The differential effects of ApoE2 isoforms on APP processing

Journal of Bioenergetics and Biomembranes, 2009

Several lines of evidence suggest mitochondrial dysfunction as a possible underlying mechanism of Alzheimer's disease (AD). Accumulation of the amyloid-β peptide (Aβ), a neurotoxic peptide implicated in the pathogenesis of AD, has been detected in brain mitochondria of AD patients and AD transgenic mouse models. In vitro evidence suggests that the Aβ causes mitochondrial dysfunction e.g. oxidative stress, mitochondrial fragmentation and decreased activity of cytochrome c oxidase and TCA cycle enzymes. Here we review the link between mitochondrial dysfunctions and AD. In particular we focus on the mechanism for Aβ uptake by mitochondria and on the recently identified Aβ degrading protease in human brain mitochondria.

Journal of Biological Chemistry, 2006

Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid ␤-protein (A␤). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zincbinding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against A␤. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu 78 in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against A␤-(1-42), A␤-(1-40), and A␤ Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 Å resolution of AtPreP allowed us to identify Cys 90 and Cys 527 that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial A␤ by hPreP may potentially be of importance in the pathology of Alzheimer disease.

Journal of Biological Chemistry, 2006

Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid ␤-protein (A␤). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zincbinding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against A␤. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu 78 in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against A␤-(1-42), A␤-(1-40), and A␤ Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 Å resolution of AtPreP allowed us to identify Cys 90 and Cys 527 that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial A␤ by hPreP may potentially be of importance in the pathology of Alzheimer disease.

Biochemical and Biophysical Research Communications, 2013

Mitochondrial dysfunction is a prominent feature of Alzheimer's disease (AD) and this can be contributed by aberrant metabolic enzyme function. But, the mechanism causing this enzymatic impairment is unclear. Amyloid precursor protein (APP) is known to be alternatively spliced to produce three major isoforms in the brain (APP695, APP751, APP770). Both APP770 and APP751 contain the Kunitz Protease Inhibitory (KPI) domain, but the former also contain an extra OX-2 domain. APP695 on the other hand, lacks both domains. In AD, up-regulation of the KPI-containing APP isoforms has been reported. But the functional contribution of this elevation is unclear. In the present study, we have expressed and compared the effect of the non-KPI containing APP695 and the KPI-containing APP751 on mitochondrial function. We found that the KPI-containing APP751 significantly decreased the expression of three major mitochondrial metabolic enzymes; citrate synthase, succinate dehydrogenase and cytochrome c oxidase (COX IV). This reduction lowers the NAD + /NADH ratio, COX IV activity and mitochondrial membrane potential. Overall, this study demonstrated that up-regulation of the KPI-containing APP isoforms is likely to contribute to the impairment of metabolic enzymes and mitochondrial function in AD.

Journal of Biological Chemistry, 2013

Background: Mitochondrial accumulation of amyloid ␤ (A␤) promotes organelle dysfunction and Alzheimer disease (AD) neuropathology. Results: IDE-Met 1 localizes in mitochondria, is present in brain, and is regulated by the master regulator of mitochondrial biogenesis. Conclusion: Mitochondrial biogenesis controls mitochondrial A␤ levels. Significance: This study identifies a molecular mechanism that links mitochondrial biogenesis with A␤ degradation, suggesting that deregulation of this pathway could induce A␤-mediated mitochondrial dysfunction. . However, the mechanisms of its expression are unknown, and its presence in brain is uncertain. We detected IDE-Met 1 in brain and showed that its expression is regulated by the mitochondrial biogenesis pathway (PGC-1␣/NRF-1). A strong positive correlation between PGC-1␣ or NRF-1 and long IDE isoform transcripts was found in non-demented brains. This correlation was weaker in Alzheimer disease. In vitro inhibition of IDE increased mitA␤ and impaired mitochondrial respiration. These changes were restored by inhibition of ␥-secretase or promotion of mitochondrial biogenesis. Our results suggest that IDE-Met 1 links the mitochondrial biogenesis pathway with mitA␤ levels and organelle functionality.

Journal of Biological …, 2007

Insulin-degrading enzyme (IDE) is a zinc metalloprotease that degrades the amyloid β-peptide, the key component of Alzheimer disease (AD)-associated senile plaques. We have previously reported evidence for genetic linkage and association of AD on chromosome ...

Alzheimer's & Dementia, 2014

Familial British dementia (FBD) is an early-onset non-amyloid-β (Aβ) cerebral amyloidosis that presents with severe cognitive decline and strikingly similar neuropathological features to those present in Alzheimer's disease (AD). FBD is associated with a T to A single nucleotide transition in the stop codon of a gene encoding BRI2, leading to the production of an elongated precursor protein. Furin-like proteolytic processing at its C-terminus releases a longer-than-normal 34 amino acid peptide, ABri, exhibiting amyloidogenic properties not seen in its 23 amino acid physiologic counterpart Bri1-23. Deposited ABri exhibits abundant post-translational pyroglutamate (pE) formation at the N-terminus, a feature seen in truncated forms of Aβ found in AD deposits, and co-exists with neurofibrillary tangles almost identical to those found in AD. We tested the impact of the FBD mutation alone and in conjunction with the pE post-translational modification on the structural properties and associated neurotoxicity of the ABri peptide. The presence of pE conferred to the ABri molecule enhanced hydrophobicity and accelerated aggregation/fibrillization properties. ABri pE was capable of triggering oxidative stress, loss of mitochondrial membrane potential and activation of caspase-mediated apoptotic mechanisms in neuronal cells, whereas homologous peptides lacking the elongated C-terminus and/or the N-terminal pE were unable to induce similar detrimental cellular pathways. The data indicate that the presence of Nterminal pE is not in itself sufficient to induce pathogenic changes in the physiologic Bri1-23 peptides but that its combination with the ABri mutation is critical for the molecular pathogenesis of FBD.

Journal of Biological Chemistry, 2003

Inherited amino acid substitutions at position 21, 22, or 23 of amyloid ␤ (A␤) lead to presenile dementia or stroke. Insulin-degrading enzyme (IDE) can hydrolyze A␤ wild type, yet whether IDE is capable of degrading A␤ bearing pathogenic substitutions is not known. We studied the degradation of all of the published A␤ genetic variants by recombinant rat IDE (rIDE). Monomeric A␤ wild type, Flemish (A21G), Italian (E22K), and Iowa (D23N) variants were readily degraded by rIDE with a similar efficiency. However, proteolysis of A␤ Dutch (E22Q) and Arctic (E22G) was significantly lower as compared with A␤ wild type and the rest of the mutant peptides. In the case of A␤ Dutch, inefficient proteolysis was related to a high content of ␤ structure as assessed by circular dichroism. All of the A␤ variants were cleaved at Glu 3 -Phe 4 and Phe 4 -Arg 5 in addition to the previously described major sites within positions 13-15 and 18 -21. SDS-stable A␤ dimers were highly resistant to proteolysis by rIDE regardless of the variant, suggesting that IDE recognizes a conformation that is available for interaction only in monomeric A␤. These results raise the possibility that upregulation of IDE may promote the clearance of soluble A␤ in hereditary forms of A␤ diseases.

Free Radical Biology and Medicine, 2012

The mitochondrial peptidasome called presequence protease (PreP) is responsible for the degradation of presequences and other unstructured peptides including the amyloid-β peptide, whose accumulation may have deleterious effects on mitochondrial function. Recent studies showed that PreP activity is reduced in Alzheimer disease (AD) patients and AD mouse models compared to controls, which correlated with an enhanced reactive oxygen species production in mitochondria. In this study, we have investigated the effects of a biologically relevant oxidant, hydrogen peroxide (H 2 O 2 ), on the activity of recombinant human PreP (hPreP). H 2 O 2 inhibited hPreP activity in a concentration-dependent manner, resulting in oxidation of amino acid residues (detected by carbonylation) and lowered protein stability. Substitution of the evolutionarily conserved methionine 206 for leucine resulted in increased sensitivity of hPreP to oxidation, indicating a possible protective role of M206 as internal antioxidant. The activity of hPreP oxidized at low concentrations of H 2 O 2 could be restored by methionine sulfoxide reductase A (MsrA), an enzyme that localizes to the mitochondrial matrix, suggesting that hPreP constitutes a substrate for MsrA. In summary, our in vitro results suggest a possible redox control of hPreP in the mitochondrial matrix and support the protective role of the conserved methionine 206 residue as an internal antioxidant.

Molecular Neurobiology, 2016

Alzheimer's disease (AD) is a multifactorial disease of wide clinical heterogenity. Overproduction of amyloid precursor protein (APP) and accumulation of β-amyloid (Aβ) and tau proteins are important hallmarks of AD. The identification of early pathomechanisms of AD is critically important for discovery of early diagnosis markers. Decreased brain metabolism is one of the earliest clinical symptoms of AD that indicate mitochondrial dysfunction in the brain. We performed the first comprehensive study integrating synaptic and non-synaptic mitochondrial proteome analysis (two-dimensional differential gel electrophoresis (2D-DIGE) and mass spectrometry) in correlation with Aβ progression in APP/PS1 mice (3, 6, and 9 months of age). We identified changes of 60 mitochondrial proteins that reflect the progressive effect of APP overproduction and Aβ accumulation on mitochondrial processes. Most of the significantly affected proteins play role in the mitochondrial electron transport chain, citric acid cycle, oxidative stress, or apoptosis. Altered expression levels of Htra2 and Ethe1, which showed parallel changes in different age groups, were confirmed also by Western blot. The common regulator bioinformatical analysis suggests the regulatory role of tumor necrosis factor (TNF) in Aβ-mediated mitochondrial protein changes. Our results are in accordance with the previous postmortem human brain proteomic studies in AD in the case of many proteins. Our results could open a new path of research aiming early mitochondrial molecular mechanisms of Aβ accumulation as a prodromal stage of human AD.