Klotho

Klotho is an endogenous human protein first described by Kuro-o et al. in Nature in 1997. Mice with a deletion in the klotho gene die at 8 to 9 weeks with accelerated aging, vascular calcification, osteopenia, sarcopenia, skin atrophy, infertility, and pulmonary emphysema, while wild-type controls live around two years [1]. Mice engineered to overexpress klotho live 20 to 30 percent longer than wild-type controls, and adult-onset klotho gene therapy in mice adds around 20 percent lifespan [2].

In humans, plasma alpha-Klotho peaks in young adulthood and declines with age; at age 80 levels are typically 50 to 60 percent of young-adult values, and decline is faster in chronic kidney disease [2]. The KL-VS genetic variant that raises klotho expression is associated with longer life and better cognitive function in some observational cohorts [2]. Higher plasma klotho correlates with longer telomeres, lower arterial stiffness, and better cognitive scores in older adults. No causal human interventional lifespan data exist.

Two Phase 1 trials started in 2025-2026. A UCSF trial led by Dena Dubal is testing a single low-dose subcutaneous injection of klotho protein in healthy older adults, with cognitive function as the primary endpoint [3]. Klothea launched trial AKL003 in February 2026, a randomized, double-blind, placebo-controlled Phase 1 study of alpha-Klotho mRNA in a lipid nanoparticle, N=21 healthy adults age 25-75, with dose escalation and repeat dosing [4]. Both trials monitor phosphate, calcium, FGF23, and anti-drug antibodies. Readouts are expected in 2026-2027 [3][4]. A separate Minicircle plasmid-based klotho gene therapy is offered outside the United States at partner clinics and has no peer-reviewed clinical data as of mid-2026 [4].

Mechanism: klotho is a coreceptor for FGF23, regulates phosphate and vitamin D metabolism, and modulates insulin and IGF-1 signaling. In mice, recombinant klotho at about 10 microgram/kg subcutaneously improves synaptic plasticity, spatial memory in the Morris water maze, and hippocampal long-term potentiation within hours to days of a single dose, an effect mediated by NMDA receptor signaling through GRIN2B [2]. Klotho overexpression reduces cellular senescence, increases FOXO3A target-gene expression, lowers IL-6 and TNF-alpha, and reduces amyloid pathology in Alzheimer mouse models [2].

Safety concerns are theoretical for now. Klotho modulates Wnt, IGF-1, and growth-factor signaling, so the cancer relationship is not settled. Pharmacologically elevated klotho could alter phosphate excretion, serum calcium, and active vitamin D through 1-alpha-hydroxylase regulation. Both Phase 1 trials are specifically powered to detect anti-drug antibody formation and other immune endpoints [3][4]. Acute rodent safety at studied doses is described as benign, and long-duration overexpression mice show no excess mortality [2].

The plain takeaway: klotho has strong preclinical support for extending lifespan and improving cognition in mice, and there is no approved klotho therapy for any indication. The first two Phase 1 human safety trials are running; expect readouts in 2026-2027. Retail supplements do not raise circulating klotho protein in any published trial.