Glucocorticoid-suppressible hyperaldosteronism (GSH), first described in 1966 (Sutherland et al. 1966), is a rare cause of familial hypertension. It presents in young adults with hypertension, hypokalaemia and suppressed plasma renin activity (features caused by the excess activity of aldosterone secretion), and is distinguished from other forms of primary hyperaldosteronism by its autosomal dominant mode of inheritance and the reversal of all its clinical and biochemical abnormalities by the administration of small doses of the synthetic glucocorticoid dexamethasone (Connell et al. 1986). GSH is also characterized by abnormally elevated levels of 18-hydroxycortisol and 18-oxocortisol, the excretion of which also falls to normal following dexamethasone administration (Chu & Ulick, 1982; Ulick et al. 1983; Gomez-Sanchez et al. 1984). The study of the production of these unusual 18-hydroxylated steroids has led to a reappraisal of the late reactions in aldosterone and cortisol synthesis by the adrenal cortex,
A Jamieson, J M C Connell, and R Fraser
Aurelie Nguyen Dinh Cat, Malou Friederich-Persson, Anna White, and Rhian M Touyz
Understanding the mechanisms linking obesity with hypertension is important in the current obesity epidemic as it may improve therapeutic interventions. Plasma aldosterone levels are positively correlated with body mass index and weight loss in obese patients is reported to be accompanied by decreased aldosterone levels. This suggests a relationship between adipose tissue and the production/secretion of aldosterone. Aldosterone is synthesized principally by the adrenal glands, but its production may be regulated by many factors, including factors secreted by adipocytes. In addition, studies have reported local synthesis of aldosterone in extra-adrenal tissues, including adipose tissue. Experimental studies have highlighted a role for adipocyte-secreted aldosterone in the pathogenesis of obesity-related cardiovascular complications via the mineralocorticoid receptor. This review focuses on how aldosterone secretion may be influenced by adipose tissue and the importance of these mechanisms in the context of obesity-related hypertension.
Amanda J Rickard and Morag J Young
The mineralocorticoid receptor (MR) and glucocorticoid receptor are ligand-activated transcription factors that have important physiological and pathophysiological actions in a broad range of cell types including monocytes and macrophages. While the glucocorticoids cortisol and corticosterone have well-described anti-inflammatory actions on both recruited and tissue resident macrophages, a role for the mineralocorticoid aldosterone in these cells is largely undefined. Emerging evidence, however, suggests that MR signalling may promote pro-inflammatory effects. This review will discuss the current understanding of the role of corticosteroid receptors in macrophages and their effect on diseases involving inflammation, with a particular focus on cardiovascular disease.
Jyotsna B Pippal and Peter J Fuller
The signature action of aldosterone in the regulation of electrolyte and fluid balance is well established. However, the role of aldosterone as an important contributor to morbidity and mortality in heart failure has gained a heightened interest in recent years, but the mechanisms of this action are not well understood. Aldosterone is the principal physiological ligand for the mineralocorticoid receptor (MR), a ligand-activated transcription factor, that also binds to the physiological glucocorticoid, cortisol. Both classes of hormones bind with similar affinity to the MR, but the molecular basis of selective and tissue-specific effects of MR ligands is not yet fully documented. The structural and functional determinants of MR function are described and their significance is discussed.
Fabio Luiz Fernandes-Rosa, Sheerazed Boulkroun, and Maria-Christina Zennaro
Primary aldosteronism (PA), the most common form of secondary hypertension, is caused in the majority of cases by unilateral aldosterone-producing adenoma (APA) or bilateral adrenal hyperplasia. Over the past few years, somatic mutations in KCNJ5, CACNA1D, ATP1A1 and ATP2B3 have been proven to be associated with APA development, representing more than 50% of sporadic APA. The identification of these mutations has allowed the development of a model for APA involving modification on the intracellular ionic equilibrium and regulation of cell membrane potential, leading to autonomous aldosterone overproduction. Furthermore, somatic CTNNB1 mutations have also been identified in APA, but the link between these mutations and APA development remains unknown. The sequence of events responsible for APA formation is not completely understood, in particular, whether a single hit or a double hit is responsible for both aldosterone overproduction and cell proliferation. Germline mutations identified in patients with early-onset PA have expanded the classification of familial forms (FH) of PA. The description of germline KCNJ5 and CACNA1H mutations has identified FH-III and FH-IV based on genetic findings; germline CACNA1D mutations have been identified in patients with very early-onset PA and severe neurological abnormalities. This review summarizes current knowledge on the genetic basis of PA, the association of driver gene mutations and clinical findings and in the contribution to patient care, plus the current understanding on the mechanisms of APA development.
G C Inglis, C J Kenyon, C Szpirer, K Klinga-Levan, R G Sutcliffe, and J M C Connell
Mouse hepatoma × rat hepatocyte hybrids that segregate rat chromosomes were used to determine the chromosomal location of the rat genes encoding 11 β-hydroxylase and aldosterone synthase (Cyp11b1 and Cyp11b2 respectively). By means of species-specific restriction fragments and microsatellite markers both genes were mapped to rat chromosome 7. The Cyp11b1 microsatellite marker was subsequently found to vary in length between and within rat strains. Furthermore, we compared the sequences of Cyp11b1 markers in two genetically hypertensive strains of rat with their normotensive counterparts. Previous studies have indicated that 11β-hydroxylase activities in Milan and Lyon hypertensive strains are different from their respective genetic controls. The Cyp11b1 microsatellite regions from Lyon hypotensive and normotensive strains of rat were similar and were both shorter by 15 bases than that of the Lyon hypertensive strain. The Cyp11b1 marker in Milan hypertensive (MHS) and normotensive (MNS) strains differ from all the Lyon strains and from each other. The MHS marker is 12 bases shorter than that of MNS rats. These differences in microsatellite length may provide useful polymorphic markers in co-segregation studies of genetic hypertension in rats.
SM MacKenzie, CJ Clark, R Fraser, CE Gomez-Sanchez, JM Connell, and E Davies
The terminal stages of cortisol and aldosterone production in the human adrenal gland are catalysed by the enzymes 11beta-hydroxylase and aldosterone synthase, which are encoded by the CYP11B1 and CYP11B2 genes respectively. Recent studies have suggested that aldosterone and cortisol are also made in other tissues such as the brain, heart and vascular system and may play a role in cardiovascular homeostasis. The aim of this study was to confirm the presence of these enzymes and localise them precisely in the rat brain. Reverse transcription-polymerase chain reaction (RT-PCR)/Southern blotting confirmed transcription of CYP11B1 and CYP11B2 in whole brain and hypothalamus minces from Wistar-Kyoto rats. 11beta-Hydroxylase and aldosterone synthase were immunolocalised in paraffin-embedded rat adrenal and brain sections using mouse monoclonal antibodies. Negative controls utilised a mouse monoclonal antibody raised against a non-mammalian epitope. In the brain, 11beta-hydroxylase and aldosterone synthase were detected in the cerebellum, especially the Purkinje cells, as well as the hippocampus. The specificities of the 11beta-hydroxylase and aldosterone synthase antibodies were confirmed by positive immunostaining of the relevant regions of the adrenal cortex. This is the first direct evidence that steroid hydroxylases involved in the final stages of corticosteroid biosynthesis are present in specific regions of the central nervous system.
S. M. Laird, J. P. Hinson, G. P. Vinson, N. Mallick, S. Kapas, and R. Teja
The involvement of the calcium messenger system in the control of steroidogenesis in the rat and bovine adrenal cortex has been studied extensively. However the role of these second messengers in the control of human adrenocortical function is not established. This was therefore studied by incubating collagenase-dispersed human adrenocortical cells with the calcium ionophore A23187 and the protein kinase C activator phorbol 12-myristate 13-acetate (TPA). The effects of the calcium channel blocker verapamil on basal and stimulated steroidogenesis were also studied.
Both TPA (1 pmol/l–10 μmol/l) and A23187 (1 nmol/l–10 μmol/l) caused a dose-dependent increase in cortisol, aldosterone and corticosterone production. Verapamil (10 μmol/l) inhibited the increase in aldosterone, corticosterone and cortisol produced in response to ACTH(1–24), potassium, and desacetyl-αMSH. Unlike previous results in the rat, these effects were not specific for aldosterone secretion.
The results suggest that, as in other species, calcium mobilization and protein kinase C activation have a role in the control of steroidogenesis in the human adrenal cortex. However, in contrast to the rat, these mechanisms appear to be involved in the control of steroidogenesis in both the zona glomerulosa and inner zone cells.
Lichun Zhou, Baohua Ma, and Xiuzhen Han
Pathological cardiac hypertrophy is associated with nearly all forms of heart failure. It develops in response to disorders such as coronary artery disease, hypertension and myocardial infarction. Angiotensin II (Ang II) has direct effects on the myocardium and promotes hypertension. Chronic elevation of Ang II can lead to pathological cardiac hypertrophy and cardiac failure. Autophagy is an important process in the pathogenesis of cardiovascular diseases. Under physiological conditions, autophagy is an essential homeostatic mechanism to maintain the global cardiac structure function by ridding damaged cells or unwanted macromolecules and organelles. Dysregulation of autophagy may play an important role in Ang II-induced cardiac hypertrophy although conflicting reports on the effects of Ang II on autophagy and cardiac hypertrophy exist. Some studies showed that autophagy activation attenuated Ang II-induced cardiac dysfunction. Others suggested that inhibition of the Ang II induced autophagy should be protective. The discrepancies may be due to different model systems and different signaling pathway involved. Ang II-induced cardiac hypertrophy may be alleviated through regulation of autophagy. This review focuses on Ang II to highlight the molecular targets and pathways identified in the prevention and treatment of Ang II-induced pathological cardiac hypertrophy by regulating autophagy.
Kazutaka Nanba, Andrew X Chen, Adina F Turcu, and William E Rainey
The H295R adrenocortical cell line is widely used for molecular analysis of adrenal functions but is known to have only modest ACTH responsiveness. The lack of ACTH response was linked to a low expression of its receptor, melanocortin 2 receptor (MC2R). We hypothesized that increasing the MC2R accessory protein (MRAP), which is required to traffic MC2R from the endoplasmic reticulum to the cell surface, would increase ACTH responsiveness. Lentiviral particles containing human MRAP-open reading frame were generated and transduced in H295R cells. Using antibiotic resistance, 18 clones were isolated for characterization. The most ACTH-responsive steroidogenic clone, H295RA, was used for further experiments. Successful induction of MRAP and increased expression of MC2R in H295RA cells was confirmed by quantitative real-time RT-PCR and protein analysis. Treatment with ACTH significantly increased aldosterone, cortisol, and dehydroepiandrosterone production in H295RA cells. ACTH also significantly increased transcript levels for all of the steroidogenic enzymes required to produce aldosterone, cortisol, and dehydroepiandrosterone, as well as MC2R mRNA. Using liquid chromatography/tandem mass spectrometry, we further revealed that the main unconjugated steroids produced in H295RA cells were 11-deoxycortisol, cortisol, and androstenedione. Treatment of H295RA cells with ACTH also acutely increased cAMP production and cellular protein levels for total and phosphorylated steroidogenic acute regulatory protein. In summary, through genetic manipulation, we have developed an ACTH-responsive human adrenocortical cell line. The cell line will provide a powerful in vitro tool for molecular analysis of physiologic and pathologic conditions involving the hypothalamic–pituitary–adrenal axis.