A Novel Population of Inner Cortical Cells in the Adrenal Gland That Displays Sexually Dimorphic Expression of Thyroid Hormone Receptor-β1

Update on Adrenarche-Still a Mystery

CONTEXT

Adrenarche marks the timepoint of human adrenal development when the cortex starts secreting androgens in increasing amounts, in healthy children at age 8-9 years, with premature adrenarche (PA) earlier. Because the molecular regulation and significance of adrenarche are unknown, this prepubertal event is characterized descriptively, and PA is a diagnosis by exclusion with unclear long-term consequences.

EVIDENCE ACQUISITION

We searched the literature of the past 5 years, including original articles, reviews, and meta-analyses from PubMed, ScienceDirect, Web of Science, Embase, and Scopus, using search terms adrenarche, pubarche, DHEAS, steroidogenesis, adrenal, and zona reticularis.

EVIDENCE SYNTHESIS

Numerous studies addressed different topics of adrenarche and PA. Although basic studies on human adrenal development, zonation, and zona reticularis function enhanced our knowledge, the exact mechanism leading to adrenarche remains unsolved. Many regulators seem involved. A promising marker of adrenarche (11-ketotestosterone) was found in the 11-oxy androgen pathway. By current definition, the prevalence of PA can be as high as 9% to 23% in girls and 2% to 10% in boys, but only a subset of these children might face related adverse health outcomes.

CONCLUSION

New criteria for defining adrenarche and PA are needed to identify children at risk for later disease and to spare children with a normal variation. Further research is therefore required to understand adrenarche. Prospective, long-term studies should characterize prenatal or early postnatal developmental pathways that modulate trajectories of birth size, early postnatal growth, childhood overweight/obesity, adrenarche and puberty onset, and lead to abnormal sexual maturation, fertility, and other adverse outcomes.

Rare Coexistence of Aldosterone-producing Adrenocortical Adenoma Confirmed by an Immunohistochemical Analysis of Steroidogenic Enzymes with Adrenal Ectopic Thyroid Tissue: A Case Report and Literature Review

A 56-year-old man presented with a history of hypertension; clinically, the patient had primary aldosteronism (PA) and a 4-cm left adrenal tumor. The left adrenal glands, resected by adrenalectomy, also contained ectopic thyroid tissue (ETT). An immunohistochemical analysis of steroid-converting enzymes revealed an aldosterone-producing adenoma (APA). Among 19 previously reported cases of adrenal ETT, 4 had adrenal hormonal abnormalities, all of which were PA. This is the first case of adrenal ETT coexisting with APA, confirmed by steroid-converting enzyme expression. Further analyses using cumulative case data are required to clarify the correlation between adrenal ETT and APA.

Current insight into the transient X-zone in the adrenal gland cortex

Mouse models have been widely used in the study of adrenal gland development and diseases. The X-zone is a unique structure of the mouse adrenal gland and lineage-tracing studies show that the X-zone is a remnant of the fetal adrenal cortex. Although the X-zone is considered analogous to the fetal zone in the human adrenal cortex, the functional significance of the X-zone has remained comparatively more obscure. The X-zone forms during the early postnatal stages of adrenal development and regresses later in a remarkable sexually dimorphic fashion. The formation and regression of the X-zone can be different in mice with different genetic backgrounds. Mouse models with gene mutations, hormone/chemical treatments, and/or gonadectomy can also display an aberrant development of the X-zone or alternatively a dysregulated X-zone regression. These models have shed light on the molecular mechanisms regulating the development and regression of these unique adrenocortical cells. This review paper briefly describes the development of the adrenal gland including the formation and regression processes of the X-zone. It also summarizes and lists mouse models that demonstrate different X-zone phenotypes.

A Brief Look at Hashimoto's Disease, Adrenal Incidentalomas, Obesity and Insulin Resistance-Could Endocrine Disruptors Be the Other Side of the Same Coin?

Hashimoto's disease (HD) is the most common cause of hypothyroidism in developed countries. The exact pathomechanism behind it has not been clearly established; however, an interplay of genetic susceptibility, environmental triggers (including diet) and epigenetic factors seems to be involved. Among the latter, increasingly more attention has been paid to some hormonally active substances, known as endocrine disruptors, which are commonly used worldwide. HD has become a condition widely reported in the media, acting as a culprit for inexplicable weight gain, chronic fatigue or weakness. Nevertheless, the recognition of HD is undeniably increasing and represents a major public health burden. At the same time, improving access to imaging tests has increased the number of incidentally diagnosed adrenal tumors. Above all, the widespread use of chest computed tomography (CT) due to the COVID-19 pandemic has contributed to frequent incidental detection of adrenal lesions. Fortunately, a vast majority of these findings are asymptomatic benign tumors with no excessive hormonal activity, and therefore, they are defined as adrenal incidentalomas (AIs). Interestingly, recent studies have indicated that patients with AIs are more prone to obesity and insulin resistance. Although mutual relationships between the thyroid and the adrenal glands have been studied widely, still, little is known about the possible pathophysiological associations between thyroid autoimmunity and the occurrence of adrenal incidentalomas. This article presents a brief review of the common endocrine disorders with a special focus on the frequently coexisting insulin resistance and/or obesity. Furthermore, in response to the recent growing interest in endocrine disruptors, with their transgenerational epigenetic effects that influence hormonal system function, a concise overview of the topic has also been included.

DHCR24, a Key Enzyme of Cholesterol Synthesis, Serves as a Marker Gene of the Mouse Adrenal Gland Inner Cortex

Steroid hormones are synthesized through enzymatic reactions using cholesterol as the substrate. In steroidogenic cells, the required cholesterol for steroidogenesis can be obtained from blood circulation or synthesized de novo from acetate. One of the key enzymes that control cholesterol synthesis is 24-dehydrocholesterol reductase (encoded by DHCR24). In humans and rats, DHCR24 is highly expressed in the adrenal gland, especially in the zona fasciculata. We recently reported that DHCR24 was expressed in the mouse adrenal gland's inner cortex and also found that thyroid hormone treatment significantly upregulated the expression of Dhcr24 in the mouse adrenal gland. In the present study, we showed the cellular expression of DHCR24 in mouse adrenal glands in early postnatal stages. We found that the expression pattern of DHCR24 was similar to the X-zone marker gene 20αHSD in most developmental stages. This finding indicates that most steroidogenic adrenocortical cells in the mouse adrenal gland do not synthesize cholesterol locally. Unlike the 20αHSD-positive X-zone regresses during pregnancy, some DHCR24-positive cells remain present in parous females. Conditional knockout mice showed that the removal of Dhcr24 in steroidogenic cells did not affect the overall development of the adrenal gland or the secretion of corticosterone under acute stress. Whether DHCR24 plays a role in conditions where a continuous high amount of corticosterone production is needed requires further investigation.

Congenital Hypothyroidism and Hyperthyroidism Alters Adrenal Gene Expression, Development, and Function

Background: The human adrenal cortex undergoes several rapid remodeling steps during its lifetime. In rodents, similar remodeling occurs postnatally in the "X-zone" layer through unknown mechanisms. Furthermore, little is known regarding the impact of thyroid hormone (TH) on adrenal glands in humans. Methods: To investigate the impact of TH on adrenal pathophysiology, we created two genetic murine models mimicking human nonautoimmune hypothyroidism and hyperthyroidism. Moreover, we analyzed serum thyrotropin (TSH) and steroid hormone concentrations in patients diagnosed with congenital hypothyroidism and premature adrenarche (PA). Results: We found that TH receptor beta-mediated hypertrophy of the X-zone significantly elevated the adrenal weights of hyperthyroid women. In the hypothyroid model, the X-zone was poorly developed in both sexes. Moreover, large reciprocal changes in the expression levels of genes that regulate adrenal cortical function were observed with both models. Unexpectedly, up- and downregulation of several genes involved in catecholamine synthesis were detected in the adrenal glands of the hypothyroid and hyperthyroid models, respectively. Furthermore, TSH and adrenal steroid concentrations correlated positively in pediatric patients with congenital hypothyroidism and PA. Conclusions: Our results revealed that congenital hypothyroidism and hyperthyroidism functionally affect adrenal gland development and related steroidogenic activity, as well as the adrenal medulla.

Bones and adrenal organogenesis: how embryonic osteocalcin influences lifelong adrenal function

Osteocalcin is a hormone produced in bones by osteoblasts during bone formation. Numerous studies have demonstrated that adrenal gland–derived glucocorticoids inhibit osteocalcin production, which can ultimately cause deleterious bones loss. This loss establishes a unidirectional endocrine relationship between the adrenal glands and bone, however, whether osteocalcin reciprocally regulates glucocorticoid secretion remains unclear. In this issue of the JCI, Yadav and colleagues address how bone-derived osteocalcin influences adrenal organogenesis and function. Using a large variety of animal models, the authors established that embryonic osteocalcin signaling, specifically through the GPR158 receptor, regulates postnatal adrenal steroid concentrations throughout life. This work has translational potential, and we await future investigations that determine whether modulating osteocalcin levels could promote endogenous adrenocortical function in adrenocortical hypoplasia and glucocorticoid deficiency.

Delayed pubarche

In healthy adolescents, delayed pubarche is generally a benign condition that is caused by a physiological discrepancy between gonadarche and adrenarche. In presence of other clinical signs and symptoms, delayed pubarche can be caused by single or multiple hormones deficiency (such as adrenal insufficiency, panhypopituitarism and hypothyroidism) and/or genetic conditions (Turner syndrome, androgen insensitivity syndrome). Exposition to endocrine disruptors has also been described as a possible cause of delay of pubic hair development. Basic blood tests, karyotype and first level imaging studies are helpful in the differential diagnosis.

Adrenal androgens, adrenarche, and zona reticularis: A human affair?

In humans, reticularis cells of the adrenal cortex fuel the production of androgen steroids, constituting the driver of numerous morphological changes during childhood. These steps are considered a precocious stage of sexual maturation and are grouped under the term "adrenarche". This review describes the molecular and enzymatic characteristics of the zona reticularis, along with the possible signals and mechanisms that control its emergence and the associated clinical features. We investigate the differences between species and discuss new studies such as genetic lineage tracing and transcriptomic analysis, highlighting the rodent inner cortex's cellular and molecular heterogeneity. The recent development and characterization of mouse models deficient for Prkar1a presenting with adrenocortical reticularis-like features prompt us to review our vision of the mouse adrenal gland maturation. We expect these new insights will help increase our understanding of the adrenarche process and the pathologies associated with its deregulation.

RNA-Seq Reveals Sub-Zones in Mouse Adrenal Zona Fasciculata and the Sexually Dimorphic Responses to Thyroid Hormone

The sex-specific prevalence of adrenal diseases has been known for a long time. However, the reason for the high prevalence of these diseases in females is not completely understood. Mouse studies have shown that the adult adrenal gland is sexually dimorphic at different levels such as transcriptome, histology, and cell renewal. Here we used RNA-seq to show that in prepubertal mice, male and female adrenal glands were not only sexually dimorphic but also responded differently to the same external stimulus. We previously reported that thyroid hormone receptor β1 (TRβ1) in the adrenal gland is mainly expressed in the inner cortex and the fate of this TRβ1-expressing cell population can be changed by thyroid hormone (triiodothyronine; T3) treatment. In the present study, we found that adrenal glands in prepubertal mice were sexually dimorphic at the level of the transcriptome. Under T3 treatment, prepubertal females had 1162 genes differentially expressed between the saline and T3 groups, whereas in males of the same age, only 512 genes were T3-responsive. Immunostaining demonstrated that several top sexually dimorphic T3-responsive genes, including Cyp2f2 and Dhcr24, were specifically expressed in the adrenal inner cortex, precisely in an area partially overlapping with the X-zone. Under T3 treatment, a unique cortical layer that surrounds the adrenal X-zone expanded significantly, forming a distinct layer peculiar to females. Our findings identified novel marker genes for the inner adrenal cortex, indicating there are different sub-zones in the zona fasciculata. The results also highlight the sex-specific response to thyroid hormone in the mouse adrenal gland.

A Direct Comparison of Thyroid Hormone Receptor Protein Levels in Mice Provides Unexpected Insights into Thyroid Hormone Action

Background: Thyroid hormone (TH) action is mediated by three major thyroid hormone receptor (THR) isoforms α1, β1, and β2 (THRA1, THRB1, and THRB2). These THRs and a fourth major but non-TH binding isoform, THRA2, are encoded by two genes Thra and Thrb. Reliable antibodies against all THR isoforms are not available, and THR isoform protein levels in mammalian tissues are often inferred from messenger RNA (mRNA) levels. Methods: We generated knock-in mouse models expressing endogenously and identically 2X hemagglutenin epitope (HA)-tagged THRs (THRA1/2, THRB1, and THRB2), which could then be detected by commercially available anti-HA antibodies. Using nuclear enrichment, immunoprecipitation, and Western blotting, we determined relative THR protein expression in 16 mouse organs. Results: In all peripheral organs tested except the liver, the predominant THR isoform was THRA1. Surprisingly, in metabolically active organs such as fat and muscle, THRB1 protein levels were up to 10 times lower than that of THRA1, while their mRNA levels appeared similar. In contrast to peripheral organs, the central nervous system (CNS) had a unique pattern with relatively low levels of both THRB1 and THRA1, and high levels of THRA2 expression. As expected, THRB2 was highly expressed in the pituitary, but a previously unknown sex-specific difference in THRB2 expression was found (female mice having higher pituitary expression than male mice). Higher THRB2 expression appears to make the central axis more sensitive to TH as both serum thyrotropin and Tshb mRNA levels were lower in female mice. Conclusions: Direct comparison of THR protein abundance in different organs using endogenously tagged HA-THR mouse lines shows that expression of THR isoforms is regulated at transcriptional and posttranscriptional levels, and in organ-specific manner. The prevalence of THRA1 and low abundance of THRB1 in majority of peripheral tissues suggest that peripheral actions of these isoforms should be revisited. A unique pattern of high THRA2 in CNS warrants further exploration of this non-TH binding isoform in brain development. Finally, THRB2, in addition to cell-specific control, is also regulated in a sex-specific manner, which may change the hypothalamus-pituitary-thyroid axis set point and perhaps metabolism in males and females.

Sex Differences in Adrenal Bmal1 Deletion-Induced Augmentation of Glucocorticoid Responses to Stress and ACTH in Mice

The circadian glucocorticoid (GC) rhythm is dependent on a molecular clock in the suprachiasmatic nucleus (SCN) and an adrenal clock that is synchronized by the SCN. To determine whether the adrenal clock modulates GC responses to stress, experiments used female and male Cyp11A1Cre/+::Bmal1Fl/Fl knockout [side-chain cleavage (SCC)-KO] mice, in which the core clock gene, Bmal1, is deleted in all steroidogenic tissues, including the adrenal cortex. Following restraint stress, female and male SCC-KO mice demonstrate augmented plasma corticosterone but not plasma ACTH. In contrast, following submaximal scruff stress, plasma corticosterone was elevated only in female SCC-KO mice. Adrenal sensitivity to ACTH was measured in vitro using acutely dispersed adrenocortical cells. Maximal corticosterone responses to ACTH were elevated in cells from female KO mice without affecting the EC50 response. Neither the maximum nor the EC50 response to ACTH was affected in male cells, indicating that female SCC-KO mice show a stronger adrenal phenotype. Parallel experiments were conducted using female Cyp11B2 (Aldosterone Synthase)Cre/+::Bmal1Fl/Fl mice and adrenal cortex-specific Bmal1-null (Ad-KO) mice. Plasma corticosterone was increased in Ad-KO mice following restraint or scruff stress, and in vitro responses to ACTH were elevated in adrenal cells from Ad-KO mice, replicating data from female SCC-KO mice. Gene analysis showed increased expression of adrenal genes in female SCC-KO mice involved in cell cycle control, cell adhesion-extracellular matrix interaction, and ligand receptor activity that could promote steroid production. These observations underscore a role for adrenal Bmal1 as an attenuator of steroid secretion that is most prominent in female mice.

Androgen receptor signalling in the male adrenal facilitates X-zone regression, cell turnover and protects against adrenal degeneration during ageing

Androgens are known to be an essential regulator of male health. Androgen receptor (AR) is widely expressed throughout the adrenal cortex, yet the wider role for androgen signalling in the adrenal remains underexplored. To investigate AR-dependent and AR-independent androgen signalling in the adrenal, we used a novel mouse model with a specific ablation of androgen receptor in the adrenal cortex with or without reduction of circulating androgen levels by castration. Our results describe AR expression in the human and mouse adrenal and highlight that the mouse is a viable model to investigate androgen signalling in the adrenal cortex. We show androgen signalling via AR is required for X-zone regression during puberty. Furthermore, cortex measurements define differences in X-zone morphology depending on whether circulating androgens or AR have been removed. We show androgens promote both cortical cell differentiation and apoptosis but are dispensable for the formation of the definitive cortex. Additionally, investigation of aged mice with AR ablation reveals severe cortex disruption, spindle cell hyperplasia and X-zone expansion. The data described herein demonstrates AR-signalling is required to facilitate X-zone regression, cell clearance and to protect against adrenal degeneration during ageing.

The transient cortical zone in the adrenal gland: the mystery of the adrenal X-zone

The X-zone is a transient cortical region enriched in eosinophilic cells located in the cortical-medullary boundary of the mouse adrenal gland. Similar to the X-zone, the fetal zone in human adrenals is also a transient cortical compartment, comprising the majority of the human fetal adrenal gland. During adrenal development, fetal cortical cells are gradually replaced by newly formed adult cortical cells that develop into outer definitive zones. In mice, the regression of this fetal cell population is sexually dimorphic. Many mouse models with mutations associated with endocrine factors have been reported with X-zone phenotypes. Increasing findings indicate that the cell fate of this aged cell population of the adrenal cortex can be manipulated by many hormonal and nonhormonal factors. This review summarizes the current knowledge of this transient adrenocortical zone with an emphasis on genes and signaling pathways that affect X-zone cells.

Adrenal steroids in female hypothyroid neonates: Unraveling an association between thyroid hormones & adrenal remodeling

CONTEXT

The adrenal gland undergoes significant remodeling during the neonatal period, an essential developmental process that still remains incompletely understood. With respect to control over the remodeling process and, specifically, the role of thyroid hormones (TH), no human studies have been published. The effect of both hypo- and hyper-thyroidism has only been evaluated in adults, focusing on the mature adrenal. Recently, Huang et al identified expression of the TH receptor β1 in the mouse adrenal X-zone and demonstrated that TH administration could alter the postnatal adrenal remodeling process.

OBJECTIVE

To address whether TH influence adrenal steroid profiles and adrenal remodeling during the neonatal period.

METHODS

We compared the adrenal steroid profile of a naturally occurring prototype, female neonates with severe congenital hypothyroidism (CH, n=22, upon diagnosis of CH), with that of euthyroid neonates (n=20).

RESULTS

Significantly higher levels of adrenal steroids (17-OH-progesterone, DHEAS, Δ4- androstenedione and testosterone) were measured in neonates with severe CH compared to euthyroid neonates, returning within normal range after euthyroid state had been established on L-thyroxine replacement therapy whereas cortisol levels did not differ. TSH values in the CH group were positively, while FT4 levels were negatively correlated with circulating adrenal steroids.

CONCLUSIONS

The hormonal profile of female neonates with severe CH suggests a more active adrenal fetal zone than controls. These data indirectly associate TH with the adrenal remodeling and maturation process in humans. Based on our results we suggest that severe hypothyroidism decelerates the involution of the adrenal fetal zone that normally occurs postnatally.

New insights into thyroid hormone action

Thyroid hormones (TH) are endocrine messengers essential for normal development and function of virtually every vertebrate. The hypothalamic-pituitary-thyroid axis is exquisitely modulated to maintain nearly constant TH (T4 and T3) levels in circulation. However peripheral tissues and the CNS control the intracellular availability of TH, suggesting that circulating concentrations of TH are not fully representative of what each cell type sees. Indeed, recent work in the field has identified that TH transporters, deiodinases and thyroid hormone receptor coregulators can strongly control tissue-specific sensitivity to a set amount of TH. Furthermore, the mechanism by which the thyroid hormone receptors regulate target gene expression can vary by gene, tissue and cellular context. This review will highlight novel insights into the machinery that controls the cellular response to TH, which include unique signaling cascades. These findings shed new light into the pathophysiology of human diseases caused by abnormal TH signaling.

Thyroid Hormones and Timing of Pubertal Onset in a Longitudinal Cohort of Females, Northern California, 2006-11

BACKGROUND

Pubertal timing is regulated by a complex interplay of hormones. Few studies have evaluated the role of thyroid hormones in pubertal onset. We investigated the associations between blood concentrations of free and total thyroxine (FT4, TT4), free triiodothyronine, and thyroid stimulating hormone and pubertal onset among females.

METHODS

Participants included 323 Kaiser Permanente Northern California members followed at annual intervals during 2004-11, who provided a blood sample during the first 3 years of the study. Thyroid hormone concentrations were measured in serum in the first blood specimen available for each participant. Pubertal onset was defined as Tanner stage ≥2 for breast (thelarche) and pubic hair (pubarche) development. Associations between thyroid hormones and pubertal onset were assessed by multivariable logistic regression and Cox proportional hazards modelling.

RESULTS

At blood draw, participants were age 6.5-10.1 (median 7.7) years, 10% had reached thelarche, and 12% had reached pubarche. Participants were followed 0-5 years after blood draw (median 4). At most recent clinical visit, participants were age 6.7-14.7 (median 12.3) years, 92% had reached thelarche, and 89% had reached pubarche. No associations were identified between having reached thelarche or pubarche at time of blood draw and thyroid hormones. Examined longitudinally, higher concentrations of pre-pubertal FT4 and TT4 were associated with earlier pubarche (adjusted hazard ratio (HR) 1.41, 95% confidence interval (CI) 1.06, 1.86; per ng/dL and aHR 1.07, 95% CI 1.02, 1.12; per μg/dL respectively).

CONCLUSIONS

Higher pre-pubertal concentrations of FT4 and TT4 are associated with earlier pubarche.