Implications of aging- and degeneration-related changes in anion exchange proteins for the maintenance of neuronal homeostasis.

Fourier-transform infrared spectroscopy was applied to examine the nature and extent of changes in membrane composition and structure during the aging process of the human erythrocyte. Analysis of the Amide I region (1700-1600 cm-1) indicates an aging-related decrease in alpha-helical structure with a concomitant increase in beta-structure. These changes can be explained by structural changes in the erythrocyte anion exchanger (band 3 or AE1) molecules, that may be caused by fragmentation, but not by aggregation. Immunohistochemical analysis of human brain tissue shows an increase in neuronal AE protein expression with age and suggests an additional increase in Alzheimer's disease. Biochemical analyses indicate that the latter may be caused by conformational changes in the AE membrane domain that are similar to those observed in AE1 during erythrocyte aging. AE proteins provide a binding site for the cytoskeleton in neurons, and AE-catalyzed chloride/bicarbonate exchange plays a major role in maintenance of neuronal pH. Thus, changes in AE structure are likely to contribute to loss of neuron homeostasis during aging and in neurodegenerative diseases.