ABNORMAL SIGNAL TRUNSDUCTION IN MESANGIAL CELLS IN DIABETES

我们之前已经证明糖尿病系膜细胞功能障碍在糖尿病肾病的发展中起重要作用。然而，糖尿病系膜细胞功能障碍的分子机制尚不清楚。有丝分裂原活化蛋白激酶（MAPK）级联已被证明在导致各种细胞功能的信号转导系统中发挥关键作用。当蛋白激酶C （PKC）被激活时，MAPK级联被激活，我们已经证明PKC在高糖条件下培养的系膜细胞中被激活。因此，在本项目中，我们试图研究MAPK级联在糖尿病系膜细胞中的特征及其异常。得到了以下结果：在系膜细胞中，MAPK级联被各种血管收缩肽和PKC激活。这种激活被增加细胞cAMP或cgmp的药物所抑制。在高糖条件下培养的系膜细胞中，MAPK级联以pkc依赖的方式被激活。MAPK下游的酶cPLA2也被激活。在糖尿病大鼠肾小球中也观察到MAPK级联的激活，胰岛素治疗可以阻止这种激活。这些结果表明，在高糖条件下培养的系膜细胞和糖尿病肾小球中，PKC活性的升高可能导致MAPK级联激活。MAPK级联的激活导致cPLA2的激活，这可能通过产生前列腺素参与肾小球高滤过的发展。因此，本研究发现的MAPK级联的激活可能在糖尿病系膜细胞功能障碍的发展中起关键作用。

We have previously shown that mesangial cell dysfunction in diabetes plays an important role in the development of diabetic nephropathy. However, the molecular mechanisms of mesangial cell disfunction in diabetes have not been clarified yet. Mitogen-activated protein kinase (MAPK) cascade has been shown to play a key role in the signal transduction system leading to various cellular functions. MAPK cascade is known to be activated when protein kinase C (PKC) is activated and we have shown that PKC is activated in mesangial cells cultured under high glucose conditions. Therefore, in this project, we have attempted to examine the charactors of MAPK cascade in mesangial cells and its abnormalities in diabetes. The following results were obtained ;1. In mesangial cells, MAPK cascade was activated by various vasoconstrictive peptides and PKC activation. This activation was inhibited by agents which increace cellular cAMP or cGMP.2. In mesangial cells cultured under high glucose conditions, MAPK cascade was activated in PKC-dependent manner. cPLA2, a enzyme downstream to MAPK,was also activated.3. The activation of MAPK cascade was also observed in glomeruli isolated from diabetic rats and this activation was prevented by the treatment with insulin.These results indicate that, in mesangial cells cultured under high glucose conditions and in diabetic glomeruli, and elevation of PKC activities may lead to the activation of MAPK cascade. The activation of MAPK cascade resulted in the activation of cPLA2, which might contribute ot the development of glomerular hyperfiltration through the production of prostanoids. Therefore, the activation of MAPK cascade found in this study might play a key role in the development of mesangial cell dysfunction in diabetes.