Upstream stimulatory factor is required for human angiotensinogen expression and differential regulation by the A-20C polymorphism

Age-Related Expression of Human AT1R Variants and Associated Renal Dysfunction in Transgenic Mice

BACKGROUND

The contribution of single nucleotide polymorphisms in transcriptional regulation of the human angiotensin receptor type I (hAT1R) gene in age-related chronic pathologies such as hypertension and associated renal disorders is not well known. The hAT1R gene has single nucleotide polymorphisms in its promoter that forms 2 haplotypes (Hap), Hap-I and Hap-II. Hap-I of AT1R gene is associated with hypertension in Caucasians. We have hypothesized here that age will alter the transcriptional environment of the cell and will regulate the expression of hAT1R gene in a haplotype-dependent manner. This could likely make subjects with Hap-I increasingly susceptible to age-associated, AT1R-mediated complications.

METHOD

We generated transgenic (TG) mice with Hap-I and Hap-II. Adults (10-12 weeks) and aged (20-24 months) TG male mice containing either Hap-I or Hap-II were divided into 4 groups to study (i) the age-associated and haplotype-specific transcriptional regulation of hAT1R gene and (ii) their physiological relevance.

RESULTS

In aged animals, TG mice with Hap-I show increased expression of hAT1R and higher blood pressure (BP); suppression of antioxidant defenses (hemoxygenase, superoxide dismutase) and antiaging molecules (ATRAP, Klotho, Sirt3); increased expression of pro-inflammatory markers (IL-6, TNFα, CRP, NOX1); and increased insulin resistance. In vivo ChIP assay shows stronger binding of transcription factor USF2 to the chromatin of Hap-I mice.

CONCLUSION

Our results suggest that in aged animals, as compared with Hap-II, the TG mice with Hap-I overexpress hAT1R gene due to the stronger transcriptional activity, thus resulting in an increase in their BP and associated renal disorders.

Metabolic Syndrome Induces Over Expression of the Human AT1R: A Haplotype-Dependent Effect With Implications on Cardio-Renal Function

BACKGROUND

The transcriptional regulation of the human angiotensin receptor subtype 1 (AT1R) gene in pathophysiologies, like the metabolic syndrome, is poorly understood. The human AT1R gene has polymorphisms in its promoter that can be arranged in 2 haplotypes. Variants -810T, -713T, -214A, and -153A always occur together (Hap-I) and variants -810A, -713G, -214C, and -153G form Hap-II. We have hypothesized that high fat diet will alter cellular transcriptional milieu and increase hAT1R gene expression in a haplotype-dependent manner. This will set up an AT1R-mediated feed-forward loop promoting inflammation, oxidative stress, and hypertension in Hap-I mice.

METHOD

Since Hap-I of the human AT1R gene is associated with hypertension in Caucasians, we generated transgenic (TG) mice with Hap-I and Hap-II and studied the physiological significance of high fat diet (HFD) on haplotype specific gene expression. Animals were fed with HFD for 20 weeks followed by blood pressure (BP) analysis and collection of their tissues for molecular and biochemical studies.

RESULTS

After HFD treatment, as compared to Hap-II, TG mice with Hap-I show increased expression of hAT1R gene and higher BP; suppression of antioxidant defenses (HO1, SOD1) and increased expression of IL-6, TNFα, IL-1β, NOX1. In vivo ChIP assay has shown that transcription factors CEBPβ, STAT3, and USF bind more strongly to the chromatin obtained from Hap-I TG mice.

CONCLUSIONS

Taken together, our results suggest, that after HFD treatment, as compared to Hap-II, the TG mice with Hap-I overexpress the AT1R gene due to the stronger transcriptional activity, thus resulting in an increase in their BP.

Potential mechanisms of hypothalamic renin-angiotensin system activation by leptin and DOCA-salt for the control of resting metabolism

The renin-angiotensin system (RAS), originally described as a circulating hormone system, is an enzymatic cascade in which the final vasoactive peptide angiotensin II (ANG) regulates cardiovascular, hydromineral, and metabolic functions. The RAS is also synthesized locally in a number of tissues including the brain, where it can act in a paracrine fashion to regulate blood pressure, thirst, fluid balance, and resting energy expenditure/resting metabolic rate (RMR). Recent studies demonstrate that ANG AT_1A receptors (Agtr1a) specifically in agouti-related peptide (AgRP) neurons of the arcuate nucleus (ARC) coordinate autonomic and energy expenditure responses to various stimuli including deoxycorticosterone acetate (DOCA)-salt, high-fat feeding, and leptin. It remains unclear, however, how these disparate stimuli converge upon and activate this specific population of AT_1A receptors in AgRP neurons. We hypothesize that these stimuli may act to stimulate local expression of the angiotensinogen (AGT) precursor for ANG, or the expression of AT_1A receptors, and thereby local activity of the RAS within the (ARC). Here we review mechanisms that may control AGT and AT_1A expression within the central nervous system, with a particular focus on mechanisms activated by steroids, dietary fat, and leptin.

Association of angiotensinogen gene SNPs and haplotypes with risk of hypertension in eastern Indian population

BACKGROUND

Angiotensinogen (AGT) enzyme comprises a vital module of RAAS system that effectively controls the blood pressure and related cardiovascular functions. Ample association studies have reported the importance of AGT variants in cardiovascular and non-cardiovascular adversities. But lately, owing to the complexity of the many anomalies, the haplotype based examination of genetic variation that facilitates the identification of polymorphic sites which are located in the vicinity of the causative polymorphic site, gets greater appreciation.

METHODS

In the present study, we have done genotype and haplotype analysis of AGT gene in reference to hypertension to confirm the association of the two in an Indian population. To accomplish this, we performed candidate SNPs analysis and construct possible haplotypes across the AGT promoter and gene region in 414 subjects (256 Hypertensive cases and 158 controls).

RESULTS

We found four SNPs (rs11568020: A-152G and rs5050: A-20C in promoter; rs4762 and rs699 in exon2) and 3 haplotypes (H4, H7 and H8) that showed a stronger positive association with hypertension. The haplotype H2 was showing protective association with hypertension.

CONCLUSION

The results of the present study confirmed and reestablished the role of AGT gene variants and their haplotypes in the causation of hypertension in Indian population and showed that haplotypes can provide stronger evidence of association.

Histone deacetylase inhibitor apicidin increases expression of the α-secretase ADAM10 through transcription factor USF1-mediated mechanisms

ADAM10 (a disintegrin and metalloproteinase domain-containing protein 10) is the α-secretase that is involved in APP (β-amyloid precursor protein) processing. Enhancement of the nonamyloidogenic APP pathway by ADAM10 provides therapeutic potential for Alzheimer's disease (AD). By using high-throughput screening that targeted ADAM10, we determined that apicidin-an inhibitor of HDACs (histone deacetylases)-significantly increased mRNA and protein levels of ADAM10 in SH-SY5Y cells. A luciferase assay revealed that the nucleotides -444 to -300 in the ADAM10 promoter were sufficient to mediate this effect. In addition, knockdown of USF1 (upstream transcription factor 1) and HDAC2/3 prevented apicidin regulation of ADAM10. Moreover, USF1 acetylation was increased by apicidin, which enhanced the association of USF1 with HDAC2/3 and with the ADAM10 promoter. We further found that apicidin did not affect the phosphorylation of ERK or USF1; however, ERK inhibitor U0126 blocked the effect of apicidin on ADAM10. Finally, apicidin increased the level of α-site C-terminal fragment from APP and reduced the production of β-amyloid peptide 1-42. Collectively, our study provides evidence that ADAM10 expression can be regulated by HDAC2/3 inhibitor apicidin via USF1-dependent mechanisms in which ERK signaling plays an important role. Thus, HDAC regulation of ADAM10 might shed new light on the understanding of AD pathology.-Hu, X.-T., Zhu, B.-L., Zhao, L.-G., Wang, J.-W., Liu, L., Lai, Y.-J., He, L., Deng, X.-J., Chen, G.-J. Histone deacetylase inhibitor apicidin increases expression of the α-secretase ADAM10 through transcription factor USF1-mediated mechanisms.

Dynamic regulation of the angiotensinogen gene by DNA methylation, which is influenced by various stimuli experienced in daily life

Angiotensinogen (AGT) has a central role in maintaining blood pressure and fluid balance. DNA methylation is an epigenomic modification maintaining a steady pattern in somatic cells. Herein we summarize the link between AGT regulation and DNA methylation. DNA methylation negatively regulates AGT expression and dynamically changes in response to continuous AGT promoter stimulation. High-salt intake and excess circulating aldosterone cause DNA demethylation around the CCAAT enhancer-binding protein-binding sites, thereby converting the phenotype of AGT expression from an inactive to an active state in visceral adipose tissue. Salt-dependent hypertension may be partially affected by increased adipose AGT expression. Because angiotensin II is a well-established aldosterone-releasing hormone, stimulation of adipose AGT by aldosterone creates a positive feedback loop. This effect is pathologically associated with obesity-related hypertension, although it would be physiologically favorable for humans to efficiently retain their body fluid. The clear difference in DNA demethylation patterns between aldosterone and cortisol indicates a difference in the respective target DNA-binding sites between mineralocorticoid and glucocorticoid receptors in the AGT promoter. Stimulation-induced interactions between transcription factors and target DNA-binding sites trigger DNA demethylation. Dynamic changes in DNA methylation occur in relaxed chromatin regions both where transcription factors actively interact and where transcription is initiated. In contrast to rapid histone modifications, DNA demethylation and remethylation will progress relatively slowly over days or years. A wide variety of stimuli in daily life will continue to slowly and dynamically change DNA methylation patterns throughout life. Wise choices of beneficial stimuli will improve health.

Renin-angiotensin-aldosterone system related gene polymorphisms and urinary total arsenic is related to chronic kidney disease

A recent study demonstrated that an increased risk of chronic kidney disease (CKD) was associated with high urinary total arsenic levels. However, whether genomic instability is related to CKD remains unclear. An association between CKD and genetic polymorphisms of regulation enzymes of the renin-angiotensin-aldosterone system (RAAS), such as angiotensin-converting enzyme (ACE), angiotensinogen (AGT), angiotensin II type I receptor (AT1R), and aldosterone synthase (CYP11B2) has not been shown. The aim of the present study was to investigate the relationship between arsenic, genetic polymorphisms of RAAS enzymes and CKD. A total of 233 patients and 449 age- and gender-matched controls were recruited from the Taipei Medical University Hospital, Taipei Municipal Wan Fang Hospital and the Shin Kong Wu Ho-Su Memorial Hospital. Concentrations of urinary arsenic were determined by a high-performance liquid chromatography-linked hydride generator, and atomic absorption spectrometry. Polymorphisms of ACE(I/D), AGT(A[-20]C), (T174M), (M235T), AT1R(A1166C) and CYP11B2(C[-344]T) were examined by polymerase chain reaction and restriction fragment length polymorphism. Subjects carrying the CYP11B2 TT genotype had a higher odds ratio (OR), 1.39 (0.96-2.01), of CKD; while those with the AGT(A[-20]C) CC genotype had an inverse OR of CKD (0.20 (0.05-0.81)), and a high-risk genotype was defined as A/A+A/C for AGT(A[-20C]) and T/T for CYP11B2(C[-344]T). The trend test showed a higher OR for CKD in patients who had either high urinary total arsenic levels or carried the high-risk genotype, or both, compared to patients with low urinary total arsenic levels, who carried the low-risk genotype, and could also be affected by the hypertension or diabetes status.

Analysis of genes causing hypertension and stroke in spontaneously hypertensive rats: gene expression profiles in the brain

Spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) are frequently used as rat models not only of essential hypertension and stroke, but also of attention-deficit hyperactivity disorder (ADHD). Normotensive Wistar-Kyoto rats (WKY) are used as the control rats in these cases. An increasing number of studies has demonstrated the critical role of the central nervous system in the development and maintenance of hypertension. In a previous study, we analyzed the gene expression profiles in the adrenal glands of SHR. Thus, in this study, we analyzed gene expression profiles in the brains of SHR in order to identify the genes responsible for causing hypertension and stroke, as well as those involved in ADHD. Using genome-wide microarray technology, we examined the gene expression profiles in the brains of 3 rat strains (SHR, SHRSP and WKY) when the rats were 3 and 6 weeks of age, a period in which the rats are considered to be in a pre-hypertensive state. Gene expression profiles in the brain were compared between SHR and WKY, and between SHRSP and SHR. A total of 179 genes showing a >4- or <-4-fold change in expression were isolated, and candidate genes were selected using two different web tools: the first tool was the Database for Annotation, Visualization and Integrated Discovery (DAVID), which was used to search for significantly enriched genes, and categorized them using Gene Ontology (GO) terms, and the second was the network explorer of Ingenuity Pathway Analysis (IPA), which was used to search for interaction networks among SHR- and SHRSP-specific genes. The IPA of SHR-specific genes revealed that prostaglandin E receptor 4 (Ptger4) is one of the candidate genes responsible for causing hypertension in SHR, and that albumin (Alb) and chymase 1 (Cma1) are also responsible for causing hypertension in SHR in the presence of angiotensinogen (Agt). Similar analyses of SHRSP-specific genes revealed that the angiotensin II receptor-associated gene (Agtrap) interacts with the FBJ osteosarcoma oncogene (Fos), and with the angiotensin II receptor type-1b (Agtr1b). As Agtrap and Agtr1b not only participate in the 'uptake of norepinephrine' and 'blood pressure', but also in the 'behavior' of SHRSP at 6 weeks of age, our data demonstrate a close association between hypertension and ADHD.

A haplotype of angiotensin receptor type 1 associated with human hypertension increases blood pressure in transgenic mice

The renin-angiotensin system plays an important role in the regulation of blood pressure via angiotensin II and the angiotensin II receptor type 1 (AT1R). Human AT1R gene promoter has four SNPs: T/A at -777, T/G at -680, A/C at -214, and A/G at -119, that are in linkage disequilibrium. Variants -777T, -680T, -214A, and -119A almost always occur together (named haplotype I), and variants -777A, -680G, -214C, and -119G almost always occur together (named haplotype II) in Caucasian subjects. Genomic DNA analyses, from 388 normotensive and 374 hypertensive subjects, link haplotype I of the human AT1R (hAT1R) gene with hypertension in Caucasians (p = 0.004, χ(2) = 8.46). Our results show increased basal promoter activity of the hAT1R gene in cells (H295R and A7r5) transfected with reporter construct containing haplotype I. We also show increased binding of the transcription factor, USF2, to oligonucleotide containing nucleoside -214A as opposed to -214C. Recombineering of a 166-kb bacterial artificial chromosome containing 68 kb of the 5'-flanking region, 45 kb of the coding sequence, and 53 kb of the 3'-flanking region of the hAT1R gene was employed to generate transgenic mice with either haplotype. We show that (a) hAT1R mRNA level is increased in the kidney and heart of transgenic mice containing haplotype I as compared with haplotype II; (b) USF2 binds more strongly to the chromatin obtained from the kidney of transgenic mice containing haplotype I as compared with haplotype II; and (c) blood pressure and oxidative stress are increased in transgenic mice containing haplotype I as compared with haplotype II.

Dynamic CCAAT/enhancer binding protein-associated changes of DNA methylation in the angiotensinogen gene

DNA methylation patterns are maintained in adult somatic cells. Recent findings, however, suggest that all methylation patterns are not preserved. We demonstrate that stimulatory signals can change the DNA methylation status at a CCAAT/enhancer binding protein (CEBP) binding site and a transcription start site and activate expression of the angiotensinogen gene (AGT). A CEBP binding site in the human AGT promoter was hypomethylated in tissues with high expression of AGT, but not in those with low expression. The transcriptional activity of AGT promoter sequences cloned into a reporter plasmid depended on DNA methylation. In cultured human cells, interleukin 6 stimulation caused DNA demethylation around a CEBP binding site and a transcription start site; demethylation was accompanied by increased CEBP-β recruitment and chromatin accessibility of the AGT promoter. DNA methylation activity decreased in the nucleus. Excess circulating aldosterone upregulated AGT expression and was accompanied by DNA hypomethylation around a CEBP binding site and a transcription start site in human visceral adipose tissue. High salt intake led to upregulation of Agt expression, DNA hypomethylation around 2 CEBP binding sites and a transcription start site, and decreased DNA methylation activity in rat visceral adipose tissue. Taken together, CEBP binding initiates chromatin relaxation and transcription, which are followed by DNA demethylation around a CEBP binding site and a transcription start site in the AGT promoter. Decreased DNA methylation activity in the nucleus may play a role in DNA demethylation. DNA demethylation switches the phenotype of AGT expression from an inactive to an active state.

Upstream stimulatory factors 1 and 2 mediate the transcription of angiotensin II binding and inhibitory protein

The angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP/Agtrap) promotes constitutive internalization of the AT1R so as to specifically inhibit the pathological activation of its downstream signaling yet preserve the base-line physiological signaling activity of the AT1R. Thus, tissue-specific regulation of Agtrap expression is relevant to the pathophysiology of cardiovascular and renal disease. However, the regulatory mechanism of Agtrap gene expression has not yet been fully elucidated. In this study, we show that the proximal promoter region from −150 to +72 of the mouse Agtrap promoter, which contains the X-box, E-box, and GC-box consensus motifs, is able to elicit substantial transcription of the Agtrap gene. Among these binding motifs, we showed that the E-box specifically binds upstream stimulatory factor (Usf) 1 and Usf2, which are known E-box-binding transcription factors. It is indicated that the E-box-Usf1/Usf2 binding regulates Agtrap expression because of the following: 1) mutation of the E-box to prevent Usf1/Usf2 binding reduces Agtrap promoter activity; 2) knockdown of Usf1 or Usf2 affects both endogenous Agtrap mRNA and Agtrap protein expression, and 3) the decrease in Agtrap mRNA expression in the afflicted kidney by unilateral ureteral obstruction is accompanied by changes in Usf1 and Usf2 mRNA. Furthermore, the results of siRNA transfection in mouse distal convoluted tubule cells and those of unilateral ureteral obstruction in the afflicted mouse kidney suggest that Usf1 decreases but Usf2 increases the Agtrap gene expression by binding to the E-box. The results also demonstrate a functional E-box-USF1/USF2 interaction in the human AGTRAP promoter, thereby suggesting that a strategy of modulating the E-box-USF1/USF2 binding has novel therapeutic potential.

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.

Gene trapping uncovers sex-specific mechanisms for upstream stimulatory factors 1 and 2 in angiotensinogen expression

A single-nucleotide polymorphism (C/A) located within an E-box at the -20 position of the human angiotensinogen (AGT) promoter may regulate transcriptional activation through differential recruitment of the transcription factors upstream stimulatory factor (USF) 1 and 2. To study the contribution of USF1 on AGT gene expression, mice carrying a (-20C) human AGT (hAGT) transgene were bred with mice harboring a USF1 gene trap allele designed to knock down USF1 expression. USF1 mRNA was reduced relative to controls in liver (9 ± 1%), perigenital adipose (16 ± 3%), kidney (17 ± 1%), and brain (34 ± 2%) in double-transgenic mice. This decrease was confirmed by electrophoretic mobility shift assay. Chromatin immunoprecipitation analyses revealed a decrease in USF1, with retention of USF2 binding at the hAGT promoter in the liver of male mice. hAGT expression was reduced in the liver and other tissues of female but not male mice. The decrease in endogenous AGT expression was insufficient to alter systolic blood pressure at baseline but caused reduced systolic blood pressure in female USF1 gene trap mice fed a high-fat diet. Treatment of USF1 knockdown males with intravenous adenoviral short hairpin RNA targeting USF2 resulted in reduced expression of USF1, USF2, and hAGT protein. Our data from chromatin immunoprecipitation assays suggests that this decrease in hAGT is attributed to decreased USF2 binding to the hAGT promoter. In conclusion, both USF1 and USF2 are essential for AGT transcriptional regulation, and distinct sex-specific and tissue-specific mechanisms are involved in the activities of these transcription factors in vivo.

Regulation of renin expression by the orphan nuclear receptors Nr2f2 and Nr2f6

Understanding the transcriptional mechanisms of renin expression is key to understanding the regulation of the renin-angiotensin system. We previously identified the nuclear receptors RAR/RXR and Nr2f6 (EAR2) as positive and negative transcriptional regulators of renin expression, respectively (Liu X, Huang X, Sigmund CD. Circ Res 92: 1033-1040, 2003). Both mediate their effects through a hormone response element (HRE) within the renin enhancer. Here, we determined whether another nuclear receptor, Nr2f2 (Coup-TFII, Arp-1), identified in a screen of proteins that bind the HRE, also regulates renin expression. Luciferase assays indicate that Nr2f2 negatively regulates the renin promoter more potently than Nr2f6. Gel-shift and chromatin immunoprecipitation (ChIP) indicate that Nr2f2 and Nr2f6 can bind directly to the renin enhancer through the HRE. Surprisingly, baseline expression of endogenous renin was not effected when Nr2f2 was knocked down in As4.1 cells, whereas knockdown of Nr2f6 increased renin expression twofold. Interestingly, however, knockdown of Nr2f2 augmented the induction of renin expression caused by retinoic acid. These data indicate that both Nr2f6 and Nr2f2 can negatively regulate the renin promoter, under baseline conditions and in response to physiological queues, respectively. Therefore, Nr2f2 may require an initiating signal that results in a change at the chromatin level or activation of another transcription factor to exert its effects. We conclude that both Nr2f2 and Nr2f6 negatively regulate renin promoter activity, but may do so by divergent mechanisms.

Role of the USF1 transcription factor in diabetic kidney disease

The predominant transcription factors regulating key genes in diabetic kidney disease have not been established. The transcription factor upstream stimulatory factor 1 (USF1) is an important regulator of glucose-mediated transforming growth factor (TGF)-β1 expression in mesangial cells; however, its role in the development of diabetic kidney disease has not been evaluated. In the present study, wild-type (WT; USF1 +/+), heterozygous (USF1 +/-), and homozygous (USF1 -/-) knockout mice were intercrossed with Akita mice (Ins2/Akita) to induce type 1 diabetes. Mice were studied up to 36 wk of age. The degree of hyperglycemia and kidney hypertrophy were similar in all groups of diabetic mice; however, the USF1 -/- diabetic mice had significantly less albuminuria and mesangial matrix expansion than the WT diabetic mice. TGF-β1 and renin gene expression and protein were substantially increased in the WT diabetic mice but not in USF1 -/- diabetic mice. The underlying pathway by which USF1 is regulated by high glucose was investigated in mesangial cell culture. High glucose inhibited AMP-activated protein kinase (AMPK) activity and increased USF1 nuclear translocation. Activation of AMPK with AICAR stimulated AMPK activity and reduced nuclear accumulation of USF1. We thus conclude that USF1 is a critical transcription factor regulating diabetic kidney disease and plays a critical role in albuminuria, mesangial matrix accumulation, and TGF-β1 and renin stimulation in diabetic kidney disease. AMPK activity may play a key role in high glucose-induced regulation of USF1.

Regulation of CCL2 expression by an upstream TALE homeodomain protein-binding site that synergizes with the site created by the A-2578G SNP

CC Chemokine Ligand 2 (CCL2) is a potent chemoattractant produced by macrophages and activated astrocytes during periods of inflammation within the central nervous system. Increased CCL2 expression is correlated with disease progression and severity, as observed in pulmonary tuberculosis, HCV-related liver disease, and HIV-associated dementia. The CCL2 distal promoter contains an A/G polymorphism at position -2578 and the homozygous -2578 G/G genotype is associated with increased CCL2 production and inflammation. However, the mechanisms that contribute to the phenotypic differences in CCL2 expression are poorly understood. We previously demonstrated that the -2578 G polymorphism creates a TALE homeodomain protein binding site (TALE binding site) for PREP1/PBX2 transcription factors. In this study, we identified the presence of an additional TALE binding site 22 bp upstream of the site created by the -2578 G polymorphism and demonstrated the synergistic effects of the two sites on the activation of the CCL2 promoter. Using chromatin immunoprecipitation (ChIP) assays, we demonstrated increased binding of the TALE proteins PREP1 and PBX2 to the -2578 G allele, and binding of IRF1 to both the A and G alleles. The presence of TALE binding sites that form inverted repeats within the -2578 G allele results in increased transcriptional activation of the CCL2 distal promoter while the presence of only the upstream TALE binding site within the -2578 A allele exerts repression of promoter activity.

Genotype-phenotype analysis of angiotensinogen polymorphisms and essential hypertension: the importance of haplotypes

OBJECTIVES

To better understand the relationship between angiotensinogen (AGT) genetic variation and essential hypertension, AGT genotypes and haplotypes were tested for association with hypertensive endophenotypes and essential hypertension.

METHODS

Two hundred and fifty-six Hypertensive Pathotype (HyperPATH)/Specialized Center of Research (SCOR) cases and 126 controls were genotyped for 24 single-nucleotide polymorphisms (SNPs) in the AGT gene. SNPs and AGT haplotypes were tested for association with plasma AGT, renal plasma flow (RPF), and essential hypertension.

RESULTS

New associations between essential hypertension, plasma AGT, and RPF are reported for alleles -1178G, 6066A, 6152A, 6233C, and 12822C. The maximum odds ratio for association of hypertension and AGT genetic variation was 2.3 [95% confidence interval (CI) 1.5-3.8; P < 0.0003] for allele 6233C. Previous associations for -1074T, -532T, -217A, -6A, and 4072C are confirmed (P < 0.05). Sodium depletion enhances associations between AGT SNPs and plasma AGT. Most individually associated SNPs, including -6A and 4072C, are found on a common complete AGT haplotype, H4 (frequency = 0.09). Individuals with haplotype H4 have significantly higher plasma AGT and reduced RPF (P < 0.003 and P < 0.0002, respectively). Other common haplotypes are not associated with increased plasma AGT levels in this data set despite the presence of the -6A and 4072C alleles, suggesting that AGT haplotype H4 is more predictive of elevated plasma AGT than is -6A or 4072C.

CONCLUSION

This study demonstrates the importance of analyzing haplotypes in addition to single genotypes in association studies. By demonstrating the dependence of AGT associations on sodium depletion status, it helps to explain previous conflicting association results.