Knockdown of Herp alleviates hyperhomocysteinemia mediated atherosclerosis through the inhibition of vascular smooth muscle cell phenotype switching

Background Phenotypic switching of vascular smooth muscle cells (VSMCs) plays a key role in atherosclerosis. We aimed to investigate whether Homocysteine-responsive endoplasmic reticulum protein (Herp) was involved in VSMC phenotypic switching and affected atheroprogression. Methods To assess the role of Herp in homocysteine (Hcy)-associated atherosclerosis, Herp −/− and LDLR −/− double knockout mice were generated and fed with a high methionine diet (HMD) to induce Hyperhomocysteinemia (HHcy). Atherosclerotic lesions, cholesterol homeostasis, endoplasmic reticulum (ER) stress activation, and the phenotype of VSMCs were assessed in vivo . We used siRNAs to knockdown Herp in cultured VSMCs to further validate our findings in vitro . Results HMD significantly activated the activating transcription factor 6 (ATF6)/Herp arm of ER stress in LDLR −/− mice, and induced the phenotypic switch of VSMCs, with the loss of contractile proteins (SMA and calponin) and an increase of OPN protein. Herp −/− /LDLR −/− mice developed reduced atherosclerotic lesions in the aortic sinus and the whole aorta when compared with LDLR −/− mice. However, Herp deficiency had no effect on diet-induced HHcy and hyperlipidemia. Inhibition of VSMC phenotypic switching, decreased proliferation and collagen accumulation were observed in Herp −/− /LDLR −/− mice when compared with LDLR −/− mice. In vitro experiments demonstrated that Hcy caused VSMC phenotypic switching, promoted cell proliferation and migration; this was reversed by Herp depletion. We achieved similar results via inhibition of ER stress using 4-phenylbutyric-acid (4-PBA) in Hcy-treated VSMCs. Conclusion Herp deficiency inhibits the phenotypic switch of VSMCs and the development of atherosclerosis, thus providing novel insights into the role of Herp in atherogenesis.