Effects of HP exposure on chondrocyte metabolism. (A,C,E,F) Expression levels of MMP-13, ADAMTS-5, Col2a1, BCL2, SOD-2, NRF2, miR-34a, miR-146a, miR-181a analyzed by quantitative real-time polymerase chain reaction PCR. (B) Apoptosis detection performed by flow cytometry analysis and measured with Annexin Alexa fluor 488 assay. Data were expressed as the percentage of positive cells for Annexin-V and propidium iodide (PI) staining. (D) Mitochondrial superoxide anion production evaluated by MitoSox Red staining at flow cytometry. Human OA chondrocytes were evaluated at basal condition and after 3~h of low sinusoidal (1–5 MPa) or static continuous (10 MPa) HP exposure. The gene expression, the ratio of apoptosis and the production of superoxide anion were referenced to the ratio of the value of interest and the value of basal condition, reported equal to 1. Data were expressed as mean ± standard deviation SD of triplicate values. * p < 0.05, ** p < 0.01, *** p < 0.001 versus basal condition.