Mechanical stress protects against chondrocyte pyroptosis through TGF-β1-mediated activation of Smad2/3 and inhibition of the NF-κB signaling pathway in an osteoarthritis model

Osteoarthritis (OA) is a degenerative disease that is difficult to cure owing to its complicated pathogenesis. Exercise therapy has been endorsed as a primary treatment option. However, it remains controversial how exercise intensity regulates OA progression. Here, a declining propensity for TGF-β1 was predicted via bioinformatics analysis of microarray GSE57218 and validated in cartilage samples obtained from arthroplasty. Based on this, cyclic tensile strain or TGF-β1 intervention was performed on human OA chondrocytes, and we found that moderate-intensity mechanical loads protected chondrocytes against pyroptosis. During this process, the elevation of TGF-β1 is mechanically stimuli-dependent and exerts an inhibitory effect on chondrocyte pyroptosis. Moreover, we elucidated that TGF-β1 activated Smad2/3 and inhibited the NF-κB signaling pathway to suppress chondrocyte pyroptosis. Furthermore, we established a rat knee OA model by intra-articular injection of monosodium iodoacetate and performed treadmill exercises of different intensities. Similar to the in vitro results, we demonstrated that moderate-intensity treadmill exercise had an outstanding chondroprotective effect. An inappropriate intensity of mechanical stimulation may aggravate OA both in vivo and in vitro. Overall, our findings demonstrated that activation of the TGF-β1/Smad2/Smad3 axis and inhibition of NF-κB coordinately inhibit chondrocyte pyroptosis under mechanical loads. This study sheds light on the future development of safe and effective exercise therapies for OA.