Evangelia Charmandari

Pediatric Stress: Hormonal Mediators and Human Development

Stress activates the central and peripheral components of the stress system, i.e., the hypothalamic-pituitary-adrenal (HPA) axis and the arousal/sympathetic system. The principal effectors of the stress system are corticotropin-releasing hormone (CRH), arginine vasopressin, the proopiomelanocortin-derived peptides α-melanocyte-stimulating hormone and β-endorphin, the glucocorticoids, and the catecholamines norepinephrine and epinephrine. Appropriate responsiveness of the stress system to stressors is a crucial prerequisite for a sense of well-being, adequate performance of tasks and positive social interactions. By contrast, inappropriate responsiveness of the stress system may impair growth and development, and may account for a number of endocrine, metabolic, autoimmune and psychiatric disorders. The development and severity of these conditions primarily depend on the genetic vulnerability of the individual, the exposure to adverse environmental factors and the timing of the stressful event(s), given that prenatal life, infancy, childhood and adolescence are critical periods characterized by increased vulnerability to stressors. The developing brain undergoes rapid growth and is characterized by high turnover of neuronal connections during the prenatal and early postnatal life. These processes and, hence, brain plasticity, slow down during childhood and puberty, and plateau in young adulthood. Hormonal actions in early life, and to a much lesser extent later, can be organizational, i.e., can have effects that last for long periods of time, often for the entire life of the individual. Hormones of the stress system and sex steroids have such effects, which influence the behavior and certain physiologic functions of individuals for life. Exposure of the developing brain to severe and/or prolonged stress may result in hyperactivity/hyperreactivity of the stress system, with resultant amygdala hyperfunction (fear reaction), decreased activity of the hippocampus (defective glucocorticoid-negative feedback, cognition), and the mesocorticolimbic dopaminergic system (dysthymia, novelty-seeking, addictive behaviors), hyperactivation of the HPA axis (hypercortisolism), suppression of reproductive, growth, thyroid and immune functions, and changes in pain perception. These changes may be accompanied by abnormal childhood, adolescent and adult behaviors, including excessive fear (‘inhibited child syndrome’) and addictive behaviors, dysthymia and/or depression, and gradual development of components of the metabolic syndrome X, including visceral obesity and essential hypertension. Prenatal stress exerted during the period of sexual differentiation may be accompanied by impairment of this process with behavioral and/or somatic sequelae. The vulnerability of individuals to develop varying degrees and/or components of the above life-long syndrome is defined by as yet unidentified genetic factors, which account for up to 60% of the variance. CRH has marked kindling and glucocorticoids have strong consolidating properties, hence both of these hormones are crucial in development and can alone produce the above syndrome. CRH and glucocorticoids may act in synergy, as in acoustic startle, while glucocorticoids may suppress or stimulate CRH, as in the hypothalamus and amygdala, respectively. A CRH type 1 receptor antagonist, antalarmin, inhibits both the development and expression of conditioned fear in rats, and has anxiolytic properties in monkeys. Profound stressors, such as those from sexual abuse, may elicit the syndrome in older children, adolescents and adults. Most frequently, chronic dysthymia and/or depression may develop in association with gastrointestinal complaints and/or the premenstrual tension syndrome. A lesser proportion of individuals may develop the classic posttraumatic stress disorder, which is characterized by hypocortisolism and intrusive and avoidance symptoms; in younger individuals it may present as dissociative personality disorder.

Tissue glucocorticoid resistance/hypersensitivity syndromes

Glucocorticoids have a broad array of life-sustaining functions and play an important role in the therapy of many diseases. Thus, changes of tissue sensitivity to glucocorticoids may be associated with and influence the course and treatment of many pathologic states. Such tissue sensitivity changes may present on either side of an optimal range, respectively as glucocorticoid resistance or hypersensitivity, and may be generalized or tissue-specific. Familial/sporadic glucocorticoid resistance syndrome caused by inactivating mutations of the glucocorticoid receptor (GR) gene is a classic monogenic disorder associated with congenital, generalized glucocorticoid insensitivity, while several autoimmune, inflammatory and allergic diseases are often associated with resistance of the inflamed tissues to glucocorticoids. On the other hand, glucocorticoid hypersensitivity has been suggested in visceral obesity-related insulin resistance associated with components of the metabolic syndrome, and in the acquired immunodeficiency syndrome (AIDS) caused by human immunodeficiency virus type-1 (HIV-1) infection. Here, we have reviewed the molecular analyses of five familial and three sporadic cases of the familial/sporadic glucocorticoid resistance syndrome and discussed the possible contribution of newly identified molecules, such as HIV-1 accessory proteins Vpr and Tat, FLICE-associated huge protein (FLASH) and chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), on the molecular regulation of GR activity, as well as their possible contribution to changes in tissue sensitivity to glucocorticoids in pathologic conditions.

Generalized Glucocorticoid Resistance: Clinical Aspects, Molecular Mechanisms, and Implications of a Rare Genetic Disorder

CONTEXT Primary generalized glucocorticoid resistance is a rare genetic condition characterized by generalized, partial, target-tissue insensitivity to glucocorticoids. We review the clinical aspects, molecular mechanisms, and implications of this disorder. EVIDENCE ACQUISITION We conducted a systematic review of the published, peer-reviewed medical literature using MEDLINE (1975 through February 2008) to identify original articles and reviews on this topic. EVIDENCE SYNTHESIS We have relied on the experience of a number of experts in the field, including our extensive personal experience. CONCLUSIONS The clinical spectrum of primary generalized glucocorticoid resistance is broad, ranging from asymptomatic to severe cases of hyperandrogenism, fatigue, and/or mineralocorticoid excess. The molecular basis of the condition has been ascribed to mutations in the human glucocorticoid receptor (hGR) gene, which impair glucocorticoid signal transduction and reduce tissue sensitivity to glucocorticoids. A consequent increase in the activity of the hypothalamic-pituitary-adrenal axis compensates for the reduced sensitivity of peripheral tissues to glucocorticoids at the expense of ACTH hypersecretion-related pathology. The study of functional defects of natural hGR mutants enhances our understanding of the molecular mechanisms of hGR action and highlights the importance of integrated cellular and molecular signaling mechanisms for maintaining homeostasis and preserving normal physiology.

Stress, the Stress System and the Role of Glucocorticoids

All living organisms have developed a highly conserved and regulatory system, the stress system, to cope with a broad spectrum of stressful stimuli that threaten, or are perceived as threatening, their dynamic equilibrium or homeostasis. This neuroendocrine system consists of the hypothalamic-pituitary-adrenal (HPA) axis and the locus caeruleus/norepinephrine-autonomic nervous system. In parallel with the evolution of the homeostasis and stress concepts from ancient Greek to modern medicine, significant advances in the field of neuroendocrinology have identified the physiologic biochemical effector molecules of the stress response. Glucocorticoids, the end-products of the HPA axis, play a fundamental role in the maintenance of both resting and stress-related homeostasis and, undoubtedly, influence the physiologic adaptive reaction of the organism against stressors. If the stress response is dysregulated in terms of magnitude and/or duration, homeostasis is turned into cacostasis with adverse effects on many vital physiologic functions, such as growth, development, metabolism, circulation, reproduction, immune response, cognition and behavior. A strong and/or long-lasting stressor may precipitate and/or cause many acute and chronic diseases. Moreover, stressors during pre-natal, post-natal or pubertal life may have a critical impact on our expressed genome. This review describes the central and peripheral components of the stress system, provides a comprehensive overview of the stress response, and discusses the role of glucocorticoids in a broad spectrum of stress-related diseases.

Peripheral CLOCK Regulates Target-Tissue Glucocorticoid Receptor Transcriptional Activity in a Circadian Fashion in Man

Context and Objective Circulating cortisol fluctuates diurnally under the control of the “master” circadian CLOCK, while the peripheral “slave” counterpart of the latter regulates the transcriptional activity of the glucocorticoid receptor (GR) at local glucocorticoid target tissues through acetylation. In this manuscript, we studied the effect of CLOCK-mediated GR acetylation on the sensitivity of peripheral tissues to glucocorticoids in humans. Design and Participants We examined GR acetylation and mRNA expression of GR, CLOCK-related and glucocorticoid-responsive genes in peripheral blood mononuclear cells (PBMCs) obtained at 8 am and 8 pm from 10 healthy subjects, as well as in PBMCs obtained in the morning and cultured for 24 hours with exposure to 3-hour hydrocortisone pulses every 6 hours. We used EBV-transformed lymphocytes (EBVLs) as non-synchronized controls. Results GR acetylation was higher in the morning than in the evening in PBMCs, mirroring the fluctuations of circulating cortisol in reverse phase. All known glucocorticoid-responsive genes tested responded as expected to hydrocortisone in non-synchronized EBVLs, however, some of these genes did not show the expected diurnal mRNA fluctuations in PBMCs in vivo. Instead, their mRNA oscillated in a Clock- and a GR acetylation-dependent fashion in naturally synchronized PBMCs cultured ex vivo in the absence of the endogenous glucocorticoid, suggesting that circulating cortisol might prevent circadian GR acetylation-dependent effects in some glucocorticoid-responsive genes in vivo. Conclusions Peripheral CLOCK-mediated circadian acetylation of the human GR may function as a target-tissue, gene-specific counter regulatory mechanism to the actions of diurnally fluctuating cortisol, effectively decreasing tissue sensitivity to glucocorticoids in the morning and increasing it at night.

A Novel Point Mutation in the KCNJ5 Gene Causing Primary Hyperaldosteronism and Early-Onset Autosomal Dominant Hypertension

CONTEXT Aldosterone production in the adrenal zona glomerulosa is mainly regulated by angiotensin II, [K(+)], and ACTH. Genetic deletion of subunits of K(+)-selective leak (KCNK) channels TWIK-related acid sensitive K(+)-1 and/or TWIK-related acid sensitive K(+)-3 in mice results in primary hyperaldosteronism, whereas mutations in the KCNJ5 (potassium inwardly rectifying channel, subfamily J, member 5) gene are implicated in primary hyperaldosteronism and, in certain cases, in autonomous glomerulosa cell proliferation in humans. OBJECTIVE The objective of the study was to investigate the role of KCNK3, KCNK5, KCNK9, and KCNJ5 genes in a family with primary hyperaldosteronism and early-onset hypertension. PATIENTS AND METHODS Two patients, a mother and a daughter, presented with severe primary hyperaldosteronism, bilateral massive adrenal hyperplasia, and early-onset hypertension refractory to medical treatment. Genomic DNA was isolated and the exons of the entire coding regions of the above genes were amplified and sequenced. Electrophysiological studies were performed to determine the effect of identified mutation(s) on the membrane reversal potentials. RESULTS Sequencing of the KCNJ5 gene revealed a single, heterozygous guanine to thymine (G → T) substitution at nucleotide position 470 (n.G470T), resulting in isoleucine (I) to serine (S) substitution at amino acid 157 (p.I157S). This mutation results in loss of ion selectivity, cell membrane depolarization, increased Ca(2+) entry in adrenal glomerulosa cells, and increased aldosterone synthesis. Sequencing of the KCNK3, KCNK5, and KCNK9 genes revealed no mutations in our patients. CONCLUSIONS These findings explain the pathogenesis in a subset of patients with severe hypertension and implicate loss of K(+) channel selectivity in constitutive aldosterone production.

Blood pressure in children and adolescents with congenital adrenal hyperplasia (21-hydroxylase deficiency): a preliminary report.

background Classical congenital adrenal hyperplasia (CAH) is characterized by a defect in cortisol and aldosterone secretion, adrenal hyperandrogenism, impaired adrenal medullary function and insulin insensitivity. The latter along with the increased tendency towards obesity raises questions whether other cardiovascular risk factors are altered in CAH.

Circadian endocrine rhythms: the hypothalamic–pituitary–adrenal axis and its actions

The stress system effectively restores the internal balance—or homeostasis—of living organisms in the face of random external or internal changes, the stressors. This highly complex system helps organisms to provide a series of neuroendocrine responses to stressors—the stress response—through coordinated activation of the hypothalamic–pituitary–adrenal (HPA) axis and the locus coeruleus/norepinephrine autonomic nervous systems. In addition to stressors, life is influenced by daily light/dark changes due to the 24‐h rotation of Earth. To adjust to these recurrent day/night cycles, the biological clock system employs the heterodimer of transcription factors circadian locomotor output cycle kaput/brain–muscle–arnt–like protein 1 (CLOCK/BMAL1), along with a set of other transcription factors, to regulate the circadian pattern of gene expression. Interestingly, the stress system, through the HPA axis, communicates with the clock system; therefore, any uncoupling or dysregulation could potentially cause several disorders, such as metabolic, autoimmune, and mood disorders. In this review, we discuss the biological function of the two systems, their interactions, and the clinical implications of their dysregulation or uncoupling.

Effects of Child- and Adolescent-Onset Endogenous Cushing Syndrome on Bone Mass, Body Composition, and Growth: A 7-Year Prospective Study Into Young Adulthood†

The long‐term effects on bone and fat mass in children with endogenous CS are unknown. In 14 children followed for 3–7 years into young adulthood after cure of CS, whereas bone mass largely recovered, persisting increases in total body and visceral fat suggests an increase risk of the metabolic syndrome.

Familial/Sporadic Glucocorticoid Resistance: Clinical Phenotype and Molecular Mechanisms

Abstract: Glucocorticoids regulate a variety of biologic processes and exert profound influences on many physiologic functions. Their actions are mediated by the glucocorticoid receptor (GR), which belongs to the nuclear receptor family of ligand‐dependent transcription factors. Alterations in tissue sensitivity to glucocorticoids may manifest as states of resistance or hypersensitivity. Glucocorticoid resistance is a rare, familial or sporadic, condition characterized by generalized, partial target‐tissue resistance to glucocorticoids. Compensatory elevations in circulating adrenocorticotropic hormone (ACTH) concentrations lead to increased production of adrenal steroids with mineralocorticoid and/or androgenic activity and their corresponding clinical manifestations, as well as increased urinary free‐cortisol excretion in the absence of symptomatology suggestive of hypercortisolism. The molecular basis of the condition has been ascribed to mutations in the GR gene, which impair normal glucocorticoid signal transduction, altering tissue sensitivity to glucocorticoids. The present review focuses on the mechanisms of GR action and the clinical manifestations and molecular mechanisms of familial/sporadic glucocorticoid resistance.