ABSTRACT
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.
Subject(s)
Endothelial Cells/metabolism , Neoplasms/physiopathology , Neovascularization, Pathologic/metabolism , Receptors, G-Protein-Coupled/deficiency , Receptors, G-Protein-Coupled/metabolism , Animals , Blotting, Western , Cell Proliferation , Computational Biology , DNA Primers/genetics , Electrophoresis, Polyacrylamide Gel , Enzyme-Linked Immunosorbent Assay , Female , Fibroblast Growth Factor 2/metabolism , Flow Cytometry , Fluorescent Antibody Technique , HeLa Cells , Humans , Mice , Mice, Inbred BALB C , Mice, Knockout , Neoplasms/metabolism , RNA, Small Interfering/genetics , Receptors, G-Protein-Coupled/genetics , Reverse Transcriptase Polymerase Chain Reaction , Vascular Endothelial Growth Factor A/metabolism , Vascular Endothelial Growth Factor Receptor-2/metabolismABSTRACT
The present study investigated the phenotype of heterozygous and homozygous neuropeptide S receptor (Npsr) deficient C57BL/6 mice in NPS- and cocaine induced hyperactivity, spontaneous and reactive locomotor activity, elevated plus maze, conditioned fear, and prepulse inhibition of the acoustic startle response. In Npsr-deficient mice, a strong reduction of spontaneous locomotor activity and of the startle magnitude was observed; heterozygous mice had an intermediate phenotype. In the other experiments, Npsr deficiency leads to no or only a very modest phenotype. These results support an important role of neuropeptide S in regulating locomotor activity.
