Hui Lin1, Tingjuan Ni2, Jie Zhang3, Liping Meng4, Feidan Gao5, Sunlei Pan4, Hangqi Luo2, Fukang Xu4, Guomei Ru6, Jufang Chi7, Hangyuan Guo8. 1. Department of Cardiology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang, China; The First Clinical Medical College, Wenzhou Medical University, Wenzhou 325000, Zhejiang, China. 2. Zhejiang University School of Medicine, Hangzhou 310000, Zhejiang, China. 3. The First Clinical Medical College, Wenzhou Medical University, Wenzhou 325000, Zhejiang, China. 4. Department of Cardiology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang, China. 5. Zhejiang Chinese Medical University, Hangzhou 310000, Zhejiang, China. 6. Medical Research Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang, China. 7. Department of Cardiology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang, China; The First Clinical Medical College, Wenzhou Medical University, Wenzhou 325000, Zhejiang, China. Electronic address: jf_chi@163.com. 8. Department of Cardiology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 312000, Zhejiang, China; The First Clinical Medical College, Wenzhou Medical University, Wenzhou 325000, Zhejiang, China. Electronic address: ghangyuan@hotmail.com.
Abstract
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.
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.