Nox4 and soluble epoxide hydrolase synergistically mediate homocysteine-induced inflammation in vascular smooth muscle cells.

BACKGROUND: Hyperhomocysteinemia leads to a vascular smooth muscle cell (VSMC) inflammatory response. Meanwhile, Nox4 dependent reactive oxygen species (ROS) signaling and soluble epoxide hydrolase (sEH)/epoxyeicosatrienoic acids (EETs) are both involved in vascular inflammation. Herein, we hypothesized that Nox4 and soluble epoxide hydrolase cross regulated during homocysteine-induced VSMC inflammation.

METHODS AND RESULTS: In cultured VSMCs, the expression of the inflammatory factors VCAM1 and ICAM1 was measured by real-time PCR and Western blotting, while supernatant MCP1 was measured by ELISA. Upon VSMC stimulation with 50 μΜ homocysteine, we observed the VCAM1 and ICAM1 mRNA levels were increased by 1.15 and 1.0 folds, respectively. The MCP1 levels in the supernatant of cultured VSMCs treated with 100 μΜ increased to 1.76 folds. As expected, homocysteine induced Nox4 expression and Nox4-dependent ROS generation. The sEH expression was also upregulated in the presence of homocysteine in a dose-dependent manner. Furthermore, we knocked down Nox4 with siRNA. Knockdown of Nox4 decreased ROS generation and homocysteine-induced sEH expression. Overexpression of Nox4 with an adenovirus stimulated sEH expression. Similarly, knockdown or chemical inhibition of sEH blunted the upregulation of Nox4 by homocysteine. In vivo, in homocysteine-fed mice, concomitant upregulation of Nox4 and sEH was associated with increased VCAM1 and ICAM1 expression in the aortic wall.

CONCLUSIONS: The inflammatory response induced by homocysteine in VSMCs was accompanied by Nox4 and sEH upregulation. Nox4 and soluble epoxide hydrolase synergistically contribute to homocysteine-induced inflammation.