Cyclin-dependent kinase inhibitor p16INK4aparticipates in matrix metalloproteinase 1 (MMP1) and MMP13 expression in mature chondrocytes. Osteoarthritis (OA) human primary chondrocytes were transfected with vector encoding for p16INK4a or empty vector (EV) for 24 hours and placed in pellet for 7 days. (A) Gene expression analysis was performed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) for p16INK4a (n = 5). (B) p16INK4a protein expression was detected by immunohistochemistry (IHC) on pellet paraffin sections. Images were taken with a ×20 objective. (C-F) MMP1, MMP13, interleukin-6 (IL-6), and IL-8 secretions were measured by enzyme-linked immunosorbent assay (ELISA) (n = 5). Data are shown as mean ± standard deviation (SD). *P <0.05.