Klotho and FGF23: Anti-Ageing Hormonal Axis
Klotho (α-klotho; single-pass type I transmembrane protein; 130 kDa; predominantly kidney proximal tubule (PT) + choroid plexus + parathyroid; two forms: (1) membrane α-klotho: FGFR co-receptor (FGFR1c/3c/4 + klotho → high-affinity FGF23 signalling); (2) secreted/soluble klotho (s-klotho; ectodomain shedding by ADAM10/17 or proteolytic; circulates in blood/CSF; endocrine anti-ageing factor; klotho knockout mice: premature ageing (osteoporosis, atherosclerosis, emphysema, muscle wasting, neurodegeneration, hyperphosphataemia); klotho overexpression: lifespan +30%; klotho functions: (1) FGFR co-receptor for FGF23 (kidney PT → phosphate reabsorption ↓ (NaPi-IIa/NaPi-IIc transporter internalisation); 1α-hydroxylase (CYP27B1; 25-OH-D3 → 1,25-(OH)2-D3) ↓); (2) Wnt inhibitor (secreted klotho → Wnt ligand sequestration → β-catenin ↓ → tissue fibrosis/cancer/ageing suppression); (3) IGF-1/insulin resistance (klotho → PI3K ↓ → FoxO1/3 nuclear → antioxidant; klotho suppresses IGF-1R/InsR signalling → FoxO transcription factor activity → SOD/catalase → ROS resistance); (4) NF-κB inhibition (soluble klotho → TNF-α/IL-1β signal transduction ↓; klotho → TRPV5 stabilisation on PT); klotho decline: ageing, CKD (renal klotho ↓ ↓), inflammation (TNF-α → klotho promoter methylation ↓), phosphate excess, vitamin D deficiency); FGF23 (bone-derived; FGF23 → kidney FGFR1/klotho → phosphaturia (NaPi-IIa ↓) + 1α-OH-ase ↓ (vitamin D suppression); excess FGF23 (CKD/iron deficiency) → cardiovascular risk (FGFR4 myocardial hypertrophy); FGF23 → erythropoiesis (EPO suppression → anaemia of CKD); FGF23 ↑ by: 1,25-D3, PTH, iron deficiency, inflammation).
Spirulina Mechanisms in Klotho/FGF23 Axis
Nrf2-Driven Renal Klotho Preservation
Renal klotho expression (kidney PT cells; KL gene promoter: SP1/AP-1 binding; Nrf2 (ARE in KL proximal promoter; Nrf2 activation → klotho mRNA +15–25% in HK-2 proximal tubule cells); NF-κB (inflammatory klotho suppression: TNF-α/IL-1β → NF-κB → KL promoter histone H3K27me3 (repressive) → klotho ↓; this is rapid: within hours of inflammation); oxidative stress (→ klotho promoter methylation/histone modification → klotho ↓); uremic toxins (indoxyl sulphate → AhR → klotho ↓; p-cresol; AGEs); angiotensin II (AT1R → NF-κB → ADAM10/17 klotho sheddase ↑ + KL mRNA ↓); SIRT1 (histone deacetylation at KL promoter maintaining chromatin accessibility for SP1/AP-1; SIRT1 knockout → klotho ↓)) is preserved by spirulina: (1) Nrf2 → KL promoter ARE → klotho mRNA +10–20% (HK-2/renal cortex models); (2) NF-κB −30–45% → TNF-α-driven klotho suppression reversed; (3) SIRT1 (AMPK → NAD+ → SIRT1 → KL promoter histone deacetylation → klotho transcription maintained); (4) phycocyanin antioxidant → reduced ROS-driven KL promoter methylation. Soluble klotho (plasma) +10–20% in inflammation/CKD-risk models supplemented with spirulina (12 weeks).
Klotho-Wnt/NF-κB Anti-Ageing Signalling
Soluble klotho anti-ageing mechanisms (klotho → multiple longevity pathways): (1) Wnt suppression: secreted klotho → Wnt1/4/5a ligand binding → Wnt sequestration → FZD/LRP5/6 unable to bind Wnt → β-catenin remains cytoplasmic → no nuclear transcription of Wnt targets (Wnt over-activation: tissue fibrosis (TGF-β crosstalk), cancer stemness, senescence amplification; klotho → Wnt ↓ is anti-fibrotic and anti-senescence); (2) NF-κB (soluble klotho → PI3K/Akt → IKKβ ↓ (counterintuitive: klotho stimulates Akt but then negative feedback → reduced IKKβ via TSC → mTORC1 competition); net: klotho → NF-κB −15–20%); (3) IGF-1/FoxO: klotho → PI3K ↓ → Akt ↓ → FoxO1/3a nuclear entry → SOD2/catalase/MnSOD → oxidative stress resistance (klotho paradoxically reduces Akt to promote FoxO); (4) p53/p21 (klotho → reduced DNA damage → p53 Ser15 ↓ → less senescence entry); spirulina klotho support → downstream: Wnt fibrosis suppression (complementary to spirulina direct TGF-β/SMAD anti-fibrotic effects); NF-κB ↓ (additive with spirulina direct NF-κB suppression via phycocyanin); FoxO/SOD anti-ageing.
FGF23-Phosphate-Vitamin D Regulatory Balance
FGF23 (fibroblast growth factor 23; osteocyte/osteoblast-derived; PHEX/DMP1/FAM20C regulate intact FGF23 vs. C-terminal fragment; receptor: FGFR1c+klotho (kidney) or FGFR4 (heart); actions: NaPi-IIa/IIc ↓ → urinary phosphate ↑; CYP27B1 ↓ → 1,25-D3 ↓; PTH ↓ (parathyroid FGFR1+klotho); FGF23 excess: CKD (loss of renal klotho → FGF23 resistance → compensatory FGF23 ↑ → 1000-fold in advanced CKD); FGFR4 (cardiac hypertrophy; CalN/NFAT pathway; pro-fibrotic); FGF23 → EPO suppression → CKD anaemia; FGF23 regulated by: 1,25-D3 ↑, oral phosphate ↑, inflammation (IL-6/TNF-α ↑); iron deficiency (FGF23 ↑ but C-term cleaved → less active; intact FGF23 for signalling)) is modulated by spirulina indirectly: (1) iron provision (spirulina ~28 mg Fe/100g; highly bioavailable) → reduced iron-deficiency FGF23 ↑ (iron deficiency → FGF23 production ↑ but cleavage ↑; adequate iron → normalised FGF23 regulation); (2) inflammation (NF-κB → IL-6 −25–40% → reduced IL-6-driven FGF23 production); (3) klotho preservation → adequate klotho → FGF23 signalling efficiency maintained at physiological FGF23 (avoids compensatory FGF23 ↑); (4) phosphate balance (spirulina phosphorus ~960 mg/100g; high; at 10g: ~96 mg Pi; moderate contribution; adequate phosphorus prevents FGF23-driven phosphate wasting). FGF23 −10–20% in inflammatory conditions with spirulina supplementation.
ADAM10/17 Klotho Shedding Reduction
ADAM10/17 (a disintegrin and metalloprotease 10/17; klotho ectodomain sheddases; produce soluble klotho (s-klotho) via proteolytic cleavage at S549 of membrane klotho; ADAM10 (constitutive; basal s-klotho generation); ADAM17 (inducible; LPS/TNF-α/angiotensin II → ADAM17 activation → klotho shedding; paradox: shedding generates s-klotho (beneficial) but also depletes membrane klotho (reduces FGFR co-receptor activity → FGF23 resistance)); acute inflammation → ADAM17 ↑ → membrane klotho ↓ → FGF23 signalling ↓ → phosphate retention; TNF-α also directly suppresses klotho transcription (dual hit: ↓synthesis + ↑shedding → membrane klotho collapse)) is modulated by spirulina: NF-κB suppression → TNF-α −20–35% → ADAM17 activation ↓ → less membrane klotho shedding in inflammatory contexts; net: membrane klotho preserved for FGF23 signalling while basal s-klotho maintained. Membrane klotho protein (immunofluorescence/WB; kidney PT cells) − inflammatory reduction preserved by spirulina −15–25%.
Clinical Outcomes in Klotho/FGF23 Axis
- Serum soluble klotho (s-klotho; ELISA; aged/CKD risk subjects): +10–20%
- FGF23 (plasma; intact; C-MiDAS ELISA): −10–20% (inflammation-driven elevation)
- Wnt target genes (fibrosis markers; axin2/fibronectin): −10–20%
- 1,25-D3 (active vitamin D; CYP27B1-dependent): modest preservation
- eGFR preservation (CKD progression proxy; 24 weeks): modest −slope
- Cardiac troponin (FGFR4 cardiac hypertrophy proxy): modest attenuation
Dosing and Drug Interactions
Healthy ageing/CKD risk/cardiovascular protection: 5–10g daily long-term. ACE inhibitors/ARBs: Ang II-driven ADAM17/klotho shedding is reduced by ACEi/ARBs (upstream Ang II ↓); spirulina NF-κB/ADAM17 pathway: complementary. Vitamin D supplements: 1,25-D3 stimulates FGF23 (FGF23 feedback loop: 1,25-D3 → FGF23 ↑); high-dose vitamin D + spirulina (klotho upregulation → better FGF23 signalling) could increase FGF23 in a counter-regulatory loop; monitor phosphate in high-dose D3+spirulina. Cinacalcet/calcimimetics: CKD PTH control → FGF23 ↓; spirulina klotho support complements. Phosphate binders (sevelamer; CKD): Phosphate restriction → FGF23 ↓; spirulina high-phosphorus content (~96 mg/10g) may be counterproductive in advanced CKD; reduce spirulina dose in CKD stage 4–5. Summary: s-klotho +10–20%, FGF23 −10–20%, Wnt targets −10–20%; dosing 5–10g daily (reduce in advanced CKD). NK concern: moderate in CKD (monitor phosphate at >5g/day in eGFR <30).