The orphan receptor APJ and its recently identified endogenous ligand, apelin, exhibit high levels of mRNA expression in the heart. However, the functional importance of apelin in the cardiovascular system is not known. In isolated perfused rat hearts, infusion of apelin (0.01 to 10 nmol/L) induced a dose-dependent positive inotropic effect (EC50: 33.1+/-1.5 pmol/L). Moreover, preload-induced increase in dP/dt(max) was significantly augmented (P<0.05) in the presence of apelin. Inhibition of phospholipase C (PLC) with U-73122 and suppression of protein kinase C (PKC) with staurosporine and GF-109203X markedly attenuated the apelin-induced inotropic effect (P<0.001). In addition, zoniporide, a selective inhibitor of Na+-H+ exchange (NHE) isoform-1, and KB-R7943, a potent inhibitor of the reverse mode Na+-Ca2+ exchange (NCX), significantly suppressed the response to apelin (P<0.001). Perforated patch-clamp recordings showed that apelin did not modulate L-type Ca2+ current or voltage-activated K+ currents in isolated adult rat ventricular myocytes. Apelin mRNA was markedly downregulated in cultured neonatal rat ventricular myocytes subjected to mechanical stretch and in vivo in two models of chronic ventricular pressure overload. The present study provides the first evidence for the physiological significance of apelin in the heart. Our results show that apelin is one of the most potent endogenous positive inotropic substances yet identified and that the inotropic response to apelin may involve activation of PLC, PKC, and sarcolemmal NHE and NCX.

Type XV collagen occurs widely in the basement membrane zones of tissues, but its function is unknown. To understand the biological role of this protein, a null mutation in the Col15a1 gene was introduced into the germ line of mice. Despite the complete lack of type XV collagen, the mutant mice developed and reproduced normally, and they were indistinguishable from their wild-type littermates. However, Col15a1-deficient mice showed progressive histological changes characteristic for muscular diseases after 3 months of age, and they were more vulnerable than controls to exercise-induced muscle injury. Despite the antiangiogenic role of type XV collagen-derived endostatin, the development of the vasculature appeared normal in the null mice. Nevertheless, ultrastructural analyses revealed collapsed capillaries and endothelial cell degeneration in the heart and skeletal muscle. Furthermore, perfused hearts showed a diminished inotropic response, and exercise resulted in cardiac injury, changes that mimic early or mild heart disease. Thus, type XV collagen appears to function as a structural component needed to stabilize skeletal muscle cells and microvessels.T ype XV collagen belongs to the heterogeneous group of non-fibril-forming collagens and is thought to be a homotrimer consisting of three ␣1(XV) collagen chains (1). It is characterized by a central highly interrupted triple helical domain and large N-and C-terminal noncollagenous domains (2-4), and it has been shown to be a chondroitin sulfate proteoglycan (5). Type XV collagen mRNAs are expressed in many tissues, but the highest mRNA levels in the mouse can be detected in the heart and skeletal muscle (4). The protein is shown by immunostaining to have a widespread tissue distribution and has been localized mainly to the basement membrane zones, although it can also be found in the fibrillar collagen matrix of some tissues (6, 7). Its function is not known, however.In terms of primary structure, type XV collagen is highly homologous with type XVIII collagen, and together they form a distinct subgroup among the collagens (1, 3). They have thrombospondin-1 sequence homology in the N terminus, seven homologous collagenous domains, and highly homologous Cterminal noncollagenous domains. Type XVIII collagen is the precursor of endostatin, which has been shown to have a potent antiangiogenic effect (8), and the highest degree of homology between collagen types XV and XVIII involves the C-terminal endostatin sequence. The corresponding fragment in type XV collagen has also been shown to have antiangiogenic activity (9, 10).To understand the biological function and significance of type XV collagen, we generated a mouse strain lacking in ␣1(XV) collagen chains by site-specific Cre-loxP-mediated deletion in embryonic stem (ES) cells (11). The data suggest a structural role for type XV collagen in providing mechanical stability between cells and the extracellular matrix in skeletal muscle fibers and microvessels. Col15a1 deficiency leads to functional rather than struct...

The natriuretic peptides, atrial (ANP) and brain natriuretic peptide (BNP) are known to suppress cardiac hypertrophy and fibrosis. Both ANP and BNP exert their bioactivities through the Npr1 receptor, and Npr1 knockout mice (Npr1K/K) exhibit marked cardiac hypertrophy and fibrosis. In this study, we investigated which genes within the hypertrophic and fibrotic pathways are influenced by the lack of Npr1 signalling. cDNA microarray and quantitative real-time PCR (RT-PCR) analyses were performed on cardiac ventricles from Npr1K/K mice. Gene expression at early and late stages during development of hypertrophy was investigated in male and female Npr1K/K mice at 8 weeks and 6 months of age. Heart weight to body weight ratios (HW:BW) were maximally increased in 8-week males (P!0 . 01), whilst HW:BW in females continued to increase progressively up to 6 months (P!0 . 01). This was despite blood pressure being similarly elevated at both the ages in male and female knockout when compared with wild-type (WT) mice (P!0 . 001). Microarray analysis identified altered gene expression at the earliest steps in the hypertrophy-signalling cascade in Npr1K/K mice, particularly calcium-calmodulin signalling and ion channels, with subsequent changes in the expression of intracellular messengers including protein kinases and transcription factors. Real-time PCR analysis confirmed significant differences in gene expression of ANP, BNP, calmodulin 1, histone deacetylase 7a (HDAC7a), protein kinase C (PKC)i, (GATA) 4, collagen 1, phospholamban and transforming growth factor-b1 in Npr1K/K mice when compared with WT (P!0 . 05). The present study implicates the calmodulin-CaMK-Hdac-Mef2 and PKC-MAPK-GATA4 pathways in Npr1 mediation of cardiac hypertrophy.

Rationale:The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels.Objective: We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV (Col15a1 ؊/؊ ) to define its functional role in the vasculature and in age-and hypertension-associated myocardial remodeling. Methods and Results:Cardiac structure and vasculature were analyzed by light and electron microscopy.Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 ؊/؊ mice. Key Words: cardiomyopathy Ⅲ collagen Ⅲ extracellular matrix Ⅲ hypertension Ⅲ microcirculation T he extracellular matrix (ECM) has an important role in cardiac remodeling, defined by the adaptive changes in left ventricular structure, geometry, and function that follow cardiovascular stress in hypertensive heart disease, cardiomyopathies, or myocardial infarction and also as a function of age. 1 Degradation of myocardial collagens results in decreased ventricular stiffness and dilatation, whereas an increase in the total interstitial collagen content and crosslinking results in a stiffer myocardium and ventricular diastolic dysfunction. 2 Cardiomyopathy may result from a variety of acquired or genetic factors. In the absence of coronary artery disease, a significant proportion of cardiomyopathies are attributable to a genetic cause, eg, hereditary forms are present in approximately 30% to 50% of patients experiencing dilative cardiomyopathy (DCM), and mutations in more than 30 genes have been linked to this disease. 3 Many defects in cytoskeletal and sarcomeric proteins involved in cardiomyocyte contraction and force production have been associated with familial DCM, but most of the genetic defects and pathophysiological mechanisms have still not been identified. 4 Recent studies using genetically modified mice suggest that altered cell-ECM interactions and cell-cell adhesion via the intercalated discs may be involved in DCM pathogenesis. [5][6]...

In patients undergoing transfemoral TAVI, the MANTA VCD showed a similar risk of VARC-2 vascular and bleeding complications compared to the ProGlide VCD, but it reduced significantly the need of additional VCDs for completion of hemostasis.

Background-Both the A 1 -and A 3 -adenosine receptors (ARs) have been implicated in mediating the cardioprotective effects of adenosine. Paradoxically, overexpression of both A 1 -AR and A 3 -AR is associated with changes in the cardiac phenotype.To evaluate the temporal relationship between AR signaling and cardiac remodeling, we studied the effects of controlled overexpression of the A 1 -AR using a cardiac-specific and tetracycline-transactivating factor-regulated promoter. Methods and Results-Constitutive A 1 -AR overexpression caused the development of cardiac dilatation and death within 6 to 12 weeks. These mice developed diminished ventricular function and decreased heart rate. In contrast, when A 1 -AR expression was delayed until 3 weeks of age, mice remained phenotypically normal at 6 weeks, and Ͼ90% of the mice survived at 30 weeks. However, late induction of A 1 -AR still caused mild cardiomyopathy at older ages (20 weeks) and accelerated cardiac hypertrophy and the development of dilatation after pressure overload. These changes were accompanied by gene expression changes associated with cardiomyopathy and fibrosis and by decreased Akt phosphorylation. Discontinuation of A 1 -AR induction mitigated cardiac dysfunction and significantly improved survival rate. Conclusions-These data suggest that robust constitutive myocardial A 1 -AR overexpression induces a dilated cardiomyopathy, whereas delaying A 1 -AR expression until adulthood ameliorated but did not eliminate the development of cardiac pathology. Thus, the inducible A 1 -AR transgenic mouse model provides novel insights into the role of adenosine signaling in heart failure and illustrates the potentially deleterious consequences of selective versus nonselective activation of adenosine-signaling pathways in the heart. (Circulation. 2006;114:2240-2250.)

Connective tissue growth factor (CTGF) is involved in the pathogenesis of various fibrotic disorders. However, its role in the heart is not clear. To investigate the role of CTGF in regulating the development of cardiac fibrosis and heart failure, we subjected mice to thoracic aortic constriction (TAC) or angiotensin II infusion, and antagonized the function of CTGF with CTGF monoclonal antibody (mAb). After 8 weeks of TAC, mice treated with CTGF mAb had significantly better preserved left ventricular (LV) systolic function and reduced LV dilatation compared with mice treated with control immunoglobulin G. CTGF mAb–treated mice exhibited significantly smaller cardiomyocyte cross-sectional area and reduced expression of hypertrophic marker genes. CTGF mAb treatment reduced the TAC-induced production of collagen 1 but did not significantly attenuate TAC-induced accumulation of interstitial fibrosis. Analysis of genes regulating extracellular matrix proteolysis showed decreased expression of plasminogen activator inhibitor-1 and matrix metalloproteinase-2 in mice treated with CTGF mAb. In contrast to TAC, antagonizing the function of CTGF had no effect on LV dysfunction or LV hypertrophy in mice subjected to 4-week angiotensin II infusion. Further analysis showed that angiotensin II–induced expression of hypertrophic marker genes or collagens was not affected by treatment with CTGF mAb. In conclusion, CTGF mAb protects from adverse LV remodeling and LV dysfunction in hearts subjected to pressure overload by TAC. Antagonizing the function of CTGF may offer protection from cardiac end-organ damage in patients with hypertension.

Piuhola, Jarkko, Markus Mä kinen, Istvá n Szokodi, and Heikki Ruskoaho. Dual role of endothelin-1 via ET A and ETB receptors in regulation of cardiac contractile function in mice. Am J Physiol Heart Circ Physiol 285: H112-H118, 2003. First published February 27, 2003 10.1152/ajpheart.00480.2002.-An increase in coronary perfusion pressure leads to increased cardiac contractility, a phenomenon known as the Gregg effect. Exogenous endothelin (ET)-1 exerts a positive inotropic effect; however, the role of endogenous ET-1 in the contractile response to elevated load is unknown. We characterized here the role of ET A and ET B receptors in regulation of contractility in isolated, perfused mouse hearts subjected to increased coronary flow. Elevation of coronary flow from 2 to 5 ml/min resulted in 80 Ϯ 10% increase in contractile force (P Ͻ 0.001). BQ-788 (ET B receptor antagonist) augmented the load-induced contractile response by 35% (P Ͻ 0.05), whereas bosentan (ET A/B receptor antagonist) and BQ-123 (ET A receptor antagonist) attenuated it by 34% and 56%, respectively (P Ͻ 0.05). CV-11974 (ANG II type 1 receptor antagonist) did not modify the increase in contractility. These results show that endogenous ET-1 is a key mediator of the Gregg effect in mouse hearts. Moreover, ET-1 has a dual role in the regulation of cardiac contractility: ET A receptor-mediated increase in contractile force is suppressed by ET B receptors. angiotensin II; coronary pressure; Gregg effect INCREASED CORONARY FLOW RATE results in an increase in cardiac oxygen consumption and contractility, a phenomenon known as the Gregg effect (6, 8). The molecular and cellular mechanisms of the Gregg effect are not completely understood. It has been suggested that changes in cardiac muscle length occur because of the increased capacity of coronary vasculature (garden hose effect), thereby leading to increased force production according to the Frank-Starling law of the heart (1). However, in a more recent study (30), it was reported that in the papillary muscle preparation the magnitude of the Gregg effect is greater than that of the Frank-Starling response. On the other hand, local regulation of cardiac contractility by capillary endothelial cells has been hypothesized to account for the Gregg effect (30). Increased coronary flow rate stimulates capillary endothelium (4), and a role for endothelial cells in the regulation of cardiac function has been demonstrated (38). Furthermore, a recent study with the papillary muscle preparation showed a role for stretch-activated ion channels in the Gregg effect (17).Elevated coronary flow has been suggested to stimulate the production and release of various vasoactive factors including nitric oxide (NO) and endothelin (ET)-1 (22, 36). Previously, the role of NO in the Gregg effect was excluded (17). ET-1 exerts a direct positive inotropic effect in guinea pig, rat, and human myocardium (12, 23). ET A receptors are considered to mediate the positive inotropic effect (15). ET B receptors also exist on cardiac myocyt...