Also known as: KP1, KP6, klotho-derived peptides, alpha-klotho peptide, klotho protein fragment
Anti-fibrotic therapy for kidney disease (preclinical)
Amount
Not standardized (preclinical IV/infusion doses)
Frequency
Single or chronic infusion (preclinical)
Duration
Acute to multiple weeks (study-dependent)
Route
IVTiming
KP1 administered as IV bolus in mouse fibrosis models. KP6 administered as chronic infusion in diabetic mouse models. No human dosing established.
Duration
Study-dependent (acute to multiple weeks)
Repeatable
Single cycle
CMP (Comprehensive Metabolic Panel)
When: Baseline
Why: Kidney and liver function baseline
Urinalysis with protein
When: Baseline
Why: Assess proteinuria relevant to kidney disease applications
Serum phosphorus and calcium
When: Baseline
Why: Klotho regulates phosphate and calcium homeostasis
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The klotho peptide refers to a family of synthetic fragments derived from the alpha-klotho protein, a 130 kDa transmembrane glycoprotein that functions as one of the most significant anti-aging factors identified in mammalian biology. First discovered in 1997 when its disruption in mice produced a syndrome resembling premature human aging, the alpha-klotho protein has since been linked to kidney protection, cognitive enhancement, cardiovascular health, and lifespan regulation. For a complete overview of klotho peptide research, this guide covers the two principal klotho-derived peptides (KP1 and KP6), their mechanisms, and the broader klotho protein's therapeutic potential.
The discovery was serendipitous: Makoto Kuro-o and colleagues at the University of Texas Southwestern Medical Center observed that mice with an insertional mutation in a then-unknown gene developed a constellation of age-related pathologies -- arteriosclerosis, osteoporosis, emphysema, skin atrophy, and infertility -- all by 8-9 weeks of age. They named the gene klotho after the Greek goddess Clotho, one of the three Fates who spins the thread of life. Conversely, transgenic mice overexpressing klotho lived approximately 20-30% longer than wild-type littermates, establishing klotho as one of the most robust mammalian longevity genes.
Two principal klotho-derived peptides have been characterized for therapeutic development:
KP1 (Klotho-Derived Peptide 1): A 30-amino-acid peptide corresponding to residues Phe57-Lys86 of human alpha-klotho. KP1 inhibits TGF-beta signaling by blocking TGF-beta receptor 2 (TbetaR2) engagement and protects against kidney fibrosis in animal models. A 2024 study further demonstrated that KP1 inhibits cellular senescence in fibrotic kidneys by restoring endogenous klotho expression.
KP6 (Klotho-Derived Peptide 6): A peptide that targets Wnt/beta-catenin signaling by binding to Wnt ligands and disrupting their engagement with LRP6, ameliorating diabetic kidney disease in mouse models. A variant, KP6T, has shown additional promise against vascular calcification in CKD models.
| Property | Details |
|---|---|
| Full name | Klotho-derived peptides (KP1, KP6) |
| Parent protein | Alpha-klotho (1014 amino acids, ~130 kDa) |
| KP1 sequence | FQGTFPDGFLWAVGSAAYQTEGGWQQHGKG (30 aa) |
| KP1 molecular weight | 3,228.42 Da |
| Research status | Preclinical (no human trials for peptides) |
| Primary targets | TGF-beta receptor 2 (KP1), Wnt/LRP6 (KP6) |
| Key publications | Nature Communications (2022), Kidney International (2022), Nature Aging (2023) |
The klotho peptide exerts its effects through distinct molecular mechanisms depending on which fragment is used. Understanding how klotho peptides work requires examining both the individual peptide mechanisms and the broader signaling pathways of the parent protein.
KP1 exerts its anti-fibrotic effects by directly binding to TGF-beta receptor type 2 (TbetaR2), which prevents TGF-beta ligands from engaging their receptor. This blocks downstream Smad2/3 phosphorylation and mitogen-activated protein kinase activation. The net effect is suppression of fibroblast activation, extracellular matrix deposition, and epithelial-mesenchymal transition, which are the hallmark processes of organ fibrosis.
In the foundational study by Yuan et al. (2022), KP1 was identified from a systematic screen of 18 overlapping peptides spanning the KL1 domain. Only KP1 demonstrated significant anti-fibrotic activity, suggesting that the specific residues Phe57-Lys86 contain a TbetaR2-binding motif that is uniquely positioned within the larger protein. When administered intravenously in mouse unilateral ureteral obstruction (UUO) models, KP1 showed preferential accumulation in injured kidneys -- a finding that suggests intrinsic tissue targeting properties, potentially mediated by increased vascular permeability or receptor density at sites of active fibrosis.
Notably, KP1 treatment also restored endogenous klotho expression in fibrotic kidneys. Since TGF-beta signaling itself suppresses klotho transcription, this creates a positive feedback loop: KP1 blocks TGF-beta, which relieves klotho suppression, which further attenuates TGF-beta signaling. A 2024 follow-up study (Yuan et al., Theranostics; PMID: 38164143) demonstrated that KP1 also inhibits cellular senescence in fibrotic kidneys by restoring klotho expression at the posttranscriptional level, expanding the therapeutic implications beyond direct anti-fibrotic activity.
KP6 acts by binding to Wnt ligands directly, preventing their engagement with the low-density lipoprotein receptor-related protein 6 (LRP6) co-receptor. This disrupts canonical Wnt/beta-catenin signaling, which is aberrantly activated in diabetic kidney disease and contributes to podocyte injury, proteinuria, and glomerulosclerosis.
The specificity of KP6 was demonstrated through a critical control experiment: a scrambled-sequence version of KP6 with identical amino acid composition but randomized order failed to bind Wnt ligands and showed no therapeutic effect. This confirmed that KP6's activity depends on its specific amino acid sequence and likely secondary structure, not merely its charge or hydrophobicity profile.
In both STZ-induced type 1 and db/db type 2 diabetic mouse models, chronic KP6 infusion reversed established proteinuria, attenuated glomerular hypertrophy, protected podocytes from injury, and ameliorated fibrotic lesions -- effects that were absent with the scrambled control peptide. A variant peptide, KP6T, has additionally been shown to block vascular calcification in CKD by inhibiting osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells through Wnt/beta-catenin pathway suppression.
The full KL1 domain of alpha-klotho enhances cognition through a distinct mechanism. Systemic elevation of klotho enriches synaptic GluN2B (an NMDA receptor subunit critical for learning and memory), enhances long-term potentiation, and induces platelet-derived factors that cross the blood-brain barrier. A single low-dose injection enhanced memory in aged nonhuman primates for up to two weeks.
The cognitive effects of klotho appear to follow an inverted U-shaped dose-response curve: low doses enhance cognition while high doses do not. This pattern, replicated across mouse and nonhuman primate studies, suggests an optimal signaling window rather than a simple dose-dependent effect.
Although they share a name, alpha-klotho and beta-klotho are encoded by different genes, expressed in different tissues, and serve distinct biological functions. Understanding these differences is essential for interpreting klotho peptide research.
Alpha-klotho is the canonical anti-aging protein. It is primarily expressed in the kidney (distal convoluted tubule), parathyroid gland, and choroid plexus of the brain. Its defining endocrine function is serving as an obligate co-receptor for fibroblast growth factor 23 (FGF23), the master regulator of phosphate homeostasis. When membrane-bound alpha-klotho forms a ternary complex with FGFR1c and FGF23, it triggers phosphaturic signaling in the kidney -- suppressing sodium-phosphate cotransporters NaPi-2a and NaPi-2c in the proximal tubule and reducing phosphate reabsorption.
Beyond its FGF23 co-receptor role, soluble alpha-klotho circulates systemically and exerts pleiotropic effects:
Beta-klotho is a distinct protein that serves as the co-receptor for a different subset of FGF ligands, primarily FGF21 and FGF19. It is expressed predominantly in the liver, pancreas, and adipose tissue rather than the kidney.
| Feature | Alpha-Klotho | Beta-Klotho |
|---|---|---|
| Gene | KL (chromosome 13) | KLB (chromosome 4) |
| Primary tissues | Kidney, parathyroid, brain | Liver, pancreas, adipose |
| FGF ligand partner | FGF23 | FGF21, FGF19 |
| Primary function | Phosphate homeostasis, anti-aging | Metabolic regulation, bile acid homeostasis |
| Soluble form | Yes (shed by ADAM10/17) | Yes (shed by ADAM10/17) |
| Aging association | Strong (declines with age) | Moderate |
| Therapeutic peptides | KP1, KP6 | None yet characterized |
The FGF21/beta-klotho axis is of major therapeutic interest for metabolic disease. FGF21 acts as a metabolic hormone that enhances insulin sensitivity, promotes fatty acid oxidation, reduces hepatic lipogenesis, and may extend lifespan in animal models. Several FGF21 analogs (pegbelfermin, efruxifermin) are in clinical trials for nonalcoholic steatohepatitis (NASH), while the GLP-1/FGF21 dual agonist approach represents an emerging therapeutic strategy. However, no beta-klotho-derived peptides have been developed to date -- the current klotho peptide research focuses exclusively on alpha-klotho fragments.
FGF23 is a bone-derived hormone that maintains serum phosphate within a narrow physiological range. The signaling cascade requires membrane-bound alpha-klotho as an obligate co-receptor:
When klotho expression declines -- as occurs in chronic kidney disease and aging -- this system becomes dysregulated. Elevated FGF23 without adequate klotho co-receptor leads to FGF23 resistance, hyperphosphatemia, vascular calcification, and left ventricular hypertrophy. This explains why CKD patients with low klotho levels have dramatically increased cardiovascular mortality.
FGF21 signals through beta-klotho/FGFR1c complexes primarily in adipose tissue and liver:
While no beta-klotho peptides exist yet, the metabolic significance of this pathway makes it a likely future target for peptide therapeutics.
Klotho's role in kidney protection extends well beyond what the individual peptides KP1 and KP6 target. The full-length protein protects the kidney through multiple overlapping pathways, making klotho peptide research in nephrology particularly promising.
Kidney fibrosis is the final common pathway of virtually all chronic kidney diseases. Klotho suppresses fibrosis through at least three mechanisms:
Podocytes -- the specialized epithelial cells of the glomerular filtration barrier -- are terminally differentiated and cannot regenerate. Their loss is a key driver of proteinuria and progressive kidney disease. Klotho protects podocytes by:
Chronic kidney disease is characterized by persistent low-grade inflammation. Klotho suppresses renal inflammation by:
CKD patients develop extensive vascular calcification driven by hyperphosphatemia and klotho deficiency. Klotho prevents vascular calcification by:
The relationship between the klotho peptide and brain function represents one of the most exciting frontiers in aging research. While the KP1 and KP6 peptides are kidney-focused, the broader klotho protein has produced compelling evidence for cognitive applications that are now entering human clinical trials.
Klotho enhances long-term potentiation (LTP), the cellular mechanism underlying learning and memory, by increasing surface expression of GluN2B-containing NMDA receptors at hippocampal synapses. GluN2B-containing receptors produce longer excitatory postsynaptic currents than GluN2A-containing receptors, allowing greater calcium influx and stronger potentiation. Pharmacological blockade of GluN2B completely abolished klotho's cognitive-enhancing effects in transgenic mice, establishing this receptor subunit as a necessary mediator.
Preclinical evidence suggests klotho may protect against multiple neurodegenerative processes:
A central question in klotho neurobiology is how a peripheral protein affects brain function. Alpha-klotho (130 kDa) is too large to freely cross the blood-brain barrier. Current evidence supports two non-mutually exclusive mechanisms:
The klotho peptide and protein field reached a major milestone in 2025 with the initiation of the first human clinical trials. UCSF researchers began a Phase 1 trial testing klotho protein (the KL1 domain, not the small peptides) in adults over 65, measuring safety, dosing, and cognitive performance on standardized tests over a 90-day period following a single subcutaneous injection. Additionally, gene therapy approaches combining klotho with follistatin are being tested for cognitive and longevity applications. These trials represent the first direct translation of decades of preclinical klotho research into human therapeutics.
The klotho peptide intersects with several of the recognized hallmarks of aging, making it one of the most broadly relevant anti-aging targets under investigation.
Klotho deficiency accelerates cellular senescence through multiple pathways, including increased p16/p21 expression, Wnt-driven senescence, and oxidative stress-induced DNA damage. KP1 has been shown to inhibit cellular senescence in fibrotic kidneys by restoring klotho expression and breaking the TGF-beta/senescence feedback loop.
Klotho maintains mitochondrial function by suppressing excessive reactive oxygen species (ROS) production through FoxO-mediated upregulation of antioxidant enzymes. Klotho-deficient mice show widespread mitochondrial dysfunction with reduced membrane potential, impaired respiratory chain function, and increased mitochondrial DNA damage.
Klotho modulates stem cell behavior through Wnt signaling regulation. Excessive Wnt signaling depletes tissue stem cell pools, while klotho's Wnt-inhibitory activity helps maintain stem cell quiescence and self-renewal capacity. This is particularly relevant in the kidney, where tubular progenitor cells require balanced Wnt signaling for tissue repair.
Age-associated chronic inflammation is both a cause and consequence of klotho decline. Klotho suppresses NF-kB-driven inflammatory gene expression, NLRP3 inflammasome activation, and endothelial dysfunction -- all of which contribute to the chronic, sterile inflammation that characterizes aging tissues.
As an endocrine factor, soluble klotho represents a form of systemic intercellular communication that declines with age. Its loss disrupts the coordinated regulation of phosphate metabolism, Wnt signaling, insulin sensitivity, and oxidative stress defense across multiple organ systems simultaneously.
The klotho peptide field divides into three research tracks with distinct timelines:
Kidney disease: KP1 and KP6 are being developed as targeted peptide therapeutics for chronic kidney disease and diabetic kidney disease, respectively. Both have demonstrated efficacy in rodent models published in Nature Communications and Kidney International. The kidney remains the most therapeutically advanced application for the small peptides, with clear molecular targets (TbetaR2 and Wnt/LRP6) and well-defined disease models.
Cognitive aging: The full klotho protein or KL1 domain has shown cognitive enhancement in mice and nonhuman primates, with the landmark 2023 Nature Aging primate study demonstrating that a single injection enhanced cognition in aged rhesus macaques. This track is now entering Phase 1 human clinical trials as of 2025.
Gene therapy: Companies including Klotho Neurosciences and Minicircle are developing klotho gene therapy approaches that would enable sustained klotho expression. These represent a distinct therapeutic modality from peptide or protein administration, with early-phase trials beginning in 2025-2026.
All klotho-derived peptide research (KP1, KP6) remains preclinical. No human clinical trials have been conducted with the small peptides, though the full klotho protein has entered Phase 1 trials for cognitive enhancement.
While klotho peptides are not available for human use, several evidence-based strategies may support endogenous klotho expression:
A Klotho-derived peptide protects against kidney fibrosis by targeting TGF-beta signaling, published in Nature Communications (Yuan Q et al., 2022; PMID: 35064106):
Klotho-derived peptide 6 ameliorates diabetic kidney disease by targeting Wnt/beta-catenin signaling, published in Kidney International (Zhou L et al., 2022; PMID: 35644285):
Klotho-derived peptide 1 inhibits cellular senescence in the fibrotic kidney, published in Theranostics (Yuan Q et al., 2024; PMID: 38164143):
Longevity factor klotho enhances cognition in aged nonhuman primates, published in Nature Aging (Castner SA et al., 2023; PMID: 37400721):
Life extension factor klotho enhances cognition, published in Cell Reports (Dubal DB et al., 2014; PMID: 24813892):
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