Astrocyte biomarkers GFAP and YKL-40 mediate early Alzheimer's disease progression

Cross-talk between amyloid beta peptides and tau proteins in Co-aggregation investigating with the combination of coarse-grained and all-atom simulations

The synergistic roles of amyloid beta (Aβ) peptides and tau proteins in the pathogenesis of Alzheimer's disease (AD) have garnered increasing attention. However, the mechanisms underlying their interactions and co-assembly remain largely unknown. Due to the rapid aggregation properties of Aβ and tau, current experimental methods face challenges in observing these interactions. In this study, we conducted coarse-grained (CG) simulations in conjunction with all-atom (AA) simulations to explore the initial stages of self-assembly of Aβ monomers in both the presence and absence of tau. The comparative results demonstrate that tau enhances the aggregation of Aβ and competes with Aβ for binding to fibrils. A gradual growth model is proposed to describe the initial co-aggregation process, wherein two specific domains of tau, R2 and R3, preferentially interact with Aβ to form dimers or trimers through electrostatic forces. Key regions have also been identified that facilitate binding with Aβ. These findings provide valuable structural and dynamic insights into the interaction between Aβ and tau, as well as the initial aggregation process, which could aid in elucidating the pathology of AD and in the development of novel therapeutic strategies for the disease.

Neuroinflammatory fluid biomarkers in patients with Alzheimer's disease: a systematic literature review

INTRODUCTION

Neuroinflammation is associated with both early and late stages of the pathophysiology of Alzheimer's disease (AD). Fluid biomarkers are gaining significance in clinical practice for diagnosis in presymptomatic stages, monitoring, and disease prognosis. This systematic literature review (SLR) aimed to identify fluid biomarkers for neuroinflammation related to clinical stages across the AD continuum and examined long-term outcomes associated with changes in biomarkers.

METHODS

The SLR was conducted per the Cochrane Handbook for Systematic Reviews of Interventions and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We used PubMed®, Embase®, and Cochrane Collaboration databases to search for articles in English (between 2012 and 2022) on AD or mild cognitive impairment due to AD, using "neuroinflammation" or other "immune" search strings. Two independent reviewers screened titles and examined data from full-text articles for the SLR.

RESULTS

After the initial screening, 54 studies were prioritized for data extraction based upon their relevance to the SLR research questions. Nine studies for YKL-40, seven studies for sTREM2, and 11 studies for GFAP examined the relationship between the neuroinflammatory biomarkers and the clinical stage of the disease. Nine longitudinal studies further explored the association of fluid biomarkers with long-term clinical outcomes of disease. Cerebrospinal fluid (CSF) levels of YKL-40 were elevated in patients with AD dementia, while CSF sTREM2 levels were more strongly associated with preclinical and early symptomatic stages of AD. Plasma GFAP levels remained consistently elevated both in patients with AD dementia and individuals in preclinical stages with β-amyloid pathology. Longitudinal changes in plasma GFAP appeared to be predictive of cognitive decline in patients over time.

DISCUSSION

Neuroinflammatory biomarkers are associated with AD progression. More longitudinal studies in the preclinical and MCI stages of AD are needed to validate fluid biomarkers for diagnosis, disease monitoring, and prognosis in clinical practice.

Emerging blood biomarkers in Alzheimer's disease: a proteomic perspective

Early detection of Alzheimer's disease (AD) remains a formidable clinical challenge, but emerging blood-based assays show promise for identifying at-risk individuals long before cognitive symptoms arise. This is the first comprehensive synthesis comparing mass-spectrometry and immunoassay platforms across multiple blood-based AD biomarkers and the first to integrate these findings into a unified roadmap for clinical implementation. In this review, we compare high-throughput mass spectrometry and ultrasensitive immunoassays for quantifying circulating amyloid-β isoforms, phosphorylated tau species (p-tau181, p-tau217), neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), YKL-40 and selected inflammatory markers. Individual biomarkers demonstrate diagnostic accuracies (AUC) up to 0.90, and integrating these protein signatures with APOE ε4 genotype, brief cognitive assessments and neuroimaging via machine-learning models boosts discrimination of preclinical AD from normal aging to over 80% accuracy. We trace the path from initial discovery through analytical validation to clinical implementation, emphasizing critical hurdles such as variability in sample collection, limited cohort diversity and regulatory requirements. Future work must standardize preanalytical protocols, extend validation across populations, refine ultrasensitive detection techniques, and combine proteomic data with genomics and other "omics" layers to move toward routine blood-based screening. These coordinated efforts provide a clear roadmap for transforming early AD diagnosis and enabling timely, personalized interventions.

Sex Differences in Biofluid Biomarkers for Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD), the most common cause of dementia, affects twice as many women as men. Moreover, sex is increasingly recognised as an important factor for AD, influencing symptom presentation, progression, disease biology, and treatment responses. In parallel, AD biomarkers are becoming more accessible with the discovery of specific and accurate blood-based biomarkers and their incorporation in AD diagnostic frameworks. This narrative review aimed to summarise sex differences in the concentration and interpretation of biofluid biomarkers for AD.

SUMMARY

Biological sex may influence both the concentration and interpretation of biofluid biomarkers for AD pathology such as amyloid-β aggregation, tau neurofibrillary tangles, neurodegeneration, or neuroinflammation. While some biofluid biomarkers display consistent sex differences in absolute levels, most biomarker levels have not been found to differ consistently by sex. Nonetheless, even biomarkers that do not differ in absolute levels display sex-specific associations with clinically relevant variables such as brain atrophy, cognitive impairment, and disease progression.

KEY MESSAGE

Sex may influence the interpretation of AD biomarkers depending on their context of use, and more research is required to develop sex-specific guidelines. Future research should aim to study sex differences and sex-specific associations with variables of interest, as well as the underlying factors driving sex differences in AD.

Relationships between neuropsychiatric symptoms, subtypes of astrocyte activities, and brain pathologies in Alzheimer's disease and Parkinson's disease

INTRODUCTION

Alzheimer's disease (AD) and Parkinson's disease (PD) are neurodegenerative diseases (NDs). This study examined astrocytic contributions to neuropsychiatric symptoms (NPS), focusing on astrocytic protein activity and its relationship with NPS severity, accounting for clinical and pathological features of NDs.

METHODS

Cerebrospinal astrocytic proteins (glial fibrillary acidic protein [GFAP], chitinase-3-like protein 1 [YKL-40], and aquaporin-4 [AQP4]) from Alzheimer's Disease Neuroimaging Initiative (ADNI) (AD) and Parkinson's Progression Markers Initiative (PPMI) (PD) were analyzed using K-means clustering. Six NPS domains, ND-specific pathologies (amyloid-beta/Aβ for AD, alpha-synuclein/αSyn for PD), and nonspecific pathology (phosphorylated tau/ptau) were assessed.

RESULTS

In both samples, three astrocytic clusters were identified, and the "highYKL|lowOthers" cluster (high YKL-40, low GFAP/AQP4) consistently showed lower ptau and NPS severity compared to the "highAll" cluster (high GFAP, YKL-40, AQP4). In PPMI, the "highYKL|lowOthers" cluster also attenuated the relationship between αSyn and NPS compared to the "highAll" cluster.

DISCUSSION

Astrocytic activity relates to NPS, highlighting astrocytic proteins as potential therapeutic targets for NPS in NDs.

HIGHLIGHTS

Astrocytic protein clusters were linked to NPS severity in AD and PD cohorts. The "highYKL|lowOthers" cluster showed lower ptau and NPS severity than "allhigh" cluster in AD and PD cohorts. Astrocytic proteins may serve as therapeutic targets for managing NPS in NDs.

Regional brain structural alterations in reward and salience networks in asthma

INTRODUCTION

Chronic systemic inflammation is highly prevalent and has deleterious effects on the brain, impacting both function and structure, and manifesting in elevations in psychological symptoms transdiagnostically. Asthma is a chronic inflammatory disease of the airway that affects more than 300 million people worldwide and is known to be highly comorbid with psychological and cognitive dysfunction. Though a growing corpus of work has identified functional brain abnormalities associated with asthma, limited research has investigated structural differences which may partially underlie functional changes. Identifying and characterizing asthma-related structural brain changes will shed light on the neurobiology through which asthma impacts mental function and has the potential to inform prophylaxis and treatment.

METHODS

We examined differences in regional brain volume, cortical thickness, and surface area, in 128 individuals with asthma compared to 134 non-asthma healthy controls. Five regions of interest were examined a priori, based on their previous implication in inflammation-related functional consequences (dorsal and ventral striatum, pallidum, and insula), or previous evidence of asthma-related structural impact (hippocampus and thalamus). We supplemented our region of interest approach with a voxel-wise whole-brain analysis. Additionally, we examined the association of brain structure with depression symptoms, asthma severity, degree of inflammation, and plasma biomarkers of neuroinflammation, neurodegeneration, and Alzheimer's disease specific pathology.

RESULTS

Compared to non-asthma control participants, those with asthma had smaller nucleus accumbens volumes, thicker orbitofrontal cortices, larger middle frontal cortex surface areas, and greater diencephalon volumes. Those with more severe asthma had smaller nucleus accumbens and dorsal striatal volumes, reduced anterior cingulate cortex surface area, and greater amygdala volume compared to those with mild asthma. In untreated asthma patients, greater depressive symptoms were associated with smaller striatal volume, suggesting a potential CNS-protective effect of medications that reduce airway inflammation in asthma. In addition, a plasma marker of astrogliosis was associated with larger diencephalon, cerebellum, brainstem, and thalamus volumes, but reduced insula thickness and surface area.

CONCLUSIONS

Patterns of structural brain changes in participants with asthma encompass key regions of reward and salience networks, which may in part give rise to the functional alterations in these networks characteristic of chronic systemic inflammation.

Plasma GFAP for populational enrichment of clinical trials in preclinical Alzheimer's disease

INTRODUCTION

Cognitively unimpaired (CU) amyloid beta (Aβ)+ individuals with elevated plasma glial fibrillary acidic protein (GFAP) have an increased risk of Alzheimer's disease (AD)-related progression. We tested the utility of plasma GFAP for population enrichment CU populations in clinical trials.

METHODS

We estimated longitudinal progression, effect size, and costs of hypothetical clinical trials designed to test an estimated 25% drug effect on reducing tau positron emission tomography (PET) accumulation in the medial temporal lobe (MTL) and temporal neocortical region (NEO-T).

RESULTS

CU GFAP+/Aβ+ individuals present an increased annual rate of change and effect size in tau PETMTL and tau PETNEO-T compared to the other groups. An enrichment strategy selecting CU GFAP+/Aβ+ individuals would require a smaller sample size (≈ 57% reduction) and fewer Aβ PET scans (≈ 74% reduction) than trials enriched with Aβ PET alone, reducing total clinical trial costs by up to 64%.

DISCUSSION

Our results suggest that clinical trials focusing on preclinical AD recruiting Aβ+ individuals with elevated GFAP levels would improve cost effectiveness.

HIGHLIGHTS

Cognitively unimpaired (CU) glial fibrillary acidic protein (GFAP)+/amyloid beta (Aβ)+ shows increased changes in tau positron emission tomography (PET) . CU GFAP+/Aβ+ enriched clinical trials require a reduced sample size compared to Aβ+ only. CU GFAP+/Aβ+ enrichment reduces Aβ PET scans required and costs. CU GFAP+/Aβ+ enrichment allows the selection of individuals at early stages of the Alzheimer's disease continuum.

Neuroimaging-derived biological brain age and its associations with glial reactivity and synaptic dysfunction cerebrospinal fluid biomarkers

Magnetic resonance Imaging (MRI)-derived brain-age prediction is a promising biomarker of biological brain aging. Accelerated brain aging has been found in Alzheimer's disease (AD) and other neurodegenerative diseases. However, no previous studies have investigated the relationship between specific pathophysiological pathways in AD and biological brain aging. Here, we studied whether glial reactivity and synaptic dysfunction are associated with biological brain aging in the earliest stages of the Alzheimer's continuum, and if these mechanisms are differently associated with AD-related cortical atrophy. We further evaluated their effects on cognitive decline. We included 380 cognitively unimpaired individuals from the ALFA+ study, for which we computed their brain-age deltas by subtracting chronological age from their brain age predicted by machine learning algorithms. We studied the cross-sectional linear associations between brain-age delta and cerebrospinal fluid (CSF) biomarkers of synaptic dysfunction (neurogranin, GAP43, synaptotagmin-1, SNAP25, and α-synuclein), glial reactivity (sTREM2, YKL-40, GFAP, and S100b) and inflammation (interleukin-6). We also studied the cross-sectional linear associations between AD signature and these CSF biomarkers, We further evaluated the mechanisms linking baseline brain-age delta and longitudinal cognitive decline by performing mediation analyses. To reproduce our findings on an independent cohort, we included 152 cognitively unimpaired and 310 mild cognitive impaired (MCI) individuals from the ADNI study. We found that higher CSF sTREM2 was associated with a younger brain-age after adjusting for AD pathology, both in ALFA+ cognitively unimpaired and in ADNI MCI individuals. Furthermore, we found that CSF sTREM2 fully mediated the link between older brain-age and cognitive decline in ALFA+. In summary, we showed that the protective microglial state reflected by higher CSF sTREM2 has a beneficial impact on biological brain aging that may partly explains the variability in cognitive decline in early AD stages, independently of AD pathology.

Associations among Angiotensin-Converting Enzyme, Neuroinflammation, and Cerebrospinal Fluid Biomarkers of Alzheimer's Disease in Non-Dementia Adults

Recent studies have identified the angiotensin-converting enzyme (ACE) gene as a potential candidate influencing Alzheimer's disease (AD) risk. It is crucial to investigate the impact of ACE on AD pathology and its underlying mechanisms. A total of 450 non-demented participants from the Alzheimer's disease Neuroimaging Initiative (ADNI) with data on cerebrospinal fluid (CSF) ACE, AD core biomarkers and inflammation-related biomarkers were included. Multiple linear regression was used to assess the associations among CSF ACE, AD core biomarkers and inflammation-related biomarkers. And we used the mediation models to investigate the potential mechanisms through which ACE influenced AD pathology. The results of multiple linear regression were shown that CSF ACE was significantly correlated with CSF Aβ42, P-tau, T-tau (all P < 0.001), and inflammation-related biomarkers (soluble triggering receptor expressed on myeloid cells 2 [sTREM2], progranulin [PGRN], glial fibrillary acidic protein [GFAP], transforming growth factor [TGF]-β1, TGF-β2, TGF-β3, tumor necrosis factor [TNF]-R1, TNF-R2, TNF-α, interleukin [IL]-21, IL-6, IL-7, IL-9, IL-10, IL-12p40, vascular cell adhesion molecule-1 [VCAM-1], and intercellular adhesion molecule-1 [ICAM-1]) (all P < 0.05). In addition, the mediation analysis results showed that the association of CSF ACE and inflammation-related biomarkers (sTREM2, PGRN, TGF-β1, TGF-β2, TNFR1, IL-6, IL-7, IL-9, and VCAM-1) mediated the correlation of CSF Aβ42 with P-tau. Our findings show that CSF ACE and neuroinflammation are correlated and that their correlation mediates the link between Aβ pathology and P-tau. This suggests ACE may play a significant role in the progression from Aβ pathology to tau pathology.

Analysis of human brain RNA-seq data reveals combined effects of 4 types of RNA modifications and 18 types of programmed cell death on Alzheimer's disease

BACKGROUND

RNA modification plays a critical role in Alzheimer's disease (AD) by modulating the expression and function of AD-related genes, thereby affecting AD occurrence and progression. Programmed cell death is closely related to neuronal death and associated with neuronal loss and cognitive function changes in AD. However, the mechanism of their joint action on AD remains unknown and requires further exploration.

METHODS

We used the MSBB RNA-seq dataset to analyze the correlation between RNA modification, programmed cell death, and AD. We used combined studies of RNA modification and programmed cell death to distinguish subgroups of patients, and the results highlight the strong correlation between RNA modification-related programmed cell death and AD. A weighted gene co-expression network was constructed, and the pivotal roles of programmed cell death genes in key modules were identified. Finally, by combining unsupervised consensus clustering, gene co-expression networks, and machine learning algorithms, an RNA modification-related programmed cell death network was constructed, and the pivotal roles of programmed cell death genes in key modules were identified. An RNA modification-related programmed cell death risk score was calculated to predict the occurrence of AD.

RESULTS

RPCD-related genes classified patients into subgroups with distinct clinical characteristics. Nineteen key genes were identified and an RPCD risk score was constructed based on the key genes. This score can be used for the diagnosis of AD and the assessment of disease progression in patients. The diagnostic efficacy of the RPCD risk score and the key genes was validated in the ROSMAP, GEO, and ADNI datasets.

CONCLUSION

This study uncovered that RNA modification-related PCD is of significance for AD progression and early prediction, providing insights from a new perspective for the study of disease mechanisms in AD.

Higher plasma soluble TREM2 correlates with reduced cerebral tau accumulation in Alzheimer's disease

Loss-of-function mutation of triggering receptor expressed on myeloid cell 2 (TREM2) is associated with increased risks for Alzheimer's disease (AD). Recent animal studies reveal that the activation of peripheral TREM2 signaling may affect cerebral β-amyloid (Aβ) and tau aggregates. However, the underlying relationship between peripheral TREM2 and brain AD pathology has not yet been well-elucidated in the aging population. In this study, we collected 318 Chinese older adults with Aβ PET and plasma biomarker measures, including soluble TREM2 (sTREM2) and glial fibrillary acidic protein (GFAP), a proxy for astrocyte reactivity. Additionally, 129 participants underwent tau PET scans. We explored the association between plasma sTREM2, GFAP, and primary AD pathology. Plasma sTREM2 was negatively associated with reduced temporal tau PET burden in participants with abnormal Aβ and tau pathology. Higher plasma sTREM2 was related to the weaker association of Aβ pathology and plasma phosphorylated tau with tau PET increases. In contrast, elevated plasma GFAP was related to greater Aβ and tau PET burden along with stronger Aβ-related tau accumulation. Finally, higher plasma sTREM2 was linked to attenuated strength of the association between plasma GFAP and tau PET increases at both pre-defined regions of interest and voxel levels. Altogether, our findings suggest distinct relationships between plasma sTREM2 and GFAP with cerebral tau pathology, providing novel insights into the roles of peripheral TREM2 signaling and astrocytic reactivity in AD neuropathological development. This study has important implications, such as targeting the peripheral TREM2 signature, which may be a potential strategy for future AD therapies.

Identification and Exploration of Immunity-Related Genes and Natural Products for Alzheimer's Disease Based on Bioinformatics, Molecular Docking, and Molecular Dynamics

BACKGROUND

Recent research highlights the immune system's role in AD pathogenesis and promising prospects of natural compounds in treatment. This study explores immunity-related biomarkers and potential natural products using bioinformatics, machine learning, molecular docking, and kinetic simulation.

METHODS

Differentially expressed genes (DEGs) in AD were analyzed using GSE5281 and GSE132903 datasets. Important AD module genes were identified using a weighted co-expression algorithm (WGCNA), and immune-related genes (IRGs) were obtained from the ImmPortPortal database. Intersecting these genes yielded important IRGs. Then, the least absolute shrinkage and selection operator (LASSO) and other methods screened common immune-related AD markers. Biological pathways were explored through Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA). The accuracy of these markers was assessed by subject operator signature (ROC) curves and validated in the GSE122063 dataset. The datasets was then subjected to immunoinfiltration analysis. Multiple compound databases were used to analyze core Chinese medicines and components. Molecular docking and kinetic simulation verification were used for further verification.

RESULTS

A total of 1360 differential genes and 5 biomarkers (PGF, GFAP, GPI, SST, NFKBIA) were identified, showing excellent diagnostic efficiency. GSEA revealed markers associated with Oxidative phosphorylation, Nicotine addiction, and Hippo signaling pathway. Immune infiltration analysis showed dysregulation in multiple immune cell types in AD brains, with significant interactions between markers and 5 immune cell types. A total of 27 possible herbs and 7 core compounds were eventually identified. The binding environment of GPI-luteolin and GPI-stigasterol was relatively stable and showed good affinity.

CONCLUSIONS

PGF, GFAP, SST, GPI, and NFKBIA were identified for early AD diagnosis, associated with immune cells and pathways in AD brains. 7 promising natural compounds, including luteolin and stigmasterol, were screened for targeting these biomarkers.

Physical Activity, Alzheimer Plasma Biomarkers, and Cognition

Importance

Physical activity (PA) is a nonpharmacological intervention for dementia prevention. The association between PA and Alzheimer disease (AD) plasma biomarkers remains underexplored.

Objective

To investigate the associations among PA; plasma biomarkers, including β-amyloid 42/40 (Aβ42/40), phosphorylated-tau217 (ptau217), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL); and cognition.

Design, Setting, and Participants

This cross-sectional study included participants with and without cognitive impairment recruited from multiple memory clinics in South Korea between May 2019 and May 2022. Data were analyzed from June to December 2024.

Exposures

PA was assessed as metabolic equivalent task minutes per week using the International Physical Activity Questionnaire and categorized into quartiles from the lowest (Q1) to the highest (Q4).

Main Outcomes and Measures

Plasma Aβ42/40, ptau217, GFAP, and NfL were measured. Cognition was assessed using the Mini-Mental State Examination (MMSE) and Clinical Dementia Rating-Sum of Boxes (CDR-SB).

Results

Among 1144 participants (mean [SD] age 70.9 [8.7] years; 744 [65.0%] female), the highest PA quartile showed significantly lower ptau217 (estimate [SE], -0.14 [0.06]; P = .01) and NfL (estimate [SE], -0.12 [0.05]; P = .01) compared with the lowest quartile. Higher PA quartiles were associated with higher MMSE scores (estimate [SE]: Q2, 0.93 [0.31]; P = .003; Q3, 0.82 [0.32]; P = .009; Q4, 0.94 [0.32]; P = .004) and lower CDR-SB scores (estimate [SE]: Q2, -0.33 [0.16]; P = .04; Q3, -0.37 [0.16]; P = .02; Q4, -0.55 [0.16]; P = .001) after adjusting for age, sex, education years, and β-amyloid uptake. In subgroup analyses according to age and cognitive status, the associations of PA and plasma biomarkers with cognition were more pronounced in the older (age ≥65 years) and cognitively impaired groups compared with the younger and cognitively unimpaired groups.

Conclusions and Relevance

These findings suggest that PA may help delay cognitive decline by modulating neurodegeneration and AD-specific tau pathologies. However, the cross-sectional design limits causal inference, and longitudinal studies are needed to confirm and clarify these associations.

Differences of longitudinal plasma biomarkers between single memory domain and multidomain subject cognitive decline: Evidence from SILCODE

BACKGROUND

Plasma biomarkers demonstrated potential in identifying amyloid pathology in early Alzheimer's disease. Different subtypes of subjective cognitive decline (SCD) may lead to different cognitive impairment conversion risks.

OBJECTIVE

To investigate the differences of plasma biomarkers in SCD subtypes individuals, which were unclear.

METHODS

The 347 individuals were involved, including 93 normal controls (NC), 76 single memory domain SCD (sd-SCD), 79 multidomain SCD (md-SCD), 55 mild cognitive impairment and 44 dementia. We investigated plasma biomarkers (Aβ42/40, p-tau181, p-tau217, NfL, and GFAP) and neuropsychological scales in the baseline and follow-up. The Kaplan-Meier survival analysis and Cox proportional hazards model were performed to investigate the risk of cognitive decline conversion. The t-test, Mann-Whitney U and multiple linear regression analysis were employed to evaluate the rate of change and correlation between PET-SUVR and plasma biomarker change.

RESULTS

In cognitively normal subjects, md-SCD exhibited lower Aβ42/40 and higher p-tau181 and p-tau217 levels. Kaplan-Meier survival analysis revealed that md-SCD group exhibited a higher risk of cognitive decline conversion compared to NC and sd-SCD. Within SCD subgroups, those with positive GFAP status showed higher conversion risk than negative. In the Cox model, the risk of conversion in the md-SCD group was 2.77 times higher than sd-SCD. The md-SCD group demonstrated a faster rate of Aβ42/40 decline than sd-SCD.

CONCLUSIONS

The study utilized plasma biomarkers to highlight the significance of staging in SCD. In cognitively normal subjects, md-SCD presents a higher risk of cognitive decline than sd-SCD, providing a valuable reference and convenient tool for early identification of individuals at risk for AD.

Molecular biomarkers of glial activation and injury in epilepsy

Increasing evidence from fluid biopsies suggests activation and injury of glial cells in epilepsy. The prevalence of clinical and subclinical seizures in neurodegenerative conditions such as Alzheimer's disease, frontotemporal dementia, and others merits review and comparison of the effects of seizures on glial markers in epilepsy and neurodegenerative diseases with concomitant seizures. Herein, we revisit preclinical and clinical reports of alterations in glial proteins in cerebrospinal fluid and blood associated with various types of epilepsy. We consider shared and distinct characteristics of changes in different age groups and sexes, in humans and animal models of epilepsy, and compare them with those reported in biofluids in neurodegenerative diseases. Our analysis indicates a significant overlap of glial response in these prevalent neurological conditions.

Brain inflammation co-localizes highly with tau in mild cognitive impairment due to early-onset Alzheimer's disease

Brain inflammation, with an increased density of microglia and macrophages, is an important component of Alzheimer's disease and a potential therapeutic target. However, it is incompletely characterized, particularly in patients whose disease begins before the age of 65 years and, thus, have few co-pathologies. Inflammation has been usefully imaged with translocator protein (TSPO) PET, but most inflammation PET tracers cannot image subjects with a low-binder TSPO rs6971 genotype. In an important development, participants with any TSPO genotype can be imaged with a novel tracer, 11C-ER176, that has a high binding potential and a more favourable metabolite profile than other TSPO tracers currently available. We applied 11C-ER176 to detect brain inflammation in mild cognitive impairment (MCI) caused by early-onset Alzheimer's disease. Furthermore, we sought to correlate the brain localization of inflammation, volume loss, elevated amyloid-β (Aβ)and tau. We studied brain inflammation in 25 patients with early-onset amnestic MCI (average age 59 ± 4.5 years, 10 female) and 23 healthy controls (average age 65 ± 6.0 years, 12 female), both groups with a similar proportion of all three TSPO-binding affinities. 11C-ER176 total distribution volume (VT), obtained with an arterial input function, was compared across patients and controls using voxel-wise and region-wise analyses. In addition to inflammation PET, most MCI patients had Aβ (n = 23) and tau PET (n = 21). For Aβ and tau tracers, standard uptake value ratios were calculated using cerebellar grey matter as region of reference. Regional correlations among the three tracers were determined. Data were corrected for partial volume effect. Cognitive performance was studied with standard neuropsychological tools. In MCI caused by early-onset Alzheimer's disease, there was inflammation in the default network, reaching statistical significance in precuneus and lateral temporal and parietal association cortex bilaterally, and in the right amygdala. Topographically, inflammation co-localized most strongly with tau (r = 0.63 ± 0.24). This correlation was higher than the co-localization of Aβ with tau (r = 0.55 ± 0.25) and of inflammation with Aβ (0.43 ± 0.22). Inflammation co-localized least with atrophy (-0.29 ± 0.26). These regional correlations could be detected in participants with any of the three rs6971 TSPO polymorphisms. Inflammation in Alzheimer's disease-related regions correlated with impaired cognitive scores. Our data highlight the importance of inflammation, a potential therapeutic target, in the Alzheimer's disease process. Furthermore, they support the notion that, as shown in experimental tissue and animal models, the propagation of tau in humans is associated with brain inflammation.

The Common Alzheimer's Disease Research Ontology (CADRO) for biomarker categorization

Biomarkers are vital to Alzheimer's disease (AD) drug development and clinical trials, and will have an increasing role in clinical care. In this narrative review, we demonstrate the use of the National Institutes on Aging/Alzheimer's Association (NIA/AA) Common Alzheimer's Disease Research Ontology (CADRO) system for the categorization of biomarkers based on the primary mechanism on which they report. We show that biomarkers are available (in various levels of validation) for all CADRO processes. Application of the CADRO system demonstrates gaps in the field where novel biomarkers are needed for specific aspects of the disease, and assays to detect and measure biological changes, in individuals with symptomatic or preclinical AD. We demonstrate the CADRO system as a means of categorizing established and candidate AD biomarkers, showing the feasibility and practicality of the system. CADRO can assist with biomarker selection for AD clinical trials and drug development, and may eventually be applied to implementing biomarkers in patient care.

Highlights

The Common Alzheimer's Disease Research Ontology (CADRO) system can be used to categorize biomarkers for drug development.We demonstrate the use of CADRO with Alzheimer's disease (AD) biomarkers.We identified AD biomarkers in each of the CADRO categories.CADRO can be incorporated into current AD drug development and clinical trial systems.

In vivo evidence of increased vascular endothelial growth factor in patients with major depressive disorder

BACKGROUND

Vascular endothelial growth factor (VEGF) is a candidate mediator of blood-brain barrier (BBB) disruption in depression. However, previous studies have mainly focused on peripheral blood VEGF levels, and the results are heterogeneous. Here we use astrocyte-derived extracellular vesicles (ADEVs) isolated from plasma to explore the in vivo changes of VEGF levels in patients with major depressive disorder (MDD).

METHODS

Thirty-five unmedicated patients with MDD and 35 healthy controls (HCs) were enrolled, and plasma ADEVs were isolated from each participant. VEGF levels in ADEVs and glial fibrillary acidic protein (GFAP) in plasma were measured. Additionally, Alix and CD81, two established extracellular vesicle markers, were quantified in ADEVs.

RESULTS

At baseline, MDD patients exhibited significantly increased levels of VEGF in ADEVs and GFAP in plasma. Following four weeks of selective serotonin reuptake inhibitor treatment, these target protein levels did not significantly change. ROC curve analysis revealed an AUC of 0.711 for VEGF in ADEVs. In exploratory analysis, VEGF levels in ADEVs were positively correlated with Alix and CD81.

LIMITATIONS

Multiple factors regulate BBB permeability. This study focused solely on VEGF and the sample size for longitudinal analysis was relatively small.

CONCLUSION

Our study is the first to confirm increased ADEV-derived VEGF levels in patients with MDD, thereby providing preliminary evidence supporting the hypothesis that the BBB is disrupted in depression.

The Taiwan-ADNI workflow toward integrating plasma p-tau217 into prediction models for the risk of Alzheimer's disease and tau burden

INTRODUCTION

We integrated plasma biomarkers from the Taiwan Alzheimer's Disease Neuroimaging Initiative and propose a workflow to identify individuals showing amyloid-positive positron emission tomography (PET) with low/intermediate tau burden based on [18F]Florzolotau PET-based quantification.

METHODS

We assessed 361 participants across the Alzheimer's disease (AD) and non-AD continuum and measured plasma phosphorylated tau (p-tau)217, p-tau181, amyloid beta (Aβ)42/40 ratio, neurofilament light chain, and glial fibrillary acidic protein levels at two medical centers. We evaluated the diagnostic potential of these biomarkers.

RESULTS

Among all plasma biomarkers, p-tau217 had the highest consistency with amyloid PET results (area under the curve = 0.94), and a cutoff value could have reduced the number of confirmatory amyloid PET scans by 57.5%. In amyloid PET-positive cases intending to use anti-amyloid therapy, p-tau217 level, along with clinical parameters, had the highest predictive ability for low/intermediate tau burden.

DISCUSSION

A two-step workflow based on p-tau217 and confirmatory amyloid PET could accurately classify AD patients showing low/intermediate tau burden.

HIGHLIGHTS

The emergence of anti-amyloid therapy increases the need to accurately diagnose Alzheimer's disease (AD). The use of plasma biomarkers, especially phosphorylated tau 217 (p-tau217), can help in the diagnosis of AD. P-tau217 is a better predictor of amyloid positron emission tomography (PET) positivity than other core biomarkers. In amyloid PET-positive individuals, p-tau217 can predict tau burden. We propose a two-step workflow to identify AD cases suitable for treatment.

Neuroglia in neurodegeneration: Amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative diseases sharing significant pathologic and genetic overlap, leading to consider these diseases as a continuum in the spectrum of their pathologic features. Although FTD compromises only specific brain districts, while ALS involves both the nervous system and the skeletal muscles, several neurocentric mechanisms are in common between ALS and FTD. Also, recent research has revealed the significant involvement of nonneuronal cells, particularly glial cells such as astrocytes, oligodendrocytes, microglia, and peripheral immune cells, in disease pathology. This chapter aims to provide an extensive overview of the current understanding of the role of glia in the onset and advancement of ALS and FTD, highlighting the recent implications in terms of prognosis and future treatment options.

Astrocyte Reactivity Polygenic Risk Score May Predict Cognitive Decline in Alzheimer's Disease

Alzheimer's disease (AD) is a polygenic disorder with a prolonged prodromal phase, complicating early diagnosis. Recent research indicates that increased astrocyte reactivity is associated with a higher risk of pathogenic tau accumulation, particularly in amyloid-positive individuals. However, few clinical tools are available to predict which individuals are likely to exhibit elevated astrocyte activation and, consequently, be susceptible to hyperphosphorylated tau-induced neurodegeneration. Polygenic risk scores (PRS) aggregate the effects of multiple genetic loci to provide a single, continuous metric representing an individual's genetic risk for a specific phenotype. We hypothesized that an astrocyte activation PRS could aid in the early detection of faster clinical decline. Therefore, we constructed an astrocyte activation PRS and assessed its predictive value for cognitive decline and AD biomarkers (i.e., cerebrospinal fluid [CSF] levels of Aβ1-42, total tau, and p-tau181) in a cohort of 791 elderly individuals. The astrocyte activation PRS showed significant main effects on cross-sectional memory (β = -0.07, p = 0.03) and longitudinal executive function (β = -0.01, p = 0.03). Additionally, the PRS interacted with amyloid positivity (p.intx = 0.02), whereby indicating that amyloid burden modifies the association between the PRS and annual rate of language decline. Furthermore, the PRS was negatively associated with CSF Aβ1-42 levels (β = -3.4, p = 0.07) and interacted with amyloid status, such that amyloid burden modifies the association between the PRS and CSF phosphorylated tau levels (p.intx = 0.08). These findings suggest that an astrocyte activation PRS could be a valuable tool for early disease risk prediction, potentially enabling intervention during the interval between pathogenic amyloid and tau accumulation.

Data-driven CSF biomarker profiling: imaging and clinical outcomes in a cohort at risk of Alzheimer's disease

BACKGROUND

Cerebrospinal fluid (CSF) biomarkers of synaptic dysfunction, neuroinflammation, and glial response, complementing Alzheimer's disease (AD) core biomarkers, have improved the pathophysiological characterization of the disease. Here, we tested the hypothesis that the co-expression of multiple CSF biomarkers will help the identification of AD-like phenotypes when biomarker positivity thresholds are not met yet.

METHODS

Two hundred and seventy cognitively unimpaired adults with family history (FH) of sporadic AD (mean age = 60.6 ± 4.85 years, 64.8% women) underwent lumbar puncture, magnetic resonance imaging (n = 266) and positron emission tomography imaging (n = 239) protocols, and clinical evaluations. CSF Aβ42, Aβ40, p-tau181, p-tau217, p-tau231, NfL, neurogranin, sTREM2, YKL40, GFAP, S100, α-Synuclein, SYT1, and SNAP25 were measured. Participants were clustered based on CSF biomarker co-expression with an agglomerative algorithm. The predictive value of the classification against brain and cognitive outcomes was evaluated.

RESULTS

Three clusters (C) were identified. Higher Aβ burden and CSF p-tau was the hallmark of C1. The other two clusters showed lower Aβ burden but higher expression of glial (C2) or synaptic markers (C3). Participants in C1 showed an AD-like clinical phenotype, comprising participants with the overall highest percentage of two parent FH and APOE-ε4 carriers, in addition to comprising more females compared to C2. C3 displayed better vascular health compared to C1. C2 were older and comprised a lower percentage of females compared to C3. C1 showed an AD-like gray matter reduction in medial temporal (notably hippocampus) and frontal regions that were not observed in Aβ42/40 + compared with Aβ42/40 - . Furthermore, Aβ42/40 - participants in C1 showed GM reduction in inferior temporal areas compared with Aβ42/40 + participants overall. C1 membership also predicted cognitive decline in executive function, but not memory, beyond Aβ + status, overall suggesting a better prognosis in Aβ42/40 + participants without C1 membership. Additionally, C1 displayed a higher rate of conversion to Aβ + (25%) over time.

CONCLUSIONS

Our results suggest that examining multiple CSF biomarkers reflecting diverse pathological pathways may complement and/or outperform AD core biomarkers and thresholding approaches to identify individuals showing a clinical and cognitive AD-like phenotype, including higher conversion to Aβ + , GM reductions and cognitive decline. The clinical utility of this approach warrants further investigation and replication in other cohorts.

Inflammatory Effects and Regulatory Mechanisms of Chitinase-3-like-1 in Multiple Human Body Systems: A Comprehensive Review

Chitinase-3-like-1 (Chi3l1), also known as YKL-40 or BRP-39, is a highly conserved mammalian chitinase with a chitin-binding ability but no chitinase enzymatic activity. Chi3l1 is secreted by various cell types and induced by several inflammatory cytokines. It can mediate a series of cell biological processes, such as proliferation, apoptosis, migration, differentiation, and polarization. Accumulating evidence has verified that Chi3l1 is involved in diverse inflammatory conditions; however, a systematic and comprehensive understanding of the roles and mechanisms of Chi3l1 in almost all human body system-related inflammatory diseases is still lacking. The human body consists of ten organ systems, which are combinations of multiple organs that perform one or more physiological functions. Abnormalities in these human systems can trigger a series of inflammatory environments, posing serious threats to the quality of life and lifespan of humans. Therefore, exploring novel and reliable biomarkers for these diseases is highly important, with Chi3l1 being one such parameter because of its physiological and pathophysiological roles in the development of multiple inflammatory diseases. Reportedly, Chi3l1 plays an important role in diagnosing and determining disease activity/severity/prognosis related to multiple human body system inflammation disorders. Additionally, many studies have revealed the influencing factors and regulatory mechanisms (e.g., the ERK and MAPK pathways) of Chi3l1 in these inflammatory conditions, identifying potential novel therapeutic targets for these diseases. In this review, we comprehensively summarize the potential roles and underlying mechanisms of Chi3l1 in inflammatory disorders of the respiratory, digestive, circulatory, nervous, urinary, endocrine, skeletal, muscular, and reproductive systems, which provides a more systematic understanding of Chi3l1 in multiple human body system-related inflammatory diseases. Moreover, this article summarizes potential therapeutic strategies for inflammatory diseases in these systems on the basis of the revealed roles and mechanisms mediated by Chi3l1.

Astroglial reactivity is a key modulator of Alzheimer's disease pathological progression

This scientific commentary refers to ‘Association of glial fibrillary acid protein, Alzheimer's disease pathology and cognitive decline’ by Peretti et al. (https://doi.org/10.1093/brain/awae211).

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

Multi-analyte proteomic analysis identifies blood-based neuroinflammation, cerebrovascular and synaptic biomarkers in preclinical Alzheimer's disease

BACKGROUND

Blood-based biomarkers are gaining grounds for the detection of Alzheimer's disease (AD) and related disorders (ADRDs). However, two key obstacles remain: the lack of methods for multi-analyte assessments and the need for biomarkers for related pathophysiological processes like neuroinflammation, vascular, and synaptic dysfunction. A novel proteomic method for pre-selected analytes, based on proximity extension technology, was recently introduced. Referred to as the NULISAseq CNS disease panel, the assay simultaneously measures ~ 120 analytes related to neurodegenerative diseases, including those linked to both core (i.e., tau and amyloid-beta (Aβ)) and non-core AD processes. This study aimed to evaluate the technical and clinical performance of this novel targeted proteomic panel.

METHODS

The NULISAseq CNS disease panel was applied to 176 plasma samples from 113 individuals in the MYHAT-NI cohort of predominantly cognitively normal participants from an economically underserved region in southwestern Pennsylvania, USA. Classical AD biomarkers, including p-tau181, p-tau217, p-tau231, GFAP, NEFL, Aβ40, and Aβ42, were independently measured using Single Molecule Array (Simoa) and correlations and diagnostic performances compared. Aβ pathology, tau pathology, and neurodegeneration (AT(N) statuses) were evaluated with [11C] PiB PET, [18F]AV-1451 PET, and an MRI-based AD-signature composite cortical thickness index, respectively. Linear mixed models were used to examine cross-sectional and Wilcoxon rank sum tests for longitudinal associations between NULISA and neuroimaging-determined AT(N) biomarkers.

RESULTS

NULISA concurrently measured 116 plasma biomarkers with good technical performance (97.2 ± 13.9% targets gave signals above assay limits of detection), and significant correlation with Simoa assays for the classical biomarkers. Cross-sectionally, p-tau217 was the top hit to identify Aβ pathology, with age, sex, and APOE genotype-adjusted AUC of 0.930 (95%CI: 0.878-0.983). Fourteen markers were significantly decreased in Aβ-PET + participants, including TIMP3, BDNF, MDH1, and several cytokines. Longitudinally, FGF2, IL4, and IL9 exhibited Aβ PET-dependent yearly increases in Aβ-PET + participants. Novel plasma biomarkers with tau PET-dependent longitudinal changes included proteins associated with neuroinflammation, synaptic function, and cerebrovascular integrity, such as CHIT1, CHI3L1, NPTX1, PGF, PDGFRB, and VEGFA; all previously linked to AD but only reliable when measured in cerebrospinal fluid. The autophagosome cargo protein SQSTM1 exhibited significant association with neurodegeneration after adjusting age, sex, and APOE ε4 genotype.

CONCLUSIONS

Together, our results demonstrate the feasibility and potential of immunoassay-based multiplexing to provide a comprehensive view of AD-associated proteomic changes, consistent with the recently revised biological and diagnostic framework. Further validation of the identified inflammation, synaptic, and vascular markers will be important for establishing disease state markers in asymptomatic AD.

Peptide-Bound Glycative, AGE and Oxidative Modifications as Biomarkers for the Diagnosis of Alzheimer's Disease-A Feasibility Study

Background: The diagnosis of Alzheimer's disease (AD) relies on core cerebrospinal fluid (CSF) biomarkers, amyloid beta (Aβ) and tau. As the brain is then already damaged, researchers still strive to discover earlier biomarkers of disease onset and the progression of AD. Glycation, advanced glycation end products (AGEs) and oxidative modifications on proteins in CSF mirror the underlying biological mechanisms that contribute to early AD pathology. However, analyzing free AGEs in the body fluids of AD patients has led to controversial results. Thus, this pilot study aimed to test the feasibility of detecting, identifying and quantifying differentially glycated, AGE or oxidatively modified peptides in CSF proteins of AD patients (n = 5) compared to a control group (n = 5). Methods: To this end, we utilized a data-dependent (DDA) nano liquid chromatography (LC) linear ion trap-Orbitrap tandem mass spectrometry (MS/MS) ) approach and database search that included over 30 glycative and oxidative modifications in four search nodes to analyze endogenous modifications on individual peptides. Furthermore, we quantified candidate peptide abundance using LC Quan. Results: We identified 299 sites of early and advanced glycation and 53 sites of oxidatively modified tryptophan. From those, we identified 17 promising candidates as putative biomarkers (receiver operating curve-area under the curve (ROC-AUC) > 0.8), albeit without statistical significance. Conclusions: The potential candidates with higher discrimination power showed correlations with established diagnostic markers, thus hinting toward the potential of those peptides as biomarkers.

Unlocking early detection of Alzheimer's disease: The emerging role of nanomaterial-based optical sensors

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disorder that affects millions of individuals worldwide. Researchers have conducted numerous studies to find accurate biomarkers for early AD diagnosis and develop more effective treatments. The main pathological hallmarks of AD are amyloid beta and Tau proteins. Other biomarkers, such as DNA, RNA, and proteins, can also be helpful in early AD diagnosis. To diagnose and treat AD promptly, it is essential to accurately measure the concentration of biomarkers in the cerebrospinal fluid or blood. However, due to the low concentrations of these biomarkers in the body, highly sensitive analytical techniques are required. To date, sensors have become increasingly important due to their high sensitivity, swift detection, and adaptable manipulation features. These qualities make them an excellent substitute for conventional instruments. Nanomaterials are commonly employed in sensors to amplify signals and improve sensitivity. This review paper summarized the integration of nanomaterials in optical sensor systems, including colorimetric, fluorescent, and surface-enhanced Raman scattering sensors for AD biomarkers detection.

Blood Astrocyte Biomarkers in Alzheimer Disease: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Neuroinflammation, particularly early astrocyte reactivity, is a significant driver of Alzheimer disease (AD) pathogenesis. It is unclear how the levels of astrocyte biomarkers change in patients across the AD continuum and which best reflect AD-related change. We performed a systematic review and meta-analysis of 3 blood astrocyte biomarkers (glial fibrillary acidic protein [GFAP], chitinase-3-like protein 1 [YKL-40], and S100B) in patients clinically diagnosed with AD.

METHODS

MEDLINE and Web of Science were searched on March 23, 2023, without restrictions on language, time, or study design, for studies reporting blood levels of the astrocyte biomarkers GFAP, YKL-40, or S100B in patients on the AD continuum (including those with mild cognitive impairment [MCI] and dementia) and a cognitively unimpaired (CU) control population. AD diagnosis was based on established diagnostic criteria and/or comprehensive multidisciplinary clinical consensus. Studies reporting indirect biomarker measures (e.g., levels of biomarker autoantibodies) were excluded. Risk of bias assessment was performed using the revised Quality Assessment of Diagnostic Accuracy Studies tool. Pooled effect sizes were determined using the Hedge g method with a random-effects model. The review was prospectively registered on PROSPERO (registration number CRD42023458305).

RESULTS

The search identified 1,186 studies; 36 met inclusion criteria (AD continuum n = 3,366, CU n = 4,115). No study was assessed to have a high risk of bias. Compared with CU individuals, patients on the AD continuum had higher GFAP and YKL-40 levels (GFAP effect size 1.15, 95% CI 0.94-1.36, p < 0.0001; YKL-40 effect size 0.38, 95% CI 0.28-0.49, p < 0.0001). Both biomarkers were elevated in more advanced clinical stages of the disease (i.e., in AD dementia compared with MCI due to AD: GFAP effect size 0.48, 95% CI 0.19-0.76, p = 0.0009; YKL-40 effect size 0.34, 95% CI 0.10-0.57, p = 0.0048). No significant differences in blood S100B levels were identified.

DISCUSSION

We demonstrated significant elevations in blood GFAP and YKL-40 levels in patients on the AD continuum compared with CU individuals. Furthermore, within the AD clinical spectrum, significant elevation correlated with more advanced disease stage. Our findings suggest that both biomarkers reflect AD-related pathology. Our findings are limited by the lack of cultural and linguistic diversity in the study populations meta-analyzed. Future meta-analyses using a biomarker-defined AD population are warranted.

Intracerebral inoculation of healthy non-transgenic rats with a single aliquot of oligomeric amyloid-β (1-42) profoundly and progressively alters brain function throughout life

One of the puzzling aspects of sporadic Alzheimer's disease (AD) is how it commences. Changes in one key brain peptide, amyloid-beta (Aβ), accompany disease progression, but whether this comprises a trigger or a consequence of AD is still a topic of debate. It is clear however that the cerebral presence of oligomeric Aβ (1-42) is a key factor in early AD-pathogenesis. Furthermore, treatment of rodent brains with oligomeric Aβ (1-42) either in vitro or in vivo, acutely impairs hippocampal synaptic plasticity, creating a link between Aβ-pathology and learning impairments. Here, we show that a once-off inoculation of the brains of healthy adult rats with oligomeric Aβ (1-42) exerts debilitating effects on the long-term viability of the hippocampus, one of the primary targets of AD. Changes are progressive: months after treatment, synaptic plasticity, neuronal firing and spatial learning are impaired and expression of plasticity-related proteins are changed, in the absence of amyloid plaques. Early changes relate to activation of microglia, whereas later changes are associated with a reconstruction of astroglial morphology. These data suggest that a disruption of Aβ homeostasis may suffice to trigger an irreversible cascade, underlying progressive loss of hippocampal function, that parallels the early stages of AD.

Astrocyte reactivity is associated with tau tangle load and cortical thinning in Alzheimer's disease

BACKGROUND

It is not fully established whether plasma β-amyloid(Aβ)42/Aβ40 and phosphorylated Tau181 (p-Tau181) can effectively detect Alzheimer's disease (AD) pathophysiology in older Chinese adults and how these biomarkers correlate with astrocyte reactivity, Aβ plaque deposition, tau tangle aggregation, and neurodegeneration.

METHODS

We recruited 470 older adults and analyzed plasma Aβ42/Aβ40, p-Tau181, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) using the Simoa platform. Among them, 301, 195, and 70 underwent magnetic resonance imaging, Aβ and tau positron emission tomography imaging. The plasma Aβ42/Aβ40 and p-Tau181 thresholds were defined as ≤0.0609 and ≥2.418 based on the receiver operating characteristic curve analysis using the Youden index by comparing Aβ-PET negative cognitively unimpaired individuals and Aβ-PET positive cognitively impaired patients. To evaluate the feasibility of using plasma Aβ42/Aβ40 (A) and p-Tau181 (T) to detect AD and understand how astrocyte reactivity affects this process, we compared plasma GFAP, Aβ plaque, tau tangle, plasma NfL, hippocampal volume, and temporal-metaROI cortical thickness between different plasma A/T profiles and explored their relations with each other using general linear models, including age, sex, APOE-ε4, and diagnosis as covariates.

RESULTS

Plasma A+/T + individuals showed the highest levels of astrocyte reactivity, Aβ plaque, tau tangle, and axonal degeneration, and the lowest hippocampal volume and temporal-metaROI cortical thickness. Lower plasma Aβ42/Aβ40 and higher plasma p-Tau181 were independently and synergistically correlated with higher plasma GFAP and Aβ plaque. Elevated plasma p-Tau181 and GFAP concentrations were directly and interactively associated with more tau tangle formation. Regarding neurodegeneration, higher plasma p-Tau181 and GFAP concentrations strongly correlated with more axonal degeneration, as measured by plasma NfL, and lower plasma Aβ42/Aβ40 and higher plasma p-Tau181 were related to greater hippocampal atrophy. Higher plasma GFAP levels were associated with thinner cortical thickness and significantly interacted with lower plasma Aβ42/Aβ40 and higher plasma p-Tau181 in predicting more temporal-metaROI cortical thinning. Voxel-wise imaging analysis confirmed these findings.

DISCUSSION

This study provides a valuable reference for using plasma biomarkers to detect AD in the Chinese community population and offers novel insights into how astrocyte reactivity contributes to AD progression, highlighting the importance of targeting reactive astrogliosis to prevent AD.

Sex-specific associations of kynurenic acid with neopterin in Alzheimer's disease

BACKGROUND

Sex differences in neuroinflammation could contribute to women's increased risk of Alzheimer's disease (AD), providing rationale for exploring sex-specific AD biomarkers. In AD, dysregulation of the kynurenine pathway (KP) contributes to neuroinflammation and there is some evidence of sex differences in KP metabolism. However, the sex-specific associations between KP metabolism and biomarkers of AD and neuroinflammation need to be explored further.

METHODS

Here we investigate sex differences in cerebrospinal fluid concentrations of seven KP metabolites and sex-specific associations with established AD biomarkers and neopterin, an indicator of neuroinflammation. This study included 311 patients with symptomatic AD and 105 age-matched cognitively unimpaired (CU) controls, followed for up to 5 years.

RESULTS

We found sex differences in KP metabolites in the AD group, with higher levels of most metabolites in men, while there were no sex differences in the CU group. In line with this, more KP metabolites were significantly altered in AD men compared to CU men, and there was a trend in the same direction in AD women. Furthermore, we found sex-specific associations between kynurenic acid and the kynurenic acid/quinolinic acid ratio with neopterin, but no sex differences in the associations between KP metabolites and clinical progression.

DISCUSSION

In our cohort, sex differences in KP metabolites were restricted to AD patients. Our results suggest that dysregulation of the KP due to increased inflammation could contribute to higher AD risk in women.

In vivo reactive astrocyte imaging using [18F]SMBT-1 in tauopathy and familial Alzheimer's disease mouse models: A multi-tracer study

BACKGROUND

Reactive astrocytes play an important role in the development of Alzheimer's disease and primary tauopathies. Here, we aimed to investigate the relationships between reactive astrocytes. Microgliosis and glucose metabolism with Tau and amyloid beta pathology by using multi-tracer imaging in widely used tauopathy and familial Alzheimer's disease mouse models.

RESULTS

Positron emission tomography imaging using [18F]PM-PBB3 (tau), [18F]florbetapir (amyloid-beta), [18F]SMBT-1 (monoamine oxidase-B), [18F]DPA-714 (translocator protein) and [18F]fluorodeoxyglucose was carried out in 3- and 7-month-old rTg4510 tau mice, 5 × FAD familial Alzheimer's disease mice and wild-type mice. Immunofluorescence staining was performed to validate the pathological distribution in the mouse brain after in vivo imaging. We found increased regional levels of [18F]PM-PBB3, [18F]SMBT-1, and [18F]DPA-714 and hypoglucose metabolism in the brains of 7-month-old rTg4510 mice compared to age-matched wild-type mice. Increased [18F]SMBT-1 uptake was observed in the brains of 3, 7-month-old 5 × FAD mice, with elevated regional [18F]florbetapir and [18F]DPA-714 uptakes in the brains of 7-month-old 5 × FAD mice, compared to age-matched wild-type mice. Positive correlations were shown between [18F]SMBT-1 and [18F]PM-PBB3, [18F]DPA-714 and [18F]PM-PBB3 in rTg4510 mice, and between [18F]florbetapir and [18F]DPA-714 SUVRs in 5 × FAD mice.

CONCLUSION

In summary, these findings provide in vivo evidence that reactive astrocytes, microglial activation, and cerebral hypoglucose metabolism are associated with tau and amyloid pathology development in animal models of tauopathy and familial Alzheimer's disease.

Alzheimer's disease pathophysiology in the Retina

The retina is an emerging CNS target for potential noninvasive diagnosis and tracking of Alzheimer's disease (AD). Studies have identified the pathological hallmarks of AD, including amyloid β-protein (Aβ) deposits and abnormal tau protein isoforms, in the retinas of AD patients and animal models. Moreover, structural and functional vascular abnormalities such as reduced blood flow, vascular Aβ deposition, and blood-retinal barrier damage, along with inflammation and neurodegeneration, have been described in retinas of patients with mild cognitive impairment and AD dementia. Histological, biochemical, and clinical studies have demonstrated that the nature and severity of AD pathologies in the retina and brain correspond. Proteomics analysis revealed a similar pattern of dysregulated proteins and biological pathways in the retina and brain of AD patients, with enhanced inflammatory and neurodegenerative processes, impaired oxidative-phosphorylation, and mitochondrial dysfunction. Notably, investigational imaging technologies can now detect AD-specific amyloid deposits, as well as vasculopathy and neurodegeneration in the retina of living AD patients, suggesting alterations at different disease stages and links to brain pathology. Current and exploratory ophthalmic imaging modalities, such as optical coherence tomography (OCT), OCT-angiography, confocal scanning laser ophthalmoscopy, and hyperspectral imaging, may offer promise in the clinical assessment of AD. However, further research is needed to deepen our understanding of AD's impact on the retina and its progression. To advance this field, future studies require replication in larger and diverse cohorts with confirmed AD biomarkers and standardized retinal imaging techniques. This will validate potential retinal biomarkers for AD, aiding in early screening and monitoring.

Multi-analyte proteomic analysis identifies blood-based neuroinflammation, cerebrovascular and synaptic biomarkers in preclinical Alzheimer's disease

Background

Blood-based biomarkers are gaining grounds for Alzheimer's disease (AD) detection. However, two key obstacles need to be addressed: the lack of methods for multi-analyte assessments and the need for markers of neuroinflammation, vascular, and synaptic dysfunction. Here, we evaluated a novel multi-analyte biomarker platform, NULISAseq CNS disease panel, a multiplex NUcleic acid-linked Immuno-Sandwich Assay (NULISA) targeting ~120 analytes, including classical AD biomarkers and key proteins defining various disease hallmarks.

Methods

The NULISAseq panel was applied to 176 plasma samples from the MYHAT-NI cohort of cognitively normal participants from an economically underserved region in Western Pennsylvania. Classical AD biomarkers, including p-tau181 p-tau217, p-tau231, GFAP, NEFL, Aβ40, and Aβ42, were also measured using Single Molecule Array (Simoa). Amyloid pathology, tau pathology, and neurodegeneration were evaluated with [11C] PiB PET, [18F]AV-1451 PET, and MRI, respectively. Linear mixed models were used to examine cross-sectional and Wilcoxon rank sum tests for longitudinal associations between NULISA biomarkers and AD pathologies. Spearman correlations were used to compare NULISA and Simoa.

Results

NULISA concurrently measured 116 plasma biomarkers with good technical performance, and good correlation with Simoa measures. Cross-sectionally, p-tau217 was the top hit to identify Aβ pathology, with age, sex, and APOE genotype-adjusted AUC of 0.930 (95%CI: 0.878-0.983). Fourteen markers were significantly decreased in Aβ-PET+ participants, including TIMP3, which regulates brain Aβ production, the neurotrophic factor BDNF, the energy metabolism marker MDH1, and several cytokines. Longitudinally, FGF2, IL4, and IL9 exhibited Aβ PET-dependent yearly increases in Aβ-PET+ participants. Markers with tau PET-dependent longitudinal changes included the microglial activation marker CHIT1, the reactive astrogliosis marker CHI3L1, the synaptic protein NPTX1, and the cerebrovascular markers PGF, PDGFRB, and VEFGA; all previously linked to AD but only reliably measured in cerebrospinal fluid. SQSTM1, the autophagosome cargo protein, exhibited a significant association with neurodegeneration status after adjusting age, sex, and APOE ε4 genotype.

Conclusions

Together, our results demonstrate the feasibility and potential of immunoassay-based multiplexing to provide a comprehensive view of AD-associated proteomic changes. Further validation of the identified inflammation, synaptic, and vascular markers will be important for establishing disease state markers in asymptomatic AD.

Recently Updated Role of Chitinase 3-like 1 on Various Cell Types as a Major Influencer of Chronic Inflammation

Chitinase 3-like 1 (also known as CHI3L1 or YKL-40) is a mammalian chitinase that has no enzymatic activity, but has the ability to bind to chitin, the polymer of N-acetylglucosamine (GlcNAc). Chitin is a component of fungi, crustaceans, arthropods including insects and mites, and parasites, but it is completely absent from mammals, including humans and mice. In general, chitin-containing organisms produce mammalian chitinases, such as CHI3L1, to protect the body from exogenous pathogens as well as hostile environments, and it was thought that it had a similar effect in mammals. However, recent studies have revealed that CHI3L1 plays a pathophysiological role by inducing anti-apoptotic activity in epithelial cells and macrophages. Under chronic inflammatory conditions such as inflammatory bowel disease and chronic obstructive pulmonary disease, many groups already confirmed that the expression of CHI3L1 is significantly induced on the apical side of epithelial cells, and activates many downstream pathways involved in inflammation and carcinogenesis. In this review article, we summarize the expression of CHI3L1 under chronic inflammatory conditions in various disorders and discuss the potential roles of CHI3L1 in those disorders on various cell types.

Ion transporter cascade, reactive astrogliosis and cerebrovascular diseases

Cerebrovascular diseases and their sequalae, such as ischemic stroke, chronic cerebral hypoperfusion, and vascular dementia are significant contributors to adult disability and cognitive impairment in the modern world. Astrocytes are an integral part of the neurovascular unit in the CNS and play a pivotal role in CNS homeostasis, including ionic and pH balance, neurotransmission, cerebral blood flow, and metabolism. Astrocytes respond to cerebral insults, inflammation, and diseases through unique molecular, morphological, and functional changes, collectively known as reactive astrogliosis. The function of reactive astrocytes has been a subject of debate. Initially, astrocytes were thought to primarily play a supportive role in maintaining the structure and function of the nervous system. However, recent studies suggest that reactive astrocytes may have both beneficial and detrimental effects. For example, in chronic cerebral hypoperfusion, reactive astrocytes can cause oligodendrocyte death and demyelination. In this review, we will summarize the (1) roles of ion transporter cascade in reactive astrogliosis, (2) role of reactive astrocytes in vascular dementia and related dementias, and (3) potential therapeutic approaches for dementing disorders targeting reactive astrocytes. Understanding the relationship between ion transporter cascade, reactive astrogliosis, and cerebrovascular diseases may reveal mechanisms and targets for the development of therapies for brain diseases associated with reactive astrogliosis.

A critical appraisal of blood-based biomarkers for Alzheimer's disease

Biomarkers that predict the clinical onset of Alzheimer's disease (AD) enable the identification of individuals in the early, preclinical stages of the disease. Detecting AD at this point may allow for more effective therapeutic interventions and optimized enrollment for clinical trials of novel drugs. The current biological diagnosis of AD is based on the AT(N) classification system with the measurement of brain deposition of amyloid-β (Aβ) ("A"), tau pathology ("T"), and neurodegeneration ("N"). Diagnostic cut-offs for Aβ1-42, the Aβ1-42/Aβ1-40 ratio, tau and hyperphosphorylated-tau concentrations in cerebrospinal fluid have been defined and may support AD clinical diagnosis. Blood-based biomarkers of the AT(N) categories have been described in the AD continuum. Cross-sectional and longitudinal studies have shown that the combination of blood biomarkers tracking neuroaxonal injury (neurofilament light chain) and neuroinflammatory pathways (glial fibrillary acidic protein) enhance sensitivity and specificity of AD clinical diagnosis and improve the prediction of AD onset. However, no international accepted cut-offs have been identified for these blood biomarkers. A kit for blood Aβ1-42/Aβ1-40 is commercially available in the U.S.; however, it does not provide a diagnosis, but simply estimates the risk of developing AD. Although blood-based AD biomarkers have a great potential in the diagnostic work-up of AD, they are not ready for the routine clinical use.

Maximizing the Clinical Value of Blood-Based Biomarkers for Mild Traumatic Brain Injury

Mild traumatic brain injury (TBI) and concussion can have serious consequences that develop over time with unpredictable levels of recovery. Millions of concussions occur yearly, and a substantial number result in lingering symptoms, loss of productivity, and lower quality of life. The diagnosis may not be made for multiple reasons, including due to patient hesitancy to undergo neuroimaging and inability of imaging to detect minimal damage. Biomarkers could fill this gap, but the time needed to send blood to a laboratory for analysis made this impractical until point-of-care measurement became available. A handheld blood test is now on the market for diagnosis of concussion based on the specific blood biomarkers glial fibrillary acidic protein (GFAP) and ubiquitin carboxyl terminal hydrolase L1 (UCH-L1). This paper discusses rapid blood biomarker assessment for mild TBI and its implications in improving prediction of TBI course, avoiding repeated head trauma, and its potential role in assessing new therapeutic options. Although we focus on the Abbott i-STAT TBI plasma test because it is the first to be FDA-cleared, our discussion applies to any comparable test systems that may become available in the future. The difficulties in changing emergency department protocols to include new technology are addressed.