Developing the potential of blood-based biomarkers for neurodegenerative disease
Creators: name: Chowdhury, Md Anisuzzaman
Publisher: name: University of Tasmania
Year: 2024

description: Neurodegenerative diseases (NDDs) are a rapidly growing problem, especially in the older population. Dementia, which is a common clinical outcome of NDDs, is now the second leading cause of death in Australia. The brain pathology associated with NDD begins to develop many years before clinical symptoms, opening a window of opportunity for early intervention. Furthermore, there is evidence that up to 40% cases of dementia could be prevented by modifying lifestyle factors. Therefore, it is critical to pick up early changes and to monitor brain health for prevention and treatment. Pathologically, each neurodegenerative disorder is defined by the accumulation of a specific protein or proteins which may be useful as biomarkers to detect NDDs. Additionally, several proteins are showing promise as biomarkers of neurodegeneration or brain health, which can be useful in monitoring disease progression or early detection of brain changes. To develop the utility of biomarkers clinically, it is essential to develop dependable biomarkers and biomarker tests that are readily accessible to predict and diagnose disease.<br>Biomarkers of brain health and pathology could be important to advance the diagnostic workup in the clinic, particularly during the early disease stages and for monitoring the effectiveness of new therapeutic strategies. These biomarkers can be measured from the biological fluids (e.g., CSF and blood). Blood-based biomarkers are ideal for disease diagnosis and monitoring as they are accessible, less invasive, and less expensive compared to other fluid biomarkers. However, various challenges exist to develop blood-based biomarkers for clinical utility. Firstly, biomarker detection in blood depends on availability of sensitive assays and appropriate biosensors. Currently, most biomarkers assays depend on antibodies, which have limitations in terms of cost, shelf-life, and batch to batch variation. Aptamers are short single stranded DNA or RNA oligonucleotides that are capable of binding specific target molecules, which could be an alternative to antibodies for biomarker assays. Secondly, while it has been documented that specific biomarkers are altered in blood of people with NDD, we do not yet understand why they are altered and whether they correlate with the pathological changes in the brain as well as functional changes. This is important to understand so that we can interpret biomarker changes and whether they actually reflect changes in the brain.<br>Therefore, the first aim of this thesis was to develop the capacity for aptamers in biomarkers assays of brain health. Brain-derived neurotrophic factor (BDNF) is an extensively investigated neurotrophin, that has been investigated in several NDDs as well as more generally in brain health. A repetitive in vitro selection technique called systematic evolution of ligands by exponential enrichment (SELEX) was used to develop aptamers against human recombinant BDNF protein and an aptamer-linked immobilised sorbent assay (ALISA) was performed to validate these aptamers against the BDNF protein. This thesis identified a DNA aptamer that showed high sensitivity and selectivity against human recombinant BDNF protein, which was confirmed by ALISA assay.<br>The second aim of this thesis was to undertake measurement of serum biomarkers of neurodegeneration and neuropathology, including neurofilament light (NfL), phosphorylated tau 181 (p-tau181), neurogranin (Ng) and neuron specific enolase (NSE) in a repressible mouse model of tauopathy (rTg4510 mice). This thesis determined how biomarkers changed when pathology induction was switched off to mimic successful treatment. Biomarkers were correlated to neuropathology and functional changes. Biomarkers were analysed using single molecular array (Simoa®) technology. This thesis found a significant difference in the levels of blood biomarkers between transgenic (TG) mice and wildtype (WT) mice that were modified by pathology removal in a sex-specific manner. The data suggests there was a correlation between blood biomarkers and brain pathology in rTg4510 mice.<br>In brief, the findings of this thesis suggest that aptamers may be developed against brain health biomarkers for use in sensitive and accessible diagnostic and detection assays. Furthermore, this thesis demonstrated that blood-biomarkers reflected the neuronal cell loss and neurodegeneration in the brain of rTg4510 mice and therefore may be useful for predicting pathology changes and monitoring therapeutic effects in clinical trials.