Decrease of HDAC4 protein determined by western blotting in human aging and OA cartilage specimens. (A) Safranin O staining was performed to show degeneration changes in the cartilage from a 61-year-old OA patient undergoing total knee arthroplasty, and the lack thereof in normal cartilage from a 60-year-old male patient and 23-year-old male patient undergoing amputation because of trauma. (B) Western blotting showed decreased expression of HDAC4 in human aging and OA cartilage. β-actin and Coomassie Blue staining was used to confirm equal loading of total proteins from cartilage samples. (C) Semi-quality by densitometry showed that the mean concentration of HDAC4 was 31% and 65% in the cartilage of OA patients (n = 6) and the 40 to 60 age group (n = 6), respectively, compared with the cartilage of the 20 to 40 age group (n = 6). *P represents that the difference was statistically significant (P <0.05). HDAC4, histone deacetylase 4; OA, osteoarthritis.