Effect of PPARG on AGEs-induced AKT/MTOR signaling-associated human chondrocytes autophagy.

Accumulation of advanced glycation end products (AGEs) in articular cartilage is thought to represent a major risk factor for osteoarthritis development. In this study we aimed to probe the role of AGEs in human chondrocytes and to determine the impact of the peroxisome proliferator-activated receptor-γ (PPARG) on AGEs-induced cell autophagy. Cell viability was measured after human chondrocytes were treated with different concentrations of AGEs with or without the PPARG inhibitor, T0070907, or agonist, pioglitazone. Autophagy activation markers (MAP2LC3, BECN1 and SQSTM1/P62), expression of PPARG and the phosphorylation levels of Akt/MTOR were determined by Western blotting; autophagosome formation was analyzed by transmission electron microscopy (TEM); autophagic flux was detected with mRFP-GFP-LC3 tandem construct. Low doses of AGEs over a short amount of time stimulated chondrocyte proliferation and autophagy by limiting phosphorylation of Akt/MTOR signaling. The addition of PPARG inhibitor T0070907 lead to defective autophagy. High dose and long exposure to AGEs inhibited cell viability and autophagy by increasing phosphorylation levels of Akt/MTOR signaling. The agonist, pioglitazone, was shown to protect cell autophagy in a dose-dependent manner. Our findings suggest AGEs can downregulate PPARG and that PPARG maintains cell viability by activating the Akt/MTOR signaling pathway as well as inducing chondrocyte autophagy.