Dimethyl fumarate and monomethyl fumarate attenuate oxidative stress and mitochondrial alterations leading to oxiapoptophagy in 158N murine oligodendrocytes treated with 7β-hydroxycholesterol

Abstract

Oxidative stress and mitochondrial dysfunction contribute to the pathogenesis of neurodegenerative diseases and favor lipid peroxidation, leading to increased levels of 7β-hydroxycholesterol (7β-OHC) which induces oxiapoptophagy (OXIdative stress, APOPTOsis, autoPHAGY). The cytoprotective effects of dimethylfumarate (DMF), used in the treatment of relapsing remitting multiple sclerosis and of monomethylfumarate (MMF), its main metabolite, were evaluated on murine oligodendrocytes 158 N exposed to 7β-OHC (50 μM, 24 h) with or without DMF or MMF (25 μM). The activity of 7β-OHC in the presence or absence DMF or MMF was evaluated on several parameters: cell adhesion; plasma membrane integrity measured with propidium iodide (PI), trypan blue and fluoresceine diacetate (FDA) assays; LDH activity; antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)); generation of lipid peroxidation products (malondialdehyde (MDA), conjugated dienes (CDs)) and protein oxidation products (carbonylated proteins (CPs)); reactive oxygen species (ROS) overproduction conducted with DHE and DHR123. The effect on mitochondria was determined with complementary criteria: measurement of succinate dehydrogenase activity, evaluation of mitochondrial potential (ΔΨm) and mitochondrial superoxide anions (O₂^●-) production using DiOC₆(3) and MitoSOX, respectively; quantification of mitochondrial mass with Mitotracker Red, and of cardiolipins and organic acids. The effects on mitochondrial and peroxisomal ultrastructure were determined by transmission electron microscopy. Intracellular sterol and fatty acid profiles were determined. Apoptosis and autophagy were characterized by staining with Hoechst 33,342, Giemsa and acridine orange, and with antibodies raised against caspase-3 and LC3. DMF and MMF attenuate 7β-OHC-induced cytotoxicity: cell growth inhibition; decreased cell viability; mitochondrial dysfunction (decrease of succinate dehydrogenase activity, loss of ΔΨm, increase of mitochondrial O₂^●- production, alteration of the tricarboxilic acid (TCA) cycle, and cardiolipins content); oxidative stress induction (ROS overproduction, alteration of GPx, CAT, and SOD activities, increased levels of MDA, CDs, and CPs); changes in fatty acid and cholesterol metabolism; and cell death induction (caspase-3 cleavage, activation of LC3-I in LC3-II). Ultrastructural alterations of mitochondria and peroxisomes were prevented. These results demonstrate that DMF and MMF prevent major dysfunctions associated with neurodegenerative diseases: oxidative stress, mitochondrial dysfunction, apoptosis and autophagy.

Keywords: 158N cells; 7β-hydroxycholesterol; Apoptosis; Autophagy; Dimethyl fumarate; Lipid profile; Mitochondria; Monomethyl fumarate; Oxiapoptophagy; Oxidative stress; Peroxisome.