PSP Ferroptosis and Iron-Dependent Cell Death

Introduction

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. ^{1Iron(ing) out parkinsonisms: The interplay of proteinopathy and ferroptosis in Parkinson's disease and tau-related parkinsonisms.2025 · Redox Biol · DOI 10.1016/j.redox.2024.103478 · PMID 39721496Open reference}

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. ^{2Deuterium Solid State NMR Studies of Intact Bacteria Treated With Antimicrobial Peptides.2020 · Front Med Technol · PMID 35047897Open reference}

flowchart TD
    IRON["Iron Accumulation<br/>(Ferritin, Transferrin)"] --> IRON_IN["Iron Influx ↑ (Fe²⁺)"]
    IRON_IN --> FENTON["Fenton Reaction"]
    FENTON --> ROS["Reactive Oxygen Species<br/>(Hydroxyl Radicals)"]
    ROS --> LP["Lipid Peroxidation<br/>(PUFA-containing PE)"]
    LP --> GPX4["GPX4 Inactivation<br/>(Glutathione Peroxidase 4)"]
    LP --> SYSTEM_XC["System Xc⁻ Inhibition<br/>(Cystine/Glutamate Antiporter)"]
    SYSTEM_XC -->|reduces| GSH["Glutathione Depletion"]
    GSH -.->|normally protects| GPX4
    GPX4 --> FERR["Ferroptosis"]
    FERR --> ND["Neuronal Death"]
    style IRON fill:#b3e5fc,stroke:#333
    style FERR fill:#ef5350,stroke:#333,color:#fff
    style ND fill:#b71c1c,stroke:#333,color:#fff

flowchart TD
    IRON["Iron Accumulation<br/>(Ferritin, Transferrin)"] --> IRON_IN["Iron Influx ↑ (Fe²⁺)"]
    IRON_IN --> FENTON["Fenton Reaction"]
    FENTON --> ROS["Reactive Oxygen Species<br/>(Hydroxyl Radicals)"]
    ROS --> LP["Lipid Peroxidation<br/>(PUFA-containing PE)"]
    LP --> GPX4["GPX4 Inactivation<br/>(Glutathione Peroxidase 4)"]
    LP --> SYSTEM_XC["System Xc⁻ Inhibition<br/>(Cystine/Glutamate Antiporter)"]
    SYSTEM_XC -->|reduces| GSH["Glutathione Depletion"]
    GSH -.->|normally protects| GPX4
    GPX4 --> FERR["Ferroptosis"]
    FERR --> ND["Neuronal Death"]
    style IRON fill:#01334a,stroke:#333
    style FERR fill:#ef5350,stroke:#333,color:#fff
    style ND fill:#b71c1c,stroke:#333,color:#fff

Ferroptosis Overview

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

Distinction from Other Cell Death Types

Iron Metabolism in PSP

Pattern of Iron Accumulation

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

Molecular Mechanisms of Iron Dysregulation

The iron accumulation in PSP results from multiple mechanisms:

1. Dysregulated Iron Transport Proteins

• 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

2. Iron Regulatory Proteins

• 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

Clinical Correlation

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

Lipid Peroxidation in PSP

Evidence of Lipid Peroxidation

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

Lipid Peroxidation Cascades

The Fenton Reaction

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:

Lipid Radical Propagation

1. Initiation: •OH abstracts hydrogen from PUFA, forming lipid radical (L•)

2. Propagation: L• reacts with O₂ to form lipid peroxyl radical (LOO•)

3. Propagation: LOO• abstracts hydrogen from adjacent PUFA, forming lipid hydroperoxide (LOOH)

4. Amplification: LOOH + Fe²⁺ → L• + Fe³⁺ + OH⁻ (continues cycle)

Membrane Vulnerability

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

Glutathione Peroxidase 4 (GPX4)

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

Evidence of GPX4 Dysfunction in PSP

• 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

System Xc⁻

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

Ferroptosis in Specific Cell Types

Neuronal Ferroptosis

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

Microglial Ferroptosis

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

Oligodendroglial Ferroptosis

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

Molecular Cross-links with Tau Pathology

Tau-Ferroptosis Interactions

Tau pathology intersects with ferroptosis through multiple mechanisms: ^{3Loss of LGR4/GPR48 causes severe neonatal salt wasting due to disrupted WNT signaling altering adrenal zonation.2023 · J Clin Invest · PMID 36538378Open reference}

1. Tau and iron: Tau directly binds iron, potentially catalyzing Fenton reactions

2. Tau and mitochondria: Tau affects mitochondrial iron handling

3. Tau and lipids: Tau alters membrane lipid composition

4. 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

Biomarkers of Ferroptosis

Blood-Based Biomarkers

CSF Biomarkers

Neuroimaging Biomarkers

• Quantitative susceptibility mapping (QSM): Detects brain iron accumulation

• R2 mapping*: Relates to iron concentration

• MRI relaxometry: Elevated R2 in basal ganglia

Therapeutic Implications

Iron Chelation Therapy

Chelators with potential in PSP:

Antioxidant Approaches

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⁻

GPX4-Enhancing Strategies

• Selenium supplementation: Supports selenoprotein synthesis

• GSH precursors: N-acetylcysteine (NAC)

• GPX4 activators: Direct pharmacological activation

Combined Approaches

Rational combination therapies for ferroptosis in PSP:

1. Iron chelation + antioxidant: Deferasirox + CoQ10

2. Lipid peroxidation inhibition + GSH support: Ferrostatin-1 + NAC

3. Mitochondrial protection + iron modulation: CoQ10 + Deferiprone

Cross-Disease Comparison: Ferroptosis in 4R-Tauopathies

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).

Overview of Ferroptosis in Each 4R-Tauopathy

Progressive Supranuclear Palsy (PSP)

PSP demonstrates the most robust evidence for ferroptosis involvement among the 4R-tauopathies:

• Iron accumulation: Marked iron deposition in the globus pallidus internus, subthalamic nucleus, and substantia nigra pars reticulata (Gomez et al., 2021)

• Lipid peroxidation: Elevated 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and F₂-isoprostanes in brain tissue and CSF

• GPX4 dysfunction: Reduced GPX4 expression in substantia nigra and globus pallidus

• System Xc⁻ alterations: Decreased SLC7A11 expression affecting glutathione synthesis

Corticobasal Degeneration (CBD)

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

Argyrophilic Grain Disease (AGD)

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

Globular Glial Tauopathy (GGT)

GGT presents unique ferroptosis considerations due to its predominant glial pathology:

• Iron accumulation: White matter iron deposition corresponding to regions of globular oligodendroglial inclusions (GOIs) (Ahmed et al., 2013)

• Oligodendroglial vulnerability: High lipid content in oligodendrocytes makes them particularly susceptible to ferroptosis

• Myelin degeneration: Iron-catalyzed lipid peroxidation may contribute to the severe white matter loss characteristic of GGT

• Astrocytic involvement: Globular astroglial inclusions (GAIs) may show iron-related stress

FTDP-17 (MAPT Mutations)

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

Comparative Table: Ferroptosis Markers Across 4R-Tauopathies

Legend: +++ = strong, ++ = moderate, + = mild, ? = unknown, ↓ = decreased

GPX4 Alterations Across 4R-Tauopathies

Glutathione peroxidase 4 (GPX4) is the central enzymatic defender against ferroptosis. Its status varies across 4R-tauopathies: ^{4Assessment of soil-soil solution distribution coefficients of global fallout (237)Np and (239)Pu in Japanese upland soils.2023 · J Environ Radioact · PMID 37454645Open reference}

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

ACSL4 in 4R-Tauopathies

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-Mediated Ferritinophagy in 4R-Tauopathies

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

1. NCOA4 binds ferritin (FTH1/FTL complex) in the cytosol

2. Autophagy receptors (e.g., NBR1) deliver the complex to autophagosomes

3. Lysosomal degradation releases iron (Fe²⁺) into the cytosol

4. 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

Lipid Peroxidation Patterns Across 4R-Tauopathies

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

Therapeutic Implications

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

Research Directions

Unresolved Questions

1. Primary vs. secondary: Is ferroptosis a primary driver or downstream consequence?

2. Cell-type specificity: Which cell types undergo ferroptosis in each 4R-tauopathy?

3. Tau intersection: How does tau pathology influence ferroptosis susceptibility?

4. Therapeutic timing: When in disease course is ferroptosis most relevant?

5. ACSL4 role: What is the precise contribution of ACSL4 to 4R-tauopathy ferroptosis?

6. Ferritinophagy dynamics: How does NCOA4-mediated iron release vary across diseases?

Emerging Research Areas

• 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

Cross-Disease Conclusions

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. ^{5Brief Report: Impact of Anti-Cancer Treatments on Outcomes of COVID-19 in Patients With Thoracic Cancers: A CCC19 Registry Analysis.2024 · Clin Lung Cancer · PMID 38744613Open reference}

Conclusions

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.