Abstract
Human mtDNA T8993G mutation is often fatal due to it inhibits significantly mitochondrial complex V (F1F0-ATPase) to cause severe ATP deficiency for clinically symptoms of neurological muscle weakness, ataxia, and retinitis pigmentosa (the so-called NARP mutation). Precisely pathological link between the mutation and its final symptoms has been limited to enhanced mitochondrial oxidative stress. Using non-invasive fluorescence probe-coupled laser scanning imaging microscopy and NARP cybrids harboring 98% mutant genes along with its parental 143B osteosarcoma cells, we demonstrated that mtDNA T8993G mutation enhanced deletion of a protective mitochondrial phospholipid, cardiolipin (CL), and altered mitochondrial dynamics during apoptotic insults of Ca2+, oxidative and lipid stress. As mtDNA T8993G mutation-induced complex V inhibition significantly hyperpolarizes mitochondrial membrane potential (∆Ψm) which enhances the driving force for mitochondrial Ca2+ (mCa2+) uniporter to take up Ca2+ during Ca2+ stress. Furthermore, we investigated in detail how mtDNA T8993G mutation augmented-mCa2+ stress affects down streams of mitochondrial pathologies including mCa2+-mediated mitochondrial reactive oxygen species (mROS) formation and mCa2+- and mROS-mediated depletion of CL. Precisely, we investigated whether and how the alterations of the activity of the mitochondrial permeability transition (MPT) at resting and during mCa2+ stress contribute to mtDNA T8993G mutation-augmented mitochondrial pathologies and apoptosis. We explored whether the modulation of the transient-MPT (t-MPT) serves as a protective target in rescuing mtDNA T8993G mutation-augmented mCa2+ stress at resting and during mCa2+ stress-induced apoptosis. Lastly, we investigated mtDNA T8993G mutation-induced complex V inhibition is a potential risk factor for Alzheimer's disease (AD) and the pathological link for long-term exposure of amyloid-beta peptide (Aβ)-induced mitochondrial toxicity and apoptosis in NARP cybrids. We demonstrated that Aβ-augmented mCa2+-independent mROS formation for CL-dependent lethal modulation of the MPT. Aβ augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize ∆Ψm and reduce Ca2+ stress. Aβ-augmented mROS oxidized and depleted CL thereby enhances mitochondrial fission and movement retardation, which promoted the NARP-augmented lethal t-MPT to switch its irreversible mode of permanent-MPT (p-MPT). Aβ-promoted p-MPT was reversed to a protective t-MPT, which preserved ∆Ψm and lowered elevated mCa2+ to sublethal levels for an enhanced mCa2+-dependent O2 consumption. We suggest that the activity of the MPT may potentially serve as a protective target in rescuing AD patients associated with NARP symptoms.