SPOP modifies neurodegenerative proteinopathy in Alzheimer’s Disease.

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PROJECT SUMMARY Aggregated pathological tau protein constitutes one of the diagnostic hallmarks of Alzheimer’s disease (AD) and related disorders (ADRD). The molecular mechanisms by which pathological tau causes dysfunction and degeneration of neurons remain incompletely understood. However, pathological tau driven neuronal dysfunction and neurodegeneration clearly cause dementia. To investigate how pathological tau contributes to neurodegeneration in AD and ADRDs, we established a transgenic model in Caenorhabditis elegans for neurodegeneration driven by human tau aggregation. By employing classical forward genetic approaches, we identified several genes whose loss of function suppresses tauopathy, including spop-1. SPOP (speckle-type POZ protein) is a conserved nuclear adaptor protein for the RING E3 ubiquitin ligase Cullin-3 (CUL3), selecting proteins for degradation in the ubiquitin proteasome system (UPS). After generating a true null allele via CRISPR- cas9, we found that loss of spop-1 dramatically decreases tau accumulation and phosphorylation without altering tau mRNA abundance, rescues lifespan, reduces neurodegeneration, and improves behavioral deficits in tau transgenic animals. In addition to its role in UPS activity, SPOP also undergoes liquid-liquid phase separation (LLPS) localizing to nuclear speckles (NS). Our previously work in C. elegans and AD neurons indicate disruptions to NS function and composition contribute to tau toxicity. Remarkably, loss of spop-1 also rescues C9orf72 dipeptide-repeat toxicity in a C. elegans model of genetic amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Our preliminary results indicate loss of spop-1 suppresses behavioral deficits in C. elegans expressing ALS-linked mutant TDP-43 as well as transgenics co-expressing TDP-43 and tau, which recalculate AD and ADRD relevant interactions. Altogether, our work led us to hypothesize that SPOP functions as a multipurpose regulator of proteinopathy in AD and ADRDs. We hypothesize SPOP-CUL3 UPS activity and SPOP LLPS/NS localization contribute to the underlying mechanisms of tauopathy. To investigate these hypothesizes the specific aims of this project are: SPECIFIC AIMS: (1) Characterize SPOP loss of function in AD/ADRD neurodegenerative proteinopathies, (2) Determine the mechanism by which SPOP loss of function suppresses tauopathy, and (3) Evaluate the translational relevance of SPOP in Alzheimer’s disease. By completing the proposed work, we will uncover new molecular understandings of disease mechanisms including how SPOP protein – as well as nuclear speckles and Cullin-3 – participate in tauopathy and related ADRD co-pathologies. This work will also provide insight into the translational relevance of SPOP in Alzheimer’s disease brains, setting the stage for future study and informing the development of novel therapeutics.