Functional biology of the primate fetal adrenal gland: advances in technology provide new insight

Fetal adrenal gland size and umbilical artery Doppler in growth-restricted fetuses

OBJECTIVES

In fetal growth restriction (FGR), Doppler ultrasound is the most important method for the detection and management. However, additional parameters are needed to improve the distinction between constitutionally small fetuses and fetuses affected by FGR.

METHODS

A total of 445 singleton pregnancies between 23 and 40 weeks of gestation were included in our retrospective study, of which 67 with FGR and 378 normal fetuses. A 2D-plane of the fetal adrenal gland was obtained and the adrenal gland ratio was measured. Spearman's correlation coefficient was calculated to assess the association of fetal Doppler and adrenal gland ratio with outcome parameters. Logistic regression analysis was performed to assess the statistical significance of "PI of the umbilical artery" and "adrenal gland ratio" as prognostic factors for intrauterine growth restriction (IUGR).

RESULTS

PI of the umbilical artery was shown to correlate with outcome parameters (WG_Delivery: r=-0.125, p=0.008; birth weight: r=-0.268, p<0.001; birth weight centile: r=-0.248, p<0.001; APGAR at 5 min: r=-0.117, p=0.014). Adrenal gland ratio showed no correlation with any of the outcome parameters. In logistic regression however, both PI of the umbilical artery and the adrenal ratio were shown to be significantly associated with fetal IUGR. When combining the two parameters, predictive value was superior to the predictive value of each individual parameter (AUC 0.738 [95% CI 0.670; 0.806]).

CONCLUSIONS

The adrenal gland ratio can be a useful addition to Doppler ultrasound when it comes to the detection of fetal FGR. Prospective studies are needed to establish references ranges and cut-off values for clinical decision-making.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

Estrogen Suppresses Interaction of Melanocortin 2 Receptor and Its Accessory Protein in the Primate Fetal Adrenal Cortex

We have shown that fetal adrenal fetal zone (FZ) volume and serum dehydroepiandrosterone sulfate (DHAS) levels were increased, whereas definitive and transitional zone (DZ/TZ) volume was unaltered, in baboons in which estrogen levels were suppressed by the administration of the aromatase inhibitor letrozole. The interaction of the melanocortin 2 receptor (MC2R) with its accessory protein (MRAP) is essential for trafficking MC2R to the adrenal cell surface for binding to ACTH. The present study determined whether the estrogen-dependent regulation of fetal adrenocortical development is mediated by ACTH and/or expression/interaction of MC2R and MRAP. Fetal pituitary proopiomelanocortin mRNA and plasma ACTH levels and fetal adrenal MC2R-MRAP interaction were assessed in baboons in which estrogen was suppressed/restored by letrozole/letrozole plus estradiol administration during the second half of gestation. Although fetal pituitary proopiomelanocortin and plasma ACTH levels and fetal adrenal MC2R and MRAP protein levels were unaltered, MC2R-MRAP interaction was 2-fold greater (P < .05) in the DZ/TZ in letrozole-treated baboons than in untreated animals and restored by letrozole plus estradiol treatment. We propose that the increasing levels of estradiol with advancing pregnancy suppress interaction of MC2R with MRAP, thereby diminishing MC2R movement to the cell membrane in the DZ/TZ. This would be expected to reduce progenitor cell proliferation in the DZ and migration to the FZ, thereby restraining FZ growth and DHAS production to maintain fetal adrenal DHAS and placental estradiol levels in a physiological range late in gestation.

Prevalence and functional consequence of TP53 mutations in pediatric adrenocortical carcinoma: a children's oncology group study

PURPOSE

Adrenocortical carcinoma (ACC) is a rare pediatric malignancy. It occurs in excess among individuals with the Li-Fraumeni syndrome, which results primarily from germline mutations in the TP53 gene. Prior series exploring frequencies of germline TP53 mutation among children with ACC have been small, geographically limited, or subject to referral bias. The functional consequence of mutations has not been related to phenotype. We provide a genotype-phenotype analysis of TP53 mutations in pediatric ACC and propose a model for tissue-specific effects based on adrenocortical ontogeny.

PATIENTS AND METHODS

Eighty-eight consecutive, unrelated children with ACC, unselected for family history, underwent germline TP53 sequencing. Rate and distribution of mutations were identified. Functional analysis was performed for novel TP53 variants. Correlation with the International Agency for Research on Cancer p53 database further delineated mutational distribution, association with family history, and risk for multiple primary malignancies (MPMs).

RESULTS

Germline mutations were present in 50% of children. These mutations did not correspond to the conventional hotspot mutations. There was a wide range of mutant protein function. Patients bearing alleles encoding protein with higher functionality were less likely to have a strong family cancer history, whereas those with greater loss of function had MPMs and/or positive family history. In patients with MPMs, ACC was the most frequent initial malignancy. Finally, we demonstrated age-dependent rates of TP53 mutation positivity.

CONCLUSION

TP53 mutations are prevalent in children with ACC but decline with age. Mutations result in a broad spectrum of functional loss. Effect of individual mutations may predict carrier and familial disease penetrance with potentially broad implications for clinical surveillance and counseling.

Placental estrogen suppresses cyclin D1 expression in the nonhuman primate fetal adrenal cortex

We have previously shown that estrogen selectively suppresses growth of the fetal zone of the baboon fetal adrenal cortex, which produces the C19-steroid precursors, eg, dehydroepiandrosterone sulfate, which are aromatized to estrogen within the placenta. In the present study, we determined whether fetal adrenal expression of cell cycle regulators are altered by estrogen and thus provide a mechanism by which estrogen regulates fetal adrenocortical development. Cyclin D1 mRNA levels in the whole fetal adrenal were increased 50% (P < .05), and the number of cells in the fetal adrenal definitive zone expressing cyclin D1 protein was increased 2.5-fold (P < .05), whereas the total number of cells in the fetal zone and fetal serum dehydroepiandrosterone sulfate levels were elevated 2-fold (P < .05) near term in baboons in which fetal serum estradiol levels were decreased by 95% (P < .05) after maternal administration of the aromatase inhibitor letrozole and restored to normal by concomitant administration of letrozole plus estradiol throughout second half of gestation. However, fetal adrenocortical expression of cyclin D2, the cyclin-dependent kinase (Cdk)-2, Cdk4, and Cdk6, and Cdk regulatory proteins p27(Kip1) and p57(Kip2) were not changed by letrozole or letrozole plus estradiol administration. We suggest that estrogen controls the growth of the fetal zone of the fetal adrenal by down-regulating cyclin D1 expression and thus proliferation of progenitor cells within the definitive zone that migrate to the fetal zone. We propose that estrogen restrains growth and function of the fetal zone via cyclin D1 to maintain estrogen levels in a physiological range during primate pregnancy.

Embryological and molecular development of the adrenal glands

In this mini review, the embryological and functional development of the adrenal glands is presented from a molecular perspective. While acknowledging that this is a highly complex series of events, the processes are described in simple and broad strokes in a single text for the reader who is interested in this field but is not an active researcher. The origin of the adrenal glands is in the mesodermal ridge as early as the fourth week of gestation. Between the eighth and ninth weeks of gestation, the adrenal glands are encapsulated and this results in the presence of a distinct organ. There have been great strides in deciphering the very complicated molecular aspects of adrenal gland development in which multiple transcription factors have been identified, directing the adrenogonadal primordium into the adrenal cortex, kidney, or bipotential gonad. Adrenocorticotrophic hormone is critical for early development of the hypothalamic-pituitary adrenal axis. Several mutations in transcription factors, responsible for normal adrenal gland development have been found to induce the familial syndrome of congenital adrenal hypoplasia or neoplasia.

100th anniversary of the discovery of the human adrenal fetal zone by Stella Starkel and Lesław Węgrzynowski: how far have we come?

Year 2010 marks a centennial anniversary of the description by Stella Starkel and Lesław Węgrzynowski, Polish students of the Faculty of Medicine, University of Lwów, the fetal zone of the human fetal adrenal gland. In 1911 both, Starkel and Węgrzynowski were graduated from the Faculty of Medicine of Lwow University. The paper appeared in the German Arch. Anat. Physiol. and its original title was "Beitrag zur Histologie der Nebeniere bei Feten und Kindern" ("Contribution to histology of adrenals of fetuses and children"). The studies were performed on 100 adrenal glands obtained from fetuses (from 6th month of gestation) and up to 5-year-old children. They described the fetal zone as a "medullary zone", also as "immature cortex", which undergoes involution in first years of life. To commemorate this discovery, this review aimed to present the most important achievements of studies on the development and involution of the human adrenal fetal zone.

Generation and application of anti-ouabain IgY antibodies

Ouabain is a bioactive hapten and is very difficult to be accurately quantified because of the lack of useful reagents. Furthermore, where ouabain is produced in the adrenal glands has not been identified. In this study, ouabain-BSA was generated for immunizing the laying hens to generate ouabain-specific IgY antibodies in chicken eggs. The anti-ouabain IgY antibodies were detected in eggs 1 week after the last immunization and their concentrations increased with time. The highest concentrations of anti-ouabain IgY antibodies reached at 1:10,240 for ELISA 5 weeks after immunization and maintained for 4 weeks in chicken eggs. Following PEG precipitation, an average of 8.5 mg of anti-ouabain IgY antibodies with a purity of 87.6% was achieved from a single egg. Further analysis revealed that the anti-ouabain IgY antibodies had little immunoreactivity to hydrocortisone, dexamethasone, cedilanid, and digoxin, indicating their high specificity, and the purified IgY antibodies effectively detected endogenous ouabain in the cytoplasm of cells predominately in the zona reticularis of rat and human adrenal glands, indicating their high immunoreactivity. Given that IgY has an unique structure and bioactive features, the generated anti-ouabain IgY antibodies may be used as a new reagent for accurately quantifying ouabain in biological studies.

Adrenal gland development and defects

The network regulating human adrenal development is complex. Studies of patients with adrenal insufficiency due to gene mutations established a central role for transcription factors GLI3, SF1 and DAX1 in the initial steps of adrenal formation. Adrenal differentiation seems to depend on adrenocorticotropic hormone (ACTH) stimulation and signalling, including biosynthesis and action of POMC, PC1, TPIT, MC2R, MRAP and ALADIN, all of which cause adrenocortical hypoplasia when mutated in humans. Studies of knockout mice revealed many more factors involved in adrenal development; however, in contrast to rodents, in humans several of those factors had no adrenal phenotype when mutated (e.g. WT1, WNT4) or, alternatively, human mutations have not (yet) been identified. Tissue profiling of fetal and adult adrenals suggested 69 genes involved in adrenal development. Among them were genes coding for steroidogenic enzymes, transcription and growth factors, signalling molecules, regulators of cell cycle and angiogenesis, and extracellular matrix proteins; however, the exact role of most of them remains to be elucidated.

Maternal melatonin stimulates growth and prevents maturation of the capuchin monkey fetal adrenal gland

The primate fetal adrenal reaches a large size relative to body weight followed by a rapid decrease in size in the postnatal period. We tested the hypothesis that maternal melatonin stimulates growth and prevents maturation of the primate fetal adrenal gland. We suppressed maternal melatonin by exposing eight pregnant capuchin monkeys to constant light (LL) from 63% to 90% gestation (term 155 days). Three of these received daily oral melatonin replacement (LL + Mel). Five mothers remaining in light:dark cycle were used as controls. Fetuses were delivered at 90% gestation. The absence of maternal melatonin selectively decreased fetal adrenal weight (Control: 488.8 +/- 51.5; LL: 363.2 +/- 27.7 and LL + Mel 519 +/- 46 mg; P < 0.05 ANOVA) without effecting fetal weight, placental weight or the weight of other fetal tissues. Changes in fetal adrenal size were accompanied by an increase in the levels of Delta5-3beta-hydroxysteroid dehydrogenase (3beta-HSD) mRNA (Control: 0.8 +/- 0.2; LL: 5.2 +/- 0.6 and LL + Mel 0.8 +/- 0.1; 3beta-HSD/18S-rRNA; P < 0.05 ANOVA). In vitro we found that maternal melatonin suppression increased basal progesterone production to levels similar to those of the adult adrenal gland (Control: 0.36 +/- 0.09; LL 0.99 +/- 0.13; LL + Mel 0.18 +/- 0.06 and adult: 0.88 +/- 0.10 ng/mg of tissue; P < 0.05 ANOVA) but no change in cortisol production. We found an increased production of cortisone (Control: 1.65 +/- 0.60; LL: 5.44 +/- 0.63; LL + Mel: 2.90 +/- 0.38 and adult: 1.70 +/- 0.45 ng/mg of tissue; P < 0.05 ANOVA). Collectively, the effects of maternal melatonin suppression and their reversion by maternal melatonin replacement suggest that maternal melatonin stimulates growth and prevents maturation of the capuchin monkey fetal adrenal gland.