Notch Signaling in CBS/PSP

Notch Signaling in CBS/PSP

Overview

Notch signaling is a highly conserved pathway that plays critical roles in neural development, adult neurogenesis, and cellular differentiation. In corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP), both classified as 4-repeat (4R) tauopathies, dysregulation of Notch signaling contributes to neuronal vulnerability and impaired repair mechanisms. This section examines Notch pathway alterations in CBS/PSP and their relationship to tau pathology. [@armstrong2020]

CBS and PSP share common pathological features of 4R tau accumulation, but exhibit distinct clinical presentations [1](https://doi.org/10.1016/S1474-4422(22)00087-0). While CBS presents with asymmetric cortical dysfunction and basal ganglia degeneration leading to apraxia, alien limb phenomena, and cortical sensory loss, PSP is characterized by vertical gaze palsy, postural instability, and axial rigidity with progressive gait disturbance. Notch signaling interacts with tau pathology through multiple mechanisms, including regulation of tau phosphorylation, modulation of neurogenesis, and control of glial cell function. Understanding these interactions may reveal novel therapeutic targets for disease modification. [@litvan2020]

Notch Signaling in CBS/PSP

Overview

Notch signaling is a highly conserved pathway that plays critical roles in neural development, adult neurogenesis, and cellular differentiation. In corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP), both classified as 4-repeat (4R) tauopathies, dysregulation of Notch signaling contributes to neuronal vulnerability and impaired repair mechanisms. This section examines Notch pathway alterations in CBS/PSP and their relationship to tau pathology. [@armstrong2020]

CBS and PSP share common pathological features of 4R tau accumulation, but exhibit distinct clinical presentations [1](https://doi.org/10.1016/S1474-4422(22)00087-0). While CBS presents with asymmetric cortical dysfunction and basal ganglia degeneration leading to apraxia, alien limb phenomena, and cortical sensory loss, PSP is characterized by vertical gaze palsy, postural instability, and axial rigidity with progressive gait disturbance. Notch signaling interacts with tau pathology through multiple mechanisms, including regulation of tau phosphorylation, modulation of neurogenesis, and control of glial cell function. Understanding these interactions may reveal novel therapeutic targets for disease modification. [@litvan2020]

The Notch pathway's role in neurodegeneration extends beyond its developmental functions. In the adult brain, Notch signaling regulates neural stem cell populations, modulates synaptic plasticity, and influences glial cell function. Dysregulation of these processes contributes to the progressive neurodegeneration observed in both CBS and PSP. [@boxer2020]

The Notch Signaling Pathway

Notch Receptors and Ligands

The Notch family includes multiple receptors and ligands with distinct expression patterns [2](https://doi.org/10.1016/j.tins.2020.09.004): [@kovacs2022]

Notch Receptors: [@williams2021]

• Notch1: Widely expressed throughout the brain, critical for neuronal function
• Notch2: Expressed in neurons and glia, important for glial development
• Notch3: Prominent in vascular cells and pericytes, affects blood-brain barrier
• Notch4: Lower expression in CNS, primarily in endothelial cells

• Delta-like (DLL1, DLL3, DLL4): Membrane-bound ligands with distinct functions
• Jagged (JAG1, JAG2): Alternative ligands with context-dependent effects

Signal Transduction

The Notch pathway involves sequential proteolytic cleavage: [@jellinger2020]

Canonical pathway steps: [@mandelkow2010]

Downstream targets: Hes (Hairy and Enhancer of Split) and Hey (Hairy/Enhancer-of-Split related with YRPW motif) transcription factors regulate genes involved in differentiation, proliferation, and survival [@mckinnon2020]

Notch in Normal Brain Function

Adult Neurogenesis

Notch signaling plays essential roles in adult neurogenesis [3](https://doi.org/10.1016/j.tins.2020.09.004):

• Neural stem cell maintenance: Notch maintains the progenitor cell pool in subventricular zone and dentate gyrus
• Neuronal differentiation: Temporal regulation of neurogenesis controls the transition from proliferation to differentiation
• Glial specification: Notch controls the choice between astrocyte and oligodendrocyte lineage

Synaptic Function

Notch contributes to synaptic plasticity through multiple mechanisms [4](https://doi.org/10.1016/j.neuroscience.2018.04.012):

• Presynaptic function: Notch regulates neurotransmitter release and vesicle cycling
• Postsynaptic density: Modulates receptor trafficking and synaptic protein synthesis
• Learning and memory: Notch activity in hippocampal neurons is required for memory consolidation
• Dendritic spine morphology: Controls spine formation and maintenance

Glial Function

Notch signaling regulates glial cell types:

• Astrocytes: Notch influences astrocyte differentiation and reactivity
• Oligodendrocytes: Controls oligodendrocyte progenitor cell proliferation and differentiation
• Microglia: Modulates microglial activation states and inflammatory responses
• Schwann cells: Peripheral nervous system myelination

Notch Dysregulation in CBS/PSP

Altered Pathway Activity

Studies suggest Notch pathway alterations in tauopathies [5](https://doi.org/10.1007/s00401-020-02171-5):

The motor cortex and basal ganglia, regions prominently affected in CBS, show particular Notch pathway alterations. Immunohistochemical studies demonstrate changes in Notch immunoreactivity in neurons with tau inclusions.

Notch-Tau Interactions

Notch signaling interacts with tau pathology in complex ways [6](https://doi.org/10.1186/s40478-014-0012-0):

• Tau phosphorylation: Notch can influence kinase pathways that phosphorylate tau
• Neurogenesis impairment: Reduced Notch signaling impairs neural repair mechanisms
• Neuronal vulnerability: Loss of Notch-mediated survival signals increases susceptibility to tau-induced death
• Synaptic dysfunction: Notch dysregulation contributes to synaptic loss

Regional Vulnerability

The pattern of Notch dysregulation in CBS/PSP follows the regional distribution of tau pathology:

• Motor cortex: Severe Notch pathway impairment in CBS
• Basal ganglia: Altered signaling in both CBS and PSP
• Hippocampus: Changes affecting memory and cognitive function
• Substantia nigra: Loss of Notch-mediated dopaminergic neuron survival

Therapeutic Implications

Targeting Notch

Therapeutic strategies targeting Notch signaling include [7](https://doi.org/10.1038/s41573-020-0089-1):

• γ-Secretase modulators: Selective pathway modulation rather than complete inhibition
• Notch antibodies: Receptor-targeted approaches
• DLL/JAG antagonists: Blocking excessive activation
• Hes/Hey inhibitors: Downstream target modulation

Clinical Considerations

Challenges in Notch-targeted therapy [8](https://doi.org/10.1016/j.tcb.2020.06.002):

• Developmental effects: Notch is essential for development; complete inhibition problematic
• BBB penetration: CNS delivery considerations for large molecules
• Selectivity: Avoiding effects on multiple Notch receptors
• Timing: Optimal intervention point may vary by disease stage

• Brain-penetrant γ-secretase modulators
• Receptor-specific antibodies
• Small molecule inhibitors of downstream targets

Cross-Links to Related Pages

• [Notch Signaling in Neurodegeneration](/mechanisms/notch-signaling-neurodegeneration) — General pathway overview
• [Notch Signaling in Parkinson's Disease](/mechanisms/notch-signaling-parkinsons) — Synucleinopathy comparison
• [Gamma-Secretase in Neurodegeneration](/mechanisms/gamma-secretase-pathway) — Proteolytic processing
• [Neurogenesis in Neurodegeneration](/mechanisms/neurogenesis-neurodegeneration) — Notch in neural stem cells
• [Synaptic Dysfunction in CBS](/mechanisms/cbs-synaptic-dysfunction) — Notch at synapses
• [4R Tauopathy Mechanisms](/mechanisms/4r-tau-cbs) — Tau isoform interactions
• [Neuroinflammation in CBS](/mechanisms/cbs-neuroinflammation) — Notch modulation of glia