Chaperone-mediated autophagy is involved in the execution of ferroptosis

Xanthohumol Protects the Rat Myocardium against Ischemia/Reperfusion Injury-Induced Ferroptosis

Ferroptosis is an iron-dependent form of cell death caused by the inactivation of glutathione peroxidase 4 (GPX4) and accumulation of lipid peroxides. Ferroptosis has been found to participate in the ischemia-reperfusion (I/R) injury, leading to heart dysfunction and myocardial cell death. Xanthohumol (XN), a prenylated flavonoid isolated from Humulus lupulus, has multiple pharmacological activities, such as anti-inflammatory and antioxidant. This study is aimed at investigating whether XN could attenuate the I/R-induced ferroptosis in cardiomyocytes and the underlying mechanisms. Cardiomyocytes were treated with Fe-SP and RSL3, and the rat hearts were treated with I/R. The results from the present study show that XN was able to protect cardiomyocytes against Fe-SP- and RSL3-induced ferroptotic cell death by decreasing the production of lipid peroxidation and ROS, chelating iron, reducing the NRF2 protein level, and modulating the protein levels of GPX4. Moreover, XN significantly decreased the mRNA levels of ferroptosis markers, Ptgs2 and Acsl4, and the protein levels of ACSL4 and NRF2 and modulated the protein levels of GPX4 in I/R-treated hearts. The findings from the present study suggest that XN might have the therapeutic potential for the I/R-induced ferroptosis injury.

Autophagy-Dependent Ferroptosis-Related Signature is Closely Associated with the Prognosis and Tumor Immune Escape of Patients with Glioma

Background

Ferroptosis is an autophagy-dependent form of cell death, sometimes called “ferritinophagy”. Its related pathway has been proven to regulate the programmed death of glioma stem cells. Mining autophagy-dependent ferroptosis-related gene (AD-FRG) signature could facilitate the discovery of mechanisms and therapeutic targets showing drug resistance to chemotherapeutic drugs.

Methods

We exhaustively searched HADB, MSigDB and FerrDb datasets and obtained 25 genes confirmed to exist in autophagy and ferroptosis death pathways. Glioma gene expression and clinicopathological data were collected from TCGA and CGGA datasets.

Results

Lasso regression and Cox regression analysis were carried out to construct a nine AD-FRGs signature (SIRT1, MTDH, HSPB1, CISD2, HMOX1, ATG7, MTOR, PRKAA2 and EIF2AK4). ROC curve showed that nine genes signature could effectively predict 1- (AUC = 0.869), 3- (AUC = 0.922) and 5-year (AUC = 0.870) survival rates. Immunohistochemical images confirmed the protein expression level of the gene model. The prognostic nomogram of risk score, age, WHO grade, isocitrate dehydrogenase (IDH) wild-type condition, 1p/19q co-deletion state was built. The calibration curve demonstrated that the prediction of the nomogram is highly consistent with the actual results. Moreover, tumor microenvironment analysis showed that the high-risk group was associated with high immune infiltration status and high tumor purity. Correlation analysis showed that the expression of SIRT1, CISD2 and HSPB1 might be related to macrophage infiltration and immunotolerance in glioma tissues.

Conclusion

Based on autophagy-dependent ferroptosis-related genes, we established gene signature and nomogram that maybe effectively predict the overall survival rate of glioma and correlate with the immunosuppressive tumor microenvironment (TME).

Abnormal Iron and Lipid Metabolism Mediated Ferroptosis in Kidney Diseases and Its Therapeutic Potential

Ferroptosis is a newly identified form of regulated cell death driven by iron-dependent phospholipid peroxidation and oxidative stress. Ferroptosis has distinct biological and morphology characteristics, such as shrunken mitochondria when compared to other known regulated cell deaths. The regulation of ferroptosis includes different molecular mechanisms and multiple cellular metabolic pathways, including glutathione/glutathione peroxidase 4(GPX4) signaling pathways, which are involved in the amino acid metabolism and the activation of GPX4; iron metabolic signaling pathways, which are involved in the regulation of iron import/export and the storage/release of intracellular iron through iron-regulatory proteins (IRPs), and lipid metabolic signaling pathways, which are involved in the metabolism of unsaturated fatty acids in cell membranes. Ferroptosis plays an essential role in the pathology of various kidneys diseases, including acute kidney injury (AKI), chronic kidney disease (CKD), autosomal dominant polycystic kidney disease (ADPKD), and renal cell carcinoma (RCC). Targeting ferroptosis with its inducers/initiators and inhibitors can modulate the progression of kidney diseases in animal models. In this review, we discuss the characteristics of ferroptosis and the ferroptosis-based mechanisms, highlighting the potential role of the main ferroptosis-associated metabolic pathways in the treatment and prevention of various kidney diseases.

Ferroptosis Signaling and Regulators in Atherosclerosis

Atherosclerosis (AS) is a major cause of cardiovascular diseases such as coronary heart disease, heart failure and stroke. Abnormal lipid metabolism, oxidative stress and inflammation are the main features of AS. Ferroptosis is an iron-driven programmed cell death characterized by lipid peroxidation, which have been proved to participate in the development and progression of AS by different signal pathways. NRF2-Keap1 pathway decreases ferroptosis associated with AS by maintaining cellular iron homeostasis, increasing the production glutathione, GPX4 and NADPH. The p53 plays different roles in ferroptosis at different stages of AS in a transcription-dependent and transcription- independent manner. The Hippo pathway is involved in progression of AS, which has been proved the activation of ferroptosis. Other transcription factors, such as ATF3, ATF4, STAT3, also involved in the occurrence of ferroptosis and AS. Certain proteins or enzymes also have a regulatory role in AS and ferroptosis. In this paper, we review the mechanism of ferroptosis and its important role in AS in an attempt to find a new relationship between ferroptosis and AS and provide new ideas for the future treatment of AS.

The V-ATPases in cancer and cell death

Transmembrane ATPases are membrane-bound enzyme complexes and ion transporters that can be divided into F-, V-, and A-ATPases according to their structure. The V-ATPases, also known as H⁺-ATPases, are large multi-subunit protein complexes composed of a peripheral domain (V1) responsible for the hydrolysis of ATP and a membrane-integrated domain (V0) that transports protons across plasma membrane or organelle membrane. V-ATPases play a fundamental role in maintaining pH homeostasis through lysosomal acidification and are involved in modulating various physiological and pathological processes, such as macropinocytosis, autophagy, cell invasion, and cell death (e.g., apoptosis, anoikis, alkaliptosis, ferroptosis, and lysosome-dependent cell death). In addition to participating in embryonic development, V-ATPase pathways, when dysfunctional, are implicated in human diseases, such as neurodegenerative diseases, osteopetrosis, distal renal tubular acidosis, and cancer. In this review, we summarize the structure and regulation of isoforms of V-ATPase subunits and discuss their context-dependent roles in cancer biology and cell death. Updated knowledge about V-ATPases may enable us to design new anticancer drugs or strategies.

Ferroptosis: A potential target for the intervention of intervertebral disc degeneration

Ferroptosis, an iron-dependent form of programmed cell death marked by phospholipid peroxidation, is regulated by complex cellular metabolic pathways including lipid metabolism, iron balance, redox homeostasis, and mitochondrial activity. Initial research regarding the mechanism of ferroptosis mainly focused on the solute carrier family 7 member 11/glutathione/glutathione peroxidase 4 (GPX4) signal pathway. Recently, novel mechanisms of ferroptosis, independent of GPX4, have been discovered. Numerous pathologies associated with extensive lipid peroxidation, such as drug-resistant cancers, ischemic organ injuries, and neurodegenerative diseases, are driven by ferroptosis. Ferroptosis is a new therapeutic target for the intervention of IVDD. The role of ferroptosis in the modulation of intervertebral disc degeneration (IVDD) is a significant topic of interest. This is a novel research topic, and research on the mechanisms of IVDD and ferroptosis is ongoing. Herein, we aim to review and discuss the literature to explore the mechanisms of ferroptosis, the relationship between IVDD and ferroptosis, and the regulatory networks in the cells of the nucleus pulposus, annulus fibrosus, and cartilage endplate to provide references for future basic research and clinical translation for IVDD treatment.

DCN released from ferroptotic cells ignites AGER-dependent immune responses

Ferroptosis is a form of inflammatory cell death for which key mediators remain obscure. Here, we report that the proteoglycan decorin (DCN) is released by cells that are dying from ferroptosis and then acts as an alarm signal to trigger innate and adaptive immune responses. The early release of DCN during ferroptosis is an active process that involves secretory macroautophagy/autophagy and lysosomal exocytosis. Once released, extracellular DCN binds to the receptor advanced glycosylation end-product-specific receptor (AGER) on macrophages to trigger the production of pro-inflammatory cytokines in an NFKB/NF-κB-dependent manner. Pharmacological and genetic inhibition of the DCN-AGER axis protects against ferroptotic death-related acute pancreatitis and limits the capacity of ferroptotic cancer cells to induce a tumor-protective immune response. Thus, DCN is an essential mediator of the inflammatory and immune consequences of ferroptosis.

Characterization of a patient-derived variant of GPX4 for precision therapy

GPX4, as the only enzyme in mammals capable of reducing esterified phospholipid hydroperoxides within a cellular context, protects cells from ferroptosis. We identified a homozygous point mutation in the GPX4 gene, resulting in an R152H coding mutation, in three patients with Sedaghatian-type spondylometaphyseal dysplasia (SSMD). With structure-based analyses and cell models, including patient fibroblasts, of this variant, we found that the missense variant destabilized a critical loop, which disrupted the active site and caused a substantial loss of enzymatic function. We also found that the R152H variant of GPX4 is less susceptible to degradation, revealing the degradation mechanism of the GPX4 protein. Proof-of-concept therapeutic treatments, which overcome the impaired R152H GPX4 activity, including selenium supplementation, selective antioxidants, and a deuterated PUFA were identified. In addition to revealing a general approach to investigating rare genetic diseases, we demonstrate the biochemical foundations for therapeutic strategies targeting GPX4.

Exosomes in triple negative breast cancer: From bench to bedside

Exosomes are lipid bilayer extracellular vesicles with a size of 30-150 nm, which can be released by various types of cells including breast cancer cells. Exosomes are enriched with multiple nucleic acids, lipids, proteins and play critical biological roles by binding to recipient cells and transmitting various biological cargos. Studies have reported that tumor-derived exosomes are involved in cancer initiation and progression, such as promoting cancer invasion and metastasis, accelerating angiogenesis, contributing to epithelial-mesenchymal transition, and enhancing drug resistance in tumors. Recently the dysregulating of exosomes has been found in triple-negative breast cancer (TNBC), relating to the clinicopathological characteristics and prognosis of TNBC patients. Considering the poor prognosis and lack of adequate response to conventional therapy of TNBC, the discovery of certain exosomes as a new target for diagnosis and treatment of TNBC may be a good choice that provides new opportunities for the early diagnosis, clinical treatment of TNBC. Here, we first discuss the innovative prognostic and predictive effects of exosomes on TNBC, as well as the practical clinical problems. Secondly, we focus on the new therapeutic areas represented by exosomes, especially the impact of introducing exosomes in TNBC treatment in the future.

The mechanisms and therapeutic targets of ferroptosis in cancer

INTRODUCTION

Ferroptosis, a form of programmed cell death, is mediated primarily by lipid peroxidation via a unique iron-dependent process. The mechanisms of ferroptosis involve the metabolisms of amino acids, irons, and lipids, and the regulation of antioxidant systems. Evidence supports the roles of ferroptosis in cancer, while metabolic reprogramming (a hallmark of cancer) renders tumor cells highly vulnerable to ferroptosis and thus provides a rationale for ferroptosis-targeted therapy for cancer.

AREA COVERED

This article examines the current understanding of the mechanisms and related signaling pathways involving ferroptosis; it focuses on novel targets in cancer and its treatment and drug resistance. The development of ferroptosis-targeted therapy, especially in combination with conventional or non-conventional therapies, are considered with dilemmas and key questions in this research area.

EXPERT OPINION

An increasing number of potential targets and ferroptosis inducers (FINs) have been identified to treat cancer. However, no specific FIN has entered clinical trials thus far, likely due to poor efficacy and high toxicity in vivo. Thus, new FINs with high selectivity and bioavailability are required to target tumor cells more specifically and potently. Particularly, the combination of FINs with chemotherapy, radiotherapy, targeted therapy, and immunotherapy warrants clinical investigation in the future.

The molecular mechanisms of ferroptosis and its role in cardiovascular disease

Ferroptosis is a programmed iron-dependent cell death characterized by accumulation of lipid peroxides (LOOH) and redox disequilibrium. Ferroptosis shows unique characteristics in biology, chemistry, and gene levels, compared to other cell death forms. The metabolic disorder of intracellular LOOH catalyzed by iron causes the inactivity of GPX4, disrupts the redox balance, and triggers cell death. Metabolism of amino acid, iron, and lipid, including associated pathways, is considered as a specific hallmark of ferroptosis. Epidemiological studies and animal experiments have shown that ferroptosis plays an important character in the pathophysiology of cardiovascular disease such as atherosclerosis, myocardial infarction (MI), ischemia/reperfusion (I/R), heart failure (HF), cardiac hypertrophy, cardiomyopathy, and abdominal aortic aneurysm (AAA). This review systematically summarized the latest research progress on the mechanisms of ferroptosis. Then we report the contribution of ferroptosis in cardiovascular diseases. Finally, we discuss and analyze the therapeutic approaches targeting for ferroptosis associated with cardiovascular diseases.

The Role of Ferroptosis in Cardiovascular Disease and Its Therapeutic Significance

Cardiovascular diseases (CVDs) are the leading cause of deaths worldwide with regulated cell death playing an important role in cardiac pathophysiology. However, the classical mode of cell death cannot fully explain the occurrence and development of heart disease. In recent years, much research has been performed on ferroptosis, a new type of cell death that causes cell damage and contributes to the development of atherosclerosis, myocardial infarction, heart failure, and other diseases. In this review, we discuss the role of different organelles in ferroptosis and also focus on the relationship between autophagy and ferroptosis. Additionally, we describe the specific mechanism by which ferroptosis contributes to the development of CVD. Finally, we summarize the current research on ferroptosis-related pathway inhibitors and the applications of clinically beneficial cardiovascular drugs.

Ferroptosis in cancer therapeutics: a materials chemistry perspective

Ferroptosis, distinct from apoptosis, is a regulated form of cell death caused by lipid peroxidation that has attracted extensive research interest since it was first defined in 2012. Over the past five years, an increasing number of studies have revealed the close relationship between ferroptosis and materials chemistry, in particular nanobiotechnology, and have concluded that nanotechnology-triggered ferroptosis is an efficient and promising antitumor strategy that provides an alternative therapeutic approach, especially for apoptosis-resistant tumors. In this review, we summarize recent advances in ferroptosis-induced tumor therapy at the intersection of materials chemistry, redox biology, and tumor biology. The biological features and molecular mechanisms of ferroptosis are first outlined, followed by a summary of the feasible strategies to induce ferroptosis using nanomaterials and the applications of ferroptosis in combined tumor therapy. Finally, the existing challenges and future development directions in this emerging field are discussed, with the aim of promoting the progress of ferroptosis-based oncotherapy in materials science and nanoscience and enriching the antitumor arsenal.

The role of ferroptosis in lung cancer

Lung cancer is one of the most common cancers in the world. Although medical treatment has made impressive progress in recent years, it is still one of the leading causes of cancer-related deaths in men and women. Ferroptosis is a type of non-apoptotic cell death modality, usually characterized by iron-dependent lipid peroxidation, rather than caspase-induced protein cleavage. Excessive or lack of ferroptosis is associated with a variety of diseases, including cancer and ischaemia-reperfusion injury. Recent preclinical evidence suggests that targeting ferroptotic pathway is a potential strategy for the treatment of lung cancer. In this review, we summarize the core mechanism and regulatory network of ferroptosis in lung cancer cells, and highlight ferroptosis induction-related tumor therapies. The reviewed information may provide new insights for targeted lung cancer therapy.

Ferroptosis: Cancer Stem Cells Rely on Iron until "to Die for" It

Cancer stem cells (CSCs) are a distinct subpopulation of tumor cells with stem cell-like features. Able to initiate and sustain tumor growth and mostly resistant to anti-cancer therapies, they are thought responsible for tumor recurrence and metastasis. Recent accumulated evidence supports that iron metabolism with the recent discovery of ferroptosis constitutes a promising new lead in the field of anti-CSC therapeutic strategies. Indeed, iron uptake, efflux, storage and regulation pathways are all over-engaged in the tumor microenvironment suggesting that the reprogramming of iron metabolism is a crucial occurrence in tumor cell survival. In particular, recent studies have highlighted the importance of iron metabolism in the maintenance of CSCs. Furthermore, the high concentration of iron found in CSCs, as compared to non-CSCs, underlines their iron addiction. In line with this, if iron is an essential macronutrient that is nevertheless highly reactive, it represents their Achilles’ heel by inducing ferroptosis cell death and therefore providing opportunities to target CSCs. In this review, we first summarize our current understanding of iron metabolism and its regulation in CSCs. Then, we provide an overview of the current knowledge of ferroptosis and discuss the role of autophagy in the (regulation of) ferroptotic pathways. Finally, we discuss the potential therapeutic strategies that could be used for inducing ferroptosis in CSCs to treat cancer.

Regulation and function of autophagy in pancreatic cancer

Oncogenic KRAS mutation-driven pancreatic ductal adenocarcinoma is currently the fourth-leading cause of cancer-related deaths in the United States. Macroautophagy (hereafter "autophagy") is one of the lysosome-dependent degradation systems that can remove abnormal proteins, damaged organelles, or invading pathogens by activating dynamic membrane structures (e.g., phagophores, autophagosomes, and autolysosomes). Impaired autophagy (including excessive activation and defects) is a pathological feature of human diseases, including pancreatic cancer. However, dysfunctional autophagy has many types and plays a complex role in pancreatic tumor biology, depending on various factors, such as tumor stage, microenvironment, immunometabolic state, and death signals. As a modulator connecting various cellular events, pharmacological targeting of nonselective autophagy may lead to both good and bad therapeutic effects. In contrast, targeting selective autophagy could reduce potential side effects of the drugs used. In this review, we describe the advances and challenges of autophagy in the development and therapy of pancreatic cancer.Abbreviations: AMPK: AMP-activated protein kinase; CQ: chloroquine; csc: cancer stem cells; DAMP: danger/damage-associated molecular pattern; EMT: epithelial-mesenchymal transition; lncRNA: long noncoding RNA; MIR: microRNA; PanIN: pancreatic intraepithelial neoplasia; PDAC: pancreatic ductal adenocarcinoma; PtdIns3K: phosphatidylinositol 3-kinase; SNARE: soluble NSF attachment protein receptor; UPS: ubiquitin-proteasome system.

Cell death in pancreatic cancer: from pathogenesis to therapy

Pancreatic cancer is a devastating gastrointestinal cancer characterized by late diagnosis, limited treatment success and dismal prognosis. Exocrine tumours account for 95% of pancreatic cancers and the most common pathological type is pancreatic ductal adenocarcinoma (PDAC). The occurrence and progression of PDAC involve multiple factors, including internal genetic alterations and external inflammatory stimuli. The biology and therapeutic response of PDAC are further shaped by various forms of regulated cell death, such as apoptosis, necroptosis, ferroptosis, pyroptosis and alkaliptosis. Cell death induced by local or systemic treatments suppresses tumour proliferation, invasion and metastasis. However, unrestricted cell death or tissue damage might result in an inflammation-related immunosuppressive microenvironment, which is conducive to tumour progression or recurrence. The precise extent to which cell death affects PDAC is not yet well described. A growing body of preclinical and clinical studies document significant correlations between mutations (for example, in KRAS and TP53), stress responses (such as hypoxia and autophagy), metabolic reprogramming and chemotherapeutic responses. Here, we describe the molecular machinery of cell death, discuss the complexity and multifaceted nature of lethal signalling in PDAC cells, and highlight the challenges and opportunities for activating cell death pathways through precision oncology treatments.

Fin56-induced ferroptosis is supported by autophagy-mediated GPX4 degradation and functions synergistically with mTOR inhibition to kill bladder cancer cells

Ferroptosis is a form of regulated cell death that emerges to be relevant for therapy-resistant and dedifferentiating cancers. Although several lines of evidence suggest that ferroptosis is a type of autophagy-dependent cell death, the underlying molecular mechanisms remain unclear. Fin56, a type 3 ferroptosis inducer, triggers ferroptosis by promoting glutathione peroxidase 4 (GPX4) protein degradation via a not fully understood pathway. Here, we determined that Fin56 induces ferroptosis and autophagy in bladder cancer cells and that Fin56-triggered ferroptosis mechanistically depends on the autophagic machinery. Furthermore, we found that autophagy inhibition at different stages attenuates Fin56-induced oxidative stress and GPX4 degradation. Moreover, we investigated the effects of Fin56 in combination with Torin 2, a potent mTOR inhibitor used to activate autophagy, on cell viability. We found that Fin56 synergizes with Torin 2 in cytotoxicity against bladder cancer cells. Collectively, our findings not only support the concept that ferroptosis is a type of autophagy-dependent cell death but imply that the combined application of ferroptosis inducers and mTOR inhibitors is a promising approach to improve therapeutic options in the treatment of bladder cancer.

N6-methyladenosine modification regulates ferroptosis through autophagy signaling pathway in hepatic stellate cells

Ferroptosis is a recently identified non-apoptotic form of cell death characterized by iron-dependent lipid peroxidation. However, the underlying exact mechanisms remain poorly understood. Here, we report that the total levels of N⁶-methyladenosine (m⁶A) modification are evidently increased upon exposure to ferroptosis-inducing compounds due to the upregulation of methylase METTL4 and the downregulation of demethylase FTO. Interestingly, RNA-seq shows that m⁶A modification appears to trigger autophagy activation by stabilizing BECN1 mRNA, which may be the potential mechanism for m⁶A modification-enhanced HSC ferroptosis. Importantly, YTHDF1 is identified as a key m⁶A reader protein for BECN1 mRNA stability, and knockdown of YTHDF1 could prevent BECN1 plasmid-induced HSC ferroptosis. Noteworthy, YTHDF1 promotes BECN1 mRNA stability and autophagy activation via recognizing the m⁶A binding site within BECN1 coding regions. In mice, erastin treatment alleviates liver fibrosis by inducing HSC ferroptosis. HSC-specific inhibition of m⁶A modification could impair erastin-induced HSC ferroptosis in murine liver fibrosis. Moreover, we retrospectively analyzed the effect of sorafenib on HSC ferroptosis and m⁶A modification in advanced fibrotic patients with hepatocellular carcinoma (HCC) receiving sorafenib monotherapy. Attractively, the m⁶A modification upregulation, autophagy activation, and ferroptosis induction occur in human HSCs. Overall, these findings reveal novel signaling pathways and molecular mechanisms of ferroptosis, and also identify m⁶A modification-dependent ferroptosis as a potential target for the treatment of liver fibrosis.

Role of chaperone-mediated autophagy in the pathophysiology including pulmonary disorders

Autophagy is a highly conserved mechanism of delivering cytoplasmic components for lysosomal degradation. Among the three major autophagic pathways, chaperone-mediated autophagy (CMA) is primarily characterized by its selective nature of protein degradation, which is mediated by heat shock cognate 71 kDa protein (HSC70: also known as HSPA8) recognition of the KFERQ peptide motif in target proteins. Lysosome-associated membrane protein type 2A (LAMP2A) is responsible for substrate binding and internalization to lysosomes, and thus, the lysosomal expression level of LAMP2A is a rate-limiting factor for CMA. Recent advances have uncovered not only physiological but also pathological role of CMA in multiple organs, including neurodegenerative disorders, kidney diseases, liver diseases, heart diseases, and cancers through the accumulation of unwanted proteins or increased degradation of target proteins with concomitant metabolic alterations resulting from CMA malfunction. With respect to pulmonary disorders, the involvement of CMA has been demonstrated in lung cancer and chronic obstructive pulmonary disease (COPD) pathogenesis through regulating apoptosis. Further understanding of CMA machinery may shed light on the molecular mechanisms of refractory disorders and lead to novel treatment modalities through CMA modulation.

Organelle-specific regulation of ferroptosis

Ferroptosis, a cell death modality characterized by iron-dependent lipid peroxidation, is involved in the development of multiple pathological conditions, including ischemic tissue damage, infection, neurodegeneration, and cancer. The cellular machinery responsible for the execution of ferroptosis integrates multiple pro-survival or pro-death signals from subcellular organelles and then 'decides' whether to engage the lethal process or not. Here, we outline the evidence implicating different organelles (including mitochondria, lysosomes, endoplasmic reticulum, lipid droplets, peroxisomes, Golgi apparatus, and nucleus) in the ignition or avoidance of ferroptosis, while emphasizing their potential relevance for human disease and their targetability for pharmacological interventions.

Trypsin-Mediated Sensitization to Ferroptosis Increases the Severity of Pancreatitis in Mice

BACKGROUND & AIMS

Pancreatitis is characterized by acinar cell death and persistent inflammation. Ferroptosis is a type of lipid peroxidation-dependent necrosis, which is negatively regulated by glutathione peroxidase 4. We studied how trypsin, a serine protease secreted by pancreatic acinar cells, affects the contribution of ferroptosis to triggering pancreatitis.

METHODS

In vitro, the mouse pancreatic acinar cell line 266-6 and mouse primary pancreatic acinar cells were used to investigate the effect of exogenous trypsin on ferroptosis sensitivity. Short hairpin RNAs were designed to silence gene expression, whereas a library of 1080 approved drugs was used to identify new ferroptosis inhibitors in 266-6 cells. In vivo, a Cre/LoxP system was used to generate mice with a pancreas-specific knockout of Gpx4 (Pdx1-Cre;Gpx4^flox/flox mice). Acute or chronic pancreatitis was induced in these mice (Gpx4^flox/flox mice served as controls) by cerulein injections or a Lieber-DeCarli alcoholic liquid diet. Pancreatic tissues, acinar cells, and serum were collected and analyzed by histology, immunoblot, quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, or immunohistochemical analyses.

RESULTS

Supraphysiological doses of trypsin (500 or 1000 ng/mL) alone did not trigger significant cell death in 266-6 cells and mouse primary pancreatic acinar cells, but did increase the sensitivity of these cells to ferroptosis upon treatment with cerulein, L-arginine, alcohol, erastin, or RSL3. Proteasome 26S subunit, non-adenosine triphosphatase 4-dependent lipid peroxidation caused ferroptosis in pancreatic acinar cells by promoting the proteasomal degradation of glutathione peroxidase 4. The drug screening campaign identified the antipsychotic drug olanzapine as an antioxidant inhibiting ferroptosis in pancreatic acinar cells. Mice lacking pancreatic Gpx4 developed more severe pancreatitis after cerulein infection or ethanol feeding than control mice. Conversely, olanzapine administration protected against pancreatic ferroptotic damage and experimental pancreatitis in Gpx4-deficient mice.

CONCLUSIONS

Trypsin-mediated sensitization to ferroptotic damage increases the severity of pancreatitis in mice, and this process can be reversed by olanzapine.

A new thiol-independent mechanism of epithelial host defense against Pseudomonas aeruginosa: iNOS/NO• sabotage of theft-ferroptosis

Ferroptosis is a redox-driven type of regulated cell death program arising from maladaptation of three metabolic pathways: glutathione homeostasis, iron handling and lipid peroxidation. Though GSH/Gpx4 is the predominant system detoxifying phospholipid hydroperoxides (PLOOH) in mammalian cells, recently Gpx4-independent regulators of ferroptosis like ferroptosis suppressor protein 1 (FSP1) in resistant cancer lines and iNOS/NO^• in M1 macrophages have been discovered. We previously reported that Pseudomonas aeruginosa (PA) utilizes its 15- lipoxygenase (pLoxA) to trigger ferroptotic death in epithelial cells by oxidizing the host arachidonoyl-phosphatidylethanolamine (ETE-PE) into pro-ferroptotic 15-hydroperoxy- arachidonyl-PE (15-HpETE-PE). Here we demonstrate that PA degrades the host GPx4 defense by activating the lysosomal chaperone-mediated autophagy (CMA). In response, the host stimulates the iNOS/NO^•-driven anti-ferroptotic mechanism to stymie lipid peroxidation and protect GPx4/GSH-deficient cells. By using a co-culture model system, we showed that macrophage-produced NO^• can distantly prevent PA stimulated ferroptosis in epithelial cells as an inter-cellular mechanism. We further established that suppression of ferroptosis in epithelial cells by NO^• is enabled through the suppression of phospholipid peroxidation, particularly the production of pro-ferroptotic 15-HpETE-PE signals. Pharmacological targeting of iNOS (NO^• generation) attenuated its anti-ferroptotic function. In conclusion, our findings define a new inter-cellular ferroptosis suppression mechanism which may represent a new strategy of the host against P. aeruginosa induced theft-ferroptosis.

Dysregulated cholesterol homeostasis results in resistance to ferroptosis increasing tumorigenicity and metastasis in cancer

Hypercholesterolemia and dyslipidemia are associated with an increased risk for many cancer types and with poor outcomes in patients with established disease. Whereas the mechanisms by which this occurs are multifactorial we determine that chronic exposure of cells to 27-hydroxycholesterol (27HC), an abundant circulating cholesterol metabolite, selects for cells that exhibit increased cellular uptake and/or lipid biosynthesis. These cells exhibit substantially increased tumorigenic and metastatic capacity. Notably, the metabolic stress imposed upon cells by the accumulated lipids requires sustained expression of GPX4, a negative regulator of ferroptotic cell death. We show that resistance to ferroptosis is a feature of metastatic cells and further demonstrate that GPX4 knockdown attenuates the enhanced tumorigenic and metastatic activity of 27HC resistant cells. These findings highlight the general importance of ferroptosis in tumor growth and metastasis and suggest that dyslipidemia/hypercholesterolemia impacts cancer pathogenesis by selecting for cells that are resistant to ferroptotic cell death.

A single genetic locus controls both expression of DPEP1/CHMP1A and kidney disease development via ferroptosis

Genome-wide association studies (GWAS) have identified loci for kidney disease, but the causal variants, genes, and pathways remain unknown. Here we identify two kidney disease genes Dipeptidase 1 (DPEP1) and Charged Multivesicular Body Protein 1 A (CHMP1A) via the triangulation of kidney function GWAS, human kidney expression, and methylation quantitative trait loci. Using single-cell chromatin accessibility and genome editing, we fine map the region that controls the expression of both genes. Mouse genetic models demonstrate the causal roles of both genes in kidney disease. Cellular studies indicate that both Dpep1 and Chmp1a are important regulators of a single pathway, ferroptosis and lead to kidney disease development via altering cellular iron trafficking.

Cell Ferroptosis: New Mechanism and New Hope for Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a leading cause of inherited retinal degeneration, with more than 60 gene mutations. Despite the genetic heterogenicity, photoreceptor cell damage remains the hallmark of RP pathology. As a result, RP patients usually suffer from reduced night vision, loss of peripheral vision, decreased visual acuity, and impaired color perception. Although photoreceptor cell death is the primary outcome of RP, the underlying mechanisms are not completely elucidated. Ferroptosis is a novel programmed cell death, with characteristic iron overload and lipid peroxidation. Recent studies, using in vitro and in vivo RP models, discovered the involvement of ferroptosis-associated cell death, suggesting a possible new mechanism for RP pathogenesis. In this review, we discuss the association between ferroptosis and photoreceptor cell damage, and its implication in the pathogenesis of RP. We propose that ferroptotic cell death not only opens up a new research area in RP, but may also serve as a novel therapeutic target for RP.

A Shortage of FTH Induces ROS and Sensitizes RAS-Proficient Neuroblastoma N2A Cells to Ferroptosis

Ferroptosis, an iron-dependent form of programmed cell death, has excellent potential as an anti-cancer therapeutic strategy in different types of tumors, especially in RAS-mutated ones. However, the function of ferroptosis for inhibiting neuroblastoma, a common child malignant tumor with minimal treatment, is unclear. This study investigated the anti-cancer function of ferroptosis inducer Erastin or RSL3 in neuroblastoma N2A cells. Our results show that Erastin or RSL3 induces ROS level and cell death and, therefore, reduces the viability of RAS-proficient N2A cells. Importantly, inhibitors to ferroptosis, but not apoptosis, ameliorate the high ROS level and viability defect in Erastin- or RSL3-treated cells. In addition, our data also show that N2A cells are much more sensitive to ferroptosis inducers than primary mouse cortical neural stem cells (NSCs) or neurons. Moreover, a higher level of ROS and PARylation is evidenced in N2A, but not NSCs. Mechanically, ferritin heavy chain 1 (Fth), the ferroxidase function to oxidate redox-active Fe²⁺ to redox-inactive Fe³⁺, is likely responsible for the hypersensitivity of N2A to ferroptosis induction since its expression is lower in N2A compared to NSCs; ectopic expression of Fth reduces ROS levels and cell death, and induces expression of GPX4 and cell viability in N2A cells. Most importantly, neuroblastoma cell lines express a significantly low level of Fth than almost all other types of cancer cell lines. All these data suggest that Erastin or RSL3 induce ferroptosis cell death in neuroblastoma N2A cells, but not normal neural cells, regardless of RAS mutations, due to inadequate FTH. This study, therefore, provides new evidence that ferroptosis could be a promising therapeutic target for neuroblastoma.

A robust ferroptosis-related gene signature predicts overall survival in clear cell renal cell carcinoma

Aims: To investigate the prognostic values and potential mechanisms of ferroptosis-related genes in clear cell renal cell carcinoma. Methods: Univariate Cox, least absolute shrinkage and selection operator regression and multivariate Cox regression analyses were employed to identify prognosis-related hub ferroptosis-related genes and establish a prognostic model. Results: The authors established a novel clinical predictive model based on seven hub ferroptosis-related genes in The Cancer Genome Atlas training cohort (n = 374) that was verified in the testing cohort (n = 156) and the entire group (n = 530). Functional analysis indicated that several carcinogenic pathways were enriched. Tumor-infiltrating cells and immunosuppressive molecules were significantly different between the two risk groups. Conclusion: Collectively, the authors successfully constructed a novel ferroptosis-related risk signature that was significantly associated with the prognosis of clear cell renal cell carcinoma.

The lysosome as a master regulator of iron metabolism

Intracellular iron fulfills crucial cellular processes, including DNA synthesis and mitochondrial metabolism, but also mediates ferroptosis, a regulated form of cell death driven by lipid-based reactive oxygen species (ROS). Beyond their established role in degradation and recycling, lysosomes occupy a central position in iron homeostasis and integrate metabolic and cell death signals emanating from different subcellular sites. We discuss the central role of the lysosome in preserving iron homeostasis and provide an integrated outlook of the regulatory circuits coupling the lysosomal system to the control of iron trafficking, interorganellar crosstalk, and ferroptosis induction. We also discuss novel studies unraveling how deregulated lysosomal iron-handling functions contribute to cancer, neurodegeneration, and viral infection, and can be harnessed for therapeutic interventions.

Ferroptosis-Inhibitory Effect and Possible Mechanisms of Ellagitannin Geraniin

The search for safe and effective ferroptosis-inhibitors has become an important topic. Geraniin, an ellagitannin bearing hexahydroxydiphenoyl (HHDP) and dehydrohexahydroxydiphenoyl (DHHDP) groups, was observed to inhibit erastin-induced ferroptosis in bone marrow-derived mesenchymal stem cells (bmMSCs). To determine the mechanism, geraniin was further analyzed using UV-vis spectra and several colorimetric assays, where its IC50 values were always much lower than that of the Trolox positive control. When interacted with several free radicals, geraniin gave no radical adduct formation (RAF) peak in the ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry. In conclusion, geraniin exhibits ferroptosis-inhibitory potential towards erastin-treated bmMSCs; such potential may mainly stem from its strong lipid peroxidation (LPO)-inhibition, Fe2+ -chelating, and antioxidant actions. Geraniin gives neither dimer nor radical adduct, owing to the bulky HHDP (or DHHDP) group; thus, it is considered as a safe and effective ferroptosis-inhibitor.

Nitric oxide protects against ferroptosis by aborting the lipid peroxidation chain reaction

Ferroptosis is a type of iron-dependent necrotic cell death, which is typically triggered by the depletion of intracellular glutathione (GSH), which is associated with increased lipid peroxidation. Nitric oxide (NO) is a highly reactive gaseous radical mediator with anti-oxidation properties that terminates lipid peroxidation reactions. In the current study, we report the anti-ferroptotic action of NOC18, an NO donor that spontaneously releases NO, in cells under various ferroptotic conditions in vitro. Our results indicate that, when mouse hepatoma Hepa 1-6 cells are incubated with NOC18, cell death induced by various ferroptotic stimuli such as cysteine (Cys) starvation, the inhibition of glutathione peroxidase 4 (GPX4) and treatment with tertiary-butyl hydroperoxide (TBHP) is significantly reduced. Treatment with NOC18 failed to improve the decrease in the levels of Cys or GSH and the accumulation of ferrous iron upon ferroptotic stimuli. The fluorescent intensity of C11-BODIPY^581/591, a probe that is used to detect lipid peroxidation products, was increased somewhat by treatment with NOC18 under conditions of Cys starvation, and the accumulation of lipid peroxidation end-products, as evidenced by the levels of 4-hydroxynonenal, were effectively suppressed. The pre-incubation of TBHP with NOC7, a short-lived NO donor completely eliminated its ability to trigger ferroptosis. These collective results indicate that NO exerts a cytoprotective action against various ferroptotic stimuli by aborting the lipid peroxidation chain reaction.

Ferroptosis-Inhibitory Difference between Chebulagic Acid and Chebulinic Acid Indicates Beneficial Role of HHDP

The search for a safe and effective inhibitor of ferroptosis, a recently described cell death pathway, has attracted increasing interest from scientists. Two hydrolyzable tannins, chebulagic acid and chebulinic acid, were selected for the study. Their optimized conformations were calculated using computational chemistry at the B3LYP-D3(BJ)/6-31G and B3LYP-D3(BJ)/6-311 + G(d,p) levels. The results suggested that (1) chebulagic acid presented a chair conformation, while chebulinic acid presented a skew-boat conformation; (2) the formation of chebulagic acid requires 762.1729 kcal/mol more molecular energy than chebulinic acid; and (3) the 3,6-HHDP (hexahydroxydiphenoyl) moiety was shown to be in an (R)- absolute stereoconfiguration. Subsequently, the ferroptosis inhibition of both tannins was determined using a erastin-treated bone marrow-derived mesenchymal stem cells (bmMSCs) model and compared to that of ferrostatin-1 (Fer-1). The relative inhibitory levels decreased in the following order: Fer-1 > chebulagic acid > chebulinic acid, as also revealed by the in vitro antioxidant assays. The UHPLC-ESI-Q-TOF-MS analysis suggested that, when treated with 16-(2-(14-carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy free radicals, Fer-1 generated dimeric products, whereas the two acids did not. In conclusion, two hydrolyzable tannins, chebulagic acid and chebulinic acid, can act as natural ferroptosis inhibitors. Their ferroptosis inhibition is mediated by regular antioxidant pathways (ROS scavenging and iron chelation), rather than the redox-based catalytic recycling pathway exhibited by Fer-1. Through antioxidant pathways, the HHDP moiety in chebulagic acid enables ferroptosis-inhibitory action of hydrolyzable tannins.

Ferroptosis and Its Potential Role in Metabolic Diseases: A Curse or Revitalization?

Ferroptosis is classified as an iron-dependent form of regulated cell death (RCD) attributed to the accumulation of lipid hydroperoxides and redox imbalance. In recent years, accumulating researches have suggested that ferroptosis may play a vital role in the development of diverse metabolic diseases, for example, diabetes and its complications (e.g., diabetic nephropathy, diabetic cardiomyopathy, diabetic myocardial ischemia/reperfusion injury and atherosclerosis [AS]), metabolic bone disease and adrenal injury. However, the specific physiopathological mechanism and precise therapeutic effect is still not clear. In this review, we summarized recent advances about the development of ferroptosis, focused on its potential character as the therapeutic target in metabolic diseases, and put forward our insights on this topic, largely to offer some help to forecast further directions.

Ferritinophagy and ferroptosis in cardiovascular disease: Mechanisms and potential applications

Ferroptosis is a type of regulated cell death driven by iron dependent accumulation of cellular reactive oxygen species (ROS) when glutathione (GSH)-dependent lipid peroxidation repair systems are compromised. Nuclear receptor co-activator 4 (NCOA4)-mediated selective autophagy of ferritin, termed ferritinophagy, involves the regulation of ferroptosis. Emerging evidence has revealed that ferritinophagy and ferroptosis exert a significant role in the occurrence and development of cardiovascular disease. In the present review, we aimed to present a brief overview of ferritinophagy and ferroptosis focusing on the underlying mechanism and regulations involved. We summarize and discuss relevant research progress on the role of ferritinophagy and ferroptosis in cardiovascular diseases accompanied with potential applications of ferritinophagy and ferroptosis modulators in the treatment of ferroptosis-associated cardiovascular diseases.

Insight into Crosstalk between Ferroptosis and Necroptosis: Novel Therapeutics in Ischemic Stroke

Ferroptosis is a nonapoptotic form of cell death characterized by iron-dependent accumulation of lipid hydroperoxides to lethal levels. Necroptosis, an alternative form of programmed necrosis, is regulated by receptor-interacting protein (RIP) 1 activation and by RIP3 and mixed-lineage kinase domain-like (MLKL) phosphorylation. Ferroptosis and necroptosis both play important roles in the pathological progress in ischemic stroke, which is a complex brain disease regulated by several cell death pathways. In the past few years, increasing evidence has suggested that the crosstalk occurs between necroptosis and ferroptosis in ischemic stroke. However, the potential links between ferroptosis and necroptosis in ischemic stroke have not been elucidated yet. Hence, in this review, we overview and analyze the mechanism underlying the crosstalk between necroptosis and ferroptosis in ischemic stroke. And we find that iron overload, one mechanism of ferroptosis, leads to mitochondrial permeability transition pore (MPTP) opening, which aggravates RIP1 phosphorylation and contributes to necroptosis. In addition, heat shock protein 90 (HSP90) induces necroptosis and ferroptosis by promoting RIP1 phosphorylation and suppressing glutathione peroxidase 4 (GPX4) activation. In this work, we try to deliver a new perspective in the exploration of novel therapeutic targets for the treatment of ischemic stroke.

Overexpression of ferroptosis defense enzyme Gpx4 retards motor neuron disease of SOD1G93A mice

Degeneration and death of motor neurons in Amyotrophic Lateral Sclerosis (ALS) are associated with increased lipid peroxidation. Lipid peroxidation is the driver of ferroptosis, an iron-dependent oxidative mode of cell death. However, the importance of ferroptosis in motor neuron degeneration of ALS remains unclear. Glutathione peroxidase 4 (Gpx4) is a key enzyme in suppressing ferroptosis by reducing phospholipid hydroperoxides in membranes. To assess the effect of increased protection against ferroptosis on motor neuron disease, we generated SOD1^G93AGPX4 double transgenic mice by cross-breeding GPX4 transgenic mice with SOD1^G93A mice, a widely used ALS mouse model. Compared with control SOD1^G93A mice, both male and female SOD1^G93AGPX4 mice had extended lifespans. SOD1^G93AGPX4 mice also showed delayed disease onset and increased motor function, which were correlated with ameliorated spinal motor neuron degeneration and reduced lipid peroxidation. Moreover, cell toxicity induced by SOD1^G93A was ameliorated by Gpx4 overexpression and by chemical inhibitors of ferroptosis in vitro. We further found that the anti-ferroptosis defense system in spinal cord tissues of symptomatic SOD1^G93A mice and sporadic ALS patients might be compromised due to deficiency of Gpx4. Thus, our results suggest that ferroptosis plays a key role in motor neuron degeneration of ALS.

Autophagy-Dependent Ferroptosis as a Therapeutic Target in Cancer

Ferroptosis is an iron-dependent form of cell death associated with the accumulation of labile iron and cytotoxic lipid peroxides. Increasing evidence reveals that ferroptosis is not a self-standing phenomenon and has close connections with other cellular events. Remarkably, recent insights show that ferroptosis is dependent on autophagy, which is a lysosomal degradation pathway responsible for the recycling of damaged cellular components under survival stress. Autophagy is capable of contributing to ferroptosis through degradation of the ferritin, an iron-storage protein, accompanied with the accumulation of iron levels and lipid ROS. The interplay between autophagy and ferroptosis also reveals emerging opportunities for novel tumor therapies, which has inspired the development of many treatment strategies capable of inducing ferroptosis in tumor cells via autophagic pathways based on molecular and nanoparticulate agents. In this review, we summarize the specific molecular and regulatory networks of autophagy-dependent ferroptosis and highlight their pathophysiological impact on various aspects of tumor cells. A perspective was also provided regarding the preliminary therapeutic exploitation of ferroptosis/autophagy crosstalk for tumor treatment.

The STING1 network regulates autophagy and cell death

Cell death and immune response are at the core of life. In past decades, the endoplasmic reticulum (ER) protein STING1 (also known as STING or TMEM173) was found to play a fundamental role in the production of type I interferons (IFNs) and pro-inflammatory cytokines in response to DNA derived from invading microbial pathogens or damaged hosts by activating multiple transcription factors. In addition to this well-known function in infection, inflammation, and immunity, emerging evidence suggests that the STING1-dependent signaling network is implicated in health and disease by regulating autophagic degradation or various cell death modalities (e.g., apoptosis, necroptosis, pyroptosis, ferroptosis, mitotic cell death, and immunogenic cell death [ICD]). Here, we outline the latest advances in our understanding of the regulating mechanisms and signaling pathways of STING1 in autophagy and cell death, which may shed light on new targets for therapeutic interventions.

Multimodal polymer encapsulated CdSe/Fe3O4 nanoplatform with improved biocompatibility for two-photon and temperature stimulated bioapplications

Multimodal polymer encapsulated CdSe/Fe₃O₄ nanoplatforms with dual optical and magnetic properties have been fabricated. We demonstrate that CdSe/Fe₃O₄ nanocapsules (NCs) upon excitation with UV radiation or NIR fs-laser excitation exhibit intense one- or two-photon emission at 535 nm, whereas the combination of an alternating magnetic field and 808 nm IR laser excitation results in heat generation. Since anticancer therapies require relatively high doses of Fe₃O₄ nanoparticles (NPs) to induce biologically relevant temperature jumps, the therapeutic effects of 0.1 and 1 mg/mL Fe₃O₄ NCs and CdSe/Fe₃O₄ NCs were investigated using breast cancer cell lines, ER-positive MCF-7, and triple-negative MDA-MB-231 cells. Improved biocompatibility of CdSe/Fe₃O₄ NCs compared to Fe₃O₄ NCs was revealed at higher NCs concentration suggesting safe potential medical applications of CdSe/Fe₃O₄ NCs. In contrast, 1 mg/mL Fe₃O₄ NCs were found to be more cytotoxic to MDA-MB-231 than MCF-7 cells through iron-induced oxidative stress, lipid peroxidation, and concomitant ferroptotic cell death. We believe that Fe₃O₄ NCs-mediated cellular response may be heterogeneous that reflects, at least in part, cancer cell genotype, molecular phenotype, and pathological classification.

Targeting ferroptosis in pancreatic cancer: a double-edged sword

Pancreatic ductal adenocarcinoma (PDAC) remains an aggressive malignancy with a 5-year survival rate below 10%. Its unique genetic makeup and tumor microenvironment produce a lack of response to current treatments, including chemotherapy, radiotherapy, and immunotherapy. Recent preclinical studies have revealed that ferroptosis, an iron-dependent form of nonapoptotic cell death driven by unrestricted lipid peroxidation, may be an attractive therapeutic goal in PDAC. Understanding the dual role of ferroptotic cell death in both promoting and suppressing tumor immunity, as well as its integrated regulatory mechanisms and signaling pathways, may lead to more effective treatment designs for clinical trials of PDAC and may minimize or delay the emergence of drug resistance or side effects.

Ferroptosis in infection, inflammation, and immunity

Ferroptosis is a type of regulated necrosis that is triggered by a combination of iron toxicity, lipid peroxidation, and plasma membrane damage. The upstream inducers of ferroptosis can be divided into two categories (biological versus chemical) and activate two major pathways (the extrinsic/transporter versus the intrinsic/enzymatic pathways). Excessive or deficient ferroptotic cell death is implicated in a growing list of physiological and pathophysiological processes, coupled to a dysregulated immune response. This review focuses on new discoveries related to how ferroptotic cells and their spilled contents shape innate and adaptive immunity in health and disease. Understanding the immunological characteristics and activity of ferroptotic death not only illuminates an intersection between cell death and immunity but may also lead to the development of novel treatment approaches for immunopathological diseases.

Mitochondrial DNA stress triggers autophagy-dependent ferroptotic death

Pancreatic cancer tends to be highly resistant to current therapy and remains one of the great challenges in biomedicine with very low 5-year survival rates. Here, we report that zalcitabine, an antiviral drug for human immunodeficiency virus infection, can suppress the growth of primary and immortalized human pancreatic cancer cells through the induction of ferroptosis, an iron-dependent form of regulated cell death. Mechanically, this effect relies on zalcitabine-induced mitochondrial DNA stress, which activates the STING1/TMEM173-mediated DNA sensing pathway, leading to macroautophagy/autophagy-dependent ferroptotic cell death via lipid peroxidation, but not a type I interferon response. Consequently, the genetic and pharmacological inactivation of the autophagy-dependent ferroptosis pathway diminishes the anticancer effects of zalcitabine in cell culture and animal models. Together, these findings not only provide a new approach for pancreatic cancer therapy but also increase our understanding of the interplay between autophagy and DNA damage response in shaping cell death.Abbreviations: ALOX: arachidonate lipoxygenase; ARNTL/BMAL1: aryl hydrocarbon receptor nuclear translocator-like; ATM: ATM serine/threonine kinase; ATG: autophagy-related; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; ER: endoplasmic reticulum; FANCD2: FA complementation group D2; GPX4: glutathione peroxidase 4; IFNA1/IFNα: interferon alpha 1; IFNB1/IFNβ: interferon beta 1; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; MDA: malondialdehyde; mtDNA: mitochondrial DNA; NCOA4: nuclear receptor coactivator 4; PDAC: pancreatic ductal adenocarcinoma; POLG: DNA polymerase gamma, catalytic subunit; qRT-PCR: quantitative polymerase chain reaction; RCD: regulated cell death; ROS: reactive oxygen species; SLC7A11: solute carrier family 7 member 11; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; TFAM: transcription factor A, mitochondrial.

Cellular degradation systems in ferroptosis

In eukaryotic cells, macromolecular homeostasis requires selective degradation of damaged units by the ubiquitin-proteasome system (UPS) and autophagy. Thus, dysfunctional degradation systems contribute to multiple pathological processes. Ferroptosis is a type of iron-dependent oxidative cell death driven by lipid peroxidation. Various antioxidant systems, especially the system xc--glutathione-GPX4 axis, play a significant role in preventing lipid peroxidation-mediated ferroptosis. The endosomal sorting complex required for transport-III (ESCRT-III)-dependent membrane fission machinery counteracts ferroptosis by repairing membrane damage. Moreover, cellular degradation systems play a dual role in regulating the ferroptotic response, depending on the cargo they degrade. The key ferroptosis repressors, such as SLC7A11 and GPX4, are degraded by the UPS. In contrast, the overactivation of selective autophagy, including ferritinophagy, lipophagy, clockophagy and chaperone-mediated autophagy, promotes ferroptotic death by degrading ferritin, lipid droplets, circadian proteins, and GPX4, respectively. Autophagy modulators (e.g., BECN1, STING1/TMEM173, CTSB, HMGB1, PEBP1, MTOR, AMPK, and DUSP1) also determine the ferroptotic response in a context-dependent manner. In this review, we provide an updated overview of the signals and mechanisms of the degradation system regulating ferroptosis, opening new horizons for disease treatment strategies.

Lipid peroxidation and the subsequent cell death transmitting from ferroptotic cells to neighboring cells

Ferroptosis regulated cell death due to the iron-dependent accumulation of lipid peroxide. Ferroptosis is known to constitute the pathology of ischemic diseases, neurodegenerative diseases, and steatohepatitis and also works as a suppressing mechanism against cancer. However, how ferroptotic cells affect surrounding cells remains elusive. We herein report the transfer phenomenon of lipid peroxidation and cell death from ferroptotic cells to nearby cells that are not exposed to ferroptotic inducers (FINs). While primary mouse embryonic fibroblasts (MEFs) and NIH3T3 cells contained senescence-associated β-galactosidase (SA-β-gal)-positive cells, they were decreased upon induction of ferroptosis with FINs. The SA-β-gal decrease was inhibited by ferroptotic inhibitors and knockdown of Atg7, pointing to the involvement of lipid peroxidation and activated autophagosome formation during ferroptosis. A transfer of cell culture medium of cells treated with FINs, type 1 or 2, caused the reduction in SA-β-gal-positive cells in recipient cells that had not been exposed to FINs. Real-time imaging of Kusabira Orange-marked reporter MEFs cocultured with ferroptotic cells showed the generation of lipid peroxide and deaths of the reporter cells. These results indicate that lipid peroxidation and its aftereffects propagate from ferroptotic cells to surrounding cells, even when the surrounding cells are not exposed to FINs. Ferroptotic cells are not merely dying cells but also work as signal transmitters inducing a chain of further ferroptosis.

Mechanisms of mitochondrial cell death

Mitochondria are double-membrane bound organelles that not only provide energy for intracellular metabolism, but also play a key role in the regulation of cell death. Mitochondrial outer membrane permeabilization (MOMP), allowing the release of intermembrane space proteins like cytochrome c, is considered a point of no return in apoptosis. MOMP is controlled by the proteins of the B-cell lymphoma 2 (BCL-2) family, including pro-and anti-apoptotic members, whose balance determines the decision between cell death and survival. Other factors such as membrane lipid environment, membrane dynamics, and inter-organelle communications are also known to influence this process. MOMP and apoptosis have been acknowledged as immunologically silent. Remarkably, a growing body of evidence indicates that MOMP can engage in various pro-inflammatory signaling functions. In this mini-review, we discuss about our current knowledge on the mechanisms of mitochondrial apoptosis, as well as the involvement of mitochondria in other kinds of programmed cell death pathways.

mTORC1 couples cyst(e)ine availability with GPX4 protein synthesis and ferroptosis regulation

Glutathione peroxidase 4 (GPX4) utilizes glutathione (GSH) to detoxify lipid peroxidation and plays an essential role in inhibiting ferroptosis. As a selenoprotein, GPX4 protein synthesis is highly inefficient and energetically costly. How cells coordinate GPX4 synthesis with nutrient availability remains unclear. In this study, we perform integrated proteomic and functional analyses to reveal that SLC7A11-mediated cystine uptake promotes not only GSH synthesis, but also GPX4 protein synthesis. Mechanistically, we find that cyst(e)ine activates mechanistic/mammalian target of rapamycin complex 1 (mTORC1) and promotes GPX4 protein synthesis at least partly through the Rag-mTORC1-4EBP signaling axis. We show that pharmacologic inhibition of mTORC1 decreases GPX4 protein levels, sensitizes cancer cells to ferroptosis, and synergizes with ferroptosis inducers to suppress patient-derived xenograft tumor growth in vivo. Together, our results reveal a regulatory mechanism to coordinate GPX4 protein synthesis with cyst(e)ine availability and suggest using combinatorial therapy of mTORC1 inhibitors and ferroptosis inducers in cancer treatment.

The Clinical Significance of Iron Overload and Iron Metabolism in Myelodysplastic Syndrome and Acute Myeloid Leukemia

Myelodysplasticsyndrome (MDS) and acute myeloid leukemia (AML) are clonal hematopoietic stem cell diseases leading to an insufficient formation of functional blood cells. Disease-immanent factors as insufficient erythropoiesis and treatment-related factors as recurrent treatment with red blood cell transfusions frequently lead to systemic iron overload in MDS and AML patients. In addition, alterations of function and expression of proteins associated with iron metabolism are increasingly recognized to be pathogenetic factors and potential vulnerabilities of these diseases. Iron is known to be involved in multiple intracellular and extracellular processes. It is essential for cell metabolism as well as for cell proliferation and closely linked to the formation of reactive oxygen species. Therefore, iron can influence the course of clonal myeloid disorders, the leukemic environment and the occurrence as well as the defense of infections. Imbalances of iron homeostasis may induce cell death of normal but also of malignant cells. New potential treatment strategies utilizing the importance of the iron homeostasis include iron chelation, modulation of proteins involved in iron metabolism, induction of leukemic cell death via ferroptosis and exploitation of iron proteins for the delivery of antileukemic drugs. Here, we provide an overview of some of the latest findings about the function, the prognostic impact and potential treatment strategies of iron in patients with MDS and AML.

Cell death in head and neck cancer pathogenesis and treatment

Many cancer therapies aim to trigger apoptosis in cancer cells. Nevertheless, the presence of oncogenic alterations in these cells and distorted composition of tumour microenvironment largely limit the clinical efficacy of this type of therapy. Luckily, scientific consensus describes about 10 different cell death subroutines with different regulatory pathways and cancer cells are probably not able to avoid all of cell death types at once. Therefore, a focused and individualised therapy is needed to address the specific advantages and disadvantages of individual tumours. Although much is known about apoptosis, therapeutic opportunities of other cell death pathways are often neglected. Molecular heterogeneity of head and neck squamous cell carcinomas (HNSCC) causing unpredictability of the clinical response represents a grave challenge for oncologists and seems to be a critical component of treatment response. The large proportion of this clinical heterogeneity probably lies in alterations of cell death pathways. How exactly cells die is very important because the predominant type of cell death can have multiple impacts on the therapeutic response as cell death itself acts as a second messenger. In this review, we discuss the different types of programmed cell death (PCD), their connection with HNSCC pathogenesis and possible therapeutic windows that result from specific sensitivity to some form of PCD in some clinically relevant subgroups of HNSCC.