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 the disease, but no medications prevent this decline. Interestingly, a fasting-mimicking diet known to activate autophagy stops this decline, and it also reverses diabetes in mice. Recent progress has increasingly recognized autophagy as a potential therapeutic target to treat diabetes because autophagy has a role in protecting β cells against pathogens and diabetic stress. However, the fundamental nature of β cell autophagy remains poorly understood, particularly in the molecular process governing autophagic membrane fission. Our recent data reveal that dynamin, a family of large GTPase proteins known to regulate endocytosis and insulin secretion, directly alters β cell autophagy. Live-cell imaging reveals that dynamin molecules translocate to autolysosomes and drive autolysosome fission. Conditional dynamin deletion causes striking autophagy defects in β cells. 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 that has not been characterized. 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. We have assembled a team with substantial expertise in β cell biology, super-resolution imaging, biochemical signaling, mouse genetic models, and diabetes to test this hypothesis. We propose three specific aims. First, we will define the role of dynamin in β cell autolysosome fission. This fission step is necessary for autolysosome-to-lysosome transformation in each autophagic cycle, but its mechanism remains poorly understood. We expect that β cells use dynamin to resolve their autolysosomes into lysosomes in autophagy. Second, we will investigate how dynamin regulates β cell microtubules to alter autophagic transport. These studies may uncover a previously unappreciated pathway for dynamin to regulate autophagy. Third, we will examine dynamin- regulated β cell autophagy in vivo. We have generated dynamin isoform-specific mouse models. These unique models make it possible to evaluate dynamin-regulated β cell autophagy in vivo and its protection against the metabolic stress of diabetes. Together, these studies will provide new insight into the molecular regulation of β cell autophagy mediated by different dynamin isoforms. Their outcomes will advance the fundamental understanding of β cell autophagy that profoundly impacts islet function and diabetes pathogenesis.