Loss of CX3CR1 increases accumulation of inflammatory monocytes and promotes gliomagenesis.

Authors:
Xi Feng
Xi Feng
Sichuan University
China
Frank Szulzewsky
Frank Szulzewsky
Max-Delbrück Center for Molecular Medicine
Germany
Alexan Yerevanian
Alexan Yerevanian
Mount Sinai School of Medicine
Zhihong Chen
Zhihong Chen
Fudan University
China
David Heinzmann
David Heinzmann
Eberhard Karls Universität Tübingen
Tübingen | Germany
Rikke Darling Rasmussen
Rikke Darling Rasmussen
Danish Cancer Society Research Center
Yeonghwan Kim
Yeonghwan Kim
Kyung Hee University
South Korea

Oncotarget 2015 Jun;6(17):15077-94

Department of Neurosciences at Cleveland Clinic, Cleveland, Ohio, USA.

The most abundant populations of non-neoplastic cells in the glioblastoma (GBM) microenvironment are resident microglia, macrophages and infiltrating monocytes from the blood circulation. The mechanisms by which monocytes infiltrate into GBM, their fate following infiltration, and their role in GBM growth are not known. Here we tested the hypothesis that loss of the fractalkine receptor CX3CR1 in microglia and monocytes would affect gliomagenesis. Deletion of Cx3cr1 from the microenvironment resulted in increased tumor incidence and shorter survival times in glioma-bearing mice. Loss of Cx3cr1 did not affect accumulation of microglia/macrophages in peri-tumoral areas, but instead indirectly promoted the trafficking of CD11b+CD45hiCX3CR1lowLy-6ChiLy-6G-F4/80-/low circulating inflammatory monocytes into the CNS, resulting in their increased accumulation in the perivascular area. Cx3cr1-deficient microglia/macrophages and monocytes demonstrated upregulation of IL1β expression that was inversely proportional to Cx3cr1 gene dosage. The Proneural subgroup of the TCGA GBM patient dataset with high IL1β expression showed shorter survival compared to patients with low IL1β. IL1β promoted tumor growth and increased the cancer stem cell phenotype in murine and human Proneural glioma stem cells (GSCs). IL1β activated the p38 MAPK signaling pathway and expression of monocyte chemoattractant protein (MCP-1/CCL2) by tumor cells. Loss of Cx3cr1 in microglia in a monocyte-free environment had no impact on tumor growth and did not alter microglial migration. These data suggest that enhancing signaling to CX3CR1 or inhibiting IL1β signaling in intra-tumoral macrophages can be considered as potential strategies to decrease the tumor-promoting effects of monocytes in Proneural GBM.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4558137PMC
http://dx.doi.org/10.18632/oncotarget.3730DOI Listing

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June 2015
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