Distinguishing α-Synuclein S129 Phosphorylation in Health and Lewy Body Dementia - SUMMARY/ABSTRACT α-Synuclein (αS) is an abundant presynaptic protein that regulates neurotransmission. αS orchestrates neurotransmitter release by synaptic vesicle cycling, clustering of synaptic vesicles, and dilation of the fusion pore during exocytosis. αS is also a central protein implicated in Parkinson’s disease (PD), PD with dementia (PDD), dementia with Lewy bodies (DLB), and Alzheimer’s disease (AD). αS-rich deposits, Lewy bodies (LB), and Lewy neurites (LN) are the pathological hallmarks of these devastating diseases. Remarkably, about 90% of αS in the LB and LN is in its serine 129 phosphorylated form (pS129). Therefore, pS129 is widely used as a surrogate marker for pathology. However, we recently demonstrated that physiological pS129 is triggered by neuronal activity and positively regulates synaptic transmission. These unexpected and intriguing results raise the critical question of whether normal and abnormal pS129 can be distinguished. We believe distinguishing normal and abnormal pS129 will help us better understand the processes leading to the pathology and refine pS129 as a marker for diseases with LBs. Eventually, these will contribute to developing meaningful therapeutic interventions. Currently, disease- modifying treatments for PD, PDD, and DLB are not available, partly due to a lack of insight into how native αS dynamics become aberrant and its consequence. The sequence of molecular events that turns the states of normal αS into pathological forms over time is a complex topic. Obviously, environmental factors, excess αS, missense mutations in αS, and other genetic risk factors influence the conversion of “good” αS into “bad”. Our long-term goal is to understand the normal biology of αS and test how their functions are compromised under pathological conditions by exploiting the factors that accelerate αS dyshomeostasis. We then seek to convert “bad αS” back to “good αS” based on the knowledge we gained from this work to mitigate symptoms of PD, LB Dementia (LBD), which includes PDD and DLB. Our objectives in this application are to (i) compare the biochemical properties of physiological and pathological pS129 and (ii) describe whether or to what extent the normal synaptic transmission mediated by pS129 is compromised in PD/LBD models. The central hypothesis flows from our recent data on pS129 being part of normal αS homeostasis: we hypothesize that dynamic activity-dependent pS129 reversibility is impaired when normal αS homeostasis is pathologically perturbed. The rationale for this project is that understanding normal and abnormal pS129 in neurons is likely to offer a solid scientific foundation whereby new strategies for preserving normal pS129 homeostasis, correcting αS imbalance, and quantifying signatures of αS pathology can be developed. To achieve the overall objectives, two specific aims will be pursued: 1. Determine whether or to what extent dynamic activity- dependent pS129 is impaired in familial and sporadic models of PD/LBD, and 2. Determine whether normal functions of pS129 are affected in αS-based PD/LBD models. It is unequivocally accepted that highly insoluble αS present in LBs mainly comprises pS129. In our recent report, we described activity-dependent physiological reversible pS129, regulated by the CaN-Plk2-PP2A pathway. In many ways, the concept of physiological pS129 is new, particularly the dynamic reversibility of pS129. In that regard, the research proposed in this application is innovative because it uses the novel concept of dynamic reversibility of pS129 to distinguish “good” and “bad” pS129. Our contributions are expected to be significant because a) our work will elucidate the differences in the biological properties of normal and abnormal pS129 that occur in physiological and pathological states, respectively; b) by establishing these distinctions, we will lay the groundwork for future studies, by us and others, to refine pS129 as a pathological marker and, potentially,
