Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, MA, USA.
Diabetes. 2012 Nov;61(11):2967-79. doi: 10.2337/db11-1824. Epub 2012 Jul 23.
To characterize glucagon-like peptide (GLP)-1 signaling and its effect on renal endothelial dysfunction and glomerulopathy. We studied the expression and signaling of GLP-1 receptor (GLP-1R) on glomerular endothelial cells and the novel finding of protein kinase A-dependent phosphorylation of c-Raf at Ser259 and its inhibition of angiotensin II (Ang II) phospho-c-Raf(Ser338) and Erk1/2 phosphorylation. Mice overexpressing protein kinase C (PKC)β2 in endothelial cells (EC-PKCβ2Tg) were established. Ang II and GLP-1 actions in glomerular endothelial cells were analyzed with small interfering RNA of GLP-1R. PKCβ isoform activation induced by diabetes decreased GLP-1R expression and protective action on the renal endothelium by increasing its degradation via ubiquitination and enhancing phospho-c-Raf(Ser338) and Ang II activation of phospho-Erk1/2. EC-PKCβ2Tg mice exhibited decreased GLP-1R expression and increased phospho-c-Raf(Ser338), leading to enhanced effects of Ang II. Diabetic EC-PKCβ2Tg mice exhibited greater loss of endothelial GLP-1R expression and exendin-4-protective actions and exhibited more albuminuria and mesangial expansion than diabetic controls. These results showed that the renal protective effects of GLP-1 were mediated via the inhibition of Ang II actions on cRaf(Ser259) and diminished by diabetes because of PKCβ activation and the increased degradation of GLP-1R in the glomerular endothelial cells.
为了描述胰高血糖素样肽（GLP）-1 的信号通路及其对肾脏内皮功能障碍和肾小球病变的影响，我们研究了 GLP-1 受体（GLP-1R）在肾小球内皮细胞中的表达和信号通路，以及蛋白激酶 A（PKA）依赖性磷酸化 c-Raf 丝氨酸 259（Ser259）及其对血管紧张素 II（Ang II）磷酸化 c-Raf（Ser338）和 Erk1/2 磷酸化的抑制作用这一新颖发现。建立了过表达蛋白激酶 C（PKC）β2 的内皮细胞（EC-PKCβ2Tg）的小鼠模型。利用 GLP-1R 的小干扰 RNA 分析了 Ang II 和 GLP-1 在肾小球内皮细胞中的作用。糖尿病引起的 PKCβ 同工型激活通过促进其泛素化降解，降低 GLP-1R 的表达，减弱 GLP-1 对肾脏内皮的保护作用，同时增强磷酸化 c-Raf（Ser338）和 Ang II 对磷酸化 Erk1/2 的激活作用。EC-PKCβ2Tg 小鼠表现出 GLP-1R 表达减少和磷酸化 c-Raf（Ser338）增加，从而增强了 Ang II 的作用。与糖尿病对照相比，糖尿病 EC-PKCβ2Tg 小鼠表现出更大的内皮 GLP-1R 表达缺失和 exendin-4 保护作用，且出现更多的白蛋白尿和系膜扩张。这些结果表明，GLP-1 的肾脏保护作用是通过抑制 Ang II 对 cRaf（Ser259）的作用介导的，而糖尿病由于 PKCβ 的激活和肾小球内皮细胞中 GLP-1R 的降解增加，导致这种作用减弱。
