The Roles And Molecular Mechanisms Of The Selenoprotein O In Cartilage Development

Se(Selenium,Se)is an essential trace element.Se exerts its beneficial properties mainly through cotranslational incorporation into selenoproteins in the form of the amino acid selenocysteine(Sec).There are 25 and 24 selenoproteins identified in humans and rodents,respectively.These include glutathione peroxidases(GPx),thioredoxin reductases(Trx R),iodothyronine deiodinases(DIO),selenophosphate synthetases 2(SPS2),and 15-k Da selenoprotein,as well as others annotated in alphabetical order from selenoprotein H to W except J.However,the functions and exact mechanisms of the most selenoproteins,including Selenoprotein O(Sel O),are still unclear.In the present study,we study the roles of Sel O in growth plate cartilage development,se well as the molecular mechanism involved.We observed that Sel O is expressed in growth plate cartilage and chondroblast ATDC5 through immunohistochemistry(IHC)and Western blot assay.Sel O knock down by using sh RNA-mediated gene silencing technique leads to abnormal growth plate structure and impaired chondrogenic differentiation of chondroblast ATDC5 cells.Sel O-knockdown cells accumulated a few cartilage glycosaminoglycans(GAGs)and decreased the activity of alkaline phosphatase(ALP).In addition,Sel O knockdown inhibited gene expression of chondrogenic gene Sox9,Col II,and aggrecan at both m RNA and protein level.These observations indicated that Sel O knockdown suppressed chondrogenic differentiation of chondroblast.Next,we found Sel O knockdown decreased chondrocyte viability in time-course dependent manner.Both cell proliferation inhibition and cell death induction attributed to the Sel O knockdown-mediated cell viability decreased,since Sel O knockdown suppressed chondrocytes proliferation through a delay in G1-phase cell cycle progression accompanied with cyclin D1 induction.Furthermore,Sel O knockdown activated the expression of Caspase-3 and induced the apoptosis of cartilage Cell death.In addition,we examined the subcellular location of Sel O.Results showed that it is a cytoplasmic protein and Sel O knockdown induced endoplasmic reticulum stress.In summary,in this paper,we described the gene expression of Sel O in the growth plate cartilage and differentiation of chondrocytes.We also elucidated the roles of Sel O on the cartilage growth and differentiation of chondrocytes.Finally,the molecular mechanisms involved in Sel O-regulated chondrocyte viability and proliferation were clarified.Therefore,we concluded that Sel O regulates the growth of growth plate cartilage by regulation of the proliferation and differentiation of chondrocyte through maintenance of endoplasmic reticulum homeostasis.