GENE-EXPRESSION OF GLUT3 GLUCOSE-TRANSPORTER REGULATED BY GLUCOSE IN-VIVO IN MOUSE-BRAIN AND IN-VITRO IN NEURONAL CELL-CULTURES FROM RAT EMBRYOS

This study was designed to determine whether glucose regulates the gen e expression of glucose transporter GLUT3 in neurons. We examined the regulation of GLUT3 mRNA by glucose in vivo in mouse brain and in vitr o by using neuronal cultures from rat embryos. Hypoglycaemia (< 30 mg/ dl), produced by 72 h of starvation, increased GLUT3 mRNA in mouse bra in by 2-fold. Hybridization studies in situ demonstrated that hypoglyc aemia-induced increases in GLUT3 mRNA expression were observed selecti vely in brain regions including the hippocampus, dentate gyrus, cerebr al cortex and piriform cortex, but not the cerebellum. Primary neurona l cultures from rat embryos deprived of glucose for 48 h also showed a n increase (4-fold over control) in GLUT3 mRNA, indicating that glucos e can directly regulate expression of GLUT3 mRNA. In contrast with hyp oglycaemia, hyperglycaemia produced by streptozotocin did not alter th e expression of GLUT3 mRNA. We also confirmed previous findings that h ypoglycaemia increases GLUT1 mRNA expression in brain. The increase in GLUT1 expression was probably limited to the blood-brain barrier in v ivo, since GLUT1 mRNA could not be detected in neurons of the mouse ce rebrum. Thus we conclude that up-regulation of neuronal GLUT3 in respo nse to glucose starvation represents a protective mechanism against en ergy depletion in neurons.