## 7 Molecular Effects of Nanoplastics in Processes of Neurotoxicity
### Nanoplastics Affect the Transcriptomics and Epigenomic in Neuronal Models
The study revealed alterations in stress response genes (_lsp27/lspB1_, _lsp70/lspA5_, and _lsp90a_), with a notable increase in mRNA expression of _lsp27/lspB1_, which plays crucial roles in neurodegenerative diseases such as AD and MS. Additionally, 30 nm PS-NPs induced altered expression of _Cu/ZnSOD1_ and catalase, along with inflammatory and mitochondrial responses in the same in vitro neural model [143]. In another study, PS-NPs beads (25 nm) were exposed for 1 day to a modified human neuronal cell model (SH-SYSY cell line) overexpressing \(\alpha\)-synuclein, a protein associated with the formation of pathological inclusions (Lewy bodies) in the brains of individuals with Parkinson's disease. The penetration of PS-NPs into the cells further increased \(\alpha\)-synuclein aggregation, suggesting potential implications for human neurodegeneration [144]. Brain organoids are complex 3D cell models differentiated from human embryonic stem cells which have emerged as innovative in vitro models for neurodevelopmental studies and neurological diseases (see, e.g., [145] for a comprehensive review). The transcriptomic analysis of DEGs in this 3D in vitro model exposed to 100 nm PS-NPs revealsthe molecular mechanisms in which _Wnt_, _PI3K-Akt_, and _TGF-beta_ signaling pathways are the most enriched [146]. The _Wnt_ and _PI3K-Akt_ are recognized signaling pathway in [PERSON]'s disease [147; 148], and _TGF-beta_ is a common feature of neurodegenerative disorders and particularly in ALS [149]. Important cues as to the comprehension of neurotoxicological effects of NPs derive from animal models, which can be used to transfer systemic data to humans. Among these, zebrafish (_Danio rerio_) is a National Institute of Health (NIH)-validated model organism for studies in (neuro)developmental toxicology due to its high genomic conservation with humans, and it represents an emerging model in toxicity studies of MPs and NPs [150]. Exposure of larval zebrafish to PS-NPs (50-200 nm) alters transcriptome analysis, affecting gene functions related to neurodegeneration and motor dysfunction. DEGs related to nervous system sub-pathways, including movement disorders, neuromuscular diseases, morphology of the nervous system, and development of neurons, are affected by NPs [151]. In the adult model, the same authors observe alterations in movement disorders and neuromuscular disease pathways, including basal ganglia, dyskinesia, and cerebellar hypoplasia. Upregulation of the membrane protein trafficking gene _ap1s2_, involved in basal ganglia disease in humans, and downregulation of _ali1_, associated with cerebellar development in mice and humans, are induced in adult zebrafish upon exposure to NPs. Additionally, multiple neuromuscular genes and cytoskeletal genes are downregulated, while genes related to synaptic signaling and pumps are upregulated. In addition, multiple neuromuscular genes (e.g., skeletal muscle subunit _mythb_ and axonal transport genes _bcd2_ and _kiflab_, encoding for axonal transport proteins in the opposite directions, retrograde vs. anterograde, respectively) and cytoskeletal gene _prph_ are downregulated. PS-NPs (25-134 nm) at concentrations which can be environmentally encountered (0.1 and 0.5 mg/L) were exposed to zebrafish to perform a battery of behavioral and gene expression assays. PS-NPs affected genes of the hypothalamic-pituitary-thyroid axis and of the dopamine metabolism [152]. These transcriptomics findings in this animal model, with structures and functions homologous to those of mammals and humans, provide crucial insights into the mechanisms of NPs implicated in promoting neurological and neuromuscular disorders. Epigenetic evaluations provide important insights into transcriptomics studies, with epigenetics encompassing a wide range of heritable changes in gene expression in response to various environmental factors, such as pollutants, diet, smoke, and lifestyle factors, without DNA sequence modifications.