A COUP-TFII Human Embryonic Stem Cell Reporter Line to Identify and Select Atrial Cardiomyocytes.

Reporter cell lines have already proven valuable in identifying, tracking, and purifying cardiac subtypes and progenitors during differentiation of human pluripotent stem cells (hPSCs). We previously showed that chick ovalbumin upstream promoter transcription factor II (COUP-TFII) is highly enriched in human atrial cardiomyocytes (CMs), but not ventricular. Here, we targeted mCherry to the COUP-TFII genomic locus in hPSCs expressing GFP from the NKX2.5 locus. This dual atrial NKX2.5EGFP/+-COUP-TFIImCherry/+ reporter line allowed identification and selection of GFP+ (G+)/mCherry+ (M+) CMs following cardiac differentiation. These cells exhibited transcriptional and functional properties of atrial CMs, whereas G+/M- CMs displayed ventricular characteristics. Via CRISPR/Cas9-mediated knockout, we demonstrated that COUP-TFII is not required for atrial specification in hPSCs. This new tool allowed selection of human atrial and ventricular CMs from mixed populations, of relevance for studying cardiac specification, developing human atrial disease models, and examining distinct effects of drugs on the atrium versus ventricle.

TECRL, a new life-threatening inherited arrhythmia gene associated with overlapping clinical features of both LQTS and CPVT.

Genetic causes of many familial arrhythmia syndromes remain elusive. In this study, whole-exome sequencing (WES) was carried out on patients from three different families that presented with life-threatening arrhythmias and high risk of sudden cardiac death (SCD). Two French Canadian probands carried identical homozygous rare variant in TECRL gene (p.Arg196Gln), which encodes the trans-2,3-enoyl-CoA reductase-like protein. Both patients had cardiac arrest, stress-induced atrial and ventricular tachycardia, and QT prolongation on adrenergic stimulation. A third patient from a consanguineous Sudanese family diagnosed with catecholaminergic polymorphic ventricular tachycardia (CPVT) had a homozygous splice site mutation (c.331+1G>A) in TECRL Analysis of intracellular calcium ([Ca2+]i) dynamics in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) generated from this individual (TECRLHom-hiPSCs), his heterozygous but clinically asymptomatic father (TECRLHet-hiPSCs), and a healthy individual (CTRL-hiPSCs) from the same Sudanese family, revealed smaller [Ca2+]i transient amplitudes as well as elevated diastolic [Ca2+]i in TECRLHom-hiPSC-CMs compared with CTRL-hiPSC-CMs. The [Ca2+]i transient also rose markedly slower and contained lower sarcoplasmic reticulum (SR) calcium stores, evidenced by the decreased magnitude of caffeine-induced [Ca2+]i transients. In addition, the decay phase of the [Ca2+]i transient was slower in TECRLHom-hiPSC-CMs due to decreased SERCA and NCX activities. Furthermore, TECRLHom-hiPSC-CMs showed prolonged action potentials (APs) compared with CTRL-hiPSC-CMs. TECRL knockdown in control human embryonic stem cell-derived CMs (hESC-CMs) also resulted in significantly longer APs. Moreover, stimulation by noradrenaline (NA) significantly increased the propensity for triggered activity based on delayed afterdepolarizations (DADs) in TECRLHom-hiPSC-CMs and treatment with flecainide, a class Ic antiarrhythmic drug, significantly reduced the triggered activity in these cells. In summary, we report that mutations in TECRL are associated with inherited arrhythmias characterized by clinical features of both LQTS and CPVT Patient-specific hiPSC-CMs recapitulated salient features of the clinical phenotype and provide a platform for drug screening evidenced by initial identification of flecainide as a potential therapeutic. These findings have implications for diagnosis and treatment of inherited cardiac arrhythmias.

Dual reporter MESP1 mCherry/w-NKX2-5 eGFP/w hESCs enable studying early human cardiac differentiation.

Understanding early differentiation events leading to cardiogenesis is crucial for controlling fate of human pluripotent stem cells and developing protocols that yield sufficient cell numbers for use in regenerative medicine and drug screening. Here, we develop a new tool to visualize patterning of early cardiac mesoderm and cardiomyocyte development in vitro by generating a dual MESP1(mCherry/w)-NKX2-5(eGFP/w) reporter line in human embryonic stem cells (hESCs) and using it to examine signals that lead to formation of cardiac progenitors and subsequent differentiation. MESP1 is a pivotal transcription factor for precardiac mesoderm in the embryo, from which the majority of cardiovascular cells arise. Transcription factor NKX2-5 is expressed upon cardiac crescent formation. Induction of cardiac differentiation in this reporter line resulted in transient expression of MESP1-mCherry, followed by continuous expression of NKX2-5-eGFP. MESP1-mCherry cells showed increased expression of mesodermal and epithelial-mesenchymal-transition markers confirming their mesodermal identity. Whole-genome microarray profiling and fluorescence-activated cell sorting analysis of MESP1-mCherry cells showed enrichment for mesodermal progenitor cell surface markers PDGFR-α, CD13, and ROR-2. No enrichment was found for the previously described KDR+PDGFR-α+ progenitors. MESP1-mCherry derivatives contained an enriched percentage of NKX2-5-eGFP and Troponin T expressing cells, indicating preferential cardiac differentiation; this was enhanced by inhibition of the Wnt-pathway. Furthermore, MESP1-mCherry derivatives harbored smooth muscle cells and endothelial cells, demonstrating their cardiac and vascular differentiation potential under appropriate conditions. The MESP1-NKX2-5 hESC reporter line allows us to identify molecular cues crucial for specification and expansion of human cardiac mesoderm and early progenitors and their differentiation to specific cardiovascular derivatives.