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Abstract Studies in recent years have highlighted an elaborate crosstalk between T cells and bone cells, suggesting that T cells may be alternative therapeutic targets for the maintenance of bone homeostasis. Here, it is reported that systemic administration of low‐dose staphylococcal enterotoxin C2 (SEC2) 2M‐118, a form of mutant superantigen, dramatically alleviates ovariectomy (OVX)‐induced bone loss via modulating T cells. Specially, SEC2 2M‐118 treatment increases trabecular bone mass significantly via promoting bone formation in OVX mice. These beneficial effects are largely diminished in T‐cell‐deficient nude mice and can be rescued by T‐cell reconstruction. Neutralizing assays determine interferon gamma (IFN‐γ) as the key factor that mediates the beneficial effects of SEC2 2M‐118 on bone. Mechanistic studies demonstrate that IFN‐γ stimulates Janus kinase/signal transducer and activator of transcription (JAK–STAT) signaling, leading to enhanced production of nitric oxide, which further activates p38 mitogen‐activated protein kinase (MAPK) and Runt‐related transcription factor 2 (Runx2) signaling and promotes osteogenic differentiation. IFN‐γ also directly inhibits osteoclast differentiation, but this effect is counteracted by proabsorptive factors tumor necrosis factor alpha (TNF‐α) and interleukin 1 beta (IL‐1β) secreted from IFN‐γ‐stimulated macrophages. Taken together, this work provides clues for developing innovative approaches which target T cells for the prevention and treatment of osteoporosis.

Abstract The knowledge of osteoarthritis (OA) has nowadays been extended from a focalized cartilage disorder to a multifactorial disease. Although recent investigations have reported that infrapatellar fat pad (IPFP) can trigger inflammation in the knee joint, the mechanisms behind the role of IPFP on knee OA progression remain to be defined. Here, dysregulated osteopontin (OPN) and integrin β3 signaling are found in the OA specimens of both human and mice. It is further demonstrated that IPFP‐derived OPN participates in OA progression, including activated matrix metallopeptidase 9 in chondrocyte hypertrophy and integrin β3 in IPFP fibrosis. Motivated by these findings, an injectable nanogel is fabricated to provide sustained release of siRNA Cd61 (RGD−Nanogel/siRNA Cd61) that targets integrins. The RGD−Nanogel possesses excellent biocompatibility and desired targeting abilities both in vitro and in vivo. Local injection of RGD−Nanogel/siRNA Cd61 robustly alleviates the cartilage degeneration, suppresses the advancement of tidemark, and reduces the subchondral trabecular bone mass in OA mice. Taken together, this study provides an avenue for developing RGD−Nanogel/siRNA Cd61 therapy to mitigate OA progression via blocking OPN‐integrin β3 signaling in IPFP.