Medical and Health Sciences, Basic Medicine, Neurosciences, Medicin och hälsovetenskap, Medicinska och farmaceutiska grundvetenskaper, Neurovetenskaper, Clinical Medicine, Neurology, Klinisk medicin, Neurologi

Significance Our results demonstrate the existence of early cellular pathways and network alterations in oligodendrocytes in the alpha-synucleinopathies Parkinson's disease and multiple system atrophy. They further reveal the involvement of an immune component triggered by alpha-synuclein protein, as well as a connection between (epi)genetic changes and immune reactivity in multiple system atrophy. The knowledge generated in this study could be used to devise novel therapeutic approaches to treat synucleinopathies. Abstract Limited evidence has shed light on how aSYN proteins affect the oligodendrocyte phenotype and pathogenesis in synucleinopathies that include Parkinson’s disease (PD) and multiple system atrophy (MSA). Here, we investigated early transcriptomic changes within PD and MSA O4+ oligodendrocyte lineage cells (OLCs) generated from patient-induced pluripotent stem cells (iPSCs). We found impaired maturation of PD and MSA O4+ OLCs compared to controls. This phenotype was associated with changes in the human leukocyte antigen (HLA) genes, the immunoproteasome subunit PSMB9, and the complement component C4b for aSYN p.A53T and MSA O4+ OLCs, but not in SNCAtrip O4+ OLCs despite high levels of aSYN assembly formation. Moreover, SNCA overexpression resulted in the development of O4+ OLCs, whereas exogenous treatment with aSYN species led to significant toxicity. Notably, transcriptome profiling of genes encoding proteins forming Lewy bodies and glial cytoplasmic inclusions revealed clustering of PD aSYN p.A53T O4+ OLCs with MSA O4+ OLCs. Our work identifies early phenotypic and pathogenic changes within human PD and MSA O4+ OLCs.