# Klotho — Research Peptide Profile

> Klotho is a 1012-amino-acid protein: mice without it age fast, mice with extra live 20-30% longer, and one dose sharpened aged monkey memory. Human trials: none.

Source: https://peptpedia.org/peptide/klotho | Published: 2026-09-18 | Last updated: 2026-09-18

Klotho is not a small peptide but a large membrane protein that rewrote aging biology: mice bred without it age rapidly, and mice with extra klotho live 20-30% longer. A single peripheral dose sharpened memory in aged monkeys in 2023. It has never been given to humans in a published trial, and consumer klotho peptide products cannot be what they claim.

## Overview

Klotho entered the literature in 1997, when Kuro-o and colleagues showed that disrupting the mouse klotho gene produced a syndrome resembling accelerated human aging: short lifespan, arteriosclerosis, osteoporosis, skin atrophy, and emphysema. The 2005 follow-up showed the reverse - transgenic overexpression extended mouse lifespan by 20-30%, partly by suppressing insulin and IGF-1 signaling, a conserved longevity pathway. The 1012-amino-acid protein sits in cell membranes as the obligatory co-receptor for FGF23, governing phosphate and vitamin D metabolism, while its extracellular domain is shed into blood, urine, and cerebrospinal fluid as soluble klotho (sKlotho) with hormone-like actions of its own. In humans, lower plasma klotho independently predicted death over six years in the InCHIANTI cohort of 804 older adults, and carriers of the KL-VS variant, which raises circulating klotho, scored better on cognitive testing across three cohorts, with mouse work pinning the mechanism to GluN2B-containing NMDA receptors. A single peripheral injection of the KL1 fragment then enhanced cognition in mice despite not crossing the blood-brain barrier, and a single low subcutaneous dose improved memory in aged rhesus macaques. Unlike senolytic approaches represented by [FOXO4-DRI](/peptide/foxo4-dri), klotho research centers on restoring a circulating factor that declines with age rather than removing damaged cells.

## Molecular Profile

- **Category:** anti-aging
- **Molecular formula:** 1012-amino-acid transmembrane glycoprotein (no fixed molecular formula)
- **Molecular weight:** ~130 kDa (full-length); ~62-65 kDa (KL1 domain fragment)
- **Also known as:** alpha-Klotho, Klotho Protein, KL, Soluble Klotho, sKlotho
- **Half-life:** Not established in humans; in rhesus macaques serum klotho was tracked to 52 hours after a single subcutaneous dose (Castner 2023)
- **Solubility:** Recombinant protein in aqueous formulation (mammalian cell expression required)
- **Storage:** Recombinant protein requires cold chain at 2-8°C. No verified consumer-grade formulation exists.

## Mechanism of Action

Membrane-bound klotho pairs with FGF receptors to form the obligatory high-affinity receptor for FGF23, the bone-derived hormone that suppresses phosphate reabsorption and vitamin D activation in the kidney - the axis that explains why klotho-deficient mice develop hyperphosphatemia and vascular calcification. Circulating soluble klotho acts beyond mineral metabolism: it suppresses insulin and IGF-1 receptor signaling (the lifespan-extending mechanism in transgenic mice), counteracts oxidative stress, and inhibits Wnt signaling in fibrosis models. In brain, klotho enhances synaptic plasticity through GluN2B-containing NMDA receptors. Peripherally delivered KL1 fragment induced GluN2B cleavage and enhanced NMDAR-dependent plasticity without entering the brain, implying a blood-to-brain signaling intermediate that remains unidentified.

## Key Research Findings

- Disrupting the klotho gene in mice caused a syndrome resembling accelerated human aging; overexpressing it extended mouse lifespan by 20-30%.
- A single low subcutaneous dose of recombinant klotho (10 mcg/kg) enhanced working memory in aged rhesus macaques; higher doses lost the effect.
- Older adults in the lowest tertile of plasma klotho had a 78% higher six-year mortality risk than those in the highest tertile (InCHIANTI cohort).
- Klotho is a 130 kDa glycoprotein requiring mammalian cell manufacturing - no consumer klotho peptide product can be verified as genuine.

## Safety & Tolerability

No human has received exogenous klotho in a published trial, so the safety picture rests on genetics and animal work. The biology itself flags the risks: klotho steers phosphate, vitamin D, and FGF23 balance, and the primate data show an inverted-U dose response where higher doses lose benefit. Material sold to consumers as klotho cannot be verified as the genuine protein.

**Human data status:** No human interventional data exist. Human evidence is limited to genetic association (the KL-VS variant) and observational cohorts linking lower circulating klotho to mortality and disease.

**Regulatory status:** Not approved by any regulatory agency, and no human trial results have been published as of 2026. No verified consumer product exists.

- Klotho disruption in mice causes hyperphosphatemia, vascular calcification, and multi-system degeneration, demonstrating that this pathway controls mineral metabolism - a risk dimension for any exogenous human use. (evidence tier: animal; [PMID 9363890](https://pubmed.ncbi.nlm.nih.gov/9363890/))
- As the obligatory FGF23 co-receptor, klotho governs phosphate and vitamin D homeostasis; manipulating it in people with kidney disease or mineral disorders carries theoretical risk that has never been clinically mapped. (evidence tier: theoretical; [PMID 30455427](https://pubmed.ncbi.nlm.nih.gov/30455427/))
- In aged macaques, a single low dose enhanced memory while higher doses did not, an inverted-U dose response that argues against informal dose escalation and complicates any self-experimentation. (evidence tier: animal; [PMID 37400721](https://pubmed.ncbi.nlm.nih.gov/37400721/))
- Low plasma klotho predicted all-cause mortality in 804 older adults (lowest versus highest tertile hazard ratio 1.78); the association does not prove that supplementation would be safe or beneficial. (evidence tier: human-observational; [PMID 21474560](https://pubmed.ncbi.nlm.nih.gov/21474560/))

## Dosing Information (Research Context)

No human dosing exists: exogenous klotho has never been administered to humans in a published trial. In the key primate study, a single subcutaneous injection of recombinant rhesus klotho at a low dose (10 mcg/kg) enhanced memory in aged macaques while higher doses did not (Castner 2023), and mouse work delivered the KL1 fragment peripherally at similar microgram-per-kilogram doses (Leon 2017). Material marketed to consumers as klotho peptide cannot be verified as the genuine protein - a 130 kDa glycoprotein requires mammalian cell manufacturing, not peptide synthesis.

| Route | Dose | Frequency | Notes |
| --- | --- | --- | --- |
| Subcutaneous (aged rhesus macaque) | 10 mcg/kg | Single dose | Castner 2023; low dose enhanced memory, higher doses did not; no human equivalent established |
| Peripheral injection (mouse) | Microgram-per-kilogram range (KL1 fragment) | Short course | Leon 2017; enhanced cognition despite no blood-brain barrier penetration |

## Researched Effects

- **Aging-Suppressor Genetics** (evidence: extensive): The klotho gene is one of the clearest single-gene levers on mammalian aging. Disrupting it in mice produced a multi-system syndrome resembling accelerated human aging, including shortened lifespan, arteriosclerosis, osteoporosis, skin atrophy, pulmonary emphysema, and infertility (PMID: 9363890). Transgenic overexpression produced the opposite phenotype: lifespan extension of 20-30% with suppression of insulin and IGF-1 signaling, tying klotho to the same longevity pathway documented in worms and flies (PMID: 16123266). Few aging-pathway genes have bidirectional lifespan evidence of this strength in mammals.
- **Cognitive Enhancement in Aging Models** (evidence: moderate): Three independent lines of evidence link klotho to cognition. Humans carrying one copy of the KL-VS variant, which elevates circulating klotho, performed better on cognitive testing across three cohorts, and mice engineered to express the variant showed enhanced hippocampal plasticity via GluN2B-containing NMDA receptors (PMID: 24813892). Peripherally administered KL1 fragment enhanced cognition and neural resilience in young, aging, and alpha-synuclein transgenic mice despite being excluded by the blood-brain barrier (PMID: 28793260). A single low subcutaneous dose of recombinant klotho then enhanced memory in aged rhesus macaques, with higher doses losing the effect (PMID: 37400721). No human has received klotho in a published trial.
- **FGF23 Co-Receptor and Mineral Metabolism** (evidence: extensive): Membrane klotho is the obligatory co-receptor that confers FGF23 specificity on FGF receptors, placing it in command of renal phosphate excretion and active vitamin D synthesis (PMID: 30455427). The klotho-FGF23 axis explains the hyperphosphatemia, vascular calcification, and bone abnormalities of klotho-deficient mice, and it is central to chronic kidney disease research, where declining renal klotho tracks with FGF23 resistance and mineral-bone disorder. This is established physiology rather than speculative biology.
- **Mortality and Aging Biomarker Association** (evidence: moderate): In the InCHIANTI cohort of 804 community-dwelling adults aged 65 and older, participants in the lowest tertile of plasma klotho (under 575 pg/mL) had a 78% higher risk of death over six years than those in the highest tertile (over 763 pg/mL), independent of age, chronic disease, vitamin D, and other covariates (PMID: 21474560). Circulating klotho declines progressively with age and tracks with cardiovascular risk and cognitive decline in observational work. These associations make klotho a candidate aging biomarker, but no intervention has been shown to raise klotho and change outcomes in humans.
- **Kidney and Cardiovascular Protection** (evidence: preliminary): Klotho is expressed most strongly in the kidney, and its loss in renal disease is linked to FGF23 resistance, phosphate retention, vascular calcification, and cardiac remodeling in animal models (PMID: 30455427). Soluble klotho also inhibits Wnt signaling in fibrosis models, a mechanism relevant to kidney and cardiac scarring. Preclinical work supports klotho replacement as a strategy in chronic kidney disease, though translation has been slowed by the manufacturing demands of a large recombinant glycoprotein.

## Research Applications

- Aging Biology and Geroscience
- Cognitive Aging Research
- FGF23 and Phosphate Physiology
- Chronic Kidney Disease Research
- Longevity Genetics

## Key Studies

### Mutation of the mouse klotho gene leads to a syndrome resembling ageing

Kuro-o M, Matsumura Y, Aizawa H, et al. — *Nature* (1997) — [PMID 9363890](https://pubmed.ncbi.nlm.nih.gov/9363890/)

The discovery paper. A mouse line carrying a disruptive insertion in the klotho gene developed a syndrome resembling accelerated human aging: short lifespan, arteriosclerosis, osteoporosis, skin atrophy, pulmonary emphysema, gonadal atrophy, and ectopic calcification. The gene encodes a single-pass transmembrane protein expressed mainly in kidney and brain choroid plexus. This work established klotho as an aging-suppressor gene and opened a new field in geroscience.

### Suppression of aging in mice by the hormone Klotho

Kurosu H, Yamamoto M, Clark JD, et al. — *Science* (2005) — [PMID 16123266](https://pubmed.ncbi.nlm.nih.gov/16123266/)

The complementary overexpression study. Transgenic mice with elevated klotho lived 20-30% longer than wild-type controls. Mechanistically, klotho suppressed insulin and IGF-1 signaling and increased resistance to oxidative stress, connecting klotho to the conserved longevity pathway established in C. elegans and Drosophila. The paper also framed klotho as a circulating hormone, because the overexpressed protein acts on tissues distant from its sites of expression.

### Plasma klotho and mortality risk in older community-dwelling adults

Semba RD, Cappola AR, Sun K, et al. — *Journals of Gerontology Series A* (2011) — [PMID 21474560](https://pubmed.ncbi.nlm.nih.gov/21474560/) | [doi:10.1093/gerona/glr058](https://doi.org/10.1093/gerona/glr058)

In the InCHIANTI cohort, plasma klotho was measured in 804 adults aged 65 and older, followed for six years. Participants in the lowest klotho tertile (under 575 pg/mL) had an all-cause mortality hazard ratio of 1.78 (95% CI 1.20-2.63) versus the highest tertile (over 763 pg/mL) after adjustment for age, education, body mass index, physical activity, lipids, cognition, vitamin D, parathyroid hormone, calcium, blood pressure, and chronic diseases. The first prospective evidence that low circulating klotho independently predicts death in humans.

### Life extension factor klotho enhances cognition

Dubal DB, Yokoyama JS, Zhu L, et al. — *Cell Reports* (2014) — [PMID 24813892](https://pubmed.ncbi.nlm.nih.gov/24813892/) | [doi:10.1016/j.celrep.2014.03.076](https://doi.org/10.1016/j.celrep.2014.03.076)

Humans carrying one copy of the KL-VS klotho variant, which raises circulating klotho levels, scored better on composite cognitive testing across three independent cohorts. In mice, elevated klotho enhanced learning and memory and strengthened hippocampal synaptic plasticity through increased GluN2B-containing NMDA receptor function, with GluN2B blockade abolishing the benefit. The study linked a human longevity-genetics variant to a defined synaptic mechanism.

### Peripheral Elevation of a Klotho Fragment Enhances Brain Function and Resilience in Young, Aging, and alpha-Synuclein Transgenic Mice

Leon J, Moreno AJ, Garay BI, et al. — *Cell Reports* (2017) — [PMID 28793260](https://pubmed.ncbi.nlm.nih.gov/28793260/) | [doi:10.1016/j.celrep.2017.07.024](https://doi.org/10.1016/j.celrep.2017.07.024)

Peripheral administration of the klotho KL1 fragment enhanced cognition and motor function in young, aging, and alpha-synuclein transgenic mice, even though the fragment does not cross the blood-brain barrier. Treatment induced cleavage of the NMDA receptor subunit GluN2B and enhanced NMDAR-dependent synaptic plasticity, and GluN2B blockade abolished the effects. The study showed that acute, intermittent peripheral dosing of a klotho fragment can drive brain benefit - a practical therapeutic concept distinct from lifelong transgenic overexpression.

### Longevity factor klotho enhances cognition in aged nonhuman primates

Castner SA, Gupta S, Wang D, et al. — *Nature Aging* (2023) — [PMID 37400721](https://pubmed.ncbi.nlm.nih.gov/37400721/) | [doi:10.1038/s43587-023-00441-x](https://doi.org/10.1038/s43587-023-00441-x)

The most translationally relevant klotho study to date. The team validated recombinant rhesus klotho in mice, then gave aged rhesus macaques a single subcutaneous injection: a low dose (10 mcg/kg) enhanced working memory, while higher doses did not, an inverted-U dose response. Serum klotho was tracked to 52 hours post-injection. The work demonstrates that a single peripheral dose of a longevity protein can improve cognition in a human-relevant species, while flagging a narrow therapeutic window.

## Frequently Asked Questions

### Is klotho actually a peptide?

No, and the distinction matters for buyers. Klotho is a 1012-amino-acid single-pass transmembrane glycoprotein of about 130 kDa - roughly 35 times larger than a typical research peptide. The circulating form is its shed extracellular domain, and the fragment studied for cognition (KL1) is still around 62-65 kDa. Producing it requires mammalian cell culture, not the solid-phase synthesis used for small peptides. Any vial sold as klotho peptide for personal use cannot be verified as the genuine protein and is very likely mislabeled.

### Has klotho been tested in humans?

No published study has administered exogenous klotho to a human as of 2026. Human evidence comes from genetics and observation: carriers of the KL-VS variant have higher circulating klotho and better cognitive scores (PMID: 24813892), and low plasma klotho independently predicted death over six years in 804 older adults (PMID: 21474560). All interventional results - cognition, lifespan, kidney protection - are from mouse and nonhuman primate work.

### What did the 2023 monkey study actually find?

Castner and colleagues gave aged rhesus macaques a single subcutaneous injection of recombinant rhesus klotho. A low dose of 10 mcg/kg enhanced working memory; higher doses did not help, an inverted-U dose response (PMID: 37400721). Serum klotho remained measurable to 52 hours. It is the strongest evidence so far that a single peripheral dose of klotho can improve cognition in a human-relevant species, and also the clearest warning that more is not better with this protein.

### Do low klotho levels predict death?

In the InCHIANTI study of 804 community-dwelling adults aged 65 and older, those in the lowest tertile of plasma klotho (under 575 pg/mL) died at a 78% higher rate over six years than those in the highest tertile, after adjusting for a long list of health covariates (PMID: 21474560). This is a prospective association, not proof of causation: no trial has shown that raising klotho reduces mortality in humans.

### What is the KL-VS variant?

KL-VS is a common haplotype of the human klotho gene. People who carry one copy (roughly a quarter of many populations) have higher circulating klotho, and in a 2014 study they performed better on cognitive testing across three independent cohorts (PMID: 24813892). Mice engineered to model the variant showed enhanced hippocampal plasticity through GluN2B-containing NMDA receptors, giving the human association a plausible mechanism. Carrying two copies does not show the same benefit, echoing the inverted-U pattern seen in the primate dosing work.

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