Stroma cell-derived factor-1α signaling enhances calcium transients and beating frequency in rat neonatal cardiomyocytes.

Stroma cell-derived factor-1α (SDF-1α) is a cardioprotective chemokine, acting through its G-protein coupled receptor CXCR4. In experimental acute myocardial infarction, administration of SDF-1α induces an early improvement of systolic function which is difficult to explain solely by an anti-apoptotic and angiogenic effect. We wondered whether SDF-1α signaling might have direct effects on calcium transients and beating frequency.Primary rat neonatal cardiomyocytes were culture-expanded and characterized by immunofluorescence staining. Calcium sparks were studied by fluorescence microscopy after calcium loading with the Fluo-4 acetoxymethyl ester sensor. The cardiomyocyte enriched cellular suspension expressed troponin I and CXCR4 but was vimentin negative. Addition of SDF-1α in the medium increased cytoplasmic calcium release. The calcium response was completely abolished by using a neutralizing anti-CXCR4 antibody and partially suppressed and delayed by preincubation with an inositol triphosphate receptor (IP3R) blocker, but not with a ryanodine receptor (RyR) antagonist. Calcium fluxes induced by caffeine, a RyR agonist, were decreased by an IP3R blocker. Treatment with forskolin or SDF-1α increased cardiomyocyte beating frequency and their effects were additive. In vivo, treatment with SDF-1α increased left ventricular dP/dtmax.These results suggest that in rat neonatal cardiomyocytes, the SDF-1α/CXCR4 signaling increases calcium transients in an IP3-gated fashion leading to a positive chronotropic and inotropic effect.

Ventricular-arterial uncoupling in heart failure with preserved ejection fraction after myocardial infarction in dogs - invasive versus echocardiographic evaluation.

BACKGROUND: Heart failure with preserved left ventricular ejection fraction and abnormal diastolic function is commonly observed after recovery from an acute myocardial infarction. The aim of this study was to investigate the physiopathology of heart failure with preserved ejection fraction in a model of healed myocardial infarction in dogs. METHODS: Echocardiography, levels of neurohormones and conductance catheter measurements of left ventricular pressure-volume relationships were obtained in 17 beagle dogs 2 months after a coronary artery ligation, and in 6 controls. RESULTS: Healed myocardial infarction was associated with preserved echocardiographic left ventricular ejection fraction (0.57 +/- 0.01, mean +/- SEM) and altered Doppler mitral indices of diastolic function. NT-proBNP was increased, aldosterone was decreased, and norepinephrine was unchanged. Invasive measurements showed a markedly decreased end-systolic elastance (2.1 +/- 0.2 vs 6.1 +/- 0.8, mmHg/ml, p < 0.001) and end-systolic elastance to effective arterial elastance ratio (0.6 +/- 0.1 vs 1.4 +/- 0.2, p < 0.001), with altered active relaxation (dP/dtmin -1992 +/- 71 vs -2821 +/- 305, mmHg/s, p < 0.01) but preserved left ventricular capacitance (70 +/- 6 vs 61 +/- 3, ml at 20 mmHg, p = NS) and stiffness constant. Among echocardiographic variables, the wall motion score index was the most reliable indicator of cardiac contractility while E', E/A and E'/A' were correlated to dP/dtmin. CONCLUSIONS: In the canine model of healed myocardial infarction induced by coronary ligation, heart failure is essentially characterized by an altered contractility with left ventricular-arterial uncoupling despite vascular compensation rather than by abnormal diastolic function.

Cardiac insulin-like growth factor-1 and cyclins gene expression in canine models of ischemic or overpacing cardiomyopathy.

BACKGROUND: Insulin-like growth factor-1 (IGF-1), transforming growth factor beta (TGFbeta) and cyclins are thought to play a role in myocardial hypertrophic response to insults. We investigated these signaling pathways in canine models of ischemic or overpacing-induced cardiomyopathy. METHODS: Echocardiographic recordings and myocardial sampling for measurements of gene expressions of IGF-1, its receptor (IGF-1R), TGFbeta and of cyclins A, B, D1, D2, D3 and E, were obtained in 8 dogs with a healed myocardial infarction, 8 dogs after 7 weeks of overpacing and in 7 healthy control dogs. RESULTS: Ischemic cardiomyopathy was characterized by moderate left ventricular systolic dysfunction and eccentric hypertrophy, with increased expressions of IGF-1, IGF-1R and cyclins B, D1, D3 and E. Tachycardiomyopathy was characterized by severe left ventricular systolic dysfunction and dilation with no identifiable hypertrophic response. In the latter model, only IGF-1 was overexpressed while IGF-1R, cyclins B, D1, D3 and E stayed unchanged as compared to controls. The expressions of TGFbeta, cyclins A and D2 were comparable in the 3 groups. The expression of IGF-1R was correlated with the thickness of the interventricular septum, in systole and diastole, and to cyclins B, D1, D3 and E expression. CONCLUSION: These results agree with the notion that IGF-1/IGF-1R and cyclins are involved in the hypertrophic response observed in cardiomyopathies.

Cell therapy with autologous bone marrow mononuclear stem cells is associated with superior cardiac recovery compared with use of nonmodified mesenchymal stem cells in a canine model of chronic myocardial infarction.

OBJECTIVE: Stem cell therapy can facilitate cardiac repair in infarcted myocardium, but the optimal cell type remains uncertain. We conducted a randomized, blind, and placebo-controlled comparison of autologous bone marrow mononuclear cell and mesenchymal stem cell therapy in a large-animal model of chronic myocardial infarction. METHODS: Eleven weeks after coronary ligation, 24 dogs received intramyocardial injections of mononuclear cells (227.106 +/- 32.106 cells), mesenchymal stem cells (232.106 +/- 40.106 cells), or placebo (n = 8 per group). Cardiac performance and remodeling were assessed up to 16 weeks' follow-up. RESULTS: At echocardiographic analysis, the wall motion score index showed a sustained improvement after mononuclear cell transfer (from 1.8 +/- 0.1 to 1.5 +/- 0.07) and a moderate late improvement after mesenchymal stem cell transfer (from 1.9 +/- 0.08 to 1.7 +/- 0.1). After mononuclear cell transfer, end-systolic elastance increased (from 2.23 +/- 0.25 to 4.42 +/- 0.55 mm Hg/mL), infarct size decreased (from 13% +/- 0.67% to 10% +/- 1.17%), N-terminal B-type natriuretic propeptide level decreased (from 608 +/- 146 to 353 +/- 118 pmol/L), and relative wall area and arterial density increased. Vascular endothelial growth factor receptor 2 expression was upregulated in the border zone. No change in cardiac contractility or histologic parameters was noted in the mesenchymal stem cell group. CONCLUSION: In a canine model of chronic myocardial infarction, bone marrow mononuclear cell transfer is superior to mesenchymal stem cell transfer in improvement of cardiac contractility and regional systolic function and reduction in infarct size and plasma N-terminal B-type natriuretic propeptide level. Functional improvement is associated with a favorable angiogenic environment and neovascularization.

Activin-A, transforming growth factor-beta, and myostatin signaling pathway in experimental dilated cardiomyopathy.

BACKGROUND: The pathogenic mechanisms of dilated cardiomyopathy are still uncertain. A number of cytokines and growth factors participate in the remodeling process of the disease. METHODS: We investigated the cardiac myostatin, transforming growth factor (TGF)beta, and activin-A/Smad growth inhibitory signaling pathway in experimental dilated cardiomyopathy. Transvenous endomyocardial biopsies of the interventricular septum were taken weekly in 15 beagle dogs during the development of heart failure (HF) induced by rapid pacing over a period of 7 weeks. Genes involved in the myostatin-TGFbeta-activin-A/Smad signaling pathway and the cardiac hypertrophic process were quantified by real-time quantitative polymerase chain reaction. Left ventricular volume, function, and mass were evaluated by echocardiography. RESULTS: Overpacing was associated with increased left ventricular volumes and decreased ejection fraction, whereas the left ventricular mass remained unchanged. TGFbeta was increased in moderate HF. Activin-A mRNA expression was 4-fold higher in overt congestive HF than at baseline. A 2-fold decrease of activin type II receptors and activin receptor interacting protein 2 gene expressions were observed, as well as a transient decrease of follistatin. Activin type I receptors, activin receptor interacting protein 1, follistatin-related gene, and myostatin remained unchanged. The inhibitory Smad 7, a negative feedback loop regulator of the Smad pathway, was overexpressed in severe HF. Gene expression of the cyclin-dependent kinase inhibitor p21, a direct target gene of the Smad pathway, was 8-fold up-regulated in HF, whereas cyclin D1 was down-regulated. CONCLUSION: We conclude that tachycardia-induced dilated cardiomyopathy is characterized by gene overexpression of the TGFbeta-activin-A/Smad signaling pathway and their target gene p21 and by the absence of ventricular hypertrophy.