This work was partially funded by the National Key Research and Development Program of China (2017YFA0105601, 2018YFA0107102), the National Natural Science Foundation of China (81970333,31901044,), and the Program for Professor of Special Appointment at Shanghai Institutions of Higher Learning (GZ2020008).

1. Cell culture and passaging
NOTE: The protocol is described using routinely cultured mouse embryonic fibroblasts (MEFs) as an example.
<ol>
	<li>Culture MEF cells in 10 cm cell culture dishes with 10 mL of Dulbecco&#39;s Modified Eagle Medium (DMEM). Incubate at 37 &#176;C and 5% CO2 and monitor the cells under a microscope at 100x magnification.</li>
	<li>Perform routine cell passaging.
	<ol>
		<li>When the cells reach 80%-90% confluency (every 3 days), wash th...

<ol>
	<li>Tao, M., 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=Animal+mitochondria:+evolution,+function,+and+disease.">Animal mitochondria: evolution, function, and disease.</a> Current Molecular Medicine. 14 (1), 115-124 (2014).</li><li>Henze, K., Martin, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolutionary+biology:+essence+of+mitochondria.">Evolutionary biology: essence of mitochondria.</a> Nature. 426 (6963), 127-128 (2003).</li><li>Kiriyama, Y., Nochi, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intra-+and+intercellular+quality+control+mechanisms+of+mitochondria.">Intra- and intercellular quality control mechanisms of mitochondria.</a> Cells. 7 (1), (2017).</li><li>Rossmann, M. P., Dubois, S. M., Agarwal, S., Zon, L. I. <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+in+development+and+disease.">Mitochondrial function in development and disease.</a> Disease Models &amp; Mechanisms. 14 (6), 048912 (2021).</li><li>Suliman, H. B., Piantadosi, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+quality+control+as+a+therapeutic+target.">Mitochondrial quality control as a therapeutic target.</a> Pharmacological Reviews. 68 (1), 20-48 (2016).</li><li>Wong, H. S., Dighe, P. A., Mezera, V., Monternier, P. A., Brand, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+superoxide+and+hydrogen+peroxide+from+specific+mitochondrial+sites+under+different+bioenergetic+conditions.">Production of superoxide and hydrogen peroxide from specific mitochondrial sites under different bioenergetic conditions.</a> Journal of Biological Chemistry. 292 (41), 16804-16809 (2017).</li><li>Zhao, R. Z., Jiang, S., Zhang, L., Yu, Z. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+electron+transport+chain,+ROS+generation+and+uncoupling+(Review).">Mitochondrial electron transport chain, ROS generation and uncoupling (Review).</a> International Journal of Molecular Medicine. 44 (1), 3-15 (2019).</li><li>Murphy, M. P., Hartley, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondria+as+a+therapeutic+target+for+common+pathologies.">Mitochondria as a therapeutic target for common pathologies.</a> Nature Reviews: Drug Discovery. 17 (12), 865-886 (2018).</li><li>Fan, H., 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+quality+control+in+cardiomyocytes:+a+critical+role+in+the+progression+of+cardiovascular+diseases.">Mitochondrial quality control in cardiomyocytes: a critical role in the progression of cardiovascular diseases.</a> Frontiers in Physiology. 11, 252 (2020).</li><li>Ma, K., 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=Mitophagy,+mitochondrial+homeostasis,+and+cell+fate.">Mitophagy, mitochondrial homeostasis, and cell fate.</a> Frontiers in Cell and Developmental Biology. 8, 467 (2020).</li><li>Kraus, F., Roy, K., Pucadyil, T. J., Ryan, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Function+and+regulation+of+the+divisome+for+mitochondrial+fission.">Function and regulation of the divisome for mitochondrial fission.</a> Nature. 590 (7844), 57-66 (2021).</li><li>Ren, L., 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+dynamics:+fission+and+fusion+in+fate+determination+of+mesenchymal+stem+cells.">Mitochondrial dynamics: fission and fusion in fate determination of mesenchymal stem cells.</a> Frontiers in Cell and Developmental Biology. 8, 580070 (2020).</li><li>Onishi, M., Yamano, K., Sato, M., Matsuda, N., Okamoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+and+physiological+functions+of+mitophagy.">Molecular mechanisms and physiological functions of mitophagy.</a> The EMBO Journal. 40 (3), 104705 (2021).</li><li>Palikaras, K., Lionaki, E., Tavernarakis, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+mitophagy+in+cellular+homeostasis,+physiology+and+pathology.">Mechanisms of mitophagy in cellular homeostasis, physiology and pathology.</a> Nature Cell Biology. 20 (9), 1013-1022 (2018).</li><li>Khaminets, A., Behl, C., Dikic, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ubiquitin-dependent+and+independent+signals+in+selective+autophagy.">Ubiquitin-dependent and independent signals in selective autophagy.</a> Trends in Cell Biology. 26 (1), 6-16 (2016).</li><li>Fritsch, L. E., Moore, M. E., Sarraf, S. A., Pickrell, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ubiquitin+and+receptor-dependent+mitophagy+pathways+and+their+implication+in+neurodegeneration.">Ubiquitin and receptor-dependent mitophagy pathways and their implication in neurodegeneration.</a> Journal of Molecular Biology. 432 (8), 2510-2524 (2020).</li><li>Narendra, D., Tanaka, A., Suen, D. F., Youle, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parkin+is+recruited+selectively+to+impaired+mitochondria+and+promotes+their+autophagy.">Parkin is recruited selectively to impaired mitochondria and promotes their autophagy.</a> Journal of Cell Biology. 183 (5), 795-803 (2008).</li><li>Lazarou, M., Jin, S. M., Kane, L. A., Youle, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+PINK1+binding+to+the+TOM+complex+and+alternate+intracellular+membranes+in+recruitment+and+activation+of+the+E3+ligase+Parkin.">Role of PINK1 binding to the TOM complex and alternate intracellular membranes in recruitment and activation of the E3 ligase Parkin.</a> Developmental Cell. 22 (2), 320-333 (2012).</li><li>Chen, M., 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=Mitophagy+receptor+FUNDC1+regulates+mitochondrial+dynamics+and+mitophagy.">Mitophagy receptor FUNDC1 regulates mitochondrial dynamics and mitophagy.</a> Autophagy. 12 (4), 689-702 (2016).</li><li>Ding, W. X., Yin, X. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitophagy:+mechanisms,+pathophysiological+roles,+and+analysis.">Mitophagy: mechanisms, pathophysiological roles, and analysis.</a> Biological Chemistry. 393 (7), 547-564 (2012).</li><li>Parzych, K. R., Klionsky, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+overview+of+autophagy:+morphology,+mechanism,+and+regulation.">An overview of autophagy: morphology, mechanism, and regulation.</a> Antioxidants and Redox Signaling. 20 (3), 460-473 (2014).</li><li>Hasegawa, J., 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=Autophagosome-lysosome+fusion+in+neurons+requires+INPP5E,+a+protein+associated+with+Joubert+syndrome.">Autophagosome-lysosome fusion in neurons requires INPP5E, a protein associated with Joubert syndrome.</a> The EMBO Journal. 35 (17), 1853-1867 (2016).</li><li>Presley, A. D., Fuller, K. M., Arriaga, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MitoTracker+Green+labeling+of+mitochondrial+proteins+and+their+subsequent+analysis+by+capillary+electrophoresis+with+laser-induced+fluorescence+detection.">MitoTracker Green labeling of mitochondrial proteins and their subsequent analysis by capillary electrophoresis with laser-induced fluorescence detection.</a> Journal of Chromatography B. Analytical Technologies in the Biomedical and Life Sciences. 793 (1), 141-150 (2003).</li><li>Chazotte, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Labeling+lysosomes+in+live+cells+with+LysoTracker.">Labeling lysosomes in live cells with LysoTracker.</a> Cold Spring Harbor Protocols. 2011 (2), 5571 (2011).</li><li>Pickles, S., Vigie, P., Youle, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitophagy+and+quality+control+mechanisms+in+mitochondrial+maintenance.">Mitophagy and quality control mechanisms in mitochondrial maintenance.</a> Current Biology. 28 (4), 170-185 (2018).</li><li>Ashrafi, G., Schwarz, T. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+pathways+of+mitophagy+for+quality+control+and+clearance+of+mitochondria.">The pathways of mitophagy for quality control and clearance of mitochondria.</a> Cell Death and Differentiation. 20 (1), 31-42 (2013).</li><li>Berezhnov, A. V., 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=Intracellular+pH+modulates+autophagy+and+mitophagy.">Intracellular pH modulates autophagy and mitophagy.</a> Journal of Biological Chemistry. 291 (16), 8701-8708 (2016).</li><li>Takemori, H., 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=Visualization+of+mitophagy+using+LysoKK,+a+7-nitro-2,1,3-benzoxadiazole-(arylpropyl)benzylamine+derivative.">Visualization of mitophagy using LysoKK, a 7-nitro-2,1,3-benzoxadiazole-(arylpropyl)benzylamine derivative.</a> Mitochondrion. 62, 176-180 (2022).</li><li>Maeda, M., 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=The+new+live+imagers+MitoMM1/2+for+mitochondrial+visualization.">The new live imagers MitoMM1/2 for mitochondrial visualization.</a> Biochemical and Biophysical Research Communications. 562, 50-54 (2021).</li><li>Feng, X. R., Yin, W., Wang, J. L., Feng, L., Kang, Y. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitophagy+promotes+the+stemness+of+bone+marrow-derived+mesenchymal+stem+cells.">Mitophagy promotes the stemness of bone marrow-derived mesenchymal stem cells.</a> Experimental Biology and Medicine. 246 (1), 97-105 (2021).</li><li>Chu, C. T., 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=Cardiolipin+externalization+to+the+outer+mitochondrial+membrane+acts+as+an+elimination+signal+for+mitophagy+in+neuronal+cells.">Cardiolipin externalization to the outer mitochondrial membrane acts as an elimination signal for mitophagy in neuronal cells.</a> Nature Cell Biology. 15 (10), 1197-1205 (2013).</li><li>Sentelle, R. D., 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=Ceramide+targets+autophagosomes+to+mitochondria+and+induces+lethal+mitophagy.">Ceramide targets autophagosomes to mitochondria and induces lethal mitophagy.</a> Nature Chemical Biology. 8 (10), 831-838 (2012).</li></ol>

The protocol described here provides a method for evaluating and monitoring the dynamic process of mitophagy in living cells, involving autophagosomes, lysosomes, and mitochondrial fission, through co-staining with cell-permeant mitochondria and lysosome dyes. The method can also be used to identify mitochondria and assess mitochondrial morphology. Both dyes used in this study should be protected from light, multiple freeze-thaw cycles should be avoided, and the dyes should be stored in single-use aliquots as much as pos...

Mitochondria are the powerhouses of nearly all eukaryotic cells1,2. In addition to ATP production through oxidative phosphorylation, mitochondria play a vital role in other processes such as bioenergetics, calcium homeostasis, free radical generation, apoptosis, and cellular homeostasis3,4,5. As mitochondria generate reactive oxygen species (ROS) from multiple complexes in the electron transport chain, they are constantly stimulated by potential oxidative stress, which can eventually lead to structural damage and dysfunction when the antioxidant defense system collapses6,7. Mitochondrial dysfunction has been found to contribute to many diseases, including metabolic disorders, neurodegeneration, and cardiovascular disease8. Therefore, it is crucial to maintain healthy mitochondrial populations and their proper function. Mitochondria are highly plastic and dynamic organelles; their morphology and function are controlled by mitochondrial quality control mechanisms, including post-translational modifications (PTM) of mitochondrial proteins, mitochondrial biogenesis, fusion, fission, and mitophagy9,10. Mitochondrial fission mediated by dynamin-related protein 1 (DRP1), a GTPase of the dynamin superfamily of proteins, results in small and round mitochondria and isolates the dysfunctional mitochondria, which can be cleared and degraded by mitophagy11,12.
Mitophagy is a cellular process that selectively degrades mitochondria by autophagy, usually occurring in damaged mitochondria following injury, aging, or stress. Subsequently, these mitochondria are delivered to lysosomes for degradation10. Thus, mitophagy is a catabolic process that helps maintain the quantity and quality of mitochondria in a healthy state in a wide range of cell types. It plays a crucial role in the restoration of cellular homeostasis under normal physiological and stress conditions13,14. Cells are characterized by a complex mitophagy mechanism, which is induced by different signals of cellular stress and developmental changes. Mitophagy regulatory pathways are classified as ubiquitin-dependent or receptor-dependent15,16; the ubiquitin-dependent autophagy is mediated by the kinase PINK1 and the recruitment of ubiquitin ligase Parkin E3 to the mitochondria17,18, while receptor-dependent autophagy involves the binding of autophagy receptors to the microtubule-associated protein light chain LC3 that mediates mitophagy in response to mitochondrial damage19.
Transmission electron microscopy (TEM) is the most commonly used method, and still one of the best methods, to observe and detect mitophagy20. The morphological features of mitophagy are autophagosomes or autolysosomes formed by the fusion of autophagosomes with lysosomes, which can be observed from electron microscopy images21. The weakness of electron microscopy (EM), however, is the inability to monitor the dynamic processes of mitophagy, such as mitochondrial depolarization, mitochondrial fission, and fusion of autophagosomes and lysosomes, in the living cell20. Thus, evaluating mitophagy through imaging living organelles is an attractive alternative method for mitochondrial research. The live cell imaging technique described here uses two fluorescent dyes to stain mitochondria and lysosomes. When mitophagy occurs, damaged or superfluous mitochondria engulfed by autophagosomes are stained green by the mitochondrial dye, while the red dye stains the lysosomes. The fusion of these autophagosomes and lysosomes, referred to as autolysosomes, causes the green and red fluorescence to overlap and manifest as yellow dots, thus indicating the occurrence of mitophagy22. The cell-permeant mitochondria dye (MitoTracker Green) contains a mildly thiol-reactive chloromethyl moiety to label mitochondria23. To label mitochondria, cells are simply incubated with the dye, which diffuses passively across the plasma membrane and accumulates in active mitochondria. This mitochondria dye can easily stain live cells, and is less effective in staining aldehyde-fixed or dead cells. The lysosome dye (LysoTracker Red) is a fluorescent acidotropic probe used for labeling and tracking acidic organelles in live cells. This dye exhibits a high selectivity for acidic organelles and can effectively label live cells at nanomolar concentrations24.
The procedures for using these fluorescent dyes in living cells, including loading the dyes and the visualization of mitochondria and lysosomes, are presented here. This method can help researchers observe mitophagy using live-cell fluorescent microscopy. It can also be used to quantify mitochondria and lysosomes, and assess mitochondrial morphology.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Automated cell counter</td>
			<td>Countstar</td>
			<td>IC1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell counting chamber slides</td>
			<td>Countstar</td>
			<td>12-0005-50</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s modified Eagle medium (DMEM)</td>
			<td>Corning</td>
			<td>10-013-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s phosphate-buffered saline (DPBS)</td>
			<td>Corning</td>
			<td>21-031-CVC</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass bottom cell culture dish (confocal dish)</td>
			<td>NEST</td>
			<td>801002</td>
			<td></td>
		</tr>
		<tr>
			<td>Image J (Rasband, NIH)</td>
			<td>NIH</td>
			<td></td>
			<td>https://imagej.nih.gov/ij/download.html</td>
		</tr>
		<tr>
			<td>Krebs&#8211;Henseleit(KHB) buffer</td>
			<td></td>
			<td></td>
			<td>Self-prepared</td>
		</tr>
		<tr>
			<td>LysoTracker Red</td>
			<td>Invitrogen</td>
			<td>1818430</td>
			<td>100 &#181;mol/L, red-fluorescent lysosome dye</td>
		</tr>
		<tr>
			<td>MitoTracker Green</td>
			<td>Invitrogen</td>
			<td>1842298</td>
			<td>200 &#181;mol/L stock, green-fluorescent mitochondria dye</td>
		</tr>
		<tr>
			<td>Mouse Embryonic Fibroblasts</td>
			<td></td>
			<td></td>
			<td>Self-prepared</td>
		</tr>
		<tr>
			<td>Objective (63x oil lens)</td>
			<td>ZEISS</td>
			<td>ZEISS LSM 880</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA 0.25%</td>
			<td>Gibico</td>
			<td>Cat# 25200056</td>
			<td></td>
		</tr>
		<tr>
			<td>ZEISS LSM 880 Confocal Laser Scanning Microscope</td>
			<td>ZEISS</td>
			<td>ZEISS LSM 880</td>
			<td></td>
		</tr>
		<tr>
			<td>ZEN Microscopy Software 2.1 (confocal microscope imaging software)</td>
			<td>ZEISS</td>
			<td>ZEN 2.1</td>
			<td></td>
		</tr>
	</tbody>
</table>

visualizing mitophagy with fluorescent dyes for mitochondria and lysosome

Mitochondria, being the powerhouses of the cell, play important roles in bioenergetics, free radical generation, calcium homeostasis, and apoptosis. Mitophagy is the primary mechanism of mitochondrial quality control and is generally studied using microscopic observation, however in vivo mitophagy assays are difficult to perform. Evaluating mitophagy by imaging live organelles is an alternative and necessary method for mitochondrial research. This protocol describes the procedures for using the cell-permeant green-fluorescent mitochondria dye MitoTracker Green and the red-fluorescent lysosome dye LysoTracker Red in live cells, including the loading of the dyes, visualization of the mitochondria and the lysosome, and expected outcomes. Detailed steps for the evaluation of mitophagy in live cells, as well as technical notes about microscope software settings, are also provided. This method can help researchers observe mitophagy using live-cell fluorescent microscopy. In addition, it can be used to quantify mitochondria and lysosomes and assess mitochondrial morphology.

MitoTracker Green is a green-fluorescent mitochondrial stain that is able to accurately localize to mitochondria. The dye can easily stain live cells and is less effective in staining aldehyde-fixed or dead cells (Figure 2). The red-fluorescent lysosome dye LysoTracker Red is capable of labeling and tracking acidic lysosomal organelles and can only stain live cells (Figure 2). Confocal microscope imaging allows the visualization of mitochondria and lysosomes sta...

Watch this Scientific Journal Video about Visualizing Mitophagy with Fluorescent Dyes for Mitochondria and Lysosome at JoVE.com

Visualizing Mitophagy with Fluorescent Dyes for Mitochondria and Lysosome

Mitophagy is the primary mechanism of mitochondrial quality control. However, the evaluation of mitophagy in vivo is hindered by the lack of reliable quantitative assays. Presented here is a protocol for the observation of mitophagy in living cells using a cell-permeant green-fluorescent mitochondria dye and a red-fluorescent lysosome dye.

Mitochondria, being the powerhouses of the cell, play important roles in bioenergetics, free radical generation, calcium homeostasis, and apoptosis. ...

This method helps to observe mitophagy in living cells using a cell permeant green-fluorescent mitochondria dye and a red-fluorescent lysosome dye. Mitophagy plays an important role in maintaining mitochondria homeostasis and various aspects of cellular function. This technique could provide a new approach to the treatment of mitochondria-related diseases.This procedure is not very complicated. Capturing clear images is very important for counting the overlay of mitochondria and lysosomes. To begin, culture mouse embryonic fibroblast or MEF cells in a 10 centimeter cell culture dish with 10 milliliters of Dulbecco's Modified Eagle Medium or DMEM.Incubate at 37 degrees Celsius and 5%carbon dioxide and monitor the cells under a microscope at 100X magnification. When the cells reach 80 to 90%confluency, wash them with two milliliters of Dulbecco's phosphate buffered saline. Then add two milliliters of 0.05%trypsin EDTA for one minute to dissociate the cells, followed by two milliliters of DMEM to stop the reaction.Centrifuge the cell suspension at 100 G for three minutes and resuspend the pellet in one milliliter DMEM. Count the cells using an automated cell counter and cell counting chamber slides and inoculate 1.5 times 10 to the sixth cells into a new 10 centimeter cell culture dish containing 10 milliliters of DMEM. For the mitophagy assay, prepare a cell suspension as described and dilute the cell suspension to one times 10 to the fifth cells per milliliter of fresh DMEM.Add two milliliters of the diluted cell suspension to a 20 millimeter confocal dish and shake the dish in a cross. Incubate at 37 degrees Celsius and 5%carbon dioxide for 24 hours. Prepare working solutions of the dyes by diluting the stock solutions.Add two microliters each of 0.2 millimolar mitochondrial dye and 50 micromolar lysosome dye to two milliliters of DMEM to obtain a working concentration of 0.2 micromolar mitochondrial dye and 50 nanomolar lysosome dye. Remove the medium from the confocal culture dish and add one milliliter of the staining solution to cover the cells. Place the cell culture dish at 37 degrees Celsius and 5%carbon dioxide for 20 to 30 minutes.Set the parameters of the confocal microscopy imaging software. For dual excitation images, use sequential excitation at 488 nanometers and 543 nanometers and collect emission at 505 to 545 nanometers and greater than 560 nanometers respectively. Remove the culture medium dish containing the dye from the incubator and add one milliliter of Krebs-Henseleit or KH buffer to the dish.To induce mitophagy, treat the cells with FCCP at one micromolar in KH buffer for 10 minutes at room temperature and immediately proceed to image the cells using the confocal microscope. Apply an appropriate amount of oil to the top of the 63X oil lens. Place the sample on the sample stage of the confocal microscope and move it directly above the objective lens.Use the imaging software to find the sample by clicking on the Locate tab in the top left corner of the software interface. Select a green filter set for the experiment. Use the coarse adjustment knob to quickly focus by moving the objective lens up and down.After the cell sample is clearly visible through the eyepiece, search and focus the area of single cells and move it to the center of the field of view. Click on the Acquisition tab in the top left corner of the software interface to acquire images. Select only the 488 nanometer channel and the frame resolution 1024 by 1024 for preview.Click on the Live tab in the top left corner to start a live scan. Adjust the field of view to the sharpest and adjust the laser power by moving the slider left or right. Keep the gain setting below 600 to avoid over exposure.Adjust the pinhole value to 156, gain value to 545 and digital offset value to zero. Select the best field of view, check the two channels and choose the frame resolution 1024 by 1024. Click Snap to acquire 2D images and save the acquired images.In this study, FFCP was used to trigger mitophagy in MEF cells for confocal imaging. Representative images of cells stained with the green-fluorescent mitochondria dye showing mitochondria and stained with the red-fluorescent lysosome dye showing lysosome are shown here. When damaged green-stained mitochondria are engulfed by red-stained lysosomes, the green and red fluorescence overlap to reveal yellow co-localized mitochondria lysosomes.The yellow dots correspond to these co-localized mitochondria lysosomes representing ongoing mitophagy and thus can be counted to evaluate the extent of mitophagy. Preparation of a working solution of dyes for mitochondria and lysosome staining and maintaining appropriate cell confluency when imaging with confocal microscopy are key steps to remember. This procedure can also be used to analyze mitochondrial number and morphology which is important for assessing mitochondrial dynamics.Mitophagy is closely associated with a variety of human diseases and this technique can be used to explore the connection between mitophagy and human diseases.

visualizing-mitophagy-with-fluorescent-dyes-for-mitochondria

Research

JoVE Journal

Biology

Labeling Stem Cells with Fluorescent Dyes for non-invasive Detection with Optical Imaging

Optical imaging (OI) is an easy, fast and inexpensive tool for in vivo monitoring of new stem cell based therapies. The technique is based on ex vivo labeling of stem cells with a fluorescent dye, subsequent intravenous injection of the labeled cells and visualization of their accumulation in specific target organs or pathologies. The presented technique demonstrates how we label human mesenchymal stem cells (hMSC) by simple incubation with the lipophilic fluorescent dye DiD (C67H103CIN2O3S) and how we label human embryonic stem cells (hESC) with the FDA approved fluorescent dye Indocyanine Green (ICG). The uptake mechanism is via adherence and diffusion of the lypophilic dye across the phospholipid cell membrane bilayer. The labeling efficiency is usually improved if the cells are incubated with the dye in serum-free media as opposed to incubation in serum-containing media. Furthermore, the addition of the transfection agent Protamine Sulfate significantly improves contrast agent uptake.

This video shows techniques for labeling of human embryonic stem cells and mesenchymal stem cells with fluorescent dyes. This technique can be used for an in vivo tracking of transplanted stem cells with optical imaging and for histopathological correlations with fluorescence microscopy.

Optical imaging (OI) is an easy, fast and inexpensive tool for in vivo monitoring of new stem cell based therapies. The technique is based on ex vivo ...

Visualizing the Live Drosophila Glial-neuromuscular Junction with Fluorescent Dyes

Our project identified GFP labeled glial structures at the developing larval fly neuromuscular synapse. To look at development of live glial-nerve-muscle synapses, we developed a larval tissue preparation that had features of live intact larvae, but also had good optical properties.  This new preparation also allowed for access of perfusates to the synapse.  We used fly larvae, immersed them in artificial hemolymph, and relaxed their normal rhythmic body contractions by chilling them. Next we dissected off the posterior segments of each animal and with a blunt insect pin pushed the mouth parts backward through the body cavity.  This everted the larval body wall, like turning a sock inside-out.  We completed the dissection with ultra-fine dissection scissors and thus exposed the visceral side of the body wall muscles. The glial structures at the NMJ expressed membrane targeted GFP under the control of glial specific promoters. The post-synaptic membrane, the SSR (Subsynaptic Reticula) in muscle expressed synaptically targeted dsRed. We needed to acutely label the motor neuron terminals, the third part of the synapse. To do this we applied primary antibodies to HRP, conjugated to a far-red emitting flurophore.  To test for dye diffusion properties into the perisynaptic space between the motor neuron terminals and the SSR, we applied a solution of large Dextran molecules conjugated to far-red emitting flurophore and collected images.

Visualizing the Live Drosophila Glial-neuromuscular Junction with Fluorescent Dyes

We described structural features of the Glia-neuromuscular synapses in a novel Inside-out tissue preparation of live fly larvae using fluorescent dyes with confocal microscopy. We labeled live neuron terminals with fluorescent primary antibodies to HRP, and also visualized the perisynaptic space with fluorescent Dextrans.

Our project identified GFP labeled glial structures at the developing larval fly neuromuscular synapse. To look at development of live glial-nerve-muscle ...

Visualizing Single-molecule DNA Replication with Fluorescence Microscopy

We describe a simple fluorescence microscopy-based real-time method for observing DNA replication at the single-molecule level. A circular, forked DNA template is attached to a functionalized glass coverslip and replicated extensively after introduction of replication proteins and nucleotides (Figure 1). The growing product double-strand DNA (dsDNA) is extended with laminar flow and visualized by using an intercalating dye. Measuring the position of the growing DNA end in real time allows precise determination of replication rate (Figure 2). Furthermore, the length of completed DNA products reports on the processivity of replication. This experiment can be performed very easily and rapidly and requires only a fluorescence microscope with a reasonably sensitive camera.


This protocol demonstrates a simple single-molecule fluorescence microscopy technique for visualizing DNA replication by individual replisomes in real time.

We describe a simple fluorescence microscopy-based real-time method for observing DNA replication at the single-molecule level. A circular, forked DNA ...

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

Symbioses, the living together of two or more organisms, are widespread throughout all kingdoms of life. As two of the most ubiquitous organisms on earth, nematodes and bacteria form a wide array of symbiotic associations that range from beneficial to pathogenic 1-3. One such association is the mutually beneficial relationship between Xenorhabdus bacteria and Steinernema nematodes, which has emerged as a model system of symbiosis 4. Steinernema nematodes are entomopathogenic, using their bacterial symbiont to kill insects 5. For transmission between insect hosts, the bacteria colonize the intestine of the nematode's infective juvenile stage 6-8. Recently, several other nematode species have been shown to utilize bacteria to kill insects 9-13, and investigations have begun examining the interactions between the nematodes and bacteria in these systems 9.
We describe a method for visualization of a bacterial symbiont within or on a nematode host, taking advantage of the optical transparency of nematodes when viewed by microscopy. The bacteria are engineered to express a fluorescent protein, allowing their visualization by fluorescence microscopy. Many plasmids are available that carry genes encoding proteins that fluoresce at different wavelengths (i.e. green or red), and conjugation of plasmids from a donor Escherichia coli strain into a recipient bacterial symbiont is successful for a broad range of bacteria. The methods described were developed to investigate the association between Steinernema carpocapsae and Xenorhabdus nematophila 14. Similar methods have been used to investigate other nematode-bacterium associations 9,15-18and the approach therefore is generally applicable.
The method allows characterization of bacterial presence and localization within nematodes at different stages of development, providing insights into the nature of the association and the process of colonization 14,16,19. Microscopic analysis reveals both colonization frequency within a population and localization of bacteria to host tissues 14,16,19-21. This is an advantage over other methods of monitoring bacteria within nematode populations, such as sonication 22or grinding 23, which can provide average levels of colonization, but may not, for example, discriminate populations with a high frequency of low symbiont loads from populations with a low frequency of high symbiont loads. Discriminating the frequency and load of colonizing bacteria can be especially important when screening or characterizing bacterial mutants for colonization phenotypes 21,24. Indeed, fluorescence microscopy has been used in high throughput screening of bacterial mutants for defects in colonization 17,18, and is less laborious than other methods, including sonication 22,25-27and individual nematode dissection 28,29.

To study the mutualism between Xenorhabdus bacteria and Steinernema nematodes, methods were developed to monitor bacterial presence and location within nematodes. The experimental approach, which can be applied to other systems, entails engineering bacteria to express the green fluorescent protein and visualizing, using fluorescence microscopy bacteria within the transparent nematode.

 
Symbioses, the living together of two or more organisms, are widespread throughout all kingdoms of life. As two of the most ubiquitous organisms on ...

Confocal Imaging of Single Mitochondrial Superoxide Flashes in Intact Heart or In Vivo

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 &deg;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.

Confocal Imaging of Single Mitochondrial Superoxide Flashes in Intact Heart or In Vivo

Confocal scanning microscopy is applied for imaging single mitochondrial events in perfused heart or skeletal muscles in live animal. Real-time monitoring of single mitochondrial processes such as superoxide flashes and membrane potential fluctuations enables the evaluation of mitochondrial function in a physiologically relevant context and during pathological perturbations.

Mitochondrion is a critical intracellular organelle responsible for energy production and intracellular signaling in eukaryotic systems. Mitochondrial ...

A Guide to Modern Quantitative Fluorescent Western Blotting with Troubleshooting Strategies

The late 1970s saw the first publicly reported use of the western blot, a technique for assessing the presence and relative abundance of specific proteins within complex biological samples. Since then, western blotting methodology has become a common component of the molecular biologists experimental repertoire. A cursory search of PubMed using the term &#8220;western blot&#8221; suggests that in excess of two hundred and twenty thousand published manuscripts have made use of this technique by the year 2014. Importantly, the last ten years have seen technical imaging advances coupled with the development of sensitive fluorescent labels which have improved sensitivity and yielded even greater ranges of linear detection. The result is a now truly Quantifiable Fluorescence based Western Blot (QFWB) that allows biologists to carry out comparative expression analysis with greater sensitivity and accuracy than ever before. Many &#8220;optimized&#8221; western blotting methodologies exist and are utilized in different laboratories. These often prove difficult to implement due to the requirement of subtle but undocumented procedural amendments. This protocol provides a comprehensive description of an established and robust QFWB method, complete with troubleshooting strategies.

The advancement of western blotting using fluorescence has allowed detection of subtle changes in protein expression enabling quantitative analyses. Here we describe a robust methodology for detection of a range of proteins across a variety of species and tissue types. A strategy to overcome common technical problems is also provided.

The late 1970s saw the first publicly reported use of the western blot, a technique for assessing the presence and relative abundance of specific proteins ...

Genetic Barcoding with Fluorescent Proteins for Multiplexed Applications

Fluorescent proteins, fluorescent dyes and fluorophores in general have revolutionized the field of molecular cell biology. In particular, the discovery of fluorescent proteins and their genes have enabled the engineering of protein fusions for localization, the analysis of transcriptional activation and translation of proteins of interest, or the general tracking of individual cells and cell populations. The use of fluorescent protein genes in combination with retroviral technology has further allowed the expression of these proteins in mammalian cells in a stable and reliable manner. Shown here is how one can utilize these genes to give cells within a population of cells their own biosignature. As the biosignature is achieved with retroviral technology, cells are barcoded &#180;indefinitely&#180;. As such, they can be individually tracked within a mixture of barcoded cells and utilized in more complex biological applications. The tracking of distinct populations in a mixture of cells is ideal for multiplexed applications such as discovery of drugs against a multitude of targets or the activation profile of different promoters. The protocol describes how to elegantly develop and amplify barcoded mammalian cells with distinct genetic fluorescent markers, and how to use several markers at once or one marker at different intensities. Finally, the protocol describes how the cells can be further utilized in combination with cell-based assays to increase the power of analysis through multiplexing.

Since the discovery of the green fluorescent protein gene, fluorescent proteins have impacted molecular cell biology. This protocol describes how expression of distinct fluorescent proteins through genetic engineering is used for barcoding individual cells. The procedure enables tracking distinct populations in a cell mixture, which is ideal for multiplexed applications.

Fluorescent proteins, fluorescent dyes and fluorophores in general have revolutionized the field of molecular cell biology. In particular, the discovery ...

Visualizing Stromule Frequency with Fluorescence Microscopy

Stromules, or "stroma-filled tubules", are narrow, tubular extensions from the surface of the chloroplast that are universally observed in plant cells but whose functions remain mysterious. Alongside growing attention on the role of chloroplasts in coordinating plant responses to stress, interest in stromules and their relationship to chloroplast signaling dynamics has increased in recent years, aided by advances in fluorescence microscopy and protein fluorophores that allow for rapid, accurate visualization of stromule dynamics. Here, we provide detailed protocols to assay stromule frequency in the epidermal chloroplasts of Nicotiana benthamiana, an excellent model system for investigating chloroplast stromule biology. We also provide methods for visualizing chloroplast stromules in vitro by extracting chloroplasts from leaves. Finally, we outline sampling strategies and statistical approaches to analyze differences in stromule frequencies in response to stimuli, such as environmental stress, chemical treatments, or gene silencing. Researchers can use these protocols as a starting point to develop new methods for innovative experiments to explore how and why chloroplasts make stromules.

Protocols to investigate the dynamics of chloroplast stromules, the stroma-filled tubules that extend from the surface of chloroplasts, are described.

Stromules, or "stroma-filled tubules", are narrow, tubular extensions from the surface of the chloroplast that are universally observed in plant cells but ...

Sensitive Measurement of Mitophagy by Flow Cytometry Using the pH-dependent Fluorescent Reporter mt-Keima

Mitophagy is a process of selective removal of damaged or unnecessary mitochondria using autophagy machinery. Close links have been found between defective mitophagy and various human diseases, including neurodegenerative diseases, cancer, and metabolic diseases. In addition, recent studies have shown that mitophagy is involved in normal cellular processes, such as differentiation and development. However, the precise role of and molecular mechanisms underlying mitophagy require further study. Therefore, it is critical to develop a robust and convenient method for measuring changes in mitophagy activity. Here, we describe a detailed protocol for quantitatively assessing mitophagy activity through flow cytometry using the mitochondria-targeted fluorescent protein Keima (mt-Keima). This flow cytometry assay can analyze mitophagy activity more rapidly and sensitively than conventional microscopy- or immunoblotting-based methods. This protocol can be applied to analyze mitophagy activity in various cell types.

Mitophagy, the selective degradation of mitochondria, has been implicated in mitochondrial homeostasis and is deregulated in various human diseases. However, convenient experimental methods for measuring mitophagy activity are very limited. Here, we provide a sensitive assay for measuring mitophagy activity using flow cytometry.

Mitophagy is a process of selective removal of damaged or unnecessary mitochondria using autophagy machinery. Close links have been found between ...

Application of Membrane and Cell Wall Selective Fluorescent Dyes for Live-Cell Imaging of Filamentous Fungi

The application of membrane and cell wall selective fluorescent dyes for live-cell imaging analyses of organelle dynamics in fungal cells started two decades ago and since then continues to contribute greatly to our understanding of the filamentous fungal lifestyle. This paper provides a practical guide for the utilization of the two membrane dyes FM 1-43 and FM 4-64 and the four cell wall stains Calcofluor White M2R, Solophenyl Flavine 7GFE 500, Pontamine Fast Scarlet 48 and Congo Red. The focus is on their low-dose application to ascertain artefact-free staining, their co-imaging properties, and their quantitative evaluation. The presented methods are applicable to all filamentous fungal samples that can be prepared in the described ways. The fundamental staining approaches can serve as starting points for adaptations to species that might require different cultivation conditions. First, biophysical and biochemical properties are reviewed as their understanding is essential for using these dyes as truly vital fluorescent stains. Secondly, step-by-step protocols are presented that detail the preparation of various fungal sample types for fluorescent live-cell imaging. Finally, example experiments illustrate different approaches to: (1) identify defects in the spatio-temporal organization of endocytosis in genetic mutants, (2) comparatively characterize shared and distinct co-localization of GFP-labeled target proteins in the endocytic pathway, (3) identify morphogenetic cell wall defects in a genetic mutant, and (4) monitor cell wall biogenesis in real time.

Vital fluorescent dyes are essential tools for live-cell imaging analyses in modern fungal cell biology. This paper details the application of established and lesser-known fluorescent dyes for tracking plasma membrane dynamics, endo-/exocytosis and cell wall morphogenesis in filamentous fungi.

The application of membrane and cell wall selective fluorescent dyes for live-cell imaging analyses of organelle dynamics in fungal cells started two ...