Objective- Dyslipidemia is a component of the metabolic syndrome, an established risk factor for atherosclerotic cardiovascular disease, and is also observed in various autoimmune and chronic ...inflammatory conditions. However, there are limited opportunities to study the impact of acquired dyslipidemia on cardiovascular and immune pathology. Approach and Results- We designed a model system that allows for the conversion to a state of acute hyperlipidemia in adult life, so that the consequences of such a transition could be observed, through conditionally deleting APOE (apolipoprotein E) in the adult mouse. The transition to hypercholesterolemia was accompanied by adaptive immune responses, including the expansion of T lymphocyte helper cell 1, T follicular helper cell, and T regulatory subsets and the formation of germinal centers. Unlike steady-state Apoe
mice, abrupt loss of APOE induced rapid production of antibodies recognizing rheumatoid disease autoantigens. Genetic ablation of the germinal center reduced both autoimmunity and atherosclerosis, indicating that the immune response that follows loss of APOE is independent of atherosclerosis but nevertheless promotes plaque development. Conclusions- Our findings suggest that immune activation in response to hyperlipidemia could contribute to a wide range of inflammatory autoimmune diseases, including atherosclerosis.
Atrial natriuretic peptide (ANP) and brain (B-type) natriuretic peptide (BNP) are circulating hormones of cardiac origin that play an important role in the regulation of intravascular blood volume ...and vascular tone. The plasma concentrations of ANP and BNP are elevated in heart failure, and they are considered to compensate for heart failure because of their diuretic, natriuretic, and vasodilating actions and inhibitory effects on renin and aldosterone secretion. Evidence is also accumulating from recent work that ANP and BNP exert their cardioprotective functions not only as circulating hormones but also as local autocrine and/or paracrine factors. In studies using cultured neonatal myocytes and fibroblasts, exogenous administration of both ANP and ANP antagonists demonstrated that ANP has antihypertrophic and antifibrotic functions. Corroborating these in vitro results, mice lacking natriuretic receptor-A (NPR-A), the receptor for ANP and BNP, develop cardiac hypertrophy and fibrosis independent of their blood pressure. Recent studies also suggest that the intracardiac natriuretic peptides/cGMP system plays a counter-regulatory role against the intracardiac renin-angiotensin-aldosterone system and TGF-beta mediated pathway. In a clinical setting, human recombinant ANP and BNP may be used for a therapy of heart failure; however, further evaluation is required in the future.
The objective of this study was to examine whether genetically determined differences in the guanylyl cyclase/natriuretic peptide receptor-A gene (Npr1) affect cardiac expression of proinflammatory ...cytokines, hypertrophic markers, nuclear factor-κB (NF-κB), and activating protein-1 (AP-1) in am Npr1 gene-dose–dependent manner. In the present studies, adult male Npr1 gene-disrupted (Npr1−/−), wild-type (Npr1+/+), and gene-duplicated (Npr1++/++) mice were used. The Npr1−/− mice showed 41 mm Hg higher systolic blood pressure and 60% greater heart weight to body weight (HW/BW) ratio; however, Npr1++/++ mice exhibited 15 mm Hg lower systolic blood pressure and 12% reduced HW/BW ratio compared with Npr1+/+ mice. Significant upregulation of gene expression of proinflammatory cytokines and hypertrophic markers along with enhanced NF-κB/AP-1 binding activities were observed in the Npr1−/− mouse hearts. Conversely, hypertrophic markers and proinflammatory cytokines gene expression as well as NF-κB/AP-1 binding activities were markedly decreased in Npr1++/++ mouse hearts compared with wild-type mice. The ventricular guanylyl cyclase activity and cGMP levels were reduced by 96% and 87%, respectively, in Npr1−/− mice; however, these parameters were amplified by 2.8-fold and 3.8-fold, respectively, in Npr1++/++ mice. Echocardiographic analysis revealed significantly increased fractional shortening in Npr1++/++ mice (P < .05) but greatly decreased in Npr1−/− mice (P < .01) hearts compared with Npr1+/+ mice. The present findings suggest that Npr1 represses the expression of cardiac proinflammatory mediators, hypertrophic markers, and NF-κB/AP-1–mediated mechanisms, which seem to be associated in an Npr1 gene-dose–dependent manner.
In humans, circulating anti-neutrophil cytoplasm autoantibodies (ANCAs) with specificity for myeloperoxidase (MPO) are strongly associated with the development of pauci-immune necrotizing and ...crescentic glomerulonephritis (NCGN). In mice, we have demonstrated that intravenous injection of mouse antibodies specific for mouse MPO induces NCGN that closely mimics the human disease. We now report that the development of NCGN in this experimental model is accompanied by glomerular accumulation of neutrophils and macrophages. Neutrophil infiltration was most conspicuous at sites of glomerular necrosis and crescent formation, with macrophages also most numerous in crescents. Lymphocytes, however, were sparse in acute lesions. Importantly, mice that were depleted of circulating neutrophils with NIMP-R14 rat monoclonal antibodies were completely protected from anti-MPO IgG-induced NCGN. These findings provide direct evidence that neutrophils play a major role in the pathogenesis of anti-MPO-induced NCGN in this animal model and implicate neutrophils in the induction of human ANCA disease. This raises the possibility that therapeutic strategies to reduce circulating neutrophils could be beneficial to patients with ANCA-induced NCGN.
Patients with Tangier disease exhibit extremely low plasma HDL concentrations resulting from mutations in the ATP-binding cassette, sub-family A, member 1 (ABCA1) protein. ABCA1 controls the ...rate-limiting step in HDL particle assembly by mediating efflux of cholesterol and phospholipid from cells to lipid-free apoA-I, which forms nascent HDL particles. ABCA1 is widely expressed; however, the specific tissues involved in HDL biogenesis are unknown. To determine the role of the liver in HDL biogenesis, we generated mice with targeted deletion of the second nucleotide-binding domain of Abca1 in liver only (Abca1(-L/-L)). Abca1(-L/-L) mice had total plasma and HDL cholesterol concentrations that were 19% and 17% those of wild-type littermates, respectively. In vivo catabolism of HDL apoA-I from wild-type mice or human lipid-free apoA-I was 2-fold higher in Abca1(-L/-L) mice compared with controls due to a 2-fold increase in the catabolism of apoA-I by the kidney, with no change in liver catabolism. We conclude that in chow-fed mice, the liver is the single most important source of plasma HDL. Furthermore, hepatic, but not extrahepatic, Abca1 is critical in maintaining the circulation of mature HDL particles by direct lipidation of hepatic lipid-poor apoA-I, slowing its catabolism by the kidney and prolonging its plasma residence time.
The ileal apical sodium bile acid cotransporter participates in the enterohepatic circulation of bile acids. In patients with primary bile acid malabsorption, mutations in the ileal bile acid ...transporter gene (Slc10a2) lead to congenital diarrhea, steatorrhea, and reduced plasma cholesterol levels. To elucidate the quantitative role of Slc10a2 in intestinal bile acid absorption, the Slc10a2 gene was disrupted by homologous recombination in mice. Animals heterozygous (Slc10a2+/–) and homozygous (Slc10a2–/–) for this mutation were physically indistinguishable from wild type mice. In the Slc10a2–/– mice, fecal bile acid excretion was elevated 10- to 20-fold and was not further increased by feeding a bile acid binding resin. Despite increased bile acid synthesis, the bile acid pool size was decreased by 80% and selectively enriched in cholic acid in the Slc10a2–/– mice. On a low fat diet, the Slc10a2–/– mice did not have steatorrhea. Fecal neutral sterol excretion was increased only 3-fold, and intestinal cholesterol absorption was reduced only 20%, indicating that the smaller cholic acid-enriched bile acid pool was sufficient to facilitate intestinal lipid absorption. Liver cholesteryl ester content was reduced by 50% in Slc10a2–/– mice, and unexpectedly plasma high density lipoprotein cholesterol levels were slightly elevated. These data indicate that Slc10a2 is essential for efficient intestinal absorption of bile acids and that alternative absorptive mechanisms are unable to compensate for loss of Slc10a2 function.
Hepatic steatosis is common in patients having severe hyperhomocysteinemia due to deficiency for cystathionine beta-synthase. However, the mechanism by which homocysteine promotes the development and ...progression of hepatic steatosis is unknown. We report here that homocysteine-induced endoplasmic reticulum (ER) stress activates both the unfolded protein response and the sterol regulatory element-binding proteins (SREBPs) in cultured human hepatocytes as well as vascular endothelial and aortic smooth muscle cells. Activation of the SREBPs is associated with increased expression of genes responsible for cholesterol/triglyceride biosynthesis and uptake and with intracellular accumulation of cholesterol. Homocysteine-induced gene expression was inhibited by overexpression of the ER chaperone, GRP78/BiP, thus demonstrating a direct role of ER stress in the activation of cholesterol/triglyceride biosynthesis. Consistent with these in vitro findings, cholesterol and triglycerides were significantly elevated in the livers, but not plasmas, of mice having diet-induced hyperhomocysteinemia. This effect was not due to impaired hepatic export of lipids because secretion of VLDL-triglyceride was increased in hyperhomocysteinemic mice. These findings suggest a mechanism by which homocysteine-induced ER stress causes dysregulation of the endogenous sterol response pathway, leading to increased hepatic biosynthesis and uptake of cholesterol and triglycerides. Furthermore, this mechanism likely explains the development and progression of hepatic steatosis and possibly atherosclerotic lesions observed in hyperhomocysteinemia.
The use of hormone replacement therapy for coronary heart disease prevention in humans has been an area of intense controversy. The atheroprotective qualities of estrogens have been challenged ...recently by several negative results of randomized clinical trials in postmenopausal women. However, the inhibitory effects of estrogens on atherogenesis are well documented in numerous animals, including atherosclerotic mouse models, but the detailed mechanisms of this protection are not understood. In this minireview, we will focus on the considerable success that has been achieved in demonstrating the atheroprotective effects of 17β-estradiol in apolipoprotein E and low-density lipoprotein receptor-deficient mice and the use of these atherosclerotic mouse models in pharmacological and genetic study designs to investigate antiatherogenic mechanisms of estrogens. Mouse models of atherosclerosis should prove beneficial to understanding the cellular and molecular mechanisms of estrogen-mediated atheroprotection and aid the development of improved therapies to confer the benefits and reduce the risks associated with hormone replacement therapy.
The molecular mechanisms leading to Non-Alcoholic Steatohepatitis (NASH) are not fully understood. In mice, NASH can be inhibited by fenofibrate, a synthetic agonist for the nuclear receptor ...peroxisome proliferator activated receptor alpha, which regulates hepatic triglyceride metabolism. This study aimed to elucidate the relation between steatosis and inflammation in NASH in a human-like hyperlipidemic mouse model.
Liver phenotype and gene expression were assessed in APOE2 knock-in mice that were fed a western-type high fat diet with or without co-administration of fenofibrate.
In response to a western diet, APOE2 knock-in mice developed NASH characterized by steatosis and inflammation. Strikingly, macrophage accumulation in the liver preceded the steatosis during progression of the disease. This phenotype was in line with gene expression patterns, which showed regulation of two major groups of genes, i.e. inflammatory and lipid genes. Fenofibrate treatment decreased hepatic macrophage accumulation and abolished steatosis. Moreover, a marked reduction in the expression of inflammatory genes occurred immediately after fenofibrate treatment.
These data indicate that inflammation might play an instrumental role during the development of NASH in this mouse model. Inhibition of NASH by fenofibrate may be due, at least in part, to its inhibitory effect on pro-inflammatory genes.
PDF
