Long-term A beta exposure augments mCa(2+)-independent mROS-mediated depletion of cardiolipin for the shift of a lethal transient mitochondrial permeability transition to its permanent mode in NARP cybrids: a protective targeting of melatonin

Mitochondrial dysfunction is a hallmark of amyloid beta-peptide (A beta)-induced neurodegeneration of Alzheimer's disease (AD). This study investigated whether mtDNA T8993G mutation-induced complex V inhibition, clinically associated with neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP), is a potential risk factor for AD and the pathological link for long-term exposure of A beta-induced mitochondrial toxicity and apoptosis in NARP cybrids. Using noninvasive fluorescence probe-coupled laser scanning imaging microscopy and NARP cybrids harboring 98% mutant genes along with its parental 143B osteosarcoma cells, we demonstrated that A beta-augmented mitochondrial Ca2+ (mCa(2+))-independent mitochondrial reactive oxygen species (mROS) formation for a cardiolipin (CL, a major mitochondrial protective phospholipid)-dependent lethal modulation of the mitochondrial permeability transition (MPT). A beta augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize mitochondrial membrane potential (Delta Psi(m)) and reduce mCa(2+) stress. A beta-augmented mROS oxidized and depleted CL, thereby enhances mitochondrial fission and movement retardation, which promoted the NARP-augmented lethal transient-MPT (t-MPT) to switch to its irreversible mode of permanent-MPT (p-MPT). Interestingly, melatonin, a multiple mitochondrial protector, markedly reduced A beta-augmented mROS formation and therefore significantly reduced mROS-mediated depolarization of Delta Psi(m), fission of mitochondria and retardation of mitochondrial movement to stabilize CL and hence the MPT. In the presence of melatonin, A beta-promoted p-MPT was reversed to a protective t-MPT, which preserved Delta Psi(m) and lowered elevated mCa(2+) to sublethal levels for an enhanced mCa(2+)-dependent O-2 consumption. Thus, melatonin may potentially rescue AD patients associated with NARP symptoms.