Role of extracellular calcium and mitochondrial oxygen species in psychosine-induced oligodendrocyte cell death.

V Voccoli,I Tonazzini,M Caleo,M Cecchini,G Signore

doi:10.1038/cddis.2014.483

Abstract

Globoid cell leukodystrophy (GLD) is a metabolic disease caused by mutations in the galactocerebrosidase (GALC) gene. GALC is a lysosomal enzyme whose function is to degrade galacto-lipids, including galactosyl-ceramide and galactosyl-sphingosine (psychosine, PSY). GALC loss of function causes progressive intracellular accumulation of PSY. It is widely held that PSY is the main trigger for the degeneration of myelinating cells and progressive white-matter loss. However, still little is known about the molecular mechanisms by which PSY imparts toxicity. Here, we address the role of calcium dynamics during PSY-induced cell death. Using the human oligodendrocyte cell line MO3.13, we report that cell death by PSY is accompanied by robust cytosolic and mitochondrial calcium (Ca2+) elevations, and by mitochondrial reactive oxygen species (ROS) production. Importantly, we demonstrate that the reduction of extracellular calcium content by the chelating agent ethylenediaminetetraacetic acid can decrease intra-mitochondrial ROS production and enhance cell viability. Antioxidant administration also reduces mitochondrial ROS production and cell loss, but this treatment does not synergize with Ca2+ chelation. Our results disclose novel intracellular pathways involved in PSY-induced death that may be exploited for therapeutic purposes to delay GLD onset and/or slow down its progression.

Highlights

Mitochondrial Ca2+ in basal conditions is maintained at low concentrations, but mitochondria are organelles that can take up high Ca2+ concentrations; different stimuli, such as nutrients, hormones or neurotransmitters that increase the cytoplasmic Ca2+ content induce intra-mitochondrial Ca2+ increase.[15]
It has been reported that some sphingolipid metabolites, such as ceramides and sphingosine, can play a crucial role in many steps of apoptosis induction as regulators of some Bcl[2] family proteins, by increasing intracellular Ca2+ levels and inducing mitochondrial stress.[18]
We found that Ca2+ chelation from the extracellular medium by ethylenediaminetetraacetic acid (EDTA) (1 mM) improves cell survival following PSY administration (Figure 5b) and reduces mitochondrial reactive oxygen species (ROS) production by 50% (Figure 5d)

Summary

Introduction

It is well established that Ca2+ is one of the main second messengers involved in apoptotic cell death in neurons and in other cell types; sustained cytosolic Ca2+ increase can activate apoptosis.[12] This can originate from extracellular influx or by release from intracellular stores like the endoplasmic reticulum.[13] Importantly, mitochondria are involved in Ca2+ homeostasis.[14] Mitochondrial Ca2+ in basal conditions is maintained at low concentrations, but mitochondria are organelles that can take up high Ca2+ concentrations; different stimuli, such as nutrients, hormones or neurotransmitters that increase the cytoplasmic Ca2+ content induce intra-mitochondrial Ca2+ increase.[15] If this increase is relevant, ROS production increases and this is associated with mitochondrial membrane destruction, release of cytochrome C and apoptosis induction.[16] During this process, proapoptotic Bcl[2] family of proteins plays a crucial role by regulating the intracellular/mitochondrial Ca2+ content, and by inducing mitochondrial permeabilization, the essential step for cytochrome C release and caspase activation.[12,17]. In order to rescue cell viability in presence of PSY, we investigated the use of Ca2+ chelation in the extracellular medium, and its possible synergic effect with antioxidant treatment

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