Alteration of Tubulin-Gi Protein Interaction in Rat Cerebral Cortex with Aging

Abstract: The ability of the tubulin dimer to interact with and to modulate the G_i function inhibiting adenylyl cyclase was examined in cerebral cortex membranes from 2-month-old and 24-month-old rats. The hydrolysis-resistant GTP analogue 5'-guanylylimidodiphosphate (GppNHp)-dependent inhibition of adenylyl cyclase was significantly decreased in cerebral cortex membranes from 24-month-old rats. Tubulin, prepared from rat brains by polymerization with GppNHp, caused inhibition of adenylyl cyclase (～28%) in 2-month-old rats. Tubulin-GppNHp-dependent inhibition of adenylyl cyclase in 24-month-old rats was significantly attenuated (～15%). In 2-month-old rats, when tubulin, polymerized with the hydrolysis-resistant photoaffinity GTP analogue ³²P] P ³(4-azidoanilido)- P ¹-5'-GTP (³²P]AAGTP), was incubated with cerebral cortex membranes, AAGTP was transferred from tubulin to G_iα. Transfer of AAGTP from tubulin to G_iα was reduced in 24-month-old rats. Furthermore, photoaffinity labeling of ³²P]AAGTP to G_iα in cortex membranes was significantly decreased in 24-month-old rats. No differences were observed in the amounts of G_sα, G_iα, or G_β subunits and tubulin, estimated by immunoblotting, in cortex membranes from 2-month-old and 24-month-old rats. These results suggest that the ability of tubulin to interact with G_i and thereby modulate the inhibitory regulation of adenylyl cyclase is reduced in the cerebral cortex of 24-month-old rats.