Localization of G protein alpha-subunits in the human fetal adrenal gland

Case Report: Severe McCune-Albright syndrome presenting with neonatal Cushing syndrome: navigating through clinical obstacles

Background

Café-au-lait skin macules, Cushing syndrome (CS), hyperthyroidism, and liver and cardiac dysfunction are presenting features of neonatal McCune-Albright syndrome (MAS), CS being the rarest endocrine feature. Although spontaneous resolution of hypercortisolism has been reported, outcome is usually unfavorable. While a unified approach to diagnosis, treatment, and follow-up is lacking, herein successful treatment and long-term follow-up of a rare case is presented.

Clinical case

An 11-day-old girl born small for gestational age presented with deterioration of well-being and weight loss. Large hyperpigmented macules on the trunk, hypertension, hyponatremia, hyperglycemia, and elevated liver enzymes were noted. ACTH-independent CS due to MAS was diagnosed. Although metyrapone (300 mg/m2/day) was started on the 25th day, complete remission could not be achieved despite increasing the dose up to 1,850 mg/m2/day. At 9 months, right total and left three-quarters adrenalectomy was performed. Cortisol decreased substantially, ACTH remained suppressed, rapid tapering of hydrocortisone to physiological dose was not tolerated, and supraphysiological doses were required for 2 months. GNAS analysis from the adrenal tissue showed a pathogenic heterozygous mutation. During 34 months of follow-up, in addition to CS due to MAS, fibrous dysplasia, hypophosphatemic rickets, and peripheral precocious puberty were detected. She is still regularly screened for other endocrinopathies.

Conclusion

Neonatal CS due to MAS is extremely rare. Although there is no specific guideline for diagnosis, treatment, or follow-up, addressing side effects and identifying treatment outcomes will improve quality of life and survival.

Three-Quarters Adrenalectomy for Infantile-Onset Cushing Syndrome due to Bilateral Adrenal Hyperplasia in McCune-Albright Syndrome

BACKGROUND

Bilateral adrenalectomy is performed in cases with infantile-onset Cushing syndrome due to bilateral adrenal hyperplasia in McCune-Albright syndrome (MAS) because severe Cushing syndrome with heart failure and liver dysfunction can have a lethal outcome. This procedure can completely ameliorate hypercortisolism, although lifetime steroid replacement therapy and steps to prevent adrenal crisis are necessary. Recently, the efficacy of unilateral adrenalectomy has been reported in adult cases of bilateral macronodular adrenal hyperplasia, but there is no consensus regarding the appropriate surgical treatment for bilateral adrenal hyperplasia in MAS.

OBJECTIVE

A 6-month-old girl presented with café-au-lait spots, short stature, central obesity, a moon face, and hypertension. Endocrinological tests and imaging studies led to the diagnosis of ACTH-independent Cushing syndrome due to bilateral adrenal hyperplasia induced by MAS. "Three-quarters adrenalectomy", namely right-sided total adrenalectomy and left-sided half adrenalectomy, was carried out. An activating mutation of the GNAS1 gene (p.Arg201Cys) was identified in the adrenal tissues. Since the operation, our patient has been in a state of clinical remission for more than 2 years.

CONCLUSION

Our original surgical intervention, three-quarters adrenalectomy, may be a new treatment option for Cushing syndrome associated with MAS.

[Recovery of Cushing syndrome revealing McCune-Albright syndrome]

Cushing syndrome (CS) is a rare feature of McCune-Albright syndrome. Treatments consist of bilateral adrenalectomy followed by lifelong glucocorticoid and mineralocorticoid treatment. However, cases of spontaneous remission of CS have been reported in the literature. We report a case of McCune-Albright syndrome with CS treated with metyrapone for 30 months with prolonged remission after a 12-year follow-up. Adrenalectomy may be avoided in some cases of CS caused by McCune-Albright syndrome. Metyrapone could be a good alternative to surgical treatment.

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.

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.

Cushing syndrome in the McCune-Albright syndrome

CONTEXT

Cushing syndrome (CS) is a rare but potentially fatal feature of McCune-Albright syndrome (MAS). Optimal management, prognostic features, and long-term follow-up of this disorder have not been described.

SETTING

The study was conducted at an academic tertiary care center.

PATIENTS

A total of 112 patients participating in a natural history study at the National Institutes of Health (NIH) were evaluated, and 21 published cases were reviewed.

INTERVENTIONS

Subjects received observation, medical management, or bilateral adrenalectomy.

MAIN OUTCOME MEASURES

We measured prevalence, prognostic factors, and natural history.

RESULTS

The prevalence of CS among NIH patients was 7.1%. The median age at diagnosis was 3 months. Clinical features included "Cushingoid facies" (66.7%), failure to thrive (60.0%), low birth weight (50.0%), liver disease (36.7%), and heart disease (26.7%). Six patients (20.0%) died, four after adrenalectomy. Death was more likely in patients with comorbid heart disease (odds ratio, 13.3; P < 0.05). Of 23 survivors, 13 underwent adrenalectomy, and 10 exhibited spontaneous resolution. Two patients with spontaneous resolution who were tested later in life (3 and 15 yr after resolution) continued to have low-level, autonomous adrenal function with biochemical adrenal insufficiency. Compared to MAS patients without CS, patients with CS were more likely to have a cognitive/developmental disorder (44.4 vs. 4.8%; P < 0.001; odds ratio, 8.8).

CONCLUSIONS

Comorbid heart and liver disease were poor prognostic markers and may indicate the need for prompt adrenalectomy. The high incidence of cognitive disorders indicates a need for close developmental follow-up and parental counseling. Patients with spontaneous resolution of CS may develop adrenal insufficiency, and they require long-term monitoring.

G protein-coupled receptor expression in the adult and fetal adrenal glands

Hormonal regulation of adrenal function occurs primarily through G protein-coupled receptors (GPCR), which may play different roles in fetal vs. adult adrenal glands. In this study, we compared the transcript levels of GPCR between fetal and adult adrenal and found that gonadotropin-releasing hormone receptor (GnRHR), latrophilin 3 receptor, G protein-coupled receptor 37, angiotensin II receptor type 2, latrophilin 2 receptor and melanocortin receptor were expressed at significantly higher levels in fetal adrenal. High GnRHR protein expression was also detected in fetal adrenal using immunohistochemical analysis. To define potential ligand sources for fetal adrenal GnRHR, we demonstrated that GnRH1 mRNA was expressed at high levels in the placenta, while fetal adrenal had high expression of GnRH2. In summary, certain GPCR particularly GnRHR were highly expressed in fetal adrenal and the expression of GnRH mRNA in the placenta and the fetal adrenal raises the possibility of endocrine and/or paracrine/autocrine influences on fetal adrenal function. However, the exact function of GnRHR in fetal adrenal remains to be determined.

G proteins immunodetection and adrenergic transduction pathways in the liver of Anguilla anguilla

G proteins are members of a highly conserved superfamily of GTPases, which includes heterotrimeric (alpha, beta, gamma) proteins acting as critical control points for transmembrane signaling. In ectothermal vertebrates, knowledge about these proteins is scarce, and our work provides the first demonstration that G(s), G(q), and G(i) proteins are all present in the liver of a fish. G(q)alpha subunits of about 42 kDa have been identified in European eel (Anguilla anguilla) liver membranes, supporting previous reports about the existence of hormone transduction pathways coupled to inositol 1,4,5-trisphosphate/Ca(2+) enhancement in fish hepatocytes. Although two G(s)alpha proteins of about 45 and 52 kDa have been reported in mammals, a single isoform of approximately 45 kDa has been recognized in eel liver. G(s)alpha and G(q)alpha proteins are involved in the epinephrine transduction pathway, leading to cAMP and Ca(2+) intracellular increments, respectively. Interestingly, both messengers significantly stimulated glucose release from eel hepatocytes but with a different time course. In fact, the Ca(2+)-dependent glucose output preceded the cAMP-mediated release by about 7 min. G(i)alpha subunits of about 40 kDa were also immunodetected, suggesting the presence of hormone receptors leading to adenylyl cyclase inhibition in eel liver; however, alpha(2)- adrenoreceptor ligands were ineffective on both enzyme activity and glucose release.

Cross signaling, cell specificity, and physiology

The literature on intracellular signal transduction presents a confusing picture: every regulatory factor appears to be regulated by all signal transduction cascades and to regulate all cell processes. This contrasts with the known exquisite specificity of action of extracellular signals in different cell types in vivo. The confusion of the in vitro literature is shown to arise from several causes: the inevitable artifacts inherent in reductionism, the arguments used to establish causal effect relationships, the use of less than adequate models (cell lines, transfections, acellular systems, etc.), and the implicit assumption that networks of regulations are universal whereas they are in fact cell and stage specific. Cell specificity results from the existence in any cell type of a unique set of proteins and their isoforms at each level of signal transduction cascades, from the space structure of their components, from their combinatorial logic at each level, from the presence of modulators of signal transduction proteins and of modulators of modulators, from the time structure of extracellular signals and of their transduction, and from quantitative differences of expression of similar sets of factors.

Identification and properties of a Gs protein in catfish liver membranes

The presence of G proteins and their involvement in adrenergic signaling has been investigated in catfish (Ictalurus melas) liver membranes. Adenylyl cyclase activity was potently stimulated by the nonhydrolyzable analog of GTP, [35S]guanosine 5'-O-(gamma-thiotriphosphate) (GTPgammaS) (maximal activation of about eightfold at 10(-5) M; half-maximal activation at 1.31 x 10(-7) M), and reduced by the competitive inhibitor of GTP, GDPbetaS (70% maximal inhibition at 10(-4) M; half-maximal inhibition at 1.98 x 10(-7) M). Forskolin dramatically enhanced enzyme activity (up to about 3500% at 100 microM), and its action was not affected by guanine nucleotides, confirming that the diterpene effect occurred only at targets downstream of the G proteins. Receptor-dependent G protein activity was evaluated by a [(35)S]GTPgammaS binding assay. At 100 microM GDP, 100 mM NaCl, and 5 mM MgCl2, after an incubation of 90 min at 20 degrees, a Kd of 18.6 nM and a Bmax of 105.7 pmol/mg protein for [35S]GTPgammaS binding to catfish liver membranes were determined. The binding of the tracer was enhanced by 1 microM epinephrine, up to a maximum of 158%, and inhibited by NF 449, a G(s)alpha-selective antagonist with half-maximal effect in the micromolar range. Immunoblotting analysis with a specific anti-G(s)alpha antibody revealed a single band of about 45 kDa mass. This result represents the first demonstration of the presence of G protein alpha(s) subunits in the liver of an ectothermal vertebrate.