Fig. 2

ERK2 can regulate USP15 and TGF-β signaling to maintain the cartilage phenotype in vivo and in vitro. a–c Overexpression or knockout of ERK2 in ATDC5 cells with TGF-β1 (10 ng/mL) or PD98059 (10 μM). d Immunofluorescence staining performed in ATDC5 cells with or without ERK2 overexpression for Col2a1, Aggrecan, and Col10a1 (scale bars = 50 μm). e The intensities of immunofluorescence of Col2a1, Aggrecan, and Col10a1 in each group were calculated, and the data were presented as the mean ± SD. f–h The expression levels of ERK2, USP15, p-SMAD2, Col2a1, Aggrecan, and MMP13 in the two groups were detected by immunohistochemistry, and the cartilage tissue morphology in the two groups were detected by HE/Safranin-O fast green staining (n = 4 for control groups in the sham surgery models, n = 4 for AAV-mediated ERK2 knockdown groups in the sham surgery models). f Scale bars = 50 μm. g Scale bars = 50 μm. h Scale bars = 200 μm. i The relative expressions of ERK2, USP15, p-SMAD2, Col2a1, Aggrecan, and MMP13 in each group were calculated via immunohistochemistry, and the hyaline cartilage thickness and OARSI scores were quantified. The data were presented as the mean ± SD. *P < 0.05, **P < 0.01, ***P < 0.001. j Relative gene expressions of Col2a1, Aggrecan, and Sox9, which are associated with cartilage anabolic metabolism, were detected by quantitative real-time PCR in both groups (n = 3 for control groups in the sham surgery models followed by quantitative real-time PCR, n = 3 for AAV-mediated ERK2 knockdown groups in the sham surgery models followed by quantitative real-time PCR). The data were presented as the mean ± SD. *P < 0.05, **P < 0.01, ***P < 0.001. All experiments were performed at least three times