Project IV: In Vivo Dissection of Genetic Modifiers on Different Stages of Synucleinopathy

PROJECT SUMMARY Project IV: In Vivo Dissection of Genetic Modifiers on Different Stages of Synucleinopathy Lewy body diseases (LBDs) are defined by the presence of intraneuronal inclusions containing misfolded alpha- synuclein (aSyn). Lewy bodies (LBs) and Lewy neurites (LNs) are also prominent in ~50% of Alzheimer’s disease (AD) patients. Postmortem studies of individuals with LBDs show that LB/LN distribution and burden in the central, peripheral and enteric nervous systems (CNS, PNS, ENS) closely parallels disease progression. Despite a clear link between aSyn pathology and neurodegeneration, the mechanisms that combine to give rise to the stereotypical non-uniform evolution of pathology observed during LBD progression remain unresolved. In particular, there is limited knowledge of how the majority of the >90 genetic risk factors currently identified for LBD modulate susceptibility to disease and contribute to the clinical heterogeneity observed in LBDs. We hypothesize that this clinical heterogeneity likely results from interactions between emerging aSyn pathology and host genetic background. Endo-lysosomal proteins are highly represented in LBD risk loci and our recent work has demonstrated that two risk genes TMEM175 and GPNMB modulate aSyn pathology through different functions. We postulate that different endo-lysosomal LBD risk genes, although ubiquitously expressed, may exert distinct effects during prodromal vs. advanced stages of disease. We will address these central questions by examining the effects of TMEM175 and GPNMB gene dose on outcome in mouse models of LBD, where synucleinopathy is seeded into different circuits representative of early vs. advanced LBD. Using aSyn fibril- based models we previously developed, we will interrogate both cell-autonomous and non-autonomous contributions of genetic factors on disease progression by comparing the pattern of pathological aSyn spread, degeneration and subsequent phenotypes between following inoculation of aSyn PFFs or human LBD-derived aSyn to different in vivo circuits that recapitulate REM-sleep disturbances that characterize prodromal LBD, or motor and limbic typically representative of later LBD stages. For each target, animals will be compared at multiple timepoints using behavioral, histological, and in silico modeling tools, thus identifying the mode and time window of influence for each specific LBD risk gene. Project IV’s studies therefore extend the work of Projects I, II and III into a whole-animal context, allowing for in vivo modeling of the roles key genetic modifiers and aSyn strains play in the spread of synucleinopathy, at different stages of disease.