Atheroprotective effects of neuronal nitric oxide synthase in apolipoprotein E knockout mice

Objective - All 3 isoforms of the nitric oxide synthase (NOS) are expressed in atherosclerotic lesions. To test whether neuronal NOS (nNOS) deficiency affects atherosclerosis, we studied apoE/nNOS alpha double knockout (DKO) and apolipoprotein E (apoE) knockout (KO) control mice. Methods and Results - Lesion area was significantly increased in male DKO (66%) mice after 14 weeks and in female DKO animals (31%) after 24 weeks of "western" diet. Moreover, mean arterial blood pressure was significantly reduced in female DKO animals. Immunohistochemistry revealed nNOS expression in the neointima of KO mice. In DKO animals, residual nNOS staining was caused by the presence of nNOS splice variants. Whereas nNOS alpha was present in vessels of KO and absent in DKO animals, nNOS gamma was expressed in KO and DKO mice. Conclusion - nNOS alpha protects against atherosclerosis as nNOS alpha deletion leads to an increase in plaque formation in apoE/nNOS alpha DKO mice. Female DKO mice showed a significant reduction in mean arterial blood pressure. Additionally, we found expression of nNOS splice variants in vessels of apoE KO mice. Our data highlights nNOS alpha overexpression as a potential therapeutic strategy and naturally occurring splice variants that lack exon 2 of the nNOS gene as a potential risk factor for vascular disease.