Processive proteolysis by γ-secretase and the mechanism of Alzheimer’s disease

2012 ◽  
Vol 393 (9) ◽  
pp. 899-905 ◽  
Author(s):  
Michael S. Wolfe
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Transmembrane Domain ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
Amyloid Β Protein ◽  
Loss Of Function ◽  
Gain Of Function ◽  
C Terminus ◽  
Secretase Activity

Abstract γ-Secretase is a membrane-embedded protease complex with presenilin as the catalytic component. Cleavage within the transmembrane domain of the amyloid β-protein precursor (APP) by γ-secretase produces the C-terminus of the amyloid β-peptide (Aβ), a proteolytic product prone to aggregation and strongly linked to Alzheimer’s disease (AD). Presenilin mutations are associated with early-onset AD, but their pathogenic mechanisms are unclear. One hypothesis is that these mutations cause AD through a toxic gain of function, changing γ-secretase activity to increase the proportion of 42-residue Aβ over the more soluble 40-residue form. A competing hypothesis is that the mutations cause AD through a loss of function, by reducing γ-secretase activity. However, γ-secretase apparently has two types of activities, an endoproteolytic function that first cuts APP to generate a 48/49-residue form of Aβ, and a carboxypeptidase activity that processively trims these longer Aβ intermediates approximately every three residues to form shorter, secreted forms. Recent studies suggest a resolution of the gain-of-function vs. loss-of-function debate: presenilin mutations may increase the proportion of longer, more aggregation-prone Aβ by specifically decreasing the trimming activity of γ-secretase. That is, the reduction of this particular proteolytic function of presenilin, not its endoproteolytic activity, may lead to the neurotoxic gain of function.

scholarly journals A Super-Resolved View of the Alzheimer’s Disease-Related Amyloidogenic Pathway in Hippocampal Neurons

2021 ◽  
pp. 1-20
Author(s):  
Yang Yu ◽  
Yang Gao ◽  
Bengt Winblad ◽  
Lars Tjernberg ◽  
Sophia Schedin Weiss
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Hippocampal Neurons ◽  
Three Dimensional ◽  
Amyloid Β ◽  
Stimulated Emission ◽  
Amyloid Β Peptide ◽  
Primary Neurons ◽  
Amyloid Β Protein ◽  
Early Endosomes

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 (Aβ 42), which is a key player in Alzheimer’s disease. Objective: Our aim was to clarify the subcellular locations of the amyloidogenic AβPP processing in primary neurons, including the intracellular pools of the immediate substrate, AβPP C-terminal fragment (APP-CTF) and the product (Aβ 42). 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 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, where we were able to show that the liberated N- and C-terminal fragments were sorted into distinct vesicles budding from the early endosomes in soma. Lack of colocalization of Aβ 42 and APP-CTF in soma suggested that γ-secretase cleavage occurs in neurites. Indeed, APP-CTF was, in line with Aβ 42 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 Aβ 42 were localized in different compartments. Conclusion: These findings provide critical super-resolved insight into amyloidogenic AβPP processing in primary neurons.

Selective Secretase Targeting for Alzheimer’s Disease Therapy

2021 ◽  
pp. 1-17
Author(s):  
Alvaro Miranda ◽  
Enrique Montiel ◽  
Henning Ulrich ◽  
Cristian Paz
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Β ◽  
Amyloid Plaques ◽  
Neuroprotective Activity ◽  
Amyloid Β Protein ◽  
Secretase Activity ◽  
Membrane Bound ◽  
Aβ Production ◽  
Bace 1

Alzheimer’s disease (AD) is associated with marked atrophy of the cerebral cortex and accumulation of amyloid plaques and neurofibrillary tangles. Amyloid plaques are formed by oligomers of amyloid-β (Aβ) in the brain, with a length of 42 and 40 amino acids. α-secretase cleaves amyloid-β protein precursor (AβPP) producing the membrane-bound fragment CTFα and the soluble fragment sAβPPα with neuroprotective activity; β-secretase produces membrane-bound fragment CTFβ and a soluble fragment sAβPPβ. After α-secretase cleavage of AβPP, γ-secretase cleaves CTFα to produce the cytoplasmic fragment AICD and P3 in the non-amyloidogenic pathway. CTFβ is cleaved by γ-secretase producing AICD as well as Aβ in amyloidogenic pathways. In the last years, the study of natural products and synthetic compounds, such as α-secretase activity enhancers, β-secretase inhibitors (BACE-1), and γ-secretase activity modulators, have been the focus of pharmaceuticals and researchers. Drugs were improved regarding solubility, blood-brain barrier penetration, selectivity, and potency decreasing Aβ42. In this regard, BACE-1 inhibitors, such as Atabecestat, NB-360, Umibecestat, PF-06751979, Verubecestat, LY2886721, Lanabecestat, LY2811376, and Elenbecestat, were submitted to phase I-III clinical trials. However, inhibition of Aβ production did not recover cognitive functions or reverse the disease. Novel strategies are being developed, aiming at a partial reduction of Aβ production, such as the development of γ-secretase modulators or α-secretase enhancers. Such therapeutic tools shall focus on slowing down or minimizing the progression of neuronal damage. Here, we summarize structures and the activities of the latest compounds designed for AD treatment, with remarkable in vitro, in vivo, and clinical phase activities.

scholarly journals Human Albumin Impairs Amyloid β-peptide Fibrillation Through its C-terminus: From docking Modeling to Protection Against Neurotoxicity in Alzheimer's disease

2019 ◽  
Vol 17 ◽  
pp. 963-971 ◽  
Author(s):  
Pol Picón-Pagès ◽  
Jaume Bonet ◽  
Javier García-García ◽  
Joan Garcia-Buendia ◽  
Daniela Gutierrez ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Β ◽  
Human Albumin ◽  
Amyloid Β Peptide ◽  
C Terminus

scholarly journals Increased soluble TREM2 in cerebrospinal fluid is associated with reduced cognitive and clinical decline in Alzheimer’s disease

2019 ◽  
Vol 11 (507) ◽  
pp. eaav6221 ◽  
Author(s):  
Michael Ewers ◽  
Nicolai Franzmeier ◽  
Marc Suárez-Calvet ◽  
Estrella Morenas-Rodriguez ◽  
Miguel Angel Araque Caballero ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Cerebrospinal Fluid ◽  
Amyloid Β ◽  
Elderly Subjects ◽  
Amyloid Β Peptide ◽  
Loss Of Function ◽  
Clinical Progression ◽  
Cognitively Normal ◽  
Soluble Trem2

Loss of function of TREM2, a key receptor selectively expressed by microglia in the brain, contributes to the development of Alzheimer’s disease (AD). We therefore examined whether soluble TREM2 (sTREM2) concentrations in cerebrospinal fluid (CSF) were associated with reduced rates of cognitive decline and clinical progression in subjects with AD or mild cognitive impairment (MCI). We measured sTREM2 in CSF samples from 385 elderly subjects, including cognitively normal controls, individuals with MCI, and subjects with AD dementia (follow-up period: mean, 4 years; range 1.5 to 11.5 years). In subjects with AD defined by evidence of CSF Aβ1–42 (amyloid β-peptide 1 to 42; A+) and CSF p-tau181 (tau phosphorylated on amino acid residue 181; T+), higher sTREM2 concentrations in CSF at baseline were associated with attenuated decline in memory and cognition. When analyzed in clinical subgroups, an association between higher CSF sTREM2 concentrations and subsequent reduced memory decline was consistently observed in individuals with MCI or AD dementia, who were positive for CSF Aβ1–42 and CSF p-tau181 (A+T+). Regarding clinical progression, a higher ratio of CSF sTREM2 to CSF p-tau181 concentrations predicted slower conversion from cognitively normal to symptomatic stages or from MCI to AD dementia in the subjects who were positive for CSF Aβ1–42 and CSF p-tau181. These results suggest that sTREM2 is associated with attenuated cognitive and clinical decline, a finding with important implications for future clinical trials targeting the innate immune response in AD.

The proteins BACE1 and BACE2 and β-secretase activity in normal and Alzheimer's disease brain

2007 ◽  
Vol 35 (3) ◽  
pp. 574-576 ◽  
Author(s):  
J.H. Stockley ◽  
C. O'Neill
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
Protein Levels ◽  
Rate Limiting Step ◽  
Secretase Activity ◽  
Aβ Amyloid ◽  
Ad Alzheimer’S Disease ◽  
And Function

The insidious progression of AD (Alzheimer's disease) is believed to be linked closely to the production, accumulation and aggregation of the ∼4.5 kDa protein fragment called Aβ (amyloid β-peptide). Aβ is produced by sequential cleavage of the amyloid precursor protein by two enzymes referred to as β- and γ-secretase. β-Secretase is of central importance, as it catalyses the rate-limiting step in the production of Aβ and was identified 7 years ago as BACE1 (β-site APP-cleaving enzyme 1). Soon afterwards, its homologue BACE2 was discovered, and both proteins represent a new subclass of the aspartyl protease family. Studies examining the regulation and function of β-secretase in the normal and AD brain are central to the understanding of excessive production of Aβ in AD, and in targeting and normalizing this β-secretase process if it has gone awry in the disease. Several reports indicate this, showing increased β-secretase activity in AD, with recent findings by our group showing changes in β-secretase enzyme kinetics in AD brain caused by an increased Vmax. This article gives a brief review of studies which have examined BACE1 protein levels and β-secretase activity in control and AD brain, considering further the expression of BACE2 in the human brain.

scholarly journals Structural Studies Providing Insights into Production and Conformational Behavior of Amyloid-β Peptide Associated with Alzheimer’s Disease Development

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2897
Author(s):  
Anatoly S. Urban ◽  
Konstantin V. Pavlov ◽  
Anna V. Kamynina ◽  
Ivan S. Okhrimenko ◽  
Alexander S. Arseniev ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Molecular Mechanisms ◽  
Transmembrane Domain ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Conformational Behavior ◽  
Amyloid Β Peptide ◽  
Structural Studies ◽  
Aβ Production

Alzheimer’s disease is the most common type of neurodegenerative disease in the world. Genetic evidence strongly suggests that aberrant generation, aggregation, and/or clearance of neurotoxic amyloid-β peptides (Aβ) triggers the disease. Aβ accumulates at the points of contact of neurons in ordered cords and fibrils, forming the so-called senile plaques. Aβ isoforms of different lengths are found in healthy human brains regardless of age and appear to play a role in signaling pathways in the brain and to have neuroprotective properties at low concentrations. In recent years, different substances have been developed targeting Aβ production, aggregation, interaction with other molecules, and clearance, including peptide-based drugs. Aβ is a product of sequential cleavage of the membrane glycoprotein APP (amyloid precursor protein) by β- and γ-secretases. A number of familial mutations causing an early onset of the disease have been identified in the APP, especially in its transmembrane domain. The mutations are reported to influence the production, oligomerization, and conformational behavior of Aβ peptides. This review highlights the results of structural studies of the main proteins involved in Alzheimer’s disease pathogenesis and the molecular mechanisms by which perspective therapeutic substances can affect Aβ production and nucleation.

Mutations in the Amyloid-β Protein Precursor Reduce Mitochondrial Function and Alter Gene Expression Independent of 42-Residue Amyloid-β Peptide

2021 ◽  
pp. 1-11
Author(s):  
Chad A. Pope ◽  
Heather M. Wilkins ◽  
Russell H. Swerdlow ◽  
Michael S. Wolfe
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Mitochondrial Function ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
Amyloid Β Protein ◽  
Human Neuroblastoma ◽  
Altered Expression ◽  
Protein Precursor ◽  
Β Protein

Background: Dominant missense mutations in the amyloid-β protein precursor (AβPP) cause early-onset familial Alzheimer’s disease (FAD) and are associated with changes in the production or properties of the amyloid-β peptide (Aβ), particularly of the 42-residue variant (Aβ 42) that deposits in the Alzheimer’s disease (AD) brain. Recent findings, however, show that FAD mutations in AβPP also lead to increased production of longer Aβ variants of 45–49 residues in length. Objective: We aimed to test neurotoxicity of Aβ 42 vis-á-vis longer variants, focusing specifically on mitochondrial function, as dysfunctional mitochondria are implicated in the pathogenesis of AD. Methods: We generated SH-SY5Y human neuroblastoma cells stably expressing AβPP mutations that lead to increased production of long Aβ peptides with or without Aβ 42. These AβPP-expressing cells were tested for oxygen consumption rates (OCR) under different conditions designed to interrogate mitochondrial function. These cell lines were also examined for expression of genes important for mitochondrial or neuronal structure and function. Results: The mutant AβPP-expressing cells showed decreased basal OCRs as well as decreased OCRs associated with mitochondrial ATP production, even more so in the absence of Aβ 42 production. Moreover, mutant AβPP-expressing cells producing longer forms of Aβ displayed altered expression of certain mitochondrial- and neuronal-associated genes, whether or not Aβ 42 was produced. Conclusion: These findings suggest that mutant AβPP can cause mitochondrial dysfunction that is associated with long Aβ but not with Aβ 42.

A Novel Cell-based β-secretase Enzymatic Assay for Alzheimer’s Disease

2019 ◽  
Vol 16 (2) ◽  
pp. 128-134
Author(s):  
Bruno De Araujo Herculano ◽  
Zhe Wang ◽  
Weihong Song
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Culture Media ◽  
Amyloid Β ◽  
Chimeric Protein ◽  
Enzymatic Assay ◽  
Amyloid Β Protein ◽  
Reporter System ◽  
Physiological Conditions ◽  
Secretase Activity

Background: Deposition of the amyloid β protein (Aβ) into neuritic plaques is the neuropathological hallmark of Alzheimer’s Disease (AD). Aβ is generated through the cleavage of the Amyloid Precursor Protein (APP) by β-secretase and γ-secretase. Currently, the evaluation of APP cleavage by β-secretase in experimental settings has largely depended on models that do not replicate the physiological conditions of this process. Objective: To establish a novel live cell-based β-secretase enzymatic assay utilizing a novel chimeric protein that incorporates the natural sequence of APP and more closely replicates its cleavage by β-secretase under physiological conditions. Methods: We have developed a chimeric protein construct, ASGβ, incorporating the β-site cleavage sequence of APP targeted by β-secretase and its intracellular trafficking signal into a Phosphatase-eGFP secreted reporter system. Upon cleavage by β-secretase, ASGβ releases a phosphatase-containing portion that can be measured in the culture medium, and an intracellular fraction that can be detected through Western Blot. Subsequently, we have generated a cell line stably expressing ASGβ that can be utilized to assay β-secretase in real time. Results: ASGβ is specifically targeted by β-secretase, being cleaved exclusively at the site responsible for the generation of Aβ. Dosage response to β-secretase inhibitors shows that β-secretase activity can be positively correlated to phosphatase activity in culture media. Conclusion: Our findings suggest this system could be a high-throughput tool to screen compounds that aim to modulate β-secretase activity and Aβ production under physiological conditions, as well as evaluating factors that regulate this cleavage.

scholarly journals The Extreme C Terminus of Presenilin 1 Is Essential for γ-Secretase Complex Assembly and Activity

2004 ◽  
Vol 279 (44) ◽  
pp. 45564-45572 ◽  
Author(s):  
Anna Bergman ◽  
Hanna Laudon ◽  
Bengt Winblad ◽  
Johan Lundkvist ◽  
Jan Näslund
Keyword(s):  
Transmembrane Domain ◽  
Amyloid Β ◽  
Presenilin 1 ◽  
Amyloid Β Peptide ◽  
Terminal Part ◽  
Complex Assembly ◽  
Terminal Fragment ◽  
C Terminus ◽  
Secretase Activity ◽  
Endoproteolytic Cleavage

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.

scholarly journals Probing Mechanisms and Therapeutic Potential of γ-Secretase in Alzheimer’s Disease

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 388
Author(s):  
Michael S. Wolfe
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Therapeutic Potential ◽  
Amyloid Β ◽  
Amyloid Β Protein ◽  
Chemical Probes ◽  
Protein Substrates ◽  
Β Protein ◽  
Secretase Activity

The membrane-embedded γ-secretase complex carries out hydrolysis within the lipid bilayer in proteolyzing nearly 150 different membrane protein substrates. Among these substrates, the amyloid precursor protein (APP) has been the most studied, as generation of aggregation-prone amyloid β-protein (Aβ) is a defining feature of Alzheimer’s disease (AD). Mutations in APP and in presenilin, the catalytic component of γ-secretase, cause familial AD, strong evidence for a pathogenic role of Aβ. Substrate-based chemical probes—synthetic peptides and peptidomimetics—have been critical to unraveling the complexity of γ-secretase, and small drug-like inhibitors and modulators of γ-secretase activity have been essential for exploring the potential of the protease as a therapeutic target for Alzheimer’s disease. Such chemical probes and therapeutic prototypes will be reviewed here, with concluding commentary on the future directions in the study of this biologically important protease complex and the translation of basic findings into therapeutics.

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