A major element in the pathophysiology of type 2 diabetes is inadequate insulin secretion in response to insulin resistance. Identifying the molecular mechanisms responsible for the impaired human beta cell response to insulin resistance and therapies optimal for islet survival and function has been slowed by both experimental limitations. Most studies of the islet response to insulin resistance have been performed with rodent islets, but human and rodent islets differ substantially in architecture, cell composition, proliferative capacity, susceptibility to injury, and ability to form islet amyloid. Most studies of human beta cells in experiments intended to mimic insulin resistance (in vitro exposure to fat, glucose, oxidative stress, etc.) have been conducted in vitro because there has been a lack of methodology to study human beta cells in situ. Our team of investigators proposes studies to directly address these gaps in our scientific knowledge using new models and approaches to study the response of human islets in response to insulin resistance in vivo by testing two hypotheses: 1) insulin resistance promotes a multi-level response in human islets (changes in gene expression, ER stress, vascularity);and 2) some currently used therapies for type 2 diabetes are advantageous in promoting islet function and survival in the setting of insulin resistance. The studies will utilize new models that allow human islets to be studied after transplantation into immunodeficient mice that have genetic or dietary forms of insulin resistance (GLUT4 knockout, ob/ob mice, and high fat feeding). We propose three aims: 1) Define the molecular, cellular and vascular changes in human beta cells when they are challenged with insulin resistance in vivo. 2) Investigate which current therapies for type 2 diabetes preserve and/or enhance human beta cell function or survival when human islets are challenged with insulin resistance in vivo. 3) Determine if the in vivo changes in human beta cells in response to insulin resistance resolve when the challenge of insulin resistance is removed. By assessing beta cell function, gene expression, function, and survival, these studies should provide insight and understanding into the islet dysfunction of type 2 diabetes and into which therapeutic agents are most effective in improving human islet function and survival.
Type 2 diabetes is a major health problem in the VA system (as many as 20% of the VA population are afflicted with diabetes) and thus, diabetes is a major source of morbidity and mortality. Current treatment is inadequate and the proposed studies will improve our understanding of how insulin secretion becomes impaired and what are the optimal therapies for type 2 diabetes.