Objectives: The main target of current drugs for alleviating bone loss is osteoclasts.However, the long-term application of such drugs will also cause side effects. Therefore, it is of great need to develop new and safer therapeutics for osteoporosis. In recent years, drug development based on gut microbiota has gradually attracted attention. This manuscript investigates the inhibitory effect of urolithin B (UB) on osteoclastogenesis and differentiation in vitro and in ovariectomized (OVX) mice.Materials and Methods: CCK-8 was used to analyse the cytotoxicity of UB; BMMs cells were differentiated into osteoclasts by RANKL, and respectively treated with 1, 5, and 25 μmol/L UB during this process. After one week of intervention, tartrateresistant acid phosphatase (TRAP) staining was used to analyse the number and average area of osteoclasts. F-actin staining and immunofluorescence staining were conducted to evaluate the morphology and function of osteoclasts. Bone resorption function of osteoclasts was detected by Pit Formation Assay. The expression of osteoclast-related protein genes in RAW264.7 cells were investigated via western blot and RT-PCR assays. Western blot analysis of RANKL-mediated activation of MAPK/NF-κB pathway after 0, 5, 15, 30, 60 min of intervention. For in vivo experiments, OVX mice received intraperitoneal injection of 10, 50 mg/kg every two days, 8 weeks later, the femurs of mice were taken for morphological analysis, and the serum content of CTX-1, a bone metabolism index, was analysed.Results: UB could inhibit the osteoclast differentiation of rankl-induced bone marrow macrophages (BMMs) and RAW264.7 cells in vitro, suppress the uptake activity of Yajun Li, Qi Zhuang, Lihong Tao and Kai Zheng equal contribution.

Osteoporosis (OP) is mainly manifested by bone loss and bone degeneration. OP is considered a risk factor for pathological fractures, as well as impacts the health of middle-aged and elderly individuals. Drug therapy remains the main treatment scheme for OP; however, its efficacy is limited and has been associated with serious side effects. Therefore, it is important to develop new, effective, and safe treatment methods for OP. Avicularin (AL) is a flavonoid and quercetin derivative from various plants. Our study showed that AL disrupts osteoclast activation and resorptive function via inhibition of the RANKL-induced osteoclast differentiation together with the resorption capacity of bone marrow-derived macrophages (BMMs). Hence, AL prevents the activation and resorptive activity of osteoclasts. The results of qPCR showed that genes related to osteoclasts exhibited downregulated expression after AL treatment. Furthermore, AL inhibited RANKL-induced phosphorylation as well as degradation of the inhibitor IκBα of the NF-κB pathway, together with P65 phosphorylation in BMMs. We used an OP mouse model that was established by ovariectomy (OVX). Relative to untreated OP mice, mice that received AL treatment showed a significant increase in bone mineral density; however, the expression of TRAP, NFATC1, mmp9, and CTX-1 was significantly reduced. These results indicate that AL disrupts osteoclastogenesis via inhibition of the NF-κB pathway, which in turn improves OVX-induced OP.

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Background: Osteoarthritis is a common chronic degenerative disease, and recently, an increasing number of studies have shown that immunity plays an important role in the progression of osteoarthritis, which is exacerbated by local inflammation. The role of N6-methyladenine (m6A) modification in immunity is being explored. However, the role of m6A modification in regulating the immune microenvironment of osteoarthritis remains unknown. In this study, we sought to discuss the association between the N6-methyladenine (m6A) modification and the immune microenvironment of osteoarthritis.Methods: First, the data and gene expression profiles of 139 samples, including 33 healthy samples and 106 osteoarthritis samples, were obtained from the Genetics osteoARthritis and Progression (GARP) study. Then the differences in m6A regulators between healthy individuals and osteoarthritis patients were analyzed. The correlation between m6A regulators and immune characteristics was also investigated by single-sample gene set enrichment analysis (ssGSEA). Principal component analysis (PCA), Gene Set Variation Analysis (GSVA) enrichment analysis, weighted gene coexpression network analysis (WGCNA), and Associated R packages were used to identify the m6A phenotype and its biological functions.Results: A total of 23 m6A regulators were involved in this study. We found a close correlation between most m6A regulators in all samples as well as in osteoarthritis samples. VIRMA and LRPPRC were the most highly correlated m6A regulators and showed a positive correlation, whereas VIRMA and RBM15B were the most negatively correlated. M6A regulators are associated with osteoarthritis immune characteristics. For example, MDSC cell abundance was strongly correlated with RBM15B and HNRNPC. Meanwhile, RBM15B and HNRNPC were important effectors of natural killer cell immune responses. IGFBP3 is an important regulator of cytolytic activity immune function. We performed an unsupervised consensus cluster analysis of the osteoarthritis samples based on the expression of 23 m6A regulators. Three different m6A subtypes of osteoarthritis were identified, including 27 samples in subtype C1, 21 samples in subtype C2, and 58 samples in subtype C3. Different m6A subtypes have unique biological pathways and play different roles in the immune microenvironment of osteoarthritis.Conclusion: The m6A modification plays a crucial role in the diversity and complexity of the immune microenvironment in osteoarthritis.

Periprosthetic osteolysis (PPO), caused by wear particles, has become a major cause of joint replacement failure. Secondary surgery after joint replacement poses a serious threat to public health worldwide. Therefore, determining how to effectively inhibit wear particle-induced PPO has become an urgent issue. Recently, the interaction between osteogenic inhibition and wear particles at the biological interface of the implant has been found to be an important factor in the pathological process. Previous studies have found that the central nervous system plays an important role in the regulation of bone formation and bone remodeling. Dopamine (DA), an important catecholamine neurotransmitter, plays an integral role in the physiological and pathological processes of various tissues through its corresponding receptors. Our current study found that upregulation of dopamine first receptors could be achieved by activating the Wnt/β-catenin pathway, improving osteogenesis in vivo and in vitro, and significantly reducing the inhibition of titanium particle-induced osteogenesis. Overall, these findings suggest that dopamine first receptor (D1R) may be a plausible target to promote osteoblast function and resist wear particle-induced PPO.