Angiotensinogen polymorphism M235T, hypertension, and nephropathy in insulin-dependent diabetes

Associations between angiotensinogen M235T polymorphisms and the risk of diabetic nephropathy: A meta-analysis

AIMS

The aim of the present study was to clarify the potential relationship of angiotensinogen (AGT) M235T polymorphism and diabetic nephropathy (DN) risk.

METHODS

Comprehensive electronic search in Pubmed, Web of Science, EBSCO, Embase, the Cochrane Library and China National Knowledge Infrastructure (CNKI) to find original articles about the association between AGT M235T polymorphism and DN risk published before 27 September 2017. Literature quality assessment was performed with the Newcastle-Ottawa Scale. Heterogeneity across studies was assessed using I² statistics. Random-effects model or Fixed-effects model was used to estimate the odds ratios (ORs) with 95% confidence intervals (CIs). Sensitivity analyses to assess the influence of individual studies on the pooled estimate. Publication bias was investigated using funnel plots and Egger's regression test. Analyses were performed by using Stata 15.0.

RESULTS

Overall, 20 eligible studies involving a total of 3822 cases and 3911 controls were included in our meta-analysis. The results showed that AGT M235T polymorphism significantly increased DN risk in recessive model (T/T versus M/T + M/M: OR = 1.35, 95%CI (1.07-1.69), I² = 63.8%, Z = 2.56, P = 0.010), homozygote model (T/T versus M/M: OR = 1.46, 95%CI (1.11-1.92), I² = 62.4%, Z = 2.69, P = 0.007) and allele model (T versus M: OR = 1.17, 95%CI (1.01-1.35), I² = 72.5%, Z = 2.14, P = 0.032); Subgroup analysis by ethnicity showed that AGT M235T polymorphism significantly increased DN risk in recessive model (T/T versus M/T + M/M: OR = 1.39, 95%CI (1.06-1.81), I² = 66.6%, Z = 2.42, P = 0.016), homozygote model (T/T versus M/M: OR = 1.47, 95%CI (1.08-2.01), I² = 67.7%, Z = 2.47, P = 0.013) and allele model (T versus M: OR = 1.18, 95%CI (1.02-1.37), I² = 69.4%, Z = 2.26, P = 0.024) in Caucasian DM population; Subgroup analysis by clinical subtype of DM also showed that AGT M235T polymorphism significantly increased DN risk in recessive model (T/T versus M/T + M/M: OR = 1.28, 95%CI (1.05-1.57), I² = 21.3%, Z = 2.40, P = 0.016), homozygote model (T/T versus M/M: OR = 1.41, 95%CI (1.04-1.92), I² = 30.2%, Z = 2.23, P = 0.026) and allele model (T versus M: OR = 1.14, 95%CI (1.03-1.28), I² = 35.5%, Z = 2.44, P = 0.015) in type 1 diabetes patients.

CONCLUSION

Our study showed that AGT M235T homozygous mutation significantly increase DN risk in Caucasian DM population and type 1 diabetes patients.

Neuromarkers of the common angiotensinogen polymorphism in healthy older adults: A comprehensive assessment of white matter integrity and cognition

The common angiotensinogen (AGT) M268T polymorphism (rs699; historically referred to as M235T) has been identified as a significant risk factor for cerebrovascular pathologies, yet it is unclear if healthy older adults carrying the threonine amino acid variant have a greater risk for white matter damage in specific fiber tracts. Further, the impact of the threonine variant on cognitive function remains unknown. The present study utilized multiple indices of diffusion tensor imaging (DTI) and neuropsychological assessment to examine the integrity of specific white matter tracts and cognition between individuals with homozygous genotypes of M268T (MetMet n=27, ThrThr n=27). Differences in subcortical hyperintensity (SH) volume were also examined between groups. Results indicated that the threonine variant was associated with significantly reduced integrity in the superior longitudinal fasciculus (SLF) and the cingulate gyrus segment of the cingulum bundle (cingulum CG) compared to those with the methionine variant, and poorer cognitive performance on tests of attention/processing speed and language. Despite these associations, integrity of these tracts did not significantly mediate relationships between cognition and genetic status, and SH did not differ significantly between groups. Collectively our results suggest that the threonine variant of M268T is a significant risk factor for abnormalities in specific white matter tracts and cognitive domains in healthy older adults, independent of SH burden.

Genetics of hypertension: discoveries from the bench to human populations

Hypertension is a complex trait that is influenced by both heritable and environmental factors. The search for genes accounting for the susceptibility to hypertension has driven parallel efforts in human research and in research using experimental animals in controlled environmental settings. Evidence from rodent models of genetic hypertension and human Mendelian forms of hypertension and hypotension have yielded mechanistic insights into the pathways that are perturbed in blood pressure homeostasis, most of which converge at the level of renal sodium reabsorption. However, the bridging of evidence from these very diverse approaches to identify mechanisms underlying hypertension susceptibility and the translation of these findings to human populations and public health remain a challenge. Furthermore, findings from genome-wide association studies still require functional validation in experimental models. In this review, we highlight results and implications from key studies in experimental and clinical hypertension to date.

Role of the renin angiotensin system in diabetic nephropathy

Diabetic nephropathy has been the cause of lot of morbidity and mortality in the diabetic population. The renin angiotensin system (RAS) is considered to be involved in most of the pathological processes that result in diabetic nephropathy. This system has various subsystems which contribute to the disease pathology. One of these involves angiotensin II (Ang II) which shows increased activity during diabetic nephropathy. This causes hypertrophy of various renal cells and has a pressor effect on arteriolar smooth muscle resulting in increased vascular pressure. Ang II also induces inflammation, apoptosis, cell growth, migration and differentiation. Monocyte chemoattractant protein-1 production responsible for renal fibrosis is also regulated by RAS. Polymorphism of angiotensin converting enzyme (ACE) and Angiotensinogen has been shown to have effects on RAS. Available treatment modalities have proven effective in controlling the progression of nephropathy. Various drugs (based on antagonism of RAS) are currently in the market and others are still under trial. Amongst the approved drugs, ACE inhibitors and angiotensin receptor blockers (ARBs) are widely used in clinical practice. ARBs are shown to be superior to ACE inhibitors in terms of reducing proteinuria but the combined role of ARBs with ACE inhibitors in diabetic nephropathy is under debate.

Angiotensinogen gene T235 variant: a marker for the development of persistent microalbuminuria in children and adolescents with type 1 diabetes mellitus

AIM

We examined genetic polymorphisms in the renin-angiotensin system (RAS) coding for angiotensin I-converting enzyme (ACE) insertion/deletion (I/D) for angiotensinogen (AGT) M235T and angiotensin II receptor type 1 (AGTR1) A1166C as predictors for the development of microalbuminuria (MA) in children with type 1 diabetes mellitus (T1DM).

METHODS

Four hundred fifty-three (215 males, 238 females) T1DM children [median (interquartile range): age, 16.7 years (13.9-18.3); diabetes duration, 6.9 years (3.3-10.8); age at diagnosis, 9.1 years (5.8-11.8)] were followed prospectively from diagnosis until the development of MA (two of three consecutive overnight urine samples with albumin excretion rates of > or =20 and <200 microg/min). Kaplan-Meier survival curves and Cox proportional multivariate model estimated the probability of developing MA and the relative risk for MA among different variables.

RESULTS

MA developed in 41 (9.1%) subjects. The frequencies of genotypes were as follows: ACE-II 112 (25%), ACE-ID 221 (49%), and ACE-DD 117 (26%) (n=450); AGT-MM 144 (32%), AGT-MT 231 (51%), and AGT-TT 77 (17%) (n=452); AGTR1-AA 211 (47%), AGTR1-AC 204 (45%), and AGTR1-CC 37 (8%) (n=452). The cumulative risk for the development of MA was higher in ACE-DD versus ACE-ID/II groups (log-rank test, P=.05), and a trend was noticed when AGT-TT was compared to AGT-MT/MM groups (log-rank test, P=.08). AGT-TT polymorphism conferred a fourfold increased risk for MA compared to AGT-MM/MT (hazard ratio=3.8; 95% confidence interval=1.43-10.3; P=.008).

INTERPRETATION

Our findings suggest that RAS gene polymorphism at AGT M235T is a strong predictor for early MA in young T1DM subjects.

Association of the angiotensinogen M235T and angiotensin-converting enzyme insertion/deletion gene polymorphisms in Turkish type 2 diabetic patients with and without nephropathy

OBJECTIVE

Recent studies have suggested an association between a deletion variant of the angiotensin-converting enzyme (ACE) gene and diabetic nephropathy. However, this finding has not been confirmed by all investigators. Furthermore, an M235T variant of the angiotensinogen (AGT) gene has been associated with hypertension, an important risk factor for the development and progression of diabetic nephropathy.

RESEARCH DESIGN AND METHODS

We investigated the relationship of the ACE insertion/deletion (I/D) and AGT M235T gene polymorphisms in Turkish patients with type 2 diabetes mellitus (DM) with and without diabetic nephropathy. A total of 102 individuals were screened for the presence of the ACE I/D and AGT M235T polymorphism: 46 individuals who had type 2 DM with diabetic nephropathy and, as controls, 56 individuals who had type 2 DM without diabetic nephropathy. Gene polymorphisms were determined by the specific melting temperature (T(m)) values of the resulting amplicons after real-time online polymerase chain reaction and melting curve analysis.

RESULTS

The frequencies of the ACE DD, ID, and II genotypes were 34.8%, 37.0%, and 28.3%, respectively, among type 2 diabetic patients with nephropathy, and 33.9%, 42.9%, 23.2%, respectively (P=.788), in the control subjects without diabetic nephropathy. On the other hand, the frequencies of the AGT MM, MT, and TT genotypes among the same groups were 26.1%, 52.2%, 21.7% and 26.8%, 57.1%, 16.1%, respectively (P=.758).

CONCLUSIONS

There were no differences in the frequencies of the AGT M235T and ACE I/D genotypes between Turkish patients with type 2 DM with and without nephropathy.

Chronic renal insufficiency among Asian Indians with type 2 diabetes: I. Role of RAAS gene polymorphisms

Background

Renal failure in diabetes is mediated by multiple pathways. Experimental and clinical evidences suggest that renin-angiotensin-aldosterone system (RAAS) has a crucial role in diabetic kidney disease. A relationship between the RAAS genotypes and chronic renal insufficiency (CRI) among type 2 diabetes subjects has therefore been speculated. We investigated the contribution of selected RAAS gene polymorphisms to CRI among type 2 diabetic Asian Indian subjects.

Methods

Twelve single nucleotide polymorphisms (SNPs) from six genes namely-renin (REN), angiotensinogen (ATG), angiotensin converting enzyme I (ACE), angiotensin II type 1 receptor (AT1) and aldosterone synthase (CYP11B2) gene from the RAAS pathway and one from chymase pathway were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method and tested for their association with diabetic CRI using a case-control approach. Successive cases presenting to study centres with type 2 diabetes of ≥2 years duration and moderate CRI diagnosed by serum creatinine ≥3 mg/dl after exclusion of non-diabetic causes of CRI (n = 196) were compared with diabetes subjects with no evidence of renal disease (n = 225). Logistic regression analysis was carried out to correlate various clinical parameters with genotypes, and to study pair wise interactions between SNPs of different genes.

Results

Of the 12 SNPs genotyped, Glu53Stop in AGT and A>T (-777) in AT1 genes, were monomorphic and not included for further analysis. We observed a highly significant association of Met235Thr SNP in angiotensinogen gene with CRI (O.R. 2.68, 95%CI: 2.01–3.57 for Thr allele, O.R. 2.94, 95%CI: 1.88–4.59 for Thr/Thr genotype and O.R. 2.68, 95%CI: 1.97–3.64 for ACC haplotype). A significant allelic and genotypic association of T>C (-344) SNP in aldosterone synthase gene (O.R. 1.57, 95%CI: 1.16–2.14 and O.R. 1.81, 95%CI: 1.21–2.71 respectively), and genotypic association of GA genotype of G>A (-1903) in chymase gene (O.R. 2.06, 95%CI: 1.34–3.17) were also observed.

Conclusion

SNPs Met235Thr in angiotensinogen, T>C (-344) in aldosterone synthase, and G>A (-1903) in chymase genes are significantly associated with diabetic chronic renal insufficiency in Indian patients and warrant replication in larger sample sets. Use of such markers for prediction of susceptibility to diabetes specific renal disease in the ethnically Indian population appears promising.

Assessing genetic susceptibility to diabetic nephropathy

Diabetic nephropathy is a serious complication of diabetes and the leading cause of end-stage renal disease. Studies indicate both environmental and genetic factors contribute to the development and progression of diabetic nephropathy. In particular, epidemiological evidence shows a familial clustering of nephropathy in siblings with diabetes, supporting an important role of genetic susceptibility in the pathogenesis of diabetic nephropathy. A common approach in genetic research is assessment of candidate gene polymorphisms using case-control analysis; a number of studies have evaluated predictable candidate genes for diabetic nephropathy. In contrast, only a few studies have used a whole genome approach, such as scanning of micro-satellite markers, in the assessment of genetic susceptibility to diabetic nephropathy. A whole genome linkage analysis using families of Pima Indians showed susceptibility loci for diabetic nephropathy on chromosome 3, 7, and 20. Another linkage analysis using discordant sib-pairs of Caucasian families with type 1 diabetes identified a critical area on chromosome 3q. However, these results have been inconclusive and further investigation is required. Recently, a genome-wide, case-control analysis identifying susceptibility genes for diabetic nephropathy was performed. As a result, a single nucleotide polymorphism in exon 23 of the solute carrier family 12 (sodium-chloride cotransporter) member 3 gene was found to be strongly associated with diabetic nephropathy. Although further assessment of this polymorphism is needed, this strategy offers great promise in the identification of genetic factors predisposing patients to diabetic nephropathy. Identification of genetic susceptibility markers may offer new hope in the diagnosis and treatment of diabetic nephropathy.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Génétique des complications du diabète : néphropathie

Diabetic nephropathy is present in 35 to 45% of Type 1 diabetic patients after 15-20 yrs of diabetes duration. Glycaemic control and diabetes duration are the major risk factors for diabetic nephropathy. Hypertension which is twice as common in diabetics than in the general population, as well as ethnic origin play an important role too. However, as not all diabetic patients will develop diabetic nephropathy, this support the hypothesis for factors of genetic susceptibility (or of protection!) to diabetic nephropathy. Familial aggregation studies supporting this concept of genetic susceptibility, and studies on candidate genes polymorphisms and their association (or lack of association) with diabetic nephropathy (angiotensin-converting enzyme, angiotensinogen and atrial natriuretic peptide genes) are reviewed. Available data from candidate genes studies support a possible implication of vasoactive genes polymorphisms in the development of diabetic nephropathy, but the risk appears to be weak. Ongoing and future studies should aim to detect gene polymorphisms with strong effects, or to identify the association and/or interaction between polymorphisms and diabetic nephropathy.

Single Strand Conformation Polymorphism (SSCP) as a quick and reliable method to genotype M235T polymorphism of angiotensinogen gene

OBJECTIVES

Conflicting results on the relationship between M235T polymorphism of angiotensinogen (AGT) gene and diabetic nephropathy are reported in the literature, probably due to the small number of subjects, to different inclusion criteria and the different genotype analysis methods used. The aim of the present study was to set up a fast, cheap and reliable method to allow the genotyping of M235T polymorphism in a large number of subjects.

DESIGN AND METHODS

We developed in our laboratory a new specifically designed PCR-SSCP method for M235T genotyping whose specificity was compared with that of Allele Specific PCR (ASPCR) and Mutagenically Separated PCR (MS-PCR). The exact M235T genotype was estabilished by direct sequencing. The new PCR-SSCP method was then used to genotype a population of 1171 hypertensive, normoalbuminuric type II diabetes mellitus patients. The patients were also genotyped for ACE I/D polymorphism. For comparison a group of hypertensive non diabetic patients (n = 88) were also screened.

RESULTS

The PCR-SSCP method identified the M235T polymorphism with no misinterpretation at variance with ASPCR and MS-PCR methods that showed a preferential amplification of the T allele. The rare Y248C polymorphism of the AGT gene was also detected by PCR-SSCP. In diabetic hypertensive patients the prevalence of TT genotype was higher than in normotensive healthy controls and equivalent to that found in hypertensive non diabetic patients.

CONCLUSIONS

The PCR-SSCP method for detection of M235T polymorphism is a powerful and sensitive tool for rapid, cheap and efficient screening of a large number of samples. The results obtained with this method demonstrate an association of the TT genotype of AGT gene with hypertension, both in diabetic and non diabetic patients.

Genomic strategies for diabetic nephropathy

Insight into the molecular mechanisms that underlie the origin and progression of diabetic nephropathy remains limited in part because conventional research tools have restricted investigators to focus on single genes or isolated pathways. Microarray technologies provide opportunities for evaluating genetic factors and environmental effects at a genomic scale during the pathogenesis of diabetic nephropathy. Despite the enormous power of the microarray technology, there are several pitfalls that need to be considered. This article discusses conceptual, practical, statistical, and logistical considerations for the use of microarrays in studies of experimental and human diabetic renal disease. New knowledge in this field will facilitate new approaches for molecular diagnosis and drug discovery.

Dinucleotide repeat polymorphism of matrix metalloproteinase-9 gene is associated with diabetic nephropathy

BACKGROUND

Although genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, the definitive gene has not been identified. To identify the genetic marker for diabetic nephropathy, we examined the association between the (A-C)n dinucleotide repeat polymorphism upstream of the matrix metalloproteinase-9 (MMP-9) gene and diabetic nephropathy in a group of Japanese patients with type 2 diabetes.

METHODS

Patients were divided into three groups based on their urinary albumin excretion rate (AER) and the stage of diabetic retinopathy as follows: uncomplicated group (U), normal albuminuria (AER <20 microg/min) without proliferative retinopathy and with the duration of diabetes more than 20 years (N = 32); microalbuminuria group (M), 20 < or = AER < 200 microg/min (N = 155); overt nephropathy group (O), AER > or = 200 microg/min (N = 63). The region containing the dinucleotide repeat upstream of MMP-9 gene was amplified by polymerase chain reaction (PCR). The amplified products were analyzed with 7% formamide/urea acrylamide gel electrophoresis. The promoter constructs of the MMP-9 gene were transfected with the CMV-beta-galactosidase construct into 293 cells using the liposome method. Twenty-four hours after transfection, cells were harvested, and luciferase and beta-galactosidase activities were measured.

RESULTS

Nine alleles of the dinucleotide repeat polymorphism (17 to 25 repeats) were identified, and the frequency of each allele in diabetic subjects was not different from that in nondiabetic controls. The frequency of the allele containing 21 repeats (A21) was most abundant (42.4% in control and 45.6% in diabetic subjects), followed by the allele with 23 repeats (A23; 35.4% in control and 27.6% in diabetic subjects). The A21 allele was less frequent in M and O than U (O, 38.9%; M, 45.5%; U, 59.3%, chi2 = 7.18; P < 0.05, O vs. U), while the frequency of the alleles other than A21 was not different among each group. The calculated odds ratio for nephropathy in the noncarrier, heterozygote, or homozygote of A21 allele was 3.38, 1.97, and 0.2, respectively. Furthermore, the promoter assay for the MMP-9 gene revealed that the A21 allele had a higher promoter activity compared with other alleles. No significant correlation was observed between serum MMP-9 concentrations and the MMP-9 gene polymorphism.

CONCLUSION

These results indicate that the patients with A21 allele of the MMP-9 gene may be protected from the development and progression of diabetic nephropathy. Thus, the microsatellite polymorphism upstream of the MMP-9 gene could be a useful genetic marker for diabetic nephropathy.

Diabetes mellitus and diabetes-associated vascular disease

Diabetes-related cardiovascular disease remains the leading cause of death in patients with type 2 diabetes. Hypertension is common among diabetics and has the same pathogenetic mechanisms as insulin resistance, in which the activated renin-angiotensin system contributes to the emerging high blood pressure and hyperglycemia. Hyperglycemia is one of the triggering factors for vascular dysfunction and clotting abnormalities and, therefore, for accelerated atherosclerosis in diabetes. Glycated hemoglobin levels, as a reflection of the degree of glycemia, are strongly associated with the risk of cardiovascular disease in diabetics and in the general population. Tight glycemic control, the treatment of dyslipidemia and raised blood pressure, in addition to the use of antiplatelet therapy, all powerfully reduce the risks associated with diabetes. Furthermore, angiotensin-converting enzyme inhibitors might offer additional cardioprotection to diabetics above that provided by blood pressure reduction.

Angiotensinogen M235T and chymase gene CMA/B polymorphisms are not associated with nephropathy in type II diabetes

BACKGROUND

Several studies have suggested that the same genetic factors may be involved in the predisposition to both essential hypertension and diabetic nephropathy, but the molecular mechanism underlying this predisposition still remains unclear. In particular, the role of genes involved in blood-pressure regulation and angiotensin II action is still controversial. This study examines a possible association between angiotensinogen M235T and chymase gene CMA/B polymorphisms with the presence of nephropathy in type II diabetic Caucasians.

METHODS

For the purposes of the study, 323 microalbuminuric and 127 overt proteinuric cases, together with 243 normoalbuminuric controls with long-duration diabetes were selected from a group of 941 type II diabetic patients with established renal status.

RESULTS

No differences in the genotype distributions or allele frequencies of the examined polymorphisms between the study groups were observed. The study groups were also stratified by gender, diabetes duration, level of glycaemic control, body mass index, hypertension, and retinopathy status, but still no distortion in the distributions of genotypes of any of the examined polymorphisms in any of the strata was shown.

CONCLUSIONS

Our study provided evidence against an association between angiotensinogen M235T or chymase gene CMA/B polymorphisms and the presence of incipient or overt nephropathy in Caucasian patients with type II diabetes.

Angiotensin II and its receptors in the diabetic kidney

Studies using either angiotensin-converting enzyme inhibitors or type 1 (AT(1)) angiotensin II (ANG II)-receptor blockers indicate that ANG II is a mediator of progressive injury in diabetic nephropathy. However, suppression of the systemic renin-angiotensin system (RAS) generally has been shown in diabetes mellitus. Evidence suggests that intrarenal RASs within glomeruli and proximal tubules may be activated with hyperglycemia, leading to stimulation of local ANG II production, which may exert feedback inhibition of systemic renin release. Once formed, intrarenal ANG II exerts most of its well-described effects through binding to AT(1) receptors that are abundantly present in cells of the glomeruli, tubules, vasculature, and interstitium. Thus, AT(1)-receptor activation increases vascular resistance, reduces renal blood flow, and stimulates production of extracellular matrix in the mesangium and tubulointerstitium. Recent studies suggest that the adult kidney also expresses type 2 (AT(2)) ANG II receptors in glomeruli, tubular segments, and vasculature. AT(2)-receptor activation is associated with increased intrarenal nitric oxide production, stimulation of natriuresis, and inhibition of cell growth and matrix synthesis, effects that oppose those of kidney AT(1) receptors. A number of studies have shown a reduction in kidney AT(1)-receptor expression in diabetic nephropathy, suggesting that the balance between AT(1)- and AT(2)-receptor-mediated cell-signaling events may be a determinant of progression rate in diabetic nephropathy and that unopposed stimulation of AT(2) receptors by ANG II with use of AT(1)-receptor blockers may contribute to the beneficial properties of these agents. Determination of the expression pattern of AT(2) receptors in diabetes and further definition of the role of AT(2) receptors in opposing the detrimental effects of AT(1) receptors may lead to more selective targeting of the RAS in diabetic nephropathy.

Angiotensin I-converting enzyme gene insertion/deletion and angiotensinogen M235T polymorphisms: risk of chronic renal failure. End-Stage Renal Disease Study Group

BACKGROUND

Chronic renal failure (CRF) is a complex phenotype that results from an underlying kidney disease and superimposing environmental and genetic factors. The aim of our study was to evaluate the role of polymorphisms in the genes encoding for components of the renin-angiotensin system (RAS) in the development and/or progression of CRF.

METHODS

Two hundred forty-seven family trios (patients with CRF and both parents; 120 with primary chronic glomerulonephritis, 80 with interstitial nephritis, and 47 with type 1 diabetes with nephropathy) were examined, and transmission/disequilibrium test (TDT) was used to evaluate allele transmission from heterozygous parents to affected offspring.

RESULTS

The D allele of the angiotensin I-converting enzyme (ACE) gene insertion/deletion polymorphism was transmitted significantly more frequently than expected for no association among all examined trios and in the subgroup of patients with interstitial nephritis. The angiotensinogen 235T allele was transmitted significantly more frequently to patients with CRF than expected for no association, but the effect was seen only in patients with interstitial nephritis. The presence of the DD or ID genotype was associated with a faster rate of decline of renal function, which was not observed for the angiotensinogen M235T polymorphism. For chymase gene and angiotensin II receptor type 1 gene, allele transmission did not deviate significantly from a random proportion of 50:50%.

CONCLUSIONS

The results of this study suggest that ACE gene insertion/deletion and angiotensinogen M235T polymorphisms contribute to the increased risk for the development of CRF, but the magnitude of the effect within subsets of patients with specific etiologies of CRF must be evaluated further.

Genetic polymorphisms of the renin-angiotensin system and complications of insulin-dependent diabetes mellitus

OBJECTIVE

Patients with insulin-dependent diabetes mellitus (IDDM) have a high risk of developing diabetic nephropathy, retinopathy and cardiovascular diseases. The contribution of gene polymorphisms of the renin angiotensin system to these complications is controversial and may differ among populations.

METHODS

In 257 Dutch IDDM patients (188 with urinary albumin excretion (UAE) <30 mg/24 h), logistic regression analysis was used to study the relationships among, on the one hand, the insertion/deletion gene polymorphism of the angiotensin-converting enzyme gene (ACE-ID), the M235T gene polymorphism of the angiotensinogen gene (AGT-M235T), and the A1166C gene polymorphism of the angiotensin type 1 receptor gene (AT1-A1166C), and, on the other hand, UAE, retinopathy, hypertension, and coronary heart disease.

RESULTS

The T-allele of the AGT-M235T polymorphism was associated with an increased risk of an elevated UAE (odds ratio (OR) 3.03; 95% confidence interval (CI) 1.06-8.61), but only when interaction with the D-allele of the ACE-ID polymorphism was considered. A previously described positive interaction between the T-allele of the AGT-M235T polymorphism and the D-allele of the ACE-ID polymorphism could not be confirmed. The T-allele was also associated with an increased risk of retinopathy (OR 3.89, 95% CI 1.79-8.47). The CC-genotype of the AT1-A1166C polymorphism was associated with hypertension (OR 3.58; 95% CI 1. 23-10.37).

CONCLUSIONS

In a Dutch IDDM population, including 69 patients with (incipient) diabetic nephropathy, the T-allele of the AGT-M235T polymorphism is associated with an elevated UAE and diabetic retinopathy and the CC-genotype of the AT1-A1166C polymorphism is associated with hypertension. A previously described interaction between the AGT-M235T and the ACE-ID polymorphisms could not be confirmed. Since the number of nephropathic patients in this study is small, these conclusions must be interpreted with caution.

Regulated expression of human angiotensinogen gene by hepatocyte nuclear factor 4 and chicken ovalbumin upstream promoter-transcription factor

We previously identified various upstream and downstream regulatory elements and factors important for hepatic expression of the human angiotensinogen (ANG) gene, the precursor of vasoactive octapeptide angiotensin II. In the present study, to further investigate the molecular mechanism of human ANG transcriptional regulation, we generated transgenic mice carrying the fusion gene composed of the 1. 3-kilobase promoter of the human ANG gene, its downstream enhancer, and the chloramphenicol acetyltransferase reporter gene. Because expression of the chloramphenicol acetyltransferase gene was observed strongly in the liver and weakly in the kidney, we suspected that hepatocyte nuclear factor (HNF) 4 with a tissue expression pattern similar to that of the reporter gene would regulate ANG transcription. In vitro assays indicated that HNF4 bound to the promoter elements and strongly activated the ANG transcription, but that chicken ovalbumin upstream promoter transcription factor (COUP-TF), a transcriptional repressor, dramatically repressed human ANG transcription through the promoter elements and the downstream enhancer core elements. Furthermore, COUP-TF dramatically decreased the human ANG transcription in the mouse liver by the Helios Gene Gun system in vivo. These results suggest that an interplay between HNF4 and COUP-TF could be important in hepatic human ANG transcription.

Polymorphisms of angiotensin-converting enzyme and angiotensinogen genes in type 2 diabetic sibships in relation to albumin excretion rate

Familial clustering of altered albumin excretion and nephropathy risk has been described in both type 1 and type 2 diabetes; moreover, an association of micro-macroalbuminuria and diabetic retinopathy has been recently reported in a large number of white families with type 2 diabetes. Conflicting reports, mainly comparing affected with unaffected unrelated subjects, have suggested a possible role of some genotypes of the renin-angiotensin system in conferring nephropathy risk in type 2 diabetes. To examine the role of genetic factors in influencing albuminuria in families, we studied the relation of angiotensin-converting enzymes (ACE) and angiotensinogen (AGN) genotypes with albumin excretion rate in a population of affected siblings of type 2 diabetic probands. We determined ACE insertion/deletion polymorphism and two polymorphisms of the AGN gene (T174M and M235T) in 160 families with at least one affected member. Defining proband as the patient with the longest known duration of diabetes, we compared the allelic distribution in diabetic probands with and without altered albumin excretion and in their siblings. Allelic distribution of these polymorphisms was similar in the two groups of probands, as well as in their siblings. Identity-by-State (IBS) analysis showed a link between AGN locus and arterial hypertension in these siblings, which was independent from the degree of renal involvement. Thus, our findings suggest that in white families with type 2 diabetes, there is no linkage between the degree of albumin excretion and ACE and AGN polymorphisms, whereas the latter is related to arterial hypertension, as previously found in patients without diabetes but with essential hypertension.

Polymorphisms in the genes encoding for human kinin receptors and the risk of end-stage renal failure: results of transmission/disequilibrium test. The End-Stage Renal Disease Study Group

There is evidence that environmental factors and genetic predisposition affect the development of end-stage renal disease (ESRD). The role of kinin peptides in renal pathology has been also suggested, and a nephroprotective effect of kinins, mediated by B1 and B2 kinin receptors, has been postulated. Recently, two novel sequence differences in the B1R gene were identified, and the C allele of the G-->C substitution at position -699 in the promoter region of the B1R gene was found to be less frequent among patients with ESRD compared with healthy control subjects. In this study, the association between B1R and B2R polymorphisms and ESRD was examined using a family-based study design: transmission/disequilibrium test. B1R gene G-->C substitution at position -699 in the promoter region and B2R gene C-->T transition at position 181 in exon 2 were genotyped in 247 family trios: offspring affected with ESRD and both parents. The less common alleles of both polymorphisms (B1R C allele and B2R T allele) were transmitted from heterozygous parents to offspring affected with ESRD less frequently than expected (37 and 36%, respectively; P < 0.05). In conclusion, results obtained in this study support a hypothesis of the protective role of bradykinin receptor gene polymorphisms in the development of ESRD.

Plasma renin and prorenin and renin gene variation in patients with insulin-dependent diabetes mellitus and nephropathy

BACKGROUND

The most striking abnormality in the renin angiotensin system in diabetic nephropathy (DN) is increased plasma prorenin. Renin is thought to be low or normal in DN. In spite of altered (pro)renin regulation the renin gene has not been studied for contribution to the development of DN.

METHODS

We studied plasma renin, prorenin, and four polymorphic markers of the renin gene in 199 patients with IDDM and DN, and in 192 normoalbuminuric IDDM controls matched for age, sex, and duration of diabetes. Plasma renin and total renin were measured by immunoradiometric assays. Genotyping was PCR-based.

RESULTS

Plasma renin was increased in patients with nephropathy (median (range), 26.3 (5.2-243.3) vs 18.3 (4.2-373.5) microU/ml in the normoalbuminuric group, P<0.0001). Prorenin levels were elevated out of proportion to renin levels in nephropathic patients (789 (88-5481) vs 302 (36-2226) microU/ml, P<0.0001). Proliferative retinopathy had an additive effect on plasma prorenin, but not on renin. DN was associated with a BglI RFLP in the first intron of the renin gene (bb-genotype: n=106 vs 82 in DN and normoalbuminuric patients respectively, P=0.037), but not with three other polymorphisms in the renin gene. A trend for association of higher prorenin levels with the DN-associated allele of this renin polymorphism was observed in a subgroup of patients with DN (bb vs Bb+BB, P=0.07).

CONCLUSIONS

The results indicate that in DN there is an increase in both renin and prorenin levels. A renin gene polymorphism may contribute weakly to DN. Although speculative, one of the renin gene alleles could lead to increased renin gene expression, leading to higher renin and prorenin levels. These may play a role in the pathogenesis of DN.

Association between AGT codon 235 polymorphism and variation in serum concentrations of creatinine and urea in Canadian Oji-Cree

Finding the genetic determinants of intermediate quantitative traits, such as serum creatinine and urea, might aid in finding the determinants of disease phenotypes, such as renal failure, that are, in part, defined according to threshold values imposed upon such traits. We evaluated the association between common variation in the gene encoding angiotensinogen, AGT, and the serum concentrations of creatinine and urea in non-diabetic Canadian Oji-Cree. We determined genotypes of the AGT codon 235 polymorphism among 502 non-diabetic Oji-Cree. We used multivariate analysis of variance to identify significant determinants of variation in serum concentrations of creatinine and urea and of systolic and diastolic blood pressure. We found significant associations between the AGT codon 235 genotype and serum concentrations of creatinine and urea (p = 0.017 and 0.049, respectively) and systolic blood pressure (p = 0.041). Compared with subjects with the other two genotypes, homozygotes for AGT T235/T235 had significantly lower serum concentrations of creatinine and urea and significantly higher mean systolic blood pressure. The findings suggest that the AGT T235 allele is a determinant of intermediate traits related to renal function in these aboriginal Canadians.

Association between AGT T235 variant and microalbuminuria in Canadian Oji-Cree with type 2 diabetes mellitus

OBJECTIVE

To assess the association between the common variation in the gene encoding angiotensinogen, AGT, and the presence of microalbuminuria in Canadian Oji-Cree with type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

We compared the frequencies of the AGT promoter and M235T polymorphisms among three subgroups of adult Oji-Cree: 50 subjects who had type 2 diabetes with microalbuminuria, 6 subjects who had type 2 diabetes without albuminuria and 302 non-diabetic, normotensive subjects.

RESULTS

We found the AGT T235 allele was present at a significantly higher frequency, and that T235/T235 homozygotes were significantly more prevalent, among the subjects who had type 2 diabetes with microalbuminuria than among the subjects in the other two groups.

CONCLUSIONS

The findings suggest that the AGT T235 allele is a determinant of the nephropathy susceptibility related to type 2 diabetes in these aboriginal Canadians.

M235T angiotensinogen gene polymorphism and cardiovascular renal risk

OBJECTIVE

In this meta-analysis, we attempted to derive pooled estimates for the putative associations between various cardiovascular-renal disorders and the M235T polymorphism of the angiotensinogen gene.

METHODS

Case-control studies were combined, using the Mantel and Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the intrastudy mean of the MM genotype as denominator.

RESULTS

The computerized database used for this analysis included 69 reports with an overall sample size of 27,906 subjects. Overall, possession of the T allele was associated with an increased risk of hypertension. In comparison with the MM reference group (number of studies, n = 32), the excess risk was 31% (P = 0.001) in TT homozygotes and 11% (P = 0.03) in TM heterozygotes. The sensitivity analysis showed that this association was present only in whites (T allelic frequency, f = 42.2%), but not in blacks (f = 77.0%) or Asians (f = 78.0%). Atherosclerotic complications (n = 12), renal microvascular disorders (n = 13), cardiomyopathy (n = 2) or diabetic retinopathy (n = 3) were not correlated with the M235T polymorphism. Publication bias was observed for hypertension, but not for coronary heart disease, including myocardial infarction, and for microvascular nephropathy. Furthermore, in comparison with the MM control group, the circulating angiotensinogen levels (n = 8) were raised by 11 and 7% (P = 0.01) in TT and TM subjects, respectively. In contrast, plasma levels of the angiotensin I converting enzyme (n = 4) and body mass index (n = 15) were not associated with the T allele.

CONCLUSION

The T allele encoding angiotensinogen is not associated with atherosclerotic or microvascular complications, but in Caucasians behaves as a marker for hypertension. This association, which may have been inflated by publication bias, does not necessarily imply causality.

Molecular variation of the human angiotensinogen core promoter element located between the TATA box and transcription initiation site affects its transcriptional activity

Recent genetic studies indicate that several molecular variants discovered in angiotensinogen (AG), the precursor of vasoactive octapeptide angiotensin II, could potentially be responsible for inherited predisposition to human blood pressure variation. We have previously shown that a ubiquitously expressed nuclear factor, AGCF1, bound to AGCE1 (AG core promoter element 1 including the core nucleotides, CTCGTG, CTC-type) located between the TATA box and transcription initiation site (positions -25 to -1) is an authentic regulator of human AG transcription. In the present study, we showed that AGCF1 has biologically and immunologically similar properties to those of a helix-loop-helix nuclear factor USF1 and examined the effects of two other naturally occurring molecular variants (ATCGTG, ATC-type and ATTGTG, ATT-type) found in the AGCE1 position on the human AG transcriptional activity. Competitive gel-shift and transfection experiments demonstrated that the transcriptional activity for the CTC- and ATC-type promoters was 2.5 times higher than that for the ATT-type through the alteration of AGCF1-binding affinity. These results suggest the possible involvement of USF1 as a component in AGCF1 formation and the potential importance of AGCE1 variation in blood pressure regulation through human AG expression.

Synergistic effect of angiotensin II type 1 receptor genotype and poor glycaemic control on risk of nephropathy in IDDM

We investigated the contribution of polymorphisms in the angiotensin II type 1 receptor gene (AGTR1) to renal complications in an inception cohort of 152 insulin-dependent diabetic (IDDM) patients examined 15-21 years after diabetes onset. This nested case-control study included 79 normoalbuminuric control subjects and 73 cases with evidence of nephropathy ranging from microalbuminuria to overt proteinuria. Subjects were genotyped for two AGTR1 polymorphisms (T573-->C and A1166-->C), and an adjacent CA repeat microsatellite. Allele C1166 and the 140 bp allele of the microsatellite were more frequent among nephropathy cases than normoalbuminuric control subjects (0.322 vs 0.247, and 0.618 vs 0.521, respectively), but these differences were not statistically significant. Although not significant by themselves, the AGTR1 polymorphisms contributed significantly to the risk of diabetic nephropathy when accompanied by poor glycaemic control. Among patients with frequent severe hyperglycaemia during the first decade of diabetes, the relative risk of nephropathy among allele C1166 carriers was 12.1 (95% CI: 3.7-39.8), whereas it was only 1.4 (95% CI: 0.6-3.5) among allele A1166 homozygotes. The difference between relative risks was highly significant (chi(2) = 8.25, p = 0.004 with 1 df). A similar pattern of higher risk of microalbuminuria, specifically among those carriers of allele C1166 who had poor glycaemic control was also found in an independent study of a cross-sectional sample of 551 IDDM individuals, although the effect was smaller in magnitude. We conclude that DNA sequence differences in the AGTR1 gene may modify the noxious effects of hyperglycaemia on the kidney. Allele C1166 carriers might especially benefit from nephropathy prevention programmes.

ATF-like element contributes to hepatic activation of human angiotensinogen promoter

Angiotensinogen is the precursor protein of angiotensin II that is involved in regulating blood pressure and electrolyte homeostasis, and it is mainly synthesized in the liver. In the present study, we analyzed the human angiotensinogen proximal promoter region by means of Chloramphenicol acetyltransferase assays, and suggested that the region from -106 to +44 is sufficient for hepatoma cell line (HepG2)-specific expression. Electrophoretic mobility shift assays using ALE (ATF-like element, -102 to -87) fragment identified CREB/ATF family nuclear factors and novel ones, ALF (ALE-binding factor). The deletion and in vivo competition of ALE decreased the human angiotensinogen promoter activity. Furthermore, the heterologous promoter analysis demonstrated that ALE acts as a HepG2-dependent activating element. These results indicate that ALE plays an important role in hepatic expression of human angiotensinogen gene.

Contribution of genetic polymorphism in the renin-angiotensin system to the development of renal complications in insulin-dependent diabetes: Genetique de la Nephropathie Diabetique (GENEDIAB) study group

Diabetic nephropathy is a glomerular disease due to uncontrolled diabetes and genetic factors. It can be caused by glomerular hypertension produced by capillary vasodilation, due to diabetes, against constitutional glomerular resistance. As angiotensin II increases glomerular pressure, we studied the relationship between genetic polymorphisms in the renin-angiotensin system-angiotensin I converting enzyme (ACE), angiotensinogen (AGT), and angiotensin II, subtype 1, receptor-and the renal involvement of insulin-dependent diabetic subjects with proliferative retinopathy: those exposed to the risk of nephropathy due to diabetes. Of 494 subjects recruited in 17 centers in France and Belgium (GENEDIAB Study), 157 (32%) had no nephropathy, 104 (21%) incipient (microalbuminuria), 126 (25 %) established (proteinuria), and 107 (22%) advanced (plasma creatinine > or = 150 micromol/liter or renal replacement therapy) nephropathy. The severity of renal involvement was associated with ACE insertion/deletion (I/D) polymorphism: chi2 for trend 5.135, P = 0.023; adjusted odds ratio attributable to the D allele 1.889 (95% CI 1.209-2.952, P = 0.0052). Renal involvement was not directly linked to other polymorphisms. However, ACE I-D and AGT M235T polymorphisms interacted significantly (P = 0.0166): in subjects with ACE ID and DD genotypes, renal involvement increased from the AGT MM to TT genotypes. Thus, genetic determinants that affect renal angiotensin II and kinin productions are risk factors for the progression of glomerular disease in uncontrolled insulin-dependent diabetic patients.