Regulation of Pancreatic β-Cell Regeneration in the Normoglycemic 60% Partial-Pancreatectomy Mouse

Abstract

β-Cell mass is determined by a dynamic balance of proliferation, neogenesis, and apoptosis. The precise mechanisms underlying compensatory β-cell mass (BCM) homeostasis are not fully understood. To evaluate the processes that maintain normoglycemia and regulate BCM during pancreatic regeneration, C57BL/6 mice were analyzed for 15 days following 60% partial pancreatectomy (Px). BCM increased in Px mice from 2 days onwards and was ∼68% of the shams by 15 days, partly due to enhanced β-cell proliferation. A transient ∼2.8-fold increase in the prevalence of β-cell clusters/small islets at 2 days post-Px contributed substantially to BCM augmentation, followed by an increase in the number of larger islets at 15 days. To evaluate the signaling mechanisms that may regulate this compensatory growth, we examined key intermediates of the insulin signaling pathway. We found insulin receptor substrate (IRS)2 and enhanced-activated Akt immunoreactivity in islets and ducts that correlated with increased pancreatic duodenal homeobox (PDX)1 expression. In contrast, forkhead box O1 expression was decreased in islets but increased in ducts, suggesting distinct PDX1 regulatory mechanisms in these tissues. Px animals acutely administered insulin exhibited further enhancement in insulin signaling activity. These data suggest that the IRS2-Akt pathway mediates compensatory β-cell growth by activating β-cell proliferation with an increase in the number of β-cell clusters/small islets.