Abstract 399: Abnormal Lipoprotein Metabolism in Mice Lacking All Nitric Oxide Synthase Isoforms
Background: Nitric oxide (NO) is synthesized by 3 NO synthase (NOS) isoforms: nNOS, iNOS, and eNOS. We have recently succeeded in developing mice lacking all NOS isoforms (triply n/i/eNOS−/ − mice) (PNAS 2005). In this study, we examined lipoprotein metabolism in those mice.
Methods and Results: Experiments were performed in 3-month-old male wild-type (WT), singly nNOS−/ −, iNOS−/ −, eNOS−/ −, and triply n/i/eNOS−/ − mice maintained on a regular diet (n=7–9). Plasma levels of total cholesterol (mg/dl) were significantly higher in the nNOS−/ − (121±2), iNOS−/ − (154±8), eNOS−/ − (154±6) and the triply n/i/eNOS−/ − mice (152±8) than in the WT mice (104±3) (all P<0.05). Plasma levels of high-density lipoprotein (HDL) cholesterol (mg/dl) were also significantly more elevated in the nNOS−/ − (98±2), iNOS−/ − (121±9), eNOS−/ − (146±3) and the triply n/i/eNOS−/ − mice (105±7) than in the WT mice (65±1) (all P<0.05). In contrast, plasma levels of low-density lipoprotein (LDL) cholesterol (mg/dl) and small dense LDL particle (mg/dl) were both markedly increased only in the triply n/i/eNOS−/ − mice (29.3±2 and 17.5±4, respectively, both P<0.05), but not in any singly NOS−/ − mice, as compared with the WT mice (9.9±0.8 and 5.7±0.5, respectively). Plasma HDL and LDL are bound to the HDL receptor (SR-B1) and the LDL receptor in the liver, respectively, and metabolized in hepatocytes. Notably, the hepatic SR-B1 expression (SR-B1/actin) (evaluated by Western blotting) was significantly more reduced in the singly nNOS−/ − (0.51±0.02), iNOS−/ − (0.51±0.03), eNOS−/ − (0.43±0.04) and the triply n/i/eNOS−/ − mice (0.50±0.02) than in the WT mice (0.65±0.01) (all P<0.05), while the LDL receptor expression (LDL/actin) was markedly decreased only in the triply n/i/eNOS−/ − mice (0.78±0.04), but not in any singly NOS−/ − mice, as compared with the WT mice (1.14±0.03) (P<0.05), suggesting that these lower expressions of the hepatic SR-B1 and LDL receptors may account for the higher levels of plasma HDL and LDL in the singly and triply NOS−/ −mice.
Conclusions: These results indicate for the first time that complete disruption of all NOSs results in abnormal lipoprotein metabolism in mice in vivo, demonstrating a critical role of endogenous NOSs system in maintaining lipoprotein homeostasis.