Fibroblast Growth Factors and Vascular Endothelial Growth Factor Promote Cardiac Reprogramming under Defined Conditions

Fibroblasts can be directly reprogrammed into cardiomyocyte-like cells (iCMs) by overexpression of cardiac transcription factors, including Gata4, Mef2c, and Tbx5; however, this process is inefficient under serum-based culture conditions, in which conversion of partially reprogrammed cells into fully reprogrammed functional iCMs has been a major hurdle. Here, we report that a combination of fibroblast growth factor (FGF) 2, FGF10, and vascular endothelial growth factor (VEGF), termed FFV, promoted cardiac reprogramming under defined serum-free conditions, increasing spontaneously beating iCMs by 100-fold compared with those under conventional serum-based conditions. Mechanistically, FFV activated multiple cardiac transcriptional regulators and converted partially reprogrammed cells into functional iCMs through the p38 mitogen-activated protein kinase and phosphoinositol 3-kinase/AKT pathways. Moreover, FFV enabled cardiac reprogramming with only Mef2c and Tbx5 through the induction of cardiac reprogramming factors, including Gata4. Thus, defined culture conditions promoted the quality of cardiac reprogramming, and this finding provides new insight into the mechanism of cardiac reprogramming.

Direct In Vivo Reprogramming with Sendai Virus Vectors Improves Cardiac Function after Myocardial Infarction

Direct cardiac reprogramming holds great promise for regenerative medicine. We previously generated directly reprogrammed induced cardiomyocyte-like cells (iCMs) by overexpression of Gata4, Mef2c, and Tbx5 (GMT) using retrovirus vectors. However, integrating vectors pose risks associated with insertional mutagenesis and disruption of gene expression and are inefficient. Here, we show that Sendai virus (SeV) vectors expressing cardiac reprogramming factors efficiently and rapidly reprogram both mouse and human fibroblasts into integration-free iCMs via robust transgene expression. SeV-GMT generated 100-fold more beating iCMs than retroviral-GMT and shortened the duration to induce beating cells from 30 to 10 days in mouse fibroblasts. In vivo lineage tracing revealed that the gene transfer of SeV-GMT was more efficient than retroviral-GMT in reprogramming resident cardiac fibroblasts into iCMs in mouse infarct hearts. Moreover, SeV-GMT improved cardiac function and reduced fibrosis after myocardial infarction. Thus, efficient, non-integrating SeV vectors may serve as a powerful system for cardiac regeneration.

Tbx6 Induces Nascent Mesoderm from Pluripotent Stem Cells and Temporally Controls Cardiac versus Somite Lineage Diversification

The mesoderm arises from pluripotent epiblasts and differentiates into multiple lineages; however, the underlying molecular mechanisms are unclear. Tbx6 is enriched in the paraxial mesoderm and is implicated in somite formation, but its function in other mesoderms remains elusive. Here, using direct reprogramming-based screening, single-cell RNA-seq in mouse embryos, and directed cardiac differentiation in pluripotent stem cells (PSCs), we demonstrated that Tbx6 induces nascent mesoderm from PSCs and determines cardiovascular and somite lineage specification via its temporal expression. Tbx6 knockout in mouse PSCs using CRISPR/Cas9 technology inhibited mesoderm and cardiovascular differentiation, whereas transient Tbx6 expression induced mesoderm and cardiovascular specification from mouse and human PSCs via direct upregulation of Mesp1, repression of Sox2, and activation of BMP/Nodal/Wnt signaling. Notably, prolonged Tbx6 expression suppressed cardiac differentiation and induced somite lineages, including skeletal muscle and chondrocytes. Thus, Tbx6 is critical for mesoderm induction and subsequent lineage diversification.

Single-Construct Polycistronic Doxycycline-Inducible Vectors Improve Direct Cardiac Reprogramming and Can Be Used to Identify the Critical Timing of Transgene Expression

Direct reprogramming is a promising approach in regenerative medicine. Overexpression of the cardiac transcription factors Gata4, Mef2c, and Tbx5 (GMT) or GMT plus Hand2 (GHMT) directly reprogram fibroblasts into cardiomyocyte-like cells (iCMs). However, the critical timing of transgene expression and the molecular mechanisms for cardiac reprogramming remain unclear. The conventional doxycycline (Dox)-inducible temporal transgene expression systems require simultaneous transduction of two vectors (pLVX-rtTA/pLVX-cDNA) harboring the reverse tetracycline transactivator (rtTA) and the tetracycline response element (TRE)-controlled transgene, respectively, leading to inefficient cardiac reprogramming. Herein, we developed a single-construct-based polycistronic Dox-inducible vector (pDox-cDNA) expressing both the rtTA and TRE-controlled transgenes. Fluorescence activated cell sorting (FACS) analyses, quantitative RT-PCR, and immunostaining revealed that pDox-GMT increased cardiac reprogramming three-fold compared to the conventional pLVX-rtTA/pLVX-GMT. After four weeks, pDox-GMT-induced iCMs expressed multiple cardiac genes, produced sarcomeric structures, and beat spontaneously. Co-transduction of pDox-Hand2 with retroviral pMX-GMT increased cardiac reprogramming three-fold compared to pMX-GMT alone. Temporal Dox administration revealed that Hand2 transgene expression is critical during the first two weeks of cardiac reprogramming. Microarray analyses demonstrated that Hand2 represses cell cycle-promoting genes and enhances cardiac reprogramming. Thus, we have developed an efficient temporal transgene expression system, which could be invaluable in the study of cardiac reprogramming.

Tbx6 induces cardiomyocyte proliferation in postnatal and adult mouse hearts

Cardiovascular disease is a leading cause of death worldwide. Mammalian cardiomyocytes (CMs) proliferate during embryonic development, whereas they largely lose their regenerative capacity after birth. Defined factors expressed in cardiac progenitors or embryonic CMs may activate the cell cycle and induce CM proliferation in postnatal and adult hearts. Here, we report that the overexpression of Tbx6, enriched in the cardiac mesoderm (progenitor cells), induces CM proliferation in postnatal and adult mouse hearts. By screening 24 factors enriched in cardiac progenitors or embryonic CMs, we found that only Tbx6 could induce CM proliferation in primary cultured postnatal rat CMs. Intriguingly, it did not induce the proliferation of cardiac fibroblasts. We next generated a recombinant adeno-associated virus serotype 9 vector encoding Tbx6 (AAV9-Tbx6) for transduction into mouse CMs in vivo. The subcutaneous injection of AAV9-Tbx6 into neonatal mice induced CM proliferation in postnatal and adult mouse hearts. Mechanistically, Tbx6 overexpression upregulated multiple cell cycle activators including Aurkb, Mki67, Ccna1, and Ccnb2 and suppressed the tumor suppressor Rb1. Thus, Tbx6 promotes CM proliferation in postnatal and adult mouse hearts by modifying the expression of cell cycle regulators.

Prevalence of the Academic Research Consortium high bleeding risk criteria in patients undergoing endovascular therapy for peripheral artery disease in lower extremities

The Academic Research Consortium (ARC) recently published a definition of patients at high bleeding risk (HBR) undergoing percutaneous coronary intervention. However, the prevalence of the ARC-HBR criteria in patients undergoing endovascular therapy (EVT) for peripheral artery disease in lower extremities has not been thoroughly investigated. This study sought to investigate the prevalence and impact of the ARC-HBR criteria in patients undergoing EVT. We analyzed 277 consecutive patients who underwent their first EVT from July 2011 to September 2019. We applied the full ARC-HBR criteria to the study population. The primary end point was a composite outcome of all-cause mortality, Bleeding Academic Research Consortium 3 or 5 bleeding, and lower limb amputation within 12 months of EVT. Among the 277 patients, 193 (69.7%) met the ARC-HBR criteria. HBR patients had worse clinical outcomes compared with non-HBR patients at 12 months after EVT, including a higher incidence of the composite primary outcome (19.2% vs. 3.6%, p < 0.001) and all-cause death (7.8% vs. 0%, p = 0.007). In a multivariate Cox proportional hazards regression analysis, presence of the ARC-HBR criteria [hazard ratio (HR) 4.15, 95% confidence interval (CI) 1.25-13.80, p = 0.020], body mass index (HR 1.13, 95% CI 1.01-1.27, p = 0.042), diabetes mellitus (HR 2.70, 95% CI 1.28-5.69, p = 0.009), hyperlipidemia (HR 0.41, 95% CI 0.21-0.80, p = 0.009), and infrapopliteal lesions (HR 3.51, 95% CI 1.63-7.56, p = 0.001) were independent predictors of the primary composite outcome. Approximately 70% of Japanese patients undergoing EVT met the ARC-HBR criteria, and its presence was strongly associated with adverse outcomes within 12 months of EVT.

A woman complicated by sudden cardiac arrest owing to spontaneous coronary artery dissection after stillbirth

Spontaneous coronary artery dissection (SCAD) is the most important cause of acute coronary syndrome in pregnant women. Pregnancy-associated SCAD frequently occurs in the third trimester or postpartum period. However, little is known regarding the relationship between the occurrence of SCAD and stillbirth. We describe here a 41-year-old woman complicated by sudden cardiac arrest owing to SCAD in the distal segment of the right coronary artery 13 days after stillbirth. After contacting emergency medical services, she was resuscitated by an automated external defibrillator because the initial electrocardiographic waveform was ventricular fibrillation. After cardiopulmonary resuscitation, the diagnosis of SCAD was confirmed by coronary angiography and intracoronary imaging, including intravascular ultrasound and optical coherence tomography. The patient was managed with conservative medical therapy because the culprit lesion was present in the distal segment of the right coronary artery and coronary blood flow was preserved. No major adverse cardiovascular events, including recurrent ventricular arrhythmia, were observed during hospitalization. Our findings indicate that pregnancy-associated SCAD leading to sudden cardiac arrest may occur in the postpartum period, even after stillbirth. Intravascular imaging plays a pivotal role in diagnosing SCAD. <Learning objective: Pregnancy-associated spontaneous coronary artery dissection (SCAD) is a relatively rare but well-known cause of acute coronary syndrome in pregnant or postpartum women. However, whether the risk of pregnancy-associated SCAD in the postpartum period is different between normal birth and stillbirth remains unknown. Pregnancy-associated SCAD leading to sudden cardiac arrest owing to acute myocardial ischemia may occur in postpartum women, regardless of fetal survival.>.

A case of atrial septal defect with right-to-left shunting without pulmonary hypertension

We report a case of a 54-year-old man with atrial septal defect who presented with oxygen desaturation on pulse oximetry. Cardiac magnetic resonance imaging and transesophageal echocardiography showed right-to-left shunting through an atrial septal defect, which was confirmed by superior vena cavography and suggested Eisenmenger syndrome. However, cardiac catheterization revealed a normal pulmonary arterial pressure. Simultaneous measurement of interatrial pressure identified two transient interatrial pressure gradient points, where the right atrial pressure was higher than the left atrial pressure. The patient was finally diagnosed with atrial septal defect without pulmonary hypertension. Right-to-left shunting was primarily caused by a transient interatrial pressure gradient due to a time delay in both initial atrial contraction and completion of passive ventricular filling between the right and left sides of the heart. Surgical closure of the atrial septal defect was performed, and hypoxemia improved. This is the first report of right-to-left shunting without pulmonary hypertension caused by a transient interatrial pressure gradient due to a time delay between the right and left cardiac cycles. Precise assessment of the simultaneous interatrial pressure in addition to diagnostic imaging played a pivotal role in clarifying the etiology of this rare condition.

Learning objective

Atrial septal defect with right-to-left shunting without Eisenmenger syndrome is a rare condition. We identified transient interatrial pressure gradients associated with a time delay in both initial atrial contraction and completion of the passive ventricular filling phase, which we considered as the primary mechanism underpinning right-to-left shunting. Simultaneous measurement of interatrial pressure played a pivotal role in elucidating the hemodynamics and abnormal shunt flow mechanism.