β-cell NCK1 is reduced in type 2 diabetes, impairing the unfolded protein response and insulin secretion while revealing sex-specific adaptation

Abstract

Type 2 diabetes is characterized by failure of pancreatic {beta} cells to adapt insulin secretion to metabolic demand, causing {beta} cell function and reduced {beta} cell mass. The unfolded protein response (UPR) is central to adaptation by maintaining endoplasmic reticulum homeostasis and supporting insulin biosynthesis, secretion, proliferation, and survival. NCK1, is an adaptor protein that regulates insulin biosynthesis and UPR activation, positioning it at the crossroads of several processes essential for {beta} cell function. We found in mouse and human islets that NCK1 expression was upregulated by glucose and reduced in individuals living with type 2 diabetes. We thus explored the importance of {beta} cell NCK1 in endocrine function and glucose homeostasis using INS 1 cells, mouse and human islets, and {beta} cell specific knockout male and female mice (NCK1{beta}KO). Loss of {beta} cell NCK1 disrupted the UPR and impaired insulin gene expression, insulin content, and glucose stimulated insulin secretion in vitro. Unexpectedly, these intrinsic {beta} cell defects triggered sex-specific adaptive responses at the organismal level, revealing distinct strategies to reshape glucose homeostasis. Under high fat/high sucrose diet, both NCK1{beta}KO female and male mice increased pancreatic insulin content, but females exhibited impaired insulin secretion associated with an increased number of small islets and reduced PERK pathway activation resulting in mild glucose intolerance. In contrast, males NCK1{beta}KO mice had improved insulin secretion associated with islet expansion, {beta} cell proliferation, and increased PERK pathway activation leading to enhanced glucose tolerance. These findings identify NCK1 as a regulator of {beta} cell insulin synthesis, secretion, and UPR signaling, and reveal sex specific adaptive mechanisms to metabolic stress. Thus, reduced NCK1 in islets from people living type 2 diabetes may contribute to {beta} cell dysfunction.