Comprehensive gene-expression survey identifies wif1 as a modulator of cardiomyocyte differentiation

In Vivo and In Vitro Cartilage Differentiation from Embryonic Epicardial Progenitor Cells

The presence of cartilage tissue in the embryonic and adult hearts of different vertebrate species is a well-recorded fact. However, while the embryonic neural crest has been historically considered as the main source of cardiac cartilage, recently reported results on the wide connective potential of epicardial lineage cells suggest they could also differentiate into chondrocytes. In this work, we describe the formation of cardiac cartilage clusters from proepicardial cells, both in vivo and in vitro. Our findings report, for the first time, cartilage formation from epicardial progenitor cells, and strongly support the concept of proepicardial cells as multipotent connective progenitors. These results are relevant to our understanding of cardiac cell complexity and the responses of cardiac connective tissues to pathologic stimuli.

Dissecting the cellular landscape and transcriptome network in viral myocarditis by single-cell RNA sequencing

Coxsackievirus B3 (CVB3)-induced myocarditis is commonly employed to study viral pathogenesis in mice. Chronically affected mice may develop dilated cardiomyopathy, which may involve the mediation of immune and nonimmune cells. To dissect this complexity, we performed single-cell RNA sequencing on heart cells from healthy and myocarditic mice, leading us to note significant proportions of myeloid cells, T cells, and fibroblasts. Although the transcriptomes of myeloid cells were mainly of M2 phenotype, the Th17 cells, CTLs, and Treg cells had signatures critical for cytotoxic functions. Fibroblasts were heterogeneous expressing genes important in fibrosis and regulation of inflammation and immune responses. The intercellular communication networks revealed unique interactions and signaling pathways in the cardiac cellulome, whereas myeloid cells and T cells had upregulated unique transcription factors modulating cardiac remodeling functions. Together, our data suggest that M2 cells, T cells, and fibroblasts may cooperatively or independently participate in the pathogenesis of viral myocarditis.

Intrauterine Programming of Diabetes Induced Cardiac Embryopathy

BACKGROUND

Maternal hyperglycemia is a well-recognized risk factor for fetal congenital heart disease. However, the underlying cellular and molecular mechanisms are not well characterized. We hypothesize that maternal hyperglycemia leading to congenital heart are linked to abnormal DNA methylation and mRNA expression at cardiac specific loci.

METHODS

Hyperglycemia was induced in normal 8-week old CD-1 female mice with a one-time intraperitoneal injection of 150 mg/kg of streptozotocin (STZ) 2 weeks prior to mating. Histological analysis of fetal cardiac morphology was evaluated for malformations on embryonic day (E) 16.5 of control pups and pups exposed to maternal hyperglycemia. We used a massively-parallel sequencing-based methylation sensitive restriction based assay to examine genome-wide cytosine methylation levels at >1.65 million loci in neonatal hearts on post-natal (P) day 0. Functional validation was performed with real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Cardiac structural defects occurred in 28% of the pups (n=12/45) of hyperglycemic dams versus 7% (n=4/61) of controls. Notable phenotypes were hypoplastic left or right ventricle, double outlet right ventricle, ventricular septal defect, and left ventricular outflow tract obstruction. A 10-fold increase in DNA methylation of gene promoter regions was seen in many cardiac important genes in the experimental versus control P0 neonates and have corresponding decreases in gene expression in 21/32 genes functionally validated.

CONCLUSION

Maternal hyperglycemia alters DNA methylation and mRNA expression of some cardiac genes during heart development. Quantitative, genome-wide assessment of cytosine methylation can be used as a discovery platform to gain insight into the mechanisms of hyperglycemia-induced cardiac anomalies.

Proepicardium: Current Understanding of its Structure, Induction, and Fate

The proepicardium (PE) is a transitory extracardiac embryonic structure which plays a crucial role in cardiac morphogenesis and delivers various cell lineages to the developing heart. The PE arises from the lateral plate mesoderm (LPM) and is present in all vertebrate species. During development, mesothelial cells of the PE reach the naked myocardium either as free-floating aggregates in the form of vesicles or via a tissue bridge; subsequently, they attach to the myocardium and, finally, form the third layer of a mature heart-the epicardium. After undergoing epithelial-to-mesenchymal transition (EMT) some of the epicardial cells migrate into the myocardial wall and differentiate into fibroblasts, smooth muscle cells, and possibly other cell types. Despite many recent findings, the molecular pathways that control not only proepicardial induction and differentiation but also epicardial formation and epicardial cell fate are poorly understood. Knowledge about these events is essential because molecular mechanisms that occur during embryonic development have been shown to be reactivated in pathological conditions, for example, after myocardial infarction, during hypertensive heart disease or other cardiovascular diseases. Therefore, in this review we intended to summarize the current knowledge about PE formation and structure, as well as proepicardial cell fate in animals commonly used as models for studies on heart development. Anat Rec, 302:893-903, 2019. © 2018 Wiley Periodicals, Inc.

Gene network analysis: from heart development to cardiac therapy

Networks offer a flexible framework to represent and analyse the complex interactions between components of cellular systems. In particular gene networks inferred from expression data can support the identification of novel hypotheses on regulatory processes. In this review we focus on the use of gene network analysis in the study of heart development. Understanding heart development will promote the elucidation of the aetiology of congenital heart disease and thus possibly improve diagnostics. Moreover, it will help to establish cardiac therapies. For example, understanding cardiac differentiation during development will help to guide stem cell differentiation required for cardiac tissue engineering or to enhance endogenous repair mechanisms. We introduce different methodological frameworks to infer networks from expression data such as Boolean and Bayesian networks. Then we present currently available temporal expression data in heart development and discuss the use of network-based approaches in published studies. Collectively, our literature-based analysis indicates that gene network analysis constitutes a promising opportunity to infer therapy-relevant regulatory processes in heart development. However, the use of network-based approaches has so far been limited by the small amount of samples in available datasets. Thus, we propose to acquire high-resolution temporal expression data to improve the mathematical descriptions of regulatory processes obtained with gene network inference methodologies. Especially probabilistic methods that accommodate the intrinsic variability of biological systems have the potential to contribute to a deeper understanding of heart development.

β-Catenin stabilization promotes proliferation and increase in cardiomyocyte number in chick embryonic epicardial explant culture

Cardiomyocyte (CM) differentiation from proepicardial organ- (PEO) and embryonic epicardium (eEpi)-derived cells or EPDCs in a developing heart emerges as a wide interest in purview of cardiac repair and regenerative medicine. eEpi originates from the precursor PEO and EPDCs, which contribute to several cardiac cell types including smooth muscle cells, fibroblasts, endothelial cells, and CMs during cardiogenesis. Here in this report, we have analyzed several cardiac lineage-specific marker gene expressions between PEO and eEpi cells. We have found that PEO-derived cells show increased level of CM lineage-specific marker gene expression compared to eEpi cells. Moreover, Wnt signaling activation results in increased level of CM-specific marker gene expression in both PEO and eEpi cells in culture. Interestingly, Wnt signaling activation also increases the number of proliferating and sarcomeric myosin (Mf20)-positive cells in eEpi explant culture. Together, this data suggests that eEpi cells as a source for CM differentiation and Wnt signaling mediator, β-catenin, might play an important role in CM differentiation from eEpi cells in culture.

Transcriptional Profiling of Cultured, Embryonic Epicardial Cells Identifies Novel Genes and Signaling Pathways Regulated by TGFβR3 In Vitro

The epicardium plays an important role in coronary vessel formation and Tgfbr3^-/- mice exhibit failed coronary vessel development associated with decreased epicardial cell invasion. Immortalized Tgfbr3^-/- epicardial cells display the same defects. Tgfbr3^+/+ and Tgfbr3^-/- cells incubated for 72 hours with VEH or ligands known to promote invasion via TGFβR3 (TGFβ1, TGFβ2, BMP2), for 72 hours were harvested for RNA-seq analysis. We selected for genes >2-fold differentially expressed between Tgfbr3^+/+ and Tgfbr3^-/- cells when incubated with VEH (604), TGFβ1 (515), TGFβ2 (553), or BMP2 (632). Gene Ontology (GO) analysis of these genes identified dysregulated biological processes consistent with the defects observed in Tgfbr3^-/- cells, including those associated with extracellular matrix interaction. GO and Gene Regulatory Network (GRN) analysis identified distinct expression profiles between TGFβ1-TGFβ2 and VEH-BMP2 incubated cells, consistent with the differential response of epicardial cells to these ligands in vitro. Despite the differences observed between Tgfbr3^+/+ and Tgfbr3^-/- cells after TGFβ and BMP ligand addition, GRNs constructed from these gene lists identified NF-ĸB as a key nodal point for all ligands examined. Tgfbr3^-/- cells exhibited decreased expression of genes known to be activated by NF-ĸB signaling. NF-ĸB activity was stimulated in Tgfbr3^+/+ epicardial cells after TGFβ2 or BMP2 incubation, while Tgfbr3^-/- cells failed to activate NF-ĸB in response to these ligands. Tgfbr3^+/+ epicardial cells incubated with an inhibitor of NF-ĸB signaling no longer invaded into a collagen gel in response to TGFβ2 or BMP2. These data suggest that NF-ĸB signaling is dysregulated in Tgfbr3^-/- epicardial cells and that NF-ĸB signaling is required for epicardial cell invasion in vitro. Our approach successfully identified a signaling pathway important in epicardial cell behavior downstream of TGFβR3. Overall, the genes and signaling pathways identified through our analysis yield the first comprehensive list of candidate genes whose expression is dependent on TGFβR3 signaling.

Wnt signaling in the heart fields: Variations on a common theme

Wnt signaling plays an essential role in development and differentiation. Heart development is initiated with the induction of precardiac mesoderm requiring the tightly and spatially controlled regulation of canonical and noncanonical Wnt signaling pathways. The role of Wnt signaling in subsequent development of the heart fields is to a large extent unclear. We will discuss the role of Wnt signaling in the development of the arterial and venous pole of the heart, highlighting the dual roles of Wnt signaling with respect to its time- and dosage-dependent effects and the balance between the canonical and noncanonical signaling. Canonical signaling appears to be involved in retaining the cardiac precursors in a proliferative and precursor state, whereas noncanonical signaling promotes their differentiation. Thereafter, both canonical and noncanonical signaling regulate specific steps in differentiation of the cardiac compartments. Because heart development is a contiguous, rather than a sequential, process, analyses tend only to show a single timeframe of development. The repetitive alternating and reciprocal effect of canonical and noncanonical signaling is lost when studied in homogenates. Without the simultaneous in vivo visualization of the different Wnt signaling pathways, the mechanism of Wnt signaling in heart development remains elusive.

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.

Wnt inhibitory factor 1 (Wif1) is regulated by androgens and enhances androgen-dependent prostate development

Fetal prostate development from urogenital sinus (UGS) epithelium requires androgen receptor (AR) activation in UGS mesenchyme (UGM). Despite growing awareness of sexually dimorphic gene expression in the UGS, we are still limited in our knowledge of androgen-responsive genes in UGM that initiate prostate ductal development. We found that WNT inhibitory factor 1 (Wif1) mRNA is more abundant in male vs. female mouse UGM in which its expression temporally and spatially overlaps androgen-responsive steroid 5α-reductase 2 (Srd5a2). Wif1 mRNA is also present in prostatic buds during their elongation and branching morphogenesis. Androgens are necessary and sufficient for Wif1 expression in mouse UGS explant mesenchyme, and testicular androgens remain necessary for normal Wif1 expression in adult mouse prostate stroma. WIF1 contributes functionally to prostatic bud formation. In the presence of androgens, exogenous WIF1 protein increases prostatic bud number and UGS basal epithelial cell proliferation without noticeably altering the pattern of WNT/β-catenin-responsive Axin2 or lymphoid enhancer binding factor 1 (Lef1) mRNA. Wif1 mutant male UGSs exhibit increased (Sfrp)2 and (Sfrp)3 expression and form the same number of prostatic buds as the wild-type control males. Collectively our results reveal Wif1 as one of the few known androgen-responsive genes in the fetal mouse UGM and support the hypothesis that androgen-dependent Wif1 expression is linked to the mechanism of androgen-induced prostatic bud formation.

Cardiac regeneration from activated epicardium

In contrast to lower vertebrates, the mammalian heart has a very limited regenerative capacity. Cardiomyocytes, lost after ischemia, are replaced by fibroblasts. Although the human heart is able to form new cardiomyocytes throughout its lifespan, the efficiency of this phenomenon is not enough to substitute sufficient myocardial mass after an infarction. In contrast, zebrafish hearts regenerate through epicardial activation and initiation of myocardial proliferation. With this study we obtain insights into the activation and cellular contribution of the mammalian epicardium in response to ischemia. In a mouse myocardial infarction model we analyzed the spatio-temporal changes in expression of embryonic epicardial, EMT, and stem cell markers and the contribution of cells of the Wt1-lineage to the infarcted area. Though the integrity of the epicardial layer overlaying the infarct is lost immediately after the induction of the ischemia, it was found to be regenerated at three days post infarction. In this regenerated epicardium, the embryonic gene program is transiently re-expressed as well as proliferation. Concomitant with this activation, Wt1-lineage positive subepicardial mesenchyme is formed until two weeks post-infarction. These mesenchymal cells replace the cardiomyocytes lost due to the ischemia and contribute to the fibroblast population, myofibroblasts and coronary endothelium in the infarct, and later also to the cardiomyocyte population. We show that in mice, as in lower vertebrates, an endogenous, epicardium-dependent regenerative response to injury is induced. Although this regenerative response leads to the formation of new cardiomyocytes, their number is insufficient in mice but sufficient in lower vertebrates to replace lost cardiomyocytes. These molecular and cellular analyses provide basic knowledge essential for investigations on the regeneration of the mammalian heart aiming at epicardium-derived cells.

Epicardial progenitor cells in cardiac development and regeneration

The epicardium forms an epithelial layer on the surface of the heart. It is derived from a cluster of mesothelial cells, which is termed the proepicardium. The proepicardium gives rise not only to the epicardium but also to epicardium-derived cells. These cells populate the myocardial wall and differentiate into smooth muscle cells, fibroblast, and possibly endothelial cells. In this review, the formation of the proepicardium is discussed. Marker genes, suitable to identify these cells in the embryo and in the adult, are introduced. Recent evidence suggests that the PE is made up of distinct cell populations. These cell lineages can be distinguished on the basis of marker gene expression and differ in their differentiation potential. The role of the epicardium as a resource for cardiac stem cells and its importance in cardiac regeneration is also discussed.

The role of glypicans in Wnt inhibitory factor-1 activity and the structural basis of Wif1's effects on Wnt and Hedgehog signaling

Proper assignment of cellular fates relies on correct interpretation of Wnt and Hedgehog (Hh) signals. Members of the Wnt Inhibitory Factor-1 (WIF1) family are secreted modulators of these extracellular signaling pathways. Vertebrate WIF1 binds Wnts and inhibits their signaling, but its Drosophila melanogaster ortholog Shifted (Shf) binds Hh and extends the range of Hh activity in the developing D. melanogaster wing. Shf activity is thought to depend on reinforcing interactions between Hh and glypican HSPGs. Using zebrafish embryos and the heterologous system provided by D. melanogaster wing, we report on the contribution of glypican HSPGs to the Wnt-inhibiting activity of zebrafish Wif1 and on the protein domains responsible for the differences in Wif1 and Shf specificity. We show that Wif1 strengthens interactions between Wnt and glypicans, modulating the biphasic action of glypicans towards Wnt inhibition; conversely, glypicans and the glypican-binding “EGF-like” domains of Wif1 are required for Wif1's full Wnt-inhibiting activity. Chimeric constructs between Wif1 and Shf were used to investigate their specificities for Wnt and Hh signaling. Full Wnt inhibition required the “WIF” domain of Wif1, and the HSPG-binding EGF-like domains of either Wif1 or Shf. Full promotion of Hh signaling requires both the EGF-like domains of Shf and the WIF domains of either Wif1 or Shf. That the Wif1 WIF domain can increase the Hh promoting activity of Shf's EGF domains suggests it is capable of interacting with Hh. In fact, full-length Wif1 affected distribution and signaling of Hh in D. melanogaster, albeit weakly, suggesting a possible role for Wif1 as a modulator of vertebrate Hh signaling.

In developing organisms, cells choose between alternative fates in order to make appropriately patterned tissues, and misregulation of those choices can underlie both developmental defects and cancers. Cells often make these decisions because of signals received from neighboring cells, such as those mediated by the secreted signaling proteins of the Wnt and Hedgehog (Hh) families. While signaling can be regulated by the levels of signaling or receptor proteins expressed by cells, another level of control is exerted by proteins that bind signaling proteins outside of cells and either inhibit or promote the signaling process. In the fruitfly Drosophilamelanogaster, the secreted Shifted protein has been shown to bind Hh and to increase Hh signaling, likely by reinforcing interactions between Hh and cell surface proteins of the glypican family. We provide evidence that the vertebrate homolog of Shifted, Wnt Inhibitory Factor-1 (Wif1), inhibits Wnt activity by a similar mechanism, reinforcing interactions between Wnts and glypicans in a manner that sequesters Wnts from their receptors. We also examine the structural basis for the specificities of Wif1 and Shifted for Wnt and Hh signaling, respectively, and provide evidence that Wif1, although a potent inhibitor of Wnt activity, influences D. melanogaster Hh signaling.

Origin and fates of the proepicardium

The embryonic heart initially consists of only two cell layers, the endocardium and the myocardium. The epicardium, which forms an epithelial layer on the surface of the heart, is derived from a cluster of mesothelial cells developing at the base of the venous inflow tract of the early embryonic heart. This cell cluster is termed the proepicardium and gives rise not only to the epicardium but also to epicardium-derived cells. These cells populate the myocardial wall and differentiate into smooth muscle cells and fibroblasts, while the contribution to the vascular endothelial lineage is uncertain. In this review we will discuss the signaling molecules involved in recruiting mesodermal cells to undergo proepicardium formation and guide these cells to the myocardial surface. Marker genes which are suitable to follow these cells during proepicardium formation and cell migration will be introduced. We will address whether the proepicardium consists of a homogenous cell population or whether different cell lineages are present. Finally the role of the epicardium as a source for cardiac stem cells and its importance in cardiac regeneration, in particular in the zebrafish and mouse model systems is discussed.