Tumor necrosis factor receptor 1 induces interleukin‐6 upregulation through NF‐kappaB in a rat neuropathic pain model

Peripheral nerve injury resulting in neuropathic pain induces the upregulation of interleukin (IL)-6 and tumor necrosis factor-alpha, which binds to tumor necrosis factor receptor 1 (TNFR1) and induces NF-kappaB and p38 MAPK activation in the spinal cord and dorsal root ganglia (DRG). We here investigated whether TNFR1 regulates IL-6 expression through NF-kappaB or p38 MAPK activations in the spinal cord and DRG in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal treatment with a TNFR1 antisense oligonucleotide (ASO) significantly inhibited CCI-elevated IKKs phosphorylation, IkB-alpha degradation, the nuclear translocation, phosphorylation, and DNA-binding activity of NF-kappaB, p38 MAPK activation, and IL-6 mRNA and protein expression in the spinal cord and DRG. Interestingly, CCI remarkably elevated IKKalpha and p65 phosphorylations in the spinal cord rather than in the DRG. In addition, NF-kappaB decoy, but not p38 MAPK inhibitor, SB203580 reduced CCI-elevated IL-6 expression in the spinal cord and DRG. Therefore, these data suggest that TNFR1 induces IL-6 upregulation and neuropathic pain through NF-kappaB, but not p38 MAPK activation in the spinal cord and DRG and that the NF-kappaB/IL-6 pathways in the DRG may be less dependent on TNFR1 than the spinal cord pathway.