PROJECT III SUMMARY/ABSTRACT Heterogeneity of Outcomes in Synucleinopathies: Insights from Genomics and Proteomics While patients with Lewy body disorders (LBD) share the core feature of deposition of misfolded alpha-synuclein (aSyn) into neuropathological inclusions, they exhibit pronounced heterogeneity in both initial clinical phenomenology, as well as in trajectory of cognitive outcomes. The reasons for these differences in phenomenology among synucleinopathy patients are not well understood, but these differences matter greatly for quality of life for patients and their families, as well as costs to the healthcare system. The central tenet of this Project is that host characteristics play an important role in determining which LBD patients manifest with cognitive impairment at disease onset vs. years into disease vs. decades into disease vs. not at all. The goal of Project III is to investigate the host characteristics represented by common genetic risk variants (associated with risk for DLB, PD, and cognitive impairment in the LBD), as well as those host characteristics represented in protein biomarker signatures, in order to uncover mechanisms that drive cognitive decline in the LBD. We will do this through three specific aims. SPECIFIC AIM 1: Assign target genes to loci associated with risk for LBD as well as cognitive decline within PD. More than 90 loci have been reported to associate with PD risk or DLB risk by GWAS, with additional loci reported to associate with cognitive decline within PD. The vast majority of these loci are non-coding, and target genes are unclear. We will assign target genes based on colocalization analyses, comparing our work with existing reports and confirming expression quantitative trait locus (eQTL) effects in PD brain tissue with allele-specific expression (ASE) assays. SPECIFIC AIM 2: Perform causal inference analyses for biomarkers associating with cognitive outcome in PD. We will perform CSF biomarker screens and investigate biomarker leads emerging from these CSF screens as well as our previously-performed plasma biomarker screens of thousands of proteins in multiple cohorts of PD patients. We will evaluate these leads for a causal role in cognitive decline by performing Mendelian randomization-based causal inference analyses. SPECIFIC AIM 3: Determine effects of nominated targets on development of aSyn pathology in cortical iPSC-N. Preliminary data suggest that Aims 1 and 2 will generate 20-40 potential targets for downstream manipulation in induced pluripotent stem cell-derived neurons (iPSC-N). We will prioritize these leads based on the strength of both the genomic and proteomic evidence in order to select 5-15 targets. We will use CRISPR- based techniques to manipulate expression of the selected targets in cortical iPSC-N, in order to determine effects on uptake of fibrillar aSyn, cell-to-cell transmission of aSyn species, and development of aSyn pathology.