Measurement of Oxygen Consumption Rates in Intact Caenorhabditis elegans

Summary

Mitochondrial respiration is critical for organismal survival; therefore, oxygen consumption rate is an excellent indicator of mitochondrial health. In this protocol, we describe the use of a commercially available respirometer to measure basal and maximal oxygen consumption rates in live, intact, and freely-motile Caenorhabditis elegans.

Abstract

Optimal mitochondrial function is critical for healthy cellular activity, particularly in cells that have high energy demands like those in the nervous system and muscle. Consistent with this, mitochondrial dysfunction has been associated with a myriad of neurodegenerative diseases and aging in general. Caenorhabditis elegans have been a powerful model system for elucidating the many intricacies of mitochondrial function. Mitochondrial respiration is a strong indicator of mitochondrial function and recently developed respirometers offer a state-of-the-art platform to measure respiration in cells. In this protocol, we provide a technique to analyze live, intact C. elegans. This protocol spans a period of ~7 days and includes steps for (1) growing and synchronization of C. elegans, (2) preparation of compounds to be injected and hydration of probes, (3) drug loading and cartridge equilibration, (4) preparation of worm assay plate and assay run, and (5) post-experiment data analysis.

Introduction

Adenosine triphosphate (ATP), the main source of cellular energy, is produced in the mitochondria by enzymes in the electron transport chain (ETC) located in the inner mitochondrial membrane. Pyruvate, a key metabolite utilized for mitochondrial ATP production, is imported into the mitochondrial matrix where it is decarboxylated to produce acetyl coenzyme A (CoA). Subsequently, acetyl CoA enters the citric acid cycle resulting in the generation of nicotinamide adenine dinucleotide (NADH), a key electron carrier molecule. As electrons from NADH are passed to oxygen via the ETC, protons build up in the mitochondrial intermembrane space, which results in the generation o....

Protocol

NOTE: Figure 2 provides a schematic overview of the full protocol.

1. Growth and synchronization of nematode population^9,10

1. Transfer L4 larvae of desired genetic backgrounds (e.g., N2 [wild type] and sel-12 animals) onto nematode growth media (NGM) plates (see Table 1 for recipe) freshly seeded with a lawn of Escherichia coli (OP50)¹¹. Use at least two 100 mm or three 60 mm plates for each strain. Incubate the worms at the appropriate growth temperature (between 15–25 °C) for 3R....

Results

Using the protocol described herein, OCR of wild type animals and three different sel-12 mutant strains were determined. sel-12 encodes the C. elegans ortholog of presenilin¹⁷. Mutations in human presenilin are the most common genetic aberration associated with the development of familial Alzheimer's disease¹⁸. Our studies have shown elevated mitochondrial calcium levels in sel-12 mutant animals compared t.......

Discussion

Mitochondrial respiration is an insightful indicator of mitochondrial function; therefore, being able to measure the oxygen consumption rates in a biological system, whether in vitro or in vivo is highly valuable. Respirometers sense oxygen levels using porphyrin-based phosphors that get quenched by oxygen or via amperometric oxygen sensors that rely on the generation of an electric current proportional to oxygen pressure. Clark electrode falls into the latter category and has been used extensively in literature, especia.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
100 mm, 60 mm Petri dishes	Kord-Valmark Labware Products	2900, 2901
1.5 mL centrifuge tubes	Globe Scientific	6285
15 mL conical tubes	Corning	430791
22 × 22 mm coverslip	Globe Scientific	1404-10
50 mL conical tubes	Corning	430829
Agar	Fisher Scientific	BP1423-2
Bacto peptone	BD, Bacto	211677
Bacto tryptone	BD, Bacto	211705
Bacto yeast extract	BD, Bacto	212705
Bleach	Generic
Calcium chloride dihydrate (CaCl2·2H2O)	Fisher Scientific	C79-500
Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP)	Abcam	ab120081
Cholesterol	Fisher Scientific	C314-500
Deionized water (dH2O)
Dimethyl sulfoxide (DMSO)	Thomas Scientific	C987Y85
Glass Pasteur pipettes	Krackeler Scientific	6-72050-900
Magnesium sulfate heptahydrate (MgSO4·7H2O)	Fisher Scientific	BP213-1
Potassium phosphate dibasic (K2HPO4)	Fisher Scientific	BP363-1
Potassium phosphate monobasic (KH2PO4)	Fisher Scientific	P285-500
Sodium chloride	Fisher Scientific	BP358-10
Sodium hydroxide (NaOH)	Fisher Scientific	BP359-500
Sodium phosphate dibasic anhydrous (Na2HPO4)	Fisher Scientific	BP332-1
Seahorse XFp Analyzer	Agilent
Seahorse XFp FluxPak	Agilent	103022-100
Sodium Azide	Sigma-Aldrich	S2002