Spontaneous Myocardial Infarction in Mice Lacking All Nitric Oxide Synthase Isoforms

Abstract

Background-The roles of nitric oxide (NO) in the cardiovascular system have been investigated extensively in pharmacological studies with NO synthase (NOS) inhibitors and in studies with NOS isoform-deficient mice. However, because of the nonspecificity of the NOS inhibitors and the compensatory interactions among NOS isoforms (nNOS, iNOS, and eNOS), the ultimate roles of endogenous NO derived from the entire NOS system are still poorly understood. In this study, we examined this point in mice deficient in all 3 NOS isoforms (triply n/i/eNOS Ϫ/Ϫ mice) that we have recently developed. Methods and Results-The triply n/i/eNOSϪ/Ϫ mice, but not singly eNOS Ϫ/Ϫ mice, exhibited markedly reduced survival, possibly due to spontaneous myocardial infarction accompanied by severe coronary arteriosclerotic lesions. Furthermore, the triply n/i/eNOS Ϫ/Ϫ mice manifested phenotypes that resembled metabolic syndrome in humans, including visceral obesity, hypertension, hypertriglyceridemia, and impaired glucose tolerance. Importantly, activation of the renin-angiotensin system was noted in the triply n/i/eNOS Ϫ/Ϫ mice, and long-term oral treatment with an angiotensin II type 1 receptor blocker significantly suppressed coronary arteriosclerotic lesion formation and the occurrence of spontaneous myocardial infarction and improved the prognosis of those mice, along with ameliorating the metabolic abnormalities. Conclusions-These results provide the first direct evidence that genetic disruption of the whole NOS system causes spontaneous myocardial infarction associated with multiple cardiovascular risk factors of metabolic origin in mice in vivo through the angiotensin II type 1 receptor pathway, demonstrating the critical role of the endogenous NOS system in maintaining cardiovascular and metabolic homeostasis.

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

“…It has been reported that SREBP-2 activity and LDL receptor expression were decreased in HFD-fed n/i/eNOSs −/− mice associated with severe dyslipidemia (Yatera et al 2010). Although it has been reported that serum lipids levels are increased in ND-fed n/i/eNOSs −/− mice (Nakata et al 2008), we showed that SREBP-2 activity and LDL receptor expression were decreased even in ND-fed n/i/eNOSs −/− mice in the present study.…”

“…In the present study, we used HFD-fed WT mice as a model of metabolic disorder. On the other hands, we fed NOSs −/− (eNOS −/− , n/eNOSs −/− and n/i/ eNOSs −/− ) mice with ND since these mice are known as animal models of metabolic disorders (Nakata et al 2008). In the skeletal muscle, the long-term treatment with fasudil significantly increased ACC activity but not AMPK activity in both HFD-fed WT mice and n/i/eNOSs −/− mice.…”

“…On the other hand, eNOS inactivation has been thought to be up-stream mechanisms of metabolic disorders (Duplain et al 2001;Nakata et al 2008;Sansbury et al 2012). Both eNOS −/− and n/i/eNOSs −/− mice show the phenotypes of metabolic syndrome (Duplain et al 2001;Nakata et al 2008), while in endothelium-specific eNOS transgenic mice, diet-induced hypercholesterolemia was prevented (Sansbury et al 2012). These findings suggest that eNOS inactivation is up-stream of metabolic disorder, but not the simple result of endothelial dysfunction.…”

“…hypertension, diabetes and dyslipidemia) further accelerate endothelial dysfunction (Shimokawa 1999). eNOS is thought to be an up-stream molecule of metabolic disorder, because either eNOS −/− mice or n/i/eNOSs −/− mice showed the phenotypes of metabolic syndrome (Duplain et al 2001;Nakata et al 2008) and conversely, in endothelium-specific eNOS transgenic mice, diet-induced hypercholesterolemia was prevented (Sansbury et al 2012). Moreover, activity of sterol regulatory element-binding protein (SREBP)-2, a transcriptional factor for cholesterol metabolism and expression of lowdensity lipoprotein (LDL) receptor were decreased in highfat diet (HFD)-fed n/i/eNOSs −/− mice with resultant severe dyslipidemia (Yatera et al 2010).…”

Nitric Oxide Synthases and Heart Failure ― Lessons from Genetically Manipulated Mice

“…The n/i/eNOS / mice are unexpectedly viable and appear normal, but their survival and fertility rates are markedly reduced as compared with wild-type (WT) mice. The n/i/ eNOS / mice spontaneously develop cardiovascular diseases, including hypertension, dyslipidemia, and arteriosclerosis [56,57]. It, however, remains to be determined whether or not the NOS system plays a role in maintaining cardiac architecture and function.…”