Jeffrey Kristin D, Alejandro Emilyn U, Luciani Dan S, Kalynyak Tatyana B, Hu Xiaoke, Li Hong, Lin Yalin, Townsend R Reid, Polonsky Kenneth S, Johnson James D
Diabetes Research Group, Laboratory of Molecular Signalling in Diabetes, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada.
Proc Natl Acad Sci U S A. 2008 Jun 17;105(24):8452-7. doi: 10.1073/pnas.0711232105. Epub 2008 Jun 11.
Obesity is a principal risk factor for type 2 diabetes, and elevated fatty acids reduce beta-cell function and survival. An unbiased proteomic screen was used to identify targets of palmitate in beta-cell death. The most significantly altered protein in both human islets and MIN6 beta-cells treated with palmitate was carboxypeptidase E (CPE). Palmitate reduced CPE protein levels within 2 h, preceding endoplasmic reticulum (ER) stress and cell death, by a mechanism involving CPE translocation to Golgi and lysosomal degradation. Palmitate metabolism and Ca(2+) flux were also required for CPE proteolysis and beta-cell death. Chronic palmitate exposure increased the ratio of proinsulin to insulin. CPE null islets had increased apoptosis in vivo and in vitro. Reducing CPE by approximately 30% using shRNA also increased ER stress and apoptosis. Conversely, overexpression of CPE partially rescued beta-cells from palmitate-induced ER stress and apoptosis. Thus, carboxypeptidase E degradation contributes to palmitate-induced beta-cell ER stress and apoptosis. CPE is a major link between hyperlipidemia and beta-cell death pathways in diabetes.
肥胖是2型糖尿病的主要危险因素，脂肪酸水平升高会降低β细胞功能并导致其死亡。我们采用无偏差蛋白质组学筛选方法来确定棕榈酸酯在β细胞死亡中的作用靶点。在用棕榈酸酯处理的人胰岛和MIN6 β细胞中，变化最显著的蛋白质是羧肽酶E（CPE）。棕榈酸酯在2小时内降低了CPE蛋白水平，早于内质网（ER）应激和细胞死亡，其机制涉及CPE转运至高尔基体并被溶酶体降解。CPE的蛋白水解和β细胞死亡还需要棕榈酸酯代谢和Ca(2+)通量。长期暴露于棕榈酸酯会增加胰岛素原与胰岛素的比例。CPE基因敲除的胰岛在体内和体外的细胞凋亡均增加。使用短发夹RNA（shRNA）将CPE降低约30%也会增加内质网应激和细胞凋亡。相反，CPE的过表达可部分挽救β细胞免受棕榈酸酯诱导的内质网应激和细胞凋亡。因此，羧肽酶E的降解导致了棕榈酸酯诱导的β细胞内质网应激和细胞凋亡。CPE是高脂血症与糖尿病中β细胞死亡途径之间的主要联系。
