Small Extracellular Vesicles from Neural Cells: Physiological and Pathological Roles, and Potential in Neurodegenerative Therapy

Small extracellular vesicles (sEVs) have emerged as central mediators of intercellular communication in the central nervous system (CNS) and are increasingly recognized for their dual roles in the pathogenesis and treatment of neurodegenerative diseases (NDDs). In disease contexts, sEVs facilitate the intercellular dissemination of pathogenic proteins and nucleic acids, thereby contributing to the propagation of Alzheimer's disease (AD) and Parkinson's disease (PD) pathology. Conversely, their intrinsic biocompatibility, capacity to traverse brain barriers, and inherent organotropic properties position sEVs as highly promising nanocarriers for CNS drug delivery. While mesenchymal stem cell-derived sEVs have been widely investigated in preclinical NDD models, accumulating evidence suggests that sEVs derived from neural cells, including neural stem cells, neurons, astrocytes, microglia, oligodendrocytes, and brain endothelial cells may offer superior brain targeting, disease relevance, and functional efficacy. This review provides a comprehensive and critical analysis of current knowledge on neural cell-derived sEVs, encompassing their physiological roles in brain homeostasis, their involvement in AD and PD pathogenesis, and their emerging therapeutic applications. We discuss cell-type-specific sEV cargo profiles, mechanisms underlying blood-brain and blood-cerebrospinal fluid barrier traversal, and recent advances in endogenous and exogenous engineering strategies that enhance cargo loading, targeting precision, and therapeutic performance. Importantly, we address key translational challenges that currently limit clinical implementation. By integrating mechanistic insights with therapeutic and engineering perspectives, this review highlights neural cell-derived sEVs as a biologically informed and versatile platform, underscoring their potential to advance next-generation neuro-nanomedicine for NDDs.