staining of ferroptosis-induced medulloblastoma cells for flow cytometric detection of lipid hydroperoxides

FACS Analysis of Lipid Hydroperoxides in Ferroptotic Medulloblastoma Cells

Ferroptosis is a newly contextualized, reactive oxygen species (ROS)-dependent type of cell death1. Besides ROS, iron plays a crucial role(s) in this type of cell death, hence the name2. The final and executive step of ferroptosis is the iron-catalyzed accumulation of oxidative damage of lipids in the plasma membrane that eventually leads to compromised membrane integrity and selective permeability, and, finally, cell death by bubbling. Lipid hydroperoxidation event is a naturally occurring phenomenon; however, its propagation throughout the cellular membrane is prevented by the antioxidant defense of the cell. The major player in this context is Se-protein glutathione peroxidase 4 (GPx4), which can approach the membrane and convert lipid hydroperoxides into their less toxic alcohol derivatives3. The reducing power for GPx4 is mainly, but not exclusively, provided by glutathione (GSH), a tripeptide composed of the non-essential amino acids: glycine, glutamate, and cysteine. The rate-limiting amino acid for the biosynthesis of GSH is cysteine4. Although cysteine is classified as a non-essential amino acid, its requirements can easily exceed its internal production in highly proliferative cells (such as cancer cells). It thus has been re-classified in the group of semi-essential amino acids. The necessary import of cysteine occurs mainly through the Xc- system, which allows the import of the oxidized (dominant) form of cysteine (aka cystine) at the expense of glutamate export5. The Xc- system is composed of a Na+-independent, Cl--dependent transport subunit, known as xCT, and a chaperon subunit, known as CD98. Until recently, the anti-ferroptotic properties of the xCT-GSH-GPx4 axis have been seen as unique and irreplicable6. However, in 2019, an alternative anti-ferroptotic pathway, consisting of ubiquinol (Coenzyme Q10) and its regenerative enzyme - ferroptosis suppressor protein 1 (FSP1), has been described7,8. Soon afterward, yet another lipid hydroperoxide detoxifying system involving GTP cyclohydrolase-1/tetrahydrobiopterin (GCH1/BH4) has been reported9. Nonetheless, the central role of the xCT-GSH-GPx4 axis in the prevention of ferroptosis seems not to be challenged.
Over the past decade, ferroptosis has been extensively studied in a variety of tumor types, showing great potential as an anti-cancer strategy (reviewed by Lei et al.10). Furthermore, it has been reported that cancer cells exhibiting high resistance to conventional chemotherapeutics and/or a propensity to metastasize are surprisingly sensitive to ferroptosis inducers, such as inhibitors of GPx411,12,13. However, in the context of brain tumors, the potential of ferroptotic inducers remains largely understudied. While this type of cell death has been closely associated with cerebral ischemia-reperfusion injury14and neurodegenerative diseases15, its potential in the context of brain tumors has mainly been limited to glioblastoma, the most common malignant craniocerebral tumor (reviewed by Zhuo et al.16). On the other hand, the sensitivity of medulloblastoma, the most common malignant pediatric brain tumor and a leading cause of childhood mortality, to ferroptosis inducers remains largely unexplored. To the best of our knowledge, there is scarce peer-reviewed literature linking ferroptosis and medulloblastoma. Nonetheless, some studies have revealed that iron plays a crucial role in the survival, proliferation, and tumorigenic potential of both medulloblastoma and glioblastoma cancer stem cells (CSCs)17,18, potentially rendering them more vulnerable to ferroptosis induction. This is particularly significant as medulloblastoma is notorious for its subpopulation of CSCs, or tumor-initiating/propagating cells, which appear to be largely responsible for tumor chemoresistance, dissemination, and relapse19.
Sensitivity to ferroptosis induction is typically investigated by measuring lipid hydroperoxide content/accumulation, which may or may not lead to cell death. The most commonly used ferroptosis inducers are (1) erastin, an inhibitor of the xCT transporter20,(2) RSL3, an inhibitor of the GPx4 enzyme2, and/or (3) iron donors, such as ferro-ammonium citrate (FAC)21. Lipid hydroperoxide content is assessed using the selective probe BODIPY 581/591 C1122, which has excitation and emission maxima at 581/591 nm in its reduced state. Upon interaction with and oxidation by lipid hydroperoxides, the probe shifts its excitation and emission maxima to 488/510 nm. Typically, a significant increase in lipid hydroperoxide content precedes ferroptotic cell death. Since ferroptosis is not a programmed cell death, there is no molecular signaling cascade leading to its execution. Therefore, the only way to confirm it is to monitor lipid hydroperoxide content and use specific inhibitors for this type of cell death, such as ferrostatin 123. Ferrostatin 1 is a lipophilic antioxidant that can penetrate the lipid compartment of the cell and detoxify lipid hydroperoxides, thereby preventing ferroptotic events.

Author Spotlight: Tracing the Ferroptotic Signatures and Cell Death Dynamics in Medulloblastoma for Advanced Therapeutics 

Revealing the Ferroptotic Phenotype of Medulloblastoma

The ultimate goal of our research is to develop new therapeutics for pediatric cancers such as myoblastoma. For this purpose, our team develops new model systems highlighting the genetic background of the disease, as well as exploiting new therapeutic avenues. In the recent years, single cell genomics have revealed how impaired lineage commitment influences clinical outcome of pediatric cancers, as well as response to the treatments, and ultimately the development of treatment resistant cell populations within the tumor.The spectrum of neural progenitor differentiated state appears to underlie the clinical outcome of pediatric cancer. Main challenges are to understand these highly plastic known or insufficiently progenitors within the tumors, as well as developing new therapeutic that are more efficient and less harmful for these diseases. From this standpoint, our research on ferroptosis appears extremely promising.Iron dependence is one of the main vulnerabilities of cancer cells, also known as cancer stem cells, all the essential element. Iron is double-edged sword as its reaction with reactive oxygen species can lead to the specific type of cell death, which is called ferroptosis. Our data clearly showed that ferroptosis is a great potential against this type of cancer cells.

Staining of Ferroptosis-Induced Medulloblastoma Cells for Flow Cytometric Detection of Lipid Hydroperoxides

To begin, seed and culture wild type medulloblastoma cell lines in a six well plate. After 24 hours, add the appropriate ferroptosis inducing agent to the cells and incubate the plate at 37 degrees Celsius with 5%carbon dioxide. After six hours of treatment, observe the cells under a light microscope for cell rounding.Using an aspirator, remove the media and floating cells from the plate under a Laminar airflow. To wash the cells, add two milliliters of PBS, swirl gently and aspirate the PBS out. Next, add two milliliters of the probe working solution and incubate the plate in the dark.Light, microscopic images of the DAOY wild type cells treated with one micromolar of Erastin showed round bubbling cells indicating a ferroptotic phenotype.

Research

JoVE Journal

Cancer Research

The interaction of iron and oxygen is an integral part of the development of life on Earth. Nonetheless, this unique chemistry continues to fascinate and ...