Investigation of mitochondrial function represents an important parameter of cardiac physiology as mitochondria are involved in energy metabolism, oxidative stress, apoptosis, aging, mitochondrial encephalomyopathies and drug toxicity. Given this, technologies to measure cardiac mitochondrial function are in demand. One technique that employs an integrative approach to measure mitochondrial function is respirometric oxidative phosphorylation (OXPHOS) analysis.
The principle of respirometric OXPHOS assessment is centered around measuring oxygen concentration utilizing a Clark electrode. As the permeabilized fiber bundle consumes oxygen, oxygen concentration in the closed chamber declines. Using selected substrate-inhibitor-uncoupler titration protocols, electrons are provided to specific sites of the electron transport chain, allowing evaluation of mitochondrial function. Prior to respirometric analysis of mitochondrial function, mechanical and chemical preparatory techniques are utilized to permeabilize the sarcolemma of muscle fibers. Chemical permeabilization employs saponin to selectively perforate the cell membrane while maintaining cellular architecture.
This paper thoroughly describes the steps involved in preparing saponin-skinned cardiac fibers for oxygen consumption measurements to evaluate mitochondrial OXPHOS. Additionally, troubleshooting advice as well as specific substrates, inhibitors and uncouplers that may be used to determine mitochondria function at specific sites of the electron transport chain are provided. Importantly, the described protocol may be easily applied to cardiac and skeletal tissue of various animal models and human samples.
20 Related JoVE Articles!
Direct Imaging of ER Calcium with Targeted-Esterase Induced Dye Loading (TED)
Institutions: University of Wuerzburg, Max Planck Institute of Neurobiology, Martinsried, Ludwig-Maximilians University of Munich.
Visualization of calcium dynamics is important to understand the role of calcium in cell physiology. To examine calcium dynamics, synthetic fluorescent Ca2+
indictors have become popular. Here we demonstrate TED (= targeted-esterase induced dye loading), a method to improve the release of Ca2+
indicator dyes in the ER lumen of different cell types. To date, TED was used in cell lines, glial cells, and neurons in vitro
. TED bases on efficient, recombinant targeting of a high carboxylesterase activity to the ER lumen using vector-constructs that express Carboxylesterases (CES). The latest TED vectors contain a core element of CES2 fused to a red fluorescent protein, thus enabling simultaneous two-color imaging. The dynamics of free calcium in the ER are imaged in one color, while the corresponding ER structure appears in red. At the beginning of the procedure, cells are transduced with a lentivirus. Subsequently, the infected cells are seeded on coverslips to finally enable live cell imaging. Then, living cells are incubated with the acetoxymethyl ester (AM-ester) form of low-affinity Ca2+
indicators, for instance Fluo5N-AM, Mag-Fluo4-AM, or Mag-Fura2-AM. The esterase activity in the ER cleaves off hydrophobic side chains from the AM form of the Ca2+
indicator and a hydrophilic fluorescent dye/Ca2+
complex is formed and trapped in the ER lumen. After dye loading, the cells are analyzed at an inverted confocal laser scanning microscope. Cells are continuously perfused with Ringer-like solutions and the ER calcium dynamics are directly visualized by time-lapse imaging. Calcium release from the ER is identified by a decrease in fluorescence intensity in regions of interest, whereas the refilling of the ER calcium store produces an increase in fluorescence intensity. Finally, the change in fluorescent intensity over time is determined by calculation of ΔF/F0
Cellular Biology, Issue 75, Neurobiology, Neuroscience, Molecular Biology, Biochemistry, Biomedical Engineering, Bioengineering, Virology, Medicine, Anatomy, Physiology, Surgery, Endoplasmic Reticulum, ER, Calcium Signaling, calcium store, calcium imaging, calcium indicator, metabotropic signaling, Ca2+, neurons, cells, mouse, animal model, cell culture, targeted esterase induced dye loading, imaging
Mechanical Stimulation-induced Calcium Wave Propagation in Cell Monolayers: The Example of Bovine Corneal Endothelial Cells
Institutions: KU Leuven.
Intercellular communication is essential for the coordination of physiological processes between cells in a variety of organs and tissues, including the brain, liver, retina, cochlea and vasculature. In experimental settings, intercellular Ca2+
-waves can be elicited by applying a mechanical stimulus to a single cell. This leads to the release of the intracellular signaling molecules IP3
that initiate the propagation of the Ca2+
-wave concentrically from the mechanically stimulated cell to the neighboring cells. The main molecular pathways that control intercellular Ca2+
-wave propagation are provided by gap junction channels through the direct transfer of IP3
and by hemichannels through the release of ATP. Identification and characterization of the properties and regulation of different connexin and pannexin isoforms as gap junction channels and hemichannels are allowed by the quantification of the spread of the intercellular Ca2+
-wave, siRNA, and the use of inhibitors of gap junction channels and hemichannels. Here, we describe a method to measure intercellular Ca2+
-wave in monolayers of primary corneal endothelial cells loaded with Fluo4-AM in response to a controlled and localized mechanical stimulus provoked by an acute, short-lasting deformation of the cell as a result of touching the cell membrane with a micromanipulator-controlled glass micropipette with a tip diameter of less than 1 μm. We also describe the isolation of primary bovine corneal endothelial cells and its use as model system to assess Cx43-hemichannel activity as the driven force for intercellular Ca2+
-waves through the release of ATP. Finally, we discuss the use, advantages, limitations and alternatives of this method in the context of gap junction channel and hemichannel research.
Cellular Biology, Issue 77, Molecular Biology, Medicine, Biomedical Engineering, Biophysics, Immunology, Ophthalmology, Gap Junctions, Connexins, Connexin 43, Calcium Signaling, Ca2+, Cell Communication, Paracrine Communication, Intercellular communication, calcium wave propagation, gap junctions, hemichannels, endothelial cells, cell signaling, cell, isolation, cell culture
Ratiometric Biosensors that Measure Mitochondrial Redox State and ATP in Living Yeast Cells
Institutions: Columbia University, Columbia University.
Mitochondria have roles in many cellular processes, from energy metabolism and calcium homeostasis to control of cellular lifespan and programmed cell death. These processes affect and are affected by the redox status of and ATP production by mitochondria. Here, we describe the use of two ratiometric, genetically encoded biosensors that can detect mitochondrial redox state and ATP levels at subcellular resolution in living yeast cells. Mitochondrial redox state is measured using redox-sensitive Green Fluorescent Protein (roGFP) that is targeted to the mitochondrial matrix. Mito-roGFP contains cysteines at positions 147 and 204 of GFP, which undergo reversible and environment-dependent oxidation and reduction, which in turn alter the excitation spectrum of the protein. MitGO-ATeam is a Förster resonance energy transfer (FRET) probe in which the ε subunit of the Fo
-ATP synthase is sandwiched between FRET donor and acceptor fluorescent proteins. Binding of ATP to the ε subunit results in conformation changes in the protein that bring the FRET donor and acceptor in close proximity and allow for fluorescence resonance energy transfer from the donor to acceptor.
Bioengineering, Issue 77, Microbiology, Cellular Biology, Molecular Biology, Biochemistry, life sciences, roGFP, redox-sensitive green fluorescent protein, GO-ATeam, ATP, FRET, ROS, mitochondria, biosensors, GFP, ImageJ, microscopy, confocal microscopy, cell, imaging
Viability Assays for Cells in Culture
Institutions: Duquesne University.
Manual cell counts on a microscope are a sensitive means of assessing cellular viability but are time-consuming and therefore expensive. Computerized viability assays are expensive in terms of equipment but can be faster and more objective than manual cell counts. The present report describes the use of three such viability assays. Two of these assays are infrared and one is luminescent. Both infrared assays rely on a 16 bit Odyssey Imager. One infrared assay uses the DRAQ5 stain for nuclei combined with the Sapphire stain for cytosol and is visualized in the 700 nm channel. The other infrared assay, an In-Cell Western, uses antibodies against cytoskeletal proteins (α-tubulin or microtubule associated protein 2) and labels them in the 800 nm channel. The third viability assay is a commonly used luminescent assay for ATP, but we use a quarter of the recommended volume to save on cost. These measurements are all linear and correlate with the number of cells plated, but vary in sensitivity. All three assays circumvent time-consuming microscopy and sample the entire well, thereby reducing sampling error. Finally, all of the assays can easily be completed within one day of the end of the experiment, allowing greater numbers of experiments to be performed within short timeframes. However, they all rely on the assumption that cell numbers remain in proportion to signal strength after treatments, an assumption that is sometimes not met, especially for cellular ATP. Furthermore, if cells increase or decrease in size after treatment, this might affect signal strength without affecting cell number. We conclude that all viability assays, including manual counts, suffer from a number of caveats, but that computerized viability assays are well worth the initial investment. Using all three assays together yields a comprehensive view of cellular structure and function.
Cellular Biology, Issue 83, In-cell Western, DRAQ5, Sapphire, Cell Titer Glo, ATP, primary cortical neurons, toxicity, protection, N-acetyl cysteine, hormesis
Confocal Imaging of Single Mitochondrial Superoxide Flashes in Intact Heart or In Vivo
Institutions: University of Washington.
Mitochondrion is a critical intracellular organelle responsible for energy production and intracellular signaling in eukaryotic systems. Mitochondrial dysfunction often accompanies and contributes to human disease. Majority of the approaches that have been developed to evaluate mitochondrial function and dysfunction are based on in vitro
or ex vivo
measurements. Results from these experiments have limited ability in determining mitochondrial function in vivo
. Here, we describe a novel approach that utilizes confocal scanning microscopy for the imaging of intact tissues in live aminals, which allows the evaluation of single mitochondrial function in a real-time manner in vivo
. First, we generate transgenic mice expressing the mitochondrial targeted superoxide indicator, circularly permuted yellow fluorescent protein (mt-cpYFP). Anesthetized mt-cpYFP mouse is fixed on a custom-made stage adaptor and time-lapse images are taken from the exposed skeletal muscles of the hindlimb. The mouse is subsequently sacrificed and the heart is set up for Langendorff perfusion with physiological solutions at 37 °C. The perfused heart is positioned in a special chamber on the confocal microscope stage and gentle pressure is applied to immobilize the heart and suppress heart beat induced motion artifact. Superoxide flashes are detected by real-time 2D confocal imaging at a frequency of one frame per second. The perfusion solution can be modified to contain different respiration substrates or other fluorescent indicators. The perfusion can also be adjusted to produce disease models such as ischemia and reperfusion. This technique is a unique approach for determining the function of single mitochondrion in intact tissues and in vivo
Physiology, Issue 81, Heart Diseases, Metabolic Diseases, Microscopy, Confocal, Time-Lapse Imaging, Physiological Processes, Confocal imaging, mt-cpYFP transgenic mice, Superoxide flashes, Single mitochondrial measurement, Langendorff perfused heart, Skeletal muscles, in vivo
Analysis of Oxidative Stress in Zebrafish Embryos
Institutions: University of Torino, Vesalius Research Center, VIB.
High levels of reactive oxygen species (ROS) may cause a change of cellular redox state towards oxidative stress condition. This situation causes oxidation of molecules (lipid, DNA, protein) and leads to cell death. Oxidative stress also impacts the progression of several pathological conditions such as diabetes, retinopathies, neurodegeneration, and cancer. Thus, it is important to define tools to investigate oxidative stress conditions not only at the level of single cells but also in the context of whole organisms. Here, we consider the zebrafish embryo as a useful in vivo
system to perform such studies and present a protocol to measure in vivo
oxidative stress. Taking advantage of fluorescent ROS probes and zebrafish transgenic fluorescent lines, we develop two different methods to measure oxidative stress in vivo
: i) a “whole embryo ROS-detection method” for qualitative measurement of oxidative stress and ii) a “single-cell ROS detection method” for quantitative measurements of oxidative stress. Herein, we demonstrate the efficacy of these procedures by increasing oxidative stress in tissues by oxidant agents and physiological or genetic methods. This protocol is amenable for forward genetic screens and it will help address cause-effect relationships of ROS in animal models of oxidative stress-related pathologies such as neurological disorders and cancer.
Developmental Biology, Issue 89, Danio rerio, zebrafish embryos, endothelial cells, redox state analysis, oxidative stress detection, in vivo ROS measurements, FACS (fluorescence activated cell sorter), molecular probes
Inducing Plasticity of Astrocytic Receptors by Manipulation of Neuronal Firing Rates
Institutions: University of California Riverside, University of California Riverside, University of California Riverside.
Close to two decades of research has established that astrocytes in situ
and in vivo
express numerous G protein-coupled receptors (GPCRs) that can be stimulated by neuronally-released transmitter. However, the ability of astrocytic receptors to exhibit plasticity in response to changes in neuronal activity has received little attention. Here we describe a model system that can be used to globally scale up or down astrocytic group I metabotropic glutamate receptors (mGluRs) in acute brain slices. Included are methods on how to prepare parasagittal hippocampal slices, construct chambers suitable for long-term slice incubation, bidirectionally manipulate neuronal action potential frequency, load astrocytes and astrocyte processes with fluorescent Ca2+
indicator, and measure changes in astrocytic Gq GPCR activity by recording spontaneous and evoked astrocyte Ca2+
events using confocal microscopy. In essence, a “calcium roadmap” is provided for how to measure plasticity of astrocytic Gq GPCRs. Applications of the technique for study of astrocytes are discussed. Having an understanding of how astrocytic receptor signaling is affected by changes in neuronal activity has important implications for both normal synaptic function as well as processes underlying neurological disorders and neurodegenerative disease.
Neuroscience, Issue 85, astrocyte, plasticity, mGluRs, neuronal Firing, electrophysiology, Gq GPCRs, Bolus-loading, calcium, microdomains, acute slices, Hippocampus, mouse
Bladder Smooth Muscle Strip Contractility as a Method to Evaluate Lower Urinary Tract Pharmacology
Institutions: University of Pittsburgh School of Medicine, University of Pittsburgh School of Medicine.
We describe an in vitro
method to measure bladder smooth muscle contractility, and its use for investigating physiological and pharmacological properties of the smooth muscle as well as changes induced by pathology. This method provides critical information for understanding bladder function while overcoming major methodological difficulties encountered in in vivo
experiments, such as surgical and pharmacological manipulations that affect stability and survival of the preparations, the use of human tissue, and/or the use of expensive chemicals. It also provides a way to investigate the properties of each bladder component (i.e.
smooth muscle, mucosa, nerves) in healthy and pathological conditions.
The urinary bladder is removed from an anesthetized animal, placed in Krebs solution and cut into strips. Strips are placed into a chamber filled with warm Krebs solution. One end is attached to an isometric tension transducer to measure contraction force, the other end is attached to a fixed rod. Tissue is stimulated by directly adding compounds to the bath or by electric field stimulation electrodes that activate nerves, similar to triggering bladder contractions in vivo
. We demonstrate the use of this method to evaluate spontaneous smooth muscle contractility during development and after an experimental spinal cord injury, the nature of neurotransmission (transmitters and receptors involved), factors involved in modulation of smooth muscle activity, the role of individual bladder components, and species and organ differences in response to pharmacological agents. Additionally, it could be used for investigating intracellular pathways involved in contraction and/or relaxation of the smooth muscle, drug structure-activity relationships and evaluation of transmitter release.
The in vitro
smooth muscle contractility method has been used extensively for over 50 years, and has provided data that significantly contributed to our understanding of bladder function as well as to pharmaceutical development of compounds currently used clinically for bladder management.
Medicine, Issue 90, Krebs, species differences, in vitro, smooth muscle contractility, neural stimulation
F1FO ATPase Vesicle Preparation and Technique for Performing Patch Clamp Recordings of Submitochondrial Vesicle Membranes
Institutions: Yale University.
Mitochondria are involved in many important cellular functions including metabolism, survival1
, development and, calcium signaling2
. Two of the most important mitochondrial functions are related to the efficient production of ATP, the energy currency of the cell, by oxidative phosphorylation, and the mediation of signals for programmed cell death3
The enzyme primarily responsible for the production of ATP is the F1FO-ATP synthase, also called ATP synthase4-5
. In recent years, the role of mitochondria in apoptotic and necrotic cell death has received considerable attention. In apoptotic cell death, BCL-2 family proteins such as Bax enter the mitochondrial outer membrane, oligomerize and permeabilize the outer membrane, releasing pro-apoptotic factors into the cytosol6
. In classic necrotic cell death, such as that produced by ischemia or excitotoxicity in neurons, a large, poorly regulated increase in matrix calcium contributes to the opening of an inner membrane pore, the mitochondrial permeability transition pore or mPTP. This depolarizes the inner membrane and causes osmotic shifts, contributing to outer membrane rupture, release of pro-apoptotic factors, and metabolic dysfunction. Many proteins including Bcl-xL7
interact with F1FO ATP synthase, modulating its function. Bcl-xL interacts directly with the beta subunit of F1FO ATP synthase, and this interaction decreases a leak conductance within the F1FOATPasecomplex, increasing the net transport of H+ by F1FO during F1FO ATPase activity8
and thereby increasing mitochondrial efficiency. To study the activity and modulation of the ATP synthase, we isolated from rodent brain submitochondrial vesicles (SMVs) containing F1FO ATPase. The SMVs retain the structural and functional integrity of the F1FO ATPase as shown in Alavian et al
. Here, we describe a method that we have used successfully for the isolation of SMVs from rat brain and we delineate the patch clamp technique to analyze channel activity (ion leak conductance) of the SMVs.
Neuroscience, Issue 75, Medicine, Biomedical Engineering, Molecular Biology, Cellular Biology, Biochemistry, Neurobiology, Anatomy, Physiology, F1FO ATPase, mitochondria, patch clamp, electrophysiology, submitochondrial vesicles, Bcl-xL, cells, rat, animal model
Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes
Institutions: University of Arkansas for Medical Sciences .
The protein kinase C (PKC) family of isozymes is involved in numerous physiological and pathological processes. Our recent data demonstrate that PKC regulates mitochondrial function and cellular energy status. Numerous reports demonstrated that the activation of PKC-a and PKC-ε improves mitochondrial function in the ischemic heart and mediates cardioprotection. In contrast, we have demonstrated that PKC-α and PKC-ε are involved in nephrotoxicant-induced mitochondrial dysfunction and cell death in kidney cells. Therefore, the goal of this study was to develop an in vitro
model of renal cells maintaining active mitochondrial functions in which PKC isozymes could be selectively activated or inhibited to determine their role in regulation of oxidative phosphorylation and cell survival. Primary cultures of renal proximal tubular cells (RPTC) were cultured in improved conditions resulting in mitochondrial respiration and activity of mitochondrial enzymes similar to those in RPTC in vivo
. Because traditional transfection techniques (Lipofectamine, electroporation) are inefficient in primary cultures and have adverse effects on mitochondrial function, PKC-ε mutant cDNAs were delivered to RPTC through adenoviral vectors. This approach results in transfection of over 90% cultured RPTC.
Here, we present methods for assessing the role of PKC-ε in: 1. regulation of mitochondrial morphology and functions associated with ATP synthesis, and 2. survival of RPTC in primary culture. PKC-ε is activated by overexpressing the constitutively active PKC-ε mutant. PKC-ε is inhibited by overexpressing the inactive mutant of PKC-ε. Mitochondrial function is assessed by examining respiration, integrity of the respiratory chain, activities of respiratory complexes and F0
-ATPase, ATP production rate, and ATP content. Respiration is assessed in digitonin-permeabilized RPTC as state 3 (maximum respiration in the presence of excess substrates and ADP) and uncoupled respirations. Integrity of the respiratory chain is assessed by measuring activities of all four complexes of the respiratory chain in isolated mitochondria. Capacity of oxidative phosphorylation is evaluated by measuring the mitochondrial membrane potential, ATP production rate, and activity of F0
-ATPase. Energy status of RPTC is assessed by determining the intracellular ATP content. Mitochondrial morphology in live cells is visualized using MitoTracker Red 580, a fluorescent dye that specifically accumulates in mitochondria, and live monolayers are examined under a fluorescent microscope. RPTC viability is assessed using annexin V/propidium iodide staining followed by flow cytometry to determine apoptosis and oncosis.
These methods allow for a selective activation/inhibition of individual PKC isozymes to assess their role in cellular functions in a variety of physiological and pathological conditions that can be reproduced in in vitro
Cellular Biology, Issue 71, Biochemistry, Molecular Biology, Genetics, Pharmacology, Physiology, Medicine, Protein, Mitochondrial dysfunction, mitochondria, protein kinase C, renal proximal tubular cells, reactive oxygen species, oxygen consumption, electron transport chain, respiratory complexes, ATP, adenovirus, primary culture, ischemia, cells, flow cytometry
Multi-parameter Measurement of the Permeability Transition Pore Opening in Isolated Mouse Heart Mitochondria
Institutions: University of Washington, Seattle.
The mitochondrial permeability transition pore (mtPTP) is a non specific channel that forms in the inner mitochondrial membrane to transport solutes with a molecular mass smaller than 1.5 kDa. Although the definitive molecular identity of the pore is still under debate, proteins such as cyclophilin D, VDAC and ANT contribute to mtPTP formation. While the involvement of mtPTP opening in cell death is well established1
, accumulating evidence indicates that the mtPTP serves a physiologic role during mitochondrial Ca2+
, bioenergetics and redox signaling 3
mtPTP opening is triggered by matrix Ca2+
but its activity can be modulated by several other factors such as oxidative stress, adenine nucleotide depletion, high concentrations of Pi, mitochondrial membrane depolarization or uncoupling, and long chain fatty acids4
. In vitro
, mtPTP opening can be achieved by increasing Ca2+
concentration inside the mitochondrial matrix through exogenous additions of Ca2+
(calcium retention capacity). When Ca2+
levels inside mitochondria reach a certain threshold, the mtPTP opens and facilitates Ca2+
release, dissipation of the proton motive force, membrane potential collapse and an increase in mitochondrial matrix volume (swelling) that ultimately leads to the rupture of the outer mitochondrial membrane and irreversible loss of organelle function.
Here we describe a fluorometric assay that allows for a comprehensive characterization of mtPTP opening in isolated mouse heart mitochondria. The assay involves the simultaneous measurement of 3 mitochondrial parameters that are altered when mtPTP opening occurs: mitochondrial Ca2+
handling (uptake and release, as measured by Ca2+
concentration in the assay medium), mitochondrial membrane potential, and mitochondrial volume. The dyes employed for Ca2+
measurement in the assay medium and mitochondrial membrane potential are Fura FF, a membrane impermeant, ratiometric indicator which undergoes a shift in the excitation wavelength in the presence of Ca2+
, and JC-1, a cationic, ratiometric indicator which forms green monomers or red aggregates at low and high membrane potential, respectively. Changes in mitochondrial volume are measured by recording light scattering by the mitochondrial suspension. Since high-quality, functional mitochondria are required for the mtPTP opening assay, we also describe the steps necessary to obtain intact, highly coupled and functional isolated heart mitochondria.
Cellular Biology, Issue 67, Mitochondria, respiration, mitochondrial permeability transition pore (mPTP), membrane potential, swelling, calcium, spectrofluorometer
Bioenergetic Profile Experiment using C2C12 Myoblast Cells
Institutions: Novato, CA, University of Alabama at Birmingham - UAB, North Billerica, MA.
The ability to measure cellular metabolism and understand mitochondrial dysfunction, has enabled scientists worldwide to advance their research in understanding the role of mitochondrial function in obesity, diabetes, aging, cancer, cardiovascular function and safety toxicity.
Cellular metabolism is the process of substrate uptake, such as oxygen, glucose, fatty acids, and glutamine, and subsequent energy conversion through a series of enzymatically controlled oxidation and reduction reactions. These intracellular biochemical reactions result in the production of ATP, the release of heat and chemical byproducts, such as lactate and CO2
into the extracellular environment.
Valuable insight into the physiological state of cells, and the alteration of the state of those cells, can be gained through measuring the rate of oxygen consumed by the cells, an indicator of mitochondrial respiration - the Oxygen Consumption Rate - or OCR. Cells also generate ATP through glycolysis, i.e.: the conversion of glucose to lactate, independent of oxygen. In cultured wells, lactate is the primary source of protons. Measuring the lactic acid produced indirectly via protons released into the extracellular medium surrounding the cells, which causes acidification of the medium provides the Extra-Cellular Acidification Rate - or ECAR.
In this experiment, C2C12 myoblast cells are seeded at a given density in Seahorse cell culture plates. The basal oxygen consumption (OCR) and extracellular acidification (ECAR) rates are measured to establish baseline rates. The cells are then metabolically perturbed by three additions of different compounds (in succession) that shift the bioenergetic profile of the cell.
This assay is derived from a classic experiment to assess mitochondria and serves as a framework with which to build more complex experiments aimed at understanding both physiologic and pathophysiologic function of mitochondria and to predict the ability of cells to respond to stress and/or insults.
Cellular Biology, Issue 46, Mitochondrial dysfunction, cellular, bioenergetics, metabolism, cancer, obesity, diabetes, aging, neurodegeneration
Monitoring Dynamic Changes In Mitochondrial Calcium Levels During Apoptosis Using A Genetically Encoded Calcium Sensor
Institutions: University of Texas Medical Branch.
Dynamic changes in intracellular calcium concentration in response to various stimuli regulates many cellular processes such as proliferation, differentiation, and apoptosis1
. During apoptosis, calcium accumulation in mitochondria promotes the release of pro-apoptotic factors from the mitochondria into the cytosol2
. It is therefore of interest to directly measure mitochondrial calcium in living cells in situ
during apoptosis. High-resolution fluorescent imaging of cells loaded with dual-excitation ratiometric and non-ratiometric synthetic calcium indicator dyes has been proven to be a reliable and versatile tool to study various aspects of intracellular calcium signaling. Measuring cytosolic calcium fluxes using these techniques is relatively straightforward. However, measuring intramitochondrial calcium levels in intact cells using synthetic calcium indicators such as rhod-2 and rhod-FF is more challenging. Synthetic indicators targeted to mitochondria have blunted responses to repetitive increases in mitochondrial calcium, and disrupt mitochondrial morphology3
. Additionally, synthetic indicators tend to leak out of mitochondria over several hours which makes them unsuitable for long-term experiments. Thus, genetically encoded calcium indicators based upon green fluorescent protein (GFP)4
targeted to mitochondria have greatly facilitated measurement of mitochondrial calcium dynamics. Here, we describe a simple method for real-time measurement of mitochondrial calcium fluxes in response to different stimuli. The method is based on fluorescence microscopy of 'ratiometric-pericam' which is selectively targeted to mitochondria. Ratiometric pericam is a calcium indicator based on a fusion of circularly permuted yellow fluorescent protein and calmodulin4
. Binding of calcium to ratiometric pericam causes a shift of its excitation peak from 415 nm to 494 nm, while the emission spectrum, which peaks around 515 nm, remains unchanged. Ratiometric pericam binds a single calcium ion with a dissociation constant in vitro
of ~1.7 μM4
. These properties of ratiometric pericam allow the quantification of rapid and long-term changes in mitochondrial calcium concentration. Furthermore, we describe adaptation of this methodology to a standard wide-field calcium imaging microscope with commonly available filter sets. Using two distinct agonists, the purinergic agonist ATP and apoptosis-inducing drug staurosporine, we demonstrate that this method is appropriate for monitoring changes in mitochondrial calcium concentration with a temporal resolution of seconds to hours. Furthermore, we also demonstrate that ratiometric pericam is also useful for measuring mitochondrial fission/fragmentation during apoptosis. Thus, ratiometric pericam is particularly well suited for continuous long-term measurement of mitochondrial calcium dynamics during apoptosis.
Cellular Biology, Issue 50, Ratiometric pericam, mitochondria, calcium, apoptosis, staurosporine, live cell imaging
Determination of Mitochondrial Membrane Potential and Reactive Oxygen Species in Live Rat Cortical Neurons
Institutions: Loyola University Chicago.
Mitochondrial membrane potential (ΔΨm) is critical for maintaining the physiological function of the respiratory chain to generate ATP. A significant loss of ΔΨm renders cells depleted of energy with subsequent death. Reactive oxygen species (ROS) are important signaling molecules, but their accumulation in pathological conditions leads to oxidative stress. The two major sources of ROS in cells are environmental toxins and the process of oxidative phosphorylation. Mitochondrial dysfunction and oxidative stress have been implicated in the pathophysiology of many diseases; therefore, the ability to determine ΔΨm and ROS can provide important clues about the physiological status of the cell and the function of the mitochondria.
Several fluorescent probes (Rhodamine 123, TMRM, TMRE, JC-1) can be used to determine Δψm in a variety of cell types, and many fluorescence indicators (Dihydroethidium, Dihydrorhodamine 123, H2
DCF-DA) can be used to determine ROS. Nearly all of the available fluorescence probes used to assess ΔΨm or ROS are single-wavelength indicators, which increase or decrease their fluorescence intensity proportional to a stimulus that increases or decreases the levels of ΔΨm or ROS. Thus, it is imperative to measure the fluorescence intensity of these probes at the baseline level and after the application of a specific stimulus. This allows one to determine the percentage of change in fluorescence intensity between the baseline level and a stimulus. This change in fluorescence intensity reflects the change in relative levels of ΔΨm or ROS. In this video, we demonstrate how to apply the fluorescence indicator, TMRM, in rat cortical neurons to determine the percentage change in TMRM fluorescence intensity between the baseline level and after applying FCCP, a mitochondrial uncoupler. The lower levels of TMRM fluorescence resulting from FCCP treatment reflect the depolarization of mitochondrial membrane potential. We also show how to apply the fluorescence probe H2
DCF-DA to assess the level of ROS in cortical neurons, first at baseline and then after application of H2
. This protocol (with minor modifications) can be also used to determine changes in ∆Ψm and ROS in different cell types and in neurons isolated from other brain regions.
Neuroscience, Issue 51, Mitochondrial membrane potential, reactive oxygen species, neuroscience, cortical neurons
Screening Assay for Oxidative Stress in a Feline Astrocyte Cell Line, G355-5
Institutions: Western University of Health Sciences, Western University of Health Sciences, Products.
An often-suggested mechanism of virus induced neuronal damage is oxidative stress. Astrocytes have an important role in controlling oxidative stress of the Central Nervous System (CNS). Astrocytes help maintain a homeostatic environment for neurons as well as protecting neurons from Reactive Oxygen Species (ROS). CM-H2DCFDA is a cell-permeable indicator for the presence of ROS. CM-H2
DCFDA enters the cell as a non-fluorescent compound, and becomes fluorescent after cellular esterases remove the acetate groups, and the compound is oxidized. The number of cells, measured by flow cytometry, that are found to be green fluorescing is an indication of the number of cells that are in an oxidative state. CM-H2
DCFDA is susceptible to oxidation by a large number of different ROS. This lack of specificity, regarding which ROS can oxidize CM-H2
DCFDA, makes this compound a valuable regent for use in the early stages of a pathogenesis investigation, as this assay can be used to screen for an oxidative cellular environment regardless of which oxygen radical or combination of ROS are responsible for the cellular conditions. Once it has been established that ROS are present by oxidation of CM-H2
DCFDA, then additional experiments can be performed to determine which ROS or combination of ROSs are involved in the particular pathogenesis process. The results of this study demonstrate that with the addition of hydrogen peroxide an increase in CM-H2
DCFDA fluoresce was detected relative to the saline controls, indicating that this assay is a valuable test for detecting an oxidative environment within G355-5 cells, a feline astrocyte cell line.
Neuroscience, Issue 53, Astrocytes, oxidative stress, flow cytometry, CM-H2DCFDA
Production and Detection of Reactive Oxygen Species (ROS) in Cancers
Institutions: Baylor College of Medicine.
Reactive oxygen species include a number of molecules that damage DNA and RNA and oxidize proteins and lipids (lipid peroxydation). These reactive molecules contain an oxygen and include H2
(hydrogen peroxide), NO (nitric oxide), O2-
(oxide anion), peroxynitrite (ONOO-
), hydrochlorous acid (HOCl), and hydroxyl radical (OH-
Oxidative species are produced not only under pathological situations (cancers, ischemic/reperfusion, neurologic and cardiovascular pathologies, infectious diseases, inflammatory diseases 1
, autoimmune diseases 2
, etc…) but also during physiological (non-pathological) situations such as cellular metabolism 3, 4
. Indeed, ROS play important roles in many cellular signaling pathways (proliferation, cell activation 5, 6
, migration 7
etc..). ROS can be detrimental (it is then referred to as "oxidative and nitrosative stress") when produced in high amounts in the intracellular compartments and cells generally respond to ROS by upregulating antioxidants such as superoxide dismutase (SOD) and catalase (CAT), glutathione peroxidase (GPx) and glutathione (GSH) that protects them by converting dangerous free radicals to harmless molecules (i.e. water). Vitamins C and E have also been described as ROS scavengers (antioxidants).
Free radicals are beneficial in low amounts 3
. Macrophage and neutrophils-mediated immune responses involve the production and release of NO, which inhibits viruses, pathogens and tumor proliferation 8
. NO also reacts with other ROS and thus, also has a role as a detoxifier (ROS scavenger). Finally NO acts on vessels to regulate blood flow which is important for the adaptation of muscle to prolonged exercise 9, 10
. Several publications have also demonstrated that ROS are involved in insulin sensitivity 11, 12
Numerous methods to evaluate ROS production are available. In this article we propose several simple, fast, and affordable assays; these assays have been validated by many publications and are routinely used to detect ROS or its effects in mammalian cells. While some of these assays detect multiple ROS, others detect only a single ROS.
Medicine, Issue 57, reactive oxygen species (ROS), stress, ischemia, cancer, chemotherapy, immune response
Fluorescence-based Measurement of Store-operated Calcium Entry in Live Cells: from Cultured Cancer Cell to Skeletal Muscle Fiber
Institutions: Robert Wood Johnson Medical School , Robert Wood Johnson Medical School , University of Missouri-Kansas City.
Store operated Ca2+
entry (SOCE), earlier termed capacitative Ca2+
entry, is a tightly regulated mechanism for influx of extracellular Ca2+
into cells to replenish depleted endoplasmic reticulum (ER) or sarcoplasmic reticulum (SR) Ca2+
. Since Ca2+
is a ubiquitous second messenger, it is not surprising to see that SOCE plays important roles in a variety of cellular processes, including proliferation, apoptosis, gene transcription and motility. Due to its wide occurrence in nearly all cell types, including epithelial cells and skeletal muscles, this pathway has received great interest3,4
. However, the heterogeneity of SOCE characteristics in different cell types and the physiological function are still not clear5-7
The functional channel properties of SOCE can be revealed by patch-clamp studies, whereas a large body of knowledge about this pathway has been gained by fluorescence-based intracellular Ca2+
measurements because of its convenience and feasibility for high-throughput screening. The objective of this report is to summarize a few fluorescence-based methods to measure the activation of SOCE in monolayer cells, suspended cells and muscle fibers5,8-10
. The most commonly used of these fluorescence methods is to directly monitor the dynamics of intracellular Ca2+
using the ratio of F340nm
(510 nm for emission wavelength) of the ratiometric Ca2+
indicator Fura-2. To isolate the activity of unidirectional SOCE from intracellular Ca2+
release and Ca2+
extrusion, a Mn2+
quenching assay is frequently used. Mn2+
is known to be able to permeate into cells via SOCE while it is impervious to the surface membrane extrusion processes or to ER uptake by Ca2+
pumps due to its very high affinity with Fura-2. As a result, the quenching of Fura-2 fluorescence induced by the entry of extracellular Mn2+
into the cells represents a measurement of activity of SOCE9
. Ratiometric measurement and the Mn+2
quenching assays can be performed on a cuvette-based spectrofluorometer in a cell population mode or in a microscope-based system to visualize single cells. The advantage of single cell measurements is that individual cells subjected to gene manipulations can be selected using GFP or RFP reporters, allowing studies in genetically modified or mutated cells. The spatiotemporal characteristics of SOCE in structurally specialized skeletal muscle can be achieved in skinned muscle fibers by simultaneously monitoring the fluorescence of two low affinity Ca2+
indicators targeted to specific compartments of the muscle fiber, such as Fluo-5N in the SR and Rhod-5N in the transverse tubules9,11,12
Cellular Biology, Issue 60, Mn quenching, 2-APB, Fura-2, Orai1, esophageal squamous cell carcinoma, skinned muscle fiber
Visualization of Vascular Ca2+ Signaling Triggered by Paracrine Derived ROS
Institutions: Temple University , University of Washington.
Oxidative stress has been implicated in a number of pathologic conditions including ischemia/reperfusion damage and sepsis. The concept of oxidative stress refers to the aberrant formation of ROS (reactive oxygen species), which include O2•-
, and hydroxyl radicals. Reactive oxygen species influences a multitude of cellular processes including signal transduction, cell proliferation and cell death1-6
. ROS have the potential to damage vascular and organ cells directly, and can initiate secondary chemical reactions and genetic alterations that ultimately result in an amplification of the initial ROS-mediated tissue damage. A key component of the amplification cascade that exacerbates irreversible tissue damage is the recruitment and activation of circulating inflammatory cells. During inflammation, inflammatory cells produce cytokines such as tumor necrosis factor-α (TNFα) and IL-1 that activate endothelial cells (EC) and epithelial cells and further augment the inflammatory response7
. Vascular endothelial dysfunction is an established feature of acute inflammation. Macrophages contribute to endothelial dysfunction during inflammation by mechanisms that remain unclear. Activation of macrophages results in the extracellular release of O2•-
and various pro-inflammatory cytokines, which triggers pathologic signaling in adjacent cells8
. NADPH oxidases are the major and primary source of ROS in most of the cell types. Recently, it is shown by us and others9,10
that ROS produced by NADPH oxidases induce the mitochondrial ROS production during many pathophysiological conditions. Hence measuring the mitochondrial ROS production is equally important in addition to measuring cytosolic ROS. Macrophages produce ROS by the flavoprotein enzyme NADPH oxidase which plays a primary role in inflammation. Once activated, phagocytic NADPH oxidase produces copious amounts of O2•-
that are important in the host defense mechanism11,12
. Although paracrine-derived O2•-
plays an important role in the pathogenesis of vascular diseases, visualization of paracrine ROS-induced intracellular signaling including Ca2+
mobilization is still hypothesis. We have developed a model in which activated macrophages are used as a source of O2•-
to transduce a signal to adjacent endothelial cells. Using this model we demonstrate that macrophage-derived O2•-
lead to calcium signaling in adjacent endothelial cells.
Molecular Biology, Issue 58, Reactive oxygen species, Calcium, paracrine superoxide, endothelial cells, confocal microscopy
Enhancement of Apoptotic and Autophagic Induction by a Novel Synthetic C-1 Analogue of 7-deoxypancratistatin in Human Breast Adenocarcinoma and Neuroblastoma Cells with Tamoxifen
Institutions: University of Windsor, Brock University.
Breast cancer is one of the most common cancers amongst women in North America. Many current anti-cancer treatments, including ionizing radiation, induce apoptosis via DNA damage. Unfortunately, such treatments are non-selective to cancer cells and produce similar toxicity in normal cells. We have reported selective induction of apoptosis in cancer cells by the natural compound pancratistatin (PST). Recently, a novel PST analogue, a C-1 acetoxymethyl derivative of 7-deoxypancratistatin (JCTH-4), was produced by de novo synthesis and it exhibits comparable selective apoptosis inducing activity in several cancer cell lines. Recently, autophagy has been implicated in malignancies as both pro-survival and pro-death mechanisms in response to chemotherapy. Tamoxifen (TAM) has invariably demonstrated induction of pro-survival autophagy in numerous cancers. In this study, the efficacy of JCTH-4 alone and in combination with TAM to induce cell death in human breast cancer (MCF7) and neuroblastoma (SH-SY5Y) cells was evaluated. TAM alone induced autophagy, but insignificant cell death whereas JCTH-4 alone caused significant induction of apoptosis with some induction of autophagy. Interestingly, the combinatory treatment yielded a drastic increase in apoptotic and autophagic induction. We monitored time-dependent morphological changes in MCF7 cells undergoing TAM-induced autophagy, JCTH-4-induced apoptosis and autophagy, and accelerated cell death with combinatorial treatment using time-lapse microscopy. We have demonstrated these compounds to induce apoptosis/autophagy by mitochondrial targeting in these cancer cells. Importantly, these treatments did not affect the survival of noncancerous human fibroblasts. Thus, these results indicate that JCTH-4 in combination with TAM could be used as a safe and very potent anti-cancer therapy against breast cancer and neuroblastoma cells.
Cancer Biology, Issue 63, Medicine, Biochemistry, Breast adenocarcinoma, neuroblastoma, tamoxifen, combination therapy, apoptosis, autophagy
Cytosolic Calcium Measurements in Renal Epithelial Cells by Flow Cytometry
Institutions: University of Witten/Herdecke, University of Witten/Herdecke.
A variety of cellular processes, both physiological and pathophysiological, require or are governed by calcium, including exocytosis, mitochondrial function, cell death, cell metabolism and cell migration to name but a few. Cytosolic calcium is normally maintained at low nanomolar concentrations; rather it is found in high micromolar to millimolar concentrations in the endoplasmic reticulum, mitochondrial matrix and the extracellular compartment. Upon stimulation, a transient increase in cytosolic calcium serves to signal downstream events. Detecting changes in cytosolic calcium is normally performed using a live cell imaging set up with calcium binding dyes that exhibit either an increase in fluorescence intensity or a shift in the emission wavelength upon calcium binding. However, a live cell imaging set up is not freely accessible to all researchers. Alternative detection methods have been optimized for immunological cells with flow cytometry and for non-immunological adherent cells with a fluorescence microplate reader. Here, we describe an optimized, simple method for detecting changes in epithelial cells with flow cytometry using a single wavelength calcium binding dye. Adherent renal proximal tubule epithelial cells, which are normally difficult to load with dyes, were loaded with a fluorescent cell permeable calcium binding dye in the presence of probenecid, brought into suspension and calcium signals were monitored before and after addition of thapsigargin, tunicamycin and ionomycin.
Cellular Biology, Issue 92, Kidney, FACS, second messenger, proximal tubule, calcium indicators, probenecid, endoplasmic reticulum, ionomycin