CX3CR1 modulates acute disc herniation-induced pain via regulating local inflammation and spinal microglia activation

Inflammation is a key driver of disc herniation, a major cause of back pain and disability. Heterogeneous macrophages infiltrated at disc hernia sites, yet their role in disease pathology and pain remains unclear. This study investigates the role of CX3CR1⁺ macrophages and microglia in local inflammation and pain using transgenic mouse models and surgically induced disc herniation model.

A lumbar annular puncture model was applied to three global transgenic mouse strains: CCR2^RFP/+/CX3CR1^GFP/+ dual-reporter mice to trace monocyte infiltration, and CX3CR1^GFP/+ and CX3CR1^GFP/GFP mice to investigate CX3CR1-contribution to disc herniation induced local inflammation and neuroinflammation in dorsal root ganglia (DRG) and spinal cord. Behavioral assays were used to evaluate mechanical sensitivity.

Disc herniation induced peak inflammatory cell infiltration at hernia sites at 1-week post injury, reduced by 4 weeks in both CX3CR1^GFP/+ and CX3CR1^GFP/GFP mice. CX3CR1^GFP/+ mice displayed more CD11b⁺ and F4/80⁺ macrophages, less disc height and higher mechanical sensitivity than CX3CR1^GFP/GFP mice. Both genotypes exhibited increased microglial activation in the ipsilateral dorsal horn of spinal cord compared to contralateral sides by 1 week, while CX3CR1^GFP/+ microglia showed higher lysosomal activity and changes in morphology than CX3CR1^GFP/GFP microglia. Ipsilateral DRGs from CX3CR1^GFP/+ mice showed elevated CX3CR1⁺ and F4/80⁺ cells, substance P, and calcitonin gene-related peptide, compared to CX3CR1^GFP/GFP at 1 week.

These findings indicate a mechanistic role of CX3CR1 in mediating inflammation and pain in disc herniation. Targeting CX3CR1 may disrupt the signal interactions between disc, DRG, and spinal cords.