Stéphane Germain

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

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Publications (79)508.76 Total impact

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    ABSTRACT: Significance: The results from the present study show that fibroblast growth factor-2 (FGF-2) priming is more efficient than hypoxia at increasing dental pulp stem cells derived from deciduous teeth (SHED)-induced vascularization compared with nonprimed controls. Together, these data demonstrate that FGF-2 priming enhances the angiogenic potential of SHED through the secretion of both hepatocyte growth factor and vascular endothelial growth factor.
    Full-text · Article · Jan 2016 · STEM CELLS TRANSLATIONAL MEDICINE
  • Claire Bouleti · Nathan Mewton · Stéphane Germain
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    ABSTRACT: Primary percutaneous coronary intervention (PCI) is the best available reperfusion strategy for acute ST-segment elevation myocardial infarction (STEMI), with nearly 95% of occluded coronary vessels being reopened in this setting. Despite re-establishing epicardial coronary vessel patency, primary PCI may fail to restore optimal myocardial reperfusion within the myocardial tissue, a failure at the microvascular level known as no-reflow (NR). NR has been reported to occur in up to 60% of STEMI patients with optimal coronary vessel reperfusion. When it does occur, it significantly attenuates the beneficial effect of reperfusion therapy, leading to poor outcomes. The pathophysiology of NR is complex and incompletely understood. Many phenomena are known to contribute to NR, including leukocyte infiltration, vasoconstriction, activation of inflammatory pathways and cellular oedema. Vascular damage and haemorrhage may also play important roles in the establishment of NR. In this review, we describe the pathophysiological mechanisms of NR and the tools available for diagnosing it. We also describe the microvasculature and the endothelial mechanisms involved in NR, which may provide relevant therapeutic targets for reducing NR and improving the prognosis for patients.
    No preview · Article · Nov 2015 · Archives of cardiovascular diseases
  • Rümeyza Bascetin · Laurent Muller · Stéphane Germain · Caroline Gorin

    No preview · Conference Paper · Sep 2015
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    ABSTRACT: Sprouting angiogenesis is stimulated by vascular endothelial growth factor (VEGF165) that is localized in the extracellular matrix (ECM) and binds to heparan sulfate (HS)-bearing proteins known as heparan sulfate proteoglycans (HSPGs). VEGF165 presentation by HSPGs enhances VEGF receptor-2 (VEGFR2) signaling. We investigated the effect of TG2, which binds to HSPGs, on the interaction between VEGF165 and HS and angiogenesis. Mice with tg2 deficiency showed transiently enhanced retina vessel formation and increased vascularization of VEGF165-containing Matrigel implants. In addition, endothelial cells in which TG2 was knocked down exhibited enhanced VEGF165-induced sprouting and migration, which was associated with increased phosphorylation of VEGFR2 at Tyr(951) and its targets Src and Akt. TG2 knockdown did not affect the phosphorylation of VEGFR2 at Tyr(1175) or cell proliferation in response to VEGF165 and sprouting or signaling in response to VEGF121. Decreased phosphorylation of VEGFR2 at Tyr(951) was due to ECM-localized TG2, which reduced the binding of VEGF165 to endothelial ECM in a manner that required its ability to bind to HS but not its catalytic activity. Surface plasmon resonance assays demonstrated that TG2 impeded the interaction between VEGF165 and HS. These results show that TG2 controls the formation of VEGF165-HSPG complexes and suggest that this regulation could be pharmacologically targeted to modulate developmental and therapeutic angiogenesis. Copyright © 2015, American Association for the Advancement of Science.
    Full-text · Article · Jul 2015 · Science Signaling

  • No preview · Article · Apr 2015 · Archives of Cardiovascular Diseases Supplements
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    ABSTRACT: No-reflow in ST-segment elevation acute myocardial infarction (STEMI) is associated with a poor clinical prognosis. Its pathophysiological mechanisms are not fully elucidated yet but enhanced vascular permeability plays a key role in this phenomenon. Angiopoietin-like 4 (ANGPTL4) has been implicated in vascular permeability in experimental models of acute myocardial infarction (AMI). We therefore sought to investigate whether baseline ANGPTL4 serum levels are associated with no-reflow after primary percutaneous coronary intervention (PPCI). We studied a group of 41 patients presenting with a first STEMI within 12h of onset of symptoms and who underwent successful PPCI. Blood samples were obtained from all patients on admission before the start of the procedure, for ANGPTL4 level measurement. No-reflow was assessed by cardiac magnetic resonance imaging (MRI), the reference method. MRI-detected no-reflow was observed in 20 patients (48.8%). Variables independently associated with no-reflow on multivariate logistic regression analysis were: lower ANGPTL4 serum levels (odds ratio 0.82, 95% CI 0.70-0.98, P=0.02), higher troponin T peak (odds ratio 1.03, 95% CI 1.00-1.05, P=0.03), higher incidence of left anterior descending coronary artery (LAD) as culprit artery (odds ratio 14.61, 95% CI 1.24-172.49, P=0.03), and higher C-reactive protein levels (odds ratio 1.18, 95% CI 1.00-1.39, P=0.05). ANGPTL4 serum levels predict MRI-detected no-reflow after successful PPCI in STEMI patients. Given the recently demonstrated therapeutic role of ANGPTL4 in diminishing no-reflow and limiting infarct size in pre-clinical animal models, these findings in humans may open up new possibilities in the field of research. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
    Preview · Article · Mar 2015 · International journal of cardiology
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    ABSTRACT: Purpose: Developing strategies to overcome resistance to sunitinib is a major challenge in human renal-cell carcinoma (RCC). We hypothesized that sunitinib-induced tumor necrosis-associated hypoxia could interact with renal cancer stem-cells in patients with metastatic RCC. Experimental design: We studied tissue samples from seven patients with primary metastatic RCC, before and after sunitinib treatment, and from six xenograft models derived from human RCC. Two xenograft models were responders to sunitinib, the four others were non-responders. CD133/CXCR4 co-expressing cells derived from the two responder xenograft models were used for in vitro studies. Results: In the seven primary RCC, we identified a significantly larger number of CD133/CXCR4-coexpressing cells in peri-necrotic versus peri-vascular areas. Their numbers also significantly increased after treatment, in peri-necrotic areas. We reproduced these clinical and pathological results in all six RCC xenograft models with again a preferential peri-necrotic distribution of CD133-expressing cells. Necrosis occurred at Day7 in the two responder models treated with sunitinib, while it occurred at Day21 in the untreated controls and in the four non-responder models. Strikingly, when we studied the 6 RCC xenograft models at the time necrosis, whether spontaneous or sunitinib-induced, occurred, necrosis area correlated with stem-cell number in all 120 xenografted RCCs. When studied under experimental hypoxia, the number of CD133/CXCR4 co-expressing cells and their tumorigenic potency increased while their sensitivity to sunitinib decreased. Conclusions: In human RCC, sunitinib was able to generate resistance to its own therapeutic effect via induced hypoxia in peri-necrotic areas where cancer stem cells were found in increased numbers. Copyright © 2014, American Association for Cancer Research.
    No preview · Article · Dec 2014 · Clinical Cancer Research
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    ABSTRACT: Creating a “pulp tissue equivalent” constitutes a promising therapeutic approach to replace the current endodontic treatment. Objectives: To assess whether a pretreatment in hypoxia increases the ability of Dental Pulp Stem Cells (DPSC) to generate a functional dentino-pulpal tissue. Methods: in vitro: To study DPSC behavior under hypoxic conditions, human-DPSC seeded in 3D collagen matrix were cultured at either 20 or 1%O2 for 3 hours to 3 days and the expression of pro-angiogenic factors was analyzed. To study the ability of hypoxia to enhance odontoblastic differentiation, compressed matrices seeded with DPSC were cultured in osteogenic medium for 14 days, with or without hypoxic pretreatment (24 or 72h, 1% O2). Mineralization was assessed by counting positive nodules for von Kossa staining and by electronic microscopy. In vivo: 24h hypoxia pretreated or not mouse-DPSC were seeded in 3D collagen matrix enclosed in a tooth slice and implanted subcutaneously in each side of mice (n=12). A weekly monitoring was performed by echo-doppler and completed by a micro-CT analysis after IV injection of contrast agent. Ex vivo, immunohistochemistry was performed using markers for blood vessels (von Willebrand factor and Alpha smooth muscle Actin) and sensitive fibers (Calcitonin Gene Related Peptide). Results: Our in vitro approaches show that DPSC adapt to hypoxia and respond with a significant increase of pro-angiogenic factor expression, especially after a 24h treatment. In addition, the number of mineralization nodules was increased when cells were pretreated with hypoxia. In vivo, dynamic examinations and quantification of vessel number and area by immunohistochemistry show a significant increase (respectively x2 and x5) (p<0,001) of neovascularization in the implanted matrix when cells were pretreated with hypoxia. Sensitive innervation was also observed around vessels. Conclusion: This work indicates that hypoxic pretreatment enhances DPSC capacity to (re)create a vascularized and innerved dental pulp tissue.
    Full-text · Conference Paper · Sep 2014
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    Preview · Article · Jul 2014 · Medecine sciences: M/S
  • L. Muller · C. Monnot · S. Germain
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    ABSTRACT: Hypoxia regulates composition of both the vascular basement membrane (BM) and the extracellular matrix (ECM) by modulating deposition, cross-linking, posttranslational modifications, and rearrangement events but also degradation. Hypoxia-driven remodeling of the ECM includes highly temporally and spatially coordinated processes that eventually affect angiogenesis leading to blood vessel formation from existing blood vessels. Hypoxia thereby affects the mechanical properties of the vascular milieu as well as matricellular proteins expression and function and availability of angiogenesis-regulating growth factors such as vascular endothelial growth factor (VEGF). ECM composition and stiffness may be required for optimal VEGFR2 expression and vascular development in vitro and in vivo (Mammoto et al. Nature 2009), but how it might control signaling pathways such as VEGFR2 signaling is not fully appreciated yet. Thus, vascular BM and ECM composition affects vascular microenvironment architecture and interaction with angiogenic growth factors but also exerts mechanical forces controlled by physical interactions between vascular cells and the ECM that cooperate in regulating angiogenesis.
    No preview · Article · Jul 2014
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    ABSTRACT: The protein tyrosine phosphatase 1B (PTP1B) modulates tyrosine kinase receptors, among which is the vascular endothelial growth factor receptor type 2 (VEGFR2), a key component of angiogenesis. Because PTP1B deficiency in mice improves left ventricular (LV) function 2 mo after myocardial infarction (MI), we hypothesized that enhanced angiogenesis early after MI via activated VEGFR2 contributes to this improvement. At 3 d after MI, capillary density was increased at the infarct border of PTP1B(-/-) mice [+7±2% vs. wild-type (WT), P = 0.05]. This was associated with increased extracellular signal-regulated kinase 2 phosphorylation and VEGFR2 activation (i.e., phosphorylated-Src/Src/VEGFR2 and dissociation of endothelial VEGFR2/VE-cadherin), together with higher infiltration of proangiogenic M2 macrophages within unchanged overall infiltration. In vitro, we showed that PTP1B inhibition or silencing using RNA interference increased VEGF-induced migration and proliferation of mouse heart microvascular endothelial cells as well as fibroblast growth factor (FGF)-induced proliferation of rat aortic smooth muscle cells. At 8 d after MI in PTP1B(-/-) mice, increased LV capillary density (+21±3% vs. WT; P<0.05) and an increased number of small diameter arteries (15-50 μm) were likely to participate in increased LV perfusion assessed by magnetic resonance imaging and improved LV compliance, indicating reduced diastolic dysfunction. In conclusion, PTP1B deficiency reduces MI-induced heart failure promptly after ischemia by enhancing angiogenesis, myocardial perfusion, and diastolic function.-Besnier, M., Galaup, A., Nicol, L., Henry, J.-P, Coquerel, D., Gueret, A., Mulder, P., Brakenhielm, E., Thuillez, C., Germain, S., Richard, V., Ouvrard-Pascaud, A. Enhanced angiogenesis and increased cardiac perfusion after myocardial infarction in protein tyrosine phosphatase 1B-deficient mice.
    Full-text · Article · Apr 2014 · The FASEB Journal
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    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.
    Full-text · Article · Apr 2014 · Vascular Cell
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    ABSTRACT: Connexin 40 (Cx40) is expressed by the renin-producing cells (RSCs) of the kidneys and the endothelial cells of blood vessels. Cx40 null mice (Cx40(-/-)) feature a much increased renin synthesis and secretion, which results in chronic hypertension, and also display an altered endothelium-dependent relaxation of the aorta because of reduced eNOS levels and nitric oxide production. To discriminate the effect of Cx40 in renin secretion and vascular signaling, we targeted Cx40 to either the RSCs or the endothelial cells of Cx40 null mice. When compared with Cx40(-/-) controls, the animals expressing Cx40 in RSCs were less hypertensive and featured reduced renin levels, still numerous RSCs outside the wall of the afferent arterioles. In contrast, mice expressing Cx40 in the endothelial cells were as hypertensive as Cx40(-/-) mice, in spite of control levels of Cx37 and eNOS. Our data show that blood pressure is improved by restoration of Cx40 expression in RSCs but not in endothelial cells, stressing the prominent role of renin in the mouse hypertension linked to loss of Cx40.
    Full-text · Article · Mar 2014 · Hypertension

  • No preview · Article · Nov 2013 · Wound Repair and Regeneration
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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.
    No preview · Article · Sep 2013 · Cancer Chemotherapy and Pharmacology
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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.
    No preview · Article · Aug 2013 · Critical care medicine
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    ABSTRACT: Background: No-reflow in ST-segment elevation acute myocardial infarction (STEMI) is associated with a poor clinical prognosis. Its pathophysiologal mechanisms are not totally elucidated yet but enhanced vascular permeability plays a key role in this process. ANGPTL4 has been implicated in vascular permeability in experimental models of AMI. We therefore sought to investigate whether baseline ANGPTL4 serum levels are associated with no-reflow after primary percutaneous coronary intervention (PPCI). Methods: A group of 41 consecutive patients with a first STEMI, undergoing successful PPCI within 12h of onset of symptoms were enrolled. Blood samples were obtained from all patients on admission for ANGPTL4 levels measurement. No-reflow was assessed by cardiac magnetic resonance imaging (MRI), the reference method. Results: MRI-detected no-reflow was observed in 20 patients (48.8%). Variables independently associated with no-reflow at multivariate logistic regression analysis were: lower ANGPTL4 plasma levels (odds ratio 0.82, 95% CI 0.70-0.98, P=0.02), higher troponin T peak (odds ratio 1.03, 95% CI 1.00-1.05, P=0.03), higher incidence of left anterior descending coronary artery (LAD) as culprit artery (odds ratio 14.61, 95% CI 1.24-172.49, P=0.03), and higher C-reactive protein levels (odds ratio 1.18, 95% CI 1.00-1.39, P=0.05). Conclusion: ANGPTL4 serum levels predict MRI-detected no-reflow after successful PPCI in STEMI patients. Given the recently demonstrated therapeutic role of ANGPTL4 in diminishing no-reflow and therefore infarct size in pre-clinical animal models, these findings in humans may open new fields of research.
    Preview · Article · Aug 2013 · European Heart Journal
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    ABSTRACT: AimsGiven the impact of vascular injuries and oedema on brain damage caused during stroke, vascular protection represents a major medical need. We hypothesized that angiopoietin-like 4 (ANGPTL4), a regulator of endothelial barrier integrity, might exert a protective effect during ischaemic stroke.Methods and resultsUsing a murine transient ischaemic stroke model, treatment with recombinant ANGPTL4 led to significantly decreased infarct size and improved behaviour. Quantitative characteristics of the vascular network (density and branchpoints) were preserved in ANGPTL4-treated mice. Integrity of tight and adherens junctions was also quantified and ANGPTL4-treated mice displayed increased VE-cadherin and claudin-5-positive areas. Brain oedema was thus significantly decreased in ANGPTL4-treated mice. In accordance, vascular damage and infarct severity were increased in angptl4-deficient mice thus providing genetic evidence that ANGPTL4 preserves brain tissue from ischaemia-induced alterations. Altogether, these data show that ANGPTL4 protects not only the global vascular network, but also interendothelial junctions and controls both deleterious inflammatory response and oedema.Mechanistically, ANGPTL4 counteracted VEGF signalling and thereby diminished Src-signalling downstream from VEGFR2. This led to decreased VEGFR2-VE-cadherin complex disruption, increased stability of junctions and thus increased endothelial cell barrier integrity of the cerebral microcirculation. In addition, ANGPTL4 prevented neuronal loss in the ischaemic area.Conclusion These results, therefore, show ANGPTL4 counteracts the loss of vascular integrity in ischaemic stroke, by restricting Src kinase signalling downstream from VEGFR2. ANGPTL4 treatment thus reduces oedema, infarct size, neuronal loss, and improves mice behaviour. These results suggest that ANGPTL4 constitutes a relevant target for vasculoprotection and cerebral protection during stroke.
    Full-text · Article · May 2013 · European Heart Journal
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    Preview · Article · Mar 2013 · Journal of the American College of Cardiology

  • No preview · Article · May 2012 · Vascular Pharmacology

Publication Stats

2k Citations
508.76 Total Impact Points

Institutions

  • 2011-2015
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • Pierre and Marie Curie University - Paris 6
      • Ecole Doctorale Physiologie et physiopathologie
      Lutetia Parisorum, Île-de-France, France
  • 1994-2015
    • Collège de France
      • Center for Interdisciplinary Research in Biology
      Lutetia Parisorum, Île-de-France, France
  • 2014
    • Université René Descartes - Paris 5
      Lutetia Parisorum, Île-de-France, France
  • 2013
    • Hôpital La Pitié Salpêtrière (Groupe Hospitalier "La Pitié Salpêtrière - Charles Foix")
      Lutetia Parisorum, Île-de-France, France
  • 2008-2009
    • Hôpital Européen Georges-Pompidou (Hôpitaux Universitaires Paris-Ouest)
      Lutetia Parisorum, Île-de-France, France
  • 2006-2007
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France