Lin Yan-Jie, Juan Chi-Chang, Kwok Ching-Fai, Hsu Yung-Pei, Shih Kuang-Chung, Chen Chin-Chang, Ho Low-Tone
Institute of Physiology, National Yang-Ming University, Taipei, Taiwan; Department of Medical Research, Taipei Veterans General Hospital, Taipei, Taiwan.
Institute of Physiology, National Yang-Ming University, Taipei, Taiwan; Faculty of Medicine, National Yang-Ming University, Taipei, Taiwan.
Biochem Biophys Res Commun. 2015 May 8;460(3):497-503. doi: 10.1016/j.bbrc.2015.03.017. Epub 2015 Mar 28.
Endothelin-1 (ET-1) is known as potent vasoconstrictor, by virtue of its mitogenic effects, and may deteriorate the process of hypertension and atherosclerosis by aggravating hyperplasia and migration in VSMCs. Our previous study demonstrated that insulin infusion caused sequential induction of hyperinsulinemia, hyperendothelinemia, insulin resistance, and then hypertension in rats. However, the underlying mechanism of ET-1 interfere insulin signaling in VSMCs remains unclear. To characterize insulin signaling during modest insulin resistant syndrome, we established and monitored rats by feeding high fructose-diet (HFD) until high blood pressure and modest insulin resistance occurred. To explore the role of ET-1/ETAR during insulin resistance, ETAR expression, ET-1 binding, and insulin signaling were investigated in the HFD-fed rats and cultured A-10 VSMCs. Results showed that high blood pressure, tunica medial wall thickening, plasma ET-1 and insulin, and accompanied with modest insulin resistance without overweight and hyperglycemia occurred in early-stage HFD-fed rats. In the endothelium-denuded aorta from HFD-fed rats, ETAR expression, but not ETBR, and ET-1 binding in aorta were increased. Moreover, decreasing of insulin-induced Akt phosphorylation and increasing of insulin-induced ERK phosphorylation were observed in aorta during modest insulin resistance. Interestingly, in ET-1 pretreated VSMCs, the increment of insulin-induced Akt phosphorylation was decreased whereas the increment of insulin-induced ERK phosphorylation was increased. In addition, insulin potentiated ET-1-induced VSMCs migration and proliferation due to increasing ET-1 binding. ETAR antagonist reversed effects of ET-1 on insulin-induced signaling and VSMCs migration and proliferation. In summary, modest insulin resistance syndrome accompanied with hyperinsulinemia leading to the potentiation on ET-1-induced actions in aortic VSMCs. ET-1 via ETAR pathway suppressed insulin-induced AKT activation, whereas remained insulin-induced ERK activation. ET-1 and insulin synergistically potentiated migration and proliferation mainly through ETAR/ERK dependent pathway, which is dominant in VSMCs during modest insulin resistance syndrome. Therefore, ET-1 and ETAR are potential targets responsible for the observed synergism effect in the hypertensive atherosclerotic process through enhancement of ET-1 binding, ET-1 binding, ETAR expression, and ET-1-induced mitogenic actions in aortic VSMCs.
内皮素-1（ET-1）因其促有丝分裂作用而被认为是一种强效血管收缩剂，它可能通过加剧血管平滑肌细胞（VSMCs）的增生和迁移而使高血压和动脉粥样硬化进程恶化。我们之前的研究表明，给大鼠输注胰岛素会依次导致高胰岛素血症、高内皮素血症、胰岛素抵抗，进而引发高血压。然而，ET-1干扰VSMCs中胰岛素信号传导的潜在机制仍不清楚。为了明确适度胰岛素抵抗综合征期间的胰岛素信号传导特征，我们通过喂食高果糖饮食（HFD）建立并监测大鼠，直至出现高血压和适度胰岛素抵抗。为了探究ET-1/内皮素A受体（ETAR）在胰岛素抵抗中的作用，我们对喂食HFD 的大鼠和培养的A-10 VSMCs中的ETAR表达、ET-1结合及胰岛素信号传导进行了研究。结果显示，早期喂食HFD的大鼠出现了高血压、血管中膜增厚、血浆ET-1和胰岛素升高，同时伴有适度胰岛素抵抗，但无超重和高血糖。在喂食HFD大鼠的去内皮主动脉中，ETAR表达增加，而ETB受体（ETBR）未增加，主动脉中的ET-1结合也增加。此外，在适度胰岛素抵抗期间，主动脉中观察到胰岛素诱导的Akt磷酸化减少，胰岛素诱导的细胞外信号调节激酶（ERK）磷酸化增加。有趣的是，在ET-1预处理的VSMCs中，胰岛素诱导的Akt磷酸化增加减少，而胰岛素诱导的ERK磷酸化增加。此外，由于ET-1结合增加，胰岛素增强了ET-1诱导的VSMCs迁移和增殖。ETAR拮抗剂可逆转ET-1对胰岛素诱导信号传导以及VSMCs迁移和增殖的影响。总之，适度胰岛素抵抗综合征伴有高胰岛素血症，导致主动脉VSMCs中ET-1诱导作用增强。ET-1通过ETAR途径抑制胰岛素诱导的AKT激活，而胰岛素诱导的ERK激活则得以保留。ET-1和胰岛素主要通过ETAR/ERK依赖性途径协同增强迁移和增殖，这在适度胰岛素抵抗综合征期间的VSMCs中占主导地位。因此，ET-1和ETAR是通过增强ET-1结合、ET-1结合、ETAR表达以及ET-1诱导的主动脉VSMCs有丝分裂作用，在高血压动脉粥样硬化进程中产生协同效应的潜在靶点。
