Reduced pathological angiogenesis and tumor growth in mice lacking GPR4, a proton sensing receptor
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The G protein-coupled receptor GPR4 is activated by acidic pH and recent evidence indicates that it is expressed in endothelial cells. In agreement with these reports, we observe a high correlation of GPR4 mRNA expression with endothelial marker genes, and we confirm expression and acidic pH dependent function of GPR4 in primary human vascular endothelial cells. GPR4-deficient mice were generated; these are viable and fertile and show no gross abnormalities. However, these animals show a significantly reduced angiogenic response to VEGF (vascular endothelial growth factor), but not to bFGF (basic fibroblast growth factor), in a growth factor implant model. Accordingly, in two different orthotopic models, tumor growth is strongly reduced in mice lacking GPR4. Histological analysis of tumors indicates reduced tumor cell proliferation as well as altered vessel morphology, length and density. Moreover, GPR4 deficiency results in reduced VEGFR2 (VEGF Receptor 2) levels in endothelial cells, accounting, at least in part, for the observed phenotype. Our data suggest that endothelial cells sense local tissue acidosis via GPR4 and that this signal is required to generate a full angiogenic response to VEGF.
KeywordsAngiogenesis Acidosis Hypoxia Endothelium Tumor
We would like to thank Melanie Muller, Juliane Vauxlaire, Corinne Manlius, Marina Maurer, Agnes Feige, Barbara Wilmering-Wetter, Marianne Lemaister, Thierry Doll, Imke Renz-Albrecht and Caterina Safina for excellent technical help, John Monahan for help with Affymetrix analysis, Julie Boisclair for help in characterizing the GPR4 deficient mice, Andreas Theuer for writing the program for Ki67 quantification and Jeanette Wood, Georg Martiny-Baron and Francesco Hofmann for support and critical discussions.
Conflict of interest
Thomas Suply, Bérangère Ricoux, Eric Billy, Christian Schnell, Birgit U Baumgarten, Sauveur Michel Maira, Claudia Koelbing, Mireille Ferretti, Bernd Kinzel, Matthias Müller, Klaus Seuwen and Marie-Gabrielle Ludwig are employees of Novartis AG, Switzerland. Lorenza Wyder is a former employee of Novartis AG.
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