APEX1 regulation of aldosterone synthase gene transcription is disrupted by a common polymorphism in humans.

RATIONALE: The genetic mechanisms underlying hypertension are unclear, but relative aldosterone excess, present in ≈10% of hypertensive patients, is known to be a heritable trait. This phenotype associates with a T/C single nucleotide polymorphism (SNP) at position -344 of the aldosterone synthase gene (CYP11B2). However, deletion of this SNP has no effect on gene transcription. We have identified another T/C SNP at -1651, in tight linkage disequilibrium with the -344 SNP and here investigate its functional effect on CYP11B2 transcription. OBJECTIVE: We assessed the effect on transcriptional activity of the -1651 T/C SNP in vivo and in vitro and propose the mechanism by which transcriptional activity is altered. METHODS AND RESULTS: We demonstrated that the SNP at -1651 exerts significant allele-dependent effects on CYP11B2 transcription. We confirm binding of the transcriptional repressor APEX1 to -1651T, which is associated with reduced transcriptional activity in relation to the less strongly bound -1651C. We show that inhibiting APEX1 by small molecule inhibition or small interfering RNA (SiRNA) leads to increased CYP11B2 transcription. In addition, overexpression of APEX1 is associated with reduced transcriptional activity. Finally, we also show that -1651T associates with lower excretion rates of aldosterone metabolites in human subjects. CONCLUSIONS: We conclude that APEX1 is a novel transcriptional repressor of CYP11B2 and that differential APEX1 binding at -1651 of CYP11B2 results in altered gene expression. This mechanism may contribute to the observed relationship between CYP11B2 genotype and aldosterone phenotype in a subgroup of hypertensive patients.

Central mineralocorticoid receptors, sympathetic activity, and hypertension.

Recent evidence highlighting the presence of cortico-steroid receptors in the central nervous system has prompted further investigation regarding their role in the pathogenesis of hypertension. The sympathetic nervous system, an important factor in the pathogenesis of hypertension, is influenced by sodium and volume status. Activation of central nervous system mineralocorticoid receptors is known to affect sympathetic activity, although the processes that underpin this phenomenon are incompletely understood. This article reviews some of the recent advances in this area, particularly mechanisms by which the mineralo-corticoid receptor maintains selectivity for its ligand within the central nervous system, its role in salt appetite, and the possibility of local production of corticosteroids. In addition, the links between central mineralocorticoid receptor activation, stress, sympathetic activity, and hypertension are discussed.

Drug Insight: eplerenone, a mineralocorticoid-receptor antagonist.

Increasing recognition of the role of aldosterone in cardiovascular disease has been supported by a significant body of evidence from animal models. This evidence has been translated into clinical practice, and large-scale, randomized, placebo-controlled trials have confirmed the beneficial effects of mineralocorticoid blockade in patients with heart failure. As a consequence, there has been a resurgence in the use of mineralocorticoid-receptor antagonists in clinical practice that has prompted the search for a potent and specific antagonist without the sexual side effects of spironolactone. Eplerenone, a mineralocorticoid-receptor antagonist with minimal binding to the progesterone and androgen receptors, is now licensed for treatment of heart failure in Europe and heart failure and hypertension in the US; it has also been proposed as a treatment for a variety of cardiovascular conditions. This article reviews the current concepts of the actions of aldosterone at a cellular level. Recent findings regarding its role as a cardiovascular hormone, both in animal models and human studies, are discussed. We also describe the development of mineralocorticoid-receptor blockers following the isolation of aldosterone and discuss the subsequent search for a specific mineralocorticoid antagonist. In addition we detail the effects of eplerenone in a number of clinical situations and outline its potential future applications.

Common Polymorphisms at the CYP17A1 Locus Associate With Steroid Phenotype: Support for Blood Pressure Genome-Wide Association Study Signals at This Locus.

Genome-wide association studies implicate the CYP17A1 gene in human blood pressure regulation although the causative polymorphisms are as yet unknown. We sought to identify common polymorphisms likely to explain this association. We sequenced the CYP17A1 locus in 60 normotensive individuals and observed 24 previously identified single-nucleotide polymorphisms with minor allele frequency >0.05. From these, we selected, for further studies, 7 polymorphisms located ≤ 2 kb upstream of the CYP17A1 transcription start site. In vitro reporter gene assays identified 3 of these (rs138009835, rs2150927, and rs2486758) as having significant functional effects. We then analyzed the association between the 7 polymorphisms and the urinary steroid metabolites in a hypertensive cohort (n=232). Significant associations included that of rs138009835 with aldosterone metabolite excretion; rs2150927 associated with the ratio of tetrahydrodeoxycorticosterone to tetrahydrodeoxycortisol, which we used as an index of 17α-hydroxylation. Linkage analysis showed rs138009835 to be the only 1 of the 7 polymorphisms in strong linkage disequilibrium with the blood pressure-associated polymorphisms identified in the previous studies. In conclusion, we have identified, characterized, and investigated common polymorphisms at the CYP17A1 locus that have functional effects on gene transcription in vitro and associate with corticosteroid phenotype in vivo. Of these, rs138009835--which we associate with changes in aldosterone level--is in strong linkage disequilibrium with polymorphisms linked by genome-wide association studies to blood pressure regulation. This finding clearly has implications for the development of high blood pressure in a large proportion of the population and justifies further investigation of rs138009835 and its effects.

Progress in the identification of responsible genes and molecular mechanisms in primary aldosteronism.

Aldosterone, the mineralocorticoid hormone, plays an important role in blood regulation. Autonomous secretion of aldosterone is known as primary aldosteronism (PA), the most common cause of secondary hypertension. PA comprises a group of heterogenous disorders which makes their classification and management challenging. With the advent of the genomic era several germline and somatic mutations have been identified that are involved in the pathogenesis of primary aldosteronism. This article will review our current knowledge of the genetic mechanisms of familial hyperaldosterism, somatic mutations in genes encoding electrolyte channels and other potential genetic mechanisms implicated in the dysregulation of aldosterone production from in vitro and animal models. There is potential for novel targeted therapies and diagnosis for subsets of patient. The challenges to achieve them are highlighted in this review.

Short- and long-term changes in plasma inflammatory markers associated with preeclampsia.

Preeclampsia is characterized by hypertension, dyslipidemia, and increased systemic inflammatory response and has been associated with an increased maternal risk of cardiovascular disease later in life. Low-grade chronic inflammation is a risk factor for cardiovascular disease. This study examined changes in inflammatory markers prospectively during pregnancy, the current inflammatory status of women who had a pregnancy complicated by preeclampsia 20 years previously against matched controls, and the association between inflammatory genes and risk of preeclampsia in a case (n=106) control (n=212) study. In control pregnancies (n=34), mean interleukin-10 (IL-10) levels increased 38% (P=0.012) and tumor necrosis factor-alpha (TNF-alpha) by 33% (P=0.024) between the first and third trimesters. The mean preeclampsia group IL-10 and TNF-alpha rose by 43% (P=0.013 and P=0.0065, respectively) from the first to the third trimester. In women with preeclampsia only, plasma IL-6 increased from the first to the third trimester (1.66 [2.04] to 2.94 [2.47] pg/mL; P=0.0004). Twenty years after the index pregnancy, women who had had preeclampsia demonstrated significantly higher IL-6 to IL-10 ratio (3.96 [6.07] versus 2.12 [1.89]; P=0.034) compared with a healthy index pregnancy 20 years previously, that persisted after adjustment for smoking and current body mass index. The IL-1beta (C-511T), IL-6 (G-174C), TNF-alpha (G-308A), E-selectin (S128R), intercellular adhesion molecule-1 (K469E), and C-reactive protein (C1059G) polymorphisms were not associated with risk of developing preeclampsia. In conclusion, preeclampsia is associated with short- and long-term changes in inflammatory status.