Alzheimer’s disease (AD) is the leading cause of death in people with Down syndrome (DS). The triplication of chromosome 21, which harbours the amyloid precursor protein gene (APP), genetically predisposes these individuals to develop a genetically determined form of AD (DS-associated AD, or DSAD), whose pathology begins a decade before the mean age of dementia onset. Although cerebrospinal fluid and blood biomarkers such as β-amyloid or pTau217 have advanced considerably in recent years, they capture only part of the disease that also involves neuroinflammation, oxidative stress and synaptic failure. Therefore, there is a need to explore new molecular pathways to better understand its progression.
In this context, extracellular vesicles (EVs) have attracted growing interest: they are tiny particles released by virtually all cells, carrying molecules that reflect the identity and environment of their cell of origin. Brain-derived EVs (BDEVs) can cross the barrier that protects the brain and reach the peripheral bloodstream, where those derived from neurons (NDEVs) and from a type of inflammatory brain cell, astrocytes (ADEVs), can be selectively enriched, offering a non-invasive “window” into the central nervous system. Most EV studies have relied on assays that measure a single protein. By contrast, ultrasensitive platforms such as NULISAseq allow many proteins to be measured at once with extremely high sensitivity but had not yet been applied to EVs. This study, published in Alzheimer’s Research & Therapy, represents its first application to characterize BDEVs in plasma across the AD continuum in DS.
What was done in this study?
This cross-sectional, proof-of-concept study included plasma samples from 57 participants: 14 controls without Down syndrome or cognitive impairment, 20 adults with DS asymptomatic for AD (aDS) and 23 symptomatic (sDS). From these plasma samples, NDEVs and ADEVs were enriched separately and then analyzed with the NULISAseq CNS panel, which quantifies 127 central nervous system and inflammatory proteins. Detectability was compared against the Olink platform using data from an independent cohort, differential protein profiles were characterized between groups, and their correlation with established AD plasma biomarkers (pTau217, NfL and GFAP) was assessed.
Main results
- NULISAseq showed superior detectability in ADEVs (87.4% of the panel’s total proteins) than Olink (11.9%) in an independent cohort, confirming its suitability for analyzing the low-abundance proteins of EVs.
- The characterization revealed signatures of neurodegeneration, inflammation and vascular/metabolic stress.
- NDEVs showed the broadest changes, with an increase in the metabolic-stress marker PGK1 and a gradual increase in the inflammatory protein CXCL10, as well as in the axonal and neuronal injury markers NEFH and NPY across the disease continuum.
- ADEVs showed a more restricted profile, dominated by changes in phosphorylated α-synuclein (pSNCA129), associated with synaptic dysfunction, and the vascular-stress marker FLT1.
- FLT1 in ADEVs, and CXCL10, NEFH, PGK1 and NPY in NDEVs, correlated significantly with AD plasma biomarkers, reinforcing their biological relevance.
Why does it matter?
This work is the first to apply NULISAseq technology to cell-type-specific brain-derived extracellular vesicles. Capturing what happens in the brain usually requires invasive procedures such as lumbar puncture, and in plasma the signals of brain origin are often so diluted that many remain undetected. This study shows that, by isolating the vesicles released by neurons and inflammatory cells from blood, these signals can be recovered and, moreover, can be attributed to a specific cell type, which current plasma biomarkers do not always distinguish. Thus, BDEVs complement plasma biomarkers such as pTau217, NfL or GFAP, by revealing which cells are affected and through which pathways, helping to prioritize new therapeutic targets and biomarkers in Down syndrome-associated Alzheimer’s disease.