Altered expression of p53 mRNA in the brain and pituitary during repeated immobilization stress: negative correlation with glucocorticoid receptor mRNA levels

Chronic stress from adolescence to adulthood increases adiposity and anxiety in rats with decreased expression of Krtcap3

We previously identified Keratinocyte-associated protein 3, Krtcap3, as a novel adiposity gene, but subsequently found that its impact on adiposity may depend on environmental stress. To more thoroughly understand the connection between Krtcap3, adiposity, and stress, we exposed wild-type (WT) and Krtcap3 knock-out (KO) rats to chronic stress then measured adiposity and behavioral outcomes. We found that KO rats displayed lower basal stress than WT rats under control conditions and exhibited metabolic and behavioral responses to chronic stress exposure. Specifically, stress-exposed KO rats gained more weight, consumed more food when socially isolated, and displayed more anxiety-like behaviors relative to control KO rats. Meanwhile, there were minimal differences between control and stressed WT rats. At study conclusion stress-exposed KO rats had increased corticosterone (CORT) relative to control KO rats with no differences between WT rats. In addition, KO rats, independent of prior stress exposure, had an increased CORT response to removal of their cage-mate (psychosocial stress), which was only seen in WT rats when exposed to chronic stress. Finally, we found differences in expression of the glucocorticoid receptor, Nr3c1, in the pituitary and colon between control and stress-exposed KO rats that were not present in WT rats. These data support that Krtcap3 expression affects stress response, potentially via interactions with Nr3c1, with downstream effects on adiposity and behavior. Future work is necessary to more thoroughly understand the role of Krtcap3 in the stress response.

Expression of glucocorticoid and mineralocorticoid receptor genes co-varies with a stress-related colour signal in barn owls

Glucocorticoid hormones are important intermediates between an organism and its environment. They enable an organism to adjust its behavioural and physiological processes in response to environmental changes by binding to mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) expressed in many tissues, including the integument. The regulation of glucocorticoids co-varies with melanin-based colouration in numerous species, an association that might result from pleiotropic effects of genes in the melanocortin system and evolve within a signalling context. Most studies have focused on the circulating levels of glucocorticoids disregarding the receptors that mediate their action, and that might partly account for the covariation between the regulation of stress and melanin-based colouration. We investigated the association of the expression levels of GR and MR genes with melanin-based colouration in the growing feathers of nestling barn owls (Tyto alba). We also explored the association between GR and MR expression levels and the expression of genes related to the melanocortin system and melanogenesis to better understand the origin of the link between the expression of receptors to which corticosterone binds and melanin-based colouration. Nestling barn owls displaying larger eumelanic black feather spots expressed GR and MR at lower levels than smaller-spotted individuals. However, we found that the expression of the GR and MR genes was positively rather than negatively correlated with the expression of genes involved in the deposition of melanin pigments at the time we sampled the nestlings. This provides mixed evidence of the association between melanin-based traits and MR and GR gene expression. The finding that the expression of GR and MR was positively associated with the expression of the PCSK2 gene (encoding one of the protein convertase responsible for the production of hormone peptide ACTH and α-MSH) suggests that the melanocortin system may be implicated in the establishment of the covariation between melanin-based colour and the expression of receptors to which glucocorticoids bind. However, further studies investigating the expression of melanin-based traits with stress-related endpoints at different time points of feather development will be necessary to understand better the proximate mechanism linking melanin-based traits with stress.

Sub-acute restraint stress progressively increases oxidative/nitrosative stress and inflammatory markers while transiently upregulating antioxidant gene expression in the rat hippocampus

We have previously demonstrated that acute stress decreases neuronal nitric oxide synthase (NOS) expression in the hippocampus despite increased concentrations of nitric oxide which may indicate feedback inhibition of neuronal NOS expression via inducible NOS-derived nitric oxide. Moreover, the hippocampus undergoes an initial oxidative/nitrosative insult that is rapidly followed by upregulation of protective antioxidants, including the zinc-binding metallothioneins, in order to counter this and restore redox balance following acute stress exposure. In the present study, we have utilized indicators of oxidative/nitrosative stress, members of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway, antioxidant metallothioneins, and neuroinflammatory markers to observe the changes occurring in the hippocampus following short term repeated stress exposure. Male Wistar rats were subjected to control conditions or 6 h of restraint stress applied for 1, 2, or 3 days (n = 8 per group) after which the hippocampus was isolated for redox assays and relative gene expression. The hippocampus showed increased oxidative stress, transient dys-homeostasis of total zinc, and increased expression of the Nrf2 pathway members. Moreover, repeated stress increased nitrosative status, nitric oxide metabolites, and 3-nitrotyrosine, indicative of nitrosative stress in the hippocampus. However, levels of neuronal NOS decreased over all stress treatment groups, while increases were observed in inducible NOS and xanthine dehydrogenase. In addition to inducible NOS, mRNA expression of other inflammatory markers including interleukin-6 and interleukin-1β also increased even in the presence of increased anti-inflammatory glucocorticoids. Together, these results demonstrate that despite increases in antioxidant expression, sub-acute stress causes an inflammatory phenotype in the hippocampus by inducing oxidative/nitrosative stress, zinc dys-homeostasis, and the accumulation of nitrotyrosinated proteins which is likely driven by increased inducible NOS signaling.

Rapid Down-Regulation of Glucocorticoid Receptor Gene Expression in the Dentate Gyrus after Acute Stress in vivo: Role of DNA Methylation and MicroRNA Activity

BACKGROUND

Although glucocorticoid receptors (GRs) in the hippocampus play a vital role in the regulation of physiological and behavioural responses to stress, the regulation of receptor expression remains unclear. This work investigates the molecular mechanisms underpinning stress-induced changes in hippocampal GR mRNA levels in vivo.

METHODS

Male Wistar rats were killed either under baseline conditions or after forced swim stress (FSS; 15 min in 25°C water). Rat hippocampi were micro-dissected (for mRNA, microRNA, and DNA methylation analysis) or frozen whole (for chromatin immunoprecipitation). In an additional experiment, rats were pre-treated with RU486 (a GR antagonist) or vehicle.

RESULTS

FSS evoked a dentate gyrus-specific reduction in GR mRNA levels. This was related to an increased DNMT3a protein association with a discreet region of the Nr3c1 (GR gene) promoter, shown here to undergo increased DNA methylation after FSS. FSS also caused a time-dependent increase in the expression of miR-124a, a microRNA known to reduce GR mRNA expression, which was inversely correlated with a reduction in GR mRNA levels 30 min after FSS. FSS did not affect GR binding to a putative negative glucocorticoid response element within the Nr3c1 gene.

CONCLUSIONS

Acute stress results in decreased GR mRNA expression specifically in the dentate gyrus. Our results indicate that a complex interplay of multiple molecular mechanisms - including increased DNA methylation of discrete CpG residues within the Nr3c1 gene, most likely facilitated by DNMT3a, and increased expression of miR-124a - could be responsible for these changes.

p53 cooperates with Sp1 to regulate breed-dependent expression of glucocorticoid receptor in the liver of preweaning piglets

Previous studies indicate that Chinese indigenous pig breeds demonstrate distinct pattern of glucocorticoid receptor (GR) expression, which is associated with their unique growth and metabolic phenotypes. Here we sought to unravel the transcriptional mechanisms underlying the breed-specific hepatic GR expression in preweaning Chinese Erhualian (EHL) and Western Large White (LW) piglets. Total GR mRNA and the predominant GR mRNA variant 1-9/10 were expressed significantly higher in EHL compared with LW piglets (P<0.01), which was associated with more enriched histone H3 acetylation on 1-9/10 promoter (P<0.05). Nuclear content of transcription factor specificity protein 1 (Sp1) was significantly lower in EHL piglets, yet its binding to GR 1-9/10 promoter was significantly higher in EHL piglets, as revealed by chromatin immunoprecipitation assays. Although p53 binding to GR promoter 1-9/10 did not differ between breeds, expression of p53 mRNA and protein, as well as its binding to Sp1, were significantly higher in EHL piglets. Moreover, p53 activator doxorubicin significantly enhanced GR 1-9/10 promoter activity in HepG2 cells at 100 nM, which was associated with significantly higher protein content of p53 and GR. Sp1 inhibitor, mithramycin A, significantly inhibited (P<0.05) the basal activity of GR promoter 1-9/10 and completely blocked doxorubicin -induced activation of GR promoter 1-9/10. These data indicate that higher hepatic GR expression in EHL piglets attributes mainly to the enhanced transcription of GR promoter 1-9/10, which is achieved from breed-specific interaction of p53 and Sp1 on porcine GR 1-9/10 promoter.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Regulation of glucocorticoid receptor transcription and nuclear translocation during single and repeated immobilization stress

We have previously reported reduced glucocorticoid receptor (GR) mRNA levels in the hippocampus and hypothalamic paraventricular nucleus (PVN) during repeated immobilization, which is potentially associated with persistent activation of the hypothalamic-pituitary-adrenocortical axis. We used in situ hybridization and Western blot to examine the transcriptional regulation of the GR gene, GR nuclear translocation, and expression of cytosolic heat shock protein 90 (hsp90), a chaperone protein essential for GR nuclear translocation, in the hippocampus, PVN, and anterior pituitary (AP) during single immobilization (sIMO) and the final immobilization on d 7 after daily IMO for 6 days (rIMO). As with GR mRNA, GR heteronuclear RNA levels decreased in the hippocampus and PVN and increased in the AP during sIMO and rIMO, indicating that the GR mRNA levels in these regions were regulated at the transcriptional level. In both sIMO and rIMO, nuclear GR levels were significantly increased in the hippocampus, medial basal hypothalamus (MBH), and AP. However, GR nuclear translocation was reduced in the hippocampus, unchanged in the MBH, and enhanced in the AP during rIMO, as compared with sIMO. Cytosolic hsp90 expression was unchanged in the hippocampus and MBH, whereas it significantly increased in the AP at 30 min during rIMO but not during sIMO. These results suggest that the site-specific changes in GR nuclear translocation during sIMO vs. rIMO are partially linked to hsp90 responses to immobilization. The reduced nuclear translocation of GR in the hippocampus during rIMO may reflect decreased glucocorticoid-mediated negative feedback on the hypothalamic-pituitary-adrenocortical axis.

Immunohistochemical expression of Bcl-2, p53 and caspase-9 in hypothalamus magnocellular centers of nNOS knockout mice following water deprivation

We studied the interactions between apoptosis regulator proteins (Bcl-2, p53 and caspase-9) and neuronal nitric oxide in vasopressinergic magnocellular centers of the hypothalamus using neuronal nitric oxide synthase (nNOS) gene knockout mice. nNOS gene deletion resulted in accumulation of Bcl-2, p53 and caspase-9 in the paraventricular (PVN) and supraoptic (SON) nuclei in controls. Dehydration increased the levels of all three apoptosis regulator proteins studied in nuclei of wild type mice. In the hypothalamus magnocellular centers of nNOS knockout mice, however, expression of Bcl-2, p53 and caspase-9 was unchanged after dehydration. The number of magnocellular neurons did not change in the SON and PVN of nNOS deficient mice compared to wild type, and after dehydration, cell death was not observed in either nucleus of wild type or knockout mice despite activation of apoptosis regulator protein expression. Thus, we demonstrated that gene disruption of nNOS prevents activation of Bcl-2, p53 and caspase-9 expression during water deprivation, and that nNOS deficiency did not affect survival of magnocellular neurons of the hypothalamus.

Intrauterine growth retardation affects expression and epigenetic characteristics of the rat hippocampal glucocorticoid receptor gene

Studies in humans and rats suggest that intrauterine growth retardation (IUGR) permanently resets the hypothalamic-pituitary-adrenal (HPA) axis. HPA axis reprogramming may involve persistently altered expression of the hippocampal glucocorticoid receptor (hpGR), an important regulator of HPA axis reactivity. Persistent alteration of gene expression, long after the inciting event, is thought to be mediated by epigenetic mechanisms that affect mRNA and mRNA variant expression. GR mRNA variants in both humans and rats include eleven 5′-end variants and GRα, the predominant 3′-end variant. The 3′-end variants associated with glucocorticoid resistance in humans (GRβ, GRγ, GRA, and GRP) have not been reported in rats. We hypothesized that in the rat hippocampus IUGR would decrease total GR mRNA, increase GRβ, GRγ, GRA, and GRP, and affect epigenetics of the GR gene at birth (D0) and at 21 days of life (D21). IUGR increased hpGR and exon 1.7 hpGR mRNA in males at D0 and D21, associated with increased trimethyl H3/K4 at exon 1.7 at both time points. IUGR also increased hpGRγ in males at D0 and D21, associated with increased acetyl H3/K9 at exon 3 at both time points. hpGRA increased in female IUGR rats at D0 and D21. In addition, our data support the existence of hpGRβ and hpGRP in the rat. IUGR has sex-specific, persistent effects on GR expression and its histone code. We speculate that postnatal changes in hippocampal GR variant and total mRNA expression may underlie IUGR-associated HPA axis reprogramming.

Programming neuroendocrine stress axis activity by exposure to glucocorticoids during postembryonic development of the frog, Xenopus laevis

Exposure to elevated glucocorticoids during early mammalian development can have profound, long-term consequences for health and disease. However, it is not known whether such actions occur in nonmammalian species, and if they do, whether the molecular physiological mechanisms are evolutionarily conserved. We investigated the effects of dietary restriction, which elevates endogenous corticosterone (CORT), or exposure to exogenous CORT added to the aquarium water of Xenopus laevis tadpoles on later-life measures of growth, feeding behavior, and neuroendocrine stress axis activity. Dietary restriction of prometamorphic tadpoles reduced body size at metamorphosis, but juvenile frogs increased food intake, showed catch-up growth through 21 d after metamorphosis, and had elevated whole-body CORT content compared with controls. Dietary restriction causes increased CORT in tadpoles, so to mimic this increase, we treated tadpoles with 100 nm CORT or vehicle for 5 or 10 d and then reared juvenile frogs to 2 months after metamorphosis. Treatment with CORT decreased body weight at metamorphosis, but juvenile frogs showed catch-up growth and had elevated basal plasma (CORT). Immunohistochemical analysis showed that CORT exposure as a tadpole led to decreased glucocorticoid receptor immunoreactivity in brain regions involved with stress axis regulation and in the anterior pituitary gland of juvenile frogs. The elevated CORT in juvenile frogs, which could result from decreased negative feedback owing to down-regulation of glucocorticoid receptor, may drive the hyperphagic response. Taken together, our findings suggest that long-term, stable phenotypic changes in response to elevated glucocorticoids early in life are an ancient and conserved feature of the vertebrate lineage.

Distribution and corticosteroid regulation of glucocorticoid receptor in the brain of Xenopus laevis

Glucocorticoids (GCs) play essential roles in physiology, development, and behavior that are mediated largely by the glucocorticoid receptor (GR). Although the GR has been intensively studied in mammals, very little is known about the GR in nonmammalian tetrapods. We analyzed the distribution and GC regulation of GR in the brain of the frog Xenopus laevis by immunohistochemistry. GR-immunoreactive (GR-ir) cells were widely distributed, with the highest densities in the medial pallium (mp; homolog of the mammalian hippocampus), accumbens, anterior preoptic area (POA; homolog of the mammalian paraventricular nucleus), Purkinje cell layer of the cerebellum, and rostral anterior pituitary gland (location of corticotropes). Lower but distinct GR-ir was observed in the internal granule cell layer of the olfactory bulbs, dorsal and lateral pallium, striatum, various subfields of the amygdala, bed nucleus of the stria terminalis (BNST), optic tectum, various tegmental nuclei, locus coeruleus, raphe nuclei, reticular nuclei, and the nuclei of the trigeminal motor nerves. Treatment with corticosterone (CORT) for 4 days significantly decreased GR-ir in the POA, mp, medial amygdala (MeA), BNST, and rostral pars distalis. Treatment with the corticosteroid synthesis inhibitor metyrapone (MTP) also significantly reduced GR-ir in the POA, mp, MeA and BNST, but not in the rostral pars distalis. Replacement with a low dose of CORT in MTP-treated animals reversed these effects in brain. Thus, chronic increase or decrease in circulating corticosteroids reduces GR-ir in regions of the frog brain. Our results show that the central distribution of GR-ir and regulation by corticosteroids are highly conserved among vertebrates.

Repeated unpredictable stress and antidepressants differentially regulate expression of the bcl-2 family of apoptotic genes in rat cortical, hippocampal, and limbic brain structures

Apoptosis has been proposed as a contributing cellular mechanism to the structural alterations that have been observed in stress-related mood disorders. Antidepressants, on the other hand, are hypothesized to exert trophic and/or neuroprotective actions. The present study examined the regulation of the major antiapoptotic (Bcl-2, Bcl-xl) and proapoptotic (Bax) genes by repeated unpredictable stress (an animal model of depression) and antidepressant treatments (ADT). In adult rats, exposure to unpredictable stress reduced Bcl-2 mRNA levels in the central nucleus of the amygdala (CeA), cingulate (Cg), and frontal (Fr) cortices. Bcl-xl mRNA was significantly decreased in hippocampal subfields. In contrast, chronic administration of clinically effective antidepressants from four different classes, ie fluoxetine, reboxetine, tranylcypromine, and electroconvulsive seizures (ECS) upregulated Bcl-2 mRNA expression in the Cg, Fr, and CeA. Reboxetine, tranylcypromine, and ECS selectively increased Bcl-xl, but not Bcl-2 mRNA expression in the hippocampus. Chemical ADT but not ECS, robustly enhanced Bcl-2 expression in the medial amygdaloid nucleus and ventromedial hypothalamus. Fluoxetine did not influence Bcl-xl expression in the hippocampus, but it was the only ADT that decreased Bax expression in this region. In the CeA, again in direct contrast to the stress effects, exposure to all classes of ADTs significantly increased Bcl-2 mRNA. The selective regulation of Bcl-xl and Bax in hippocampal subfields and of Bcl-2 in the Cg cortex, amygdala, and hypothalamus suggests that these cellular adaptations contribute to the long-term neural plastic adaptations to stress and ADTs in cortical, hypothalamic, and limbic brain structures.

Glucocorticoid receptor mRNA expression in the hippocampal formation of male rats before and after pubertal development in response to acute or repeated stress

Numerous studies have established that adolescence is marked by substantial changes in stress reactivity and hippocampal function. Glucocorticoid receptors (GRs) in the hippocampus are imperative in corticosterone-dependent gene transcription when glucocorticoid levels are relatively high, such as during periods of stress. As reported previously, in reaction to acute stress, prepubertal animals show a significantly more protracted corticosterone response compared to adults. Chronic stress, however, results in a higher peak response, but a faster return to baseline in prepubertal compared to adult animals. Thus, depending on the developmental stage and experience of the animal, the hippocampus is exposed to different concentrations and durations of corticosterone. The present set of experiments assessed the effects of acute or repeated stress on GR mRNA expression in the dorsal and ventral hippocampal formation either before or after pubertal maturation in male rats. We found that acute stress results in a significant decrease in GR mRNA in the CA1 pyramidal cell layer and dentate gyrus in the dorsal and ventral hippocampal formation of both prepubertal and adult males. In response to repeated stress, we found no differences in GR expression in either the dorsal or ventral hippocampus. Thus, despite the dramatic differences in corticosterone concentration following stress at these two developmental stages, the stress-induced changes in GR expression in the hippocampus before and after pubertal maturation were more similar than different. These data point to a dissociation between differential stress-induced corticosterone responses and regulation of hippocampal GR levels in prepubertal and adult animals.

Inclusion of the glucocorticoid receptor in a hypothalamic pituitary adrenal axis model reveals bistability

BACKGROUND

The body's primary stress management system is the hypothalamic pituitary adrenal (HPA) axis. The HPA axis responds to physical and mental challenge to maintain homeostasis in part by controlling the body's cortisol level. Dysregulation of the HPA axis is implicated in numerous stress-related diseases.

RESULTS

We developed a structured model of the HPA axis that includes the glucocorticoid receptor (GR). This model incorporates nonlinear kinetics of pituitary GR synthesis. The nonlinear effect arises from the fact that GR homodimerizes after cortisol activation and induces its own synthesis in the pituitary. This homodimerization makes possible two stable steady states (low and high) and one unstable state of cortisol production resulting in bistability of the HPA axis. In this model, low GR concentration represents the normal steady state, and high GR concentration represents a dysregulated steady state. A short stress in the normal steady state produces a small perturbation in the GR concentration that quickly returns to normal levels. Long, repeated stress produces persistent and high GR concentration that does not return to baseline forcing the HPA axis to an alternate steady state. One consequence of increased steady state GR is reduced steady state cortisol, which has been observed in some stress related disorders such as Chronic Fatigue Syndrome (CFS).

CONCLUSION

Inclusion of pituitary GR expression resulted in a biologically plausible model of HPA axis bistability and hypocortisolism. High GR concentration enhanced cortisol negative feedback on the hypothalamus and forced the HPA axis into an alternative, low cortisol state. This model can be used to explore mechanisms underlying disorders of the HPA axis.

What is the functional significance of chronic stress-induced CA3 dendritic retraction within the hippocampus?

Chronic stress produces consistent and reversible changes within the dendritic arbors of CA3 hippocampal neurons, characterized by decreased dendritic length and reduced branch number. This chronic stress-induced dendritic retraction has traditionally corresponded to hippocampus-dependent spatial memory deficits. However, anomalous findings have raised doubts as to whether a CA3 dendritic retraction is sufficient to compromise hippocampal function. The purpose of this review is to outline the mechanism underlying chronic stress-induced CA3 dendritic retraction and to explain why CA3 dendritic retraction has been thought to mediate spatial memory. The anomalous findings provide support for a modified hypothesis, in which chronic stress is proposed to induce CA3 dendritic retraction, which then disrupts hypothalamic-pituitary-adrenal axis activity, leading to dysregulated glucocorticoid release. The combination of hippocampal CA3 dendritic retraction and elevated glucocorticoid release contributes to impaired spatial memory. These findings are presented in the context of clinical conditions associated with elevated glucocorticoids.

Effect of voluntary wheel running on circadian corticosterone release and on HPA axis responsiveness to restraint stress in Sprague-Dawley rats

Adaptations of the hypothalamic-pituitary-adrenal (HPA) axis to voluntary exercise in rodents are not clear, because most investigations use forced-exercise protocols, which are associated with psychological stress. In the present study, we examined the effects of voluntary wheel running on the circadian corticosterone (Cort) rhythm as well as HPA axis responsiveness to, and recovery from, restraint stress. Male Sprague-Dawley rats were divided into exercise (E) and sedentary (S) groups, with E rats having 24-h access to running wheels for 5 wk. Circadian plasma Cort levels were measured at the end of each week, except for week 5 when rats were exposed to 20 min of restraint stress, followed by 95 min of recovery. Measurements of glucocorticoid receptor content in the hippocampus and anterior pituitary were performed using Western blotting at the termination of the restraint protocol. In week 1, circadian Cort levels were twofold higher in E compared with S animals, but the levels progressively decreased in the E group throughout the training protocol to reach similar values observed in S by week 4. During restraint stress and recovery, Cort values were similar between E and S, as was glucocorticoid receptor content in the hippocampus and pituitary gland after death. Compared with E, S animals had higher plasma ACTH levels during restraint. Taken together, these data indicate that 5 wk of wheel running are associated with normal circadian Cort activity and normal negative-feedback inhibition of the HPA axis, as well as with increased adrenal sensitivity to ACTH after restraint stress.

Uteroplacental insufficiency alters hepatic expression, phosphorylation, and activity of the glucocorticoid receptor in fetal IUGR rats

Uteroplacental insufficiency (UPI) induces persistent changes in hepatic gene expression secondary to altered chromatin dynamics in the intrauterine growth- restricted (IUGR) rat liver. The glucocorticoid receptor (GR) is a transcription factor that when activated can induce changes in chromatin structure. To begin the process of identifying pathways by which IUGR affects chromatin structure, we hypothesized that UPI in the rat induces a significant increase in endogenous glucocorticoids (corticosterone) and increases GR expression and activation. To prove our hypothesis, we induced IUGR through bilateral uterine artery ligation of the pregnant rat. At day 1, UPI significantly increased corticosterone levels and was associated with increased total GR mRNA and protein levels in the liver, as well as increased hepatic phosphorylation of GR serine 211. Moreover, cyclin-dependent kinase 2 (CDK2) cyclinA/CDK2 protein levels, which selectively phosphorylate GR serine 211, were also significantly increased. To assess activity of the GR, we measured protein levels of the transcription factor p53 whose levels are downregulated, at least in part, by active GR. In this study, UPI decreased p53 protein and its downstream target Bax mRNA levels. We conclude that UPI in rats affects GR expression and activity in the liver. We speculate that these alterations early in life may contribute to the changes in chromatin structure and gene expression previously described in the IUGR liver.

Chronic stress, depression and antidepressants: effects on gene transcription in the hippocampus

Depressive disorders are among the most frequent forms of mental illness. Both genetic and environmental factors, such as stress, are involved in the etiology of depression. Therefore, chronic stress paradigms in laboratory animals constitute an important tool for research in this field. The molecular bases of chronic stress/depression are largely unknown, although a large amount of information has been accumulated during recent years. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as well as structural and physiological alterations in the hippocampus and neocortex are known to occur. Modifications in the expression level of some genes, such as brain-derived neurotrophic factor, cAMP-response-element binding protein, serotonin receptors and HPA axis components were consistently associated in a number of experimental models. However, recent results suggest that several synaptic proteins, transcription factors and proteins involved in neuronal growth/differentiation, are also modified in their expression in experimental models of chronic stress. In general, these alterations can be reversed by treatment with antidepressants. Thus, a complex pattern of gene expression leading to stress/depression is starting to emerge. We summarize here recent findings on the alterations of gene expression in the hippocampus of chronically stressed and antidepressant treated animals.