Reciprocal Regulation of Cyclooxygenase (COX)‐1 and COX‐2 Expression in Murine Resident and Elicited Peritoneal Macrophages by Lipopolysaccharide

Abstract

Macrophages express COX‐1 and COX‐2 that are involved in the biosynthesis of prostanoids including prostaglandin E2 (PGE2). In this study, we examined the relative expression of COX‐1 and COX‐2 in murine resident (RPM) and thioglycollate‐elicited peritoneal macrophages (EPM) and determined the influence of lipopolysaccharide (LPS) on their gene expression and functions. Freshly harvested RPM and EPM from C57Bl/6J mice were allowed to adhere on cell culture plates and incubated with LPS (0.1 to 100 ng/ml) for 4 h for measuring COX‐1 and COX‐2 mRNA expression by quantitative RT‐PCR. To monitor COX‐1 and COX‐2 protein expression, Western blot analyses were carried out after incubating macrophages with LPS for 2, 4, 8, 16 and 24 h. The production of PGE2 and TNF‐α by RPM and EPM were monitored as functional indices. The study revealed that, in comparison to EPM, RPM constitutively express markedly higher levels of COX‐1 (12‐fold) and COX‐2 (3.5‐fold) mRNA and produce substantially higher quantities of PGE2 when stimulated with LPS. In contrast, EPM generate considerably lower levels of PGE2 and higher levels of TNF‐α than RPM when activated with LPS. Incubation of RPM or EPM with LPS resulted in marked increases in COX‐2 mRNA (up to 1000 fold) and protein expression. On the other hand, LPS challenge significantly inhibited COX‐1 mRNA (60 to 90%) and protein expression in both RPM and EPM. These results demonstrate that LPS reciprocally regulate the expression of COX‐1 and COX‐2 in murine peritoneal macrophages. Furthermore, the newly recruited peritoneal macrophages seem to undergo plausible phenotype switching from high‐TNFα/low‐PGE2 producing EPM to low‐TNFα/high‐PGE2 producing RPM. (Supported by NIH R01‐HL070101 and Carey Arthritis Fund).