A(-20)C polymorphism of the angiotensinogen gene and progression of IgA nephropathy

Risk given by AGT polymorphisms in inducing susceptibility to essential hypertension among isolated populations from a remote region of China: A case-control study among the isolated populations

INTRODUCTION

Hypertension is a serious risk factor affecting up to 30% of the world's population with a heritability of more than 30-50%. The aim of this study was to investigate the contribution of the polymorphisms localized in the angiotensinogen (AGT) gene, a main component of the renin-angiotensin-aldosterone system, in inducing the susceptibility to essential hypertension (EH) among isolated populations (Yi and Hani minorities) with low prevalence rate from the remote region of Yunnan in China.

METHODS

A case-control association study was performed, and all subjects were genotyped for the seven single nucleotide polymorphisms localized in the AGT region by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

Three polymorphisms, i.e. rs5046, rs5049, and rs2478544, were significantly associated with EH among the Hani minority. The associations, found in the Yi minority, did not reach a conclusive level of statistical significance. The polymorphisms of rs2478544 and rs5046 caused the transformations of exonic splicing enhancer sites and transcription factor binding sites, respectively, in the bioinformatic analyses. The haplotype-rs5046T, rs5049A, rs11568020G, rs3789679C, rs2478544C was susceptible for EH among the Hani minority.

CONCLUSION

Our findings suggested that the AGT polymorphisms have played a vital role in determining an individual's susceptibility to EH among the isolated population, which would be helpful for EH management in the remote mountainous region of Yunnan in China.

Angiotensinogen promoter polymorphisms predict low diffusing capacity in U.S. and Spanish IPF cohorts

BACKGROUND

Single nucleotide polymorphisms (SNPs) in angiotensinogen (AGT) at positions -20 and -6 are associated with increased severity and progression of various fibrotic diseases. Our earlier work demonstrated that the progression of idiopathic pulmonary fibrosis (IPF) was associated with the A-6 allele. This study examined the hypothesis that the homozygous CC genotype at -20 and the AA genotype at -6 would confer worse measures of pulmonary function (measured by pulmonary function tests) in IPF.

METHODS

Multiple logistic regression analysis was applied to a NIH Lung Tissue Research Consortium cohort and a Spanish cohort, while also adjusting for covariates to determine the effects of these SNPs on measures of pulmonary function.

RESULTS

Analysis demonstrated that the CC genotype at -20 was strongly associated with reduced diffusing capacity in males in both cohorts (p = 0.0028 for LTRC and p = 0.017 for the Spanish cohort). In females, the AA genotype was significantly associated with lower FVC (p = 0.0082) and V alv (p = 0.022). In males, the haplotype CA at -20 and -6 in AGT was also strongly associated with reduced diffusing capacity in both cohorts.

CONCLUSIONS

This study is the first to demonstrate an association of AGT polymorphisms (-20A > C and -6G > A) with lower measures of pulmonary function in IPF. It is also the first to relate the effect of gender in lung fibrosis with polymorphisms in AGT.

Association of aldosterone synthase (CYP11B2) gene -344T/C polymorphism with the risk of primary chronic glomerulonephritis in the Polish population

INTRODUCTION

We evaluate whether angiotensinogen AGT M235T (rs699), angiotensin-converting enzyme ACE (I/D) (rs4646994) and aldosterone synthase CYP11B2 -344C/T (rs1799998) polymorphisms can be genetic risk factors of chronic glomerulonephritis (GN) in the Polish population.

MATERIALS AND METHODS

The study was conducted in 140 patients with primary chronic GN: mesangial proliferative GN (MesPGN) (n = 49), IgA nephropathy (IgAN) (n = 31), membranous nephropathy (MN) (n = 27), focal segmental glomerulosclerosis (FSGS) (n = 25), membranoproliferative GN (MPGN) (n = 4), and minimal change disease (MCD) (n = 4), and controls (n = 187). Genotypes were determined by HRM curve analysis for AGT M235T, by PCR and agarose gel separation for ACE (I/D), and by PCR-RFLP for CYP11B2 -344C/T.

RESULTS

We found a significant association of the CYP11B2 -344C/T polymorphism in the recessive model with all subtypes of GN (OR = 1.925 (95% CI = 1.152-3.219, p = 0.0118, p(corr) = 0.0354)). We also observed that the CYP11B2 -344C/T polymorphism in the recessive model may also be an independent significant risk factor of IgAN (OR = 2.743 (95% CI = 1.219-6.172, p = 0.0122, p(corr) = 0.0366)), FSGS (OR = 2.895 (95% CI = 1.200-6.985, p = 0.0145, p(corr) = 0.0435)), and all proliferative GNs (MesPGN, IgAN, MPGN) (OR = 2.171 (95% CI = 1.211-3.894, p = 0.0084, p(corr) = 0.0252)).

CONCLUSION

Our results suggest that the CYP11B2 -344C/T polymorphism might be an independent risk factor of IgAN, FSGS and all proliferative chronic GNs.

Allele-specific expression of angiotensinogen in human subcutaneous adipose tissue

The angiotensinogen gene is genetically linked with hypertension, but the mechanistic basis for association of sequence variants in the promoter and coding region of the gene remains unclear. An E-box at position -20 has been hypothesized to control the level of angiotensinogen expression, but its mechanistic importance for angiotensinogen expression in human tissues is uncertain. We developed an allele-specific polymerase chain reaction-based assay to distinguish between angiotensinogen mRNA derived from variants at the -20 position (rs5050) in the angiotensinogen promoter in adipose tissues obtained during surgery. The assay takes advantage of linkage disequilibrium between the rs5050 (located in the promoter) and rs4762 (located in the coding region) single nucleotide polymorphisms. This strategy allowed us to assess the level of allele-specific expression in A-20C heterozygous subjects comparing the relative proportion of each allele with the total, thus eliminating the problem of variability in the level of total angiotensinogen mRNA among subjects. We show that angiotensinogen mRNA derived from the -20C allele is expressed significantly higher than that derived from the -20A allele in subcutaneous adipose tissue, and increased expression correlates with enriched chromatin binding of upstream stimulatory factor-2 to the -20C E-box compared with -20A. This may be depot selective because we were unable to detect these differences in omental adipose. This provides the first data directly comparing expression of angiotensinogen mRNA and differential transcription factor binding derived from 2 variant alleles in human tissue where the ratio of expression of one allele to another can be accurately determined.

A candidate gene approach to genetic prognostic factors of IgA nephropathy--a result of Polymorphism REsearch to DIstinguish genetic factors Contributing To progression of IgA Nephropathy (PREDICT-IgAN)

BACKGROUND

Renal prognosis of IgA nephropathy (IgAN) is affected by environmental and genetic factors. Other studies demonstrated that some atherosclerotic disease-related genes were significantly associated with renal prognosis.

METHODS

The Polymorphism REsearch to DIstinguish genetic factors Contributing To progression of IgAN (PREDICT-IgAN) was a multicentre retrospective observational study to investigate associations between progression of IgAN (a 50% increase of serum creatinine level and slope of eGFR) and a hundred atherosclerotic disease-related gene polymorphisms, mainly single nucleotide polymorphisms (SNPs) in 320 IgAN patients who had more than a normal range of urinary protein (> or =0.25 g/day) at diagnosis.

RESULTS

During 8.3 +/- 4.2 years of a follow-up period, 83 patients (25.9%) developed progression. In log-rank tests, glycoprotein Ia GPIa C807T and G873A and intercellular adhesion molecule-1 ICAM-1 A1548G (K469E) were found to be significantly associated with progression even after adjustment for multiple comparisons by the method of Bonferroni (adjusted P = 0.0174, 0.0176 and 0.0430, respectively). In a multivariate Cox proportional-hazards model, GPIa 807TT (873CC) [versus 807TT, adjusted hazard ratio 2.05 (95% confidence interval 1.13-3.71)] and ICAM-1 1548GG [versus 1548AA, 2.55 (1.40-4.65)] were identified as independent genetic predictors of progression, along with conventional clinical prognostic factors such as eGFR, urinary protein and use of antihypertensives at diagnosis.

CONCLUSIONS

PREDICT-IgAN distinguished GPIa C807T/ G873A and ICAM-1 A1548G from multiple athero- sclerotic disease-related gene polymorphisms by their predictive indicator for progression of IgAN.

Genetic polymorphisms and the risk of accelerated renal function decline in women

Background

Reduced glomerular filtration rate is an important predictor of cardiovascular disease and death. Genetic polymorphisms, particularly in genes involved in the renin-angiotensin system (RAS), may influence the rate of renal function decline.

Methodology/Principal Findings

We examined the relation between specific single nucleotide polymorphisms (SNPs), including those in the RAS, apolipoprotein E and alpha-adducin, and renal function decline assessed by estimated glomerular filtration rate (eGFR) over an 11-year period in 2578 Caucasian participants of the Nurses' Health Study. Logistic regression was used to examine the associations between genotype and risk of eGFR decline of ≥25%.

Results

After 11 years between creatinine measurements, the eGFR declined by ≥25% in 423 of 2578 (16%) women. The angiotensinogen (AGT) A-20C polymorphism was associated with a higher risk of renal function decline when two risk alleles were present than if one or no alleles were present (CC vs AA and AC) OR 1.83 (95% CI 1.02–3.26; p = 0.04). The angiotensin II type 1 receptor (AT₁R) A1166C polymorphism was marginally associated with a higher risk of renal function decline when two risk alleles were present (CC vs AA, OR = 1.41; 95% CI 0.98–2.01; p = 0.06). The alpha-adducin G460W polymorphism was associated with a lower risk of renal function decline when any number of risk alleles were present (WG vs GG, OR = 0.78, 95% CI 0.61–0.99, p = 0.04; WW vs GG, OR = 0.46; 95% CI 0.20–1.07, p = 0.07). Linear regression analysis with change in eGFR as the outcome showed a larger decline of 3.5 (95% CI 0.5 to 6.4, p = 0.02) ml/min/1.73 m² in AGT A-20C CC homozygotes. No other polymorphisms were significantly associated with renal function decline or absolute change in eGFR over the study period.

Conclusions

Genetic variants in the angiotensinogen, angiotensin II type 1 receptor and alpha-adducin genes may contribute to loss of renal function in the general female Caucasian population.

Association of angiotensin II type 2 receptor gene A1818T polymorphism with progression of immunoglobulin A nephropathy in Korean patients

We determined the relationship between the progression of immunoglobulin A nephropathy (IgAN) and the A1818T polymorphism in intron 2 of Angiotensin II type 2 receptor (AT2R) gene, which might play protective roles in the pathogenesis of IgAN. Patients with biopsy-proven IgAN were recruited from the registry of the Progressive REnal disease and Medical Informatics and gEnomics Research (PREMIER) which was sponsored by the Korean Society of Nephrology. A1818T polymorphism of AT2R gene was analyzed with PCR-RFLP method and the association with the progression of IgAN, which was defined as over 50% increase in baseline serum creatinine level, was analyzed with survival analysis. Among the 480 patients followed for more than 10 months, the group without T allele had significantly higher rates of progression of IgAN than the group with T allele (11.4% vs. 3.9%, p=0.024), although there were no significant differences in the baseline variables such as initial serum creatinine level, the degree of proteinuria, and blood pressure. In the Cox's proportional hazard model, the hazard ratio of disease progression in the patients with T allele was 0.221 (95% confidence interval for Exp(B): 0.052-0.940, p=0.041) compared to that of without T allele. In conclusion, A1818T polymorphism of AT2R gene was associated with the progression of IgAN.

Toll-like receptor 9 affects severity of IgA nephropathy

Environmental pathogens are suspected to aggravate renal injury in IgA nephropathy (IgAN), but neither underlying mechanisms nor specific exogenous antigens have been identified. In this study, a genome-wide scan of ddY mice, which spontaneously develop IgAN, was performed, and myeloid differentiation factor 88 (MyD88) was identified as a candidate gene for progression of renal injury (chi(2) = 21.103, P = 0.00017). For evaluation of the potential influence of environmental pathogens on progression of renal injury, ddY mice were housed in either conventional or specific pathogen-free conditions. Expression of genes encoding toll-like receptors (TLR) and the signaling molecule MyD88 were quantified by real-time reverse transcription-PCR in splenocytes. Although the housing conditions did not affect the prevalence of IgAN, the severity of renal injuries was higher in the conventionally housed group. Mice that had IgAN and were housed in conventional conditions had higher levels of TLR9 and MyD88 transcripts than mice that had IgAN and were housed in specific pathogen-free conditions. Furthermore, nasal challenge with CpG-oligodeoxynucleotides, which are ligands for TLR9, aggravated renal injury, led to strong Th1 polarization, and increased serum and mesangial IgA. For investigation of whether these results may be generalizable to humans, single-nucleotide polymorphisms in the TLR9 and MyD88 genes were analyzed in two cohorts of patients with IgAN; an association was observed between TLR9 polymorphisms and disease progression. In summary, these findings suggest that activation of the TLR9/MyD88 pathway by common antigens may affect the severity of IgAN.

Impact of selectin gene polymorphisms on rapid progression to end-stage renal disease in patients with IgA nephropathy

OBJECTIVE

It is evident that leukocyte infiltration plays an important role in the pathogenesis of IgA nephropathy (IgAN). Selectin is one of the key adhesion molecules involved in leukocyte infiltration. Recent studies demonstrated a significant association between the selectin gene polymorphisms and susceptibility to IgAN. However, the impact of selectin gene polymorphisms on the progression to end-stage renal disease (ESRD) has not been studied.

PATIENTS AND METHODS

To evaluate the influence of the selectin gene polymorphisms on the progression of IgAN, we designed specific primers for PCR genotyping and analyzed the association of selectin gene polymorphisms with the declining rate in renal function to its ESRD.

RESULTS

A total of 61 hemodialysis patients were enrolled in the study. The mean age at renal biopsy was 33.0+/-13.3 years old, and the mean age at the start of hemodialysis was 41.2+/-13.8 years old. The mean interval between the time points of renal biopsy and the start of hemodialysis was 8.2+/-6.5 years (ranging from 0 to 33 years). The interval was significantly longer in IgAN patients with a homoallele of C in C1402T, C1402/C1402, of the E-selectin gene, or a homoallele of C in C712T, C712/C712, of the L-selectin gene compared to others. The haplotype, which is a combination of C1402/C1402 and C712/C712, is able to distinguish the group that is at least a better prognosis than the severest prognostic one.

CONCLUSION

This study provides a possible association between the selectin gene polymorphisms and the rapid progression to ESRD in IgAN patients.

Genetics of common progressive renal disease

Familial aggregation of common chronic kidney diseases provides a unique opportunity to investigate the susceptibility genetic and environmental factors. In the past decade, a wealth of new data has become available concerning the genetic susceptibility leading to numerous nephropathies. Knowledge of the genetic components allows better understanding of initiation and progression of these chronic kidney diseases. In addition, one can envision that identification of genetically susceptible individuals might lead to earlier diagnosis and potential reversal of the current epidemic of end-stage renal disease. The goal of the current discussion is to review various issues pertaining to the role of genetic factors in common chronic kidney diseases, as exemplified by two leading causes of end-stage renal diseases worldwide, nephropathy of type 2 diabetes and IgA nephropathy. The genetic and environmental interplay leading to the nephropathies is highlighted.

Polymorphism of renin-angiotensin system genes in IgA nephropathy

BACKGROUND AND AIMS

Individuals are prone to disease because of certain disease-susceptible genes. The angiotensin I-converting enzyme (ACE) gene insertion/deletion (I/D), the angiotensinogen (AGT) gene, M235T, and the angiotensin II type 1 receptor (ATR) gene, A1166C, polymorphisms have been associated with IgA nephropathy (IgAN) and its progression. Several studies on Caucasians and Japanese patients have reported contradictory results. We determined these polymorphisms in 118 Chinese patients with IgAN and 94 healthy Chinese subjects to assess their clinical impact.

METHODS

Genotyping was performed with DNA isolated from peripheral leucocytes, polymerase chain reaction amplification of the polymorphic sequence, restriction enzymes digestion, and separation and identification of DNA fragments. Clinical data at renal biopsy and final status on renal function were determined from patients' records.

RESULTS

Comparing all IgAN patients with controls, AGT and ATR genotype distributions were similar, whereas there was a significant increase in the ACE DD genotype (P < 0.05). When comparing patients with end-stage renal failure (IgAN-ESRF) and those without (IgAN-nonESRF), there was no difference among the three gene polymorphisms. In contrast, there were significant differences in higher male prevalence (P < 0.05), increased serum creatinine at presentation (P < 0.05), more sclerosis (P < 0.01) and higher tubulointerstitial lesion score (P < 0.001) in the IgAN-ESRF group.

CONCLUSION

Among the ACE, AGT and ATR gene polymorphisms, only the DD genotype may predispose the individual to IgAN in the Chinese population. None are significant for prognosticating ESRF.

Natural history of idiopathic IgA nephropathy and factors predictive of disease outcome

Among the numerous studies published in the last 20 years that have calculated the actuarial renal survival and tried to individuate the prognostic role of the clinical and histologic features present at the onset of the disease or the time of biopsy, we chose to critically analyze the results of the most valid (23 studies). Actuarial renal survival at 10 years in adults was between 80% and 85% in most of the European, Asian, and Australian studies, but was lower than this in studies from the United States and exceeded 90% in the few studies on children. Concordance existed in this selected literature on the fact that impairment of renal function, severe proteinuria, and arterial hypertension are the strongest and more reliable clinical predictors of an unfavorable outcome. Extent of proteinuria during follow up was an even stronger predictor. In adult patients, a high score of the glomerular and tubulointerstitial lesions predicted a more rapid progression. When the single lesions were analyzed separately, glomerular sclerosis and interstitial fibrosis appeared to be the strongest, most reliable predictors of unfavorable prognosis. More controversial was the role of crescents and capsular adhesions.

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers for IgA nephropathy

The lengthy course of IgA nephropathy and the possibility of good outcomes without therapy suggest nontoxic therapies such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs.) Among patients with IgA nephropathy, both ACE inhibitors and ARBs reduce the transglomerular passage of large, but not small, molecules, reducing proteinuria. The antiproteinuric effects of ACE inhibitors and ARBs are probably equivalent. Dual ACE inhibitor-ARB therapy reduces proteinuria by 54% to 73% and is more effective than either agent alone. To determine whether ACE inhibitors or ARBs preserve renal function long-term, one must rely on trials studying nondiabetic, proteinuric renal diseases rather than on trials specific to IgA nephropathy. Among this group of patients, several randomized, controlled trials, including the AIPRI trial, the REIN trial, and a metaanalysis of 11 randomized, controlled trials, have established clearly that the ACE inhibitors preserve renal function. There is no reason to believe that this information is not applicable to IgA nephropathy. The COOPERATE trial, in which 50% of the subjects had IgA nephropathy, established that ACE inhibitors and ARBs preserve renal function equally, and that dual ACE inhibitor-ARB therapy preserves renal function more effectively than either therapy alone. These data suggest that most individuals with proteinuric renal diseases, including IgA nephropathy, should be treated with ACE inhibitors and ARBs, ideally in combination. Polymorphisms of the angiotensinogen gene, the ACE gene, and the angiotensin II type I receptor gene have, so far, failed to predict either susceptibility to or progression of IgA nephropathy. However, the D allele of the ID polymorphism, particularly the DD genotype, could predict a favorable response to renin-angiotensin blockade.

A-20C angiotensinogen gene polymorphism and proteinuria in childhood IgA nephropathy

We have previously reported that the TT genotype of the angiotensinogen gene and the ID/DD genotype of the angiotensin-converting enzyme gene are associated with increased severity of proteinuria in IgA nephropathy in Japanese children. Recently it was reported that polymorphism at -20 from adenine to cytosine in the angiotensinogen gene, increasing the level of this transcript, was associated with the progression of renal dysfunction in adult IgA nephropathy. We therefore investigated whether this polymorphism is involved in IgA nephropathy in Japanese children. We identified this polymorphism in 105 children with IgA nephropathy and 119 healthy adults using polymerase chain reaction/restriction fragment length polymorphism analysis. At the time of biopsy, all patients had normal blood pressure and renal function. There were no differences in the genotypes and allele frequencies of this polymorphism between patients with IgA nephropathy and controls. The number of patients with the AC/CC genotype showing heavy proteinuria (>or=1.0 g/day per m(2) body surface area) at biopsy was significantly higher than that with the AA genotype ( P=0.039, chi-squared test). The AC/CC genotype of this polymorphism may be associated with an increased severity of proteinuria, suggesting that this polymorphism may play a significant role in the progression of IgA nephropathy in Japanese children.

Angiotensinogen gene variation and renoprotective efficacy of renin-angiotensin system blockade in IgA nephropathy

BACKGROUND

Blockade of the renin-angiotensin system (RAS) is well documented to be renoprotective; however, not all patients with glomerulonephritis respond well to this therapy. The interindividual variation in response to the RAS blockade may be in part genetically determined, whereas the results have been controversial.

METHODS

We investigated whether the therapeutic efficacy of angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin receptor blocker on renal prognosis is modified by the angiotensinogen gene (AGT) polymorphism in immunoglobulin A nephropathy (IgAN). In total, 259 patients with histologically proven IgAN were analyzed for clinical manifestations, renal survival, and their associations with AGT A(-20)C and M235T.

RESULTS

The renal prognosis of 110 patients, who received ACE inhibitors/angiotensin receptor blocker during their clinical course, was significantly better than those without ACE inhibitors/angiotensin receptor blockers despite higher blood pressures and heavier proteinuria. The Cox proportional hazards regression model showed an increased hazard ratio (HR) for urinary protein (more than 1.0 g/day) of 3.346 (P = 0.0001), hypertension of 1.949 (P = 0.01), deteriorated renal function of 3.040 (P < 0.0001), no ACE inhibitor/angiotensin receptor blocker administration of 2.725 (P = 0.0004), and the T235 and C(-20) haplotype of 1.608 (P = 0.0322). Only in patients carrying at least one M235 and A(-20) haplotype did the administration of ACE inhibitors/angiotensin receptor blockers have no significant effect on the prognosis of renal function (Kaplan-Meier, log rank test, chi2 = 0.700; P = 0.4028), whereas it was significant in patients who had other haplotypes of AGT (chi2 = 11.805; P = 0.0006).

CONCLUSION

This study provides evidence that the M235T and A(-20)C genotype of AGT can influence the therapeutic efficacy of a RAS blockade on the renal survival in IgAN.

The efficacy of tonsillectomy on long-term renal survival in patients with IgA nephropathy

BACKGROUND

Little information has been available until now about the clinical efficacy of tonsillectomy on long-term renal survival of patients with idiopathic immunoglobulin A nephropathy (IgAN).

METHODS

To investigate the effect of tonsillectomy on long-term renal survival, we reviewed the clinical course of 118 patients with idiopathic biopsy-diagnosed IgAN from 1973 to 1980. Of those, 48 patients received tonsillectomy and 70 patients did not. The starting point of observation was defined as the time of the diagnostic renal biopsy, and the end point as when requiring the first dialysis. Up to 2001, the mean observation time was 192.9 +/- 74.8 months (48-326 months). Renal survival and impact of covariates were evaluated by Kaplan-Meier analysis and Cox proportional hazards regression model.

RESULTS

Age, gender, amount of urinary protein excretion, serum creatinine, serum IgA, blood pressure, and histopathologic findings at the time of renal biopsy and treatments during the observation period were not significantly different between patients with and without tonsillectomy. Five (10.4%) of the patients with tonsillectomy and 18 (25.7%) of the patients without tonsillectomy finally required dialysis therapy (chi-square test, P = 0.0393). By Kaplan-Meier analysis, renal survival rates were 89.6% and 63.7% at 240 months in the patients with and without tonsillectomy, respectively, and were significantly different (log-rank test, P = 0.0329). In the multivariate Cox regression model, tonsillectomy (hazard ratio, 0.22; 95% CI, 0.06 to 0.76; P = 0.0164) had a significant effect on renal outcome.

CONCLUSION

These results indicate that tonsillectomy has a favorable effect on long-term renal survival in patients with IgAN.