Cocultures of fetal and adult cardiomyocytes yield rhythmically beating rod shaped heart cells from adult rats

Cardiomyocyte Contractility and Autophagy in a Premature Senescence Model of Cardiac Aging

Globally, cardiovascular diseases are the leading cause of death in the aging population. While the clinical pathology of the aging heart is thoroughly characterized, underlying molecular mechanisms are still insufficiently clarified. The aim of the present study was to establish an in vitro model system of cardiomyocyte premature senescence, culturing heart muscle cells derived from neonatal C57Bl/6J mice for 21 days. Premature senescence of neonatal cardiac myocytes was induced by prolonged culture time in an oxygen-rich postnatal environment. Age-related changes in cellular function were determined by senescence-associated β-galactosidase activity, increasing presence of cell cycle regulators, such as p16, p53, and p21, accumulation of protein aggregates, and restricted proteolysis in terms of decreasing (macro-)autophagy. Furthermore, the culture system was functionally characterized for alterations in cell morphology and contractility. An increase in cellular size associated with induced expression of atrial natriuretic peptides demonstrated a stress-induced hypertrophic phenotype in neonatal cardiomyocytes. Using the recently developed analytical software tool Myocyter, we were able to show a spatiotemporal constraint in spontaneous contraction behavior during cultivation. Within the present study, the 21-day culture of neonatal cardiomyocytes was defined as a functional model system of premature cardiac senescence to study age-related changes in cardiomyocyte contractility and autophagy.

Effective and steady differentiation of a clonal derivative of P19CL6 embryonal carcinoma cell line into beating cardiomyocytes

The P19CL6 cell line is a useful model to study cardiac differentiation in vitro. However, large variations were noticed in the differentiation rates among previous reports as well as our individual experiments. To overcome the unstable differentiation, we established P19CL6-A1, a new clonal derivative of P19CL6 that could differentiate into cardiomyocytes more efficiently and stably than the parent using the double stimulation with 5-Aza and DMSO based on the previous report. We also introduced a new software, Visorhythm, that can analyze the temporal variations in the beating rhythms and can chart correlograms displaying the oscillated rhythms. Using P19CL6-A1-derived cardiomyocytes and the software, we demonstrated that the correlograms could clearly display the enhancement of beating rates by cardiotonic reagents. These indicate that a combination of P19CL6-A1 and Visorhythm is a useful tool that can provide invaluable assistance in inotropic drug discovery, drug screening, and toxicity testing.

Phenylephrine and sustained acidosis activate the neonatal rat cardiomyocyte Na+/H+ exchanger through phosphorylation of amino acids Ser770 and Ser771

The mammalian Na(+)/H(+) exchanger isoform 1 (NHE1) is a ubiquitously expressed membrane protein that regulates intracellular pH in the myocardium. NHE1 is also important in mediating myocardial hypertrophy, and the blockage of NHE1 activity prevents hypertrophy and reduces ischemia-reperfusion injury in animal models. We recently demonstrated that extracellular-regulated kinase (ERK)-mediated activation of NHE1 occurs during ischemia-reperfusion of the myocardium. To understand the regulation of NHE1 in the myocardium by phosphorylation, we expressed a series of adenoviruses that express wild-type and mutant cDNA for NHE1. All exogenous cDNA for NHE1 had additional mutations [Leu(163)Phe/Gly(174)Ser], which increases NHE1 resistance to EMD-87580 (a specific blocker of NHE1) 100-fold, and allowed the measurement of exogenous NHE1 while inhibiting endogenous NHE1. By examining the effects of a series of mutations of the NHE1 cytosolic region, we determined that the amino acids Ser(770) and Ser(771) were essential for the acute activation of NHE1 activity in rat cardiomyocytes. The specific mutation of either residue prevented the rapid activation of exchanger activity by a sustained intracellular acidosis through ERK-dependent pathways. The same amino acids were critical to phenylephrine-mediated, ERK-dependent activation of NHE1 activity and increased the phosphorylation in intact rat cardiomyocytes. The results demonstrate that both sustained intracellular acidosis and phenylephrine rapidly activate the NHE1 protein in intact cardiac cells through ERK-dependent pathways that act on a common pathway mediated by amino acids Ser(770) and Ser(771) of the cytosolic tail of the protein.

Cardiomyocyte transplantation into the failing heart-new therapeutic approach for heart failure?

Heart failure, frequently the consequence of irreversible myocardial damage with subsequent formation of akinetic scar tissue, is a highly prevalent disease, and in its advanced stages associated with high mortality. The transplantation of exogenous cells with the inherent ability to contract has been put forward as one potential treatment strategy to increase contractility and cardiac performance. Besides skeletal myoblasts or stem cells from various sources, immature cardiomyocytes, such as fetal or neonatal cardiomyocytes, have been transplanted into normal, cryoinjured, infarcted myocardium, as well as into models of global heart failure. Survival of transplanted immature cardiomyocytes has been demonstrated up to 6-7 months, accompanied by vascularization of the grafted tissue. Transplants developed sarcomeric structures and other morphological features of differentiation. The principal possibility of cell-to-cell coupling between graft and host cells was demonstrated after cardiomyocyte transplantation into normal hearts and in some studies in damaged myocardium. But most long-term follow-up investigations in models of myocardial infarction reported that optimal integration of the engrafted cells appeared to be hindered by scar tissue, separating the transplant from the host. Nonetheless, in several studies, improved parameters of cardiac performance were demonstrated ex-vivo and in vivo. Potential mechanisms might involve beneficial effects on the remodeling process. In this review, we critically evaluate the potential value of cardiomyocyte transplantation as a new approach in the treatment of the syndrome of "heart failure".