Roles of autophagy and transcription factor EB (TFEB) in β-cell viability and function

Diabetes affects more than 500 million people worldwide and results in serious health complications that contribute to millions of deaths annually. Diabetes is characterized by high blood glucose levels resulting from insufficient insulin production due to dysfunction and loss of insulin-producing pancreatic β-cells. The success of islet transplantation as a functional cure for autoimmune type 1 diabetes is also hindered by dysfunction and death of transplanted β-cells. Autophagy is a conserved cellular process that helps maintain cell function and survival by lysosomal degradation and recycling of damaged cellular components under stress. However, the role of autophagy in β-cell survival under hypoxia and following islet transplantation remains unclear. Furthermore, recent evidence suggests that failure of β-cell autophagy may contribute to β-cell dysfunction and the development of both type 1 and type 2 diabetes, but the underlying mechanisms are not understood. This dissertation investigates the importance of autophagy and lysosomal homeostasis in pancreatic β-cells under diabetes- and transplantation-relevant stress. We created a mouse model with β-cell-specific deletion of the autophagy-related gene Atg5 and demonstrated that basal autophagy is essential for maintaining glucose tolerance and β-cell survival. We further found that autophagy protects β-cells under hypoxic stress and during islet transplantation, as loss of autophagy exacerbated β-cell death and islet graft failure. Prolonged hypoxia was found to impair autophagic flux, and this was associated with lysosomal dysfunction and decreased β-cell levels of Tfeb, a transcriptional master regulator of lysosomes and autophagy. By pharmacologically activating Tfeb, we were able to restore lysosomal function and improve β-cell viability under stress. To further understand the role of Tfeb in β-cells, we generated a β-cell-specific Tfeb knockout mouse. Loss of β-cell Tfeb made the mice more susceptible to streptozotocin-induced hyperglycemia but did not worsen glucose tolerance under high-fat diet-induced stress, possibly due to compensation by the related transcription factor Tfe3. The research in this dissertation highlights the protective role of autophagy in β-cells under stress and identifies Tfeb dysregulation as a factor in pathogenic β-cell autophagy loss. Targeting Tfeb may offer a therapeutic strategy to improve clinical islet transplantation outcomes and enhance β-cell resilience in diabetes.