RESUMO
Ca(2+) extrusion from the ß-cell is mediated by two processes the Na/Ca exchanger (NCX) and the plasma membrane Ca(2+) -ATPase (PMCA). Gain of function studies show that overexpression of NCX or PMCA leads to endoplasmic reticulum (ER) Ca(2+) depletion with subsequent ER stress, decrease in ß-cell proliferation and ß-cell death by apoptosis. Interestingly, chronic exposure to cytokines or high free fatty acid concentrations also induce ER Ca(2+) depletion and ß-cell death in diabetes. Loss of function studies show, on the contrary, that heterozygous inactivation of NCX1 (Ncx1(+/-)) leads to an increase in ß-cell function (insulin production and release), and a fivefold increase in both ß-cell mass and proliferation. The mutation also increases ß-cell resistance to hypoxia, and Ncx1(+/-) islets show a two to four times higher rate of diabetes cure than Ncx1(+/+) islets when transplanted in diabetic animals. Thus, down-regulation of the Na/Ca exchanger leads to various changes in ß-cell function that are opposite to the major abnormalities seen in diabetes. This provides a unique model for the prevention and treatment of ß-cell dysfunction in diabetes and following islet transplantation.
