Oxidized arachidonic and adrenic PEs navigate cells to ferroptosis

Abstract

Enigmatic lipid peroxidation products have been claimed as the proximate executioners of ferroptosis - a specialized death program triggered by insufficiency of glutathione peroxidase 4 (GPX4). Here, by using quantitative redox lipidomics, reverse genetics, bioinformatics and systems biology we discovered that execution of ferroptosis involves a highly organized oxygenation center, whereby only one class of phospholipids, phosphatidylethanolamines (PE), undergoes oxidation in the ER-associated compartments with the specificity towards two fatty acyls – arachidonoyl (AA) and adrenoyl (AdA). Suppression of AA or AdA esterification into PE by genetic or pharmacological inhibition of acyl-CoA synthase 4 acts as a specific anti-ferroptotic rescue pathway. Lipoxygenases (LOX) generate doubly- and triply-oxygenated (15-hydroperoxy)-di-acylated PE species which act as death signals while tocopherols and tocotrienols suppress LOX and protect against ferroptosis suggesting an unforeseen homeostatic physiological role of vitamin E. This oxidative PE death pathway may also represent a target for drug discovery.

PEBP1 Wardens Ferroptosis by Enabling Lipoxygenase Generation of Lipid Death Signals

“…Therefore, we employed a GPX4 inhibitor, RSL3 (which chemically inactivates the enzyme and suppresses its expression), to block the enzymatic reduction of 15-HpETE-PE (Kagan et al, 2017; Skouta et al, 2014). RSL3 induced death of HAEC, PHKC, HK2 and HT22 cells (Figure S3) that was prevented by several prototypical inhibitors of ferroptosis, including ferrostatin-1 (Figure S3C–F).…”

“…While historically these free oxygenated PUFA were associated with many signaling functions, lately it has become obvious that a more diversified group of PLox represent a much richer signaling language albeit with a poorly understood role. It has been shown that AA-PEox are required for normal functions of many types of leukocytes (Aldrovandi et al, 2017; Morgan et al, 2009), are meaningful signals in phagocytosis of apoptotic cells (Uderhardt et al, 2012) and represent crucial death signals in ferroptosis (Kagan et al, 2017). …”

“…The reverse hexagonal phase arrangements of PEs – less ordered than the bilayer membrane regions – are likely the preferred areas of 15LO-driven oxygenation reactions (Kagan et al, 2017). Here we discovered that a redox phospholipoxysome , comprising PUFA-PE and PUFA-PEox as the substrates and products of oxygenation reactions as well as catalytic/regulatory proteins, 15LO, PEBP1 and GPX4, constitutes a redox assembly regulating ferroptosis.…”

“…We recently identified OOH-phosphatidylethanolamines (OOH-PE) as ferroptotic death signals and showed that the balance between the production of OOH-PE metabolites by 15LO and their reduction to hydroxy-(OH)-metabolites by GPX4 serves as a pivot point between cell survival and ferroptosis (Kagan et al, 2017). LOs are effective in oxygenation of free PUFA liberated from PLs by Ca 2+ -dependent phospholipases A 2 feeding the subsequent oxygenation stages.…”

Directing eicosanoid esterification into phospholipids

“…Also, 12-HETE-d8 is not incorporated into platelet PE during the timescale of agonist-stimulated 12-HETE-PE generation, indicating that exogenous and endogenously generated eicosanoids are somehow sensed differently and suggesting that cell compartmentalization is an important factor (13). Last, two recent studies by Kagan, Conrad, and coworkers (23,24) showed that ACLS4 shapes lipid composition, including formation of oxidized arachidonate and adrenic acid-PEs by lipoxygenase, during a cell death process called ferroptosis.…”