Publications by authors named "Valeria Petronilli"

35 Publications

High-Conductance Channel Formation in Yeast Mitochondria is Mediated by F-ATP Synthase e and g Subunits.

Cell Physiol Biochem 2018 13;50(5):1840-1855. Epub 2018 Nov 13.

Department of Biomedical Sciences, University of Padova, Padova,

Background/aims: The permeability transition pore (PTP) is an unselective, Ca2+-dependent high conductance channel of the inner mitochondrial membrane whose molecular identity has long remained a mystery. The most recent hypothesis is that pore formation involves the F-ATP synthase, which consistently generates Ca2+-activated channels. Available structures do not display obvious features that can accommodate a channel; thus, how the pore can form and whether its activity can be entirely assigned to F-ATP synthase is the matter of debate. In this study, we investigated the role of F-ATP synthase subunits e, g and b in PTP formation.

Methods: Yeast null mutants for e, g and the first transmembrane (TM) α-helix of subunit b were generated and evaluated for mitochondrial morphology (electron microscopy), membrane potential (Rhodamine123 fluorescence) and respiration (Clark electrode). Homoplasmic C23S mutant of subunit a was generated by in vitro mutagenesis followed by biolistic transformation. F-ATP synthase assembly was evaluated by BN-PAGE analysis. Cu2+ treatment was used to induce the formation of F-ATP synthase dimers in the absence of e and g subunits. The electrophysiological properties of F-ATP synthase were assessed in planar lipid bilayers.

Results: Null mutants for the subunits e and g display dimer formation upon Cu2+ treatment and show PTP-dependent mitochondrial Ca2+ release but not swelling. Cu2+ treatment causes formation of disulfide bridges between Cys23 of subunits a that stabilize dimers in absence of e and g subunits and favors the open state of wild-type F-ATP synthase channels. Absence of e and g subunits decreases conductance of the F-ATP synthase channel about tenfold. Ablation of the first TM of subunit b, which creates a distinct lateral domain with e and g, further affected channel activity.

Conclusion: F-ATP synthase e, g and b subunits create a domain within the membrane that is critical for the generation of the high-conductance channel, thus is a prime candidate for PTP formation. Subunits e and g are only present in eukaryotes and may have evolved to confer this novel function to F-ATP synthase.
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http://dx.doi.org/10.1159/000494864DOI Listing
November 2018

Arginine 107 of yeast ATP synthase subunit g mediates sensitivity of the mitochondrial permeability transition to phenylglyoxal.

J Biol Chem 2018 09 9;293(38):14632-14645. Epub 2018 Aug 9.

From the Consiglio Nazionale delle Ricerche Institute of Neuroscience and Department of Biomedical Sciences, University of Padova, Padova 35131, Italy and

Modification with arginine-specific glyoxals modulates the permeability transition (PT) of rat liver mitochondria, with inhibitory or inducing effects that depend on the net charge of the adduct(s). Here, we show that phenylglyoxal (PGO) affects the PT in a species-specific manner (inhibition in mouse and yeast, induction in human and mitochondria). Following the hypotheses (i) that the effects are mediated by conserved arginine(s) and (ii) that the PT is mediated by the F-ATP synthase, we have narrowed the search to 60 arginines. Most of these residues are located in subunits α, β, γ, ϵ, a, and c and were excluded because PGO modification did not significantly affect enzyme catalysis. On the other hand, yeast mitochondria lacking subunit g or bearing a subunit g R107A mutation were totally resistant to PT inhibition by PGO. Thus, the effect of PGO on the PT is specifically mediated by Arg-107, the only subunit g arginine that has been conserved across species. These findings are evidence that the PT is mediated by F-ATP synthase.
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http://dx.doi.org/10.1074/jbc.RA118.004495DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6153276PMC
September 2018

The idebenone metabolite QS10 restores electron transfer in complex I and coenzyme Q defects.

Biochim Biophys Acta Bioenerg 2018 09 22;1859(9):901-908. Epub 2018 Apr 22.

CNR Neuroscience Institute and Department of Biomedical Sciences, University of Padova, Padova, Italy. Electronic address:

Idebenone is a hydrophilic short-chain coenzyme (Co) Q analogue, which has been used as a potential bypass of defective complex I in both Leber Hereditary Optic Neuropathy and OPA1-dependent Dominant Optic Atrophy. Based on its potential antioxidant effects, it has also been tested in degenerative disorders such as Friedreich's ataxia, Huntington's and Alzheimer's diseases. Idebenone is rapidly modified but the biological effects of its metabolites have been characterized only partially. Here we have studied the effects of quinones generated during in vivo metabolism of idebenone with specific emphasis on 6-(9-carboxynonyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone (QS10). QS10 partially restored respiration in cells deficient of complex I or of CoQ without inducing the mitochondrial permeability transition, a detrimental effect of idebenone that may offset its potential benefits [Giorgio et al. (2012) Biochim. Biophys. Acta 1817: 363-369]. Remarkably, respiration was largely rotenone-insensitive in complex I deficient cells and rotenone-sensitive in CoQ deficient cells. These findings indicate that, like idebenone, QS10 can provide a bypass to defective complex I; and that, unlike idebenone, QS10 can partially replace endogenous CoQ. In zebrafish (Danio rerio) treated with rotenone, QS10 was more effective than idebenone in allowing partial recovery of respiration (to 40% and 20% of the basal respiration of untreated embryos, respectively) and allowing zebrafish survival (80% surviving embryos at 60 h post-fertilization, a time point at which all rotenone-treated embryos otherwise died). We conclude that QS10 is potentially more active than idebenone in the treatment of diseases caused by complex I defects, and that it could also be used in CoQ deficiencies of genetic and acquired origin.
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http://dx.doi.org/10.1016/j.bbabio.2018.04.006DOI Listing
September 2018

The unique histidine in OSCP subunit of F-ATP synthase mediates inhibition of the permeability transition pore by acidic pH.

EMBO Rep 2018 02 7;19(2):257-268. Epub 2017 Dec 7.

Consiglio Nazionale delle Ricerche Institute of Neuroscience, Padova, Italy

The permeability transition pore (PTP) is a Ca-dependent mitochondrial channel whose opening causes a permeability increase in the inner membrane to ions and solutes. The most potent inhibitors are matrix protons, with channel block at pH 6.5. Inhibition is reversible, mediated by histidyl residue(s), and prevented by their carbethoxylation by diethylpyrocarbonate (DPC), but their assignment is unsolved. We show that PTP inhibition by H is mediated by the highly conserved histidyl residue (H112 in the human mature protein) of oligomycin sensitivity conferral protein (OSCP) subunit of mitochondrial FF (F)-ATP synthase, which we also show to undergo carbethoxylation after reaction of mitochondria with DPC. Mitochondrial PTP-dependent swelling cannot be inhibited by acidic pH in H112Q and H112Y OSCP mutants, and the corresponding megachannels (the electrophysiological counterpart of the PTP) are insensitive to inhibition by acidic pH in patch-clamp recordings of mitoplasts. Cells harboring the H112Q and H112Y mutations are sensitized to anoxic cell death at acidic pH. These results demonstrate that PTP channel formation and its inhibition by H are mediated by the F-ATP synthase.
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http://dx.doi.org/10.15252/embr.201744705DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5797955PMC
February 2018

Alisporivir rescues defective mitochondrial respiration in Duchenne muscular dystrophy.

Pharmacol Res 2017 Nov 9;125(Pt B):122-131. Epub 2017 Sep 9.

Department of Biomedical Sciences and CNR Neuroscience Institute, University of Padova, Padova, Italy. Electronic address:

Duchenne muscular dystrophy (DMD) is a severe muscle disease of known etiology without effective, or generally applicable therapy. Mitochondria are affected by the disease in animal models but whether mitochondrial dysfunction is part of the pathogenesis in patients remains unclear. We show that primary cultures obtained from muscle biopsies of DMD patients display a decrease of the respiratory reserve, a consequence of inappropriate opening of the permeability transition pore (PTP). Treatment with the cyclophilin inhibitor alisporivir - a cyclosporin A derivative that desensitizes the PTP but does not inhibit calcineurin - largely restored the maximal respiratory capacity without affecting basal oxygen consumption in cells from patients, thus reinstating a normal respiratory reserve. Treatment with alisporivir, but not with cyclosporin A, led to a substantial recovery of respiratory function matching improved muscle ultrastructure and survival of sapje zebrafish, a severe model of DMD where muscle defects are close to those of DMD patients. Alisporivir was generally well tolerated in HCV patients and could be used for the treatment of DMD.
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http://dx.doi.org/10.1016/j.phrs.2017.09.001DOI Listing
November 2017

Calcium and regulation of the mitochondrial permeability transition.

Cell Calcium 2018 03 10;70:56-63. Epub 2017 May 10.

Department of Biomedical Sciences and CNR Neuroscience Institute, University of Padova, Italy. Electronic address:

Recent years have seen renewed interest in the permeability transition pore, a high conductance channel responsible for permeabilization of the inner mitochondrial membrane, a process that leads to depolarization and Ca release. Transient openings may be involved in physiological Ca homeostasis while long-lasting openings may trigger and/or execute cell death. In this review we specifically focus (i) on the hypothesis that the PTP forms from the F-ATP synthase and (ii) on the mechanisms through which Ca can reversibly switch this energy-conserving nanomachine into an energy-dissipating device.
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http://dx.doi.org/10.1016/j.ceca.2017.05.004DOI Listing
March 2018

Ca binding to F-ATP synthase β subunit triggers the mitochondrial permeability transition.

EMBO Rep 2017 07 15;18(7):1065-1076. Epub 2017 May 15.

Department of Biomedical Sciences, University of Padova, Padova, Italy

F-ATP synthases convert the electrochemical energy of the H gradient into the chemical energy of ATP with remarkable efficiency. Mitochondrial F-ATP synthases can also undergo a Ca-dependent transformation to form channels with properties matching those of the permeability transition pore (PTP), a key player in cell death. The Ca binding site and the mechanism(s) through which Ca can transform the energy-conserving enzyme into a dissipative structure promoting cell death remain unknown. Through , and studies we (i) pinpoint the "Ca-trigger site" of the PTP to the catalytic site of the F-ATP synthase β subunit and (ii) define a conformational change that propagates from the catalytic site through OSCP and the lateral stalk to the inner membrane. T163S mutants of the β subunit, which show a selective decrease in Ca-ATP hydrolysis, confer resistance to Ca-induced, PTP-dependent death in cells and developing zebrafish embryos. These findings are a major advance in the molecular definition of the transition of F-ATP synthase to a channel and of its role in cell death.
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http://dx.doi.org/10.15252/embr.201643354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5494526PMC
July 2017

Melanocytes from Patients Affected by Ullrich Congenital Muscular Dystrophy and Bethlem Myopathy have Dysfunctional Mitochondria That Can be Rescued with Cyclophilin Inhibitors.

Front Aging Neurosci 2014 20;6:324. Epub 2014 Nov 20.

CNR National Research Council of Italy, Institute of Molecular Genetics , Bologna , Italy ; SC Laboratory of Musculoskeletal Cell Biology, IOR , Bologna , Italy.

Ullrich congenital muscular dystrophy and Bethlem myopathy are caused by mutations in collagen VI (ColVI) genes, which encode an extracellular matrix protein; yet, mitochondria play a major role in disease pathogenesis through a short circuit caused by inappropriate opening of the permeability transition pore, a high-conductance channel, which causes a shortage in ATP production. We find that melanocytes do not produce ColVI yet they bind it at the cell surface, suggesting that this protein may play a trophic role and that its absence may cause lesions similar to those seen in skeletal muscle. We show that mitochondria in melanocytes of Ullrich congenital muscular dystrophy and Bethlem myopathy patients display increased size, reduced matrix density, and disrupted cristae, findings that suggest a functional impairment. In keeping with this hypothesis, mitochondria (i) underwent anomalous depolarization after inhibition of the F-ATP synthase with oligomycin, and (ii) displayed decreased respiratory reserve capacity. The non-immunosuppressive cyclophilin inhibitor NIM811 prevented mitochondrial depolarization in response to oligomycin in melanocytes from both Ullrich congenital muscular dystrophy and Bethlem myopathy patients, and partially restored the respiratory reserve of melanocytes from one Bethlem myopathy patient. These results match our recent findings on melanocytes from patients affected by Duchenne muscular dystrophy (Pellegrini et al., 2013), and suggest that skin biopsies may represent a minimally invasive tool to investigate mitochondrial dysfunction and to evaluate drug efficacy in ColVI-related myopathies and possibly in other muscle wasting conditions like aging sarcopenia.
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http://dx.doi.org/10.3389/fnagi.2014.00324DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4238408PMC
December 2014

Peptide-based carbon nanotubes for mitochondrial targeting.

Nanoscale 2013 Oct 1;5(19):9110-7. Epub 2013 Aug 1.

Department of Chemical and Pharmaceutical Sciences, University of Trieste, Piazzale Europa 1, Trieste, 34127, Italy.

In the present study, we report the design and synthesis of peptide-based-multi-walled carbon nanotubes (MWCNTs) to target mitochondria. Targeting these intracellular organelles might open the way to develop alternative systems to address diseases related to genetic mutations in mitochondrial (mt)-DNA, by delivering therapeutic oligonucleotides. The first step towards mitochondrial delivery of this type of nucleic acid was to target MWCNTs to mitochondria by covalent functionalization with a well-known endogenous mitochondrial targeting sequence (MTS). The subcellular localization of the conjugates, which were fluorescently labeled, in murine RAW 264.7 macrophages and human HeLa cells was then studied using different microscopy techniques, such as wide-field epifluorescence microscopy, confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). The localization of the MTS-MWCNT conjugates into mitochondria was further confirmed by analyzing the isolated organelles using TEM.
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http://dx.doi.org/10.1039/c3nr02694aDOI Listing
October 2013

Dimers of mitochondrial ATP synthase form the permeability transition pore.

Proc Natl Acad Sci U S A 2013 Apr 25;110(15):5887-92. Epub 2013 Mar 25.

Consiglio Nazionale delle Ricerche Institute of Neuroscience and Department of Biomedical Sciences, University of Padova, 35121 Padua, Italy.

Here we define the molecular nature of the mitochondrial permeability transition pore (PTP), a key effector of cell death. The PTP is regulated by matrix cyclophilin D (CyPD), which also binds the lateral stalk of the FOF1 ATP synthase. We show that CyPD binds the oligomycin sensitivity-conferring protein subunit of the enzyme at the same site as the ATP synthase inhibitor benzodiazepine 423 (Bz-423), that Bz-423 sensitizes the PTP to Ca(2+) like CyPD itself, and that decreasing oligomycin sensitivity-conferring protein expression by RNAi increases the sensitivity of the PTP to Ca(2+). Purified dimers of the ATP synthase, which did not contain voltage-dependent anion channel or adenine nucleotide translocator, were reconstituted into lipid bilayers. In the presence of Ca(2+), addition of Bz-423 triggered opening of a channel with currents that were typical of the mitochondrial megachannel, which is the PTP electrophysiological equivalent. Channel openings were inhibited by the ATP synthase inhibitor AMP-PNP (γ-imino ATP, a nonhydrolyzable ATP analog) and Mg(2+)/ADP. These results indicate that the PTP forms from dimers of the ATP synthase.
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http://dx.doi.org/10.1073/pnas.1217823110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625323PMC
April 2013

The effects of idebenone on mitochondrial bioenergetics.

Biochim Biophys Acta 2012 Feb 4;1817(2):363-9. Epub 2011 Nov 4.

Department of Biomedical Sciences, University of Padova, Padova, Italy.

We have studied the effects of idebenone on mitochondrial function in cybrids derived from one normal donor (HQB17) and one patient harboring the G3460A/MT-ND1 mutation of Leber's Hereditary Optic Neuropathy (RJ206); and in XTC.UC1 cells bearing a premature stop codon at amino acid 101 of MT-ND1 that hampers complex I assembly. Addition of idebenone to HQB17 cells caused mitochondrial depolarization and NADH depletion, which were inhibited by cyclosporin (Cs) A and decylubiquinone, suggesting an involvement of the permeability transition pore (PTP). On the other hand, addition of dithiothreitol together with idebenone did not cause PTP opening and allowed maintenance of the mitochondrial membrane potential even in the presence of rotenone. Addition of dithiothreitol plus idebenone, or of idebenol, to HQB17, RJ206 and XTC.UC1 cells sustained membrane potential in intact cells and ATP synthesis in permeabilized cells even in the presence of rotenone and malonate, and restored a good level of coupled respiration in complex I-deficient XTC.UC1 cells. These findings demonstrate that idebenol can feed electrons at complex III. If the quinone is maintained in the reduced state, a task that in some cell types appears to be performed by dicoumarol-sensitive NAD(P)H:quinone oxidoreductase 1 [Haefeli et al. (2011) PLoS One 6, e17963], electron transfer to complex III may allow reoxidation of NADH in complex I deficiencies.
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http://dx.doi.org/10.1016/j.bbabio.2011.10.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3265671PMC
February 2012

Properties of Ca(2+) transport in mitochondria of Drosophila melanogaster.

J Biol Chem 2011 Dec 7;286(48):41163-70. Epub 2011 Oct 7.

Consiglio Nazionale delle Ricerche Institute of Neuroscience and Department of Biomedical Sciences, University of I-35121 Padova, Italy.

We have studied the pathways for Ca(2+) transport in mitochondria of the fruit fly Drosophila melanogaster. We demonstrate the presence of ruthenium red (RR)-sensitive Ca(2+) uptake, of RR-insensitive Ca(2+) release, and of Na(+)-stimulated Ca(2+) release in energized mitochondria, which match well characterized Ca(2+) transport pathways of mammalian mitochondria. Following larger matrix Ca(2+) loading Drosophila mitochondria underwent spontaneous RR-insensitive Ca(2+) release, an event that in mammals is due to opening of the permeability transition pore (PTP). Like the PTP of mammals, Drosophila Ca(2+)-induced Ca(2+) release could be triggered by uncoupler, diamide, and N-ethylmaleimide, indicating the existence of regulatory voltage- and redox-sensitive sites and was inhibited by tetracaine. Unlike PTP-mediated Ca(2+) release in mammals, however, it was (i) insensitive to cyclosporin A, ubiquinone 0, and ADP; (ii) inhibited by P(i), as is the PTP of yeast mitochondria; and (iii) not accompanied by matrix swelling and cytochrome c release even in KCl-based medium. We conclude that Drosophila mitochondria possess a selective Ca(2+) release channel with features intermediate between the PTP of yeast and mammals.
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http://dx.doi.org/10.1074/jbc.M111.268375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3308830PMC
December 2011

The translocator protein (peripheral benzodiazepine receptor) mediates rat-selective activation of the mitochondrial permeability transition by norbormide.

Biochim Biophys Acta 2011 Dec 26;1807(12):1600-5. Epub 2011 Aug 26.

C.N.R. Institute of Neurosciences at the Department of Biomedical Sciences, University of Padova, Italy.

We have investigated the mechanism of rat-selective induction of the mitochondrial permeability transition (PT) by norbormide (NRB). We show that the inducing effect of NRB on the PT (i) is inhibited by the selective ligands of the 18kDa outer membrane (OMM) translocator protein (TSPO, formerly peripheral benzodiazepine receptor) protoporphyrin IX, N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide and 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one; and (ii) is lost in digitonin mitoplasts, which lack an intact OMM. In mitoplasts the PT can still be induced by the NRB cationic derivative OL14, which contrary to NRB is also effective in intact mitochondria from mouse and guinea pig. We conclude that selective NRB transport into rat mitochondria occurs via TSPO in the OMM, which allows its translocation to PT-regulating sites in the inner membrane. Thus, species-specificity of NRB toward the rat PT depends on subtle differences in the structure of TSPO or of TSPO-associated proteins affecting its substrate specificity.
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http://dx.doi.org/10.1016/j.bbabio.2011.08.007DOI Listing
December 2011

A glutamine synthetase inhibitor increases survival and decreases cytokine response in a mouse model of acute liver failure.

Liver Int 2011 Sep 31;31(8):1209-21. Epub 2011 May 31.

Department of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, MI, USA.

Background: Acute liver failure (ALF) can be induced in mice by administering Escherichia coli lipopolysaccharide (LPS) and D-galactosamine (D-GalN), which induce an inflammatory response involving tumour necrosis factor (TNF)-α production and a hepatocyte-specific transcriptional block. Under these conditions, binding of TNF-α to its cognate receptor on hepatocytes eventually leads to their apoptosis.

Aims: As part of an effort to identify drugs to treat this disease model, we have investigated whether the glutamine synthetase inhibitor methionine sulfoximine (MSO) could play a protective role, given its effectiveness in the inhibition of brain swelling associated with hyperammonaemia.

Methods: Mouse survival, glutamine synthetase activity, hepatocyte apoptosis and induction of inflammatory cytokines were measured in mice treated with MSO before an intraperitoneal injection of LPS/D-GalN. The effect of MSO on viability and on TNF-α release was also assessed on inflammatory and liver cells.

Results: We have found that, in mice treated with LPS/D-GalN, MSO (i) drastically increases animal survival; (ii) sharply reduces glutamine synthetase activity, without inhibiting its other target, γ-glutamyl cysteine synthetase; (iii) inhibits death receptor-mediated apoptosis in hepatocytes upstream to cytokine binding; (iv) strongly reduces the overall inflammatory cytokine response, including a significant decrease in TNF-α induction in vivo and ex vivo, and in the interferon-γ level and signalling.

Conclusions: These results demonstrate that the MSO target glutamine synthetase is required for the early steps of the cytokine response to endotoxins, and that its pharmacological inhibition may be exploited to treat inflammation.
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http://dx.doi.org/10.1111/j.1478-3231.2011.02553.xDOI Listing
September 2011

Regulation of the inner membrane mitochondrial permeability transition by the outer membrane translocator protein (peripheral benzodiazepine receptor).

J Biol Chem 2011 Jan 9;286(2):1046-53. Epub 2010 Nov 9.

Department of Biomedical Sciences, Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Padova, I-35121 Padova, Italy.

We studied the properties of the permeability transition pore (PTP) in rat liver mitochondria and in mitoplasts retaining inner membrane ultrastructure and energy-linked functions. Like mitochondria, mitoplasts readily underwent a permeability transition following Ca(2+) uptake in a process that maintained sensitivity to cyclosporin A. On the other hand, major differences between mitochondria and mitoplasts emerged in PTP regulation by ligands of the outer membrane translocator protein of 18 kDa, TSPO, formerly known as the peripheral benzodiazepine receptor. Indeed, (i) in mitoplasts, the PTP could not be activated by photo-oxidation after treatment with dicarboxylic porphyrins endowed with protoporphyrin IX configuration, which bind TSPO in intact mitochondria; and (ii) mitoplasts became resistant to the PTP-inducing effects of N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide and of other selective ligands of TSPO. Thus, the permeability transition is an inner membrane event that is regulated by the outer membrane through specific interactions with TSPO.
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http://dx.doi.org/10.1074/jbc.M110.172486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3020711PMC
January 2011

The mitochondrial permeability transition from yeast to mammals.

FEBS Lett 2010 Jun 14;584(12):2504-9. Epub 2010 Apr 14.

Department of Biomedical Sciences, CNR Institute of Neuroscience, University of Padova, Padova, Italy.

Regulated permeability changes have been detected in mitochondria across species. We review here their key features, with the goal of assessing whether a "permeability transition" similar to that observed in higher eukaryotes is present in other species. The recent discoveries (i) that treatment with cyclosporin A (CsA) unmasks an inhibitory site for inorganic phosphate (Pi) [Basso, E., Petronilli, V., Forte, M.A. and Bernardi, P. (2008) Phosphate is essential for inhibition of the mitochondrial permeability transition pore by cyclosporin A and by cyclophilin D ablation. J. Biol. Chem. 283, 26307-26311], the classical inhibitor of the permeability transition of yeast and (ii) that under proper experimental conditions a matrix Ca(2+)-dependence can be demonstrated in yeast as well [Yamada, A., Yamamoto, T., Yoshimura, Y., Gouda, S., Kawashima, S., Yamazaki, N., Yamashita, K., Kataoka, M., Nagata, T., Terada, H., Pfeiffer, D.R. and Shinohara Y. (2009) Ca(2+)-induced permeability transition can be observed even in yeast mitochondria under optimized experimental conditions. Biochim. Biophys. Acta 1787, 1486-1491] suggest that the mitochondrial permeability transition has been conserved during evolution.
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http://dx.doi.org/10.1016/j.febslet.2010.04.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2878904PMC
June 2010

Cyclophilin D modulates mitochondrial F0F1-ATP synthase by interacting with the lateral stalk of the complex.

J Biol Chem 2009 Dec 29;284(49):33982-8. Epub 2009 Sep 29.

Department of Biomedical Sciences and the Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Padova, I-35121 Padova, Italy.

Blue native gel electrophoresis purification and immunoprecipitation of F(0)F(1)-ATP synthase from bovine heart mitochondria revealed that cyclophilin (CyP) D associates to the complex. Treatment of intact mitochondria with the membrane-permeable bifunctional reagent dimethyl 3,3-dithiobis-propionimidate (DTBP) cross-linked CyPD with the lateral stalk of ATP synthase, whereas no interactions with F(1) sector subunits, the ATP synthase natural inhibitor protein IF1, and the ATP/ADP carrier were observed. The ATP synthase-CyPD interactions have functional consequences on enzyme catalysis and are modulated by phosphate (increased CyPD binding and decreased enzyme activity) and cyclosporin (Cs) A (decreased CyPD binding and increased enzyme activity). Treatment of MgATP submitochondrial particles or intact mitochondria with CsA displaced CyPD from membranes and activated both hydrolysis and synthesis of ATP sustained by the enzyme. No effect of CsA was detected in CyPD-null mitochondria, which displayed a higher specific activity of the ATP synthase than wild-type mitochondria. Modulation by CyPD binding appears to be independent of IF1, whose association to ATP synthase was not affected by CsA treatment. These findings demonstrate that CyPD association to the lateral stalk of ATP synthase modulates the activity of the complex.
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http://dx.doi.org/10.1074/jbc.M109.020115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797168PMC
December 2009

Modulation of mitochondrial K(+) permeability and reactive oxygen species production by the p13 protein of human T-cell leukemia virus type 1.

Biochim Biophys Acta 2009 Jul 11;1787(7):947-54. Epub 2009 Feb 11.

Department of Oncology and Surgical Sciences, University of Padova, I-35128 Padova, Italy.

Human T-cell leukemia virus type-1 (HTLV-1) expresses an 87-amino acid protein named p13 that is targeted to the inner mitochondrial membrane. Previous studies showed that a synthetic peptide spanning an alpha helical domain of p13 alters mitochondrial membrane permeability to cations, resulting in swelling. The present study examined the effects of full-length p13 on isolated, energized mitochondria. Results demonstrated that p13 triggers an inward K(+) current that leads to mitochondrial swelling and confers a crescent-like morphology distinct from that caused by opening of the permeability transition pore. p13 also induces depolarization, with a matching increase in respiratory chain activity, and augments production of reactive oxygen species (ROS). These effects require an intact alpha helical domain and strictly depend on the presence of K(+) in the assay medium. The effects of p13 on ROS are mimicked by the K(+) ionophore valinomycin, while the protonophore FCCP decreases ROS, indicating that depolarization induced by K(+) vs. H(+) currents has different effects on mitochondrial ROS production, possibly because of their opposite effects on matrix pH (alkalinization and acidification, respectively). The downstream consequences of p13-induced mitochondrial K(+) permeability are likely to have an important influence on the redox state and turnover of HTLV-1-infected cells.
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http://dx.doi.org/10.1016/j.bbabio.2009.02.001DOI Listing
July 2009

Switch from inhibition to activation of the mitochondrial permeability transition during hematoporphyrin-mediated photooxidative stress. Unmasking pore-regulating external thiols.

Biochim Biophys Acta 2009 Jul 1;1787(7):897-904. Epub 2009 Apr 1.

C.N.R. Institute of Neurosciences at the Department of Biomedical Sciences, University of Padova, Italy.

We have studied the mitochondrial permeability transition pore (PTP) under oxidizing conditions with mitochondria-bound hematoporphyrin, which generates reactive oxygen species (mainly singlet oxygen, (1)O(2)) upon UV/visible light-irradiation and promotes the photooxidative modification of vicinal targets. We have characterized the PTP-modulating properties of two major critical sites endowed with different degrees of photosensitivity: (i) the most photovulnerable site comprises critical histidines, whose photomodification by vicinal hematoporphyrin causes a drop in reactivity of matrix-exposed (internal), PTP-regulating cysteines thus stabilizing the pore in a closed conformation; (ii) the most photoresistant site coincides with the binding domains of (external) cysteines sensitive to membrane-impermeant reagents, which are easily unmasked when oxidation of internal cysteines is prevented. Photooxidation of external cysteines promoted by vicinal hematoporphyrin reactivates the PTP after the block caused by histidine photodegradation. Thus, hematoporphyrin-mediated photooxidative stress can either inhibit or activate the mitochondrial permeability transition depending on the site of hematoporphyrin localization and on the nature of the substrate; and selective photomodification of different hematoporphyrin-containing pore domains can be achieved by fine regulation of the sensitizer/light doses. These findings shed new light on PTP modulation by oxidative stress.
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http://dx.doi.org/10.1016/j.bbabio.2009.03.014DOI Listing
July 2009

Respiratory complex I dysfunction due to mitochondrial DNA mutations shifts the voltage threshold for opening of the permeability transition pore toward resting levels.

J Biol Chem 2009 Jan 1;284(4):2045-52. Epub 2008 Dec 1.

Department of Evolutionary and Experimental Biology, University of Bologna, 40126 Bologna, Italy.

We have studied mitochondrial bioenergetics in HL180 cells (a cybrid line harboring the T14484C/ND6 and G14279A/ND6 mtDNA mutations of Leber hereditary optic neuropathy, leading to an approximately 50% decrease of ATP synthesis) and XTC.UC1 cells (derived from a thyroid oncocytoma bearing a disruptive frameshift mutation in MT-ND1, which impairs complex I assembly). The addition of rotenone to HL180 cells and of antimycin A to XTC.UC1 cells caused fast mitochondrial membrane depolarization that was prevented by treatment with cyclosporin A, intracellular Ca2+ chelators, and antioxidant. Both cell lines also displayed an anomalous response to oligomycin, with rapid onset of depolarization that was prevented by cyclosporin A and by overexpression of Bcl-2. These findings indicate that depolarization by respiratory chain inhibitors and oligomycin was due to opening of the mitochondrial permeability transition pore (PTP). A shift of the threshold voltage for PTP opening close to the resting potential may therefore be the underlying cause facilitating cell death in diseases affecting complex I activity. This study provides a unifying reading frame for previous observations on mitochondrial dysfunction, bioenergetic defects, and Ca2+ deregulation in mitochondrial diseases. Therapeutic strategies aimed at normalizing the PTP voltage threshold may be instrumental in ameliorating the course of complex I-dependent mitochondrial diseases.
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http://dx.doi.org/10.1074/jbc.M807321200DOI Listing
January 2009

Phosphate is essential for inhibition of the mitochondrial permeability transition pore by cyclosporin A and by cyclophilin D ablation.

J Biol Chem 2008 Sep 6;283(39):26307-11. Epub 2008 Aug 6.

Department of Biomedical Sciences and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Padova, Viale Giuseppe Colombo 3, I-35121 Padova, Italy.

Energized mouse liver mitochondria displayed the same calcium retention capacity (a sensitive measure of the propensity of the permeability transition pore (PTP) to open) irrespective of whether phosphate, arsenate, or vanadate was the permeating anion. Unexpectedly, however, phosphate was specifically required for PTP desensitization by cyclosporin A (CsA) or by genetic inactivation of cyclophilin D (CyP-D). Indeed, when phosphate was replaced by arsenate, vanadate, or bicarbonate, the inhibitory effects of CsA and of CyP-D ablation on the PTP disappeared. After loading with the same amount of Ca(2+) in the presence of arsenate or vanadate but in the absence of phosphate, the sensitivity of the PTP to a variety of inducers was identical in mitochondria from wild-type mice, CyP-D-null mice, and wild-type mice treated with CsA. These findings call for a reassessment of conclusions on the role of the PTP in cell death that are based on the effects of CsA or of CyP-D ablation.
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http://dx.doi.org/10.1074/jbc.C800132200DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2546556PMC
September 2008

Hexokinase II detachment from mitochondria triggers apoptosis through the permeability transition pore independent of voltage-dependent anion channels.

PLoS One 2008 Mar 19;3(3):e1852. Epub 2008 Mar 19.

CNR Institute of Neuroscience and Department of Biomedical Sciences, University of Padova, Padova, Italy.

Type II hexokinase is overexpressed in most neoplastic cells, and it mainly localizes on the outer mitochondrial membrane. Hexokinase II dissociation from mitochondria triggers apoptosis. The prevailing model postulates that hexokinase II release from its mitochondrial interactor, the voltage-dependent anion channel, prompts outer mitochondrial membrane permeabilization and the ensuing release of apoptogenic proteins, and that these events are inhibited by growth factor signalling. Here we show that a hexokinase II N-terminal peptide selectively detaches hexokinase II from mitochondria and activates apoptosis. These events are abrogated by inhibiting two established permeability transition pore modulators, the adenine nucleotide translocator or cyclophilin D, or in cyclophilin D knock-out cells. Conversely, insulin stimulation or genetic ablation of the voltage-dependent anion channel do not affect cell death induction by the hexokinase II peptide. Therefore, hexokinase II detachment from mitochondria transduces a permeability transition pore opening signal that results in cell death and does not require the voltage-dependent anion channel. These findings have profound implications for our understanding of the pathways of outer mitochondrial membrane permeabilization and their inactivation in tumors.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001852PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267038PMC
March 2008

Assessing the molecular basis for rat-selective induction of the mitochondrial permeability transition by norbormide.

Biochim Biophys Acta 2007 Jul 14;1767(7):980-8. Epub 2007 Apr 14.

Department of Pharmacology and Anesthesiology/Pharmacology Division, University of Padova, Padova, Italy.

It was recently demonstrated that the rat-selective toxicant norbormide also induces rat-selective opening of the permeability transition pore (PTP) in isolated mitochondria. Norbormide is a mixture of endo and exo stereoisomers; however, only the endo forms are lethal to rats. In the present study we tested both endo and exo isomers as well as neutral and cationic derivatives of norbormide to: (i) verify if the PTP-regulatory activity by norbormide is stereospecific; (ii) define the structural features of norbormide responsible for PTP-activation, (iii) elucidate the basis for the drug species-specificity. Our results show that: (i) norbormide isomers affect PTP in a rat-selective fashion; however, no relevant differences between lethal and non-lethal forms are observed suggesting that drug regulation of PTP-activity and lethality in rats are unrelated phenomena; (ii) a (phenylvinyl)pyridine moiety represents the key element conferring the PTP-activating effect; (iii) cationic derivatives of rat-active compounds accumulate in the matrix via the membrane potential and activate the PTP also in mouse and guinea pig mitochondria. These findings suggest that the norbormide-sensitive PTP-target is present in all species examined, and is presumably located on the matrix side. The species-selectivity may depend on the unique properties of a transport system allowing drug internalisation in rat mitochondria.
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http://dx.doi.org/10.1016/j.bbabio.2007.04.002DOI Listing
July 2007

The mitochondrial permeability transition from in vitro artifact to disease target.

FEBS J 2006 May;273(10):2077-99

Department of Biomedical Sciences and CNR Institute of Neurosciences, University of Padova, Italy.

The mitochondrial permeability transition pore is a high conductance channel whose opening leads to an increase of mitochondrial inner membrane permeability to solutes with molecular masses up to approximately 1500 Da. In this review we trace the rise of the permeability transition pore from the status of in vitro artifact to that of effector mechanism of cell death. We then cover recent results based on genetic inactivation of putative permeability transition pore components, and discuss their meaning for our understanding of pore structure. Finally, we discuss evidence indicating that the permeability transition pore plays a role in pathophysiology, with specific emphasis on in vivo models of disease.
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http://dx.doi.org/10.1111/j.1742-4658.2006.05213.xDOI Listing
May 2006

The mitochondrial effects of small organic ligands of BCL-2: sensitization of BCL-2-overexpressing cells to apoptosis by a pyrimidine-2,4,6-trione derivative.

J Biol Chem 2006 Apr 14;281(15):10066-72. Epub 2006 Feb 14.

Department of Biomedical Sciences and Consiglio Nazionale delle Ricerche Institute of Neurosciences, University of Padova, Viale Giuseppe Colombo 3, I-35121 Padua, Italy.

We have investigated the mitochondrial effects of BH3I-2', Chelerythrine, and HA14-1, small organic molecules that share the ability to bind the BH3 domain of BCL-2. All compounds displayed a biphasic effect on mitochondrial respiration with uncoupling at low concentrations and respiratory inhibition at higher concentrations, the relative uncoupling potency being BH3I-2' (half-maximal uncoupling at about 80 nm) > Chelerythrine (half-maximal uncoupling at about 2 microm) > HA14-1 (half-maximal uncoupling at about 20 microm). At concentrations lower than required for uncoupling all compounds sensitized the permeability transition pore (PTP) to opening both in isolated mitochondria and intact cells. To assess whether the effects on BCL-2 binding, PTP induction and respiration could be due to different structural determinants we have tested a set of HA14-1 analogs from the Hoffmann-La Roche chemical library. We have identified 5-(6-chloro-2,4-dioxo-1,3,4,10-tetrahydro-2H-9-oxa-1,3-diaza-anthracen-10-yl)-pyrimidine-2,4,6-trione (EM20-25) as a molecule devoid of effects on respiration that is able to induce PTP opening, to disrupt the BCL-2/BAX interactions in situ and to activate caspase-9 in BCL-2-overexpressing cells. EM20-25 neutralized the antiapoptotic activity of overexpressed BCL-2 toward staurosporine and sensitized BCL-2-expressing cells from leukemic patients to the killing effects of staurosporine, chlorambucil, and fludarabine. These results provide a proof of principle that the potentially toxic effects of BCL-2 ligands on mitochondrial respiration are not essential for their antiapoptotic activity and represent an important step forward in the development of tumor-selective drugs acting on BCL-2.
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http://dx.doi.org/10.1074/jbc.M513708200DOI Listing
April 2006

Species-specific modulation of the mitochondrial permeability transition by norbormide.

Biochim Biophys Acta 2005 Jun 19;1708(2):178-86. Epub 2005 Mar 19.

C.N.R., Institute of Biomedical Technologies/Padova Unit, Department of Biology, University of Padova, Viale Giuseppe Colombo 3, 35121 Padova, Italy.

In the present study, we show that norbormide stimulates the opening of the permeability transition pore (PTP) in mitochondria from various organs of the rat but not of guinea pig and mouse. Norbormide does not affect the basic parameters that modulate the PTP activity since the proton electrochemical gradient, respiration, phosphorylation and Ca(2+) influx processes are only partially affected. On the other hand, norbormide induces rat-specific changes in the fluidity of the lipid interior of mitochondrial membranes, as revealed by fluorescence anisotropy of various reporter molecules. Such changes increase the PTP open probability through the internal Me(2+) regulatory site. The lack of PTP opening by norbormide is matched by a negligible perturbation of internal lipid domains in guinea pig and mouse, suggesting that the drug does not gain access to the matrix in the mitochondria from these species. Consistent with this interpretation, we demonstrate a preferential interaction of norbormide with the mitochondrial surface leading to alterations of the Me(2+) binding affinity for the external PTP regulatory site. Our findings indicate that norbormide affects Me(2+) binding to the regulatory sites of the PTP, and suggest that the drug could be taken up by a mitochondrial transport system unique to the rat. The characterization of the norbormide target may lead to a better understanding of the mechanisms underlying the mitochondrial PTP as well as to the identification of species-specific drugs that affect mitochondrial function.
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http://dx.doi.org/10.1016/j.bbabio.2005.03.002DOI Listing
June 2005

Discrimination between two steps in the mitochondrial permeability transition process.

Int J Biochem Cell Biol 2005 Sep 26;37(9):1858-68. Epub 2005 Apr 26.

C.N.R. Institute of Biomedical Technologies/Padova Unit, Italy.

It is well known that a lag phase generally elapses between the addition of inducers of the mitochondrial permeability transition and the opening of the pore. To advance our present understanding as regards the significance of this phenomenon, we used experimental approaches which are sensitive to different aspects of the permeability transition process. The pore conformation was sensed by the fluorescence anisotropy changes of hematoporphyrin-labelled mitochondria. Membrane permeabilization was ascertained by following the matrix swelling consequent to external solute equilibration. We show that the anisotropy changes of mitochondria-bound hematoporphyrin precede both membrane depolarization (proton permeation) and matrix swelling (solute permeation), thus sensing a step of the permeability transition process that involves the pore in its closed state. We suggest that the opening of the pore is preceded by a structural remodelling of mitochondrial domains containing hematoporphyrin-near, pore-regulating histidines. Such a perturbation is strongly inhibited at acidic matrix pH and completely blocked by cyclosporin A. In sucrose-based media the opening of the pore can be strongly delayed, as compared to salt-based media, a fact which probably reflects perturbation of mitochondrial membranes by sugar. We conclude that the mitochondrial permeability transition could be described as an at least two-step process which is mainly regulated by conformational changes of the pore components.
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http://dx.doi.org/10.1016/j.biocel.2005.04.001DOI Listing
September 2005

Properties of the permeability transition pore in mitochondria devoid of Cyclophilin D.

J Biol Chem 2005 May 25;280(19):18558-61. Epub 2005 Mar 25.

Department of Biomedical Sciences and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Padova, Viale Giuseppe Colombo 3, I-35121 Padova, Italy.

We have studied the properties of the permeability transition pore (PTP) in mitochondria from the liver of mice where the Ppif gene encoding for mitochondrial Cyclophilin D (CyP-D) had been inactivated. Mitochondria from Ppif-/- mice had no CyP-D and displayed a striking desensitization of the PTP to Ca2+, in that pore opening required about twice the Ca2+ load necessary to open the pore in strain-matched, wild-type mitochondria. Mitochondria lacking CyP-D were insensitive to Cyclosporin A (CsA), which increased the Ca2+ retention capacity only in mitochondria from wild-type mice. The PTP response to ubiquinone 0, depolarization, pH, adenine nucleotides, and thiol oxidants was similar in mitochondria from wild-type and Ppif-/- mice. These experiments demonstrate that (i) the PTP can form and open in the absence of CyP-D, (ii) that CyP-D represents the target for PTP inhibition by CsA, and (iii) that CyP-D modulates the sensitivity of the PTP to Ca2+ but not its regulation by the proton electrochemical gradient, adenine nucleotides, and oxidative stress. These results have major implications for our current understanding of the PTP and its modulation in vitro and in vivo.
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http://dx.doi.org/10.1074/jbc.C500089200DOI Listing
May 2005

Induction of the mitochondrial permeability transition by the DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine. Sorting cause and consequence of mitochondrial dysfunction.

Biochim Biophys Acta 2004 Jul;1658(1-2):58-63

Dipartimento di Chimica Biologica, Università di Padova, Viale G. Colombo 3, I-35121 Padova, Italy.

The alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) alters DNA and stimulates the activity of poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme involved in DNA repair. The consumption of cellular NAD(+) by PARP-1 is accompanied by ATP depletion, mitochondrial depolarization and release of proapoptotic proteins, but whether a causal relationship exists among these events remains an open question. Most of cellular NAD(+) is stored in the mitochondrial matrix and becomes available for cytosolic and nuclear processes only after its release through the permeability transition pore (PTP), a voltage-gated inner membrane channel. Here we have explored whether MNNG affects mitochondrial function upstream of PARP-1 activation. We show that MNNG has a dual effect on isolated mitochondria. At relatively low concentrations (up to 0.1 mM), it selectively sensitizes the PTP to opening, while at higher concentrations (above 0.5 mM) it inhibits carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP)-stimulated respiration. MNNG caused PTP opening and activation of the mitochondrial proapoptotic pathway in intact HeLa cells, which resulted in cell death that could be prevented by the PTP inhibitor CsA. We conclude that a key event in MNNG-dependent cell death is induction of PTP opening that occurs independently of PARP-1 activation.
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http://dx.doi.org/10.1016/j.bbabio.2004.05.005DOI Listing
July 2004

Arachidonic acid released by phospholipase A(2) activation triggers Ca(2+)-dependent apoptosis through the mitochondrial pathway.

J Biol Chem 2004 Jun 7;279(24):25219-25. Epub 2004 Apr 7.

Department of Biomedical Sciences, Consiglio Nazionale delle Ricerche Institute of Neuroscience at the University of Padova, Viale Giuseppe Colombo 3, I-35121 Padova, Italy.

We studied the effects of the divalent cation ionophore A23187 on apoptotic signaling in MH1C1 cells. Addition of A23187 caused a fast rise of cytosolic Ca(2+) ([Ca(2+)](c)), which returned close to the resting level within about 40 s. The [Ca(2+)](c) rise was immediately followed by phospholipid hydrolysis, which could be inhibited by aristolochic acid or by pretreatment with thapsigargin in Ca(2+)-free medium, indicating that the Ca(2+)-dependent cytosolic phospholipase A(2) (cPLA(2)) was involved. These early events were followed by opening of the mitochondrial permeability transition pore (PTP) and by apoptosis in about 30% of the cell population. In keeping with a cause-effect relationship between addition of A23187, activation of cPLA(2), PTP opening, and cell death, all events but the [Ca(2+)](c) rise were prevented by aristolochic acid. The number of cells killed by A23187 was doubled by treatment with 0.5 microm MK886 and 5 microm indomethacin, which inhibit arachidonic acid metabolism through the 5-lipoxygenase and cyclooxygenase pathway, respectively. Consistent with the key role of free arachidonic acid, its levels increased within minutes of treatment with A23187; the increase being more pronounced in the presence of MK886 plus indomethacin. Cell death was preceded by cytochrome c release and cleavage of caspase 9 and 3, but not of caspase 8. All these events were prevented by aristolochic acid and by the PTP inhibitor cyclosporin A. Thus, A23187 triggers the apoptotic cascade through the release of arachidonic acid by cPLA(2) in a process that is amplified when transformation of arachidonic acid into prostaglandins and leukotrienes is inhibited. These findings identify arachidonic acid as the causal link between A23187-dependent perturbation of Ca(2+) homeostasis and the effector mechanisms of cell death.
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http://dx.doi.org/10.1074/jbc.M310381200DOI Listing
June 2004