substrate-uncoupler-inhibitor-titration for mitochondrial respiration analysis in drosophila melanogaster

Analyzing Mitochondrial Physiology and Bioenergetics in Fruit Flies

Mitochondria are cellular organelles that control important functions, including apoptotic regulation, calcium homeostasis, and participation in biosynthetic pathways. By possessing autonomous genetic material, they are capable of contributing to cellular maintenance and repair processes. Their structure houses the electron transport chain and oxidative phosphorylation, both crucial for cellular energy1,2,3. In particular, energy control is achieved through adenosine triphosphate (ATP) production via oxidative phosphorylation (OXPHOS)2. Disruption of energy metabolism with impairment of mitochondrial functions occurs both in cell survival and death4,5, frequently associated with a wide range of human pathologies, such as cancer, and neurodegenerative diseases such as Parkinson&#39;s Disease (PD)3,6.
PD is a chronic, progressive, and neurological disorder. The primary cause of this disease is the death of brain cells, especially in the substantia nigra, which are responsible for the production of the neurotransmitter dopamine, which controls movement6,7,8. The earliest observation that linked Parkinsonism to mitochondrial dysfunction was made in 1988, in experimental models using toxins that inhibit the respiratory chain Complex I9.
Currently, there are several methods to evaluate mitochondrial dysfunction10,11,12,13; however, compared to conventional approaches, high-resolution respirometry (HRR) presents superior sensitivity and advantages13,14. For example, HRR protocols allow the evaluation of the whole mitochondrial respiratory chain function or the activity of specific mitochondrial complexes14,15. Mitochondrial dysfunctions can be assessed in intact cells, isolated mitochondria, or even ex vivo10,11,13,14.
Mitochondrial dysfunctions are closely associated with many pathological and physiological processes. It is therefore important to study mitochondrial physiology and bioenergetics using genetically and experimentally tractable model systems. In this regard, research on Drosophila melanogaster, the fruit fly, has several advantages. This model shares fundamental cellular characteristics and processes with humans, including the use of DNA as genetic material, common organelles, and conserved molecular pathways involved in development, immunity, and cell signaling. In addition, fruit flies have a rapid life cycle, easy maintenance, low cost, high throughput, and fewer ethical concerns, thus constituting an invaluable tool for dissecting complex cellular processes16,17,18,19,20.
Furthermore, a homolog of the PTEN-induced putative kinase 1 (pink1) gene is expressed in D. melanogaster. It plays a crucial role in the removal of damaged mitochondria through the process of mitophagy8. In humans, mutations in this gene predispose individuals to an autosomal recessive familial form of PD associated with mitochondrial dysfunction8,21,22,23. Consequently, the fruit fly is a powerful animal model for studies on the pathophysiology of PD and screening of drug candidates focusing on mitochondrial dysfunction and bioenergetics. Therefore, the present work explains how to analyze mitochondrial function in a model of PD from D. melanogaster using the HRR technique in the OROBOROS with the Substrate-Uncoupler-Inhibitor-Titration (SUIT) protocol.

Author Spotlight: Exploring Mitochondrial Function and Chemical Toxicity Using Drosophila melanogaster 

Analyzing Mitochondrial Function in a Drosophila melanogaster PINK1B9-Null Mutant Using High-resolution Respirometry

Our research uses Drosophila melanogaster as an experimental model to understand mitochondrial function in disease and chemical toxicity. Some questions we want to answer are, how does PINK-1 mutation affect mitochondrial function and how is this linked to Parkinson's Disease? How can we revert, or avert, the mitochondrial dysfunction associated with this mutation?High-resolution respirometry requires specialized training for precise operation and data analysis. In addition, the system we used doesn't allow working with several samples simultaneously and is not educated for high-throughput analysis. Since it's only possible to run two samples at the same time, the experimental design must be well delineated.Our findings indicate progressive impairment of the mitochondrial function we face in PINK1-Null mutants, which is characterized by decrease in OXPHOS CI link, and ETS CI&CII link, and a metabolic metabolic shift in ATP production from oxidative to glycolytic in pathways. These findings are closely related to Parkinson's Disease pathophysiology. One of the key points of high-resolution respirometry is its ability to provide direct and accurate measurements of oxygen consumption, allowing for detailed analysis of mitochondrial function and cellular metabolism.Also, it's versatile. It can be used for wide range of sample types, including isolated mitochondria. Considering that mitochondrial dysfunction is a common feature of neurodegenerative diseases, such as Parkinson's disease, in the future, we will focus on investigating how mitochondrial function and energy elevation could be important targets for therapies directed to neurodegenerative diseases.

Watch this Scientific Journal Video about Substrate-Uncoupler-Inhibitor-Titration for Mitochondrial Respiration Analysis in Drosophila melanogaster at JoVE.com

Substrate-Uncoupler-Inhibitor-Titration for Mitochondrial Respiration Analysis in Drosophila melanogaster  

Substrate-Uncoupler-Inhibitor-Titration for Mitochondrial Respiration Analysis in Drosophila melanogaster

After calibrating polarographic oxygen sensors, remove the stoppers and open the chambers. Wash the stoppers and chambers with 100%ethanol, 70%ethanol, and distilled water. Transfer the flies into a microcentrifuge tube.Add 200 microliters of chilled MiR05 buffer into the tube and homogenize the flies by applying gentle pressure with four to six strokes of the pestle. Using a micropipette, transfer the homogenized fly suspension into the chamber. Cover the chamber with a stopper without introducing air bubbles.Next, click on the layout menu and select Option 5, Flow by Corrected Volume. Another new window will open. Here, in the space, experimental code, name the experiment.In the sample field, name each sample in its respective chamber A and B.Then set the unit field to Unit and in the concentration field, define the chamber volume as one per milliliter. To start the high-resolution respirometry, ensure that the oxygen flux signal is steady on the positive value. Add digitonin to permeabilize the mitochondrial membrane.Then add pyruvate, malate, and proline substrates until the oxygen flux increases and stabilizes. Press the F4 key on the keyboard and enter the name of the reagent to mark the event. Add ADP to couple the mitochondrial respiratory chain, and wait for the increase and stabilization of the oxygen flux.Then add succinate and measure the oxygen flux. TO inhibit ATP synthase, add oligomycin and examine for a decrease in oxygen flux. After the red line stabilizes, uncouple the mitochondrial electron transfer using 0.25-micromolar FCCP until maximum oxygen consumption is reached, demonstrated by the rise of the red line.Next, add rotenone complex I inhibitor and wait for the decrease and stabilization of the oxygen flux. Then add malonate complex II inhibitor and measure the oxygen flux. Finally, add antimycin complex III inhibitor and wait for the decrease, followed by the increase and stabilization of the oxygen flux.Click on the GraphPad Prism software to extract the oxygen flux values from the graphs. OXPHOS CI refers to the value of oxygen flux after adding ADP. Then use the given formula to calculate OXHPOS CII.Using the following equation, calculate the ETS CI and CII oxygen values for the uncouples and inhibitors. Then calculate the ATP synthesis as the difference between the OXPHOS and LEAK. Finally, calculate the OXPHOS by LEAK ratio to determine the respiratory control ratio.The oxygen flux in both OXHPOS CI and OXPHOS CI and CII states was significantly reduced in PINK1 B9 null flies. compared to control flies. Additionally, the oxygen flux in ETS CI, ETS CII, and ETS CI and CII state were lower in PINK1 B9 null flies, indicating an impaired electron transfer system compared to the control flies.The disruption in the flux of electrons affects the OXPHOS process, leading to reduced ATP synthesis in the PINK1 B9 null flies. The reduction in the respiratory control ratio of null flies suggests mitochondrial uncoupling, indicating that the mitochondria were less efficient at utilizing oxygen and producing ATP.

substrate-uncoupler-inhibitor-titration-for-mitochondrial-respiration

Research

JoVE Journal

Biochemistry

104 Views.  Federal University of Santa Maria. After calibrating polarographic oxygen sensors, remove the stoppers and open the chambers. Wash the stoppers and chambers with 100%ethanol, 70%ethanol, and distilled water. Transfer the flies into a microcentrifuge tube.Add 200 microliters of chilled MiR05 buffer into the tube and homogenize the flies by applying gentle pressure with four to six strokes of the pestle. Using a micropipette, transfer the homogenized fly suspension into the chamber. Cover the chamber with a stopper withou...