Glutathione peroxidase 4 and vitamin E cooperatively prevent hepatocellular degeneration

Abstract

The selenoenzyme glutathione peroxidase 4 (Gpx4) is an essential mammalian glutathione peroxidase, which protects cells against detrimental lipid peroxidation and governs a novel form of regulated necrotic cell death, called ferroptosis. To study the relevance of Gpx4 and of another vitally important selenoprotein, cytosolic thioredoxin reductase (Txnrd1), for liver function, mice with conditional deletion of Gpx4 in hepatocytes were studied, along with those lacking Txnrd1 and selenocysteine (Sec) tRNA (Trsp) in hepatocytes. Unlike Txnrd1- and Trsp-deficient mice, Gpx4−/− mice died shortly after birth and presented extensive hepatocyte degeneration. Similar to Txnrd1-deficient livers, Gpx4−/− livers manifested upregulation of nuclear factor (erythroid-derived)-like 2 (Nrf2) response genes. Remarkably, Gpx4−/− pups born from mothers fed a vitamin E-enriched diet survived, yet this protection was reversible as subsequent vitamin E deprivation caused death of Gpx4-deficient mice ~4 weeks thereafter. Abrogation of selenoprotein expression in Gpx4−/− mice did not result in viable mice, indicating that the combined deficiency aggravated the loss of Gpx4 in liver. By contrast, combined Trsp/Txnrd1-deficient mice were born, but had significantly shorter lifespans than either single knockout, suggesting that Txnrd1 plays an important role in supporting liver function of mice lacking Trsp. In sum our study demonstrates that the ferroptosis regulator Gpx4 is critical for hepatocyte survival and proper liver function, and that vitamin E can compensate for its loss by protecting cells against deleterious lipid peroxidation.

Lethal dysregulation of energy metabolism during embryonic vitamin E deficiency

“…Thus, E− embryos experience dysregulation of energy metabolism, a phenomenon that is a major driver of cellular dysfunction and death as an ultimate consequence of VitE deficiency. Potentially, ferroptosis, a mechanism of programmed cell death due to increased lipid peroxidation [40,41], which is dependent on GPx4 and GSH, as well as VitE to prevent cell death [7], is responsible for the embryonic lethality. Notably, VitE has been suggested to function as a lipoxygenase inhibitor and thus preventing the generation of oxidized arachidonic and adrenic PE, which have been identified as lipid signaling molecules for ferroptosis [42].…”

“…Could dysregulation of this antioxidant network cause embryonic mortality? Maternal VitE supplementation in mice prevents GPx4 knockdown-induced lethality in offspring [7], suggesting that VitE is necessary both 1) to generate lipid hydroperoxides from peroxyl radicals (the lipid hydroperoxides then function as GPx4 substrates) and 2) in the absence of GPx4 to prevent alkoxyl radicals, which arise from the spontaneous oxidation of lipid hydroperoxides, to reinitiate lipid peroxidation.…”

Oxidized arachidonic and adrenic PEs navigate cells to ferroptosis

“…Thus not only free radical scavenging but also competition with the oxidation substrates for the binding site of the protein (“corking” mechanism) may be an important factor contributing to the inhibition of stereo-specific LOX-driven oxidations. Several reports documented efficiency of Vitamin E as a protector of cells against ferroptotic death in vitro 38–40 . In previous publication 18 , we reported that α-tocopherol was effective in preventing ferroptosis in nM-range of concentrations.…”

“…More importantly, this protective effect of vitamin E was also realized in vivo 41 . It has been established that “Gpx4 −/− pups born from mothers fed a vitamin E-enriched diet survived, yet this protection was reversible as subsequent vitamin E deprivation caused death of GPX4-deficient mice ~4 weeks thereafter” 38 . Thus vitamin E can be considered as an effective anti-ferroptotic agent.…”

Vitamin E deficiency during embryogenesis in zebrafish causes lasting metabolic and cognitive impairments despite refeeding adequate diets

“…Excessive glutamate is neurotoxic [58] and may be a consequence of compromised mitochondria [59]; additional experiments regarding the regulation of neuronal intracellular glutamate levels are required to determine whether these mechanisms also apply to our VitE deficiency model. Importantly, VitE supplementation successfully prevents ferroptosis [60] and associated neurological impairments [61], while VitE deficiency exacerbates the latter [62], indicating that ferroptosis may constitute a biological rationale for the consequences of embryonic VitE deficiency we observed in E− larvae.…”