Interactions of cyclophilin with the mitochondrial inner membrane and regulation of the permeability transition pore, and cyclosporin A-sensitive channel

The oligomycin-sensitivity conferring protein of mitochondrial ATP synthase: emerging new roles in mitochondrial pathophysiology

The oligomycin-sensitivity conferring protein (OSCP) of the mitochondrial F(O)F1 ATP synthase has long been recognized to be essential for the coupling of proton transport to ATP synthesis. Located on top of the catalytic F1 sector, it makes stable contacts with both F1 and the peripheral stalk, ensuring the structural and functional coupling between F(O) and F1, which is disrupted by the antibiotic, oligomycin. Recent data have established that OSCP is the binding target of cyclophilin (CyP) D, a well-characterized inducer of the mitochondrial permeability transition pore (PTP), whose opening can precipitate cell death. CyPD binding affects ATP synthase activity, and most importantly, it decreases the threshold matrix Ca²⁺ required for PTP opening, in striking analogy with benzodiazepine 423, an apoptosis-inducing agent that also binds OSCP. These findings are consistent with the demonstration that dimers of ATP synthase generate Ca²⁺-dependent currents with features indistinguishable from those of the PTP and suggest that ATP synthase is directly involved in PTP formation, although the underlying mechanism remains to be established. In this scenario, OSCP appears to play a fundamental role, sensing the signal(s) that switches the enzyme of life in a channel able to precipitate cell death.

Structure based design, synthesis, pharmacophore modeling, virtual screening, and molecular docking studies for identification of novel cyclophilin D inhibitors

Cyclophilin D (CypD) is a peptidyl prolyl isomerase F that resides in the mitochondrial matrix and associates with the inner mitochondrial membrane during the mitochondrial membrane permeability transition. CypD plays a central role in opening the mitochondrial membrane permeability transition pore (mPTP) leading to cell death and has been linked to Alzheimer's disease (AD). Because CypD interacts with amyloid beta (Aβ) to exacerbate mitochondrial and neuronal stress, it is a potential target for drugs to treat AD. Since appropriately designed small organic molecules might bind to CypD and block its interaction with Aβ, 20 trial compounds were designed using known procedures that started with fundamental pyrimidine and sulfonamide scaffolds know to have useful therapeutic effects. Two-dimensional (2D) quantitative structure-activity relationship (QSAR) methods were applied to 40 compounds with known IC50 values. These formed a training set and were followed by a trial set of 20 designed compounds. A correlation analysis was carried out comparing the statistics of the measured IC50 with predicted values for both sets. Selectivity-determining descriptors were interpreted graphically in terms of principle component analyses. These descriptors can be very useful for predicting activity enhancement for lead compounds. A 3D pharmacophore model was also created. Molecular dynamics simulations were carried out for the 20 trial compounds with known IC50 values, and molecular descriptors were determined by 2D QSAR studies using the Lipinski rule-of-five. Fifteen of the 20 molecules satisfied all 5 Lipinski rules, and the remaining 5 satisfied 4 of the 5 Lipinski criteria and nearly satisfied the fifth. Our previous use of 2D QSAR, 3D pharmacophore models, and molecular docking experiments to successfully predict activity indicates that this can be a very powerful technique for screening large numbers of new compounds as active drug candidates. These studies will hopefully provide a basis for efficiently designing and screening large numbers of more potent and selective inhibitors for CypD treatment of AD.

Thyroid hormone, thyromimetics, and metabolic efficiency

Thyroid hormone (TH) has long been recognized as a major modulator of metabolic efficiency, energy expenditure, and thermogenesis. TH effects in regulating metabolic efficiency are transduced by controlling the coupling of mitochondrial oxidative phosphorylation and the cycling of extramitochondrial substrate/futile cycles. However, despite our present understanding of the genomic and nongenomic modes of action of TH, its control of mitochondrial coupling still remains elusive. This review summarizes historical and up-to-date findings concerned with TH regulation of metabolic energetics, while integrating its genomic and mitochondrial activities. It underscores the role played by TH-induced gating of the mitochondrial permeability transition pore (PTP) in controlling metabolic efficiency. PTP gating may offer a unified target for some TH pleiotropic activities and may serve as a novel target for synthetic functional thyromimetics designed to modulate metabolic efficiency. PTP gating by long-chain fatty acid analogs may serve as a model for such strategy.

Calcium signaling in the liver

Intracellular free Ca(2+) ([Ca(2+)]i) is a highly versatile second messenger that regulates a wide range of functions in every type of cell and tissue. To achieve this versatility, the Ca(2+) signaling system operates in a variety of ways to regulate cellular processes that function over a wide dynamic range. This is particularly well exemplified for Ca(2+) signals in the liver, which modulate diverse and specialized functions such as bile secretion, glucose metabolism, cell proliferation, and apoptosis. These Ca(2+) signals are organized to control distinct cellular processes through tight spatial and temporal coordination of [Ca(2+)]i signals, both within and between cells. This article will review the machinery responsible for the formation of Ca(2+) signals in the liver, the types of subcellular, cellular, and intercellular signals that occur, the physiological role of Ca(2+) signaling in the liver, and the role of Ca(2+) signaling in liver disease.

Molecular Dissection of Cyclosporin A's Neuroprotective Effect Reveals Potential Therapeutics for Ischemic Brain Injury

After the onset of brain ischemia, a series of events leads ultimately to the death of neurons. Many molecules can be pharmacologically targeted to protect neurons during these events, which include glutamate release, glutamate receptor activation, excitotoxicity, Ca²⁺ influx into cells, mitochondrial dysfunction, activation of intracellular enzymes, free radical production, nitric oxide production, and inflammation. There have been a number of attempts to develop neuroprotectants for brain ischemia, but many of these attempts have failed. It was reported that cyclosporin A (CsA) dramatically ameliorates neuronal cell damage during ischemia. Some researchers consider ischemic cell death as a unique process that is distinct from both apoptosis and necrosis, and suggested that mitochondrial dysfunction and Δψ collapse are key steps for ischemic cell death. It was also suggested that CsA has a unique neuroprotective effect that is related to mitochondrial dysfunction. Here, I will exhibit examples of neuroprotectants that are now being developed or in clinical trials, and will discuss previous researches about the mechanism underlying the unique CsA action. I will then introduce the results of our cDNA subtraction experiment with or without CsA administration in the rat brain, along with our hypothesis about the mechanism underlying CsA’s effect on transcriptional regulation.

Metabolic dysfunction in pulmonary hypertension: the expanding relevance of the Warburg effect

BACKGROUND

Pulmonary hypertension (PH) is an enigmatic vascular syndrome characterized by increased pulmonary arterial pressure and adverse remodelling of the pulmonary arterioles and often of the right ventricle. Drawing parallels with tumourigenesis, recent endeavours have explored the relationship between metabolic dysregulation and PH pathogenesis.

DESIGN

We will discuss the general mechanisms by which cellular stressors such as hypoxia and inflammation alter cellular metabolism. Based on those principles, we will explore the development of a corresponding metabolic pathophenotype in PH, with a focus on WHO Groups I and III, and the implications that these alterations may have for future treatment of this disease.

RESULTS

Investigation of metabolic dysregulation in both the pulmonary vasculature and right ventricle during PH pathogenesis has provided a more unifying understanding of how disparate disease triggers coordinate end-stage disease manifestations. Namely, as defined originally in various cancers, the Warburg effect describes a chronic shift in energy production from mitochondrial oxidative phosphorylation to glycolysis. In many cases, this Warburg phenotype may serve as a central causative mechanism for PH progression, largely driving cellular hyperproliferation and resistance to apoptosis. Consequently, new therapeutic strategies have been increasingly pursued that target the Warburg phenotype. Finally, new technologies are increasingly becoming available to probe more completely the complexities of metabolic cellular reprogramming and may reveal distinct metabolic pathways beyond the Warburg effect that drive PH.

CONCLUSION

Studies of metabolic dysregulation in PH are just emerging but may offer powerful therapeutic means to prevent or even reverse disease progression at the molecular level.

The mitochondrial permeability transition pore: a mystery solved?

The permeability transition (PT) denotes an increase of the mitochondrial inner membrane permeability to solutes with molecular masses up to about 1500 Da. It is presumed to be mediated by opening of a channel, the permeability transition pore (PTP), whose molecular nature remains a mystery. Here I briefly review the history of the PTP, discuss existing models, and present our new results indicating that reconstituted dimers of the F_OF₁ ATP synthase form a channel with properties identical to those of the mitochondrial megachannel (MMC), the electrophysiological equivalent of the PTP. Open questions remain, but there is now promise that the PTP can be studied by genetic methods to solve the large number of outstanding problems.

Neuroglobin overexpression inhibits oxygen-glucose deprivation-induced mitochondrial permeability transition pore opening in primary cultured mouse cortical neurons

Neuroglobin (Ngb) is an endogenous neuroprotective molecule against hypoxic/ischemic brain injury, but the underlying mechanisms remain largely undefined. Our recent study revealed that Ngb can bind to voltage-dependent anion channel (VDAC), a regulator of mitochondria permeability transition (MPT). In this study we examined the role of Ngb in MPT pore (mPTP) opening following oxygen-glucose deprivation (OGD) in primary cultured mouse cortical neurons. Co-immunoprecipitation (Co-IP) and immunocytochemistry showed that the binding between Ngb and VDAC was increased after OGD compared to normoxia, indicating the OGD-enhanced Ngb-VDAC interaction. Ngb overexpression protected primary mouse cortical neurons from OGD-induced neuronal death, to an extent comparable to mPTP opening inhibitor, cyclosporine A (CsA) pretreatment. We further measured the role of Ngb in OGD-induced mPTP opening using Ngb overexpression and knockdown approaches in primary cultured neurons, and recombinant Ngb exposure to isolated mitochondria. Same as CsA pretreatment, Ngb overexpression significantly reduced OGD-induced mPTP opening markers including mitochondria swelling, mitochondrial NAD(+) release, and cytochrome c (Cyt c) release in primary cultured neurons. Recombinant Ngb incubation significantly reduced OGD-induced NAD(+) release and Cyt c release from isolated mitochondria. In contrast, Ngb knockdown significantly increased OGD-induced neuron death, and increased OGD-induced mitochondrial NAD(+) release and Cyt c release as well, and these outcomes could be rescued by CsA pretreatment. In summary, our results demonstrated that Ngb overexpression can inhibit OGD-induced mPTP opening in primary cultured mouse cortical neurons, which may be one of the molecular mechanisms of Ngb's neuroprotection.

Physiologic functions of cyclophilin D and the mitochondrial permeability transition pore

This review focuses on the role of cyclophilin D (CypD) as a prominent mediator of the mitochondrial permeability transition pore (MPTP) and subsequent effects on cardiovascular physiology and pathology. Although a great number of reviews have been written on the MPTP and its effects on cell death, we focus on the biology surrounding CypD itself and the non-cell death physiologic functions of the MPTP. A greater understanding of the physiologic functions of the MPTP and its regulation by CypD will likely suggest novel therapeutic approaches for cardiovascular disease, both dependent and independent of programmed necrotic cell death mechanisms.  

Dimers of mitochondrial ATP synthase form the permeability transition pore

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.

Cyclophilin 40 alters UVA-induced apoptosis and mitochondrial ROS generation in keratinocytes

The CyP40 protein encoded by PPID gene is a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerate the folding of proteins. The CyP40 protein has been shown to possess PPIase activity and, similar to other family members, can bind to the immunosuppressant drug cyclosporin A (CsA). In this study, we created keratinocyte cell lines with CyP40 being stably knocked down using viral particles containing shRNA for CyP40 which knocked down the expression level of CyP40 transcripts by 90-99%. The proliferation rates of the cell lines with silenced CyP40 were decreased compared to the control cells. After UVA irradiation, the rate of apoptosis was found to be significantly lower in CyP40 silenced cell lines than it was in control cells. Moreover, mitochondrial membrane potential (MMP) was found to be less dissipated and mitochondrial permeability transition pore (MPTP) less active in cells with knocked down CyP40 than in control cells after UVA irradiation. Also, less mitochondrial superoxide was detected in the cells with silenced CyP40 compared to control cells after UVA exposure. Moreover, silencing of CyP40 partially modulates expression of key genes involved in mitochondrial pore formation including CyPD, ANTs and VDAC family members. The ability of CyP40 to regulate UV induced apoptosis implicates this protein as a potential target for therapy in cancer cells.

A Model of Hypoxia-Reoxygenation on Isolated Adult Mouse Cardiomyocytes

The use of in vitro experimental models of hypoxia-reoxygenation (H/R) that mimic in vivo ischemia-reperfusion represents a powerful tool to investigate cardioprotective strategies against myocardial infarction. Most in vitro studies are performed using neonatal cardiac cells or immortalized embryonic cardiac cell lines which may limit the extrapolation of the results. We developed an H/R model using adult cardiomyocytes freshly isolated from mice and compared its characteristics to the in vivo ischemia-reperfusion conditions. First, cell death was assessed at different values of pH medium during hypoxia (6.2 vs 7.4) to simulate extracellular pH during in vivo ischemia. Cardiomyocyte mortality was aggravated with hypoxia under acidic pH. We next evaluated the relationship between the duration of hypoxia and cell death. Hypoxia time-dependently reduced myocyte viability (−24%, −36%, −53%, and −74% with 1, 1.5, 2, and 3 hours of hypoxia followed by 17 hours of reoxygenation, respectively). We then focused on the duration of reoxygenation as cardioprotective strategies have been reported to have different effects with short and long durations of reperfusion. We observed that cardiomyocyte mortality was increased when the duration of reoxygenation was increased from 2 h to 17 hours. Finally, we used our characterized model to investigate the cardioprotective effect of regular treadmill exercise. Myocyte viability was significantly greater in exercised when compared to sedentary mice (44% and 26%, respectively). Similarly, mice submitted to in vivo ischemia-reperfusion elicited infarct sizes reaching 27%, 43%, and 55% with 20, 30, and 45 minutes of coronary artery occlusion. In addition, infarct size was significantly reduced by exercise. In conclusion, this H/R model of cardiomyocytes freshly isolated from adult mice shows similar characteristics to the in vivo ischemia-reperfusion conditions. The comparison of in vivo and in vitro settings represents a powerful approach to investigate cardioprotective strategies and to distinguish between direct and indirect cardiomyocyte-dependent mechanisms.

Inhibition of complex I regulates the mitochondrial permeability transition through a phosphate-sensitive inhibitory site masked by cyclophilin D

Inhibition of the mitochondrial permeability transition pore (PTP) has proved to be an effective strategy for preventing oxidative stress-induced cell death, and the pore represents a viable cellular target for drugs. Here, we report that inhibition of complex I by rotenone is more effective at PTP inhibition than cyclosporin A in tissues that express low levels of the cyclosporin A mitochondrial target, cyclophilin D; and, conversely, that tissues in which rotenone does not affect the PTP are characterized by high levels of expression of cyclophilin D and sensitivity to cyclosporin A. Consistent with a regulatory role of complex I in the PTP-inhibiting effects of rotenone, the concentrations of the latter required for PTP inhibition precisely match those required to inhibit respiration; and a similar effect is seen with the antidiabetic drug metformin, which partially inhibits complex I. Remarkably (i) genetic ablation of cyclophilin D or its displacement with cyclosporin A restored PTP inhibition by rotenone in tissues that are otherwise resistant to its effects; and (ii) rotenone did not inhibit the PTP unless phosphate was present, in striking analogy with the phosphate requirement for the inhibitory effects of cyclosporin A [Basso et al. (2008) J. Biol. Chem. 283, 26307-26311]. These results indicate that inhibition of complex I by rotenone or metformin and displacement of cyclophilin D by cyclosporin A affect the PTP through a common mechanism; and that cells can modulate their PTP response to complex I inhibition by modifying the expression of cyclophilin D, a finding that has major implications for pore modulation in vivo.

Propofol and magnesium attenuate isoflurane-induced caspase-3 activation via inhibiting mitochondrial permeability transition pore

Background

The inhalation anesthetic isoflurane has been shown to open the mitochondrial permeability transition pore (mPTP) and induce caspase activation and apoptosis, which may lead to learning and memory impairment. Cyclosporine A, a blocker of mPTP opening might attenuate the isoflurane-induced mPTP opening, lessening its ripple effects. Magnesium and anesthetic propofol are also mPTP blockers. We therefore set out to determine whether propofol and magnesium can attenuate the isoflurane-induced caspase activation and mPTP opening.

Methods

We investigated the effects of magnesium sulfate (Mg²⁺), propofol, and isoflurane on the opening of mPTP and caspase activation in H4 human neuroglioma cells stably transfected to express full-length human amyloid precursor protein (APP) (H4 APP cells) and in six day-old wild-type mice, employing Western blot analysis and flowcytometry.

Results

Here we show that Mg²⁺ and propofol attenuated the isoflurane-induced caspase-3 activation in H4-APP cells and mouse brain tissue. Moreover, Mg²⁺ and propofol, the blockers of mPTP opening, mitigated the isoflurane-induced mPTP opening in the H4-APP cells.

Conclusion

These data illustrate that Mg²⁺ and propofol may ameliorate the isoflurane-induced neurotoxicity by inhibiting its mitochondrial dysfunction. Pending further studies, these findings may suggest the use of Mg²⁺ and propofol in preventing and treating anesthesia neurotoxicity.

Anesthetics isoflurane and desflurane differently affect mitochondrial function, learning, and memory

OBJECTIVE

There are approximately 8.5 million Alzheimer disease (AD) patients who need anesthesia and surgery care every year. The inhalation anesthetic isoflurane, but not desflurane, has been shown to induce caspase activation and apoptosis, which are part of AD neuropathogenesis, through the mitochondria-dependent apoptosis pathway. However, the in vivo relevance, underlying mechanisms, and functional consequences of these findings remain largely to be determined.

METHODS

We therefore set out to assess the effects of isoflurane and desflurane on mitochondrial function, cytotoxicity, learning, and memory using flow cytometry, confocal microscopy, Western blot analysis, immunocytochemistry, and the fear conditioning test.

RESULTS

Here we show that isoflurane, but not desflurane, induces opening of mitochondrial permeability transition pore (mPTP), increase in levels of reactive oxygen species, reduction in levels of mitochondrial membrane potential and adenosine-5'-triphosphate, activation of caspase 3, and impairment of learning and memory in cultured cells, mouse hippocampus neurons, mouse hippocampus, and mice. Moreover, cyclosporine A, a blocker of mPTP opening, attenuates isoflurane-induced mPTP opening, caspase 3 activation, and impairment of learning and memory. Finally, isoflurane may induce the opening of mPTP via increasing levels of reactive oxygen species.

INTERPRETATION

These findings suggest that desflurane could be a safer anesthetic for AD patients as compared to isoflurane, and elucidate the potential mitochondria-associated underlying mechanisms, and therefore have implications for use of anesthetics in AD patients, pending human study confirmation.

The permeability transition pore as a Ca(2+) release channel: new answers to an old question

Mitochondria possess a sophisticated array of Ca²⁺ transport systems reflecting their key role in physiological Ca²⁺ homeostasis. With the exception of most yeast strains, energized organelles are endowed with a very fast and efficient mechanism for Ca²⁺ uptake, the ruthenium red (RR)-sensitive mitochondrial Ca²⁺ uniporter (MCU); and one main mechanism for Ca²⁺ release, the RR-insensitive 3Na⁺–Ca²⁺ antiporter. An additional mechanism for Ca²⁺ release is provided by a Na⁺ and RR-insensitive release mechanism, the putative 3H⁺–Ca²⁺ antiporter. A potential kinetic imbalance is present, however, because the V_max of the MCU is of the order of 1400 nmol Ca²⁺ mg⁻¹ protein min⁻¹ while the combined V_max of the efflux pathways is about 20 nmol Ca²⁺ mg⁻¹ protein min⁻¹. This arrangement exposes mitochondria to the hazards of Ca²⁺ overload when the rate of Ca²⁺ uptake exceeds that of the combined efflux pathways, e.g. for sharp increases of cytosolic [Ca²⁺]. In this short review we discuss the hypothesis that transient opening of the Ca²⁺-dependent permeability transition pore may provide mitocondria with a fast Ca²⁺ release channel preventing Ca²⁺ overload. We also address the relevance of a mitochondrial Ca²⁺ release channel recently discovered in Drosophila melanogaster, which possesses intermediate features between the permeability transition pore of yeast and mammals.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Phosphate is not an absolute requirement for the inhibitory effects of cyclosporin A or cyclophilin D deletion on mitochondrial permeability transition

CypD (cyclophilin D) has been established as a critical regulator of the MPT (mitochondrial permeability transition) pore, and pharmacological or genetic inhibition of CypD attenuates MPT in numerous systems. However, it has recently been suggested that the inhibitory effects of CypD inhibition only manifest when P(i) (inorganic phosphate) is present, and that inhibition is lost when P(i) is replaced by As(i) (inorganic arsenate) or V(i) (inorganic vanadate). To test this, liver mitochondria were isolated from wild-type and CypD-deficient (Ppif-/-) mice and then incubated in buffer containing P(i), As(i) or V(i). MPT was induced under both energized and de-energized conditions by the addition of Ca2+, and the resultant mitochondrial swelling was measured spectrophotometrically. For pharmacological inhibition of CypD, wild-type mitochondria were pre-incubated with CsA (cyclosporin A) before the addition of Ca2+. In energized and de-energized mitochondria, Ca2+ induced MPT regardless of the anion present, although the magnitude differed between P(i), As(i) and V(i). However, in all cases, pre-treatment with CsA significantly inhibited MPT. Moreover, these effects were independent of mouse strain, organ type and rodent species. Similarly, attenuation of Ca2+-induced MPT in the Ppif-/- mitochondria was still observed irrespective of whether P(i), As(i) or V(i) was present. We conclude that the pharmacological and genetic inhibition of CypD is still able to attenuate MPT even in the absence of P(i).

Peripheral benzodiazepine receptor regulates vascular endothelial activations via suppression of the voltage-dependent anion channel-1

Peripheral benzodiazepine receptor (PBR) is a multifunctional protein mainly found on the outer mitochondrial membrane. PBR expression is increased by tumor necrosis factor-α (TNF-α) in endothelial cells. Adenoviral overexpression of PBR inhibits monocyte adhesion, VCAM-1, and ICAM-1 expression in TNF-α-activated endothelial cells. Rotenone, cyclosporine A, and bongkrekic acid suppress TNF-α-induced VCAM-1 expression. Overexpression of PBR inhibits voltage-dependent anion channel-1 (VDAC-1) expression and the silencing of PBR increases VDAC-1 expression in endothelial cells. Moreover, TNF-α-induced VCAM-1 expression is suppressed by VDAC-1 gene silencing. PBR overexpression significantly decreases TNF-α-induced mitochondrial reactive oxygen species and MnSOD expression. These results suggest that PBR can inhibit endothelial activation and this action is related to the inhibition of mitochondrial ROS and/or VDAC-1 expression in endothelial cells.

Induction of the permeability transition pore in cells depleted of mitochondrial DNA

Respiratory complexes are believed to play a role in the function of the mitochondrial permeability transition pore (PTP), whose dysregulation affects the process of cell death and is involved in a variety of diseases, including cancer and degenerative disorders. We investigated here the PTP in cells devoid of mitochondrial DNA (ρ(0) cells), which lack respiration and constitute a model for the analysis of mitochondrial involvement in several pathological conditions. We observed that mitochondria of ρ(0) cells maintain a membrane potential and that this is readily dissipated after displacement of hexokinase (HK) II from the mitochondrial surface by treatment with either the drug clotrimazole or with a cell-permeant HK II peptide, or by placing ρ(0) cells in a medium without serum and glucose. The PTP inhibitor cyclosporin A (CsA) could decrease the mitochondrial depolarization induced by either HK II displacement or by nutrient depletion. We also found that a fraction of the kinases ERK1/2 and GSK3α/β is located in the mitochondrial matrix of ρ(0) cells, and that glucose and serum deprivation caused concomitant ERK1/2 inhibition and GSK3α/β activation with the ensuing phosphorylation of cyclophilin D, the mitochondrial target of CsA. GSK3α/β inhibition with indirubin-3'-oxime decreased PTP-induced cell death in ρ(0) cells following nutrient ablation. These findings indicate that ρ(0) cells are equipped with a functioning PTP, whose regulatory mechanisms are similar to those observed in cancer cells, and suggest that escape from PTP opening is a survival factor in this model of mitochondrial diseases. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

Mitochondrial Ca(2+) as a key regulator of mitochondrial activities

Mitochondria play a central role in cell biology, not only as producers of ATP but also as regulators of the Ca(2+) signal. The translocation by respiratory chain protein complexes of H(+) across the ion-impermeable inner membrane generates a very large H(+) electrochemical gradient that can be employed not only by the H(+) ATPase to run the endoergonic reaction of ADP phosphorylation, but also to accumulate cations into the matrix. Mitochondria can rapidly take up Ca(2+) through an electrogenic pathway, the uniporter, that acts to equilibrate Ca(2+) with its electrochemical gradient, and thus accumulates the cation into the matrix, and they can release it through two exchangers (with H(+) and Na(+), mostly expressed in non-excitable and excitable cells, respectively), that utilize the electrochemical gradient of the monovalent cations to prevent the attainment of electrical equilibrium.The uniporter, due to its low Ca(2+) affinity, demands high local Ca(2+) concentrations to work. In different cell systems these high Ca(2+) concentration microdomains are generated, upon cell stimulation, in proximity of the plasma membrane and the sarco/endoplasmic reticulum Ca(2+) channels.Recent work has revealed the central role of mitochondria in signal transduction pathways: evidence is accumulating that, by taking up Ca(2+), they not only modulate mitochondrial activities but also tune the cytosolic Ca(2+) signals and their related functions. This review analyses recent developments in the area of mitochondrial Ca(2+) signalling and attempts to summarize cell physiology aspects of the mitochondrial Ca(2+) transport machinery.

Cyclosporine-A as a neuroprotective agent against stroke: its translation from laboratory research to clinical application

Stoke remains a leading cause of death and disability with limited treatment options. Extensive research has been aimed at studying cell death events that accompany stroke and how to use these same cell death pathways as potential therapeutic targets for treating the disease. The mitochondrial permeability transition pore (MPTP) has been implicated as a major factor associated with stroke-induced neuronal cell death. MPTP activation and increased permeability has been shown to contribute to the events that lead to cell death. Cyclosporine A (CsA), a widely used immunosuppressant in transplantation and rheumatic medicine, has been recently shown to possess neuroprotective properties through its ability to block the MPTP, which in turn inhibits neuronal damage. This newfound CsA-mediated neuroprotection pathway prompted research on its use to prevent cell death in stroke and other neurological conditions. Preclinical studies are being conducted in hopes of establishing the safety and efficacy guidelines for CsA use in human trials as a potential neuroprotective agent against stroke. In this review, we provide an overview of the current laboratory and clinical status of CsA neuroprotection.

The effects of idebenone on mitochondrial bioenergetics

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 aminoacid 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.

Post-injury administration of the mitochondrial permeability transition pore inhibitor, NIM811, is neuroprotective and improves cognition after traumatic brain injury in rats

Mitochondrial dysfunction is known to play a pivotal role in cell death mechanisms following traumatic brain injury (TBI). N-methyl-4-isoleucine-cyclosporin (NIM811), a non-immunosuppressive cyclosporin A (CsA) analog, inhibits the mitochondrial permeability transition pore (mPTP) and has been shown to be neuroprotective following TBI in mice. However, the translation of the neuroprotective effects of mPTP inhibitors, including CsA and NIM811, into improved cognitive end points has yet to be fully investigated. Therefore, to build upon these results, a severe unilateral controlled cortical impact model of TBI was used in the present study to establish a dose-response curve for NIM811 in rats. The findings demonstrate that the neuroprotection afforded by NIM811 is dose dependent, with the 10 mg/kg dose being the most effective dose. Once the dose response was established, we evaluated the effect of the optimal dose of NIM811 on behavior, mitochondrial bioenergetics, and mitochondrial oxidative damage following TBI. For behavioral studies, rats were administered NIM811 at 15 min and 24 h post-injury, with cognitive testing beginning 10 days post-injury. Mitochondrial studies involved a single injection of NIM811 at 15 min post-injury followed by mitochondrial isolation at 6 h post-injury. The results revealed that the optimal dose of NIM811 improves cognition, improves mitochondrial functioning, and reduces oxidative damage following TBI.

Cyclophilin D and the mitochondrial permeability transition in kidney proximal tubules after hypoxic and ischemic injury

Mitochondrial matrix cyclophilin D (CyPD) is known to promote development of the mitochondrial permeability transition (MPT). Kidney proximal tubule cells are especially prone to deleterious effects of mitochondrial damage because of their dependence on oxidative mitochondrial metabolism for ATP production. To clarify the role of CyPD and the MPT in proximal tubule injury during ischemia-reperfusion (I/R) and hypoxia-reoxygenation (H/R), we assessed freshly isolated tubules and in vivo injury in wild-type (WT) and Ppif(-/-) CyPD-null mice. Isolated mouse tubules developed a sustained, nonesterified fatty acid-mediated energetic deficit after H/R in vitro that could be substantially reversed by delipidated albumin and supplemental citric acid cycle substrates but was not modified by the absence of CyPD. Susceptibility of WT and Ppif(-/-) tubules to the MPT was increased by H/R but was less in normoxic and H/R Ppif(-/-) than WT tubules. Correction of the energetic deficit that developed during H/R strongly increased resistance to the MPT. Ppif(-/-) mice were resistant to I/R injury in vivo spanning a wide range of severity. The data clarify involvement of the MPT in oxygen deprivation-induced tubule cell injury by showing that the MPT does not contribute to the initial bioenergetic deficit produced by H/R but the deficit predisposes to subsequent development of the MPT, which contributes pathogenically to kidney I/R injury in vivo.

Pharmacological interventions for spinal cord injury: where do we stand? How might we step forward?

Despite numerous studies reporting some measures of efficacy in the animal literature, there are currently no effective therapies for the treatment of traumatic spinal cord injuries (SCI) in humans. The purpose of this review is to delineate key pathophysiological processes that contribute to neurological deficits after SCI, as well as to describe examples of pharmacological approaches that are currently being tested in clinical trials, or nearing clinical translation, for the therapeutic management of SCI. In particular, we will describe the mechanistic rationale to promote neuroprotection and/or functional recovery based on theoretical, yet targeted pathological events. Finally, we will consider the clinical relevancy for emerging evidence that pharmacologically targeting mitochondrial dysfunction following injury may hold the greatest potential for increasing tissue sparing and, consequently, the extent of functional recovery following traumatic SCI.

A calcineurin-independent mechanism of angiogenesis inhibition by a nonimmunosuppressive cyclosporin A analog

Cyclosporin A (CsA) is a widely used immunosuppressant drug. Its immunosuppressive activity occurs through the inhibition of the protein phosphatase calcineurin via formation of a ternary complex with cyclophilin A (CypA). CsA also inhibits endothelial cell proliferation and angiogenesis. This has been thought to occur through calcineurin inhibition as well. However, CsA is also a potent inhibitor of cyclophilins, a class of prolyl isomerases. Because calcineurin inhibition requires binding, and therefore inhibition of CypA, the relative contributions of calcineurin and cyclophilin inhibition in antiangiogenesis have not been addressed. We have taken a chemical biology approach to explore this question by dissociating the two activities of CsA at the molecular level. We have identified a nonimmunosuppressive analog of CsA that does not inhibit calcineurin but maintains inhibition of endothelial cell proliferation and in vivo angiogenesis. The same analog also maintains inhibition of all cyclophilin isoforms tested. We also show that a second, structurally distinct, cyclophilin inhibitor is sufficient to block endothelial cell proliferation. These results suggest that the inhibition of cyclophilins may play a larger role in the antiangiogenic activity of CsA than previously believed, and that cyclophilins may be potential antiangiogenic drug targets.

A Review of Laboratory and Clinical Data Supporting the Safety and Efficacy of Cyclosporin A in Traumatic Brain Injury

For decades, cyclosporin A (CsA) has proved to be safe and effective for use in transplantation. In the past 10 years, this agent has shown neuroprotective effects in animal models of traumatic brain injury (TBI). This review article provides a critical overview of the literature on CsA neuroprotective effects in animal studies and current findings of clinical trials in the treatment of TBI with an emphasis on the possible CsA molecular mechanism of action. Animal data provide compelling evidence of the therapeutic benefits of CsA in TBI, but the outcome indices are heterogeneous with respect to the animal model of TBI as well as the route, dose, and timing of CsA administration. Similarly, clinical studies (phase II trials) adapting almost identical patient inclusion criteria have demonstrated the safety of CsA use in TBI, but the clinical trials are also heterogeneous based on study design, especially with regard to the variable timing of CsA administration after TBI. In view of the translational shortcomings of the preclinical studies and the rather pilot nature of the limited clinical trials that recently reached phase III, we offer guidance on the future directions of laboratory investigations on CsA that could improve the safety and efficacy of this agent in subsequent larger clinical trials.

Ischemic postconditioning: from receptor to end-effector

Ischemic preconditioning, a robust cardioprotective intervention, has limited clinical efficacy because it must be initiated before myocardial ischemia. Conversely, ischemic postconditioning, repeated brief reocclusions of a coronary artery after release of prolonged coronary occlusion, provides cardioprotection in clinically feasible settings, that is, coronary angioplasty. Ischemic postconditioning's signaling is being investigated to identify pharmacological triggers that could be used without angioplasty. In initial minutes of reperfusion H(+) washes out of previously ischemic cells. pH rises enabling mitochondrial permeability transition pores (MPTPs) to form leading to cessation of ATP production and cell necrosis. Coronary reocclusions maintain sufficient acidosis to keep MPTP closed while signaling is initiated that can generate endogenous antagonists of MPTP formation even after cellular pH normalizes. Reintroduction of oxygen generates reactive oxygen species that activate protein kinase C to increase sensitivity of adenosine A(2b) receptors allowing adenosine released from ischemic cells to bind leading to activation of phosphatidylinositol 3-kinase and extracellular signal-regulated kinase 1/2. Phosphatidylinositol 3-kinase activation results in phosphorylation of Akt promoting activation of nitric oxide synthase and nitric oxide production, which inhibits glycogen synthase kinase-3β, perhaps the final cytosolic signaling step before inhibition of MPTP formation. Interference with MPTP may be the final step that determines cell salvage.

Pretreatment with the ciclosporin derivative NIM811 reduces delayed neuronal death in the hippocampus after transient forebrain ischaemia

OBJECTIVES

There have been several previous studies showing that ciclosporin, a ligand for cyclophilin D (CypD), reduces mitochondrial permeability transition (mPT) and ameliorates delayed neuronal death. NIM811 is a non-immunosuppressive ciclosporin derivative that also inhibits mPT, but has significantly less cytotoxicity than ciclosporin. Actually, in animal experiments, several investigators have reported that NIM811 ameliorates central nervous system disorders, such as traumatic brain injury, transient focal cerebral ischaemia and spinal cord injury. Therefore, we evaluated whether the ciclosporin derivative, NIM811 reduces mPT and ameliorates delayed neuronal death in the hippocampal CA1 sectors in mice when subjected to transient forebrain ischaemia.

METHODS

Male C57BL/6 mice were treated with 50 mg/kg ciclosporin, 10, 50 or 100 mg/kg NIM811 or phosphate-buffered saline. At 30 min post-injection, all mice were subjected to 20 min bilateral common carotid artery occlusion (BCCAO). To estimate delayed neuronal death, the sections were prepared for HE staining and terminal deoxynucleotidyl transferase-mediated dUTP end-labelling (TUNEL) staining at 72 h after 20 min BCCAO. Furthermore, using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide (JC-1) staining technique, we evaluated whether NIM811 (1, 10, 100 or 1000 microm) inhibited mPT in the neurons exposed to 100 microm glutamate.

RESULTS

Both delayed neuronal injury and apoptosis in the hippocampal CA1 sectors were significantly ameliorated at 72 h after transient forebrain ischaemia in the mice treated with 100 mg/kg NIM811 or 50 mg/kg ciclosporin. The treatments with 100 microm and 1,000 microm NIM811 significantly inhibited the reduction of mitochondrial membrane potential in the neurons exposed to 100 microm glutamate.

CONCLUSIONS

These findings strongly suggest that NIM811 inhibits mPT and ameliorates delayed neuronal death in mice subjected to transient forebrain ischaemia.

Ethanol sensitizes mitochondria to the permeability transition by inhibiting deacetylation of cyclophilin-D mediated by sirtuin-3

Ethanol increases the vulnerability of mitochondria to induction of the mitochondrial permeability transition (MPT). Cyclophilin-D activity enhances the potential for the permeability transition pore (PTP) to open. In the present study, we demonstrate that ethanol and its metabolism sensitize the PTP to opening, in part by increasing the acetylation and activity of cyclophilin-D. This effect of ethanol is mediated by inhibiting the activity of sirtuin-3, an NAD(+) dependent deacetylase that is localized to the mitochondrial matrix. The ethanol-enhanced acetylation of cyclophilin-D also increases the interaction of cyclophilin-D with the adenine nucleotide translocator-1 (ANT-1) and is dependent on ethanol metabolism. Moreover, activation of AMPK, a known positive modulator of sirtuin activity, prevented the ethanol-induced suppression of sirtuin-3 activity and the attendant increase of cyclophilin-D acetylation, activity and association with ANT-1. Additionally, AMPK reactivation of sirtuin-3 prevented the sensitization to the MPT and the enhancement of cell killing by TNF in cells exposed to ethanol.

p53 and TIGAR regulate cardiac myocyte energy homeostasis under hypoxic stress

Bioenergetic homeostasis is altered in heart failure and may play an important role in pathogenesis. p53 has been implicated in heart failure, and although its role in regulating tumorigenesis is well characterized, its activities on cellular metabolism are just beginning to be understood. We investigated the role of p53 and its transcriptional target gene TP53-induced glycolysis and apoptosis regulator (TIGAR) in myocardial energy metabolism under conditions simulating ischemia that can lead to heart failure. Expression of p53 and TIGAR was markedly upregulated after myocardial infarction, and apoptotic myocytes were decreased by 42% in p53-deficient mouse hearts compared with those in wild-type mice. To examine the effect of p53 on energy metabolism, cardiac myocytes were exposed to hypoxia. Hypoxia induced p53 and TIGAR expression in a p53-dependent manner. Knockdown of p53 or TIGAR increased glycolysis with elevated fructose-2,6-bisphosphate levels and reduced myocyte apoptosis. Hypoxic stress decreased phosphocreatine content and the mitochondrial membrane potential of myocytes without changes in ATP content, the effects of which were prevented by the knockdown of TIGAR. Inhibition of glycolysis by 2-deoxyglucose blocked these bioenergetic effects and TIGAR siRNA-mediated prevention of apoptosis, and, in contrast, overexpression of TIGAR reduced glucose utilization and increased apoptosis. Our data demonstrate that p53 and TIGAR inhibit glycolysis in hypoxic myocytes and that inhibition of glycolysis is closely involved in apoptosis, suggesting that p53 and TIGAR are significant mediators of cellular energy homeostasis and cell death under ischemic stress.

The molecular identity of the mitochondrial Ca2+ sequestration system

There is ample evidence to suggest that a dramatic decrease in mitochondrial Ca(2+) retention may contribute to the cell death associated with stroke, excitotoxicity, ischemia and reperfusion, and neurodegenerative diseases. Mitochondria from all studied tissues can accumulate and store Ca(2+) , but the maximum Ca(2+) storage capacity varies widely and exhibits striking tissue specificity. There is currently no explanation for this fact. Precipitation of Ca(2+) and phosphate in the mitochondrial matrix has been suggested to be the major form of storage of accumulated Ca(2+) in mitochondria. How this precipitate is formed is not known. The molecular identity of almost all proteins involved in Ca(2+) transport, storage and formation of the permeability transition pore is also unknown. This review summarizes studies aimed at identifying these proteins, and describes the properties of a known mitochondrial protein that may be involved in Ca(2+) transport and the structure of the permeability transition pore.

Cyclosporine A: impact on mitochondrial function in endothelial cells

INTRODUCTION

Although cyclosporine A (CSA) is considered to be an efficient immunosuppressive compound in transplantation, vascular side effects like arterial hypertension, neurologic complications and other adverse reactions occur. Interference of CSA with mitochondrial function may be responsible for these side effects.

METHODS

We evaluated the effect of CSA on mitochondrial and glycolytic function by measuring fatty acid oxidation (FAO), activities of respiratory chain complexes (RC) and citratesynthase (CS), lactate/pyruvate-ratios, energy-rich phosphates as well as activities of some glycolytic enzymes in human umbilical vein endothelial cells.

RESULTS

After 48 h of CSA incubation, global FAO, RC-complexes 1 + 3; 4 and 5 as well as CS were compromised while energy charges were not reduced. Lactate/pyruvate-ratios increased; cellular lactate dehydrogenase (LDH)-, hexokinase- and phosphofructokinase-activities were not impaired by CSA. Moderate cellular toxicity, assessed by LDH leakage, appeared only at the highest CSA concentration.

CONCLUSION

Part of CSA toxicity may arise from alterations in mitochondrial function as judged by impaired FAO and respiratory chain enzymes. To some extent, energy balance seems to be maintained by cytosolic energy production. Although only demonstrated for endothelial cells, it is conceivable that such effects will alter energy metabolism of different organs with high oxidative energy demands.

Mitochondrial Ca2+ transport and permeability transition in zebrafish (Danio rerio)

We have studied mitochondrial Ca(2+) transport and the permeability transition (PT) in the teleost zebrafish (Danio rerio), a key model system for human diseases. Permeabilized zebrafish embryo cells displayed a mitochondrial energy-dependent Ca(2+) uptake system that, like the Ca(2+) uniporter of mammals, was inhibited by ruthenium red. Zebrafish mitochondria underwent a Ca(2+)-dependent PT that displayed Pi-dependent desensitization by cyclosporin A, and responded appropriately to key modulators of the mammalian PT pore (voltage, pH, ubiquinone 0, dithiol oxidants and cross linkers, ligands of the adenine nucleotide translocator, arachidonic acid). Opening of the pore was documented in intact cells, where it led to death that could largely be prevented by cyclosporin A. Our results represent a necessary step toward the use of zebrafish for the screening and validation of PTP inhibitors of potential use in human diseases, as recently shown for collagen VI muscular dystrophy [Telfer et al., 2010].

The mitochondrial permeability transition from yeast to mammals

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.

Cyclophilin D in mitochondrial pathophysiology

Cyclophilins are a family of peptidyl-prolyl cis-trans isomerases whose enzymatic activity can be inhibited by cyclosporin A. Sixteen cyclophilins have been identified in humans, and cyclophilin D is a unique isoform that is imported into the mitochondrial matrix. Here we shall (i) review the best characterized functions of cyclophilin D in mitochondria, i.e. regulation of the permeability transition pore, an inner membrane channel that plays an important role in the execution of cell death; (ii) highlight new regulatory interactions that are emerging in the literature, including the modulation of the mitochondrial F1FO ATP synthase through an interaction with the lateral stalk of the enzyme complex; and (iii) discuss diseases where cyclophilin D plays a pathogenetic role that makes it a suitable target for pharmacologic intervention.

Downmodulation of Bcl-2 sensitizes metastatic LNCaP-LN3 cells to undergo apoptosis via the intrinsic pathway

BACKGROUND

We explored the mechanisms of apoptosis after Bcl-2 protein downmodulation in metastatic LNCaP-LN3 cells (LN3).

METHODS

LNCaP, LNCaP-Pro5 (Pro5) and LN3 cells were cultured in 5% charcoal-stripped serum (CSS) or in R1881 (synthetic androgen) and bicalutamide (synthetic anti-androgen) and growth inhibition was assessed. Expression levels of androgen receptor (AR) and Bcl-2 were determined. LN3 cells were transfected with small interfering RNA Bcl-2 (siRNA Bcl-2) or control siRNA oligonucleotides. Rates of apoptosis and proliferation were obtained. Cytochrome c localization in treated and control cells was assessed +/- cyclosporine A (CsA). Caspases 9, 3, and poly (ADP-ribose) polymerase cleavage (PARP) were measured upon downmodulation of Bcl-2; and cell growth inhibition in vitro after Bcl-2 modulation combined with docetaxel chemotherapy was determined.

RESULTS

LN3 cells maintained growth under castrate conditions in vitro. AR protein amplification did not explain castrate-resistant LN3 cell growth. Bcl-2 protein levels in LN3 cells were significantly higher than in Pro5 cells, and were effectively downmodulated by siRNA Bcl-2. Subsequently increased apoptosis and decreased proliferation mediated by cytochrome c was noted and this was reversed by CsA. siRNA Bcl-2-transfected LN3 cells exhibited elevated levels of caspases 9, 3, and PARP cleavage. Exposure of LN3 cells to docetaxel led to increased apoptosis, and simultaneous downmodulation of Bcl-2 substantially enhanced this effect.

CONCLUSIONS

Downmodulation of Bcl-2 in metastatic castrate-resistant LNCaP-LN3 cells led to apoptosis via a cytochrome c-dependent pathway that was enhanced with docetaxel treatment.

Cyclophilin D is required for mitochondrial removal by autophagy in cardiac cells

Autophagy is a highly regulated intracellular degradation process by which cells remove cytosolic long-lived proteins and damaged organelles. The mitochondrial permeability transition (MPT) results in mitochondrial depolarization and increased reactive oxygen species production, which can trigger autophagy. Therefore, we hypothesized that the MPT may have a role in signaling autophagy in cardiac cells. Mitochondrial membrane potential was lower in HL-1 cells subjected to starvation compared to cells maintained in full medium. Mitochondrial membrane potential was preserved in starved cells treated with cyclosporin A (CsA), suggesting the MPT pore is associated with starvation-induced depolarization. Starvation-induced autophagy in HL-1 cells, neonatal rat cardiomyocytes and adult mouse cardiomyocytes was inhibited by CsA. Starvation failed to induce autophagy in CypD-deficient murine cardiomyocytes, whereas in myocytes from mice overexpressing CypD the levels of autophagy were enhanced even under fed conditions. Collectively, these results demonstrate a role for CypD and the MPT in the initiation of autophagy. We also analyzed the role of the MPT in the degradation of mitochondria by biochemical analysis and electron microscopy. HL-1 cells subjected to starvation in the presence of CsA had higher levels of mitochondrial proteins (by Western blot), more mitochondria and less autophagosomes (by electron microscopy) than cells starved in the absence of CsA. Our results suggest a physiologic function for CypD and the MPT in the regulation of starvation-induced autophagy. Starvation-induced autophagy regulated by CypD and the MPT may represent a homeostatic mechanism for cellular and mitochondrial quality control.

The consequences of mitochondrial amyloid beta-peptide in Alzheimer's disease

The Abeta (amyloid-beta peptide) has long been associated with Alzheimer's disease, originally in the form of extracellular plaques. However, in the present paper we review the growing evidence for the role of soluble intracellular Abeta in the disease progression, with particular reference to Abeta found within the mitochondria. Once inside the cell, Abeta is able to interact with a number of targets, including the mitochondrial proteins ABAD (amyloid-binding alcohol dehydrogenase) and CypD (cyclophilin D), which is a component of the mitochondrial permeability transition pore. Interference with the normal functions of these proteins results in disruption of cell homoeostasis and ultimately cell death. The present review explores the possible mechanisms by which cell death occurs, considering the evidence presented on a molecular, cellular and in vivo level.

Extramitochondrial Ca2+ in the nanomolar range regulates glutamate-dependent oxidative phosphorylation on demand

We present unexpected and novel results revealing that glutamate-dependent oxidative phosphorylation (OXPHOS) of brain mitochondria is exclusively and efficiently activated by extramitochondrial Ca²⁺ in physiological concentration ranges (S_0.5 = 360 nM Ca²⁺). This regulation was not affected by RR, an inhibitor of the mitochondrial Ca²⁺ uniporter. Active respiration is regulated by glutamate supply to mitochondria via aralar, a mitochondrial glutamate/aspartate carrier with regulatory Ca²⁺-binding sites in the mitochondrial intermembrane space providing full access to cytosolic Ca²⁺. At micromolar concentrations, Ca²⁺ can also enter the intramitochondrial matrix and activate specific dehydrogenases. However, the latter mechanism is less efficient than extramitochondrial Ca²⁺ regulation of respiration/OXPHOS via aralar. These results imply a new mode of glutamate-dependent OXPHOS regulation as a demand-driven regulation of mitochondrial function. This regulation involves the mitochondrial glutamate/aspartate carrier aralar which controls mitochondrial substrate supply according to the level of extramitochondrial Ca²⁺.

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

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.

Ca(2+) transfer from the ER to mitochondria: when, how and why

The heterogenous subcellular distribution of a wide array of channels, pumps and exchangers allows extracellular stimuli to induce increases in cytoplasmic Ca(2+) concentration ([Ca(2+)]c) with highly defined spatial and temporal patterns, that in turn induce specific cellular responses (e.g. contraction, secretion, proliferation or cell death). In this extreme complexity, the role of mitochondria was considered marginal, till the direct measurement with targeted indicators allowed to appreciate that rapid and large increases of the [Ca(2+)] in the mitochondrial matrix ([Ca(2+)]m) invariably follow the cytosolic rises. Given the low affinity of the mitochondrial Ca(2+) transporters, the close proximity to the endoplasmic reticulum (ER) Ca(2+)-releasing channels was shown to be responsible for the prompt responsiveness of mitochondria. In this review, we will summarize the current knowledge of: i) the mitochondrial and ER Ca(2+) channels mediating the ion transfer, ii) the structural and molecular foundations of the signaling contacts between the two organelles, iii) the functional consequences of the [Ca(2+)]m increases, and iv) the effects of oncogene-mediated signals on mitochondrial Ca(2+) homeostasis. Despite the rapid progress carried out in the latest years, a deeper molecular understanding is still needed to unlock the secrets of Ca(2+) signaling machinery.

Induction of a non-specific permeability transition in mitochondria from Yarrowia lipolytica and Dipodascus (Endomyces) magnusii yeasts

In this study we used tightly-coupled mitochondria from Yarrowia lipolytica and Dipodascus (Endomyces) magnusii yeasts, possessing a respiratory chain with the usual three points of energy conservation. High-amplitude swelling and collapse of the membrane potential were used as parameters for demonstrating induction of the mitochondrial permeability transition due to opening of a pore (mPTP). Mitochondria from Y. lipolytica, lacking a natural mitochondrial Ca(2+) uptake pathway, and from D. magnusii, harboring a high-capacitive, regulated mitochondrial Ca(2+) transport system (Bazhenova et al. J Biol Chem 273:4372-4377, 1998a; Bazhenova et al. Biochim Biophys Acta 1371:96-100, 1998b; Deryabina and Zvyagilskaya Biochemistry (Moscow) 65:1352-1356, 2000; Deryabina et al. J Biol Chem 276:47801-47806, 2001) were very resistant to Ca(2+) overload. However, exposure of yeast mitochondria to 50-100 microM Ca(2+) in the presence of the Ca(2+) ionophore ETH129 induced collapse of the membrane potential, possibly due to activation of the fatty acid-dependent Ca(2+)/nH(+)-antiporter, with no classical mPTP induction. The absence of response in yeast mitochondria was not simply due to structural limitations, since large-amplitude swelling occurred in the presence of alamethicin, a hydrophobic, helical peptide, forming voltage-sensitive ion channels in lipid membranes. Ca(2+)- ETH129-induced activation of the Ca(2+)/H(+)-antiport system was inhibited and prevented by bovine serum albumin, and partially by inorganic phosphate and ATP. We subjected yeast mitochondria to other conditions known to induce the permeability transition in animal mitochondria, i.e., Ca(2+) overload (in the presence of ETH129) combined with palmitic acid (Mironova et al. J Bioenerg Biomembr 33:319-331, 2001; Sultan and Sokolove Arch Biochem Biophys 386:37-51, 2001), SH-reagents, carboxyatractyloside (an inhibitor of the ADP/ATP translocator), depletion of intramitochondrial adenine nucleotide pools, deenergization of mitochondria, and shifting to acidic pH values in the presence of high phosphate concentrations. None of the above-mentioned substances or conditions induced a mPTP-like pore. It is thus evident that the permeability transition in yeast mitochondria is not coupled with Ca(2+) uptake and is differently regulated compared to the mPTP of animal mitochondria.

Role of glycogen synthase kinase-3beta in cardioprotection

Limitation of infarct size by ischemic/pharmacological pre- and postconditioning involves activation of a complex set of cell-signaling pathways. Multiple lines of evidence implicate the mitochondrial permeability transition pore (mPTP) as a key end effector of ischemic/pharmacological pre- and postconditioning. Increasing the ROS threshold for mPTP induction enhances the resistance of cardiomyocytes to oxidant stress and results in infarct size reduction. Here, we survey and synthesize the present knowledge about the role of glycogen synthase kinase (GSK)-3beta in cardioprotection, including pre- and postconditioning. Activation of a wide spectrum of cardioprotective signaling pathways is associated with phosphorylation and inhibition of a discrete pool of GSK-3beta relevant to mitochondrial signaling. Therefore, GSK-3beta has emerged as the integration point of many of these pathways and plays a central role in transferring protective signals downstream to target(s) that act at or in proximity to the mPTP. Bcl-2 family proteins and mPTP-regulatory elements, such as adenine nucleotide translocator and cyclophilin D (possibly voltage-dependent anion channel), may be the functional downstream target(s) of GSK-3beta. Gaining a better understanding of these interactions to control and prevent mPTP induction when appropriate will enable us to decrease the negative impact of the reperfusion-induced ROS burst on the fate of mitochondria and perhaps allow us to limit propagation of damage throughout and between cells and consequently, to better limit infarct size.

The cyclophilin inhibitor Debio 025 normalizes mitochondrial function, muscle apoptosis and ultrastructural defects in Col6a1-/- myopathic mice

BACKGROUND AND PURPOSE

We have investigated the therapeutic effects of the selective cyclophilin inhibitor D-MeAla(3)-EtVal(4)-cyclosporin (Debio 025) in myopathic Col6a1(-/-) mice, a model of muscular dystrophies due to defects of collagen VI.

EXPERIMENTAL APPROACH

We studied calcineurin activity based on NFAT translocation; T cell activation based on expression of CD69 and CD25; propensity to open the permeability transition pore in mitochondria and skeletal muscle fibres based on the ability to retain Ca(2+) and on membrane potential, respectively; muscle ultrastructure by electronmicroscopy; and apoptotic rates by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assays in Col6a1(-/-) mice before after treatment with Debio 025.

KEY RESULTS

Debio 025 did not inhibit calcineurin activity, yet it desensitizes the mitochondrial permeability transition pore in vivo. Treatment with Debio 025 prevented the mitochondrial dysfunction and normalized the apoptotic rates and ultrastructural lesions of myopathic Col6a1(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

Desensitization of the mitochondrial permeability transition pore can be achieved by selective inhibition of matrix cyclophilin D without inhibition of calcineurin, resulting in an effective therapy of Col6a1(-/-) myopathic mice. These findings provide an important proof of principle that collagen VI muscular dystrophies can be treated with Debio 025. They represent an essential step towards an effective therapy for Ullrich Congenital Muscular Dystrophy and Bethlem Myopathy, because Debio 025 does not expose patients to the potentially harmful effects of immunosuppression.