血管收縮素 II 活化腎絲球體環間膜細胞磷脂醯肌醇 3 激酶 ; 之訊息傳遞 路徑及 HIF-1α 的累積
血管收縮素 II 會在人體血管組織釋放血管內皮生長因子 (VEGF) ,並調節 VEGF 引起血 管增生,而血管增生為糖尿病腎病變發展的主要病理過程。因此血管收縮素 II (angioten sin II , Ang II) 為潛在導致腎硬化的病因。由於在血管平滑肌細胞中 HIF-1a 會影響 VE GF 表現,本研究主要探討血管收縮素 II 在腎絲球體環間膜細胞是否會刺激 HIF-1α 的 增加,並了解其訊號傳遞路徑。在腎絲球環間膜細胞中,血管收縮素 II 可以活化磷脂 醯肌醇 3 激酶 (PI 3-kinase , PI3-K) 路徑並造成 PDK1 及 Akt 的磷酸化,同時也會造成 HIF-1α 堆積,由於 PI3-K 之抑制劑 LY294002 可抑制血管收縮素 II 所刺激的 HIF-1α 增加,血管收縮素 II 應是經由 PI3-K 路徑而造成 HIF-1α 堆積,且 HIF-1α 表現與血管 增生有關,因此血管收縮素 II 可能經 PI3-K 路徑而造成 HIF-1α 的累積,並進一步產生 血管增生情形,本研究將有助於了解腎絲球硬化時血管收縮素 II 所扮演的角色。
除此之外血管收縮素 II 也可以藉由訊號傳遞調控細胞凋亡以決定細胞之存亡。血管收 縮素 II 有兩條路徑可調控細胞生存;在 PC12W cells 中血管收縮素 II 可藉著合成 sphing omyelin ,及活化神經磷脂酵素 (sphingomyelinase) 而細胞內產生 ceramide 並造成細 胞凋亡。另外,血管收縮素 II 則可透過活化 cAMP 、 PI3-K 等訊號路徑使細胞生長。故本論文第二部分探討 PI3-K 及神經磷脂酵素兩條路徑間之調控關係,進而了解血管收 縮素 II 調節腎絲球體環間膜細胞生長平衡之訊號傳遞方式。結果發現以血管收縮素 II 或 cAMP 處理腎絲球體環間膜細胞 30 分鐘可經由 PI3-K 路徑而活化下游之 PDK1 、 Ak t 之磷酸化;但若以神經醯胺 (ceramide) 或 cAMP 前處理腎絲球體環間膜細胞,則可將 血管收縮素 II 所活化之 Akt 去磷酸化;因此血管收縮素 II 可能藉由 PI3-K 及 cAMP 活 化 Akt 之路徑使細胞增生,另外又可透過神經醯胺 (ceramide) 活化 PKCζ 抑制細胞存 亡訊號 Akt 之活化,結論為 PI3-K 、 cAMP 與神經醯胺 (ceramide) 之訊號路徑間 cross- talk ,可藉此調節腎絲球體環間膜細胞生長平衡。
Angiotensin II activaties PI 3-kinase dependent pathway and HIF-1α accumulation in glomerular mesangial cells
The potential pathogenic role of angiotensin-II (Ang II) in glomeruloscerosis is not clear. Angiogenesis is one the major features of several pathological processes of a number of nephropathies. Ang II stimulates th e release of vascular endothelial growth factor (VEGF) from human vascular tissues. VEGF is a family of p otent cytokines, which act to induce angiogenesis. VEGF is up-regulated by Ang II during angiogenesis in hamster sponge granulomas. On the other hand, hypoxia-inducible factor-1 (HIF-1) controls the expression of a number of genes including vascular endothelial growth factor (VEGF) in vascular smooth muscle cells . We hypothesized that angiogenesis is induced by hypoxic conditions and regulated by the hypoxia-induci ble factor 1 (HIF-1). In the present study, we investigate whether Ang II stimulates the accumulation of HI F-1a and the role of PI3-K signaling pathway in this effect. We demonstrated that Ang II (100 nM) increas e HIF-1a protein expression in mesangial cells. Ang II (100 nM) activated PI3-K, PDK-1 and Akt in a dose dependent manner. Because Ang II-induced HIF-1a expression was blocked by the PI3-K inhibitor (LY294 002). The induction of HIF-a by Ang II is mediated through PI3-K dependent pathway.