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
Angiotensin II activaties PI 3-kinase dependent pathway and HIF-1α accumulation in glomerular mesangial cells
中文摘要
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 (angiotensin 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 VEGF 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sphingomyelin，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、Akt 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。
英文摘要
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 the release of vascular endothelial growth factor (VEGF) from human vascular tissues. VEGF is a family of potent 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-inducible factor 1 (HIF-1). In the present study, we investigate whether Ang II stimulates the accumulation of HIF-1a and the role of PI3-K signaling pathway in this effect. We demonstrated that Ang II (100 nM) increase 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 (LY294002). The induction of HIF-a by Ang II is mediated through PI3-K dependent pathway.
Angiotensin II mediates both pro- and anti-apoptotic signaling cascades that determine survival and death decisions. In PC12W cells, Ang II induces
sphingomyelin synthesis, which in turn leads to an increase in intracellular ceramide and apoptosis. Conversely, PI3-K is involved in regulating cell survival and
proliferation pathways. Akt is a major downstream target of PI3-K involved in angiotensin II-induced proliferation. In the present study, we investigate cross-talk between the PI3-K and sphingomyelinase pathways as a mechanism for regulation of mesangial cell survival/death decisions. Ang II (100 nM) exposure of rat mesangial cells activated PI3-K, PDK-1 and Akt in a dose dependent manner. The Ang
II-stimulated effects can be mimicked by incubating mesangials cells with dibutyryl cAMP. Treatment of the cells with C2-ceramides blocked Ang II- or cAMP- induced PI3-K and Akt activation and results in a significant increase in cell death. As a composite, these studies suggest that Ang II mediates proliferation pathway through cAMP and PI3-K/Akt/PKB pathways, whereas ceramides and activation of PKCz inhibits the survival signal.
