Stromal Cell-SLIT3/Cardiomyocyte-ROBO1 Axis Regulates Pressure Overload-Induced Cardiac Hypertrophy.

BACKGROUND: Recently shown to regulate cardiac development, the secreted axon guidance molecule SLIT3 maintains its expression in the postnatal heart. Despite its known expression in the cardiovascular system after birth, SLIT3's relevance to cardiovascular function in the postnatal state remains unknown. As such, the objectives of this study were to determine the postnatal myocardial sources of SLIT3 and to evaluate its functional role in regulating the cardiac response to pressure overload stress. METHODS: We performed in vitro studies on cardiomyocytes and myocardial tissue samples from patients and performed in vivo investigation with SLIT3 and ROBO1 (roundabout homolog 1) mutant mice undergoing transverse aortic constriction to establish the role of SLIT3-ROBO1 in adverse cardiac remodeling. RESULTS: We first found that SLIT3 transcription was increased in myocardial tissue obtained from patients with congenital heart defects that caused ventricular pressure overload. Immunostaining of hearts from WT (wild-type) and reporter mice revealed that SLIT3 is secreted by cardiac stromal cells, namely fibroblasts and vascular mural cells, within the heart. Conditioned media from cardiac fibroblasts and vascular mural cells both stimulated cardiomyocyte hypertrophy in vitro, an effect that was partially inhibited by an anti-SLIT3 antibody. Also, the N-terminal, but not the C-terminal, fragment of SLIT3 and the forced overexpression of SLIT3 stimulated cardiomyocyte hypertrophy and the transcription of hypertrophy-related genes. We next determined that ROBO1 was the most highly expressed roundabout receptor in cardiomyocytes and that ROBO1 mediated SLIT3's hypertrophic effects in vitro. In vivo, Tcf21+ fibroblast and Tbx18+ vascular mural cell-specific knockout of SLIT3 in mice resulted in decreased left ventricular hypertrophy and cardiac fibrosis after transverse aortic constriction. Furthermore, α-MHC+ cardiomyocyte-specific deletion of ROBO1 also preserved left ventricular function and abrogated hypertrophy, but not fibrosis, after transverse aortic constriction. CONCLUSIONS: Collectively, these results indicate a novel role for the SLIT3-ROBO1-signaling axis in regulating postnatal cardiomyocyte hypertrophy induced by pressure overload.

Mapping Chromatin Occupancy of Ppp1r1b-lncRNA Genome-Wide Using Chromatin Isolation by RNA Purification (ChIRP)-seq.

Long non-coding RNA (lncRNA) mediated transcriptional regulation is increasingly recognized as an important gene regulatory mechanism during development and disease. LncRNAs are emerging as critical regulators of chromatin state; yet the nature and the extent of their interactions with chromatin remain to be fully revealed. We have previously identified Ppp1r1b-lncRNA as an essential epigenetic regulator of myogenic differentiation in cardiac and skeletal myocytes in mice and humans. We further demonstrated that Ppp1r1b-lncRNA function is mediated by the interaction with the chromatin-modifying complex polycomb repressive complex 2 (PRC2) at the promoter of myogenic differentiation transcription factors, TBX5 and MyoD1. Herein, we employed unbiased chromatin isolation by RNA purification (ChIRP) and high throughput sequencing to map the repertoire of Ppp1r1b-lncRNA chromatin occupancy genome-wide in the mouse muscle myoblast cell line. We uncovered a total of 99732 true peaks corresponding to Ppp1r1b-lncRNA binding sites at high confidence (p-value < 1E-5) and enrichment score ≥ 10). The Ppp1r1b-lncRNA-binding sites averaged 558 bp in length and were distributed widely within the coding and non-coding regions of the genome. Approximately 46% of these true peaks were mapped to gene elements, of which 1180 were mapped to experimentally validated promoter sequences. Importantly, the promoter-mapped binding sites were enriched in myogenic transcription factors and heart development while exhibiting focal interactions with known motifs of proximal promoters and transcription initiation by RNA Pol-II, including TATA-box, transcription initiator motif, CCAAT-box, and GC-box, supporting Ppp1r1b-lncRNA role in transcription initiation of myogenic regulators. Remarkably, nearly 40% of Ppp1r1b-lncRNA-binding sites mapped to gene introns were enriched with the Homeobox family of transcription factors and exhibited TA-rich motif sequences, suggesting potential motif-specific Ppp1r1b-lncRNA-bound introns. Lastly, more than 136521 enhancer sequences were detected in Ppp1r1b-lncRNA-occupancy sites at high confidence. Among these enhancers, 3390 (12%) exhibited cell type/tissue-specific enrichment in fetal heart and muscles. Together, our findings provide further insights into the genome-wide Ppp1r1b-lncRNA: Chromatin interactome that may dictate its function in myogenic differentiation and potentially other cellular and biological processes.

Mapping Chromatin Occupancy of Ppp1r1b-lncRNA Genome-Wide Using Chromatin Isolation by RNA Purification (ChIRP)-seq.

Long non-coding RNA (lncRNA) mediated transcriptional regulation is increasingly recognized as an important gene regulatory mechanism during development and disease. LncRNAs are emerging as critical regulators of chromatin state; yet the nature and the extent of their interactions with chromatin remain to be fully revealed. We have previously identified Ppp1r1b-lncRNA as an essential epigenetic regulator of myogenic differentiation in cardiac and skeletal myocytes in mice and humans. We further demonstrated that Ppp1r1b-lncRNA function is mediated by the interaction with the chromatin-modifying complex polycomb repressive complex 2 (PRC2) at the promoter of myogenic differentiation transcription factors, TBX5 and MyoD1. Herein, we employed an unbiased chromatin isolation by RNA purification (ChIRP) and high throughput sequencing to map the repertoire of Ppp1r1b-lncRNA chromatin occupancy genome-wide in the mouse muscle myoblast cell line. We uncovered a total of 99732 true peaks corresponding to Ppp1r1b-lncRNA binding sites at high confidence (P-value < 1e-5 and enrichment score ≥ 10). The Ppp1r1b-lncRNA-binding sites averaged 558 bp in length and were distributed widely within the coding and non-coding regions of the genome. Approximately 46% of these true peaks were mapped to gene elements, of which 1180 were mapped to experimentally validated promoter sequences. Importantly, the promoter-mapped binding sites were enriched in myogenic transcription factors and heart development while exhibiting focal interactions with known motifs of proximal promoters and transcription initiation by RNA polII, including TATA, transcription initiator, CCAAT-box, and GC-box, supporting Ppp1r1b-lncRNA role in transcription initiation of myogenic regulators. Remarkably, nearly 40% of Ppp1r1b-lncRNA-binding sites mapped to gene introns, were enriched with the Homeobox family of transcription factors, and exhibited TA-rich motif sequences, suggesting potential motif specific Ppp1r1b-lncRNA-bound introns. Lastly, more than 136521enhancer sequences were detected in Ppp1r1b-lncRNA-occupancy sites at high confidence. Among these enhancers,12% exhibited cell type/tissue-specific enrichment in fetal heart and muscles. Together, our findings provide further insights into the genome-wide Ppp1r1b-lncRNA: Chromatin interactome that may potentially dictate its function in myogenic differentiation and potentially other cellular and biological processes.

Whole-Exome Sequencing Identifies Homozygote Nonsense Variants in LMOD2 Gene Causing Infantile Dilated Cardiomyopathy.

As an essential component of the sarcomere, actin thin filament stems from the Z-disk extend toward the middle of the sarcomere and overlaps with myosin thick filaments. Elongation of the cardiac thin filament is essential for normal sarcomere maturation and heart function. This process is regulated by the actin-binding proteins Leiomodins (LMODs), among which LMOD2 has recently been identified as a key regulator of thin filament elongation to reach a mature length. Few reports have implicated homozygous loss of function variants of LMOD2 in neonatal dilated cardiomyopathy (DCM) associated with thin filament shortening. We present the fifth case of DCM due to biallelic variants in the LMOD2 gene and the second case with the c.1193G>A (p.W398*) nonsense variant identified by whole-exome sequencing. The proband is a 4-month male infant of Hispanic descent with advanced heart failure. Consistent with previous reports, a myocardial biopsy exhibited remarkably short thin filaments. However, compared to other cases of identical or similar biallelic variants, the patient presented here has an unusually late onset of cardiomyopathy during infancy. Herein, we present the phenotypic and histological features of this variant, confirm the pathogenic impact on protein expression and sarcomere structure, and discuss the current knowledge of LMOD2-related cardiomyopathy.

Post-Transcriptional Modification by Alternative Splicing and Pathogenic Splicing Variants in Cardiovascular Development and Congenital Heart Defects.

Advancements in genomics, bioinformatics, and genome editing have uncovered new dimensions in gene regulation. Post-transcriptional modifications by the alternative splicing of mRNA transcripts are critical regulatory mechanisms of mammalian gene expression. In the heart, there is an expanding interest in elucidating the role of alternative splicing in transcriptome regulation. Substantial efforts were directed toward investigating this process in heart development and failure. However, few studies shed light on alternative splicing products and their dysregulation in congenital heart defects (CHDs). While elegant reports showed the crucial roles of RNA binding proteins (RBPs) in orchestrating splicing transitions during heart development and failure, the impact of RBPs dysregulation or genetic variation on CHDs has not been fully addressed. Herein, we review the current understanding of alternative splicing and RBPs' roles in heart development and CHDs. Wediscuss the impact of perinatal splicing transition and its dysregulation in CHDs. We further summarize the discoveries made of causal splicing variants in key transcription factors that are implicated in CHDs. An improved understanding of the roles of alternative splicing in heart development and CHDs may potentially inform novel preventive and therapeutic advancements for newborn infants with CHDs.

A novel murine model of atrial fibrillation by diphtheria toxin-induced injury.

The treatment of atrial fibrillation (AF) continues to be a significant clinical challenge. While genome-wide association studies (GWAS) are beginning to identify AF susceptibility genes (Gudbjartsson et al., Nature, 2007, 448, 353-357; Choi et al., Circ. Res., 2020, 126, 200-209; van Ouwerkerk et al., Circ. Res., 2022, 127, 229-243), non-genetic risk factors including physical, chemical, and biological environments remain the major contributors to the development of AF. However, little is known regarding how non-genetic risk factors promote the pathogenesis of AF (Weiss et al., Heart Rhythm, 2016, 13, 1868-1877; Chakraborty et al., Heart Rhythm, 2020, 17, 1,398-1,404; Nattel et al., Circ. Res., 2020, 127, 51-72). This is, in part, due to the lack of a robust and reliable animal model induced by non-genetic factors. The currently available models using rapid pacing protocols fail to generate a stable AF phenotype in rodent models, often requiring additional genetic modifications that introduce potential sources of bias (Schüttler et al., Circ. Res., 2020, 127, 91-110). Here, we report a novel murine model of AF using an inducible and tissue-specific activation of diphtheria toxin (DT)-mediated cellular injury system. By the tissue-specific and inducible expression of human HB-EGF in atrial myocytes, we developed a reliable, robust and scalable murine model of AF that is triggered by a non-genetic inducer without the need for AF susceptibility gene mutations.

Recessive ciliopathy mutations in primary endocardial fibroelastosis: a rare neonatal cardiomyopathy in a case of Alstrom syndrome.

Among neonatal cardiomyopathies, primary endocardial fibroelastosis (pEFE) remains a mysterious disease of the endomyocardium that is poorly genetically characterized, affecting 1/5000 live births and accounting for 25% of the entire pediatric dilated cardiomyopathy (DCM) with a devastating course and grave prognosis. To investigate the potential genetic contribution to pEFE, we performed integrative genomic analysis, using whole exome sequencing (WES) and RNA-seq in a female infant with confirmed pathological diagnosis of pEFE. Within regions of homozygosity in the proband genome, WES analysis revealed novel parent-transmitted homozygous mutations affecting three genes with known roles in cilia assembly or function. Among them, a novel homozygous variant [c.1943delA] of uncertain significance in ALMS1 was prioritized for functional genomic and mechanistic analysis. Loss of function mutations of ALMS1 have been implicated in Alstrom syndrome (AS) [OMIM 203800], a rare recessive ciliopathy that has been associated with cardiomyopathy. The variant of interest results in a frameshift introducing a premature stop codon. RNA-seq of the proband's dermal fibroblasts confirmed the impact of the novel ALMS1 variant on RNA-seq reads and revealed dysregulated cellular signaling and function, including the induction of epithelial mesenchymal transition (EMT) and activation of TGFß signaling. ALMS1 loss enhanced cellular migration in patient fibroblasts as well as neonatal cardiac fibroblasts, while ALMS1-depleted cardiomyocytes exhibited enhanced proliferation activity. Herein, we present the unique pathological features of pEFE compared to DCM and utilize integrated genomic analysis to elucidate the molecular impact of a novel mutation in ALMS1 gene in an AS case. Our report provides insights into pEFE etiology and suggests, for the first time to our knowledge, ciliopathy as a potential underlying mechanism for this poorly understood and incurable form of neonatal cardiomyopathy. KEY MESSAGE: Primary endocardial fibroelastosis (pEFE) is a rare form of neonatal cardiomyopathy that occurs in 1/5000 live births with significant consequences but unknown etiology. Integrated genomics analysis (whole exome sequencing and RNA sequencing) elucidates novel genetic contribution to pEFE etiology. In this case, the cardiac manifestation in Alstrom syndrome is pEFE. To our knowledge, this report provides the first evidence linking ciliopathy to pEFE etiology. Infants with pEFE should be examined for syndromic features of Alstrom syndrome. Our findings lead to a better understanding of the molecular mechanisms of pEFE, paving the way to potential diagnostic and therapeutic applications.

Case Report: Whole Exome Sequencing Identifies Compound Heterozygous Variants in TSFM Gene Causing Juvenile Hypertrophic Cardiomyopathy.

We report a case of hypertrophic cardiomyopathy and lactic acidosis in a 3-year-old female. Cardiac and skeletal muscles biopsies exhibited mitochondrial hyperplasia with decreased complex IV activity. Whole exome sequencing identified compound heterozygous variants, p.Arg333Trp and p.Val119Leu, in TSFM, a nuclear gene that encodes a mitochondrial translation elongation factor, resulting in impaired oxidative phosphorylation and juvenile hypertrophic cardiomyopathy.

Gene-environment regulation of chamber-specific maturation during hypoxemic perinatal circulatory transition.

Chamber-specific and temporally regulated perinatal cardiac growth and maturation is critical for functional adaptation of the heart and may be altered significantly in response to perinatal stress, such as systemic hypoxia (hypoxemia), leading to significant pathology, even mortality. Understanding transcriptome regulation of neonatal heart chambers in response to hypoxemia is necessary to develop chamber-specific therapies for infants with cyanotic congenital heart defects (CHDs). We sought to determine chamber-specific transcriptome programming during hypoxemic perinatal circulatory transition. We performed transcriptome-wide analysis on right ventricle (RV) and left ventricle (LV) of postnatal day 3 (P3) mouse hearts exposed to perinatal hypoxemia. Hypoxemia decreased baseline differences between RV and LV leading to significant attenuation of ventricular patterning (AVP), which involved several molecular pathways, including Wnt signaling suppression and cell cycle induction. Notably, robust changes in RV transcriptome in hypoxemic condition contributed significantly to the AVP. Remarkably, suppression of epithelial mesenchymal transition (EMT) and dysregulation of the TP53 signaling were prominent hallmarks of the AVP genes in neonatal mouse heart. Furthermore, members of the TP53-related gene family were dysregulated in the hypoxemic RVs of neonatal mouse and cyanotic Tetralogy of Fallot hearts. Integrated analysis of chamber-specific transcriptome revealed hypoxemia-specific changes that were more robust in RVs compared with LVs, leading to previously uncharacterized AVP induced by perinatal hypoxemia. Remarkably, reprogramming of EMT process and dysregulation of the TP53 network contributed to transcriptome remodeling of neonatal heart during hypoxemic circulatory transition. These insights may enhance our understanding of hypoxemia-induced pathogenesis in newborn infants with cyanotic CHD phenotypes. KEY MESSAGES: During perinatal circulatory transition, transcriptome programming is a major driving force of cardiac chamber-specific maturation and adaptation to hemodynamic load and external environment. During hypoxemic perinatal transition, transcriptome reprogramming may affect chamber-specific growth and development, particularly in newborns with congenital heart defects (CHDs). Chamber-specific transcriptome changes during hypoxemic perinatal transition are yet to be fully elucidated. Systems-based analysis of hypoxemic neonatal hearts at postnatal day 3 reveals chamber-specific transcriptome signatures during hypoxemic perinatal transition, which involve attenuation of ventricular patterning (AVP) and repression of epithelial mesenchymal transition (EMT). Key regulatory circuits involved in hypoxemia response were identified including suppression of Wnt signaling, induction of cellular proliferation and dysregulation of TP53 network.

Echocardiographic markers of pulmonary hemodynamics and right ventricular hypertrophy in rat models of pulmonary hypertension.

Echocardiography is the gold standard non-invasive technique to diagnose pulmonary hypertension. It is also an important modality used to monitor disease progression and response to treatment in patients with pulmonary hypertension. Surprisingly, only few studies have been conducted to validate and standardize echocardiographic parameters in experimental animal models of pulmonary hypertension. We sought to define cut-off values for both invasive and non-invasive measures of pulmonary hemodynamics and right ventricular hypertrophy that would reliably diagnose pulmonary hypertension in three different rat models. The study was designed in two phases: (1) a derivation phase to establish the cut-off values for invasive measures of right ventricular systolic pressure, Fulton's index (right ventricular weight/left ventricle + septum weight), right ventricular to body weight ratio, and non-invasive echocardiographic measures of pulmonary arterial acceleration time, pulmonary arterial acceleration time to ejection time ratio and right ventricular wall thickness in diastole in the hypoxic and monocrotaline rat models of pulmonary hypertension and (2) a validation phase to test the performance of the cut-off values in predicting pulmonary hypertension in an independent cohort of rats with Sugen/hypoxia-induced pulmonary hypertension. Our study demonstrates that right ventricular systolic pressure ≥35.5 mmHg and Fulton's Index ≥0.34 are highly sensitive (>94%) and specific (>91%) cut-offs to distinguish animals with pulmonary hypertension from controls. When pulmonary arterial acceleration time/ejection time and right ventricular wall thickness in diastole were both measured, a result of either pulmonary arterial acceleration time/ejection time ≤0.25 or right ventricular wall thickness in diastole ≥1.03 mm detected right ventricular systolic pressure ≥35.5 mmHg or Fulton's Index ≥0.34 with a sensitivity of 88% and specificity of 100%. With properly validated non-invasive echocardiography measures of right ventricular performance in rats that accurately predict invasive measures of pulmonary hemodynamics, future studies can now utilize these markers to test the efficacy of different treatments with preclinical therapeutic modeling.

COVID-19: molecular diagnostics overview.

The last day of 2019 delivered the first report to the World Health Organization (WHO) about a group of cases of pneumonia of unknown etiology in Wuhan, China. Subsequent investigations identified the new comer, a novel coronavirus related to severe acute respiratory syndrome coronavirus (SARS-CoV) and thus was termed as SARS-CoV-2. Being very contagious, the new virus led the era of "COVID-19" which is the acronym of "coronavirus disease 2019," evoking an imminent threat to global health security with unprecedented devastating challenges to human kind. In this article, we provide a molecular overview on the SARS-CoV-2 virus and summarize tremendous efforts that have been made to develop a rapid confirmatory diagnostic test for COVID-19. The diagnostic performances of the available tests are analyzed based on the best current information from the early research.

p38 Mitogen-activated protein kinase regulates chamber-specific perinatal growth in heart.

In the mammalian heart, the left ventricle (LV) rapidly becomes more dominant in size and function over the right ventricle (RV) after birth. The molecular regulators responsible for this chamber-specific differential growth are largely unknown. We found that cardiomyocytes in the neonatal mouse RV had lower proliferation, more apoptosis, and a smaller average size compared with the LV. This chamber-specific growth pattern was associated with a selective activation of p38 mitogen-activated protein kinase (MAPK) activity in the RV and simultaneous inactivation in the LV. Cardiomyocyte-specific deletion of both the Mapk14 and Mapk11 genes in mice resulted in loss of p38 MAPK expression and activity in the neonatal heart. Inactivation of p38 activity led to a marked increase in cardiomyocyte proliferation and hypertrophy but diminished cardiomyocyte apoptosis, specifically in the RV. Consequently, the p38-inactivated hearts showed RV-specific enlargement postnatally, progressing to pulmonary hypertension and right heart failure at the adult stage. Chamber-specific p38 activity was associated with differential expression of dual-specific phosphatases (DUSPs) in neonatal hearts, including DUSP26. Unbiased transcriptome analysis revealed that IRE1α/XBP1-mediated gene regulation contributed to p38 MAPK-dependent regulation of neonatal cardiomyocyte proliferation and binucleation. These findings establish an obligatory role of DUSP/p38/IRE1α signaling in cardiomyocytes for chamber-specific growth in the postnatal heart.

Ppp1r1b-lncRNA inhibits PRC2 at myogenic regulatory genes to promote cardiac and skeletal muscle development in mouse and human.

Long noncoding RNAs (lncRNAs) have emerged as critical epigenetic regulators and play important roles in cardiac development and congenital heart disease. In a previous study, we identified a novel lncRNA, Ppp1r1b, with expression highly correlated with myogenesis. However, the molecular mechanism that underlies Ppp1r1b-lncRNA function in myogenic regulation is unknown. By silencing Ppp1r1b-lncRNA, mouse C2C12 and human skeletal myoblasts failed to develop fully differentiated myotubes. Myogenic differentiation was also impaired in PPP1R1B-lncRNA deficient human-induced pluripotent stem cell-derived cardiomyocytes (hiPSCs-CMs). The expression of myogenic transcription factors, including MyoD, Myogenin, and Tbx5, as well as sarcomere proteins, was significantly suppressed in Ppp1r1b-lncRNA inhibited myoblast cells and neonatal mouse heart. Histone modification analysis revealed increased H3K27 tri-methylation at MyoD1 and Myogenin promoters in GapmeR treated C2C12 cells. Furthermore, Ppp1r1b-lncRNA was found to bind to Ezh2, and chromatin isolation by RNA purification (ChIRP) assay revealed enriched interaction of Ppp1r1b-lncRNA with Myod1 and Tbx5 promoters, suggesting that Ppp1r1b-lncRNA induces transcription of myogenic transcription factors by interacting with the polycomb repressive complex 2 (PRC2) at the chromatin interface. Correspondingly, the silencing of Ppp1r1b-lncRNA increased EZH2 binding at promoter regions of myogenic transcription factors. Therefore, our results suggest that Ppp1r1b-lncRNA promotes myogenic differentiation through competing for PRC2 binding with chromatin of myogenic master regulators during heart and skeletal muscle development.

Gene-environment regulatory circuits of right ventricular pathology in tetralogy of fallot.

The phenotypic spectrum of congenital heart defects (CHDs) is contributed by both genetic and environmental factors. Their interactions are profoundly heterogeneous but may operate on common pathways as in the case of hypoxia signaling during postnatal heart development in the context of CHDs. Tetralogy of Fallot (TOF) is the most common cyanotic (hypoxemic) CHD. However, how the hypoxic environment contributes to TOF pathogenesis after birth is poorly understood. We performed Genome-wide transcriptome analysis on right ventricle outflow tract (RVOT) specimens from cyanotic and noncyanotic TOF. Co-expression network analysis identified gene modules specifically associated with clinical diagnosis and hypoxemia status in the TOF hearts. In particular, hypoxia-dependent induction of myocyte proliferation is associated with E2F1-mediated cell cycle regulation and repression of the WNT11-RB1 axis. Genes enriched in epithelial mesenchymal transition (EMT), fibrosis, and sarcomere were also repressed in cyanotic TOF patients. Importantly, transcription factor analysis of the hypoxia-regulated modules suggested CREB1 as a putative regulator of hypoxia/WNT11-RB1 circuit. The study provides a high-resolution landscape of transcriptome programming associated with TOF phenotypes and unveiled hypoxia-induced regulatory circuit in cyanotic TOF. Hypoxia-induced cardiomyocyte proliferation involves negative modulation of CREB1 activity upstream of the WNT11-RB1 axis. KEY MESSAGES: Genetic and environmental factors contribute to congenital heart defects (CHDs). How hypoxia contributes to Tetralogy of Fallot (TOF) pathogenesis after birth is unclear. Systems biology-based analysis revealed distinct molecular signature in CHDs. Gene expression modules specifically associated with cyanotic TOF were uncovered. Key regulatory circuits induced by hypoxia in TOF pathogenesis after birth were unveiled.

Fetal Mouse Cardiovascular Imaging Using a High-frequency Ultrasound (30/45MHZ) System.

Congenital heart defects (CHDs) are the most common cause of childhood morbidity and early mortality. Prenatal detection of the underlying molecular mechanisms of CHDs is crucial for inventing new preventive and therapeutic strategies. Mutant mouse models are powerful tools to discover new mechanisms and environmental stress modifiers that drive cardiac development and their potential alteration in CHDs. However, efforts to establish the causality of these putative contributors have been limited to histological and molecular studies in non-survival animal experiments, in which monitoring the key physiological and hemodynamic parameters is often absent. Live imaging technology has become an essential tool to establish the etiology of CHDs. In particular, ultrasound imaging can be used prenatally without surgically exposing the fetuses, allowing maintaining their baseline physiology while monitoring the impact of environmental stress on the hemodynamic and structural aspects of cardiac chamber development. Herein, we use the High-Frequency Ultrasound (30/45) system to examine the cardiovascular system in fetal mice at E18.5 in utero at the baseline and in response to prenatal hypoxia exposure. We demonstrate the feasibility of the system to measure cardiac chamber size, morphology, ventricular function, fetal heart rate, and umbilical artery flow indices, and their alterations in fetal mice exposed to systemic chronic hypoxia in utero in real time.

Wnt11 regulates cardiac chamber development and disease during perinatal maturation.

Ventricular chamber growth and development during perinatal circulatory transition is critical for functional adaptation of the heart. However, the chamber-specific programs of neonatal heart growth are poorly understood. We used integrated systems genomic and functional biology analyses of the perinatal chamber specific transcriptome and we identified Wnt11 as a prominent regulator of chamber-specific proliferation. Importantly, downregulation of Wnt11 expression was associated with cyanotic congenital heart defect (CHD) phenotypes and correlated with O2 saturation levels in hypoxemic infants with Tetralogy of Fallot (TOF). Perinatal hypoxia treatment in mice suppressed Wnt11 expression and induced myocyte proliferation more robustly in the right ventricle, modulating Rb1 protein activity. Wnt11 inactivation was sufficient to induce myocyte proliferation in perinatal mouse hearts and reduced Rb1 protein and phosphorylation in neonatal cardiomyocytes. Finally, downregulated Wnt11 in hypoxemic TOF infantile hearts was associated with Rb1 suppression and induction of proliferation markers. This study revealed a previously uncharacterized function of Wnt11-mediated signaling as an important player in programming the chamber-specific growth of the neonatal heart. This function influences the chamber-specific development and pathogenesis in response to hypoxia and cyanotic CHDs. Defining the underlying regulatory mechanism may yield chamber-specific therapies for infants born with CHDs.

A Path to Implement Precision Child Health Cardiovascular Medicine.

Congenital heart defects (CHDs) affect approximately 1% of live births and are a major source of childhood morbidity and mortality even in countries with advanced healthcare systems. Along with phenotypic heterogeneity, the underlying etiology of CHDs is multifactorial, involving genetic, epigenetic, and/or environmental contributors. Clear dissection of the underlying mechanism is a powerful step to establish individualized therapies. However, the majority of CHDs are yet to be clearly diagnosed for the underlying genetic and environmental factors, and even less with effective therapies. Although the survival rate for CHDs is steadily improving, there is still a significant unmet need for refining diagnostic precision and establishing targeted therapies to optimize life quality and to minimize future complications. In particular, proper identification of disease associated genetic variants in humans has been challenging, and this greatly impedes our ability to delineate gene-environment interactions that contribute to the pathogenesis of CHDs. Implementing a systematic multileveled approach can establish a continuum from phenotypic characterization in the clinic to molecular dissection using combined next-generation sequencing platforms and validation studies in suitable models at the bench. Key elements necessary to advance the field are: first, proper delineation of the phenotypic spectrum of CHDs; second, defining the molecular genotype/phenotype by combining whole-exome sequencing and transcriptome analysis; third, integration of phenotypic, genotypic, and molecular datasets to identify molecular network contributing to CHDs; fourth, generation of relevant disease models and multileveled experimental investigations. In order to achieve all these goals, access to high-quality biological specimens from well-defined patient cohorts is a crucial step. Therefore, establishing a CHD BioCore is an essential infrastructure and a critical step on the path toward precision child health cardiovascular medicine.

Decoding the Long Noncoding RNA During Cardiac Maturation: A Roadmap for Functional Discovery.

BACKGROUND: Cardiac maturation during perinatal transition of heart is critical for functional adaptation to hemodynamic load and nutrient environment. Perturbation in this process has major implications in congenital heart defects. Transcriptome programming during perinatal stages is an important information but incomplete in current literature, particularly, the expression profiles of the long noncoding RNAs (lncRNAs) are not fully elucidated. METHODS AND RESULTS: From comprehensive analysis of transcriptomes derived from neonatal mouse heart left and right ventricles, a total of 45 167 unique transcripts were identified, including 21 916 known and 2033 novel lncRNAs. Among these lncRNAs, 196 exhibited significant dynamic regulation along maturation process. By implementing parallel weighted gene co-expression network analysis of mRNA and lncRNA data sets, several lncRNA modules coordinately expressed in a developmental manner similar to protein coding genes, while few lncRNAs revealed chamber-specific patterns. Out of 2262 lncRNAs located within 50 kb of protein coding genes, 5% significantly correlate with the expression of their neighboring genes. The impact of Ppp1r1b-lncRNA on the corresponding partner gene Tcap was validated in cultured myoblasts. This concordant regulation was also conserved in human infantile hearts. Furthermore, the Ppp1r1b-lncRNA/Tcap expression ratio was identified as a molecular signature that differentiated congenital heart defect phenotypes. CONCLUSIONS: The study provides the first high-resolution landscape on neonatal cardiac lncRNAs and reveals their potential interaction with mRNA transcriptome during cardiac maturation. Ppp1r1b-lncRNA was identified as a regulator of Tcap expression, with dynamic interaction in postnatal cardiac development and congenital heart defects.

Maternal Calorie Restriction Causing Uteroplacental Insufficiency Differentially Affects Mammalian Placental Glucose and Leucine Transport Molecular Mechanisms.

We examined the effect of mild (Mi; ∼25%) and moderate (Mo; ∼50%) maternal calorie restriction (MCR) vs ad libitum-fed controls on placental glucose and leucine transport impacting fetal growth potential. We observed in MiMCR a compensatory increase in transplacental (TP) glucose transport due to increased placental glucose transporter isoform (GLUT)-3 but no change in GLUT1 protein concentrations. This change was paralleled by increased glut3 mRNA and 5-hydroxymethylated cytosines with enhanced recruitment of histone 3 lysine demethylase to the glut3 gene locus. To assess the biologic relevance of placental GLUT1, we also examined glut1 heterozygous null vs wild-type mice and observed no difference in placental GLUT3 and TP or intraplacental glucose and leucine transport. Both MCR states led to a graded decrease in TP and intraplacental leucine transport, with a decline in placental L amino acid transporter isoform 2 (LAT2) concentrations and increased microRNA-149 (targets LAT2) and microRNA-122 (targets GLUT3) expression in MoMCR alone. These changes were accompanied by a step-wise reduction in uterine and umbilical artery Doppler blood flow with decreased fetal left ventricular ejection fraction and fractional shortening. We conclude that MiMCR transactivates placental GLUT3 toward preserving TP glucose transport in the face of reduced leucine transport. This contrasts MoMCR in which a reduction in placental GLUT3 mediated glucose transport with a reciprocal increase in miR-122 expression was encountered. A posttranscriptional reduction in LAT2-mediated leucine transport also occurred with enhanced miR-149 expression. Both MCR states, although not affecting placental GLUT1, resulted in uteroplacental insufficiency and fetal growth restriction with compromised cardiovascular health.

Hematopoietic progenitors are required for proper development of coronary vasculature.

RATIONALE: During embryogenesis, hematopoietic cells appear in the myocardium prior to the initiation of coronary formation. However, their role is unknown. OBJECTIVE: Here we investigate whether pre-existing hematopoietic cells are required for the formation of coronary vasculature. METHODS AND RESULTS: As a model of for hematopoietic cell deficient animals, we used Runx1 knockout embryos and Vav1-cre; R26-DTA embryos, latter of which genetically ablates 2/3 of CD45(+) hematopoietic cells. Both Runx1 knockout embryos and Vav1-cre; R26-DTA embryos revealed disorganized, hypoplastic microvasculature of coronary vessels on section and whole-mount stainings. Furthermore, coronary explant experiments showed that the mouse heart explants from Runx1 and Vav1-cre; R26-DTA embryos exhibited impaired coronary formation ex vivo. Interestingly, in both models it appears that epicardial to mesenchymal transition is adversely affected in the absence of hematopoietic progenitors. CONCLUSION: Hematopoietic cells are not merely passively transported via coronary vessel, but substantially involved in the induction of the coronary growth. Our findings suggest a novel mechanism of coronary growth.