Myofibroblasts Electrotonically Coupled to Cardiomyocytes Alter Conduction: Insights at the Cellular Level from a Detailed In silico Tissue Structure Model

Fibrotic myocardial remodeling is typically accompanied by the appearance of myofibroblasts (MFBs). In vitro, MFBs were shown to slow conduction and precipitate ectopic activity following gap junctional coupling to cardiomyocytes (CMCs). To gain further mechanistic insights into this arrhythmogenic MFB-CMC crosstalk, we performed numerical simulations in cell-based high-resolution two-dimensional tissue models that replicated experimental conditions. Cell dimensions were determined using confocal microscopy of single and co-cultured neonatal rat ventricular CMCs and MFBs. Conduction was investigated as a function of MFB density in three distinct cellular tissue architectures: CMC strands with endogenous MFBs, CMC strands with coating MFBs of two different sizes, and CMC strands with MFB inserts. Simulations were performed to identify individual contributions of heterocellular gap junctional coupling and of the specific electrical phenotype of MFBs. With increasing MFB density, both endogenous and coating MFBs slowed conduction. At MFB densities of 5-30%, conduction slowing was most pronounced in strands with endogenous MFBs due to the MFB-dependent increase in axial resistance. At MFB densities >40%, very slow conduction and spontaneous activity was primarily due to MFB-induced CMC depolarization. Coating MFBs caused non-uniformities of resting membrane potential, which were more prominent with large than with small MFBs. In simulations of MFB inserts connecting two CMC strands conduction delays increased with increasing insert lengths and block appeared for inserts >1.2 mm. Thus, electrophysiological properties of engineered CMC-MFB co-cultures depend on MFB density, MFB size and their specific positioning in respect to CMCs. These factors may influence conduction characteristics in the heterocellular myocardium

Electrical Coupling Between Micropatterned Cardiomyocytes and Stem Cells

To understand how stem cells functionally couple with native cardiomyocytes is crucial for cell-based therapies to restore the loss of cardiomyocytes that occurs during heart infarction and other cardiac diseases. Due to the complexity of the in vivo environment, our knowledge of cell coupling is heavily dependent on cell-culture models. However, conventional in vitro studies involve undefined cell shapes and random length of cell-cell contacts in addition to the presence of multiple homotypic and heterotypic contacts between interacting cells. Thus, it has not been feasible to study electrical coupling corresponding to isolated specific types of cell contact modes. To address this issue, we used microfabrication techniques to develop different geometrically-defined stem cell-cardiomyocyte contact assays to comparatively and quantitatively study functional stem cell-cardiomyocyte electrical coupling. Through geometric confinements, we will construct a matrix of identical microwells, and each was constructed as a specific microenvironment. Using laser-guided cell micropatterning technique, individual stem cells or cardiomyocytes can be deposited into the microwells to form certain contact mode. In this research, we firstly constructed an in-vivo like cardiac muscle fiber microenvironment, and the electrical conductivity of stem cells was investigated by inserting stem cells as cellular bridges. Then, the electrical coupling between cardiomyocytes and stem cells was studied at single-cell level by constructing contact-promotive/-preventive microenvironments

Generation of left ventricle-like cardiomyocytes with improved structural, functional, and metabolic maturity from human pluripotent stem cells

Decreased left ventricle (LV) function caused by genetic mutations or injury often leads to debilitating and fatal cardiovascular disease. LV cardiomyocytes are, therefore, a potentially valuable therapeutical target. Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are neither homogeneous nor functionally mature, which reduces their utility. Here, we exploit cardiac development knowledge to instruct differentiation of hPSCs specifically toward LV cardiomyocytes. Correct mesoderm patterning and retinoic acid pathway blocking are essential to generate near-homogenous LV-specific hPSC-CMs (hPSC-LV-CMs). These cells transit via first heart field progenitors and display typical ventricular action potentials. Importantly, hPSC-LV-CMs exhibit increased metabolism, reduced proliferation, and improved cytoarchitecture and functional maturity compared with age-matched cardiomyocytes generated using the standard WNT-ON/WNT-OFF protocol. Similarly, engineered heart tissues made from hPSC-LV-CMs are better organized, produce higher force, and beat more slowly but can be paced to physiological levels. Together, we show that functionally matured hPSC-LV-CMs can be obtained rapidly without exposure to current maturation regimes

Characterizing Cardiac Electrophysiology during Radiofrequency Ablation : An Integrative Ex vivo, In silico, and In vivo Approach

Catheter ablation is a major treatment for atrial tachycardias. Hereby, the precise monitoring of the lesion formation is an important success factor. This book presents computational, wet-lab, and clinical studies with the aim of evaluating the signal characteristics of the intracardiac electrograms (IEGMs) recorded around ablation lesions from different perspectives. The detailed analysis of the IEGMs can optimize the description of durable and complex lesions during the ablation procedure

Stem Cell Research on Cardiology

Even today, cardiovascular diseases are the main cause of death worldwide, and therapeutic approaches are very restricted. Due to the limited regenerative capabilities of terminally differentiated cardiomyocytes post injury, new strategies to treat cardiac patients are urgently needed. Post myocardial injury, resident fibroblasts begin to generate the extracellular matrix, resulting in fibrosis, and finally, cardiac failure. Recently, preclinical investigations and clinical trials raised hope in stem cell-based approaches, to be an effective therapy option for these diseases. So far, several types of stem cells have been identified to be promising candidates to be applied for treatment: cardiac progenitor cells, bone marrow derived stem cells, embryonic and induced pluripotent stem cells, as well as their descendants. Furthermore, the innovative techniques of direct cardiac reprogramming of cells offered promising options for cardiovascular research, in vitro and in vivo. Hereby, the investigation of underlying and associated mechanisms triggering the therapeutic effects of stem cell application is of particular importance to improve approaches for heart patients. This Special Issue of Cells provides the latest update in the rapidly developing field of regenerative medicine in cardiology

Recombinant Human Neuregulin-1 in Myocardial Ischaemia-Reperfusion Injury and Chronic Heart Failure

Neuregulin-1, a ligand of the ErbB family of receptor tyrosine kinases is produced by endocardial and myocardial microvascular endothelial cells and acts in a paracrine fashion on adjacent cardiac myocytes. Neuregulin-1-ErbB signalling critically regulates cardiac development and the adaptation of the heart to injury; inhibiting apoptosis, inducing cardiomyocyte proliferation and improving cardiac function and survival in animal models of cardiomyopathy.Neuregulin-1-ErbB signalling also involves pathways involved in protecting against ischaemia-reperfusion injury. This thesis reports the first human studies exploring the acute and chronic haemodynamic responses to a series of recombinant human Neuregulin-1 (rhNeuregulin-1) infusions in patients with stable chronic heart failure and also reports a series of studies aimed at enhancing cardiac preservation in heart transplantation by rhNeuregulin-1 supplementation of a cardiac storage solution. During a 6-hour rhNeuregulin-1 infusion cardiac output increased by 30% (p<0.01), pulmonary artery wedge pressure and systemic vascular resistance decreased 30% and 20% respectively at two hours (p<0.01). A 47% reduction in serum noradrenaline, a 55% reduction in serum aldosterone and a 3.6-fold increase in N-terminal fragment of B-type natriuretic peptide levels were concurrently observed (p<0.001). These acute haemodynamic effects were sustained, as demonstrated by a 12% increase in left ventricular ejection fraction from 32.2±2.0% (baseline) to 36.1±2.3% (mean±1SE, p<0.001) at 84 days. The therapy was well tolerated. In a rodent model of global ischaemia-reperfusion injury, rhNeuregulin-1 supplemented Celsior storage solution improved functional recovery of hearts after 6 hours of hypothermic storage, an effect abrogated by the phosphatidylinositol-3-kinase inhibitor, wortmannin. When storage times were extended out to 10 hours, rhNeuregulin-1 further enhanced cardiac preservation when used in combination with other activators of pro-survival pathways (p<0.01). Functional improvements were accompanied by increased phosphorylation of Akt, extracellular signal-regulated protein kinases 1/2, signal transducer and activator of transcription 3 and glycogen synthase kinase 3β (Western blotting) and a reduction in the cleaved form of caspase-3 (immunohistochemical staining). rhNeuregulin-1produces favourable acute and chronic haemodynamic effects in patients with stable chronic heart failure on optimal medical therapy and improves preservation of the rat heart after prolonged hypothermic storage. It shows promise as a novel therapy in heart failure and transplantation