MKP-1 switches arginine metabolism from nitric oxide synthase to arginase following endotoxin challenge

Centers for 1 Perinatal Research and 2 Gene Therapy, Columbus Children's Research Institute, Department of Pediatrics, The Ohio State University, Columbus, Ohio; and 3 Department of Pediatrics, Children's Foundation Research Center at Le Bonheur Children's Medical Center, University of Tennessee Health Sciences Center at Memphis, Memphis, Tennessee Submitted 26 March 2006 ; accepted in final form 17 April 2007 L -Arginine ( L -arg) is metabolized to nitric oxide (NO) by inducible NO synthase (iNOS) or to urea and L -ornithine ( L -orn) by arginase. NO is involved in the inflammatory response, whereas arginase is the first step in polyamine and proline synthesis necessary for tissue repair and wound healing. Mitogen-activated protein kinases (MAPK) mediate LPS-induced iNOS expression, and MAPK phosphatase-1 (MKP-1) plays a crucial role in limiting MAPK signaling in macrophages. We hypothesized that MKP-1, by attenuating iNOS expression, acts as a switch changing L -arg metabolism from NO production to L -orn production after endotoxin administration. To test this hypothesis, we performed studies in RAW264.7 macrophages stably transfected with an MKP-1 expression vector in thioglyollate-elicited peritoneal macrophages harvested from wild-type and Mkp-1 –/– mice, as well as in vivo in wild-type and Mkp-1 –/– mice. We found that overexpression of MKP-1 resulted in lower iNOS expression and NO production but greater urea production in response to LPS. Although deficiency of MKP-1 resulted in greater iNOS expression and NO production and lower urea production in response to LPS, neither the overexpression nor the deficiency of MKP-1 had any substantial effect on the expression of the arginases. lung injury; macrophage; ornithine; mitogen-activated protein kinases Address for reprint requests and other correspondence: L. D. Nelin, Center for Perinatal Research, Columbus Children's Research Inst., 700 Children's Dr.-W207, Columbus, OH 43205 (e-mail: NelinL{at}pediatrics.ohio-state.edu )