Regulation of the genes for arginase isoforms and related enzymes in mousemacrophages by lipopolysaccharide

Arginase exists in two isoforms, the hepatic (arginase I) and extrahepatic types (arginase II). Arginase I is markedly induced in rat peritoneal macro phages and rat tissues in vivo by bacterial lipopolysaccharide (LPS). In co ntrast, both arginase I and arginase II are induced in LPS-activated mouse peritoneal macrophages. In the present study, expression of arginase isofor ms and related enzymes was studied in mouse tissues in vivo and in peritone al macrophages with RNA blot and immunoblot analyses and enzyme assay. When mice were injected intraperitoneally with LPS, inducible nitric oxide synt hase (iNOS) and arginase II were induced early in the lung and spleen. mRNA s for argininosuccinate synthase (AS) and ornithine decarboxylase (ODC) wer e also induced early. In comparison, arginase I was induced later in the lu ng. Early induction of iNOS, arginase II, AS, ODC, and cationic amino acid transporter 2 and late induction of arginase I were observed in LPS-activat ed peritoneal macrophages. These results indicate that the genes for the tw o arginase isoforms are regulated differentially. Possible roles of the arg inase isoforms in the regulation of nitric oxide production and in polyamin e synthesis are discussed.