粒線體 DNA T8993G 突變細胞質融合株中粒線體功能失調和細胞凋亡之機制探討

Mechanistic Investigation on Mitochondrial Dysfunction and Apoptosis in mtDNA T8993G Mutation Cybrids

蕭嘉偉(Chia-Wei Hsiao)

指導教授 ： 黎耀基 ； 周美智

國立清華大學/生命科學院/生物科技研究所/博士(2012年)

摘要

人類粒線體 DNA突變（mtDNA T8993G）會抑制粒線體複合體五（F1F0-ATPase），造成三磷酸腺苷（ATP）不足、進而導致死亡，臨床上常伴隨神經性肌肉無力、運動失調、視網膜色素病變（neurological muscle weakness、 ataxia、retinitis pigmentosa，所以又稱 NARP 突變）等症狀。該突變與其症狀之間的確切病理關係仍只受限在粒線體氧化壓力方面的研究。藉由非侵入式螢光探針搭配雷射掃描影像顯微鏡和 NARP 細胞質融合株 (帶有98% 突變基因) 及其親帶 143B 骨髓瘤細胞 (對照組)，我們證明在鈣離子、氧化、脂質等壓力下，該突變會增加粒線體保護性磷脂質－心磷脂 (cardiolipin) 缺失，並改變粒線體動態。由於該突變抑制粒線體複合體五會使粒線體膜電位過極化，進而增加粒線體鈣單向轉運體 (mCa2+ uniporter) 的驅動力。當鈣離子壓力存在下，會增加鈣離子的吸收。因此我們更進一步深入探討該突變造成的鈣離子壓力如何去影響粒線體病變，包括鈣離子引發的粒線體活性氧屬自由基 (mROS) 形成、粒線體鈣離子、氧化壓力造成的心磷脂缺失。更確切來說，我們是探討該突變如何去影響粒線體過渡性通透 (MPT) 的活性，進而引發該突變造成的病變和細胞凋亡。我們探索暫時性粒線體過渡性通透 (t-MPT) 的調節如何在鈣離子壓力造成的細胞凋亡時，扮演保護性的角色。最後我們研究該突變引發的粒線體複合體五抑制是阿茲海默症的潛在風險因子，並且和長期暴露在乙型澱粉樣胜肽 (amyloid-beta peptide) 造成的毒性和細胞凋亡有關。我們證明乙型澱粉樣胜肽造成的非粒線體鈣離子依賴的粒線體活性氧屬自由基形成，會造成心磷脂依賴的粒線體過渡性通透致死調節。乙型澱粉樣胜肽不但增加粒線體活性氧屬自由基，也會增加粒線體活性氧屬自由基的傳播速度，造成粒線體膜電位去極化，降低鈣離子壓力。乙型澱粉樣胜肽造成的粒線體活性氧屬自由基會氧化和耗盡心磷脂，接著使粒線體斷裂、移動遲緩，並促使該突變造成的致死暫時性粒線體過渡性通透轉變成不可逆的永久性粒線體過渡性通透 (p-MPT)。而乙型澱粉樣胜肽造成的永久性粒線體過渡性通透，如果被還原成保護性的暫時性粒線體過渡性通透，則能維持膜電位並降低粒線體鈣離子到非致死程度，並增加粒線體鈣離子依賴的氧氣消耗。我們認為調控粒線體過渡性通透的活性也許有潛力成為和 NARP 症狀相關的阿茲海默病患的治療標的。

關鍵字

粒線體 DNA 突變 ； 神經性肌肉無力 ； 運動失調 ； 視網膜色素病變 ； 心磷脂 ； 粒線體活性氧屬自由基 ； 粒線體過渡性通透 ； 粒線體鈣離子 ； 乙型澱粉樣胜肽

並列摘要

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.

並列關鍵字

mtDNA T8993G ； neurological muscle weakness ； ataxia ； retinitis pigmentosa ； cardiolipin ； mROS ； MPT ； mCa2+ ； amyloid-beta peptide

參考文獻

91. Pagani, L. and A. Eckert, Amyloid-Beta interaction with mitochondria. Int J Alzheimers Dis, 2011. 2011: p. 925050.

1. Kao, S.H., H.T. Chao, and Y.H. Wei, Multiple deletions of mitochondrial DNA are associated with the decline of motility and fertility of human spermatozoa. Mol Hum Reprod, 1998. 4(7): p. 657-66.

2. Senior, A.E., ATP synthesis by oxidative phosphorylation. Physiol Rev, 1988. 68(1): p. 177-231.

3. Mitchell, P., Coupling of phosphorylation to electron and hydrogen transfer by a chemi-osmotic type of mechanism. Nature, 1961. 191: p. 144-8.

4. Schon, E.A., et al., Therapeutic prospects for mitochondrial disease. Trends Mol Med, 2010. 16(6): p. 268-76.