Biochemical and Ionic signaling mechanisms for ACTH-stimulated cortisol production

Computational approaches for identifications of altered ion channels in keratoconus

BACKGROUND

Keratoconus is an etiologically complex, degenerative corneal disease that eventually leads to loss of corneal integrity. Cells in corneal epithelium and endothelium express various types of ion channels that play important roles in ocular pathology. This emphasizes the need of understanding alterations of ion channels in keratoconus.

METHOD

Differential gene expression analysis was performed to identify deregulated ion channels in keratoconus patients using transcriptomic data. Thereafter correlation analysis of ion channel expression was performed to obtain the changed correlation between ion channels' expression in keratoconus patients versus control samples. Moreover, Protein-protein interaction networks and a pathway map was constructed to identify cellular processes altered due to the deregulation of ion channels. Furthermore, drugs interacting with deregulated ion channels were identified.

RESULTS

Total 75 ion channels were found to be deregulated in keratoconus, of which 12 were upregulated and 63 were downregulated. Correlations between ion channel expressions found to be different in control and keratoconus samples. Thereafter, protein-protein interactions network was generated to identify hub ion channels in network. Furthermore, the pathway map was constructed to depict calcium signalling, MAPK signalling, synthesis and secretion of cortisol, and cAMP signalling. The 19 FDA- approved drugs that interact with the 6 deregulated ion channels were identified.

CONCLUSION

Down-regulation of voltage-gated calcium channels can be attributed to reduced cell proliferation and differentiation. Additionally, deregulated ion channels in 3',5'- cyclic adenosine monophosphate signalling may be responsible for elevated cortisol level in progressive keratoconus patients.

Effect of resuscitation of cryopreserved porcine adrenal glands at 26 °C on their recovery and functioning under xenotransplantation

The study is devoted to the effect of lowered resuscitation temperature (26 °C) on cryopreserved porcine adrenal glands functional activity in vitro and in vivo under xenotransplantation. The adrenals were collected from newborn pigs, cryopreserved with 5 % DMSO at a rate of 1 °C/min, resuscitated at 26 or 37 °C for 48 h (5 % CO2, DMEM), embedded into small intestinal submucosa, and transplanted to bilaterally adrenalectomized rats. It has been shown that the glands resuscitated at 26 °C have suppressed free-radical processes and can produce cortisol and aldosterone in vitro, and may lead to elevated blood levels of these hormones. Moreover, the adrenal grafts maintain blood glucose levels and promote the formation of glycogen stores. Thus, the resuscitation at 26 °C can improve the quality of grafts and favor the introduction and application of the cryopreserved organs and tissues for transplantation in clinical and experimental practice.

Different cell compositions and a novel somatic KCNJ5 variant found in a patient with bilateral adrenocortical adenomas secreting aldosterone and cortisol

INTRODUCTION

This study aimed to explore the possible pathogenesis of a rare case of co-existing Cushing's syndrome (CS) and primary aldosteronism (PA) caused by bilateral adrenocortical adenomas secreting aldosterone and cortisol, respectively.

METHODS

A 41-year-old Chinese woman with severe hypertension and hypokalemia for 5 and 2 years, respectively, was referred to our hospital. She had a Cushingoid appearance. Preoperative endocrinological examinations revealed autonomous cortisol and aldosterone secretion. Computed tomography revealed bilateral adrenal adenomas. Subsequently, adrenal vein sampling and sequential left and right partial adrenalectomy indicated the presence of a left aldosterone-producing tumor and a right cortisol-producing tumor. Pathological examination included immunohistochemical analysis of the resected specimens. Secretions of aldosterone and cortisol were observed both in vivo and in vitro. Further, whole-exome sequencing was performed for DNA that was extracted from peripheral blood leukocytes and bilateral adrenal adenomas in order to determine whether the patient had relevant variants associated with PA and CS.

RESULTS

Immunohistochemical staining revealed that the left adenoma primarily comprised clear cells expressing CYP11B2, whereas the right adenoma comprised both eosinophilic compact and clear cells expressing CYP11B1. The mRNA levels of steroidogenic enzymes (including CYP11B1 and CYP17A1) were high in the right adenoma, whereas CYP11B2 was highly expressed in the left adenoma. A novel somatic heterozygous missense variant-KCNJ5 c.503T > G (p.L168R)-was detected in the left adrenal adenoma, but no other causative variants associated with PA and CS were detected in the peripheral blood or right adrenocortical adenoma. In the primary cell culture of the resected hyperplastic adrenal adenomas, verapamil and nifedipine, which are two calcium channel blockers, markedly inhibited the secretion of both aldosterone and cortisol.

CONCLUSION

We present an extremely rare case of bilateral adrenocortical adenomas with distinct secretion of aldosterone and cortisol. The heterogeneity of the tumor cell compositions of aldosterone- and cortisol-producing adenoma (A/CPA) and somatic mutation of KCNJ5 may have led to different hormone secretions in the bilateral adrenal adenomas.

Sodium background currents in endocrine/neuroendocrine cells: Towards unraveling channel identity and contribution in hormone secretion

In endocrine/neuroendocrine tissues, excitability of secretory cells is patterned by the repertoire of ion channels and there is clear evidence that extracellular sodium (Na⁺) ions contribute to hormone secretion. While voltage-gated channels involved in action potential generation are well-described, the background 'leak' channels operating near the resting membrane potential are much less known, and in particular the channels supporting a background entry of Na⁺ ions. These background Na⁺ currents (called here 'I_Nab') have the ability to modulate the resting membrane potential and subsequently affect action potential firing. Here we compile and analyze the data collected from three endocrine/neuroendocrine tissues: the anterior pituitary gland, the adrenal medulla and the endocrine pancreas. We also model how I_Nab can be functionally involved in cellular excitability. Finally, towards deciphering the physiological role of I_Nab in endocrine/neuroendocrine cells, its implication in hormone release is also discussed.

The pathogenic role of the GIP/GIPR axis in human endocrine tumors: emerging clinical mechanisms beyond diabetes

The glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone produced in the gastrointestinal tract in response to nutrients. GIP has a variety of effects on different systems, including the potentiation of insulin secretion from pancreatic β-cells after food intake (i.e. incretin effect), which is probably the most important. GIP effects are mediated by the GIP receptor (GIPR), a G protein-coupled receptor expressed in several tissues, including islet β-cells, adipocytes, bone cells, and brain. As well as its involvement in metabolic disorders (e.g. it contributes to the impaired postprandial insulin secretion in type 2 diabetes (T2DM), and to the pathogenesis of obesity and associated insulin resistance), an inappropriate GIP/GIPR axis activation of potential diagnostic and prognostic value has been reported in several endocrine tumors in recent years. The ectopic GIPR expression seen in patients with overt Cushing syndrome and primary bilateral macronodular adrenal hyperplasia or unilateral cortisol-producing adenoma has been associated with an inverse rhythm of cortisol secretion, with low fasting morning plasma levels that increase after eating. On the other hand, most acromegalic patients with an unusual GH response to oral glucose suppression have GIPR-positive somatotropinomas, and a milder phenotype, and are more responsive to medical treatment. Neuroendocrine tumors are characterized by a strong GIPR expression that may correlate positively or inversely with the proliferative index MIB-1, and that seems an attractive target for developing novel radioligands. The main purpose of this review is to summarize the role of the GIP/GIPR axis in endocrine neoplasia, in the experimental and the clinical settings.

Short- and long-term effects of lipoprotein apheresis on plasma hormones in patients with therapy-resistant dyslipidemia

BACKGROUND AND AIMS

Lipoprotein apheresis (LA) is a highly effective method to improve the clinical and metabolic situation in patients with therapy-resistant disorders of lipid metabolism. Cholesterol is the substrate for the synthesis of all steroid hormones. If repeated massive reduction of LDL-cholesterol may interfere with human adrenal steroidogenesis, and could become clinically relevant is unknown, so far. Thus, the aim of this study was to determine possible short- and long-term effects of LA on blood plasma levels of ACTH, cortisol, aldosterone, DHEAS, renin and testosterone.

METHODS

In total, 39 patients, treated with one of four LA techniques were studied: 1. Lipid Filtration (LF; n = 7), 2. Dextran Sulfate Adsorption (DSA; n = 7), 3. Membrane Filtration Optimised Novel Extracorporeal Treatment (MONET; n = 8), and 4. Direct Absorption of Lipoproteins (DALI; n = 15). Hormone levels were analyzed before and after five LA sessions with an interval of 20 weeks covering a total observation time of two years. In addition patients were comprehensively characterized by clinical and laboratory data.

RESULTS

Patients treated with LA revealed an acute reduction of steroid hormones and ACTH, independent of apheresis technology but no long-term insufficiency in steroidogenesis was observed. Plasma renin levels were stable in LF patients and were highly elevated in patients under DSA, MONET and DALI apheresis throughout the observation period.

CONCLUSIONS

In summary, these data suggest that although different LA techniques considerably differ in their acute effects on hormone levels during LA, they did not alter long-term hormone levels sustainably.

Evidence in Favor of an Alternative Glucocorticoid Synthesis Pathway During Acute Experimental Chagas Disease

It is well-established that infectious stress activates the hypothalamus-pituitary-adrenal axis leading to the production of pituitary adrenocorticotropin (ACTH) and adrenal glucocorticoids (GCs). Usually, GC synthesis is mediated by protein kinase A (PKA) signaling pathway triggered by ACTH. We previously demonstrated that acute murine Chagas disease courses with a marked increase of GC, with some data suggesting that GC synthesis may be ACTH-dissociated in the late phase of this parasitic infection. Alternative pathways of GC synthesis have been reported in sepsis or mental diseases, in which interleukin (IL)-1β, prostaglandin E2 (PGE2), and/or cAMP-activated guanine nucleotide exchange factor 2 (EPAC2) are likely to play a role in this regard. Accordingly, we have searched for the existence of an ACTH-independent pathway in an experimental model of a major parasitic disease like Chagas disease, in addition to characterizing potential alternative pathways of GC synthesis. To this end, C57BL/6 male mice were infected with T. cruzi (Tc), and evaluated throughout the acute phase for several parameters, including the kinetic of GC and ACTH release, the adrenal level of MC2R (ACTH receptor) expression, the p-PKA/PKA ratio as ACTH-dependent mechanism of signal transduction, as well as adrenal expression of IL-1β and its receptor, EPAC2 and PGE2 synthase. Our results reveal the existence of two phases involved in GC synthesis during Tc infection in mice, an initial one dealing with the well-known ACTH-dependent pathway, followed by a further ACTH-hyporesponsive phase. Furthermore, inflamed adrenal microenvironment may tune the production of intracellular mediators that also operate upon GC synthesis, like PGE2 synthase and EPAC2, as emerging driving forces for GC production in the advanced course of Tc infection. In essence, GC production seems to be associated with a biphasic action of PGE2, suggesting that the effect of PGE2/cAMP in the ACTH-independent second phase may be mediated by EPAC2.

Quantification of a Glucocorticoid Profile in Non-pooled Samples Is Pivotal in Stress Research Across Vertebrates

Vertebrates are faced continuously with a variety of potential stressful stimuli and react by a highly conserved endocrine stress response. An immediate catecholamine mediated response increases plasma glucose levels in order to prepare the organism for the "fight or flight" reaction. In addition, in a matter of minutes after this (nor)adrenaline release, glucocorticoids, in particular cortisol or corticosterone depending on the species, are released through activation of the hypothalamic-pituitary-interrenal (HPI) axis in fish or hypothalamic-pituitary-adrenal (HPA) axis in other vertebrates. These plasma glucocorticoids are well documented and widely used as biomarker for stress across vertebrates. In order to study the role of glucocorticoids in acute and chronic stress and gain in-depth insight in the stress axis (re)activity across vertebrates, it is pivotal to pin-point the involved molecules, to understand the mechanisms of how the latter are synthesized, regulated and excreted, and to grasp their actions on a plethora of biological processes. Furthermore, in-depth knowledge on the characteristics of the tissues as well as on the analytical methodologies available for glucocorticoid quantification is needed. This manuscript is to be situated in the multi-disciplinary research topic of glucocorticoid action across vertebrates which is linked to a wide range of research domains including but not limited to biochemistry, ecology, endocrinology, ethology, histology, immunology, morphology, physiology, and toxicology, and provides a solid base for all interested in stress, in particular glucocorticoid, related research. In this framework, internationally validated confirmation methods for quantification of a glucocorticoid profile comprising: (i) the dominant hormone; (ii) its direct precursors; (iii) its endogenously present phase I metabolites; and (iv) the most abundant more polar excreted exogenous phase I metabolites in non-pooled samples are pivotal.

A Novel Phenotype of Familial Hyperaldosteronism Type III: Concurrence of Aldosteronism and Cushing's Syndrome

CONTEXT

To date, all the familial hyperaldosteronism type III (FH-III) patients reported presenting with typical primary aldosteronism (PA), without showing other adrenal hormone abnormalities.

OBJECTIVE

This study characterized a novel phenotype of FH-III and explored the possible pathogenesis.

PATIENTS AND METHODS

A male patient presented with severe hypertension and hypokalemia at the age of 2 years and developed Cushing's syndrome at 20 years. He was diagnosed with PA and Cushing's syndrome on the basis of typical biochemical findings. He had massive bilateral adrenal hyperplasia and underwent left adrenalectomy. KCNJ5 was sequenced, and secretion of aldosterone and cortisol were observed both in vivo and in vitro.

RESULTS

A heterozygous germline p.Glu145Gln mutation of KCNJ5 was identified. ARMC5, PRKAR1A, PDE8B, PDE11A, and PRKACA genes and β-catenin, P53 immunoactivity were normal in the adrenal. CYP11B2 was highly expressed, whereas mRNA expression of CYP11B1, CYP17A1, and STAR was relatively low in the hyperplastic adrenal, compared with normal adrenal cortex and other adrenal diseases. In the primary cell culture of the resected hyperplastic adrenal, verapamil and nifedipine, two calcium channel blockers, markedly inhibited the secretion of both aldosterone and cortisol and the mRNA expression of CYP11B1, CYP11B2, CYP17A1, and STAR.

CONCLUSIONS

We presented the first FH-III patient who had both severe PA and Cushing's syndrome. Hypersecretion of cortisol might be ascribed to overly large size of the hyperplastic adrenal because CYP11B1 expression was relatively low in his adrenal. Like aldosterone, synthesis and secretion of cortisol in the mutant adrenal may be mediated by voltage-gated Ca²⁺ channels.

Inhibition of TREK-2 K(+) channels by PI(4,5)P2: an intrinsic mode of regulation by intracellular ATP via phosphatidylinositol kinase

TWIK-related two-pore domain K(+) channels 1 and 2 (TREKs) are activated under various physicochemical conditions. However, the directions in which they are regulated by PI(4,5)P2 and intracellular ATP are not clearly presented yet. In this study, we investigated the effects of ATP and PI(4,5)P2 on overexpressed TREKs (HEK293T and COS-7) and endogenously expressed TREK-2 (mouse astrocytes and WEHI-231 B cells). In all of these cells, both TREK-1 and TREK-2 currents were spontaneously increased by dialysis with ATP-free pipette solution for whole-cell recording (ITREK-1,w-c and ITREK-2w-c) or by membrane excision for inside-out patch clamping without ATP (ITREK-1,i-o and ITREK-2,i-o). Steady state ITREK-2,i-o was reversibly decreased by 3 mM ATP applied to the cytoplasmic side, and this reduction was prevented by wortmannin, a PI-kinase inhibitor. An exogenous application of PI(4,5)P2 inhibited the spontaneously increased ITREKs,i-o, suggesting that intrinsic PI(4,5)P2 maintained by intracellular ATP and PI kinase may set the basal activity of TREKs in the intact cells. The inhibition of intrinsic TREK-2 by ATP was more prominent in WEHI-231 cells than astrocytes. Interestingly, unspecific screening of negative charges by poly-L-lysine also inhibited ITREK-2,i-o. Application of PI(4,5)P2 after the poly-L-lysine treatment showed dose-dependent dual effects, initial activation and subsequent inhibition of ITREK-2,i-o at low and high concentrations, respectively. In HEK293T cells coexpressing TREK-2 and a voltage-sensitive PI(4,5)P2 phosphatase, sustained depolarization increased ITREK-2,w-c initially (<5 s) but then decreased the current below the control level. In HEK293T cells coexpressing TREK-2 and type 3 muscarinic receptor, application of carbachol induced transient activation and sustained suppression of ITREK-2,w-c and cell-attached ITREK-2. The inhibition of TREK-2 by unspecific electrostatic quenching, extensive dephosphorylation, or sustained hydrolysis of PI(4,5)P2 suggests the existence of dual regulatory modes that depend on PI(4,5)P2 concentration.

60 YEARS OF POMC: Adrenal and extra-adrenal functions of ACTH

The pituitary adrenocorticotropic hormone (ACTH) plays a pivotal role in homeostasis and stress response and is thus the major component of the hypothalamo-pituitary-adrenal axis. After a brief summary of ACTH production from proopiomelanocortin (POMC) and on ACTH receptor properties, the first part of the review covers the role of ACTH in steroidogenesis and steroid secretion. We highlight the mechanisms explaining the differential acute vs chronic effects of ACTH on aldosterone and glucocorticoid secretion. The second part summarizes the effects of ACTH on adrenal growth, addressing its role as either a mitogenic or a differentiating factor. We then review the mechanisms involved in steroid secretion, from the classical Cyclic adenosine monophosphate second messenger system to various signaling cascades. We also consider how the interaction between the extracellular matrix and the cytoskeleton may trigger activation of signaling platforms potentially stimulating or repressing the steroidogenic potency of ACTH. Finally, we consider the extra-adrenal actions of ACTH, in particular its role in differentiation in a variety of cell types, in addition to its known lipolytic effects on adipocytes. In each section, we endeavor to correlate basic mechanisms of ACTH function with the pathological consequences of ACTH signaling deficiency and of overproduction of ACTH.

Signaling Interactions in the Adrenal Cortex

The major physiological stimuli of aldosterone secretion are angiotensin II (AII) and extracellular K(+), whereas cortisol production is primarily regulated by corticotropin (ACTH) in fasciculata cells. AII triggers Ca(2+) release from internal stores that is followed by store-operated and voltage-dependent Ca(2+) entry, whereas K(+)-evoked depolarization activates voltage-dependent Ca(2+) channels. ACTH acts primarily through the formation of cAMP and subsequent protein phosphorylation by protein kinase A. Both Ca(2+) and cAMP facilitate the transfer of cholesterol to mitochondrial inner membrane. The cytosolic Ca(2+) signal is transferred into the mitochondrial matrix and enhances pyridine nucleotide reduction. Increased formation of NADH results in increased ATP production, whereas that of NADPH supports steroid production. In reality, the control of adrenocortical function is a lot more sophisticated with second messengers crosstalking and mutually modifying each other's pathways. Cytosolic Ca(2+) and cGMP are both capable of modifying cAMP metabolism, while cAMP may enhance Ca(2+) release and voltage-activated Ca(2+) channel activity. Besides, mitochondrial Ca(2+) signal brings about cAMP formation within the organelle and this further enhances aldosterone production. Maintained aldosterone and cortisol secretion are optimized by the concurrent actions of Ca(2+) and cAMP, as exemplified by the apparent synergism of Ca(2+) influx (inducing cAMP formation) and Ca(2+) release during response to AII. Thus, cross-actions of parallel signal transducing pathways are not mere intracellular curiosities but rather substantial phenomena, which fine-tune the biological response. Our review focuses on these functionally relevant interactions between the Ca(2+) and the cyclic nucleotide signal transducing pathways hitherto described in the adrenal cortex.

Much more than a leak: structure and function of K₂p-channels

Over the last decade, we have seen an enormous increase in the number of experimental studies on two-pore-domain potassium channels (K2P-channels). The collection of reviews and original articles compiled for this special issue of Pflügers Archiv aims to give an up-to-date summary of what is known about the physiology and pathophysiology of K2P-channels. This introductory overview briefly describes the structure of K2P-channels and their function in different organs. Its main aim is to provide some background information for the 19 reviews and original articles of this special issue of Pflügers Archiv. It is not intended to be a comprehensive review; instead, this introductory overview focuses on some unresolved questions and controversial issues, such as: Do K2P-channels display voltage-dependent gating? Do K2P-channels contribute to the generation of action potentials? What is the functional role of alternative translation initiation? Do K2P-channels have one or two or more gates? We come to the conclusion that we are just beginning to understand the extremely complex regulation of these fascinating channels, which are often inadequately described as 'leak channels'.

Steroidogenesis-adrenal cell signal transduction

The purpose of this article is to review fundamentals in adrenal gland histophysiology. Key findings regarding the important signaling pathways involved in the regulation of steroidogenesis and adrenal growth are summarized. We illustrate how adrenal gland morphology and function are deeply interconnected in which novel signaling pathways (Wnt, Sonic hedgehog, Notch, β-catenin) or ionic channels are required for their integrity. Emphasis is given to exploring the mechanisms and challenges underlying the regulation of proliferation, growth, and functionality. Also addressed is the fact that while it is now well-accepted that steroidogenesis results from an enzymatic shuttle between mitochondria and endoplasmic reticulum, key questions still remain on the various aspects related to cellular uptake and delivery of free cholesterol. The significant progress achieved over the past decade regarding the precise molecular mechanisms by which the two main regulators of adrenal cortex, adrenocorticotropin hormone (ACTH) and angiotensin II act on their receptors is reviewed, including structure-activity relationships and their potential applications. Particular attention has been given to crucial second messengers and how various kinases, phosphatases, and cytoskeleton-associated proteins interact to ensure homeostasis and/or meet physiological demands. References to animal studies are also made in an attempt to unravel associated clinical conditions. Many of the aspects addressed in this article still represent a challenge for future studies, their outcome aimed at providing evidence that the adrenal gland, through its steroid hormones, occupies a central position in many situations where homeostasis is disrupted, thus highlighting the relevance of exploring and understanding how this key organ is regulated. © 2014 American Physiological Society. Compr Physiol 4:889-964, 2014.

Dose-response downregulation within the span of single interpulse intervals

Pituitary ACTH drives adrenal glucocorticoid (cortisol) pulses via a time-delayed asymptotic dose-response process. To test the postulate that ACTH stimulates cortisol secretion dynamically (unequally during the initiation and termination of a cortisol secretory burst), a mathematical formalism was developed in which dose-response hysteretic shifts were allowed, but not required, within the time evolution of ACTH-cortisol pulse pairs. A dual-waveform deconvolution model was used to quantify cortisol secretion rates and reconstruct ACTH concentration profiles in 28 healthy adults previously sampled every 10 min for 24 h in the unstressed state (8,120 measurements). ACTH concentration-cortisol secretion dose-response functions were then estimated in each subject 1) without hysteresis (base model) and with allowances for possible hysteresis in 2) ACTH potency, 3) adrenal sensitivity, and 4) ACTH efficacy. Model residual error was 40% lower in the potency and sensitivity models and 20% lower in the efficacy model than in the base model (P < 0.001). Mean time shifts for inferable hysteretic inflection were model-independent, i.e., grand mean (95% confidence interval) 22 (12-39) min after the onset of a cortisol secretory burst. Half-maximally effective ACTH concentrations (EC(50)) differed before and after hysteretic inflection within individual pulses: 1) 9.4 and 54 ng/l in the potency model (P < 0.001) and 2) 8.9 and 123 ng/l in the sensitivity model (P < 0.001) compared with 16 ng/l in the no-hysteresis model (P < 0.001). In the efficacy-shift model, estimated maximal ACTH drive varied by 17-fold within cortisol secretory bursts (from 22 to 1.3 nmol.l(-1).min cortisol secretion(-1), P < 0.001). The collective results introduce the basis for modeling the dynamics of rapid, reversible physiological downregulation within the span of single interpulse intervals in vivo. This construct should have utility in parsing mechanisms of physiological regulation in other integrative systems.

Differential regulation and roles of urocortins in human adrenal H295R cells

Three urocortins (Ucns) are known as members of the corticotropin-releasing factor (CRF) family of peptides and serve as natural ligands for CRF receptors. Ucn1 and Ucn3 exhibit potent effects on the adrenal system via the CRF receptors. This study aimed to explore the regulation and roles of Ucns in the adrenal system using human adrenal carcinoma H295R cells, which express Ucn1, Ucn2, Ucn3, CRF receptor type 1 (CRF(1) receptor), and CRF receptor type 2a (CRF(2a) receptor) mRNA. Forskolin, which stimulates adenylate cyclase and then increases intracellular cAMP production, was shown to transiently decrease Ucn1 and Ucn2 mRNA levels, but increase Ucns 1-3 mRNA levels in H295R cells. Steroidogenic acute regulatory protein, Cyp11beta1, and Cyp11beta2 mRNA levels, and both cortisol and aldosterone secretions were elevated by Ucn1. Cell viability was reduced by both Ucn1 and Ucn3 via the CRF(2) receptor in H295R cells. Ucn1 and Ucn3 increased the expression of the cAMP-response element binding protein and extracellular signal-related kinase (ERK) phosphorylations. The ERK and protein kinase A pathways were involved in Ucn3-decreased cell viability.

Possible contribution of 2-aminoethoxydiphenyl-borate-sensitive Ca2+ mobilization to adrenocorticotropin-induced glucocorticoid synthesis in rat adrenocortical cells

Cytoplasmic calcium ([Ca(2+)](i)) provided through voltage-dependent Ca(2+) channels (VDCC) plays an important role in adrenocorticotropin (ACTH)-induced steroidogenesis in adrenocortical cells. To identify alternative mechanisms for [Ca(2+)](i) supply, we investigated the 2-aminoethoxydiphenyl borate (2APB)-sensitive pathway as one of the possible signaling pathways involved in [Ca(2+)](i) supply for ACTH-induced steroidogenesis. In monolayers of cultured rat adrenal fasciculate and reticularis cells, ACTH at 10(-11) M stimulated corticosterone synthesis without increasing intracellular cAMP, and corticosterone synthesis was decreased by 10 microM 2APB by 51.8% (6.71 +/- 0.97 vs. 3.23 +/- 0.05 ng/mL/4 hours; p<0.05). Furthermore, 2APB significantly decreased the 10(-11) M ACTH-stimulated [Ca(2+)](i). ACTH increased the intracellular inositol-1,4,5-trisphosphate (IP3) content with a peak at 10(-13) M ACTH, which illustrates the possibility that ACTH activates IP3/diacylglycerol- dependent protein kinase C signal transduction. However, the difference in ACTH concentrations between that responsible for the IP3 increase and steroidogenesis without elevated cAMP, suggest a hypothesis that IP3 is not required for steroidogenesis, but does involve an unknown messenger, which stimulates the release of Ca(2+) from the ER or the subsequent store-operated Ca(2+) entry (SOCE). The pregnenolone concentration in the culture medium was increased by ACTH, which was significantly suppressed by 2APB, showing that the 2APB-sensitive Ca(2+) supply affects cholesterol transport into the mitochondrial membrane via steroidogenic acute regulatory protein. Therefore, the SOCE may contribute to ACTH-induced steroidogenesis in the mitochondrial region. In conclusion, the [Ca(2+)](i) used for steroidogenesis may be derived from a 2APB-sensitive pathway and via VDCCs, particularly at physiological concentrations of ACTH. We suggest that ACTH receptors activate steroidogenesis via inositol triphosphate, or an unknown downstream messenger, which could be inhibited by 2APB.

beta-cell function in obese-hyperglycemic mice [ob/ob Mice]

This review summarizes key aspects of what has been learned about the physiology of pancreatic islets and leptin deficiency from studies in obese ob/ob mice. ob/ob Mice lack functional leptin. They are grossly overweight and hyperphagic particularly at young ages and develop severe insulin resistance with hyperglycemia and hyperinsulinemia. ob/ob Mice have large pancreatic islets. The beta-cells respond adequately to most stimuli, and ob/ob mice have been used as a rich source of pancreatic islets with high insulin release capacity. ob/ob Mice can perhaps be described as a model for the prediabetic state. The large capacity for islet growth and insulin release makes ob/ob mice a good model for studies on how beta-cells can cope with prolonged functional stress.

Curcumin inhibits ACTH- and angiotensin II-stimulated cortisol secretion and Ca(v)3.2 current

Adrenocorticotropic hormone and angiotensin II stimulate cortisol secretion from bovine adrenal zona fasciculata cells by the activation of adenylate cyclase and phospholipase C-coupled receptors. Curcumin (1- 20 muM), a compound found in the spice turmeric, inhibited cortisol secretion stimulated by ACTH, AngII, and 8CPT-cAMP. Curcumin also suppressed ACTH-stimulated increases in mRNAs coding for steroid acute regulatory protein and CYP11a1 steroid hydroxylase. In whole cell patch clamp recordings from AZF cells, curcumin at slightly higher concentrations also inhibited Ca(v)3.2 current. These results identify curcumin as an effective inhibitor of ACTH- and AngII-stimulated cortisol secretion. The inhibition of Ca(v)3.2 current by curcumin may contribute to its suppression of secretion.

Acute arterial thrombosis in the absence of inflammation: the stress-related anti-inflammatory hormone ACTH participates in platelet-mediated thrombosis

OBJECTIVE

Despite the reciprocal relationship that exists between inflammation and thrombosis, we asked whether thrombosis can develop without inflammation, and whether stress-related hormones (ACTH and cortisol) influence platelet-mediated thrombosis.

METHODS

We investigated the role of ACTH and cortisol in platelet aggregation, as well as on the circulating levels of IL-6 in pigs subjected to different treatments. In control animals, deep vessel wall injury (DVWI) was induced in the right common carotid artery, while in the animals under study DVWI was induced 60 min after ACTH administration (subgroup 1) or not at all (subgroup 2). In an ex vivo study we evaluated whether ACTH or cortisol modulates platelet aggregation. Indeed, we assessed whether blocking the P2Y platelet receptors inhibits the effect of ACTH on platelet aggregation. Finally, we assessed whether ACTH mobilizes intracellular calcium and modulates intracellular cAMP in platelets ex vivo.

RESULTS

We found that the suppression of inflammation following ACTH administration was accompanied by acute arterial thrombosis in the zone of injury in vivo. Furthermore, ACTH but not cortisol amplifies the platelet aggregation induced ex vivo by agonists. Platelets do not express ACTH receptors which may explain why ACTH does not reduce intracellular levels of cAMP in platelets. Nevertheless, supraphysiological concentrations of ACTH increase calcium mobilization in platelets.

CONCLUSION

These results indicate for the first time that ACTH may fulfil an important role in acute arterial thrombosis by increasing the platelet aggregation induced by agonists, probably via a G(q)-coupled pathway.

Diminished expression of ACTH signaling proteins and steroidogenic limiting factors in adrenocortical cells isolated from halothane nn pigs

Previous studies demonstrated significantly lower plasma cortisol level in homozygous halothane-positive (Hal nn) pigs, as compared with homozygous halothane-negative (Hal NN) pigs. To determine whether such difference is attributed to the fundamental alterations in adrenocortical function, F1 offsprings from Pietrain (Hal nn)xErhualian (Hal NN) were intercrossed to produce F2 sibling pigs with segregated genotypes. Adrenocortical cells were isolated from the Hal nn and Hal NN F2 pigs, respectively, and cultured with or without ACTH challenge. Cortisol levels in culture medium, as well as the content of MC2R, cAMP, CREB, phosphorylated CREB (pCREB), StAR and P450scc in adrenocortical cell lysates, were determined. Cortisol, cAMP, StAR and P450scc levels were significantly lower in Hal nn adrenocortical cells under basal condition without ACTH challenge. ACTH significantly increased cortisol level in the medium and the protein content of MC2R, StAR, P450scc in adrenocortical cell lysates, regardless of genotypes. Total CREB protein content was not different between genotypes and treatments, whereas pCREB content exhibited significant effects of genotype and treatment, being higher in Hal NN than in Hal nn under basal condition and in response to ACTH challenge. These results indicate that the compromised cAMP/PKA/pCREB signaling pathway of ACTH and diminished expression of limiting factors in adrenocortical steroidogenesis (StAR and P450scc) may contribute to the significantly lower plasma cortisol levels in Hal nn pigs.

Mechanisms of adrenocorticotropin-induced activation of extracellularly regulated kinase 1/2 mitogen-activated protein kinase in the human H295R adrenal cell line

The role of ACTH in stimulating or inhibiting growth of adrenal cells has been a subject of some controversy. Reports that ACTH may stimulate ERK/MAPK in Y1 cells have suggested a role for cAMP in this process. In attempting to extend this work, the ACTH responses in the human H295R cell line have been studied. This cell line makes only a very modest cAMP response to ACTH, yet the ERK1/2 response is highly reproducible and immediate but not prolonged. It is minimally reduced by the protein kinase A inhibitor, H89, but unaffected by protein kinase C and calcium inhibitors. Inhibition of epidermal growth factor receptor or other tyrosine kinase receptor transactivation was without effect, as was inhibition of c-Src activity or c-Src phosphorylation. The most effective inhibitor of this pathway was dansylcadaverine, an inhibitor of receptor internalization. These findings imply that ACTH-induced ERK1/2 activation in H295R cells is dependent on a mechanism distinct from that by which most G protein-coupled receptors activate ERK1/2 but that nevertheless seems to depend on receptor internalization.

Transcriptional regulation of adrenocortical steroidogenic gene expression

By serving as ligands for nuclear and plasma membrane receptors, steroid hormones are key regulators of a diverse array of physiological processes. These hormones are synthesized from cholesterol in tissues such as the adrenal cortex, ovaries, testes, and placenta. Because steroid hormones control the expression of numerous genes, steroidogenic cells utilize multiple mechanisms that ensure tight control of the synthesis of these molecules. This review will give an overview of the molecular mechanisms by which the expression of steroidogenic genes is regulated in the human adrenal cortex.

Role of calcium messenger systems in ACTH-induced cortisol production in bovine adrenal fasciculo-reticularis cells

We investigated the regulation of each intracellular signal transduction system including cyclic AMP (cAMP)-dependent and calcium (Ca2+) messenger systems in bovine adrenal fasciculo-reticularis cells to clarify the exact mode of action of ACTH. Pretreatment with primaquine and quinacrine, which are phospholipase A2 inhibitors, significantly inhibited cortisol production activated by both low and high concentrations of ACTH. Therefore, it seems that metabolites induced by phospholipase A2 are quite essential for cortisol synthesis induced by ACTH, either at low or high concentrations. At low concentrations of ACTH (10(-13)-10(-12) M), significant increases of cytosolic calcium ([Ca2+]i), but not of cAMP, were observed. Calphostin C, a specific protein kinase C inhibitor, apparently suppressed cortisol production activated by low concentrations of ACTH, while H-89, a specific inhibitor of cAMP-dependent protein kinase, did not. These findings suggest that, at physiologically low concentrations, ACTH activates [Ca2+]i and phospholipase A2 without affecting cAMP formation, resulting in an increased biosynthesis of cortisol, partly via protein kinase C-dependent processes. At high concentrations, ACTH (10(-9)-10(-7) M) induced an increase of cAMP and [Ca2+]i. The cortisol production induced by high concentrations of ACTH was significantly inhibited by pretreatment with calphostin C, H-89 and H-7, suggesting the participation of cAMP-dependent protein kinase and protein kinase C systems in the regulation of cortisol production in the presence of high concentrations of ACTH. In conclusion, cytosolic calcium is biphasically enhanced by ACTH, although cAMP accumulation is increased only by high concentrations of ACTH. A phospholipase A2-dependent process may partly play a crucial role in the regulation of cortisol biosynthesis, when stimulated by low and high concentrations of ACTH.

Interaction of the melanocortin 2 receptor with nucleoporin 50: evidence for a novel pathway between a G-protein-coupled receptor and the nucleus

The adrenocorticotropin (ACTH) receptor (melanocortin 2 receptor, or MC2R) is the smallest G-protein-coupled receptor that, when activated by the peptide hormone ACTH, stimulates cAMP production and adrenal steroidogenesis. Receptor expression is dependent on a specific membrane trafficking process involving an accessory protein (melanocortin 2 receptor accessory protein, or MRAP) and other unidentified components. In an attempt to discover novel receptor interacting proteins, the C-terminal tail of the MC2R was used to screen a mouse adrenal Y6 cell cDNA library using the bacterial two-hybrid system. This identified the nucleoporin Nup 50 (Npap60) as the major full-length interacting protein. Interaction was confirmed by a GST pulldown assay and by coimmunoprecipitation in human H295R cells (which express both proteins endogenously). Deletion analysis identified the region between residues 143 and 466 in Nup50 as being required for interaction with the MC2R. Stimulation of H295R cells with ACTH (10(-6) M) was followed by a gradual translocation of the Nup50-MC2R complex from the membrane to the nucleus after 30 min. This time course is most consistent with MC2R internalization dynamics and may suggest a novel role for Nup50.

Mechanisms of disease: the adrenocorticotropin receptor and disease

The action of the peptide hormone adrenocorticotropin (ACTH) to stimulate glucocorticoid production by the adrenal gland is an essential physiologic process, yet is dependent on a single unique genetic component--the ACTH receptor or melanocortin 2 receptor. Genetic defects that cause abnormalities in this receptor or in a protein required for its expression at the cell surface result in a potentially fatal disease (familial glucocorticoid deficiency). Overexpression of this receptor or inability to desensitize it is found in adrenal adenomas or hyperplasia associated with glucocorticoid overproduction (Cushing syndrome). These disorders are uncommon, but there are considerable data to show that the hypothalamo-pituitary-adrenal axis is overactive, or in some circumstances underactive, in more common situations including depressive illness and septic shock. The origin of these latter disturbances is undoubtedly complex and multifactorial, but there is good evidence that a component of this phenomenon is an altered responsiveness of the ACTH receptor to ACTH. Understanding the basis of ACTH responsiveness might, therefore, contribute to the understanding of disorders such as these and perhaps enable the hypothalamo-pituitary-adrenal axis to be manipulated beneficially in these circumstances.

A genome-wide assessment of adrenocorticotropin action in the Y1 mouse adrenal tumor cell line

This report summarizes the genome-wide effects of ACTH on transcript accumulation in mouse adrenal Y1 cells and the relative contributions of the cAMP-, protein kinase C- and Ca(2+)-dependent signaling pathways to these actions of the hormone. ACTH affected the accumulation of 1386 transcripts, a much larger number than previously appreciated. The cAMP signaling pathway accounted for approximately 56% of the ACTH effects whereas the protein kinase C- and Ca(2+)-dependent pathways made smaller contributions to ACTH action. Approximately 38% of the ACTH-affected transcripts could not be assigned to these signaling pathways and thus represent candidates for regulation via other mechanisms. The set of ACTH-regulated transcripts included clusters with functions in steroid metabolism, cell proliferation and alternative splicing. Collectively, our results suggest that Y1 adrenal cells undergo extensive remodeling upon prolonged stimulation with ACTH. The functional implications of ACTH on alternative splicing are explored.

Liver X receptors regulate adrenal steroidogenesis and hypothalamic-pituitary-adrenal feedback

The nuclear hormone receptors liver X receptor alpha (LXRalpha) (NR1H3) and LXRbeta (NR1H2) are established regulators of cholesterol, lipid, and glucose metabolism and are attractive drug targets for the treatment of diabetes and cardiovascular disease. Adrenal steroid hormones including glucocorticoids and mineralocorticoids are known to interfere with glucose metabolism, insulin signaling, and blood pressure regulation. Here we present genome-wide expression profiles of LXR-responsive genes in both the adrenal and the pituitary gland. LXR activation in cultured adrenal cells inhibited expression of multiple steroidogenic genes and consequently decreased adrenal steroid hormone production. In addition, LXR agonist treatment elevated ACTH mRNA expression and hormone secretion from pituitary cells both in vitro and in vivo. Reduced expression of the glucocortioid-activating enzyme 11beta-hydroxysteroid dehydrogenase 1 in pituitary cells upon LXR activation suggests blunting of the negative feedback of glucocorticoids by LXRs. In conclusion, LXRs independently interfere with the hypothalamic-pituitary-adrenal axis regulation at the level of the pituitary and the adrenal gland.

Global profiles of gene expression induced by adrenocorticotropin in Y1 mouse adrenal cells

ACTH regulates the steroidogenic capacity, size, and structural integrity of the adrenal cortex through a series of actions involving changes in gene expression; however, only a limited number of ACTH-regulated genes have been identified, and these only partly account for the global effects of ACTH on the adrenal cortex. In this study, a National Institute on Aging 15K mouse cDNA microarray was used to identify genome-wide changes in gene expression after treatment of Y1 mouse adrenocortical cells with ACTH. ACTH affected the levels of 1275 annotated transcripts, of which 46% were up-regulated. The up-regulated transcripts were enriched for functions associated with steroid biosynthesis and metabolism; the down- regulated transcripts were enriched for functions associated with cell proliferation, nuclear transport and RNA processing, including alternative splicing. A total of 133 different transcripts, i.e. only 10% of the ACTH-affected transcripts, were represented in the categories above; most of these had not been described as ACTH-regulated previously. The contributions of protein kinase A and protein kinase C to these genome-wide effects of ACTH were evaluated in microarray experiments after treatment of Y1 cells and derivative protein kinase A-defective mutants with pharmacological probes of each pathway. Protein kinase A-dependent signaling accounted for 56% of the ACTH effect; protein kinase C-dependent signaling accounted for an additional 6%. These results indicate that ACTH affects the expression profile of Y1 adrenal cells principally through cAMP- and protein kinase A- dependent signaling. The large number of transcripts affected by ACTH anticipates a broader range of actions than previously appreciated.