Author + information
- 1Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Capital Medical University
- 2Key Laboratory of Remodeling-Related Cardiovascular Diseases, Ministry of Education
- 3Beijing Anzhen Hospital of Capital Medical University and Beijing Institute of Heart Lung and Blood Vessel Diseases, Beijing, China
Hypoxia is intimately linked to atherosclerosis and inflammation. Hypoxia inducible factor 2α(HIF2α)is a key transcription factor for cellular adaptive responses to hypoxia,but its role in atherosclerosis remains unclear.In this study,we sought to determine the contribution of HIF2a activation in vascular smooth muscle cells(VSMC)to the development of atherosclerosis.
HIF2a expression were evaluated in human atherosclerotic samples or aortic roots of atherosclerotic ApoE-/-mice.Hypoxic probe and HIF2a were colocalized with a-SMA,a marker for VSMCs in atherosclerotic plaques, indicating an activation of HIF2a in VSMC during atherosclerosis. To explore the role of HIF2a in atherosclerosis, VSMC-specific HIF2a knockout mice were generated and crossed with ApoE-/-mice to establish Hif2αΔSMC/ApoE-/-or the littermate Hif2αF/F/ApoE-/-mice.The mice were given normal diet and high fat diet for 12 weeks and detect serum triglycerides,cholesterol.Then the aorta were stained with oil red O to observe plaque areas and the aortic sinus were stained with HE, masson and oil red O to detect plaque areas and necrotic plaque areas.Hif2αΔSMC/ApoE-/-mice and Hif2αF/F/ApoE-/-mice primary VSMCs were treated with oxLDL and detect the expression of pro-inflammatory genes such as mcp-1,icam1.Co-culture assays for macrophages and primary VSMCs to investigate its effects on macrophage recruitment after oxLDL treatment.
As shown by en face oil red O staining, there was no significant difference of plaque area in aortas between Hif2αΔSMC/ApoE-/-and Hif2αF/F/ApoE-/-mice fed with control diet for 12 weeks.However,when challenged with high-cholesterol diet for 12 weeks, there was much less atherosclerotic plaques in aortas from Hif2αΔSMC/ApoE -/-mice compared with aortas from Hif2αF/F/ApoE-/-mice (12.28%±0.97%vs19.51%±1.59%,n=10,p<0.001).Ablation of HIF2a in VSMCs also dramatically reduced plaques areas in aortic sinus (95.73′103μm2±5.04′103μm2 in Hif2αΔSMC/ApoE-/-mice vs121.3′103μm2±5.00′103μm2 in Hif2αF/F/ApoE-/-mice,n=10,p<0.001). Morphological analysis demonstrated a significant reduction of necrotic plaque areas in aortic sinus from Hif2αΔSMC/ApoE-/-mice compared with Hif2αF/F/ApoE-/-mice (5.66′103μm2±0.79′103 μm2 vs 10.05′103μm2±1.68′103μm2,n=10,p<0.05).All these data suggest that disruption of HIF2a in VSMCs promotes the development of atherosclerosis.Mechanistically,deficiency of HIF2a in VSMCs did not alter serum triglycerides, cholesterol or lipoprotein profiles, indicating that dysregulation of lipid metabolism might not contribute to the exacerbated atherosclerosis upon HIF2a activation in VSMCs. However, a remarkable decrease of macrophage infiltration into atherosclerotic plaques was observed in the Hif2αΔSMC/ApoE-/-mice in vivo. Furthermore, several pro-inflammatory genes, such as mcp1 and icam1 were downregulated in aortas from Hif2αΔSMC/ApoE-/-mice and HIF2a-deficient primary VSMCs upon oxLDL stimulation. Co-culture assays for macrophages and primary VSMCs revealed that disruption of HIF2a in VMSCs abrogated macrophage migration after oxLDL treatment. The above data indicate that ablation of VMSC HIF2a may reduce atherogenesis via inhibition of macrophage recruitment and infiltration into vessel walls, although the further molecular links are still under investigation.
Our study provides evidence that HIF2a activation in VSMCs promotes atherosclerosis, and thus HIF2a may serve as a novel therapeutic target for atherosclerotic cardiovascular diseases.