Autophagy in Diabetes

Diabetes mellitus is characterized by decreased insulin secreti on and action. Decreased insulin secretion results from a reduction in mass and/or function of pancreatic β-cells. Apoptosis, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress responses have been suggested as mechanisms for the changes in β -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 β-cell mass in autophagy-deficient mice. Pancreatic insulin content was also decreased due to the decreased β-cell mass and the reduced number of insulin granules. Morphological analysis of these β-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 β-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 β-cell homeostasis, dysregulated autophagy may possibly be involved in insulin resistance. (Korean Diabetes J 33:453-457, 2009)