Evangelos P. Daskalopoulos

Interventions in Wnt signaling as a novel therapeutic approach to improve myocardial infarct healing

Following myocardial infarction, wound healing takes place in the infarct area where the non-viable cardiac tissue is replaced by a scar. Inadequate wound healing or insufficient maintenance of the extracellular matrix in the scar can lead to excessive dilatation of the ventricles, one of the hallmarks of congestive heart failure. Therefore, it is important to better understand the wound-healing process in the heart and to develop new therapeutic agents that target the infarct area in order to maintain an adequate cardiac function. One of these potential novel therapeutic targets is Wnt signaling. Wnt signaling plays an important role in embryonic myocardial development but in the adult heart the pathway is thought to be silent. However, there is increasing evidence that components of the Wnt pathway are re-expressed during cardiac repair, implying a regulatory role. Recently, several studies have been published where the effect of interventions in Wnt signaling on infarct healing has been studied. In this review, we will summarize the results of these studies and discuss the effects of these interventions on the different cell types that are involved in the wound healing process.

Targeting the Wnt/frizzled signaling pathway after myocardial infarction: A new tool in the therapeutic toolbox?

Wnt/frizzled signaling in the adult heart is quiescent under normal conditions; however it is reactivated after myocardial infarction (MI). Any intervention at the various levels of this pathway can modulate its signaling. Several studies have targeted Wnt/frizzled signaling after MI with the majority of them indicating that the inhibition of the pathway is beneficial since it improves infarct healing and prevents heart failure. This suggests that blocking the Wnt/frizzled signaling pathway could be a potential novel therapeutic target to prevent the adverse cardiac remodeling after MI.

The Janus face of myofibroblasts in the remodeling heart

Abstract Cardiac fibrosis is a process that is associated with multiple forms of cardiac remodeling. There is an ongoing debate whether fibrosis is good or bad for cardiac function. On the one hand, deposition of extracellular matrix is indispensable for the wound healing in the injured heart; on the other hand, interstitial fibrosis can lead to stiffening of the ventricular wall and adverse remodeling. A common denominator of cardiac fibrosis is the appearance of myofibroblasts that possess smooth muscle-like contractile properties and can synthesize extracellular matrix. Traditionally, these cells were considered to merely derive from resident fibroblasts in the ventricular wall. However, recent insights suggest that myofibroblasts can originate from cell types as diverse as epicardial cells, resident mesenchymal stem cells and circulating fibrocytes. In this review, we will describe the origin(s) of the myofibroblasts in different forms of cardiac remodeling. We will also address the question whether specific mediators that are involved in the transdifferentiation of these myofibroblasts from their precursors can be identified. This would be of relevance in order to design specific interventions that would attenuate the adverse fibrotic deposition whilst preserving the favorable aspects of the fibrotic response.

Cardiac (myo)fibroblast: Novel Strategies for its Targeting Following Myocardial Infarction

Following myocardial infarction (MI), a dynamic and complex process called wound healing is initiated, aiming to produce a robust scar and limit adverse remodeling of the left ventricle (LV). Cardiac fibroblasts (CFs) - the most populous cardiac cell-type - differentiate into myofibroblasts under the influence of post-MI mechanical stress, transforming growth factor β (TGF-β) and various inflammatory signals. Myofibroblasts are contractile cells that start producing extracellular matrix (ECM) components and secrete factors that orchestrate wound healing, but also promote adverse cardiac remodeling that can progress to life-threatening heart failure (HF). Due to their vital role in the wound healing and LV remodeling after MI, (myo)fibroblasts have been receiving more and more attention lately as targets for anti-HF treatment strategies. In this review, we will summarize the current knowledge regarding the cardiac (myo)fibroblast characteristics, discuss the signaling pathways and the factors that affect their migration, proliferation and differentiation post-MI, as well as their ECM-depositing capabilities. Finally, we will provide an overview of the latest innovative research that is targeting the (myo)fibroblast, in an attempt to limit adverse remodeling and prevent HF.

UM206, a selective Frizzled antagonist, attenuates adverse remodeling after myocardial infarction in swine

Modulation of Wnt/Frizzled signaling with UM206 reduced infarct expansion and prevented heart failure development in mice, an effect that was accompanied by increased myofibroblast presence in the infarct, suggesting that Wnt/Frizzled signaling has a key role in cardiac remodeling following myocardial infarction (MI). This study investigated the effects of modulation of Wnt/Frizzled signaling with UM206 in a swine model of reperfused MI. For this purpose, seven swine with MI were treated with continuous infusion of UM206 for 5 weeks. Six control swine were treated with vehicle. Another eight swine were sham-operated. Cardiac function was determined by echo in awake swine. Infarct mass was estimated at baseline by heart-specific fatty acid-binding protein ELISA and at follow-up using planimetry. Components of Wnt/Frizzled signaling, myofibroblast presence, and extracellular matrix were measured at follow-up with qPCR and/or histology. Results show that UM206 treatment resulted in a significant decrease in infarct mass compared with baseline (−41±10%), whereas infarct mass remained stable in the Control-MI group (+3±17%). Progressive dilation of the left ventricle occurred in the Control-MI group between 3 and 5 weeks after MI, while adverse remodeling was halted in the UM206-treated group. mRNA expression for Frizzled-4 and the Frizzled co-receptor LRP5 was increased in UM206-treated swine as compared with Control-MI swine. Myofibroblast presence was significantly lower in infarcted tissue of the UM206-treated animals (1.53±0.43% vs 3.38±0.61%) at 5 weeks follow-up. This study demonstrates that UM206 treatment attenuates adverse remodeling in a swine model of reperfused MI, indicating that Wnt/Frizzled signaling is a promising target to improve infarct healing and limit post-MI remodeling.

Loss of Mouse P2Y6 Nucleotide Receptor Is Associated with Physiological Macrocardia and Amplified Pathological Cardiac Hypertrophy

The study of the mechanisms leading to cardiac hypertrophy is essential to better understand cardiac development and regeneration. Pathological conditions such as ischemia or pressure overload can induce a release of extracellular nucleotides within the heart. We recently investigated the potential role of nucleotide P2Y receptors in cardiac development. We showed that adult P2Y4-null mice displayed microcardia resulting from defective cardiac angiogenesis. Here we show that loss of another P2Y subtype called P2Y6, a UDP receptor, was associated with a macrocardia phenotype and amplified pathological cardiac hypertrophy. Cardiomyocyte proliferation and size were increased in vivo in hearts of P2Y6-null neonates, resulting in enhanced postnatal heart growth. We then observed that loss of P2Y6 receptor enhanced pathological cardiac hypertrophy induced after isoproterenol injection. We identified an inhibitory effect of UDP on in vitro isoproterenol-induced cardiomyocyte hyperplasia and hypertrophy. The present study identifies mouse P2Y6 receptor as a regulator of cardiac development and cardiomyocyte function. P2Y6 receptor could constitute a therapeutic target to regulate cardiac hypertrophy.

Targeting Wnt signaling to improve wound healing after myocardial infarction.

Myocardial infarction is one of the major causes of left ventricular dilatation, frequently leading to heart failure. In the last decade, the wound healing process that takes place in the infarct area after infarction has been recognized as a novel therapeutic target to attenuate left ventricular dilatation and preserve an adequate cardiac function. In this chapter, we discuss the role of Wnt signaling in the wound healing process after infarction, with a specific focus on its modulating effect on myofibroblast characteristics.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

Attenuation of post-infarction remodeling in rats by sustained myocardial growth hormone administration.

Abstract Prevention of left ventricular remodeling is an important therapeutic target post-myocardial infarction. Experimentally, treatment with growth hormone (GH) is beneficial, but sustained local administration has not been thoroughly investigated. We studied 58 rats (322 ± 4 g). GH was administered via a biomaterial-scaffold, following in vitro and in vivo evaluation of degradation and drug-release curves. Treatment consisted of intra-myocardial injection of saline or alginate-hydrogel, with or without GH, 10 min after permanent coronary artery ligation. Echocardiographic and histologic remodeling-indices were examined 3 weeks post-ligation, followed by immunohistochemical evaluation of angiogenesis, collagen, macrophages and myofibroblasts. GH-release completed at 3 days and alginate-degradation at ∼7 days. Alginate + GH consistently improved left ventricular end-diastolic and end-systolic diameters, ventricular sphericity, wall tension index and infarct-thickness. Microvascular-density and myofibroblast-count in the infarct and peri-infarct areas were higher after alginate + GH. Macrophage-count and collagen-content did not differ between groups. Early, sustained GH-administration enhances angiogenesis and myofibroblast-activation and ameliorates post-infarction remodeling.

Central Sympathetic Activation and Arrhythmogenesis during Acute Myocardial Infarction: Modulating Effects of Endothelin-B Receptors

Sympathetic activation during acute myocardial infarction (MI) is an important arrhythmogenic mechanism, but the role of central autonomic inputs and their modulating factors remain unclear. Using the in vivo rat-model, we examined the effects of clonidine, a centrally acting sympatholytic agent, in the presence or absence of myocardial endothelin-B (ETB) receptors. We studied wild-type (n = 20) and ETB-deficient rats (n = 20) after permanent coronary ligation, with or without pretreatment with clonidine. Cardiac rhythm was continuously recorded for 24 h by implantable telemetry devices, coupled by the assessment of autonomic and heart failure indices. Sympathetic activation and arrhythmogenesis were more prominent in ETB-deficient rats during the early phase post-ligation. Clonidine improved these outcomes throughout the observation period in ETB-deficient rats, but only during the delayed phase in wild-type rats. However, this benefit was counterbalanced by atrioventricular conduction abnormalities and by higher incidence of heart failure, the latter particularly evident in ETB-deficient rats. Myocardial ETB-receptors attenuate the arrhythmogenic effects of central sympathetic activation during acute MI. ETB-receptor deficiency potentiates the sympatholytic effects of clonidine and aggravates heart failure. The interaction between endothelin and sympathetic responses during myocardial ischemia/infarction and its impact on arrhythmogenesis and left ventricular dysfunction merits further investigation.