Cardiac Fibrosis In Mice Research Articles

Defective peroxisomal proliferators activated receptor gamma activity due to dominant‐negative mutation synergizes with hypertension to accelerate cardiac fibrosis in mice

AimsHumans with inactivating mutations in peroxisomal proliferators activated receptor gamma (PPARγ) typically develop a complex metabolic syndrome characterized by insulin resistance, diabetes, lipodystrophy, hypertension, and dyslipidaemia which is likely to increase their cardiovascular risk. Despite evidence that the activation of PPARγ may prevent cardiac fibrosis and hypertrophy, recent evidence has suggested that pharmacological activation of PPARγ causes increased cardiovascular mortality. In this study, we investigated the effects of defective PPARγ function on the development of cardiac fibrosis and hypertrophy in a murine model carrying a human dominant-negative mutation in PPARγ.Methods and resultsMice with a dominant-negative point mutation in PPARγ (P465L) and their wild-type (WT) littermates were treated with either subcutaneous angiotensin II (AngII) infusion or saline for 2 weeks. Heterozygous P465L and WT mice developed a similar increase in systolic blood pressure, but the mutant mice developed significantly more severe cardiac fibrosis to AngII that correlated with increased expression of profibrotic genes. Both groups similarly increased the heart weight to body weight ratio compared with saline-treated controls. There were no differences in fibrosis between saline-treated WT and P465L mice.ConclusionThese results show synergistic pathogenic effects between the presence of defective PPARγ and AngII-induced hypertension and suggest that patients with PPARγ mutation and hypertension may need more aggressive therapeutic measures to reduce the risk of accelerated cardiac fibrosis.

Prostanoids in health and disease

The prostanoids are a family of lipid mediators generated by the action of cyclooxygenase on a 20-carbon unsaturated fatty acid, arachidonic acid. Prostanoids are generated widely in response to diverse stimuli and, acting in a paracrine or autocrine manner, play important roles in normal physiology and disease. This review summarizes the current knowledge on prostanoid generation and the roles of individual mediators, their biosynthetic pathways, and their receptors in health and disease.

Severe deficiency of coagulation Factor VII results in spontaneous cardiac fibrosis in mice

Mice genetically modified to produce low levels (approximately 1% of wild-type) of coagulation FVII presented with echocardiographic evidence of heart abnormalities. Decreases in ventricular size and reductions in systolic and diastolic functions were found, suggestive of a restrictive cardiomyopathy and consistent with an infiltrative myopathic process. Microscopic analysis of mouse hearts showed severe patchy fibrosis in the low-FVII mice. Haemosiderin deposition was discovered in hearts of these mice, along with increases in inflammatory cell number, ultimately resulting in widespread collagen deposition. Significant increases in mRNA levels of TGFbeta, TNFalpha and several matrix metalloproteinases in low-FVII mice, beginning at early ages, supported a state of cardiac remodelling associated with the fibrotic pathology. Mechanistic time-course studies suggested that cardiac fibrosis in low-FVII mice originated from bleeding in heart tissue, resulting in the recruitment of leukocytes, which released inflammatory mediators and induced collagen synthesis and secretion. These events led to necrosis of cardiomyocytes and collagen deposition, characteristics of cardiac fibrosis. The results of this study demonstrated that haemorrhagic and inflammatory responses to a severe FVII deficiency resulted in the development of cardiac fibrosis, observed echocardiographically as a restrictive cardiomyopathy, with compromised ventricular diastolic and systolic functions.

A FVII Deficiency Induces Cardiac Fibrosis in Mice Resulting in Systolic and Diastolic Dysfunction.

Mice severely deficient in coagulation Factor (F)VII that survive to adulthood have been developed, thus allowing the study of spontaneous bleeding and inflammatory phenotypes under conditions of a deficiency of extrinsic coagulation, especially in organs e.g., the heart, that continually undergo normal mechanical challenge. Mice genetically modified to produce very low levels (∼1% of wild-type) of coagulation FVII (FVIItTA/tTA) spontaneously developed heart abnormalities that were revealed by echocardiography. There were no significant differences between groups at baseline for the hemodynamic and respiratory parameters: temperature and heart rate (HR). The end-systolic functions of FVIItTA/tTA mice heart were comparable to wild-type (WT) controls. However, there were significant changes in the end-diastolic parameters of FVIItTA/tTA hearts. The diameter at end-diastole in FVIItTA/tTA mice was smaller compared to WT mice, which was due to the stiffness of the interventricular wall. When viewed from the parasternal short-axis, these mice had evidence of hypokinesis, indicating alteration of the elastic properties of the left ventricular (LV) wall. Correspondingly, the stroke volume, ejection fraction, fractional shortening, and cardiac output were lower in FVIItTA/tTA mice, compared to WT mice. Mitral valve inflow was compromised in FVIItTA/tTA mice, as demonstrated by the reduced early/late (E/A) filling ratio. We found that the spontaneous impaired cardiac function in FVIItTA/tTA mice was associated with an increased ratio of heart weight to body weight. Decreases in ventricular size, accompanied by reductions in systolic and diastolic functions, suggest a restrictive cardiomyopathy, consistent with an infiltrative myopathic process. Microscopic analysis of mouse hearts showed severe patchy fibrosis in FVIItTA/tTA mice. Hemosiderin deposition in hearts of these mice, along with large increases in inflammatory cells, ultimately resulting in widespread collagen deposition, were found. Significant increases in mRNA levels of TGF-beta, TNF-alpha, and a variety of matrix metalloproteinases, beginning at early ages in FVIItTA/tTA mice, supported the fibrotic pathology. The results of this study demonstrated that hemorrhagic and inflammatory responses to a severe FVII deficiency resulted in the development of cardiac fibrosis, manifest echocardiographically as a restrictive cardiomyopathy, with significantly compromised ventricular diastolic and systolic functions. These data also suggest that a FVII deficiency differentially regulates the expression level of inflammation and extracellular matrix proteins, which result in compromised cardiac function.

Adenovirus-mediated delivery of relaxin reverses cardiac fibrosis in mice with fibrotic cardiomyopathy

Adenovirus-mediated delivery of relaxin reverses cardiac fibrosis in mice with fibrotic cardiomyopathy

Increased insulin, triglycerides, reactive oxygen species, and cardiac fibrosis in mice with a mutation in the helicase domain of the Werner syndrome gene homologue

Werner Syndrome (WS) is a rare disorder characterized by the premature onset of a number of age-related diseases. The gene responsible for WS encodes a DNA helicase/exonuclease protein. Previously, we generated a mouse model lacking part of the helicase domain of the murine Wrn homologue. Mutant Wrn Δhel/Δhel mice developed severe cardiac interstitial fibrosis in addition to tumors. Further analyses of these mice on the pure C57Bl/6 genetic background revealed abnormal increases in visceral fat deposition, fasting blood triglyceride and cholesterol levels followed by insulin resistance and high blood glucose levels. These phenotypes were more severe in mutant females than mutant males. In addition, adult mice had clear hemodynamic signs of aortic stenosis. All these symptoms appeared before the onset of cardiomyopathy and are known to cause heart failure. Interestingly, Wrn Δhel/Δhel adult mice (but not juveniles) showed higher levels of serum and cardiac tissue reactive oxygen species followed in time by an increase in cardiac oxidative DNA damage, all this prior to cardiac fibrosis.

Angiotensin II antagonism fails to ameliorate bleomycin-induced pulmonary fibrosis in mice

Based on current evidence, transforming growth factor (TGF)-beta plays a central pathogenic role in the development of pulmonary fibrosis. There is growing evidence that angiotensin II can serve as a stimulus for TGF-beta-mediated lung fibrosis. However, the role of angiotensin II in the pathobiology of pulmonary fibrosis in vivo remains unclear and the therapeutic potential for targeting angiotensin II in a bleomycin-induced pulmonary fibrosis model is not well known. Therefore, the aim of this study was to test whether the angiotensin II antagonist, losartan, attenuated the development of bleomycin-induced pulmonary fibrosis in two distinct murine strains, C57/BL6 and Sv129. This was determined by histopathology and quantification of collagen content by hydroxyproline assay. Despite demonstrable angiotensin II antagonism in vivo and a reduction in measures of acute lung injury, losartan therapy, at a dose shown to reduce renal and cardiac fibrosis in mice, failed to significantly ameliorate bleomycin-induced pulmonary fibrosis. In conclusion, these data suggest that the pulmonary fibrotic disease process in vivo is not solely dependent on angiotensin II activity and the potential for angiotensin II receptor blockers as a therapeutic strategy in patients with pulmonary fibrosis may be limited.

Overexpression of urokinase by macrophages or deficiency of plasminogen activator inhibitor type 1 causes cardiac fibrosis in mice.

Several studies implicate elevated matrix metalloproteinase activity as a cause of cardiac fibrosis. However, it is unknown whether other proteases can also initiate cardiac fibrosis. Because absence of urokinase plasminogen activator (uPA) prevents development of cardiac fibrosis after experimental myocardial infarction in mice, we hypothesized that elevated activity of uPA or deficiency of the uPA inhibitor plasminogen activator inhibitor-1 (PAI-1) might cause cardiac fibrosis. We used mice with scavenger-receptor (SR)-directed, macrophage-targeted uPA overexpression (SR-uPA+/0 mice) and PAI-1 null mice to test these hypotheses. Our studies revealed that SR-uPA+/0 mice developed cardiac fibrosis beginning between 5 and 10 weeks of age. Fibrosis was preceded by cardiac macrophage accumulation, implicating uPA-secreting macrophages as important contributors to development of fibrosis. A key role for uPA-secreting macrophages in development of cardiac fibrosis was supported by experiments in which recipients of bone marrow transplants from SR-uPA+/0 donors but not nontransgenic donors developed cardiac macrophage accumulation and fibrosis. SR-uPA+/0 mice and recipients of SR-uPA+/0 bone marrow had neither macrophage accumulation nor fibrosis in other major organs despite the presence of higher levels of uPA in these organs than in hearts. PAI-1 null mice but not congenic, age-matched controls also developed macrophage accumulation and fibrosis in hearts but not in other organs. We conclude: (1) either elevated macrophage uPA expression or PAI-1 deficiency is sufficient to cause cardiac macrophage accumulation and fibrosis; (2) macrophages are important contributors to the development of cardiac fibrosis; and (3) the heart is particularly sensitive to the effects of excess uPA activity.

Angiotensin II type 2 receptor is essential for left ventricular hypertrophy and cardiac fibrosis in chronic angiotensin II-induced hypertension.

The roles of angiotensin II (Ang II) in the regulation of heart function under normal and pathological conditions have been well documented. Although 2 types of Ang II receptor (AT(1) and AT(2)) are found in various proportions, most studies have focused on AT(1)-coupled events. In the present study, we examined the hypothesis that signaling by AT(2) is important to the development of left ventricular hypertrophy and cardiac fibrosis by Ang II infusion in mice lacking the AT(2) gene (Agtr2-/Y). Male Agtr2-/Y and age-matched wild-type (WT) mice were treated long-term with Ang II, infused at a rate of 4.2 ng. kg(-1). min(-1) for 3 weeks. Ang II elevated systolic blood pressure to comparable levels in Agtr2-/Y and WT mice. WT mice developed prominent concentric cardiac hypertrophy, prominent fibrosis, and impaired diastolic relaxation after Ang II infusion. In contrast, there was no cardiac hypertrophy in Agtr2-/Y mice. Agtr2-/Y mice, however, did not show signs of heart failure or impairment of ventricular relaxation and only negligible fibrosis after Ang II infusion. The absence of fibrosis may be a clue to the absence of impairment in ventricular relaxation and account for the normal left ventricular systolic and diastolic performances in Agtr2-/Y mice. Chronic loss of AT(2) by gene targeting abolished left ventricular hypertrophy and cardiac fibrosis in mice with Ang II-induced hypertension.

Reversibility of cardiac fibrosis in mice chronically infected with Trypanosoma cruzi, under specific chemotherapy

This investigation was performed to verify the effect of specific chemotherapy (Benznidazole or MK-436) on the inflammatory and fibrotic cardiac alterations in mice chronically infected with the strains 21 SF (Type II) and Colombian (Type III) of Trypanosoma cruzi. To obtain chronically infected mice, two groups of 100 Swiss mice each, were infected with either the 21 SF or the Colombian strain (2 x 10(4) and 5 x 10(4) blood forms respectively). The rate of mortality in the acute phase was of 80% for both groups. Twenty surviving mice chronically infected with the 21 SF strain and 20 with the Colombian strain were then divided in treated and untreated groups. Excluding those that died during the course of treatment, 14 mice chronically infected with the 21 SF strain and 15 with the Colombian strain were finally evaluated in the present study. Chemotherapy was performed with Benznidazole (N-benzil-2-nitro-1-imidazolacetamide) in the dose of 100 mg/k.b.w/day, for 60 days, or with the MK-436 (3(1-methyl-5 nitroimidazol-2-yl) in two daily doses of 250 mg/k.b.w, for 20 days. Parasitological cure tests were performed (xenodiagnosis, haemoculture, subinoculation of the blood into newborn mice), and serological indirect immunofluorescence test. The treated and untreated mice as well as intact controls were killed at different periods after treatment and the heart were submitted to histopathological study with hematoxilineosin and picrosirius staining; ultrastructural study; collagen immunotyping, fibronectin and laminin identification by immunofluorescence tests. the untreated controls either infected with 21 SF or Colombian strain, showed inflammatory and fibrotic alterations that were mild to moderate with the 21 SF strain and intense with the Colombian strain. Redpicrosirius staining showed bundles of collagen in the interstitial space and around cardiac fibers. Increased deposits of matritial components and collagen fibers, macrophages and fibroblasts appeared at the ultrastructural examination. Deposits of fibronectin, laminin, pro-III and IV collagens were seen, most intense in those infected with the Colombian strain. Treated mice, parasitologically cured, presented clear-cut regression of the inflammatory lesions and of the interstitial matrix thickening. Mice infected with the Colombian strain and treated with MK-436, was parasitologically cured in 5/6 cases and showed mild inflammatory infiltration and fibrosis. The mice treated with Benznidazole (Colombian strain) did not cure and showed moderate fibrosis and inflammation. Treatment of the mice infected with the 21 SF with Benznidazole determined parasitological cure of all animals, that showed mild inflammation and fibrosis of the myocardium.(ABSTRACT TRUNCATED AT 400 WORDS)