engleski

Cholesterol-mediated oxidative stress in Niemann-Pick type C disease involves a defect in the activity of superoxide dismutase

Niemann-Pick type C (NPC) disease is an inherited, neurodegenerative lysosomal storage disorder caused by mutations in NPC1/2 genes. At the cellular level, the most prominent feature of the NPC disease is lysosomal sequestration of low density lipoprotein derived cholesterol. The mechanisms underlying the progressive neurodegeneration in the NPC disease are still not fully established. In addition to defects in intracellular lipid transport and disturbed endo/lysosomal pathway, a number of studies are consistent with increased oxidative stress being a contributing factor in the pathophysiology of NPC disease. Moreover, abnormalities in mitochondria, the main source of reactive oxygen species in the cell, have also been reported in NPC. Interestingly, it was shown that mitochondrial cholesterol content was higher in NPC1-deficient cells than in wild-type (wt) cells. To determine the effect of cholesterol accumulation on oxidative stress in NPC, we analysed antioxidant defence systems in CHOwt and CHO NPC1-null cells. We measured the concentration of total glutathione and activity of antioxidant enzymes superoxide dismutase (SOD) and catalase. While the concentrations of glutathione and catalase activity do not seem to be affected, our results show a significantly higher activity of SOD in NPC1-null cells. Under conditions of oxidative stress (treatment with hydrogen peroxide), NPC1-null cells show lower SOD activity than wt cells indicating a defect in the antioxidant defence. We confirmed that the observed alterations in SOD activity in NPC1-null cells are partially due to disturbed activity of mitochondrial SOD (SOD2). The expression levels of SOD1 (cytosolic) and SOD2 are not changed in NPC1-null cells vs. wt cells. Additionally, we showed that the defect in SOD activity in NPC1-null cells is dependent on cholesterol levels since cholesterol depletion in these cells completely reversed SOD activity to the levels as in wt cells. Our results indicate that mitochondria are especially susceptible to oxidative stress caused by cholesterol accumulation in NPC. Our findings suggest that oxidative stress might contribute to the NPC disease and that lipid storage reducing therapies could protect against this pathological process.

cholesterol ; Niemann-Pick type C disease ; oxidative stress ; superoxide dismutase

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