HEART DEVELOPMENT. Integration of Bmp and Wnt signaling by Hopx specifies commitment of cardiomyoblasts

A spatiotemporal cell atlas of cardiopulmonary progenitor cell allocation during development

The heart and lung co-orchestrate their development during organogenesis. The mesoderm surrounding both the developing heart and anterior foregut endoderm provides instructive cues guiding cardiopulmonary development. Additionally, it serves as a source of cardiopulmonary progenitor cells (CPPs) expressing Wnt2 that give rise to both cardiac and lung mesodermal cell lineages. Despite the mesoderm's critical importance to both heart and lung development, mechanisms guiding CPP specification are unclear. To address this, we lineage traced Wnt2+ CPPs at E8.5 and performed single-cell RNA sequencing on collected progeny across the developmental lifespan. Using computational analyses, we created a CPP-derived cell atlas that revealed a previously underappreciated spectrum of CPP-derived cell lineages, including all lung mesodermal lineages, ventricular cardiomyocytes, and epicardial and pericardial cells. By integrating spatial mapping with computational cell trajectory analysis and transcriptional profiling, we have provided a potential molecular and cellular roadmap for cardiopulmonary development.

HOPX as a tumour-suppressive protein in T-cell acute lymphoblastic leukaemia

The homeodomain protein homeobox (HOPX), a multifaceted regulator of cellular functions and developmental processes, is predominantly expressed in stem cells across diverse tissues; it has also emerged as a tumour suppressor in various solid cancers. However, its role in haematological malignancies still remains undefined. This study aimed to elucidate its significance in T-cell acute lymphoblastic leukaemia (T-ALL). We firstly uncovered a novel link between reduced HOPX expression, its promoter hypermethylation and increased tumour burden in patients with T-ALL, suggesting its tumour-suppressive role. Next, we induced T-ALL by transducing intracellular NOTCH1 (ICN1) into mice with either conditional knock-in at the Rosa26 locus or knockout of Hopx. We found that T-ALL development was markedly accelerated and impeded in backgrounds with low and high Hopx expression respectively. Further analysis revealed Hopx's roles in modulating the Wnt-β-catenin pathway, a pivotal regulator of the downstream Myc signalling involved in T-ALL transformation and progression.

Terminal α1,2-fucosylation of glycosphingolipids by FUT1 is a key regulator in early cell-fate decisions

The embryonic cell surface is rich in glycosphingolipids (GSLs), which change during differentiation. The reasons for GSL subgroup variation during early embryogenesis remain elusive. By combining genomic approaches, flow cytometry, confocal imaging, and transcriptomic data analysis, we discovered that α1,2-fucosylated GSLs control the differentiation of human pluripotent cells (hPCs) into germ layer tissues. Overexpression of α1,2-fucosylated GSLs disrupts hPC differentiation into mesodermal lineage and reduces differentiation into cardiomyocytes. Conversely, reducing α1,2-fucosylated groups promotes hPC differentiation and mesoderm commitment in response to external signals. We find that bone morphogenetic protein 4 (BMP4), a mesodermal gene inducer, suppresses α1,2-fucosylated GSL expression. Overexpression of α1,2-fucosylated GSLs impairs SMAD activation despite BMP4 presence, suggesting α-fucosyl end groups as BMP pathway regulators. Additionally, the absence of α1,2-fucosylated GSLs in early/late mesoderm and primitive streak stages in mouse embryos aligns with the hPC results. Thus, α1,2-fucosylated GSLs may regulate early cell-fate decisions and embryo development by modulating cell signaling.

A primate-specific endogenous retroviral envelope protein sequesters SFRP2 to regulate human cardiomyocyte development

Endogenous retroviruses (ERVs) occupy a significant part of the human genome, with some encoding proteins that influence the immune system or regulate cell-cell fusion in early extra-embryonic development. However, whether ERV-derived proteins regulate somatic development is unknown. Here, we report a somatic developmental function for the primate-specific ERVH48-1 (SUPYN/Suppressyn). ERVH48-1 encodes a fragment of a viral envelope that is expressed during early embryonic development. Loss of ERVH48-1 led to impaired mesoderm and cardiomyocyte commitment and diverted cells to an ectoderm-like fate. Mechanistically, ERVH48-1 is localized to sub-cellular membrane compartments through a functional N-terminal signal peptide and binds to the WNT antagonist SFRP2 to promote its polyubiquitination and degradation, thus limiting SFRP2 secretion and blocking repression of WNT/β-catenin signaling. Knockdown of SFRP2 or expression of a chimeric SFRP2 with the ERVH48-1 signal peptide rescued cardiomyocyte differentiation. This study demonstrates how ERVH48-1 modulates WNT/β-catenin signaling and cell type commitment in somatic development.

Glioblastoma Neurovascular Progenitor Orchestrates Tumor Cell Type Diversity

Glioblastoma (GBM) is the deadliest form of primary brain tumor with limited treatment options. Recent studies have profiled GBM tumor heterogeneity, revealing numerous axes of variation that explain the molecular and spatial features of the tumor. Here, we seek to bridge descriptive characterization of GBM cell type heterogeneity with the functional role of individual populations within the tumor. Our lens leverages a gene program-centric meta-atlas of published transcriptomic studies to identify commonalities between diverse tumors and cell types in order to decipher the mechanisms that drive them. This approach led to the discovery of a tumor-derived stem cell population with mixed vascular and neural stem cell features, termed a neurovascular progenitor (NVP). Following in situ validation and molecular characterization of NVP cells in GBM patient samples, we characterized their function in vivo. Genetic depletion of NVP cells resulted in altered tumor cell composition, fewer cycling cells, and extended survival, underscoring their critical functional role. Clonal analysis of primary patient tumors in a human organoid tumor transplantation system demonstrated that the NVP has dual potency, generating both neuronal and vascular tumor cells. Although NVP cells comprise a small fraction of the tumor, these clonal analyses demonstrated that they strongly contribute to the total number of cycling cells in the tumor and generate a defined subset of the whole tumor. This study represents a paradigm by which cell type-specific interrogation of tumor populations can be used to study functional heterogeneity and therapeutically targetable vulnerabilities of GBM.

Ketogenic diet does not promote triple-negative and luminal mammary tumor growth and metastasis in experimental mice

Ketogenic diets (KDs) can improve the well-being and quality of life of breast cancer patients. However, data on the effects of KDs on mammary tumors are inconclusive, and the influence of KDs on metastasis in general remains to be investigated. We therefore assessed the impact of a KD on growth and metastasis of triple negative murine 4T1 mammary tumors, and on the progression of luminal breast tumors in an autochthonous MMTV-PyMT mouse model. We found that KD did not influence the metastasis of 4T1 and MMTV-PyMT mammary tumors, but impaired 4T1 tumor cell proliferation in vivo, and also temporarily reduced 4T1 primary tumor growth. Notably, the ketogenic ratio (the mass of dietary fat in relation to the mass of dietary carbohydrates and protein) that is needed to induce robust ketosis was twice as high in mice as compared to humans. Surprisingly, only female but not male mice responded to KD with a sustained increase in blood β-hydroxybutyrate levels. Together, our data show that ketosis does not foster primary tumor growth and metastasis, suggesting that KDs can be safely applied in the context of luminal breast cancer, and may even be advantageous for patients with triple negative tumors. Furthermore, our data indicate that when performing experiments with KDs in mice, the ketogenic ratio needed to induce ketosis must be verified, and the sex of the mice should also be taken into account.

Stem cell-based therapies for heart failure management: a narrative review of current evidence and future perspectives

Heart failure (HF) is a prevalent and debilitating global cardiovascular condition affecting around 64 million individuals, placing significant strain on healthcare systems and diminishing patients' quality of life. The escalating prevalence of HF underscores the urgent need for innovative therapeutic approaches that target the root causes and aim to restore normal cardiac function. Stem cell-based therapies have emerged as promising candidates, representing a fundamental departure from conventional treatments focused primarily on symptom management. This review explores the evolving landscape of stem cell-based therapies for HF management. It delves into the mechanisms of action, clinical evidence from both positive and negative outcomes, ethical considerations, and regulatory challenges. Key findings include the potential for improved cardiac function, enhanced quality of life, and long-term benefits associated with stem cell therapies. However, adverse events and patient vulnerabilities necessitate stringent safety assessments. Future directions in stem cell-based HF therapies include enhancing efficacy and safety through optimized stem cell types, delivery techniques, dosing strategies, and long-term safety assessments. Personalized medicine, combining therapies, addressing ethical and regulatory challenges, and expanding access while reducing costs are crucial aspects of the evolving landscape.

On the involvement of the second heart field in congenital heart defects

Congenital heart defects (CHD) affect 1 in 100 live births and result from defects in cardiac development. Growth of the early heart tube occurs by the progressive addition of second heart field (SHF) progenitor cells to the cardiac poles. The SHF gives rise to ventricular septal, right ventricular and outflow tract myocardium at the arterial pole, and atrial, including atrial septal myocardium, at the venous pole. SHF deployment creates the template for subsequent cardiac septation and has been implicated in cardiac looping and in orchestrating outflow tract development with neural crest cells. Genetic or environmental perturbation of SHF deployment thus underlies a spectrum of common forms of CHD affecting conotruncal and septal morphogenesis. Here we review the major properties of SHF cells as well as recent insights into the developmental programs that drive normal cardiac progenitor cell addition and the origins of CHD.

A genome-wide CRISPR screen identifies BRD4 as a regulator of cardiomyocyte differentiation

Human induced pluripotent stem cell (hiPSC) to cardiomyocyte (CM) differentiation has reshaped approaches to studying cardiac development and disease. In this study, we employed a genome-wide CRISPR screen in a hiPSC to CM differentiation system and reveal here that BRD4, a member of the bromodomain and extraterminal (BET) family, regulates CM differentiation. Chemical inhibition of BET proteins in mouse embryonic stem cell (mESC)-derived or hiPSC-derived cardiac progenitor cells (CPCs) results in decreased CM differentiation and persistence of cells expressing progenitor markers. In vivo, BRD4 deletion in second heart field (SHF) CPCs results in embryonic or early postnatal lethality, with mutants demonstrating myocardial hypoplasia and an increase in CPCs. Single-cell transcriptomics identified a subpopulation of SHF CPCs that is sensitive to BRD4 loss and associated with attenuated CM lineage-specific gene programs. These results highlight a previously unrecognized role for BRD4 in CM fate determination during development and a heterogenous requirement for BRD4 among SHF CPCs.

Homeodomain-only protein suppresses proliferation and contributes to differentiation- and age-related reduced CD8+ T cell expansion

T cell activation is a tightly controlled process involving both positive and negative regulators. The precise mechanisms governing the negative regulators in T cell proliferation remain incompletely understood. Here, we report that homeodomain-only protein (HOPX), a homeodomain-containing protein, and its most abundant isoform HOPXb, negatively regulate activation-induced proliferation of human T cells. We found that HOPX expression progressively increased from naïve (TN) to central memory (TCM) to effector memory (TEM) cells, with a notable upregulation following in vitro stimulation. Overexpression of HOPXb leads to a reduction in TN cell proliferation while HOPX knockdown promotes proliferation of TN and TEM cells. Furthermore, we demonstrated that HOPX binds to promoters and exerts repressive effects on the expression of MYC and NR4A1, two positive regulators known to promote T cell proliferation. Importantly, our findings suggest aging is associated with increased HOPX expression, and that knockdown of HOPX enhances the proliferation of CD8+ T cells in older adults. Our findings provide compelling evidence that HOPX serves as a negative regulator of T cell activation and plays a pivotal role in T cell differentiation and in age-related-reduction in T cell proliferation.

HOPX-associated molecular programs control cardiomyocyte cell states underpinning cardiac structure and function

Genomic regulation of cardiomyocyte differentiation is central to heart development and function. This study uses genetic loss-of-function human-induced pluripotent stem cell-derived cardiomyocytes to evaluate the genomic regulatory basis of the non-DNA-binding homeodomain protein HOPX. We show that HOPX interacts with and controls cardiac genes and enhancer networks associated with diverse aspects of heart development. Using perturbation studies in vitro, we define how upstream cell growth and proliferation control HOPX transcription to regulate cardiac gene programs. We then use cell, organoid, and zebrafish regeneration models to demonstrate that HOPX-regulated gene programs control cardiomyocyte function in development and disease. Collectively, this study mechanistically links cell signaling pathways as upstream regulators of HOPX transcription to control gene programs underpinning cardiomyocyte identity and function.

Cardiac Progenitor Cells of the First and Second Heart Fields

The heart forms from the first and second heart fields, which contribute to distinct regions of the myocardium. This is supported by clonal analyses, which identify corresponding first and second cardiac cell lineages in the heart. Progenitor cells of the second heart field and its sub-domains are controlled by a gene regulatory network and signaling pathways, which determine their behavior. Multipotent cells in this field can also contribute cardiac endothelial and smooth muscle cells. Furthermore, the skeletal muscles of the head and neck are clonally related to myocardial cells that form the arterial and venous poles of the heart. These lineage relationships, together with the genes that regulate the heart fields, have major implications for congenital heart disease.

Epigenetics

Epigenetics is the study of heritable changes to the genome and gene expression patterns that are not caused by direct changes to the DNA sequence. Examples of these changes include posttranslational modifications to DNA-bound histone proteins, DNA methylation, and remodeling of nuclear architecture. Collectively, epigenetic changes provide a layer of regulation that affects transcriptional activity of genes while leaving DNA sequences unaltered. Sequence variants or mutations affecting enzymes responsible for modifying or sensing epigenetic marks have been identified in patients with congenital heart disease (CHD), and small-molecule inhibitors of epigenetic complexes have shown promise as therapies for adult heart diseases. Additionally, transgenic mice harboring mutations or deletions of genes encoding epigenetic enzymes recapitulate aspects of human cardiac disease. Taken together, these findings suggest that the evolving field of epigenetics will inform our understanding of congenital and adult cardiac disease and offer new therapeutic opportunities.

The benign nature and rare occurrence of cardiac myxoma as a possible consequence of the limited cardiac proliferative/ regenerative potential: a systematic review

BACKGROUND

Cardiac Myxoma is a primary tumor of heart. Its origins, rarity of the occurrence of primary cardiac tumors and how it may be related to limited cardiac regenerative potential, are not yet entirely known. This study investigates the key cardiac genes/ transcription factors (TFs) and signaling pathways to understand these important questions.

METHODS

Databases including PubMed, MEDLINE, and Google Scholar were searched for published articles without any date restrictions, involving cardiac myxoma, cardiac genes/TFs/signaling pathways and their roles in cardiogenesis, proliferation, differentiation, key interactions and tumorigenesis, with focus on cardiomyocytes.

RESULTS

The cardiac genetic landscape is governed by a very tight control between proliferation and differentiation-related genes/TFs/pathways. Cardiac myxoma originates possibly as a consequence of dysregulations in the gene expression of differentiation regulators including Tbx5, GATA4, HAND1/2, MYOCD, HOPX, BMPs. Such dysregulations switch the expression of cardiomyocytes into progenitor-like state in cardiac myxoma development by dysregulating Isl1, Baf60 complex, Wnt, FGF, Notch, Mef2c and others. The Nkx2-5 and MSX2 contribute predominantly to both proliferation and differentiation of Cardiac Progenitor Cells (CPCs), may possibly serve roles based on the microenvironment and the direction of cell circuitry in cardiac tumorigenesis. The Nkx2-5 in cardiac myxoma may serve to limit progression of tumorigenesis as it has massive control over the proliferation of CPCs. The cardiac cell type-specific genetic programming plays governing role in controlling the tumorigenesis and regenerative potential.

CONCLUSION

The cardiomyocytes have very limited proliferative and regenerative potential. They survive for long periods of time and tightly maintain the gene expression of differentiation genes such as Tbx5, GATA4 that interact with tumor suppressors (TS) and exert TS like effect. The total effect such gene expression exerts is responsible for the rare occurrence and benign nature of primary cardiac tumors. This prevents the progression of tumorigenesis. But this also limits the regenerative and proliferative potential of cardiomyocytes. Cardiac Myxoma develops as a consequence of dysregulations in these key genes which revert the cells towards progenitor-like state, hallmark of CM. The CM development in carney complex also signifies the role of TS in cardiac cells.

Benzophenone induces cardiac developmental toxicity in zebrafish embryos by upregulating Wnt signaling

Benzophenone (BP) is found in many popular consumer products, such as cosmetics. BP potential toxicity to humans and aquatic organisms has emerged as an increased concern. In current study, we utilized a zebrafish model to assess BP-induced developmental cardiotoxicity. Following BP exposure, zebrafish embryos exhibited developmental toxicity, including increased mortality, reduced hatchability, delayed yolk sac absorption, and shortened body length. Besides, BP exposure induced cardiac defects in zebrafish embryos, comprising pericardial edema, reduced myocardial contractility and rhythm disturbances, and altered expression levels of cardiac developmental marker genes. Mechanistically, BP exposure disturbed the redox state and increased the level of apoptosis in zebrafish cardiomyocytes. Transcriptional expression levels of Wnt signaling genes, involving lef1, axin2, and β-catenin, were upregulated after BP treatment. Inhibition of Wnt signaling with IWR-1 could rescue the BP-induced cardiotoxicity in zebrafish. In summary, BP exposure causes cardiotoxicity via upregulation of the Wnt signaling pathway in zebrafish embryos.

An integrated single-cell analysis of human adrenal cortex development

The adrenal glands synthesize and release essential steroid hormones such as cortisol and aldosterone, but many aspects of human adrenal gland development are not well understood. Here, we combined single-cell and bulk RNA sequencing, spatial transcriptomics, IHC, and micro-focus computed tomography to investigate key aspects of adrenal development in the first 20 weeks of gestation. We demonstrate rapid adrenal growth and vascularization, with more cell division in the outer definitive zone (DZ). Steroidogenic pathways favored androgen synthesis in the central fetal zone, but DZ capacity to synthesize cortisol and aldosterone developed with time. Core transcriptional regulators were identified, with localized expression of HOPX (also known as Hop homeobox/homeobox-only protein) in the DZ. Potential ligand-receptor interactions between mesenchyme and adrenal cortex were seen (e.g., RSPO3/LGR4). Growth-promoting imprinted genes were enriched in the developing cortex (e.g., IGF2, PEG3). These findings reveal aspects of human adrenal development and have clinical implications for understanding primary adrenal insufficiency and related postnatal adrenal disorders, such as adrenal tumor development, steroid disorders, and neonatal stress.

Interferon hyperactivity impairs cardiogenesis in Down syndrome via downregulation of canonical Wnt signaling

Congenital heart defects (CHDs) are frequent in children with Down syndrome (DS), caused by trisomy of chromosome 21. However, the underlying mechanisms are poorly understood. Here, using a human-induced pluripotent stem cell (iPSC)-based model and the Dp(16)1Yey/+ (Dp16) mouse model of DS, we identified downregulation of canonical Wnt signaling downstream of increased dosage of interferon (IFN) receptors (IFNRs) genes on chromosome 21 as a causative factor of cardiogenic dysregulation in DS. We differentiated human iPSCs derived from individuals with DS and CHDs, and healthy euploid controls into cardiac cells. We observed that T21 upregulates IFN signaling, downregulates the canonical WNT pathway, and impairs cardiac differentiation. Furthermore, genetic and pharmacological normalization of IFN signaling restored canonical WNT signaling and rescued defects in cardiogenesis in DS in vitro and in vivo. Our findings provide insights into mechanisms underlying abnormal cardiogenesis in DS, ultimately aiding the development of therapeutic strategies.

HOPX is a tumor-suppressive biomarker that corresponds to T cell infiltration in skin cutaneous melanoma

BACKGROUND

Skin cutaneous melanoma (SKCM) is the most threatening type of skin cancer. Approximately 55,000 people lose their lives every year due to SKCM, illustrating that it seriously threatens human life and health. Homeodomain-only protein homeobox (HOPX) is the smallest member of the homeodomain family and is widely expressed in a variety of tissues. HOPX is involved in regulating the homeostasis of hematopoietic stem cells and is closely related to the development of tumors such as breast cancer, nasopharyngeal carcinoma, and head and neck squamous cell carcinoma. However, its function in SKCM is unclear, and further studies are needed.

METHODS

We used the R language to construct ROC (Receiver-Operating Characteristic) curves, KM (Kaplan‒Meier) curves and nomograms based on databases such as the TCGA and GEO to analyze the diagnostic and prognostic value of HOPX in SKCM patients. Enrichment analysis, immune scoring, GSVA (Gene Set Variation Analysis), and single-cell sequencing were used to verify the association between HOPX expression and immune infiltration. In vitro experiments were performed using A375 cells for phenotypic validation. Transcriptome sequencing was performed to further analyze HOPX gene-related genes and their signaling pathways.

RESULTS

Compared to normal cells, SKCM cells had low HOPX expression (p < 0.001). Patients with high HOPX expression had a better prognosis (p < 0.01), and the marker had good diagnostic efficacy (AUC = 0.744). GO/KEGG (Gene Ontology/ Kyoto Encyclopedia of Genes and Genomes) analysis, GSVA and single-cell sequencing analysis showed that HOPX expression is associated with immune processes and high enrichment of T cells and could serve as an immune checkpoint in SKCM. Furthermore, cellular assays verified that HOPX inhibits the proliferation, migration and invasion of A375 cells and promotes apoptosis and S-phase arrest. Interestingly, tumor drug sensitivity analysis revealed that HOPX also plays an important role in reducing clinical drug resistance.

CONCLUSION

These findings suggest that HOPX is a blocker of SKCM progression that inhibits the proliferation of SKCM cells and promotes apoptosis. Furthermore, it may be a new diagnostic and prognostic indicator and a novel target for immunotherapy in SKCM patients.

Single-cell analysis of the postnatal dorsal V-SVZ reveals a role for Bmpr1a signaling in silencing pallial germinal activity

The ventricular-subventricular zone (V-SVZ) is the largest neurogenic region of the postnatal forebrain, containing neural stem cells (NSCs) that emerge from both the embryonic pallium and subpallium. Despite of this dual origin, glutamatergic neurogenesis declines rapidly after birth, while GABAergic neurogenesis persists throughout life. We performed single-cell RNA sequencing of the postnatal dorsal V-SVZ for unraveling the mechanisms leading to pallial lineage germinal activity silencing. We show that pallial NSCs enter a state of deep quiescence, characterized by high bone morphogenetic protein (BMP) signaling, reduced transcriptional activity and Hopx expression, while in contrast, subpallial NSCs remain primed for activation. Induction of deep quiescence is paralleled by a rapid blockade of glutamatergic neuron production and differentiation. Last, manipulation of Bmpr1a demonstrates its key role in mediating these effects. Together, our results highlight a central role of BMP signaling in synchronizing quiescence induction and blockade of neuronal differentiation to rapidly silence pallial germinal activity after birth.

Metabolism-based cardiomyocytes production for regenerative therapy

Human pluripotent stem cells (hPSCs) are currently used in clinical applications such as cardiac regenerative therapy, studying disease models, and drug screening for heart failure. Transplantation of hPSC-derived cardiomyocytes (hPSC-CMs) can be used as an alternative therapy for heart transplantation. In contrast to differentiated somatic cells, hPSCs possess unique metabolic programs to maintain pluripotency, and understanding their metabolic features can contribute to the development of technologies that can be useful for their clinical applications. The production of hPSC-CMs requires stepwise specification during embryonic development and metabolic regulation is crucial for proper embryonic development. These metabolic features have been applied to hPSC-CM production methods, such as mesoderm induction, specifications for cardiac progenitors, and their maturation. This review describes the metabolic programs in hPSCs and the metabolic regulation in hPSC-CM production for cardiac regenerative therapy.

Mechanisms regarding cardiac toxicity triggered by up-regulation of miR-144 in larval zebrafish upon exposure to triclosan

Although triclosan (TCS) is ubiquitously detected in environmental media and organisms, little information is available on its cardiotoxicity and underlying mechanisms. Herein, acute TCS exposure (0.69-1.73 μM) to zebrafish from embryos (6 hpf) to larvae (72 hpf) resulted in cardiac development defects, including increased angle between atrium and ventricle, prolonged SV-BA distance, linearized heart and pericardial cyst in 72-hpf larvae. These malformations resulted from interfered oxidative-stress pathways, reflecting in accumulated ROS and MDA and inhibited SOD and CAT activities. By RT-qPCR, the transcription levels of four cardiac development-related marker genes were significantly up-regulated except for gata4. Besides, miR-144 was identified as a regulatory molecule of TCS-induced cardiac defects by integrating analyses of artificial intervene expression and RNA-Seq data. Interestingly, the target genes of miR-144 were found and interacted with the above marker genes through constructing protein-protein interaction networks. After intervening the expression of miR-144 by microinjecting and activating Wnt pathway by an agonist BML-284, we confirmed that up-regulated miR-144 suppressed the expression of angiogenesis-related genes and negatively regulated Wnt pathway, further triggering angiogenesis disorders and cardiac phenotypic malformation. These findings unravel the underlying molecular mechanisms regarding TCS-induced cardiac development toxicity, and contribute to early warning and risk management of TCS.

The second heart field: the first 20 years

In 2001, three independent groups reported the identification of a novel cluster of progenitor cells that contribute to heart development in mouse and chicken embryos. This population of progenitor cells was designated as the second heart field (SHF), and a new research direction in heart development was launched. Twenty years have since passed and a comprehensive understanding of the SHF has been achieved. This review provides retrospective insights in to the contribution, the signaling regulatory networks and the epithelial properties of the SHF. It also includes the spatiotemporal characteristics of SHF development and interactions between the SHF and other types of cells during heart development. Although considerable efforts will be required to investigate the cellular heterogeneity of the SHF, together with its intricate regulatory networks and undefined mechanisms, it is expected that the burgeoning new technology of single-cell sequencing and precise lineage tracing will advance the comprehension of SHF function and its molecular signals. The advances in SHF research will translate to clinical applications and to the treatment of congenital heart diseases, especially conotruncal defects, as well as to regenerative medicine.

Identification of a Novel GRHL3/HOPX/Wnt/β-Catenin Proto-oncogenic Axis in Squamous Cell Carcinoma of the Esophagus

BACKGROUND & AIMS

Esophageal squamous cell carcinoma (ESCC) is an aggressive malignancy with a poor long-term prognosis. The molecular mechanisms underlying the initiation and progression of this tumor are largely unknown. The transcription factor GRHL3 functions as a potent tumor suppressor in SCC of skin, head, and neck. This study aims to determine whether GRHL3 also plays a role in the homeostasis of the esophageal epithelium and in the development of ESCC.

METHODS

The effects of Grhl3 deletion on squamous epithelial homeostasis in embryos and adult mice were examined using immunohistochemistry, transmission electron microscopy, and real-time polymerase chain reaction. The conditionally deleted mice were subsequently used to determine susceptibility to ESCC. Whole-transcriptome sequencing (RNA-seq) was performed on ESCC in wild-type and Grhl3 deleted animals. To decipher the signaling pathways, real-time polymerase chain reaction, immunohistochemistry, analysis of chromatin immunoprecipitation sequencing, chromatin immunoprecipitation-polymerase chain reaction, and RNA seq datasets were used. Primary human samples were used to validate the findings in the mouse model.

RESULTS

Loss of Grhl3 perturbs the proliferation-differentiation balance in the esophageal epithelium, thereby increasing the susceptibility to esophageal carcinogenesis in adult mice. Grhl3 imparts its tumor suppressor function by regulating the expression of HOPX. We have identified the Wnt/β-catenin pathway as the downstream effectors of GRHL3 and HOPX through our integrated approach using patient-derived ESCC samples and mouse models.

CONCLUSIONS

GRHL3 conveys its tumor suppressor function in ESCC through regulating its target gene HOPX, which limits Wnt/β-catenin signaling. Targeted therapies to inhibit this pathway could be a potential treatment strategy for ESCC patients with reduced GRHL3 expression.

Wif1 Mediates Coordination of Bone Morphogenetic Protein and Wnt Signaling in Neural and Glioma Stem Cells

Wnts, bone morphogenetic protein (BMP), and fibroblast growth factor (FGF) are paracrine signaling pathways implicated in the niche control of stem cell fate decisions. BMP-on and Wnt-off are the dominant quiescent niche signaling pathways in many cell types, including neural stem cells (NSCs). However, among the multiple inhibitory family members of the Wnt pathway, those with direct action after BMP4 stimulation in NSCs remain unclear. We examined 11 Wnt inhibitors in NSCs after BMP4 treatment. Wnt inhibitory factor 1 (Wif1) has been identified as the main factor reacting to BMP4 stimuli. RNA sequencing confirmed that Wif1 was markedly upregulated after BMP4 treatment in different gene expression analyses. Similar to the functional role of BMP4, Wif1 significantly decreased the cell cycle of NSCs and significantly inhibited cell proliferation (P < 0.05). Combined treatment with BMP4 and Wif1 significantly enhanced the inhibition of cell growth compared with the single treatment (P < 0.05). Wif1 expression was clearly lower in glioblastoma and low-grade glioma samples than in normal samples (P < 0.05). A functional analysis revealed that both BMP4 and Wif1 could decrease glioma cell growth. These effects were abrogated by the BMP inhibitor Noggin. The collective findings demonstrate that Wif1 plays a key role in quiescent NSC homeostasis and glioma cell growth downstream of BMP-on signaling. The functional roles of Wif1/BMP4 in glioma cells may provide a technical basis for regenerative medicine, drug discovery, and personal molecular therapy in future clinical treatments.

Cardiac Development in the Presence of Cadmium: An in Vitro Study Using Human Embryonic Stem Cells and Cardiac Organoids

BACKGROUND

Exposure to cadmium (Cd) is associated with cardiovascular diseases. Maternal Cd exposure is a significant risk factor for congenital heart disease. However, mechanisms of Cd on developmental cardiotoxicity are not well defined.

OBJECTIVES

We evaluated the effects of Cd on the different stages (mesoderm, cardiac induction, cardiac function) of cardiac development using an early embryo development in vitro model and two- or three-dimensional (2- or 3D) cardiomyocyte and cardiac organoid formation models mimicking early cardiac development.

METHODS

Embryonic stem cells (ESCs) form 3D aggregates, called embryoid bodies, that recapitulate events involved with early embryogenesis (e.g., germ layer formation). This model was used for early germ layer formation and signaling pathway identification. The 2D cardiomyocyte differentiation from the NKX2-5eGFP/w human ESCs model was used to explore the effects of Cd exposure on cardiomyocyte formation and to model mesoderm differentiation and cardiac induction, allowing us to explore different developmental windows of Cd toxicity. The 3D cardiac organoid model was used in evaluating the effects of Cd exposure on contractility and cardiac development.

RESULTS

Cd (0.6μM; 110 ppb) lowered the differentiation of embryoid bodies to mesoderm via suppression of Wnt/β-catenin-signaling pathways. During early mesoderm induction, the mesoderm-associated transcription factors MESP1 and EOMES showed a transient up-regulation, which decreased later in the cardiac induction stage. Cd (0.15μM) lowered mesoderm formation and cardiac induction through suppression of the transcription factors and mesoderm marker genes HAND1, SNAI2, HOPX, and the cardiac-specific genes NKX2-5, GATA4, troponin T, and alpha-actinin. In addition, Cd-induced histone modifications for both gene activation (H3K4me3) and repression (H3K27me3), which play vital roles in regulating mesoderm commitment markers. The effects of Cd inhibition on cardiomyocyte differentiation were confirmed in 3D cardiac organoids.

DISCUSSION

In conclusion, using a human ESC-derived 2D/3D in vitro differentiation model system and cardiac organoids, we demonstrated that low-dose Cd suppressed mesoderm formation through mesoderm gene histone modification, thus inhibiting cardiomyocyte differentiation and cardiac induction. The studies provide valuable insights into cellular events and molecular mechanisms associated with Cd-induced congenital heart disease. https://doi.org/10.1289/EHP11208.

Hedgehog signaling activates a mammalian heterochronic gene regulatory network controlling differentiation timing across lineages

Many developmental signaling pathways have been implicated in lineage-specific differentiation; however, mechanisms that explicitly control differentiation timing remain poorly defined in mammals. We report that murine Hedgehog signaling is a heterochronic pathway that determines the timing of progenitor differentiation. Hedgehog activity was necessary to prevent premature differentiation of second heart field (SHF) cardiac progenitors in mouse embryos, and the Hedgehog transcription factor GLI1 was sufficient to delay differentiation of cardiac progenitors in vitro. GLI1 directly activated a de novo progenitor-specific network in vitro, akin to that of SHF progenitors in vivo, which prevented the onset of the cardiac differentiation program. A Hedgehog signaling-dependent active-to-repressive GLI transition functioned as a differentiation timer, restricting the progenitor network to the SHF. GLI1 expression was associated with progenitor status across germ layers, and it delayed the differentiation of neural progenitors in vitro, suggesting a broad role for Hedgehog signaling as a heterochronic pathway.

Single Cell Sequencing Reveals Mechanisms of Persistent Truncus Arteriosus Formation after PDGFRα and PDGFRβ Double Knockout in Cardiac Neural Crest Cells

Persistent truncus arteriosus (PTA) is an uncommon and complex congenital cardiac malformation accounting for about 1.2% of all congenital heart diseases (CHDs), which is caused by a deficiency in the embryonic heart outflow tract’s (OFT) septation and remodeling. PDGFRα and PDGFRβ double knockout (DKO) in cardiac neural crest cells (CNCCs) has been reported to cause PTA, but the underlying mechanisms remain unclear. Here, we constructed a PTA mouse model with PDGFRα and PDGFRβ double knockout in Pax3+ CNCCs and described the condensation failure into OFT septum of CNCC-derived cells due to disturbance of cell polarity in the DKO group. In addition, we further explored the mechanism with single-cell RNA sequencing. We found that two main cell differentiation trajectories into vascular smooth muscle cells (VSMCs) from cardiomyocytes (CMs) and mesenchymal cells (MSs), respectively, were interrupted in the DKO group. The process of CM differentiation into VSMC stagnated in a transitional CM I-like state, which contributed to the failure of OFT remodeling and muscular septum formation. On the other hand, a Penk+ transitional MS II cluster closely related to cell condensation into the OFT septum disappeared, which led to the OFT’s septation absence directly. In conclusion, the disturbance of CNCC-derived cells caused by PDGFRα and PDGFRβ knockout can lead to the OFT septation disorder and the occurrence of PTA.

Dissecting mechanisms of chamber-specific cardiac differentiation and its perturbation following retinoic acid exposure

The specification of distinct cardiac lineages occurs before chamber formation and acquisition of bona fide atrial or ventricular identity. However, the mechanisms underlying these early specification events remain poorly understood. Here, we performed single cell analysis at the murine cardiac crescent, primitive heart tube and heart tube stages to uncover the transcriptional mechanisms underlying formation of atrial and ventricular cells. We find that progression towards differentiated cardiomyocytes occurs primarily based on heart field progenitor identity, and that progenitors contribute to ventricular or atrial identity through distinct differentiation mechanisms. We identify new candidate markers that define such differentiation processes and examine their expression dynamics using computational lineage trajectory methods. We further show that exposure to exogenous retinoic acid causes defects in ventricular chamber size, dysregulation in FGF signaling and a shunt in differentiation towards orthogonal lineages. Retinoic acid also causes defects in cell-cycle exit resulting in formation of hypomorphic ventricles. Collectively, our data identify, at a single cell level, distinct lineage trajectories during cardiac specification and differentiation, and the precise effects of manipulating cardiac progenitor patterning via retinoic acid signaling.

HOPX: A Unique Homeodomain Protein in Development and Tumor Suppression

Simple Summary

Homeobox (HOX) genes encode homeodomain proteins that regulate a wide range of molecular pathways. The homeodomain is highly conserved and binds to DNA. One exception is homeodomain-only protein (HOPX) that lacks DNA-binding capacity. HOPX plays a crucial role in development and its functional impairment is associated with a variety of diseases, including cancer. Loss of HOPX function occurs in a wide range of cancer types, where it functions as a tumor suppressor gene. Understanding the molecular mechanisms by which HOPX regulates carcinogenesis will likely lead to the development of new therapeutic approaches.

Abstract

Homeobox genes are master regulators of morphogenesis and differentiation by acting at the top of genetic hierarchies and their deregulation is associated with a variety of human diseases. They usually contain a highly conserved sequence that codes for the homeodomain of the protein, a specialized motif with three α helices and an N-terminal arm that aids in DNA binding. However, one homeodomain protein, HOPX, is unique among its family members in that it lacks the capacity to bind DNA and instead functions by interacting with transcriptional regulators. HOPX plays crucial roles in organogenesis and is expressed in both embryonic and adult stem cells. Loss of HOPX expression is common in cancer, where it functions primarily as a tumor suppressor gene. In this review, we describe the function of HOPX in development and discuss its role in carcinogenesis.

LncRNAs and their RBPs: How to influence the fate of stem cells?

Stem cells are distinctive cells that have self-renewal potential and unique ability to differentiate into multiple functional cells. Stem cell is a frontier field of life science research and has always been a hot spot in biomedical research. Recent studies have shown that long non-coding RNAs (lncRNAs) have irreplaceable roles in stem cell self-renewal and differentiation. LncRNAs play crucial roles in stem cells through a variety of regulatory mechanisms, including the recruitment of RNA-binding proteins (RBPs) to affect the stability of their mRNAs or the expression of downstream genes. RBPs interact with different RNAs to regulate gene expression at transcriptional and post-transcriptional levels and play important roles in determining the fate of stem cells. In this review, the functions of lncRNAs and their RBPs in self-renewal and differentiation of stem cell are summarized. We focus on the four regulatory mechanisms by which lncRNAs and their RBPs are involved in epigenetic regulation, signaling pathway regulation, splicing, mRNA stability and subcellular localization and further discuss other noncoding RNAs (ncRNAs) and their RBPs in the fate of stem cells. This work provides a more comprehensive understanding of the roles of lncRNAs in determining the fate of stem cells, and a further understanding of their regulatory mechanisms will provide a theoretical basis for the development of clinical regenerative medicine.

The cortical hem lacks stem cell potential despite expressing SOX9 and HOPX

The adult dentate gyrus (DG) of rodents hosts a neural stem cell (NSC) niche capable of generating new neurons throughout life. The embryonic origin and molecular mechanisms underlying formation of DG NSCs are still being investigated. We performed a bulk transcriptomic analysis on mouse developing archicortex conditionally deleted for Sox9, a SoxE transcription factor controlling both gliogenesis and NSC formation, and identified Hopx, a recently identified marker of both prospective adult DG NSCs and astrocytic progenitors, as being downregulated. We confirm SOX9 is required for HOPX expression in the embryonic archicortex. In particular, we found that both NSC markers are highly expressed in the cortical hem (CH), while only weakly in the adjacent dentate neuroepithelium (DNE), suggesting a potential CH embryonic origin for DG NSCs. However, we demonstrate both in vitro and in vivo that the embryonic CH, as well as its adult derivatives, lacks stem cell potential. Instead, deletion of Sox9 in the DNE affects both HOPX expression and NSC formation in the adult DG. We conclude that HOPX expression in the CH is involved in astrocytic differentiation downstream of SOX9, which we previously showed regulates DG development by inducing formation of a CH-derived astrocytic scaffold. Altogether, these results suggest that both proteins work in a dose-dependent manner to drive either astrocytic differentiation in CH or NSC formation in DNE.

Landscape of Hopx expression in cells of the immune system

Homeodomain only protein (Hopx) is a regulator of cell differentiation and function, and it has also emerged as a crucial marker of specific developmental and differentiation potentials. Hopx expression and functions have been identified in some stem cells, tumors, and in certain immune cells. However, expression of Hopx in immune cells remains insufficiently characterized. Here we report a comprehensive pattern of Hopx expression in multiple types of immune cells under steady state conditions. By utilizing single-cell RNA sequencing (scRNA-seq) and flow cytometric analysis, we characterize a constitutive expression of Hopx in specific subsets of CD4⁺ and CD8⁺ T cells and B cells, as well as natural killer (NK), NKT, and myeloid cells. In contrast, Hopx expression is not present in conventional dendritic cells and eosinophils. The utility of identifying expression of Hopx in immune cells may prove vital in delineating specific roles of Hopx under multiple immune conditions.

Physiologic biomechanics enhance reproducible contractile development in a stem cell derived cardiac muscle platform

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) allow investigations in a human cardiac model system, but disorganized mechanics and immaturity of hPSC-CMs on standard two-dimensional surfaces have been hurdles. Here, we developed a platform of micron-scale cardiac muscle bundles to control biomechanics in arrays of thousands of purified, independently contracting cardiac muscle strips on two-dimensional elastomer substrates with far greater throughput than single cell methods. By defining geometry and workload in this reductionist platform, we show that myofibrillar alignment and auxotonic contractions at physiologic workload drive maturation of contractile function, calcium handling, and electrophysiology. Using transcriptomics, reporter hPSC-CMs, and quantitative immunofluorescence, these cardiac muscle bundles can be used to parse orthogonal cues in early development, including contractile force, calcium load, and metabolic signals. Additionally, the resultant organized biomechanics facilitates automated extraction of contractile kinetics from brightfield microscopy imaging, increasing the accessibility, reproducibility, and throughput of pharmacologic testing and cardiomyopathy disease modeling.

Investigations of human cardiac disease involving human pluripotent stem cell-derived cardiomyocytes are limited by the disorganized presentation of biomechanical cues resulting in cell immaturity. Here the authors develop a platform of micron-scale 2D cardiac muscle bundles to precisely deliver physiologic cues, improving reproducibility and throughput.

Heart organoids and tissue models for modeling development and disease

Organoids, or miniaturized organs formed in vitro, hold potential to revolutionize how researchers approach and answer fundamental biological and pathological questions. In the context of cardiac biology, development of a bona fide cardiac organoid enables study of heart development, function, and pathogenesis in a dish, providing insight into the nature of congenital heart disease and offering the opportunity for high-throughput probing of adult heart disease and drug discovery. Recently, multiple groups have reported novel methods for generating in vitro models of the heart; however, there are substantial conceptual and methodological differences. In this review we will evaluate recent cardiac organoid studies through the lens of the core principles of organoid technology: patterned self-organization of multiple cell types resembling the in vivo organ. Based on this, we will classify systems into the following related types of tissues: developmental cardiac organoids, chamber cardiac organoids, microtissues, and engineered heart tissues. Furthermore, we highlight the interventions which allow for organoid formation, such as modulation of highly conserved cardiogenic signaling pathways mediated by developmental morphogens. We expect that consolidation and categorization of existing organoid models will help eliminate confusion in the field and facilitate progress towards creation of an ideal cardiac organoid.

Control of cardiomyocyte differentiation timing by intercellular signaling pathways

Congenital Heart Disease (CHD), malformations of the heart present at birth, is the most common class of life-threatening birth defect (Hoffman (1995) [1], Gelb (2004) [2], Gelb (2014) [3]). A major research challenge is to elucidate the genetic determinants of CHD and mechanistically link CHD ontogeny to a molecular understanding of heart development. Although the embryonic origins of CHD are unclear in most cases, dysregulation of cardiovascular lineage specification, patterning, proliferation, migration or differentiation have been described (Olson (2004) [4], Olson (2006) [5], Srivastava (2006) [6], Dunwoodie (2007) [7], Bruneau (2008) [8]). Cardiac differentiation is the process whereby cells become progressively more dedicated in a trajectory through the cardiac lineage towards mature cardiomyocytes. Defects in cardiac differentiation have been linked to CHD, although how the complex control of cardiac differentiation prevents CHD is just beginning to be understood. The stages of cardiac differentiation are highly stereotyped and have been well-characterized (Kattman et al. (2011) [9], Wamstad et al. (2012) [10], Luna-Zurita et al. (2016) [11], Loh et al. (2016) [12], DeLaughter et al. (2016) [13]); however, the developmental and molecular mechanisms that promote or delay the transition of a cell through these stages have not been as deeply investigated. Tight temporal control of progenitor differentiation is critically important for normal organ size, spatial organization, and cellular physiology and homeostasis of all organ systems (Raff et al. (1985) [14], Amthor et al. (1998) [15], Kopan et al. (2014) [16]). This review will focus on the action of signaling pathways in the control of cardiomyocyte differentiation timing. Numerous signaling pathways, including the Wnt, Fibroblast Growth Factor, Hedgehog, Bone Morphogenetic Protein, Insulin-like Growth Factor, Thyroid Hormone and Hippo pathways, have all been implicated in promoting or inhibiting transitions along the cardiac differentiation trajectory. Gaining a deeper understanding of the mechanisms controlling cardiac differentiation timing promises to yield insights into the etiology of CHD and to inform approaches to restore function to damaged hearts.

Cardiac toxicity assessment of pendimethalin in zebrafish embryos

Pendimethalin (PND) is one of the best sellers of selective herbicide in the world and has been frequently detected in the water. However, little is known about its effects on cardiac development. In this study, we used zebrafish to investigate the developmental and cardiac toxicity of PND. We exposed the zebrafish embryos with a serial of concentrations at 3, 4, and 5 mg/L at 5.5-72 h post-fertilization (hpf). We found that PND exposure can reduce the heart rate, survival rate, and body length of zebrafish embryos. Furthermore, we identified many malformations including pericardial and yolk sac edema, spinal deformity, and cardiac looping abnormality. In addition, PND increased the expression of reactive oxygen species and malondialdehyde and reduced the activity of superoxide dismutase (Antioxidant enzymes); We examined the expression of cardiac development-related genes and the apoptosis markers, and found changes of the following marker: vmhc, nppa, tbx5a, nkx2.5, gata4, tbx2b and FoxO1, bax, bcl-2, p53, casp-9, casp-3. Our data showed that activation of Wnt pathway can rescue the cardiac abnormalities caused by PND. Our results provided new evidence for the toxicity of PND and suggested that the PND residual should be treated as a hazard in the environment.

Ectopic expression of Id1 or Id3 inhibits transcription of the GATA-4 gene in P19CL6 cells under differentiation condition

Inhibitor of DNA binding (Id) is a dominant negative form of the E-box binding basic-helix-loop-helix (bHLH) transcription factor since it is devoid of the basic region required for DNA binding and forms an inactive hetero dimer with bHLH proteins. The E-box sequence located in the promoter region of the GATA-binding protein 4 (GATA-4) gene is essential for transcriptional activation in P19CL6 cells. These cells differentiate into cardiomyocytes and start to express GATA-4, which further triggers cardiac-specific gene expression. In this study, expression plasmids for Ids tagged with human influenza hemagglutinin (HA)-FLAG were constructed and introduced into P19CL6 cells. The stable clones expressing the recombinant Id proteins (Id1 or Id3) were isolated. The GATA-4 gene expression in these clones under differentiation condition in the presence of 1% dimethyl sulfoxide (DMSO) was repressed, with concomitant abolishment of the transcription of α-myosin heavy chain (α-MHC), which is a component of cardiac myofibrils. Thus, the increased expression of Id protein could affect GATA-4 gene expression and negatively regulate the differentiation of P19CL6 cells.

Lenvatinib exposure induces hepatotoxicity in zebrafish via inhibiting Wnt signaling

Lenvatinib is a multi-kinase inhibitor for widely treating thyroid cancer. However, little studies have been done about it or its toxicity on embryonic development of vertebrate. In this study, we used zebrafish to assess the effect of lenvatinib on early embryonic development. Exposure of zebrafish embryos to 58, 117, 176 nM lenvatinib induced abnormal embryonic development, such as decreased heart rate, pericardial edema, delayed yolk absorption, and bladder atrophy. Lenvatinib exposure reduced liver area and down-regulated liver developmental related genes. The proliferation of hepatocytes and the expression of apoptosis-related genes were significantly reduced.by Lenvatinib. Furthermore, the imbalance of liver metabolism and abnormal liver tissue structure were observed in adult zebrafish after Lenvatinib exposure. Oxidative stress was up-regulated by lenvatinib and astaxanthin partially rescued hepatic developmental defects via downregulating oxidative stress. After lenvatinib exposure, Wnt signaling was down-regulated, and activation of Wnt signaling partially rescued hepatic developmental defects. Therefore, these results suggested that lenvatinib might induce zebrafish hepatotoxicity by down-regulating Wnt signaling related genes and inducing oxidative stress. This study provides a reference for the potential hepatotoxicity of lenvatinib during embryonic development and raises health concern about the potential harm of exposure to lenvatinib for foetuses.

HOPX Exhibits Oncogenic Activity during Squamous Skin Carcinogenesis

Cutaneous squamous cell carcinomas (SCCs) are frequent heterogeneous tumors arising from sun-exposed regions of the skin and characterized by complex pathogenesis. HOPX is a member of the homeodomain-containing superfamily of proteins holding an atypical homeodomain unable to bind to DNA. First discovered in the heart as a regulator of cardiac development, in the skin, HOPX modulates the terminal differentiation of keratinocytes. There is a particular interest in studying HOPX in squamous skin carcinogenesis because it has the atypical structure and the functional duality as an oncogene and a tumor suppressor gene, reported in different malignancies. In this study, we analyzed the effects of HOPX knockdown and overexpression on SCC tumorigenicity in vitro and in vivo. Our data show that HOPX knockdown in SCC cells inhibits their proliferative and invasive activity through the acceleration of apoptosis. We established that methylation of two alternative HOPX promoters leads to differential expression of HOPX transcripts in normal keratinocytes and SCC cells. Importantly, we report that HOPX acts as an oncogene in the pathogenesis of SCC probably through the activation of the second alternative promoter and the modulation of apoptosis.

Understanding Heart Field Progenitor Cells for Modeling Congenital Heart Diseases

PURPOSE OF REVIEW

Heart development is a meticulously coordinated process that involves the specification of two distinct populations of cardiac progenitor cells, namely the first and the second heart field. Disruption of heart field progenitors can result in congenital heart defects. In this review, we aim to describe the signaling pathways and transcription factors that link heart field development and congenital heart disease.

RECENT FINDINGS

Single-cell transcriptomics, lineage-tracing mouse models, and stem cell-based in vitro modeling of cardiogenesis have significantly improved the spatiotemporal characterization of cardiac progenitors. Additionally, novel functional genomic studies have now linked more genetic variants with congenital heart disease. Dysregulation of cardiac progenitor cells causes malformations that can be lethal. Ongoing research will continue to shed light on cardiac morphogenesis and help us better understand and treat patients with congenital heart disease.

The Role of Epigenetics in Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect among newborns worldwide and contributes to significant infant morbidity and mortality. Owing to major advances in medical and surgical management, as well as improved prenatal diagnosis, the outcomes for these children with CHD have improved tremendously so much so that there are now more adults living with CHD than children. Advances in genomic technologies have discovered the genetic causes of a significant fraction of CHD, while at the same time pointing to remarkable complexity in CHD genetics. For this reason, the complex process of cardiogenesis, which is governed by multiple interlinked and dose-dependent pathways, is a well investigated process. In addition to the sequence of the genome, the contribution of epigenetics to cardiogenesis is increasingly recognized. Significant progress has been made dissecting the epigenome of the heart and identified associations with cardiovascular diseases. The role of epigenetic regulation in cardiac development/cardiogenesis, using tissue and animal models, has been well reviewed. Here, we curate the current literature based on studies in humans, which have revealed associated and/or causative epigenetic factors implicated in CHD. We sought to summarize the current knowledge on the functional role of epigenetics in cardiogenesis as well as in distinct CHDs, with an aim to provide scientists and clinicians an overview of the abnormal cardiogenic pathways affected by epigenetic mechanisms, for a better understanding of their impact on the developing fetal heart, particularly for readers interested in CHD research.

Cardiac Development: A Glimpse on Its Translational Contributions

Cardiac development is a complex developmental process that is initiated soon after gastrulation, as two sets of precardiac mesodermal precursors are symmetrically located and subsequently fused at the embryonic midline forming the cardiac straight tube. Thereafter, the cardiac straight tube invariably bends to the right, configuring the first sign of morphological left–right asymmetry and soon thereafter the atrial and ventricular chambers are formed, expanded and progressively septated. As a consequence of all these morphogenetic processes, the fetal heart acquired a four-chambered structure having distinct inlet and outlet connections and a specialized conduction system capable of directing the electrical impulse within the fully formed heart. Over the last decades, our understanding of the morphogenetic, cellular, and molecular pathways involved in cardiac development has exponentially grown. Multiples aspects of the initial discoveries during heart formation has served as guiding tools to understand the etiology of cardiac congenital anomalies and adult cardiac pathology, as well as to enlighten novels approaches to heal the damaged heart. In this review we provide an overview of the complex cellular and molecular pathways driving heart morphogenesis and how those discoveries have provided new roads into the genetic, clinical and therapeutic management of the diseased hearts.

The role of HOPX in normal tissues and tumor progression

The homeodomain-only protein homeobox (HOPX) as the smallest homeodomain protein, lacks certain conserved residues required for DNA binding. Through our literature search, we reviewed the current understandings of HOPX in normal tissues and tumor progression. HOPX was initially identified as a critical transcription factor in various normal tissues, which interacted with serum response factor (SRF) or other substance to regulate normal physiological function. However, HOPX is at a low expression or methylation level in tumors. These data indicated that HOPX may play a very important role in regulating differentiation phenotype and tumor suppressive function. We predicted the prognosis of HOPX in tumors from TCGA database and discussed the downstream genes of HOPX. To understand how HOPX is involved in the mechanisms between physical and pathological conditions could lead to novel therapeutic strategies for treatment.

Design of synthetic microenvironments to promote the maturation of human pluripotent stem cell derived cardiomyocytes

Cardiomyocyte like cells derived from human pluripotent stem cells (hPSC-CMs) have a good application perspective in many fields such as disease modeling, drug screening and clinical treatment. However, these are severely hampered by the fact that hPSC-CMs are immature compared to adult human cardiomyocytes. Therefore, many approaches such as genetic manipulation, biochemical factors supplement, mechanical stress, electrical stimulation and three-dimensional culture have been developed to promote the maturation of hPSC-CMs. Recently, establishing in vitro synthetic artificial microenvironments based on the in vivo development program of cardiomyocytes has achieved much attention due to their inherent properties such as stiffness, plasticity, nanotopography and chemical functionality. In this review, the achievements and deficiency of reported synthetic microenvironments that mainly discussed comprehensive biological, chemical, and physical factors, as well as three-dimensional culture were mainly discussed, which have significance to improve the microenvironment design and accelerate the maturation of hPSC-CMs.

Single-cell analysis of developing and azoospermia human testicles reveals central role of Sertoli cells

Clinical efficacy of treatments against non-obstructive azoospermia (NOA), which affects 1% of men, are currently limited by the incomplete understanding of NOA pathogenesis and normal spermatogenic microenvironment. Here, we profile >80,000 human testicular single-cell transcriptomes from 10 healthy donors spanning the range from infant to adult and 7 NOA patients. We show that Sertoli cells, which form the scaffold in the testicular microenvironment, are severely damaged in NOA patients and identify the roadmap of Sertoli cell maturation. Notably, Sertoli cells of patients with congenital causes (Klinefelter syndrome and Y chromosome microdeletions) are mature, but exhibit abnormal immune responses, while the cells in idiopathic NOA (iNOA) are physiologically immature. Furthermore, we find that inhibition of Wnt signaling promotes the maturation of Sertoli cells from iNOA patients, allowing these cells to regain their ability to support germ cell survival. We provide a novel perspective on the development of diagnostic methods and therapeutic targets for NOA.

Non-obstructive azoospermia affects 1% of men. Here, authors perform single-cell transcriptomic analysis of human testicular cells from healthy donors and non-obstructive azoospermia patients and find that inhibition of Wnt signaling promotes the maturation of Sertoli cells from patients.

Single-Cell Transcriptomics of Engineered Cardiac Tissues From Patient-Specific Induced Pluripotent Stem Cell-Derived Cardiomyocytes Reveals Abnormal Developmental Trajectory and Intrinsic Contractile Defects in Hypoplastic Right Heart Syndrome

Background

To understand the intrinsic cardiac developmental and functional abnormalities in pulmonary atresia with intact ventricular septum (PAIVS) free from effects secondary to anatomic defects, we performed and compared single‐cell transcriptomic and phenotypic analyses of patient‐ and healthy subject–derived human‐induced pluripotent stem cell–derived cardiomyocytes (hiPSC‐CMs) and engineered tissue models.

Methods and Results

We derived hiPSC lines from 3 patients with PAIVS and 3 healthy subjects and differentiated them into hiPSC‐CMs, which were then bioengineered into the human cardiac anisotropic sheet and human cardiac tissue strip custom‐designed for electrophysiological and contractile assessments, respectively. Single‐cell RNA sequencing (scRNA‐seq) of hiPSC‐CMs, human cardiac anisotropic sheet, and human cardiac tissue strip was performed to examine the transcriptomic basis for any phenotypic abnormalities using pseudotime and differential expression analyses. Through pseudotime analysis, we demonstrated that bioengineered tissue constructs provide pro‐maturational cues to hiPSC‐CMs, although the maturation and development were attenuated in PAIVS hiPSC‐CMs. Furthermore, reduced contractility and prolonged contractile kinetics were observed with PAIVS human cardiac tissue strips. Consistently, single‐cell RNA sequencing of PAIVS human cardiac tissue strips and hiPSC‐CMs exhibited diminished expression of cardiac contractile apparatus genes. By contrast, electrophysiological aberrancies were absent in PAIVS human cardiac anisotropic sheets.

Conclusions

Our findings were the first to reveal intrinsic abnormalities of cardiomyocyte development and function in PAIVS free from secondary effects. We conclude that hiPSC‐derived engineered tissues offer a unique method for studying primary cardiac abnormalities and uncovering pathogenic mechanisms that underlie sporadic congenital heart diseases.

HOPX regulates bone marrow-derived mesenchymal stromal cell fate determination via suppression of adipogenic gene pathways

Previous studies of global binding patterns identified the epigenetic factor, EZH2, as a regulator of the homeodomain-only protein homeobox (HOPX) gene expression during bone marrow stromal cell (BMSC) differentiation, suggesting a potential role for HOPX in regulating BMSC lineage specification. In the present study, we confirmed that EZH2 direct binds to the HOPX promoter region, during normal growth and osteogenic differentiation but not under adipogenic inductive conditions. HOPX gene knockdown and overexpression studies demonstrated that HOPX is a promoter of BMSC proliferation and an inhibitor of adipogenesis. However, functional studies failed to observe any affect by HOPX on BMSC osteogenic differentiation. RNA-seq analysis of HOPX overexpressing BMSC during adipogenesis, found HOPX function to be acting through suppression of adipogenic pathways associated genes such as ADIPOQ, FABP4, PLIN1 and PLIN4. These findings suggest that HOPX gene target pathways are critical factors in the regulation of fat metabolism.

Single-Cell Transcriptome Analysis Maps the Developmental Track of the Human Heart

The heart is the central organ of the circulatory system, and its proper development is vital for maintaining human life. Here, we used single-cell RNA sequencing to profile the gene expression landscapes of ∼4,000 cardiac cells from human embryos and identified four major types of cells: cardiomyocytes (CMs), cardiac fibroblasts, endothelial cells (ECs), and valvar interstitial cells (VICs). Atrial and ventricular CMs acquired distinct features early in heart development. Furthermore, both CMs and fibroblasts show stepwise changes in gene expression. As development proceeds, VICs may be involved in the remodeling phase, and ECs display location-specific characteristics. Finally, we compared gene expression profiles between humans and mice and identified a series of unique features of human heart development. Our study lays the groundwork for elucidating the mechanisms of in vivo human cardiac development and provides potential clues to understand cardiac regeneration.