Beta-cell replacement strategies for the future management of insulin-dependent diabetes will require amplification of pancreatic islet tissue in vitro for transplantation or induction of new islets by stimulating islet growth within the diabetic patient. Accordingly, fundamental issues to address before these goals can be met will be the identification and manipulation of mechanisms that efficiently expand functional beta-cell mass. We have developed and characterized both normoglycemic and transiently hyperglycemic glucose-infused rats whereby a rapid expansion of beta-cell mass occurs without proliferation. These rats exhibit striking increases in the prevalence of beta-cell neogenesis associated with both the ductal epithelium and acinar tissue. The potential contribution of these nascent beta-cells to new or pre-existing islets is not known. We have also recently identified key insulin-signaling intermediates associated with the expression of beta-cell transcription factors in these tissues. However, the interplay of growth factors and integrated signaling pathways that control compensatory beta-cell neogenesis and islet mass expansion are far from being resolved. We propose that a principal mechanism mediating beta-cell neogenesis and islet mass expansion during a glucose challenge is activation of the insulin-signaling pathway through IRS-2 and the downstream serine/threonine protein kinase B/Akt (Akt). Using our glucose infusion models, we propose to initially focus on the insulin-signaling pathway's activation of beta-cell neogenic events occurring in ducts. We will then examine the nature and mechanisms by which islet beta-cell mass rapidly increases. Finally, we will determine the source of the """"""""acinar-associated"""""""" beta-cells and investigate the mechanism of how they may contribute to pre-existing or, possibly, new islets. These studies will establish the foundation for future endeavors to exploit signaling pathways and the factors involved to manipulate and efficiently expand functional beta-cell mass for potential therapies to treat type 1 and severe type 2 diabetic patients.
