scholarly journals The cellular expression and proteolytic processing of the amyloid precursor protein is independent of TDP-43

2020 ◽  
Vol 40 (4) ◽  
Author(s):  
David A. Hicks ◽  
Alys C. Jones ◽  
Stuart M. Pickering-Brown ◽  
Nigel M. Hooper
Keyword(s):  
Amyloid Precursor Protein ◽  
Amyloid Β ◽  
Proteolytic Processing ◽  
Precursor Protein ◽  
Aβ Peptides ◽  
App Processing ◽  
Cellular Expression ◽  
Aβ Generation ◽  
Human Neuronal Cells ◽  
Inducible Cell Line

Abstract Alzheimer’s disease (AD) is a neurodegenerative condition, of which one of the cardinal pathological hallmarks is the extracellular accumulation of amyloid β (Aβ) peptides. These peptides are generated via proteolysis of the amyloid precursor protein (APP), in a manner dependent on the β-secretase, BACE1 and the multicomponent γ-secretase complex. Recent data also suggest a contributory role in AD of transactive response DNA binding protein 43 (TDP-43). There is little insight into a possible mechanism linking TDP-43 and APP processing. To this end, we used cultured human neuronal cells to investigate the ability of TDP-43 to interact with APP and modulate its proteolytic processing. Immunocytochemistry showed TDP-43 to be spatially segregated from both the extranuclear APP holoprotein and its nuclear C-terminal fragment. The latter (APP intracellular domain) was shown to predominantly localise to nucleoli, from which TDP-43 was excluded. Furthermore, neither overexpression of each of the APP isoforms nor siRNA-mediated knockdown of APP had any effect on TDP-43 expression. Doxycycline-stimulated overexpression of TDP-43 was explored in an inducible cell line. Overexpression of TDP-43 had no effect on expression of the APP holoprotein, nor any of the key proteins involved in its proteolysis. Furthermore, increased TDP-43 expression had no effect on BACE1 enzymatic activity or immunoreactivity of Aβ1-40, Aβ1-42 or the Aβ1-40:Aβ1-42 ratio. Also, siRNA-mediated knockdown of TDP-43 had no effect on BACE1 immunoreactivity. Taken together, these data indicate that TDP-43 function and/or dysfunction in AD is likely independent from dysregulation of APP expression and proteolytic processing and Aβ generation.

scholarly journals The intact Kunitz domain protects the amyloid precursor protein from being processed by matriptase-2

2016 ◽  
Vol 397 (8) ◽  
pp. 777-790 ◽  
Author(s):  
Anna-Madeleine Beckmann ◽  
Konstantin Glebov ◽  
Jochen Walter ◽  
Olaf Merkel ◽  
Martin Mangold ◽  
...  
Keyword(s):  
Amyloid Precursor Protein ◽  
Iron Homeostasis ◽  
Amyloid Β ◽  
Proteolytic Processing ◽  
Precursor Protein ◽  
App Processing ◽  
Kunitz Domain ◽  
Membrane Bound ◽  
Aβ Generation ◽  
Slow Binding Inhibitor

Abstract Proteolytic processing of the amyloid precursor protein (APP) leads to amyloid-β (Aβ) peptides. So far, the mechanism of APP processing is insufficiently characterized at the molecular level. Whereas the knowledge of Aβ generation by several proteases has been expanded, the contribution of the Kunitz-type protease inhibitor domain (KPI) present in two major APP isoforms to the complex proteolytic processing of APP is poorly understood. In this study, we have identified KPI-containing APP as a very potent, slow-binding inhibitor for the membrane-bound proteolytic regulator of iron homeostasis matriptase-2 by forming stable complexes with its target protease in HEK cells. Inhibition and complex formation depend on the intact KPI domain. By inhibiting matriptase-2, KPI-containing APP is protected from matriptase-2-mediated proteolysis within the Aβ region, thus preventing the generation of N-terminally truncated Aβ.

scholarly journals Effects of the amyloid precursor protein Glu693→Gln ‘Dutch’ mutation on the production and stability of amyloid β-protein

1999 ◽  
Vol 340 (3) ◽  
pp. 703-709 ◽  
Author(s):  
Deborah J. WATSON ◽  
Dennis J. SELKOE ◽  
David B. TEPLOW
Keyword(s):  
Amyloid Precursor Protein ◽  
Disease Process ◽  
Amyloid Β ◽  
Cerebral Haemorrhage ◽  
Proteolytic Processing ◽  
Precursor Protein ◽  
Amyloid Β Protein ◽  
Aβ Peptides ◽  
Β Protein ◽  
Dutch Mutation

Hereditary cerebral haemorrhage with amyloidosis, Dutch type (HCHWA-D), is a cerebral amyloidosis characterized by prominent vascular deposits and fatal haemorrhages. The disorder is caused by a point mutation in codon 693 of the gene encoding the amyloid precursor protein (APP), resulting in a Glu → Gln amino acid substitution at position 22 of the amyloid β-protein (Aβ) region. The pathogenetic mechanisms of HCHWA-D are unknown but could involve alterations in the proteolytic processing of APP and in amyloid fibril formation. We examined Aβ production and stability by using cultured human embryonic kidney 293 cells stably expressing wild-type or ‘Dutch’ APP. Radiosequencing and quantitative immunoprecipitation experiments showed that cells expressing Dutch APP secreted increased quantities of Aβ peptides beginning at Asp1, and of truncated peptides beginning at Val18 and Phe19. The ratio of levels of 4 kDa (Aβ) to 3 kDa (p3) peptides remained constant due to co-ordinate decreases in other peptide species. Novel truncated or elongated peptides were not observed. Pulse-chase experiments showed that the Dutch mutation did not affect the stability of the Aβ or p3 populations. These results are consistent with a disease process in which the Dutch mutation results in the production of Aβ peptides with enhanced propensities for fibrillogenesis, leading to accelerated vascular deposition and disease.

scholarly journals Distinct anterograde trafficking pathways of BACE1 and amyloid precursor protein from the TGN and the regulation of amyloid-β production

2020 ◽  
Vol 31 (1) ◽  
pp. 27-44 ◽  
Author(s):  
Jing Zhi A. Tan ◽  
Lou Fourriere ◽  
Jingqi Wang ◽  
Franck Perez ◽  
Gaelle Boncompain ◽  
...  
Keyword(s):  
Amyloid Precursor Protein ◽  
Secretory Pathway ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Primary Neurons ◽  
App Processing

The anterograde trafficking of BACE1 and the potential processing of amyloid precursor protein along the secretory pathway remain poorly defined. Our findings reveal that Golgi exit of BACE1 and APP in primary neurons is tightly regulated, resulting in their segregation along different transport routes, which limits APP processing.

The Absence of Myelin Basic Protein Reduces Non-Amyloidogenic Processing of Amyloid Precursor Protein

2021 ◽  
Vol 18 ◽  
Author(s):  
Chika Seiwa ◽  
Ichiro Sugiyama ◽  
Makoto Sugawa ◽  
Hiroaki Murase ◽  
Chiaki Kudoh ◽  
...  
Keyword(s):  
Amyloid Precursor Protein ◽  
Myelin Basic Protein ◽  
Basic Protein ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Amyloid Β Protein ◽  
Pathological Feature ◽  
Novel Therapy ◽  
App Processing ◽  
App Metabolism

Background: The accumulation of amyloid β-protein (Aβ) in the brain is a pathological feature of Alzheimer’s disease (AD). Aβ peptides originate from amyloid precursor protein (APP). APP can be proteolytically cleaved through amyloidogenic or non-amyloidogenic pathways. The molecular effects on APP metabolism / processing may be influenced by myelin and the breakdown of myelin basic protein (MBP) in AD patients and mouse models of AD pathology. Methods: We directly tested whether MBP can alter influence APP processing in MBP-/- mice, known as Shiverer (shi/shi) mice, in which no functional MBP is produced due to gene breakage from the middle of MBP exon II. Results: A significant reduction of the cerebral sAPPα level in Shiverer (shi/shi) mice was found, although the levels of both total APP and sAPPβ remain unchanged. The reduction of sAPPα was considered to be due to the changes in the expression levels of a disintegrin and metalloproteinase-9 (ADAM9) catalysis and non-amyloid genic processing of APP in the absence of MBP because it binds to ADAM9. MBP -/- mice exhibited increased Aβ oligomer production. Conclusion: Together, these findings suggest that in the absence of MBP, there is a marked reduction of non-amyloidogenic APP processing to sAPPα, and targeting myelin of oligodendrocytes may be a novel therapy for the prevention and treatment of AD.

scholarly journals Transcriptional Regulation of BACE1, the β-Amyloid Precursor Protein β-Secretase, by Sp1

2004 ◽  
Vol 24 (2) ◽  
pp. 865-874 ◽  
Author(s):  
Michelle A. Christensen ◽  
Weihui Zhou ◽  
Hong Qing ◽  
Anna Lehman ◽  
Sjaak Philipsen ◽  
...  
Keyword(s):  
Gene Expression ◽  
Transcription Factor ◽  
Amyloid Precursor Protein ◽  
Proteolytic Processing ◽  
Precursor Protein ◽  
Transcriptional Level ◽  
Response Element ◽  
App Processing ◽  
Transcription Factor Sp1 ◽  
Β Amyloid

ABSTRACT Proteolytic processing of the β-amyloid precursor protein (APP) at the β site is essential to generate Aβ. BACE1, the major β-secretase involved in cleaving APP, has been identified as a type 1 membrane-associated aspartyl protease. We have cloned a 2.1-kb fragment upstream of the human BACE1 gene and identified key regions necessary for promoter activity. BACE1 gene expression is controlled by a TATA-less promoter. The region of bp −619 to +46 is the minimal promoter to control the transcription of the BACE1 gene. Several putative cis-acting elements, such as a GC box, HSF-1, a PU box, AP1, AP2, and lymphokine response element, are found in the 5′ flanking region of the BACE1 gene. Transcriptional activation and gel shift assays demonstrated that the BACE1 promoter contains a functional Sp1 response element, and overexpression of the transcription factor Sp1 potentiates BACE gene expression and APP processing to generate Aβ. Furthermore, Sp1 knockout reduced BACE1 expression. These results suggest that BACE1 gene expression is tightly regulated at the transcriptional level and that the transcription factor Sp1 plays an important role in regulation of BACE1 to process APP generating Aβ in Alzheimer's disease.

scholarly journals A novel mechanism for the regulation of amyloid precursor protein metabolism

2002 ◽  
Vol 158 (1) ◽  
pp. 79-89 ◽  
Author(s):  
Qi Chen ◽  
Hideo Kimura ◽  
David Schubert
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Cell Adhesion ◽  
Amyloid Precursor Protein ◽  
Proteasome Inhibitors ◽  
Amyloid Β ◽  
Cellular Adhesion ◽  
Precursor Protein ◽  
Amyloid Β Peptide ◽  
App Processing

Modifier of cell adhesion protein (MOCA; previously called presenilin [PS] binding protein) is a DOCK180-related molecule, which interacts with PS1 and PS2, is localized to brain areas involved in Alzheimer's disease (AD) pathology, and is lost from the soluble fraction of sporadic Alzheimer's disease (AD) brains. Because PS1 has been associated with γ-secretase activity, MOCA may be involved in the regulation of β-amyloid precursor protein (APP) processing. Here we show that the expression of MOCA decreases both APP and amyloid β-peptide secretion and lowers the rate of cell-substratum adhesion. In contrast, MOCA does not lower the secretion of amyloid precursor-like protein (APLP) or several additional type 1 membrane proteins. The phenotypic changes caused by MOCA are due to an acceleration in the rate of intracellular APP degradation. The effect of MOCA expression on the secretion of APP and cellular adhesion is reversed by proteasome inhibitors, suggesting that MOCA directs nascent APP to proteasomes for destruction. It is concluded that MOCA plays a major role in APP metabolism and that the effect of MOCA on APP secretion and cell adhesion is a downstream consequence of MOCA-directed APP catabolism. This is a new mechanism by which the expression of APP is regulated.

scholarly journals Contribution of the endosomal-lysosomal and proteasomal systems in Amyloid-β Precursor Protein derived fragments processing

2018 ◽  
Author(s):  
Caroline Evrard ◽  
Pascal Kienlen-Campard ◽  
Rémi Opsomer ◽  
Bernadette Tasiaux ◽  
Jean-Noël Octave ◽  
...  
Keyword(s):  
Amyloid Β ◽  
Full Length ◽  
Precursor Protein ◽  
Degradation Pathways ◽  
Aβ Peptides ◽  
Hek 293 ◽  
App Processing ◽  
Amyloid Deposits ◽  
App Metabolism ◽  
Carboxy Terminal

AbstractAβ peptides, the major components of amyloid deposits of Alzheimer’s disease, are released following sequential cleavages by secretases of its precursor named the amyloid precursor protein (APP). In addition to secretases, degradation pathways, in particular the endosomal/lysosomal and proteasomal systems have also been reported to contribute to APP processing. However, the respective role of each of these pathways towards APP metabolism remains to be established. To address this, we used HEK 293 cells and primary neurons expressing full-length APPWT or the β-secretase-derived C99 fragments (β-CTFs) in which degradation pathways were selectively blocked using pharmacological drugs. APP metabolites, including carboxy-terminal fragments (CTFs), soluble APP (sAPP) and Aβ peptides were studied. In this report, we show that APP-CTFs produced from endogenous or overexpressed full-length APP are mainly processed by γ-secretase and the endosomal/lysosomal pathway, while in sharp contrast, overexpressed C99 alone is mainly degraded by the proteasome and to a lesser extent by γ-secretase.

scholarly journals Fyn Tyrosine Kinase Elicits Amyloid Precursor Protein Tyr682 Phosphorylation in Neurons from Alzheimer’s Disease Patients

Cells ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 1807
Author(s):  
Filomena Iannuzzi ◽  
Rossana Sirabella ◽  
Nadia Canu ◽  
Thorsten J. Maier ◽  
Lucio Annunziato ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Tyrosine Kinase ◽  
Amyloid Precursor Protein ◽  
Neurodegenerative Disorder ◽  
Amyloid Β ◽  
Adaptor Protein ◽  
Precursor Protein ◽  
App Processing ◽  
Fyn Tyrosine Kinase

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder with a few early detection strategies. We previously proposed the amyloid precursor protein (APP) tyrosine 682 (Tyr682) residue as a valuable target for the development of new innovative pharmacologic or diagnostic interventions in AD. Indeed, when APP is phosphorylated at Tyr682, it is forced into acidic neuronal compartments where it is processed to generate neurotoxic amyloid β peptides. Of interest, Fyn tyrosine kinase (TK) interaction with APP Tyr682 residue increases in AD neurons. Here we proved that when Fyn TK was overexpressed it elicited APP Tyr682 phosphorylation in neurons from healthy donors and promoted the amyloidogenic APP processing with Aβ peptides accumulation and neuronal death. Phosphorylation of APP at Tyr (pAPP-Tyr) increased in neurons of AD patients and AD neurons that exhibited high pAPP-Tyr also had higher Fyn TK activity. Fyn TK inhibition abolished the pAPP-Tyr and reduced Aβ42 secretion in AD neurons. In addition, the multidomain adaptor protein Fe65 controlled the Fyn-mediated pAPP-Tyr, warranting the possibility of targeting the Fe65-APP-Fyn pathway to develop innovative strategies in AD. Altogether, these results strongly emphasize the relevance of focusing on pAPP Tyr682 either for diagnostic purposes, as an early biomarker of the disease, or for pharmacological targeting, using Fyn TKI.

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