The TGF-beta 1 gene codon 10 polymorphism contributes to the genetic predisposition to nephropathy in Type 1 diabetes

Association between polymorphisms of cytokine genes and diabetic nephropathy: A comprehensive systematic review and meta-analysis

AIM

Diabetic nephropathy (DN) is one of the microvascular complications of diabetes, leading to renal failure. In this study, we sought to systematically investigate the cytokine gene polymorphisms association with DN.

METHODS

A structured bibliographic search on PubMed, Scopus, and EMBASE databases has been performed to identify related papers. The odds ratio and corresponding 95% confidence intervals (CIs) were calculated to estimate the association.

RESULTS

Overall, the pooled results showed that the dominant models of TNF-α rs1800629, IL-1β rs16944, IL-8 rs4073, and IL-10 rs1800896 were associated with increased susceptibility to DN. Also, the pooled analyses of the mutant allele vs wild allele of TNF-α rs1800629, rs1799964, IL-1β rs16944, and IL-8 rs4073 were associated with increased susceptibility to DN. Rs1800629, rs16944, rs4073, and rs1800896 polymorphisms were significantly associated with DN susceptibility, suggesting its potential use as a genetic risk marker in the population.

TGF-Beta as a Master Regulator of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications in diabetes mellitus and the leading cause of end-stage renal disease. TGF-β is a pleiotropic cytokine and has been recognized as a key mediator of DN. However, anti-TGF-β treatment for DN remains controversial due to the diverse role of TGF-β1 in DN. Thus, understanding the regulatory role and mechanisms of TGF-β in the pathogenesis of DN is the initial step towards the development of anti-TGF-β treatment for DN. In this review, we first discuss the diverse roles and signaling mechanisms of TGF-β in DN by focusing on the latent versus active TGF-β1, the TGF-β receptors, and the downstream individual Smad signaling molecules including Smad2, Smad3, Smad4, and Smad7. Then, we dissect the regulatory mechanisms of TGF-β/Smad signaling in the development of DN by emphasizing Smad-dependent non-coding RNAs including microRNAs and long-non-coding RNAs. Finally, the potential therapeutic strategies for DN by targeting TGF-β signaling with various therapeutic approaches are discussed.

Polymorphisms in the heme oxygenase-1 and bone morphogenetic protein receptor type 1b genes and estimated glomerular filtration rate in Brazilian sickle cell anemia patients

INTRODUCTION

Mutations affecting genes involved in oxidative and signaling pathways may be associated with kidney disease in sickle cell anemia. We determined the allele and genotype frequencies of some polymorphisms in the promoter regions of the Heme Oxygenase-1 (HMOX1) [rs2071746 (A>T) and (GT)n repeats, short (S) and long (L) alleles] and Bone Morphogenetic Protein Receptor type-1B (BMPR1B) [rs17022863 (A>G), rs4331783 (A>G) and rs1470409 (A>G)] genes in 75 adult patients with sickle cell anemia and 160 healthy controls and investigated whether these polymorphisms may influence the estimated glomerular filtration rate for the patients.

METHODS

The single nucleotide polymorphisms were genotyped using the TaqMan assays, the HMOX1(GT)n repeats were determined by polymerase chain reaction fragment size analysis and the estimated glomerular filtration rate was calculated by the Modification of Diet in Renal Disease formula.

RESULTS

Regarding the HMOX1rs2071746, the estimated glomerular filtration rate median was significantly higher in TT patients (p=0.019), including when TT was compared with AT+AA (p=0.009); for the (GT)n repeats, the estimated glomerular filtration rate medians of SS, SL and LL significantly differed (p=0.009), being the LL estimated glomerular filtration rate median significantly higher, when compared with the LS+SS (p=0.005). These results suggest that both the homozygotes, TT for rs2071746 and LL for (GT)n repeats, lead to a higher risk of developing renal complications. Concerning the BMPR1B, the frequencies of GG for rs17022863 and AA for rs4331783 were significantly higher in patients than in controls (p=0.002 and p=0.008, respectively), however no association with estimated glomerular filtration rate was found.

CONCLUSION

These results contribute to a better understanding of the genetic factors related to the development of nephropathy in sickle cell anemia patients.

Dynamic changes of activator protein 1 and collagen I expression in the sclera of myopia guinea pigs

AIM

To investigate the dynamic changes of activator protein 1 (AP1) and collagen I expression in the sclera of form-deprivation myopic model in guinea pigs.

METHODS

A form-deprivation myopic model in guinea pigs were established with the left eye covered for 2 to 6wk (FDM group). Normal control group (n=25) were untreated. Changes in refractive power and axial length (AL) were measured and recorded at different time points. Expressions of AP1 and collagen 1 of the sclera were measured with Western blotting and reverse transcription-polymerase chain reaction (RT-PCR). The relationship between AP1 and collagen I levels was analyzed.

RESULTS

After 0, 2, 4, 6wk, and 4/-1wk of form-deprivation, the diopter in the FDM group was gradually changed (2.08±0.31, -1.23±0.68, -4.17±0.58, -7.07±0.55, and -2.67±0.59 D, respectively, P<0.05), and the AL was gradually increased (5.90±0.38, 6.62±0.37, 7.30±0.35, 7.99±0.31, and 6.97±0.32 mm, respectively, P<0.05). With the prolongation of covered time, the protein expressions of AP1 and collagen I in the FDM group were gradually down-regulated (all P<0.05); the mRNA expressions of them were also gradually down-regulated (all P<0.05); and there was positive correlation between them. The control group had no obvious change in each index (all P>0.05).

CONCLUSION

AP1 may be an important transcription factor involved in the regulation of collagen I synthesis and degradation during myopic scleral remodeling.

Transforming growth factor-β1 and diabetic nephropathy

Transforming growth factor-β1 (TGF-β1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-β1. TGF-β1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-β1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-β1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-β1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-β1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-β1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-β1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-β1 in diabetic nephropathy.

The rs1800471 Polymorphism of TGFB1 Gene, Serum TGF-Beta1 Level and Chronic Kidney Disease Progression

The aim of the study was to investigate whether rs1800471 polymorphism in TGFB1 gene is associated with the development and progression of non-diabetic chronic kidney disease. Moreover, we examined the serum TGF-beta1 concentration and its association with that polymorphism and progression of the disease. We applied two different methodological approaches. Firstly, a family based study was carried out, comprised of 109 patients with non-diabetic chronic kidney disease and their 218 healthy parents, using the transmission/disequilibrium test. The rs1800471 polymorphism and serum TGF-beta1 level were determined in all subjects. Serum TGF-beta1 concentration was also measured in 40 healthy controls. Secondly, we performed a case-control orientated study to determine whether rs1800471 polymorphism and other factors influence the progression of renal impairment. We found no relationships between rs1800471 polymorphism allele transfer and the incidence or progression of non-diabetic chronic kidney disease. We found, however, that the serum TGF-beta1 was significantly higher in patients than in controls. In conclusion, rs1800471 polymorphism in TGFB1 gene does not have an impact on the development and progression of non-diabetic chronic kidney disease caused by primary glomerulopathy and chronic interstitial nephritis. The increased serum TGF-beta1 concentration in such patients suggests its role in the pathomechanism of the disease. Circulating TGF-beta1 level is determined in a multifactorial way, not by rs1800471 polymorphism in TGFB1 gene.

The genetics of diabetic nephropathy

Up to 40% of patients with type 1 and type 2 diabetes will develop diabetic nephropathy (DN), resulting in chronic kidney disease and potential organ failure. There is evidence for a heritable genetic susceptibility to DN, but despite intensive research efforts the causative genes remain elusive. Recently, genome-wide association studies have discovered several novel genetic variants associated with DN. The identification of such variants may potentially allow for early identification of at risk patients. Here we review the current understanding of the key molecular mechanisms and genetic architecture of DN, and discuss the merits of employing an integrative approach to incorporate datasets from multiple sources (genetics, transcriptomics, epigenetic, proteomic) in order to fully elucidate the genetic elements contributing to this serious complication of diabetes.

The association of cytokine gene polymorphism with reflux nephropathy

OBJECTIVE

To identify genetic risk factors for the progression of vesicoureteral reflux (VUR) to reflux nephropathy, we examined polymorphisms of multiple cytokine genes among VUR patients with or without renal scarring.

METHODS

A total of 238 VUR patients aged between 1 and 18 years with (n = 113) or without renal scarring (n = 125) were included. The presence of renal scarring was demonstrated by renal parenchymal examination using Technetium-99m dimercaptosuccinate scintigraphy. Sera of the patients were examined for tumor necrosis factor-alpha (TNF-α, -308), transforming growth factor-beta1 (TGF-β1, +869, +915), interleukin-6 (IL-6, -174), interleukin-10 (IL-10, -1082, -819, -592) and interferon-gamma (IFN-γ, +874) gene polymorphisms using the polymerase chain reaction sequence-specific primer method.

RESULTS

Among patients with renal scarring, frequencies for the T/T G/C and C/C G/C genotypes of TGF-β1 gene (p = 0.003), GCC/GCC genotype of IL-10 gene (p = 0.015), GC phenotype of IL-6 gene (p = 0.001) and T/T genotype of IFN-γ gene (p = 0.001) were higher compared to patients without renal scarring. Regarding the TNF-α gene, among patients with low grade VUR only, the G/G genotype was associated with an increased risk.

CONCLUSIONS

Certain genotypes of cytokine gene polymorphisms seem to be associated with an increased or decreased susceptibility to reflux nephropathy, which may explain why only a proportion of VUR patients progress to reflux nephropathy. This information may aid in prediction of prognosis and implementing more aggressive management strategies at earlier stages. Further immunogenetic studies may identify novel targets for the management and prevention of the condition.

Association of rs1800471 polymorphism of TGFB1 gene with chronic kidney disease occurrence and progression and hypertension appearance

INTRODUCTION

Transforming growth factor β1 (TGF-β1) is a cytokine involved in the process of pathological tissue sclerosis, which is part of the pathophysiological mechanism of end stage renal disease development. The aim of the study was to evaluate the association of the single nucleotide polymorphism rs1800471 of the TGFB1 gene with chronic kidney disease (CKD) occurrence and progression as well as hypertension appearance.

MATERIAL AND METHODS

It was a case-control study where 109 patients with CKD and 111 very old people were enrolled. The association of the studied polymorphism with mentioned diseases was assessed in the whole study group as well as in the subgroups stratified according to the underlying etiology of CKD: nephropathy in type 1 diabetes (n = 13), chronic glomerulonephritis (n = 50) and chronic interstitial nephritis (n = 46).

RESULTS

No association of CKD progression with rs1800471 polymorphism was observed. The C allele was identified as the one associated with higher risk of the disease occurrence in the dominant model of inheritance (p = 0.035). The C allele in women, opposite to male gender, was associated with higher risk of CKD development (p = 0.038). GG genotype was associated with elevated risk of hypertension appearance (p = 0,0021).

CONCLUSIONS

Due to the lack of accordance with previously performed studies it is still impossible to state an unequivocal conclusion regarding the association between rs1800471 polymorphism of the TGFB1 gene and risk of CKD occurrence and progression as well as hypertension appearance. That is why it is necessary to perform further studies in this field.

Contribution of TGFβ1 codon 10 polymorphism to high myopia in an ethnic Kashmiri population from India

This study looks at novel variants of the TGFβ1 gene and their potential association with high myopia in an ethnic population from Kashmir, India. Allele frequencies of 247 Kashmiri subjects (from India) with high myopia and 176 ethnically matched healthy controls were tested for Hardy-Weinberg disequilibrium. The genotype and allele frequencies were evaluated using chi-square or Fisher's exact tests. One of the three SNPs in codon 10 showed a significant difference between patients and control subjects (rs1982073: p genotype = 0.003, p allele = 0.001). There were no statistically significant differences between patients and control subjects for the other two SNPs, rs1800471 at codon 25 and a novel variant at codon 52. SNP rs1982073, substituting proline with leucine, appeared to be significantly associated with high myopia (p < 0.05). In silico predictions show that substitutions are likely to have an impact on the structure and functional properties of the protein, making it imperative to understand their functional consequences in relation to high myopia.

Cellular mechanisms of tissue fibrosis. 1. Common and organ-specific mechanisms associated with tissue fibrosis

Fibrosis is a pathological scarring process that leads to destruction of organ architecture and impairment of organ function. Chronic loss of organ function in most organs, including bone marrow, heart, intestine, kidney, liver, lung, and skin, is associated with fibrosis, contributing to an estimated one third of natural deaths worldwide. Effective therapies to prevent or to even reverse existing fibrotic lesions are not yet available in any organ. There is hope that an understanding of common fibrosis pathways will lead to development of antifibrotic therapies that are effective in all of these tissues in the future. Here we review common and organ-specific pathways of tissue fibrosis.

Association between the T869C polymorphism of transforming growth factor-beta 1 and diabetic nephropathy: a meta-analysis

Accumulating evidence has suggested that transforming growth factor-beta 1 (TGF-β1) is a functional candidate for diabetic nephropathy (DN). However, association studies investigating the relationship of TGF-β1 gene T869C polymorphism and DN generate inconsistent results. To comprehensively clarify this issue, we performed a meta-analysis to evaluate the impact of the polymorphism on DN. We searched studies from PubMed and China National Knowledge Infrastructure (CNKI) through March 2011. Pooled ORs were calculated under allelic/additive/dominant/recessive/over-dominant genetic models. Nine studies with 1776 cases and 1740 controls were included. Our results indicated that C allele of T869C conferred a significantly increased risk of DN compared with T allele (OR = 1.25, 95% CI: 1.05-1.48) for allelic contrast. Similar results were also found under additive (OR = 1.57, 95% CI: 1.10-2.23) and dominant (OR = 1.40, 95% CI: 1.06-1.85) genetic models. However, subgroup analyses stratified by types of diabetes showed that significantly increased risks were only observed in type 2 diabetic patients, and the association persistently existed in further analysis for Asian populations. As for type 1 diabetic subjects, no significant association was detected under all the genetic models (P > 0.05). Our meta-analysis suggested that the TGF-β1 T869C polymorphism conferred an elevated risk of DN. However, significant associations were only observed in type 2 diabetic patients.

Renal gene and protein expression signatures for prediction of kidney disease progression

Although chronic kidney disease (CKD) is common, only a fraction of CKD patients progress to end-stage renal disease. Molecular predictors to stratify CKD populations according to their risk of progression remain undiscovered. Here we applied transcriptional profiling of kidneys from transforming growth factor-beta1 transgenic (Tg) mice, characterized by heterogeneity of kidney disease progression, to identify 43 genes that discriminate kidneys by severity of glomerular apoptosis before the onset of tubulointerstitial fibrosis in 2-week-old animals. Among the genes examined, 19 showed significant correlation between mRNA expression in uninephrectomized left kidneys at 2 weeks of age and renal disease severity in right kidneys of Tg mice at 4 weeks of age. Gene expression profiles of human orthologs of the 43 genes in kidney biopsies were highly significantly related (R(2) = 0.53; P < 0.001) to the estimated glomerular filtration rates in patients with CKD stages I to V, and discriminated groups of CKD stages I/II and III/IV/V with positive and negative predictive values of 0.8 and 0.83, respectively. Protein expression patterns for selected genes were successfully validated by immunohistochemistry in kidneys of Tg mice and kidney biopsies of patients with IgA nephropathy and CKD stages I to V, respectively. In conclusion, we developed novel mRNA and protein expression signatures that predict progressive renal fibrosis in mice and may be useful molecular predictors of CKD progression in humans.

Lack of association between TGF-beta-1 genotypes and microalbuminuria in essential hypertensive men

BACKGROUND

Polymorphisms within the gene for transforming growth factor (TGF)-beta-1, a pro-fibrogenic cytokine pathophysiologically involved in hypertension and hypertensive target damage, might modulate the biological activity of the encoded protein. Through that mechanism, they might contribute to microalbuminuria, a marker of subclinical renal damage and a correlate of systemic inflammation and endothelial dysfunction in hypertension, a possibility never before tested. For this reason, we assessed the association of four TGF-beta-1 polymorphic variants (C-509T, Leu(10)-->Pro, Arg(25)-->Pro, Thr(263)-->Ile) with albuminuria in uncomplicated essential hypertensive men, using (circulating active + acid-activatable latent) TGF-beta-1 levels as an indirect index of their in vivo biological activity. Because of the close pathophysiological link of TGF-beta-1 with the renin-angiotensin system, we also tested the behaviour of the angiotensin converting enzyme (ACE) deletion/insertion (D/I) polymorphism.

METHODS

Albuminuria (three overnight collections), office and 24-h BP, left ventricular mass index (LVMI), BMI, renal function, glucose, lipids, plasma TGF-beta-1 (n = 162, ELISA) were measured in 222 genetically unrelated, never-treated, uncomplicated Caucasian hypertensive men. ACE D/I polymorphisms were analysed by the polymerase chain reaction technique or a 5' nuclease assay with further restriction analysis when required.

RESULTS

Urine albumin levels or microalbuminuria (albuminuria > or =15 microg/min) did not differ by TGF-beta-1 genotypes, but both parameters were more frequent in ACE D/D homozygotes. Plasma TGF-beta-1 was similar across genetic backgrounds and was unrelated to albuminuria. Cardiovascular, renal, metabolic parameters were homogeneously distributed across genotypes.

CONCLUSIONS

In contrast to its link with the ACE D/I genotype, microalbuminuria was independent of TGF-beta-1 polymorphism in this group of never-treated, uncomplicated essential hypertensive men.

TGF-beta1 gene polymorphisms and primary vesicoureteral reflux in childhood

The aim of this study was to assess the association between the transforming growth factor-beta1 (TGF-beta1) gene polymorphisms rs1800469 (commonly known as T-509C) and rs1982073 (commonly known as Leu (10)-->Pro) and primary vesicoureteral reflux (VUR) and renal scarring. Using a case-control approach, we examined 121 children with primary VUR and 169 controls. Genotyping of the TGF-beta1 gene polymorphisms was performed by restriction fragment length polymorphism (RFLP) analysis. The (99m)Tc-DMSA- or (99m)Tc-unitiol-single photon emission computed tomography method was used to evaluate renal scars in 84 of 121 VUR children. Statistical analysis revealed differences in rs1800469 genotype frequencies between VUR patients and controls (p = 0.0021). Our data demonstrate that individuals homozygous for the TT genotype are at risk of primary VUR [odds ratio (95% confidence interval) = 2.7 (1.46-5.08)]. Distribution of the rs1982073 polymorphism was similar in VUR children and controls. In terms of renal scarring, patients were stratified into non-scar and scar subgroups, and no differences in the genotype frequencies of either polymorphism was found. Previous reports have shown that the TT genotype of the rs1800469 polymorphism is a risk factor for renal scarring in primary VUR, and the results of our study suggest that this same polymorphism is associated with susceptibility to this congenital uropathy.

Diabetes-induced upregulation of urotensin II and its receptor plays an important role in TGF-beta1-mediated renal fibrosis and dysfunction

Urotensin II (UII) was identified as the ligand for a novel G protein-coupled receptor, GPR14. UII was found not only to have a potent vasoconstrictive action but also to have profibrotic effects in the heart. The present study was to define whether UII and GPR14 also play important roles in diabetes-induced renal fibrosis and dysfunction. Diabetic rats were induced using streptozotocin, and the rat proximal tubular epithelial cells (NRK-52E) were used for the in vitro mechanism study. Results showed that expression of UII and GPR14 was significantly upregulated at both mRNA and protein levels in the diabetic kidneys compared with controls. The upregulated expressions of UII and GPR14 in the kidney were accompanied by significant increases in the renal profibrotic factor transforming growth factor (TGF)-beta1 expression, the renal extracellular matrix (fibronectin and collagen IV) accumulation, and the renal dysfunction (increases in urinal N-acetyl-beta-d-glucosaminidase content, 24-h urinary retinol-binding protein excretion rate, and decrease in creatinine clearance rate). Exposure of NRK-52E cells to 10(-8) mol/l UII for 48 h caused a significant increase of TGF-beta1, but not ANG II, production that was GPR14- and calcium-dependent, since GPR14 small-interfering RNA and calcium channel blocker nimodipine or calcium chelator EDTA all could abolish the induction of TGF- beta1 by UII. Furthermore, exposure of NRK-52E cells to TGF-beta1 or ANG II also increased UII and GPR14 mRNA expressions. These results suggested that diabetes-induced upregulation of UII and GPR14, most likely through autocrine and/or paracrine mechanisms, plays an important role in TGF-beta1-mediated renal fibrosis and dysfunction.

Recent advancement of understanding pathogenesis of type 1 diabetes and potential relevance to diabetic nephropathy

Type 1 diabetes mellitus is an autoimmune disease characterized by progressive destruction of pancreatic beta cells by genetic and environmental factors which leads to an absolute dependence of insulin for survival and maintenance of health. Although the majority of mechanisms of beta cell destruction remain unclear, many molecules, including proinflammatory cytokines and chemokines such as tumor necrosis factor alpha and monocyte chemoattractant protein-1, are implicated in the development of beta cell damage. Furthermore, beta cell destruction is enhanced by the Th1 and Th17 subsets of CD4+ T cells. In contrast, there are mechanisms involved in the maintenance of peripheral tolerance by regulatory T cells, the function of which depends on the pleiotropic cytokine transforming growth factor beta. Development and progression of renal injuries in patients with diabetic nephropathy are also associated with several growth factors and proinflammatory cytokines, including tumor necrosis factor alpha, insulin-like growth factor-1, monocyte chemoattractant protein-1, vascular endothelial growth factor, and transforming growth factor beta. Although the pathogenic mechanisms underlying type 1 diabetes and diabetic nephropathy are principally different, i.e., autoimmunity and inflammation, some common factors, including susceptibility genes and proinflammatory cytokines, are involved in both mechanisms, including infiltrating cell recruitment, upregulation of other cytokines and chemokines, or apoptosis.

TGF-β1 and TSC-22 Gene Polymorphisms and Susceptibility to Microvascular Complications in Type 2 Diabetes

BACKGROUND/AIM

There is a strong evidence for the involvement of genetic factors in diabetic microvascular complications. The aim of our study was to investigate the role of molecular variants of the TGF-beta1 (transforming growth factor beta 1) and the TSC-22 (transforming growth factor beta stimulated clone 22) genes in diabetic nephropathy and diabetic retinopathy in type 2 diabetes.

METHODS

A case-control study was conducted in 503 patients and 400 healthy subjects. DNA samples were genotyped by polymerase chain reaction and restriction fragment length polymorphism methods.

RESULTS

Among the patients, 245 had diabetic nephropathy, 195 had retinopathy, and 168 were free from complications. All subjects were genotyped for T869C and C -509T polymorphisms of the TGF-beta1 gene and for -396 polymorphism of the TSC-22 gene. A significantly increased frequency of the CC genotype of the T869C polymorphism was observed in patients with nephropathy and retinopathy (33 and 48%, respectively, vs. 19 and 15%, respectively, in controls and patients free from complications). The frequency of the C allele was also higher (0.58 for nephropathy and 0.64 for retinopathy vs. 0.42 in controls). The G allele of the TSC-22 polymorphism was associated with an increased risk of diabetic nephropathy (frequency 0.15 vs. 0.07 and 0.06, respectively, in patients free from complications and controls). An interaction was observed between the G allele of the TSC-22 polymorphism and the C-allele of the TGF-beta polymorphism.

CONCLUSIONS

Our data suggest the association of TGF-beta T869C gene polymorphism with an increased risk of nephropathy and retinopathy in type 2 diabetes patients. It interacts with the TSC-22 gene involved in the TGF-beta signaling pathway, promoting the development of diabetic nephropathy.

Familial Clustering of Chronic Kidney Disease

The incidence and prevalence rates of most forms of chronic kidney disease (CKD) had steadily been increasing for the past 30 years, although these rates now appear to have reached a plateau. It is clear that an individual's likelihood of developing progressive CKD results from complex interactions between multiple genetic and environmental factors. Familial clustering of CKD and end-stage renal disease (ESRD) is observed among all the common etiologies of nephropathy. This article reviews the epidemiology of the familial clustering of kidney disease, as well as potential environmental and genetic contributors. The related impact of familial clustering of cardiovascular disease (CVD) and the impact of CVD on the current epidemic of ESRD is also discussed. It is imperative that nephrologists and primary care physicians recognize that individuals who have relatives with advanced nephropathy are themselves at high risk for subsequent kidney disease, proteinuria, and atherosclerotic cardiovascular complications. Until kidney failure genes are identified, it is reasonable to use "family history" (FH) as a surrogate marker for risk of future nephropathy. The detection of kidney disease genes holds great promise for detecting novel pathways that initiate renal fibrosis and lead to progressive loss of renal function. These pathways are likely to offer new therapies that may slow or halt development of chronic kidney failure.

Estimated glomerular filtration rate in sickle cell anemia is associated with polymorphisms of bone morphogenetic protein receptor 1B

Renal disease is common in sickle cell anemia. In this exploratory work, we used data from a longitudinal study of the natural history of sickle cell disease to examine the hypothesis that polymorphisms (SNPs) in selected candidate genes are associated with glomerular filtration rate (GFR). DNA samples and clinical and laboratory data were available for 1,140 patients with sickle cell anemia. GFR was estimated using the Cockcroft-Gault and Schwartz formulas for adults and children, respectively. We examined approximately 175 haplotype tagging (ht) SNPs in about 70 genes of the TGFbeta/BMP pathway for their association with GFR using linear regression. Four SNPs in BMPR1B, a bone morphogenetic protein (BMP) receptor gene, yielded statistically significant associations (P values ranging from 0.015 to 0.046). Three haplotypes in this gene were also associated with GFR. The TGF-beta/BMP pathway has been associated with the development of diabetic nephropathy, which has some features in common with sickle cell nephropathy. Our results suggest that, as with other subphenotypes of sickle cell disease, renal function may be genetically modulated.

Common polymorphisms of the PAI1 gene do not play a major role in the development of diabetic nephropathy in Type 1 diabetes

AIM

Plasminogen activator inhibitor 1 (PAI1) plays a key role in the regulation of extracellular matrix (ECM) degradation. ThePAI1 gene is therefore an excellent candidate gene for diabetic nephropathy. The aim of this study was to employ gene resequencing to identify common DNA polymorphisms in thePAI1gene, and subsequently assess haplotype tagged single nucleotide polymorphisms(htSNPs) using a case control design. METHODS All nine exons, exon-intron boundaries, introns 1, 4 and 7 and approximately 3 kb upstream and 5 kb downstream of thePAI1 gene were screened for DNA polymorphisms in 15 case and 15 control subjects using WAVE denaturing high-performance liquid chromatography technology and confirmed by DNA sequencing. Polymorphisms were genotyped in 86 healthy individuals using direct sequencing and haplotype tagged single nucleotide polymorphisms (htSNPs) identified. Genotyping of the htSNPs was performed in 583 Type 1 diabetic patients (222 with nephropathy, 361 without nephropathy)using Pyrosequencing.

RESULTS

Twenty-one polymorphisms with a minor allele frequency (MAF)>1%were identified; 14 had a MAF> or =10%. Five htSNPs [c.-1968_69insG, c.43 G-->A (Ala15Thr), c.1092-105 A-->G, c.*1737 G-->A, c.*3711 C-->T] were identified. Haplotype frequencies were similar in case and control groups (likelihood ratio chi2 test,P=0.66).

CONCLUSION

It is unlikely that common polymorphisms of thePAI1 gene strongly influence susceptibility to diabetic nephropathy in the White Type 1 diabetic population.

Resequencing of genes for transforming growth factor beta1 (TGFB1) type 1 and 2 receptors (TGFBR1, TGFBR2), and association analysis of variants with diabetic nephropathy

Background

Diabetic nephropathy is the leading cause of end stage renal failure in the western world. There is substantial epidemiological evidence supporting a genetic predisposition to diabetic nephropathy, however the exact molecular mechanisms remain unknown. Transforming growth factor (TGFβ1) is a crucial mediator in the pathogenesis of diabetic nephropathy.

Methods

We investigated the role of five known single nucleotide polymorphisms (SNPs) in the TGFB1 gene for their association with diabetic nephropathy in an Irish, type 1 diabetic case (n = 272) control (n = 367) collection. The activity of TGFβ1 is facilitated by the action of type 1 and type 2 receptors, with both receptor genes (TGFBR1 and TGFBR2) shown to be upregulated in diabetic kidney disease. We therefore screened TGFBR1 and TGFBR2 genes for genomic variants using WAVE™ (dHPLC) technology and confirmed variants by direct capillary sequencing. Allele frequencies were determined in forty-eight healthy individuals. Data for all SNPs was assessed for Hardy Weinberg equilibrium, with genotypes and allele frequencies compared using the χ² test for contingency tables. Patterns of linkage disequilibrium were established and common haplotypes estimated.

Results

Fifteen variants were identified in these genes, seven of which are novel, and putatively functional SNPs were subsequently genotyped using TaqMan™, Invader™ or Pyrosequencing^® technology. No significant differences (p > 0.1) were found in genotype or allele distributions between cases and controls for any of the SNPs assessed.

Conclusion

Our results suggest common variants in TGFB1, TGFBR1 and TGFBR2 genes do not strongly influence genetic susceptibility to diabetic nephropathy in an Irish Caucasian population.

Diabetic nephropathy: leveraging mouse genetics

PURPOSE OF REVIEW

Advances in mouse genetics have made this species particularly useful as a model for human disease. This review will summarize recent advances regarding the pathogenesis of diabetic nephropathy discovered in mice.

RECENT FINDINGS

Diabetic nephropathy has been characterized in novel genetic models of murine diabetes including the Akita, Ove26, and ICER-Igamma mice. Mutagenesis resources targeting every gene of the genome and the importance of inbred genetic background are discussed.

SUMMARY

Through the use of these resources mouse models should provide new insight into the pathogenesis of diabetic nephropathy, and complement human studies and validate the identity of candidate genes contributing to diabetic nephropathy.

A genome-wide DNA microsatellite association screen to identify chromosomal regions harboring candidate genes in diabetic nephropathy

In an effort to accelerate the identification of susceptibility genes in diabetic nephropathy, the first genome-wide fluorescence-based DNA microsatellite (n=6000) association screen was performed, using pools of genomic DNA derived from Irish patients with (cases; n=200) and without (controls; n=200) type 1 diabetic nephropathy. Allele image profiles were generated for 5353 (89.2%) microsatellite markers for both case and control pools. Allele counts (estimated from allele image profiles) were compared in case versus control groups, and empirical P values were generated. Markers then were ranked on the basis of their empirical P values (lowest to highest). Repeat PCR amplification and electrophoresis of pooled samples were performed systematically on ranked markers until the 50 most associated markers with consistent results were identified. DNA samples that composed the pools then were genotyped individually for these markers. Two markers on chromosome 10, D10S558 (Pcorrected=0.005) and D10S1435 (Pcorrected=0.016), revealed statistically significant associations with diabetic nephropathy. An additional four markers (D6S281, D4S2937, D2S291, and D17S515) also are worthy of further investigation. Relevant functional candidate genes have been identified in the vicinity of these markers, demonstrating the feasibility of low-resolution genome-wide microsatellite association screening to identify possible candidate genes for diabetic nephropathy.