Ca2+-induced permeability transition in human lymphoblastoid cell mitochondria from normal and Huntington's disease individuals

Huntington's disease (HD) is associated with expansion of polyglutamine tract in a protein named huntingtin (htt) that is expressed in virtually all body tissues. Thus mutated htt (HD-htt) might affect all organs, although clinical manifestations of HD are associated with selective loss of corticostriatal neurons of the brain. In this work we studied how HD-htt affects mitochondria in human peripheral blood cells. We compared various functions of mitochondria isolated from cultured lymphoblastoid cells derived from three HD patients with juvenile onset of the disease(HD-LBM) and three age-matched control (C-LBM) individuals. Respiratory parameters in different metabolic states, with succinate and glutamate plus malate were the same for all control and HD cell lines. State 4 membrane potential in HD-LBM was slightly lower than in C-LBM. The calcium retention capacity (CRC) of mitochondria was estimated using simultaneously several methods to register permeability transition (PT). We found that LBM do not undergo swelling upon Ca2+-induced PT, and do not increase CRC in the presence of ADP+ oligomycin. Although each cell line had different CRC values, qualitatively PT was different in C-LBM and HD-LBM. With C-LBM cyclosporin A (CsA) increased CRC significantly, while with HD-LBM CsA was ineffective. In C-LBM depolarization of mitochondria and a large pore opening (PT) always occurred simultaneously. In HD-LBM depolarization occurred at 20-50% lower Ca2+ loads than PT. We suggest that HD-htt promotes low H+ conductance of the mitochondria by interacting with proteins at the contacts sites without directly promoting PT or hampering mitochondrial oxidative phosphorylation.