Profiling of Midbrain Neuronal Vulnerability in Parkinson's Disease

Project Summary/Abstract Parkinson’s disease (PD) is the second leading neurodegenerative disorder in the United States with patients manifesting motor and psychiatric complications. As the global population ages, the prevalence of PD will increase accompanied by emotional and economic burden. PD is characterized by the degeneration of neuromelanin-containing dopaminergic (DA) neurons in the substantia nigra (SN). It remains poorly understood how this degeneration occurs. The use of single-cell RNA sequencing has significantly advanced our understanding of neurodegenerative disease–several studies in mouse midbrains identify the heterogeneity of DA neurons; however, limited studies have been conducted in human samples. To fill this gap, we have performed single-nucleus RNA sequencing (snRNAseq) and profiled the cells from healthy and PD human SN, which identified a novel degenerating neuronal population in PD that is highly enriched with RIT2 but lacks tyrosine hydroxylase (TH), a typical marker for DA neurons (RIT2+/TH-). It is not known whether non-DA neurons in the SN are also vulnerable in PD. Immunostaining of aged healthy and PD human and murine SN samples validated the distinct RIT2 populations (RIT2+/TH+, RIT2+/TH-). This proposal aims to characterize distinct RIT2 neuronal subpopulations in the SN to elucidate its cellular heterogeneity and to identify potential mechanisms underlying the complexity of PD symptoms. The driving hypotheses are that subpopulations of RIT2 neurons in the SN are distinct from DA neurons with unique morphology, function, and circuits (AIM 1) and that RIT2 neuronal subpopulations in the SN are vulnerable to PD-associated pathogenesis (AIM 2). Aim 1 will characterize the novel RIT2-expressing neuronal subpopulations in mouse SN. Aim 2 will assess the vulnerability of RIT2 neuronal subpopulations in both PD mouse models and human midbrain neurons. These studies will elucidate whether non-DA neurons in the SN are degenerating in PD and they will characterize distinct RIT2 subpopulations in the SN, providing mechanistic insights into the complexity of PD and identify pathways warranting further exploration for therapeutic development. This proposal is highly innovative because it will characterize a novel midbrain neuron type with vulnerability in PD that may lead to insights into resilience mechanisms. This proposal will also generate several novel model systems in both mice and hiPSC, which will be available to the research community. Completion of this proposal will provide rigorous multidisciplinary training for the candidate in assessing cell circuit innervations, transcriptomics, cell viability, and functional testing of neuronal subpopulations in transgenic mice and hiPSCs. This fellowship will enrich and accelerate the career of a promising PhD student with demonstrated dedication to research in aging-related neurodegenerative disorders and education. The training will be conducted in a highly multidisciplinary and collaborative environment in the Department of Neuroscience at Icahn School of Medicine at Mount Sinai, a leading institution with emphasis in translational and transformative discoveries.