Abstract

Diabetes mellitus is characterized by decreased insulin secretion and action. Decreased insulin secretion results from a reduction in mass and/or function of pancreatic beta-cells. Apoptosis, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress responses have been suggested as mechanisms for the changes in beta-cells in type 2 diabetes; however, the underlying causes have not been clearly elucidated. Autophagy is an intracellular process that maintains cellular homeostasis through degradation and recycling of organelles. Recently, we reported reduction of beta-cell mass in autophagy-deficient mice. Pancreatic insulin content was also decreased due to the decreased beta-cell mass and the reduced number of insulin granules. Morphological analysis of these beta-cells revealed an accumulation of ubiquitinated proteins, swollen mitochondria, and distended ER. Insulin secretory function ex vivo was also impaired. As a result, autophagy-deficient mice showed hypoinsulinemia and hyperglycemia. These results suggested that autophagy is necessary to maintain the structure, mass and function of beta-cells. In addition, as autophagy may play a protective role against ER stress and rejuvenate organelle function, impaired autophagy may lead to mitochondrial dysfunction and ER stress, which have been implicated as causes of insulin resistance. Therefore, in addition to beta-cell homeostasis, dysregulated autophagy may possibly be involved in insulin resistance.

• Keywords: Autophagy;Diabetes mellitus;Endoplasmic reticulum;Insulin-secreting cells;Mitochondria;