Ferroptosis is a non-apoptotic form of cell death induced by small molecules in specific tumour types, and in engineered cells overexpressing oncogenic RAS. Yet, its relevance in non-transformed cells and tissues is unexplored and remains enigmatic. Here, we provide direct genetic evidence that the knockout of glutathione peroxidase 4 (Gpx4) causes cell death in a pathologically relevant form of ferroptosis. Using inducible Gpx4^−/− mice, we elucidate an essential role for the glutathione/Gpx4 axis in preventing lipid-oxidation-induced acute renal failure and associated death. We furthermore systematically evaluated a library of small molecules for possible ferroptosis inhibitors, leading to the discovery of a potent spiroquinoxalinamine derivative called Liproxstatin-1, which is able to suppress ferroptosis in cells, in Gpx4^−/− mice, and in a pre-clinical model of ischaemia/reperfusion-induced hepatic damage. In sum, we demonstrate that ferroptosis is a pervasive and dynamic form of cell death, which, when impeded, promises substantial cytoprotection.

Bioactive peptide LL-37/hCAP18, the only human member of the cathelicidin family, plays important roles in killing various pathogens, as well as in immune modulation. We demonstrate that LL-37 is internalized by human macrophages in a time-, dose-, temperature-, and peptide sequence–dependent endocytotic process. Both clathrin- and caveolae/lipid raft–mediated endocytosis pathways are involved in LL-37 internalization. We find that the P2X₇ receptor (P2X₇R) plays an important role in LL-37 internalization by human macrophages because significantly less internalized LL-37 was detected in macrophages pretreated with P2X₇R antagonists or, more specifically, in differentiated THP-1 cells in which the P2X₇R gene had been silenced. Furthermore, this P2X₇R-mediated LL-37 internalization is primarily connected to the clathrin-mediated endocytosis pathway. In addition, our results demonstrate that internalized LL-37 traffics to endosomes and lysosomes and contributes to intracellular clearance of bacteria by human macrophages, coinciding with increased reactive oxygen species and lysosome formation. Finally, we show that human macrophages have the potential to import LL-37 released from activated human neutrophils. In conclusion, our study unveils a novel mechanism by which human macrophages internalize antimicrobial peptides to improve their intracellular pathogen clearance.

Resolution of acute inflammation is an active process coordinated by proresolving lipid mediators (SPMs) such as lipoxins (LXs) and resolvins (Rvs), which are formed by the concerted action of 2 lipoxygenases (LOs). Because the exact molecular mechanisms of SPM biosynthesis are not completely understood, we aimed to investigate LX and D‐type Rv formation in human leukocytes and HEK293T cells overexpressing leukotriene (LT) pathway enzymes. Activity assays in precursor (15‐hydroxyeicosatetraenoic acids, 17‐HDoHE)‐treated granulocytes [polymorphonuclear leukocytes (PMNLs)] showed a strict dependence of LXA ₄ /RvD ₁ biosynthesis on cell integrity, and incubation with recombinant human 5‐LO did not lead to LX or Rv formation. Pharmacologic inhibition of 5‐LO activating protein (FLAP) by MK‐886 inhibited LXA ₄ /RvD ₁ biosynthesis in precursor‐treated PMNLs (drug concentration causing 50% inhibition ∼0.3/0.2 μM), as did knockdown of the enzyme in MM6 cells, and precursor‐treated HEK293T overexpressing 5‐LO produced high amounts of LXA ₄ only in the presence of FLAP. In addition, inhibition of cytosolic phospholipase A _2α (cPLA _2α ) interfered with LXA ₄ /RvD ₁ formation from exogenous precursors in PMNLs. Furthermore, inhibition of the LT synthases LTA ₄ hydrolase and LTC ₄ synthase in PMNL/platelet coincubations augmented LXA ₄ levels. These findings show that several enzymes known to be involved in the biosynthesis of proinflammatory LTs, such as FLAP and cPLA _2α , also contribute to LX and Rv formation.—Lehmann, C., Homann, J., Ball, A.‐K., Blöcher, R., Kleinschmidt, T. K., Basavarajappa, D., Angioni, C., Ferreirós, N., Häfner, A.‐K., Rådmark, O., Proschak, E., Haeggström, J. Z., Geisslinger, G., Parnham, M. J., Steinhilber, D., Kahnt, A. S. Lipoxin and resolvin biosynthesis is dependent on 5‐lipoxygenase activating protein. FASEB J. 29, 5029–5043 (2015). www.fasebj.org

Glaucoma is a complex multifactorial eye disease manifesting in retinal ganglion cell (RGC) death and optic nerve degeneration, ultimately causing irreversible vision loss. Research in recent years has significantly enhanced our understanding of RGC degenerative mechanisms in glaucoma. It is evident that high intraocular pressure (IOP) is not the only contributing factor to glaucoma pathogenesis. The equilibrium of pro-survival and pro-death signalling pathways in the retina strongly influences the function and survival of RGCs and optic nerve axons in glaucoma. Molecular evidence from human retinal tissue analysis and a range of experimental models of glaucoma have significantly contributed to unravelling these mechanisms. Accumulating evidence reveals a wide range of molecular signalling pathways that can operate -either alone or via intricate networks - to induce neurodegeneration. The roles of several molecules, including neurotrophins, interplay of intracellular kinases and phosphates, caveolae and adapter proteins, serine proteases and their inhibitors, nuclear receptors, amyloid beta and tau, and how their dysfunction affects retinal neurons are discussed in this review. We further underscore how anatomical alterations in various animal models exhibiting RGC degeneration and susceptibility to glaucoma-related neuronal damage have helped to characterise molecular mechanisms in glaucoma. In addition, we also present different regulated cell death pathways that play a critical role in RGC degeneration in glaucoma.