The undifferentiated cell zone is a stem cell zone in adult rat adrenal cortex

The changes in adrenal developmental programming and homeostasis in offspring induced by glucocorticoids exposure during pregnancy

Clinically, synthetic glucocorticoids are often used to treat maternal and fetal related diseases, such as preterm birth and autoimmune diseases. Although its clinical efficacy is positive, it will expose the fetus to exogenous glucocorticoids. Adverse environments during pregnancy (e.g., exogenous glucocorticoids exposure, malnutrition, infection, hypoxia, and stress) can lead to fetal overexposure to endogenous maternal glucocorticoids. Basal glucocorticoids levels in utero are crucial in determining fetal tissue maturation and its postnatal fate. As the synthesis and secretion organ of glucocorticoids, the adrenal development is crucial for the growth and development of the body. Studies have found that glucocorticoids exposure during pregnancy could cause abnormal fetal adrenal development, which could last after birth or even adulthood. As the key organ of fetal-originated adult disease, the adrenal developmental programming has a profound impact on the health of offspring, which can lead to many chronic diseases in adulthood. However, the aberrant adrenal development in offspring caused by glucocorticoids exposure during pregnancy and its intrauterine programming mechanism have not been systematically clarified. Therefore, this review summarizes recent research progress on the short and long-term hazards of aberrant adrenal development induced by glucocorticoids exposure during pregnancy, which is of great significance for the analysis of aberrant adrenal development and clarify the intrauterine origin mechanism of fetal-originated adult disease.

RNA-Seq reveals ACTH-induced steroid hormone pathway participating in goat adrenal gland response to castration

The content of androgen from adrenal is elevated under castration, and the mechanisms of compensatory secretion of adrenal androgen remain unknown. This study was designed to compare the transcript profiles between adrenals from noncastrated, orchiectomized and immunocastrated Yiling goats. Fifteen goats were randomly divided into three groups: pVAX-asd injection (control) group, pVAX-B2L-(G4S)3-kisspeptin-54-asd immunization (PBK-asd) group, and surgical castration (SC) group. Subsequently, serum was collected every two weeks after the initial immunization for hormone assays. At week 14 after immunization, adrenal glands were collected for transcriptome sequencing and qPCR. Serum testosterone concentration was significantly reduced in PBK-asd and SC group, demonstrating the effectiveness of castration. Both surgical and immunized castration resulted in adrenal hyperplasia, and thickness of adrenal cortex elevated. The specific genes involving castration were enriched in many pathways, including Steroid hormone biosynthesis pathway. The adrenocorticotropic hormone (ACTH), which promotes the production of adrenal steroids, and dehydroepiandrosterone (DHEA), a steroid hormone secreted by adrenal glands, both increased after castration. Further construction of co-expression network for transcription genes and traits (including adrenal weight and cortex thickness, ACTH and DHEA concentration) showed that the trait-related genes were enriched in multiple steroid-related pathways. These results showed that adrenal compensatory hyperplasia and androgen secretion caused by castration may involve in ACTH-induced steroid hormone synthesis.

Salt-Sensitive Hypertension in GR+/- Rats Is Accompanied with Dysregulation in Adrenal Soluble Epoxide Hydrolase and Polyunsaturated Fatty Acid Pathways

Mutations within the glucocorticoid receptor (GR) gene locus lead to glucocorticoid resistance which is characterized by several clinical symptoms such as adrenal gland hyperplasia and salt-sensitive hypertension, although the underlying mechanisms are still unknown. We studied GR haploinsufficient (GR^+/−) Sprague Dawley rats which, on a standard diet, showed significantly increased plasma aldosterone and corticosterone levels and an adrenocortex hyperplasia accompanied by a normal systolic blood pressure. Following a high salt diet, these rats developed salt-sensitive hypertension and maintained elevated enzyme-soluble epoxide hydrolase (sEH) in adrenal glands, while sEH was significantly decreased in wild-type rats. Furthermore, GR^+/− rats showed dysregulation of the equilibrated linoleic and arachidonic acid pathways, with a significant increase of less active metabolites such as 8,9-DiHETrE. In Sprague Dawley rats, GR haploinsufficiency induced steroid disturbances, which provoked hypertension only in combination with high salt intake, which was accompanied by disturbances in sEH and fatty acid metabolism. Our results suggest that sEH inhibition could be a potential target to treat hypertension in patients with GR haploinsufficiency.

Adrenal cortex renewal in health and disease

Resident progenitor and/or stem cell populations in the adult adrenal cortex enable cortical cells to undergo homeostatic renewal and regeneration after injury. Renewal occurs predominantly in the outer layers of the adrenal gland but newly formed cells undergo centripetal migration, differentiation and lineage conversion in the process of forming the different functional steroidogenic zones. Over the past 10 years, advances in the genetic characterization of adrenal diseases and studies of mouse models with altered adrenal phenotypes have helped to elucidate the molecular pathways that regulate adrenal tissue renewal, several of which are fine-tuned via complex paracrine and endocrine influences. Moreover, the adrenal gland is a sexually dimorphic organ, and testicular androgens have inhibitory effects on cell proliferation and progenitor cell recruitment in the adrenal cortex. This Review integrates these advances, including the emerging role of sex hormones, into existing knowledge on adrenocortical cell renewal. An in-depth understanding of these mechanisms is expected to contribute to the development of novel therapies for severe endocrine diseases, for which current treatments are unsatisfactory.

Developmental mechanisms of adrenal cortex formation and their links with adult progenitor populations

The adrenal cortex is the main steroid producing organ of the human body. Studies on adrenal tissue renewal have been neglected for many years, but recent intensified research has seen tremendous progress in our understanding of the formation and homeostasis of this organ. However, cell turnover of the adrenal cortex appears to be complex and several cell populations have been identified that can differentiate into steroidogenic cells and contribute to adrenal cortex renewal. The purpose of this review is to provide an overview of how the adrenal cortex develops and how stem cell populations relate to its developmental progenitors. Finally, we will summarize present and future approaches to harvest the potential of progenitor/stem cells for future cell replacement therapies.

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

Prenatal glucocorticoids exposure and fetal adrenal developmental programming

Clinically, we apply synthetic glucocorticoids to treat fetal and maternal diseases, such as premature labor and autoimmune diseases. Although its clinical efficacy is positive, the fetus will be exposed to exogenous synthetic glucocorticoids. Prenatal adverse environments (such as xenobiotics exposure, malnutrition, infection, hypoxia and stress) can cause fetuses overexposure to excessive endogenous maternal glucocorticoids. The level of glucocorticoids is the key to fetal tissue maturation and postnatal fate. A large number of studies have found that prenatal glucocorticoids exposure can lead to fetal adrenal dysplasia and dysfunction, continuing after birth and even into adulthood. As the core organ of fetal-originated adult diseases, fetal adrenal dysplasia is closely related to the susceptibility and occurrence of multiple chronic diseases, and there are also obvious gender differences. However, its intrauterine programming mechanisms have not been fully elucidated. This review summarizes recent advances in prenatal glucocorticoids exposure and fetal adrenal developmental programming alterations, which is of great significance for explaining adrenal developmental toxicity and the intrauterine origin of fetal-originated adult diseases.

Role of Transcription Factor Oct4 in Postnatal Development and Function of the Adrenal Cortex

We analyzed the expression of transcriptional factor Oct4 in rat adrenal cortical cells during postnatal development. It was found that Oct4 is expressed by typical cortical cells of the zona glomerulosa, zona fasciculata, and zona reticularis in pubertal and postpubertal periods. The maximum number of Oct4⁺ cells was found in the zona glomerulosa. An inverse correlation between the number of Oct4⁺ glomerulosa cells and serum level of aldosterone both in pubertal and postpubertal periods was revealed. After puberty, the number of Oct4⁺ glomerulosa cells directly correlated with the number of Ki-67⁺ cells. A hypothesis was put forward that Oct4 is involved in postnatal morphogenesis, regeneration, and functioning of the adrenal cortex.

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.

Regeneration of Functional Adrenal Tissue Following Bilateral Adrenalectomy

It is assumed that after complete bilateral adrenalectomy (ADX), no adrenal tissue will redevelop and adrenal hormone levels will remain low and unaffected by stress. However, anecdotal observations in animals and in patients suggest that under some unknown circumstances the opposite can occur. Herein, we studied whether adrenalectomized rats can develop an alternative source of systemic corticosterone after complete bilateral ADX with minimal replacement therapy. Male and female rats underwent either a standard ADX, in which the glands were removed with minimal surrounding adipose tissue, or an extensive ADX, in which glands were removed with most surrounding adipose tissue. Excised glands were histologically tested for completeness, and corticosterone replacement was nullified within 1 to 3 weeks postoperatively. In four experiments and in both excision approaches, some rats gradually reestablished baseline corticosterone levels and stress response in a time-dependent manner, but differences were observed in the reestablishing rates: 80% in standard ADX vs 20% in extensive ADX. Upon searching for the source of corticosterone secretion, we were surprised to find functional macroscopic foci of adrenocortical tissue without medullary tissue, mostly proximal to the original location. Chronic stress accelerated corticosterone level reestablishment. We hypothesized that underlying this phenomenon were preexisting ectopic microscopic foci of adrenocortical-like tissue or a few adrenal cells that were pre-embedded in surrounding tissue or detached from the excised gland upon removal. We concluded that adrenalectomized animals may develop compensatory mechanisms and suggest that studies employing ADX consider additional corticosterone supplementation, minimize stress, and verify the absence of circulating corticosterone.

Molecular Mechanisms of Stem/Progenitor Cell Maintenance in the Adrenal Cortex

The adrenal cortex is characterized by three histologically and functionally distinct zones: the outermost zona glomerulosa (zG), the intermediate zona fasciculata, and the innermost zona reticularis. Important aspects of the physiology and maintenance of the adrenocortical stem/progenitor cells have emerged in the last few years. Studies have shown that the adrenocortical cells descend from a pool of progenitors that are localized in the subcapsular region of the zG. These cells continually undergo a process of centripetal displacement and differentiation, which is orchestrated by several paracrine and endocrine cues, including the pituitary-derived adrenocorticotrophic hormone, and angiotensin II. However, while several roles of the endocrine axes on adrenocortical function are well established, the mechanisms coordinating the maintenance of an undifferentiated progenitor cell pool with self-renewal capacity are poorly understood. Local factors, such as the composition of the extracellular matrix (ECM) with embedded signaling molecules, and the activity of major paracrine effectors, including ligands of the sonic hedgehog and Wnt signaling pathways, are thought to play a major role. Particularly, the composition of the ECM, which exhibits substantial differences within each of the three histologically distinct concentric zones, has been shown to influence the differentiation status of adrenocortical cells. New data from other organ systems and different experimental paradigms strongly support the conclusion that the interactions of ECM components with cell-surface receptors and secreted factors are key determinants of cell fate. In this review, we summarize established and emerging data on the paracrine and autocrine regulatory loops that regulate the biology of the progenitor cell niche and propose a role for bioengineered ECM models in further elucidating this biology in the adrenal.

Hedgehog signaling and steroidogenesis

Since its discovery nearly 30 years ago, the Hedgehog (Hh) signaling pathway has been shown to be pivotal in many developmental and pathophysiological processes in several steroidogenic tissues, including the testis, ovary, adrenal cortex, and placenta. New evidence links the evolutionarily conserved Hh pathway to the steroidogenic organs, demonstrating how Hh signaling can influence their development and homeostasis and can act in concert with steroids to mediate physiological functions. In this review, we highlight the role of the components of the Hh signaling pathway in steroidogenesis of endocrine tissues.

Regulation of the adrenocortical stem cell niche: implications for disease

Stem cells are endowed with the potential for self-renewal and multipotency. Pluripotent embryonic stem cells have an early role in the formation of the three germ layers (ectoderm, mesoderm and endoderm), whereas adult tissue stem cells and progenitor cells are critical mediators of organ homeostasis. The adrenal cortex is an exceptionally dynamic endocrine organ that is homeostatically maintained by paracrine and endocrine signals throughout postnatal life. In the past decade, much has been learned about the stem and progenitor cells of the adrenal cortex and the multiple roles that these cell populations have in normal development and homeostasis of the adrenal gland and in adrenal diseases. In this Review, we discuss the evidence for the presence of adrenocortical stem cells, as well as the various signalling molecules and transcriptional networks that are critical for the embryological establishment and postnatal maintenance of this vital population of cells. The implications of these pathways and cells in the pathophysiology of disease are also addressed.

Development of monoclonal antibodies against human CYP11B1 and CYP11B2

1. The final enzymes in the biosynthesis of aldosterone and cortisol are by the cytochrome P450 CYP11B2 and CYP11B1, respectively. The enzymes are 93% homologous at the amino acid level and specific antibodies have been difficult to generate. 2. Mice and rats were immunized with multiple peptides conjugated to various immunogenic proteins and monoclonal antibodies were generated. The only peptide sequences that generated specific antibodies were amino acids 41-52 for the CYP11B2 and amino acids 80-90 for the CYP11B1 enzyme. 3. The mouse monoclonal CYP11B2-41 was specific and sensitive for use in western blots and produced specific staining of the zona glomerulosa of normal adrenal glands. The rat monoclonal CYP11B1-80 also detected a single band by western blot and detected only the zona fasciculata. Triple immunofluorescence of the adrenal demonstrated that the CYP11B1 and the CYP11B2 did not co-localize, while as expected the CYP11B1 co-localized with the 17α-hydroxylase.

Enucleation-induced rat adrenal gland regeneration: expression profile of selected genes involved in control of adrenocortical cell proliferation

Enucleation-induced adrenal regeneration is a highly controlled process; however, only some elements involved in this process have been recognized. Therefore, we performed studies on regenerating rat adrenals. Microarray RNA analysis and QPCR revealed that enucleation resulted in a rapid elevation of expression of genes involved in response to wounding, defense response, and in immunological processes. Factors encoded by these genes obscure possible priming effects of various cytokines on initiation of regeneration. In regenerating adrenals we identified over 100 up- or downregulated genes involved in adrenocortical cell proliferation. The changes were most significant at days 2-3 after enucleation and their number decreased during regeneration. For example, expression analysis revealed a notable upregulation of the growth arrest gene, Gadd45, only 24 hours after surgery while expression of cyclin B1 and Cdk1 genes was notably elevated between days 1-8 of regeneration. These changes were accompanied by changes in expression levels of numerous growth factors and immediate-early transcription factors genes. Despite notable differences in mechanisms of adrenal and liver regeneration, in regenerating adrenals we identified genes, the expression of which is well recognized in regenerating liver. Thus, it seems legitimate to suggest that, in the rat, the general model of liver and adrenal regeneration demonstrate some degree of similarity.

Expression of selected genes involved in steroidogenesis in the course of enucleation-induced rat adrenal regeneration

The enucleation-induced (EI) rapid proliferation of adrenocortical cells is followed by their differentiation, the degree of which may be characterized by the expression of genes directly and indirectly involved in steroid hormone biosynthesis. In this study, out of 30,000 transcripts of genes identified by means of Affymetrix Rat Gene 1.1 ST Array, we aimed to select genes (either up- or downregulated) involved in steroidogenesis in the course of enucleation-induced adrenal regeneration. On day 1, we found 32 genes with altered expression levels, 15 were upregulated and 17 were downregulated [i.e., 3β-hydroxysteroid dehydrogenase (Hsd3β), nuclear receptor subfamily 0, group B, member 1 (Nr0b1), cytochrome P450 aldosterone synthase (Cyp11b2) and sterol O-acyltransferase 1 (Soat1)]. On day 15, the expression of only 2 genes was increased and that of 3 was decreased. The investigated genes were clustered according to an hierarchical clustering algorithm and 4 clusters were obtained. Quantitative PCR (qPCR) confirmed the much lower mRNA expression levels of steroidogenic acute regulatory protein (StAR) during the regeneration process compared to the control, while the cholesterol side-chain cleavage enzyme (cholesterol desmolase; Cyp11a1) and Hsd3β genes presented similar expression profiles throughout the entire regeneration process. Cyp11b2 mRNA levels remained very low during the whole regeneration period. Fatty acid binding protein 6 (Fabp6) was markedly upregulated, whereas hormone-sensitive lipase (Lipe) was downregulated. The expression of Soat1 was lowest on regeneration day 1 and, subsequently, its expression increased from there on, reaching levels higher than the control. Dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (Dax-1) mRNA levels were lowest on day 1 of the experiment; however, throughout the entire experimental period, there were no statistically significant differences observed. After the initial decrease in steroidogenic factor 1 (Sf-1) mRNA levels observed on the 1st day of the experiment, a marked upregulation in its expression was observed from there on. Data from the current study strongly suggest the role of Fabp6, Lipe and Soat1 in supplying substrates of regenerating adrenocortical cells for steroid synthesis. Our results indicate that during the first days of adrenal regeneration, intense synthesis of cholesterol may occur, which is then followed by its conversion into cholesteryl esters. Moreover, our data demonstrated that in enucleation-induced regeneration, the restoration of genes involved in glucocorticoid synthesis is notably shorter than that of those involved in aldosterone synthesis.

Cell proliferation, movement and differentiation during maintenance of the adult mouse adrenal cortex

Appropriate maintenance and regeneration of adult endocrine organs is important in both normal physiology and disease. We investigated cell proliferation, movement and differentiation in the adult mouse adrenal cortex, using different 5-bromo-2'-deoxyuridine (BrdU) labelling regimens and immunostaining for phenotypic steroidogenic cell markers. Pulse-labelling showed that cell division was largely confined to the outer cortex, with most cells moving inwards towards the medulla at around 13-20 µm per day, though a distinct labelled cell population remained in the outer 10% of the cortex. Pulse-chase-labelling coupled with phenotypic immunostaining showed that, unlike cells in the inner cortex, most BrdU-positive outer cortical cells did not express steroidogenic markers, while co-staining for BrdU and Ki67 revealed that some outer cortical BrdU-positive cells were induced to proliferate following acute adrenocorticotropic hormone (ACTH) treatment. Extended pulse-chase-labelling identified cells in the outer cortex which retained BrdU label for up to 18-23 weeks. Together, these observations are consistent with the location of both slow-cycling stem/progenitor and transiently amplifying cell populations in the outer cortex. Understanding the relationships between these distinct adrenocortical cell populations will be crucial to clarify mechanisms underpinning adrenocortical maintenance and long-term adaptation to pathophysiological states.

Dlk1 up-regulates Gli1 expression in male rat adrenal capsule cells through the activation of β1 integrin and ERK1/2

The development and maintenance of the zones of the adrenal cortex and their steroidal output are extremely important in the control of gluconeogenesis, the stress response, and blood volume. Sonic Hedgehog (Shh) is expressed in the adrenal cortex and signals to capsular cells, which can respond by migrating into the cortex and converting into a steroidogenic phenotype. Delta-like homologue 1 (Dlk1), a member of the Notch/Delta/Serrate family of epidermal growth factor-like repeat-containing proteins, has a well-established role in inhibiting adipocyte differentiation. We demonstrate that Shh and Dlk1 are coexpressed in the outer undifferentiated zone of the male rat adrenal and that Dlk1 signals to the adrenal capsule, activating glioma-associated oncogene homolog 1 transcription in a β1 integrin- and Erk1/2-dependent fashion. Moreover, Shh and Dlk1 expression inversely correlates with the size of the zona glomerulosa in rats after manipulation of the renin-angiotensin system, suggesting a role in the homeostatic maintenance of the gland.

The permissive role of prolactin as a regulator of luteinizing hormone action in the female mouse ovary and extragonadal tumorigenesis

Transgenic female mice overexpressing the hCGβ subunit (hCGβ(+)) and producing elevated levels of luteinizing hormone (LH)/hCG bioactivity present as young adults with enhanced ovarian steroidogenesis, precocious puberty, and infertility. They subsequently develop pituitary prolactinomas, high circulating prolactin (PRL) levels, and marked mammary gland lobuloalveolar development followed by adenocarcinomas. None of these phenotypes appear in gonadectomized mice, indicating that the hCG-induced aberrations of ovarian function are responsible for the extragonadal phenotypes. PRL receptor-deficient (PRLR(-/-)) female mice are sterile, despite ovulating, due to a failure of embryo implantation, as a consequence of decreased ovarian LH receptor (Lhcgr) expression and inadequate corpus luteum formation and progesterone production. To study further the presumed permissive role of PRL in the maintenance of gonadal responsiveness to LH/hCG stimulation, we crossed the hCGβ(+) and PRLR(-/-) mice. The double-mutant hCGβ(+)/PRLR(-/-) females remained sterile with an ovarian phenotype similar to PRLR(-/-) mice, indicating that LH action, Lhcgr expression, and consequent luteinization are not possible without simultaneous PRL signaling. The high frequency of pituitary prolactinomas in PRLR(-/-) mice was not affected by transgenic hCGβ expression. In contrast, none of the hCGβ(+)/PRLR(-/-) females showed either mammary gland lobuloalveolar development or tumors, and the increased mammary gland Wnt-5b expression, possibly responsible for the tumorigenesis in hCGβ(+) mice, was absent in double-mutant mice. Hence, high LH/hCG stimulation is unable to compensate for missing PRL signaling in the maintenance of luteal function. PRL thus appears to be a major permissive regulator of LH action in the ovary and of its secondary extragonadal effects.

Epimedium flavonoids counteract the side effects of glucocorticoids on hypothalamic-pituitary-adrenal axis

Our previous studies demonstrated that the epimedium herb, when simultaneously used with GCs, counteracted suppressive effects of GCs on the HPA axis without adverse influence on the therapeutic action of GCs. Here, total flavones were extracted from the epimedium flavonoids (EFs) and then used to investigate whether EFs provide protective effects on the HPA axis. We found that GCs induced a significant decrease in body weight gain, adrenal gland weight gain, and plasma adrenocorticotropin (ACTH) and corticosterone levels. After treatment with EFs, body weight gain, adrenal gland weight gain, and plasma corticosterone level were significantly restored, whilst plasma ACTH level was partially elevated. EFs were also shown to promote cell proliferation in the outer layer of adrenal cortex and to enhance the migration of newly divided cells toward the inner layer. To elucidate the underlying mechanisms, the mRNA expression of insulin-like growth factor II (IGF-II) was measured, and EFs significantly upregulated IGF-II expression. Our results indicated that EFs counteract the suppression of the HPA axis induced by GCs. This may involve both the ACTH and IGF-II pathways and thereby promote regeneration of the adrenal cortex suggesting a potential clinical application of EFs against the suppressive effects of GCs on the HPA axis.

Melanocortin receptor accessory proteins in adrenal gland physiology and beyond

The melanocortin receptor (MCR) family consists of five G-protein-coupled receptors (MC1R-MC5R) with diverse physiological roles. MC1R controls pigmentation, MC2R is a critical component of the hypothalamic-pituitary-adrenal axis, MC3R and MC4R have a vital role in energy homeostasis and MC5R is involved in exocrine function. The melanocortin receptor accessory protein (MRAP) and its paralogue MRAP2 are small single-pass transmembrane proteins that have been shown to regulate MCR expression and function. In the adrenal gland, MRAP is an essential accessory factor for the functional expression of the MC2R/ACTH receptor. The importance of MRAP in adrenal gland physiology is demonstrated by the clinical condition familial glucocorticoid deficiency, where inactivating MRAP mutations account for ∼20% of cases. MRAP is highly expressed in both the zona fasciculata and the undifferentiated zone. Expression in the undifferentiated zone suggests that MRAP could also be important in adrenal cell differentiation and/or maintenance. In contrast, the role of adrenal MRAP2, which is highly expressed in the foetal gland, is unclear. The expression of MRAPs outside the adrenal gland is suggestive of a wider physiological purpose, beyond MC2R-mediated adrenal steroidogenesis. In vitro, MRAPs have been shown to reduce surface expression and signalling of all the other MCRs (MC1,3,4,5R). MRAP2 is predominantly expressed in the hypothalamus, a site that also expresses a high level of MC3R and MC4R. This raises the intriguing possibility of a CNS role for the MRAPs.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Transgenic GATA-4 expression induces adrenocortical tumorigenesis in C57Bl/6 mice

A link between elevated luteinizing hormone (LH) levels, GATA-4 and LH receptor (LHCGR) expression and gonadotropin-dependent adrenocortical tumorigenesis in humans and mice has been shown. To assess the mechanistic tumorigenic interrelationships between these factors, we transgenically expressed Gata4 under the 21-hydroxylase promoter (Cyp21a1, 21-OH) in C57Bl/6N mice. There was a gradual age-dependent increase of GATA-4 expression only in 21-OH-GATA-4 (TG) female adrenals, in association with slowly progressing neoplasia of non-steroidogenic spindle-shaped A cells in the subcapsular cortex. Gonadectomy (GDX), apparently through direct action of elevated serum LH, markedly enhanced the adrenocortical neoplasia, which now also appeared in GDX TG males. The neoplastic areas of the post-GDX TG adrenals contained, besides A cells, larger lipid-laden, steroidogenically active and LHCGR-positive B cells. Prolonged (>10 months) exposure to elevated post-GDX LH levels resulted in formation of adrenocortical adenomas in the TG mice. Intact and GDX TG mouse adrenals displayed elevated FOG-2 and decreased GATA-6 expression. Additionally, increased expression/activation of components of the Inhbb-Acvr2a-Acvr1c-Smad2/3 signaling system was observed in 12-month-old GDX TG adrenals. Our findings show that two distinct GATA-4-dependent populations of neoplastic adrenocortical cells form: non-steroidogenic LH-independent A cells and steroidogenic LH-dependent B cells.

Label-free enrichment of adrenal cortical progenitor cells using inertial microfluidics

Passive and label-free isolation of viable target cells based on intrinsic biophysical cellular properties would allow for cost savings in applications where molecular biomarkers are known as well as potentially enable the separation of cells with little-to-no known molecular biomarkers. We have demonstrated the purification of adrenal cortical progenitor cells from digestions of murine adrenal glands utilizing hydrodynamic inertial lift forces that single cells and multicellular clusters differentially experience as they flow through a microchannel. Fluorescence staining, along with gene expression measurements, confirmed that populations of cells collected in different outlets were distinct from one another. Furthermore, primary murine cells processed through the device remained highly viable and could be cultured for 10 days in vitro. The proposed target cell isolation technique can provide a practical means to collect significant quantities of viable intact cells required to translate stem cell biology to regenerative medicine in a simple label-free manner.

Sonic hedgehog signaling during adrenal development

It has been speculated for a number of years that Sonic hedgehog (Shh) signaling plays an important role in adrenal development. Over the past two years several reports have described the expression and function of Shh pathway genes in the adrenal cortex, using primarily mouse models. The key findings are that Shh signals produced by a population of partially differentiated cortical cells located in the outer cortex/zona glomerulosa are received by non-cortical mesenchymal cells located predominantly in the overlying capsule. This signal is required for growth of both the capsule and the cortex, but not for cortical zonation or steroidogenic cell differentiation. Using molecular genetic tools to define the adrenocortical cell lineages that are descended from both Shh signaling and receiving cells, both capsule and cortical cells were found to have properties of adrenocortical stem and/or progenitor cells. Here we place these observations within the context of prior studies on adrenal development, postnatal adrenal maintenance and adrenocortical stem/progenitor cell lineages.

Transition from organogenesis to stem cell maintenance in the mouse adrenal cortex

Mice showing mosaic expression of an appropriate marker gene that is activated during development provide simple tools for investigating cell lineages. We used the mosaic β-galactosidase staining patterns in adrenal cortices of 21OH/ LacZ transgenic mice to study both organogenesis and maintenance of the adult tissue. Randomly orientated mosaic patterns present in embryonic day 14.5 (E14.5) adrenals changed progressively during the perinatal period from discrete spots, via patches and radial arrays, to radial stripes, which first emerged between postnatal days 0 and 7 (P0 and P7). The mosaic radial stripe pattern was fully established by P21 and remained unchanged throughout the adult period (8-52 weeks). The mouse adrenal gland grew continuously between E14.5 and P21, including the period during which stripes emerge. Ki67-positive, proliferative cells in the adrenal cortex were mainly localized to the outer cell layers between E18.5 and P3. By P10, cell proliferation had increased, and the proliferative region had expanded but was still mainly confined to the outer cortex. Correlation of changes in mosaic patterns in 21OH/LacZ adrenal cortices with the locations of adrenocortical cell proliferation suggest that the radial stripes arise by edge-biased growth during the perinatal period, even if they are maintained by stem cells in adults. The stability of the adult stripe pattern suggests that stem cell function is unchanged between 8 and 52 weeks.

Moving toward personalized cell-based interventions for adrenal cortical disorders: part 2--Human diseases and tissue engineering

Transdifferentiation of an individual's own cells into functional differentiated cells to replace an organ's lost function would be a personalized approach to therapeutics. In this two part series, we will describe the progress toward establishing functional transdifferentiated adrenal cortical cells. In this article (Part 2), we describe the disorders of the adrenal cortex, therefore establishing why there is the need for personalized cell-based therapy for individuals with these disorders. We then present our pilot studies of cell transdifferentiation toward an adrenal cortical fate using genes described in the first article of this pair (Part 1).

Moving toward personalized cell-based interventions for adrenal cortical disorders: part 1--Adrenal development and function, and roles of transcription factors and signaling proteins

Transdifferentiation of an individual's own cells into functional differentiated cells to replace an organ's lost function would be a personalized approach to therapeutics. In this two part series, we will describe the progress toward establishing functional transdifferentiated adrenal cortical cells. In this article (Part 1), we describe adrenal development and function, and discuss genes involved in these processess and selected for use in our pilot studies of transdifferentiation that are presented in the second article (Part 2).

Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit

Continuous efforts have been devoted to unraveling the biophysiology and development of the human fetal adrenal cortex, which is structurally and functionally unique from other species. It plays a pivotal role, mainly through steroidogenesis, in the regulation of intrauterine homeostasis and in fetal development and maturation. The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone and its sulfate, precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis. Recent studies employing modern technologies such as gene expression profiling and laser capture microdissection have revealed that development and/or function of the fetal adrenal cortex may be regulated by a panoply of molecules, including transcription factors, extracellular matrix components, locally produced growth factors, and placenta-derived CRH, in addition to the primary regulator, fetal pituitary ACTH. The role of the fetal adrenal cortex in human pregnancy and parturition appears highly complex, probably due to redundant and compensatory mechanisms regulating these events. Mounting evidence indicates that actions of hormones operating in the human feto-placental unit are likely mediated by mechanisms including target tissue responsiveness, local metabolism, and bioavailability, rather than changes only in circulating levels. Comprehensive study of such molecular mechanisms and the newly identified factors implicated in adrenal development should help crystallize our understanding of the development and physiology of the human fetal adrenal cortex.

Localisation of the melanocortin-2-receptor and its accessory proteins in the developing and adult adrenal gland

The melanocortin-2-receptor (MC2R)/MC2R accessory protein (MRAP) complex is critical to the production of glucocorticoids from the adrenal cortex. Inactivating mutations in either MC2R or MRAP result in the clinical condition familial glucocorticoid deficiency. The localisation of MC2R together with MRAP within the adrenal gland has not previously been reported. Furthermore, MRAP2, a paralogue of MRAP, has been shown in vitro to have a similar function to MRAP, facilitating MC2R trafficking and responsiveness to ACTH. Despite similar MC2R accessory functions, in vivo, patients with inactivating mutations of MRAP fail to be rescued by a functioning MRAP2 gene, suggesting differences in adrenal expression, localisation and/or function between the two MRAPs. In this study on the rat adrenal gland, we demonstrate that while MRAP and MC2R are highly expressed in the zona fasciculata, MRAP2 is expressed throughout the adrenal cortex in low quantities. In the developing adrenal gland, both MRAP and MRAP2 are equally well expressed. The MC2R/MRAP2 complex requires much higher concentrations of ACTH to activate compared with the MC2R/MRAP complex. Interestingly, expression of MC2R and MRAP in the undifferentiated zone would support the notion that ACTH may play an important role in adrenal cell differentiation and maintenance.

Localization of Sonic hedgehog secreting and receiving cells in the developing and adult rat adrenal cortex

Sonic hedgehog signaling was recently demonstrated to play an important role in murine adrenal cortex development. The organization of the rat adrenal differs from that of the mouse, with the zona glomerulosa and zona fasciculata separated by an undifferentiated zone in the rat, but not in the mouse. In the present study we aimed to determine the mRNA expression patterns of Sonic hedgehog and the hedgehog signaling pathway components Patched-1 and Gli1 in the developing and adult rat adrenal. Sonic hedgehog expression was detected at the periphery of the cortex in cells lacking CYP11B1 and CYP11B2 expression, while signal-receiving cells were localized in the overlying capsule mesenchyme. Using combined in situ hybridization and immunohistochemistry we found that the cells expressing Sonic hedgehog lie between the CYP11B2 and CYP11B1 layers, and thus Sonic hedgehog expression defines one cell population of the undifferentiated zone.

Endogenous biotin as a marker of adrenocortical cells with steroidogenic potential

Interpretation of adrenal cortex phenotypes is greatly facilitated by simultaneous examination of multiple markers at single cell resolution. However, the availability of multiple appropriate antibodies can be rate limiting, while their cognate antigens are often subject to variable accessibility. Specific markers not subject to these constraints thus have obvious utility. Here we report that endogenous biotin, when detected in fixed, frozen tissue sections using fluorescent streptavidin, is a specific marker of apparently all cells with steroidogenic potential in the murine adrenal cortex. While streptavidin stains presteroidogenic and mature cortical cells, it does not label the adrenal capsule, medulla or vascular endothelium. Developmental profiles reveal adrenal endogenous biotin labeling from E13.5 through adulthood. Comparisons with zonal markers, hypothalamic-pituitary-adrenal (HPA) axis-remodeled tissue, transgenic Shh-nLacZ or Gli1-nLacZ animals, and Shh mutant embryos further demonstrate the utility of this approach. Fluorescent streptavidin applied using a simple one-step staining protocol thus provides a potent counterstain for use in adrenal analyses.

Alteration of subcapsular adrenocortical zonation in humans with aging: the progenitor zone predominates over the previously well-developed zona glomerulosa after 40 years of age

Few studies have examined functional adrenal zonation throughout human life. Adrenals from 61 surgical/autopsy patients from 1 day old to 92 years old who had no clinical endocrinological/mineralocorticoid abnormalities were assessed for immunohistochemically defined adrenal zonation. The zona glomerulosa (zG) was well developed in all 11 patients ranging in age from newborn to the 30s. After 40 years of age, however, the zG occupied less than one-quarter of the adrenal circumference, suggestive of zG involution. The other subcapsular areas were occupied by the progenitor zone (zP), which expressed neither cytochrome P450(aldo) nor P450(11β) but 3β-hydroxysteroid dehydrogenase and P450scc, although some autopsy cases had adrenals with zG zonation because of secondary aldosteronism, and others who had experienced severe stresses showed subcapsular zona fasciculata (zF). In conclusion, the adrenal cortex consists of homogeneous zG-topped columns from birth to adolescence. Subsequently, in the fifth decade of life, the cortex is reconstituted by integration of three types of cortical columns: scattered zG-topped columns and zonal zP-topped columns, the latter having the ability for bidirectional differentiation into either zG-topped columns or zF-topped columns, according to secondary aldosteronism or the presence of severe stresses. Such adrenocortical remodeling is ascribed to high-sodium/low-potassium diets.

Adrenocortical zonation in humans under normal and pathological conditions

CONTEXT

Aldosterone synthase (CYP11B2) and steroid 11 beta-hydroxylase (CYP11B1) catalyze the terminal steps for aldosterone and cortisol syntheses, respectively, thereby determining the functional differentiation of human adrenocortical cells. Little is known, however, about how the cells expressing the enzymes are actually distributed in the adrenals under normal and pathological conditions.

OBJECTIVE

The objective of the study was to determine the localization of CYP11B2 and -B1 in human adrenal specimens by using developed antibodies capable of distinguishing the two enzymes from each other.

RESULTS

Under normal conditions, CYP11B2 was sporadically detected in the zona glomerulosa, whereas CYP11B1 was entirely detected in the zonae fasciculata-reticularis. Adrenocortical cells lacking both enzymes were observed in the outer cortical regions. In addition to conventional zonation, we found a variegated zonation consisting of a subcapsular cell cluster expressing CYP11B2, which we termed aldosterone-producing cell cluster, and a CYP11B1-expressing area. Aldosterone-producing adenomas differed in cell populations expressing CYP11B2 from one another, whereas CYP11B1-expressing and double-negative cells were also intermingled. Adenomas from patients with Cushing's syndrome expressed CYP11B1 entirely but not CYP11B2, resulting in atrophic nontumor glands. The nontumor portions of both types of adenomas bore frequently one or more aldosterone-producing cell clusters, which sustained CYP11B2 expression markedly under the conditions of the suppressed renin-angiotensin system.

CONCLUSION

Immunohistochemistry of the human normal adrenal cortex for CYP11B2 and CYP11B1 revealed a variegated zonation with cell clusters constitutively expressing CYP11B2. This technique may provide a pathological confirmatory diagnosis of adrenocortical adenomas.

Targeted disruption of Sonic Hedgehog in the mouse adrenal leads to adrenocortical hypoplasia

Development of the mammalian adrenal gland is regulated by a diverse network of growth and transcription factors. Disruptions in these pathways often result in adrenal insufficiency because of adrenal hypoplasia. Several lines of evidence have suggested that the Hedgehog signaling pathway, which controls many aspects of tissue and organ patterning, may play a direct role in adrenal morphogenesis as well. Therefore, we examined the role of Sonic Hedgehog (Shh), a member of the Hedgehog family, in mouse adrenal development. We show that Shh and its downstream effectors Gli1, Gli2, and Gli3 are expressed in the adrenal cortex throughout development, and that Shh is required for normal adrenal organogenesis. Conditional inactivation of Shh in the adrenal cortex using a Cre-loxP system resulted in severe hypoplasia and disorganization of the cortex. In mice carrying the targeted mutation (Shh(fl/fl;SF-1/Cre+)), adrenal mass was significantly reduced and the cortex failed to encapsulate the adrenal medulla. Taken together, these results establish a direct role for Shh signaling in normal adrenal development.

Shh signaling regulates adrenocortical development and identifies progenitors of steroidogenic lineages

The adrenal cortex is a critical steroidogenic endocrine tissue, generated at least in part from the coelomic epithelium of the urogenital ridge. Neither the intercellular signals that regulate cortical development and maintenance nor the lineage relationships within the adrenal are well defined. We have explored adrenal Shh activity and found that Shh is expressed in relatively undifferentiated steroidogenic cells, which signal to the overlying capsule and subjacent nonsteroidogenic mesenchyme cells that we also find are progenitors of steroidogenic lineages. Shh-expressing cells also generate all steroidogenic cell types, but not nonsteroidogenic ones. Shh mutant adrenals have a thin capsule and small cortex. Our findings both support a novel dual lineage, Shh-independent and Shh-dependent, model of adrenocortical development, and identify distinct populations of adrenocortical progenitor and candidate stem cells.

Basic fibroblast growth factor delivery enhances adrenal cortical cellular regeneration

The effective delivery of angiogenic factors is a useful strategy for the engineering of vascularized tissues. When adrenal cortical cells were implanted in mice under the renal capsule, the size of the implant was reduced to about 100 microm in thickness after 8 weeks. Either low (approximately 2 microg) levels of basic fibroblast growth factor (bFGF) or high (approximately12 microg) levels of bFGF were encapsulated into poly-lactic-co-glycolic acid microspheres, and these bFGF-encapsulated microspheres were coimplanted with adrenal cortical cells. After 56 days, the implants with low and high levels of bFGF weighed five and eight times more, respectively, than the implants without bFGF delivery. The implants with bFGF-encapsulated microspheres also contained significantly more cells than the implants without bFGF delivery. The levels of adrenal cortical gene expression were not significantly changed with bFGF delivery. The implants with high levels of bFGF also had a more uniform distribution of anti-CD31 immunofluorescence. Based on the increased number of cells that expressed adrenal cortical genes, the delivery of bFGF enhanced adrenal cortical cellular regeneration, possibly through an angiogenic response.

Transplantation of adrenal cortical progenitor cells enriched by Nile red

BACKGROUND

The adrenal cortex may contain progenitor cells useful for tissue regeneration. Currently there are no established methods to isolate these cells.

MATERIAL AND METHODS

Murine adrenal cells were sorted into a Nile-red-bright (NR(bright)) and a Nile-red-dim (NR(dim)) population of cells according to their degree of cholesterol content revealed by Nile red fluorescence. The cells were transplanted under the renal capsule to determine their ability for regeneration.

RESULTS

The NR(bright) cells contained an abundance of lipid droplets, whereas the NR(dim) cells contained little. The NR(bright) cells expressed Sf1 and the more differentiated adrenal cortical genes, including Cyp11a1, Cyp11b1, and Cyp11b2, whereas the NR(dim) cells expressed Sf1 but not the more differentiated adrenal cortical genes. After 56 d of implantation in unilateral adrenalectomized mice, the NR(dim) cells expressed Sf1 and the more differentiated adrenal cortical genes, whereas the NR(bright) cells ceased to express Sf1 as well as the more differentiated adrenal cortical genes. NR(dim) cells also proliferated in the presence of basic fibroblast growth factor.

CONCLUSIONS

The population of NR(dim) cells contained adrenal cortical progenitor cells that can proliferate and give rise to differentiated daughter cells. These cells may be useful for adrenal cortical regeneration.

In search of adrenocortical stem and progenitor cells

Scientists have long hypothesized the existence of tissue-specific (somatic) stem cells and have searched for their location in different organs. The theory that adrenocortical organ homeostasis is maintained by undifferentiated stem or progenitor cells can be traced back nearly a century. Similar to other organ systems, it is widely believed that these rare cells of the adrenal cortex remain relatively undifferentiated and quiescent until needed to replenish the organ, at which time they undergo proliferation and terminal differentiation. Historical studies examining cell cycle activation by label retention assays and regenerative potential by organ transplantation experiments suggested that the adrenocortical progenitors reside in the outer periphery of the adrenal gland. Over the past decade, the Hammer laboratory, building on this hypothesis and these observations, has endeavored to understand the mechanisms of adrenocortical development and organ maintenance. In this review, we summarize the current knowledge of adrenal organogenesis. We present evidence for the existence and location of adrenocortical stem/progenitor cells and their potential contribution to adrenocortical carcinomas. Data described herein come primarily from studies conducted in the Hammer laboratory with incorporation of important related studies from other investigators. Together, the work provides a framework for the emerging somatic stem cell field as it relates to the adrenal gland.

Adrenal hyperplasia and tumours in mice in connection with aberrant pituitary-gonadal function

Gonadectomy induces in certain inbred stains of mice adrenal hyperplasia and tumorigenesis, originating from the putative subcapsular stem/progenitor cell layer. This response is apparently triggered by the elevated post-gonadectomy levels of luteinising hormone (LH), followed by ectopic upregulation of adrenal LH/chorionic gonadotrophin (CG) receptors (Lhcgr). The clear strain dependence of this adrenal response to gonadectomy prompted us to study its genetic basis. Tumorigenic DBA/2J and non-tumorigenic C57BL/6J mice, as well as their F2 and backcrosses, were studied by whole genome linkage analysis. Gonadectomy induced similar upregulation of adrenal Lhcgr in both parental strains and their crosses, irrespective of the tumour status, indicating that ectopic expression of this receptor is not the immediate cause of tumours. Linkage analysis revealed one major significant quantitative trait locus (QTL) for the tumorigenesis on chromosome 8, modulated by epistasis with another QTL on chromosome 18. Hence, post-gonadectomy adrenal tumorigenesis in DBA/2J mice is a dominant trait, not a direct consequence of adrenal Lhcgr expression, and is driven by a complex genetic architecture. A promising candidate gene in the tumorigenesis linkage region is Sfrp1 (secreted frizzled-related protein 1), a tumour suppressor gene, which was down-regulated in the neoplastic tissue. Our findings may have relevance to the human pathogenesis of macronodular adrenal hyperplasia and postmenopausal adrenocortical tumours. A distinctly different adrenal response was observed in TG mice overexpressing LH or CG, or a constitutively activated form of the follicle-stimulating hormone receptor (Fshr). These mice developed perimedullary hyperlasia of foamy multinucleated cells, reminding of macrophages and filled with lipofuscin. Similar response was observed in TG mice overexpressing aromatase (CYP19). The cause of this response is not related to direct LH/CG action, but merely to adrenal response to chronically elevated oestrogen levels. This phenotype is reminiscent of the rare 'black adenomas' of the human adrenal cortex.

Decreased p44/42 mitogen-activated protein kinase phosphorylation in gender- or hormone-related but not during age-related adrenal gland growth in mice

Postnatal growth of the mouse adrenal gland shows a characteristic gender-dependent pattern, resulting in an almost 2-fold higher adrenal weight in 11-wk-old female vs. male mice. We demonstrated that the higher weight of the adrenal glands in female mice is due to a significantly (P < 0.05) increased growth rate in female mice and a shorter growth phase of the adrenal glands in male mice (P < 0.05). To address the signaling mechanisms underlying these differential growth patterns, we evaluated the phosphorylation levels of p44/42 and p38 MAPK. In female mice, age-dependent reductions of p38 MAPK phosphorylation were found between wk 3 and 9 (47% reduction; P < 0.05). At the age of 11 wk, the p38 MAPK phosphorylation level in female adrenal glands was about 60% lower than in the male counterparts (P < 0.01). Similarly, the phosphorylation level of p44/42 MAPK was 50% lower in female adrenal glands (P < 0.001). Reduced activation of p44/42 MAPK was also observed after growth stimulation of the adrenal glands in male mice after ACTH treatment (-36%; P < 0.001) or by expression of a GH transgene (-34%; P < 0.001), whereas p38 MAPK, JNK, or PDK1 activation was unaffected. From our findings in three independent mouse models where partial deactivation of p44/42 MAPK was observed under conditions of elevated growth, we suggest a function of p44/42 MAPK for adrenal growth and a role of p44/42 MAPK for the integration of different endocrine stimuli.

Is the adrenal cortex a target for gonadotropins?

The human adrenal cortex expresses low levels of luteinizing hormone/chorionic gonadotropin receptors (LHCGR), a characteristic gonad-specific G-protein coupled receptor (GPCR). LHCGR levels increase in the adrenal cortex after exposure to chronically elevated gonadotropins (e.g. after gonadectomy). In fact, heightened ectopic LHCGR levels are observed in a subclass of human adrenocortical tumors, and gonadotropin-responsive adrenocortical hyperplasia and tumors occur in several animal species. These findings suggest that adrenocortical responsiveness to LH/CG might be a physiological phenomenon that is amplified in the presence of elevated gonadotropin levels. Such increased gonadotropin action can induce pathologies ranging from adrenocorticotropic hormone (ACTH)-independent Cushing syndrome to malignant adrenal tumors. The authors review the current information on adrenocortical responses to gonadotropins in experimental animals and humans.

Lesions of the adrenal cortex

CONTEXT

In surgical pathology practice adrenal cortical tumors are rare. However, in autopsy series adrenal cortical nodules are found frequently. These are now being identified more commonly in life when the abdomen is scanned for other disease. It is important to differentiate between benign and malignant lesions as adrenal cortical carcinoma is an aggressive tumor. Molecular genetic investigations are providing new information on both pathogenesis of adrenal tumors and basic adrenal development and physiology.

OBJECTIVE

To provide an overview of current knowledge on adrenal cortical development and structure that informs our understanding of genetic diseases of the adrenal cortex and adrenal cortical tumors.

DATA SOURCES

Literature review using PubMed via the Endnote bibliography tool.

CONCLUSIONS

The understanding of basic developmental and physiologic processes permits a better understanding of diseases of the adrenal cortex. The information coming from investigation of the molecular pathology of adrenal cortical tumors is beginning to provide additional tests for the assessment of malignant potential in diagnosis but the mainstay remains traditional histologic analysis.

Distribution of cells expressing Jun and Fos proteins and synthesizing DNA in the adrenal cortex of hypophysectomized rats: regulation by ACTH and FGF2

Protein expression of the early response genes, jun and fos, has been suggested to play an important role in the in vitro and in vivo proliferation of adrenal cells. To elucidate the immunolocalization of proliferative cells and the patterns of adrenal gland expression of members of the activating protein-1 (AP-1) family of oncogenes, we used hypophysectomized rats. The effects of adrenocorticotropic hormone (ACTH) and fibroblast growth factor 2 (FGF2) on Fos and Jun protein expression were investigated, and DNA synthesis was assessed by using bromodeoxyuridine (BrdU) incorporation. No change was detectable in the adrenal cortex at 2 days after hypophysectomy, although a reduction occurred in the number of BrdU-positive cells in the zona fasciculata. This hypophysectomy-induced early phase of adrenal cortex atrophy in the zona fasciculata was correlated with JunB protein induction, suggesting the formation of an inhibitory AP-1 complex. Accumulation of c-Jun/JunD and c-Fos/FosB, but not of JunB, in the zona fasciculata and zona reticularis implied that, after ACTH stimulation, these proteins were the principal AP-1 components in these zones. In these same zones, ACTH increased BrdU-positive cell counts, indicating that the composition of the AP-1 complex in these zones was proliferation-related. However, FGF2 induced an antagonistic modulation of the response to ACTH, by reducing the numbers of Jun-/Fos-positive cells and inhibiting DNA synthesis. Our results implicate the AP-1 family of transcription factors (in particular, the dynamics within the Jun protein family) in the regulation of cell control during ACTH-induced proliferation of the adrenal cortex.

Disabled-2 is expressed in adrenal zona glomerulosa and is involved in aldosterone secretion

The differentiation of the adrenal cortex into functionally specific zones is probably due to differential temporal gene expression during fetal growth, development, and adulthood. In our search for adrenal zona glomerulosa-specific genes, we found that Disabled-2 (Dab2) is expressed in the zona glomerulosa of the rat adrenal gland using a combination of laser capture microdissection, mRNA amplification, cDNA microarray hybridization, and real-time RT-PCR. Dab2 is an alternative spliced mitogen-regulated phosphoprotein with features of an adaptor protein and functions in signal transduction, endocytosis, and tissue morphogenesis during embryonic development. We performed further studies to analyze adrenal Dab2 localization, regulation, and role in aldosterone secretion. We found that Dab2 is expressed in the zona glomerulosa and zona intermedia of the rat adrenal cortex. Low-salt diet treatment increased Dab2-long isoform expression at the mRNA and protein level in the rat adrenal gland, whereas high-salt diet treatment did not cause any significant modification. Angiotensin II infusion caused a transient increase in both Dab2 isoform mRNAs in the rat adrenal gland. Dab2 overexpression in H295R human adrenocortical cells caused an increase in aldosterone synthase expression and up-regulated aldosterone secretion under angiotensin II-stimulated conditions. In conclusion, Dab2 is an adrenal gland zona glomerulosa- and intermedia-expressed gene that is regulated by aldosterone secretagogues such as low-salt diet or angiotensin II and is involved in aldosterone synthase expression and aldosterone secretion. Dab2 may therefore be a modulator of aldosterone secretion and be involved in mineralocorticoid secretion abnormalities.