GPX4 in cell death, autophagy, and disease

Figures & data

Figure 1. Differences among GPX family members. Briefly, human GPX members can be divided into groups of selenoproteins (GPX1, 2, 3, 4, and 6) and non-selenoproteins (GPX5, 7, and 8) with different subcellular locations, spatial structures, and molecular masses.

Table 1. Developmental and disease phenotypes associated with GPX4 deficiency in mice.

Name	Annotation	Isoform	Allele	Phenotype	Salvage	Reference
gpx4^−/− mice	Mice that are homozygous for a gpx4 null allele	Constitutive	Homozygous	Embryos die at E7.5	NA	[11,12]
Gpx4± mice	Mice that are heterozygous for a gpx4 null allele	Constitutive	Heterozygous	50% reduction in GPX4 expression and sensitivity to oxidative stress	Culture under low oxygen	[13]
				GPX4 activity and selenium concentrations are lower in mouse tissues	Administration of paraquat	[14]
				Longer median lifespan and reduced/delayed severity of age-related pathologies, such as fatal neoplastic lymphoma and glomerulonephritis	NA	[15]
				GPX4 activity is 50% reduced in lung fibroblasts and is susceptible to oxidative cytotoxicity	NA	[16]
ngpx4 KO mice	Mice with a targeted deletion of the nGpx4 gene	nGPX4/nPHGPx	Homozygous	Defective chromatin condensation and abnormal morphology in spermatozoa	NA	[17]
				Easier depolymerization of spermatozoa at all stages of epididymal maturation and accelerated dispersion of sperm chromatin in oocytes	NA	[18]
mgpx4-KO mice	Mice with a targeted deletion of the mGpx4 gene	mGPX4	Homozygous	Retinal degeneration and photoreceptor apoptotic death	Administration of vitamin E	[19]
Inducible gpx4-KO mice	Inducible loss of Gpx4 in the kidney	Constitutive	Homozygous	Massive lipid peroxidation and cell death (apoptosis and ferroptosis) occur	Reconstitution of wild-type GPX4, adding α-tocopherol, or the knockdown of AIFM1	[20]
				Massive lipid peroxidation and cell death (apoptosis and ferroptosis) occur	Administration of liproxstatin-1	[21]
Neuron-specific gpx4-KO mice	Knockout of Gpx4 in mouse cerebral cortex and hippocampus	Conditional	Homozygous	Neuron-specific gpx4-KO mice exhibits irregular gait at P10 and a hyperexcitable phenotype at P12	NA	[20]
Tg(sGPX4)/gpx4-/- mice	Mice that are null for endogenous Gpx4 but express a short form of the GPX4 protein	Constitutive	Homozygous	Rescue the lethal phenotype of gpx4-null	NA	[22]
mgpx4-KO mice	Mice specifically deficient in mitochondrial Gpx4	mGPX4	Homozygous	Impaired sperm quality and structural abnormalities lead to infertility	Intracytoplasmic sperm injection	[23]
				Retinal degeneration	Vitamin E-enriched diet	[19]
Spermatocyte-specific gpx4-KO mice	Depletion of Gpx4 in murine spermatocyte	Conditional	Homozygous	Mice are infertile and have significantly reduced sperm counts	NA	[24]
Keratinocyte-specific gpx4-KO mice	Depletion of Gpx4 in murine keratinocyte	Conditional	Heterozygous	Epidermal hyperplasia, dermal inflammatory infiltrates, malformed hair follicles, and alopecia in perinatal mice	Adding celecoxib to the diet	[25]
Gpx4_U46S mice	Mice express a catalytically inactive mutant form of Gpx4	Constitutive	Homozygous	Died at embryonic stage E7.5	NA	[26]
			Heterozygous	Subfertility and damaged sperm
gpx4 KO Sec46Ala-Gpx4+/+ knockin mice	Homozygous gpx4-knockout mice expressing a catalytically inactive Gpx4 mutant (Sec46Ala)	Constitutive	Homozygous	Mice are not viable, but undergo intrauterine resorption between E 6 and E7	NA	[27]
			Heterozygous	Mice are viable, fertile and show no major phenotypic changes
TΔgpx4/Δgpx4 mice	T cell-specific gpx4-deficient mice	Conditional	Homozygous	T cells lacking Gpx4 fail to expand and protect against infection	Diet supplementation of high dosage of vitamin E	[28]
gpx4-NIKO mice	Conditional ablation of Gpx4 in neurons	Conditional	Homozygous	Rapid motor neuron degeneration and paralysis	Administration of liproxstatin-1	[29]
Mx1-cre/Gpx4F/F (Gpx4Δ) mice	Loss of Gpx4 in murine hematopoietic cells	Conditional	Homozygous	Develop necroptosis-related anemia	Administration of vitamin E or knockout of Ripk3	[30]
Hepatocyte-specific gpx4-KO mice	Depletion of Gpx4 in murine hepatocyte	Conditional	Homozygous	Die shortly after birth and present extensive hepatocyte degeneration	Vitamin E-enriched diet	[31]
gpx4-BIKO mice	Mice with conditional deletion of Gpx4 in forebrain neurons	Conditional	Homozygous	Exhibit significant deficits in spatial learning, memory function, and cognition	Administration of liproxstatin-1	[32]
gpx4Mye-/- mice	Myeloid cell-specific gpx4-knockout mice	Conditional	Homozygous	Susceptible to pyroptosis-related lethal infection	Administration of vitamin E, PLCG1 inhibitor, genetic Casp11 deletion, or Gsdmd inactivation	[33]
Gpx4cys/cys mice	Mice with a targeted mutation of the catalytically active Sec to Cys of Gpx4	Conditional	Homozygous	Exhibit severe spontaneous seizures or hyperactivity; Gpx4^cys/cys mice survive until the pre-weaning stage only on a mixed genetic background	NA	[34]
gpx4fl/fl;Cd19-Cre mice	Mice with gpx4 deletion in B cells	Conditional	Homozygous	Significant decrease in marginal zone B cells and splenic B1 cells, and subsequent decrease in antibody response to infection	NA	[35]
Pdx1-Cre; gpx4flox/flox mice	Mice with gpx4 deletion in pancreas	Conditional	Homozygous	Increased sensitivity to pancreatitis induced by cerulean or a Lieber-DeCarli alcoholic liquid diet	Administration of olanzapine	[36]
				Promote pancreatitis induced by cerulean or L-arginine	Administration of liproxstatin-1	[37]
Pdx1-Cre; KrasG12D/+; gpx4−/− mice (KCG mice)	Mice with gpx4 deletion in KrasG12D-driven pancreatic cancer			Promote Kras^G12D-driven tumorigenesis
gpx4fl/fl;LysM-cre mice	Mice with gpx4 deletion in macrophages	Conditional	Homozygous	Increased sensitivity to ferroptosis following IL4 overexpression and nematode infection	Exposure to nitric oxide	[38]
MRL/lpr mice	Mice with neutrophil-specific Gpx4 haploinsufficiency	Conditional	Homozygous	Systemic lupus erythematosus features including autoantibodies, neutropenia, skin lesions, and proteinuria	Administration of liproxstatin-1	[39]
T-KO mice	Mice with gpx4 deletion in CD4+ T cells	Conditional	Homozygous	Peripheral CD8^+ T cells are severely reduced, but CD4^+ T cells display relatively normal naive and effector cell populations in unchallenged mice	Selenium supplementation	[40]
Col2a1-CreERT; gpx4flox/flox mice (gpx4-CKO mice)	Mice with gpx4 deletion in osteoarthritis model	Conditional	Homozygous	Aggravate the development of osteoarthritis	Administration of CoQ10 and inhibition of calcium channels	[41]

Figure 2. GPX4 isoenzymes. The GPX4 protein has three isoforms (cGPX4, mGPX4, and nGPX4) encoded by distinct 1a and 1b exons. They exhibit overlapping and distinct functions in regulating development and cell death.

Figure 3. Role of GPX4 in lipid peroxidation. Polyunsaturated fatty acids (PUFAs) are major components of cell membrane phospholipid bilayers and are susceptible to oxidative damage that produces the toxic lipid oxidation product PLOOH. In contrast, membrane system xc⁻ is a heterodimeric complex composed of SLC7A11 and SLC3A2, which mediates cystine uptake into cells that is followed by GSH synthesis via the GCLC-GSS pathway. GSH is a co-factor in the catalytic cycle of GPX4 that detoxifies PLOOH to the lipid alcohol PLOH. Therefore, the pharmacological inhibition of GCLC, SLC7A11, and GPX4 using indicated small-molecular compounds can promote or enhance lipid peroxidation.

Figure 4. Expression and modification of GPX4. (A) Multiple transcription factors are required for GPX4 expression. As a selenoprotein, Sec-tRNA^[Ser]Sec requires a Sec insertion sequence element in Gpx4 mRNA. (B) GPX4 can undergo ubiquitination (Ub), phosphorylation (P), sumoylation (Su) and alkylation (Alk) at specific sites. (C) Both the UPS and autophagy are involved in GPX4 protein degradation.

Figure 5. GPX4 and cell death. Regulated cell death mechanisms have been studied in a wide range of oxidative stress models. The overexpression of GPX4 blocks cell death, whereas GPX4 depletion induces cell death in a cell-type and stimulus-dependent manner. For example, GPX4 has been demonstrated to be a negative regulator of apoptosis (A), necroptosis (B), pyroptosis (C), ferroptosis (D), or parthanatos (E).

Figure 6. GPX4 and autophagy. Autophagy is a dynamic degradation process that involves the formation of multiple membrane structures. In addition to the classical autophagic machinery, the induction of autophagy-dependent ferroptosis requires specific proteins, such as TMEM164, which is responsible for the formation of phagophores for autophagosome generation. The selective degradation of pro-survival proteins or organelles by autophagy promotes ferroptosis, including the passive release of DAMPs. On the other hand, the early secretion of inflammatory mediators such as DCN during ferroptosis is involved in secretory autophagy mediated by the fusion of the plasma membrane. The autophagic degradation of GPX4 is mediated by different mechanisms. For example, copper and erastin can promote GPX4 degradation by using autophagic receptors TAXIBP1 and SQSTM1, respectively. In addition to macroautophagy, CMA also mediates GPX4 degradation in response to erastin. This process can be inhibited by phosphorylated CKB at T133, which leads to GPX4 phosphorylation at S104.

Figure 7. Dual roles of GPX4 in cancer. The loss of GPX4 results in cell death and tissue damage. On the one hand, chronic inflammation may occur, leading to DAMP-mediated macrophage polarization in the tumor microenvironment, which can promote tumor growth. On the other hand, acute cell death caused by the loss of GPX4 can clear tumor cells and release DAMPs, activating anti-tumor immunity. GPX4 is widely expressed in cancer cells and immune cells, including DCs, CD8 T cells, and neutrophils. However, current GPX4 inhibitors are nonselective and can also cause immune cell death, leading to inhibition of anti-tumor immunity.

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