Anti-aging Hormone Klotho Research Articles

Antiaging hormone Klotho derived from renal distal-convolution regulates calcium but not phosphate homeostasis

Soluble-Klotho (sKl) is the shed ectodomain of the transmembrane protein-Klotho (mKl) that exhibits pleiotropic actions, including lifespan extension, mineral metabolism, slowing-down kidney diseases and cardioprotection. The sKl is derived from the kidneys, but what type/s of renal cells secrete it is unknown. Secondly the respective roles of mKl versus sKl in regulating mineral metabolism is unclear due to the lack of appropriate in vivo models. Here, using scRNA-seq of renal distal-convolution (DC) cells, we found an unexpected pattern revealing that Klotho transcripts ( Kl) are moderately expressed in overall distal convoluted tubule (DCT), but highly enriched in the end of DCT and in connecting tubule (CNT). Immunohistochemistry further confirmed this pattern for mKl protein as well. Next, Kl was knocked-out only in renal DC to check if it affects sKl production. Interestingly, deleting Kl in the DCT and late-DCT+CNT in mice showed ~20% and ~80% reduction in sKl levels, respectively. Expectedly, knocking-out Kl along the entire DC in mice (Kl-KO DC ) abolished sKl levels. Furthermore, we found that compared to control mice, Kl-KO DC mice exhibited reduced renal TRPV5-Ca 2+ channel expression, profound calciuria, and loss of bone mineral density. The RNA-seq of automated-sorted DC cells from Kl-KO DC mice revealed enhanced caveolae-mediated endocytosis of TRPV5. On the other hand, Kl-KO DC mice had normal phosphate metabolism as confirmed by unchanged serum FGF23, serum phosphate, urinary phosphate excretion, and renal NaPi-IIa expression. Our findings reveal that a small population of renal DC cells accounts for the sKl levels. The lack of sKl may leads to disturbed Ca 2+ homeostasis and bone loss without affecting phosphate balance in mice. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Reduced Levels of the Antiaging Hormone Klotho are Associated With Increased Aortic Stiffness in Diabetic Kidney Disease

Aortic pulse wave velocity (Ao-PWV) predicts cardiovascular and kidney disease in type 2 diabetes (T2D). Klotho is a circulating antiaging hormone (sKlotho) with putative cardiorenal protective effects. The relationship between sKlotho and Ao-PWV in diabetic kidney disease (DKD) is unknown. In a cross-sectional cohort study, the correlation of sKlotho measured by a validated immunoassay, and Ao-PWV measured by applanation tonometry, was investigated in 172 participants with T2D and early stage DKD (all had estimated glomerular filtration rate [eGFR] >45 ml/min) on stable renin angiotensin system (RAS) inhibition. In cultured human aortic smooth muscle cells (HASMCs) stimulated with angiotensin II (AngII), the effects of recombinant human sKlotho pretreatment were assessed on intracellular calcium ([Ca2+]i) responses and expression of proteins associated with proosteogenic HASMC phenotypes. Mean (range) age of the cohort was 61.3 years (40-82) and 65% were male. Mean (±SD) Ao-PWV was 11.4 (±2.3) m/s, eGFR 78.8 (±23.5) and median (interquartile range) sKlotho of 358.5 (194.2-706.3) pg/ml. In multivariable linear regression analyses, we observed a statistically significant inverse relationship between sKlotho and Ao-PWV, which was independent of clinical risk factors for cardiorenal disease. Pretreatment of cultured HASMC with sKlotho significantly attenuated AngII-stimulated [Ca2+]i transients and reduced osteogenic collagen (Col1a2) expression. In individuals with T2D and early DKD, lower levels of sKlotho are associated with increased Ao-PWV. Taken together with the direct effect of sKlotho on mediators of aortic wall stiffness invitro, these findings may explain the enhanced risk of cardiorenal disease in DKD.

The Anti-Aging Hormone Klotho Promotes Retinal Pigment Epithelium Cell Viability and Metabolism by Activating the AMPK/PGC-1α Pathway

Initially discovered by Makuto Kuro-o in 1997, Klotho is a putative aging-suppressor gene when overexpressed and accelerates aging when deleted in mice. Previously, we showed that α-Klotho regulates retinal pigment epithelium (RPE) functions and protects against oxidative stress. However, the mechanisms by which Klotho influences RPE and retinal homeostasis remain elusive. Here, by performing a series of in vitro and in vivo experiments, we demonstrate that Klotho regulates cell viability under oxidative stress, mitochondrial gene expression and activity by inducing the phosphorylation of AMPK and p38MAPK, which in turn phosphorylate and activate CREB and ATF2, respectively, triggering PGC-1α transcription. The inhibition of Klotho in human RPE cells using CRISPR-Cas9 gene editing confirmed that a lack of Klotho negatively affects RPE functions, including mitochondrial activity and cell viability. Proteomic analyses showed that myelin sheath and mitochondrial-related proteins are downregulated in the RPE/retina of Kl-/- compared to WT mice, further supporting our biochemical observations. We conclude that Klotho acts upstream of the AMPK/PGC-1α pathway and regulates RPE/retinal resistance to oxidative stress, mitochondrial function, and gene and protein expressions. Thus, KL decline during aging could negatively impact retinal health, inducing age-related retinal degeneration.

Renal effects of growth hormone in health and in kidney disease

Growth hormone (GH) and its mediator insulin-like growth factor-1 (IGF-1) have manifold effects on the kidneys. GH and IGF receptors are abundantly expressed in the kidney, including the glomerular and tubular cells. GH can act either directly on the kidneys or via circulating or paracrine-synthesized IGF-1. The GH/IGF-1 system regulates glomerular hemodynamics, renal gluconeogenesis, tubular sodium and water, phosphate, and calcium handling, as well as renal synthesis of 1,25 (OH)2 vitamin D3 and the antiaging hormone Klotho. The latter also acts as a coreceptor of the phosphaturic hormone fibroblast-growth factor 23 in the proximal tubule. Recombinant human GH (rhGH) is widely used in the treatment of short stature in children, including those with chronic kidney disease (CKD). Animal studies and observations in acromegalic patients demonstrate that GH-excess can have deleterious effects on kidney health, including glomerular hyperfiltration, renal hypertrophy, and glomerulosclerosis. In addition, elevated GH in patients with poorly controlled type 1 diabetes mellitus was thought to induce podocyte injury and thereby contribute to the development of diabetic nephropathy. This manuscript gives an overview of the physiological actions of GH/IGF-1 on the kidneys and the multiple alterations of the GH/IGF-1 system and its consequences in patients with acromegaly, CKD, nephrotic syndrome, and type 1 diabetes mellitus. Finally, the impact of short- and long-term treatment with rhGH/rhIGF-1 on kidney function in patients with kidney diseases will be discussed.

Regulation of muscle stem cell function.

Regeneration of skeletal muscle is a finely tuned process which is depending on muscle stem cells, a population of stem cells in skeletal muscle which is also termed satellite cells. Muscle stem cells are a prerequisite for regeneration of skeletal muscle. Of note, the muscle stem cell population is heterogeneous and subpopulations can be identified depending on gene expression or phenotypic traits. However, all muscle stem cells express the transcription factor Pax7 and their functionality is tightly controlled by intrinsic signaling pathways and extrinsic signals. The latter ones include signals form the stem cell niche as well as circulating factors such as growth factors and hormones. Among them are Wnt proteins, growth factors like IGF-1 or FGF-2 and hormones such as thyroid hormones and the anti-aging hormone Klotho. A highly orchestrated interplay between those factors and muscle stem cells is important for their full functionality and ultimately regeneration of skeletal muscle as outlined here.

Klotho Ameliorates Renal Fibrosis in a Murine Model of ADTKD‐UMOD by Enhancing UMOD secretion and Downregulation of TGFBI

Heterozygous Uromodulin (UMOD) mutations cause autosomal dominant tubulo‐interstitial kidney disease (ADTKD). ADTKD‐UMOD is a model for renal fibrosis.Currently, no therapies are available for ADTKD‐UMOD. The antiaging hormone Klotho improves glomerular disease, hypertension, uremic cardiomyopathy, and acute kidney injury (AKI). We tested if Klotho ameliorates renal fibrosis and tubular disease in a murine model of ADTKD‐UMOD.To generate a more pronounced phenotype we used homozygous UmodC93F/C93F mice. Mice were crossed with mice overexpressing Klotho (TgKl). We compared the phenotype with wild‐type (WT), TgKl, and UmodC93F/C93F mice (8 animals per group). We studied blood pressure, urine and blood samples at ages of 6 and 13 months. In different animals of the four groups, we harvested kidneys at 3 months to perform quantitative proteome analysis via LC‐MS/MS on renal outer medulla.Compared to UmodC93F/C93F mice, TgKl/UmodC93F/C93F had better renal function as indicated by significantly lower BUN, creatinine, and cystatin C values, and less renal fibrosis. PTH and FGF23 improved significantly in TgKl/UmodC93F/C93F vs. UmodC93F/C93F mice. Mutant UMOD is retained in the endoplasmic reticulum. We found that relative urinary UMOD secretion was higher in TgKl/UmodC93F/C93F vs. UmodC93F/C93F. No major serum electrolyte differences were found among the four groups. Urinary studies in TgKl/UmodC93F/C93F mice showed less urinary wasting of Na+, Ca2+, Mg2+ and Phosphorus than in UmodC93F/C93F mice. Compared to UmodC93F/C93F, Klotho‐overexpressing animals had significantly lower systolic and diastolic blood pressures. Markers of cardiac hypertrophy such as ANP, BNP, and MYH7 mRNA were significantly lower in TgKl/UmodC93F/C93F than in UmodC93F/C93F animals. We confirmed impaired unfolded protein response (UPR) and autophagy in UmodC93F/C93F compared to WT mice. However, improved renal function and fibrosis in Klotho‐overexpressing mice were not due to changes in UPR or autophagy. Therefore, we performed an unbiased proteomics approach. We identified 262 downregulated and 179 upregulated proteins in kidneys. Analyzing proteins by signaling pathways, we identified in TgKl/UmodC93F/C93F vs. UmodC93F/C93F animals downregulation of Transforming growth factor‐beta‐induced protein (TGFBI) together with collagens Col1a1, Col4a3, Col4a4, Col4a5, Col6a1, Col6a2, Col6a3, Col12a1, Col14a1, prolargin, biglycan, and osteoglycin/mimecan. We confirmed lower Col1a1 mRNA expression with qPCR.We show that Klotho improves renal outcome in ADTKD‐UMOD by increasing urinary UMOD secretion and ameliorating renal fibrosis by downregulation of TGFBI and collagen. TGFBI is secreted by mesenchymal stromal cells and infiltrating macrophages and stimulates collagen synthesis. Infiltrating macrophages are an important part of AKI and ADTKD‐UMOD. Our data reveal a new specific target for treatment of renal fibrosis.Support or Funding InformationNIH R03 DK111776, NIH P30 DK079328, and CCRAC Senior Investigator Bridge Award, Children’s Health DallasAt 6 and 13 months TgKl/UmodC93F/C93F show significantly lower BUN, creatinine, and cystatin C values.Figure 1STRING analysis showing networks formed by downregulated proteins in renal outer medulla of TgKl/UmodC93F/C93F compared to UmodC93F/C93F mice. Red circle outlines downregulated TGFBI and collagens.Figure 2

Peripheral levels of the anti-aging hormone Klotho in patients with depression.

Klotho is a humoral factor with pleiotropic effects. Most notably, Klotho deficiency is associated with a phenotype comprising organ manifestations accompanying aging including atherosclerosis and cognitive impairment. Research on the role of Klotho in affective disorder is scarce, which is surprising in light of the fact that depression is associated with accelerated cellular aging as well as aging-related phenotypes and comorbidity observed in Klotho deficiency. Soluble α-Klotho (sKlotho) serum levels in patients with a major depressive episode and either undergoing electroconvulsive therapy (n = 16) or a monotherapy with an antidepressant (n = 37) were investigated. We measured the sKlotho serum levels in those patients before and after treatment and compared the baseline levels with those of age-matched healthy controls (n = 39). No group differences were found between the baseline sKlotho levels of patients and controls (573.5pg/ml vs. 563.8pg/ml; p = 0.80) and between pre- and post-treatment in the patients with depression (563.8pg/ml vs. 561.8pg/ml; p = 0.15), when treated either with electroconvulsive therapy or antidepressant. The major limitation of our study might be that peripheral material such as serum might not reliably reflect processes in the central nervous system. In sum, this first study on peripheral sKlotho levels in a clinical sample cannot confirm a global Klotho dysregulation in depression as it has been already suggested by others. Nonetheless, further preclinical and clinical studies on the involvement of Klotho in affective disorders should be carried out.

From the Literature

From the Literature

Klotho expression is a prerequisite for proper muscle stem cell function and regeneration of skeletal muscle

BackgroundKlotho is a well-known anti-aging hormone, which serves as a suppressor of aging through a variety of mechanisms. Aging of skeletal muscle is concomitant with a decrease in muscle stem cell function resulting in impaired regeneration.MethodsHere we investigate the functional role of the anti-aging hormone Klotho for muscle stem cell function after cardiotoxin-induced injury of skeletal muscle using a klotho hypomorphic mouse line, which is characterized by a premature aging phenotype. Furthermore, we perform floating single myofiber cultures with their adjacent muscle stem cells to investigate the interplay between canonical Wnt signaling and Klotho function.ResultsWe demonstrate that muscle stem cell numbers are significantly decreased in klotho hypomorphic mice. Furthermore, we show that muscle stem cell function is also severely impaired upon loss of klotho expression, in culture and during regeneration in vivo. Moreover, we demonstrate that addition of recombinant Klotho protein inhibits aberrant excessive Wnt signaling in aged muscle stem cells thereby restoring their functionality.ConclusionsThe anti-aging hormone Klotho counteracts aberrant canonical Wnt signaling in muscle stem cells and might be one of the naturally occurring inhibitors of canonical Wnt signaling in skeletal muscle.

Klotho Deficiency Disrupts Hematopoietic Stem Cell Development and Erythropoiesis

Klotho deficiency is a characteristic feature of chronic kidney disease in which anemia and cardiovascular complications are prevalent. Disruption of the Klotho gene in mice results in hypervitaminosis D and a syndrome resembling accelerated aging that includes osteopenia and vascular calcifications. Given that the bone microenvironment and its cellular components considerably influence hematopoiesis, in the present study, we addressed the in vivo role of klotho in blood cell formation and differentiation. Herein, we report that genetic ablation of Klotho in mice results in a significant increase in erythropoiesis and a decrease in the hematopoietic stem cell pool size in the bone marrow, leading to impaired hematopoietic stem cell homing in vivo. Our data also suggest that high vitamin D levels are only partially responsible for these hematopoietic changes in Klotho(-/-) mice. Importantly, we found similar hematopoietic abnormalities in Klotho(-/-) fetal liver cells, suggesting that the effects of klotho in hematopoietic stem cell development are independent of the bone microenvironment. Finally, injection of klotho protein results in hematopoietic changes opposite to the ones observed in Klotho(-/-) mice. These observations unveil a novel role for the antiaging hormone klotho in the regulation of prenatal and postnatal hematopoiesis and provide new insights for the development of therapeutic strategies targeting klotho to treat hematopoietic disorders associated with aging.

The Epithelial Calcium Channel TRPV5 Is Regulated Differentially by Klotho and Sialidase

The transient receptor potential vanilloid type 5 (TRPV5) Ca(2+) channel facilitates transcellular Ca(2+) transport in the distal convoluted tubule (DCT) of the kidney. The channel is glycosylated with a complex type N-glycan and it has been postulated that hydrolysis of the terminal sialic acid(s) stimulate TRPV5 activity. The present study delineates the role of the N-glycan in TRPV5 activity using biochemical assays in Human Embryonic Kidney 293 cells expressing TRPV5, isoelectric focusing and total internal reflection fluorescent microscopy. The anti-aging hormone klotho and other glycosidases stimulate TRPV5-dependent Ca(2+) uptake. Klotho was found to increase the plasma membrane stability of TRPV5, via the TRPV5 N-glycan. Sialidase mimicked this stimulatory action. However, this effect was independent of the N-glycosylation state of TRPV5, since the N-glycosylation mutant (TRPV5(N358Q)) was activated to the same extent. We showed that the increased TRPV5 activity after sialidase treatment is caused by inhibition of lipid raft-mediated internalization. In addition, sialidase modified the N-glycan of transferrin, a model glycoprotein, differently from klotho. Previous studies showed that after klotho treatment, galectin-1 binds the TRPV5 N-glycan and thereby increases TRPV5 activity. However, galectin-3, but not galectin-1, was expressed in the DCT. Furthermore, an increase in TRPV5-mediated Ca(2+) uptake was detected after galectin-3 treatment. In conclusion, two distinct TRPV5 stimulatory mechanisms were demonstrated; a klotho-mediated effect that is dependent on the N-glycan of TRPV5 and a sialidase-mediated stimulation that is lipid raft-dependent and independent of the N-glycan of TRPV5.

Unilateral ureteral obstruction: beyond obstruction

Unilateral ureteral obstruction is a popular experimental model of renal injury. However, the study of the kidney response to urinary tract obstruction is only one of several advantages of this model. Unilateral ureteral obstruction causes subacute renal injury characterized by tubular cell injury, interstitial inflammation and fibrosis. For this reason, it serves as a model both of irreversible acute kidney injury and of events taking place during human chronic kidney disease. Being a unilateral disease, it is not useful to study changes in global kidney function, but has the advantage of a low mortality and the availability of an internal control (the non-obstructed kidney). Experimental unilateral ureteral obstruction has illustrated the molecular mechanisms of apoptosis, inflammation and fibrosis, all three key processes in kidney injury of any cause, thus providing information beyond obstruction. Recently this model has supported key concepts on the role in kidney fibrosis of epithelial-mesenchymal transition, tubular epithelial cell G2/M arrest, the anti-aging hormone Klotho and renal innervation. We now review the experimental model and its contribution to identifying novel therapeutic targets in kidney injury and fibrosis, independently of the noxa.

New Approaches to Pathogenesis and Management of Hypertension

New Approaches to Pathogenesis and Management of Hypertension

A molecularly guided tour along the nephron

The kidney is an intriguingly multifaceted organ controlling many vital body functions. Therefore, the kidney orchestrates a large set of tasks including the maintenance of the body fluid balance and thereby the blood pressure, the reabsorption of glucose, amino acids and other nutrients, the excretion of sodium, potassium, calcium, magnesium, and other electrolytes, and the control of the acid/base balance. In addition, the kidney produces hormones and proteins exerting important general physiological roles. For instance, the biological active form of vitamin D is mainly produced in the kidney through the conversion of 25hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 by the renal enzyme 25-hydroxyvitamin D-1-α-hydroxylase. In addition, the antiaging hormone klotho is primarily produced in the kidney and controls overall mineral metabolism. Also, the glycoprotein erythropoietin is generated here and enhances the oxygen-carrying capacity of the blood by activating the production of erythrocytes by the bone marrow. The importance of these renal hormones is sadly demonstrated by the severe symptoms accompanying chronic kidney diseases. The kidney is an anatomically complex structure consisting of a large number of nephrons, the functional units of the kidney. Each nephron begins with a glomerulus that filters blood entering the kidney. This filtrate then flows along the length of the nephron. The major function of the epithelial cells lining the nephron is the reabsorption of water and small molecules from the filtrate into the blood and the secretion of wastes from the blood into the urine. To this end, the kidney is equipped with a host of transport proteins including ion channels, electrolyte transporters, and pumps within specific epithelial cells along the various tubule segments. In recent years, our understanding of the molecular nature of these transport proteins has made major progress through the application of functional expression cloning techniques using Xenopus laevis oocytes and the identification of gene defects in inherited renal tubular transport disorders. The regulation of these transport processes is constantly challenged by a demanding and greatly variable environment including an acidic luminal pH, a high medullary osmolarity, and a variability in blood and urinary flow as well as in the composition of the prourine [4]. The activity of these transporters can basically be controlled at several discrete levels. First, the expression level of the particular transporter can be regulated by specific hormones. Second, trafficking of the transporter to the designated plasma membrane can be controlled by intracellular signaling processes. Third, the activity of the transport protein present at the plasma membrane can be subject to various extra-en intracellular regulatory mechanisms. Ample timely physiological studies have addressed these various regulatory aspects of renal transport processes. New key physiological mechanisms have emerged from these recent investigations particularly through a multidisciplinary approach using model cells and organisms. The complexity in structure and function of the kidney is increasingly revealed by these investigations. To do justice to this fact, a standard nomenclature has been disseminated to facilitate the renal physiologist [14]. Consequently, this special issue has been divided according to the main parts of the nephron including the proximal tubule, the loop of Henle, the distal convoluted tubule, the connecting tubule, and the collecting duct. In this guided tour along the nephron, world-renowned renal physiologists highlight the Pflugers Arch Eur J Physiol (2009) 458:1–3 DOI 10.1007/s00424-009-0661-3

Calcium and phosphate homeostasis: Concerted interplay of new regulators

Calcium (Ca2+) and phosphate (Pi) are essential to many vital physiological processes. Consequently the maintenance of Ca2+ and Pi homeostasis is essential to a healthy existence. This occurs through the concerted action of intestinal, renal, and skeletal regulatory mechanisms. Ca2+ and Pi handling by these organs is under tight hormonal control. Disturbances in their homeostasis have been linked to pathophysiological disorders including chronic renal insufficiency, kidney stone formation, and bone abnormalities. Importantly, the kidneys fine‐tune the amount of Ca2+ and Pi retained in the body by altering their (re)absorption from the glomerular filtrate. The ion transport proteins involved in this process have been studied extensively. Recently, new key players have been identified in the regulation of the Ca2+ and Pi balance. Novel regulatory mechanisms and their implications were introduced for the antiaging hormone klotho and fibroblast growth factor member 23 (FGF23). Importantly, transgenic mouse models, exhibiting disturbances in Ca2+ and Pi balance, have been of great value in the elucidation of klotho and FGF23 functioning. This review highlights the current knowledge and ongoing research into Ca2+ and Pi homeostasis, emphasizing findings from several relevant knockout mouse models.

Regulation of the epithelial calcium channel TRPV5 by extracellular factors

Recent studies have greatly increased our knowledge concerning the regulation of renal calcium handling. This review focuses on newly identified calciotropic factors present in the pro-urine and the mechanisms by which they control the transient receptor potential channel vanilloid subtype 5 (TRPV5) which forms the gatekeeper of active renal calcium reabsorption. The antiaging hormone klotho regulates TRPV5 activity via a novel mechanism modifying its glycosylation status, thereby entrapping the channel at the cell surface. Functional characterization of tissue kallikrein knockout mice revealed that these animals exhibit a pronounced hypercalciuria, comparable to the calcium leak observed in TRPV5 knockout mice. Recently, it has been demonstrated that tissue kallikrein stimulates active calcium reabsorption via the bradykinin receptor type 2 pathway involving protein kinase C-dependent activation of TRPV5. Finally, the extracellular pH appears to act as a dynamic switch controlling cell surface expression of TRPV5. Unraveling the molecular mechanisms of TRPV5 channel regulation by the antiaging hormone klotho, tissue kallikrein and extracellular pH demonstrated the existence of novel regulatory mechanisms of active calcium reabsorption acting from the tubular lumen.

Recent advances in renal tubular calcium reabsorption

Knowledge of renal Ca2+ reabsorption has evolved greatly in recent years. This review focuses on two recent discoveries concerning passive and active Ca2+ reabsorption. The thiazide diuretics are known for their hypocalciuric effect. Recently, it has been demonstrated that TRPV5-knockout mice, in which active Ca2+ reabsorption in the distal convoluted tubule is completely abolished, show the same sensitivity towards thiazides as wild-type mice. This indicates that thiazide affects Ca2+ reabsorption indirectly via contraction of the extracellular volume, independent of active Ca2+ reabsorption in the distal convoluted tubule, thereby increasing passive paracellular Ca2+ transport in the proximal tubule. Moreover, the antiaging hormone Klotho regulates Ca2+ reabsorption in the distal convoluted tubule via a novel molecular mechanism. Klotho stabilizes the TRPV5 Ca2+ channel in the plasma membrane by deglycosylation of the protein. By showing that thiazide-induced hypercalciuria is due to increased passive Ca2+ reabsorption in the proximal tubule, a long-standing issue has been solved, underlining the importance of proximal paracellular Ca2+ reabsorption. Moreover, the molecular mechanism by which the antiaging hormone Klotho regulates TRPV5 activity may prove to be generally applicable in Klotho-mediated prevention of aging.

Regulation of Oxidative Stress by the Anti-aging Hormone Klotho*♦

klotho is an aging suppressor gene and extends life span when overexpressed in mice. Klotho protein was recently demonstrated to function as a hormone that inhibits insulin/insulin-like growth factor-1 (IGF-1) signaling. Here we show that Klotho protein increases resistance to oxidative stress at the cellular and organismal level in mammals. Klotho protein activates the FoxO forkhead transcription factors that are negatively regulated by insulin/IGF-1 signaling, thereby inducing expression of manganese superoxide dismutase. This in turn facilitates removal of reactive oxygen species and confers oxidative stress resistance. Thus, Klotho-induced inhibition of insulin/IGF-1 signaling is associated with increased resistance to oxidative stress, which potentially contributes to the anti-aging properties of klotho.