Transforming Growth Factor β1 Regulates the Expression of Cyclooxygenase in Cultured Cortical Astrocytes and Neurons

Abstract

The hypothesis that transforming growth factor beta1 (TGFbeta1) regulates the synthesis of prostaglandins by CNS tissue was tested by using purified cultures of cortical astrocytes or neurons that were obtained from rat pups on postnatal day 4 or 5 or fetuses on gestational day 16, respectively. The cells were exposed to TGFbeta1 for 2 days. The synthesis of prostaglandins depends upon the production and conversion of arachidonic acid, steps that are catalyzed by phospholipase A2 (PLA2) and cyclooxygenase (COX), respectively. Prostaglandin E2 (PGE2) concentration was determined by radioimmunoassay. The expression of cytosolic PLA2 and COX (the constitutive COX1 and the inducible COX2) was assessed by using immunohistochemical and quantitative immunoblotting procedures. Astrocytes produced much more PGE2 than neurons, suggesting that glial cells are an important source of PGE2 in the CNS. TGFbeta1 increased the production of PGE2 by astrocytes and neurons in a concentration-dependent manner. Furthermore, TGFbeta1 enhanced COX activity; the inhibitor indomethacin completely blocked TGFbeta1-mediated PGE2 synthesis. Cultured astrocytes and neurons expressed the three enzymes: cytosolic PLA2, COX1, and COX2. Cytosolic PLA2 expression was unaffected by TGFbeta1 treatment. In contrast, COX expression was altered by TGFbeta1 treatment in a concentration-dependent fashion. COX1 was increased by TGFbeta1, but only in astrocytes. TGFbeta1 increased COX2 expression in astrocytes and neurons. Thus, TGFbeta1-induced increases in PGE2 concentration are regulated by COX. This study suggests that TGFbeta1 is an important regulator of immune and inflammatory processes in the CNS.