Membrane Dynamics and Cation Handling in Ferroptosis

Apoptotic cell death induced by copper (II), manganese (II) and silver (I) complexes containing bridging dicarboxylate and 1,10-phenanthroline ligands: one of the multi-modes of anticancer activity?

Cu(II), Mn(II) and Ag(I) complexes incorporating bridging dicarboxylate and 1,10-phenanthroline ligands have exhibited anti-cancer potential with significant in vitro and in vivo cytotoxic efficacies. Our study focuses on regulated cell death process of apoptosis as a mode of action of the anti-cancer activity by the complexes. Cytotoxicity screening of the complexes demonstrated all the metal-dicarboxylate-phenanthroline complexes exhibit superior activity compared to their non-phenanthroline containing precursors, in addition to cisplatin. The Cu(II) and Mn(II) complexes were shown to induce reactive oxygen species (ROS) but this was not observed for the Ag(I) analogues. Furthermore, apoptosis was found to be induced by all the metal-phenanthroline complexes to varying degrees contingent on the type of metal centre in the complex. Apoptotic gene expression analysis established the predominant activation of the intrinsic apoptotic pathway, with co-stimulation of the extrinsic pathway observed in some cases. The mechanistic data provided within this study highlights the multi-modal activity of the metal-phenanthroline complexes contingent on the type of metal present, warranting continued investigation of their biological modes of action beyond apoptosis induction.

Ferroptosis in plant immunity

Plant cell death is mediated by calcium, iron, and reactive oxygen species (ROS) signaling in plant immunity. The reconstruction of a nucleotide-binding leucine-rich-repeat receptor (NLR) supramolecular structure, called the resistosome, is intimately involved in the hypersensitive response (HR), a type of cell death involved in effector-triggered immunity (ETI). Iron is a crucial redox catalyst in various cellular reactions. Ferroptosis is a regulated, non-apoptotic form of iron- and ROS-dependent cell death in plants. Pathogen infections trigger iron accumulation and ROS bursts in plant cells, leading to lipid peroxidation via the Fenton reaction and subsequent ferroptosis in plant cells similar to that in mammalian cells. The small-molecule inducer erastin triggers iron-dependent lipid ROS accumulation and glutathione depletion, leading to HR cell death in plant immunity. Calcium (Ca2+) is another major mediator of plant immunity. Cytoplasmic Ca2+ influx through calcium-permeable channels, the resistosomes, mediates iron- and ROS-dependent ferroptotic cell death under reduced glutathione reductase (GR) expression levels in the ETI response. Acibenzolar-S-methyl (ASM), a plant defense activator, enhances Ca2+ influx, ROS and iron accumulation, and lipid peroxidation to trigger ferroptotic cell death. These breakthroughs suggest a potential role for Ca2+ signaling in ferroptosis and its coordination with iron and ROS signaling in plant immunity. In this review, we highlight the essential roles of calcium, iron, and ROS signaling in ferroptosis during plant immunity and discuss advances in the understanding of how Ca2+-mediated ferroptotic cell death orchestrates effective plant immune responses against invading pathogens.

Recommendations for robust and reproducible research on ferroptosis

Ferroptosis is a necrotic, non-apoptotic cell death modality triggered by unrestrained iron-dependent lipid peroxidation. By unveiling the regulatory mechanisms of ferroptosis and its relevance to various diseases, research over the past decade has positioned ferroptosis as a promising therapeutic target. The rapid growth of this research field presents challenges, associated with potentially inadequate experimental approaches that may lead to misinterpretations in the assessment of ferroptosis. Typical examples include assessing whether an observed phenotype is indeed linked to ferroptosis, and selecting appropriate animal models and small-molecule modulators of ferroptotic cell death. This Expert Recommendation outlines state-of-the-art methods and tools to reliably study ferroptosis and increase the reproducibility and robustness of experimental results. We present highly validated compounds and animal models, and discuss their advantages and limitations. Furthermore, we provide an overview of the regulatory mechanisms and the best-studied players in ferroptosis regulation, such as GPX4, FSP1, SLC7A11 and ACSL4, discussing frequent pitfalls in experimental design and relevant guidance. These recommendations are intended for researchers at all levels, including those entering the expanding and exciting field of ferroptosis research.

Conjugated fatty acids drive ferroptosis through chaperone-mediated autophagic degradation of GPX4 by targeting mitochondria

Conjugated fatty acids (CFAs) have been known for their anti-tumor activity. However, the mechanism of action remains unclear. Here, we identify CFAs as inducers of glutathione peroxidase 4 (GPX4) degradation through chaperone-mediated autophagy (CMA). CFAs, such as (10E,12Z)-octadecadienoic acid and α-eleostearic acid (ESA), induced GPX4 degradation, generation of mitochondrial reactive oxygen species (ROS) and lipid peroxides, and ultimately ferroptosis in cancer cell lines, including HT1080 and A549 cells, which were suppressed by either pharmacological blockade of CMA or genetic deletion of LAMP2A, a crucial molecule for CMA. Mitochondrial ROS were sufficient and necessary for CMA-dependent GPX4 degradation. Oral administration of an ESA-rich oil attenuated xenograft tumor growth of wild-type, but not that of LAMP2A-deficient HT1080 cells, accompanied by increased lipid peroxidation, GPX4 degradation and cell death. Our study establishes mitochondria as the key target of CFAs to trigger lipid peroxidation and GPX4 degradation, providing insight into ferroptosis-based cancer therapy.

PRDX6 dictates ferroptosis sensitivity by directing cellular selenium utilization

Selenium-dependent glutathione peroxidase 4 (GPX4) is the guardian of ferroptosis, preventing unrestrained (phospho)lipid peroxidation by reducing phospholipid hydroperoxides (PLOOH). However, the contribution of other phospholipid peroxidases in ferroptosis protection remains unclear. We show that cells lacking GPX4 still exhibit substantial PLOOH-reducing capacity, suggesting a contribution of alternative PLOOH peroxidases. By scrutinizing potential candidates, we found that although overexpression of peroxiredoxin 6 (PRDX6), a thiol-specific antioxidant enzyme with reported PLOOH-reducing activity, failed to prevent ferroptosis, its genetic loss sensitizes cancer cells to ferroptosis. Mechanistically, we uncover that PRDX6, beyond its known peroxidase activity, acts as a selenium-acceptor protein, facilitating intracellular selenium utilization and efficient selenium incorporation into selenoproteins, including GPX4. Its physiological significance was demonstrated by reduced GPX4 expression in Prdx6-deficient mouse brains and increased sensitivity to ferroptosis in PRDX6-deficient tumor xenografts in mice. Our study highlights PRDX6 as a critical player in directing cellular selenium utilization and dictating ferroptosis sensitivity.

Improving understanding of ferroptosis: Molecular mechanisms, connection with cellular senescence and implications for aging

In the face of cell damage, cells can initiate a response ranging from survival to death, the balance being crucial for tissue homeostasis and overall health. Cell death, in both accidental and regulated forms, plays a fundamental role in maintaining tissue homeostasis. Among the regulated mechanisms of cell death, ferroptosis has garnered attention for its iron-dependent phospholipid (PL) peroxidation and its implications in aging and age-related disorders, as well as for its therapeutic relevance. In this review, we provide an overview of the mechanisms, regulation, and physiological and pathological roles of ferroptosis. We present new insights into the relationship between ferroptosis, cellular senescence and aging, emphasizing how alterations in ferroptosis pathways contribute to aging-related tissue dysfunction. In addition, we examine the therapeutic potential of ferroptosis in aging-related diseases, offering innovative insights into future interventions aimed at mitigating the effects of aging and promoting longevity.

Targeting ferroptosis for treating kidney disease

Ferroptosis is a type of regulated cell death hallmarked by iron-mediated excessive lipid oxidation. Over the past decade since the coining of the term ferroptosis, advances in research have led to the identification of intracellular processes that regulate ferroptosis such as GSH-GPX4 pathway and FSP1-coenzyme Q10/vitamin K pathway. From a disease perspective, the involvement of ferroptosis in pathological conditions including kidney disease has attracted attention. In terms of renal pathophysiology, ferroptosis has been widely investigated for its involvement in ischemia-reperfusion injury, nephrotoxin-induced kidney damage and other renal diseases. Therefore, therapeutic interventions targeting ferroptosis are expected to become a new therapeutic approach for these diseases. However, when considering cell death as a therapeutic target, careful consideration must be given to (i) in which type of cells, (ii) which type of cell death mode, and (iii) in which stage or temporal window of the disease. In the next decade, elucidation of the true involvement of ferroptosis in kidney disease setting in human, and development of clinically applicable and effective therapeutic drugs that target ferroptosis are warranted.

Oxidative Metabolism as a Cause of Lipid Peroxidation in the Execution of Ferroptosis

Ferroptosis is a type of nonapoptotic cell death that is characteristically caused by phospholipid peroxidation promoted by radical reactions involving iron. Researchers have identified many of the protein factors that are encoded by genes that promote ferroptosis. Glutathione peroxidase 4 (GPX4) is a key enzyme that protects phospholipids from peroxidation and suppresses ferroptosis in a glutathione-dependent manner. Thus, the dysregulation of genes involved in cysteine and/or glutathione metabolism is closely associated with ferroptosis. From the perspective of cell dynamics, actively proliferating cells are more prone to ferroptosis than quiescent cells, which suggests that radical species generated during oxygen-involved metabolism are responsible for lipid peroxidation. Herein, we discuss the initial events involved in ferroptosis that dominantly occur in the process of energy metabolism, in association with cysteine deficiency. Accordingly, dysregulation of the tricarboxylic acid cycle coupled with the respiratory chain in mitochondria are the main subjects here, and this suggests that mitochondria are the likely source of both radical electrons and free iron. Since not only carbohydrates, but also amino acids, especially glutamate, are major substrates for central metabolism, dealing with nitrogen derived from amino groups also contributes to lipid peroxidation and is a subject of this discussion.