New Insights into the Molecular Mechanisms of Islet Dysfunction in Human Diabetes
Walker, John T.
Pancreatic islets are central in the control of blood glucose and their dysfunction is a hallmark of diabetes. Incomplete knowledge of islet biology currently prevents diagnostic and therapeutic approaches based on molecular features in most forms of diabetes. Furthermore, there are significant experimental barriers to translation, including the difficulty in obtaining and mechanistically studying primary human islets which have known differences between common model systems. Thus, the primary goal of my research was to investigate the molecular mechanisms of human islet dysfunction in numerous forms of diabetes. Our team developed new approaches to mechanistically study human islets and pancreatic tissue, allowing us to manipulate the systemic environment and alter cellular and molecular features of the islet. To understand the pathogenesis of post-transplantation diabetes, we defined how immunosuppressive agents cause β cell dysfunction in vivo that is both reversible and preventable. We further highlighted the utility of in vivo models by showing that SGLT2 inhibitors, a commonly used diabetes medication, act indirectly on human islets through changes in blood glucose. To achieve efficient genetic and cellular manipulation of the human islet, we developed a novel pseudoislet system. Using genetically-encoded biosensors and a microfluidic device, we demonstrated cell-specific GPCR signaling pathways and investigated the formation and function of α cell-enriched pseudoislets. To identify critical features of human diabetes, we performed integrated analyses of tissue and islets, highlighting atypical findings of substantial insulin secretion in isolated islets from a donor with type 1 diabetes. We also used this integrative approach to identify disease driving mechanisms in human type 2 diabetes (T2D) and showed that β cell dysfunction, rather than loss, defines early T2D and that this is characterized by a disrupted islet microenvironment and RFX6-mediated transcriptional dysregulation. Given the substantial role of islet-enriched transcription factors in multiple forms of diabetes, we utilized both single cell RNA-seq and shRNA knockdown experiments to investigate transcriptional regulatory networks and islet function controlled by RFX6, MAFA, MAFB, and ARX. Overall, my work provides new molecular insights into islet physiology and pathophysiology and paves the way for more effective and precise diagnosis and treatment of individuals with diabetes.