Role of the Wnt-Frizzled system in cardiac pathophysiology: a rapidly developing, poorly understood area with enormous potential

Wnt signaling pathway in cardiac fibrosis: New insights and directions

OBJECTIVE

Wnt signaling pathway significantly participates in cardiac fibrosis and CFs activation. Therefore, we reviewed current evidence on the new perspectives and biological association between Wnt signaling pathway and cardiac fibrosis.

DESIGN AND METHODS

A PubMed database search was performed for studies of Wnt signaling pathway in cardiac fibrosis and CFs activation.

RESULTS

Numerous studies have shown that the Wnt signaling pathway significantly participates in cardiac fibrosis pathogenesis. The aim of this review is to describe the present knowledge about the Wnt signaling pathway significantly participating in cardiac fibrosis and CFs activation, and look ahead on new perspectives of Wnt signaling pathway research. Moreover, we will discuss the different insights that interact with the Wnt signaling pathway-regulated cardiac fibrosis. The Wnt proteins are glycoproteins that bind to the Fz receptors on the cell surface, which lead to several important biological functions, such as cell differentiation and proliferation. There are several signals among the characterized pathways of cardiac fibrosis, including Wnt/β-catenin signaling. In this review, new insight into the Wnt signaling pathway in cardiac fibrosis pathogenesis is discussed, with special emphasis on Wnt/β-catenin.

CONCLUSION

It seems reasonable to suggest the potential targets of Wnt signaling pathway and it can be developed as a therapeutic target for cardiac fibrosis.

Secreted Frizzled-related Protein 5 Diminishes Cardiac Inflammation and Protects the Heart from Ischemia/Reperfusion Injury

Wnt signaling has diverse actions in cardiovascular development and disease processes. Secreted frizzled-related protein 5 (Sfrp5) has been shown to function as an extracellular inhibitor of non-canonical Wnt signaling that is expressed at relatively high levels in white adipose tissue. The aim of this study was to investigate the role of Sfrp5 in the heart under ischemic stress. Sfrp5 KO and WT mice were subjected to ischemia/reperfusion (I/R). Although Sfrp5-KO mice exhibited no detectable phenotype when compared with WT control at baseline, they displayed larger infarct sizes, enhanced cardiac myocyte apoptosis, and diminished cardiac function following I/R. The ischemic lesions of Sfrp5-KO mice had greater infiltration of Wnt5a-positive macrophages and greater inflammatory cytokine and chemokine gene expression when compared with WT mice. In bone marrow-derived macrophages, Wnt5a promoted JNK activation and increased inflammatory gene expression, whereas treatment with Sfrp5 blocked these effects. These results indicate that Sfrp5 functions to antagonize inflammatory responses after I/R in the heart, possibly through a mechanism involving non-canonical Wnt5a/JNK signaling.

Identification of Region-Specific Myocardial Gene Expression Patterns in a Chronic Swine Model of Repaired Tetralogy of Fallot

Surgical repair of Tetralogy of Fallot (TOF) is highly successful but may be complicated in adulthood by arrhythmias, sudden death, and right ventricular or biventricular dysfunction. To better understand the molecular and cellular mechanisms of these delayed cardiac events, a chronic animal model of postoperative TOF was studied using microarrays to perform cardiac transcriptomic studies. The experimental study included 12 piglets (7 rTOF and 5 controls) that underwent surgery at age 2 months and were further studied after 23 (+/- 1) weeks of postoperative recovery. Two distinct regions (endocardium and epicardium) from both ventricles were analyzed. Expression levels from each localization were compared in order to decipher mechanisms and signaling pathways leading to ventricular dysfunction and arrhythmias in surgically repaired TOF. Several genes were confirmed to participate in ventricular remodeling and cardiac failure and some new candidate genes were described. In particular, these data pointed out FRZB as a heart failure marker. Moreover, calcium handling and contractile function genes (SLN, ACTC1, PLCD4, PLCZ), potential arrhythmia-related genes (MYO5B, KCNA5), and cytoskeleton and cellular organization-related genes (XIRP2, COL8A1, KCNA6) were among the most deregulated genes in rTOF ventricles. To our knowledge, this is the first comprehensive report on global gene expression profiling in the heart of a long-term swine model of repaired TOF.

Inhibition of Wnt6 by Sfrp2 regulates adult cardiac progenitor cell differentiation by differential modulation of Wnt pathways

Wnt signaling has recently emerged as an important regulator of cardiac progenitor cell proliferation and differentiation, but the exact mechanisms by which Wnt signaling modulates these effects are not known. Understanding these mechanisms is essential for advancing our knowledge of cardiac progenitor cell biology and applying this knowledge to enhance cardiac therapy. Here, we explored the effects of Sfrp2, a canonical Wnt inhibitor, in adult cardiac progenitor cell (CPC) differentiation and investigated the molecular mechanisms involved. Our data show that Sfrp2 treatment can promote differentiation of CPCs after ischemia-reperfusion injury. Treatment of CPCs with Sfrp2 inhibited CPC proliferation and primed them for cardiac differentiation. Sfrp2 binding to Wnt6 and inhibition of Wnt6 canonical pathway was essential for the inhibition of CPC proliferation. This inhibition of Wnt6 canonical signaling by Sfrp2 was important for activation of the non-canonical Wnt/Planar Cell Polarity (PCP) pathway through JNK, which in turn induced expression of cardiac transcription factors and CPC differentiation. Taken together, these results demonstrate a novel role of Sfrp2 and Wnt6 in regulating the dynamic process of CPC proliferation and differentiation, as well as providing new insights into the mechanisms of Wnt signaling in cardiac differentiation.

Angiotensin II increases secreted frizzled-related protein 5 (sFRP5) expression through AT1 receptor/Rho/ROCK1/JNK signaling in cardiomyocytes

Secreted frizzled-related protein 5 (sFRP5) is a novel adipokine that functions as an inhibitor of Wnt signaling and is involved in embryonic development, proliferation, atherosclerosis, and apoptosis. Studies have shown that sFRP1-4 is expressed in cardiomyocytes, and sFRP3 and sFRP4 are elevated during heart failure. However, it is unclear whether sFRP5 is expressed in cardiomyocytes or cardiac hypertrophy, and as regards the effects of sFRP5 in the process. Here, we report the expression and the corresponding mechanisms of sFRP5 in angiotensin II (Ang II)-induced cardiomyocyte hypertrophy. Neonatal rat ventricular myocytes were exposed to increasing concentrations of Ang II for 12-72 h. Y27632 was used to block ROCK signal. PD98059, SB203580, and SP600125 were used to inhibit ERK1/2, p38 MAPK, and JNK signaling pathways, respectively, and anisomycin was used to activate JNK pathway. RT-PCR and Western-blot determined the expressions of sFRP5. BNP, TNF-α, ROCK1, ROCK2, MYPT1, and JNK were examined through Western-blot analysis. Ang II increased sFRP5 mRNA and protein levels in a time- and dose-dependent manner. Telmisartan, Y27632 and SP600125 effectively suppressed the expression of sFRP5. sFRP5 downregulated BNP and TNF-α expressions in hypertrophic cardiomyocytes. sFRP5 is expressed in cardiomyocytes, and upregulated in Ang II-induced cardiomyocyte hypertrophy through the AT1 receptor/Rho/ROCK1/JNK signaling pathway. sFRP5 may play an important role during cardiomyocyte hypertrophy.

Gene expression changes controlling distinct adaptations in the heart and skeletal muscle of a hibernating mammal

Throughout the hibernation season, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) experiences extreme fluctuations in heart rate, metabolism, oxygen consumption, and body temperature, along with prolonged fasting and immobility. These conditions necessitate different functional requirements for the heart, which maintains contractile function throughout hibernation, and the skeletal muscle, which remains largely inactive. The adaptations used to maintain these contractile organs under such variable conditions serves as a natural model to study a variety of medically relevant conditions including heart failure and disuse atrophy. To better understand how two different muscle tissues maintain function throughout the extreme fluctuations of hibernation we performed Illumina HiSeq 2000 sequencing of cDNAs to compare the transcriptome of heart and skeletal muscle across the circannual cycle. This analysis resulted in the identification of 1,076 and 1,466 differentially expressed genes in heart and skeletal muscle, respectively. In both heart and skeletal muscle we identified a distinct cold-tolerant mechanism utilizing peroxisomal metabolism to make use of elevated levels of unsaturated depot fats. The skeletal muscle transcriptome also shows an early increase in oxidative capacity necessary for the altered fuel utilization and increased oxygen demand of shivering. Expression of the fetal gene expression profile is used to maintain cardiac tissue, either through increasing myocyte size or proliferation of resident cardiomyocytes, while skeletal muscle function and mass are protected through transcriptional regulation of pathways involved in protein turnover. This study provides insight into how two functionally distinct muscles maintain function under the extreme conditions of mammalian hibernation.

Wnt signalling suppresses voltage-dependent Na⁺ channel expression in postnatal rat cardiomyocytes

Wnt signalling plays crucial roles in heart development, but is normally suppressed postnatally. In arrhythmogenic conditions, such as cardiac hypertrophy and heart failure, Wnt signalling is reactivated. To explore the potential role of Wnt signalling in arrhythmogenic electrical remodelling, we examined voltage-dependent ion channels in cardiomyocytes. Treatment of neonatal rat ventricular myocytes with either recombinant Wnt3a protein or CHIR-99021 (CHIR, a glycogen synthase kinase-3β inhibitor) caused a dose-dependent increase in Wnt target gene expression (Axin2 and Lef1), indicating activation of the Wnt/β-catenin pathway. Cardiac Na(+) current (INa) density was reduced by Wnt3a (-20 ± 4 vs. control -59 ± 7 pA pF(-1) , at -30 mV) or CHIR (-22 ± 5 pA pF(-1) ), without changes in steady-state activation, inactivation or repriming kinetics. Wnt3a and CHIR also produced dose-dependent reductions in the mRNA level of Scn5a (the cardiac Na(+) channel α subunit gene), as well as a 56% reduction (by Wnt3a) in the Nav 1.5 protein level. Consistent with INa reduction, action potentials in Wnt3a-treated neonatal rat ventricular myocytes had a lower upstroke amplitude (91 ± 3 vs. control 137 ± 2 mV) and decreased maximum upstroke velocity (70 ± 10 vs. control 163 ± 15 V s(-1)). In contrast, inward rectifier K(+) current and L-type Ca(2+) channels were not affected by Wnt3a treatment. Taken together, our data indicate that the Wnt/β-catenin pathway suppresses INa in postnatal cardiomyocytes and may contribute to ion channel remodelling in heart disease.

Activation of Wnt/β-catenin/GSK3β signaling during the development of diabetic cardiomyopathy

BACKGROUND

As Wnt/β-catenin/glycogen synthase kinase 3β (GSK3β) signaling has been implicated in myocardial injury and diabetic cardiomyopathy (DCM) is a major part of diabetic cardiovascular complications, we therefore investigated the alterations of Wnt/β-catenin/GSK3β signaling during the development of DCM.

METHODS

The rat model of diabetes mellitus (DM) was established using a single intraperitoneal injection of streptozotocin (STZ, 60 mg/kg). The alterations of Wnt/β-catenin/GSK3β signaling were determined 4, 8, and 12 weeks following DM using Western blotting, immunohistochemistry, and quantitative real-time reverse transcriptase polymerase chain reaction. Cardiac pathology changes were evaluated using hematoxylin and eosin, Masson trichromatic, and terminal dUTP nick-end labeling staining.

RESULTS

Histological analyses revealed that DM induced significant myocardial injury and progressive cardiomyocyte apoptosis. The protein and mRNA levels of Wnt2, β-catenin, and c-Myc were progressively increased 4, 8, and 12 weeks following DM. The expression of T-cell factor 4 and phosphorylated of GSK3β on Ser9 were progressively increased. However, the expression of the endogenous Wnt inhibitor Dickkopf-1 was increased after STZ injection and then decreased as DCM developed.

CONCLUSION

Wnt/β-catenin/GSK3β signaling pathway is activated in the development of DCM. Further investigation into the role of Wnt signaling during DCM will functionally find novel therapeutic target for DCM.

1,25-Vitamin D3 promotes cardiac differentiation through modulation of the WNT signaling pathway

Cardiovascular disease (CVD) remains the leading cause of death worldwide. Low levels of vitamin D are associated with high risk of myocardial infarction, even after controlling for factors associated with coronary artery disease. A growing body of evidence indicates that vitamin D plays an important role in CVD-related signaling pathways. However, little is known about the molecular mechanism by which vitamin D modulates heart development. The WNT signaling pathway plays a pivotal role in tissue development by controlling stem cell renewal, lineage selection and, even more importantly, heart development. In this study, we examined the role of 1,25-D3 (the active form of vitamin D) on cardiomyocyte proliferation, apoptosis, cell phenotype, cell cycle progression and differentiation into cardiomyotubes. We determined that the addition of 1,25-D3 to cardiomyocytes cells: i) inhibits cell proliferation without promoting apoptosis; ii) decreases expression of genes related to the regulation of the cell cycle; iii) promotes formation of cardiomyotubes; iv) induces the expression of casein kinase-1-α1, a negative regulator of the canonical WNT signaling pathway; and v) increases the expression of the noncanonical WNT11, which it has been demonstrated to induce cardiac differentiation during embryonic development and in adult cells. In conclusion, we postulate that vitamin D promotes cardiac differentiation through a negative modulation of the canonical WNT signaling pathway and by upregulating the expression of WNT11. These results indicate that vitamin D repletion to prevent and/or improve cardiovascular disorders that are linked with abnormal cardiac differentiation, such as post infarction cardiac remodeling, deserve further study.

Porcupine is not required for the production of the majority of Wnts from primary human astrocytes and CD8+ T cells

Wnts are small secreted glycoproteins that are highly conserved among species. To date, 19 Wnts have been described, which initiate a signal transduction cascade that is either β-catenin dependent or independent, culminating in the regulation of hundreds of target genes. Extracellular release of Wnts is dependent on lipidation of Wnts by porcupine, a membrane-bound-O-acyltransferase protein in the endoplasmic reticulum. Studies demonstrating the requirement of porcupine for Wnts production are based on cell line and non-human primary cells. We evaluated the requirement for porcupine for Wnts production in human primary astrocytes and CD8+ T cells. Using IWP-2, an inhibitor of porcupine, or siRNA targeting porcupine, we demonstrate that porcupine is not required for the release of Wnt 1, 3, 5b, 6,7a, 10b, and 16a. While IWP had no effect on Wnt 2b release, knockdown of porcupine by siRNA reduced Wnt 2b release by 60%. These data indicate that porcupine-mediated production of Wnts is context dependent and is not required for all Wnts production, suggesting that alternative mechanisms exist for Wnts production.

Cell-cell interaction in the heart via Wnt/β-catenin pathway after cardiac injury

The adult mammalian heart predominantly comprises myocytes, fibroblasts, endothelial cells, smooth muscle cells, and epicardial cells arranged in a precise three-dimensional framework. Following cardiac injury, the spatial arrangement of cells is disrupted as different populations of cells are recruited to the heart in a temporally regulated manner. The alteration of the cellular composition of the heart after cardiac injury thus enables different phenotypes of cells to interact with each other in a spatio-temporal-dependent manner. It can be argued that the integrated study of such cellular interactions rather than the examination of single populations of cells can provide more insights into the biology of cardiac repair especially at an organ-wide level. Many signalling systems undoubtedly mediate such cross talk between cells after cardiac injury. The Wnt/β-catenin system plays an important role during cardiac development and disease. Here, we describe how cell populations in the heart after cardiac injury mediate their interactions via the Wnt/β-catenin pathway, determine how such interactions can affect a cardiac repair response and finally suggest an integrated approach to study cardiac cellular interactions.

Fibroblast-mediated pathways in cardiac hypertrophy

Under normal physiological conditions, cardiac fibroblasts are the primary producers of extracellular matrix and supply a mechanical scaffold for efficacious heart contractions induced by cardiomyocytes. In the hypertrophic heart, cardiac fibroblasts provide a pivotal contribution to cardiac remodeling. Many growth factors and extracellular matrix components secreted by cardiac fibroblasts induce and modify cardiomyocyte hypertrophy. Recent evidence revealed that cardiomyocyte-cardiac fibroblast communications are complex and multifactorial. Many growth factors and molecules contribute to cardiac hypertrophy via different roles that include induction of hypertrophy and the feedback hypertrophic response, fine-tuning of adaptive hypertrophy, limitation of left ventricular dilation, and modification of interstitial changes. This review focuses on recent work and topics and provides a mechanistic insight into cardiomyocyte-cardiac fibroblast communication in cardiac hypertrophy. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

Cilia and coordination of signaling networks during heart development

Primary cilia are unique sensory organelles that coordinate a wide variety of different signaling pathways to control cellular processes during development and in tissue homeostasis. Defects in function or assembly of these antenna-like structures are therefore associated with a broad range of developmental disorders and diseases called ciliopathies. Recent studies have indicated a major role of different populations of cilia, including nodal and cardiac primary cilia, in coordinating heart development, and defects in these cilia are associated with congenital heart disease. Here, we present an overview of the role of nodal and cardiac primary cilia in heart development.

Arrhythmogenic right ventricular dysplasia/cardiomyopathy type 1: a light on molecular mechanisms

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited cardiomyopathy associated with cardiac arrhythmias originating in the right ventricle, heart failure, and sudden cardiac death. Development of ARVD/C type 1 has been attributed to differential expression of transforming growth factor beta 3 (TGF β 3). Several mechanisms underlying the molecular basis of ARVD/C type 1 have been proposed. Evaluating previously described mechanisms might elucidate how TGF β 3 contributes to disease progression in ARVD/C type 1. Here we review how TGF β 3 can induce fibrogenesis through Smad and/or β -catenin signaling. Moreover, the role of apoptosis is addressed. Finally the extent to which the immune system has been demonstrated to be a modulating and amplifying agent in the onset and progression of ARVD/C in general is discussed.

Stem cell signaling as a target for novel drug discovery: recent progress in the WNT and Hedgehog pathways

One of the most exciting fields in biomedical research over the past few years is stem cell biology, and therapeutic application of stem cells to replace the diseased or damaged tissues is also an active area in development. Although stem cell therapy has a number of technical challenges and regulatory hurdles to overcome, the use of stem cells as tools in drug discovery supported by mature technologies and established regulatory paths is expected to generate more immediate returns. In particular, the targeting of stem cell signaling pathways is opening up a new avenue for drug discovery. Aberrations in these pathways result in various diseases, including cancer, fibrosis and degenerative diseases. A number of drug targets in stem cell signaling pathways have been identified. Among them, WNT and Hedgehog are two most important signaling pathways, which are the focus of this review. A hedgehog pathway inhibitor, vismodegib (Erivedge), has recently been approved by the US FDA for the treatment of skin cancer, while several drug candidates for the WNT pathway are entering clinical trials. We have discovered that the stem cell signaling pathways respond to traditional Chinese medicines. Substances isolated from herbal medicine may act specifically on components of stem cell signaling pathways with high affinities. As many of these events can be explained through molecular interactions, these phenomena suggest that discovery of stem cell-targeting drugs from natural products may prove to be highly successful.