Abstract A30: Hypoxia induces macrophage polarization and re-education towards an M2 phenotype in glioblastoma
Authors: Leblond Marine M. , Gérault Aurélie N. , Corroyer-Dulmont Aurélien , Petit Edwige , Bernaudin Myriam , Valable Samuel 
Published: May 2016

Introduction: Hypoxia, resulting in a decrease in tissue oxygen tension, is a main characteristic of glioblastoma (GBM) and is associated to a poor life expectancy of GBM patients (Spence et al., 2008). In the same time, it is now known that GBM are also inflammatory tumors and that macrophages (MΦ) are the most abundant immune cells found in these tumors (Badie et al., 2000). MΦ present in tissue can be polarized into at least two distinct phenotypes: the M1 phenotype (with antitumoral activity) and the M2 phenotype (with protumoral activity) (Mantovani et al., 2002), the most often phenotype found in patients with GBM (Lu-Emerson et al., 2013). However, factors responsible for their migration and phenotype acquisition in the context of GBM are not yet identified. The aim of this study was to evaluate, in vivo, the impact of hypoxia on MΦ tropism and polarization in a preclinical model of human GBM that progressively evolves towards severe hypoxia and, in vitro, the effect of hypoxia on MΦ polarization and re-education.

Method: Animal models consisted of injection of human GBM U251 cells into the brain of immunodeficient rats. Hypoxia has been evaluated by pimonidazole and CAIX staining. MΦ have been detected on brain slices through a CD68 staining and polarization toward M1 or M2 phenotype with iNOS and Arginase1 staining, respectively. In parallel, murine primary cultures of MΦ have been freshly prepared from bone marrow. M0, M1 and M2 MΦ have been exposed to moderate (1% oxygen) or severe (0.2% oxygen) hypoxia for 24h and their phenotypes have been characterized by RT-qPCR and enzymatic assays.

Results: In the U251 model, we have shown that MΦ migrated at the tumor site only when hypoxia takes place. We also demonstrated that the acquisition of the M2 phenotype was clearly a dynamic process with hypoxia as the major trigger for this transition. Furthermore, MΦ present at the shell of the tumor express M1 markers unlike MΦ found in hypoxic zones which exhibit M2 markers. In support of these in vivo findings, M0 but also M1 MΦ cultured in 1% or 0.2% oxygen displayed a phenotype close to that of M2 MΦ whose this phenotype was further reinforced by severe hypoxia.

Conclusion: In this study, using a human preclinical GBM model which progressively develops severe hypoxia, we showed that the presence of MΦ in the tumor depends on presence or not of hypoxia. We have also shown that hypoxia polarizes and re-educates MΦ towards M2 MΦ but also that it fine-tunes the M2 phenotype. These results highlight the effect of hypoxia in the aggressiveness of GBM and may help to improve therapies for these tumors by taking in account that hypoxia drives MΦ towards a protumoral phenotype.

Acknowledgements: Conseil Régional de Basse-Normandie, Université de Caen Basse-Normandie, Archade, CNRS, the European Regional Development Fund of Basse-Normandie (FEDER), “l'Europe s'engage en Basse Normandie” and the French Ministère de l'Enseignement Supérieur et de la Recherche (MESR).

Citation Format: Marine M. Leblond, Aurélie N. Gérault, Aurélien Corroyer-Dulmont, Edwige Petit, Myriam Bernaudin, Samuel Valable. Hypoxia induces macrophage polarization and re-education towards an M2 phenotype in glioblastoma. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr A30.