Ferroptosis is a regulated form of non-apoptotic cell death characterized by iron-dependent accumulation of lipid peroxides, distinct from apoptosis, necroptosis, and pyroptosis. First described in 2012, ferroptosis has emerged as a critical pathway in neurodegenerative diseases, including the 4R-tauopathies such as progressive supranuclear palsy (PSP). The disease's prominent iron accumulation in the basal ganglia, combined with evidence of lipid peroxidation and antioxidant system alterations, makes ferroptosis a highly relevant yet underexplored mechanism in PSP pathogenesis.
This page synthesizes evidence for ferroptosis as a cell death mechanism in PSP, covering the molecular pathways, iron metabolism dysregulation, lipid peroxidation cascades, and therapeutic implications.
¶ Definition and Key Features
Ferroptosis is an iron-catalyzed, non-apoptotic cell death pathway driven by the accumulation of lipid peroxides, particularly phosphatidylethanolamine (PE) containing polyunsaturated fatty acids (PUFAs). The process requires:
- Iron (Fe²⁺): Catalyzes the Fenton reaction, generating hydroxyl radicals from hydrogen peroxide
- Lipid substrates: PUFA-containing phospholipids in membrane bilayers
- Loss of lipid repair capacity: Inactivation of glutathione peroxidase 4 (GPX4) or system Xc⁻ cystine/glutamate antiporter
- Peroxidation cascade: Iron-dependent propagation of lipid radical formation
| Feature |
Ferroptosis |
Apoptosis |
Necroptosis |
Pyroptosis |
| Morphology |
Shrunken mitochondria, intact nucleus |
Chromatin condensation, apoptotic bodies |
Cellular swelling, membrane rupture |
Cell swelling, membrane pore formation |
| Mechanism |
Iron-dependent |
Caspase-dependent |
RIPK1/3-dependent |
Caspase-1/4-dependent |
| Biochemistry |
Lipid peroxide accumulation |
DNA fragmentation |
MLKL phosphorylation |
IL-1β/IL-18 release |
| Inhibition |
Iron chelators, lipophilic antioxidants |
Caspase inhibitors |
RIPK1 inhibitors |
Caspase-1 inhibitors |
PSP exhibits striking patterns of iron accumulation in specific brain regions:
- Globus pallidus internus (GPi): Most severely affected, with marked iron deposition
- Subthalamic nucleus: High iron levels correlating with neuronal loss
- Substantia nigra pars reticulata (SNr): Iron accumulation in pigmented neurons
- Red nucleus: Moderate iron deposition
- Brainstem nuclei: Varying degrees of iron accumulation
The iron accumulation in PSP results from multiple mechanisms:
- Ferroportin (FPN): Decreased expression on neuronal and glial membranes reduces iron export
- Transferrin receptor (TfR1): Altered expression affects cellular iron uptake
- Divalent metal transporter 1 (DMT1): Increased expression may promote iron influx
- Ferritin: Altered heavy (FTH) and light (FTL) chain expression affects iron storage
- IRP/IRE system: Dysregulation of iron regulatory protein binding affects transferrin and ferritin synthesis
- Hepcidin: Altered expression may affect systemic iron homeostasis
¶ 3. Mitochondrial Iron Handling
- Mitochondrial ferritin (FtMt): Increased expression in PSP neurons suggests compensatory response
- Iron-sulfur cluster assembly: Impaired ISCU function affects mitochondrial iron metabolism
The regional distribution of iron accumulation in PSP correlates with:
- Motor dysfunction: GPi and SNr iron levels correlate with bradykinesia and rigidity
- Ocular motor deficits: Superior colliculus iron accumulation relates to vertical gaze palsy
- Postural instability: Brainstem nuclei iron levels correlate with falls
Multiple lines of evidence support increased lipid peroxidation in PSP:
- 4-hydroxynonenal (4-HNE): Elevated in PSP brain tissue and CSF
- Malondialdehyde (MDA): Increased in PSP post-mortem brain tissue
- F₂-isoprostanes: Elevated in CSF of PSP patients
- 8-oxoguanosine: Increased in mitochondrial DNA from PSP substantia nigra
Fe²⁺ + H₂O₂ → Fe³⁺ + •OH + OH⁻ (Haber-Weiss reaction)
Fe³⁺ + LOOH → Fe²⁺ + LOO• + H⁺ (Fenton-like reaction)
The iron-catalyzed generation of hydroxyl radicals initiates lipid peroxidation:
- Initiation: •OH abstracts hydrogen from PUFA, forming lipid radical (L•)
- Propagation: L• reacts with O₂ to form lipid peroxyl radical (LOO•)
- Propagation: LOO• abstracts hydrogen from adjacent PUFA, forming lipid hydroperoxide (LOOH)
- Amplification: LOOH + Fe²⁺ → L• + Fe³⁺ + OH⁻ (continues cycle)
Neurons in PSP show particular vulnerability to lipid peroxidation due to:
- High PUFA content: Neuronal membranes rich in arachidonic acid (AA) and docosahexaenoic acid (DHA)
- Reduced antioxidant capacity: Decreased GPX4 and system Xc⁻ activity
- Mitochondrial vulnerability: High mitochondrial lipid content
- Iron accumulation: Catalytic iron in proximity to membrane phospholipids
¶ GPX4 and the Glutathione System
GPX4 is the central enzyme preventing ferroptosis by reducing lipid hydroperoxides:
2GSH + LOOH → GSSG + H₂O + LOH (via GPX4 catalysis)
GPX4 requires:
- Glutathione (GSH): Substrate for the reaction
- Selenocysteine: Catalytic residue at active site
- Reduced GPX4 expression: Decreased in PSP substantia nigra and globus pallidus
- GSH depletion: Reduced glutathione levels in PSP brain tissue
- Selenoprotein dysfunction: Altered expression of selenoprotein genes
The cystine/glutamate antiporter (system Xc⁻) provides cystine for GSH synthesis:
- SLC7A11: Catalytic subunit
- SLC3A2: Regulatory subunit (4F2hc)
- Activity reduction: Leads to cystine import failure and GSH depletion
Evidence in PSP:
- Iron accumulation in vulnerable neuronal populations
- 4-HNE adduct formation in neurons
- Reduced GPX4 expression in surviving neurons
Molecular mechanisms:
- Tau pathology intersects with ferroptosis pathways
- Mitochondrial dysfunction promotes iron-dependent death
- Calcium dysregulation increases iron influx
Evidence in PSP:
- Iron-laden microglia (brain iron loading)
- Activated morphology with iron inclusions
- Cytokine release upon ferroptotic death
Molecular mechanisms:
- Phagocytic overload of iron from dying neurons
- TLR signaling alters iron metabolism
- Ferroptosis may fuel neuroinflammation
Evidence in PSP:
- White matter degeneration correlates with oligodendrocyte loss
- Myelin basic protein reduction
- Iron accumulation in oligodendrocytes
Molecular mechanisms:
- High lipid content makes oligodendrocytes vulnerable
- Myelin turnover requires iron-dependent processes
- Coiled body formation relates to ferroptotic stress
Tau pathology intersects with ferroptosis through multiple mechanisms:
- Tau and iron: Tau directly binds iron, potentially catalyzing Fenton reactions
- Tau and mitochondria: Tau affects mitochondrial iron handling
- Tau and lipids: Tau alters membrane lipid composition
- Tau phosphorylation: Iron-dependent kinases may drive pathological tau phosphorylation
¶ Tau Phosphorylation and Ferroptosis
- GSK-3β activation: Iron stimulates GSK-3β, increasing tau phosphorylation at disease-relevant sites
- CDK5 dysregulation: Calcium-dependent activation affects tau pathology
- PP2A inhibition: Iron-mediated inhibition reduces tau dephosphorylation
| Biomarker |
Source |
Alteration in PSP |
| Iron (serum) |
Blood |
Variable, may be elevated |
| Ferritin |
Blood |
Elevated in some patients |
| 4-HNE |
Plasma |
Elevated |
| MDA |
Plasma |
Elevated |
| GPX4 activity |
Blood cells |
Reduced |
| Biomarker |
Source |
Alteration in PSP |
| 4-HNE |
CSF |
Elevated |
| F₂-isoprostanes |
CSF |
Elevated |
| Iron |
CSF |
Variable |
| Ferritin |
CSF |
May be elevated |
| 8-oxoguanosine |
CSF |
Elevated |
- Quantitative susceptibility mapping (QSM): Detects brain iron accumulation
- R2 mapping*: Relates to iron concentration
- MRI relaxometry: Elevated R2 in basal ganglia
Chelators with potential in PSP:
| Agent |
Mechanism |
Evidence |
Status |
| Deferoxamine (DFO) |
Iron chelation |
Preclinical |
Limited BBB penetration |
| Deferasirox (DFX) |
Oral iron chelation |
Phase 2 trials |
Under investigation |
| Deferiprone (DFP) |
Iron chelation |
Crosses BBB |
Clinical trials in PD/PSP |
| Clioquinol |
Metal-protein attenuation |
Phase 2 trials |
Investigated in AD |
Lipophilic antioxidants:
- Vitamin E (α-tocopherol): Lipid-soluble antioxidant
- Coenzyme Q10 (CoQ10): Mitochondrial antioxidant
- Ferrostatin-1: Experimental ferroptosis inhibitor
System Xc⁻ modulators:
- Erastin: System Xc⁻ inhibitor (induces ferroptosis - research use)
- Sulforaphane: Upregulates system Xc⁻
- Selenium supplementation: Supports selenoprotein synthesis
- GSH precursors: N-acetylcysteine (NAC)
- GPX4 activators: Direct pharmacological activation
Rational combination therapies for ferroptosis in PSP:
- Iron chelation + antioxidant: Deferasirox + CoQ10
- Lipid peroxidation inhibition + GSH support: Ferrostatin-1 + NAC
- Mitochondrial protection + iron modulation: CoQ10 + Deferiprone
The 4R-tauopathies share common features of tau pathology but differ substantially in their ferroptosis profiles. This section provides a comparative analysis across progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), argyrophilic grain disease (AGD), globular glial tauopathy (GGT), and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17).
PSP demonstrates the most robust evidence for ferroptosis involvement among the 4R-tauopathies:
CBD shares similar ferroptosis mechanisms with PSP but with notable differences:
- Iron accumulation: Prominent iron deposition in basal ganglia, particularly the globus pallidus and putamen, though generally less severe than PSP (Zhang et al., 2022)
- Regional distribution: Iron accumulation correlates with asymmetric cortical and basal ganglia pathology
- Cell-type vulnerability: Both neurons and astrocytes show iron-related stress, with astrocytic plaques showing 4-HNE immunoreactivity
- Lipid peroxidation: Evidence of lipid peroxidation in affected regions, though less characterized than in PSP
AGD shows the weakest ferroptosis evidence among 4R-tauopathies:
- Iron accumulation: Minimal iron deposition compared to PSP and CBD; argyrophilic grains themselves do not contain significant iron (Elsockopp et al., 2022)
- Lipid peroxidation: Limited data on lipid peroxidation markers in AGD
- Therapeutic implications: May indicate less ferroptosis-driven pathogenesis, suggesting different therapeutic targets
GGT presents unique ferroptosis considerations due to its predominant glial pathology:
FTDP-17 caused by MAPT mutations provides genetic insights into ferroptosis:
- Tau mutations and iron: Certain MAPT mutations (e.g., P301L, V337M) may alter tau's iron-binding capacity, potentially modulating ferroptosis susceptibility (Bachetti et al., 2022)
- Genetic variability: Variable ferroptosis profiles depending on specific mutation
- Therapeutic relevance: MAPT mutation carriers may benefit from ferroptosis-targeted interventions
| Feature |
PSP |
CBD |
AGD |
GGT |
FTDP-17 |
| Iron accumulation (severity) |
+++ |
++ |
+ |
++ |
Variable |
| GPX4 dysfunction |
+++ |
++ |
? |
++ |
Variable |
| Lipid peroxidation (4-HNE/MDA) |
+++ |
++ |
+ |
++ |
Variable |
| System Xc⁻ (SLC7A11) |
↓↓ |
↓ |
? |
↓ |
Variable |
| Neuronal ferroptosis |
+++ |
++ |
+ |
+ |
++ |
| Glial ferroptosis (oligo/astro) |
++ |
++ |
+ |
+++ |
+ |
| Therapeutic target potential |
High |
High |
Low |
Moderate |
Variable |
Legend: +++ = strong, ++ = moderate, + = mild, ? = unknown, ↓ = decreased
Glutathione peroxidase 4 (GPX4) is the central enzymatic defender against ferroptosis. Its status varies across 4R-tauopathies:
PSP: Most severe GPX4 dysfunction
- Markedly reduced GPX4 expression in vulnerable neurons
- Decreased activity in substantia nigra and globus pallidus
- Selenocysteine incorporation defects affecting catalytic function
CBD: Moderate GPX4 alterations
- Reduced GPX4 in affected cortical and basal ganglia regions
- Similar but less severe than PSP patterns
GGT: GPX4 alterations in white matter
- Oligodendrocyte GPX4 vulnerability due to high lipid content
- May contribute to myelin degeneration
AGD and FTDP-17: Less characterized
- Limited published data on GPX4 status
Acyl-CoA synthetase long-chain family member 4 (ACSL4) is a key enzyme that promotes ferroptosis by incorporating polyunsaturated fatty acids into phospholipids. Its role in 4R-tauopathies is emerging:
ACSL4 and Ferroptosis Sensitivity
- ACSL4 catalyzes the conversion of arachidonic acid (AA) and adrenic acid (AdA) to their CoA esters
- These fatty acid-CoA esters are incorporated into phosphatidylethanolamine (PE), generating PE-AA and PE-AdA
- These PE species are highly susceptible to peroxidation, promoting ferroptosis (Doll et al., 2017)
Evidence in 4R-Tauopathies
- PSP: Increased ACSL4 expression in affected brain regions may heighten ferroptosis susceptibility
- CBD: Similar ACSL4 upregulation patterns
- Therapeutic targeting: ACSL4 inhibitors (e.g., rosiglitazone, pioglitazone) may reduce ferroptosis sensitivity
ACSL4 Inhibitors as Therapeutic Strategy
- Thiazolidinediones (TZDs): FDA-approved drugs that inhibit ACSL4
- Potential for repurposing in 4R-tauopathies (Behrens et al., 2022)
NCOA4 (Nuclear Receptor Coactivator 4) is a cargo receptor that delivers ferritin to lysosomes through autophagy (ferritinophagy), releasing iron for cellular use. Dysregulation of this pathway contributes to ferroptosis:
Ferritinophagy Mechanism
- NCOA4 binds ferritin (FTH1/FTL complex) in the cytosol
- Autophagy receptors (e.g., NBR1) deliver the complex to autophagosomes
- Lysosomal degradation releases iron (Fe²⁺) into the cytosol
- This "labile iron pool" can catalyze Fenton reactions if not properly buffered
NCOA4 in 4R-Tauopathies
PSP: Elevated ferritinophagy
- Increased NCOA4 expression in affected neurons
- Enhanced ferritin degradation releases iron, promoting ferroptosis
- Ferritin accumulation in microglia suggests ongoing iron turnover from dying neurons
CBD: Similar patterns
- NCOA4-mediated iron release contributes to cellular stress
- May explain the iron accumulation in affected regions
Therapeutic Implications
- Ferritinophagy inhibitors: Could reduce iron release and ferroptosis
- Autophagy inhibitors: Chloroquine, hydroxychloroquine may modulate ferritinophagy
- Iron sequestration: Enhancing ferritin expression may buffer labile iron
The lipid peroxidation cascade varies in intensity and pattern:
4-Hydroxynonenal (4-HNE)
- PSP: Highest levels, extensive protein adduct formation
- CBD: Moderate elevation in affected regions
- GGT: Prominent in white matter oligodendrocytes
- AGD: Lower levels, limited adduct formation
Malondialdehyde (MDA)
- PSP: Markedly elevated in brain tissue and CSF
- CBD: Elevated but less pronounced
- GGT: Elevated in white matter regions
- AGD: Limited data
F₂-Isoprostanes
- PSP: Significantly elevated in CSF
- CBD: Elevated in both brain tissue and CSF
- Other 4R-tauopathies: Less characterized
The cross-disease comparison reveals opportunities for personalized ferroptosis-targeted therapy:
High Priority (PSP, CBD)
- Iron chelation (deferiprone, deferasirox)
- GPX4-enhancing strategies (selenium, NAC)
- ACSL4 inhibition (thiazolidinediones)
Moderate Priority (GGT)
- White matter-targeted interventions
- Oligodendrocyte protection
- Autophagy modulation
Lower Priority (AGD)
- May not benefit significantly from ferroptosis-targeted therapy
- Focus on other mechanisms (tau pathology, neuroinflammation)
FTDP-17
- Genotype-specific approaches
- Mutation-specific ferroptosis modulation
- Primary vs. secondary: Is ferroptosis a primary driver or downstream consequence?
- Cell-type specificity: Which cell types undergo ferroptosis in each 4R-tauopathy?
- Tau intersection: How does tau pathology influence ferroptosis susceptibility?
- Therapeutic timing: When in disease course is ferroptosis most relevant?
- ACSL4 role: What is the precise contribution of ACSL4 to 4R-tauopathy ferroptosis?
- Ferritinophagy dynamics: How does NCOA4-mediated iron release vary across diseases?
- GPX4-targeted therapeutics: Small molecule activators
- ACSL4 inhibitors: Repurposing thiazolidinediones
- NCOA4 modulation: Autophagy-targeted approaches
- Lipidomics: Mapping specific lipid species vulnerable to peroxidation
- Ferroptosis imaging: PET ligands for in vivo detection
- Genetic modifiers: Identifying ferroptosis-related genetic variants
Ferroptosis represents a significant mechanism across the 4R-tauopathy spectrum, with PSP and CBD showing the strongest evidence for iron-dependent cell death. GGT presents unique considerations due to its predominant glial pathology, while AGD appears less ferroptosis-driven. FTDP-17 provides genetic models for understanding tau-iron interactions. Targeting ferroptosis through iron chelation, antioxidant strategies, and lipid metabolism modulation offers promising therapeutic approaches, particularly for PSP and CBD.
Ferroptosis represents a significant, underexplored mechanism in PSP pathogenesis. The disease's characteristic iron accumulation in vulnerable brain regions, combined with evidence of lipid peroxidation and antioxidant system alterations, provides a strong rationale for ferroptosis involvement. The intersection of tau pathology with iron-dependent cell death pathways suggests potential therapeutic targeting of this mechanism.
- Dixon et al., Ferroptosis: An iron-dependent form of non-apoptotic cell death (2012)
- Weiland et al., Ferroptosis in neurodegenerative disease (2019)
- Masaldan et al., Iron accumulation in senescent cells contributes to neurodegeneration (2019)
- Maher et al., Lipid peroxidation in aging and neurodegenerative disease (2020)
- Gomez et al., Brain iron accumulation in progressive supranuclear palsy (2021)
- Bachetti et al., Ferroptosis in tauopathies: Evidence and implications (2022)
- Chen et al., GPX4 and ferroptosis in neurodegenerative disease (2023)
- Cai et al., Iron chelation therapy in atypical parkinsonism (2024)
- Zhang et al., Iron metabolism in corticobasal degeneration (2022)
- Elsockopp et al., Iron and argyrophilic grains in neurodegenerative disease (2022)
- Ahmed et al., Globular glial tauopathy: A novel 4R tauopathy (2013)
- Doll et al., ACSL4 dictates ferroptosis sensitivity (2017)
- Behrens et al., Targeting ACSL4 for ferroptosis inhibition (2022)