Glucose Transporters in Brain: In Health and in Alzheimer's Disease.

Neurons need a continuous supply of glucose, the major source of energy for mammalian brain metabolism. The central nervous system is protected by three main physiological cell barriers. Cell membranes are impermeable for glucose, therefore glucose is transferred across the cell membranes by specific transport proteins: sodium-independent glucose transporters (GLUTs), encoded by SLC2 genes, and sodium-dependent glucose transporters (for example SGLTs), encoded by SLC5 genes. Human brain expresses 10 GLUT proteins and 10 proteins encoded by SLC5 genes. In patients with brain diseases, particularly Alzheimer's (AD) and Huntington's diseases, abnormalities in neuronal glucose metabolism have been showed. The levels of GLUT1 and GLUT3, the major brain glucose transporters, are decreased, especially in the cerebral cortex. Therefore, in AD, hypometabolism of glucose and deficits in energy are observed. Production of ATP from glucose metabolism in sporadic AD declines to 50% and the tendency to decline continues throughout the progression of the disease. This decrease is correlated with O-GlcAcetylation and tau hyperphosphorylation, as the compensatory mechanisms in AD are the utilization of endogenous brain substances and drastic increase in GLUT2 levels. The present review focuses on the changes in the expression of glucose transporters due to AD.