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

Abstract

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.

Autophagy: A double-edged sword in intervertebral disk degeneration

“…Xu and colleagues have demonstrated that intermittent cyclic mechanical tension (ICMT) induces the calcification of rat CEP chondrocytes through downregulation of transforming growth factor-β1 (TGF-β1) expression in vitro [118]. A later study by these authors found that the same cells loaded with ICMT show decreased autophagy and the palpable calcification, whereas ICMT-mediated calcification is partially reversed by administration of rapamycin [119]. Thus, autophagy may play a protective role in the process of CEP calcification induced by ICMT.…”

Autophagy and mechanotransduction in outflow pathway cells

“…The signaling pathways and the physiological roles varies depending on the cell type and experimental model. Autophagy was found to protect end plate chondrocytes from intermittent cyclic mechanical tension-induced calcification, playing a key role in bone homeostasis (Xu et al, 2014). In contrast, application of cyclic mechanical stress caused autophagic cell death in tenofibroblast through activation of PGE2 production (Chen et al, 2015).…”

Tumor necrosis factor-α: a key contributor to intervertebral disc degeneration

“…However, the role of autophagy in the process of IDD is still controversial. Some studies suggest autophagy as a protective mechanism [117,118]. Other reports showed that autophagy promotes the development of IDD [119,120].…”