Full-length membrane-bound tumor necrosis factor-α acts through tumor necrosis factor receptor 2 to modify phenotype of sensory neurons

Neuropathic pain resulting from spinal hemisection or selective spinal nerve ligation is characterized by an increase in membrane-bound tumor necrosis factor-alpha (mTNF alpha) in spinal microglia without detectable release of soluble TNF alpha (sTNF alpha). In tissue culture, we showed that a full-length transmembrane cleavage-resistant TNF alpha (CRTNF alpha) construct can act through cell-cell contact to activate neighboring microglia. We undertook the current study to test the hypothesis that mTNF alpha expressed in microglia might also affect the phenotype of primary sensory afferents, by determining the effect of CRTNF alpha expressed from COS-7 cells on gene expression in primary dorsal root ganglia (DRG) neurons. Co-culture of DRG neurons with CRTNF alpha-expressing COS-7 cells resulted in a significant increase in the expression of voltage-gated sodium channel isoforms Na(V)1.7 and Na(V)1.8, and voltage-gated calcium channel subunit Ca(V)3.2 at both mRNA and protein levels, and enhanced CCL2 expression and release from the DRG neurons. Exposure to sTNF alpha produced an increase only in CCL2 expression and release. Treatment of the cells with an siRNA against tumor necrosis factor receptor 2 (TNFR2) significantly reduced CRTNF alpha-induced gene expression changes in DRG neurons, whereas administration of CCR2 inhibitor had no significant effect on CRTNF alpha-induced increase in gene expression and CCL2 release in DRG neurons. Taken together, the results of this study suggest that mTNF alpha expressed in spinal microglia can facilitate pain signaling by up-regulating the expression of cation channels and CCL2 in DRG neurons in a TNFR2-dependent manner. (c) 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.