Klotho is a target gene of PPAR-gamma

Interrogating the estrogen-mediated regulation of adrenocortical Klotho expression using ovariectomized albino rat model exposed to repeated restraint stress

Reproductive aging is associated with altered stress response and many other menopausal symptoms. Little is known about the adrenal expression of the anti-aging protein Klotho or how it is modulated by estrogen in ovariectomized stressed rats. Fifty-six Wistar female rats were assigned into seven equal groups. Sham-operated (Sham), sham stressed (Sham/STS), ovariectomized (OVR), ovariectomized stressed (OVR/STS), ovariectomized stressed rosiglitazone-treated (OVR/STS/R), ovariectomized stressed estrogen-treated (OVR/STS/E), and ovariectomized stressed estrogen/GW9662 co-treated (OVR/STS/E/GW) groups. All stressed rats were subjected daily to a one-hour restraint stress test for 19 days. At the end of the experiment, blood was collected for serum corticosterone (CORT) analysis. Adrenal tissues were obtained and prepared for polymerase chain reaction (PCR) assay, hematoxylin and eosin (H&E), immunohistochemistry-based identification of Klotho and PPAR-γ, and Oil Red O (ORO) staining. The rise in serum CORT was negligible in the OVR/STS group, in contrast to the Sham/STS group. The limited CORT response in the former group was restored by estrogen and rosiglitazone and blocked by estrogen/GW9226 co-administration. ORO-staining revealed a more evident reduction in the adrenal fat in the OVR/STS group, which was reversed by estrogen and counteracted by GW. Also, there was a comparable expression pattern of Klotho and PPAR-γ in the adrenals. The adrenal Klotho decreased in the OVR/STS group, but was reversed by estrogen treatment. GW9226/estrogen co-treatment interfered with the regulatory effect of estrogen on Klotho. The study suggested modulation of the adrenal Kotho expression by estrogen, in the ovariectomized rats subjected to a restraint stress test. This estrogen-provided adrenal protection might be mediated by PPAR-γ activation.

Hypermethylation of Klotho and Peroxisome Proliferator-Activated Receptor γ Concomitant with Overexpression of DNA Methyltransferase 1 in Adenomyosis

Cellular senescence is known to be involved in tissue repair, but its role in adenomyosis remains unclear. This study was tasked to evaluate the expression of Klotho, a well-known aging-suppressing protein, as well as PPARγ and DNMT1 in adenomyotic lesions (AD) in comparison with that of control endometrium (CT). We performed immunohistochemistry analysis of markers of cellular senescence p16 and p21, along with Klotho, PPARγ and DNMT1 in CT and AD samples, followed by the quantification of gene expression of Klotho, PPARγ and DNMT1 in epithelial organoids derived from AD and CT samples and methylation-specific PCR to evaluate promoter methylation status. The effect of forced expression and knockdown of DNMT1 on Klotho and PPARγ expression in ectopic endometrial epithelial cells was evaluated. We found that both p16 and p21 immunoreactivity in AD was significantly higher while that of Klotho and PPARγ was significantly lower than CT samples, which was concomitant with elevated immunoexpression of DNMT1. The results were confirmed by transcriptional analysis using epithelial organoids derived from AD and CT samples. In addition, the promoter regions of both Klotho and PPARγ genes were hypermethylated in AD as compared with CT, and treatment with HDAC and DNMT inhibitors reactivated the expression of both Klotho and PPARγ. Forced expression of DNMT1 resulted in downregulation of both Klotho and PPARγ but its knockdown increased their expression. Thus, overexpression of DNMT1 seems to facilitate the promoter hypermethylation of both Klotho and PPARγ in AD, resulting in their reduced expression that is suggestive of the role of senescence in adenomyosis.

The current and emerging Klotho-enhancement strategies

Klotho is well known as a gene with antiaging properties. It has membrane and soluble forms, providing a unique system that controls various metabolic processes essential to health and disease. Klotho deficiency has been revealed to be associated with various aging-related disorders. Based on its various known and unknown protective properties, upregulating the Klotho gene may be a possible therapeutic and/or preventive approach in aging-related complications. Some agents, such as hormonal compounds, renin-angiotensin system inhibitors, antioxidants, peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists, statins, vitamin D receptor agonists, antioxidants, anti-inflammatory agents, mammalian target of rapamycin (mTOR) signaling inhibitors, and receptor-interacting serine/threonine-protein kinase 1 (RIPK1) inhibitors, can possibly lead to the upregulation and elevation of Klotho levels. Demethylation and deacetylation of the Klotho gene can also be considered other possible Klotho-enhancement methods. Some emerging techniques, such as RNA modifications, gene therapy, gene editing, and exosome therapy, probably have the potential to be applied for increasing Klotho. In the present study, these current and emerging Klotho-enhancement strategies and their underlying mechanisms were comprehensively reviewed, which could highlight some potential avenues for future research.

The Importance of α-Klotho in Depression and Cognitive Impairment and Its Connection to Glutamate Neurotransmission-An Up-to-Date Review

Depression is a serious neuropsychiatric disease affecting an increasing number of people worldwide. Cognitive deficits (including inattention, poor memory, and decision-making difficulties) are common in the clinical picture of depression. Cognitive impairment has been hypothesized to be one of the most important components of major depressive disorder (MDD; referred to as clinical depression), although typical cognitive symptoms are less frequent in people with depression than in people with schizophrenia or bipolar disorder (BD; sometimes referred to as manic-depressive disorder). The importance of α-Klotho in the aging process has been well-documented. Growing evidence points to the role of α-Klotho in regulating other biological functions, including responses to oxidative stress and the modulation of synaptic plasticity. It has been proven that a Klotho deficit may contribute to the development of various nervous system pathologies, such as behavioral disorders or neurodegeneration. Given the growing evidence of the role of α-Klotho in depression and cognitive impairment, it is assumed that this protein may be a molecular link between them. Here, we provide a research review of the role of α-Klotho in depression and cognitive impairment. Furthermore, we propose potential mechanisms (related to oxidative stress and glutamatergic transmission) that may be important in α-Klotho-mediated regulation of mental and cognitive function.

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

BACKGROUND AND AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Histamine deficiency inhibits lymphocyte infiltration in the submandibular gland of aged mice via increased anti-aging factor Klotho

OBJECTIVES

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various tissues and is induced by proinflammatory cytokines such as TNFα. As they age, C57BL/6 mice show auto-antibody deposition and lymphocyte infiltration into various tissues, including salivary glands. However, the mechanism underlying cell infiltration and the change in HDC expression in salivary glands with aging remain unclear. Thus, we aimed to elucidate the relationship between histamine and inflammaging.

METHODS

We investigated the change in histology and HDC expression in the major salivary glands (parotid, submandibular, and sublingual) of 6-week- and 9-month-old wild-type mice. We also determined the histological changes, cytokine expression, and anti-aging factor Klotho in the salivary glands of 9-month-old wild-type and HDC-deficient (HDC-KO) mice.

RESULTS

Cell infiltration was observed in the submandibular gland of 9-month-old wild-type mice. Although most cells infiltrating the submandibular glands were CD3-positive and B220-positive lymphocytes, CD11c-positive and F4/80-positive monocyte lineages were also detected. HDC, TNFα, and IL-1β mRNA expression increased in the submandibular gland of 9-month-old wild-type mice. The expression of PPARγ, an anti-inflammatory protein, declined in 9-month-old wild-type mice, and Klotho expression increased in 9-month-old HDC-KO mice. Immunohistochemistry showed that Klotho-positive cells disappeared in the submandibular gland of 9-month-old wild-type mice, while Klotho was detected in all salivary glands in HDC-KO mice of the same age.

CONCLUSION

Our findings demonstrate the multifunctionality of histamine and can aid in the development of novel therapeutic methods for inflammatory diseases such as Sjogren's syndrome and age-related dysfunctions.

Programmed ageing: decline of stem cell renewal, immunosenescence, and Alzheimer's disease

The characteristic maximum lifespan varies enormously across animal species from a few hours to hundreds of years. This argues that maximum lifespan, and the ageing process that itself dictates lifespan, are to a large extent genetically determined. Although controversial, this is supported by firm evidence that semelparous species display evolutionarily programmed ageing in response to reproductive and environmental cues. Parabiosis experiments reveal that ageing is orchestrated systemically through the circulation, accompanied by programmed changes in hormone levels across a lifetime. This implies that, like the circadian and circannual clocks, there is a master 'clock of age' (circavital clock) located in the limbic brain of mammals that modulates systemic changes in growth factor and hormone secretion over the lifespan, as well as systemic alterations in gene expression as revealed by genomic methylation analysis. Studies on accelerated ageing in mice, as well as human longevity genes, converge on evolutionarily conserved fibroblast growth factors (FGFs) and their receptors, including KLOTHO, as well as insulin-like growth factors (IGFs) and steroid hormones, as key players mediating the systemic effects of ageing. Age-related changes in these and multiple other factors are inferred to cause a progressive decline in tissue maintenance through failure of stem cell replenishment. This most severely affects the immune system, which requires constant renewal from bone marrow stem cells. Age-related immune decline increases risk of infection whereas lifespan can be extended in germfree animals. This and other evidence suggests that infection is the major cause of death in higher organisms. Immune decline is also associated with age-related diseases. Taking the example of Alzheimer's disease (AD), we assess the evidence that AD is caused by immunosenescence and infection. The signature protein of AD brain, Aβ, is now known to be an antimicrobial peptide, and Aβ deposits in AD brain may be a response to infection rather than a cause of disease. Because some cognitively normal elderly individuals show extensive neuropathology, we argue that the location of the pathology is crucial - specifically, lesions to limbic brain are likely to accentuate immunosenescence, and could thus underlie a vicious cycle of accelerated immune decline and microbial proliferation that culminates in AD. This general model may extend to other age-related diseases, and we propose a general paradigm of organismal senescence in which declining stem cell proliferation leads to programmed immunosenescence and mortality.

Klotho Upregulation via PPARγ Contributes to the Induction of Brain Ischemic Tolerance by Cerebral Ischemic Preconditioning in Rats

Cerebral ischemic preconditioning (CIP)-induced brain ischemic tolerance protects neurons from subsequent lethal ischemic insult. However, the specific mechanisms underlying CIP remain unclear. In the present study, we explored the hypothesis that peroxisome proliferator-activated receptor gamma (PPARγ) participates in the upregulation of Klotho during the induction of brain ischemic tolerance by CIP. First we investigated the expression of Klotho during the brain ischemic tolerance induced by CIP. Lethal ischemia significantly decreased Klotho expression from 6 h to 7 days, while CIP significantly increased Klotho expression from 12 h to 7 days in the hippocampal CA1 region. Inhibition of Klotho expression by its shRNA blocked the neuroprotection induced by CIP. These results indicate that Klotho participates in brain ischemic tolerance by CIP. Furthermore, we tested the role of PPARγ in regulating Klotho expression after CIP. CIP caused PPARγ protein translocation to the nucleus in neurons in the CA1 region of the hippocampus. Pretreatment with GW9962, a PPARγ inhibitor, significantly attenuated the upregulation of Klotho protein and blocked the brain ischemic tolerance induced by CIP. Taken together, it can be concluded that Klotho upregulation via PPARγ contributes to the induction of brain ischemic tolerance by CIP.

The Value of Klotho in Kidney Transplantation

Kidney transplant recipients have better survival rates and improved quality of life than long-term dialysis patients. However, delayed graft function, immunosuppressive therapy nephrotoxicity, and rejection episodes may compromise graft and patient survival. The KL gene is highly expressed in kidney tubular cells and encodes the antiaging and kidney-protective protein Klotho, which has membrane-anchored and soluble forms and regulates mineral metabolism. Klotho expression decreases during acute kidney injury or chronic kidney disease, and human chronic kidney disease shares features of accelerated aging with murine Klotho deficiency. In this work, we review clinical studies on the relationship between Klotho and kidney transplantation. Specifically, we address the dynamics of serum and kidney Klotho levels in donors and kidney transplant recipients, the role of Klotho as a marker of current graft function and graft outcomes, and the potential impact of Klotho on kidney protection in the transplantation context. A better understanding of the potential biomarker and therapeutic utility of Klotho in kidney transplant recipients may provide new insights into the control of graft function and new therapeutic strategies to preserve allograft function.

Deciphering the role of lipoproteins and lipid metabolic alterations in ageing and ageing-associated renal fibrosis

Fibrosis is the ultimate pathological feature of many chronic diseases, and ageing a major risk factor for fibrotic diseases. Current therapies are limited to those that reduce the rate of functional decline in patients with mild to moderate disease, but few interventions are available to specifically target the pathogenesis of fibrosis. In this context, new treatments that can significantly improve survival time and quality of life for these patients are urgently needed. In this review, we outline both the synthesis and metabolism of lipids and lipoproteins associated with ageing-associated renal fibrosis and the prominent contribution of lipids and lipidomics in the discovery of biomarkers that can be used for the prevention, diagnosis, and treatment of renal ageing and fibrosis. Next, we describe the effect of dyslipidaemia on ageing-related renal fibrosis and the pathophysiological changes in the kidney caused by dyslipidaemia. We then summarize the enzymes, transporters, transcription factors, and RNAs that contribute to dysregulated lipid metabolism in renal fibrosis and discuss their role in renal fibrosis in detail. We conclude by discussing the progress in research on small molecule therapeutic agents that prevent and treat ageing and ageing-associated renal fibrosis by modulating lipid metabolism. A growing number of studies suggest that restoring aberrant lipid metabolism may be a novel and promising therapeutic strategy to combat ageing and ageing-associated renal fibrosis.

Klotho, Oxidative Stress, and Mitochondrial Damage in Kidney Disease

Reducing oxidative stress stands at the center of a prevention and control strategy for mitigating cellular senescence and aging. Kidney disease is characterized by a premature aging syndrome, and to find a modulator targeting against oxidative stress, mitochondrial dysfunction, and cellular senescence in kidney cells could be of great significance to prevent and control the progression of this disease. This review focuses on the pathogenic mechanisms related to the appearance of oxidative stress damage and mitochondrial dysfunction in kidney disease. In this scenario, the anti-aging Klotho protein plays a crucial role by modulating signaling pathways involving the manganese-containing superoxide dismutase (Mn-SOD) and the transcription factors FoxO and Nrf2, known antioxidant systems, and other known mitochondrial function regulators, such as mitochondrial uncoupling protein 1 (UCP1), B-cell lymphoma-2 (BCL-2), Wnt/β-catenin, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1 alpha), transcription factor EB, (TFEB), and peroxisome proliferator-activated receptor gamma (PPAR-gamma). Therefore, Klotho is postulated as a very promising new target for future therapeutic strategies against oxidative stress, mitochondria abnormalities, and cellular senescence in kidney disease patients.

Klotho's impact on diabetic nephropathy and its emerging connection to diabetic retinopathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide and is a significant burden on healthcare systems. α-klotho (klotho) is a protein known for its anti-aging properties and has been shown to delay the onset of age-related diseases. Soluble klotho is produced by cleavage of the full-length transmembrane protein by a disintegrin and metalloproteases, and it exerts various physiological effects by circulating throughout the body. In type 2 diabetes and its complications DN, a significant decrease in klotho expression has been observed. This reduction in klotho levels may indicate the progression of DN and suggest that klotho may be involved in multiple pathological mechanisms that contribute to the onset and development of DN. This article examines the potential of soluble klotho as a therapeutic agent for DN, with a focus on its ability to impact multiple pathways. These pathways include anti-inflammatory and oxidative stress, anti-fibrotic, endothelial protection, prevention of vascular calcification, regulation of metabolism, maintenance of calcium and phosphate homeostasis, and regulation of cell fate through modulation of autophagy, apoptosis, and pyroptosis pathways. Diabetic retinopathy shares similar pathological mechanisms with DN, and targeting klotho may offer new insights into the prevention and treatment of both conditions. Finally, this review assesses the potential of various drugs used in clinical practice to modulate klotho levels through different mechanisms and their potential to improve DN by impacting klotho levels.

Role of Klotho Protein in Neuropsychiatric Disorders: A Narrative Review

Neuropsychiatric disorders are comprised of diseases having both the neurological and psychiatric manifestations. The increasing burden of the disease on the population worldwide makes it necessary to adopt measures to decrease the prevalence. The Klotho is a single pass transmembrane protein that decreases with age, has been associated with various pathological diseases, like reduced bone mineral density, cardiac problems and cognitive impairment. However, multiple studies have explored its role in different neuropsychiatric disorders. A comprehensive search was undertaken in the Pubmed database for articles with the keywords "Klotho" and "neuropsychiatric disorders". The available literature, based on the above search strategy, has been compiled in this brief narrative review to describe the emerging role of Klotho in various neuropsychiatric disorders. The Klotho levels were decreased in various neuropsychiatric disorders except for bipolar disorder. A suppressed Klotho protein levels induced oxidative stress and incited pro-inflammatory conditions significantly contributing to the pathophysiology of neuropsychiatric disorder. The increasing evidence of altered Klotho protein levels in cognition-decrement-related disorders warrants its consideration as a biomarker in various neuropsychiatric diseases. However, further evidence is required to understand its role as a therapeutic target.

A systematic review and meta-analysis demonstrating Klotho as an emerging exerkine

Klotho is an anti-aging protein with several therapeutic roles in the pathophysiology of different organs, such as the skeletal muscle and kidneys. Available evidence suggests that exercise increases Klotho levels, regardless of the condition or intervention, shedding some light on this anti-aging protein as an emergent and promising exerkine. Development of a systematic review and meta-analysis in order to verify the role of different exercise training protocols on the levels of circulating soluble Klotho (S-Klotho) protein. A systematic search of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE through PubMed, EMBASE, CINAHL, CT.gov, and PEDro. Randomized and quasi-randomized controlled trials that investigated effects of exercise training on S-Klotho levels. We included 12 reports in the analysis, comprising 621 participants with age ranging from 30 to 65 years old. Klotho concentration increased significantly after chronic exercise training (minimum of 12 weeks) (Hedge' g [95%CI] 1.3 [0.69-1.90]; P < 0.0001). Moreover, exercise training increases S-Klotho values regardless of the health condition of the individual or the exercise intervention, with the exception of combined aerobic + resistance training. Furthermore, protocol duration and volume seem to influence S-Klotho concentration, since the effect of the meta-analysis changes when subgrouping these variables. Altogether, circulating S-Klotho protein is altered after chronic exercise training and it might be considered an exerkine. However, this effect may be influenced by different training configurations, including protocol duration, volume, and intensity.

Impact of cytotoxic agents or apoptosis stimulants on αklotho in MDCK, NRK-52E and HK2 kidney cells

αKlotho is a transmembrane protein acting as a co-receptor for FGF23, a bone hormone regulating renal phosphate and vitamin D metabolism. αKlotho expression is controlled by PPARγ. Soluble αklotho (sKL) regulates cellular signaling impacting stress resistance and death. αKlotho deficiency causes early onset of aging-associated diseases while its overexpression markedly increases lifespan. Cellular stress due to cytotoxic therapeutics or apoptosis induction through caspase activation or serum deficiency may result in cell death. Owing to αklotho's role in cellular stress and aging, this study explored the effect of cytotoxic agents or apoptosis stimulants on cellular αklotho expression. Experiments were performed in renal MDCK, NRK-52E and HK-2 cells. Gene expression was determined by qRT-PCR, sKL by ELISA, apoptosis and necrosis by annexin V binding and a fluorescent DNA dye, and cell viability by MTT assay. Cytostatic drugs cisplatin, paclitaxel, and doxorubicin as well as apoptosis induction with caspase 3 activator PAC-1 and serum deprivation induced αklotho and PPARG gene expression while decreasing viability and proliferation and inducing apoptosis of MDCK and NRK-52E cells to a variable extent. PPARγ antagonism attenuated up-regulation of αklotho in MDCK cells. In HK-2 cells, αklotho gene expression and sKL protein were down-regulated by chemotherapeutics. SKL serum levels in patients following chemotherapy were not significantly changed. In summary, potentially fatal stress results in up-regulation of αKlotho gene expression in MDCK and NRK-52E cells and down-regulation in HK-2 cells. These results indicate that different renal cell lines may exhibit completely different regulation of αklotho.

Cholecalciferol supplementation effectively improved tertiary hyperparathyroidism, FGF23 resistance and lowered coronary calcification score: a prospective study

INTRODUCTION

Tertiary hyperparathyroidism (THPT) and vitamin D deficiency are commonly seen in kidney transplant recipients, which may result in persistently elevated fibroblast growth factor 23 (FGF23) level after transplantation and decreased graft survival. The aim of this study is to evaluate the effect of vitamin D supplementation on THPT, FGF23-alpha Klotho (KLA) axis and cardiovascular complications after transplantation.

MATERIALS AND METHODS

Two hundred nine kidney transplant recipients were included and further divided into treated and untreated groups depending on whether they received vitamin D supplementation. We tracked the state of THPT, bone metabolism and FGF23-KLA axis within 12 months posttransplant and explored the predictors and risk factors for intact FGF23 levels, KLA levels, THPT and cardiovascular complications in recipients.

RESULTS

Vitamin D supplementation significantly improved FGF23 resistance, THPT and high bone turnover status, preserved better graft function and prevented coronary calcification in the treated group compared to the untreated group at month 12. The absence of vitamin D supplementation was an independent risk factor for THPT and a predictor for intact FGF23 and KLA levels at month 12. Age and vitamin D deficiency were independent risk factors for coronary calcification in recipients at month 12.

CONCLUSION

Vitamin D supplementation effectively improved THPT, FGF23 resistance and bone metabolism, preserved graft function and prevented coronary calcification after transplantation.

Pathobiology of the Klotho Antiaging Protein and Therapeutic Considerations

The α-Klotho protein (henceforth denoted Klotho) has antiaging properties, as first observed in mice homozygous for a hypomorphic Klotho gene (kl/kl). These mice have a shortened lifespan, stunted growth, renal disease, hyperphosphatemia, hypercalcemia, vascular calcification, cardiac hypertrophy, hypertension, pulmonary disease, cognitive impairment, multi-organ atrophy and fibrosis. Overexpression of Klotho has opposite effects, extending lifespan. In humans, Klotho levels decline with age, chronic kidney disease, diabetes, Alzheimer’s disease and other conditions. Low Klotho levels correlate with an increase in the death rate from all causes. Klotho acts either as an obligate coreceptor for fibroblast growth factor 23 (FGF23), or as a soluble pleiotropic endocrine hormone (s-Klotho). It is mainly produced in the kidneys, but also in the brain, pancreas and other tissues. On renal tubular-cell membranes, it associates with FGF receptors to bind FGF23. Produced in bones, FGF23 regulates renal excretion of phosphate (phosphaturic effect) and vitamin D metabolism. Lack of Klotho or FGF23 results in hyperphosphatemia and hypervitaminosis D. With age, human renal function often deteriorates, lowering Klotho levels. This appears to promote age-related pathology. Remarkably, Klotho inhibits four pathways that have been linked to aging in various ways: Transforming growth factor β (TGF-β), insulin-like growth factor 1 (IGF-1), Wnt and NF-κB. These can induce cellular senescence, apoptosis, inflammation, immune dysfunction, fibrosis and neoplasia. Furthermore, Klotho increases cell-protective antioxidant enzymes through Nrf2 and FoxO. In accord, preclinical Klotho therapy ameliorated renal, cardiovascular, diabetes-related and neurodegenerative diseases, as well as cancer. s-Klotho protein injection was effective, but requires further investigation. Several drugs enhance circulating Klotho levels, and some cross the blood-brain barrier to potentially act in the brain. In clinical trials, increased Klotho was noted with renin-angiotensin system inhibitors (losartan, valsartan), a statin (fluvastatin), mTOR inhibitors (rapamycin, everolimus), vitamin D and pentoxifylline. In preclinical work, antidiabetic drugs (metformin, GLP-1-based, GABA, PPAR-γ agonists) also enhanced Klotho. Several traditional medicines and/or nutraceuticals increased Klotho in rodents, including astaxanthin, curcumin, ginseng, ligustilide and resveratrol. Notably, exercise and sport activity increased Klotho. This review addresses molecular, physiological and therapeutic aspects of Klotho.

Orally-active, clinically-translatable senolytics restore α-Klotho in mice and humans

BACKGROUND

α-Klotho is a geroprotective protein that can attenuate or alleviate deleterious changes with ageing and disease. Declines in α-Klotho play a role in the pathophysiology of multiple diseases and age-related phenotypes. Pre-clinical evidence suggests that boosting α-Klotho holds therapeutic potential. However, readily clinically-translatable, practical strategies for increasing α-Klotho are not at hand. Here, we report that orally-active, clinically-translatable senolytics can increase α-Klotho in mice and humans.

METHODS

We examined α-Klotho expression in three different human primary cell types co-cultured with conditioned medium (CM) from senescent or non-senescent cells with or without neutralizing antibodies. We assessed α-Klotho expression in aged, obese, and senescent cell-transplanted mice treated with vehicle or senolytics. We assayed urinary α-Klotho in patients with idiopathic pulmonary fibrosis (IPF) who were treated with the senolytic drug combination, Dasatinib plus Quercetin (D+Q).

FINDINGS

We found exposure to the senescent cell secretome reduces α-Klotho in multiple nonsenescent human cell types. This was partially prevented by neutralizing antibodies against the senescence-associated secretory phenotype (SASP) factors, activin A and Interleukin 1α (IL-1α). Consistent with senescent cells' being a cause of decreased α-Klotho, transplanting senescent cells into younger mice reduced brain and urine α-Klotho. Selectively removing senescent cells genetically or pharmacologically increased α-Klotho in urine, kidney, and brain of mice with increased senescent cell burden, including naturally-aged, diet-induced obese (DIO), or senescent cell-transplanted mice. D+Q increased α-Klotho in urine of patients with IPF, a disease linked to cellular senescence.

INTERPRETATION

Senescent cells cause reduced α-Klotho, partially due to their production of activin A and IL-1α. Targeting senescent cells boosts α-Klotho in mice and humans. Thus, clearing senescent cells restores α-Klotho, potentially opening a novel, translationally-feasible avenue for developing orally-active small molecule, α-Klotho-enhancing clinical interventions. Furthermore, urinary α-Klotho may prove to be a useful test for following treatments in senolytic clinical trials.

FUNDING

This work was supported by National Institute of Health grants AG013925 (J.L.K.), AG062413 (J.L.K., S.K.), AG044271 (N.M.), AG013319 (N.M.), and the Translational Geroscience Network (AG061456: J.L.K., T.T., N.M., S.B.K., S.K.), Robert and Arlene Kogod (J.L.K.), the Connor Group (J.L.K.), Robert J. and Theresa W. Ryan (J.L.K.), and the Noaber Foundation (J.L.K.). The previous IPF clinical trial was supported by the Claude D. Pepper Older Americans Independence Centers at WFSM (AG021332: J.N.J., S.B.K.), UTHSCA (AG044271: A.M.N.), and the Translational Geroscience Network.

The Role of Peroxisome Proliferator-Activated Receptors in Kidney Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Accumulating evidence suggests that PPARs may play an important role in the pathogenesis of kidney disease. All three members of the PPAR subfamily, PPARα, PPARβ/δ, and PPARγ, have been implicated in many renal pathophysiological conditions, including acute kidney injury, diabetic nephropathy, and chronic kidney disease, among others. Emerging data suggest that PPARs may be potential therapeutic targets for renal disease. This article reviews the physiological roles of PPARs in the kidney and discusses the therapeutic utility of PPAR agonists in the treatment of kidney disease.

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

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

The role of FoxO1 and its modulation with small molecules in the development of diabetes mellitus: A review

Diabetes mellitus type 2 (T2D) is one of the metabolic disorders suffered by a global human being. Certain factors, such as lifestyle and heredity, can increase a person's tendency for T2D. Various genes and proteins play a role in the development of insulin resistance and ultimately diabetes in which one central protein that is discussed in this review is FoxO1. In this review, we regard FoxO1 activation as detrimental, promote high plasma glucose level, and induce insulin resistance. Indeed, many contrasting studies arise since FoxO1 is an important protein to alleviate oxidative stress and promote cell survival, for example, also by preventing hyperglycemic-induced cell death. Inter-relation to PPARG, another important protein in metabolism, is also discussed. Ultimately, we discussed contrasting approaches of targeting FoxO1 to combat diabetes mellitus by small molecules.

Dominant factors of the phosphorus regulatory network differ under various dietary phosphate loads in healthy individuals

BACKGROUND

The purpose of this study was to explore the contribution of each factor of the phosphorus metabolism network following phosphorus diet intervention via Granger causality analysis.

METHODS

In this study, a total of six healthy male volunteers were enrolled. All participants sequentially received regular, low-, and high-phosphorus diets. Consumption of each diet lasted for five days, with a 5-day washout period between different diets. Blood and urinary samples were collected on the fifth day of consumption of each diet at 9 time points (00:00, 04:00, 08:00, 10:00, 12:00, 14:00, 16:00, 20:00, 24:00) for measurements of serum levels of phosphate, calcium, PTH, FGF23, BALP, α-Klotho, and 1,25 D and urinary phosphorus excretion. Granger causality and the centrality of the above variables in the phosphorus network were analyzed by pairwise panel Granger causality analysis using the time-series data.

RESULTS

The mean age of the participants was 28.5 ± 2.1 years. By using Granger causality analysis, we found that the α-Klotho level had the strongest connection with and played a key role in influencing the other variables. In addition, urinary phosphorus excretion was frequently regulated by other variables in the network of phosphorus metabolism following a regular phosphorus diet. After low-phosphorus diet intervention, serum phosphate affected the other factors the most, and the 1,25 D level was the main outcome factor, while urinary phosphorus excretion was the most strongly associated variable in the network of phosphorus metabolism. After high-phosphorus diet intervention, FGF23 and 1,25 D played a more critical role in active regulation and passive regulation in the Granger causality analysis.

CONCLUSIONS

Variations in dietary phosphorus intake led to changes in the central factors involved in phosphorus metabolism.

Modulatory effect of euxanthone in liver cancer-bearing obese mice: crosstalk between PPARγ and TIMP3 signalling axes

Liver cancer is one of the prominent cancer-associated fatal diseases with > 80% of cases befall in low-middle resource nations worldwide. In the current study, we studied the effect of euxanthone (EUX) on obesity-associated liver cancer using a high-fat diet-fed mouse model of diethylnitrosamine (DEN)-provoked hepatocellular carcinoma. Mice with 2 weeks of age were intraperitoneally injected with diethylnitrosamine (DEN) 25 mg/kg b.w. After 4 weeks, the mice were divided into four groups with low-fat diet (LFD), high-fat diet (HFD), and EUX treatment groups with or without PPARγ inhibitor (GW9662). We observed that TIMP3, E-cadherin, and Klotho expressions were downmodulated, while MMP9, ADAM17, and Wnt signalling biofactors (Wnt5a, Wnt3a and β-catenin) were upmodulated in the HFD groups. Nevertheless, these aberrations were reciprocated by the treatment with EUX; at the same time, co-administration of PPARγ inhibitor ablated the anti-cancer effects of EUX, indicating that PPARγ activation is a pivotal mechanism underpinning the negative regulation of oncogenic factors by EUX. Together, these results imply that EUX might be a viable therapeutic option in the treatment of obesity-associated hepatocarcinogenesis.

Understanding the Stony Bridge between Osteoporosis and Vascular Calcification: Impact of the FGF23/Klotho axis

A relationship between osteoporosis (OP) and vascular calcification (VC) is now proposed. There are common mechanisms underlying the regulation of them. Fibroblast growth factor- (FGF-) 23 and Klotho are hormones associated with the metabolic axis of osteovascular metabolism. Most recently, it was suggested that the FGF23-klotho axis is associated with increasing incidence of fractures and is potentially involved in the progression of the aortic-brachial stiffness ratio. Herein, we discussed the potential role of the FGF23/Klotho axis in the pathophysiology of OP and VC. We want to provide an update review in order to allow a better understanding of the potential role of the FGF23/Klotho axis in comorbidity of OP and VC. We believe that a better understanding of the relationship between both entities can help in proposing new therapeutic targets for reducing the increasing prevalence of OP and VC in the aging population.

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.

Role of Klotho in the Development of Essential Hypertension

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

Redirecting drug repositioning to discover innovative cosmeceuticals

Skin appearance is essential for self-esteem and quality of life; consequently, skin care products represent a huge market. In particular, cosmeceuticals constitute a hybrid category of skin care formulations, at the interphase of cosmetics and pharmaceuticals, rationally designed to target (patho) physiological mechanisms aiming to enhance skin health and appearance. Cosmeceuticals are marketed as anti-ageing, anti-wrinkle, hair regrowth, skin whitening and wound healing agents with special emphasis on scar-free healing. An overview on recent cutting-edge advances concerning the discovery and development of enhanced performance cosmeceuticals by drug repositioning approaches is presented here. In this context, we propose "target repositioning," a new term, to highlight that druggable protein targets implicated in multiple diseases (hubs in the diseasome) can be exploited to accelerate the discovery of molecularly targeted cosmeceuticals that can promote skin health as an added benefit, which is a novel concept not described before. In this direction, emphasis is placed on the role of mouse models, for often untreatable skin diseases, as well as recent breakthroughs on monogenic rare skin syndromes, in promoting compound repositioning to innovative cosmeceuticals.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

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

The Interplay of WNT and PPARγ Signaling in Vascular Calcification

Vascular calcification (VC), the ectopic deposition of calcium phosphate crystals in the vessel wall, is one of the primary contributors to cardiovascular death. The pathology of VC is determined by vascular topography, pre-existing diseases, and our genetic heritage. VC evolves from inflammation, mediated by macrophages, and from the osteochondrogenic transition of vascular smooth muscle cells (VSMC) in the atherosclerotic plaque. This pathologic transition partly resembles endochondral ossification, involving the chronologically ordered activation of the β-catenin-independent and -dependent Wingless and Int-1 (WNT) pathways and the termination of peroxisome proliferator-activated receptor γ (PPARγ) signal transduction. Several atherosclerotic plaque studies confirmed the differential activity of PPARγ and the WNT signaling pathways in VC. Notably, the actively regulated β-catenin-dependent and -independent WNT signals increase the osteochondrogenic transformation of VSMC through the up-regulation of the osteochondrogenic transcription factors SRY-box transcription factor 9 (SOX9) and runt-related transcription factor 2 (RUNX2). In addition, we have reported studies showing that WNT signaling pathways may be antagonized by PPARγ activation via the expression of different families of WNT inhibitors and through its direct interaction with β-catenin. In this review, we summarize the existing knowledge on WNT and PPARγ signaling and their interplay during the osteochondrogenic differentiation of VSMC in VC. Finally, we discuss knowledge gaps on this interplay and its possible clinical impact.

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

Fibroblast growth factor 2 exacerbates inflammation in adipocytes through NLRP3 inflammasome activation

Chronic inflammation in adipose tissue is the hallmark of obesity and a major risk factor for the development of obesity-induced insulin resistance. NLRP3 inflammasome regulates the maturation and secretion of pro-inflammatory cytokines, such as IL-1β and IL-18, and was recently discovered to be involved in obesity-related metabolic diseases. Fibroblast growth factors (FGFs) such as FGF1, FGF10, and FGF21 are adipokines that regulate adipocyte development and metabolism, but reports on the effect of other FGFs on adipocytes are lacking. In the present study, the novel role of FGF2 in NLRP3 inflammasome activation was elucidated. Our results showed that FGF2 levels were increased during adipocyte differentiation and in the adipose tissue of high-fat diet (HFD)-induced obese mice. Recombinant FGF2 treatment upregulated inflammasome markers such as NLRP3, which was further exaggerated by TNF-ɑ treatment. Interestingly, β-Klotho, a co-receptor of FGF21, was significantly decreased by FGF2 treatment. Results from mice confirmed the positive correlation between FGF2 and NLRP3 expression in epididymal and subcutaneous adipose tissue, while exercise training effectively reversed HFD-induced NLRP3 expression as well as FGF2 levels in both adipose depots. Our results suggest that FGF2 is an adipokine that may exacerbate the inflammatory response in adipocytes through NLRP3 inflammasome activation.

Epigenetic and non-epigenetic regulation of Klotho in kidney disease

Klotho is a novel renoprotective anti-aging protein available in membrane-bound or soluble form. Klotho is expressed in brain, pancreas, and other solid organs but shows highest expression levels in the kidney. Klotho sustains normal kidney physiology but Klotho regulation also contributes to the progression of kidney disease. Systemic and intrarenal levels of Klotho fall drastically during acute kidney injury, kidney fibrosis, diabetic nephropathy, and other forms of chronic kidney disease, etc. Moreover, exogenous supplementation or overexpression of endogenous Klotho attenuates kidney disease. The regulation of endogenous Klotho expression involves epigenetic as well as non-epigenetic mechanisms. The epigenetic modifications such as DNA methylation, post-translational histone modifications, miRNAs regulate the change in Klotho expression in kidney disease. Non-epigenetic mechanisms such as ER stress, Wnt signaling, activation of the renin angiotensin system (RAS), excessive reactive oxygen species and cytokine generation, albumin overload, and PPAR-γ signaling also contribute to Klotho regulation. Evolving evidence highlight the capacity of natural products to regulate Klotho expression in kidney disease. All these preclinical data suggest that Klotho could be a novel biomarker as well as therapeutic target. Here we review the different mechanisms of Klotho regulation in the context of Klotho as a biomarker and potential therapeutic agent.

Klotho, Aging, and the Failing Kidney

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in the diseasome of aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology. A range of senotherapeutic strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists and indirect approaches, via modulation of the foodome and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes within the diseasome of aging.

The effect of 6 weeks of high intensity interval training on myelin biomarkers and demyelination in experimental autoimmune encephalomyelitis model

Exercise has been shown to increase myelin biomarkers such as klotho and PLP and improve clinical and pathological symptoms using the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS). In the present study, we evaluated whether 6 weeks of high-intensity interval training (HIIT) prior to induction of EAE increase klotho and/or PLP and attenuate the severity of symptoms and/or disease progression in EAE model. Our data demonstrate that HIIT increased klotho and PLP and decreased disability. These proteins are associated with maintaining myelination and further research is required to examine potential clinical relevance.

Sodium butyrate protects against oxidative stress in human nucleus pulposus cells via elevating PPARγ-regulated Klotho expression

We investigated the involvement of klotho in the inhibition of oxidative stress by sodium butyrate (NaB) in human nucleus pulposus cells (NPCs). NPCs were pretreated with different concentrations of NaB for 2 h before stimulation with tert-butyl hydroperoxide (TBHP). NaB alleviated TBHP-induced oxidative injury in the NPCs, as evident by the reduced accumulation of mitochondrial superoxide, intracellular reactive oxygen species, and malondialdehyde, and increased activities of superoxide dismutase and glutathione peroxidase. Flow cytometry and western blotting showed that TBHP-induced apoptosis of NPCs was inhibited by NaB. NaB also reduced the TBHP-induced release of proteases that degrade the extracellular matrix, including matrix metalloproteinases 3 and 13, and ADAMTS-4 (a disintegrin and metalloproteinase with thrombospondin motifs 4). Intriguingly, NaB significantly reversed TBHP-induced klotho suppression. However, the protective effects of NaB on NPCs were abolished by klotho-specific small interfering RNA (siRNA). TBHP stimulation had no obvious effects on total or nuclear expression of peroxisome proliferator-activated receptor γ (PPARγ), but significantly reduced PPARγ acetylation and transcriptional activity, which were restored by NaB. TBHP stimulation also promoted the nuclear translocation of histone deacetylase 3 (HDAC3) and enhanced the association between HDAC3 and PPARγ in the nucleus, but this interaction was substantially disrupted by NaB. siRNA-induced HDAC3 knockdown significantly increased PPARγ acetylation and transactivation, reversing the TBHP-induced suppression of klotho. Therefore, NaB alleviates TBHP-induced oxidative stress in human NPCs by elevating PPARγ-regulated klotho expression. HDAC3 may be a critical HDAC subtype that mediates the regulation of PPARγ activity by NaB under oxidative stress.

Intermedin alleviates pathological cardiac remodeling by upregulating klotho

Cardiac remodeling is accompanied by cardiac hypertrophy, fibrosis, dysfunction, and eventually leading to heart failure. Intermedin (IMD), as a paracrine/autocrine peptide, has a protective effect in cardiovascular diseases. In this study, we elucidated the role and the underlying mechanism of IMD in pathological remodeling. Pathological remodeling mouse models were induced by abdominal aorta constriction for 4 weeks or angiotensin II (Ang II) infusion for 2 weeks in wildtype, IMD-overexpression, IMD-knockout and klotho-knockdown mice. Western blot, real-time PCR, histological staining, echocardiography and hemodynamics were used to detect the role of IMD in cardiac remodeling. Cardiac hypertrophy, fibrosis and dysfunction were significantly aggravated in IMD-knockout mice versus wildtype mice, and the expression of klotho was downregulated. Conversely, cardiac remodeling was alleviated in IMD-overexpression mice, and the expression of klotho was upregulated. Hypertension induced by Ang II infusion rather than abdominal aorta constriction was mitigated by IMD. However, the cardioprotective effect of IMD was blocked in klotho-knockdown mice. Similar results were found in cultured neonatal rat cardiomyocytes, which was pretreated with IMD before Ang II stimulation. Mechanistically, IMD inhibited the phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and the activity of calcineurin to protect against cardiac hypertrophy through upregulating klotho in vivo and in vitro. Furthermore, peroxisome proliferator-activated receptor γ (PPARγ) might mediate IMD upregulating klotho. In conclusion, pathological remodeling may be alleviated by endogenous IMD, which inhibits the expression of calcineurin and p-CaMKII by upregulating klotho via the PPARγ pathway. It suggested that IMD might be a therapeutic target for heart disease.

The Klotho proteins in health and disease

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.

αKlotho-FGF23 interactions and their role in kidney disease: a molecular insight

Following the serendipitous discovery of the ageing suppressor, αKlotho (αKl), several decades ago, a growing body of evidence has defined a pivotal role for its various forms in multiple aspects of vertebrate physiology and pathology. The transmembrane form of αKl serves as a co-receptor for the osteocyte-derived mineral regulator, fibroblast growth factor (FGF)23, principally in the renal tubules. However, compelling data also suggest that circulating soluble forms of αKl, derived from the same source, may have independent homeostatic functions either as a hormone, glycan-cleaving enzyme or lectin. Chronic kidney disease (CKD) is of particular interest as disruption of the FGF23-αKl axis is an early and common feature of disease manifesting in markedly deficient αKl expression, but FGF23 excess. Here we critically discuss recent findings in αKl biology that conflict with the view that soluble αKl has substantive functions independent of FGF23 signalling. Although the issue of whether soluble αKl can act without FGF23 has yet to be resolved, we explore the potential significance of these contrary findings in the context of CKD and highlight how this endocrine pathway represents a promising target for novel anti-ageing therapeutics.

Fibroblast Growth Factor 23 and Klotho in AKI

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.

Exercise training increases the S-Klotho plasma levels in sedentary middle-aged adults: A randomised controlled trial. The FIT-AGEING study

This study aimed to investigate the effects of different training modalities on the soluble Klotho (S-Klotho) plasma levels in sedentary middle-aged adults. A total of 74 middle-aged adults (53.4 ± 5.0 years old; 52.7% women) were enrolled in the FIT-AGEING study. We conducted a 12-week randomised controlled trial. The participants were randomly assigned to 4 different groups: (i) a control group (no exercise), (ii) a physical activity recommendation from the World Health Organization group (PAR), (iii) a high intensity interval training group (HIIT), and (iv) a high intensity interval training group adding whole-body electromyostimulation training group (HIIT-EMS). S-Klotho plasma levels, anthropometric measurements, and body composition variables were measured before and after the intervention programme. All exercise training modalities induced an increase in the S-Klotho plasma levels (all P ≤ 0.019) without statistical differences between them (all P ≥ 0.696). We found a positive association between changes in lean mass index and changes in the S-Klotho plasma levels, whereas a negative association was reported between changes in fat mass outcomes and changes in the S-Klotho plasma levels after our intervention study. In conclusion, our results suggest that the link between exercise training and the increase in S-Klotho plasma levels could be mediated by a decrease of fat mass and an increase of lean mass.

The greater effect of high-intensity interval training versus moderate-intensity continuous training on cardioprotection against ischemia-reperfusion injury through Klotho levels and attenuate of myocardial TRPC6 expression

BACKGROUND

Myocardial ischemia-reperfusion (IR) injury is a leading cause of death all over the world, so developing practical approaches to promote cardioprotection against IR injury is essential. Exercise training is an effective strategy to improve cardioprotection. Hence, the purpose of this study was to investigate the effect of short-term preconditioning with two types of high-intensity interval training (HIIT) and moderate intensity continuous training (MICT) on klotho and TRPC6 mechanisms in cardioprotection.

METHODS

Eighty Male Wistar rats (250-300 g) were randomly divided into 7 groups, including Control, HIIT, MICT, Sham, IR, HIIT+IR, and MICT+IR. Training was performed in 5 consecutive days. HIIT protocol consisted of running on the treadmill at intervals 85-90% vo₂max that separated by slow intensity periods at 50-60% vo₂max. MICT program was performed at 70% VO₂max at the same running distance with HIIT groups. The cardiac IR injury was induced by LAD occlusion followed by reperfusion. ELISA kit was used in order to measure the plasma levels of klotho, LDH and CK-MB, and TRPC6 expression was determined using the western blot technique. Data were analyzed using one way ANOVA and Tukey's post hoc tests.

RESULTS

The results of this study showed that both types of exercise training programs significantly increase plasma levels of klotho and reduce the infarct size and heart injury. In addition, the exercise training decreased the amount of TRPC6 channels expression during IR. However, the effect of HIIT on increasing the klotho and cardioprotection was greater compared to MICT.

CONCLUSIONS

Based on the results, even a short-term of aerobic exercise training, especially HIIT, promotes cardioprotection against IR injury and decreases infarct size via an increase in klotho and attenuate of protein expression of myocardial TRPC6 during IR.

Reduced lifespan of mice lacking catalase correlates with altered lipid metabolism without oxidative damage or premature aging

The relationship between the mechanisms that underlie longevity and aging and the metabolic alterations due to feeding conditions has not been completely defined. In the present work, through the deletion of the gene encoding catalase, hydrogen peroxide (H₂O₂) was uncovered as a relevant regulator of longevity and of liver metabolism. Mice lacking catalase (Cat^-/-) fed ad libitum with a regular diet showed a shorter lifespan than wild type mice, which correlated with reduced body weight, blood glucose levels and liver fat accumulation, but not with increased oxidative damage or consistent premature aging. High fat diet (HFD) and fasting increased oxidative damage in the liver of wild type animals but, unexpectedly, this was not the case for that of Cat^-/- mice. Interestingly, although HFD feeding similarly increased the body weight of Cat^-/- and wild-type mice, hyperglycemia and liver steatosis did not develop in the former. Fat accumulation due to fasting, on the other hand, was diminished in mice lacking catalase, which correlated with increased risk of death and low ketone body blood levels. Alteration in expression of some metabolic genes in livers of catalase deficient mice was consistent with reduced lipogenesis. Specifically, Pparγ2 expression up-regulation in response to a HFD and down-regulation upon fasting was lower and higher, respectively, in livers of Cat^-/- than of wild type mice, and a marked decay was observed during Cat^-/- mice aging. We propose that catalase regulates lipid metabolism in the liver by an evolutionary conserved mechanism that is determinant of lifespan without affecting general oxidative damage.

Serum klotho is inversely associated with metabolic syndrome in chronic kidney disease: results from the KNOW-CKD study

BACKGROUND

Metabolic syndrome (MS) is prevalent in chronic kidney disease (CKD). Klotho, a protein linked to aging, is closely associated with CKD. Each component of MS and klotho has an association. However, little is known about the association between klotho and MS per se. We investigated the association between serum klotho levels and MS using baseline cross-sectional data obtained from a large Korean CKD cohort.

METHODS

Of the 2238 subjects recruited in the KoreaN Cohort Study for Outcome in Patients With Chronic Kidney Disease (KNOW-CKD) between 2011 and 2016, 484 patients with missing data on serum klotho and extreme klotho values (values lower than the detectable range or > 6000 pg/mL) or with autosomal dominant polycystic kidney disease patients were excluded. The data of the remaining 1754 subjects were included in the present study. MS was defined using the revised National Cholesterol Education Program Adult Treatment Panel (NCEP-ATP) III criteria. Serum klotho levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

Mean patient age was 54.9 ± 12.1 years and 1110 (63.3%) were male. The prevalence of MS among all study subjects was 63.7% (n = 1118). The median serum klotho level was 527 pg/mL (interquartile range [IQR]: 418-656 pg/mL). Serum klotho level was significantly lower in MS patients than patients without MS (Median [IQR]; 521 pg/mL [413, 651] vs. 541 pg/mL [427, 676], respectively; P = 0.012). After adjusting for age, sex, estimated glomerular filtration rate, and overt proteinuria, serum klotho was independently associated with MS (adjusted odds ratio [OR], 0.44; 95% confidence interval, 0.23-0.82; P = 0.010). Furthermore, the adjusted OR for MS was found to be significantly increased at serum klotho levels of < 518 pg/mL (receiver operating characteristic curve cut-off value).

CONCLUSIONS

Serum klotho was inversely associated with the presence of MS in patients with CKD.

TRIAL REGISTRATION

This trial was registered on ClinicalTrials.gov on 26 June 2012 ( https://clinicaltrials.gov;NCT01630486 ).

Influence of exogenous growth hormone administration on circulating concentrations of α-klotho in healthy and chronic kidney disease subjects: a prospective, single-center open case-control pilot study

BACKGROUND

The CKD-associated decline in soluble α-Klotho (α-Klotho) levels is considered detrimental. Some studies suggest a direct induction of α-Klotho concentrations by growth hormone (GH). In the present study, the effect of exogenous GH administration on α-Klotho concentrations in a clinical cohort with mild chronic kidney disease (CKD) and healthy subjects was studied.

METHODS

A prospective, single-center open case-control pilot study was performed involving 8 patients with mild CKD and 8 healthy controls matched for age and sex. All participants received subcutaneous GH injections (Genotropin®, 20 mcg/kg/day) for 7 consecutive days. α-Klotho concentrations were measured at baseline, after 7 days of therapy and 1 week after the intervention was stopped.

RESULTS

α-Klotho concentrations were not different between CKD-patients and healthy controls at baseline (554 (388-659) vs. 547 (421-711) pg/mL, P = 0.38). Overall, GH therapy increased α-Klotho concentrations from 554 (405-659) to 645 (516-754) pg/mL, P < 0.05). This was accompanied by an increase of IGF-1 concentrations from 26.8 ± 5.0 nmol/L to 61.7 ± 17.7 nmol/L (P < 0.05). GH therapy induced a trend toward increased α-Klotho concentrations both in the CKD group (554 (388-659) to 591 (358-742) pg/mL (P = 0.19)) and the healthy controls (547 (421-711) pg/mL to 654 (538-754) pg/mL (P = 0.13)). The change in α-Klotho concentration was not different for both groups (P for interaction = 0.71). α-Klotho concentrations returned to baseline levels within one week after the treatment (P < 0.05).

CONCLUSIONS

GH therapy increases α-Klotho concentrations in subjects with normal renal function or stage 3 CKD. A larger follow-up study is needed to determine whether the effect size is different between both groups or in patients with more severe CKD.

TRIAL REGISTRATION

This trial is registered in EudraCT ( 2013-003354-24 ).

Association of circular Klotho and insulin-like growth factor 1 with cardiac hypertrophy indexes in athlete and non-athlete women following acute and chronic exercise

Owing to the role of insulin-like growth factor 1 (IGF-I) in cardiac hypertrophy and the ability of Klotho in inhibiting the IGF-I action, we investigated effects of exercise on plasma Klotho and IGF-I and their association with cardiac hypertrophy. In this study, 10 non-athlete and 10 athlete women underwent a Bruce test (acute exercise) and 12-weeks water aerobics training (chronic exercise). Electrocardiographic parameters, plasma IGF-I and Klotho levels were measured in different time courses. The exercise training could significantly increase left ventricular end-diastolic diameter index (LVEDDI) in the non-athletes. Plasma levels of IGF-I significantly increased following acute and chronic exercises. The Klotho levels at the baseline were higher in athletes than non-athletes and its levels significantly increased immediately after acute exercise in both groups. The Klotho levels significantly decreased in non-athletes 24 h after chronic exercise, but its level was still higher than the baseline in the athletes. We found positive and negative correlations between cardiac hypertrophy indexes (LVEDDI and left ventricular mass index) with respectively IGF-I and Klotho. In conclusion, we found a stimulatory effect of acute and chronic exercises on plasma IGF-I and Klotho and association of IGF-I with exercise-induced cardiac hypertrophy. Moreover, Klotho could act as a negative regulator for exercise-induced cardiac hypertrophy.

High-intensity physical exercise increases serum α-klotho levels in healthy volunteers

The recently discovered klotho proteins have roles in a diverse range of metabolic processes with the oldest protein, α-klotho, implicated in various cellular pathways in energy, glucose, and phosphate metabolism. Circulating soluble klotho (sKl), derived from membrane α-klotho cleavage, not only has effects on ion channels and insulin signaling pathways, but is inversely associated with mortality. Effects of physical exercise on sKl have not been well studied. The effect of a single high-intensity standardized exercise on sKl and serum phosphate (sPi) levels in healthy adults was investigated. A standard Bruce protocol treadmill exercise was undertaken by 10 fasting healthy volunteers. sKl, sPi, and blood glucose levels were measured in samples collected 1-week prior, immediately pre (T_pre), 0 (T_post), 30 (T₃₀), 240 (T₂₄₀) min, and 1-week after exercise. Median (interquartile range) age of participants was 47.5 (44-51) years; five (50%) were male. All study participants achieved at least 90% predicted maximum heart rate (MHR). sKl increased acutely after exercise (T_pre median 448 pg/mL vs. T_post median 576 pg/mL; p < 0.01). There was a nonsignificant sPi decline at T₃₀ (T_pre 0.94 ± 0.12 mmol/L vs. T₃₀ 0.83 ± 0.22 mmol/L). Exercise led to a reduction in blood glucose by T₂₄₀ with median glucose levels at T_pre, T_post, T₃₀, and T₂₄₀ of 6.0, 6.5, 6.3, and 5.7 mmol/L, respectively. In conclusion, a single high-intensity exercise session is associated with a transient increase in sKl, a delayed reduction in blood glucose, and a nonsignificant decrease in sPi levels in healthy adults. The evaluation of long-term effects of cardiovascular fitness programs on sKl and sPi in healthy individuals and disease cohorts are required to identify potential lifestyle modifications to help improve chronic disease management and long-term outcomes.

Klotho and PPAR Gamma Activation Mediate the Renoprotective Effect of Losartan in the 5/6 Nephrectomy Model

Renin angiotensin system (RAS) blockade reduces the progression of chronic kidney disease (CKD) independently of its antihypertensive effect. Ang II-induced fibrosis can be mediated by molecules such as klotho, peroxisome proliferator-activate receptor γ (PPAR-γ), and the Wnt/β-catenin pathway; however, the interaction among these molecules and RAS activation is not completely known. The aim of this study was to investigate a possible link between RAS, PPAR-γ, and Klotho in the 5/6 nephrectomy (NX) animals. NX rats presented hypertension that was blunted by both losartan and propranolol, however, only losartan was able to reduce the expression levels of fibronectin FSP1 and TGF-β in the remnant kidney. The anti-fibrotic Klotho and PPAR-γ were reduced in the remnant kidney, and losartan, but not propranolol, restored their levels. In contrast, the profibrotic Wnt 7a and Wnt 3 were upregulated and losartan prevented the increase in Wnts. In vitro, Ang II induced a decrease in both klotho and in PPAR-γ in Madin-Darby canine kidney (MDCK) cells, and this effect was blunted by losartan. However, klotho expression was increased by pioglitazone, an agonist of PPAR-γ, and suppressed by BADGE, an antagonist of PPAR-γ, suggesting that the effect of Ang II downregulating klotho is mediated by PPAR-γ. These data suggest that activation of the Wnt pathway together with downregulation of PPAR-γ that in turn suppresses klotho contribute to potentiating the profibrotic effect of Ang II.