Name: assessing lysosomal alkalinization in the intestine of live caenorhabditis elegans
Uploaded: 2018-04-13T14:30:00
Description: Watch this Scientific Journal Video about Assessing Lysosomal Alkalinization in the Intestine of Live Caenorhabditis elegans at JoVE.com

We would like to thank the Caenorhabditis Genetics Center for strains, the Natural Sciences and Engineering Research Council (NSERC), and the Canada Foundation for Innovation (CFI) for funding. We would like to thank Dr. Lizhen Chen (Department of Cell Systems and Anatomy, UT Health San Antonio) for allowing unrestricted use of her lab facilities for all C. elegans experiments as well as Dr. Exing Wang (Associate Director, Optical Imaging Facility, UT Health San Antonio) for assistance with confocal microscopy. We would also like to thank Dr. Myron Ignatius for providing support and encouragement to facilitate the video shoot.

1. Stain and Image intestinal lysosomes
<ol>
	<li>Seed nematode growth media (NGM) plates with OP50
	<ol>
		<li>Prepare NGM plates as per the recommended protocol19 and allow the closed plates to dry for 2 days at room temperature.</li>
		<li>Inoculate OP50 bacteria into sterile Luria Broth (LB) broth and grow in a shaking incubator or water bath at 37 &#176;C for 36 h or until the OD is between 0.2 and 0.4. Avoid using a bacterial culture with OD &#62;1 or OD &#60;0.2.</li>
		<...

<ol>
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A variety of cellular and molecular events contribute to aging, influenced by life history traits and genetic factors. Our recent study22 suggests that the reproductive cycle plays an important role in controlling the fitness of the soma through the regulation of lysosomal pH dynamics. We showed that lysosomal-mediated proteolysis is promoted while animals actively reproduce by upregulation of v-ATPase transcription, which in turn ensures acidic lysosomes. Upon the end of reproduction, v-ATPase ex...

The appearance of protein aggregates is widely accepted to be a hallmark of aging in eukaryotic cells1,2,3, and the formation of which is thought to be among the principle drivers of cellular senescence4,5,6,7. There is growing evidence that as cells age, protein catabolism is impaired, leading to an increase in protein aggregation. The collapse of proteolysis in aging cells involves an impairment of autophagy8 as well as proteasome-mediated protein degradation9. Finally, irreversible protein oxidation is increased in old cells, further impairing protein catabolism10.
Autophagy was initially thought to be a non-selective process for bulk degradation of damaged proteins, but recent studies have indicated that autophagy is highly selective to the catabolism of protein aggregates and dysfunctional organelles that are not amenable to degradation via other protein clearance mechanisms11. During the process of autophagy, damaged and aggregated proteins are sequestered into a double-membrane vesicle called the autophagosome. This autophagosome then fuses with the acidic organelles called lysosomes, which leads to degradation of the autophagosome cargo12. Lysosomes represent the end-point of the autophagic pathway and participate in different cellular processes such as membrane repair, transcriptional control and nutrient sensing; highlighting their centralized role in cellular homeostasis (reviewed in ref. 13). Several studies have shown an association between an age-dependent decrease in lysosomal function and various neurodegenerative disorders13. Consistently, restoring lysosomal function in older cells can delay the onset of aging-related phenotypes14,15. Studies of the composition of the intralumen milieu suggest that the collapse of lysosomal function in older cells is not due to a reduction in the production of lysosomal proteases16. Alternatively, it has been proposed that loss of intralysosomal acidity, a critical requirement of its enzymatic activity, may underlie the drop in lysosome-mediated proteolysis17. To be able to explore this hypothesis, it is essential to develop reagents and protocols to probe dynamic changes in lysosomal pH in live cells in a replicable and consistent manner.
The intestine of C. elegans is the major metabolic tissue in worms and it is a critical regulator of systemic homeostasis and lifespan. We have developed assays to evaluate changes in the acidity of the lumen of intestinal lysosomes of worms to determine how lysosome-mediated proteolysis contributes to aging. Though pH-sensitive fluorophores have been used previously in C. elegans to mark intestinal lysosomes, there hasn&#39;t yet been an effort to establish a successful protocol that can detect small increases in lysosomal pH in vivo18. Here, we provide a protocol that can be used to detect loss of lysosomal acidity in the intestinal cells of C. elegans using a simple and convenient feeding protocol that incorporates a pH-sensitive fluorophore (cDCFDA) into OP50 food.

<table border="0" cellpadding="0" cellspacing="0" width="1166">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:475px;">OP50 (E. coli)</td>
			<td style="width:188px;">Caenorhabditis Genetics Center</td>
			<td style="width:119px;"></td>
			<td style="width:385px;">Order online at https://cgc.umn.edu/strain/OP50</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">5(6)-carboxy-2&#8217;,7&#8217;-dichlorofluorescein diacetate&#160;</td>
			<td style="width:188px;">ThermoFisher</td>
			<td style="width:119px;">C369</td>
			<td>Commonly known as cDCFDA</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:475px;">9-diethylamino-5H-benzo(a)phenoxazine-5-one and (3-{2-[(1H,1&#39;H-2,2&#39;-bipyrrol-5-yl-kappaN(1))methylidene]-2H-pyrrol-5-yl-kappaN}-N-[2-(dimethylamino)ethyl]propanamidato)(difluoro)boron</td>
			<td style="width:188px;">ThermoFisher</td>
			<td style="width:119px;">L7528</td>
			<td>Commonly known as Lysotracker Red</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Confocal microscope (e.g. Zeiss LSM 510)</td>
			<td style="width:188px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">ImageJ</td>
			<td style="width:188px;"></td>
			<td style="width:119px;"></td>
			<td>Download for free from https://imagej.nih.gov/ij/download.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">LB Broth powder</td>
			<td style="width:188px;">ThermoFisher</td>
			<td style="width:119px;">22700041</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Bacto Agar</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">A5306-1KG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">NaCl</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">S9888</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Bacto Peptone</td>
			<td style="width:188px;">Fisher Scientific</td>
			<td style="width:119px;">S71604</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Cholesterol powder</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">C3045&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">CaCl2</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">449709</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">MgSO4</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">M7506</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">K3PO4</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">P5629</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Sodium Azide</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">S2002</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">DMSO</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">D8418</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Microscope Slides</td>
			<td style="width:188px;">VWR</td>
			<td style="width:119px;">48311-703</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Cover Slips</td>
			<td style="width:188px;">ThermoFisher</td>
			<td style="width:119px;">3406</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Agarose</td>
			<td style="width:188px;">Sigma</td>
			<td style="width:119px;">A6013</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Incubator</td>
			<td style="width:188px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:475px;">Mirror or other smooth flat surface</td>
			<td style="width:188px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

assessing lysosomal alkalinization in the intestine of live caenorhabditis elegans

The nematode Caenorhabditis elegans (C. elegans) is a model system that is widely used to study longevity and developmental pathways. Such studies are facilitated by the transparency of the animal, the ability to do forward and reverse genetic assays, the relative ease of generating fluorescently labeled proteins, and the use of fluorescent dyes that can either be microinjected into the early embryo or incorporated into its food (E. coli strain OP50) to label cellular organelles (e.g. 9-diethylamino-5H-benzo(a)phenoxazine-5-one and (3-{2-[(1H,1&#39;H-2,2&#39;-bipyrrol-5-yl-kappaN(1))methylidene]-2H-pyrrol-5-yl-kappaN}-N-[2-(dimethylamino)ethyl]propanamidato)(difluoro)boron). Here, we present the use of a fluorescent pH-sensitive dye that stains intestinal lysosomes, providing a visual readout of dynamic, physiological changes in lysosomal acidity in live worms. This protocol does not measure lysosomal pH, but rather aims to establish a reliable method of assessing physiological relevant variations in lysosomal acidity. cDCFDA is a cell-permeant compound that is converted to the fluorescent fluorophore 5-(and-6)-carboxy-2&#39;,7&#39;-dichlorofluorescein (cDCF) upon hydrolysis by intracellular esterases. Protonation inside lysosomes traps cDCF in these organelles, where it accumulates. Due to its low pKa of 4.8, this dye has been used as a pH sensor in yeast. Here we describe the use of cDCFDA as a food supplement to assess the acidity of intestinal lysosomes in C. elegans. This technique allows for the detection of alkalinizing lysosomes in live animals, and has a broad range of experimental applications including studies on aging, autophagy, and lysosomal biogenesis.

cDCFDA stains lysosomes in a pH-dependent manner, and its low pKa and ready uptake into lysosomes makes it an ideal pH sensor21. cDCFDA staining intensity is inversely proportional to lysosomal pH (i.e. staining intensity increases as pH decreases)18,22. cDCFDA signals are consistently weak in lysosomes of animals treated with 20 mM of chloroquine, an inhibitor of lysosomal acidification, and in wo...

Watch this Scientific Journal Video about Assessing Lysosomal Alkalinization in the Intestine of Live Caenorhabditis elegans at JoVE.com

Assessing Lysosomal Alkalinization in the Intestine of Live Caenorhabditis elegans

A step-by-step guide to probe loss of lysosomal acidity in the intestine of C. elegans using the pH-sensitive vital dye 5(6)-carboxy-2&#39;,7&#39;-dichlorofluorescein diacetate (cDCFDA)

Assessing Lysosomal Alkalinization in the Intestine of Live Caenorhabditis elegans

The nematode Caenorhabditis elegans (C. elegans) is a model system that is widely used to study longevity and developmental pathways. Such studies are ...

The overall goal of this procedure is to assess a relative loss of lysosomal acidity in the intestinal lysosomes of C.elegans. This method can help answer key questions in the field of autophagy by indirectly providing information about lysosomal function and protein degradation. The main advantage of this technique is that it is simple, inexpensive, convenient, and reproducible.We first had the idea for this method when we observed the staining technique being used for assessing vacuolar alkalinization in yeast. Visual demonstration of this method is important because certain steps, such as adding cDCFDA to OP50 food and imaging control two day old wild type worms are critical. After preparing the NGM plates, let the plates dry in room temperature for two days with the lid closed.Then, inoculate the OP50 bacteria in the sterile Luria broth. After inoculating, leave the inoculant in the incubator until the OD is between 0.2 and 0.4. Then, place a drop of the OP50 inoculant in the center of the dry NGM plate.Next, use a spreader to spread the inoculant in patch roughly two by two centimeters. Approximately after 15 minutes, invert the OP50 plate after the inoculant has dried up. Then, incubate the plate at 37 degrees Celsius for 36 hours.Once the incubation is over, transfer the plate at four degrees Celsius til use. Then, prepare a working stock of 10 millimolar cDCFDA in M9 buffer. Store the cDCFDA solution away from light at minus 20 degrees Celsius.Then, pipette 100 microliters of 10 millimolar cDCFDA to cover the entire OP50 patch uniformly on the plate. Leave the cDCFDA plates in a dark box on the bench top for about 30 minutes. After the cDCFDA has permeated the OP50 patch completely, transfer 20 worms on the plate, then leave the plate in inverted condition for about 14 hours at 20 degrees Celsius.Next, take two strips of labeling tapes and place them 1.5 inches apart on a smooth, flat mirror surface. Then, coat the surface of the mirror with water repellent spray, and remove the excess liquid out. Next, melt 2%agarose in distilled water in the microwave.After the agarose has liquified, place a drop of agarose between the two strips of the tapes and cover the drop with the microscope slide. After the agarose has solidified in the shape of a circular pad under the slide, flip the slide. Then, add 10 to 15 microliters of five millimolar sodium azide on the agarose pad.Now, transfer the worms from the cDCFDA supplemented plate to a clean NGM plate without any OP50. Let the worms move around for a few seconds for the OP50 to be removed from their surface. Then, transfer the worm on the agarose pad containing five millimolar sodium azide.Quickly cover the agarose pad with a cover slip. Next, use 60X magnification lens and capture images in a single plane of the intestine from two day old wild type and mutant worms. Then, open ImageJ and click on the file.Then, click Open to open the file that needs to be quantified. After the image has loaded, use the oval-shaped Selection Tool to select the region of interest. Then, click Analyze, and finally, Measure to quantify the fluorescence intensity of the region of interest.To study the lysosomal functional activity, cDCFDA staining intensity is quantified using confocal imaging. In this image, there is a robust cDCFDA fluorescence signal intensity in the intestinal lysosomes of wild type day two C.Elegans. This indicates a functionally competent acidic lysosome.On the contrary, the fluorescence intensity is considerably suppressed in the intestinal lysosomes of wild type day eight old worms. This is in comparison to the intestinal lysosomes of day two worms. The result indicated the presence of functionally incompetent alkaline lysosome in day eight old worms.Interestingly, the cDCFDA fluorescence in intensity is also markedly reduced in both day two and eight old RNAi worms when compared to the wild type worm. Here, the vha gene, encoding the vacuolar ATPase subunits in the lysosomal lining has been knocked down in the day two and day eight old worms. Once mastered, this entire staining and microscopy regimen can be completed in less than 18 hours, if performed properly.While attempting this procedure, it is important to remember to incubate worms in cDCFDA supplement in OP50 food for at least 14 hours. After watching this video, you should have a good understanding of how to assess loss of lysosomal acidity in the intestinal lysosomes of live C.elegans.

Research

JoVE Journal

Developmental Biology

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