Familial Alzheimer's disease (FAD), caused by mutations in Presenilin (PSEN1/2) and Amyloid Precursor Protein (APP) genes, is associated with an early age at onset (AAO) of symptoms. AAO is ...relatively consistent within families and between carriers of the same mutations, but differs markedly between individuals carrying different mutations. Gaining a mechanistic understanding of why certain mutations manifest several decades earlier than others is extremely important in elucidating the foundations of pathogenesis and AAO. Pathogenic mutations affect the protease (PSEN/γ-secretase) and the substrate (APP) that generate amyloid β (Aβ) peptides. Altered Aβ metabolism has long been associated with AD pathogenesis, with absolute or relative increases in Aβ42 levels most commonly implicated in the disease development. However, analyses addressing the relationships between these Aβ42 increments and AAO are inconsistent. Here, we investigated this central aspect of AD pathophysiology via comprehensive analysis of 25 FAD-linked Aβ profiles. Hypothesis- and data-driven approaches demonstrate linear correlations between mutation-driven alterations in Aβ profiles and AAO. In addition, our studies show that the Aβ (37 + 38 + 40) / (42 + 43) ratio offers predictive value in the assessment of 'unclear' PSEN1 variants. Of note, the analysis of PSEN1 variants presenting additionally with spastic paraparesis, indicates that a different mechanism underlies the aetiology of this distinct clinical phenotype. This study thus delivers valuable assays for fundamental, clinical and genetic research as well as supports therapeutic interventions aimed at shifting Aβ profiles towards shorter Aβ peptides.
γ‐Secretase complexes (GSECs) are multimeric membrane proteases involved in a variety of physiological processes and linked to Alzheimer's disease (AD). Presenilin (PSEN, catalytic subunit), ...Nicastrin (NCT), Presenilin Enhancer 2 (PEN‐2), and Anterior Pharynx Defective 1 (APH1) are the essential subunits of GSECs. Mutations in PSEN and the Amyloid Precursor Protein (APP) cause early‐onset AD. GSECs successively cut APP to generate amyloid‐β (Aβ) peptides of various lengths. AD‐causing mutations destabilize GSEC‐APP/Aβn interactions and thus enhance the production of longer Aβs, which elicit neurotoxic events underlying pathogenesis. Here, we investigated the molecular strategies that anchor GSEC and APP/Aβn during the sequential proteolysis. Our studies reveal that a direct interaction between NCT ectodomain and APPC99 influences the stability of GSEC‐Aβn assemblies and thereby modulates Aβ length. The data suggest a potential link between single‐nucleotide variants in NCSTN and AD risk. Furthermore, our work indicates that an extracellular interface between the protease (NCT, PSEN) and the substrate (APP) represents the target for compounds (GSMs) modulating Aβ length. Our findings may guide future rationale‐based drug discovery efforts.
Synopsis
γ‐Secretase mediated cleavage of APP defines the length of Aβ peptides. Alzheimer's disease causing mutations destabilize γ‐secretase – APP interactions and thus promote the production of longer, amyloidogenic Aβs. Here, we investigated the molecular strategies securing γ‐secretase – APP interactions.
NCT ectodomain establishes a direct, short distance interaction with APP ectodomain.
NCT‐APP interface influences the stability of γ‐secretase – APP interactions and thereby modulates Aβ length.
NCT ectodomain influences the response towards compounds modulating Aβ length.
The data suggest a potential link between single nucleotide variants in NCSTN and AD risk.
A direct interaction between the gamma secretase subunit Nicastrin and APP regulates the stability and processivity of the γ‐secretase/substrate complex to affect Aβ length and Alzheimer disease pathogenicity.
Sequential proteolysis of the amyloid precursor protein (APP) by γ‐secretases generates amyloid‐β (Aβ) peptides and defines the proportion of short‐to‐long Aβ peptides, which is tightly connected to ...Alzheimer's disease (AD) pathogenesis. Here, we study the mechanism that controls substrate processing by γ‐secretases and Aβ peptide length. We found that polar interactions established by the APPC99 ectodomain (ECD), involving but not limited to its juxtamembrane region, restrain both the extent and degree of γ‐secretases processive cleavage by destabilizing enzyme–substrate interactions. We show that increasing hydrophobicity, via mutation or ligand binding, at APPC99‐ECD attenuates substrate‐driven product release and rescues the effects of Alzheimer's disease‐associated pathogenic γ‐secretase and APP variants on Aβ length. In addition, our study reveals that APPC99‐ECD facilitates the paradoxical production of longer Aβs caused by some γ‐secretase inhibitors, which act as high‐affinity competitors of the substrate. These findings assign a pivotal role to the substrate ECD in the sequential proteolysis by γ‐secretases and suggest it as a sweet spot for the potential design of APP‐targeting compounds selectively promoting its processing by these enzymes.
Synopsis
Sequential proteolysis of amyloid precursor protein (APP) by γ‐secretase generates various amyloid‐β (Aβ) peptides, whose length correlates with pathogenicity of Alzheimer's disease (AD)‐associated mutations. Here, the ectodomain of the APP substrate is found to define Aβ length by promoting product release and destabilizing enzyme–substrate interactions.
Polar residues in the APPC99 ectodomain (APPC99‐ECD) drive product release by destabilizing enzyme–substrate interactions.
Increased hydrophobicity in the substrate ECD increases both efficiency and extent of sequential γ‐secretase‐mediated proteolysis of APP and Notch.
γ‐Secretase inhibitors (GSIs) DAPT and semagacestat act as high‐affinity competitors of substrates.
GSI‐mediated displacement of partially digested Aβ peptides, facilitated by the APPC99‐ECD, explains paradoxical increases in longer Aβ peptides.
Mitigation of APPC99‐ECD‐driven product release rescues the increased production of longer Aβ peptides linked to pathogenic variants in γ‐secretase and APP.
How γ‐secretase cleaves and processes the amyloid precursor protein depends on the hydrophobicity of its ectodomain, with implications for disease mechanism and drug discovery.
Alzheimer's disease (AD) pathogenesis has been linked to the accumulation of longer, aggregation‐prone amyloid β (Aβ) peptides in the brain. Γ‐secretases generate Aβ peptides from the amyloid ...precursor protein (APP). Γ‐secretase modulators (GSMs) promote the generation of shorter, less‐amyloidogenic Aβs and have therapeutic potential. However, poorly defined drug–target interactions and mechanisms of action have hampered their therapeutic development. Here, we investigate the interactions between the imidazole‐based GSM and its target γ‐secretase—APP using experimental and in silico approaches. We map the GSM binding site to the enzyme–substrate interface, define a drug‐binding mode that is consistent with functional and structural data, and provide molecular insights into the underlying mechanisms of action. In this respect, our analyses show that occupancy of a γ‐secretase (sub)pocket, mediating binding of the modulator's imidazole moiety, is sufficient to trigger allosteric rearrangements in γ‐secretase as well as stabilize enzyme–substrate interactions. Together, these findings may facilitate the rational design of new modulators of γ‐secretase with improved pharmacological properties.
Synopsis
Modulators of γ‐secretase activity (GSMs) that shift amyloid‐β (Aβ) production towards the shorter non‐amyloidogenic peptides while sparing critical γ‐secretase‐mediated signalling cascades are promising agents in the fight against Alzheimer's disease. Here, insights into the underlying drug‐target interactions and GSM mode of action may help to overcome current limitations to their rational further therapeutic development.
The binding pocket of a potent imidazole‐based GSM (GSM III) maps towards the γ‐secretase‐amyloid precursor protein (APP) (enzyme‐substrate) interface.
The binding mode of GSM III at the γ‐secretase—APP interface reveals a dual mechanism of action, as activator and stabilizer of γ‐secretases.
Occupancy of a sub‐pocket in γ‐secretase is sufficient to allosterically activate γ‐secretase and to stabilize enzyme—substrate interactions.
This dual mode of action enhances the generation of short and non‐toxic Aβ peptides.
Insights into drug‐target interactions and mode of action of an imidazole‐based γ‐secretase modulator may facilitate rational design of next‐generation compounds for treatment of Alzheimer's disease.
The out-of-equilibrium dynamics of quantum systems is one of the most
fascinating problems in physics, with outstanding open questions on
issues such as relaxation to equilibrium. An area of ...particular interest
concerns few-body systems, where quantum and thermal fluctuations are
expected to be especially relevant. In this contribution, we present
numerical results demonstrating the impact of conserved quantities (or
‘charges’) in the outcomes of out-of-equilibrium measurements starting
from realistic equilibrium states on a few-body system implementing the
Dicke model.
Ultracold polar molecules as qudits Sawant, Rahul; Blackmore, Jacob A; Gregory, Philip D ...
New journal of physics,
01/2020, Letnik:
22, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We discuss how the internal structure of ultracold molecules, trapped in the motional ground state of optical tweezers, can be used to implement qudits. We explore the rotational, fine and hyperfine ...structure of 40Ca19F and 87Rb133Cs, which are examples of molecules with 2 and 1 electronic ground states, respectively. In each case we identify a subset of levels within a single rotational manifold suitable to implement a four-level qudit. Quantum gates can be implemented using two-photon microwave transitions via levels in a neighboring rotational manifold. We discuss limitations to the usefulness of molecular qudits, arising from off-resonant excitation and decoherence. As an example, we present a protocol for using a molecular qudit of dimension d = 4 to perform the Deutsch algorithm.
Juvenile myelomonocytic leukemia (JMML) is a rare and severe myelodysplastic and myeloproliferative neoplasm of early childhood initiated by germline or somatic RAS-activating mutations. Genetic ...profiling and whole-exome sequencing of a large JMML cohort (118 and 30 cases, respectively) uncovered additional genetic abnormalities in 56 cases (47%). Somatic events were rare (0.38 events/Mb/case) and restricted to sporadic (49/78; 63%) or neurofibromatosis type 1 (NF1)-associated (8/8; 100%) JMML cases. Multiple concomitant genetic hits targeting the RAS pathway were identified in 13 of 78 cases (17%), disproving the concept of mutually exclusive RAS pathway mutations and defining new pathways activated in JMML involving phosphoinositide 3-kinase (PI3K) and the mTORC2 complex through RAC2 mutation. Furthermore, this study highlights PRC2 loss (26/78; 33% of sporadic JMML cases) that switches the methylation/acetylation status of lysine 27 of histone H3 in JMML cases with altered RAS and PRC2 pathways. Finally, the association between JMML outcome and mutational profile suggests a dose-dependent effect for RAS pathway activation, distinguishing very aggressive JMML rapidly progressing to acute myeloid leukemia.
PDF
