Apolipoprotein E4-driven effects on inflammatory and neurotrophic factors in peripheral extracellular vesicles from cognitively impaired, no dementia participants who converted to Alzheimer's disease

Challenges associated with using extracellular vesicles as biomarkers in neurodegenerative disease

INTRODUCTION

The hunt for new biomarkers - for the diagnosis of subcategories of disease, or for the monitoring of the efficacy of novel therapeutics - is an increasingly relevant challenge in the current era of precision medicine. In neurodegenerative research, the aim is to look for simple tools which can predict cognitive or motor decline early, and to determine whether these can also be used to test the efficacy of new interventions. Extracellular vesicles (EVs) are thought to play an important role in intercellular communication and have been shown to play a vital role in a number of diseases.

AREAS COVERED

The aim of this review is to examine what we know about EVs in neurodegeneration and to discuss their potential to be diagnostic and prognostic biomarkers in the future. It will cover the techniques used to isolate and study EVs and what is currently known about their presence in neurodegenerative diseases. In particular, we will discuss what is required for standardization in biomarker research, and the challenges associated with using EVs within this framework.

EXPERT OPINION

The technical challenges associated with isolating EVs consistently, combined with the complex techniques required for their efficient analysis, might preclude 'pure' EV populations from being used as effective biomarkers. Whilst biomarker discovery is important for more effective diagnosis, monitoring, prediction and prognosis in neurodegenerative disease, reproducibility and ease-of-use should be the priorities.

Implication of Circulating Extracellular Vesicles-Bound Amyloid-β42 Oligomers in the Progression of Alzheimer's Disease

BACKGROUND

The perplex interrelation between circulating extracellular vesicles (cEVs) and amyloid-β (Aβ) deposits in the context of Alzheimer's disease (AD) is poorly understood.

OBJECTIVE

This study aims to 1) analyze the possible cross-linkage of the neurotoxic amyloid-β oligomers (oAβ) to the human cEVs, 2) identify cEVs corona proteins associated with oAβ binding, and 3) analyze the distribution and expression of targeted cEVs proteins in preclinical participants converted to AD 5 years later (Pre-AD).

METHODS

cEVs were isolated from 15 Pre-AD participants and 15 healthy controls selected from the Canadian Study of Health and Aging. Biochemical, clinical, lipid, and inflammatory profiles were measured. oAβ and cEVs interaction was determined by nanoparticle tracking analysis and proteinase K digestion. cEVs bound proteins were determined by ELISA.

RESULTS

oAβ were trapped by cEVs and were topologically bound to their external surface. We identified surface-exposed proteins functionally able to conjugate oAβ including apolipoprotein J (apoJ), apoE and RAGE, with apoJ being 30- to 130-fold higher than RAGE and apoE, respectively. The expression of cEVs apoJ was significantly lower in Pre-AD up to 5 years before AD onset.

CONCLUSION

Our findings suggest that cEVs might participate in oAβ clearance and that early dysregulation of cEVs could increase the risk of conversion to AD.

Biomarker and therapeutic potential of peripheral extracellular vesicles in Alzheimer's disease

Extracellular vesicles (EVs) are cell-derived nanoparticles with an important role in intercellular communication, even across brain barriers. The bidirectional brain-barrier crossing capacity of EVs is supported by research identifying neuronal markers in peripheral EVs, as well as the brain delivery of peripherally administered EVs. In addition, EVs are reflective of their cellular origin, underlining their biomarker and therapeutic potential when released by diseased and regenerative cells, respectively. Both characteristics are of interest in Alzheimer's disease (AD) where the current biomarker profile is solely based on brain-centered readouts and effective therapeutic options are lacking. In this review, we elaborate on the role of peripheral EVs in AD. We focus on bulk EVs and specific EV subpopulations including bacterial EVs (bEVs) and neuronal-derived EVs (nEVs), which have mainly been studied from a biomarker perspective. Furthermore, we highlight the therapeutic potential of peripherally administered EVs whereby research has centered around stem cell derived EVs.

Relationships of APOE Genotypes With Small RNA and Protein Cargo of Brain Tissue Extracellular Vesicles From Patients With Late-Stage AD

Background and Objectives

Variants of the apolipoprotein E (APOE) gene are the greatest known risk factors for sporadic Alzheimer disease (AD). Three major APOE isoform alleles, ε2, ε3, and ε4, encode and produce proteins that differ by only 1-2 amino acids but have different binding partner interactions. Whereas APOE ε2 is protective against AD relative to ε3, ε4 is associated with an increased risk for AD development. However, the role of APOE in gene regulation in AD pathogenesis has remained largely undetermined. Extracellular vesicles (EVs) are lipid bilayer-delimited particles released by cells to dispose of unwanted materials and mediate intercellular communication, and they are implicated in AD pathophysiology. Brain-derived EVs (bdEVs) could act locally in the tissue and reflect cellular changes. To reveal whether APOE genotype affects EV components in AD brains, bdEVs were separated from patients with AD with different APOE genotypes for parallel small RNA and protein profile.

Methods

bdEVs from late-stage AD brains (BRAAK stages 5-6) from patients with APOE genotypes ε2/3 (n = 5), ε3/3 (n = 5), ε3/4 (n = 6), and ε4/4 (n = 6) were separated using our published protocol into a 10,000g pelleted extracellular fraction (10K) and a further purified EV fraction. Counting, sizing, and multiomic characterization by small RNA sequencing and proteomic analysis were performed for 10K, EVs, and source tissue.

Results

Comparing APOE genotypes, no significant differences in bdEV total particle concentration or morphology were observed. Overall small RNA and protein profiles of 10K, EVs, and source tissue also did not differ substantially between different APOE genotypes. However, several differences in individual RNAs (including miRNAs and tRNAs) and proteins in 10K and EVs were observed when comparing the highest and lowest risk groups (ε4/4 and ε2/3). Bioinformatic analysis and previous publications indicate a potential regulatory role of these molecules in AD.

Discussion

For patients with late-stage AD in this study, only a few moderate differences were observed for small RNA and protein profiles between APOE genotypes. Among these, several newly identified 10K and EV-associated molecules may play roles in AD progression. Possibly, larger genotype-related differences exist and are more apparent in or before earlier disease stages.

Proteomics Studies in Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis

Gestational Diabetes Mellitus (GDM) is the most common metabolic complication during pregnancy and is associated with serious maternal and fetal complications such as pre-eclampsia and stillbirth. Further, women with GDM have approximately 10 times higher risk of diabetes later in life. Children born to mothers with GDM also face a higher risk of childhood obesity and diabetes later in life. Early prediction/diagnosis of GDM leads to early interventions such as diet and lifestyle, which could mitigate the maternal and fetal complications associated with GDM. However, no biomarkers identified to date have been proven to be effective in the prediction/diagnosis of GDM. Proteomic approaches based on mass spectrometry have been applied in various fields of biomedical research to identify novel biomarkers. Although a number of proteomic studies in GDM now exist, a lack of a comprehensive and up-to-date meta-analysis makes it difficult for researchers to interpret the data in the existing literature. Thus, we undertook a systematic review and meta-analysis on proteomic studies and GDM. We searched MEDLINE, EMBASE, Web of Science and Scopus from inception to January 2022. We searched Medline, Embase, CINHAL and the Cochrane Library, which were searched from inception to February 2021. We included cohort, case-control and observational studies reporting original data investigating the development of GDM compared to a control group. Two independent reviewers selected eligible studies for meta-analysis. Data collection and analyses were performed by two independent reviewers. The PROSPERO registration number is CRD42020185951. Of 120 articles retrieved, 24 studies met the eligibility criteria, comparing a total of 1779 pregnant women (904 GDM and 875 controls). A total of 262 GDM candidate biomarkers (CBs) were identified, with 49 CBs reported in at least two studies. We found 22 highly replicable CBs that were significantly different (nine CBs were upregulated and 12 CBs downregulated) between women with GDM and controls across various proteomic platforms, sample types, blood fractions and time of blood collection and continents. We performed further analyses on blood (plasma/serum) CBs in early pregnancy (first and/or early second trimester) and included studies with more than nine samples (nine studies in total). We found that 11 CBs were significantly upregulated, and 13 CBs significantly downregulated in women with GDM compared to controls. Subsequent pathway analysis using Database for Annotation, Visualization and Integrated Discovery (DAVID) bioinformatics resources found that these CBs were most strongly linked to pathways related to complement and coagulation cascades. Our findings provide important insights and form a strong foundation for future validation studies to establish reliable biomarkers for GDM.

Differential Effects of APOE Genotype on MicroRNA Cargo of Cerebrospinal Fluid Extracellular Vesicles in Females With Alzheimer's Disease Compared to Males

Multiple biological factors, including age, sex, and genetics, influence Alzheimer's disease (AD) risk. Of the 6.2 million Americans living with Alzheimer's dementia in 2021, 3.8 million are women and 2.4 million are men. The strongest genetic risk factor for sporadic AD is apolipoprotein E-e4 (APOE-e4). Female APOE-e4 carriers develop AD more frequently than age-matched males and have more brain atrophy and memory loss. Consequently, biomarkers that are sensitive to biological risk factors may improve AD diagnostics and may provide insight into underlying mechanistic changes that could drive disease progression. Here, we have assessed the effects of sex and APOE-e4 on the miRNA cargo of cerebrospinal fluid (CSF) extracellular vesicles (EVs) in AD. We used ultrafiltration (UF) combined with size exclusion chromatography (SEC) to enrich CSF EVs (e.g., Flotillin+). CSF EVs were isolated from female and male AD or controls (CTLs) that were either APOE-e3,4 or -e3,3 positive (n = 7/group, 56 total). MiRNA expression levels were quantified using a custom TaqMan™ array that assayed 190 miRNAs previously found in CSF, including 25 miRNAs that we previously validated as candidate AD biomarkers. We identified changes in the EV miRNA cargo that were affected by both AD and sex. In total, four miRNAs (miR-16-5p, -331-3p, -409-3p, and -454-3p) were significantly increased in AD vs. CTL, independent of sex and APOE-e4 status. Pathway analysis of the predicted gene targets of these four miRNAs with identified pathways was highly relevant to neurodegeneration (e.g., senescence and autophagy). There were also three miRNAs (miR-146b-5p, -150-5p, and -342-3p) that were significantly increased in females vs. males, independent of disease state and APOE-e4 status. We then performed a statistical analysis to assess the effect of APOE genotype in AD within each sex and found that APOE-e4 status affects different subsets of CSF EV miRNAs in females vs. males. Together, this study demonstrates the complexity of the biological factors associated with AD risk and the impact on EV miRNAs, which may contribute to AD pathophysiology.

Effect of APOE ε4 allele on levels of apolipoproteins E, J, and D, and redox signature in circulating extracellular vesicles from cognitively impaired with no dementia participants converted to Alzheimer's disease

INTRODUCTION

The substantial link between apolipoprotein E (APOE) ε4 allele and oxidative stress may underlie enhanced Alzheimer's disease (AD) risk. Here, we studied the impact of APOE ε4 on the level of apolipoproteins with antioxidant activities along with oxidative markers in circulating extracellular vesicles (cEVs) and plasma from cognitively impaired-not demented (CIND) individuals converted to AD (CIND-AD).

METHODS

Apolipoproteins E, J, and D and antioxidant response markers were determined in cEVs and plasma using immunoblotting, electrochemical examination, and spectrofluorimetry.

RESULTS

Total antioxidant capacity and apolipoprotein D levels in cEVs, as judged by regression analysis and cognitive performance correlations, allowed us to differentiate CIND APOE ε4 carriers from controls and to predict their progression to AD 5 years later.

DISCUSSION

Our findings support the pathological redox linkage between APOE ε4 and AD onset and suggest the use of cEVs oxidative signature in early AD diagnosis.