α‐Synuclein Promotes the Expression and Release of Neurofilament Light Chain from Oligodendrocytes in a Murine Model: Implication for Multiple System Atrophy?

OBJECTIVE: The understanding of neurofilament light chain (NfL) presence and release in oligodendrocytes is limited. This study aims to determine the NfL expression in oligodendrocytes, investigate whether excess ɑ-synuclein (α-syn) impacts NfL expression, release, and functions in oligodendrocytes, as well as detect plasma NfL-positive oligodendrocyte-derived extracellular vesicles (ODEVs) changes in patients with multiple system atrophy (MSA), Parkinson's disease (PD), and healthy controls (HCs). METHODS: NfL expression in oligodendrocytes was assessed using RNAscope and immunofluorescence staining in human and mouse brain slices, as well as flow cytometry in mouse brain single-cells. The MO3.13 oligodendrocyte cell line was used to mimic MSA pathology with α-syn overexpression or preformed fibril treatment. NfL levels were detected in cell line, brain tissues and condition media, and the differences between MSA pathology and controls were compared. Plasma NfL-positive ODEVs were quantified using nano-scale flow cytometry in a cohort of 101 MSA patients, 96 PD patients, and 97 HCs. RESULTS: Both NEFL mRNA and NfL protein showed co-localization with typical oligodendrocyte marker anti-2,3-cyclic nucleotide-3-phosphodiesterase (CNPase). A total of 58.5% of CNPase-positive oligodendrocytes co-expressed NfL. Increased α-syn load elevates NfL expression in both oligodendrocyte cell line and MSA patient brain slices. NfL overexpression inhibited oligodendrocyte maturation, but did not affect α-syn-induced cell viability deficits. α-Syn promoted oligodendrocytic NfL release via extracellular vesicles. Plasma NfL-positive ODEVs were elevated in MSA patients compared to PD and HCs. INTERPRETATION: These findings suggest additional cellular roles for NfL in oligodendrocytes beyond its established function in neurons and have potential implications for the neurodegenerative pathophysiology of MSA. ANN NEUROL 2025;98:1364-1379.