Impaired regulation of brain mitochondria by extramitochondrial Ca2+ in transgenic Huntington disease rats.
Huntington disease (HD) is characterized by polyglutamine expansions of huntingtin (htt), but the underlying pathomechanisms have remained unclear. We studied brain mitochondria of transgenic HD rats with 51 glutamine repeats (htt(51Q)), modeling the adult form of HD. Ca(free)(2+) up to 2 mum activated state 3 respiration of wild type mitochondria with glutamate/malate or pyruvate/malate as substrates. Ca(free)(2+) above 2 mum inhibited respiration via cyclosporin A-dependent permeability transition (PT). Ruthenium red, an inhibitor of the mitochondrial Ca(2+) uniporter, did not affect the Ca(2+)-dependent activation of respiration but reduced Ca(2+)-induced inhibition. Thus, Ca(2+) activation was mediated exclusively by extramitochondrial Ca(2+), whereas inhibition was promoted also by intramitochondrial Ca(2+). In contrast, htt(51Q) mitochondria showed a deficient state 3 respiration, a lower sensitivity to Ca(2+) activation, and a higher susceptibility to Ca(2+)-dependent inhibition. Furthermore htt(51Q) mitochondria exhibited a diminished membrane potential stability in response to Ca(2+), lower capacities and rates of Ca(2+) accumulation, and a decreased Ca(2+) threshold for PT in a substrate-independent but cyclosporin A-sensitive manner. Compared with wild type, Ca(2+)-induced inhibition of respiration of htt(51Q) mitochondria was less sensitive to ruthenium red, indicating the involvement of extramitochondrial Ca(2+). In conclusion, we demonstrate a novel mechanism of mitochondrial regulation by extramitochondrial Ca(2+). We suggest that specific regulatory Ca(2+) binding sites on the mitochondrial surface, e.g. the glutamate/aspartate carrier (aralar), mediate this regulation. Interactions between htt(51Q) and distinct targets such as aralar and/or the PT pore may underlie mitochondrial dysregulation leading to energetic depression, cell death, and tissue atrophy in HD.
Gellerich
Frank N
FN
KeyNeurotek Pharmaceuticals AG, ZENIT Technology Park, 39120 Magdeburg, Germany. frank.gellerich@keyneurotek.de
Gizatullina
Zemfira
Z
Nguyen
Huu P
HP
Trumbeckaite
Sonata
S
Vielhaber
Stefan
S
Seppet
Enn
E
Zierz
Stephan
S
Landwehrmeyer
Bernhard
B
Riess
Olaf
O
von Hörsten
Stephan
S
Striggow
Frank
F
D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D004396:Coloring Agents / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000235:genetics; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects / Q000235:genetics; D051381:Rats; D055647:Rats, Transgenic; D012430:Ruthenium Red / Q000494:pharmacology
D004396:Coloring Agents; D004791:Enzyme Inhibitors; C499524:Htt protein, rat; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012430:Ruthenium Red; D016572:Cyclosporine; D002118:Calcium