PERK EIF2alpha kinase regulates cell proliferation, insulin synthesis and secretion in pancreatic beta cells.

摘要

Insulin synthesis and secretion, as well as cell proliferation are under tight regulation in pancreatic beta-cells to maintain glucose homeostasis. Dysfunction in any of these aspects leads to development of diabetes. PERK (EIF2AK3) is essential for normal development and function of the insulin-secreting beta-cell. Genetic ablation of PERK in humans and mice results in permanent neonatal diabetes featuring insufficient beta-cell mass, impaired insulin synthesis and ablated insulin secretion. However, previous attempts to identify the primary functions of PERK were confounded by those severe abnormalities within PERK-deficient beta-cells. Here, I used a newly developed and highly specific inhibitor of PERK to determine the immediate effects of acute PERK activity inhibition. Stimulated subcellular Ca2+ signaling and insulin secretion in human and rodent beta-cells was found to be rapidly reduced as a consequence of acute inhibition of PERK. These PERK-dependent dysfunctions stem from alterations in store-operated Ca2+ entry, sarcoplasmic-endoplasmic reticulum Ca2+ ATPase activity, and possibly some of the transient receptor potential channels. I also found that PERK regulates calcineurin, and pharmacological inhibition of calcineurin results in similar defects on stimulus-secretion coupling. My findings by using PERK inhibitor demonstrate that PERK acutely regulates beta-cell Ca2+ signaling and insulin secretion.;In addition, I used an alternative strategy to identify the primary functions of PERK by examining mice with one copy of the loss-of function Perk mutation (Perk heterozygous mice). Longitudinal studies were conducted to assess serum glucose and insulin, intracellular insulin synthesis and storage, insulin secretion, and beta-cell proliferation in Perk heterozygous mice. I found that Perk heterozygous mice first exhibited elevated proinsulin synthesis, changes in ER chaperone expression, and enhanced insulin secretion during neonatal and juvenile development, followed by enhanced beta-cell proliferation and a substantial increase in beta-cell mass at the adult stage. These effects of Perk heterozygosity are opposite to what has been learned from previously studies using Perk knockout mice and therefore suggest an inverted U-shaped dose effect on insulin production and secretion with half-dosage (Perk heterozygotes) defining the maximum. Moreover, because commonly used sensitive markers for ER stress were not differentially expressed in Perk heterozygous mice, these PERK-dependent differences are not likely to entail the well-known function of PERK in ER stress response.;Taken together my thesis work suggests that PERK has two major functions in the pancreatic beta-cells: 1) acutely regulating insulin secretion through modulation of Ca2+ dynamics in a calcineurin-dependent pathway; and 2) impacting proinsulin folding and quality control in a longer-term through modulation of ER chaperone expression. These two major functions of PERK coordinate with each other and influence whole-body insulin production and glucose homeostasis.