GPX4 (Glutathione Peroxidase 4)

Overview

GPX4 (Glutathione Peroxidase 4), also known as phospholipid hydroperoxide glutathione peroxidase (PHGPx), is a unique member of the glutathione peroxidase family that directly reduces lipid hydroperoxides in cellular membranes. Unlike other GPX enzymes that require free hydrogen peroxide, GPX4 can reduce complex lipid hydroperoxides embedded within phospholipid bilayers, making it the master regulator of ferroptosis—a regulated cell death pathway driven by iron-dependent lipid peroxidation.^{1Inactivation of the ferroptosis regulator Gpx4 triggers acute renal failure2014 · Nature Cell Biology · DOI 10.1038/ncb3064Open reference}

Structure and Domains

GPX4 is a 197-amino acid protein with a molecular weight of approximately 22 kDa. Unlike other selenoproteins, GPX4 contains a selenocysteine (Sec) residue at its active site (position 46 in humans), which is encoded by an in-frame UGA codon that normally signals translation termination.^{2Selenium utilization by GPX4 is required to prevent hydroperoxide-induced ferroptosis2018 · Cell · DOI 10.1016/j.cell.2017.11.048Open reference}

Key structural features:

• Active site selenocysteine: Essential for the high catalytic efficiency of lipid hydroperoxide reduction

• Three functional isoforms: Cytosolic (cGPX4), mitochondrial (mGPX4), and nuclear (nGPX4), generated from alternative translation initiation sites

• SECIS element: A stem-loop structure in the 3’ UTR required for selenocysteine incorporation

The crystal structure reveals a compact globular protein with the selenocysteine positioned in a surface-accessible pocket that accommodates phospholipid substrates.^{3Structural basis for catalytic activity of glutathione peroxidase 42007 · Biochemical Journal · DOI 10.1042/BJ20070428Open reference}

Normal Function

GPX4 serves as the primary defense against lipid peroxidation in cellular membranes:^{4Glutathione peroxidases2013 · Biochimica et Biophysica Acta · DOI 10.1016/j.bbagen.2012.11.020Open reference}

1. Lipid hydroperoxide reduction: Directly reduces lipid hydroperoxides (LOOH) to corresponding alcohols (LOH) using glutathione (GSH) as a cofactor

2. Ferroptosis suppression: Prevents the accumulation of oxidized phospholipids that trigger ferroptotic cell death

3. Sperm maturation: Essential for male fertility; mitochondrial GPX4 is a structural component of the sperm mitochondrial capsule

4. Redox signaling: Modulates lipid-derived signaling molecules

The catalytic cycle involves:

GPX4-SeH + LOOH → GPX4-SeOH + LOH
GPX4-SeOH + GSH → GPX4-SeSG + H2O  
GPX4-SeSG + GSH → GPX4-SeH + GSSG

Role in Neurodegeneration

Ferroptosis and Neurodegeneration

GPX4 dysfunction is increasingly recognized as central to neurodegenerative diseases through ferroptosis:^{5Ferroptosis: A regulated cell death nexus linking metabolism, redox biology, and disease2017 · Cell · DOI 10.1016/j.cell.2017.09.021Open reference}

Alzheimer’s Disease:

• GPX4 expression is reduced in AD brain tissue

• Lipid peroxidation markers are elevated in AD patients and correlate with cognitive decline

• Aβ oligomers can trigger ferroptosis by depleting glutathione

• GPX4 haplodeficiency accelerates Aβ pathology in mouse models^{6Ablation of the ferroptosis inhibitor glutathione peroxidase-4 in forebrain neurons accelerates neurodegeneration2017 · Autophagy · DOI 10.1080/15548627.2016.1277304Open reference}

Parkinson’s Disease:

• Iron accumulation in the substantia nigra creates conditions favorable for ferroptosis

• α-Synuclein aggregates can sequester GPX4, impairing its function

• GPX4 activators protect dopaminergic neurons in PD models

• GPX4 deficiency sensitizes neurons to ferroptotic death^{7Ferroptosis, a newly characterized form of cell death in Parkinson's disease that is regulated by PKC2021 · Neurobiology of Disease · DOI 10.1016/j.nbd.2021.105610Open reference}

Amyotrophic Lateral Sclerosis:

• GPX4 levels are decreased in spinal motor neurons of ALS patients

• SOD1 mutations increase susceptibility to ferroptosis

• GPX4 overexpression extends survival in ALS mouse models

Multiple Sclerosis:

• Ferroptosis contributes to oligodendrocyte death in MS lesions

• GPX4 expression is reduced in active demyelinating lesions

Molecular Mechanisms

The ferroptosis pathway involves several key players that intersect with GPX4:^{8Ferroptosis: mechanisms, biology and role in disease2021 · Nature Reviews Molecular Cell Biology · DOI 10.1038/s41580-020-00324-8Open reference}

1. Iron accumulation: Increases labile iron pool, promoting Fenton chemistry

2. Polyunsaturated fatty acids (PUFAs): Substrates for lipid peroxidation

3. System Xc-: Cystine/glutamate antiporter that supplies cysteine for GSH synthesis

4. FSP1/AIFM2: Parallel ferroptosis suppressor that acts independently of GPX4

5. NRF2: Transcriptional regulator of GPX4 and antioxidant genes

Therapeutic Targeting

GPX4 Activation Strategies

Several approaches are being explored to enhance GPX4 function:^{9Broadening horizons: The role of ferroptosis in cancer2021 · Nature Reviews Clinical Oncology · DOI 10.1038/s41571-020-00462-0Open reference}

Strategy	Mechanism	Status
Selenocysteine supplementation	Supports GPX4 synthesis	Preclinical
GPX4 mimetics	Small molecule antioxidants	Research phase
Gene therapy	GPX4 overexpression	Preclinical models
GSH precursors (NAC, GSH-EE)	Provides cofactor	Clinical use

Ferroptosis Inhibitors

Indirect approaches to support GPX4 function:^{10On the mechanisms of cytoprotection by ferrostatin-1 and liproxstatin-1 and the role of lipid peroxidation in ferroptotic cell death2017 · ACS Central Science · DOI 10.1021/acscentsci.7b00028Open reference}

• Deferoxamine: Iron chelator that reduces lipid peroxidation

• Liproxstatin-1: Direct ferroptosis inhibitor

• Ferrostatin-1: Lipid radical scavenger

• Vitamin E: Lipid-soluble antioxidant

System Xc- Modulators

• Dimethyl fumarate: Activates NRF2, increases GSH synthesis

• Sulfasalazine: Inhibits System Xc- (caution: may promote ferroptosis)

Protein Interactions

Interacting Partner	Function	Relevance
Glutathione (GSH)	Essential cofactor	Substrate for peroxide reduction
FSP1/AIFM2	Parallel ferroptosis suppressor	Redundant protection pathway
NRF2	Transcription factor	Regulates GPX4 expression
Ferroportin	Iron exporter	Reduces labile iron pool
ACSL4	Fatty acid metabolism	Generates PUFA-PL substrates

Key Publications

1. Friedmann Angeli et al., Inactivation of the ferroptosis regulator Gpx4 triggers acute renal failure (2014) — Nature Cell Biology. Landmark study establishing GPX4 as the master regulator of ferroptosis.

2. Yang et al., Regulation of ferroptotic cancer cell death by GPX4 (2014) — Cell. Characterization of GPX4’s role in ferroptosis regulation.

3. Hambright et al., Ablation of the ferroptosis inhibitor glutathione peroxidase-4 in the forebrain accelerates neurodegeneration (2017) — Autophagy. Demonstrates GPX4’s neuroprotective role in vivo.

4. Chen et al., ATF4 promotes neuroprotection in ferroptosis by regulating the SLC7A11-GPX4 axis (2023) — Demonstrates the stress response pathway regulating GPX4 in neurons.

5. Stockwell et al., Ferroptosis: A Regulated Cell Death Nexus Linking Metabolism, Redox Biology, and Disease (2017) — Cell. Comprehensive review of ferroptosis mechanisms.

See Also

• Ferroptosis

• FSP1/AIFM2

• Ferritin Heavy Chain

• NRF2

• Iron Metabolism in Neurodegeneration

• Glutathione System