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Osteoarthritis (OA), in which M1 macrophage polarization in the synovium exacerbates disease progression, is a major cause of cartilage degeneration and functional disabilities. Therapeutic strategies of OA designed to interfere with the polarization of macrophages have rarely been reported. Here, we report that SHP099, as an allosteric inhibitor of src-homology 2-containing protein tyrosine phosphatase 2 (SHP2), attenuated osteoarthritis progression by inhibiting M1 macrophage polarization. We demonstrated that M1 macrophage polarization was accompanied by the overexpression of SHP2 in the synovial tissues of OA patients and OA model mice. Compared to wild-type (WT) mice, myeloid lineage conditional Shp2 knockout (cKO) mice showed decreased M1 macrophage polarization and attenuated severity of synovitis, an elevated expression of cartilage phenotype protein collagen II (COL2), and a decreased expression of cartilage degradation markers collagen X (COL10) and matrix metalloproteinase 3 (MMP3) in OA cartilage. Further mechanistic analysis showed thatSHP099 inhibited lipopolysaccharide (LPS)-induced Toll-like receptor (TLR) signaling mediated by nuclear factor kappa B (NF-κB) and PI3K–AKT signaling. Moreover, intra-articular injection of SHP099 also significantly attenuated OA progression, including joint synovitis and cartilage damage. These results indicated that allosteric inhibition of SHP2 might be a promising therapeutic strategy for the treatment of OA.

Background: Cartilage repair has been a challenge in the field of orthopaedics for decades, highlighting the significance of investigating potential therapeutic drugs. In this study, we explored the effect of the SHP2 inhibitor SHP099, a small-molecule drug, on cartilage repair. Methods: Human synovial mesenchymal stem cells (SMSCs) were isolated, and their three-way differentiation potential was examined. After treatment with chondrogenic medium, the chondrogenic effect of SHP099 on SMSCs was examined by western blot, qPCR, and immunofluorescence (IF). Micro-mass culture was also used to detect the effect of SHP099. To explore the chondrogenic effects of SHP099 in vivo, full-thickness cartilage defects with microfractures were constructed in the right femoral trochlea of New Zealand White rabbits. Intraarticular injection of SHP099 or normal saline was performed twice a week for 6 weeks. Cartilage repair was evaluated by haematoxylin and eosin (HE) staining and safranin O/fast green staining. Immunohistochemistry (IHC) for collagen II (COL2) was also conducted to verify the abundance of cartilage extracellular matrix after SHP099 treatment. The mechanism involving yes-associated protein (YAP) and WNT signalling was investigated in vitro. Results: SMSCs isolated from human synovium have optimal multi-differentiation potential. SHP099 increased chondrogenic marker (SOX9, COL2) expression and decreased hypertrophic marker (COL10, RUNX2) expression in SMSCs. In micro-mass culture, the SHP099-induced cartilage tissues had a better result of Safranin O and Toluidine blue staining and are enriched in cartilage-specific collagen II. Inhibition of YAP and WNT signalling was also observed. Moreover, compared to the normal saline group at 6 weeks, intraarticular injection of SHP099 resulted in better defect filling, forming increased hyaline cartilage-like tissue with higher levels of glycosaminoglycan (GAG) and COL2. Conclusion: SHP099 promotes the repair of rabbit full-thickness cartilage defects, representing a potential therapeutic drug for cartilage repair. The Translational potential of this article: This study provides evidence that SHP2 inhibition promotes chondrogenesis and the repair of cartilage in defect area, which could be a novel therapeutic approach for cartilage repair.

Abstract Osteoarthritis (OA) is the major course of joint deterioration, in which M1 macrophage-driven synovitis exacerbates the pathological process. However, precise therapies for M1 macrophage to decrease synovitis and attenuate OA progression have been scarcely proposed. Transient receptor potential vanilloid 1 (TRPV1) is a cation channel that has been implicated in pain perception and inflammation. In this study, we investigated the role of TRPV1 in the M1 macrophage polarization and pathogenesis of OA. We demonstrated that TRPV1 expression and M1 macrophage infiltration were simultaneously increased in both human and rat OA synovium. More than 90% of the infiltrated M1 macrophages expressed TRPV1. In the rat OA model, intra-articular injection of capsaicin (CPS), a specific TRPV1 agonist, significantly attenuated OA phenotypes, including joint swelling, synovitis, cartilage damage, and osteophyte formation. CPS treatment markedly reduced M1 macrophage infiltration in the synovium. Further mechanistic analyses showed that TRPV1-evoked Ca2+ influx promoted the phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and facilitated the nuclear localization of nuclear factor-erythroid 2-related factor 2 (Nrf2), which ultimately resulted in the inhibition of M1 macrophage polarization. Taken together, our findings establish that TRPV1 attenuates the progression of OA by inhibiting M1 macrophage polarization in synovium via the Ca2+/CaMKII/Nrf2 signaling pathway. These results highlight the effect of targeting TRPV1 for the development of a promising therapeutic strategy for OA.

Knee osteoarthritis (KOA) is the most common form of joint degeneration with increasing prevalence and incidence in recent decades. KOA is a molecular disorder characterized by the interplay of numerous molecules, a considerable number of which can be detected in body fluids, including synovial fluid, urine, and blood. However, the current diagnosis and treatment of KOA mainly rely on clinical and imaging manifestations, neglecting its molecular pathophysiology. The mismatch between participants’ molecular characteristics and drug therapeutic mechanisms might explain the failure of some disease-modifying drugs in clinical trials. Hence, according to the temporal alteration of representative molecules, we propose a novel molecular classification of KOA divided into pre-KOA, early KOA, progressive KOA, and end-stage KOA. Then, progressive KOA is furtherly divided into four subtypes as cartilage degradation-driven, bone remodeling-driven, inflammation-driven, and pain-driven subtype, based on the major pathophysiology in patient clusters. Multiple clinical findings of representatively investigated molecules in recent years will be reviewed and categorized. This molecular classification allows for the prediction of high-risk KOA individuals, the diagnosis of early KOA patients, the assessment of therapeutic efficacy, and in particular, the selection of homogenous patients who may benefit most from the appropriate therapeutic agents.