Anderson P W, Zhang X Y, Tian J, Correale J D, Xi X P, Yang D, Graf K, Law R E, Hsueh W A
Department of Medicine, University Southern California Medical School, Los Angeles, USA.
Kidney Int. 1996 Sep;50(3):745-53. doi: 10.1038/ki.1996.372.
Angiotensin II (Ang II) and insulin are implicated in the mesangial cell hypertrophy and excessive accumulation of mesangial matrix seen in glomerulosclerosis. Therefore, the effects of Ang II with and without insulin on mRNA levels of several important extracellular matrix genes and transforming growth factor beta-1 (TGF-beta 1) were examined. Ang II alone (1 microM) added to quiescent, murine mesangial cells in serum-free, insulin-free media slightly but not significantly increased TGF-beta 1, fibronectin, collagen I, collagen IV and laminin message levels. The slight elevations in message expression were reversed by losartan, suggesting that these modest effects are mediated by the AT-1 receptor. Ang II alone also had no significant effects on TGF-beta 1 and extracellular matrix message levels in quiescent rat mesangial cells. In contrast, significant increases in mRNA for collagen 1 (6-fold), collagen IV (4-fold), fibronectin 1 (4-fold) and TGF-beta 1 (2-fold) were seen with insulin alone (10(-6)M) in rat mesangial cells, and a dose-response effect could be demonstrated for insulin (10(-9) to 10(-6)M). Ang II plus insulin further significantly increased collagen I (9-fold), collagen IV (9-fold), fibronectin 1 (5-fold) and TGF-beta 1 (3-fold) message expression. These effects were partially reversed in the presence of losartan. The Northern analyses were supported by measurements of active and total TGF-beta 1 activity (pg/ml/ 5 x 10(6) cells): 1145 +/- 76 and 1960 +/- 199, serum free control; 1121 +/- 92 and 1932 +/- 214, Ang II (10(-6)M); 4589 +/- 103 (P < 0.001 vs. control) and 11071 +/- 1952 (P < 0.01 vs. control), insulin (10(-6)M); and 6881 +/- 183 (P < 0.001 vs. control) and 16626 +/- 1435 (P < 0.01 vs. control), insulin plus Ang II. These results suggest that insulin, itself, significantly increases TGF-beta 1 and extracellular matrix gene expression in rat mesangial cells. Ang II alone has modest effects, while Ang II and insulin have additive effects. To explain the mechanism of these additive effects, we investigated the action of Ang II on insulin signaling and the effect of insulin on Ang II AT1 receptor mRNA expression. Ang II did not enhance insulin-induced insulin receptor substrate-1 (IRS-1) phosporylation or phosphatidylinositol3 (PI-3) kinase activity, but did enhance insulin-induced mitogen activated protein (MAP) kinase activity. Insulin increased message levels of AT1 receptor by twofold. These results suggest that enhancement of MAP kinase activity and AT1 receptor regulation by insulin may contribute to the additive effects of insulin and Ang II in mesangial cells.
血管紧张素II（Ang II）和胰岛素与肾小球硬化中所见的系膜细胞肥大和系膜基质过度积聚有关。因此，研究了有无胰岛素时Ang II对几种重要细胞外基质基因和转化生长因子β-1（TGF-β1）mRNA水平的影响。在无血清、无胰岛素培养基中，单独添加Ang II（1微摩尔）至静止的小鼠系膜细胞，可使TGF-β1、纤连蛋白、I型胶原、IV型胶原和层粘连蛋白的信息水平略有升高，但无统计学意义。洛沙坦可逆转信息表达的轻微升高，提示这些适度效应是由AT-1受体介导的。单独的Ang II对静止的大鼠系膜细胞中的TGF-β1和细胞外基质信息水平也无显著影响。相比之下，单独使用胰岛素（10^(-6)M）可使大鼠系膜细胞中I型胶原（6倍）、IV型胶原（4倍）、纤连蛋白1（4倍）和TGF-β1（2倍）的mRNA显著增加，且可证明胰岛素存在剂量反应效应（10^(-9)至10^(-6)M）。Ang II加胰岛素可进一步显著增加I型胶原（9倍）、IV型胶原（9倍）、纤连蛋白1（5倍）和TGF-β1（3倍）的信息表达。在洛沙坦存在的情况下，这些效应部分被逆转。Northern分析得到了活性和总TGF-β1活性（皮克/毫升/5×10^6个细胞）测量结果的支持：无血清对照为1145±76和1960±199；Ang II（10^(-6)M）为1121±92和1932±214；胰岛素（10^(-6)M）为4589±103（与对照相比P<0.001）和11071±1952（与对照相比P<0.01）；胰岛素加Ang II为6881±183（与对照相比P<0.001）和16626±1435（与对照相比P<0.01）。这些结果表明，胰岛素本身可显著增加大鼠系膜细胞中TGF-β1和细胞外基质基因的表达。单独的Ang II有适度效应，而Ang II和胰岛素有相加效应。为解释这些相加效应的机制，我们研究了Ang II对胰岛素信号传导的作用以及胰岛素对Ang II AT1受体mRNA表达的影响。Ang II未增强胰岛素诱导的胰岛素受体底物-1（IRS-1）磷酸化或磷脂酰肌醇3（PI-3）激酶活性，但增强了胰岛素诱导的丝裂原活化蛋白（MAP）激酶活性。胰岛素使AT1受体的信息水平增加了两倍。这些结果表明，胰岛素对MAP激酶活性的增强及对AT1受体的调节可能有助于胰岛素和Ang II在系膜细胞中的相加效应。
