Propionibacterium acnes contributes to low back pain via upregulation of NGF in TLR2-NF-κB/JNK or ROS pathway

Propionibacterium acnes infection in intervertebral discs (IVDs) is a newly identified cause of low back pain (LBP). In the present study, we aimed to determine whether the nerve growth factor (NGF), a critical pro-algesic factor, is involved in P. acnes-induced LBP. After co-culturing with P. acnes, nucleus pulposus cells (NPCs) produced NGF, which was upregulated after inoculation of P. acnes into IVDs of rats. In addition, administration of P. acnes into rat IVDs leads to significant mechanical allodynia and cold hyperreflexia, and significant upregulation of the pain-related factors, including substance P (SP), calcitonin gene-related peptide (CGRP), and Transient Receptor Potential Vanilloid 1 (TRPV1), in rat dorsal root ganglia (DRG), suggesting that P. acnes-inoculated rats had obvious discogenic LBP. However, inhibition of NGF bioactivity significantly ameliorated P. acnes-induced discogenic LBP, suggesting that P. acnes induced LBP via NGF. Finally, an in vitro mechanism study demonstrated that P. acnes stimulated NPCs to secrete NGF via TLR-2 receptor and NF-κB p65/JNK pathway, or ROS-related pathway. Therefore, P. acnes had a strong association with LBP by stimulating NPCs to secrete NGF via the TLR2-NF- κB/JNK or ROS-related pathway. These findings propose a novel potential therapeutic strategy for LBP.