Methylation Of Bone SOST Impaired The Transactivation Of Transcriptional Factors SP7 RUNX2 And ER? In Osteoporosis Patients

Objective:Sclerostin(SOST)is a glycoprotein secreted mainly by osteocytes in bone tissue and encoded by SOST gene.It is an important regulator of bone formation and an effective inhibitor of bone formation.It is produced by osteoblasts,not osteoblasts.Loss of SOST gene leads to Van Buchem disease.Inhibition of sclerosing protein(a glycoprotein secreted by osteocytes)has become a new therapeutic modality(OP)for osteoporosis through the key role of Wnt/beta-catenin signaling regulator.DNA methylation contributes to the regulation of SOST expression in human bone cells,but the mechanism is unclear.Methods:12 cases of fracture with postmenopausal osteoporosis and 8 cases of fracture with postmenopausal non-osteoporosis were compared to explore the mechanism of SOST methylation and its effect on osteoporosis.We found two CpG-rich regions in SOST:two CpG islands were identified in the 2 kb region upstream of the SOST transcription initiation site.CpG island 1 is located at 1560?1287,CpG 4,and CpG Island 2 is located at-441?-181,10 CpG sites.The bone biopsy results of OP patients and non OP patients were analyzed by BSP.Results:methylation of CpG island 1 in OP patients was 77.5%,which was significantly higher than that in patients without OP(62.5%).In OP(88.2%)patients,CpG Island 2 methylation was also significantly higher than that without OP(60.1%).The expression of SOST in serum and bone decreased in osteoporosis patients.Bisulfite sequencing PCR showed a high methylation rate in patients with osteoporosis.We identified OSTIX(SP7),RUNT-related transcription factor 2(RUNX2)and estrogen receptor a(ERa)as candidate transcription factors for activating SOST expression.In addition,in AzadC demethylated MG-63 cells,AzadC treated MG-63 cells showed a significant increase in SOST expression,and when transcription factors were overexpressed,the expression of SOST was significantly higher than that of AzadC alone.This indicates that SOST demethylation increases the trans activation of SP7,RUNX2 and ER a in MG-63 cells.Overexpression of AzadC and SOST in MG-63 cells revealed changes in cell proliferation and apoptosis.ChIP experiments showed that hypermethylation was associated with the reduction of SP7,RUNX2 and ERa-binding SOST promoters in osteoporotic patients.Conclusions:In general,DNA methylation may be involved in regulating SOST expression during osteoblast-osteoblast transformation by blocking the binding of transcription factors to proximal promoters.The increase of promoter methylation in OP is a compensatory resistance mechanism,which reduces the concentration of serum sclerosing protein and the inhibition of Wnt signal transduction in an attempt to promote bone formation.This study provides a new perspective for the role of SOST methylation in osteoporosis.