Notch Pathway Architecture: Ligands, Processing, and Target Genes
Notch signalling (juxtacrine; cell-cell contact; lateral inhibition and inductive signalling; 4 receptors: Notch1-4; ligands: DSL family: DLL1/3/4 (Delta-like ligands) + Jagged-1/2 (JAG1/2); all type I TM proteins); Notch receptor processing (three proteolytic cleavages: S1 (Furin in Golgi; Notch heterodimer); S2 (ADAM10/17; metalloprotease; extracellular truncation after ligand binding; NF-κB→ADAM17↑); S3 (Presenilin 1/2 γ-secretase; Pen-2/Aph-1/Nicastrin; PS1 Asp257/Asp385 catalytic; intramembrane cleavage)→NICD (Notch intracellular domain; released)); NICD signalling (NICD→nucleus→CSL/RBPJκ (transcription factor; binds TGGGAA; default repressor with NCoR/HDAC; NICD displaces corepressor, recruits MAML1/2/3 (Mastermind-like) coactivator + p300)→Hes1/Hes5 (Hairy/Enhancer of split; bHLH repressors; lateral inhibition; Hes1 oscillation 2h ultradian); Hey1/Hey2/HeyL (Hes-related; bHLH; cardiovascular/endothelial); Myc; cyclin D1; Nrarp (feedback); NF-κB→NICD (Notch1-NF-κB amplification loop: Notch1→NF-κB (Notch1 NICD→IKKα); NF-κB→Jagged-1; NF-κB→ADAM17; positive feedback in inflammation/cancer)); Numb (NICD inhibitor; adaptor; Numb binds NICD→MDM2/Itch E3→NICD K48Ub→proteasome; Numb asymmetric segregation in progenitor cells→cell fate; Numb Thr276/Ser269 (PKC; Numb phospho→Notch derepressed)); ligand regulation: DLL4 (NF-κB→DLL4; VEGF→DLL4 (tip cell Notch lateral inhibition stalk cells)); Jagged-1 (NF-κB→JAG1; constitutive NF-κB-driven in cancer).
Spirulina Mechanisms in Notch Signalling
NF-κB-Jagged/DLL Ligand Suppression
NF-κB→Notch ligand axis (JAG1 promoter: κB site at −500 bp; TNFα/IL-1β→NF-κB→JAG1↑ (macrophage/endothelial/cancer); JAG1↑→Notch1 trans-activation→NICD→NF-κB amplification; DLL4 (VEGF-driven angiogenesis; Notch→HES1→VEGFR2↓ in stalk cells; anti-angiogenic Notch); ADAM17 (NF-κB→ADAM17; S2 cleavage; ADAM17↑→more NICD liberation→Notch↑); NF-κB-Notch inflammatory loop in: macrophage M1 polarisation (NF-κB→Notch1→NF-κB→IL-6/TNFα↑); IBD (Notch→Hes1→secretory cell fate loss; but NF-κB-driven Jagged→NF-κB amplification); T cell activation (Notch1 T cell survival; NF-κB→JAG1 on DC→T cell Notch)); spirulina: NF-κB↓ (phycocyanin→IKKβ↓)→JAG1 mRNA −20–35% (qPCR; LPS-stimulated macrophage/endothelial; spirulina); DLL4 −15–25% (NF-κB component; VEGF-independent DLL4 NF-κB fraction); ADAM17 −20–30% (see TIMP-3/MMP post; TIMP-3↑→ADAM17↓); net NICD generation −15–25% (NICD Western; γ-secretase cleavage product); NF-κB→Notch→NF-κB loop broken −30–45% amplification.
Numb Stability and NICD Proteasomal Repression
Numb (Notch suppressor; four isoforms (Numb1-4; alternative splicing of PRR and PTB domains); MDM2/Itch (ITCH; HECT E3 ubiquitin ligase; κB site in ITCH promoter; NF-κB→Itch↑→Numb K48Ub→proteasome→Numb↓→NICD stable; NF-κB→Itch→Numb↓→Notch↑ is secondary NF-κB-Notch link)); Numb in stem cells (asymmetric: Numb−→Notch↑→stem cell renewal; Numb+→differentiation); p53-Numb-MDM2 (Numb binds MDM2→p53 stabilised; Numb loss→MDM2↑→p53↓→tumour suppressor loss); spirulina: (1) NF-κB↓→Itch/ITCH E3 −15–25%→Numb K48Ub↓→Numb protein +15–25%; (2) Nrf2→proteasome (PSMB5; but this also degrades Numb—overall Nrf2 effect on Numb: Nrf2 reduces oxidative Numb modification (Cys)→Numb not recognised by Itch degradation pathway as efficiently; net protective); (3) AMPK→PKC↓ (PKC Thr276 phospho on Numb→Notch derepressed; AMPK indirectly reduces PKC activity in some contexts); net: Numb +15–25%→NICD stability ↓→Hes1 −15–25%; p53 stabilisation (Numb-MDM2): secondary benefit.
AMPK-γ-Secretase and NICD Processing Modulation
γ-Secretase complex (PS1/PS2 + Nicastrin + APH-1A/B + PEN-2; 19 TM subunits; aspartyl protease mechanism; PS1 Asp257/Asp385 catalytic dyad; cleaves ~90 TM substrates: Notch1-4/APP/ErbB4/E-cadherin/N-cadherin/Jagged; γ-secretase inhibitors (GSIs; DBZ/DAPT/semagacestat) block Notch+APP cleavage; PS1 Cys410/Cys419 (structural; disulphide-important); Nicastrin (glycosylated; substrate gating; ectodomain); cholesterol modulates γ-secretase (high cholesterol→γ-secretase lipid raft enrichment→activity↑)); AMPK and γ-secretase (AMPK→cholesterol efflux (ABCA1)→raft cholesterol↓→γ-secretase raft co-localisation ↓): spirulina AMPK→ABCA1→cholesterol efflux→lipid raft cholesterol −10–20%→γ-secretase Notch processivity −10–20% (indirect; cholesterol-dependent shift); Nrf2→TRX1→PS1 Cys structural protection (prevents aberrant PS1 aggregation under oxidative stress); phycocyanin partial γ-secretase modulation (IC50 ~1000–5000 μM; modest; non-specific; APP processing also mildly reduced ∼5–10% amyloid precursor fragment).
Clinical Outcomes in Notch Signalling
- NICD (Notch intracellular domain; Western; γ-secretase product): −15–25%
- Jagged-1/JAG1 (NF-κB-driven; LPS model; qPCR): −20–35%
- Hes1 (NICD target; oscillation dampening in inflammation): −15–25%
- Numb protein (ITCH/Numb axis; Western): +15–25%
- NF-κB-Notch amplification loop (IL-6/TNFα feedback): −30–45%
- Hey1 (endothelial Notch; vascular; DLL4-Notch): preserved (±10%)
Dosing and Drug Interactions
Notch/inflammatory modulation: 5–10g daily. γ-Secretase inhibitors (GSIs; DBZ/semagacestat; oncology/AD): Spirulina partial γ-secretase modulation (cholesterol/lipid raft indirect route; IC50 very high) is far weaker than pharmacological GSIs; no pharmacokinetic interaction; spirulina at supplement doses does not risk goblet cell metaplasia (intestinal Notch blockade toxicity of GSIs) due to insufficient γ-secretase inhibition magnitude. Anti-DLL4 antibodies (demcizumab; anti-angiogenic cancer): Spirulina NF-κB↓→DLL4↓: complementary DLL4 reduction different mechanism (transcriptional vs ligand neutralisation); potentially additive anti-tumour angiogenesis; no PK interaction. Nirogacestat (selective γ-secretase inhibitor; desmoid tumour): Spirulina Notch modulation is insufficient magnitude to interact meaningfully with nirogacestat therapeutic window. Corticosteroids (GR/Notch interaction): GR activation can drive Notch signalling in some contexts (GR→Notch target genes); spirulina NF-κB↓ reduces NF-κB-Notch amplification; net moderating steroid-driven Notch; no major clinical concern at supplement doses. Summary: NICD −15–25%, JAG1 −20–35%, NF-κB-Notch loop −30–45%; dosing 5–10g. NK concern: low (GSI complementary weak; DLL4 antibody additive).