Klotho usually refers to α-Klotho, a protein involved in mineral balance and studied for its connections with aging and brain function. It can remain attached to a cell membrane or circulate after its outer portion is released. Genetically increasing Klotho has prolonged life in mice, and particular administered protein preparations have improved memory-task performance in mice and aged rhesus macaques. The human studies discussed here measured the body’s own Klotho or KLOTHO gene variants observationally; they do not show that Klotho treatment improves memory or extends life.
Overview
α-Klotho is a large protein with two extracellular regions called KL1 and KL2. The membrane-associated form and its released outer region have related but distinct settings and functions. β-Klotho is a different family member that supports different hormone signals. A vial or study described only as “Klotho” needs a species, fragment and preparation before its results can be interpreted. Chen et al. (2018), Hu et al. (2016)
Molecular profile
- Profile form
- α-Klotho; membrane-associated protein and released extracellular forms distinguished by study Source
- Protein regions
- KL1 and KL2 extracellular domains Source
- 2017 mouse-study preparation
- Recombinant α-Klotho fragment, residues 35–982 with a histidine tag; not one universal Klotho product Source
- 2023 primate-study preparation
- Recombinant rhesus α-Klotho extracellular protein Source
Forms and derivatives
Membrane and shed α-Klotho
The membrane form participates in FGF23 signaling. Cleavage releases its outer portion, which can circulate; circulating measurements also depend on production and clearance.
β-Klotho
A different Klotho family member supporting different endocrine FGF signals; it is not an alias for α-Klotho.
αKL-F fragment and rhesus recombinant protein
The 2017 study administered a tagged α-Klotho fragment to mice; the 2023 study used rhesus recombinant protein in monkeys. Species and fragment are part of the tested material.
KLOTHO gene variants and transgenic elevation
An inherited human variant or lifelong mouse transgene changes endogenous protein biology. These are distinct from assigning an administered protein preparation.
In the 2017 mouse brain study, Leon and colleagues used a recombinant α-Klotho fragment corresponding to residues 35–982 with a histidine tag. The 2023 primate study used a recombinant rhesus form. These preparations differ from lifelong extra production caused by a mouse transgene, from a person’s natural circulating protein, and from gene or messenger-RNA approaches intended to change protein production. Leon et al. (2017), Castner et al. (2023)
Uses and research areas
Klotho biology is studied in kidney and mineral regulation, survival, memory and neurological disease. Each setting asks a different question. The original gene-defect mice had multiple severe disorders and shortened lives; later overexpression experiments asked whether animals producing more protein lived longer. Cognitive studies then tested genetic elevation or administered fragments in specific tasks. Kuro-o et al. (1997), Kurosu et al. (2005), Dubal et al. (2014)
Human cohort studies ask whether a blood measurement or inherited gene variant predicts an outcome. Those associations can motivate experiments, but kidney function, other illness and many lifelong differences may influence both Klotho and health. An association does not identify the effect of adding a manufactured protein later in life. Semba et al. (2011)
Mechanism of action
A scaffold for mineral-regulating hormone signals
Chen and colleagues showed how α-Klotho holds the hormone FGF23 beside a fibroblast growth factor receptor so that signaling can occur. FGF23 helps regulate phosphate and vitamin D balance. The protein’s structure supported a binding scaffold function rather than the sugar-cleaving enzyme action once inferred from its resemblance to other proteins. This established role helps explain why changing Klotho can have consequences beyond a memory test. Chen et al. (2018)
Peripheral protein can influence the brain without demonstrated brain entry
Leon and colleagues found improved mouse memory-related behavior after administering α-Klotho fragment outside the brain, compared with a control preparation without the fragment. The tagged fragment was not detected entering brain tissue in their assay, and endogenous hippocampal Klotho did not rise. Synapses—the contacts through which neurons communicate—showed a greater lasting increase in signaling strength after stimulation, a form of synaptic plasticity involving NMDA receptors. Blocking the GluN2B component of those receptors abolished the reported effects. Leon et al. (2017)
Park and colleagues later found that peripheral Klotho increased signals released by platelets, blood cells involved in clotting and intercellular communication. Inhibiting platelet activation blocked cognitive enhancement in mice. Giving platelet factor 4, or PF4, could improve cognition, but Klotho still worked in mice lacking PF4. Other signals therefore appear to contribute; the results do not establish one complete blood-to-brain mechanism in people. Park et al. (2023)
Pharmacokinetics
The clearest primate estimate is small and preparation-specific. Castner and colleagues sampled serum after subcutaneous recombinant rhesus Klotho in two aged female monkeys. At the highest tested dose, 30 micrograms per kilogram, samples at 4, 28 and 52 hours informed an exploratory estimated half-life of 29.5 hours, assuming that the peak occurred at four hours. The figure reports eight samples from two animals. No confidence interval for that half-life was supplied. Sparse sampling and an assumed peak make this an exploratory estimate rather than an established human half-life. Castner et al. (2023), Extended Data Figure 2
Hu and colleagues separately traced labeled recombinant mouse α-Klotho in rats. Kidney removal prolonged its circulating half-life four- to five-fold, and labeled material accumulated in kidneys and urine. Those rat experiments show why kidney handling matters, while different species, labels and protein preparations prevent a direct numerical comparison with the primate estimate. Hu et al. (2016)
Research findings
Gene manipulation established biological importance in mice
Kuro-o and colleagues’ 1997 mice with severely reduced Klotho expression developed short survival, infertility and multiple disorders resembling aspects of aging. This disease model established the importance of the gene, without reproducing ordinary human aging. In 2005, Kurosu and colleagues tested two mouse lines that produced extra Klotho. Compared with mice without the introduced Klotho transgene, reported lifespan increases were 20.0% and 30.8% in males, and 18.8% and 19.0% in females. The animals produced extra protein through a transgene; this was not a late-life injection experiment. Kuro-o et al. (1997), Kurosu et al. (2005)
Aged monkeys remembered reward locations more accurately
Castner and colleagues studied 18 rhesus macaques aged 15–28 years, using overlapping subsets for different treatments and repeated testing sessions. Monkeys watched food being hidden and later chose its location after a delay. After the lower tested Klotho amount, they made more correct choices than after phosphate-buffered saline without protein; the reported improvement persisted for at least two weeks. The higher tested doses did not establish improved performance. They also did not establish impaired performance, so the result cannot define a safe or optimal human amount. Castner et al. (2023)
The animals had extensive prior task training and previous research exposure, and only one type of cognitive task was tested. Robertson and colleagues’ 2026 reanalysis of the same data broadly retained the main pattern after changing statistical models and identified analytic errors. Reanalysis of existing animals strengthens understanding of that experiment but supplies no independent primate replication or human treatment result. Robertson et al. (2026)
Human associations remain separate from treatment benefit
Semba and colleagues measured endogenous plasma Klotho in 804 Italian adults aged at least 65. During six years, 194 participants died. People in the lowest Klotho third had a higher adjusted rate of death than those in the highest third: hazard ratio 1.78, with a 95% confidence interval from 1.20 to 2.63. The investigators measured protein concentrations; they did not assign people to Klotho treatment. Semba et al. (2011)
In 2026, Luthra and colleagues linked a KLOTHO gene variant with better executive cognition in two Parkinson disease cohorts. The accompanying intervention evidence came from mice genetically producing more Klotho: cognition and synaptic measures improved, but motor function did not. This combination supplies a human association and animal causal evidence, with different populations and outcomes on each side. Luthra et al. (2026)
Safety and tolerability
The administered recombinant preparations remain experimental. The selected studies do not establish an approved treatment for human aging, a clinical cognitive benefit or long-term human tolerability. A naturally occurring protein can have different effects when its amount, location, fragment, species or duration of exposure changes. The mineral-regulating biology, possible immune responses to a manufactured protein and repeated-exposure effects require direct assessment rather than reassurance from endogenous concentrations. Chen et al. (2018), Leon et al. (2017), Castner et al. (2023)
In the monkey experiment, higher tested doses failed to improve the task despite greater circulating protein increases. This prevents assuming that raising Klotho further produces more benefit. The study’s size and duration could not determine uncommon adverse effects, long-term mineral consequences or risks from a different product.
What the research means
Klotho has a well-supported physiological role and several promising experimental observations. The most direct administered-protein cognitive evidence comes from mice and a small rhesus study. Longer survival in transgenic mice, better monkey performance and lower mortality among people with higher endogenous Klotho measure different events. Together they justify further research; they do not establish that a Klotho product extends healthy human life or treats dementia.
FAQs
Is Klotho a small peptide?
α-Klotho is a large protein with two extracellular domains. Some studies administer an engineered fragment or the released outer region. Molecular form, species and preparation determine which experiment a product resembles. Chen et al. (2018), Leon et al. (2017)
Did Klotho extend lifespan in people?
The survival extension came from genetically modified mice that produced more Klotho. The human mortality study observed endogenous blood concentrations without assigning treatment. Neither establishes a survival benefit from giving Klotho to people. Kurosu et al. (2005), Semba et al. (2011)
What did the monkey memory study actually test?
Aged rhesus macaques watched a food reward being hidden, waited, then chose a location. A lower tested dose of rhesus Klotho improved correct choices compared with phosphate-buffered saline without protein. Higher tested doses did not establish improvement. The experiment involved overlapping subsets of 18 monkeys and one task. Castner et al. (2023)
Must the administered protein enter the brain to have an effect?
In the 2017 mouse study, a tagged α-Klotho fragment was not detected crossing into brain tissue in the reported assay, although brain-related outcomes changed. Later mouse work implicated platelet signals, while leaving several possible messengers unresolved. Leon et al. (2017), Park et al. (2023)
Is 29.5 hours an established human Klotho half-life?
That estimate came from serum samples in only two aged female rhesus macaques after a particular subcutaneous recombinant preparation. It assumed a peak at four hours and supplied no half-life confidence interval. It cannot determine a human product’s clearance. Castner et al. (2023), Extended Data Figure 2
Did the 2026 Parkinson study treat people with Klotho?
The human component associated an inherited KLOTHO variant with executive cognition in two Parkinson cohorts. The intervention experiments involved genetically modified mice; cognition improved while motor function did not. Luthra et al. (2026)
Comparisons and related reading
References
Identifies a mouse gene defect associated with shortened survival and multiple aging-like disorders. This was a genetic disease model, not a trial of administered protein.
Two genetically modified mouse lines producing extra Klotho lived longer than their wild-type controls. Lifelong gene overexpression differs from beginning protein treatment in an older person.
Shows how the extracellular protein holds FGF23 and its receptor together. This defines a mineral-regulation role and argues against treating α-Klotho simply as a sugar-cleaving enzyme.
Rat tracer and blood-sampling experiments identify kidney production and clearance of circulating Klotho. Human blood samples support a renal source; people did not receive the recombinant tracer.
Human gene-variant associations and genetically modified mice address different kinds of evidence. Mice producing more Klotho performed better on memory tests; the human participants were not assigned Klotho treatment.
Tests a recombinant α-Klotho fragment outside the brain in several mouse settings. Memory-related effects occurred without detectable entry of the tagged fragment into brain tissue in the reported assay.
Aged rhesus macaques remembered hidden reward locations more accurately after the lower tested dose of rhesus Klotho. Higher tested doses did not establish improvement. The small longitudinal study does not establish a human cognitive benefit.
Mouse experiments suggest platelet signals can relay some peripheral Klotho effects to the brain. PF4 could improve cognition, but deleting PF4 did not abolish the Klotho effect, so this is not a single necessary messenger.
Observational follow-up of older adults links lower circulating Klotho with higher mortality. Measuring an endogenous protein does not test whether administering it changes survival.
Two human Parkinson cohorts linked a KLOTHO variant with better executive cognition. The intervention work was in transgenic mice, whose cognitive and synaptic outcomes improved while motor function did not.
Reanalyzes the same primate data rather than enrolling new monkeys. The main pattern persisted after revised statistical models; the report identifies problems with the original analytic choices.
Glossary
- Extracellular domain
- The portion of a membrane protein that lies outside the cell and may be released by cleavage.
- Recombinant protein
- A protein produced using an engineered expression system; its sequence and preparation need to be specified.
- Transgenic mouse
- A mouse carrying introduced genetic material that changes its protein production.
- Synaptic plasticity
- The ability of connections between nerve cells to change their signaling strength.
- Hazard ratio
- A comparison of event rates over follow-up; an observational ratio does not by itself establish cause.
- FGF23
- A hormone that helps regulate phosphate and vitamin D balance through receptors supported by α-Klotho.