P4-166: Overexpression of amyloid precursor protein causes abnormal mitochondrial dynamics via differential modulation of mitochondrial fission/fusion proteins

Abstract

Mitochondrial dysfunction is a prominent feature of Alzheimer disease and while both the amyloid precursor protein (APP) and amyloid-beta are present in mitochondria, their involvement in mitochondrial dysfunction is unclear. To investigate this further, in this study, we evaluated the effect of mutant APP and amyloid-beta on mitochondrial morphology and distribution in M17 neuroblastoma cells using confocal microscopy, electron microscopy, and immunoblot analysis. Using confocal microscopy analysis, we found that around 40% M17 cells overexpressing WT APP (APPwt M17 cells) and more than 80% M17 cells overexpressing APPswe mutant (APPswe M17 cells) displayed fragmented punctiform mitochondria and also demonstrated an abnormal uneven mitochondrial distribution with mitochondria accumulating around the perinuclear area with more remote cytoplasmic areas being devoid of mitochondria. Notably, these abnormalities were abolished by treatment of the cells with BACE inhibitor IV which is able to efficiently block amyloid-beta production. These morphological observations were confirmed by electron microscopic analysis. Immunoblot analysis revealed that levels of DLP1 and OPA1 were significantly decreased while levels of Fis1 were significantly increased in APPwt and APPswe M17 cells. Testifying to the mechanistic import of these observations, overexpression of WT DLP1 in these cells rescued the abnormal mitochondrial distribution and differentiation capability upon retinoic acid treatment but exacerbated mitochondrial fragmentation, MMP reduction and ROS production. Conversely, the overexpression of WT OPA1 rescued abnormal mitochondrial fragmentation, MMP reduction and ROS production but failed to restore normal mitochondrial distribution. Based on these data, we conclude that APP or amyloid-beta cause impairments in the balance of mitochondrial fission and fusion through differential modulation of DLP1, OPA1 and Fis1 that results in mitochondrial fragmentation and distribution abnormalities which likely contribute to mitochondrial dysfunction in Alzheimer disease. Work in the authors' laboratories is supported by the National Institutes of Health (AG024028) and Alzheimer's Association (IIRG-07–60196).