The mechanism of G protein-mediated cardiac fibrosis

细胞内Ca^2+浓度（[Ca^2+]i）的持续升高与许多细胞事件有关。我们报道了通过典型瞬时受体电位3/6 （TRPC3/6）通道途径持续的Ca^2+内流导致活化T细胞核因子（NFAT）的激活，这是一种Ca^2+应答转录因子，并介导大鼠新生心肌细胞的肥厚反应。我们还证明了TRPC6通道参与内皮素(ET)-1治疗心脏成纤维细胞持续Ca^2+内流和NFAT激活。组成活性（CA） G_α<12>或G_α<13>的表达增加了TRPC6蛋白的表达和基础CA ^2+内流活性。ET-1通过G_α<12/13>、活性氧（ROS）和c-Jun n -末端激酶（JNK）依赖途径增加TRPC6蛋白水平。NFAT被持续增加的[Ca^2+]激活；通过上调TRPC6。来自p115-RhoGEF g蛋白信号域调控因子和JNK抑制剂SP600125的G_α<12/13>-ROS-JNK途径抑制et -1诱导的肌成纤维细胞形成标记蛋白表达的增加。过表达TRPC6和CA-NFAT可抑制et -1诱导的肌成纤维细胞形成，而TRPC6 sirna和环孢素a可增强其形成。这些结果提示G_α<12/13>在心脏成纤维细胞中具有两种相反的作用。首先，G_α<12/13>介导et -1诱导的肌成纤维细胞形成。其次，G_α<12/13>介导TRPC6上调和NFAT激活，负调控et -1诱导的肌成纤维细胞形成。此外，TRPC6介导心肌细胞的肥厚反应，但抑制心脏成纤维细胞的纤维化反应。因此，TRPC6在心肌细胞和成纤维细胞中介导相反的反应。

Sustained elevation of intracellular Ca^2+ concentration ([Ca^2+]i) has been implicated in many cellular events. We reported that sustained Ca^2+ influx through canonical transient receptor potential 3/6 (TRPC3/6) channels pathway leads to the activation of nuclear factor of activated T cells (NFAT), a Ca^2+-responsive transcriptional factor, and meditates hypertrophic responses in rat neonatal cardiac myocytes. We also demonstrated that TRPC6 channels participates in sustained Ca^2+ influx and NFAT activation by endothelin (ET)-1 treatment in cardiac fibroblasts. Expression of constitutively active (CA) G_α<12> or G_α<13> increased the expression of TRPC6 proteins and basal Ca^2+ influx activity. The treatment with ET-1 increased TRPC6 protein levels through G_α<12/13>, reactive oxygen species (ROS), and c-Jun N-terminal kinase (JNK)-dependent pathways. NFAT is activated by sustained increase in [Ca^2+]; through upregulated TRPC6. A G_α<12/13>-inhibitory polypeptide derived from regulator of G-protein signaling domain of p115-RhoGEF and a JNK inhibitor, SP600125, suppressed the ET-1-induced increase in expression of marker proteins of myofibroblast formation through G_α<12/13>-ROS-JNK pathway. The ET-1-induced myofibroblast formation was suppressed by overexpression of TRPC6 and CA-NFAT, while enhanced by TRPC6 siRNAs and cyclosporine A. These results suggest two opposite roles of G_α<12/13> in cardiac fibroblasts. First, G_α<12/13> mediate ET-1-induced myofibroblast formation. Second, G_α<12/13> mediate TRPC6 upregulation and NFAT activation that negatively regulates ET-1-induced myofibroblast formation. Furthermore, TRPC6 mediates hypertrophic responses in cardiac myocytes but suppresses fibrotic responses in cardiac fibroblasts. Thus, TRPC6 mediates opposite responses in cardiac myocytes and fibroblasts.