Bone is a dynamic organ continuously undergoing shaping, repairing and remodeling. The homeostasis of bone is maintained by the balance between osteoblastic bone formation and osteoclastic bone resorption. Osteoclasts (OCs) are specialized multinucleated cells derived from hematopoietic stem cells (HSCs) or monocytes/macrophage progenitor cells. There are different stages during osteoclastogenesis, and one of the most important steps to form functional osteoclasts is realized by cell-cell fusion. In our study, microarray was performed to detect the expression profiles of lncRNA, mRNA, circRNA and miRNA at different stages during osteoclastogenesis of RAW264.7 cells. Often changed RNAs were selected and clustered among the four groups with Venn analysis. The results revealed that expressions of 518 lncRNAs, 207 mRNAs, 24 circRNAs and 37 miRNAs were often altered at each stage during OC differentiation. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathway analysis were performed to predict the functions of differentially expressed lncRNAs and co-expressed potential targeting genes. Co-expression networks of lncRNA-mRNA and circRNA-miRNA were constructed based on the correlation analysis between the differentially expressed RNAs. The present study provided a systematic perspective on the potential function of non-coding RNAs (ncRNAs) during osteoclastogenesis.

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In this study, for the first time we discovered that the M1/M2 macrophage phenotype ratio is increased in bone marrow of ovariectomized (OVX) osteoporotic C57BL/6 mice. Considering estrogen is the main variable, we assumed that estrogen participated in this alteration. To determine whether and how estrogen contributes to the change of the M1/M2 ratio, we first isolated bone marrow macrophages (BMMs) from mice femur and stimulated the cells with lipopolysaccharide (LPS)/interferon γ (IFN-γ) for M1 polarization and interleukin 4 (IL-4)/IL-13 for M2 polarization. M1 and M2 macrophages were then exposed to RANKL stimulation, we found that M2 macrophage but not M1 macrophage differentiated into functional osteoclast leading to increased M1/M2 ratio. Intriguingly, 17β-estradiol (E2) pretreatment prevented osteoclastogenesis from M2 macrophages. By constructing shRNA lentivirus interfering the expression of different estrogen receptors in M2 macrophages, we found that estrogen protects M2 macrophage from receptor activator of nuclear factor κB ligand (RANKL) stimulation selectively through estrogen receptor α (ERα) and the downstream blockage of NF-κB p65 nuclear translocation. Animal studies showed that ERα selective agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT) was able to replicate the therapeutic effects of E2 in treating osteoporotic OVX mice. Together, our findings reveal that estrogen deficiency-mediated M2 macrophage osteoclastogenesis leads to increased M1/M2 ratio in OVX mice. Reducing the M1/M2 ratio is a potential therapeutic target in treating postmenopausal osteoporosis. © 2017 American Society for Bone and Mineral Research.

Although bone marrow-derived mesenchymal stromal cells (BMSCs) are a main cell source for tissue-engineered bone (TEB), the clinical use of BMSCs is restricted due to the invasive bone marrow aspiration procedure and the decline in available number of mesenchymal stromal cells (MSCs) and differentiation potential with increasing age. Umbilical cord-derived MSCs (UCMSCs) are likely to be a promising alternative cell source for TEB due to their higher availability and potential to proliferate and differentiate. To assess this possibility, we studied bone morphogenetic protein 2 (BMP2)-induced osteogenic differentiation and activation of signaling pathways in UCMSCs and BMSCs. UCMSCs showed a phenotype and differentiation potential similar to that of BMSCs. After 14 days of BMP2 treatment, the overall expression of several osteogenic-specific phenotypes (type I collagen, osteopontin, and osteocalcin) was similar for UCMSCs and BMSCs. The signaling pathway by which BMP2 induced differentiation of both cell types involved the membrane receptor-initiated signals including SMADs, P38, and extracellular regulated kinase. The similar characteristics of BMP2-induced osteogenic differentiation of UCMSCs and BMSCs in vitro would support the use of UCMSCs in TEB.

The objective of this study is to design a graphene‐based miRNA transfection drug delivery system for antiresorptive therapy. An efficient nonviral gene delivery system is developed using polyethylenimine (PEI) functionalized graphene oxide (GO) complex loaded with miR‐7b overexpression plasmid. GO‐PEI complex exhibits excellent transfection efficiency within the acceptable range of cytotoxicity. The overexpression of miR‐7b after GO‐PEI‐miR‐7b transfection significantly abrogates osteoclast (OC) fusion and bone resorption activity by hampering the expression of an essential fusogenic molecule dendritic cell‐specific transmembrane protein. However, osteoclastogenesis occurs without cell–cell fusion and preosteoclast (POC) is preserved. Through preservation of POC, GO‐PEI‐miR‐7b transfection promotes mesenchymal stem cell osteogenesis and endothelial progenitor cells angiogenesis in the coculture system. Platelet‐derived growth factor‐BB secreted by POC is increased by GO‐PEI‐miR‐7b both in vitro and in vivo. In treating osteoporotic ovariectomized mice, GO‐PEI‐miR‐7b significantly enhances bone mineral density, bone volume as well as bone vascularization through increasing CD31hiEmcnhi cell number. This study provides a cell–cell fusion targeted miRNA transfection drug delivery strategy in treating bone disorders with excessive osteoclastic bone resorption.