# Non-human primate models of Parkinson's disease: Decoding pathogenesis and advancing therapies

Sihui Zhang, Lin Yuan, Zihan Wu, Xuguang Du, Jacek Z. Kubiak, Feng Yue, Xuejing Yan, Gaolin Jiang, Yongye Huang

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Sihui Zhang, Lin Yuan, Zihan Wu, Xuguang Du, Jacek Z. Kubiak, et al. Non-human primate models of Parkinson's disease: Decoding pathogenesis and advancing therapies. Brain-x, 2025, 3 (2), pp.e70032. 10.1002/brx2.70032. hal-05158518

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# Non-human primate models of Parkinson's disease: Decoding pathogenesis and advancing therapies

Sihui Zhang<fnref n="1" />

Lin Yuan<fnref n="2" /> ID

Zihan Wu<fnref n="1" />

Xuguang Du<fnref n="3" />

Jacek Z. Kubiak<fnref n="4" />,<fnref n="5" />

Feng Yue<fnref n="6" />

Xuejing Yan<fnref n="7" />,<fnref n="8" />,<fnref n="9" />

Gaolin Jiang<fnref n="1" />

Yongye Huang<fnref n="1" />,<fnref n="10" /> ID

**Correspondence**

Yongye Huang.

Email: huangyongye@mail.neu.edu.cn; huangyongye88@163.com

**Funding information**

National Natural Science Foundation of China,
Grant/Award Numbers: 82201594, 81502582;
National Key Research and Development Program
of China, Grant/Award Number:
2023YFF1000200; Natural Science Foundation of
Liaoning Province, Grant/Award Number: 2022-
MS-228; Open Project of State Key Laboratory of
Animal Biotech Breeding, Grant/Award Number:
2025SKLAB6-13; Science and Technology Plan
Joint Project of Liaoning Province-Doctoral
Research Start-Up Fund Project, Grant/Award
Number: 2023-BSBA-361; Polish Ministry of
Education and Science, Grant/Award Number:
612/2023

**Abstract**

Parkinson's disease (PD) is a neurodegenerative disorder in which the clinical manifestations include resting tremor, bradykinesia, akinesia, rigidity, and postural instability. The disease can be accompanied by non-motor symptoms such as depression and insomnia. The leading factors in the initiation of this disease include genetic alteration, exposure to toxins, and age. However, the exact mechanisms underlying the pathogenesis of PD remain elusive. Animal models play a critical role in the research on the pathogenesis and treatment of PD. Non-human primates share similar characteristics with humans, particularly in motor and cognitive abilities and the complexity of the neural structure. Non-human primate models for PD can be roughly classified into spontaneous, neurotoxin-based, and gene-editing models. Although having several current limitations, non-human primate models can play an increasingly important role in the research on PD, especially given the rapid development of novel methods in neuroscience.

**KEYWORDS**

6-OHDA, α-synuclein, MPTP, Non-human primate, Parkinson

Sihui Zhang, Lin Yuan and Zihan Wu contributed equally to this work.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2025 The Author(s). *Brain-X* published by John Wiley & Sons Australia, Ltd on behalf of Aiuohui Medical Technology.

<footnote n="1">¹College of Life and Health Sciences, Northeastern University, Shenyang, Liaoning, China</footnote>

<footnote n="2">²Laboratory of Research in Parkinson's Disease and Related Disorders, Health Sciences Institute, China Medical University, Shenyang, Liaoning, China</footnote>

<footnote n="3">³State Key Laboratory of Animal Biotech Breeding, Frontiers Science Center for Molecular Design Breeding (MOE), College of Biological Sciences, China Agricultural University, Beijing, China</footnote>

<footnote n="4">⁴Dynamics and Mechanics of Epithelia Group, Faculty of Medicine, CNRS, Institute of Genetics and Development of Rennes (IGDR), University Rennes, Rennes, France</footnote>

<footnote n="5">⁵Laboratory of Molecular Oncology and Innovative Therapies, Military Institute of Medicine - National Research Institute, Warsaw, Poland</footnote>

<footnote n="6">⁶Key Laboratory of Biomedical Engineering of Hainan Province, School of Biomedical Engineering, Hainan University, Haikou, Hainan, China</footnote>

<footnote n="7">⁷Department of Neurology, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China</footnote>

<footnote n="8">⁸Key Laboratory for Neurological Big Data of Liaoning Province, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China</footnote>

<footnote n="9">⁹Shenyang Clinical Medical Research Center for Difficult and Serious Diseases of the Nervous System, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China</footnote>

<footnote n="10">¹⁰Key Laboratory of Bioresource Research and Development of Liaoning Province, College of Life and Health Sciences, Northeastern University, Shenyang, Liaoning, China</footnote>
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# 1 | INTRODUCTION

Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by loss of nigrostriatal dopaminergic neurons and the aggregation of α-synuclein-rich inclusions known as Lewy bodies and Lewy neurites.[1,2] The prevalence of PD increases with age, and most cases occur at over 60 years of age.[3,4] The clinical manifestations of PD include motor syndromes such as resting tremor, bradykinesia, akinesia, rigidity, and postural instability. The disease is often accompanied by non-motor symptoms, including depression, constipation, and sleep disturbance.[5,6] The exact etiology of Parkinson's pathological changes is not fully understood. Genetic factors, environmental causes, aging, and oxidative stress may contribute to the degenerative death of dopaminergic neurons in PD. The role of genetic factors in the pathogenesis of PD has received increasing attention from researchers. Mutations of the autosomal dominant genes Leucine-rich repeat kinase 2 (LRRK2), α-synuclein (SNCA), and the autosomal recessive genes parkin (PRKN), protein deglycase (DJ-1), and PTEN-induced kinase 1 (PINK1) are associated with the pathogenesis of the disease.[7,8] Some lifestyle habits, such as smoking, coffee drinking, and drug taking, may also play a role in PD.[9] Treatment for PD by the dopamine precursor drug levodopa is still recognized as the most effective approach, although the drug's efficacy diminishes over time and can cause drug-induced tremors.[10,11]

Post-mortem neuropathological confirmation is the current gold standard for the definitive diagnosis of PD.[12,13] Experimental models are urgently needed to gain a clearer understanding of this complex disease and explore more effective therapeutic approaches. The heterogeneity in the etiology and pathology of PD requires a variety of models that can replicate different aspects of the disease. On this point, animal models appear to be superior to cell models. Models of the disease are generally constructed using neurotoxin-based or gene-based approaches employing a variety of animals, such as rodents, non-human primates, zebrafish, *Caenorhabditis elegans*, and *Drosophila*.[14,15] In neurotoxin-induced models, chemicals such as 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, and paraquat have been used to replicate the disease. Genetic manipulation of PD-related genes, such as SNCA, LRRK2, PINK1, Parkin, and DJ-1, is commonly employed in the construction of transgenic models. Neurotoxins can mimic the dopaminergic neurodegeneration caused by environmental factors that are associated with PD. In addition, neurotoxins generally induce intense and rapid cell loss in the substantia nigra pars compacta, resulting in motor symptoms and behavioral changes but lacking the formation of Lewy bodies.[16] In contrast, gene-based models not only exhibit various cell loss and motor symptoms but also display alpha-nucleotide pathology.[17] Different species of animals employed for disease models have their own advantages and limitations.

## Key points

### What is known about this topic?

* Parkinson's disease (PD) is a neurodegenerative condition characterized by key clinical symptoms that include resting tremor, bradykinesia, akinesia, rigidity, and postural instability. The primary factors contributing to the onset of the disease include genetic changes, exposure to toxins, and aging. Non-human primates exhibit considerable similarities to humans, particularly in terms of motor skills, cognitive functions, and the complexity of their neural structures. Non-human primate models for PD can be categorized into three main types: spontaneous, neurotoxin-based, and gene-editing models.

### What does this study add?

* Recent advancements in deciphering the pathogenesis and developing therapies for PD based on the utility of non-human primate models are reviewed. This article systematically discusses the current limitations of non-human primate models that need to be addressed to realize a more effective modeling of PD. This review also provides future perspectives in combining animal models with novel neuroscience technologies to advance therapeutic approaches for neurological diseases.

The motor and cognitive abilities, as well as the neuroanatomical complexities of non-human primates, are highly similar to those of human beings (Figure 1). Therefore, non-human primate models of PD are being increasingly recognized as the most powerful tools for revealing the pathophysiology of PD and evaluating therapeutic strategies for the disease.[18,19] Non-human primate models can provide insight into the resolution of relevant clinical problems associated with PD. Thus, this review presents an overview of non-human primate models of PD.

# 2 | ANIMAL MODELS OF PD: THE ADVANTAGE OF UTILIZING NON-HUMAN PRIMATES

Exploring the neural network dysfunction that leads to specific symptoms and treatment-related complications requires a variety of models. Besides these, some therapeutic approaches also demand models for experimental validation before clinical application. Animal models are essential for the study of the cellular and molecular mechanisms of neurodegenerative diseases. Rodents and non-mammalian
<figure><img src="image_5.png" /><figcaption>**FIGURE 1** Non-human primates share many similarities with human beings. Non-human primate models for Parkinson's disease can be roughly classified into spontaneous, drug-induced, and gene-editing models. MPTP, rotenone, and paraquat can cross the blood-brain barrier. In contrast, 6-OHDA must be injected intracerebrally into specific sites and transported to dopaminergic neurons via DAT. 6-OHDA, MPP⁺, and rotenone all inhibit the activity of mitochondrial complex I, damage the oxidative respiratory chain, and selectively damage dopaminergic neurons. Paraquat entry into dopaminergic neurons also induces oxidative stress, ultimately leading to neuronal death. Different genes can be targeted using gene editing techniques, such as CRISPR/Cas9, and transferred to specific brain regions of monkeys via different delivery methods. 6-OHDA, 6-hydroxydopamine; CRISPR, Clustered Regularly Interspaced Short Palindromic Repeats; DA, Dopamine; DAT, Dopamine transporter; DJ-1, Parkinsonism Associated Deglycase; LRRK2, Leucine-Rich Repeat Kinase 2; MAO-B, Monoamine Oxidase B; MPP⁺, 1-methyl-4-phenylpyridinium; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; PINK1, PTEN Induced Kinase 1; SNCA, α-Synuclein; ZFN, Zinc-Finger Nuclease.</figcaption></figure>

species are the most common models used for establishing animal models of PD.

There are several advantages to using rodents to construct PD models. Nigrostriatal dopaminergic degeneration is directly related to motor deficits and can be observed in these animals. The observation and measurement of such motor deficits can be easily manipulated by a range of behavioral tests, most of which involve measuring

locomotion, grip strength, or forepaw strength. In addition, some non-motor symptoms are frequently reported in rodents with partial nigrostriatal lesions.[20] However, there are also significant differences between rodents and humans including genomic, molecular, and anatomical characteristics. For example, the mouse brain and the human brain do not develop in the same way. Human brains take more than 10 months to fully develop, whereas rodent brains take only
<figure><img src="image_6.png" /></figure>

21 days to form, resulting in significant differences in their structures.[21] In terms of anatomy, the stratified structure of the substantia nigra in rodents is not as clear as that in humans, the content of melanin granules (neuromelanin) is very low, difficult to observe in gross anatomy, and the volume of the substantia nigra and the number of dopaminergic neurons are significantly less than that in humans. In humans, the substantia nigra—striatum pathway is spatially more complex, with dopaminergic neurons in the substantia nigra projecting into the dorsolateral region of the striatum, and the human striatum (including the putamen and caudate nuclei) is highly differentiated and responsible for the integration of motor, emotional, and cognitive functions. In rodents, the nigrostriatal projection has a low degree of differentiation, and the degree of regionalization within the striatum is also low, primarily focusing on motor regulation.[22] The expression level of the human dopamine transporter (DAT) is high, resulting in efficient transport of dopamine. However, the number of dopaminergic neurons in rodents is relatively low, and the expression level of DAT is significantly lower than that in humans, resulting in a lower efficiency of dopamine reuptake and affecting the dynamics of dopamine. PD is characterized by selective, progressive death of dopaminergic neurons in the substantia nigra, accompanied by aggregation of α-synuclein to form Lewy bodies (Figure 2).[23,24] This degenerative change gradually accumulates. Rodent models, often induced by neurotoxins, lack such progressive features and fail to exhibit Lewy body pathology, limiting the mechanistic study of protein misfolding. These differences determine the neuropathological differences in the brain between the rodent models and patients with neurodegenerative diseases. Thus, although rodent models are widely used in mechanistic studies at the cellular and molecular levels, there are still shortcomings in these models that prevent them from definitively and effectively reflecting PD.

In recent decades, non-mammalian model species, such as *C. elegans*, *Drosophila*, and zebrafish, have also been extensively used for PD research due to the ease of genetic manipulation, rapid reproductive cycles, low maintenance costs, and clearly delineated neuropathology and behavior.[25] These models have generally been applied to the study of molecular mechanisms and in drug screening. For example, research using zebrafish found that the YIAEDAER (Tyr-Ile-Ala-Glu-Asp-Ala-Glu-Arg) peptide may have neuro-protective effects against MPTP-induced locomotor impairment and degeneration of Dopamine (DA) neurons.[26] The zebrafish brain has a neurotransmitter system and a functional blood-brain barrier (BBB) similar to that of humans.[25] Moreover, zebrafish also possesses a ventral brain homologous to the mammalian substantia nigra, making the species increasingly popular for PD research. However, findings from these non-mammalian models are difficult to translate into real human disease treatment. Therefore, there is still a demand for other suitable PD models.

Primates are an ancient and diversified group of animals that includes lemurs, lorises, tarsiers, monkeys, apes, and

humans. Therefore, there is a close genetic relationship between humans and non-human primates (Figure 1). Furthermore, in contrast to rodents and non-mammals, non-human primates share many more characteristics with humans in terms of physiology, genetics, immunology, and pathology.[27,28] The motor and cognitive abilities as well as the neuroanatomical complexity of non-human primates are very similar to those of humans. For example, non-human primate models can simulate the early or premotor stages of PD, such as sleep disorders.[29] Thus, non-human primate models have profound implications for the clinical detection and treatment of PD. These models also enable a more detailed assessment of the development of different brain structures involved in the pathology of PD and the exploration of novel therapeutic approaches such as deep brain stimulation (DBS).

# 3 | STRATEGIES FOR ESTABLISHING NON-HUMAN PRIMATE PD MODELS

## 3.1 | Neurotoxic models

Several PD symptoms can be induced by neurotoxins. Neurotoxins can trigger mitochondrial dysfunction via inhibition of complex I in the respiratory chain, thereby inducing the production of reactive oxygen species (ROS) that decrease the permeability of the mitochondrial membrane (Figure 1). Many proteins, including tumor necrosis factor and cytochrome c, then cross the mitochondrial membrane into the cytoplasm, triggering cell apoptosis and neurodegeneration. Among these neurotoxins, 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) have been employed to establish PD models for the study of the pathogenesis of PD-associated neurodegeneration. In addition to these traditional neurotoxins, pesticides such as rotenone and herbicides such as paraquat are toxic to neurons and thus have been suggested to increase the risk of PD.[30,31] Therefore, animal models have also been constructed by utilizing rotenone and paraquat.

### 3.1.1 | The existing drug-induced Parkinson's models

#### MPTP

MPTP, which was first synthesized as a byproduct of the synthesis of 1-methyl-4-phenyl-4-propionpiperidine (MPPP), is commonly used in the construction of PD models. Due to its lipophilic nature, MPTP can easily cross the BBB and be taken up by dopaminergic neurons. MPTP can be oxidized by monoamine oxidase B into 1-methyl-4-phenylpyridinium (MPP+), a metabolite toxic to astrocytes.[32] After being released into the parenchyma, MPP+ is rapidly absorbed by dopaminergic neurons through the DAT as MPP+ is structurally similar to dopamine.[33] Furthermore, MPP+ leads to the
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<figure><img src="image_8.png" /><figcaption>**FIGURE 2** Key mechanisms and genetic influences in the pathogenesis of PD. (A) Coronal sections of the midbrain in healthy and PD states. Compared to the healthy state, in the PD state, there is significant loss of DA neurons, leading to depigmentation of the substantia nigra. (B) Mechanistic pathways of α-synuclein toxicity and cellular dysfunction in PD. The misfolding and aggregation of α-synuclein, progressing from monomers to toxic oligomers and fibrils, contribute to neurotoxicity in DA neurons. In the center, α-synuclein is depicted to highlight its central role in influencing all known signaling pathways associated with PD. Genetic variants, such as those in SNCA, LRRK2, and GBA1, affect key cellular processes, including vesicle transport, retromer function, autophagy, and lysosomal degradation. Environmental toxins such as rotenone and paraquat exacerbate mitochondrial dysfunction, oxidative stress, and protein aggregation, thereby further disrupting cellular homeostasis. Together, these mechanisms converge to drive the degeneration of DA neurons, a hallmark of PD. ALAS1, 5'-Aminolevulinate Synthase 1; ASAH1, N-Acylsphingosine Amidohydrolase 1; ATP13A2, ATPase Cation Transporting 13A2; COQ7, Coenzyme Q7, Hydroxylase; CTSB, Cathepsin B; DA, Dopamine; DJ-1, Parkinsonism Associated Deglycase; FBXO7, F-box Protein 7; GAK, Cyclin G Associated Kinase; GALC, Galactosylceramidase; GBA1, Glucosylceramidase Beta 1; LRRK2, Leucine -Rich Repeat Kinase 2; MCCC1, Methylcrotonyl-CoA Carboxylase Subunit 1; MCOLN1, Mucolipin TRP Cation Channel 1; PD, Parkinson's disease; PINK1, PTEN Induced Kinase 1; RAB7L1, RAB29, Member RAS Oncogene Family-Like 1; SCARB2, Scavenger Receptor Class B Member 2; SLC17A5, Solute Carrier Family 17 Member 5; SMPD1, Sphingomyelin Phosphodiesterase 1; TMEM175, Transmembrane Protein 175; VPS13C, Vacuolar Protein Sorting 13 Homolog C.</figcaption></figure>
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inhibition of complex I, resulting in a rapid decrease in the adenosine triphosphate concentration in the striatum and substantia nigra, which in turn triggers oxidative stress, ultimately leading to the apoptosis and necrosis of dopaminergic neurons and neuroinflammation.[32] Systemic administration of MPTP results in catecholaminergic loss in both the central and peripheral nervous systems. In MPTP-induced PD models in mice and non-human primates, similar symptoms, including dopaminergic cell loss, decreased striatal dopamine levels, and neuroinflammation, have been reported. Rats are reported to be resistant to MPTP.[34] Monkeys receiving MPTP treatment exhibited several Parkinsonian motor phenotypes, including bradykinesia, akinesia, tremor, rigidity, and postural instability.[35] Furthermore, the stability and severity of these hallmark symptoms are dependent on the dosage and regimen of MPTP treatment.

In non-human primates, MPTP is typically administered systemically and is usually delivered via arterial infusion (Table 1). Dopaminergic neurodegeneration is the key

pathological feature of the MPTP-induced PD model.[45] Non-human primates treated with MPTP also display pathologies that replicate PD-like olfactory[46] and sleep disturbance[47] symptoms. MPTP-induced models result in rapid and localized degeneration of dopaminergic neurons, whereas PD in humans progresses slowly and affects multiple brain regions, including non-dopaminergic systems.[48,49] Another important feature of MPTP treatment is that monkeys need 2–3 months to display stable PD symptoms. In addition, these symptoms can only be maintained within a few months because of the limited duration of MPTP unless further doses are administered. Therefore, most MPTP-induced PD models are generated via multiple low-dose intracarotid injections. It has been demonstrated that MPTP treatment with chronic delivery and low daily dose can induce a progressive model with unrecovered dopamine loss.[50] Although it takes longer to generate the PD model via multiple administrations of MPTP, the animals manifest much more stable Parkinsonian symptoms,

<table><caption>TABLE 1 A partial summary of neurotoxin-induced non-human primate PD models.</caption><thead><tr><th>Neurotoxin</th><th>Strain</th><th>Dose &amp; route</th><th>Behavioral features</th><th>Pathological features</th></tr></thead><tbody><tr><td rowspan="5">MPTP: Complex I inhibitor</td><td>Rhesus monkeys (Macaca mulatta), 6.1 years[36]</td><td>Intravenous injection: 0.3 mg/kg twice a week for 3 months</td><td>Parkinsonian symptoms (a higher Parkinson's disease score)</td><td>Loss of TH<sup>+</sup> neurons and dopaminergic neurons in substantia nigra</td></tr><tr><td>Cynomogus monkeys (Macaca fascicularis), 5.6 &plusmn; 1.0 years,[37] 4 years[38]</td><td>Intramuscular injection: Each 0.45 mg/kg/week for 5 weeks, and a cumulative dose of 2.25 mg/kg</td><td>Changes in Parkinsonian motor symptom severity scores</td><td>Increased volume in striatum, midbrain &amp; other dopaminergic neurons</td></tr><tr><td rowspan="3">Marmosets (Callithrix jacchus),[39] 5 years,[40] 2–5 years[41]</td><td>Intravenous injection: 0.25–0.5 mg/kg/week</td><td>Stable motor disability</td><td>Reduced TH<sup>+</sup> neurons; loss of nigral dopaminergic neurons</td></tr><tr><td>Subcutaneous injections: 2 mg/kg for 5 days</td><td>Postural tremors, bradykinesia, cognitive impairment, sleep disturbance</td><td>- n/a</td></tr><tr><td>Subcutaneous injections: 2 mg/kg for 2 days and 1 mg/kg for next 3 days</td><td>Akinesia, rigidity, postural instability, tremor, and abnormal blinking</td><td>Loss of TH<sup>+</sup> neurons and degeneration of DA neurons</td></tr><tr><td rowspan="2">Squirrel monkey (Saimiri sciureus)[42]</td><td>Subcutaneous injections: (Group 1) 2 mg/kg for 3 days; (Group 1) 1 mg/kg for 3 days</td><td>Increased anxiety, depression or psychosis</td><td>Group 1: 19.07% of TH<sup>+</sup> versus control<br>Group 2: 4 neurons 5.7% of TH<sup>+</sup> neurons versus control</td></tr><tr><td>Over 12-year-old<br>MPTP: Only one single subcutaneous injection of 1.75 mg/kg</td><td>Abnormal posture of the head, trunk, and limbs; bradykinesia and tremor</td><td>Loss of TH<sup>+</sup> neurons; reduction of dopaminergic cells; significant depletion of dopamine and dopamine metabolites in the striatum; upregulation of &alpha;-synuclein in dopaminergic neurons</td></tr><tr><td rowspan="2">6-OHDA: Produce ROS and inhibit complex I</td><td>Marmoset (C. jacchus), 22–35 months[43]</td><td>Injection: 2 &mu;L of 4 mg/mL in 0.01% ascorbate made at a rate of 0.5 &mu;L/min</td><td>Bend posture; decreased movement or motor control; tremor; increased time spent on the ipsilateral side</td><td>Dopaminergic cell loss in substantia nigra</td></tr><tr><td>Rhesus monkeys (M. mulatta), 5–17 years[44]</td><td>Intravenous injection: The final dose is 50 mg/kg</td><td>No motor deficits</td><td>Decreased TH<sup>+</sup> neurons in substantia nigra; no &alpha;-synuclein aggregation</td></tr></tbody></table>

Abbreviations: 6-OHDA, 6-hydroxydopamine; DA, Dopamine; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; PD, Parkinson's disease; ROS, reactive oxygen species.
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including tremor, bradykinesia, and impaired balance.[51] In these models, the topographic pattern of dopaminergic cell loss in the striatum replicates that of PD. However, another important feature, the formation of Lewy bodies, has never been induced by MPTP treatment.[33] Nonetheless, in non-human primates, MPTP leads to the upregulation of α-synuclein in degenerating neuron cell bodies following acute exposure, whereas accumulation and aggregation of α-synuclein follow chronic exposure.[42,52] In recent decades, MPTP has been widely administered to non-human primates for testing drugs for their anti-Parkinsonian activity.[53,54]

## 6-OHDA

In 1974, the first PD animal model was established by the intracerebral injection of 6-OHDA,[55] a well-known dopamine analog. The reason for applying intracerebral injection was that 6-OHDA cannot cross the BBB. After being injected into the brain, 6-OHDA enters dopaminergic and noradrenergic neurons through monoamine transporters. Then, it rapidly self-oxidizes, producing ROS such as hydroxyl radicals, superoxide radicals, and hydrogen peroxide. These compounds can disrupt the function of complex I, leading to the dysfunction of mitochondria.[33]

The 6-OHDA-induced models have been widely used to elucidate the mechanism of dopaminergic neuronal death and to develop neuroprotective and therapeutic strategies.[56-58] Injection of 6-OHDA into the substantia nigra pars compacta or the striatum results in a distinctive pattern of neuronal degeneration.[32] For example, in rats, 6-OHDA directly injected into the striatum will damage the axon terminals and induce dopaminergic neuron degeneration in the substantia nigra.[59] Injection of 6-OHDA into the substantia nigra immediately leads to relatively serious dopaminergic neuronal degeneration. The same phenomenon is also observed in non-human primates.[60] In marmosets, the unilateral injection of 6-OHDA into the nigro-striatal pathway resulted in a massive reduction of approximately 98% of dopaminergic neurons, accompanied by long-term behavioral deficits.[43,61] However, none of the 6-OHDA toxicity models have induced the formation of Lewy bodies, although 6-OHDA has been reported to interact with SNCA.[62]

### 3.1.2 | The non-existing drug-induced Parkinson's models

#### Paraquat

Ten pesticides have been found to be directly toxic to dopaminergic neurons.[63] Paraquat, acting as an herbicide, is also reported to be neurotoxic. Despite its polarity, paraquat can penetrate the BBB via a neutral amino acid carrier.[64] Paraquat has structural similarity to MPP⁺. However, rather than inhibiting complex I as MPP⁺ does, paraquat exerts its neural toxicity through cellular redox cycling, the system that protects against oxidative stress in neuronal cells.[64] Among animal models induced by paraquat, substantia nigra

pars compacta dopaminergic neuron degeneration accompanied by SNCA inclusions has been observed in mice,[65] and dopamine depletion has been observed in rats.[66] However, paraquat-induced PD-like phenomena in monkeys differ from those in mice. Exposure to paraquat reduces nicotinic receptor-evoked dopamine in the monkey striatum,[67] whereas dopaminergic function in mice is unaffected by paraquat treatment. The different performance of paraquat emphasizes the importance of evaluating symptoms in suitable animal models. However, paraquat has not yet been widely used to generate a non-human primate PD model.

#### Rotenone

Rotenone is a highly lipophilic molecule. Therefore, it can easily cross the BBB. Similar to paraquat, rotenone induces dopaminergic neurodegeneration by enhancing oxidative stress. Rotenone also functions by inhibiting complex I, thereby evoking the production of ROS, which leads to mitochondrial dysfunction. Rotenone injection induces PD-like symptoms in a dose-dependent manner: a high concentration of rotenone injection results in massive dopaminergic cell loss, whereas low doses of rotenone administration induce selective nigrostriatal cell loss.[68,69] In rodent PD models induced by rotenone, the mice typically display dopaminergic neurodegeneration, the formation of Lewy bodies, and some motor deficits.[68,70,71] Rotenone also presents oxidative toxicity in primates. However, there is not yet a non-human primate model induced by rotenone.

### 3.2 | Genetic models

Genetic animal models generated by gene knockout, knockdown, or knock-in techniques contribute to the study of the molecular mechanisms underlying PD pathology. SNCA was the first gene linked to familial PD.[72] Afterward, the autosomal dominant genes LRRK2 and UCH-L1 and the autosomal recessive genes PRKN, DJ-1, and PINK1 were discovered to be related to both familial and sporadic PD. Genetic mutations are recognized as critical risk factors for both familial and sporadic PD. Mutation of these genes resulted in partial PD symptoms in non-human primates, whereas mutation of other parts of the genes did not induce any of the hallmarks of PD.

The rapid development of genetic modification techniques has contributed to the generation of non-human primate PD models. Although transgenic non-human primate models established by germline genome editing have displayed some of the hallmarks of PD, the long life cycle and the lack of non-human primate embryonic stem cells limit their widespread use. It has been reported that some neurological phenotypes appear at the early stage of an animal's life without degenerative progression with age in genetic models.[73] Age is a major risk factor for PD.[74] However, age-dependent PD symptoms are difficult to replicate in animal models. Thus, viral vector-mediated gene transfer combined with nuclease-mediated genome editing
<figure><img src="image_11.png" /></figure>

<table><caption>TABLE 2 A partial summary of genetic non-human primate PD models.</caption><thead><tr><th>Gene</th><th>Species</th><th>Mutation &amp; route</th><th>Behavioral features</th><th>Pathological features</th></tr></thead><tbody><tr><td>SNCA/α-synuclein</td><td>Rhesus monkey<sup>[83]</sup></td><td>Transgenic: Lentiviral vector mediated, injected into 133 MII oocytes, expression of mutant α-synuclein (A53T)</td><td>Age-dependent non-motor symptoms: Cognitive defects and anxiety behavior</td><td>No apparent degeneration in the brain</td></tr><tr><td rowspan="2">Common marmoset (Callithrix jacchus)<sup>[84,85]</sup></td><td>rAAV-mediated expression of A53T α-syn in the SN of adult marmosets</td><td>1. Head position bias</td><td>1. Nigral dopamine neuron cell loss<br>2. α-syn positive cytoplasmic inclusions<br>3. Loss of TH<sup>+</sup> neurons</td></tr><tr><td>rAAV-mediated expression of human WT α-syn in the ventral midbrain of adult marmosets</td><td>1. Head position bias &amp; full body rotation</td><td>1. Dopaminergic neurodegeneration<br>2. Loss of oligodendroglial cells in the cerebral peduncle<br>3. Deposition of α-syn and ubiquitin</td></tr><tr><td>DJ-1</td><td>Rhesus monkey (Macaca mulatta)<sup>[86]</sup></td><td>AAV-delivered CRISPR/Cas9 mediated loss-of-function mutations in DJ-1 in adult monkeys</td><td>No PD clinical symptoms</td><td>1. Nigral dopaminergic cell loss</td></tr><tr><td>PINK1</td><td>Rhesus monkey (M. mulatta)<sup>[87]</sup></td><td>CRISPR/Cas9-mediated PINK1 KO with double disruption in both exon 2 &amp; exon 4 of PINK1 in one-cell stage embryos</td><td>No PD clinical symptoms</td><td>1. Less severe neurodegeneration in brains</td></tr><tr><td>PINK1 &amp; DJ-1</td><td>Rhesus monkey (M. mulatta)<sup>[86]</sup></td><td>AAV9-delivered CRISPR/Cas9 mediated double mutation of PINK1 exon 3 and DJ-1 in the substantia nigra of adult monkeys</td><td>1. Bradykinesia, tremor, postural instability</td><td>1. Nigral dopaminergic neuron loss<br>2. α-synuclein pathology</td></tr></tbody></table>

Abbreviations: DJ-1, protein deglycase; PD, Parkinson's disease; PINK-1, PTEN-induced kinase 1; rAAV, recombinant Adeno-associated Virus; SNCA, α-synuclein; WT, wild type.

technology (i.e., CRISPR/Cas9) or gene knockdown via RNAi has been suggested as an ideal method to produce PD phenotypes in adult monkeys (Figure 1). These techniques can modify the endogenous genome at specific target loci. Stereotaxic injection in the brain can deliver a viral vector carrying the CRISPR/Cas9 system into the substantia nigra regions of adult monkeys, thereby substantially shortening the generation of PD symptoms. This strategy also makes it more efficient to study age-dependent symptoms by modifying targeted genes in adult monkeys of different ages.

## 3.2.1 | Constructed models

### α-synuclein

MPTP can largely replicate the clinical motor symptoms and nigrostriatal dopaminergic loss observed in PD.[75] However, MPTP cannot induce α-synuclein pathology. Therefore, transgenic models are used to mimic α-synuclein pathology and conduct preclinical trials. The protein α-synuclein, a major biomarker for PD, is massively present in the presynaptic terminals. Under normal conditions, α-synuclein interacts with membranes and plays a key role in vesicular dynamics.[76,77] In pathological conditions, α-synuclein can form toxic intraneuronal protein inclusions, known as Lewy bodies, and often generates dystrophic neurites.[78,79] Generally, Lewy bodies and dystrophic neurites are primarily composed of α-synuclein and its phosphorylated form. A variety of mutations in α-synuclein have been

identified, including A53T, A30P, E46K, H50Q, G51D, and A53E.[7,80–82]

The first α-synuclein transgenic non-human primate models were established by introducing A53T mutant α-synuclein in rhesus monkeys. The monkeys showed age-related non-motor symptoms, including cognitive defects and anxiety phenotypes[83] (Table 2). Mutant α-synuclein transgenic rhesus monkeys display non-motor symptoms in an age-dependent manner. The oldest monkeys in the experiments displayed stereotypic behavior (repetitive, unchanging movements without goals or functions) but did not have sleep disorders or non-motor symptoms. This suggests that in the early stages of the disease, the mutant α-synuclein is more likely to affect emotional behavior rather than sleep function.

Because of the long life cycle of non-human primates and age-dependent pathology, stereoscopic injection with a viral vector is considered a relatively efficient method for generating genetic PD models. Adeno-associated virus (AAV) vectors are robust gene transfer tools for introducing α-synuclein into the brains of non-human primates.[88] Recombinant AAV containing wild type (WT) or mutant α-synuclein was injected into the brains of adult monkeys to construct α-synuclein-based non-human primate PD models. Recombinant AAV-mediated expression in the WT and A53T α-syn in the substantia nigra of adult marmosets produced a significant loss of TH-positive neurons, accompanied by motor impairment, including head position bias compatible with the magnitude of nigral dopamine neuron
<figure><img src="image_12.png" /></figure>

cell loss at 16 weeks after injection.[84] Although α-synuclein-positive cytoplasmic inclusions were observed in the monkeys, evidence of ubiquitin staining was lacking. In another study, the long-term effects of overexpressing WT and A53T mutant α-synuclein in the substantia nigra of marmosets were examined.[85] One year post-injection, marmosets with A53T α-synuclein expression exhibited a more consistent neurodegeneration than the WT group.[85] Importantly, α-synuclein aggregation present in the primate midbrain was positive for ubiquitin staining,[89] indicating that Lewy bodies could be successfully induced in a non-human primate model.

Seeding, which involves the direct administration of exogenous α-synuclein fibrils, can produce aggregation of Lewy body inclusions. Macaques and marmosets administered with α-synuclein fibrils exhibited nigro-striatal dopaminergic neurodegeneration after injection.[74,90] However, none of these animal models showed motor deficits for more than 1 year post-injection.

Overall, more time is needed to generate non-human primate PD models via regulating α-synuclein expression, while the extent of DA neurodegeneration still does not fully mimic human PD symptoms.[91] However, these models are useful for examining the etiology and pathology of PD, particularly in understanding the mechanism of α-synuclein-related symptoms. Furthermore, the establishment of an α-synuclein-based PD model could also lead to the development of PD treatments via targeting Lewy bodies.

### PTEN-induced kinase 1

PINK1, a neuroprotective serine/threonine kinase, is involved in protecting against mitochondrial dysfunction and promoting neuronal differentiation.[92] PINK1 mutations are closely associated with early-onset recessive PD.[93,94] When mitochondria become damaged, PINK1 accumulates on the outer membrane via its N-terminal mitochondrial targeting sequence.[95] Subsequently, PINK1 phosphorylates Parkin to activate its E3 ubiquitin ligase activity and recruits Parkin to dysfunctional mitochondria, thereby mediating protein degradation in proteasomes.[96,97] In a recent research study, severe neurodegeneration in the brain occurred in PINK1 mutant monkeys, despite the absence of dysfunction in mitochondrial morphology or dynamics, although the animals exhibited significant decreases in several proteins related to neuronal function.[98] This finding suggests that PINK1 could act as a functional cytoplasmic kinase to maintain neuronal survival in the primate brain. In summary, PINK1 kinase activity is critical for the survival of mitochondria and neurons, while dysfunction of its kinase may be involved in the pathogenesis of PD.

It is difficult to replicate PD behavior using PINK1 mutant models in mice and pigs. There is no typical degeneration of dopaminergic neurons in the brains of mice with endogenous PINK1 mutations,[99,100] even when the mice were produced via knockout of PINK1 together with both PRKN and DJ-1.[101] In pigs, disrupting PINK1 and PRKN by targeted CRISPR/Cas9 induced neither

neurodegeneration nor PD phenotypes,[102] even when combined with mutation of DJ-1.[103] In contrast to the selective expression of PINK1 in the primate brain, endogenous PINK1 protein in the mouse brain is difficult to detect. Both transgenic and viral-vector-mediated PINK1 mutant mouse models are more sensitive to MPTP-induced dopaminergic (IDA) neurodegeneration,[1,4–106] and PINK1 knockout mice show an enhanced loss of dopaminergic neurons under SNCA overexpression.[107]

CRISPR/Cas9-targeted PINK1 in non-human primates results in several types of mutation-dependent animal models. Single-exon targeted mutations are reportedly insufficient to model PD phenotypes in monkeys.[108] Monkey models with double disruption in both exon 2 and exon 4 of PINK1 exhibit severe neurodegeneration in the brain,[87] indicating that PINK1 is essential for the survival of neurons in the primate brain. Nevertheless, the model failed to elicit clinical symptoms of PD.[87] In a recent study, a viral vector was directly injected into the substantia nigra of adult monkeys to co-edit both PINK1 and DJ-1, resulting in severe loss of dopaminergic cells.[86] Importantly, almost all the classic PD symptoms, including motor deficits (bradykinesia, tremor, and postural instability) as well as α-synuclein pathology, were manifested in the model. Generally, a deficiency of PINK1, or in combination with related genes, in the brains of non-human primates leads to neurodegeneration in the substantia nigra, contributing to the pathogenesis of PD.

## 3.2.2 | Non-constructed models

### PRKN/Parkin

Parkin is an E3 ubiquitin ligase that plays an important role in proteasomal degradation. Once activated by phosphorylation, Parkin is recruited from the cytosol to the damaged mitochondria, where it will ubiquitinate substrates of the mitochondria to trigger selective mitophagy,[109] leading to neuronal apoptosis. Various types of Parkin mutations have resulted in loss-of-function related to disease.[96] There are more than 200 mutations in Parkin that have been found in approximately 50% of familial and 20% of idiopathic early-onset PD.[47]

General Parkin knock-out mouse models have been generated. Consistent with the inhibition of complexes I and IV, Parkin-null mice exhibit mitochondrial dysfunction and oxidative damage.[110] However, although Parkin-null mice exhibited nigrostriatal deficits, no losses of dopaminergic neurons or impairment of the nigrostriatal dopaminergic system were observed, nor the aggregation of α-synuclein,[111,112] indicating that Parkin mutant animal models do not fully replicate the pathology of PD. Certainly, a monogenic Parkin mutant model based on large animals such as non-human primates and pigs has not yet been generated. Nonetheless, in induced pluripotent stem cell (iPSC)-derived neurons from PD patients, it has been reported that mutation of PRKN results in abnormal mitochondrial function and
<figure><img src="image_13.png" /></figure>

reduced dopamine levels.[113] Thus, the PRKN mutant iPSC model can be used to characterize mitochondrial morphology and study the function of Parkin as well as its role in the etiology of PD.

### *DJ-1*

The DJ-1 gene is associated with rare autosomal recessive early-onset PD.[114] DJ-1 encodes an antioxidant protein that together with PINK1 protects neurons from oxidative stress.[115] DJ-1 is a critical modulator in PINK1/parkin-mediated mitophagy[116] and prevents the formation of metabolites and protein damage.[117] Human DJ-1 has three cysteine residues: Cys46, Cys53, and Cys106. Besides Cys106, Cys46 is the most active cysteine residue in DJ-1, as shown by NPSB-B chemical probes.[118] Peroxidized Cys46 readily forms a disulfide bond with the adjacent depolymerized Cys53, but the mutants (C46A and C53A) do not form a Cys46-Cys53 disulfide bond cross-link, which increases the oxidation of Cys106.[118] The DJ-1 C46A mutant has a twisted and unstable structure, and all three mutants cause dopaminergic neurons to lose their antioxidant capacity.[118] This suggests that all three cysteine residues, including the Cys46-Cys53 disulfide linkage crosslink, are required for DJ-1 to be structurally intact and function as an antioxidant protein.

DJ-1 is also involved in the correct folding of α-synuclein, which inhibits α-synuclein aggregation in the pathogenesis of PD.[119] Studies have shown that the substitution of L166P results in the loss of the homodimer structure of DJ-1.[120] DJ-1 is present in Lewy bodies, and the interaction between α-synuclein and wild-type DJ-1 (wDJ-1) or L166P mutant DJ-1 (mDJ-1) has been investigated by molecular dynamics simulation. The results showed that α-synuclein bound more tightly to mutant mDJ-1 than to wDJ-1. The mDJ-1 bound α-synuclein complex represents a stable conformation and forms a complex that may exacerbate Lewy body formation.[120] Loss of nigral dopaminergic cells was induced in DJ-1 deficient monkeys via the CRISPR/Cas9 system.[86] Nonetheless, this monkey model did not elicit other hallmarks or clinical symptoms of PD, probably because the degree of neurodegeneration was not high enough. At present, there are no monogenic DJ-1 mutant non-human primate models being generated.

## 4 | ADVANTAGES AND CURRENT LIMITATIONS OF NON-HUMAN PRIMATE MODELS

### 4.1 | Advantages

Non-human primate models, such as monkeys and apes, play a critical role in biomedical research due to their genetic, anatomical, and physiological similarities to humans.[121] Non-human primates share a high degree of genetic homology with humans (e.g., chimpanzees share ~98% of their DNA with humans). Their physiological systems, such as

immune response, brain structure, and cardiovascular function, closely resemble those of humans. This similarity is important in neuroscience research. Non-human primates possess complex brains and cognitive functions, making them ideal for studying brain disorders, neural circuits, and behavior. Diseases such as Alzheimer's, Parkinson's, and mental illnesses can be effectively modeled. Non-human primates are valuable for studying infectious diseases, such as HIV/AIDS, Ebola, and SARS-CoV-2, as their immune systems respond similarly to pathogens and thus can serve as key models in vaccine development and testing.[122,123] The findings from non-human primate research are often more directly applicable to humans compared to other animal models, thereby reducing the translational gap. This is critical in drug development and toxicology testing.[124,125]

### 4.2 | Current limitations

The non-human primate models also have significant limitations that need to be addressed for future research to be more effective. These limitations primarily relate to the absence of certain PD symptoms, difficulties in replicating human disease pathology, and ethical considerations. Non-human primate models often fail to replicate the full spectrum of non-motor symptoms associated with PD, such as depression, anxiety, cognitive decline, sleep disturbances, and autonomic dysfunction.[126,127] These symptoms significantly affect patients, but the models are still being developed. Non-human primate models often rely on neurotoxins to induce PD-like symptoms, as discussed in Section 3.1. However, these models do not capture the progressive nature of PD. Genetic factors (e.g., mutations in LRRK2, SNCA, and PINK1) have been implicated in PD; however, genetic manipulation in non-human primates remains technically challenging as it is both costly and time-intensive.[128] Existing genetic non-human primate models do not yet replicate the complex interplay between genetic and environmental factors seen in human PD.[129] Technologies such as organoids, computational models, and human-iPSCs are advancing.[130,131] The development of brain organoid models provides a physiological platform for the study of PD. However, iPSC-derived brain organoids require a long maturation time and may not accurately represent the epigenetic and cellular environment of the diseased brain. Recent studies have proposed a novel approach to directly generate 3D-iDA neuronal organoids from human fibroblasts.[132] These 3D iDA organoids were more similar to the human brain in its older stages and could accurately replicate PD pathology. Creation of 3D iDA neuron-astrocyte assemblies by introducing astrocytes revealed that healthy astrocytes and A53T mutant IDA assemblies exhibited the protective effect of astrocytes, but A53T mutant astrocytes gradually led to neuronal degeneration and Lewy bodies in the assembly.[132] Constructing non-human primate models is also expensive,[133,134] hindering their widespread application.
<figure><img src="image_14.png" /></figure>

Moreover, non-human primates are highly intelligent social animals capable of experiencing pain, stress, and suffering, which raises significant ethical questions. There is growing public opposition to non-human primate research, especially when it involves invasive procedures or prolonged pain. In addition, strict ethical guidelines and regulatory frameworks (e.g., the 3Rs: Replace, Reduce, Refine) often limit the scope and pace of research involving non-human primates. This often leads to ethical reviews that can delay research times and stringent benefit standards that increase operating costs.[134] However, ethical review is indispensable for scientific research.

## 5 | FUTURE PERSPECTIVES

It is essential to emphasize the importance of ethics and the ethical requirements for the use of experimental animals.

In specific practices, we must first emphasize the “Replacement” inherent in the use of non-animal models (such as organoids and computer simulations) in lieu of Non-human Primates (NHPs). If NHPs must be used, they must be shown to be irreplaceable, for example, in studies of the immune response or long-term complications of peritoneal dialysis that cannot be adequately modeled in rodents. The accuracy of the model is the most important factor. It is critical to develop models that simulate the progression of PD and susceptibility to age-related neurodegeneration. Research may focus on inducing slow, cumulative neurodegeneration in both dopaminergic and non-dopaminergic systems to better align with the progression of human disease. Efforts should be made to replicate the full range of symptoms of PD, including non-motor manifestations such as cognitive decline, mood disorders, and autonomic dysfunction. This may involve neural networks targeting a wider range of PD effects, such as in the limbic system and brainstem. Moreover, cross-species comparisons of PD susceptibility and defense mechanisms (in rodents and primates) may yield new insights into PD prevention and treatment in humans. At the same time, the use of animal models must be planned in detail, possibly involving the supplementation of non-human primate studies with rodent models, computational methods, or organoid systems to reduce the reliance on non-human primates.[129,134] This could significantly reduce the use of non-human primate models, thereby reducing research costs and difficulties.

In terms of “Reduction,” the experiments should minimize the number of animals used by optimizing the experimental design (e.g., cross-control, longitudinal monitoring). For example, a single NHP can be reused for data acquisition at multiple time points, provided that animal welfare is not compromised. Significant improvements in model design, experimental approaches, and ethical frameworks are necessary to address current limitations and optimize the translational potential of these models. To construct an accurate PD model, it is necessary to enhance the practicality of non-human primate models, such as by combining existing models of MPTP-induced damage with genetic

mutation models to mimic the slow degradation of both dopaminergic and non-dopaminergic systems. AAV-mediated gene precision therapy and delivery systems, together with CRISPR/Cas9, have huge potential.[1,5–137] It is feasible to construct non-human primate PD models using genetic techniques accompanied by proper neurotoxin treatment. Researchers have discovered an approach known as TARGET-seq (Tagging projections by AAV-mediated RetroGrade Enrichment of Transcriptomes) that can identify molecularly distinct subpopulations of human dopamine neurons, identify candidate transcription factors along the developmental trajectory of dopamine neurons that may control subtype identity, and explore cells for clinical stem cell therapies using molecular targets.[138,139]

The final item of the “3R principles” is “Refinement,” which means minimizing animal suffering, such as using noninvasive imaging (magnetic resonance imaging [MRI] or ultrasound) to monitor peritoneal fibrosis rather than repeated surgical sampling. We should employ minimally invasive surgical techniques and improve post-operative care to minimize animal suffering. During the phenotypic study phase, the use of non-invasive imaging techniques, such as functional MRI or positron emission tomography, can help track subtle changes caused by disease and validate phenomena such as neuroinflammation and protein aggregation in non-human primates. DBS[140,141] and brain-computer interfaces (BCI)[142] connect the direct communication between the brain and external devices and can obtain the signal regulation mode of the brain network through the integration of interdisciplinary communication, such as artificial intelligence,[143] to examine treatments and rehabilitation mechanisms for PD. BCIs and noninvasive DBS have been shown to be effective in PD patients for pain relief.[144,145]

## 6 | CONCLUSION

Brain science is considered the final frontier of the life sciences, and various interventions in the diagnosis and treatment of brain diseases must be tested in animals before being applied to humans. In this article, we summarize the drug-induced and genetic models that can be used to generate non-human primate models, but some of these models have not yet been applied to non-human primates. Non-human primates are the most similar model animals to humans in terms of both genes and neurological and immune systems. Thus, the effective construction of non-human primate models is crucial for PD research.

The importance of non-human primate models in the study of PD and similar brain diseases cannot be overstated, but it is also necessary to consider the ethical and moral constraints imposed by society. Researchers need to develop innovative solutions that consider the advantages and disadvantages of non-human primate models. In the near future, applying these animal models in combination with novel technologies, such as BCI, to explore new therapeutic approaches for neurological diseases will be a bonus.
<figure><img src="image_15.png" /></figure>

## AUTHOR CONTRIBUTIONS

**Sihui Zhang**: Investigation; writing—original draft. **Lin Yuan**: Investigation; visualization; conceptualization; writing—original draft. **Zihan Wu**: Investigation; writing—original draft. **Xuguang Du**: Investigation; visualization; data curation. **Jacek Z. Kubiak**: Methodology; validation; resources. **Feng Yue**: Methodology; validation; resources. **Xuejing Yan**: Methodology; validation; resources. **Gaolin Jiang**: Visualization. **Yongye Huang**: Conceptualization; methodology; resources; supervision; writing—review and editing.

## ACKNOWLEDGMENTS

This study was funded by the National Natural Science Foundation of China (82201594, 81502582), National Key R&D Program of China (2023YFF1000200), the Natural Science Foundation of Liaoning Province (2022-MS-228), the Open Project of State Key Laboratory of Animal Biotech Breeding (2025SKLAB6-13), the Science and Technology Plan Joint Project of Liaoning Province-Doctoral Research Start-Up Fund Project (2023-BSBA-361), and the Polish Ministry of Education and Science (612/2023 at WIM-PIB).

## CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

## DATA AVAILABILITY STATEMENT

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

## ETHICS STATEMENT

Ethics approval was not needed in this study.

## ORCID

Lin Yuan https://orcid.org/0000-0002-6583-7333

Yongye Huang https://orcid.org/0000-0002-9083-250X

## REFERENCES

1. Kalia LV, Lang AE. Parkinson's disease. *Lancet*. 2015;386(9996):896-912. https://doi.org/10.1016/s0140-6736(14)61393-3

2. Li S-Y, Gong X-Y, Ndikuryayo F, Yang W-C. The emerging role of mitochondria oxygen redox in pathological progression of neurodegenerative disorders. *Ageing Res Rev*. 2025;104:102660. https://doi.org/10.1016/j.arr.2025.102660

3. Tysnes OB, Storstein A. Epidemiology of Parkinson's disease. *J Neural Transm*. 2017;124(8):901-905. https://doi.org/10.1007/s00702-017-1686-y

4. El Hayek M, Lobo Jofili Lopes JLM, LeLaurin JH, et al. Type, timing, frequency, and durability of outcome of physical therapy for Parkinson disease: a systematic review and meta-analysis. *JAMA Netw Open*. 2023;6(7):e2324860. https://doi.org/10.1001/jamane tworkopen.2023.24860

5. Tolosa E, Garrido A, Scholz SW, Poewe W. Challenges in the diagnosis of Parkinson's disease. *Lancet Neurol*. 2021;20(5):385-397. https://doi.org/10.1016/s1474-4422(21)00030-2

6. Thakur J, Godad A. Deciphering the role of neuropeptides as biomarkers for early diagnosis of Parkinson's disease. *Life Sci*. 2025; 363:123376. https://doi.org/10.1016/j.lfs.2025.123376

7. Dawson TM, Ko HS, Dawson VL. Genetic animal models of Parkinson's disease. *Neuron*. 2010;66(5):646-661. https://doi.org/10.1016/j.neuron.2010.04.034

8. Hu S, Tan J, Qin L, et al. Molecular chaperones and Parkinson's disease. *Neurobiol Dis*. 2021;160:105527. https://doi.org/10.1016/j.nbd.2021.105527

9. Domenighetti C, Sugier PE, Sreelatha AAK, et al. Mendelian randomisation study of smoking, alcohol, and coffee drinking in relation to Parkinson's disease. *J Parkinsons Dis*. 2022;12(1):267-282. https://doi.org/10.3233/JPD-212851

10. Poewe W. Treatments for Parkinson disease—past achievements and current clinical needs. *Neurology*. 2009;72(7_suppl_2):S65-S73. https://doi.org/10.1212/WNL.0b013e31819908ce

11. Hauser RA, Espay AJ, Ellenbogen AL, et al. IPX203 vs immediate-release carbidopa-levodopa for the treatment of motor fluctuations in Parkinson disease: the RISE-PD randomized clinical trial. *JAMA Neurol*. 2023;80(10):1062-1069. https://doi.org/10.1001/jamaneurol.2023.2679

12. da Costa Caiado MJ, Dolga AM, den Dunnen WFA. Iron(ing) out parkinsonisms: the interplay of proteinopathy and ferroptosis in Parkinson's disease and tau-related parkinsonisms. *Redox Biol*. 2025;79:103478. https://doi.org/10.1016/j.redox.2024.103478

13. Mayà G, Iranzo A, Gaig C, et al. Post-mortem neuropathology of idiopathic rapid eye movement sleep behaviour disorder: a case series. *Lancet Neurol*. 2024;23(12):1238-1251. https://doi.org/10.1016/s1474-4422(24)00402-2

14. Yu C, Cassar IR, Sambangi J, Grill WM. Frequency-specific opto-genetic deep brain stimulation of subthalamic nucleus improves parkinsonian motor behaviors. *J Neurosci*. 2020;40(22):4323-4334. https://doi.org/10.1523/jneurosci.3071-19.2020

15. Zhang C, Chen S, Li X, et al. Progress in Parkinson's disease animal models of genetic defects: characteristics and application. *Biomed Pharmacother*. 2022;155:113768. https://doi.org/10.1016/j.biopha.2022.113768

16. Blesa J, Przedborski S. Parkinson's disease: animal models and dopaminergic cell vulnerability. *Front Neuroanat*. 2014;8:155. https://doi.org/10.3389/fnana.2014.00155

17. Dovonou A, Bolduc C, Soto Linan V, Gora C, Peralta Iii MR, Lévesque M. Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions. *Transl Neurodegener*. 2023;12(1):36. https://doi.org/10.1186/s40035-023-00368-8

18. Capitanio JP, Emborg ME. Contributions of non-human primates to neuroscience research. *Lancet*. 2008;371(9618):1126-1135. https://doi.org/10.1016/s0140-6736(08)60489-4

19. Yin P, Li S, Li XJ, Yang W. New pathogenic insights from large animal models of neurodegenerative diseases. *Protein Cell*. 2022;13(10):707-720. https://doi.org/10.1007/s13238-022-00912-8

20. Commons KG, Cholanians AB, Babb JA, Ehlinger DG. The rodent forced swim test measures stress-coping strategy, not depression-like behavior. *ACS Chem Neurosci*. 2017;8(5):955-960. https://doi.org/10.1021/acschemneuro.7b00042

21. Otani T, Marchetto MC, Gage FH, Simons BD, Livesey FJ. 2D and 3D stem cell models of primate cortical development identify species-specific differences in progenitor behavior contributing to brain size. *Cell Stem Cell*. 2016;18(4):467-480. https://doi.org/10.1016/j stem.2016.03.003

22. Plum S, Steinbach S, Attems J, et al. Proteomic characterization of neuromelanin granules isolated from human substantia nigra by laser-microdissection. *Sci Rep*. 2016;6(1):37139. https://doi.org/10.1038/srep37139

23. Surmeier DJ, Obeso JA, Halliday GM. Selective neuronal vulnerability in Parkinson disease. *Nat Rev Neurosci*. 2017;18(2):101-113. https://doi.org/10.1038/nrn.2016.178

24. Zhang Q-S, Heng Y, Mou Z, Huang J-Y, Yuan Y-H, Chen N-H. Reassessment of subacute MPTP-treated mice as animal model of Parkinson's disease. *Acta Pharmacol Sin*. 2017;38(10):1317-1328. https://doi.org/10.1038/aps.2017.49
25. Najib NHM, Nies YH, Abd Halim SAS, et al. Modeling Parkinson's disease in zebrafish. *CNS Neurol Disord: Drug Targets*. 2020;19(5): 386-399. https://doi.org/10.2174/1871527319666200708124117

26. Ren Q, Jiang X, Zhang S, et al. Neuroprotective effect of YIAE-DAER peptide against Parkinson's disease like pathology in zebrafish. *Biomed Pharmacother*. 2022;147:112629. https://doi.org/10.1016/j.biopha.2022.112629

27. Zhang R, Quan H, Wang Y, Luo F. Neurogenesis in primates versus rodents and the value of non-human primate models. *Natl Sci Rev*. 2023;10(11):1-23. https://doi.org/10.1093/nsr/nwad248

28. Deycmar S, Gomes B, Charo J, Ceppi M, Cline JM. Spontaneous, naturally occurring cancers in non-human primates as a translational model for cancer immunotherapy. *J Immunother Cancer*. 2023;11(1): e005514. https://doi.org/10.1136/jitc-2022-005514

29. Bezard E, Fernagut PO. Premotor parkinsonism models. *Parkinsonism Relat Disord*. 2014;20(Suppl 1):S17-S19. https://doi.org/10.1016/s1353-8020(13)70007-5

30. Kamel F. Epidemiology. Paths from pesticides to Parkinson's. *Science*. 2013;341(6147):722-723. https://doi.org/10.1126/science.1243619

31. Vellingiri B, Chandrasekhar M, Sri Sabari S, et al. Neurotoxicity of pesticides – a link to neurodegeneration. *Ecotoxicol Environ Saf*. 2022;243:113972. https://doi.org/10.1016/j.ecoenv.2022.113972

32. Dauer W, Przedborski S. Parkinson's disease: mechanisms and models. *Neuron*. 2003;39(6):889-909. https://doi.org/10.1016/s0896-6273(03)00568-3

33. Schober A. Classic toxin-induced animal models of Parkinson's disease: 6-OHDA and MPTP. *Cell Tissue Res*. 2004;318(1):215-224. https://doi.org/10.1007/s00441-004-0938-y

34. Chiueh CC, Markey SP, Burns RS, Johannessen JN, Jacobowitz DM, Kopin IJ. Neurochemical and behavioral effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rat, guinea pig, and monkey. *Psychopharmacol Bull*. 1984;20(3):548-553.

35. Hughes AJ, Daniel SE, Kilford L, Lees AJ. Accuracy of clinical diagnosis of idiopathic Parkinson's disease: a clinico-pathological study of 100 cases. *J Neurol Neurosurg Psychiatry*. 1992;55(3):181-184. https://doi.org/10.1136/jnnp.55.3.181

36. Su LY, Li H, Lv L, et al. Melatonin attenuates MPTP-induced neurotoxicity via preventing CDK5-mediated autophagy and SNCA/α-synuclein aggregation. *Autophagy*. 2015;11(10):1745-1759. https://doi.org/10.1080/15548627.2015.1082020

37. Jeong HS, Lee SR, Kim JE, et al. Brain structural changes in cynomolgus monkeys administered with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine: a longitudinal voxel-based morphometry and diffusion tensor imaging study. *PLoS One*. 2018;13(1):e0189804. https://doi.org/10.1371/journal.pone.0189804

38. Carmona-Abellan M, Martínez-Valbuena I, DiCaudo C, Marcilla I, Luquin MR. Cardiac sympathetic innervation in the MPTP non-human primate model of Parkinson disease. *Clin Auton Res*. 2019;29(4):415-425. https://doi.org/10.1007/s10286-019-00620-0

39. Choudhury GR, Daadi MM. Charting the onset of Parkinson-like motor and non-motor symptoms in non-human primate model of Parkinson's disease. *PLoS One*. 2018;13(8):e0202770. https://doi.org/10.1371/journal.pone.0202770

40. Yun JW, Ahn JB, Kwon E, et al. Behavior, PET and histology in novel regimen of MPTP marmoset model of Parkinson's disease for long-term stem cell therapy. *Tissue Eng Regen Med*. 2016;13(1):100-109. https://doi.org/10.1007/s13770-015-0106-3

41. Phillips KA, Ross CN, Spross J, et al. Behavioral phenotypes associated with MPTP induction of partial lesions in common marmosets (*Callithrix jacchus*). *Behav Brain Res*. 2017;325(pt A):51-62. https://doi.org/10.1016/j.bbr.2017.02.010

42. Purisai MG, McCormack AL, Langston WJ, Johnston LC, Di Monte DA. Alpha-synuclein expression in the substantia nigra of MPTP-lesioned non-human primates. *Neurobiol Dis*. 2005;20(3):898-906. https://doi.org/10.1016/j.nbd.2005.05.028

43. Eslamboli A, Baker HF, Ridley RM, Annett LE. Sensorimotor deficits in a unilateral intrastriatal 6-OHDA partial lesion model of Parkinson's disease in marmoset monkeys. *Exp Neurol*. 2003;183(2):418-429. https://doi.org/10.1016/s0014-4886(03)00139-0

44. Joers V, Vermilyea SC, Dilley K, Emborg ME. Systemic administration of 6-OHDA to rhesus monkeys upregulates HLA-DR expression in brain microvasculature. *J Inflamm Res*. 2014;7:139-149. https://doi.org/10.2147/jir.s67285

45. Bové J, Perier C. Neurotoxin-based models of Parkinson's disease. *Neuroscience*. 2012;211:51-76. https://doi.org/10.1016/j.neuroscience.2011.10.057

46. Mitsumoto Y, Mori A, Ohashi S, Nakai M, Moriizumi T. Differential effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the olfactory bulb and the striatum in mice. *Neurosci Res*. 2005;51(1):111-115. https://doi.org/10.1016/j.neures.2004.09.012

47. Schulte C, Gasser T. Genetic basis of Parkinson's disease: inheritance, penetrance, and expression. *Appl Clin Genet*. 2011;4:67-80. https://doi.org/10.2147/tacg.S11639

48. Masilamoni GJ, Smith Y. Chronic MPTP administration regimen in monkeys: a model of dopaminergic and non-dopaminergic cell loss in Parkinson's disease. *J Neural Transm*. 2018;125(3):337-363. https://doi.org/10.1007/s00702-017-1774-z

49. Niu J, Zhong Y, Jin C, et al. Positron emission tomography imaging of synaptic dysfunction in Parkinson's disease. *Neurosci Bull*. 2024;40(6):743-758. https://doi.org/10.1007/s12264-024-01188-0

50. Meissner W, Prunier C, Guilloteau D, Chalon S, Gross CE, Bezard E. Time-course of nigrostriatal degeneration in a progressive MPTP-lesioned macaque model of Parkinson's disease. *Mol Neurobiol*. 2003;28(3):209-218. https://doi.org/10.1385/MN:28:3:209

51. Kikuchi T, Morizane A, Doi D, et al. Human iPS cell-derived dopaminergic neurons function in a primate Parkinson's disease model. *Nature*. 2017;548(7669):592-596. https://doi.org/10.1038/nature23664

52. Kowall NW, Hantraye P, Brouillet E, Beal MF, McKee AC, Ferrante RJ. MPTP induces alpha-synuclein aggregation in the substantia nigra of baboons. *Neuroreport*. 2000;11(1):211-213. https://doi.org/10.1097/00001756-200001170-00041

53. Ohno Y, Okita E, Kawai-Uchida M, et al. Anti-parkinsonian activity of the adenosine A(2A) receptor antagonist/inverse agonist KW-6356 as monotherapy in MPTP-treated common marmosets. *Eur J Pharmacol*. 2023;950:175773. https://doi.org/10.1016/j.ejphar.2023.175773

54. Bourque M, Grégoire L, Patel W, Dickens D, Snodgrass R, Di Paolo T. AV-101, a pro-drug antagonist at the NMDA receptor glycine site, reduces L-Dopa induced dyskinesias in MPTP monkeys. *Cells*. 2022;11(22):3530. https://doi.org/10.3390/cells11223530

55. Ungerstedt U, Ljungberg T, Steg G. Behavioral, physiological, and neurochemical changes after 6-hydroxydopamine-induced degeneration of the nigro-striatal dopamine neurons. *Adv Neurol*. 1974;5:421-426.

56. Gronlier E, Volle J, Coizet V, et al. Evoked responses to single pulse electrical stimulation reveal impaired striatal excitability in a rat model of Parkinson's disease. *Neurobiol Dis*. 2023;185:106266. https://doi.org/10.1016/j.nbd.2023.106266

57. Liu W, Zhang R, Feng H, Luo J, Zhu H. Increased expression of Nav1.6 of reactive astrocytes in the globus pallidus is closely associated with motor deficits in a model of Parkinson's disease. *Glia*. 2023;71(12):2850-2865. https://doi.org/10.1002/glia.24455

58. Dong LG, An MQ, Gu HY, et al. PACAP/PAC1-R activation contributes to hyperalgesia in 6-OHDA-induced Parkinson's disease model rats via promoting excitatory synaptic transmission of spinal dorsal horn neurons. *Acta Pharmacol Sin*. 2023;44(12):2418-2431. https://doi.org/10.1038/s41401-023-01141-3

59. Perese DA, Ulman J, Viola J, Ewing SE, Bankiewicz KS. A 6-hydroxydopamine-induced selective parkinsonian rat model. *Brain Res*. 1989;494(2):285-293. https://doi.org/10.1016/0006-8993(89)90597-0

60. Emborg ME. Nonhuman primate models of Parkinson's disease. *ILAR J*. 2007;48(4):339-355. https://doi.org/10.1093/ilar.48.4.339
<figure><img src="image_16.png" /></figure>

61. Annett LE, Rogers DC, Hernandez TD, Dunnett SB. Behavioural analysis of unilateral monoamine depletion in the marmoset. *Brain*. 1992;115(Pt 3):825-856. https://doi.org/10.1093/brain/115.3.825

62. Alves da Costa C, Dunys J, Brau F, Wilk S, Cappai R, Checler F. 6-Hydroxydopamine but not 1-methyl-4-phenylpyridinium abolishes alpha-synuclein anti-apoptotic phenotype by inhibiting its proteasomal degradation and by promoting its aggregation. *J Biol Chem*. 2006;281(14):9824-9831. https://doi.org/10.1074/jbc.M513903200

63. Paul KC, Krolewski RC, Lucumi Moreno E, et al. A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides. *Nat Commun*. 2023;14(1):2803. https://doi.org/10.1038/s41467-023-38215-z

64. Chia SJ, Tan EK, Chao YX. Historical perspective: models of Parkinson's disease. *Int J Mol Sci*. 2020;21(7):2464. https://doi.org/10.3390/ijms21072464

65. Manning-Bog AB, McCormack AL, Li J, Uversky VN, Fink AL, Di Monte DA. The herbicide paraquat causes up-regulation and aggregation of alpha-synuclein in mice: paraquat and alpha-synuclein. *J Biol Chem*. 2002;277(3):1641-1644. https://doi.org/10.1074/jbc.C100560200

66. Ossowska K, Wardas J, Smiałowska M, et al. A slowly developing dysfunction of dopaminergic nigrostriatal neurons induced by long-term paraquat administration in rats: an animal model of preclinical stages of Parkinson's disease? *Eur J Neurosci*. 2005;22:1294-1304. https://doi.org/10.1111/j.1460-9568.2005.04301.x

67. O'Leary KT, Parameswaran N, Johnston LC, McIntosh JM, Di Monte DA, Quik M. Paraquat exposure reduces nicotinic receptor-evoked dopamine release in monkey striatum. *J Pharmacol Exp Therapeut*. 2008;327(1):124-129. https://doi.org/10.1124/jpet.108.141861

68. Inden M, Kitamura Y, Abe M, Tamaki A, Takata K, Taniguchi T. Parkinsonian rotenone mouse model: reevaluation of long-term administration of rotenone in C57BL/6 mice. *Biol Pharm Bull*. 2011;34(1):92-96. https://doi.org/10.1248/bpb.34.92

69. Van Laar AD, Webb KR, Keeney MT, et al. Transient exposure to rotenone causes degeneration and progressive parkinsonian motor deficits, neuroinflammation, and synucleinopathy. *npj Parkinson's Dis*. 2023;9(1):121. https://doi.org/10.1038/s41531-023-00561-6

70. von Wrangel C, Schwabe K, John N, Krauss JK, Alam M. The rotenone-induced rat model of Parkinson's disease: behavioral and electrophysiological findings. *Behav Brain Res*. 2015;279:52-61. https://doi.org/10.1016/j.bbr.2014.11.002

71. Fehér M, Márton Z, Szabó Á, et al. Downregulation of PACAP and the PAC1 receptor in the basal ganglia, substantia nigra and centrally projecting Edinger-Westphal nucleus in the rotenone model of Parkinson's disease. *Int J Mol Sci*. 2023;24(14):11843. https://doi.org/10.3390/ijms241411843

72. Polymeropoulos MH, Lavedan C, Leroy E, et al. Mutation in the alpha-synuclein gene identified in families with Parkinson's disease. *Science*. 1997;276(5321):2045-2047. https://doi.org/10.1126/science.276.5321.2045

73. Yan S, Wang CE, Wei W, et al. TDP-43 causes differential pathology in neuronal versus glial cells in the mouse brain. *Hum Mol Genet*. 2014;23(10):2678-2693. https://doi.org/10.1093/hmg/ddt662

74. Recasens A, Dehay B, Bové J, et al. Lewy body extracts from Parkinson disease brains trigger α-synuclein pathology and neurodegeneration in mice and monkeys. *Ann Neurol*. 2014;75(3):351-362. https://doi.org/10.1002/ana.24066

75. Joers V, Masilamoni G, Kempf D, et al. Microglia, inflammation and gut microbiota responses in a progressive monkey model of Parkinson's disease: a case series. *Neurobiol Dis*. 2020;144:105027. https://doi.org/10.1016/j.nbd.2020.105027

76. Lautenschläger J, Stephens AD, Fusco G, et al. C-terminal calcium binding of α-synuclein modulates synaptic vesicle interaction. *Nat Commun*. 2018;9(1):712. https://doi.org/10.1038/s41467-018-03111-4

77. Tóth G, Gardai SJ, Zago W, et al. Targeting the intrinsically disordered structural ensemble of α-synuclein by small molecules as a

potential therapeutic strategy for Parkinson's disease. *PLoS One*. 2014;9(2):e87133. https://doi.org/10.1371/journal.pone.0087133

78. Isonaka R, Sullivan P, Goldstein DS. Pathophysiological significance of α-synuclein in sympathetic nerves: in vivo observations. *Neurology*. 2025;104(3):e210215. https://doi.org/10.1212/wnl.00000000000210215

79. Shahmoradian SH, Lewis AJ, Genoud C, et al. Lewy pathology in Parkinson's disease consists of crowded organelles and lipid membranes. *Nat Neurosci*. 2019;22(7):1099-1109. https://doi.org/10.1038/s41467-019-10423-2

80. Zarranz JJ, Alegre J, Gómez-Esteban JC, et al. The new mutation, E46K, of alpha-synuclein causes Parkinson and Lewy body dementia. *Ann Neurol*. 2004;55(2):164-173. https://doi.org/10.1002/ana.10795

81. Xu B, Fan F, Liu Y, Liu Y, Zhou L, Yu H. Distinct effects of familial Parkinson's disease-associated mutations on α-synuclein phase separation and amyloid aggregation. *Biomolecules*. 2023;13(5):726. https://doi.org/10.3390/biom13050726

82. Watt KJC, Meade RM, Williams RJ, Mason JM. Anionic lipid vesicles have differential effects on the aggregation of early onset-associated α-synuclein missense mutants. *J Biol Chem*. 2022;298(12):102565. https://doi.org/10.1016/j.jbc.2022.102565

83. Niu Y, Guo X, Chen Y, et al. Early Parkinson's disease symptoms in α-synuclein transgenic monkeys. *Hum Mol Genet*. 2015;24(8):2308-2317. https://doi.org/10.1093/hmg/ddu748

84. Kirik D, Annett LE, Burger C, Muzyczka N, Mandel RJ, Björklund A. Nigrostriatal alpha-synucleinopathy induced by viral vector-mediated overexpression of human alpha-synuclein: a new primate model of Parkinson's disease. *Proc Natl Acad Sci USA*. 2003;100(5):2884-2889. https://doi.org/10.1073/pnas.0536383100

85. Eslamboli A, Romero-Ramos M, Burger C, et al. Long-term consequences of human alpha-synuclein overexpression in the primate ventral midbrain. *Brain*. 2007;130(pt 3):799-815. https://doi.org/10.1093/brain/awl382

86. Li H, Wu S, Ma X, et al. Co-editing PINK1 and DJ-1 genes via adeno-associated virus-delivered CRISPR/Cas9 system in adult monkey brain elicits classical parkinsonian phenotype. *Neurosci Bull*. 2021;37(9):1271-1288. https://doi.org/10.1007/s12264-021-00732-6

87. Yang W, Liu Y, Tu Z, et al. CRISPR/Cas9-mediated PINK1 deletion leads to neurodegeneration in rhesus monkeys. *Cell Res*. 2019;29(4):334-336. https://doi.org/10.1038/s41422-019-0142-y

88. Chuapoco MR, Flytzanis NC, Goeden N, et al. Adeno-associated viral vectors for functional intravenous gene transfer throughout the non-human primate brain. *Nat Nanotechnol*. 2023;18(10):1241-1251. https://doi.org/10.1038/s41565-023-01419-x

89. Marmion DJ, Kordower JH. α-Synuclein non-human primate models of Parkinson's disease. *J Neural Transm*. 2018;125(3):385-400. https://doi.org/10.1007/s00702-017-1720-0

90. Burns RS, Chiueh CC, Markey SP, Ebert MH, Jacobowitz DM, Kopin IJ. A primate model of parkinsonism: selective destruction of dopaminergic neurons in the pars compacta of the substantia nigra by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. *Proc Natl Acad Sci USA*. 1983;80(14):4546-4550. https://doi.org/10.1073/pnas.80.14.4546

91. Morissette M, Di Paolo T. Non-human primate models of PD to test novel therapies. *J Neural Transm*. 2018;125(3):291-324. https://doi.org/10.1007/s00702-017-1722-y

92. Matsuda S, Kitagishi Y, Kobayashi M. Function and characteristics of PINK1 in mitochondria. *Oxid Med Cell Longev*. 2013;2013:601587. https://doi.org/10.1155/2013/601587

93. Bakhit Y, Ibrahim MO, Tesson C, et al. Intrafamilial and interfamilial heterogeneity of PINK1-associated Parkinson's disease in Sudan. *Parkinsonism Relat Disord*. 2023;111:105401. https://doi.org/10.1016/j.parkreldis.2023.105401

94. Hu J, Waters CH, Spiegelman D, et al. Gene-based burden analysis of damaging private variants in PRKN, PARK7 and PINK1 in Parkinson's disease cohorts of European descent. *Neurobiol Aging.*
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

2022;119:136-138. https://doi.org/10.1016/j.neurobiolaging.2022.07.012

95. Valente EM, Abou-Sleiman PM, Caputo V, et al. Hereditary early-onset Parkinson's disease caused by mutations in PINK1. *Science*. 2004;304(5674):1158-1160. https://doi.org/10.1126/science.1096284

96. Pickrell Alicia M, Youle RJ. The roles of PINK1, parkin, and mitochondrial fidelity in Parkinson's disease. *Neuron*. 2015;85(2):257-273. https://doi.org/10.1016/j.neuron.2014.12.007

97. Gasser T. Molecular pathogenesis of Parkinson disease: insights from genetic studies. *Expet Rev Mol Med*. 2009;11:e22. https://doi.org/10.1017/s1462399409001148

98. Yang W, Guo X, Tu Z, et al. PINK1 kinase dysfunction triggers neurodegeneration in the primate brain without impacting mitochondrial homeostasis. *Protein Cell*. 2022;13(1):26-46. https://doi.org/10.1007/s13238-021-00888-x

99. Zhou H, Falkenburger BH, Schulz JB, Tieu K, Xu Z, Xia XG. Silencing of the Pink1 gene expression by conditional RNAi does not induce dopaminergic neuron death in mice. *Int J Biol Sci*. 2007;3(4):242-250. https://doi.org/10.7150/ijbs.3.242

100. Kitada T, Pisani A, Porter DR, et al. Impaired dopamine release and synaptic plasticity in the striatum of PINK1-deficient mice. *Proc Natl Acad Sci USA*. 2007;104(27):11441-11446. https://doi.org/10.1073/pnas.0702717104

101. Kitada T, Tong Y, Gautier CA, Shen J. Absence of nigral degeneration in aged parkin/DJ-1/PINK1 triple knockout mice. *J Neurochem*. 2009;111(3):696-702. https://doi.org/10.1111/j.1471-4159.2009.06350.x

102. Zhou X, Xin J, Fan N, et al. Generation of CRISPR/Cas9-mediated gene-targeted pigs via somatic cell nuclear transfer. *Cell Mol Life Sci*. 2015;72(6):1175-1184. https://doi.org/10.1007/s00018-014-1744-7

103. Wang X, Cao C, Huang J, et al. One-step generation of triple gene-targeted pigs using CRISPR/Cas9 system. *Sci Rep*. 2016;6(1):20620. https://doi.org/10.1038/srep20620

104. Van der Perren A, Van den Haute C, Baekelandt V. Viral vector-based models of Parkinson's disease. *Curr Top Behav Neurosci*. 2015;22:271-301. https://doi.org/10.1007/7854_2014_310

105. Luna E, Luk KC. Bent out of shape: α-synuclein misfolding and the convergence of pathogenic pathways in Parkinson's disease. *FEBS Lett*. 2015;589(24, pt A):3749-3759. https://doi.org/10.1016/j.febslet.2015.10.023

106. Haque ME, Mount MP, Safarpour F, et al. Inactivation of Pink1 gene in vivo sensitizes dopamine-producing neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and can be rescued by autosomal recessive Parkinson disease genes, Parkin or DJ-1. *J Biol Chem*. 2012;287(27):23162-23170. https://doi.org/10.1074/jbc.M112.346437

107. Oliveras-Salvá M, Macchi F, Coessens V, et al. Alpha-synuclein-induced neurodegeneration is exacerbated in PINK1 knockout mice. *Neurobiol Aging*. 2014;35(11):2625-2636. https://doi.org/10.1016/j.neurobiolaging.2014.04.032

108. Chen ZZ, Wang JY, Kang Y, et al. PINK1 gene mutation by pair truncated sgRNA/Cas9-D10A in cynomolgus monkeys. *Zool Res*. 2021;42(4):469-477. https://doi.org/10.24272/j.issn.2095-8137.2021.023

109. Narendra D, Tanaka A, Suen DF, Youle RJ. Parkin is recruited selectively to impaired mitochondria and promotes their autophagy. *J Cell Biol*. 2008;183(5):795-803. https://doi.org/10.1083/jcb.200809125

110. Palacino JJ, Sagi D, Goldberg MS, et al. Mitochondrial dysfunction and oxidative damage in parkin-deficient mice. *J Biol Chem*. 2004;279(18):18614-18622. https://doi.org/10.1074/jbc.M401135200

111. Goldberg MS, Fleming SM, Palacino JJ, et al. Parkin-deficient mice exhibit nigrostriatal deficits but not loss of dopaminergic neurons. *J Biol Chem*. 2003;278(44):43628-43635. https://doi.org/10.1074/jbc.M308947200

112. Von Coelln R, Thomas B, Savitt JM, et al. Loss of locus coeruleus neurons and reduced startle in Parkin null mice. *Proc Natl Acad Sci*.

USA. 2004;101(29):10744-10749. https://doi.org/10.1073/pnas.0401297101

113. Yokota M, Kakuta S, Shiga T, et al. Establishment of an in vitro model for analyzing mitochondrial ultrastructure in PRKN-mutated patient iPSC-derived dopaminergic neurons. *Mol Brain*. 2021;14(1):58. https://doi.org/10.1186/s13041-021-00771-0

114. Kumaran R, Vandrovcova J, Luk C, et al. Differential DJ-1 gene expression in Parkinson's disease. *Neurobiol Dis*. 2009;36(2):393-400. https://doi.org/10.1016/j.nbd.2009.08.011

115. Ariga H, Takahashi-Niki K, Kato I, Maita H, Niki T, Iguchi-Ariga SM. Neuroprotective function of DJ-1 in Parkinson's disease. *Oxid Med Cell Longev*. 2013;2013:683920-683929. https://doi.org/10.1155/2013/683920

116. Imberechts D, Kinnart I, Wauters F, et al. DJ-1 is an essential downstream mediator in PINK1/parkin-dependent mitophagy. *Brain*. 2022;145(12):4368-4384. https://doi.org/10.1093/brain/awac313

117. Heremans IP, Caligiore F, Gerin I, et al. Parkinson's disease protein PARK7 prevents metabolite and protein damage caused by a glycolytic metabolite. *Proc Natl Acad Sci USA*. 2022;119(4):e2111338119. https://doi.org/10.1073/pnas.2111338119

118. Song IK, Kim MS, Ferrell JE, Jr., Shin DH, Lee KJ. Stepwise oxidations play key roles in the structural and functional regulations of DJ-1. *Biochem J*. 2021;478(19):3505-3525. https://doi.org/10.1042/bc20210245

119. Dolgacheva LP, Berezhnov AV, Fedotova EI, Zinchenko VP, Abramov AY. Role of DJ-1 in the mechanism of pathogenesis of Parkinson's disease. *J Bioenerg Biomembr*. 2019;51(3):175-188. https://doi.org/10.1007/s10863-019-09798-4

120. Alipour M, Hajipour-Verdom B, Zali A, et al. Interaction of α-synuclein with DJ-1 in homodimer and L166P mutant monomer forms in Parkinson's disease: a molecular dynamics study. *J Biomol Struct Dyn*. 2025:1-8. https://doi.org/10.1080/07391102.2024.2446660

121. Zhang X, Lai GY, Volpe G, et al. Towards a primate single-cell atlas. *Zool Res*. 2022;43(4):691-694. https://doi.org/10.24272/j.issn.2095-8137.2022.212

122. Li Q, Chen Y, Zhang W, et al. Mpox virus Clade IIb infected *Cynomolgus macaques* via mimic natural infection routes closely resembled human mpox infection. *Emerg Microb Infect*. 2024;13(1):2332669. https://doi.org/10.1080/22221751.2024.2332669

123. Saturday T, van Doremalen N. Pathogenesis of severe acute respiratory syndrome coronavirus-2 in non-human primates. *Curr Opin Virol*. 2023;63:101375. https://doi.org/10.1016/j.coviro.2023.101375

124. Anwar IJ, DeLaura I, Ladowski JM, et al. CD154 blockade effectively controls antibody-mediated rejection in highly sensitized non-human primate kidney transplant recipients. *Sci Transl Med*. 2025;17(779):eadn8130. https://doi.org/10.1126/scitranslmed.adn8130

125. Haggag AZ, Xu J, Butcher L, et al. Non-clinical and first-in-human characterization of ECC5004/AZD5004, a novel once-daily, oral small-molecule GLP-1 receptor agonist. *Diabetes Obes Metabol*. 2025;27(2):551-562. https://doi.org/10.1111/ dom.16047

126. Li C, Xiao Z, Li Y, et al. Deep learning-based activity recognition and fine motor identification using 2D skeletons of cynomolgus monkeys. *Zool Res*. 2023;44(5):967-980. https://doi.org/10.24272/j.issn.2095-8137.2022.449

127. Cesaroni V, Blandini F, Cerri S. Dyskinesia and Parkinson's disease: animal model, drug targets, and agents in preclinical testing. *Expert Opin Ther Targets*. 2022;26(10):837-851. https://doi.org/10.1080/14728222.2022.2153036

128. Sanchez G, Varaschin RK, Büeler H, Marcogliese PC, Park DS, Trudeau LE. Unaltered striatal dopamine release levels in young Parkin knockout, Pink1 knockout, DJ-1 knockout and LRRK2 R1441G transgenic mice. *PLoS One*. 2014;9(4):e94826. https://doi.org/10.1371/journal.pone.0094826

129. Yao YG, Lu L, Ni RJ, et al. Study of tree shrew biology and models: a booming and prosperous field for biomedical research. *Zool Res*. 2024;45(4):877-909. https://doi.org/10.24272/j.issn.2095-8137.2024.199
<figure><img src="image_19.png" /></figure>

130. Chemla A, Arena G, Sacripanti G, et al. Parkinson's disease mutant Miro1 causes mitochondrial dysfunction and dopaminergic neuron loss. *Brain*. 2025;6:awaf051. https://doi.org/10.1093/brain/awaf051

131. Yi LX, Woon HR, Saw G, Zeng L, Tan EK, Zhou ZD. Induced pluripotent stem cell-related approaches to generate dopaminergic neurons for Parkinson's disease. *Neural Regen Res*. 2025;20(11):3193-3206. https://doi.org/10.4103/nrr.Nrr-d-24-00771

132. Kim H, Kang S, Cho B, An S, Kim Y, Kim J. Parkinson's disease modeling using directly converted 3D induced dopaminergic neuron organoids and assembloids. *Adv Sci (Weinh)*. 2025;12(14):e2412548. https://doi.org/10.1002/advs.202412548

133. Yao YG. Creating animal models, why not use the Chinese tree shrew (*Tupaia belangeri chinensis*)? *Zool Res*. 2017;38(3):118-126. https://doi.org/10.24272/j.issn.2095-8137.2017.032

134. Li H, Mei L, Nie X, et al. The tree shrew model of Parkinson disease: a cost-effective alternative to non-human primate models. *Lab Invest*. 2024;104(11):102145. https://doi.org/10.1016/j.labinv.2024.102145

135. Luo S, Jiang H, Li Q, et al. An adeno-associated virus variant enabling efficient ocular-directed gene delivery across species. *Nat Commun*. 2024;15(1):3780. https://doi.org/10.1038/s41467-024-48221-4

136. Wiseman JP, Scarrott JM, Alves-Cruzeiro J, et al. Pre-clinical development of AP4B1 gene replacement therapy for hereditary spastic paraplegia type 47. *EMBO Mol Med*. 2024;16(11):2882-2917. https://doi.org/10.1038/s44321-024-00148-5

137. Drouyer M, Merjane J, Nedelkoska T, et al. Enhanced AAV transduction across preclinical CNS models: a comparative study in human brain organoids with cross-species evaluations. *Mol Ther Nucleic Acids*. 2024;35(3):102264. https://doi.org/10.1016/j.omtn.2024.102264

138. Fiorenzano A, Storm P, Sozzi E, et al. TARGET-seq: linking single-cell transcriptomics of human dopaminergic neurons with their target specificity. *Proc Natl Acad Sci USA*. 2024;121(47):e2410331121. https://doi.org/10.1073/pnas.2410331121

139. Lai MS, Sørensen MH, Lee K, Chu JM, Chang RC. 3D mapping of direct VTA-CA2 circuit with potential involvement in Parkinson's disease degeneration. *Neurobiol Dis*. 2024;202:106723. https://doi.org/10.1016/j.nbd.2024.106723

140. Senova S, Poupon C, Dauguet J, et al. Optogenetic tractography for anatomo-functional characterization of cortico-subcortical neural circuits in non-human primates. *Sci Rep*. 2018;8(1):3362. https://doi.org/10.1038/s41598-018-21486-8

141. Köhler RM, Binns TS, Merk T, et al. Dopamine and deep brain stimulation accelerate the neural dynamics of volitional action in Parkinson's disease. *Brain*. 2024;147(10):3358-3369. https://doi.org/10.1093/brain/awae219

142. Zhang H, Jiao L, Yang S, et al. Brain-computer interfaces: the innovative key to unlocking neurological conditions. *Int J Surg*. 2024;110(9):5745-5762. https://doi.org/10.1097/js9.0000000000002022

143. Jia Y, Oyken M, Kim RQ, et al. Development of inhibitors, probes, and PROTAC provides a complete toolbox to study PARK7 in the living cell. *J Med Chem*. 2024;67(10):7935-7953. https://doi.org/10.1021/acs.jmedchem.3c02410

144. Merk T, Peterson V, Lipski WJ, et al. Electrocorticography is superior to subthalamic local field potentials for movement decoding in Parkinson's disease. *eLife*. 2022;11:e75126. https://doi.org/10.7554/eLife.75126

145. Neumann WJ, Gilron R, Little S, Tinkhauser G. Adaptive deep brain stimulation: from experimental evidence toward practical implementation. *Mov Disord*. 2023;38(6):937-948. https://doi.org/10.1002/mds.29415

**How to cite this article:** Zhang S, Yuan L, Wu Z, et al. Non-human primate models of Parkinson's disease: decoding pathogenesis and advancing therapies. *Brain-X*. 2025;3:e70032. https://doi.org/10.1002/brx2.70032