In vitro effects of polyglutamine tracts on Ca2+-dependent depolarization of rat and human mitochondria: relevance to Huntington's disease.
The mechanisms by which neurons die in CAG triplet repeat (polyglutamine) disorders, such as Huntington's disease, are uncertain; however, mitochondrial dysfunction and disordered calcium homeostasis have been implicated. We previously demonstrated abnormal mitochondrial calcium handling in Huntington's disease cell lines and transgenic mice. To examine whether these abnormalities might arise in part from direct effects of the expanded polyglutamine tract contained in mutant huntingtin, we have exposed normal rat liver and human lymphoblast mitochondria to glutathione S-transferase fusion proteins containing polyglutamine tracts of 0, 19, or 62 residues. Similar to bovine serum albumin, each of the protein constructs nonspecifically inhibited succinate-supported respiration, independent of polyglutamine tract length. There was a small but significant reduction of mitochondrial membrane potential (state 4) only in the presence of the pathological-length polyglutamine tract. With successive addition of small Ca(2+) aliquots, mitochondria exposed to pathological-length polyglutamine tracts (approximately 5 microM) depolarized much earlier and to a greater extent than those exposed to the other protein constructs. These results suggest that the mitochondrial calcium handling defects seen in Huntington's disease cell lines and transgenic mice may be due, in part, to direct, deleterious effects of mutant huntingtin on mitochondria.
Panov
Alexander V
AV
Emory Center for Neurodegenerative Diseases, Emory University School of Medicine, Whitehead Biomedical Research Building, 615 Michael Street, Room 575, Atlanta, GA 30322, USA. apanov@emory.edu
Burke
James R
JR
Strittmatter
Warren J
WJ
Greenamyre
J Timothy
JT
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D016764:Cell Polarity / Q000187:drug effects / Q000502:physiology*; D019069:Cell Respiration; D002478:Cells, Cultured; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000473:pathology*; D007425:Intracellular Membranes; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000235:genetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D010455:Peptides / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D010539:Permeability; D051381:Rats; D011917:Rats, Inbred Lew; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology
C086055:HTT protein, human; C499524:Htt protein, rat; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011994:Recombinant Proteins; C097188:polyglutamine; D005982:Glutathione Transferase; D002118:Calcium