MS Brain Vesicles Reveal Hidden Synaptic and Mitochondrial Damage in White Matter

Multiple sclerosis is classically defined by inflammatory demyelinating lesions, but substantial pathology also occurs in normal-appearing white matter (NAWM)—regions that look intact on conventional imaging yet harbor neurodegeneration, axonal injury, and subtle inflammation. Understanding what is happening at the molecular level in NAWM is critical because it may drive progressive disability even when overt lesions are absent. Extracellular vesicles (EVs), membrane-enclosed nanoparticles released by all cells, carry molecular cargo reflective of their cell of origin and disease state, making them promising windows into CNS biology.

This study, from Johns Hopkins University and Cleveland Clinic, isolated and characterized EVs from postmortem NAWM of four MS patients and four age-matched controls using a rigorous pipeline: differential centrifugation followed by size exclusion chromatography (SEC), with EV-rich fractions collected and validated by nanoflow cytometry, single-particle interferometric reflectance imaging (SP-IRIS/ExoView), and transmission electron microscopy (TEM). EV yield, size, and morphology were statistically similar between MS and control samples, confirming that quantity differences did not confound downstream analyses.

Despite the small sample size, proteomics revealed biologically compelling differences. MS NAWM EVs showed significant downregulation of synaptic proteins (consistent with known synaptic pathology in MS) and mitochondrial proteins (reflecting metabolic dysfunction), while complement cascade proteins and inflammatory mediators were markedly upregulated. Pathway enrichment analyses highlighted aging-related signatures as well, suggesting that compartmentalized neuroinflammation in MS may accelerate cellular aging processes within the CNS. Cell-type deconvolution of the EV proteomes indicated a shift away from neuronal EV origin toward increased astrocytic contribution in MS, aligning with known astrogliosis in MS NAWM.

A particularly translational finding is that several proteomic changes identified in these CNS tissue-derived EVs overlap with changes previously reported in circulating brain-derived EVs from MS patients. This cross-validation supports the hypothesis that plasma-derived brain EVs can serve as non-invasive surrogates for CNS tissue pathology—a concept with significant implications for biomarker development and disease monitoring without requiring tissue biopsy.

The study is strengthened by adherence to MISEV2023 guidelines and use of multiple orthogonal characterization methods, and by its focus on NAWM—a clinically important but understudied compartment. However, the small sample size (n=4 per group), postmortem tissue limitations, and demographic differences (all MS patients were female; controls were mixed sex) introduce potential confounders. Nevertheless, this work establishes a valuable molecular reference dataset and points toward EVs as active mediators—not merely bystanders—of synaptic loss, mitochondrial failure, and complement-driven neuroinflammation in MS.