Vascular endothelial growth factor promotes cardiomyocyte differentiation of embryonic stem cells

Neuregulin-1 promotes cardiomyocyte differentiation of genetically engineered embryonic stem cell clones

Embryonic stem (ES) cell-derived cardiomyocytes (ESCMs) must be specifically purified in order to prevent teratoma formation, and this confusing issue has hampered their clinical application. We therefore investigated a technique to generate pure labeled ESCMs for possible use in cardiac repair. We generated transgenic ES cell lines expressing enhanced green fluorescent protein (EGFP) under the transcriptional control of the alpha-cardiac myosin heavy chain (alpha-MHC) promoter. Differentiated EGFP-positive ES cells displayed characteristics of CMs. Furthermore, neuregulin-1 (NRG-1) upregulated the expression of the cardiac-restricted transcription factors Nkx2.5 and GATA-4, as well as differentiated CM factors (alpha-MHC, beta-MHC). Immunohistochemistry demonstrated that NRG-1 increased expression of cardiac-specific troponin T in the beating foci of the embryoid bodies. This work revealed a potential method for specifically labeling and enriching ESCMs by combining genetically-engineered ES cell clones and exogenous growth factor treatment.

Lineage specification of Flk-1+ progenitors is associated with divergent Sox7 expression in cardiopoiesis

Embryonic stem cell differentiation recapitulates the diverse phenotypes of a developing embryo, traceable according to markers of lineage specification. At gastrulation, the vascular endothelial growth factor (VEGF) receptor, Flk-1 (KDR), identifies a mesoderm-restricted potential of embryonic stem cells. The multi-lineage propensity of Flk-1(+) progenitors mandates the mapping of fate-modifying co-factors in order to stratify differentiating cytotypes and predict lineage competency. Here, Flk-1-based selection of early embryonic stem cell progeny separated a population depleted of pluripotent (Oct4, Sox2) and endoderm (Sox17) markers. The gene expression profile of the Flk-1(+) population was notable for a significant upregulation in the vasculogenic Sox7 transcription factor, which overlapped with the emergence of primordial cardiac transcription factors GATA-4, Myocardin and Nkx2.5. Sorting the parental Flk-1(+) pool with the chemokine receptor CXCR4 to enrich the cardiopoietic subpopulation uncovered divergent Sox7 expression, with a 7-fold induction in non-cardiac compared to cardiac progenitors. Bioinformatic resolution sequestered a framework of gene expression relationship between Sox transcription factor family members and the Flk-1/CXCR4 axes with significant integration of beta-catenin signaling. Thus, differential Sox7 gene expression presents a novel biomarker profile, and possible regulatory switch, to distinguish cardiovascular pedigrees within Flk-1(+) multi-lineage progenitors.

Endothelial differentiation of hematopoietic stem and progenitor cells from patients with multiple myeloma

PURPOSE

Vasculogenesis is a physiologic process typical of fetal development in which new blood vessels develop from undifferentiated precursors (or angioblasts). In tumors, near angiogenesis, vasculogenesis contributes to the formation of the microvascular plexus that is important for diffusion. Here, we show that hematopoietic stem and progenitor cells (HSPC) of multiple myeloma (MM) patients are able to differentiate into cells with endothelial phenotype on exposure to angiogenic cytokines.

EXPERIMENTAL DESIGN

Circulating HSPCs were purified with an anti-CD133 antibody from patients with newly diagnosed MM before autologous transplantation and exposed to vascular endothelial growth factor (VEGF), fibroblast growth factor-2 and insulin-like growth factor in a 3-week culture.

RESULTS

HSPCs gradually lost CD133 expression and acquired VEGF receptor-2, factor VIII-related antigen, and vascular endothelial-cadherin expression. The expression pattern overlapped with paired MM endothelial cells (MMEC). During culture, cells adhered to fibronectin, spread, and acquired an endothelial cell shape. Differentiated HSPCs also became capillarogenic in the Matrigel assay with maximal activity at the third week of culture. Bone marrow biopsies revealed HSPCs inside the neovessel wall in patients with MM but not in those with monoclonal gammopathy of undetermined significance.

CONCLUSIONS

In patients with MM, but not in those with monoclonal gammopathy of undetermined significance, HSPCs contribute to the neovessel wall building together with MMECs. Therefore, besides angiogenesis, HSPC-linked vasculogenesis contributes to neovascularization in MM patients. Tentatively, we hypothesize that in HSPC cultures a multipotent cell population expressing low VEGF receptor-2 levels corresponds to the endothelial progenitor cell precursor and seems to be the MMEC precursor.

MAPK/ERK signalling mediates VEGF-induced bone marrow stem cell differentiation into endothelial cell

Multi-potent adult progenitor cells (MAPCs) differentiate into endothelial cells (ECs) in the presence of vascular endothelial growth factor (VEGF). The mechanism(s) of VEGF-induced differentiation of MAPCs to ECs are not yet known. We, therefore, examined the role of mitogen-activated protein kinase/extracellular signal-regulated kinase (p42/44-MAPK/ERK1/2) signalling in endothelial differentiation from bone marrow stem cells. We observed that VEGF stimulation of MAPCs for 14 days results in a significant expression of endothelial-specific gene and/or proteins including von Willebrand factor (vWF), vascular endothelial-cadherin (VE-cadherin), VEGF receptor-2 (VEGFR2), and CD31. Up-regulation of EC-specific markers was accompanied by a cobblestone morphology, expression of endothelial nitric oxide synthase (eNOS), and Dil-Ac-LDL uptake, typical for EC morphology and function. VEGF induced a sustained activation of p42 MAPK/ERK, but not that of p44 MAPK/ERK during the course of MAPCs differentiation in a time-dependent manner up to 14 days. VEGF-induced activation of p42 MAPK/ERK also led to the nuclear translocation of MAPK/ERK1/2. Incubation of MAPCs with MAPK/ERK1/2 phosphorylation inhibitor PD98059 blocked the sustained VEGF-induced MAPK/ERK1/2 phosphorylation as well as its nuclear translocation in the differentiating MAPCs. Inhibition of MAPK/ERK1/2 phosphorylation by PD98059 also blocked the expression of EC-specific genes in these cells and their differentiation to ECs. These data suggest that VEGF induces MAPC differentiation into EC via a. MAPK/ERK1/2 signalling pathway-mediated mechanism in vitro.

Genomic chart guiding embryonic stem cell cardiopoiesis

Gene expression analysis of embryonic stem cells undergoing guided cardiogenic differentiation reveals the molecular fingerprint for committing to cardiac cell fate.

Background

Embryonic stem cells possess a pluripotent transcriptional background with the developmental capacity for distinct cell fates. Simultaneous expression of genetic elements for multiple outcomes obscures cascades relevant to specific cell phenotypes. To map molecular patterns critical to cardiogenesis, we interrogated gene expression in stem cells undergoing guided differentiation, and defined a genomic paradigm responsible for confinement of pluripotency.

Results

Functional annotation analysis of the transcriptome of differentiating embryonic stem cells exposed downregulated components of DNA replication, recombination and repair machinery, cell cycling, cancer mechanisms, and RNA post-translational modifications. Concomitantly, cardiovascular development, cell-to-cell signaling, cell development and cell movement were upregulated. These simultaneous gene ontology rearrangements engaged a repertoire switch that specified lineage development. Bioinformatic integration of genomic and gene ontology data further unmasked canonical signaling cascades prioritized within discrete phases of cardiopoiesis. Examination of gene relationships revealed a non-stochastic network anchored by integrin, WNT/β-catenin, transforming growth factor β and vascular endothelial growth factor pathways, validated by manipulation of selected cascades that promoted or restrained cardiogenic yield. Moreover, candidate genes within anchor pathways acted as nodes that organized correlated expression profiles into functional clusters, which collectively orchestrated and secured an overall cardiogenic theme.

Conclusion

The present systems biology approach reveals a dynamically integrated and tractable gene network fundamental to embryonic stem cell specification, and represents an initial step towards resolution of a genomic cardiopoietic atlas.

Dynamic transcription programs during ES cell differentiation towards mesoderm in serum versus serum-freeBMP4 culture

Background

Expression profiling of embryonic stem (ES) cell differentiation in the presence of serum has been performed previously. It remains unclear if transcriptional activation is dependent on complex growth factor mixtures in serum or whether this process is intrinsic to ES cells once the stem cell program has been inactivated. The aims of this study were to determine the transcriptional programs associated with the stem cell state and to characterize mesoderm differentiation between serum and serum-free culture.

Results

ES cells were differentiated as embryoid bodies in 10% FBS or serum-free media containing BMP4 (2 ng/ml), and expression profiled using 47 K Illumina(R) Sentrix arrays. Statistical methods were employed to define gene sets characteristic of stem cell, epiblast and primitive streak programs. Although the initial differentiation profile was similar between the two culture conditions, cardiac gene expression was inhibited in serum whereas blood gene expression was enhanced. Also, expression of many members of the Kruppel-like factor (KLF) family of transcription factors changed dramatically during the first few days of differentiation. KLF2 and KLF4 co-localized with OCT4 in a sub-nuclear compartment of ES cells, dynamic changes in KLF-DNA binding activities occurred upon differentiation, and strong bio-informatic evidence for direct regulation of many stem cell genes by KLFs was found.

Conclusion

Down regulation of stem cell genes and activation of epiblast/primitive streak genes is similar in serum and defined media, but subsequent mesoderm differentiation is strongly influenced by the composition of the media. In addition, KLF family members are likely to be important regulators of many stem cell genes.

Endocardiogenesis in embryoid bodies: Novel markers identified by gene expression profiling

Endocardial cells and cardiomyocytes differentiate from the cardiogenic mesoderm at about the same time during development. Although in vitro embryonic stem (ES) cell systems have been used to study the differentiation of various types of cell lineages, including cardiomyocytes, smooth muscle cells, and vascular endothelial cells, differentiation of endocardial cells, or endocardiogenesis, has not been well reported, because of a lack of specific molecular markers. In our search for cardiogenesis-associated genes expressed in embryoid bodies, we found several genes expressed in the heart region of mouse embryos, but not in cardiomyocytes. To identify the cell types expressing these genes, CD31(+) cells were taken from mouse embryos on embryonic day (E)8.5 and E9.5 and sorted, then their transcripts were analyzed using quantitative RT-PCR analyses. In those embryos, Gata4 and Nfatc1, as well as newly identified Cgnl1 and Dok4 were found to be preferentially expressed in endocardial cells, but not in yolk sac endothelial cells, while Cdh5 and Kdr were expressed in both cardiac and yolk sac endothelial cells. Immunohistochemical analyses of embryoid bodies revealed that some CD31(+) cells co-expressing Gata4 and Nfatc1 were located in close proximity to cardiomyocytes. These results suggest that embryoid bodies express endocardial specific genes and likely generate endocardial cells along with cardiomyocytes. Further, they indicate that these new marker genes are useful to study the origin and induction of endocardial cells, and identify other endocardial markers.

VEGF is critical for spontaneous differentiation of stem cells into cardiomyocytes

Cardiomyocyte regeneration is limited in adult life and is not sufficient to compensate for cell loss with myocardial infarction. Hence, the identification of a useful source of cardiomyocyte progenitors is of great interest for possible use in regenerative therapy. In this study, we isolated stem cells derived from human subcutaneous adipose tissue. The expression of Nkx2.5 and GATA-4 can be observed by PCR directly after extraction and during cultivation in some of these cells. Cardiac Troponin T and myosin light chain-2v become positive after 12 days of cultivation. To define respective factors responsible for spontaneous differentiation, we measured VEGF level in ADSC conditioned medium. Our data showed that ADSC secrete significant amount of VEGF (283.5pg per microgram DNA) and that anti-VEGF receptor antibodies blocked the cardiac differentiation. In conclusion, we demonstrated the spontaneous differentiation of human subcutaneous adipose-derived stem cells into a cardiomyocyte phenotype under standard culturing conditions.