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Aims Pathological cardiac remodelling is characterized by cardiomyocyte (CM) hypertrophy and fibroblast activation, which can ultimately lead to maladaptive hypertrophy and heart failure (HF). Genome-wide expression analysis on heart tissue has been instrumental for the identification of molecular mechanisms at play. However, these data were based on signals derived from all cardiac cell types. Here, we aimed for a more detailed view on molecular changes driving maladaptive CM hypertrophy to aid in the development of therapies to reverse pathological remodelling. Methods and results Utilizing CM-specific reporter mice exposed to pressure overload by transverse aortic banding and CM isolation by flow cytometry, we obtained gene expression profiles of hypertrophic CMs in the more immediate phase after stress, and CMs showing pathological hypertrophy. We identified subsets of genes differentially regulated and specific for either stage. Among the genes specifically up-regulated in the CMs during the maladaptive phase we found known stress markers, such as Nppb and Myh7 , but additionally identified a set of genes with unknown roles in pathological hypertrophy, including the platelet isoform of phosphofructokinase (PFKP). Norepinephrine-angiotensin II treatment of cultured human CMs induced the secretion of N-terminal-pro-B-type natriuretic peptide (NT-pro-BNP) and recapitulated the up-regulation of these genes, indicating conservation of the up-regulation in failing CMs. Moreover, several genes induced during pathological hypertrophy were also found to be increased in human HF, with their expression positively correlating to the known stress markers NPPB and MYH7. Mechanistically, suppression of Pfkp in primary CMs attenuated stress-induced gene expression and hypertrophy, indicating that Pfkp is an important novel player in pathological remodelling of CMs. Conclusion Using CM-specific transcriptomic analysis, we identified novel genes induced during pathological hypertrophy that are relevant for human HF, and we show that PFKP is a conserved failure-induced gene that can modulate the CM stress response. [ABSTRACT FROM AUTHOR]

The efficiency of the repair process following ischemic cardiac injury is a crucial determinant for the progression into heart failure and is controlled by both intra- and intercellular signaling within the heart. An enhanced understanding of this complex interplay will enable better exploitation of these mechanisms for therapeutic use. We used single-cell transcriptomics to collect gene expression data of all main cardiac cell types at different time-points after ischemic injury. These data unveiled cellular and transcriptional heterogeneity and changes in cellular function during cardiac remodeling. Furthermore, we established potential intercellular communication networks after ischemic injury. Follow up experiments confirmed that cardiomyocytes express and secrete elevated levels of beta-2 microglobulin in response to ischemic damage, which can activate fibroblasts in a paracrine manner. Collectively, our data indicate phase-specific changes in cellular heterogeneity during different stages of cardiac remodeling and allow for the identification of therapeutic targets relevant for cardiac repair. Molenaar et al. use scRNA-seq to profile cardiac cell gene expression changes at three time points following ischemic injury. They observe that B2M is secreted by cardiomyocytes following injury, promoting scar formation. This data may be useful in finding therapeutic targets for cardiac repair [ABSTRACT FROM AUTHOR]

The significance of cardiac stem cell (CSC) populations for cardiac regeneration remains disputed. Here, we apply the most direct definition of stem cell function (the ability to replace lost tissue through cell division) to interrogate the existence of CSCs. By singlecell mRNA sequencing and genetic lineage tracing using two Ki67 knockin mouse models, we map all proliferating cells and their progeny in homoeostatic and regenerating murine hearts. Cycling cardiomyocytes were only robustly observed in the early postnatal growth phase, while cycling cells in homoeostatic and damaged adultmyocardium represented various noncardiomyocyte cell types. Proliferative postdamage fibroblasts expressing follistatin-like protein 1 (FSTL1) closely resemble neonatal cardiac fibroblasts and form the fibrotic scar. Genetic deletion of Fstl1 in cardiac fibroblasts results in postdamage cardiac rupture. We find no evidence for the existence of a quiescent CSC population, for transdifferentiation of other cell types toward cardiomyocytes, or for proliferation of significant numbers of cardiomyocytes in response to cardiac injury. [ABSTRACT FROM AUTHOR]

Heart failure is the leading cause of death worldwide. Identification of factors that promote cardiac repair is of major importance. Here we show that the transcription factor ZEB2 confers cardioprotective effects after ischemia. Exposure of cardiomyocyte-specific ZEB2 knock out mice to a myocardial infarction reduced survival and impaired cardiac contractility and infarct healing. Conversely, cardiomyocyte-specific ZEB2 overexpression improved survival, infarct healing and cardiac function. To unveil the molecular mechanisms behind the cardioprotective effects of ZEB2 we performed mass spectrometry on conditioned medium from cardiomyocytes overexpressing ZEB2. We identified TMSB4, PTMA, RACK1 and DYNLL1 as main circulating factors in response to ZEB2 overexpression, which were reported to be cardioprotective, pro-angiogenic or anti-apoptotic. In line with this observation, we could validate the regulation of those factors in our gain- and loss-of-function mouse models, suggesting a role of ZEB2 in regulating their expression and release from cardiomyocytes in vivo. To test for the therapeutic effect of increasing the level of ZEB2 specifically in cardiomyocytes after ischemic injury we made use of both AAV9-mediated ZEB2 delivery directly to the heart and systemic antimiR-208 delivery that causes Zeb2 de-repression specifically in heart muscle cells. Both approaches prevented cardiac dysfunction after ischemic damage and promoted the activation of a cardioprotective gene program. Our data suggest that the increase in ZEB2 in cardiomyocytes in response to stress protects the heart from ischemic damage via non cell autonomous effects of cardioprotective factors. These findings reveal ZEB2 as a cardioprotective factor during ischemic injury, which may hold great promise for future heart failure therapies. [ABSTRACT FROM AUTHOR]