Form Of Klotho Research Articles

P1549Serum soluble Klotho is associated with extent of coronary artery calcification in patients with stable angina pectoris undergoing percutaneous coronary intervention

Abstract Background Klotho, which was originally identified as an aging suppressor, is a key regulator of bone and mineral metabolism. Transmembrane and soluble forms of Klotho protein have been identified. The transmembrane form serves as an obligate co-receptor for fibroblast growth factor 23 (FGF23). However, the physiological importance of soluble form of Klotho has not been determined. Purpose The present study aimed to test the hypothesis that circulating soluble Klotho levels can predict the presence or extent of coronary artery calcification (CAC) in patients with coronary artery disease. Methods We analyzed CAC of culprit lesions in patients with 75 stable angina pectoris who were not on dialysis and were scheduled for percutaneous coronary intervention (PCI) following intravascular ultrasound (IVUS). Arc and length of each calcium within the culprit lesion was measured by IVUS. The main outcome measure was the calcium index; a volumetric IVUS-derived measure which was calculated as total calcium length/lesion length × maximal calcium arc/360°. Low calcium index was defined as calcium index <0.042 of the first quartile value. Serum Klotho and FGF23 were measured before PCI. Patients were divided into two groups according to median serum Klotho value: low-Klotho (n=37, ≤460 pg/mL) and high-Klotho group (n=38, >460 pg/mL). Results Compared with patients with low-Klotho, those with high-Klotho had higher estimated glomerular filtration rate (eGFR) (69±20 vs. 55±16 mL/min/1.73 m2, p<0.001), lower FGF23 levels (51±24 vs. 67±41 pg/mL, p=0.010). Patients with high-Klotho had significantly lower calcium index than those with low-Klotho (0.17±0.21 vs. 0.24±0.23, p=0.043). Serum Klotho levels correlated significantly and inversely with calcium index (r=−0.31, p=0.006). The correlation between Klotho and calcium index was pronounced at analysis in patients with eGFR <60 mL/min/1.73 m2 (r=−0.52, p<0.001). Logistic regression analysis showed that high-Klotho is a sole significant independent factor associated with low calcium index (odds ratio 7.17, p=0.004). Presence of high-Klotho had high sensitivity and negative predictive value for identifying low calcium index (83% and 92%, respectively). Conclusions Serum Klotho values were independently and inversely associated with the degree of CAC assessed by IVUS. These findings have important clinical implications for serum Klotho as a biomarker that reflects the extent of CAC.

Evaluation of serum soluble klotho protein in patients with different degrees of chronic kidney disease

Objectives The aim of this study was to investigate serum α-klotho as a new biomarker for the diagnosis of chronic kidney disease (CKD), especially in its early stages. Background α-Klotho is a novel antiaging protein that was identified as a regulator of calcium and phosphate homeostasis, which is highly expressed in the kidney. The soluble form of klotho acts as an endocrine substance that exerts multiple actions including the modulation of renal solute transport and protection of the kidney. Methods A case–control study was conducted at the Clinical Pathology Department, Menoufia University Hospitals, Faculty of Medicine, during the period from January 2015 to November 2016. Sixty-eight patients suffering from CKD who were admitted to the hospital during the period from January 2015 to November 2016 were included in this study. In addition, 10 apparently healthy subjects with matching age and gender formed the control group. Routine laboratory investigations performed were: hemoglobin, urea, creatinine, uric acid, calcium (Ca2), phosphate (PO4), and albumin and the estimated glomerular filtration rate were measured and the α-klotho protein level was measured by ELISA. Results Serum soluble α-klotho protein levels were significantly lower in CKD patients compared with normal controls. Besides, α-klotho protein levels were positively correlated with estimated glomerular filtration rate, hemoglobin and were negatively correlated with renal function tests and phosphate. Conclusion Soluble α-klotho levels are significantly decreased in CKD not only in the advanced stages but also in the early stages.

The couple fibroblast growth factor 23 (FGF23)/Klotho

The fibrobalst growth factor 23 (FGF23) is a protein secreted in the plasma by bone cells. FGF23 controls phosphate and calcitriol plasma concentration. Its main physiological targets are the kidney and the parathyroid gland. Its production is stimulated by phosphate intake and plasma calcitriol levels. FGF23 binds a receptor at the cell surface that is composed by the association of a FGF receptor with the protein Klotho. Klotho expression is restricted to few organs including the kidney and the parathyroid gland. Klotho, which is expressed at the cell surface, can also be released in the plasma after an enzymatic cleavage. The role of the circulating form of Klotho is unknown. In addition to its role as a co-receptor Klotho may control the stability of the renal sodium phosphate transporter NPT2a and the calcium channel TRPV5 via enzymatic properties. FGF23 or Klotho gene disruption in mice leads to similar phenotypes except for the levels of FGF23, undetectable or increased respectively. FGF23 plasma concentration rises from the early stage of renal insufficiency to prevent plasma phosphate concentration from increasing. In parallel Klotho production seems to diminish. These modifications trigger the secondary hyperparathyroidism observed in renal insufficiency. The increase in FGF23 concentration and the decrease in Klotho levels are associated in animals and in human as well to an augmentation of mortality especially from cardiovascular causes and to heart modification: hypertrophy or dysfunction.

Factors Those Up Regulate <i>Klotho</i> and Glutathione Peroxidase-1 Gene Expression Improve Renal Function in Rats with Acute Renal Failure

Acute Renal Failure (ARF) has traditionally been defined as the abrupt and progressive loss of kidney functions resulting in the retention of urea and other nitrogenous waste products associated with interstitial inflammation, tubular injury and increasing Tumor Necrosis Factor (TNF). Mortality in patients with ARF remains high >50% in severely ill patients. Klotho gene is a new anti-aging gene. Genetic mutation of klotho gene causes multiple premature aging-like phenotypes and shortens lifespan. Klotho gene is highly expressed in the kidney and a soluble form of klotho functions as an endocrine substance that exerts multiple actions including the modulation of renal solute transport and the protection of the kidney. This study aimed to clarify the pre treatment and/or post treatment effect of vitamin E as an antioxidant on kidney functions, klotho gene expression and glutathione peroxidase-1 gene expression among rats with acute renal failure. Using glycerol as oxidative stress factor to cause acute renal failure and Real time PCR for assessment of gene expression of target gene in the control and treated groups. Our results demonstrated that the vitamin E (I± tocopherol) as antioxidant factor decreased the kidney injuries as pre renal failure administer and improve kidney function as post renal failure administer. Those effects were through up regulating the Klotho as anti aging gene and the Glutathione Peroxidase (GPx-1) as antioxidant gene expression in the kidney tissue. We concluded that factors those up regulate the klotho gene expression can use as protective factors against kidney injuries and to improve kidney function in renal failure.

The endocrine role of the skeleton.

In recent years, many advances have been made in the understanding of the role of the skeleton in whole body pathophysiology. The original vision of the bone as a static tissue with limited functions is now completely abolished. Indeed it is now well established that bone is a dynamic connective tissue subjected to a continuous process of resorption and formation. This activity is crucial, since correct bone homeostasis, skeleton integrity, and mechanical properties rely on a perfect coupling between osteoclasts and osteoblasts functions. Indeed recent studies demonstrated that the bone remodelling process is an important regulator of many functions not only limited to the bone, but also correlated with the whole body physiology. In this special issue, experts in the bone field addressed the interplay between bone and energy metabolism, immune system, male fertility, and kidney and documented how bone has emerged as an endocrine “gland.” In particular, osteocalcin is indicated as a key factor mediating the endocrine functions of bone, with special focus on glucose metabolism and male fertility. J. Shao et al. described how osteocalcin targets β-cells in the pancreas and adipocytes to regulate insulin production and sensitivity and Leydig cells to control testicular function. Moreover the authors reviewed the mechanisms regulating osteocalcin production and activation, with particular attention to 1α,25-dihydroxyvitamin D3 and vitamin K, and reported studies in humans supporting the relevance of osteocalcin in energy metabolism and highlighting differences between men and mice as well as aspects requiring further investigation. M. F. Faienza et al. analyzed the bone-pancreas loop, focusing the attention not only on osteocalcin, but also on other proteins, such as osteoprotegerin, vitamin D, gastric inhibitory polypeptide (GIP), and adiponectin, involved in the regulation of insulin function and glucose metabolism. Antiresorptive drugs might impact the bone-pancreas interplay; however conflicting results exist on this aspect and deserve further efforts from the scientific community. In particular, the development of new drugs simultaneously targeting the skeleton, glucose metabolism, and the adipose tissue can be envisaged. Besides the effects of bone osteocalcin on male fertility, the endocrine role of oestrogens on human male skeleton was also discussed in this special issue in the paper by V. Rochira et al. The authors described the effects exerted by oestrogens in the physiological events occurring in male bone throughout life such as longitudinal skeletal growth, skeletal proportion, achievement of peak bone mass, and maintenance of bone mineral density. Moreover the authors discussed clinical aspects of oestrogen deficiency. In separate chapters, the interplay between bone and kidney is presented. Y. Takei et al. described how bone homeostasis is finely regulated by a complex mechanism including FGFs (fibroblast growth factors)/FGF receptors signalling. In particular they emphasized how FGF23, expressed by osteocytes/osteoblasts, reduces the levels of serum phosphate and 1,25(OH)2D3 and the relevance of its coreceptor αKlotho, produced by kidney distal tubular cells, in the physiologic regulation of mineral metabolism. In a clinical study S. Rotondi et al. investigated whether a soluble form of Klotho could represent a marker of renal damage of CKD- (chronic kidney disease-) MBD (mineral bone disorder), indicative of the cross-talk between bone and kidney, and concluded that soluble Klotho could be considered an early marker of mineral metabolism impairment in renal disease. Finally, bone diseases, such as osteopetrosis and osteoporosis, are revisited with the special focus on their relevance for the endocrine role of the skeleton and on the relationship with other diseases, respectively. Indeed, A. E. Coudert et al. described how osteoclast dysfunctions lead to osteopetrosis and have allowed shedding some lights on several aspects of the bone biology that were not well known, discovering the interaction between bone and stomach, insulin metabolism, male fertility, immune system, bone marrow, and fat. Regarding osteoporosis studies, P. Jackuliak and J. Payer analyzed the osteoporosis risk in diabetic patients. Moreover the authors made clinical considerations and discussed the use of bone mineral density and the trabecular bone score to study different bone properties, quantity and quality, respectively. M. Bolanowski et al. investigated how many hormonal disorders such as Cushing's syndrome, hyperprolactinemia, acromegaly, hypogonadism, and hypopituitarism influence bone metabolism and can result in secondary osteoporosis. This special issue should be of interest for basic and clinical researchers since it covers a wide range of topics regarding bone research. Original studies and reviews have been published with the aim to report and summarize the latest findings regarding the relevance of the skeleton in the whole body physiology.

Identification of cleavage sites leading to the shed form of the anti-aging protein klotho.

Membrane protein shedding is a critical step in many normal and pathological processes. The anti-aging protein klotho (KL), mainly expressed in kidney and brain, is secreted into the serum and CSF, respectively. KL is proteolytically released, or shed, from the cell surface by ADAM10 and ADAM17, which are the α-secretases that also cleave the amyloid precursor protein and other proteins. The transmembrane KL is a coreceptor with the FGF receptor for FGF23, whereas the shed form acts as a circulating hormone. However, the precise cleavage sites in KL are unknown. KL contains two major cleavage sites: one close to the juxtamembrane region and another between the KL1 and KL2 domains. We identified the cleavage site involved in KL release by mutating potential sheddase(s) recognition sequences and examining the production of the KL extracellular fragments in transfected COS-7 cells. Deletion of amino acids T958 and L959 results in a 50–60% reduction in KL shedding, and an additional P954E mutation results in further reduction of KL shedding by 70–80%. Deletion of amino acids 954–962 resulted in a 94% reduction in KL shedding. This mutant also had moderately decreased cell surface expression, yet had overall similar subcellular localization as that of WT KL, as demonstrated by immunofluorescence. Cleavage-resistant mutants could function as a FGFR coreceptor for FGF23, but they lost activity as a soluble form of KL in proliferation and transcriptional reporter assays. Cleavage between the KL1 and KL2 domains is dependent on juxtamembrane cleavage. Our results shed light onto mechanisms underlying KL release from the cell membrane and provide a target for potential pharmacologic interventions aimed at regulating KL secretion.