Analysis of 14 candidate genes for diabetic nephropathy on chromosome 3q in European populations: strongest evidence for association with a variant in the promoter region of the adiponectin gene

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

Genetic and epigenetic background of diabetic kidney disease

Diabetic kidney disease (DKD) is a severe diabetic complication that affects up to half of the individuals with diabetes. Elevated blood glucose levels are a key underlying cause of DKD, but DKD is a complex multifactorial disease, which takes years to develop. Family studies have shown that inherited factors also contribute to the risk of the disease. During the last decade, genome-wide association studies (GWASs) have emerged as a powerful tool to identify genetic risk factors for DKD. In recent years, the GWASs have acquired larger number of participants, leading to increased statistical power to detect more genetic risk factors. In addition, whole-exome and whole-genome sequencing studies are emerging, aiming to identify rare genetic risk factors for DKD, as well as epigenome-wide association studies, investigating DNA methylation in relation to DKD. This article aims to review the identified genetic and epigenetic risk factors for DKD.

Novel susceptibility loci identified in a genome-wide association study of type 2 diabetes complications in population of Latvia

BACKGROUND

Type 2 diabetes complications cause a serious emotional and economical burden to patients and healthcare systems globally. Management of both acute and chronic complications of diabetes, which dramatically impair the quality of patients' life, is still an unsolved issue in diabetes care, suggesting a need for early identification of individuals with high risk for developing diabetes complications.

METHODS

We performed a genome-wide association study in 601 type 2 diabetes patients after stratifying them according to the presence or absence of four types of diabetes complications: diabetic neuropathy, diabetic nephropathy, macrovascular complications, and ophthalmic complications.

RESULTS

The analysis revealed ten novel associations showing genome-wide significance, including rs1132787 (GYPA, OR = 2.71; 95% CI = 2.02-3.64) and diabetic neuropathy, rs2477088 (PDE4DIP, OR = 2.50; 95% CI = 1.87-3.34), rs4852954 (NAT8, OR = 2.27; 95% CI = 2.71-3.01), rs6032 (F5, OR = 2.12; 95% CI = 1.63-2.77), rs6935464 (RPS6KA2, OR = 2.25; 95% CI = 6.69-3.01) and macrovascular complications, rs3095447 (CCDC146, OR = 2.18; 95% CI = 1.66-2.87) and ophthalmic complications. By applying the targeted approach of previously reported susceptibility loci we managed to replicate three associations: MAPK14 (rs3761980, rs80028505) and diabetic neuropathy, APOL1 (rs136161) and diabetic nephropathy.

CONCLUSIONS

Together these results provide further evidence for the implication of genetic factors in the development of type 2 diabetes complications and highlight several potential key loci, able to modify the risk of developing these conditions. Moreover, the candidate variant approach proves a strong and consistent effect for multiple variants across different populations.

Identification of C3 as a therapeutic target for diabetic nephropathy by bioinformatics analysis

The pathogenesis of diabetic nephropathy is not completely understood, and the effects of existing treatments are not satisfactory. Various public platforms already contain extensive data for deeper bioinformatics analysis. From the GSE30529 dataset based on diabetic nephropathy tubular samples, we identified 345 genes through differential expression analysis and weighted gene coexpression correlation network analysis. GO annotations mainly included neutrophil activation, regulation of immune effector process, positive regulation of cytokine production and neutrophil-mediated immunity. KEGG pathways mostly included phagosome, complement and coagulation cascades, cell adhesion molecules and the AGE-RAGE signalling pathway in diabetic complications. Additional datasets were analysed to understand the mechanisms of differential gene expression from an epigenetic perspective. Differentially expressed miRNAs were obtained to construct a miRNA-mRNA network from the miRNA profiles in the GSE57674 dataset. The miR-1237-3p/SH2B3, miR-1238-5p/ZNF652 and miR-766-3p/TGFBI axes may be involved in diabetic nephropathy. The methylation levels of the 345 genes were also tested based on the gene methylation profiles of the GSE121820 dataset. The top 20 hub genes in the PPI network were discerned using the CytoHubba tool. Correlation analysis with GFR showed that SYK, CXCL1, LYN, VWF, ANXA1, C3, HLA-E, RHOA, SERPING1, EGF and KNG1 may be involved in diabetic nephropathy. Eight small molecule compounds were identified as potential therapeutic drugs using Connectivity Map.

Identification of hub genes in diabetic kidney disease via multiple-microarray analysis

Background

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease; however, the underlying molecular mechanisms remain unclear. Recently, bioinformatics analysis has provided a comprehensive insight toward the molecular mechanisms of DKD. Here, we re-analyzed three mRNA microarray datasets including a single-cell RNA sequencing (scRNA-seq) dataset, with the aim of identifying crucial genes correlated with DKD and contribute to a better understanding of DKD pathogenesis.

Methods

Three datasets including GSE131882, GSE30122, and GSE30529 were utilized to find differentially expressed genes (DEGs). The potential functions of DEGs were analyzed by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. A protein-protein interaction (PPI) network was constructed, and hub genes were selected with the top three molecular complex detection (MCODE) score. A correlation analysis between hub genes and clinical indicators was also performed.

Results

In total, 84 upregulated DEGs and 49 downregulated DEGs were identified. Enriched pathways of the upregulated DEGs included extracellular matrix (ECM) receptor interaction, focal adhesion, human papillomavirus infection, malaria, and cell adhesion molecules. The downregulated DEGs were mainly enriched in ascorbate and aldarate metabolism, arginine and proline metabolism, endocrine- and other factor-regulated calcium reabsorption, mineral absorption and longevity regulating pathway, and multiple species signaling pathway. Seventeen hub genes were identified, and correlation analysis between unexplored hub genes and clinical features of DKD suggested that EGF, KNG1, GADD45B, and CDH2 might have reno-protective roles in DKD. Meanwhile, ATF3, B2M, VCAM1, CLDN4, SPP1, SOX9, JAG1, C3, and CD24 might promote the progression of DKD. Finally, most hub genes were found present in the immune cells of diabetic kidneys, which suggest the important role of inflammation infiltration in DKD pathogenesis.

Conclusions

In this study, we found seventeen hub genes using a scRNA-seq contained multiple-microarray analysis, which enriched the present understanding of molecular mechanisms underlying the pathogenesis of DKD in cells' level and provided candidate targets for diagnosis and treatment of DKD.

Association of Proteins Modulating Immune Response and Insulin Clearance During Gestation with Antenatal Complications in Patients with Gestational or Type 2 Diabetes Mellitus

Background: The purpose of the study is to establish and quantitatively assess protein markers and their combination in association with insulin uptake that may be have value for early prospective recognition of diabetic fetopathy (DF) as a complication in patients with diabetes mellitus during gestation. Methods: Proteomic surveying and accurate quantitative measurement of selected proteins from plasma samples collected from the patients with gestational diabetes mellitus (GDM) and type 2 diabetes mellitus (T2DM) who gave birth of either healthy or affected by maternal diabetes newborns was performed using mass spectrometry. Results: We determined and quantitatively measured several proteins, including CRP, CEACAM1, CNDP1 and Ig-family that were significantly differed in patients that gave birth of newborns with signs of DF. We found that patients with newborns associated with DF are characterized by significantly decreased CEACAM1 (113.18 ± 16.23 ng/mL and 81.09 ± 10.54 ng/mL in GDM and T2DM, p < 0.005) in contrast to control group (515.6 ± 72.14 ng/mL, p < 0.005). On the contrary, the concentration of CNDP1 was increased in DF-associated groups and attained 49.3 ± 5.18 ng/mL and 37.7 ± 3.34 ng/mL (p < 0.005) in GDM and T2DM groups, respectively. Among other proteins, dramatically decreased concentration of IgG4 and IgA2 subclasses of immunoglobulins were noticed. Conclusion: The combination of the measured markers may assist (AUC = 0.893 (CI 95%, 0.785–0.980) in establishing the clinical finding of the developing DF especially in patients with GDM who are at the highest risk of chronic insulin resistance.

Multiple-microarray analysis for identification of hub genes involved in tubulointerstial injury in diabetic nephropathy

Diabetic nephropathy (DN) is a primary cause of renal failure. However, studies providing renal gene expression profiles of diabetic tubulointerstitial injury are scarce and its molecular mechanisms still await clarification. To identify vital genes involved in the diabetic tubulointerstitial injury, three microarray data sets from gene expression omnibus (GEO) were downloaded. A total of 127 differentially expressed genes (DEGs) were identified by limma package. Gene set enrichment analysis (GSEA) plots showed that sister chromatid cohesion was the most significant enriched gene set positively correlated with the DN group while retinoid X receptor binding was the most significant enriched gene set positively correlated with the control group. Enriched Gene Ontology (GO) annotations and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of DEGs mostly included extracellular matrix organization, extracellular space, extracellular matrix structural constituent, and Staphylococcus aureus infection. Twenty hub genes from three significant modules were ascertained by Cytoscape. Correlation analysis and subgroup analysis between hub genes and clinical features of DN showed that ALB, ANXA1, APOH, C3, CCL19, COL1A2, COL3A1, COL4A1, COL6A3, CXCL6, DCN, EGF, HRG, KNG1, LUM, SERPINA3, SPARC, SRGN, and TIMP1 may involve in diabetic tubulointerstitial injury. ConnectivityMap analysis indicated the most significant three compounds are 5182598, thapsigargin and 5224221. In conclusion, this study may provide new insights into the molecular mechanisms underlying diabetic tubulointerstitial injury as well as potential targets for diagnosis and therapeutics of DN.

Association of Interleukin-6 -174G/C Polymorphism with the Risk of Diabetic Nephropathy in Type 2 Diabetes: A Meta-analysis

Previous studies reported the association between interleukin-6 (IL-6) -174G/C gene polymorphism and the risk of diabetic nephropathy in type 2 diabetes mellitus (T2DN). However, the results remain controversial. In the present study, we conducted a meta-analysis to further examine this relationship between IL-6-174G/C gene polymorphism and T2DN. Three databases (PubMed, SinoMed and ISI Web of Science) were used to search clinical case-control studies about IL-6-174G/C polymorphism and T2DN published until Apr. 14, 2018. Fixed- or random-effects models were used to calculate the effect sizes of odds ratio (OR) and 95% confidence intervals (95% CI). Moreover, subgroup analysis was performed in terms of the excretion rate of albuminuria. All the statistical analyses were conducted using Stata 12.0. A total of 11 case-control studies were included in this study, involving 1203 cases of T2DN and 1571 cases of T2DM without DN. Meta-analysis showed that there was an association between IL-6-174G/C polymorphism and increased risk of T2DN under the allelic and recessive genetic models (G vs. C: OR=1.10, 95%CI 1.03-1.18, P=0.006; GG vs. CC+GC: OR=1.11, 95%CI 1.02-1.21 P=0.016). In the subgroup analysis by albuminuria, a significant association of IL-6-174G/C polymorphism with risk of T2DN was noted in the microalbuminuria group under the recessive model (OR=1.54, 95% CI 1.02-2.32, _P=0.038). In conclusion, this meta-analysis suggests that IL-6-174G/C gene polymorphism is associated with the risk of T2DN.

Genome-wide association study identifies new susceptibility loci for diabetic nephropathy in Korean patients with type 2 diabetes mellitus

Genetic factors are considered to be important in the pathogenesis of diabetic nephropathy (DN). Despite several genome-wide association studies (GWASs) demonstrating that specific polymorphisms of candidate genes were associated with DN, there were some limitations in previous studies. We conducted a GWAS using customized DNA chips to identify novel susceptibility loci for DN in Korean. We analyzed a total of 414 DN cases and 474 normoalbuminuric diabetic hyper-controls across two stages using customized DNA chips containing 98 667 single nucleotide polymorphisms (SNPs). We explored the associations between SNPs and DN in samples from 87 DN cases, mostly confirmed by renal biopsy, and 104 diabetic hyper-controls, and replicated these associations in independent cohort samples with 327 DN cases and 370 diabetic hyper-controls. The top significant SNPs from the discovery samples were selected for replication in the independent cohort. rs3765156 in PIK3C2B was significantly associated with DN in the replication cohort after multiple test. The SNPs identified in our study provide new insights into the pathogenesis of DN in the Korean population. Additional studies are needed to determine biological effects and clinical utility of our findings.

T-cadherin gene variants are associated with nephropathy in subjects with type 1 diabetes

Background

High plasma adiponectin levels are associated with diabetic nephropathy (DN). T-cadherin gene (CDH13) variants have been shown to be associated with adiponectin levels. We investigated associations between allelic variations of CDH13 and DN in subjects with type 1 diabetes.

Methods

Two CDH13 polymorphisms were analysed in 1297 Caucasian subjects with type 1 diabetes from the 'Survival Genetic Nephropathy' (SURGENE) (n = 340, 10-year follow-up), 'Genesis France-Belgium' (GENESIS) (n = 501, 5-year follow-up for n = 462) and 'Génétique de la Néphropathie Diabétique' (GENEDIAB) (n = 456, 9-year follow-up for n = 283) cohorts. Adiponectin levels were measured in plasma samples from GENESIS and GENEDIAB cohorts.

Results

Pooled analysis of GENEDIAB and GENESIS studies showed that baseline plasma adiponectin levels were higher in subjects with established/advanced DN at inclusion (P < 0.0001) and in subjects who developed end-stage renal disease (ESRD) at follow-up (P < 0.0001). The minor allele of rs3865188 was associated with lower adiponectin levels (P = 0.006). rs11646213 [odds ratio (OR) 1.47; 95% confidence interval (CI) 1.18-1.85; P = 0.0009] and rs3865188 (OR 0.71; 95% CI 0.57-0.90; P = 0.004) were associated with baseline prevalence of established/advanced DN. These polymorphisms were also associated with the risk of ESRD (0.006 < P < 0.03). The association between rs11646213 (but not rs3865188) and renal function remained significant after adjustment for plasma adiponectin. In SURGENE, rs11646213 [hazard ratio (HR) 1.69; 95% CI 1.01-2.71; P = 0.04] and rs3865188 (HR 0.74; 95% CI 0.55-0.99; P = 0.04) were associated with risk of renal events (defined as progression to more severe DN stages).

Conclusions

Plasma adiponectin levels are associated with the prevalence of DN and the incidence of ESRD in patients with type 1 diabetes. CDH13 polymorphisms are also associated with the prevalence and incidence of DN, and with the incidence of ESRD in these patients. The association between CDH13 and DN may be due to pleiotropic effects, both dependent and independent of plasma adiponectin levels.

Association of genetic variants with diabetic nephropathy

Diabetic nephropathy accounts for the most serious microvascular complication of diabetes mellitus. It is suggested that the prevalence of diabetic nephropathy will continue to increase in future posing a major challenge to the healthcare system resulting in increased morbidity and mortality. It occurs as a result of interaction between both genetic and environmental factors in individuals with both type 1 and type 2 diabetes. Genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, and various research efforts are being executed worldwide to identify the susceptibility gene for diabetic nephropathy. Numerous single nucleotide polymorphisms have been found in various genes giving rise to various gene variants which have been found to play a major role in genetic susceptibility to diabetic nephropathy. The risk of developing diabetic nephropathy is increased several times by inheriting risk alleles at susceptibility loci of various genes like ACE, IL, TNF-α, COL4A1, eNOS, SOD2, APOE, GLUT, etc. The identification of these genetic variants at a biomarker level could thus, allow the detection of those individuals at high risk for diabetic nephropathy which could thus help in the treatment, diagnosis and early prevention of the disease. The present review discusses about the various gene variants found till date to be associated with diabetic nephropathy.

Meta-analysis of diabetic nephropathy associated genetic variants in inflammation and angiogenesis involved in different biochemical pathways

Background

Diabetes mellitus is the most common chronic endocrine disorder, affecting an estimated population of 382 million people worldwide. It is associated with microvascular and macrovascular complications, including diabetic nephropathy (DN); primary cause of end-stage renal disease. Different inflammatory and angiogenic molecules in various pathways are important modulators in the pathogenesis and progression of diabetic nephropathy. Differential disease risk in DN may be partly attributable to genetic susceptibility. In this meta-analysis, we aimed to determine which of the previously investigated genetic variants in these pathways are significantly associated with the development of DN and to examine the functional role of these genes.

Methods

A systematic search was conducted to collect and analyze all studies published till June 2013; that investigated the association between genetic variants involved in inflammatory cytokines and angiogenesis and diabetic nephropathy. Genetic variants associated with DN were selected and analyzed by using Comprehensive Meta Analysis software. Pathway analysis of the genes with variants showing significant positive association with DN was performed using Genomatix Genome Analyzer (Genomatix, Munich, Germany).

Results

After the inclusion and exclusion criteria for this analysis, 34 studies were included in this meta-analysis. 11 genetic variants showed significant positive association with DN in a random-effects meta-analysis. These included genetic variants within or near VEGFA, CCR5, CCL2, IL-1, MMP9, EPO, IL-8, ADIPOQ and IL-10. rs1800871 (T) genetic variant in IL-10 showed protective effect for DN. Most of these eleven genetic variants were involved in GPCR signaling and receptor binding pathways whereas four were involved in chronic kidney failure. rs833061 [OR 2.08 (95% CI 1.63-2.66)] in the VEGFA gene and rs3917887 [OR 2.04 (95% CI 1.64-2.54)] in the CCL2 gene showed the most significant association with the risk of diabetic nephropathy.

Conclusions

Our results indicate that 11 genetic variants within or near VEGFA, CCR5, CCL2, IL-1, MMP9, EPO, IL-8, ADIPOQ and IL-10 showed significant positive association with diabetic nephropathy. Gene Ontology or pathway analysis showed that these genes may contribute to the pathophysiology of DN. The functional relevance of the variants and their pathways can lead to increased biological insights and development of new therapeutic targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-014-0103-8) contains supplementary material, which is available to authorized users.

Genetics of diabetes complications

Chronic hyperglycemia and duration of diabetes are the major risk factors associated with development of micro- and macrovascular complications of diabetes. Although it is believed that hyperglycemia induces damage to the particular cell subtypes, e.g., mesangial cells in the renal glomerulus, capillary endothelial cells in the retina, and neurons and Schwann cells in peripheral nerves, the exact mechanisms underlying these damaging defects are not yet well understood. Clustering of micro- and macrovascular complications in families of patients with diabetes suggests a strong genetic susceptibility. However, until now only a handful number of genetic variants were reported to be associated with either nephropathy (ACE, ELMO1, FRMD3, and AKR1B1) or retinopathy (VEGF, AKR1B1, and EPO), and only a few studies were carried out for genetic susceptibility to cardiovascular diseases (ADIPOQ, GLUL) in patients with diabetes. It is, therefore, obvious that the accumulation of more data from larger studies and better phenotypically characterized cohorts is needed to facilitate genetic discoveries and unravel novel insights into the pathogenesis of diabetic complications.

Adiponectin gene (ADIPOQ) polymorphisms correlate with the progression of nephropathy in Taiwanese male patients with type 2 diabetes

AIMS

Polymorphisms of the ADIPOQ gene were associated with diabetic nephropathy (DN) in case-control studies predominantly among European populations. Gender may modify the ADIPOQ associated risk for DN. We investigated the association of 18 ADIPOQ polymorphisms with DN in a prospective Taiwanese cohort of type 2 diabetes (T2D) and explored whether gender plays a role in this genetic association.

METHODS

Selected single nucleotide polymorphisms (SNPs) of ADIPOQ were genotyped in 566 T2D patients with normoalbuminuria at baseline. DN was defined based on urinary albumin-to-creatinine ratio (ACR). The Cox proportional hazard model was used to explore the association of individual SNP to DN events under different genetic models over a 6-year follow-up period. Analyses were further stratified by gender.

RESULTS

In male patients, the adjusted hazard ratios under the recessive models were 1.81 for rs2241766 TT (vs. GT+GG, 95% CI=1.10-2.96, p=0.019) and 1.89 for rs1063537 CC (vs. CT+TT, 95% CI=1.15-3.11, p=0.013). In the Kaplan-Meier survival curve, males carrying rs2241766 TT (vs. GT+GG, p=0.050) and rs1063537 CC (vs. CT+TT, p=0.037) recessive homozygotes also had a reduced nephropathy-free survival rate. SNPs rs2241767 and rs2082940, both in strong correlation with tag SNP rs1063537 (r(2)≥ 0.96), were also associated with DN progression in males. In females, ADIPOQ polymorphisms were not associated with the progression of DN.

CONCLUSIONS

ADIPOQ genetic polymorphisms rs2241766 (+45T>G), rs1063537, rs2241767 and rs2082940 were correlated with the progression of DN in Taiwanese male patients with T2D. The role of gender in this ADIPOQ genetic association needs to be further investigated in other populations.

Carnosinases, their substrates and diseases

Carnosinases are Xaa-His dipeptidases that play diverse functions throughout all kingdoms of life. Human isoforms of carnosinase (CN1 and CN2) under appropriate conditions catalyze the hydrolysis of the dipeptides carnosine (β-alanyl-l-histidine) and homocarnosine (γ-aminobutyryl-l-histidine). Alterations of serum carnosinase (CN1) activity has been associated with several pathological conditions, such as neurological disorders, chronic diseases and cancer. For this reason the use of carnosinase levels as a biomarker in cerebrospinal fluid (CSF) has been questioned. The hydrolysis of imidazole-related dipeptides in prokaryotes and eukaryotes is also catalyzed by aminoacyl-histidine dipeptidases like PepD (EC 3.4.13.3), PepV (EC 3.4.13.19) and anserinase (EC 3.4.13.5). The review deals with the structure and function of this class of enzymes in physiological and pathological conditions. The main substrates of these enzymes, i.e., carnosine, homocarnosine and anserine (β-alanyl-3-methyl-l-histidine) will also be described.

Urinary excretion of high molecular weight adiponectin is an independent predictor of decline of renal function in type 2 diabetes

Adiponectin and urinary adiponectin excretions have been ascribed a function in glomerular physiology and seem to indicate vascular disease in diabetes. The aim of this study was to compare the urinary excretion of albumin and adiponectin as predictors for decline of renal function in patients with type 2 diabetes and early kidney disease. Over 141 patients were screened for renal function (estimated GFR, ml/min*1.73 m(2)), albumin excretion rate (AER, mg/24 h), total as well as high molecular weight (HMW) urinary adiponectin excretion (ng/mol u-creatinine). AER and adiponectin excretion were studied as predictors of renal function after 1 year. After 1 year, 36 patients were in the upper quartile of eGFR decline and defined as progressors (delta eGFR = - 12.3 ± 6.3) while the remaining 105 patients were defined as non-progressors (delta eGFR = 1.4 ± 6.0). At baseline, HMW-adiponectin excretion was positively correlated with HbA1c (p < 0.001) and negatively with eGFR (p < 0.001), but not with AER (p = 0.14). Progressors showed increased urinary HMW-adiponectin at baseline (158[IQR41/479] vs. 65[24/168] ng/mol; p < 0.01), while total adiponectin (182[101/1534] vs. 345[118/1361] ng/mol) and AER (48[23/109] vs. 46[25/108] mg/24 h) excretion showed no differences between the groups. Multivariate logistic regression showed that HMW-adiponectin excretion was an independent predictor of renal progression in all patients (OR 1.86 [95 % CI 1.34-2.59]; p < 0.01), especially in those (n = 45) with normal AER at baseline (OR 2.16 [95 % CI 1.1-4.56]; p < 0.05). Urinary HMW-adiponectin but not AER improved the prediction of progressors in ROC analysis (AUC 0.72 [95 % CI 0.63-0.81] vs. 0.80 [95 % CI 0.71-0.90], p < 0.05). In conclusion, urinary HMW-adiponectin excretion may identify diabetes patients at increased risk for progression of kidney disease.

Adiponectin gene polymorphisms and susceptibility to diabetic nephropathy: a meta-analysis

Adiponectin (ADIPOQ) plays an important role in the pathogenesis of diabetic nephropathy (DN) and previous studies regarding the association between ADIPOQ polymorphisms and DN risk reported conflicting results. To derive a more precise estimation of this association, we performed a meta-analysis to assess the association between four ADIPOQ polymorphisms [-11391G > A (rs17300539), -11377C > G (rs266729), +45T > G (rs2241766), and +276G > T (rs1501299)] and risk for DN. Odds ratios (ORs) with corresponding 95% confidence intervals (95% CIs) were pooled to assess the association between four aforementioned polymorphisms and susceptibility to DN. Based on the included criteria, we selected 13 articles, among which 7 studies (cases/controls: 2749/7585) for -11391G > A, 8 studies for -11377C > G (3074/3842), 9 studies for +45T > G (2654/7710), and 10 studies for +276G > T (2812/7821), respectively. Our meta-analysis indicated no evidence heterogeneity among the included studies; thus, the fixed-effects model was used. Overall, there was an association between ADIPOQ -11391A allele with increased DN risk (OR = 1.186, 95% CI: 1.051-1.338, p = 0.006). Subgroup by ethnicity suggested significant association between +45T > G polymorphism and DN risk among Caucasians (OR = 1.122, 95% CI: 1.007-1.250, p = 0.038). Sensitivity analysis suggested exclusion of any single study did not materially alter the overall pooled ORs above. Future studies are needed to validate these findings.

Urinary adiponectin excretion rises with increasing albuminuria in type 1 diabetes

AIM

Urinary adiponectin (u-adiponectin) excretion has been suggested to reflect early glomerular damage. Inspired by this, we studied the levels of u-adiponectin in type 1 diabetic patients with different levels of urinary albumin excretion (UAE).

METHODS

U-adiponectin was analysed by ELISA in type 1 diabetic patients: Fifty-eight with normoalbuminuria (<30mg albumin/24h), 43 with persistent microalbuminuria (30-300mg/24h) and 44 with persistent macroalbuminuria (>300mg/24h). For comparison, a control group of 55 healthy individuals was included.

RESULTS

U-adiponectin increased with increasing levels of UAE (p<0.01). U-adiponectin median (interquartile range): Normoalbuminuria 0.38 (0.14-1.31), microalbuminuria 1.12 (0.20-2.68), macroalbuminuria 9.20 (1.10-23.35) and controls 0.09 (0.06-0.24) μg/g creatinine. Levels were unrelated to sex, age, cholesterol, diastolic BP and BMI. U-adiponectin was weakly associated with increasing systolic BP and HbA1c (r(2)<0.1, p<0.05), but strongly related to increasing UAE (r(2)=0.57, p<0.001) and decreasing eGFR (r(2)=0.26, p<0.001). The relationship between UAE and u-adiponectin was significant in all groups and independent of eGFR, BMI, BP and HbA1c. Furthermore, u-adiponectin was associated with markers of tubular damage (p<0.01).

CONCLUSION

U-adiponectin rises with increasing levels of UAE in patients with type 1 diabetes. This is in accordance with the hypothesis that loss of adiponectin may reflect glomerular and/or tubular damage.

Genetic association of adiponectin with type 2 diabetes in Jordanian Arab population

Adiponectin, a protein exclusively secreted by adipose tissue and present at low levels in obese individuals, is now widely recognized as a key determinant of insulin sensitivity and protection against obesity-associated metabolic syndrome. In Jordan, prevalence of diabetes (17.1%) is twice that of the United States (7.8%). In this study, we examined the contribution of the promoter variant rs266729 (-11377C>G) of the ADIPOQ gene as a risk factor for diabetic patients in Jordan. DNA was extracted from blood samples for patients and controls .Polymerase chain reaction and restriction fragment length polymorphism were used to genotype this variant. A total of 420 type 2 diabetic patients and 230 controls were successfully genotyped. The results showed a significant genotypic (p=0.00001) and allelic (p=0.01) association with variant in the diabetic patients as compared to controls. This suggests that the ADIPOQ gene plays a major role in increasing the risk of diabetes, at least in the Jordanian Arab population.

IGF2BP2 and IGF2 genetic effects in diabetes and diabetic nephropathy

OBJECTIVE

The IGF2BP2 gene is located on chromosome 3q27.2 within a region linked to type 1 diabetes (T1D), type 2 diabetes (T2D) and diabetic nephropathy (DN). Its protein functionally binds to 5'-UTR of the imprinting IGF2 gene. The present study aims to evaluate the IGF2BP2-IGF2 genetic effects in diabetes and DN.

MATERIALS AND METHODS

Three cohorts including T1D with and without DN (n=1139) of European descents from the GoKinD study, Swedish T1D with and without DN (n=303) and Czech control subjects without diabetes, T1D, T2D with and without DN (n=1418) were enrolled in TaqMan genotyping experiments for IGF2BP2 rs4402960 and IGF2 rs10770125. Igf2bp2 gene expression in kidney tissues of db/db and control mice at the ages of 5 and 26 weeks was examined with real time RT-PCR and Western blot.

RESULTS

An association of IGF2BP2 rs4402960 with T2D in the Czech population was replicated. This IGF2BP2 polymorphism (P=0.037, OR=0.69 95% CI 0.49-0.98) was found to be associated with DN in male not in female patients with T1D selected from the GoKinD study. In the analyses of combined the GoKinD, Czech and Swedish populations, the association between IGF2BP2 polymorphism and DN in male patients with T1D was still significant (P=0.030, OR=0.73, 95% CI 0.54-0.97). IGF2 rs10770125 was also associated with DN in male T1D patients of the GoKinD population (P=0.038, OR=0.67 95% CI 0.46-0.98). There might be a genetic interaction between IGF2BP2 and IGF2 (P=0.05). The Igf2bp2 gene expression levels were increased in the kidneys of db/db mice compared to controls at the age of 5weeks but not at 26 weeks.

CONCLUSIONS

The present study has replicated the association of IGF2BP2 rs4402960 with T2D in the Czech population and provided data suggesting that IGF2BP2 may have genetic interaction with IGF2 with a protective effect against DN in male patients with T1D.

Single-nucleotide polymorphisms and haplotypes in the adiponectin gene contribute to the genetic risk for type 2 diabetes in Tunisian Arabs

Adiponectin is an adipocyte-produced protein involved in regulating glucose, lipid, and energy metabolism, and is encoded by ADIPOQ (APM1) gene. ADIPOQ polymorphisms were previously associated with type 2 diabetes (T2DM) in Caucasian and non-Caucasian populations. We investigated the contribution of 13 polymorphisms in the promoter, coding regions, and 3'untranslated region of ADIPOQ gene to T2DM in 917 patients and 748 normoglycemic control subjects. ADIPOQ genotyping was done by allelic discrimination method. Of the 13 ADIPOQ variants analyzed, higher minor allele frequency of rs16861194 (P<0.001), rs17300539 (P<0.001), rs266729 (P<0.001), rs822396 (P=0.02), rs2241767 (P=0.03), and rs1063538 (P=0.02) were seen in T2DM cases. Varied association of ADIPOQ genotypes with T2DM was seen according to the genetic model used: rs17300539 and rs266729 were significantly associated with T2DM under the three models, while rs16861194 was association with T2DM under additive and dominant models, and rs822396, rs2241766, and rs1063538 were associated with T2DM under the dominant models only. Haploview analysis revealed low linkage disequilibrium between the ADIPOQ variants, resulting in high haplotype diversity, and two blocks were identified, each differentially associated with T2DM. These results support a significant association of ADIPOQ gene polymorphism with T2DM in Tunisian Arabs.

Insights into the genetic architecture of diabetic nephropathy

Diabetic nephropathy (DN) is a devastating complication of type 1 and type 2 diabetes and leads to increased morbidity and premature mortality. Susceptibility to DN has an inherent genetic basis as evidenced by familial aggregation and ethnic-specific prevalence rates. Progress in identifying the underlying genetic architecture has been arduous with the realization that a single locus of large effect does not exist, unlike in predisposition to non-diabetic nephropathy in individuals with African ancestry. Numerous risk variants have been identified, each with a nominal effect, and they collectively contribute to disease. These results have identified loci targeting novel pathways for disease susceptibility. With continued technological advances and development of new analytic methods, additional genetic variants and mechanisms (e.g., epigenetic variation) will be identified and help to elucidate the pathogenesis of DN. These advances will lead to early detection and development of novel therapeutic strategies to decrease the incidence of disease.

PPARγ as a therapeutic target in diabetic nephropathy and other renal diseases

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor that regulates many important physiological processes including glucose and lipid metabolism, energy homeostasis, cell proliferation, inflammation, immunity and reproduction. The current review aims to summarize and discuss recent findings evaluating the protective effects of PPARγ against kidney diseases with a focus on diabetic nephropathy. We will also delineate the potential underlying mechanisms.

RECENT FINDINGS

PPARγ plays important roles in renal physiology and pathophysiology. Agonists of PPARγ exert protective effects against various kidney diseases including diabetic nephropathy, ischemic renal injury, IgA nephropathy, chemotherapy-associated kidney damage, polycystic kidney diseases and age-related kidney diseases via both systemic and renal actions.

SUMMARY

PPARγ agonists are effective in delaying and even preventing the progression of many renal diseases, especially diabetic nephropathy. PPARγ may represent a promising target for the treatment of renal diseases.

Genetic and functional effects of membrane metalloendopeptidase on diabetic nephropathy development

BACKGROUND/AIMS

Vasopeptidase as an agent inhibits membrane metalloendopeptidase (MME, also known as neutral endopeptidase). MME is widely distributed in the body and particularly abundant in the kidney. The MME gene is located on chromosome 3q25.1 within a linkage region for diabetic nephropathy (DN). The present study aims to evaluate the genetic and functional effects of MME in the development of DN.

METHODS

A case-control genetic study of the MME gene in type 1 diabetes (T1D) patients with and without DN (n = 578/599) was performed. All subjects were selected from the Genetics of Kidneys in Diabetes study. Genotyping was performed with TagMan allelic discrimination. Mme mRNA and protein expression levels in kidney tissues of db/db mice at the ages of 5, 12 and 26 weeks were analyzed with TaqMan real-time RT-PCR and Western blot.

RESULTS

The haplotype A-C constructed with single nucleotide polymorphisms (SNPs) rs3796268A/G and rs3773885C/T in the MME gene was found to be associated with DN (p = 0.015, OR = 1.33, 95% CI 1.05-1.68) in female T1D patients. Further analyses of renal traits in T1D patients with DN and end-stage renal disease according to the genotypes of SNP rs3773885 indicated that the C allele carriers had higher serum creatinine levels compared to the subjects carrying T allele in both females and males. Mme expression at mRNA and protein levels was upregulated in kidneys of db/db mice at the ages of 12 and 26 weeks (p = 0.017 and <0.001) but not at the age of 5 weeks compared to the controls.

CONCLUSIONS

The present study provides the first evidence that MME has genetic and biological effects on the development of DN, and suggests that the inhibition of MME expression in the kidney with the agent of vasopeptidase may be a useful therapeutic approach for this disease.

Relationship between ADIPOQ gene, circulating high molecular weight adiponectin and albuminuria in individuals with normal kidney function: evidence from a family-based study

AIMS/HYPOTHESIS

Insulin resistance is associated with reduced serum adiponectin and increased albuminuria levels. Thus, one would anticipate an inverse relationship between circulating adiponectin and albuminuria. However, several studies have described a 'paradoxical' elevation of serum adiponectin in patients with elevated albuminuria. These findings may have been confounded by the presence of diseases and related treatments known to affect circulating adiponectin and albuminuria. We therefore studied the relationship between circulating adiponectin and albuminuria in the absence of such confounders.

METHODS

To this purpose, the relationship between adiponectin isoforms and albumin:creatinine ratio (ACR) was investigated in a family-based sample of 634 non-diabetic untreated white individuals with normal kidney function. We also investigated whether the two variables share a common genetic background and addressed the specific role of the gene encoding adiponectin on that background by genotyping several ADIPOQ single nucleotide polymorphisms (SNPs).

RESULTS

ACR was directly associated with high molecular weight (HMW) adiponectin isoform (p = 0.024). The two variables shared some genetic correlation (ρ(g) = 0.38, p = 0.04). ADIPOQ promoter SNP rs17300539 was associated with HMW adiponectin (p = 4.8 × 10(-5)) and ACR (p =0.0027). The genetic correlation between HMW adiponectin and ACR was no longer significant when SNP rs17300539 was added to the model, thus reinforcing the role of this SNP in determining both traits.

CONCLUSIONS/INTERPRETATION

Our study shows a positive, independent correlation between HWM adiponectin and ACR. ADIPOQ variability is associated with HMW adiponectin and ACR, and explains some of the common genetic background shared by these traits, thus suggesting that ADIPOQ and HMW adiponectin modulate albuminuria levels.

Hyperadiponectinemia is independent of kidney function, diabetes duration, and control in type 1 diabetic patients without microangiopathy

INTRODUCTION

High total adiponectin (ADPN) levels were reported in type 1 diabetes (T1D) and related to long diabetes duration and nephropathy. We studied whether ADPN and its specific isoforms were elevated in T1D without microangiopathy and whether they were related to kidney function.

MATERIALS AND METHODS

Total, high, medium, and low molecular weight ADPN and insulin levels were measured in 47 consecutive normoalbuminuric, normotensive T1D patients without retinopathy and in 47 age-, sex-, and body mass index-matched controls. Glomerular filtration rate was estimated by (51)Cr-EDTA plasma clearance.

RESULTS

Total and high molecular weight ADPN ratio were higher in T1D patients than in controls. ADPN levels were not related to anthropometric measures, whereas they were in controls. In T1D, ADPN levels were not related to glycosylated hemoglobin, diabetes duration, or glomerular filtration rate. Peripheral insulin levels were higher in T1D patients than in controls, but they were not related to ADPN levels. In controls, insulin levels were positively related to total ADPN.

CONCLUSION

In T1D without microangiopathy, high ADPN levels could not be related to anthropometric diabetes parameters, kidney function, or high insulin levels. The nature of this elevation remains unknown.

Effects of MCF2L2, ADIPOQ and SOX2 genetic polymorphisms on the development of nephropathy in type 1 Diabetes Mellitus

Background

MCF2L2, ADIPOQ and SOX2 genes are located in chromosome 3q26-27, which is linked to diabetic nephropathy (DN). ADIPOQ and SOX2 genetic polymorphisms are found to be associated with DN. In the present study, we first investigated the association between MCF2L2 and DN, and then evaluated effects of these three genes on the development of DN.

Methods

A total of 1177 type 1 diabetes patients with and without DN from the GoKinD study were genotyped with TaqMan allelic discrimination. All subjects were of European descent.

Results

Leu359Ile T/G variant in the MCF2L2 gene was found to be associated with DN in female subjects (P = 0.017, OR = 0.701, 95%CI 0.524-0.938) but not in males. The GG genotype carriers among female patients with DN had tendency decreased creatinine and cystatin levels compared to the carriers with either TT or TG genotypes. This polymorphism MCF2L2-rs7639705 together with SNPs of ADIPOQ-rs266729 and SOX2-rs11915160 had combined effects on decreased risk of DN in females (P = 0.001).

Conclusion

The present study provides evidence that MCF2L2, ADIPOQ and SOX2 genetic polymorphisms have effects on the resistance of DN in female T1D patients, and suggests that the linkage with DN in chromosome 3q may be explained by the cumulated genetic effects.

Increased plasma adiponectin closely associates with vascular endothelial dysfunction in type 2 diabetic patients with diabetic nephropathy

Several studies found that adiponectin, an adipokine withstands atherosclerosis in vivo, is significantly increased in subjects with diabetic nephropathy (DN), but its clinical meaning remains unclear. For its structural similarity to complement C1q and collagen, we performed this study to explore the relationship between adiponectin and the vascular endothelial function alterations in DN patients. 50 type 2 diabetic patients without clinical cardiovascular complications were assigned to control group, microalbuminuria group (Micro-MA), and macroalbuminuria group (Macro-MA) according to the Mogensen's criteria. Plasma adiponectin and soluble vascular cell adhesion molecule-1 (sVCAM-1) were detected. Flow-mediated dilatation (FMD), nitroglycerin-induced dilatation (NID) and cardiologic parameters were measured by ultrasound cardiogram. Plasma adiponectin level was significantly and gradually increased in agreement with the amount of urine albumin excretion. sVCAM-1 was higher in Micro-MA and Macro-MA patients than in the controls, but it was comparable between the former 2 groups. FMD and NID were both remarkably decreased in Macro-MA group compared with Micro-MA and control group. For the whole subjects, plasma adiponectin was negatively related to FMD (r=-0.397, P<0.01) and NID (r=-0.413, P<0.01). These results suggest that increased plasma adiponectin may predict co-existing vascular endothelial dysfunction in DN patients.

Unravelling the genetic basis of renal diseases; from single gene to multifactorial disorders

Chronic kidney disease is common with up to 5% of the adult population reported to have an estimated glomerular filtration rate of < 60 ml/min/1.73 m(2). A large number of pathogenic mutations have been identified that are responsible for 'single gene' renal disorders, such as autosomal dominant polycystic kidney disease and X-linked Alport syndrome. These single gene disorders account for < 15% of the burden of end-stage renal disease that requires dialysis or kidney transplantation. It has proved more difficult to identify the genetic susceptibility underlying common, complex, multifactorial kidney conditions, such as diabetic nephropathy and hypertensive nephrosclerosis. This review describes success to date and explores strategies currently employed in defining the genetic basis for a number of renal disorders. The complementary use of linkage studies, candidate gene and genome-wide association analyses are described and a collation of renal genetic resources highlighted.

Association of ADIPOQ genetic variants and plasma adiponectin isoforms with the risk of incident renal events in type 2 diabetes

BACKGROUND

Adiponectin levels are high in cases of diabetic nephropathy, but it remains unclear whether these high levels are a cause or a consequence of the disease. We investigated the possible association of polymorphisms in the adiponectin gene and baseline adiponectin levels with the incidence of renal events in subjects with type 2 diabetes.

METHODS

We studied three adiponectin polymorphisms (-11391G > A, +45T > G and +276G > T) in 3086 subjects with type 2 diabetes and high levels of albumin excretion from the diabetes, hypertension, microalbuminuria or proteinuria, cardiovascular events and ramipril (DIABHYCAR) trial. Baseline concentrations of total adiponectin and of adiponectin isoforms were determined in cases with incident renal events and in controls matched for sex, age, body mass index (BMI) and adiponectin genotype. We used another cohort of type 2 diabetes patients-the survie, diabète de type 2 et génétique(SURDIAGENE) study (n = 1004)-for the replication of genetic data.

RESULTS

In DIABHYCAR, the -11391A and +45G alleles were associated with a higher incidence of renal events [hazard ratio (HR) = 1.73; 95% confidence interval (CI), 1.10-2.71; and HR = 1.68; 95% CI, 1.14-2.47, respectively]. The haplotype containing susceptibility alleles, -11391A/+45G/+276G, was more frequent in cases with renal events (5.1% vs. 1.9% in those without, P = 0.005). In SURDIAGENE, the -11391A/+45G/+276G haplotype was also associated with renal events (5.6% vs. 1.9% in those without, P = 0.03). In DIABHYCAR, all isoforms were more abundant in subjects carrying the -11391A or +45G alleles. Medium- (MMW) and low-molecular weight (LMW) isoforms were more abundant in cases with renal events.

CONCLUSIONS

In subjects with type 2 diabetes and early renal dysfunction, adiponectin gene variants are determinants of the renal risk. The -11391A and +45G alleles may affect renal risk by leading to high circulating adiponectin concentrations, at least those of MMW and LMW isoforms.

The V16A polymorphism in SOD2 is associated with increased risk of diabetic nephropathy and cardiovascular disease in type 1 diabetes

AIMS/HYPOTHESIS

Hyperglycaemia increases oxidative stress and may thereby increase the risk of diabetic complications, including diabetic nephropathy. Cells are protected from oxidative damage by, for example, the manganese superoxide dismutase enzyme (MnSOD), but the functional polymorphism V16A affects the localisation of MnSOD and therefore its ability to scavenge superoxide radicals. In a Danish cohort of type 1 diabetes patients, we sought to confirm previous findings of association between the V allele and the risk of diabetic nephropathy and to investigate the influence of this polymorphism on the development of cardiovascular disease.

METHODS

Type 1 diabetes patients attending the Steno Diabetes Center, Gentofte, Denmark, between 1993 and 2001 were enrolled in this study. A total of 441 cases with diabetic nephropathy (albumin excretion > or =300 mg/24 h) and 314 controls with persistent normoalbuminuria (<30 mg/24 h), despite diabetes of duration > or =20 years, were identified. The median duration of diabetes was 35 years (range 12-73 years).

RESULTS

We confirmed the significant association between carrier status of the V allele and diabetic nephropathy. The association was independent of age at diabetes onset, HbA(1c), sex, smoking and diabetes duration (OR 1.7, 95% CI 1.2-2.4). The VV and AV genotypes considered together also predicted the risk of cardiovascular disease, independently of age at follow-up, HbA(1c), sex, smoking, systolic blood pressure, cholesterol and nephropathy status. The hazard ratio was 1.6 (95% CI 1.0-2.5).

CONCLUSIONS/INTERPRETATION

The MnSOD V16A polymorphism is involved in the development of nephropathy caused by type 1 diabetes and seems to predict cardiovascular disease during follow-up.

Biomarkers of adiponectin: plasma protein variation and genomic DNA polymorphisms

Adiponectin is secreted by white adipose tissue and exists as the most abundant adipokine in the human plasma. Recent research has indicated that plasma adiponectin levels are inversely correlated with body mass index (BMI) and insulin resistance. Reduction of plasma adiponectin levels is commonly observed in the patients with type 2 diabetes (T2D) and/or in those who are obese in comparison with healthy control individuals. The adiponectin (AdipoQ) gene has a moderate linkage disequilibrium (LD), but two small LD blocks are observed, respectively, in the promoter region and the boundary of exon 2-intron 2. Genetic association studies have demonstrated that single nucleotide polymorphisms (SNPs) +45G15G(T/G) in exon 2 and +276G/T in intron 2 of the AdipoQ gene confer the risk susceptibility to the development of T2D, obesity and diabetic nephropathy (DN). The SNPs in the promoter region, including −11426A/G, −11377C/G and −11391G/A, are found to be associated with T2D and DN. Recent research has indicated that the promoter polymorphisms interfere with the AdipoQ promoter activity. The haplotypes constructed by the promoter polymorphisms and SNP +276G/T in intron 2 are associated with circulating adiponectin levels. This review summarises genetic and pathophysiological relevancies of adiponectin and discusses about the biomarkers of adiponectin plasma protein variation and genomic DNA polymorphisms.

Gender-specific association between the kininogen 1 gene variants and essential hypertension in Chinese Han population

BACKGROUND

Kininogens serve as the precursors of potent vasoactive kinin peptides and also function as cysteine proteinase inhibitors.

METHOD

Given its potential role in blood pressure homeostasis, a tagging single nucleotide polymorphism (SNP) based case-control study was conducted to explore the association between kininogen 1 gene common variants and essential hypertension in Chinese Han population. Four tagging SNPs were selected on the basis of the HapMap database and further genotyped in 2411 patients with essential hypertension and 2348 controls from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA in China).

RESULTS

A significant gender-specific association between the kininogen 1 gene common variants and essential hypertension was observed. In male, but not female participants, rs2304456 CC genotype and rs4686799 TT genotype were significantly related to hypertension [odds ratio (OR) = 2.20, 95% confidence interval (CI): 1.24-3.90, P = 0.007 and OR = 1.31, 95% CI: 1.04-1.66, P = 0.025, respectively]. The haplotypes G-C-C-T and the A-A-T-T were significantly associated with essential hypertension in the male population with adjusted OR 1.43 (P < 0.001) and OR 1.24 (P = 0.001), respectively. The haplotype G-A-C-T was in significant association with essential hypertension (OR = 1.42, P = 0.003) as well as systolic blood pressure (P = 0.005) and diastolic blood pressure (P = 0.015).

CONCLUSION

This is the first association study of the kininogen 1 gene with essential hypertension. Both single-locus and haplotype analyses indicated the kininogen 1 gene was associated with essential hypertension and blood pressure traits in the Chinese male population.

Functional annotations of diabetes nephropathy susceptibility loci through analysis of genome-wide renal gene expression in rat models of diabetes mellitus

BACKGROUND

Hyperglycaemia in diabetes mellitus (DM) alters gene expression regulation in various organs and contributes to long term vascular and renal complications. We aimed to generate novel renal genome-wide gene transcription data in rat models of diabetes in order to test the responsiveness to hyperglycaemia and renal structural changes of positional candidate genes at selected diabetic nephropathy (DN) susceptibility loci.

METHODS

Both Affymetrix and Illumina technologies were used to identify significant quantitative changes in the abundance of over 15,000 transcripts in kidney of models of spontaneous (genetically determined) mild hyperglycaemia and insulin resistance (Goto-Kakizaki-GK) and experimentally induced severe hyperglycaemia (Wistar-Kyoto-WKY rats injected with streptozotocin [STZ]).

RESULTS

Different patterns of transcription regulation in the two rat models of diabetes likely underlie the roles of genetic variants and hyperglycaemia severity. The impact of prolonged hyperglycaemia on gene expression changes was more profound in STZ-WKY rats than in GK rats and involved largely different sets of genes. These included genes already tested in genetic studies of DN and a large number of protein coding sequences of unknown function which can be considered as functional and, when they map to DN loci, positional candidates for DN. Further expression analysis of rat orthologs of human DN positional candidate genes provided functional annotations of known and novel genes that are responsive to hyperglycaemia and may contribute to renal functional and/or structural alterations.

CONCLUSION

Combining transcriptomics in animal models and comparative genomics provides important information to improve functional annotations of disease susceptibility loci in humans and experimental support for testing candidate genes in human genetics.

A single nucleotide polymorphism alters the sequence of SP1 binding site in the adiponectin promoter region and is associated with diabetic nephropathy among type 1 diabetic patients in the Genetics of Kidneys in Diabetes Study

OBJECTIVE

The adiponectin promoter single nucleotide polymorphism (SNP) -11391G/A is found to be associated with nephropathy in type 1 diabetic (T1D) patients among Danish, but not French, Finnish, and Swedish populations. In the present study, we identified the binding sites for transcriptional factors in the adiponectin promoter region and also evaluated the association between adiponectin promoter polymorphisms and diabetic nephropathy (DN) in T1D patients.

MATERIALS AND METHODS

Three adiponectin promoter SNPs, including -11377C/G, -11391G/A, and -11426A/G, were genotyped with dynamic allele-specific hybridization. The subjects included 1177 American T1D patients (622 females/555 males) with or without DN. All patients are of European descent and selected from the Genetics of Kidneys in Diabetes (GoKinD) study.

RESULTS

We identified four binding sites of transcriptional stimulatory protein (SP1) in the adiponectin putative promoter and found that the G allele of SNP -11377C/G altered the sequence for one of the SP1 binding sites. This polymorphism was significantly associated with DN in female T1D patients (P=.022, OR=1.352, 95% CI=1.044-1.752). Further analyses indicated the common diplotype (haplotypic genotype) H1/H1, constructed with SNPs -11377C/G and -11391G/A, was significantly associated with DN in females (P=.013), while the association of another diplotype H1/H2 with DN in females was of borderline significance (P=.071).

CONCLUSIONS

The present study thus provides the first evidence that SNP -11377C/G alters the sequence in one of the SP1 binding sites in the adiponectin promoter region. This polymorphism, together with another promoter SNP -11391G/A, may confer susceptibility to the development of DN in T1D patients among the GoKinD population.

Annotated chromosome maps for renal disease

A combination of linkage analyses and association studies are currently employed to promote the identification of genetic factors contributing to inherited renal disease. We have standardized and merged complex genetic data from disparate sources, creating unique chromosomal maps to enhance genetic epidemiological investigations. This database and novel renal maps effectively summarize genomic regions of suggested linkage, association, or chromosomal abnormalities implicated in renal disease. Chromosomal regions associated with potential intermediate clinical phenotypes have been integrated, adding support for particular genomic intervals. More than 500 reports from medical databases, published scientific literature, and the World Wide Web were interrogated for relevant renal-related information. Chromosomal regions highlighted for prioritized investigation of renal complications include 3q13-26, 6q22-27, 10p11-15, 16p11-13, and 18q22. Combined genetic and physical maps are effective tools to organize genetic data for complex diseases. These renal chromosome maps provide insights into renal phenotype-genotype relationships and act as a template for future genetic investigations into complex renal diseases. New data from individual researchers and/or future publications can be readily incorporated to this resource via a user-friendly web-form accessed from the website: www.qub.ac.uk/neph-res/CORGI/index.php.

Role of PPARgamma in renoprotection in Type 2 diabetes: molecular mechanisms and therapeutic potential

DN (diabetic nephropathy) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of ESRD (end-stage renal disease), accounting for millions of deaths worldwide. TZDs (thiazolidinediones) are synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma), which is involved in many important physiological processes, including adipose differentiation, lipid and glucose metabolism, energy homoeostasis, cell proliferation, inflammation, reproduction and renoprotection. A large body of research over the past decade has revealed that, in addition to their insulin-sensitizing effects, TZDs play an important role in delaying and preventing the progression of chronic kidney disease in Type 2 diabetes. Although PPARgamma activation by TZDs is in general considered beneficial for the amelioration of diabetic renal complications in Type 2 diabetes, the underlying mechanism(s) remains only partially characterized. In this review, we summarize and discuss recent findings regarding the renoprotective effects of PPARgamma in Type 2 diabetes and the potential underlying mechanisms.

Genetics of diabetic nephropathy

Genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, and research efforts have been invested worldwide to identify the susceptibility gene for diabetic nephropathy. Although, several candidate genes were shown to be associated with the disease, the results were not always consistent; most of the genes conferring susceptibility to diabetic nephropathy remain to be identified. Recent development of the single nucleotide polymorphism (SNP) typing technology and collation of information on linkage disequilibrium in the human genome have facilitated genome-wide association studies (GWASs) for investigating novel disease-susceptibility genes across the entire human genome. GWASs are considered a powerful and promising approach and are expected to be useful for identifying convincing susceptibility genes for several common diseases; however, to date, these studies have not been able to completely cover the entire human genome.

Association of adiponectin gene polymorphisms with type 2 diabetes in an African American population enriched for nephropathy

OBJECTIVE

Polymorphisms in the adiponectin gene (ADIPOQ) have been associated with type 2 diabetes and diabetic nephropathy in type 1 diabetes, in mostly European-derived populations.

RESEARCH DESIGN AND METHODS

A comprehensive association analysis of 24 single-nucleotide polymorphisms (SNPs) in the adiponectin gene was performed for type 2 diabetes and diabetic nephropathy in African Americans.

RESULTS

The minor allele (A) in a single SNP in intron 1 (rs182052) was associated with diabetic nephropathy (P = 0.0015, odds ratio [OR] 1.37, CI 1.13-1.67, dominant model) in an African American sample of 851 case subjects with diabetic nephropathy and 871 nondiabetic control subjects in analyses incorporating adjustment for varying levels of racial admixture. This association remained significant after adjustment of the data for BMI, age, and sex (P = 0.0013-0.0004). We further tested this SNP for association with longstanding type 2 diabetes without nephropathy (n = 317), and evidence of association was also significant (P = 0.0054, OR 1.46, CI 1.12-1.91, dominant model) when compared with the same set of 871 nondiabetic control subjects. Combining the type 2 diabetes and diabetic nephropathy samples into a single group of case subjects (n = 1,168) resulted in the most significant evidence of association (P = 0.0003, OR 1.40, CI 1.17-1.67, dominant model). Association tests between age at onset of type 2 diabetes and the rs182052 genotypes also revealed significant association between the presence of the minor allele (A/A or A/G) and earlier onset of type 2 diabetes.

CONCLUSIONS

The SNP rs182052 in intron 1 of the adiponectin gene is associated with type 2 diabetes in African Americans.

Association of genetic variants at 3q22 with nephropathy in patients with type 1 diabetes mellitus

Diabetic nephropathy (DN) is the primary cause of morbidity and mortality in patients with type 1 diabetes mellitus (T1DM) and affects about 30% of these patients. We have previously localized a DN locus on chromosome 3q with suggestive linkage in Finnish individuals. Linkage to this region has also been reported earlier by several other groups. To fine map this locus, we conducted a multistage case-control association study in T1DM patients, comprising 1822 cases with nephropathy and 1874 T1DM patients free of nephropathy, from Finland, Iceland, and the British Isles. At the screening stage, we genotyped 3072 tag SNPs, spanning a 28 Mb region, in 234 patients and 215 controls from Finland. SNPs that met the significance threshold of p < 0.01 at this stage were followed up by a series of sample sets. A genetic variant, rs1866813, in the noncoding region at 3q22 was associated with increased risk of DN (overall p = 7.07 x 10(-6), combined odds ratio [OR] of the allele = 1.33). The estimated genotypic ORs of this variant in all Finnish samples suggested a codominant effect, resulting in significant association, with a p value of 4.7 x 10(-5) (OR = 1.38; 95% confidence interval = 1.18-1.62). Additionally, an 11 kb segment flanked by rs62408925 and rs1866813, two strongly correlated variants (r(2) = 0.95), contains three elements highly conserved across multiple species. Independent replication will clarify the role of the associated variants at 3q22 in influencing the risk of DN.

G/T substitution in intron 1 of the UNC13B gene is associated with increased risk of nephropathy in patients with type 1 diabetes

OBJECTIVE

Genetic and environmental factors modulate the susceptibility to diabetic nephropathy, as initiating and/or progression factors. The objective of the European Rational Approach for the Genetics of Diabetic Complications (EURAGEDIC) study is to identify nephropathy susceptibility genes. We report molecular genetic studies for 127 candidate genes for nephropathy.

RESEARCH DESIGN AND METHODS

Polymorphisms were identified through sequencing of promoter, exon, and flanking intron gene regions and a database search. A total of 344 nonredundant SNPs and nonsynonymous variants were tested for association with diabetic nephropathy (persistent albuminuria >/=300 mg/24 h) in a large type 1 diabetes case/control (1,176/1,323) study from three European populations.

RESULTS

Only one SNP, rs2281999, located in the UNC13B gene, was significantly associated with nephropathy after correction for multiple testing. Analyses of 21 additional markers fully characterizing the haplotypic variability of the UNC13B gene showed consistent association of SNP rs13293564 (G/T) located in intron 1 of the gene with nephropathy in the three populations. The odds ratio (OR) for nephropathy associated with the TT genotype was 1.68 (95% CI 1.29-2.19) (P = 1.0 x 10(-4)). This association was replicated in an independent population of 412 case subjects and 614 control subjects (combined OR of 1.63 [95% CI 1.30-2.05], P = 2.3 x 10(-5)).

CONCLUSIONS

We identified a polymorphism in the UNC13B gene associated with nephropathy. UNC13B mediates apopotosis in glomerular cells in the presence of hyperglycemia, an event occurring early in the development of nephropathy. We propose that this polymorphism could be a marker for the initiation of nephropathy. However, further studies are needed to clarify the role of UNC13B in nephropathy.

Metabolic phenotypes, vascular complications, and premature deaths in a population of 4,197 patients with type 1 diabetes

OBJECTIVE

Poor glycemic control, elevated triglycerides, and albuminuria are associated with vascular complications in diabetes. However, few studies have investigated combined associations between metabolic markers, diabetic kidney disease, retinopathy, hypertension, obesity, and mortality. Here, the goal was to reveal previously undetected association patterns between clinical diagnoses and biochemistry in the FinnDiane dataset.

RESEARCH DESIGN AND METHODS

At baseline, clinical records, serum, and 24-h urine samples of 2,173 men and 2,024 women with type 1 diabetes were collected. The data were analyzed by the self-organizing map, which is an unsupervised pattern recognition algorithm that produces a two-dimensional layout of the patients based on their multivariate biochemical profiles. At follow-up, the results were compared against all-cause mortality during 6.5 years (295 deaths).

RESULTS

The highest mortality was associated with advanced kidney disease. Other risk factors included 1) a profile of insulin resistance, abdominal obesity, high cholesterol, triglycerides, and low HDL(2) cholesterol, and 2) high adiponectin and high LDL cholesterol for older patients. The highest population-adjusted risk of death was 10.1-fold (95% CI 7.3-13.1) for men and 10.7-fold (7.9-13.7) for women. Nonsignificant risk was observed for a profile with good glycemic control and high HDL(2) cholesterol and for a low cholesterol profile with a short diabetes duration.

CONCLUSIONS

The self-organizing map analysis enabled detailed risk estimates, described the associations between known risk factors and complications, and uncovered statistical patterns difficult to detect by classical methods. The results also suggest that diabetes per se, without an adverse metabolic phenotype, does not contribute to increased mortality.

The PPAR gamma 2 Pro12Ala variant predicts ESRD and mortality in patients with type 1 diabetes and diabetic nephropathy

The Pro12Ala polymorphism in the peroxisome proliferator-activated receptor-gamma 2 gene is suggested to associate with diabetic nephropathy and cardiovascular disease in type 2 diabetes. The aim of this study was to investigate the polymorphism in relation to diabetic nephropathy, end-stage renal disease (ESRD), mortality and cardiovascular (CVD) events in type 1 diabetic patients. This prospective observational follow-up study included 415 type 1 diabetic patients with overt diabetic nephropathy (252 men; age 42.2+/-10.4 years [mean+/-SD], duration of diabetes 28.3+/-8.8 years, GFR 66+/-8.8 ml/min) and 428 patients with longstanding type 1 diabetes and persistent normoalbuminuria (230 men; age 45.4+/-11.6 years, duration of diabetes 27.8+/-10.1 years).

FOLLOW-UP

8.1 (0.0-12.8) years (median [range]). There where no significant differences between cases and controls in genotype (p=0.51) or allele frequencies (p=0.25). Cox regression analysis revealed a covariate-adjusted hazard ratio (HR) for all-cause mortality in patients with the Ala/Ala genotype of 2.44 (1.23-4.84). The Pro12Ala polymorphism did not predict CVD events. However, the Ala/Ala genotype predicts ESRD (covariate-adjusted HR 2.60 (1.11-6.07)). Furthermore, Carriers of the Ala-allele had a higher rate of decline in GFR (p=0.040). In conclusion, the Pro12Ala polymorphism is not associated with type 1 diabetic nephropathy. The Ala-allele is associated with enhanced decline in GFR and predicts ESRD and all-cause mortality in patients with nephropathy.

Genetic predictors of renal failure

BACKGROUND

Both environmental and genetic factors contribute to the development and progression of chronic kidney disease. The completion of the human genome sequence and advances in genomic technology make possible identification of gene variants associated with renal failure.

OBJECTIVE

This review discusses the relevant genetic studies in chronic kidney disease, with particular emphasis on the most common causes of end stage renal failure, diabetic nephropathy and glomerulonephritis.

METHODS

Most of the studies presented were performed in recent years and employed association studies, both population-based and with candidate genes, as well as the genome-wide association and genome-wide scan approaches.

RESULTS/CONCLUSION

Increasing evidence supports an important role of genetic susceptibility in the development and progression of renal failure. Identification of disease genes will allow the identification of patients at high risk and the development of new strategies to prevent or delay the renal disease process.