IN-VITRO AND IN-VIVO INDUCTION OF HEME OXYGENASE-1 IN RAT GLIAL-CELLS- POSSIBLE INVOLVEMENT OF NITRIC-OXIDE PRODUCTION FROM INDUCIBLE NITRIC-OXIDE SYNTHASE

To determine whether heme oxygenase-l (HO-1) protein is induced by end ogenous nitric oxide (NO) in rat glial cultures, we examined the effec ts of lipopolysaccharide (LPS), interferon-gamma (IFN-gamma), and NO d onors such as S-nitroso-N-acetylpenicillamine (SNAP), in mixed glial c ells and in vivo rat hippocampus. In cultured glial cells, treatment w ith LPS induced the expression of 130-kd inducible NO synthase (iNOS) after 6 h, and NO2- accumulation and enhancement of the protein level of 33-kd HO-1 after 12 h. In addition, treatment with SNAP induced HO- 1 expression after 6 h. Although NOS inhibitors such as N-G-nitro-L-ar ginine (NNA) and N-G-methyl-L-arginine did not change LPS-induced iNOS expression, these inhibitors suppressed both NO2- accumulation and th e enhancement of HO-1. Immunocytochemistry showed that treatment with LPS for 24 h induced iNOS immunoreactivity predominantly in ameboid mi croglia, while this treatment induced HO-l-immunoreactivity in both mi croglia and astrocytes. In in vivo rat hippocampus, microinjection of LPS plus IFN-gamma, or SNAP after 24 h also induced HO-1 immunoreactiv ity in reactive microglia and astrocytes. In addition, intraperitoneal administration of NNA inhibited HO-1 immunoreactivity induced by the microinjection of LPS plus IFN-gamma. These results suggest that endog enous NO production by iNOS in microglia causes autocrine and paracrin e induction of HO-1 protein in microglia and astrocytes in vitro and i n rat brain. (C) 1998 Wiley-Liss, Inc.