REORIENTATION OF PROSTANOID PRODUCTION ACCOMPANIES ACTIVATION OF ADULT MICROGLIAL CELLS IN CULTURE

Using morphological, immunocytochemical, and functional parameters we have previously shown that highly purified adult rat microglial cells undergo a process of ''activation'' when cultured in a serum-containin g medium in the absence of added proinflammatory substances or other f actors (Slepko and Levi: Glia 16:241-246, 1996), Here we studied the l ipopolysaccharide (LPS)-evoked production of two prostanoids, thrombox ane A(2) (measured as thromboxane B-2) (TXB2) and prostaglandin E-2 (P GE(2)), as a function of microglial ''activation.'' LPS induced a grea ter time- and dose-dependent release of TXB2, compared to PGE(2), in t he less ''activated'' cells, Further ''activation'' led to amplified s ynthesis of PGE(2) and not of TXB2, so that the TXB2/PGE(2) ratio chan ged from 2.2 to 0.25 between the 2nd and 4th day in culture. Western b lot experiments showed. that the LPS-evoked expression of the inducibl e form of cyclooxygenase (COX) was markedly higher in cells exhibiting a more ''activated'' phenotype, The expression of the constitutive is oform of COX was Ia tr in an conditions, was slightly greater in more ''activated'' cells, and was not affected by LPS, Neither progression in microglial ''activation'' nor LPS treatment enhanced thromboxane sy nthase activity. We hypothesize that reorientation of prostanoid synth esis toward a major production of PGE(2) in the more ''activated'' cel ls can be largely attributed to an increased inducibility of cellular COX expression, combined with the inability of thromboxane synthase to cope with the increased availability of the COX product prostaglandin H-2 (PGH(2)), the common precursor of TXA(2) and PGE(2). In view of t he different, and at times opposite, functional activity of TXB2 and P GE(2), the described change in prostanoid production pattern may contr ibute to the role of ''activated'' microglia in inflammation and host defense. (C) 1997 Wiley-Liss, Inc.