AGE-RELATED RESPONSES OF NEURONAL MITOCHONDRIA TO A-BETA AND GLUTAMATE





Gregory J. Brewer*, John R. Torricelli, Nicole Capps (gbrewer@siumed.edu)

Neurology, Medical Microbiology and Immunology, Southern Illinois University Sch. Med.62794



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). The mechanism of this increased killing involves age-related increases in condensed nuclei and caspase activation, suggestive of an apoptotic mechanism. In an age-related manner, mitochondria could be set to trigger apoptosis at an earlier point or fewer mitochondria could fail to maintain adequate energy levels under stress. A potential role for mitochondrial deficiencies in this process was studied with measures of mitochondrial mass and membrane potential in individual neurons isolated from embryonic, middle-age (12 month) and old (24 month) rat brains. The fluorescent dye nonylacridine orange was used to label mitochondrial cardiolipin. Even after regeneration in a common culture medium, neurons from old animals showed a 45% lower nonylacridine 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 for 20 min., 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 :M A$(25-35). These results suggest an age-related decline in regeneration of mitochondria in culture and age-related deficits in function in response to stressors. Supported by NIH AG13435.






Key words: mitochondria, stress, beta-amyloid, glutamate, neuron culture







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