Kirk L. Peterson

ErbB2 is essential in the prevention of dilated cardiomyopathy

Amplification of the gene encoding the ErbB2 (Her2/neu) receptor tyrosine kinase is critical for the progression of several forms of breast cancer. In a large-scale clinical trial, treatment with Herceptin (trastuzumab), a humanized blocking antibody against ErbB2, led to marked improvement in survival. However, cardiomyopathy was uncovered as a mitigating side effect, thereby suggesting an important role for ErbB2 signaling as a modifier of human heart failure. To investigate the physiological role of ErbB2 signaling in the adult heart, we generated mice with a ventricular-restricted deletion of Erbb2. These ErbB2-deficient conditional mutant mice were viable and displayed no overt phenotype. However, physiological analysis revealed the onset of multiple independent parameters of dilated cardiomyopathy, including chamber dilation, wall thinning and decreased contractility. Additionally, cardiomyocytes isolated from these conditional mutants were more susceptible to anthracycline toxicity. ErbB2 signaling in cardiomyocytes is therefore essential for the prevention of dilated cardiomyopathy.

The knockout of miR-143 and -145 alters smooth muscle cell maintenance and vascular homeostasis in mice: Correlates with human disease

Mechanisms controlling vascular smooth muscle cell (VSMC) plasticity and renewal still remain to be elucidated completely. A class of small RNAs called microRNAs (miRs) regulate gene expression at the post-transcriptional level. Here, we show a critical role of the miR-143/145 cluster in SMC differentiation and vascular pathogenesis, also through the generation of a mouse model of miR-143 and -145 knockout (KO). We determined that the expression of miR-143 and -145 is decreased in acute and chronic vascular stress (transverse aortic constriction and in aortas of the ApoE KO mouse). In human aortic aneurysms, the expression of miR-143 and -145 was significantly decreased compared with control aortas. In addition, overexpression of miR-143 and -145 decreased neointimal formation in a rat model of acute vascular injury. An in-depth analysis of the miR-143/145 KO mouse model showed that this miR cluster is expressed mostly in the SMC compartment, both during development and postnatally, in vessels and SMC-containing organs. Loss of miR-143 and miR-145 expression induces structural modifications of the aorta, because of an incomplete differentiation of VSMCs. In conclusion, our results show that the miR-143/145 gene cluster has a critical role during SMC differentiation and strongly suggest its involvement in the reversion of the VSMC differentiation phenotype that occurs during vascular disease.

Transthoracic Echocardiography in Models of Cardiac Disease in the Mouse

BACKGROUND Transthoracic echocardiography (M-mode and Doppler) offers a noninvasive approach for in vivo evaluation of the mouse heart. The present study examines its usefulness for assessing the morphological/functional phenotype of the left ventricle (LV) in several transgenic and surgical murine models of cardiac disease. METHODS AND RESULTS Observations were made in 83 intact, anesthetized mice. In mice with a surgical arteriovenous fistula, volume overload and LV dilation were detected. In normal mice, echocardiographic indexes of increased contractility (dobutamine) were confirmed by LV dP/dtmax. In transgenic mice with overexpression of the beta 2-adrenergic receptor, heart rate and mean velocity of circumferential fiber shortening were increased, indicating enhanced contractility. In colony screening of transgenic mice overexpressing the H-ras gene, 45% had increased LV wall thickness (> 0.9 mm), and those showing a striking increase were selected for breeding. In mice with LV hypertrophy (aortic constriction) and normal mice, the actual LV mass determined by echocardiography correlated well (r = .93), and 95% confidence limits were determined. The maximum intraobserver and interobserver coefficients of variation for M-mode data were 0.03 +/- 0.29 mm (+/- 2 SD), < 10% for LV internal dimensions but 27% to 30% for wall thickness. CONCLUSIONS These studies provide the first application of transthoracic echocardiography for morphological/functional characterization of the cardiac phenotype in transgenic and surgical murine models, including (1) high reliability for detecting LV chamber dilation and function; (2) reliability (and its limits) for determining abnormal LV wall thickness and LV mass; (3) identification of marked, sometimes asymmetrical, hypertrophy in a transgenic model of hypertrophic cardiomyopathy; and (4) usefulness for transgenic colony screening to identify markedly abnormal phenotypes.

Defects in caveolin-1 cause dilated cardiomyopathy and pulmonary hypertension in knockout mice

Caveolins are important components of caveolae, which have been implicated in vesicular trafficking and signal transduction. To investigate the in vivo significance of Caveolins in mammals, we generated mice deficient in the caveolin-1 (cav-1) gene and have shown that, in the absence of Cav-1, no caveolae structures were observed in several nonmuscle cell types. Although cav-1−/− mice are viable, histological examination and echocardiography identified a spectrum of characteristics of dilated cardiomyopathy in the left ventricular chamber of the cav-1-deficient hearts, including an enlarged ventricular chamber diameter, thin posterior wall, and decreased contractility. These animals also have marked right ventricular hypertrophy, suggesting a chronic increase in pulmonary artery pressure. Direct measurement of pulmonary artery pressure and histological analysis revealed that the cav-1−/− mice exhibit pulmonary hypertension, which may contribute to the right ventricle hypertrophy. In addition, the loss of Cav-1 leads to a dramatic increase in systemic NO levels. Our studies provided in vivo evidence that cav-1 is essential for the control of systemic NO levels and normal cardiopulmonary function.

A cardiac myocyte vascular endothelial growth factor paracrine pathway is required to maintain cardiac function

The role of the cardiac myocyte as a mediator of paracrine signaling in the heart has remained unclear. To address this issue, we generated mice with cardiac myocyte-specific deletion of the vascular endothelial growth factor gene, thereby producing a cardiomyocyte-specific knockout of a secreted factor. The hearts of these mice had fewer coronary microvessels, thinned ventricular walls, depressed basal contractile function, induction of hypoxia-responsive genes involved in energy metabolism, and an abnormal response to β-adrenergic stimulation. These findings establish the critical importance of cardiac myocyte-derived vascular endothelial growth factor in cardiac morphogenesis and determination of heart function. Further, they establish an adult murine model of hypovascular nonnecrotic cardiac contractile dysfunction.

Requirement for Ca2+/calmodulin–dependent kinase II in the transition from pressure overload–induced cardiac hypertrophy to heart failure in mice

Ca2+/calmodulin-dependent kinase II (CaMKII) has been implicated in cardiac hypertrophy and heart failure. We generated mice in which the predominant cardiac isoform, CaMKIIdelta, was genetically deleted (KO mice), and found that these mice showed no gross baseline changes in ventricular structure or function. In WT and KO mice, transverse aortic constriction (TAC) induced comparable increases in relative heart weight, cell size, HDAC5 phosphorylation, and hypertrophic gene expression. Strikingly, while KO mice showed preserved hypertrophy after 6-week TAC, CaMKIIdelta deficiency significantly ameliorated phenotypic changes associated with the transition to heart failure, such as chamber dilation, ventricular dysfunction, lung edema, cardiac fibrosis, and apoptosis. The ratio of IP3R2 to ryanodine receptor 2 (RyR2) and the fraction of RyR2 phosphorylated at the CaMKII site increased significantly during development of heart failure in WT mice, but not KO mice, and this was associated with enhanced Ca2+ spark frequency only in WT mice. We suggest that CaMKIIdelta contributes to cardiac decompensation by enhancing RyR2-mediated sarcoplasmic reticulum Ca2+ leak and that attenuating CaMKIIdelta activation can limit the progression to heart failure.

Rebuilding a Damaged Heart Long-Term Survival of Transplanted Neonatal Rat Cardiomyocytes After Myocardial Infarction and Effect on Cardiac Function

Background—The long-term effects of cardiac cell transplantation on cardiac function are unknown. Therefore, we tested the survival and functional impact of rat neonatal cardiac myocytes up to 6 months after transplantation into infarcted hearts. Methods and Results—Cardiomyocytes from male neonatal Fischer 344 rats (1 to 2 days, 3 to 5×106) or medium was injected into the infarcts of adult syngeneic female animals 1 week after left coronary artery ligation. Six months later, implanted cardiomyocytes were still present by quantitative TaqMan polymerase chain reaction and histology. In all treated hearts, discrete lumps of cells were present within the infarct scar, which was not observed in media-injected hearts typified by a transmural infarct scar. Infarct thickness was greater in treated animals versus control animals (909±97 versus 619±43 &mgr;m, P <0.02), whereas infarct size and left ventricular volumes were similar. By biplane angiography, left ventricular ejection fractions at 6 months were greater (0.36±0.03 versus 0.25±0.02, P <0.01) and significantly less infarct zone dyskinesis was seen (0.30±0.08 versus 0.55±0.07, P =0.035, lateral projection) in treated animals versus control animals. Conclusions—Grafted neonatal cardiomyocytes were present in infarcts 6 months after transplantation; they thickened the wall of the left ventricle and were associated with enhanced ejection fraction and reduced paradoxical systolic bulging of the infarct. Therefore, neonatal cardiac cell transplants exhibit long-term survival in a myocardial infarct model and contribute to long-term improved cardiac function. These results suggest that a damaged heart can be rebuilt.

Temporal response of left ventricular performance to mitral valve surgery.

We separated MR patients into two subgroups. In 12 subjects (group 1) with preoperative EDD = 5.94 0.42 cm, ESD = 3.55 ± 0.43 cm, and EF = 0.70 ± 0.05, EF fell slightly by 6 months after surgery to 0.59 ± 0.10 (p < 0.01), but remained within the normal range. Concomitantly, left ventricular hypertrophy regressed, as CSA was 24.2 6.5 cm2 before and 18.6 ± 2.4 cm2 after surgery (p < 0.01). contrast, in four subjects (group 2) with preoperative EDD = 8.07 ± 0.35 cm, ESD = 5.69 ± 0.70 cm, and EF = 0.57 ± 0.05, left ventricular function progressively deteriorated after surgery, with EF falling 0.26 ± 0.06 (p < 0.01). In the latter group left ventricular hypertrophy did not regress (CSA = 31.5 ± 4.5 cm2 before and 31.9 ± 3.4 cm2 after surgery, NS). Techniques for myocardial preservation during mitral valve surgery did not differ between the MR and MS groups. In group 2 MR subjects, there was no evidence of intraoperative myocardial infarction.

Acute Pulmonary Thromboembolism Has Its Evolution Been Redefined

Despite nearly 4 decades of creative scientific and clinical scrutiny by physicians and surgeons, worldwide pulmonary thromboembolism remains a dreaded, life-threatening illness. Older statistics estimate that in the United States, acute pulmonary thromboembolism afflicts 500 000 to 600 000 persons annually and is either a primary or secondary cause of death in 150 000 to 200 000 of these individuals.1 2 Extrapolation of a population-based study from data accumulated in 1985 through 1986 in Worcester, Mass, suggests that each year there are ≈170 000 new cases of clinically recognized venous thromboembolism treated in short-stay hospitals and 99 000 hospitalizations for recurrent disease.3 When the disease process was followed from the time of clinical recognition, the 1-year mortality rate in a national multicenter project (PIOPED) was reported as ≈25%, with 2.5% dying from pulmonary embolism itself and most patients dying from the major diseases that are associated with pulmonary thromboembolism, including cancer, various infections, cardiovascular diseases, and other pulmonary diseases.4 Other studies have reported that in patients without preexisting cardiac or pulmonary disease, the 1-year mortality rate ranged from 3% to 9%.5 6 If a massive pulmonary embolism occurs associated with systemic hypotension, the in-hospital mortality rate is ≈18%.7 The persistence of pulmonary hypertension after embolization has been associated with increased mortality rates; the higher the pulmonary artery pressure, the lower the survival rate at 5 years.8 Furthermore, it has been predicted, with admitted imprecision, that 0.01% of patients develop what is now commonly referred to as chronic pulmonary thromboembolic pulmonary hypertension.9 Although these statistics are often reiterated, they likely belie an accurate description of the natural history of the disease. In fact, there are a number of impediments to precise characterization of the incidence and course of the disease: (1) many episodes of …

Resident fibroblast lineages mediate pressure overload–induced cardiac fibrosis

Activation and accumulation of cardiac fibroblasts, which result in excessive extracellular matrix deposition and consequent mechanical stiffness, myocyte uncoupling, and ischemia, are key contributors to heart failure progression. Recently, endothelial-to-mesenchymal transition (EndoMT) and the recruitment of circulating hematopoietic progenitors to the heart have been reported to generate substantial numbers of cardiac fibroblasts in response to pressure overload-induced injury; therefore, these processes are widely considered to be promising therapeutic targets. Here, using multiple independent murine Cre lines and a collagen1a1-GFP fusion reporter, which specifically labels fibroblasts, we found that following pressure overload, fibroblasts were not derived from hematopoietic cells, EndoMT, or epicardial epithelial-to-mesenchymal transition. Instead, pressure overload promoted comparable proliferation and activation of two resident fibroblast lineages, including a previously described epicardial population and a population of endothelial origin. Together, these data present a paradigm for the origins of cardiac fibroblasts during development and in fibrosis. Furthermore, these data indicate that therapeutic strategies for reducing pathogenic cardiac fibroblasts should shift from targeting presumptive EndoMT or infiltrating hematopoietically derived fibroblasts, toward common pathways upregulated in two endogenous fibroblast populations.