Adrenocortical cells with stem/progenitor cell properties: recent advances

Role of NR5A1 Gene Mutations in Disorders of Sex Development: Molecular and Clinical Features

Disorders/differences of sex development (DSDs) are defined as broad, heterogenous groups of congenital conditions characterized by atypical development of genetic, gonadal, or phenotypic sex accompanied by abnormal development of internal and/or external genitalia. NR5A1 gene mutation is one of the principal genetic alterations implicated in causing DSD. This review outlines the role of NR5A1 gene during the process of gonadal development in humans, provides an overview of the molecular and functional characteristics of NR5A1 gene, and discusses potential clinical phenotypes and additional organ diseases due to NR5A1 mutations. NR5A1 mutations were analyzed in patients with 46,XY DSD and 46,XX DSD both during the neonatal and pubertal periods. Loss of function of the NR5A1 gene causes several different phenotypes, including some associated with disease in additional organs. Clinical phenotypes may vary, even among patients carrying the same NR5A1 variant, indicating that there is no specific genotype-phenotype correlation. Genetic tests are crucial diagnostic tools that should be used early in the diagnostic pathway, as early as the neonatal period, when gonadal dysgenesis is the main manifestation of NR5A1 mutation. NR5A1 gene mutations could be mainly associated with amenorrhea, ovarian failure, hypogonadism, and infertility during puberty. Fertility preservation techniques should be considered as early as possible.

FGF/FGFR signaling in adrenocortical development and tumorigenesis: novel potential therapeutic targets in adrenocortical carcinoma

FGF/FGFR signaling regulates embryogenesis, angiogenesis, tissue homeostasis and wound repair by modulating proliferation, differentiation, survival, migration and metabolism of target cells. Understandably, compelling evidence for deregulated FGF signaling in the development and progression of different types of tumors continue to emerge and FGFR inhibitors arise as potential targeted therapeutic agents, particularly in tumors harboring aberrant FGFR signaling. There is first evidence of a dual role of the FGF/FGFR system in both organogenesis and tumorigenesis, of which this review aims to provide an overview. FGF-1 and FGF-2 are expressed in the adrenal cortex and are the most powerful mitogens for adrenocortical cells. Physiologically, they are involved in development and maintenance of the adrenal gland and bind to a family of four tyrosine kinase receptors, among which FGFR1 and FGFR4 are the most strongly expressed in the adrenal cortex. The repeatedly proven overexpression of these two FGFRs also in adrenocortical cancer is thus likely a sign of their participation in proliferation and vascularization, though the exact downstream mechanisms are not yet elucidated. Thus, FGFRs potentially offer novel therapeutic targets also for adrenocortical carcinoma, a type of cancer resistant to conventional antimitotic agents.

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.

Flow-dependent differentiation of cultured adrenal cells under different stimuli

It still remains unclear how the functional organisation of the adrenal cortex arises. One aim of this study was to create a setup which allows for the establishment of a concentration gradient in vitro. This was achieved by a continuous flow of medium through the culture flask which caused differences in glucose and cortisol concentrations as well as in pH values between the sites of inflow and outflow of medium. Using real-time polymerase chain reaction, we found that a continuous supply of 1 ml medium per hour significantly increased the expression of MC2R, CYP11B1 and CYP17A1 genes of NCI-H295R cells in the distal area of the flask as compared with the proximal part. The expression of the AT1R showed a reverse regulation. The addition of dexamethasone to the medium led to an increase in gene expression of MC2R while AT1R was downregulated. Moreover, we detected a higher expression of CYP11B2 and a decreased expression of CYP11B1 when endothelial cell-conditioned medium (ECCM) was added to the inflow. Our experiments show that a directed medium delivery system creates different gradients and affects the functional differentiation of the NCI-H295R cells. Also, our results emphasise that products of endothelial cells have additional effects on the differentiation of the cultured adrenal cortical cells. Our results are in support that the regulation of the adrenal zonation is possible through different concentration gradients.

MANAGEMENT OF ENDOCRINE DISEASE: Regenerative therapies in autoimmune Addison's disease

The treatment for autoimmune Addison's disease (AAD) has remained virtually unchanged in the last 60 years. Most patients have symptoms that are relatively well controlled with exogenous steroid replacement, but there may be persistent symptoms, recurrent adrenal crisis and poor quality of life, despite good compliance with optimal current treatments. Treatment with conventional exogenous steroid therapy is also associated with premature mortality, increased cardiovascular risk and complications related to excessive steroid replacement. Hence, novel therapeutic approaches have emerged in the last decade attempting to improve the long-term outcome and quality of life of patients with AAD. This review discusses the recent developments in treatment innovations for AAD, including the novel exogenous steroid formulations with the intention of mimicking the physiological biorhythm of cortisol secretion. Our group has also carried out a few studies attempting to restore endogenous glucocorticoid production via immunomodulatory and regenerative medicine approaches. The recent advances in the understanding of adrenocortical stem cell biology, and adrenal plasticity will also be discussed to help comprehend the science behind the therapeutic approaches adopted.

Neural differentiation potential of sympathoadrenal progenitors derived from fresh and cryopreserved neonatal porcine adrenal glands

Stem/progenitor cells are thought to have the potential in the treatment of severe neurodegenerative diseases. Recently, sympathoadrenal progenitors expressing specific markers of neural crest derivatives and capable to differentiate into neurons were discovered in adult bovine and human adrenal glands, but there was no reported data on cryopreservation of sympathoadrenal progenitors. The aim of the present study was to examine the neural differentiation potential of sympathoadrenal progenitors derived from fresh and cryopreserved neonatal porcine adrenal glands. Considering impact of various initial state of frozen biomaterial on cell recovery, we carried out a comparative estimation of cryopreservation outcome both for adrenal tissue fragments and isolated primary cells. The estimation consisted of determining cell yield, viability, ability to adhere, proliferate and differentiate in vitro. Cells isolated from the fresh adrenal glands were cultured until confluence. A formation of sympathoadrenal progenitors-embedded spherical cell colonies, whose cells are differentiated then into βIII-tubulin-positive cells with neuron-like morphology, was observed on the monolayer. The colonies were well preserved after cryopreservation of cell culture with a cooling rate of 1 °C/min in the cryoprotectant media containing 5-15% of dimethylsulfoxide. Adrenal tissue fragments were cryopreserved in the presence of 10% dimethylsulfoxide at the cooling rates of 0.3; 1: 5; 40 and > 100 °C/min. Sympathoadrenal progenitors were recovered after cryopreservation with 0.3 °C/min cooling rate but not higher.

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.

POD-1/Tcf21 overexpression reduces endogenous SF-1 and StAR expression in rat adrenal cells

During gonad and adrenal development, the POD-1/capsulin/TCF21transcription factor negatively regulates SF-1/NR5A1expression, with higher SF-1 levels being associated with increased adrenal cell proliferation and tumorigenesis. In adrenocortical tumor cells, POD-1 binds to the SF-1 E-box promoter region, decreasing SF-1 expression. However, the modulation of SF-1 expression by POD-1 has not previously been described in normal adrenal cells. Here, we analyzed the basal expression of Pod-1 and Sf-1 in primary cultures of glomerulosa (G) and fasciculata/reticularis (F/R) cells isolated from male Sprague-Dawley rats, and investigated whether POD-1 overexpression modulates the expression of endogenous Sf-1 and its target genes in these cells. POD-1 overexpression, following the transfection of pCMVMycPod-1, significantly decreased the endogenous levels of Sf-1 mRNA and protein in F/R cells, but not in G cells, and also decreased the expression of the SF-1 target StAR in F/R cells. In G cells overexpressing POD-1, no modulation of the expression of SF-1 targets, StAR and CYP11B2, was observed. Our data showing that G and F/R cells respond differently to ectopic POD-1 expression emphasize the functional differences between the outer and inner zones of the adrenal cortex, and support the hypothesis that SF-1 is regulated by POD-1/Tcf21 in normal adrenocortical cells lacking the alterations in cellular physiology found in tumor cells.

Practical approaches for evaluating adrenal toxicity in nonclinical safety assessment

The adrenal gland has characteristic morphological and biochemical features that render it particularly susceptible to the actions of xenobiotics. As is the case with other endocrine organs, the adrenal gland is under the control of upstream organs (hypothalamic-pituitary system) in vivo, often making it difficult to elucidate the mode of toxicity of a test article. It is very important, especially for pharmaceuticals, to determine whether a test article-related change is caused by a direct effect or other associated factors. In addition, antemortem data, including clinical signs, body weight, food consumption and clinical pathology, and postmortem data, including gross pathology, organ weight and histopathologic examination of the adrenal glands and other related organs, should be carefully monitored and evaluated. During evaluation, the following should also be taken into account: (1) species, sex and age of animals used, (2) metabolic activation by a cytochrome P450 enzyme(s) and (3) physicochemical properties and the metabolic pathway of the test article. In this review, we describe the following crucial points for toxicologic pathologists to consider when evaluating adrenal toxicity: functional anatomy, blood supply, hormone production in each compartment, steroid biosynthesis, potential medulla-cortex interaction, and species and gender differences in anatomical features and other features of the adrenal gland which could affect vulnerability to toxic effects. Finally practical approaches for evaluating adrenal toxicity in nonclinical safety studies are discussed.

Steroidogenic organ development and homeostasis: A WT1-centric view

Adrenal and gonads are the main steroidogenic organs and are central to regulate body homeostasis in the vertebrate organism. Although adrenals and gonads are physically separated in the adult organism, both organs share a common developmental origin, the adrenogonadal primordium. One of the key genes involved in the development of both organs is the Wilms' tumor suppressor WT1, which encodes a zinc finger protein that has fascinated the scientific community for more than two decades. This review will provide an overview of the processes leading to the development of these unique organs with a particular focus on the multiple functions WT1 serves during adrenogonadal development. In addition, we will highlight some recent findings and open questions on how maintenance of steroidogenic organs is achieved in the adult organism.

Two-pore domain potassium channels in the adrenal cortex

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

Steroidogenesis-adrenal cell signal transduction

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

Adrenocortical zonation, renewal, and remodeling

The adrenal cortex is divided into concentric zones. In humans the major cortical zones are the zona glomerulosa, zona fasciculata, and zona reticularis. The adrenal cortex is a dynamic organ in which senescent cells are replaced by newly differentiated ones. This constant renewal facilitates organ remodeling in response to physiological demand for steroids. Cortical zones can reversibly expand, contract, or alter their biochemical profiles to accommodate needs. Pools of stem/progenitor cells in the adrenal capsule, subcapsular region, and juxtamedullary region can differentiate to repopulate or expand zones. Some of these pools appear to be activated only during specific developmental windows or in response to extreme physiological demand. Senescent cells can also be replenished through direct lineage conversion; for example, cells in the zona glomerulosa can transform into cells of the zona fasciculata. Adrenocortical cell differentiation, renewal, and function are regulated by a variety of endocrine/paracrine factors including adrenocorticotropin, angiotensin II, insulin-related growth hormones, luteinizing hormone, activin, and inhibin. Additionally, zonation and regeneration of the adrenal cortex are controlled by developmental signaling pathways, such as the sonic hedgehog, delta-like homolog 1, fibroblast growth factor, and WNT/β-catenin pathways. The mechanisms involved in adrenocortical remodeling are complex and redundant so as to fulfill the offsetting goals of organ homeostasis and stress adaptation.

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.

Functional zonation of the rat adrenal cortex: the development and maintenance

The adrenal cortex of mammals consists of three concentric zones, i.e., the zona glomerulosa (zG), the zona fasciculata (zF), and the zona reticularis (zR), which secrete mineralocorticoids, glucocorticoids, and adrenal androgens, respectively. In 1994, we identified immunohistochemically a new zone between zG and zF of the rat adrenal gland. The zone appeared to be devoid of any significant endocrine functions specific to adrenocortical zones, therefore, we designated the zone as "undifferentiated cell zone (zU)". Further, BrdU (5-bromo-2'-deoxyuridine)-incorporating cells (cells in S-phase) were concentrated at the outer region and the inner region of zU, and these cells proliferated and migrated bidirectionally: toward zG centrifugally and toward zF centripetally. We proposed that cells in and around zU are stem/progenitor cells of the rat adrenal cortex, maintaining functional zonation of the adrenal cortex. The view is consistent with observations reported recently that Sonic hedgehog (Shh), an important factor in embryonic development and adult stem cell maintenance, exists in zU of the rat adrenal gland and the Shh-containing cells seem to migrate bidirectionally.

WT1 maintains adrenal-gonadal primordium identity and marks a population of AGP-like progenitors within the adrenal gland

Adrenal glands and gonads share a common primordium (AGP), but the molecular events driving differentiation are poorly understood. Here we demonstrate that the Wilms tumor suppressor WT1 is a key factor defining AGP identity by inhibiting the steroidogenic differentiation process. Indeed, ectopic expression of WT1 precludes differentiation into adrenocortical steroidogenic cells by locking them into a progenitor state. Chromatin immunoprecipitation experiments identify Tcf21 and Gli1 as direct targets of WT1. Moreover, cell lineage tracing analyses identify a long-living progenitor population within the adrenal gland, characterized by the expression of WT1, GATA4, GLI1, and TCF21, that can generate steroidogenic cells in vivo. Strikingly, gonadectomy dramatically activates these WT1(+) cells and leads to their differentiation into gonadal steroidogenic tissue. Thus, our data describe a mechanism of response to organ loss by recreating hormone-producing cells at a heterotopic site.

NGF induces adult stem Leydig cells to proliferate and differentiate during Leydig cell regeneration

Nerve growth factor (NGF) has been reported to be involved in male reproductive physiology. However, few reports have described the activity of NGF during Leydig cell development. The objective of the present study was to examine the role of NGF during stem-Leydig-cell (SLC) regeneration. We investigated the effects of NGF on Leydig-cell (LC) regeneration by measuring mRNA levels in the adult rat testis after ethane dimethanesulfonate (EDS) treatment. Furthermore, we used the established organ culture model of rat seminiferous tubules to examine the regulation of NGF during SLC proliferation and differentiation using EdU staining, real-time PCR and western blotting. Progenitor Leydig cells (PLCs) and immature Leydig cells (ILCs) were also used to investigate the effects of NGF on LCs at different developmental stages. NGF mRNA levels changed significantly during Leydig-cell regeneration in vivo. In vitro, NGF significantly promoted the proliferation of stem Leydig cells and also induced steroidogenic enzyme gene expression and 3β-HSD protein expression. The data from PLCs and ILCs showed that NGF could increase Cyclin D1 and Hsd 17b3 mRNA levels in PLCs and Cyclin D1 mRNA levels in ILCs. These results indicate that NGF may play an important role during LC regeneration by regulating the proliferation and differentiation of LCs at different developmental stages, from SLCs to PLCs and from PLCs to ILCs. The discovery of this effect of NGF on Leydig cells will provide useful information for developing new potential therapies for PADAM (Partial Androgen Deficiency in the Aging Male).

Dicer deficiency reveals microRNAs predicted to control gene expression in the developing adrenal cortex

MicroRNAs (miRNAs) are small, endogenous, non-protein-coding RNAs that are an important means of posttranscriptional gene regulation. Deletion of Dicer, a key miRNA processing enzyme, is embryonic lethal in mice, and tissue-specific Dicer deletion results in developmental defects. Using a conditional knockout model, we generated mice lacking Dicer in the adrenal cortex. These Dicer-knockout (KO) mice exhibited perinatal mortality and failure of the adrenal cortex during late gestation between embryonic day 16.5 (E16.5) and E18.5. Further study of Dicer-KO adrenals demonstrated a significant loss of steroidogenic factor 1-expressing cortical cells that was histologically evident as early as E16.5 coincident with an increase in p21 and cleaved-caspase 3 staining in the cortex. However, peripheral cortical proliferation persisted in KO adrenals as assessed by staining of proliferating cell nuclear antigen. To further characterize the embryonic adrenals from Dicer-KO mice, we performed microarray analyses for both gene and miRNA expression on purified RNA isolated from control and KO adrenals of E15.5 and E16.5 embryos. Consistent with the absence of Dicer and the associated loss of miRNA-mediated mRNA degradation, we observed an up-regulation of a small subset of adrenal transcripts in Dicer-KO mice, most notably the transcripts coded by the genes Nr6a1 and Acvr1c. Indeed, several miRNAs, including let-7, miR-34c, and miR-21, that are predicted to target these genes for degradation, were also markedly down-regulated in Dicer-KO adrenals. Together these data suggest a role for miRNA-mediated regulation of a subset of genes that are essential for normal adrenal growth and homeostasis.

Massive neonatal adrenal enlargement due to cytomegaly, persistence of the transient cortex, and hyperplasia of the permanent cortex: findings in Cushing syndrome associated with hemihypertrophy

Described in this article is the massive enlargement of both adrenal glands in 3 newborns-2 girls and 1 boy. Two had hemihypertrophy and other congenital abnormalities but no identified genetic mutation; the third had genetically proven Beckwith-Wiedemann syndrome. Two had severe Cushing syndrome, the third had hypercortisolemia but no clinical Cushing syndrome. Bilateral adrenalectomy cured Cushing syndrome in the 2 with severe symptoms; total adrenal weight in these patients was 44 and 53 g, respectively. Unilateral adrenalectomy was performed in the third patient: the gland weighed 52 g; postoperatively, the patient's hypercortisolemia normalized, and, concomitantly, the enlarged contralateral adrenal gland had a 5-fold decrease in size with slight enlargement 6 years postoperatively. Microscopically, the 3 patients had similar pathology: massive adrenal enlargement due to a combination of cytomegaly, persistence of the transient cortex, and hyperplasia of the permanent cortex. The pathologic findings were most likely the result of the genetic mutation identified in 1 patient and of an unknown mutation in the remaining 2 patients.

Angiogenesis in the course of enucleation-induced adrenal regeneration--expression of selected genes and proteins involved in development of capillaries

Enucleation-induced rapid proliferation of adrenocortical cells and restoration of adrenals structure requires formation of new blood vessels. The performed studies aimed to select from around 30,000 transcripts, identified by means of Affymetrix(®) Rat Gene 1.1 ST Array, the genes involved in angiogenesis in the course of enucleation-induced adrenal regeneration and to characterize their expression levels in regenerating gland between days 1 and 15 after surgery. At day 1 of regeneration almost 2000 genes showed more than 2-fold up/down-regulation. At days 1-3 after surgery the highest expression demonstrated genes involved in the development of inflammation and blood clot formation. From around 2000 genes we selected genes involved in angiogenesis. During the regeneration 62 genes involved in angiogenesis were identified as up- or down-regulated. Some data were also validated by QPCR. Levels of Vegfa and Kdr (Vegfr-2) mRNAs were very low at day 1 of regeneration and remained unchanged thereafter. The highest expression of Figf gene was found at day 5 while that of Vwf gene at days 1 and 2 after surgery. Levels of Thy1 mRNA increased notably between days 2 and 5 of the experiment. In comparison to control rats, Mc2r (ACTH receptor) expression was lowered at day 1 of the experiment and remained unchanged thereafter. This suggests that enucleation-induced adrenal neoangiogenesis does not require elevated expression of ACTH receptor. Results of our studies strongly suggest that enucleation-induced adrenal regeneration is an angiogenesis-dependent process. Moreover, immunohistochemistry suggests that regenerating adrenal parenchymal cells release numerous angiogenic factors which paracrinally may regulate formation of new vessels.

In vivo evidence for the crucial role of SF1 in steroid-producing cells of the testis, ovary and adrenal gland

Adrenal and gonadal steroids are essential for life and reproduction. The orphan nuclear receptor SF1 (NR5A1) has been shown to regulate the expression of enzymes involved in steroid production in vitro. However, the in vivo role of this transcription factor in steroidogenesis has not been elucidated. In this study, we have generated steroidogenic-specific Cre-expressing mice to lineage mark and delete Sf1 in differentiated steroid-producing cells of the testis, the ovary and the adrenal gland. Our data show that SF1 is a regulator of the expression of steroidogenic genes in all three organs. In addition, Sf1 deletion leads to a radical change in cell morphology and loss of identity. Surprisingly, sexual development and reproduction in mutant animals were not compromised owing, in part, to the presence of a small proportion of SF1-positive cells. In contrast to the testis and ovary, the mutant adult adrenal gland showed a lack of Sf1-deleted cells and our studies suggest that steroidogenic adrenal cells during foetal stages require Sf1 to give rise to the adult adrenal population. This study is the first to show the in vivo requirements of SF1 in steroidogenesis and provides novel data on the cellular consequences of the loss of this protein specifically within steroid-producing 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.

Adrenocortical stem and progenitor cells: implications for adrenocortical carcinoma

The continuous centripetal repopulation of the adrenal cortex is consistent with a population of cells endowed with the stem/progenitor cell properties of self-renewal and pluripotency. The adrenocortical capsule and underlying undifferentiated cortical cells are emerging as critical components of the stem/progenitor cell niche. Recent genetic analysis has identified various signaling pathways including Sonic Hedgehog (Shh) and Wnt as crucial mediators of adrenocortical lineage and organ homeostasis. Shh expression is restricted to the peripheral cortical cells that express a paucity of steroidogenic genes but give rise to the underlying differentiated cells of the cortex. Wnt/β-catenin signaling maintains the undifferentiated state and adrenal fate of adrenocortical stem/progenitor cells, in part through induction of its target genes Dax1 and inhibin-α, respectively. The pathogenesis of ACC, a rare yet highly aggressive cancer with an extremely poor prognosis, is slowly emerging from studies of the stem/progenitor cells of the adrenal cortex coupled with the genetics of familial syndromes in which ACC occurs. The frequent observation of constitutive activation of Wnt signaling due to loss-of-function mutations in the tumor suppressor gene APC or gain-of-function mutation in β-catenin in both adenomas and carcinomas, suggests perhaps that the Wnt pathway serves an early or initiating insult in the oncogenic process. Loss of p53 might be predicted to cooperate with additional genetic insults such as IGF2 as both are the most common genetic abnormalities in malignant versus benign adrenocortical neoplasms. It is unclear whether other factors such as Pod1 and Pref1, which are implicated in stem/progenitor cell biology in the adrenal and/or other organs, are also implicated in the etiology of adrenocortical carcinoma. The rarity and heterogeneous presentation of ACC makes it difficult to identify the cellular origin and the molecular progression to cancer. A more complete understanding of adrenocortical stem/progenitor cell biology will invariably aid in characterization of the molecular details of ACC tumorigenesis and may offer new options for therapeutic intervention.

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.

Adrenocortical cell transplantation reverses a murine model of adrenal failure

PURPOSE

Although adrenal insufficiency can be managed with steroid replacement, transplantation of adrenocortical cells may represent a more definitive therapy.

METHODS

An adrenal failure model was created by adding stress to mice that underwent staged bilateral adrenalectomy. Murine adrenocortical cells were seeded onto collagen sponges. The grafts were implanted under the renal capsule during the first adrenalectomy. Some mice had an additional graft placed next to the kidney. A contralateral adrenalectomy and a laparotomy were performed 1 week after the first adrenalectomy. Two weeks later, blood was collected for corticosterone measurement; and implants were retrieved for adrenal-specific messenger RNA analysis and histology. Mice that underwent the same procedures but received a graft without cells served as controls.

RESULTS

Control group mortality was 100%. Mice that had only one cell-seeded implant had 42% survival, whereas mice that had 2 cell-seeded implants had 100% survival. Retrieved implants demonstrated viable cells and expression of adrenocortical genes. The plasma corticosterone concentration in animals that survived was similar to that in normal mice.

CONCLUSION

Cells transplantation restored the adrenocortical function in these mice. Further optimization of this technique could bring a curative therapy to patients with adrenal insufficiency.

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.

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.

The Wnt/beta-catenin pathway in adrenocortical development and cancer

Signaling by the Wnt family of secreted glycolipoproteins plays key roles in embryonic development of organisms ranging from nematodes to mammals and is also implicated in several types of human cancers. Canonical Wnt signaling functions by regulating the translocation of β-catenin to the nucleus, where it controls key gene expression programs through interaction with Tcf/Lef and other families of transcription factors. Wnts can also act through non-canonical pathways that do not involve β-catenin activation, but implicate small GTPases/JNK kinase and intracellular calcium. Here we review recent studies that have revealed the expression of several components of Wnt/β-catenin signaling in the adrenal cortex and discovered a key role for this pathway in the regulation of proliferation/differentiation of progenitor cells and in tumorigenesis of that endocrine organ.

Diverse functions of Hedgehog signaling in formation and physiology of steroidogenic organs

Adrenal, testis, and ovary are steroidogenic organs derived from a common primordium that consists of steroidogenic factor 1 (SF1)-positive precursor cells. SF1 not only defines the steroidogenic lineages in these organs but also controls their differentiation. Recent evidence implicates the Hedgehog (Hh) signaling pathway as a downstream regulator of SF1 in the appearance of steroidogenic cells in these organs. The Hh signaling pathway serves as a common crosstalk component, yet has evolved diverse functions in the expansion and differentiation of the steroidogenic cells in a tissue-specific manner. The purpose of this review is to compare and contrast the different roles of Hh signaling in these three organs during development.

Alternative strategies for the treatment of classical congenital adrenal hyperplasia: pitfalls and promises

Despite decades of different treatment algorithms, the management of congenital adrenal hyperplasia (CAH) remains clinically challenging. This is due to the inherent difficulty of suppressing adrenal androgen production using near physiological dosing of glucocorticoids (GC). As a result, alternating cycles of androgen versus GC excess can occur and may lead to short stature, obesity, virilization, and alterations in puberty. Novel therapeutic alternatives, including new and more physiological means of GC delivery, inhibitors at the level of CRH or ACTH secretion and/or action, as well as “rescue strategies”, such as GnRH analogs, anti-androgens, aromatase inhibitors, and estrogen receptor blockers, are available; many of these agents, however, still require active investigation in CAH. Bilateral adrenalectomy is effective but it is also still an experimental approach. Gene therapy and stem cells, to provide functional adrenal cortical tissue, are at preclinical stage but provide exciting avenues for a potential cure for CAH.

Cushing's syndrome and fetal features resurgence in adrenal cortex-specific Prkar1a knockout mice

Carney complex (CNC) is an inherited neoplasia syndrome with endocrine overactivity. Its most frequent endocrine manifestation is primary pigmented nodular adrenocortical disease (PPNAD), a bilateral adrenocortical hyperplasia causing pituitary-independent Cushing's syndrome. Inactivating mutations in PRKAR1A, a gene encoding the type 1 α-regulatory subunit (R1α) of the cAMP–dependent protein kinase (PKA) have been found in 80% of CNC patients with Cushing's syndrome. To demonstrate the implication of R1α loss in the initiation and development of PPNAD, we generated mice lacking Prkar1a specifically in the adrenal cortex (AdKO). AdKO mice develop pituitary-independent Cushing's syndrome with increased PKA activity. This leads to autonomous steroidogenic genes expression and deregulated adreno-cortical cells differentiation, increased proliferation and resistance to apoptosis. Unexpectedly, R1α loss results in improper maintenance and centrifugal expansion of cortisol-producing fetal adrenocortical cells with concomitant regression of adult cortex. Our data provide the first in vivo evidence that loss of R1α is sufficient to induce autonomous adrenal hyper-activity and bilateral hyperplasia, both observed in human PPNAD. Furthermore, this model demonstrates that deregulated PKA activity favors the emergence of a new cell population potentially arising from the fetal adrenal, giving new insight into the mechanisms leading to PPNAD.

Carney complex is a rare familial disease characterized by a predisposition to develop multiple endocrine tumors and highly morbid syndromes due to endocrine overactivities. Its most frequent endocrine manifestation, hypersecretion of glucocorticoids i.e. Cushing's syndrome, is caused by micronodular adrenal gland hyperplasia, an unusual neoplasia which combines both hyperplastic and atrophic areas. Inactivating mutations of the gene encoding the regulatory subunit 1α (R1α) of the cAMP–dependent protein kinase were frequently found in these patients, but the causal link between loss of R1α and onset of this adrenal disorder had not yet been established. Here, we describe the first mouse model mimicking this disease and provide mechanistic insights into endocrine overactivity and neoplastic transformation. Indeed, we show that lack of R1α induces autonomous expression of genes involved in steroid biosynthesis and resurgence of hyperplastic fetal-like cells with concomitant defects in cell renewal of the adult cortex. Our data therefore represent a substantial conceptual advance on the cellular dynamics involved in adrenal gland homeostasis. They suggest that regression of fetal structures may be important to establish normal endocrine functions and to allow cell renewal in the definitive cortex. Failure to clear out cells of fetal features in R1α-deficient adrenals leads to morbid hyperplasia.

Molecular aspects of steroidogenic factor 1 (SF-1)

Steroidogenic factor 1 (SF-1, also called Ad4BP and NR5A1) is a nuclear receptor with critical roles in steroidogenic tissues, as well as in the brain and pituitary. In particular, SF-1 has emerged as an essential regulator of adrenal and gonadal functions and development. In the last few years, our knowledge on SF-1 has increased considerably at all levels, from the gene to the protein, and on its specific roles in different physiological processes. In this review, we discuss the current understanding on SF-1 with focus on the parameters that control the transcriptional capacity of SF-1 and the mechanisms that ensure proper stage- and tissue-specific expression of the gene encoding SF-1.

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.

Review paper: origin and molecular pathology of adrenocortical neoplasms

Neoplastic adrenocortical lesions are common in humans and several species of domestic animals. Although there are unanswered questions about the origin and evolution of adrenocortical neoplasms, analysis of human tumor specimens and animal models indicates that adrenocortical tumorigenesis involves both genetic and epigenetic alterations. Chromosomal changes accumulate during tumor progression, and aberrant telomere function is one of the key mechanisms underlying chromosome instability during this process. Epigenetic changes serve to expand the size of the uncommitted adrenal progenitor population, modulate their phenotypic plasticity (i.e., responsiveness to extracellular signals), and increase the likelihood of subsequent genetic alterations. Analyses of heritable and spontaneous types of human adrenocortical tumors documented alterations in either cell surface receptors or their downstream effectors that impact neoplastic transformation. Many of the mutations associated with benign human adrenocortical tumors result in dysregulated cyclic adenosine monophosphate signaling, whereas key factors and/or signaling pathways associated with adrenocortical carcinomas include dysregulated expression of the IGF2 gene cluster, activation of the Wnt/beta-catenin pathway, and inactivation of the p53 tumor suppressor. A better understanding of the factors and signaling pathways involved in adrenal tumorigenesis is necessary to develop targeted pharmacologic and genetic therapies.

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.

Dax-1 and steroid receptor RNA activator (SRA) function as transcriptional coactivators for steroidogenic factor 1 in steroidogenesis

The nuclear receptor steroidogenic factor 1 (SF-1) is essential for adrenal development and steroidogenesis. The atypical orphan nuclear receptor Dax-1 binds to SF-1 and represses SF-1 target genes. Paradoxically, however, loss-of-function mutations of Dax-1 also cause adrenal hypoplasia, suggesting that Dax-1 may function as an SF-1 coactivator under some circumstances. Indeed, we found that Dax-1 can function as a dosage-dependent SF-1 coactivator. Both SF-1 and Dax-1 bind to steroid receptor RNA activator (SRA), a coactivator that functions as an RNA. The coactivator TIF2 also associates with Dax-1 and synergistically coactivates SF-1 target gene transcription. A naturally occurring Dax-1 mutation inhibits this transactivation, and the mutant Dax-1-TIF2 complex mislocalizes in living cells. Coactivation by Dax-1 is abolished by SRA knockdown. The expression of the steroidogenic gene products steroidogenic acute regulatory protein (StAR) and melanocortin 2 receptor is reduced in adrenal Y1 cells following the knockdown of endogenous SRA. Similarly, the knockdown of endogenous Dax-1 downregulates the expression of the steroidogenic gene products CYP11A1 and StAR in both H295R adrenal and MA-10 Leydig cells. These findings reveal novel functions of SRA and Dax-1 in steroidogenesis and adrenal biology.

Estrogen deficiency leads to telomerase inhibition, telomere shortening and reduced cell proliferation in the adrenal gland of mice

Estrogen deficiency mediates aging, but the underlying mechanism remains to be fully determined. We report here that estrogen deficiency caused by targeted disruption of aromatase in mice results in significant inhibition of telomerase activity in the adrenal gland in vivo. Gene expression analysis showed that, in the absence of estrogen, telomerase reverse transcriptase (TERT) gene expression is reduced in association with compromised cell proliferation in the adrenal gland cortex and adrenal atrophy. Stem cells positive in c-kit are identified to populate in the parenchyma of adrenal cortex. Analysis of telomeres revealed that estrogen deficiency results in significantly shorter telomeres in the adrenal cortex than that in wild-type (WT) control mice. To further establish the causal effects of estrogen, we conducted an estrogen replacement therapy in these estrogen-deficient animals. Administration of estrogen for 3 weeks restores TERT gene expression, telomerase activity and cell proliferation in estrogen-deficient mice. Thus, our data show for the first time that estrogen deficiency causes inhibitions of TERT gene expression, telomerase activity, telomere maintenance, and cell proliferation in the adrenal gland of mice in vivo, suggesting that telomerase inhibition and telomere shortening may mediate cell proliferation arrest in the adrenal gland, thus contributing to estrogen deficiency-induced aging under physiological conditions.

Developmental links between the fetal and adult zones of the adrenal cortex revealed by lineage tracing

The nuclear receptor Ad4BP/SF-1 is essential for development of the adrenal cortex and the gonads, which derive from a common adrenogonadal primordium. The adrenal cortex subsequently forms morphologically distinct compartments: the inner (fetal) and outer (definitive or adult) zones. Despite considerable effort, the mechanisms that mediate the differential development of the adrenal and gonadal primordia and the fetal and adult adrenal cortices remain incompletely understood. We previously identified a fetal adrenal-specific enhancer (FAdE) in the Ad4BP/SF-1 locus that directs transgene expression to the fetal adrenal cortex and demonstrated that this enhancer is autoregulated by Ad4BP/SF-1. We now combine the FAdE with the Cre/loxP system to trace cell lineages in which the FAdE was active at some stage in development. These lineage-tracing studies establish definitively that the adult cortex derives from precursor cells in the fetal cortex in which the FAdE was activated before the organization into two distinct zones. The potential of these fetal adrenocortical cells to enter the pathway that eventuates in cells of the adult cortex disappeared by embryonic day 14.5. Thus, these studies demonstrate a direct link between the fetal and adult cortices involving a transition that must occur before a specific stage of development.

Deoxyribonucleic acid methylation controls cell type-specific expression of steroidogenic factor 1

Steroidogenic factor 1 (SF1) is expressed in a time- and cell-specific manner in the endocrine system. In this study we present evidence to support that methylation of CpG sites located in the proximal promoter of the gene encoding SF1 contributes to the restricted expression pattern of this nuclear receptor. DNA methylation analyses revealed a nearly perfect correlation between the methylation status of the proximal promoter and protein expression, such that it was hypomethylated in cells that express SF1 but hypermethylated in nonexpressing cells. Moreover, in vitro methylation of this region completely repressed reporter gene activity in transfected steroidogenic cells. Bisulfite sequencing of DNA from embryonic tissue demonstrated that the proximal promoter was unmethylated in the developing testis and ovary, whereas it was hypermethylated in tissues that do not express SF1. Together these results indicate that the DNA methylation pattern is established early in the embryo and stably inherited thereafter throughout development to confine SF1 expression to the appropriate tissues. Chromatin immunoprecipitation analyses revealed that the transcriptional activator upstream stimulatory factor 2 and RNA polymerase II were specifically recruited to this DNA region in cells in which the proximal promoter is hypomethylated, providing functional support for the fact that lack of methylation corresponds to a transcriptionally active gene. In conclusion, we identified a region within the SF1/Sf1 gene that epigenetically directs cell-specific expression of SF1.

Targeted disruption of beta-catenin in Sf1-expressing cells impairs development and maintenance of the adrenal cortex

The nuclear receptor steroidogenic factor 1 (Sf1, Nr5a1) is essential for adrenal development and regulates genes that specify differentiated adrenocortical function. The transcriptional coactivator beta-catenin reportedly synergizes with Sf1 to regulate a subset of these target genes; moreover, Wnt family members, signaling via beta-catenin, are also implicated in adrenocortical development. To investigate the role of beta-catenin in the adrenal cortex, we used two Sf1/Cre transgenes to inactivate conditional beta-catenin alleles. Inactivation of beta-catenin mediated by Sf1/Cre(high), a transgene expressed at high levels, caused adrenal aplasia in newborn mice. Analysis of fetal adrenal development with Sf1/Cre(high)-mediated beta-catenin inactivation showed decreased proliferation in presumptive adrenocortical precursor cells. By contrast, the Sf1/Cre(low) transgene effected a lesser degree of beta-catenin inactivation that did not affect all adrenocortical cells, permitting adrenal survival to reveal age-dependent degeneration of the cortex. These results define crucial roles for beta-catenin--presumably as part of the Wnt canonical signaling pathway--in both embryonic development of the adrenal cortex and in maintenance of the adult organ.