Clinical and Serologic Manifestations of Autoimmune Disease in MRL-lpr/lpr Mice Lacking Nitric Oxide Synthase Type 2

Abstract

Nitric oxide (NO) is an important mediator of the inflammatory response. MRL–lpr/lpr mice overexpress inducible nitric oxide synthase (NOS2) and overproduce NO in parallel with the development of an autoimmune syndrome with a variety of inflammatory manifestations. In previous studies, we showed that inhibiting NO production with the nonselective nitric oxide synthase (NOS) inhibitor NG-monomethyl–arginine reduced glomerulonephritis, arthritis, and vasculitis in MRL–lpr/lpr mice. To define further the role of NO and NOS2 in disease in MRL–lpr/lpr mice, mice with targeted disruption of NOS2 were produced by homologous recombination and bred to MRL–lpr/lpr mice to the N4 generation. MRL–lpr/lpr littermates homozygous for disrupted NOS2 (−/−), heterozygous for disrupted NOS2 (+/−), or wildtype (+/+) were derived for this study. Measures of NO production were markedly decreased in the MRL-lpr/lpr (−/−) mice compared with MRL-lpr/lpr (+/+) mice, with intermediate production by the MRL-lpr/lpr (+/−) mice. There was no detectable NOS2 protein by immunoblot analysis of the spleen, liver, kidney, and peritoneal macrophages of the (−/−) animals, whereas that of (+/+) was high and (+/−) intermediate. The (−/−) mice developed glomerular and synovial pathology similar to that of the (+/−) and (+/+) mice. However, (−/−) mice and (+/−) mice had significantly less vasculitis of medium-sized renal vessels than (+/+) mice. IgG rheumatoid factor levels were significantly lower in the (−/−) mice as compared with (+/+) mice, but levels of anti-DNA antibodies were comparable in all groups. Our findings show that NO derived from NOS2 has a variable impact on disease manifestations in MRL-lpr/lpr mice, suggesting heterogeneity in disease mechanisms.

Inflammatory Properties of IgG Modified by Oxygen Radicals and Peroxynitrite

“…Thus, the studies described here involving the effects of the oxidants on the business end of the Ab molecules, the Ag binding domains, suggest that one of the possible beneficial effects of NO and oxygen radicals may reside in their ability to decrease the formation of immunocomplexes. Pertinent to this discussion is the observation that rodents with absent inducible NO synthase developed inflammatory arthritis of similar magnitude to their wild-type counterparts (25,26), although other pathologic processes such as vasculitis were ameliorated (26).…”

The role of nitric oxide in abnormal T cell signal transduction in systemic lupus erythematosus

“…Oral administration of either N G -monomethyl-L-arginine, a nonspecific NOS inhibitor, or L-N 6− (1-iminoethyl) lysine (L-NIL), an iNOS-specific inhibitor, prevented the development of glomerulonephritis, reduced the intensity of arthritis, and lowered renal pathology scores in MRL-lpr/lpr mice [63]. However, MRL/lpr iNOS knockout mice develop renal disease similar to the wild-type animal [64]. Belmont and colleagues reported elevated serum nitrite levels, an in vivo marker of NO production, in lupus patients [65,66].…”

Activated Macrophages Direct Apoptosis and Suppress Mitosis of Mesangial Cells

“…However, the only available study of glomerulonephritis in NOS-2 Ϫ/Ϫ mice was in a model of mild nephrotoxic nephritis with little M infiltration of glomeruli (29), and apoptosis was not assessed. Furthermore, the equivocal data on NO in glomerulonephritis published to date (in which two studies show amelioration of disease (30,31): two show no difference (29,32), and one shows exacerbation (33)) have concentrated on conventional parameters of glomerular injury rather than apoptosis or remodeling. Therefore, additional experiments will be required to confirm a role for Mderived NO in regulating MC number in glomerulonephritis models exhibiting degrees of M infiltration comparable with that observed in human disease (34,35), in which M number may approach MC number (comparable with the in vitro ratio employed in our experiments).…”