Involvement of the choroid plexus in Alzheimer's disease pathophysiology: findings from mouse and human proteomic studies.

BACKGROUND: Structural and functional changes of the choroid plexus (ChP) have been reported in Alzheimer's disease (AD). Nonetheless, the role of the ChP in the pathogenesis of AD remains largely unknown. We aim to unravel the relation between ChP functioning and core AD pathogenesis using a unique proteomic approach in mice and humans. METHODS: We used an APP knock-in mouse model, APPNL-G-F, exhibiting amyloid pathology, to study the association between AD brain pathology and protein changes in mouse ChP tissue and CSF using liquid chromatography mass spectrometry. Mouse proteomes were investigated at the age of 7 weeks (n = 5) and 40 weeks (n = 5). Results were compared with previously published human AD CSF proteomic data (n = 496) to identify key proteins and pathways associated with ChP changes in AD. RESULTS: ChP tissue proteome was dysregulated in APPNL-G-F mice relative to wild-type mice at both 7 and 40 weeks. At both ages, ChP tissue proteomic changes were associated with epithelial cells, mitochondria, protein modification, extracellular matrix and lipids. Nonetheless, some ChP tissue proteomic changes were different across the disease trajectory; pathways related to lysosomal function, endocytosis, protein formation, actin and complement were uniquely dysregulated at 7 weeks, while pathways associated with nervous system, immune system, protein degradation and vascular system were uniquely dysregulated at 40 weeks. CSF proteomics in both mice and humans showed similar ChP-related dysregulated pathways. CONCLUSIONS: Together, our findings support the hypothesis of ChP dysfunction in AD. These ChP changes were related to amyloid pathology. Therefore, the ChP could become a novel promising therapeutic target for AD.

Microfluidic Interfaces for Chronic Bidirectional Access to the Brain.

Two-photon polymerization (TPP) is an additive manufacturing technique with micron-scale resolution that is rapidly gaining ground for a range of biomedical applications. TPP is particularly attractive for the creation of microscopic three-dimensional structures in biocompatible and noncytotoxic resins. Here, TPP is used to develop microfluidic interfaces which provide chronic fluidic access to the brain of preclinical research models. These microcatheters can be used for either convection-enhanced delivery (CED) or for the repeated collection of liquid biopsies. In a brain phantom, infusions with the micronozzle result in more localized distribution clouds and lower backflow compared to a control catheter. In mice, the delivery interface enables faster, more precise, and physiologically less disruptive fluid injections. A second microcatheter design enables repeated, longitudinal sampling of cerebrospinal fluid (CSF) over time periods as long as 250 days. Moreover, further in vivo studies demonstrate that the blood-CSF barrier is intact after chronic implantation of the sampling interface and that samples are suitable for downstream molecular analysis for the identification of nucleic acid- or peptide-based biomarkers. Ultimately, the versatility of this fabrication technique implies a great translational potential for simultaneous drug delivery and biomarker tracking in a range of human neurological diseases.

High-precision K isotopic analysis of cerebrospinal fluid and blood serum microsamples via multicollector inductively coupled plasma-mass spectrometry equipped with 1013 Ω faraday cup amplifier resistors.

BACKGROUND: Potassium isotopic analysis is increasingly performed in both geological and biological contexts as a result of the introduction of MC-ICP-MS instrumentation either equipped with a collision/reaction cell or having the capability of working at "extra-high" mass resolution in order to deal with spectral interference caused by argon hydride (ArH+) ions. Potassium plays an important role in the central nervous system, and its isotopic analysis could provide an enhanced insight into the corresponding processes, but K isotopic analysis of cerebrospinal fluid is challenging due to the small volume, a few microliter only, typically available. This work aimed at developing a method for determining the K isotopic signature of serum and cerebrospinal fluid at a final K concentration of 25 ng mL-1 using Faraday cup amplifiers equipped with a 1013 Ω resistor. RESULTS: Potassium isotope ratios obtained for reference materials measured at a final K concentration of 25 ng mL-1 were in excellent agreement with the corresponding reference values and the internal and external precision for the δ41K value was 0.11 ‰ (2SE, N = 50) and 0.10 ‰ (2SD, N = 6), respectively. The robustness against the presence of matrix elements and the concentration mismatch between sample and standard observed at higher K concentrations is preserved at low K concentration. Finally, K isotopic analysis of serum and cerebrospinal fluid (3-12 µL of sample) of healthy mice of both sexes was performed, revealing a trend towards an isotopically lighter signature for serum and cerebrospinal fluid from female individuals, however being significant for serum only. SIGNIFICANCE: This work provides a robust method for high-precision K isotopic analysis at a concentration of 25 ng mL-1. By monitoring both K isotopes, 39K and 41K, with Faraday cups connected to amplifiers with 1013 Ω resistors, accurate K isotope ratio results are obtained with a two-fold improvement in internal and external precision compared to those obtained with the set-up with traditional 1011 Ω resistors. The difference in the K isotope ratio in CSF and serum between the sexes, is possibly indicating an influence of the sex or hormones on the fractionation effects accompanying cellular uptake/release.

Safety and efficacy of faecal microbiota transplantation in patients with mild to moderate Parkinson's disease (GUT-PARFECT): a double-blind, placebo-controlled, randomised, phase 2 trial.

Background: Dysregulation of the gut microbiome has been implicated in Parkinson's disease (PD). This study aimed to evaluate the clinical effects and safety of a single faecal microbiota transplantation (FMT) in patients with early-stage PD. Methods: The GUT-PARFECT trial, a single-centre randomised, double-blind, placebo-controlled trial was conducted at Ghent University Hospital between December 01, 2020 and December 12, 2022. Participants (aged 50-65 years, Hoehn and Yahr stage 2) were randomly assigned to receive nasojejunal FMT with either healthy donor stool or their own stool. Computer-generated randomisation was done in a 1:1 ratio through permutated-block scheduling. Treatment allocation was concealed for participants and investigators. The primary outcome measure at 12 months was the change in the Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) motor score obtained during off-medication evaluations. Intention-to-treat analysis was performed using a mixed model for repeated measures analysis. This completed trial is registered on ClinicalTrials.gov (NCT03808389). Findings: Between December 2020 and December 2021, FMT procedures were conducted on 46 patients with PD: 22 in the healthy donor group and 24 in the placebo group. Clinical evaluations were performed at baseline, 3, 6, and 12 months post-FMT. Full data analysis was possible for 21 participants in the healthy donor group and 22 in the placebo group. After 12 months, the MDS-UPDRS motor score significantly improved by a mean of 5.8 points (95% CI -11.4 to -0.2) in the healthy donor group and by 2.7 points (-8.3 to 2.9) in the placebo group (p = 0.0235). Adverse events were limited to temporary abdominal discomfort. Interpretation: Our findings suggested a single FMT induced mild, but long-lasting beneficial effects on motor symptoms in patients with early-stage PD. These findings highlight the potential of modulating the gut microbiome as a therapeutic approach and warrant a further exploration of FMT in larger cohorts of patients with PD in various disease stages. Funding: Flemish PD patient organizations (VPL and Parkili), Research Foundation Flanders (FWO), Biocodex Microbiota Foundation.

The Spreading and Effects of Human Recombinant α-Synuclein Preformed Fibrils in the Cerebrospinal Fluid of Mice.

Parkinson's disease (PD) patients harbor seeding-competent α-synuclein (α-syn) in their cerebrospinal fluid (CSF), which is mainly produced by the choroid plexus (ChP). Nonetheless, little is known about the role of the CSF and the ChP in PD pathogenesis. To address this question, we used an intracerebroventricular (icv) injection mouse model to assess CSF α-syn spreading and its short- and long-term consequences on the brain. Hereby, we made use of seeding-competent, recombinant α-syn preformed fibrils (PFF) that are known to induce aggregation and subsequent spreading of endogenous α-syn in stereotactic tissue injection models. Here, we show that icv-injected PFF, but not monomers (Mono), are rapidly removed from the CSF by interaction with the ChP. Additionally, shortly after icv injection both Mono and PFF were detected in the olfactory bulb and striatum. This spreading was associated with increased inflammation and complement activation in these tissues as well as leakage of the blood-CSF barrier. Despite these effects, a single icv injection of PFF didn't induce a decline in motor function. In contrast, daily icv injections over the course of 5 days resulted in deteriorated grip strength and formation of phosphorylated α-syn inclusions in the brain 2 months later, whereas dopaminergic neuron levels were not affected. These results point toward an important clearance function of the CSF and the ChP, which could mediate removal of PFF from the brain, whereby chronic exposure to PFF in the CSF may negatively impact blood-CSF barrier functionality and PD pathology.

Inflammasome signaling is dispensable for ß-amyloid-induced neuropathology in preclinical models of Alzheimer's disease.

Background: Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting memory and cognition. The disease is accompanied by an abnormal deposition of ß-amyloid plaques in the brain that contributes to neurodegeneration and is known to induce glial inflammation. Studies in the APP/PS1 mouse model of ß-amyloid-induced neuropathology have suggested a role for inflammasome activation in ß-amyloid-induced neuroinflammation and neuropathology. Methods: Here, we evaluated the in vivo role of microglia-selective and full body inflammasome signalling in several mouse models of ß-amyloid-induced AD neuropathology. Results: Microglia-specific deletion of the inflammasome regulator A20 and inflammasome effector protease caspase-1 in the AppNL-G-F and APP/PS1 models failed to identify a prominent role for microglial inflammasome signalling in ß-amyloid-induced neuropathology. Moreover, global inflammasome inactivation through respectively full body deletion of caspases 1 and 11 in AppNL-G-F mice and Nlrp3 deletion in APP/PS1 mice also failed to modulate amyloid pathology and disease progression. In agreement, single-cell RNA sequencing did not reveal an important role for Nlrp3 signalling in driving microglial activation and the transition into disease-associated states, both during homeostasis and upon amyloid pathology. Conclusion: Collectively, these results question a generalizable role for inflammasome activation in preclinical amyloid-only models of neuroinflammation.

An immunological puzzle: The adaptive immune system fuels Alzheimer's disease pathology.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by a concerning rise in prevalence. It is projected that the number of affected individuals will reach a staggering 150 million by 2050. While recent advancements in monoclonal antibodies targeting Aß have shown some clinical effects, there is an urgent need for improved therapies to effectively address the impeding surge of AD patients worldwide. To achieve this, a deeper understanding of the intricate mechanisms underlying the disease is crucial. In recent years, mounting evidence has underscored the vital role of the innate immune system in AD pathology. However, limited findings persist regarding the involvement of the adaptive immune system. Here, we report on the impact of the adaptive immune system on various aspects of AD by using AppNL-G-F mice crossed into a Rag2-/- background lacking mature adaptive immune cells. In addition, to simulate the continuous exposure to various challenges such as infections that is commonly observed in humans, the innate immune system was activated through the repetitive induction of peripheral inflammation. We observed a remarkably improved performance on complex cognitive tasks when a mature adaptive immune system is absent. Notably, this observation is pathologically associated with lower Aß plaque accumulation, reduced glial activation, and better-preserved neuronal networks in the mice lacking a mature adaptive immune system. Collectively, these findings highlight the detrimental role of the adaptive immune system in AD and underscore the need for effective strategies to modulate it for therapeutic purposes.

Limitations of PLX3397 as a microglial investigational tool: peripheral and off-target effects dictate the response to inflammation.

Microglia, the resident macrophages of the central nervous system (CNS), play a critical role in CNS homeostasis and neuroinflammation. Pexidartinib (PLX3397), a colony-stimulating factor 1 (CSF1) receptor inhibitor, is widely used to deplete microglia, offering flexible options for both long-term depletion and highly versatile depletion-repopulation cycles. However, the potential impact of PLX3397 on peripheral (immune) cells remains controversial. Until now, the microglia-specificity of this type of compounds has not been thoroughly evaluated, particularly in the context of peripherally derived neuroinflammation. Our study addresses this gap by examining the effects of PLX3397 on immune cells in the brain, liver, circulation and bone marrow, both in homeostasis and systemic inflammation models. Intriguingly, we demonstrate that PLX3397 treatment not only influences the levels of tissue-resident macrophages, but also affects circulating and bone marrow immune cells beyond the mononuclear phagocyte system (MPS). These alterations in peripheral immune cells disrupt the response to systemic inflammation, consequently impacting the phenotype irrespective of microglial depletion. Furthermore, we observed that a lower dose of PLX3397, which does not deplete microglia, demonstrates similar (non-)MPS effects, both in the periphery and the brain, but fails to fully replicate the peripheral alterations seen in the higher doses, questioning lower doses as a 'peripheral control' strategy. Overall, our data highlight the need for caution when interpreting studies employing this compound, as it may not be suitable for specific investigation of microglial function in the presence of systemic inflammation.

Proteomic comparison between non-purified cerebrospinal fluid and cerebrospinal fluid-derived extracellular vesicles from patients with Alzheimer's, Parkinson's and Lewy body dementia.

Dementia is a leading cause of death worldwide, with increasing prevalence as global life expectancy increases. The most common neurodegenerative disorders are Alzheimer's disease (AD), dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). With this study, we took an in-depth look at the proteome of the (non-purified) cerebrospinal fluid (CSF) and the CSF-derived extracellular vesicles (EVs) of AD, PD, PD-MCI (Parkinson's disease with mild cognitive impairment), PDD and DLB patients analysed by label-free mass spectrometry. This has led to the discovery of differentially expressed proteins that may be helpful for differential diagnosis. We observed a greater number of differentially expressed proteins in CSF-derived EV samples (N = 276) compared to non-purified CSF (N = 169), with minimal overlap between both datasets. This finding suggests that CSF-derived EV samples may be more suitable for the discovery phase of a biomarker study, due to the removal of more abundant proteins, resulting in a narrower dynamic range. As disease-specific markers, we selected a total of 39 biomarker candidates identified in non-purified CSF, and 37 biomarker candidates across the different diseases under investigation in the CSF-derived EV data. After further exploration and validation of these proteins, they can be used to further differentiate between the included dementias and may offer new avenues for research into more disease-specific pharmacological therapeutics.

Gut microbiota regulates blood-cerebrospinal fluid barrier function and Aß pathology.

Accumulating evidence indicates that gut microbiota dysbiosis is associated with increased blood-brain barrier (BBB) permeability and contributes to Alzheimer's disease (AD) pathogenesis. In contrast, the influence of gut microbiota on the blood-cerebrospinal fluid (CSF) barrier has not yet been studied. Here, we report that mice lacking gut microbiota display increased blood-CSF barrier permeability associated with disorganized tight junctions (TJs), which can be rescued by recolonization with gut microbiota or supplementation with short-chain fatty acids (SCFAs). Our data reveal that gut microbiota is important not only for the establishment but also for the maintenance of a tight barrier. Also, we report that the vagus nerve plays an important role in this process and that SCFAs can independently tighten the barrier. Administration of SCFAs in AppNL-G-F mice improved the subcellular localization of TJs at the blood-CSF barrier, reduced the ß-amyloid (Aß) burden, and affected microglial phenotype. Altogether, our results suggest that modulating the microbiota and administering SCFAs might have therapeutic potential in AD via blood-CSF barrier tightening and maintaining microglial activity and Aß clearance.

Bacterial extracellular vesicles: an emerging avenue to tackle diseases.

A growing body of research, especially in recent years, has shown that bacterial extracellular vesicles (bEVs) are one of the key underlying mechanisms behind the pathogenesis of various diseases like pulmonary fibrosis, sepsis, systemic bone loss, and Alzheimer's disease. Given these new insights, bEVs are proposed as an emerging vehicle that can be used as a diagnostic tool or to tackle diseases when used as a therapeutic target. To further boost the understanding of bEVs in health and disease we thoroughly discuss the contribution of bEVs in disease pathogenesis and the underlying mechanisms. In addition, we speculate on their potential as novel diagnostic biomarkers and how bEV-related mechanisms can be exploited as therapeutic targets.

Alzheimer's Disease and Age-Related Changes in the Cu Isotopic Composition of Blood Plasma and Brain Tissues of the APPNL-G-F Murine Model Revealed by Multi-Collector ICP-Mass Spectrometry.

Alzheimer's' disease (AD) is characterized by the formation of ß-amyloid (Aß) plaques and neurofibrillary tangles of tau protein in the brain. Aß plaques are formed by the cleavage of the ß-amyloid precursor protein (APP). In addition to protein aggregations, the metabolism of the essential mineral element Cu is also altered during the pathogenesis of AD. The concentration and the natural isotopic composition of Cu were investigated in blood plasma and multiple brain regions (brain stem, cerebellum, cortex, and hippocampus) of young (3-4 weeks) and aged (27-30 weeks) APPNL-G-F knock-in mice and wild-type controls to assess potential alterations associated with ageing and AD. Tandem inductively coupled plasma-mass spectrometry (ICP-MS/MS) was used for elemental analysis and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for high-precision isotopic analysis. The blood plasma Cu concentration was significantly altered in response to both age- and AD-related effects, whereas the blood plasma Cu isotope ratio was only affected by the development of AD. Changes in the Cu isotopic signature of the cerebellum were significantly correlated with the changes observed in blood plasma. The brain stem showed a significant increase in Cu concentration for both young and aged AD transgenic mice compared with healthy controls, whereas the Cu isotopic signature became lighter as a result of age-related changes. In this work, ICP-MS/MS and MC-ICP-MS provided relevant and complementary information on the potential role of Cu in ageing and AD.

Experimental hepatic encephalopathy causes early but sustained glial transcriptional changes.

Hepatic encephalopathy (HE) is a common complication of liver cirrhosis, associated with high morbidity and mortality, for which no brain-targeted therapies exist at present. The interplay between hyperammonemia and inflammation is thought to drive HE development. As such, astrocytes, the most important ammonia-metabolizing cells in the brain, and microglia, the main immunomodulatory cells in the brain, have been heavily implicated in HE development. As insight into cellular perturbations driving brain pathology remains largely elusive, we aimed to investigate cell-type specific transcriptomic changes in the HE brain. In the recently established mouse bile duct ligation (BDL) model of HE, we performed RNA-Seq of sorted astrocytes and microglia at 14 and 28 days after induction. This revealed a marked transcriptional response in both cell types which was most pronounced in microglia. In both cell types, pathways related to inflammation and hypoxia, mechanisms commonly implicated in HE, were enriched. Additionally, astrocytes exhibited increased corticoid receptor and oxidative stress signaling, whereas microglial transcriptome changes were linked to immune cell attraction. Accordingly, both monocytes and neutrophils accumulated in the BDL mouse brain. Time-dependent changes were limited in both cell types, suggesting early establishment of a pathological phenotype. While HE is often considered a unique form of encephalopathy, astrocytic and microglial transcriptomes showed significant overlap with previously established gene expression signatures in other neuroinflammatory diseases like septic encephalopathy and stroke, suggesting common pathophysiological mechanisms. Our dataset identifies key molecular mechanisms involved in preclinical HE and provides a valuable resource for development of novel glial-directed therapeutic strategies.

Helicobacter pylori-derived outer membrane vesicles contribute to Alzheimer's disease pathogenesis via C3-C3aR signalling.

The gut microbiota represents a diverse and dynamic population of microorganisms that can influence the health of the host. Increasing evidence supports the role of the gut microbiota as a key player in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD). Unfortunately, the mechanisms behind the interplay between gut pathogens and AD are still elusive. It is known that bacteria-derived outer membrane vesicles (OMVs) act as natural carriers of virulence factors that are central players in the pathogenesis of the bacteria. Helicobacter pylori (H. pylori) is a common gastric pathogen and H. pylori infection has been associated with an increased risk to develop AD. Here, we are the first to shed light on the role of OMVs derived from H. pylori on the brain in healthy conditions and on disease pathology in the case of AD. Our results reveal that H. pylori OMVs can cross the biological barriers, eventually reaching the brain. Once in the brain, these OMVs are taken up by astrocytes, which induce activation of glial cells and neuronal dysfunction, ultimately leading to exacerbated amyloid-ß pathology and cognitive decline. Mechanistically, we identified a critical role for the complement component 3 (C3)-C3a receptor (C3aR) signalling in mediating the interaction between astrocytes, microglia and neurons upon the presence of gut H. pylori OMVs. Taken together, our study reveals that H. pylori has a detrimental effect on brain functionality and accelerates AD development via OMVs and C3-C3aR signalling.

Differential plasticity and fate of brain-resident and recruited macrophages during the onset and resolution of neuroinflammation.

Microglia and border-associated macrophages (BAMs) are brain-resident self-renewing cells. Here, we examined the fate of microglia, BAMs, and recruited macrophages upon neuroinflammation and through resolution. Upon infection, Trypanosoma brucei parasites invaded the brain via its border regions, triggering brain barrier disruption and monocyte infiltration. Fate mapping combined with single-cell sequencing revealed microglia accumulation around the ventricles and expansion of epiplexus cells. Depletion experiments using genetic targeting revealed that resident macrophages promoted initial parasite defense and subsequently facilitated monocyte infiltration across brain barriers. These recruited monocyte-derived macrophages outnumbered resident macrophages and exhibited more transcriptional plasticity, adopting antimicrobial gene expression profiles. Recruited macrophages were rapidly removed upon disease resolution, leaving no engrafted monocyte-derived cells in the parenchyma, while resident macrophages progressively reverted toward a homeostatic state. Long-term transcriptional alterations were limited for microglia but more pronounced in BAMs. Thus, brain-resident and recruited macrophages exhibit diverging responses and dynamics during infection and resolution.

Choroid plexus-derived extracellular vesicles exhibit brain targeting characteristics.

The brain is protected against invading organisms and other unwanted substances by tightly regulated barriers. However, these central nervous system (CNS) barriers impede the delivery of drugs into the brain via the blood circulation and are therefore considered major hurdles in the treatment of neurological disorders. Consequently, there is a high need for efficient delivery systems that are able to cross these strict barriers. While most research focuses on the blood-brain barrier (BBB), the design of drug delivery platforms that are able to cross the blood-cerebrospinal fluid (CSF) barrier, formed by a single layer of choroid plexus epithelial cells, remains a largely unexplored domain. The discovery that extracellular vesicles (EVs) make up a natural mechanism for information transfer between cells and across cell layers, has stimulated interest in their potential use as drug delivery platform. Here, we report that choroid plexus epithelial cell-derived EVs exhibit the capacity to home to the brain after peripheral administration. Moreover, these vesicles are able to functionally deliver cargo into the brain. Our findings underline the therapeutic potential of choroid plexus-derived EVs as a brain drug delivery vehicle via targeting of the blood-CSF interface.

A mouse model of hepatic encephalopathy: bile duct ligation induces brain ammonia overload, glial cell activation and neuroinflammation.

Hepatic encephalopathy (HE) is a common complication of chronic liver disease, characterized by an altered mental state and hyperammonemia. Insight into the brain pathophysiology of HE is limited due to a paucity of well-characterized HE models beyond the rat bile duct ligation (BDL) model. Here, we assess the presence of HE characteristics in the mouse BDL model. We show that BDL in C57Bl/6j mice induces motor dysfunction, progressive liver fibrosis, liver function failure and hyperammonemia, all hallmarks of HE. Swiss mice however fail to replicate the same phenotype, underscoring the importance of careful strain selection. Next, in-depth characterisation of metabolic disturbances in the cerebrospinal fluid of BDL mice shows glutamine accumulation and transient decreases in taurine and choline, indicative of brain ammonia overload. Moreover, mouse BDL induces glial cell dysfunction, namely microglial morphological changes with neuroinflammation and astrocyte reactivity with blood-brain barrier (BBB) disruption. Finally, we identify putative novel mechanisms involved in central HE pathophysiology, like bile acid accumulation and tryptophan-kynurenine pathway alterations. Our study provides the first comprehensive evaluation of a mouse model of HE in chronic liver disease. Additionally, this study further underscores the importance of neuroinflammation in the central effects of chronic liver disease.

Recent insights into viral infections as a trigger and accelerator in alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder for which only symptomatic medication is available, except for the recently FDA-approved aducanumab. This lack of effective treatment urges us to investigate alternative paths that might contribute to disease development. In light of the recent SARS-CoV-2 pandemic and the disturbing neurological complications seen in some patients, it is desirable to (re)investigate the viability of the viral infection theory claiming that a microbe could affect AD initiation and/or progression. Here, we review the most important evidence for this theory with a special focus on two viruses, namely HSV-1 and SARS-CoV-2. Moreover, we discuss the possible involvement of extracellular vesicles (EVs). This overview will contribute to a more rational approach of potential treatment strategies for AD patients.

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.