Activation of TLR4/CCL2 in Intact Neurons Drives Radicular Injury-Induced Global Nerve Trunk Hypersensitivity in Radiculopathy Preclinical Models.

Introduction: The distribution of pain in painful radiculopathy extends beyond the region innervated by the injured nerve. This phenomenon may arise due to the interaction between damaged nerve fibers and intact ones within the same nerve trunk. However, the underlying mechanisms remain unclear. Methods: An L5 spinal nerve compression rat model was established. RNA sequencing (RNA-seq) was performed to identify altered signaling pathways in the L4 dorsal root ganglia (DRG). Nociceptive behaviors were evaluated by von Frey testing and gait analysis. Immunofluorescence stainings were employed to analyze protein expression levels. Primary DRG neurons were cultured for in vitro validation of key molecular pathways. Results: We observed that degenerated L5 nerve fibers released damage-associated molecular patterns (DAMPs), which may activate Toll-like receptor 4 (TLR4) signaling in intact L4 nerve fibers mingling in the sciatic nerve. This activation led to increased expression of C-C chemokine ligand 2 (CCL2), which induced macrophage infiltration and upregulation of ion channels in the L4 DRG. Administration of TAK-242, a TLR4 antagonist, reduced the neuronal expression of CCL2 in the L4 DRG and attenuated pain-like behavior in nerve-compression rats. Conclusion: Our findings demonstrate that L5 spinal nerve lesions activate TLR4/CCL2 signaling in adjacent uninjured L4 neurons within the sciatic nerve, leading to a global nerve trunk hypersensitivity. Targeting the TLR4/CCL2 pathway may provide a novel therapeutic strategy for the management of radiculopathy.