IFNα differentially disrupts stimulus-secretion coupling in pancreatic alpha and beta cells

Abstract

Aims/hypothesis: IFN contributes to early islet inflammation and beta cell immunogenicity in type 1 diabetes, but its direct effects on endocrine cell function remain incompletely understood. We investigated whether acute IFN exposure disrupts glucose-regulated insulin and glucagon secretion and whether the underlying alterations in stimulus-secretion coupling differ between beta and alpha cells. Methods: Male and female mice received IFN before an IPGTT, during which blood glucose and serum insulin and glucagon concentrations were measured. Hormone secretion and intracellular Ca2+ dynamics were assessed in isolated mouse islets and in MIN6, EndoC-{beta}H1 and TC1.9 cells following IFN exposure. Sarco/endoplasmic reticulum Ca2+-ATPase 2 (SERCA2) protein levels and SERCA activity were measured in microsome-enriched fractions. Mitochondrial respiration was evaluated in intact and digitonin-permeabilised cells, including separate assessment of NADH-linked and succinate-linked pathways. Results: Acute IFN administration activated interferon signalling in isolated islets and altered glucose and hormone responses in vivo. IFN increased glucose area under the curve in male mice but did not significantly affect glucose tolerance in female mice. The circulating insulin response to glucose was reduced in both sexes, while basal serum glucagon was reduced in female mice. In isolated islets, IFN reduced glucose-stimulated insulin secretion in males and reduced 3-isobutyl-1-methylxanthine-potentiated insulin secretion in both sexes. IFN also diminished glucose-mediated suppression of glucagon secretion in islets and attenuated the inhibitory effects of glucose and insulin in TC1.9 cells. Intracellular Ca2+ signalling was impaired in primary islet cells and endocrine cell lines. IFN did not significantly affect cell viability, reactive oxygen species production, proliferation or endocrine cell composition. IFN reduced SERCA2 protein levels in MIN6 and EndoC-{beta}H1 cells and impaired SERCA function in both models. By contrast, IFN did not alter SERCA2 abundance or SERCA activity in TC1.9 cells but reduced mitochondrial respiratory parameters. In permeabilised TC1.9 cells, NADH-linked respiration was reduced, whereas succinate-linked respiration, mitochondrial mass and respiratory-chain complex abundance remained unchanged. Conclusions/interpretation: Acute IFN exposure disrupts endocrine cell stimulus-secretion coupling in the absence of cytotoxicity. Although intracellular Ca2+ signalling was impaired in both beta and alpha cells, the associated alterations were cell-type selective, involving reduced SERCA2 abundance and SERCA activity in beta cells and impaired NADH-linked mitochondrial respiration in alpha cells. These findings extend the pathogenic role of IFN beyond immune activation and beta cell immunogenicity to include direct dysregulation of insulin and glucagon secretion.