Abstract
Mitochondrial dysfunction has been implicated in cell death in many neurodegenerative diseases. Diminished activity of the α‐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 α‐keto‐β‐methyl‐n‐valeric acid (KMV), a structural analogue of α‐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. © 2003 Wiley‐Liss, Inc.