Disrupted Endoplasmic Reticulum Ca 2+ Handling: A Harβinger of β-Cell Failure.

The β-cell workload increases in the setting of insulin resistance and reduced β-cell mass, which occurs in type 2 and type 1 diabetes, respectively. The prolonged elevation of insulin production and secretion during the pathogenesis of diabetes results in β-cell ER stress. The depletion of β-cell Ca 2+ ER during ER stress activates the unfolded protein response, leading to β-cell dysfunction. Ca 2+ ER is involved in many pathways that are critical to β-cell function, such as protein processing, tuning organelle and cytosolic Ca 2+ handling, and modulating lipid homeostasis. Mutations that promote β-cell ER stress and deplete Ca 2+ ER stores are associated with or cause diabetes (e.g., mutations in ryanodine receptors and insulin). Thus, improving β-cell Ca 2+ ER handling and reducing ER stress under diabetogenic conditions could preserve β-cell function and delay or prevent the onset of diabetes. This review focuses on how mechanisms that control β-cell Ca 2+ ER are perturbed during the pathogenesis of diabetes and contribute to β-cell failure.