Therapeutic Strategies to Increase Human β-Cell Growth and Proliferation by Regulating mTOR and GSK-3/β-Catenin Pathways

摘要

This perspective delineates approaches to develop therapeutic strategies to stimulate the proliferative potentialof adult human β-cells in vitro. Previous findings demonstrated that nutrients, through regulation of mTOR signaling,promote regenerative processes including DNA synthesis, cell cycle progression and β-cell proliferation in rodent isletsbut rarely in human islets. Recently, we discovered that regulation of the Wnt/GSK-3/β-catenin pathway by directlyinhibiting GSK-3 with pharmacologic agents, in combination with nutrient activation of mTOR, was required to increasegrowth and proliferation in human islets. Studies also revealed that nuclear translocation of β-catenin in response to GSK-3 inhibition regulated these processes and was rapamycin sensitive, indicating a role for mTOR. Human islets displayed ahigh level of insulin resistance consistent with the inability of exogenous insulin to activate Akt and engage the Wntpathway by GSK-3 inhibition. This insulin resistance in human islets is not present in rodent islets and may explain thedifferential requirement in human islets to inhibit GSK-3 to enhance these regenerative processes. Human islets exhibitednormal insulin secretion but a loss of insulin content, which was independent of all treatment conditions. The loss ofinsulin content may be related to insulin resistance, the isolation process or culture conditions. In this perspective, weprovide strategies to enhance the proliferative capacity of adult human β-cells and highlight important differencesbetween human and rodent islets: the lack of a nutrient response, requirement for direct GSK-3 inhibition, insulinresistance and loss of insulin content that emphasize the physiological significance of conducting studies in human islets.