MITOCHONDRIAL ROLE IN AGE-RELATED RESPONSES OF NEURONS TO A-BETA AND GLUTAMATE





Gregory J. Brewer*, John R. Torricelli, Nicole Capps, Jason Nash

Neurology, Medical Microbiology & Immunology, Southern Illinois Univ. Sch.Med. 62794-9626



A clearer understanding on how the mitochondrial theory of aging applies to the brain under stress and neurodegenerative disorders could provide new targets for successful ageing. Our model of neurons isolated and cultured from aged rat brain hippocampus indicates an age-related increase in susceptibility to death for these neurons following exposure to stressors such as glutamate and A-beta (Brewer, Neurobiol. Aging 19:561). Since these cells regenerate similarly in identical culture medium, we infer that intrinsic differences exist in these cells. We hypothesize that the impact of mitochondria impairment in aged neurons becomes evident with stress. Mitochondria from old neurons are could be set to trigger apoptosis at an earlier point or there could be less mitochondria with age. We measured mitochondrial mass with the fluorescent dye nonylacridine orange (NAO) in individual neurons isolated from embryonic, middle-age (12 month)and old (24 month) rat brains. Even after regeneration in a common culture medium, neurons from old animals showed a 45% lower NAO fluorescence normalized to the size of each cell compared to middle-age neurons. Rhodamine 123 (R123) fluorescence was used to monitor mitochondrial membrane polarization. Resting R123 fluorescence/cell was 40% lower for old neurons compared to middle-age neurons. In response to glutamate, R123 fluorescence/cell declined for old neurons, remained unchanged for middle-age neurons and increased for embryonic neurons. These results suggest that glutamate caused old neurons to lose their mitochondrial membrane potential faster than middle-age or embryonic neurons. A similar result was obtained over a 6 hr. time course for neurons exposed to 25 ?MA?(25-35). Levels of anti-apoptotic bcl-2 and pro-apoptotic bax were evaluated by immunocytology. The density of bax increased with age. These results suggest an age-related decline in regeneration of mitochondria in culture and age-related deficits in resting mitochondrial function that were exacerbated in response to stressors. Supported by NIH AG13435 and the Alzheimer Association.




Key words: neuron, mitochondria, glutamate, A-beta







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