Klotho
Klotho is a transmembrane protein and circulating hormone that functions as a co-receptor for FGF23, regulates phosphate homeostasis, suppresses aging-related signaling pathways, and protects against kidney disease, neurodegeneration, and cardiovascular calcification.
Klotho is a type I transmembrane protein originally identified in 1997 as an aging-suppressor gene in mice, where its disruption caused a syndrome resembling accelerated human aging. The protein exists in two primary forms: membrane-bound alpha-klotho, which serves as an obligate co-receptor for fibroblast growth factor 23 (FGF23), and soluble klotho (shed ectodomain), which circulates as an endocrine hormone with pleiotropic anti-aging effects.
Overview
The klotho gene was discovered by Kuro-o et al. in 1997 when an insertional mutation in mice produced a phenotype strikingly reminiscent of human aging: shortened lifespan, arteriosclerosis, osteoporosis, skin atrophy, emphysema, and ectopic calcification. Conversely, overexpression of klotho extended mouse lifespan by 20-30%. The gene encodes a single-pass transmembrane protein predominantly expressed in the kidney distal convoluted tubule, choroid plexus of the brain, and parathyroid gland.
Alpha-klotho and beta-klotho are encoded by different genes (KL and KLB, respectively) and serve distinct biological functions. Alpha-klotho is the canonical aging-suppressor that partners with FGF23 to regulate phosphate and vitamin D metabolism. Beta-klotho partners with FGF19 and FGF21 to regulate bile acid synthesis and energy metabolism, respectively. This article focuses on alpha-klotho unless otherwise noted.
Soluble klotho is generated by proteolytic cleavage of the extracellular domain by ADAM10 and ADAM17 (alpha-secretases), releasing it into blood, urine, and cerebrospinal fluid. Circulating klotho levels decline with age, chronic kidney disease, and various pathological states, and low klotho levels are independently associated with all-cause mortality.
Mechanism of Action
Klotho exerts its biological effects through both receptor-dependent and receptor-independent mechanisms:
FGF23 Co-receptor Function: Membrane-bound klotho forms a ternary complex with FGF23 and FGFR1c in the kidney, converting the low-affinity FGF23-FGFR interaction (Kd ~200 nM) into a high-affinity signaling complex (Kd ~2-10 nM). This complex activates the RAS-MAPK and PI3K-AKT cascades, leading to downregulation of NaPi-IIa and NaPi-IIc sodium-phosphate cotransporters in the proximal tubule, promoting renal phosphate excretion. It simultaneously suppresses 1-alpha-hydroxylase (CYP27B1) and induces 24-hydroxylase (CYP24A1), reducing active vitamin D (1,25(OH)2D3) levels. Urakawa et al. (2006) demonstrated that klotho is required for FGF23 signal transduction.
Insulin/IGF-1 Signaling Suppression: Soluble klotho inhibits insulin and IGF-1 receptor autophosphorylation, reducing downstream PI3K/AKT signaling. This derepresses FoxO transcription factors (FoxO1, FoxO3a, FoxO4), which translocate to the nucleus and activate expression of manganese superoxide dismutase (MnSOD) and catalase, enhancing cellular antioxidant defenses. Kurosu et al. (2005) showed that klotho extends lifespan through inhibition of insulin/IGF-1 signaling.
Wnt Signaling Modulation: Soluble klotho binds directly to Wnt ligands (particularly Wnt3a and Wnt1) and inhibits canonical Wnt/beta-catenin signaling. While Wnt signaling is essential for development, its chronic activation in aging tissues promotes cellular senescence and stem cell exhaustion. Liu et al. (2007) identified klotho as an endogenous Wnt antagonist with implications for renal fibrosis.
Anti-calcification: Soluble klotho directly suppresses phosphate uptake by vascular smooth muscle cells and inhibits TGF-beta1-induced epithelial-to-mesenchymal transition (EMT), both of which drive vascular calcification. It also maintains endothelial integrity by preserving VE-cadherin expression and inhibiting TRPC6 channel-mediated calcium influx.
Sialidase Activity: The KL1 domain possesses weak sialidase (neuraminidase) activity that modifies glycans on TRPV5 and ROMK1 ion channels, increasing their cell surface retention and activity, which regulates renal calcium reabsorption and potassium secretion.
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Klotho
**Klotho** is a type I transmembrane protein originally identified in 1997 as an
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Research
Longevity and Aging
The foundational discovery by Kuro-o et al. (1997) showed that klotho-deficient mice develop a syndrome resembling accelerated aging with a median lifespan of ~61 days. Overexpression of klotho in transgenic mice extended median lifespan by 20-30% compared to wild-type littermates, establishing klotho as a bona fide aging-suppressor gene. The KL-VS variant (a functional haplotype containing F352V and C370S substitutions) has been associated with longevity and higher circulating klotho levels in multiple human cohorts. Arking et al. (2002) identified KL-VS heterozygosity as associated with extended human longevity, though homozygosity was detrimental.
Circulating klotho levels decline progressively with age, beginning around age 40, with levels in individuals over 70 approximately 50% lower than in young adults. Yamazaki et al. (2010) developed the first ELISA for soluble klotho, enabling clinical measurement and establishing reference ranges (~250-1100 pg/mL in healthy adults).
Inflammation and Oxidative Stress
Soluble klotho functions as an endogenous anti-inflammatory and antioxidant factor. It suppresses NF-kappaB activation in endothelial cells, reduces TNF-alpha and IL-6 production, and directly upregulates MnSOD and catalase expression through FoxO derepression. Klotho-deficient mice exhibit elevated markers of systemic inflammation and oxidative damage, while klotho overexpression reduces oxidative DNA damage (8-OHdG) and lipid peroxidation (4-HNE) across multiple tissues. These anti-inflammatory properties contribute to klotho's protective effects in kidney, brain, and cardiovascular tissues.
Neuroprotection and Cognitive Function
Klotho is highly expressed in the brain choroid plexus, and its deficiency causes cognitive impairment, hippocampal degeneration, and impaired myelination. Dubal et al. (2014) demonstrated in a landmark Cell Reports study that klotho overexpression enhances cognition in mice across multiple ages and genetic backgrounds, with effects mediated through enhancement of NMDA receptor-dependent synaptic plasticity via GluN2B subunit enrichment. In humans, a single copy of the KL-VS variant is associated with larger prefrontal cortical volume and better cognitive performance. Yokoyama et al. (2015) found that KL-VS heterozygosity protects against cognitive decline in APOE4 carriers, suggesting klotho modulation could counteract Alzheimer's risk.
Cardiovascular Protection
Klotho protects against vascular calcification, endothelial dysfunction, and cardiac hypertrophy. Xie et al. (2012) showed that soluble klotho inhibits phosphate-induced vascular smooth muscle cell calcification and osteoblastic differentiation. Klotho-deficient mice develop extensive vascular and soft tissue calcification driven by hyperphosphatemia and unchecked Wnt signaling. Hu et al. (2013) demonstrated that klotho suppresses cardiac hypertrophy by inhibiting TRPC6 channel activity, identifying a direct cardioprotective mechanism.
In human epidemiological studies, lower circulating klotho levels are independently associated with increased risk of cardiovascular events, coronary artery disease, and all-cause mortality. Klotho also protects endothelial function by upregulating nitric oxide (NO) production through increased endothelial nitric oxide synthase (eNOS) activity and by suppressing angiotensin II-induced oxidative stress in vascular smooth muscle cells.
Phosphate Metabolism and Mineral Homeostasis
The klotho-FGF23 axis is the master regulator of phosphate homeostasis. In the kidney, klotho enables FGF23 to suppress phosphate reabsorption by downregulating NaPi-IIa/IIc transporters in the proximal tubule. Simultaneously, FGF23-klotho signaling suppresses 1-alpha-hydroxylase, reducing active vitamin D synthesis and thereby decreasing intestinal phosphate absorption. Disruption of this axis (as in CKD) leads to hyperphosphatemia, secondary hyperparathyroidism, vascular calcification, and the mineral bone disorder characteristic of advanced kidney disease. Shimada et al. (2004) established FGF23 as a phosphaturic hormone, and subsequent work identified klotho as the essential co-receptor enabling FGF23 signaling specificity.
Kidney Disease
The kidney is the primary site of klotho expression, and renal klotho levels are profoundly reduced in chronic kidney disease (CKD), making klotho deficiency a hallmark of CKD. Hu et al. (2011) demonstrated that klotho deficiency exacerbates renal fibrosis through activation of Wnt/beta-catenin signaling, and that exogenous klotho administration attenuates fibrosis in animal models. Klotho loss precedes and predicts CKD progression, and restoration of klotho protects against acute kidney injury (AKI) by suppressing oxidative stress, inflammation, and apoptosis. Doi et al. (2011) showed that klotho inhibits TGF-beta1-induced EMT in renal tubular cells, a key driver of renal fibrosis.
Safety Profile
Klotho is an endogenous protein with well-characterized physiological functions, providing a favorable theoretical safety framework. In preclinical studies, exogenous recombinant klotho administration has not produced significant adverse effects at doses used in published research.
Known safety considerations include:
- Phosphate homeostasis: Excessive klotho/FGF23 axis activation could theoretically cause hypophosphatemia, though this has not been observed at preclinical therapeutic doses
- Vitamin D suppression: Klotho-mediated FGF23 signaling suppresses 1,25(OH)2D3 synthesis; chronic supraphysiological klotho could impair vitamin D-dependent calcium absorption
- Insulin sensitivity: Klotho suppresses insulin/IGF-1 signaling, which is beneficial for longevity but could theoretically impair glucose homeostasis at excessive doses
- Wnt inhibition: Chronic Wnt suppression could impair tissue regeneration and stem cell function, particularly in bone and intestinal epithelium
- Immunogenicity: Recombinant protein therapy carries risk of anti-drug antibody formation with chronic administration
- Long-term data: No human clinical trials have been completed; safety profile relies on preclinical models and observational human genetic data
Pharmacokinetic Profile
Klotho — Pharmacokinetic Curve
Recombinant protein injection (research); gene therapy (experimental)Quick Start
- Route
- Recombinant protein injection (research); gene therapy (experimental)
Molecular Structure
- Formula
- Complex glycoprotein (~130 kDa with glycosylation)
Research Indications
Anti-Aging
Single low-dose klotho injection enhanced memory in aged nonhuman primates (Nature Aging 2023). Meta-analysis of 6,645 subjects confirmed positive correlation between klotho levels and cognitive function.
Klotho deficiency is strongly linked to kidney pathology. Supplementation inhibits TGF-β signaling and protects against renal fibrosis. Klotho-derived peptide KP6 shows promise for diabetic kidney disease.
Meta-analysis of 14 studies found low klotho levels correlate with greater cardiovascular mortality risk. Klotho inhibits vascular calcification and cardiac hypertrophy in preclinical models.
Klotho overexpression extends lifespan 20-30% in mice. Klotho-deficient mice show accelerated aging with multi-organ atrophy. Inhibits four aging pathways: TGF-β, IGF-1, Wnt, and NF-κB.
Recombinant klotho protects against insulitis in diabetic models and myocardial ischemia-reperfusion injury. Human klotho levels decline from around age 40.
Research Protocols
intracerebroventricular Injection
- Routes: Intravenous (recombinant protein), intramuscular (AAV gene therapy), intracerebroventricular (CNS studies).
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
intramuscular Injection
- Gene therapy: AAV-klotho constructs delivering klotho gene intramuscularly in mice increased circulating klotho for >12 weeks (Ravikumar et al., 2014). - Routes: Intravenous (recombinant protein), intramuscular (AAV gene therapy), intracerebroventricular (CNS studies).
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
intravenous Injection
- Routes: Intravenous (recombinant protein), intramuscular (AAV gene therapy), intracerebroventricular (CNS studies).
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
intranasal Injection
- CNS delivery: Intrathecal and intranasal klotho delivery being investigated for neurodegenerative diseases, bypassing the blood-brain barrier.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
oral
No oral klotho supplement exists — the protein is not orally bioavailable.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
intrathecal Injection
- CNS delivery: Intrathecal and intranasal klotho delivery being investigated for neurodegenerative diseases, bypassing the blood-brain barrier.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| In mice | 0.01-0.1 mg | Per protocol | — |
Interactions
Peptide Interactions
Both target metabolic homeostasis and longevity. Klotho via insulin/IGF-1 suppression, MOTS-c via AMPK activation. Mechanistic rationale for complementary anti-aging effects.
What to Expect
What to Expect
Effects begin within hours of administration based on half-life of ~1-2 hours (soluble klotho in circulation)
Duration: Acute injury models: 1-7 days treatment.
CKD models: 4-12 weeks sustained delivery.
Gene therapy: AAV-klotho constructs delivering klotho gene intramuscularly in mice increased circulating klotho for >12 weeks .
Continued use as directed
Quality Indicators
What to look for
- Human clinical trials conducted
- Extensive peer-reviewed research base
- Oral administration available
Caution
- Limited human data available
Frequently Asked Questions
References (18)
- [1]Kuro-o M, Matsumura Y, Aizawa H, et al Mutation of the mouse klotho gene leads to a syndrome resembling ageing Nature (1997)
- [14]Chen G, Liu Y, Goetz R, et al Alpha-klotho is a non-enzymatic molecular scaffold for FGF23 hormone signalling Nature (2018)
- [13]Yokoyama JS, Sturm VE, Bonham LW, et al Variation in longevity gene KLOTHO is associated with greater cortical volumes Ann Clin Transl Neurol (2015)
- [2]Kurosu H, Yamamoto M, Clark JD, et al Suppression of aging in mice by the hormone klotho Science (2005)
- [3]Urakawa I, Yamazaki Y, Shimada T, et al Klotho converts canonical FGF receptor into a specific receptor for FGF23 Nature (2006)
- [6]Yamazaki Y, Imura A, Urakawa I, et al Establishment of sandwich ELISA for soluble alpha-klotho measurement Biochem Biophys Res Commun (2010)
- [8]Doi S, Zou Y, Togao O, et al Klotho inhibits transforming growth factor-beta1 (TGF-beta1) signaling and suppresses renal fibrosis and cancer metastasis in mice J Biol Chem (2011)
- [9]Xie J, Cha SK, An SW, et al Cardioprotection by klotho through downregulation of TRPC6 channels in the mouse heart Nat Commun (2012)
- [10]Hu MC, Shi M, Gillings N, et al Recombinant alpha-klotho may be prophylactic and therapeutic for acute to chronic kidney disease progression and uremic cardiomyopathy Kidney Int (2013)
- [11]
- [12]Ravikumar P, Ye J, Zhang J, et al Alpha-klotho protects against oxidative damage in pulmonary epithelia Am J Physiol Lung Cell Mol Physiol (2014)
- [4]Liu H, Fergusson MM, Castilho RM, et al Augmented Wnt signaling in a mammalian model of accelerated aging Science (2007)
- [5]Arking DE, Krebsova A, Macek M Sr, et al Association of human aging with a functional variant of klotho Proc Natl Acad Sci USA (2002)
- [7]Hu MC, Shi M, Zhang J, et al Klotho deficiency causes vascular calcification in chronic kidney disease J Am Soc Nephrol (2011)
- [18]Chen et al — Soluble klotho protects against vascular calcification through the PI3K/AKT/FOXO1 pathway Cardiovasc Res (2022)
- [15]Castner SA, Gupta S, Wang D, et al Longevity factor klotho enhances cognition in aged nonhuman primates Nature Aging (2023)
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