Mechanistic basis for endoplasmic reticulum-driven cytoprotection by selective autophagy in neurons

SUMMARY. Neurodegenerative diseases, as age-dependent disorders, represent a rising hazard to human health in America, given the rapidly growing number of seniors in its population. For this reason, the development of novel therapies to treat neurodegenerative diseases has become a national priority. These disorders are often characterized by the incorrect folding of certain proteins, accumulation of cytotoxic macromolecular structures, and changes in intracellular stress response capacity - our proposal aims to identify a means to resolve these conditions. Numerous labs over the last decade have elucidated mechanisms underlying selective autophagy - the process by which damaged organelles, protein aggregates, or misfolded proteins are targeted to the autophagosome for degradation in the lysosome. Our understanding of autophagy is that it controls a large fraction of regulated protein homeostasis in human cells, particularly post-mitotic cells (i.e., a cell that does not divide) like neurons. While autophagy is broadly associated with the turnover of proteins or organelles, several autophagy-related genes have been specifically genetically linked with aging and neurodegenerative cellular signaling pathways. Despite these advances, our understanding of how neuronal cells use and rely on specific forms of autophagy via specialized proteins called receptors is incomplete for several reasons. First, most studies have focused on a small number of well-studied receptors, and systematic approaches aimed at uncovering the global contribution of known and other possible receptors are lacking, leaving major gaps in our understanding of the many roles these proteins may play. Second, the majority of studies have focused on processes in cancer cell lines in culture, and we know very little about the cell type-relevant roles of selective autophagy receptors in neuronal homeostasis. Third, although we know that selective autophagy receptors are regulated dynamically, we still have a relatively rudimentary understanding of the signaling pathways that control receptor engagement in physiological or stress-induced states. Here, we propose a series of experiments that seek to address limitations in our understanding of the neuronal selective autophagy pathways, their regulation, and their function. In the first series of experiments (AIM 1), we will build on preliminary data to elucidate the role of an endoplasmic reticulum membrane-bound receptor we identified to be regulated upon nutrient stress in neurons, and reveal the molecular mechanisms involved in its regulation and the nature of the substrate turned over. A second series of experiments (AIM 2) will be focused on investigating the cellular specificity across neuroimmune cell subtypes, response to pathological cues modeled in iPSCs, and functional and physiological relevance using knock-out mouse models. Together, these studies will quantitatively, mechanistically, and functionally address gaps in our understanding of the neuronal relevant functions of this selective autophagy pathway and the mechanisms by which substrates are selected for lysosomal recycling.