Daniel J. Lips

Human embryonic stem cell-derived cardiomyocytes survive and mature in the mouse heart and transiently improve function after myocardial infarction

Regeneration of the myocardium by transplantation of cardiomyocytes is an emerging therapeutic strategy. Human embryonic stem cells (HESC) form cardiomyocytes readily but until recently at low efficiency, so that preclinical studies on transplantation in animals are only just beginning. Here, we show the results of the first long-term (12 weeks) analysis of the fate of HESC-derived cardiomyocytes transplanted intramyocardially into healthy, immunocompromised (NOD-SCID) mice and in NOD-SCID mice that had undergone myocardial infarction (MI). Transplantation of mixed populations of differentiated HESC containing 20-25% cardiomyocytes in control mice resulted in rapid formation of grafts in which the cardiomyocytes became organized and matured over time and the noncardiomyocyte population was lost. Grafts also formed in mice that had undergone MI. Four weeks after transplantation and MI, this resulted in significant improvement in cardiac function measured by magnetic resonance imaging. However, at 12 weeks, this was not sustained despite graft survival. This suggested that graft size was still limiting despite maturation and organization of the transplanted cells. More generally, the results argued for requiring a minimum of 3 months follow-up in studies claiming to observe improved cardiac function, independent of whether HESC or other (adult) cell types are used for transplantation.

MEK1-ERK2 Signaling Pathway Protects Myocardium From Ischemic Injury In Vivo

Background—Myocardial infarction causes a rapid and largely irreversible loss of cardiac myocytes that can lead to sudden death, ventricular dilation, and heart failure. Members of the mitogen-activated protein kinase (MAPK) signaling cascade have been implicated as important effectors of cardiac myocyte cell death in response to diverse stimuli, including ischemia-reperfusion injury. Specifically, activation of the extracellular signal–regulated kinases 1/2 (ERK1/2) has been associated with cardioprotection, likely through antagonism of apoptotic regulatory pathways. Methods and Results—To establish a causal relationship between ERK1/2 signaling and cardioprotection, we analyzed Erk1 nullizygous gene-targeted mice, Erk2 heterozygous gene-targeted mice, and transgenic mice with activated MEK1-ERK1/2 signaling in the heart. Although MEK1 transgenic mice were largely resistant to ischemia-reperfusion injury, Erk2+/− gene-targeted mice showed enhanced infarction areas, DNA laddering, and terminal deoxynucleotidyl transferase–mediated dUTP biotin nick-end labeling (TUNEL) compared with littermate controls. In contrast, enhanced MEK1-ERK1/2 signaling protected hearts from DNA laddering, TUNEL, and preserved hemodynamic function assessed by pressure-volume loop recordings after ischemia-reperfusion injury. Conclusions—These data are the first to demonstrate that ERK2 signaling is required to protect the myocardium from ischemia-reperfusion injury in vivo.

Molecular determinants of myocardial hypertrophy and failure: alternative pathways for beneficial and maladaptive hypertrophy

The implementation of molecular biological approaches has led to the discovery of single genetic variations that contribute to the development of cardiac failure. In the present review, the characteristics that are invariably associated with the development of failure in experimental animals and clinical studies are discussed, which may provide attractive biological targets in the treatment of human heart failure. Findings from the Framingham studies have provided evidence that the presence of left ventricular hypertrophy is the main risk factor for subsequent development of heart failure in man. Conventional views identify myocardial hypertrophy as a compensatory response to increased workload, prone to evoke disease. Recent findings in genetic models of myocardial hypertrophy and human studies have provided the molecular basis for a novel concept, which favours the existence of either compensatory or maladaptive forms of hypertrophy, of which only the latter leads the way to cardiac failure. Furthermore, the concept that hypertrophy compensates for augmented wall stress is probably outdated. In this article, we provide the molecular pathways that can distinguish beneficial from maladaptive hypertrophy.

MCIP1 overexpression suppresses left ventricular remodeling and sustains cardiac function after myocardial infarction

Pathological remodeling of the left ventricle (LV) after myocardial infarction (MI) is a major cause of heart failure. Although cardiac hypertrophy after increased loading conditions has been recognized as a clinical risk factor for human heart failure, it is unknown whether post-MI hypertrophic remodeling of the myocardium is beneficial for cardiac function over time, nor which regulatory pathways play a crucial role in this process. To address these questions, transgenic (TG) mice engineered to overexpress modulatory calcineurin-interacting protein-1 (MCIP1) in the myocardium were used to achieve cardiac-specific inhibition of calcineurin activation. MCIP1-TG mice and their wild-type (WT) littermates, were subjected to MI and analyzed 4 weeks later. At 4 weeks after MI, calcineurin was activated in the LV of WT mice, which was significantly reduced in MCIP1-TG mice. WT mice displayed a 78% increase in LV mass after MI, which was reduced by 38% in MCIP1-TG mice. Echocardiography indicated marked LV dilation and loss of systolic function in WT-MI mice, whereas TG-MI mice displayed a remarkable preservation of LV geometry and contractility, a pronounced reduction in myofiber hypertrophy, collagen deposition, and &bgr;-MHC expression compared with WT-MI mice. Together, these results reveal a protective role for MCIP1 in the post-MI heart and suggest that calcineurin is a crucial regulator of postinfarction-induced pathological LV remodeling. The improvement in functional, structural, and molecular abnormalities in MCIP1-TG mice challenges the adaptive value of post-MI hypertrophy of the remote myocardium. The full text of this article is available online at http://circres.ahajournals.org.

Estrogen Receptor β Protects the Murine Heart Against Left Ventricular Hypertrophy

Background—Left ventricular hypertrophy (LVH) displays significant gender-based differences. 17&bgr;-estradiol (E2) plays an important role in this process because it can attenuate pressure overload hypertrophy via 2 distinct estrogen receptors (ERs): ER&agr; and ER&bgr;. However, which ER is critically involved in the modulation of LVH is poorly understood. We therefore used ER&agr;-deficient (ER&agr;−/−) and ER&bgr;-deficient (ER&bgr;−/−) mice to analyze the respective ER-mediated effects. Methods and Results—Respective ER-deficient female mice were ovariectomized and were given E2 or placebo subcutaneously using 60-day release pellets. After 2 weeks, they underwent transverse aortic constriction (TAC) or sham operation. In ER&agr;−/− animals, TAC led to a significant increase in ventricular mass compared with sham operation. E2 treatment reduced TAC induced cardiac hypertrophy significantly in wild-type (WT) and ER&agr;−/− mice but not in ER&bgr;−/− mice. Biochemical analysis showed that E2 blocked the increased phosphorylation of p38–mitogen-activated protein kinase observed in TAC-treated ER&agr;−/− mice. Moreover, E2 led to an increase of ventricular atrial natriuretic factor expression in WT and ER&agr;−/− mice. Conclusions—These findings demonstrate that E2, through ER&bgr;-mediated mechanisms, protects the murine heart against LVH.

Calcineurin Aβ Gene Targeting Predisposes the Myocardium to Acute Ischemia-Induced Apoptosis and Dysfunction

Abstract— Cardiovascular disease is the leading cause of mortality and morbidity within the industrialized nations of the world, with coronary heart disease (CHD) accounting for as much as 66% of these deaths. Acute myocardial infarction is a typical sequelae associated with long-standing coronary heart disease resulting in large scale loss of ventricular myocardium through both apoptotic and necrotic cell death. In this study, we investigated the role that the calcium calmodulin-activated protein phosphatase calcineurin (PP2B) plays in modulating cardiac apoptosis after acute ischemia-reperfusion injury to the heart. Calcineurin A &bgr; gene–targeted mice showed a greater loss of viable myocardium, enhanced DNA laddering and TUNEL, and a greater loss in functional performance compared with strain-matched wild-type control mice after ischemia-reperfusion injury. RNA expression profiling was performed to uncover potential mechanisms associated with this loss of cardioprotection. Interestingly, calcineurin A &bgr;−/− hearts were characterized by a generalized downregulation in gene expression representing approximately 6% of all genes surveyed. Consistent with this observation, nuclear factor of activated T cells (NFAT)-luciferase reporter transgenic mice showed reduced expression in calcineurin A &bgr;−/− hearts at baseline and after ischemia-reperfusion injury. Finally, expression of an activated NFAT mutant protected cardiac myocytes from apoptotic stimuli, whereas directed inhibition of NFAT augmented cell death. These results represent the first genetic loss-of-function data showing a prosurvival role for calcineurin-NFAT signaling in the heart.

Diagnosing diastolic heart failure.

increasing evidence supports the existence of left ventricular diastolic dysfunction as an important cause of congestive heart failure, present in up to 40% of heart failure patients.

Left ventricular pressure–volume measurements in mice: Comparison of closed–chest versus open–chest approach

AbstractObjectiveWe investigated whether in vivo closed–chest left ventricular pressure–volume measurements would yield similar values for LV hemodynamics compared with open–chest PV measurements under several anesthetics.MethodsThe right common carotid of C57Bl/6 mice was cannulated with a combined pressure–conductance catheter and inserted retrogradely into the left ventricle in the closed–chest model. The open–chest model consisted of an abdominal approach involving the opening of the thoracic cavity by transverse opening of the diaphragm and ventricular catheterization by apical stab. Measurements were performed under urethane or pentobarbital intraperitoneal injection anesthesia.ResultsCardiac function in the open–chest model was characterized by larger ejection fraction and stroke volume with a leftward shift in ventricular volume compared to the closed–chest model. Further observed characteristics include low endsystolic pressure and arterial–ventricular coupling mismatch in the openchest model. Arrhythmias were not detected in either model.ConclusionMurine cardiac function determination via open–chest or closed–chest protocols is sensitive, reproducible and comparable. The choice for open– or closed–chest pressure–volume measurements in mice depends on the aims of the study.

Oestrogen modulates cardiac ischaemic remodelling through oestrogen receptor-specific mechanisms.

Aim:  Observational and clinical studies suggest different responses upon sex hormone replacement therapy in ischaemic heart disease. Few studies, however, have examined the impact of oestrogen receptor‐dependent mechanisms on the extent of injury after myocardial infarction (MI). Therefore, we set out to evaluate the effect of oestrogen (E2) replacement on infarct size and remodelling, and the respective role of the oestrogen receptors (ER)α and ‐β in this process, using ERα‐ and ERβ‐deficient mice.

Cardiac Hypertrophic Signaling the Good, the Bad and the Ugly

All cells in multi-cellular organisms must be able to sense their surrounding environment and and respond based upon this information. In a similar fashion, cardiac muscle cells are equipped with a specialized protein machinery composed of detection systems (receptors), intermediate proteins within the cell for information transduction (intracellular signal transducers) and nuclear components specialized in changing the genetic profile of the cell (transcription factors). This integrated system is the subject of part of the biological sciences that studies “signal transduction” or shortly “signaling”, and topics the molecular mechanisms by which transfer of biological - information at the cellular level is converted. Cardiac signaling systems provide crucial information for cells to decide about differentiation status, death or metabolic control. As such, it is not surprising that many signaling malfunctions underly human diseases. For example, cancer evolves following inactivating mutations in growth-inhibitory pathways, resulting in specialized cells with proliferative advantages over its neighbouring cells[1]. Diabetes results from defects in the insulin-signaling pathway used to control blood glucose levels[2]. Certain forms of achrondoplasia (dwarfism) result from mutations in the receptor tyrosine kinase for fibroblast growth factor, [3] while in agammaglobulinaemia (failure to produce immunoglobulins in the blood), a mutation in the B-cell tyrosine kinase Btk results in a failure of this enzyme to respond to activation of the enzyme phosphatidylinositol-3-OH kinase (PI-3K) [4].