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.

MITO-Luc/GFP zebrafish model to assess spatial and temporal evolution of cell proliferation in vivo.

We developed a novel reporter transgenic zebrafish model called MITO-Luc/GFP zebrafish in which GFP and luciferase expression are under the control of the master regulator of proliferation NF-Y. In MITO-Luc/GFP zebrafish it is possible to visualize cell proliferation in vivo by fluorescence and bioluminescence. In this animal model, GFP and luciferase expression occur in early living embryos, becoming tissue specific in juvenile and adult zebrafish. By in vitro and ex vivo experiments we demonstrate that luciferase activity in adult animals occurs in intestine, kidney and gonads, where detectable proliferating cells are located. Further, by time lapse experiments in live embryos, we observed a wave of GFP positive cells following fin clip. In adult zebrafish, in addition to a bright bioluminescence signal on the regenerating tail, an early unexpected signal coming from the kidney occurs indicating not only a fin cell proliferation, but also a systemic response to tissue damage. Finally, we observed that luciferase activity was inhibited by anti-proliferative interventions, i.e. 5FU, cell cycle inhibitors and X-Rays. In conclusion, MITO-Luc/GFP zebrafish is a novel animal model that may be crucial to assess the spatial and temporal evolution of cell proliferation in vivo.

Myocardial infarction induces embryonic reprogramming of epicardial c-kit(+) cells: role of the pericardial fluid.

Stem cells expressing c-kit have been identified in the adult epicardium. In mice, after myocardial infarction, these cells proliferate, migrate to the injury site and differentiate toward myocardial and vascular phenotype. We hypothesized that, acutely after myocardial infarction, pericardial sac integrity and pericardial fluid (PF) may play a role on epicardial cell gene expression, proliferation and differentiation. Microarray analysis indicated that, in the presence of an intact pericardial sac, myocardial infarction modulated 246 genes in epicardial cells most of which were related to cell proliferation, cytoskeletal organization, wound repair and signal transduction. Interestingly, WT1, Tbx18 and RALDH2, notably involved in epicardial embryonic development, were markedly up-regulated. Importantly, coexpression of stem cell antigen c-kit and WT1 and/or Tbx18 was detected by immunohistochemistry in the mouse epicardium during embryogenesis as well as in adult mouse infarcted heart. Injection of human pericardial fluid from patients with acute myocardial ischemia (PFMI) in the pericardial cavity of non-infarcted mouse hearts, enhanced, epicardial cell proliferation and WT1 expression. Further, PFMI supplementation to hypoxic cultured human epicardial c-kit(+) cells increased WT1 and Tbx18 mRNA expression. Finally, insulin-like growth factor 1, hepatocyte growth factor and high mobility group box 1 protein, previously involved in cardiac c-kit(+) cell proliferation and differentiation, were increased in PFMI compared to the pericardial fluid of non ischemic patients. In conclusion, myocardial infarction reactivates an embryonic program in epicardial c-kit(+) cells; soluble factors released in the pericardial fluids following myocardial necrosis may play a role in this process.

Regulated expression pattern of gremlin during zebrafish development.

Xenopus laevis Gremlin has been isolated as a novel dorsalizing factor, belonging to a family of secreted proteins with axial patterning activity . In a search for genes that control development in zebrafish (Danio rerio), we have identified a sequence homologous to Xenopus gremlin. This paper describes the cloning of zebrafish gremlin (grm) and its expression pattern during development. Our results show that grm encodes a maternal transcript, and the zygotic transcription is turned on at the mid-blastula transition (MBT), when grm is detected in the entire blastoderm. In the gastrula grm becomes restricted to the dorsolateral region of the embryo, and during somitogenesis it is strongly expressed in the presomitic mesoderm and developing somites, and in the ventral neural tube. From 24 hpf to 48 hpf, we show that grm transcription is downregulated in the whole embryo, even though Grm protein is still present and localized into the entire myotome at 48-72 hpf. Finally, grm transcript is strongly downregulated in fibroblast growth factor-8 (fgf8) and sonic hedgehog (shh) mutants, thus implicating a putative role of Fgf/Shh signalling loop in grm expression regulation.

Identification and expression pattern of mago nashi during zebrafish development.

In a search for zebrafish genes expressed during early stages of development, we have identified two ESTs encoding proteins related to Drosophila mago nashi. Zebrafish mago nashi codes for a small protein with no clearly identified functional domains, and which is highly conserved during evolution. This paper describes the identification and a detailed gene expression analysis of zebrafish mago nashi during development. Our results demonstrate that mago nashi encodes a maternal transcript detected in both blastomeres and yolk cell at the 1-2 cell stages, and in the blastoderm during segmentation. We show that a putative microtubule-mediated transport of mago nashi mRNA from the vegetal hemisphere into animal blastomeres determines the localization of the transcript in the animal pole, immediately after fertilization. Furthermore, the microtubule array contained into the yolk cell seems to be responsible for the high level of mago nashi transcript detected in the central blastomeres at the 8-16 cell stages. Zygotic mago nashi is expressed into the dorsal-marginal region during gastrulation, and starting from somitogenesis to 24 hpf, the expression domain becomes progressively restricted to the developing neural tube and paraxial structures, and ventrally to the pronephric ducts.

Hypoxia/reoxygenation cardiac injury and regeneration in zebrafish adult heart.

AIMS: the adult zebrafish heart regenerates spontaneously after injury and has been used to study the mechanisms of cardiac repair. However, no zebrafish model is available that mimics ischemic injury in mammalian heart. We developed and characterized zebrafish cardiac injury induced by hypoxia/reoxygenation (H/R) and the regeneration that followed it. METHODS AND RESULTS: adult zebrafish were kept either in hypoxic (H) or normoxic control (C) water for 15 min; thereafter fishes were returned to C water. Within 2-6 hours (h) after reoxygenation there was evidence of cardiac oxidative stress by dihydroethidium fluorescence and protein nitrosylation, as well as of inflammation. We used Tg(cmlc2:nucDsRed) transgenic zebrafish to identify myocardial cell nuclei. Cardiomyocyte apoptosis and necrosis were evidenced by TUNEL and Acridine Orange (AO) staining, respectively; 18 h after H/R, 9.9±2.6% of myocardial cell nuclei were TUNEL(+) and 15.0±2.5% were AO(+). At the 30-day (d) time point myocardial cell death was back to baseline (n = 3 at each time point). We evaluated cardiomyocyte proliferation by Phospho Histone H3 (pHH3) or Proliferating Cell Nuclear Antigen (PCNA) expression. Cardiomyocyte proliferation was apparent 18-24 h after H/R, it achieved its peak 3-7d later, and was back to baseline at 30d. 7d after H/R 17.4±2.3% of all cardiomyocytes were pHH3(+) and 7.4±0.6% were PCNA(+) (n = 3 at each time point). Cardiac function was assessed by 2D-echocardiography and Ventricular Diastolic and Systolic Areas were used to compute Fractional Area Change (FAC). FAC decreased from 29.3±2.0% in normoxia to 16.4±1.8% at 18 h after H/R; one month later ventricular function was back to baseline (n = 12 at each time point). CONCLUSIONS: zebrafish exposed to H/R exhibit evidence of cardiac oxidative stress and inflammation, myocardial cell death and proliferation. The initial decrease in ventricular function is followed by full recovery. This model more closely mimics reperfusion injury in mammals than other cardiac injury models.

Gene transfer into human cord blood-derived CD34(+) cells by adeno-associated viral vectors.

OBJECTIVE: Bone marrow-derived CD34(+) cells are currently used in clinical trials in patients with ischemic heart disease. An option to enhance activity of injected progenitors may be offered by genetic engineering of progenitor cells with angiogenic growth factors. Recombinant adeno-associated viral vectors (rAAV) have emerged as a leading gene transfer systems. In contrast to other vector systems in use for genetic engineering of CD34(+) cells, rAAV-mediated gene expression does not depend on vector integration. This is relevant for application in regenerative medicine of ischemic tissues, where transient transgene expression is likely sufficient to achieve therapeutic benefits. MATERIALS AND METHODS: We compared three different human AAV serotypes, packaged as pseudotypes by a helper virus-free production method, for their transduction efficiency in human cord blood-derived CD34(+) cells. We further assessed the impact of vector genome conformation, of alpha(v)beta(5) and alpha(5)beta(1) integrin availability and of the transcription-modulating drugs retinoic acid and Trichostatin A on rAAV-mediated human CD34(+) cell transduction. RESULTS: We provide, for the first time, evidence that hCD34(+) cells can be reproducibly transduced with high efficiency by self-complementary rAAV2 without inducing cytotoxicity or interfering with their differentiation potential. We further show the involvement of alpha(5)beta(1) integrin as a crucial AAV2 internalization receptor and a function for transcription-modulating drugs in enhancing rAAV-mediated transgene expression. CONCLUSION: This study represents a first step toward translation of a combined cellular/rAAV-based therapy of ischemic disease.

Role of HIF-1alpha in proton-mediated CXCR4 down-regulation in endothelial cells.

AIMS: Acidification is associated with a variety of pathological and physiological conditions. In the present study, we aimed at investigating whether acidic pH may regulate endothelial cell (EC) functions via the chemokine receptor CXCR4, a key modulator of EC biological activities. METHODS AND RESULTS: Exposure of ECs to acidic pH reversibly inhibited mRNA and protein CXCR4 expression, CXCL12/stromal cell-derived factor (SDF)-1-driven EC chemotaxis in vitro, and CXCR4 expression and activation in vivo in a mouse model. Further, CXCR4 signalling impaired acidosis-induced rescue from apoptosis in ECs. The inhibition of CXCR4 expression occurred transcriptionally and was hypoxia-inducible factor (HIF)-1alpha-dependent as demonstrated by both HIF-1alpha and HIF-1alpha dominant negative overexpression, by HIF-1alpha silencing, and by targeted mutation of the -29 to -25 hypoxia response element (HRE) in the -357/-59 CXCR4 promoter fragment. Moreover, chromatin immunoprecipitation (ChIP) analysis showed endogenous HIF-1alpha binding to the CXCR4 promoter that was enhanced by acidification. CONCLUSION: The results of the present study identify CXCR4 as a key player in the EC response to acidic pH and show, for the first time, that HRE may function not only as an effector of hypoxia, but also as an acidosis response element, and raise the possibility that this may constitute a more general mechanism of transcriptional regulation at acidic pH.

Functional and hierarchical interactions among zebrafish vox/vent homeobox genes.

The vertebrate Vox/Vent family of transcription factors plays a crucial role in the establishment of the dorsoventral (DV) axis, by repressing organizer genes such as bozozok/dharma, goosecoid, and chordino. In Danio rerio (zebrafish), members of the vox/vent gene family (vox/vega1, vent/vega2, and ved) are thought to share expression patterns and functional properties. Bringing novel insights in the differential activity of the zebrafish vox/vent genes, we propose a critical role for the ved gene in DV patterning of vertebrate embryos. ved is not only expressed as a maternal gene, but it also appears to function as a repressor of dorsal factors involved in organizer formation. At early- and mid-gastrula stage, ved appears to be finely controlled by antagonist crosstalks in a complex regulatory network, involving gradients of bone morphogenetic protein (BMP) activity, dorsal factors, and vox/vent family members. We show that ved transcripts are ventrally restricted by BMP factors such as bmp2b, bmp7, smad5, and alk8, and by dorsal factors (chd and gsc). Alteration of ved expression in both vox and vent deletion mutants and vox and vent mRNAs-injected embryos, suggests that vox and vent function downstream of BMP signaling to negatively regulate ved expression. This inhibitory role is emphasized by a vox and vent redundant activity, compared with single gene effects.