Overexpression of Amyloid-β Protein Precursor Induces Mitochondrial Oxidative Stress and Activates the Intrinsic Apoptotic Cascade

Abstract

Alzheimer's disease (AD) is a debilitating cognitive disorder which is characterized pathologically by amyloid-β plaques and neurofibrillary tangles. Aberrant processing of amyloid beta protein precursor (AβPP) into amyloid-β fragments underlies the formation of senile plaques. Moreover, amyloid-β fragments, particularly Aβ42, exert direct toxic effects within neurons including the induction of mitochondrial oxidative stress (MOS). Interestingly, individuals with Down Syndrome (DS) frequently develop early onset AD as a major co-morbid phenotype. One hypothesis for AD associated with DS involves the overexpression of wild type (WT) AβPP protein, due to its location on chromosome 21. However, the mechanism by which the overexpression of WT AβPP might trigger MOS and induce cell death is presently unclear. Here we show that transient overexpression of DsRed2-tagged AβPP (WT) in CHO cells induces the activation of caspase-3 and nuclear fragmentation indicative of apoptosis. AβPP localizes to the mitochondrial fraction of transfected CHO cells and its overexpression causes glutathione (GSH)-sensitive opening of the mitochondrial permeability transition pore (mPTP) and cytochrome c release. MOS and intrinsic apoptosis induced by AβPP were significantly inhibited by the co-expression of Bcl-2 or treatment with either GSH or Boc, a pan-caspase inhibitor. Furthermore, the mPTP inhibitor, cyclosporin A, also significantly protected CHO cells from apoptosis induced by AβPP overexpression. Finally, co-treatment with a β-secretase inhibitor did not significantly protect CHO cells from AβPP overexpression and Aβ42 levels were undetectable in transfected CHO cells. Therefore, the mechanism of AβPP induced MOS and apoptosis is independent of the production of Aβ42. However, a γ-secretase inhibitor showed significant protection of the CHO cells against AβPP overexpression. Thus, suggesting a possible role of the AβPP intracellular domain in this apoptotic pathway. These data indicate that overexpression of WT AβPP is sufficient to induce MOS and intrinsic apoptosis, suggesting a novel pro-oxidant role for AβPP at the mitochondria in AD and DS disease pathologies.

Significant Modifications of the Salivary Proteome Potentially Associated with Complications of Down Syndrome Revealed by Top-down Proteomics

“…Indeed, it has been demonstrated that A␤ protein induces mitochondrial oxidative stress, suggesting a novel pro-oxidant role for A␤ protein, which may be relevant in AD and DS disease pathologies (34).…”

Induction of Bax-dependent neuronal apoptosis by Amyloid-β Protein Precursor (AβPP) requires its localization to functional mitochondria

“…Here, we used a cobalt/calcein assay, in which if the mPTP is activated, CoCl2 is released from the matrix of the mitochondria into the cytosol allowing it to react with and quench the fluorescence (green) signal of calcein which is localized in the cytoplasm. In our previous study, we showed that AβPP overexpression activates the mPTP in CHO cells [16]. However, in HT22 cells no significant activation of the mPTP was observed with AβPP overexpression ( Figure 3A, right panel).…”

“…While it has been well documented that Aβ fragments induce cell death both in vitro and in vivo, there is emerging evidence that AβPP and its intracellular domain (AICD) may also contribute to AD pathogenesis [16][17][18][19]27,28]. In this study, the overexpression of AβPP in a mouse hippocampal cell line induced a caspase-dependent and Bax-mediated apoptotic pathway which appeared to be largely independent of AβPP processing.…”

“…AβPP inserts into the mitochondrial translocases, TOM 40 and TIM 23, and as a result has the potential to induce mitochondrial dysfunction [15]. In this context, we have previously shown that overexpression of full length WT AβPP induces intrinsic apoptosis in Chinese hamster ovary (CHO) cells, independently of Aβ production [16]. Our previous study is in agreement with others showing that full length WT AβPP can induce apoptosis in the human SH-SY5Y neuroblastoma and differentiated NBP2 neuroblastoma cell lines [17,18].…”

Rheumatoid Arthritis and Alzheimer Disease: Possible Cellular and Molecular Links

“…Among them, CyclosporinA (CsA), preventing mitochondrial-membrane damage, seems to attenuate both the β-amyloid and Tau proteins induced neuronal apoptosis [31] and the oxidative stress [32]. CsA also seems to prevent APP overexpression and amyloidogenic peptides overproduction [33] but conversely it has been described to enhance Tau phosphorylation.…”