Mitochondrial impairment and oxidative stress compromise autophagosomal degradation of α-synuclein in oligodendroglial cells.

Abstract

α-Synuclein (α-syn)-containing glial cytoplasmic inclusions originating in oligodendrocytes are characteristically observed in multiple system atrophy. The mechanisms of glial cytoplasmic inclusion formation remain rather elusive. α-Syn over-expression, uptake from the environment, oxidative stress or impairment of the proteolytic degradation systems have been discussed. Here, we investigated whether in oligodendrocytes autophagy plays a major role in the degradation and aggregation of endogenously expressed α-syn and of α-syn taken up from the extracellular environment. Furthermore, we studied whether in cells with impaired mitochondria the accumulation and aggregation of exogenously added α-syn is promoted. Using primary cultures of rat brain oligodendrocytes and an oligodendroglial cell line, genetically engineered to express green fluorescent protein-microtubule-associated light chain 3 with or without α-syn to monitor the autophagic flux, we demonstrate that both exogenously applied α-syn and α-syn stably expressed endogenously are effectively degraded by autophagy and do not affect the autophagic flux per se. Mitochondrial impairment with the protonophore carbonyl cyanide 3-chlorophenylhydrazone or 3-nitropropionic acid disturbs the autophagic pathway and leads to the accumulation of exogenously applied α-syn and enhances its propensity to form aggregates intracellularly. Thus, mitochondrial dysfunction and oxidative stress, which occur over time and are significant pathological features in synucleinopathies, have an impact on the autophagic pathway and participate in pathogenesis. Glial cytoplasmic inclusions are characteristically observed in multiple system atrophy, their occurrence might be related to failure in protein degradation systems. Here, we show that in oligodendrocytes autophagy is the major route of α-synuclein degradation which is either endogenously expressed or added exogenously (1, 2). Mitochondrial impairment (3) disturbs the autophagic flux and leads to the accumulation of exogenously applied α-synuclein, and enhances its propensity to form aggregates intracellulary (4).