A novel microRNA regulates osteoclast differentiation via targeting protein inhibitor of activated STAT3 (PIAS3).

MicroRNAs (miRNAs) involve in the regulation of a wide range of physiological processes. Recent studies suggested that miRNAs might play a role in osteoclast differentiation. Here, we identify a new miRNA (miR-9718) in primary mouse osteoclasts that promotes osteoclast differentiation by repressing protein inhibitor of activated STAT3 (PIAS3) at the post-transcriptional level. MiR-9718 was found to be transcribed during osteoclastogenesis, which was induced by macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL). Overexpression of miR-9718 in RAW 264.7 cells promoted M-CSF and RANKL-induced osteoclastogenesis, whereas inhibition of miR-9718 attenuated it. PIAS3 was predicted to be a target of miR-9718. Luciferase reporter gene validated the prediction. Transfection of pre-miR-9718 in RAW 264.7 cells induced by both M-CSF and RANKL inhibited expression of PIAS3 protein, while the mRNA levels of PIAS3 were not attenuated. In vivo, our study showed that silencing of miR-9718 using a specific antagomir inhibited bone resorption and increased bone mass in mice receiving ovariectomy (OVX) and in sham-operated control mice. Thus, our study showed that miR-9718 played an important role in osteoclast differentiation via targeting PIAS3 both in vitro and in vivo.

Relationship between serum TGF-ß1, OPG levels and osteoporotic risk in native Chinese women.

BACKGROUND: Cytokines including transforming growth factor beta 1 (TGF-ß1) and osteoprotegerin (OPG) are closely related to bone metabolism. However, the relationships between TGF-ß1, OPG and risk of osteoporosis in native Chinese women are unknown. Our research indicated that there is a positive correlation between TGF-ß1 and bone mineral density (BMD) T-score, and a negative correlation between OPG and T-score. The risk of osteoporosis is reduced as TGF-ß1 increases and increases as OPG was raised. We investigated correlations of BMD T-scores with circulating TGF-ß1 and BMD T-scores with circulating OPG in healthy native Chinese women, and to study the effects of changes in TGF-ß1 and OPG on osteoporosis. METHODS: This was a cross-sectional study of 691 healthy native Chinese women aged 20-80 years. Concentrations of serum TGF-ß1 and OPG were determined. BMD T-scores at the posteroanterior spine, left hip, and forearm were measured by dual-energy X-ray absorptiometry. RESULTS: There were positive correlations between serum TGF-ß1 and T-scores at the various skeletal sites (r=0.167-0.285, all P=0.000) and negative correlations between serum OPG and T-scores (r=-0.179 to -0.270, all P=0.007-0.000). After adjusting for age and BMI, correlations between TGF-ß1 and T-score at the lumbar vertebrae and ultradistal forearm, and between OPG and T-score at the ultradistal forearm in premenopausal subjects, remained statistically significant. Multivariate linear stepwise analysis showed that TGF-ß1 could explain 1.9-8.3% of T-score variation at each skeletal site. OPG could explain 2.4-4.4% of T-score variation. When TGF-ß1 and OPG concentrations were grouped according to quartile intervals, T-score and the prevalence and risk of osteoporosis varied with changes in the cytokines. CONCLUSIONS: The risk of osteoporosis in native Chinese women increased as circulating TGF-ß1 was reduced and OPG was raised.

miR-93/Sp7 function loop mediates osteoblast mineralization.

microRNAs (miRNAs) play pivotal roles in osteoblast differentiation. However, the mechanisms of miRNAs regulating osteoblast mineralization still need further investigation. Here, we performed miRNA profiling and identified that miR-93 was the most significantly downregulated miRNA during osteoblast mineralization. Overexpression of miR-93 in cultured primary mouse osteoblasts attenuated osteoblast mineralization. Expression of the Sp7 transcription factor 7 (Sp7, Osterix), a zinc finger transcription factor and critical regulator of osteoblast mineralization, was found to be inversely correlated with miR-93. Then Sp7 was confirmed to be a target of miR-93. Overexpression of miR-93 in cultured osteoblasts reduced Sp7 protein expression without affecting its mRNA level. Luciferase reporter assay showed that miR-93 directly targeted Sp7 by specifically binding to the target coding sequence region (CDS) of Sp7. Experiments such as electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP), and promoter luciferase reporter assay confirmed that Sp7 bound to the promoter of miR-93. Furthermore, overexpression of Sp7 reduced miR-93 transcription, whereas blocking the expression of Sp7 promoted miR-93 transcription. Our study showed that miR-93 was an important regulator in osteoblast mineralization and miR-93 carried out its function through a novel miR-93/Sp7 regulatory feedback loop. Our findings provide new insights into the roles of miRNAs in osteoblast mineralization.