FUNCTIONAL EXPRESSION OF THE CXC-CHEMOKINE RECEPTOR-4 FUSIN ON MOUSE MICROGLIAL CELLS AND ASTROCYTES/

The mRNA for the seven-transmembrane-spanning G protein-coupled recept or fusin/CXCR-4 is expressed in primary mouse astrocyte cultures and t he transformed mouse microglial cell line, N9. Cell surface expression of fusin in these cells was confirmed by staining with a polyclonal a nti-fusin Ab. The functional capacity of this chemokine receptor was e xamined by evaluating the calcium responses following stimulation of g lial cells with the CXC-chemokine, stromal-derived cell factor-la (SDF -1 alpha). Both astrocytes and microglial cells mobilized calcium foll owing stimulation with chemically synthesized SDF-1 alpha. SDF-1 alpha - and carbachol-mediated calcium responses of astrocytes were partiall y inhibited by treatment with pertussis toxin (PTx), suggesting recept or coupling to a combination of G alpha(i) and other G proteins. In co ntrast, the calcium responses of microglial cells to SDF-1 alpha were completely PTx sensitive, while responses to carbachol stimulation wer e PTx resistant. The ability of SDF-1 alpha to induce glial cell migra tion was also examined. Synthetic SDF-1 alpha was a potent chemoattrac tant for mouse microglial cells at ligand concentrations of 10 to 500 ng/ml; peak responses were noted at 100 ng/ml. In contrast, astrocytes did not migrate toward a gradient of SDF-1 alpha. The failure of SDF- 1 alpha to induce astrocyte migration was specific, as another chemoki ne, macrophage inflammatory protein-1 alpha, triggered astrocyte chemo taxis.