Autophagy protects end plate chondrocytes from intermittent cyclic mechanical tension induced calcification

Calcification of end plate chondrocytes is a major cause of intervertebral disc (IVD) degeneration. However, the underlying molecular mechanism of end plate chondrocyte calcification is still unclear. The aim of this study was to clarify whether autophagy in end plate chondrocytes could protect the calcification of end plate chondrocytes. Previous studies showed that intermittent cyclic mechanical tension (ICMT) contributes to the calcification of end plate chondrocytes in vitro. While autophagy serves as a cell survival mechanism, the relationship of autophagy and induced end plate chondrocyte calcification by mechanical tension in vitro is unknown. Thus, we investigated autophagy, the expression of the autophagy genes, Beclin-1 and LC3, and rat end plate chondrocyte calcification by ICMT. The viability of end plate chondrocytes was examined using the LIVE/DEAD viability/cytotoxicity kit. The reverse transcription-polymerase chain reaction and western blotting were used to detect the expression of Beclin-1; LC3; type I, II and X collagen; aggrecan; and Sox-9 genes. Immunofluorescent and fluorescent microscopy showed decreased autophagy in the 10- and 20-day groups loaded with ICMT. Additionally, Alizarin red and alkaline phosphatase staining detected the palpable calcification of end plate chondrocytes after ICMT treatment. We found that increased autophagy induced by short-term ICMT treatment was accompanied by an insignificant calcification of end plate chondrocytes. To the contrary, the suppressive autophagy inhibited by long-term ICMT was accompanied by a more significant calcification. The process of calcification induced by ICMT was partially resisted by increased autophagy activity induced by rapamycin, implicating that autophagy may prevent end plate chondrocyte calcification.