Rapamycin Inhibits Nf-ΚB Activation by Autophagy to Reduce Catabolism in Human Chondrocytes

Osteoarthritis is a disease that is accompanied by inflammation and catabolic disorders in the cartilage. Rapamycin is a good autophagy activator and has an inhibitory effect on inflammation, and autophagy can remove waste generated by catabolic disorders and delay the destruction of cartilage by inflammation. This study was designed to evaluate the effect of rapamycin upon the catabolism in human chondrocytes and unravel underlying mechanism.

Rapamycin can inhibit the overexpression of inflammatory catabolic genes by activating autophagy, and can suppress the NF-κB signaling pathway in chondrocytes to break the positive feedback loop with inflammatory factors and reduce the rate and level of inflammation progression.

C57 mice and SW1353 cells were cultured and osteoblastic arthritis was formed by destabilization of the medial meniscus surgery; 10 ng/ml of IL-1β was added to the cells to produce inflammatory chondrocytes, and a non-cytotoxic concentration of 20 nM Rapamycin was used as the self-activator. Autophagy levels were verified by quantitative analysis of autophagy markers of LC3 and ATG5, and it was verified that rapamycin can activate autophagy. Autophagy inhibition was induced by ATG5 siRNA by comparing the presence of rapamycin treatment in inflammatory chondrocytes. The expression of the degrading gene and chemokine was evaluated by qPCR. Rapamycin down-regulated the expression of MMP-3 and -9, ADAMTS5, CCL-1, -2, and -5 induced by inflammation. Quantitative analysis of IκBα and P-P65 was used to analyze the interaction between the NF-κB pathway and autophagy in inflammation. Activation of the NF-κB pathway by inflammatory stimulation, P-P65 nuclear translocation, and degradation of IκBα protein were attenuated, respectively. Autophagy inhibited the activation of NF-κB signaling pathway in inflammatory chondrocytes. Conclusions: Rapamycin can inhibit the overexpression of inflammatory catabolic genes by activating autophagy, and can suppress the NF-κB signaling pathway in chondrocytes to break the positive feedback loop with inflammatory factors and reduce the rate and level of inflammation progression.