Knockdown of macrophage inhibitory cytokine-1 in RPMI-8226 human multiple myeloma cells inhibits osteoclastic differentiation through inhibiting the RANKL-Erk1/2 signaling pathway

Administration of zoledronic acid alleviates osteoporosis in HIV patients by suppressing osteoclastogenesis via regulating RANKL expression

Background

Osteoporosis is a common phenomenon in HIV patients on tenofovir treatment, but its underlying mechanisms remain to be explored.

Methods

Quantitative real-time PCR was performed to analyze the expression of miR-302, miR-101, miR-145 and osteoclast-specific genes in the serum of HIV patients treated with tenofovir and ZOL. ELISA was used to evaluate the expression of RANKL, SMAD3 and PRKACB in the serum of these patients. Luciferase assay was carried out to explore the inhibitory effects of miR-302, miR-101 and miR-145 on the expression of PRKACB, RANKL and SMAD3, respectively. Western blot was used to examine the expression of genes involved in NF‑κB and JNK signaling pathways.

Results

ZOL treatment significantly suppressed the expression of CTx and osteocalcin in HIV patients treated with tenofovir. The BMD loss of HIV patients treated with tenofovir was effectively hindered by ZOL treatment. Mechanistically, the expression of miR-302, miR-101, miR-145, RANKL, SMAD3 and PRKACB in the serum was remarkably activated by ZOL treatment. Luciferase assays showed that miR-302, miR-101 and miR-145 effectively suppressed the expression of PRKACB, RANKL and SMAD3, respectively, through binding to their 3′ UTR. Furthermore, ZOL treatment notably restored the normal expression of osteoclast‑specific genes while activating NF‑κB and JNK signaling pathways.

Conclusion

The findings of this study demonstrated that administration of ZOL suppressed the expression of RANKL via modulating signaling pathways of miR-101-3p/RANKL, miR-302/PRKACB/RANKL and miR-145/SMAD3/RANKL. Furthermore, down-regulated expression of RANKL by ZOL treatment alleviated osteoporosis in HIV-positive subjects treated with tenofovir.

Zoledronic acid inhibits osteoclast differentiation and function through the regulation of NF-κB and JNK signalling pathways

It is well known that extensive osteoclast formation plays a key role in osteoporosis in post‑menopausal women and the elderly. The suppression of extensive osteoclastogenesis and bone resorption may be an effective preventive strategy for osteoporosis. Zoledronic acid (ZOL) has been indicated to play an essential role in regulating bone mineral density and has already been used in large clinical trials. However, the effects of ZOL on osteoclastogenesis remain to be fully elucidated. Therefore, the present study aimed to determine the effects of ZOL on osteoclastogenesis, and to explore the corresponding signalling pathways. By using a cell viability assay, as well as in vitro osteoclastogenesis, immunofluorescence and resorption pit assays, we demonstrated that ZOL (0.1‑5 µM) suppressed receptor activator of nuclear factor‑κB ligand (RANKL)‑induced osteoclast differentiation and bone resorptive activity. Furthermore, western blot analysis and reverse transcription‑quantitative PCR indicated that ZOL inhibited the RANKL‑induced activation of NF‑κB and the phosphorylation of JNK in RAW264.7 cells, and subsequently decreased the expression of osteoclastogenesis‑associated genes, including calcitonin receptor, tartrate‑resistant acid phosphatase and dendritic cell‑specific transmembrane protein. ZOL inhibited osteoclast formation and resorption in vitro by specifically suppressing NF‑κB and JNK signalling. On the whole, the findings of this study indicate that ZOL may serve as a potential agent for the treatment of osteoclast‑associated diseases, including osteoporosis.

The antimicrobial peptide, human β-defensin-1, potentiates in vitro osteoclastogenesis via activation of the p44/42 mitogen-activated protein kinases

Previous studies have demonstrated increased expression and raised levels of human β-defensin (hBD)-1 in gingival tissue and crevicular fluid of patients with chronic periodontitis and peri-implantitis, oral bone-resorbing diseases caused by enhanced osteoclastogenesis. Therefore, we aimed to investigate the effect of hBD-1 on osteoclast formation and function and to elucidate the involved signaling pathway in vitro. Human peripheral blood mononuclear cells (PBMCs) were first incubated with various doses of hBD-1 and cell viability was assayed by MTT. PBMCs were treated with macrophage-colony stimulating factor and receptor activator of nuclear factor kappa-B ligand (RANKL) in the presence or absence of non-toxic doses of hBD-1. In vitro osteoclastogenesis was analyzed by tartrate-resistant acid phosphatase (TRAP) staining, osteoclast-specific gene expression, and a resorption pit assay. Involvement of mitogen-activated protein kinases (MAPKs) was studied by immunoblotting and specific MAPK inhibitors. HBD-1 potentiated induction of in vitro osteoclastogenesis by RANKL, as shown by significantly increased number of TRAP-positive multinuclear cells and resorption areas on the dentin slices, and further up-regulated expressions of osteoclast-specific genes compared to those by RANKL treatment (p <0.05). However, hBD-1 treatment without RANKL failed to induce formation of osteoclast-like cells. A significant and further increase in transient phosphorylation of the p44/42 MAPKs was demonstrated by hBD-1 co-treatment (p<0.05), consistent with the inhibitory effect by pretreatment with U0126 or PD98059 on hBD-1-enhanced osteoclastogenesis. Collectively, hBD-1 potentiates the induction of in vitro osteoclastogenesis by RANKL via enhanced phosphorylation of the p44/42 MAPKs.