Effect Of Selenoprotein S On Hydrogen Peroxide-induced Osteogenic Differentiation Of Vascular Smooth Muscle Cells And Related Signaling Pathways

Vascular calcification, the presence of calcium phosphate deposits in the vessel wall, is a common pathological feature of atherosclerotic cardiovascular diseases, type Ⅱ diabetes and chronic renal failure. Vascular calcification is an active, complex and highly controlled process similar to that of the bone formation. The calcification of medial artery which is surrounded by vascular smooth muscle cells（VSMCs） is a critical event in vascular calcification. Previous studies have shown that oxidative stress promoted VSMCs differentiate to osteoblast-like cells. Selenoprotein S（SelS）, as a glucose-regulated protein with a series of biological functions, has been confirmed to be associated with diabetes, cardiovascular diseases, and so on. VSMCs cultured in calcifying medium containing β-glycerophosphate and dexamethasone were used as a in vitro vascular calcification model. SelS expression was decreased by RNA intereference technology. We investigated the effect of SelS on hydrogen peroxide（H₂O₂）-induced osteogenic differentiation of VSMCs and related signaling pathways in this work.We found that SelS was regulated by H₂O₂ in VSMCs in a concentrations-dependent manner, characterized by the increase of SelS protein level. Meanwhile, SelS knock-down significantly aggravated the oxidative damage induced by H₂O₂ in calcifying VSMCs. Moreover, SelS knock-down enhanced VSMCs osteogenic differentiation and calcification induced by H₂O₂, as demonstrated by the increase of the calcium deposits, alkaline phosphatase（ALP） activity and the protein expression level of osteoblast specific transcription factor Runx2 and ALP. Real-time fluorescent quantitative PCR results showed that the mRNA expression levels of Runx2 and two other bone-related markers type I collagen（Col I） and osteocalcin（OC） were all increased in SelS knock-down VSMCs. Malondialdehyde（MDA） and superoxide dismutase（SOD） as oxidative stress markers, SelS knock-down increased MDA accumulation in calcifying VSMCs, but had no significant effect on SOD activity. In addition, we found that protein kinase B（Akt） phosphorylation responded to H₂O₂-induced oxidative stress more rapidly than extracellular signal-regulated kinase（ERK） phosphorylation in calcifying VSMCs, and SelS knock-down exacerbated H₂O₂-induced phosphorylation of Akt and ERK.In conclusion, the present study suggested that SelS responded to oxidative stress in VSMCs and SelS knock-down promoted oxidative stress-induced VSMCs osteogenic differentiation and calcification through activating the phosphorylation of Akt and ERK. These results indicated a potential inhibitory effect of SelS on oxidative stress-induced vascular calcification to a certain extent.