Limited effects of dysfunctional macroautophagy on the accumulation of extracellularly derived \u03b1-synuclein in oligodendroglia: implications for MSA pathogenesis

Lisa Fellner,Regina Irschick,Dominik Brueck,Edith Buchinger,Nadia Stefanova,Gregor K Wenning

doi:10.1186/s12868-018-0431-2

Lisa Fellner, Regina Irschick + Show 4 more

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https://doi.org/10.1186/s12868-018-0431-2

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Abstract

BackgroundThe progressive neurodegenerative disorder multiple system atrophy (MSA) is characterized by α-synuclein-positive (oligodendro-) glial cytoplasmic inclusions (GCIs). A connection between the abnormal accumulation of α-synuclein in GCIs and disease initiation and progression has been postulated. Mechanisms involved in the formation of GCIs are unclear. Abnormal uptake of α-synuclein from extracellular space, oligodendroglial overexpression of α-synuclein, and/or dysfunctional protein degradation including macroautophagy have all been discussed. In the current study, we investigated whether dysfunctional macroautophagy aggravates accumulation of extracellular α-synuclein in the oligodendroglia.ResultsWe show that oligodendroglia uptake monomeric and fibrillar extracellular α-synuclein. Blocking macroautophagy through bafilomycin A1 treatment or genetic knockdown of LC3B does not consistently change the level of incorporated α-synuclein in oligodendroglia exposed to extracellular soluble/monomeric or fibrillar α-synuclein, however leads to higher oxidative stress in combination with fibrillar α-synuclein treatment. Finally, we detected no evidence for GCI-like formation resulting from dysfunctional macroautophagy in oligodendroglia using confocal microscopy.ConclusionIn summary, isolated dysfunctional macroautophagy is not sufficient to enhance abnormal accumulation of uptaken α-synuclein in vitro, but may lead to increased production of reactive oxygen species in the presence of fibrillar α-synuclein. Multiple complementary pathways are likely to contribute to GCI formation in MSA.

Highlights

The progressive neurodegenerative disorder multiple system atrophy (MSA) is characterized by α-synuclein-positive glial cytoplasmic inclusions (GCIs)
No GCI-like formation of α-syn upon macroautophagy blocking was found in the used oligodendroglial cell culture model suggesting that multiple complementary factors are likely to contribute to GCI formation in MSA
To determine whether recombinant sol and fib α-syn incorporation from the extracellular space is comparable in primary murine oligodendroglia and human MO 3.13 oligodendroglial cell line, we analyzed different parameters including the percentage of cells with α-syn inclusions (Fig. 1a), the number of inclusions per cell (Fig. 1b) and the total area of inclusion per cell in μm2 (Fig. 1c). 24 h after incubation with both α-syn forms, small incorporations of α-syn were found in around 15–20% of the analyzed primary and MO 3.13 oligodendroglia

Summary

Introduction

The progressive neurodegenerative disorder multiple system atrophy (MSA) is characterized by α-synuclein-positive (oligodendro-) glial cytoplasmic inclusions (GCIs). Abnormal uptake of α-synuclein from extracellular space, oligodendroglial overexpression of α-synuclein, and/or dysfunctional protein degradation including macroautophagy have all been discussed. MSA is characterized by α-synuclein (α-syn)-positive glial cytoplasmic inclusions (GCIs) occurring predominantly in oligodendroglial cells [1]. Incorporation of α-syn by oligodendroglia either released by dying neurons into the extracellular space or by cell-tocell propagation represents an alternative mechanism of GCI formation [20,21,22]. Pathological accumulation of α-syn in the cytoplasm of oligodendroglia might be explained by a primary oligodendroglial injury [31] such as deficits in the cellular protein degradation mechanisms [11, 32, 33]

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