Wnt signaling: an essential regulator of cardiovascular differentiation, morphogenesis and progenitor self-renewal

A cocktail method for promoting cardiomyocyte differentiation from bone marrow-derived mesenchymal stem cells

A growing body of evidence supports the argument that bone marrow-derived mesenchymal stem cells (MSCs) can differentiate into cardiomyocyte-like cells in an appropriate cellular environment, but the differentiation rate is low. A cocktail method was designed: we investigated the role of 5-azacytidine (5-aza), salvianolic acid B (SalB), and cardiomyocyte lysis medium (CLM) in inducing MSCs to acquire the phenotypical characteristics of cardiomyocytes. The fourth-passage MSCs were treated with 5-aza, SalB, CLM, 5-aza+salB, 5-aza+CLM, SalB+CLM, and 5-aza+SalB+CLM for 2 weeks. Immunofluorescence results showed that cTnT expression in the 5-aza+salB+CLM group was stronger than other groups. Real-time qPCR and Western blotting analyses showed that cTnT, alpha-cardiac actin, mef-2c, Cx43, and GSK-3beta expression increased while beta-catenin expression decreased. The salB+5-aza+CLM group had the most evident effects. SalB combined with 5-aza and CLM improved cardiomyocyte differentiation from MSCs. In the MSCs differentiation process, the Wnt/beta-catenin signaling pathway had been inhibited.

Smad1 transcription factor integrates BMP2 and Wnt3a signals in migrating cardiac progenitor cells

In vertebrate embryos, cardiac progenitor cells (CPCs) undergo long-range migration after emerging from the primitive streak during gastrulation. Together with other mesoderm progenitors, they migrate laterally and then toward the ventral midline, where they form the heart. Signals controlling the migration of different progenitor cell populations during gastrulation are poorly understood. Several pathways are involved in the epithelial-to-mesenchymal transition and ingression of mesoderm cells through the primitive streak, including fibroblast growth factors and wingless-type family members (Wnt). Here we focus on early CPC migration and use live video microscopy in chicken embryos to demonstrate a role for bone morphogenetic protein (BMP)/SMA and MAD related (Smad) signaling. We identify an interaction of BMP and Wnt/glycogen synthase kinase 3 beta (GSK3β) pathways via the differential phosphorylation of Smad1. Increased BMP2 activity altered migration trajectories of prospective cardiac cells and resulted in their lateral displacement and ectopic differentiation, as they failed to reach the ventral midline. Constitutively active BMP receptors or constitutively active Smad1 mimicked this phenotype, suggesting a cell autonomous response. Expression of GSK3β, which promotes the turnover of active Smad1, rescued the BMP-induced migration phenotype. Conversely, expression of GSK3β-resistant Smad1 resulted in aberrant CPC migration trajectories. De-repression of GSK3β by dominant negative Wnt3a restored normal migration patterns in the presence of high BMP activity. The data indicate the convergence of BMP and Wnt pathways on Smad1 during the early migration of prospective cardiac cells. Overall, we reveal molecular mechanisms that contribute to the emerging paradigm of signaling pathway integration in embryo development.

The four and a half LIM-domain 2 controls early cardiac cell commitment and expansion via regulating β-catenin-dependent transcription

The multiphasic regulation of the Wnt/β-catenin canonical pathway is essential for cardiogenesis in vivo and in vitro. To achieve tight regulation of the Wnt/β-catenin signaling, tissue- and cell-specific coactivators and repressors need to be recruited. The identification of such factors may help to elucidate mechanisms leading to enhanced cardiac differentiation efficiency in vitro as well as promote regeneration in vivo. Using a yeast-two-hybrid screen, we identified four-and-a-half-LIM-domain 2 (FHL2) as a cardiac-specific β-catenin interaction partner and activator of Wnt/β-catenin-dependent transcription. We analyzed the role of this interaction for early cardiogenesis in an in vitro model by making use of embryoid body cultures from mouse embryonic stem cells (ESCs). In this model, stable FHL2 gain-of-function promoted mesodermal cell formation and cell proliferation while arresting cardiac differentiation in an early cardiogenic mesodermal progenitor state. Mechanistically, FHL2 overexpression enhanced nuclear accumulation of β-catenin and activated Wnt/β-catenin-dependent transcription leading to sustained upregulation of the early cardiogenic gene Igfbp5. In an alternative P19 cell model, transient FHL2 overexpression led to early activation of Wnt/β-catenin-dependent transcription, but not sustained high-level of Igfbp5 expression. This resulted in enhanced cardiogenesis. We propose that early Wnt/β-catenin-dependent transcriptional activation mediated by FHL2 is important for the transition to and expansion of early cardiogenic mesodermal cells. Collectively, our findings offer mechanistic insight into the early cardiogenic code and may be further exploited to enhance cardiac progenitor cell activity in vitro and in vivo.

Decreased expression of Dkk1 and Dkk3 in human clear cell renal cell carcinoma

The expression patterns of the Dickkopf (Dkk) family of proteins varies in different cancers. In the present study, the expression levels of Dkk1 and Dkk3 were investigated in clear cell renal cell carcinoma (ccRCC) tissues. Dkk1 and Dkk3 serum levels were also examined in patients with ccRCC, and the association between clinicopathological features and Dkk levels was investigated. Serum Dkk1 and Dkk3 were quantified using ELISA in 64 patients with ccRCC and in 30 healthy individuals (controls). The expression levels of Dkk1 and Dkk3 were analyzed in tumor and adjacent normal tissues obtained from patients with ccRCC (n=20) using quantitative polymerase chain reaction (qPCR), western blot analysis and immunohistochemistry. The mean serum levels of Dkk1 and Dkk3 in the patients with ccRCC were significantly lower than those in the healthy controls. Furthermore, the serum Dkk1 levels were significantly lower at higher tumor‑node‑metastasis stages and tumor grades. qPCR, western blot analysis and immunohistochemistry revealed a significant decrease in the Dkk1 and Dkk3 mRNA and protein levels in the tumor tissues compared with the adjacent normal tissues. Consequently, Dkk1 and Dkk3 may present a novel molecular target for the diagnosis and therapeutic treatment of ccRCC.

The rejuvenation of aged stem cells for cardiac repair

Rejuvenation is one of the greatest challenges of modern science. Aging affects every tissue and organ in the body, leading to a deterioration of normal function and inhibition of repair mechanisms. Cell therapy has received much attention for its potential to regenerate organs, but in the context of cardiac repair, the initial clinical trials in aged patients did not replicate the dramatic benefits recorded in preclinical studies with young animals. The benefits of autologous cell therapy are reduced in the elderly, the largest target group for regenerative medicine. Adult stem cell functionality decreases with age which impairs tissue regeneration. In this review we discuss the age-related changes in stem cell function, with particular attention to stem cell therapy in heart disease. We also focus on possible mechanisms of adult stem cell aging and targets for rejuvenation strategies to reverse the aging process. We provide useful insights on how to apply this knowledge to advance cellular therapies for heart disease.

Serum level of DKK-1 and its prognostic potential in non-small cell lung cancer

Background

The aim of the present study was to measure the serum level of dickkopf-1(DKK-1) in patients with non-small cell lung cancer (NSCLC), and to determine the prognostic potential of serum DKK-1 in NSCLC.

Material and methods

The present study included a total of 150 patients with NSCLC and 150 healthy controls. Serum level of DKK-1 was measured by enzyme-linked immunosorbent assay (ELISA). Numerical variables were recorded as means ± standard deviation (SD) and analyzed by independent t-tests. Categorical variables were presented as rates and analyzed by using the chi-square test or Fisher’s exact test. The overall survival was analyzed by log-rank test, and survival curves were plotted according to Kaplan–Meier.

Results

We found that serum DKK-1 level was significantly higher in patients with NSCLC than healthy controls. Mean serum DKK-1 level was 31.42 ± 6.32 ng/ml in the NSCLC group and 14.12 ± 3.29 ng/ml in the healthy control group (p <0.01). Serum DKK-1 level expression level was significantly positively correlated with TNM stage (p = 0.009), lymph node involvement(p = 0.001), and distant metastases(p < 0.001).

In the multivariate Cox proportional hazards analysis, high DKK-1 expression was independently associated with poor survival (P < 0.001; HR = 3.98; 95% CI =2.19-4.83).

Conclusions

In conclusion, our results showed that DKK-1 was overexpressed in NSCLC, and DKK-1 in serum was a good predictor of poor prognosis in patients with NSCLC. More researches are needed in the future to clarify the detailed mechanism of DKK-1 in the carcinogenesis and metastasis of NSCLC.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1471414150119415.

microRNA expression profiling of heart tissue during fetal development

microRNAs (miRNAs) are important both in early cardiogenesis and in the process of heart maturation. The aim of this study was to determine the stage-specific expression of miRNAs in human fetal heart in order to identify valuable targets for further study of heart defects. Affymetrix microarrays were used to obtain miRNA expression profiles from human fetal heart tissue at 5, 7, 9 and 23 weeks of gestation. To identify differentially expressed miRNAs at each time-point, linear regression analysis by the R limma algorithm was employed. Hierarchical clustering analysis was conducted with Cluster 3.0 software. Gene Ontology analysis was carried out for miRNAs from different clusters. Commonalities in miRNA families and genomic localization were identified, and the differential expression of selected miRNAs from different clusters was verified by quantitative polymerase chain reaction (qPCR). A total of 703 miRNAs were expressed in human fetal heart. Of these, 288 differentially expressed miRNAs represented 5 clusters with different expression trends. Several clustered miRNAs also shared classification within miRNA families or proximal genomic localization. qPCR confirmed the expression patterns of selected miRNAs. miRNAs within the 5 clusters were predicted to target genes vital for heart development and to be involved in cellular signaling pathways that affect heart structure formation and heart-associated cellular events. In conclusion, to the best of our knowledge, this is the first miRNA expression profiling study of human fetal heart tissue. The stage-specific expression of specific miRNAs suggests potential roles at distinct time-points during fetal heart development.

Overexpression of Wnt11 promotes chondrogenic differentiation of bone marrow-derived mesenchymal stem cells in synergism with TGF-β

Bone marrow-derived mesenchymal stem cells (MSCs), the most widely used cell source for cartilage tissue engineering, are multipotent cells which have been shown to differentiate into various mesenchyme-lineage cell types including chondrocytes. However, the molecular mechanisms controlling the chondrogenic differentiation of MSCs remain to be fully elucidated. It has been demonstrated that Wnt signaling involves regulating chondrogenesis and MSC differentiation. The aim of the present study was to investigate the role of Wnt11, a member of noncanonical Wnts, in MSCs during chondrogenic differentiation. We observed that overexpression of Wnt11 inhibited proliferation of MSCs and caused a G0/G1 cell cycle arrest. The expression level of chondrogenic markers, aggrecan and Collagen II, was significantly increased in MSCs transduced with Wnt11 as compared with non-transduced cells or MSCs transduced with the empty lentiviral vector. Furthermore, ectopic expression of Wnt11 stimulated gene expression of chondrogenic regulators, SRY-related gene 9, Runt-related transcription factor 2, and Indian hedgehog. Finally, Wnt11 overexpression promoted chondrogenic differentiation of MSCs in synergism with TGF-β. Collectively, these results indicate that Wnt11 plays a crucial role in regulating MSC chondrogenic differentiation.

WIF1 causes dysfunction of heart in transgenic mice

Wnt activity is a key regulator of cardiac progenitor cell self-renewal, differentiation and morphogenesis. However, Wnt inhibitory factor 1 (WIF1), a antagonists of Wnt signaling activity, its potential effects on heart development has not yet been approached by either in vivo or in vitro studies. Here, the expression of WIF1 was regulated in a different way in the dilated and hypertrophic cardiomyopathy heart from transgenic mice by mutations in cardiac troponin T, cTnT(R141W) and cTnT(R92Q). The heart tissue specific transgenic mice of WIF1 was studied using M-mode echocardiography and histologic analyses. Production levels of an array of effectors and transcription factors that impact cellular organization and tissue morphology were measured. The effects of WIF1 on β-catenin pathway could be reversed by LiCl regarding signaling pathways and effector and respondent molecules in H9c2 cells, consistent with the expression levels of c-myc, natriuretic peptide precursor type B and skeletal muscle actin α1. Among the most noteworthy findings were that WIF1 impaired the function and structure of heart, and the effects on β-catenin pathway maybe the course of the former. It is anticipated that our findings will contribute to expansion of our understanding of WIF1 biological function on heart development and possible modes of treatment of heart diseases.

Embryonic heart progenitors and cardiogenesis

The mammalian heart is a highly specialized organ, comprised of many different cell types arising from distinct embryonic progenitor populations during cardiogenesis. Three precursor populations have been identified to contribute to different myocytic and nonmyocytic cell lineages of the heart: cardiogenic mesoderm cells (CMC), the proepicardium (PE), and cardiac neural crest cells (CNCCs). This review will focus on molecular cues necessary for proper induction, expansion, and lineage-specific differentiation of these progenitor populations during cardiac development in vivo. Moreover, we will briefly discuss how the knowledge gained on embryonic heart progenitor biology can be used to develop novel therapeutic strategies for the management of congenital heart disease as well as for improvement of cardiac function in ischemic heart disease.

A network study of chinese medicine xuesaitong injection to elucidate a complex mode of action with multicompound, multitarget, and multipathway

Chinese medicine has evolved from thousands of years of empirical applications and experiences of combating diseases. It has become widely recognized that the Chinese medicine acts through complex mechanisms featured as multicompound, multitarget and multipathway. However, there is still a lack of systematic experimental studies to elucidate the mechanisms of Chinese medicine. In this study, the differentially expressed genes (DEGs) were identified from myocardial infarction rat model treated with Xuesaitong Injection (XST), a Chinese medicine consisting of the total saponins from Panax notoginseng (Burk.) F. H. Chen (Chinese Sanqi). A network-based approach was developed to combine DEGs related to cardiovascular diseases (CVD) with lines of evidence from the literature mining to investigate the mechanism of action (MOA) of XST on antimyocardial infarction. A compound-target-pathway network of XST was constructed by connecting compounds to DEGs validated with literature lines of evidence and the pathways that are functionally enriched. Seventy potential targets of XST were identified in this study, of which 32 were experimentally validated either by our in vitro assays or by CVD-related literatures. This study provided for the first time a network view on the complex MOA of antimyocardial infarction through multiple targets and pathways.

WNT3A promotes hematopoietic or mesenchymal differentiation from hESCs depending on the time of exposure

We investigated the role of canonical WNT signaling in mesoderm and hematopoietic development from human embryonic stem cells (hESCs) using a recombinant human protein-based differentiation medium (APEL). In contrast to prior studies using less defined culture conditions, we found that WNT3A alone was a poor inducer of mesoderm. However, WNT3A synergized with BMP4 to accelerate mesoderm formation, increase embryoid body size, and increase the number of hematopoietic blast colonies. Interestingly, inclusion of WNT3A or a GSK3 inhibitor in methylcellulose colony-forming assays at 4 days of differentiation abrogated blast colony formation but supported the generation of mesospheres that expressed genes associated with mesenchymal lineages. Mesospheres differentiated into cells with characteristics of bone, fat, and smooth muscle. These studies identify distinct effects for WNT3A, supporting the formation of hematopoietic or mesenchymal lineages from human embryonic stem cells, depending upon differentiation stage at the time of exposure.

Activin-A in diabetes-induced cardiac malformations in embryos

BACKGROUND

Heart defects are the most common abnormalities in infants of diabetic mothers. Cardiac malformation is associated with altered expression of the genes in the transforming growth factor β system, including inhibin βA, which forms activin-A as a homodimer and functions through its effectors, Smad2 and Smad3. This study aimed to investigate the role of activin-A in diabetes-induced cardiac malformations.

METHODS

Diabetes mellitus in female mice (C57BL/6J) was induced via intravenous injection of streptozotocin. The expression of inhibin βA protein and phosphorylation of Smad2 and Smad3 in the embryonic hearts were examined using immunohistochemical, in situ proximity ligation, and immunoblot assays. Embryos and endocardial cushions of nondiabetic mice were cultured in a high concentration of glucose and treated with activin-A. Mitosis was examined using BrdU incorporation assay and immunohistochemistry of phosphorylated histone H3. Migration of the endocardial cells was assessed using a collagen-based cell migration assay.

RESULTS

The levels of inhibin βA expression and Smad2 and Smad3 activation were significantly reduced by maternal diabetes. Treatment with activin-A significantly increased cell proliferation in the myocardium and migration of endocardial cells, compared with those in vehicle-treated high glucose group, to the level in the euglycemic control group.

CONCLUSIONS

Maternal diabetes suppresses the expression of inhibin βA protein, as well as the activation of Smad2 and Smad3. Activin-A rescues cell proliferation in the myocardium and migration of the endocardial cells suppressed by hyperglycemia. The activin-Smad2/3 signaling system appears to play a role in cardiac malformation in diabetic embryopathy.

CG0009, a novel glycogen synthase kinase 3 inhibitor, induces cell death through cyclin D1 depletion in breast cancer cells

Glycogen synthase kinase 3α/β (GSK3α/β) is a constitutively active serine/threonine kinase involved in multiple physiological processes, such as protein synthesis, stem cell maintenance and apoptosis, and acts as a key suppressor of the Wnt-β-catenin pathway. In the present study, we examined the therapeutic potential of a novel GSK3 inhibitor, CG0009, in the breast cancer cell lines, BT549, HS578T, MDA-MB-231, NCI/ADR-RES, T47D, MCF7 and MDA-MB-435, from the NCI-60 cancer cell line panel. Assessment of cytotoxicity, apoptosis and changes in estrogen-signaling proteins was performed using cell viability assays, Western blotting and quantitative real-time PCR. CG0009 enhanced the inactivating phosphorylation of GSK3α at Ser21 and GSK3β at Ser9 and simultaneously decreased activating phosphorylation of GSK3β at Tyr216, and induced caspase-dependent apoptosis independently of estrogen receptor α (ERα) expression status, which was not observed with the other GSK3 inhibitors examined, including SB216763, kenpaullone and LiCl. CG0009 treatment (1 µmol/L) completely ablated cyclin D1 expression in a time-dependent manner in all the cell lines examined, except T47D. CG0009 alone significantly activated p53, leading to relocation of p53 and Bax to the mitochondria. GSK3 inhibition by CG0009 led to slight upregulation of the β-catenin target genes, c-Jun and c-Myc, but not cyclin D1, indicating that CG0009-mediated cyclin D1 depletion overwhelms the pro-survival signal of β-catenin, resulting in cell death. Our findings suggest that the novel GSK3 inhibitor, CG0009, inhibits breast cancer cell growth through cyclin D1 depletion and p53 activation, and may thus offer an innovative therapeutic approach for breast cancers resistant to hormone-based therapy.

Spheroid formation and enhanced cardiomyogenic potential of adipose-derived stem cells grown on chitosan

Mesenchymal stem cells may differentiate into cardiomyocytes and participate in local tissue repair after heart injury. In the current study, rat adipose-derived adult stem cells (ASCs) grown on chitosan membranes were observed to form cell spheroids after 3 days. The cell seeding density and surface modification of chitosan with Arg-Gly-Asp-containing peptide had an influence on the sizes of ASC spheroids. In the absence of induction, these spheroids showed an increased level of cardiac marker gene expression (Gata4, Nkx2-5, Myh6, and Tnnt2) more than 20-fold versus cells on the tissue culture polystyrene (TCPS) dish. Induction by 5-azacytidine or p38 MAP kinase inhibitor (SB202190) did not further increase the cardiac marker gene expression of these spheroids. Moreover, the enhanced cardiomyogenic potential of the spheroids was highly associated with the chitosan substrates. When ASC spheroids were plated onto TCPS with either basal or cardiac induction medium for 9 days, the spheroids spread into a monolayer and the positive effect on cardiomyogenic marker gene expression disappeared. The possible role of calcium ion and the up-regulation of adhesion molecule P-selectin and chemokine receptor Cxcr4 were demonstrated in ASC spheroids. Applying these spheroids to the chronic myocardial infarction animal model showed better functional recovery versus single cells after 12 weeks. Taken together, this study suggested that the ASC spheroids on chitosan may form as a result of calcium ion signaling, and the transplantation of these spheroids may offer a simple method to enhance the efficiency of stem cell-based therapy in myocardial infarction.

Secreted Wnt modulators in symptomatic aortic stenosis

Background

Valve calcification and inflammation play key roles in the development of aortic stenosis (AS). The Wnt pathways have been linked to inflammation, bone metabolism, angiogenesis, and heart valve formation. We hypothesized that soluble Wnt modulators may be dysregulated in symptomatic AS.

Methods and Results

We measured circulating levels (n=136) and aortic valve tissue expression (n=16) of the secreted Wnt modulators secreted frizzled related protein-3, dickkopf-1 (DKK-1), and Wnt inhibitory factor-1 (WIF-1) by enzyme immunoassay, immunostaining, and RT-PCR in patients with symptomatic, severe AS and investigated associations with echocardiographic parameters of AS and cardiac function. Finally, we assessed the prognostic value of these Wnt modulators in relation to all-cause mortality (n=35) during long-term follow-up (median 4.6 years; survivors, 4.8 years; nonsurvivors, 1.9 years) in these patients. Our main findings were: (1) serum levels of all Wnt modulators were markedly elevated in patients with symptomatic AS (mean increase 231% to 278%, P<0.001), (2) all Wnt modulators were present in calcified aortic valves but correlated poorly with systemic levels or degree of AS, (3) some modulators (ie, WIF-1) were associated with the degree of myocardial function and valvular calcification, (4) all Wnt modulators, and DKK-1 in particular, predicted long-term mortality in these patients also after adjusting for conventional predictors including NT-proBNP.

Conclusions

Together, these in vivo data support the involvement of Wnt signaling in the development of AS and suggest that circulating Wnt modulators should be further investigated as risk markers in larger AS populations, including patients with asymptomatic disease.

Emerging strategies for spatiotemporal control of stem cell fate and morphogenesis

Stem cell differentiation is regulated by the complex interplay of multiple parameters, including adhesive intercellular interactions, cytoskeletal and extracellular matrix remodeling, and gradients of agonists and antagonists that individually and collectively vary as a function of spatial locale and temporal stages of development. Current approaches to direct stem cell differentiation focus on systematically understanding the relative influences of microenvironmental perturbations and simultaneously engineering platforms aimed at recapitulating physicochemical aspects of tissue morphogenesis. This review focuses on novel approaches to control the spatiotemporal dynamics of stem cell signaling and morphogenic remodeling to direct the differentiation of stem cells and develop functional tissues for in vitro screening and regenerative medicine technologies.

Differential expression profile of MicroRNAs during differentiation of cardiomyocytes exposed to polychlorinated biphenyls

Exposure to persistent environmental pollutants, such as polychlorinated biphenyls (PCBs), is a risk factor for the development of congenital heart defects. MicroRNAs (miRNAs) have been shown to be involved in cardiac development. The objective of this study was to investigate changes in miRNA expression profiles during the differentiation of cardiomyocytes exposed to PCBs. For that purpose, PCBs (Aroclor 1254) at a concentration of 2.5 μmol/L were added on day 0 of differentiation of P19 mouse embryonal carcinoma cells into cardiac myocytes. The relative expression of miRNA genes was determined by miRNA microarray and real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR) analyses. The microarray results revealed that 45 miRNAs, of which 14 were upregulated and 31 were downregulated, were differentially expressed in P19 cells treated with PCBs compared with control cells. The miRNA expression data was validated with real-time RT-PCR. The expression of certain potential target genes (Wnt1) was found to be reduced in P19 cells treated with PCBs, whereas the expression of other potential predicted target genes (GSK3β) was increased. Our results demonstrate a critical role of miRNAs in mediating the effect of PCBs during the differentiation of P19 cells into cardiac myocytes.

Differentiation of human embryonic stem cells and induced pluripotent stem cells to cardiomyocytes: a methods overview

Since human embryonic stem cells were first differentiated to beating cardiomyocytes a decade ago, interest in their potential applications has increased exponentially. This has been further enhanced over recent years by the discovery of methods to induce pluripotency in somatic cells, including those derived from patients with hereditary cardiac diseases. Human pluripotent stem cells have been among the most challenging cell types to grow stably in culture, but advances in reagent development now mean that most laboratories can expand both embryonic and induced pluripotent stem cells robustly using commercially available products. However, differentiation protocols have lagged behind and in many cases only produce the cell types required with low efficiency. Cardiomyocyte differentiation techniques were also initially inefficient and not readily transferable across cell lines, but there are now a number of more robust protocols available. Here, we review the basic biology underlying the differentiation of pluripotent cells to cardiac lineages and describe current state-of-the-art protocols, as well as ongoing refinements. This should provide a useful entry for laboratories new to this area to start their research. Ultimately, efficient and reliable differentiation methodologies are essential to generate desired cardiac lineages to realize the full promise of human pluripotent stem cells for biomedical research, drug development, and clinical applications.

Frizzled homolog proteins, microRNAs and Wnt signaling in cancer

Wnt signaling pathways play important roles in tumorigenesis and are initiated by binding of Wnt to various receptors including frizzleds (FZDs). FZDs are one of several families of receptors comprised of FZD/LRP/ROR2/RYK in the Wnt signaling pathway. Expression of some FZD receptors are up regulated, thereby activating the Wnt signaling pathway and is correlated with cancer malignancy and patient outcomes (recurrence and survival) in many cancers. The FZD family contains ten genes in humans and their function has not been completely examined including the regulatory mechanisms of FZD genes in cancer. Knockdown of FZDs may suppress the Wnt signaling pathway resulting in decreased cell growth, invasion, motility and metastasis of cancer cells. Recently a number of microRNAs (miRNAs) have been identified and reported to be important in several cancers. MiRNAs regulate target gene expression at both the transcription and translation levels. The study of miRNA is a newly emerging field and promises to be helpful in understanding the pathogenesis of FZDs in cancer. In addition, miRNAs may be useful in regulating FZDs in cancer cells. Therefore, the aim of this review is to discuss current knowledge of the functional mechanisms of FZDs in cancer, including regulation by miRNAs and the potential for possible use of miRNAs and FZDs in future clinical applications.

Stem cell factor gene transfer promotes cardiac repair after myocardial infarction via in situ recruitment and expansion of c-kit+ cells

RATIONALE

There is growing evidence that the myocardium responds to injury by recruiting c-kit(+) cardiac progenitor cells to the damage tissue. Even though the ability of exogenously introducing c-kit(+) cells to injured myocardium has been established, the capability of recruiting these cells through modulation of local signaling pathways by gene transfer has not been tested.

OBJECTIVE

To determine whether stem cell factor gene transfer mediates cardiac regeneration in a rat myocardial infarction model, through survival and recruitment of c-kit(+) progenitors and cell-cycle activation in cardiomyocytes, and explore the mechanisms involved.

METHODS AND RESULTS

Infarct size, cardiac function, cardiac progenitor cells recruitment, fibrosis, and cardiomyocyte cell-cycle activation were measured at different time points in controls (n=10) and upon stem cell factor gene transfer (n=13) after myocardial infarction. We found a regenerative response because of stem cell factor overexpression characterized by an enhancement in cardiac hemodynamic function: an improvement in survival; a reduction in fibrosis, infarct size and apoptosis; an increase in cardiac c-kit(+) progenitor cells recruitment to the injured area; an increase in cardiomyocyte cell-cycle activation; and Wnt/β-catenin pathway induction.

CONCLUSIONS

Stem cell factor gene transfer induces c-kit(+) stem/progenitor cell expansion in situ and cardiomyocyte proliferation, which may represent a new therapeutic strategy to reverse adverse remodeling after myocardial infarction.

Wnt5a and Wnt11 are essential for second heart field progenitor development

Wnt/β-catenin has a biphasic effect on cardiogenesis, promoting the induction of cardiac progenitors but later inhibiting their differentiation. Second heart field progenitors and expression of the second heart field transcription factor Islet1 are inhibited by the loss of β-catenin, indicating that Wnt/β-catenin signaling is necessary for second heart field development. However, expressing a constitutively active β-catenin with Islet1-Cre also inhibits endogenous Islet1 expression, reflecting the inhibitory effect of prolonged Wnt/β-catenin signaling on second heart field development. We show that two non-canonical Wnt ligands, Wnt5a and Wnt11, are co-required to regulate second heart field development in mice. Loss of Wnt5a and Wnt11 leads to a dramatic loss of second heart field progenitors in the developing heart. Importantly, this loss of Wnt5a and Wnt11 is accompanied by an increase in Wnt/β-catenin signaling, and ectopic Wnt5a/Wnt11 inhibits β-catenin signaling and promotes cardiac progenitor development in differentiating embryonic stem cells. These data show that Wnt5a and Wnt11 are essential regulators of the response of second heart field progenitors to Wnt/β-catenin signaling and that they act by restraining Wnt/β-catenin signaling during cardiac development.

Sca-1 knockout impairs myocardial and cardiac progenitor cell function

RATIONALE

Cardiac progenitor cells are important for maintenance of myocardial structure and function, but molecular mechanisms governing these progenitor cells remain obscure and require elucidation to enhance regenerative therapeutic approaches.

OBJECTIVE

To understand consequences of stem cell antigen-1 (Sca-1) deletion on functional properties of c-kit+ cardiac progenitor cells and myocardial performance using a Sca-1 knock-out/green fluorescent protein knock-in reporter mouse (ScaKI).

METHODS AND RESULTS

Genetic deletion of Sca-1 results in early-onset cardiac contractile deficiency as determined by echocardiography and hemodynamics as well as age-associated hypertrophy. Resident cardiac progenitor cells in ScaKI mice do not respond to pathological damage in vivo, consistent with observations of impaired growth and survival of ScaKI cardiac progenitor cells in vitro. The molecular basis of the defect in ScaKI cardiac progenitor cells is associated with increased canonical Wnt signaling pathway activation consistent with molecular characteristics of lineage commitment.

CONCLUSIONS

Genetic deletion of Sca-1 causes primary cardiac defects in myocardial contractility and repair consistent with impairment of resident cardiac progenitor cell proliferative capacity associated with altered canonical Wnt signaling.

Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update

The mammalian stress-activated families of mitogen-activated protein kinases (MAPKs) were first elucidated in 1994, and by 2001, substantial progress had been made in identifying the architecture of the pathways upstream of these kinases as well as in cataloguing candidate substrates. This information remains largely sound. Nevertheless, an informed understanding of the physiological and pathophysiological roles of these kinases remained to be accomplished. In the past decade, there has been an explosion of new work using RNAi in cells, as well as transgenic, knockout and conditional knockout technology in mice that has provided valuable insight into the functions of stress-activated MAPK pathways. These findings have important implications in our understanding of organ development, innate and acquired immunity, and diseases such as atherosclerosis, tumorigenesis, and type 2 diabetes. These new developments bring us within striking distance of the development and validation of novel treatment strategies. Herein we first summarize the molecular components of the mammalian stress-regulated MAPK pathways and their regulation as described thus far. We then review some of the in vivo functions of these pathways.

Importance of myocyte-nonmyocyte interactions in cardiac development and disease

Emerging data in the field of cardiac development as well as repair and regeneration indicate a complex and important interplay between endocardial, epicardial, and myofibroblast populations that is critical for cardiomyocyte differentiation and postnatal function. For example, epicardial cells have been shown to generate cardiac myofibroblasts and may be one of the primary sources for this cell lineage during development. Moreover, paracrine signaling from the epicardium and endocardium is critical for proper development of the heart and pathways such as Wnt, fibroblast growth factor, and retinoic acid signaling have been shown to be key players in this process. Despite this progress, interactions between nonmyocyte cells and cardiomyocytes in the heart are still poorly understood. We review the various nonmyocyte-myocyte interactions that occur in the heart and how these interactions, primarily through signaling networks, help direct cardiomyocyte differentiation and regulate postnatal cardiac function.

Signaling in cell differentiation and morphogenesis

All the information to make a complete, fully functional living organism is encoded within the genome of the fertilized oocyte. How is this genetic code translated into the vast array of cellular behaviors that unfold during the course of embryonic development, as the zygote slowly morphs into a new organism? Studies over the last 30 years or so have shown that many of these cellular processes are driven by secreted or membrane-bound signaling molecules. Elucidating how the genetic code is translated into instructions or signals during embryogenesis, how signals are generated at the correct time and place and at the appropriate level, and finally, how these instructions are interpreted and put into action, are some of the central questions of developmental biology. Our understanding of the causes of congenital malformations and disease has improved substantially with the rapid advances in our knowledge of signaling pathways and their regulation during development. In this article, I review some of the signaling pathways that play essential roles during embryonic development. These examples show some of the mechanisms used by cells to receive and interpret developmental signals. I also discuss how signaling pathways downstream from these signals are regulated and how they induce specific cellular responses that ultimately affect cell fate and morphogenesis.

Exogenous high-mobility group box 1 protein injection improves cardiac function after myocardial infarction: involvement of Wnt signaling activation

Exogenous high-mobility group box 1 protein (HMGB1) injection could prevent left ventricular remodeling and enhance left ventricular function during myocardial infarction (MI). However, the mechanism remains unclear. This paper was to investigate in the mechanism of cardioprotection of HMGB1 during MI in rats. Anesthetized male rats were treated once with HMGB1 (200 ng) 4 h after MI and then executed after 7 and 28 days, respectively. Cardiac function, collagen deposition, and dishevelled-1 and β-catenin protein expression were measured. After MI 7 days or 28 days, the left ventricular ejection fraction (LVEF) was significantly decreased compared to that of sham-operated control group (P < 0.05). However, the LVEF HMGB1-treated groups were significantly higher compared to those of the MI group in both 7 days and 28 days (P < 0.05). The collagen volume fraction was significantly reduced in the HMGB1-treated group in infarcted border zone. HMGB1 could activate the expression of dishevelled-1 and β-catenin proteins (P < 0.05). Our study suggested that exogenous high-mobility group box 1 protein injection improves cardiac function after MI, which may be involved in Wnt/β-catenin signaling activation.

Overexpression of Dickkopf-3 induces apoptosis through mitochondrial pathway in human colon cancer

AIM: To investigate the mechanisms of the biological roles of Dickkopf-3 (Dkk-3) in cell invasion, survival and apoptosis in colon cancer cells.

METHODS: Three human colon cancer cell lines, i.e., HT-29, LoVo and SW480, were used. Overexpression of Dkk-3 induced by pEGFP-N1-Dkk-3-GFP plasmid in LoVo cells was performed using Lipofectamine 2000 reagent. Reverse transcription polymerase chain reaction and Western blotting were performed to determine the mRNA and protein expression levels of Dkk-3, respectively. Cell proliferation assay, cell cycle analysis, hoechst 33258 assay and Matrigel invasion assay were performed on Dkk-3 overexpressing transfectants.

RESULTS: The mRNA and protein expressions of Dkk-3 in HT-29 (mRNA: 0.06 ± 0.02, protein: 0.06 ± 0.01) and LoVo (mRNA: 0.07 ± 0.02, protein: 0.07 ± 0.02) cells were significantly lower than that in SW480 cells (mRNA: 0.92 ± 0.04, protein: 0.69 ± 0.13; all P < 0.05), and the greatest levels of invasiveness was in LoVo cells. Dkk-3 overexpression inhibited the proliferation and invasion of LoVo cells and induced cell cycle arrest at G₀/G₁ phase and subsequent apoptosis, as indicated by increased chromatin condensation and fragments, upregulated Bax and cytochrome c protein, downregulated survivin and Bcl-2 protein, and the activation of caspase-3 and caspase-9. Furthermore, Dkk-3 overexpression reduced the accumulation of cytosolic fraction of β-catenin.

CONCLUSION: Dkk-3 overexpression induced apoptosis in human colon cancer possibly through the mitochondrial pathway. Dkk-3 may be involved in the Wnt/β-catenin signaling pathways in colon cancer.

Frizzled7 as an emerging target for cancer therapy

Wnt proteins are secreted glycoproteins that bind to the N-terminal extra-cellular cysteine-rich domain of the Frizzled (Fzd) receptor family. The Fzd receptors can respond to Wnt proteins in the presence of Wnt co-receptors to activate the canonical and non-canonical Wnt pathways. Recent studies indicated that, among the Fzd family, Fzd7 is the Wnt receptor most commonly upregulated in a variety of cancers including colorectal cancer, hepatocellular carcinoma and triple negative breast cancer. Fzd7 plays an important role in stem cell biology and cancer development and progression. In addition, it has been demonstrated that siRNA knockdown of Fzd7, the anti-Fzd7 antibody or the extracellular peptide of Fzd7 (soluble Fzd7 peptide) displayed anti-cancer activity in vitro and in vivo mainly due to the inhibition of the canonical Wnt signaling pathway. Furthermore, pharmacological inhibition of Fzd7 by small interfering peptides or a small molecule inhibitor suppressed β-catenin-dependent tumor cell growth. Therefore, targeted inhibition of Fzd7 represents a rational and promising new approach for cancer therapy.

Human cardiac progenitor cell grafts as unrestricted source of supernumerary cardiac cells in healthy murine hearts

Human heart harbors a population of resident progenitor cells that can be isolated by stem cell antigen-1 antibody and expanded in culture. These cells can differentiate into cardiomyocytes in vitro and contribute to cardiac regeneration in vivo. However, when directly injected as single cell suspension, less than 1%-5% survive and differentiate. Among the major causes of this failure are the distressing protocols used to culture in vitro and implant progenitor cells into damaged hearts. Human cardiac progenitors obtained from the auricles of patients were cultured as scaffoldless engineered tissues fabricated using temperature-responsive surfaces. In the engineered tissue, progenitor cells established proper three-dimensional intercellular relationships and were embedded in self-produced extracellular matrix preserving their phenotype and multipotency in the absence of significant apoptosis. After engineered tissues were leant on visceral pericardium, a number of cells migrated into the murine myocardium and in the vascular walls, where they integrated in the respective textures. The study demonstrates the suitability of such an approach to deliver stem cells to the myocardium. Interestingly, the successful delivery of cells in murine healthy hearts suggests that myocardium displays a continued cell cupidity that is strictly regulated by the limited release of progenitor cells by the adopted source. When an unregulated cell source is added to the system, cells are delivered to the myocardium. The exploitation of this novel concept may pave the way to the setup of new protocols in cardiac cell therapy.

How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

Wnt/β-catenin signalling is known to play many roles in metazoan development and tissue homeostasis. Misregulation of the pathway has also been linked to many human diseases. In this review, specific aspects of the pathway's involvement in these processes are discussed, with an emphasis on how Wnt/β-catenin signalling regulates gene expression in a cell and temporally specific manner. The T-cell factor (TCF) family of transcription factors, which mediate a large portion of Wnt/β-catenin signalling, will be discussed in detail. Invertebrates contain a single TCF gene that contains two DNA-binding domains, the high mobility group (HMG) domain and the C-clamp, which increases the specificity of DNA binding. In vertebrates, the situation is more complex, with four TCF genes producing many isoforms that contain the HMG domain, but only some of which possess a C-clamp. Vertebrate TCFs have been reported to act in concert with many other transcription factors, which may explain how they obtain sufficient specificity for specific DNA sequences, as well as how they achieve a wide diversity of transcriptional outputs in different cells.

Imaging cardiac extracellular matrices: a blueprint for regeneration

Once damaged, cardiac tissue does not readily repair and is therefore a primary target of regenerative therapies. One regenerative approach is the development of scaffolds that functionally mimic the cardiac extracellular matrix (ECM) to deliver stem cells or cardiac precursor populations to the heart. Technological advances in micro/nanotechnology, stem cell biology, biomaterials and tissue decellularization have propelled this promising approach forward. Surprisingly, technological advances in optical imaging methods have not been fully utilized in the field of cardiac regeneration. Here, we describe and provide examples to demonstrate how advanced imaging techniques could revolutionize how ECM-mimicking cardiac tissues are informed and evaluated.

Possible involvement of Wnt11 in colorectal cancer progression

Our previous report revealed that the expression of Frizzled-7 (FZD7) in colorectal cancer (CRC) and its possible role in CRC progression. In this study we measured the expression levels of candidate FZD7 ligands, Wnt3 and Wnt11 in colon cancer cell lines (n = 7) and primary CRC tissues (n = 133) by quantitative RT-PCR. We also examined the functional effects of Wnt11 with the use of Wnt11 transfectants of colon cancer HCT-116 cells. Wnt11 transfectants showed the increased proliferation and migration/invasion activities compared to mock cells. Western blot analysis of transfectants revealed that phosphorylation of JNK and c-jun was increased after Wnt11 transfection. Wnt11 mRNA expression was significantly higher in the stage I, II, III, or IV tumor tissues than in non-tumor tissues (overall P < 0.003), while there was no significant difference in Wnt3 mRNA expression between tumor and non-tumor tissues. In addition, Wnt11 mRNA expression was significantly higher in patients with recurrence or death after surgery than in those with no recurrence (disease free) after surgery (P = 0.018). We also compared the expression levels of Wnt11 mRNA with those of FZD7 mRNA in the same CRC samples. Wnt11 mRNA expression was significantly higher in patients with higher FZD7 mRNA levels than in those with lower FZD7 mRNA levels (P = 0.0005). The expression levels of Wnt11 mRNA were correlated with those of FZD7 mRNA (P < 0.0001). These data suggest that Wnt11 may play an important role in CRC progression.

Wnt2 accelerates cardiac myocyte differentiation from ES-cell derived mesodermal cells via non-canonical pathway

The efficient induction of cardiomyocyte differentiation from embryonic stem (ES) cells is crucial for cardiac regenerative medicine. Although Wnts play important roles in cardiac development, complex questions remain as to when, how and what types of Wnts are involved in cardiogenesis. We found that Wnt2 was strongly up-regulated during cardiomyocyte differentiation from ES cells. Therefore, we investigated when and how Wnt2 acts in cardiogenesis during ES cell differentiation. Wnt2 was strongly expressed in the early developing murine heart. We applied this embryonic Wnt2 expression pattern to ES cell differentiation, to elucidate Wnt2 function in cardiomyocyte differentiation. Wnt2 knockdown revealed that intrinsic Wnt2 was essential for efficient cardiomyocyte differentiation from ES cells. Moreover, exogenous Wnt2 increased cardiomyocyte differentiation from ES cells. Interestingly, the effects on cardiogenesis of intrinsic Wnt2 knockdown and exogenous Wnt2 addition were temporally restricted. During cardiomyocyte differentiation from ES cells, Wnt2 didn't activate canonical Wnt pathway but utilizes JNK/AP-1 pathway which is required for cardiomyocyte differentiation from ES cells. Therefore we conclude that Wnt2 plays strong positive stage-specific role in cardiogenesis through non-canonical Wnt pathway in murine ES cells.

Histone H1 recruitment by CHD8 is essential for suppression of the Wnt-β-catenin signaling pathway

Members of the chromodomain helicase DNA-binding (CHD) family of proteins are thought to regulate gene expression. Among mammalian CHD proteins, CHD8 was originally isolated as a negative regulator of the Wnt-β-catenin signaling pathway that binds directly to β-catenin and suppresses its transactivation activity. The mechanism by which CHD8 inhibits β-catenin-dependent transcription has been unclear, however. Here we show that CHD8 promotes the association of β-catenin and histone H1, with formation of the trimeric complex on chromatin being required for inhibition of β-catenin-dependent transactivation. A CHD8 mutant that lacks the histone H1 binding domain did not show such inhibitory activity, indicating that histone H1 recruitment is essential for the inhibitory effect of CHD8. Furthermore, either depletion of histone H1 or expression of a dominant negative mutant of this protein resulted in enhancement of the response to Wnt signaling. These observations reveal a new mode of regulation of the Wnt signaling pathway by CHD8, which counteracts β-catenin function through recruitment of histone H1 to Wnt target genes. Given that CHD8 is expressed predominantly during embryogenesis, it may thus contribute to setting a threshold for responsiveness to Wnt signaling that operates in a development-dependent manner.

Distinct phases of Wnt/β-catenin signaling direct cardiomyocyte formation in zebrafish

Normal heart formation requires reiterative phases of canonical Wnt/β-catenin (Wnt) signaling. Understanding the mechanisms by which Wnt signaling directs cardiomyocyte (CM) formation in vivo is critical to being able to precisely direct differentiated CMs from stem cells in vitro. Here, we investigate the roles of Wnt signaling in zebrafish CM formation using heat-shock inducible transgenes that increase and decrease Wnt signaling. We find that there are three phases during which CM formation is sensitive to modulation of Wnt signaling through the first 24 h of development. In addition to the previously recognized roles for Wnt signaling during mesoderm specification and in the pre-cardiac mesoderm, we find a previously unrecognized role during CM differentiation where Wnt signaling is necessary and sufficient to promote the differentiation of additional atrial cells. We also extend the previous studies of the roles of Wnt signaling during mesoderm specification and in pre-cardiac mesoderm. Importantly, in pre-cardiac mesoderm we define a new mechanism where Wnt signaling is sufficient to prevent CM differentiation, in contrast to a proposed role in inhibiting cardiac progenitor (CP) specification. The inability of the CPs to differentiate appears to lead to cell death through a p53/Caspase-3 independent mechanism. Together with a report for an even later role for Wnt signaling in restricting proliferation of differentiated ventricular CMs, our results indicate that during the first 3days of development in zebrafish there are four distinct phases during which CMs are sensitive to Wnt signaling.

Planar cell polarity signaling pathway in congenital heart diseases

Congenital heart disease (CHD) is a common cardiac disorder in humans. Despite many advances in the understanding of CHD and the identification of many associated genes, the fundamental etiology for the majority of cases remains unclear. The planar cell polarity (PCP) signaling pathway, responsible for tissue polarity in Drosophila and gastrulation movements and cardiogenesis in vertebrates, has been shown to play multiple roles during cardiac differentiation and development. The disrupted function of PCP signaling is connected to some CHDs. Here, we summarize our current understanding of how PCP factors affect the pathogenesis of CHD.

Wnt signaling exerts an antiproliferative effect on adult cardiac progenitor cells through IGFBP3

RATIONALE

Recent work in animal models and humans has demonstrated the presence of organ-specific progenitor cells required for the regenerative capacity of the adult heart. In response to tissue injury, progenitor cells differentiate into specialized cells, while their numbers are maintained through mechanisms of self-renewal. The molecular cues that dictate the self-renewal of adult progenitor cells in the heart, however, remain unclear.

OBJECTIVE

We investigate the role of canonical Wnt signaling on adult cardiac side population (CSP) cells under physiological and disease conditions.

METHODS AND RESULTS

CSP cells isolated from C57BL/6J mice were used to study the effects of canonical Wnt signaling on their proliferative capacity. The proliferative capacity of CSP cells was also tested after injection of recombinant Wnt3a protein (r-Wnt3a) in the left ventricular free wall. Wnt signaling was found to decrease the proliferation of adult CSP cells, both in vitro and in vivo, through suppression of cell cycle progression. Wnt stimulation exerted its antiproliferative effects through a previously unappreciated activation of insulin-like growth factor binding protein 3 (IGFBP3), which requires intact IGF binding site for its action. Moreover, injection of r-Wnt3a after myocardial infarction in mice showed that Wnt signaling limits CSP cell renewal, blocks endogenous cardiac regeneration and impairs cardiac performance, highlighting the importance of progenitor cells in maintaining tissue function after injury.

CONCLUSIONS

Our study identifies canonical Wnt signaling and the novel downstream mediator, IGFBP3, as key regulators of adult cardiac progenitor self-renewal in physiological and pathological states.

Regulation of insulin-like growth factor signaling by Yap governs cardiomyocyte proliferation and embryonic heart size

The Hippo signaling pathway regulates growth of the heart and other tissues. Hippo pathway kinases influence the activity of various targets, including the transcriptional coactivator Yap, but the specific role of Yap in heart growth has not been investigated. We show that Yap is necessary and sufficient for embryonic cardiac growth in mice. Deletion of Yap in the embryonic mouse heart impeded cardiomyocyte proliferation, causing myocardial hypoplasia and lethality at embryonic stage 10.5. Conversely, forced expression of a constitutively active form of Yap in the embryonic heart increased cardiomyocyte number and heart size. Yap activated the insulin-like growth factor (IGF) signaling pathway in cardiomyocytes, resulting in inactivation of glycogen synthase kinase 3β, which led to increased abundance of β-catenin, a positive regulator of cardiac growth. Our results point to Yap as a critical downstream effector of the Hippo pathway in the control of cardiomyocyte proliferation and a nexus for coupling the IGF, Wnt, and Hippo signaling pathways with the developmental program for heart growth.

Continuous antagonism by Dkk1 counter activates canonical Wnt signaling and promotes cardiomyocyte differentiation of embryonic stem cells

Embryonic stem (ES) cells give rise to mesodermal progenitors that differentiate to hematopoietic and cardiovascular cells. The wnt signaling pathway plays multiple roles in cardiovascular development through a network of intracellular effectors. To monitor global changes in wnt signaling during ES cell differentiation, we generated independent ES cell lines carrying the luciferase gene under promoters that uniquely respond to specific wnt pathway branches. Our results show that successive, mutually exclusive waves of noncanonical and canonical wnt signaling precede mesoderm differentiation. Blocking the initial noncanonical JNK/AP-1 signaling with SP60125 aborts cardiovascular differentiation and promotes hematopoiesis, whereas interference with the subsequent peak of canonical wnt signaling using Dkk1 has the opposite effect. Dkk1 blockade triggers counter mechanisms that lead to delayed and extended activation of canonical wnt signaling and mesoderm differentiation that appear to favor the cardiomyocytic lineage at the expense of hematopoietic cells. The cardiomyocytic yield can be further enhanced by overexpression of Wnt11 leading to approximately 95-fold enrichment in contracting cells. Our results suggest that the initial noncanonical wnt signaling is necessary for subsequent activation of canonical signaling and that the latter operates under a regulatory loop which responds to suppression with hyperactivation of compensatory mechanisms. This model provides new insights on wnt signaling during ES cell differentiation and points to a method to induce cardiomyocytic differentiation without precise timing of wnt signaling manipulation. Taking into account the heterogeneity of pluripotent cells, these findings might present an advantage to enhance the cardiogenic potential of stem cells.

Rspo1/Wnt signaling promotes angiogenesis via Vegfc/Vegfr3

Here, we show that a novel Rspo1-Wnt-Vegfc-Vegfr3 signaling pathway plays an essential role in developmental angiogenesis. A mutation in R-spondin1 (rspo1), a Wnt signaling regulator, was uncovered during a forward-genetic screen for angiogenesis-deficient mutants in the zebrafish. Embryos lacking rspo1 or the proposed rspo1 receptor kremen form primary vessels by vasculogenesis, but are defective in subsequent angiogenesis. Endothelial cell-autonomous inhibition of canonical Wnt signaling also blocks angiogenesis in vivo. The pro-angiogenic effects of Rspo1/Wnt signaling are mediated by Vegfc/Vegfr3(Flt4) signaling. Vegfc expression is dependent on Rspo1 and Wnt, and Vegfc and Vegfr3 are necessary to promote angiogenesis downstream from Rspo1-Wnt. As all of these molecules are expressed by the endothelium during sprouting stages, these results suggest that Rspo1-Wnt-VegfC-Vegfr3 signaling plays a crucial role as an endothelial-autonomous permissive cue for developmental angiogenesis.

LEOPARD-type SHP2 mutant Gln510Glu attenuates cardiomyocyte differentiation and promotes cardiac hypertrophy via dysregulation of Akt/GSK-3β/β-catenin signaling

LEOPARD syndrome (LS) is an autosomal dominant inherited multisystemic disorder. Most cases involve mutations in the PTPN11 gene, which encodes the protein tyrosine phosphatase Src homology 2-containing protein phosphatase 2 (SHP2). LS frequently causes severe hypertrophic cardiomyopathy (HCM), even from the fetal period. However, the molecular pathogenesis has not been clearly elucidated. Here, we analyzed the roles of the LS-type SHP2 mutant Gln510Glu (Q510E), which showed the most severe type of HCM in LS, in cardiomyocyte differentiation, and in morphological changes. We generated mutant P19CL6 cell lines, the most convenient cardiomyocyte differentiation model, which continuously expressed SHP2-Q510E, SHP2-D61N (Noonan-type mutant), wild-type SHP2, and green fluorescent protein (native SHP2 expression only). SHP2-Q510E mutant P19CL6 cells showed significant attenuation of myofibrillogenesis, with increased proliferative activity. Mature cardiomyocytes from the SHP2-Q510E mutant were significantly larger than those of controls and the other mutants. However, expression of cardiac-specific transcriptional factors (Gata4, Tbx5, and Nkx2.5) did not differ significantly between the LS-type SHP2-Q510E mutants and the other mutants and controls. Our results indicate that SHP2-Q510E mutants can differentiate into cardiac progenitors but are inhibited from undergoing terminal differentiation into mature cardiomyocytes. In contrast, Akt and glycogen synthase kinase (GSK)-3β phosphorylation were upregulated, and nuclear β-catenin at the late stage of differentiation was highly accumulated in SHP2-Q510E mutant P19CL6 cells. Supplementation with the phosphoinositide 3-kinase/Akt inhibitor LY-294002 during the late stage of differentiation was found to partially restore myofibrillogenesis while suppressing the increase in size of individual mature cardiomyocytes derived from the SHP2-Q510E mutants. Our findings suggest that dysregulation of the Akt/GSK-3β/β-catenin pathway can contribute to the pathogenesis of HCM in LS patients, not only through hypertrophic changes in individual cardiac cells but also via the expansion of cardiac progenitors.

A biochemical screen for identification of small-molecule regulators of the Wnt pathway using Xenopus egg extracts

Misregulation of the Wnt pathway has been shown to be responsible for a variety of human diseases, most notably cancers. Screens for inhibitors of this pathway have been performed almost exclusively using cultured mammalian cells or with purified proteins. We have previously developed a biochemical assay using Xenopus egg extracts to recapitulate key cytoplasmic events in the Wnt pathway. Using this biochemical system, we show that a recombinant form of the Wnt coreceptor, LRP6, regulates the stability of two key components of the Wnt pathway (β-catenin and Axin) in opposing fashion. We have now fused β-catenin and Axin to firefly and Renilla luciferase, respectively, and demonstrate that the fusion proteins behave similarly as their wild-type counterparts. Using this dual luciferase readout, we adapted the Xenopus extracts system for high-throughput screening. Results from these screens demonstrate signal distribution curves that reflect the complexity of the library screened. Of several compounds identified as cytoplasmic modulators of the Wnt pathway, one was further validated as a bona fide inhibitor of the Wnt pathway in cultured mammalian cells and Xenopus embryos. We show that other embryonic pathways may be amendable to screening for inhibitors/modulators in Xenopus egg extracts.

Pronephric tubulogenesis requires Daam1-mediated planar cell polarity signaling

Canonical β-catenin-mediated Wnt signaling is essential for the induction of nephron development. Noncanonical Wnt/planar cell polarity (PCP) pathways contribute to processes such as cell polarization and cytoskeletal modulation in several tissues. Although PCP components likely establish the plane of polarization in kidney tubulogenesis, whether PCP effectors directly modulate the actin cytoskeleton in tubulogenesis is unknown. Here, we investigated the roles of Wnt PCP components in cytoskeletal assembly during kidney tubule morphogenesis in Xenopus laevis and zebrafish. We found that during tubulogenesis, the developing pronephric anlagen expresses Daam1 and its interacting Rho-GEF (WGEF), which compose one PCP/noncanonical Wnt pathway branch. Knockdown of Daam1 resulted in reduced expression of late pronephric epithelial markers with no apparent effect upon early markers of patterning and determination. Inhibiting various points in the Daam1 signaling pathway significantly reduced pronephric tubulogenesis. These data indicate that pronephric tubulogenesis requires the Daam1/WGEF/Rho PCP pathway.

Cancer chemotherapy induces cardiotoxicity by targeting cardiac stem cells

Overwhelming data indicate that cancer survivors are at higher risk of cardiovascular diseases because chemotherapy induces cardiotoxicity. Mechanistic explanation of this phenomenon is necessary to advise the clinical practice on the prevention of cardiotoxicity in cancer patients. Here we propose that chemotherapy induces cardiotoxicity by inadvertently interrupting the homeostasis of cardiac stem cells and depleting the resident cardiac stem cells pool. As a result, the heart loses the capability of regeneration and repair and demonstrates the cardiotoxicity symptoms. Our hypothesis is supported by several lines of emerging evidence: the high incidence of cardiotoxicity in paediatric cancer patients who still have more cardiac stem cells in the myocardium; the rescue of anthracycline cardiomyopathy by injection of cardiac stem cells; and the adverse cardiotoxicity induced by inhibitors of oncogenic kinases or pathways which target cardiac stem cells besides cancer cells. This may promote our growing appreciation that cardiac stem cells represent new targets of chemotherapy that contribute to cardiotoxicity and open up novel strategies for the preservation or expansion of the cardiac stem cells pool to overcome cardiotoxicity associated with chemotherapy.

Restriction of hepatic competence by Fgf signaling

Hepatic competence, or the ability to respond to hepatic-inducing signals, is regulated by a number of transcription factors broadly expressed in the endoderm. However, extrinsic signals might also regulate hepatic competence, as suggested by tissue explant studies. Here, we present genetic evidence that Fgf signaling regulates hepatic competence in zebrafish. We first show that the endoderm posterior to the liver-forming region retains hepatic competence: using transgenic lines that overexpress hepatic inducing signals following heat-shock, we found that at late somitogenesis stages Wnt8a, but not Bmp2b, overexpression could induce liver gene expression in pancreatic and intestinal bulb cells. These manipulations resulted in the appearance of ectopic hepatocytes in the intestinal bulb. Second, by overexpressing Wnt8a at various stages, we found that as embryos develop, the extent of the endodermal region retaining hepatic competence is gradually reduced. Most significantly, we found, using gain- and loss-of-function approaches, that Fgf10a signaling regulates this gradual reduction of the hepatic-competent domain. These data provide in vivo evidence that endodermal cells outside the liver-forming region retain hepatic competence and show that an extrinsic signal, Fgf10a, negatively regulates hepatic competence.