Control of cell proliferation in the rat adrenal gland in vivo by the renin-angiotensin system

Elevated luteinizing hormone receptor signaling or selenium treatment leads to comparable changes in adrenal cortex histology and androgen-AR/ZIP9 signaling

The importance and regulation of adrenal androgen production and signaling are not completely understood and are scarcely studied. In addition, there is still a search for appropriate animal models and experimental systems for the investigation of adrenal physiology and disease. Therefore, the main objective of the study was to evaluate the effect of luteinizing hormone (LH) signaling and selenium (Se2+) exposure on androgen adrenal signaling via canonical androgen receptor (AR), and membrane androgen receptor acting as zinc transporter (zinc- and iron-like protein 9; ZIP9). For herein evaluations, adrenals isolated from transgenic mice with elevated LH receptor signaling (KiLHRD582G) and adrenals obtained from rabbits used for ex vivo adenal cortex culture and exposure to Se2+ were utilized. Tissues were assessed for morphological, morphometric, and Western blot analyses and testosterone and zinc level measurements.Comparison of adrenal cortex histology and morphometric analysis in KiLHRD582G mice and Se2+-treated rabbits revealed cell hypertrophy. No changes in the expression of proliferating cell nuclear antigen (PCNA) were found. In addition, AR expression was decreased (p < 0.001) in both KiLHRD582G mouse and Se2+-treated rabbit adrenal cortex while expression of ZIP9 showed diverse changes. Its expression was increased (P < 0.001) in KiLHRD582G mice and decreased (P < 0.001) in Se2+-treated rabbits but only at the dose 10 ug/100 mg/ tissue. Moreover, increased testosterone levels (P < 0.05) and zinc levels were detected in the adrenal cortex of KiLHRD582G mice whereas in rabbit adrenal cortex treated with Se2+, the effect was the opposite (P < 0.001).

ACTH signalling and adrenal development: lessons from mouse models

The melanocortin-2-receptor (MC2R), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC2R in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency (FGD), a potentially fatal disease characterised by isolated cortisol deficiency. MC2R mutations cause ~25% of cases. The discovery of a MC2R accessory protein MRAP, mutations of which account for ~20% of FGD, has provided insight into MC2R trafficking and signalling. MRAP is a single transmembrane domain accessory protein highly expressed in the adrenal gland and essential for MC2R expression and function. Mouse models helped elucidate the action of ACTH. The Mc2r-knockout (Mc2r - / - ) mice was the first mouse model developed to have adrenal insufficiency with deficiencies in glucocorticoid, mineralocorticoid and catecholamines. We recently reported the generation of the Mrap - / - mice which better mimics the human FGD phenotype with isolated glucocorticoid deficiency alone. The adrenal glands of adult Mrap - / - mice were grossly dysmorphic with a thickened capsule, deranged zonation and deranged WNT4/beta-catenin and sonic hedgehog (SHH) pathway signalling. Collectively, these mouse models of FGD highlight the importance of ACTH and MRAP in adrenal progenitor cell regulation, cortex maintenance and zonation.

Regulation of zonation and homeostasis in the adrenal cortex

The adult adrenal cortex is organized into concentric zones, each specialized to produce distinct steroid hormones. Cellular composition of the cortex is highly dynamic and subject to diverse signaling controls. Cortical homeostasis and regeneration rely on centripetal migration of steroidogenic cells from the outer to the inner cortex, which is accompanied by direct conversion of zona glomerulosa (zG) into zona fasciculata (zF) cells. Given the important impact of tissue structure and growth on steroidogenic function, it is essential to understand the mechanisms governing adrenal zonation and homeostasis. Towards this end, we review the distinctions between each zone by highlighting their morphological and ultra-structural features, discuss key signaling pathways influencing zonal identity, and evaluate current evidence for long-term self-renewing stem cells in the adult cortex. Finally, we review data supporting zG-to-zF transdifferentiation/direct conversion as a major mechanism of adult cortical renewal.

Functional Zonation of the Adult Mammalian Adrenal Cortex

The standard model of adrenocortical zonation holds that the three main zones, glomerulosa, fasciculata, and reticularis each have a distinct function, producing mineralocorticoids (in fact just aldosterone), glucocorticoids, and androgens respectively. Moreover, each zone has its specific mechanism of regulation, though ACTH has actions throughout. Finally, the cells of the cortex originate from a stem cell population in the outer cortex or capsule, and migrate centripetally, changing their phenotype as they progress through the zones. Recent progress in understanding the development of the gland and the distribution of steroidogenic enzymes, trophic hormone receptors, and other factors suggests that this model needs refinement. Firstly, proliferation can take place throughout the gland, and although the stem cells are certainly located in the periphery, zonal replenishment can take place within zones. Perhaps more importantly, neither the distribution of enzymes nor receptors suggest that the individual zones are necessarily autonomous in their production of steroid. This is particularly true of the glomerulosa, which does not seem to have the full suite of enzymes required for aldosterone biosynthesis. Nor, in the rat anyway, does it express MC2R to account for the response of aldosterone to ACTH. It is known that in development, recruitment of stem cells is stimulated by signals from within the glomerulosa. Furthermore, throughout the cortex local regulatory factors, including cytokines, catecholamines and the tissue renin-angiotensin system, modify and refine the effects of the systemic trophic factors. In these and other ways it more and more appears that the functions of the gland should be viewed as an integrated whole, greater than the sum of its component parts.

The endocrine dyscrasia that accompanies menopause and andropause induces aberrant cell cycle signaling that triggers re-entry of post-mitotic neurons into the cell cycle, neurodysfunction, neurodegeneration and cognitive disease

This article is part of a Special Issue "SBN 2014". Sex hormones are physiological factors that promote neurogenesis during embryonic and fetal development. During childhood and adulthood these hormones support the maintenance of brain structure and function via neurogenesis and the formation of dendritic spines, axons and synapses required for the capture, processing and retrieval of information (memories). Not surprisingly, changes in these reproductive hormones that occur with menopause and during andropause are strongly correlated with neurodegeneration and cognitive decline. In this connection, much evidence now indicates that Alzheimer's disease (AD) involves aberrant re-entry of post-mitotic neurons into the cell cycle. Cell cycle abnormalities appear very early in the disease, prior to the appearance of plaques and tangles, and explain the biochemical, neuropathological and cognitive changes observed with disease progression. Intriguingly, a recent animal study has demonstrated that induction of adult neurogenesis results in the loss of previously encoded memories while decreasing neurogenesis after memory formation during infancy mitigated forgetting. Here we review the biochemical, epidemiological and clinical evidence that alterations in sex hormone signaling associated with menopause and andropause drive the aberrant re-entry of post-mitotic neurons into an abortive cell cycle that leads to neurite retraction, neuron dysfunction and neuron death. When the reproductive axis is in balance, gonadotropins such as luteinizing hormone (LH), and its fetal homolog, human chorionic gonadotropin (hCG), promote pluripotent human and totipotent murine embryonic stem cell and neuron proliferation. However, strong evidence supports menopausal/andropausal elevations in the LH:sex steroid ratio as driving aberrant mitotic events. These include the upregulation of tumor necrosis factor; amyloid-β precursor protein processing towards the production of mitogenic Aβ; and the activation of Cdk5, a key regulator of cell cycle progression and tau phosphorylation (a cardinal feature of both neurogenesis and neurodegeneration). Cognitive and biochemical studies confirm the negative consequences of a high LH:sex steroid ratio on dendritic spine density and human cognitive performance. Prospective epidemiological and clinical evidence in humans supports the premise that rebalancing the ratio of circulating gonadotropins:sex steroids reduces the incidence of AD. Together, these data support endocrine dyscrasia and the subsequent loss of cell cycle control as an important etiological event in the development of neurodegenerative diseases including AD, stroke and Parkinson's disease.

LGR5 Activates Noncanonical Wnt Signaling and Inhibits Aldosterone Production in the Human Adrenal

CONTEXT

Aldosterone synthesis and cellularity in the human adrenal zona glomerulosa (ZG) is sparse and patchy, presumably due to salt excess. The frequency of somatic mutations causing aldosterone-producing adenomas (APAs) may be a consequence of protection from cell loss by constitutive aldosterone production.

OBJECTIVE

The objective of the study was to delineate a process in human ZG, which may regulate both aldosterone production and cell turnover.

DESIGN

This study included a comparison of 20 pairs of ZG and zona fasciculata transcriptomes from adrenals adjacent to an APA (n = 13) or a pheochromocytoma (n = 7).

INTERVENTIONS

Interventions included an overexpression of the top ZG gene (LGR5) or stimulation by its ligand (R-spondin-3).

MAIN OUTCOME MEASURES

A transcriptome profile of ZG and zona fasciculata and aldosterone production, cell kinetic measurements, and Wnt signaling activity of LGR5 transfected or R-spondin-3-stimulated cells were measured.

RESULTS

LGR5 was the top gene up-regulated in ZG (25-fold). The gene for its cognate ligand R-spondin-3, RSPO3, was 5-fold up-regulated. In total, 18 genes associated with the Wnt pathway were greater than 2-fold up-regulated. ZG selectivity of LGR5, and its absence in most APAs, were confirmed by quantitative PCR and immunohistochemistry. Both R-spondin-3 stimulation and LGR5 transfection of human adrenal cells suppressed aldosterone production. There was reduced proliferation and increased apoptosis of transfected cells, and the noncanonical activator protein-1/Jun pathway was stimulated more than the canonical Wnt pathway (3-fold vs 1.3-fold). ZG of adrenal sections stained positive for apoptosis markers.

CONCLUSION

LGR5 is the most selectively expressed gene in human ZG and reduces aldosterone production and cell number. Such conditions may favor cells whose somatic mutation reverses aldosterone inhibition and cell loss.

Diagnosis and management of primary aldosteronism: an updated review

Primary aldosteronism (PA) is the most common secondary form of arterial hypertension, with a particularly high prevalence among patients with resistant hypertension. Aldosterone has been found to be associated with cardiovascular toxicity. Prolonged aldosteronism leads to higher incidence of cardiac events, glomerular hyperfiltration, and potentially bone/metabolic sequels. The wider application of aldosterone/renin ratio as screening test has substantially contributed to increasing diagnosis of PA. Diagnosis of PA consists of two phases: screening and confirmatory testing. Adrenal imaging is often inaccurate for differentiation between an adenoma and hyperplasia, and adrenal venous sampling is essential for selecting the appropriate treatment modality. The etiologies of PA have two main subtypes: unilateral (aldosterone-producing adenoma) and bilateral (micro- or macronodular hyperplasia). Aldosterone-producing adenoma is typically managed with unilateral adrenalectomy, while bilateral adrenal hyperplasia is amenable to pharmacological approaches using mineralocorticoid antagonists. Short-term treatment outcome following surgery is determined by factors such as preoperative blood pressure level and hypertension duration, but evidence regarding long-term treatment outcome is still lacking. However, directed treatments comprising of unilateral adrenalectomy or mineralocorticoid antagonists still potentially reduce the toxicities of aldosterone. Utilizing a physician-centered approach, we intend to provide up-dated information on the etiology, diagnosis, and the management of PA.

K+ channel mutations in adrenal aldosterone-producing adenomas and hereditary hypertension

Endocrine tumors such as aldosterone-producing adrenal adenomas (APAs), a cause of severe hypertension, feature constitutive hormone production and unrestrained cell proliferation; the mechanisms linking these events are unknown. We identify two recurrent somatic mutations in and near the selectivity filter of the potassium (K(+)) channel KCNJ5 that are present in 8 of 22 human APAs studied. Both produce increased sodium (Na(+)) conductance and cell depolarization, which in adrenal glomerulosa cells produces calcium (Ca(2+)) entry, the signal for aldosterone production and cell proliferation. Similarly, we identify an inherited KCNJ5 mutation that produces increased Na(+) conductance in a Mendelian form of severe aldosteronism and massive bilateral adrenal hyperplasia. These findings explain pathogenesis in a subset of patients with severe hypertension and implicate loss of K(+) channel selectivity in constitutive cell proliferation and hormone production.

Sodium depletion increases sympathetic neurite outgrowth and expression of a novel TMEM35 gene-derived protein (TUF1) in the rat adrenal zona glomerulosa

The adrenal zona glomerulosa (ZG) secretes aldosterone to regulate sodium balance. Chronic sodium restriction increases aldosterone accompanied by ZG expansion. The ZG is innervated by sympathetic, vasoactive intestinal polypeptide (VIP) and neuropeptide tyrosine (NPY), and sensory, calcitonin gene-related peptide, nerves. It is unclear whether innervation is affected by ZG growth. Therefore, we measured neurite outgrowth in the ZG of adult male rats after dietary sodium manipulation. In response to 1 wk sodium restriction, VIP and NPY fibers elongated in parallel with expansion of the ZG, shown by aldosterone synthase (AS) expression, but calcitonin gene-related peptide fibers were not affected. Sodium repletion resulted in parallel regression in VIP and NPY fiber length and AS expression. These results show that sympathetic, but not sensory, innervation is coordinated with ZG growth. Mediators underlying changes in innervation are unknown; therefore, we characterized a novel gene TMEM35 [termed the unknown factor-1 (TUF1) due to its unknown function] that shows extensive overlap with AS in ZG. After sodium restriction, TUF1 expanded in parallel with the ZG. TUF1 bound the low-affinity neurotrophin receptor, p75NTR, which was expressed in NPY fibers and showed a response similar to TUF1 after sodium manipulation. TUF1- p75NTR binding was competitively displaced by nerve growth factor but not by TUF1 lacking the p75NTR binding motif. Moreover, TUF1 mRNA in rat ZG cells increased after angiotensin II exposure in vitro. Collectively, these findings suggest that TMEM35/TUF1 is a candidate for modulating neurite outgrowth in the ZG after sodium depletion.

The pregnancy hormones human chorionic gonadotropin and progesterone induce human embryonic stem cell proliferation and differentiation into neuroectodermal rosettes

INTRODUCTION

The physiological signals that direct the division and differentiation of the zygote to form a blastocyst, and subsequent embryonic stem cell division and differentiation during early embryogenesis, are unknown. Although a number of growth factors, including the pregnancy-associated hormone human chorionic gonadotropin (hCG) are secreted by trophoblasts that lie adjacent to the embryoblast in the blastocyst, it is not known whether these growth factors directly signal human embryonic stem cells (hESCs).

METHODS

Here we used hESCs as a model of inner cell mass differentiation to examine the hormonal requirements for the formation of embryoid bodies (EB's; akin to blastulation) and neuroectodermal rosettes (akin to neurulation).

RESULTS

We found that hCG promotes the division of hESCs and their differentiation into EB's and neuroectodermal rosettes. Inhibition of luteinizing hormone/chorionic gonadotropin receptor (LHCGR) signaling suppresses hESC proliferation, an effect that is reversed by treatment with hCG. hCG treatment rapidly upregulates steroidogenic acute regulatory protein (StAR)-mediated cholesterol transport and the synthesis of progesterone (P4). hESCs express P4 receptor A, and treatment of hESC colonies with P4 induces neurulation, as demonstrated by the expression of nestin and the formation of columnar neuroectodermal cells that organize into neural tubelike rosettes. Suppression of P4 signaling by withdrawing P4 or treating with the P4-receptor antagonist RU-486 inhibits the differentiation of hESC colonies into EB's and rosettes.

CONCLUSIONS

Our findings indicate that hCG signaling via LHCGR on hESC promotes proliferation and differentiation during blastulation and neurulation. These findings suggest that trophoblastic hCG secretion and signaling to the adjacent embryoblast could be the commencement of trophic support by placental tissues in the growth and development of the human embryo.

Gene expression profile in rat adrenal zona glomerulosa cells stimulated with aldosterone secretagogues

The mineralocorticoid aldosterone, mainly produced by the adrenal gland, is essential for life, but an abnormally excessive secretion causes severe pathological effects including hypertension and target organ injury in the heart and kidney. The aim of this study was to determine the gene regulatory network triggered by aldosterone secretagogues in a nontransformed cell system. Freshly isolated rat adrenal zona glomerulosa cells were stimulated with the two main aldosterone secretagogues, angiotensin II and potassium, for 2 h and subjected to whole genome expression studies using multiple biological and bioinformatics tools. Several genes were differentially expressed by ANG II (n = 133) or potassium (n = 216). Genes belonging to the nucleic acid binding and transcription factor activity categories were significantly enriched. A subset of the most regulated genes was confirmed by real-time RT-PCR, and then their expression was analyzed in time curve studies. Differentially expressed genes were grouped according to their time response expression pattern, and their promoter regions were analyzed for common regulatory transcription factor binding sites. Finally, data mining with gene promoters, transcription factors, and literature databases was performed to generate gene interaction networks for either ANG II or potassium. This paper provides for the first time a complete study of the genes that are regulated, and the interaction between them, by aldosterone secretagogues in rat adrenal cells. Increasing our knowledge of adrenal physiology and gene regulation in nontransformed cell systems could lead us to a better approach for the discovery of candidate genes involved in pathological conditions of the adrenal cortex.

Zone-specific cell proliferation during adrenocortical regeneration after enucleation in rats

A quantitative analysis of zone-specific proliferation was done to determine the recovery of adrenal cortical zonation during regeneration after enucleation. Adult male rats underwent adrenal enucleation [unilateral enucleation (ULE)] or sham surgery, both accompanied by contralateral adrenalectomy. At 2, 5, 10, and 28 days, blood and adrenals were collected to assess functional recovery. Adrenal sections were immunostained for Ki67 (proliferation), cytochrome P-450 aldosterone synthase (P-450aldo, glomerulosa), and cytochrome P-450 11beta-hydroxylase (P-45011beta, fasciculata). Unbiased stereology was used to count proliferating glomerulosa and fasciculata cells. Recovery of fasciculata secretory function occurred by 28 days as reflected by plasma ACTH and corticosterone, whereas glomerulosa function reflected by plasma aldosterone remained low at 28 days. At 5 days, ULE adrenals showed increased Ki67+ cells in the glomerulosa and inner fasciculata, whereas at 10 and 28 days increased proliferation was restricted to the outer fasciculata. These data show that enucleation results in transient elevations in glomerulosa and inner fasciculata cell proliferation followed by a delayed increase in the outer fasciculata. To assess adrenal growth in enucleated adrenals previously suppressed by the presence of an intact adrenal, rats underwent ULE and sham surgery; after 4 wk, the intact adrenal was removed and enucleated adrenals were collected at 2, 5, and 10 days. Overall, proliferation was delayed in this model, but at 5 days, Ki67+ cells increased in the outer fasciculata, whereas by 10 days, increased proliferation occurred in the outer and inner fasciculata. The key novel finding of increased proliferation in the inner fasciculata suggests that the delayed growth of the enucleated adrenal results in part from a regenerative response.

Zone-specific cell proliferation during compensatory adrenal growth in rats

Compensatory adrenal growth after unilateral adrenalectomy (ULA) leads to adrenocortical hyperplasia. Because zonal growth contributions are not clear, we characterized the phenotype of cortical cells that proliferate using immunofluorescence histochemistry and zone-specific cell counting. Rats underwent ULA, sham adrenalectomy (sham), or no surgery and were killed at 2 or 5 days. Adrenals were weighed and sections immunostained for Ki67 (proliferation), cytochrome P-450 aldosterone synthase (P450aldo, glomerulosa), and cytochrome P-450 11beta-hydroxylase (P45011beta, fasciculata). Unbiased stereology was used to count proliferating glomerulosa and fasciculata cells. Adrenal weight increased after ULA compared with sham and no surgery at both time points, and there was no difference between sham and no surgery. However, either ULA or sham increased Ki67-positive cells in the outer fasciculata at both time points compared with no surgery. Outer fasciculata-restricted proliferation is thus associated with adrenal weight gain in ULA but not sham. Experiment repetition using proliferating cell nuclear antigen and bromodeoxyuridine showed similar results. After ULA, adrenal DNA, RNA, and protein increased at both time points, whereas after sham, only adrenal DNA increased at 2 days. Compensatory growth thus results from hyperplasia and hypertrophy, whereas sham induces only a transient adrenal hyperplasia. Dexamethasone pretreatment prevented the increase in adrenal weight after ULA and blocked Ki67 labeling in the outer fasciculata but not zona glomerulosa in all groups. These results clearly show that the outer fasciculata is the primary adrenal zone responsible for compensatory growth, responding to steroid-suppressible stress signals that alone are ineffective in increasing adrenal mass.

Angiotensin II AT1 receptor stimulates Na+ -K+ATPase activity through a pathway involving PKC-zeta in rat thyroid cells

Angiotensin II (Ang II) receptor subtype 1, AT1, is expressed by the rat thyroid. A relationship between thyroid function and several components of the renin-angiotensin system has also been established, but the Ang II cellular effects in thyrocytes and its transduction signalling remain undefined. The aim of the present paper was to investigate the modulation of the activity of the Na(+)-K(+)ATPase by Ang II and its intracellular transduction pathway in PC-Cl3 cells, an established epithelial cell line derived from rat thyroid. Here we have demonstrated, by RT-PCR analysis, the expression of mRNA for the Ang II AT1 receptor in PC-Cl3 cells; mRNA for the Ang II AT2 receptor was not detected. Ang II was not able to affect the intracellular Ca(2+) concentration in fura-2-loaded cells, but it stimulated the translocation from the cytosol to the plasma membrane of atypical protein kinase C-zeta (PKC-zeta) and -iota (PKC-) isoforms with subsequent phosphorylation of the extracellular signal-regulated kinases 1 and 2 (ERK1 and 2). Translocated atypical PKCs displayed temporally different activations, the activation of PKC-zeta being the fastest. PC-Cl3 cells stimulated with increasing Ang II concentrations showed dose- and time-dependent activation of the Na(+)-K(+)ATPase activity, which paralleled the PKC-zeta translocation time course. Na(+)-K(+)ATPase activity modulation was dependent on PKC activation since the PKC antagonist staurosporine abolished the stimulatory effect of Ang II. The inhibition of the ERK kinases 1 and 2 (MEK1 and 2) by PD098059 (2'-amino-3'-methoxyflavone) failed to block the effect of Ang II on the Na(+)-K(+)ATPase activity. In conclusion, our results suggest that Ang II modulates Na(+)-K(+)ATPase activity in PC-Cl3 cells through the AT1 receptor via activation of atypical PKC-zeta while the Ang II-activated PKC- appears to have other as yet unknown functions.

Transcription of the prorenin gene in normal and diseased breast

The angiotensin II type 1 (AT1) receptor is present in a wide variety of human and animal tissues, and is particularly abundant in epithelial cells. Because of this, and because it is known that tissue renin angiotensin systems (RASs) exist that have specific local functions, we investigated the expression and localisation of components of the RAS in normal and diseased breast tissue. Using a monoclonal antibody to the AT1 receptor, immunocytochemistry confirmed that the AT1 receptor was characteristically distributed in ductal epithelial cells in both normal and malignant tissue, and in most, although not all, cells in invasive tumours. Transcription of prorenin mRNA was studied by in situ hybridisation, using a DIG-ddUTP tail-labelled probe specific for the human prorenin gene. In normal tissue, and in cases of ductal carcinoma in situ, prorenin mRNA was distributed in myoepithelial cells and in a band of connective tissue cells completely surrounding the AT1-containing ductal epithelial cells. This prorenin transcribing tissue was disrupted and attenuated in invasive tumours, and in some of these, prorenin mRNA transcription could not be detected at all. Functions ascribed to the tissue RASs include regulation of mitosis and tissue modelling, as well as fluid and electrolyte transport. The results presented here strongly suggest the possibility that a tissue RAS may also be present in the breast, closely coupled to the provision of angiotensin II to the AT1 receptors in ductal epithelial cells. This mechanism is disrupted in cancer.