Anne Labonté’s research while affiliated with University of Quebec in Montreal and other places

Alzheimer’s disease (AD) is associated with presymptomatic changes in brain morphometry and accumulation of abnormal tau and amyloid-beta pathology. Studying the development of brain changes prior to symptoms onset may lead to early diagnostic biomarkers and a better understanding of AD pathophysiology. AD pathology is thought to arise from a combination of protein accumulation and spreading via neural connections, but how these processes influence brain atrophy progression in the presymptomatic phases remains unclear. Individuals with a family history of AD (FHAD) have an elevated risk of AD, providing an opportunity to study the presymptomatic phase. Here we used structural MRI from three databases (Alzheimer’s Disease Neuroimaging Initiative, Pre-symptomatic Evaluation of Experimental or Novel Treatments for Alzheimer Disease and Montreal Adult Lifespan Study) to map atrophy progression in FHAD and AD and assess the constraining effects of structural connectivity on atrophy progression. Cross-sectional and longitudinal data up to four years were used to perform atrophy progression analysis in FHAD and AD compared to controls. Positron emission tomography radiotracers were also used to quantify the distribution of abnormal tau and amyloid-beta protein isoforms at baseline. We first derived cortical atrophy progression maps using deformation-based morphometry from 153 FHAD, 156 AD, and 116 controls with similar age, education, and sex at baseline. We next examined the spatial relationship between atrophy progression and spatial patterns of tau aggregates and amyloid-beta plaques deposition, structural connectivity, and neurotransmitter receptor and transporter distributions. Our results show that there were similar patterns of atrophy progression in FHAD and AD, notably in the cingulate, temporal, and parietal cortices, with more widespread and severe atrophy in AD. Both tau and amyloid-beta pathology tended to accumulate in regions that were structurally connected in FHAD and AD. The pattern of atrophy and its progression also aligned with existing structural connectivity in FHAD. In AD, our findings suggest that atrophy progression results from pathology propagation that occurred earlier, on a previously intact connectome. Moreover, a relationship was found between serotonin receptor spatial distribution and atrophy progression in AD. The current study demonstrates that regions showing atrophy progression in FHAD and AD present with specific connectivity and cellular characteristics, uncovering some of the mechanisms involved in preclinical and clinical neurodegeneration.

Background In mouse models of amyloidosis, macrophage receptor 1 (MSR1) and neprilysin (NEP) have been shown to interact to reduce amyloid burden in the brain. Objective The purpose of this study is to analyze these two gene products in combination with apolipoproteins and Aβ1-42 in the cerebrospinal fluid (CSF) and plasma of individuals at different stages of Alzheimer’s disease (AD), as well as in autopsied brain samples from ROSMAP (Religious Orders Study and Memory and Aging Project). Methods CSF/plasma levels of MSR1 and NEP were measured using the sensitive primer extension assay technology. CSF Aβ1-42 was assessed with ELISA, while CSF ApoE and ApoJ were measured with the Luminex’s multiplex technology. Brain MSR1, APOE, and CLU (APOJ) mRNA levels were measured with RNA-Seq and contrasted to amyloid plaques pathology using CERAD staging. Results While plasma and CSF MSR1 levels are significantly correlated, this correlation was not observed for NEP. In addition to be highly correlated to one another, CSF levels of both MSR1 and NEP are strongly correlated with AD status and CSF Aβ1-42, ApoE, and ApoJ levels. In the cortical tissues of subjects from ROSMAP, MSR1 mRNA levels are correlated with CLU mRNA levels and the CERAD scores but not with APOE mRNA levels. Conclusion The discrepancies observed between CSF/plasma levels of MSR1 and NEP with CSF Aβ1-42 and ApoE concentrations can be explained by many factors, such as the disease stage or the involvement of the blood-brain barrier breakdown that leads to the infiltration of peripheral monocytes or macrophages.

Background Synaptic dysfunction is a central pathologic feature of Alzheimer’s disease (AD), with synaptic loss even preceding neuronal loss in specific brain regions. In healthy individuals, synaptic function and plasticity are orchestrated through the complex integration of signaling inputs generated by cell surface receptors. Methods In this study, we investigate the role of one such receptor, protein tyrosine phosphatase receptor sigma (PTPRS), in the context of Alzheimer’s disease. Publicly available datasets (BRAINEAC, ROSMAP, ADC1) and a cohort of asymptomatic but “at risk” individuals (PREVENT‐AD) were used to explore the relationship between PTPRS and various Alzheimer’s disease biomarkers. Results We identified that PTPRS rs10415488 variant C shows features of neuroprotection against early phospho (181)‐tau pathology (p<0.005) and synaptic degeneration (GAP‐43, p<0.001) in Alzheimer’s disease. In brain tissues, PTPRS protein abundance was significantly correlated with the quantity of two markers of synaptic integrity: SNAP25(R²=0.20, p < 0.0001) and SYT‐1(R²=0.12, p < 0.0001). We also found the presence of sexual dimorphism for PTPRS, with higher CSF concentrations in males (p<0.001) than females. Male carriers for variant C exhibit a 10‐month delay in the onset of AD (p <0.05). One molecular function of PTPRS we chose to explore is macrophagy, given the implication of this biological process in the response against neurodegeneration. Macrophagy‐associated LC3 immunoreactivity occurs in most dystrophic neurites in AD and co‐localized with abnormal P‐tau in most neurofibrillary tangles. In the ROSMAP subjects, LC3 cortical protein levels were found to be significant reduced in C carriers Conclusions PTPRS acts as a soluble, secreted neuroprotective receptor, found in the extracellular space in Alzheimer’s disease. These findings also highlight the functional importance of synaptic plasticity in the protection against neurodegenerative diseases.

Background The heterogeneous etiology of “sporadic” Alzheimer’s disease (sAD) includes genetic influences. To better understand synaptic dysfunction in AD pathogenesis, we used protein quantitative train loci (pQTL) assessments and a polygenic risk score (PRS) to examine the relationship between synaptic integrity and longitudinal cognitive performance in the presymptomatic phase of the disease. Method The PREVENT‐AD cohort includes symptom‐free elderly participants at risk of AD because of their family history. A second resource, the Quebec Founder Population (QFP) brain bank, derives from the descendants of the 17th and 18th century French settlers in Eastern Canada. We used Olink Proximity Extension Assays to measure the soluble synaptic proteins ADAM 22 (post‐synaptic) and ADAM23 (pre‐synaptic) in 120 CSFs, while immunoprecipitated SYT1 (pre‐synaptic) and SNAP25 (pos‐synaptic) were analyzed in 141 CSF samples using a quadrupole–orbitrap mass spectrometer. The Repeatable Battery for Assessment of Neuropsychological Status (RBANS) indicated cognitive trajectory. Genotyping was performed using the Illumina Infinium Omni 2.5M‐8 array. Cortical RNAs (n=86) from the QFP cohort were processed using GeneChip WT Pico Kit. Statistical analyses included sex, education and APOE e4 status as covariates. Result Among PREVENT‐AD participants who remained cognitively unimpaired over the past 11 years, we observed significant correlations between a PRS constructed from pQTL ADAM 22 CSF concentrations and delayed memory (R² = 0.06, p = 0.0132), visuospatial constructional memory (R² = 0.274, p = 0.00408) and total index scale (R² = 0.202, p = 0.0454), but only trend‐levels association with immediate memory (R² = 0.1, p = 0.0747). We also found similar correlations between PRS constructed from of CSF ADAM 23, CSF SYT1, CSF SNAP25 concentrations and the different RBANS subscales. Significantly lower cortical mRNA levels for ADAM22 (p = 0.062), ADAM23 (p = 0.0030), SYT1 (p = 0.033) and SNAP25 (p = 0.0036) were found in the autopsied AD brains compared to autopsied control brains. Conclusion CSF synaptic protein levels show promising correlations with emerging cognitive deficits and provide insights toward a possible compensatory mechanism in the early presymptomatic phase of the disease.

Background The immune complement system is key to the elimination of redundant neural connections in the brain through a process called synaptic pruning. In neurodegenerative diseases such as Alzheimer's disease (AD), this system may result in excessive synapse loss, leading to brain atrophy and cognitive impairment. While increased cerebrospinal fluid (CSF) levels of complement proteins have been observed in patients with AD dementia, no studies have yet investigated the role of complement in the pre‐symptomatic phase of AD, nor throughout its progression. Method We used Luminex technology to assess complement protein levels in 566 CSF samples obtained over five years from 160 high‐risk asymptomatic subjects with familial history of AD [the PREVENT‐AD cohort; Breitner et al, 2016: JPAD 3,(4) 236]. Baseline complement levels were contrasted with CSF biomarkers of AD pathology (Aβ42, p(181) and total tau, NFL) and markers of synaptic dysfunction (GAP‐43, SYT1, SNAP‐25, ADAM22, ADAM23). Analyses were stratified by sex and ApoE4 carrier status. Currently pending are additional longitudinal analyses probing complement levels versus PET‐quantified cerebral amyloid and tau deposition, MRI volume of AD‐implicated structures, and cognitive ability (RBANS). Result Preliminary analyses revealed significant positive associations between complement proteins and p‐(181)tau (C1q: R² = .238, p < .0001; C3: R² = .041, p = .0099; C3b: R² = .027, p = .0384; Factor H: R² = .128, p < .0001) and total tau levels (C1q: R² = .247, p < .0001; C3: R² = .023, p = .0543; Factor H: R² = .128, p < .0001). Complement relationships with synaptic protein levels were more significant overall in females, which showed the following associations [GAP‐43 (C1q: R² = .389, p < .0001; Factor H: R² = .315, p = .0002); SNAP‐25 (C1q: R² = .367, p < .0001; C3: R² = .106, p = .0459; Factor H: R² = .278, p = .0072); SYT1 (C1q: R² = .316, p = .0002; Factor H: R² = .246, p = .0015)]. Conclusion There is a clear association between complement levels, tau pathology, and synaptic markers in the asymptomatic phase of AD, especially in women. Longitudinal and multimodal investigation is ongoing to further characterize these relationships.

Background Scavenger receptors (SR) are a group of receptors involved in the endocytosis of various ligands, such as modified LDL and soluble β‐amyloid, which connects them to Alzheimer’s disease (AD). SCARF2 (SREC‐II) is part of the SR family, but unlike other scavenger receptors, internalizes a low amount of modified LDL. Its main function revolves around the binding of Aβ (Vo et al. 2023). Other studies found SCARF2 to be a SCARF1 inhibitor (Ishii et al. 2002). This study compares gene expression and protein levels of SCARF2 in post‐mortem brain tissue of AD and control subjects, as well as in the CSF of participants with a family history of AD. The goal is to track the progression of AD using the expression pattern of SCARF2. Method SCARF2 CSF protein levels were assessed in the PREVENT‐AD (PRe‐symptomatic EValuation of Experimental or Novel Treatments for Alzheimer’s Disease) cohort which is composed of asymptomatic subjects with parental history of AD. SCARF2 has been measured with a primer extension assay using Olink technology. ELISA immunoassay has been used to quantify SCARF2 protein levels in frontal cortex homogenates of 86 brains from the Douglas Bell Canada Brain Bank (DBCBB). mRNA prevalence was measured using Gene Chip Clariom D human microarray. All statistical analyses were performed using JMP pro 17 software. Result SCARF2 Protein levels, but not mRNA, are significantly lower in brains with AD (p<0.001). SCARF2 protein display a strong negative association with plaques bound Aβ, despite being a well‐established Aβ receptor (R² = 0.277, p<0.0001). Interestingly, CSF protein levels correlate positively with AD biomarkers such as total and phosphorylated(181) tau (R² = 0.235, p<0.0001; R² = 0.288, p<0.0001) and Aβ to a lesser extent (R² = 0.045, p = 0.0318). Conclusion Our study unveils a distinctive role for SCARF2 in AD pathogenesis. Despite being a known Aβ receptor, SCARF2 exhibits lower cortical protein levels in AD brains, inversely linked to plaques bound Aβ. In contrast, elevated CSF SCARF2 protein levels correlate positively with CSF AD biomarkers in the presymptomatic phase of the disease; suggesting differential response to amyloid and tau deposition. These findings shed light on the intricate interplay of SCARF2 in AD pathophysiology, offering potential avenues for further research.

Background Inflammation is central to Alzheimer Disease (AD), as astrocyte reactivity accompanies the appearance of Aβ and phosphorylated tau (Bellaver et al., 2023). As expected, therefore, AD patients have elevated levels of CSF inflammatory cytokines (Onyango et al., 2021). To understand the importance of these phenomena, exploration of individual inflammatory markers before and at the time of dementia onset is needed. To uncover key CK/Rs involved in the early pathogenesis of AD, we investigated selected cytokines and their receptors (CK/Rs) in the preclinical stages of the disease. Method We analyzed 433 longitudinal CSF samples from 104 participants in the PREVENT‐AD cohort. These persons, who were symptom‐free at baseline but at enhanced risk of developing AD because of their family history, have now been followed for over 10 years. We used ELISA to analyze Aβ42, p181, and total tau in the CSF [Fujirebio Innotest, Ghent, Belgium], while CK/Rs were assayed using the Olink proximity extension assay Target 96 Inflammation panel [Upsala, Sweden]. Linear mixed model analyses controlled for participant age and APOE4 status. Result We found that IL10RB, IL18, and CD40 levels in the CSF were significantly associated with both p(181)tau and Aβ42 levels in the CSF over time. IL10RB, IL18, and CD40 each showed significant positive association with p(181)tau levels across time (F(1,213.191) = 7.013, p = 0.009; F(1,237.624) = 9.972, p = 0.002; F(1,246.859) = 8.211, p = 0.005). The longitudinal effects of IL10RB and IL18 on Aβ42 were contingent on both sex and time (F(5,55.406) = 2.548, p = 0.038; F(5,54.792) = 4.280, p = 0.002), while the significantly positive association of CD40 levels on Aβ42 across time was stronger in females than in males (F(1, 59.669) = 4.099, p = 0.047). Conclusion These investigations of CSF proteins in preclinical AD persons identified inflammatory markers that exhibited specific relationships with p(181)tau and Aβ42 across time and sex. These results may guide further study of biomarkers for detection of AD in its preclinical stages, and/or therapeutic strategies. Of special importance, characterization of the pathogenesis of pre‐symptomatic AD may facilitate development of early interventions for the prevention of AD dementia.

Background Clusterin is a major cholesterol transporter in the central nervous system (CNS) and different SNPs in the CLU gene have been associated with Alzheimer’s disease (AD) risk. The rs11136000_T variant in the CLU gene has been shown to decrease the risk of AD. In this work, we investigate the role of the CLU rs11136000_T protective variant and of the clusterin protein throughout different phases of the AD spectrum. Method Levels of clusterin, Tau, phospho(181) Tau (p‐tau), and Aß were measured using ELISA and synaptic proteins were measured using immunoprecipitation followed by mass spectroscopy in the CSF of cognitively unimpaired individuals. Flortaucipir PET was used to measure tau deposition and 18F‐NAV4694 PET was used to measure amyloid burden in the same subjects. ELISA was used to measure clusterin levels and RT‐PCR was used to measure mRNA levels in cortical areas of autopsied‐confirmed controls and AD subjects. Genotype was performed using Illumina Infinium Omni2.5M‐8 microarray. Result There was no effect of the protective genotype on the levels of PET biomarkers, CSF biomarkers or synaptic proteins in cognitively unimpaired individuals. CSF clusterin levels were positively associated with Aß (p = 0.021), total‐tau (p<0.001), p‐tau (p<0.001), synaptotagmin (p<0.001), SNAP 25 (p = 00006), GAP 43 (p = 0.00055) and neurogranin (p = 0.0086) in the CSF and with amyloid deposition in the hippocampus (p = 0.018) and tau retention in the entorhinal cortex (p = 0.0082) and temporal pole (p = 0.0124) in cognitively unimpaired individuals at high risk for AD. Clusterin is increased in the brain of individuals who are homozygous for the CLU_T variant (p = 0.04) and in AD patients compared to age‐matched controls (p = 0.024). mRNA levels are increased in individuals homozygous for the CLU_T variant (p = 0.003), but there are no significant differences in AD patients compared to controls (p = 0.07). Conclusion Our work shows significant correlation between CSF clusterin and the main AD biomarkers (PET and CSF) and synaptic proteins before disease onset, in subjects at high risk for the disease. In the later stage of the disease, clusterin protein and CLU mRNA levels are increased as a function of genotype and disease status, suggesting that CLU may play a protective role by increases in gene expression in the CNS.

Background: Assay-vendor independent quality control (QC) samples for neurochemical dementia diagnostics (NDD) biomarkers are so far commercially unavailable. This requires that NDD laboratories prepare their own QC samples, for example by pooling leftover cerebrospinal fluid (CSF) samples. Objective: To prepare and test alternative matrices for QC samples that could facilitate intra- and inter-laboratory QC of the NDD biomarkers. Methods: Three matrices were validated in this study: (A) human pooled CSF, (B) Aβ peptides spiked into human prediluted plasma, and (C) Aβ peptides spiked into solution of bovine serum albumin in phosphate-buffered saline. All matrices were tested also after supplementation with an antibacterial agent (sodium azide). We analyzed short- and long-term stability of the biomarkers with ELISA and chemiluminescence (Fujirebio Europe, MSD, IBL International), and performed an inter-laboratory variability study. Results: NDD biomarkers turned out to be stable in almost all samples stored at the tested conditions for up to 14 days as well as in samples stored deep-frozen (at – 80°C) for up to one year. Sodium azide did not influence biomarker stability. Inter-center variability of the samples sent at room temperature (pooled CSF, freeze-dried CSF, and four artificial matrices) was comparable to the results obtained on deep-frozen samples in other large-scale projects. Conclusion: Our results suggest that it is possible to replace self-made, CSF-based QC samples with large-scale volumes of QC materials prepared with artificial peptides and matrices. This would greatly facilitate intra- and inter-laboratory QC schedules for NDD measurements.

Apolipoprotein B (APOB), a receptor-binding protein present in cholesterol-rich lipoproteins, has been implicated in Alzheimer's disease (AD). High levels of APOB-containing low-density lipoproteins (LDL) are linked to the pathogenesis of both early-onset familial and late-onset sporadic AD. Rare coding mutations in the APOB gene are associated with familial AD, suggesting a role for APOB-bound lipoproteins in the central nervous system. This research explores APOB gene regulation across the AD spectrum using four cohorts: BRAINEAC (elderly control brains), DBCBB (controls, AD brains), ROSMAP (controls, MCI, AD brains), and ADNI (control, MCI, AD clinical subjects). APOB protein levels, measured via mass spectrometry and ELISA, positively correlated with AD pathology indices and cognition, while APOB mRNA levels showed negative correlations. Brain APOB protein levels are also correlated with cortical Aβ levels. A common coding variant in the APOB gene locus affected its expression but didn't impact AD risk or brain cholesterol concentrations, except for 24-S-hydroxycholesterol. Polymorphisms in the CYP27A1 gene, notably rs4674344, were associated with APOB protein levels. A negative correlation was observed between brain APOB gene expression and AD biomarker levels. CSF APOB correlated with Tau pathology in presymptomatic subjects, while cortical APOB was strongly associated with cortical Aβ deposition in late-stage AD. The study discusses the potential link between blood-brain barrier dysfunction and AD symptoms in relation to APOB neurobiology. Overall, APOB's involvement in lipoprotein metabolism appears to influence AD pathology across different stages of the disease.