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Rationale: Cardiac-expressed long noncoding RNAs (lncRNAs) are important for cardiomyocyte (CM) differentiation and function. Several lncRNAs have been identified and characterized for early CM lineage commitment, however those in later CM lineage specification and maturation remain less well studied. Moreover, unique atrial / ventricular lncRNA expression has never been studied in detail., Objectives: Here, we characterized a novel ventricular myocyte-restricted lncRNA, not expressed in atrial myocytes, and conserved only in primates., Methods and Results: First, we performed single cell RNA-seq on human pluripotent stem cell derived cardiomyocytes (hPSC-CM) at the late stages of 2, 6 and 12 weeks of differentiation. Weighted correlation network analysis identified core gene modules, including a set of lncRNAs highly abundant and predominantly expressed in the human heart. A lncRNA (we call VENTHEART, VHRT) co-expressed with cardiac maturation and ventricular-specific genes MYL2 and MYH7, and was expressed in fetal and adult human ventricles, but not atria. CRISPR-mediated deletion of the VHRT gene led to impaired CM sarcomere formation and significant disruption of the ventricular CM gene program. Indeed, a similar disruption was not observed in VHRT KO hPSC-derived atrial CM, suggesting that VHRT exhibits only ventricular myocyte subtype-specific effects. Optical recordings validated that loss of VHRT significantly prolonged action potential duration at 90 % repolarization (APD 90 ) for ventricular-like, but not atrial-like, CMs., Conclusion: This reports the first lncRNA that is exclusively required for proper ventricular, and not atrial, CM specification and function., Competing Interests: Declaration of competing interest P.L.S and K.H.L are co-founders and shareholders of Ternion Biosciences., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Adult mammalian cardiomyocytes have limited proliferative capacity, but in specifically induced contexts they traverse through cell-cycle reentry, offering the potential for heart regeneration. Endogenous cardiomyocyte proliferation is preceded by cardiomyocyte dedifferentiation (CMDD), wherein adult cardiomyocytes revert to a less matured state that is distinct from the classical myocardial fetal stress gene response associated with heart failure. However, very little is known about CMDD as a defined cardiomyocyte cell state in transition., Methods: Here, we leveraged 2 models of in vitro cultured adult mouse cardiomyocytes and in vivo adeno-associated virus serotype 9 cardiomyocyte-targeted delivery of reprogramming factors ( Oct4 , Sox2 , Klf4 , and Myc ) in adult mice to study CMDD. We profiled their transcriptomes using RNA sequencing, in combination with multiple published data sets, with the aim of identifying a common denominator for tracking CMDD., Results: RNA sequencing and integrated analysis identified Asparagine Synthetase ( Asns ) as a unique molecular marker gene well correlated with CMDD, required for increased asparagine and also for distinct fluxes in other amino acids. Although Asns overexpression in Oct4 , Sox2 , Klf4 , and Myc cardiomyocytes augmented hallmarks of CMDD, Asns deficiency led to defective regeneration in the neonatal mouse myocardial infarction model, increased cell death of cultured adult cardiomyocytes, and reduced cell cycle in Oct4 , Sox2 , Klf4 , and Myc cardiomyocytes, at least in part through disrupting the mammalian target of rapamycin complex 1 pathway., Conclusions: We discovered a novel gene Asns as both a molecular marker and an essential mediator, marking a distinct threshold that appears in common for at least 4 models of CMDD, and revealing an Asns /mammalian target of rapamycin complex 1 axis dependency for dedifferentiating cardiomyocytes. Further study will be needed to extrapolate and assess its relevance to other cell state transitions as well as in heart regeneration., Competing Interests: Disclosures None.

The pleiotropic benefits of statins in cardiovascular diseases that are independent of their lipid-lowering effects have been well documented, but the underlying mechanisms remain elusive. Here we show that simvastatin significantly improves human induced pluripotent stem cell-derived endothelial cell functions in both baseline and diabetic conditions by reducing chromatin accessibility at transcriptional enhanced associate domain elements and ultimately at endothelial-to-mesenchymal transition (EndMT)-regulating genes in a yes-associated protein (YAP)-dependent manner. Inhibition of geranylgeranyltransferase (GGTase) I, a mevalonate pathway intermediate, repressed YAP nuclear translocation and YAP activity via RhoA signaling antagonism. We further identified a previously undescribed SOX9 enhancer downstream of statin-YAP signaling that promotes the EndMT process. Thus, inhibition of any component of the GGTase-RhoA-YAP-SRY box transcription factor 9 (SOX9) signaling axis was shown to rescue EndMT-associated endothelial dysfunction both in vitro and in vivo, especially under diabetic conditions. Overall, our study reveals an epigenetic modulatory role for simvastatin in repressing EndMT to confer protection against endothelial dysfunction.

Single-cell technology has become an indispensable tool in cardiovascular research since its first introduction in 2009. Here, we highlight the recent remarkable progress in using single-cell technology to study transcriptomic and epigenetic heterogeneity in cardiac disease and development. We then introduce the key concepts in single-cell multi-omics modalities that apply to cardiovascular research. Lastly, we discuss some of the trending concepts in single-cell technology that are expected to propel cardiovascular research to the next phase of single-cell research., (© 2023. Springer Nature Limited.)

Doxorubicin is an anthracycline widely used for the treatment of various cancers; however, the drug has a common deleterious side effect, namely a dose-dependent cardiotoxicity. Doxorubicin treatment increases the generation of reactive oxygen species, which leads to oxidative stress in the cardiac cells and ultimately DNA damage and cell death. The most common DNA lesion produced by oxidative stress is 7,8-dihydro-8-oxoguanine (8-oxoguanine), and the enzyme responsible for its repair is the 8-oxoguanine DNA glycosylase (OGG1), a base excision repair enzyme. Here, we show that the OGG1 deficiency has no major effect on cardiac function at baseline or with pressure overload; however, we found an exacerbation of cardiac dysfunction as well as a higher mortality in Ogg1 knockout mice treated with doxorubicin. Our transcriptomic analysis also showed a more extensive dysregulation of genes in the hearts of Ogg1 knockout mice with an enrichment of genes involved in inflammation. These results demonstrate that OGG1 attenuates doxorubicin-induced cardiotoxicity and thus plays a role in modulating drug-induced cardiomyopathy., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2022 Chukwuemeka George Anene-Nzelu et al.)

The Human Genome Project marked a major milestone in the scientific community as it unravelled the ~3 billion bases that are central to crucial aspects of human life. Despite this achievement, it only scratched the surface of understanding how each nucleotide matters, both individually and as part of a larger unit. Beyond the coding genome, which comprises only ~2% of the whole genome, scientists have realized that large portions of the genome, not known to code for any protein, were crucial for regulating the coding genes. These large portions of the genome comprise the 'non-coding genome'. The history of gene regulation mediated by proteins that bind to the regulatory non-coding genome dates back many decades to the 1960s. However, the original definition of 'enhancers' was first used in the early 1980s. In this Review, we summarize benchmark studies that have mapped the role of cardiac enhancers in disease and development. We highlight instances in which enhancer-localized genetic variants explain the missing link to cardiac pathogenesis. Finally, we inspire readers to consider the next phase of exploring enhancer-based gene therapy for cardiovascular disease., (© 2021. Springer Nature Limited.)

We determined the relationships between DNA sequence variation and DNA methylation using blood samples from 3,799 Europeans and 3,195 South Asians. We identify 11,165,559 SNP-CpG associations (methylation quantitative trait loci (meQTL), P < 10 -14 ), including 467,915 meQTL that operate in trans. The meQTL are enriched for functionally relevant characteristics, including shared chromatin state, High-throuhgput chromosome conformation interaction, and association with gene expression, metabolic variation and clinical traits. We use molecular interaction and colocalization analyses to identify multiple nuclear regulatory pathways linking meQTL loci to phenotypic variation, including UBASH3B (body mass index), NFKBIE (rheumatoid arthritis), MGA (blood pressure) and COMMD7 (white cell counts). For rs6511961 , chromatin immunoprecipitation followed by sequencing (ChIP-seq) validates zinc finger protein (ZNF)333 as the likely trans acting effector protein. Finally, we used interaction analyses to identify population- and lineage-specific meQTL, including rs174548 in FADS1, with the strongest effect in CD8 + T cells, thus linking fatty acid metabolism with immune dysregulation and asthma. Our study advances understanding of the potential pathways linking genetic variation to human phenotype., (© 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.)

The role of DNA methylation in cardiomyocyte physiology and cardiac disease remains a matter of controversy. We have recently provided evidence for an important role of DNMT3A in human cardiomyocyte cell homeostasis and metabolism, using engineered heart tissue (EHT) generated from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes carrying a knockout of the de novo DNA methyltransferase DNMT3A. Unlike isogenic control EHT, knockout EHT displayed morphological abnormalities such as lipid accumulations inside cardiomyocytes associated with impaired mitochondrial metabolism, as well as functional defects and impaired glucose metabolism. Here, we analyzed the role of DNMT3A in the setting of cardiac hypertrophy. We induced hypertrophic signaling by treatment with 50 nM endothelin-1 and 20 μM phenylephrine for one week and assessed EHT contractility, morphology, DNA methylation, and gene expression. While both knockout EHTs and isogenic controls showed the expected activation of the hypertrophic gene program, knockout EHTs were protected from hypertrophy-related functional impairment. Conversely, hypertrophic treatment prevented the metabolic consequences of a loss of DNMT3A, i.e. abolished lipid accumulation in cardiomyocytes likely by partial normalization of mitochondrial metabolism and restored glucose metabolism and metabolism-related gene expression of knockout EHT. Together, these data suggest an important role of DNA methylation not only for cardiomyocyte physiology, but also in the setting of cardiac disease., (Copyright © 2021 University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. Published by Elsevier Ltd.. All rights reserved.)

Loss of insulin-secreting pancreatic β cells through apoptosis contributes to the progression of type 2 diabetes, but underlying mechanisms remain elusive. Here, we identify a pathway in which the cell death inhibitor ARC paradoxically becomes a killer during diabetes. While cytoplasmic ARC maintains β cell viability and pancreatic architecture, a pool of ARC relocates to the nucleus to induce β cell apoptosis in humans with diabetes and several pathophysiologically distinct mouse models. β cell death results through the coordinate downregulation of serpins (serine protease inhibitors) not previously known to be synthesized and secreted by β cells. Loss of the serpin α 1 -antitrypsin from the extracellular space unleashes elastase, triggering the disruption of β cell anchorage and subsequent cell death. Administration of α 1 -antitrypsin to mice with diabetes prevents β cell death and metabolic abnormalities. These data uncover a pathway for β cell loss in type 2 diabetes and identify an FDA-approved drug that may impede progression of this syndrome., Competing Interests: Declaration of interests David Lomas is an inventor on the patent PCT/GB2019/051761 for a small molecule treatment of antitrypsin deficiency. This small molecule has not been used in this work., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: DNA methylation acts as a mechanism of gene transcription regulation. It has recently gained attention as a possible therapeutic target in cardiac hypertrophy and heart failure. However, its exact role in cardiomyocytes remains controversial. Thus, we knocked out the main de novo DNA methyltransferase in cardiomyocytes, DNMT3A, in human induced pluripotent stem cells. Functional consequences of DNA methylation-deficiency under control and stress conditions were then assessed in human engineered heart tissue from knockout human induced pluripotent stem cell-derived cardiomyocytes., Methods: DNMT3A was knocked out in human induced pluripotent stem cells by CRISPR/Cas9gene editing. Fibrin-based engineered heart tissue was generated from knockout and control human induced pluripotent stem cell-derived cardiomyocytes. Development and baseline contractility were analyzed by video-optical recording. Engineered heart tissue was subjected to different stress protocols, including serum starvation, serum variation, and restrictive feeding. Molecular, histological, and ultrastructural analyses were performed afterward., Results: Knockout of DNMT3A in human cardiomyocytes had three main consequences for cardiomyocyte morphology and function: (1) Gene expression changes of contractile proteins such as higher atrial gene expression and lower MYH7/MYH6 ratio correlated with different contraction kinetics in knockout versus wild-type; (2) Aberrant activation of the glucose/lipid metabolism regulator peroxisome proliferator-activated receptor gamma was associated with accumulation of lipid vacuoles within knockout cardiomyocytes; (3) Hypoxia-inducible factor 1α protein instability was associated with impaired glucose metabolism and lower glycolytic enzyme expression, rendering knockout-engineered heart tissue sensitive to metabolic stress such as serum withdrawal and restrictive feeding., Conclusion: The results suggest an important role of DNA methylation in the normal homeostasis of cardiomyocytes and during cardiac stress, which could make it an interesting target for cardiac therapy.

Rationale: Identifying genetic markers for heterogeneous complex diseases such as heart failure is challenging and requires prohibitively large cohort sizes in genome-wide association studies to meet the stringent threshold of genome-wide statistical significance. On the other hand, chromatin quantitative trait loci, elucidated by direct epigenetic profiling of specific human tissues, may contribute toward prioritizing subthreshold variants for disease association., Objective: Here, we captured noncoding genetic variants by performing epigenetic profiling for enhancer H3K27ac chromatin immunoprecipitation followed by sequencing in 70 human control and end-stage failing hearts., Methods and Results: We have mapped a comprehensive catalog of 47 321 putative human heart enhancers and promoters. Three thousand eight hundred ninety-seven differential acetylation peaks (FDR [false discovery rate], 5%) pointed to pathways altered in heart failure. To identify cardiac histone acetylation quantitative trait loci (haQTLs), we regressed out confounding factors including heart failure disease status and used the G-SCI (Genotype-independent Signal Correlation and Imbalance) test 1 to call out 1680 haQTLs (FDR, 10%). RNA sequencing performed on the same heart samples proved a subset of haQTLs to have significant association also to gene expression (expression quantitative trait loci), either in cis (180) or through long-range interactions (81), identified by Hi-C (high-throughput chromatin conformation assay) and HiChIP (high-throughput protein centric chromatin) performed on a subset of hearts. Furthermore, a concordant relationship between the gain or disruption of TF (transcription factor)-binding motifs, inferred from alternative alleles at the haQTLs, implied a surprising direct association between these specific TF and local histone acetylation in human hearts. Finally, 62 unique loci were identified by colocalization of haQTLs with the subthreshold loci of heart-related genome-wide association studies datasets., Conclusions: Disease and phenotype association for 62 unique loci are now implicated. These loci may indeed mediate their effect through modification of enhancer H3K27 acetylation enrichment and their corresponding gene expression differences (bioRxiv: https://doi.org/10.1101/536763). Graphical Abstract: A graphical abstract is available for this article.

Background: Primary valvular heart disease is a prevalent cause of morbidity and mortality in both industrialized and developing countries. Although the primary consequence of valvular heart disease is myocardial dysfunction, treatment of valvular heart diseases centers around valve repair or replacement rather than prevention or reversal of myocardial dysfunction. This is particularly evident in primary mitral regurgitation (MR), which invariably results in eccentric hypertrophy and left ventricular (LV) failure in the absence of timely valve repair or replacement. The mechanism of LV dysfunction in primary severe MR is entirely unknown., Methods: Here, we developed the first mouse model of severe MR. Valvular damage was achieved by severing the mitral valve leaflets and chords with iridectomy scissors, and MR was confirmed by echocardiography. Serial echocardiography was performed to follow up LV morphology and systolic function. Analysis of cardiac tissues was subsequently performed to evaluate valve deformation, cardiomyocyte morphology, LV fibrosis, and cell death. Finally, dysregulated pathways were assessed by RNA-sequencing analysis and immunofluorescence., Results: In the ensuing 15 weeks after the induction of MR, gradual LV dilatation and dysfunction occurred, resulting in severe systolic dysfunction. Further analysis revealed that severe MR resulted in a marked increase in cardiac mass and increased cardiomyocyte length but not width, with electron microscopic evidence of sarcomere disarray and the development of sarcomere disruption. From a mechanistic standpoint, severe MR resulted in activation of multiple components of both the mammalian target of rapamycin and calcineurin pathways. Inhibition of mammalian target of rapamycin signaling preserved sarcomeric structure and prevented LV remodeling and systolic dysfunction. Immunohistochemical analysis uncovered a differential pattern of expression of the cell polarity regulator Crb2 (crumbs homolog 2) along the longitudinal axis of cardiomyocytes and close to the intercalated disks in the MR hearts. Electron microscopy images demonstrated a significant increase in polysome localization in close proximity to the intercalated disks and some areas along the longitudinal axis in the MR hearts., Conclusions: These results indicate that LV dysfunction in response to severe MR is a form of maladaptive eccentric cardiomyocyte hypertrophy and outline the link between cell polarity regulation and spatial localization protein synthesis as a pathway for directional cardiomyocyte growth.

A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. We recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes 1,2 and that Meis1, a three amino acid loop extension (TALE) family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest 3 . Here we report that Hoxb13 acts as a cofactor of Meis1 in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can extend the postnatal window of cardiomyocyte proliferation and reactivate the cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1-Hoxb13 double-knockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and improved left ventricular systolic function following myocardial infarction, as demonstrated by echocardiography and magnetic resonance imaging. Chromatin immunoprecipitation with sequencing demonstrates that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and cell cycle. Finally, we show that the calcium-activated protein phosphatase calcineurin dephosphorylates Hoxb13 at serine-204, resulting in its nuclear localization and cell cycle arrest. These results demonstrate that Meis1 and Hoxb13 act cooperatively to regulate cardiomyocyte maturation and proliferation and provide mechanistic insights into the link between hyperplastic and hypertrophic growth of cardiomyocytes.

Human pluripotent stem cells (hPSCs)-derived cardiovascular progenitor cells (CVPCs) are a promising source for myocardial repair, while the mechanisms remain largely unknown. Extracellular vesicles (EVs) are known to mediate cell-cell communication, however, the efficacy and mechanisms of hPSC-CVPC-secreted EVs (hCVPC-EVs) in the infarct healing when given at the acute phase of myocardial infarction (MI) are unknown. Here, we report the cardioprotective effects of the EVs secreted from hESC-CVPCs under normoxic (EV-N) and hypoxic (EV-H) conditions in the infarcted heart and the long noncoding RNA (lncRNA)-related mechanisms. The hCVPC-EVs were confirmed by electron microscopy, nanoparticle tracking, and immunoblotting analysis. Injection of hCVPC-EVs into acutely infracted murine myocardium significantly improved cardiac function and reduced fibrosis at day 28 post MI, accompanied with the improved vascularization and cardiomyocyte survival at border zones. Consistently, hCVPC-EVs enhanced the tube formation and migration of human umbilical vein endothelial cells (HUVECs), improved the cell viability, and attenuated the lactate dehydrogenase release of neonatal rat cardiomyocytes (NRCMs) with oxygen glucose deprivation (OGD) injury. Moreover, the improvement of the EV-H in cardiomyocyte survival and tube formation of HUVECs was significantly better than these in the EV-N. RNA-seq analysis revealed a high abundance of the lncRNA MALAT1 in the EV-H. Its abundance was upregulated in the infarcted myocardium and cardiomyocytes treated with hCVPC-EVs. Overexpression of human MALAT1 improved the cell viability of NRCM with OGD injury, while knockdown of MALAT1 inhibited the hCVPC-EV-promoted tube formation of HUVECs. Furthermore, luciferase activity assay, RNA pull-down, and manipulation of miR-497 levels showed that MALAT1 improved NRCMs survival and HUVEC tube formation through targeting miR-497. These results reveal that hCVPC-EVs promote the infarct healing through improvement of cardiomyocyte survival and angiogenesis. The cardioprotective effects of hCVPC-EVs can be enhanced by hypoxia-conditioning of hCVPCs and are partially contributed by MALAT1 via targeting the miRNA.

The neonatal mammalian heart is capable of regeneration for a brief window of time after birth. However, this regenerative capacity is lost within the first week of life, which coincides with a postnatal shift from anaerobic glycolysis to mitochondrial oxidative phosphorylation, particularly towards fatty-acid utilization. Despite the energy advantage of fatty-acid beta-oxidation, cardiac mitochondria produce elevated rates of reactive oxygen species when utilizing fatty acids, which is thought to play a role in cardiomyocyte cell-cycle arrest through induction of DNA damage and activation of DNA-damage response (DDR) pathway. Here we show that inhibiting fatty-acid utilization promotes cardiomyocyte proliferation in the postnatatal heart. First, neonatal mice fed fatty-acid deficient milk showed prolongation of the postnatal cardiomyocyte proliferative window, however cell cycle arrest eventually ensued. Next, we generated a tamoxifen-inducible cardiomyocyte-specific, pyruvate dehydrogenase kinase 4 (PDK4) knockout mouse model to selectively enhance oxidation of glycolytically derived pyruvate in cardiomyocytes. Conditional PDK4 deletion resulted in an increase in pyruvate dehydrogenase activity and consequently an increase in glucose relative to fatty-acid oxidation. Loss of PDK4 also resulted in decreased cardiomyocyte size, decreased DNA damage and expression of DDR markers and an increase in cardiomyocyte proliferation. Following myocardial infarction, inducible deletion of PDK4 improved left ventricular function and decreased remodelling. Collectively, inhibition of fatty-acid utilization in cardiomyocytes promotes proliferation, and may be a viable target for cardiac regenerative therapies., Competing Interests: Competing interests None of the authors have competing interests

Background: The human genome folds in 3 dimensions to form thousands of chromatin loops inside the nucleus, encasing genes and cis-regulatory elements for accurate gene expression control. Physical tethers of loops are anchored by the DNA-binding protein CTCF and the cohesin ring complex. Because heart failure is characterized by hallmark gene expression changes, it was recently reported that substantial CTCF-related chromatin reorganization underpins the myocardial stress-gene response, paralleled by chromatin domain boundary changes observed in CTCF knockout., Methods: We undertook an independent and orthogonal analysis of chromatin organization with mouse pressure-overload model of myocardial stress (transverse aortic constriction) and cardiomyocyte-specific knockout of Ctcf. We also downloaded published data sets of similar cardiac mouse models and subjected them to independent reanalysis., Results: We found that the cardiomyocyte chromatin architecture remains broadly stable in transverse aortic constriction hearts, whereas Ctcf knockout resulted in ≈99% abolition of global chromatin loops. Disease gene expression changes correlated instead with differential histone H3K27-acetylation enrichment at their respective proximal and distal interacting genomic enhancers confined within these static chromatin structures. Moreover, coregulated genes were mapped out as interconnected gene sets on the basis of their multigene 3D interactions., Conclusions: This work reveals a more stable genome-wide chromatin framework than previously described. Myocardial stress-gene transcription responds instead through H3K27-acetylation enhancer enrichment dynamics and gene networks of coregulation. Robust and intact CTCF looping is required for the induction of a rapid and accurate stress response.

Background: Immune adaptation with aging is a major of health outcomes. Studies in humans have mainly focus on αβ T cells while γδ T cells have been neglected despite their role in immunosurveillance. We investigated the impact of aging on γδ T cell subsets phenotypes, functions, senescence and their molecular response to stress., Methods: Peripheral blood of young and old donors in Singapore have been used to assess the phenotype, functional capacity, proliferation capacity and gene expression of the various γδ T cell subsets. Peripheral blood mononuclear cells from apheresis cones and young donors have been used to characterize the telomere length, epigenetics profile and DNA damage response of the various γδ T cell subsets phenotype., Findings: Our data shows that peripheral Vδ2+ phenotype, functional capacity (cytokines, cytotoxicity, proliferation) and gene expression profile are specific when compared against all other αβ and γδ T cells in aging. Hallmarks of senescence including telomere length, epigenetic profile and DNA damage response of Vδ2+ also differs against all other αβ and γδ T cells., Interpretation: Our results highlight the differential impact of lifelong stress on γδ T cells subsets, and highlight possible mechanisms that enable Vδ2+ to be resistant to cellular aging. The new findings reinforce the concept that Vδ2+ have an "innate-like" behavior and are more resilient to the environment as compared to "adaptive-like" Vδ1+ T cells., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

The mammalian heart contains heterogeneous cell types contributing to pathological changes in cardiac disease. In this Comment, we explore how single-cell transcriptomic approaches are unveiling intricate cellular mechanisms and gene co-expression networks that regulate the workings, and failings, of the heart.

Cardiac regeneration may revolutionize treatment for heart failure but endogenous progenitor-derived cardiomyocytes in the adult mammalian heart are few and pre-existing adult cardiomyocytes divide only at very low rates. Although candidate genes that control cardiomyocyte cell cycle re-entry have been implicated, expression heterogeneity in the cardiomyocyte stress-response has never been explored. Here, we show by single nuclear RNA-sequencing of cardiomyocytes from both mouse and human failing, and non-failing adult hearts that sub-populations of cardiomyocytes upregulate cell cycle activators and inhibitors consequent to the stress-response in vivo. We characterize these subgroups by weighted gene co-expression network analysis and discover long intergenic non-coding RNAs (lincRNA) as key nodal regulators. KD of nodal lincRNAs affects expression levels of genes related to dedifferentiation and cell cycle, within the same gene regulatory network. Our study reveals that sub-populations of adult cardiomyocytes may have a unique endogenous potential for cardiac regeneration in vivo.Adult mammalian cardiomyocytes are predominantly binucleated and unable to divide. Using single nuclear RNA-sequencing of cardiomyocytes from mouse and human failing and non-failing adult hearts, See et al. show that some cardiomyocytes respond to stress by dedifferentiation and cell cycle re-entry regulated by lncRNAs.

Cardiovascular disease remains the number one global cause of death and presents as multiple phenotypes in which the interplay between cardiomyocytes and cardiac fibroblasts (CFs) has become increasingly highlighted. Fetal and adult CFs influence neighboring cardiomyocytes in different ways. Thus far, a detailed comparison between the two is lacking. Using a genome-wide approach, we identified and validated 2 crucial players for maintaining the adult primary human CF phenotype. Knockdown of these factors induced significant phenotypical changes, including senescence and reduced collagen gene expression. These may now represent novel therapeutic targets against deleterious functions of CFs in adult cardiovascular disease.