Tissue expression and source of circulating αKlotho

Dynamic single cell transcriptomics defines kidney FGF23/KL bioactivity and novel segment-specific inflammatory targets

Fibroblast growth factor 23 (FGF23) via its coreceptor αKlotho (KL) provides critical control of phosphate metabolism, which is altered in both rare and very common syndromes. However, the spatial-temporal mechanisms dictating kidney FGF23 functions remain poorly understood. Thus, developing approaches to modify specific FGF23-dictated pathways has proven problematic. Herein, wild type mice were injected with rFGF23 for one, four and 12h and kidney FGF23 bioactivity was determined at single cell resolution. Computational analysis identified distinct epithelial, endothelial, stromal, and immune cell clusters, with differential expressional analysis uniquely tracking FGF23 bioactivity at each time point. FGF23 actions were sex independent but critically relied upon constitutive KL expression mapped within proximal tubule (segments S1-S3) and distal convoluted tub/connecting tubule cell sub-populations. Temporal KL-dependent FGF23 responses drove unique and transient cellular identities, including genes in key MAPK-signaling and vitamin D-metabolic pathways via early- (transcription factor AP-1-related) and late-phase (initiation factor EIF2 signaling) transcriptional regulons. Combining ATACseq/RNAseq data from a cell line stably expressing KL with the in vivo scRNAseq pinpointed genomic accessibility changes in MAPK-dependent genes, including the identification of FGF23-dependent early growth factor-1 distal enhancers. Finally, we identified unexpected crosstalk between FGF23-mediated MAPK signaling and pro inflammatory TNF receptor activation via transcription factor NF-κB, which blocked FGF23 bioactivity in vitro and in vivo. Collectively, our findings have uncovered novel pathways at the single cell level that likely influence FGF23-dependent disease mechanisms.

Aging Impairs the Capacity of Cardiac Functional Recovery Following Endotoxemia: Modulation of Myocardial Klotho Level for Remedy

INTRODUCTION

Endotoxemic/septic cardiac dysfunction occurs frequently in elderly patients undergoing major surgery and contributes to postsurgery morbidity and mortality. This study evaluated the effect of aging on cardiac functional recovery following endotoxemia and explored therapeutic approaches for promotion of the recovery.

METHODS

A small dose of endotoxin (0.5 mg/kg, iv) was administered to young adult (3-4 mo) and old (18-22 mo) mice with or without subsequent treatment with recombinant interleukin-37 (IL-37, 50 μg/kg, iv) or recombinant Klotho (10 μg/kg, iv). Cardiac function was analyzed using a microcatheter at 24, 48, and 96 h following administration of endotoxin. Myocardial levels of Klotho, intercellular adhesion molecule-1, and IL-6 were determined by immunoblotting and Enzyme-linked immunosorbent assay.

RESULTS

Compared to young adult endotoxemic mice, old endotoxemic mice had worse cardiac dysfunction accompanied by greater myocardial levels of intercellular adhesion molecule-1 and IL-6 at each time point and failed to fully recover cardiac function by 96 h. The exacerbated and prolonged myocardial inflammation and cardiac dysfunction in old endotoxemic mice were associated with lower myocardial Klotho level and its further reduction by endotoxemia. Interestingly, recombinant IL-37 up-regulated myocardial Klotho level in old mice with or without endotoxemia and treatment of old endotoxemic mice with IL-37 improved myocardial inflammation resolution and cardiac functional recovery. Similarly, recombinant Klotho suppressed myocardial inflammatory response and promoted inflammation resolution in old endotoxemic mice, leading to complete recovery of cardiac function by 96 h.

CONCLUSIONS

Myocardial Klotho insufficiency in old mice exacerbates myocardial inflammatory response, impairs inflammation resolution and hinders cardiac functional recovery. IL-37 is capable of up-regulating myocardial Klotho level to promote myocardial inflammation resolution and cardiac functional recovery in old endotoxemic mice.

Klotho antiaging protein: molecular mechanisms and therapeutic potential in diseases

Klotho, initially introduced as an anti-aging protein, is expressed in the brain, pancreas, and most prominently in the kidney. The two forms of Klotho (membrane-bound and soluble form) have diverse pharmacological functions such as anti-inflammatory, anti-oxidative, anti-fibrotic, tumour-suppressive etc. The membrane-bound form plays a pivotal role in maintaining kidney homeostasis by regulating fibroblast growth factor 23 (FGF 23) signalling, vitamin D metabolism and phosphate balance. Klotho deficiency has been linked with significantly reduced protection against various kidney pathological phenotypes, including diabetic kidney disease (DKD), which is a major cause of chronic kidney disease leading to end-stage kidney disease. Owing to the pleiotropic actions of klotho, it has shown beneficial effects in DKD by tackling the complex pathophysiology and reducing kidney inflammation, oxidative stress, as well as fibrosis. Moreover, the protective effect of klotho extends beyond DKD in other pathological conditions, including cardiovascular diseases, alzheimer's disease, cancer, inflammatory bowel disease, and liver disease. Therefore, this review summarizes the relationship between Klotho expression and various diseases with a special emphasis on DKD, the distinct mechanisms and the potential of exogenous Klotho supplementation as a therapeutic strategy. Future research into exogenous Klotho could unravel novel treatment avenues for DKD and other diseases.

Association Between Serum α-Klotho Levels and Diabetic Kidney Disease Prevalence in Middle-Aged and Elderly US Patients with Diabetes: A Cross-Sectional Study Using NHANES 2007-2016 Data

INTRODUCTION

Diabetic kidney disease (DKD) represents a significant microvascular complication associated with diabetes and serves as a major contributor to end-stage renal disease. While many studies have highlighted the renal protective effects of the anti-aging protein Klotho, the potential link between Klotho and DKD within individuals with diabetes remains a subject of debate, and comprehensive studies utilizing large population-based databases are still needed.

METHODS

This cross-sectional study, which is representative of the national population, examined data from US patients with diabetes aged 40-79 years, collected during the 2007-2016 cycles of the National Health and Nutrition Examination Survey (NHANES). Serum α-Klotho levels were determined using enzyme-linked immunosorbent assay (ELISA) techniques. Given that serum Klorho levels are not normally distributed, our analysis is based on values converted from the natural logarithm of Klotho. To assess the association between Klotho levels and the prevalence of DKD, multivariate regression models were utilized, taking into account potential confounding factors. Furthermore, we applied smooth curve fitting and segmented regression analyses to investigate possible threshold effects and identify inflection points. Subgroup analyses and cross-tests were performed to assess the consistency of associations in the general population.

RESULTS

The investigation included 4490 individuals with diabetes, with an median age of 60.0 years and 48.2% of them being male. Among these participants, 1352 (30.1%) were diagnosed with DKD. The fully adjusted model (model 3) indicated a significant inverse relationship between Klotho levels and DKD prevalence. Statistical analysis showed that in fully adjusted model 3, each 1-unit increase in log-transformed Klotho was associated with a 42% reduction in DKD prevalence [OR 0.58, 95% CI (0.42, 0.80), p = 0.002]. Further analysis using smooth curve fitting revealed a U-shaped relationship between Klotho levels and DKD prevalence, with an inflection point at 6.82 (after natural logarithm conversion).

CONCLUSIONS

This study identified a U-shaped relationship between Klotho levels and the prevalence of DKD in middle-aged and older adults with diabetes in the USA, with an inflection point of 6.82 (after natural logarithm conversion). Prior to this threshold, the relationship between Klotho and DKD prevalence was negatively correlated, while after the inflection point, the relationship became positive. Future studies are recommended to investigate the causal relationship behind this relationship.

The bone-heart axis in the pathogenesis of cardiovascular diseases: A narrative review

Cardiovascular diseases (CVDs) cause about 30% of deaths worldwide, increasing social and economic burden in our societies. Although the treatment of the canonical cardiovascular risk factors has reduced the impact of CVDs on morbidity and mortality in the past few years, they continue to represent a major health problem. The definition of the biological properties of the bone-heart axis has led to new insights in the pathogenesis of CVDs; hence, the aim of this review is to try to elucidate the role of this axis on the susceptibility to CVDs. There is evidence that the bone interacts with extra-skeletal organs, including the cardiovascular system, through its endocrine functions. Clinical and experimental data strongly indicate that the interplay between the bone and the cardiovascular system represents a future tool for the prevention, diagnosis and treatment of CVDs. The identification of these non-canonical cardiovascular risk factors could prompt pharmacological research towards new target therapy aimed at precision medicine.

Identification of the enzymatic cleavage relationship between anti-aging protein α-Klotho and Alzheimer's disease biomarker BACE1

BackgroundThe α-Klotho is known to be involved in longevity and various age-related diseases, including cognitive impairment. BACE1, an important enzyme associated with the pathological process of Alzheimer's disease (AD), serves as a biomarker for predicting changes in cognitive function. Although both proteins are closely linked to age-related cognitive function, the mechanism of their interaction remains unclear.ObjectiveTo identify the enzymatic digestion relation between α-Klotho and BACE1 and the specific cleavage site.MethodsThirty elderly and forty-five young individuals were recruited. The cleavage product was identified by Coomassie blue staining, western blot, and MALDI-TOF mass spectrometry. The concentrations of plasma proteins were measured by ELISA.ResultsA new protein product was identified after the digestion reaction. BACE1 cleaved the α-Klotho peptide 951-981 at the F-T residues. When the F-T residues were replaced with K-K, BACE1 was unable to cleave the mutant peptide. The plasma levels of α-Klotho were significantly lower in elderly participants than in young participants (p < 0.0001). However, there was no significant difference in plasma BACE1 levels between elderly and young participants (p = 0.164). In elderly adults, there was a significant positive correlation between plasma BACE1 and α-Klotho protein levels (p = 0.009, r = 0.469), while this correlation was not observed in young adults (p = 0.170, r = -0.208).ConclusionsThe anti-aging protein α-Klotho is a substrate of BACE1 with a specific cleavage site at F-T. The BACE1/α-Klotho pathway may serve as a common axis for age-related cognitive decline.

Interaction Effect of Estimated Pulse Wave Velocity and Serum Klotho Level on Chronic Kidney Disease

Objectives

Older individuals usually have greater arterial stiffness, lower serum Klotho levels and a greater incidence of chronic kidney disease (CKD). The current study aimed to evaluate the interaction effect of estimated pulse wave velocity (ePWV) and serum Klotho levels on CKD in Americans.

Methods

Data from the National Health and Nutrition Examination Survey database from 2007 to 2016 were used. Participants with data for the assessment of ePWV and serum Klotho and for the assessment of CKD were enrolled. The associations between ePWV and serum Klotho levels were analyzed via restricted cubic spline analysis and a linear regression model. The associations between exposure factors and CKD prevalence were assessed via a logistic regression model. Subgroup analysis was performed for each confounding factor to assess the robustness of the results.

Results

This study enrolled 13,273 participants, 3859 of whom were CKD patients. CKD patients had higher ePWV (9.66 ± 1.75 m/s vs. 8.48 ± 1.64 m/s, p < 0.001) and lower levels of serum Klotho (816.35 ± 290.47 pg/mL vs. 869.87 ± 315.87 pg/mL, p < 0.001). A significant negative linear association was found between ePWV and serum Klotho. According to the fully adjusted model, a significant interaction effect between ePWV and serum Klotho was observed on the risk of CKD (p < 0.001). Compared with individuals with a lower ePWV and higher serum Klotho, individuals with an increased ePWV and lower serum Klotho had a significantly elevated risk of CKD (OR: 1.847, 95% confidence interval: 1.467-2.325; p < 0.001). The subgroup analysis revealed that the results were robust.

Conclusions

The study demonstrated significant interaction effect of ePWV and serum Klotho on the prevalence of CKD. Individuals with increased ePWV and decreased serum Klotho levels had the highest risk of CKD. The assessment of the combination of ePWV and serum Klotho for CKD management should be considered routine in clinical practice.

Systemic immunoinflammatory indexes in albuminuric adults are negatively associated with α-klotho: evidence from NHANES 2007-2016

BACKGROUND

Systemic Immune-Inflammation Index (SII) is a novel inflammatory biomarker closely associated with the inflammatory response and chronic kidney disease. Klotho is implicated as a pathogenic factor in the progression of kidney disease, and supplementation of Klotho may delay the progression of chronic kidney disease by inhibiting the inflammatory response. Our aim is to investigate the potential relationship between SII and Klotho in adult patients in the United States and explore the differences in the populations with and without albuminuria.

METHODS

We conducted a cross-sectional study recruiting adult participants with complete data on SII, Klotho, and urine albumin-to-creatinine ratio (ACR) from the National Health and Nutrition Examination Survey from 2007 to 2016. SII was calculated as platelet count × neutrophil count/lymphocyte count, with abnormal elevation defined as values exceeding 330 × 10^9/L. Albuminuria was defined as ACR >30 mg/g. Weighted multivariable regression analysis and subgroup analysis were employed to explore the independent relationship between SII and Klotho.

RESULTS

Our study included a total of 10,592 individuals. In all populations, non-albuminuria population, and proteinuria population with ACR ≥ 30, participants with abnormally elevated SII levels, as compared to those with SII less than 330 × 10^9/L, showed a negative correlation between elevated SII levels and increased Klotho, which persisted after adjusting for covariates.

CONCLUSIONS

There is a negative correlation between SII and Klotho in adult patients in the United States. This finding complements previous research but requires further analysis through large prospective studies.

Associations Between Urinary Phthalate Metabolites and Decreased Serum α-Klotho Level: A Cross-Sectional Study Among US Adults in Middle and Old Age

Phthalates are widely used chemicals with ubiquitous human exposure. Evidence indicated that phthalate exposure was associated with an increased risk of aging-related diseases. Klotho is a transmembrane protein with anti-aging functions, and its association with phthalates remains unknown. To find the association between phthalate exposure and serum α-Klotho, a cross-sectional study was performed in 4482 adults (40-79 years old) who completed the National Health and Nutrition Examination Survey (NHANES) (2007-2016). As shown in the results of multivariable linear regression analyses, mono(carboxynonyl) phthalate (MCNP) and mono-n-butyl phthalate (MBP) were inversely associated with α-Klotho, and the regression coefficients of MCNP and MBP were -1.14 (95% confidence interval (CI): -2.00, -0.27) and -0.08 (95% CI: -0.14, -0.02). Subgroup analyses based on the quartiles of each phthalate metabolite showed that both MCNP and MBP were only inversely associated with α-Klotho in the subgroups of the highest levels. For mono-isobutyl phthalate (MIBP), the inverse association with α-Klotho was only statistically significant in the subgroup of the lowest level, and the regression coefficient was -26.87 (95% CI: -52.53, -1.21). Our findings suggest that α-Klotho might be involved in the association of phthalate exposure with aging-related diseases. Future research investigating the causality between phthalates and α-Klotho and its underlying mechanisms is encouraged.

Predictive value of bone metabolism markers in the progression of diabetic kidney disease: a cross-sectional study

Objective

This study aimed to investigate the relationship between bone metabolism markers, including serum klotho, fibroblast growth factor 23 (FGF23), 25(OH)D3, iPTH, calcium (Ca), and PHOS and the progression of diabetic kidney disease (DKD) in patients with type 2 diabetes mellitus (T2DM). Additionally, the predictive value of these markers for DKD progression was evaluated.

Methods

This study involved 126 patients with T2DM between May 2021 and March 2023. DKD staging was assessed based on urinary protein excretion rates and estimated glomerular filtration rate (eGFR). The study evaluated serum concentrations of klotho, FGF23, 25(OH)D3, iPTH, Ca and PHOS across various stages and examined their relationships with clinical parameters. Receiver operating characteristic (ROC) curve analysis was utilized to determine the predictive accuracy of these bone metabolism markers for DKD. Multivariate linear and logistic regression analyses identified risk factors linked to DKD severity.

Results

Among the 126 participants, 30 had non-DKD with normal proteinuria, while 96 had DKD, categorized as 31 with stage III DKD (microproteinuria), 34 with stage IV DKD, and 31 with stage V DKD (massive proteinuria). With advancing DKD from stage III to V, levels of klotho, 25(OH)D3, and Ca decreased significantly, whereas FGF23, iPTH and PHOS levels increased markedly. Klotho is significantly positively correlated with eGFR (r = 0.285, P = 0.001.) and negative correlations with serum creatinine (Scr) and UACR (r = -0.255, P = 0.004; r = -0.260, P = 0.011). FGF23 was positively related to systolic blood pressure (SBP) (r = 0.224, P = 0.012), but negatively with eGFR (r = -0.294, P = 0.001). Additionally, 25(OH)D3 exhibited significant negative correlations with several adverse clinical biomarkers, and both iPTH, Ca and PHOS were strongly associated with DKD progression (P<0.05). ROC analysis showed high predictive accuracy for DKD using these bone metabolism markers, with a combined area under the curve (AUC) of 0.846. Multivariate logistic regression analysis reinforced the significance of these markers in DKD progression.

Conclusion

Bone metabolism markers, such as klotho, FGF23, 25(OH)D3, iPTH, Ca and PHOS are intricately linked to DKD progression and may function as valuable predictive biomarkers.

Distinct role of Klotho in long bone and craniofacial bone: skeletal development, repair and regeneration

Bone defects are highly prevalent diseases caused by trauma, tumors, inflammation, congenital malformations and endocrine abnormalities. Ideally effective and side effect free approach to dealing with bone defects remains a clinical conundrum. Klotho is an important protein, which plays an essential role in regulating aging and mineral ion homeostasis. More recently, research revealed the function of Klotho in regulating skeleton development and regeneration. Klotho has been identified in mesenchymal stem cells, osteoblasts, osteocytes and osteoclasts in different skeleton regions. The specific function and regulatory mechanisms of Klotho in long bone and craniofacial bone vary due to their different embryonic development, ossification and cell types, which remain unclear and without conclusion. Moreover, studies have confirmed that Klotho is a multifunctional protein that can inhibit inflammation, resist cancer and regulate the endocrine system, which may further accentuate the potential of Klotho to be the ideal molecule in inducing bone restoration clinically. Besides, as an endogenous protein, Klotho has a promising potential for clinical therapy without side effects. In the current review, we summarized the specific function of Klotho in long bone and craniofacial skeleton from phenotype to cellular alternation and signaling pathway. Moreover, we illustrated the possible future clinical application for Klotho. Further research on Klotho might help to solve the existing clinical difficulties in bone healing and increase the life quality of patients with bone injury and the elderly.

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.

X-linked hypophosphataemia

X-linked hypophosphataemia is a genetic disease caused by defects in the phosphate regulating endopeptidase homolog X-linked (PHEX) gene and is characterised by X-linked dominant inheritance. The main consequence of PHEX deficiency is increased production of the phosphaturic hormone fibroblast growth factor 23 (FGF23) in osteoblasts and osteocytes. Chronic exposure to circulating FGF23 is responsible for renal phosphate wasting and decreased synthesis of calcitriol, which decreases intestinal phosphate absorption. These mechanisms result in lifelong hypophosphataemia, impaired growth plate and bone matrix mineralisation, and diverse manifestations in affected children and adults, including some debilitating morbidities and possibly increased mortality. Important progress has been made in disease knowledge and management over the past decade; in particular, targeting FGF23 is a therapeutic approach that has substantially improved outcomes. However, patients affected by this complex disease need lifelong care and innovative treatment strategies, such as gene repair of PHEX, are necessary to further limit the disease burden.

Dynamic Single Cell Transcriptomics Defines Kidney FGF23/KL Bioactivity and Novel Segment-Specific Inflammatory Targets

FGF23 via its coreceptor αKlotho (KL) provides critical control of phosphate metabolism, which is altered in rare and very common syndromes, however the spatial-temporal mechanisms dictating renal FGF23 functions remain poorly understood. Thus, developing approaches to modify specific FGF23-dictated pathways has proven problematic. Herein, wild type mice were injected with rFGF23 for 1, 4 and 12h and renal FGF23 bioactivity was determined at single cell resolution. Computational analysis identified distinct epithelial, endothelial, stromal, and immune cell clusters, with differential expressional analysis uniquely tracking FGF23 bioactivity at each time point. FGF23 actions were sex independent but critically relied upon constitutive KL expression mapped within proximal tubule (S1-S3) and distal tubule (DCT/CNT) cell sub-populations. Temporal KL-dependent FGF23 responses drove unique and transient cellular identities, including genes in key MAPK- and vitamin D-metabolic pathways via early- (AP-1-related) and late-phase (EIF2 signaling) transcriptional regulons. Combining ATACseq/RNAseq data from a cell line stably expressing KL with the in vivo scRNAseq pinpointed genomic accessibility changes in MAPK-dependent genes, including the identification of FGF23-dependent EGR1 distal enhancers. Finally, we isolated unexpected crosstalk between FGF23-mediated MAPK signaling and pro-inflammatory TNF receptor activation via NF-κB, which blocked FGF23 bioactivity in vitro and in vivo . Collectively, our findings have uncovered novel pathways at the single cell level that likely influence FGF23-dependent disease mechanisms.

Translational statement

Inflammation and elevated FGF23 in chronic kidney disease (CKD) are both associated with poor patient outcomes and mortality. However, the links between these manifestations and the effects of inflammation on FGF23-mediated mineral metabolism within specific nephron segments remain unclear. Herein, we isolated an inflammatory pathway driven by TNF/NF-κB associated with regulating FGF23 bioactivity. The findings from this study could be important in designing future therapeutic approaches for chronic mineral diseases, including potential combination therapies or early intervention strategies. We also suggest that further studies could explore these pathways at the single cell level in CKD models, as well as test translation of our findings to interactions of chronic inflammation and elevated FGF23 in human CKD kidney datasets.

α-Klotho levels in girls with central precocious puberty: potential as a diagnostic and monitoring marker

Background

Recent studies suggest a link between the Klotho protein, sex hormones, and insulin-like growth factor-1 (IGF-1), indicating that α-Klotho levels may rise during puberty, including in central precocious puberty (CPP) cases. This study aimed to explore α-Klotho levels in girls with CPP to assess its potential as a diagnostic and monitoring tool for this condition.

Methods

In total, 139 girls, comprising 82 patients diagnosed with CPP and 57 healthy prepubertal controls, were enrolled in this study. From March 2020 to May 2023, we assessed both α-Klotho levels and clinical parameters. α-Klotho concentrations were measured using an α-Klotho ELISA kit. For the girls with CPP, we additionally analyzed samples taken 6 months after GnRH agonist treatment.

Results

α-Klotho levels were higher in the CPP group compared with the control (CPP group: 2529 ± 999 ng/mL; control group: 1802 ± 675 pg/mL) (P < 0.001), and its level modest decreased after 6 months of GnRH agonist treatment (2147± 789 pg/mL) (P < 0.001). The association between α-Klotho and IGF-1 SDS, follicular stimulating hormone and baseline luteinizing hormone was assessed by partial correlation after adjusting for age, BMI SDS (r= 0.416, p= <0.001; r= 0.261, p= 0.005; r= 0.278, p= 0.002), respectively. Receiver operating characteristic curve analysis identified an α-Klotho cut-off differentiating CPP from controls, with a cut-off of 1914 pg/mL distinguishing girls with CPP from controls with a sensitivity of 69.5% and specificity of 70.2%; the area under the curve was 0.723.

Conclusion

The findings of our study are the first step towards deciphering the role of α-Klotho in puberty induction. With additional data and further research, α-Klotho could potentially be utilized as a significant diagnostic and monitoring tool for CPP.

Association of serum soluble α‑klotho with risk of kidney stone disease: a population-based cross-sectional study

BACKGROUND

The aim of the study was to explore the association of serum soluble klotho with kidney stone disease (KSD) in the general population over the age of 40 years in the United States.

METHODS

We integrated the data in National Health and Nutrition Examination Survey from 2007 to 2016 years. The relationship between serum soluble α‑klotho and prevalence of KSD was analyzed by constructing weighted multivariable logistic regression model, restricted cubic spline (RCS) curve, and subgroup analyses.

RESULTS

In the study, a total of 13,722 individuals were included in our study. A U-shaped association between serum soluble klotho and the risk of KSD was shown by the RCS curve (P value for nonlinear < 0.05). In the full adjusted model, compared with the lowest quartile of serum soluble α‑klotho, the adjusted odd ratios (95% confidence intervals) for KSD across the quartiles were (0.999 (0.859, 1.164), 1.005 (0.858, 1.176), and 1.061 (0.911, 1.235)). Subgroup analyses also showed that the U-shaped association of serum soluble α‑klotho with KSD was found among subjects who were age < 60 years, female or male, with or without hypertension, and BMI ≥ 30 kg/m2.

CONCLUSIONS

Our findings suggested that serum klotho levels had a U-shaped correlation with risk of KSD. When the Klotho level is at 818.66 pg/mL, prevalence of KSD is lowest. Therefore, maintaining a certain level of serum soluble α‑klotho could prevent the occurrence of KSD.

Endocrine FGFs and their signaling in the brain: Relevance for energy homeostasis

Since their discovery in 2000, there has been a continuous expansion of studies investigating the physiology, biochemistry, and pharmacology of endocrine fibroblast growth factors (FGFs). FGF19, FGF21, and FGF23 comprise a subfamily with attributes that distinguish them from typical FGFs, as they can act as hormones and are, therefore, referred to as endocrine FGFs. As they participate in a broad cross-organ endocrine signaling axis, endocrine FGFs are crucial lipidic, glycemic, and energetic metabolism regulators during energy availability fluctuations. They function as powerful metabolic signals in physiological responses induced by metabolic diseases, like type 2 diabetes and obesity. Pharmacologically, FGF19 and FGF21 cause body weight loss and ameliorate glucose homeostasis and energy expenditure in rodents and humans. In contrast, FGF23 expression in mice and humans has been linked with insulin resistance and obesity. Here, we discuss emerging concepts in endocrine FGF signaling in the brain and critically assess their putative role as therapeutic targets for treating metabolic disorders.

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.

Analysis of serum insulin-like growth factor-1, fibroblast growth factor 23, and Klotho levels in girls with rapidly progressive central precocious puberty

To study the levels of serum insulin-like growth factor 1 (IGF-1), fibroblast growth factor 23 (FGF23), and Klotho, and to study their relationship with girls with rapidly progressive central precocious puberty (RP-CPP). This is a cross-sectional study on the progression rate of central precocious puberty in girls, who complained of breast development before the age of 8 years and were followed between June 2021 and June 2022. At the same time, 28 healthy girls less than 8 years old who had not started puberty were recruited as the control group. The physical examination and laboratory evaluation of each group was completed. Only patients with CPP received pelvic ultrasound examination and bone age test. Bone age index (BAI), basal LH levels (BLH), basal LH levels/basal FSH levels (BFSH), peak LH (PLH)/peak FSH (PFSH), IGF-1, Klotho, FGF23, and ovarian volume in the RP-CPP group were higher than those in slowly progressive CPP (SP-CPP) group. In the RP-CPP group, IGF-1 was correlated with Klotho, FGF23, and BLH; Klotho was correlated with FGF23 and BLH; FGF23 was correlated with BLH.

CONCLUSION

The BLH, FGF23, Klotho, and IGF-1 have a certain correlation with RP-CPP, which may play an important role in the speed of girls' sexual development.

WHAT IS KNOWN

• The association between IGF-1 and RP-CPP.

WHAT IS NEW

• We found the association between FGF23, Klotho and RP-CPP.

Association between serum soluble α-klotho and bone mineral density (BMD) in middle-aged and older adults in the United States: a population-based cross-sectional study

BACKGROUND

Osteoporosis is a degenerative disease defined by low bone mineral density, has a high prevalence, and causes fractures at multiple sites throughout the body, greatly affecting the quality of patients. α-Klotho is an endocrine factor involved in the regulation of various metabolic processes in humans, and its role in bone metabolism has attracted widespread attention. The relationship between α-klotho and bone mineral density has not been uniformly recognized, and no large-scale correlation analysis has been conducted in the middle-aged and elderly population.

OBJECTIVE

To determine the relationship between α-klotho and bone mineral density in middle-aged and elderly people.

METHODS

Population data of 3120 individuals aged 40-79 years were obtained from the NHANES database for the period 2011-2016. Regression analysis was performed using a general linear model with serum α-klotho as the independent variable and total bone mineral density, thoracic bone mineral density, lumbar bone mineral density, pelvic bone mineral density, and trunk bone mineral density as the dependent variables, respectively. The generalized additive model was also used for smoothing curve fitting and threshold effect analysis.

RESULTS

Serum α-klotho was positively correlated with total bone mineral density at lg (Klotho) < 2.97 and with thoracic bone mineral density at lg (Klotho) > 2.69 (β = 0.05, p = 0.0006), and negatively correlated (β = -0.27, p = 0.0341) with lumbar bone mineral density at lg (Klotho) < 2.69. It also positively correlated with trunk bone mineral density (β = 0.027, p = 0.03657) and had no segmental effect but did not correlate with pelvic bone mineral density. The positive association of serum α-klotho with those aged 40-49 years, female, non-Hispanic White, and without hypertension was clearer. In the population with diabetes, a significantly positive association between total (β = 0.15, p = 0.01), thoracic (β = 0.23, p = 0.0404), and lumbar (β = 0.22, p = 0.0424) bone mineral density and α-klotho was observed.

CONCLUSIONS

α-Klotho has different relationships with total, thoracic, lumbar, and trunk bone mineral density. Among them, the positive correlation between α-klotho and trunk bone mineral density is more valuable for predicting osteoporosis. The significant effect of α-klotho on bone mineral density in diabetes patients suggests its potential as a predictive marker of diabetes progression.

Transcriptome analysis of renal ischemia/reperfusion (I/R) injury in BAFF and BAFF-R deficient mice

Acute kidney injury (AKI) accompanies with high morbidity and mortality. Incomplete renal recovery can lead to chronic and finally end-stage kidney disease, which results in the requirement of lifelong dialysis or kidney transplantation. Consequently, finding predictive biomarker and therefore developing preventive therapeutic approaches is an urgent need. For this purpose, a better understanding of the mechanism underlying AKI is necessary. The cytokine BAFF (B cell activating factor) is related to AKI by supporting B cells, which in turn play an important role in inflammatory processes and the production of antibodies. In our study, we investigated the role of BAFF and its receptor BAFF-R in the early phase of AKI. Therefore, we performed the well-established ischemia/reperfusion (I/R) model in BAFF (B6.129S2-Tnfsf13btm1Msc/J) and BAFF-R (B6(Cg)-Tnfrsf13ctm1Mass/J) deficient mice. Transcriptome of ischemic and contralateral control kidneys was analyzed and compared to wildtype littermates. We detected the upregulation of Lcn2, Lyz2, Cd44, Fn1 and Il1rn in ischemic kidneys as well as the downregulation of Kl. Furthermore, we revealed different expression patterns in BAFF and BAFF-R knockout mice. Compared to wildtype littermates, up- and downregulation of each investigated gene were higher in BAFF-R knockout and lower in BAFF knockout. Our findings indicate a positive impact of BAFF knockout in early phase of AKI, while BAFF-R knockout seems to worsen I/R injury. In addition, our study shows for the first time a remarkable renal upregulation of Lyz2 in a murine I/R model. Therefore, we consider Lyz2 as conceivable predictive or early biomarker in case of I/R and AKI.

Analysis of the association between serum antiaging humoral factor klotho and cardiovascular disease potential risk factor apolipoprotein B in general population

Cardiovascular disease (CVD) is a prevalent health issue, and various risk factors contribute to its development, including blood lipids, blood pressure, diabetes, smoking, and alcohol consumption. Apolipoprotein B (ApoB) is related to CVD. ApoB is present on the surface of low-density lipoprotein (LDL), and its cellular recognition and LDL uptake are mainly achieved through recognition. It plays a crucial role in the diagnosis and treatment of CVD. This study aims to investigate the relationship between Klotho and ApoB in the general population of the United States as the correlation between serum Klotho and apoB is currently unknown. These findings could potentially guide the development of future treatments for CVD. This study utilized data from the National Health and Nutrition Examination Survey (NHANES) collected between 2007 and 2016. A linear regression model and smooth curve fitting were conducted to analyze the relationship between serum Klotho and apoB. The results indicate a negative correlation between serum Klotho concentration and apoB concentration (β = -71.7; 95% confidence interval [CI]: -120.8, -22.6; P = .005). After adjusting for confounding variables, the negative correlation between apoB concentration and serum Klotho concentration became more significant (β = -91.8; 95% CI: -151.3, -32.2; P = .004). When apoB concentration was converted from a continuous variable to a categorical variable (tertiles: T1 <0.8 g/L; T2: ≥0.8 g/L to <1.0 g/L; T3: ≥1.0 g/L), the serum klotho level of participants in the highest tertile (≥1.0 g/L) was -44.8 pg/mL (95% CI: -86.3, -3.2; P = .040) lower than that in the lowest tertile (<0.8 g/L). The smooth curve fitting diagram revealed differences in the relationship between serum Klotho concentration and apoB among individuals with different CVD risk factors. This study demonstrates a significant negative correlation between serum Klotho concentration and apoB concentration, even after controlling for confounding factors. The findings suggest that serum Klotho and apoB may be involved in the development of CVD, and targeting these factors could be a potential approach for CVD prevention and treatment.

Individual nutrients and serum klotho levels in adults aged 40-79 years

Several dietary factors (including adherence to the Mediterranean diet or higher nut intake) seem to positively affect circulating antiaging Klotho protein levels; yet, a description of possible relationships between individual nutrients and Klotho activity has not been evaluated. We analyzed the association of dietary intake of individual macro- and micronutrients and nonnutritive food components with circulating Klotho levels in a sample of 40- to 79-year-old US adults. Data from the 2015-2016 National Health and Nutrition Examination Survey were analyzed. Nutrient/food component intakes were calculated in relation to total energy intake using the nutrient density method, and available pristine serum samples were analyzed for serum Klotho concentrations. The final study sample consisted of 2637 participants (mean age 59.0 ± 10.7 years; 52% women). Higher Klotho concentrations were found with higher intake of carbohydrates (p < .001), total sugars (p < .001), dietary fibers (p < .001), vitamin D (p = .05), total folates (p = .015), and copper (p = .018). The results of the regression analysis with a crude model showed significant associations among five nutrients/food components (carbohydrates, alcohol, total sugars, dietary fibers, and niacin) and soluble Klotho levels across the sample. After adjusting the models for age and gender, the nutrient/food component-Klotho association remained significant for carbohydrates, total sugars, and alcohol (p < .05). Dietary exposure to individual nutrients and nonnutritive food components appears to be associated with Klotho activity; however, additional research is needed to investigate the relationship between cause and effect in diet composition-Klotho interplay.

Up-regulation of Myocardial Klotho Expression to Promote Cardiac Functional Recovery in Old Mice following Endotoxemia

Objective

Endotoxemic cardiac dysfunction contributes to greater morbidity and mortality in elderly patients with sepsis. This study tested the hypothesis that Klotho insufficiency in aging heart exaggerates and prolongs myocardial inflammation to hinder cardiac function recovery following endotoxemia.

Methods

Endotoxin (0.5 mg/kg, iv) was administered to young adult (3-4 months) and old (18-22 months) mice with or without subsequent treatment with recombinant interleukin-37 (IL-37, 50 μg/kg, iv) or recombinant Klotho (10 μg/kg, iv). Cardiac function was analyzed using a microcatheter 24, 48 and 96 h later. Myocardial levels of Klotho, ICAM-1, VCAM-1 and IL-6 were determined by immunoblotting and ELISA.

Results

In comparison to young adult mice, old mice had worse cardiac dysfunction accompanied by greater myocardial levels of ICAM-1, VCAM-1 and IL-6 at each time point following endotoxemia and failed to fully recover cardiac function by 96 h. The exacerbated myocardial inflammation and cardiac dysfunction were associated with endotoxemia-caused further reduction of lower myocardial Klotho level in old mice. Recombinant IL-37 promoted inflammation resolution and cardiac functional recovery in old mice. Interestingly, recombinant IL-37 markedly up-regulated myocardial Klotho levels in old mice with or without endotoxemia. Similarly, recombinant Klotho suppressed myocardial inflammatory response and promoted inflammation resolution in old endotoxemic mice, leading to complete recovery of cardiac function by 96 h.

Conclusion

Myocardial Klotho insufficiency in old endotoxemic mice exacerbates myocardial inflammatory response, impairs inflammation resolution and thereby hinders cardiac functional recovery. IL-37 is capable of up-regulating myocardial Klotho expression to improve cardiac functional recovery in old endotoxemic mice.

mTORC1-induced bone marrow-derived mesenchymal stem cell exhaustion contributes to the bone abnormalities in klotho-deficient mice of premature aging

Stem cell exhaustion is a hallmark of aging. Klotho-deficient mice (kl/kl mice) is a murine model that mimics human aging with significant bone abnormalities. The aim of this study is using kl/kl mice to investigate the functional change of bone marrow-derived mesenchymal stem cells (BMSCs) and explore the underlying mechanism. We found klotho-deficiency leads to bone abnormalities. In addition, kl/kl BMSCs manifested hyper-active proliferation but functional declined both in vivo and in vitro. mTORC1 activity was higher in freshly isolated kl/kl BMSCs and autophagy in kl/kl BMSCs were significantly decreased, possibly through mTORC1 activation. Conditional medium containing soluble Klotho protein (sKL) rescued hyper-proliferation of kl/kl BMSCs by inhibiting mTORC1 activity and restoring autophagy. Finally, intraperitoneally injection of mTORC1 inhibitor rapamycin restored BMSC quiescence, ameliorated bone phenotype and increased lifespan of kl/kl mice in vivo. This research highlights a therapeutic strategy to maintain the homeostasis of adult stem cell pool for healthy bone aging.

Soluble Klotho protects against glomerular injury through regulation of ER stress response

αKlotho (Klotho) has well established renoprotective effects; however, the molecular pathways mediating its glomerular protection remain incompletely understood. Recent studies have reported that Klotho is expressed in podocytes and protects glomeruli through auto- and paracrine effects. Here, we examined renal expression of Klotho in detail and explored its protective effects in podocyte-specific Klotho knockout mice, and by overexpressing human Klotho in podocytes and hepatocytes. We demonstrate that Klotho is not significantly expressed in podocytes, and transgenic mice with either a targeted deletion or overexpression of Klotho in podocytes lack a glomerular phenotype and have no altered susceptibility to glomerular injury. In contrast, mice with hepatocyte-specific overexpression of Klotho have high circulating levels of soluble Klotho, and when challenged with nephrotoxic serum have less albuminuria and less severe kidney injury compared to wildtype mice. RNA-seq analysis suggests an adaptive response to increased endoplasmic reticulum stress as a putative mechanism of action. To evaluate the clinical relevance of our findings, the results were validated in patients with diabetic nephropathy, and in precision cut kidney slices from human nephrectomies. Together, our data reveal that the glomeruloprotective effects of Klotho is mediated via endocrine actions, which increases its therapeutic potential for patients with glomerular diseases.

FGF23 Actions in CKD-MBD and other Organs During CKD

Fibroblast growth factor 23 (FGF23) is a new endocrine product discovered in the past decade. In addition to being related to bone diseases, it has also been found to be related to kidney metabolism and parathyroid metabolism, especially as a biomarker and a key factor to be used in kidney diseases. FGF23 is upregulated as early as the second and third stages of chronic kidney disease (CKD) in response to relative phosphorus overload. The early rise of FGF23 has a protective effect on the body and is essential for maintaining phosphate balance. However, with the decline in renal function, eGFR (estimated glomerular filtration rate) declines, and the phosphorus excretion effect caused by FGF23 is weakened. It eventually leads to a variety of complications, such as bone disease (Chronic Kidney Disease-Mineral and Bone Metabolism Disorder), vascular calcification (VC), and more. Monoclonal antibodies against FGF23 are currently used to treat genetic diseases with increased FGF23. CKD is also a state of increased FGF23. This article reviews the current role of FGF23 in CKD and discusses the crosstalk between various organs under CKD conditions and FGF23. Studying the effect of hyperphosphatemia on different organs of CKD is important. The prospect of FGF23 for therapy is also discussed.

Association between Serum Soluble α-Klotho and Urinary Albumin Excretion in Middle-Aged and Older US Adults: NHANES 2007-2016

(1) Background: Preclinical and clinical studies on the anti-aging effect of α-Klotho are emerging. Urinary albumin excretion (UAE) is a well-known biomarker of kidney injury and generalized damage in the cardiovascular system. However, the potential relationship between α-Klotho and UAE is limited and controversial. This study aimed to quantify this relationship in the general middle-aged and elderly population from the National Health and Nutrition Survey (NHANES) 2007-2016. (2) Methods: Serum α-Klotho was measured by enzyme-linked immunosorbent assay. UAE was assessed by the albumin-to-creatinine ratio (ACR). After adjusting for several confounding variables, the relationship between α-Klotho and ACR was analyzed by weighted multivariable logistic regression, subgroup analysis, and interaction tests. A generalized additive model (GAM) with smooth functions using the two-piecewise linear regression model was used to examine the potential nonlinear relationship between α-Klotho and ACR. (3) Results: Among 13,584 participants aged 40-79 years, we observed an independent and significant negative correlation between α-Klotho and ACR (β = -12.22; 95% CI, -23.91, -0.53, p = 0.0448) by multivariable logistic regression analysis, especially in those with age ≥ 60 years, pulse pressure (PP) ≥ 60 mmHg, hypertension or diabetes. We further discovered the nonlinear relationship between α-Klotho and ACR by GAM, revealing the first negative and then positive correlations with an inflection point of 9.91 pg/mL between α-Klotho and ACR. (4) Conclusions: A dose-response relationship between α-Klotho and ACR was demonstrated, and the negative correlation therein indicated that α-Klotho has potential as a serum marker and prophylactic or therapeutic agent despite its metabolic and effective mechanisms needing to be further explored.

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.

Pathophysiology and genetics of salt-sensitive hypertension

Most hypertensive cases are primary and heavily associated with modifiable risk factors like salt intake. Evidence suggests that even small reductions in salt consumption reduce blood pressure in all age groups. In that regard, the ACC/AHA described a distinct set of individuals who exhibit salt-sensitivity, regardless of their hypertensive status. Data has shown that salt-sensitivity is an independent risk factor for cardiovascular events and mortality. However, despite extensive research, the pathogenesis of salt-sensitive hypertension is still unclear and tremendously challenged by its multifactorial etiology, complicated genetic influences, and the unavailability of a diagnostic tool. So far, the important roles of the renin-angiotensin-aldosterone system, sympathetic nervous system, and immune system in the pathogenesis of salt-sensitive hypertension have been studied. In the first part of this review, we focus on how the systems mentioned above are aberrantly regulated in salt-sensitive hypertension. We follow this with an emphasis on genetic variants in those systems that are associated with and/or increase predisposition to salt-sensitivity in humans.

Soluble α-klotho and heparin modulate the pathologic cardiac actions of fibroblast growth factor 23 in chronic kidney disease

Fibroblast growth factor (FGF) 23 is a phosphate-regulating hormone that is elevated in patients with chronic kidney disease and associated with cardiovascular mortality. Experimental studies showed that elevated FGF23 levels induce cardiac hypertrophy by targeting cardiac myocytes via FGF receptor isoform 4 (FGFR4). A recent structural analysis revealed that the complex of FGF23 and FGFR1, the physiologic FGF23 receptor in the kidney, includes soluble α-klotho (klotho) and heparin, which both act as co-factors for FGF23/FGFR1 signaling. Here, we investigated whether soluble klotho, a circulating protein with cardio-protective properties, and heparin, a factor that is routinely infused into patients with kidney failure during the hemodialysis procedure, regulate FGF23/FGFR4 signaling and effects in cardiac myocytes. We developed a plate-based binding assay to quantify affinities of specific FGF23/FGFR interactions and found that soluble klotho and heparin mediate FGF23 binding to distinct FGFR isoforms. Heparin specifically mediated FGF23 binding to FGFR4 and increased FGF23 stimulatory effects on hypertrophic growth and contractility in isolated cardiac myocytes. When repetitively injected into two different mouse models with elevated serum FGF23 levels, heparin aggravated cardiac hypertrophy. We also developed a novel procedure for the synthesis and purification of recombinant soluble klotho, which showed anti-hypertrophic effects in FGF23-treated cardiac myocytes. Thus, soluble klotho and heparin act as independent FGF23 co-receptors with opposite effects on the pathologic actions of FGF23, with soluble klotho reducing and heparin increasing FGF23-induced cardiac hypertrophy. Hence, whether heparin injections during hemodialysis in patients with extremely high serum FGF23 levels contribute to their high rates of cardiovascular events and mortality remains to be studied.

Gender-specific soluble α-klotho levels as marker of GH deficiency in children: a case-control study

PURPOSE

To evaluate circulating soluble α-klotho (sαKL) levels in GHD children before and after 12 months of GH treatment (GHT).

METHODS

Auxological and basal metabolic parameters, oral glucose tolerance test for glucose and insulin levels, insulin sensitivity indices and klotho levels were evaluated before and after 12 months of follow-up in 58 GHD children and 56 healthy controls.

RESULTS

At baseline, GHD children showed significantly lower growth velocity standard deviation score (SDS) (p < 0.001), bone/chronological age ratio (p < 0.001), GH peak and area under the curve (AUC) after arginine test (ARG) (both p < 0.001) and glucagon stimulation test (GST) (p < 0.001 and 0.048, respectively), IGF-1 (p < 0.001), with higher BMI (SDS) (p < 0.001), WC (SDS) (p = 0.003) and sαKL (p < 0.001) than controls. After 12 months of GHT, GHD children showed a significant increase in height (SDS) (p < 0.001), growth velocity (SDS) (p < 0.001), bone/chronological age ratio (p < 0.001) IGF-1 (p < 0.001), fasting insulin (p < 0.001), Homa-IR (p < 0.001) and sαKL (p < 0.001) with a concomitant decrease in BMI (SDS) (p = 0.002) and WC (SDS) (p = 0.038) than baseline. At ROC curve analysis, we identified a sαKL cut-off to discriminate controls and GHD children of 1764.4 pg/mL in females and 1339.4 pg/mL in males. At multivariate analysis, the independent variables significantly associated with sαKL levels after 12 months of GHT were the oral disposition index (p = 0.004, β = 0.327) and IGF-1 (p = 0.019, β = 0.313).

CONCLUSIONS

Gender-related sαKL may be used as a marker of GHD combined to GH and IGF-1. Insulin and IGF-1 are independently associated with sαKL values after 12 months of GHT.

Klotho in Osx+-mesenchymal progenitors exerts pro-osteogenic and anti-inflammatory effects during mandibular alveolar bone formation and repair

Maxillofacial bone defects are commonly seen in clinical practice. A clearer understanding of the regulatory network directing maxillofacial bone formation will promote the development of novel therapeutic approaches for bone regeneration. The fibroblast growth factor (FGF) signalling pathway is critical for the development of maxillofacial bone. Klotho, a type I transmembrane protein, is an important components of FGF receptor complexes. Recent studies have reported the presence of Klotho expression in bone. However, the role of Klotho in cranioskeletal development and repair remains unknown. Here, we use a genetic strategy to report that deletion of Klotho in Osx-positive mesenchymal progenitors leads to a significant reduction in osteogenesis under physiological and pathological conditions. Klotho-deficient mensenchymal progenitors also suppress osteoclastogenesis in vitro and in vivo. Under conditions of inflammation and trauma-induced bone loss, we find that Klotho exerts an inhibitory function on inflammation-induced TNFR signaling by attenuating Rankl expression. More importantly, we show for the first time that Klotho is present in human alveolar bone, with a distinct expression pattern under both normal and pathological conditions. In summary, our results identify the mechanism whereby Klotho expressed in Osx+-mensenchymal progenitors controls osteoblast differentiation and osteoclastogenesis during mandibular alveolar bone formation and repair. Klotho-mediated signaling is an important component of alveolar bone remodeling and regeneration. It may also be a target for future therapeutics.

Klotho: An Emerging Factor With Ergogenic Potential

Sarcopenia and impaired cardiorespiratory fitness are commonly observed in older individuals and patients with chronic kidney disease (CKD). Declines in skeletal muscle function and aerobic capacity can progress into impaired physical function and inability to perform activities of daily living. Physical function is highly associated with important clinical outcomes such as hospitalization, functional independence, quality of life, and mortality. While lifestyle modifications such as exercise and dietary interventions have been shown to prevent and reverse declines in physical function, the utility of these treatment strategies is limited by poor widespread adoption and adherence due to a wide variety of both perceived and actual barriers to exercise. Therefore, identifying novel treatment targets to manage physical function decline is critically important. Klotho, a remarkable protein with powerful anti-aging properties has recently been investigated for its role in musculoskeletal health and physical function. Klotho is involved in several key processes that regulate skeletal muscle function, such as muscle regeneration, mitochondrial biogenesis, endothelial function, oxidative stress, and inflammation. This is particularly important for older adults and patients with CKD, which are known states of Klotho deficiency. Emerging data support the existence of Klotho-related benefits to exercise and for potential Klotho-based therapeutic interventions for the treatment of sarcopenia and its progression to physical disability. However, significant gaps in our understanding of Klotho must first be overcome before we can consider its potential ergogenic benefits. These advances will be critical to establish the optimal approach to future Klotho-based interventional trials and to determine if Klotho can regulate physical dysfunction.

Vitamin D Actions: The Lung Is a Major Target for Vitamin D, FGF23, and Klotho

Vitamin D is well known for its role as a calcium regulator and in maintenance of phosphate homeostasis in musculoskeletal health, and fibroblast growth factor 23 (FGF23) and its coreceptor α-klotho are known for their roles as regulators of serum phosphate levels. However, apart from these classical actions, recent data point out a relevant role of vitamin D and FGF23/klotho in lung health. The expression of the vitamin D receptor by different cell types in the lung and the fact that those cells respond to vitamin D or can locally produce vitamin D indicate that the lung represents a target for vitamin D actions. Similarly, the presence of the four FGF receptor isoforms in the lung and the ability of FGF23 to stimulate pulmonary cells support the concept that the lung is a target for FGF23 actions, whereas the contribution of klotho is still undetermined. This review will give an overview on how vitamin D or FGF23/klotho may act on the lung and interfere positively or negatively with lung health. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Fibroblast growth factor 23-Klotho and hypertension: experimental and clinical mechanisms

Hypertension (HTN) and chronic kidney disease (CKD) are increasingly recognized in pediatric patients and represent risk factors for cardiovascular morbidity and mortality later in life. In CKD, enhanced tubular sodium reabsorption is a leading cause of HTN due to augmented extracellular fluid volume expansion. The renin-angiotensin-aldosterone system (RAAS) upregulates various tubular sodium cotransporters that are also targets of the hormone fibroblast growth factor 23 (FGF23) and its co-receptor Klotho. FGF23 inhibits the activation of 1,25-dihydroxyvitamin D that is a potent suppressor of renin biosynthesis. Here we review the complex interactions and disturbances of the FGF23-Klotho axis, vitamin D, and the RAAS relevant to blood pressure regulation and discuss the therapeutic strategies aimed at mitigating their pathophysiologic contributions to HTN.

The intersection of Mineralocorticoid Receptor (MR) activation and the FGF23 - Klotho cascade. A Duopoly that promotes renal and cardiovascular injury

The nexus of CKD and cardiovascular disease (CVD) amplifies the morbidity and mortality of CKD, emphasizing the need for defining and establishing therapeutic initiatives to modify and abrogate the progression of CKD and concomitant CV risks. In addition to the traditional CV risk factors, disturbances of mineral metabolism are specific risk factors that contribute to the excessive CV mortality in patients with CKD. These risk factors include dysregulations of circulating factors that modulate phosphate metabolism including fibroblast growth factor 23 (FGF23) and soluble Klotho. Reduced circulating levels and suppressed renal klotho expression may be associated with adverse outcomes in CKD patients. While elevated circulating concentrations or locally produced FGF23 in the strained heart exert pro-hypertrophic mechanisms on the myocardium, Klotho attenuates tissue fibrosis, progression of CKD, cardiomyopathy, endothelial dysfunction, vascular stiffness, and vascular calcification. Mineralocorticoid receptor (MR) activation in non-classical targets, mediated by aldosterone and other ligands, amplifies CVD in CKD. In concert, we detail how the interplay of elevated FGF23, activation of the MR, and concomitant reductions of circulating Klotho in CKD, may potentiate each other's deleterious effects on kidney and the heart, thereby contributing to the initiation and progression of kidney and cardiac functional deterioration, acting through multipronged albeit complementary mechanistic pathways.

Correlation Between Soluble Klotho and Vascular Calcification in Chronic Kidney Disease: A Meta-Analysis and Systematic Review

Background: The correlation between soluble Klotho (sKlotho) level and vascular calcification (VC) in patients with chronic kidney disease (CKD) remains controversial. Using meta-analysis, we aimed to address this controversy and assess the feasibility of applying sKlotho as a biomarker for VC. Methods: Medical electronic databases were thoroughly searched for eligible publications on the association between sKlotho level and VC in CKD patients. Effectors, including correlation coefficients (r), odds ratios (ORs), hazard ratio (HR) or β-values, and 95% confidence intervals (CIs) were extracted and combined according to study design or effector calculation method. Pooled effectors were generated using both random-effects models and fixed-effects models according to I 2-value. Origin of heterogeneity was explored by sensitivity analysis and subgroup analysis. Results: Ten studies with 1,204 participants from a total of 1,199 publications were eligible and included in this meta-analysis. The combined correlation coefficient (r) was [-0.33 (-0.62, -0.04)] with significant heterogeneity (I 2 = 89%, p < 0.001) based on Spearman correlation analysis, and this significant association was also demonstrated in subgroups. There was no evidence of publication bias. The combined OR was [3.27 (1.70, 6.30)] with no evidence of heterogeneity (I 2 = 0%, p = 0.48) when sKlotho was treated as a categorical variable or [1.05 (1.01, 1.09)] with moderate heterogeneity (I 2 = 63%, p = 0.10) when sKlotho was treated as a continuous variable based on multivariate logistic regression. No significant association was observed and the pooled OR was [0.29 (0.01, 11.15)] with high heterogeneity (I 2 = 96%, p < 0.001) according to multivariate linear regression analysis. There was an inverse association between sKlotho and parathyroid hormone levels. The combined coefficient (r) was [-0.20 (-0.40, -0.01)] with significant heterogeneity (I 2 = 86%, p < 0.001), and without obvious publication bias. No significant association was found between sKlotho and calcium or phosphate levels. Conclusion: There exists a significant association between decreased sKlotho level and increased risk of VC in CKD patients. This raises the possibility of applying sKlotho as a biomarker for VC in CKD populations. Large, prospective, well-designed studies or interventional clinical trials are required to validate our findings.

Localization of fibroblast growth factor 23 protein in the rat hypothalamus

Fibroblast growth factor 23 (FGF23) is an endocrine growth factor and known to play a pivotal role in phosphate homeostasis. Interestingly, several studies point towards a function of FGF23 in the hypothalamus. FGF23 classically activates the FGF receptor 1 in the presence of the co-receptor αKlotho, of both gene expression in the brain was previously established. However, studies on gene and protein expression of FGF23 in the brain are scarce and have been inconsistent. Therefore, our aim was to localise FGF23 gene and protein expression in the rat brain with focus on the hypothalamus. Also, we investigated the protein expression of αKlotho. Adult rat brains were used to localise and visualise FGF23 and αKlotho protein in the hypothalamus by immunofluorescence labelling. Furthermore, western blots were used for assessing hypothalamic FGF23 protein expression. FGF23 gene expression was investigated by qPCR in punches of the arcuate nucleus, lateral hypothalamus, paraventricular nucleus, choroid plexus, ventrolateral thalamic nucleus and the ventromedial hypothalamus. Immunoreactivity for FGF23 and αKlotho protein was found in the hypothalamus, third ventricle lining and the choroid plexus. Western blot analysis of the hypothalamus confirmed the presence of FGF23. Gene expression of FGF23 was not detected, suggesting that the observed FGF23 protein is not brain-derived. Several FGF receptors are known to be present in the brain. Therefore, we conclude that the machinery for FGF23 signal transduction is present in several brain areas, indeed suggesting a role for FGF23 in the brain.

Circulating α-klotho regulates metabolism via distinct central and peripheral mechanisms

Emerging evidence implicates the circulating α-klotho protein as a prominent regulator of energy balance and substrate metabolism, with diverse, tissue-specific functions. Despite its well-documented ubiquitous role inhibiting insulin signaling, α-klotho elicits potent antidiabetic and anti-obesogenic effects. α-Klotho facilitates insulin release and promotes β cell health in the pancreas, stimulates lipid oxidation in liver and adipose tissue, attenuates hepatic gluconeogenesis, and increases whole-body energy expenditure. The mechanisms underlying α-klotho's peripheral functions are multifaceted, including hydrolyzing transient receptor potential channels, stimulating integrin β1➔focal adhesion kinase signaling, and activating PPARα via inhibition of insulin-like growth factor receptor 1. Moreover, until recently, potential metabolic roles of α-klotho in the central nervous system remained unexplored; however, a novel α-klotho➔fibroblast growth factor receptor➔PI3kinase signaling axis in the arcuate nucleus of the hypothalamus has been identified as a critical regulator of energy balance and glucose metabolism. Overall, the role of circulating α-klotho in the regulation of metabolism is a new focus of research, but accumulating evidence identifies this protein as an encouraging therapeutic target for Type 1 and 2 Diabetes and obesity. This review analyzes the new literature investigating α-klotho-mediated regulation of metabolism and proposes impactful future directions to progress our understanding of this complex metabolic protein.

Soluble Alpha Klotho in Acromegaly: Comparison With Traditional Markers of Disease Activity

CONTEXT

Soluble alpha klotho (sαKL) has been linked to growth hormone (GH) action, but systematic evaluation and comparisons with traditional biomarkers in acromegaly are lacking.

OBJECTIVE

To evaluate the potential of sαKL to aid classification of disease activity.

METHODS

This retrospective study at 2 academic centers included acromegaly patients before surgery (A, n = 29); after surgery (controlled, discordant, or uncontrolled) without (B1, B2, B3, n = 28, 11, 8); or with somatostatin analogue treatment (C1, C2, C3, n = 17, 11, 5); nonfunctioning pituitary adenomas (n = 20); and healthy controls (n = 31). sαKL was measured by immunoassay and compared with traditional biomarkers (random and nadir GH, insulin-like growth factor I [IGF-I], IGF binding protein 3). Associations with disease activity were assessed.

RESULTS

sαKL was correlated to traditional biomarkers, particularly IGF-I (rs=0.80, P <0.0001). High concentrations before treatment (A, median, interquartile range: 4.04 × upper limit of normal [2.26-8.08]) dropped to normal after treatment in controlled and in most discordant patients. A cutoff of 1548 pg/mL for sαKL discriminated controlled (B1, C1) and uncontrolled (B3, C3) patients with 97.8% (88.4%-99.9%) sensitivity and 100% (77.1%-100%) specificity. sαKL was below the cutoff in 84% of the discordant subjects. In the remaining 16%, elevated sαKL and IGF-I persisted, despite normal random GH. Sex, age, body mass index, and markers of bone and calcium metabolism did not significantly affect sαKL concentrations.

CONCLUSION

Our data support sαKL as a biomarker to assess disease activity in acromegaly. sαKL exhibits close association with GH secretory status, large dynamic range, and robustness toward biological confounders. Its measurement could be helpful particularly when GH and IGF-I provide discrepant information.

Role of Klotho in the Development of Essential Hypertension

Klotho has antiaging properties, and serum levels decrease with physiological aging and aging-related diseases, such as hypertension, cardiovascular, and chronic kidney disease. Klotho deficiency in mice results in accelerated aging and cardiovascular injury, whereas Klotho supplementation slows down the progression of aging-related diseases. The pleiotropic functions of Klotho include, but are not limited to, inhibition of insulin/IGF-1 (insulin-like growth factor 1) and WNT (wingless-related integration site) signaling pathways, suppression of oxidative stress and aldosterone secretion, regulation of calcium-phosphate homeostasis, and modulation of autophagy with inhibition of apoptosis, fibrosis, and cell senescence. Accumulating evidence shows an interconnection between Klotho deficiency and hypertension, and Klotho gene polymorphisms are associated with hypertension in humans. In this review, we critically review the current understanding of the role of Klotho in the development of essential hypertension and the most important underlying pathways involved, such as the FGF23 (fibroblast growth factor 23)/Klotho axis, aldosterone, Wnt5a/RhoA, and SIRT1 (Sirtuin1). Based on this critical review, we suggest avenues for further research.

Roles for fibroblast growth factor-23 and α-Klotho in acute kidney injury

Acute kidney injury is a global disease with high morbidity and mortality. Recent studies have revealed that the fibroblast growth factor-23-α-Klotho axis is closely related to chronic kidney disease, and has multiple biological functions beyond bone-mineral metabolism. However, although dysregulation of fibroblast growth factor-23-α-Klotho has been observed in acute kidney injury, the role of fibroblast growth factor-23-α-Klotho in the pathophysiology of acute kidney injury remains largely unknown. In this review, we describe recent findings regarding fibroblast growth factor-23-α-Klotho, which is mainly involved in inflammation, oxidative stress, and hemodynamic disorders. Further, based on these recent results, we put forth novel insights regarding the relationship between the fibroblast growth factor-23-α-Klotho axis and acute kidney injury, which may provide new therapeutic targets for treating acute kidney injury.

Salt causes aging-associated hypertension via vascular Wnt5a under Klotho deficiency

Aging is associated with a high prevalence of hypertension due to elevated susceptibility of BP to dietary salt, but its mechanism is unknown. Serum levels of Klotho, an anti-aging factor, decline with age. We found that high salt (HS) increased BP in aged mice and young heterozygous Klotho-knockout mice and was associated with increased vascular expression of Wnt5a and p-MYPT1, which indicate RhoA activity. Not only the Wnt inhibitor LGK974 and the Wnt5a antagonist Box5 but Klotho supplementation inhibits HS-induced BP elevation, similarly to the Rho kinase inhibitor fasudil, associated with reduced p-MYPT1 expression in both groups of mice. In cultured vascular smooth muscle cells, Wnt5a and angiotensin II (Ang II) increased p-MYPT1 expression but knockdown of Wnt5a with siRNA abolished Ang II-induced upregulation of p-MYPT1, indicating that Wnt5a is indispensable for Ang II-induced Rho/ROCK activation. Notably, Klotho inhibited Wnt5a- and Ang II-induced upregulation of p-MYPT1. Consistently, Klotho supplementation ameliorated HS-induced augmentation of reduced renal blood flow (RBF) response to intra-arterial infusion of Ang II and the thromboxane A2 analog U46619, which activated RhoA in both groups of mice and were associated with the inhibition of BP elevation, suggesting that abnormal response of RBF to Ang II contributes to HS-induced BP elevation. Thus, Klotho deficiency underlies aging-associated salt-sensitive hypertension through vascular non-canonical Wnt5a/RhoA activation.

Association Between the Anti-Aging Gene Klotho and Selected Rheumatologic Autoimmune Diseases

Klotho long recognized for its role in anti-aging, is potentially implicated in the pathogenesis of rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis. Aging of the immune system coincides with the inability of the body to recognize self-antigens, which often leads to autoimmune responses. The role of Klotho in these autoimmune diseases should be of high interest; however, few articles have been published exploring the role of Klotho in the pathogenesis, organ involvement, or clinical manifestation of rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis. Herein, we discuss information gathered from peer-reviewed publications to describe the emerging role of Kl in these select rheumatologic autoimmune diseases.

Alginate Oligosaccharide Ameliorates D-Galactose-Induced Kidney Aging in Mice through Activation of the Nrf2 Signaling Pathway

Aging is an independent risk factor for the development of age-related progressive kidney injury. As a part of the aging process, kidney aging has been indicated to be associated with oxidative stress-induced damage. Ameliorating oxidative damage is therefore considered a promising strategy for delaying kidney aging. Alginate oligosaccharide (AOS) has been reported to have a wide range of biological and pharmacological activities. However, no studies have focused on the role of AOS in delaying the kidney aging process. In this study, we aimed to evaluate the potential effects of AOS on kidney aging and its possible mechanisms. Subcutaneous injection of D-galactose (D-gal) (200 mg·kg⁻¹·d⁻¹) in C57BL/6J mice for 8 weeks was used to establish the aging model. AOS (200 mg·kg⁻¹·d⁻¹) was administered via oral gavage for the last four weeks. As a result, AOS inhibited the D-gal-induced upregulation of aging markers and significantly improved the kidney index and kidney function of D-gal-induced mice. In addition, AOS ameliorated the degree of tissue damage and fibrosis in the aging kidney. To further explore the potential mechanisms by which AOS attenuates the kidney aging process, the associated oxidative stress-induced damage was analyzed in depth. The data showed that AOS upregulated the expression of Klotho and decreased malondialdehyde levels by increasing the expression of antioxidant enzymes. Furthermore, our results suggested that AOS activated the nuclear factor erythrogen-2 associated factor 2 (Nrf2) pathway by promoting Nrf2 nuclear translocation in aging mice and upregulated the downstream expression of heme oxygenase-1 (HO-1) and NADPH quinone oxidoreductase 1 (NQO1). In conclusion, the present study demonstrated that AOS is a promising agent for attenuating kidney aging, and the underlying molecular mechanisms are related to the activation of the Nrf2 signaling pathway.

Centrally circulating α-klotho inversely correlates with human obesity and modulates arcuate cell populations in mice

Objective

Our laboratory recently identified the centrally circulating α-klotho protein as a novel hypothalamic regulator of food intake and glucose metabolism in mice. The current study aimed to investigate novel molecular effectors of central α-klotho in the arcuate nucleus of the hypothalamus (ARC), while further deciphering its role regulating energy balance in both humans and mice.

Methods

Cerebrospinal fluid (CSF) was collected from 22 adults undergoing lower limb orthopedic surgeries, and correlations between body weight and α-klotho were determined using an α-klotho enzyme-linked immunosorbent assay (ELISA) kit. To investigate the effects of α-klotho on energy expenditure (EE), 2-day intracerebroventricular (ICV) treatment was performed in diet-induced obesity (DIO) mice housed in TSE Phenomaster indirect calorimetry metabolic cages. Immunohistochemical staining for cFOS and patch clamp electrophysiology were used to determine the effects of central α-klotho on proopiomelanocortin (POMC) and tyrosine hydroxylase (TH) neurons. Additional stainings were performed to determine novel roles for central α-klotho to regulate non-neuronal cell populations in the ARC. Lastly, ICV pretreatment with fibroblast growth factor receptor (FGFR) or PI3kinase inhibitors was performed to determine the intracellular signaling involved in α-klotho-mediated regulation of ARC nuclei.

Results

Obese/overweight human subjects had significantly lower CSF α-klotho concentrations compared to lean counterparts (1,044 ± 251 vs. 1616 ± 218 pmol/L, respectively). Additionally, 2 days of ICV α-klotho treatment increased EE in DIO mice. α-Klotho had no effects on TH neuron activity but elicited varied responses in POMC neurons, with 44% experiencing excitatory and 56% experiencing inhibitory effects. Inhibitor experiments identified an α-klotho→FGFR→PI3kinase signaling mechanism in the regulation of ARC POMC and NPY/AgRP neurons. Acute ICV α-klotho treatment also increased phosphorylated ERK in ARC astrocytes via FGFR signaling.

Conclusion

Our human CSF data provide the first evidence that impaired central α-klotho function may be involved in the pathophysiology of obesity. Furthermore, results in mouse models identify ARC POMC neurons and astrocytes as novel molecular effectors of central α-klotho. Overall, the current study highlights prominent roles of α-klotho→FGFR→PI3kinase signaling in the homeostatic regulation of ARC neurons and whole-body energy balance.

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Human CSF α-klotho concentrations exhibit a strong, inverse correlation with body weight and BMI.

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ICV α-klotho treatment increases energy expenditure in DIO mice.

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α-Klotho.→FGFR→PI3kinase signaling modulates ARC NPY/AgRP and POMC neurons.

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α-Klotho.→FGFR→ERK signaling regulates ARC astrocytes.