A major investment of the Kulkarni lab is in investigating the significance of the growth factor (e.g. insulin and IGF) signaling pathways in the modulation of glucose sensing of beta cells, proinsulin processing, mitochondrial function, protection against apoptosis and ER stress and in regulating the expression of transcription factors in islet cells. We continue to create genetic models to examine the roles of insulin and IGF-1 and -2 receptors and their substrates (insulin receptor substrates; IRS-1,2,3,4) and proteins downstream (e.g. Akt, FoxO1, PDX-1) in islet biology. For example, we have used Cre-LoxP and Flp-Frt techniques to create beta- or alpha-cell-specific knockout of multiple proteins to complement in vitro models using primary islets from humans and rodents and derived beta and alpha cell lines from the knockouts. Using these powerful and unique reagents we are investigating cross-talk between insulin, IGF-I, glucose and incretin (glucagon like-peptide-1) and leptin signaling mechanisms in islet cells. A major effort is directed towards evaluating specificity of insulin versus IGF signaling and their substrates in islet cell biology during embryonic and adult life. We are studying pathways utilized by lymphocytes that allow regeneration of beta cells in type 1 diabetes using NOD mice. To investigate the high incidence of type 2 diabetes in obese individuals we propose a potential link between adipocyte-derived factors (e.g. leptin) and growth factor signaling pathways at the level of the islet, to underlie islet function and growth. This hypothesis is being examined using islet-cell-specific knockouts of insulin and/or IGF-1 receptors and their substrates and the leptin receptor (ObRb) in mice. These studies will advance the field on several fronts – first, it will allow us to gain greater insights into the fundamental physiological mechanisms that govern the normal proliferation of the cell types and secretory function of the pancreatic islets; second, it will provide a physiological basis to identify targets in signaling pathways that would be useful to design potential therapeutic strategies to prevent islet cell death and to plan alternative approaches to generate new beta cells to prevent and/or cure type 1 and type 2 diabetes.
While there continues to be debate regarding the origin of human and rodent islet cells, a major focus in our laboratory is to derive induced pluripotent stem (iPS) cells from skin fibroblasts and/or blood cells derived from living human donors (MODY and type 1 and type 2 diabetes patients) and rodent models with the long term goal of differentiating them into mature islet cells (e.g. insulin, glucagon secreting cells). There is also a focus on differentiating iPS cells into cells that are targets for complications observed in patients with type 1 and type 2 diabetes (e.g. vascular endothelial cells, neuronal cells, kidney cells, retinal pericytes). These approaches allow us to generate unique cells that maintain the genetic make-up of the living individual that would otherwise be unavailable, with the potential for characterizing their signaling properties, and for screening drugs to identity the most effective medications for individual patients. We are using transplantation and parabiotic approaches and techniques that allow us to investigate inter-organ communication and the identification of circulating islet cell growth factors (e.g. between islets and liver or white/brown adipose). Identification of these putative factors will have the potential for harnessing them into therapeutics to enhance functional beta cell mass to counter type 1 and type 2 diabetes.