Wnt/ß-Catenin Stimulation and Laminins Support Cardiovascular Cell Progenitor Expansion from Human Fetal Cardiac Mesenchymal Stromal Cells.

The intrinsic regenerative capacity of human fetal cardiac mesenchymal stromal cells (MSCs) has not been fully characterized. Here we demonstrate that we can expand cells with characteristics of cardiovascular progenitor cells from the MSC population of human fetal hearts. Cells cultured on cardiac muscle laminin (LN)-based substrata in combination with stimulation of the canonical Wnt/ß-catenin pathway showed increased gene expression of ISL1, OCT4, KDR, and NKX2.5. The majority of cells stained positive for PDGFR-α, ISL1, and NKX2.5, and subpopulations also expressed the progenitor markers TBX18, KDR, c-KIT, and SSEA-1. Upon culture of the cardiac MSCs in differentiation media and on relevant LNs, portions of the cells differentiated into spontaneously beating cardiomyocytes, and endothelial and smooth muscle-like cells. Our protocol for large-scale culture of human fetal cardiac MSCs enables future exploration of the regenerative functions of these cells in the context of myocardial injury in vitro and in vivo.

Exploration of human, rat, and rabbit embryonic cardiomyocytes suggests K-channel block as a common teratogenic mechanism.

AIMS: Several drugs blocking the rapidly activating potassium (K(r)) channel cause malformations (including cardiac defects) and embryonic death in animal teratology studies. In humans, these drugs have an established risk for acquired long-QT syndrome and arrhythmia. Recently, associations between cardiac defects and spontaneous abortions have been reported for drugs widely used in pregnancy (e.g. antidepressants), with long-QT syndrome risk. To investigate whether a common embryonic adverse-effect mechanism exists in the human, rat, and rabbit embryos, we made a comparative study of embryonic cardiomyocytes from all three species. METHODS AND RESULTS: Patch-clamp and quantitative-mRNA measurements of K(r) and slowly activating K (K(s)) channels were performed on human, rat, and rabbit primary cardiomyocytes and cardiac samples from different embryo-foetal stages. The K(r) channel was present when the heart started to beat in all species, but was, in contrast to human and rabbit, lost in rats in late organogenesis. The specific K(r)-channel blocker E-4031 prolonged the action potential in a species- and development-dependent fashion, consistent with the observed K(r)-channel expression pattern and reported sensitive periods of developmental toxicity. E-4031 also increased the QT interval and induced 2:1 atrio-ventricular block in multi-electrode array electrographic recordings of rat embryos. The K(s) channel was expressed in human and rat throughout the embryo-foetal period but not in rabbit. CONCLUSION: This first comparison of mRNA expression, potassium currents, and action-potential characteristics, with and without a specific K(r)-channel blocker in human, rat, and rabbit embryos provides evidence of K(r)-channel inhibition as a common mechanism for embryonic malformations and death.

Ischemia-reperfusion injury and pregnancy initiate time-dependent and robust signs of up-regulation of cardiac progenitor cells.

To explore how cardiac regeneration and cell turnover adapts to disease, different forms of stress were studied for their effects on the cardiac progenitor cell markers c-Kit and Isl1, the early cardiomyocyte marker Nkx2.5, and mast cells. Adult female rats were examined during pregnancy, after myocardial infarction and ischemia-reperfusion injury with/out insulin like growth factor-1(IGF-1) and hepatocyte growth factor (HGF). Different cardiac sub-domains were analyzed at one and two weeks post-intervention, both at the mRNA and protein levels. While pregnancy and myocardial infarction up-regulated Nkx2.5 and c-Kit (adjusted for mast cell activation), ischemia-reperfusion injury induced the strongest up-regulation which occurred globally throughout the entire heart and not just around the site of injury. This response seems to be partly mediated by increased endogenous production of IGF-1 and HGF. Contrary to c-Kit, Isl1 was not up-regulated by pregnancy or myocardial infarction while ischemia-reperfusion injury induced not a global but a focal up-regulation in the outflow tract and also in the peri-ischemic region, correlating with the up-regulation of endogenous IGF-1. The addition of IGF-1 and HGF did boost the endogenous expression of IGF and HGF correlating to focal up-regulation of Isl1. c-Kit expression was not further influenced by the exogenous growth factors. This indicates that there is a spatial mismatch between on one hand c-Kit and Nkx2.5 expression and on the other hand Isl1 expression. In conclusion, ischemia-reperfusion injury was the strongest stimulus with both global and focal cardiomyocyte progenitor cell marker up-regulations, correlating to the endogenous up-regulation of the growth factors IGF-1 and HGF. Also pregnancy induced a general up-regulation of c-Kit and early Nkx2.5+ cardiomyocytes throughout the heart. Utilization of these pathways could provide new strategies for the treatment of cardiac disease.

Islet-1 cells are cardiac progenitors present during the entire lifespan: from the embryonic stage to adulthood.

The aim of this study was to longitudinally characterize the distribution of cells actively expressing the progenitor transcription factor islet-1 (Isl1+) during the embryonic life, the postnatal period, and adulthood. In this study, we have used direct immunohistochemical staining toward the protein Isl1 in a longitudinal rat model. Cells actively expressing Isl1 were traced in embryos from gestational day (GD) 11 until adulthood. In early cardiac development (GD 11), the Isl1+ progenitors were located in a greater abundance in the paracardiac regions, areas suggested to be the second heart field. To a lesser extent, Isl1+ cells were present within the bulbotruncal region and the truncus arteriosus. During the following days until GD 15, the Isl1+ cells were mainly observed at the proximal outflow tract (OFT) and at the inflow area of the right atrium. No Isl1+ cells were detected in the left ventricle. Compared with GD 11, more Isl1+ cells seemed to co-express cardiomyocyte markers and a minority of the Isl1+ cells was undifferentiated. Unexpectedly, only few undifferentiated Isl1+ cells were Ki67+ while a lot of TnT+ cardiomyocytes were proliferating in the ventricles. After birth, immature Isl1+ cells were still present in the OFT where they resided until adulthood. Our data suggest that during embryogenesis, Isl1+ cells migrate from extracardiac regions into the proximal part of the heart, proliferating and giving rise to cardioblasts. Unexpectedly, only a minority of the Isl1+ cells while a majority of ventricular cardiomyocytes were proliferating. The Isl1+ cell pool persists into adulthood, which might open up new strategies to repair damaged myocardium.

Early first trimester human embryonic cardiac Islet-1 progenitor cells and cardiomyocytes: Immunohistochemical and electrophysiological characterization.

The aims of this study were to systematically characterize the distribution, proliferation, and differentiation of Islet-1(+)(Isl1(+)) progenitor cells in the early first trimester human embryonic heart during which period most of the organogenesis takes place. In hearts of gestational week 5 to 10 Isl1(+)cells were identified and mainly clustered in the outflow tract and to a lesser extent in the atria and in the right ventricle. Some of the clusters were also troponin T(+). Unexpectedly a only few Isl1(+)cells were Ki67(+)while in the ventricles a majority of Isl1(-)troponinT(+)cells were Ki67(+). Cultures derived from the digested embryonic heart developed into spontaneously beating cardiospheres. At harvest cells in these cardiospheres showed frequent expression of troponin T(+)and Nkx2.5(+), while Isl1 was expressed only in scattered cells. Only a minority of the cultured cells expressed Ki67. The cardiospheres could be frozen, thawed, and recultured to beating cardiospheres. In a multielectrode array system, the beating cardiospheres were responsive to adrenergic stimulation and exhibited rate-dependent action potential duration. In conclusion, the early first trimester human embryonic heart expresses clusters of Isl1(+)cells, some of which differentiate into cardiomyocytes. Unexpectedly, only a minority of the Isl1(+)cells, while a majority of ventricular cardiomyocytes, were proliferating. Spontaneously beating cardiospheres could be derived from the human embryonic heart and these cardiospheres showed functional frequency control.

Costimulation blockade induces tolerance to HESC transplanted to the testis and induces regulatory T-cells to HESC transplanted into the heart.

In order to study the ability of costimulation blockade to induce tolerance to human embryonic stem cells (HESC), severe combined immunodeficient (SCID), and immunocompetent C57BL/6 mice treated with costimulation blockade received intratesticular and intramyocardial HESC transplants. All SCID mice with intratesticular HESC transplants developed teratoma. When SCID mice were transplanted intramyocardially, only two of five mice developed teratoma-like tumors. C57BL/6 mice transplanted intratesticularly and treated with costimulation blockade all developed teratoma and were surrounded by CD4(+)CD25(+)Foxp3(+) T-cells, while isotype control treated recipients rejected their grafts. Most C57BL/6 mice transplanted intramyocardially and treated with costimulation blockade demonstrated lymphocytic infiltrates 1 month after transplantation, whereas one maintained its graft. Isolation of regulatory T-cells from intramyocardial transplanted recipients treated with costimulation blockade demonstrated specificity toward undifferentiated HESC and down-regulated naive T-cell activation toward HESC. These results demonstrate that costimulation blockade is sufficiently robust to induce tolerance to HESC in the immune-privileged environment of the testis. HESC specific regulatory T-cells developed to HESC transplanted to the heart and the success of transplantation was similar to that seen in SCID mice.

Erythropoietin has an antiapoptotic effect after myocardial infarction and stimulates in vitro aortic ring sprouting.

Aims were to explore if darbepoietin-alpha in mouse can induce angiogenesis and if moderate doses after myocardial infarction stimulates periinfarct capillary and arteriolar densities, cell proliferation, and apoptosis. Myocardial infarction was induced by ligation of LAD. Mouse aortic rings (0.8mm) were cultured in matrigel and the angiogenic sprouting was studied after addition of darbepoietin-alpha with and without VEGF-165. After 12 days the hemoglobin concentration was 25% higher in the darbepoietin-alpha treated mice than in the control group. No difference in capillary densities in the periinfarct or noninfarcted areas was seen with darbepoietin-alpha. Cell proliferation was about 10 times higher in the periinfarct area than in the noninfarcted wall. Darbepoietin-alpha treatment led to a decrease of cell proliferation (BrdU, (p<0.02)) and apoptosis (TUNEL, p<0.005) with about 30% in the periinfarct area. Darbepoietin-alpha and VEGF-165 both independently induced sprouting from aortic rings. The results suggest that darbepoietin-alpha can induce angiogenesis but that moderate doses after myocardial infarction are not angiogenic but antiapoptotic.