Osteoarthritis (OA) is a common degenerative joint disease. The pathogenesis of OA is closely related to inflammatory responses and apoptosis of chondrocytes. Hyperoside (Hyp), a natural flavonoid compound, exerts multiple bioactivities in various diseases. Our study aims to investigate the anti-arthritic effects of Hyp and delineate the potential mechanism at the cellular level. Murine chondrocytes were stimulated with interleukin-1β (IL-1β) with or without Hyp treatment. CCK-8 assay was used to evaluate the cytotoxic effect of Hyp. DCFH-DA was used to detect intracellular ROS. Annexin V-FITC/PI method was applied to examine apoptosis of chondrocytes. The anti-arthritic effects of Hyp and related mechanisms were investigated by examining and analyzing relative markers through quantitative PCR, western blot analysis and immunofluorescent staining. C57BL/6 mice were performed the destabilized medial meniscus (DMM) surgery to establish OA model and then injected intraperitoneally with Hyp (20 mg/kg)) for 4 or 8 weeks. Finally, mice were sacrificed and knee joints were collected for histological observation and analysis. Hyp inhibited IL-1β-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Additionally, Hyp attenuated IL-1β-induced destruction of the extracellular matrix (ECM) by downregulating the expression of MMPs and ADAMTS5, and meanwhile upregulating the expression of collagen II, aggrecan, and SOX9. Also, Hyp pretreatment reduced IL-1β-induced overproduction of ROS and apoptosis of chondrocytes. Mechanistically, Hypexerted anti-inflammatory effects by partly suppressing the PI3K/AKT/NF-κB and the MAPK signaling pathways, enhancing the Nrf2/HO-1 to limit the activation of NF-κB. Moreover, Hyp played an anti-apoptotic effect via the Nrf2/ROS/BAX/Bcl-xlaxis. In vivo, cartilage degradation was attenuated with a lower OARSI score in Hyp-treated group compared to the DMM group. Our study demonstrated that anti-arthritic effects of Hyp in vitro and in vivo, indicating Hyp might serve as a potential agent for the treatment of OA.

N6-methyladenosine (m6A) is the most prevalent internal mRNA modification. m6A can be installed by the methyltransferase complex and removed by demethylases, which are involved in regulating post-transcriptional expression of target genes. RNA methylation is linked to various inflammatory states, including autoimmunity, infection, metabolic disease, cancer, neurodegenerative diseases, heart diseases, and bone diseases. However, systematic knowledge of the relationship between m6A modification and inflammation in human diseases remains unclear. In this review, we will discuss the association between m6A modification and inflammatory response in diseases, especially the role, mechanisms, and potential clinical application of m6A as a biomarker and therapeutic target for inflammatory diseases.

Osteoclasts are multinucleated giant cells with the ability to degrade bone tissue, and are closely related to abnormal bone metabolic diseases. Endoplasmic reticulum (ER) is an organelle responsible for protein modification, quality control, and transportation. The accumulation of unfolded or misfolded proteins in ER cavity induces ER stress. Double-stranded RNA-dependent protein kinase-like ER kinase (PERK) is an ER stress-sensing protein, which is ubiquitous in eukaryotic cells. Systemic PERK knockout mice show severe bone loss, suggesting that PERK is of great significance for maintaining the normal growth and development of bone tissue, but the role of PERK in osteoclastogenesis is still unclear. In this study, we found that PERK was significantly activated during RANKL-induced osteoclast differentiation; knockdown of PERK by siRNA and inhibition of PERK by GSK2606414, respectively, had significant negative regulatory effects on the formation and bone resorption of osteoclasts. PERK inhibitor GSK2606414 down-regulated the mRNA levels and protein expression of osteoclast differentiation marker genes, and inhibited RANKL-induced activation of Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Treatment with PERK inhibitor GSK2606414 in ovariectomized mouse model significantly suppressed bone loss and osteoclast formation. Thapsigargin activated ER stress to enhance autophagy, while GSK2606414 had a significant inhibitory effect on autophagy flux and autophagosome formation. Antioxidant N-acetylcysteine (NAC) could inhibit the expression of PERK phosphorylation, osteoclast-related proteins and autophagy-related proteins, but the use of PERK activator CCT020312 can reverse inhibition effect of NAC. Our findings demonstrate a key role for PERK in osteoclast differentiation and suggest its therapeutic potential.

Bone marrow mesenchymal stem cells (BMSCs) differentiation dysfunction is a common pathological phenotype of several prevalent metabolic and genetic bone diseases. Pyruvate kinase muscle isoenzyme 2 (PKM2) regulates the last step of glycolysis, and its role in BMSCs differentiation is still unknown. In this study, the influence of PKM2 on osteogenesis and adipogenesis was assessed in vitro and in vivo. We found that DASA-58 (the activator of PKM2) reduced the enzymatic activity of ALP, and inhibited the levels of osteogenic marker genes, especially RUNX2, which is a crucial transcription factor for osteogenesis. Besides, we provided evidence that C3k, an inhibitor of PKM2, caused increase in mitochondrial membrane potential and maintained low levels of ROS, and promoted mitochondrial fusion. Furthermore, after treatment with DASA-58, the level of active β-catenin gradually decreased, which also inhibited the transport of active β-catenin into the nucleus, but C3k obviously promoted its nuclear translocation. As for adipogenesis, PKM2 activation increased the expression of adipogenic related genes and decreased active-β-catenin expression, whereas treatment of C3k had the opposite effect. In addition, C3k significantly attenuated ovariectomy-induced trabecular bone loss in vivo. Our findings helped uncover the molecular mechanisms underlying PKM2 regulation of BMSCs differentiation.