The Role Of SMOC1 Gene In Aortic Valve Interstitial Cells And Related Mechanisms

Objective: Calcific aortic valve stenosis(Calcific aortic valve stenosis,CAS)is the most common form of heart valve disease.However,the molecular mechanisms underlying late aortic valve calcification are not well understood.Recent studies demonstrated BMP2 are highly expressed in calcific stenotic aortic valves and thought to play critical roles in aortic valve calcification.In this study,the role of BMP antagonist SMOC1 in regulating function of human aortic valve intersititial cell(hAVICs)and differentiation to osteoblastic phenotypes,and how SMOC1 regulates BMP2/Smad1 pathway were assessed.Methods: The expression of SMOC1 in normal and calcifc aortic valves were performed by immunohistochemistry.hAVICs were isolated from the healthy donor aortic valves and cultured in standard media or osteogenic medium.Adenoviral transduction was carried out to over-express either SMOC1/green fluorescent protein(Ad-SMOC1/GFP)or Ad-null/GFP alone(control).The effect of SMOC1 on hAVICs function in vitro was analyzed in terms of cell proliferation,migration,apoptosis and response to osteogenic medium.Then we explored the regulation and associated mechanism of BMP2/Smad1 pathway by SMOC1 through biochemical analysis.Results: SMOC1 located on the endothelium of normal aortic valves with higher expression on aortic side and was upregulated in calcific aortic valves.Overexpression of SMOC1 inhibited proliferation of hAVICs with no effects on cell migration and apoptosis.Moreover,Overexpression of SMOC1 inhibited osteoblastic differentiation and calcification induced by osteogenic medium in hAVICs.Further biochemical analysis revealed that SMOC1 inhibited BMP2/Smad1 signaling not through MAPK pathway and mTOR pathway in hAVICs.Specially in MC3T3 cells,SMOC1 downregulated level of pSmad1/5 possibly through Smad1 polyubiquitination and proteasome-mediated degradation by increasing level of Smurf1.While in hAVICs,SMOC1 downregulated mRNA level of BMPR2 after treated with BMP2 for 48 h,accompanied with significantly increasing level of has-miR-19 a.Moreover,SMOC1 could reduce the inhibitory effect of MAPKAP1 on MEKK2 due to combination with the MEKK2 competition to MAPKAP1,and then upregulated the phosphorylation levels of JNK and p38,which role was not involved in BMP2/Smad1 signaling.Conclusions: Our results indicate a novel and important role for SMOC1 in the proliferation and calcification of hAVICs,suggesting that SMOC1 may be involved in valvular fibrosis and calcification in the pathogenesis of CAS through regulating BMP2/Smad1 pathway.