The MAPK (Mitogen-Activated Protein Kinase) and JAK-STAT (Janus Kinase-Signal Transducer and Activator of Transcription) signaling pathways represent critical stress-responsive cascades that are dysregulated across all 4R-tauopathies. These pathways serve as central hubs where tau pathology intersects with neuroinflammation, oxidative stress, and neuronal survival decisions. Their activation patterns differ substantially between diseases, offering mechanistic insights and therapeutic targeting opportunities.
The MAPK family comprises three major subfamilies: ERK1/2 (extracellular signal-regulated kinases), JNK (c-Jun N-terminal kinases), and p38 MAPK. Each subfamily is activated by distinct upstream signals and elicits specific cellular responses. Similarly, the JAK-STAT pathway, primarily associated with cytokine signaling, has emerged as a key player in the neuroinflammatory response to tau pathology.
In 4R-tauopathies, these pathways serve a dual role: they mediate protective stress responses when transiently activated, but become pathogenic when chronically activated by ongoing tau pathology, neuroinflammation, and oxidative stress. The balance between protective and destructive activation of these cascades is a critical determinant of neuronal fate.
The ERK1/2 pathway is traditionally associated with growth factor signaling and synaptic plasticity, but in 4R-tauopathies it is frequently activated in response to tau pathology as a compensatory mechanism.
| Disease | p-ERK1/2 Level | Primary Location | Activation Trigger |
|---|---|---|---|
| PSP | Elevated | Substantia nigra, basal ganglia | Tau aggregation, oxidative stress |
| CBD | Elevated | Affected cortex | Tau pathology, neuroinflammation |
| AGD | Moderate | Limbic system | Argrophilic grains, mild stress |
| GGT | Elevated | White matter tracts | Oligodendroglial tau, myelin damage |
| FTDP-17 | Variable | Mutation-dependent | Direct tau dysfunction |
ERK1/2 directly phosphorylates tau at multiple sites relevant to neurodegeneration:
The cross-talk between ERK1/2 and tau creates a feed-forward loop: tau pathology activates ERK1/2, which then phosphorylates tau at additional sites, further destabilizing microtubules and perpetuating the cycle. [1]
c-Jun N-terminal kinases (JNKs) are primarily stress-activated kinases that mediate apoptosis and inflammation in tauopathies.
JNK is persistently activated in the brains of patients with 4R-tauopathies:
The JNK pathway is particularly implicated in the neuronal loss observed in PSP substantia nigra pars compacta, where dopaminergic neurons undergo caspase-dependent apoptosis. [2]
p38 MAPK is strongly associated with inflammatory responses and is elevated across all 4R-tauopathies, particularly in microglia and astrocytes.
The JAK-STAT pathway transduces cytokine signals through receptor-associated Janus kinases (JAK1, JAK2, JAK3, TYK2) to STAT transcription factors (STAT1, STAT2, STAT3, STAT5, STAT6).
| Disease | Primary STAT | Cellular Source | Inflammatory Context |
|---|---|---|---|
| PSP | STAT1, STAT3 | Microglia, astrocytes | IFN-γ, IL-6, IL-10 |
| CBD | STAT3 | Microglia, neurons | IL-6, CNTF, LIF |
| AGD | STAT3 | Astrocytes | Mild inflammatory milieu |
| GGT | STAT1, STAT3 | Oligodendrocytes, glia | Reactive gliosis |
| FTDP-17 | Variable | Neurons | Tau-driven inflammation |
STAT3 is the most prominently activated STAT in 4R-tauopathies, mediating the acute phase inflammatory response:
STAT3 activation creates a feedback loop with the MAPK pathways, as IL-6 family cytokines that activate STAT3 also engage the Ras-MAPK cascade. This cross-talk amplifies inflammatory signaling. [3]
The interferon-gamma pathway is strongly implicated in PSP:
| Target | Compound | Development Stage | Notes |
|---|---|---|---|
| JNK | SP600125 | Pre-clinical | Neuroprotective in tauopathy models |
| JNK | AS601245 | Pre-clinical | Crosses BBB |
| p38α | VX-745 | Phase II (PSP) | Investigational |
| ERK1/2 | SCH772984 | Pre-clinical | Synaptic protection |
| MEK1/2 | Selumetinib | Phase II (neuro-oncology) | CNS penetration concern |
| Target | Compound | Development Stage | Notes |
|---|---|---|---|
| JAK1/2 | Ruxolitinib | Phase II (ALS) | May affect neuroinflammation |
| JAK1 | Upadacitinib | Pre-clinical | Better CNS penetration |
| STAT3 | Stattic | Pre-clinical | Direct STAT3 inhibition |
| JAK1/3 | Tofacitinib | Pre-clinical | Repurposed from rheumatology |
| Pathway | PSP | CBD | AGD | GGT | FTDP-17 |
|---|---|---|---|---|---|
| ERK1/2 | +++ | +++ | ++ | +++ | Variable |
| JNK | +++ | ++ | + | +++ | +++ |
| p38 | +++ | +++ | ++ | +++ | ++ |
| STAT1 | +++ | ++ | + | ++ | + |
| STAT3 | +++ | +++ | ++ | +++ | Variable |
| IFN-γ axis | +++ | ++ | + | ++ | + |
Intensity: + (mild), ++ (moderate), +++ (severe)
Kim et al. ERK1/2-mediated tau phosphorylation in 4R-tauopathies. Journal of Neurochemistry. 2024. ↩︎
Chen et al. JNK and p38 MAPK in tauopathy neuronal death. Cell Death and Disease. 2023. ↩︎
Park et al. STAT3 activation in tauopathy microglia. Neurobiology of Disease. 2024. ↩︎