Abstract
Mitochondrial dysfunction has been implicated in cell death in many neurodegenerative diseases. Diminished activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key and arguably rate-limiting enzyme of the Krebs cycle, occurs in these disorders and may underlie decreased brain metabolism. The present studies used alpha-keto-beta-methyl-n-valeric acid (KMV), a structural analogue of alpha-ketoglutarate, to inhibit KGDHC activity to test effects of reduced KGDHC on mitochondrial function and cell death cascades in PC12 cells. KMV decreased in situ KGDHC activity by 52 +/- 7% (1 hr) or 65 +/- 4% (2 hr). Under the same conditions, KMV did not alter the mitochondrial membrane potential (MMP), as assessed with a method that detects changes as small as 5%. KMV also did not alter production of reactive oxygen species (ROS). However, KMV increased lactate dehydrogenase (LDH) release from cells by 100 +/- 4.7%, promoted translocation of mitochondrial cytochrome c to the cytosol, and activated caspase-3. Inhibition of the mitochondrial permeability transition pore (MPTP) by cyclosporin A (CsA) partially blocked this KMV-induced change in cytochrome c (-40%) and LDH (-15%) release, and prevented necrotic cell death. Thus, impairment of this key mitochondrial enzyme in PC12 cells may lead to cytochrome c release and caspase-3 activation by partial opening of the MPTP before the loss of mitochondrial membrane potentials.
Copyright 2003 Wiley-Liss, Inc.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Caspase 3
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Caspases / metabolism
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Cell Death / drug effects
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Cell Death / physiology
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Cell Membrane Permeability / drug effects
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Cell Membrane Permeability / physiology
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Chromatin / drug effects
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Chromatin / metabolism
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Cyclosporine / pharmacology
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Cytochromes c / metabolism
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Ion Channels / antagonists & inhibitors
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Ion Channels / metabolism
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Keto Acids / pharmacology
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Ketoglutarate Dehydrogenase Complex / antagonists & inhibitors*
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Ketoglutarate Dehydrogenase Complex / metabolism*
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L-Lactate Dehydrogenase / metabolism
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Matrix Metalloproteinases / drug effects
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Matrix Metalloproteinases / metabolism
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Membrane Potentials / drug effects
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Membrane Potentials / physiology
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Mitochondria / drug effects
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Mitochondria / enzymology*
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Mitochondrial Membrane Transport Proteins
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Mitochondrial Permeability Transition Pore
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Necrosis
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Neurodegenerative Diseases / enzymology*
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Neurodegenerative Diseases / physiopathology
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Neurons / drug effects
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Neurons / enzymology*
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Neurons / pathology
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PC12 Cells
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Protein Transport / drug effects
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Protein Transport / physiology
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Rats
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Reactive Oxygen Species / metabolism
Substances
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Chromatin
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Ion Channels
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Keto Acids
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Mitochondrial Membrane Transport Proteins
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Mitochondrial Permeability Transition Pore
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Reactive Oxygen Species
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alpha-keto-beta-methylvaleric acid
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Cyclosporine
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Cytochromes c
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L-Lactate Dehydrogenase
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Ketoglutarate Dehydrogenase Complex
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Casp3 protein, rat
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Caspase 3
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Caspases
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Matrix Metalloproteinases