CALCIUM HOMEOSTASIS AND REACTIVE OXYGEN SPECIES PRODUCTION IN CELLS TRANSFORMED BY MITOCHONDRIA FROM INDIVIDUALS WITH SPORADIC ALZHEIMERS-DISEASE

Alzheimer's disease (AD) is associated with defects in mitochondrial f unction. Mitochondrial-based disturbances in calcium homeostasis, reac tive oxygen species (ROS) generation, and amyloid metabolism have been implicated in the pathophysiology of sporadic AD. The cellular conseq uences of mitochondrial dysfunction, however, are not known. To examin e these consequences, mitochondrially transformed cells (cybrids) were created from AD patients or disease-free controls. Mitochondria from platelets were fused to rho(0) cells created by depleting the human ne uroblastoma line SH-SY5Y of its mitochondrial DNA (mtDNA). AD cybrids demonstrated a 52% decrease in electron transport chain (ETC) complex IV activity but no difference in complex I activity compared with cont rol cybrids or SH-SY5Y cells. This mitochondrial dysfunction suggests a transferable mtDNA defect associated with AD. ROS generation was ele vated in the AD cybrids. AD cybrids also displayed an increased basal cytosolic calcium concentration mediated release, Furthermore, they re covered more slowly from an elevation in cytosolic calcium induced by the InsP(3) agonist carbachol. Mitochondrial calcium buffering plays a major role after this type of perturbation, beta-amyloid (25-35) pept ide delayed the initiation of calcium recovery to a carbachol challeng e and slowed the recovery rate. Nerve growth factor reduced the carbac hol-induced maximum and moderated the recovery kinetics. Succinate inc reased ETC activity and partially restored the AD cybrid recovery rate . These subtle alterations in calcium homeostasis and ROS generation m ight lead to increased susceptibility to cell death under circumstance s not ordinarily toxic.