APP-derived peptides reflect neurodegeneration in frontotemporal dementia

Soluble Aβ pathology predicts neurodegeneration and cognitive decline independently on p-tau in the earliest Alzheimer's continuum: Evidence across two independent cohorts

INTRODUCTION

Identifying the link between early Alzheimer's disease (AD) pathological changes and neurodegeneration in asymptomatic individuals may lead to the discovery of preventive strategies. We assessed longitudinal brain atrophy and cognitive decline as a function of cerebrospinal fluid (CSF) AD biomarkers in two independent cohorts of cognitively unimpaired (CU) individuals.

METHODS

We used longitudinal voxel-based morphometry (VBM) in combination with hippocampal subfield segmentation. Changes in neuroimaging and cognitive variables were inspected using general linear models (GLMs) adjusting by age, sex, apolipoprotein E (APOE) status, follow-up time, and years of education.

RESULTS

In both cohorts, baseline CSF amyloid beta (Aβ) biomarkers significantly predicted medial temporal lobe (MTL) atrophy rates and episodic memory (EM) decline independently of CSF phosphorylated tau (p-tau).

DISCUSSION

Our data suggest that soluble Aβ dyshomeostasis triggers MTL longitudinal atrophy and EM decline independently of CSF p-tau. Our data underscore the need for secondary preventive strategies at the earliest stages of the AD pathological cascade.

HIGHLIGHTS

We assessed brain atrophy and cognitive decline in asymptomatic individuals. Aβ biomarkers predicted MTL atrophy independently of p-tau. Our results underscore the importance of undertaking Alzheimer's preclinical trials.

Establishing Co-Culture Blood–Brain Barrier Models for Different Neurodegeneration Conditions to Understand Its Effect on BBB Integrity

The blood–brain barrier (BBB) is a functional interface that provides selective permeability, protection from toxic substances, transport of nutrients, and clearance of brain metabolites. Additionally, BBB disruption has been shown to play a role in many neurodegenerative conditions and diseases. Therefore, the aim of this study was to establish a functional, convenient, and efficient in vitro co-cultured BBB model that can be used for several physiological conditions related to BBB disruption. Mouse brain-derived endothelial (bEnd.3) and astrocyte (C8-D1A) cells were co-cultured on transwell membranes to establish an intact and functional in vitro model. The co-cultured model and its effects on different neurological diseases and stress conditions, including Alzheimer’s disease (AD), neuroinflammation, and obesity, have been examined by transendothelial electrical resistance (TEER), fluorescein isothiocyanate (FITC) dextran, and tight junction protein analyses. Scanning electron microscope images showed evidence of astrocyte end-feet processes passing through the membrane of the transwell. Moreover, the co-cultured model showed effective barrier properties in the TEER, FITC, and solvent persistence and leakage tests when compared to the mono-cultured model. Additionally, the immunoblot results showed that the expression of tight junction proteins such as zonula occludens-1 (ZO-1), claudin-5, and occludin-1 was enhanced in the co-culture. Lastly, under disease conditions, the BBB structural and functional integrity was decreased. The present study demonstrated that the co-cultured in vitro model mimicked the BBB’s structural and functional integrity and, under disease conditions, the co-cultured model showed similar BBB damages. Therefore, the present in vitro BBB model can be used as a convenient and efficient experimental tool to investigate a wide range of BBB-related pathological and physiological studies.

Endo-lysosomal protein concentrations in CSF from patients with frontotemporal dementia caused by CHMP2B mutation

Introduction

Increasing evidence implicates proteostatic dysfunction as an early event in the development of frontotemporal dementia (FTD). This study aimed to explore potential cerebrospinal fluid (CSF) biomarkers associated with the proteolytic systems in genetic FTD caused by CHMP2B mutation.

Methods

Combining solid-phase extraction and parallel reaction monitoring mass spectrometry, a panel of 47 peptides derived from 20 proteins was analyzed in CSF from 31 members of the Danish CHMP2B-FTD family.

Results

Compared with family controls, mutation carriers had significantly higher levels of complement C9, lysozyme and transcobalamin II, and lower levels of ubiquitin, cathepsin B, and amyloid precursor protein.

Discussion

Lower CSF ubiquitin concentrations in CHMP2B mutation carriers indicate that ubiquitin levels relate to the specific disease pathology, rather than all-cause neurodegeneration. Increased lysozyme and complement proteins may indicate innate immune activation. Altered levels of amyloid precursor protein and cathepsins have previously been associated with impaired lysosomal proteolysis in FTD.

Highlights

CSF markers of proteostasis were explored in CHMP2B-mediated frontotemporal dementia (FTD).31 members of the Danish CHMP2B-FTD family were included.We used solid-phase extraction and parallel reaction monitoring mass spectrometry.Six protein levels were significantly altered in CHMP2B-FTD compared with controls.Lower CSF ubiquitin levels in patients suggest association with disease mechanisms.

New developments of biofluid-based biomarkers for routine diagnosis and disease trajectories in frontotemporal dementia

Frontotemporal dementia (FTD) covers a spectrum of neurodegenerative disorders with different phenotypes, genetic backgrounds, and pathological states. Its clinicopathological diversity challenges the diagnostic process and the execution of clinical trials, calling for specific diagnostic biomarkers of pathologic FTD types. There is also a need for biomarkers that facilitate disease staging, quantification of severity, monitoring in clinics and observational studies, and for evaluation of target engagement and treatment response in clinical trials. This review discusses current FTD biofluid-based biomarker knowledge taking into account the differing applications. The limitations, knowledge gaps, and challenges for the development and implementation of such markers are also examined. Strategies to overcome these hurdles are proposed, including the technologies available, patient cohorts, and collaborative research initiatives. Access to robust and reliable biomarkers that define the exact underlying pathophysiological FTD process will meet the needs for specific diagnosis, disease quantitation, clinical monitoring, and treatment development.

Blood-brain barrier dysfunction and reduced cerebrospinal fluid levels of soluble amyloid precursor protein-β in patients with subcortical small-vessel disease

Introduction

Subcortical small-vessel disease (SSVD) is the most common vascular cognitive disorder. However, because no disease-specific cerebrospinal fluid (CSF) biomarkers are available for SSVD, our aim was to identify such markers.

Methods

We included 170 healthy controls and patients from the Gothenburg Mild Cognitive Impairment (MCI) study clinically diagnosed with SSVD dementia, Alzheimer's disease (AD), or mixed AD/SSVD. We quantified CSF levels of amyloid-β (Aβ)x-38, Aβx-40, Aβx-42, as well as soluble amyloid precursor protein (sAPP)-α and sAPP-β.

Results

sAPP-β was lower in SSVD patients than in AD patients and controls. Receiver-operating characteristic (ROC) analyses showed that sAPP-β moderately separated SSVD from AD and controls. Moreover, the CSF/serum albumin ratio was elevated exclusively in SSVD and could moderately separate SSVD from the other groups in ROC analyses.

Discussion

SSVD has a biomarker profile that differs from that of AD and controls, and to some extent also from mixed AD/SSVD, suggesting that signs of blood-brain barrier (BBB) dysfunction and sAPP-β could be additional tools to diagnose SSVD.

Highlights

Patients with subcortical small-vessel disease (SSVD) exhibited reduced levels of sAPP-β and disturbances of the blood-brain barrier (BBB).This biochemical pattern is different from that of Alzheimer's disease (AD) and to some degree from that of mixed AD/SSVD.Our findings are speaking in favor of the concept that SSVD is a distinct vascular cognitive disorder (VCD) form.

The Aβ1-42/Aβ1-40 ratio in CSF is more strongly associated to tau markers and clinical progression than Aβ1-42 alone

BACKGROUND

Cerebrospinal fluid (CSF) Aβ1-42 levels and the Aβ1-42/Aβ1-40 ratio are markers of amyloid pathology, but previous studies suggest that their levels might be influenced by additional pathophysiological processes.

AIMS

To compare Aβ1-42 and the Aβ1-42/Aβ1-40 ratio in CSF in different neurodegenerative disorders and study their association with other biomarkers (tTau, pTau181, and NfL) and with cognitive and functional progression.

METHODS

We included all participants from the Sant Pau Initiative on Neurodegeneration (SPIN) with CSF Aβ1-42 and Aβ1-42/Aβ1-40. Participants had diagnoses of Alzheimer's disease (AD), dementia with Lewy bodies, frontotemporal lobar degeneration-related syndromes, non-neurodegenerative conditions, or were cognitively normal. We classified participants as "positive" or "negative" according to each marker. We compared CSF levels of tTau, pTau181, and NfL between concordant and discordant groups through ANCOVA and assessed differences in cognitive (MMSE, FCSRT) and functional (GDS, CDR-SOB) progression using Cox regression and linear-mixed models.

RESULTS

In the 1791 participants, the agreement between Aβ1-42 and Aβ1-42/Aβ1-40 was 78.3%. The Aβ1-42/Aβ1-40 ratio showed a stronger correlation with tTau and pTau181 than Aβ1-42 and an agreement with tTau and pTau181 of 73.1% and 77.1%, respectively. Participants with a low Aβ1-42/Aβ1-40 ratio showed higher tTau and pTau181 and worse cognitive and functional prognosis, regardless of whether they were positive or negative for Aβ1-42. The results were consistent across stages, diagnostic categories, and use of different cutoffs.

CONCLUSION

Although Aβ1-42 and Aβ1-42/Aβ1-40 are considered markers of the same pathophysiological pathway, our findings provide evidence favoring the use of the Aβ1-42/Aβ1-40 ratio in clinical laboratories in the context of AD.

Pathophysiological Underpinnings of Extra-Motor Neurodegeneration in Amyotrophic Lateral Sclerosis: New Insights From Biomarker Studies

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) lie at opposing ends of a clinical, genetic, and neuropathological continuum. In the last decade, it has become clear that cognitive and behavioral changes in patients with ALS are more frequent than previously recognized. Significantly, these non-motor features can impact the diagnosis, prognosis, and management of ALS. Partially overlapping neuropathological staging systems have been proposed to describe the distribution of TAR DNA-binding protein 43 (TDP-43) aggregates outside the corticospinal tract. However, the relationship between TDP-43 inclusions and neurodegeneration is not absolute and other pathophysiological processes, such as neuroinflammation (with a prominent role of microglia), cortical hyperexcitability, and synaptic dysfunction also play a central role in ALS pathophysiology. In the last decade, imaging and biofluid biomarker studies have revealed important insights into the pathophysiological underpinnings of extra-motor neurodegeneration in the ALS-FTLD continuum. In this review, we first summarize the clinical and pathophysiological correlates of extra-motor neurodegeneration in ALS. Next, we discuss the diagnostic and prognostic value of biomarkers in ALS and their potential to characterize extra-motor neurodegeneration. Finally, we debate about how biomarkers could improve the diagnosis and classification of ALS. Emerging imaging biomarkers of extra-motor neurodegeneration that enable the monitoring of disease progression are particularly promising. In addition, a growing arsenal of biofluid biomarkers linked to neurodegeneration and neuroinflammation are improving the diagnostic accuracy and identification of patients with a faster progression rate. The development and validation of biomarkers that detect the pathological aggregates of TDP-43 in vivo are notably expected to further elucidate the pathophysiological underpinnings of extra-motor neurodegeneration in ALS. Novel biomarkers tracking the different aspects of ALS pathophysiology are paving the way to precision medicine approaches in the ALS-FTLD continuum. These are essential steps to improve the diagnosis and staging of ALS and the design of clinical trials testing novel disease-modifying treatments.

Investigating drug–target interactions in frontotemporal dementia using a network pharmacology approach

Background

Frontotemporal dementia (FTD) is the second most common type of dementia in individuals aged below 65 years with no current cure. Current treatment plan is the administration of multiple medications. This has the issue of causing adverse effects due to unintentional drug–drug interactions. Therefore, there exists an urgent need to propose a novel targeted therapy that can maximize the benefits of FTD-specific drugs while minimizing its associated adverse side effects.

In this study, we implemented the concept of network pharmacology to understand the mechanism underlying FTD and highlight specific drug–gene and drug–drug interactions that can provide an interesting perspective in proposing a targeted therapy against FTD.

Results

We constructed protein–protein, drug–gene and drug–drug interaction networks to identify highly connected nodes and analysed their importance in associated enriched pathways. We also performed a historeceptomics analysis to determine tissue-specific drug interactions.

Through this study, we were able to shed light on the APP gene involved in FTD. The APP gene which was previously known to cause FTD cases in a small percentage is now being extensively studied owing to new reports claiming its participation in neurodegeneration. Our findings strengthen this hypothesis as the APP gene was found to have the highest node degree and betweenness centrality in our protein–protein interaction network and formed an essential hub node between disease susceptibility genes and neuroactive ligand–receptors.

Our findings also support the study of FTD being presented as a case of substance abuse. Our protein–protein interaction network highlights the target genes common to substance abuse (nicotine, morphine and cocaine addiction) and neuroactive ligand–receptor interaction pathways, therefore validating the cognitive impairment caused by substance abuse as a symptom of FTD.

Conclusions

Our study abandons the one-target one-drug approach and uses networks to define the disease mechanism underlying FTD. We were able to highlight important genes and pathways involved in FTD and analyse their relation with existing drugs that can provide an insight into effective medication management.

Sex differences in the behavioral variant of frontotemporal dementia: A new window to executive and behavioral reserve

INTRODUCTION

Biological sex is an increasingly recognized factor driving clinical and structural heterogeneity in Alzheimer's disease, but its role in the behavioral variant of frontotemporal dementia (bvFTD) is unknown.

METHODS

We included 216 patients with bvFTD and 235 controls with magnetic resonance imaging (MRI) from a large multicenter cohort. We compared the clinical characteristics and cortical thickness between men and women with bvFTD and controls. We followed the residuals approach to study behavioral and cognitive reserve.

RESULTS

At diagnosis, women with bvFTD showed greater atrophy burden in the frontotemporal regions compared to men despite similar clinical characteristics. For a similar amount of atrophy, women demonstrated better-than-expected scores on executive function and fewer changes in apathy, sleep, and appetite than men.

DISCUSSION

Our findings suggest that women might have greater behavioral and executive reserve than men, and neurodegeneration must be more severe in women to produce symptoms similar in severity to those in men.

Diagnostic Utility of Measuring Cerebral Atrophy in the Behavioral Variant of Frontotemporal Dementia and Association With Clinical Deterioration

IMPORTANCE

The presence of atrophy on magnetic resonance imaging can support the diagnosis of the behavioral variant of frontotemporal dementia (bvFTD), but reproducible measurements are lacking.

OBJECTIVE

To assess the diagnostic and prognostic utility of 6 visual atrophy scales (VAS) and the Magnetic Resonance Parkinsonism Index (MRPI).

DESIGN, SETTING, AND PARTICIPANTS

In this diagnostic/prognostic study, data from 235 patients with bvFTD and 225 age- and magnetic resonance imaging-matched control individuals from 3 centers were collected from December 1, 1998, to September 30, 2019. One hundred twenty-one participants with bvFTD had high confidence of frontotemporal lobar degeneration (FTLD) (bvFTD-HC), and 19 had low confidence of FTLD (bvFTD-LC). Blinded clinicians applied 6 previously validated VAS, and the MRPI was calculated with a fully automated approach. Cortical thickness and subcortical volumes were also measured for comparison. Data were analyzed from February 1 to June 30, 2020.

MAIN OUTCOMES AND MEASURES

The main outcomes of this study were bvFTD-HC or a neuropathological diagnosis of 4-repeat (4R) tauopathy and the clinical deterioration rate (assessed by longitudinal measurements of Clinical Dementia Rating Sum of Boxes). Measures of cerebral atrophy included VAS scores, the bvFTD atrophy score (sum of VAS scores in orbitofrontal, anterior cingulate, anterior temporal, medial temporal lobe, and frontal insula regions), the MRPI, and other computerized quantifications of cortical and subcortical volumes. The areas under the receiver operating characteristic curve (AUROC) were calculated for the differentiation of participants with bvFTD-HC and bvFTD-LC and controls. Linear mixed models were used to evaluate the ability of atrophy measures to estimate longitudinal clinical deterioration.

RESULTS

Of the 460 included participants, 296 (64.3%) were men, and the mean (SD) age was 62.6 (11.4) years. The accuracy of the bvFTD atrophy score for the differentiation of bvFTD-HC from controls (AUROC, 0.930; 95% CI, 0.903-0.957) and bvFTD-HC from bvFTD-LC (AUROC, 0.880; 95% CI, 0.787-0.972) was comparable to computerized measures (AUROC, 0.973 [95% CI, 0.954-0.993] and 0.898 [95% CI, 0.834-0.962], respectively). The MRPI was increased in patients with bvFTD and underlying 4R tauopathies compared with other FTLD subtypes (14.1 [2.0] vs 11.2 [2.6] points; P < .001). Higher bvFTD atrophy scores were associated with faster clinical deterioration in bvFTD (1.86-point change in Clinical Dementia Rating Sum of Boxes score per bvFTD atrophy score increase per year; 95% CI, 0.99-2.73; P < .001).

CONCLUSIONS AND RELEVANCE

Based on these study findings, in bvFTD, VAS increased the diagnostic certainty of underlying FTLD, and the MRPI showed potential for the detection of participants with underlying 4R tauopathies. These widely available measures of atrophy can also be useful to estimate longitudinal clinical deterioration.

Plasma and cerebrospinal fluid ABeta42 for the differential diagnosis of Alzheimer's disease dementia in participants diagnosed with any dementia subtype in a specialist care setting

BACKGROUND

Dementia is a syndrome that comprises many differing pathologies, including Alzheimer's disease dementia (ADD), vascular dementia (VaD) and frontotemporal dementia (FTD). People may benefit from knowing the type of dementia they live with, as this could inform prognosis and may allow for tailored treatment. Beta-amyloid (1-42) (ABeta42) is a protein which decreases in both the plasma and cerebrospinal fluid (CSF) of people living with ADD, when compared to people with no dementia. However, it is not clear if changes in ABeta42 are specific to ADD or if they are also seen in other types of dementia. It is possible that ABeta42 could help differentiate ADD from other dementia subtypes.

OBJECTIVES

To determine the accuracy of plasma and CSF ABeta42 for distinguishing ADD from other dementia subtypes in people who meet the criteria for a dementia syndrome.

SEARCH METHODS

We searched MEDLINE, and nine other databases up to 18 February 2020. We checked reference lists of any relevant systematic reviews to identify additional studies.

SELECTION CRITERIA

We considered cross-sectional studies that differentiated people with ADD from other dementia subtypes. Eligible studies required measurement of participant plasma or CSF ABeta42 levels and clinical assessment for dementia subtype.

DATA COLLECTION AND ANALYSIS

Seven review authors working independently screened the titles and abstracts generated by the searches. We collected data on study characteristics and test accuracy. We used the second version of the 'Quality Assessment of Diagnostic Accuracy Studies' (QUADAS-2) tool to assess internal and external validity of results. We extracted data into 2 x 2 tables, cross-tabulating index test results (ABeta42) with the reference standard (diagnostic criteria for each dementia subtype). We performed meta-analyses using bivariate, random-effects models. We calculated pooled estimates of sensitivity, specificity, positive predictive values, positive and negative likelihood ratios, and corresponding 95% confidence intervals (CIs). In the primary analysis, we assessed accuracy of plasma or CSF ABeta42 for distinguishing ADD from other mixed dementia types (non-ADD). We then assessed accuracy of ABeta42 for differentiating ADD from specific dementia types: VaD, FTD, dementia with Lewy bodies (DLB), alcohol-related cognitive disorder (ARCD), Creutzfeldt-Jakob disease (CJD) and normal pressure hydrocephalus (NPH). To determine test-positive cases, we used the ABeta42 thresholds employed in the respective primary studies. We then performed sensitivity analyses restricted to those studies that used common thresholds for ABeta42.

MAIN RESULTS

We identified 39 studies (5000 participants) that used CSF ABeta42 levels to differentiate ADD from other subtypes of dementia. No studies of plasma ABeta42 met the inclusion criteria. No studies were rated as low risk of bias across all QUADAS-2 domains. High risk of bias was found predominantly in the domains of patient selection (28 studies) and index test (25 studies). The pooled estimates for differentiating ADD from other dementia subtypes were as follows: ADD from non-ADD: sensitivity 79% (95% CI 0.73 to 0.85), specificity 60% (95% CI 0.52 to 0.67), 13 studies, 1704 participants, 880 participants with ADD; ADD from VaD: sensitivity 79% (95% CI 0.75 to 0.83), specificity 69% (95% CI 0.55 to 0.81), 11 studies, 1151 participants, 941 participants with ADD; ADD from FTD: sensitivity 85% (95% CI 0.79 to 0.89), specificity 72% (95% CI 0.55 to 0.84), 17 studies, 1948 participants, 1371 participants with ADD; ADD from DLB: sensitivity 76% (95% CI 0.69 to 0.82), specificity 67% (95% CI 0.52 to 0.79), nine studies, 1929 participants, 1521 participants with ADD. Across all dementia subtypes, sensitivity was greater than specificity, and the balance of sensitivity and specificity was dependent on the threshold used to define test positivity.

AUTHORS' CONCLUSIONS

Our review indicates that measuring ABeta42 levels in CSF may help differentiate ADD from other dementia subtypes, but the test is imperfect and tends to misdiagnose those with non-ADD as having ADD. We would caution against the use of CSF ABeta42 alone for dementia classification. However, ABeta42 may have value as an adjunct to a full clinical assessment, to aid dementia diagnosis.

Brain cell-derived exosomes in plasma serve as neurodegeneration biomarkers in male cynomolgus monkeys self-administrating oxycodone

Background

The United States is currently facing an opioid crisis. Novel tools to better comprehend dynamic molecular changes in the brain associated with the opioid abuse are limited. Recent studies have suggested the usefulness of plasma exosomes in better understanding CNS disorders. However, no study has ever characterized exosomes (small extracellular vesicles of endocytic origin) secreted by brain cells to understand the potential neurodegenerative effects of long-term oxycodone self-administration (SA).

Methods

MRI of Cynomolgus monkeys (Macaca fascicularis) was performed to assess alterations in gray matter volumes with oxycodone SA. We isolated total exosomes (TE) from the plasma of these monkeys; from TE, we pulled-out neuron-derived exosomes (NDE), astrocytes-derived exosomes (ADE), and microglia-derived exosomes (MDE) using surface biomarkers L1CAM (L1 cell adhesion molecule), GLAST (Glutamate aspartate transporter) and TMEM119 (transmembrane protein119), respectively.

Findings

We observed a significantly lower gray matter volume of specific lobes of the brain (frontal and parietal lobes, and right putamen) in monkeys with ∼3 years of oxycodone SA compared to controls. Higher expression of neurodegenerative biomarkers (NFL and α-synuclein) correlates well with the change in brain lobe volumes in control and oxycodone SA monkeys. We also identified a strong effect of oxycodone SA on the loading of specific miRNAs and proteins associated with neuro-cognitive disorders. Finally, exosomes subpopulation from oxycodone SA group activated NF-κB activity in THP1- cells.

Interpretation

These results provide evidence for the utility of brain cells-derived exosomes from plasma in better understanding and predicting the pro-inflammatory and neurodegenerative consequence of oxycodone SA.

Funding

NIH

Fluid Biomarkers of Frontotemporal Lobar Degeneration

A timely diagnosis of frontotemporal degeneration (FTD) is frequently challenging due to the heterogeneous symptomatology and poor phenotype-pathological correlation. Fluid biomarkers that reflect FTD pathophysiology could be instrumental in both clinical practice and pharmaceutical trials. In recent years, significant progress has been made in developing biomarkers of neurodegenerative diseases: amyloid-β and tau in cerebrospinal fluid (CSF) can be used to exclude Alzheimer's disease, while neurofilament light chain (NfL) is emerging as a promising, albeit nonspecific, marker of neurodegeneration in both CSF and blood. Gene-specific biomarkers such as PGRN in GRN mutation carriers and dipeptide repeat proteins in C9orf72 mutation carriers are potential target engagement markers in genetic FTD trials. Novel techniques capable of measuring very low concentrations of brain-derived proteins in peripheral fluids are facilitating studies of blood biomarkers as a minimally invasive alternative to CSF. A major remaining challenge is the identification of a biomarker that can be used to predict the neuropathological substrate in sporadic FTD patients.