<i>Propionibacterium acnes</i> induces intervertebral disc degeneration by promoting nucleus pulposus cell apoptosis via the TLR2/JNK/mitochondrial-mediated pathway

Evidence suggests that intervertebral disc degeneration (IVDD) can be induced by <i>Propionibacterium acnes</i> (<i>P. acnes</i>), although the underlying mechanisms are unclear. In this study, we analyzed the pathological changes in degenerated human intervertebral discs (IVDs) infected with <i>P. acnes</i>. Compared with <i>P. acnes</i>-negative samples, <i>P. acnes</i>-positive IVDs showed increased apoptosis of nucleus pulposus cells (NPCs) concomitant with severe IVDD. Then, a <i>P. acnes</i>-inoculated IVD animal model was established, and severe IVDD was induced by <i>P. acnes</i> infection by promoting NPC apoptosis. The results suggested that <i>P.</i><i>acnes</i>-induced apoptosis of NPCs via the Toll-like receptor 2 (TLR2)/c-Jun N-terminal kinase (JNK) pathway and mitochondrial-mediated cell death. In addition, <i>P. acnes</i> was found to activate autophagy, which likely plays a role in apoptosis of NPCs. Overall, these findings further validated the involvement of <i>P. acnes</i> in the pathology of IVDD and provided evidence that <i>P. acnes</i>-induced apoptosis of NPCs via the TLR2/JNK pathway is likely responsible for the pathology of IVDD.