Inhibition of alpha-ketoglutarate dehydrogenase complex promotes cytochrome c release from mitochondria, caspase-3 activation, and necrotic cell death.
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.
D000818:Animals; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D007651:Keto Acids / Q000494:pharmacology; D007655:Ketoglutarate Dehydrogenase Complex / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009336:Necrosis; D019636:Neurodegenerative Diseases / Q000201:enzymology* / Q000503:physiopathology; D009474:Neurons / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D016716:PC12 Cells; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism
D002843:Chromatin; D007473:Ion Channels; D007651:Keto Acids; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017382:Reactive Oxygen Species; C016211:alpha-keto-beta-methylvaleric acid; D016572:Cyclosporine; D045304:Cytochromes c; D007770:L-Lactate Dehydrogenase; D007655:Ketoglutarate Dehydrogenase Complex; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D020782:Matrix Metalloproteinases