Excitotoxicity and overnutrition additively impair metabolic function and identity of pancreatic β-cells

A sustained increase in intracellular Ca²⁺ concentration (referred to herein as excitotoxicity), brought on by chronic metabolic stress, may contribute to pancreatic b-cell failure. To determine the additive effects of excitotoxicity and overnutrition on b-cell function and gene expression, we analyzed the impact of a high fat diet (HFD) on Abcc8 knock-out mice. Excitotoxicity caused b-cells to be more susceptible to HFD-induced impairment of glucose homeostasis, and these effects were mitigated by verapamil, a Ca²⁺ channel blocker. Excitotoxicity, overnutrition and the combination of both stresses caused similar but distinct alterations in the b-cell transcriptome, including additive increases in genes associated with mitochondrial energy metabolism, fatty acid b-oxidation and mitochondrial biogenesis, and their key regulator Ppargc1a. Overnutrition worsened excitotoxicity-induced mitochondrial dysfunction, increasing metabolic inflexibility and mitochondrial damage. In addition, excitotoxicity and overnutrition, individually and together, impaired both b-cell function and identity by reducing expression of genes important for insulin secretion, cell polarity, cell junction, cilia, cytoskeleton, vesicular trafficking, and regulation of b-cell epigenetic and transcriptional program. Sex had an impact on all b-cell responses, with male animals exhibiting greater metabolic stress-induced impairments than females. Together, these findings indicate that a sustained increase in intracellular Ca²⁺, by altering mitochondrial function and impairing b-cell identity, augments overnutrition-induced b-cell failure.