Small extracellular vesicles as emerging biomarkers and therapeutic targets in neurodegenerative diseases.

Small extracellular vesicles (sEVs) have rapidly emerged as versatile mediators of intercellular communication with significant potential to transform the diagnosis and treatment of neurodegenerative diseases (NDDs). Increasing evidence shows that sEVs not only participate in the propagation of pathogenic proteins but also serve as accessible, CNS-informative carriers of molecular signatures that reflect neuronal, glial, and systemic disease processes. This dual role positions sEVs at the intersection of biomarker discovery and therapeutic innovation. In the diagnostic domain, advances in immunoaffinity capture, single-vesicle analysis, and multi-omics profiling have enabled increasingly precise characterization of neuron-, astrocyte-, and microglia-derived sEVs, revealing candidate markers for Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and related disorders. However, translation remains limited by methodological heterogeneity, a lack of large-scale validation, and the need for standardized pre-analytical and analytical pipelines aligned with the ISEV/MISEV guidelines. On the therapeutic front, native and engineered sEVs, particularly those derived from mesenchymal and neural stem cells, demonstrate promising neuroprotective effects, including the modulation of neuroinflammation; the enhancement of synaptic resilience; and the delivery of antioxidant, anti-amyloid, or gene-modifying cargo across the blood-brain barrier. Scalable GMP manufacturing, cargo-loading strategies, targeting specificity, and long-term safety remain key challenges for clinical translation. This narrative review synthesizes current advances in sEV-based biomarkers and therapeutics, outlines technological and regulatory barriers, and proposes a translational roadmap spanning mechanistic discovery, platform standardization, and integration into precision-medicine frameworks. Collectively, emerging data position sEVs as powerful tools capable of reshaping the diagnostic and therapeutic landscape of NDDs, provided that coordinated multidisciplinary efforts address the remaining gaps in validation, scalability, and regulatory readiness.