The impact of genetic removal of GFAP and/or vimentin on glutamine levels and transport of glucose and ascorbate in astrocytes

The importance of the intermediate filament (IF) proteins glial fibrillary acidic protein (GFAP) and vimentin for astrocyte function was studied by in vestigating astrocytes prepared from GFAP-/-and/or vimentin-/- mice. The ra te of glucose uptake through facilitative hexose transporters was not affec ted by depletion of GFAP or vimentin. Similarly, the absence of these IF pr oteins did not affect ascorbate uptake, under control or cyclic AMP-stimula ted conditions, or ascorbate efflux through volume-sensitive organic anion channels. However, compared with wild-type astrocytes, glutamine concentrat ions were increased up to 200% in GFAP-/- astrocytes and up to 150% in GFAP +/-astrocytes and this increase was not dependent on the presence of viment in. GFAP-/- astrocytes in culture still contain Ifs (made of vimentin and n estin), whereas GFAP-/-vim-/- cultured astrocytes lack Ifs. Thus, glutamine levels appear to correlate inversely with GFAP, rather than depend on the presence of Ifs per se. Furthermore, the effect of GFAP is dose-dependent s ince the glutamine concentration in GFAP+/- astrocytes falls between those in wild-type and GFAP-/-astrocytes.