Klotho

Overview

Klotho's discovery in 1997 by Kuro-o and colleagues created a new paradigm for aging biology. The group was studying hypertension when they identified a mouse mutant with a dramatically accelerated aging phenotype: premature arteriosclerosis, osteoporosis, emphysema, skin atrophy, and early death by 8–9 weeks. The causative mutation was in a previously unknown gene — they named it klotho, after one of the Greek Fates who spins the thread of life.

The klotho protein (also called α-Klotho to distinguish it from β-Klotho and γ-Klotho, related proteins with different functions) has since been identified as one of the most compelling anti-aging factors discovered. Conversely, klotho overexpression extends mouse lifespan by 20–30%.

Mechanism

Two Forms of Klotho

Transmembrane klotho: The full-length membrane-bound form (1,012 amino acids in humans). Acts as a co-receptor with FGFR1 for FGF23 signaling. Located primarily in kidney tubules, parathyroid glands, and choroid plexus.

Soluble klotho (sKL): Generated by α-secretase shedding of the transmembrane ectodomain, or by alternative splicing. Circulates in blood and CSF. The form most relevant to systemic anti-aging effects.

FGF23-Dependent Functions (Mineral Homeostasis)

When acting as FGF23 co-receptor:

1. FGF23 + FGFR1 + klotho → activates ERK/MAPK signaling in kidney
2. Suppresses renal phosphate reabsorption (phosphaturia) → lowers serum phosphate
3. Suppresses CYP27B1 (reduces 1,25-OH vitamin D synthesis)
4. Net effect: lower phosphate, lower active vitamin D

Hyperphosphatemia is emerging as a driver of aging phenotypes (vascular calcification, oxidative stress) — klotho's anti-phosphatemic function is thus anti-aging in this pathway.

FGF23-Independent Functions (Anti-Aging)

Soluble klotho has multiple FGF23-independent actions:

| Function | Mechanism | Effect | |----------|-----------|--------| | Nrf2 activation | Suppresses PI3K-Akt-FOXO inhibition of Nrf2 | ↑ Antioxidant defense | | Wnt inhibition | Binds Wnt ligands; prevents fibrosis | ↓ Organ fibrosis | | TGF-β inhibition | Inhibits TGF-β co-receptor | ↓ Renal/cardiac fibrosis | | TRPC1 modulation | Ion channel regulation | Cardiac protection | | FOXO activation | Insulin/IGF-1 signaling suppression | Longevity pathways |

KL-VS Polymorphism

Approximately 20% of humans carry one copy of the KL-VS variant (a haplotype with F352V and C370S substitutions). Heterozygous carriers have ~10–16% higher circulating klotho, better cognitive function with aging, and lower cardiovascular risk in population studies. Homozygous carriers, paradoxically, show decreased klotho (possibly due to protein misfolding). This human natural experiment provides compelling evidence for klotho's aging-protective role.

Ways to Increase Endogenous Klotho

Since exogenous recombinant klotho remains experimental, research on klotho-boosting approaches is active:

• Exercise (acute aerobic exercise transiently raises serum klotho)
• Vitamin D status (adequate levels support klotho expression)
• Caloric restriction (modest evidence)
• PPAR-γ agonists (in animal models)
• Reducing phosphate intake (dietary)