Endogenous inhibitors of hypertrophy in concentric versus eccentric hypertrophy.

Left ventricular (LV) hypertrophy (LVH) is an adaptive response to hemodynamic overload, but also contributes to the pathogenesis of heart failure. LVH can be concentric (cLVH) but subsequent dilatation and progression to eccentric hypertrophy (eLVH) may lead to global pump failure. Recently, several endogenous molecular inhibitors of hypertrophy have been identified. Using real-time PCR, we compared the myocardial mRNA expression of these inhibitors in pressure-overload induced cLVH (severe aortic stenosis) and in volume overload-induced eLVH (severe mitral regurgitation) in patients, and during the progression from cLVH to eLVH in pressure overload in rat. Each of these genes showed a unique temporal expression profile. Strikingly, except for SOCS-3, changes in gene expression of these negative regulators in rat cLVH and eLVH vs sham were recapitulated in human cLVH and eLVH. In particular, VDUP-1 and MCIP-1 were high in cLVH but expression levels were normal in eLVH, both in rat and human. These data indicate that during the progression of LVH, both in pressure and volume overload, expression levels of endogenous inhibitors of hypertrophy are modified and that these changes may have pathophysiological significance. In particular, MCIP-1 (the endogenous calcineurin inhibitor) and VDUP-1 (the endogenous inhibitor of thioredoxin) are potential molecular switches in the progression of LV hypertrophy.

Applanation tonometry in mice: a novel noninvasive technique to assess pulse wave velocity and arterial stiffness.

Arterial stiffening is the root cause of a range of cardiovascular complications, including myocardial infarction, left ventricular hypertrophy, stroke, renal failure, dementia, and death, and a hallmark of the aging process. The most important in vivo parameter of arterial stiffness is pulse wave velocity (PWV). Clinically, PWV is determined noninvasively using applanation tonometry. Unlike the clinical value of arterial stiffness and PWV, techniques to determine PWV in mice are scarce. The only way to determine aortic PWV noninvasively in the mouse is by using ultrasound echo Doppler velocimetry. It is a fast, efficient, and accurate technique, but the required tools are expensive and technically complex. Here, we describe the development and validation of a novel technique to assess carotid-femoral PWV noninvasively in mice. This technique is based on applanation tonometry as used clinically. We were able to establish a reproducible reference value in wild-type mice (3.96±0.05 m/s) and to detect altered carotid-femoral PWV values in endothelial nitric oxide synthase knockout mice (4.66±0.05 m/s; P<0.001 compared with control), and in mice sedated with sodium pentobarbital (2.89±0.17 m/s; P<0.001 compared with control). Also, carotid-femoral PWV was pharmacologically modulated and measured in a longitudinal experiment with endothelial nitric oxide synthase knockout mice to demonstrate the applicability of this technique. In general, applanation tonometry can be used to measure carotid-femoral PWV noninvasively in mice. The experimental setup is simple, and the technical requirements are basic, making this technique readily implementable in any mouse model-based research facility interested in arterial stiffness.

Left ventricular diastolic dysfunction and myocardial stiffness in diabetic mice is attenuated by inhibition of dipeptidyl peptidase 4.

AIMS: Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, which contributes to an increasing prevalence of heart failure with a preserved LV ejection fraction. We investigated the effects of sitagliptin (SITA), an inhibitor of dipeptidylpeptidase-4 (DPP-4) and anti-diabetic drug, on LV structure and function of obese mice with Type 2 DM. METHODS AND RESULTS: Obese Type 2 diabetic mice (Lepr(db/db), BKS.Cg-Dock7(m)+/+ Lepr(db)/J), displaying increased cardiomyocyte and LV stiffness at the age of 16 weeks, were treated with SITA (300 mg/kg/day) or vehicle for 8 weeks. SITA severely impaired serum DPP-4 activity, but had no effect on glycaemia. Invasive haemodynamic recordings showed that SITA reduced LV passive stiffness and increased LV stroke volume; LV end-systolic elastance remained unchanged. In addition, SITA reduced resting tension of isolated single cardiomyocytes and intensified phosphorylation of the sarcomeric protein titin. SITA also increased LV concentrations of cGMP and increased activity of protein kinase G (PKG). In vitro activation of PKG decreased resting tension of cardiomyocytes from vehicle-treated mice, but had no effect on resting tension of cardiomyocytes from SITA-treated mice. CONCLUSIONS: In obese Type 2 diabetic mice, in the absence of hypoglycaemic effects, inhibition of DPP-4 decreases LV passive stiffness and improves global LV performance. These effects seem at least partially mediated by stimulatory effects on the myocardial cGMP-PKG pathway and, hence, on the phosphorylation status of titin and the hereto coupled cardiomyocyte stiffness modulus.

Role of neuregulin-1/ErbB2 signaling in endothelium-cardiomyocyte cross-talk.

Neuregulin-1 (NRG-1), a cardioactive growth factor released from endothelial cells, has been shown to be indispensable for the normal function of the adult heart by binding to ErbB4 receptors on cardiomyocytes. In the present study, we have investigated to what extent ErbB2, the favored co-factor of ErbB4 for heterodimerization, participates in the cardiac effects of endothelium-derived NRG-1. In addition, in view of our previously described anti-adrenergic effects of NRG-1, we have studied which neurohormonal stimuli affect endothelial NRG-1 expression and release and how this may fit into a broader frame of cardiovascular physiology. Immunohistochemical staining of rat heart and aorta showed that NRG-1 expression was restricted to the endocardial endothelium and the cardiac microvascular endothelium (CMVE); by contrast, NRG-1 expression was absent in larger coronary arteries and veins and in aortic endothelium. In rat CMVE in culture, NRG-1 mRNA and protein expression was down-regulated by angiotensin II and phenylephrine and up-regulated by endothelin-1 and mechanical strain. CMVE-derived NRG-1 was shown to phosphorylate cardiomyocyte ErbB2, an event prevented by a 24-h preincubation of myocytes with monoclonal ErbB2 antibodies. Pretreating cardiomyocytes with these inhibitory anti-ErbB2 antibodies significantly attenuated CMVE-induced cardiomyocyte hypertrophy and abolished the protective actions of CMVE against cardiomyocyte apoptosis. Accordingly, ErbB2 signaling participated in the paracrine survival and growth controlling effects of NRG-1 on cardiomyocytes in vitro, explaining the cardiotoxicity of ErbB2 antibodies in patients. Cardiac NRG-1 synthesis occurs in endothelial cells adjacent to cardiac myocytes and is sensitive to factors related to the regulation of blood pressure.

Mesenchymal stem cell adhesion to cardiac microvascular endothelium: activators and mechanisms.

Circulating stem cells home within the myocardium, probably as the first step of a tissue regeneration process. This step requires adhesion to cardiac microvascular endothelium (CMVE). In this study, we studied mechanisms of adhesion between CMVE and mesenchymal stem cells (MSCs). Adhesion was studied in vitro and in vivo. Isolated 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-labeled rat MSCs were allowed to adhere to cultured CMVE in static and dynamic conditions. Either CMVE or MSCs were pretreated with cytokines [IL-1beta, IL-3, IL-6, stem cell factor, stromal cell-derived factor-1, or TNF-alpha, 10 ng/ml]. Control or TNF-alpha-treated MSCs were injected intracavitarily in rat hearts in vivo. In baseline in vitro conditions, the number of MSCs that adhered to CMVE was highly dependent on the flow rate of the superfusing medium but remained significant at venous and capillary shear stress amplitudes. Activation of both CMVE and MSCs with TNF-alpha or IL-1beta before adhesion concentration dependently increased adhesion of MSCs at each studied level of shear stress. Consistently, in vivo, activation of MSCs with TNF-alpha before injection significantly enhanced cardiac homing of MSCs. TNF-alpha-induced adhesion could be completely blocked by pretreating either CMVE or MSCs with anti-VCAM-1 monoclonal antibodies but not by anti-ICAM-1 antibodies. Adhesion of circulating MSCs in the heart appears to be an endothelium-dependent process and is sensitive to modulation by activators of both MSCs and endothelium. Inflammation and the expression of VCAM-1 but not ICAM-1 on both cell types have a regulatory effect on MSC homing in the heart.