Diabetes mellitus and the key role of endoplasmic reticulum stress in pancreatic β cells.

Insufficient insulin secretion by pancreatic β cells is central to the pathogenesis of diabetes mellitus. As insulin is synthesized in the endoplasmic reticulum (ER), perturbations in ER homeostasis lead to ER stress and activate the ER stress response. Over the past two decades, considerable data have accumulated on the role of β cell ER stress in diabetes mellitus. Several monogenic forms of diabetes mellitus are caused by excessive ER stress, perturbed ER stress response signalling or impaired ER-Golgi protein trafficking. These pathways are now recognized to contribute to β cell failure in both type 1 and type 2 diabetes mellitus. This Review considers the role of β cell ER stress in common forms of diabetes mellitus and examines whether it is a cause or a consequence of these diseases. The strong genetic evidence for a causal role of ER stress in 15 monogenic forms of diabetes mellitus is summarized, and the effects of ER stress on human β cell differentiation, function and survival are described. Although definitive proof is lacking that ER stress responses can be therapeutically targeted to improve β cell function in diabetes mellitus, existing and novel treatments that aim to restore ER homeostasis are also outlined.