Sex-dependent pronociceptive role of spinal α5-GABAA receptor and its epigenetic regulation in neuropathic rodents

Extrasynaptic alpha(5)-subunit containing GABA(A)(alpha(5)-GABA(A)) receptors participate in chronic pain. Previously, we reported a sex difference in the action of alpha(5)-GABA(A)receptors in dysfunctional pain. However, the underlying mechanisms remain unknown. The aim of this study was to examine this sexual dimorphism in neuropathic rodents and the mechanisms involved. Female and male Wistar rats or ICR mice were subjected to nerve injury followed by alpha(5)-GABA(A)receptor inverse agonist intrathecal administration, L-655,708. The drug produced an antiallodynic effect in nerve-injured female rats and mice, and a lower effect in males. We hypothesized that changes in alpha(5)-GABA(A)receptor, probably influenced by hormonal and epigenetic status, might underlie this sex difference. Thus, we performed qPCR and western blot. Nerve injury increased alpha(5)-GABA(A)mRNA and protein in female dorsal root ganglia (DRG) and decreased them in DRG and spinal cord of males. To investigate the hormonal influence over alpha(5)-GABA(A)receptor actions, we performed nerve injury to ovariectomized rats and reconstituted them with 17 beta-estradiol (E2). Ovariectomy abrogated L-655,708 antiallodynic effect and E2 restored it. Ovariectomy decreased alpha(5)-GABA(A)receptor and estrogen receptor alpha protein in DRG of neuropathic female rats, while E2 enhanced them. Since DNA methylation might contribute to alpha(5)-GABA(A)receptor down-regulation in males, we examined CpG island DNA methylation of alpha(5)-GABA(A)receptor coding gene through pyrosequencing. Nerve injury increased methylation in male, but not female rats. Pharmacological inhibition of DNA methyltransferases increased alpha(5)-GABA(A)receptor and enabled L-655,708 antinociceptive effect in male rats. These results suggest that alpha(5)-GABA(A)receptor is a suitable target to treat chronic pain in females.

Automated summary

This study examined the sexual dimorphism in neuropathic rodents regarding alpha(5)-GABA(A) receptors, revealing an increase in receptor expression in DRG of nerve-injured females and a decrease in males. Ovariectomy abolished the antiallodynic effect of L-655,708 in females, which was restored by estradiol supplementation. In males, DNA methylation inhibition increased the receptor expression and enabled the antinociceptive effect, suggesting a potential treatment target for chronic pain in females.