Journal articles on the topic 'APP and amyloid fragments'
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1
Yokota, Masayuki, Takaomi C. Saido, Eiichi Tani, Ikuya Yamaura, and Nobutaka Minami. "Cytotoxic Fragment of Amyloid Precursor Protein Accumulates in Hippocampus after Global Forebrain Ischemia." Journal of Cerebral Blood Flow & Metabolism 16, no. 6 (November 1996): 1219–23. http://dx.doi.org/10.1097/00004647-199611000-00016.
Abstract:
We developed an antibody specific to β-amyloid precursor protein (βAPP) fragments possessing the exact amino terminus of the β-amyloid peptide and examined its induction in postischemic hippocampus. In control hippocampus, this APP fragment was lightly observed in pyramidal neurons of CA sectors and dentate granule cells. Transient forebrain ischemia enhanced accumulation of the APP fragment in CA1 pyramidal neurons. Seven days after the ischemia, while the APP fragment was still observed in dentate granule cells and CA3 neurons, it disappeared in dead CA1 neurons. While astrocytes did not show in any immunoreactivity throughout the experiment, those in the CA1 sector showed moderate immunoreactivity 7 days after the ischemia. The APP fragment has a cytotoxic effect on cultured neurons. These results suggest that the accumulation of the cytotoxic APP fragment in CA1 neurons may play a role in the development of delayed neuronal death after the ischemic insult.
2
Chyung, Abraham S. C., Barry D. Greenberg, David G. Cook, Robert W. Doms, and Virginia M. Y. Lee. "Novel β-Secretase Cleavage of β-Amyloid Precursor Protein in the Endoplasmic Reticulum/Intermediate Compartment of NT2N Cells." Journal of Cell Biology 138, no. 3 (August 11, 1997): 671–80. http://dx.doi.org/10.1083/jcb.138.3.671.
Abstract:
Previous studies have demonstrated that NT2N neurons derived from a human embryonal carcinoma cell line (NT2) constitutively process the endogenous wild-type β-amyloid precursor protein (APP) to amyloid β peptide in an intracellular compartment. These studies indicate that other proteolytic fragments generated by intracellular processing must also be present in these cells. Here we show that the NH2-terminal fragment of APP generated by β-secretase cleavage (APPβ) is indeed produced from the endogenous full length APP (APPFL). Pulse–chase studies demonstrated a precursor–product relationship between APPFL and APPβ as well as intracellular and secreted APPβ fragments. In addition, trypsin digestion of intact NT2N cells at 4°C did not abolish APPβ recovered from the cell lysates. Furthermore, the production of intracellular APPβ from wild-type APP appears to be a unique characteristic of postmitotic neurons, since intracellular APPβ was not detected in several non-neuronal cell lines. Significantly, production of APPβ occurred even when APP was retained in the ER/ intermediate compartment by inhibition with brefeldin A, incubation at 15°C, or by expression of exogenous APP bearing the dilysine ER retrieval motif.
3
Niederst, Emily D., Sol M. Reyna, and Lawrence S. B. Goldstein. "Axonal amyloid precursor protein and its fragments undergo somatodendritic endocytosis and processing." Molecular Biology of the Cell 26, no. 2 (January 15, 2015): 205–17. http://dx.doi.org/10.1091/mbc.e14-06-1049.
Abstract:
Deposition of potentially neurotoxic Aβ fragments derived from amyloid precursor protein (APP) at synapses may be a key contributor to Alzheimer's disease. However, the location(s) of proteolytic processing and subsequent secretion of APP fragments from highly compartmentalized, euploid neurons that express APP and processing enzymes at normal levels is not well understood. To probe the behavior of endogenous APP, particularly in human neurons, we developed a system using neurons differentiated from human embryonic stem cells, cultured in microfluidic devices, to enable direct biochemical measurements from axons. Using human or mouse neurons in these devices, we measured levels of Aβ, sAPPα, and sAPPβ secreted solely from axons. We found that a majority of the fragments secreted from axons were processed in the soma, and many were dependent on somatic endocytosis for axonal secretion. We also observed that APP and the β-site APP cleaving enzyme were, for the most part, not dependent on endocytosis for axonal entry. These data establish that axonal entry and secretion of APP and its proteolytic processing products traverse different pathways in the somatodendritic compartment before axonal entry.
4
Lee, Ming-Sum, Shih-Chu Kao, Cynthia A. Lemere, Weiming Xia, Huang-Chun Tseng, Ying Zhou, Rachael Neve, Michael K. Ahlijanian, and Li-Huei Tsai. "APP processing is regulated by cytoplasmic phosphorylation." Journal of Cell Biology 163, no. 1 (October 13, 2003): 83–95. http://dx.doi.org/10.1083/jcb.200301115.
Abstract:
Amyloid-β peptide (Aβ) aggregate in senile plaque is a key characteristic of Alzheimer's disease (AD). Here, we show that phosphorylation of amyloid precursor protein (APP) on threonine 668 (P-APP) may play a role in APP metabolism. In AD brains, P-APP accumulates in large vesicular structures in afflicted hippocampal pyramidal neurons that costain with antibodies against endosome markers and the β-secretase, BACE1. Western blot analysis reveals increased levels of T668-phosphorylated APP COOH-terminal fragments in hippocampal lysates from many AD but not control subjects. Importantly, P-APP cofractionates with endosome markers and BACE1 in an iodixanol gradient and displays extensive colocalization with BACE1 in rat primary cortical neurons. Furthermore, APP COOH-terminal fragments generated by BACE1 are preferentially phosphorylated on T668 verses those produced by α-secretase. The production of Aβ is significantly reduced when phosphorylation of T668 is either abolished by mutation or inhibited by T668 kinase inhibitors. Together, these results suggest that T668 phosphorylation may facilitate the BACE1 cleavage of APP to increase Aβ generation.
5
Feng, Fei, Yuanyuan Li, Nanqu Huang, and Yong Luo. "Icaritin, an inhibitor of beta-site amyloid cleaving enzyme-1, inhibits secretion of amyloid precursor protein in APP-PS1-HEK293 cells by impeding the amyloidogenic pathway." PeerJ 7 (December 10, 2019): e8219. http://dx.doi.org/10.7717/peerj.8219.
Abstract:
Background Icaritin (ICT) is a prenylflavonoid derivative from Epimedium brevicornum Maxim. ICT has been shown to have neuroprotective effects. We investigate how ICT affects secretion of amyloid precursor protein (APP). Methods We exposed APP-PS1-HEK293 cells to ICT to investigate its effect on beta-site amyloid cleaving enzyme (BACE)1. Cell viability was evaluated by MTT and lactate dehydrogenase (LDH) assays. The half-maximal inhibitory concentration (IC50) of ICT for BACE1 was measured using fluorescence resonance energy transfer. Effects of ICT on the mRNA expression of APP were assessed by quantitative polymerase chain reaction, and protein expression was measured by western blotting and immunofluorescence. Results Icaritin inhibited BACE1 activity and IC50 was 5.70 ± 1.09 μM. Compared with the control group, at ICT concentrations of 5 μM and 10 μM, the viability increased and LDH leakage decreased in APP-PS1-293 cells. Also, mRNA expression of A disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) increased, while that of BACE1 and presenilin-1 (PS1) decreased, upon ICT treatment. Western blotting and immunofluorescence confirmed that protein expression of ADAM10, BACE1 and PS1 showed the same trend. Expression of the APP fragments sAPPβ and C-terminal fragment β decreased, while that of sAPPα increased, upon ICT treatment. Expression of amyloid β peptides in APP-PS1-HEK293 cells was lower in ICT-treated groups compared with that in the control group. Conclusions Icaritin, as a BACE1 inhibitor, inhibits APP secretion in APP-PS1-HEK293 cells by impeding the amyloidogenic pathway.
6
Ghiso, J., A. Rostagno, J. E. Gardella, L. Liem, P. D. Gorevic, and B. Frangione. "A 109-amino-acid C-terminal fragment of Alzheimer's-disease amyloid precursor protein contains a sequence, -RHDS-, that promotes cell adhesion." Biochemical Journal 288, no. 3 (December 15, 1992): 1053–59. http://dx.doi.org/10.1042/bj2881053.
Abstract:
Amyloid beta (A beta), the major constituent of the fibrils composing senile plaques and vascular amyloid deposits in Alzheimer's disease (AD) and related disorders, is a 39-42-residue self-aggregating degradation peptide of a larger multidomain membrane glycoprotein designated amyloid precursor protein (APP). An array of biological functions has been assigned to different APP domains, including growth regulation, neurotoxicity, inhibitory activity of serine proteinases and promotion of cell-cell and cell-matrix interactions. A beta is generated through an as-yet-unknown catabolic pathway that by-passes or inhibits the cleavage of APP within the A beta sequence. We have identified a 16 kDa intermediate APP C-terminal fragment containing A beta in leptomeningeal vessels of aged normal individuals and AD patients by means of its immunoreactivity with a panel of four different anti-(APP C-terminal) antibodies, indicating a different pathway of APP processing. Previous studies have indicated that the APP C-terminal domain is the most likely to be involved in cell-matrix interactions. A 109-amino-acid construct C109 with a sequence analogous to the C-terminal of APP (positions 587-695 of APP695), similar in length and immunoreactivity to the 16 kDa fragment, was found to promote cell adhesion. By use of synthetic peptides, this activity was initially located to the extracellular 28 residues of A beta. Inhibition studies demonstrated that the sequence RHDS (amino acids 5-8 of A beta, corresponding to residues 601-604 of APP695 was responsible for the adhesion-promoting activity. The interaction is dependent on bivalent cations and can be blocked either by the tetrapeptides RHDS and RGDS or by an anti-(beta 1 integrin) antibody. Thus, through integrin-like surface receptors, APP or its derivative proteolytic fragments containing the sequence RHDS may modulate cell-cell or cell-matrix interactions.
7
Cook, J. J., K. R. Wildsmith, D. B. Gilberto, M. A. Holahan, G. G. Kinney, P. D. Mathers, M. S. Michener, et al. "Acute -Secretase Inhibition of Nonhuman Primate CNS Shifts Amyloid Precursor Protein (APP) Metabolism from Amyloid- Production to Alternative APP Fragments without Amyloid- Rebound." Journal of Neuroscience 30, no. 19 (May 12, 2010): 6743–50. http://dx.doi.org/10.1523/jneurosci.1381-10.2010.
8
Yu, Yang, Yang Gao, Bengt Winblad, Lars O. Tjernberg, and Sophia Schedin-Weiss. "A Super-Resolved View of the Alzheimer’s Disease-Related Amyloidogenic Pathway in Hippocampal Neurons." Journal of Alzheimer's Disease 83, no. 2 (September 14, 2021): 833–52. http://dx.doi.org/10.3233/jad-215008.
Abstract:
Background: Processing of the amyloid-β protein precursor (AβPP) is neurophysiologically important due to the resulting fragments that regulate synapse biology, as well as potentially harmful due to generation of the 42 amino acid long amyloid β-peptide (Aβ42), which is a key player in Alzheimer’s disease. Objective: Our aim was to clarify the subcellular locations of the fragments involved in the amyloidogenic pathway in primary neurons with a focus on Aβ42 and its immediate substrate AβPP C-terminal fragment (APP-CTF). To overcome the difficulties of resolving these compartments due to their small size, we used super-resolution microscopy. Methods: Mouse primary hippocampal neurons were immunolabelled and imaged by stimulated emission depletion (STED) microscopy, including three-dimensional three-channel imaging, and quantitative image analyses. Results: The first (β-secretase) and second (γ-secretase) cleavages of AβPP were localized to functionally and distally distinct compartments. The β-secretase cleavage was observed in early endosomes in soma, where we were able to show that the liberated N- and C-terminal fragments were sorted into distinct vesicles budding from the early endosomes. Lack of colocalization of Aβ42 and APP-CTF in soma suggested that γ-secretase cleavage occurs in neurites. Indeed, APP-CTF was, in line with Aβ42 in our previous study, enriched in the presynapse but absent from the postsynapse. In contrast, full-length AβPP was not detected in either the pre- or the postsynaptic side of the synapse. Furthermore, we observed that endogenously produced and endocytosed Aβ42 were localized in different compartments. Conclusion: These findings provide critical super-resolved insight into amyloidogenic AβPP processing in primary neurons.
9
Stieren, Emily S., Amina El Ayadi, Yao Xiao, Efraín Siller, Megan L. Landsverk, Andres F. Oberhauser, José M. Barral, and Darren Boehning. "Ubiquilin-1 Is a Molecular Chaperone for the Amyloid Precursor Protein." Journal of Biological Chemistry 286, no. 41 (August 18, 2011): 35689–98. http://dx.doi.org/10.1074/jbc.m111.243147.
Abstract:
Alzheimer disease (AD) is associated with extracellular deposition of proteolytic fragments of amyloid precursor protein (APP). Although mutations in APP and proteases that mediate its processing are known to result in familial, early onset forms of AD, the mechanisms underlying the more common sporadic, yet genetically complex forms of the disease are still unclear. Four single-nucleotide polymorphisms within the ubiquilin-1 gene have been shown to be genetically associated with AD, implicating its gene product in the pathogenesis of late onset AD. However, genetic linkage between ubiquilin-1 and AD has not been confirmed in studies examining different populations. Here we show that regardless of genotype, ubiquilin-1 protein levels are significantly decreased in late onset AD patient brains, suggesting that diminished ubiquilin function may be a common denominator in AD progression. Our interrogation of putative ubiquilin-1 activities based on sequence similarities to proteins involved in cellular quality control showed that ubiquilin-1 can be biochemically defined as a bona fide molecular chaperone and that this activity is capable of preventing the aggregation of amyloid precursor protein both in vitro and in live neurons. Furthermore, we show that reduced activity of ubiquilin-1 results in augmented production of pathogenic amyloid precursor protein fragments as well as increased neuronal death. Our results support the notion that ubiquilin-1 chaperone activity is necessary to regulate the production of APP and its fragments and that diminished ubiquilin-1 levels may contribute to AD pathogenesis.
10
Ono, Kenji, Mikio Niwa, Hiromi Suzuki, Nahoko Bailey Kobayashi, Tetsuhiko Yoshida, and Makoto Sawada. "Signal Sequence-Dependent Orientation of Signal Peptide Fragments to Exosomes." International Journal of Molecular Sciences 23, no. 6 (March 15, 2022): 3137. http://dx.doi.org/10.3390/ijms23063137.
Abstract:
Signal peptides (SPs) not only mediate targeting to the endoplasmic reticulum (ER) but also play important roles as biomarkers and substances with physiological activity in extracellular fluids including blood. SPs are thought to be degraded intracellularly, making it unclear how they are transported from the ER to the extracellular fluid. In a recent study, we showed that a C-terminal fragment of the SP of a type I membrane protein, amyloid precursor protein (APP), was secreted into the extracellular fluid via exosomes using transformed HEK293 cells expressing APP SP flanking a reporter protein. In the present study, we demonstrate that a N-terminal fragment of the SP from a type II membrane protein, human placental secreted alkaline phosphatase (SEAP), is contained in exosomes and secreted into the extracellular fluid using HEK-Blue hTLR3 cells, which express both a human toll-like receptor 3 gene and an inducible SEAP reporter gene. When HEK-Blue hTLR3 cells were stimulated with a TLR3 ligand, a N-terminal fragment of SEAP SP in exosomes was increased in parallel with SEAP secretion in a concentration-dependent manner. These results indicated that SP fragments are exosomal components. In addition, migrating SP fragments were determined by characteristics of the signal–anchor sequence of membrane proteins. Furthermore, we found that SP fragments could bind to calmodulin (CALM), which is a cytosolic protein and also a component of exosomes, suggesting its involvement in the transportation of SP fragments from the endoplasmic reticulum to exosomes.
11
Xie, Zhongcong, Yuanlin Dong, Uta Maeda, Weiming Xia, and Rudolph E. Tanzi. "RNA Interference Silencing of the Adaptor Molecules ShcC and Fe65 Differentially Affect Amyloid Precursor Protein Processing and Aβ Generation." Journal of Biological Chemistry 282, no. 7 (December 14, 2006): 4318–25. http://dx.doi.org/10.1074/jbc.m609293200.
Abstract:
The amyloid precursor protein (APP) and its pathogenic by-product amyloid-β protein (Aβ) play central roles in Alzheimer disease (AD) neuropathogenesis. APP can be cleaved by β-secretase (BACE) and α-secretase to produce APP-C99 and APP-C83. These C-terminal fragments can then be cleaved by γ-secretase to produce Aβ and p3, respectively. p3 has been reported to promote apoptosis, and Aβ is the key component of senile plaques in AD brain. APP adaptor proteins with phosphotyrosine-binding domains, including ShcA (SHC1), ShcC (SHC3), and Fe65 (APBB1), can bind to and interact with the conserved YENPTY motif in the APP-C terminus. Here we have described for the first time the effects of RNA interference (RNAi) silencing of ShcA, ShcC, and Fe65 expression on APP processing and Aβ production. RNAi silencing of ShcC led to reductions in the levels of APP-C-terminal fragments (APP-CTFs) and Aβ in H4 human neuroglioma cells stably overexpressing full-length APP (H4-FL-APP cells) but not in those expressing APP-C99 (H4-APP-C99 cells). RNAi silencing of ShcC also led to reductions in BACE levels in H4-FL-APP cells. In contrast, RNAi silencing of the homologue ShcA had no effect on APP processing or Aβ levels. RNAi silencing of Fe65 increased APP-CTF levels, although also decreasing Aβ levels in H4-FL-APP cells. These findings suggest that pharmacologically blocking interaction of APP with ShcC and Fe65 may provide novel therapeutic strategies against AD.
12
Marttinen, Mikael, Catarina B. Ferreira, Kaisa M. A. Paldanius, Mari Takalo, Teemu Natunen, Petra Mäkinen, Luukas Leppänen, et al. "Presynaptic Vesicle Protein SEPTIN5 Regulates the Degradation of APP C-Terminal Fragments and the Levels of Aβ." Cells 9, no. 11 (November 15, 2020): 2482. http://dx.doi.org/10.3390/cells9112482.
Abstract:
Alzheimer’s disease (AD) is a neurodegenerative disease characterized by aberrant amyloid-β (Aβ) and hyperphosphorylated tau aggregation. We have previously investigated the involvement of SEPTIN family members in AD-related cellular processes and discovered a role for SEPTIN8 in the sorting and accumulation of β-secretase. Here, we elucidated the potential role of SEPTIN5, an interaction partner of SEPTIN8, in the cellular processes relevant for AD, including amyloid precursor protein (APP) processing and the generation of Aβ. The in vitro and in vivo studies both revealed that the downregulation of SEPTIN5 reduced the levels of APP C-terminal fragments (APP CTFs) and Aβ in neuronal cells and in the cortex of Septin5 knockout mice. Mechanistic elucidation revealed that the downregulation of SEPTIN5 increased the degradation of APP CTFs, without affecting the secretory pathway-related trafficking or the endocytosis of APP. Furthermore, we found that the APP CTFs were degraded, to a large extent, via the autophagosomal pathway and that the downregulation of SEPTIN5 enhanced autophagosomal activity in neuronal cells as indicated by altered levels of key autophagosomal markers. Collectively, our data suggest that the downregulation of SEPTIN5 increases the autophagy-mediated degradation of APP CTFs, leading to reduced levels of Aβ in neuronal cells.
13
Hao, Candy Yan, Michael S. Perkinton, William Wai-Lun Chan, Ho Yin Edwin Chan, Christopher C. J. Miller, and Kwok-Fai Lau. "GULP1 is a novel APP-interacting protein that alters APP processing." Biochemical Journal 436, no. 3 (May 27, 2011): 631–39. http://dx.doi.org/10.1042/bj20110145.
Abstract:
Altered production of Aβ (amyloid-β peptide), derived from the proteolytic cleavage of APP (amyloid precursor protein), is believed to be central to the pathogenesis of AD (Alzheimer's disease). Accumulating evidence reveals that APPc (APP C-terminal domain)-interacting proteins can influence APP processing. There is also evidence to suggest that APPc-interacting proteins work co-operatively and competitively to maintain normal APP functions and processing. Hence, identification of the full complement of APPc-interacting proteins is an important step for improving our understanding of APP processing. Using the yeast two-hybrid system, in the present study we identified GULP1 (engulfment adaptor protein 1) as a novel APPc-interacting protein. We found that the GULP1–APP interaction is mediated by the NPTY motif of APP and the GULP1 PTB (phosphotyrosine-binding) domain. Confocal microscopy revealed that a proportion of APP and GULP1 co-localized in neurons. In an APP–GAL4 reporter assay, we demonstrated that GULP1 altered the processing of APP. Moreover, overexpression of GULP1 enhanced the generation of APP CTFs (C-terminal fragments) and Aβ, whereas knockdown of GULP1 suppressed APP CTFs and Aβ production. The results of the present study reveal that GULP1 is a novel APP/APPc-interacting protein that influences APP processing and Aβ production.
14
Kuentzel, S. L., S. M. Ali, R. A. Altman, B. D. Greenberg, and T. J. Raub. "The Alzheimer β-amyloid protein precursor/protease nexin-II is cleaved by secretase in a trans-Golgi secretory compartment in human neuroglioma cells." Biochemical Journal 295, no. 2 (October 15, 1993): 367–78. http://dx.doi.org/10.1042/bj2950367.
Abstract:
Alzheimer beta-amyloid protein precursor (beta APP) is expressed endogenously and abundantly by human neuroglioma (H4) cells. Its secretory processing has been shown to involve discrete proteolysis within the beta A4 region, thus preventing beta-amyloid formation, by an enzyme which has been referred to as ‘beta APP secretase’. This cleavage results in secretion of a soluble N-terminal 135 kDa protein and retention of an integral membrane C-terminal fragment within the cell. The membrane-associated C-terminal fragment is sorted to lysosomes where it undergoes limited degradation. We show here that most newly synthesized beta APP is degraded via a non-lysosomal pathway before maturation in H4 cells, and most mature beta APP is processed predominantly by the so-called secretase. The rapid kinetics of appearance/disappearance of a cleaved 135 kDa protein within a microsomal fraction and the slow accumulation of this form in the extracellular medium indicated that secretase cleaves beta APP in an intracellular compartment. Low-temperature block (20 degrees C) was used to demonstrate that beta APP is cleaved within a late Golgi compartment after sulphation which occurs in the trans-Golgi network (TGN). This is consistent with (1) the immunolocalization of most of the beta APP within a Golgi compartment that reacts with wheat germ agglutinin, (2) the fact that less than 1.5% of the total mature full-length beta APP is present at the plasma membrane and (3) subcellular fractionation studies which showed that the mature full-length and intracellular cleaved beta APPs co-sediment with a membrane fraction that is slightly more dense than the plasma membrane. This study provides evidence that most of the beta APP secretase in H4 cells is intracellular, and confirms that the resulting C-terminal fragment is delivered to lysosomes immediately after cleavage. These results are discussed with regard to the possibility that mature full-length beta APP escapes secretase cleavage and is delivered directly from the TGN to the lysosome without passing through the plasma membrane. Either pathway will result in the generation of amyloidogenic fragments.
15
Ono, Kenji, Mikio Niwa, Hiromi Suzuki, Nahoko Bailey Kobayashi, Tetsuhiko Yoshida, and Makoto Sawada. "Calmodulin as a Key Regulator of Exosomal Signal Peptides." Cells 12, no. 1 (December 30, 2022): 158. http://dx.doi.org/10.3390/cells12010158.
Abstract:
Signal peptides (SPs) and their fragments play important roles as biomarkers and substances with physiological functions in extracellular fluid. We previously reported that SP fragments were released into extracellular fluid via exosomes and bound to calmodulin (CaM), an exosomal component, in a cell-free system. However, it currently remains unclear whether CaM intracellularly interacts with SP fragments or is involved in the trafficking of these fragments to exosomes. Therefore, the present study examined the binding of CaM to SP fragments in T-REx AspALP cells, transformed HEK293 cells expressing amyloid precursor protein (APP) SP flanking a reporter protein, and their exosomes. APP SP fragments were detected in exosomes from T-REx AspALP cells in the absence of W13, a CaM inhibitor, but were present in lower amounts in exosomes from W13-treated cells. Cargo proteins, such as Alix, CD63, and CD81, were increased in W13-treated T-REx AspALP cells but were decreased in their exosomes. Furthermore, CaM interacted with heat shock protein 70 and CD81 in T-REx AspALP cells and this increased in the presence of W13. APP SP fragments were detected in intracellular CaM complexes in the absence of W13, but not in its presence. These results indicate that CaM functions as a key regulator of the transport of SP fragments into exosomes and plays novel roles in the sorting of contents during exosomal biogenesis.
16
Annaert, Wim G., Lyne Levesque, Kathleen Craessaerts, Inge Dierinck, Greet Snellings, David Westaway, Peter St George-Hyslop, Barbara Cordell, Paul Fraser, and Bart De Strooper. "Presenilin 1 Controls γ-Secretase Processing of Amyloid Precursor Protein in Pre-Golgi Compartments of Hippocampal Neurons." Journal of Cell Biology 147, no. 2 (October 18, 1999): 277–94. http://dx.doi.org/10.1083/jcb.147.2.277.
Abstract:
Mutations of presenilin 1 (PS1) causing Alzheimer's disease selectively increase the secretion of the amyloidogenic βA4(1-42), whereas knocking out the gene results in decreased production of both βA4(1-40) and (1-42) amyloid peptides (De Strooper et al. 1998). Therefore, PS1 function is closely linked to the γ-secretase processing of the amyloid precursor protein (APP). Given the ongoing controversy on the subcellular localization of PS1, it remains unclear at what level of the secretory and endocytic pathways PS1 exerts its activity on APP and on the APP carboxy-terminal fragments that are the direct substrates for γ-secretase. Therefore, we have reinvestigated the subcellular localization of endogenously expressed PS1 in neurons in vitro and in vivo using confocal microscopy and fine-tuned subcellular fractionation. We show that uncleaved PS1 holoprotein is recovered in the nuclear envelope fraction, whereas the cleaved PS fragments are found mainly in post-ER membranes including the intermediate compartment (IC). PS1 is concentrated in discrete sec23p- and p58/ERGIC-53–positive patches, suggesting its localization in subdomains involved in ER export. PS1 is not found to significant amounts beyond the cis-Golgi. Surprisingly, we found that APP carboxy-terminal fragments also coenrich in the pre-Golgi membrane fractions, consistent with the idea that these fragments are the real substrates for γ-secretase. Functional evidence that PS1 exerts its effects on γ-secretase processing of APP in the ER/IC was obtained using a series of APP trafficking mutants. These mutants were investigated in hippocampal neurons derived from transgenic mice expressing PS1wt or PS1 containing clinical mutations (PS1M146L and PS1L286V) at physiologically relevant levels. We demonstrate that the APP-London and PS1 mutations have additive effects on the increased secretion of βA4(1-42) relative to βA4(1-40), indicating that both mutations operate independently. Overall, our data clearly establish that PS1 controls γ42-secretase activity in pre-Golgi compartments. We discuss models that reconcile this conclusion with the effects of PS1 deficiency on the generation of βA4(1-40) peptide in the late biosynthetic and endocytic pathways.
17
Cater, Michael A., Kelly T. McInnes, Qiao-Xin Li, Irene Volitakis, Sharon La Fontaine, Julian F. B. Mercer, and Ashley I. Bush. "Intracellular copper deficiency increases amyloid-β secretion by diverse mechanisms." Biochemical Journal 412, no. 1 (April 25, 2008): 141–52. http://dx.doi.org/10.1042/bj20080103.
Abstract:
In Alzheimer's disease there is abnormal brain copper distribution, with accumulation of copper in amyloid plaques and a deficiency of copper in neighbouring cells. Excess copper inhibits Aβ (amyloid β-peptide) production, but the effects of deficiency have not yet been determined. We therefore studied the effects of modulating intracellular copper levels on the processing of APP (amyloid precursor protein) and the production of Aβ. Human fibroblasts genetically disposed to copper accumulation secreted higher levels of sAPP (soluble APP ectodomain)α into their medium, whereas fibroblasts genetically manipulated to be profoundly copper deficient secreted predominantly sAPPβ and produced more amyloidogenic β-cleaved APP C-termini (C99). The level of Aβ secreted from copper-deficient fibroblasts was however regulated and limited by α-secretase cleavage. APP can be processed by both α- and β-secretase, as copper-deficient fibroblasts secreted sAPPβ exclusively, but produced primarily α-cleaved APP C-terminal fragments (C83). Copper deficiency also markedly reduced the steady-state level of APP mRNA whereas the APP protein level remained constant, indicating that copper deficiency may accelerate APP translation. Copper deficiency in human neuroblastoma cells significantly increased the level of Aβ secretion, but did not affect the cleavage of APP. Therefore copper deficiency markedly alters APP metabolism and can elevate Aβ secretion by either influencing APP cleavage or by inhibiting its degradation, with the mechanism dependent on cell type. Overall our results suggest that correcting brain copper imbalance represents a relevant therapeutic target for Alzheimer's disease.
18
Maarouf, Chera L., Tyler A. Kokjohn, Charisse M. Whiteside, MiMi P. Macias, Walter M. Kalback, Marwan N. Sabbagh, Thomas G. Beach, Robert Vassar, and Alex E. Roher. "Molecular Differences and Similarities between Alzheimer's Disease and the 5XFAD Transgenic Mouse Model of Amyloidosis." Biochemistry Insights 6 (January 2013): BCI.S13025. http://dx.doi.org/10.4137/bci.s13025.
Abstract:
Transgenic (Tg) mouse models of Alzheimer's disease (AD) have been extensively used to study the pathophysiology of this dementia and to test the efficacy of drugs to treat AD. The 5XFAD Tg mouse, which contains two presenilin-1 and three amyloid precursor protein (APP) mutations, was designed to rapidly recapitulate a portion of the pathologic alterations present in human AD. APP and its proteolytic peptides, as well as apolipoprotein E and endogenous mouse tau, were investigated in the 5XFAD mice at 3 months, 6 months, and 9 months. AD and nondemented subjects were used as a frame of reference. APP, amyloid-beta (Aβ) peptides, APP C-terminal fragments (CT99, CT83, AICD), β-site APP-cleaving enzyme, and APLP1 substantially increased with age in the brains of 5XFAD mice. Endogenous mouse tau did not show age-related differences. The rapid synthesis of Aβ and its impact on neuronal loss and neuroinflammation make the 5XFAD mice a desirable paradigm to model AD.
19
Pang, Keliang, Richeng Jiang, Wei Zhang, Zhengyi Yang, Lin-Lin Li, Makoto Shimozawa, Simone Tambaro, et al. "An App knock-in rat model for Alzheimer’s disease exhibiting Aβ and tau pathologies, neuronal death and cognitive impairments." Cell Research 32, no. 2 (November 17, 2021): 157–75. http://dx.doi.org/10.1038/s41422-021-00582-x.
Abstract:
AbstractA major obstacle in Alzheimer’s disease (AD) research is the lack of predictive and translatable animal models that reflect disease progression and drug efficacy. Transgenic mice overexpressing amyloid precursor protein (App) gene manifest non-physiological and ectopic expression of APP and its fragments in the brain, which is not observed in AD patients. The App knock-in mice circumvented some of these problems, but they do not exhibit tau pathology and neuronal death. We have generated a rat model, with three familiar App mutations and humanized Aβ sequence knocked into the rat App gene. Without altering the levels of full-length APP and other APP fragments, this model exhibits pathologies and disease progression resembling those in human patients: deposit of Aβ plaques in relevant brain regions, microglia activation and gliosis, progressive synaptic degeneration and AD-relevant cognitive deficits. Interestingly, we have observed tau pathology, neuronal apoptosis and necroptosis and brain atrophy, phenotypes rarely seen in other APP models. This App knock-in rat model may serve as a useful tool for AD research, identifying new drug targets and biomarkers, and testing therapeutics.
20
Hajdú, István, Barbara M. Végh, András Szilágyi, and Péter Závodszky. "Beta-Secretase 1 Recruits Amyloid-Beta Precursor Protein to ROCK2 Kinase, Resulting in Erroneous Phosphorylation and Beta-Amyloid Plaque Formation." International Journal of Molecular Sciences 24, no. 13 (June 21, 2023): 10416. http://dx.doi.org/10.3390/ijms241310416.
Abstract:
The amyloidogenic processing of APP depends on two events: its phosphorylation by ROCK2 (at Thr654) and the phosphorylation of the APP-cleaving enzyme BACE1 (at Ser498). However, the mechanisms and structural details of APP-ROCK2 and BACE1-ROCK2 binding are unknown. Using direct physical methods in combination with an in silico approach, we found that BACE1 binds into the substrate-binding groove of ROCK2 with a low affinity (Kd = 18 µM), while no binding of APP to ROCK2 alone could be detected. On the other hand, a strong association (Kd = 3.5 nM) of APP to the weak ROCK2-BACE1 complex was observed, although no stable ternary complex was detected, i.e., BACE1 was displaced by APP. We constructed a sequential functional model: (1) BACE1 weakly binds to ROCK2 and induces an allosteric conformational change in ROCK2; (2) APP strongly binds to the ROCK2-BACE1 complex, and BACE1 is released; and (3) ROCK2 phosphorylates APP at Thr654 (leading to a longer stay in the early endosome during APP processing). Direct fluorescence titration experiments showed that the APP646–664 or APP665–695 fragments did not bind separately to the ROCK2-BACE1 complex. Based on these observations, we conclude that two binding sites are involved in the ROCK2-APP interaction: (1) the substrate-binding groove, where the APP646–664 sequence containing Thr654 sits and (2) the allosteric binding site, where the APP665–695 sequence binds. These results open the way to attack the allosteric site to prevent APP phosphorylation at Thr654 by ROCK2 without inhibiting the activity of ROCK2 towards its other substrates.
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Crino, Peter B., Barry Greenberg, John A. Martin, Virginia M. Y. Lee, William D. Hill, and John Q. Trojanowski. "β-Amyloid Peptide and Amyloid Precursor Proteins in Olfactory Mucosa of Patients with Alzheimer's Disease, Parkinson's Disease, and down Syndrome." Annals of Otology, Rhinology & Laryngology 104, no. 8 (August 1995): 655–61. http://dx.doi.org/10.1177/000348949510400812.
Abstract:
Dystrophic neurites are present in olfactory epithelium (OE) of patients with Alzheimer's disease (AD), Parkinson's disease (PD), and Down syndrome (DS) and occasionally in normal individuals. Cultured olfactory neuroblasts from AD patients generate carboxy terminal amyloid precursor protein (APP) fragments that contain β-amyloid (Aβ), but it is not known if deposits of Aβ and/or APP fragments occur in the OE of individuals with or without AD, PD, or DS. To determine if Aβ accumulates in the OE in situ, we probed postmortem samples of olfactory mucosa from patients with AD, PD and AD (PD/AD), and DS and AD (DS/AD), as well as from controls, using polyclonal and monoclonal antibodies to Aβ and flanking sequences in APPs. Samples of OE also were examined by thioflavin-S and electron microscopy. Labeling of Aβ was observed in 10 of 12 AD cases, 2 of 3 PD/AD cases, 3 of 4 DS/AD cases, 3 of 10 adult controls, and 4 of 6 fetal cases. The Aβ staining was seen in the basal third of the OE, in axons projecting through the lamina propria, and in metaplastic respiratory epithelium within the OE. Antibodies to other APP domains stained the OE of patients and controls. Thioflavin-S staining was present in the basal third of the OE of 8 of 9 AD patients and several PD/AD and DS/AD patients, but only in rare cells of 3 controls. Electron microscopy did not reveal amyloid fibrils in the OE. These data suggest that deposition of Aβ occurs in a variety of circumstances and is not restricted to patients with AD, PD, or DS.
22
Ghiso, J., T. Wisniewski, R. Vidal, A. Rostagno, and B. Frangione. "Epitope map of two polyclonal antibodies that recognize amyloid lesions in patients with Alzheimer's disease." Biochemical Journal 282, no. 2 (March 1, 1992): 517–22. http://dx.doi.org/10.1042/bj2820517.
Abstract:
Two synthetic peptides with sequences identical with those of fragments of the extracellular domain of the Alzheimer's-disease amyloid precursor protein (APP) were used to raise antibodies. SP28 comprises positions 597-624 of the APP695 isoform, whereas SP41 extends towards the N-terminus (amino acids 584-624) and contains the entire SP28 peptide. Using e.l.i.s.a. and inhibition experiments we identified the two beta-turn-containing segments 602-607 and 617-624 as the epitopes recognized by anti-SP41 and anti-SP28 respectively. Both antibodies immunolabelled amyloid lesions in brains from Alzheimer's-disease patients and patients with related disorders, whereas they were unreactive in control brains. However, when probed on immunoblots, anti-SP28 failed to detect full-length APP from baculovirus-infected Sf9 cells, and anti-SP41 reacted weakly compared with other anti-APP antisera. The data suggest that these antibodies are directed to conformational epitopes not existent in the native molecules but present after alternative APP processing.
23
van den Hurk, Wilhelmina H., Heidi J. J. Willems, Marjon Bloemen, and Gerard J. M. Martens. "Novel Frameshift Mutations near Short Simple Repeats." Journal of Biological Chemistry 276, no. 15 (January 3, 2001): 11496–98. http://dx.doi.org/10.1074/jbc.m011040200.
Abstract:
In patients with Alzheimer's disease or Down's syndrome, the cerebellar cortex exhibits protein deposits in neurofibrillary tangles and neuritic plaques. Recently, the deposits have been shown to contain protein fragments of ubiquitin-B and amyloid precursor protein (APP) with an aberrant carboxyl terminus resulting from frameshift mutations (dinucleotide deletions; ΔGU or ΔGA) in or adjacent to GAGAG motifs in their mRNAs, a process referred to as molecular misreading. We have now used a bacterial expression system with the green fluorescent protein as a reporter to screen gene transcripts from aged controls, Alzheimer's disease, and Down's syndrome for molecular misreading. Novel frameshift mutations at a number of locations in the transcripts of the ubiquitin-B and APP genes were discovered (ΔGA, ΔG, ΔGU, ΔGG, ΔCA, ΔAU, ΔA, ΔAA, ΔC, ΔU, and insertion of an A). Interestingly, most mutations were in close proximity of short simple repeats (GAGAG, GGUGGU, GAGACACACA, UCAUCAUCA, CAAACAAA, and GAAGAAGAA), demonstrating that the GAGAG motif does not constitute the only hot spot for transcriptional errors. Unlike the previously detected aberrant APP fragments, some of the novel ones have the potential to generate the neurotoxic peptide β-amyloid. We conclude that during aging molecular misreading is a widespread phenomenon.
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Yao, Yinan, Seong Su Kang, Yiyuan Xia, Zhi-Hao Wang, Xia Liu, Thorsten Muller, Yi E. Sun, and Keqiang Ye. "A delta-secretase-truncated APP fragment activates CEBPB, mediating Alzheimer’s disease pathologies." Brain 144, no. 6 (April 20, 2021): 1833–52. http://dx.doi.org/10.1093/brain/awab062.
Abstract:
Abstract Amyloid-β precursor protein (APP) is sequentially cleaved by secretases and generates amyloid-β, the major components in senile plaques in Alzheimer’s disease. APP is upregulated in human Alzheimer’s disease brains. However, the molecular mechanism of how APP contributes to Alzheimer’s disease pathogenesis remains incompletely understood. Here we show that truncated APP C586-695 fragment generated by δ-secretase directly binds to CCAAT/enhancer-binding protein beta (CEBPB), an inflammatory transcription factor, and enhances its transcriptional activity, escalating Alzheimer’s disease-related gene expression and pathogenesis. The APP C586-695 fragment, but not full-length APP, strongly associates with CEBPB and elicits its nuclear translocation and augments the transcriptional activities on APP itself, MAPT (microtubule-associated protein tau), δ-secretase and inflammatory cytokine mRNA expression, finally triggering Alzheimer’s disease pathology and cognitive disorder in a viral overexpression mouse model. Blockade of δ-secretase cleavage of APP by mutating the cleavage sites reduces its stimulatory effect on CEBPB, alleviating amyloid pathology and cognitive dysfunctions. Clearance of APP C586-695 from 5xFAD mice by antibody administration mitigates Alzheimer’s disease pathologies and restores cognitive functions. Thus, in addition to the sequestration of amyloid-β, APP implicates in Alzheimer’s disease pathology by activating CEBPB upon δ-secretase cleavage.
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Xie, Zhongcong, Yuanlin Dong, Uta Maeda, Paul Alfille, Deborah J. Culley, Gregory Crosby, and Rudolph E. Tanzi. "The Common Inhalation Anesthetic Isoflurane Induces Apoptosis and Increases Amyloid β Protein Levels." Anesthesiology 104, no. 5 (May 1, 2006): 988–94. http://dx.doi.org/10.1097/00000542-200605000-00015.
Abstract:
Background The common inhalation anesthetic isoflurane has previously been reported to enhance the aggregation and cytotoxicity of the Alzheimer disease-associated amyloid beta protein (Abeta), the principal peptide component of cerebral beta-amyloid deposits. Methods H4 human neuroglioma cells stably transfected to express human full-length wild-type amyloid precursor protein (APP) were exposed to 2% isoflurane for 6 h. The cells and conditioned media were harvested at the end of the treatment. Caspase-3 activation, processing of APP, cell viability, and Abeta levels were measured with quantitative Western blotting, cell viability kit, and enzyme-linked immunosorbent assay sandwich. The control condition consisted of 5% CO2 plus 21% O2 and balanced nitrogen, which did not affect caspase-3 activation, cell viability, APP processing, or Abeta generation. Results Two percent isoflurane caused apoptosis, altered processing of APP, and increased production of Abeta in H4 human neuroglioma cell lines. Isoflurane-induced apoptosis was independent of changes in Abeta and APP holoprotein levels. However, isoflurane-induced apoptosis was potentiated by increased levels of APP C-terminal fragments. Conclusion A clinically relevant concentration of isoflurane induces apoptosis, alters APP processing, and increases Abeta production in a human neuroglioma cell line. Because altered processing of APP leading to accumulation of Abeta is a key event in the pathogenesis of Alzheimer disease, these findings may have implications for use of this anesthetic agent in individuals with excessive levels of cerebral Abeta and elderly patients at increased risk for postoperative cognitive dysfunction.
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Huttunen, Henri J., Suzanne Y. Guénette, Camilla Peach, Christopher Greco, Weiming Xia, Doo Yeon Kim, Cory Barren, Rudolph E. Tanzi, and Dora M. Kovacs. "HtrA2 Regulates β-Amyloid Precursor Protein (APP) Metabolism through Endoplasmic Reticulum-associated Degradation." Journal of Biological Chemistry 282, no. 38 (August 6, 2007): 28285–95. http://dx.doi.org/10.1074/jbc.m702951200.
Abstract:
Alzheimer disease-associated β-amyloid peptide is generated from its precursor protein APP. By using the yeast two-hybrid assay, here we identified HtrA2/Omi, a stress-responsive chaperone-protease as a protein binding to the N-terminal cysteinerich region of APP. HtrA2 coimmunoprecipitates exclusively with immature APP from cell lysates as well as mouse brain extracts and degrades APP in vitro. A subpopulation of HtrA2 localizes to the cytosolic side of the endoplasmic reticulum (ER) membrane where it contributes to ER-associated degradation of APP together with the proteasome. Inhibition of the proteasome results in accumulation of retrotranslocated forms of APP and increased association of APP with HtrA2 and Derlin-1 in microsomal membranes. In cells lacking HtrA2, APP holoprotein is stabilized and accumulates in the early secretory pathway correlating with elevated levels of APP C-terminal fragments and increased Aβ secretion. Inhibition of ER-associated degradation (either HtrA2 or proteasome) promotes binding of APP to the COPII protein Sec23 suggesting enhanced trafficking of APP out of the ER. Based on these results we suggest a novel function for HtrA2 as a regulator of APP metabolism through ER-associated degradation.
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Grangeon, Lou, Kévin Cassinari, Stéphane Rousseau, Bernard Croisile, Maïté Formaglio, Olivier Moreaud, Jean Boutonnat, et al. "Early-Onset Cerebral Amyloid Angiopathy and Alzheimer Disease Related to an APP Locus Triplication." Neurology Genetics 7, no. 5 (September 8, 2021): e609. http://dx.doi.org/10.1212/nxg.0000000000000609.
Abstract:
Background and ObjectiveTo report a triplication of the amyloid-β precursor protein (APP) locus along with relative messenger RNA (mRNA) expression in a family with autosomal dominant early-onset cerebral amyloid angiopathy (CAA) and Alzheimer disease (AD).MethodsFour copies of the APP gene were identified by quantitative multiplex PCR of short fluorescent fragments, fluorescent in situ hybridization (FISH), and array comparative genomic hybridization. APP mRNA levels were assessed using reverse-transcription–digital droplet PCR in the proband's whole blood and compared with 10 controls and 9 APP duplication carriers.ResultsBeginning at age 39 years, the proband developed severe episodic memory deficits with a CSF biomarker profile typical of AD and multiple lobar microbleeds in the posterior regions on brain MRI. His father had seizures and recurrent cerebral hemorrhage since the age of 37 years. His cerebral biopsy showed abundant perivascular amyloid deposits, leading to a diagnosis of CAA. In the proband, we identified 4 copies of a 506-kb region located on chromosome 21q21.3 and encompassing the whole APP gene without any other gene. FISH suggested that the genotype of the proband was 3 copies/1 copy corresponding to an APP locus triplication, which was consistent with the presence of 2 APP copies in the healthy mother and with the paternal medical history. Analysis of the APP mRNA level showed a 2-fold increase in the proband and a 1.8 fold increase in APP duplication carriers compared with controls.DiscussionIncreased copy number of APP is sufficient to cause AD and CAA, with likely earlier onset in case of triplication compared with duplication.
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Jowsey, Paul A., and Peter G. Blain. "Fe65 Ser228 is phosphorylated by ATM/ATR and inhibits Fe65–APP-mediated gene transcription." Biochemical Journal 465, no. 3 (January 22, 2015): 413–21. http://dx.doi.org/10.1042/bj20140656.
Abstract:
APP (amyloid precursor protein) processing generates cytotoxic amyloid β-peptides (Aβ) and a transcriptionally active protein fragment (AICD). In the present study, we identify a novel ATM/ATR phosphorylation site in the APP-binding protein Fe65. Phosphorylation of this site decreases the transcriptional activity of the Fe65–APP complex.
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Nguyen, Khue Vu. "The human β-amyloid precursor protein: biomolecular and epigenetic aspects." Biomolecular Concepts 6, no. 1 (March 1, 2015): 11–32. http://dx.doi.org/10.1515/bmc-2014-0041.
Abstract:
AbstractBeta-amyloid precursor protein (APP) is a membrane-spanning protein with a large extracellular domain and a much smaller intracellular domain. APP plays a central role in Alzheimer’s disease (AD) pathogenesis: APP processing generates β-amyloid (Aβ) peptides, which are deposited as amyloid plaques in the brains of AD individuals; point mutations and duplications of APP are causal for a subset of early-onset familial AD (FAD) (onset age <65 years old). However, these mutations in FAD represent a very small percentage of cases (∼1%). Approximately 99% of AD cases are nonfamilial and late-onset, i.e., sporadic AD (SAD) (onset age >65 years old), and the pathophysiology of this disorder is not yet fully understood. APP is an extremely complex molecule that may be functionally important in its full-length configuration, as well as the source of numerous fragments with varying effects on neural function, yet the normal function of APP remains largely unknown. This article provides an overview of our current understanding of APP, including its structure, expression patterns, proteolytic processing and putative functions. Importantly, and for the first time, my recent data concerning its epigenetic regulation, especially in alternative APP pre-mRNA splicing and in the control of genomic rearrangements of the APP gene, are also reported. These findings may provide new directions for investigating the role of APP in neuropathology associated with a deficiency in the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGprt) found in patients with Lesch-Nyhan syndrome (LNS) and its attenuated variants (LNVs). Also, these findings may be of significance for research in neurodevelopmental and neurodegenerative disorders in which the APP gene is involved in the pathogenesis of diseases such as autism, fragile X syndrome (FXS) and AD, with its diversity and complexity, SAD in particular. Accurate quantification of various APP-mRNA isoforms in brain tissues is needed, and antisense drugs are potential treatments.
30
Wang, Bo-Jeng, Guor Mour Her, Ming-Kuan Hu, Yun-Wen Chen, Ying-Tsen Tung, Pei-Yi Wu, Wen-Ming Hsu, et al. "ErbB2 regulates autophagic flux to modulate the proteostasis of APP-CTFs in Alzheimer’s disease." Proceedings of the National Academy of Sciences 114, no. 15 (March 28, 2017): E3129—E3138. http://dx.doi.org/10.1073/pnas.1618804114.
Abstract:
Proteolytic processing of amyloid precursor protein (APP) C-terminal fragments (CTFs) by γ-secretase underlies the pathogenesis of Alzheimer’s disease (AD). An RNA interference screen using APP-CTF [99-residue CTF (C99)]- and Notch-specific γ-secretase interaction assays identified a unique ErbB2-centered signaling network that was predicted to preferentially govern the proteostasis of APP-C99. Consistently, significantly elevated levels of ErbB2 were confirmed in the hippocampus of human AD brains. We then found that ErbB2 effectively suppressed autophagic flux by physically dissociating Beclin-1 from the Vps34–Vps15 complex independent of its kinase activity. Down-regulation of ErbB2 by CL-387,785 decreased the levels of C99 and secreted amyloid-β in cellular, zebrafish, and mouse models of AD, through the activation of autophagy. Oral administration of an ErbB2-targeted CL-387,785 for 3 wk significantly improves the cognitive functions of APP/presenilin-1 (PS1) transgenic mice. This work unveils a noncanonical function of ErbB2 in modulating autophagy and establishes ErbB2 as a therapeutic target for AD.
31
Vaillant-Beuchot, Loan, Arnaud Mary, Raphaëlle Pardossi-Piquard, Alexandre Bourgeois, Inger Lauritzen, Fanny Eysert, Paula Fernanda Kinoshita, et al. "Accumulation of amyloid precursor protein C-terminal fragments triggers mitochondrial structure, function, and mitophagy defects in Alzheimer’s disease models and human brains." Acta Neuropathologica 141, no. 1 (October 20, 2020): 39–65. http://dx.doi.org/10.1007/s00401-020-02234-7.
Abstract:
AbstractSeveral lines of recent evidence indicate that the amyloid precursor protein-derived C-terminal fragments (APP-CTFs) could correspond to an etiological trigger of Alzheimer’s disease (AD) pathology. Altered mitochondrial homeostasis is considered an early event in AD development. However, the specific contribution of APP-CTFs to mitochondrial structure, function, and mitophagy defects remains to be established. Here, we demonstrate in neuroblastoma SH-SY5Y cells expressing either APP Swedish mutations, or the β-secretase-derived APP-CTF fragment (C99) combined with β- and γ-secretase inhibition, that APP-CTFs accumulation independently of Aβ triggers excessive mitochondrial morphology alteration (i.e., size alteration and cristae disorganization) associated with enhanced mitochondrial reactive oxygen species production. APP-CTFs accumulation also elicit basal mitophagy failure illustrated by enhanced conversion of LC3, accumulation of LC3-I and/or LC3-II, non-degradation of SQSTM1/p62, inconsistent Parkin and PINK1 recruitment to mitochondria, enhanced levels of membrane and matrix mitochondrial proteins, and deficient fusion of mitochondria with lysosomes. We confirm the contribution of APP-CTFs accumulation to morphological mitochondria alteration and impaired basal mitophagy in vivo in young 3xTgAD transgenic mice treated with γ-secretase inhibitor as well as in adeno-associated-virus-C99 injected mice. Comparison of aged 2xTgAD and 3xTgAD mice indicates that, besides APP-CTFs, an additional contribution of Aβ to late-stage mitophagy activation occurs. Importantly, we report on mitochondrial accumulation of APP-CTFs in human post-mortem sporadic AD brains correlating with mitophagy failure molecular signature. Since defective mitochondria homeostasis plays a pivotal role in AD pathogenesis, targeting mitochondrial dysfunctions and/or mitophagy by counteracting early APP-CTFs accumulation may represent relevant therapeutic interventions in AD.
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Dorval, Véronique, Matthew J. Mazzella, Paul M. Mathews, Ronald T. Hay, and Paul E. Fraser. "Modulation of Aβ generation by small ubiquitin-like modifiers does not require conjugation to target proteins." Biochemical Journal 404, no. 2 (May 14, 2007): 309–16. http://dx.doi.org/10.1042/bj20061451.
Abstract:
The sequential processing of the APP (amyloid precursor protein) by the β- and γ-secretase and generation of the Aβ (amyloid-β) peptide is a primary pathological factor in AD (Alzheimer's disease). Regulation of the processing or turnover of these proteins represents potential targets for the development of AD therapies. Sumoylation is a process by which SUMOs (small ubiquitin-like modifiers) are covalently conjugated to target proteins, resulting in a number of functional consequences. These include regulation of protein–protein interactions, intracellular trafficking and protein stability, which all have the potential to impact on several aspects of the amyloidogenic pathway. The present study examines the effects of overexpression and knockdown of the major SUMO isoforms (SUMO1, 2 and 3) on APP processing and the production of Aβ peptides. SUMO3 overexpression significantly increased Aβ40 and Aβ42 secretion, which was accompanied by an increase in full-length APP and its C-terminal fragments. These effects of SUMO3 were independent of its covalent attachment or chain formation, as mutants lacking the motifs responsible for SUMO chain formation or SUMO conjugation led to similar changes in Aβ. SUMO3 overexpression also up-regulated the expression of the transmembrane protease BACE (β-amyloid-cleaving enzyme), but failed to affect levels of several other unrelated proteins. Suppression of SUMO1 or combined SUMO2+3 by RNA interference did not affect APP levels or Aβ production. These findings confirm a specific effect of SUMO3 overexpression on APP processing and the production of Aβ peptides but also suggest that endogenous sumoylation is not essential and likely plays an indirect role in modulating the amyloid processing pathway.
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Bussiere, Oulès, Mary, Vaillant-Beuchot, Martin, Manaa, Vallée, et al. "Upregulation of the Sarco-Endoplasmic Reticulum Calcium ATPase 1 Truncated Isoform Plays a Pathogenic Role in Alzheimer’s Disease." Cells 8, no. 12 (November 28, 2019): 1539. http://dx.doi.org/10.3390/cells8121539.
Abstract:
Dysregulation of the Endoplasmic Reticulum (ER) Ca2+ homeostasis and subsequent ER stress activation occur in Alzheimer Disease (AD). We studied the contribution of the human truncated isoform of the sarco-endoplasmic reticulum Ca2+ ATPase 1 (S1T) to AD. We examined S1T expression in human AD-affected brains and its functional consequences in cellular and transgenic mice AD models. S1T expression is increased in sporadic AD brains and correlates with amyloid β (Aβ) and ER stress chaperone protein levels. Increased S1T expression was also observed in human neuroblastoma cells expressing Swedish-mutated β-amyloid precursor protein (βAPP) or treated with Aβ oligomers. Lentiviral overexpression of S1T enhances in return the production of APP C-terminal fragments and Aβ through specific increases of β-secretase expression and activity, and triggers neuroinflammation. We describe a molecular interplay between S1T-dependent ER Ca2+ leak, ER stress and βAPP-derived fragments that could contribute to AD setting and/or progression.
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Augutis, Kristin, Markus Axelsson, Erik Portelius, Gunnar Brinkmalm, Ulf Andreasson, Mikael K. Gustavsson, Clas Malmeström, et al. "Cerebrospinal fluid biomarkers of β-amyloid metabolism in multiple sclerosis." Multiple Sclerosis Journal 19, no. 5 (October 15, 2012): 543–52. http://dx.doi.org/10.1177/1352458512460603.
Abstract:
Background: Amyloid precursor protein (APP) and amyloid β (Aβ) peptides are intensely studied in neuroscience and their cerebrospinal fluid (CSF) measurements may be used to track the metabolic pathways of APP in vivo. Reduced CSF levels of Aβ and soluble APP (sAPP) fragments are reported in inflammatory diseases, including multiple sclerosis (MS); but in MS, the precise pathway of APP metabolism and whether it can be affected by disease-modifying treatments remains unclear. Objective: To characterize the CSF biomarkers of APP degradation in MS, including the effects of disease-modifying therapy. Methods: CSF samples from 87 MS patients (54 relapsing–remitting (RR) MS; 33 secondary progressive (SP) MS and 28 controls were analyzed for sAPP and Aβ peptides by immunoassays, plus a subset of samples was analyzed by immunoprecipitation and mass spectrometry (IP-MS). Patients treated with natalizumab or mitoxantrone were examined at baseline, and after 1–2 years of treatment. Results: CSF sAPP and Aβ peptide levels were reduced in MS patients; but they increased again towards normal, after natalizumab treatment. A multivariate model of IP-MS-measured Aβ species separated the SPMS patients from controls, with RRMS patients having intermediate levels. Conclusions: We confirmed and extended our previous observations of altered CSF sAPP and Aβ peptide levels in MS patients. We found that natalizumab therapy may be able to counteract the altered APP metabolism in MS. The CSF Aβ isoform distribution was found to be distinct in SPMS patients, as compared to the controls.
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K. Lakshmana, Madepalli, Subhojit Roy, Kaihong Mi, and David E. Kang. "Amyloidogenic Processing of APP in Lipid Rafts." Open Biology Journal 3, no. 1 (March 19, 2010): 21–31. http://dx.doi.org/10.2174/18741967010030100021.
Abstract:
Increased generation of amyloid β peptide (Aβ) derived from amyloid precursor protein (APP) is the primary pathological characteristic of Alzheimer’s disease (AD). However, the sub cellular compartment in which APP undergoes cleavage by secretases to generate Aβ is not precisely known. Compelling evidences suggest that amyloidogenic processing of APP occurs in lipid rafts. An indirect support for lipid raft processing of APP includes the localization of Aβ, APP C-terminal fragments (CTFs), APP holoprotein and secretases in the lipid raft microdomains, although few studies failed to find APP in the lipid rafts. The indirect support also comes from both experimental and clinical studies involving modulation of cholesterol levels and its effect on Aβ generation. Moderate depletion of cholesterol results in significant reduction in Aβ levels and increased dietary intake of cholesterol leads to higher levels of Aβ production suggesting that amyloidogenic processing of APP strongly depends on cholesterol levels and therefore on lipid raft integrity. More convincing evidence that lipid rafts are critical for amyloidogenic processing of APP comes from studies using antibody-mediated co-patching of APP and BACE1 which results in lipid raft association of APP and BACE1 and increased Aβ generation. Further, an endosome/lipid raft targeting of β-secretase inhibitor by sterol-mediated anchoring leading to reduced Aβ generation also suggests that lipid rafts are pivotal for amyloidogenic processing of APP. In the absence of an effective therapy for AD, proteins responsible for delivery of APP to lipid rafts including LRP, RanBP9 and ApoER2 may be excellent therapeutic targets in AD.
36
Tan, Jing Zhi A., and Paul A. Gleeson. "The trans-Golgi network is a major site for α-secretase processing of amyloid precursor protein in primary neurons." Journal of Biological Chemistry 294, no. 5 (December 13, 2018): 1618–31. http://dx.doi.org/10.1074/jbc.ra118.005222.
Abstract:
Amyloid precursor protein (APP) is processed along the amyloidogenic pathway by the β-secretase, BACE1, generating β-amyloid (Aβ), or along the nonamyloidogenic pathway by α-secretase, precluding Aβ production. The plasma membrane is considered the major site for α-secretase–mediated APP cleavage, but other cellular locations have not been rigorously investigated. Here, we report that APP is processed by endogenous α-secretase at the trans-Golgi network (TGN) of both transfected HeLa cells and mouse primary neurons. We have previously shown the adaptor protein complex, AP-4, and small G protein ADP-ribosylation factor–like GTPase 5b (Arl5b) are required for efficient post-Golgi transport of APP to endosomes. We found here that AP-4 or Arl5b depletion results in Golgi accumulation of APP and increased secretion of the soluble α-secretase cleavage product sAPPα. Moreover, inhibition of γ-secretase following APP accumulation in the TGN increases the levels of the membrane-bound C-terminal fragments of APP from both α-secretase cleavage (α-CTF, named C83 according to its band size) and BACE1 cleavage (β-CTF/C99). The level of C83 was ∼4 times higher than that of C99, indicating that α-secretase processing is the major pathway and that BACE1 processing is the minor pathway in the TGN. AP-4 silencing in mouse primary neurons also resulted in the accumulation of endogenous APP in the TGN and enhanced α-secretase processing. These findings identify the TGN as a major site for α-secretase processing in HeLa cells and primary neurons and indicate that both APP processing pathways can occur within the TGN compartment along the secretory pathway.
37
Szögi, Titanilla, Ildikó Schuster, Emőke Borbély, Andrea Gyebrovszki, Zsolt Bozsó, János Gera, Róbert Rajkó, Miklós Sántha, Botond Penke, and Lívia Fülöp. "Effects of the Pentapeptide P33 on Memory and Synaptic Plasticity in APP/PS1 Transgenic Mice: A Novel Mechanism Presenting the Protein Fe65 as a Target." International Journal of Molecular Sciences 20, no. 12 (June 22, 2019): 3050. http://dx.doi.org/10.3390/ijms20123050.
Abstract:
Regulated intramembrane proteolysis (RIP) of the amyloid precursor protein (APP) leads to the formation of fragments, among which the intracellular domain of APP (AICD) was also identified to be a causative of early pathological events. AICD-counteracting proteins, such as Fe65, may serve as alternative therapeutic targets of Alzheimer’s disease (AD). The detection of elevated levels of Fe65 in the brains of both human patients and APP transgenic mice may further strengthen the hypothesis that influencing the interaction between Fe65 and APP may have a beneficial effect on the course of AD. Based on a PXP motif, proven to bind to the WW domain of Fe65, a new pentapeptide was designed and tested. The impedimental effect of P33 on the production of beta amyloid (Aβ) (soluble fraction and aggregated plaques) and on the typical features of the AD pathology (decreased dendritic spine density, synaptic markers, elevated inflammatory reactions) was also demonstrated. Significant enhancements of both learning ability and memory function were observed in a Morris water maze paradigm. The results led us to formulate the theory that P33 acts by altering the conformation of Fe65 via binding to its WW domain, consequently hindering any interactions between Fe65 and key members involved in APP processing.
38
Kuznetsov, I. A., and A. V. Kuznetsov. "Simulating the effect of formation of amyloid plaques on aggregation of tau protein." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2220 (December 2018): 20180511. http://dx.doi.org/10.1098/rspa.2018.0511.
Abstract:
In this paper, we develop a mathematical model that enables the investigation of the production and intracellular transport of amyloid precursor protein (APP) and tau protein in a neuron. We also investigate the aggregation of APP fragments into amyloid-β (Aβ) as well as tau aggregation into tau oligomers and neurofibrillary tangles. Using the developed model, we investigate how Aβ aggregation can influence tau transport and aggregation in both the soma and the axon. We couple the Aβ and tau agglomeration processes by assuming that the value of the kinetic constant that describes the autocatalytic growth (self-replication) reaction step of tau aggregation is proportional to the Aβ concentration. The model predicts that APP and tau are distributed differently in the axon. While APP has a uniform distribution along the axon, tau's concentration first decreases and then increases towards the synapse. Aβ is uniformly produced along the axon while misfolded tau protein is mostly produced in the proximal axon. The number of Aβ and tau polymers originating from the axon is much smaller than the number of Aβ and tau polymers originating from the soma. The rate of production of misfolded tau polymers depends on how strongly their production is facilitated by Aβ.
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Masi, Mirco, Fabrizio Biundo, André Fiou, Marco Racchi, Alessia Pascale, and Erica Buoso. "The Labyrinthine Landscape of APP Processing: State of the Art and Possible Novel Soluble APP-Related Molecular Players in Traumatic Brain Injury and Neurodegeneration." International Journal of Molecular Sciences 24, no. 7 (April 2, 2023): 6639. http://dx.doi.org/10.3390/ijms24076639.
Abstract:
Amyloid Precursor Protein (APP) and its cleavage processes have been widely investigated in the past, in particular in the context of Alzheimer’s Disease (AD). Evidence of an increased expression of APP and its amyloidogenic-related cleavage enzymes, β-secretase 1 (BACE1) and γ-secretase, at the hit axon terminals following Traumatic Brain Injury (TBI), firstly suggested a correlation between TBI and AD. Indeed, mild and severe TBI have been recognised as influential risk factors for different neurodegenerative diseases, including AD. In the present work, we describe the state of the art of APP proteolytic processing, underlining the different roles of its cleavage fragments in both physiological and pathological contexts. Considering the neuroprotective role of the soluble APP alpha (sAPPα) fragment, we hypothesised that sAPPα could modulate the expression of genes of interest for AD and TBI. Hence, we present preliminary experiments addressing sAPPα-mediated regulation of BACE1, Isthmin 2 (ISM2), Tetraspanin-3 (TSPAN3) and the Vascular Endothelial Growth Factor (VEGFA), each discussed from a biological and pharmacological point of view in AD and TBI. We finally propose a neuroprotective interaction network, in which the Receptor for Activated C Kinase 1 (RACK1) and the signalling cascade of PKCβII/nELAV/VEGF play hub roles, suggesting that vasculogenic-targeting therapies could be a feasible approach for vascular-related brain injuries typical of AD and TBI.
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Netzer, William J., Karima Bettayeb, Subhash C. Sinha, Marc Flajolet, Paul Greengard, and Victor Bustos. "Gleevec shifts APP processing from a β-cleavage to a nonamyloidogenic cleavage." Proceedings of the National Academy of Sciences 114, no. 6 (January 23, 2017): 1389–94. http://dx.doi.org/10.1073/pnas.1620963114.
Abstract:
Neurotoxic amyloid-β peptides (Aβ) are major drivers of Alzheimer’s disease (AD) and are formed by sequential cleavage of the amyloid precursor protein (APP) by β-secretase (BACE) and γ-secretase. Our previous study showed that the anticancer drug Gleevec lowers Aβ levels through indirect inhibition of γ-secretase activity. Here we report that Gleevec also achieves its Aβ-lowering effects through an additional cellular mechanism. It renders APP less susceptible to proteolysis by BACE without inhibiting BACE enzymatic activity or the processing of other BACE substrates. This effect closely mimics the phenotype of APP A673T, a recently discovered mutation that protects carriers against AD and age-related cognitive decline. In addition, Gleevec induces formation of a specific set of APP C-terminal fragments, also observed in cells expressing the APP protective mutation and in cells exposed to a conventional BACE inhibitor. These Gleevec phenotypes require an intracellular acidic pH and are independent of tyrosine kinase inhibition, given that a related compound lacking tyrosine kinase inhibitory activity, DV2-103, exerts similar effects on APP metabolism. In addition, DV2-103 accumulates at high concentrations in the rodent brain, where it rapidly lowers Aβ levels. This study suggests that long-term treatment with drugs that indirectly modulate BACE processing of APP but spare other BACE substrates and achieve therapeutic concentrations in the brain might be effective in preventing or delaying the onset of AD and could be safer than nonselective BACE inhibitor drugs.
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Hoe, Hyang-Sook, David Wessner, Uwe Beffert, Amanda G. Becker, Yasuji Matsuoka, and G. William Rebeck. "F-Spondin Interaction with the Apolipoprotein E Receptor ApoEr2 Affects Processing of Amyloid Precursor Protein." Molecular and Cellular Biology 25, no. 21 (November 1, 2005): 9259–68. http://dx.doi.org/10.1128/mcb.25.21.9259-9268.2005.
Abstract:
ABSTRACT A recent study showed that F-spondin, a protein associated with the extracellular matrix, interacted with amyloid precursor protein (APP) and inhibited β-secretase cleavage. F-spondin contains a thrombospondin domain that we hypothesized could interact with the family of receptors for apolipoprotein E (apoE). Through coimmunoprecipitation experiments, we demonstrated that F-spondin interacts with an apoE receptor (apoE receptor 2 [ApoEr2]) through the thrombospondin domain of F-spondin and the ligand binding domain of ApoEr2. Full-length F-spondin increased coimmunoprecipitation of ApoEr2 and APP in transfected cells and primary neurons and increased surface expression of APP and ApoEr2. Full-length F-spondin, but none of the individual F-spondin domains, increased cleavage of APP and ApoEr2, resulting in more secreted forms of APP and ApoEr2 and more C-terminal fragments (CTF) of these proteins. In addition, full-length F-spondin, but not the individual domains, decreased production of the β-CTF of APP and Aβ in transfected cells and primary neurons. The reduction in APP β-CTF was blocked by receptor-associated protein (RAP), an inhibitor of lipoprotein receptors, implicating ApoEr2 in the altered proteolysis of APP. ApoEr2 coprecipitated with APP α- and β-CTF, and F-spondin reduced the levels of APP intracellular domain signaling, suggesting that there are also intracellular interactions between APP and ApoEr2, perhaps involving adaptor proteins. These studies suggest that the extracellular matrix molecule F-spondin can cluster APP and ApoEr2 together on the cell surface and affect the processing of each, resulting in decreased production of Aβ.
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Schmitt, T. L. "Thyroid epithelial cells produce large amounts of the Alzheimer beta- amyloid precursor protein (APP) and generate potentially amyloidogenic APP fragments." Journal of Clinical Endocrinology & Metabolism 80, no. 12 (December 1, 1995): 3513–19. http://dx.doi.org/10.1210/jc.80.12.3513.
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Schmitt, T. L., E. Steiner, P. Klingler, H. Lassmann, and B. Grubeck-Loebenstein. "Thyroid epithelial cells produce large amounts of the Alzheimer beta-amyloid precursor protein (APP) and generate potentially amyloidogenic APP fragments." Journal of Clinical Endocrinology & Metabolism 80, no. 12 (December 1995): 3513–19. http://dx.doi.org/10.1210/jcem.80.12.8530592.
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Mori, Takashi, Naoki Koyama, Tatsuya Segawa, Masahiro Maeda, Nobuhiro Maruyama, Noriaki Kinoshita, Huayan Hou, Jun Tan, and Terrence Town. "Methylene Blue Modulates β-Secretase, Reverses Cerebral Amyloidosis, and Improves Cognition in Transgenic Mice." Journal of Biological Chemistry 289, no. 44 (August 25, 2014): 30303–17. http://dx.doi.org/10.1074/jbc.m114.568212.
Abstract:
Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in the brains of patients with Alzheimer disease (AD). Here, we tested whether the experimental agent methylene blue (MB), used for treatment of methemoglobinemia, might improve AD-like pathology and behavioral deficits. We orally administered MB to the aged transgenic PSAPP mouse model of cerebral amyloidosis and evaluated cognitive function and cerebral amyloid pathology. Beginning at 15 months of age, animals were gavaged with MB (3 mg/kg) or vehicle once daily for 3 months. MB treatment significantly prevented transgene-associated behavioral impairment, including hyperactivity, decreased object recognition, and defective spatial working and reference memory, but it did not alter nontransgenic mouse behavior. Moreover, brain parenchymal and cerebral vascular β-amyloid deposits as well as levels of various Aβ species, including oligomers, were mitigated in MB-treated PSAPP mice. These effects occurred with inhibition of amyloidogenic APP proteolysis. Specifically, β-carboxyl-terminal APP fragment and β-site APP cleaving enzyme 1 protein expression and activity were attenuated. Additionally, treatment of Chinese hamster ovary cells overexpressing human wild-type APP with MB significantly decreased Aβ production and amyloidogenic APP proteolysis. These results underscore the potential for oral MB treatment against AD-related cerebral amyloidosis by modulating the amyloidogenic pathway.
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Hefter, Dimitri, Susann Ludewig, Andreas Draguhn, and Martin Korte. "Amyloid, APP, and Electrical Activity of the Brain." Neuroscientist 26, no. 3 (November 29, 2019): 231–51. http://dx.doi.org/10.1177/1073858419882619.
Abstract:
The Amyloid Precursor Protein (APP) is infamous for its proposed pivotal role in the pathogenesis of Alzheimer’s disease (AD). Much research on APP focusses on potential contributions to neurodegeneration, mostly based on mouse models with altered expression or mutated forms of APP. However, cumulative evidence from recent years indicates the indispensability of APP and its metabolites for normal brain physiology. APP contributes to the regulation of synaptic transmission, plasticity, and calcium homeostasis. It plays an important role during development and it exerts neuroprotective effects. Of particular importance is the soluble secreted fragment APPsα which mediates many of its physiological actions, often counteracting the effects of the small APP-derived peptide Aβ. Understanding the contribution of APP for normal functions of the nervous system is of high importance, both from a basic science perspective and also as a basis for generating new pathophysiological concepts and therapeutic approaches in AD. In this article, we review the physiological functions of APP and its metabolites, focusing on synaptic transmission, plasticity, calcium signaling, and neuronal network activity.
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BORCHARDT, Thilo, James CAMAKARIS, Roberto CAPPAI, Colin L. MASTERS, Konrad BEYREUTHER, and Gerd MULTHAUP. "Copper inhibits β-amyloid production and stimulates the non-amyloidogenic pathway of amyloid-precursor-protein secretion." Biochemical Journal 344, no. 2 (November 24, 1999): 461–67. http://dx.doi.org/10.1042/bj3440461.
Abstract:
Previous studies have demonstrated that amyloid precursor protein (APP) can bind and reduce Cu(II) to Cu(I), leading to oxidative modification of APP. In the present study we show that adding copper to Chinese-hamster ovary (CHO) cells greatly reduced the levels of amyloid Aβ peptide (Aβ) both in parental CHO-K1 and in copper-resistant CHO-CUR3 cells, which have lower intracellular copper levels. Copper also caused an increase in the secretion of the APP ectodomain, indicating that the large decrease in Aβ release was not due to a general inhibition in protein secretion. There was an increase in intracellular full-length APP levels which paralleled the decrease in Aβ generation, suggesting the existence of two distinct regulating mechanisms, one acting on Aβ production and the other on APP synthesis. Maximal inhibition of Aβ production and stimulation of APP secretion was achieved in CHO-K1 cells at about 10 μM copper and in CHO-CUR3 cells at about 50 μM copper. This dose ‘window of opportunity’ at which copper promoted the non-amyloidogenic pathway of APP was confirmed by an increase in the non-amyloidogenic p3 fragment produced by α-secretase cleavage. Our findings suggest that copper or copper agonists might be useful tools to discover novel targets for anti-Alzheimer drugs and may prove beneficial for the prevention of Alzheimer's disease.
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Barron, A. M., M. Cake, G. Verdile, and R. N. Martins. "Ovariectomy and 17β-Estradiol Replacement Do Not Alter β-Amyloid Levels in Sheep Brain." Endocrinology 150, no. 7 (March 12, 2009): 3228–36. http://dx.doi.org/10.1210/en.2008-1252.
Abstract:
The benefits of estrogen replacement as a preventative treatment for Alzheimer’s disease (AD) are subject to debate. Because the effects of estrogen depletion and replacement on accumulation of the neurotoxic β-amyloid (Aβ) peptide in transgenic animal models of AD have been variable, we examined Aβ levels and oxidative stress in a nontransgenic animal model. Sheep have traditionally been used as a model for human reproduction; however because they share 100% sequence homology with the human form of Aβ, they may also have potential as a nontransgenic model for Aβ biology. The effect of ovariectomy and estrogen replacement administered for 6 months via slow-release implant was examined in the brain of 4.5-yr-old sheep. Aβ levels were measured by ELISA, and protein levels of the amyloid precursor protein (APP), APP C-terminal fragments (C100), and presenilin-1 were examined semiquantitatively by Western blot as markers of APP processing. Markers of oxidative stress were examined semiquantitatively by Western blot [4-hydroxy-2(E)-nonenal] and oxyblot (protein carbonyls). We found no effects of estrogen depletion and supplementation in terms of AD-related biochemical markers, including Aβ levels, APP processing, and oxidative stress levels. Evidence of a trend toward increased P450 side-chain cleavage enzyme levels in the hippocampus of ovariectomized and estrogen supplemented sheep suggests that neurosteroidogenesis may compensate for gonadal estrogen depletion; however, these findings cannot explain the lack of effect of estrogen supplementation on APP processing. It is possible that supraphysiological doses of estrogen are necessary to yield antiamyloidogenic and antioxidative benefits in ovariectomized sheep.
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Paschou, Maria, Danai Liaropoulou, Vasileia Kalaitzaki, Spiros Efthimiopoulos, and Panagiota Papazafiri. "Knockdown of Amyloid Precursor Protein Increases Ion Channel Expression and Alters Ca2+ Signaling Pathways." International Journal of Molecular Sciences 24, no. 3 (January 24, 2023): 2302. http://dx.doi.org/10.3390/ijms24032302.
Abstract:
Although the physiological role of the full-length Amyloid Precursor Protein (APP) and its proteolytic fragments remains unclear, they are definitively crucial for normal synaptic function. Herein, we report that the downregulation of APP in SH-SY5Y cells, using short hairpin RNA (shRNA), alters the expression pattern of several ion channels and signaling proteins that are involved in synaptic and Ca2+ signaling. Specifically, the levels of GluR2 and GluR4 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPAR) were significantly increased with APP knockdown. Similarly, the expression of the majority of endoplasmic reticulum (ER) residing proteins, such as the ER Ca2+ channels IP3R (Inositol 1,4,5-triphosphate Receptor) and RyR (Ryanodine Receptor), the Ca2+ pump SERCA2 (Sarco/endoplasmic reticulum Ca2+ ATPase 2) and the ER Ca2+ sensor STIM1 (Stromal Interaction Molecule 1) was upregulated. A shift towards the upregulation of p-AKT, p-PP2A, and p-CaMKIV and the downregulation of p-GSK, p-ERK1/2, p-CaMKII, and p-CREB was observed, interconnecting Ca2+ signal transduction from the plasma membrane and ER to the nucleus. Interestingly, we detected reduced responses to several physiological stimuli, with the most prominent being the ineffectiveness of SH-SY5Y/APP- cells to mobilize Ca2+ from the ER upon carbachol-induced Ca2+ release through IP3Rs and RyRs. Our data further support an emerging yet perplexing role of APP within a functional molecular network of membrane and cytoplasmic proteins implicated in Ca2+ signaling.
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Li, Wei, Xiang Gao, Junle Ren, Ting An, and Yan Liu. "High Expression and Purification of Amino-Terminal Fragment of Human Amyloid Precursor Protein inPichia pastorisand Partial Analysis of Its Properties." BioMed Research International 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/836429.
Abstract:
The cleaved amino-terminal fragment of human amyloid precursor protein (N-APP) binds death receptor 6 (DR6) and triggers a caspase-dependent self-destruction process, which was suggested to contribute to Alzheimer’s disease. To investigate the N-APP-DR6-induced degeneration pathway at the molecular level, obtaining abundant and purified N-APP is fundamental and critical. The recombinant N-APP has been produced in mammalian expression system. However, the cost and yield disadvantages of mammalian expression system make it less ideal for protein mass production. Here, we successfully expressed and purified recombinant N-terminal 18-285 amino acid residues of human amyloid precursor protein from the methylotrophic yeastPichia pastoriswith a high yield of 50 mg/L. Flow cytometry indicated the purified N-APP-induced obvious apoptosis of human neuroblastoma SHEP cells.
50
Bergman, Anna, Hanna Laudon, Bengt Winblad, Johan Lundkvist, and Jan Näslund. "The Extreme C Terminus of Presenilin 1 Is Essential for γ-Secretase Complex Assembly and Activity." Journal of Biological Chemistry 279, no. 44 (August 20, 2004): 45564–72. http://dx.doi.org/10.1074/jbc.m407717200.
Abstract:
The γ-secretase complex catalyzes the cleavage of the amyloid precursor protein in its transmembrane domain resulting in the formation of the amyloid β-peptide and the cytoplasmic APP intracellular domain. The active γ-secretase complex is composed of at least four subunits: presenilin (PS), nicastrin, Aph-1, and Pen-2, where the presence of all components is critically required for γ-cleavage to occur. The PS proteins are themselves subjected to endoproteolytic cleavage resulting in the generation of an N-terminal and a C-terminal fragment that remain stably associated as a heterodimer. Here we investigated the effects of modifications on the C terminus of PS1 on PS1 endoproteolysis, γ-secretase complex assembly, and activity in cells devoid of endogenous PS. We report that certain mutations and, in particular, deletions of the PS1 C terminus decrease γ-secretase activity, PS1 endoproteolysis, and γ-secretase complex formation. We demonstrate that the N- and C-terminal PS1 fragments can associate with each other in mutants having C-terminal truncations that cause loss of interaction with nicastrin and Aph-1. In addition, we show that the C-terminal fragment of PS1 alone can mediate interaction with nicastrin and Aph-1 in PS null cells expressing only the C-terminal fragment of PS1. Taken together, these data suggest that the PS1 N- and C-terminal fragment intermolecular interactions are independent of an association with nicastrin and Aph-1, and that nicastrin and Aph-1 interact with the C-terminal part of PS1 in the absence of an association with full-length PS1 or the N-terminal fragment.