Expression of glucose transporter GLUT3 by endotoxin in cultured rat astrocytes: The role of nitric oxide

Abstract

The induction of nitric oxide (NO) synthase in astrocytes by endotoxin and/or cytokine treatment is associated with increased glucose consumption and glycolysis, but the mechanism whereby this phenomenon occurs remains obscure. In this work, we have addressed this issue and found that incubation of cultured rat astrocytes with lipopolysaccharide (LPS; 1 μg/mL) for 24 h increased the level of constitutively expressed GLUT1 glucose transporter mRNA, and triggered GLUT3 mRNA expression, which was absent in normal astrocytes. The occurrence of GLUT3 protein after LPS treatment was corroborated by western blotting and immunocytochemistry. A 4-h incubation of astrocytes in the absence of glucose, or under an oxygen-poor (3%) atmosphere also resulted in GLUT3 mRNA overexpression. Experiments performed with 2-deoxy-D-[U-14C]glucose (at 0.1 mM of D-glucose) confirmed that LPS (0.1-10 μg/mL) dose-dependently increased the rate of glucose uptake (by a factor of 1.6 at 1 μg/mL of LPS), which was paralleled with the increase in NO synthesis. Furthermore, blockade of NO synthase with 2-amino-5,6-dihydro-6-methyl-(4H)-1,3-thiazine (AMT; 50 μM) partially (by 45%) prevented the LPS-mediated increase in glucose uptake. Finally, incubation of astrocytes with the NO donor 1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen- 1-ium-1,2-diolate (DETA; 100 μM) increased by a factor of 1.4 the rate of glucose uptake. We conclude that the increase in GLUT3-driven glucose uptake in astrocytes would have a neuroprotective role under conditions in which NO formation is combined with hypoglycaemia, such as in brain ischemia.