Bouzakri Karim, Ribaux Pascale, Halban Philippe A
Department of Genetic Medicine and Development, University Medical Center, University of Geneva, CH-1211 Geneva 4, Switzerland.
Department of Genetic Medicine and Development, University Medical Center, University of Geneva, CH-1211 Geneva 4, Switzerland.
J Biol Chem. 2009 Oct 9;284(41):27892-27898. doi: 10.1074/jbc.M109.048058. Epub 2009 Aug 18.
Obesity and type 2 diabetes present partially overlapping phenotypes with systemic inflammation as a common feature, raising the hypothesis that elevated cytokine levels may contribute to peripheral insulin resistance as well as the decreased beta cell functional mass observed in type 2 diabetes. In healthy humans, TNF-alpha infusion induces skeletal muscle insulin resistance. We now explore the impact of TNF-alpha on primary beta cell function and the underlying signaling pathways. Human and rat primary beta cells were sorted by FACS and cultured for 24 h +/- 20 ng/ml TNF-alpha to explore the impact on apoptosis, proliferation, and short-term insulin secretion (1 h, 2.8 mm glucose followed by 1 h, 16.7 mm glucose at the end of the 24-h culture period) as well as key signaling protein phosphorylation and expression. Prior exposure to TNF-alpha for 24 h inhibits glucose-stimulated insulin secretion from primary beta cells. This is associated with a decrease in glucose-stimulated phosphorylation of key proteins in the insulin signaling pathway including Akt, AS160, and other Akt substrates, ERK as well as the insulin receptor. Strikingly, TNF-alpha treatment decreased IRS-2 protein level by 46 +/- 7% versus control, although mRNA expression was unchanged. While TNF-alpha treatment increased MAP4K4 mRNA expression by 33 +/- 5%, knockdown of MAP4K4 by siRNA-protected beta cells against the detrimental effects of TNF-alpha on both insulin secretion and signaling. We thus identify MAP4K4 as a key upstream mediator of TNF-alpha action on the beta cell, making it a potential therapeutic target for preservation of beta cell function in type 2 diabetes.
肥胖和2型糖尿病呈现出部分重叠的表型，全身炎症是其共同特征，这引发了一种假说，即细胞因子水平升高可能导致外周胰岛素抵抗以及2型糖尿病中观察到的β细胞功能质量下降。在健康人类中，输注肿瘤坏死因子-α（TNF-α）会诱导骨骼肌胰岛素抵抗。我们现在探讨TNF-α对原代β细胞功能及其潜在信号通路的影响。通过荧光激活细胞分选术（FACS）对人和大鼠的原代β细胞进行分选，并在±20 ng/ml TNF-α的条件下培养24小时，以探讨其对细胞凋亡、增殖和短期胰岛素分泌（24小时培养期结束时，先1小时2.8 mmol/L葡萄糖刺激，随后1小时16.7 mmol/L葡萄糖刺激）以及关键信号蛋白磷酸化和表达的影响。预先暴露于TNF-α 24小时会抑制原代β细胞的葡萄糖刺激的胰岛素分泌。这与胰岛素信号通路中关键蛋白（包括Akt、AS160和其他Akt底物、细胞外信号调节激酶（ERK）以及胰岛素受体）的葡萄糖刺激的磷酸化减少有关。令人惊讶的是，与对照组相比，TNF-α处理使胰岛素受体底物-2（IRS-2）蛋白水平降低了46±7%，尽管mRNA表达未改变。虽然TNF-α处理使丝裂原活化蛋白激酶4激酶4（MAP4K4）mRNA表达增加了33±5%，但通过小干扰RNA（siRNA）敲低MAP4K4可保护β细胞免受TNF-α对胰岛素分泌和信号传导的有害影响。因此，我们确定MAP4K4是TNF-α对β细胞作用的关键上游介质，使其成为2型糖尿病中保护β细胞功能的潜在治疗靶点。
