GOLM1 Stimulation of Glutamine Metabolism Promotes Osteoporosis via Inhibiting Osteogenic Differentiation of BMSCs

Background/Aims: Bone marrow mesenchymal stem cells (BMSCs) play an essential role in osteoporosis. However, the molecular mechanisms and the involvement of glutamine metabolism in osteogenic BMSCs differentiation and osteoporosis remain largely unclear. In this study, we investigated the role of Golgi membrane protein 1 (GOLM1) and glutamine metabolism in BMSCs differentiation and osteoporosis. Methods: Osteogenic differentiation-inducing media (Odi) was used to induce the osteogenic differentiation of BMSCs. The mRNA expression of GOLM1, ALP, Runx2, Osx, BSP and OCN was determined by qRT-PCR assay. Western blot assay was used to analyze GOLM1, p-mTOR, mTOR, p-S6 and S6 abundance in GOLM1 silencing and over-expressed BMSCs. Glutamine uptake, intracellular glutamine, glutamate and α-KG level was detected using indicated Kits. GOLM1 antibody, glutamine metabolism inhibitors EGCG and BPTES were used to treat ovariectomy (OVX)-induced osteoporosis. Bone mineral density and bone volume relative to tissue volume (%) were analyzed by micro-CT. Serum was collected from osteoporosis patients and healthy participants and subjected to GOLM1 determination using ELISA Kit. Results: GOLM1 expression and glutamine metabolism were suppressed by Odi. GOLM1 blockage or inhibition of glutamine metabolism promoted the osteogenic differentiation of BMSCs induced by Odi. GOLM1 activated glutamine metabolism depending on the mTOR signaling pathway. In vivo, GOLM1 antibody or combination of glutamine inhibitor EGCG and BPTES rescued the osteoporosis in an OVX-operated mouse model. Serum GOLM1 level was increased in the patients of osteoporosis compared with healthy people. Conclusion: GOLM1 stimulates glutamine metabolism to suppress the osteogenic differentiation of BMSCs and to promote osteoporosis. Therefore, GOLM1 activation of glutamine metabolism is a potential target for osteoporosis

Methylation of bone SOST impairs SP7, RUNX2, and ERα transactivation in patients with postmenopausal osteoporosis

Sclerostin (SOST), a glycoprotein predominantly secreted by bone tissue osteocytes, is an important regulator of bone formation, and loss of SOST results in Van Buchem disease. DNA methylation regulates SOST expression in human osteocytes, although the detailed underlying mechanisms remain unknown. In this study, we compared 12 patients with bone fractures and postmenopausal osteoporosis with eight patients without postmenopausal osteoporosis to understand the mechanisms via which SOST methylation affects osteoporosis. Serum and bone SOST expression was reduced in patients with osteoporosis. Bisulfite sequencing-polymerase chain reaction (PCR) revealed that the methylation rate was higher in patients with osteoporosis. We identified osterix (SP7), Runt-related transcription factor 2 (RUNX2), and estrogen receptor  (ER) as candidate transcription factors activating SOST expression. Increased SOST methylation impaired the transactivation function of SP7, RUNX2, and ER in MG-63 cells. AzadC treatment and SOST overexpression in MG-63 cells altered cell proliferation and apoptosis. Chromatin immunoprecipitation showed that higher methylation was associated with reduced SP7, RUNX2, and ER binding to the SOST promoter in patients with osteoporosis. Our studies provide new insight into the role of SOST methylation in osteoporosis.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author