Osteoarthritis (OA) is the most common arthritis that is characterized by the progressive synovial inflammation and loss of articular cartilage. Although GYY4137 is a novel and slow-releasing hydrogen sulfide (H₂S) donor with potent anti-inflammatory properties that may modulate the progression of OA, its underlying mechanism remains unclear. In this study, we validated the protective role of GYY4137 against OA pathological courses and elucidated its underlying regulatory mechanisms. Cell transfection, immunofluorescence staining, EdU assay, transmission electron microscopy, mitochondrial membrane potential measurement, electrophoretic mobility shift assay, sulfhydration assay, qPCR and western blot assays were performed in the primary mouse chondrocytes or the mouse macrophage cell line raw 264.7 for in vitro study. DMM-induced OA mice model and Macrophage-specific p65 knockout (p65^f/f LysM-CreER^T2) mice on the C57BL/6 background were used for in vivo study. We found that GYY4137 can alleviate OA progress by suppressing synovium pyroptosis in vivo. Moreover, our in vitro data revealed that GYY4137 attenuates inflammation-induced NLRP3 and caspase-1 activation and results in a decrease of IL-1β production in macrophages. Mechanistically, GYY4137 increased persulfidation of NF-kB p65 in response to inflammatory stimuli that results in a decrease of cellular reactive oxygen species (ROS) accumulation and ameliorates mitochondrial dysfunctions. Using site-directed mutagenesis, we showed that H₂S persulfidates cysteine38 in p65 protein and hampers p65 transcriptional activity, and p65 mutant impaired macrophage responses to GYY4137. These findings suggest a mechanism by which GYY4137 through redox modification of p65 participates in inhibiting NLRP3 activation by OA to regulate inflammatory responses. Thus, we propose that GYY4137 represents a promising novel therapeutic strategy for the treatment of OA.

Tumor necrosis factor-alpha (TNF-α) promotes osteoclasts differentiation to enhance bone resorption and inhibits osteoblasts differentiation to impair bone formation, which plays a central role in the development of postmenopausal osteoporosis (PMOP). Recent studies implicated an important role of circular RNAs (circRNAs) in osteoporosis. The purpose of this study is to investigate whether circRNAs might be implicated in TNF-α-regulated osteoclasts differentiation and osteoblasts differentiation in PMOP. QRT-PCR was applied to detect expression of circRNA-circHmbox1 and miR-1247-5p in TNF-α-induced osteoclasts differentiation. Western blot, TRAP staining, alkaline phosphatase staining, alizarin red S staining, transwell and cell transfection were conducted to confirm that TNF-α inhibited osteoblasts differentiation by exosomal with low circHmbox1 expression from osteoclasts. Bioinformatics analysis and luciferase reporter revealed the mechanisms of the circHmbox1/miR-1247-5p/B cell lymphoma 6 (Bcl6) interaction. In this study, we found that the level of circRNA-circHmbox1 was obviously reduced in TNF-α-induced osteoclast formation in vivo and in vitro. CircHmbox1 could inhibit RANKL-induced osteoclasts differentiation primarily through binding to microRNA-1247-5p. TNF-α decreased osteoblasts differentiation by exosomal with low circHmbox1 expression from osteoclasts. Mechanistic studies showed that microRNA-1247-5p regulated osteoclasts differentiation and osteoblasts differentiation by targeting Bcl6, which was confirmed to play opposite roles in osteoblasts differentiation and osteoclasts differentiation. Our results provide evidence that circHmbox1-targeting miR-1247-5p is involved in the regulation of bone metabolisms by TNF-α in PMOP.

Osteoarthritis (OA) is one of the most frequent chronic joint diseases with the increasing life expectancy. The main characteristics of the disease are loss of articular cartilage, subchondral bone sclerosis and synovium inflammation. Physical measures, drug therapy and surgery are the mainstay of treatments for OA, whereas drug therapies are mainly limited to analgesics, glucocorticoids, hyaluronic acids and some alternative therapies because of single therapeutic target of OA joints. Baicalein, a traditional Chinese medicine extracted from Scutellaria baicalensis Georgi, has been widely used in anti‐inflammatory therapies. Previous studies revealed that baicalein could alleviate cartilage degeneration effectively by acting on articular chondrocytes. However, the mechanisms involved in baicalein‐mediated protection of the OA are not completely understood in consideration of integrality of arthrosis. In this study, we found that intra‐articular injection of baicalein ameliorated subchondral bone remodelling. Further studies showed that baicalein could decrease the number of differentiated osteoblasts by inhibiting pre‐osteoblasts proliferation and promoting pre‐osteoblasts apoptosis. In addition, baicalein impaired angiogenesis of endothelial cells and inhibited proliferation of synovial cells. Taken together, these results implicated that baicalein might be an effective medicine for treating OA by regulating multiple targets.

Background: Calcium ion (Ca²⁺) signals are required for osteoclast differentiation. Previous study showed that transient receptor potential vanilloid 5 (TRPV5) is an essential Ca²⁺ transporter in osteoclastogenesis and bone resorption. TRPV5 and TRPV6 represent two highly homologous members within the transient receptor potential (TRP) superfamily. However, the role of TRPV6 in bone metabolism is still controversial and little is known about the involvement of TRPV6 in receptor activator of nuclear factor κ-B ligand (RANKL)-induced osteoclastogenesis. Methods: In our study, gene knockout mice, RNA interference, western blot, quantitative real-time PCR, tartrate-resistant acid phosphatase (TRAP) staining, pit formation assay, histomorphometry and measurement of serum parameters were employed to investigate the role of TRPV6 in bone homeostasis, osteoclastogenesis and bone resorption. Results: We found that TRPV6 depletion results in noticeable destruction of bone microarchitecture in TRPV6 knockout mice (TRPV6^-/-), suggesting that TRPV6 is a critical regulator in bone homeostasis. Inactivation of Trpv6 had no effect on osteoblastic bone formation. However, quantification of the TRAP staining showed a significantly increased osteoclast number and surface area in the metaphyseal area of femurs bone sections derived from TRPV6^-/- mice. In agreement with our observations from TRPV6^-/- mice, TRPV6 depletion in vitro significantly increased osteoclasts differentiation and bone resorption activity. Conclusion: Based on these results above, we can draw conclusions that TRPV6 plays an essential role in bone metabolism and is a critical regulator in osteoclasts differentiation and bone resorption.

Hydrogen sulfide (H₂S), a gasotransmitter, plays an important role in the regulation of bone homeostasis. However, the precise effect of H₂S on osteoclasts was still elusive. The goal of this study was to determine the potential role of H₂S in regulation of osteoclasts and the underlying mechanisms by which H₂S affected osteoclastogenesis. The present study applied western blot, quantitative real-time PCR, tartrate-resistant acid phosphatase staining, pit formation assay, immunofluorescence confocal microscopy, transmission electron microscopy, and annexin v-fluorescein isothiocyanate/propidium iodide double-staining assay. The results showed that the expressions of cystathionine b-synthase (CBS) and cystathionine c-lyase (CSE) were obviously increased in osteoclast differentiation induced by the receptor activator of nuclear factor kappa-Β ligand (RANKL). In addition, H₂S promoted RANKL-induced osteoclastogenesis and inhibited apoptosis of mature osteoclasts. Mechanistically, H₂S inhibited autophagy in Raw 264.7 cells. Autophagy activator (rapamycin) alleviated the induction of osteoclast differentiation by H₂S. Further studies showed that H₂S inhibited autophagy by activating the PI3K/AKT/mTOR signaling pathway. Taken together, our results implicated that exogenous H₂S could promote osteoclastogenesis by activating the PI3K/AKT/mTOR pathway to downregulate autophagy.