Glucocorticoid receptor variants: clinical implications

Common polymorphisms in the glucocorticoid receptor gene are associated with adrenocortical responses to psychosocial stress

Chronic dysregulation of hypothalamus-pituitary-adrenal axis activity is related to several stress-related disorders. Evidence suggests that polymorphisms in the glucocorticoid receptor (GR) gene may have an impact on this neuroendocrine system. In the present investigation, 112 healthy males were studied to estimate the impact of three GR gene polymorphisms (BclI RFLP, N363S, ER22/23EK) on cortisol and ACTH responses to psychosocial stress (Trier Social Stress Test) and pharmacological stimulation (1 microg ACTH(1-24), 0.5 mg dexamethasone). Because only four ER22/23EK heterozygotes were identified, these subjects were not statistically analyzed. Compared with subjects with the wild-type GR genotype (n = 36), 363S allele carriers (n = 10) showed significantly increased salivary cortisol responses to stress, whereas the BclI genotype GG (n = 18) was associated with a diminished cortisol response. BclI heterozygotes and homozygotes (GG) exhibited a trend toward lower ACTH responses, compared with wild-type subjects and 363S carriers. The cortisol response to ACTH(1-24) administration was not significantly different between genotypes. After dexamethasone ingestion, 363S carriers showed a trend toward an enhanced cortisol suppression. This is the first report documenting an impact of GR gene polymorphisms on cortisol (and perhaps ACTH) responses to psychosocial stress. These variants may contribute to the individual vulnerability for hypothalamus-pituitary-adrenal-related disorders.

Hypothalamic-pituitary-adrenocortical system and mood disorders: highlights from mutant mice

In recent years, refined molecular technologies and the generation of genetically engineered mice have allowed to specifically target individual genes involved in the regulation of the hypothalamic-pituitary-adrenocortical (HPA) system. Given the fundamental role of the corticotropin-releasing hormone (CRH) system in anxiety, stress-associated pathologies, and mood disorders, we describe genetic modifications of the genes that encode proteins integral to the CRH/CRH receptor system with particular emphasis on conditional gene-targeting strategies. The profile of results, consistent with current knowledge of CRH function from more traditional assays, indicates that enhancement of the CRH function is associated with an activation of the HPA system, an anxious phenotype, alterations in cognitive performance, reductions in food intake, and disturbances of autonomic functions. In general, blockade of CRH activity produces the opposite effects, namely an anxiety-reduced phenotype. Molecular genetic strategies for conditional inactivation or overexpression of the glucocorticoid receptor contribute to our understanding of the genetics of endocrine activity and behavior, the most complex form of biological organization. In addition, we introduce mice with a genetic manipulation in the function of the blood-brain barrier as an animal model for the study of neuroendocrine regulation and, in particular, of HPA system activity. By use of mice deficient for abcb1- (also called multidrug resistance gene 1, mdr1-) type P glycoproteins, it was shown most recently that abcb1-type P glycoproteins control the access of endogenous glucocorticoids into the central nervous system. Thus, the ABCB1-type P glycoprotein function exerts a profound influence on activity and regulation of the HPA system under both basal conditions and during stress. Taken together, these genetically engineered mice are valuable tools for increasing our understanding of HPA system dysregulation in anxiety and stress-related pathologies, including human affective disorders. The identification and detailed characterization of these molecular pathways will ultimately lead to the development of novel neuropharmacological intervention strategies.

Polymorphisms in Genes Involved in the Corticosteroid Response and the Outcome of Childhood Acute Lymphoblastic Leukemia

BACKGROUND

Considerable variability in sensitivity to corticosteroids (CS) has been observed among individuals with regard to both the natural and synthetic compounds. The role of genetic polymorphisms in modulating CS function, and hence in disease susceptibility, has been extensively analyzed. Their impact on therapeutic response still remains to be explored. The role of cytochrome P450 (CYP) 3A4 in corticosteroid metabolism, and that of the glucocorticoid receptor (NR3C1) in regulation of responsive genes, renders CYP3A4 and NR3C1 polymorphisms as potential candidates for pharmacogenetic analysis.

AIM

The aim of the study was to analyze the role of these polymorphisms in the outcome of a disease treated with CS drugs.

METHODS

Towards this aim we analyzed the CYP3A4-290A/G substitution and three NR3C1 polymorphisms (200G/A, 1220A/G and BclI RFLP) in 222 children with acute lymphoblastic leukemia (ALL) whose treatment protocols, among other components, contained corticosteroid drugs.

RESULTS

The analysis of survival probabilities in relation to the indicated genotypes showed only an association between homozygosity for allele G of the NR3C1 BclI RFLP polymorphism and overall survival (univariate and multivariate hazard ratio [HR] 2.7, 95% confidence interval [CI] 1.0, 7.6 and 5.2, 95% CI 1.4, 18.9, respectively). The association reflects a correlation with disease progression and prognosis, and may vary depending on risk of relapse.

CONCLUSION

A reduction in survival probability in children with ALL was associated with homozygosity for G allele of the NR3C1BclI RFLP polymorphism, particularly in certain patient subgroups. Further analysis is required to replicate this finding and to understand the mechanism underlying the observed association.

CRH, Stress, and Major Depression: A Psychobiological Interplay

Major depressive disorder (MDD) is a complex disease and is one of the leading causes of disability in our society. The provoking factors are multiple; acute and chronic psychological stress, severe early trauma experiences, somatic disease, and genetic factors all play a role. This review focuses on hyperdrive of corticotropin-releasing hormone (CRH) as the fundamental neurobiological correlate of MDD. CRH plays a key role in the adaptation to acute stress, but chronic CRH hyperdrive leads to a number of disadvantageous emotional and somatic effects. The evidence that the HPA axis is hyperactive in MDD, probably as a result of a primary hyperdrive of CRH, comes from multiple sources: biochemical studies, functional HPA axis tests, neuroimaging and postmortem studies, and clinical trials with HPA axis-related compounds. The liability to develop CRH hyperdrive is probably partly genetic. For a number of relevant genes, transgenic animal studies and human association studies indicate a role in HPA axis regulation and the liability to develop CRH hyperdrive. These data are reviewed. Finally, early adverse experience can produce a lasting effect on HPA axis regulation as well, probably leading to a lifelong tendency to develop chronic CRH hyperdrive in response to stress. This has been shown in a number of animal studies, and recently some data in humans with early trauma have become available as well. Taken together, these findings allow formulating an integrative hypothesis, with CRH hyperdrive at the core, bridging the old dichotomy between biology and psychology in our thinking about MDD.

Glucocorticoids and invasive fungal infections

Since the 1990s, opportunistic fungal infections have emerged as a substantial cause of morbidity and mortality in profoundly immunocompromised patients. Hypercortisolaemic patients, both those with endogenous Cushing's syndrome and, much more frequently, those receiving exogenous glucocorticoid therapy, are especially at risk of such infections. This vulnerability is attributed to the complex dysregulation of immunity caused by glucocorticoids. We critically review the spectrum and presentation of invasive fungal infections that arise in the setting of hypercortisolism, and the ways in which glucocorticoids contribute to their pathogenesis. A better knowledge of the interplay between glucocorticoid-induced immunosuppression and invasive fungal infections should assist in earlier recognition and treatment of such infections. Efforts to decrease the intensity of glucocorticoid therapy should help to improve outcomes of opportunistic fungal infections.

Relationship between dexamethasone-inhibited lysozyme activity in peripheral mononuclear leukocytes and the cortisol and glucocorticoid receptor response to dexamethasone

The assessment of lysozyme activity in mononuclear leukocytes (MNLs) following the in vitro administration of dexamethasone (DEX) provides a measure of peripheral glucocorticoid sensitivity. The goal of the present study was to determine the relationship between the IC(50) of lysozyme activity following such challenge, and the cortisol response to oral administration of 0.50 mg DEX in 18 healthy subjects. The results demonstrated a robust association between the IC(50) and both cortisol decline and percent suppression of cortisol in response to low-dose DEX. However, this measure was uncorrelated with pre or post DEX cortisol levels or GR number. The high correlation between the inhibitory effect of DEX on lysozyme synthesis and two measures reflecting cortisol suppression in response to oral DEX reflects the similarities of GC responsiveness in both in vivo and in vitro models, and suggests that the in vitro assessment of lysozyme activity in MNLs may be useful in the study of neuropsychiatric or other clinical disorder.

Functional analysis of three genetic polymorphisms in the glucocorticoid receptor gene

Glucocorticoids are widely used as potent anti-inflammatory drugs. Glucocorticoids exert their pharmacological effects by binding to a glucocorticoid receptor (GR), which promotes expression of its target genes or suppresses transcription mediated by other transcriptional factors, such as nuclear factor-kappaB (NF-kappaB). To identify genetic polymorphisms affecting glucocorticoid responses, the GR gene was sequenced, and two novel single nucleotide alterations, 1510A>T (T504S) and 1952C>T (S651F), were identified in addition to an adenine base insertion at nucleotide 2314 (2314insA). mRNA expression levels of T504S and S651F were comparable with that of the wild type (WT), whereas the mRNA level of 2314insA was reduced to approximately 36% of the WT level. Protein expression was reduced to approximately 66% of WT levels in S651F and to approximately 6% in 2314insA. No significant change was seen in the T504S variant levels. The instability of the 2314insA mRNA, S651F protein, and 2314insA protein was confirmed by time course experiments. The transcriptional activity of S651F and 2314insA was also reduced to approximately 63 and 2% of the WT levels, respectively, in the luciferase reporter assay. Moreover, the inhibitory effect of GR on NF-kappaB transactivation was reduced to approximately 81 and 12% of the WT levels for S651F and 2314insA, respectively. These results indicated that the overall transcriptional activity and inhibitory effect on NF-kappaB transactivation of S651F and 2314insA have partially reduced and almost abrogated, respectively, almost paralleling their reduced protein expression levels caused by mRNA and/or protein instabilities. Thus, these two variations were suggested to influence the response to glucocorticoid treatment.

Very low levels of the glucocorticoid receptor beta isoform in the human hippocampus as shown by Taqman RT-PCR and immunocytochemistry

The hippocampus is an important target for glucocorticoid hormones. Glucocorticoid receptor (GR) mediated feedback in this area is important for control of behavioural adaptation. An alternative splice variant, the GRbeta (GRbeta) isoform, does not bind ligand and has been proposed to inhibit classic GRalpha-mediated transactivation of target genes. Hence, an increased ratio of GRbeta to GRalpha may induce relative corticosteroid-resistance, as e.g. presumed to occur in major depression. To investigate whether GRbeta is involved in the human hippocampus, we studied GRalpha and GRbeta expression levels in postmortem hippocampal tissue of control subjects by quantitative PCR (Taqman RT-PCR) and immunocytochemistry. Taqman RT-PCR demonstrated a very low relative abundance of GRbeta in the human hippocampus (GRalpha:GRbeta ratio approximately 14,500:1). Immunohistochemical analysis confirmed the occurrence of isolated profiles indeed displaying nuclear staining in the main hippocampal subregions. Subsequent double immunofluorescent analysis revealed that >98% of these GRbeta positive cells were double positive for leucocyte common antigen, that identifies exclusively blood-derived cells of haematopoietic origin, including microglia. We conclude that GRbeta is present in very low amounts in the control human hippocampus, and that of these low numbers of cells, notably, almost all are derived from blood which is inevitably present in postmortem tissue. A functionally relevant role for the GRbeta in control of the human hippocampus is therefore not very likely. Whether this is altered in disease conditions awaits further research.

Rapidly developing Cushing syndrome in a 4-year-old patient during combined treatment with itraconazole and inhaled budesonide

A 4-year-old boy with cystic fibrosis developed hypertension, rapid weight gain and a moon face 2 weeks after starting a combined treatment of oral itraconazole and inhaled budesonide for a suspected allergic bronchopulmonary aspergillosis. Adrenal suppression was documented and found to persist 3 months after stopping this combined treatment.

CONCLUSION

To the best of our knowledge, this is the first time that an iatrogenic Cushing syndrome in a young child with cystic fibrosis after such combined treatment is reported. The inhibition of cytochrome P4503A by intraconazole and a higher glucocorticoid tissue sensitivity is suggested as the underlying mechanism.

HPA axis and memory

The hormones of the hypothalamus-pituitary-adrenal (HPA) axis influence memory in situations of acute and chronic stress. The present review tries to summarize the current state of knowledge by describing the enhancing as well as the impairing effects of stress or glucocorticoid (GC) treatment documented in animals and humans. GCs secreted during the acquisition of a stressful task facilitate consolidation. However, acute stress (or GC treatment) unrelated to the task impairs performance. The effects of acute stress are additionally modulated by gender, age and the emotional valence of the learning material. Chronic stress in rodents has mostly impairing effects on memory and hippocampal integrity. However, other regions of the brain, such as the prefrontal cortex, are also sensitive to stress. In humans, similar observations have been reported in several patient populations as well as in older subjects. The potential to reverse these effects using behavioural or pharmacological approaches needs to be explored.