Our goal is to elucidate molecular mechanism for neuroprotective autophagy in Huntington's disease (HD) and determine therapeutic potential for selective autophagy in treating the disease. HD is caused by an aberrant expansion of CAG repeat (polyQ) in the HTT gene, which leads to a toxic gain-of-function in the mutant huntingtin (mHTT) protein. Despite over 20 years' research, disease-modifying therapeutics is unavailable. Thus, elucidation of the disease mechanism and mHTT clearance pathways is pivotal for the success of therapeutic development. Autophagy is a catabolic cellular pathway that clears protein aggregates and injured organelles through lysosomes as a quality control system. PolyQ-expanded protein aggregates including fragments of HTT can be degraded by selective autophagy, and thus selective autophagy is considered a drug target for HD. However, autophagy is a complex process subjected to tight regulation, and how exactly autophagy selectively degrade mHTT remains poorly understood. We previously showed that ULK1 regulates p62-mediated selective autophagy under proteotoxic stress. In the context of mHTT, however, we reported dysregulation of ULK1 kinase activity that connects to reduced VPS34 activity and aberrant p62-selective autophagy in the brains of HD model zQ175. Our current study suggests that ULK1 deficiency accelerates mHTT-mediated toxicity. The data thus provides strong evidence for the role of ULK1-p62 mediated selective autophagy in regulating mHTT toxicity. We hypothesize that ULK1 and p62 are promising modifiers of HD disease progression. We propose (1) to determine the role and mechanism for ULK1-p62 signaling in the degradation of mHTT through selective autophagy; (2) to investigate pathogenic mechanism that mHTT disrupts ULK1 kinase activity and causes ULK1 deficiency-mediated selective autophagy impairment and neurotoxicity; (3) determine ULK1 kinase activity as a therapeutic target to inhibit mHtt-mediated neurotoxicity using animal models through genetic and pharmacological approaches. Our study is expected to reveal molecular mechanism for ULK1 protective function against HD and validate ULK1 kinase activity as a drug target for the clearance of mHTT and offering neuroprotection.
