Compression stress induces nucleus pulposus cell autophagy by inhibition of the PI3K/AKT/mTOR pathway and activation of the JNK pathway

Abstract

ABSTRACT Purpose: Reactive oxygen species (ROS) are related to compression stress-induced nucleus pulposus (NP) cell autophagy, but the specific mechanism is unknown in compression stress-induced intervertebral disc degeneration (IVDD). Here, we discuss the specific molecular mechanism and explore whether ROS scavengers could be employed as specific drugs to inhibit compression stress-induced IVDD. Methods: Rat NP cells were exposed to 1.0 MPa compression and pretreatment with the ROS scavenger N-acetylcysteine (NAC) or the JNK-selective inhibitor SP600125 not. Intracellular ROS production was monitored by confocal microscopy. Autophagy was detected by observing the NP cell ultrastructural features using TEM and examining autophagic vacuoles by flow cytometry. The levels of autophagy-associated molecules, the JNK pathway and the PI3K/AKT/mTOR pathway were analyzed by western blotting. Results: Compression-mediated autophagy in rat NP cells was implicated in ROS generation. The ROS scavenger NAC could protect compression-induced NP cell injures by inhibiting ROS production. And SP600125, a JNK inhibitor, attenuated compression-induced NP cell autophagy. Additionally, this is the first report showing that compression induces autophagy in rat NP cells by impeding the compression-induced ROS dependent PI3K/AKT/mTOR pathway and the ROS independent activation of JNK pathway. And the involvement of JNK pathway was in different mechanism of action that when inhibited leaded to increased cell death, increased generation of ROS but decreased autophagy. Conclusions: These results show a new regulatory mechanism involving ROS-mediated autophagy in rat NP cells, which may provide ideas for drug development to improve compression stress-induced IVDD and help avoid eventual surgical treatment of IVD herniation.