Protein kinase A activity controls the regulation of T-type CaV3.2 channels by Gbetagamma dimers

Low voltage-activated (LVA), T-type, calcium channels mediate diverse biological functions and are inhibited by Gbetagamma dimers, yet the molecular events required for channel inhibition remain unknown. Here, we identify protein kinase A (PKA) as a molecular switch that allows Gbeta(2)gammax dimers to effect voltage-independent inhibition of Ca(v)3.2 channels. Inhibition requires phosphorylation of Ser(1107), a critical serine residue on the II-III loop of the channel pore protein. S1107A prevents inhibition of unitary currents by recombinant Gbeta(2)gamma(2) dimers but does not disrupt dimer binding nor change its specificity. Gbetagamma dimers released upon receptor activation also require PKA activity for their inhibitory actions. Hence, dopamine inhibition of Ca(v)3.2 whole cell current is precluded by Gbetagamma-scavenger proteins or a peptide that blocks PKA catalytic activity. Fittingly, when used alone at receptor-selective concentrations, D(1) or D(2) agonists do not elicit channel inhibition yet together synergize to inhibit Ca(v)3.2 channel currents. We propose that a dual-receptor regulatory mechanism is used by dopamine to control Ca(v)3.2 channel activity. This mechanism, for example, would be important in aldosterone producing adrenal glomerulosa cells where channel dysregulation would lead to overproduction of aldosterone and consequent cardiac, renal, and brain target organ damage.

Altered corticosteroid biosynthesis in essential hypertension: A digenic phenomenon

Aldosterone plays an important role in electrolyte and blood pressure homeostasis. Our studies have focused on the role of aldosterone in essential hypertension. We have shown that plasma aldosterone and ARR are heritable characteristics and that aldosterone concentrations in older subjects are inversely correlated with birthweight and positively correlated with blood pressure. Aldosterone levels are also associated with polymorphic variation in the CYP11B2 gene, which encodes aldosterone synthase, the enzyme responsible for aldosterone production. Interestingly, CYP11B2 polymorphisms are also associated with less efficient activity of 11beta-hydroxylase, encoded by the neighbouring, highly homologous CYP11B1 gene. We propose that a digenic effect leads to increased aldosterone production, with inefficient 11beta-hydroxylation causing a long-term increase in ACTH drive to the adrenal gland and enhanced expression of CYP11B2, thereby resulting in chronically raised aldosterone secretion in response to factors such as angiotensin II and potassium. In susceptible subjects this is likely, over many years, to result in hypertension with relative aldosterone excess.

Development of an adrenocorticotropin-responsive human adrenocortical carcinoma cell line

CONTEXT

The molecular mechanisms regulating adrenal steroidogenesis continue to be defined. The only current human adrenocortical cell line is the NCI-H295 and its substrains. One of the strains, H295R, has retained the ability to respond to angiotensin II (Ang II); however, it lacks ACTH responsiveness. An ACTH-responsive human adrenocortical model would add significantly to studies directed at defining the molecular control of corticosteroid biosynthesis.

OBJECTIVE

The objective of the study was to develop a human adrenal cell line that retained both Ang II- and ACTH-regulated corticosteroid production.

DESIGN

Human adrenocortical carcinoma (HAC) cells were isolated from an adrenal tumor removed from a girl presenting with virilization and hypertension. Clonal populations of cells were established and characterized. HAC cells were treated with ACTH, Ang II, and forskolin, followed by examination of steroidogenic enzyme mRNA expression using quantitative real-time PCR and steroid production.

RESULTS

HAC clone 15 (HAC15) cells responded to treatment with ACTH, Ang II, and forskolin, with increased cortisol and aldosterone production. ACTH, Ang II, and forskolin also increased expression of mRNA, encoding all enzymes needed for cortisol and aldosterone biosynthesis, namely steroidogenic acute regulatory protein, cholesterol side-chain cleavage, cytochrome P450 17alpha-hydroxylase-17, 20-lyase, 3beta-hydroxysteroid dehydrogenase type II, 21-hydroxylase, 11beta-hydroxylase, and 11beta-aldosterone synthase. In addition, the cells expressed mRNA for ACTH receptor (MC2R) and Ang II receptor. MC2R protein was also expressed in HAC15 cells.

CONCLUSION

The current study describes the development and characterization of an ACTH- and Ang II-responsive human adrenal cell line. The HAC15 cell line should provide an important model system for defining the molecular mechanisms regulating aldosterone and cortisol production.

Gonadal modulation of in vitro steroidogenic properties of dispersed adrenocortical cells from Sceloporus lizards

Effects of adrenal corticosteroids on reproductive and endocrine functions of the gonads are well known, but reciprocal effects of gonadal hormones on the hypothalamo-pituitary-adrenal (HPA) axis and on adrenocortical steroidogenesis in particular have received much less attention. We investigated effects of gonadectomy and testosterone (T) replacement on adrenocortical cell function in a year-long field study of male Sceloporus undulatus (Eastern Fence Lizard) and in a shorter term laboratory study with male Sceloporus jarrovii (Yarrow's Spiny Lizard). We also compared females to males in Sceloporus virgatus (Striped Plateau Lizard) and investigated effects of gonadectomy in short-term laboratory experiment on females of this species. As measured by in vitro production of progesterone (P(4)), corticosterone (B), and aldosterone (ALDO), sensitivity of adrenocortical cells to corticotrophin (ACTH) was lower in control males than females of S. virgatus. In S. jarrovii males, cellular sensitivity to ACTH was reduced by orchiectomy but was not restored to levels of intact controls by T replacement. By contrast, in S. undulatus, cellular sensitivity to ACTH was not affected by orchiectomy alone but was reduced by T replacement in orchiectomized males. Maximal rates of steroid production were less consistently affected by experimental treatments, but were lower in males than in females of S. virgatus and were dramatically reduced by T replacement in orchiectomized S. undulatus males. Overall, our experiments clearly demonstrate two distinct sources of variation in functional capacities of dispersed adrenocortical cells isolated from Sceloporus lizards: (1) naturally occurring differences between males and females (Carsia and John-Alder, 2003), and (2) species-dependent changes in response to surgical gonadectomy with or without exogenous testosterone. Sex differences and functional lability in adrenocortical cells are probably widespread among vertebrates and may be an important component of variation in output of the HPA.

[Molecular basics of aldosterone and cortisol synthesis in normal adrenals and adrenocortical adenomas]

The aim of the study is to present genes encoding enzymatic proteins of aldosterone and cortisol synthesis pathway, methods of their transcriptional activity measurement, mRNA expression of the genes in normal adrenal cortex, in adrenocortical adenomas excised from patients with Conn and Cushing syndromes, as well as in adrenocortical adenomas excised from patients, in which hormonal activity of the tumour was not confirmed. According to presented papers mRNA expression of analyzed genes is best known in tissue obtained from tumours excised from patients with Conn syndrome. On the other hand transcriptional activity of the genes within the other adrenocortical adenomas is documented in lesser degree. It concerns particularly analyses of tissue material obtained from patients, in which hormonal activity of adrenal tumours was not confirmed with biochemical tests. It should be also considered, that the frame of reference for the majority of molecular analyses of adrenocortical tumour tissues was material obtained from little number of normal adrenals, what decreases in some degree credibility of obtained results. Mentioned above remarks may be the basis for conduction of further investigations based on larger material, obtained both from normal adrenals and adrenocortical adenomas.

New mechanisms to control aldosterone synthesis

Arterial hypertension is a frequent and leading cardiovascular risk factor, and primary aldosteronism is a well-recognized cause of secondary hypertension. Aldosterone is the basic regulator of extracellular fluid volume and electrolyte balance. Alterations in plasma aldosterone levels significantly contribute to the development and the severity of hypertension. Adrenal steroidogenesis is controlled by two major feedback loops: the hypothalamic-pituitary-adrenal axis, which regulates cortisol synthesis, and the renin-angiotensin-aldosterone system, which directs aldosterone production. In addition to angiotensin, potassium, and corticotropin-which belong to the classic stimulators of aldosterone-neuropeptides, catecholamines, and prostaglandins are also known to stimulate aldosterone synthesis. Recently, several new mechanisms have been characterized that control the release of aldosterone by adrenocortical cells, among them endothelial cell-derived factors and adipokines. Further identification and characterization of these factors may help in the development of novel therapies for the treatment of arterial hypertension, various metabolic diseases, and other disorders.

Metastin stimulates aldosterone synthesis in human adrenal cells

Kisspeptins, including metastin, are encoded by the KiSS-1 gene and play an important role in regulating the hypothalamic gonadotropin-releasing hormone (GnRH) system via G protein-coupled receptor 54 (GPR54, also called KiSS-1R). Normally, metastin (also called Kp-54) levels are quite low, except during pregnancy, when levels increase 1000-fold over those found in men and nonpregnant women. However, the potential hormonal role of metastin in the fetal and maternal circulation is unknown. In this study, the authors examine the levels of GPR54 mRNA expression in human adult and fetal adrenals using quantitative real-time reverse-transcriptase polymerase chain reaction (RT-PCR). In addition, they examine the effects of metastin on steroidogenesis and steroidogenic enzyme mRNA levels in fetal adrenal cells and in the H295R adrenocortical cell line using enzyme immunoassay and RT-PCR techniques. The authors demonstrate that GPR54 mRNA is significantly higher (50-fold) in human fetal adrenals than in adult adrenals. Immunohistochemical studies have demonstrated that the GPR54 protein is predominantly expressed in the neocortex of human fetal adrenals in the third trimester. Metastin increases aldosterone production (approximately 2-fold) in both fetal neocortex adrenal cells and H295R adrenal cells, with a maximal increase seen at 100 nM. In addition, metastin increased angiotensin II (Ang II)-stimulated aldosterone production by approximately 1.5-fold. Metastin also increased the ability of the H295R cells to metabolize exogenously added pregnenolone to aldosterone but had no effect on the expression of aldosterone synthase (CYP11B2). These results suggest that the high fetal/maternal levels of metastin seen during pregnancy may affect adrenal production of aldosterone.

Bilateral aldosterone-producing adenomas: differentiation from bilateral adrenal hyperplasia

BACKGROUND

Primary aldosteronism (PA) is a common curable disease of secondary hypertension. Most such patients have either idiopathic bilateral adrenal hyperplasia (BAH) or unilateral aldosterone-producing adenoma (APA). Bilateral APAs are reportedly extremely rare.

AIM

To compare the distinctive characteristics, clinical course, and outcomes of bilateral APA vs. BAH.

DESIGN

Retrospective record review.

METHODS

From July 1994 to Jan 2007, 190 patients diagnosed with PA underwent surgical intervention at our hospital. Bilateral APA was diagnosed in 7/164 patients with histologically-proven APA. Twenty-one patients diagnosed as BAH, and 21 randomly selected of unilateral APA patients, matched by age and sex served as controls.

RESULTS

Patients with bilateral APA had similar blood pressure, arterial blood gas analysis, spot urinary potassium to creatinine ratio and clinical symptoms to those with BAH, but lower serum potassium levels (p = 0.027), lower plasma renin activity (p = 0.037), and higher plasma aldosterone concentrations (p = 0.029). Aldosterone-renin ratio (ARR) after administration of 50 mg captopril was higher in bilateral APA than in BAH patients (p = 0.023), but not different between unilateral APA and BAH (p = 0.218). A cut-off of ARR >100 ng/dl per ng/ml/h and plasma aldosterone >20 ng/dl after captopril significantly differentiated bilateral APA from BAH. Bilateral subtotal adrenalectomy normalized blood pressure and biochemistry in all patients with bilateral APA.

DISCUSSION

Bilateral APA, presenting simultaneously or sequentially, may not be a rare disease, accounting for 4.3% of APA in this sample. The clinical presentations of bilateral functional adenoma are not different from BAH, but patients with low serum potassium and ARR >100 after captopril should be carefully evaluated for bilateral adenoma.

The transcription of steroidogenic genes in the human cerebellum and hippocampus: a comparative survey of normal and Alzheimer's tissue

Steroid actions on brain tissue have been implicated in processes such as blood pressure regulation and neurodegeneration, including the progression of Alzheimer's disease (AD). mRNAs from all of the genes required for de novo synthesis from cholesterol of aldosterone and corticosterone (equivalent to cortisol in humans) have been identified in rat brain, together with abundant steroid hormone receptors, but the situation in human brain requires clarification. We used real-time RT-PCR to assess whether transcription of 13 steroid-associated genes occurs in human hippocampus and cerebellum, and to identify whether transcription of these genes is significantly altered in cases of AD. Frozen post-mortem samples of hippocampus and cerebellum from patients with AD (n=7) and age-matched controls free from neurological disease at the time of death (n=9) were used. We found all of the genes under investigation to be transcribed within normal and AD hippocampus and cerebellum except for CYP11B1 (11beta-hydroxylase), CYP11B2 (aldosterone synthase) and CYP17 (17alpha-hydroxylase). No significant differences in mRNA levels were observed between the AD tissue and the equivalent control tissue, although significant regional differences in gene transcription were observed between hippocampus and cerebellum in AD and control samples. The absence of key mRNAs from human hippocampus and cerebellum rules out the de novo generation of aldosterone, cortisol or the sex steroids within these regions. However, the pattern of gene expression does suggest that the mineralocorticoid 11-deoxycorticosterone can be generated de novo. There is no evidence of a link between AD and altered steroid biosynthesis within human hippocampus and cerebellum.

The role of adrenal steroidogenesis in arterial hypertension

Adrenal aldosterone production, the major regulator of salt and water retention, is discussed with respect to hypertensive diseases. Physiological aldosterone production is tightly regulated, either stimulated or inhibited, in the adrenal zona glomerulosa by both circulating factors and/or by locally derived endothelial factors. Arterial hypertension caused by volume overload is the leading clinical symptom indicating increased mineralocorticoid hormones. Excessive aldosterone production is seen in adenomatous disease of the adrenals. The balance between stimulatory/proliferative and antagonistic signaling is disturbed by expression of altered receptor subtypes in the adenomas. Increased aldosterone production without a detectable adenoma is the most frequent form of primary aldosteronism. Both increased sensitivity to agonistic signals and activating polymorphisms within the aldosterone synthase gene (CYP11B2) have been associated with excessive aldosterone production. 17alpha-Hydroxylase deficiency and glucocorticoidremediable aldosteronism can also cause excessive mineralocorticoid synthesis. In contrast, the severe form of pregnancy-induced hypertension, preeclampsia, is characterized by a compromised volume expansion in the presence of inappropriately low aldosterone levels. Initial evidence suggests that compromised CYP11B2 is causative, and that administration of NaCl lowered blood pressure in pregnant patients with low aldosterone availability due to a loss of function.

Aldosterone-induced coronary dysfunction in transgenic mice involves the calcium-activated potassium (BKCa) channels of vascular smooth muscle cells

BACKGROUND

Cardiomyocyte-specific overexpression of aldosterone synthase in male (MAS) mice induces a nitric oxide-independent coronary dysfunction. Because calcium-activated potassium (BKCa) channels are essential for vascular smooth muscle cell (VSMC) relaxation, we hypothesized that aldosterone alters their expression and/or function in VSMCs.

METHODS AND RESULTS

Left coronary artery segments were isolated from MAS or male wild-type mice and mounted in a wire myograph. Responses to acetylcholine were assessed (in the presence of a nitric oxide synthase inhibitor) without or with the cyclooxygenase inhibitor diclofenac, the KCa inhibitors charybdotoxin plus apamin, or the BKCa inhibitor iberiotoxin. Expression of BKCa was quantified in hearts by real-time quantitative polymerase chain reaction and Western blot and in isolated coronary arteries by polymerase chain reaction. The effect of aldosterone on BKCa expression also was studied in cultured rat aortic VSMCs. Acetylcholine-mediated coronary relaxation was markedly decreased in MAS mice and was prevented by spironolactone. Diclofenac did not affect the MAS-induced impairment in the responses to acetylcholine, whereas charybdotoxin plus apamin virtually abolished the relaxation in both male wild-type and MAS mice. After iberiotoxin, relaxation to acetylcholine was decreased to a larger extent in male wild-type than in MAS, leading to similar levels of relaxation. BKCa-alpha and -beta1 subunit expressions were significantly decreased in MAS heart and coronary arteries. In cultured VSMCs, aldosterone induced a concentration-dependent decrease in BKCa expression, which was prevented by spironolactone.

CONCLUSIONS

Aldosterone overexpression altered VSMC BKCa expression and coronary BKCa-dependent relaxation. The resulting alteration of relaxing responses may contribute to the deleterious effects of aldosterone in cardiovascular diseases. BKCa channels may therefore be useful therapeutic targets in cardiovascular diseases.

Body mass index predicts aldosterone production in normotensive adults on a high-salt diet

CONTEXT

The mechanisms underlying obesity-mediated cardiovascular disease are not fully understood. Aldosterone and insulin resistance both are associated with obesity and cardiovascular disease.

OBJECTIVES

The objectives of this study were to test the hypotheses that aldosterone production is elevated and associated with insulin resistance in overweight adults on a high-sodium diet.

PARTICIPANTS/INTERVENTIONS

Healthy normotensive adults were categorized as lean body mass index (BMI) less than 25 kg/m(2) (n = 63) or overweight BMI 25 kg/m(2) or greater (n = 57). After 7 d of a high-sodium diet, participants fasted overnight and remained supine throughout hemodynamic and laboratory assessments and angiotensin II (AngII) stimulation.

RESULTS

The overweight group, compared with the lean group, had higher 24-h urinary aldosterone (9.0 +/- 0.8 vs. 6.6 +/- 0.5 microg per 24 h; P = 0.003) and higher AngII-stimulated serum aldosterone (11.4 +/- 1.0 vs. 9.0 +/- 0.6 ng/dl; P = 0.04). There were no differences in 24-h urinary cortisol or sodium or supine measurements of plasma renin activity, serum aldosterone, or serum potassium. The homeostasis model assessment of insulin resistance was predicted by urinary aldosterone excretion (r = 0.32, P = 0.03) and serum aldosterone response to AngII stimulation (r = 0.28, P = 0.02) independent of age and BMI.

CONCLUSION

Urinary aldosterone excretion and AngII-stimulated aldosterone are increased in overweight, compared with lean, normotensive adults. The correlation of these measures of aldosterone production with insulin resistance suggests a potential role for aldosterone in the pathophysiology of obesity-mediated insulin resistance.

Induction of 5-aminolevulinate synthase by activators of steroid biosynthesis

Different cytochromes P450 are involved in steroid biosynthesis. These cytochromes have heme as the prosthetic group. We previously reported that ACTH, an activator of glucocorticoid biosynthesis in adrenal, requires heme biosynthesis for a maximal response. In the present study, we investigated the effect of ACTH, and the effect of two activators of the adrenal mineralocorticoid synthesis, endothelin-1 and low sodium diet on 5-aminolevulinate-synthase (ALA-s) mRNA. ALA-s is the rate-limiting enzyme in heme biosynthesis. It was found that infusion of rats with ACTH for 1 h caused an increase of adrenal ALA-s mRNA and activity accompanied by an increase in plasma corticosterone. CYP21, a cytochrome involved in the synthesis of both corticosterone and aldosterone, was not modified at the RNA level in adrenal glands by 1 h of ACTH infusion. Consistently, infusion of endothelin-1 for 1 h increased ALA-s mRNA and aldosterone content in adrenal gland without modifying CYP21 mRNA levels. To study if ALA-s is also regulated by the main physiological stimuli that increase adrenal mineralocorticoid secretion, we fed rats with low salt diet for 2 or 15 days. Low salt diet treatment increased adrenal gland ALA-s mRNA levels. On the other hand, the rapid stimulation of ALA-s mRNA by ACTH which acts through cyclic AMP was confirmed in H295R human adrenocortical cells, the only human adrenal cell line that has a steroid secretion pattern and regulation similar to primary cultures of adrenal cells. Our findings suggest that the acute activation of adrenal steroidogenic cytochromes by trophic hormones involves an increase in heme biosynthesis which will favor the production of active cytochromes.

[Determining aldosterone in the adrenal veins in order to establish uni- or bilateral aldosterone production in patients with primary hyperaldosteronism]

In 3 patients, men aged 60, 55 and 60, respectively, with hypertension due to primary hyperaldosteronism, the aldosterone level in the adrenal veins was determined for the purpose of further diagnosis. In two patients, unilateral adrenal enlargement on the CT-scan was accompanied by overproduction ofaldosterone, in one case in a non-enlarged adrenal gland and in the other case in both adrenals. The first patient underwent adrenalectomy of the non-enlarged adrenal gland, while in the second patient surgery was decided against. The third patient had bilateral adrenal gland enlargement on the CT-scan with a surgically treatable, unilateral overproduction ofaldosterone. Now that determination ofthe aldosterone:renin ratio in plasma as a screening method in selected patients with hypertension is being used more often, primary hyperaldosteronism turns out to be more common than was previously thought. For differentiation between unilateral and bilateral overproduction of aldosterone, imaging of the adrenals, for example with CT, is insufficiently accurate. Aldosterone determination in the adrenal veins can distinguish between unilateral and bilateral overproduction of aldosterone with great accuracy, which has important therapeutic consequences.

Down-regulation of D2 dopamine receptor and increased protein kinase Cmu phosphorylation in aldosterone-producing adenoma play roles in aldosterone overproduction

CONTEXT

The mechanism associated with the overproduction of aldosterone by aldosterone-producing adenomas (APA) is unknown.

OBJECTIVE

The objective of the study was to explore the role of the D2 dopamine receptor (D2R) on aldosterone synthesis and secretion and clarify the clinical importance of this role on aldosterone overproduction in APA.

RESULTS

D2R expression in APA was examined in 24 patients and was much less than that in the nontumorous adrenal cortex. D2R mRNA levels in APA were inversely correlated with CYP11B2 mRNA levels and the patient's plasma aldosterone concentration. Angiotensin II (AII)-stimulated aldosterone secretion and CYP11B2 mRNA expression in human adenocarcinoma cells (H295R) was attenuated by the D2 agonist, bromocriptine (BMC). BMC selectively attenuated AII-induced protein kinase C (PKC)-mu phosphorylation and its translocation to the cell membrane. PKCmu-specific short-hairpin RNA significantly decreased AII-induced CYP11B2 mRNA expression and aldosterone secretion. BMC also attenuated the AII-induced increase in cytoplasmic calcium, partially through an inhibition of cytoplasmic inositol 1,4,5 triphosphate production. Despite similar total PKCmu levels in APA and the nontumorous adrenal cortex, expression of phosphorylated PKCmu in APA was much higher.

CONCLUSION

This is the first study to demonstrate that the D2R modulated aldosterone secretion and synthesis through a specific attenuation of PKCmu activity, as well as the intracellular calcium level. Down-regulation of the D2R in APA, in turn, increased PKCmu activity and led to overproduction of aldosterone in affected patients. The D2R may thus serve as a potential treatment target for primary aldosteronism.

Angiotensin II reactivation and aldosterone escape phenomena in renin–angiotensin–aldosterone system blockade: is oral renin inhibition the solution?

This editorial considers the use of the first selective oral renin inhibitor, aliskiren, in reducing angiotensin (Ang) II reactivation or aldosterone (ALDO) escape during renin-angiotensin-aldosterone system (RAAS) inhibition. RAAS blockade with angiotensin converting enzyme inhibitors (ACEIs) and/or angiotensin receptor AT(1) blockers (ARBs) is very useful for the treatment of arterial hypertension, chronic heart failure (CHF), atherosclerosis and diabetes. 'Ang II reactivation' and 'ALDO escape' or 'breakthrough' have been observed during either ACEI or ARB treatment, and may attenuate the clinical benefit of RAAS blockade. Renin and Ang I accumulate during ACE inhibition, and might overcome the ability of an ACEI to effectively suppress ACE activity. There is also data suggesting that 30 - 40% of Ang II formation in the healthy human during RAAS activation is formed via renin-dependent, but ACE-independent, pathways. Moreover, ACE gene polymorphisms contribute to the modulation and adequacy of the neurohormonal response to long-term ACE inhibition, at least in patients with CHF (up to 45% of CHF patients have elevated Ang II levels despite the long-term use of an ACEI) or diabetes. The reactivated Ang II promotes ALDO secretion and sodium reabsorption. ALDO breakthrough also occurs during long-term ARB therapy, mainly by an AT(2)-dependent mechanism. This was related to target-organ damage in animal models. Oral renin inhibition with aliskiren has showed excellent efficacy and safety in the treatment of hypertension. Aliskiren can be co-administered with ACEIs, ARBs or hydrochlorothiazide. Furthermore, there is evidence suggesting that aliskiren reduces Ang II reactivation in ACE inhibition and ALDO escape during treatment with an ACEI or an ARB, at least to the degree that this is associated with the RAAS. For RAAS-independent ALDO production, the combination of aliskiren with eplerenone might prove useful.

Interacting influence of potassium and polychlorinated biphenyl on cortisol and aldosterone biosynthesis

Giving human adrenocortical H295R cells 14 mM KCl for 24 h significantly induced not only aldosterone biosynthesis but also cortisol biosynthesis. Pre-treating the cells with polychlorinated biphenyl 126 (PCB126) further increased potassium-induced aldosterone and cortisol productions in a dose-dependent manner, but all examined concentrations of PCB126 had little effect on the yields of precursor steroids progesterone and 17-OH-progesterone. Subsequent examinations revealed that CYP11B1 and CYP11B2 genes, responsible for the respective final steps of the cortisol and aldosterone biosynthetic pathways, exhibited increased responsiveness to PCB126 under high potassium. While 10(-5) M PCB126 was needed to induce a significant increase in the basal mRNA abundance of either gene, PCB126 could enhance potassium-induced mRNA expression of CYP11B1 at 10(-7) M and CYP11B2 at 10(-9) M. Actually, potassium and PCB126 synergistically upregulated mRNA expression of both genes. Potassium raised the transcriptional rates of CYP11B1 and CYP11B2 probably through a conserved Ad5 cis-element, whereas PCB126 appeared to regulate these two genes at the post-transcriptional level. Positive potassium-PCB126 synergism was also detected in CYP11B2 enzyme activity estimated by aldosterone/progesterone ratio. In contrast, potassium and PCB126 increased CYP11B1 enzyme activity or cortisol/17-OH-progesterone ratio additively. Moreover, potassium improved the time effect of PCB126 on gene expression and enzyme activity of CYP11B2, but not the PCB126 time response of CYP11B1. These data demonstrated that potassium differentially enhanced the potency of PCB126 to induce CYP11B1- and CYP11B2-mediated steroidogenesis.

Tumor necrosis factor-alpha regulates steroidogenesis, apoptosis, and cell viability in the human adrenocortical cell line NCI-H295R

TNF-alpha regulates the hypothalamo-pituitary-adrenal axis at several levels. It has been shown to modify adrenal steroidogenesis in many species, and it is supposed to act as an auto/paracrine factor. However, its significance in human adrenocortical function remains unclear. Therefore, we investigated the effect of TNF-alpha on adrenal steroidogenesis, expression of the key steroidogenic genes, apoptosis, and cell viability in the human adrenocortical cell line NCI-H295R. TNF-alpha treatment (1 nM for 48 h) decreased the basal production of cortisol, androstenedione, dehydroepiandrosterone sulfate (DHEAS), and aldosterone (14, 18, 35, and 52%, respectively), and the 8-bromo-cAMP-induced production of cortisol, androstenedione, dehydroepiandrosterone (DHEA), and DHEAS (44, 66, 58, and 48%, respectively). However, when the steroid production data were normalized by the cell number, TNF-alpha increased the basal production of cortisol, androstenedione, DHEA, DHEAS, and aldosterone (137, 121, 165, 73, and 28%, respectively), and the 8-bromo-cAMP-induced production of cortisol, DHEAS, and aldosterone (122, 121, and 256%, respectively). This was accompanied by a parallel increase in the expression of the genes encoding for the steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase 2, and 17-hydroxylase/17,20-lyase (74, 200, and 50%, respectively; quantitative real-time RT-PCR analysis). TNF-alpha increased caspase 3/7 activity (an indicator of apoptosis) and decreased cell viability dose and time dependently. The effect of TNF-alpha on apoptosis was neutralized by a monoclonal TNF-alpha antibody. These findings indicate that TNF-alpha is a potent regulator of steroidogenesis and cell viability in adrenocortical cells. TNF-alpha may have physiological and/or pathophysiological significance as an endocrine and/or paracrine/autocrine regulator of adrenocortical function.

Association between aldosterone production and variation in the 11beta-hydroxylase (CYP11B1) gene

CONTEXT

Variation in the region of chromosome 8 including the genes steroid 11beta-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) influences mineralocorticoid and glucocorticoid metabolism. However, the relative importance of polymorphisms in CYP11B1 and CYP11B2 in determining these phenotypes is unknown.

OBJECTIVE

Our objective was to investigate genetic influences of the CYP11B1 and CYP11B2 genes on mineralocorticoid metabolism.

DESIGN

We measured 24-h urinary excretion of the key metabolites of the principal mineralocorticoids, glucocorticoids and androgens secreted by the adrenal cortex. We genotyped polymorphisms spanning the CYP11B1 and CYP11B2 genes, which together capture all common variations at the locus.

PARTICIPANTS

Participants included 573 members of 105 British Caucasian families ascertained on a hypertensive proband.

MAIN OUTCOME MEASURES

We assessed heritability of urinary tetrahydroaldosterone (THAldo) excretion and association of THAldo excretion with genotype.

RESULTS

The heritability of THAldo excretion was 52% (P < 10(-6)). There was significant association between THAldo and genotype at several of the CYP11B1/B2 polymorphisms. The strongest association was observed at the rs6387 (2803A/G) polymorphism in intron 3 of CYP11B1 (P = 0.0004). Association followed a codominant model with a 21% higher THAldo excretion per G allele. Genotype at rs6387 accounted for 2.1% of the total population variability of THAldo. We found significant association between THAldo excretion and urinary total androgen excretion, urinary tetrahydrodeoxycortisol level, and urinary cortisol metabolites (all P < 0.001).

CONCLUSIONS

Aldosterone synthesis is highly heritable and is affected by genotype at CYP11B1. Our findings support the hypothesis that genetically determined differences in 11-hydroxylation efficiency can have downstream effects on mineralocorticoid synthesis. Such effects may be of relevance to the development of low-renin essential hypertension.