Name: measuring mitochondrial substrate flux in recombinant perfringolysin o-permeabilized cells
Uploaded: 2021-08-13T14:30:00
Description: Watch this Scientific Journal Video about Measuring Mitochondrial Substrate Flux in Recombinant Perfringolysin O-Permeabilized Cells at JoVE.com

The authors thank the staff members of the Department of Physiology in the Faculty of Medicine in Hradec Kr&#225;lov&#233; and the Department of Pathophysiology in the Third Faculty of Medicine for the help with chemicals and samples preparation. This work was supported by Charles University grant programs PROGRES Q40/02, Czech Ministry of Health grant NU21-01-00259, Czech science foundation grant 18-10144 and INOMED project CZ.02.1.01/0.0/0.0/18_069/0010046 funded by the Ministry of Education, Youth and Sports of the Czech Republic and by the European Union.

1. One day before the assay
<ol>
	<li>Preparation of reagents and substrates.
	<ol>
		<li>Mitochondrial assay solution (MAS): Prepare stock solutions of all reagents as described in Table 1. Warm the stocks of mannitol and sucrose to 37 &#176;C to dissolve completely. Mix the reagents to prepare 2x MAS, then warm the mixture to 37 &#176;C. Adjust the pH with 5N KOH to 7.4 (~7 mL), then add water to bring the volume up to 1 L. Filter-sterilize&#160;and store the aliquots at -20 &#176;C until the measure...

<ol>
	<li>Gerencser, A. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+microplate-based+respirometry+with+correction+for+oxygen+diffusion.">Quantitative microplate-based respirometry with correction for oxygen diffusion.</a> Analytical Chemistry. 81 (16), 6868-6878 (2009).</li><li>Murphy, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+function,+biology,+and+role+in+disease:+A+scientific+statement+from+the+American+Heart+Association.">Mitochondrial function, biology, and role in disease: A scientific statement from the American Heart Association.</a> Circulation Research. 118 (12), 1960-1991 (2016).</li><li>Owen, O. E., Kalhan, S. C., Hanson, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+key+role+of+anaplerosis+and+cataplerosis+for+citric+acid+cycle+function.">The key role of anaplerosis and cataplerosis for citric acid cycle function.</a> Journal of Biological Chemistry. 277 (34), 30409-30412 (2002).</li><li>Nicholls, D. G., Ferguson, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Bioenergetics 3. , (2002).</li><li>Brand, M. D., Nicholls, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessing+mitochondrial+dysfunction+in+cells.">Assessing mitochondrial dysfunction in cells.</a> Biochemical Journal. 435 (2), 297-312 (2011).</li><li>Sta&#328;kov&#225;, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptation+of+mitochondrial+substrate+flux+in+a+mouse+model+of+nonalcoholic+fatty+liver+disease.">Adaptation of mitochondrial substrate flux in a mouse model of nonalcoholic fatty liver disease.</a> International Journal of Molecular Sciences. 21 (3), 1101 (2020).</li><li>Salabei, J. K., Gibb, A. A., Hill, B. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+measurement+of+respiratory+activity+in+permeabilized+cells+using+extracellular+flux+analysis.">Comprehensive measurement of respiratory activity in permeabilized cells using extracellular flux analysis.</a> Nature Protocols. 9 (2), 421-438 (2014).</li><li>Divakaruni, A. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thiazolidinediones+are+acute,+specific+inhibitors+of+the+mitochondrial+pyruvate+carrier.">Thiazolidinediones are acute, specific inhibitors of the mitochondrial pyruvate carrier.</a> Proceedings of the National Academy of Sciences of the United States of America. 110 (14), 5422-5427 (2011).</li><li>Divakaruni, A. S., Rogers, G. W., Murphy, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+mitochondrial+function+in+permeabilized+cells+using+the+seahorse+XF+analyzer+or+a+Clark-type+oxygen+electrode.">Measuring mitochondrial function in permeabilized cells using the seahorse XF analyzer or a Clark-type oxygen electrode.</a> Current Protocols in Toxicology. 60, 1-16 (2014).</li><li>Elkalaf, M., T&#367;ma, P., Weiszenstein, M., Pol&#225;k, J., Trnka, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+probe+Methyltriphenylphosphonium+(TPMP)+inhibits+the+Krebs+cycle+enzyme+2-Oxoglutarate+dehydrogenase.">Mitochondrial probe Methyltriphenylphosphonium (TPMP) inhibits the Krebs cycle enzyme 2-Oxoglutarate dehydrogenase.</a> PLoS One. 11 (8), 0161413 (2016).</li><li>Rogers, G. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+throughput+microplate+respiratory+measurements+using+minimal+quantities+of+isolated+mitochondria.">High throughput microplate respiratory measurements using minimal quantities of isolated mitochondria.</a> PLoS One. 6 (7), 21746 (2011).</li></ol>

This protocol is a modification of previously published studies7,8,9,10 and the product user guide. In contrast to the manufacturer&#39;s protocol, 2x MAS is used instead of 3x MAS, since 2&#215; MAS is easier to dissolve and does not form precipitations after freezing. Frozen 2x MAS aliquots can be stored up to six months and show consistent results. Another difference is including ADP in the ...

Microplate-based respirometry has revolutionized mitochondrial research by enabling the study of cellular respiration of a small sample size1. Cellular respiration is generally considered as an indicator of mitochondrial function or &#39;dysfunction&#39;, despite the fact that the mitochondrial range of functions extends beyond energy production2. In aerobic conditions, mitochondria extract the energy stored in different substrates by breaking down and converting these substrates into metabolic intermediates that can fuel the citric acid cycle3 (Figure 1). The continuous flux of substrates is essential for the flow of the citric acid cycle to generate high energy &#39;electron donors&#39;, which deliver electrons to the electron transport chain that generates a proton gradient across the inner mitochondrial membrane, enabling ATP-synthase to phosphorylate ADP to ATP4. Therefore, an experimental design to assay mitochondrial respiration must include the sample nature (intact cells, permeabilized cells, or isolated mitochondria) and mitochondrial substrates.
Cells keep a store of indigenous substrates5, and mitochondria oxidize several types of substrates simultaneously6, which complicates the interpretation of results obtained from experiments performed on intact cells. A common approach to investigate mitochondrial ability to oxidize a selected substrate is to isolate mitochondria or permeabilize the investigated cells5. Although isolated mitochondria are ideal for quantitative studies, the isolation process is laborious. It faces technical difficulties such as the need for large sample size, purity of the yield, and reproducibility of the technique5. Permeabilized cells offer a solution for the disadvantages of mitochondrial isolation; however, routine permeabilizing agents of detergent nature are not specific and may damage mitochondrial membranes5.
Recombinant perfringolysin O (rPFO) was offered as a selective plasma membrane permeabilizing agent7, and it was used successfully in combination with an extracellular flux analyzer in several studies7,8,9,10. We have modified a protocol using rPFO to screen mitochondrial substrate flux using XFe96 extracellular flux analyzer. In this protocol, four different substrate oxidizing pathways in two cellular phenotypes are compared while having sufficient replicates and the proper control for each tested material.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Adinosine 5&#8242; -diphosphate monopotassium salt dihydrate</td>
			<td>Merck</td>
			<td>A5285</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Antimycin A</td>
			<td>Merck</td>
			<td>A8674</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Bovine serum albumin</td>
			<td>Merck</td>
			<td>A3803</td>
			<td>store at 2 - 8 &#176;C</td>
		</tr>
		<tr>
			<td>Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone</td>
			<td>Merck</td>
			<td>C2920</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>Merck</td>
			<td>D8418</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>D-Mannitol</td>
			<td>Merck</td>
			<td>63559</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s phosphate buffered saline</td>
			<td>Gibco</td>
			<td>14190-144</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Ethylene glycol-bis(2-aminoethylether)-N,N,N&#8242;,N&#8242;-tetraacetic acid</td>
			<td>Merck</td>
			<td>03777</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Merck</td>
			<td>H7523</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>L(-)Malic acid disodium salt</td>
			<td>Merck</td>
			<td>M9138</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>L-Glutamic acid sodium salt hydrate</td>
			<td>Merck</td>
			<td>G5889</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Magnissium chloride hexahydrate</td>
			<td>Merck</td>
			<td>M2670</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Oligomycin</td>
			<td>Merck</td>
			<td>O4876</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Palmitoyl-DL-carnitine chloride</td>
			<td>Merck</td>
			<td>P4509</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Potassium hydroxide</td>
			<td>Merck</td>
			<td>484016</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Merck</td>
			<td>P5655</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Rotenone</td>
			<td>Merck</td>
			<td>R8875</td>
			<td>store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Seahorse Wave Desktop Software</td>
			<td>Agilent technologies</td>
			<td></td>
			<td>Download from www.agilent.com</td>
		</tr>
		<tr>
			<td>Seahorse XFe96 Analyzer</td>
			<td>Agilent technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Seahorse XFe96 FluxPak</td>
			<td>Agilent technologies</td>
			<td>102416-100</td>
			<td>XFe96 sensor cartridges and XF96 cell culture microplates</td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td>Merck</td>
			<td>P2256</td>
			<td>store at 2 - 8 &#176;C</td>
		</tr>
		<tr>
			<td>Sodium succinate dibasic hexahydrate</td>
			<td>Merck</td>
			<td>S2378</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Merck</td>
			<td>S7903</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>Water</td>
			<td>Merck</td>
			<td>W3500</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>XF calibrant</td>
			<td>Agilent technologies</td>
			<td>100840-000</td>
			<td>store at RT</td>
		</tr>
		<tr>
			<td>XF Plasma membrane permeabilizer</td>
			<td>Agilent technologies</td>
			<td>102504-100</td>
			<td>Recombinant perfringolysin O (rPFO) - Aliquot and store at -20 &#176;C</td>
		</tr>
	</tbody>
</table>

measuring mitochondrial substrate flux in recombinant perfringolysin o-permeabilized cells

Mitochondrial substrate flux is a distinguishing characteristic of each cell type, and changes in its components such as transporters, channels, or enzymes are involved in the pathogenesis of several diseases. Mitochondrial substrate flux can be studied using intact cells, permeabilized cells, or isolated mitochondria. Investigating intact cells encounters several problems due to simultaneous oxidation of different substrates. Besides, several cell types contain internal stores of different substrates that complicate results interpretation. Methods such as mitochondrial isolation or using permeabilizing agents are not easily reproducible. Isolating pure mitochondria with intact membranes in sufficient amounts from small samples is problematic. Using non-selective permeabilizers causes various degrees of unavoidable mitochondrial membrane damage. Recombinant perfringolysin O (rPFO) was offered as a more appropriate permeabilizer, thanks to its ability to selectively permeabilize plasma membrane without affecting mitochondrial integrity. When used in combination with microplate respirometry, it allows testing the flux of several mitochondrial substrates with enough replicates within one experiment while using a minimal number of cells. In this work, the protocol describes a method to compare mitochondrial substrate flux of two different cellular phenotypes or genotypes and can be customized to test various mitochondrial substrates or inhibitors.

Start by normalizing the results to the second measurement of baseline respiration to show values as oxygen consumption rate percentage (OCR%). The results of the assay are shown in Figures 5, Figure 6, Figure 7, and Figure 8. It is important to assign the proper background wells for each group and inactivate the background wells of other groups. Fi...

Watch this Scientific Journal Video about Measuring Mitochondrial Substrate Flux in Recombinant Perfringolysin O-Permeabilized Cells at JoVE.com

Measuring Mitochondrial Substrate Flux in Recombinant Perfringolysin O-Permeabilized Cells

In this work, we describe a modified protocol to test mitochondrial respiratory substrate flux using recombinant perfringolysin O in combination with microplate-based respirometry. With this protocol, we show how metformin affects mitochondrial respiration of two different tumor cell lines.

Mitochondrial substrate flux is a distinguishing characteristic of each cell type, and changes in its components such as transporters, channels, or ...

Because it tests mitochondria substrate flux that can be affected with different pathologies or treatments. For example, today we will use it to reveal cancer cell response to Metformin treatment. It requires a minimal number of cells while having sufficient replicates and appropriate control for each distinct material.The analyzer is for research use only. This technique can identify errors in mitochondrial metabolism and can be used to evaluate warriors drugs affecting mitochondria. Demonstrating the procedure will be Karolina Vaneckova an undergraduate student and research technician from my laboratory.To begin seed A549 cells at a density of 20, 000 cells per well in columns, two to 11 of a seahorse XF 96 cell culture micro-plate. Leaving columns one and 12 empty as background wells. Fill the blank Wells with an equal volume of the cell culture medium, then incubate the cells at 37 degrees Celsius in a humidified incubator with 5%carbon dioxide for cell attachment.After three to four hours, add 100 microliters of cell culture medium in the Wells. Treat the experimental group columns seven to 11 with one millimolar Metformin and the control group with an equal volume of sterile distilled water, then return the plate to the incubator. For hydrating the sensors, pipette 200 microliters of sterile water per well into the utility plate.Then carefully return the sensor cartridge while immersing the sensor in water. Incubate the cartridge in a carbon dioxide free incubator at 37 degrees Celsius till the next day. Switch on the analyzer and the control unit.Start the instrument control and data acquisition software, and design the assay protocol as described in the text manuscript. Under group definitions, create four injection strategies where port A differs according to the injected substrate and name the strategies after the substrates or abbreviations. Assign Oligomycin to port B, FCCP to port C and Rotenone Antimycin A mixture to port D.Create and name eight groups, under the plate map, assign groups to the corresponding Wells.Then save the protocol as a ready to use template. Leave the analyzer switch on to allow the temperature to stabilize overnight. The next day, discard the water from the utility plate and add 200 microliters of the pre-warmed calibrant per well in the utility plate.Return the cartridge to the carbon dioxide free incubator until the time of the assay. Maintain a source of humidity inside the incubator and turn off or reduce the fan speed to a minimum, to avoid rapid evaporation of the calibrant. Prepare five milliliters of the working solution of the substrates and inhibitors with pre-warmed two times mitochondrial assay solution, 5%BSA and sterile water as described in the text manuscript.Next, load the injector ports with substrate and inhibitors as described in the tax manuscript. For calibration under the run assay tab, click on the start run to start the assay. Insert the loaded censor cartridge and wait for the calibration to complete.Prepare a 20 milliliters of assay medium, by mixing two times mitochondrial assay solution, sterile water and 5%BSA in a 50 milliliter tube. Add two microliters of 10 micromolar recombinant perfringolysin O, to attain a concentration of one nanomolar. And re-suspend the mixture with gentle pipetting, avoiding shaking and vortexing.Incubate the tube at 37 degrees Celsius until use. Use a multi-channel pipette to wash the cells and the empty blank Wells two times, using pre-warmed calcium and magnesium free PBS solution. Discard the PBS and add 180 microliters of the pre-warmed assay medium for cell permeabilization.Immediately after permeabilization replace the utility plate of the calibrated sensor cartridge with the cell plate containing permeabilized cells and start the measurement. The treatment group had a higher rate of succinate induced respiration. The response of A549 cells to Metformin treatment was higher than Hep G2.For the pyruvate malate induced respiration, A549 cells showed increased induction compared to Hep G2 cells between five to 15 minutes.Similar results were obtained for glutamate malate induced respiration and palmitoylcarnitine malate induced respiration. To attain the right concentration of substrate and inhibitors. The right volume must be loaded into the right port.When a change in a metabolic pathway of a certain substrate is identified, it will be necessary to assess the function of the enzymes and transporters involved in that pathway.

measuring-mitochondrial-substrate-flux-recombinant-perfringolysin-o

Research

JoVE Journal

Biology

A Method For Production of Recombinant mCD1d Protein in Insect Cells.

CD1 proteins constitute a third class of antigen-presenting molecules. They are cell surface glycoproteins, expressed as approximately 50-kDa glycosylated heavy chains that are noncovalently associated with beta2-microglobulin. They bind lipids rather than peptides. Although their structure confirms the similarity of CD1 proteins to MHC class I and class II antigen presenting molecules, the mCD1d groove is relatively narrow, deep, and highly hydrophobic and it has two binding pockets instead of the several shallow pockets described for the classical MHC-encoded antigen-presenting molecules. Based upon their amino acid sequences, such a hydrobphobic groove provides an ideal environment for the binding of lipid antigens. The Natural Killer T (NKT) cells use their TCR to recognize glycolipids bound to or presented by CD1d. T cells reactive to lipids presented by CD1 have been involved in the protection against autoimmune and infectious diseases and in tumor rejection. Thus, the ability to identify, purify , and track the response of CD1-reactive NKT cell is of great importance . The generation of tetramers of alpha Galactosyl ceramide (a-Galcer) with CD1d has significant insight into the biology of NKT cells. Tetramers constructed from other CD1 molecules have also been generated and these new reagents have greatly expanded the knowledge of the functions of lipid-reactive T cells, with potential use in monitoring the response to lipid-based vaccines and in the diagnosis of autoimmune diseases and other treatments.

A Method to prepare Insect cells and infect them with baculovirus for the the purpose of production of recombinant mCD1d proteinand generating mCD1d tetramers.

CD1 proteins constitute a third class of antigen-presenting molecules. They are cell surface glycoproteins, expressed as approximately 50-kDa glycosylated ...

Probing for Mitochondrial Complex Activity in Human Embryonic Stem Cells

Mitochondria are cytoplasmic organelles that have a primary role in cellular metabolism and homeostasis, regulation of the cell signaling network, and programmed cell death. Mitochondria produce ATP, regulate the cytoplasmic redox state and Ca2+ balance, catabolize fatty acids, synthesize heme, nucleotides, steroid hormones, amino acids, and help assemble iron-sulfur clusters in proteins. Mitochondria also have an essential role in heat production. Mutations of the mitochondrial genome cause several types of human disorder. The accumulation of mtDNA mutations correlates with aging and is suspected to have an important role in the development of cancer. Due to their vitally important role in all cell types, the function of mitochondria must also be critical for stem cells. Key advances have been made in our understanding of stem cell viability, proliferation, and differentiation capacity. But the functional activity of stem cells, in particular their energy status, was not yet been studied in detail. Almost nothing is known about the mitochondrial properties of human embryonic stem cells (hESCs) and their differentiated precursor progeny. One way to understand and evaluate the role of mitochondria in hESC function and developmental potential is to directly measure the activity of mitochondrial respiratory complexes. Here, we describe high resolution clear native gel electrophoresis and subsequent in gel activity visualization as a method for analyzing the five respiratory chain complexes of hESCs.

In this video, we will show you how the mitochondrial respiratory chain complexes of human embryonic stem cells can be analyzed using in gel activity assays.

Mitochondria are cytoplasmic organelles that have a primary role in cellular metabolism and homeostasis, regulation of the cell signaling network, and ...

Measuring Glutathione-induced Feeding Response in Hydra

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. The movement of prey organisms causes mechanosensory discharge of the stinging cells called nematocysts from hydra, which are inserted into the prey. The feeding response in hydra, which includes curling of the tentacles to bring the prey towards the mouth, opening of the mouth and consequent engulfing of the prey, is triggered by GSH present in the fluid released from the injured prey. To be able to identify the molecular mechanism of the feeding response in hydra which is unknown to date, it is necessary to establish an assay to measure the feeding response. Here, we describe a simple method for the quantitation of the feeding response in which the distance between the apical end of the tentacle and mouth of hydra is measured and the ratio of such distance before and after the addition of GSH is determined. The ratio, called the relative tentacle spread, was found to give a measure of the feeding response. This assay was validated using a starvation model in which starved hydra show an enhanced feeding response in comparison with daily fed hydra.

Here we describe a simple assay for the quantification of the feeding response in hydra induced by the reduced form of glutathione. This assay relies on measuring the distance between the apical end of the tentacle and mouth of hydra.

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. ...

Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy

Apart from their essential role in generating ATP, mitochondria also act as local calcium (Ca2+) buffers to tightly regulate intracellular Ca2+ concentration. To do this, mitochondria utilize the electrochemical potential across their inner membrane (&#916;&#936;m) to sequester Ca2+. The influx of Ca2+ into the mitochondria stimulates three rate-limiting dehydrogenases of the citric acid cycle, increasing electron transfer through the oxidative phosphorylation (OXPHOS) complexes. This stimulation maintains &#916;&#936;m, which is temporarily dissipated as the positive calcium ions cross the mitochondrial inner membrane into the mitochondrial matrix.
We describe here a method for simultaneously measuring mitochondria Ca2+ uptake and &#916;&#936;m in live cells using confocal microscopy. By permeabilizing the cells, mitochondrial Ca2+ can be measured using the fluorescent Ca2+ indicator Fluo-4, AM, with measurement of &#916;&#936;m using the fluorescent dye tetramethylrhodamine, methyl ester, perchlorate (TMRM). The benefit of this system is that there is very little spectral overlap between the fluorescent dyes, allowing accurate measurement of mitochondrial Ca2+ and &#916;&#936;m simultaneously. Using the sequential addition of Ca2+ aliquots, mitochondrial Ca2+ uptake can be monitored, and the concentration at which Ca2+ induces mitochondrial membrane permeability transition and the loss of &#916;&#936;m determined.

Mitochondria can utilize the electrochemical potential across their inner membrane (&#916;&#936;m) to sequester calcium (Ca2+), allowing them to shape cytosolic Ca2+ signaling within the cell. We describe a method for simultaneously measuring mitochondria Ca2+ uptake and &#916;&#936;m in live cells using fluorescent dyes and confocal microscopy.

Apart from their essential role in generating ATP, mitochondria also act as local calcium (Ca2+) buffers to tightly regulate intracellular Ca2+ ...

Assessing Autophagic Flux by Measuring LC3, p62, and LAMP1 Co-localization Using Multispectral Imaging Flow Cytometry

Autophagy is a catabolic pathway in which normal or dysfunctional cellular components that accumulate during growth and differentiation are degraded via the lysosome and are recycled. During autophagy, cytoplasmic LC3 protein is lipidated and recruited to the autophagosomal membranes. The autophagosome then fuses with the lysosome to form the autolysosome, where the breakdown of the autophagosome vesicle and its contents occurs. The ubiquitin-associated protein p62, which binds to LC3, is also used to monitor autophagic flux. Cells undergoing autophagy should demonstrate the co-localization of p62, LC3, and lysosomal markers. Immunofluorescence microscopy has been used to visually identify LC3 puncta, p62, and/or lysosomes on a per-cell basis. However, an objective and statistically rigorous assessment can be difficult to obtain. To overcome these problems, multispectral imaging flow cytometry was used along with an analytical feature that compares the bright detail images from three autophagy markers (LC3, p62 and lysosomal LAMP1) and quantifies their co-localization, in combination with LC3 spot counting to measure autophagy in an objective, quantitative, and statistically robust manner.

Here, multispectral imaging flow cytometry with an analytical feature that compares bright detail images of 3 autophagy markers and quantifies their co-localization, along with LC3 spot counting, was used to measure autophagy in an objective, quantitative, and statistically robust manner.

Autophagy is a catabolic pathway in which normal or dysfunctional cellular components that accumulate during growth and differentiation are degraded via ...

A Graphical User Interface for Software-assisted Tracking of Protein Concentration in Dynamic Cellular Protrusions

Filopodia are dynamic, finger-like cellular protrusions associated with migration and cell-cell communication. In order to better understand the complex signaling mechanisms underlying filopodial initiation, elongation and subsequent stabilization or retraction, it is crucial to determine the spatio-temporal protein activity in these dynamic structures. To analyze protein function in filopodia, we recently developed a semi-automated tracking algorithm that adapts to filopodial shape-changes, thus allowing parallel analysis of protrusion dynamics and relative protein concentration along the whole filopodial length. Here, we present a detailed step-by-step protocol for optimized cell handling, image acquisition and software analysis. We further provide instructions for the use of optional features during image analysis and data representation, as well as troubleshooting guidelines for all critical steps along the way. Finally, we also include a comparison of the described image analysis software with other programs available for filopodia quantification. Together, the presented protocol provides a framework for accurate analysis of protein dynamics in filopodial protrusions using image analysis software.

We present a software solution for semi-automated tracking of relative protein concentration along the length of dynamic cellular protrusions.

Filopodia are dynamic, finger-like cellular protrusions associated with migration and cell-cell communication. In order to better understand the complex ...

Transient Expression and Cellular Localization of Recombinant Proteins in Cultured Insect Cells

Heterologous protein expression systems are used for the production of recombinant proteins, the interpretation of cellular trafficking/localization, and the determination of the biochemical function of proteins at the sub-organismal level. Although baculovirus expression systems are increasingly used for protein production in numerous biotechnological, pharmaceutical, and industrial applications, nonlytic systems that do not involve viral infection have clear benefits but are often overlooked and underutilized. Here, we describe a method for generating nonlytic expression vectors and transient recombinant protein expression. This protocol allows for the efficient cellular localization of recombinant proteins and can be used to rapidly discern protein trafficking within the cell. We show the expression of four&#160;recombinant proteins in a commercially available insect cell line, including two aquaporin proteins from the insect Bemisia tabaci, as well as subcellular marker proteins specific for the cell plasma membrane and for intracellular lysosomes. All recombinant proteins were produced as chimeras with fluorescent protein markers at their carboxyl termini, which allows for the direct detection of the recombinant proteins. The double transfection of cells with plasmids harboring constructs for the genes of interest and a known subcellular marker allows for live cell imaging and improved validation of cellular protein localization.

Nonlytic insect cell expression systems are underutilized for production, cellular trafficking/localization, and recombinant protein functional analysis. Here, we describe methods to generate expression vectors and subsequent transient protein expression in commercially available lepidopteran cell lines. The co-localization of Bemisia tabaci aquaporins with subcellular fluorescent marker proteins is also presented.

Heterologous protein expression systems are used for the production of recombinant proteins, the interpretation of cellular trafficking/localization, and ...

Measurement of Energy Metabolism in Explanted Retinal Tissue Using Extracellular Flux Analysis

High acuity vision is a heavily energy-consuming process, and the retina has developed several unique adaptations to precisely meet such demands while maintaining transparency of the visual axis. Perturbations to this delicate balance cause blinding illnesses, such as diabetic retinopathy. Therefore, the understanding of energy metabolism changes in the retina during disease is imperative to the development of rational therapies for various causes of vison loss. The recent advent of commercially-available extracellular flux analyzers has made the study of retinal energy metabolism more accessible. This protocol describes the use of such an analyzer to measure contributions to retinal energy supply through its two principle arms - oxidative phosphorylation and glycolysis - by quantifying changes in oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) as proxies for these pathways. This technique is readily performed in explanted retinal tissue, facilitating assessment of responses to multiple pharmacologic agents in a single experiment. Metabolic signatures in retinas from animals lacking rod photoreceptor signaling are compared to wild-type controls using this method. A major limitation in this technique is the lack of ability to discriminate between light-adapted and dark-adapted energy utilization, an important physiologic consideration in retinal tissue.

This technique describes real time recording of oxygen consumption and extracellular acidification rates in explanted mouse retinal tissues using an extracellular flux analyzer.

High acuity vision is a heavily energy-consuming process, and the retina has developed several unique adaptations to precisely meet such demands while ...

Measuring Diurnal Rhythms in Autophagic and Proteasomal Flux

Cells employ several methods for recycling unwanted proteins and other material, including lysosomal and non-lysosomal pathways. The main lysosome-dependent pathway is called autophagy, while the primary non-lysosomal method for protein catabolism is the ubiquitin-proteasome system. Recent studies in model organisms suggest that the activity of both autophagy and the ubiquitin-proteasome system is not constant across the day but instead varies according to a daily (circadian) rhythm. The ability to measure biological rhythms in protein turnover is important for understanding how cellular quality control is achieved and for understanding the dynamics of specific proteins of interest. Here we present a standardized protocol for quantifying autophagic and proteasomal flux in vivo that captures the circadian component of protein turnover. Our protocol includes details for mouse handling, tissue processing, fractionation, and autophagic flux quantification using mouse liver as the starting material.

We describe our protocol for measuring biological rhythms in protein catabolism via autophagy and the proteasome in mouse liver.

Cells employ several methods for recycling unwanted proteins and other material, including lysosomal and non-lysosomal pathways. The main ...

Development of a Mobile Mitochondrial Physiology Laboratory for Measuring Mitochondrial Energetics in the Field

Mitochondrial energetics is a central theme in animal biochemistry and physiology, with researchers using mitochondrial respiration as a metric to investigate metabolic capability. To obtain the measures of mitochondrial respiration, fresh biological samples must be used, and the entire laboratory procedure must be completed within approximately 2 h. Furthermore, multiple pieces of specialized equipment are required to perform these laboratory assays. This creates a challenge for measuring mitochondrial respiration in the tissues of wild animals living far from physiology laboratories as live tissue cannot be preserved for very long after collection in the field. Moreover, transporting live animals over long distances induces stress, which can alter mitochondrial energetics.
This manuscript introduces the Auburn University (AU) MitoMobile, a mobile mitochondrial physiology laboratory that can be taken into the field and used on-site to measure mitochondrial metabolism in tissues collected from wild animals. The basic features of the mobile laboratory and the step-by-step methods for measuring isolated mitochondrial respiration rates are presented. Additionally, the data presented validate the success of outfitting the mobile mitochondrial physiology laboratory and making mitochondrial respiration measurements. The novelty of the mobile laboratory lies in the ability to drive to the field and perform mitochondrial measurements on the tissues of animals captured on site.

We designed and constructed a mobile laboratory to measure respiration rates in isolated mitochondria of wild animals captured at field locations. Here, we describe the design and outfitting of a mobile mitochondrial laboratory and the associated laboratory protocols.