Linagliptin ameliorated interleukin-29-induced reduction of extracellular matrix genes through the nuclear factor erythroid 2-related factor 2 (Nrf2)/sry-type high-mobility-group box (SOX)-9 axis in an in vitro study on C-28/I2 chondrocytes

Osteoarthritis (OA) is a severe orthopedic disease commonly observed in the elderly population and is closely related to the degradation of extracellular matrix (ECM) in cartilage tissues. Interleukin-29 (IL-29) is a cytokine that has been recently linked with the progression of OA. However, the physiological roles of IL-29 in ECM genes and function are unknown. Linagliptin is a novel dipeptidyl peptidase-4 (DPP-4) inhibitor recently reported to exert significant anti-inflammatory properties. In this study, we used IL-29 to stimulate C-28/I2 chondrocytes to build an inflammatory injury model. We aimed to investigate the protective effect of Linagliptin on IL-29-induced degradation of ECM. We found that IL-29 stimulation reduced the expressions of Col2a1 and Acan in C-28/I2 chondrocytes, and this effect was mediated by SRY-related high-mobility group box gene-9 (SOX-9), as we showed that overexpression of SOX-9 could rescue the reduction of Col2a1 and Acan. Interestingly, we found that IL-29 stimulation pronouncedly promoted the expression of DPP-4. Treatment with 100 nM of the DPP-4 inhibitor Linagliptin ameliorated IL-29-induced expressions of SOX-9, Col2a1, and Acan. Lastly, the nuclear level of nuclear factor erythroid 2-related factor 2 (Nrf2) was dramatically declined in IL-29-challenged chondrocytes and the protective effects of Linagliptin on the expressions of SOX-9, Col2a1, and Acan were abolished by the knockdown of Nrf2. Taken together, our data reveal that Linagliptin ameliorated IL-29-induced reduction of ECM genes partially through the Nrf2/SOX-9 axis in C-28/I2 chondrocytes. Further in vivo and clinical studies will be done to clarify the protective benefits of Linagliptin in OA.