Depletion Of Cardiolipin Research Articles

In Search of the Holy Grail: Toward a Unified Hypothesis on Mitochondrial Dysfunction in Age-Related Diseases.

Cardiolipin (CL) is a mitochondrial signature phospholipid that plays a pivotal role in mitochondrial dynamics, membrane structure, oxidative phosphorylation, mtDNA bioenergetics, and mitophagy. The depletion or abnormal acyl composition of CL causes mitochondrial dysfunction, which is implicated in the pathogenesis of aging and age-related disorders. However, the molecular mechanisms by which mitochondrial dysfunction causes age-related diseases remain poorly understood. Recent development in the field has identified acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase upregulated by oxidative stress, as a key enzyme that promotes mitochondrial dysfunction in age-related diseases. ALCAT1 catalyzes CL remodeling with very-long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA). Enrichment of DHA renders CL highly sensitive to oxidative damage by reactive oxygen species (ROS). Oxidized CL becomes a new source of ROS in the form of lipid peroxides, leading to a vicious cycle of oxidative stress, CL depletion, and mitochondrial dysfunction. Consequently, ablation or the pharmacological inhibition of ALCAT1 have been shown to mitigate obesity, type 2 diabetes, heart failure, cardiomyopathy, fatty liver diseases, neurodegenerative diseases, and cancer. The findings suggest that age-related disorders are one disease (aging) manifested by different mitochondrion-sensitive tissues, and therefore should be treated as one disease. This review will discuss a unified hypothesis on CL remodeling by ALCAT1 as the common denominator of mitochondrial dysfunction, linking mitochondrial dysfunction to the development of age-related diseases.

Cardiolipin depletion-induced changes in the Trypanosoma brucei proteome.

The mitochondrial signature glycerophospholipid, cardiolipin (CL), binds to transporters of the inner mitochondrial membrane and plays a central role in formation and stability of respiratory supercomplexes. Functional and structural requirement of CL for mitochondrial membrane proteins has been studied in vitro using purified reconstituted proteins or in CL synthesis knockout cells that are viable under specific growth conditions. However, no information is available on mitochondrial function, protein stability, or expression levels in cells during CL depletion. In contrast to yeast and mammalian cells, CL synthesis is essential in Trypanosoma brucei. By stable isotope labeling with amino acids in cell culture and mass spectrometry, we analyzed protein levels in T. brucei procyclic forms at different time points during depletion of CL using tightly controllable conditional CL synthase knockout mutants and identified a set of novel CL-dependent proteins (CLDPs) with unknown functions. Depletion of individual CLDPs using knockout or knockdown technologies showed that although CL synthesis is essential, expression of a given CLDP is not. In addition, ablation of CL synthesis leads to respiratory supercomplex instability and altered mitochondrial ultrastructure and function. Our findings suggest that CL may bind to and affect many more proteins in eukaryotes than previously thought.-Schädeli, D., Serricchio, M., Ben Hamidane, H., Loffreda, A., Hemphill, A., Beneke, T., Gluenz, E., Graumann, J., Bütikofer, P. Cardiolipin depletion-induced changes in the Trypanosoma brucei proteome.

Maspin binds to cardiolipin in mitochondria and triggers apoptosis.

A central question in cell biology is how cells respond to stress signals and biochemically regulate apoptosis. One critical pathway involves the change of mitochondrial function and release of cytochrome c to initiate apoptosis. In response to apoptotic stimuli, we found that maspin-a noninhibitory member of the serine protease inhibitor superfamily-translocates from the cytosol to mitochondria and binds to cardiolipin in the inner mitochondrial membrane. Biolayer interferometry assay revealed that recombinant maspin binds cardiolipin with an apparent Kd,of ∼15.8 μM and competes with cytochrome c (apparent Kd of ∼1.31 μM) for binding to cardiolipin-enriched membranes. A hydrophobic, lysine-rich domain in maspin consists of 27 aa, is located at position 268-294, and is responsible for the interaction of this protein with cardiolipin. Depletion of cardiolipin in cells significantly prevents maspin binding to the inner mitochondrial membrane and decreases cytochrome c release and apoptosis. Alteration to maspin's cardiolipin binding domain changes its ability to bind cardiolipin, and tumor cells expressing this mutant have a low frequency of apoptosis. We propose a model of apoptosis in which maspin binds to cardiolipin, displaces cytochrome c from the membrane, and facilitates its release to the cytoplasm.-Mahajan, N., Hoover, B., Rajendram, M., Shi, H. Y., Kawasaki, K., Weibel, D. B., Zhang, M. Maspin binds to cardiolipin in mitochondria and triggers apoptosis.

Probing the Effect of Cardiolipin on the Redox-Partner Recognition between Cytochrome C2 and Cytochrome Bc1 Complex

Cytochrome c (cyt. c) and cytochrome bc1 (bc1) complex are redox proteins that participate in the electron transport chain of the mitochondria, with cyt. c shuttling electrons from bc1 complex to complex IV. Cyt. c and bc1 complex reside in the inner membrane of the mitochondria, which is rich in the negatively-charged cardiolipin (CL). CL concentration in mitochondria varies upon different physiological conditions, and in some cases, a depletion of CL leads to a reduced bc1 complex activity. In this study, the redox-partner recognition between cyt. c and bc1 complex is examined using molecular dynamic (MD) and Brownian dynamics (BD) simulations with variations in CL concentration and salinity. First, MD simulations were performed to equilibrate cyt c2 and bc1 complex with membranes of different CL concentrations to obtain atomistic representations of their in situ configurations. Then, for each CL concentration, the electrostatic potential profile as well as hydrophobic interactions under different salinities were determined; to serve as input parameters for BD simulations. Then, for each redox state of cyt. c2 and that of bc1 complex, as well as for each of the above-mentioned CL concentration, a set of 10 independent 200 microsecond BD simulations were performed to sample the binding likelihood between the two proteins. Our result shows that a match between the redox state of cyt. c2 and that of bc1 complex promotes the binding of the two proteins in all different conditions. However, the ability of cyt. c2 to distinguish bc1 complex from the membrane surface is susceptible to the corresponding electrostatic potential profile, which can be significantly modified by variations in CL concentration and salinity.

Let's face the fats: palmitate restores cellular redox state in the diabetic heart.

Let's face the fats: palmitate restores cellular redox state in the diabetic heart.

Ethanolamine ameliorates mitochondrial dysfunction in cardiolipin-deficient yeast cells

Cardiolipin (CL) is a signature phospholipid of the mitochondria required for the formation of mitochondrial respiratory chain (MRC) supercomplexes. The destabilization of MRC supercomplexes is the proximal cause of the pathology associated with the depletion of CL in patients with Barth syndrome. Thus, promoting supercomplex formation could ameliorate mitochondrial dysfunction associated with CL depletion. However, to date, physiologically relevant small-molecule regulators of supercomplex formation have not been identified. Here, we report that ethanolamine (Etn) supplementation rescues the MRC defects by promoting supercomplex assembly in a yeast model of Barth syndrome. We discovered this novel role of Etn while testing the hypothesis that elevating mitochondrial phosphatidylethanolamine (PE), a phospholipid suggested to overlap in function with CL, could compensate for CL deficiency. We found that the Etn supplementation rescues the respiratory growth of CL-deficient Saccharomyces cerevisiae cells in a dose-dependent manner but independently of its incorporation into PE. The rescue was specifically dependent on Etn but not choline or serine, the other phospholipid precursors. Etn improved mitochondrial function by restoring the expression of MRC proteins and promoting supercomplex assembly in CL-deficient cells. Consistent with this mechanism, overexpression of Cox4, the MRC complex IV subunit, was sufficient to promote supercomplex formation in CL-deficient cells. Taken together, our work identifies a novel role of a ubiquitous metabolite, Etn, in attenuating mitochondrial dysfunction caused by CL deficiency.

Increased mitophagy in the skeletal muscle of spinal and bulbar muscular atrophy patients

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disorder caused by polyglutamine expansion in the androgen receptor (AR) and characterized by the loss of lower motor neurons. Here we investigated pathological processes occurring in muscle biopsy specimens derived from SBMA patients and, as controls, age-matched healthy subjects and patients suffering from amyotrophic lateral sclerosis (ALS) and neurogenic atrophy. We detected atrophic fibers in the muscle of SBMA, ALS and neurogenic atrophy patients. In addition, SBMA muscle was characterized by the presence of a large number of hypertrophic fibers, with oxidative fibers having a larger size compared with glycolytic fibers. Polyglutamine-expanded AR expression was decreased in whole muscle, yet enriched in the nucleus, and localized to mitochondria. Ultrastructural analysis revealed myofibrillar disorganization and streaming in zones lacking mitochondria and degenerating mitochondria. Using molecular (mtDNA copy number), biochemical (citrate synthase and respiratory chain enzymes) and morphological (dark blue area in nicotinamide adenine dinucleotide-stained muscle cross-sections) analyses, we found a depletion of the mitochondria associated with enhanced mitophagy. Mass spectrometry analysis revealed an increase of phosphatidylethanolamines and phosphatidylserines in mitochondria isolated from SBMA muscles, as well as a 50% depletion of cardiolipin associated with decreased expression of the cardiolipin synthase gene. These observations suggest a causative link between nuclear polyglutamine-expanded AR accumulation, depletion of mitochondrial mass, increased mitophagy and altered mitochondrial membrane composition in SBMA muscle patients. Given the central role of mitochondria in cell bioenergetics, therapeutic approaches toward improving the mitochondrial network are worth considering to support SBMA patients.

Phosphatidylcholine Affects Inner Membrane Protein Translocases of Mitochondria

Two protein translocases transport precursor proteins into or across the inner mitochondrial membrane. The presequence translocase (TIM23 complex) sorts precursor proteins with a cleavable presequence either into the matrix or into the inner membrane. The carrier translocase (TIM22 complex) inserts multispanning proteins into the inner membrane. Both protein import pathways depend on the presence of a membrane potential, which is generated by the activity of the respiratory chain. The non-bilayer-forming phospholipids cardiolipin and phosphatidylethanolamine are required for the activity of the respiratory chain and therefore to maintain the membrane potential for protein import. Depletion of cardiolipin further affects the stability of the TIM23 complex. The role of bilayer-forming phospholipids like phosphatidylcholine (PC) in protein transport into the inner membrane and the matrix is unknown. Here, we report that import of presequence-containing precursors and carrier proteins is impaired in PC-deficient mitochondria. Surprisingly, depletion of PC does not affect stability and activity of respiratory supercomplexes, and the membrane potential is maintained. Instead, the dynamic TIM23 complex is destabilized when the PC levels are reduced, whereas the TIM22 complex remains intact. Our analysis further revealed that initial precursor binding to the TIM23 complex is impaired in PC-deficient mitochondria. We conclude that reduced PC levels differentially affect the TIM22 and TIM23 complexes in mitochondrial protein transport.

Elimination of chronic lymphocytic leukemia cells in stromal microenvironment by targeting CPT with an antiangina drug perhexiline.

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the western countries and is currently incurable due in part to difficulty in eliminating the leukemia cells protected by stromal microenvironment. Based on previous observations that CLL cells exhibit mitochondrial dysfunction and altered lipid metabolism and that carnitine palmitoyltransferases (CPT) play a major role in transporting fatty acid into mitochondria to support cancer cell metabolism, we tested several clinically relevant inhibitors of lipid metabolism for their ability to eliminate primary CLL cells. We discovered that Perhexiline, an anti-angina agent that inhibits CPT, was highly effective in killing CLL cells in stromal microenvironment at clinically achievable concentrations. These effective concentrations caused low toxicity to normal lymphocytes and normal stromal cells. Mechanistic study revealed that CLL cells expressed high levels of CPT1 and CPT2. Suppression of fatty acid transport into mitochondria by inhibiting CPT using Perhexiline resulted in a depletion of cardiolipin, a key component of mitochondrial membranes, and compromised mitochondrial integrity leading to rapid depolarization and massive CLL cell death. The therapeutic activity of Perhexiline was further demonstrated in vivo using a CLL transgenic mouse model. Perhexiline significantly prolonged the overall animal survival by only 4 drug injections. Our study suggests that targeting CPT using an anti-angina drug is able to effectively eliminate leukemia cells in vivo, and is a novel therapeutic strategy for potential clinical treatment of CLL.

Abstract 2697: A novel therapeutic strategy to effectively kill CLL cells in stromal microenvironment by targeting lipid metabolism

Abstract The tissue microenvironment promotes cancer cell survival and drug resistance, and thus presents a major challenge in cancer treatment. Recent study suggests that the microenvironmental protection of chronic lymphocytic leukemia (CLL) cells is particular important due to the unique metabolic properties of CLL cells. Emerging evidence suggests that altered fatty acid metabolism may be associated with the pathogenesis of CLL and could potentially provide a biochemical basis for targeting CLL. In the current study, we tested three classes of compounds that respectively inhibit the de novo fatty acids synthesis (FASN), block the transport of fatty acids from cytosol into mitochondria, or suppress fatty acid oxidation, for their ability to kill CLL cells in the presence and absence of bone marrow stromal cells. While all three inhibitors exhibited cytotoxic effect again CLL cells when the leukemia cells were culture alone, only the compound that inhibited the transport of fatty acids into mitochondria was highly effective in killing CLL in the presence of bone marrow stromal cells. Mechanistic study revealed that the cytotoxicity was not due to inhibition of ATP generation through mitochondrial β-oxidation of fatty acids, since there was no significant decrease in mitochondrial respiratory activity. We further showed that inhibition of FA transport into mitochondria suppressed biosynthesis of mitochondrial phospholipid, leading to a significant depletion of cardiolipin (CL), which is essential for maintaining mitochondrial membrane integrity. Depletion of CL by the FA transport inhibitor in CLL cells resulted in mitochondrial depolarization, release of cytochrome c, and massive apoptosis. Since this cell death process was through the intrinsic pathway and could not be rescued by the stromal environment, this might explain why inhibition of FA transport into the mitochondrial was highly effective in killing CLL cells in the presence of stromal cells. Importantly, we found that inhibition of FA transport had low toxicity in normal lymphocytes and stromal cells, suggesting that the normal cells might be less dependent on FA transport for cardiolipin biosynthesis. In summary, our study suggests that inhibition of FA transport into the mitochondria is a novel therapeutic strategy to effectively and selectively kill CLL cells in stromal microenvironment, and may potentially improve the clinical outcome of CLL treatment. Citation Format: Panpan Liu, Jinyun Liu, Marcia A. Ogasawara, Helene Pelicano, Ruihua Xu, Michael J. Keating, Peng Huang. A novel therapeutic strategy to effectively kill CLL cells in stromal microenvironment by targeting lipid metabolism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2697. doi:10.1158/1538-7445.AM2014-2697

Electron flow into cytochrome c coupled with reactive oxygen species from the electron transport chain converts cytochrome c to a cardiolipin peroxidase: role during ischemia–reperfusion

BackgroundCytochrome c (Cyt c) is a mobile component of the electron transport chain (ETC.) which contains a tightly coordinated heme iron. In pathologic settings, a key ligand of the cyt c's heme iron, methionine (Met80), is oxidized allowing cyt c to participate in reactions as a peroxidase with cardiolipin as a target. Myocardial ischemia (ISC) results in ETC. blockade and increased production of reactive oxygen species (ROS). We hypothesized that during ischemia–reperfusion (ISC-REP); ROS generation coupled with electron flow into cyt c would oxidize Met80 and contribute to mitochondrial-mediated ETC. damage. MethodsMitochondria were incubated with specific substrates and inhibitors to test the contributions of ROS and electron flow into cyt c. Subsequently, cyt c and cardiolipin were analyzed. To test the pathophysiologic relevance, mouse hearts that underwent ISC-REP were tested for methionine oxidation in cyt c. ResultsThe combination of substrate/inhibitor showed that ROS production and electron flux through cyt c are essential for the oxidation of methionine residues that lead to cardiolipin depletion. The content of cyt c methionine oxidation increases following ISC-REP in the intact heart. ConclusionsIncrease in intra-mitochondrial ROS coupled with electron flow into cyt c, oxidizes cyt c followed by depletion of cardiolipin. ISC-REP increases methionine oxidation, supporting that cyt c peroxidase activity can form in the intact heart. General significanceThis study identifies a new site in the ETC. that is damaged during cardiac ISC-REP. Generation of a neoperoxidase activity of cyt c favors the formation of a defective ETC. that activates signaling for cell death.

MtDNA T8993G Mutation-Induced F1F0-ATP Synthase Defect Augments Mitochondrial Dysfunction Associated with hypoxia/reoxygenation: The Protective Role of Melatonin

BackgroundF1F0-ATP synthase (F1F0-ATPase) plays important roles in regulating mitochondrial function during hypoxia, but the effect of F1F0-ATPase defect on hypoxia/reoxygenation (H/RO) is unknown. The aim of this study was to investigate how mtDNA T8993G mutation (NARP)-induced inhibition of F1F0-ATPase modulates the H/RO–induced mitochondrial dysfunction. In addition, the potential for melatonin, a potent antioxidant with multiple mitochondrial protective properties, to protect NARP cells exposed to H/RO was assessed.Methods And FindingsNARP cybrids harboring 98% of mtDNA T8993G genes were established as an in vitro model for cells with F1F0-ATPase defect; their parental osteosarcoma 143B cells were studied for comparison. Treating the cells with H/RO using a hypoxic chamber resembles ischemia/reperfusion in vivo. NARP significantly enhanced apoptotic death upon H/RO detected by MTT assay and the trypan blue exclusion test of cell viability. Based on fluorescence probe-coupled laser scanning imaging microscopy, NARP significantly enhanced mitochondrial reactive oxygen species (mROS) formation and mitochondrial Ca2+ (mCa2+) accumulation in response to H/RO, which augmented the depletion of cardiolipin, resulting in the retardation of mitochondrial movement. With stronger H/RO stress (either with longer reoxygenation duration, longer hypoxia duration, or administrating secondary oxidative stress following H/RO), NARP augmented H/RO-induced mROS formation to significantly depolarize mitochondrial membrane potential (ΔΨm), and enhance mCa2+ accumulation and nitric oxide formation. Also, NARP augmented H/RO-induced mROS oxidized and depleted cardiolipin, thereby promoting permanent mitochondrial permeability transition, retarded mitochondrial movement, and enhanced apoptosis. Melatonin markedly reduced NARP-augmented H/RO-induced mROS formation and therefore significantly reduced mROS-mediated depolarization of ΔΨm and accumulation of mCa2+, stabilized cardiolipin, and then improved mitochondrial movement and cell survival. ConclusionNARP-induced inhibition of F1F0-ATPase enhances mROS formation upon H/RO, which augments the depletion of cardiolipin and retardation of mitochondrial movement. Melatonin may have the potential to rescue patients with ischemia/reperfusion insults, even those associated with NARP symptoms.

Hypoxic preconditioning-induced mitochondrial protection is not disrupted in a cell model of mtDNA T8993G mutation-induced F1F0-ATP synthase defect: the role of mitochondrial permeability transition

Transient opening of the mitochondrial permeability transition pore plays a crucial role in hypoxic preconditioning-induced protection. Recently, the cyclophilin-D component of the mitochondrial permeability transition pore has been shown to interact with and regulate the F1F0-ATP synthase. However, the precise role of the F1F0-ATP synthase and the interaction between cyclophilin-D and F1F0-ATP synthase in the mitochondrial permeability transition pore and hypoxic preconditioning remain uncertain. Here we found that a 1-h hypoxic preconditioning delayed apoptosis and improved cell survival after stimulation with various apoptotic inducers including H2O2, ionomycin, and arachidonic acid in mitochondrial DNA T8993G mutation (NARP) osteosarcoma 143B cybrids, an F1F0-ATP synthase defect cell model. This hypoxic preconditioning protected NARP cybrid cells against focal laser irradiation-induced oxidative stress by suppressing reactive oxygen species formation and preventing the depletion of cardiolipin. Furthermore, the protective functions of transient opening of the mitochondrial permeability transition pore in both NARP cybrids and wild-type 143B cells can be augmented by hypoxic preconditioning. Disruption of the interaction between cyclophilin-D and F1F0-ATP synthase by cyclosporin A attenuated the mitochondrial protection induced by hypoxic preconditioning in both NARP cybrids and wild-type 143B cells. Our results demonstrate that the interaction between cyclophilin-D and F1F0-ATP synthase is important in the hypoxic preconditioning-induced cell protection. This finding improves our understanding of the mechanism of mitochondrial permeability transition pore opening in cells in response to hypoxic preconditioning, and will be helpful in further developing new pharmacological agents targeting hypoxia–reoxygenation injury and mitochondria-mediated cell death

Phosphatidylethanolamine and Cardiolipin Differentially Affect the Stability of Mitochondrial Respiratory Chain Supercomplexes

The mitochondrial inner membrane contains two non-bilayer‐forming phospholipids, phosphatidylethanolamine (PE) and cardiolipin (CL). Lack of CL leads to destabilization of respiratory chain supercomplexes, a reduced activity of cytochrome c oxidase, and a reduced inner membrane potential Δψ. Although PE is more abundant than CL in the mitochondrial inner membrane, its role in biogenesis and assembly of inner membrane complexes is unknown. We report that similar to the lack of CL, PE depletion resulted in a decrease of Δψ and thus in an impaired import of preproteins into and across the inner membrane. The respiratory capacity and in particular the activity of cytochrome c oxidase were impaired in PE-depleted mitochondria, leading to the decrease of Δψ. In contrast to depletion of CL, depletion of PE did not destabilize respiratory chain supercomplexes but favored the formation of larger supercomplexes (megacomplexes) between the cytochrome bc1 complex and the cytochrome c oxidase. We conclude that both PE and CL are required for a full activity of the mitochondrial respiratory chain and the efficient generation of the inner membrane potential. The mechanisms, however, are different since these non-bilayer‐forming phospholipids exert opposite effects on the stability of respiratory chain supercomplexes.

Long‐term Aβ exposure augments mCa2+‐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 β-peptide (Aβ)-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 Aβ-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 Aβ-augmented mitochondrial Ca(2+) (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). Aβ augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize mitochondrial membrane potential (∆Ψ(m)) and reduce mCa(2+) stress. Aβ-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 Aβ-augmented mROS formation and therefore significantly reduced mROS-mediated depolarization of ∆Ψ(m), fission of mitochondria and retardation of mitochondrial movement to stabilize CL and hence the MPT. In the presence of melatonin, Aβ-promoted p-MPT was reversed to a protective t-MPT, which preserved ∆Ψ(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.

MtDNA T8993G Mutation-Induced Mitochondrial Complex V Inhibition Augments Cardiolipin-Dependent Alterations of Mitochondrial Dynamics During Oxidative, Ca2+ and Lipid Insults in NARP Cybrids: A Potential Therapeutic Target

Mitochondrial dynamics including morphological fission and mitochondrial movement are essential to normal mitochondrial and cellular physiology. This study investigated how mtDNA T8993G (NARP)-induced inhibition of mitochondrial complex V altered mitochondrial dynamics in association with a protective mitochondrial phospholipid, cardiolipin (CL), as a potential therapeutic target. NARP cybrids harboring 98% of mtDNA T8993G genes and its parental osteosarcoma 143B cells were studied for comparison, and protection provided by melatonin, a potent mitochondrial protector, was explored. We demonstrate for the first time that NARP mutation significantly enhances apoptotic death as a result of three distinct lethal mitochondrial apoptotic insults including oxidative, Ca2+ and lipid stress. In addition, NARP significantly augmented pathological depletion of CL. NARP-augmented depletion of CL results in enhanced retardation of mitochondrial movement and fission and later swelling of mitochondria during all insults. These results suggest that CL is a common and crucial pathological target for mitochondrial apoptotic insults. Furthermore, CL possibly plays a central role in regulating mitochondrial dynamics that are associated with NARP-augmented mitochondrial pathologies. Intriguingly, melatonin, by differentially preserving CL during various stresses (oxidation > Ca2+ > lipid), rescues differentially CL-altered mitochondrial dynamics and cell death (oxidation > Ca2+ > lipid). Thus, melatonin, in addition to being a mitochondrial antioxidant to antagonize mitochondrial oxidative stress, a mitochondrial permeability transition modulator to antagonize mitochondrial Ca2+ stress, may stabilize directly CL to prevent its oxidization and/or depletion and, therefore, it exerts great potential in rescuing CL-dependent mitochondrial dynamics-associated mitochondrial pathologies for treatment of NARP-induced pathologies and diseases.

MtDNA T8993G mutation‐induced mitochondrial complex V inhibition augments cardiolipin‐dependent alterations in mitochondrial dynamics during oxidative, Ca2+, and lipid insults in NARP cybrids: a potential therapeutic target for melatonin

Mitochondrial dynamics including morphological fission and mitochondrial movement are essential to normal mitochondrial and cellular physiology. This study investigated how mtDNA T8993G (NARP)-induced inhibition of mitochondrial complex V altered mitochondrial dynamics in association with a protective mitochondrial phospholipid, cardiolipin (CL), as a potential therapeutic target. NARP cybrids harboring 98% of mtDNA T8993G genes and its parental osteosarcoma 143B cells were studied for comparison, and protection provided by melatonin, a potent mitochondrial protector, was explored. We demonstrate for the first time that NARP mutation significantly enhances apoptotic death as a result of three distinct lethal mitochondrial apoptotic insults including oxidative, Ca(2+), and lipid stress. In addition, NARP significantly augmented pathological depletion of CL. NARP-augmented depletion of CL results in enhanced retardation of mitochondrial movement and fission and later swelling of mitochondria during all insults. These results suggest that CL is a common and crucial pathological target for mitochondrial apoptotic insults. Furthermore, CL possibly plays a central role in regulating mitochondrial dynamics that are associated with NARP-augmented mitochondrial pathologies. Intriguingly, melatonin, by differentially preserving CL during various stresses (oxidation > Ca(2+) > lipid), rescues differentially CL-altered mitochondrial dynamics and cell death (oxidation > Ca(2+) > lipid). Thus, melatonin, in addition to being a mitochondrial antioxidant to antagonize mitochondrial oxidative stress, a mitochondrial permeability transition modulator to antagonize mitochondrial Ca(2+) stress, may stabilize directly CL to prevent its oxidization and/or depletion and, therefore, exerts great potential in rescuing CL-dependent mitochondrial dynamics-associated mitochondrial pathologies for treatment of NARP-induced pathologies and diseases.

Combined Genetic and Metabolic Manipulation of Lipids in Rhodobacter sphaeroides Reveals Non-Phospholipid Substitutions in Fully Active Cytochrome c Oxidase

A specific requirement for lipids, particularly cardiolipin (CL), in cytochrome c oxidase (CcO) has been reported in many previous studies using mainly in vitro lipid removal approaches in mammalian systems. Our accompanying paper shows that CcO produced in markedly CL-depleted Rhodobacter sphaeroides displays wild-type properties in all respects, likely allowed by quantitative substitution with other negatively charged lipids. To further examine the structural basis for the lipid requirements of R. sphaeroides CcO and the extent of interchangeability between lipids, we employed a metabolic approach to enhance the alteration of the lipid profiles of the CcO-expressing strains of R. sphaeroides in vivo using a phosphate-limiting growth medium in addition to the CL-deficient mutation. Strikingly, the purified CcO produced under these conditions still maintained wild-type function and characteristics, in spite of even greater depletion of cardiolipin compared to that of the CL-deficient mutant alone (undetectable by MS) and drastically altered profiles of all the phospholipids and non-phospholipids. The lipids in the membrane and in the purified CcO were identified and quantified by ESI and MALDI mass spectrometry and tandem mass spectrometry. Comparison between the molecular structures of those lipids that showed major changes provides new insight into the structural rationale for the flexible lipid requirements of CcO from R. sphaeroides and reveals a more comprehensive interchangeability network between different phospholipids and non-phospholipids.

Cardiolipin Deficiency in Rhodobacter sphaeroides Alters the Lipid Profile of Membranes and of Crystallized Cytochrome Oxidase, but Structure and Function Are Maintained

Many recent studies highlight the importance of lipids in membrane proteins, including in the formation of well-ordered crystals. To examine the effect of changes in one lipid, cardiolipin, on the lipid profile and the production, function, and crystallization of an intrinsic membrane protein, cytochrome c oxidase, we mutated the cardiolipin synthase (cls) gene of Rhodobacter sphaeroides, causing a >90% reduction in cardiolipin content in vivo and selective changes in the abundances of other lipids. Under these conditions, a fully native cytochrome c oxidase (CcO) was produced, as indicated by its activity, spectral properties, and crystal characteristics. Analysis by MALDI tandem mass spectrometry (MS/MS) revealed that the cardiolipin level in CcO crystals, as in the membranes, was greatly decreased. Lipid species present in the crystals were directly analyzed for the first time using MS/MS, documenting their identities and fatty acid chain composition. The fatty acid content of cardiolipin in R. sphaeroides CcO (predominantly 18:1) differs from that in mammalian CcO (18:2). In contrast to the cardiolipin dependence of mammalian CcO activity, major depletion of cardiolipin in R. sphaeroides did not impact any aspect of CcO structure or behavior, suggesting a greater tolerance of interchange of cardiolipin with other lipids in this bacterial system.

MtDNA T8993G-Augmented Mitochondrial Stresses Upon mCa2+ Overload and its Protection by Melatonin in a NARP Cybrid

Mitochondrial DNA (mtDNA) T8993G mutation inhibits specifically mitochondrial F1F0-ATPase (complex V) for severe ATP deficiency and is clinically associated with neurological muscle weakness, ataxia, and retinitis pigmentosa so called NARP mutation. At present, detail T8993G-associated mitochondrial mechanisms as well as its therapeutic strategies are limited. Using time-lapse laser scanning dual fluorescence imaging microscopy, this study investigated T8993G-altered apoptotic mitochondrial pathology particular upon mCa2+ stress and protection by melatonin, previously reported to protect mCa2+ stress-mediated apoptosis (Hsu et al., 2009 JPR in press). In comparison to its parental osteosarcoma 143B and mtDNA less (ρ0) cells, T8993G induced significant hyperpolarization of mitochondrial membrane potential (ΔΨm) and potentiated greatly ionomycin-induced mCa2+ stress. T8993G-augmented mCa2+ stress subsequently elicited rigorously generation of mitochondrial oxygen species (mROS), depletion of cardiolipin (CL) and activation of the mitochondrial permeability transition (MPT). In contract, ρ0 cells, with much depolarized ΔΨm, suffered less mCa2+ stress, mROS formation, CL depletion and the MPT opening. Interestingly, melatonin reduced significantly peak amplitude of the ionomycin-induced mCa2+ transient and antagonized efficiently mCa2+-augmented mROS generation for a reduced depletion of CL and activation of the MPT. In addition, melatonin prevented “oxidation free mCa2+”-mediated MPT suggesting its direct targeting on the MPT. Melatonin-enhanced tail amplitude of mCa2+ transient possibly due to the reduced MPT-dependent depolarization of ΔΨm, however, did not enhance mCa2+ stress-mediated pathology in NARP cybrids possibly as melatonin-elevated mCa2+ improved mitochondrial respiratory. Thus, the administration of melatonin may provide potential improvement for the treatment of mtDNA T8993G-associated NARP syndromes and diseases.