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Glucose protection from MPP+-induced apoptosis depends on mitochondrial membrane potential and ATP synthase
R M Chalmers-Redman1, A D Fraser, G W Carlile
1Department of Neurology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, New York, 10029-6574, USA.
Abstract:
MPP+ inhibits mitochondrial complex I and alpha-ketoglutarate dehydrogenase causing necrosis or apoptosis of catecholaminergic neurons. Low glucose levels or glycolytic blockade has been shown to potentiate MPP+ toxicity. We found that MPP+ caused concentration-dependent apoptosis of neuronally differentiated PC12 cells and that glucose, but not pyruvate, supplementation reduced apoptosis. Oligomycin concentrations sufficient to inhibit ATP synthase blocked the decreased apoptosis afforded by glucose supplementation. Laser-scanning confocal microscope imaging of chloromethyl-tetramethylrosamine methyl ester fluorescence to estimate DeltaPsiM showed that MPP+ and atractyloside reduced DeltaPsiM, while cyclosporin A (CSA) and glucose supplementation reversed decreases in DeltaPsiM caused by MPP+. Oligomycin blocked the effect of glucose supplementation on DeltaPsiM. These findings show that (i) MPP+-induced and atractyloside-induced apoptosis are associated with reduced DeltaPsiM; (ii) CSA maintains DeltaPsiM and reduces MPP+-induced apoptosis; and (iii) glucose supplementation maintains DeltaPsiM, likely by glycolytic ATP-dependent proton pumping at ATP synthase and reduces MPP+-induced apoptosis.
Insights
MPP+ toxicity, which causes neuron death, is reduced by glucose supplementation. Glucose maintains mitochondrial membrane potential (DeltaPsiM) by supporting ATP production, thereby preventing apoptosis.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- MPP+ (1-methyl-4-phenylpyridinium) is a neurotoxin that inhibits mitochondrial complex I and alpha-ketoglutarate dehydrogenase.
- MPP+ induces necrosis or apoptosis in catecholaminergic neurons, with toxicity potentiated by low glucose or glycolytic blockade.
Purpose of the Study:
- To investigate the protective effect of glucose supplementation against MPP+-induced apoptosis in neuronally differentiated PC12 cells.
- To elucidate the role of mitochondrial membrane potential (DeltaPsiM) in MPP+-induced apoptosis and the mechanism of glucose-mediated protection.
Main Methods:
- PC12 cells were treated with MPP+ at varying concentrations.
- Glucose or pyruvate supplementation was used to assess effects on apoptosis.
- Mitochondrial membrane potential (DeltaPsiM) was measured using chloromethyl-tetramethylrosamine methyl ester fluorescence.
- Inhibition of ATP synthase by oligomycin and effects of cyclosporin A (CSA) were evaluated.
Main Results:
- MPP+ induced concentration-dependent apoptosis in PC12 cells.
- Glucose supplementation, but not pyruvate, significantly reduced MPP+-induced apoptosis.
- MPP+ and atractyloside decreased DeltaPsiM; CSA and glucose reversed these decreases.
- Oligomycin blocked the protective effects of glucose on both apoptosis and DeltaPsiM.
Conclusions:
- MPP+-induced apoptosis is associated with a reduction in mitochondrial membrane potential (DeltaPsiM).
- Cyclosporin A (CSA) maintains DeltaPsiM and reduces MPP+-induced apoptosis.
- Glucose supplementation preserves DeltaPsiM, likely via glycolytic ATP-dependent proton pumping at ATP synthase, thereby reducing MPP+-induced apoptosis.