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Aims: Congenital heart disease (CHD) frequently occurs in newborns due to abnormal formation of the heart or major blood vessels. Mutations in the GATA4 gene, which encodes GATA binding protein 4, are responsible for atrial septal defect (ASD), a common CHD. This study aims to gain insights into the molecular mechanisms of CHD using human induced pluripotent stem cells (iPSCs) from a family cohort with ASD. Methods and Results: Patient-specific iPSCs possess the same genetic information as the donor and can differentiate into various cell types from all three germ layers in vitro , thus presenting a promising approach for disease modeling and molecular mechanism research. Here, we generated a patient-specific iPSC line (iPSC-G4 T280M ) from a family cohort carrying a hereditary ASD mutation in GATA4 gene (T280M), as well as a human embryonic stem cell line (ESC-G4 T280M ) carrying the isogenic T280M mutation using the CRISPR/Cas9 genome editing method. The GATA4-mutant iPSCs and ESCs were then differentiated into cardiomyocytes (CMs) to model GATA4 mutation-associated ASD. We observed an obvious defect in cell proliferation in cardiomyocytes derived from both GATA4 T280M -mutant iPSCs (iPSC-G4 T280M -CMs) and ESCs (ESC-G4 T280M -CMs), while the impaired proliferation ability of iPSC-G4 T280M -CMs could be restored by gene correction. Integrated analysis of RNA-Seq and ChIP-Seq data indicated that FGF16 is a direct target of wild-type GATA4. However, the T280M mutation obstructed GATA4 occupancy at the FGF16 promoter region, leading to impaired activation of FGF16 transcription. Overexpression of FGF16 in GATA4-mutant cardiomyocytes rescued the cell proliferation defect. The direct relationship between GATA4 T280M and ASD was demonstrated in a human iPSC model for the first time. Conclusions: In summary, our study revealed the molecular mechanism of the GATA4 T280M mutation in ASD. Understanding the roles of the GATA4-FGF16 axis in iPSC-CMs will shed light on heart development and provide novel insights for the treatment of ASD and other CHD disorders.

Cardiomyocytes differentiated from human embryonic stem cells (hESCs) represent a promising cell source for heart repair, disease modeling and drug testing. However, improving the differentiation efficiency and maturation of hESC-derived cardiomyocytes (hESC-CMs) is still a major concern. Retinoic acid (RA) signaling plays multiple roles in heart development, and studies on RA can provide clues for understanding cardiomyocyte differentiation and maturation. In this study, we studied the roles of RA during cardiomyocyte differentiation and maturation, systematically. After adding RA at different stages of cardiomyocyte differentiation, we compared the efficiency of differentiation by quantitative real-time PCR and flow cytometry. We found that RA treatment at the lateral mesoderm stage (days 2-4) significantly improved cardiomyocyte differentiation, as evidenced by the upregulation of TNNT2, NKX2.5 and MYH6 on day 10 of differentiation. In addition, flow cytometry showed that the proportion of differentiated cardiomyocytes in the RA-treated group was significantly higher than that in control group. Furthermore, RA was added at different time intervals after purification to induce cardiomyocyte maturation. Our results demonstrated that RA treatment on days 15-20 increased cardiomyocyte area, sarcomere length, multinucleation and mitochondrial copy number, and promoted RNA splicing switch. Importantly, RA-treated cardiomyocytes showed decreased glycolysis and enhanced mitochondrial oxidative phosphorylation, with the increased utilization of fatty acid and exogenous pyruvate but not glutamine. In conclusion, our data indicated that RA treatment at an early time window (days 2-4) promotes the efficiency of cardiomyocyte differentiation and that RA treatment post beating (days 15-20) promotes cardiomyocyte metabolic maturation. The biphasic effects of RA provide new insights for improving cardiomyocyte differentiation and quality.

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) can differentiate into spontaneously beating cardiomyocytes in vitro, and hold great promise for cardiovascular disease modeling, therapy and drug discovery. However, these applications were hampered by low yield and purity of the in vitro differentiated cardiomyocytes. Although miRNAs represent a type of potential candidates to promote cardiac differentiation, most of cardiomyocyte-enriched miRNAs have not been functionally investigated until now. This study investigated the roles of MIR148A family in cardiac differentiation from hESCs. The MIR148A family is composed of MIR148A , MIR148B and MIR152 , three highly conserved miRNAs sharing same seed sequences. The expression levels of all MIR148A family members were progressively increased during cardiac differentiation in vitro. By using CRISPR-Cas9-mediated knockout, we demonstrated that triple knockout of MIR148A family ( MIR148A -TKO), rather than individual knockout of each members, could grossly inhibited TNNT2 + cardiomyocyte generation. Ectopic expression of MIR152 significantly restored the cardiac differentiation efficiency of MIR148A -TKO hESCs. The transcriptome analysis identified a total of 1071 upregulated genes and 766 down-regulated genes in the MIR148A -TKO hESC-derived cells compared to wild-type hESC-derived cells at day 4 of cardiac differentiation. Gene Ontology analysis revealed that most genes down-regulated in MIR148A -TKO hESC-derived cells were involved in the events of lateral/cardiac mesoderm development, while the up-regulated genes were mainly involved in the events of paraxial/somitic development. Furthermore, the NOTCH ligand Delta-like1 ( DLL1 ) was validated as the target gene of MIR148A family, and the knockdown of DLL1 could inhibit target gene expression of Notch signaling pathway, and promote cardiac differentiation of MIR148A -TKO hESCs. Our findings demonstrate a new function of MIR148A family during cardiac differentiation. Synergistic inhibition of DLL1 -mediated Notch signaling represents a major mechanism for the MIR148A family to inhibit undesired lineage formation and promote hESC differentiation into cardiomyocytes.

Rationale: Aging is one of the most significant risk factors for cardiovascular diseases, and the incidence of myocardial ischemia increases dramatically with age. Some studies have reported that cardiosphere-derived cells (CDCs) could benefit the injured heart. Nevertheless, the convincing evidence on CDC-induced improvement of aging heart is still limited. Objective: In this study, we tested whether the CDCs isolated from neonatal mice could benefit cardiac function in aging mice. Methods and Results: We evaluated cardiac function of PBS- (n=15) and CDC-injected (n=19) aging mice. Echocardiography indicated that left ventricular (LV) ejection fraction (57.46%±3.57% versus 57.86%±2.44%) and LV fraction shortening (30.67%±2.41% versus 30.51%±1.78%) showed similar values in PBS- and CDC-injected mice. The diastolic wall thickness of LV was significantly increased after CDC injection, resulting in reduced diastolic LV volume. The pulse-wave Doppler and tissue Doppler imaging indicated that aging mice receiving PBS or CDC injection presented similar values of the peak early transmitral flow velocity, the peak late transmitral flow velocity, the ratio of the peak early transmitral flow velocity to the peak late transmitral flow velocity, and the ratio of the peak early transmitral flow velocity to the peak early diastolic mitral annular velocity, respectively. Pressure-volume loop experiment indicated that the LV end-diastolic pressure-volume relationship and end-systolic pressure-volume relationship were comparable in both PBS- and CDC-injected mice. Postmortem analysis of aging mouse hearts showed similar fibrotic degree in the 2 groups. In addition, the aging markers showed comparable expression levels in both PBS- and CDC-injected mice. The systemic aging performance measures, including exercise capacity, hair regrowth capacity, and inflammation, showed no significant improvement in CDC-injected mice. Finally, the telomere length was comparable between PBS- and CDC-injected mice. Conclusions: Together, these results indicate that CDCs do not improve heart function and systemic performances in aging mice.

Background: Circular RNAs (circRNAs) are regarded as a novel class of noncoding RNA regulators. Although a number of circRNAs have been identified by bioinformatics analysis of RNA-seq data, the tissue- and disease-specific circRNAs are still to be uncovered to promote their application in basic research and clinical practice. The purpose of this study was to explore the circRNA profiles in human induced pluripotent stem cells (hiPSCs) and hiPSC-derived cardiomyocytes (hiPSC-CMs), and identify cardiac or disease-specific circRNAs. Methods: Human iPSCs were generated from fibroblasts, and then further differentiated to hiPSC-CMs by modulating WNT signaling in RPMI+B27 medium. Following high-throughput RNA sequencing, circRNAs were extracted and quantified by a combined strategy known as CIRCexplorer. Integrative analysis was performed to illuminate the correlation between circRNAs and their parental linear isoforms. Cardiac and disease-specific expression of circRNAs was confirmed by quantitative reverse-transcription PCR. Results: In this study, a total of 5602 circRNAs were identified in hiPSCs and hiPSC-CMs. Our data indicated, for the first time, a more enriched expression of circRNAs in differentiated cardiomyocytes than undifferentiated hiPSCs. In addition to the host gene-dependent expression, our integrative analysis also identified a number of circRNAs showing host gene-independent expression in hiPSCs and hiPSC-CMs. CircRNAs including circSLC8A1 , circCACNA1D , circSPHKAP and circALPK2 showed a cardiac-selective expression during cardiac differentiation and human heart-specific enrichment in fetal tissues. Furthermore, circSLC8A1 abnormally increased in heart tissues from patients suffering from dilated cardiomyopathy (DCM). Conclusions: CircRNAs are highly enriched in hiPSC-differentiated CMs, and cardiac-specific circRNAs such as circSLC8A1 , circCACNA1D , circSPHKAP and circALPK2 may serve as biomarkers of CMs. Detection of the excessive expression of circSLC8A1 provides a potential approach for pathological status indication of heart disease.

Introduction: The injured heart undergoes a major process of cellular apoptosis in the initial stage of MI, therefore, the most fundamental method to prevent post-MI remodeling is to suppress cardiomyocyte apoptosis. In this study, we have illustrated the key role of long noncoding RNA, Maternally expressed gene 3 ( Meg3 ), on cardiomyocyte apoptosis and the underlying mechanisms in heart. Methods: Neonatal murine cardiomyocytes and human ESC-derived cardiomyocytes were subjected to hypoxia, and cellular apoptosis was evaluated with Annexin V assay. The Meg3 regulation by p53 was measured by luciferase reporter assay. The complex of Meg3 and RNA-binding protein FUS (Fused in sarcoma) was determined by EMSA and RIP. Adeno-Associated Virus serotype 9 (AAV9) system was employed to knock down Meg3 in cardiomyocytes in vivo, and the cardiac function was evaluated by echocardiography and ex-vivo assays. Results: We first found that Meg3 was progressively upregulated in the murine injured heart after MI, and it showed the pro-apoptotic functions in primary cardiomyocytes. Meg3 could be directly upregulated by p53 during hypoxia condition, and was involved in apoptotic regulation via its direct binding with FUS. The Meg3 knockdown in cardiomyocytes by AAV9 system could preserve heart function in murine myocardial infarction. Moreover, its pro-apoptotic function was conserved in human cardiomyocytes. Conclusion: Together, these results indicate that p53-induced Meg3 - FUS complex plays an important role on cardiomyocyte apoptosis post-MI, and its specific knockdown in cardiomyocytes with AAV9 system represents a promising method to treat myocardial infarction.