Upregulation of the klotho gene expression by thyroid hormone and during adipose differentiation in 3T3-L1 adipocytes

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

BACKGROUND AND STUDY AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Triiodothyronine and Protein Malnutrition Could Influence Pulse Wave Velocity in Pre-Dialysis Chronic Kidney Disease Patients

Cardiovascular diseases (CVD) are the first cause of chronic kidney disease (CKD) mortality. For personalized improved medicine, detecting correctable markers of CVD can be considered a priority. The aim of this study was the evaluation of the impact of nutritional, hormonal and inflammatory markers on brachial-ankle Pulse Wave Velocity (PWV) in pre-dialysis CKD patients. A cross-sectional observational study was conducted on 68 pre-dialysis CKD patients (median age of 69 years, 41.2% with diabetes mellitus, 52.9% male). Laboratory data were collected, including levels of prolactin, triiodothyronine, TGF α, IL-6, and IL-1β. The high values of brachial-ankle PWV were associated with reduced muscle mass (p = 0.001, r = -0.44), low levels of total cholesterol (p = 0.04, r = -0.26), triglycerides (p = 0.03, r = -0.31), triiodothyronine (p = 0.04, r = -0.24), and prolactin (p = 0.02, r = -0.27). High PWV was associated with advanced age (p < 0.001, r = 0.19). In the multivariate analysis, reduced muscle mass (p = 0.018), low levels of triiodothyronine (p = 0.002), and triglycerides (p = 0.049) were significant predictors of PWV, but age (p < 0.001) remained an important factor. In conclusion, reduced triiodothyronine together with markers of malnutrition and age were associated with PWV in pre-dialysis CKD patients.

Low Free Triiodothyronine as a More Sensitive Predictor of Survival Than Total Testosterone among Dialysis Men

BACKGROUND

Some endocrine disorders, previously considered benign, may be related to a poorer prognosis for patients with renal failure. Both low serum free triiodothyronine (fT3) and low total testosterone (TT) concentrations have been considered as predictors of death in dialysis patients, but the results of studies are inconsistent. In our study, we evaluated the relationships of the serum thyroid hormone levels and the total testosterone levels with survival in male dialysis patients.

METHODS

Forty-eight male dialysis patients, 31 on hemodialysis (HD) and 17 on peritoneal dialysis (PD), aged 61.4 ± 10.0, 59.2 ± 12.2 years, respectively, were included in the study. Serum thyroid hormones and total testosterone were measured.

RESULTS

During the 12-month follow-up, nine all-cause deaths were recorded. The concentrations of fT3 were significantly lower in those who died than in the survivors (p = 0.001). We did not observe any statistically considerable differences between the group of men who died and the rest of the participants in terms of the total serum testosterone concentration (p = 0.350). Total testosterone positively correlated with fT3 (r = 0.463, p = 0.009) in the HD group.

CONCLUSIONS

In the group of male dialysis patients, the serum concentration of fT3 had a better prognostic value in terms of survival than the total testosterone. A linear relationship between the fT3 levels and testosterone levels in men undergoing hemodialysis may confirm the hypothesis that some of the hormonal changes observed in chronic kidney disease (CKD) may have a common cause.

Association of serum Klotho levels with cancer and cancer mortality: Evidence from National Health and Nutrition Examination Survey

BACKGROUND

Klotho has both anticancer and hormone-like functions. But the research on Klotho and cancer is mainly based on animal experiments and small-scale clinical research, thus we explored the association between serum Klotho and cancer and cancer mortality based on the National Health and Nutrition Survey (NHANES).

METHODS

Participants were employed from the NHANES 2007-2016, excluding pregnant, chronic renal insufficiency, and incomplete data of cancer questionnaire and serum Klotho level. The association of serum Klotho with cancer and mortality was analyzed by weighted Logistic regression, weighted Cox regression and competitive risk model, respectively. Correlations between serum Klotho and testosterone and estradiol levels were analyzed by Spearman correlation and restricted cubic spline respectively.

RESULTS

We found Klotho had an inverse effect with risk of pan-cancer (all p < 0.02), with each unit increase in Klotho (1ug/g creatinine) associated with a 0.9%-2.2% reduction in the risk of cancer, and higher levels showing a stronger negative association (all p-trend <= 0.0005). Whereas, we did not observe any association between serum Klotho level with all-cause mortality and cancer-specific mortality (all p > 0.05). Then, stratified analysis found that people aged 60-79, female, overweight and non-Hispanic whites or Mexican Americans were less likely to develop cancer. In addition, there was a strong nonlinear and linear positive correlation of Klotho with estradiol (p-nonlinear = 0.0178) and testosterone only among male participants (β = -0.513, p = 0.0137), respectively.

CONCLUSIONS

We found an inverse association between serum Klotho and cancer, but without cancer mortality. And this effect may be partially mediated by estradiol and testosterone. Further prospective studies are needed to prove these findings.

Effects of thyroxine and propylthiouracil on feeding behavior and the expression of hypothalamic appetite-regulating peptides and thyroid function in goldfish (Carassius auratus)

There is poor evidence for an association between thyroidal state, feeding and appetite regulation in fish. We assessed how an altered thyroid state influences feeding behavior, food intake and expression of hypothalamic appetite-regulating peptides (Klotho-α and Klotho-β; orexin, OX; cholecystokinin, CCK; agouti-related peptide, AgRP; cannabinoid receptor 1, CB1) in goldfish. We also measured the expressions of hypothalamic, pituitary and liver transcripts that regulate the thyroid [thyrotropin-releasing hormone (TRH), thyrotropin-releasing hormone receptor (TRH-R) type 1, thyroid stimulating hormone beta (TSHβ), deiodinases (DIO2, DIO3), UDP-glucuronosyltransferase (UGT1A1), thyroid receptor alpha and beta (TRα, TRβ)], and circulating levels of total thyroxine (tT₄) and total triiodothyronine (tT₃). Goldfish were implanted with propylthiouracil (PTU) or T₄ osmotic pumps for 12 days. T₄- treatment increased feeding behavior but not food intake, increased central TSHβ and DIO2, and hepatic DIO2 transcript expression and increased central DIO3 mRNA. Under hyperthyroid conditions, hypothalamic Klotho and CCK expressions were downregulated, suggesting an increased metabolic state and a hypothalamic response to regulate energy balance. AgRP, OX and CB1 were not affected by T₄ treatment. PTU had no effect on any of the parameters examined, suggesting it is not a sensitive thyroid inhibitor in fish. Overall, we show that unlike in mammals, hyperthyroid conditions in goldfish do not lead to an increased desire or need to consume food, furthering evidence for a weak link between the thyroid and appetite.

Thyroid disease in end-stage renal disease

PURPOSE OF REVIEW

Hypothyroidism is a highly prevalent endocrine disorder in the end-stage renal disease (ESRD) population, yet many cases may remain latent and undiagnosed.

RECENT FINDINGS

Epidemiologic data show that there is a nearly five-fold higher prevalence of hypothyroidism in advanced chronic kidney disease (CKD) patients vs. those without CKD. Given that the metabolism, degradation, and excretion of thyroid hormone and its metabolites, as well as the regulation of the hypothalamic-pituitary-thyroid axis may be altered in ESRD, certain considerations should be made when interpreting thyroid functional tests in these patients. Growing evidence shows that hypothyroidism and other thyroid functional test derangements are associated with higher risk of cardiovascular disease, worse patient-centered outcomes, and survival in the advanced CKD population, including those with ESRD. Although limited data examining treatment of hypothyroidism suggests benefit, further studies of the efficacy and safety of thyroid hormone supplementation, including clinical trials and rigorous longitudinal observational studies are needed to inform the management of thyroid dysfunction in CKD.

SUMMARY

Given the high burden of hypothyroidism in ESRD patients, and potential ill effects on their cardiovascular health, patient-centered outcomes, and survival, further research is needed to inform the optimal management of thyroid dysfunction in this population.

Human alternative Klotho mRNA is a nonsense-mediated mRNA decay target inefficiently spliced in renal disease

Klotho is a renal protein involved in phosphate homeostasis, which is downregulated in renal disease. It has long been considered an antiaging factor. Two Klotho gene transcripts are thought to encode membrane-bound and secreted Klotho. Indeed, soluble Klotho is detectable in bodily fluids, but the relative contributions of Klotho secretion and of membrane-bound Klotho shedding are unknown. Recent advances in RNA surveillance reveal that premature termination codons, as present in alternative Klotho mRNA (for secreted Klotho), prime mRNAs for degradation by nonsense-mediated mRNA decay (NMD). Disruption of NMD led to accumulation of alternative Klotho mRNA, indicative of normally continuous degradation. RNA IP for NMD core factor UPF1 resulted in enrichment for alternative Klotho mRNA, which was also not associated with polysomes, indicating no active protein translation. Alternative Klotho mRNA transcripts colocalized with some P bodies, where NMD transcripts are degraded. Moreover, we could not detect secreted Klotho in vitro. These results suggest that soluble Klotho is likely cleaved membrane-bound Klotho only. Furthermore, we found that, especially in acute kidney injury, splicing of the 2 mRNA transcripts is dysregulated, which was recapitulated by various noxious stimuli in vitro. This likely constitutes a novel mechanism resulting in the downregulation of membrane-bound Klotho.

Tissue expression and source of circulating αKlotho

αKlotho (Klotho), a type I transmembrane protein and a coreceptor for Fibroblast Growth Factor-23, was initially thought to be expressed only in a limited number of tissues, most importantly the kidney, parathyroid gland and choroid plexus. Emerging data may suggest a more ubiquitous Klotho expression pattern which has prompted reevaluation of the restricted Klotho paradigm. Herein we systematically review the evidence for Klotho expression in various tissues and cell types in humans and other mammals, and discuss potential reasons behind existing conflicting data. Based on current literature and tissue expression atlases, we propose a classification of tissues into high, intermediate and low/absent Klotho expression. The functional relevance of Klotho in organs with low expression levels remain uncertain and there is currently limited data on a role for membrane-bound Klotho outside the kidney. Finally, we review the evidence for the tissue source of soluble Klotho, and conclude that the kidney is likely to be the principal source of circulating Klotho in physiology.

The Antiaging Gene Klotho Regulates Proliferation and Differentiation of Adipose-Derived Stem Cells

Klotho was originally discovered as an aging-suppressor gene. The purpose of this study was to investigate whether secreted Klotho (SKL) affects the proliferation and differentiation of adipose-derived stem cells (ADSCs). RT-PCR and Western blot analysis showed that short-form Klotho was expressed in mouse ADSCs. The Klotho gene mutation KL(-/-) significantly decreased proliferation of ADSCs and expression of pluripotent transcription factors (Nanog, Sox-2, and Oct-4) in mice. The adipogenic differentiation of ADSCs was also decreased in KL(-/-) mice. Incubation with Klotho-deficient medium decreased ADSC proliferation, pluripotent transcription factor levels, and adipogenic differentiation, which is similar to what was found in KL(-/-) mice. These results indicate that Klotho deficiency suppresses ADSC proliferation and differentiation. Interestingly, treatment with recombinant SKL protein rescued the Klotho deficiency-induced impairment in ADSC proliferation and adipogenic differentiation. SKL also regulated ADSCs' differentiation to other cell lineages (osteoblasts, myofibroblasts), indicating that SKL maintains stemness of ADSCs. It is intriguing that overexpression of SKL significantly increased PPAR-γ expression and lipid formation in ADSCs following adipogenic induction, indicating enhanced adipogenic differentiation. Overexpression of SKL inhibited expression of TGFβ1 and its downstream signaling mediator Smad2/3. This study demonstrates, for the first time, that SKL is essential to the maintenance of normal proliferation and differentiation in ADSCs. Klotho regulates adipogenic differentiation in ADSCs, likely via inhibition of TGFβ1 and activation of PPAR-γ. Stem Cells 2016;34:1615-1625.

Associations between Thyroid Hormones, Calcification Inhibitor Levels and Vascular Calcification in End-Stage Renal Disease

Introduction

Vascular calcification is a common, serious and elusive complication of end-stage renal disease (ESRD). As a pro-calcifying risk factor, non-thyroidal illness may promote vascular calcification through a systemic lowering of vascular calcification inhibitors such as matrix-gla protein (MGP) and Klotho.

Methods and Material

In 97 ESRD patients eligible for living donor kidney transplantation, blood levels of thyroid hormones (fT3, fT4 and TSH), total uncarboxylated MGP (t-ucMGP), desphospho-uncarboxylated MGP (dp-ucMGP), descarboxyprothrombin (PIVKA-II), and soluble Klotho (sKlotho) were measured. The degree of coronary calcification and arterial stiffness were assessed by means of cardiac CT-scans and applanation tonometry, respectively.

Results

fT3 levels were inversely associated with coronary artery calcification (CAC) scores and measures of arterial stiffness, and positively with dp-ucMGP and sKlotho concentrations. Subfractions of MGP, PIVKA-II and sKlotho did not associate with CAC scores and arterial stiffness. fT4 and TSH levels were both inversely associated with CAC scores, but not with arterial stiffness.

Discussion

The positive associations between fT3 and dp-ucMGP and sKlotho suggest that synthesis of MGP and Klotho is influenced by thyroid hormones, and supports a link between non-thyroidal illness and alterations in calcification inhibitor levels. However, the absence of an association between serum calcification inhibitor levels and coronary calcification/arterial stiffness and the fact that MGP and Klotho undergo post-translational modifications underscore the complexity of this association. Further studies, measuring total levels of MGP and membrane bound Klotho, should examine this proposed pathway in further detail.

Thyroid functional disease: an under-recognized cardiovascular risk factor in kidney disease patients

Thyroid functional disease, and in particular hypothyroidism, is highly prevalent among chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. In the general population, hypothyroidism is associated with impaired cardiac contractility, endothelial dysfunction, atherosclerosis and possibly higher cardiovascular mortality. It has been hypothesized that hypothyroidism is an under-recognized, modifiable risk factor for the enormous burden of cardiovascular disease and death in CKD and ESRD, but this has been difficult to test due to the challenge of accurate thyroid functional assessment in uremia. Low thyroid hormone levels (i.e. triiodothyronine) have been associated with adverse cardiovascular sequelae in CKD and ESRD patients, but these metrics are confounded by malnutrition, inflammation and comorbid states, and hence may signify nonthyroidal illness (i.e. thyroid functional test derangements associated with underlying ill health in the absence of thyroid pathology). Thyrotropin is considered a sensitive and specific thyroid function measure that may more accurately classify hypothyroidism, but few studies have examined the clinical significance of thyrotropin-defined hypothyroidism in CKD and ESRD. Of even greater uncertainty are the risks and benefits of thyroid hormone replacement, which bear a narrow therapeutic-to-toxic window and are frequently prescribed to CKD and ESRD patients. In this review, we discuss mechanisms by which hypothyroidism adversely affects cardiovascular health; examine the prognostic implications of hypothyroidism, thyroid hormone alterations and exogenous thyroid hormone replacement in CKD and ESRD; and identify areas of uncertainty related to the interplay between hypothyroidism, cardiovascular disease and kidney disease requiring further investigation.

Molecular basis of Klotho: from gene to function in aging

The discovery of the Klotho (KL) gene, which was originally identified as a putative aging-suppressor gene, has generated tremendous interest and has advanced understanding of the aging process. In mice, the overexpression of the KL gene extends the life span, whereas mutations to the KL gene shorten the life span. The human KL gene encodes the α-Klotho protein, which is a multifunctional protein that regulates the metabolism of phosphate, calcium, and vitamin D. α-Klotho also may function as a hormone, although the α-Klotho receptor(s) has not been found. Point mutations of the KL gene in humans are associated with hypertension and kidney disease, which suggests that α-Klotho may be essential to the maintenance of normal renal function. Three α-Klotho protein types with potentially different functions have been identified: a full-length transmembrane α-Klotho, a truncated soluble α-Klotho, and a secreted α-Klotho. Recent evidence suggests that α-Klotho suppresses the insulin and Wnt signaling pathways, inhibits oxidative stress, and regulates phosphatase and calcium absorption. In this review, we provide an update on recent advances in the understanding of the molecular, genetic, biochemical, and physiological properties of the KL gene. Specifically, this review focuses on the structure of the KL gene and the factors that regulate KL gene transcription, the key sites in the regulation of α-Klotho enzyme activity, the α-Klotho signaling pathways, and the molecular mechanisms that underlie α-Klotho function. This current understanding of the molecular biology of the α-Klotho protein may offer new insights into its function and role in aging.

Nonthyroidal illness: a risk factor for coronary calcification and arterial stiffness in patients undergoing peritoneal dialysis?

OBJECTIVES

Low triiodothyronine levels, as part of the nonthyroidal illness syndrome, are common in dialysis patients and have repeatedly been shown to be associated with increased (cardiovascular) mortality rates. We hypothesized that increased vascular calcification may mediate this relationship.

METHODS

A total of 84 patients from the Stockholm region receiving maintenance peritoneal dialysis were included in the study. Serum concentrations of free triiodothyronine (fT3), thyroxine and thyroid-stimulating hormone were measured. Coronary artery calcium (CAC) scores were assessed by cardiac computed tomography scans. Surrogates of arterial stiffness included aortic diastolic and systolic blood pressures, pulse pressure, augmentation pressure and Buckberg's subendocardial viability ratio measured by pulse waveform analyses. Patients were subsequently followed, and events of death and censoring were recorded. Thyroid hormone concentrations were associated with CAC scores, measures of arterial stiffness and all-cause mortality. The associations between CAC scores and arterial stiffness surrogates and mortality were also determined to evaluate a possible causal pathway.

RESULTS

Both CAC scores and arterial stiffness surrogates were substantially higher in individuals with low fT3 levels. These associations persisted in multivariate logistic and linear regression analyses. During a median (interquartile range) follow-up of 32 (22-42) months, 24 patients died. Both fT3 levels below the median value [HR crude 4.1, 95% confidence interval (CI) 1.4-12.6] and CAC scores above the median value (HR crude 5.8, 95% CI 1.7-20.1) were strongly associated with mortality.

CONCLUSIONS

In patients undergoing peritoneal dialysis, fT3 levels were strongly associated with arterial stiffness, coronary artery calcification and mortality. We speculate that the association between nonthyroidal illness and mortality may be partly mediated by acceleration of vascular calcification.

Nonthyroidal illness and the cardiorenal syndrome

The cardiorenal syndrome represents a final common pathway for renal and congestive heart failure and heralds a poor prognosis. Factors that link the failing heart and the failing kidneys--the so-called cardiorenal connectors--are, therefore, of clinical and therapeutic interest. Alterations in the levels and function of thyroid hormones that fit the spectrum of nonthyroidal illnesses could be considered to be cardiorenal connectors as both renal failure and heart failure progress with the development of nonthyroidal illness. In addition, circumstantial evidence suggests that nonthyroidal illness can induce deterioration in the function of the heart and the kidneys via multiple pathways. As a consequence, these reciprocal associations could result in a vicious cycle of deterioration that likely contributes to increased mortality. In this Review, we describe the evidence for a pathophysiological role of nonthyroidal illness in the cardiorenal syndrome. We also discuss the available data from studies that have investigated the efficacy of thyroid hormone replacement therapy in patients with renal failure and the rationale for interventional trials to examine the effects of normalization of the thyroid hormone profile in patients with renal failure and congestive heart failure.

Thyroid hormone signaling and homeostasis during aging

Studies in humans and in animal models show negative correlations between thyroid hormone (TH) levels and longevity. TH signaling is implicated in maintaining and integrating metabolic homeostasis at multiple levels, notably centrally in the hypothalamus but also in peripheral tissues. The question is thus raised of how TH signaling is modulated during aging in different tissues. Classically, TH actions on mitochondria and heat production are obvious candidates to link negative effects of TH to aging. Mitochondrial effects of excess TH include reactive oxygen species and DNA damage, 2 factors often considered as aging accelerators. Inversely, caloric restriction, which can retard aging from nematodes to primates, causes a rapid reduction of circulating TH, reducing metabolism in birds and mammals. However, many other factors could link TH to aging, and it is these potentially subtler and less explored areas that are highlighted here. For example, effects of TH on membrane composition, inflammatory responses, stem cell renewal and synchronization of physiological responses to light could each contribute to TH regulation of maintenance of homeostasis during aging. We propose the hypothesis that constraints on TH signaling at certain life stages, notably during maturity, are advantageous for optimal aging.

Biological significance of a thyroid hormone-regulated secretome

The thyroid hormone, 3,3,5-triiodo-L-thyronine (T3), modulates several physiological processes, including cellular growth, differentiation, metabolism and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Several intracellular and extracellular protein candidates are regulated by T3. Moreover, T3-regulated secreted proteins participate in physiological processes or cellular transformation. T3 has been employed as a marker in several disorders, such as cardiovascular disorder in chronic kidney disease, as well as diseases of the liver, immune system, endocrine hormone metabolism and coronary artery. Our group subsequently showed that T3 regulates several tumor-related secretory proteins, leading to cancer progression via alterations in extracellular matrix proteases and tumor-associated signaling pathways in hepatocellular carcinomas. Therefore, elucidation of T3/thyroid hormone receptor-regulated secretory proteins and their underlying mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a detailed summary on the known secretory proteins regulated by T3 and their physiological significance. This article is part of a Special Issue entitled: An Updated Secretome.

Chronic kidney disease: a clinical model of premature aging

Premature aging is a process associated with a progressive accumulation of deleterious changes over time, an impairment of physiologic functions, and an increase in the risk of disease and death. Regardless of genetic background, aging can be accelerated by the lifestyle choices and environmental conditions to which our genes are exposed. Chronic kidney disease is a common condition that promotes cellular senescence and premature aging through toxic alterations in the internal milieu. This occurs through several mechanisms, including DNA and mitochondria damage, increased reactive oxygen species generation, persistent inflammation, stem cell exhaustion, phosphate toxicity, decreased klotho expression, and telomere attrition. Because recent evidence suggests that both increased local signaling of growth factors (through the nutrient-sensing mammalian target of rapamycin) and decreased klotho expression are important modulators of aging, interventions that target these should be tested in this prematurely aged population.

A contemporary atlas of the mouse diaphragm: myogenicity, vascularity, and the Pax3 connection

The thoracic diaphragm is a unique skeletal muscle composed of costal, crural, and central tendon domains. Although commonly described in medical textbooks, newer insights into the diaphragm cell composition are scarce. Here, using reporter mice, combined with gene expression analyses of whole tissues and primary cultures, we compared the diaphragm domains and their myogenic progenitors (i.e., Pax3/7 satellite cells). The outcomes of these analyses underscore the similarities between the myogenic aspects of the costal and crural domains. Expression levels of all myogenic genes examined (except Pax3) were strongly affected in mdx (dystrophin-null) mice and accompanied by an increase in fibrosis- and adiposity-related gene expression. Cell culture studies further indicated the presence of a non-myogenic Pax3-expressing population, potentially related to vascular mural cells. We additionally investigated the diaphragm vasculature. XLacZ4 and Sca1-GFP transgenes allowed a fine definition of the arterial and microvasculature network based on reporter expression in mural cells and capillary endothelium, respectively. We also provide insights into the organization of the diaphragm venous system, especially apparent in the central tendon and exhibiting arcades lined with fat-containing cells. The novel information in this "contemporary atlas" can be further explored in the context of diaphragm pathology and genetic disorders.

Dietary and genetic evidence for enhancing glucose metabolism and reducing obesity by inhibiting klotho functions

Klotho is a multifunctional protein involved in numerous biological functions, ranging from mineral ion metabolism to signaling activities. Recent studies have identified klotho as a target gene for peroxisome proliferator-activated receptor-γ (PPAR-γ), a master regulator of adipocyte differentiation, and an adipogenesis-promoting factor. In a similar line of observation, eliminating klotho function from mice resulted in the generation of lean mice with almost no detectable fat tissue. In contrast to the klotho-knockout mice (11.7±0.3 g at 9 wk), leptin-deficient (ob/ob) mice are severely obese (49.3±0.6 g at 9 wk), due to excessive fat accumulation. To study the in vivo role of klotho in obesity, we have generated and characterized ob/ob mice lacking klotho activity [ob/ob-klotho double-knockout (DKO) mice]. The ob/ob mice started to get bigger from 3 wk onward and gained almost 2 times more weight than their wild-type (WT) counterparts (WT vs. ob/ob: 34.8±1.3 vs. 65.5±1.2 g at 21 wk). The generated ob/ob-klotho DKO mice were not only viable throughout their adulthood but also showed markedly reduced fat tissue accumulation compared to their ob/ob littermates. The ob/ob-klotho DKO mice had significantly (P<0.01) less retroperitoneal, mesenteric, and epididymal fat accumulation, compared to their ob/ob counterparts. Similarly, the fatty liver that was consistently observed in the ob/ob mice was eliminated in the ob/ob-klotho DKO mice. Such structural improvement in the liver was also evident from markedly reduced fasting blood glucose levels in ob/ob-klotho DKO mice, compared to their ob/ob counterparts (ob/ob vs. ob/ob-klotho DKO: 266 ± 36 vs. 65±2 mg/dl). Finally, to study whether the absence of klotho can induce resistance to high-fat-diet-induced obesity, we provided a high-fat (60%) diet to klotho-knockout mice and compared them with normal-fat (20%) diet-fed klotho-knockout mice. No significant difference in body weight was detected in klotho-knockout mice fed either the normal-fat diet or high-fat diet, while WT mice fed the high-fat diet gradually gained body weight, compared to the normal-fat-diet-fed counterparts. The results of our dietary and genetic manipulation studies provide in vivo evidence for a role of klotho in obesity and offer a novel target to manipulate obesity and associated complications.

Identification of nesfatin-1 in human and murine adipose tissue: a novel depot-specific adipokine with increased levels in obesity

Nesfatin-1 is a recently identified anorexigenic peptide derived from its precursor protein, nonesterified fatty acid/nucleobindin 2 (NUCB2). Although the hypothalamus is pivotal for the maintenance of energy homeostasis, adipose tissue plays an important role in the integration of metabolic activity and energy balance by communicating with peripheral organs and the brain via adipokines. Currently no data exist on nesfatin-1 expression, regulation, and secretion in adipose tissue. We therefore investigated NUCB2/nesfatin-1 gene and protein expression in human and murine adipose tissue depots. Additionally, the effects of insulin, dexamethasone, and inflammatory cytokines and the impact of food deprivation and obesity on nesfatin-1 expression were studied by quantitative RT-PCR and Western blotting. We present data showing NUCB2 mRNA (P < 0.001), nesfatin-1 intracellular protein (P < 0.001), and secretion (P < 0.01) were significantly higher in sc adipose tissue compared with other depots. Also, nesfatin-1 protein expression was significantly increased in high-fat-fed mice (P < 0.01) and reduced under food deprivation (P < 0.01) compared with controls. Stimulation of sc adipose tissue explants with inflammatory cytokines (TNFalpha and IL-6), insulin, and dexamethasone resulted in a marked increase in intracellular nesfatin-1 levels. Furthermore, we present evidence that the secretion of nesfatin-1 into the culture media was dramatically increased during the differentiation of 3T3-L1 preadipocytes into adipocytes (P < 0.001) and after treatments with TNF-alpha, IL-6, insulin, and dexamethasone (P < 0.01). In addition, circulating nesfatin-1 levels were higher in high-fat-fed mice (P < 0.05) and showed positive correlation with body mass index in human. We report that nesfatin-1 is a novel depot specific adipokine preferentially produced by sc tissue, with obesity- and food deprivation-regulated expression.

Klotho: a novel phosphaturic substance acting as an autocrine enzyme in the renal proximal tubule

Klotho has profound effects on phosphate metabolism, but the mechanisms of how Klotho affects phosphate homeostasis is unknown. We detected Klotho in the proximal tubule cell, brush border, and urinary lumen, where phosphate homeostasis resides. Increasing Klotho in the kidney and urine chronically by transgenic overexpression or acutely by intravenous infusion caused hypophosphatemia, phosphaturia from decreased proximal phosphate reabsorption, and decreased activity and protein of the principal renal phosphate transporter NaPi-2a. The phosphaturic effect was present in FGF23-null mice, indicating a direct action distinct from Klotho's known role as a coreceptor for FGF23. Direct inhibition of NaPi-2a by Klotho was confirmed in cultured cells and in cell-free membrane vesicles characterized by acute inhibition of transport activity followed by decreased cell surface protein. Transport inhibition can be mimicked by recombinant beta-glucuronidase and is associated with proteolytic degradation and reduced surface NaPi-2a. The inhibitory effect of Klotho on NaPi-2a was blocked by beta-glucuronidase inhibitor but not by protease inhibitor. Klotho is a novel phosphaturic substance that acts as an enzyme in the proximal tubule urinary lumen by modifying glycans, which cause decreased transporter activity, followed by proteolytic degradation and possibly internalization of NaPi-2a from the apical membrane.

Klotho: an antiaging protein involved in mineral and vitamin D metabolism

Klotho gene mutation leads to a syndrome strangely resembling chronic kidney disease patients undergoing dialysis with multiple accelerated age-related disorders, including hypoactivity, sterility, skin thinning, muscle atrophy, osteoporosis, vascular calcifications, soft-tissue calcifications, defective hearing, thymus atrophy, pulmonary emphysema, ataxia, and abnormalities of the pituitary gland, as well as hypoglycemia, hyperphosphatemia, and paradoxically high-plasma calcitriol levels. Conversely, mice overexpressing klotho show an extended existence and a slow aging process through a mechanism that may involve the induction of a state of insulin and oxidant stress resistance. Two molecules are produced by the klotho gene, a membrane bound form and a circulating form. However, their precise biological roles and molecular functions have been only partly deciphered. Klotho can act as a circulating factor or hormone, which binds to a not yet identified high-affinity receptor and inhibits the intracellular insulin/insulin-like growth factor-1 (IGF-1) signaling cascade; klotho can function as a novel beta-glucuronidase, which deglycosylates steroid beta-glucuronides and the calcium channel transient receptor potential vallinoid-5 (TRPV5); as a cofactor essential for the stimulation of fibroblast growth factor (FGF) receptor by FGF23. The two last functions have propelled klotho to the group of key factors regulating mineral and vitamin D metabolism, and have also stimulated the interest of the nephrology community. The purpose of this review is to provide a nephrology-oriented overview of klotho and its potential implications in normal and altered renal function states.

The differential effects of age on the association of KLOTHO gene polymorphisms with coronary artery disease

The Klotho knockout mouse is thought to be a good animal model for human aging. Recent studies have reported on the association of KLOTHO gene mutation with cardiovascular disease in humans. We observed the frequencies of single nucleotide polymorphisms, that is, G-395A in the promoter region, C1818T in exon 4, and a functional variant, KL-VS, of KLOTHO gene in Koreans, and we investigated their relationships with the presence of coronary artery disease (CAD) in patients who had undergone coronary angiograms. A total of 274 subjects who underwent coronary angiograms because of chest pain were enrolled, and their blood pressure, body mass index, fasting blood glucose level, and lipid profiles were measured. Genotypings were performed on samples of their blood with real-time polymerase chain reaction. Two single nucleotide polymorphisms, G-395A and C1818T, complied with Hardy-Weinberg equilibrium. For the KL-VS genotype, 1 homozygote subject for the adverse allele was detected among the entire population (GG for F352V and CC for C370S). When the subjects were classified into 4 groups according to the number of stenotic vessels, there were no differences among the mean values of the cardiovascular risk factors, except for age and the fasting blood glucose levels, which showed a significant difference between that of the normal and the diseased vessel groups. There were no differences in the prevalence of CAD according to the genotypes of the G-395A polymorphism; however, for the C1818T polymorphism, those subjects with the T allele showed a lower prevalence of CAD than those with the CC genotype. When the subjects were divided into 2 groups according to age, in the group younger than 60 years, T allele carriers of the C1818T polymorphism showed a lower prevalence of CAD than did the noncarriers. In the group older than 60 years, A allele carriers of the G-395A polymorphism showed a lower prevalence of CAD than did the noncarriers. On the haplotype analysis, the GG-CC haplotype showed an increased risk for CAD with an odds ratio of 2.594 (95% confidence interval, 1.385-4.858; P = 0.003). Differential effects of age were observed in the association of KLOTHO G-395A and C1818T polymorphisms with CAD in Koreans. The KL-VS variant seems to be rarely found in the Korean population. These results infer the possibility of the KLOTHO gene being a candidate gene of atherosclerosis in humans, and further research on this topic needs to be done.

Klotho protein promotes adipocyte differentiation

Mice with homozygous disruption of the klotho exhibit multiple age-related disorders and have barely detectable amounts of white adipose tissue. Although klotho expression in cultured adipocytes has been reported, little is known about its function in adipocytes. In the present study, we investigated the role of klotho on adipocyte differentiation. Adipocyte differentiation was induced by incubation of confluent 3T3-L1 cells with insulin, dexamethasone, and 1-methyl-3-isobutyl-xanthin. Klotho-siRNA and expression vector were produced for klotho suppression and overexpression, respectively. Klotho protein was purified for determination of the hormonal effect of klotho. Klotho mRNA and protein expression increased up to the 3rd d of differentiation. A peroxisome proliferator-activated receptor-gamma agonist increased klotho expression during the early period of adipocyte differentiation. The mRNA expression of adipocyte differentiation markers, such as CCAAT/enhancer-binding protein (C/EBP)alpha, C/EBPbeta, C/EBPdelta, peroxisome proliferator-activated receptor-gamma, and fatty acid binding protein 4, was decreased by klotho suppression, and increased 1.9- to 3.8-fold by klotho overexpression. The results of Oil Red O staining also suggested that klotho overexpression promoted adipocyte differentiation. Klotho protein stimulation resulted in a 2.4- to 4.6-fold increase in mRNA expression of differentiation markers compared with control, and the time course depended on adipocyte induction status. Western blot analysis showed that protein levels of C/EBPalpha and C/EBPdelta were increased by Klotho protein stimulation. These results suggest that klotho works as a hormonal factor to promote adipocyte differentiation in the early days, during the period of transient proliferation in the differentiation process, and that klotho may play an essential role in adipocyte differentiation.

Oxidative stress decreases klotho expression in a mouse kidney cell line

BACKGROUND/AIMS

Defects in klotho gene expression in the mouse result in a syndrome that resembles human aging. We recently identified expression of klotho in a mouse inner medullary collecting duct (mIMCD3) cell line for the first time, and in the present study we explored the physiological relevance of the regulation of klotho expression in the presence of oxidant stress injury.

METHODS

Klotho expression was analyzed by real-time PCR, Western blot, and immuocytochemical staining during exposure to hydrogen peroxide (H2O2). Overexpression of the klotho gene was induced by klotho adenoviruses, and the number of apoptotic cells was counted by flowcytometry.

RESULTS

Oxidant stress injury by H2O2 dose-dependently reduced klotho expression and diminished klotho staining. There were fewer apoptotic cells among the klotho-transfected cells than among the control cells.

CONCLUSION

Klotho is expressed in cell line mIMCD3, and the klotho gene may be involved in the process of oxidative stress injury and apoptosis in this cell line.