Opposing Roles of Nitric Oxide and Rho-Kinase in Lipid Metabolism in Mice

Dyslipidemia is a life-style disorder and is one of the important risk factors of cardiovascular diseases. Nitric oxide (NO) exerts beneficial effects on lipid metabolism through activation of hepatic sterol regulatory element-binding protein (SREBP)-2, a transcriptional factor for cholesterol metabolism and expression of LDL receptor, while Rho-kinase, an effecter protein of small G protein, RhoA, contributes to the pathogenesis of metabolic syndrome through suppressing the whole body energy consumption. However, the crosstalk between NO and Rho-kinase in regulation of lipid metabolism remains to be elucidated. In the present study, we used male wild-type (WT) mice and mice lacking three isoforms of NO synthase (NOSs(-/-)). WT mice were fed either normal diet (ND) or high-fat diet (HFD), while NOSs(-/-) mice were fed ND with or without a selective Rho-kinase inhibitor, fasudil (100 mg/kg/day), for 6 weeks. At 6 weeks, plasma NOx concentration was significantly decreased and Rho-kinase activity and lipid levels were significantly elevated in HFD-fed WT mice and NOSs(-/-) mice compared with ND-fed WT mice. In the liver, SREBP-2 activity was reduced in NOSs(-/-) mice. Fasudil ameliorated lipid levels in HFD-fed WT mice and NOSs(-/-) mice without affecting SREBP-2 activity or LDL receptor expression, whereas it significantly enhanced phosphorylation of AMP-activated kinase (AMPK) in the liver and skeletal muscle. Importantly, the beneficial metabolic effects of fasudil were absent in HFD-fed AMPK(-/-) mice. These results provide the first evidence that NO and Rho-kinase play opposing roles for the lipid metabolism, suggesting that Rho-kinase inhibitors could be novel therapeutic agents of dyslipidemia.