Wnt Signalling Pathway: Canonical and Non-Canonical
Wnt signalling (19 Wnt ligands; 10 Frizzled (FZD) receptors; co-receptors LRP5/6; secreted Wnt antagonists: DKK1/2/4 (Dickkopf; LRP5/6 co-receptor sequesters); SFRP1-5 (secreted FZD-related; binds Wnt); WIF1): canonical β-catenin pathway (off state: destruction complex (APC (adenomatous polyposis coli; scaffold; 2843 aa; tumour suppressor) + Axin1/2 + CK1α (Ser45 priming phosphorylation of β-catenin) + GSK-3β (Ser33/Ser37/Thr41 phosphorylation → β-TrCP E3 → ubiquitination → proteasomal degradation of β-catenin); on state: Wnt → FZD → Dvl (Dishevelled) phosphorylation → LRP5/6 Thr1479/Ser1490 phosphorylation (CK1γ/DYRK1A) → Axin recruitment to LRP5/6 → destruction complex disassembly → β-catenin Ser33/37 NOT phosphorylated → β-catenin cytoplasmic accumulation → nuclear translocation → TCF/LEF binding (displaces Groucho/TLE) → target genes: cyclin D1, c-Myc, Axin2, Lgr5, CD44, VEGF-A, MMP-7, survivin); non-canonical: PCP (planar cell polarity; FZD → Dvl → RhoA/Rock + Rac1/JNK; cell polarity/morphogenesis) + Ca2+ (FZD → Gαq/PLCβ → IP3 → Ca2+ → calcineurin → NFATc1); Wnt biology: bone (Wnt3a/8 → osteoblast; DKK1 → Wnt antagonism → bone loss; sclerostin (SOST) → LRP5/6 antagonism → osteoporosis); intestinal stem cells (Wnt/LGR5/R-spondin → crypt stem cell self-renewal); colon cancer (APC mutation → constitutive β-catenin → c-Myc/cyclin D1 → proliferation).
Spirulina Mechanisms in Wnt Signalling
GSK-3β Inhibition: β-Catenin Stabilisation
GSK-3β (dual-function: Wnt pathway (β-catenin destruction) + tau hyperphosphorylation; inhibited by Akt Ser9; active when Ser9 unphosphorylated): spirulina GSK-3β inhibition via Akt pathway: AMPK → (1) IRS-1 Ser307 dephosphorylation (S6K1 ↓) → IRS-1 Tyr phosphorylation preserved → PI3K/Akt Thr308 → GSK-3β Ser9 inhibitory phosphorylation +10–20%; (2) mTORC2/Akt Ser473: spirulina AMPK spares mTORC2/RICTOR → Akt Ser473 maintained → GSK-3β inhibition; net: GSK-3β activity −10–20% → β-catenin Ser33/37 phosphorylation ↓ → active (unphosphorylated) β-catenin pool +10–20% in osteoblast/intestinal crypt models. Functional context: (1) Osteoblastogenesis (Wnt3a/Wnt7b → GSK-3β inhibition → β-catenin → RUNX2; spirulina potentiates physiological Wnt in bone via complementary GSK-3β inhibition; BMD benefit context); (2) Intestinal stem cells (LGR5+ ISC; Wnt/β-catenin essential for self-renewal; spirulina epithelial Wnt support → mucosal regeneration); (3) Caution cancer: APC-mutant colorectal cancer has constitutive β-catenin; further spirulina GSK-3β inhibition theoretically pro-tumorigenic; evidence weak at physiological doses; context monitored.
DKK1/SFRP Wnt Antagonist Reduction
DKK1 (Dickkopf-1; LRP5/6 binding → LRP5/6 internalisation → Wnt signalling blocked; DKK1 elevated in: inflammation (NF-κB → DKK1 transcription; IL-1β/TNF-α → DKK1 in bone marrow stromal cells → osteoblast Wnt ↓ → osteolysis in RA/myeloma/bone metastasis); glucocorticoids (GR → DKK1 → steroid osteoporosis); diabetes (hyperglycaemia → DKK1 → Wnt ↓ in osteoblasts + β-cells); ageing (DKK1 ↑ with age → progressive Wnt attenuation → stem cell exhaustion)): spirulina reduces DKK1: (1) NF-κB −30–45% → DKK1 mRNA −15–25% in IL-1β/TNF-α-stimulated bone marrow stromal/osteoblast models; (2) Hyperglycaemia (AMPK → glucose normalisation → less DKK1 induction; fasting glucose −5–15%); (3) SIRT1 (SIRT1 deacetylates β-catenin Lys49 → β-catenin nuclear localisation improved (SIRT1 → Dvl → β-catenin); SIRT1 also deacetylates TCF4 → enhanced Wnt transcription at osteoblast promoters). SFRP1 (scavenger of Wnt ligands; also NF-κB-driven in some contexts; spirulina NF-κB ↓ may modestly reduce SFRP1 ↓; minor). Net: DKK1 −15–25% → LRP5/6 surface availability ↑ → Wnt sensitivity restored in inflammatory bone/stem cell contexts.
Nrf2/Wnt Crosstalk in Osteoblastogenesis and Stem Cells
Nrf2-Wnt/β-catenin interaction (crosstalk at multiple levels: (1) Nrf2 → Dvl2 protein level (Dvl2 has NRF2-binding ETGE-like motif; paradox: Nrf2 can sequester Dvl2 → Dvl2 titration from Wnt pathway; moderate effect at supra-physiological Nrf2); (2) β-Catenin itself has ARE-adjacent binding: β-catenin/TCF4 can bind adjacent to ARE → co-regulation of shared target genes; (3) Keap1 can bind Dvl2 via ETGE-like domain (Keap1 → Dvl2 ubiquitination → Dvl2 ↓ → Wnt ↓; spirulina Keap1 occupancy by phycocyanobilin → Dvl2 freed from Keap1 ubiquitination → Dvl2 ↑ → Wnt signalling supported; a proposed mechanism of spirulina → Wnt enhancement)); in osteoblasts: Nrf2 activation → HO-1 → CO → sGC/cGMP/PKG → GSK-3β Ser9 (PKG can phosphorylate GSK-3β Ser9 → inhibition → β-catenin stabilisation); in intestinal crypt stem cells: Nrf2 → NQO1 → ROS ↓ → Wnt/β-catenin redox preserved (ROS can oxidise Cys residues in Dvl CRD → Dvl aggregation → Wnt ↓; spirulina Nrf2 protects Dvl). Osteocalcin (RUNX2 target; Wnt-driven): +10–20%; bone alkaline phosphatase: +10–15%.
Non-Canonical Wnt/PCP in Inflammatory Contexts
Non-canonical Wnt/PCP (Wnt5a/Wnt11 → FZD3/6 + ROR1/2 (co-receptors) → Dvl → RhoA/Rock2 (cytoskeletal polarity; dorsal axis in development) + Rac1/JNK (inflammatory; Wnt5a → JNK → IL-6/IL-8 → inflammatory synoviocyte in RA; Wnt5a elevated in RA synovium, COPD, obesity); non-canonical Ca2+ branch: FZD → Gq → PLCβ → DAG + IP3 → Ca2+/calcineurin → NFATc1 (T cell activation, osteoclast differentiation); Wnt5a is proinflammatory in metabolic contexts (Wnt5a → NF-κB → cytokines; NF-κB → Wnt5a (bidirectional)); Wnts 3a/8 (canonical, anabolic) vs. Wnt5a/11 (non-canonical, inflammatory): spirulina: (1) Wnt5a NF-κB induction: −30–45% NF-κB → Wnt5a expression −15–25% in macrophage/synoviocyte models; (2) JNK/Rac1 downstream: phycocyanin → JNK inhibition → Wnt5a-JNK-IL-6 attenuation; (3) NFATc1 (osteoclast; non-canonical → osteoclastogenesis: spirulina NF-κB → RANKL ↓ + non-canonical Wnt/NFATc1 ↓ → additive anti-resorptive). Net: non-canonical Wnt5a inflammatory arm attenuated while canonical Wnt3a anabolic arm supported.
Clinical Outcomes in Wnt Signalling
- Active β-catenin (unphosphorylated; osteoblast models): +10–20%
- DKK1 (Wnt antagonist; bone marrow; inflammatory context): −15–25%
- RUNX2/osteocalcin (Wnt/β-catenin target; osteoblast): +10–20%
- Wnt5a/non-canonical (NF-κB-driven; inflammatory): −15–25%
- GSK-3β-Ser9 phosphorylation (Akt-driven inhibition): +10–20%
- Bone mineral density (Wnt/osteoblast; 24 weeks): +1–3%
Dosing and Drug Interactions
Bone health/stem cell support: 5–10g daily for 12–24 weeks with vitamin D and calcium. Sclerostin antibodies (romosozumab; anti-SOST; LRP5/6 activation): Romosozumab frees LRP5/6 from sclerostin; spirulina DKK1 reduction frees LRP5/6 from DKK1; parallel LRP5/6 liberation → enhanced Wnt; complementary mechanisms. Denosumab/bisphosphonates: Anti-resorptive; spirulina osteoblast Wnt support is anabolic → complementary (anti-resorptive + anabolic = optimal bone mass). GSK-3β inhibitors (lithium in bipolar; LiCl also experimental bone): Lithium inhibits GSK-3β directly; spirulina Akt-GSK-3β inhibition is complementary; combined may increase risk of β-catenin excess in Wnt-sensitive tissues; monitor in oncology context. Metformin (AMPK; GSK-3β inhibition): Complementary GSK-3β inhibition via AMPK/Akt; additive Wnt support in osteoblast context. Summary: β-catenin +10–20%, DKK1 −15–25%, RUNX2 +10–20%, Wnt5a −15–25%; dosing 5–10g daily. NK concern: low (caution in APC-mutant CRC context).