Abstract
We have previously shown that anti-hyperalgesic effects of cannabinoid agonists under inflammatory condition are much greater in male than female, and that inflammatory cytokines upregulate cannabinoid receptor type 1 (CB1) expression in male, but not female, trigeminal ganglia (TG) in a testosterone-dependent manner. In this study, we investigated the mechanisms underlying the testosterone-mediated regulation of peripheral CB1 expression. We hypothesized that testosterone upregulates CB1 through transcriptional modulation by androgen receptor (AR). Interleukin-1 beta (IL-1β), a pro-inflammatory cytokine, upregulated CB1 mRNA expression in TG of male rats. The cytokine-induced upregulation was prevented by the pretreatment with flutamide, a specific antagonist for AR, but not by ICI 182,780, a specific antagonist for estrogen receptor, suggesting that the effects of testosterone are not mediated by estradiol, a testosterone metabolite. The expression levels of AR and IL-1β receptors were comparable between male and female TG, suggesting that the male specific IL-1β effects on CB1 upregulation occurs downstream to these receptors. The chromatin immunoprecipitation assay showed AR binding to the CB1 promoter in the rat TG. Furthermore, luciferase reporter assay revealed that AR activated the CB1 gene in response to testosterone or dihydrotestosterone treatment. These experiments provided compelling evidence that testosterone regulates CB1 gene transcription in TG through AR following cytokine stimulation. These results should provide mechanistic bases for understanding cytokine-hormone-neuron interactions in peripheral cannabinoid systems, and have important clinical implications for pain patients in whom testosterone level is naturally low, gradually declining or pharmacologically compromised.