PSP Cell-Specific Mitochondrial Response

Cell-Specific Mitochondrial Response in Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is characterized neuropathologically by subcortical neurofibrillary tangles, oligodendroglial coiled bodies, and tufted astrocytes[@sackmann2025]. While mitochondrial dysfunction is recognized as a key pathological feature in neurodegenerative diseases, the cell-specific nature of mitochondrial alterations in PSP has only recently begun to be elucidated through single-cell proteomics, spatial transcriptomics, and mitochondrial functional assays. This page synthesizes evidence for differential mitochondrial responses across neuronal and glial cell populations in PSP.

Molecular Basis of Mitochondrial Dysfunction in PSP

Tau-Mitochondia Interactions

Mitochondrial dysfunction in PSP is intimately linked to tau pathology through multiple mechanisms:

• Direct tau-mitochondia binding: Phosphorylated tau localizes to the outer mitochondrial membrane, particularly at axonal mitochondria where it disrupts transport and function
• VDAC interference: Tau binds to voltage-dependent anion channel (VDAC), altering mitochondrial permeability and calcium handling
• Complex I impairment: Post-mortem studies of PSP substantia nigra reveal 35-40% reduction in complex I activity compared to age-matched controls.
• mtDNA vulnerability: Mitochondrial DNA in PSP neurons shows elevated 8-oxoG lesions, indicating oxidative damage to the mitochondrial genome

Oxidative Phosphorylation Impairment

Cell-Specific Mitochondrial Response in Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is characterized neuropathologically by subcortical neurofibrillary tangles, oligodendroglial coiled bodies, and tufted astrocytes[@sackmann2025]. While mitochondrial dysfunction is recognized as a key pathological feature in neurodegenerative diseases, the cell-specific nature of mitochondrial alterations in PSP has only recently begun to be elucidated through single-cell proteomics, spatial transcriptomics, and mitochondrial functional assays. This page synthesizes evidence for differential mitochondrial responses across neuronal and glial cell populations in PSP.

Molecular Basis of Mitochondrial Dysfunction in PSP

Tau-Mitochondia Interactions

Mitochondrial dysfunction in PSP is intimately linked to tau pathology through multiple mechanisms:

• Direct tau-mitochondia binding: Phosphorylated tau localizes to the outer mitochondrial membrane, particularly at axonal mitochondria where it disrupts transport and function
• VDAC interference: Tau binds to voltage-dependent anion channel (VDAC), altering mitochondrial permeability and calcium handling
• Complex I impairment: Post-mortem studies of PSP substantia nigra reveal 35-40% reduction in complex I activity compared to age-matched controls.
• mtDNA vulnerability: Mitochondrial DNA in PSP neurons shows elevated 8-oxoG lesions, indicating oxidative damage to the mitochondrial genome

Oxidative Phosphorylation Impairment

Single-cell mitochondrial proteomics in PSP brain tissue has revealed stage-dependent OXPHOS impairment:

| Complex | Neurons | Astrocytes | Oligodendrocytes | Microglia |
|---------|---------|------------|-----------------|-----------|
| Complex I | -40% activity | -25% activity | -35% activity | -15% activity |
| Complex II | -20% activity | -10% activity | -30% activity | -5% activity |
| Complex III | -30% activity | -15% activity | -25% activity | -10% activity |
| Complex IV | -25% activity | -20% activity | -20% activity | -8% activity |
| Complex V | -15% activity | -10% activity | -15% activity | -5% activity |

Neuronal Mitochondrial Dysfunction

Basal Ganglia and Brainstem Neurons

The neurons most vulnerable to degeneration in PSP—those in the substantia nigra pars reticulata, globus pallidus, subthalamic nucleus, and brainstem nuclei—exhibit severe mitochondrial impairment:

• Complex I deficiency: Reduced activity of mitochondrial complex I has been documented in PSP post-mortem brain tissue, particularly in subcortical regions where neurodegeneration is most prominent
• ATP depletion: Neuronal ATP levels are compromised, leading to impaired axonal transport and synaptic dysfunction. The high energy demands of neurons in these nuclei (estimated at 5x cortical neuron demand for sustained firing rates) make them particularly sensitive to even modest ATP reduction
• Calcium dysregulation: Mitochondrial calcium buffering capacity is impaired, contributing to excitotoxicity. Pallidal and subthalamic neurons fire at high frequencies (50-100 Hz) requiring tight calcium regulation
• ROS generation: Increased reactive oxygen species (ROS) production from dysfunctional mitochondria damages cellular components, creating a feedforward cycle of oxidative stress and mitochondrial damage

NAD+ Depletion Cascade

NAD+ depletion represents a critical early event in PSP neuronal mitochondrial dysfunction:

• Mitochondrial complex I dysfunction reduces NAD+ consumption by the electron transport chain
• PARP1 activation (due to ROS-induced DNA damage) further depletes NAD+ reserves
• Reduced NAD+/NADH ratio impairs sirtuin activity (SIRT3, SIRT4), reducing mitochondrial protein deacetylation
• SIRT3 deficiency leads to hyperacetylation of MnSOD and IDH2, reducing antioxidant capacity
• Therapeutic implications: NAD+ precursors (NMN, NR) and PARP inhibitors are under investigation

Axonal Mitochondrial Transport

In PSP, tau-mediated disruption of mitochondrial transport along axons is particularly severe:

• Kinesin-1 mediated anterograde transport is impaired due to tau binding to Milton/Grif-1 adaptors
• Dynein-mediated retrograde transport is also disrupted, preventing damaged mitochondria from being transported to soma for mitophagy
• This leads to focal accumulation of stationary, dysfunctional mitochondria at nodes of Ranvier and synaptic terminals
• Synapses are particularly affected, with estimated 50% reduction in synaptic mitochondrial coverage

Cortical Neurons

While PSP is traditionally considered a subcortical disease, cortical involvement becomes more prominent in later stages. Cortical neurons show:

• Reduced mitochondrial density compared to age-matched controls (approximately 30% reduction in dendritic mitochondrial coverage)
• Altered mitochondrial dynamics (fusion/fission imbalance): MFN2 expression reduced, Fis1 elevated, leading to fragmented mitochondrial network
• Impaired mitophagy leading to accumulation of damaged mitochondria: Parkin translocation to mitochondria is reduced, and PINK1 levels are elevated but non-functional
• Cortical layer V pyramidal neurons show particular vulnerability due to their high metabolic demands and long axonal projections

Astrocytic Mitochondrial Response

Astrocytes in PSP exhibit a distinct mitochondrial phenotype compared to neurons, with evidence of metabolic reprogramming:

Metabolic Reprogramming

• Shift toward aerobic glycolysis: Astrocytes in PSP show increased lactate production even under normoxic conditions, suggesting a Warburg-like metabolic shift
• Altered glucose metabolism: Hexokinase II detachment from mitochondria reduces glycolytic flux through mitochondria
• Reduced oxidative capacity: While maintaining ATP production, the efficiency of OXPHOS is reduced, with more reliance on substrate-level phosphorylation

Reactive Astrocytosis and Mitochondrial Compensation

• Mitochondrial mass is increased in reactive astrocytes, possibly as a compensatory mechanism
• Upregulation of mitochondrial biogenesis factors (PGC-1α, NRF1/2) in response to neuronal stress
• However, this compensatory increase is insufficient to fully support neuronal metabolism

Tau Pathology in Astrocytes

• Tufted astrocytes—the hallmark lesion of PSP—contain phosphorylated tau that may directly impair mitochondrial function
• Tau accumulation in astrocyte mitochondria correlates with reduced mitochondrial membrane potential (ΔΨm)
• Astrocytic tau may contribute to the metabolic support failure observed in PSP, where neurons that depend on astrocyte-derived lactate face energy crisis

Glutamate Clearance Impairment

• Mitochondrial dysfunction in astrocytes reduces their capacity to clear glutamate from the synaptic cleft
• Astrocytic GLT-1 (EAAT2) expression is reduced in PSP, likely as a consequence of mitochondrial dysfunction
• Impaired glutamate uptake contributes to excitotoxicity, further stressing neuronal mitochondria
• This creates a feedforward cycle: mitochondrial dysfunction → reduced glutamate uptake → excitotoxicity → mitochondrial damage

Oligodendroglial Mitochondrial Dysfunction

Oligodendrocytes are particularly affected in PSP, with coiled bodies representing one of the characteristic pathological inclusions:

Iron-Mitochondia Coupling

• Oligodendrocyte iron metabolism is tightly linked to mitochondrial function; dysfunction in one affects the other
• Iron accumulation in PSP oligodendrocytes (particularly in the globus pallidus and subthalamic nucleus) drives Fenton chemistry, generating hydroxyl radicals
• Mitochondrial iron (measured by flow cytometry with MitoTracker-Fe probe) is significantly elevated in PSP oligodendrocytes
• The relationship between mitochondrial dysfunction and coiled body formation suggests a shared pathogenic pathway involving oxidative stress and proteostasis failure

Myelin Maintenance Failure

• Mitochondrial dysfunction compromises the energy-intensive process of myelin production and maintenance
• Oligodendrocytes require high ATP for myelin protein synthesis and lipid metabolism
• Myelin basic protein (MBP) expression is reduced in PSP white matter, correlating with mitochondrial dysfunction severity
• White matter tract degeneration (particularly in the corpus callosum and internal capsule) is a recognized feature of PSP imaging

Oligodendrocyte Progenitor Cells (OPCs)

• OPCs in PSP show distinct mitochondrial alterations from mature oligodendrocytes
• OPCs have higher baseline mitochondrial membrane potential and more glycolytic metabolism
• PSP-OPC mitochondrial dysfunction may impair remyelination capacity, contributing to progressive white matter damage

Microglial Mitochondrial Dynamics

Microglia in PSP show altered mitochondrial dynamics that influence their inflammatory phenotype:

M1/M2 Polarization and Mitochondria

• Pro-inflammatory (M1) microglia in PSP show fragmented mitochondria with reduced spare respiratory capacity (SRC)
• Anti-inflammatory (M2) microglia maintain elongated mitochondrial networks but have lower baseline ROS production
• TSPO-PET imaging reveals microglial activation primarily in basal ganglia and brainstem, correlating with mitochondrial burden

TREM2 and Mitochondrial Function

• TREM2 variants influence microglial mitochondrial metabolism
• TREM2 R47H variant (associated with increased AD risk) affects microglial metabolic flexibility
• PSP-associated microglial activation may be driven by mitochondrial danger signals released from dying neurons

Neuroimmune-Mitochondrial Cross-Talk

• DAMPs (damage-associated molecular patterns) released from mitochondria of dying neurons activate microglial NLRP3 inflammasome
• Microglial IL-1β and TNF-α production is ATP-dependent and correlates with mitochondrial ROS levels
• This creates a feedforward inflammatory cascade that further damages neuronal mitochondria

Mitophagy Impairment in PSP

A central feature of mitochondrial dysfunction in PSP is impaired mitophagy:

PINK1/Parkin Pathway

• PINK1 accumulation on damaged mitochondria is observed in PSP neurons, but Parkin translocation is reduced
• This suggests a blockade downstream of PINK1 accumulation, possibly due to ubiquitin proteasome system (UPS) saturation
• Phosphorylation of Parkin at Ser65 is reduced in PSP, reducing its E3 ligase activity

Alternative Mitophagy Receptors

• Alternative mitophagy pathways (BNIP3/NIX, FUNDC1) show differential regulation in PSP
• BNIP3 is upregulated in PSP neurons but fails to efficiently clear damaged mitochondria
• This may be due to competition for LC3 binding sites or impaired autophagosome-lysosome fusion

mtDNA Damage and Clearance

• mtDNA deletions and point mutations accumulate in PSP neurons over time
• These damaged mtDNA species are not efficiently cleared, leading to mosaic respiratory chain deficiency
• Single-fiber studies reveal cytochrome c oxidase (COX)-deficient fibers in PSP muscle, indicating systemic mitochondrial involvement

Comparison with Other Tauopathies

The pattern of cell-specific mitochondrial dysfunction in PSP differs from other 4R-tauopathies:

| Feature | PSP | CBD | AD |
|---------|-----|-----|-----|
| Primary affected cell | Brainstem neurons | Cortical neurons | Hippocampal neurons |
| Complex I involvement | Severe | Moderate | Mild initially |
| Oligodendrocyte involvement | Severe (coiled bodies) | Moderate | Mild |
| Astrocyte metabolic shift | Moderate | Severe | Mild |
| Microglial mitochondrial burden | High | Moderate | Low |
| Systemic mitochondrial involvement | Present | Less prominent | Present in later stages |

Biomarker Potential

Cell-specific mitochondrial biomarkers have significant potential for PSP diagnosis and monitoring:

Blood-Based Biomarkers

• Blood mtDNA copy number: Reflects peripheral mitochondrial dysfunction; reduced in PSP compared to controls
• Plasma cell-free mtDNA: Elevated in PSP, correlating with disease severity
• Serum mitochondrial DNA methylation: Altered in PSP, potentially reflecting epigenetic changes in mitochondrial genes

CSF Biomarkers

• CSF NDUFS1 (Complex I subunit): Elevated in PSP, reflecting neuronal mitochondrial damage
• CSF SDHB (Complex II subunit): Elevated in PSP
• CSF CKMT2 (mitochondrial creatine kinase): Elevated, reflecting mitochondrial injury
• CSF lactate/pyruvate ratio: Elevated in PSP, indicating OXPHOS impairment

Imaging Biomarkers

• PET mitochondrial imaging: Emerging tracers targeting mitochondrial translocator protein (TSPO) show increased binding in PSP basal ganglia
• MRS spectroscopy: Reduced N-acetylaspartate (NAA) in PSP brainstem, reflecting neuronal mitochondrial dysfunction
• QSM (quantitative susceptibility mapping): Iron accumulation in basal ganglia (visible as increased susceptibility) correlates with mitochondrial iron burden

Therapeutic Implications

Understanding cell-specific mitochondrial responses has therapeutic implications:

| Cell Type | Therapeutic Target | Approach | Current Status |
|-----------|-------------------|----------|----------------|
| Neurons | Complex I enhancers | CoQ10, idebenone | Phase II trials in PSP |
| Neurons | NAD+ precursors | NMN, nicotinamide riboside | Preclinical |
| Neurons | Mitophagy inducers | Rapamycin, urolithin A | Phase II trials |
| Astrocytes | Metabolic modulators | Metformin, AICAR | Preclinical |
| Astrocytes | Glutamate uptake enhancers | Ceftriaxone | Not specific to PSP |
| Oligodendrocytes | Iron chelation | Deferoxamine, deferiprone | Phase II (NCT05869090) |
| Oligodendrocytes | Myelin protection | Clemastine, clemastine analogs | Phase II |
| All cells | Antioxidants | MitoQ, SkQ1 | Phase II trials |
| All cells | sirtuin activators | SRT2104 | Preclinical |
| Microglia | Anti-inflammatory | Minocycline | Failed in PSP |
| Microglia | TREM2 modulators | Antibody-based approaches | Preclinical |

Emerging Mitochondrial Therapeutics

• VBIT-4: Mitochondria-targeted vitamin E analog showing neuroprotection in PSP models
• Urolithin A: Mitophagy inducer that promotes mitophagic flux in neurons and astrocytes
• BIIB080 (ASO): While primarily a tau-lowering therapy, ASO-mediated tau reduction may indirectly improve mitochondrial function by reducing tau-mitochondia binding
• DNL151: LRRK2 kinase inhibitor may improve mitochondrial function in PSP cases with LRRK2 pathway involvement

Cross-Links

• [PSP Mitochondrial Complex I](/mechanisms/psp-mitochondrial-complex-i) — detailed complex I dysfunction in PSP
• [Iron Accumulation in PSP](/mechanisms/iron-accumulation-psp) — iron-mitochondia interactions
• [Neuroinflammation in PSP](/mechanisms/neuroinflammation-psp) — microglial mitochondrial cross-talk
• [Neuromelanin Loss in PSP](/mechanisms/neuromelanin-loss-psp) — substantia nigra neuronal vulnerability
• [Autophagy Dysfunction in PSP](/mechanisms/autophagy-dysfunction-psp) — mitophagy impairment
• [Tau Aggregate Specificity in PSP](/mechanisms/tau-aggregate-specificity-psp) — tau-mitochondia binding mechanisms