Oxidative stress promotes uptake, accumulation, and oligomerization of extracellular α-synuclein in oligodendrocytes

The accumulation and aggregation of α-synuclein (α-Syn) in glial cytoplasmic inclusions originating in oligodendrocytes is a characteristic hallmark of multiple system atrophy, a progressive adult onset neurodegenerative disorder. The origin of α-Syn deposition in oligodendrocytes in multiple system atrophy is still unclear, but the uptake of α-Syn from the environment after neuronal secretion has been discussed. The present study was undertaken to investigate the consequences of α-Syn uptake from the environment in cultured oligodendroglial cells and its localization and potential to form intracellular aggregates in the absence or presence of the microtubule-associated protein tau, which has been demonstrated to act synergistically with α-Syn. Primary rat brain oligodendrocytes and clonal oligodendroglial OLN-93 cells were incubated with human recombinant soluble and pre-aggregated α-Syn. The data show that oligodendrocytes are capable to take up and internalize soluble and pre-aggregated α-Syn from their growth medium. In a time-dependent manner, α-Syn oligomerizes and small intracellular aggregates are formed. These do not exert cytotoxic responses or mitochondrial impairment. Oxidative stress exerted by hydrogen peroxide further promotes α-Syn oligomer formation and leads to an enlargement of the aggregates. This process is not affected or modified by the presence of tau in OLN-93 cells. Furthermore, membrane lipid modification by docosahexaenoic acid promotes α-Syn uptake and oligomerization, indicating that changing the membrane lipid composition and structure contributes to the protein aggregation process and pathological events. Hence, although α-Syn taken up by oligodendrocytes from the environment is not toxic per se, under conditions of oxidative stress, which might occur during chronic disease progression and aging, aggregates are enlarged and eventually may contribute to cytotoxicity and cellular death.