calcimycin and 3-nitropropionic-acid

Changes in mitochondrial integrity, reactive oxygen species release and Ca2+ handling are proposed to be involved in the pathogenesis of many neurological disorders including methylmalonic acidaemia and Huntington's disease, which exhibit partial mitochondrial respiratory inhibition. In this report, we studied the mechanisms by which the respiratory chain complex II inhibitors malonate, methylmalonate and 3-nitropropionate affect rat brain mitochondrial function and neuronal survival. All three compounds, at concentrations which inhibit respiration by 50%, induced mitochondrial inner membrane permeabilization when in the presence of micromolar Ca2+ concentrations. ADP, cyclosporin A and catalase prevented or delayed this effect, indicating it is mediated by reactive oxygen species and mitochondrial permeability transition (PT). PT induced by malonate was also present in mitochondria isolated from liver and kidney, but required more significant respiratory inhibition. In brain, PT promoted by complex II inhibition was stimulated by increasing Ca2+ cycling and absent when mitochondria were pre-loaded with Ca2+ or when Ca2+ uptake was prevented. In addition to isolated mitochondria, we determined the effect of methylmalonate on cultured PC12 cells and freshly prepared rat brain slices. Methylmalonate promoted cell death in striatal slices and PC12 cells, in a manner attenuated by cyclosporin A and bongkrekate, and unrelated to impairment of energy metabolism. We propose that under conditions in which mitochondrial complex II is partially inhibited in the CNS, neuronal cell death involves the induction of PT.

Topics: Animals; Antimycin A; Bongkrekic Acid; Brain; Calcimycin; Calcium; Catalase; Cell Survival; Cyclosporins; Dose-Response Relationship, Drug; Drug Interactions; Electron Transport Complex II; Enzyme Inhibitors; Female; In Vitro Techniques; Ionophores; Malonates; Membrane Potentials; Methylmalonic Acid; Mitochondria; NADP; Neurons; Nitro Compounds; Oxygen Consumption; PC12 Cells; Permeability; Propionates; Rats; Rotenone; Tacrolimus; Tetrazolium Salts; Thiazoles; Uncoupling Agents

Huntington's disease (HD) is caused by a polyglutamine expansion in the amino-terminal region of huntingtin. Mutant huntingtin is proteolytically cleaved by caspases, generating amino-terminal aggregates that are toxic for cells. The addition of calpains to total brain homogenates also leads to cleavage of wild-type huntingtin, indicating that proteolysis of mutant and wild-type huntingtin may play a role in HD. Here we report that endogenous wild-type huntingtin is promptly cleaved by calpains in primary neurons. Exposure of primary neurons to glutamate or 3-nitropropionic acid increases intracellular calcium concentration, leading to loss of intact full-length wild-type huntingtin. This cleavage could be prevented by calcium chelators and calpain inhibitors. Degradation of wild-type huntingtin by calcium-dependent proteases thus occurs in HD neurons, leading to loss of wild-type huntingtin neuroprotective activity.

Topics: Animals; Blotting, Western; Brain; Calcimycin; Calcium; Calpain; Cell-Free System; Cells, Cultured; Densitometry; Glutamic Acid; Huntingtin Protein; Ionophores; Nerve Tissue Proteins; Neurons; Nitro Compounds; Nuclear Proteins; Propionates; Protein Binding; Rats; Rats, Sprague-Dawley; Time Factors