Abstract 1214: Accelerated Vascular Lesion Formation in Mice Lacking All Nitric Oxide Synthases in vivo
Background: Nitric oxide (NO) is synthesized by 3 NO synthases (NOSs). Due to the substantial compensation among the 3 NOSs, the role of the whole NOS system in vascular lesion formation remains to be fully elucidated. In this study, we addressed this point in mice lacking all 3 NOS genes (triply n/i/eNOS−/ − mice) that we have recently developed (PNAS 2005).
Methods: Permanent ligation of a unilateral carotid artery was performed in 2-month-old male wild-type (WT), singly nNOS−/ −, iNOS−/ −, and eNOS−/ −, and triply n/i/eNOS−/ − mice (n=12–16). Two weeks later, histological changes of the ligated carotid arteries were examined by hematoxylin-eosin staining. NOS isoform expressions were assessed by immunostaining.
Results: At 2 weeks after the carotid artery ligation, neointimal formation, constrictive vascular remodeling, and adventitial infiltration of inflammatory leukocytes were noted in the ligated arteries of all strains. While the neointimal formation (intima/media ratio, 0.19±0.02 in WT) was noted in eNOS−/ − (0.58±0.03) and nNOS−/ − mice (0.51±0.03), it was most accelerated in the triply n/i/eNOS−/ − mice (1.01±0.08, P<0.01 vs. other strains). Similarly, while the constrictive vascular remodeling (vascular circumference ratio, 0.95±0.05 in WT) was noted in iNOS−/ − (0.79±0.02) and nNOS−/ − mice (0.80±0.02), it was most accelerated in the triply n/i/eNOS−/ −mice (0.70±0.03, P<0.05 vs. other strains). In addition, while the adventitial infiltration of inflammatory leukocytes (cell number, 52±9 in WT) was noted in nNOS−/ − (100±6), iNOS−/ − (84±5) and eNOS−/ − mice (94±6), it was again most accelerated in the triply n/i/eNOS−/ − mice (272±23, P<0.01 vs. other strains). In WT mice, after the carotid artery ligation, the expression of eNOS was limited to the endothelium, iNOS was induced mainly in vascular smooth muscle cells (VSMC) and the adventitia, and nNOS was upregulated in all the endothelium, VSMC, and the adventitia (n=8 each). In contrast, none of such NOS expressions were noted in the triply n/i/eNOS−/ − mice (n=8).
Conclusions: These results provide the first evidence that the NOS system plays an important protective role, in a cooperative manner, against inflammatory vascular lesion formation caused by blood flow disruption in mice in vivo.