Studies of Brain-Derived Small Extracellular Vesicles in Neurodegenerative Disease Biomarker Development

Abstract

Alzheimer's disease (AD) is a pathophysiologically complex and heterogeneous condition and the predominant form of dementia in aging individuals, which may be responsible for as many as 70% of dementia cases. Conventional hallmarks of AD have provided limited information about the underlying molecular mechanisms facilitating the disease onset and cognitive impairment. Furthermore, concomitant pathological phenomena, such as brain insulin dysregulation, have yet to be explained in the context of the disease. Moreover, without the use of specialized imaging facilities, most, if not all current biomarkers of AD, cannot identify brain region-specific molecular changes during the disease progression. Firstly, we sought to establish whether we could develop a novel method capable of characterizing the surface proteome of brain tissue-derived sEV with high specificity—this would require a strategy adept at minimizing contamination from intravesicular proteins and proteins of the digested parent tissue, thereby permitting a more precise surface biomarker identification. Secondly, we were prompted by the potential of brain-derived sEV cargo, specifically their microRNA (miRNA) profiles, as a prospective diagnostic tool which could provide a less-invasive distinction between healthy and neuropathological changes of the brain, offering new outlook in the detection of neurodegenerative diseases. Finally, we hypothesized that sEV originating from discrete brain regions might display unique surface proteomes that would not only allow for their identification, and subsequent enrichment, within peripheral biofluids, such as plasma, but also mirror the specific pathological changes indicative of various neurological conditions. The experiments outlined in this thesis provide evidence that sEV can be used not only as a novel biomarker for neurodegenerative diseases, including AD, but may also provide an improved specificity over other blood-based biomarkers as their surface proteins enable brain region-specific identification.