Stéphane Germain

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (36)267.78 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Dicer is an RNase III enzyme that cleaves double stranded RNA and generates functional interfering RNAs that act as important regulators of gene and protein expression. Dicer plays an essential role during mouse development because the deletion of the dicer gene leads to embryonic death. In addition, dicer-dependent interfering RNAs regulate postnatal angiogenesis. However, the role of dicer is not yet fully elucidated during vascular development. In order to explore the functional roles of the RNA interference in vascular biology, we developed a new constitutive Cre/loxP-mediated inactivation of dicer in tie2 expressing cells. We show that cell-specific inactivation of dicer in Tie2 expressing cells does not perturb early blood vessel development and patterning. Tie2-Cre; dicerfl/fl mutant embryos do not show any blood vascular defects until embryonic day (E)12.5, a time at which hemorrhages and edema appear. Then, midgestational lethality occurs at E14.5 in mutant embryos. The developing lymphatic vessels of dicer-mutant embryos are filled with circulating red blood cells, revealing an impaired separation of blood and lymphatic vasculature. Thus, these results show that RNA interference perturbs neither vasculogenesis and developmental angiogenesis, nor lymphatic specification from venous endothelial cells but actually provides evidence for an epigenetic control of separation of blood and lymphatic vasculature.
    Vascular cell. 04/2014; 6(1):9.
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    ABSTRACT: Sunitinib is an inhibitor of tyrosine-kinase receptors, and no biomarker predictive of sunitinib response is available. The purpose of this preclinical study was to show whether sunitinib molecular targets could be used as biomarkers to assess tumor response to sunitinib in human cancer cell line xenografts of three different tumor types. Using mice xenografted with liver, breast and renal carcinoma cell lines, we sequentially analyzed the effect of 7-day sunitinib treatment on tumor and vascular compartments. In all xenografts, microvessel damage occurred from Day 1. Tumor damage also occurred in liver, breast, but not in renal xenografts. Using specific human and mouse probes for genes encoding sunitinib targets, we showed a significant relation between apoptotic tumor cell numbers and human PDGFRΒ and RET mRNA expression in liver cancer and to human VEGFR2 expression in breast cancer xenografts. In contrast, in renal cancer xenografts, vascular effect evaluated by measuring endothelial cell apoptosis was related to mouse Vegfr1, Vegfr2 and Vegfa-164 expression. This study identifies sunitinib vascular and tumor effects according to different tumor types and shows that sunitinib molecular targets used as biomarkers enable assessment of therapeutic response.
    Cancer Chemotherapy and Pharmacology 09/2013; · 2.80 Impact Factor
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    ABSTRACT: As adenosine monophosphate (AMP)-activated protein kinase both controls cytoskeleton organization in endothelial cells and exerts anti-inflammatory effects, we here postulated that it could influence vascular permeability and inflammation, thereby counteracting cardiac wall edema during sepsis. Controlled animal study. University research laboratory. C57BL/6J, α1AMPK, and α1AMPK mice. Sepsis was triggered in vivo using a sublethal injection of lipopolysaccharide (O55B5, 10 mg/kg), inducing systolic left ventricular dysfunction. Left ventricular function, edema, vascular permeability, and inflammation were assessed in vivo in both wild-type mice (α1AMPK) and α1AMP-activated protein kinase-deficient mice (α1AMPK). The 5-aminoimidazole-4-carboxamide riboside served to study the impact of AMP-activated protein kinase activation on vascular permeability in vivo. The integrity of endothelial cell monolayers was also examined in vitro after lipopolysaccharide challenge in the presence of aminoimidazole-4-carboxamide riboside and/or after α1AMP-activated protein kinase silencing. α1AMP-activated protein kinase deficiency dramatically impaired tolerance to lipopolysaccharide challenge. Indeed, α1AMPK exhibited heightened cardiac vascular permeability after lipopolysaccharide challenge compared with α1AMPK. Consequently, an increase in left ventricular mass corresponding to exaggerated wall edema occurred in α1AMPK, without any further decrease in systolic function. Mechanistically, the lipopolysaccharide-induced α1AMPK cardiac phenotype could not be attributed to major changes in the systemic inflammatory response but was due to an increased disruption of interendothelial tight junctions. Accordingly, AMP-activated protein kinase activation by aminoimidazole-4-carboxamide riboside counteracted lipopolysaccharide-induced hyperpermeability in wild-type mice in vivo as well as in endothelial cells in vitro. This effect was associated with a potent protection of zonula occludens-1 linear border pattern in endothelial cells. Our results demonstrate for the first time the involvement of a signaling pathway in the control of left ventricular wall edema during sepsis. AMP-activated protein kinase exerts a protective action through the preservation of interendothelial tight junctions. Interestingly, exaggerated left ventricular wall edema was not coupled with aggravated systolic dysfunction. However, it could contribute to diastolic dysfunction in patients with sepsis.
    Critical care medicine 08/2013; · 6.37 Impact Factor
  • Ariane Galaup, Stéphane Germain
    Medecine sciences: M/S 02/2012; 28(2):133-5. · 0.56 Impact Factor
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    ABSTRACT: Increased permeability, predominantly controlled by endothelial junction stability, is an early event in the deterioration of vascular integrity in ischemic disorders. Hemorrhage, edema, and inflammation are the main features of reperfusion injuries, as observed in acute myocardial infarction (AMI). Thus, preservation of vascular integrity is fundamental in ischemic heart disease. Angiopoietins are pivotal modulators of cell-cell junctions and vascular integrity. We hypothesized that hypoxic induction of angiopoietin-like protein 4 (ANGPTL4) might modulate vascular damage, infarct size, and no-reflow during AMI. We showed that vascular permeability, hemorrhage, edema, inflammation, and infarct severity were increased in angptl4-deficient mice. We determined that decrease in vascular endothelial growth factor receptor 2 (VEGFR2) and VE-cadherin expression and increase in Src kinase phosphorylation downstream of VEGFR2 were accentuated after ischemia-reperfusion in the coronary microcirculation of angptl4-deficient mice. Both events led to altered VEGFR2/VE-cadherin complexes and to disrupted adherens junctions in the endothelial cells of angptl4-deficient mice that correlated with increased no-reflow. In vivo injection of recombinant human ANGPTL4 protected VEGF-driven dissociation of the VEGFR2/VE-cadherin complex, reduced myocardial infarct size, and the extent of no-reflow in mice and rabbits. These data showed that ANGPTL4 might constitute a relevant target for therapeutic vasculoprotection aimed at counteracting the effects of VEGF, thus being crucial for preventing no-reflow and conferring secondary cardioprotection during AMI.
    Circulation 11/2011; 125(1):140-9. · 15.20 Impact Factor
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    ABSTRACT: Proper vessel maturation, remodeling of endothelial junctions, and recruitment of perivascular cells is crucial for establishing and maintaining vessel functions. In proliferative retinopathies, hypoxia-induced angiogenesis is associated with disruption of the vascular barrier, edema, and vision loss. Therefore, identifying factors that regulate vascular maturation is critical to target pathological angiogenesis. Given the conflicting role of angiopoietin-like-4 (ANGPTL4) reported in the current literature using gain of function systems both in vitro and in vivo, the goal of this study was to characterize angiogenesis, focusing on perinatal retinal vascularization and pathological circumstances in angpl4-deficient mice. We report altered organization of endothelial junctions and pericyte coverage, both leading to impaired angiogenesis and increased vascular leakage that were eventually caught up, suggesting a delay in vessel maturation. In a model of oxygen-induced retinopathy, pathological neovascularization, which results from tissue hypoxia, was also strongly inhibited in angptl4-deficient mice. This study therefore shows that ANGPTL4 tunes endothelial cell junction organization and pericyte coverage and controls vascular permeability and angiogenesis, both during development and in pathological conditions.
    Journal of Biological Chemistry 10/2011; 286(42):36841-36851. · 4.65 Impact Factor
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    ABSTRACT: Rapidly progressive glomerulonephritis (RPGN) is a life-threatening clinical syndrome and a morphological manifestation of severe glomerular injury that is marked by a proliferative histological pattern ('crescents') with accumulation of T cells and macrophages and proliferation of intrinsic glomerular cells. We show de novo induction of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in intrinsic glomerular epithelial cells (podocytes) from both mice and humans with RPGN. HB-EGF induction increases phosphorylation of the epidermal growth factor receptor (EGFR, also known as ErbB1) in mice with RPGN. In HB-EGF-deficient mice, EGFR activation in glomeruli is absent and the course of RPGN is improved. Autocrine HB-EGF induces a phenotypic switch in podocytes in vitro. Conditional deletion of the Egfr gene from podocytes of mice alleviates the severity of RPGN. Likewise, pharmacological blockade of EGFR also improves the course of RPGN, even when started 4 d after the induction of experimental RPGN. This suggests that targeting the HB-EGF-EGFR pathway could also be beneficial in treatment of human RPGN.
    Nature medicine 09/2011; 17(10):1242-50. · 27.14 Impact Factor
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    ABSTRACT: Sprouting angiogenesis is associated with extensive extracellular matrix (ECM) remodeling. The molecular mechanisms involved in building the vascular microenvironment and its impact on capillary formation remain elusive. We therefore performed a proteomic analysis of ECM from endothelial cells maintained in hypoxia, a major stimulator of angiogenesis. Here, we report the characterization of lysyl oxidase-like protein-2 (LOXL2) as a hypoxia-target expressed in neovessels and accumulated in the endothelial ECM. LOXL2 belongs to the lysyl oxidase family of secreted enzymes involved in ECM crosslinking. Knockdown experiments in Tg(fli1:egfp)y1 zebrafish embryos resulted in lack of intersegmental vessel circulation and demonstrated LOXL2 involvement in proper capillary formation. Further investigation in vitro by loss and gain of function experiments confirmed that LOXL2 was required for tubulogenesis in 3D fibrin gels and demonstrated that this enzyme was required for collagen IV assembly in the ECM. In addition, LOXL2 depletion down-regulated cell migration and proliferation. These data suggest a major role for LOXL2 in the organization of endothelial basal lamina and in the downstream mechanotransductive signaling. Altogether, our study provides the first evidence for the role of LOXL2 in regulating angiogenesis through collagen IV scaffolding.
    Blood 08/2011; 118(14):3979-89. · 9.06 Impact Factor
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    ABSTRACT: Proper vessel maturation, remodeling of endothelial junctions, and recruitment of perivascular cells is crucial for establishing and maintaining vessel functions. In proliferative retinopathies, hypoxia-induced angiogenesis is associated with disruption of the vascular barrier, edema, and vision loss. Therefore, identifying factors that regulate vascular maturation is critical to target pathological angiogenesis. Given the conflicting role of angiopoietin-like-4 (ANGPTL4) reported in the current literature using gain of function systems both in vitro and in vivo, the goal of this study was to characterize angiogenesis, focusing on perinatal retinal vascularization and pathological circumstances in angpl4-deficient mice. We report altered organization of endothelial junctions and pericyte coverage, both leading to impaired angiogenesis and increased vascular leakage that were eventually caught up, suggesting a delay in vessel maturation. In a model of oxygen-induced retinopathy, pathological neovascularization, which results from tissue hypoxia, was also strongly inhibited in angptl4-deficient mice. This study therefore shows that ANGPTL4 tunes endothelial cell junction organization and pericyte coverage and controls vascular permeability and angiogenesis, both during development and in pathological conditions.
    Journal of Biological Chemistry 08/2011; 286(42):36841-51. · 4.65 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Rapidly progressive glomerulonephritis (RPGN) is a life-threatening clinical syndrome and a morphological manifestation of severe glomerular injury that is marked by a proliferative histological pattern ('crescents') with accumulation of T cells and macrophages and proliferation of intrinsic glomerular cells. We show de novo induction of heparin-binding epidermal growth factor–like growth factor (HB-EGF) in intrinsic glomerular epithelial cells (podocytes) from both mice and humans with RPGN. HB-EGF induction increases phosphorylation of the epidermal growth factor receptor (EGFR, also known as ErbB1) in mice with RPGN. In HB-EGF–deficient mice, EGFR activation in glomeruli is absent and the course of RPGN is improved. Autocrine HB-EGF induces a phenotypic switch in podocytes in vitro. Conditional deletion of the Egfr gene from podocytes of mice alleviates the severity of RPGN. Likewise, pharmacological blockade of EGFR also improves the course of RPGN, even when started 4 d after the induction of experimental RPGN. This suggests that targeting the HB-EGF–EGFR pathway could also be beneficial in treatment of human RPGN.
    Nature medicine 01/2011; 17(11):1521. · 27.14 Impact Factor
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    ABSTRACT: To determine the role of Wnt antagonist Dickkopf (DKK) 1 in human endothelial colony-forming cells (ECFCs) in view of the emerging importance of Wnt pathways in vascular biology. Endothelial progenitor cells have been proposed to be crucial in tumor neovascularization. Recombinant DKK1 has been tested in ECFC angiogenic properties in vitro. DKK1 enhanced ECFC proliferation and the capacity of ECFCs to form pseudotubes in Matrigel. These effects have been attributed to enhancement of vascular endothelial growth factor receptor 2, SDF-1, and CXCR4. DKK1 gene silencing has been realized on ECFCs and mesenchymal stem cells, and we found that DKK1 silencing in the 2 cell types decreased their angiogenic potential. We then examined the possible role of DKK1 in tumor neovasculogenesis and found that blood vessels of breast cancer tissues expressed DKK1 far more strongly in human breast tumors than in normal breast tissues. By studying 62 human breast tumors, we found a significant positive correlation between DKK1 expression and von Willebrand factor. In vivo, DKK1 strongly enhanced the vascularization of Matrigel plugs and increased tumor size in a xenograft model of human breast carcinoma in nude mice. DKK1 enhances angiogenic properties of ECFCs in vitro and is required for ECFC and mesenchymal stem cell angiogenic phenotypes in vivo. DKK1 also increases tumoral angiogenesis. Thus, we demonstrated a major role of DKK1 in angiogenic processes.
    Arteriosclerosis Thrombosis and Vascular Biology 12/2010; 30(12):2544-52. · 6.34 Impact Factor
  • Stéphane Germain, Anne Eichmann
    Nature medicine 07/2010; 16(7):752-4. · 27.14 Impact Factor
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    ABSTRACT: Angiogenesis is a highly coordinated tissue remodeling process leading to blood vessel formation. Hypoxia triggers angiogenesis via induction of expression of growth factors such as vascular endothelial growth factor (VEGF). VEGF instructs endothelial cells to form tip cells, which lead outgrowing capillary sprouts, whereas Notch signaling inhibits sprout formation. Basement membrane deposition and mechanical cues from the extracellular matrix (ECM) induced by hypoxia may participate to coordinated vessel sprouting in conjunction with the VEGF and Notch signaling pathways. Hypoxia regulates ECM composition, deposition, posttranslational modifications and rearrangement. In particular, hypoxia-driven vascular remodeling is dynamically regulated through modulation of ECM-modifying enzyme activities that eventually affect both matricellular proteins and growth factor availability. Better understanding of the complex interplay between endothelial cells and soluble growth factors and mechanical factors from the ECM will certainly have significant implications for understanding the regulation of developmental and pathological angiogenesis driven by hypoxia.
    Current opinion in hematology 03/2010; 17(3):245-51. · 5.19 Impact Factor
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    ABSTRACT: We have previously shown that angiopoietin-like 4 (angptl4) mRNA, a hypoxia-inducible gene, is highly expressed in clear cell renal-cell carcinoma (ccRCC), the most common subtype of RCC for which no specific marker is available. We here investigated whether angptl4 mRNA 1) could be a useful diagnostic and/or prognostic marker of ccRCC in a large and comprehensive retrospective series, 2) induction is dependent on the VHL status of tumors. Using in situ hybridization, we report that angptl4 mRNA is expressed in 100% of both sporadic (n = 102) and inherited (n = 6) primary ccRCCs, without any statistical association with nuclear grade (p = 0.39), tumor size (p = 0.09), stage grouping (p = 0.17), progression-free survival (p = 0.94), and overall survival (p = 0.80). Angptl4 mRNA was also expressed in 26 (87%) of 30 secondary ccRCCs but neither in any other secondary RCCs (n = 7). In contrast, angptl4 mRNA was neither expressed in 94% non-ccRCC renal tumors (papillary RCCs (n = 46), chromophobe RCCs (n = 28), and oncocytomas (n = 9)), nor in non-renal clear cell carcinomas (n = 39). Angptl4 expression was also examined in tumors associated (n = 23) or not associated (n = 66) with VHL disease. 40 (98%) hemangioblastomas expressed angptl4 whereas all pheochromocytomas (n = 23) and pancreatic tumors (n = 25) were angptl4-negative, whatever their VHL status. Angptl4 mRNA expression was highly associated with ccRCC (p = 1.5 10(-49), Chi square test) allowing to define its expression as a diagnosis marker for primary ccRCC. Moreover, angptl4 mRNA allows to discriminate the renal origin of metastases of clear-cell carcinomas arising from various organs. Finally, inactivation of VHL gene is neither necessary nor sufficient for angptl4 mRNA induction.
    PLoS ONE 01/2010; 5(4):e10421. · 3.73 Impact Factor
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    ABSTRACT: Mechanisms governing muscle satellite cell withdrawal from cell cycle to enter into quiescence remain poorly understood. We studied the role of angiopoietin 1 (Ang1) and its receptor Tie-2 in the regulation of myogenic precursor cell (mpc) fate. In human and mouse, Tie-2 was preferentially expressed by quiescent satellite cells in vivo and reserve cells (RCs) in vitro. Ang1/Tie-2 signaling, through ERK1/2 pathway, decreased mpc proliferation and differentiation, increased the number of cells in G0, increased expression of RC-associated markers (p130, Pax7, Myf-5, M-cadherin), and downregulated expression of differentiation-associated markers. Silencing Tie-2 had opposite effects. Cells located in the satellite cell neighborhood (smooth muscle cells, fibroblasts) upregulated RC-associated markers by secreting Ang1 in vitro. In vivo, Tie-2 blockade and Ang1 overexpression increased the number of cycling and quiescent satellite cells, respectively. We propose that Ang1/Tie-2 signaling regulates mpc self-renewal by controlling the return to quiescence of a subset of satellite cells.
    Cell stem cell 10/2009; 5(3):298-309. · 23.56 Impact Factor
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    ABSTRACT: We investigated the causes of microvessel immaturity and destabilization in human atherosclerotic lesions. Human atherosclerotic carotid plaques (n = 24) were classified as non-haemorrhagic (NH) or haemorrhagic (Hem), according to their macroscopic aspect and haemoglobin content. Plaque microvessel density and maturity were quantified by immunohistochemistry. Expression of angiogenic factors was studied by immunohistochemistry, in situ hybridization, and ELISA. Plaque-conditioned media were tested for plasmin and elastase activities and for their ability to degrade angiogenic factors and to induce smooth muscle cell migration. Microvessel density and leucocyte infiltration were increased in Hem compared with NH plaques. Plaque vasculature appeared vulnerable as indicated by the absence of alpha-actin-positive mural cells in most plaque vessels. Despite increased numbers of angiogenic factor-expressing microvessels and leucocytes in Hem plaques, lower levels of vascular endothelial growth factor, placental growth factor, and angiopoietin-1 were found in conditioned media from Hem plaques. However, NH and Hem plaques released similar levels of the vascular destabilizing factor, angiopoietin-2. Addition of recombinant angiogenic factors to plaque extracts showed that all factors but angiopoietin-2 were selectively degraded by plasmin and/or elastase released from Hem plaques. Furthermore, conditioned media from Hem plaques showed a reduced ability to induce smooth muscle cell migration. Our results provide evidence that immaturity of plaque vessels is associated with the degradation of angiogenic factors by haemorrhage-conveyed leucocytes and proteases.
    Cardiovascular research 08/2009; 85(1):184-93. · 5.80 Impact Factor
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    ABSTRACT: Increased permeability of, and bleeding from, microvessels within the atheromatous arterial wall participate in atherothrombosis progression. The VEGF family and angiopoietin system components govern microvessel development and maturation. Serine protease activities are proportional to atherothrombosis progression and linked to intraplaque hemorrhage. Here we investigated the relationship between angiogenic factors and proteases in human hemorrhagic and non-hemorrhagic atheromatous carotid samples by immunohistochemistry, in situ hybridization and ELISA. Plaque activity of plasmin and leukocyte elastase and proteolysis of angiogenic factors by plaque extracts were determined. Smooth muscle cell migration induced by hemorrhagic and nonhemorrhagic plaques was assessed. The absence of á-actin-positive cells characterized microvessels in hemorrhagic areas in spite of similar expression of VEGF and angiopoietin system components in microvessels of hemorrhagic and non-hemorrhagic areas. However, VEGF, PlGF and angiopoietin-1 levels were signifi cantly decreased in hemorrhagic compared to non-hemorrhagic plaques, whereas angiopoietin-2 did not change and soluble Tie-2 levels increased. Consequently, smooth muscle cell migration stimulatory activity of hemorrhagic plaques was reduced. Recombinant PlGF, VEGF and angiopoietin-1 added to plaque extracts were only degraded by hemorrhagic lesions. This proteolysis was prevented by inhibitors of plasmin and elastase, whose activity was increased in hemorrhagic plaques. No degradation was observed for angiopoietin-2. Decreased angiogenic factor levels caused by proteolysis may destabilize plaque microvessels via impairment of mural cell recruitment, thus leading to a vicious circle of intraplaque hemorrhages and lesion progression.
    Archives of Cardiovascular Diseases - ARCH CARDIOVASC DIS. 01/2009; 102.
  • Archives of Cardiovascular Diseases - ARCH CARDIOVASC DIS. 01/2009; 102.
  • Archives of Cardiovascular Diseases - ARCH CARDIOVASC DIS. 01/2009; 102.
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    ABSTRACT: Angiopoietin-like 4 (ANGPTL4) is involved in angiogenesis and lipid metabolism. It is secreted by liver and adipose tissues and cleaved to generate circulating coiled-coil domain (CCD) and fibrinogen-like domain (FLD) fragments. The full-length ANGPTL4 produced by hypoxic endothelial cells interacts with the extracellular matrix (ECM). The ECM-bound and soluble forms of ANGPTL4 have antiangiogenic properties. We carried out a structure-function analysis to investigate the regulation of ANGPTL4 bioactivity in endothelial cells. We found that the recombinant CCD binds to the ECM, whereas the FLD is released into the medium. The CCD, like the full-length ANGPTL4, binds to heparan and dermatan sulfates in surface plasmon resonance assays and inhibits endothelial cell adhesion, motility, and tubule-like formation. In endothelial cells, ANGPTL4 is processed in the secretion medium after release from the ECM. This processing is altered by the proprotein convertases inhibitor alpha1-PDX and abolished by the mutation of the (161)RRKR(164) cleavage site without modification of the ECM binding and release. These data suggest that the full-length form, which interacts with heparan sulfate proteoglycans via its CCD, is protected from proteolysis by proprotein convertases and constitutes the major active pool of ANGPTL4 in hypoxic endothelial cells.
    The FASEB Journal 12/2008; 23(3):940-9. · 5.70 Impact Factor

Publication Stats

658 Citations
200 Downloads
2k Views
267.78 Total Impact Points

Institutions

  • 2011–2012
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2007–2011
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
  • 2006–2010
    • Unité Inserm U1077
      Caen, Lower Normandy, France
  • 2003–2010
    • Collège de France
      Lutetia Parisorum, Île-de-France, France