Osteoporosis is a common metabolic bone disease, influenced by genetic and environmental factors, that increases bone fragility and fracture risk and, therefore, has a serious adverse effect on the quality of life of patients. However, epigenetic mechanisms involved in the development of osteoporosis remain unclear. There is accumulating evidence that epigenetic modifications may represent mechanisms underlying the links of genetic and environmental factors with increased risk of osteoporosis and bone fracture. Some RNAs, such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), have been shown to be epigenetic regulators with significant involvement in the control of gene expression, affecting multiple biological processes, including bone metabolism. This review summarizes the results of recent studies on the mechanisms of miRNA-, lncRNA-, and circRNA-mediated osteoporosis associated with osteoblasts and osteoclasts. Deeper insights into the roles of these three classes of RNA in osteoporosis could provide unique opportunities for developing novel diagnostic and therapeutic approaches to this disease.

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The roles of miRNA, lncRNA and circRNA in the development of osteoporosis

The goal of the present study is to identify the differential expression of circular RNA (circRNA), miRNA, and piwi-interacting RNA (piRNA) after lineage commitment towards osteo- and chondrogenesis of human bone marrow mesenchymal stromal cells (hMSCs). The cells were maintained for 7 days in either osteogenic or chondrogenic medium. RNA sequencing was performed to assess the expression of miRNA and piRNA, while RNA hybridization arrays were used to identify which circRNA were differentially expressed. qPCR validation of a selection of targets for both osteogenic and chondrogenic differentiation was carried out. The differential expression of several circRNA, miRNA, and piRNA was identified and validated. The expression of total and circular isoforms of FKBP5 was upregulated both in osteo- and chondrogenesis and it was influenced by the presence of dexamethasone. ZEB1, FADS2, and SMYD3 were also identified as regulated in differentiation and/or by dexamethasone. In conclusion, we have identified a set of different non-coding RNAs that are differentially regulated in early osteogenic and chondrogenic differentiation, paving the way for further investigation to understand how dexamethasone controls the expression of those genes and what their function is in MSC differentiation.

Differential Regulation of circRNA, miRNA, and piRNA during Early Osteogenic and Chondrogenic Differentiation of Human Mesenchymal Stromal Cells.

As one of the most common chronic diseases in the world, osteoporosis occurs especially in postmenopausal women. Circular RNAs (circRNAs) are emerging as major drivers in human disease. The aim of the present study was to analyse circRNA expression profiles in osteoporosis and to explore the clinical significance and the regulatory molecular mechanism of hsa_circ_0006859 during osteoporosis. Exosomes were isolated from clinically collected serum samples. A circRNA microarray was performed to screen differentially expressed circRNAs. Quantitative real-time PCR (qRT-PCR) and western blot were performed to analyse target gene mRNA expression and protein expression. Alizarin red staining (ARS) was performed to evaluate the mineralization ability of human bone marrow mesenchymal stem cells (hBMSCs). Oil Red O staining was performed to evaluate the lipid droplet formation ability of hBMSCs. Bioinformatics analysis and the luciferase reporter assay were performed to investigate the interaction between two genes. Hsa_circ_0006859 was identified as one of the most upregulated circRNAs in the microarray analysis. Hsa_circ_0006859 in exosomes was upregulated in osteoporosis patients compared to healthy controls. Hsa_circ_0006859 differentiated osteopenia or osteoporosis patients from healthy controls with high sensitivity and specificity. Hsa_circ_0006859 suppressed osteoblastic differentiation and promoted adipogenic differentiation of hBMSCs. Hsa_circ_0006859 directly bound to miR-431-5p, and ROCK1 was identified as a novel target gene of miR-431-5p. Hsa_circ_0006859 is a competing endogenous RNA (ceRNA) of miR-431-5p that promotes ROCK1 expression. Hsa_circ_0006859 suppressed osteogenesis and promoted adipogenesis by sponging miR-431-5p to upregulate ROCK1. Exosomal hsa_circ_0006859 is a potential biomarker for postmenopausal osteoporosis and controls the balance between osteogenesis and adipogenesis in hBMSCs by sponging miR-431-5p.

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Exosomal hsa_circ_0006859 is a potential biomarker for postmenopausal osteoporosis and enhances adipogenic versus osteogenic differentiation in human bone marrow mesenchymal stem cells by sponging miR-431-5p.

Circular RNA YAP1 attenuates osteoporosis through up-regulation of YAP1 and activation of Wnt/β-catenin pathway.

Little is known about the implications of circRNAs in the effects of melatonin (MEL) on bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation and osteoporosis (OP) progression. The aim of our study was to investigate circRNAs in MEL-regulated BMSC differentiation and OP progression. BMSC osteogenic differentiation was measured by qRT-PCR, western blot (WB), Alizarin Red, and alkaline phosphatase (ALP) staining. Differential circRNA and mRNA profiles of BMSCs treated by MEL were characterized by deep sequencing, followed by validation using RT-PCR, Sanger sequencing, and qRT-PCR. Silencing and overexpression of circ_0003865 were conducted for functional investigations. The sponged microRNAs and targeted mRNAs were predicted by bioinformatics and validated by qRT-PCR, RNA pull-down, and dual-luciferase reporter assay. The function of miR-3653-3p and circ_0003865/miR-3653-3p/growth arrest-specific gene 1 (GAS1) cascade was validated for the osteogenic differentiation of BMSCs by CCK-8, qRT-PCR, WB, Alizarin Red, and ALP staining. The effects of circ_0003865 on OP development were tested in murine OP model. MEL promoted osteogenic differentiation of BMSCs. RNA sequencing revealed significant alterations in circRNA and mRNA profiles associated with multiple biological processes and signaling pathways. Circ_0003865 expression in BMSCs was significantly decreased by MEL treatment. Silencing of circ_0003865 had no effect on proliferation while promoted osteogenic differentiation of BMSCs. Overexpression of circ_0003865 abrogated the promotion of BMSC osteogenic differentiation induced by MEL, but proliferation of BMSCs induced by MEL had no change whether circ_0003865 was overexpression or not. Furthermore, circ_0003865 sponged miR-3653-3p to promote GAS1 expression in BMSCs. BMSC osteogenic differentiation was enhanced by miR-3653-3p overexpression while BMSC proliferation was not affected. By contrast, miR-3653-3p silencing mitigated the promoted BMSC osteogenic differentiation caused by circ_0003865 silencing, but had no effect on proliferation. Finally, circ_0003865 silencing repressed OP development in mouse model. MEL promotes BMSC osteogenic differentiation and inhibits OP pathogenesis by suppressing the expression of circ_0003865, which regulates GAS1 gene expression via sponging miR-3653-3p.

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Melatonin promotes bone marrow mesenchymal stem cell osteogenic differentiation and prevents osteoporosis development through modulating circ_0003865 that sponges miR-3653-3p

Yonggang Liu

Papers

circRNA_0016624 could sponge miR-98 to regulate BMP2 expression in postmenopausal osteoporosis.

Graphene oxide leads to mitochondrial-dependent apoptosis by activating ROS-p53-mPTP pathway in intestinal cells.