The effect of pioglitazone on aldosterone and cortisol production in HAC15 human adrenocortical carcinoma cells

Pioglitazone belongs to the class of drugs called thiazolidinediones (TZDs), which are widely used as insulin sensitizers in the treatment of diabetes. A major side effect of TZDs is fluid retention. The steroid hormone aldosterone also promotes sodium and fluid retention; however, the effect of pioglitazone on aldosterone production is controversial. We analyzed the effect of pioglitazone alone and in combination with angiotensin II (AngII) on the late rate-limiting step of adrenocortical steroidogenesis in human adrenocortical carcinoma HAC15 cells. Treatment with pioglitazone for 24 h significantly increased the expression of CYP11B2 and enhanced AngII-induced CYP11B2 expression. Despite the observed changes in mRNA levels, pioglitazone significantly inhibited AngII-induced aldosterone production and CYP11B2 protein levels. On the other hand, pioglitazone stimulated the expression of the unfolded protein response (UPR) marker DDIT3, with this effect occurring at early times and inhibitable by the PPARγ antagonist GW9962. The levels of DDIT3 (CHOP) and phospho-eIF2α (Ser51), a UPR-induced event that inhibits protein translation, were also increased. Thus, pioglitazone promotes CYP11B2 expression but nevertheless inhibits aldosterone production in AngII-treated HAC15 cells, likely by blocking global protein translation initiation through DDIT3 and phospho-eIF2α. In contrast, pioglitazone promoted AngII-induced CYP11B1 expression and cortisol production. Since cortisol enhances lipolysis, this result suggests the possibility that PPARs, activated by products of fatty acid oxidation, stimulate cortisol secretion to promote utilization of fatty acids during fasting. In turn, the ability of pioglitazone to stimulate cortisol production could potentially underlie the effects of this drug on fluid retention.

Protein kinase C and Src family kinases mediate angiotensin II-induced protein kinase D activation and acute aldosterone production

Recent evidence has shown a role for the serine/threonine protein kinase D (PKD) in the regulation of acute aldosterone secretion upon angiotensin II (AngII) stimulation. However, the mechanism by which AngII activates PKD remains unclear. In this study, using both pharmacological and molecular approaches, we demonstrate that AngII-induced PKD activation is mediated by protein kinase C (PKC) and Src family kinases in primary bovine adrenal glomerulosa cells and leads to increased aldosterone production. The pan PKC inhibitor Ro 31-8220 and the Src family kinase inhibitors PP2 and Src-1 inhibited both PKD activation and acute aldosterone production. Additionally, like the dominant-negative serine-738/742-to-alanine PKD mutant that cannot be phosphorylated by PKC, the dominant-negative tyrosine-463-to-phenylalanine PKD mutant, which is not phosphorylatable by the Src/Abl pathway, inhibited acute AngII-induced aldosterone production. Taken together, our results demonstrate that AngII activates PKD via a mechanism involving Src family kinases and PKC, to underlie increased aldosterone production.

Angiotensin II-induced protein kinase D activates the ATF/CREB family of transcription factors and promotes StAR mRNA expression

Aldosterone synthesis is initiated upon the transport of cholesterol from the outer to the inner mitochondrial membrane, where the cholesterol is hydrolyzed to pregnenolone. This process is the rate-limiting step in acute aldosterone production and is mediated by the steroidogenic acute regulatory (StAR) protein. We have previously shown that angiotensin II (AngII) activation of the serine/threonine protein kinase D (PKD) promotes acute aldosterone production in bovine adrenal glomerulosa cells, but the mechanism remains unclear. Thus, the purpose of this study was to determine the downstream signaling effectors of AngII-stimulated PKD activity. Our results demonstrate that overexpression of the constitutively active serine-to-glutamate PKD mutant enhances, whereas the dominant-negative serine-to-alanine PKD mutant inhibits, AngII-induced StAR mRNA expression relative to the vector control. PKD has been shown to phosphorylate members of the activating transcription factor (ATF)/cAMP response element binding protein (CREB) family of leucine zipper transcription factors, which have been shown previously to bind the StAR proximal promoter and induce StAR mRNA expression. In primary glomerulosa cells, AngII induces ATF-2 and CREB phosphorylation in a time-dependent manner. Furthermore, overexpression of the constitutively active PKD mutant enhances the AngII-elicited phosphorylation of ATF-2 and CREB, and the dominant-negative mutant inhibits this response. Furthermore, the constitutively active PKD mutant increases the binding of phosphorylated CREB to the StAR promoter. Thus, these data provide insight into the previously reported role of PKD in AngII-induced acute aldosterone production, providing a mechanism by which PKD may be mediating steroidogenesis in primary bovine adrenal glomerulosa cells.

Aldosterone synthase inhibition in hypertension

Hypertension is an established risk factor for stroke, premature coronary artery disease and heart failure. Control of elevated blood pressure has been shown to result in significant reduction of cardiovascular risk. Aldosterone, the final product of the renin-angiotensin-aldosterone system (RAAS), not only causes salt and water reabsorbtion in the kidneys through its effect on the mineralocorticoid hormone receptor (MR), but also an MR-independent effect, not regulated by conventional MR blockade. Although many pharmacological agents target different levels of the RAAS cascade, these generally result in elevated renin concentration and plasma renin activity. This upstream feedback response subsequently results in elevated levels of angiotensin II, a potent vasoconstrictor and stimulus to aldosterone release. This aldosterone breakthrough counteracts the long-term blood pressure-lowering effect of these agents. Therefore the development of a new class of pharmacologic agents that directly inhibit the production of aldosterone may prove clinically useful in reducing aldosterone and thereby controlling elevated blood pressure.

PCP4: a regulator of aldosterone synthesis in human adrenocortical tissues

Purkinje cell protein 4 (PCP4) is a calmodulin (CaM)-binding protein that accelerates calcium association and dissociation with CaM. It has been previously detected in aldosterone-producing adenomas (APA), but details on its expression and function in adrenocortical tissues have remained unknown. Therefore, we performed the immunohistochemical analysis of PCP4 in the following tissues: normal adrenal (NA; n=15), APA (n=15), cortisol-producing adenomas (n=15), and idiopathic hyperaldosteronism cases (IHA; n=5). APA samples (n=45) were also submitted to quantitative RT-PCR of PCP4, CYP11B1, and CYP11B2, as well as DNA sequencing for KCNJ5 mutations. Transient transfection analysis using PCP4 siRNA was also performed in H295R adrenocortical carcinoma cells, following ELISA analysis, and CYP11B2 luciferase assays were also performed after PCP4 vector transfection in order to study the regulation of PCP4 protein expression. In our findings, PCP4 immunoreactivity was predominantly detected in APA and in the zona glomerulosa of NA and IHA. In APA, the mRNA levels of PCP4 were significantly correlated with those of CYP11B2 (P<0.0001) and were significantly higher in cases with KCNJ5 mutation than WT (P=0.005). Following PCP4 vector transfection, CYP11B2 luciferase reporter activity was significantly higher than controls in the presence of angiotensin-II. Knockdown of PCP4 resulted in a significant decrease in CYP11B2 mRNA levels (P=0.012) and aldosterone production (P=0.011). Our results indicate that PCP4 is a regulator of aldosterone production in normal, hyperplastic, and neoplastic human adrenocortical cells.

Role of D2 dopamine receptor in adrenal cortical cell proliferation and aldosterone-producing adenoma tumorigenesis

Aldosterone-producing adenoma (APA) and bilateral adrenal hyperplasia are the two characteristic types of primary aldosteronism. Dysregulation of adrenal cortical cell proliferation contributes to both diseases. We previously demonstrated that APA expressed less dopamine D2 receptor than the respective non-tumor tissue and might contribute to the overproduction of aldosterone. As activation of D2 receptor inhibits the proliferation of various cells, downregulation of D2 receptor in APA may play a role in the tumorigenesis of APA. In this study, we demonstrate that D2 receptor plays a role in angiotensin II (AII)-stimulated adrenal cortical cell proliferation. The D2 receptor agonist, bromocriptine, inhibited AII-stimulated cell proliferation in primary cultures of the normal human adrenal cortex and APA through attenuating AII-induced phosphorylation of PK-stimulated cyclin D1 protein expression and cell proliferation. D2 receptor also inhibited AII-induced ERK1/2 phosphorylation. Our results demonstrate that, in addition to inhibiting aldosterone synthesis/production, D2 receptor exerts an anti-proliferative effect in adrenal cortical and APA cells by attenuating PKCμ and ERK phosphorylation. The lower level of expression of D2 receptor in APA may augment cell proliferation and plays a crucial role in the tumorigenesis of APA. Our novel finding suggests a new therapeutic target for primary aldosteronism.

Aberrant gonadotropin-releasing hormone receptor (GnRHR) expression and its regulation of CYP11B2 expression and aldosterone production in adrenal aldosterone-producing adenoma (APA)

Aberrant expression of gonadotropin-releasing hormone receptor (GnRHR) has been reported in human adrenal tissues including aldosterone-producing adenoma (APA). However, the details of its expression and functional role in adrenals are still not clear. In this study, quantitative RT-PCR analysis revealed the mean level of GnRHR mRNA was significantly higher in APAs than in human normal adrenal (NA) (P=0.004). GnRHR protein expression was detected in human NA and neoplastic adrenal tissues. In H295R cells transfected with GnRHR, treatment with GnRH resulted in a concentration-dependent increase in CYP11B2 reporter activity. Chronic activation of GnRHR with GnRH (100nM), in a cell line with doxycycline-inducible GnRHR (H295R-TR/GnRHR), increased CYP11B2 expression and aldosterone production. These agonistic effects were inhibited by blockers for the calcium signaling pathway, KN93 and calmidazolium. These results suggest GnRH, through heterotopic expression of its receptor, may be a potential regulator of CYP11B2 expression levels in some cases of APA.

Prognosis of primary aldosteronism in Japan: results from a nationwide epidemiological study

The Research Committee of Disorders of Adrenal Hormones, Japan, undertook a nationwide epidemiological study of primary aldosteronism (PA). The present study was undertaken as a part of this study to reveal the relationship between type of treatment and the prognosis of PA. In the primary survey, 4161 patients with PA during the period January 1, 2003-December 31, 2007 were reported from 3252 departments of internal medicine, pediatrics and urology. In the secondary survey, a questionnaire that requested detailed clinical information on individual patients was sent to those departments reporting patients in the primary survey. In total, data on 1706 patients with PA were available in the present study. Among patients with bilateral or unilateral aldosterone-producing adenoma, after adjustment for age at which prognosis was examined, sex, surgical treatment and medical treatment, surgical treatment was significantly associated with amelioration of hypertension (adjusted odds ratio [OR]: 0.47 [95% confidence interval (CI): 0.29-0.77]) and hypokalemia (adjusted OR: 0.17 [95% CI: 0.11-0.29]). No significant relationship was observed between medical treatment and such prognosis in this group of patients. Among patients with bilateral or unilateral adrenal hyperplasia, surgical, but not medical, treatment was significantly associated with amelioration of hypokalemia (adjusted OR: 0.23 [95% CI: 0.06-0.74]), while there was no relationship between surgical or medical treatment and the prognosis of hypertension. In conclusion, surgery offered a better prognosis of PA than medication with regards to hypertension and hypokalemia, with the limitation that a new anti-aldosterone drug, eplerenone, was not available during the study period.

Vitamin D receptor, an important transcription factor associated with aldosterone-producing adenoma

OBJECTIVE

To explore the endocrine mechanisms of aldosterone-producing adenoma (APA) by using the microarray expression profiles of normal and APA samples.

METHODS

The gene expression profile GSE8514 was downloaded from Gene Expression Omnibus database, including samples from normal adrenals (n = 5) and APAs (n = 10). The differentially expressed genes (DEGs) were identified by samr package and endocrine DEGs were obtained according to Clinical Genome Database. Then, functional enrichment analysis of screened DEGs was performed by DAVID (Database for Annotation, Visualization and Integrated Discovery). Finally, a regulatory network was constructed to screen endocrine genes related with adrenal dysfunction and pathway enrichment analysis for the constructed network was performed.

RESULTS

A total of 2149 DEGs were identified including 379 up- and 1770 down-regulated genes. And 26 endocrine genes were filtered from the DEGs. Furthermore, the down-regulated DEGs are mainly related to protein kinase cascade, response to molecule of bacterial origin, response to lipopolysaccharide, cellular macromolecule catabolic process and macromolecule catabolic process, while the up-regulated DEGs are related with regulation of ion transport. The target genes of VDR (vitamin D receptor), one of the three endocrine genes differentially expressed in the regulatory network, were endocrine genes including CYP24A1 (25-hydroxyvitamin D-24-hydroxylase) and PTH (parathyroid hormone). Three pathways may be associated with APA pathogenesis including cytokine-cytokine receptor interaction, pathways in cancer and autoimmune thyroid disease.

CONCLUSION

The VDR is the most significant transcription factor and related endocrine genes might play important roles in the endocrine mechanisms of APA.

Vascular aldosterone production at the pre-diabetic stage of young Otsuka Long-Evans Tokushima Fatty (OLETF) rats, compared with Long-Evans Tokushima Otsuka (LETO) rats

We examined the ability of aortic smooth muscle cells (AoSMC) prepared from spontaneously diabetic rats to produce aldosterone (Aldo) and the regulatory mechanism that controls their Aldo production. AoSMC of 6 week-old Long-Evans Tokushima Otsuka (LETO: the control group) and 6 week-old Otsuka Long-Evans Tokushima Fatty (OLETF: the type 2 diabetes group) rats were used in the present experiments. CYP11B2 (Aldo synthetase) mRNA expression was detected in both the LETO and OLETF AoSMC. Basal Aldo production was significantly greater (4-5 fold higher) in the OLETF AoSMC culture medium than in the LETO AoSMC culture medium. When AoSMC were co-incubated with high-density lipoproteins (HDL), supplying cholesterol as a substrate for steroidogenesis in rats, angiotensin II (AII) significantly increased greater Aldo production in the OLETF AoSMC than in the LETO AoSMC. The present data suggested that future onset of diabetic vascular dysfunction is partly caused by excess Aldo production by AoSMC in young OLETF rats. Concomitant stimulation by HDL and AII resulted in elevated Aldo production in the OLETF and the LETO AoSMC, and also demonstrated that AII-induced Aldo production is greatly enhanced by HDL in OLETF, rather than in LETO. In conclusion, our data clearly demonstrated that Aldo production in the OLETF AoSMC was significantly higher than in the LETO AoSMC, suggesting possible future onset of vascular dysfunction in diabetes, induced by local Aldo production in the AoSMC.

Extramitochondrial OPA1 and adrenocortical function

We have previously described that silencing of the mitochondrial protein OPA1 enhances mitochondrial Ca(2+) signaling and aldosterone production in H295R adrenocortical cells. Since extramitochondrial OPA1 (emOPA1) was reported to facilitate cAMP-induced lipolysis, we hypothesized that emOPA1, via the enhanced hydrolysis of cholesterol esters, augments aldosterone production in H295R cells. A few OPA1 immunopositive spots were detected in ∼40% of the cells. In cell fractionation studies OPA1/COX IV (mitochondrial marker) ratio in the post-mitochondrial fractions was an order of magnitude higher than that in the mitochondrial fraction. The ratio of long to short OPA1 isoforms was lower in post-mitochondrial than in mitochondrial fractions. Knockdown of OPA1 failed to reduce db-cAMP-induced phosphorylation of hormone-sensitive lipase (HSL), Ca(2+) signaling and aldosterone secretion. In conclusion, OPA1 could be detected in the post-mitochondrial fractions, nevertheless, OPA1 did not interfere with the cAMP - PKA - HSL mediated activation of aldosterone secretion.

Spironolactone prevents dietary-induced metabolic syndrome by inhibiting PI3-K/Akt and p38MAPK signaling pathways

OBJECTIVES

Aim of the study is to evaluate the impact of spironolactone (SPL) on indexes of metabolic syndrome (MS) and further investigate the mechanisms underlying its protective effects.

METHODS

A rat model of MS was established by administering a fat- and salt-enriched diet (FS diet). The occurrence of MS was examined by measurement of blood pressure (BP), aldosterone (ALD) content, blood lipid (BL), glucose and insulin levels. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Pancreatic gland tissue injury was assessed by β-cell apoptosis. Mineralocorticoid receptor (MR) activity, phosphatidylinositol 3- kinase/Akt (PI3-K/Akt), and phosphorylation of p38MAPK (Pp38MAPK) in pancreatic gland tissue were evaluated by western blot analysis.

RESULTS

SPL prevented hypertension, and dyslipidemia during MS induced by the intake of FS diet, but had no effect on K+ and Na+ disturbances. Furthermore, SPL significantly attenuated ALD and MR expression levels after FS diet. Finally, SPL inhibited phosphorylation protein kinase B (p- PKB) activation in the pancreatic gland tissue, a downstream target of PI3-K, and phosphorylation of p38MAPK pathway, critical for cellular apoptosis.

CONCLUSIONS

This study demonstrates that SPL exerts a protective effect on hypertension and dyslipidemia. This protective effect may depend, at least in part, on MAPK and PI3-K pathways.

QRFP induces aldosterone production via PKC and T-type calcium channel-mediated pathways in human adrenocortical cells: evidence for a novel role of GPR103

Hormonal regulation of adrenal function occurs primarily through activation of GPCRs. GPCRs are central to many of the body's endocrine and neurotransmitter pathways. Recently, it was shown that activation of GPR103 by its ligand QRFP induced feeding, locomotor activity, and metabolic rate, and QRFP is bioactive in adipose tissue of obese individuals. Given that the adrenal gland is a pivotal organ for energy balance and homeostasis, we hypothesized that GPR103 and QRFP are involved in steroidogenic responses. Using qRT-PCR and immunohistochemistry, we mapped both GPR103 and QRFP in human fetal and adult adrenal gland as well as rat adrenals. Both were primarily localized in the adrenal cortex but not in the medulla. Activation of GPR103 in human adrenocortical H295R cells led to a decrease in forskolin-increased cAMP and an increase of intracellular Ca(2+) levels. In addition, treatment of H295R cells with QRFP induced aldosterone and cortisol secretion as measured by ELISA. These increases were accompanied by increased expression and activity of StAR, CYB11B1, and CYP11B2 as assessed by qRT-PCR and luciferase reporter assay, respectively. Using specific inhibitors, we also demonstrated that aldosterone induction involves MAPK, PKC, and/or T-type Ca(2+) channel-dependent pathways. These novel data demonstrate that QRFP induces adrenal steroidogenesis in vitro by regulating key steroidogenic enzymes involving MAPK/PKC and Ca(2+) signaling pathways.

Increased expression of (pro)renin receptor in aldosterone-producing adenomas

(Pro)renin receptor ((P)RR) is a specific receptor for renin and prorenin. The aim of the present study is to clarify expression and possible pathophysiological roles of (P)RR in aldosterone-producing adenomas (APAs) and other adrenal tumors. Expression of (P)RR was studied by immunocytochemistry, western blot analysis and real-time RT-PCR in adrenal tumor tissues obtained at surgery. Immunocytochemistry showed that (P)RR was expressed in normal adrenal glands and tumor tissues of adrenocortical tumors including APAs. In the normal adrenal glands, positive (P)RR immunostaining was observed in both adrenal cortex and medulla, with higher (P)RR immunostaining observed in zona glomerulosa and zona reticularis. Positive (P)RR immunostaining was also observed in the adrenocortical tumors, with elevated (P)RR immunostaining found in APAs, particularly in compact cells. By contrast, no apparent (P)RR immunostaining was observed in pheochromocytomas. Western blot analysis showed a band of (P)RR protein in normal adrenal glands and adrenocortical tumors at the position of 35 kDa. The relative expression levels of (P)RR protein were higher in tumor tissues of APAs than in attached non-neoplastic adrenal tissues of APAs. Real-time RT-PCR showed that expression levels of (P)RR mRNA were significantly increased in tumor tissues of APAs compared with other adrenal tumor tissues and attached non-neoplastic adrenal tissues of APAs. The present study has shown for the first time that expression of (P)RR is elevated in tumor tissues of APAs, raising the possibility that (P)RR may play pathophysiological roles in APAs, such as aldosterone secretion and cell proliferation.

Genetics of mineralocorticoid excess: an update for clinicians

Aldosterone plays a major role in the regulation of sodium and potassium homeostasis and blood pressure. More recently, aldosterone has emerged as a key hormone mediating end organ damage. In extreme cases, dysregulated aldosterone production leads to primary aldosteronism (PA), the most common form of secondary hypertension. However, even within the physiological range, high levels of aldosterone are associated with an increased risk of developing hypertension over time. PA represents the most common and curable form of hypertension, with a prevalence that increases with the severity of hypertension. Although genetic causes underlying glucocorticoid-remediable aldosteronism, one of the three Mendelian forms of PA, were established some time ago, somatic and inherited mutations in the potassium channel GIRK4 have only recently been implicated in the formation of aldosterone-producing adenoma (APA) and in familial hyperaldosteronism type 3. Moreover, recent findings have shown somatic mutations in two additional genes, involved in maintaining intracellular ionic homeostasis and cell membrane potential, in a subset of APAs. This review summarizes our current knowledge on the genetic determinants that contribute to variations in plasma aldosterone and renin levels in the general population and the genetics of familial and sporadic PA. Various animal models that have significantly improved our understanding of the pathophysiology of excess aldosterone production are also discussed. Finally, we outline the cardiovascular, renal, and metabolic consequences of mineralocorticoid excess beyond blood pressure regulation.

Lessons from the gene expression pattern of the rat zona glomerulosa

We recently identified hundreds of transcripts with differential expression in rat zona glomerulosa (zG) and zona fasciculata. Although the genes up-regulated in the zG may be playing important roles in aldosterone production, the relationship between most of these genes and aldosterone production has not been uncovered. Because aldosterone, in the presence of a high sodium diet, is now considered a significant cardiovascular risk factor, in this review we performed gene ontology and pathway analyses on the same microarray data to better define the genes that may influence zG function. Overall, we identified a number of genes that may be involved in aldosterone production through transforming growth factor β (TGF-β), WNT, calcium, potassium, and ACTH signaling pathways. The list of genes we present in the current report may become an important tool for researchers working on primary aldosteronism and aldosterone-related cardiovascular diseases.

KCNJ5 mutations in aldosterone producing adenoma and relationship with adrenal cortex remodeling

Somatic mutations of KCNJ5, coding for the potassium channel GIRK4, have recently been implicated in the formation of aldosterone producing adenoma (APA). While a causal link between KCNJ5 mutations, membrane depolarization and aldosterone production has been established, the precise mechanism by which these mutations promote cell proliferation and APA formation remains unclear. The aim of our study was to correlate KCNJ5 mutation status with morphological and functional characteristics of the adrenal cortex adjacent to APA. While GIRK4 was expressed in APA and in the zona glomerulosa of the adjacent cortex, significantly lower levels were detected in APA harboring a KCNJ5 mutation. There was no correlation between KCNJ5 mutation status and the morphological measures of adrenal cortex remodeling, including nodulation, vascularization and expression of CYP11B2. The cell composition of APA was not significantly different between groups. These results indicate that KCNJ5 mutations are not correlated with adrenal cortex remodeling in APA.

A role for phospholipase D in angiotensin II-induced protein kinase D activation in adrenal glomerulosa cell models

The mineralocorticoid aldosterone plays an important role in regulating blood pressure, with excess causing hypertension and exacerbating cardiovascular disease. Previous studies have indicated a role for both phospholipase D (PLD) and protein kinase D (PKD) in angiotensin II (AngII)-regulated aldosterone production in adrenal glomerulosa cells. Therefore, the relationship between AngII-activated PLD and PKD was determined in two glomerulosa cell models, primary bovine zona glomerulosa (ZG) and HAC15 human adrenocortical carcinoma cells, using two inhibitors, 1-butanol and the reported PLD inhibitor, fluoro-2-indolyl des-chlorohalopemide (FIPI). FIPI was first confirmed to decrease PLD activation in response to AngII in the two glomerulosa cell models. Subsequently, it was shown that both 1-butanol and FIPI inhibited AngII-elicited PKD activation and aldosterone production. These results indicate that PKD is downstream of PLD and suggest that PKD is one of the mechanisms through which PLD promotes aldosterone production in response to AngII in adrenal glomerulosa cells.

Characterization of NCI-H295R cells as an in vitro model of hyperaldosteronism

In depth analysis of key molecular mechanisms involved in functional autonomy of aldosterone secretion is hampered by the lack of tumor cell lines that reflect functional characteristics of aldosterone producing adenomas. Herein, we describe the characteristics of the adrenocortical carcinoma cell line NCI-H295R and its suitability as a model of hyperaldosteronism in relation to different culture conditions. Steroid profiling revealed that NCI-H295R cells predominantly secrete cortisol, while aldosterone and other steroids are released at much lower concentrations. However, aldosterone output specifically increased in response to different stimuli such as ACTH and angiotensin II, and in particular to potassium in a dose dependent manner. NCI-H295R cells readily formed spheroids under specific culture conditions, a method widely used for the enrichment of progenitor cells. Unexpectedly, spheroid cells excelled with higher aldosterone concentration and higher expression levels of the steroidogenic enzymes StAR, 3βHSD, CYP17, SF-1, and the MC2-receptor. Further investigations revealed that this phenomenon is mainly attributed to epithelial growth factor (EGF) and particularly fibroblast growth factor (FGF), which are both essential ingredients in the spheroid culture medium. Aldosterone release under the combinatory influence of EGF and FGF was not higher than the effect of FGF alone. Spheroid growth per se, therefore, does not ensure an enrichment of less differentiated cell types in this cell line.

Characterization of steroidogenic enzyme expression in aldosterone-producing adenoma: a comparison with various human adrenal tumors

We analyzed the expression profiles of several steroidogenic enzymes in normal adrenals, aldosterone-producing adenomas (APA), cortisol-producing adenomas combined with Cushing's syndrome (CPA) or with subclinical Cushing's syndrome (SCPA), and nonfunctioning adrenal adenomas (NFA) to clarify the nature and characteristics of steroidogenesis in APA. Clinical data were collected for all subjects. In resected adrenal glands (normal adrenals, APA, CPA, SCPA, and NFA), the mRNA expression levels of the CYP17, HSD3B2, CYP11B1, and CYP11B2 genes were studied using real-time quantitative PCR and immunohistochemistry. The CYP11B2 mRNA level in APA was significantly higher than that in other groups. The CYP17/HSD3B2 ratio for mRNA in APA was significantly lower than those in the other groups. Low ratio of CYP17/HSD3B2 with high expression of CYP11B2 seems to explain steroidogenic characteristics of APA.

Female sex hormones are associated with the reduction of serum sodium and hypertension complications in patients with aldosterone-producing adenoma

This study was conducted to evaluate gender-related differences in clinical characteristics and vascular complications in patients with aldosterone-producing adenomas (APA). Clinical characteristics, biochemical markers and incidence of vascular complications were compared by gender in 187 consecutive patients with APA confirmed by pathological diagnosis. Patients were separated into two groups based on ages either older or younger than 49 years, the average age of menopause among Chinese women (<49 y and ≥49 y). Males had significantly higher BMI than females in the age group of <49 years (p = 0.017). In the <49 years group, males had significantly higher serum sodium levels (p = 0.003). However, no such gender differences in clinical characteristics were observed in patients ≥49 years. A higher proportion of vascular complications was observed in males as compared to females aged <49 years but the difference was not statistically significant (51.4% vs. 34.8%, p = 0.105). The only gender difference observed in vascular complications between patients aged ≥49 years was that a significantly greater proportion of males had cerebrovascular complication compared to females (p = 0.006). Our data suggest that female sex hormones are implicated in reducing serum sodium concentration and vascular complications in female APA patients.

An in vivo role of bone morphogenetic protein-6 in aldosterone production by rat adrenal gland

Aldosterone is synthesized in the zona glomerulosa of the adrenal cortex. We previously reported the presence of a functional BMP system including BMP-6 in human adrenocortical cells. BMP-6 contributes to Ang II-induced aldosterone production by activating Smad signaling, in which endogenous BMP-6 action is negatively controlled by Ang II in vitro. In the present study, we examined the in vivo role of BMP-6 in regulation of aldosterone by neutralizing endogenous BMP-6 in rats treated with immunization against BMP-6. Three-week-old male rats were actively immunized with rat mature BMP-6 antigen conjugated with keyhole limpet hemocyanin (KLH). The immunization treatment had no effect on bilateral adrenal weight or its ratio to body weight. Urinary aldosterone excretion was time-dependently increased during the 8-week observation period in the control group. Of note, the level of urinary aldosterone excretion in BMP-6-KLH-immunized rats was significantly reduced compared to that in the control group, suggesting that endogenous BMP-6 contributes to the induction of aldosterone production in vivo. Moreover, the level of urinary aldosterone/creatinine after 8-week treatment was significantly lowered by treatment with BMP-6-KLH. In contrast, with chronic Ang II treatment, urinary aldosterone and creatinine-corrected values at 8 weeks were not significantly different between the two groups, suggesting that the effects of BMP-6-KLH were impaired under the condition of chronic treatment with Ang II. The mRNA levels of Cyp11b2, but not those of Star, P450scc and 3βhsd2, were significantly decreased in adrenal tissues isolated from BMP-6-KLH-immunized rats after 8-week treatment. Furthermore, the ratio of plasma aldosterone level to corticosterone was significantly decreased by immunization with BMP-6-KLH. Collectively, the results indicate that endogenous BMP-6 is functionally linked to aldosterone synthesis by the zona glomerulosa in the adrenal cortex in vivo.

Minireview: aldosterone biosynthesis: electrically gated for our protection

Aldosterone produced by adrenal zona glomerulosa (ZG) cells plays an important role in maintaining salt/water balance and, hence, blood pressure homeostasis. However, when dysregulated, aldosterone advances renal and cardiovascular disease states. Multiple steps in the steroidogenic pathway require Ca(2+), and the sustained production of aldosterone depends on maintained Ca(2+) entry into the ZG cell. Nevertheless, the recorded membrane potential of isolated ZG cells is extremely hyperpolarized, allowing the opening of only a small fraction of low-voltage-activated Ca(2+) channels of the Ca(v)3.x family, the major Ca(2+) conductance on the ZG cell membrane. As a consequence, to activate sufficient Ca(2+) channels to sustain the production of aldosterone, aldosterone secretagogs would be required to affect large decreases in membrane voltage, a requirement that is inconsistent with the exquisite sensitivity of aldosterone production in vivo to small changes (0.1 mm) in extracellular K(+). In this review, we evaluate the contribution of membrane voltage and voltage-dependent Ca(2+) channels to the control of aldosterone production and consider data highlighting the electrical excitability of the ZG cell. This intrinsic capacity of ZG cells to behave as electrical oscillators provides a platform from which to generate a recurring Ca(2+) signal that is compatible with the lengthy time course of steroidogenesis and provides an alternative model for the physiological regulation of aldosterone production that permits both amplitude and temporal modulation of the Ca(2+) signal.

Effect of KCNJ5 mutations on gene expression in aldosterone-producing adenomas and adrenocortical cells

CONTEXT

Primary aldosteronism is a heterogeneous disease that includes both sporadic and familial forms. A point mutation in the KCNJ5 gene is responsible for familial hyperaldosteronism type III. Somatic mutations in KCNJ5 also occur in sporadic aldosterone producing adenomas (APA).

OBJECTIVE

The objective of the study was to define the effect of the KCNJ5 mutations on gene expression and aldosterone production using APA tissue and human adrenocortical cells.

METHODS

A microarray analysis was used to compare the transcriptome profiles of female-derived APA samples with and without KCNJ5 mutations and HAC15 adrenal cells overexpressing either mutated or wild-type KCNJ5. Real-time PCR validated a set of differentially expressed genes. Immunohistochemical staining localized the KCNJ5 expression in normal adrenals and APA.

RESULTS

We report a 38% (18 of 47) prevalence of KCNJ5 mutations in APA. KCNJ5 immunostaining was highest in the zona glomerulosa of NA and heterogeneous in APA tissue, and KCNJ5 mRNA was 4-fold higher in APA compared with normal adrenals (P < 0.05). APA with and without KCNJ5 mutations displayed slightly different gene expression patterns, notably the aldosterone synthase gene (CYP11B2) was more highly expressed in APA with KCNJ5 mutations. Overexpression of KCNJ5 mutations in HAC15 increased aldosterone production and altered expression of 36 genes by greater than 2.5-fold (P < 0.05). Real-time PCR confirmed increases in CYP11B2 and its transcriptional regulator, NR4A2.

CONCLUSIONS

KCNJ5 mutations are prevalent in APA, and our data suggest that these mutations increase expression of CYP11B2 and NR4A2, thus increasing aldosterone production.