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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., (© The Author(s) 2024. Published by Oxford University Press on behalf of the ERA.)

The kidney is a metabolically active organ that requires energy to drive processes such as tubular reabsorption and secretion, and shows a decline in function with advancing age. Various molecular mechanisms, including genomic instability, telomere attrition, inflammation, autophagy, mitochondrial function, and changes to the sirtuin and Klotho signalling pathways, are recognized regulators of individual lifespan and pivotal factors that govern kidney ageing. Thus, mechanisms that contribute to ageing not only dictate renal outcomes but also exert a substantial influence over life expectancy. Conversely, kidney dysfunction, in the context of chronic kidney disease (CKD), precipitates an expedited ageing trajectory in individuals, leading to premature ageing and a disconnect between biological and chronological age. As CKD advances, age-related manifestations such as frailty become increasingly conspicuous. Hence, the pursuit of healthy ageing necessitates not only the management of age-related complications but also a comprehensive understanding of the processes and markers that underlie systemic ageing. Here, we examine the hallmarks of ageing, focusing on the mechanisms by which they affect kidney health and contribute to premature organ ageing. We also review diagnostic methodologies and interventions for premature ageing, with special consideration given to the potential of emerging therapeutic avenues to target age-related kidney diseases., (© 2024. Springer Nature Limited.)

Fibroblast growth factor 23 (FGF23) is a circulating hormone derived from the bone whose release is controlled by many factors and exerts a multitude of systemic actions. There are congenital and acquired disorders of increased and decreased FGF23 levels. In chronic kidney disease (CKD), elevations of FGF23 levels can be 1000-fold above the upper physiological limit. It is still debated whether this high FGF23 in CKD is a biomarker or causally related to morbidity and mortality. Data from human association studies support pathogenicity, while experimental data are less robust. Knowledge of the biology and pathobiology of FGF23 has generated a plethora of means to reduce FGF23 bioactivity at many levels that will be useful for therapeutic translations. This article summarizes these approaches and addresses several critical questions that still need to be answered., (© The Author(s) 2021. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.)

Klotho gene was originally recognized as a putative aging-suppressor and its prominent age-regulating effects are mostly attributed to the modulation of mineral homeostasis in the kidney. However, recent studies link alterations in hippocampal Klotho expression with cognitive impairment and neurodegenerative diseases. This suggests that hippocampal neurons require Klotho for health and proper functionality. Klotho protects against neuronal dysfunction and regulates several intracellular signaling pathways including oxidative stress response, inflammation, DNA damage, autophagy, endoplasmic reticulum stress response, and multiple types of cell death. Specifically, this chapter covers the current knowledge as to how Klotho protein affects the hippocampal neuronal cells, with special attention paid to underlying molecular mechanisms, and thus influences hippocampal development, hippocampal-dependent cognition, behavior, and motor skills as well as mediates neurodegenerative processes., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Soluble Klotho (sKL) is closely related to insulin resistance, which is a major factor in the progression of diabetic cardiomyopathy (DCM). The purpose of this study was to investigate the role of sKL in the regulation of DCM and the mechanism involved. A mouse model of type 2 diabetes was induced by high-fat diet and streptozotocin injection. An insulin-resistant cardiac fibroblast model was established by high glucose and high insulin. KL gene overexpression was achieved in vivo and vitro through transfection with an adenovirus-harboring KL-cDNA. Gene overexpression was used to evaluate the role of sKL in the pathophysiologic characteristics of DCM. Insulin-resistant cardiac fibroblasts reduced sKL expression and collagen deposition. Diabetic mice constructed by streptozotocin exhibited severe insulin resistance, inflammation, fibrosis, left ventricular dysfunction, and sKL downregulation. The overexpression of sKL mitigated insulin resistance and metabolic disturbance; inflammation, fibrosis, and upregulated collagen I/III content ratio in diabetic state were significantly reduced. Our findings were accompanied by notable moderation of cardiac function. Further, blunted phosphorylation of Akt was restored with sKL gene overexpression, and activated phosphorylation of extracellular signal-regulated kinase 1/2 in DCM was reduced. Our results suggest that sKL protein overexpression exerts a defensive measure by ameliorating selective insulin resistance in mouse DCM, thus revealing its underlying mechanism for potential human DCM treatment., (© 2021 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

The extracellular matrix (ECM) is a structural framework that has many important physiological functions which include maintaining tissue structure and integrity, serving as a barrier to invading pathogens, and acting as a reservoir for bioactive molecules. This cellular scaffold is made up of various types of macromolecules including heparan sulfate proteoglycans (HSPGs). HSPGs comprise a protein core linked to the complex glycosaminoglycan heparan sulfate (HS), the remodeling of which is important for many physiological processes such as wound healing as well as pathological processes including cancer metastasis. Turnover of HS is tightly regulated by a single enzyme capable of cleaving HS side chains: heparanase. Heparanase upregulation has been identified in many inflammatory diseases including atherosclerosis, fibrosis, and cancer, where it has been shown to play multiple roles in processes such as epithelial-mesenchymal transition, angiogenesis, and cancer metastasis. Heparanase expression and activity are tightly regulated. Understanding the regulation of heparanase and its downstream targets is attractive for the development of treatments for these diseases. This review provides a comprehensive overview of the regulators of heparanase as well as the enzyme's downstream gene and protein targets, and implications for the development of new therapeutic strategies.

Chronic kidney disease (CKD) has been associated with a higher risk of cardiovascular disease (CVD). CKD patients present a decrease in the levels of the protein Klotho that accompanies the decrease in kidney function. This protein has been related to protective effects against CVD. However, it is unclear whether circulating Klotho, and its expression in peripheral blood cells (PBCs) are also associated with subclinical atherosclerosis in CKD. The present study aimed to study the relationship between Klotho and subclinical atherosclerosis in a population of patients with moderate to severe CKD. We determined the serum levels and gene expression in PBCs levels of Klotho and three inflammatory cytokines in 103 patients with CKD and investigated their relationship with two surrogate markers of subclinical atherosclerotis: ankle-brachial index (ABI) and carotid intima-media thickness (CIMT). Patients with subclinical atherosclerosis presented lower serum and PBCs expression levels of Klotho. Both variables were associated with the presence of subclinical atherosclerosis, being directly related with ABI and inversely with CIMT (P < 0.0001 for both). Multiple regression analysis demonstrated that both variables were significant determinants for ABI (adjusted R 2  = 0.511, P < 0.0001) and CIMT (adjusted R 2  = 0.445, P < 0.0001), independently of traditional and emergent cardiovascular risk factors. Moreover, both constituted protective factors against subclinical atherosclerosis [OR: 0.993 (P = 0.002) and 0.231 (P = 0.025), respectively]. Receiver operating characteristic analysis pointed to the utility of serum Klotho (area under the curve [AUC]: 0.817, 95% CI: 0.736-0.898, P < 0.001) and its gene expression in PBCs (AUC: 0.742, 95% CI: 0.647-0.836, P < 0.001) to distinguish subclinical atherosclerosis. The reductions in serum and PBCs expression levels of Klotho in CKD patients are independently associated with the presence of for subclinical atherosclerosis. Further research exploring whether therapeutic approaches to maintain or elevate Klotho could reduce the impact of CVD in CKD patients is warranted., (© 2021. The Author(s).)

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., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Chronic gastritis caused by Helicobacter pylori ( H. pylori ) infection has been widely recognized as the most important risk factor for gastric cancer. Analysis of the interaction between the key participants in gastric mucosal immunity and H. pylori infection is expected to provide important insights for the treatment of chronic gastritis and the prevention of gastric cancer. Heparanase is an endoglycosidase that degrades heparan sulfate, resulting in remodeling of the extracellular matrix thereby facilitating the extravasation and migration of immune cells towards sites of inflammation. Heparanase also releases heparan sulfate-bound cytokines and chemokines that further promote directed motility and recruitment of immune cells. Heparanase is highly expressed in a variety of inflammatory conditions and diseases, but its role in chronic gastritis has not been sufficiently explored. In this study, we report that H. pylori infection promotes up-regulation of heparanase in gastritis, which in turn facilitates the colonization of H. pylori in the gastric mucosa, thereby aggravating gastritis. By sustaining continuous activation, polarization and recruitment of macrophages that supply pro-inflammatory and pro-tumorigenic cytokines (i.e., IL-1, IL-6, IL-1β, TNF-α, MIP-2, iNOS), heparanase participates in the generation of a vicious circle, driven by enhanced NFκB and p38-MAPK signaling, that supports the development and progression of gastric cancer. These results suggest that inhibition of heparanase may block this self-sustaining cycle, and thereby reduce the risk of gastritis and gastric cancer., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Tang, Tang, Lei, Yang, Wang, Hu, Xie, Liu, Vlodavsky and Yang.)

Competing Interests: None declared.

Dietary salt intake increases blood pressure (BP) but the salt sensitivity of BP differs between individuals. The interplay of ageing, genetics and environmental factors, including malnutrition and stress, contributes to BP salt sensitivity. In adults, obesity is often associated with salt-sensitive hypertension. The children of women who experience malnutrition during pregnancy are at increased risk of developing obesity, diabetes and salt-sensitive hypertension as adults. Similarly, the offspring of mice that are fed a low-protein diet during pregnancy develop salt-sensitive hypertension in association with aberrant DNA methylation of the gene encoding type 1A angiotensin II receptor (AT 1A R) in the hypothalamus, leading to upregulation of hypothalamic AT 1A R and renal sympathetic overactivity. Ageing is also associated with salt-sensitive hypertension. In aged mice, promoter methylation leads to reduced kidney production of the anti-ageing factor Klotho and a decrease in circulating soluble Klotho. In the setting of Klotho deficiency, salt-induced activation of the vascular Wnt5a-RhoA pathway leads to ageing-associated salt-sensitive hypertension, potentially as a result of reduced renal blood flow and increased peripheral resistance. Thus, kidney mechanisms and aberrant DNA methylation of certain genes are involved in the development of salt-sensitive hypertension during fetal development and old age. Three distinct paradigms of epigenetic memory operate on different timescales in prenatal malnutrition, obesity and ageing.

During the evolution of skeletons, terrestrial vertebrates acquired strong bones made of calcium-phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate ions, they created the bone when and where they wanted simply by providing a cue for precipitation. To secure this strategy, they acquired a novel endocrine system to strictly control the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion, thereby maintaining phosphate homeostasis. The FGF23-Klotho endocrine system, when disrupted in mice, results in hyperphosphatemia and vascular calcification. Besides, mice lacking Klotho or FGF23 suffer from complex aging-like phenotypes, which are alleviated by placing them on a low- phosphate diet, indicating that phosphate is primarily responsible for the accelerated aging. Phosphate acquires the ability to induce cell damage and inflammation when precipitated with calcium. In the blood, calcium-phosphate crystals are adsorbed by serum protein fetuin-A and prevented from growing into large precipitates. Consequently, nanoparticles that comprised calcium-phosphate crystals and fetuin-A, termed calciprotein particles (CPPs), are generated and dispersed as colloids. CPPs increase in the blood with an increase in serum phosphate and age. Circulating CPP levels correlate positively with vascular stiffness and chronic non-infectious inflammation, raising the possibility that CPPs may be an endogenous pro-aging factor. Terrestrial vertebrates with the bone made of calcium- phosphate may be destined to age due to calcium-phosphate in the blood.

Acute kidney injury is a global disease with high morbidity and mortality. Recent studies have revealed that the fibroblast growth factor-23-α-Klotho axis is closely related to chronic kidney disease, and has multiple biological functions beyond bone-mineral metabolism. However, although dysregulation of fibroblast growth factor-23-α-Klotho has been observed in acute kidney injury, the role of fibroblast growth factor-23-α-Klotho in the pathophysiology of acute kidney injury remains largely unknown. In this review, we describe recent findings regarding fibroblast growth factor-23-α-Klotho, which is mainly involved in inflammation, oxidative stress, and hemodynamic disorders. Further, based on these recent results, we put forth novel insights regarding the relationship between the fibroblast growth factor-23-α-Klotho axis and acute kidney injury, which may provide new therapeutic targets for treating acute kidney injury., Competing Interests: Declaration of competing interest All the authors declared no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Klotho was initially introduced as an antiaging molecule. Klotho deficiency significantly reduces lifespan, and its overexpression extends it and protects against various pathological phenotypes, especially renal disease. It was shown to regulate phosphate and calcium metabolism, protect against oxidative stress, downregulate apoptosis, and have antiinflammatory and antifibrotic properties. The course of diabetes mellitus and diabetic nephropathy resembles premature cellular senescence and causes the activation of various proinflammatory and profibrotic processes. Klotho was shown to exert many beneficial effects in these disorders. The expression of Klotho protein is downregulated in early stages of inflammation and diabetic nephropathy by proinflammatory factors. Therefore, its therapeutic effects are diminished in this disorder. Significantly lower urine levels of Klotho may serve as an early biomarker of renal involvement in diabetes mellitus. Recombinant Klotho administration and Klotho overexpression may have immunotherapeutic potential for the treatment of both diabetes and diabetic nephropathy. Therefore, the current manuscript aims to characterize immunopathologies occurring in diabetes and diabetic nephropathy, and tries to match them with antiinflammatory actions of Klotho. It also gives reasons for Klotho to be used in diagnostics and immunotherapy of these disorders.

Alzheimer's disease (AD) is considered a prevalent neurological disorder with a neurodegenerative nature in elderly people. Oxidative stress and neuroinflammation due to amyloid β (Aβ) peptides are strongly involved in AD pathogenesis. Klotho is an anti-aging protein with multiple protective effects that its deficiency is involved in development of age-related disorders. In this study, we investigated the beneficial effect of Klotho pretreatment at different concentrations of 0.5, 1, and 2 nM against Aβ1-42 toxicity at a concentration of 20 μM in human SH-SY5Y neuroblastoma cells. Our findings showed that Klotho could significantly and partially restore cell viability and decrease reactive oxygen species (known as ROS) and improve superoxide dismutase activity (SOD) in addition to reduction of caspase 3 activity and DNA fragmentation following Aβ1-42 challenge. In addition, exogenous Klotho also reduced inflammatory biomarkers consisting of nuclear factor-kB (NF-kB), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in Aβ-exposed cells. Besides, Klotho caused downregulation of Wnt1 level, upregulation of phosphorylated cyclic AMP response element binding (pCREB), and mRNA levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) with no significant alteration of epsilon isoform of protein kinase C (PKCε) after Aβ toxicity. In summary, Klotho could alleviate apoptosis, oxidative stress, and inflammation in human neuroblastoma cells after Aβ challenge and its beneficial effect is partially exerted through appropriate modulation of Wnt1/pCREB/Nrf2/HO-1 signaling.

During the evolution of skeletons, vertebrates acquired the bone made of calcium phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate, vertebrates create the bone when and where they want simply by providing a cue for precipitation. To secure this strategy, a new endocrine system has evolved that strictly controls the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion and maintain phosphate homeostasis. The FGF23-Klotho endocrine system, when disrupted, results in hyperphosphatemia and ectopic precipitation of calcium phosphate in mice and humans. In addition to disturbed phosphate homeostasis, mice lacking Klotho suffer from premature aging. They exhibit multiple organ atrophy, arteriosclerosis characterized by vascular calcification, cardiac hypertrophy, sarcopenia, cognition impairment, frailty, and a shortened life span associated with chronic non-infectious inflammation. Restoration of the phosphate balance by placing Klotho- or FGF23-deficient mice on low phosphate diet rescued them from the aging-like phenotypes, indicating that phosphate was responsible for the accelerated aging. The similar pathophysiology is universally observed in patients with chronic kidney disease (CKD), rendering advanced CKD a clinical model of accelerated aging. CKD patients bear colloidal nanoparticles containing calcium phosphate in the blood, which are termed calciprotein particles (CPPs). CPPs have the ability to induce cell damage and inflammation, potentially contributing to accelerated aging. Terrestrial vertebrates with the bone made of calcium phosphate may be destined to age due to ectopic calcium phosphate., (© 2021 Elsevier Inc. All rights reserved.)

Background: Hyperoxia (HO) causes kidney injury in preterm infants; however, whether these effects are modifiable is unknown. We hypothesized that administration of exogenous soluble Klotho, a kidney-derived antioxidant, would attenuate HO-induced kidney injury during postnatal nephrogenesis in rats., Methods: Sprague Dawley neonatal rats assigned to normoxia (21% O 2 ) or HO (85% O 2 ) groups from postnatal day (P) 1 to 21 were randomly assigned to receive alternate day intraperitoneal injections of recombinant Klotho or placebo for 3 weeks. They were recovered in normoxia for an additional 3 weeks and sacrificed at 6 weeks. Renal artery resistance and pulsatility indices, tubular injury scores, glomerular area, and renal antioxidant capacity were assessed., Results: Rodents exposed to HO during postnatal nephrogenesis had reduced kidney Klotho expression, glomerulomegaly, and higher tubular injury scores. Exogenous Klotho administration improved renal perfusion as indicated by decreases in both resistance and pulsatility indices and increased antioxidant enzyme expression., Conclusions: HO exposure during postnatal nephrogenesis in rodents results in a decline in kidney Klotho expression, decreased renal perfusion, enlarged glomerular size, and tubular injury. The exogenous administration of Klotho attenuated HO-induced kidney injury and augmented antioxidant capacity.

Currently, no treatment exists to improve semen quality in most infertile men. Here, we demonstrate systemic and direct effects of Fibroblast growth factor 23 (FGF23) and Klotho, which normally regulate vitamin D and mineral homeostasis, on testicular function. Direct effects are plausible because KLOTHO is expressed in both germ cells and spermatozoa and forms with FGFR1 a specific receptor for the bone-derived hormone FGF23. Treatment with FGF23 increased testicular weight in wild-type mice, while mice with global loss of either FGF23 or Klotho had low testicular weight, reduced sperm count, and sperm motility. Mice with germ cell-specific Klotho (gcKL) deficiency neither had a change in sperm count nor sperm motility. However, a tendency toward fewer pregnancies was detected, and significantly fewer Klotho heterozygous pups originated from gcKL knockdown mice than would be expected by mendelian inheritance. Moreover, gcKL mice had a molecular phenotype with higher testicular expression of Slc34a2 and Trpv5 than wild-type littermates, which suggests a regulatory role for testicular phosphate and calcium homeostasis. KLOTHO and FGFR1 were also expressed in human germ cells and spermatozoa, and FGF23 treatment augmented the calcium response to progesterone in human spermatozoa. Moreover, cross-sectional data revealed that infertile men with the highest serum Klotho levels had significantly higher serum Inhibin B and total sperm count than men with the lowest serum Klotho concentrations. In conclusion, this translational study suggests that FGF23 and Klotho influence gonadal function and testicular mineral ion homeostasis both directly and indirectly through systemic changes in vitamin D and mineral homeostasis., (© 2020 Federation of American Societies for Experimental Biology.)

Klotho is a transmembrane protein with a wide spectrum of activity. The human Klotho gene shows 86% amino acid identity with the mouse protein. Many important pleiotropic functions of the Klotho protein have been revealed. Amongst them, there is a regulation of nitric oxide production, suppression of oxidative stress and inflammation, influence on the insulin-like growth factors and fibroblast growth factors signaling, modulation of calcium and phosphate metabolism, synthesis of vitamin D and other. Two forms of the Klotho protein are known. The secreted form strongly inhibits the oxidative stress, and, in humans, is more dominant than the membrane form. Studies on a mouse model resulted in the finding of the anti-aging effect of the Klotho protein. This activity is mainly associated with the suppression of oxidative stress, as well as it could be related to neuroprotective, cardioprotective, and metabolic functions.It might be speculated that Klotho, regarded as a neuroprotective factor, may have therapeutical applications in the future in the treatment of demyelinating and neurodegenerative disorders, especially multiple sclerosis (MS) and Alzheimer's disease (AD). The Klotho through inhibition of oxidative stress possesses cardioprotective properties. Of note, one functional variant of Klotho is a risk factor for coronary disease as well as some nucleotide polymorphisms are associated with carotid arteriosclerosis. Moreover, the Klotho protein can inhibit Angiotensin II-induced cardiomyocyte hypertrophy. All those effects indicate that the Klotho protein may be useful in the therapy of heart failure and hypertension. Undoubtedly, metabolic disturbances play an important role in the pathogenesis of many neurodegenerative and cardiovascular diseases. The metabolic effects of the Klotho protein are strongly connected with its neuroprotective and cardioprotective activity. This protein affects adipogenesis, metabolism of glucose and lipids as well as calcium-phosphate system by influence on the activity of fibroblast growth factors (FGF19, FGF23, FGF21). Finally, it has been revealed that the Klotho protein has antitumor activity. Besides, the FGF-Klotho system may have a role in longevity and aging-related disorders.

α-Klotho is a circulating factor with well-documented antiaging properties. However, the central role of α-klotho in metabolism remains largely unexplored. The current study investigated the potential role of central α-klotho to modulate neuropeptide Y/agouti-related peptide (NPY/AgRP)-expressing neurons, energy balance, and glucose homeostasis. Intracerebroventricular administration of α-klotho suppressed food intake, improved glucose profiles, and reduced body weight in mouse models of type 1 and 2 diabetes. Furthermore, central α-klotho inhibition via an anti-α-klotho antibody impaired glucose tolerance. Ex vivo patch clamp electrophysiology and immunohistochemical analysis revealed that α-klotho suppresses NPY/AgRP neuron activity, at least in part, by enhancing miniature inhibitory postsynaptic currents. Experiments in hypothalamic GT1-7 cells observed that α-klotho induces phosphorylation of AKT ser473 , ERK thr202/tyr204 , and FOXO1 ser256 as well as blunts AgRP gene transcription. Mechanistically, fibroblast growth factor receptor 1 (FGFR1) inhibition abolished the downstream signaling of α-klotho, negated its ability to modulate NPY/AgRP neurons, and blunted its therapeutic effects. Phosphatidylinositol 3 kinase (PI3K) inhibition also abolished α-klotho's ability to suppress food intake and improve glucose clearance. These results indicate a prominent role of hypothalamic α-klotho/FGFR1/PI3K signaling in the modulation of NPY/AgRP neuron activity and maintenance of energy homeostasis, thus providing new insight into the pathophysiology of metabolic disease., (© 2020 by the American Diabetes Association.)

Introduction: Among the family of fibroblast growth factors (FGFs), FGF19, FGF21, and FGF23 act as circulating hormones and are called endocrine FGFs. FGF19 and FGF21 regulate bile acid and energy homeostasis, respectively, whereas FGF23 regulates vitamin D and phosphate homeostasis. Accumulating evidence suggests that FGF23 plays a critical role in disturbed mineral metabolisms, left ventricular hypertrophy, immunosuppression, inflammation, among others in patients with chronic kidney disease (CKD), highlighting the potential both as a biomarker and a therapeutic target. Several studies have also examined the potential role of FGF19 and FGF21 in CKD patients., Areas Covered: In this review, we present a brief overview of the biology of FGF19, FGF21, and FGF23, and summarize recent clinical and experimental studies on the pathophysiological roles of endocrine FGFs, mainly FGF23, in CKD patients., Expert Opinion: Among the endocrine FGFs, FGF23 represents the most promising biomarker in CKD patients. If future studies confirm that FGF23 is directly toxic in CKD patients, FGF23 could be regarded as a therapeutic target and its measurement would be valuable if applied in clinical practice. Despite their potentially important roles, the clinical relevance of FGF19 and FGF21 in CKD patients is unclear, and much more studies are required.

Background: Longevity gene klotho (KL) is associated with age-related phenotypes including lifespan, cardiometabolic disorders, cognition, and brain morphology, in part, by conferring protection against inflammation. We hypothesized that the KL/inflammation association might be altered in the presence of psychiatric stress and operate via epigenetic pathways. We examined KL polymorphisms, and their interaction with posttraumatic stress disorder (PTSD) symptoms, in association with KL DNA methylation in blood. We further examined KL DNA methylation as a predictor of longitudinal changes in a peripheral biomarker of inflammation (C-reactive protein; CRP)., Methods: The sample comprised 309 white non-Hispanic military veterans (93.5 % male; mean age: 32 years, range: 19-65; 30 % PTSD per structured diagnostic interview); 111 were reassessed approximately two years later., Results: Analyses revealed a methylation quantitative trait locus at rs9527025 (C370S, previously implicated in numerous studies of aging) in association with a Cytosine-phosphate-Guanine site (cg00129557; B = -.65, p =  1.29 X 10 -20 ), located within a DNase hypersensitivity site in the body of KL. There was also a rs9527025 x PTSD severity interaction (B = .004, p = .035) on methylation at this locus such that the minor allele was associated with reduced cg00129557 methylation in individuals with few or no PTSD symptoms while this effect was attenuated in those with elevated levels of PTSD. Path models revealed that methylation at cg00129557 was inversely associated with CRP over time (B = -.14, p = .005), controlling for baseline CRP. There was also an indirect effect of rs9527025 X PTSD on subsequent CRP via cg00129557 methylation (indirect B = -.002, p = .033)., Conclusions: Results contribute to our understanding of the epigenetic correlates of inflammation in PTSD and suggest that KL methylation may be a mechanism by which KL genotype confers risk vs. resilience to accelerated aging in those experiencing traumatic stress., (Copyright © 2020. Published by Elsevier Ltd.)

Background: Long-term exposure to bioincompatible peritoneal dialysate causes the loss of mesothelial cells and accumulation of matrix proteins, leading to an increase in the thickness of the submesothelial layer, thereby limiting the long-term effectiveness of peritoneal dialysis (PD). However, the detailed molecular mechanisms underlying the process of peritoneal fibrosis have not been clearly elucidated. Wnt/β-catenin signaling pathway activation has been suggested to play a pivotal role in the development of organ fibrosis. Moreover, Klotho protein can regulate Wnt/β-catenin signaling. We examined the role of Klotho protein in reducing peritoneal fibrosis by inhibiting Wnt/β-catenin signaling., Methods: The β-catenin-activated transgenic (BAT) driving expression of nuclear β-galactosidase reporter transgenic (BAT-LacZ) mice, the alpha-Klotho gene under control of human elongation factor 1 alpha promoter [Klotho transgenic (KLTG) and C57BL/6 background] and C57BL/6 mice [wild-type (WT)] were used. The mice received daily intraperitoneal (i.p.) injections of 4.25% glucose with lactate (PD solution) or saline as a control for 4 weeks. Other mice received daily i.p. injections of the same volume of saline (normal control)., Results: After exposure to PD, Wnt signal activation was observed on the peritoneal mesothelial cells in WT-PD mice. The peritoneal fibrosis was also accelerated in WT-PD mice. The protein expression of β-catenin and Wnt-inducible genes were also remarkably increased in WT-PD mice. On the other hand, KLTG-PD mice attenuated activation of Wnt/β-catenin signaling after exposure to PD and ameliorated the progression of peritoneal fibrosis., Conclusions: Overexpression of Klotho protein protects the peritoneal membrane through attenuation of the Wnt/β-catenin signaling pathway. The availability of recombinant Klotho protein would provide a novel potential therapeutic target in peritoneal fibrosis., (© The Author(s) 2020. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.)

Membrane Alpha Klotho (α-klotho) is expressed in the kidney and functions as a co-receptor of FGF receptors (FGFRs) to activate specific fibroblast growth factor 23 (FGF23) signal pathway. FGF23 is produced in bones and participates in mineral homeostasis. The extracellular domain of transmembrane αklotho can be cleaved by proteases and released into the circulation as soluble α-klotho. Klotho deficiency is a pathogenic factor for chronic kidney disease progression and cardiovascular diseases. The FGF23 excess may also contribute to cardiovascular diseases where its pathogenic effect acts via the FGFR4 and independently of α-klotho. The decline in serum α-klotho followed by a rise in serum FGF23 at an early stage of chronic kidney disease can serve as a robust predictor for risk of cardiovascular diseases and mortality in both CKD patients and the general population. The first randomized trials suggest the possibility to reduce FGF23 excess in chronic kidney disease by controlling the phosphate serum using phosphate binders and reducing PTH levels with calcimimetic drug. New strategies emerge, including the administration of α-klotho recombinant and the use of epidrugs in order to correct the klotho deficiency. The FGR4 inhibitors are promising to limit the development of left ventricular hypertrophy linked to FGF23 excess. Finally, a better understanding of the molecular mechanisms of FGF23/α-klotho axis will allow us to find new strategic approaches and improve the CKD patient's management and their outcomes., (Copyright © 2019 Société francophone de néphrologie, dialyse et transplantation. Published by Elsevier Masson SAS. All rights reserved.)

Fibroblast growth factor (FGF) 23 and αKlotho are circulating mineral regulatory substances that also have a very diverse range of actions. Acute kidney injury (AKI) is a state of high FGF23 and low αKlotho. Clinical association data for FGF23 are strong, but the basic pathobiology of FGF23 in AKI is rather sparse. Conversely, preclinical data supporting a pathogenic role of αKlotho in AKI are strong, but the human data are still being generated. This pair of substances can potentially serve as diagnostic and prognostic biomarkers. FGF23 blockade and αKlotho restoration can have prophylactic and therapeutic utility in AKI. The literature to date is briefly reviewed in this article., (© 2020 S. Karger AG, Basel.)

Klotho is a putative aging suppressor gene that is primarily expressed in renal tubular epithelial cells. Its expression has been reported to protect against fibrosis in human chronic kidney disease. However, the roles of klotho in epithelial-mesenchymal transition (EMT) and renal fibrosis are yet to be elucidated. The present study aimed to investigate the putative roles of klotho in angiotensin (Ang) II-induced damage of renal tubular epithelial cells. NRK-52E rat cells were treated with various combinations of Ang II, the Ang-converting enzyme inhibitor fosinopril (Fos) and the Ang II receptor antagonist valsartan (Val). The levels of transforming growth factor (TGF)-β1, soluble klotho, α-smooth muscle actin (α-SMA) and E-cadherin in NRK-52E culture supernatants were measured using enzyme-linked immunosorbent assays. Furthermore, the mRNA and protein expression of TGF-β1, klotho, α-SMA and E-cadherin was detected using semiquantitative reverse transcription-polymerase chain reaction, immunocytochemistry and Western blot analysis. The results demonstrated that Ang II inhibited the expression of klotho and E-cadherin, while it upregulated the expression of TGF-β1 and α-SMA, in NRK52E cells. Fos and/or Val were revealed to enhance klotho and E-cadherin expression, and suppress the expression of TGF-β1 and α-SMA, compared with the Ang II-only group. Furthermore, a positive linear correlation was detected between the expression of klotho and E-cadherin, while negative linear correlations with klotho expression were detected for TGF-β1 and α-SMA expression. In conclusion, the expression of klotho was demonstrated to be enhanced following treatment with Fos and Val in Ang II-treated NRK-52E cells. The present results indicate that klotho may be involved in the inhibition of Ang II-induced EMT in renal tubular epithelial cells. Therefore, klotho may serve as a protective factor in renal tubulointerstitial fibrosis and aid the treatment of chronic kidney disease (CKD) patients using precision therapy., (Copyright 2020 Biolife Sas. www.biolifesas.org.)

Hyalinosis is a vascular lesion affecting the renal vasculature and contributing to aging-related renal function decline. We assessed whether arteriolar hyalinosis is caused by Klotho deficiency, a state known to induce both renal and vascular phenotypes associated with aging. Histochemistry was used to assess hyalinosis in Klotho -/- kidneys, compared with Klotho +/- and wild-type littermates. Immunohistochemistry was used to investigate vascular lesion composition and the different layers of the vascular wall. Finally, spironolactone was used to inhibit calcification in kl/kl mice, and vascular lesions were characterized in the kidney. Arteriolar hyalinosis was detected in Klotho -/- mice, which was present up to the afferent arterioles. Hyalinosis was accompanied by loss of α-smooth muscle actin expression, whereas the endothelial lining was mostly intact. Hyalinous lesions were positive for IgM and iC3b/c/d, indicating subendothelial leakage of plasma proteins. The presence of extracellular matrix proteins suggested increased production by smooth muscle cells (SMCs). Finally, in Klotho -/- mice with marked vascular calcification, treatment with spironolactone allowed for replacement of calcification by hyalinosis. Klotho deficiency potentiates both endothelial hyperpermeability and SMC dedifferentiation. In the absence of a calcification-inducing stimulus, SMCs assume a synthetic phenotype in response to subendothelial leakage of plasma proteins. In the kidney, this results in arteriolar hyalinosis, which contributes to the decline in renal function. Klotho may play a role in preventing aging-related arteriolar hyalinosis., (Copyright © 2019 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Comorbidity is common as age increases, and currently prescribed treatments often ignore the interconnectedness of the involved age-related diseases. The presence of any one such disease usually increases the risk of having others, and new approaches will be more effective at increasing an individual's health span by taking this systems-level view into account. In this study, we developed gene therapies based on 3 longevity associated genes (fibroblast growth factor 21 [FGF21], αKlotho, soluble form of mouse transforming growth factor-β receptor 2 [sTGFβR2]) delivered using adeno-associated viruses and explored their ability to mitigate 4 age-related diseases: obesity, type II diabetes, heart failure, and renal failure. Individually and combinatorially, we applied these therapies to disease-specific mouse models and found that this set of diverse pathologies could be effectively treated and in some cases, even reversed with a single dose. We observed a 58% increase in heart function in ascending aortic constriction ensuing heart failure, a 38% reduction in α-smooth muscle actin (αSMA) expression, and a 75% reduction in renal medullary atrophy in mice subjected to unilateral ureteral obstruction and a complete reversal of obesity and diabetes phenotypes in mice fed a constant high-fat diet. Crucially, we discovered that a single formulation combining 2 separate therapies into 1 was able to treat all 4 diseases. These results emphasize the promise of gene therapy for treating diverse age-related ailments and demonstrate the potential of combination gene therapy that may improve health span and longevity by addressing multiple diseases at once., Competing Interests: Conflict of interest statement: N.D., D.O., and G.M.C. are founders of Rejuvenate Bio. N.D. and G.M.C. are named inventors on a patent application related to the technologies described in this article., (Copyright © 2019 the Author(s). Published by PNAS.)

Obese women have higher risk of bearing breast tumors that are highly aggressive and resistant to therapies. Tumor-promoting effects of obesity occur locally via adipose inflammation and related alterations to the extracellular matrix (ECM) as well as systemically via circulating metabolic mediators (e.g., free fatty acids, FFA) associated with excess adiposity and implicated in toll-like receptor-mediated activation of macrophages-key cellular players in obesity-related cancer progression. Although the contribution of macrophages to proneoplastic effects of obesity is well documented, the role of ECM components and their enzymatic degradation is less appreciated. We show that heparanase, the sole mammalian endoglucuronidase that cleaves heparan sulfate in ECM, is preferentially expressed in clinical/experimental obesity-associated breast tumors. Heparanase deficiency abolished obesity-accelerated tumor progression in vivo . Heparanase orchestrated a complex molecular program that occurred concurrently in adipose and tumor tissue and sustained the cancer-promoting action of obesity. Heparanase was required for adipose tissue macrophages to produce inflammatory mediators responsible for local induction of aromatase, a rate-limiting enzyme in estrogen biosynthesis. Estrogen upregulated heparanase in hormone-responsive breast tumors. In subsequent stages, elevated levels of heparanase induced acquisition of procancerous phenotype by tumor-associated macrophages, resulting in activation of tumor-promoting signaling and acceleration of breast tumor growth under obese conditions. As techniques to screen for heparanase expression in tumors become available, these findings provide rational and a mechanistic basis for designing antiheparanase approaches to uncouple obesity and breast cancer in a rapidly growing population of obese patients. SIGNIFICANCE: This study reveals the role of heparanase in promoting obesity-associated breast cancer and provides a mechanistically informed approach to uncouple obesity and breast cancer in a rapidly growing population of obese patients., (©2019 American Association for Cancer Research.)

The glycocalyx is a dense layer of carbohydrate chains involved in numerous and fundamental biological processes, such as cellular and tissue homeostasis, inflammation and disease development. Composed of membrane-bound glycoproteins, sulfated proteoglycans and glycosaminoglycan side-chains, this structure is particularly essential for blood vascular barrier functions and leukocyte diapedesis. Interestingly, whilst the glycocalyx of blood vascular endothelium has been extensively studied, little is known about the composition and function of this glycan layer present on tissue-associated lymphatic vessels (LVs). Here, we applied confocal microscopy to characterize the composition of endothelial glycocalyx of initial lymphatic capillaries in murine cremaster muscles during homeostatic and inflamed conditions using an anti-heparan sulfate (HS) antibody and a panel of lectins recognizing different glycan moieties of the glycocalyx. Our data show the presence of HS, α-D-galactosyl moieties, α2,3-linked sialic acids and, to a lesser extent, N-Acetylglucosamine moieties. A similar expression profile was also observed for LVs of mouse and human skins. Interestingly, inflammation of mouse cremaster tissues or ear skin as induced by TNF-stimulation induced a rapid (within 16 h) remodeling of the LV glycocalyx, as observed by reduced expression of HS and galactosyl moieties, whilst levels of α2,3-linked sialic acids remains unchanged. Furthermore, whilst this response was associated with neutrophil recruitment from the blood circulation and their migration into tissue-associated LVs, specific neutrophil depletion did not impact LV glycocalyx remodeling. Mechanistically, treatment with a non-anticoagulant heparanase inhibitor suppressed LV HS degradation without impacting neutrophil migration into LVs. Interestingly however, inhibition of glycocalyx degradation reduced the capacity of initial LVs to drain interstitial fluid during acute inflammation. Collectively, our data suggest that rapid remodeling of endothelial glycocalyx of tissue-associated LVs supports drainage of fluid and macromolecules but has no role in regulating neutrophil trafficking out of inflamed tissues via initial LVs., (Copyright © 2019 Arokiasamy, King, Boulaghrasse, Poston, Nourshargh, Wang and Voisin.)

Approximately 20% of the world's population will be around or above 65 years of age by the next decade. Out of these, 40% are suspected to have cardiovascular diseases as a cause of mortality. Arteriosclerosis, characterized by increased vascular calcification, impairing Windkessel effect and tissue perfusion, and determining end-organ damage, is a hallmark of vascular pathology in the elderly population. Risk factors accumulated during aging affect the normal physiological and vascular aging process, which contributes to the progression of arteriosclerosis. Traditional risk factors, age-associated diseases, and respective regulating mechanisms influencing vascular calcification and vascular stiffness have been extensively studied for many years. Despite the well-known fact that aging alone can induce vascular damage, specific mechanisms that implicate physiological aging in vascular calcification, contributing to vascular stiffness, are poorly understood. This review focuses on mechanisms activated during normal aging, for example, cellular senescence, autophagy, extracellular vesicles secretion, and oxidative stress, along with the convergence of premature aging models' pathophysiology, such as Hutchinson-Gilford Progeria (prelamin accumulation) and Klotho deficiency, to understand vascular calcification in aging. Understanding the mechanisms of vascular damage in aging that intersect with age-associated diseases and risk factors is crucial to foster innovative therapeutic targets to mitigate cardiovascular disease. Visual Overview- An online visual overview is available for this article.

This study investigated the protective effects of melatonin (MT) against cisplatin (CP)-induced acute kidney injury in rats as well as its possible mechanism of action associated with anti-aging protein Klotho. The following four experimental groups were evaluated: vehicle control, CP (7 mg/kg), CP&MT20 (20 mg/kg/day), and CP&MT40 (40 mg/kg/day). The concomitant administration of MT significantly ameliorated CP-induced acute kidney injury in rats, as evidenced by increased kidney weight, increased serum levels of blood urea nitrogen and creatinine, and increased incidence of histopathological alterations with renal tubular cell apoptosis. In addition, MT treatment protected kidney tissue against oxidative damages and significantly upregulated the expression level of Klotho decreased by CP treatment, resulting in reduced phosphorylation of protein kinase B (AKT) and forkhead box O (FOXO) as well as reduced expression levels of B-cell lymphoma 2-associated X protein (Bax) and caspase-3. MT not only partially regulated oxidative stress via AKT/FOXO signaling, but also reduced apoptosis caused by CP by inhibiting the Bax/caspase-3 pathway. Our results indicated that MT could prevent acute kidney injury induced by CP in rats, presumably through upregulating the expression of Klotho, resulting in elevated anti-oxidant and anti-apoptotic properties., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Aims and Background: Alpha Klotho is a transmembrane protein that serves as co-receptor for FGF23. Ectodomain of membrane bound α Klotho may be shed by membrane bound proteases (activated, among other factors, by tumor necrosis factor (TNF)-α) generating the soluble form of the protein (sKl) that functions as a hormone by itself. It modulates calcium influx into cells, blunts IGF-1/Insulin signaling, promotes synthesis of antioxidants, generally slows down tumor progression, delays cell senescence, is neuroprotective and promotes oligodendrocyte maturation and myelin synthesis, and muscle rejuvenation. It may be involved in inflammation and exerts antifibrogenic effects. Some of these pathways may become altered in alcoholism or liver cirrhosis, but data are scattered and scarce and an update is required., Method: Literature survey., Results and Conclusions: Alcohol consumption in non-alcoholics is inversely related to sKl, but alcoholic cirrhotics showed higher-than-normal sKl values in association with liver function derangement. In hepatoma cells, the intensity of Klotho staining was related to faster tumor progression and a shortened life span. Among severe alcoholic cirrhotics sKl is directly related to serum TNF-α levels, and, inversely, to brain atrophy. Given the antioxidant, anti-inflammatory, and antifibrogenic effects of Klotho, perhaps the increase in cirrhosis (and in other inflammatory conditions, such as sepsis or cancer) reflects an attempt to regulate increased inflammation, but clinical and experimental research is urgently needed in this field., (© The Author(s) 2019. Medical Council on Alcohol and Oxford University Press. All rights reserved.)

Klotho gene polymorphisms have been implicated in healthy aging, but inconsistences in findings from previous case-control studies have raised concerns regarding the associations between KLOTHO gene polymorphisms and susceptibility to aging-related diseases and longevity. Hence, this meta-analysis was performed. We assessed the associations between two polymorphisms (G-395 A/rs1207568 and F352 V/rs9536314) and five parameters (urolithiasis, cognitive impairment, cardiovascular disease, cancer, and longevity) by calculating pooled odds ratios with 95% confidence intervals. According to the pooled results, the G allele of the G-395 A polymorphism conferred a significantly higher risk of urolithiasis; G-395 A was related to the susceptibility to cardiovascular disease under allele, dominant, and recessive models. There was no significant association between the G-395 A polymorphism and cognitive impairment among the elderly. The F allele of the F352 V polymorphism protected against breast and ovarian cancer susceptibility. Interestingly, based on the results of the subgroup analysis, the F352 V polymorphism was associated with the overall risk of neoplasms in BRCA1 mutation carriers but not in BRCA2 mutation carriers. Moreover, the F allele played a protective role in determining human longevity. In conclusion, Klotho G-395 A polymorphisms were associated with urolithiasis and cardiovascular disease but not with cognitive impairment. Additionally, Klotho F352 V polymorphisms were associated with cancers and longevity., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Bacterial endotoxins have been shown to induce prosurvival autophagy or apoptosis in fibroblasts and thus impair the wound healing process. Endoplasmic reticulum has been proposed as a molecular switch between these processes and klotho protein possessing pleiotropic characteristics seems to be involved in both processes, however the exact molecular mechanism is unknown. In this study, we have evaluated the effect of klotho silencing on human fibroblasts exposed to a non-toxic dose of lipopolysaccharide in terms of in vitro wound healing ability. We show for the first time, that klotho silencing in fibroblasts intensified lipopolysaccharide-induced oxidative stress and inflammatory response, what resulted in genomic instability, p-eIF2a-mediated ER stress, retardation of prosurvival autophagy, induction of apoptotic cell death and finally in impaired wound closure. Therefore, our data suggest that klotho serves as a part of cellular defense mechanism engaged in providing protection against bacterial infections during wound healing by modulating ER-signaling crosstalk between autophagy and apoptosis.

Purpose of Review: The current review examines what is known about the FGF-23/α-Klotho co-dependent and independent pathophysiological effects, and whether FGF-23 and/or α-Klotho are potential therapeutic targets., Recent Findings: FGF-23 is a hormone derived mainly from bone, and α-Klotho is a transmembrane protein. Together they form a trimeric signaling complex with FGFRs in target tissues to mediate the physiological functions of FGF-23. Local and systemic factors control FGF-23 release from osteoblast/osteocytes in bone, and circulating FGF-23 activates FGFR/α-Klotho complexes in kidney proximal and distal renal tubules to regulate renal phosphate excretion, 1,25 (OH)2D metabolism, sodium and calcium reabsorption, and ACE2 and α-Klotho expression. The resulting bone-renal-cardiac-immune networks provide a new understanding of bone and mineral homeostasis, as well as identify other biological effects FGF-23. Direct FGF-23 activation of FGFRs in the absence of α-Klotho is proposed to mediate cardiotoxic and adverse innate immune effects of excess FGF-23, particularly in chronic kidney disease, but this FGF-23, α-Klotho-independent signaling is controversial. In addition, circulating soluble Klotho (sKl) released from the distal tubule by ectodomain shedding is proposed to have beneficial health effects independent of FGF-23., Summary: Separation of FGF-23 and α-Klotho independent functions has been difficult in mammalian systems and understanding FGF-23/α-Klotho co-dependent and independent effects are incomplete. Antagonism of FGF-23 is important in treatment of hypophosphatemic disorders caused by excess FGF-23, but its role in chronic kidney disease is uncertain. Administration of recombinant sKl is an unproven therapeutic strategy that theoretically could improve the healt span and lifespan of patients with α-Klotho deficiency.

Acute kidney injury (AKI) is associated with many of the same mineral metabolite abnormalities that are observed in chronic kidney disease. These include increased circulating levels of the osteocyte-derived, vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23), and decreased renal expression of klotho, the co-receptor for FGF23. Recent data have indicated that increased FGF23 and decreased klotho levels in the blood and urine could serve as novel predictive biomarkers of incident AKI, or as novel prognostic biomarkers of adverse outcomes in patients with established AKI. In addition, because FGF23 and klotho exert numerous classic as well as off-target effects on a variety of organ systems, targeting their dysregulation in AKI may represent a unique opportunity for therapeutic intervention. We review the pathophysiology, kinetics, and regulation of FGF23 and klotho in animal and human studies of AKI, and we discuss the challenges and opportunities involved in targeting FGF23 and klotho therapeutically., (Copyright © 2018. Published by Elsevier Inc.)

The Klotho proteins, αKlotho and βKlotho, are essential components of endocrine fibroblast growth factor (FGF) receptor complexes, as they are required for the high-affinity binding of FGF19, FGF21 and FGF23 to their cognate FGF receptors (FGFRs). Collectively, these proteins form a unique endocrine system that governs multiple metabolic processes in mammals. FGF19 is a satiety hormone that is secreted from the intestine on ingestion of food and binds the βKlotho-FGFR4 complex in hepatocytes to promote metabolic responses to feeding. By contrast, under fasting conditions, the liver secretes the starvation hormone FGF21, which induces metabolic responses to fasting and stress responses through the activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system following binding to the βKlotho-FGFR1c complex in adipocytes and the suprachiasmatic nucleus, respectively. Finally, FGF23 is secreted by osteocytes in response to phosphate intake and binds to αKlotho-FGFR complexes, which are expressed most abundantly in renal tubules, to regulate mineral metabolism. Growing evidence suggests that the FGF-Klotho endocrine system also has a crucial role in the pathophysiology of ageing-related disorders, including diabetes, cancer, arteriosclerosis and chronic kidney disease. Therefore, targeting the FGF-Klotho endocrine axes might have therapeutic benefit in multiple systems; investigation of the crystal structures of FGF-Klotho-FGFR complexes is paving the way for the development of drugs that can regulate these axes.

Klotho is highly expressed in the kidney, while soluble Klotho is detectable in the blood, urine, and cerebrospinal fluid, and has multiple hormone-like functions. The role of Klotho in kidney injury has attracted more and more attentions from researchers. Emerging evidence revealed that the transient deficiency of Klotho is an early event of acute kidney injury (AKI), whereas, in chronic kidney disease, this deficiency is sustained not only in the kidney, but also in other organ systems. Therefore, Klotho could be a potential biomarker for early diagnosis of AKI, as well as for its progression to chronic kidney disease. Moreover, Klotho might have therapeutic value to renal injury. Nevertheless, there are only few studies on the involvement of Klotho in post AKI repair. This review focused on the role of Klotho in not only kidney injury, but also its repair, in particular the relationship between Klotho and cell fate (autophagy/apoptosis/necrosis), repair/regeneration, Wnt/β-catenin and erythropoietin receptor, one of the Klotho effectors.

BACKGROUND Klotho protein has been shown to act as a hormone on the cardiovascular system, and to have specific protective effects on vascular endothelial cells. The aim of this study was to investigate the mechanisms of the anti-oxidative and anti-apoptotic effects of klotho protein on hydrogen peroxide (H₂O₂)-induced apoptosis and endoplasmic reticulum oxidative stress in human umbilical vein endothelial cells (HUVECs). MATERIAL AND METHODS HUVECs were cultured in vitro and treated with H₂O₂. The MTT assay evaluated cell viability of H₂O₂-treated HUVECs, and flow cytometry measured cell apoptosis. An enzyme-linked immunosorbent assay (ELISA) measured the levels of nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-6. Western blot was used to detect the expression of the proteins, 78 kD glucose-regulated protein (GRP78), CCAAT-enhancer-binding protein homologous protein (CHOP), caspase-3, caspase-9, caspase-12, and AKT. The effects of LY294002, a pharmacological inhibitor of PI3K, were evaluated. RESULTS Klotho protein increased the viability of H2O2-treated HUVECs and reduced the expression of NO, TNF-α, and IL-6. Klotho protein reduced the rate of apoptosis of H₂O₂-treated HUVECs and downregulated the expression of proteins associated with endoplasmic reticulum oxidative stress, GRP78 and CHOP, and the expression of the apoptotic proteins, caspase-3, caspase-9, and caspase-12, and activated the phosphorylation of AKT. The addition of LY294002 inhibited klotho protein downregulation of GRP78, CHOP, caspase-3, caspase-9, and caspase-12 expression. CONCLUSIONS In HUVECs, klotho protein suppressed apoptosis mediated by endoplasmic reticulum oxidative stress by activation of the PI3K/AKT pathway.

Chronic kidney disease (CKD) is an inherently systemic disease that refers to a long-term loss of kidney function. The progression of CKD has repercussions for other organs, leading to many kinds of extrarenal complications. Intensive studies are now being undertaken to reveal the risk factors and pathophysiological mechanism of this disease. During the past 20 years, increasing evidence from clinical and basic studies has indicated that klotho, which was initially known as an anti-aging gene and is mainly expressed in the kidney, is significantly correlated with the development and progression of CKD and its complications. Here, we discuss in detail the role and pathophysiological implications of klotho in ion disorders, the inflammation response, vascular calcification, mineral bone disorders, and renal fibrosis in CKD. Based on the pathogenic mechanism of klotho deficiency and klotho decline in urine early in CKD stage 2 and even earlier in CKD stage 1, it is not difficult to understand that soluble klotho can serve as an early and sensitive marker of CKD. Moreover, the prevention of klotho decline by several mechanisms can attenuate renal injuries, retard CKD progression, ameliorate extrarenal complications, and improve renal function. In this review, we focus on the functions and pathophysiological implications of klotho in CKD and its extrarenal complications as well as its potential applications as a diagnostic and/or prognostic biomarker for CKD and as a novel treatment strategy to improve and decrease the burden of comorbidity in CKD.

Aging is characterized by a reduced ability to defend against stress, an inability to maintain homeostasis, and an increased risk of disease. In this study, a metabolomics approach was used to identify novel metabolic pathways that are perturbed in a mouse model of accelerated aging (SAMP1/kl-/-) and to gain new insights into the metabolic associations of the metformin derivative HL156A. Extensive inflammation and calcification were observed in the tissues of the SAMP1/kl-/- mice with premature aging. In mouse embryonic fibroblasts (MEFs) obtained from SAMP1/kl-/- mice, we observed that HL156A induced FOXO1 expression through inhibition of the IGF-1/AKT/mTOR signaling pathways. Treatment of HL156A decreased reactive oxygen species production and enhanced mitochondrial transmembrane potential in SAMP1/kl-/- MEFs. A metabolomic profile analysis showed that HL156A increased the GSH/GSSG ratio in the kidneys of SAMP1/kl-/- mice (8-12 weeks old). In addition, treating SAMP1/kl-/- mice with HL156A (30 mg/kg) for 4 weeks improved survival and decreased the significant elevation of oxidized GSH (GSSG) that was observed in SAMP1/kl-/- mice. In histological sections, HL156A administered SAMP1/kl-/- mice exhibited a decrease in excessive calcification. Based on these findings, we conclude that the new metformin derivative HL156A may inhibit oxidative damage by inducing glutathione metabolism and antioxidant pathways.

αKlotho is a gene regulator of aging, increasing life expectancy when overexpressed and accelerating the development of aging phenotypes when inhibited. In mice, expression levels of the secreted isoform Klotho (s-KL) are very high in the brain, suggesting that s-KL activity may have an important role in the nervous system. Here we study the functional relevance at behavioural level of modifying s-KL levels in the aging brain. We used AAVrh10 vectors to deliver and sustained expression of s-KL in 6- and 12-month-old wild-type C57BL/6J males. This study demonstrates for we believe the first time in vivo that 6 months after a single injection of s-KL into the central nervous system, long-lasting and quantifiable enhancement of learning and memory capabilities are found. More importantly, cognitive improvement is also observable in 18-month-old mice treated once, at 12 months of age. These findings demonstrate the therapeutic potential of s-KL as a treatment for cognitive decline associated with aging.

Aggregated metastatic cancer cells, referred to as circulating tumor cell (CTC) clusters, are present in the blood of cancer patients and contribute to cancer metastasis. However, the origin of CTC clusters, especially intravascular aggregates, remains unknown. Here, we employ suspension culture methods to mimic CTC cluster formation in the circulation of breast cancer patients. CTC clusters generated using these methods exhibited an increased metastatic potential that was defined by the overexpression of heparanase (HPSE). Heparanase induced FAK- and ICAM-1-dependent cell adhesion, which promoted intravascular cell aggregation. Moreover, knockdown of heparanase or inhibition of its activity with JG6, a heparanase inhibitor, was sufficient to block the formation of cell clusters and suppress breast cancer metastasis. Our data reveal that heparanase-mediated cell adhesion is critical for metastasis mediated by intravascular CTC clusters. We also suggest that targeting the function of heparanase in cancer cell dissemination might limit metastatic progression.

Background: Klotho is a well-known anti-aging hormone, which serves as a suppressor of aging through a variety of mechanisms. Aging of skeletal muscle is concomitant with a decrease in muscle stem cell function resulting in impaired regeneration., Methods: Here we investigate the functional role of the anti-aging hormone Klotho for muscle stem cell function after cardiotoxin-induced injury of skeletal muscle using a klotho hypomorphic mouse line, which is characterized by a premature aging phenotype. Furthermore, we perform floating single myofiber cultures with their adjacent muscle stem cells to investigate the interplay between canonical Wnt signaling and Klotho function., Results: We demonstrate that muscle stem cell numbers are significantly decreased in klotho hypomorphic mice. Furthermore, we show that muscle stem cell function is also severely impaired upon loss of klotho expression, in culture and during regeneration in vivo. Moreover, we demonstrate that addition of recombinant Klotho protein inhibits aberrant excessive Wnt signaling in aged muscle stem cells thereby restoring their functionality., Conclusions: The anti-aging hormone Klotho counteracts aberrant canonical Wnt signaling in muscle stem cells and might be one of the naturally occurring inhibitors of canonical Wnt signaling in skeletal muscle.

The pathogenesis of parathyroid gland hyperplasia is poorly understood, and a better understanding is essential if there is to be improvement over the current strategies for prevention and treatment of secondary hyperparathyroidism. Here we investigate the specific role of Klotho expressed in the parathyroid glands (PTGs) in mediating parathyroid hormone (PTH) and serum calcium homeostasis, as well as the potential interaction between calcium-sensing receptor (CaSR) and Klotho. We generated mouse strains with PTG-specific deletion of Klotho and CaSR and dual deletion of both genes. We show that ablating CaSR in the PTGs increases PTH synthesis, that Klotho has a pivotal role in suppressing PTH in the absence of CaSR, and that CaSR together with Klotho regulates PTH biosynthesis and PTG growth. We utilized the tdTomato gene in our mice to visualize and collect PTGs to reveal an inhibitory function of Klotho on PTG cell proliferation. Chronic hypocalcemia and ex vivo PTG culture demonstrated an independent role for Klotho in mediating PTH secretion. Moreover, we identify an interaction between PTG-expressed CaSR and Klotho. These findings reveal essential and interrelated functions for CaSR and Klotho during parathyroid hyperplasia., Competing Interests: The authors declare no conflict of interest.

The mitotic spindle, assembled by microtubule organization center (MTOC), is a critical structure required for proper chromosome segregation during mitosis. Studies demonstrated that defects of mitotic spindle assembling would result in chromosome instability, associating with oncogenesis. In this study, we identified that heparanase (HPSE) was localized on MTOC in mitotic cells. Induced expression of HPSE in human airway epithelial cells promoted mitotic spindle formation, and silencing of HPSE expression disrupted the mitotic spindle formation, resulting in chromosome instability, including chromosome mis-segregation and increased micronuclei formation. In conclusion, HPSE is an important protein in regulation of mitotic spindle and loss of HPSE function on MTOC associates with chromosome instability, indicating that loss of HPSE on MTOC may play critical roles in oncogenesis.

Duchenne muscular dystrophy (DMD) is a muscle wasting disease in which inflammation influences the severity of pathology. We found that the onset of muscle inflammation in the mdx mouse model of DMD coincides with large increases in expression of pro-inflammatory cytokines [tumor necrosis factor-α (TNFα); interferon gamma (IFNγ)] and dramatic reductions of the pro-myogenic protein Klotho in muscle cells and large increases of Klotho in pro-regenerative, CD206+ macrophages. Furthermore, TNFα and IFNγ treatments reduced Klotho in muscle cells and increased Klotho in macrophages. Because CD206+/Klotho+ macrophages were concentrated at sites of muscle regeneration, we tested whether macrophage-derived Klotho promotes myogenesis. Klotho transgenic macrophages had a pro-proliferative influence on muscle cells that was ablated by neutralizing antibodies to Klotho and conditioned media from Klotho mutant macrophages did not increase muscle cell proliferation in vitro. In addition, transplantation of bone marrow cells from Klotho transgenic mice into mdx recipients increased numbers of myogenic cells and increased the size of muscle fibers. Klotho also acted directly on macrophages, stimulating their secretion of TNFα. Because TNFα is a muscle mitogen, we tested whether the pro-proliferative effects of Klotho on muscle cells were mediated by TNFα and found that increased proliferation caused by Klotho was reduced by anti-TNFα. Collectively, these data show that pro-inflammatory cytokines contribute to silencing of Klotho in dystrophic muscle, but increase Klotho expression by macrophages. Our findings also show that macrophage-derived Klotho can promote muscle regeneration by expanding populations of muscle stem cells and increasing muscle fiber growth in dystrophic muscle., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The aim was to evaluate the role of klotho in the pathogenesis of systemic sclerosis (SSc), through the measurement of its serum concentration in SSc patients compared to healthy controls, and to assess the association with cutaneous and visceral involvement. Blood samples obtained from both SSc patients and healthy controls were analysed by an ELISA assay for the detection of human klotho. SSc patients were globally evaluated for disease activity and assessed through the modified Rodnan's Skin Score, Medsger's scale, pulmonary function tests, 2D-echocardiography, nailfold capillaroscopy and laboratory tests. Our cohort consisted of 69 SSc patients (61 females, mean age 64.5±12.5 years, median disease duration 9.0 (IQR 8) years) and 77 healthy controls (28 females, mean age 49.7±10.2 years). In the group of SSc patients, 19 (27.5%) suffered from a diffuse form of SSc. All patients were receiving IV prostanoids, and some of them were concomitantly treated with immunosuppressive drugs (prednisone, hydroxychloroquine, mofetil mycophenolate, methotrexate, cyclosporin A and azathioprine). The median serum concentration of klotho was significantly lower in patients compared to controls (0.23 ng/mL vs 0.60 ng/mL; p<0.001). However, Spearman's test showed no significant association between klotho serum levels and disease activity, concerning either clinical, laboratory or instrumental findings. Our data show a significant deficit of klotho in SSc patients although any significant association was detected between klotho serum concentration and the clinical, laboratory or instrumental features of the disease. However, due to the limits of the study, further investigations are required.

BACKGROUND Anthracyclines-induced cardiotoxicity has become one of the major restrictions of their clinical applications. Klotho showed cardioprotective effects. This study aimed to investigate the effects and possible mechanisms of klotho on doxorubicin (DOX)-induced cardiotoxicity. MATERIAL AND METHODS Rats and isolated myocytes were exposed to DOX and treated with exogenous klotho. Specific inhibitors and siRNAs silencing MAPKs were also used to treat the animals and/or myocytes. An invasive hemodynamic method was used to determine cardiac functions. Intracellular ROS generation was evaluated by DHE staining. Western blotting was used to determine the phosphorylation levels of JNK, ERK, and p38 MAPKs in plasma extracts and Nrf2 in nuclear extracts. Nuclear translocation of Nrf2 in myocytes was evaluated by immunohistochemistry. Cell apoptosis was evaluated by TUNEL assay and flow cytometry. RESULTS Klotho treatment improved DOX-induced cardiac dysfunction in rats. The DOX-induced ROS accumulation and cardiac apoptosis were attenuated by klotho. Impaired phosphorylations of MAPKs, Nrf2 translocation and expression levels of HO1 and Prx1 were also attenuated by klotho treatment. However, the anti-oxidant and anti-apoptotic effects of klotho on DOX-exposed myocardium and myocytes were impaired by both specific inhibitors and siRNAs against MAPKs. Moreover, the recovery effects of klotho on phosphorylations of MAPKs, Nrf2 translocation and expression levels of HO1 and Prx1 were also impaired by specific inhibitors and siRNAs against MAPKs. CONCLUSIONS By recovering the activation of MAPKs signaling, klotho improved cardiac function loss which was triggered by DOX-induced ROS mediated cardiac apoptosis.