Stress, glucocorticoid hormones, and hippocampal neural progenitor cells: implications to mood disorders

The hypothalamic-pituitary-adrenal (HPA) axis and its end-effectors glucocorticoid hormones play central roles in the adaptive response to numerous stressors that can be either internal or external. Thus, this system has a strong impact on the brain hippocampus and its major functions, such as cognition, memory as well as behavior and mood. The hippocampal area of the adult brain contains neural stem cells or more committed neural progenitor cells, which retain throughout the human life the ability of self-renewal and to differentiate into multiple neural cell lineages, such as neurons, astrocytes and oligodendrocytes. Importantly, these characteristic cells contribute significantly to the above-indicated functions of the hippocampus, while various stressors and glucocorticoids influence proliferation, differentiation and fate of these cells. This review offers an overview of the current understanding on the interactions between the HPA axis/glucocorticoid stress-responsive system and hippocampal neural progenitor cells by focusing on the actions of glucocorticoids. Also addressed is a further discussion on the implications of such interactions to the pathophysiology of mood disorders

G protein β interacts with the glucocorticoid receptor and suppresses its transcriptional activity in the nucleus

Extracellular stimuli that activate cell surface receptors modulate glucocorticoid actions via as yet unclear mechanisms. Here, we report that the guanine nucleotide-binding protein (G protein)–coupled receptor-activated WD-repeat Gβ interacts with the glucocorticoid receptor (GR), comigrates with it into the nucleus and suppresses GR-induced transactivation of the glucocorticoid-responsive genes. Association of Gγ with Gβ is necessary for this action of Gβ. Both endogenous and enhanced green fluorescent protein (EGFP)–fused Gβ2 and Gγ2 proteins were detected in the nucleus at baseline, whereas a fraction of EGFP-Gβ2 and DsRed2-GR comigrated to the nucleus or the plasma membrane, depending on the exposure of cells to dexamethasone or somatostatin, respectively. Gβ2 was associated with GR/glucocorticoid response elements (GREs) in vivo and suppressed activation function-2–directed transcriptional activity of the GR. We conclude that the Gβγ complex interacts with the GR and suppresses its transcriptional activity by associating with the transcriptional complex formed on GR-responsive promoters

Liver X Receptors Regulate the Transcriptional Activity of the Glucocorticoid Receptor: Implications for the Carbohydrate Metabolism

GLUCOCORTICOIDS are steroid hormones that strongly influence intermediary carbohydrate metabolism by increasing the transcription rate of glucose-6-phosphatase (G6Pase), a key enzyme of gluconeogenesis, and suppress the immune system through the glucocorticoid receptor (GR). The liver X receptors (LXRs), on the other hand, bind to cholesterol metabolites, heterodimerize with the retinoid X receptor (RXR), and regulate the cholesterol turnover, the hepatic glucose metabolism by decreasing the expression of G6Pase, and repress a set of inflammatory genes in immune cells. Since the actions of these receptors overlap with each other, we evaluated the crosstalk between the GR- and LXR-mediated signaling systems. Transient transfection-based reporter assays and gene silencing methods using siRNAs for LXRs showed that overexpression/ligand (GW3965) activation of LXRs/RXRs repressed GR-stimulated transactivation of certain glucocorticoid response element (GRE)-driven promoters in a gene-specific fashion. Activation of LXRs by GW3965 attenuated dexamethasone-stimulated elevation of circulating glucose in rats. It also suppressed dexamethasone-induced mRNA expression of hepatic glucose-6-phosphatase (G6Pase) in rats, mice and human hepatoma HepG2 cells, whereas endogenous, unliganded LXRs were required for dexamethasone-induced mRNA expression of phosphoenolpyruvate carboxylase. In microarray transcriptomic analysis of rat liver, GW3965 differentially regulated glucocorticoid-induced transcriptional activity of about 15% of endogenous glucocorticoid-responsive genes. To examine the mechanism through which activated LXRs attenuated GR transcriptional activity, we examined LXRα/RXRα binding to GREs. Endogenous LXRα/RXRα bound GREs and inhibited GR binding to these DNA sequences both in in vitro and in vivo chromatin immunoprecipitation assays, while their recombinant proteins did so on classic or G6Pase GREs in gel mobility shift assays. We propose that administration of LXR agonists may be beneficial in glucocorticoid treatment- or stress-associated dysmetabolic states by directly and gene-specifically attenuating the transcriptional activity of the GR on glucose and/or lipid metabolism

The Role of S-Palmitoylation of the Human Glucocorticoid Receptor (hGR) in Mediating the Nongenomic Glucocorticoid Actions

Background: Many rapid nongenomic glucocorticoid actions are mediated by membrane-bound glucocorticoid receptors (GRs). S-palmitoylation is a lipid post-translational modification that mediates the membrane localization of some steroid receptors. A highly homologous amino acid sequence (663YLCM KTLLL671) is present in the ligand-binding domain of hGRα, suggesting that hGRα might also undergo S-palmitoylation. Aim: To investigate the role of the motif 663YLCMKTLLL671 in membrane localization of the hGRα and in mediating rapid nongenomic glucocorticoid signaling. Methods and Results: We showed that the mutant receptors hGRαY663A, hGRαC665A and hGRαLL670/671AA, and the addition of the palmitoylation inhibitor 2-bromopalmitate did not prevent membrane localization of hGRα and co-localization with caveolin-1, and did not influence the biphasic activation of mitogen-activated protein kinase (MAPK) signaling pathway in the early time points. Finally, the hGRα was not shown to undergo S-palmitoylation. Conclusions: The motif 663YLCMKTLLL671 does not play a role in membrane localization of hGRα and does not mediate the nongenomic glucocorticoid actions.  

Cohort profile: molecular signature in pregnancy (MSP): longitudinal high-frequency sampling to characterise cross-omic trajectories in pregnancy in a resource-constrained setting

A successful pregnancy relies on the interplay of various biological systems. Deviations from the norm within a system or intersystemic interactions may result in pregnancy-associated complications and adverse pregnancy outcomes. Systems biology approaches provide an avenue of unbiased, in-depth phenotyping in health and disease. The molecular signature in pregnancy (MSP) cohort was established to characterise longitudinal, cross-omic trajectories in pregnant women from a resource constrained setting. Downstream analysis will focus on characterising physiological perturbations in uneventful pregnancies, pregnancy-associated complications and adverse outcomes.; First trimester pregnant women of Karen or Burman ethnicity were followed prospectively throughout pregnancy, at delivery and until 3 months post partum. Serial high-frequency sampling to assess whole blood transcriptomics and microbiome composition of the gut, vagina and oral cavity, in conjunction with assessment of gene expression and microbial colonisation of gestational tissue, was done for all cohort participants.; 381 women with live born singletons averaged 16 (IQR 15-18) antenatal visits (13 094 biological samples were collected). At 5% (19/381) the preterm birth rate was low. Other adverse events such as maternal febrile illness 7.1% (27/381), gestational diabetes 13.1% (50/381), maternal anaemia 16.3% (62/381), maternal underweight 19.2% (73/381) and a neonate born small for gestational age 20.2% (77/381) were more often observed than preterm birth.; Results from the MSP cohort will enable in-depth characterisation of cross-omic molecular trajectories in pregnancies from a population in a resource-constrained setting. Moreover, pregnancy-associated complications and unfavourable pregnancy outcomes will be investigated at the same granular level, with a particular focus on population relevant needs such as effect of tropical infections on pregnancy. More detailed knowledge on multiomic perturbations will ideally result in the development of diagnostic tools and ultimately lead to targeted interventions that may disproportionally benefit pregnant women from this resource-limited population.; NCT02797327

Chrousos syndrome: a seminal report, a phylogenetic enigma and the clinical implications of glucocorticoid signalling changes

P>Background Glucocorticoids regulate a broad spectrum of physiologic functions and play important roles in resting and stress homeostasis. Their actions are mediated by the nuclear glucocorticoid receptor (GR). Design Using a patient as a stimulus, we reviewed briefly the area of Primary Generalized Glucocorticoid Resistance in man and nonhuman primates. Results In man, Primary Generalized Glucocorticoid Resistance is a rare sporadic or familial syndrome characterized by target-tissue insensitivity to glucocorticoids and compensatory elevations in adrenocorticotropic hormone (ACTH), leading to increased secretion of cortisol and adrenal steroids with mineralocorticoid and/or androgenic activity, and causing hypermineralocorticoidism and hyperandrogenism without Cushing stigmata. The presentation, diagnosis and therapy of this condition are summarized. Many or, most likely, all New World primates have markedly elevated cortisol and ACTH, and resistance to dexamethasone suppression, without any pathology. These primates in fact have ‘pan-steroid/sterol’ resistance, including all five steroid hormones and 1,25-dihydroxy-vitamin D. In humans, the molecular basis of Primary Generalized Glucocorticoid Resistance has been mainly ascribed to recent mutations in the GR gene, which impair glucocorticoid signal transduction. In contrast, in the primates, steroid/sterol signalling systems have adapted under yet unknown selective pressures or genetic drift over many million years. Of course, other molecules of the signaling pathways may also be involved in both states. There are now a host of human states associated with tissue-specific pathologic glucocorticoid target tissue changes. These include allergic, autoimmune, inflammatory and lymphoproliferative disorders. Conclusions In recognition of Professor George P. Chrousos’ extensive ground-breaking research in this field, and for the sake of brevity, we propose that ‘Chrousos syndrome’ is used instead of ‘Primary Generalized Familial or Sporadic Glucocorticoid Resistance’

Acetylation-mediated epigenetic regulation of glucocorticoid receptor activity: Circadian rhythm-associated alterations of glucocorticoid actions in target tissues

Glucocorticoids influence organ functions through the glucocorticoid receptor, a protein acetylated and deacetylated by several histone acetyltransferases and deacetylases. We reported that the circadian rhythm-related transcription factor “Clock”, a key component of the biological CLOCK with inherent histone acetyltransferase activity, acetylates glucocorticoid receptor lysines within its hinge region-a “lysine cluster” containing a KXKK motif-and represses its transcriptional activity. This Clock-induced repression of the glucocorticoid receptor activity is inversely phased to the diurnally circulating glucocorticoids and may act as a local counter regulatory mechanism to the actions of these hormones. Importantly, uncoupling of the central CLOCK-regulated hypothalamic-pituitary-adrenal axis and peripheral CLOCK-mediated alterations of glucocorticoid action, such as chronic stress and frequent trans-time zone travel or night-shift work, may cause functional hypercortisolism and contribute to various pathologies. Thus, acetylation-mediated epigenetic regulation of the glucocorticoid receptor may be essential for the maintenance of proper time-integrated glucocorticoid action, significantly influencing human well-being and longevity. Published by Elsevier Ireland Ltd

Ikaros transcription factors: flying between stress and inflammation

The hypothalamic-pituitary-adrenal axis (a major component of the stress system) and the immune system contribute to the maintenance of homeostasis at rest and during stress. Because of their essential roles for the survival of self and species, the activities of these systems have evolutionarily developed in parallel and are intertwined at many levels. In this issue of the JCI, Ezzat et al. demonstrate that Ikaros, a differentiation factor of leukocyte lineage, also influences the maturation of the fetal pituitary corticotroph and, hence, the secretion of adrenocorticotropic hormone before and after birth. These results indicate that Ikaros is an ontogenetic and phylogenetic integrator of the stress and immune systems and that abnormalities in its function may produce endocrine and/or immune pathologies

Glucocorticoid Signaling in the Cell Expanding Clinical Implications to Complex Human Behavioral and Somatic Disorders

Glucocorticoids contribute to the maintenance of basal and stress-related homeostasis in all higher organisms, and influence a large proportion of the expressed human genome, and their effects spare almost no organs or tissues. Glucocorticoids regulate many functions of the central nervous system, such as arousal, cognition, mood, sleep, the activity and direction of intermediary metabolism, the maintenance of a proper cardiovascular tone, the activity and quality of the immune and inflammatory reaction, including the manifestations of the sickness syndrome, and growth and reproduction. The numerous actions of glucocorticoids are mediated by a set of at least 16 glucocorticoid receptor (GR) isoforms forming homo- or hetero-dimers. The GRs consist of multifunctional domain proteins operating as ligand-dependent transcription factors that interact with many other cell signaling systems, including large and small G proteins. The presence of multiple GR monomers and homo- or hetero-dimers expressed in a cell-specific fashion at different quantities with quantitatively and qualitatively different transcriptional activities suggest that the glucocorticoid signaling system is highly stochastic. Glucocorticoids are heavily involved in human pathophysiology and influence life expectancy. Common behavioral and/or somatic complex disorders, such as anxiety, depression, insomnia, chronic pain and fatigue syndromes, obesity, the metabolic syndrome, essential hypertension, diabetes type 2, atherosclerosis with its cardiovascular sequelae, and osteoporosis, as well as autoimmune inflammatory and allergic disorders, all appear to have a glucocorticoid-regulated component