Soluble Klotho is associated with mortality and cardiovascular events in hemodialysis

Effect of heart failure and atrial fibrillation on cardiorespiratory fitness in hemodialysis patients

PURPOSE

Heart failure (HF) and atrial fibrillation (AF) are highly prevalent in hemodialysis. They are well-known significant modifiers of the disease associations with cardiovascular outcomes, but there is a lack of evidence regarding the effects of HF and AF on cardiorespiratory fitness. This study is the first to examine the possible association of the presence of HF and AF with exercise intolerance in patients undergoing hemodialysis.

METHODS

This analysis included 40 sex- and age-matched participants [10 hemodialysis patients with HF or AF, 10 hemodialysis patients without HF or AF, 10 patients with HF or AF without chronic kidney disease (CKD) and 10 healthy controls] that underwent CPET and spirometry examinations. The total of patients with HF had preserved ejection fraction.

RESULTS

VO2peak(ml/kg/min) showed a graded increase between hemodialysis patients with HF or AF, hemodialysis patients without HF or AF, non-CKD patients with HF or AF and controls (13.17 ± 2.45 vs 15.26 ± 3.29 vs 19.64 ± 5.84 vs 25.11 ± 6.94 ml/kg/min, p < 0.001); VO2peak(ml/min) followed the same pattern (1172 ± 197 vs 1269 ± 314 vs 1817 ± 583 vs 1952 ± 592 ml/min respectively, p = 0.001). VO2peak(%predicted), VO2AT(ml/kg/min), VO2AT(ml/min) and maximal work load significantly differed between the study groups, with a tendency for higher values from hemodialysis patients to non-CKD patients with HF or AF and to healthy controls. FEV1 and FVC levels were similar between the study groups. In the whole population, VO2peak(ml/kg/min) showed a positive correlation with hemoglobin (r = 0.663, p < 0.001) and negative correlations with high-sensitivity cardiac troponin I (r = - 0.493, p = 0.001) and BNP (r = - 0.479, p = 0.002).

CONCLUSION

Hemodialysis patients have low exercise tolerance, and the presence of HF or AF is associated with further decreased values of VO2peak, the most important determinant of cardiorespiratory fitness.

Lessons from Klotho mouse models to understand mineral homeostasis

AIM

Klotho, a key component of the endocrine fibroblast growth factor receptor-fibroblast growth factor axis, is a multi-functional protein that impacts renal electrolyte handling. The physiological significance of Klotho will be highlighted in the regulation of calcium, phosphate, and potassium metabolism.

METHODS

In this review, we compare several murine models with different renal targeted deletions of Klotho and the insights into the molecular and physiological function that these models offer.

RESULTS

In vivo, Klotho deficiency is associated with severely impaired mineral metabolism, with consequences on growth, longevity and disease development. Additionally, we explore the perspectives of Klotho in renal pathology and vascular events, as well as potential Klotho treatment options.

CONCLUSION

This comprehensive review emphasizes the use of Klotho to shed light on deciphering the renal molecular in vivo mechanisms in electrolyte handling, as well as novel therapeutic interventions.

Serum Klotho Is Elevated in Patients with Acute Myocardial Infarction and Could Predict Poor In-Hospital Prognosis

INTRODUCTION

Klotho has emerged as a potential protective factor for cardiovascular diseases recently. Nevertheless, the levels of serum Klotho in acute coronary syndrome (ACS) have not been reported. Hence, we undertook a study to investigate the potential correlation between serum Klotho and ACS patients.

METHOD

This observational cohort study was conducted at Peking University People's Hospital between May 2016 and April 2020. Upon admission, we collected the patients' clinical data and conducted ELISA tests to measure their serum Klotho levels.

RESULT

A total of 349 patients were enrolled in this study, including 14 patients with UA and 335 patients with AMI. We observed that serum Klotho levels were obviously higher in the AMI group compared to the UA group (median 479.8 vs. 233.8 pg/mL, p = 0.035). In addition, serum Klotho levels were positively correlated with cardiac function and more pronounced in patients who died in the hospital (median 721.1 vs. 468.3 pg/mL, p < 0.001). A logistic regression analysis indicated that age ≥ 78 years old, HR ≥ 90 bpm, Killip classification ≥ 3 grade, and serum Klotho > 645.0 pg/mL were risk factors for poor prognosis.

CONCLUSIONS

Serum Klotho is obviously increased in patients with AMI and with a positive correlation with cardiac function, and its elevation could serve as a predictor of poor prognosis in ACS patients.

The association between klotho and kidney and cardiovascular outcomes: a comprehensive systematic review and meta-analysis

Background

Chronic kidney disease (CKD) and end-stage renal disease (ESKD) are significant global health challenges associated with progressive kidney dysfunction and numerous complications, including cardiovascular disease and mortality. This study aims to explore the potential association between plasma klotho levels and various prognostic outcomes in CKD and ESKD, including all-cause mortality, cardiovascular events, metabolic syndrome development and adverse renal events necessitating renal replacement therapies.

Methods

A literature search was conducted through 3 June 2024 using the electronic databases Cochrane Library, Ovid MEDLINE, CINAHL, Web of Science, SCOPUS and PubMed. This systematic review adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

Results

Fourteen studies were included. For all-cause mortality, comparing CKD patients with low versus high klotho levels showed a significant association {odds ratio [OR] 1.81 [95% confidence interval (CI) 1.34-2.44], P = .0001}, with substantial heterogeneity (I 2 = 69%). Excluding one study reduced heterogeneity (I 2 = 43%) while maintaining significance [OR 1.97 (95% CI 1.45-2.66), P < .0001]. Cardiovascular mortality was higher in patients with low klotho levels [OR 2.11 (95% CI 1.61-2.76), P < .00001], with low heterogeneity (I 2 = 25%). Excluding one study eliminated heterogeneity (I 2 = 0%) while maintaining significance [OR 2.39 (95% CI 1.83-3.12), P < .00001]. Composite cardiovascular events did not differ significantly between low and high klotho groups [OR 1.51 (95% CI 0.82-2.77), P = .18], but with high heterogeneity (I 2 = 72%). Patients with low klotho levels had a higher risk of adverse renal events [OR 2.36 (95% CI 1.37-4.08), P = .002], with moderate heterogeneity (I 2 = 61%). Sensitivity analysis reduced heterogeneity (I 2 = 0%) while maintaining significance [OR 3.08 (95% CI 1.96-4.85), P < .00001]. Specifically, for ESKD or kidney replacement therapy risk, low klotho levels were associated with an increased risk [OR 2.30 (95% CI 1.26-4.21), P = .007]. Similarly, CKD progression risk was higher in patients with lower klotho levels [OR 2.48 (95% CI 1.45-4.23), P = .0009].

Conclusion

Lower serum klotho levels serve as a significant predictor of adverse outcomes, including increased risks of all-cause mortality, cardiovascular mortality and progression to end-stage kidney disease among CKD patients.

Pentoxifylline ameliorates subclinical atherosclerosis progression in patients with type 2 diabetes and chronic kidney disease: a randomized pilot trial

BACKGROUND

Diabetic kidney disease (DKD) is associated with a higher risk of cardiovascular disease (CVD). Pentoxifylline (PTF), a nonselective phosphodiesterase inhibitor with anti-inflammatory, antiproliferative, and antifibrotic actions, has demonstrated renal benefits in both clinical trials and meta-analyses. The present work aimed to study the effects of PTF on the progression of subclinical atherosclerosis (SA) in a population of patients with diabetes and moderate to severe chronic kidney disease (CKD).

METHODS

In this open-label, randomized controlled, prospective single-center pilot study the evolution of carotid intima-media thickness (CIMT) and ankle-brachial index (ABI) were determined in 102 patients with type 2 diabetes mellitus and CKD assigned to PTF, aspirin or control groups during 18 months. We also determined the variations in the levels of inflammatory markers and Klotho (KL), a protein involved in maintaining cardiovascular health, and their relationship with the progression of SA.

RESULTS

Patients treated with PTF presented a better evolution of CIMT, increased KL mRNA levels in peripheral blood cells (PBCs) and reduced the inflammatory state. The progression of CIMT values was inversely related to variations in KL both in serum and mRNA expression levels in PBCs. Multiple regression analysis demonstrated that PTF treatment and variations in mRNA KL expression in PBCs, together with changes in HDL, were significant determinants for the progression of CIMT (adjusted R2 = 0.24, P < 0.001) independently of traditional risk factors. Moreover, both variables constituted protective factors against a worst progression of CIMT [OR: 0.103 (P = 0.001) and 0.001 (P = 0.005), respectively].

CONCLUSIONS

PTF reduced SA progression assessed by CIMT variation, a beneficial effect related to KL gene expression in PBCs.

TRIAL REGISTRATION

The study protocol code is PTF-AA-TR-2009 and the trial was registered on the European Union Drug Regulating Authorities Clinical Trials (EudraCT #2009-016595-77). The validation date was 2010-03-09.

Biomarkers of chronic kidney disease in older individuals: navigating complexity in diagnosis

Chronic kidney disease (CKD) in older individuals is a matter of growing concern in the field of public health across the globe. Indeed, prevalence of kidney function impairment increases with advancing age and is often exacerbated by age-induced modifications of kidney function, presence of chronic diseases such as diabetes, hypertension, and cardiovascular disorders, and increased burden related to frailty, cognitive impairment and sarcopenia. Accurate assessment of CKD in older individuals is crucial for timely intervention and management and relies heavily on biomarkers for disease diagnosis and monitoring. However, the interpretation of these biomarkers in older patients may be complex due to interplays between CKD, aging, chronic diseases and geriatric syndromes. Biomarkers such as serum creatinine, estimated glomerular filtration rate (eGFR), and albuminuria can be significantly altered by systemic inflammation, metabolic changes, and medication use commonly seen in this population. To overcome the limitations of traditional biomarkers, several innovative proteins have been investigated as potential, in this review we aimed at consolidating the existing data concerning the geriatric aspects of CKD, describing the challenges and considerations in using traditional and innovative biomarkers to assess CKD in older patients, highlighting the need for integration of the clinical context to improve biomarkers' accuracy.

U-shaped association between serum Klotho and all-cause mortality in US cardiovascular patients: a prospective cohort study

Background

Increased levels of serum Klotho have been associated with a reduced risk of several cardiovascular diseases (CVD). However, limited studies exist on the association between serum Klotho and mortality in patients with CVD.

Methods

We collected data from CVD patients in the National Health and Nutrition Examination Survey (NHANES) spanning 2007 to 2016. We linked NHANES data with the National Death Index to determine the survival status of participants. Univariate and multivariable Cox regression models were used to investigate the relationship between serum Klotho levels and mortality in CVD patients. The relationship between serum Klotho quartiles and mortality in CVD patients was visualized using Kaplan-Meier (KM) curves and restricted cubic spine. Finally, subgroup analyses were used to examine the association between serum Klotho and all-cause mortality in different populations.

Results

1905 patients with CVD were finally enrolled in our study with a mean follow-up of 7.1 years. The average age of the participants was 63.4 years, with 58.40% being male. KM showed that lower Klotho levels were associated with lower survival rates. After adjusting for potential confounders, patients with higher serum Klotho levels had lower all-cause mortality (Q1: 1.00, Q2: 0.58 (0.42-0.80), Q3: 0.69 (0.47-1.01), and Q4:0.64 (0.45-0.92). However, the relationship between serum Klotho levels and cardiovascular mortality was not statistically significant. Dose-response analysis shows a U-shaped relationship between serum Klotho levels and all-cause mortality in patients with CVD (P nonlinear=0.002). Subgroup analysis indicated that participants with a history of hypertension had a higher risk of all-cause mortality in serum Klotho Q4 compared to Q1 (P trend <0.05).

Conclusion

The relationship between serum Klotho levels and all-cause mortality in CVD patients exhibits a U-shaped association. The underlying mechanisms of this association need further investigation.

The optimal cut-off values of Klotho for predicting all-cause and cardiovascular mortality among chronic kidney disease: results from NHANES

To explore the optimal cut-off values of Klotho for predicting all-cause and cardiovascular mortality among chronic kidney disease (CKD) patients. Klotho was measured in 40-79-year-old individuals in the NHANES 2007-2016. A total of 2418 patients with stage 1-4 CKD were included. The optimal cut-off values of Klotho were utilized using receiver operator characteristic (ROC) curves and be verified on the effects of all-cause and cardiovascular mortality. Restricted cubic splines were used to examine the relationship between Klotho and all-cause and cardiovascular mortality with the optimal cutpoints as the reference. After a mean follow-up period of 87.9 months, 535 deaths occurred and 188 died of cardiovascular disease. Cubic splines showed that the risk of all-cause and cardiovascular mortality increased gradually for Klotho < 700 pg/ml. ROC curves revealed that the optimal cut-off values of Klotho for all-cause and cardiovascular mortality are 548.8 pg/ml and 660.9 pg/ml, respectively. Compared to patients with higher levels of Klotho, HRs (95% CIs) for all-cause and cardiovascular mortality were 1.52 (1.23, 1.87) and 1.58 (1.13, 2.22) among patients with lower levels of Klotho, respectively, in the multivariate model (P < .0001 and P = 0.008). Our findings revealed the optimal cut-off values of Klotho for all-cause and cardiovascular mortality in CKD.

Soluble Klotho, a Potential Biomarker of Chronic Kidney Disease-Mineral Bone Disorders Involved in Healthy Ageing: Lights and Shadows

Shortly after the discovery of Klotho, interest grew in its potential role in chronic kidney disease (CKD). There are three isoforms of the Klotho protein: αKlotho, βKlotho and γKlotho. This review will focus on αKlotho due to its relevance as a biomarker in CKD. αKlotho is synthesized mainly in the kidneys, but it can be released into the bloodstream and urine as soluble Klotho (sKlotho), which undertakes systemic actions, independently or in combination with FGF23. It is usually accepted that sKlotho levels are reduced early in CKD and that lower levels of sKlotho might be associated with the main chronic kidney disease-mineral bone disorders (CKD-MBDs): cardiovascular and bone disease. However, as results are inconsistent, the applicability of sKlotho as a CKD-MBD biomarker is still a matter of controversy. Much of the inconsistency can be explained due to low sample numbers, the low quality of clinical studies, the lack of standardized assays to assess sKlotho and a lack of consensus on sample processing, especially in urine. In recent decades, because of our longer life expectancies, the prevalence of accelerated-ageing diseases, such as CKD, has increased. Exercise, social interaction and caloric restriction are considered key factors for healthy ageing. While exercise and social interaction seem to be related to higher serum sKlotho levels, it is not clear whether serum sKlotho might be influenced by caloric restriction. This review focuses on the possible role of sKlotho as a biomarker in CKD-MBD, highlighting the difference between solid knowledge and areas requiring further research, including the role of sKlotho in healthy ageing.

FGF23 and klotho at the intersection of kidney and cardiovascular disease

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD). As CKD progresses, CKD-specific risk factors, such as disordered mineral homeostasis, amplify traditional cardiovascular risk factors. Fibroblast growth factor 23 (FGF23) regulates mineral homeostasis by activating complexes of FGF receptors and transmembrane klotho co-receptors. A soluble form of klotho also acts as a 'portable' FGF23 co-receptor in tissues that do not express klotho. In progressive CKD, rising circulating FGF23 levels in combination with decreasing kidney expression of klotho results in klotho-independent effects of FGF23 on the heart that promote left ventricular hypertrophy, heart failure, atrial fibrillation and death. Emerging data suggest that soluble klotho might mitigate some of these effects via several candidate mechanisms. More research is needed to investigate FGF23 excess and klotho deficiency in specific cardiovascular complications of CKD, but the pathophysiological primacy of FGF23 excess versus klotho deficiency might never be precisely resolved, given the entangled feedback loops that they share. Therefore, randomized trials should prioritize clinical practicality over scientific certainty by targeting disordered mineral homeostasis holistically in an effort to improve cardiovascular outcomes in patients with CKD.

Klotho and lean mass as novel cardiovascular risk factors in hemodialysis patients

Background

Patients with chronic kidney disease (CKD) present a higher risk of cardiovascular (CV) morbidity and mortality compared with the general population. While there are several well-established traditional CV risk factors, few studies have addressed novel potential risk factors such as α-Klotho, asymmetric dimethylarginine (ADMA) and lean mass.

Methods

This was an observational, prospective, single-center, cohort study that included prevalent hemodialysis (online hemodiafiltration) adult patients. By univariate logistic regression models, univariate and multivariate Cox proportional hazards models, and Kaplan-Meier analysis, we evaluated the association between the levels of α-Klotho, ADMA and lean mass, with the risk of peripheral vascular disease (PVD), CV events and all-cause mortality in these patients.

Results

A total of 200 HD patients was included. We found that increased levels of log-α-Klotho were significantly associated with decreased odds of both PVD [odds ratio (OR) 0.521, 95% confidence interval (CI) 0.270-0.954, P = .034] and CV events (OR 0.415, 95% CI 0.203-0.790, P = .01), whereas increased levels of log-ADMA were only significantly associated with increased odds of PVD (OR 13.482, 95% CI 5.055-41.606, P < .001). We also found that the levels of log-α-Klotho (HR 0.357, 95% CI 0.140-0.906, P < .05) and lean mass (HR 0.187, 95% CI 0.042-0.829, P < .05), but not log-ADMA, were significantly associated with the risk of all-cause mortality, even after adjusting for possible confounding variables.

Conclusions

Novel long-term clinical associations were generated that support α-Klotho and lean mass as novel CV risk factors in hemodialysis patients.

Klotho inhibits IGF1R/PI3K/AKT signalling pathway and protects the heart from oxidative stress during ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) of the heart involves the activation of oxidative and proapoptotic pathways. Simultaneously Klotho protein presents anti-aging, antiapoptotic and antioxidative properties. Therefore, this study aimed to evaluate the effect of Klotho protein on oxidative stress in hearts subjected to IRI. Isolated rat hearts perfused with the Langendorff method were subjected to ischemia, followed by reperfusion, in the presence or absence of recombinant rat Klotho protein. The factors involved in the activation of insulin-like growth factor receptor (IGF1R)/phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) signalling pathway were evaluated. IRI caused activation of the IGF1R (p = 0.0122)/PI3K (p = 0.0022) signalling, as compared to the aerobic control group. Infusion supply of Klotho protein during IRI significantly reduced the level of phospho-IGF1R (p = 0.0436), PI3K (p = 0.0218) and phospho-AKT (p = 0.0020). Transcriptional activity of forkhead box protein O3 (FOXO3) was reduced (p = 0.0207) in hearts subjected to IRI, compared to aerobic control. Administration of Klotho decreased phosphorylation of FOXO3 (p = 0.0355), and enhanced activity of glutathione peroxidase (p = 0.0452) and superoxide dismutase (p = 0.0060) in IRI + Klotho group. The levels of reactive oxygen/nitrogen species (ROS/RNS) (p = 0.0480) and hydrogen peroxide (H2O2) (p = 0.0460), and heart injury (p = 0.0005) were significantly increased in hearts from the IRI group in comparison to the aerobic group. Klotho reduced NADPH oxidase 2 (NOX2) (p = 0.0390), ROS/RNS (p = 0.0435) and H2O2 (p = 0.0392) levels, and heart damage (p = 0.0286) in the hearts subjected to IRI. In conclusion, Klotho contributed to the protection of the heart against IRI and oxidative stress via inhibition of the IGF1R/PI3K/AKT pathway, thus can be recognized as a novel cardiopreventive/cardioprotective agent.

Cardiomyopathy in chronic kidney disease: clinical features, biomarkers and the contribution of murine models in understanding pathophysiology

The cardiorenal syndrome (CRS) is described as a multi-organ disease encompassing bidirectionally heart and kidney. In CRS type 4, chronic kidney disease (CKD) leads to cardiac injury. Different pathological mechanisms have been identified to contribute to the establishment of CKD-induced cardiomyopathy, including a neurohormonal dysregulation, disturbances in the mineral metabolism and an accumulation of uremic toxins, playing an important role in the development of inflammation and oxidative stress. Combined, this leads to cardiac dysfunction and cardiac pathophysiological and morphological changes, like left ventricular hypertrophy, myocardial fibrosis and cardiac electrical changes. Given that around 80% of dialysis patients suffer from uremic cardiomyopathy, the study of cardiac outcomes in CKD is clinically highly relevant. The present review summarizes clinical features and biomarkers of CKD-induced cardiomyopathy and discusses underlying pathophysiological mechanisms recently uncovered in the literature. It discloses how animal models have contributed to the understanding of pathological kidney-heart crosstalk, but also provides insights into the variability in observed effects of CKD on the heart in different CKD mouse models, covering both "single hit" as well as "multifactorial hit" models. Overall, this review aims to support research progress in the field of CKD-induced cardiomyopathy.

The fibroblast growth factor-Klotho axis at molecular level

Klotho is a recently discovered protein that has positive effects on all systems of the body, for example, regulating calcium and phosphorus metabolism, protecting nerves, delaying aging and so on. Fibroblast growth factors (FGFs) are a group of polypeptides that function throughout the body by binding with cell surface FGF receptors (FGFRs). Endocrine FGFs require Klotho as a co-receptor for FGFRs. There is increasing evidence that Klotho participates in calcium and phosphorus regulation and metabolic regulation via the FGF-Klotho axis. Moreover, soluble Klotho can function as a separate hormone to regulate homeostasis on various ion channels and carrier channels on the cell surface. This review mainly explains the molecular basis of the membrane signaling mechanism of Klotho.

An evaluation of both serum Klotho/FGF-23 and apelin-13 for detection of diabetic nephropathy

PURPOSE

The aim of our study is to evaluate whether serum Klotho/FGF-23 and apelin-13 can be used as new biomarkers for detection of development of nephropathy.

METHODS

In this cross-sectional study, 88 type 2 diabetes mellitus (T2DM) patients and 38 healthy controls were included. The mean duration of T2DM was 11.4 ± 9.7 years. T2DM individuals were categorized into two groups as group 1 with e-GFR < 60 mL/min/1.73 m2 and group 2 with e-GFR > 60 mL/min/1.73 m2. They were also divided into two groups according to their 24 h urine albumin levels, classifying them as follows: normoalbuminuria if less than 30 mg/day and albuminuria if more than 30 mg/day.

RESULTS

Mean serum Klotho levels in the T2DM group were observed to be significantly higher than in the control group. Serum apelin-13 levels were observed to be significantly lower in the T2DM group compared to the control group (p < 0.001). In the diabetic group, apelin-13 levels were positively correlated with age, waist circumference, and albuminuria while they were negatively correlated with e-GFR. Apelin-13 levels were seen to be significantly higher in group 1 (p < 0.001).

CONCLUSION

Apelin-13 levels were found to be significantly higher in individuals with diabetic nephropathy than in those without diabetic nephropathy. In the diabetic group, a significant relationship was detected between apelin-13 levels and albumin excretion. Based on these findings, we consider that serum Klotho and apelin-13 levels may have a protective effect on diabetic nephropathy and can additionally be used as a biomarker to predict diabetic nephropathy.

Association of Klotho with Coronary Artery Disease in Subjects with Type 2 Diabetes Mellitus and Preserved Kidney Function: A Case-Control Study

Circulating Klotho levels are significantly reduced in subjects with type 2 diabetes mellitus (T2DM) and in kidney disease patients. In this work, the relationship between Klotho levels and the coronary artery disease (CAD) burden in subjects with T2DM and preserved kidney function was analyzed. For this, we performed a cross-sectional case-control study involving 133 subjects with T2DM and 200 age-, sex- and CAD-incidence-matched, non-diabetic patients undergoing non-emergency diagnostic coronary angiography. All of them were non-albuminuric and with normal glomerular filtration rates. The concentrations of serum Klotho, fibroblast growth factor 23, and inflammatory markers were also measured. As expected, the serum Klotho concentration was lower in the T2DM group (12.3% lower, p = 0.04). However, within the group of patients with T2DM, those subjects with CAD presented significantly higher Klotho levels than those without significant coronary stenosis (314.5 (6.15-562.81) vs. 458.97 (275.2-667.2) pg/mL; p = 0.02). Multiple regression analysis revealed that serum Klotho was positively related with stenosis values exclusively in subjects with T2DM (adjusted R2 = 0.153, p < 0.01). Moreover, logistic regression analysis showed that Klotho was positively associated with the presence of significant CAD in the group of T2DM patients (OR: 1.001; p = 0.041). Our data suggest that higher levels of circulating Klotho in subjects with T2DM and preserved kidney function are associated with the presence of significant CAD.

Epidemiology and Risk Factors for Stroke in Chronic Kidney Disease: A Narrative Review

Patients with chronic kidney disease (CKD) have a higher risk ofboth ischemic and hemorrhagic stroke. This association appears to be partly independent from the higher prevalence of established risk factors for stroke in patients with CKD, including hypertension and atrial fibrillation. In the present review we aim to discuss the impact of CKD on the risk of stroke and stroke-related consequences, and explore the pathophysiology underpinning the increased risk of stroke in patients with CKD. We cover the clinical association between renal dysfunction and cerebrovascular disease including stroke, silent brain infarct, cerebral small vessel disease, microbleeds, and white matter hyperintensity, and discuss the underlying mechanisms.

Association between soluble α-klotho and mortality risk in middle-aged and older adults

Introduction

Studies on association of α-klotho levels with mortality risk in general population are relatively scarce and inconclusive. Therefore, we conducted a population-based cohort study to investigate the relationship between soluble α-klotho and all-cause mortality in a nationally representative sample of middle-aged and older adults in the United States (U.S.).

Methods

The study population was 2007-2016 National Health and Nutrition Examination Survey (NHANES) participants, totaling 13,583 adults aged 40-79 years. Participants were divided into 7 groups by septile of α-klotho levels. We linked the NHANES data to the National Death Index to determine participants' survival status. End of follow-up was participants' death date or December 31, 2019.

Results

We observed that males, current smokers, older age, higher body mass index, and lower estimated glomerular filtration rate correlated to lower α-klotho levels, while hepatitis C virus infection correlated to higher α-klotho. The population mortality rate was 11.8 per 10,000 person-months (1,490 deaths); group 1 (the first septile) had higher mortality risk compared with group 2 through group 7. By weighted Cox regression with adjustment for potential confounders, we found that group 2 through group 6, but not group 7, were associated with 25% to 35% lower risk of all-cause mortality compared with group 1. When compared with group 4, we observed that both group 1 (HR: 1.46, 95% CI 1.13-1.88) and group 7 (HR: 1.38, 95% CI 1.09-1.74) were associated with higher mortality risk.

Conclusion

In summary, among middle-aged and older U.S. adults, we observed a non-linear association between soluble α-klotho and all-cause mortality, with individuals at the two extremes at increased risk of death.

Klotho prevents transforming growth factor-β2-induced senescent-like morphological changes in the retinal pigment epithelium

Degenerative changes of the retinal pigment epithelium (RPE) triggered by transforming growth factor-β2 (TGF-β2) and oxidative stress play a critical role in the progression of age-related macular degeneration (AMD). The expression of α-klotho, an antiaging protein, declines with age, increasing the risk factors for age-related diseases. Here, we investigated the protective effects of soluble α-klotho on TGF-β2-induced RPE degeneration. The morphological changes induced by TGF-β2, including epithelial-mesenchymal transition (EMT), were attenuated in the mouse RPE by the intravitreal injection (IVT) of α-klotho. In ARPE19 cells, EMT and morphological alterations by TGF-β2 were attenuated by co-incubation with α-klotho. TGF-β2 decreased miR-200a accompanied by zinc finger e-box binding homeobox1 (ZEB1) upregulation and EMT, all of which were prevented by α-klotho co-treatment. Inhibitor of miR-200a mimicked TGF-β2-induced morphological changes, which were recovered by ZEP1 silencing, but not by α-klotho, implying the upstream regulation of α-klotho on miR-200a-ZEP1-EMT axis. α-Klotho inhibited receptor binding of TGF-β2, Smad2/3 phosphorylation, extracellular signal-regulated protein kinase 1/2 (ERK1/2)-a mechanistic target of rapamycin (mTOR) activation and oxidative stress via NADPH oxidase 4 (NOX4) upregulation. Furthermore, α-klotho recovered the TGF-β2-induced mitochondrial activation and superoxide generation. Interestingly, TGF-β2 upregulated α-klotho expression in the RPE cells, and genetic suppression of endogenous α-klotho aggravated TGF-β2-induced oxidative stress and EMT. Lastly, α-klotho abrogated senescence-associated signaling molecules and phenotypes induced by long-term incubation with TGF-β2. Hence, our findings indicate that the antiaging α-klotho plays a protective role against EMT and degeneration of the RPE, demonstrating the therapeutic potential for age-related retinal diseases, including the dry type of AMD.

α-Klotho: An Early Risk-Predictive Biomarker for Acute Kidney Injury in Patients with Acute Myocardial Infarction

Background

Acute kidney injury (AKI) was a common and serious complication in patients with acute myocardial infarction (AMI). Novel biomarkers and therapies were deficient and imperative for AKI's early diagnosis and therapy after AMI. α-Klotho was considered as an early biomarker and potential therapy for AKI recently. Previous studies reported that the expression of α-Klotho was decreased in AKI rodents, and supplement of α-Klotho alleviated kidney injury. Nevertheless, its effect has not been studied in patients presenting with AMI.

Methods

A total of 155 consecutive diagnosed with AMI at emergency department whose eGFR >60 ml/min ∗ 1.73 m2 were enrolled in this prospective observational cohort study which conducted between May 2016 and April 2019 in Peking University People's Hospital. AKI was defined according to the KDIGO criteria in 2012. At admission, the clinical data of patients were collected and serum α-Klotho was tested by ELISA. The relationship between α-Klotho, serum creatinine, eGFR, systolic pressure, BNP, LVEF, and Hgb of AKI were analyzed and their discrimination performances were compared. The association variables were calculated (adjusted odds ratio) with a confidence interval (CI) of 95% by binary logistic regression. And, we followed up the incidence of CKD and rehospitalization after patients' discharge in one year. Our study was approved by the ethics committee (no. 2016PHB042-01).

Results

AKI incidence was 17.4% (27/155) during hospitalization. Compared to patients without AKI, the AKI group had obviously higher mortality and was more female and had higher incidence of chronic kidney disease, worse cardiac function, more cardiac complications, larger doses of diuretics, and less use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker. By contrary to previous animal experiments, we found serum α-Klotho levels were increased significantly in AKI patients (740.2 ± 306.8 vs. 419.0 ± 272.6 pg/mL, p < 0.001). And, the areas under the receiver operating curves indicated serum α-Klotho levels had a superior discriminative power for predicting AKI after AMI compared with other risk factors (0.792, 95% CI, 0.706-0.878, p < 0.001). Meanwhile, logistic regression model indicates extensive anterior myocardial infarction, Killip classification ≥2 grade, α-Klotho ≥516.9 pg/mL, eGFR (decrease per 10 ml/min ∗ 1.73 m2), Hgb, and nonuse of ACEI/ARB were the risk factors of AKI after AMI. Moreover, one-year follow-up presented AMI patients developed CKD had higher α-Klotho levels (739.7 ± 315.2 vs. 443.8 ± 292.5 pg/mL, p = 0.001), but no significant difference in rehospitalization. And, patients with α-Klotho ≥516.9 pg/ml was 6.699 times more likely to develop CKD than those with α-Klotho <516.9 pg/ml (relative risk 6.699, 95% CI 1.631-27.519, p = 0.007).

Conclusion

Compared with traditional cardiac and renal biomarkers, serum α-Klotho could be a more appropriate predict biomarker for AKI after AMI in patients' eGFR >60 ml/min ∗ 1.73 m2. Higher α-Klotho levels are related to the development of AKI during hospitalization and suggest a higher prevalence of CKD after discharge. By contrary to animal experiments, whether the increased expression of α-Klotho could be a protective factor secreted by AKI after AMI, is remained to be further studied.

Role of Klotho and AGE/RAGE-Wnt/β-Catenin Signalling Pathway on the Development of Cardiac and Renal Fibrosis in Diabetes

Fibrosis plays an important role in the pathogenesis of long-term diabetic complications and contributes to the development of cardiac and renal dysfunction. The aim of this experimental study, performed in a long-term rat model, which resembles type 1 diabetes mellitus, was to investigate the role of soluble Klotho (sKlotho), advanced glycation end products (AGEs)/receptor for AGEs (RAGE), fibrotic Wnt/β-catenin pathway, and pro-fibrotic pathways in kidney and heart. Diabetes was induced by streptozotocin. Glycaemia was maintained by insulin administration for 24 weeks. Serum and urine sKlotho, AGEs, soluble RAGE (sRAGE) and biochemical markers were studied. The levels of Klotho, RAGEs, ADAM10, markers of fibrosis (collagen deposition, fibronectin, TGF-β1, and Wnt/β-catenin pathway), hypertrophy of the kidney and/or heart were analysed. At the end of study, diabetic rats showed higher levels of urinary sKlotho, AGEs and sRAGE and lower serum sKlotho compared with controls without differences in the renal Klotho expression. A significant positive correlation was found between urinary sKlotho and AGEs and urinary albumin/creatinine ratio (uACR). Fibrosis and RAGE levels were significantly higher in the heart without differences in the kidney of diabetic rats compared to controls. The results also suggest the increase in sKlotho and sRAGE excretion may be due to polyuria in the diabetic rats.

Hypertension and cardiomyopathy associated with chronic kidney disease: epidemiology, pathogenesis and treatment considerations

Chronic kidney disease (CKD) is a complex condition with a prevalence of 10-15% worldwide. An inverse-graded relationship exists between cardiovascular events and mortality with kidney function which is independent of age, sex, and other risk factors. The proportion of deaths due to heart failure and sudden cardiac death increase with progression of chronic kidney disease with relatively fewer deaths from atheromatous, vasculo-occlusive processes. This phenomenon can largely be explained by the increased prevalence of CKD-associated cardiomyopathy with worsening kidney function. The key features of CKD-associated cardiomyopathy are increased left ventricular mass and left ventricular hypertrophy, diastolic and systolic left ventricular dysfunction, and profound cardiac fibrosis on histology. While these features have predominantly been described in patients with advanced kidney disease on dialysis treatment, patients with only mild to moderate renal impairment already exhibit structural and functional changes consistent with CKD-associated cardiomyopathy. In this review we discuss the key drivers of CKD-associated cardiomyopathy and the key role of hypertension in its pathogenesis. We also evaluate existing, as well as developing therapies in the treatment of CKD-associated cardiomyopathy.

Soluble klotho as an effective biomarker to characterize inflammatory states

BACKGROUND & AIMS

Soluble α-Klotho (s-Klotho) is a circulating protein with pleiotropic effects that mainly induce protective effects. Our study investigates the associations between s-Klotho and several established inflammatory biomarkers, with the aim of examining whether s-Klotho levels are representative of inflammatory states.

METHODS

A total of 11,128 eligible participants from NHANES 2007-2016 were included in our study. Levels of four inflammatory biomarkers, uric acid (UA), C-reactive protein (CRP), white blood cell (WBC) count, and mean platelet volume (MPV), were examined for their relationship with s-Klotho levels. Sub-analyses sorted the total population by gender and into four quartiles. Linear regression models were used to evaluate the strengths of associations.

RESULTS

All four inflammatory biomarkers were significantly associated with s-Klotho levels. UA, CRP, and WBC count showed an inverse association, while MPV showed a direct one. Of the four markers, UA was most strongly correlated with s-Klotho levels (β coefficient: -28.89 in unadjusted model, p<.001), and this relationship was stronger in women than in men (β coefficient of UA in men: -22.01, p<.001; in women: -31.54, p<.001). In addition, all four biomarkers manifested stronger associations with s-Klotho in higher quartiles, and the highest absolute values of β coefficients appeared in Q4 vs. Q1.

CONCLUSION

s-Klotho is significantly associated with well-recognized inflammatory biomarkers. A decrease in s-Klotho levels implies a general inflammatory status; therefore, s-Klotho serves as a potential biomarker that is inversely correlated with inflammatory conditions. Further applications in clinical practice will provide us with a better understanding of its role.Key messagesSoluble α-Klotho (s-Klotho) levels are significantly associated with the inflammatory markers uric acid, C-reactive protein, white blood cell count, and mean platelet volume.S-Klotho is involved in inflammatory processes and plays a protective role.S-Klotho may serve as an inverse indicator of inflammation.

Association between serum Klotho concentration and all-cause and cardiovascular mortality among American individuals with hypertension

BACKGROUND AND AIMS

Evidence indicates that serum Klotho concentration is associated with mortality in patients with chronic kidney disease (CKD). However, evidence on this association among people with hypertension is scarce. Therefore, we aimed to examine the association between serum Klotho concentration and all-cause and cardiovascular mortality in American patients with hypertension.

METHODS AND RESULTS

We included 6,778 participants with hypertension from the National Health and Nutrition Examination Survey (NHANES) 2007-2014. A Cox proportional hazard model was used to compute the hazard ratios (HRs) and 95% confidence intervals (CIs). The correlation between serum Klotho concentration and mortality was determined using restricted cubic spline and piecewise linear regression analyses. During 36,714 person-years of follow-up, 575 deaths were documented. Lower serum Klotho concentration was associated with increased all-cause mortality, but not cardiovascular mortality after multivariate adjustment. According to spline analysis, the correlation between serum Klotho concentration and all-cause mortality was non-linear (P < 0.001), and the threshold value was 574 pg/mL. The HR below the threshold point was 0.79 (95% CI: 0.67-0.93); no significant difference was found above the threshold point.

CONCLUSION

Higher serum Klotho concentration was associated with lower all-cause mortality, but not cardiovascular mortality in patients with hypertension with or without chronic renal impairment.

Serum Levels of α-Klotho, Inflammation-Related Cytokines, and Mortality in Hemodialysis Patients

It has been hypothesized that α-Klotho deficiency might contribute to chronic inflammation in patients with end-stage renal disease (ESRD), especially those on hemodialysis (HD). Serum Klotho levels by some authors are considered a potential predictor of cerebrovascular events. Therefore, we analyzed serum levels of α-Klotho with ELISA and inflammation-related cytokines in HD patients. Sixty-seven HD patients and 19 healthy people were recruited between November 2017 and June 2021. A Cytometric Bead Array (CBA) was used to determine the level of different cytokines: IL-12p70, TNF, IL-10, IL-6, IL-1β, and IL-8. A human Klotho ELISA kit was used to determine the level of α-Klotho in the plasma samples of HD patients. There was no difference in serum levels of α-Klotho between HD patients and healthy people. Patients had increased serum IL-6 and IL-8. Significant positive correlations existed between the concentration of α-Klotho and the serum concentrations of IL-12p70, IL-10, and IL-1β. However, in a multivariable linear regression analysis, only patients' age was associated independently with α-Klotho level. Serum α-Klotho was not associated with higher mortality risk in HD patients. While these results draw attention to potential relationships between α-Klotho proteins and inflammatory markers in HD patients, our cross-sectional study could not confirm the pathogenic link between α-Klotho, inflammation, and cardiovascular mortality.

Strategies to lower fibroblast growth factor 23 bioactivity

Fibroblast growth factor 23 (FGF23) is a circulating hormone derived from the bone whose release is controlled by many factors and exerts a multitude of systemic actions. There are congenital and acquired disorders of increased and decreased FGF23 levels. In chronic kidney disease (CKD), elevations of FGF23 levels can be 1000-fold above the upper physiological limit. It is still debated whether this high FGF23 in CKD is a biomarker or causally related to morbidity and mortality. Data from human association studies support pathogenicity, while experimental data are less robust. Knowledge of the biology and pathobiology of FGF23 has generated a plethora of means to reduce FGF23 bioactivity at many levels that will be useful for therapeutic translations. This article summarizes these approaches and addresses several critical questions that still need to be answered.

The controversy of klotho as a potential biomarker in chronic kidney disease

Klotho is an identified longevity gene with beneficial pleiotropic effects on the kidney. Evidence shows that a decline in serum Klotho level occurs in early chronic kidney disease (CKD) and continues as CKD progresses. Klotho deficiency is associated with poor clinical outcomes and CKD mineral bone disorders (CKD-MBD). Klotho has been postulated as a candidate biomarker in the evaluation of CKD. However, the evidence for the clinical significance of the relationship between Klotho and kidney function, CKD stage, adverse kidney and/or non-kidney outcomes, and CKD-MBD remains inconsistent and in some areas, contradictory. Therefore, there is uncertainty as to whether Klotho is a potential biomarker in CKD; a general consensus regarding the clinical significance of Klotho in CKD has not been reached, and there is limited evidence synthesis in this area. To address this, we have systematically assessed the areas of controversy, focusing on the inconsistencies in the evidence base. We used a PICOM strategy to search for relevant studies and the Newcastle–Ottawa Scale scoring to evaluate included publications. We reviewed the inconsistent clinical findings based on the relationship of Klotho with CKD stage, kidney and/or non-kidney adverse outcomes, and CKD-MBD in human studies. Subsequently, we assessed the underlying sources of the controversies and highlighted future directions to resolve these inconsistencies and clarify whether Klotho has a role as a biomarker in clinical practice in CKD.

Outcomes in Patients with Chronic Kidney Disease and End Stage Renal Disease and Durable Left Ventricular Assist Device: Insights from United States Renal Data System Database

BACKGROUND

There is paucity of data regarding durable LVAD outcomes in patients with chronic kidney disease (CKD) stage 3-5 and CKD stage 5 on dialysis (ESRD: end stage renal disease).

METHODS

We conducted a retrospective study of Medicare beneficiaries with ESRD and 5% sample of CKD with LVAD (2006 to 2018) to determine one-year outcomes utilizing the United States Renal Data System (USRDS) database. The LVAD implantation, comorbidities and outcomes were identified using appropriate ICD-9 and ICD-10 codes.

RESULTS

We identified 496 CKD and 95 ESRD patients who underwent LVAD implantation. The ESRD patients were younger (59 vs 66 years; p <0.001), had more Blacks (40% vs 24.6%; p=0.009), compared to the CKD group. One-year mortality (49.5% vs 30.9%; p <0.001) and index mortality (27.4% vs 16.7%; p=0.014) was higher in ESRD. Subgroup analysis showed significantly higher mortality in ESRD vs CKD 3 (49.5% vs 30.2%, adjusted p=0.009), but no significant difference in mortality between stage 3 vs 4/5 (30.2% vs 30.8%; adjusted p=0.941). There was no significant difference in secondary outcomes (bleeding, stroke, and sepsis/infection) during follow-up between two groups.

CONCLUSIONS

Patients with ESRD undergoing LVAD implantation had significantly higher index and 1-year mortality compared to CKD patients.

Recombinant Klotho Protein Ameliorates Myocardial Ischemia/Reperfusion Injury by Attenuating Sterile Inflammation

Currently, no effective therapy and potential target have been elucidated for preventing myocardial ischemia and reperfusion injury (I/R). We hypothesized that the administration of recombinant klotho (rKL) protein could attenuate the sterile inflammation in peri-infarct regions by inhibiting the extracellular release of high mobility group box-1 (HMGB1). This hypothesis was examined using a rat coronary artery ligation model. Rats were divided into sham, sham+ rKL, I/R, and I/R+ rKL groups (n = 5/group). Administration of rKL protein reduced infarct volume and attenuated extracellular release of HMGB1 from peri-infarct tissue after myocardial I/R injury. The administration of rKL protein inhibited the expression of pro-inflammatory cytokines in the peri-infarct regions and significantly attenuated apoptosis and production of intracellular reactive oxygen species by myocardial I/R injury. Klotho treatment significantly reduced the increase in the levels of circulating HMGB1 in blood at 4 h after myocardial ischemia. rKL regulated the levels of inflammation-related proteins. This is the first study to suggest that exogenous administration of rKL exerts myocardial protection effects after I/R injury and provides new mechanistic insights into rKL that can provide the theoretical basis for clinical application of new adjunctive modality for critical care of acute myocardial infarction.

Monthly Continuous Erythropoietin Receptor Activator Versus Weekly Epoetin-Beta, Similar Hemoglobinization but Different Anisocytosis Degree in Hemodialysis Patients: A Randomized Controlled Trial

Background

The monthly continuous erythropoietin receptor activator (CERA) utilization maintains stable hemoglobin (Hb) after conversion from weekly epoetin-β (EB); however, how the different pharmacologic properties affect the red blood cell (RBC) size determined by RBC distribution width (RDW) has not been evaluated yet. We assess the potential differences in iron metabolism, plasma erythropoietin (EPO), hepcidin, and soluble α-Klotho (α-Klotho) levels as an emergent hematopoiesis factor.

Methods

Thirty-seven chronic hemodialysis patients were included from January 2010 to November 2011 and randomized (1:1) to continue with EB or to convert to monthly CERA. Primary outcome was the mean change in Hb between groups at months 0, 3 and 6, and the percentage of patients who maintained stable Hb (Hb ± 1 g/dL from baseline level to month 6). Secondary outcomes were the influence on the erythropoietic process and iron metabolism markers. Thirty-one patients completed the study (CERA: n = 15, EB: n = 16).

Results

The mean (95% confidence interval (CI)) Hb difference between groups was 0.28 g/dL (-0.36 to 0.93). There was no difference between the percentages of patients with stable Hb levels. In the CERA group RDW values increased progressively (interaction erythropoietin-stimulating agent (ESA) type and time on RDW values, F (1.57, 45.60) = 17.17, P < 0.01, partial η² = 0.37) and the mean corpuscular volume changed at the different time points, (F (2, 28) = 29.12, P = 0.03, partial η² = 0.23). During the evaluation period, in the CERA group, EPO was higher, and hepcidin and ferritin decreased significantly. α-Klotho decreased in both groups and correlated negatively with the changes on the RDW and positively with transferrin and serum iron. The number of serious adverse events was higher at the CERA group.

Conclusions

Monthly CERA maintained Hb concentrations; however, it showed a significant effect on RDW, probably due to its impact on the EPO and hepcidin levels. α-Klotho decreased significantly in both groups, and its changes correlated with the changes in iron metabolism. Whether the RDW evolution was associated with the serious adverse events (SAEs) is a feasible hypothesis that needs to be confirmed in large studies.

Inflammation as A Precursor of Atherothrombosis, Diabetes and Early Vascular Aging

Vascular disease was for a long time considered a disease of the old age, but it is becoming increasingly clear that a cumulus of factors can cause early vascular aging (EVA). Inflammation plays a key role in vascular stiffening and also in other pathologies that induce vascular damage. There is a known and confirmed connection between inflammation and atherosclerosis. However, it has taken a long time to prove the beneficial effects of anti-inflammatory drugs on cardiovascular events. Diabetes can be both a product of inflammation and a cofactor implicated in the progression of vascular disease. When diabetes and inflammation are accompanied by obesity, this ominous trifecta leads to an increased incidence of atherothrombotic events. Research into earlier stages of vascular disease, and documentation of vulnerability to premature vascular disease, might be the key to success in preventing clinical events. Modulation of inflammation, combined with strict control of classical cardiovascular risk factors, seems to be the winning recipe. Identification of population subsets with a successful vascular aging (supernormal vascular aging-SUPERNOVA) pattern could also bring forth novel therapeutic interventions.

Klotho and Mesenchymal Stem Cells: A Review on Cell and Gene Therapy for Chronic Kidney Disease and Acute Kidney Disease

Chronic kidney disease (CKD) and acute kidney injury (AKI) are public health problems, and their prevalence rates have increased with the aging of the population. They are associated with the presence of comorbidities, in particular diabetes mellitus and hypertension, resulting in a high financial burden for the health system. Studies have indicated Klotho as a promising therapeutic approach for these conditions. Klotho reduces inflammation, oxidative stress and fibrosis and counter-regulates the renin-angiotensin-aldosterone system. In CKD and AKI, Klotho expression is downregulated from early stages and correlates with disease progression. Therefore, the restoration of its levels, through exogenous or endogenous pathways, has renoprotective effects. An important strategy for administering Klotho is through mesenchymal stem cells (MSCs). In summary, this review comprises in vitro and in vivo studies on the therapeutic potential of Klotho for the treatment of CKD and AKI through the administration of MSCs.

Fibroblast Growth Factor-23-Klotho Axis in Cardiorenal Syndrome: Mediators and Potential Therapeutic Targets

Cardiorenal syndrome (CRS) is a complex disorder that refers to the category of acute or chronic kidney diseases that induce cardiovascular disease, and inversely, acute or chronic heart diseases that provoke kidney dysfunction. There is a close relationship between renal and cardiovascular disease, possibly due to the presence of common risk factors for both diseases. Thus, it is well known that renal diseases are associated with increased risk of developing cardiovascular disease, suffering cardiac events and even mortality, which is aggravated in those patients with end-stage renal disease or who are undergoing dialysis. Recent works have proposed mineral bone disorders (MBD) as the possible link between kidney dysfunction and the development of cardiovascular outcomes. Traditionally, increased serum phosphate levels have been proposed as one of the main factors responsible for cardiovascular damage in kidney patients. However, recent studies have focused on other MBD components such as the elevation of fibroblast growth factor (FGF)-23, a phosphaturic bone-derived hormone, and the decreased expression of the anti-aging factor Klotho in renal patients. It has been shown that increased FGF-23 levels induce cardiac hypertrophy and dysfunction and are associated with increased cardiovascular mortality in renal patients. Decreased Klotho expression occurs as renal function declines. Despite its expression being absent in myocardial tissue, several studies have demonstrated that this antiaging factor plays a cardioprotective role, especially under elevated FGF-23 levels. The present review aims to collect the recent knowledge about the FGF-23-Klotho axis in the connection between kidney and heart, focusing on their specific role as new therapeutic targets in CRS.

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.

Cardiovascular remodeling as a result of fibroblast growth factor-23 (FGF-23)/Klotho imbalance in patients with CKD

BACKGROUND

In chronic kidney disease (CKD) cardiovascular remodeling (CVR) is very frequent compared with general population and, as suppose, may be associated with «new» renal risk factors. The aim of study was to estimate association of new serum biomarkers (FGF-23, Klotho) and traditional biomarker of cardiac damage-serum Troponin I (sTr-I) with signs of CVR.

METHODS

One hundred thirty CKD G1-5D patients without cardiovascular disease (CVD) clinical manifestation were included. We measured serum FGF-23, Klotho and sTr-I. The instrumental methods were: echocardiography, SphygmoCor test [Pulse Wave Velocity (PWV), Central (aortic) Blood Pressure (CBP), Subendocardial Blood Supply (SBS)].

RESULTS

FGF-23 level correlated with: sTr-I (r = 0.512; p < 0.01), eccentric left ventricular hypertrophy, LVH (r = 0.543; p < 0.01), SBS (r = - 0.499; p < 0.05). There were no differences of FGF-23 level in patients with normal and high CBP. Klotho correlated with concentric LVH (r = - 0.451; p < 0.01), PWV (r = - 0.667; p < 0.001), Cardiac Calcification Score, CCS (r = - 0.581; p < 0.01). Multivariate analysis revealed positive independent association of FGF-23 with eccentric LVH (OR = 1.036, 95% CI (1.004-1.068); p = 0.038). Klotho was a negative determinant for concentric LVH (OR = 0.990, 95% CI 0.987-0.994; p < 0.001), increased PWV (OR = 0.984, 95% CI (0.977-0.991); p < 0.001) and CCS (OR = 0.991, 95% CI (0.988-0.995); p < 0.001). In addition, multivariate analysis revealed a relationship between serum Klotho (OR = 0.980, 95% CI (0.964-0.996); p = 0.016), FGF-23 (OR = 3.145, 95% CI (1.020-9.695); p = 0.046) and troponin I level.

CONCLUSION

In CKD patients without CVD clinical manifestation increased serum FGF-23 level and decreased Klotho are associated with CVR: FGF-23 with eccentric LVH (independently of CBP), Klotho determinate concentric LVH, PWV and CCS. Moderately elevated sTr-I levels may be a manifestation of FGF-23/Klotho imbalance in CKD.

Klotho as a biomarker of subclinical atherosclerosis in patients with moderate to severe chronic kidney disease

Chronic kidney disease (CKD) has been associated with a higher risk of cardiovascular disease (CVD). CKD patients present a decrease in the levels of the protein Klotho that accompanies the decrease in kidney function. This protein has been related to protective effects against CVD. However, it is unclear whether circulating Klotho, and its expression in peripheral blood cells (PBCs) are also associated with subclinical atherosclerosis in CKD. The present study aimed to study the relationship between Klotho and subclinical atherosclerosis in a population of patients with moderate to severe CKD. We determined the serum levels and gene expression in PBCs levels of Klotho and three inflammatory cytokines in 103 patients with CKD and investigated their relationship with two surrogate markers of subclinical atherosclerotis: ankle-brachial index (ABI) and carotid intima-media thickness (CIMT). Patients with subclinical atherosclerosis presented lower serum and PBCs expression levels of Klotho. Both variables were associated with the presence of subclinical atherosclerosis, being directly related with ABI and inversely with CIMT (P < 0.0001 for both). Multiple regression analysis demonstrated that both variables were significant determinants for ABI (adjusted R2 = 0.511, P < 0.0001) and CIMT (adjusted R2 = 0.445, P < 0.0001), independently of traditional and emergent cardiovascular risk factors. Moreover, both constituted protective factors against subclinical atherosclerosis [OR: 0.993 (P = 0.002) and 0.231 (P = 0.025), respectively]. Receiver operating characteristic analysis pointed to the utility of serum Klotho (area under the curve [AUC]: 0.817, 95% CI: 0.736-0.898, P < 0.001) and its gene expression in PBCs (AUC: 0.742, 95% CI: 0.647-0.836, P < 0.001) to distinguish subclinical atherosclerosis. The reductions in serum and PBCs expression levels of Klotho in CKD patients are independently associated with the presence of for subclinical atherosclerosis. Further research exploring whether therapeutic approaches to maintain or elevate Klotho could reduce the impact of CVD in CKD patients is warranted.

The Effects of Cholecalciferol Supplementation on FGF23 and α-Klotho in Hemodialysis Patients With Hypovitaminosis D: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

Vitamin D-fibroblast growth factor-23 (FGF-23)-klotho forms an axis that takes part at least in cardiovascular complications in patients with chronic kidney disease. This study aimed to assess the effects of cholecalciferol supplementation on FGF23 and α-klotho in patients with hypovitaminosis D requiring hemodialysis.

METHODS

In a single-center, parallel-arm, randomized, double-blind, placebo-controlled trial, 86 patients with hypovitaminosis D requiring hemodialysis were enrolled. The patients were randomized into 2 groups (n = 43 each) to receive either 50,000 IU of cholecalciferol or placebo every week for 12 weeks. Accordingly, the serum levels of FGF23 and klotho were measured by ELISA and compared between both groups.

RESULTS

Serum 25OH(D) levels increased in participants who received cholecalciferol supplementation compared with participants who received placebo (P = .006). In addition, serum FGF23 decreased and α-klotho levels increased in the supplemented group compared with placebo. However, the before-after differences between cholecalciferol supplement and placebo were significant only for α-klotho (P = .035). These effects were not accompanied by changes in the levels of phosphate, total and ionized calcium, and intact parathyroid hormone.

CONCLUSION

Cholecalciferol supplementation of 50,000 IU for 12 weeks increases α-klotho levels in the serum of kidney failure patients undergoing hemodialysis. This may suggest that patients receiving maintenance hemodialysis can benefit from using cholecalciferol supplementation and increase in serum α-klotho levels.

Effect of vitamin D receptor activators on serum Klotho levels in 3b–4 stages chronic кidney disease patients: a prospective randomized study

Background. High risk of cardiovascular events is among leading problems in chronic kidney disease (CKD). Serum Klotho is supposed to be cardio- and nephroprotective; modification of its levels may be important in CKD. Aim. To evaluate the impact of vitamin D receptor activators (VDRA) on Klotho serum levels in CKD 3b4 stages patients. Materials and methods. Study included 90 CKD 3b4 stages patients who had elevated serum levels of parathyroid hormone (PTH). From them, 47 patients (group 1) started to treat with the selective VDRA (zemplar 1 mcg/day), and 43 patients (group 2) started to treat with non-selective VDRA (alfacalcidol 0.25 mcg/day). At baseline and after 12 months we conducted routine examination, serum Klotho measurement, and broad cardiovascular examination. Results. The patients who managed to maintain a target serum PTH level, had higher Klotho serum level (p=0.037) at the end of the study. Patients who used selective VDRA significantly more often reached the target PTH level (p=0.032), had higher serum Klotho levels (p=0.037), and glomerular filtration rate (eGFR) level (p=0.048) than patients who used non-selective VDRA. In addition, patients treated with alfacalcidol more than 6 months, more often had hypercalcemia (p=0.047) and hyperphosphatemia (p=0.035). Group 2 showed higher: pulse wave velocity (p=0.051), left ventricular myocardial mass index (p=0.033), and more advanced heart valve calcification (p=0.038). Conclusion. Successful parathyroid hormone level control with vitamin D receptor activators was associated with higher serum Klotho, selective agents having shown greater effect. Long-term treatment with selective vitamin D receptor activators may contribute to cardiovascular calcification prevention by modifying Klotho levels.

New Insights into the Role of FGF-23 and Klotho in Cardiovascular Disease in Chronic Kidney Disease Patients

Alterations of fibroblast growth factor 23 (FGF-23) and Klotho levels are considered to be the earliest biochemical abnormality of chronic kidney disease - mineral and bone disease (CKDMBD) syndrome. Moreover, emerging data suggests that the dysregulated FGF-23 and Klotho axis has many effects on the cardiovascular (CV) system and contributes significantly to the increased CV morbidity and mortality rates of CKD patients. This review examines recent evidence on the role of FGF-23 and Klotho in the development and progression of CV complications of uremia namely cardiac hypertrophy, uremic cardiomyopathy, and atherosclerotic and arteriosclerotic vascular lesions. Moreover, the available evidence on their associations with adverse clinical outcomes are summarized. Undoubtedly, more studies are needed to further elucidate the effects of FGF-23 and Klotho on the heart and vessels and to gain insights into their prognostic value as CV risk factors. Finally, large prospective studies are required to test the hypothesis that modification of their levels would have a favourable impact on the unacceptably high mortality rates of these patient populations.

A Decreased Level of Soluble Klotho Can Predict Cardiovascular Death in No or Mild Abdominal Aortic Calcification Hemodialysis Patients

Background: Soluble Klotho plays an important role in cardiovascular disease and death in chronic kidney disease (CKD). We assessed the relationship between serum soluble Klotho (sKL) level and outcome in MHD patients.

Methods: Soluble Klotho was detected by ELISA. Cox regression analysis and Kaplan-Meier analysis showed the relationship between sKL and cardiovascular disease (CVD) mortality in maintenance hemodialysis (MHD) patients.

Results: There were 45 cases (35.2%) of all-cause death and 36 cases (28.1%) of CVD mortality. Multivariate linear regression analysis showed that Log[iPTH] (γ = −0.224, P = 0.015) was an independent predictor of sKL level. Cox regression showed that lower sKL was associated with higher CVD mortality rate [OR = 0.401, 95% CI (0.183–0.867), P = 0.022]. Kaplan-Meier analysis showed that the CVD mortality rate increased significantly in patients with low sKL (P = 0.006). Compared with high sKL patients, low sKL patients with no or mild vascular calcification [aortic calcification score (AACs) ≤ 4] had no significant difference in all-cause mortality rate. The CVD mortality rate was significantly lower in high sKL patients (P = 0.004) than in those with low sKL. In the severe calcification group (AACs ≥ 5), all-cause and CVD mortality rates were similar between different sKL groups (P = 0.706 and 0.488, respectively). The area under the receiver-operating characteristic curve (AUC) of soluble Klotho for predicting the CVD in MHD patients with AACs ≤ 4 was 0.796 (0.647–0.946, P = 0.017), sensitivity was 0.921, and specificity was 0.50 for a cutoff value of 307.69 pg/ml.

Conclusions: Lower sKL was associated with higher CVD mortality rate. Lower sKL concentration in MHD patients with no or mild calcification can predict CVD mortality.

The Multifunctional Contribution of FGF Signaling to Cardiac Development, Homeostasis, Disease and Repair

The current focus on cardiovascular research reflects society’s concerns regarding the alarming incidence of cardiac-related diseases and mortality in the industrialized world and, notably, an urgent need to combat them by more efficient therapies. To pursue these therapeutic approaches, a comprehensive understanding of the mechanism of action for multifunctional fibroblast growth factor (FGF) signaling in the biology of the heart is a matter of high importance. The roles of FGFs in heart development range from outflow tract formation to the proliferation of cardiomyocytes and the formation of heart chambers. In the context of cardiac regeneration, FGFs 1, 2, 9, 16, 19, and 21 mediate adaptive responses including restoration of cardiac contracting rate after myocardial infarction and reduction of myocardial infarct size. However, cardiac complications in human diseases are correlated with pathogenic effects of FGF ligands and/or FGF signaling impairment. FGFs 2 and 23 are involved in maladaptive responses such as cardiac hypertrophic, fibrotic responses and heart failure. Among FGFs with known causative (FGFs 2, 21, and 23) or protective (FGFs 2, 15/19, 16, and 21) roles in cardiac diseases, FGFs 15/19, 21, and 23 display diagnostic potential. The effective role of FGFs on the induction of progenitor stem cells to cardiac cells during development has been employed to boost the limited capacity of postnatal cardiac repair. To renew or replenish damaged cardiomyocytes, FGFs 1, 2, 10, and 16 were tested in (induced-) pluripotent stem cell-based approaches and for stimulation of cell cycle re-entry in adult cardiomyocytes. This review will shed light on the wide range of beneficiary and detrimental actions mediated by FGF ligands and their receptors in the heart, which may open new therapeutic avenues for ameliorating cardiac complications.

Klotho: A possible mechanism of action of SGLT2 inhibitors preventing episodes of acute kidney injury and cardiorenal complications of diabetes

Diabetes and cardiorenal comorbidities are major global health concerns, with high economic burdens and mortality rates. Sodium glucose co-transporter-2 inhibitors (SGLT2is) are novel US Food and Drug Administration (FDA)-approved antihyperglycemics with unexpected protective potential against cardiorenal diseases in patients with or without type 2 diabetes mellitus (T2DM). Despite initial concerns, the incidence of episodes of acute kidney injury (AKI) was significantly lower in patients taking SGLT2i compared with other therapies or placebo. Evolving data suggest a link between SGLT2is and the anti-aging protein Klotho in the amelioration of diabetes and cardiorenal diseases. Here, we consider Klotho and SGLT2is as a novel therapeutic approach for the management of AKI and other cardiorenal complications in patients with or without diabetes.

Citrate high volume on-line hemodiafiltration modulates serum Interleukin-6 and Klotho levels: the multicenter randomized controlled study "Hephaestus"

BACKGROUND

Studies addressing the anti-inflammatory properties of citrate dialysate enrolled patients in both hemodialysis (HD) and hemodiafiltration (HDF), the latter not adjusted for adequate convective exchange. This is a potential source of confounding in that HDF itself has anti-inflammatory effects regardless of the buffer, and optimal clinical outcomes are related to the amount of convection.

METHODS

To distinguish the merits of the buffer from those of convection, we performed a 6-month, prospective, randomized, crossover AB-BA study. Comparisons were made during the 3-month study period of on-line HDF with standard dialysate containing three mmol of acetic acid (OL-HDFst) and the 3-month of OL-HDF with dialysate containing one mmol of citric acid (OL-HDFcit). Primary outcome measure of the study was interleukin-6 (IL-6). Klotho, high sensitivity C-reactive protein (hsCRP), fetuin and routine biochemical parameters were also analyzed.

RESULTS

We analyzed 47 patients (mean age 64 years, range 27-84 years) enrolled in 10 participating Nephrology Units. Convective volumes were around 25 L/session with 90 percent of sessions > 20 L and ß2-microglobulin reduction rate 76% in both HDFs. Baseline median IL-6 values in OL-HDFst were 5.6 pg/ml (25:75 interquartile range IQR 2.9:10.6) and in OL-HDFcit 6.6 pg/ml (IQR 3.4:11.4 pg/ml). The difference was not statistically significant (p 0.88). IL-6 values were lower during OL-HDFcit than during OL-HDFst, both when analyzed as the median difference of overall IL-6 values (p 0.02) and as the median of pairwise differences between the baseline and the 3-month time points (p 0.03). The overall hsCRP values too, were lower during OL-HDFcit than during OL-HDFst (p 0.01). Klotho levels showed a time effect (p 0.02) and the increase was significant only during OL-HDFcit (p 0.01).

CONCLUSIONS

Citrate buffer modulated IL-6, hsCRP and Klotho levels during high volume OL-HDF. These results are not attributable to differences in the dialysis technology that was applied and may suggest a potential biological effect of citrate on CKD-associated inflammatory state. ClinicalTrials.gov identifier NCT02863016.

Role of Fibroblast Growth Factor 23 (FGF23) and αKlotho in Cancer

Together with fibroblast growth factors (FGFs) 19 and 21, FGF23 is an endocrine member of the family of FGFs. Mainly secreted by bone cells, FGF23 acts as a hormone on the kidney, stimulating phosphate excretion and suppressing formation of 1,25(OH)₂D₃, active vitamin D. These effects are dependent on transmembrane protein αKlotho, which enhances the binding affinity of FGF23 for FGF receptors (FGFR). Locally produced FGF23 in other tissues including liver or heart exerts further paracrine effects without involvement of αKlotho. Soluble Klotho (sKL) is an endocrine factor that is cleaved off of transmembrane Klotho or generated by alternative splicing and regulates membrane channels, transporters, and intracellular signaling including insulin growth factor 1 (IGF-1) and Wnt pathways, signaling cascades highly relevant for tumor progression. In mice, lack of FGF23 or αKlotho results in derangement of phosphate metabolism and a syndrome of rapid aging with abnormalities affecting most organs and a very short life span. Conversely, overexpression of anti-aging factor αKlotho results in a profound elongation of life span. Accumulating evidence suggests a major role of αKlotho as a tumor suppressor, at least in part by inhibiting IGF-1 and Wnt/β-catenin signaling. Hence, in many malignancies, higher αKlotho expression or activity is associated with a more favorable outcome. Moreover, also FGF23 and phosphate have been revealed to be factors relevant in cancer. FGF23 is particularly significant for those forms of cancer primarily affecting bone (e.g., multiple myeloma) or characterized by bone metastasis. This review summarizes the current knowledge of the significance of FGF23 and αKlotho for tumor cell signaling, biology, and clinically relevant parameters in different forms of cancer.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

αKlotho (called Klotho here) is a membrane protein that serves as the coreceptor for the circulating hormone fibroblast growth factor 23 (FGF23). Klotho is also cleaved and released as a circulating substance originating primarily from the kidney and exerts a myriad of housekeeping functions in just about every organ. The vital role of Klotho is shown by the multiorgan failure with genetic deletion in rodents, with certain features reminiscent of human disease. The most common causes of systemic Klotho deficiency are AKI and CKD. Preclinical data on Klotho biology have advanced considerably and demonstrated its potential diagnostic and therapeutic value; however, multiple knowledge gaps exist in the regulation of Klotho expression, release, and metabolism; its target organs; and mechanisms of action. In the translational and clinical fronts, progress has been more modest. Nonetheless, Klotho has potential clinical applications in the diagnosis of AKI and CKD, in prognosis of progression and extrarenal complications, and finally, as replacement therapy for systemic Klotho deficiency. The overall effect of Klotho in clinical nephrology requires further technical advances and additional large prospective human studies.

Higher Serum-Soluble α-Klotho Level Does Not Predict Longer Survival after Stroke

Results

There were 5 recurrent strokes and 89 deaths during the 36-month follow-up. Even though no significant differences in OS and SFS between soluble α-Klotho level tertile groups were recorded, unexpectedly, OS and SFS were highest in patients with the lowest soluble α-Klotho concentrations. Moreover, the Cox proportional models adjusted for established risk factors, kidney function, and the severity of stroke revealed that each 100 pg/mL increase in soluble α-Klotho levels was associated with decreased OS (HR = 0.951 (0.908-0.995), p < 0.05) and SFS (HR = 0.949 (0.908-0.993), p < 0.05). In addition, the α-Klotho to iFGF23 index was predicting neither OS nor SFS.

Conclusion

Soluble α-Klotho levels in serum were not related to the severity of neurological deficits and long-term outcomes in patients with IS. No neuroprotective effect of soluble α-Klotho levels in patients with IS was demonstrated.

New Potential Biomarkers for Chronic Kidney Disease Management-A Review of the Literature

The prevalence of chronic kidney disease (CKD) is increasing worldwide, and the mortality rate continues to be unacceptably high. The biomarkers currently used in clinical practice are considered relevant when there is already significant renal impairment compromising the early use of potentially successful therapeutic interventions. More sensitive and specific biomarkers to detect CKD earlier on and improve patients' prognoses are an important unmet medical need. The aim of this review is to summarize the recent literature on new promising early CKD biomarkers of renal function, tubular lesions, endothelial dysfunction and inflammation, and on the auspicious findings from metabolomic studies in this field. Most of the studied biomarkers require further validation in large studies and in a broad range of populations in order to be implemented into routine CKD management. A panel of biomarkers, including earlier biomarkers of renal damage, seems to be a reasonable approach to be applied in clinical practice to allow earlier diagnosis and better disease characterization based on the underlying etiologic process.

Serum soluble Klotho is inversely related to coronary artery calcification assessed by intravascular ultrasound in patients with stable coronary artery disease

BACKGROUND

Although the Klotho gene is recognized as an aging-suppressor gene, the clinical significance of its soluble product, soluble Klotho, in coronary artery disease (CAD) has not been completely determined. The relationship between soluble Klotho and coronary artery calcification (CAC) was investigated in patients with stable CAD.

METHODS

CAC in culprit lesions was analyzed in 75 non-dialysis patients with stable CAD who were scheduled for percutaneous coronary intervention (PCI) following intravascular ultrasound (IVUS). The main outcome measure was the calcium index (CalcIndex), a volumetric IVUS-derived measure of total calcification per culprit lesion. A low CalcIndex was defined as a first-quartile calcium index (<0.042). Patients were divided into two groups according to the median serum Klotho value: low Klotho (n = 37, ≤460 pg/mL) and high Klotho (n = 38, >460 pg/mL).

RESULTS

The CalcIndex was significantly lower in patients with high than with low Klotho. Patients with high Klotho had a significantly higher prevalence of a low CalcIndex than those with low Klotho. The number of angiographic moderate-severe CACs in whole coronary arteries was significantly decreased in patients with high Klotho compared to low Klotho. Serum Klotho levels correlated significantly and inversely with the CalcIndex. This relationship was pronounced in patients with estimated glomerular filtration rate <60 mL/min/1.73 m². Logistic regression analysis showed that high Klotho was associated with a low CalcIndex independent of classical coronary risk factors and markers of mineral metabolism.

CONCLUSIONS

High serum soluble Klotho levels are associated with a low degree of CAC in non-dialysis, stable CAD patients treated by PCI.

Klotho: a link between cardiovascular and non-cardiovascular mortality

Klotho is a membrane-bound protein acting as an obligatory coreceptor for fibroblast growth factor 23 (FGF23) in the kidney and parathyroid glands. The extracellular portion of its molecule may be cleaved and released into the blood and produces multiple endocrine effects. Klotho exerts anti-inflammatory and antioxidative activities that may explain its ageing suppression effects evidenced in mice; it also modulates mineral metabolism and FGF23 activities and limits their negative impact on cardiovascular system. Clinical studies have found that circulating Klotho is associated with myocardial hypertrophy, coronary artery disease and stroke and may also be involved in the pathogenesis of salt-sensitive hypertension with a mechanism sustained by inflammatory cytokines. As a consequence, patients maintaining high serum levels of Klotho not only show decreased cardiovascular mortality but also non-cardiovascular mortality. Klotho genetic polymorphisms may influence these clinical relationships and predict cardiovascular risk; rs9536314 was the polymorphism most frequently involved in these associations. These findings suggest that Klotho and its genetic polymorphisms may represent a bridge between inflammation, salt sensitivity, hypertension and mortality. This may be particularly relevant in patients with chronic kidney disease who have decreased Klotho levels in tissues and blood.

Enhanced Klotho availability protects against cardiac dysfunction induced by uraemic cardiomyopathy by regulating Ca2+ handling

BACKGROUND AND PURPOSE

Klotho is a membrane-bound or soluble protein, originally identified as an age-suppressing factor and regulator of mineral metabolism. Klotho deficiency is associated with the development of renal disease, but its role in cardiac function in the context of uraemic cardiomyopathy is unknown.

EXPERIMENTAL APPROACH

We explored the effects of Klotho on cardiac Ca2+ cycling. We analysed Ca2+ handling in adult cardiomyocytes from Klotho-deficient (kl/kl) mice and from a murine model of 5/6 nephrectomy (Nfx). We also studied the effect of exogenous Klotho supplementation, by chronic recombinant Klotho treatment, or endogenous Klotho overexpression, using transgenic mice overexpressing Klotho (Tg-Kl), on uraemic cardiomyopathy. Hearts from Nfx mice were used to study Ca2+ sensitivity of ryanodine receptors and their phosphorylation state.

KEY RESULTS

Cardiomyocytes from kl/kl mice showed decreased amplitude of intracellular Ca2+ transients and cellular shortening together with an increase in pro-arrhythmic Ca2+ events compared with cells from wild-type mice. Cardiomyocytes from Nfx mice exhibited the same impairment in Ca2+ cycling as kl/kl mice. Changes in Nfx cardiomyocytes were explained by higher sensitivity of ryanodine receptors to Ca2+ and their increased phosphorylation at the calmodulin kinase type II and protein kinase A sites. Ca2+ mishandling in Nfx-treated mice was fully prevented by chronic recombinant Klotho administration or transgenic Klotho overexpression.

CONCLUSIONS AND IMPLICATIONS

Klotho emerges as an attractive therapeutic tool to improve cardiac Ca2+ mishandling observed in uraemic cardiomyopathy. Strategies that improve Klotho availability are good candidates to protect the heart from functional cardiac alterations in renal disease.