Background: Eosinophils are involved in various inflammatory processes including allergic inflammation during which angiogenesis has been documented. Angiogenesis is most likely connected to the hypoxia which characterizes inflamed tissues. Eosinophils produce VEGF and are pro-angiogenic. However, to the best of our knowledge no study has been performed to verify the existence of a direct link between eosinophils, hypoxia and angiogenesis in allergic inflammation.Objective: To characterize eosinophil function and angiogenic potential under hypoxic conditions.Methods: Human peripheral blood eosinophils were cultured in normoxic or hypoxic conditions with or without cytokines. Viability and apoptosis were assessed by Annexin V/PI staining. Anti- or pro-apoptotic protein levels, HIF-1α levels and MAPK phosphorylation were analyzed by immunoblot analysis. Angiogenic mediator release was evaluated by ELISA.Results: Hypoxic eosinophils were more viable than normoxic ones after up to three days. In addition in hypoxia, anti-apoptotic Bcl-XL protein levels increased more than pro-apoptotic Bax levels. Hypoxia increased VEGF and IL-8 release. In hypoxic eosinophils high levels of HIF-1α were observed, particularly in the presence of GM-CSF. MAPK, particularly ERK1/2 inhibitors, decreased hypoxia-mediated VEGF release and HIF-1α expression.Conclusion: Eosinophils respond to hypoxia by up-regulation of survival and of some of their pro-angiogenic functions indicating a correlation between eosinophilic inflammation and angiogenesis.
Bibliographical noteFunding Information:
F. Levi-Schaffer is affiliated with the David R. Bloom Center of Pharmacy and the Brettler Center for Pharmacology at the School of Pharmacy, The Hebrew University of Jerusalem. This work was funded by grants from the Aimwell Charitable Trust Foundation (UK), the David R. Bloom Center of Pharmacy, and The David Sydney Davis Fund for Emphysema Related Research and by a donation in memory of Mrs. Muriel Turk (UK). We wish to thank Dr. Bruce Mazer for his critical reading of the manuscript and Dr. Ilaria Puxeddu for many helpful discussions.