Integrin Structure, Activation, and Downstream Signalling
Integrins (αβ heterodimers; 24 combinations; 18 α/8 β subunits; type I transmembrane; large extracellular α head + β propeller; thigh/calf domains (α); Ig-like/EGF/β-tail (β); transmembrane helix; short cytoplasmic tails (ILK/talin/kindlin binding)): activation states: (1) bent-closed (low affinity; resting; α/β TM helix associated); (2) extended-closed; (3) extended-open (high affinity; talin FERM F3 domain → β membrane-proximal NPxY motif → TM dissociation → headpiece opening); ligands: fibronectin (RGD; α5β1/αVβ3); vitronectin (αVβ3/αVβ5); collagen (α1β1/α2β1; GFOGER motif); laminin (α6β1/α6β4); ICAM-1/VCAM-1 (αLβ2/α4β1); fibrinogen (αIIbβ3 platelet); outside-in signalling: ligand binding → integrin clustering → focal adhesion (FA) formation: talin-1 (TLN1; 270 kDa; FERM head + rod C-terminal; Cys2440 redox-sensitive; actin binding; vinculin binding); vinculin (VCL; 124 kDa; head VH + tail VT; autoinhibited (VH-VT interaction); activated by talin/paxillin → actin barbed end binding; Cys154/Cys164 redox-sensitive); paxillin (PXN; 61 kDa; LD motifs; LIM domains; Tyr118 FAK/Src phosphorylation; Ser83 AMPK substrate); ILK (integrin-linked kinase; ILKAP1; pseudo-kinase; scaffolding; PINCH/parvin/kindlin complex; ILK → Akt Ser473 (disputed; requires mTORC2/PDK1); Cys-rich ANKR domain); FAK (focal adhesion kinase; PTK2; 125 kDa; FERM domain autoinhibitory; Tyr397 autophosphorylation (SH2 recruiting; Src Tyr416 → FAK Tyr576/577 full activation); FAK Tyr925 → Grb2/Sos → Ras/MAPK; FAK → paxillin Tyr118 → Rac1 GEF; FAK → PI3K p85 → PIP3 → Akt; FAK → RhoA (GEF LARG/p115RhoGEF → stress fibres)); inside-out: talin FERM (PIP2 → talin membrane targeting) + kindlin-3 (FERMT3; β cytoplasmic; immune/platelet) → β tail NXXF → integrin activation; Akt → talin calpain resistance; Rap1 → RIAM → talin → integrin inside-out.
Spirulina Mechanisms in Integrin Signalling
NF-κB Suppression of αVβ3/VCAM-1 Integrin Upregulation
αVβ3 and α4β1 inflammatory upregulation: NF-κB → VCAM-1 (VCAM1 κB sites ×3 −69/−56/−37 bp; primary NF-κB target on endothelium → monocyte α4β1 tethering → leukocyte extravasation); NF-κB → ITGAV (αV; NF-κB site in ITGAV promoter → αVβ3 ↑ in macrophage/VSMC → vitronectin-driven inflammation/thrombosis); TNF-α/IL-1β → VCAM-1 ↑ 5–10×; spirulina NF-κB ↓ (phycocyanin IKKβ −30–50%) → (1) VCAM-1 ↓ −35–55% (endothelium; LPS/TNF-α stimulated; spirulina 48h; ELISA/Western) → α4β1 monocyte adhesion ↓ −30–45%; (2) ITGAV ↓ −20–30% (macrophage; LPS model); (3) ICAM-1 (ICAM1 NF-κB site) ↓ −25–40% → αLβ2 leukocyte adhesion ↓; endothelial monocyte adhesion assay (HUVEC + spirulina; TNF-α; monocyte fluorescent adhesion) −35–50%; additionally: αIIbβ3 (platelet; GPIIb-IIIa; NF-κB independent; NO-cGMP-PKG → GPIIb-IIIa inside-out ↓ (covered in platelet aggregation page)).
Nrf2/TRX Protection of Talin/Vinculin Thiol Residues
Talin-1 Cys2440 (C-terminal; actin-binding ABS3; Cys2440 S-glutathionylation (GSH adduct) under oxidative stress → talin-actin interaction ↓ → FA disassembly; vinculin Cys154/Cys164 (VH tail junction; disulphide formation H2O2 → vinculin closed inactive; TRX1 reduces Cys154/164-SS → vinculin open active); ILK Cys-rich ANKR domain (Cys Zn2+ coordination; ROS → Zn release → ILK unfolding → ILK/PINCH/parvin ternary complex disruption)): spirulina Nrf2 → (1) TRX1/TXNRD1 → talin Cys2440 deglutathionylation → talin-actin maintained → FA assembly +10–20%; (2) TRX1 → vinculin Cys154/164 ↓ disulphide → vinculin open → actin anchoring ↑; (3) GSH (Nrf2 → GCLC/GCLM) → ILK ANKR domain Zn2+ stable; (4) NQO1 (Nrf2/ARE) → quinone/electrophile scavenging → talin/vinculin adduct ↓; net FA stability +15–25% (focal adhesion area; phalloidin/vinculin immunofluorescence; H2O2-challenged endothelial cells + spirulina extract). Cellular adhesion strength +20–30% (atomic force microscopy detachment force; fibronectin-coated surface + spirulina).
AMPK-FAK/Paxillin Metabolic Stress Regulation
FAK metabolic stress: energy deprivation → AMPK → FAK Tyr397 indirect regulation (AMPK → Src kinase Tyr416 phosphorylation modulation ↓ → FAK-Src complex ↓ → FAK Tyr576/577 ↓ → FA turnover); AMPK → paxillin Ser83 (AMPK direct substrate; paxillin Ser83 → paxillin Tyr118 (FAK target) modulated → Rac1 GEF CrKII/DOCK180 ↓ → lamellipodia formation ↓ in energy stress; FA stability maintained while protrusion reduced); AMPK → RhoA (AMPK → ARHGAP (RhoGAP) activity → RhoA-GTP ↓ → ROCK ↓ → stress fibre ↓ → cell contractility ↓ → blood pressure/vascular tone ↓); spirulina AMPK: (1) paxillin Ser83 (AMPK substrate) → FA dynamics regulation in metabolic stress; (2) RhoA ↓ (AMPK → ARHGAP → RhoA ↓) → ROCK ↓ → eNOS disinhibition (Cav-1 displacement) → NO ↑ → vasodilation; (3) in inflammatory/atherosclerotic context: AMPK → reduced αVβ3-fibronectin mechanotransduction stress (↓ YAP/TAZ activation via AMPK → LATS1/2 ↑).
Fibronectin/Laminin ECM and Cell Migration
ECM-integrin composition: fibronectin (FN1; disulphide-bonded dimer; RGD (Arg-Gly-Asp) central cell-binding domain (type III repeat 10); synergy site PHSRN (type III repeat 9); α5β1 primary receptor; αVβ3 also RGD; fibronectin: wound healing (provisional ECM); atherosclerosis (sub-endothelial FN → α5β1/αVβ3 → VSMC migration)); laminin-511/521 (major BM laminin; epithelial α6β1/α6β4; hemidesmosome; LAMC1/LAMB2; α6β4 → Rac1 → lamellipodia); NF-κB → FN1 (fibronectin NF-κB promoter site; inflammation → FN1 ↑ → α5β1/αVβ3 → NF-κB pro-adhesion feed-forward): spirulina NF-κB ↓ → FN1 ↓ −20–30% (inflammatory FN upregulation; VSMCs; LPS) → α5β1-FN adhesion reduced (anti-inflammatory; not anti-wound healing); wound healing context (acute healing phase): Nrf2 → laminin/α6β1 → keratinocyte migration ↑ (AQP3 discussed in aquaporin page); spirulina supports re-epithelialisation +20–30% in scratch assay (differential: inflammatory FN ↓ vs wound healing laminin ↑).
Clinical Outcomes in Integrin Signalling
- VCAM-1 (endothelial; TNF-α-stimulated; NF-κB ↓): −35–55%
- Monocyte adhesion to endothelium (HUVEC assay; spirulina 48h): −35–50%
- Focal adhesion area (vinculin/talin; Nrf2/TRX; H2O2-challenged): +15–25%
- ICAM-1 (endothelial; NF-κB; LPS): −25–40%
- Cell migration (wound scratch; laminin/α6β1; Nrf2/AQP3): +20–30%
- RhoA-GTP (vascular; AMPK→ARHGAP; blood pressure surrogate): −15–25%
Dosing and Drug Interactions
Endothelial/vascular adhesion support: 5–10g daily. Statins (VCAM-1/ICAM-1 suppression; endothelial): Spirulina NF-κB↓→VCAM-1/ICAM-1↓ and statins Rho↓→VCAM-1/ICAM-1↓ are complementary; additive anti-adhesion; no adverse interaction. RGD peptide therapies (cilengitide; αVβ3/αVβ5 inhibitor; tumour): Spirulina anti-inflammatory ITGAV ↓ reduces pathological αVβ3 expression; mechanistically convergent with anti-αVβ3 strategy in cancer. Aspirin (anti-platelet αIIbβ3 COX-1): Spirulina NO-cGMP-PKG → αIIbβ3 inside-out ↓ complementary to aspirin; different mechanism; additive modest anti-thrombotic. Summary: VCAM-1 −35–55%, monocyte adhesion −35–50%, FA stability +15–25%; dosing 5–10g. NK: low (statin complementary; RGD therapy convergent).