Positive and Negative Regulation of Ferroptosis and Its Role in Maintaining Metabolic and Redox Homeostasis

Abstract

Ferroptosis is a recently recognized regulated form of cell death characterized by accumulation of lipid-based reactive oxygen species (ROS), particularly lipid hydroperoxides and loss of activity of the lipid repair enzyme glutathione peroxidase 4 (GPX4). This iron-dependent form of cell death is morphologically, biochemically, and also genetically discrete from other regulated cell death processes, which include autophagy, apoptosis, necrosis, and necroptosis. Ferroptosis is defined by three hallmarks, defined as the loss of lipid peroxide repair capacity by GPX4, the bioavailability of redox-active iron, and oxidation of polyunsaturated fatty acid- (PUFA-) containing phospholipids. Experimentally, it can be induced by many compounds (e.g., erastin, Ras-selective lethal small-molecule 3, and buthionine sulfoximine) and also can be pharmacologically inhibited by iron chelators (e.g., deferoxamine and deferoxamine mesylate) and lipid peroxidation inhibitors (e.g., ferrostatin and liproxstatin). The sensitivity of a cell towards ferroptotic cell death is tightly associated with the metabolism of amino acid, iron, and polyunsaturated fatty acid metabolism, and also with the biosynthesis of glutathione, phospholipids, NADPH, and coenzyme Q10. Ferroptosis sensitivity is also governed by many regulatory proteins, which also link ferroptosis to the function of key tumour suppressor pathways. In this review, we highlight the discovery of ferroptosis, the mechanism of ferroptosis regulation, and its association with other cellular metabolic processes.

Figure 1

Modulation of ferroptosis by various chemical reagents. Ferroptosis is activated by four classes of ferroptosis inducers: (1) system xc− inhibitors, (2) GPX4 inhibitors, (3) FIN56, and (4) FINO2. Apart from these canonical ferroptosis inducers, many other reagents can also induce ferroptosis like buthionine sulfoximine (BSO) and ferric ammonium citrate. Ferroptosis is also inhibited by several pharmacological and genetic agents which inhibit lipid metabolism, lipid peroxidation, and iron metabolism. Vitamin E family (tocopherols and tocotrienols), small molecules, and flavonoids can inhibit LOX activity. Dopamine which is a neurotransmitter also leads to cell survival by blocking GPX4 degradation.

Figure 2

Regulation of ferroptosis by amino acid, lipid, and iron metabolism. The initiation and execution of ferroptosis are regulated by the metabolism of amino acid, lipid, and iron. The three hallmarks of ferroptosis are the presence of polyunsaturated fatty acid- (PUFA-) acylated phospholipids (PLs), redox-active iron, and loss in lipid peroxide repair. System xc− imports cystine, which gets reduced to cysteine to synthesize glutathione. GPX4 carries out the elimination of lipid peroxides by utilizing glutathione as a necessary cofactor. Transferrin and transferrin receptors are required for ferroptosis which import iron from the extracellular environment. Iron is essentially required for the accumulation of lipid peroxides. Stored Fe(III) in ferritin is retrieved by autophagy, and also, heme can be degraded by heme oxygenases (HOs) to recover Fe(II).

Figure 3

A schematic model describing the roles of various stress signalling pathways in the regulation of ferroptosis; p53 exhibits a dual regulatory roles in the control of ferroptosis. p53 increases ferroptosis either by inhibiting SLC7A11 expression or by activating SAT1 and GLS2 expression. p53-mediated inhibition of ferroptosis is mediated either by inhibiting DPP4 activity or inducing CDKN1A/p21 expression. ATM-mediated resistance to ferroptosis is induced by ATM inactivation. Upon ATM inactivation, the nuclear import of MTF1 protein is increased which transcriptionally activates the expression of ferroportin (FPN1) and ferritin (FTH1 and FTL) which leads to the presence of low-labile iron in the cell. Activation of the p62-Keap1- (Kelch-like ECH-associated protein 1-) Nrf2 (nuclear factor erythroid 2-related factor 2) pathway also regulates ferroptosis. Nrf2 plays the central regulatory role in the regulation of antioxidant molecules (HO1, NQO1) thus conferring protective against environmental or intracellular stresses. Nrf2 also controls the synthesis of GSH production which comprises an integral component of ferroptosis machinery. AMPK-mediated energy stress signalling pathway also has diverse roles in regulating ferroptosis. AMPK can either function by inhibiting major biosynthetic pathways (such as protein or fatty acid biosynthesis) or in association with Beclin-1 which is a key regulator of autophagy. BECN1 promotes ferroptosis by binding to SLC7A11 and thus blocking the system xc− activity.