Real-time flow cytometry analysis of permeability transition in isolated mitochondria

Jujuboside A improves insomnia by maintaining mitochondrial homeostasis in prefrontal neurons

OBJECTIVE

Jujuboside A (JB-A) is the major component of Semen Ziziphi Spinosae (SZS), a traditional Chinese herbal medicine used to treat sleep with clinical efficacy. This is the first study to investigate the effects of JB-A on mitochondrial structure and function in the prefrontal cortex of the insomnia model mice.

METHODS

Young adult C57BL/6 mice were induced to develop insomnia by P-chlorophenylalanine. After 14 d of JB-A treatment via gavage, anxiety level was assessed using the open field and elevated plus maze tests. Next, the mitochondrial metabolic activity and morphological changes in the prefrontal cortex of each group of mice, as well as their effects on mitochondrial membrane potential, oxidative phosphorylation levels, and cytochrome c (Cyt c) content in neurons were measured.

RESULTS

In our mouse model, JB-A ameliorated anxiety-like behaviors; up-regulated the membrane potential (Δψm) and had a therapeutic effect on the metabolic activity and damaged microscopic structure of mitochondria in the prefrontal cortex; effectively improved mitochondrial function by increasing the expression of Cyt c oxidase I and IV proteins, ATPase activity, and ATP content; and reduced the accumulation of Cyt c in the neuronal cytoplasm while inhibiting mitochondrial permeability transition pore (mPTP) opening.

CONCLUSIONS

JB-A can improve insomnia by restoring mitochondrial intracellular oxidative phosphorylation, regulating mPTP to maintain mitochondrial homeostasis, and alleviating structural damage, providing a scientific basis for finding new targets for insomnia treatment.

Apoptosis Due to After-effects of Acute Ethanol Exposure in Brain Cortex: Intrinsic and Extrinsic Signaling Pathways

Alcohol hangover is the combination of negative mental and physical symptoms which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration approaches zero. We previously demonstrated that hangover provokes mitochondrial dysfunction, oxidative stress, imbalance in antioxidant defenses, and impairment in cellular bioenergetics. Chronic and acute ethanol intake induces neuroapoptosis but there are no studies which evaluated apoptosis at alcohol hangover. The aim of the present work was to study alcohol residual effects on intrinsic and extrinsic apoptotic signaling pathways in mice brain cortex. Male Swiss mice received i.p. injection of ethanol (3.8 g/kg) or saline. Six hours after injection, at alcohol hangover onset, mitochondria and tissue lysates were obtained from brain cortex. Results indicated that during alcohol hangover a loss of granularity of mitochondria and a strong increment in mitochondrial permeability were observed, indicating the occurrence of swelling. Alcohol-treated mice showed a significant 35% increase in Bax/Bcl-2 ratio and a 5-fold increase in the ratio level of cytochrome c between mitochondria and cytosol. Caspase 3, 8 and 9 protein expressions were 32%, 33% and 20% respectively enhanced and the activity of caspase 3 and 6 was 30% and 20% increased also due to the hangover condition. Moreover, 38% and 32% increments were found in PARP1 and p53 protein expression respectively and on the contrary, SIRT-1 was almost 50% lower than controls due to the hangover condition. The present work demonstrates that alcohol after-effects could result in the activation of mitochondrial and non-mitochondrial apoptosis pathways.

Direct count of fluorescent microspheres in a microfluidic chip based on the capillary electrophoresis method

Fluorescent microspheres (FMs) are tiny particles with special functions that are widely employed in biological research. Counting of microscale FMs is a great challenge by capillary electrophoresis. Herein we developed a method to count 2 μm FMs based on a microfluidic chip with a gradual change in inner size. Such a microfluidic chip can inhibit sample blocking at the inlet of the capillary. The results showed that FMs migrated in the wide part of the microchannel side by side, and then passed through the narrow part one by one. There was a linear relationship between the number of peaks in the electropherogram and concentration of FMs if they were running in the microchannel for more than 20 min. A high separation voltage may lead to aggregation of FMs in the microchannels, and about 2 × 10⁴ FMs can be counted within 30 min by this microfluidic chip.

Isolated Mitochondria State after Myocardial Ischemia-Reperfusion Injury and Cardioprotection: Analysis by Flow Cytometry

Rationale: Mitochondria are key organelles involved in cell survival and death during the acute phenomena of myocardial ischemia-reperfusion (i.e., myocardial infarction). To investigate the functions of isolated mitochondria such as calcium retention capacity, oxidative phosphorylation, and reactive oxygen species (ROS) production, already established methods are based on extramitochondrial measurements of the whole mitochondria population. Objective: The aim of this study was to develop a reliable and well-characterized method for multiparametric analysis of isolated single mitochondrion by flow cytometry (FC) in the context of myocardial infarction. The advantage of FC is the possibility to give a simultaneous analysis of morphological parameters (side and forward scatters: SSC and FSC) for each mitochondrion, combined with intramitochondrial measurements of several biological markers, such as ROS production or membrane potential (Δφm), using specific fluorescent probes. Methods and Results: For this study, a rat model of ischemia-reperfusion and a protective approach of post-conditioning using low reperfusion pressure was used. Thanks to the use of specific probes (NAO, MTR, TMRM, DilC1, and DHR123) combined with flow cytometry, we propose a method: (i) to identify mitochondrial populations of interest based on quality criteria (NAO/TMRM double staining); (ii) to monitor their morphological criteria, especially during swelling due to calcium overload; and (iii) to compare mitochondrial functions (membrane potential and ROS production) in different experimental groups. Applied to mitochondria from ischemic hearts, these measurements revealed that individual mitochondria are altered and that cardioprotection by low-pressure reperfusion reduces damage, as expected. Conclusions: Our results highlight FC as a reliable and sensitive method to investigate changes in mitochondrial functions and morphology in pathological conditions that disrupts their activity such as the case in ischemia-reperfusion. This methodological approach can be extended to other pathologies involving mitochondrial dysfunctions. Moreover, FC offers the possibility to work with very small amounts of isolated mitochondria, a factor that may limit the use of classical methods.

Isolated Mitochondrial Preparations and In organello Assays: A Powerful and Relevant Ex vivo Tool for Assessment of Brain (Patho)physiology

Mitochondria regulate multiple aspects of neuronal development, physiology, plasticity, and pathology through their regulatory roles in bioenergetic, calcium, redox, and cell survival/death signalling. While several reviews have addressed these different aspects, a comprehensive discussion focussing on the relevance of isolated brain mitochondria and their utilities in neuroscience research has been lacking. This is relevant because the employment of isolated mitochondria rather than their in situ functional evaluation, offers definitive evidence of organelle-specificity, negating the interference from extra mitochondrial cellular factors/signals. This mini-review was designed primarily to explore the commonly employed in organello analytical assays for the assessment of mitochondrial physiology and its dysfunction, with a particular focus on neuroscience research. The authors briefly discuss the methodologies for biochemical isolation of mitochondria, their quality assessment, and cryopreservation. Further, the review attempts to accumulate the key biochemical protocols for in organello assessment of a multitude of mitochondrial functions critical for neurophysiology, including assays for bioenergetic activity, calcium and redox homeostasis, and mitochondrial protein translation. The purpose of this review is not to examine each and every method or study related to the functional assessment of isolated brain mitochondria, but rather to assemble the commonly used protocols of in organello mitochondrial research in a single publication. The hope is that this review will provide a suitable platform aiding neuroscientists to choose and apply the required protocols and tools to address their particular mechanistic, diagnostic, or therapeutic question dealing within the confines of the research area of mitochondrial patho-physiology in the neuronal perspective.

Fabrication of a label-free electrochemical aptasensor to detect cytochrome c in the early stage of cell apoptosis

A label-free direct electrochemical aptasensor is presented for the identification of cytochrome c (Cyt c) at the nM concentration level. Carbon nanofibers (CNF), as a highly conductive material, were used to modify a glassy carbon electrode (GCE) and thus increase its conductivity. Moreover, to enhance the immobilization of aptamers (Apt) on the electrode surface, graphene oxide functionalized with aspartic acid (GOAsp) was added to the surface. Aspartic acid with countless carboxyl groups (-COOH) on its surface caused more aptamers to be immobilized on the electrode surface. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were used to monitor the step-by-step fabrication of the label-free direct electrochemical aptasensor. The label-free quantification of Cyt c was also done by the direct electron transfer between the Fe(III)/Fe(II)-heme redox-active sites which were selectively bound to the aptamers on the GCE and the surface of the electrode. Under optimum conditions, the peak currents of differential pulse voltammograms at 0.26 V (vs. Ag/AgCl) were used for calibration. The proposed aptasensor performs in a wide dynamic range from 10 nM to 100 µM with a low detection limit of 0.74 nM for cytochrome c. It also has high selectivity as well as acceptable stability. These advantages make the biosensor capable of detecting early-stage apoptotic cells that contribute to early cancer diagnosis.

Measurement of fish freshness: Flow cytometry analysis of isolated muscle mitochondria

Mitochondria are real sensors of the physiological status of tissues. After the death of an animal, they maintain physiological activity for several days. This activity is highly dependent on the availability of nutrients in the tissue. In this study, flow cytometry was used to measure the membrane potential of mitochondria isolated from European seabass (Dicentrarchus labrax) red muscle stored in ice for seven days in order to characterize fish freshness. Two probes, TMRM and Rhodamine 123, were used to measure mitochondrial potential. During the first few days (D0 to D3), isolated mitochondria maintained high potential, and then lost their potential (from D3 to D5), but were always re-polarizable after addition of substrates (glutamate, malate and succinate). From D7, the mitochondria were more strongly depolarized and were difficult to repolarize by the substrates. Using flow cytometry, we demonstrated that mitochondria were an excellent marker to confirm seabass freshness.

Lung injury after cardiopulmonary bypass: Alternative treatment prospects

Although the lung injury caused by cardiopulmonary bypass (CPB) has been extensively investigated, the incidence and mortality of lung injury after CPB remain a prominent clinical problem. The poor outcome has been attributed to multifactorial etiology, including the systemic inflammatory response and ischemia reperfusion (I/R) injury during CPB. Lung injury after CPB is a complex pathophysiological process and has many clinical manifestations of mild to severe disease. Which is associated with prognosis. To alleviate this lung injury, interventions that address the pathogenesis are particularly important. This review summarizes the pathogenesis, mechanism and treatment options of lung injury after CPB, such as lung protection with intralipid.

Species-Specific Urothelial Toxicity with an anti-HIV Non-Catalytic Site Integrase Inhibitor (NCINI) is Related to Unusual pH-Dependent Physicochemical Changes

GS-9695 and GS-9822 are next generation Non-Catalytic Site Integrase Inhibitors (NCINIs) with significantly improved potency against HIV compared with previous drugs such as BI-224436. Development stopped due to vacuolation of the bladder urothelium seen in cynomolgus monkey but not in rat; this lesion was absent in equivalent preclinical studies with BI-224436 (tested in dog and rat). Lesions were unlikely to be attributable to target since NCINIs specifically target viral integrase protein and no mammalian homologue is known. Secondary pharmacology studies, mitochondrial toxicity studies, immunophenotyping and analysis of proteins implicated in cell-cell interactions and/or bladder integrity (e-cadherin, pan-cytokeratin, uroplakins) failed to offer any plausible explanation for the species-specificity of the lesion. Since it was characterized by inflammation and disruption of urothelial morphology, we investigated physicochemical changes in the bladder of cynomolgus monkey (urinary pH 5.5-7.4) that might not occur in the bladder of rats (urinary pH 7.3-8.5). In measurements of surface activity, GS-9822 showed an unusual transition from a monolayer to a bilayer at the air/water interface with decreasing pH, attributed to the strong association between drug molecules in adjacent bilayer leaflets and expected to be highly disruptive to the urothelium. Structural analysis of GS-9822 and GS-9695 showed zwitterionic characteristics over the range of pH expected in cynomolgus monkey but not rat urine. This exotic surface behaviour is unlikely with BI-224436 since it would transition from neutral to cationic (never zwitterionic) with decreasing pH. These data provide useful insights to guide discovery and development of NCINIs, related compounds and zwitterions.

Drug-induced hepatic steatosis in absence of severe mitochondrial dysfunction in HepaRG cells: proof of multiple mechanism-based toxicity

Steatosis is a liver lesion reported with numerous pharmaceuticals. Prior studies showed that severe impairment of mitochondrial fatty acid oxidation (mtFAO) constantly leads to lipid accretion in liver. However, much less is known about the mechanism(s) of drug-induced steatosis in the absence of severe mitochondrial dysfunction, although previous studies suggested the involvement of mild-to-moderate inhibition of mtFAO, increased de novo lipogenesis (DNL), and impairment of very low-density lipoprotein (VLDL) secretion. The objective of our study, mainly carried out in human hepatoma HepaRG cells, was to investigate these 3 mechanisms with 12 drugs able to induce steatosis in human: amiodarone (AMIO, used as positive control), allopurinol (ALLO), D-penicillamine (DPEN), 5-fluorouracil (5FU), indinavir (INDI), indomethacin (INDO), methimazole (METHI), methotrexate (METHO), nifedipine (NIF), rifampicin (RIF), sulindac (SUL), and troglitazone (TRO). Hepatic cells were exposed to drugs for 4 days with concentrations decreasing ATP level by less than 30% as compared to control and not exceeding 100 × Cmax. Among the 12 drugs, AMIO, ALLO, 5FU, INDI, INDO, METHO, RIF, SUL, and TRO induced steatosis in HepaRG cells. AMIO, INDO, and RIF decreased mtFAO. AMIO, INDO, and SUL enhanced DNL. ALLO, 5FU, INDI, INDO, SUL, RIF, and TRO impaired VLDL secretion. These seven drugs reduced the mRNA level of genes playing a major role in VLDL assembly and also induced endoplasmic reticulum (ER) stress. Thus, in the absence of severe mitochondrial dysfunction, drug-induced steatosis can be triggered by different mechanisms, although impairment of VLDL secretion seems more frequently involved, possibly as a consequence of ER stress.

Engineering Living Mitochondria with AIE Photosensitizer for Synergistic Cancer Cell Ablation

Photodynamic therapy (PDT) has been increasingly studied in cancer treatment, and several factors have been identified to limit the PDT therapeutic efficiency. Taking Bcl-2 protein as an example, its overexpressing in cancer cells could strengthen the antioxidant and antiapoptotic capability of the cells, making PDT less effective in cancer cell treatment. To address this issue, we developed an engineered living system by integrating an aggregation-induced emission photosensitizer (AIE PS) with bioactive mitochondria (Mito-AIEgen-lipid) for enhanced PDT. The AIE PS engineered mitochondria could not only change the energetic metabolism of cancer cells from aerobic glycolysis to normal oxide phosphorylation for cancer cell growth inhibition but also activate the apoptotic pathway and reduce the expression of antiapoptotic protein Bcl-2. This specific organelle-based living system holds great promise to enhance the therapeutic efficiency of PDT by integrating the advantages of synthetic organic small molecules with biological components.

Single organelle analysis to characterize mitochondrial function and crosstalk during viral infection

Mitochondria are key for cellular metabolism and signalling processes during viral infection. We report a methodology to analyse mitochondrial properties at the single-organelle level during viral infection using a recombinant adenovirus coding for a mitochondrial tracer protein for tagging and detection by multispectral flow cytometry. Resolution at the level of tagged individual mitochondria revealed changes in mitochondrial size, membrane potential and displayed a fragile phenotype during viral infection of cells. Thus, single-organelle and multi-parameter resolution allows to explore altered energy metabolism and antiviral defence by tagged mitochondria selectively in virus-infected cells and will be instrumental to identify viral immune escape and to develop and monitor novel mitochondrial-targeted therapies.

Mechanistic Landscape of Membrane-Permeabilizing Peptides

Membrane permeabilizing peptides (MPPs) are as ubiquitous as the lipid bilayer membranes they act upon. Produced by all forms of life, most membrane permeabilizing peptides are used offensively or defensively against the membranes of other organisms. Just as nature has found many uses for them, translational scientists have worked for decades to design or optimize membrane permeabilizing peptides for applications in the laboratory and in the clinic ranging from antibacterial and antiviral therapy and prophylaxis to anticancer therapeutics and drug delivery. Here, we review the field of membrane permeabilizing peptides. We discuss the diversity of their sources and structures, the systems and methods used to measure their activities, and the behaviors that are observed. We discuss the fact that "mechanism" is not a discrete or a static entity for an MPP but rather the result of a heterogeneous and dynamic ensemble of structural states that vary in response to many different experimental conditions. This has led to an almost complete lack of discrete three-dimensional active structures among the thousands of known MPPs and a lack of useful or predictive sequence-structure-function relationship rules. Ultimately, we discuss how it may be more useful to think of membrane permeabilizing peptides mechanisms as broad regions of a mechanistic landscape rather than discrete molecular processes.

Mitochondrial damage-associated molecular patterns released by lung transplants are associated with primary graft dysfunction

Primary graft dysfunction (PGD) is a major limitation in short- and long-term lung transplant survival. Recent work has shown that mitochondrial damage-associated molecular patterns (mtDAMPs) can promote solid organ injury, but whether they contribute to PGD severity remains unclear. We quantitated circulating plasma mitochondrial DNA (mtDNA) in 62 patients, before lung transplantation and shortly after arrival to the intensive care unit. Although all recipients released mtDNA, high levels were associated with severe PGD development. In a mouse orthotopic lung transplant model of PGD, we detected airway cell-free damaged mitochondria and mtDNA in the peripheral circulation. Pharmacologic inhibition or genetic deletion of formylated peptide receptor 1 (FPR1), a chemotaxis sensor for N-formylated peptides released by damaged mitochondria, inhibited graft injury. An analysis of intragraft neutrophil-trafficking patterns reveals that FPR1 enhances neutrophil transepithelial migration and retention within airways but does not control extravasation. Using donor lungs that express a mitochondria-targeted reporter protein, we also show that FPR1-mediated neutrophil trafficking is coupled with the engulfment of damaged mitochondria, which in turn triggers reactive oxygen species (ROS)-induced pulmonary edema. Therefore, our data demonstrate an association between mtDAMP release and PGD development and suggest that neutrophil trafficking and effector responses to damaged mitochondria are drivers of graft damage.

An efficient and assumption-free method to approximate protein level distribution in the two-states gene expression model

Stochastic fluctuations at each step of gene expression might influence protein levels distributions across cell populations. However, current methods to model protein distribution of intrinsic gene expression dynamics are either computationally inefficient or rely on ad hoc assumptions, e.g., that the gene is always active. Taking advantage of the simple form of lower-order moments of distribution, we developed an efficient and assumption-free protein distribution approximation method (EFPD), for the two state gene expression model to accurately approximate the distribution. By EFPD, we computed nearly identical intensity of gene expression regulation at mRNA and protein level, implying a profound link between transcription and translation. Finally, by extending EFPD to approximate the distribution of protein level at any arbitrary temporal state, we proposed an explanation for the role of stochastic noise in gene expression in the context of a continuously changing environment. EFPD can be a powerful tool for modeling the particular molecular mechanisms of targeted gene expression pattern.

An Effective, Versatile, and Inexpensive Device for Oxygen Uptake Measurement

In the last ten years, the use of fluorescent probes developed to measure oxygen has resulted in several marketed devices, some unreasonably expensive and with little flexibility. We have explored the use of the effective, versatile, and inexpensive Redflash technology to determine oxygen uptake by a number of different biological samples using various layouts. This technology relies on the use of an optic fiber equipped at its tip with a membrane coated with a fluorescent dye (www.pyro-science.com). This oxygen-sensitive dye uses red light excitation and lifetime detection in the near infrared. So far, the use of this technology has mostly been used to determine oxygen concentration in open spaces for environmental studies, especially in aquatic media. The oxygen uptake determined by the device can be easily assessed in small volumes of respiration medium and combined with the measurement of additional parameters, such as lactate excretion by intact cells or the membrane potential of purified mitochondria. We conclude that the performance of by this technology should make it a first choice in the context of both fundamental studies and investigations for respiratory chain deficiencies in human samples.

Identification and Characterization of Mitochondrial Subtypes in Caenorhabditis elegans via Analysis of Individual Mitochondria by Flow Cytometry

Mitochondrial bioenergetics has been implicated in a number of vital cellular and physiological phenomena, including aging, metabolism, and stress resistance. Heterogeneity of the mitochondrial membrane potential (Δψ), which is central to organismal bioenergetics, has been successfully measured via flow cytometry in whole cells but rarely in isolated mitochondria from large animal models. Similar studies in small animal models, such as Caenorhabditis elegans (C. elegans), are critical to our understanding of human health and disease but lack analytical methodologies. Here we report on new methodological developments that make it possible to investigate the heterogeneity of Δψ in C. elegans during development and in tissue-specific studies. The flow cytometry methodology described here required an improved collagenase-3-based mitochondrial isolation procedure and labeling of mitochondria with the ratiometric fluorescent probe JC-9. To demonstrate feasibility of tissue-specific studies, we used C. elegans strains expressing blue-fluorescent muscle-specific proteins, which enabled identification of muscle mitochondria among mitochondria from other tissues. This methodology made it possible to observe, for the first time, critical changes in Δψ during C. elegans larval development and provided direct evidence of the elevated bioenergetic status of muscle mitochondria relative to their counterparts in the rest of the organism. Further application of these methodologies can help tease apart bioenergetics and other biological complexities in C. elegans and other small animal models used to investigate human disease and aging.

Long-chain acylcarnitines determine ischaemia/reperfusion-induced damage in heart mitochondria

The accumulation of long-chain fatty acids (FAs) and their CoA and carnitine esters is observed in the ischaemic myocardium after acute ischaemia/reperfusion. The aim of the present study was to identify harmful FA intermediates and their detrimental mechanisms of action in mitochondria and the ischaemic myocardium. In the present study, we found that the long-chain acyl-CoA and acylcarnitine content is increased in mitochondria isolated from an ischaemic area of the myocardium. In analysing the FA derivative content, we discovered that long-chain acylcarnitines, but not acyl-CoAs, accumulate at concentrations that are harmful to mitochondria. Acylcarnitine accumulation in the mitochondrial intermembrane space is a result of increased carnitine palmitoyltransferase 1 (CPT1) and decreased carnitine palmitoyltransferase 2 (CPT2) activity in ischaemic myocardium and it leads to inhibition of oxidative phosphorylation, which in turn induces mitochondrial membrane hyperpolarization and stimulates the production of reactive oxygen species (ROS) in cardiac mitochondria. Thanks to protection mediated by acyl-CoA-binding protein (ACBP), the heart is much better guarded against the damaging effects of acyl-CoAs than against acylcarnitines. Supplementation of perfusion buffer with palmitoylcarnitine (PC) before occlusion resulted in a 2-fold increase in the acylcarnitine content of the heart and increased the infarct size (IS) by 33%. A pharmacologically induced decrease in the mitochondrial acylcarnitine content reduced the IS by 44%. Long-chain acylcarnitines are harmful FA intermediates, accumulating in ischaemic heart mitochondria and inducing inhibition of oxidative phosphorylation. Therefore, decreasing the acylcarnitine content via cardioprotective drugs may represent a novel treatment strategy.

Alcohol hangover induces mitochondrial dysfunction and free radical production in mouse cerebellum

Alcohol hangover (AH) is defined as the temporary state after alcohol binge-like drinking, starting when ethanol (EtOH) is absent in plasma. Previous data indicate that AH induces mitochondrial dysfunction and free radical production in mouse brain cortex. The aim of this work was to study mitochondrial function and reactive oxygen species production in mouse cerebellum at the onset of AH. Male mice received a single i.p. injection of EtOH (3.8g/kg BW) or saline solution. Mitochondrial function was evaluated 6h after injection (AH onset). At the onset of AH, malate-glutamate and succinate-supported state 4 oxygen uptake was 2.3 and 1.9-fold increased leading to a reduction in respiratory control of 55% and 48% respectively, as compared with controls. Decreases of 38% and 16% were found in Complex I-III and IV activities. Complex II-III activity was not affected by AH. Mitochondrial membrane potential and mitochondrial permeability changes were evaluated by flow cytometry. Mitochondrial membrane potential and permeability were decreased by AH in cerebellum mitochondria. Together with this, AH induced a 25% increase in superoxide anion and a 92% increase in hydrogen peroxide production in cerebellum mitochondria. Related to nitric oxide (NO) metabolism, neuronal nitric oxide synthase (nNOS) protein expression was 52% decreased by the hangover condition compared with control group. No differences were found in cerebellum NO production between control and treated mice. The present work demonstrates that the physiopathological state of AH involves mitochondrial dysfunction in mouse cerebellum showing the long-lasting effects of acute EtOH exposure in the central nervous system.

Zinc and calcium modulate mitochondrial redox state and morphofunctional integrity

Zinc and calcium have highly interwoven functions that are essential for cellular homeostasis. Here we first present a novel real-time flow cytometric technique to measure mitochondrial redox state and show it is modulated by zinc and calcium, individually and combined. We then assess the interactions of zinc and calcium on mitochondrial H2O2 production, membrane potential (ΔΨm), morphological status, oxidative phosphorylation (OXPHOS), complex I activity, and structural integrity. Whereas zinc at low doses and both cations at high doses individually and combined promoted H2O2 production, the two cations individually did not alter mitochondrial redox state. However, when combined at low and high doses the two cations synergistically suppressed and promoted, respectively, mitochondrial shift to a more oxidized state. Surprisingly, the antioxidants vitamin E and N-acetylcysteine showed pro-oxidant activity at low doses, whereas at high antioxidant doses NAC inhibited OXPHOS and dyscoupled mitochondria. Individually, zinc was more potent than calcium in inhibiting OXPHOS, whereas calcium more potently dissipated the ΔΨm and altered mitochondrial volume and ultrastructure. The two cations synergistically inhibited OXPHOS but antagonistically dissipated ΔΨm and altered mitochondrial volume and morphology. Overall, our study highlights the importance of zinc and calcium in mitochondrial redox regulation and functional integrity. Importantly, we uncovered previously unrecognized bidirectional interactions of zinc and calcium that reveal distinctive foci for modulating mitochondrial function in normal and disease states because they are potentially protective or damaging depending on conditions.

Silencing of uncoupling protein 2 by small interfering RNA aggravates mitochondrial dysfunction in cardiomyocytes under septic conditions

Uncoupling protein 2 (UCP2) regulates the production of mitochondrial reactive oxygen species (ROS) and cellular energy transduction under physiological or pathological conditions. In this study, we aimed to determine whether mitochondrial UCP2 plays a protective role in cardiomyocytes under septic conditions. In order to mimic the septic condition, rat embryonic cardiomyoblast-derived H9C2 cells were cultured in the presence of lipopolysaccharide (LPS) plus peptidoglycan G (PepG) and small interfering RNA (siRNA) against UCP2 (siUCP2) was used to suppress UCP2 expression. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR), western blot analysis, transmission electron microscopy (TEM), confocal microscopy and flow cytometry (FCM) were used to detect the mRNA levels, protein levels, mitochondrial morphology and mitochondrial membrane potential (MMP or ΔΨm) in qualitative and quantitative analyses, respectively. Indicators of cell damage [lactate dehydrogenase (LDH), creatine kinase (CK), interleukin (IL)-6 and tumor necrosis factor (TNF)-α in the culture supernatant] and mitochondrial function [ROS, adenosine triphosphate (ATP) and mitochondrial DNA (mtDNA)] were detected. Sepsis enhanced the mRNA and protein expression of UCP2 in the H9C2 cells, damaged the mitochondrial ultrastructure, increased the forward scatter (FSC)/side scatter (SSC) ratio, increased the CK, LDH, TNF-α and IL-6 levels, and lead to the dissipation of MMP, as well as the overproduction of ROS; in addition, the induction of sepsis led to a decrease in ATP levels and the deletion of mtDNA. The silencing of UCP2 aggravated H9C2 cell damage and mitochondrial dysfunction. In conclusion, our data demonstrate that mitochondrial morphology and funtion are damaged in cardiomyocytes under septic conditions, while the silencing of UCP2 using siRNA aggravated this process, indicating that UCP2 may play a protective role in cardiomyocytes under septic conditions.

Treatment of human cells derived from MERRF syndrome by peptide-mediated mitochondrial delivery

BACKGROUND AIMS

The feasibility of delivering mitochondria using the cell-penetrating peptide Pep-1 for the treatment of MERRF (myoclonic epilepsy with ragged red fibers) syndrome, which is caused by point mutations in the transfer RNA genes of mitochondrial DNA, is examined further using cellular models derived from patients with MERRF syndrome.

METHODS

Homogenesis of mitochondria (wild-type mitochondria) isolated from normal donor cells with about 83.5% preserved activity were delivered into MERRF fibroblasts by Pep-1 conjugation (Pep-1-Mito).

RESULTS

Delivered doses of 52.5 μg and 105 μg Pep-1-Mito had better delivered efficiency and mitochondrial biogenesis after 15 days of treatment. The recovery of mitochondrial function in deficient cells receiving 3 days of treatment with peptide-mediated mitochondrial delivery was comprehensively demonstrated by restoration of oxidative phosphorylation subunits (complex I, III and IV), mitochondrial membrane potential, adenosine triphosphate synthesis and reduction of reactive oxygen species production. The benefits of enhanced mitochondrial regulation depended on the function of foreign mitochondria and not the existence of mitochondrial DNA and can be maintained for at least 21 days with dramatically elongated mitochondrial morphology. In contrast to delivery of wild-type mitochondria, the specific regulation of Pep-1-Mito during MERRF syndrome progression in cells treated with mutant mitochondria was reflected by the opposite performance, with increase in reactive oxygen species production and matrix metalloproteinase activity.

CONCLUSIONS

The present study further illustrates the feasibility of mitochondrial intervention therapy using the novel approach of peptide-mediated mitochondrial delivery and the benefit resulting from mitochondria-organelle manipulation.

The induction of mitochondria-mediated apoptosis in cancer cells by ruthenium(II) asymmetric complexes

Four ruthenium(ii) asymmetric complexes, [Ru(bpy)2(PAIDH)](2+) (bpy = 2,2'-bipyridine, PAIDH = 2-pyridyl-1H-anthra[1,2-d]imidazole-6,11-dione, ), [Ru(phen)2(PAIDH)](2+) (phen = 1,10-phenanthroline, ), [Ru(dmp)2(PAIDH)](2+) (dmp = 4,7-dimethyl-1,10-phenanthroline, ) and [Ru(dip)2(PAIDH)](2+) (dip = 4,7-diphenyl-1,10-phenanthroline, ), have been synthesized and characterized. These complexes displayed potent anti-proliferation activity against various cancer cell lines and had high selectivity between tumor cells and normal cells. HeLa cells exhibited the highest sensitivity to complex , accounting for the greatest cellular uptake. Complex was shown to accumulate preferentially in the mitochondria of HeLa cells and induced apoptosis via the mitochondrial pathway, which involved ROS generation, mitochondrial membrane potential depolarisation, and Bcl-2 and caspase family members activation. These results demonstrated that complex induced cancer cell apoptosis by acting on mitochondrial pathways.

Mitochondria are the primary target in the induction of apoptosis by chiral ruthenium(II) polypyridyl complexes in cancer cells

A series of novel chiral ruthenium(II) polypyridyl complexes (Δ-Ru1, Λ-Ru1, Δ-Ru2, Λ-Ru2, Δ-Ru3, Λ-Ru3) were synthesized and evaluated to determine their antiproliferative activities. Colocalization, inductively coupled plasma mass spectrometry, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay studies showed that these ruthenium(II) complexes accumulated preferentially in the mitochondria and exhibited cytotoxicity against various cancer cells in vitro. The complex Δ-Ru1 is of particular interest because it was found to have half-maximal inhibitory concentrations comparable to those of cisplatin and better activity than cisplatin against a cisplatin-resistant cell line, A549-CP/R. Δ-Ru1 induced alterations in the mitochondrial membrane potential and triggered intrinsic mitochondria-mediated apoptosis in HeLa cells, which involved the regulation of Bcl-2 family members and the activation of caspases. Taken together, these data suggest that Δ-Ru1 may be a novel mitochondria-targeting anticancer agent.

Nanofluidic platform for single mitochondria analysis using fluorescence microscopy

Using nanofluidic channels in PDMS of cross section 500 nm × 2 μm, we demonstrate the trapping and interrogation of individual, isolated mitochondria. Fluorescence labeling demonstrates the immobilization of mitochondria at discrete locations along the channel. Interrogation of mitochondrial membrane potential with different potential sensitive dyes (JC-1 and TMRM) indicates the trapped mitochondria are vital in the respiration buffer. Fluctuations of the membrane potential can be observed at the single mitochondrial level. A variety of chemical challenges can be delivered to each individual mitochondrion in the nanofluidic system. As sample demonstrations, increases in the membrane potential are seen upon introduction of OXPHOS substrates into the nanofluidic channel. Introduction of Ca(2+) into the nanochannels induces mitochondrial membrane permeabilization (MMP), leading to depolarization, observed at the single mitochondrial level. A variety of applications in cancer biology, stem cell biology, apoptosis studies, and high throughput functional metabolomics studies can be envisioned using this technology.

Prediction of liver injury induced by chemicals in human with a multiparametric assay on isolated mouse liver mitochondria

Drug-induced liver injury (DILI) in humans is difficult to predict using classical in vitro cytotoxicity screening and regulatory animal studies. This explains why numerous compounds are stopped during clinical trials or withdrawn from the market due to hepatotoxicity. Thus, it is important to improve early prediction of DILI in human. In this study, we hypothesized that this goal could be achieved by investigating drug-induced mitochondrial dysfunction as this toxic effect is a major mechanism of DILI. To this end, we developed a high-throughput screening platform using isolated mouse liver mitochondria. Our broad spectrum multiparametric assay was designed to detect the global mitochondrial membrane permeabilization (swelling), inner membrane permeabilization (transmembrane potential), outer membrane permeabilization (cytochrome c release), and alteration of mitochondrial respiration driven by succinate or malate/glutamate. A pool of 124 chemicals (mainly drugs) was selected, including 87 with documented DILI and 37 without reported clinical hepatotoxicity. Our screening assay revealed an excellent sensitivity for clinical outcome of DILI (94 or 92% depending on cutoff) and a high positive predictive value (89 or 82%). A highly significant relationship between drug-induced mitochondrial toxicity and DILI occurrence in patients was calculated (p < 0.001). Moreover, this multiparametric assay allowed identifying several compounds for which mitochondrial toxicity had never been described before and even helped to clarify mechanisms with some drugs already known to be mitochondriotoxic. Investigation of drug-induced loss of mitochondrial integrity and function with this multiparametric assay should be considered for integration into basic screening processes at early stage to select drug candidates with lower risk of DILI in human. This assay is also a valuable tool for assessing the mitochondrial toxicity profile and investigating the mechanism of action of new compounds and marketed compounds.

Characterization of functionally distinct mitochondrial subpopulations

Mitochondrial stress results in changes in mitochondrial function, morphology and homeostasis (biogenesis, fission/fusion, mitophagy) and may lead to changes in mitochondrial subpopulations. While flow cytometric techniques have been developed to quantify features of individual mitochondria related to volume, Ca(2+) concentration, mtDNA content, respiratory capacity and oxidative damage, less information is available concerning the identification and characterization of mitochondrial subpopulations, particularly in epithelial cells. Mitochondria from rabbit kidneys were stained with molecular probes for cardiolipin content (nonyl acridine orange, NAO) and membrane potential (tetramethylrhodamine, TMRM) and analyzed using flow cytometry. We validated that side scatter was a better indicator of volume and that as side scatter (SSC) decreased mitochondrial volume increased. Furthermore, those mitochondria with the highest NAO content had greater side scattering and were most highly charged. Mitochondria with average NAO content were of average side scattering and maintained an intermediate charge. Those mitochondria with low NAO content had minimal side scattering and exhibited minimal charge. Upon titration with the uncoupler carbonylcyanide-4-(trifluoromethoxy)-phenylhydrazone (FCCP), it was found that the high NAO content subpopulations were more resistant to uncoupling than lower NAO content populations. Ca(2+)-induced swelling of mitochondria was evaluated using probability binning (PB) analyses of SSC. Interestingly, only 30% of the mitochondria showed changes in response to Ca(2+), which was blocked by cyclosporine A. In addition, the small, high NAO content mitochondria swelled differentially in response to Ca(2+) over time. Our results demonstrate that flow cytometry can be used to identify mitochondrial subpopulations based on high, mid and low NAO content and/or volume/complexity. These subpopulations showed differences in membrane potential, volume, and responses to uncoupling and Ca(2+)-induced swelling.

Elevated skeletal muscle apoptotic signaling following glutathione depletion

Oxidative stress has a well-established role in numerous intracellular signaling pathways, including apoptosis. Glutathione is an important cellular antioxidant and is the most abundant low molecular weight thiol in the cell. Although previous work has shown a link between glutathione and apoptosis, this relationship has not been defined in skeletal muscle. The present investigation examined the effect of glutathione depletion on skeletal muscle apoptotic signaling, and mitochondrial apoptotic-susceptibility. Administration of L: -buthionine-[S,R]-sulfoximine (BSO; 30 mM in drinking water for 10 days) caused glutathione depletion in whole muscle and isolated mitochondria, as well as elevated muscle catalase protein content and reactive oxygen species (ROS) generation. Glutathione depletion was associated with elevated DNA fragmentation, mitochondrial Bax levels, Poly(ADP-ribose) polymerase (PARP) cleavage, and calpain activity; however, caspase-3, -8, and -9 activity were not altered. BSO administration was also associated with higher cytosolic and nuclear protein levels of apoptosis-inducing factor (AIF), but not cytochrome c, second mitochondria-derived activator of caspase (Smac), or endonuclease G (EndoG). In addition, isolated mitochondria from BSO animals demonstrated significantly lower membrane potential, increased Ca(2+)-induced permeability transition pore opening, and greater basal and ROS-induced AIF and cytochrome c release. These results demonstrate that glutathione depletion in skeletal muscle increases caspase-independent signaling, as well as augments mitochondrial-associated apoptotic events to subsequent cell death stimuli.

Glutathione preconditioning ameliorates mitochondria dysfunction during warm pulmonary ischemia-reperfusion injury

OBJECTIVES

Reduced glutathione (GSH) has been shown to improve pulmonary graft preservation. Mitochondrial dysfunction is regarded to be the motor of ischemia-reperfusion injury (IR) in solid organs. We have shown previously that IR induces pulmonary mitochondrial damage. This study elucidates the impact of GSH preconditioning on the integrity and function of pulmonary mitochondria in the setting of warm pulmonary IR.

METHODS

Wistar rats were subjected to control, sham, and to two-study-group conditions (IR30/60 and GSH-IR30/60) receiving IR with or without GSH preconditioning. Rats were anesthetized and received mechanical ventilation. Pulmonary in situ clamping followed by reperfusion generated IR. Mitochondria were isolated from pulmonary tissue. Respiratory chain complexes activities (I-IV) were analyzed by polarography. Mitochondrial viability (Ca2+-induced swelling) and membrane integrity (citrate synthase assay) were determined. Subcellular-fractional cytochrome C-content (Cyt C) was quantified by enzyme-linked immunosorbent assay (ELISA). Mitochondrial membrane potential (ΔΨm) was analyzed by fluorescence-activated cell sorting (FACS) after energizing and uncoupling. Inflammatory activation was determined by myeloperoxidase activity (MPO), matrix-metalloproteinase 9 (MMP-9) activity by gel zymography.

RESULTS

Pulmonary IR significantly reduced mitochondrial viability in combination with ΔΨm hyper-polarization. GSH preconditioning improved mitochondrial viability and normalized ΔΨm. Cyt C was reduced after IR; GSH protected from Cyt C liberation. Respiratory chain complex activities (I, II, III) declined during IR; GSH protected complex II function. GSH also protected from MMP-9 and neutrophil sequestration (P>.05).

CONCLUSIONS

GSH preconditioning is effective to prevent mitochondrial death and improves complex II function during IR, but not mitochondrial membrane stability. GSH-mediated amelioration of ΔΨm hyper-polarization appears to be the key factor of mitochondrial protection.

HIV-1 Tat protein directly induces mitochondrial membrane permeabilization and inactivates cytochrome c oxidase

The Trans-activator protein (Tat) of human immunodeficiency virus (HIV) is a pleiotropic protein involved in different aspects of AIDS pathogenesis. As a number of viral proteins Tat is suspected to disturb mitochondrial function. We prepared pure synthetic full-length Tat by native chemical ligation (NCL), and Tat peptides, to evaluate their direct effects on isolated mitochondria. Submicromolar doses of synthetic Tat cause a rapid dissipation of the mitochondrial transmembrane potential (ΔΨ_m) as well as cytochrome c release in mitochondria isolated from mouse liver, heart, and brain. Accordingly, Tat decreases substrate oxidation by mitochondria isolated from these tissues, with oxygen uptake being initially restored by adding cytochrome c. The anion-channel inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) protects isolated mitochondria against Tat-induced mitochondrial membrane permeabilization (MMP), whereas ruthenium red, a ryanodine receptor blocker, does not. Pharmacologic inhibitors of the permeability transition pore, Bax/Bak inhibitors, and recombinant Bcl-2 and Bcl-XL proteins do not reduce Tat-induced MMP. We finally observed that Tat inhibits cytochrome c oxidase (COX) activity in disrupted mitochondria isolated from liver, heart, and brain of both mouse and human samples, making it the first described viral protein to be a potential COX inhibitor.

Glycine preconditioning to ameliorate pulmonary ischemia reperfusion injury in rats

This study examines the impact of glycine (Gly) preconditioning on ischemia reperfusion (IR)-induced pulmonary mitochondrial injury to research the previously, in pig lungs, demonstrated Gly-dependent amelioration of pulmonary IR injury. IR injury was induced in rat lungs by 30 min pulmonary hilum clamping followed by 60 min reperfusion time. Rats were subjected to controls, shams and two study groups (IR30/60, Gly-IR30/60) receiving 37.5 mg Gly i.v. or not before IR induction. The wet/dry-weight ratio, mitochondria viability (MV), membrane integrity (MI), respiratory chain complex (RCC) activities, mitochondrial membrane potential (ΔΨm) and cytochrome C (Cyt C) content were analysed. In IR30/60, RCC and MV were impaired; Cyt C loss and MI combined with matrix metalloproteinase-9 (MMP-9) activation and ΔΨm alteration were observed when compared with controls. In Gly-IR30/60, complex II function and mitochondrial viability were protected during IR, and MMP-9 activation combined with tissue-water content accumulation and ΔΨm alteration were ameliorated. Cyt C loss, mitochondrial membranes damage, tissue GSH oxidation or neutrophil sequestration was not extenuated in Gly-IR30/60. Gly ameliorates IR-associated mitochondrial dysfunction and decay of viability and normalizes ΔΨm but does not protect from Cyt C liberation and mitochondrial membrane damage. Our data suggest that the previously described effect of Gly preconditioning results at least partially from mitochondrial protection. A dose-finding study is necessary to improve results of Gly preconditioning.

Metallothioneins and energy budget indices in cadmium and copper exposed spiders Agelena labyrinthica in relation to their developmental stage, gender and origin

The aim of our studies was to explain the role of metallothioneins (MTs) in the neutralization of excessive amounts of metals (essential: copper (Cu) and toxic: cadmium (Cd)) and to describe the energy status in metal-exposed spiders Agelena labyrinthica in relation to its developmental stage, gender and origin. Juvenile, female and male spiders were collected from three variously polluted habitats, transferred to the laboratory and exposed to the metals in their diet. Cu and Cd accumulation in the body and exuviae, bioaccumulation factor, percentage of metallothionein positive cells, MT concentration, percentage of cells with depolarized mitochondria, ATP concentration and ADP/ATP ratio were measured and calculated. Cu appeared to be regulated and its excess is eliminated via, among others, the molting process, while Cd was rather accumulated by the spiders. The level of MTs increased significantly mainly in females exposed to both metals, irrespectively of the pollution degree of their site of origin, indicating a defensive role of the proteins. In general, even if both the MT level and the energy status indices were positively correlated with Cd and Cu concentrations in the spider body, the energy status of A. labyrinthica did not seem disturbed.

Ischemia-reperfusion injury-induced pulmonary mitochondrial damage

BACKGROUND

Mitochondrial dysfunction is a key factor in solid organ ischemia-reperfusion (IR) injury. Impaired mitochondrial integrity predisposes to cellular energy depletion, free radical generation, and cell death. This study analyzed mitochondrial damage induced by warm pulmonary IR.

METHODS

Anesthetized Wistar rats received mechanical ventilation. Pulmonary clamping was followed by reperfusion to generate IR injury. Rats were subjected to control, sham, and to 2 study group conditions: 30 minutes of ischemia without reperfusion (IR30/0), or ischemia followed by 60 minutes of reperfusion (IR30/60). Pulmonary edema was quantified by wet/dry-weight ratio. Polarography determined activities of respiratory chain complexes. Mitochondrial viability was detected by using Ca(2+)-induced swelling, and integrity by citrate synthase assay. Enzyme-linked immunosorbent assay determined cytochrome C content. Mitochondrial membrane potential (ΔΨm) stability was analyzed by flow cytometry using JC1, inflammation by myeloperoxidase (MPO) activity, and matrix-metalloproteinase-9 (MMP-9) activity by gel zymography, respectively.

RESULTS

In IR30/60 rats, tissue water content was elevated from 80.6 % (sham) to 86.9%. After ischemia, ΔΨm showed hyperpolarization and rapid decline after uncoupling compared with controls. IR, but not ischemia alone, impaired respiratory chain function complexes I, II and III (p < 0.05). Mitochondrial viability (p < 0.001) and integrity (p < 0.01) was impaired after ischemia and IR, followed by mitochondrial cytochrome C loss (p < 0.05). Increased activation of MPO (p < 0.01) and MMP-9 (p < 0.001) was induced by reperfusion after ischemia.

CONCLUSIONS

Ischemia-related ΔΨm hyper-polarization induces reperfusion-associated mitochondrial respiratory chain dysfunction in parallel with tissue inflammation and degradation. Controlling ΔΨm during ischemia might reduce IR injury.

Use of human cancer cell lines mitochondria to explore the mechanisms of BH3 peptides and ABT-737-induced mitochondrial membrane permeabilization

Current limitations of chemotherapy include toxicity on healthy tissues and multidrug resistance of malignant cells. A number of recent anti-cancer strategies aim at targeting the mitochondrial apoptotic machinery to induce tumor cell death. In this study, we set up protocols to purify functional mitochondria from various human cell lines to analyze the effect of peptidic and xenobiotic compounds described to harbour either Bcl-2 inhibition properties or toxic effects related to mitochondria. Mitochondrial inner and outer membrane permeabilization were systematically investigated in cancer cell mitochondria versus non-cancerous mitochondria. The truncated (t-) Bid protein, synthetic BH3 peptides from Bim and Bak, and the small molecule ABT-737 induced a tumor-specific and OMP-restricted mitochondrio-toxicity, while compounds like HA-14.1, YC-137, Chelerythrine, Gossypol, TW-37 or EM20-25 did not. We found that ABT-737 can induce the Bax-dependent release of apoptotic proteins (cytochrome c, Smac/Diablo and Omi/HtrA2 but not AIF) from various but not all cancer cell mitochondria. Furthermore, ABT-737 addition to isolated cancer cell mitochondria induced oligomerization of Bax and/or Bak monomers already inserted in the mitochondrial membrane. Finally immunoprecipatations indicated that ABT-737 induces Bax, Bak and Bim desequestration from Bcl-2 and Bcl-xL but not from Mcl-1L. This study investigates for the first time the mechanism of action of ABT-737 as a single agent on isolated cancer cell mitochondria. Hence, this method based on MOMP (mitochondrial outer membrane permeabilization) is an interesting screening tool, tailored for identifying Bcl-2 antagonists with selective toxicity profile against cancer cell mitochondria but devoid of toxicity against healthy mitochondria.

Mitochondria as a source of mechanical signals in cardiomyocytes

AIMS

The myofibrillar and nuclear compartments in cardiomyocytes are known to be sensitive to extracellular mechanical stimuli. Recently, we have shown that alterations in the mitochondrial ionic balance in cells in situ are associated with considerably increased mitochondrial volume. Theoretically, this swelling of mitochondria could impose mechanical constraints on the myofibrils and nuclei in their vicinity. Thus, we studied whether modulation of mitochondrial volume in cardiomyocytes in situ has a mechanical effect on the myofibrillar and nuclear compartments.

METHODS AND RESULTS

We used the measurement of passive force developed by saponin-permeabilized mouse ventricular fibres as a sensor for compression of the myofibrils. Osmotic compression induced by dextran caused an increase in passive force. Similarly, mitochondrial swelling induced by drugs that alter ionic homeostasis (alamethicin and propranolol) markedly augmented passive force (confirmed by confocal microscopy). Diazoxide, a mitochondrial ATP-sensitive potassium channel opener known to cause moderate mitochondrial swelling, also increased passive force (by 28 +/- 5% at 10% stretch, P < 0.01). This effect was completely blocked by 5-hydroxydecanoate (5-HD), a putative specific inhibitor of these channels. Mitochondrial swelling induced by alamethicin and propranolol led to significant nuclear deformation, which was visualized by confocal microscopy. Furthermore, diazoxide decreased nuclear volume, calculated using three-dimensional reconstructed images, in a 5-HD-dependent manner by 12 +/- 2% (P < 0.05). This corresponds to an increase in intracellular pressure of 2.1 +/- 0.3 kPa.

CONCLUSION

This study is the first to demonstrate that mitochondria are able to generate internal pressure, which can mechanically affect the morphological and functional properties of intracellular organelles.

Sorting of Leishmania-bearing dendritic cells reveals subtle parasite-induced modulation of host-cell gene expression

Once in the mouse skin, Leishmania (L) amazonensis amastigotes are hosted by professional mononuclear phagocytes such as dendritic cells (DCs). When monitored after parasite inoculation, the frequency of amastigote-hosting DCs is very low (<1%) in both the skin and skin-draining lymph nodes. Therefore, we designed and validated an efficient procedure to purify live amastigotes-hosting DCs with the objective to facilitate quantitative and qualitative analysis of such rare cells. To this end, a L. amazonensis transgenic parasite expressing DsRed2 fluorescent protein was generated and added to mouse bone marrow-derived DC cultures. Then, a high speed sorting procedure, performed in BSL-2 containment, was setup to pick out only DCs hosting live amastigotes. This study reveals, for the first time, a unique transcript pattern from sorted live amastigotes-hosting DCs that would have been undetectable in unsorted samples. It was indeed possible to highlight a significant and coordinated up-regulation of L-arginine transporter and arginase2 transcripts in Leishmania-hosting DCs compared to un-parasitized DCs. These results indicate that arginine catabolism for polyamine generation is dominating over L-arginine catabolism for NO generation. In conclusion, this approach provides a powerful method for further characterisation, of amastigote-hosting DCs in the skin and the skin-draining lymph nodes.

Safranine O as a fluorescent probe for mitochondrial membrane potential studied on the single particle level and in suspension

The permeant cationic dye safranine O is often used to measure mitochondrial membrane potential due to the dependence of both its absorption and fluorescence on mitochondrial energization, which causes its oligomerization inside mitochondria. In the present study we have used fluorescent correlation spectroscopy (FCS) to record the fluorescence changes on a micro level, i.e. under conditions permitting resolution of contributions from single particles (molecules of the dye and stained mitochondria). We have shown that the decrease in fluorescence signal from a suspension of energized mitochondria stained with a high safranine concentration (10 microM) is explained by the decrease in dye concentration in the medium in parallel with the accumulation of the dye inside the mitochondria, which results in fluorescence quenching. With 1 microM safranine O, the fluorescence rise after energization is caused by the accumulation of the dye up to a level not sufficient for full fluorescence quenching and also by the higher intensity of mitochondrial fluorescence on immersion of the dye in the hydrophobic milieu. Besides the estimation of the inner mitochondrial membrane potential, this approach also assesses the concentration of fluorescent particles. The non-monotonic dependence of the FCS parameter 1/G(tau-->0) on the concentration of mitochondrial protein suggests heterogeneity of the system with respect to fluorescence of particles. An important advantage of the described method is its high sensitivity, which allows measurements with low concentrations and quantities of mitochondrial protein in samples (less than 10 microg).

Guidelines for the use and interpretation of assays for monitoring cell death in higher eukaryotes

Cell death is essential for a plethora of physiological processes, and its deregulation characterizes numerous human diseases. Thus, the in-depth investigation of cell death and its mechanisms constitutes a formidable challenge for fundamental and applied biomedical research, and has tremendous implications for the development of novel therapeutic strategies. It is, therefore, of utmost importance to standardize the experimental procedures that identify dying and dead cells in cell cultures and/or in tissues, from model organisms and/or humans, in healthy and/or pathological scenarios. Thus far, dozens of methods have been proposed to quantify cell death-related parameters. However, no guidelines exist regarding their use and interpretation, and nobody has thoroughly annotated the experimental settings for which each of these techniques is most appropriate. Here, we provide a nonexhaustive comparison of methods to detect cell death with apoptotic or nonapoptotic morphologies, their advantages and pitfalls. These guidelines are intended for investigators who study cell death, as well as for reviewers who need to constructively critique scientific reports that deal with cellular demise. Given the difficulties in determining the exact number of cells that have passed the point-of-no-return of the signaling cascades leading to cell death, we emphasize the importance of performing multiple, methodologically unrelated assays to quantify dying and dead cells.

Mitochondrial function and apoptotic susceptibility in aging skeletal muscle

During aging, skeletal muscle undergoes sarcopenia, a condition characterized by a loss of muscle cell mass and alterations in contractile function. The origin of these decrements is unknown, but evidence suggests that they can be partly attributed to mitochondrial dysfunction. To characterize the nature of this dysfunction, we investigated skeletal muscle contractile properties, subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondrial biogenesis and function, as well as apoptotic susceptibility in young (6 months old) and senescent (36 months old) Fischer 344 Brown Norway rats. Muscle mass and maximal force production were significantly lower in the 36-month group, which is indicative of a sarcopenic phenotype. Furthermore, contractile activity in situ revealed greater fatigability in the 36-month compared to the 6-month animals. This decrement could be partially accounted for by a 30% lower mitochondrial content in fast-twitch muscle from 36-month animals, as well as lower protein levels of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha. Enzyme activities and glutamate-induced oxygen consumption rates in isolated SS and IMF mitochondria were similar between age groups. However, mitochondrial reactive oxygen species (ROS) production during state 3 respiration was approximately 1.7-fold greater in mitochondria isolated from 36-month compared to 6-month animals, and was accompanied by a 1.8-fold increase in the DNA repair enzyme 8-oxoguanine glycosylase 1 in fast-twitch muscle. Basal rates of release of cytochrome c and endonuclease G in SS mitochondria were 3.5- to 7-fold higher from senescent animals. These data suggest that the age-related sarcopenia and muscle fatigability are associated with enhanced ROS production, increased mitochondrial apoptotic susceptibility and reduced transcriptional drive for mitochondrial biogenesis.

Polyphyllin D induces mitochondrial fragmentation and acts directly on the mitochondria to induce apoptosis in drug-resistant HepG2 cells

We previously showed that polyphyllin D (PD) produced a stronger apoptotic effect in R-HepG2 with multi-drug resistance (MDR) than that in its parent HepG2 cells without MDR. In this study, PD was found to elicit mitochondrial fragmentation in live cells by using total internal reflection fluorescence microscopy (TIRFM). When mitochondria were isolated and treated directly with PD, a stronger swelling, deeper transmembrane depolarization, and more apoptosis-inducing factor (AIF) release were observed from the mitochondria of R-HepG2 than that of HepG2. These observations suggest that PD is a potent anti-cancer agent that bypasses MDR and elicits apoptosis via mitochondrial injury.

Evaluating mitochondrial membrane potential in cells

Permeant cationic fluorescent probes are widely employed to monitor mitochondrial transmembrane potential and its changes. The application of such potential-dependent probes in conjunction with both fluorescence microscopy and fluorescence spectroscopy allows the monitoring of mitochondrial membrane potential in individual living cells as well as in large population of cells. These approaches to the analysis of membrane potential is of extremely high value to obtain insights into both the basic energy metabolism and its dysfunction in pathologic cells. However, the use of fluorescent molecules to probe biological phenomena must follow the awareness of some principles of fluorescence emission, quenching, and quantum yield since it is a very sensitive tool, but because of this extremely high sensitivity it is also strongly affected by the environment. In addition, the instruments used to monitor fluorescence and its changes in biological systems have also to be employed with cautions due to technical limits that may affect the signals. We have therefore undertaken to review the most currently used analytical methods, providing a summary of practical tips that should precede data acquisition and subsequent analysis. Furthermore, we discuss the application and feasibility of various techniques and discuss their respective strength and weakness.

CE-LIF analysis of mitochondria using uncoated and dynamically coated capillaries

This report is the first demonstration of the use of uncoated and dynamically coated capillaries for the separation of individual mitochondria via CE. Currently, the analysis of individual mitochondria relies upon fused-silica capillaries coated with a hydrophilic polymer (e.g. poly(acryloylaminopropanol)), which is used to minimize adsorption to the capillary surface. Both uncoated fused-silica capillaries and 0.2% w/w poly(vinyl alcohol) dynamic coating solutions are used to successfully analyze isolated individual mitochondrial particles using CE-LIF. While it was possible to separate mouse liver mitochondria on an uncoated capillary, rat liver mitochondria proved to have strong adsorption characteristics that only allowed them to be adequately separated with a PVA dynamic coating or a poly(acryloylaminopropanol) (AAP) capillary. The possible causes for this adsorption are analyzed and discussed. This study shows that uncoated and dynamically coated capillaries can be used in place of AAP-coated capillaries to analyze mitochondria and suggests the use of these capillaries for the analysis of other organelles, offering a greatly simplified method for the analysis of individual organelles.

Methods for the assessment of mitochondrial membrane permeabilization in apoptosis

Mitochondrial membrane permeabilization (MMP) is considered as the "point-of-no-return" in numerous models of programmed cell death. Indeed, mitochondria determine the intrinsic pathway of apoptosis, and play a major role in the extrinsic route as well. MMP affects the inner and outer mitochondrial membranes (IM and OM, respectively) to a variable degree. OM permeabilization culminates in the release of proteins that normally are confined in the mitochondrial intermembrane space (IMS), including caspase activators (e.g. cytochrome c) and caspase-independent death effectors (e.g. apoptosis-inducing factor). Partial IM permeabilization disrupts mitochondrial ion and volume homeostasis and dissipates the mitochondrial transmembrane potential (DeltaPsi(m)). The assessment of early mitochondrial alterations allows for the identification of cells that are committed to die but have not displayed yet the apoptotic phenotype. Several techniques to measure MMP by cytofluorometry and fluorescence microscopy have been developed. Here, we summarize the currently available methods for the detection of MMP, and provide a comparative analysis of these techniques.