An integrated view of lipid metabolism in ferroptosis revisited via lipidomic analysis

Abstract

Ferroptosis is a form of regulated cell death characterized by iron-dependent lipid peroxidation. This process contributes to cellular and tissue damage in various human diseases, such as cardiovascular diseases, neurodegeneration, liver disease, and cancer. Although polyunsaturated fatty acids (PUFAs) in membrane phospholipids are preferentially oxidized, saturated/monounsaturated fatty acids (SFAs/MUFAs) also influence lipid peroxidation and ferroptosis. In this review, we first explain how cells differentially synthesize SFA/MUFAs and PUFAs and how they control fatty acid pools via fatty acid uptake and β-oxidation, impacting ferroptosis. Furthermore, we discuss how fatty acids are stored in different lipids, such as diacyl or ether phospholipids with different head groups; triglycerides; and cholesterols. Moreover, we explain how these fatty acids are released from these molecules. In summary, we provide an integrated view of the diverse and dynamic metabolic processes in the context of ferroptosis by revisiting lipidomic studies. Thus, this review contributes to the development of therapeutic strategies for ferroptosis-related diseases.

Fig. 1. Fatty acid biosynthesis and ferroptosis.

Arachidonic acid (AA, C20:4) is an n-6 polyunsaturated fatty acid that can be synthesized from linoleic acid (C18:2) by fatty acid desaturases (FADSs) and elongation of very long-chain fatty acid proteins (ELOVLs) or taken up directly from the environment. AA and its elongation product, adrenic acid (AdA), are incorporated into membrane phospholipids via acyl-CoA synthetase long-chain family member 4 (ACSL4) and lysophosphatidylcholine acyltransferase 3 (LPCAT3). PE-AA and PE-AdA are considered the most vulnerable phospholipids to peroxidation, which may be mediated by lipoxygenases or via nonenzymatic autoxidation reactions. Peroxidation is followed by the generation of lipid radicals, such as the phospholipid peroxyl radical (PLOO∙), which contributes to the lipid peroxidation chain reaction and, ultimately, to ferroptosis. Ferroptosis can be prevented by reducing lipid hydroperoxides to lipid alcohols via glutathione peroxidase 4 (GPX4) or by directly halting lipid radicals via ferroptosis suppressor protein (FSP1)/CoQ₁₀/vitamin K (VK). The de novo lipogenesis (DNL) pathway contributes to the pool of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs). Although nonessential polyunsaturated fatty acids (PUFAs), such as n-7 and n-9 PUFAs, can be synthesized by FADS2 (Δ6 desaturase), mammals cannot synthesize essential PUFAs, such as n-3 and n-6 fatty acids, because they lack of Δ12 and Δ15 desaturases. Nonetheless, through the DNL pathway, SFAs, and MUFAs contribute to the abundance of n-6 PUFAs, positively or negatively impacting ferroptosis. Abbreviations: ACC acetyl-CoA carboxylase, AMPK AMP-activated protein kinase, FASN fatty acid synthase, GSH glutathione, GSSG glutathione disulfide, SCD1 stearoyl-CoA desaturase-1.

Fig. 2. The Kennedy pathway and Lands cycle in ferroptosis.

The Kennedy pathway is critical for de novo phosphatidylethanolamine (PE) and phosphatidylcholine (PC) synthesis. Phospholipase A2 (PLA2) enzymes, including cytosolic PLA2 (cPLA2), calcium-independent phospholipase A2 (iPLA2), and lipoprotein-associated PLA2 (Lp-PLA2), cleave the sn-2 position of phospholipids, contributing to lysophosphatidylethanolamine (LPE) and lysophosphatidylcholine (LPC) recycling. The sn-2 position of phospholipids favors PUFAs, and PLA2 enzymes release PUFAs, such as AA and oxidized AA, from phospholipids. Abbreviations: CCT choline-phosphate cytidylyltransferase, CK choline kinase, CPT1 choline phosphotransferase 1, DAG diacylglycerol, ECT ethanolamine-phosphate cytidylyltransferase, EPT1 ethanolaminephosphotransferase 1, G3P glycerol-3-phosphate, LPA lysophosphatidic acid, PA phosphatidic acid, PLD phospholipase D.

Fig. 3. Integrated view of the metabolism of fatty acids and various lipids.

The DNL pathways and exogenous supply determine the abundance of fatty acids through the fatty acid transporters CD36 and FATP and the LDL receptor (LDLR). Free fatty acids can be stored in neutral lipids such as triacylglycerols (TAGs), cholesteryl esters (CEs), and phospholipids. Several enzymes release fatty acids from these stores, resulting in either lipid remodeling or degradation via β-oxidation. Although PUFAs in phospholipids are regarded as pro-ferroptotic lipids, the roles of the remodeling pathways of these lipids in ferroptosis are still unclear. ACSL enzymes that catalyze fatty acyl-CoA synthesis play various roles, including fatty acid oxidation, phospholipid synthesis, TAG synthesis, and CE synthesis. Abbreviations: ACAT1 acyl-coenzyme A cholesterol acyltransferase 1, ACSL acyl-CoA synthetase long-chain, ATGL adipose triglyceride lipase, DGAT1 diacylglycerol O-acyltransferase 1, DNL de novo lipogenesis farnesyl, PP farnesyl pyrophosphate, HILPDA hypoxia-inducible lipid droplet associated, isopentenyl PP isopentenyl pyrophosphate, LCAT lecithin–cholesterol acyltransferase, SOAT1 sterol O-acyltransferase 1.

Fig. 4. Schematic showing the diacyl and ether phospholipid synthesis pathways during ferroptosis.

a Diacyl phospholipids contain two fatty acyl chains, each linked with an ester bond, whereas ether lipids consist of a fatty alkyl chain connected by an ether bond or a fatty alkenyl chain connected by a vinyl ether bond at the sn-1 position. b Diacyl and ether lipid synthesis mechanisms. Lysophosphatidic acid (LPA) can be synthesized directly from glycerol-3-phosphate (G3P) in the ER or mitochondria by glycerol-3-phosphate acyltransferase (GPAT) or indirectly from G3P by acyl-dihydroxyacetone phosphate (acyl-DHAP) in peroxisomes, followed by diacyl phospholipid synthesis. The peroxisomal enzymes fatty acyl-CoA reductases (FAR1/2) generate fatty alcohol (FA-OH), which is then replaced with alkyl-DHAP via alkylglycerone phosphate synthase (AGPS), resulting in ether lipid synthesis. Alkenyl-ether lipids, known as plasmalogens, are synthesized from alkyl-ether lipids by TMEM189. ePE-AA and ePC-AA can be synthesized from eLPE, eLPC, and AA-CoA by LPCAT family enzymes or from PC-AA by TMEM164, which transfers the AA chain from PC-AA to an eLPE or eLPC. Although both diacyl- and ether phospholipids containing PUFAs are prone to lipid peroxidation, their relative contributions to initial lipid peroxidation and ferroptosis may be context dependent. Abbreviations: G3PDH glyceraldehyde 3-phosphate dehydrogenase, GNPAT glyceronephosphate O-acyltransferase, PA phosphatidic acid, alkyl-DHAP alkyl-dihydroxyacetone phosphate, TMEM164 transmembrane protein 164, TMEM189 transmembrane protein 189, AGP 1-O-Alky glycerol-3-phosphate.