PROJECT SUMMARY Diabetes affects over 30 million Americans, yet its epidemic is still rising at an alarming rate. The progressive decline of pancreatic β cell function and mass is a hallmark of diabetes, but no medications prevent this decline. Interestingly, a fasting-mimicking diet known to activate autophagy stops this decline and reverses diabetes in mice. Accordingly, recent progress has increasingly recognized autophagy as a potential therapeutic target to treat diabetes because of its role in protecting β cells against pathogens and metabolic stress. However, the basic nature of β cell autophagy remains poorly understood, particularly in the molecular process governing autophagic membrane fission. Our recent data uncover that dynamin, a subfamily of large GTPases known to regulate endocytosis and insulin secretion, directly alters β cell autophagy. Live-cell imaging suggests that dynamin molecules can translocate to autolysosomes and drive autolysosome fission. Dynamin deletion causes striking autophagy defects in β cells in vitro and in vivo. These new findings fuel tremendous interest in understanding the molecule mechanisms at play throughout the β cell autophagy cycle. We hypothesize that dynamin plays a direct and crucial role in β cell autophagy flux that has not been characterized previously. Mechanistically, we suspect that dynamin regulates β cell autophagy through regulating autolysosome fission and autophagic transport. These processes may be essential to protect β cells against chronic metabolic stress toward diabetes. To test the hypothesis, we have generated dynamin isoform-specific mouse models, which allow evaluating dynamin-regulated β cell autophagy and its protection against metabolic stress associated with diabetes. We have assembled a team with substantial expertise in β cell biology, super-resolution imaging, biochemical signaling, and diabetes. We will focus on three specific aims. First, define the role of dynamin in β cell autolysosome fission. The fission step is necessary for autolysosome-to-lysosome transformation in each autophagic cycle of β cells, but its mechanism remains poorly understood. Second, identify the role of dynamin in regulating autophagic transport via microtubule modulation. This aim may uncover a previously unappreciated pathway for dynamin to regulate autophagy in β cells. Third, examine how dynamin regulates β cell autophagic responses upon metabolic stress in vivo. Together, these studies will provide new insights into the autophagic turnover in β cells and its regulation by different dynamin isoforms. The results will advance the fundamental understanding of β cell autophagy cycles that profoundly impacts islet function and diabetes pathogenesis.