The Role of Alpha-Klotho as a Universal Tumor Suppressor

Association Between Serum Klotho and Chronic Obstructive Pulmonary Disease in US Middle-Aged and Older Individuals: A Cross-Sectional Study from NHANES 2013-2016

Purpose

This study sought to examine the potential association between serum Klotho levels and the prevalence of COPD in the United States.

Patients and Methods

This study was a cross-sectional analysis involving 4361 adults aged 40-79 years participating in the US National Health and Nutrition Examination Survey (NHANES) conducted between 2013 and 2016. Our investigation utilized multivariate logistic regression and restricted cubic spline (RCS) regression to explore the potential correlation between serum Klotho concentrations and the prevalence of COPD. Additionally, we conducted stratified and interaction analyses to evaluate the consistency and potential modifiers of this relationship.

Results

In this study encompassing 4631 patients (with an average age of 57.6 years, 47.5% of whom were male), 445 individuals (10.2%) were identified as having COPD. In the fully adjusted model, ln-transformed serum Klotho was negatively associated with COPD (OR = 0.71; 95% CI: 0.51-0.99; p = 0.043). Meanwhile, compared with quartile 1, serum Klotho levels in quartiles 2-4 yielded odds ratios (ORs) (95% CI) for COPD were 0.84 (0.63~1.11), 0.76 (0.56~1.02), 0.84 (0.62~1.13), respectively. A negative relationship was observed between the ln-transformed serum Klotho and occurrence of COPD (nonlinear: p = 0.140). the association between ln-transformed serum Klotho and COPD were stable in stratified analyses.

Conclusion

Serum Klotho was negatively associated with the incidence of COPD, when ln-transformed Klotho concentration increased by 1 unit, the risk of COPD was 29% lower.

Protein interaction networks characterizing the A549 cells Klotho transfected are associated with activated pro-apoptotic Bim and suppressed Wnt/β-catenin signaling pathway

Invasive assays and lung tumor-bearing mice models using a human lung adenocarcinoma cell line A549 cells transfected with the Klotho (KL) gene, A549/KL cells, have confirmed that KL suppresses invasive/metastatic potential. This study aimed to identify the co-expression protein networks and proteomic profiles associated with A549/KL cells to understand how Klotho protein expression affects molecular networks associated with lung carcinoma malignancy. A two-step application of a weighted network correlation analysis to the cells' quantitative proteome datasets of a total of 6,994 proteins, identified by mass spectrometry-based proteomic analysis with data-independent acquisition (DIA), identified one network module as most significantly associated with the A549/KL trait. Upstream analyses, confirmed by western blot, implicated the pro-apoptotic Bim (Bcl-2-like protein 11) as a master regulator of molecular networks affected by Klotho. GeneMANIA interaction networks and quantitative proteome data implicated that Klotho interacts with two signaling axes: negatively with the Wnt/β-catenin axis, and positively by activating Bim. Our findings might contribute to the development of future therapeutic strategies.

Revealing the tumor suppressive sequence within KL1 domain of the hormone Klotho

Klotho, a 1012 amino acid transmembrane protein, is a potent tumor suppressor in different cancer types. Klotho is composed of two internal repeats KL1 and KL2, and the tumor suppressor activity is primarily attributed to the KL1 domain. Despite its significant role in regulating various cancer-related pathways, the precise mechanism underlying its tumor suppressor activity remains unresolved. In this study, we aimed to identify the sequence responsible for the tumor suppressor function of Klotho and gain insights into its mechanism of action. To accomplish this, we generated expression vectors of truncated KL1 at the C and N-terminal regions and evaluated their ability to inhibit the colony formation of several cancer cell lines. Our findings demonstrated that truncated KL1 1-340 (KL340) effectively inhibited colony formation similar to KL1, while truncated KL1 1-320 (KL320) lost this activity. Furthermore, this correlated with the inhibitory effect of KL1 and KL340 on the Wnt/β-catenin pathway, whereas KL320 had no effect. Transcriptomic analysis of MCF-7 cells expressing the constructs revealed enriched pathways associated with tumor suppressor activity in KL1 and KL340. Interestingly, the α-fold predictor tool highlighted distinct differences in the α and β sheets of the TIM barrel fold of the truncated Klotho constructs, adding to our understanding of their structural variations. In summary, this study identified the 340 N-terminal amino acids as the sequence that possesses Klotho's tumor suppressor activity and reveals a critical role in the 320-340 sequence for this function. It also provides a foundation for the development of Klotho-based therapeutic approaches for cancer treatment.

Klotho in Cancer: Potential Diagnostic and Prognostic Applications

Klotho proteins, αKlotho, βKlotho, and γKlotho, exert tumor-suppressive activities via the fibroblast growth factor receptors and multiple cell-signaling pathways. There is a growing interest in Klotho proteins as potential diagnostic and prognostic biomarkers for multiple diseases. However, recent advances regarding their roles and potential applications in cancer remain disperse and require an integrated analysis. The present review analyzed research articles published between 2012 and 2022 in the Cochrane and Scopus scientific databases to study the role of Klotho in cancer and their potential as tools for diagnosing specific cancer types, predicting tumor aggressiveness and prognosis. Twenty-six articles were selected, dealing with acute myeloid leukemia and with bladder, breast, colorectal, esophageal, gastric, hepatocellular, ovarian, pancreatic, prostatic, pulmonary, renal, and thyroid cancers. αKlotho was consistently associated with improved prognosis and may be useful in estimating patient survival. A single study reported the use of soluble αKlotho levels in blood serum as a tool to aid the diagnosis of esophageal cancer. γKlotho was associated with increased aggressiveness of bladder, breast, and prostate cancer, and βKlotho showed mixed results. Further clinical development of Klotho-based assays will require careful identification of specific tumor subtypes where Klotho proteins may be most valuable as diagnostic or prognostic tools.

The role of α-klotho in human cancer: molecular and clinical aspects

Klotho is a well-established longevity hormone. Its most prominent function is the regulation of phosphate homeostasis. However, klotho possesses multiple pleiotropic activities, including inhibition of major signaling pathways, reducing oxidative stress and suppressing inflammation. These activities are tightly associated with cancer, and klotho was discovered as a universal tumor suppressor. We review here novel molecular aspects of klotho activity in cancer, focusing on its structure-function relationships and clinical aspects regarding its expression, blood levels, clinical risk, and prognostic value in the clinical setting. In addition, the potential benefit of klotho treatment combined with chemotherapy, biological therapy, or immunotherapy, are discussed. Finally, as klotho was shown in preclinical models to inhibit cancer development and growth, we discuss various approaches to developing klotho-based therapies.

Pathobiology of the Klotho Antiaging Protein and Therapeutic Considerations

The α-Klotho protein (henceforth denoted Klotho) has antiaging properties, as first observed in mice homozygous for a hypomorphic Klotho gene (kl/kl). These mice have a shortened lifespan, stunted growth, renal disease, hyperphosphatemia, hypercalcemia, vascular calcification, cardiac hypertrophy, hypertension, pulmonary disease, cognitive impairment, multi-organ atrophy and fibrosis. Overexpression of Klotho has opposite effects, extending lifespan. In humans, Klotho levels decline with age, chronic kidney disease, diabetes, Alzheimer’s disease and other conditions. Low Klotho levels correlate with an increase in the death rate from all causes. Klotho acts either as an obligate coreceptor for fibroblast growth factor 23 (FGF23), or as a soluble pleiotropic endocrine hormone (s-Klotho). It is mainly produced in the kidneys, but also in the brain, pancreas and other tissues. On renal tubular-cell membranes, it associates with FGF receptors to bind FGF23. Produced in bones, FGF23 regulates renal excretion of phosphate (phosphaturic effect) and vitamin D metabolism. Lack of Klotho or FGF23 results in hyperphosphatemia and hypervitaminosis D. With age, human renal function often deteriorates, lowering Klotho levels. This appears to promote age-related pathology. Remarkably, Klotho inhibits four pathways that have been linked to aging in various ways: Transforming growth factor β (TGF-β), insulin-like growth factor 1 (IGF-1), Wnt and NF-κB. These can induce cellular senescence, apoptosis, inflammation, immune dysfunction, fibrosis and neoplasia. Furthermore, Klotho increases cell-protective antioxidant enzymes through Nrf2 and FoxO. In accord, preclinical Klotho therapy ameliorated renal, cardiovascular, diabetes-related and neurodegenerative diseases, as well as cancer. s-Klotho protein injection was effective, but requires further investigation. Several drugs enhance circulating Klotho levels, and some cross the blood-brain barrier to potentially act in the brain. In clinical trials, increased Klotho was noted with renin-angiotensin system inhibitors (losartan, valsartan), a statin (fluvastatin), mTOR inhibitors (rapamycin, everolimus), vitamin D and pentoxifylline. In preclinical work, antidiabetic drugs (metformin, GLP-1-based, GABA, PPAR-γ agonists) also enhanced Klotho. Several traditional medicines and/or nutraceuticals increased Klotho in rodents, including astaxanthin, curcumin, ginseng, ligustilide and resveratrol. Notably, exercise and sport activity increased Klotho. This review addresses molecular, physiological and therapeutic aspects of Klotho.

Phosphate and Cellular Senescence

Cellular senescence is one type of permeant arrest of cell growth and one of increasingly recognized contributor to aging and age-associated disease. High phosphate and low Klotho individually and synergistically lead to age-related degeneration in multiple organs. Substantial evidence supports the causality of high phosphate in cellular senescence, and potential contribution to human aging, cancer, cardiovascular, kidney, neurodegenerative, and musculoskeletal diseases. Phosphate can induce cellular senescence both by direct phosphotoxicity, and indirectly through downregulation of Klotho and upregulation of plasminogen activator inhibitor-1. Restriction of dietary phosphate intake and blockage of intestinal absorption of phosphate help suppress cellular senescence. Supplementation of Klotho protein, cellular senescence inhibitor, and removal of senescent cells with senolytic agents are potential novel strategies to attenuate phosphate-induced cellular senescence, retard aging, and ameliorate age-associated, and phosphate-induced disorders.

A Transgenic Model Reveals the Role of Klotho in Pancreatic Cancer Development and Paves the Way for New Klotho-Based Therapy

Simple Summary

We aimed to study the role of the anti-aging protein klotho and its secreted isoform, sKL, in pancreatic cancer. Three in vivo models, including a novel genetic mouse model and bioinformatics analyses, indicated klotho as a tumor suppressor in pancreatic ductal adenocarcinoma, and unveiled a unique klotho DNA hypermethylation pattern in pancreatic tumors. These results possess significant prognostic value, and further suggest that sKL may serve as a therapeutic agent for pancreatic ductal adenocarcinoma.

Abstract

Klotho is an anti-aging transmembrane protein, which can be shed and can function as a hormone. Accumulating data indicate that klotho is a tumor suppressor in a wide array of malignancies, and designate the subdomain KL1 as the active region of the protein towards this activity. We aimed to study the role of klotho as a tumor suppressor in pancreatic ductal adenocarcinoma (PDAC). Bioinformatics analyses of The Cancer Genome Atlas (TCGA) datasets revealed a correlation between the survival of PDAC patients, levels of klotho expression, and DNA methylation, and demonstrated a unique hypermethylation pattern of klotho in pancreatic tumors. The in vivo effects of klotho and KL1 were examined using three mouse models. Employing a novel genetic model, combining pancreatic klotho knockdown with a mutation in Kras, the lack of klotho contributed to PDAC generation and decreased mousece survival. In a xenograft model, administration of viral particles carrying sKL, a spliced klotho isoform containing the KL1 domain, inhibited pancreatic tumors. Lastly, treatment with soluble sKL prolonged survival of Pdx1-Cre; Kras^G12D/+;Trp53^R172H/+ (KPC) mice, a model known to recapitulate human PDAC. In conclusion, this study provides evidence that klotho is a tumor suppressor in PDAC. Furthermore, these data suggest that the levels of klotho expression and DNA methylation could have prognostic value in PDAC patients, and that administration of exogenous sKL may serve as a novel therapeutic strategy to treat PDAC.

Klotho as Potential Autophagy Regulator and Therapeutic Target

The protein Klotho can significantly delay aging, so it has attracted widespread attention. Abnormal downregulation of Klotho has been detected in several aging-related diseases, such as Alzheimer’s disease, kidney injury, cancer, chronic obstructive pulmonary disease (COPD), vascular disease, muscular dystrophy and diabetes. Conversely, many exogenous and endogenous factors, several drugs, lifestyle changes and genetic manipulations were reported to exert therapeutic effects through increasing Klotho expression. In recent years, Klotho has been identified as a potential autophagy regulator. How Klotho may contribute to reversing the effects of aging and disease became clearer when it was linked to autophagy, the process in which eukaryotic cells clear away dysfunctional proteins and damaged organelles: the abovementioned diseases involve abnormal autophagy. Interestingly, growing evidence indicates that Klotho plays a dual role as inducer or inhibitor of autophagy in different physiological or pathological conditions through its influence on IGF-1/PI3K/Akt/mTOR signaling pathway, Beclin 1 expression and activity, as well as aldosterone level, which can help restore autophagy to beneficial levels. The present review examines the role of Klotho in regulating autophagy in Alzheimer’s disease, kidney injury, cancer, COPD, vascular disease, muscular dystrophy and diabetes. Targeting Klotho may provide a new perspective for preventing and treating aging-related diseases.

Impact of Fasting Status on the Use of Klotho as a Biomarker

BACKGROUND

Klotho is a protein secreted physiologically in humans. It acts like a hormone that regulates many biological processes. It is also a novel serological biomarker that is increasingly used as a predictive factor for several physiological and psychological conditions. Surprisingly, there is no consensus about the fasting state of the patient who is tested for klotho. Most studies are done on fasting patients, although others are done without concern about fasting status. There is a lack of evidence about this variable in klotho serological testing. Performing fasting tests on patients can be deleterious and can affect compliance. We investigated the effect of fasting status on klotho serological value.

METHODS

We conducted an observational study in which klotho serology was evaluated in a fasting state and 2 h after a meal. In total, 35 participants came to the laboratory without having eaten for 10 h. Blood samples were taken on arrival at our laboratory and 2 h after eating a standardized meal.

RESULTS

The mean age of our participants was 32.7 years old. There were 13 men and 22 women. In the fasting state, the klotho value was 1060.5 pg/mL (SD: 557.5 pg/mL). At 2 h after the meal, the klotho value was 1077.5 pg/mL (SD: 576.9 pg/mL). Statistical tests showed no difference before and after a meal in our study (P = 0.2425).

CONCLUSIONS

Our results suggest that it is not necessary to perform klotho serology in a fasting state.

In search of alternatively spliced alpha-Klotho Kl1 protein in mouse brain

Alpha‐Klotho is a multi‐functional protein essential for maintenance of a myriad of cell functions. αKlotho is a single transmembrane protein with a large extracellular segment consisting of two domains (termed Kl1 and Kl2) which is shed into the extracellular fluid by proteolytic cleavage to furnish circulating soluble αKlotho. Based on cDNA sequence, an alternatively spliced mRNA is predicted to translate to a putative soluble αKlotho protein in mouse and human with only the Kl1 domain that represents a “spliced αKlotho Kl1” (spKl1) and is released from the cell without membrane targeting or cleavage. The existence of this protein remains in silico for two decades. We generated a novel antibody (anti‐spE15) against the 15 amino acid epitope (E15; VSPLTKPSVGLLLPH) which is not present in Kl1 or full‐length αKlotho and validated its specific reactivity against spKl1 in vitro. Using anti‐spE15 and two well‐established anti‐αKlotho monoclonal antibodies, we performed immunoblots, immunoprecipitation, and immunohistochemistry to investigate for expression of spKl1 in the mouse brain. We found anti‐spE15 labeling in mouse brain but were not able to see co‐labelling of Kl1 and spE15 epitopes on the same protein, which is the pre‐requisite for the existence of a spKl1 polypeptide, indicating that anti‐spE15 likely binds to another protein other than the putative spKl1. In isolated choroid plexus from mouse brain, we found strong staining with anti‐spE15, but did not find the spliced αKlotho transcript. We conclude that using reliable reagents and inclusion of proper controls, there is no evidence of the spKl1 protein in the mouse brain.

microRNAs and Corresponding Targets Involved in Metastasis of Colorectal Cancer in Preclinical In Vivo Models

The high death toll of colorectal cancer patients is due to metastatic disease which is difficult to treat. The liver is the preferred site of metastasis, followed by the lungs and peritoneum. In order to identify new targets and new modalities of intervention we surveyed the literature for microRNAs (miRs) which modulate metastasis of colorectal cancer in preclinical in vivo models. We identified 12 up-regulated and 19 down-regulated miRs corresponding to the latter criterium. The vast majority (n=16) of identified miRs are involved in modulation of epithelial-mesenchymal transition (EMT). Other categories of metastasis-related miRs exhibit tumor- and metastasis-suppressing functions, modulation of signaling pathways, transmembrane receptors and a class of miRs, which interfere with targets which do not fit into these categories. Finally, we discuss the principles of miR inhibition and reconstitution of function, prospective clinical evaluation of with miR-related agents in the context of clinical evaluation in metastasis relevant settings.

Klotho gene G395A and C1818T polymorphisms in acromegaly: Association with clinical presentation and comorbidities

BACKGROUND

Klotho is a new identified anti-ageing gene with tumour suppressor activities. Current data suggest that there is a tight relationship between Klotho protein and growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis.

PURPOSE

This study aimed to investigate the possible association of Klotho gene polymorphisms with acromegaly and to assess whether these polymorphisms contribute to clinical characteristics, comorbidities and biochemical variables in these patients.

METHODS

The study included 52 patients with acromegaly and 52 unrelated healthy subjects. The Klotho G395A and C1818T polymorphisms were assessed by Sanger sequencing. Serum levels of sKlotho were determined by ELISA method.

RESULTS

Subjects carrying GA genotype of Klotho G395A polymorphism had 3.27 times higher risk of developing acromegaly [odds ratio (OR), 3.27; 95% confidence interval (CI): 1.37-7.81; p = .023]. The A allele of G395A was significantly associated with acromegaly risk (OR, 2.27; 95% CI: 1.1-4.72; p = .022). No association was observed between the studied polymorphisms and disease characteristics including age at acromegaly diagnosis, size of adenoma, baseline GH and IGF-1 concentrations, and final outcome. G395A polymorphism was associated with the presence of malignancy (OR, 2.24, 95% CI: 1.63-3.08; p = .019) and colorectal polyps (OR, 1.99; 95% CI: 1.02-3.88; p = .047) in patients with acromegaly. Serum sKlotho levels were significantly higher and correlated with GH and IGF-1 levels among acromegaly patients. There was no association between the studied polymorphisms and sKlotho levels.

CONCLUSIONS

Klotho G395A polymorphism is associated with acromegaly susceptibility and increased risk of malignancy and colorectal polyps in these patients.

Antiaging gene Klotho regulates epithelial-mesenchymal transition and increases sensitivity to pemetrexed by inducing lipocalin-2 expression

Epithelial-mesenchymal transition (EMT) is considered to serve an important role in the metastatic/invasive ability of cancer cells, in the acquisition of drug resistance, and in metabolic reprogramming. In the present study, it was hypothesized that the Klotho gene is involved in the metastatic/invasive ability of lung cancer. We previously reported an association between Klotho expression and overall survival in patients with small cell lung cancer and large cell neuroendocrine cancer. We also found that Klotho expression was associated with EMT-related molecules in lung squamous cell carcinoma. The present study aimed to analyze the function of the Klotho gene and to elucidate its relevance to the regulation of the EMT. For this purpose, GFP-Klotho plasmids were transfected into lung adenocarcinoma cells (A549) and cell lines with stable expression (A549/KL-1 and A549/KL-2) were established. A549/KL-1 cells expressed higher levels of Klotho protein by western blot analysis compared with A549/KL-2 cells. In western blotting of A549 and A549/KL-1 cells, the expression of the mesenchymal marker N-cadherin was found to be completely inhibited in A549/KL-1 cells suggesting that Klotho expression may regulate the EMT in cancer cells via the inhibition of N-cadherin. The results of the sensitivity tests demonstrated that A549/KL-1 cells were significantly more sensitive to pemetrexed compared with A549 cells (IC₅₀ A549/KL-1 vs. A549 cells, 0.1 µM vs. 0.7 µM). The results of the microarray analysis demonstrated that a very high level of lipocalin-2 (LCN2) expression was induced in the A549/KL-1 cells. Klotho overexpression completely suppressed the expression of mesenchymal markers, such as N-cadherin and Snail1 (Snail). The results of the present study suggested that there may be a new mechanism of action for the antitumor effects of pemetrexed, namely, LCN2-mediated modulation of N-cadherin expression. Klotho expression during cancer treatment has great potential as a predictor for efficacy of pemetrexed and as a factor in the selection of personalized medicine for postoperative adjuvant chemotherapy.

Association of a single nucleotide polymorphism combination pattern of the Klotho gene with non-cardiovascular death in patients with chronic kidney disease

Background

Chronic kidney disease (CKD) is associated with an elevated risk of all-cause mortality, with cardiovascular death being extensively investigated. However, non-cardiovascular mortality represents the biggest percentage, showing an evident increase in recent years. Klotho is a gene highly expressed in the kidney, with a clear influence on lifespan. Low levels of Klotho have been linked to CKD progression and adverse outcomes. Single nucleotide polymorphisms (SNPs) of the Klotho gene have been associated with several diseases, but studies investigating the association of Klotho SNPs with non-cardiovascular death in CKD populations are lacking.

Methods

The main aim of this study was to assess whether 11 Klotho SNPs were associated with non-cardiovascular death in a subpopulation of the National Observatory of Atherosclerosis in Nephrology (NEFRONA) study (n = 2185 CKD patients).

Results

After 48 months of follow-up, 62 cardiovascular deaths and 108 non-cardiovascular deaths were recorded. We identified a high non-cardiovascular death risk combination of SNPs corresponding to individuals carrying the most frequent allele (G) at rs562020, the rare allele (C) at rs2283368 and homozygotes for the rare allele (G) at rs2320762 (rs562020 GG/AG + rs2283368 CC/CT + rs2320762 GG). Among the patients with the three SNPs genotyped (n = 1016), 75 (7.4%) showed this combination. Furthermore, 95 (9.3%) patients showed a low-risk combination carrying all the opposite genotypes (rs562020 AA + rs2283368 TT + rs2320762 GT/TT). All the other combinations [n = 846 (83.3%)] were considered as normal risk. Using competing risk regression analysis, we confirmed that the proposed combinations are independently associated with a higher {hazard ratio [HR] 3.28 [confidence interval (CI) 1.51–7.12]} and lower [HR 6 × 10⁻⁶ (95% CI 3.3 × 10⁻⁷–1.1 × 10⁻⁵)] risk of suffering a non-cardiovascular death in the CKD population of the NEFRONA cohort compared with patients with the normal-risk combination.

Conclusions

Determination of three SNPs of the Klotho gene could help in the prediction of non-cardiovascular death in CKD.

Klotho and the Treatment of Human Malignancies

Klotho was first discovered as an anti-ageing protein linked to a number of age-related disease processes, including cardiovascular, renal, musculoskeletal, and neurodegenerative conditions. Emerging research has also demonstrated a potential therapeutic role for Klotho in cancer biology, which is perhaps unsurprising given that cancer and ageing share similar molecular hallmarks. In addition to functioning as a tumour suppressor in numerous solid tumours and haematological malignancies, Klotho represents a candidate therapeutic target for patients with these diseases, the majority of whom have limited treatment options. Here, we examine contemporary evidence evaluating the anti-neoplastic effects of Klotho and describe the modulation of downstream oncogenic signalling pathways, including Wnt/β-catenin, FGF, IGF1, PIK3K/AKT, TGFβ, and the Unfolded Protein Response. We also discuss possible approaches to developing therapeutic Klotho and consider technological advances that may facilitate the delivery of Klotho through gene therapy.

Klotho rewires cellular metabolism of breast cancer cells through alteration of calcium shuttling and mitochondrial activity

Klotho is a transmembrane protein, which can be shed and act as a circulating hormone and is involved in regulating cellular calcium levels and inhibition of the PI3K/AKT pathway. As a longevity hormone, it protects normal cells from oxidative stress, and as a tumor suppressor it inhibits growth of cancer cells. Mechanisms governing these differential activities have not been addressed. Altered cellular metabolism is a hallmark of cancer and dysregulation of mitochondrial activity is a hallmark of aging. We hypothesized that klotho exerts its differential effects through regulation of these two hallmarks. Treatment with klotho inhibited glycolysis, reduced mitochondrial activity and membrane potential only in cancer cells. Accordingly, global metabolic screen revealed that klotho altered pivotal metabolic pathways, amongst them glycolysis and tricarboxylic acid cycle in breast cancer cells. Alteration of metabolic activity and increased AMP/ATP ratio lead to LKB1-dependent AMPK activation. Indeed, klotho induced AMPK phosphorylation; furthermore, inhibition of LKB1 partially abolished klotho's tumor suppressor activity. By diminishing deltapsi (Δψ) klotho also inhibited mitochondria Ca²⁺ shuttling thereby impairing mitochondria communication with SOCE leading to reduced Ca²⁺ influx by SOCE channels. The reduced SOCE was followed by ER Ca²⁺ depletion and stress. These data delineate mechanisms mediating the differential effects of klotho toward cancer versus normal cells, and indicate klotho as a potent regulator of metabolic activity.

FLI-1 mediates tumor suppressor function via Klotho signaling in regulating CRC

Colorectal cancer (CRC) is an aggressive malignancy with a high incidence and mortality rate. Although a targeting therapy has been developed, the 5-year survival rate is still very low in CRC patients with distant metastasis. Thus, the identification of new targets is still significant for improving CRC treatment. Klotho is a tumor suppressor, and its expression is aberrant in CRC. In this study, the roles of the FLI-1 gene in regulating Klotho gene expression and Klotho-associated signaling, as well as the effects of FLI-1 on colony formation, invasion, and apoptosis were investigated in CRC cell lines. The methylation of the FLI-1 gene was analyzed using a commercial methylation kit. Results showed that FLI-1 messenger RNA and protein expression were downregulated in six CRC cell lines when compared with the normal colon mucosal epithelial cell line, which negatively correlated with the level of DNA methylation. Silencing of FLI-1 gene expression decreased Klotho protein expression and phosphorylation of β-catenin protein at Thr⁴¹ /Ser⁴⁵ , but increased Wnt3a and β-catenin protein expression and IGF-1R phosphorylation in HT29 cells. In contrast to silencing FLI-1, overexpressing FLI-1 significantly increased Klotho protein expression and phosphorylation of β-catenin protein at Thr⁴¹ /Ser⁴⁵ , but decreased Wnt3a and β-catenin protein expression and IGF-1R phosphorylation in Caco-2 cells. Silencing of FLI-1 gene expression significantly increased colony formation and invasion, but decreased apoptosis in HT29 cells. In contrast, overexpressing the FLI-1 gene significantly decreased colony formation and invasion, but increased apoptosis in Caco-2 cells. These findings suggest that FLI-1 functions as a tumor suppressor in CRC cells and positively regulates Klotho signaling. Hypermethylation may be one of the causes of the loss of FLI-1 gene expression in CRC cells.

Rab8 GTPase regulates Klotho-mediated inhibition of cell growth and progression by directly modulating its surface expression in human non-small cell lung cancer

BACKGROUND

The klotho (KL) gene is an anti-aging gene that has recently been shown to also function as a general tumor suppressor. However, there is currently only limited information regarding the potential molecular signals for regulation of Klotho without identifying precise molecular mechanisms or interactions.

METHODS

We performed a mass spectrometry (MS) assay to screen candidate proteins complexed with Klotho derived from immunoprecipitation in human non-small cell lung cancer (NSCLC) cells, and identified Rab8 to be the protein that most prominently interacts with Klotho. We further investigated whether Rab8 can regulate trafficking of Klotho and which process it would modulate using surface biotinylation assay, immunofluorescence and fluorescence ratio microscopy. Furthermore, we explored whether Rab8 is involved in Klotho-mediated function in NSCLC, and verified the results which we found in vivo using xenograft mouse model.

FINDINGS

We report discovery of Rab8 as a Klotho-interacting protein that acts as a critical modulator of Klotho surface expression in human NSCLC. In particular, we report that Rab8 is co-localized and associated with Klotho, and Klotho trafficking is regulated by Rab8. Moreover, we found that Rab8 modulates surface levels of Klotho via a post-biosynthetic pathway, as opposed to an endocytic pathway. Furthermore, we demonstrate that Rab8 is involved in Klotho-mediated regulation of cell proliferation, migration, invasiveness, epithelial-mesenchymal transition (EMT), and Wnt-β-catenin signaling in NSCLC. Additionally, Rab8 overexpression was also found to increase Klotho-mediated inhibition of NSCLC tumorigenesis in vivo.

INTERPRETATION

Overall, our findings suggest that Rab8 GTPase can regulate Klotho-mediated inhibition of Wnt signaling activity by modulating translocation of Klotho onto the cell surface, which in turn affects Klotho-mediated inhibition of cell proliferation, migration and invasiveness in NSCLC. These results have important implications for the development of new therapeutic targets, Klotho-related research in the context of NSCLC as well as other areas, and provide a working model for Rab8 function in the context of cancer and cancer biology.

Exercise training increases the S-Klotho plasma levels in sedentary middle-aged adults: A randomised controlled trial. The FIT-AGEING study

This study aimed to investigate the effects of different training modalities on the soluble Klotho (S-Klotho) plasma levels in sedentary middle-aged adults. A total of 74 middle-aged adults (53.4 ± 5.0 years old; 52.7% women) were enrolled in the FIT-AGEING study. We conducted a 12-week randomised controlled trial. The participants were randomly assigned to 4 different groups: (i) a control group (no exercise), (ii) a physical activity recommendation from the World Health Organization group (PAR), (iii) a high intensity interval training group (HIIT), and (iv) a high intensity interval training group adding whole-body electromyostimulation training group (HIIT-EMS). S-Klotho plasma levels, anthropometric measurements, and body composition variables were measured before and after the intervention programme. All exercise training modalities induced an increase in the S-Klotho plasma levels (all P ≤ 0.019) without statistical differences between them (all P ≥ 0.696). We found a positive association between changes in lean mass index and changes in the S-Klotho plasma levels, whereas a negative association was reported between changes in fat mass outcomes and changes in the S-Klotho plasma levels after our intervention study. In conclusion, our results suggest that the link between exercise training and the increase in S-Klotho plasma levels could be mediated by a decrease of fat mass and an increase of lean mass.

Study of the association of DHEAS, testosterone and cortisol with S-Klotho plasma levels in healthy sedentary middle-aged adults

BACKGROUND

α-Klotho is a recently discovered gene that accelerates ageing when disrupted and extends lifespan when overexpressed. The age-related decline in DHEAS and testosterone secretion and the increase in cortisol are associated with a rise of frailty and mortality.

OBJECTIVE

To investigate the association of DHEAS, cortisol and testosterone plasma levels with S-Klotho plasma levels in healthy sedentary middle-aged adults.

METHODS

73 (39 women) healthy middle-aged sedentary adults (45-65 years old) were recruited for the present study. The blood samples were collected in the morning after fasting for 12 h.

RESULTS

DHEAS was positively associated with S-Klotho in men (β = 0.521, R² = 0.248, P = 0.002), whereas no association was observed in women (P ≥ 0.201). Testosterone was positively associated with S-Klotho in both men and women (β = 0.360, R² = 0.099, P = 0.047; β = 0.431, R² = 0.161, P = 0.010, respectively). No association was found between cortisol and S-Klotho neither in men nor in women (all P ≥ 0.141). The association between DHEAS and testosterone with S-Klotho in men disappeared after adjusting by age (all P ≥ 0.151). Nevertheless, the association between testosterone (β = 0.397, R² = 0.423, P = 0.011) and S-Klotho in women remained after adjusting by age.

CONCLUSIONS

DHEAS and testosterone were positively associated with S-Klotho in healthy sedentary middle-aged men while only testosterone was positively associated in women.

The Role of the Anti-Aging Protein Klotho in IGF-1 Signaling and Reticular Calcium Leak: Impact on the Chemosensitivity of Dedifferentiated Liposarcomas

By inhibiting Insulin-Like Growth Factor-1-Receptor (IGF-1R) signaling, Klotho (KL) acts like an aging- and tumor-suppressor. We investigated whether KL impacts the aggressiveness of liposarcomas, in which IGF-1R signaling is frequently upregulated. Indeed, we observed that a higher KL expression in liposarcomas is associated with a better outcome for patients. Moreover, KL is downregulated in dedifferentiated liposarcomas (DDLPS) compared to well-differentiated tumors and adipose tissue. Because DDLPS are high-grade tumors associated with poor prognosis, we examined the potential of KL as a tool for overcoming therapy resistance. First, we confirmed the attenuation of IGF-1-induced calcium (Ca²⁺)-response and Extracellular signal-Regulated Kinase 1/2 (ERK1/2) phosphorylation in KL-overexpressing human DDLPS cells. KL overexpression also reduced cell proliferation, clonogenicity, and increased apoptosis induced by gemcitabine, thapsigargin, and ABT-737, all of which are counteracted by IGF-1R-dependent signaling and activate Ca²⁺-dependent endoplasmic reticulum (ER) stress. Then, we monitored cell death and cytosolic Ca²⁺-responses and demonstrated that KL increases the reticular Ca²⁺-leakage by maintaining TRPC6 at the ER and opening the translocon. Only the latter is necessary for sensitizing DDLPS cells to reticular stressors. This was associated with ERK1/2 inhibition and could be mimicked with IGF-1R or MEK inhibitors. These observations provide a new therapeutic strategy in the management of DDLPS.

Klotho suppresses colorectal cancer through modulation of the unfolded protein response

Klotho is an anti-aging transmembrane protein, which can be shed and function as a hormone. Accumulating data indicate klotho as a tumor suppressor in a wide array of malignancies and indicate the subdomain KL1 as the active region of the protein. We aimed to study the role of klotho as a tumor suppressor in colorectal cancer. Bioinformatics analyses of TCGA datasets indicated reduced klotho mRNA levels in human colorectal cancer, along with negative regulation of klotho expression by hypermethylation of the promoter and 1st exon, and hypomethylation of an area within the gene. Overexpression or treatment with klotho or KL1 inhibited proliferation of colorectal cancer cells in vitro. The in vivo activity of klotho and KL1 was examined using two models recapitulating development of tumors in the normal colonic environment of immune-competent mice. Treatment with klotho inhibited formation of colon polyps induced by the carcinogen azoxymethane, and KL1 treatment slowed growth of orthotopically-implanted colorectal tumors. Gene expression array revealed that klotho and KL1 expression enhanced the unfolded protein response (UPR) and this was further established by increased levels of spliced XBP1, GRP78 and phosphorylated-eIF2α. Furthermore, attenuation of the UPR partially abrogated klotho tumor suppressor activity. In conclusion, this study indicates klotho as a tumor suppressor in colorectal cancer and identifies, for the first time, the UPR as a pathway mediating klotho activities in cancer. These data suggest that administration of exogenous klotho or KL1 may serve as a novel strategy for prevention and treatment of colorectal cancer.

Assessment of the circulating klotho protein in lung cancer patients

The anti-aging factor, klotho has been identified as a tumor suppressor in various human cancers, including lung cancer. In vitro studies provided evidence that klotho expression influences the characteristics of lung cancer cells, however, in vivo results are lacking. The aim of our study was to evaluate whether circulating klotho protein might serve as a potential biomarker of lung cancer. Blood samples were taken from 45 newly diagnosed lung cancer patients (31 NSCLC, 14 SCLC) and 43 control subjects. Plasma klotho concentration was measured using ELISA. No difference in plasma klotho values was detected between patients and control subjects (366.3 (257.9-486.8) vs. 383.5 (304.6-489.7) pg/ml respectively (median (IQR)); p > 0.05). Plasma klotho levels in patients with distant metastasis did not differ from less advanced stage disease (354.2 (306.9-433.3 vs. 328.5 (242.5-419.7) pg/ml, p > 0.05). In contrast, analyzed with one-way ANOVA, significant difference (p = 0.04) was found between the examined histological types of lung cancer: adenocarcinoma (353 (329.4-438.5) pg/ml), squamous cell carcinoma (308 (209.6-348.1) pg/ml) and small cell lung cancer (388.8 (289.9-495.4) pg/ml). However, Tukey's post hoc test did not reveal significant difference between any pairs of histological groups. There was no difference between any histological subtype and health either. Our results suggest that circulating klotho protein cannot be considered as a biomarker for lung cancer. Further studies are warranted in order to examine the relationship between klotho expression in lung tissue and circulating levels of the protein, and to explore its mechanism of action in lung cancer.

Klotho inhibits EGF-induced cell migration in Caki-1 cells through inactivation of EGFR and p38 MAPK signaling pathways

Klotho is a single-pass transmembrane protein with documented anti-cancer properties. Recent reports have implicated Klotho as an inhibitor of transforming growth factor β1 induced cell migration in renal fibrosis. Overexpression of epidermal growth factor receptor (EGFR) is known to promote tumor initiation and progression in clear-cell renal cell carcinoma (cRCC). We tested our hypothesis that Klotho inhibits EGF-mediated cell migration in cRCC by interfering with the EGFR signaling complex and mitogen-activated protein kinase (MAPK) pathways. We performed cell adhesion, migration, and biochemical studies in vitro using Caki-1 cell line. In addition, we validated the cell culture studies with expression analysis of six de-identified FFPE tissues from primary and metastatic cRCC patients. Our studies show that Klotho inhibited EGF-induced Caki-1 de-adhesion and decreased spreading on collagen type 1. Klotho also inhibited EGF-induced α2β1 integrin-dependent cell migration on collagen type 1. To test the involvement of MAPK pathways in EGF-induced Caki-1 cell motility, the cells were pretreated with either SB203580, a specific p38 MAPK inhibitor, or Klotho. SB203580 blocked the EGF-induced Caki-1 cell migration. Klotho had a comparable inhibitory effect. Our FFPE clinical specimens revealed decreased Klotho mRNA expression compared to a control, non-cancer kidney tissue. The decrease in Klotho mRNA levels correlated with increased c-Src expression, while E-Cadherin was relatively reduced in metastatic FFPE specimens where Klotho was least expressed. Taken together, these results suggest that secreted Klotho inhibits EGF-induced pro-migratory cell morphological changes and migration in Caki-1 cells. Our data additionally suggest that decreased Klotho expression may be involved in cRCC metastasis.

Phosphate toxicity and tumorigenesis

In this article, we briefly summarized evidence that cellular phosphate burden from phosphate toxicity is a pathophysiological determinant of cancer cell growth. Tumor cells express more phosphate cotransporters and store more inorganic phosphate than normal cells, and dysregulated phosphate homeostasis is associated with the genesis of various human tumors. High dietary phosphate consumption causes the growth of lung and skin tumors in experimental animal models. Additional studies show that excessive phosphate burden induces growth-promoting cell signaling, stimulates neovascularization, and is associated with chromosome instability and metastasis. Studies have also shown phosphate is a mitogenic factor that affects various tumor cell growth. Among epidemiological evidence linking phosphate and tumor formation, the Health Professionals Follow-Up Study found that high dietary phosphate levels were independently associated with lethal and high-grade prostate cancer. Further research is needed to determine how excessive dietary phosphate consumption influences initiation and promotion of tumorigenesis, and to elucidate prognostic benefits of reducing phosphate burden to decrease tumor cell growth and delay metastatic progression. The results of such studies could provide the basis for therapeutic modulation of phosphate metabolism for improved patient outcome.

Alteration in the serum concentrations of FGF19, FGFR4 and βKlotho in patients with thyroid cancer

INTRODUCTION

βKlotho (βKL) is known to act as co-receptor for fibroblast growth factor receptor 4 (FGFR4) which is the main cognate receptor for fibroblast growth factor 19 (FGF19). Dysregulation of this FGF19/FGFR4/βKL signaling axis has been implicated in the pathogenesis of several cancers. However, its role in the pathogenesis of thyroid cancer has not been determined.

MATERIALS AND METHODS

The aim of this study was to assess FGF19, FGFR4 and βKL concentrations in a group of 36 patients with papillary thyroid cancer (PTC), 11 patients with follicular thyroid cancer (FTC), 9 patients with anaplastic thyroid cancer (ATC) and a group of 19 subjects with multinodular nontoxic goiter (MNG). The control group consisted of 20 healthy volunteers. Serum FGF19, FGFR4 and βKL concentrations were measured using specific ELISA methods.

RESULTS

Significantly lower concentrations of βKL and higher concentrations of FGF19 were found in patients with PTC, FTC and ATC as compared with MNG group and controls. An elevation of FGFR4 serum concentration was observed in all thyroid cancer groups in comparison to MNG group and controls; however, in FTC group it was statistically insignificant. A positive correlation was found between βKL and FGFR4 concentrations in PTC patients. The levels of βKL, FGF19 and FGFR4 did not differ significantly between MNG group and healthy controls.

CONCLUSIONS

Our results indicate that a disrupted FGF19/FGFR4/βKL signaling pathway may play a role in the development of thyroid cancers. However, further studies are needed to elucidate the molecular mechanism of the neoplastic transition of thyroid epithelial cells.

Acute lung injury complicating acute kidney injury: A model of endogenous αKlotho deficiency and distant organ dysfunction

The lung interfaces with atmospheric oxygen via a large surface area and is perfused by the entire venous return bearing waste products collected from the whole body. It is logical that the lung is endowed with generous anti-oxidative capacity derived both locally and from the circulation. The single-pass pleiotropic alpha-Klotho (αKlotho) protein was discovered when its genetic disruption led to premature multi-organ degeneration and early death. The extracellular domain of αKlotho is cleaved by secretases and released into circulation as endocrine soluble αKlotho protein, exerting wide-ranging cytoprotective effects including anti-oxidation on distant organs including the lung, which exhibits high sensitivity to circulating αKlotho insufficiency. Because circulating αKlotho is derived mainly from the kidney, acute kidney injury (AKI) leads to systemic αKlotho deficiency that in turn increases the risks of pulmonary complications, i.e., edema and inflammation, culminating in the acute respiratory distress syndrome. Exogenous αKlotho increases endogenous anti-oxidative capacity partly via activation of the Nrf2 pathway to protect lungs against injury caused by direct hyperoxia exposure or AKI. This article reviews the current knowledge of αKlotho antioxidation in the lung in the setting of AKI as a model of circulating αKlotho deficiency, an under-recognized condition that weakens innate cytoprotective defenses and contributes to the dysfunction in distant organs.