Ferroptosis: process and function

Ferroptosis, a new form of cell death, and its relationships with tumourous diseases

Ferroptosis is a newly discovered type of cell death that differs from traditional apoptosis and necrosis and results from iron‐dependent lipid peroxide accumulation. Ferroptotic cell death is characterized by cytological changes, including cell volume shrinkage and increased mitochondrial membrane density. Ferroptosis can be induced by two classes of small‐molecule substances known as class 1 (system X_c⁻ inhibitors) and class 2 ferroptosis inducers [glutathione peroxidase 4 (GPx4) inhibitors]. In addition to these small‐molecule substances, a number of drugs (e.g. sorafenib, artemisinin and its derivatives) can induce ferroptosis. Various factors, such as the mevalonate (MVA) and sulphur‐transfer pathways, play pivotal roles in the regulation of ferroptosis. Ferroptosis plays an unneglectable role in regulating the growth and proliferation of some types of tumour cells, such as lymphocytoma, ductal cell cancer of the pancreas, renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). Here, we will first introduce the discovery of and research pertaining to ferroptosis; then summarize the induction mechanisms and regulatory pathways of ferroptosis; and finally, further elucidate the roles of ferroptosis in human tumourous diseases.

Antiferroptotic activity of non-oxidative dopamine

Dopamine is a neurotransmitter that has many functions in the nervous and immune systems. Ferroptosis is a non-apoptotic form of regulated cell death that is involved in cancer and neurodegenerative diseases. However, the role of dopamine in ferroptosis remains unidentified. Here, we show that the non-oxidative form of dopamine is a strong inhibitor of ferroptotic cell death. Dopamine dose-dependently blocked ferroptosis in cancer (PANC1 and HEY) and non-cancer (MEF and HEK293) cells following treatment with erastin, a small molecule ferroptosis inducer. Notably, dopamine reduced erastin-induced ferrous iron accumulation, glutathione depletion, and malondialdehyde production. Mechanically, dopamine increased the protein stability of glutathione peroxidase 4, a phospholipid hydroperoxidase that protects cells against membrane lipid peroxidation. Moreover, dopamine suppressed dopamine receptor D4 protein degradation and promoted dopamine receptor D5 gene expression. Thus, our findings uncover a novel function of dopamine in cell death and provide new insight into the regulation of iron metabolism and lipid peroxidation by neurotransmitters.

Myoinositol Attenuates the Cell Loss and Biochemical Changes Induced by Kainic Acid Status Epilepticus

Identification of compounds preventing or modifying the biochemical changes that underlie the epileptogenesis process and understanding the mechanism of their action are of great importance. We have previously shown that myoinositol (MI) daily treatment for 28 days prevents certain biochemical changes that are triggered by kainic acid (KA) induced status epilepticus (SE). However in these studies we have not detected any effects of MI on the first day after SE. In the present study we broadened our research and focused on other molecular and morphological changes at the early stages of SE induced by KA and effects of MI treatment on these changes. The increase in the amount of voltage-dependent anionic channel-1 (VDAC-1), cofilin, and caspase-3 activity was observed in the hippocampus of KA treated rats. Administration of MI 4 hours later after KA treatment abolishes these changes, whereas diazepam treatment by the same time schedule has no significant influence. The number of neuronal cells in CA1 and CA3 subfields of hippocampus is decreased after KA induced SE and MI posttreatment significantly attenuates this reduction. No significant changes are observed in the neocortex. Obtained results indicate that MI posttreatment after KA induced SE could successfully target the biochemical processes involved in apoptosis, reduces cell loss, and can be successfully used in the future for translational research.

Identification of ACSL4 as a biomarker and contributor of ferroptosis

Ferroptosis, a recently identified form of non-apoptotic cell death, is involved in several physiological and pathological processes. Although lipid peroxidation plays a central role in triggering ferroptosis, the essential regulator of lipid metabolism in ferroptosis remains poorly defined. Here, we show that acyl-CoA synthetase long-chain family member 4 (ACSL4) is required for ferroptotic cancer cell death. Compared with ferroptosis-sensitive cells (e.g., HepG2 and HL60), the expression of ACSL4 was remarkably downregulated in ferroptosis-resistant cells (e.g., LNCaP and K562). In contrast, the expression of other ACSLs, including ACSL1, ACSL3, ACSL5, and ACSL6, did not correlate with ferroptosis sensitivity. Moreover, knockdown of ACSL4 by specific shRNA inhibited erastin-induced ferroptosis in HepG2 and HL60 cells, whereas overexpression of ACSL4 by gene transfection restored sensitivity of LNCaP and K562 cells to erastin. Mechanically, ACSL4-mediated production of 5-hydroxyeicosatetraenoic acid (5-HETE) contributed to ferroptosis. Pharmacological inhibition of 5-HETE production by zileuton limited ACSL4 overexpression-induced ferroptosis. Collectively, these results indicate that ACSL4 is not only a sensitive monitor of ferroptosis, but also an important contributor of ferroptosis.

Autophagy promotes ferroptosis by degradation of ferritin

Macroautophagy/autophagy is an evolutionarily conserved degradation pathway that maintains homeostasis. Ferroptosis, a novel form of regulated cell death, is characterized by a production of reactive oxygen species from accumulated iron and lipid peroxidation. However, the relationship between autophagy and ferroptosis at the genetic level remains unclear. Here, we demonstrated that autophagy contributes to ferroptosis by degradation of ferritin in fibroblasts and cancer cells. Knockout or knockdown of Atg5 (autophagy-related 5) and Atg7 limited erastin-induced ferroptosis with decreased intracellular ferrous iron levels, and lipid peroxidation. Remarkably, NCOA4 (nuclear receptor coactivator 4) was a selective cargo receptor for the selective autophagic turnover of ferritin (namely ferritinophagy) in ferroptosis. Consistently, genetic inhibition of NCOA4 inhibited ferritin degradation and suppressed ferroptosis. In contrast, overexpression of NCOA4 increased ferritin degradation and promoted ferroptosis. These findings provide novel insight into the interplay between autophagy and regulated cell death.

Metallothionein-1G facilitates sorafenib resistance through inhibition of ferroptosis

Hepatocellular carcinoma (HCC) is a major cause of cancer-related death worldwide and currently has the fastest rising incidence of all cancers. Sorafenib was originally identified as an inhibitor of multiple oncogenic kinases and remains the only approved systemic therapy for advanced HCC. However, acquired resistance to sorafenib has been found in HCC patients, which results in poor prognosis. Here, we show that metallothionein (MT)-1G is a critical regulator and promising therapeutic target of sorafenib resistance in human HCC cells. The expression of MT-1G messenger RNA and protein is remarkably induced by sorafenib but not other clinically relevant kinase inhibitors (e.g., erlotinib, gefitinib, tivantinib, vemurafenib, selumetinib, imatinib, masitinib, and ponatinib). Activation of the transcription factor nuclear factor erythroid 2-related factor 2, but not p53 and hypoxia-inducible factor 1-alpha, is essential for induction of MT-1G expression following sorafenib treatment. Importantly, genetic and pharmacological inhibition of MT-1G enhances the anticancer activity of sorafenib in vitro and in tumor xenograft models. The molecular mechanisms underlying the action of MT-1G in sorafenib resistance involve the inhibition of ferroptosis, a novel form of regulated cell death. Knockdown of MT-1G by RNA interference increases glutathione depletion and lipid peroxidation, which contributes to sorafenib-induced ferroptosis.

CONCLUSION

These findings demonstrate a novel molecular mechanism of sorafenib resistance and suggest that MT-1G is a new regulator of ferroptosis in HCC cells. (Hepatology 2016;64:488-500).

Loss of NCB5OR in the cerebellum disturbs iron pathways, potentiates behavioral abnormalities, and exacerbates harmaline-induced tremor in mice

Iron dyshomeostasis has been implicated in many diseases, including a number of neurological conditions. Cytosolic NADH cytochrome b5 oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues and is capable of reducing ferric iron in vitro. We previously reported that global gene ablation of NCB5OR resulted in early-onset diabetes and altered iron homeostasis in mice. To further investigate the specific effects of NCB5OR deficiency on neural tissue without contributions from known phenotypes, we generated a conditional knockout (CKO) mouse that lacks NCB5OR only in the cerebellum and midbrain. Assessment of molecular markers in the cerebellum of CKO mice revealed changes in pathways associated with cellular and mitochondrial iron homeostasis. (59)Fe pulse-feeding experiments revealed cerebellum-specific increased or decreased uptake of iron by 7 and 16 weeks of age, respectively. Additionally, we characterized behavioral changes associated with loss of NCB5OR in the cerebellum and midbrain in the context of dietary iron deprivation-evoked generalized iron deficiency. Locomotor activity was reduced and complex motor task execution was altered in CKO mice treated with an iron deficient diet. A sucrose preference test revealed that the reward response was intact in CKO mice, but that iron deficient diet consumption altered sucrose preference in all mice. Detailed gait analysis revealed locomotor changes in CKO mice associated with dysfunctional proprioception and locomotor activation independent of dietary iron deficiency. Finally, we demonstrate that loss of NCB5OR in the cerebellum and midbrain exacerbated harmaline-induced tremor activity. Our findings suggest an essential role for NCB5OR in maintaining both iron homeostasis and the proper functioning of various locomotor pathways in the mouse cerebellum and midbrain.

Induction of ferroptotic cell death for overcoming cisplatin resistance of head and neck cancer

Inhibition of key molecules related to ferroptosis, cystine/glutamate antiporter and glutathione peroxidase, may induce eradication of chemotherapy/radiotherapy-resistant cancer cells. The present study investigated whether ferroptosis could overcome head and neck cancer (HNC) resistance to cisplatin treatment. Three cisplatin-resistant HNC cell lines (AMC-HN3R, -HN4R, and -HN9R) and their parental lines were used. The effects of cystine and glutamate alteration and pharmacological and genetic inhibition of cystine/glutamate antiporter were assessed by measuring viability, death, reactive oxygen species production, protein expression, and preclinical mouse tumor xenograft models. Conditioned media with no cystine or glutamine excess induced ferroptosis of both cisplatin-sensitive and -resistant HNC cells without any apparent changes to necrosis and apoptosis markers. The cystine/glutamate antiporter inhibitors erastin and sulfasalazine inhibited HNC cell growth and accumulated lipid reactive oxygen species, thereby inducing ferroptosis. Genetic silencing of cystine/glutamate antiporter with siRNA or shRNA treatment also induced effective ferroptotic cell death of resistant HNC cells and enhanced the cisplatin cytotoxicity of resistant HNC cells. Pharmacological and genetic inhibition of cystine/glutamate antiporter significantly sensitized resistant HNC cells to cisplatin in vitro and in vivo. Pharmacological and genetic inhibition of cystine/glutamate antiporter overcomes the cisplatin resistance of HNC cells by inducing ferroptosis.

Necroptosis: A new way of dying?

This review embarks upon a cell death journey from the discovery of apoptosis and necrosis through to the coalescence of these: necroptosis. The mechanisms of 2 emerging necrotic cell death pathways, pyroptosis and ferroptosis, will be explored before delving into apoptotic and necroptotic signaling cascades, highlighting the complex interplay between molecular players. The involvement of the ripoptosome, interferon signaling and DNA damage in necroptosis will be discussed briefly. The major focus is on necroptosis initiation by tumor necrosis factor-α (TNFα) and its cognate receptor TNFR1, caspase-independent RIP1/RIP3/MLKL necrosome activation and cell death propagation by damage-associated molecular pattern (DAMP) release. Finally, the implications of a complex cell death signaling network will be revealed in the context of cancer biology and therapy. The clinical contribution of the discovery of necroptosis as an unequivocally new way of dying is monumental and could drastically alter cancer therapy strategies in the future.

Iron homeostasis: transport, metabolism, and regulation

PURPOSE OF REVIEW

Iron is essential for normal cellular function and many diseases result from disturbances in iron homeostasis. This review describes some of the recent key advances in iron transport and its regulation, how this relates to iron-related disorders, and emerging therapies for these diseases.

RECENT FINDINGS

The iron-regulatory hormone hepcidin and its target, the iron exporter ferroportin (FPN), play central roles in iron homeostasis. Recent studies have expanded our understanding of how hepcidin is regulated in response to stimulated erythropoiesis and have added some new players to the complex network of factors that influences hepcidin expression. Novel structural insights into how FPN transports iron have been an important addition to the field, as has the recognition that some zinc transporters such as ZIP14 can transport iron. Investigations into cardiac iron homeostasis have revealed a key role for FPN, and transferrin receptor 1, which is essential for cellular iron uptake, has been shown to be critical for normal immune function.

SUMMARY

The increased understanding of mechanisms of iron homeostasis that has resulted from recent research has greatly improved our ability to diagnose and manage iron-related disorders, and has offered new therapies for this important class of human diseases.

ROS homeostasis and metabolism: a dangerous liason in cancer cells

Tumor cells harbor genetic alterations that promote a continuous and elevated production of reactive oxygen species. Whereas such oxidative stress conditions would be harmful to normal cells, they facilitate tumor growth in multiple ways by causing DNA damage and genomic instability, and ultimately, by reprogramming cancer cell metabolism. This review outlines the metabolic-dependent mechanisms that tumors engage in when faced with oxidative stress conditions that are critical for cancer progression by producing redox cofactors. In particular, we describe how the mitochondria has a key role in regulating the interplay between redox homeostasis and metabolism within tumor cells. Last, we will discuss the potential therapeutic use of agents that directly or indirectly block metabolism.

Transplantation of bone marrow mesenchymal stem cells alleviates hepatic ischemia-reperfusion injury in rats

AIM: To assess the therapeutic effects of transplantation of bone marrow mesenchymal stem cells (BMSCs) on hepatic ischemia-reperfusion injury (HIRI) in rats and explore the underlying mechanism.

METHODS: BMSCs were isolated from bone tissues of SD rats, cultured, and identified. SD rats were randomly divided into three groups: a control group, an HIRI group and a BMSCs transplantation group. HIRI was induced by the pringle occlusion method. After hepatic ischemia-reperfusion injury induction, blood samples were taken at 1, 2, and 3 weeks. Serum alanine transaminase (ALT), aspartate transaminase (AST), malondialdehyde (MDA), superoxide dismutase (SOD), interleukin (IL)-18 and tumor necrosis factor-α (TNF-α) were determined. Liver pathological changes were assessed by HE staining after 2 wk. Expression of hepatocyte growth factor (HGF) and alpha-smooth muscle protein (α-SMA) in the liver was detected by RT-PCR and Western blot.

RESULTS: At 1 wk, the levels of serum ALT, AST, IL-18, TNF-α and MDA in the transplantation group and HIRI group were significantly higher than those in the control group (P < 0.05 for all), and the levels of serum SOD were lower than that in the control group (P < 0.05). At 2 wk, the levels of serum ALT, AST, IL-18, TNF-α and MDA in the transplantation group were significantly lower than those in the HIRI group (P < 0.05 for all), but the level of serum MDA was higher and the level of serum SOD was lower in the transplantation group than in the control group (P < 0.05 for both). Hepatic degeneration, necrosis and fibrosis in the transplantation group were reduced significantly compared with the HIRI group (P < 0.05). HGF expression in the liver tissue was significantly higher and α-SMA expression was significantly lower in the transplantation group than in the HIRI group (P < 0.05 for both).

CONCLUSION: Transplantation of BMSCs can alleviate hepatic ischemia-reperfusion injury via mechanism possibly associated with inhibiting inflammatory factors and enhancing anti-oxidation.