Amyloid β-induced ER stress is enhanced under mitochondrial dysfunction conditions.
ABSTRACT Previously we reported that endoplasmic reticulum (ER)-mitochondria crosstalk is involved in amyloid-β (Aβ)-induced apoptosis. Now we show that mitochondrial dysfunction affects the ER stress response triggered by Aβ using cybrids that recreate the defect in mitochondrial cytochrome c oxidase (COX) activity detected in platelets from Alzheimer's disease (AD) patients. AD and control cybrids were treated with Aβ or classical ER stressors and the ER stress-mediated apoptotic cell death pathway was accessed. Upon treatment, we found increased glucose-regulated protein 78 (GRP78) levels and caspase-4 activation (ER stress markers) which were more pronounced in AD cybrids. Treated AD cybrids also exhibited decreased cell survival as well as increased caspase-3-like activity, poli-ADP-ribose-polymerase (PARP) levels and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells. Finally, we showed that Aβ-induced caspase-3 activation in both cybrid cell lines was prevented by dantrolene, thus implicating ER Ca(2+) release in ER stress-mediated apoptosis. Our results demonstrate that mitochondrial dysfunction occurring in AD patients due to COX inhibition potentiates cell susceptibility to Aβ-induced ER stress. This study further supports the close communication between ER and mitochondria during apoptosis in AD.
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ABSTRACT: The E3 ubiquitin ligase HRD1 is found in the endoplasmic reticulum membrane of brain neurons and is involved in endoplasmic reticulum-associated degradation. We previously demonstrated that suppression of HRD1 expression in neurons causes accumulation of amyloid precursor protein, resulting in amyloid β production associated with endoplasmic reticulum stress and apoptosis. Furthermore, HRD1 levels are significantly decreased in the cerebral cortex of Alzheimer's disease patients because of its insolubility. The mechanisms that affect HRD1 solubility are not well understood. We here show that HRD1 protein was insolubilized by oxidative stress but not by other Alzheimer's disease-related molecules and stressors, such as amyloid β, tau, and endoplasmic reticulum stress. Furthermore, we raise the possibility that modifications of HRD1 by 4-hydroxy-2-nonenal, an oxidative stress marker, decrease HRD1 protein solubility and the oxidative stress led to the accumulation of HRD1 into the aggresome. Thus, oxidative stress-induced HRD1 insolubilization might be involved in a vicious cycle of increased amyloid β production and amyloid β-induced oxidative stress in Alzheimer's disease pathogenesis.PLoS ONE 01/2014; 9(5):e94576. · 3.73 Impact Factor
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ABSTRACT: Mitochondrial DNA (mtDNA) damage and the generation of reactive oxygen species have been associated with and implicated in the development and progression of Alzheimer's disease. To study how mtDNA damage affects reactive oxygen species and amyloid beta (Aβ) pathology in vivo, we generated an Alzheimer's disease mouse model expressing an inducible mitochondrial-targeted endonuclease (Mito-PstI) in the central nervous system. Mito-PstI cleaves mtDNA causing mostly an mtDNA depletion, which leads to a partial oxidative phosphorylation defect when expressed during a short period in adulthood. We found that a mild mitochondrial dysfunction in adult neurons did not exacerbate Aβ accumulation and decreased plaque pathology. Mito-PstI expression altered the cleavage pathway of amyloid precursor protein without increasing oxidative stress in the brain. These data suggest that mtDNA damage is not a primary cause of Aβ accumulation.Neurobiology of aging 05/2013; · 5.94 Impact Factor
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ABSTRACT: Although the accumulation of the neurotoxic peptide β-amyloid (Aβ) in the central nervous system is a hallmark of Alzheimer's disease, whether Aβ acts in astrocytes is unclear, and downstream functional consequences have yet to be defined. Here, we show that cytosolic Ca2+ dysregulation, induced by a neurotoxic fragment (Aβ25–35), caused apoptosis in a concentration-dependent manner, leading to cytoplasmic Ca2+ mobilization from extra- and intracellular sources, mainly from the endoplasmic reticulum (ER) via IP3 receptor activation. This mechanism was related to Aβ-mediated apoptosis by the intrinsic pathway because the expression of pro-apoptotic Bax was accompanied by its translocation in cells transfected with GFP-Bax. Aβ-mediated apoptosis was reduced by BAPTA-AM, a fast Ca2+ chelator, indicating that an increase in intracellular Ca2+ was involved in cell death. Interestingly, the Bax translocation was dependent on Ca2+ mobilization from IP3 receptors because pre-incubation with xestospongin C, a selective IP3 receptor inhibitor, abolished this response. Taken together, these results provide evidence that Aβ dysregulation of Ca2+ homeostasis induces ER depletion of Ca2+ stores and leads to apoptosis; this mechanism plays a significant role in Aβ apoptotic cell death and might be a new target for neurodegeneration treatments.European Journal of Neuroscience 05/2014; · 3.75 Impact Factor