Cholecystokinin-A Signaling Regulates Automaticity of Pacemaker Cardiomyocytes.

Aims: The behavior of pacemaker cardiomyocytes (PCs) in the sinoatrial node (SAN) is modulated by neurohormonal and paracrine factors, many of which signal through G-protein coupled receptors (GPCRs). The aims of the present study are to catalog GPCRs that are differentially expressed in the mammalian SAN and to define the acute physiological consequences of activating the cholecystokinin-A signaling system in isolated PCs.

Methods And Results: Using bulk and single cell RNA sequencing datasets, we identify a set of GPCRs that are differentially expressed between SAN and right atrial tissue, including several whose roles in PCs and in the SAN have not been thoroughly characterized.

ATAC-Seq Reveals an Enhancer That Regulates Sinoatrial Node Development and Function.

Rationale: Cardiac pacemaker cells (PCs) in the sinoatrial node (SAN) have a distinct gene expression program that allows them to fire automatically and initiate the heartbeat. Although critical SAN transcription factors, including Isl1 (Islet-1), Tbx3 (T-box transcription factor 3), and Shox2 (short-stature homeobox protein 2), have been identified, the -regulatory architecture that governs PC-specific gene expression is not understood, and discrete enhancers required for gene regulation in the SAN have not been identified.

Objective: To define the epigenetic profile of PCs using comparative ATAC-seq (assay for transposase-accessible chromatin with sequencing) and to identify novel enhancers involved in SAN gene regulation, development, and function.

Premature MicroRNA-1 Expression Causes Hypoplasia of the Cardiac Ventricular Conduction System.

Mammalian cardiac Purkinje fibers (PFs) are specified from ventricular trabecular myocardium during mid-gestation and undergo limited proliferation before assuming their final form. MicroRNA-1 (miR-1), a negative regulator of proliferation, is normally expressed in the heart at low levels during the period of PF specification and outgrowth, but expression rises steeply after birth, when myocardial proliferation slows and postnatal cardiac maturation and growth commence. Here, we test whether premature up-regulation and overexpression of miR-1 during the period of PF morphogenesis influences PF development and function.

RNA sequencing of mouse sinoatrial node reveals an upstream regulatory role for Islet-1 in cardiac pacemaker cells.

Rationale: Treatment of sinus node disease with regenerative or cell-based therapies will require a detailed understanding of gene regulatory networks in cardiac pacemaker cells (PCs).

Objective: To characterize the transcriptome of PCs using RNA sequencing and to identify transcriptional networks responsible for PC gene expression.

Methods And Results: We used laser capture microdissection on a sinus node reporter mouse line to isolate RNA from PCs for RNA sequencing.

Allogeneic cardiospheres safely boost cardiac function and attenuate adverse remodeling after myocardial infarction in immunologically mismatched rat strains.

Objectives: We sought to characterize the immunologic profile of allogeneic cardiospheres, which are 3-dimensional, self-assembling, cardiac-derived microtissues, and to evaluate their safety and efficacy in repairing ischemic heart tissue.

Background: Intramyocardial injection of autologous cardiospheres ameliorates remodeling and improves global function in infarcted myocardium. It is as yet unknown whether allogeneic cardiospheres are similarly effective without eliciting deleterious immune reactions.

Cardiomyocyte proliferation and progenitor cell recruitment underlie therapeutic regeneration after myocardial infarction in the adult mouse heart.

Cardiosphere-derived cells (CDCs) have been shown to regenerate infarcted myocardium in patients after myocardial infarction (MI). However, whether the cells of the newly formed myocardium originate from the proliferation of adult cardiomyocytes or from the differentiation of endogenous stem cells remains unknown. Using genetic fate mapping to mark resident myocytes in combination with long-term BrdU pulsing, we investigated the origins of postnatal cardiomyogenesis in the normal, infarcted and cell-treated adult mammalian heart.

Functional performance of human cardiosphere-derived cells delivered in an in situ polymerizable hyaluronan-gelatin hydrogel.

The vast majority of cells delivered into the heart by conventional means are lost within the first 24 h. Methods are needed to enhance cell retention, so as to minimize loss of precious material and maximize effectiveness of the therapy. We tested a cell-hydrogel delivery strategy.

Magnetic enhancement of cell retention, engraftment, and functional benefit after intracoronary delivery of cardiac-derived stem cells in a rat model of ischemia/reperfusion.

The efficiency of stem cell transplantation is limited by low cell retention. Intracoronary (IC) delivery is convenient and widely used but exhibits particularly low cell retention rates. We sought to improve IC cell retention by magnetic targeting.

Transplantation of platelet gel spiked with cardiosphere-derived cells boosts structural and functional benefits relative to gel transplantation alone in rats with myocardial infarction.

The emerging field of stem cell therapy and biomaterials has begun to provide promising strategies for the treatment of ischemic cardiomyopathy. Platelet gel and cardiosphere-derived cells (CDCs) are known to be beneficial when transplanted separately post-myocardial infarction (MI). We hypothesize that pre-seeding platelet gel with CDCs can enhance therapeutic efficacy.

Intramyocardial injection of platelet gel promotes endogenous repair and augments cardiac function in rats with myocardial infarction.

Objectives: This study sought to explore the therapeutic potential of platelet gel for the treatment of myocardial infarction.

Background: Cardiac dysfunction after acute myocardial infarction is a major cause of heart failure. Current therapy relies on prompt reperfusion and blockage of secondary maladaptive pathways by small molecules.

Safety and efficacy of allogeneic cell therapy in infarcted rats transplanted with mismatched cardiosphere-derived cells.

Background: Cardiosphere-derived cells (CDCs) are an attractive cell type for tissue regeneration, and autologous CDCs are being tested clinically. However, autologous therapy necessitates patient-specific tissue harvesting and cell processing, with delays to therapy and possible variations in cell potency. The use of allogeneic CDCs, if safe and effective, would obviate such limitations.

Transcriptional suppression of connexin43 by TBX18 undermines cell-cell electrical coupling in postnatal cardiomyocytes.

T-box transcription factors figure prominently in embryonic cardiac cell lineage specifications. Mesenchymal precursor cells expressing Tbx18 give rise to the heart's pacemaker, the sinoatrial node (SAN). We sought to identify targets of TBX18 transcriptional regulation in the heart by forced adenoviral overexpression in postnatal cardiomyocytes.

Dedifferentiation and proliferation of mammalian cardiomyocytes.

Background: It has long been thought that mammalian cardiomyocytes are terminally-differentiated and unable to proliferate. However, myocytes in more primitive animals such as zebrafish are able to dedifferentiate and proliferate to regenerate amputated cardiac muscle.

Methodology/principal Findings: Here we test the hypothesis that mature mammalian cardiomyocytes retain substantial cellular plasticity, including the ability to dedifferentiate, proliferate, and acquire progenitor cell phenotypes.

Intermolecular cross-linking of Na+-Ca2+ exchanger proteins: evidence for dimer formation.

The cardiac Na (+)-Ca (2+) exchanger (NCX1) is modeled to contain nine transmembrane segments (TMS) with a pair of oppositely oriented, conserved sequences called the alpha-repeats that are important in ion transport. Residue 122 in the alpha-1 repeat is in proximity to residue 768 in TMS 6, and the two residues can be cross-linked . During studies on the substrate specificity of this intramolecular cross-link, we found evidence that NCX1 can form dimers.