Biology subjects

Chavez-Gutierrez, L.

Publications and source records attributed to Chavez-Gutierrez, L..

6 recordsLinked to original sources

bioRxiv2024

Unbiased data-driven analysis of five amyloid-beta peptides for biomarker investigations in familial Alzheimer's disease

Structured AbstractO_ST_ABSINTRODUCTIONC_ST_ABSChanges to the relative abundance of amyloid-beta (A{beta}) peptides are hallmarks of Alzheimers disease (AD). iPSC-derived neurons offer a physiological model of A{beta} production. We employed unbiased, data-driven analyses to investigate combinations of A{beta} peptides as AD biomarkers and the relative contribution of peptides to AD pathogenesis. METHODSWe measured A{beta}37, A{beta}38, A{beta}40, A{beta}42 and A{beta}43 in ten iPSC-neuronal cultures from PSEN1 mutation carriers. We combined these data with published cell model data and used linear weighted combinations to 1) distinguish AD from controls, and 2) predict age-at-onset for PSEN1 mutations. RESULTSData-driven approaches distinguished A{beta}42 and A{beta}43 from shorter peptides, providing unbiased evidence for their contribution to disease. Weighted linear combinations of A{beta} peptides outperform A{beta}42/40 and provide insights into relative peptide contribution as biomarkers; the optimal ratio for all data is represented as (21 {middle dot} A{beta}37 + 10 {middle dot} A{beta}38 + 69 {middle dot} A{beta}40)/(94 {middle dot} A{beta}42 + 6 {middle dot} A{beta}43). DISCUSSIONThe algorithm discovered herein can be further refined to improve biomarkers for AD.

neuroscience↗

bioRxiv2024

Spectrum of gamma-Secretase dysfunction as a unifying predictor of ADAD age at onset across PSEN1, PSEN2 and APP causal genes

Autosomal Dominant Alzheimers Disease (ADAD), caused by mutations in Presenilins (PSEN1/2) and Amyloid Precursor Protein (APP) genes, typically manifests before age 65. Age at symptom onset (AAO) is relatively consistent among carriers of the same PSEN1 mutation, but more variable for PSEN2 and APP variants, with these mutations associated with later AAOs than PSEN1. Understanding this clinical variability is crucial for developing predictive models and tailored interventions in ADAD. Biochemical in vitro assessment of {gamma}-secretase function is valuable in evaluating PSEN1 variant pathogenicity, disease onset and progression. Here, we examined A{beta} profiles relationships to AAO across causal genes. Our analysis showed linear correlations between mutation-induced shifts in A{beta} profiles and AAO for PSEN2 and APP mutations. Integration with PSEN1 data revealed parallel but shifted correlations, indicating a common pathogenic mechanism with gene-specific onset timing shifts. Our data support a unified model of ADAD pathogenesis wherein {gamma}-secretase dysfunction and shifts in A{beta} profiles define disease onset. This biochemical analysis of ADAD causality and established quantitative relationships deepen our understanding of ADAD pathogenesis, offering potential for predictive AAO modelling with implications for clinical practice, genetic research and development of therapeutic strategies modulating {gamma}-secretase across ADAD forms and potentially more broadly in AD. SummaryWe examined the relationships between (full) A{beta} peptide profiles and age at symptom onset (AAO) across all Alzheimers disease causal genes. Our findings establish a quantitative framework for mutations pathogenicity assessment and AAO prediction; with implications for clinical practice, genetic counselling, fundamental and translational research.

neuroscience↗

bioRxiv2024

Resistance to PSEN1-selective γ-secretase inhibitors in T-cell acute lymphoblastic leukemia

PSEN1-selective gamma-secretase inhibitors (GSI), such as MRK-560, are a potential option for the treatment of T-cell acute lymphoblastic leukemia (T-ALL) with NOTCH1 activating mutations, as these show less toxicity compared to broad-spectrum GSIs. However, an important challenge with targeted therapies for cancer treatment is the rapid development of drug resistance. We therefore investigated if PSEN1 mutations could confer resistance to MRK-560 in T-ALL. We performed a CRISPR-mediated mutagenesis screen in a T-ALL cell line to identify mutations leading to MRK-560 resistance and confirmed these findings in additional cell lines. We identified 3 types of resistance mutations. Mutations at the enzyme-drug interface directly disrupt the interaction of MRK-560 with PSEN1. Mutations at the enzyme-substrate interface cause a shift in relative binding affinities towards drug and/or substrate. The third resistance mechanism involves a mutation at the enzyme-substrate interface that hinders the entrance of MRK-560 to the binding pocket. These findings contribute to the understanding of the PSEN1-selectivity of MRK-560 and can help to design other PSEN1-selective GSIs to overcome resistance in cancer therapy.

cancer biology↗

bioRxiv2023

APP substrate ectodomain defines A beta length by restraining gamma-secretase processivity and facilitating product release

Sequential proteolysis of the amyloid precursor protein (APP) by {gamma}-secretases (GSECs) generates amyloid-{beta} (A{beta}) and defines the proportion of short-to-long A{beta} peptides, which is tightly connected to Alzheimers disease (AD) pathogenesis. Here, we study the mechanism controlling substrate processing by GSECs and defining product 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 GSEC processive cleavage by destabilizing enzyme-substrate (E-S) interactions. We show that increasing hydrophobicity at APPC99-ECD - due to mutation or ligand binding - attenuates this substrate-driven product release mechanism, and rescues the effects that AD pathogenic variants exert on A{beta} profiles. In addition, our study reveals that APPC99-ECD facilitates the paradoxical production of longer A{beta}s caused by some GSEC inhibitors that act as high-affinity competitors to the substrate. These findings assign a pivotal role to the substrate ECD in the sequential proteolysis by GSEC and suggest it as a sweet spot for the potential design of APP targeting compounds selectively promoting its processing by GSEC.

biochemistry↗

bioRxiv2023

Structure of γ-secretase (PSEN1/APH-1B) in complex with Aβ46 provides insights into amyloid-β processing and modulation by the APH-1B isoform

Deposition of amyloid-{beta} (A{beta}) peptides in the brain is a hallmark of Alzheimers disease. A{beta}s are generated through sequential proteolysis of the amyloid precursor protein by the {gamma}-secretase complexes (GSECs). A{beta} peptide length, which is modulated by the Presenilin (PSEN) and APH-1 subunits of GSEC, is critical for Alzheimers pathogenesis. Despite high relevance, mechanistic understanding of the proteolysis of A{beta}, and its modulation by APH-1, remain incomplete. Here, we report cryo-EM structures of human GSEC (PSEN1/APH-1B) reconstituted into lipid nanodiscs in apo form and in complex with the intermediate A{beta}46 substrate. We found a divergent APH-1 loop to be involved with PSEN1 in substrate-binding-induced concerted rearrangements. Upstream the catalytic site, A{beta}46 structure is similar to the endopeptidase substrates and is stabilised by polar interactions including a previously unseen interaction with PSEN1 loop1. The hybrid {beta}-sheet was not observed downstream the catalytic site.

molecular biology↗

bioRxiv2023

Alzheimer's disease linked Aβ42 exerts product feedback inhibition on γsecretase impairing downstream cell signaling

Amyloid {beta} (A{beta}) peptides accumulating in the brain are proposed to trigger Alzheimers disease (AD). However, molecular cascades underlying their toxicity are poorly defined. Here, we explored a novel hypothesis for A{beta}42 toxicity that arises from its proven affinity for {gamma}-secretases. We hypothesized that the reported increases in A{beta}42, particularly in the endolysosomal compartment, promote the establishment of a product feedback inhibitory mechanism on {gamma}-secretases, and thereby impair downstream signaling events. We show that human A{beta}42 peptides, but neither murine A{beta}42 nor human A{beta}17-42 (p3), inhibit {gamma}-secretases and trigger accumulation of unprocessed substrates in neurons, including C-terminal fragments (CTFs) of APP, p75 and pan-cadherin. Moreover, A{beta}42 treatment dysregulated cellular homeostasis, as shown by the induction of p75-dependent neuronal death in two distinct cellular systems. Our findings raise the possibility that pathological elevations in A{beta}42 contribute to cellular toxicity via the {gamma}-secretase inhibition, and provide a novel conceptual framework to address A{beta} toxicity in the context of {gamma}-secretase-dependent homeostatic signaling.

biochemistry↗