Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging.

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

Signaling cascade that mediates endothelial nitric oxide synthase activation induced by atrial natriuretic peptide.

UNLABELLED: Atrial natriuretic peptide (ANP) induces activation of nitric oxide-synthase (NOS). AIMS: to identify the isoform of NOS involved in ANP effects, to study whether ANP modifies NOS expression and to investigate the signaling pathways and receptors involved in NOS stimulation. NOS activation induced by ANP would be mediated by endothelial NOS (eNOS) since neuronal or inducible NOS inhibition did not alter ANP effect. The peptide induced no changes in eNOS protein expression. NOS activity stimulated by ANP, in the kidney, aorta and left ventricle, was partially abolished by the NPR-A/B antagonist, as well as PKG inhibition, but no difference in atria was observed. 8-Br-cGMP partially mimicked the effect of ANP on NOS in all tissues. NOS stimulation by ANP in atria disappeared when G protein was inhibited, but this effect was partial in the other tissues. Calmodulin antagonist abolished NOS stimulation via ANP. Inhibition of the PLC, PKC or PI3 kinase/Akt pathway failed to alter NOS activation induced by ANP. ANP would activate eNOS in the aorta, heart and kidney without modifying the expression of the enzyme. ANP would interact with NPR-C coupled via G proteins leading to the activation of Ca(2+)-calmodulin-dependent NOS in atria; while in ventricle, aorta and kidney, ANP could also interact with NPR-A/B, increasing cGMP, which in turns activates PKG to stimulate eNOS.

Neuronal and endothelial nitric oxide synthase gene knockout mice

Targeted disruption of the neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) genes has led to knockout mice that lack these isoforms. These animal models have been useful to study the roles of nitric oxide (NO) in physiologic processes. nNOS knockout mice have enlarged stomachs and defects in the inhibitory junction potential involved in gastrointestinal motility. eNOS knockout mice are hypertensive and lack endothelium-derived relaxing factor activity. When these animals are subjected to models of focal ischemia, the nNOS mutant mice develop smaller infarcts, consistent with a role for nNOS in neurotoxicity following cerebral ischemia. In contrast, eNOS mutant mice develop larger infarcts, and show a more pronounced hemodynamic effect of vascular occlusion. The knockout mice also show that nNOS and eNOS isoforms differentially modulate the release of neurotransmitters in various regions of the brain. eNOS knockout mice respond to vessel injury with greater neointimal proliferation, confirming that reduced NO levels seen in endothelial dysfunction change the vessel response to injury. Furthermore, eNOS mutant mice still show a protective effect of female gender, indicating that the mechanism of this protection cannot be limited to upregulation of eNOS expression. The eNOS mutant mice also prove that eNOS modulates the cardiac contractile response to ß-adrenergic agonists and baseline diastolic relaxation. Atrial natriuretic peptide, upregulated in the hearts of eNOS mutant mice, normalizes cGMP levels and restores normal diastolic relaxation.

Regulation of human luteal steroidogenesis in vitro by nitric oxide.

To evaluate the effect of nitric oxide (NO.) in human corpus luteum (CL) function, we investigated the expression and the presence of NO. synthase (NOS) in the human CL and the action of NO. on the in vitro luteal steroid production. The expression of endothelial NOS (eNOS) in early, mid-, and late CL was assessed by reverse transcriptase polymerase chain reaction (RT-PCR) and the immunohistochemical study was performed in human CL histological sections by using monoclonal antibodies (MAbs) against the distinct NOS isoforms. In addition, seven human mid-CLs were enzymatically dispersed, and the cells were cultured with NO. donor compounds. Steroid production was measured in the culture media by specific radioimmunoassay. The results show that the expression of eNOS was highly detected in mid- and early CL, and to a lesser extent, in late CL. Meanwhile, the immunohistochemical study indicated that both isoenzymes of NOS were expressed in mid-human CL, eNOS being the more abundant isoform present. On the other hand, functional studies showed that NO. donors (L-arginine [L-Arg] and sodium nitroprusside) elicited an inhibitory action on steroid synthesis, preferentially on estradiol production by the luteal cell cultures (p < 0.05). In conclusion, the NO-NOS system is present in the human CL, and it may serve as a modulator of the in vitro human luteal steroidogenesis.