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The amyloid [beta]-peptide (A[beta]) has been suggested to exert its toxicity intracellularly. Mitochondrial functions can be negatively affected by A[beta] and accumulation of A[beta] has been detected in mitochondria. Because A[beta] is not likely to be produced locally in mitochondria, we decided to investigate the mechanisms for mitochondrial A[beta] uptake. Our results from rat mitochondria show that A[beta] is transported into mitochondria via the translocase of the outer membrane (TOM) machinery. The import was insensitive to valinomycin, indicating that it is independent of the mitochondrial membrane potential. Subfractionation studies following the import experiments revealed A[beta] association with the inner membrane fraction, and immunoelectron microscopy after import showed localization of A[beta] to mitochondrial cristae. A similar distribution pattern of A[beta] in mitochondria was shown by immunoelectron microscopy in human cortical brain biopsies obtained from living subjects with normal pressure hydrocephalus. Thus, we present a unique import mechanism for A[beta] in mitochondria and demonstrate both in vitro and in vivo that A[beta] is located to the mitochondrial cristae. Importantly, we also show that extracellulary applied A[beta] can be internalized by human neuroblastoma cells and can colocalize with mitochondrial markers. Together, these results provide further insight into the mitochondrial uptake of A[beta], a peptide considered to be of major significance in Alzheimer's disease. Alzheimer disease | protein import | human brain biopsies

N-Methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity may depend, in part, on the generation of nitric oxide ([NO.sup..]) and superoxide anion ([Mathematical Expression Omitted]), which react to form peroxynitrite ([OONO.sup.-]). This form of neurotoxicity is thought to contribute to a final common pathway of injury in a wide variety of acute and chronic neurologic disorders, including focal ischemia, trauma, epilepsy, Huntington disease, Alzheimer disease, amyotrophic lateral sclerosis, AIDS dementia, and other neurodegenerative diseases. Here, we report that exposure of cortical neurons to relatively short durations or low concentrations of NMDA, S-nitrosocystelne, or 3-morpholinosydnonimine, which generate low levels of peroxynitrite, induces a delayed form of neurotoxicity ptedominated by apoptotic features. Pretreatment with superoxide dismutase-and catalase to scavenge [Mathematical Expression Omitted] partially prevents the apoptotic process triggered by S-nitrosocysteine or 3--morpholinosydnonimine. In contrast, intense exposure to high concentrations of NMDA or peroxyrutrite induces necrotic cell damage characterized by acute swelling and lysis, which cannot be ameliorated by superoxide dismutase and catalase. Thus, depending on the intensity of the initial insult, NMDA or nitric oxide/superoxide can result in either apoptotic or necrotic neuronal cell damage.

It is well-established that subcompartments of endoplasmic reticulum (ER) are in physical contact with the mitochondria. These lipid raft-like regions of ER are referred to as mitochondria-associated ER membranes (MAMs), and they play an important role in, for example, lipid synthesis, calcium homeostasis, and apoptotic signaling. Perturbation of MAM function has previously been suggested in Alzheimer's disease (AD) as shown in fibroblasts from AD patients and a neuroblastoma cell line containing familial presenilin-2 AD mutation. The effect of AD pathogenesis on the ER-mitochondria interplay in the brain has so far remained unknown. Here, we studied ER-mitochondria contacts in human AD brain and related AD mouse and neuronal cell models. We found uniform distribution of MAM in neurons. Phosphofurin acidic cluster sorting protein-2 and σ1 receptor, two MAM-associated proteins, were shown to be essential for neuronal survival, because siRNA knockdown resulted in degeneration. Up-regulated MAM-associated proteins were found in the AD brain and amyloid precursor protein (APP)Swe/Lon mouse model, in which up-regulation was observed before the appearance of plaques. By studying an ER-mitochondria bridging complex, inositol-1,4,5-triphosphate receptor-voltage-dependent anion channel, we revealed that nanomolar concentrations of amyloid β-peptide increased inositol-1,4,5-triphosphate receptor and voltage-dependent anion channel protein expression and elevated the number of ER-mitochondria contact points and mitochondrial calcium concentrations. Our data suggest an important role of ER-mitochondria contacts and cross-talk in AD pathology. [ABSTRACT FROM AUTHOR]

The amyloid β-peptide (Aβ) has been suggested to exert its toxicity intracellularly. Mitochondrial functions can be negatively affected by Aβ and accumulation of Aβ has been detected in mitochondria. Because Aβ is not likely to be produced locally in mitochondria, we decided to investigate the mechanisms for mitochondrial Aβ uptake. Our results from rat mitochondria show that Aβ is transported into mitochondria via the translocase of the outer membrane (TOM) machinery. The import was insensitive to valinomycin, indicating that it is independent of the mitochondrial membrane potential. Subfractionation studies following the import experiments revealed Aβ association with the inner membrane fraction, and immunoelectron microscopy after import showed localization of Aβ to mitochondrial cristae. A similar distribution pattern of Aβ in mitochondria was shown by immunoelectron microscopy in human cortical brain biopsies obtained from living subjects with normal pressure hydrocephalus. Thus, we present a unique import mechanism for Aβ in mitochondria and demonstrate both in vitro and in vivo that Aβ is located to the mitochondrial cristae. Importantly, we also show that extracellulary applied Aβ can be internalized by human neuroblastoma cells and can colocalize with mitochondrial markers. Together, these results provide further insight into the mitochondrial uptake of Aβ, a peptide considered to be of major significance in Alzheimer's disease. [ABSTRACT FROM AUTHOR]

The amyloid beta-peptide (Abeta) has been suggested to exert its toxicity intracellularly. Mitochondrial functions can be negatively affected by Abeta and accumulation of Abeta has been detected in mitochondria. Because Abeta is not likely to be produced locally in mitochondria, we decided to investigate the mechanisms for mitochondrial Abeta uptake. Our results from rat mitochondria show that Abeta is transported into mitochondria via the translocase of the outer membrane (TOM) machinery. The import was insensitive to valinomycin, indicating that it is independent of the mitochondrial membrane potential. Subfractionation studies following the import experiments revealed Abeta association with the inner membrane fraction, and immunoelectron microscopy after import showed localization of Abeta to mitochondrial cristae. A similar distribution pattern of Abeta in mitochondria was shown by immunoelectron microscopy in human cortical brain biopsies obtained from living subjects with normal pressure hydrocephalus. Thus, we present a unique import mechanism for Abeta in mitochondria and demonstrate both in vitro and in vivo that Abeta is located to the mitochondrial cristae. Importantly, we also show that extracellulary applied Abeta can be internalized by human neuroblastoma cells and can colocalize with mitochondrial markers. Together, these results provide further insight into the mitochondrial uptake of Abeta, a peptide considered to be of major significance in Alzheimer's disease.