Association of polymorphisms in the klotho gene with severity of non-diabetic ESRD in African Americans

Role of deleterious nsSNPs of klotho protein and their drug response: a computational mechanical insights

Worldwide, the burden of chronic kidney disease (CKD) has increased rapidly and is a lethal disease. The klotho protein plays a vital role in the regulatory mechanism in the progression of CKD. Particularly the decreased expression of klothoand its genetic variations might affect the potency of drugs. This study aims to identify a new drug molecule, which works equipotential in all types of klotholike wild and mutant variants. All non-synonymous SNPs were predicted by several SNP tools. Where, two missense variants were examined as vulnerable, significantly damaging, and also involved in the structural conformational changes of the protein. Based on structure-based screening, E-pharmacophore screening, binding mode analysis, binding free energy analysis, QM/MM, and molecular dynamics analysis a lead compound (Lifechemical_F2493-2038) was identified as an effective agonistic molecule hence the identified Lifechemical_F2493-2038 compound is well bound to the wild and mutant proteins which found to increase the expression of klotho.Communicated by Ramaswamy H. Sarma.

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.

Association of Genetic Variants of Klotho with BP Responses to Dietary Sodium or Potassium Intervention and Long-Term BP Progression

OBJECTIVES

Klotho (KL) plays pivotal roles in the progression of salt-sensitive hypertension. Salt-sensitive hypertension was associated with KL genotypes. We aimed to explore the association of common genetic variants of KL with individual blood pressure (BP) responses to sodium and potassium through a dietary intervention study as well as long-term BP progression.

METHODS

We conducted family-based dietary interventions among 344 participants from 126 families in rural villages of northern China in 2004. Subjects sequentially underwent a baseline diet, a low-salt diet (51.3 mmol/day Na), a high-salt diet (307.8 mmol/day Na), and a high-salt + potassium supplementation diet (307.8 mmol/day Na + 60 mmol/day K). After dietary intervention, we followed up with these participants in 2009 and 2012. The associations between 6 single-nucleotide polymorphisms (SNPs) of KL and phenotypes were analyzed through a linear mixed-effects model.

RESULTS

SNPs rs211247 and rs1207568 were positively correlated with the BP response to high-salt diet in the dominant model after adjusting for confounders (β = 1.670 and 2.163, p = 0.032 and 0.005, respectively). BPs rs526906 and rs525014 were in a haplotype block. Block rs526906-rs525014 was positively correlated with diastolic BP response to potassium and potassium sensitivity in the additive model (β = 0.845, p = 0.032). In addition, regression analysis indicated that rs211247 was associated with long-term systolic BP alterations after 8 years of follow-up in the recessive model (β = 20.47, p = 0.032).

CONCLUSIONS

Common variants of the KL gene might modify individual BP sensitivity to sodium or potassium and influence the long-term progression of BP, suggesting a potential role in the development of salt-sensitive hypertension. Thus, KL may be a new early intervention target for salt-sensitive hypertension.

Donor Klotho KL-VS Polymorphism Predicts Allograft Glomerulosclerosis and Early Post-Transplant Kidney Function

BACKGROUND

The Klotho protein, encoded by the KL (Klotho) gene, exerts antiaging and antifibrotic effects. The KL-VS genotype diminishes Klotho expression and correlates with cardiovascular death, heart failure, and chronic kidney disease progression. The aim of this study was to analyze the contribution of donor Klotho rs9536314 and rs9527025 polymorphisms (KL-VS genotype) to renal allograft morphology and function in the early post-transplant period.

METHODS

Clinical data and biopsy reports of 170 deceased donor transplantations were retrieved from standard medical files. Donor DNA was genotyped for rs9527025 and rs9536314 SNPs using custom TaqMan assays.

RESULTS

As rs9527025 remained in full linkage with rs9536314, we report results for the latter. The analyses were performed for G dominant model (GG+GT vs TT). We found an association between reported SNP alleles, morphologic changes in the peritransplant biopsy, and kidney function 3 months after engraftment. A chronic glomerulopathy score of >0 was found in 12.2% of GG+GT cases and in 3.2% of TT cases (P = .023). For G allele carriers, the third month's median estimated glomerular filtration rate value was 35.0 (range, 20.4-76.6 mL/min), while for TT haplotype, the value was 46.3 (range, 15.5-96.8 mL/min), P = .001. At the third post-transplant month, proteinuria incidence was higher for organs with G allele than with TT haplotype (24.4% vs 9.5%; P = .030; odds ratio 3.09; 95% confidence interval 1.22-7.69).

CONCLUSION

Deceased donor KL-VS polymorphism, altering protein dimerization and coreceptor function, predicts early renal transplant glomerular lesions and function. Further analyses for mentioned effect durability are necessary.

ETHICS STATEMENT

This study complies with the Helsinki Congress and the Istanbul Declaration regarding donor source. Donors were not prisoners, and were not paid or coerced.

Association of the rs495392 Klotho polymorphism with atheromatosis progression in patients with chronic kidney disease

Background

Prevalence of atherosclerotic cardiovascular disease and its rate of progression are higher in patients with chronic kidney disease (CKD) compared with the general population. Mineral metabolism parameters have been shown to be involved in the increased velocity of atheromatosis progression. The aim of this study is to determine the role of 11 single-nucleotide polymorphisms (SNPs) of the Klotho gene on the rate of atherosclerosis progression in CKD.

Methods

This was a multicentre, prospective, observational study of 1439 CKD patients from the NEFRONA cohort. Carotid and femoral ultrasounds were performed at baseline and after 24 months in 10 arterial territories. Progression of atheromatosis was defined as an increase in the number of territories with plaque. Genotyping of 11 SNPs of the Klotho gene was performed and its association with atheromatosis progression was determined by multivariate logistic regression.

Results

Bivariate analysis showed that none of the 11 SNPs was associated with atheroma plaque prevalence, but 3 of them (rs495392, rs562020 and rs567170) showed association with atheromatosis progression. The multivariate analysis revealed that only rs495392 showed a statistically significant association with atheromatosis progression, after adjustment for several parameters known to affect it in CKD patients. Thus, the presence of one allele T was associated with a reduction of 30% of the odds of progression, whereas the presence of the two T alleles was associated with a decrease close to 50%.

Conclusions

The presence of the allele T of the SNP rs495392 of the Klotho gene is associated with a decrease in the odds of progression of atheromatosis in CKD patients.

FGF23-αKlotho as a paradigm for a kidney-bone network

The vertebrate endoskeleton is not a mere frame for muscle attachment to facilitate locomotion, but is a massive organ integrated with many physiologic functions including mineral and energy metabolism. Mineral balance is maintained by tightly controlled ion fluxes that are external (intestine and kidney) and internal (between bone and other organs), and are regulated and coordinated by many endocrine signals between these organs. The endocrine fibroblast growth factors (FGFs) and Klotho gene families are complex systems that co-evolved with the endoskeleton. In particular, FGF23 and αKlotho which are primarily derived from bone and kidney respectively, are critical in maintaining mineral metabolism where each of these proteins serving highly diverse roles; abound with many unanswered questions regarding their upstream regulation and downstream functions. Genetic lesions of components of this network produce discreet disturbances in many facets of mineral metabolism. One acquired condition with colossal elevations of FGF23 and suppression of αKlotho is chronic kidney disease where multiple organ dysfunction contributes to the morbidity and mortality. However, the single most important group of derangements that encompasses the largest breadth of complications is mineral metabolism disorders. Mineral metabolic disorders in CKD impact negatively and significantly on the progression of renal disease as well as extra-renal complications. Knowledge of the origin, nature, and impact of phosphate, FGF23, and αKlotho derangements is pivotal to understanding the pathophysiology and treatment of CKD.

Influence of Klotho gene polymorphisms on vascular gene expression and its relationship to cardiovascular disease

Klotho protein has been associated with beneficial effects that contribute to the maintenance of cardiovascular health. Diverse studies suggest that alterations in the levels of this molecule may be associated with pathophysiological abnormalities that result in increased cardiovascular risk. The primary aim of this proof-of-concept study was to analyse the existence of a potential link between Klotho gene polymorphisms and the expression level of this gene in the vascular wall, and additionally with the incidence of cardiovascular disease and cardiovascular risk factors. Our results indicate that the variant G-395A, located in the promoter region, influences Klotho gene vascular expression and is associated with the incidence of diabetes. Similarly, the exonic variant KL-VS was associated with the incidence of atherosclerotic vascular disease and coronary artery disease. Moreover, vascular expression levels of Klotho were related with the incidence of diabetes mellitus and coronary artery disease. These findings, which need to be confirmed in larger studies, suggest a potential role of Klotho in the pathogenesis of vascular damage.

The Irish Kidney Gene Project--Prevalence of Family History in Patients with Kidney Disease in Ireland

BACKGROUND

The prevalence of kidney disease (KD) due to inherited genetic conditions in Ireland is unknown. The aim of this study was to characterise an adult kidney disease population in Ireland and to identify familial clusters of kidney disease within the population.

METHODS

This was a multicenter cross-sectional study of patients with kidney disease in the Republic of Ireland, from January 2014 to September 2014, recruiting from dialysis units and out-patient renal departments. A survey was performed by collecting data on etiology of kidney disease and whether a family history of kidney disease exists. Medical records were cross-referenced to confirm the etiology of kidney disease.

RESULTS

A total of 1,840 patients were recruited with a mean age of 55.9 years (range 17-94.5) and a male predominance (n = 1,095; 59.5%). A positive family history was reported by 629 participants (34.2%). Excluding polycystic kidney disease (n = 134, 7.3%), a positive family history was reported by 495 participants (26.9%). Kidney disease due to an unknown etiology was the commonest etiology in the non-polycystic kidney disease group with a positive family history (10.6%, n = 67). Kidney diseases that are not classically associated with familial inheritance including tubulo-interstitial kidney disease, congenital abnormalities of the kidney and urinary tract and glomerulonephritis demonstrated familial clustering.

CONCLUSION

In an Irish non-polycystic kidney disease population, 26.9% reports a positive family history. The commonest etiology of kidney disease in the positive family history cohort, excluding autosomal dominant polycystic kidney disease, was kidney disease due to unknown etiology. Examining families with kidney disease provides an opportunity to better understand disease pathogenesis and potentially identify genetic predispositions to kidney disease.

FGF-23, α-Klotho Gene Polymorphism and Their Relationship with the Markers of Bone Metabolism in Chronic Peritoneal Dialysis Patients

OBJECTIVE

The aim of the present study was to evaluate the variations of some major bone metabolism markers with reference to klotho gene polymorphism (KGP) and bone mineral density (BMD) values in patients on chronic peritoneal dialysis (CPD).

MATERIALS AND METHODS

In 51 CPD patients and 40 healthy persons, assays for intact parathormone (iPTH), fibroblast growth factor 23 (FGF-23), osteoprotegerin (OPG), osteocalcin (OC), procollagen type-1 N terminal propeptide (PINP), beta- crosslaps (beta CTx), tartrate resistant acid phosphatase (TRAP5b), bone alkaline phosphatase (BAP), 1,25(OH)D3, and 25(OH)D3 and α-klotho gene mutations were performed.

RESULTS

In CPD patients, 1,25(OH)D3 and 25(OH)D3 deficiency rates were 96% and 94% respectively. iPTH (249 pg/mL vs 39 pg/mL) and FGF-23 (1089 RU/mL vs 153 RU/mL), OPG, OC, PINP, beta CTx, TRAP5b levels were significantly higher in patients. iPTH levels and whole-body BMD values were negatively correlated in patients. The rate of KGP was similar in all groups.

CONCLUSION

In CPD patients, besides vitamin D deficiency, high levels of OPG, OC, PINP, beta CTx, TRAP5b were evident. Positive correlation between iPTH levels and BAP and PINP levels suggested a diagnostic value for those markers during the management of CKD MBD. On the other hand, high serum TRAP5b concentrations did not seem to be affected by neither calcitriol treatment nor the severity of hyperparathyroidism. iPTH and FGF-23 levels and whole-body BMD values showed a significant negative correlation. We were unable to show any correlation between KGP and any of the CKD-MBD parameters measured in this study.

APOL1 null alleles from a rural village in India do not correlate with glomerulosclerosis

BACKGROUND

Among African-Americans, genome wide association revealed a strong correlation between the G1 and G2 alleles of APOL1 (apolipoproteinL1, also called trypanolytic factor) and kidney diseases including focal and segmental glomerulosclerosis, HIV-associated nephropathy and hypertensive nephrosclerosis. In the prevailing hypothesis, heterozygous APOL1 G1 and G2 alleles increase resistance against Trypanosoma that cause African sleeping sickness, resulting in positive selection of these alleles, but when homozygous the G1 and G2 alleles predispose to glomerulosclerosis. While efforts are underway to screen patients for G1 and G2 alleles and to better understand "APOL1 glomerulopathy," no data prove that these APOL1 sequence variants cause glomerulosclerosis. G1 and G2 correlate best with glomerulosclerosis as recessive alleles, which suggests a loss of function mutation for which proof of causality is commonly tested with homozygous null alleles. This test cannot be performed in rodents as the APOL gene cluster evolved only in primates. However, there is a homozygous APOL1 null human being who lives in a village in rural India. This individual and his family offer a unique opportunity to test causality between APOL1 null alleles and glomerulosclerosis.

METHODS AND FINDINGS

We obtained clinical data, blood and urine from this APOL1 null patient and 50 related villagers. Based on measurements of blood pressure, BUN, creatinine, albuminuria, genotyping and immunoblotting, this APOL1 null individual does not have glomerulosclerosis, nor do his relatives who carry APOL1 null alleles.

CONCLUSIONS

This small study cannot provide definitive conclusions but the absence of glomerulosclerosis in this unique population is consistent with the possibility that African-American glomerulosclerosis is caused, not by loss of APOL1 function, but by other mechanisms including a subtle gain of function or by the "genetic hitchhiking" of deleterious mutations in a gene linked to APOL1 G1 and G2.

The association of Klotho polymorphism with disease progression and mortality in IgA nephropathy

BACKGROUNDS

IgA nephropathy (IgAN) is the most common primary glomerulonephritis causing end stage renal disease (ESRD), and vasculopathy is known to involve disease progression. Klotho, a gene related to aging, has been reported to play a role in atherosclerosis and endothelial dysfunction. We investigated whether klotho gene polymorphism affect clinical course of IgAN.

METHODS

The data registered for PREMIER study which enrolled the patients with biopsy proven IgAN were analyzed. Two single nucleotide polymorphisms for klotho gene, G395A of promoter region and C1818T of exon 4, were examined, and investigated the association klotho genotypes with the progression of IgAN and patient survival.

RESULTS

Clinical data from 973 patients confirmed about survival were analyzed. The allele frequency was 0.830 and 0.170 for allele G and A, and 0.816 and 0.184 for allele C and T, which were complied with Hardy-Weinberg equilibrium (p=0.996 and 0.531 respectively). Death was observed more frequently in A-allele carriers of G395A polymorphism (0.7 vs. 2.6 %, GG vs. GA+AA, p=0.022). Renal survival in Kaplan-Meier survival curve was also worse in same group (p=0.04).

CONCLUSION

Klotho gene polymorphism was associated with patient survival and disease progression of IgAN.

Stochastic model search with binary outcomes for genome-wide association studies

Objective

The spread of case–control genome-wide association studies (GWASs) has stimulated the development of new variable selection methods and predictive models. We introduce a novel Bayesian model search algorithm, Binary Outcome Stochastic Search (BOSS), which addresses the model selection problem when the number of predictors far exceeds the number of binary responses.

Materials and methods

Our method is based on a latent variable model that links the observed outcomes to the underlying genetic variables. A Markov Chain Monte Carlo approach is used for model search and to evaluate the posterior probability of each predictor.

Results

BOSS is compared with three established methods (stepwise regression, logistic lasso, and elastic net) in a simulated benchmark. Two real case studies are also investigated: a GWAS on the genetic bases of longevity, and the type 2 diabetes study from the Wellcome Trust Case Control Consortium. Simulations show that BOSS achieves higher precisions than the reference methods while preserving good recall rates. In both experimental studies, BOSS successfully detects genetic polymorphisms previously reported to be associated with the analyzed phenotypes.

Discussion

BOSS outperforms the other methods in terms of F-measure on simulated data. In the two real studies, BOSS successfully detects biologically relevant features, some of which are missed by univariate analysis and the three reference techniques.

Conclusion

The proposed algorithm is an advance in the methodology for model selection with a large number of features. Our simulated and experimental results showed that BOSS proves effective in detecting relevant markers while providing a parsimonious model.

Lack of association of Klotho gene variants with valvular and vascular calcification in Caucasians: a candidate gene study of the Framingham Offspring Cohort

BACKGROUND

Valvular and vascular calcification are important early aging phenotypes and represent risk factors for cardiovascular morbidity and mortality. Klotho is a gene primarily expressed in the kidney that has an important role in calcium-phosphate homeostasis. The functional KL-VS variant of Klotho has been associated with aging and cardiovascular disease in human studies, but its role in valvular and vascular calcification remains unknown. We performed a candidate gene study in the Framingham Offspring Cohort to evaluate the effect of KL-VS variant of the Klotho gene on valvular calcification.

METHODS

We analyzed the Klotho KL-VS genotype (rs9536314) from the Affymetrix 550K genome-wide dataset, distributed by dbGAP, on 1389 cases and 2139 controls from the Framingham Heart Study Offspring Cohort. Allele and genotype frequencies were compared between cases and controls. Valvular calcification was defined as presence of calcification on the mitral annulus or the aortic valve as determined by echocardiography. A sensitivity analysis of coronary artery calcification by electron beam computed tomography was performed on 1363 patients.

RESULTS

The frequency of the TT versus the TG allele was not different between the cases and the controls (39 versus 41%). The KL-VS variant of Klotho was not associated with valvular or vascular calcification, despite adequate power to detect association (86% for odds ratios ≥1.2). In sensitivity analyses, no association (P > 0.001) between other common variants of Klotho, β-Klotho or fibroblast growth factor-23 and the end points of valvular or vascular calcification was observed.

CONCLUSIONS

In our adequately powered candidate gene study, we did not observe an association with the functional KL-VS variant of Klotho and presence of valvular or vascular calcification. Future studies aimed at combining cohorts with echocardiographic phenotypes need to be conducted to identify genetic variants associated with valvular calcification.