Yano Naohiro, Suzuki Daisuke, Endoh Masayuki, Cao Tram N, Dahdah John R, Tseng Andy, Stabila Joan P, McGonnigal Bethany G, Padbury James F, Tseng Yi-Tang
Department of Pediatrics, Women & Infants Hospital, The Warren Alpert Medical School of Brown University, Providence, RI 02903, USA.
Biochem J. 2009 Sep 14;423(1):129-43. doi: 10.1042/BJ20082277.
Diabetic nephropathy is associated with mesangial ECM (extracellular matrix) accumulation. We have shown that AT-1R [Ang II (angiotensin II) type I receptor] signalling induces ECM proteins via transactivation of PI3K (phosphoinositide 3-kinase) in mesangial cells. In the present study, we examined the mechanisms underlying the effect of high ambient glucose on cell proliferation and ECM expansion in a mesangial context. High glucose induced increases in PI3K activity, proliferation and ECM accumulation in mesangial cells. These effects were abrogated by losartan, an AT-1R antagonist, but not by [Sar1,Thr8]-Ang II (Sar is sarcosine), an inactive analogue of Ang II, or by a neutralizing antibody against Ang I/II. Overexpression of a constitutively active PI3Kalpha or AT-1R alone was sufficient to induce similar changes by high glucose. In contrast, overexpression of an inactive AT-1R lowered the basal levels and rendered the cells non-responsive to high glucose. Moreover, cells overexpressing wild-type AT-1R had enhanced sensitivity to acute Ang II stimulation. These cells, however, did not respond to conditioned medium obtained from mesangial cells cultured in high glucose. We further demonstrated that iAng (intracellular Ang II) can be induced by high glucose but only under certain conditions. Efficient suppression of iAng by short hairpin RNA against angiotensinogen, however, did not affect high glucose-induced effects on MES-13 cells. These results suggest that high ambient glucose induces activation of AT-1R in an Ang II-independent manner to transactivate PI3K, resulting in proliferation and ECM accumulation in mesangial cells.
糖尿病肾病与系膜细胞外基质（ECM）积聚有关。我们已经表明，AT-1R[血管紧张素II（Ang II）I型受体]信号通过系膜细胞中PI3K（磷脂酰肌醇3-激酶）的反式激活诱导ECM蛋白。在本研究中，我们研究了高环境葡萄糖对系膜细胞中细胞增殖和ECM扩张影响的潜在机制。高糖诱导系膜细胞中PI3K活性增加、细胞增殖和ECM积聚。这些作用被AT-1R拮抗剂氯沙坦消除，但不被Ang II的无活性类似物[Sar1，Thr8]-Ang II（Sar是肌氨酸）或抗Ang I/II的中和抗体消除。单独过表达组成型活性PI3Kα或AT-1R足以诱导高糖引起的类似变化。相反，过表达无活性的AT-1R降低了基础水平并使细胞对高糖无反应。此外，过表达野生型AT-1R的细胞对急性Ang II刺激的敏感性增强。然而，这些细胞对从高糖培养的系膜细胞获得的条件培养基无反应。我们进一步证明，细胞内Ang II（iAng）可由高糖诱导，但仅在某些条件下。然而，用针对血管紧张素原的短发夹RNA有效抑制iAng并不影响高糖对MES-13细胞的诱导作用。这些结果表明，高环境葡萄糖以Ang II非依赖性方式诱导AT-1R激活，从而反式激活PI3K，导致系膜细胞增殖和ECM积聚。
