Etude des effets de l’hypoxie cyclique et du TNFalpha sur les cellules endothéliales : Activation du facteur NF-kappaB et d’un phénotype pro-inflammatoire et pro-angiogénique

  • Déborah Desmet

Student thesis: Doc typesDoctor of Sciences

Abstract

Cycling hypoxia, which is periods of hypoxia followed by reoxygenation, is a hallmark of solid tumors that originate from the instability of the tumor blood flow. Cycling hypoxia may influence cancer cell as well as endothelial cell physiology and is described to favour survival and pro-angiogenic phenotype in endothelial cells. However, the molecular mechanisms underlying these effects remain largely unknown. The hypoxia-reoxygenation cycles are thought to induce oxidative stress in the tumor vasculature that could activate an anti-oxidant response in endothelial cells. Solid tumors are also characterized by a pro-inflammatory environment generated by cancer and immune cells, the major pro-inflammatory mediator being TNFα. In this work, we investigated the specific effects of cycling hypoxia, compared to continuous hypoxia and normoxia, on the activation of Nrf2 and NF-κB pathways in EA.hy926 endothelial cells and HUVEC by tBHQ and SIN-1, or TNFα respectively. We showed that cycling hypoxia inhibited Nrf2 response to tBHQ or SIN-1 by up-regulating the Nrf2 inhibitor Bach1. On the other hand, cycling hypoxia increased the activation of NF-κB initiated by TNFα in endothelial cells, probably by slowing down the negative feedback loop engaged by newly synthesized IκBα. The pro-inflammatory response initiated by TNFα was further enhanced by cycling hypoxia as both IL-8 and ICAM-1 were overexpressed at gene and protein levels. Furthermore, cycling hypoxia fostered elevated IL-6 secretion independently of gene regulation. Silencing of p65 and of HIF-1α expression with targeting siRNA highlighted the implication of NF-κB, but not of HIF-1, in the up-regulated secretion of IL-6 and the accumulation of ICAM-1. Finally, we showed that cycling hypoxia induced a strong increase in the migratory ability of EA.hy926 endothelial cells, suggesting an effect toward a pro-angiogenic phenotype. Endothelial cells exposed to cycling hypoxia and stimulated with TNFα thus seem to participate to the development of a pro-inflammatory environment potentially beneficial for tumor growth and metastasis
Date of Award6 Sept 2012
Original languageFrench
Awarding Institution
  • University of Namur
SupervisorCarine Michiels (Supervisor), Olivier Féron (Jury), Jacques Piette (Jury), Nathalie Caron (Jury), Martine Raes (Jury) & Thierry Arnould (President)

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