Mitochondrial Reactive Oxygen Species Generation and Calcium Increase Induced by Visible Light in Astrocytes

Male Infertility and Oxidative Stress: A Focus on the Underlying Mechanisms

Reactive oxygen species (ROS) play a critical role in defining the functional competence of human spermatozoa. When generated in moderate amounts, ROS promote sperm capacitation by facilitating cholesterol efflux from the plasma membrane, enhancing cAMP generation, inducing cytoplasmic alkalinization, increasing intracellular calcium levels, and stimulating the protein phosphorylation events that drive the attainment of a capacitated state. However, when ROS generation is excessive and/or the antioxidant defences of the reproductive system are compromised, a state of oxidative stress may be induced that disrupts the fertilizing capacity of the spermatozoa and the structural integrity of their DNA. This article focusses on the sources of ROS within this system and examines the circumstances under which the adequacy of antioxidant protection might become a limiting factor. Seminal leukocyte contamination can contribute to oxidative stress in the ejaculate while, in the germ line, the dysregulation of electron transport in the sperm mitochondria, elevated NADPH oxidase activity, or the excessive stimulation of amino acid oxidase action are all potential contributors to oxidative stress. A knowledge of the mechanisms responsible for creating such stress within the human ejaculate is essential in order to develop better antioxidant strategies that avoid the unintentional creation of its reductive counterpart.

Short-wave Infrared Neural Stimulation Drives Graded Sciatic Nerve Activation Across A Continuum of Wavelengths

Infrared neural stimulation (INS) is an optical stimulation technique which uses coherent light to stimulate nerves and neurons and which shows increased spatial selectivity compared to electrical stimulation. This could improve deep brain, high channel count, or vagus nerve stimulation. In this study, we seek to understand the wavelength dependence of INS in the near-infrared optical window. Rat sciatic nerves were excised ex vivo and stimulated with wavelengths between 700 and 900 nm. Recorded compound nerve action potentials (CNAPs) showed that stimulation was maximized in the 700 nm window despite comparable laser power levels across wavelengths. Computational models demonstrated that wavelength-based activation dependencies were not a result of passive optical properties. This data demonstrates that INS is both wavelength and power level dependent, which inform stimulation systems to actively target neural microcircuits in humans.

Comparing the performance of mScarlet-I, mRuby3, and mCherry as FRET acceptors for mNeonGreen

Förster Resonance Energy Transfer (FRET) has become an immensely powerful tool to profile intra- and inter-molecular interactions. Through fusion of genetically encoded fluorescent proteins (FPs) researchers have been able to detect protein oligomerization, receptor activation, and protein translocation among other biophysical phenomena. Recently, two bright monomeric red fluorescent proteins, mRuby3 and mScarlet-I, have been developed. These proteins offer much improved physical properties compared to previous generations of monomeric red FPs that should help facilitate more general adoption of Green/Red FRET. Here we assess the ability of these two proteins, along with mCherry, to act as a FRET acceptor for the bright, monomeric, green-yellow FP mNeonGreen using intensiometric FRET and 2-photon Fluorescent Lifetime Imaging Microscopy (FLIM) FRET techniques. We first determined that mNeonGreen was a stable donor for 2-photon FLIM experiments under a variety of imaging conditions. We then tested the red FP's ability to act as FRET acceptors using mNeonGreen-Red FP tandem construct. With these constructs we found that mScarlet-I and mCherry are able to efficiently FRET with mNeonGreen in spectroscopic and FLIM FRET. In contrast, mNeonGreen and mRuby3 FRET with a much lower efficiency than predicted in these same assays. We explore possible explanations for this poor performance and determine mRuby3's protein maturation properties are a major contributor. Overall, we find that mNeonGreen is an excellent FRET donor, and both mCherry and mScarlet-I, but not mRuby3, act as practical FRET acceptors, with the brighter mScarlet-I out performing mCherry in intensiometric studies, but mCherry out performing mScarlet-I in instances where consistent efficiency in a population is critical.

Azulene-Derived Fluorescent Probe for Bioimaging: Detection of Reactive Oxygen and Nitrogen Species by Two-Photon Microscopy

Two-photon fluorescence microscopy has become an indispensable technique for cellular imaging. Whereas most two-photon fluorescent probes rely on well-known fluorophores, here we report a new fluorophore for bioimaging, namely azulene. A chemodosimeter, comprising a boronate ester receptor motif conjugated to an appropriately substituted azulene, is shown to be an effective two-photon fluorescent probe for reactive oxygen species, showing good cell penetration, high selectivity for peroxynitrite, no cytotoxicity, and excellent photostability.

Mouse embryonic stem cell-derived cardiomyocytes cease to beat following exposure to monochromatic light: association with increased ROS and loss of calcium transients

We earlier established the mouse embryonic stem (ES) cell "GS-2" line expressing enhanced green fluorescent protein (EGFP) and have been routinely using it to understand the molecular regulation of differentiation into cardiomyocytes. During such studies, we made a serendipitous discovery that functional cardiomyocytes derived from ES cells stopped beating when exposed to blue light. We observed a gradual cessation of contractility within a few minutes, regardless of wavelength (nm) ranges tested: blue (~420-495), green (~510-575), and red (~600-700), with green light manifesting the strongest impact. Following shifting of cultures back into the incubator (darkness), cardiac clusters regained beatings within a few hours. The observed light-induced contractility-inhibition effect was intrinsic to cardiomyocytes and not due to interference from other cell types. Also, this was not influenced by any physicochemical parameters or intracellular EGFP expression. Interestingly, the light-induced cardiomyocyte contractility inhibition was accompanied by increased intracellular reactive oxygen species (ROS), which could be abolished in the presence of N-acetylcysteine (ROS quencher). Besides, the increased intracardiomyocyte ROS levels were incidental to the inhibition of calcium transients and suppression of mitochondrial activity, both being essential for sarcomere function. To the best of our knowledge, ours is the first report to demonstrate the monochromatic light-mediated inhibition of contractions of cardiomyocytes with no apparent loss of cell viability and contractility. Our findings have implications in cardiac cell biology context in terms of 1) mechanistic insights into light impact on cardiomyocyte contraction, 2) potential use in laser beam-guided (cardiac) microsurgery, photo-optics-dependent medical diagnostics, 3) transient cessation of hearts during coronary artery bypass grafting, and 4) functional preservation of hearts for transplantation.

Redox-Responsive Fluorescent Polycarbonates Based on Selenide for Chemotherapy of Triple-Negative Breast Cancer

Transient increase of reactive oxygen species (ROS) is vital for some physiological processes, whereas the chronic and sustained high ROS level is usually implicated in the inflammatory diseases and cancers. Herein, we report the innovative redox-responsive theranostic micellar nanoparticles that are able to load anticancer drugs through coordination and hydrophobic interaction and to fluorescently monitor the intracellular redox status. The nanoparticles were formed by the amphiphilic block copolymers composed of a PEG segment and a selenide-containing hydrophobic polycarbonate block with a small fraction of coumarin-based chromophore. Under the alternative redox stimulation that might be encountered in the physiological process of some healthy cells, these nanoparticles underwent the reversible changes in size, morphology, and fluorescence intensity. With the assistance of small model compounds, we clarified the chemistry behind these changes, that is, the redox triggered reversible transformation between selenide and selenoxide. Upon the monotonic oxidation similar to the sustained high ROS level of cancer cells, the nanoparticles could be disrupted completely, which was accompanied by the drastic decrease in fluorescence. Cisplatin and paclitaxel were simultaneously coloaded in the nanoparticles with a moderate efficacy, and the coordination between selenide and platinum improved the stability of the drug-loaded nanoparticles against dilution. The naked nanoparticles are cytocompatible, whereas the dual drug-loaded nanoparticles exhibited a concentration dependent and synergistic cytotoxicity to triple-negative breast cancer (TNBC) cells. Of importance, the drug-loaded nanoparticles are much more toxic to TNBC cells than to normal cells due in part to ROS overproduction in the former cell lines.

Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3-OHM and AFMK in RBA1 astrocytes

Cyclic 3-hydroxymelatonin (C3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria-targeted protection beyond as a mitochondrial antioxidant during ionomycin-induced mitochondrial Ca²⁺ (mCa²⁺ ) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time-lapse digital imaging microscopy, this study investigated whether C3-OHM and AFMK also provide mitochondrial levels of protection during ionomycin-induced mCa²⁺ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3-OHM and AFMK prevented specifically mCa²⁺ -mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS-mediated depolarization of mitochondrial membrane potential (△Ψ_m ) and permanent lethal opening of the MPT (p-MPT). The antioxidative effects of AFMK, however, were less potent than that of C3-OHM. Whether C3-OHM and AFMK targeted directly the MPT was investigated under a condition of "oxidation free-Ca²⁺ stress" using a classic antioxidant vitamin E to remove mCa²⁺ -mediated mROS stress and the potential antioxidative effects of C3-OHM and AFMK. Intriguingly, two compounds still effectively postponed "oxidation free-Ca²⁺ stress"-mediated depolarization of △Ψ_m and p-MPT. Measurements using a MPT pore-specific indicator Calcein further identified that C3-OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t-MPT), a critical mechanism to reduce overloaded mROS and mCa²⁺ . These multiple layers of mitochondrial protection provided by C3-OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS- and mCa²⁺ -mediated MPT-associated apoptotic stresses and may provide therapeutic benefits against astrocyte-mediated neurodegeneration in the CNS.

Multiwavelength Light-Responsive Au/B-TiO2 Janus Micromotors

Conventional photocatalytic micromotors are limited to the use of specific wavelengths of light due to their narrow light absorption spectrum, which limits their effectiveness for applications in biomedicine and environmental remediation. We present a multiwavelength light-responsive Janus micromotor consisting of a black TiO₂ microsphere asymmetrically coated with a thin Au layer. The black TiO₂ microspheres exhibit absorption ranges between 300 and 800 nm. The Janus micromotors are propelled by light, both in H₂O₂ solutions and in pure H₂O over a broad range of wavelengths including UV, blue, cyan, green, and red light. An analysis of the particles' motion shows that the motor speed decreases with increasing wavelength, which has not been previously realized. A significant increase in motor speed is observed when exploiting the entire visible light spectrum (>400 nm), suggesting a potential use of solar energy, which contains a great portion of visible light. Finally, stop-go motion is also demonstrated by controlling the visible light illumination, a necessary feature for the steerability of micro- and nanomachines.

Synchronism in mitochondrial ROS flashes, membrane depolarization and calcium sparks in human carcinoma cells

Mitochondria are major producers of reactive oxygen species (ROS) in many cells including cancer cells. However, complex interrelationships between mitochondrial ROS (mitoROS), mitochondrial membrane potential (ΔΨm) and Ca²⁺ are not completely understood. Using human carcinoma cells, we further highlight biphasic ROS dynamics: - gradual mitoROS increase followed by mitoROS flash. Also, we demonstrate heterogeneity in rates of mitoROS generation and flash initiation time. Comparing mitochondrial and near-extra-mitochondrial signals, we show that mechanisms of mitoROS flashes in single mitochondria, linked to mitochondrial permeability transition pore opening (ΔΨm collapse) and calcium sparks, may involve flash triggering by certain levels of external ROS released from the same mitochondria. In addition, mitochondria-mitochondria interactions can produce wave propagations of mitoROS flashes and ΔΨm collapses in cancer cells similar to phenomena of ROS-induced ROS release (RIRR). Our data suggest that in cancer cells RIRR, activation of mitoROS flashes and mitochondrial depolarization may involve participation of extramitochondrial-ROS produced either by individual mitochondria and/or by neighboring mitochondria. This could represent general mechanisms in ROS-ROS signaling with suggested role in both mitochondrial and cellular physiology and signaling.

Bystander effects elicited by single-cell photo-oxidative blue-light stimulation in retinal pigment epithelium cell networks

‘Bystander effect’ refers to the induction of biological effects in cells not directly targeted. The retinal pigment epithelium consists of hexagonal cells, forming a monolayer interconnected by gap junctions (GJs). Oxidative stress initiated in an individual cell by photostimulation (488 nm) triggered changes in reactive oxygen species (ROS), Ca²⁺ and mitochondrial membrane potential (ψ_m). The Ca²⁺ signal was transmitted to neighboring cells slowly and non-uniformly; the ROS signal spread fast and radially. Increased Ca²⁺ levels were associated with a loss in ψ_m. GJ blockers prevented the spreading of the Ca²⁺, but not the ROS-related signal. The GJ-mediated Ca²⁺ wave was associated with cell death by 24 h, requiring endoplasmic reticulum–mitochondria Ca²⁺ transfer. Ensuing cell death was correlated with baseline Ca²⁺ levels, and baseline Ca²⁺ levels were correlated with pigmentation. Hence, local oxidative stress in a donor cell can trigger changes in certain connected recipient cells, a signal that required GJ communication and an ROS-Ca²⁺ dual-hit. Finally, damage apparently occurred in susceptible cells, which correlated with baseline Ca²⁺ levels.

A reversible ratiometric two-photon lysosome-targeted probe for real-time monitoring of pH changes in living cells

A reversible ratiometric two-photon lysosome-targeted probe that can monitor real-time pH changes in living cells.

A Golgi-localized two-photon probe for imaging zinc ions

We report a two-photon fluorescent probe which shows a strong two photon excited fluorescence enhancement in response to Zn(2+), easy loading into the cells, Golgi-localizing ability, low cytotoxicity, and high photostability. Two-photon microscopy imaging revealed that this probe allows for real-time monitoring of the changes in Golgi Zn(2+) as well as their 3D distributions in live cells and tissues.

A ratiometric two-photon probe for quantitative imaging of mitochondrial pH values

Mitochondrial pH (pHmito) is known to be alkaline (near 8.0) and has emerged as a potential factor for mitochondrial function and disorder. We have developed a ratiometric two-photon probe (CMP1) for quantitative analysis of pHmito in live cells and tissues. This probe is designed to function by controlling the intramolecular charge transfer from 2-naphthol, having an ideal pKa value (7.86 ± 0.05) in the cells to monitor pHmito. This transition results in a marked yellow to red emission color change in response to pH alterations from 6.0 to 9.0. CMP1 exhibits easy loading, selective and robust staining ability of mitochondria, low cytotoxicity, and bright two-photon excited fluorescence in situ, thereby allowing quantitative imaging of the pHmito in live cells and tissues. The ratiometric TPM imaging clearly reveals that subcellular distribution of the pHmito values is heterogeneous, with the pHmito values in the perinuclear region being higher than those at the periphery of the cells. The changes of pHmito values on carbonyl cyanide m-chlorophenyl hydrazone (CCCP) treatment and autophagic processes were also investigated along with their morphological alterations at specific subcellular positions. We also used CMP1 to visualize the pHmito values of Parkinson's disease model astrocytes as well as living hippocampal tissues. Our results demonstrate that CMP1 will be useful as a quantitative imaging probe to study pHmito in biomedical research.

Recent advances in hydrogen peroxide imaging for biological applications

Mounting evidence supports the role of hydrogen peroxide (H2O2) in physiological signaling as well as pathological conditions. However, the subtleties of peroxide-mediated signaling are not well understood, in part because the generation, degradation, and diffusion of H2O2 are highly volatile within different cellular compartments. Therefore, the direct measurement of H2O2 in living specimens is critically important. Fluorescent probes that can detect small changes in H2O2 levels within relevant cellular compartments are important tools to study the spatial dynamics of H2O2. To achieve temporal resolution, the probes must also be photostable enough to allow multiple readings over time without loss of signal. Traditional fluorescent redox sensitive probes that have been commonly used for the detection of H2O2 tend to react with a wide variety of reactive oxygen species (ROS) and often suffer from photostablilty issues. Recently, new classes of H2O2 probes have been designed to detect H2O2 with high selectivity. Advances in H2O2 measurement have enabled biomedical scientists to study H2O2 biology at a level of precision previously unachievable. In addition, new imaging techniques such as two-photon microscopy (TPM) have been employed for H2O2 detection, which permit real-time measurements of H2O2 in vivo. This review focuses on recent advances in H2O2 probe development and optical imaging technologies that have been developed for biomedical applications.

Are the mitochondrial respiratory complexes blocked by NO the targets for the laser and LED therapy?

Effects of laser (442 and 532 nm) and light-emitting diode (LED) (650 nm) radiation on mitochondrial respiration and mitochondrial electron transport rate (complexes II-III and IV) in the presence of nitric oxide (NO) were investigated. It was found that nitric oxide (300 nM-10 μM) suppresses mitochondrial respiration. Laser irradiation of mitochondria (442 nm, 3 J cm(-2)) partly restored mitochondrial respiration (approximately by 70 %). Irradiation with green laser (532 nm) or red LED (650 nm) in the same dose had no reliable effect. Evaluation of mitochondrial electron transport rate in complexes II-III and IV and effects of nitric oxide demonstrated almost similar sensitivity of complex II-III and IV to NO, with approximately 50 % inhibition at NO concentration of 3 μM. Subsequent laser or LED irradiation (3 J cm(-2)) showed partial recovery of electron transport only in complex IV and only under irradiation with blue light (442 nm). Our results support the hypothesis of the crucial role of cytochrome c oxidase (complex IV) in photoreactivation of mitochondrial respiration suppressed by NO.

Impedance-based cell culture platform to assess light-induced stress changes with antagonist drugs using retinal cells

This Article describes an unprecedented, simple, and real-time in vitro analytical tool to measure the luminous effect on the time responses function of retinal ganglion cells (RGC-5) by electric cell substrate impedance sensing (ECIS) system. The ECIS system was used for the continuous measurement of different color light-induced effects on the response of cells that exposed to protective drugs. The measurement suggests that the association of photo-oxidative stress was mediated by reactive oxygen species (ROS), which plays a critical role that leads to cell stress, damages, and retinopathy, resulting in eye degenerative diseases. Continuous light radiation caused time-dependent decline of RGC-5 response and resulted in photodamage within 10 h due to adenosine 5'-triphosphate depletion and increased ROS level, which is similar to in vivo photodamage. The ECIS results were correlated with standard cell viability assay. ECIS is very helpful to determine the protective effects of analyzed drugs such as β-carotene, quercetin, agmatine, and glutathione in RGC-5 cells, and the maximum drug activity of nontoxic safer drug concentrations was found to be 0.25, 0.25, 0.25, and 1.0 mM, respectively. All drugs show protection against light radiation toxicity in a dose-dependent manner; the most effective drug was found to be glutathione. The proposed system identifies the phototoxic effects in RGC-5 and provides high throughput drug screening for photo-oxidative stress during early stages of drug discovery. This study is convenient and potential enough for the direct measurements of the photoprotective effect in vitro and would be of broad interest in the field of therapeutics.

Dual phases of respiration chain defect-augmented mROS-mediated mCa 2+ stress during oxidative insult in normal and ρ 0 RBA1 astrocytes

Mitochondrial respiratory chain (RC) deficits, resulting in augmented mitochondrial ROS (mROS) generation, underlie pathogenesis of astrocytes. However, mtDNA-depleted cells (ρ⁰) lacking RC have been reported to be either sensitive or resistant to apoptosis. In this study, we sought to determine the effects of RC-enhanced mitochondrial stress following oxidative insult. Using noninvasive fluorescence probe-coupled laser scanning imaging microscopy, the ability to resist oxidative stress and levels of mROS formation and mitochondrial calcium (mCa²⁺) were compared between two different astrocyte cell lines, control and ρ⁰ astrocytes, over time upon oxidative stress. Our results showed that the cytoplasmic membrane becomes permeated with YO-PRO-1 dye at 150 and 130 minutes in RBA-1 and ρ⁰ astrocytes, respectively. In contrast to RBA-1, 30 minutes after 20 mM H₂O₂ exposure, ρ⁰ astrocytes formed marked plasma membrane blebs, lost the ability to retain Mito-R, and showed condensation of nuclei. Importantly, H₂O₂-induced ROS and accompanied mCa²⁺ elevation in control showed higher levels than ρ⁰ at early time point but vice versa at late time point. Our findings underscore dual phase of RC-defective cells harboring less mitochondrial stress due to low RC activity during short-term oxidative stress but augmented mROS-mediated mCa²⁺ stress during severe oxidative insult.

Long-term Aβ exposure augments mCa2+-independent mROS-mediated depletion of cardiolipin for the shift of a lethal transient mitochondrial permeability transition to its permanent mode in NARP cybrids: a protective targeting of melatonin

Mitochondrial dysfunction is a hallmark of amyloid β-peptide (Aβ)-induced neurodegeneration of Alzheimer's disease (AD). This study investigated whether mtDNA T8993G mutation-induced complex V inhibition, clinically associated with neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP), is a potential risk factor for AD and the pathological link for long-term exposure of Aβ-induced mitochondrial toxicity and apoptosis in NARP cybrids. Using noninvasive fluorescence probe-coupled laser scanning imaging microscopy and NARP cybrids harboring 98% mutant genes along with its parental 143B osteosarcoma cells, we demonstrated that Aβ-augmented mitochondrial Ca(2+) (mCa(2+))-independent mitochondrial reactive oxygen species (mROS) formation for a cardiolipin (CL, a major mitochondrial protective phospholipid)-dependent lethal modulation of the mitochondrial permeability transition (MPT). Aβ augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize mitochondrial membrane potential (∆Ψ(m)) and reduce mCa(2+) stress. Aβ-augmented mROS oxidized and depleted CL, thereby enhances mitochondrial fission and movement retardation, which promoted the NARP-augmented lethal transient-MPT (t-MPT) to switch to its irreversible mode of permanent-MPT (p-MPT). Interestingly, melatonin, a multiple mitochondrial protector, markedly reduced Aβ-augmented mROS formation and therefore significantly reduced mROS-mediated depolarization of ∆Ψ(m), fission of mitochondria and retardation of mitochondrial movement to stabilize CL and hence the MPT. In the presence of melatonin, Aβ-promoted p-MPT was reversed to a protective t-MPT, which preserved ∆Ψ(m) and lowered elevated mCa(2+) to sublethal levels for an enhanced mCa(2+)-dependent O(2) consumption. Thus, melatonin may potentially rescue AD patients associated with NARP symptoms.

Hyperuricemia induces endothelial dysfunction via mitochondrial Na+/Ca2+ exchanger-mediated mitochondrial calcium overload

BACKGROUND

Uric acid (UA) has proven to be a causal agent in endothelial dysfunction in which ROS production plays an important role. Calcium overload in mitochondria can promote the mitochondrial production of ROS. We hypothesize that calcium transduction in mitochondria contributes to UA-induced endothelial dysfunction.

METHODS AND RESULTS

We first demonstrated that high concentrations of UA cause endothelial dysfunction, marked by a reduction in eNOS protein expression and NO release in vitro. We further found that a high concentration of UA increased levels of [Ca2+]mito, total intracellular ROS, H2O2, and mitochondrial O2·-, and Δψmito but not the [Ca2+]cyt level. When the mitochondrial calcium channels NCXmito and MCU were blocked by CGP-37157 and Ru360, respectively, the UA-induced increases in the levels of [Ca2+]mito and total intracellular ROS were significantly reduced. Mitochondrial levels of O2·- and Δψmito were reduced by inhibition of NCXmito but not of MCU. Moreover, inhibition of NCXmito, but not of MCU, blocked the UA-induced reductions in eNOS protein expression and NO release.

CONCLUSIONS

The increased generation of mitochondrial O2·- induced by a high concentration of UA is triggered by mitochondrial calcium overload and ultimately leads to endothelial dysfunction. In this process, the activation of NCXmito is the major cause of the influx of calcium into mitochondria. Our results provide a new pathophysiological mechanism for UA-induced endothelial dysfunction and may offer a new therapeutic target for clinicians.

mtDNA T8993G mutation-induced mitochondrial complex V inhibition augments cardiolipin-dependent alterations in mitochondrial dynamics during oxidative, Ca(2+), and lipid insults in NARP cybrids: a potential therapeutic target for melatonin

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

Measurements of intracellular calcium signals in polarized primary cultures of normal and cystic fibrosis human airway epithelia

The airways are continuously challenged by a variety of stimuli including bacteria, viruses, allergens, and inflammatory factors that act as agonists for G protein-coupled receptors (GPCR). Intracellular calcium (Ca(2+) (i)) mobilization in airway epithelia in response to extracellular stimuli regulates key airway innate defense functions, e.g., Ca(2+)-activated Cl(-) secretion, ciliary beating, mucin secretion, and inflammatory responses. Because Ca(2+) (i) mobilization in response to luminal stimuli is larger in CF vs. normal human airway epithelia, alterations in Ca(2+) (i) signals have been associated with the pathogenesis of CF airway disease. Hence, assessment of Ca(2+) (i) signaling has become an important area of CF research. This chapter will focus on measurements of cytoplasmic and mitochondrial Ca(2+) signals resulting from GPCR activation in polarized primary cultures of normal and CF human bronchial epithelia (HBE).

Oxidative stress caused by mitochondrial calcium overload

Mitochondrial oxidative stress has been reported as the result of respiratory complex anomalies, genetic defects, or insufficient oxygen or glucose supply. Although Ca(2+) has no direct effect on respiratory chain function or oxidation/reduction process, mitochondrial Ca(2+) overload can lead to reactive oxygen species (ROS) increase. Even though Ca(2+) is well known for its role as crucial second messenger in modulating many cellular physiological functions, Ca(2+) overload is detrimental to mitochondrial function and may present as an important cause of mitochondrial ROS generation. Possible mechanisms include Ca(2+) stimulated increase of metabolic rate, Ca(2+) stimulated nitric oxide production, Ca(2+) induced cytochrome c dissociation, Ca(2+) induced cardiolipin peroxidation, Ca(2+) induced mitochondrial permeability transition pore opening with release of cytochrome c and GSH-antioxidative enzymes, and Ca(2+)-calmodulin dependent protein kinases activation. Different mechanisms may exist under different mitochondrial preparations (isolated mitochondria vs. mitochondria in intact cells), tissue sources, animal species, or inhibitors used. Furthermore, mitochondrial ROS rise can modulate Ca(2+) dynamics and augment Ca(2+) surge. The reciprocal interactions between Ca(2+) induced ROS increase and ROS modulated Ca(2+) upsurge may cause a feedforward, self-amplified loop createing cellular damage far beyond direct Ca(2+) induced damage.

Visualization of melatonin's multiple mitochondrial levels of protection against mitochondrial Ca(2+)-mediated permeability transition and beyond in rat brain astrocytes

Melatonin protects cells against various types of oxidative stress-induced apoptosis due primarily to its ability to effectively scavenge pathological and disease condition-augmented generation of mitochondrial reactive oxygen species (mROS). Once produced, mROS indiscriminately damage mitochondrial components and more importantly they crucially activate directly the mitochondrial permeability transition (MPT), one of the critical mechanisms for initiating post mitochondrial apoptotic signaling. Whether or not melatonin targets directly the MPT, however, remains inconclusive, particularly during oxidative stress. This study, thus, investigated this possibility of an 'oxidation free Ca(2+) stress' in the presence of vitamin E after ionomycin exposure as a sole Ca(2+)-mediated MPT in order to exclude melatonin's primary antioxidative effects as well as Ca(2+)-mediated oxidative stress. The studies were carried out using cultured rat brain astrocytes RBA-1. With the application of laser scanning multiple fluorescence imaging microscopy, we visualized for the first time multiple mitochondrial protective effects provided by melatonin during Ca(2+) stress. First, melatonin, due to its primary antioxidative actions, completely prevented mCa(2+)-induced mROS formation during ionomycin exposure. Secondly, when melatonin(')s antioxidative effects were prevented due to the addition of vitamin E, melatonin significantly prevented mCa(2+)-mediated MPT and apoptosis suggesting its direct targeting of the MPT. Surprisingly, in the presence of cyclosporin A, a MPT inhibitor, melatonin reduced further mCa(2+)-mediated apoptosis during ionomycin exposure also suggesting its targeting beyond the MPT. As astrocytes are actively involve in regulating synaptic transmission and neurovascular coupling in the CNS, these multiple mitochondrial layers of protection provided by melatonin against mCa(2+)-and/or mROS-mediated apoptosis in astrocytes may be crucial for future therapeutic prevention and treatment of astrocyte-mediated neurodegenerative diseases in the CNS.

Melatonin protects the mitochondria from oxidative damage reducing oxygen consumption, membrane potential, and superoxide anion production

The role of melatonin in improving mitochondrial respiratory chain activity and increasing ATP production in different experimental conditions has been widely reported. To date, however, the mechanism(s) involved are largely unknown. Using high-resolution respirometry, fluorometry and spectrophotometry we studied the effects of melatonin on normal mitochondrial functions. Mitochondria were recovered from mouse liver cells and incubated in vitro with melatonin at concentrations ranging from 1 nm to 1 mm. Melatonin decreased oxygen consumption concomitantly with its concentration, inhibited any increase in oxygen flux in the presence of an excess of ADP, reduced the membrane potential, and consequently inhibited the production of superoxide anion and hydrogen peroxide. At the same time it maintained the efficiency of oxidative phosphorylation and ATP synthesis while increasing the activity of the respiratory complexes (mainly complexes I, III, and IV). The effects of melatonin appeared to be due to its presence within the mitochondria, since kinetic experiments clearly showed its incorporation into these organelles. Our results support the hypothesis that melatonin, together with hormones such as triiodothyronine, participates in the physiological regulation of mitochondrial homeostasis.

Reactive oxygen species play a central role in the activity of cationic liposome based cancer vaccine

Recently, we developed a simple and potent therapeutic liposome cancer vaccine consisting of a peptide antigen and a cationic lipid. The molecular mechanism of the adjuvanticity of cationic liposome was studied and described in the current report. First, cationic DOTAP liposome, but not the neutral liposome DOPC, was shown to generate reactive oxygen species (ROS) in mouse bone marrow-derived dendritic cells (BMDC). ROS generation by DOTAP was required for ERK and p38 activation and downstream chemokine/cytokine induction. Furthermore, ROS were shown to be involved in the expression of the co-stimulatory molecules CD86/CD80 induced by DOTAP. However, as the DOTAP concentration increased from 50 to 800 microM, the apoptotic marker Annexin V and ROS double positive cells increased, suggesting that high dose of DOTAP-generated ROS causes cell apoptosis. In vivo, optimal amount of ROS in the draining lymph nodes (DLN) and anti-tumor (HPV positive TC-1 tumor) activity induced by E7 peptide (antigen derived from E7 oncoprotein of human papillomavirus (HPV) type 16) formulated in 100 nmol DOTAP were attenuated by incorporating DOPC in the formulation, suggesting that ROS are essential for the vaccine induced anti-tumor activity. Moreover, 600 nmol DOTAP/E7 generated huge amount of ROS in the DLN and showed no activity of tumor regression. Interestingly, 600 nmol DOTAP/E7-induced ROS were tuned down to the same level induced by 100 nmol DOTAP/E7 by adding DOPC in the formulation and this formulation showed tumor regression activity. In conclusion, DOTAP is an active DC stimulator resulting in the activation of ERK and p38 and induction of chemokines, cytokines and co-stimulatory molecules mediated by appropriate amount of ROS. Our data elucidated an important mechanism of adjuvant activity of cationic liposome and could facilitate rational design of synthetic lipid based adjuvants and vaccine formulation.

Effects of low power laser irradiation on intracellular calcium and histamine release in RBL-2H3 mast cells

Although laser irradiation has been reported to promote skin wound healing, the mechanism is still unclear. As mast cells are found to accumulate at the site of skin wounds we hypothesized that mast cells might be involved in the biological effects of laser irradiation. In this work the mast cells, RBL-2H3, were used in vitro to investigate the effects of laser irradiation on cellular responses. After laser irradiation, the amount of intracellular calcium ([Ca2+]i) was increased, followed by histamine release, as measured by confocal fluorescence microscopy with Fluo-3/AM staining and a fluorescence spectrometer with o-phthalaldehyde staining, respectively. The histamine release was mediated by the increment of [Ca2+]i from the influx of the extracellular buffer solution through the cation channel protein, transient receptor potential vanilloid 4 (TRPV4). The TRPV4 inhibitor, Ruthenium Red (RR) can effectively block such histamine release, indicating that TRPV4 was the key factor responding to laser irradiation. These induced responses of mast cells may provide an explanation for the biological effects of laser irradiation on promoting wound healing, as histamine is known to have multi-functions on accelerating wound healing.

Zinc is a novel intracellular second messenger

Zinc is an essential trace element required for enzymatic activity and for maintaining the conformation of many transcription factors; thus, zinc homeostasis is tightly regulated. Although zinc affects several signaling molecules and may act as a neurotransmitter, it remains unknown whether zinc acts as an intracellular second messenger capable of transducing extracellular stimuli into intracellular signaling events. In this study, we report that the cross-linking of the high affinity immunoglobin E receptor (Fcɛ receptor I [FcɛRI]) induced a release of free zinc from the perinuclear area, including the endoplasmic reticulum in mast cells, a phenomenon we call the zinc wave. The zinc wave was dependent on calcium influx and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase activation. The results suggest that the zinc wave is involved in intracellular signaling events, at least in part by modulating the duration and strength of FcɛRI-mediated signaling. Collectively, our findings indicate that zinc is a novel intracellular second messenger.

'To repair or not to repair - no longer a question': repair of mitochondrial DNA shielding against age and cancer

The role of mitochondria in energy production and apoptosis is well known. The role of mitochondria and particularly the role of the mitochondria's own genome, mitochondrial (mt) DNA, in the process of ageing were postulated decades ago. However, this was discussed, debated and more or less disposed of. Recent data from elegant mouse models now confirm that mutations of mtDNA do indeed play a central and pivotal role in the ageing process. Newer reports also indicate a possible role of mtDNA mutations in the carcinogenesis of several organs. But is damaged mtDNA repaired, or is it simply degraded and discarded? This question appears to be answered now. According to recent data, mitochondria possess functional repair mechanisms such as base excision repair, double-strand break repair and mismatch repair, yet nucleotide excision repair has so far not been detected.

Full developmental potential of mammalian preimplantation embryos is maintained after imaging using a spinning-disk confocal microscope

Fluorescent live imaging of cells and embryos at subcellular resolution poses significant challenges for biologists due to morbidity and mortality ensuing from phototoxicity. Here we report the use of a spinning-disk confocal microscope to image mouse and bovine preimplantation embryos without impairing their developmental potential. We also present data indicating that this imaging technique does not affect the functionality of subcellular components as assessed by reactive oxygen species (ROS) production, caspase activity, and DNA integrity. Spinning-disk confocal microscopy was also useful in determining cell number and allocation in transgenic bovine blastocysts. We conclude that this imaging method is suitable for monitoring preimplantation embryos.

Mitochondrion-targeted photosensitizer enhances the photodynamic effect-induced mitochondrial dysfunction and apoptosis

Recently, the mitochondrion has been considered as a novel pharmacological target for anticancer therapy due to its crucial role involved in arbitrating cell apoptosis. We have previously demonstrated that 488-nm laser irradiation induced a specific mitochondrial reactive oxygen species (mROS) formation and apoptotic death. In this study, we used a second generation of photosensitizers, the benzoporphyrin-derivative monoacid ring A (BPD-MA). We investigated specifically mechanisms at the mitochondrial level for BPD-MA coupled with 690-nm laser irradiation, the photodynamic effect (PDE) of BPD-MA, using conventional and laser scanning imaging microscopy in intact C6 glioma cells. We demonstrated BPD-MA localized mainly in the mitochondrial area. The phototoxicity induced by 1-10 J 690-nm laser irradiation was minor as compared to that induced by 488-nm laser irradiation. Unlike other mitochondrion-targeted photosensitizers, the dark toxicity induced by BPD-MA (0.05-5 mg/mL, effective doses used for the PDE) was relatively low. Nevertheless, the PDE of BPD-MA using 0.5 mg/mL coupled with 5J 690-nm irradiation induced profound and rapid (< 1 min) mitochondrial swelling, mROS formation, and severe plasma membrane blebbing as compared to that induced by 488-nm laser irradiation (< 10 min). Later, the PDE of BPD-MA resulted in positive propidium iodide cell-death stain and positive TUNEL apoptotic nuclear stain and DNA laddering. Finally, the PDT of BPD-MA also instantaneously promoted the mitochondrion to diminish its covalent binding with a mitochondrial marker, MitoTracker Green. We conclude that the PDT of BPD-MA targeted primarily and compellingly the mitochondrion to induce effective mitochondria-mediated apoptosis and thus may serve as a powerful photosensitizer for clinical cancer therapy.

Visualizing common deletion of mitochondrial DNA-augmented mitochondrial reactive oxygen species generation and apoptosis upon oxidative stress

Common deletion (CD) 4977 bp of mitochondrial DNA (mtDNA) disrupt specifically mitochondrial complex I, IV and V on the electron transport chain (ETC) and is closely associated with wide spectrums of clinical manifestations. To quantitatively investigate how CD-induced ETC defect alters mitochondrial reactive oxygen species (mROS) generation as well as down stream apoptotic signaling, we employed an established array of human CD cytoplasmic hybrids (cybrids) harboring 0%-80% of CD. Pathological effects of CD on the mitochondria were visualized at single cell level by the application of fluorescent probes coupled with conventional and multiphoton imaging microscopy. Intriguingly, we observed CD-augmented mROS generation omitted "threshold effect". CD-augmented mROS generation was associated with depolarized mitochondrial membrane potential (DeltaPsi(m)). Upon oxidative stress, the amount of CD-augmented mROS generation was greatly enhanced to cause pathological apoptotic deterioration including opening of the mitochondrial permeability transition, cytochrome c release, phosphatidylserine externalization and DNA fragmentation. In addition, heterogeneous mitochondrial dysfunctions were found in cybrids containing 80% of CD (D cybrids), i.e., low sensitive-D (LS-D, roughly 80%) and a super sensitive-D (SS-D, 20%). As compared to LS-D, SS-D had higher resting mROS level but slightly hyperpolarized DeltaPsi(m). Upon H2O2 treatment, much faster generation of mROS was observed which induced a faster depolarization of DeltaPsi(m) and later apoptotic deterioration in SS-D. We proposed a dose-dependent, feed-forward and self-accelerating vicious cycle of mROS production might be initiated in CD-induced ETC defect without threshold effect. As CD-augmented mROS generation is obligated to cause an enhanced pathological apoptosis, precise detection of CD-augmented mROS generation and their degree of heterogeneity in single cells may serve as sensitive pathological indexes for early diagnosis, prognosis and treatment of CD-associated diseases.

Enhanced Generation of Mitochondrial Reactive Oxygen Species in Cybrids Containing 4977-bp Mitochondrial DNA Deletion

The poor bioenergetic state in mitochondria containing mtDNA with the 4977-bp deletion has been well documented. However, information on mitochondrial reactive oxygen species (ROS) generation at rest or under intense oxidative stress in mitochondria lacking the 4977-bp mtDNA fragment inside intact living cells was insufficient. We used cybrids containing truncated mtDNA lacking the 4977-bp fragment and measured ROS levels inside cybrids by fluorescence probe, 2',7'-dichlorodihydrofluorescein (DCF), and confocal microscopy. Mitochondrial ROS at resting state was slightly higher in cybrids containing 4977-bp deletion mtDNA as compared to cybrids without mtDNA defects. For intense oxidative stress treatment, cybrids were treated with 5 mM H2O2 for 10 min. Consecutive DCF images were acquired after H2O2 had been washed away. Progressive increase of DCF signals, especially in the mitochondrial area, was observed in cybrids containing 4977-bp deletion mtDNA, even long after the brief, intense H2O2 treatment. This result suggests that a feed-forward, self-accelerating vicious cycle of mitochondrial ROS production could be initiated in cybrids containing 4977-bp deletion fragment mitochondria after brief, intense H2O2 treatment. This mechanism may play an important role in the pathophysiology of the disease process caused by mitochondria containing mtDNA with the 4977-bp deletion.

Repair of mitochondrial DNA in aging and carcinogenesis

Mitochondria are responsible for the generation of energy in the form of adenosine triphosphate. These organelles contain their own genetic material, mitochondrial (mt) DNA. This mtDNA has been hypothesized to play a role in the processes of aging and carcinogenesis. Initial reports have shown that there is no repair of cyclobutylpyrimidine dimers (CPD). More recent reports indicate however, that the mitochondrion contains several defence mechanisms against endogenous or exogenous damaging agents such as ultraviolet radiation or oxidative damage. The role of these defence mechanisms in the removal of mitochondrial DNA damage and the link to aging and carcinogenesis-associated processes are discussed in this review.

Endogenous fluorescence imaging of somatosensory cortical activities after discrimination learning in rats

Aerobic energy metabolism in the brain is reflected as changes in the green fluorescence of mitochondrial flavoproteins, and the activity-dependent changes in endogenous fluorescence are applicable for functional brain imaging. To understand the roles of cortical plasticity in discrimination learning, we used flavoprotein fluorescence imaging to visualize changes of neural activities in the rat primary somatosensory cortex (SI) after learning. Rats were trained to discriminate floor vibration at rewarded and unrewarded frequencies. After this discrimination learning was accomplished in 3-5 days, the rats were anesthetized with urethane (1.5 g/kg, i.p.), and neural responses were recorded in SI during flutter stimuli applied to the contralateral hindpaw. The fluorescence responses to the stimuli at unrewarded frequencies were selectively depressed in the trained rats, which had behaviorally neglected unrewarded stimuli. The depression of cortical responses was not observed in the rats trained with rewarded stimuli only. Therefore, the stimulus-specific depression in SI might explain a part of neural mechanisms underlying discrimination behavior. To reproduce the stimulus-specific depression of cortical responses in anesthetized rats, tetanic cortical stimulation was paired with flutter stimulation applied to the hindpaw. Selective depression of fluorescence responses or field potentials in SI was induced by the paired stimulation. Our findings suggest that some intracortical circuits in SI are specifically tuned to and modulated by unrewarded stimuli of a particular frequency while SI neurons are responsive to both of rewarded and unrewarded stimuli. The present results indicate the usefulness of flavoprotein fluorescence imaging for investigating somatosensory cortical plasticity after learning.

Effect of sesaminol glucosides on β-amyloid-induced PC12 cell death through antioxidant mechanisms

Several lines of evidence support that beta-amyloid (Abeta)-induced neurotoxicity is mediated through the generation of reactive oxygen species (ROS) and elevation of intracellular calcium. In this study, we have investigated protective effects of sesaminol glucosides on Abeta-induced oxidative cell death in cultured rat pheochromocytoma (PC12) cells. Sesaminol glucoside (50-250microg/ml) decreased Abeta(25-35)-induced ROS generation, formation of 8-oxodG, a form of oxidative DNA and elevation of intracellular calcium level concomitant with prevention of apoptotic cell death dose dependently. Sesaminol glucoside (50-250microg/ml) also effectively decreased Abeta1-42 and ADDL form of Abeta1-42 as well as the combination of H2O2 with FeSO4-induced cell damages. In mechanistic study, sesaminol glucosides attenuated Abeta25-35-induced activation of redox transcription factor nuclear factor-kappaB NF-kappaB through inhibition of p50 translocation and IkappaB phosphorylation, and blocked NF-kappaB-dependent luciferase activity in addition to the inhibitory effect on Abeta25-35-induced activation of ERK kinase signal pathway. Consistent with the inhibitory effect on Abeta25-35-induced stress-induced cell death, sesaminol glucosides decreased expression of pro-apoptotic gene p53, and Bax and caspase-3, but enhanced expression of anti-apoptotic Bcl-2. Moreover, the protective effects of sesaminol glucoside on Abeta25-35-induced ROS generation, NF-kappaB activation and cell death were further enhanced with glutathione. This study therefore suggests that sesaminol glucosides have protective effect on Abeta-induced neuronal cell death, and its effect may be through antioxidative property.