Dynamin function in beta cell autophagy

Medical College Of Wisconsin, Milwaukee WI

Investigators

Abstract

PROJECT SUMMARY Diabetes affects over 30 million Americans, yet its epidemic is still rising at an alarming rate. The progressive decline of pancreatic ? 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 ? cells against pathogens and diabetic stress. However, the fundamental nature of ? 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 ? cell autophagy. Live-cell imaging reveals that dynamin molecules translocate to autolysosomes and drive autolysosome fission. Conditional dynamin deletion causes striking autophagy defects in ? cells. These new findings fuel tremendous interest in understanding the molecule mechanisms at play throughout the ? cell autophagy cycle. We hypothesize that dynamin plays a direct and crucial role in ? cell autophagy that has not been characterized. Mechanistically, we suspect that dynamin regulates ? cell autophagy through regulating autolysosome fission and autophagic transport. These processes may be essential to protect ? cells against chronic metabolic stress. We have assembled a team with substantial expertise in ? 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 ? 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 ? cells use dynamin to resolve their autolysosomes into lysosomes in autophagy. Second, we will investigate how dynamin regulates ? 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 ? cell autophagy in vivo. We have generated dynamin isoform-specific mouse models. These unique models make it possible to evaluate dynamin-regulated ? 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 ? cell autophagy mediated by different dynamin isoforms. Their outcomes will advance the fundamental understanding of ? cell autophagy that profoundly impacts islet function and diabetes pathogenesis.