Name: Detection of Mitophagy in Caenorhabditis elegans and Mammalian Cells Using Organelle-Specific Dyes (Video) | JoVE
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Description: Watch this Scientific Journal Video about Detection of Mitophagy in Caenorhabditis elegans and Mammalian Cells Using Organelle-Specific Dyes at JoVE.com

We thank members of the Gross laboratory for the critical reading of the manuscript and their comments and advice. We thank the Caenorhabditis Genetics Center (CGC), which is funded by the National Institutes of Health Office of Research Infrastructure Programs (P40 OD010440), for providing some of the strains. This research was supported by a grant from Vitalunga Ltd and the Israel Science Foundation (grant No. 989/19). The graphical abstract figure (Figure 1) was generated with BioRender.com.

NOTE: For the convenience of the readers, we have divided the protocol into two parts: one focuses on the protocol for measuring mitophagy in C. elegans, and the other focuses on the protocol for measuring mitophagy in liver cells. The list of materials can be found in the Table of Materials provided.
1. The C. elegans protocol
<ol>
	<li>Preparing the nematode growth medium (NGM) plates and Escherichia coli OP50 bacterial stock<br ...

Quantifying Mitophagy in C. elegans and a Liver Cancer Cell Line

<ol>
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Y., Mizushima, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysosome+biology+in+autophagy.">Lysosome biology in autophagy.</a> Cell Discovery. 6, 6 (2020).</li><li>Katayama, 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=Visualizing+and+modulating+mitophagy+for+therapeutic+studies+of+neurodegeneration.">Visualizing and modulating mitophagy for therapeutic studies of neurodegeneration.</a> Cell. 181 (5), 1176-1187 (2020).</li><li>Shpilka, 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=UPR(mt)+scales+mitochondrial+network+expansion+with+protein+synthesis+via+mitochondrial+import+in+Caenorhabditis+elegans.">UPR(mt) scales mitochondrial network expansion with protein synthesis via mitochondrial import in Caenorhabditis elegans.</a> Nature Communications. 12, 479 (2021).</li><li>Liao, Z., 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+degradation+of+TMEM166+by+autophagy+promotes+AMPK+activation+to+protect+SH-SY5Y+cells+exposed+to+MPP().">The degradation of TMEM166 by autophagy promotes AMPK activation to protect SH-SY5Y cells exposed to MPP().</a> Cells. 11 (17), 2706 (2022).</li><li>Srivastava, 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=Distinct+designer+diamines+promote+mitophagy,+and+thereby+enhance+healthspan+in+C.+elegans+and+protect+human+cells+against+oxidative+damage.">Distinct designer diamines promote mitophagy, and thereby enhance healthspan in C. elegans and protect human cells against oxidative damage.</a> Autophagy. 19 (2), 474-504 (2022).</li><li>Georgakopoulos, N. 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Multiple mitophagy pathways involve various proteins and biomolecules (e.g., cardiolipin29). However, the endpoint of these pathways is similar-the degradation of mitochondria by lysosomal enzymes12,13. Indeed, several methods use this endpoint to quantify mitophagy. However, some methods, such as electron microscopy, demand access to costly equipment, trained experts, and an extended preparation time for the specimens and analysis. Furthe...

Mitochondria are essential for all aerobic animals, including humans. They convert the chemical energy of biomolecules to adenosine triphosphate (ATP) via oxidative phosphorylation1, synthesize heme2, degrade fatty acids through &#946; oxidation3, regulate calcium4 and iron5 homeostasis, control cell death by apoptosis6, and generate reactive oxygen species (ROS), which play a vital role in redox homeostasis7. Two complementary and opposite processes maintain the integrity and proper function of the mitochondria: the synthesis of new mitochondrial components (biogenesis) and the selective removal of damaged ones through mitochondrial autophagy (i.e., mitophagy)8.
Several mitophagy pathways are mediated by enzymes, such as PINK1/Parkin, and receptors, including FUNDC1, FKBP8, and BNIP/NIX9,10. Notably, the selective degradation of mitochondrial components can occur independently of the autophagosome machinery (i.e., through mitochondrial-derived vesicles)11. However, the endpoints of the different selective mitophagy pathways are similar&#160;(i.e.,mitochondrial degradation by lysosomal enzymes)12,13. For this reason, various methods for identifying and measuring mitophagy rely on the colocalization of mitochondrial and lysosomal markers14,15,16,17 and decreased levels of mitochondrial proteins/mitochondrial DNA18.
Below is a concise description of the existing experimental methodologies for measuring mitophagy in animal cells using fluorescence microscopy, emphasizing the mitophagy endpoint phase.
Mitophagy biosensors 
Mitochondrial degradation occurs within the acidic environment of the lysosome19. Therefore, mitochondrial components, including proteins, experience a shift from a neutral to an acidic pH at the endpoint of the mitophagy process. This pattern underpins the mechanism of action of several mitophagy biosensors, including mito-Rosella18 and tandem mCherry-GFP-FIS114. These sensors contain a pH-sensitive green fluorescence protein (GFP) and a pH-insensitive red fluorescence protein (RFP). Therefore, at the endpoint of mitophagy, the green-to-red fluorescence ratio drops significantly due to the quenching of the GFP fluorophore. The major limitations of these sensors are (1) possible F&#246;rster resonance energy transfer (FRET) between the fluorophores; (2) the differential maturation rate of GFP and RFP; (3) dissociation between the GFP and RFP due to proteolytic cleavage of the polypeptide that connects them; (4) fluorescence-emission overlap; and (5) differential fluorophore brightness and quenching15,16.
A sensor that overcomes some of these limitations is the Keima mitochondrial sensor17. The mt-Keima sensor (derived from the coral protein Keima) displays a single emission peak (620 nm). However, its excitation peaks are pH-sensitive. As a result, there is a transition from a green excitation (440 nm) to a red one (586 nm) when shifting from a high pH to an acidic pH16,17. A more recent mitophagy sensor, Mito-SRAI, has advanced the field by allowing for measurements in fixed biological samples20. However, despite the many advantages of genetic sensors, such as the ability to express them in specific tissues/cells and target them to distinct mitochondrial compartments, they also have limitations. One limitation is that the genetic sensors need to be expressed in cells or animals, which can be time-consuming and resource-intensive.
Additionally, the expression of the sensors within mitochondria themselves may influence the mitochondrial function. For example, expressing mitochondrial GFP (mtGFP) in the C. elegans worm body wall muscles expands the mitochondrial network21. This phenotype depends on the function of the stress-activated transcription factor ATFS-1, which plays an essential role in the activation of unfolded protein response in mitochondria (UPRmt)21. Therefore, although genetically encoded mitochondria/mitophagy biosensors are extremely useful for monitoring mitochondria homeostasis in vivo, they may affect the very process they are designed to measure.
Mitochondria/lysosome-specific antibodies and dyes 
Another strategy for testing mitochondrial/lysosome colocalization is to use antibodies against mitochondrial/lysosomal proteins, such as the mitochondrial outer membrane protein TOM20 and lysosomal-associated membrane protein 1 (LAMP1)22. In most cases, secondary antibodies that are conjugated to a fluorophore are used to detect the fluorescence signal via microscopy. Another strategy is to combine genetic constructs with mitochondrial/lysosomal dyes, such as expressing a LAMP1::GFP fusion construct in cells while staining them with a red mitochondrial dye (e.g., Mitotracker Red)16. These methodologies, while effective, require specific antibodies and often involve working with fixed specimens or generating cells/transgenic animals expressing fluorescently labeled mitochondria/lysosomes.
Here, we outline the utilization of a commercial lysosome/mitochondria/nuclear staining kit for assessing the mitophagy-activating properties of synthetic diamine O,O (octane-1,8-diyl)bis(hydroxylamine), hereafter referred to as VL-85023, in C. elegans worms and the human cancer cell line Hep-3B (Figure 1). The staining kit contains a mixture of lysosomal/mitochondrial/nuclear-targeted dyes that specifically stain these organelles23. We previously used this kit to demonstrate the mitophagy activity of 1,8 diaminooctane (hereafter referred to as VL-004) in C. elegans23. Importantly, we validated the staining kit results with the mito-Rosella biosensor and qPCR measurements of the mitochondrial:nuclear DNA content23. This staining kit offers the following advantages. First, there is no need to generate transgenic animals or cells expressing a mitochondrial biosensor. Therefore, we can study unmodified wild-type animals or cells and, thus, save much time, money, and labor. Moreover, as mentioned, expressing mitochondrial biosensors can change the mitochondrial function. Second, the kit is cost-effective, easy to use, and fast. Third, although we demonstrate the method in C. elegans and human cells, it could be modified for other cell types and organisms.
With that said, like any method, the staining kit protocol has drawbacks. For example, the incubation of the worms with the reagent is carried out in the absence of food (we have seen that even dead bacteria significantly decrease the staining efficiency). Although the incubation time is relatively short, it is possible that even in this time frame, homeostatic responses may be altered, including mitophagy. In addition, the binding of the dyes to the ER/mitochondrial/nuclear proteins and other biomolecules may affect the activities of these organelles. Moreover, unlike mitophagy measurement with genetic sensors, we work with worms and cells that have undergone chemical fixation. Therefore, it is impossible to continue monitoring the same worms/cells at different times. Hence, we recommend combining different methodologies to validate the function of mitophagy in a particular physiological process. Below, we present new data demonstrating that VL-850 induces robust mitophagy in C. elegans worms and Hep-3B cells. Therefore, these data further support the hypothesis that VL-850 extends the lifespan of C. elegans and protects C. elegans from oxidative damage through the induction of healthy mitophagy. We have used the proton ionophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), which is a potent mitophagy inducer24, as a positive control.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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			<td>Reagent or resource</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Analytical balance</td>
			<td>Mettler-Toledo</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Agar</td>
			<td>BD-Difco</td>
			<td>214010</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Peptone</td>
			<td>BD-Difco</td>
			<td>211677</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Tryptone</td>
			<td>BD-Difco</td>
			<td>211705</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Yeast extract</td>
			<td>BD-Difco</td>
			<td>212750</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td>Sigma</td>
			<td>C1016</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP)</td>
			<td>Sigma</td>
			<td>C2920</td>
			<td></td>
		</tr>
		<tr>
			<td>Chemicals</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cholestrol</td>
			<td>Thermo Fisher</td>
			<td>C/5360/48</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM high glucose</td>
			<td>Biological Industries</td>
			<td>01-055-1A</td>
			<td></td>
		</tr>
		<tr>
			<td>Double distilled water (DDW)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Phosphate Buffered Saline (PBS)</td>
			<td>Biological Industries</td>
			<td>02-023-1A</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS heat inactivated</td>
			<td>Invitrogen</td>
			<td>M7514</td>
			<td></td>
		</tr>
		<tr>
			<td>Gluteradehyde (25%)</td>
			<td>Sigma</td>
			<td>G5882</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES Buffer 1 M</td>
			<td>Biological Industries</td>
			<td>03-025-1B</td>
			<td></td>
		</tr>
		<tr>
			<td>L-gluatamine</td>
			<td>Biological Industries</td>
			<td>03-020-1B</td>
			<td></td>
		</tr>
		<tr>
			<td>Lysosome/Mitochondria/Nuclear Staining Cytopainter Reagent</td>
			<td>Abcam</td>
			<td>ab139487</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Sulfate</td>
			<td>Sigma</td>
			<td>M7506</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonidet P 40</td>
			<td>Sigma</td>
			<td>74385</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformalydehyde (16%)</td>
			<td>Electron Microscopy Sciences</td>
			<td>15720</td>
			<td></td>
		</tr>
		<tr>
			<td>Poloxamer 188 Solution</td>
			<td>Sigma</td>
			<td>P5556</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium dihydrogen phosphate</td>
			<td>Millipore</td>
			<td>1.04873.1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate dibasic</td>
			<td>Sigma</td>
			<td>P3786</td>
			<td></td>
		</tr>
		<tr>
			<td>SeaKem LE Agarose</td>
			<td>Lonza</td>
			<td>50004</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Bio-Lab</td>
			<td>1903059100</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide</td>
			<td>Gadot</td>
			<td>1310732</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic dodecahydrate</td>
			<td>Sigma</td>
			<td>4273</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetracycline hydrochloride</td>
			<td>Sigma</td>
			<td>87128-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA</td>
			<td>Biological Industries</td>
			<td>03-052-1A</td>
			<td></td>
		</tr>
		<tr>
			<td>VL-850: 1,8-diaminooxy-octane</td>
			<td>Patented</td>
			<td></td>
			<td></td>
		</tr>
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			<td>Glass/Plastic Disposables</td>
			<td></td>
			<td></td>
			<td></td>
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		<tr>
			<td>0.22 &#956;m syringe filter</td>
			<td>Millex GV</td>
			<td>SLGV033RS</td>
			<td></td>
		</tr>
		<tr>
			<td>1.7 mL Micro Centrifuge Tubes</td>
			<td>Lifegene</td>
			<td>LMCT1.7B-500</td>
			<td></td>
		</tr>
		<tr>
			<td>10 cm Petri plates</td>
			<td>Corning</td>
			<td>430167</td>
			<td></td>
		</tr>
		<tr>
			<td>1,000 mL Erlenmeyer Flask</td>
			<td>IsoLab, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>15 mL Sterile Polypropylene tube</td>
			<td>Lifegene</td>
			<td>LTB15-500</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm Petri dishes</td>
			<td>Bar Naor</td>
			<td>BN9015810</td>
			<td></td>
		</tr>
		<tr>
			<td>500&#160;mL vacuum filter/storage bottle system, 0.22&#160;&#956;m</td>
			<td>Lifegene</td>
			<td>LG-FPE205500S</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL Sterile Polypropylene tube</td>
			<td>Lifegene</td>
			<td>LTB50-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Deckgl&#228;ser Microscope cover glass 24 x 60 mm</td>
			<td>Marienfeld</td>
			<td>101152</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass test tubes (10 mL- 13 x 100 mm) Borosilicate glass</td>
			<td>Pyrex</td>
			<td>99445-13</td>
			<td></td>
		</tr>
		<tr>
			<td>iBiDi 8 well &#956;-slides</td>
			<td>iBiDi</td>
			<td>80826</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope cover glass 24 x 40 mm</td>
			<td>Bar Naor</td>
			<td>BN1052421ECALN</td>
			<td></td>
		</tr>
		<tr>
			<td>Platinum iridium 0.25 mM wire</td>
			<td>World Precision Instruments</td>
			<td>PT1002</td>
			<td></td>
		</tr>
		<tr>
			<td>Instruments</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cell counter CellDrop BF</td>
			<td>DeNovix</td>
			<td>CellDrop BF-UNLTD</td>
			<td></td>
		</tr>
		<tr>
			<td>Microspin FV-2400</td>
			<td>Biosan</td>
			<td>BS-010201-AAA</td>
			<td></td>
		</tr>
		<tr>
			<td>Nikon Yokogawa W1 Spinning Disk confocal microscope with DAPI, FITC, and TRITC filters and bright-field, with a 60x CFI Plan-Apochromat Lambda type lens (air lens) and NIS-Elements software</td>
			<td>Nikon</td>
			<td>CSU-W1</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus SZ61 stereo microscope</td>
			<td>Olympus</td>
			<td>SZ61</td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Mettler-Toledo</td>
			<td>MT30019032</td>
			<td></td>
		</tr>
		<tr>
			<td>Revolver Adjustable Lab Rotator</td>
			<td>Labnet</td>
			<td>H5600</td>
			<td></td>
		</tr>
	</tbody>
</table>

detection of mitophagy in caenorhabditis elegans and mammalian cells using organelle-specific dyes

Mitochondria are essential for various biological functions, including energy production, lipid metabolism, calcium homeostasis, heme biosynthesis, regulated cell death, and the generation of reactive oxygen species (ROS). ROS are vital for key biological processes. However, when uncontrolled, they can lead to oxidative injury, including mitochondrial damage. Damaged mitochondria release more ROS, thereby intensifying cellular injury and the disease state. A homeostatic process named mitochondrial autophagy (mitophagy) selectively removes damaged mitochondria, which are then replaced by new ones. There are multiple mitophagy pathways, with the common endpoint being the breakdown of the damaged mitochondria in lysosomes. 
Several methodologies, including genetic sensors, antibody immunofluorescence, and electron microscopy, use this endpoint to quantify mitophagy. Each method for examining mitophagy has its advantages, such as specific tissue/cell targeting (with genetic sensors) and great detail (with electron microscopy). However, these methods often require expensive resources, trained personnel, and a lengthy preparation time before the actual experiment, such as for creating transgenic animals. Here, we present a cost-effective alternative for measuring mitophagy using commercially available fluorescent dyes targeting mitochondria and lysosomes. This method effectively measures mitophagy in the nematode Caenorhabditis elegans and human liver cells, which indicates its potential efficiency in other model systems.

Detection of Mitophagy in Caenorhabditis elegans and Mammalian Cells Using Organelle-Specific Dyes

Induction of a robust mitophagy response in both C. elegans worms and Hep-3B cells with VL-850 
VL-850 protects C. elegans worms and human keratinocytes (HaCaT cells) from oxidative stress23. To further explore its mechanism of action, we examined whether VL-850 induces mitophagy in C. elegans and other human cells. To test this, we exposed C. elegans worms (young adults, 3 days post-L1) to 62.5 &#181;M VL-850, 5 &#181;M FCCP (positive cont...

Watch this Scientific Journal Video about Detection of Mitophagy in Caenorhabditis elegans and Mammalian Cells Using Organelle-Specific Dyes at JoVE.com

Detection of Mitophagy in Caenorhabditis elegans and Mammalian Cells Using Organelle-Specific Dyes (Video) | JoVE 

Exploring mitophagy through electron microscopy, genetic sensors, and immunofluorescence requires costly equipment, skilled personnel, and a significant time investment. Here, we demonstrate the efficacy of a commercial fluorescence dye kit in quantifying the mitophagy process in both Caenorhabditis elegans and a liver cancer cell line.

Mitochondria are essential for various biological functions, including energy production, lipid metabolism, calcium homeostasis, heme biosynthesis, ...