Different roles of Akt and mechanistic target of rapamycin in serum-dependent chondroprotection of human osteoarthritic chondrocytes

Despite various animal serums being used widely to culture chondrocytes, the regulatory mechanism of serum on chondrocyte activities has not been elucidated. In the present study, human osteoarthritis (OA) chondrocytes were used to perform in vitro investigations on the effect of different concentrations of bovine fetal serum on extracellular matrix synthesis, cell proliferation and autophagy using the Cell Counting Kit-8 analysis, a laser-scanning confocal microscope, and western blot analysis. The results demonstrated that 5% serum exerted a chondroprotective effect more than the other concentrations of serum, as it simultaneously promoted cell proliferation, autophagy, and ECM synthesis in human OA chondrocytes. Furthermore, the decreased mechanistic target of rapamycin (mTOR) and increased Akt were observed in 5% serum-treated OA chondrocytes. Either mTOR or Akt inhibitor influenced the effect of 5% serum on cell proliferation and autophagy in human OA chondrocytes, which was associated with LC-3B or B-cell lymphoma-2 (Bcl-2) signal molecules. Consistent with previous studies, the present study proposes that 5% serum promotes cell proliferation via the Akt/Bcl-2 axis and induces autophagy via the mTOR/LC-3B axis in human OA chondrocytes. Furthermore, the different roles of Akt and mTOR in the cell processes of human OA chondrocytes require consideration for preclinical and clinical therapy of OA.