Endothelial Nitric Oxide Synthase (eNOS) Knockout Mice Have Defective Mitochondrial β-Oxidation

Abstract

OBJECTIVE— Recent observations indicate that the delivery of nitric oxide by endothelial nitric oxide synthase (eNOS) is not only critical for metabolic homeostasis, but could also be important for mitochondrial biogenesis, a key organelle for free fatty acid (FFA) oxidation and energy production. Because mice deficient for the gene of eNOS (eNOS^−/−) have increased triglycerides and FFA levels, in addition to hypertension and insulin resistance, we hypothesized that these knockout mice may have decreased energy expenditure and defective β-oxidation. RESEARCH DESIGN AND METHODS— Several markers of mitochondrial activity were assessed in C57BL/6J wild-type or eNOS^−/− mice including the energy expenditure and oxygen consumption by indirect calorimetry, in vitro β-oxidation in isolated mitochondria from skeletal muscle, and expression of genes involved in fatty acid oxidation. RESULTS— eNOS^−/− mice had markedly lower energy expenditure (−10%, P < 0.05) and oxygen consumption (−15%, P < 0.05) than control mice. This was associated with a roughly 30% decrease of the mitochondria content (P < 0.05) and, most importantly, with mitochondrial dysfunction, as evidenced by a markedly lower β-oxidation of subsarcolemmal mitochondria in skeletal muscle (−30%, P < 0.05). Finally, impaired mitochondrial β-oxidation was associated with a significant increase of the intramyocellular lipid content (30%, P < 0.05) in gastrocnemius muscle. CONCLUSIONS— These data indicate that elevated FFA and triglyceride in eNOS^−/− mice result in defective mitochondrial β-oxidation in muscle cells.