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Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder with a range of cardiovascular, skeletal, craniofacial and cutaneous manifestations. LDS type 4 is caused by mutations in TGFβ ligand 2 (TGFB2) and based on the family pedigrees described to date, appears to have a milder clinical phenotype, often presenting with isolated aortic disease. We sought to investigate its molecular basis in a new pedigree. We identified a missense variant p.(Arg320Cys) (NM_003238.3) in a highly evolutionary conserved region of TGFB2 in a new LDS type 4 pedigree with multiple cases of aortic aneurysms and dissections. There was striking upregulation of TGFB1 and TGFB2 expression on immunofluorescent staining, and western blotting of the aortic tissue from the index case confirming the functional importance of the variant. This case highlights the striking paradox of predicted loss-of-function mutations in TGFB2 causing enhanced TGFβ signaling in this emerging familial aortopathy.

Primary aldosteronism accounts for 5%–10% of hypertension and in a third of cases is caused by autonomous aldosterone production by adenomas (APA). Somatic mutations in the potassium channel encoded by KCNJ5have been detected in surgically removed APAs. To better understand the role of these mutations, we resequenced the KCNJ5channel in a large Australian primary aldosteronism cohort. KCNJ5mutations were detected in 37 APAs (45% of the cohort), including previously reported E145Q (n = 3), G151R (n = 20), and L168R (n = 13) mutations. In addition, we found a novel 12-bp in-frame insertion mutation (c.414–425dupGCTTTCCTGTTC, A139_F142dup) that duplicates the AFLF sequence in the pore helix upstream of the selectivity filter. Expressed in Xenopus oocytes, the A139_F142dup mutation depolarized the oocytes and produced a G-protein-sensitive Na+current with altered K+selectivity and loss of inward rectification but retained Ba2+sensitivity. Transfected into H295R cells, A139_F142dup increased basal aldosterone release 2.3-fold over the wild type. This was not increased further by incubation with angiotensin II. Although the A139_F142dup mutant trafficked to the plasma membrane of H295R cells, it showed reduced tetramer stability and surface expression compared with the wild-type channel. This study confirms the frequency of somatic KCNJ5mutations in APAs and the novel mutation identified (A139_F142dup) extend the phenotypic range of the known KCNJ5APA mutations. Being located in the pore helix, it is upstream of the previously reported mutations and shares some features in common with selectivity filter mutants but additionally demonstrates insensitivity to angiotensin II and decreased channel stability.

Adrenal aldosterone-producing adenomas (APAs) are an increasingly recognized cause of primary aldosteronism, and somatic mutations within the KCNJ5gene encoding an inwardly rectifying Kchannel (also called GIRK4 or Kir3.4) have been identified by several groups including our own. We identified the previously noted G151R and L168R mutations in the region of a selectivity filter of the channel as well as a previously unreported 3-base deletion, delI157. Here, we report the functional properties of KCNJ5channels carrying this novel delI157 mutation.

Carotid-femoral pulse wave velocity (CFPWV) is a heritable measure of aortic stiffness that is strongly associated with increased risk for major cardiovascular disease events.

Sodium and chloride transport play a fundamental role in many physiological processes. In the kidney, sodium secretion and reabsorption are essential to maintain the extracellular volume and, thus, blood pressure (BP). In vascular smooth muscle, it is important for contractility and in the nervous system for the functioning of GABAergic neurons. Hence, the emergence of a WNKSPAKOSR1 kinase cascade that activates NaCl cotransporters has widespread physiological implications. This review gives an overview of the actions of SPAK and OSR1 kinases on NaCl cotransporters and highlights their possible therapeutic potential.

A high salt intake in industrialized countries is an important cardiovascular risk factor. It remains at typically twice the maximum recommended levels of 5–6 g/day, and halving this would have enormous public health benefit in preventing stroke and cardiovascular disease. Salt homeostasis can also be affected pharmacologically by diuretic drugs that target mechanisms within the distal kidney nephron to cause salt wasting. Indeed, thiazide‐type diuretics are among the most widely used agents in the management of hypertension and work by blocking NCCT, the NaCl‐transporter in the distal nephron. The biology of this membrane transporter was not previously well understood until the discovery of the molecular basis of a rare familial form of hypertension called Gordon syndrome (pseudohypoaldosteronism type 2, PHAII). This has established that the NCCT transporter is dynamically regulated in the kidney by WNK kinases and a signaling cascade using a second kinase called SPAK. Common polymorphisms in the SPAK gene have recently been shown to affect blood pressure in human cohorts and removing its function lowers blood pressure in mice. The SPAK‐deficient mouse actually has a phenotype reminiscent of Gitelman syndrome. This suggests that specific inhibitors of SPAK kinase may provide a novel class of diuretic drugs to lower blood pressure through salt wasting. The expectation is that SPAK inhibitors would mimic the on‐target effects of thiazides but not their adverse off‐target effects. An antihypertensive drug that could lower blood pressure with the efficacy of a thiazide without producing metabolic side effects such as hyperuricaemia or impaired glucose tolerance is therapeutically very attractive. It also exemplifies how data coming from the rare monogenic hypertension syndromes can together with genome‐wide association studies in hypertension deliver novel druggable targets.

The regulation of sodium reabsorption by the distal kidney is fundamental to blood pressure control. The clinical success of thiazide diuretics as antihypertensive drugs underscores the importance of its target, the thiazide-sensitive sodium/chloride cotransporter (NCC), in this process. However, thiazides are often ineffective as monotherapy and have significant side-effects. An understanding of NCC regulation at a molecular level may allow the design of better tolerated and more effective antihypertensive agents. The aim of this review is to provide an overview of the recent developments in the regulation of NCC, highlighting a potential new therapeutic target for the treatment of hypertension.

Regulation of the SLC12 family of membrane transporters including NCCT involves a scaffold of interacting proteins including the STE 20 kinase SPAK and the WNK kinases, WNK 1 and WNK 4, which are mutated in the hypertensive syndrome of pseudohypoaldosteronism type 2 (PHAII). WNK4 regulates NCCT by affecting forward trafficking to the surface membrane. Studies in using kinase dead WNK4 site mutants have produced inconsistent results with regard to the necessity of kinase function for NCCT regulation. Dynamic inhibition of WNK4 by small molecules may bring clarity to this issue however WNK4 is naturally resistant to commercial MAP kinase inhibitors owing to steric constraints prohibiting entry of small molecules to the active site. Using an approach similar to that used in p38 and ERK, we show that a single substitution in WNK4 (T261G) dramatically enhances its susceptibility to the inhibitors SB 202190 and SB 203580.Xenopus

The epithelial Na+ channel (ENaC) forms the rate limiting step in transepithelial Na+ absorption across aldosterone- responsive tissues such as the distal nephron. After more than a decade of investigation it is clear that the mechanisms of ENaC regulation are complex with an array of ENaC-regulatory proteins having been identified. A variety of monogenic syndromes of low renin hypertension have been identified that serve, through different mechanisms, to upregulate distal tubular ENaC activity. One of the most extensively studied, Liddle's syndrome, results predominantly from mutations in the C-termini of β and γ-ENaC subunits leading to a failure of Nedd4-2 (neuronal precursor cell-expressed and developmentally down-regulated protein 4-2) mediated channel endocytosis and an increased expression of ENaC at the cell surface. The role of ENaC subunit polymorphisms as determinants of essential hypertension has been investigated in a number of studies. The T594M mutation in the β-subunit of ENaC, for example, has been screened in large study populations and there is conflicting evidence that it co-segregates with blood pressure. Reasons for such controversies are discussed. The authors conclude that ENaC is a pivotal convergence point in blood pressure regulation and that future studies must identify better ways to measure distal tubular ENaC activity and investigate the importance of combination polymorphisms of ENaC subunits and their regulatory proteins as genetic determinants of hypertension.

The novel serine/threonine kinases (with no lysine kinases or WNKs), WNK1 and WNK4, are encoded by the disease genes for Gordon syndrome (PRKWNK1 and PRKWNK4), a rare monogenic syndrome of hypertension and hyperkalemia. These proteins alter the expression of the thiazide-sensitive Na/Cl cotransporter (NCCT) in Xenopus laevisoocytes, although the details are controversial. We describe here our own experience and confirm that kinase-dead WNK4 (318D>A) is unable to affect Na+fluxes through the thiazide-sensitive Na/Cl transporter (NCCT) or its membrane expression as an ECFP-NCCT fusion protein. However, the kinase domain is not sufficient for a functional WNK4 since deletion of the acidic motif (a motif unique to WNK family members) completely abolishes functional activity. Indeed, the NH2terminal of WNK4 (1–620) containing the kinase domain and acidic motif retains full activity, but does not interact directly with NCCT in pull-down assays. Coexpression of WNK1 antagonizes the action of WNK4, and kinase-dead WNK1 (368D>A) or WNK1 carrying a WNK4 disease mutation (565Q>E) behaves in the same way as wild-type WNK1. This suggests kinase activity and charge conservation within the acidic motif are not essential for the WNK1-WNK4 interaction. We also report that WNK4 probably reduces surface expression largely through an effect on forward trafficking. Hence, the effect of WNK4 on NCCT expression is mimicked by dynamin, but the dominant-negative K44A dynamin mutant does not block the action of WNK4 itself. These results further highlight important differences in the mechanism by which WNK kinases affect expression of NCCT vs. other membrane proteins such as ROMK.

Arterial stiffness is an independent determinant of cardiovascular risk, and there is evidence that it has a strong genetic component. Fibrillin-1 (FBN-1) is the disease gene for Marfan's syndrome and an FBN-1 polymorphism has been associated with large artery stiffening and elevated pulse pressure (PP) in patients with cardiovascular disease. The aim of this study was to investigate the possible influence of the common FBN-1 genotypes on arterial stiffness in a large cohort of healthy individuals.

Preeclampsia is a serious complication of pregnancy in which the fetus receives an inadequate supply of blood due to failure of trophoblast invasion. There is evidence that the condition has an immunological basis. The only known polymorphic histocompatibility antigens on the fetal trophoblast are HLA-C molecules. We tested the idea that recognition of these molecules by killer immunoglobulin receptors (KIRs) on maternal decidual NK cells is a key factor in the development of preeclampsia. Striking differences were observed when these polymorphic ligand: receptor pairs were considered in combination. Mothers lacking most or all activating KIR (AA genotype) when the fetus possessed HLA-C belonging to the HLA-C2 group were at a greatly increased risk of preeclampsia. This was true even if the mother herself also had HLA-C2, indicating that neither nonself nor missing-self discrimination was operative. Thus, this interaction between maternal KIR and trophoblast appears not to have an immune function, but instead plays a physiological role related to placental development. Different human populations have a reciprocal relationship between AA frequency and HLA-C2 frequency, suggesting selection against this combination. In light of our findings, reproductive success may have been a factor in the evolution and maintenance of human HLA-C and KIR polymorphisms.

The human β1-adrenoceptor (β1-AR) is an important therapeutic target for cardiovascular diseases and has two common functional polymorphisms (49S>G and 389R>G). These polymorphisms have only been studied in isolation, however, and not in the context of the four haplotypes (SR, SG, GR and GG) that exist in native β1-ARs.

Matrix γ-carboxyglutamic acid protein (MGP) is a mineral-binding extracellular matrix protein synthesized by vascular smooth muscle cells (VSMCs) and chondrocytes that is thought to be a key regulator of tissue calcification. In this study, we identified four polymorphisms in the promoter region of the human MGP gene. Transfection studies showed that the G−7A and T−138C polymorphisms have an important impact on in vitropromoter activity when transiently transfected into VSMCs. We found that one of these polymorphisms (T−138C) is significantly correlated with serum MGP levels in human subjects. Promoter deletion analysis showed that this polymorphism lies in a region of the promoter critical for transcription in VSMCs. This region contains a potential activating protein-1 (AP-1) binding element located between −142 and −136. We have demonstrated that the T−138C polymorphism results in altered binding of an AP-1 complex to this region. The −138T allelic variant binds AP-1 complexes consisting primarily of c-Jun, JunB and its partners Fra-1 and Fra-2 in rat VSMC. Furthermore, the −138T variant form of the promoter was induced following phorbol 12-myristate 13-acetate treatment, while the −138C variant was refractive to phorbol 12-myristate 13-acetate treatment, confirming that AP-1 factors preferentially bind to the −138T variant. This study therefore suggests that a common polymorphism of the MGP promoter influences binding of the AP-1 complex, which may lead to altered transcription and serum levels. This could have important implications for diseases such as atherosclerosis and aortic valve stenosis, since it strongly suggests a genetic basis for regulation of tissue calcification.

Mutation scanning of the β1-adrenoceptor gene has identified a polymorphism, G389R, that markedly affects G-protein coupling of the receptor and resulting cAMP production. We have investigated the effect of this functionally active polymorphism on clinical response to β-adrenoceptor blockade. Two cohorts of untreated hypertensive patients randomly assigned to a β1-selective β-blocker at the start of antihypertensive therapy were studied retrospectively to see if the G389R polymorphism influenced the response in terms of blood pressure and heart rate. The blood pressure and heart rate responses to treatment were assessed 4 weeks later and compared with the G389R genotype, ascertained by PCR/restriction fragment length polymorphism. The falls in blood pressure and heart rate for the first group (n = 92) by genotype were: GG, 20.1±3.5/13.9±2.7 mmHg (systolic/diastolic blood pressure), 18.4±2.2 beats/min; GR, 20.0±2.2/15.0±1.3 mmHg, 16.5±1.5 beats/min; RR, 20.8±2.3/13.4±1.1 mmHg, 16.0±1.4 beats/min. For the second group (n = 55) the corresponding falls were: GG, 17.0±4.3/11.2±3.4 mmHg, 12.0±3.5 beats/min; GR, 16.6±1.8/14.4±1.1 mmHg, 13.1±2.1 beats/min; RR, 18.0±1.6/13.0±1.4 mmHg, 14.4±1.4 beats/min. The G389R genotype also failed to have a significant effect on pretreatment blood pressure or heart rate in either group. These data suggest that, despite clear functional differences between the G389R receptor variants expressed in vitro, the polymorphism does not affect the haemodynamic response of hypertensive subjects to chronic β1-adrenoceptor blockade.

Primary aldosteronism (PA) may account for 5–10 of patients with hypertension. Recently, a family with florid PA and marked zona fasciculata (ZF) hyperplasia was reported to have a germ-line mutation within KCNJ5(encodes a potassium channel) 1. Somatic mutations were also identified in eight of 22 large, apparently sporadic aldosterone-producing adenomas (APAs) 1.