Tumor necrosis factor alpha and interleukin-1beta stimulate the expression of cyclooxygenase II but do not alter prostaglandin E2 receptor mRNA levels in cultured dorsal root ganglia cells.

ABSTRACT

Tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL-1beta) are pro-inflammatory cytokines capable of altering the sensitivity of sensory neurons. Because sensitization elicited by IL-1beta and TNFalpha is blocked by inhibition of the inducible enzyme, cyclooxygenase-II (COX-2), we examined whether these cytokines could increase COX-2 expression in dorsal root ganglion (DRG) cultures. Treatment of cell cultures with either IL-1beta or TNFalpha increases immunoreactive COX-2, as measured by immunoblotting, in a time- and concentration-dependent manner. A 24-h pretreatment with 10 ng/ml IL-1beta or 50 ng/ml TNFalpha augmented COX-2 expression 50- and 8-fold over basal levels, respectively. Immunohistochemistry established the presence of COX-2-like immunoreactivity in both neuronal and non-neuronal cells in culture. The addition of IL-1 receptor antagonist blocked the induction of COX-2 expression by IL-1beta, but did not alter TNFalpha-stimulated increases in COX-2, indicating that the mechanism of TNFalpha is not limited to increasing the expression of IL-1beta. The basal and TNFalpha-induced expression of COX-2 was not dependent on the presence of NGF in the growth media. IL-1beta and TNFalpha treatment for 24 h enhanced prostaglandin E2 (PGE2) production 2-4-fold, which was blocked by pretreatment with the COX-2 inhibitor, NS-398. Exposing cultures to PGE2, IL-1beta, or TNFalpha for 24 h did not alter PGE2 receptor (EP) mRNA levels. These results indicate that TNFalpha and IL-1beta induce the functional expression of COX-2 but not EP receptors in DRG cells in culture and suggest that cytokine-induced sensitization of sensory neurons is secondary to prostaglandin production and not alterations in EP receptors.