eNOS and iNOS knockout mice

The first eNOS knockout mice were generated by disrupting the region that encodes for the NADPH ribose and adenine binding sites, which are essential for catalytic activity. These mice are viable, fertile and exhibit no gross anatomic abnormalities, despite the absence of detectable eNOS mRNA, protein or enzymatic activity. eNOS knockout mice show abnormalities in vascular relaxation, blood pressure regulation, and cardiac contractility. They are a useful animal model for endothelial dysfunction, as they show increased propensity to form neointima in response to vessel injury, and accelerated and more severe diet-induced atherosclerosis in the apolipoprotein E (apoE) knockout mouse model. Several additional strains of eNOS knockout mice have also been reported. In one strain, the eNOS gene was disrupted at the calmodulin binding site, encoded by exons 12 and 13, in another strain, the NADPH ribose and adenine binding sites were disrupted, similar to the first eNOS knockout mice. Three separate groups independently disrupted the iNOS gene. MacMicking et al. deleted the promoter region and the first four exons, including the initiation codon ATG. Wei et al. in an attempt to delete the first five exons of the gene, created a genomic rearrangement of the iNOS gene that results in an aberrant transcript, but no detectable iNOS activity. Laubach et al. disrupted the calmodulin, FAD, and FMN binding domains of iNOS, and found no detectable iNOS mRNA or protein. In all cases, expression of iNOS cannot be induced in the iNOS mutant mice under conditions that induce iNOS in wild-type animals. Peritoneal macrophages from all of the iNOS mutant mice are deficient in NO and nitrite production. None of the mutants demonstrate abnormalities in growth, fertility, or gross histopathology.