Rainey Lab Research Projects

I. Regulation of Zonation of the Mammalian Adrenal Cortex

The human adrenal cortex is a multifunctional organ responsible for the secretion of mineralocorticoids, glucocorticoids, and sex steroid precursors. These three classes of steroids have distinct roles in endocrine physiology and are produced within distinct adrenal zones – the zona glomerulosa (ZG), zona fasciculata (ZF) and zona reticularis (ZR), respectively. Interestingly, the adrenal gland consistently replenishes its cell population through “centripetal migration” of cells from the outermost ZG through the ZF and ZR to the border of the adrenal medulla. As cells migrate inward, they change their morphology and expression pattern of key enzymes involved in steroid biosynthesis (Fig 1). It is the selective expression of the enzymes involved in steroid production that cause the zones to produce specific steroid classes. However, the mechanisms that lead to the conversion of cells to different zonal phenotypes remain poorly defined.

Using in vivo and in vitro adrenal models, our laboratory focuses on the mechanisms that drive the zonal conversion of adrenal cells. Understanding these processes will provide novel therapeutic targets for adrenal diseases.

II. Biology of Adrenal Androgens

The human adrenal cortex produces a series of androgens and androgen precursors. The two most characterized are dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S), which exhibit a unique pattern of production across human aging (Fig 1). The mechanisms regulating the production of DHEA/DHEA-S remain elusive. Adrenarche refers to the onset of DHEA and DHEA-S production from the adrenal zona reticularis (ZR) that can be detected around 6 years of age (Fig 1). The phenotypic result of adrenarche is pubarche or the development of axillary and pubic hair that occurs in both girls and boys at about age 8 to 9. The phenomenon of adrenarche is unique to human and to some old-world primates. Importantly, the mechanisms (hormonal or otherwise) that control the expansion of the process of adrenarche including the expansion of the ZR and the and production of DHEA remain poorly defined. There is no evidence that DHEA-S is the steroid that is responsible for the clinical phenomena that characterize adrenarche. From this perspective, adrenal androgen production remains one of the least understood of endocrine processes.

We have characterized the development of the DHEA-S-secreting cells within the ZR using a unique collection of normal adrenal glands and immunohistochemistry for the enzymes involved in steroid production. We have mainly focused on: 1) 3β-hydroxysteroid dehydrogenase (HSD3B2) which has the unique ability to divert precursors from the pathway leading to DHEA-S thereby inhibiting its biosynthesis, and 2) the allosteric protein cytochrome b5 type A (CYB5A) that enhances the 17,20-lyase activity of the enzyme CYP17A1 (17α-hydroxylase/17, 20-lyase), which is required for DHEA-S synthesis. The relative absence of ZR HSD3B2 expression/activity combined with the augmenting expression of CYB5A in the expanding ZR facilitates DHEA and DHEA-S synthesis through the pre-adrenarche period to adult life (Fig 2). In addition, we are now taking the novel approach of applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) to defining the adrenal-produced steroids that could be involved in the phenotypic changes occurring during adrenarche.

The adrenal can cause childhood androgen excess in several diseases, which include certain forms of congenital adrenal hyperplasia (CAH) and premature adrenarche (PremA). PremA is characterized by early rise in DHEAS and early development of pubic or axillary hair before age 8 y in girls and 9 y in boys. While PremA was previously thought to be a benign disorder, recently studies have suggested that it is an early indicator of increased likelihood of having insulin resistance and polycystic ovary syndrome (PCOS). Our laboratory group hopes to identify the mechanisms and bioactive androgens involved in normal and PremA. Understanding adrenarche may improve our understanding of the mechanisms and treatments for disorders of androgen excess in children and women.

III. Primary Aldosteronism

There is growing evidence that chronic inappropriate elevations in circulating aldosterone cause cardiovascular, renal and other pathologic complications. Primary aldosteronism (PA) is the major cause of endocrine-related hypertension and has been proposed to affect ~6-8% of overall hypertensive population and ~20% of patients with resistant hypertension. The most common causes of PA are aldosterone-producing adenomas (APA) and bilateral adrenal hyperplasia (BAH). Rarer forms of PA include unilateral adrenal hyperplasia, aldosterone-producing adrenocortical carcinoma, and familial PA. PA occurs, in part, due to the disruption of the tightly regulated and site-specific expression of the steroidogenic enzyme, CYP11B2 (aldosterone synthase). The use of next-generation sequencing has resulted in identification of several somatic and germline mutations that are responsible for excess aldosterone production in APA and familial PA, respectively. Gene affected by these mutations include KCNJ5 (potassium channel), ATP1A1 (Na⁺/K⁺ transporter), ATP2B3 (Calcium pump), CACNA1D (L-type calcium channel), and CACNA1H (T-type calcium channel) which all cause inappropriate aldosterone production, mostly through increased intracellular calcium concentration.

Figure. Cellular mechanisms resulting in inappropriate aldosterone production in adrenal cells with gene mutation. (from Adrenal Disorders: Physiology, Pathophysiology and Treatment: Springer Nature, In Press)

We have developed international collaborations to determine the adrenal cellular origins that cause PA. Nationally we participated in collaborations with adrenal experts that include: Celso Gomez-Sanchez (University of Mississippi), Anand Vaidya (Harvard Medical School), Constantine Stratakis (NIH), Debbie Cohen (University of Pennsylvania), James Luther (Vanderbilt University), Lester Thompson (Woodland Hills Medical Center, California). Internationally, we have developed collaborations in Europe, Australia and Japan. These include collaborative projects with Franco Mantero (University of Padua, Padua, Italy), Paulo Mulatero (University of Torino, Italy), Silvia Monticone (University of Torino, Italy), Gian-Paulo Rossi (university of Padua, Padua, Italy), Martin Reincke (Ludwig-Maximilians-Universität München, Germany), Felix Beuschlein (Universitätsspital Zürich, Switzerland), and Michael Stowasser (University of Queensland, Australia). Each of these investigators have strong referral programs for adrenal disease. Last but not least, for many years we have worked closely with Hironobu Sasano (Tohoku University, Japan), Yasuhiro Nakamura (Tohoku University, Japan), and Fumitoshi Satoh (Tohoku University, Japan) who are experts on endocrine pathology and endocrinology. With these collaborators, we are working to define the cellular and molecular mechanisms causing this disease. In addition we are working to improve the ability to diagnose primary aldosteronism through the advanced measurement of hybrid-steroids that are only produced in certain forms of this disease. Together we work towards having a better understanding of molecular characteristics of PA that will provide improved diagnostic methods and novel targeted therapeutics.

IV. Cushing's Syndrome

Chronic exposure to endogenous glucocorticoid excess in patients with Cushing’s syndrome (CS) is associated with a cluster of complications, which negatively impact morbidity and mortality, including visceral obesity, dyslipidemia, hypertension and type 2 diabetes. CS and subclinical CS (SCS), caused by overproduction of cortisol from the adrenal gland, has a combined incidence of 8 per 10,000 people per year. CS can be divided into two subgroups, adrenocorticotropic hormone (ACTH)-dependent Cushing’s Disease and ACTH-independent CS. The latter is often called "adrenal CS”. Cortisol-producing adenomas (CPA) are the most common cause of adrenal CS and SCS. The use of next-generation sequencing has allowed the identification of somatic mutations that cause autonomous cortisol production in half of CPA. The most frequently altered gene is PRKACA, encoding the catalytic subunit α of protein kinase A (PKA). Somatic hot-spot mutation in PRKACA causes constitutive PKA activation, leading to phosphorylation of downstream targets and excess cortisol production. Activating PRKACA somatic mutations have been identified in approximately 35% of CPA. Other affected genes in CPA include GNAS, PRKAR1A, and CTNNB1. However, the genetic causes of over half of CPA are still unknown. In addition, the genotype and its steroidogenic impact (that results in disease) has not been well studied.

We have developed international referral center collaborations to determine the genetic landscape of adrenal CS. Our national collaborations include adrenal experts: Mouhammed Habra and Paul Graham (MD Anderson Cancer Center), Constantine Stratakis (NIH) and James Luther (Vanderbilt University). Together, we are working to define the cellular and molecular mechanisms causing adrenal CS. Accurate genetic and detailed histologic characterization and in vitro mechanistic studies will provide a better understanding of the molecular pathogenesis of CPA, leading to the identification of molecular targets for new functional diagnostics for adrenal CS.