Role Of Orphan Nuclear Receptor Nur77 In Low Shear Stress Induced Mice Carotid Artery Remodeling And Underlying Mechanism

OBJIECTIVE To investigate the change of orphan nuclear receptor Nur77 expression in low shear stress induced carotid artery remodeling, and the underlying mechanisms.METHODS 1) 6-8 weeks old male C57BL/6 mice were randomly divided into sham group and vascular remodeling group, partial ligation of left carotid artery branches was used to generate low shear stress induced vascualr remodeling. 4 weeks after the operation, left common carotid arteries were harvested. HE staining was used to analyze intima-media area and thickness of carotid artery,Verhoeff-Van Gieson staining was performed to show elastin, collagen was detected by Picro Sirius Red staing, Nur77 was marked by immunofluoescence staining, and DHE fluorescence probe was used to observe ROS in vascular remodeling. 2) Primary rat vascular smooth muscle cells(VSMC) were cultured and stimulated with ox-LDL?7-KC?9-HODE?13-HODE?H2O2and its inhibitor N-acetylcysteine(NAC). Western blotting and Real Time PCR were used to detect the expression of Nur77. 3) 6-8 weeks old male Nur77-/- mice and C57BL/6 mice were used to generate carotid artery remodeling, 4 weeks after operation, left common carotid arteries were harvested, the same methods were used to analyze morpology changes as mentioned above, immunofluoescence staining was used to detect the expression of MMP9 and PCNA, cell apoptosis was observed by TUNEL staining.RESULTS 1) The intima-media area and thickness were notably increased in LSS group than the sham group(p<0.01), elastic lamina broke and disorganized in LSS group, also local ROS increased(p<0.01), the expression of Nur77 protein increased(p<0.01),and most of Nur77 expressed in VSMCs; 2) ox-LDL??7-KC?9-HODE?13-HODE?H2O2 induced the expression of Nur77,in contrary,NAC treatment reverse the phenomenon.3) After 4 weeks of the operation, the intima-media area was significantly greater in Nur77-/- mice than that in C57BL/6 mice(p < 0.01). Verhoeff-Van Gieson staining shows more disorganized and interrupted elastin fibers in Nur77-/-mice. MMP9 protein level is higher in Nur77-/- mice than in C57BL/6 mice(p<0.01). As for the proliferation and apoptosis of VSMC, the staining of PCNA shows increased proliferation in both type of mice, the Nur77-/- mice suffers more(P<0.01); However, there is no obvious difference in the level of VSMC apoptosis between these two types of mice(P>0.05).CONCLUSION Orphan nuclear receptor Nur77 is upregulated in low shear stress induced carotid artery remodeling, and most of Nur77 expresses in VSMCs, which may be induced by oxidative stress; Increased expression of Nur77 may inhibit VSMCs proliferation, upregulate MMP9 activity, and inhibit low shear stress induced carotid artery remodeling.