New Insights into the Mechanism of Action of Soluble Klotho

Hyperphosphatemia in Kidney Failure: Pathophysiology, Challenges, and Critical Role of Phosphorus Management

Phosphorus is one of the most abundant minerals in the body and plays a critical role in numerous cellular and metabolic processes. Most of the phosphate is deposited in bones, 14% is present in soft tissues as various organic phosphates, and only 1% is found in extracellular space, mainly as inorganic phosphate. The plasma inorganic phosphate concentration is closely maintained between 2.5 and 4.5 mg/dL by intertwined interactions between fibroblast growth factor 23 (FGF-23), parathyroid hormone (PTH), and vitamin D, which tightly regulate the phosphate trafficking across the gastrointestinal tract, kidneys, and bones. Disruption of the strict hemostatic control of phosphate balance can lead to altered cellular and organ functions that are associated with high morbidity and mortality. In the past three decades, there has been a steady increase in the prevalence of kidney failure (KF) among populations. Individuals with KF have unacceptably high mortality, and well over half of deaths are related to cardiovascular disease. Abnormal phosphate metabolism is one of the major factors that is independently associated with vascular calcification and cardiovascular mortality in KF. In early stages of CKD, adaptive processes involving FGF-23, PTH, and vitamin D occur in response to dietary phosphate load to maintain plasma phosphate level in the normal range. However, as the CKD progresses, these adaptive events are unable to overcome phosphate retention from continued dietary phosphate intake and overt hyperphosphatemia ensues. As these hormonal imbalances and the associated adverse consequences are driven by the underlying hyperphosphatemic state in KF, it appears logical to strictly control serum phosphate. Conventional dialysis is inadequate in removing phosphate and most patients require dietary restrictions and pharmacologic interventions to manage hyperphosphatemia. However, diet control comes with many challenges with adherence and may place patients at risk for inadequate protein intake and malnutrition. Phosphate binders help to reduce phosphate levels but come with a sizable pill burden and high financial costs and are associated with poor adherence and psychosocial issues. Additionally, long-term use of binders may increase the risk of calcium, lanthanum, or iron overload or promote gastrointestinal side effects that exacerbate malnutrition and affect quality of life. Given the aforesaid challenges with phosphorus binders, novel therapies targeting small intestinal phosphate absorption pathways have been investigated. Recently, tenapanor, an agent that blocks paracellular absorption of phosphate via inhibition of enteric sodium-hydrogen exchanger-3 (NHE3) was approved for the treatment of hyperphosphatemia in KF. While various clinical tools are now available to manage hyperphosphatemia, there is a lack of convincing clinical data to demonstrate improvement in outcomes in KF with the lowering of phosphorus level. Conceivably, deleterious effects associated with hyperphosphatemia could be attributable to disruptions in phosphorus-sensing mechanisms and hormonal imbalance thereof. Further exploration of mechanisms that precisely control phosphorus sensing and regulation may facilitate development of strategies to diminish the deleterious effects of phosphorus load and improve overall outcomes in KF.

Association between serum α-klotho levels and the incidence of diabetic kidney disease and mortality in type 2 diabetes: evidence from a Chinese cohort and the NHANES database

BACKGROUND

The α-klotho is crucial in diabetes and its related complications. This study seeks to explore the link between α-klotho levels and the risk of diabetic kidney disease (DKD) as well as all-cause and cardiovascular mortality among individuals with type 2 diabetes mellitus (T2DM).

METHODS

The investigation involved 126 Chinese T2DM patients and 4,451 individuals from the National Health and Nutrition Examination Survey (NHANES) database. To evaluate the relationship between α-klotho levels and DKD risk, multivariate logistic regression was utilized. Additionally, restricted cubic spline (RCS) regression analysis was conducted to examine the nonlinear relationship between α-klotho levels and DKD incidence. RCS analysis was employed to explore the correlation between α-klotho and both all-cause and cardiovascular mortality.

RESULTS

In the Chinese cohort, α-klotho levels were notably elevated in T2DM group compared to DKD group. The NHANES data revealed a significant inverse relationship between α-klotho levels and DKD risk. Nonlinear analysis further illustrated a substantial nonlinear connection between α-klotho levels and DKD risk. Serum α-klotho levels below 880.78 pg/mL were linked to increased DKD risk in T2DM patients. When compared to the T2DM group, the DKD group had markedly higher all-cause and cardiovascular mortality rates, with the α-klotho low group (e.g., Q1) exhibiting lower survival compared to other groups. Cox regression findings indicated that elevated α-klotho levels could mitigate all-cause mortality in T2DM patients. The relationship between α-klotho levels and all-cause mortality was also nonlinear, with the minimal risk found at α-klotho levels between 776.95 pg/mL and 812.69 pg/mL, varying by gender.

CONCLUSION

There exists a notable association between α-klotho levels and DKD risk, along with mortality in T2DM patients, with varying effects based on gender. These results highlight the potential importance of α-klotho as both a biomarker and a therapeutic target.

Genetically determined α-Klotho levels and causal association with aging-related lung diseases

BACKGROUND

Abnormal α-Klotho (KL) levels play an essential role in the pathogenesis of aging-related lung diseases. However, the correlation between circulating KL levels and aging-related lung diseases has not been determined. This study aimed to determine whether circulating KL levels causally affect aging-related lung diseases using Mendelian randomization (MR).

METHODS

Five KL-associated Single-nucleotide polymorphisms (SNPs) were analyzed using two-sample MR to assess their effects on three aging-related lung diseases: idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), and lung cancer.

RESULTS

Based on a main casual effects model with MR analyses by the inverse variance weighted (IVW) method including multiplicative random-effects model (IVW-mre) and fixed-effects inverse variance-weighted model (IVW-fe), genetically predicted circulating KL levels were negatively related with risk of IPF (Odds ratio (ORIVW-mre), 0.999, 95 % CI, 0.999-1.000, PIVW-mre = 0.008; OR IVW-fe, 0.999, 95 % CI, 0.999-1.000, PIVW-fe = 0.042). Inversely, the circulating levels of KL displayed no clear association with COPD and lung cancer. No pleiotropy was detected.

CONCLUSIONS

Genetically predicted circulating KL was causally associated with a lower risk of IPF, suggesting a protective effect in preventing IPF risk. Therefore, KL may be a promising target for the prevention and therapeutic intervention in patients with IPF.

Longevity mechanisms in cardiac aging: exploring calcium dysregulation and senescence

Cardiac aging is a multistep process that results in a loss of various structural and functional heart abilities, increasing the risk of heart disease. Since its remarkable discovery in the early 1800s, when limestone is heated, calcium's importance has been defined in numerous ways. It can help stiffen shells and bones, function as a reducing agent in chemical reactions, and play a central role in cellular signalling. The movement of calcium ions in and out of cells and between those is referred to as calcium signalling. It influences the binding of the ligand, enzyme activity, electrochemical gradients, and other cellular processes. Calcium signalling is critical for both contraction and relaxation under the sliding filament model of heart muscle. However, with age, the heart undergoes changes that lead to increases in cardiac dysfunction, such as myocardial fibrosis, decreased cardiomyocyte function, and noxious disturbances in calcium homeostasis. Additionally, when cardiac tissues age, cellular senescence, a state of irreversible cell cycle arrest, accumulates and begins to exacerbate tissue inflammation and fibrosis. This review explores the most recent discoveries regarding the role of senescent cell accumulation and calcium signalling perturbances in cardiac aging. Additionally, new treatment strategies are used to reduce aged-related heart dysfunction by targeting senescent cells and modulating calcium homeostasis.

Klotho in age-related cardiovascular diseases: Insights into mitochondrial dysfunction and cell death

Aging is a major risk factor for the development of cardiovascular diseases (CVD), leading to specific alterations in the heart and vasculature. Besides, the mechanisms and intracellular pathways of aging and the factors affecting it are still not completely clear. Age-related complications such as oxidative stress, decreased autophagy, mitochondrial dysfunction, inflammatory responses, and cardiac dysfunction are associated with relative Klotho deficiency. Klotho, an anti-aging protein, with anti-oxidative and anti-inflammatory properties, has been shown to modulate calcium regulation and autophagy. It also protects against endothelial dysfunction by increasing nitric oxide production. Furthermore, emerging research has revealed that klotho significantly impacts vascular smooth muscle cells (VSMC) energetics and survival. This article has focused on recent advances in using Klotho in age-related CVD and summarizes the pre-clinical evidence supporting this approach. Based on the research, Klotho could provide more therapeutic options for ameliorating aging-related CVD.

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.

Dysregulation of Circadian Markers, HAT1 and Associated Epigenetic Proteins, and the Anti-Aging Protein KLOTHO in Placenta of Pregnant Women with Chronic Venous Disease

Background: Chronic venous disease (CVD) is a vascular disorder common among pregnant women, due to the impairment in the venous function associated with the mechanical, hemodynamical, and hormonal changes that occur during pregnancy. CVD is linked to venous hypertension, inflammation, oxidative stress, and hypoxia, which alter placental structure and function, as demonstrated in previous works. The placenta fulfills several roles in fetal development and maternal well-being by mediating nutrient exchange; acting as a mechanical, chemical, and immunological shield; and producing essential hormones, making it crucial to investigate the effects of CVD in this organ. Patients and methods: This work specifically analyzes the gene expression of circadian markers (CLOCK, BMAL1, PER1, and PER2), epigenetic regulators (HAT1 and associated molecules like histones H3, H4, RBBP7, and ASF1), and the anti-aging protein KLOTHO in placental tissue of pregnant women with CVD (CVD-PW, N = 98) compared to healthy pregnant controls (HC-PW, N = 82), using RT-qPCR and immunohistochemistry (IHC) to determine protein expression. Results: Our study demonstrates that the placentas of CVD-PW exhibit the reduced gene and protein levels of circadian regulators (clock, bmal1, per1, and per2), increased expression of hat1 and related proteins (h3, h4, rbbp7, and asf1), and decreased klotho expression, indicative of accelerated aging. Conclusions: These findings highlight profound molecular disturbances in the placentas of women with CVD, offering insights into the disease's pathophysiology and potential implications for maternofetal well-being. While this study deepens our understanding of the relationship between CVD and placental dysfunction, further research is required to fully elucidate these mechanisms and their long-term effects.

Klotho protects INS-1 pancreatic β-cells from senescence and enhances mitochondrial function

Aging is an important contributing factor for β-cell failure which could lead to the development of type 2 diabetes (T2D). Aging β-cell exhibits signs of senescence and develops senescence-associated secretory phenotype (SASP), causing the senescence and dysfunction of neighboring cells through paracrine action. Klotho is recognized as an anti-aging gene, and the corresponding protein is α-Klotho (KL). KL exerts potent anti-aging effects on multiple cell types, but its role in β-cell aging remains unclear. Here we showed that pancreatic INS-1 cell (a rat insulinoma cell line commonly used to study pancreatic β-cell function) developed the typical hallmarks of senescent cells when treated with doxorubicin in vitro, and this was accompanied by downregulation of endogenous KL expression. Supplementation with exogenous KL protein protected pancreatic INS-1 cell against senescence, as indicated by downregulation of senescent markers and SA-β-gal staining. Notably, these effects were associated with improved mitochondrial ATP production and mitochondrial dynamic balance, as well as reduced ROS production. Our study further revealed that INS-1 cell treated with doxorubicin exhibited a reduced insulin secretion response to glucose stimulation, while supplementation with KL could reverse this effect. Our results indicate the important role of KL in regulating β-cell senescence and provide new mechanistic insights into its role in β-cell aging.

Potential of Klotho as a Biomarker for Overwork: A Study of Frontline Medical Workers

OBJECTIVE

This study evaluates the utility of serum s-αKlotho levels as a quantifiable biomarker for overwork.

METHODS

Frontline medical workers aged 20-55 years from Yiling People's Hospital of Yichang were recruited. Criteria included nonsmokers, non-heavy drinkers, no chronic medication use, and no acute illnesses recently. Participants worked over 10 hours per day, 60 hours weekly, and had at least 3 years of experience. A control group was matched except for work conditions. Data were collected through surveys, and serum levels were measured.

RESULTS

Significant differences in serum Klotho were found between overwork and control groups. The overwork group had higher median s-αKlotho levels (49.99 pg/mL) compared to controls (27.88 pg/mL).

CONCLUSION

Overworked medical workers exhibited elevated serum s-αKlotho, suggesting s-αKlotho as a potential biomarker for overwork. Future research should use multicenter designs with larger samples to validate findings.

Impact of 24-week supervised concurrent exercise on S-Klotho and vitamin D levels: A randomized controlled trial

This study aimed to investigate the effects 24 weeks of supervised exercise training at different intensities on S-Klotho and 25-hydroxyvitamin D plasma levels in young adults. This report was based on a secondary analysis from the ACTIBATE single-center unblinded randomized controlled trial (ClinicalTrials.gov ID: NCT02365129). A total of 144 young adults (~34% men and ~66% women) aged between 18 and 25 years took part in the study. The participants were randomly assigned to 3 different groups: (i) concurrent exercise training program based on the international physical activity recommendations at vigorous intensity (Ex-Vigorous group), (ii) at moderate intensity (Ex-Moderate group), and (iii) control group (no exercise). S-Klotho and 25-hydroxyvitamin D plasma levels were determined before and after the 24-week intervention programme. A significant decrease of 25-hydroxyvitamin D plasma levels were identified across time in all groups (p < 0.001), whereas no significant differences across time were observed in S-Klotho plasma levels (p = 0.497). There was no time x group interaction neither in S-Klotho nor in 25-hydroxyvitamin D plasma levels (all p > 0.7). In summary, our results showed that 24 weeks of supervised concurrent exercise training does not induce significant changes on S-Klotho and 25-hydroxyvitamin D independently of the exercise intensity in young adults.

Klotho relieves H2O2-induced lens epithelial cell damage via suppression of NOX4

BACKGROUND

Age-related cataract (ARC) is a common eye disease and represents a common contributing factor to visual damage and loss. Klotho is a longevity gene and has been reported to participate in aging-related disorders. This work aims to investigate the potential role of klotho in ARC.

METHODS

In human lens epithelial cells (HLECs) induced by varying concentrations of hydrogen peroxide (H2O2), CCK-8 assay was used to detect cell viability. DCFH-DA probe was used to detect reactive oxygen species (ROS) level. Western blot was used to detect klotho expression. JC-1 fluorochrome assay was used to detect mitochondrial membrane potential (MMP). The concentrations of oxidative stress markers malondialdehyde (MDA) and superoxide dismutase (SOD) were detected by related assay kits. Flow cytometry analysis, immunofluorescence staining and western blot were used to detect cell apoptosis. SA-β-gal staining and western blot were used to detect cell senescence.

RESULTS

Klotho expression was decreased in HLECs induced by increasing concentrations of H2O2. Overexpression of klotho significantly inhibited ROS generation, decreased MDA content, increased SOD content, promoted cell viability and suppressed cell apoptosis and senescence in H2O2-induced HLECs. Furthermore, klotho down-regulated NOX4 expression and NOX4 elevation partially reversed the effects of klotho on H2O2-induced HLECs.

CONCLUSIONS

To sum up, klotho may down-regulate NOX4 to protect against H2O2-induced HLECs damage. This finding suggested the potential therapeutic use of klotho in ARC, which needs further investigation.

Decreased Alpha Klotho Expression in Placentas Exposed to Severe Maternal Vascular Malperfusion

BACKGROUND

Placental maternal vascular malperfusion (MVM) is characterized by accelerated villous maturation and has been associated with a decrease in the antiaging protein, alpha-klotho (AK). Our aim was to characterize AK protein and gene expression in the placenta and fetal organs.

METHODS

We utilized 2 cohorts. First, we characterized AK protein expression in an autopsy cohort where cases were defined as MVM as the cause of fetal death compared to a stillborn control population. Second, we characterized placental and umbilical cord blood AK gene expression in a liveborn population with and without MVM.

RESULTS

We found decreased protein expression in the villous trophoblastic cells of placentas exposed to severe MVM and decreased AK gene expression in placental tissue exposed to MVM. We did not see any statistically significant differences in fetal organ or umbilical cord blood AK expression based on the presence or absence of MVM. Furthermore, in liveborn infants, we also found increased odds of preterm birth with lower placental AK expression.

CONCLUSIONS

Decreased AK gene and protein expression in the placenta in the setting of MVM is consistent with the theory of placental aging in MVM and is associated with increased odds of preterm birth.

The role of Klotho and sirtuins in sleep-related cardiovascular diseases: a review study

The prevalence of sleep disorders has been reported from 1.6% to 56.0%, worldwide. Sleep deprivation causes cardiovascular diseases (CVDs) including atherosclerosis, vascular aging, hypertension, heart dysfunction, reduced heart rate variability, and cardiac arrhythmia. Reduced tissue oxygen causes various CVDs by activating pro-inflammatory factors and increasing oxidative stress. Sleep disorders are more important and prevalent in older people and cause more severe cardiovascular complications. On the other hand, the reduction of Klotho level, an age-dependent protein whose expression decreases with age, is associated with age-related diseases. Sirtuins, class III histone deacetylases, also are among the essential factors in postponing cellular aging and increasing the lifespan of organisms, and they do this by regulating different pathways in the cell. Sirtuins and Klotho play an important role in the pathophysiology of CVDS and both have anti-oxidative stress and anti-inflammatory activity. Studies have shown that the levels of Klotho and sirtuins are altered in sleep disorders. In this article, alterations of Klotho and sirtuins in sleep disorders and in the development of sleep-related CVDs were reviewed and the possible signaling pathways were discussed. The inclusion criteria were studies with keywords of different types of sleep disorders and CVDs, klotho, SIRT1-7, and sirtuins in PubMed, Scopus, Embase، Science Direct، Web of Sciences and Google Scholar by the end of 2023. The studies revealed there is a bidirectional relationship between sleep disorders and the serum and tissue levels of Klotho and sirtuins and sleep related-CVDs.

Klotho in pregnancy and intrauterine development-potential clinical implications: a review from the European Renal Association CKD-MBD Working Group

Intrauterine development is crucial for life-long health; therefore, elucidation of its key regulators is of interest for their potential prognostic and therapeutic implications. Originally described as a membrane-bound anti-aging protein, Klotho has evolved as a regulator of numerous functions in different organ systems. Circulating Klotho is generated by alternative splicing or active shedding from cell membranes. Recently, Klotho was identified as a regulator of placental function, and while Klotho does not cross the placental barrier, increased levels of circulating α-Klotho have been identified in umbilical cord blood compared with maternal blood, indicating that Klotho may also play a role in intrauterine development. In this narrative review, we discuss novel insights into the specific functions of the Klotho proteins in the placenta and in intrauterine development, while summarizing up-to-date knowledge about their structures and functions. Klotho plays a role in stem cell functioning, organogenesis and haematopoiesis. Low circulating maternal and foetal levels of Klotho are associated with preeclampsia, intrauterine growth restriction, and an increased perinatal risk for newborns, indicating a potential use of Klotho as biomarker and therapeutic target. Experimental administration of Klotho protein indicates a neuro- and nephroprotective potential, suggesting a possible future role of Klotho as a therapeutic agent. However, the use of Klotho as intervention during pregnancy is as yet unproven. Here, we summarize novel evidence, suggesting Klotho as a key regulator for healthy pregnancies and intrauterine development with promising potential for clinical use.

Klotho accelerates the progression of polycystic ovary syndrome through promoting granulosa cell apoptosis and inflammation†

The morbidity of polycystic ovary syndrome (PCOS) is in highly increasing rate nowadays. PCOS not only affects the fertility in women, but also threatens the health of whole life. Hence, to find the prognostic risk factors is of great value. However, the effective predictors in clinical practice of PCOS are still in blackness. In this study, we found Klotho (KL) was increased in follicular fluid (FF) and primary luteinized granulosa cells (GCs) from PCOS patients with hyperandrogenism. Furthermore, we found follicular KL was negatively correlated with numbers of mature oocytes, and positively correlated with serum testosterone, LH, and LH/FSH levels menstrual cycle and number of total antral follicles in PCOS patients. In primary luteinized GCs, the increased KL was accompanied with upregulation of cell apoptosis and inflammation-related genes. In ovaries of PCOS mice and cultured human KGN cell line, KL was up-regulated and accompanied by apoptosis, inflammation, and mitochondrial dysfunction. Therefore, our findings suggest new mechanisms for granulosa cell injury and revealed to target inhibit KL maybe a new therapeutic strategy for treatment of PCOS.

Soluble klotho induces the heat shock factor 1 through EGR1 expression

Klotho is an antiaging protein that has multiple functions. The purpose of this study is to investigate whether soluble klotho plays a role in cellular stress response pathways. We found that klotho deficiency (kl-/-) largely decreased HSF1 levels and impaired heat shock protein expression. Interestingly, recombinant soluble klotho-induced HSF1 and HSPs such as HSP90, HSP70, and HSP27 in kl-/- mouse embryonic fibroblasts (MEFs). Soluble Klotho treatment also induced cell proliferation and HSF1 promoter activity in MEF kl-/- cells in a concentration-dependent manner. Furthermore, using point mutagenesis, we identified regulatory/binding sites of transcription factors EGR1 regulated by soluble klotho in the HSF1 promoter. Taken together, our findings unravel the molecular basis of klotho and provide molecular evidence supporting a direct interaction between soluble klotho and HSF1-mediated stress response pathway.

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.

Anti-Inflammatory Role of the Klotho Protein and Relevance to Aging

The α-Klotho protein (hereafter Klotho) is an obligate coreceptor for fibroblast growth factor 23 (FGF23). It is produced in the kidneys, brain and other sites. Klotho insufficiency causes hyperphosphatemia and other anomalies. Importantly, it is associated with chronic pathologies (often age-related) that have an inflammatory component. This includes atherosclerosis, diabetes and Alzheimer's disease. Its mode of action in these diseases is not well understood, but it inhibits or regulates multiple major pathways. Klotho has a membrane form and a soluble form (s-Klotho). Cytosolic Klotho is postulated but not well characterized. s-Klotho has endocrine properties that are incompletely elucidated. It binds to the FGF receptor 1c (FGFR1c) that is widely expressed (including endothelial cells). It also attaches to soluble FGF23, and FGF23/Klotho binds to FGFRs. Thus, s-Klotho might be a roaming FGF23 coreceptor, but it has other functions. Notably, Klotho (cell-bound or soluble) counteracts inflammation and appears to mitigate related aging (inflammaging). It inhibits NF-κB and the NLRP3 inflammasome. This inflammasome requires priming by NF-κB and produces active IL-1β, membrane pores and cell death (pyroptosis). In accord, Klotho countered inflammation and cell injury induced by toxins, damage-associated molecular patterns (DAMPs), cytokines, and reactive oxygen species (ROS). s-Klotho also blocks the TGF-β receptor and Wnt ligands, which lessens fibrotic disease. Low Klotho is associated with loss of muscle mass (sarcopenia), as occurs in aging and chronic diseases. s-Klotho counters the inhibitory effects of myostatin and TGF-β on muscle, reduces inflammation, and improves muscle repair following injury. The inhibition of TGF-β and other factors may also be protective in diabetic retinopathy and age-related macular degeneration (AMD). This review examines Klotho functions especially as related to inflammation and potential applications.

Klotho: molecular mechanisms and emerging therapeutics in central nervous system diseases

Klotho is recognized as an aging-suppressor protein that is implicated in a variety of processes and signaling pathways. The anti-inflammatory, anti-apoptotic, anti-oxidant, and anti-tumor bioactivities of klotho have extended its application in neurosciences and made the protein popular for its lifespan-extending capacity. Furthermore, it has been demonstrated that klotho levels would reduce with aging and numerous pathologies, particularly those related to the central nervous system (CNS). Evidence supports the idea that klotho can be a key therapeutic target in CNS diseases such as amyotrophic lateral sclerosis, Parkinson's disease, stroke, and Alzheimer's disease. Reviewing the literature suggests that the upregulation of klotho expression regulates various signaling pathways related to autophagy, oxidative stress, inflammation, cognition, and ferroptosis in neurological disorders. Therefore, it has been of great interest to develop drugs or agents that boost or restore klotho levels. In this regard, the present review was designed and aimed to gather the delegated documents regarding the therapeutic potential of Klotho in CNS diseases focusing on the molecular and cellular mechanisms.

Association between the triglyceride-glucose index and serum soluble Klotho in middle-aged and older adults from NHANES 2007-2016

Klotho, an anti-aging protein, is believed to participate in metabolic diseases and play a potential protective role by regulating insulin sensitivity. This study aimed to explore the relationship between the triglyceride-glucose (TyG) index (a simple marker of insulin resistance) and serum soluble Klotho (S-Klotho) levels. The cross-sectional study comprised 5237 adults aged 40-79 years who participated in the National Health and Nutrition Examination Surveys (NHANES) 2007-2016. The TyG index was calculated as ln [fasting triglycerides (mg/dL) × fasting glucose (mg/dL)/2]. The serum levels of S-Klotho were measured by enzyme-linked immunosorbent assay. The association between the TyG index and S-Klotho levels was investigated by multiple linear regression models, smoothed curve fitting, segmented linear regression models, subgroup analyses, and interaction tests. The TyG index was inversely associated with serum S-Klotho level after full adjustment (β = - 45.11, 95% CI (- 79.53, - 10.69), P = 0.011). Furthermore, we also found a non-linear correlation and saturation phenomenon between the TyG index and serum S-Klotho levels, with a turning point of 9.56. In addition, a significant interaction effect of sex was found between the two (P for interaction < 0.001), with a more pronounced association observed in females. Further studies are required to explore the mechanisms and verify the correlation.

Placental and serum levels of human α-Klotho in preeclampsia & intra-uterine growth retardation: A potential sensitive biomarker?

INTRODUCTION

α-Klotho protein has three isoforms: a transmembrane (mKL), a shed- soluble isoform, and a circulating soluble isoform (sKL). mKL is expressed in the kidney and placenta, while sKL is detectable in blood and urine. It is known that α-Klotho levels fluctuate during pregnancy mainly in women with complications such as preeclampsia (PE) and intra-uterine growth restriction (IUGR).

METHODS

Forty-nine participants were divided into two groups: healthy and complicated pregnancy (PE, IUGR or both). Tissue samples (2 cm3) from the maternal side, Blood and urine samples were collected during pregnancy and postpartum. Samples were subjected to biochemical (WB), histological (H&E and IHC) staining as well as genetic analysis (qPCR).

RESULTS

Blood αKL levels were preserved in both healthy and complicated pregnancies. Significantly lower blood αKL concentrations were found in PE postpartum (PP) compared to levels during pregnancy, and were significantly lower compared with postpartum of a healthy pregnancy. αKL activity was reduced in complicated pregnancies vs. healthy pregnancies. Placen tal mKL levels (ELISA) and expression (WB) were lowered in complicated pregnancies compared with the healthy pregnancies group. Additionally, we found a significant decline in the expression of mKL mRNA in PE/IUGR placentas compared with the healthy group.

DISCUSSION

Several studies have focused on the involvement of αKL in normal placentation during pregnancy. Our results suggest lower function of sKL in complicated pregnancy compared with a control, and present differences in placental mKL levels as well as tissue and gene expression between healthy and complicated pregnancy. In light of our results, we conclude that complicated pregnancy is associated with in decline in mKL.

Inverse association of the systemic immune-inflammation index with serum anti-ageing protein Klotho levels in individuals with osteoarthritis: A cross-sectional study

BACKGROUND

The association between the systemic immune-inflammation index (SII) and the serum soluble-Klotho concentration (pg/ml) in osteoarthritis (OA) patients is unknown. This study aimed to investigate the relationship between the SII and serum soluble-Klotho levels in OA patients.

METHODS

All study data were obtained from the National Health and Nutrition Examination Survey (NHANES) database (n = 1852 OA patients; age range = 40-79 years). The SII and serum Klotho measurement data are from the NHANES mobile examination centre. The SII values were divided into quartiles (Q1-4: 0.02-3.36, 3.36-4.78, 4.79-6.70, and 6.70-41.75). A multivariate linear regression model was constructed to evaluate the association between the SII and serum Klotho levels in OA patients; interaction tests were conducted to test the stability of the statistical results.

RESULTS

Multivariate linear regression revealed a negative linear relationship between the SII and serum Klotho concentration in OA patients (β = -6.05; 95% CI: -9.72, -2.39). Compared to Q1, Q4 was associated with lower serum Klotho concentrations (β = -59.93; 95% CI: -96.57, -23.28). Compared with that of Q1, the β value of Q2-Q4 showed a downwards trend as the SII increased (Ptrend <0.001). The stratified analysis results indicated that the SII had a greater sensitivity in predicting serum Klotho concentrations in OA patients aged 60-79 years (Pinteraction = 0.028).

CONCLUSIONS

There was a significant negative linear correlation between the SII and serum Klotho concentration in OA patients. The SII can serve as a predictive indicator of serum Klotho concentrations in OA patients. Klotho may be a potential anti-inflammatory drug for OA treatment.

Serum klotho associated with thyroid hormone in adults: A population-based cross-sectional research

BACKGROUND AND STUDY AIM

The klotho protein, a multifunctional protein, has been shown to be associated with a wide range of endocrine diseases and has been linked to thyroid tumourigenesis. However, the relationship between serum klotho levels and thyroid hormones remains poorly understood. This study aimed to explore the correlation between serum klotho levels and thyroid hormones.

METHODS

Data was obtained from the NHANES cycles 2007-2008, 2009-2010, and 2011-2012. A total of 4674 participants were recruited for this study. Statistical analysis was using multiple linear regression analyses, and restricted cubic spline plots (RCS) to investigate the association between serum klotho levels and serum levels of thyroid hormones.

RESULTS

In the unadjusted covariate model, ln(klotho) significantly positively correlated with tT3, tT4, fT3, tT4/fT4, and tT3/fT3 (all P<0.01) and negatively correlated with TSH, tT4/tT3, and fT4/fT3 (all P<0.05). Furthermore, tT3, tT4, fT3and tT3/fT3 (P < 0.05) were still significant in the adjusted model. And it is worth noting that there is an approximately L-shaped nonlinear relationship between ln(klotho) and fT3,tT3 with a cut-off point of 6.697 (P-non-linear < 0.05). The stratification analysis showed gender and iodine level differences in the relationship between serum Klotho levels and thyroid hormones.

CONCLUSION

There is an L-shaped nonlinear relationship between ln(klotho) and fT3, tT3, suggesting that klotho could be involved in the physiological regulation of thyroid function.

In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

Investigation of α-Klotho Concentrations in Serum of Cats Affected by Hypertrophic Cardiomyopathy

Being involved in various physiological and pathophysiological mechanisms (ageing, kidney damage, cardiovascular diseases, etc.), Klotho is a parameter of increasing interest. Studies in veterinary medicine are still rare, but it is exciting to find out whether the findings obtained can be transferred to animals. The aim of this study was therefore to investigate Klotho in cats. This study addressed α-Klotho concentrations in the serum of two groups of cats: one diseased group affected by hypertrophic cardiomyopathy (n = 27) and one healthy control group (n = 35). α-Klotho concentrations in serum were measured using an ELISA. The results were evaluated in the context of several echocardiographic measurement parameters in the diseased group. No significant difference between α-Klotho concentrations in the two groups was found. A slight negative correlation was found between α-Klotho concentrations and the relation of left atrium/aorta (La/Ao) in the diseased group. Gaining initial information on α-Klotho in cats, it was not possible to draw definite conclusions concerning cardiomyopathies in this species. The assessment of Klotho should be considered in terms of its broad implications in disease processes, but it is also recommended to focus on specific disease features. Both approaches might be promising as possible applications of Klotho in veterinary medicine.

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.

Role of klotho and fibroblast growth factor 23 in arterial calcification, thickness, and stiffness: a meta-analysis of observational studies

This meta-analysis was conducted to clarify the role of klotho and fibroblast growth factor 23 (FGF-23) in human arterial remodeling across recent studies, in terms of arterial calcification, thickness, and stiffness. A systematic literature search was conducted on five databases for articles up to December 2023. Arterial calcification, thickness, and stiffness were determined using the calcification score and artery affected, carotid intima-media thickness (CIMT), and pulse wave velocity (PWV), respectively. Sixty-two studies with a total of 27,459 individuals were included in this meta-analysis. Most studies involved chronic kidney disease patients. Study designs were mostly cross-sectional with only one case-control and nine cohorts. FGF-23 was positively correlated with arterial calcification (r = 0.446 [0.254-0.611], p < 0.0001 and aOR = 1.36 [1.09-1.69], p = 0.006), CIMT (r = 0.188 [0.02-0.354], p = 0.03), and PWV (r = 0.235 [0.159-0.310], p < 0.00001). By contrast, Klotho was inversely correlated with arterial calcification (r = - 0.388 [- 0.578 to - 0.159], p = 0.001) and CIMT (r = - 0.38 [- 0.53 to - 0.207], p < 0.00001). In conclusion, FGF-23 and Klotho were associated with arterial calcification, thickness, and stiffness, clarifying their role in arterial remodeling processes.

Correlation between soluble klotho and chronic kidney disease-mineral and bone disorder in chronic kidney disease: a meta-analysis

We conducted a systematic search across medical databases, including PubMed, Web of Science, EMBASE, and Cochrane Library, up to March 2023. A total of 1944 subjects or individuals from 17 studies were included in our final analysis. The correlation coefficient (r) between sKlotho and calcium was [0.14, (0.02, 0.26)], and a moderate heterogeneity was observed (I2 = 66%, P < 0.05). The correlation coefficient (r) between Klotho and serum phosphate was [- 0.21, (- 0.37, - 0.04)], with apparent heterogeneity (I2 = 84%, P < 0.05). The correlation coefficient (r) between sKlotho and parathyroid hormone and vascular calcification was [- 0.23,(- 0.29, - 0.17); - 0.15, (- 0.23, - 0.08)], with no significant heterogeneity among the studies. (I2 = 40%, P < 0.05; I2 = 30%, P < 0.05). A significant correlation exists between low sKlotho levels and an increased risk of CKD-MBD in patients with CKD. According to the findings, sKlotho may play a role in alleviating CKD-MBD by lowering phosphorus and parathyroid hormone levels, regulating calcium levels, and suppressing vascular calcification. As analysis showed that sKlotho has an important impact on the pathogenesis and progression of CKD-MBD in CKD patients. Nonetheless, further comprehensive and high-quality studies are needed to validate our conclusions.

Klotho Stabilizes the Podocyte Actin Cytoskeleton in Idiopathic Membranous Nephropathy through Regulating the TRPC6/CatL Pathway

INTRODUCTION

The aim of this study was to explore the renoprotective effects of Klotho on podocyte injury mediated by complement activation and autoantibodies in idiopathic membranous nephropathy (IMN).

METHODS

Rat passive Heymann nephritis (PHN) was induced as an IMN model. Urine protein levels, serum biochemistry, kidney histology, and podocyte marker levels were assessed. In vitro, sublytic podocyte injury was induced by C5b-9. The expression of Klotho, transient receptor potential channel 6 (TRPC6), and cathepsin L (CatL); its substrate synaptopodin; and the intracellular Ca2+ concentration were detected via immunofluorescence. RhoA/ROCK pathway activity was measured by an activity quantitative detection kit, and the protein expression of phosphorylated-LIMK1 (p-LIMK1) and p-cofilin in podocytes was detected via Western blotting. Klotho knockdown and overexpression were performed to evaluate its role in regulating the TRPC6/CatL pathway.

RESULTS

PHN rats exhibited proteinuria, podocyte foot process effacement, decreased Klotho and Synaptopodin levels, and increased TRPC6 and CatL expression. The RhoA/ROCK pathway was activated by the increased phosphorylation of LIMK1 and cofilin. Similar changes were observed in C5b-9-injured podocytes. Klotho knockdown exacerbated podocyte injury, while Klotho overexpression partially ameliorated podocyte injury.

CONCLUSION

Klotho may protect against podocyte injury in IMN patients by inhibiting the TRPC6/CatL pathway. Klotho is a potential target for reducing proteinuria in IMN patients.

The influence of Klotho protein and prooxidant-antioxidant balance combination on the mortality of HD patients

PURPOSE

End-stage renal disease patients on chronic hemodialysis (HD) have a shortened life expectancy compared to the general population. The aim of this study was to evaluate a possible link between three new and emerging factors in renal pathophysiology: Klotho protein, telomere length in peripheral blood mononuclear cells (TL) and redox status parameters before HD (bHD) and after HD (aHD), and to test mortality prediction capability of these emerging parameters in a population of HD patients.

METHODS

The study included 130 adult patients with average age 66 (54-72), on HD (3 times per week; 4-5 h per session). Klotho level, TL, routine laboratory parameters, dialysis adequacy and redox status parameters: advanced oxidation protein products (AOPP), prooxidant-antioxidant balance (PAB), superoxide anion (O2.-), malondialdehyde (MDA), ischemia-modified albumin (IMA), total sulfhydryl group content (SHG), and superoxide dismutase (SOD) were determined.

RESULTS

Klotho concentration was significantly higher aHD; 68.2 (22.6-152.9) vs. bHD 64.2 (25.5-119.8) (p = 0.027). The observed increase in TL was not statistically significant. AOPP, PAB, SHG, and SOD activity were significantly increased aHD (p > 0.001). The patients with the highest mortality risk score (MRS) had significantly higher PAB bHD (p = 0.002). Significantly lower O2.- (p < 0.001), SHG content (p = 0.072), and IMA (p = 0.002) aHD were found in patients with the lowest MRS values. Principal component analysis revealed redox balance-Klotho factor as a significant predictor of high mortality risk (p = 0.014).

CONCLUSION

Decreased Klotho and TL attrition as well as redox status disturbance could be connected with higher mortality rate in HD patients.

Vitamin D and cancer

The role of vitamin D in the prevention of chronic diseases including cancer, has received a great deal of attention during the past few decades. The term "Cancer" represents multiple disease states with varying biological complexities. The strongest link between vitamin D and cancer is provided by ecological and studies like observational, in preclinical models. It is apparent that vitamin D exerts diverse biological responses in a tissue specific manner. Moreover, several human factors could affect bioactivity of vitamin D. The mechanism(s) underlying vitamin D initiated anti-carcinogenic effects are diverse and includes changes at the muti-system levels. The oncogenic environment could easily corrupt the traditional role of vitamin D or could ensure resistance to vitamin D mediated responses. Several researchers have identified gaps in our knowledge pertaining to the role of vitamin D in cancer. Further areas are identified to solidify the role of vitamin D in cancer control strategies.

Improving sleep quality is essential for enhancing soluble Klotho levels in hemodialysis patients

PURPOSE

Sleep and Klotho seem to share common physiological pathways in aging. However, studies investigating this relationship are very few and none of them was done with a specific patient group. The aim of this study was to investigate the association of sleep quality and soluble Klotho levels in hemodialysis patients.

METHODS

100 hemodialysis patients were included in this study. Soluble Klotho levels were obtained from each patient and Pittsburgh Sleep Quality Index was performed by all patients. Association of soluble Klotho with sleep quality was calculated.

RESULTS

Soluble Klotho levels were significantly inversely correlated with total sleep quality score (p < 0.001, r = - 0.444). Among the subscales, soluble Klotho levels were negatively correlated with subjective sleep quality (p < 0.001, r = - 0.365), sleep latency (p = 0.002, r = - 0.312), sleep disturbance (p = 0.002, r = - 0.303) and daytime dysfunction (p = 0.027, r = - 0.221). Patients who had good sleep quality scores were found to have higher soluble Klotho levels [4.15 (0.05-22.68) vs. 1.14 (0.32-17.63), p < 0.001]. In regression analysis, total sleep quality score, subjective sleep quality and age were found to be independent negative factors for soluble Klotho levels.

CONCLUSION

In this study, a significant association between sleep quality and soluble Klotho levels was revealed in hemodialysis patients. Improving sleep quality will lead to increased soluble Klotho levels, which may further slow down the aging process in hemodialysis patients.

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.

Association of Dietary Vitamin C Consumption with Serum Klotho Concentrations

BACKGROUND

Klotho is widely recognized as a protein that combats aging and possesses antioxidative characteristics, which have been implicated in the pathophysiology of numerous diseases. There is emerging evidence suggesting that the consumption of dietary nutrients, particularly those rich in antioxidants, could be associated with serum Klotho concentrations. Dietary vitamin C is one of the critical nutrients that possesses antioxidant properties. Nonetheless, the association between dietary vitamin C consumption and serum Klotho concentrations remains unclear.

OBJECTIVE

Aiming to evaluate the relationship between serum Klotho concentrations and dietary vitamin C consumption among Americans aged 40 to 79, we conducted a population-based study.

METHODS

From the National Health and Nutrition Examination Survey (NHANES) conducted between 2007 and 2016, a grand total of 11,282 individuals who met the criteria were selected as eligible participants for the study. Serum Klotho concentrations were measured using an ELISA kit that is commercially available. Trained interviewers evaluated the consumption of dietary vitamin C in the diet through a 24-hour dietary recall technique. A generalized linear model was used to evaluate the correlation between the consumption of dietary vitamin C in the diet and serum Klotho concentrations. Further examination was conducted using restricted cubic spline (RCS) analysis to explore the non-linear correlation between dietary vitamin C consumption in the diet and serum Klotho concentrations.

RESULTS

After accounting for possible confounding factors, serum Klotho concentrations rose by 1.17% (95% confidence interval (CI): 0.37%, 1.99%) with every standard deviation (SD) rise in dietary vitamin C consumption. With the first quintile of dietary vitamin C consumption as a reference, the percentage change of serum Klotho concentrations in the fifth quintile of dietary vitamin C consumption was 3.66% higher (95% CI: 1.05%, 6.32%). In older, normal-weight, and male participants, the subgroup analysis revealed a stronger correlation between dietary vitamin C consumption and serum Klotho concentrations. Analysis of RCS showed a linear positive association between dietary vitamin C consumption and the levels of serum Klotho concentrations.

CONCLUSION

The findings of this research indicate a strong and positive correlation between dietary vitamin C consumption and serum Klotho concentrations among the general adult population in the United States. Further studies are needed to validate the present findings and to explore specific mechanisms.

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.

Interaction of Klotho and sirtuins

OBJECTIVE

In this article, we review the articles that have reported the interaction between Klotho and sirtuins.

RECENT FINDINGS

Sirtuins are a family of histone deacetylase enzymes that are considered to be the main regulators of biological processes. This family is one of the essential factors for postponing aging and increasing the life span of organisms. Sirtuins play a role in regulating the function of various cellular processes such as cellular metabolism, oxidative stress, apoptosis, and inflammation. It has also been shown that various diseases are related to these enzymes. Klotho is an anti-aging protein that exists as a membrane protein as well as a soluble circulating form. The membrane type of this protein acts as a co-receptor of the FGF endocrine family. It has been shown that the Klotho gene is related to age-related diseases, including osteoporosis, coronary artery, brain diseases, diabetes, etc. At the same time, it is difficult to separate the actions of Klotho and endocrine FGFs. Several studies have shown that Klotho and sirtuins interact with each other at different regulatory levels. However, it is necessary to carry out more in-vivo investigations to create new windows towards the treatment or prevention of various diseases.

Emerging role of α-Klotho in energy metabolism and cardiometabolic diseases

BACKGROUND AND AIM

Klotho was first identified as a gene associated with aging and longevity in 1997. α-Klotho is an anti-aging protein and its role in energy metabolism, various cardiovascular diseases (CVDs), and metabolic disorders is increasingly being recognized. In this review, we aimed to outline the potential protective role and therapeutic prospects of α-Klotho in energy metabolism and cardiometabolic diseases (CMDs).

METHODS

We comprehensively reviewed the relevant literature in PubMed using the keywords 'Klotho', 'metabolism', 'cardiovascular', 'diabetes', 'obesity', 'metabolic syndrome', and 'nonalcoholic fatty liver disease'.

RESULTS

α-Klotho can be divided into membrane-bound Klotho, secreted Klotho, and the most studied circulating soluble Klotho that can act as a hormone. Klotho gene polymorphisms have been implicated in energy metabolism and CMDs. α-Klotho can inhibit insulin/insulin growth factor-1 signaling and its overexpression can lead to a 'healthy insulin resistance' and may exert beneficial effects on the regulation of glycolipid metabolism and central energy homeostasis. α-Klotho, mainly serum Klotho, has been revealed to be protective against CVDs, diabetes and its complications, obesity, and nonalcoholic fatty liver disease. Human recombinant Klotho protein/Klotho gene delivery, multiple drugs, or natural products, and exercise can increase α-Klotho expression.

CONCLUSION

Overall, α-Klotho has demonstrated its potential as a promising target for modulating energy metabolism and CMDs, and further research is needed to explore its utilization in clinical practice in the future.

Current and Emerging Markers and Tools Used in the Diagnosis and Management of Chronic Kidney Disease-Mineral and Bone Disorder in Non-Dialysis Adult Patients

Chronic kidney disease (CKD) is a significant public health concern associated with significant morbidity and has become one of the foremost global causes of death in recent years. A frequent comorbidity of CKD is secondary hyperparathyroidism (SHPT), exemplified by high serum parathyroid hormone (PTH) levels. The mineral metabolism disturbances resulting from CKD and progression to SHPT are currently considered part of the definition of chronic kidney disease-mineral and bone disorder (CKD-MBD). However, CKD-MBD does not only include abnormalities in laboratory-measured parameters; it is a complex condition characterized by dysregulation of bone turnover, mineralization, growth and strength, accompanied by vascular or another soft-tissue calcification. Together, this increases the risk of bone fractures, cardiovascular disease, and overall mortality in CKD-MBD patients. Monitoring serum markers is essential in diagnosing SHPT and CKD-MBD, and there are several recognized indicators for prognosis, optimal clinical management and treatment response in late-stage kidney disease patients receiving dialysis. However, far fewer markers have been established for patients with non-dialysis CKD. This review provides an overview of current and emerging markers and tools used in the diagnosis and management of CKD-MBD in non-dialysis adult patients.

Klotho and Fibroblast Growth Factor 23 Are Independent of Vitamin D, and Unlike Vitamin D, Are Not Associated With Graft- and Patient Survival After Kidney Transplantation

Short-term survival after kidney transplantation is excellent but long-term survival remains suboptimal. The aim of the study was to explore the relationship between soluble α-Klotho (sKlotho) and intact fibroblast growth factor 23 (iFGF23) measured 8 wk and 1 y posttransplant with long-term graft- and patient survival in a cohort of kidney transplant recipients with deficient and nondeficient vitamin D (25[OH]D) levels.

Methods

Vitamin D, sKlotho, and iFGF23 were measured 8 wk and 1 y posttransplant in 132 recipients transplanted between November 2012 and October 2013.

Results

Of the 132 kidney transplant recipients, 49 had deficient vitamin D levels (<30 nmol/L) and 83 had nondeficient vitamin D levels (≥30 nmol/L) at 8 wk posttransplant. The mean age was 51 y and the median follow-up was 7.4 y. At 1 y posttransplant, vitamin D increased significantly. There were no significant differences in sKlotho or iFGF23 levels between the 2 vitamin D groups neither at 8 wk nor 1 y. sKlotho increased significantly and iFGF23 decreased significantly in the whole cohort. During the follow-up, there were 36 graft losses (27%) and 27 deaths (20%). Ninety-four percent of the transplant recipients with nondeficient vitamin D levels were alive with a well-functioning graft after 5 y using Kaplan-Meier survival estimates, compared with 84% of the patients with deficient vitamin D levels (P = 0.014). Klotho and FGF23 levels did not influence graft- and patient survival.

Conclusions

In this nationwide cohort of kidney transplant recipients, long-term graft- and patient survival were significantly better in patients with vitamin D ≥30 nmol/L 8 wk posttransplant compared with those with vitamin D <30 nmol/L. sKlotho levels increased and iFGF23 levels decreased from 8 wk to 1 y posttransplant. Klotho and FGF23 levels were not associated with graft- and patient survival.

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.

Metformin: A New Inhibitor of the Wnt Signaling Pathway in Cancer

The biguanide drug metformin is widely used in type 2 diabetes mellitus therapy, due to its ability to decrease serum glucose levels, mainly by reducing hepatic gluconeogenesis and glycogenolysis. A considerable number of studies have shown that metformin, besides its antidiabetic action, can improve other disease states, such as polycystic ovary disease, acute kidney injury, neurological disorders, cognitive impairment and renal damage. In addition, metformin is well known to suppress the growth and progression of different types of cancer cells both in vitro and in vivo. Accordingly, several epidemiological studies suggest that metformin is capable of lowering cancer risk and reducing the rate of cancer deaths among diabetic patients. The antitumoral effects of metformin have been proposed to be mainly mediated by the activation of the AMP-activated protein kinase (AMPK). However, a number of signaling pathways, both dependent and independent of AMPK activation, have been reported to be involved in metformin antitumoral action. Among these, the Wingless and Int signaling pathway have recently been included. Here, we will focus our attention on the main molecular mechanisms involved.

The association of serum Klotho concentrations with hyperlipidemia prevalence and lipid levels among US adults: a cross-sectional study

BACKGROUND

Klotho has anti-oxidative and anti-inflammatory properties. However, little is known about whether high Klotho concentrations were associated with reduced hyperlipidemia risk and improved plasma lipid levels.

METHODS

Participants with complete data on serum Klotho and plasma lipid concentrations from the 2007-2016 National Health and Nutrition Examination Survey were included. Weighted regression models were fitted to explore the association of Klotho concentrations with hyperlipidemia risk and plasma lipid levels while restricted cubic spline models were applied to explore the dose-response relationship. Additionally, we assessed the mediating effects of C-reaction protein (CRP) on the foregoing association.

RESULTS

Individuals in the fourth and fifth quintile of serum Klotho had an adjusted odds ratio (OR) of 0.77 (95%CI: 0.65, 0.93) and 0.67 (95%CI: 0.65, 0.93) for hyperlipidemia. Doubling of serum Klotho concentrations was associated with decreased hyperlipidemia risk (OR = 0.81; 95%CI: 0.68, 0.95) and triglyceride levels (13.25 mg/dL; 95%CI: 4.02, 22.47), with a monotonic dose-response relationship. Individuals in the fourth and fifth quintile of serum Klotho had a 0.07 (95%CI: 0.002, 0.13), 0.08 (95%CI: 0.02, 0.15) and 0.05 (95%CI: -0.03, 0.12) mg/dL decreased CRP levels, with a marginally significant trend (Ptrend = 0.05).

CONCLUSIONS

Higher Klotho concentrations were associated with reduced hyperlipidemia risk and triglyceride levels. Klotho supplementation maybe a promising method to intervene and prevent hyperlipidemia, but the underlying mechanism should be further explored.

Klotho: A new therapeutic target in diabetic retinopathy?

Klotho (Kl) is considered an antiaging gene, mainly for the inhibition of the insulin-like growth factor-1 signaling. Kl exists as full-length transmembrane, which acts as co-receptor for fibroblast growth factor receptor, and in soluble forms (sKl). The sKl may exert pleiotropic effects on organs and tissues by regulating several pathways involved in the pathogenesis of diseases associated with oxidative and inflammatory state. In diabetic Patients, serum levels of Kl are significantly decreased compared to healthy subjects, and are related to duration of diabetes. In diabetic retinopathy (DR), one of the most common microvascular complications of type 2 diabetes, serum Kl levels are negatively correlated with progression of the disease. A lot of evidences showed that Kl regulates several mechanisms involved in maintaining homeostasis and functions of retinal cells, including phagocytosis, calcium signaling, secretion of vascular endothelial growth factor A (VEGF-A), maintenance of redox status, and melanin biosynthesis. Experimental data have been shown that Kl exerts positive effects on several mechanisms involved in onset and progression of DR. In particular, treatment with Kl: (1) Prevents apoptosis induced by oxidative stress in human retinal endothelial cells and in retinal pigment epithelium (RPE) cells; (2) reduces secretion of VEGF-A by RPE cells; and (3) decreases subretinal fibrosis and preserves autophagic activity. Therefore, Kl may become a novel biomarker and a good candidate for the treatment of DR.

Regulation of the Osteocyte Secretome with Aging and Disease

As the most numerous and long-lived of all bone cells, osteocytes have essential functions in regulating skeletal health. Through the lacunar-canalicular system, secreted proteins from osteocytes can reach cells throughout the bone. Furthermore, the intimate connectivity between the lacunar-canalicular system and the bone vasculature allows for the transport of osteocyte-secreted factors into the circulation to reach the entire body. Local and endocrine osteocyte signaling regulates physiological processes such as bone remodeling, bone mechanoadaptation, and mineral homeostasis. However, these processes are disrupted by impaired osteocyte function induced by aging and disease. Dysfunctional osteocyte signaling is now associated with the pathogenesis of many disorders, including chronic kidney disease, cancer, diabetes mellitus, and periodontitis. In this review, we focus on the targeting of bone and extraskeletal tissues by the osteocyte secretome. In particular, we highlight the secreted osteocyte proteins, which are known to be dysregulated during aging and disease, and their roles during disease progression. We also discuss how therapeutic or genetic targeting of osteocyte-secreted proteins can improve both skeletal and systemic health.

Fibroblast growth factor 23, klotho and heparin

PURPOSE OF REVIEW

Fibroblast growth factor (FGF) 23 is a bone-derived hormone that regulates phosphate and vitamin D metabolism by targeting the kidney. When highly elevated, such as in chronic kidney disease (CKD), FGF23 can also target the heart and induce pathologic remodeling. Here we discuss the mechanisms that underlie the physiologic and pathologic actions of FGF23, with focus on its FGF receptors (FGFR) and co-receptors.

RECENT FINDINGS

Klotho is a transmembrane protein that acts as an FGFR co-receptor for FGF23 on physiologic target cells. Klotho also exists as a circulating variant, and recent studies suggested that soluble klotho (sKL) can mediate FGF23 effects in cells that do not express klotho. Furthermore, it has been assumed that the actions of FGF23 do not require heparan sulfate (HS), a proteoglycan that acts as a co-receptor for other FGF isoforms. However, recent studies revealed that HS can be part of the FGF23:FGFR signaling complex and modulate FGF23-induced effects.

SUMMARY

sKL and HS have appeared as circulating FGFR co-receptors that modulate the actions of FGF23. Experimental studies suggest that sKL protects from and HS accelerates CKD-associated heart injury. However, the in vivo relevance of these findings is still speculative.

Genomically anchored vitamin D receptor mediates an abundance of bioprotective actions elicited by its 1,25-dihydroxyvitamin D hormonal ligand

The nuclear vitamin D receptor (VDR) mediates the actions of its physiologic 1,25-dihydroxyvitamin D3 (1,25D) ligand produced in kidney and at extrarenal sites during times of physiologic and cellular stress. The ligand-receptor complex transcriptionally controls genes encoding factors that regulate calcium and phosphate sensing/transport, bone remodeling, immune function, and nervous system maintenance. With the aid of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23), 1,25D/VDR primarily participates in an intricate network of feedback controls that govern extracellular calcium and phosphate concentrations, mainly influencing bone formation and mineralization, ectopic calcification, and indirectly supporting many fundamental roles of calcium. Beyond endocrine and intracrine effects, 1,25D/VDR signaling impacts multiple biochemical phenomena that potentially affect human health and disease, including autophagy, carcinogenesis, cell growth/differentiation, detoxification, metabolic homeostasis, and oxidative stress mitigation. Several health advantages conferred by 1,25D/VDR appear to be promulgated by induction of klotho, an anti-aging renal peptide hormone which functions as a co-receptor for FGF23 and, like 1,25D, regulates nrf2, foxo, mTOR and other cellular protective pathways. Among hundreds of genes for which expression is modulated by 1,25D/VDR either primarily or secondarily in a cell-specific manner, the resulting gene products (in addition to those expressed in the classic skeletal mineral regulatory tissues kidney, intestine, and bone), fall into multiple biochemical categories including apoptosis, cholesterol homeostasis, glycolysis, hypoxia, inflammation, p53 signaling, unfolded protein response and xenobiotic metabolism. Thus, 1,25D/VDR is a bone mineral control instrument that also signals the maintenance of multiple cellular processes in the face of environmental and genetic challenges.

Neuroprotective Role of Klotho on Dementia

Klotho, a gene found on chromosome 13q12, is involved in a variety of processes and signaling pathways in the human body related to vitamin D metabolism; cardiovascular, renal, musculoskeletal, and skin diseases; and cancer biology. However, more importantly, it has been linked to beneficial effects related to anti-aging. The levels of soluble Klotho in the blood have been found to decline with age, increasing the risk of age-related diseases. When the Klotho gene was silenced or defective, it caused a shorter lifespan. However, when the gene was overexpressed, it resulted in a longer lifespan. Klotho has positive benefits on the neurological system by causing a higher representation of useful longevity genes, preventing further neuronal damage, and offering neuroprotection. Thus, it has the potential to become a new treatment for many age-related diseases that cause dementia, including multiple sclerosis, Alzheimer's disease, and Parkinson's disease. In this review, we discuss the mechanisms of Klotho's benefits and roles on various organ systems, specifically on nervous system disorders that lead to dementia.

Anti-Inflammatory Klotho Protein Serum Concentration Correlates with Interferon Gamma Expression Related to the Cellular Activity of Both NKT-like and T Cells in the Process of Human Aging

Klotho is a beta-glucuronidase that reveals both anti-inflammatory and anti-oxidative properties that have been associated with mechanisms of aging. The study aimed to analyze the relationships between the serum concentration of soluble α-Klotho and cellular activity of two populations of lymphocytes; T and NKT-like cells corresponding to the level of cytokine secretion; i.e., IFN-γ, TNF-α, and IL-6. The studied population comprised three age groups: young individuals ('young'), seniors aged under 85 ('old'), and seniors aged over 85 ('oldest'). Both NKT-like and T cells were either non-cultured or cultured for 48 h and stimulated appropriately with IL-2, LPS or PMA with ionomycin to compare with unstimulated control cells. In all studied age groups non-cultured or cultured NKT-like cells revealed higher expressions of TNF-α, IL-6, and IFN-γ than T cells. α-Klotho concentration in serum decreased significantly in the process of aging. Intriguingly, only IFN-γ expression revealed a positive correlation with α-Klotho protein serum concentration in both non-cultured and cultured T and NKT-like cells. Since IFN-γ is engaged in the maintenance of immune homeostasis, the observed relationships may indicate the involvement of α-Klotho and cellular IFN-γ expression in the network of adaptive mechanisms developed during the process of human aging.

Klotho alleviates contrast-induced acute kidney injury by suppressing oxidative stress, inflammation, and NF-KappaB/NLRP3-mediated pyroptosis

BACKGROUND

Contrast-induced acute kidney injury (CI-AKI) is a common complication following percutaneous coronary intervention in coronary artery disease (CAD) patients with >30% incidence. Klotho is a multifunctional protein that inhibits oxidative stress and inflammation, but its role in CI-AKI is poorly understood. The present study aimed to explore the effects of klotho in CI-AKI.

METHODS

Six-week-old mice and HK-2 were divided into the control, contrast medium (CM), CM + klotho, and klotho groups. H&E staining evaluated kidney injury. Scr and BUN showed renal function. DHE probe and ELISA kit detected the levels of reactive oxygen species (ROS) in kidney tissue, superoxide dismutase (SOD), and malondialdehyde (MDA) in serum. Western blot detected the expressions of NF-κB and phosphorylated NF-κB (p-NF-κB) and pyroptosis-related protein levels of NLRP3, caspase-1, GSDMD, and cleaved-GSDMD in the kidney of CI-AKI mice. CCK-8 and lactate dehydrogenase (LDH) activity assays determined cell viability and damage. Fluorescent probe dichloro-dihydro-fluorescein diacetate (DCFH-DA) and enzyme-linked immunosorbent assay (ELISA) tested oxidative stress-related indicators. These included intracellular reactive oxygen species (ROS), superoxidase dismutase (SOD), and malondialdehyde (MDA). IL-6, TNF-α, IL-1β, and IL-18 in the cell supernatant were tested by ELISA assay and used to reflect inflammation responses. Propidium iodide (PI) staining showed the cell death of HK-2. The expressions of NF-κB, p-NF-κB and pyroptosis-related protein levels of NLRP3, caspase-1, GSDMD, and cleaved-GSDMD were detected by Western blot.

RESULTS

Exogenous klotho administration reduced kidney histopathological alterations and improved renal function in vivo. The levels of reactive oxygen species (ROS) in renal tissue, superoxide dismutase (SOD), and malondialdehyde (MDA) in serum decreased after the klotho intervention. The expression levels of p-NF-κB and pyroptosis-related proteins, including NLRP3, caspase-1, GSDMD, and cleaved-GSDMD, were decreased in CI-AKI mice after the klotho intervention. In vitro, klotho significantly inhibited CM-induced oxidative stress and the production of IL-6 and TNF-α. Moreover, it was found that klotho inhibited the activation of p-NF-κB and down-regulated pyroptosis-related protein (NLRP3, caspase-1, GSDMD, and cleaved-GSDMD).

CONCLUSION

Klotho has a protective effect on CI-AKI via suppressing oxidative stress, inflammation, and NF-κB/NLRP3-mediated pyroptosis that contributes to the potential therapy of CI-AKI.

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

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