Mechanism of action of ACTH: beyond cAMP

Optogenetic induction of chronic glucocorticoid exposure in early-life leads to blunted stress-response in larval zebrafish

Early life stress (ELS) exposure alters stress susceptibility in later life and affects vulnerability to stress-related disorders, but how ELS changes the long-lasting responsiveness of the stress system is not well understood. Zebrafish provides an opportunity to study conserved mechanisms underlying the development and function of the stress response that is regulated largely by the neuroendocrine hypothalamus-pituitary-adrenal/interrenal (HPA/I) axis, with glucocorticoids (GC) as the final effector. In this study, we established a method to chronically elevate endogenous GC levels during early life in larval zebrafish. To this end, we employed an optogenetic actuator, beggiatoa photoactivated adenylyl cyclase, specifically expressed in the interrenal cells of zebrafish and demonstrate that its chronic activation leads to hypercortisolaemia and dampens the acute-stress evoked cortisol levels, across a variety of stressor modalities during early life. This blunting of stress-response was conserved in ontogeny at a later developmental stage. Furthermore, we observe a strong reduction of proopiomelanocortin (pomc)-expression in the pituitary as well as upregulation of fkbp5 gene expression. Going forward, we propose that this model can be leveraged to tease apart the mechanisms underlying developmental programming of the HPA/I axis by early-life GC exposure and its implications for vulnerability and resilience to stress in adulthood.

The Organophosphate Esters Used as Flame Retardants and Plasticizers Affect H295R Adrenal Cell Phenotypes and Functions

Adverse effects associated with exposure to brominated flame retardants have led to regulations for their use and their replacement with organophosphate esters (OPEs). However, little is known about the impact of OPEs on the adrenal, a vital endocrine gland. Here, we used a high-content screening approach to elucidate the effects of OPEs on H295R human adrenal cell phenotypic endpoints and function. The effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a legacy brominated flame retardant, on H295R cell cytotoxicity, oxidative stress, mitochondria, lysosomes, and lipid droplets were compared with those of 6 OPEs. Most OPEs reduced oxidative stress, increased the numbers of mitochondria, decreased lysosomes, and increased lipid droplets. Two potency ranking approaches, the lowest benchmark concentration/administered equivalent dose methods and Toxicological Prioritization Index analyses, revealed that the triaryl-OPEs (isopropylated triphenyl phosphate [IPPP], tris(methylphenyl) phosphate [TMPP], and triphenyl phosphate [TPHP]) and 1 nontriaryl OPE (tris(1,3-dichloro-2-propyl) phosphate [TDCIPP]) were more potent than BDE-47. The steroidogenic activity of adrenal cells in the presence or absence of forskolin, a steroidogenic stimulus, was determined after exposure to triaryl-OPEs. The basal production of cortisol and aldosterone was increased by IPPP but decreased by TPHP or TMPP exposure; the response to forskolin was not affected by these OPEs. All 3 triaryl OPEs altered the expression of rate-limiting enzymes involved in cholesterol and steroid biosynthesis; CYP11B1 and CYP11B2 were the most prominently affected targets. The OPE chemical-specific effects on cortisol and aldosterone production were best explained by alterations in STAR expression. Thus, the adrenal may be an important target for these endocrine-disrupting chemicals.

Mosaic PRKACA duplication causing a novel and distinct phenotype of early-onset Cushing's syndrome and acral cutaneous mucinosis

SIGNIFICANCE STATEMENT

We describe a mosaic PRKACA duplication in a young infant who presented with a Carney-like complex: bilateral non-pigmented micronodular adrenal hyperplasia, severe early-onset Cushing's syndrome, and distinct acral soft tissue overgrowth due to cutaneous mucinosis. This represents a novel manifestation of PRKACA disruption and broadens the extra-adrenal phenotype of PRKACA-associated Cushing's syndrome. Our data suggest that Cushing's syndrome phenotypes arising from somatic and germline PRKACA abnormalities can exist on a spectrum. We emphasise the value of ascertaining a genetic diagnosis for PRKACA-mediated adrenal and extra-adrenal disease to guide individualised and targeted care.

HSD3B1 Expression Is Upregulated by Interleukin 4 in HT-29 Colon Cancer Cells via Multiple Signaling Pathways

3β-Hydroxysteroid dehydrogenase/isomerase is essential for the synthesis of active steroid hormones. Interleukin 4 (IL4) induces the expression of HSD3B1 in various human cancer cell lines. Here, we demonstrated that administration of IL4 to an HT-29 colon cancer cell line induced high expression of HSD3B1 at the mRNA and protein levels. In the HT-29 cells, IL4 stimulated the activity of signal transducer and activator of transcription 6 (STAT6) and promoted its binding to the STAT6-binding site in the HSD3B1 promoter. The STAT6 inhibitor significantly suppressed HSD3B1 induction by IL4 in a dose-dependent manner. Moreover, inhibition of the PI3-kinase/AKT pathway strongly suppressed the IL4-induced HSD3B1 expression. Glycogen synthase kinase 3 (GSK3), a downstream target of AKT, had a stimulatory effect on the IL4-induced HSD3B1 expression. However, IL4 stimulated the phosphorylation of AKT, which inhibited the GSK3 activity at the early stage. Hence, GSK3 potentiated the HSD3B1 levels at the late stage of the IL4 stimulation. Additionally, inhibitors of mitogen-activated protein kinases (MAPKs), ERK1/2 and p38, but not of JNK, partly reduced the HSD3B1 expression following the IL4 stimulation. We further demonstrated that IL4 potently promoted steroid synthesis. Our results indicate that IL4 induces HSD3B1 expression via multiple signaling pathways in HT-29 cells and may play a role in the regulation of steroid synthesis.

11β-HSD as a New Target in Pharmacotherapy of Metabolic Diseases

Glucocorticoids (GCs), which are secreted by the adrenal cortex, are important regulators in the metabolism of carbohydrates, lipids, and proteins. For the proper functioning of the body, strict control of their release is necessary, as increased GCs levels may contribute to the development of obesity, type 2 diabetes mellitus, hypertension, cardiovascular diseases, and other pathological conditions contributing to the development of metabolic syndrome. 11β-hydroxysteroid dehydrogenase type I (11β-HSD1) locally controls the availability of the active glucocorticoid, namely cortisol and corticosterone, for the glucocorticoid receptor. Therefore, the participation of 11β-HSD1 in the development of metabolic diseases makes both this enzyme and its inhibitors attractive targets in the pharmacotherapy of the above-mentioned diseases.

A Novel Homozygous MC2R Variant Leading to Type-1 Familial Glucocorticoid Deficiency

Context

Type 1 familial glucocorticoid deficiency (FGD) (OMIM #607397) is a rare autosomal recessive disorder due to mutations in melanocortin-2-receptor (MC2R) gene encoding the G protein-coupled adrenocorticotropic (ACTH) transmembrane receptor.

Objective

The aim of the study is to describe 2 siblings born to a healthy consanguineous family presenting with clinical and biochemical features of FGD, harboring a novel homozygous MC2R variant.

Methods

Both patients are siblings born at term via normal delivery with normal birth weights. The first sibling presented with symptoms of hypoglycemia, repeated episodes of infections starting from 2 days of age. At 18 months of age, low serum cortisol was found, and he was started on hydrocortisone replacement therapy. The second sibling developed hypoglycemia on day 1 after birth, investigations revealed low serum sodium and cortisol levels and was also commenced on hydrocortisone treatment. Whole exome sequencing (WES) and in vitro functional studies on cell line transfected with wild-type and mutant plasmid clones were undertaken.

Results

WES revealed a novel homozygous missense mutation c.326T>A, p.Leu109Gln in the MC2R gene. In-silico prediction tools predicted the effect of this mutation to be deleterious. In vitro study using HEK293 cells transfected with MC2R wild-type and mutant clones showed a defect in protein expression and cAMP generation when stimulated with ACTH.

Conclusion

Homozygous semiconserved p.Leu109Gln mutation disrupts cAMP production and MC2R protein expression leading to ACTH resistance. This study provides additional evidence that this novel pathogenic variant in MC2R results in FGD phenotypes.

Label-Free Live-Cell Imaging of Internalized Microplastics and Cytoplasmic Organelles with Multicolor CARS Microscopy

As the bioaccumulation of microplastics (MPs) is considered as a potential health risk, many efforts have been made to understand the cellular dynamics and cytotoxicity of MPs. Here, we demonstrate that label-free multicolor coherent anti-Stokes Raman scattering (CARS) microscopy enables separate vibrational imaging of internalized MPs and lipid droplets (LDs) with indistinguishable shapes and sizes in live cells. By simultaneously obtaining polystyrene (PS)- and lipid-specific CARS images at two very different frequencies, 1000 and 2850 cm^-1, respectively, we successfully identify the local distribution of ingested PS beads and native LDs in Caenorhabditis elegans. We further show that the movements of PS beads and LDs in live cells can be separately tracked in real time, which allows us to characterize their individual intracellular dynamics. We thus anticipate that our multicolor CARS imaging method could be of great use to investigate the cellular transport and cytotoxicity of MPs without additional efforts for pre-labeling to MPs.

MC2R/MRAP2 activation could affect bovine ovarian steroidogenesis potential after ACTH treatment

Stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, reducing fertility by interfering with the mechanisms that regulate the timing of events within the follicular phase of the estrous cycle. In the HPA axis, melanocortin 2 receptor (MC2R) mediates responses to adrenocorticotropic hormone (ACTH) in concert with melanocortin receptor accessory protein 2 (MRAP2). The aims of the present study were: (1) to evaluate the effects of ACTH administered in cows in the preovulatory period on the expression of the MC2R/MRAP2 complex in the dominant follicle; and (2) to analyze the involvement of Extracellular signal Regulated Kinase 1 (ERK1) signaling in the activation of MC2R and the expression of key enzymes involved in the biosynthesis of glucocorticoids (GCs) in the dominant follicle. To this end, 100 IU ACTH was administered to Holstein cows from a local dairy farm during pro-estrus every 12 h for four days until ovariectomy, which was performed before ovulation. Protein immunostaining of MC2R was higher in the dominant follicles of ACTH-treated cows (p < 0.05). Also, Western blot analysis showed higher activation of the ERK1 signaling pathway in ACTH-treated cows (p < 0.05). Finally, immunohistochemistry performed in the dominant follicles of ACTH-treated cows detected higher expression of CYP17A1 and CYP21A2 (p < 0.05). These results suggest that the bovine ovary is able to respond locally to ACTH as a consequence of stress altering the expression of relevant steroidogenic enzymes. The results also confirm that the complete GC biosynthesis pathway is present in bovine dominant follicle and therefore GCs could be produced locally.

Transcriptomic Response Dynamics of Human Primary and Immortalized Adrenocortical Cells to Steroidogenic Stimuli

Adrenal steroid hormone production is a dynamic process stimulated by adrenocorticotropic hormone (ACTH) and angiotensin II (AngII). These ligands initialize a rapid and robust gene expression response required for steroidogenesis. Here, we compare the predominant human immortalized cell line model, H295R cell, with primary cultures of adult adrenocortical cells derived from human kidney donors. We performed temporally resolved RNA-seq on primary cells stimulated with either ACTH or AngII at multiple time points. The magnitude of the expression dynamics elicited by ACTH was greater than AngII in primary cells. This is likely due to the larger population of adrenocortical cells that are responsive to ACTH. The dynamics of stimulus-induced expression in H295R cells are mostly recapitulated in primary cells. However, there are some expression responses in primary cells absent in H295R cells. These data are a resource for the endocrine community and will help researchers determine whether H295R is an appropriate model for the specific aspect of steroidogenesis that they are studying.

Neuroprotective effect of ACTH on collagenase-induced peri-intraventricular hemorrhage in newborn male rats

Peri-intraventricular hemorrhage (PIVH) is a common and serious prematurity-related complication in neonates. Adrenocorticotropic hormone (ACTH) has neuroprotective actions and is a candidate to ameliorate brain damage following PIVH. Here, we tested the efficacy of ACTH1-24 on a collagenase-induced lesion of the germinal matrix (GM) in newborn male rats. Animals received microinjection of the vehicle (PBS, 2 µl) or collagenase type VII (0.3 IU) into the GM/periventricular tissue on postnatal day (PN) 2. Twelve hours later pups received microinjection of either the agonist ACTH1-24 (0.048 mg/kg), or the antagonist SHU9119 (antagonist of MCR3/MCR4 receptors, 0.01 mg/kg), or their combination. Morphological outcomes included striatal injury extension, neuronal and glial cells counting, and immunohistochemical expression of brain lesion biomarkers ipsilateral and contralateral to the hemorrhagic site. Data were evaluated on PN 8. Collagenase induced PIVH and severe ipsilateral striatal lesion. ACTH1-24 dampened the deleterious effects of collagenase-induced hemorrhage in significantly reducing the extension of the damaged area, the striatal neuronal and glial losses, and the immunoreactive expression of the GFAP, S100β, and NG2-glia biomarkers in the affected periventricular area. SHU9119 blocked the glial density rescuing effect of ACTH1-24. ACTH1-24 could be further evaluated to determine its suitability for preclinical models of PVH in premature infants.

The hypothalamic-pituitary-adrenal axis as a substrate for stress resilience: Interactions with the circadian clock

Stress, primarily processed via the hypothalamic-pituitary-adrenal (HPA) axis, engages biological pathways throughout the brain and body which promote adaptation and survival to changing environmental demands. Adaptation to environmental challenges is compromised when these pathways are no longer functioning optimally. The physiological and behavioral mechanisms through which HPA axis function influences stress adaptation and resilience are not fully elucidated. Our understanding of stress biology and disease must take into account the complex interactions between the endocrine system, neural circuits, and behavioral coping strategies. In addition, further consideration must be taken concerning influences of other aspects of physiology, including the circadian clock which is critical for regulation of daily changes in HPA activity. While adding a layer of complexity, it also offers targets for intervention. Understanding the role of HPA function in mediating these diverse biological responses will lead to important insights about how to bolster successful stress adaptation and promote stress resilience.

Isolated glucocorticoid deficiency: Genetic causes and animal models

Hereditary adrenocorticotropin (ACTH) resistance syndromes encompass the genetically heterogeneous isolated or Familial Glucocorticoid Deficiency (FGD) and the distinct clinical entity known as Triple A syndrome. The molecular basis of adrenal resistance to ACTH includes defects in ligand binding, MC2R/MRAP receptor trafficking, cellular redox balance, cholesterol synthesis and sphingolipid metabolism. Biochemically, this manifests as ACTH excess in the setting of hypocortisolaemia. Triple A syndrome is an inherited condition involving a tetrad of adrenal insufficiency, achalasia, alacrima and neuropathy. FGD is an autosomal recessive condition characterized by the presence of isolated glucocorticoid deficiency, classically in the setting of preserved mineralocorticoid secretion. Primarily there are three established subtypes of the disease: FGD 1, FGD2 and FGD3 corresponding to mutations in the Melanocortin 2 receptor MC2R (25%), Melanocortin 2 receptor accessory protein MRAP (20%), and Steroidogenic acute regulatory protein STAR (5-10%) respectively. Together, mutations in these 3 genes account for approximately half of cases. Whole exome sequencing in patients negative for MC2R, MRAP and STAR mutations, identified mutations in minichromosome maintenance 4 MCM4, nicotinamide nucleotide transhydrogenase NNT, thioredoxin reductase 2 TXNRD2, cytochrome p450scc CYP11A1, and sphingosine 1-phosphate lyase SGPL1 accounting for a further 10% of FGD. These novel genes have linked replicative and oxidative stress and altered redox potential as a mechanism of adrenocortical damage. However, a genetic diagnosis is still unclear in about 40% of cases. We describe here an updated list of FGD genes and provide a description of relevant mouse models that, despite some being flawed, have been precious allies in the understanding of FGD pathobiology.

Autoantibodies reactive to adrenocorticotropic hormone can alter cortisol secretion in both aggressive and nonaggressive humans

Violent aggression in humans may involve a modified response to stress, but the underlying mechanisms are not well understood. Here we show that naturally present autoantibodies reactive to adrenocorticotropic hormone (ACTH) exhibit distinct epitope-binding profiles to ACTH peptide in subjects with a history of violent aggression compared with controls. Namely, while nonaggressive male controls displayed a preferential IgG binding to the ACTH central part (amino acids 11-24), subjects who had committed violent acts of aggression had IgG with increased affinity to ACTH, preferentially binding to its N terminus (amino acids 1-13). Purified IgGs from approximately half of the examined sera were able to block ACTH-induced cortisol secretion of human adrenal cells in vitro, irrespective of the source of sample (from a control subject or a violent aggressor). Nevertheless, in the resident-intruder test in mice, i.p. injection of residents with ACTH and IgG from aggressive subjects, but not from control subjects, shortened latency for the first attack against intruders. Immunohistochemical screening of violent aggressors' sera on rat brain and pituitary sections did not show IgG binding to ACTH-producing cells, but 4 of 16 sera revealed selective binding to a nonidentified antigen in vasopressinergic neurons of the hypothalamic paraventricular and supraoptic nuclei. Thus, the data show that ACTH-reactive plasmatic IgGs exhibit differential epitope preference in control and violently aggressive subjects. These IgGs can modulate ACTH-induced cortisol secretion and, hence, are involved in the regulation of the stress response. However, the possible role of ACTH-reactive autoantibodies in aggressive behavior needs further investigation.

Effect of a melanocortin type 2 receptor (MC2R) antagonist on the corticosterone response to hypoxia and ACTH stimulation in the neonatal rat

The adrenal stress response in the neonatal rat shifts from ACTH-independent to ACTH-dependent between postnatal days 2 (PD2) and 8 (PD8). This may be due to an increase in an endogenous, bioactive, nonimmunoreactive ligand to the melanocortin type 2 receptor (MC2R). GPS1574 is a newly described MC2R antagonist that we have shown to be effective in vitro. Further experimentation with GPS1574 would allow better insight into this seemingly ACTH-independent steroidogenic response in neonates. We evaluated the acute corticosterone response to hypoxia or ACTH injection following pretreatment with GPS1574 (32 mg/kg) or vehicle for GPS1574 in PD2, PD8, and PD15 rat pups. Pretreatment with GPS1574 decreased baseline corticosterone in PD2 pups but increased baseline corticosterone in PD8 and PD15 pups. GPS1574 did not attenuate the corticosterone response to hypoxia in PD2 pups and augmented the corticosterone response in PD8 and PD15 pups. GPS1574 augmented the corticosterone response to ACTH in PD2 and PD15 pups but had no significant impact on the response in PD8 pups. Baseline adrenal Mrap and Star mRNA increased from PD2 to PD15, whereas Mrap2 mRNA expression was low and did not change with age. The data suggest that GPS1574 is not a pure MC2R antagonist, but rather acts as a biasing agonist/antagonist. Its ability to attenuate or augment the adrenal response may depend on the ambient plasma ACTH concentration and/or developmental changes in early transduction steroidogenic pathway genes.

Cofilin is a cAMP effector in mediating actin cytoskeleton reorganization and steroidogenesis in mouse and human adrenocortical tumor cells

cAMP pathway plays a major role in the pathogenesis of cortisol-producing adrenocortical adenomas (CPA). cAMP-induced steroidogenesis is preceded by actin cytoskeleton reorganization, a process regulated by cofilin activity. In this study we investigated cofilin role in mediating cAMP effects on cell morphology and steroidogenesis in adrenocortical tumor cells. We demonstrated that forskolin induced cell rounding and strongly reduced phosphorylated (P)-cofilin/total cofilin ratio in Y1 (-52 ± 16%, p < 0.001) and human CPA cells (-53 ± 18%, p < 0.05). Cofilin silencing significantly reduced both forskolin-induced morphological changes and progesterone production (1.3-fold vs 1.8-fold in controls, p < 0.05), whereas transfection of wild-type or S3A (active), but not S3D (inactive) cofilin, potentiated forskolin effects on cell rounding and increased 3-fold progesterone synthesis with respect to control (p < 0.05). Furthermore, cofilin dephosphorylation by a ROCK inhibitor potentiated forskolin-induced cell rounding and steroidogenesis (2-fold increase vs forskolin alone). Finally, we found a reduced P-cofilin/total cofilin ratio and increased cofilin expression in CPA vs endocrine inactive adenomas by western blot and immunohistochemistry. Overall, these results identified cofilin as a mediator of cAMP effects on both morphological changes and steroidogenesis in mouse and human adrenocortical tumor cells.

Adrenal gland plasticity in lactating rats and mice is sufficient to maintain basal hypersecretion of corticosterone

Increased basal glucocorticoid secretion and a reduced glucocorticoid response during acute stress, despite only minor changes in the secretion of the major secretagogue adrenocorticotropic hormone (ACTH), have been documented in the peripartum period in several species. We recently showed that the adrenal gland, the site of glucocorticoid synthesis, undergoes substantial postpartum-associated plasticity in the rat at mid-lactation. Here, we asked the question whether adrenal changes already take place around parturition in the rat and in another species, namely the mouse. After demonstrating that several components of the adrenal machinery mediating cholesterol supply for steroidogenesis, including protein levels of hormone-sensitive lipase, low-density lipoprotein receptor (LDLR) and scavenger receptor class-B type-1 (SRB1), are upregulated, while hydroxymethylglutaryl coenzyme A reductase (HMGCR) is downregulated in the lactating rat one day after delivery, as previously observed at mid-lactation, we demonstrated profound changes in the mouse. In detail, protein expression of LDLR, SRB1, HMGCR and adrenal lipid store density were increased in the mouse adrenal one day after parturition as tested via western blot analysis and oil-red lipid staining, respectively. Moreover, using in vitro culture techniques, we observed that isolated adrenal explants from lactating mice secreted higher levels of corticosterone under basal conditions, but showed impaired responsiveness to ACTH, mimicking the in vivo scenario. These results suggest that mechanisms of adaptation in the maternal adrenal after delivery, namely increased cholesterol availability and decreased ACTH sensitivity, are crucial for the basal increase in circulating glucocorticoids and maternal stress hyporesponsiveness that are typical of this period.

ACTH Receptor (MC2R) Specificity: What Do We Know About Underlying Molecular Mechanisms?

Coincidentally, the release of this Research Topic in Frontiers in Endocrinology takes place 25 years after the discovery of the adrenocorticotropic hormone receptor (ACTHR) by Mountjoy and colleagues. In subsequent years, following the discovery of other types of mammalian melanocortin receptors (MCRs), ACTHR also became known as melanocortin type 2 receptor (MC2R). At present, five types of MCRs have been reported, all of which share significant sequence similarity at the amino acid level, and all of which specifically bind melanocortins (MCs)-a group of biologically active peptides generated by proteolysis of the proopiomelanocortin precursor. All MCs share an identical -H-F-R-W- pharmacophore sequence. α-Melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) are the most extensively studied MCs and are derived from the same region. Essentially, α-MSH is formed from the first 13 amino acid residues of ACTH. ACTHR is unique among MCRs because it binds one sole ligand-ACTH, which makes it a very attractive research object for molecular pharmacologists. However, much research has failed, and functional studies of this receptor are lagging behind other MCRs. The reason for these difficulties has already been outlined by Mountjoy and colleagues in their publication on ACTHR coding sequence discovery where the Cloudman S91 melanoma cell line was used for receptor expression because it was a "more sensitive assay system." Subsequent work showed that ACTHR could be successfully expressed only in endogenous MCR-expressing cell lines, since in other cell lines it is retained within the endoplasmic reticulum. The resolution of this methodological problem came in 2005 with the discovery of melanocortin receptor accessory protein, which is required for the formation of functionally active ACTHR. The decade that followed this discovery was filled with exciting research that provided insight into the molecular mechanisms underlying the action of ACTHR. The purpose of this review is to summarize the advances in this fascinating research field.

Role of cAMP/PKA pathway and T-type calcium channels in the mechanism of action of serotonin in human adrenocortical cells

In human adrenal, serotonin (5-HT), produced by mast cells located in zona glomerulosa, stimulates production of corticosteroids through a paracrine mechanism involving the 5-HT receptor type 4 (5-HT₄). The aim of the present study was to investigate the transduction mechanisms associated with activation of 5-HT₄ receptors in human adrenocortical cells. Our results show that 5-HT₄ receptors are present in the outer adrenal cortex, both in glomerulosa and fasciculata zonae. In the zona glomerulosa. 5-HT₄ receptor was detected both in immunopositive and immunonegative cells for 11β-hydroxylase, an enzyme involved in cortisol synthesis. The data demonstrate that 5-HT₄ receptors are positively coupled to adenylyl cyclases and cAMP-dependent protein kinases (PKA). The activation of the cAMP-PKA pathway is associated with calcium influx through T-type calcium channels. Both the adenylyl cyclase/PKA pathway and the calcium influx are involved in 5-HT-induced cortisol secretion.

ACTH Action on StAR Biology

Adrenocorticotropin hormone (ACTH) produced by the anterior pituitary stimulates glucocorticoid synthesis by the adrenal cortex. The first step in glucocorticoid synthesis is the delivery of cholesterol to the mitochondrial matrix where the first enzymatic reaction in the steroid hormone biosynthetic pathway occurs. A key response of adrenal cells to ACTH is activation of the cAMP-protein kinase A (PKA) signaling pathway. PKA activation results in an acute increase in expression and function of the Steroidogenic Acute Regulatory protein (StAR). StAR plays an essential role in steroidogenesis- it controls the hormone-dependent movement of cholesterol across the mitochondrial membranes. Currently StAR's mechanism of action remains a major unanswered question in the field. However, some insight may be gained from understanding the mechanism(s) controlling the PKA-dependent phosphorylation of StAR at S194/195 (mouse/human StAR), a modification that is required for function. This mini-review provides a background on StAR's biology with a focus on StAR phosphorylation. The model for StAR translation and phosphorylation at the outer mitochondrial membrane, the location for StAR function, is presented to highlight a unifying theme emerging from diverse studies.

Role of CREB on heme oxygenase-1 induction in adrenal cells: involvement of the PI3K pathway

In addition to the well-known function of ACTH as the main regulator of adrenal steroidogenesis, we have previously demonstrated its effect on the transcriptional stimulation of HO-1 expression, a component of the cellular antioxidant defense system. In agreement, we hereby demonstrate that, in adrenocortical Y1 cells, HO-1 induction correlates with a significant prevention of the generation of reactive oxygen species induced by H2O2/Fe(2+) ACTH/cAMP-dependent activation of redox-imbalanced related factors such as NRF2 or NFκB and the participation of MAPKs in this mechanism was, however, discarded based on results with specific inhibitors and reporter plasmids. We suggest the involvement of CREB in HO-1 induction by ACTH/cAMP, as transfection of cells with a dominant-negative isoform of CREB (DN-CREB-M1) decreased, while overexpression of CREB increased HO-1 protein levels. Sequence screening of the murine HO-1 promoter revealed CRE-like sites located at -146 and -37 of the transcription start site and ChIP studies indicated that this region recruits phosphorylated CREB (pCREB) upon cAMP stimulation in Y1 cells. In agreement, H89 (PKA inhibitor) or cotransfection with DN-CREB-M1 prevented the 8Br-cAMP-dependent increase in luciferase activity in cells transfected with pHO-1[-295/+74].LUC. ACTH and cAMP treatment induced the activation of the PI3K/Akt signaling pathway in a PKA-independent mechanism. Inhibition of this pathway prevented the cAMP-dependent increase in HO-1 protein levels and luciferase activity in cells transfected with pHO-1[-295/+74].LUC. Finally, here we show a crosstalk between the cAMP/PKA and PI3K pathways that affects the binding of p-CREB to its cognate element in the murine promoter of the Hmox1 gene.

Dynamic transitions in a model of the hypothalamic-pituitary-adrenal axis

Dynamic properties of a nonlinear five-dimensional stoichiometric model of the hypothalamic-pituitary-adrenal (HPA) axis were systematically investigated. Conditions under which qualitative transitions between dynamic states occur are determined by independently varying the rate constants of all reactions that constitute the model. Bifurcation types were further characterized using continuation algorithms and scale factor methods. Regions of bistability and transitions through supercritical Andronov-Hopf and saddle loop bifurcations were identified. Dynamic state analysis predicts that the HPA axis operates under basal (healthy) physiological conditions close to an Andronov-Hopf bifurcation. Dynamic properties of the stress-control axis have not been characterized experimentally, but modelling suggests that the proximity to a supercritical Andronov-Hopf bifurcation can give the HPA axis both, flexibility to respond to external stimuli and adjust to new conditions and stability, i.e., the capacity to return to the original dynamic state afterwards, which is essential for maintaining homeostasis. The analysis presented here reflects the properties of a low-dimensional model that succinctly describes neurochemical transformations underlying the HPA axis. However, the model accounts correctly for a number of experimentally observed properties of the stress-response axis. We therefore regard that the presented analysis is meaningful, showing how in silico investigations can be used to guide the experimentalists in understanding how the HPA axis activity changes under chronic disease and/or specific pharmacological manipulations.

Cortisol-secreting adrenocortical tumours in dogs and their relevance for human medicine

Spontaneous cortisol-secreting adrenocortical tumours in pet dogs are an attractive animal model for their human counterparts. Adrenal morphology and function are similar in dogs and humans, and adrenocortical tumours have comparable clinical and pathological characteristics. Their relatively high incidence in pet dogs represents a potential source of adrenocortical tumour tissue to facilitate research. The molecular characteristics of canine cortisol-secreting adrenocortical tumours suggest that they will be useful for the study of angiogenesis, the cAMP/protein kinase A pathway, and the role of Steroidogenic Factor-1 in adrenal tumourigenesis. Pet dogs with spontaneous cortisol-secreting adrenocortical tumours may also be useful in clinical testing of new drugs and in investigating the molecular background of adrenocortical tumours.

Role of EPAC in cAMP-Mediated Actions in Adrenocortical Cells

Adrenocorticotropic hormone regulates adrenal steroidogenesis mainly via the intracellular signaling molecule cAMP. The effects of cAMP are principally relayed by activating protein kinase A (PKA) and the more recently discovered exchange proteins directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). While the intracellular roles of PKA have been extensively studied in steroidogenic tissues, those of EPACs are only emerging. EPAC1 and EPAC2 are encoded by the genes RAPGEF3 and RAPGEF4, respectively. Whereas EPAC1 is ubiquitously expressed, the expression of EPAC2 is more restricted, and typically found in endocrine tissues. Alternative promoter usage of RAPGEF4 gives rise to three different isoforms of EPAC2 that vary in their N-termini (EPAC2A, EPAC2B, and EPAC2C) and that exhibit distinct expression patterns. EPAC2A is expressed in the brain and pancreas, EPAC2B in steroidogenic cells of the adrenal gland and testis, and EPAC2C has until now only been found in the liver. In this review, we discuss current knowledge on EPAC expression and function with focus on the known roles of EPAC in adrenal gland physiology.

Effect of Novel Melanocortin Type 2 Receptor Antagonists on the Corticosterone Response to ACTH in the Neonatal Rat Adrenal Gland In Vivo and In Vitro

Stress-induced increases in neonatal corticosterone demonstrate a unique shift from ACTH independence to ACTH dependence between postnatal day 2 (PD2) and day 8 (PD8) in newborn rats. This shift could be due to the binding of a bioactive, non--immunoreactive plasma ligand to the adrenocortical melanocortin 2 receptor (MC2R) (ACTH receptor). A potent MC2R antagonist would be useful to evaluate this phenomenon in the neonate. Therefore, we investigated the acute corticosterone response to ACTH(1-39) injection in rat pups pretreated with newly developed MC2R antagonists (GPS1573 and GPS1574), which have not been tested in vivo. The doses used in vivo were based on their in vitro potency, with GP1573 being more potent than GPS1574. GPS1573 (PD2 and PD8), GPS1574 (PD2 only), or vehicle were injected intraperitoneally (ip) 10 min before baseline sampling. Then, 0.001 mg/kg of ACTH(1-39) was injected ip, and subsequent blood samples obtained for the measurement of plasma corticosterone. Pretreatment of PD2 pups with GPS1573 demonstrated augmentation, rather than inhibition, of the corticosterone response to ACTH. In PD8 pups, pretreatment with 0.1 mg/kg GPS1573, but not 4 mg/kg, augmented the corticosterone response to ACTH. Pretreatment with GPS1574 attenuated the plasma corticosterone response to ACTH at 30 min in PD2 pups. The activity of these two compounds in vivo do not match their potency in vitro, with GPS1573 leading to a small augmentation of the corticosterone response to ACTH in vivo while GPS1574 resulted in inhibition.

Regulation of human (adrenal) androgen biosynthesis-New insights from novel throughput technology studies

Androgens are precursors for sex steroids and are predominantly produced in the human gonads and the adrenal cortex. They are important for intrauterine and postnatal sexual development and human reproduction. Although human androgen biosynthesis has been extensively studied in the past, exact mechanisms underlying the regulation of androgen production in health and disease remain vague. Here, the knowledge on human androgen biosynthesis and regulation is reviewed with a special focus on human adrenal androgen production and the hyperandrogenic disorder of polycystic ovary syndrome (PCOS). Since human androgen regulation is highly specific without a good animal model, most studies are performed on patients harboring inborn errors of androgen biosynthesis, on human biomaterials and human (tumor) cell models. In the past, most studies used a candidate gene approach while newer studies use high throughput technologies to identify novel regulators of androgen biosynthesis. Using genome wide association studies on cohorts of patients, novel PCOS candidate genes have been recently described. Variant 2 of the DENND1A gene was found overexpressed in PCOS theca cells and confirmed to enhance androgen production. Transcriptome profiling of dissected adrenal zones established a role for BMP4 in androgen synthesis. Similarly, transcriptome analysis of human adrenal NCI-H295 cells identified novel regulators of androgen production. Kinase p38α (MAPK14) was found to phosphorylate CYP17 for enhanced 17,20 lyase activity and RARB and ANGPTL1 were detected in novel networks regulating androgens. The discovery of novel players for androgen biosynthesis is of clinical significance as it provides targets for diagnostic and therapeutic use.

cAMP signaling in cortisol-producing adrenal adenoma

The cAMP signaling pathway is one of the major players in the regulation of growth and hormonal secretion in adrenocortical cells. Although its role in the pathogenesis of adrenocortical hyperplasia associated with Cushing's syndrome has been clarified, a clear involvement of the cAMP signaling pathway and of one of its major downstream effectors, the protein kinase A (PKA), in sporadic adrenocortical adenomas remained elusive until recently. During the last year, a report by our group and three additional independent groups showed that somatic mutations of PRKACA, the gene coding for the catalytic subunit α of PKA, are a common genetic alteration in patients with Cushing's syndrome due to adrenal adenomas, occurring in 35-65% of the patients. In vitro studies revealed that those mutations are able to disrupt the association between catalytic and regulatory subunits of PKA, leading to a cAMP-independent activity of the enzyme. Despite somatic PRKACA mutations being a common finding in patients with clinically manifest Cushing's syndrome, the pathogenesis of adrenocortical adenomas associated with subclinical hypercortisolism seems to rely on a different molecular background. In this review, the role of cAMP/PKA signaling in the regulation of adrenocortical cell function and its alterations in cortisol-producing adrenocortical adenomas will be summarized, with particular focus on recent developments.

Manipulation of Interrenal Cell Function in Developing Zebrafish Using Genetically Targeted Ablation and an Optogenetic Tool

Zebrafish offer an opportunity to study conserved mechanisms underlying the ontogeny and physiology of the hypothalamic-pituitary-adrenal/interrenal axis. As the final effector of the hypothalamic-pituitary-adrenal/interrenal axis, glucocorticoids exert both rapid and long-term regulatory functions. To elucidate their specific effects in zebrafish, transgenic approaches are necessary to complement pharmacological studies. Here, we report a robust approach to specifically manipulate endogenous concentrations of cortisol by targeting heterologous proteins to interrenal cells using a promoter element of the steroidogenic acute regulatory protein. To test this approach, we first used this regulatory region to generate a transgenic line expressing the bacterial nitroreductase protein, which allows conditional targeted ablation of interrenal cells. We demonstrate that this line can be used to specifically ablate interrenal cells, drastically reducing both basal and stress-induced cortisol concentrations. Next, we coupled this regulatory region to an optogenetic actuator, Beggiatoa photoactivated adenylyl cyclase, to increase endogenous cortisol concentrations in a blue light-dependent manner. Thus, our approach allows specific manipulations of steroidogenic interrenal cell activity for studying the effects of both hypo- and hypercortisolemia in zebrafish.

Modeling diurnal hormone profiles by hierarchical state space models

Adrenocorticotropic hormone (ACTH) diurnal patterns contain both smooth circadian rhythms and pulsatile activities. How to evaluate and compare them between different groups is a challenging statistical task. In particular, we are interested in testing (1) whether the smooth ACTH circadian rhythms in chronic fatigue syndrome and fibromyalgia patients differ from those in healthy controls and (2) whether the patterns of pulsatile activities are different. In this paper, a hierarchical state space model is proposed to extract these signals from noisy observations. The smooth circadian rhythms shared by a group of subjects are modeled by periodic smoothing splines. The subject level pulsatile activities are modeled by autoregressive processes. A functional random effect is adopted at the pair level to account for the matched pair design. Parameters are estimated by maximizing the marginal likelihood. Signals are extracted as posterior means. Computationally efficient Kalman filter algorithms are adopted for implementation. Application of the proposed model reveals that the smooth circadian rhythms are similar in the two groups but the pulsatile activities in patients are weaker than those in the healthy controls.

Granulocyte-colony stimulating factor activates JAK2/PI3K/PDE3B pathway to inhibit corticosterone synthesis in a neonatal hypoxic-ischemic brain injury rat model

OBJECTIVE

Our previous study demonstrated that granulocyte-colony stimulating factor (G-CSF)-induced neuroprotection is accompanied by an inhibition of corticosterone production in a neonatal hypoxic-ischemic (HI) rat model. The present study investigates how G-CSF inhibits corticosterone production, using adrenal cortical cells and HI rat pups.

METHODS

Cholera toxin was used to induce corticosterone synthesis in a rodent Y1 adrenal cortical cell line by increasing cyclic adenosine monophosphate (cAMP). Both corticosterone and cAMP were quantitatively measured using a commercial enzyme-linked immunosorbent assay (ELISA). The downstream signaling components of the G-CSF receptor, including Janus Kinase 2 (JAK2)/Phosphatidylinositol-3-kinase (PI3K)/Protein kinase B (Akt) and Phosphodiesterase 3B (PDE3B), were detected by western blot. Sprague-Dawley rat pups at the age of 10days (P10) were subjected to unilateral carotid artery ligation followed by hypoxia for 2.5hours. Brain infarction volumes were determined using 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining.

RESULTS

G-CSF at 30ng/ml inhibited corticosterone synthesis but lost its inhibitory effect at higher doses. The inhibitory effect of G-CSF was conferred by interfering with cAMP signaling via the activation of the JAK2/PI3K/PDE3B signaling pathway. The degradation of cAMP by G-CSF signaling reduced corticosterone production. This mechanism was further verified in the neonatal HI brain injury rat model, in which inhibition of PDE3B reversed the protective effects of G-CSF.

CONCLUSION

Our data suggest that the neuroprotective G-CSF reduces corticosterone synthesis at the adrenal level by degrading intracellular cAMP via activation of the JAK2/PI3K/PDE3B pathway.

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.

Physiological basis for the etiology, diagnosis, and treatment of adrenal disorders: Cushing's syndrome, adrenal insufficiency, and congenital adrenal hyperplasia

The hypothalamic-pituitary-adrenal (HPA) axis is a classic neuroendocrine system. One of the best ways to understand the HPA axis is to appreciate its dynamics in the variety of diseases and syndromes that affect it. Excess glucocorticoid activity can be due to endogenous cortisol overproduction (spontaneous Cushing's syndrome) or exogenous glucocorticoid therapy (iatrogenic Cushing's syndrome). Endogenous Cushing's syndrome can be subdivided into ACTH-dependent and ACTH-independent, the latter of which is usually due to autonomous adrenal overproduction. The former can be due to a pituitary corticotroph tumor (usually benign) or ectopic ACTH production from tumors outside the pituitary; both of these tumor types overexpress the proopiomelanocortin gene. The converse of Cushing's syndrome is the lack of normal cortisol secretion and is usually due to adrenal destruction (primary adrenal insufficiency) or hypopituitarism (secondary adrenal insufficiency). Secondary adrenal insufficiency can also result from a rapid discontinuation of long-term, pharmacological glucocorticoid therapy because of HPA axis suppression and adrenal atrophy. Finally, mutations in the steroidogenic enzymes of the adrenal cortex can lead to congenital adrenal hyperplasia and an increase in precursor steroids, particularly androgens. When present in utero, this can lead to masculinization of a female fetus. An understanding of the dynamics of the HPA axis is necessary to master the diagnosis and differential diagnosis of pituitary-adrenal diseases. Furthermore, understanding the pathophysiology of the HPA axis gives great insight into its normal control.

Uncoupling of secretion from growth in some hormone secretory tissues

CONTEXT

Most syndromes with benign primary excess of a hormone show positive coupling of hormone secretion to size or proliferation in the affected hormone secretory tissue. Syndromes that lack this coupling seem rare and have not been examined for unifying features among each other.

EVIDENCE ACQUISITION

Selected clinical and basic features were analyzed from original reports and reviews. We examined indices of excess secretion of a hormone and indices of size of secretory tissue within the following three syndromes, each suggestive of uncoupling between these two indices: familial hypocalciuric hypercalcemia, congenital diazoxide-resistant hyperinsulinism, and congenital primary hyperaldosteronism type III (with G151E mutation of the KCNJ5 gene).

EVIDENCE SYNTHESIS

Some unifying features among the three syndromes were different from features present among common tumors secreting the same hormone. The unifying and distinguishing features included: 1) expression of hormone excess as early as the first days of life; 2) normal size of tissue that oversecretes a hormone; 3) diffuse histologic expression in the hormonal tissue; 4) resistance to treatment by subtotal ablation of the hormone-secreting tissue; 5) causation by a germline mutation; 6) low potential of the same mutation to cause a tumor by somatic mutation; and 7) expression of the mutated molecule in a pathway between sensing of a serum metabolite and secretion of hormone regulating that metabolite.

CONCLUSION

Some shared clinical and basic features of uncoupling of secretion from size in a hormonal tissue characterize three uncommon states of hormone excess. These features differ importantly from features of common hormonal neoplasm of that tissue.

Role of soluble adenylyl cyclase in cell death and growth

cAMP signaling is an evolutionarily conserved intracellular communication system controlling numerous cellular functions. Until recently, transmembrane adenylyl cyclase (tmAC) was considered the major source for cAMP in the cell, and the role of cAMP signaling was therefore attributed exclusively to the activity of this family of enzymes. However, increasing evidence demonstrates the role of an alternative, intracellular source of cAMP produced by type 10 soluble adenylyl cyclase (sAC). In contrast to tmAC, sAC produces cAMP in various intracellular microdomains close to specific cAMP targets, e.g., in nucleus and mitochondria. Ongoing research demonstrates involvement of sAC in diverse physiological and pathological processes. The present review is focused on the role of cAMP signaling, particularly that of sAC, in cell death and growth. Although the contributions of sAC to the regulation of these cellular functions have only recently been discovered, current data suggest that sAC plays key roles in mitochondrial bioenergetics and the mitochondrial apoptosis pathway, as well as cell proliferation and development. Furthermore, recent reports suggest the importance of sAC in several pathologies associated with apoptosis as well as in oncogenesis. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to postnatal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response with a minimal increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore the phenomenon of ACTH-stimulated steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected intraperitoneally with porcine ACTH at low, moderate, or high doses (1, 4, or 20 μg/kg body wt). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 min after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3,000 pg/ml), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP-mediated pathway.

Genetics and epigenetics of adrenocortical tumors

Adrenocortical tumors are common neoplasms. Most are benign, nonfunctional and clinically irrelevant. However, adrenocortical carcinoma is a rare disease with a dismal prognosis and no effective treatment apart from surgical resection. The molecular genetics of adrenocortical tumors remain poorly understood. For decades, molecular studies relied on a small number of samples and were directed to candidate-genes. This approach, based on the elucidation of the genetics of rare genetic syndromes in which adrenocortical tumors are a manifestation, has led to the discovery of major dysfunctional molecular pathways in adrenocortical tumors, such as the IGF pathway, the Wnt pathway and TP53. However, with the advent of high-throughput methodologies and the organization of international consortiums to obtain a larger number of samples and high-quality clinical data, this paradigm is rapidly changing. In the last decade, genome-wide expression profile studies, microRNA profiling and methylation profiling allowed the identification of subgroups of tumors with distinct genetic markers, molecular pathways activation patterns and clinical behavior. As a consequence, molecular classification of tumors has proven to be superior to traditional histological and clinical methods in prognosis prediction. In addition, this knowledge has also allowed the proposal of molecular-targeted approaches to provide better treatment options for advanced disease. This review aims to summarize the most relevant data on the rapidly evolving field of genetics of adrenal disorders.

Expression of angiogenesis-related genes in canine cortisol-secreting adrenocortical tumors

The aim of this study was to evaluate the expression of angiogenesis-related genes in canine cortisol-secreting adrenocortical tumors (ATs). Quantitative RT-PCR analysis revealed mRNA encoding for vascular endothelial growth factor, vascular endothelial growth factor receptors 1 and 2, angiopoietin 1 and 2 (ANGPT1 and ANGPT2), the splice variant ANGPT2443, the ANGPT-receptor Tie2, and basic fibroblast growth factor in 38 canine cortisol-secreting ATs (26 carcinomas and 12 adenomas) and 15 normal adrenals. The relative expression of both ANGPT2 and ANGPT2443 was higher in adenomas (P = 0.020 for ANGPT2 and P = 0.002 for ANGPT2443) and carcinomas (P = 0.003 for ANGPT2 and P < 0.001 for ANGPT2443) compared with normal adrenals, and this enhanced expression was also detected with Western blot analysis. Immunohistochemistry indicated expression of ANGPT2 protein in AT cells and in vascular endothelial cells of carcinomas, whereas Tie2 was mainly present in the tumor vascular endothelial cells. The ANGPT2-to-ANGTPT1 ratio, a marker for a proangiogenic state, was higher in both adenomas (P = 0.020) and carcinomas (P = 0.043). With the use of the human H295R cortisol-producing adrenocortical carcinoma cell line, we were able to demonstrate that the ANGPT2 expression was stimulated by cyclic adenosine monophosphate and progesterone but not by cortisol. In conclusion, canine cortisol-secreting ATs have enhanced ANGPT2 expression with a concomitant shift toward a proangiogenic state. On the basis of this information, treatment modalities may be developed that interfere with ANGPT2 expression, including inhibition of the cyclic adenosine monophosphate/protein kinase A pathway, or of the effect of ANGPT2, by using specific ANGPT2 inhibitors.

Modulation of circadian glucocorticoid oscillation via adrenal opioid-CXCR7 signaling alters emotional behavior

Circulating glucocorticoid levels oscillate with a robust circadian rhythm, yet the physiological relevance of this rhythmicity remains unclear. Here, we show that modulation of circadian glucocorticoid oscillation by enhancing its amplitude leads to anxiolytic-like behavior. We observed that mice with adrenal subcapsular cell hyperplasia (SCH), a common histological change in the adrenals, are less anxious than mice without SCH. This behavioral change was found to be dependent on the higher amplitude of glucocorticoid oscillation, although the total glucocorticoid secretion is not increased in these mice. Genetic and pharmacologic experiments demonstrated that intermediate opioid peptides secreted from SCH activate CXCR7, a β-arrestin-biased G-protein-coupled receptor (GPCR), to augment circadian oscillation of glucocorticoid levels in a paracrine manner. Furthermore, recapitulating this paracrine axis by subcutaneous administration of a synthetic CXCR7 ligand is sufficient to induce anxiolytic-like behavior. Adrenocortical β-arrestin-biased GPCR signaling is a potential target for modulating circadian glucocorticoid oscillation and emotional behavior.

Hedgehog-signaling is upregulated in non-producing human adrenal adenomas and antagonism of hedgehog-signaling inhibits proliferation of NCI-H295R cells and an immortalized primary human adrenal cell line

Hedgehog (Hh)-signaling pathway is important in embryonic development. Activation of Hh-signaling is associated with tumorigenesis. Recent studies demonstrate that Hh-signaling is involved in the development of the adrenal gland in mice and is important in regulating adrenal proliferation. We studied the expression of Sonic hedgehog (SHH), Smoothened (SMO), Patched1 (PTCH1) and GLI family zinc finger 1 (GLI1) in human adrenal and in adrenocortical tumors using immunohistochemistry and semi-quantitative reverse transcriptase-polymerase chain reaction. Modulation of GLI1 and SMO messenger ribonucleic acid (mRNA) expression was investigated with forskolin. The role of Hh-signaling was studied in NCI-H295R cells and in an immortalized primary cell line using the Hh-agonist smoothened agonist (SAG) and the Hh-antagonist cyclopamine. The Hh-pathway components SHH, GLI1, PTCH1 and SMO were detectable in all adrenal glands. While in cortisol-producing adenomas (CPA), Hh-signaling expression levels were comparable to that in normal adrenal cortex, a much higher mRNA expression of GLI1, SMO and SHH was observed in non-producing adenomas (NPA). Interestingly, stimulation of cultured adrenal cells with forskolin led to a decrease in expression of GLI1 and SMO mRNAs. Antagonism of Hh-signaling resulted in a lower proliferation rate of adrenocortical cells, while Hh-agonism had no significant effect on adrenal cell proliferation. Our data show Hh-signaling activity in adult adrenal glands. Activation of the PKA pathway results in lower expression of Hh-signaling proteins. This might explain the lower expression of the Hh components GLI1 and SMO in CPA in comparison to the higher expression in NPA. Hh-signaling might be involved in the tumorigenesis of NPA.

Adrenocortical control in the neonatal rat: ACTH- and cAMP-independent corticosterone production during hypoxia

We have previously demonstrated that the neonatal corticosterone response to acute hypoxia shifts from ACTH independence to ACTH dependence between postnatal days two (PD2) and eight (PD8). Cyclic AMP (cAMP) is the obligatory intracellular second messenger of ACTH action, and we hypothesized that corticosterone production in neonatal rats shifts from a cAMP-independent mechanism to cAMP-dependent mechanism between PD2 and PD8. Plasma ACTH and corticosterone and adrenal cAMP and cGMP responses to acute severe hypoxia (8% O₂ for 5, 10, 20, 30, and 180 min) were measured in neonatal rats at PD2, PD8, and PD15. Plasma ACTH and corticosterone were measured by radioimmunoassay, and adrenal cAMP and cGMP were measured by ELISA. Plasma corticosterone-binding globulin (CBG) was measured in normoxic pups by ELISA. The largest corticosterone response was observed in PD2 pups, despite only a small increase in plasma ACTH that was not sustained. The PD2 ACTH-independent increase in corticosterone occurred with no change in adrenal cAMP or cGMP content. Plasma CBG concentration was lowest in PD2 pups. Large corticosterone responses were measured during the first 30 min of hypoxia. Differences in corticosterone responses between PD2 and PD8 pups cannot be attributed to changes in plasma protein binding capacity, and the PD2 corticosterone response is consistent with a nongenomic mechanism of action. We conclude that the sustained corticosterone response to hypoxia in PD2 pups occurs with small and transient ACTH responses and independently of increases in adrenal cAMP or cGMP.

Differential regulation of human 3β-hydroxysteroid dehydrogenase type 2 for steroid hormone biosynthesis by starvation and cyclic AMP stimulation: studies in the human adrenal NCI-H295R cell model

Human steroid biosynthesis depends on a specifically regulated cascade of enzymes including 3β-hydroxysteroid dehydrogenases (HSD3Bs). Type 2 HSD3B catalyzes the conversion of pregnenolone, 17α-hydroxypregnenolone and dehydroepiandrosterone to progesterone, 17α-hydroxyprogesterone and androstenedione in the human adrenal cortex and the gonads but the exact regulation of this enzyme is unknown. Therefore, specific downregulation of HSD3B2 at adrenarche around age 6–8 years and characteristic upregulation of HSD3B2 in the ovaries of women suffering from the polycystic ovary syndrome remain unexplained prompting us to study the regulation of HSD3B2 in adrenal NCI-H295R cells. Our studies confirm that the HSD3B2 promoter is regulated by transcription factors GATA, Nur77 and SF1/LRH1 in concert and that the NBRE/Nur77 site is crucial for hormonal stimulation with cAMP. In fact, these three transcription factors together were able to transactivate the HSD3B2 promoter in placental JEG3 cells which normally do not express HSD3B2. By contrast, epigenetic mechanisms such as methylation and acetylation seem not involved in controlling HSD3B2 expression. Cyclic AMP was found to exert differential effects on HSD3B2 when comparing short (acute) versus long-term (chronic) stimulation. Short cAMP stimulation inhibited HSD3B2 activity directly possibly due to regulation at co-factor or substrate level or posttranslational modification of the protein. Long cAMP stimulation attenuated HSD3B2 inhibition and increased HSD3B2 expression through transcriptional regulation. Although PKA and MAPK pathways are obvious candidates for possibly transmitting the cAMP signal to HSD3B2, our studies using PKA and MEK1/2 inhibitors revealed no such downstream signaling of cAMP. However, both signaling pathways were clearly regulating HSD3B2 expression.

ACTH promotes chondrogenic nodule formation and induces transient elevations in intracellular calcium in rat bone marrow cell cultures via MC2-R signaling

Adrenocorticotropic hormone (ACTH) is among several melanocortin peptide hormones that are derived from proopiomelanocortin (POMC). ACTH has been found to enhance osteogenesis and chondrogenesis. We show that, in the presence of dexamethasone, ACTH dose-dependently increases chondrogenic nodule formation in bone marrow stromal cells (BMSC) from the Wistar Kyoto (WKY) rat. The nodules consist in condensed cells highly expressing alkaline phosphatase, Sox9 and type II collagen transcripts and a proteoglycan-rich matrix. Immunoblot analysis of crude membrane fractions has shown that these cells express three melanocortin receptors (MC-R), namely MC2-R, MC3-R and MC5-R and the melanocortin 2-receptor accessory protein (MRAP). To determine which of these receptors mediate ACTH-induced effects, we have used MC-R-specific peptides and the known agonist profiles of the receptors. Neither α-MSH, a strong agonist of MC5-R, nor γ2-MSH, a strong agonist of MC3-R, duplicates ACTH effects in rat BMSC. In addition, calcium flux has been examined as a mechanism for ACTH action at the MC2-R. Consistent with MC2-R and MRAP expression patterns in the BMSC cultures, ACTH-induced transient increases in intracellular calcium are increased with dexamethasone treatment. Neither α-MSH nor γ2-MSH affects calcium flux. Dexamethasone increases MC2-R and MRAP expression and POMC peptide expression and cleavage increasing the production of the lipolytic β-lipotropic hormone product. Therefore, the effects of ACTH in rat BMSC enriched for mesenchymal progenitors are consistent with an MC2-R signaling mechanism, with dexamethasone being capable of regulating components of the melanocortin system in these cells.

Using the human melanocortin-2 receptor as a model for analyzing hormone/receptor interactions between a mammalian MC2 receptor and ACTH(1-24)

When considering the interactions between the melanocortin peptides (i.e., ACTH, α-MSH, β-MSH, γ-MSH) and the melanocortin receptors (i.e., MC1R, MC2R, MC3R, MC4R, MC5R), it appears that the structure/function relationship between ACTH and MC2R is the most complicated. Human ACTH(1-24) and the human melanocortin-2 receptor provide a useful model system for understanding how ACTH emerged as the sole ligand for the melanocortin-2 receptor of bony vertebrates. This review will discuss how studies utilizing analogs of hACTH(1-24) have revealed two critical amino acid motifs in this ligand (HFRW and KKRRP) which are required for activation of the melanocortin-2 receptor. In addition, observations on the unique activation features of the melanocortin-2 receptor, as revealed from studies on Familial Glucocorticoid Deficiency, will be considered. Finally, the evolutionary implications of the relationship between MC2R and MRAP1 will be discussed.

Systemic and local ACTH produced during inflammatory states promotes osteochondrogenic mesenchymal cell differentiation contributing to the pathologic progression of calcified atherosclerosis

There are many well-known roles for the proopiomelanocortin (POMC) derived peptides and their receptors, the melanocortin receptors (MC-R). The focus here is on the evolving role of the melanocortin system in inflammation. Chronic inflammatory states such as those occurring in diabetes and obesity are associated with both a hyperactive hypothalamic-pituitary-adrenal (HPA) axis as well as increased incidence of atherosclerosis. An inflammation-induced hyperactive HPA axis along with increased leukocyte infiltration can lead to significant exposure to melanocortin peptides, particularly ACTH, in an inflamed vasculature. Mesenchymal progenitor cells are present throughout the vasculature, express receptors for the melanocortin peptides, and respond to ACTH with increased osteochondrogenic differentiation. Coupled to the increased exposure to ACTH during HPA hyperactivity is increased glucocorticoid (GC) exposure. GCs also promote chondrogenic differentiation of mesenchymal progenitors and increase their expression of MC-R as well as their expression of POMC and its cleavage products. It is hypothesized that during inflammatory states systemically produced ACTH and glucocorticoid as well as ACTH produced locally by macrophage and other immune cells, can influence and potentiate mesenchymal progenitor cell differentiation along the osteochondrogenic lineages. In turn the increase in osteochondrogenic matrix contributes to the pathophysiological progression of the calcified atherosclerotic plaque. The roles of the melanocortin system in inflammation and its resolution have just begun to be explored. Investigations into the ACTH-induced matrix changes among mesenchymal cell populations are warranted. ACTH signaling through the MC-R represents a new therapeutic target for the prevention and treatment of calcified atherosclerosis.

Functional melanocortin-2 receptors are expressed by mouse aorta-derived mesenchymal progenitor cells

A local melanocortin system is active during tissue injury and inflammation. Thus far this system has been described as autocrine in nature where local production of pro-opiomelanocortin (POMC) peptides by leukocytes feeds back on melanocortin receptor (MC-R) expressing immune cells to quell inflammatory cytokine production. Here we present evidence that POMC peptides may generate extracellular matrix (ECM) changes by inducing matrix production by cells of the mesenchymal lineage through activation of the MC2-R. Using immunoblot, we determined that mouse aorta-derived mesenchymal progenitor cells express both MC2-R and MC3-R. These progenitors respond to treatment with ACTH by increasing collagen matrix synthesis as assessed by picrosirius red stain and (3)H-proline incorporation. ACTH also induces transient increases in intracellular calcium ([Ca(2+)](i)) as assessed using the fluorescent Ca(2+) indicator, fura-2. The ACTH-induced changes in [Ca(2+)](i) are consistent with MC2-R signaling and consist of both an intracellular release and an extracellular influx of Ca(2+). Both mouse aortic mesenchymal progenitors and mouse macrophage cells express POMC and the prohormone convertase 1/3 (PC1/3) indicating they have the potential to contribute to the local production of POMC peptides. These data demonstrate functional MC2-R expression in mouse aorta-derived mesenchymal progenitors and implicate both macrophage and mesenchymal cells as relevant sources of local POMC peptides.

Mitotane exhibits dual effects on steroidogenic enzymes gene transcription under basal and cAMP-stimulating microenvironments in NCI-H295 cells

Adrenocortical carcinoma (ACC) is an extremely rare and aggressive endocrine malignancy with a poor prognosis. The most common symptom of ACC is hypercortisolism (Cushing's syndrome), which has the highest mortality. Mitotane is used as a steroidogenesis inhibitor for Cushing's syndrome or as a chemical adrenalectomy drug for ACC. Mitotane induces adrenal cortex necrosis, mitochondrial membrane impairment, and irreversible binding to CYP proteins. In this study, we explored the molecular effect of mitotane on steroidogenesis in human adrenocortical cancer NCI-H295 cells. Mitotane (10-40μM) inhibited basal and cAMP-induced cortisol secretion but did not cause cell death. Mitotane exhibited an inhibitory effect on the basal expression of StAR and P450scc protein. Furthermore, 40μM of mitotane significantly diminished StAR, CYP11A1 and CYP21 mRNA expression. HSD3B2 and CYP17 seem to be insensitive to mitotane. The stimulatory effects of mitotane on CYP11B1 were more remarkable than its inhibitory effects. In contrast, the activation of cAMP signaling strongly elevated the expression of all these genes. Mitotane (40μM) almost completely neutralized this positive effect and returned 8-Br-cAMP-induced StAR, CYP11A1, CYP17 and CYP21 mRNA to control levels. After cAMP activation, mitotane did not change the levels of CYP11B1 mRNA. The present study demonstrates that mitotane can inhibit cortisol biosynthesis due to a non-specific interference with the gene transcription of steroidogenic enzymes under both basal and 8-Br-cAMP-activated conditions in NCI-H295 cells. We also identified that StAR and CYP11A1 key enzymes that participate in the rate-limiting step of steroidogenesis, were more sensitive to mitotane. In addition, the biphasic effect of mitotane on CYP11B1 was also elucidated.

The C-terminal domains of melanocortin-2 receptor (MC2R) accessory proteins (MRAP1) influence their localization and ACTH-induced cAMP production

ACTH binding to the human melanocortin-2 receptor (MC2R) requires the presence of the MC2R accessory protein1 isoforms, MRAPα or MRAPβ. This study evaluated the role of the isoform-specific C-terminal domains of MRAP with regard to their cellular localization, topology, interaction with MRAP2 and cAMP production. When stably expressed in HEK293/FRT cells or in B16-G4F mouse melanoma cells (an MSH receptor-deficient cell clone), MRAPα and MRAPdCT (truncated MRAP1, N-terminal only) localized mainly around the nuclear envelope and within dense intracellular endosomes, while MRAPβ exhibited a strong localization at the plasma membrane, and partially with rapid recycling endosomes. MRAPβ and MRAPdCT both exhibited dual-topology (N(cyto)/C(exo) and N(exo)/C(cyto)) at the plasma membrane whereas MRAPα exhibited only N(cyto)/C(exo) topology at the plasma membrane while adopting dual-topology in intracellular compartments. Both MRAPα and MRAP2 colocalized in intracellular compartments, as opposed to weak colocalization between MRAPβ and MRAP2. MRAP2 and MC2R enhanced the expression of MRAP1 isoforms and vice versa. Moreover, in both HEK293/FRT and B16-G4F cells, ACTH failed to activate MC2R unless MRAP1 was present. MRAP1 expression enhanced MC2R cell-surface expression as well as concentration-dependent cAMP accumulation. In the presence of human or zebrafish MC2R, MRAPβ induced the highest cAMP accumulation while MRAPdCT induced the lowest. Together, the present findings indicate that the C-terminal domains of MRAP dictate their intracellular localization in addition to regulating ACTH-induced cAMP production. These preferential localizations suggest that MRAPα is involved in MC2R targeting to the plasma membrane, while MRAPβ may enhance ACTH-MC2R coupling to cAMP production.