Homocysteine up-regulates ETB receptors via suppression of autophagy in vascular smooth muscle cells

Abstract

The change of autophagy is implicated in cardiovascular diseases (CVDs). Homocysteine (Hcy) up-regulates endothelin type B (ETB) receptors in vascular smooth muscle cells (VSMCs). However, it is unclear whether autophagy is involved in Hcy-induced-up-regulation of ETB receptors in VSMCs. The present study was designed to examine the hypothesis that Hcy up-regulates ETB receptors by inhibiting autophagy in VSMCs. Hcy treated the rat superior mesenteric artery (SMA) without endothelium in the presence and absence of AICAR, rapamycin or MHY1485 for 24 h. The contractile responses to sarafotoxin 6c (S6c) (an ETB receptor agonist) were studied using a sensitive myograph. Levels of protein expression were determined using Western blot analysis. Punctate staining of LC3B was exanimated by immunofluorescence using confocal microscopy. The results showed that Hcy inhibited AMPK, and activated mTOR, followed by impairing autophagy, and increased the levels of ETB receptor protein expression and the ETB receptor-mediated contractile responses to S6c in SMA without endothelium. However, these effects were reversed by AICAR or rapamycin. Additionally, MHY1485 up-regulated the AICAR-inhibited ETB receptor-mediated contractile response and the levels of ETB receptor protein expression in presence of Hcy. In conclusion, this suggested that Hcy up-regulated ETB receptors by inhibiting autophagy in VSMCs via AMPK/mTOR signaling pathway.