Homocysteine up-regulates endothelin type A receptor in vascular smooth muscle cells through Sirt1/ERK1/2 signaling pathway.

Sirtuin 1 (Sirt1) is a longevity gene that has protective effects in cardiovascular diseases (CVDs). The endothelin type A (ETA) receptor is involved in pathogenesis of CVDs. The extracellular signal related kinases 1 and 2 (ERK1/2) signaling pathway is involved in regulation of the ETA receptor induced by some CVD risk factors in vascular smooth muscle cells (VSMCs). Hyperhomocysteinemia (HHcy) is an independent risk factor for CVDs. The present study was designed to investigate the hypothesis that homocysteine up-regulates ETA receptor through the Sirt1/ERK1/2 signaling pathway. In vitro experiments were performed in the rat superior mesenteric artery. The rat superior mesenteric artery was cultured with or without homocysteine (Hcy) in the presence and absence of Resveratrol (Res, a Sirt1 agonist), SRT1720 (a specific Sirt1 agonist) or U0126 (an ERK1/2 signaling pathway inhibitor) in serum-free medium for 24h. In vivo, the rats received subcutaneous injections of Hcy in the presence of or absence of Res or U0126 for 3weeks. The contractile response to ET-1 was studied using a sensitive myograph. In addition, the level of protein expression was determined using western blotting. Hcy significantly increased the expression of ETA receptor and also increased the ETA receptor-mediated contractile response induced by ET-1 in vitro. These effects were inhibited by Res, SRT1720 and U0126 treatment. In addition, Hcy down-regulated the level of Sirt1, and up-regulated the level of phosphorylated ERK1/2, which was reversed upon Res or SRT1720 treatment. In vivo results showed that HHcy results in the up-regulation of ETA receptor expression, and elevated blood pressure in rats. However, Res and U0126 could block these effects, respectively. In conclusion, these results suggest that Hcy regulates ETA receptor expression via the Sirt1/ERK1/2 signaling pathway in VSMCs.