Klotho: a novel regulator of calcium and phosphorus homeostasis

Mechanism of NLRP3 Inflammasome in Epilepsy and Related Therapeutic Agents

Epilepsy is one of the most widespread and complex diseases in the central nervous system (CNS), affecting approximately 65 million people globally, an important factor resulting in neurological disability-adjusted life year (DALY) and progressive cognitive dysfunction. Medication is the most essential treatment. The currently used drugs have shown drug resistance in some patients and only control symptoms; the development of novel and more efficacious pharmacotherapy is imminent. Increasing evidence suggests neuroinflammation is involved in the occurrence and development of epilepsy, and high expression of NLRP3 inflammasome has been observed in the temporal lobe epilepsy (TLE) brain tissue of patients and animal models. The inflammasome is a crucial cause of neuroinflammation by activating IL-1β and IL-18. Many preclinical studies have confirmed that regulating NLRP3 inflammasome pathway can prevent the development of epilepsy, reduce the severity of epilepsy, and play a neuroprotective role. Therefore, regulating NLRP3 inflammasome could be a potential target for epilepsy treatment. In summary, this review describes the priming and activation of inflammasome and its biological function in the progression of epilepsy. In addition, we reviewes the current pharmacological researches for epilepsy based on the regulation of NLRP3 inflammasome, aiming to provide a basis and reference for developing novel antiepileptic drugs.

Targeting neuroendocrine abnormalities in Parkinson's disease with exercise

Parkinson's Disease (PD) is a prevalent and complex age-related neurodegenerative condition for which there are no disease-modifying treatments currently available. The pathophysiological process underlying PD remains incompletely understood but increasing evidence points to multiple system dysfunction. Interestingly, the past decade has produced evidence that exercise not only reduces signs and symptoms of PD but is also potentially neuroprotective. Characterizing the mechanistic pathways that are triggered by exercise and lead to positive outcomes will improve understanding of how to counter disease progression and symptomatology. In this review, we highlight how exercise regulates the neuroendocrine system, whose primary role is to respond to stress, maintain homeostasis and improve resilience to aging. We focus on a group of hormones - cortisol, melatonin, insulin, klotho, and vitamin D - that have been shown to associate with various non-motor symptoms of PD, such as mood, cognition, and sleep/circadian rhythm disorder. These hormones may represent important biomarkers to track in clinical trials evaluating effects of exercise in PD with the aim of providing evidence that patients can exert some behavioral-induced control over their disease.

Effects of Multiwall Carbon Nanotubes on Premature Kidney Aging: Biochemical and Histological Analysis

Carbon nanotubes (CNTs) have gained much attention due to their superb properties, which make them promising options for the reinforcing composite materials with desirable mechanical properties. However, little is known about the linkage between lung exposure to nanomaterials and kidney disease. In this study, we compared the effects on the kidneys and aging for two different types of multiwall carbon nanotubes (MWCNTs): pristine MWCNTs (PMWCNTs) and acid-treated MWCNTs (TMWCNTs), with TMWCNTs being the preferred form for use as a composite material due to its superior dispersion properties. We used tracheal instillation and maximum tolerated dose (MTD) for both types of CNTs. MTD was determined as a 10% weight loss dose in a 3-month subchronic study, and the appropriate dosage for 1-year exposure was 0.1 mg/mouse. Serum and kidney samples were analyzed using ELISA, Western blot, and immunohistochemistry after 6 months and 1 year of treatment. PMWCNT-administered mice showed the activation of pathways for inflammation, apoptosis, and insufficient autophagy, as well as decreased serum Klotho levels and increased serum levels of DKK-1, FGF-23, and sclerostin, while TMWCNTs did not. Our study suggests that lung exposure to PMWCNTs can induce premature kidney aging and highlights a possible toxic effect of using MWCNTs on the kidneys in the industrial field, further highlighting that dispersibility can affect the toxicity of the nanotubes.

The expression of anti-aging protein Klotho is increased during neural differentiation of bone marrow-derived mesenchymal stem cells

Klotho, as an antiaging protein, is involved in the maintenance and differentiation of neuronal or glial cells and, therefore, has been noticed as a potential therapeutic target for neurodegenerative disorders. Expression of Klotho has been examined in different cells and organs, however, our information about the developmental pattern of this protein during differentiation of mesenchymal stem cells (MSCs) into neuron-like cells is limited. In this study, we conducted neural differentiation of mouse bone marrow-derived-MSCs and monitored the expression of Klotho together with selected neuron-specific genes at messenger RNA (mRNA) on days 7 and 14 of differentiation using quantitative real-time PCR. In addition, Klotho status at protein level was evaluated by immunocytochemistry. The results showed a significant change in the morphology of MSCs towards neuron-like cells. These changes were observed with progressive growth and formation of cell connections towards the formation of a chain of neuron-like cells which occurred in the second week of differentiation. Morphological changes were associated with a significant increase in the expression of neuron-specific genes like pax-6, neuN and, neurofilaments (NfL). Likewise, there was an increased expression of Klotho mRNA, and accumulation of Klotho protein in neuronal cell bodies, during the cellular differentiation of MSCs. These findings provided new evidence that neuronal differentiation from the MSCs is associated with increased expression of Klotho. These data may provide insight into the importance of Klotho protein in stem cell differentiation and regeneration in response to cell death in the central nervous system.

The Interrelated Multifactorial Actions of Cortisol and Klotho: Potential Implications in the Pathogenesis of Parkinson's Disease

The pathogenesis of Parkinson's disease (PD) is complex, multilayered, and not fully understood, resulting in a lack of effective disease-modifying treatments for this prevalent neurodegenerative condition. Symptoms of PD are heterogenous, including motor impairment as well as non-motor symptoms such as depression, cognitive impairment, and circadian disruption. Aging and stress are important risk factors for PD, leading us to explore pathways that may either accelerate or protect against cellular aging and the detrimental effects of stress. Cortisol is a much-studied hormone that can disrupt mitochondrial function and increase oxidative stress and neuroinflammation, which are recognized as key underlying disease mechanisms in PD. The more recently discovered klotho protein, considered a general aging-suppressor, has a similarly wide range of actions but in the opposite direction to cortisol: promoting mitochondrial function while reducing oxidative stress and inflammation. Both hormones also converge on pathways of vitamin D metabolism and insulin resistance, also implicated to play a role in PD. Interestingly, aging, stress and PD associate with an increase in cortisol and decrease in klotho, while physical exercise and certain genetic variations lead to a decrease in cortisol response and increased klotho. Here, we review the interrelated opposite actions of cortisol and klotho in the pathogenesis of PD. Together they impact powerful and divergent mechanisms that may go on to influence PD-related symptoms. Better understanding of these hormones in PD would facilitate the design of effective interventions that can simultaneously impact the multiple systems involved in the pathogenesis of PD.

Soluble klotho as an effective biomarker to characterize inflammatory states

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

α-Klotho, Plasma Asymmetric Dimethylarginine, and Kidney Disease Progression

Rationale & Objective

We aimed to explore the associated factors of endothelial injury in chronic kidney disease (CKD) and the relationship between endothelial dysfunction and CKD prognosis.

Study Design

A prospective observational cohort study.

Setting & Participants

77 adults with CKD stages 1-5 were enrolled January 2010 to December 2010 and followed up until December 2015.

Exposure

Serum asymmetric dimethylarginine (ADMA) level at baseline, α-klotho, sodium-phosphorus synergistic transporter, and dimethylarginine-dimethylamine hydrolase expression in kidney biopsy samples.

Outcome

Initiation of kidney replacement therapy (KRT).

Analytical Approach

Kaplan-Meier analysis was used for evaluation of the incidence rate of KRT. All tests were 2 tailed, and statistical significance was defined as P < 0.05.

Results

Mean serum ADMA level of 77 patients was 64.3 ± 34.6 ng/mL. ADMA level increased with CKD stages (P = 0.06) and declining kidney function (r = −0.267; P = 0.02). The expression of α-klotho in kidney biopsy specimens also decreased. Median follow-up time was 56 (interquartile range, 50.5-62) months. Kaplan-Meier analyses showed that during a total follow-up of 6 years, the incidence of KRT initiation in the high-ADMA group was significantly higher than that in the low group (35.9% vs 13.2%; P = 0.03). ADMA level was negatively correlated with α-klotho (r = −0.233; P = 0.04) and positively correlated with phosphorus level (r = 0.243; P = 0.04). The expression of sodium-phosphorus synergistic transporter in kidney tubules, which promoted phosphorus reabsorption, and the expression of dimethylarginine-dimethylamine hydrolase isoform 1, which regulated ADMA, were decreased. Correlation analysis also showed that ADMA level decreased while age increased at baseline (r = −0.292; P = 0.01).

Limitations

Small sample size with limited longer-term follow-up.

Conclusions

Serum ADMA levels increased as kidney function declined, and high serum ADMA level was associated with incident kidney failure. Low tissue α-klotho and high levels of plasma phosphorus or tissue expression of type II sodium/phosphate cotransporter in the kidney are associated with higher circulating ADMA levels, suggesting that they may be involved in the pathogenesis of endothelial dysfunction in patients with CKD.

Genistein regulates calcium and phosphate homeostasis without activation of MEK 1/2 signalling pathway in an animal model of the andropause

Soy isoflavone genistein interplays with numerous physiological or pathophysiological processes during ageing. However, its protective role and underlying mechanisms of action in the regulation of calcium (Ca²⁺) and phosphate (Pi) homeostasis in an animal model of the andropause are yet to be fully clarified. Wistar male rats (16-month-old) were divided into sham-operated, orchidectomized, orchidectomized estradiol-treated (0.625 mg/kg b.m./day) and orchidectomized genistein-treated (30 mg/kg b.m./day) groups. Treatments were administered subcutaneously for 3 weeks, while the controls received vehicle alone. Estradiol treatment increased the expression level of fibroblast growth factor receptor (FGFR) and parathyroid hormone 1 receptor (PTH1R), and activated mitogen - activated protein kinase kinase 1/2 (MEK 1/2) signaling pathway in the kidneys. Genistein application induced a prominent gene and protein expression of Klotho and downregulated the expression of FGFR and PTH1R in the kidney of andropausal rats. Activation of protein kinase B (Akt) signalling pathway was observed, while MEK 1/2 signaling pathway wasn't altered after genistein treatment. The increase of 25 (OH) vitamin D in the serum and decrease in Ca²⁺ urine content was observed after genistein application. Our findings strongly suggest genistein as a potent biocompound with beneficial effects on the regulation of Ca²⁺ and Pi homeostasis, especially during aging process when the balance of mineral metabolism is impaired. These novel data provide closer insights into the physiological roles of genistein in the regulation of mineral homeostasis.

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.

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

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

Resveratrol Pretreatment Ameliorates Concanavalin A-Induced Advanced Renal Glomerulosclerosis in Aged Mice through Upregulation of Sirtuin 1-Mediated Klotho Expression

Aging kidneys are characterized by an increased vulnerability to glomerulosclerosis and a measurable decline in renal function. Evidence suggests that renal and systemic klotho and sirtuin 1 (SIRT1) deficiencies worsen kidney damage induced by exogenous stresses. The aim of this study was to explore whether resveratrol would attenuate concanavalin A (Con A)-induced renal oxidative stress and advanced glomerulosclerosis in aged mice. Aged male C57BL/6 mice were treated orally with resveratrol (30 mg/kg) seven times (12 h intervals) prior to the administration of a single tail-vein injection of Con A (20 mg/kg). The plasma and urinary levels of kidney damage markers were evaluated. The kidney histopathology, renal parameters, and oxidative stress levels were measured. Furthermore, klotho was downregulated in mouse kidney mesangial cells that were pretreated with 25 µM resveratrol followed by 20 µg/mL Con A. The urinary albumin/creatinine ratio, blood urea nitrogen, kidney mesangial matrix expansion, tubulointerstitial fibrosis, and renal levels of α-smooth muscle actin, transforming growth factor beta, fibronectin, procollagen III propeptide, and collagen type I significantly increased in Con A-treated aged mice. Aged mice kidneys also showed markedly increased levels of 8-hydroxydeoxyguanosine (8-OH-dG) and reactive oxygen species (ROS), with reduced superoxide dismutase activity and levels of glutathione, klotho, and SIRT1 after Con A challenge. Furthermore, in kidney mesangial cells, klotho silencing abolished the effects of resveratrol on the Con A-mediated elevation of the indices of oxidative stress and the expression of glomerulosclerosis-related factors. These findings suggest that resveratrol protects against Con A-induced advanced glomerulosclerosis in aged mice, ameliorating renal oxidative stress via the SIRT1-mediated klotho expression.

Denosumab-induced severe hypocalcaemia in a patient with vitamin D deficiency

Postmenopausal women are at increased risk of osteoporosis. Osteoporotic fractures carry an increased risk of morbidity and mortality. Denosumab is a monoclonal antibody widely used for the treatment of osteoporosis by inhibiting osteoclast-induced bone resorption. Hypocalcaemia is a known side-effect of denosumab treatment. The majority of such cases have been described in patients with underlying metastatic cancer or chronic kidney disease. We present a patient who developed severe hypocalcaemia after administration of denosumab in the context of severe vitamin D deficiency and a normal kidney function. The management was further complicated by hypophosphatemia. Following replacement of vitamin D, the patient's calcium and phosphate levels stabilised. The patient required intensive care monitoring for replacement of electrolytes. This case report emphasises the importance of screening and ongoing monitoring of risk factors for iatrogenic hypocalcaemia with denosumab treatment.

The prognostic value of soluble Klotho in patients with haemodialysis: a systematic review and meta-analysis

Aim:

The correlation between soluble Klotho (sKlotho) levels and clinical outcomes remains inconclusive for patients undergoing maintenance haemodialysis (MHD). We aimed to evaluate the potential predictive significance of sKlotho in this population by conducting a meta-analysis.

Methods:

PubMed, Embase, Web of Science and Cochrane Library were comprehensively searched for studies concerning the association between sKlotho level and clinical outcomes including cardiovascular (CV) events and all-cause mortality. The pooled hazard ratios (HR) and 95% confidence intervals (CI) were generated using either random or fixed effects models. Sensitivity and subgroup analyses were used to explore heterogeneity sources.

Results:

Eight prospective studies with 992 MHD participants were included and reduced sKlotho levels predicted more adverse outcomes in this meta-analysis. The pooled HRs and 95% CIs related to CV events, mortality, or composite outcomes were 1.73 (95% CI 1.08–2.76, p = 0.02), 2.34 (95% CI 1.34–2.07, p = 0.003) or 1.75 (95% CI 1.19–2.57, p = 0.005). Moderate heterogeneity was observed in the composite adverse outcomes (I² = 57%, p = 0.05). Age and sKlotho level were the main sources of heterogeneities in the subgroup analysis.

Conclusion:

Lower sKlotho levels were associated with more CV events and all-cause mortality, suggesting that sKlotho may have predictive value in CKD patients receiving haemodialysis.

Klotho: An Elephant in Aging Research

The year 2017 marked the 20th anniversary of the first publication describing Klotho. This single protein was and is remarkable in that its absence in mice conferred an accelerated aging, or progeroid, phenotype with a dramatically shortened life span. On the other hand, genetic overexpression extended both health span and life span by an impressive 30%. Not only has Klotho deficiency been linked to a number of debilitating age-related illnesses but many subsequent reports have lent credence to the idea that Klotho can compress the period of morbidity and extend the life span of both model organisms and humans. This suggests that Klotho functions as an integrator of organ systems, making it both a promising tool for advancing our understanding of the biology of aging and an intriguing target for interventional studies. In this review, we highlight advances in our understanding of Klotho as well as key challenges that have somewhat limited our view, and thus translational potential, of this potent protein.

Cardiovascular disease in dialysis patients

Cardiovascular disease (CVD) is a highly common complication and the first cause of death in patients with end-stage renal disease (ESRD) on haemodialysis (HD). In this population, mortality due to CVD is 20 times higher than in the general population and the majority of maintenance HD patients have CVD. This is likely due to ventricular hypertrophy as well as non-traditional risk factors, such as chronic volume overload, anaemia, inflammation, oxidative stress, chronic kidney disease–mineral bone disorder and other aspects of the ‘uraemic milieu’. Better understanding the impact of these numerous factors on CVD would be an important step for prevention and treatment. In this review we focus non-traditional CVD risk factors in HD patients.

Neferine Attenuates Acute Kidney Injury by Inhibiting NF-κB Signaling and Upregulating Klotho Expression

Purpose: Morbidity associated with and mortality from acute kidney injury (AKI) is gradually increasing, and no efficient drug is available. We explored whether neferine, a bisbenzylisoquinoline alkaloid, attenuated AKI, and the possible mechanisms in play in vivo and in vitro.

Methods: We induced AKI using ischemia-reperfusion (I/R) or lipopolysaccharide (LPS) in vivo. C57 BL/6 male mice were randomized into two groups each containing four subgroups: control, neferine, I/R or LPS, and I/R or LPS + neferine. Mice were sacrificed 24 h after AKI induction and kidneys and sera were collected. NRK-52E cells were exposed to hypoxia/reoxygenation (H/R) or LPS in vitro.

Results: Neferine pretreatment significantly alleviated kidney functional loss and pathological damage. In the AKI mouse models induced by I/R or LPS, neferine inhibited the infiltration of inflammatory cells, including granulocytes and macrophages. Both in vivo and in vitro, neferine attenuated apoptosis, suppressed inflammatory cytokine production, decreased degradation of IκB-α, and inhibited nuclear translocation of NF-κB. Furthermore, it also upregulated Klotho expression in AKI.

Conclusion: Neferine mitigated renal injury in AKI models, perhaps by suppressing the activation of NF-κB and upregulating the expression of Klotho.

Impaired function of fibroblast growth factor 23 / Klotho protein axis in prediabetes and diabetes mellitus: Promising predictor of cardiovascular risk

The discovery of clear molecular mechanisms of early cardiac and vascular complications in patients with prediabetes and known diabetes mellitus are core element of stratification at risk with predictive model creation further. Previous clinical studies have shown a pivotal role of impaired signaling axis of fibroblast growth factor 23 (FGF23), FGF23 receptor isoforms and its co-factor Klotho protein in cardiovascular (CV) complications in prediabetes and diabetes. Although there were data received in clinical studies, which confirmed a causative role of altered function of FGF-23/Klotho protein axis in manifestation of CV disease in prediabetes and type 2 diabetes mellitus (T2DM), the target therapy of these diseases directing on improvement of metabolic profiles, systemic and adipokine-relating inflammation by beneficial restoring of dysregulation in FGF-23/Klotho protein axis remain to be not fully clear. The aim of the review was to summarize findings regarding the role of impaired FGF-23/Klotho protein axis in developing CV complications in patients with prediabetes and type 2 diabetes mellitus. It has been elucidated that elevated levels of FGF-23 and deficiency of Klotho protein in peripheral blood are predictors of CV disease and CV outcomes in patients with (pre) diabetes, while predictive values of dynamic changes of the concentrations of these biomarkers require to be elucidated in detail in the future.

Administration of alpha klotho reduces liver and adipose lipid accumulation in obese mice

α-Klotho, a known anti-aging protein, exerts diverse physiological effects including: maintenance of phosphate and calcium homeostasis, modulation of cell proliferation, and enhanced buffering of reactive oxygen species. However, the role of α-Klotho in the regulation of energy metabolism is complex and poorly understood. Here we investigated the effects of 5 weeks peripheral administration of α-Klotho in high fat diet induced obese mice. Food intake, blood glucose, and body weight were measured daily. Energy expenditure was determined with indirect calorimetry and body composition with magnetic resonance imaging. Liver and adipose tissue were collected for lipid content measurements and gene expression analysis. α-Klotho-treated mice experienced reduced adiposity, increased lean mass, and elevated energy expenditure, despite no changes in food intake, body weight, or fed blood glucose levels. Lipid accumulation in liver and adipose tissue was also reduced compared to controls. Furthermore, Real-time quantitative PCR showed reduced expression of key lipogenic genes in α-Klotho treated mice in these organs. Taken together, these data suggest encouraging therapeutic potential of α-Klotho and highlight a need for further research into the specific mechanisms explaining improved body composition, elevated energy expenditure, and reduced lipid content in both liver and adipose tissue in α-Klotho-treated mice.

Rapid decline of kidney function in diabetic kidney disease is associated with high soluble Klotho levels

BACKGROUND

Klotho is found in two forms: a transmembrane form and a soluble form (s-Klotho). In order to be excreted, s-Klotho, that is too large to be filtered, will probably reach the proximal convoluted tubule by a transcytosis process. The aim of our study was to show the relationship between the levels of s-Klotho and tubular injury in patients with diabetic kidney disease (DKD), using as tubular injury marker the kidney injury molecule-1 (KIM-1).

METHODS

Our study included 63 DKD patients (stages 1-5, mean eGFR 65.15±32.45ml/min) with a mean age 58.13±12 years. In all patients we determined serum levels of: KIM-1 and s-Klotho using ELISA, urinary albumin/creatinine ratio (UACR) and reduction in the estimated glomerular filtration rate (eGFR) per year.

RESULTS

We found a strong statistically significant correlation of s-Klotho with the rate of reduction of eGFR/year (r=0.714, p=0.0004) and with the tubular injury marker KIM-1 (r=0.758, p=0.005) and strong correlations of UACR with the rate of reduction of eGFR/year (r=0.53, p<0.01), KIM-1 (r=0.49, p<0.05) and s-Klotho (r=0.52, p<0.01).

CONCLUSION

Despite previous published data, that shows a decrease of s-Klotho in chronic kidney disease, in our study the rapid annual decline of kidney function but not the level of eGFR was associated with increased s-Klotho. A possible explanation could be a more severe proximal tubule injury that could lead to a reduction of tubular excretion of s-Klotho as suggested by the correlation of s-Klotho levels with the serum levels of KIM-1.

Daidzein upregulates anti-aging protein Klotho and NaPi 2a cotransporter in a rat model of the andropause

In a rat model of the andropause we aimed to examine the influence of daidzein, soy isoflavone, on the structure and function of parathyroid glands (PTG) and the expression levels of some of the crucial regulators of Ca²⁺ and Pi homeostasis in the kidney, and to compare these effects with the effects of estradiol, serving as a positive control. Middle-aged (16-month-old) male Wistar rats were divided into the following groups: sham-operated (SO), orchidectomized (Orx), orchidectomized and estradiol-treated (Orx+E; 0.625mg/kg b.w./day, s.c.) as well as orchidectomized and daidzein-treated (Orx+D; 30mg/kg b.w./day, s.c.) group. Every treated group had a corresponding control group. PTH serum concentration was decreased in Orx+E and Orx+D groups by 10% and 21% (p<0.05) respectively, in comparison with the Orx. PTG volume was decreased in Orx+E group by 16% (p<0.05), when compared to the Orx. In Orx+E group expression of NaPi 2a was lower (p<0.05), while NaPi 2a abundance in Orx+D animals was increased (p<0.05), when compared to Orx. Expression of PTH1R was increased (p<0.05) in Orx+E group, while in Orx+D animals the same parameter was decreased (p<0.05), in comparison with Orx. Klotho expression was elevated (p<0.05) in Orx+D rats, in regard to Orx. Orx+D induced reduction in Ca²⁺/creatinine and Pi/creatinine ratio in urine by 32% and 16% (p<0.05) respectively, in comparison with Orx. In conclusion, presented results indicate the more coherent beneficial effects of daidzein compared to estradiol, on disturbed Ca²⁺ and Pi homeostasis, and presumably on bone health, in the aging male rats.

Role of Bisphosphonates in Vascular calcification and Bone Metabolism: A Clinical Summary

Background:

Vascular calcification is known to be a strong risk factor for cardiovascularadverse events and mortality. Atherosclerosis, diabetes, aging, abnormal bone mineral homeostasisand high uremic milieu such as chronic kidney disease are major factors that contribute to theprogression of vascular calcification. Several mechanisms such as the osteoblastic transition of vascularsmooth muscle cells in response to oxidative stress have shed light on the active nature ofvascular calcification, which was once thought to be a passive process. The fine interplay of regulatoryfactors such as PTH, vitamin D3, FGF 23 and klotho reflect the delicate balance between vascularcalcification and bone mineralization. Any disturbance affecting this equilibrium of the bonemineral-vascular axis results in accelerated vascular calcification.

Bisphosphonates share similar mechanism of action as statins, and hence several studies were undertakenin humans to verify if the benefits proven to be obtained in animal models extended tohuman models too. This yielded conflicting outcomes which are outlined in this review. This wasattributed mainly to inadequate sample size and flaws in the study design. Therefore, this benefitcan only be ascertained if studies addressing this are undertaken.

Conclusion:

This review seeks to highlight the pathophysiologic phenomena implicated in vascular and valvular calcification and summarize the literature available regarding the use of bisphosphonates in animal and human models. We also discuss novel treatment approaches for vascular calcification,with emphasis on chronic kidney disease and calciphylaxis.

Sex steroids and the kidney: role in renal calcium and phosphate handling

Calcium and phosphate are vital for the organism and constitute essential components of the skeleton. Serum levels are tightly hormonally regulated and maintained by exchange with three major sources: the intestines, the kidney and the bone. The effects of sex steroids on the bone have been extensively studied and it is well known that sex steroid deficiency induces bone loss, indirectly influencing renal calcium and phosphate homeostasis. However, it is unknown whether sex steroids also directly regulate renal calcium and phosphate handling, hereby potentially indirectly impacting on bone. The presence of androgen receptors (AR) and estrogen receptors (ER) in both human and rodent kidney, although their exact localization within the kidney remains debated, supports direct effects. Estrogens stimulate renal calcium reabsorption as well as phosphate excretion, while the effects of androgens are less clear. Many of the studies performed with regard to renal calcium and/or phosphate homeostasis do not correct for the calcium and phosphate fluxes from the bone and intestines, which complicates the differentiation between the direct effects of sex steroids on renal calcium and phosphate handling and the indirect effects via the bone and intestines. The objective of this study is to review the literature and current insight of the role of sex steroids in calcium and phosphate handling in the kidney.

P2X7 receptor and klotho expressions in diabetic nephropathy progression

Diabetes mellitus is characterized by increased levels of reactive oxygen species (ROS), leading to high levels of adenosine triphosphate (ATP) and the activation of purinergic receptors (P2X₇), which results in cell death. Klotho was recently described as a modulator of oxidative stress and as having anti-apoptotic properties, among others. However, the roles of P2X₇ and klotho in the progression of diabetic nephropathy are still unclear. In this context, the aim of the present study was to characterize P2X₇ and klotho in several stages of diabetes in rats. Diabetes was induced in Wistar rats by streptozotocin, while the control group rats received the drug vehicle. From the 1st to 8th weeks after the diabetes induction, the animals were placed in metabolic cages on the 1st day of each week for 24 h to analyze metabolic parameters and for the urine collection. Then, blood samples and the kidneys were collected for biochemical analysis, including Western blotting and qPCR for P2X₇ and klotho. Diabetic rats presented a progressive loss of renal function, with reduced nitric oxide and increased lipid peroxidation. The P2X₇ and klotho expressions were similar up to the 4th week; then, P2X₇ expression increased in diabetes mellitus (DM), but klotho expression presented an opposite behavior, until the 8th week. Our data show an inverse correlation between P2X₇ and klotho expressions through the development of DM, which suggests that the management of these molecules could be useful for controlling the progression of this disease and diabetic nephropathy.

Targeted inhibition of Klotho binding to fibroblast growth factor 23 prevents hypophosphetemia

Klotho is a transmembrane protein which plays significant role in the pathogenesis of phosphate ion (Pi)-related disorders. Pi accumulation in human kidney tissues results in the major metabolic disorders due to malfunctioning of Klotho-FGFR1-FGF23 trimeric complex. The potential role of Klotho in Pi metabolism was elaborated through modeling and interaction analysis of glycosyl hydrolase (GS1 and GS2) domains with Fibroblast growth factor 23 (FGF23). In order to inhibit the association of Klotho and FGF23, binding patterns of three reported hits (N-(2-chlorophenyl)-1H-indole-3-carboxamide, N-[2-(1-cyclohexen-1-yl)ethyl]-6,7,8,9-tetrahydropyrido[1,2-e]purin-4-amine and 2-(1-propyl)amino-11-chlorothiazolo[5,4-a]acridine) were evaluated through molecular docking analysis. These inhibitors effectively targeted both GS1 and GS2 domains of Klotho at the similar sites required for FGF23 binding. To further characterize the comparative binding profile of these compounds, molecular dynamics simulation assays were performed. Taken together, current study emphasizes that Klotho may be anticipated as a target molecule in familial hypophosphatemic rickets and mentioned compounds may prove to be effective therapeutic targets against hypophosphetemia induced disorders.

Soluble klotho binds monosialoganglioside to regulate membrane microdomains and growth factor signaling

Soluble klotho, the shed ectodomain of the antiaging membrane protein α-klotho, is a pleiotropic endocrine/paracrine factor with no known receptors and poorly understood mechanism of action. Soluble klotho down-regulates growth factor-driven PI3K signaling, contributing to extension of lifespan, cardioprotection, and tumor inhibition. Here we show that soluble klotho binds membrane lipid rafts. Klotho binding to rafts alters lipid organization, decreases membrane's propensity to form large ordered domains for endocytosis, and down-regulates raft-dependent PI3K/Akt signaling. We identify α2-3-sialyllactose present in the glycan of monosialogangliosides as targets of soluble klotho. α2-3-Sialyllactose is a common motif of glycans. To explain why klotho preferentially targets lipid rafts we show that clustering of gangliosides in lipid rafts is important. In vivo, raft-dependent PI3K signaling is up-regulated in klotho-deficient mouse hearts vs. wild-type hearts. Our results identify ganglioside-enriched lipid rafts to be receptors that mediate soluble klotho regulation of PI3K signaling. Targeting sialic acids may be a general mechanism for pleiotropic actions of soluble klotho.

New Insights into the Mechanism of Action of Soluble Klotho

The klotho gene encodes a type I single-pass transmembrane protein that contains a large extracellular domain, a membrane spanning segment, and a short intracellular domain. Klotho protein exists in several forms including the full-length membrane form (mKl) and a soluble circulating form [soluble klotho (sKl)]. mKl complexes with fibroblast growth factor receptors to form coreceptors for FGF23, which allows it to participate in FGF23-mediated signal transduction and regulation of phosphate and calcium homeostasis. sKl is present in the blood, urine, and cerebrospinal fluid where it performs a multitude of functions including regulation of ion channels/transporters and growth factor signaling. How sKl exerts these pleiotropic functions is poorly understood. One hurdle in understanding sKl's mechanism of action as a "hormone" has been the inability to identify a receptor that mediates its effects. In the body, the kidneys are a major source of sKl and sKl levels decline during renal disease. sKl deficiency in chronic kidney disease makes the heart susceptible to stress-induced injury. Here, we summarize the current knowledge of mKl's mechanism of action, the mechanistic basis of sKl's protective, FGF23-independent effects on the heart, and provide new insights into the mechanism of action of sKl focusing on recent findings that sKl binds sialogangliosides in membrane lipid rafts to regulate growth factor signaling.

Klotho/FGF23 Axis in Chronic Kidney Disease and Cardiovascular Disease

BACKGROUND

Membrane αKlotho (hereinafter called Klotho) is highly expressed in the kidney and functions as a coreceptor of FGF receptors (FGFRs) to activate specific fibroblast growth factor 23 (FGF23) signal pathway. FGF23 is produced in bones and participates in the maintenance of mineral homeostasis. The extracellular domain of transmembrane Klotho can be cleaved by secretases and released into the circulation as soluble Klotho. Soluble Klotho does not only weakly activate FGFRs to transduce the FGF23 signaling pathway, but also functions as an enzyme and hormonal substance to play a variety of biological functions. FGF23 exerts its biological effects through activation of FGFRs in a Klotho-dependent manner. However, extremely high FGF23 can exert its pathological action in a Klotho-independent manner.

SUMMARY

The decline in serum and urinary Klotho followed by a rise in serum FGF23 at an early stage of chronic kidney disease (CKD) functions as an early biomarker for kidney dysfunction and can also serve as a predictor for risk of cardiovascular disease (CVD) and mortality in both CKD patients and the general population. Moreover, Klotho deficiency is a pathogenic factor for CKD progression and CVD. FGF23 may also contribute to CVD. Prevention of Klotho decline, reactivation of endogenous Klotho production, or supplementation of exogenous Klotho attenuate renal fibrosis, retard CKD progression, improve mineral metabolism, ameliorate cardiomyopathy, and alleviate vascular calcification in CKD. However, the poor CVD outcome after depletion of FGF23 with FGF23 antibody stimulates the generation of a more specific inhibitor of FGF23 for CKD treatment.

KEY MESSAGE

Klotho/FGF23 may not only be diagnostic and/or prognostic biomarkers for CKD and CVD, but are also pathogenic contributors to CKD progression and CVD development. The Klotho/FGF23 axis should be a novel target for renal clinics.

Klotho-Dependent Cellular Transport Regulation

Klotho is a transmembrane protein that in humans is encoded by the hKL gene. This protein is known to have aging suppressor effects and is predominantly expressed in the distal convoluted tubule of the kidney, parathyroid glands, and choroid plexus of the brain. The Klotho protein exists in both full-length membrane form and a soluble secreted form, which exerts numerous distinct functions. The extracellular domain of Klotho can be enzymatically cleaved off and released into the systemic circulation where it functions as β-glucuronidase and a hormone. Soluble Klotho is a multifunction protein present in the biological fluids including blood, urine, and cerebrospinal fluid of mammals. Klotho deficiency leads to multiple organ failure accompanied by early appearance of multiple age-related disorders and early death, whereas overexpression of Klotho results in the opposite effects. Klotho, an enzyme and hormone, has been reported to participate in the regulation of cellular transport processes across the plasma membrane either indirectly through inhibiting calcitriol (1,25(OH)2D3) formation or other mechanism, or by directly affecting transporter proteins, including ion channels, cellular carriers, and Na(+)/K(+)-ATPase. Accordingly, Klotho protein serves as a powerful regulator of cellular transport across the plasma membrane. Importantly, Klotho-dependent cellular transport regulation implies stimulatory or inhibitory effects. Klotho has been shown to play a key role in the regulation of multiple calcium and potassium ion channels, and various cellular carriers including the Na(+)-coupled cotransporters such as NaPi-IIa, NaPi-IIb, EAAT3, and EAAT4, CreaT1 as well as Na(+)/K(+)-ATPase. These regulations are parts of the antiaging function of Klotho, which will be discussing throughout this chapter. Clearly, further experimental efforts are required to investigate the effect of Klotho on other transport proteins and underlying molecular mechanisms by which Klotho exerts its effect.

Renal Production, Uptake, and Handling of Circulating αKlotho

αKlotho is a multifunctional protein highly expressed in the kidney. Soluble αKlotho is released through cleavage of the extracellular domain from membrane αKlotho by secretases to function as an endocrine/paracrine substance. The role of the kidney in circulating αKlotho production and handling is incompletely understood, however. Here, we found higher αKlotho concentration in suprarenal compared with infrarenal inferior vena cava in both rats and humans. In rats, serum αKlotho concentration dropped precipitously after bilateral nephrectomy or upon treatment with inhibitors of αKlotho extracellular domain shedding. Furthermore, the serum half-life of exogenous αKlotho in anephric rats was four- to five-fold longer than that in normal rats, and exogenously injected labeled recombinant αKlotho was detected in the kidney and in urine of rats. Both in vivo (micropuncture) and in vitro (proximal tubule cell line) studies showed that αKlotho traffics from the basal to the apical side of the proximal tubule via transcytosis. Thus, we conclude that the kidney has dual roles in αKlotho homeostasis, producing and releasing αKlotho into the circulation and clearing αKlotho from the blood into the urinary lumen.

Serum klotho: relation to fibroblast growth factor-23 and other regulators of phosphate metabolism in children with chronic kidney disease

FGF23 and Klotho synergize to regulate phosphate homeostasis by promoting renal phosphate excretion. Chronic kidney disease (CKD) may be viewed as a state of FGF23 resistance caused by Klotho deficiency. This viewpoint explains several observations on phosphate metabolism in CKD that lack mechanistic insights. Our objectives were to correlate serum klotho and FGF-23 with other variables that regulate phosphate metabolism. We studied 40 patients with CKD on conservative treatment (group A), 44 patients with end-stage renal disease (ESRD) on regular hemodialysis (group B), 40 kidney transplant recipients (KTR) (group C) and 40 healthy controls for measuring serum klotho and FGF-23. Blood samples were withdrawn for measuring the levels of serum Calcium (Ca), Phosphorus (P), alkaline phosphatase (ALP), 1,25 (OH)2 D3, intact parathyroid hormone (PTH), FGF-23 and α klotho. The mean levels of FGF-23 and α klotho in control group were 225.78 ± 111.05 pg/ml (range: 102.4, 418.5) and 6.78 ± 1.90 ng/ml (range: 4, 11), respectively. The mean levels of FGF-23 in the 3 studied groups were 1,034.2 ± 84.6, 1,288.7 ± 131.4 and 1,008.7 ± 117.6 pg/ml, respectively. The median levels of s-klotho in the 3 studied groups were 3.15, 2.3 and 2.95, respectively. It was found that FGF-23 was significantly increased and α klotho was significantly decreased in all patients when compared with those in the control group (p < 0.001, <0.001, respectively). We found that there was a significant inverse correlation between serum Ca and α klotho in the studied groups. There was no significant correlation between FGF-23 and α klotho in the studied groups (p > 0.05). We have shown that circulating s-klotho was not related to FGF-23 in CKD, dialysis and KTR patients. In addition, we demonstrated a novel association between serum Ca and s-klotho that needs to be further studied.

Klotho: its various functions and association with sickle cell disease subphenotypes

The Klotho protein, whose gene has predominant renal expression, acts in the control of serum phosphorus and 1,25-dihydroxyvitamin D3 and regulates the function of ion channels. It also participates in the mechanism of protection against oxidative stress and acts on the vascular endothelium by inducing the production of nitric oxide. Mutations that reflect defects in the Klotho gene expression may be implicated in the onset of osteonecrosis, priapism, and leg ulcers in patients with sickle cell disease, as a result of oxidative stress and endothelial impairment, important factors in the development and severity of this disease. Previous reports regarding the association of Klotho single nucleotide polymorphisms with sickle cell disease subphenotypes have found that these polymorphisms are important to identify genetic markers of risk in these individuals and allow early and more effective therapeutic intervention.

Alpha Klotho and phosphate homeostasis

The Klotho family consists of three single-pass transmembrane proteins—αKlotho, βKlotho and γKlotho. Each of them combines with fibroblast growth factor (FGF) receptors (FGFRs) to form receptor complexes for various FGF’s. αKlotho is a co-receptor for physiological FGF23 signaling and appears essential for FGF23-mediated regulation of mineral metabolism. αKlotho protein also plays a FGF23-independent role in phosphate homeostasis. Animal experimental studies and clinical observations have demonstrated that αKlotho deficiency leads to severe hyperphosphatemia; moderate elevation of αKlotho reduces serum phosphate and extremely high αKlotho induces hypophosphatemia and high-FGF23. αKlotho maintains circulating phosphate in a narrow range by modulating intestinal phosphate absorption, urinary phosphate excretion by the kidney, and phosphate distribution into bone rather than soft tissue in concerted interaction with other calciophosphotropic hormones such as PTH, FGF23, and 1,25-(OH)₂ vitamin D. The role of αKlotho in maintenance of phosphate homeostasis is mediated by direct suppression of Na-dependent phosphate cotransporters in target organs. Therefore, αKlotho manipulation may be a novel strategy for genetic and acquired phosphate disorders and for medical conditions with αKlotho deficiency such as chronic kidney disease in future.

First evidence of TRPV5 and TRPV6 channels in human parathyroid glands: possible involvement in neoplastic transformation

The parathyroid glands play an overall regulatory role in the systemic calcium (Ca²⁺) homeostasis. The purpose of the present study was to demonstrate the presence of the Ca²⁺ channels transient receptor potential vanilloid (TRPV) 5 and TRPV6 in human parathyroid glands. Semi-quantitative and quantitative PCR was carried out to evaluate the presence of TRPV5 and TRPV6 mRNAs in sporadic parathyroid adenomas and normal parathyroid glands. Western blot and immunocytochemical assays were used to assess protein expression, cellular localization and time expression in primary cultures from human parathyroid adenoma. TRPV5 and TRPV6 transcripts were then identified both in normal and pathological tissues. Predominant immunoreactive bands were detected at 75–80 kD for both vanilloid channels. These channels co-localized with the calcium-sensing receptor (CASR) on the membrane surface, but immunoreactivity was also detected in the cytosol and around the nuclei. Our data showed that western blotting recorded an increase of protein expression of both channels in adenoma samples compared with normal glands suggesting a potential relation with the cell calcium signalling pathway and the pathological processes of these glands.

Assessment of tubular reabsorption of phosphate as a surrogate marker for phosphate regulation in chronic kidney disease

BACKGROUND/AIMS

Fibroblast growth factor 23 (FGF23) and soluble α-Klotho are emerging potential biomarkers of phosphorus and vitamin D metabolism which change in concentration in early chronic kidney disease (CKD) in order to maintain normal phosphorus levels. Tubular reabsorption of phosphate (TRP) has been commonly used to assess renal tubular phosphate transport. The aim of this study was to evaluate the usefulness of TRP as a surrogate marker of parameters of CKD-mineral bone disease (CKD-MBD) in CKD.

METHODS

A cross-sectional study was performed in 93 stable patients with predialysis CKD stage 1-5. In all patients, TRP, estimated glomerular filtration rate (eGFR), calcium, phosphate, intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, serum FGF23 and urine soluble α-Klotho levels were measured.

RESULTS

As renal function declined, TRP significantly decreased (P < 0.001; r = 0.763) and both iPTH and serum FGF23 increased (P < 0.001; r = -0.598, P < 0.001; r = -0.453, respectively). The prevalence of hyperphosphatemia, secondary hyperparathyroidism, FGF23 excess and abnormal TRP increased progressively with declining eGFR. Although TRP level changed later than FGF23, abnormal levels of both TRP and FGF23 were observed earlier than changes in iPTH and serum phosphate. Decreased TRP was found to be independently associated with decreased eGFR and increased iPTH but was not associated with urine soluble α-Klotho or serum FGF23 level in multiple linear regression analysis.

CONCLUSION

TRP is a simple, useful and cost-saving surrogate marker of the assessment of altered mineral metabolism in CKD patients and can be used as an alternative to serum FGF23, especially for mild to moderate renal insufficiency.

Phosphate transporters of the SLC20 and SLC34 families

Transport of inorganic phosphate (Pi) across the plasma membrane is essential for normal cellular function. Members of two families of SLC proteins (SLC20 and SLC34) act as Na(+)-dependent, secondary-active cotransporters to transport Pi across cell membranes. The SLC34 proteins are expressed in specific organs important for Pi homeostasis: NaPi-IIa (SLC34A1) and NaPi-IIc (SLC34A3) fulfill essential roles in Pi reabsorption in the kidney proximal tubule and NaPi-IIb (SLC34A2) mediates Pi absorption in the gut. The SLC20 proteins, PiT-1 (SLC20A1), PiT-2 (SLC20A2) are expressed ubiquitously in all tissues and although generally considered as "housekeeping" transport proteins, the discovery of tissue-specific activity, regulatory pathways and gene-related pathophysiologies, is redefining their importance. This review summarizes our current knowledge of SLC20 and SLC34 proteins in terms of their basic molecular characteristics, physiological roles, known pathophysiology and pharmacology.

Post-translational loss of renal TRPV5 calcium channel expression, Ca(2+) wasting, and bone loss in experimental colitis

BACKGROUND & AIMS

Dysregulated Ca(2+) homeostasis likely contributes to the etiology of inflammatory bowel disease-associated loss of bone mineral density. Experimental colitis leads to decreased expression of Klotho, a protein that supports renal Ca(2+) reabsorption by stabilizing the transient receptor potential vanilloid 5 (TRPV5) channel on the apical membrane of distal tubule epithelial cells.

METHODS

Colitis was induced in mice via administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) or transfer of CD4(+)interleukin-10(-/-) and CD4(+), CD45RB(hi) T cells. We investigated changes in bone metabolism, renal processing of Ca(2+), and expression of TRPV5.

RESULTS

Mice with colitis had normal serum levels of Ca(2+) and parathormone. Computed tomography analysis showed a decreased density of cortical and trabecular bone, and there was biochemical evidence for reduced bone formation and increased bone resorption. Increased fractional urinary excretion of Ca(2+) was accompanied by reduced levels of TRPV5 protein in distal convoluted tubules, with a concomitant increase in TRPV5 sialylation. In mouse renal intermedullary collecting duct epithelial (mIMCD3) cells transduced with TRPV5 adenovirus, the inflammatory cytokines tumor necrosis factor, interferon-γ, and interleukin-1β reduced levels of TRPV5 on the cell surface, leading to its degradation. Cytomix induced interaction between TRPV5 and UBR4 (Ubiquitin recoginition 4), an E3 ubiquitin ligase; knockdown of UBR4 with small interfering RNAs prevented cytomix-induced degradation of TRPV5. The effects of cytokines on TRPV5 were not observed in cells stably transfected with membrane-bound Klotho; TRPV5 expression was preserved when colitis was induced with TNBS in transgenic mice that overexpressed Klotho or in mice with T-cell transfer colitis injected with soluble recombinant Klotho.

CONCLUSIONS

After induction of colitis in mice via TNBS administration or T-cell transfer, tumor necrosis factor and interferon-γ reduced the expression and activity of Klotho, which otherwise would protect TRPV5 from hypersialylation and cytokine-induced TRPV5 endocytosis, UBR4-dependent ubiquitination, degradation, and urinary wasting of Ca(2+).

The epithelial calcium channel TRPV5 is regulated differentially by klotho and sialidase

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

The anti-aging factor α-klotho during human pregnancy and its expression in pregnancies complicated by small-for-gestational-age neonates and/or preeclampsia

OBJECTIVE

α-klotho, a protein with anti-aging properties, has been involved in important biological processes, such as calcium/phosphate metabolism, resistance to oxidative stress, and nitric oxide production in the endothelium. Recent studies have suggested a role of α-klotho in endocrine regulation of mineral metabolism and postnatal growth in infants. Yet, the role of α-klotho during pregnancy remains largely unknown. The aim of this study was to determine whether maternal plasma concentration of α-klotho changes during pregnancy and evaluate its expression in pregnancies complicated by small for gestational age (SGA) and/or preeclampsia (PE).

STUDY DESIGN

This cross-sectional study included patients in the following groups: (1) non pregnant women (n = 37); (2) uncomplicated pregnancy (n = 130); (3) PE without an SGA neonate (PE; n = 58); (4) PE with an SGA neonate (PE and SGA; n = 52); and (5) SGA neonate without PE (SGA; n = 52). Plasma concentrations of α-klotho were determined by ELISA.

RESULTS

The median plasma α-klotho concentration was higher in pregnant than in non-pregnant women. Among women with an uncomplicated pregnancy, the median plasma concentration of α-klotho increased as a function of gestational age (Spearman Rho = 0.2; p = 0.006). The median (interquartile range) plasma concentration of α-klotho in women with PE and SGA [947.6 (762-2013) pg/mL] and SGA without PE [1000 (585-1567) pg/mL] were 21% and 17% lower than that observed in women with an uncomplicated pregnancy [1206.6 (894-2012) pg/mL], (p = 0.005 and p = 0.02), respectively. Additionally, there were no significant differences in the median plasma concentration of α-klotho between uncomplicated pregnancies and women with PE without an SGA neonate (p = 0.5).

CONCLUSION

Maternal plasma concentration of α-klotho was higher during pregnancy than in a non-pregnant state. Moreover, the median maternal plasma concentration of α-klotho was lower in mothers who delivered an SGA neonate than in those with an uncomplicated pregnancy regardless of the presence or absence of PE.

Hippocampal gene expression dysregulation of Klotho, nuclear factor kappa B and tumor necrosis factor in temporal lobe epilepsy patients

Background

Previous research in animal seizure models indicates that the pleiotropic cytokine TNF is an important effector/mediator of neuroinflammation and cell death. Recently, it has been demonstrated that TNF downregulates Klotho (KL) through the nuclear factor kappa B (NFkB) system in animal models of chronic kidney disease and colitis. KL function in the brain is unclear, although Klotho knockout (Kl^−/−) mice exhibit neural degeneration and a reduction of hippocampal synapses. Our aim was to verify if the triad KL-NFKB1-TNF is also dysregulated in temporal lobe epilepsy associated with hippocampal sclerosis (TLE(HS)) patients.

Findings

We evaluated TNF, NFKB1 and KL relative mRNA expression levels by reverse transcription quantitative PCR (RT-qPCR) in resected hippocampal tissue samples from 14 TLE(HS) patients and compared them to five post mortem controls. Four reference genes were used: GAPDH, HPRT1, ENO2 and TBP. We found that TNF expression was dramatically upregulated in TLE(HS) patients (P <0.005). NFKB1 expression was also increased (P <0.03) while KL was significantly downregulated (P <0.03) in TLE(HS) patients. Hippocampal KL expression had an inverse correlation with NFKB1 and TNF.

Conclusions

Our data suggest that, similar to other inflammatory diseases, TNF downregulates KL through NFkB in TLE(HS) patients. The remarkable TNF upregulation in patients is a strong indication of hippocampal chronic inflammation. Our finding of hippocampal KL downregulation has wide implications not only for TLE(HS) but also for other neuronal disorders related to neurodegeneration associated with inflammation.

Tumour suppressor p16(INK4a) - anoikis-favouring decrease in N/O-glycan/cell surface sialylation by down-regulation of enzymes in sialic acid biosynthesis in tandem in a pancreatic carcinoma model

Tumour suppressor p16(INK4a) is known to exert cell-cycle control via cyclin-dependent kinases. An emerging aspect of its functionality is the orchestrated modulation of N/O-glycosylation and galectin expression to induce anoikis in human Capan-1 pancreatic carcinoma cells. Using chemoselective N/O-glycan enrichment technology (glycoblotting) and product characterization, we first verified a substantial decrease in sialylation. Tests combining genetic (i.e. transfection with α2,6-sialyltransferase-specific cDNA) or metabolic (i.e. medium supplementation with N-acetylmannosamine to track down a bottleneck in sialic acid biosynthesis) engineering with cytofluorometric analysis of lectin binding indicated a role of limited substrate availability, especially for α2,6-sialylation, which switches off reactivity for anoikis-triggering homodimeric galectin-1. Quantitative MS analysis of protein level changes confirmed an enhanced galectin-1 presence along with an influence on glycosyltransferases (β1,4-galactosyltransferase-IV, α2,3-sialyltransferase-I) and detected p16(INK4a) -dependent down-regulation of two enzymes in the biosynthesis pathway for sialic acid [i.e. the bifunctional UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) and N-acetylneuraminic acid 9-phosphate synthase] (P < 0.001). By contrast, quantitative assessment for the presence of nuclear CMP-N-acetylneuraminic acid synthase (which is responsible for providing the donor for enzymatic sialylation that also acts as feedback inhibitor of the epimerase activity of GNE) revealed a trend for an increase. Partial restoration of sialylation in GNE-transfected cells supports the implied role of sialic acid availability for the glycophenotype. Fittingly, the extent of anoikis was reduced in double-transfected (p16(INK4a) /GNE) cells. Thus, a second means of modulating cell reactivity to the growth effector galectin-1 is established in addition to the common route of altering α2,6-sialyltransferase expression: regulating enzymes of the pathway for sialic acid biosynthesis.

The emerging role of Klotho in clinical nephrology

Klotho is highly expressed in the kidney and a soluble form of Klotho functions as an endocrine substance that exerts multiple actions including the modulation of renal solute transport and the protection of the kidney from a variety of insults in experimental models. At present, the Klotho database is still largely preclinical, but the anticipated forthcoming impact on clinical nephrology can be immense. This manuscript puts these potentials into perspective for the clinician. There is renal and systemic Klotho deficiency in both acute kidney injury (AKI) and chronic kidney disease (CKD). Klotho plummets very early and severely in AKI and represents a pathogenic factor that exacerbates acute kidney damage. In CKD, Klotho deficiency exerts a significant impact on progression of renal disease and extra renal complications. In AKI, soluble Klotho levels in plasma and/or urine may serve as an early biomarker for kidney parenchymal injury. Restoration by exogenous supplementation or stimulation of endogenous Klotho may prevent and/or ameliorate kidney injury and mitigate CKD development. In CKD, Klotho levels may be an indicator of early disease and predict the rate of progression, and presence and severity of soft tissue calcification. The correction of Klotho deficiency may delay progression and forestall development of extra renal complications in CKD. Rarely does one find a molecule with such broad potential applications in nephrology. Klotho can possibly emerge on the horizon as a candidate for an unprecedented sole biomarker and intervention. Nephrologists should monitor the progress of the preclinical studies and the imminently emerging human database.

The secreted Klotho protein restores phosphate retention and suppresses accelerated aging in Klotho mutant mice

Klotho was identified as the responsible gene in a mutant mouse line whose disruption results in a variety of premature aging-related phenotypes. Nonetheless, the related mechanisms were still unknown. Many studies report that dietary phosphate restriction and genetic ablation of vitamin D pathways indirectly reverse premature aging processes in these mice. Furthermore, transgenic overexpression of klotho in mice extends their life span through inhibition of insulin and IGF1 signaling. We found that intraperitoneal injection of recombinant soluble Klotho protein at dose of 0.02 mg/kg every other day effectively extends the life span of kl/kl mice by 17.4%. Soluble Klotho administration also ameliorated premature aging-related phenotype, such as growth retardation, premature thymus involution and vascular calcification, and effectively enhanced urinary phosphate excretion in kl/kl mice. Klotho treatment attenuated renal fibrosis through down-regulation of transforming growth factor-β signaling as well as reduced cellular senescence through down-regulation of p21-cip1 mRNA levels. In addition, soluble Klotho treatment significantly reduced both renal and aorta calcium deposits. In conclusion, our study shows the therapeutic potential of soluble Klotho protein to treat age-related disorders in mice.

Klotho in health and disease

PURPOSE OF REVIEW

The klotho gene was originally identified as a putative aging-suppressor gene in mice that extended life span when overexpressed and induced a premature aging syndrome when disrupted. Subsequently, it became clear that the Klotho family of membrane proteins function as obligate co-receptors for endocrine fibroblast growth factors (FGFs) that regulate various metabolic processes. This review focuses on the Klotho-FGF23 endocrine system that maintains phosphate (Pi) homeostasis, and discusses the mechanism of action and the potential contribution of Klotho deficiency to acute kidney injury (AKI), chronic kidney disease (CKD) and cancer.

RECENT FINDINGS

Klotho functions as a receptor for the phosphaturic hormone FGF23. Klotho deficiency induces resistance to FGF23 and predisposition to Pi retention, which represents a critical feature of pathophysiology of CKD. The extracellular domain of Klotho protein is subject to ectodomain shedding and released into the blood and urine. Secreted Klotho functions as a humoral factor that inhibits AKI, vascular calcification, renal fibrosis, and cancer metastasis in an FGF23-independent manner.

SUMMARY

Various factors that affect Klotho expression have been identified. Prevention of Klotho decline and supplementation of Klotho can be a novel therapeutic strategy for many age-related diseases.