Expression of cyclooxygenase-2 in foetal rat hepatocytes stimulated with lipopolysaccharide and pro-inflammatory cytokines

Abstract

1. Cyclooxygenase-2 (COX-2) is involved in the biosynthesis of prostanoids in the course of inflammatory reactions. This isoenzyme is regulated at the transcription level and many cells express COX-2 upon challenge with lipopolysaccharide (LPS) or pro-inflammatory cytokines. 2. Since hepatocytes respond to LPS and pro-inflammatory stimuli, we investigated the expression of COX-2 in foetal and adult hepatocytes upon challenge with these substances. 3. COX-2 was expressed in foetal hepatocytes incubated with LPS, tumour necrosis factor-α and interleukin-1β. This response rapidly decreased after birth and was absent in hepatocytes from animals aged 2 days or more and treated under identical conditions. The expression of COX-2 was determined at the mRNA, protein and enzyme activity levels using Northern and Western blot, and following the synthesis of prostaglandin E2, respectively. The use of NS 398, a specific pharmacological inhibitor of COX-2, confirmed the expression of this isoenzyme in activated foetal hepatocytes. 4. Synergism in COX-2 expression was observed between LPS, tumour necrosis factor-α and interleukin-1β. Interleukin-6 and permeant analogues of cyclic AMP failed to induce COX-2 or to synergize with LPS. Also, transforming growth factor-β inhibited the LPS- and pro-inflammatory cytokines-dependent expression of COX-2. 5. These results indicate that foetal hepatocytes are competent to express COX-2 upon challenge with pro-inflammatory stimuli, a process lost completely in hepatocytes isolated from animals aged 2 days.