NADH oxidase signaling induces cyclooxygenase-2 expression during lipopolysaccharide stimulation in cardiomyocytes.

Cyclooxygenase-2 (COX-2) is induced in response to lipopolysaccharide (LPS). However, the signaling mechanisms of LPS-induced COX-2 expression in cardiomyocytes are not well understood. The aim of this study was to investigate the role of gp91(phox)-containing NADH oxidase signaling pathway in LPS-induced COX-2 expression in cardiomyocytes. Cultured neonatal mouse cardiomyocytes showed basal COX-2 expression and PGE2 production. In response to LPS, COX-2 expression and PGE2 production increased by two- to four-fold, which were completely blocked by a selective COX-2 inhibitor NS398. LPS also increased NADH oxidase (gp91(phox) and p47(phox) subunits) expression and superoxide generation. Deficiency of gp91(phox) or suppression of p22(phox) expression decreased NADH oxidase activity and down-regulated COX-2 expression and PGE2 production stimulated by LPS. Pharmacological inhibitors of NADH oxidase prevented LPS-induced COX-2 expression and PGE2 production. The effect of NADH oxidase was mediated through MAPK activation, since inhibition of NADH-oxidase activity prevented phosphorylation of ERK1/2, p38, and JNK1/2, as well as selective inhibition of each subfamily of MAPK by siRNAs and a dominant negative mutant of JNK1 decreased COX-2 expression and completely abrogated PGE2 production in response to LPS. Furthermore, LPS-induced NF-kappaB activation was decreased by inhibition of NADH oxidase, ERK1/2 or JNK1/2 activation, suggesting that LPS increases NF-kappaB activity and COX-2 expression via NADH oxidase-dependent activation of ERK1/2 and JNK1/2. In conclusion, NADH oxidase signaling represents a novel pathway leading to COX-2 expression via MAPK/NF-kappaB-dependent mechanisms in cardiomyocytes during LPS stimulation. Our study suggests that gp91(phox)-containing NADH oxidase is a potential therapeutic target of sepsis.