Glomerulosa Cells Research Articles

Two-pore domain potassium channels in the adrenal cortex.

The physiological control of steroid hormone secretion from the adrenal cortex depends on the function of potassium channels. The “two-pore domain K+ channels” (K2P) TWIK-related acid sensitive K+ channel 1 (TASK1), TASK3, and TWIK-related K+ channel 1 (TREK1) are strongly expressed in adrenocortical cells. They confer a background K+ conductance to these cells which is important for the K+ sensitivity as well as for angiotensin II and adrenocorticotropic hormone-dependent stimulation of aldosterone and cortisol synthesis. Mice with single deletions of the Task1 or Task3 gene as well as Task1/Task3 double knockout mice display partially autonomous aldosterone synthesis. It appears that TASK1 and TASK3 serve different functions: TASK1 affects cell differentiation and prevents expression of aldosterone synthase in the zona fasciculata, while TASK3 controls aldosterone secretion in glomerulosa cells. TREK1 is involved in the regulation of cortisol secretion in fasciculata cells. These data suggest that a disturbed function of K2P channels could contribute to adrenocortical pathologies in humans.

Effect of swimming on the production of aldosterone in rats.

It has been demonstrated that exercise is one of the stresses known to increase the aldosterone secretion. Both potassium and angiotensin II (Ang II) levels are shown to be correlated with aldosterone production during exercise, but the mechanism is still unclear. In an in vivo study, male rats were catheterized via right jugular vein (RJV), and divided into four groups namely water immersion, swimming, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitro study, rat zona glomerulosa (ZG) cells were challenged by lactate (1–10 mM) in the presence or absence of Ang II (10−8 M) for 60 min. The levels of aldosterone in plasma and medium were measured by radioimmunoassay. Cell lysates were analyzed by immunoblotting assay. After exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. Swimming for 10 min significantly increased the plasma Ang II levels in male rats. Administration of lactate plus Ang II significantly increased aldosterone production and enhanced protein expression of steroidogenic acute regulatory protein (StAR) in ZG cells. These results demonstrated that acute exercise led to the increase of both aldosterone and Ang II secretion, which is associated with lactate action on ZG cells and might be dependent on the activity of renin-angiotensin system.

Effect of Vitex agnus castus L. essential oil on stereological architecture of adrenal glands in female mice

The adrenal gland is of critical importance for a plethora of biological processes and has a pivotal role in different stages of life. The structure and function of adrenal can be affected by steroid hormones. Vitex agnus-castus L. (VAC) is a phytosterogen shrub and has been used in the treatment of many female conditions such as menstrual disorders in traditional medicine. So, this study was conducted to investigate the effects of VAC essential oil on structure of adrenal glands. In this study 20 young adult female BALB/c mice were randomly divided into four groups: group 1 as control group, group 2 received 75 mg/kg VAC, group 3 received 150 mg/kg VAC and group 4 which received 300 mg/kg VAC essential oil via gastric gavage for seven consecutive days. At the eighth day, animals were euthanized and the adrenal glands were quickly removed, weighted and fixed in buffered formalin. The samples were processed by routine and standard paraffin embedding and serially sectioned and stained by H&E. The total volume of adrenal gland, adrenal cortex and cortical zones were estimated by Cavalieri’s point-counting principle using Weibel’s multipurpose test grid M 42 . Total number of cortical cell in each zona was estimated by unbiased stereological methods. The results showed that adrenal gland mass were significantly decreased in group 4. It was also found that there are no significant differences in the zona glomerulosa volume and cell number among examined groups. The volume of cortex, zona fasciculata, zona reticularis and cell number of these regions were significantly reduced in group 4 compared to other groups (P<0.05). Finally, it can be concluded that VAC essential oil can affected adrenocortical structure. So, it should be considered with caution with high doses in traditional medicine.

Regulation of aldosterone synthesis and secretion.

Aldosterone is a steroid hormone synthesized in and secreted from the outer layer of the adrenal cortex, the zona glomerulosa. Aldosterone is responsible for regulating sodium homeostasis, thereby helping to control blood volume and blood pressure. Insufficient aldosterone secretion can lead to hypotension and circulatory shock, particularly in infancy. On the other hand, excessive aldosterone levels, or those too high for sodium status, can cause hypertension and exacerbate the effects of high blood pressure on multiple organs, contributing to renal disease, stroke, visual loss, and congestive heart failure. Aldosterone is also thought to directly induce end-organ damage, including in the kidneys and heart. Because of the significance of aldosterone to the physiology and pathophysiology of the cardiovascular system, it is important to understand the regulation of its biosynthesis and secretion from the adrenal cortex. Herein, the mechanisms regulating aldosterone production in zona glomerulosa cells are discussed, with a particular emphasis on signaling pathways involved in the secretory response to the main controllers of aldosterone production, the renin-angiotensin II system, serum potassium levels and adrenocorticotrophic hormone. The signaling pathways involved include phospholipase C-mediated phosphoinositide hydrolysis, inositol 1,4,5-trisphosphate, cytosolic calcium levels, calcium influx pathways, calcium/calmodulin-dependent protein kinases, diacylglycerol, protein kinases C and D, 12-hydroxyeicostetraenoic acid, phospholipase D, mitogen-activated protein kinase pathways, tyrosine kinases, adenylate cyclase, and cAMP-dependent protein kinase. A complete understanding of the signaling events regulating aldosterone biosynthesis may allow the identification of novel targets for therapeutic interventions in hypertension, primary aldosteronism, congestive heart failure, renal disease, and other cardiovascular disorders.

Wnt signaling inhibits adrenal steroidogenesis by cell-autonomous and non-cell-autonomous mechanisms.

Wnt/β-catenin (βcat) signaling is critical for adrenal homeostasis. To elucidate how Wnt/βcat signaling elicits homeostatic maintenance of the adrenal cortex, we characterized the identity of the adrenocortical Wnt-responsive population. We find that Wnt-responsive cells consist of sonic hedgehog (Shh)-producing adrenocortical progenitors and differentiated, steroidogenic cells of the zona glomerulosa, but not the zona fasciculata and rarely cells that are actively proliferating. To determine potential direct inhibitory effects of βcat signaling on zona fasciculata-associated steroidogenesis, we used the mouse ATCL7 adrenocortical cell line that serves as a model system of glucocorticoid-producing fasciculata cells. Stimulation of βcat signaling caused decreased corticosterone release consistent with the observed reduced transcription of steroidogenic genes Cyp11a1, Cyp11b1, Star, and Mc2r. Decreased steroidogenic gene expression was correlated with diminished steroidogenic factor 1 (Sf1; Nr5a1) expression and occupancy on steroidogenic promoters. Additionally, βcat signaling suppressed the ability of Sf1 to transactivate steroidogenic promoters independent of changes in Sf1 expression level. To investigate Sf1-independent effects of βcat on steroidogenesis, we used Affymetrix gene expression profiling of Wnt-responsive cells in vivo and in vitro. One candidate gene identified, Ccdc80, encodes a secreted protein with unknown signaling mechanisms. We report that Ccdc80 is a novel βcat-regulated gene in adrenocortical cells. Treatment of adrenocortical cells with media containing secreted Ccdc80 partially phenocopies βcat-induced suppression of steroidogenesis, albeit through an Sf1-independent mechanism. This study reveals multiple mechanisms of βcat-mediated suppression of steroidogenesis and suggests that Wnt/βcat signaling may regulate adrenal homeostasis by inhibiting fasciculata differentiation and promoting the undifferentiated state of progenitor cells.

Phospholipase D activity underlies very-low-density lipoprotein (VLDL)-induced aldosterone production in adrenal glomerulosa cells.

Aldosterone is the mineralocorticoid responsible for sodium retention, thus increased blood volume and pressure. Excessive production of aldosterone results in high blood pressure as well as renal disease, stroke, and visual loss via both direct effects and effects on blood pressure. Weight gain is often associated with increased blood pressure, but it remains unclear how obesity increases blood pressure. Obese patients typically have higher lipoprotein levels; moreover, some studies have suggested that aldosterone levels are also elevated and represent a link between obesity and hypertension. Very-low-density lipoprotein (VLDL) functions to transport triglycerides from the liver to peripheral tissues. Although previous studies have demonstrated that VLDL can stimulate aldosterone production, the mechanisms underlying this effect are largely unclear. Here we show for the first time that phospholipase D (PLD) is involved in VLDL-induced aldosterone production in both a human adrenocortical cell line (HAC15) and primary cultures of bovine zona glomerulosa cells. Our data also reveal that PLD mediates steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2) expression via increasing the phosphorylation (activation) of their regulatory transcription factors. Finally, by using selective PLD inhibitors, our studies suggest that both PLD1 and PLD2 isoforms play an important role in VLDL-induced aldosterone production.

Novel genes in primary aldosteronism.

Novel high-throughput genetic techniques have increased the pace of discoveries in the field of primary aldosteronism. Mutations in the potassium channel gene KCNJ5 are a cause of familial and sporadic forms of primary aldosteronism with around 30-40% of aldosterone-producing adenomas being affected by somatic mutations. Exome sequencing of tumors without KCNJ5 mutations revealed genetic alterations in the ATPases ATP1A1 and ATP2B3, with a combined prevalence of 5-7%. Mutations in the gene encoding a subunit of the Ca channel Cav1.3 (CACNA1D) were described with a prevalence of 5-8%. In addition, a new syndrome consisting of primary aldosteronism, seizures, and neuromuscular disease with germline CACNA1D mutations could be identified. All these genetic variants enhance Ca-mediated signalling and steroidogenesis in affected glomerulosa cells and provide the molecular basis for autonomous aldosterone secretion. Furthermore, the pattern of genetic alterations allows for subgrouping of patient cohorts with potentially distinct clinical features including sex and age distribution as well as endocrine and cardiovascular endpoints. Altogether in around 50% of aldosterone-producing adenomas, a somatic point mutation can be identified as the underlying genetic cause. These findings will provide the framework for potential identification of new biomarkers and therapeutic targets of this most common form of secondary hypertension.

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.

Channels and Pumps in Aldosterone-Producing Adenomas

Primary aldosteronism is the most common cause of secondary hypertension, with a prevalence of about 5% of the general hypertensive population and 10% of patients referred to hypertension specialty clinics. Aldosterone-producing adenomas (APAs) account for approximately 30–50% of cases of primary aldosteronism, and idiopathic hyperaldosteronism accounts for most of the rest of the cases. Aldosterone synthesis is regulated primarily by the renin-angiotensin system, potassium, ACTH, and to a lesser degree other peptides (1). Isolated adrenal zona glomerulosa and fasciculata cells from different species maintain a negative membrane resting potential determined by regulating membrane permeability to potassium (2, 3). Zona glomerulosa cells with hyperpolarized resting membrane voltages are steroidogenically inactive (4). Stimulation with angiotensin II, ACTH, or potassium results in membrane depolarization, opening of plasma membrane calcium channels, and mobilization of intracellular calcium, which increases activation of the calcium-calmodulin pathway, ultimately resulting in an increase in steroid biosynthesis and secretion (1). Several potassium channels have been described in rodent, bovine, and human adrenal cells, including inward rectifying and leak potassium currents that provide background potassium currents (reviewed in Ref. 3).

Overview of the genetic determinants of primary aldosteronism

Primary aldosteronism is the most common cause of secondary hypertension. The syndrome accounts for 10% of all cases of hypertension and is primarily caused by bilateral adrenal hyperplasia or aldosterone-producing adenoma. Over the last few years, the use of exome sequencing has significantly improved our understanding of this syndrome. Somatic mutations in the KCNJ5, ATP1A1, ATP2B3 or CACNA1D genes are present in more than half of all cases of aldosterone-producing adenoma (~40%, ~6%, ~1% and ~8%, respectively). Germline gain-of-function mutations in KCNJ5 are now known to cause familial hyperaldosteronism type III, and an additional form of genetic hyperaldosteronism has been reported in patients with germline mutations in CACNA1D. These genes code for channels that control ion homeostasis across the plasma membrane of zona glomerulosa cells. Moreover, all these mutations modulate the same pathway, in which elevated intracellular calcium levels lead to aldosterone hyperproduction and (in some cases) adrenal cell proliferation. From a clinical standpoint, the discovery of these mutations has potential implications for patient management. The mutated channels could be targeted by drugs, in order to control hormonal and overgrowth-related manifestations. Furthermore, some of these mutations are associated with high cell turnover and may be amenable to diagnosis via the sequencing of cell-free (circulating) DNA. However, genotype-phenotype correlations in patients harboring these mutations have yet to be characterized. Despite this recent progress, much remains to be done to elucidate the yet unknown mechanisms underlying sporadic bilateral adrenal hyperplasia.

English

The Indian wild caught bat, Taphozous kachhensis at Ambai Nimbai (Maharashtra) shows continuous asynchronous breeding, exhibiting a seasonal polyoestry. The adrenal gland of T. kachhensis is made up of adrenocortical and chromaffin tissues. The adrenocortical tissue is comprised of two main types of cells, the steroid cells with abundance of lipid inclusions and eosinophilic cells with eosinophilic granular cytoplasm. The chromaffin tissue is intermingled with adrenocortical tissue. They are formed of adrenaline and noradrenaline secreting cells with different electron density and variable sizes. The zona glomerulosa during estrus shows spherical nuclei with prominent nucleoli. Adrenal gland of pregnant female shows striking differences in ultrastructural features than those observed in the adrenal gland of non-pregnant female. During pregnancy, the cells of zona glomerulosa are hypertrophied and synthetically very active. The lysosomes and few lipid droplets are seen in cytoplasm of cell. The cells of zona fasciculata are large, vacuolated and arranged in cords of polygonal cells having mitochondria with tubular and lamellar cristae. The lipid droplets are observed in close association with smooth endoplasmic reticulum and mitochondria suggesting the role of these organelles in steroidogenesis. The cells of zona reticularis are loaded with lipid droplets. The mitochondria are spherical in shape with collapsed cristae. The cells of zona reticularis are in close association with blood vessels. Few lysosomal bodies are seen in the cytoplasm. Adrenal medulla consists of two types of cells depending on the presence of secretory granules. Nor-epinephrine cells are predominant in the medulla of pregnant bat while epinephrine cells are predominant in the medulla of estrus bat. Key words: Bat, adrenal gland, medulla, ultrastructure, reproductive cycle.

Minireview: Potassium Channels and Aldosterone Dysregulation: Is Primary Aldosteronism a Potassium Channelopathy?

Primary aldosteronism is the most common form of secondary hypertension and has significant cardiovascular consequences. Aldosterone-producing adenomas (APAs) are responsible for half the cases of primary aldosteronism, and about half have mutations of the G protein-activated inward rectifying potassium channel Kir3.4. Under basal conditions, the adrenal zona glomerulosa cells are hyperpolarized with negative resting potentials determined by membrane permeability to K(+) mediated through various K(+) channels, including the leak K(+) channels TASK-1, TASK-3, and Twik-Related Potassium Channel 1, and G protein inward rectifying potassium channel Kir3.4. Angiotensin II decreases the activity of the leak K(+) channels and Kir3.4 channel and decreases the expression of the Kir3.4 channel, resulting in membrane depolarization, increased intracellular calcium, calcium-calmodulin pathway activation, and increased expression of cytochrome P450 aldosterone synthase (CYP11B2), the last enzyme for aldosterone production. Somatic mutations of the selectivity filter of the Kir3.4 channel in APA results in loss of selectivity for K(+) and entry of sodium, resulting in membrane depolarization, calcium mobilization, increased CYP11B2 expression, and hyperaldosteronism. Germ cell mutations cause familial hyperaldosteronism type 3, which is associated with adrenal zona glomerulosa hyperplasia, rather than adenoma. Less commonly, somatic mutations of the sodium-potassium ATPase, calcium ATPase, or the calcium channel calcium channel voltage-dependent L type alpha 1D have been found in some APAs. The regulation of aldosterone secretion is exerted to a significant degree by activation of membrane K(+) and calcium channels or pumps, so it is not surprising that the known causes of disorders of aldosterone secretion in APA have been channelopathies, which activate mechanisms that increase aldosterone synthesis.

Mutations in KCNJ5 determines presentation and likelihood of cure in primary hyperaldosteronism

Primary hyperaldosteronism (PA) is a common cause of secondary hypertension. Two recurrent mutations (G151R and L168R) in the potassium channel gene KCNJ5 have been identified that affect the Kir3.4 potassium channel found in the cells of the zona glomerulosa of the adrenal gland. The aim of this study was to determine the prevalence of KCNJ5 mutations in an Australian cohort of patients and to correlate these findings with clinical outcome data, in order to describe the clinical impact on patients who harbour this mutation. Direct Sanger sequencing for KCNJ5 on DNA from adrenal tumour tissue of 83 patients with PA in a cohort study was undertaken and mutation status correlated with clinical outcome data. Seventy-one of 83 patients (86%) had adrenocortical adenomas and 12 patients (14%) had bilateral adrenal hyperplasia. A total of 34 (41%) patients were found to have heterozygous somatic mutations in KCNJ5, G151R and L168R. No germ line mutations were identified. Patients with mutations were predominately female (68% versus 49%) and significantly younger at presentation (48 versus 55 years). When correlated with clinical data, our results demonstrated that patients with KCNJ5 mutations were more likely to be cured following surgery without the requirement for ongoing medications. Our findings in a large Australian cohort show that patients with mutations in KCNJ5 present earlier with the signs and symptoms of PA benefit from surgical intervention. Moreover, our results highlight the importance of a thorough workup and management plan for younger patients who present with hypertension.

Regulation of aldosterone biosynthesis by the Kir3.4 (KCNJ5) potassium channel

The G-protein-activated inwardly rectifying potassium channel Kir3.4 is expressed in the zona glomerulosa cell membrane and transports potassium out of the cell. Angiotensin II stimulation of aldosterone secretion is mediated, in part, by suppression of the transcription of KCNJ5, the gene coding for Kir3.4, and blocking channel activity. This results in membrane depolarization, mobilization of intracellular calcium, activation of the calcium-calmodulin pathway and increasing gene transcription of steroidogenic enzymes required for aldosterone secretion. In 40-60% of aldosterone-producing adenomas there is a somatic mutation in the region of the KCNJ5 gene that codes for the selectivity filter that decreases potassium selectivity, allowing sodium to leak into the cells, thus depolarizing the membrane and initiating events that result in increased aldosterone synthesis. The mechanism by which mutated KCNJ5 induces cell proliferation and adenoma formation remains unclear.

WNT/β-catenin signalling is activated in aldosterone-producing adenomas and controls aldosterone production

Primary aldosteronism (PA) is the main cause of secondary hypertension, resulting from adrenal aldosterone-producing adenomas (APA) or bilateral hyperplasia. Here, we show that constitutive activation of WNT/β-catenin signalling is the most frequent molecular alteration found in 70% of APA. We provide evidence that decreased expression of the WNT inhibitor SFRP2 may be contributing to deregulated WNT signalling and APA development in patients. This is supported by the demonstration that mice with genetic ablation of Sfrp2 have increased aldosterone production and ectopic differentiation of zona glomerulosa cells. We further show that β-catenin plays an essential role in the control of basal and Angiotensin II-induced aldosterone secretion, by activating AT1R, CYP21 and CYP11B2 transcription. This relies on both LEF/TCF-dependent activation of AT1R and CYP21 regulatory regions and indirect activation of CYP21 and CYP11B2 promoters, through increased expression of the nuclear receptors NURR1 and NUR77. Altogether, these data show that aberrant WNT/β-catenin activation is associated with APA development and suggest that WNT pathway may be a good therapeutic target in PA.

Immunolocalization of murine type VI 3β-hydroxysteroid dehydrogenase in the adrenal gland, testis, skin, and placenta

The enzyme 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD) is essential for the biosynthesis of all active steroid hormones, such as those secreted from the adrenal gland, testis, ovary, skin and placenta. The 3β-HSD enzymes exist in multiple isoforms in humans and rodents. To date, six different isoforms have been identified in the mouse, and these isoforms are speculated to play different roles in different tissues. We previously showed that the murine type VI 3β-HSD isoform (Hsd3b6) is expressed specifically in the aldosterone-producing zona glomerulosa cells within the adrenal gland and that its overexpression causes abnormally increased aldosterone synthesis, revealing a crucial (or rate-limiting) role of this enzyme in steroidogenesis. However, potential contributions of this enzyme to the steroid hormone synthesis outside the adrenal glands are poorly understood. This paucity of knowledge is partly because of the lack of isoform-specific antibody that can be used for immunohistochemistry. Here, we report the development and characterization of specific antibody to Hsd3b6 and show the results of immunohistochemistry for the adrenal gland, testis, ovary, skin and placenta. As expected, Hsd3b6 immunoreactivities within the adrenal gland were essentially confined to the zona glomerulosa cells, where aldosterone is produced. By contrast, no immunopositive cells were observed in the zona fasciculata, which is where corticosterone is produced. In the gonads, while the ovaries did not show any detectable immunoreactivity to Hsd3b6, the testes displayed intense immunoreactivities within the interstitial Leydig cells, where testosterone is produced. In the skin, positive immunoreactivities to Hsd3b6 were only seen in the sebaceous glands, suggesting a specific role of this enzyme in sebaceous function. Moreover, in the placenta, Hsd3b6 was specifically found in the giant trophoblast cells surrounding the embryonic cavity, which suggests a role for this enzyme in local progesterone production that is required for proper embryonic implantation and/or maintenance of pregnancy. Taken together, our data revealed that Hsd3b6 is localized in multiple specific tissues and cell types, perhaps thereby involved in biosynthesis of a number of tissue-specific steroid hormones with different physiological roles.

Abstract 248: Leptin-mediated Cardiovascular Disease Involves Aldosterone in Female Mice and Adolescent Women

Premenopausal women have a better endothelial function than men but are more sensitive to obesity induced endothelial dysfunction (ED) and more reactive to mineralocorticoid receptor (MR) blockade. Due to its control of sympathetic activity, leptin has been reported to be the link between metabolic and cardiovascular disease (CVD) in men. Whether a similar correlation exists in females that secrete 4 times more leptin than men is unknown. Using a population based study and mice deficient (KO) in protein tyrosine phosphatase 1B (PTP1B), a leptin sensitizer, we tested the hypothesis that leptin mediated CVD involves sex specific mechanisms. Plasma leptin were 4 times higher in female mice (KO F :1648±271 vs KO M : 347±47 pg/ml; p&lt;0.05) indifferently of the genotype (WT F : 2386±765 vs WT M : 375±37 pg/ml; p&lt;0.05). PTP1B deletion increased leptin sensitivity and raised blood pressure (BP) to a similar extent in males and females (124±4 vs 126±4 respectively; WT 102±5 mmHg) but induced ED in females KO only (p&lt;0.01 vs WT and males). Sympathetic tone was assessed by measuring BP response to ganglionic blockade. Leptin sensitized males only exhibit an increased sympathetic tone, but leptin sensitized females only exhibit high plasma aldosterone levels (aldo; KO F :1234±173 vs WT F : 545±71and KO M : 624±70 pg/ml). Both leptin receptor antagonist and MR blockade restored BP in KO females. In vivo and ex vivo (aortic ring) MR blockade restored endothelial function in females KO suggesting direct aldo effects on the vessels. Neither corticosterone, potassium nor angiotensin II was increased in KO females. However aldosterone synthase expression was impressively increased in females KO only. Aldo levels are low in obese leptin receptor deficient females (333±89 pg/ml), and leptin directly stimulates aldosterone secretion in glomerulosa cells. In parallel we demonstrated that African American adolescent females secrete 4 times more leptin than males, and established a correlation between leptin and aldosterone(r=0.464, p=0.011) in female subjects only. These human and animal data suggest that leptin regulates aldo secretion in females. All together these data suggest that obesity mediated CVD is leptin dependent and involves aldo dependent mechanisms in females.

Adrenocortical Zonation Results from Lineage Conversion of Differentiated Zona Glomerulosa Cells

Lineage conversion of differentiated cells in response to hormonal feedback has yet to be described. To investigate this, we studied the adrenal cortex, which is composed of functionally distinct concentric layers that develop postnatally, the outer zona glomerulosa (zG) and the inner zona fasciculata (zF). These layers have separate functions, are continuously renewed in response to physiological demands, and are regulated by discrete hormonal feedback loops. Their cellular origin, lineage relationship, and renewal mechanism, however, remain poorly understood. Cell-fate mapping and gene-deletion studies using zG-specific Cre expression demonstrate that differentiated zG cells undergo lineage conversion into zF cells. In addition, zG maintenance is dependent on the master transcriptional regulator Steroidogenic Factor 1 (SF-1), and zG-specific Sf-1 deletion prevents lineage conversion. These findings demonstrate that adrenocortical zonation and regeneration result from lineage conversion and may provide a paradigm for homeostatic cellular renewal in other tissues.

Pharmacological characterization of FE 201874, the first selective high affinity rat V1A vasopressin receptor agonist

Distinct vasopressin receptors are involved in different physiological and behavioural functions. Presently, no selective agonist is available to specifically elucidate the functional roles of the V1A receptor in the rat, one of the most widely used animal models. FE 201874 is a new derivative of the human selective V1A receptor agonist F180. In this study, we performed a multi-approach pharmacological and functional characterization of FE 201874 to determine whether it is selective for V1A receptors. We modified an available human selective V1A receptor agonist (F180) and determined its pharmacological properties in cell lines expressing vasopressin/oxytocin receptors (affinity and coupling to second messenger cascades), in an ex vivo model (aorta ring contraction) and in vivo in rats (proliferation of adrenal cortex glomerulosa cells and lactation). FE 201874 exhibited nanomolar affinity for the rat V1A receptor; it was highly selective towards the rat V1B and V2 vasopressin receptors and behaved as a full V1A agonist in all the pharmacological tests performed. FE 201874 bound to the oxytocin receptor, but with moderate affinity, and behaved as an oxytocin antagonist in vitro, but not in vivo. On functional grounds, all the data demonstrate that FE 201874 is the first selective agonist of the rat V1A receptor isoform available. Hence, FE 201874 may have potential as a treatment for the vasodilator-induced hypotension occurring in conditions such as septic shock and could be the most suitable compound for discriminating between the behavioural effects of arginine vasopressin and oxytocin.