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The synthesis and characterisation (IR, NMR, HR-MS, and X-ray crystallography) of six oxazoline Zn complexes, containing enolate ligands derived from a series of (Z)-1-R-2-(4′,4′-dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ols (R = C6H5, C6H4-p-NO2, C6H4-p-OCH3, CF3, CH3, or CMe3) is detailed. All derivatives are air-stable solids of formula Zn(Ln)2 and are formed in the presence of the title ligands and NEt3. Reasonable yields (53%–82%) are obtained with the exception of R = CMe3 (9%); in this case, by-product formation and high solubility affected complex isolation. Crystallographic characterisation reveals that in all cases the ligands are bound in a κ2-N,O-bonding motif. Little structural diversity is noted within the series; these complexes are further placed into structural context with related Zn materials containing oxazoline, phenolate, and (or) Schiff base ligands. [ABSTRACT FROM AUTHOR]

Genome-wide association studies found that increased risk for atrial fibrillation (AF), the most common human heart arrhythmia, is associated with noncoding sequence variants located in proximity to PITX2. Cardiomyocyte-specific epigenomic and comparative genomics uncovered 2 AF-associated enhancers neighboring PITX2 with varying conservation in mice. Chromosome conformation capture experiments in mice revealed that the Pitx2c promoter directly contacted the AF-associated enhancer regions. CRISPR/Cas9- mediated deletion of a 20-kb topologically engaged enhancer led to reduced Pitx2c transcription and AF predisposition. Allele-specific chromatin immunoprecipitation sequencing on hybrid heterozygous enhancer knockout mice revealed that long-range interaction of an AF-associated region with the Pitx2c promoter was required for maintenance of the Pitx2c promoter chromatin state. Long-range looping was mediated by CCCTC-binding factor (CTCF), since genetic disruption of the intronic CTCF-binding site caused reduced Pitx2c expression, AF predisposition, and diminished active chromatin marks on Pitx2. AF risk variants located at 4q25 reside in genomic regions possessing long-range transcriptional regulatory functions directed at PITX2. [ABSTRACT FROM AUTHOR]

Summary Specialized adult somatic cells, such as cardiomyocytes (CMs), are highly differentiated with poor renewal capacity, an integral reason underlying organ failure in disease and aging. Among the least renewable cells in the human body, CMs renew approximately 1% annually. Consistent with poor CM turnover, heart failure is the leading cause of death. Here, we show that an active version of the Hippo pathway effector YAP, termed YAP5SA, partially reprograms adult mouse CMs to a more fetal and proliferative state. One week after induction, 19% of CMs that enter S-phase do so twice, CM number increases by 40%, and YAP5SA lineage CMs couple to pre-existing CMs. Genomic studies showed that YAP5SA increases chromatin accessibility and expression of fetal genes, partially reprogramming long-lived somatic cells in vivo to a primitive, fetal-like, and proliferative state. Graphical Abstract Highlights • Creation of a mouse conditionally expressing active YAP called YAP5SA • YAP5SA in adult cardiomyocytes (CMs) induces a more primitive transcriptional state • YAP5SA activates developmental enhancers • YAP5SA expression in CMs causes CM hyperplasia and overall heart hypercellularity As highly differentiated cells, cardiomyocytes have poor renewal capacity, a contributing factor to heart failure in aging and disease. Monroe et al. created a mouse conditionally overexpressing active YAP (YAP5SA) and show that YAP5SA expression induces adult cardiomyocytes to adopt a more proliferative state with fetal-like chromatin and transcriptional landscapes. [ABSTRACT FROM AUTHOR]

Summary During development, progenitors progress through transition states. The cardiac epicardium contains progenitors of essential non-cardiomyocytes. The Hippo pathway, a kinase cascade that inhibits the Yap transcriptional co-factor, controls organ size in developing hearts. Here, we investigated Hippo kinases Lats1 and Lats2 in epicardial diversification. Epicardial-specific deletion of Lats1/2 was embryonic lethal, and mutant embryos had defective coronary vasculature remodeling. Single-cell RNA sequencing revealed that Lats1/2 mutant cells failed to activate fibroblast differentiation but remained in an intermediate cell state with both epicardial and fibroblast characteristics. Lats1/2 mutant cells displayed an arrested developmental trajectory with persistence of epicardial markers and expanded expression of Yap targets Dhrs3, an inhibitor of retinoic acid synthesis, and Dpp4, a protease that modulates extracellular matrix (ECM) composition. Genetic and pharmacologic manipulation revealed that Yap inhibits fibroblast differentiation, prolonging a subepicardial-like cell state, and promotes expression of matricellular factors, such as Dpp4, that define ECM characteristics. [ABSTRACT FROM AUTHOR]

Loss of the paired-like homeodomain transcription factor 2 (Pitx2) in cardiomyocytes predisposes mice to atrial fibrillation and compromises neonatal regenerative capacity. Additionally, Pitx2 gain-of-function protects mature cardiomyocytes from ischemic injury and promotes heart repair. Here, we characterized the long-term myocardial phenotype after MI in Pitx2 conditional-knockout (Pitx2 CKO) mice. We found adipose-like tissue in Pitx2 CKO hearts 60 days after MI induced surgically at postnatal day 2 but not at day 8. Molecular and cellular analyses showed the onset of adipogenic signaling in mutant hearts after MI. Lineage tracing experiments showed a non-cardiomyocyte origin of the de novo adipose-like tissue. Interestingly, we found that Pitx2 promotes mitochondrial function through its gene regulatory network, and that the knock down of a key mitochondrial Pitx2 target gene, Cox7c, also leads to the accumulation of myocardial fat tissue. Single-nuclei RNA-Seq (snRNA-Seq) revealed that Pitx2 deficient hearts were oxidatively stressed. Our findings reveal a role for Pitx2 in maintaining proper cardiac cellular composition during heart regeneration via the maintenance of proper mitochondrial structure and function. [ABSTRACT FROM AUTHOR]

The cardiac conduction system is a network of heterogeneous cell population that initiates and propagates electric excitations in the myocardium. Purkinje fibers, a network of specialized myocardial cells, comprise the distal end of the conduction system in the ventricles. The developmental origins of Purkinje fibers and their roles during cardiac physiology and arrhythmia have been reported. However, it is not clear if they play a role during ischemic injury and heart regeneration. Here we introduce a novel tamoxifen-inducible Cre allele that specifically labels a broad range of components in the cardiac conduction system while excludes other cardiac cell types and vital organs. Using this new allele, we investigated the cellular and molecular response of Purkinje fibers to myocardial injury. In a neonatal mouse myocardial infarction model, we observed significant increase in Purkinje cell number in regenerating myocardium. RNA-Seq analysis using laser-captured Purkinje fibers showed a unique transcriptomic response to myocardial infarction. Our finds suggest a novel role of cardiac Purkinje fibers in heart injury. [Display omitted] • A novel inducible Cre strain with specific activity in cardiac conduction system. • Cardiac Purkinje fibers respond to myocardial injury. • Cardiomyocytes may contribute to Purkinje fiber expansion post injury. [ABSTRACT FROM AUTHOR]

Background: Surviving cells in the postinfarction border zone are subjected to intense fluctuations of their microenvironment. Recently, border zone cardiomyocytes have been specifically implicated in cardiac regeneration. Here, we defined their unique transcriptional and regulatory properties, and comprehensively validated new molecular markers, including Nppb, encoding B-type natriuretic peptide, after infarction.Methods: Transgenic reporter mice were used to identify the Nppb-positive border zone after myocardial infarction. Transcriptome analysis of remote, border, and infarct zones and of purified cardiomyocyte nuclei was performed using RNA-sequencing. Top candidate genes displaying border zone spatial specificity were histologically validated in ischemic human hearts. Mice in which Nppb was deleted by genome editing were subjected to myocardial infarction. Chromatin accessibility landscapes of border zone and control cardiomyocyte nuclei were assessed by using assay for transposase-accessible chromatin using sequencing.Results: We identified the border zone as a spatially confined region transcriptionally distinct from the remote myocardium. The transcriptional response of the border zone was much stronger than that of the remote ventricular wall, involving acute downregulation of mitochondrial oxidative phosphorylation, fatty acid metabolism, calcium handling, and sarcomere function, and the activation of a stress-response program. Analysis of infarcted human hearts revealed that the transcriptionally discrete border zone is conserved in humans, and led to the identification of novel conserved border zone markers including NPPB, ANKRD1, DES, UCHL1, JUN, and FOXP1. Homozygous Nppb mutant mice developed acute and lethal heart failure after myocardial infarction, indicating that B-type natriuretic peptide is required to preserve postinfarct heart function. Assay for transposase-accessible chromatin using sequencing revealed thousands of cardiomyocyte lineage-specific MEF2-occupied regulatory elements that lost accessibility in the border zone. Putative injury-responsive enhancers that gained accessibility were highly associated with AP-1 (activator protein 1) binding sites. Nuclear c-Jun, a component of AP-1, was observed specifically in border zone cardiomyocytes.Conclusions: Cardiomyocytes in a discrete zone bordering the infarct switch from a MEF2-driven homeostatic lineage-specific to an AP-1-driven injury-induced gene expression program. This program is conserved between mouse and human, and includes Nppb expression, which is required to prevent acute heart failure after infarction. [ABSTRACT FROM AUTHOR]