Cardiomyogenesis in the developing heart is regulated by c-kit-positive cardiac stem cells.

RATIONALE: Embryonic and fetal myocardial growth is characterized by a dramatic increase in myocyte number, but whether the expansion of the myocyte compartment is dictated by activation and commitment of resident cardiac stem cells (CSCs), division of immature myocytes or both is currently unknown. OBJECTIVE: In this study, we tested whether prenatal cardiac development is controlled by activation and differentiation of CSCs and whether division of c-kit-positive CSCs in the mouse heart is triggered by spontaneous Ca(2+) oscillations. METHODS AND RESULTS: We report that embryonic-fetal c-kit-positive CSCs are self-renewing, clonogenic and multipotent in vitro and in vivo. The growth and commitment of c-kit-positive CSCs is responsible for the generation of the myocyte progeny of the developing heart. The close correspondence between values computed by mathematical modeling and direct measurements of myocyte number at E9, E14, E19 and 1 day after birth strongly suggests that the organogenesis of the embryonic heart is dependent on a hierarchical model of cell differentiation regulated by resident CSCs. The growth promoting effects of c-kit-positive CSCs are triggered by spontaneous oscillations in intracellular Ca(2+), mediated by IP3 receptor activation, which condition asymmetrical stem cell division and myocyte lineage specification. CONCLUSIONS: Myocyte formation derived from CSC differentiation is the major determinant of cardiac growth during development. Division of c-kit-positive CSCs in the mouse is promoted by spontaneous Ca(2+) spikes, which dictate the pattern of stem cell replication and the generation of a myocyte progeny at all phases of prenatal life and up to one day after birth.

Endothelial fate and angiogenic properties of human CD34+ progenitor cells in zebrafish.

OBJECTIVE: The vascular competence of human-derived hematopoietic progenitors for postnatal vascularization is still poorly characterized. It is unclear whether, in the absence of ischemia, hematopoietic progenitors participate in neovascularization and whether they play a role in new blood vessel formation by incorporating into developing vessels or by a paracrine action. METHODS AND RESULTS: In the present study, human cord blood-derived CD34(+) (hCD34(+)) cells were transplanted into pre- and postgastrulation zebrafish embryos and in an adult vascular regeneration model induced by caudal fin amputation. When injected before gastrulation, hCD34(+) cells cosegregated with the presumptive zebrafish hemangioblasts, characterized by Scl and Gata2 expression, in the anterior and posterior lateral mesoderm and were involved in early development of the embryonic vasculature. These morphogenetic events occurred without apparent lineage reprogramming, as shown by CD45 expression. When transplanted postgastrulation, hCD34(+) cells were recruited into developing vessels, where they exhibited a potent paracrine proangiogenic action. Finally, hCD34(+) cells rescued vascular defects induced by Vegf-c in vivo targeting and enhanced vascular repair in the zebrafish fin amputation model. CONCLUSIONS: These results indicate an unexpected developmental ability of human-derived hematopoietic progenitors and support the hypothesis of an evolutionary conservation of molecular pathways involved in endothelial progenitor differentiation in vivo.

GATA6 reporter gene reveals myocardial phenotypic heterogeneity that is related to variations in gap junction coupling.

This study examined transgenic mice whose expression of a ß-galactosidase (lacZ) reporter is driven by a GATA6 gene enhancer. Previous investigations established that transcription of the transgene was associated with precardiac mesoderm and primary heart tube myocardium, which decreased progressively, so that its expression was no longer observed within ventricular myocardium by midgestation. Expression of this reporter in the adult was investigated for insights into myocyte homeostasis and cardiovascular biology. Morphometric analysis determined that <1% of myocytes, often found in small clusters, express this GATA6-associated reporter in the adult heart. LacZ expression was also found in the ascending aorta. Myocardial expression of the transgene was not associated with a proliferative phenotype or new myocyte formation, as lacZ-positive myocytes neither labeled with cell division markers nor following 5-bromodeoxyuridine pulse-chase experimentation. Despite exhibiting normal adherens junctions, these myocytes appeared to exhibit decreased connexin 43 gap junctions. Treatment with the gap junctional blocker heptanol both in vivo and in culture elevated myocardial ß-galactosidase activity, suggesting that deficient gap junctional communication underlies expression of the transgenic reporter. LacZ expression within the myocardium was also enhanced in response to cryoinjury and isoproterenol-induced hypertrophy. These results reveal a previously uncharacterized phenotypic heterogeneity in the myocardium and suggest that decreased gap junctional coupling leads to induction of a signaling pathway that utilizes a unique GATA6 enhancer. Upregulation of lacZ reporter gene expression following cardiac injury indicates this transgenic mouse may serve as a model for examining the transition of the heart from healthy to pathological states.

An expandable embryonic stem cell-derived Purkinje neuron progenitor population that exhibits in vivo maturation in the adult mouse cerebellum.

The directed differentiation of patient-derived induced pluripotent stem cells into cell-type specific neurons has inspired the development of therapeutic discovery for neurodegenerative diseases. Many forms of ataxia result from degeneration of cerebellar Purkinje cells, but thus far it has not been possible to efficiently generate Purkinje neuron (PN) progenitors from human or mouse pluripotent stem cells, let alone to develop a methodology for in vivo transplantation in the adult cerebellum. Here, we present a protocol to obtain an expandable population of cerebellar neuron progenitors from mouse embryonic stem cells. Our protocol is characterized by applying factors that promote proliferation of cerebellar progenitors. Cerebellar progenitors isolated in culture from cell aggregates contained a stable subpopulation of PN progenitors that could be expanded for up to 6 passages. When transplanted into the adult cerebellum of either wild-type mice or a strain lacking Purkinje cells (L7cre-ERCC1 knockout), GFP-labeled progenitors differentiated in vivo to establish a population of calbindin-positive cells in the molecular layer with dendritic trees typical of mature PNs. We conclude that this protocol may be useful for the generation and maturation of PNs, highlighting the potential for development of a regenerative medicine approach to the treatment of cerebellar neurodegenerative diseases.

The histone methyltransferase inhibitor BIX01294 enhances the cardiac potential of bone marrow cells.

Bone marrow (BM) has long been considered a potential stem cell source for cardiac repair due to its abundance and accessibility. Although previous investigations have generated cardiomyocytes from BM, yields have been low, and far less than produced from ES or induced pluripotent stem cells (iPSCs). Since differentiation of pluripotent cells is difficult to control, we investigated whether BM cardiac competency could be enhanced without making cells pluripotent. From screens of various molecules that have been shown to assist iPSC production or maintain the ES cell phenotype, we identified the G9a histone methyltransferase inhibitor BIX01294 as a potential reprogramming agent for converting BM cells to a cardiac-competent phenotype. BM cells exposed to BIX01294 displayed significantly elevated expression of brachyury, Mesp1, and islet1, which are genes associated with embryonic cardiac progenitors. In contrast, BIX01294 treatment minimally affected ectodermal, endodermal, and pluripotency gene expression by BM cells. Expression of cardiac-associated genes Nkx2.5, GATA4, Hand1, Hand2, Tbx5, myocardin, and titin was enhanced 114, 76, 276, 46, 635, 123, and 5-fold in response to the cardiogenic stimulator Wnt11 when BM cells were pretreated with BIX01294. Immunofluorescent analysis demonstrated that BIX01294 exposure allowed for the subsequent display of various muscle proteins within the cells. The effect of BIX01294 on the BM cell phenotype and differentiation potential corresponded to an overall decrease in methylation of histone H3 at lysine9, which is the primary target of G9a histone methyltransferase. In summary, these data suggest that BIX01294 inhibition of chromatin methylation reprograms BM cells to a cardiac-competent progenitor phenotype.

Early handling increases susceptibility to experimental autoimmune encephalomyelitis (EAE) in C57BL/6 male mice.

Brief maternal separations of neonatal animals can exert long-lasting effects on the reactivity of the neuroendocrine system. The aim of the present study was to investigate whether manipulations of the mother-infant interaction could affect susceptibility to immune-mediated diseases, such experimental autoimmune encephalomyelitis (EAE), and whether this effect would be mediated by changes in leptin which has been shown to regulate disease susceptibility and severity at adulthood. Given the different gender susceptibility to EAE previously described, we tested also whether early experiences could differentially affect the two genders. To this purpose, female and male C56BL/6 mice were subjected to handling (15 min daily) postnatally, from day 2 until day 14. All subjects were weaned at 21 days. At 7 weeks of age mice were immunized with MOG(35-55) to actively induce EAE. We thus determined the effect of neonatal handling on plasma concentrations of testosterone in male mice and leptin in both genders at different times post EAE induction. Our results show that early experiences influence susceptibility to EAE in a gender-specific manner, early manipulations resulting in an enhancement of sex-related differences in susceptibility. These effects were associated with changes in the testosterone profile of male subjects. Changes in leptin levels during the preclinical stage of EAE may predict a more severe disease course.

Bone marrow cells adopt the cardiomyogenic fate in vivo.

The possibility that adult bone marrow cells (BMCs) retain a remarkable degree of developmental plasticity and acquire the cardiomyocyte lineage after infarction has been challenged, and the notion of BMC transdifferentiation has been questioned. The center of the controversy is the lack of unequivocal evidence in favor of myocardial regeneration by the injection of BMCs in the infarcted heart. Because of the interest in cell-based therapy for heart failure, several approaches including gene reporter assay, genetic tagging, cell genotyping, PCR-based detection of donor genes, and direct immunofluorescence with quantum dots were used to prove or disprove BMC transdifferentiation. Our results indicate that BMCs engraft, survive, and grow within the spared myocardium after infarction by forming junctional complexes with resident myocytes. BMCs and myocytes express at their interface connexin 43 and N-cadherin, and this interaction may be critical for BMCs to adopt the cardiomyogenic fate. With time, a large number of myocytes and coronary vessels are generated. Myocytes show a diploid DNA content and carry, at most, two sex chromosomes. Old and new myocytes show synchronicity in calcium transients, providing strong evidence in favor of the functional coupling of these two cell populations. Thus, BMCs transdifferentiate and acquire the cardiomyogenic and vascular phenotypes restoring the infarcted heart. Together, our studies reveal that locally delivered BMCs generate de novo myocardium composed of integrated cardiomyocytes and coronary vessels. This process occurs independently of cell fusion and ameliorates structurally and functionally the outcome of the heart after infarction.