Accumulation of cytoplasmic glucocorticoid receptor is related to elevation of FKBP5 in lymphocytes of depressed patients

The transportosome system as a model for the retrotransport of soluble proteins

The classic model of action of the glucocorticoid receptor (GR) sustains that its associated heat-shock protein of 90-kDa (HSP90) favours the cytoplasmic retention of the unliganded GR, whereas the binding of steroid triggers the dissociation of HSP90 allowing the passive nuclear accumulation of GR. In recent years, it was described a molecular machinery called transportosome that is responsible for the active retrograde transport of GR. The transportosome heterocomplex includes a dimer of HSP90, the stabilizer co-chaperone p23, and FKBP52 (FK506-binding protein of 52-kDa), an immunophilin that binds dynein/dynactin motor proteins. The model shows that upon steroid binding, FKBP52 is recruited to the GR allowing its active retrograde transport on cytoskeletal tracks. Then, the entire GR heterocomplex translocates through the nuclear pore complex. The HSP90-based heterocomplex is released in the nucleoplasm followed by receptor dimerization. Subsequent findings demonstrated that the transportosome is also responsible for the retrotransport of other soluble proteins. Importantly, the disruption of this molecular oligomer leads to several diseases. In this article, we discuss the relevance of this transport machinery in health and disease.

Functions of the Hsp90-Binding FKBP Immunophilins

The Hsp90 chaperone is known to interact with a diverse array of client proteins. However, in every case examined, Hsp90 is also accompanied by a single or several co-chaperone proteins. One class of co-chaperone contains a tetratricopeptide repeat (TPR) domain that targets the co-chaperone to the C-terminal region of Hsp90. Within this class are Hsp90-binding peptidylprolyl isomerases, most of which belong to the FK506-binding protein (FKBP) family. Despite the common association of FKBP co-chaperones with Hsp90, it is abundantly clear that the client protein influences, and is often influenced by, the particular FKBP bound to Hsp90. Examples include Xap2 in aryl hydrocarbon receptor complexes and FKBP52 in steroid receptor complexes. In this chapter, we discuss the known functional roles played by FKBP co-chaperones and, where possible, relate distinctive functions to structural differences between FKBP members.

Nuclear receptors modulate inflammasomes in the pathophysiology and treatment of major depressive disorder

Major depressive disorder (MDD) is highly prevalent and is a significant cause of mortality and morbidity worldwide. Currently, conventional pharmacological treatments for MDD produce temporary remission in < 50% of patients; therefore, there is an urgent need for a wider spectrum of novel antidepressants to target newly discovered underlying disease mechanisms. Accumulated evidence has shown that immune inflammation, particularly inflammasome activity, plays an important role in the pathophysiology of MDD. In this review, we summarize the evidence on nuclear receptors (NRs), such as glucocorticoid receptor, mineralocorticoid receptor, estrogen receptor, aryl hydrocarbon receptor, and peroxisome proliferator-activated receptor, in modulating the inflammasome activity and depression-associated behaviors. This review provides evidence from an endocrine perspective to understand the role of activated NRs in the pathophysiology of MDD, and to provide insight for the discovery of antidepressants with novel mechanisms for this devastating disorder.

Corticosteroid receptors as a model for the Hsp90•immunophilin-based transport machinery

Steroid receptors form soluble heterocomplexes with the 90-kDa heat-shock protein (Hsp90) and other chaperones and co-chaperones. The assembly and composition of the oligomer is influenced by the presence and nature of the bound steroid. Although these receptors shuttle dynamically in and out of the nucleus, their primary localization in the absence of steroid can be mainly cytoplasmic, mainly nuclear, or partitioned into both cellular compartments. Upon steroid binding, receptors become localized to the nucleus via the transportosome, a retrotransport molecular machinery that comprises Hsp90, a high-molecular-weight immunophilin, and dynein motors. This molecular machinery, first evidenced in steroid receptors, can also be used by other soluble proteins. In this review, we dissect the complete model of this transport machinery system.

FKBP5 and early life stress affect the hippocampus by an age-dependent mechanism

Early life stress (ELS) adversely affects the brain and is commonly associated with the etiology of mental health disorders, like depression. In addition to the mood-related symptoms, patients with depression show dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, increased peripheral inflammation, and structural brain alterations. Although the underlying causes are unknown, polymorphisms in the FK506-binding protein 5 (FKBP5) gene, a regulator of glucocorticoid receptor (GR) activity, interact with childhood adversities to increase vulnerability to depressive disorders. We hypothesized that high FKBP5 protein levels combined with early life stress (ELS) would alter the HPA axis and brain, promoting depressive-like behaviors. To test this, we exposed males and females of a mouse model overexpressing FKBP5 in the brain (rTgFKBP5 mice), or littermate controls, to maternal separation for 14 days after birth. Then, we evaluated neuroendocrine, behavioral, and brain changes in young adult and aged mice. We observed lower basal corticosterone (CORT) levels in rTgFKBP5 mice, which was exacerbated in females. Aged, but not young, rTgFKBP5 mice showed increased depressive-like behaviors. Moreover, FKBP5 overexpression reduced hippocampal neuron density in aged mice, while promoting markers of microglia expression, but these effects were reversed by ELS. Together, these results demonstrate that high FKBP5 affects basal CORT levels, depressive-like symptoms, and numbers of neurons and microglia in the hippocampus in an age-dependent manner.

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High FKBP5 reduces basal corticosterone levels in mice, especially in females.

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ELS prevents FKBP5-induced susceptibility to depressive-like behavior in aged mice.

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FKBP5 overexpression reduces hippocampal neuron density in aged mice, while increasing microglial markers.

Stress modulates Ahi1-dependent nuclear localization of Ten-Eleven Translocation Protein 2

Major depression disorder (MDD) is one of the most common psychiatric diseases. Recent evidence supports that environmental stress affects gene expression and promotes the pathological process of depression through epigenetic mechanisms. Three Ten-Eleven Translocation (Tet) enzymes are epigenetic regulators of gene expression that promote 5-hydroxymethylcytosine (5hmC) modification of genes. Here, we show that the loss of Tet2 can induce depression-like phenotypes in mice. Paradoxically, using the paradigms of chronic stress, such as chronic mild stress (CMS) and chronic social defeat stress (CSDS), we found that depressive behaviors were associated with increased Tet2 expression but decreased global 5hmC level in hippocampus. We examined the genome-wide 5hmC profile in the hippocampus of Tet2 knockout mice and identified 651 dynamically hydroxymethylated regions, some of which overlapped with known depression-associated loci. We further showed that chronic stress could induce the abnormal nuclear translocation of Tet2 protein from cytosol. Through Tet2 immunoprecipitation and mass spectrum analyses, we identified a cellular trafficking protein, Abelson helper integration site-1 (Ahi1), which could interact with Tet2 protein. Ahi1 knockout or knockdown caused the accumulation of Tet2 in cytosol. The reduction of Ahi1 protein under chronic stress explained the abnormal Ahi1-dependent nuclear translocation of Tet2. These findings together provide the evidence for a critical role of modulating Tet2 nuclear translocation in regulating stress response.

The glucocorticoid receptor-FKBP51 complex contributes to fear conditioning and posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) can develop after exposure to severe psychological trauma, leaving patients with disabling anxiety, nightmares, and flashbacks. Current treatments are only partially effective, and development of better treatments is hampered by limited knowledge of molecular mechanisms underlying PTSD. We have discovered that the glucocorticoid receptor (GR) and FK506 binding protein 51 (FKBP51) form a protein complex that is elevated in PTSD patients compared with unaffected control subjects, subjects exposed to trauma without PTSD, and patients with major depressive disorder (MDD). The GR-FKBP51 complex is also elevated in fear-conditioned mice, an aversive learning paradigm that models some aspects of PTSD. Both PTSD patients and fear-conditioned mice had decreased GR phosphorylation, decreased nuclear GR, and lower expression of 14-3-3ε, a gene regulated by GR. We created a peptide that disrupts GR-FKBP51 binding and reverses behavioral and molecular changes induced by fear conditioning. This peptide reduces freezing time and increases GR phosphorylation, GR-FKBP52 binding, GR nuclear translocation, and 14-3-3ε expression in fear-conditioned mice. These experiments demonstrate a molecular mechanism contributing to PTSD and suggest that the GR-FKBP51 complex may be a diagnostic biomarker and a potential therapeutic target for preventing or treating PTSD.

Low Circulating Levels of GR, FKBP5, and SGK1 in Medicated Patients With Depression Are Not Altered by Electroconvulsive Therapy

OBJECTIVES

Hypothalamic-pituitary-adrenal axis dysregulation is frequently observed in patients with depression, with increased levels of the glucocorticoid (GC) cortisol commonly reported. Hypothalamic-pituitary-adrenal axis dysregulation may be a consequence of impaired feedback inhibition due to GC receptor (GR) impairments or dysfunction, termed "glucocorticoid resistance." Here, our objective was to assess mRNA levels of GC-related markers (GR, FKBP5, serum glucocorticoid kinase 1 [SGK1]) in patients with depression versus controls and in patient samples after electroconvulsive therapy (ECT). We also examined the relationship between these GC-related markers and 24-item Hamilton Depression Rating Scale (HAM-D24) scores to assess the utility of using them as biological markers for depression or the therapeutic response to ECT.

METHODS

GR, FKBP5, and SGK1 mRNA levels were examined in whole blood samples from 88 medicated patients with depression pre-/post-ECT and 63 controls using quantitative real-time polymerase chain reaction. Exploratory subgroup correlational analyses were performed to determine the relationship between GR, FKBP5, and SGK1 and 24-item Hamilton Depression Rating Scale scores.

RESULTS

GR, FKBP5, and SGK1 mRNA levels were significantly lower in medicated patients with depression compared with controls (P < 0.001, P = 0.03, P < 0.001, respectively), but ECT did not alter their levels (all P > 0.05). There was no relationship between GR, FKBP5, or SGK1 and 24-item Hamilton Depression Rating Scale scores.

CONCLUSIONS

GR, FKBP5, and SGK1 do not seem to be involved in the peripheral molecular response to ECT and do not represent useful biomarkers for predicting the therapeutic response to ECT in a real-world clinical setting.

Sex differences in hypothalamic-pituitary-adrenal axis regulation after chronic unpredictable stress

INTRODUCTION

Exposure to stress, mediated through the hypothalamic-pituitary-adrenal (HPA) axis, elicits sex differences in endocrine, neurological, and behavioral responses. However, the sex-specific factors that confer resilience or vulnerability to stress and stress-associated psychiatric disorders remain largely unknown. The evident sex differences in stress-related disease prevalence suggest the underlying differences in the neurobiological underpinnings of HPA axis regulation.

METHOD

Here, we used a chronic unpredictable stress (CUS) model to investigate the behavioral and biochemical responses of the HPA axis in C57BL/6 mice. Animals were tested in the open field and forced swim test to examine anxiety-like and depressive-like behaviors. Plasma corticosterone levels were measured after behavior and CUS, and glucocorticoid receptor (GR) expression and cytosolic and nuclear fractions of binding protein FKBP51 expression were taken to measure function and regulation of the stress response.

RESULTS

Our results indicate increased depressive-like behavior in males and females which correlated with increased corticosterone levels following CUS. However, females displayed more anxiety-like behaviors with and without CUS. Interestingly, we found trends toward dysregulation of GR protein expression in CUS females, and an increase in the GR inhibitory protein, FKBP51, in the cytosol of CUS males but not females.

CONCLUSION

These results suggest biochemical alterations to the HPA axis regulation which may elicit a glucocorticoid resistance in females after chronic stress and may contribute to the sex-biased vulnerability to stress-related psychiatric disorders.

Targeting the Glucocorticoid Receptor Reduces Binge-Like Drinking in High Drinking in the Dark (HDID-1) Mice

BACKGROUND

Chronic alcohol exposure can alter glucocorticoid receptor (GR) function in some brain areas that promotes escalated and compulsive-like alcohol intake. GR antagonism can prevent dependence-induced escalation in drinking, but very little is known about the role of GR in regulating high-risk nondependent alcohol intake. Here, we investigate the role of GR in regulating binge-like drinking and aversive responses to alcohol in the High Drinking in the Dark (HDID-1) mice, which have been selectively bred for high blood ethanol (EtOH) concentrations (BECs) in the Drinking in the Dark (DID) test, and in their founder line, the HS/NPT.

METHODS

In separate experiments, male and female HDID-1 mice were administered one of several compounds that inhibited GR or its negative regulator, FKBP51 (mifepristone [12.5, 25, 50, 100 mg/kg], CORT113176 [20, 40, 80 mg/kg], and SAFit2 [10, 20, 40 mg/kg]) during a 2-day DID task. EtOH consumption and BECs were measured. EtOH conditioned taste and place aversion (CTA and CPA, respectively) were measured in separate HDID-1 mice after mifepristone administration to assess GR's role in regulating the conditioned aversive effects of EtOH. Lastly, HS/NPT mice were administered CORT113176 during DID to assess whether dissimilar effects from those of HDID-1 would be observed, which could suggest that selective breeding had altered sensitivity to the effects of GR antagonism on binge-like drinking.

RESULTS

GR antagonism (with both mifepristone and CORT113176) selectively reduced binge-like EtOH intake and BECs in the HDID-1 mice, while inhibition of FKBP51 did not alter intake or BECs. In contrast, GR antagonism had no effect on EtOH intake or BECs in the HS/NPT mice. Although HDID-1 mice exhibit attenuated EtOH CTA, mifepristone administration did not enhance the aversive effects of EtOH in either a CTA or CPA task.

CONCLUSION

These data suggest that the selection process increased sensitivity to GR antagonism on EtOH intake in the HDID-1 mice, and support a role for the GR as a genetic risk factor for high-risk alcohol intake.

Transcriptional changes in the stress pathway are related to symptoms in schizophrenia and to mood in schizoaffective disorder

Altered levels of stress-signalling transcripts have been identified in post-mortem brains of people with schizophrenia, and since stress effects may be expressed throughout the body, there should be similar changes in peripheral cells. However, the extent to which these markers are altered in peripheral white blood cells of people with schizophrenia is not known. Furthermore, how peripheral cortisol and stress-related mRNA are associated with negative symptom severity and emotional states in people with schizophrenia versus schizoaffective disorder has not been determined. Whole blood samples were collected from 86 patients with either schizophrenia or schizoaffective disorder (56 people with schizophrenia and 30 people with schizoaffective disorder), and 77 healthy controls. Total RNA was isolated, cDNA was synthesized, and stress-signalling mRNA levels (for NR3C1, FKBP5, FKBP4, PTGES3 and BAG1) were determined. Stress and symptom severity scores were measured by the Depression, Anxiety and Stress Scale, and the Positive and Negative Syndrome Scale, respectively. We found increased FKBP5 mRNA, Z(156) = 2.5, p = 0.01, decreased FKBP4 mRNA, t(155) = 3.5, p ≤ 0.001, and decreased PTGES3 mRNA, t(153) = 3.0, p ≤ 0.01, in schizophrenia and schizoaffective disorder cohorts combined compared to healthy controls. Stress-related peripheral mRNA levels were differentially correlated with negative emotional states and symptom severity in schizoaffective disorder (β's = -0.45-0.56, p's = 0.05-0.001) and schizophrenia (β's = -0.34-0.38, p's = 0.04-0.03), respectively. Therefore, molecules of the stress-signalling pathway appear to differentially contribute to clinical features of schizophrenia versus schizoaffective disorder.

HIV and symptoms of depression are independently associated with impaired glucocorticoid signaling

Chronic inflammation caused by HIV infection may lead to deficient glucocorticoid (GC) signaling predisposing people living with HIV to depression and other psychiatric disorders linked to GC resistance. We hypothesized that comorbid HIV and depressive symptoms in women would synergistically associate with deficits in GC signaling. This cross-sectional study used samples obtained from the Women's Interagency HIV Study (WIHS). The Centers for Epidemiological Studies (CES-D) was used to define depression in four groups of women from the Women's Interagency HIV Study (WIHS): 1) HIV-negative, non-depressed (n = 37); 2) HIV-negative, depressed (n = 34); 3) HIV-positive, non-depressed (n = 38); and 4) HIV-positive, depressed (n = 38). To assess changes in GC signaling from peripheral blood mononuclear cells (PBMCs), we examined baseline and dexamethasone (Dex)-stimulated changes in the expression of the GC receptor (GR, gene: Nr3c1) and its negative regulator Fkbp5 via quantitative RT-PCR. GR sensitivity was evaluated in vitro by assessing the Dex inhibition of lipopolysaccharide (LPS)-stimulated IL-6 and TNF-α levels. Depressive symptoms and HIV serostatus were independently associated with elevated baseline expression of Fkbp5 and Nr3c1. Depressive symptoms, but not HIV status, was independently associated with reduced LPS-induced release of IL-6. Counter to predictions, there was no interactive association of depressive symptoms and HIV on any outcome. Comorbid depressive symptoms with HIV infection were associated with a gene expression and cytokine profile similar to that of healthy control women, a finding that may indicate further disruptions in disease adaptation.

Nuclear localized Raf1 isoform alters DNA-dependent protein kinase activity and the DNA damage response

Raf1/c-Raf is a well-characterized serine/threonine-protein kinase that links Ras family members with the MAPK/ERK signaling cascade. We have identified a novel splice isoform of human Raf1 that causes protein truncation and loss of the C-terminal kinase domain (Raf1-tr). We found that Raf1-tr has increased nuclear localization compared with full-length Raf1, and this finding was secondary to reduced binding of Raf1-tr to the cytoplasmic chaperone FK506 binding protein 5. We show that Raf1-tr has increased binding to DNA-dependent protein kinase (DNA-PK), which inhibits DNA-PK function and causes amplification of irradiation- and bleomycin-induced DNA damage. We found that the human colorectal cancer cell line, HCT-116, displayed reduced expression of Raf1-tr, and reintroduction of Raf1-tr sensitized the cells to bleomycin-induced apoptosis. Furthermore, we identified differential Raf1-tr expression in breast cancer cell lines and showed that breast cancer cells with increased Raf1-tr expression become sensitized to bleomycin-induced apoptosis. Collectively, these results demonstrate a novel Raf1 isoform in humans that has a unique noncanonical role in regulating the double-stranded DNA damage response pathway through modulation of DNA-PK function.-Nixon, B. R., Sebag, S. C., Glennon, M. S., Hall, E. J., Kounlavong, E. S., Freeman, M. L., Becker, J. R. Nuclear localized Raf1 isoform alters DNA-dependent protein kinase activity and the DNA damage response.

Different roles of CD4, CD8 and γδ T-lymphocytes in naive and vaccinated chickens during Salmonella Enteritidis infection

Lymphocytes represent the key antigen-specific leukocyte subpopulation. Despite their importance in mounting an immune response, an unbiased description of proteins expressed by chicken lymphocytes has not been presented. In this study, we therefore intravenously infected chickens with Salmonella Enteritidis, sorted CD4, CD8 and γδ T-lymphocytes from the spleen by flow cytometry and determined the proteome of each population by LC-MS/MS. CD4 T-lymphocyte characteristic proteins included ubiquitin SUMO-like domain and BAR domain containing proteins. CD8 T-lymphocyte specific proteins were characterized by purine ribonucleoside triphosphate binding and were involved in cell differentiation, cell activation and regulation of programmed cell death. γδ T-lymphocyte specific proteins exhibited enrichment of small GTPase of Rab type and GTP binding. Following infection, inducible proteins in CD4 lymphocytes included ribosomal proteins and downregulated proteins localized to the lysosome. CD8 T-lymphocytes induced MCM complex proteins, proteins required for DNA replication and machinery for protein processing in the endoplasmic reticulum. Proteins inducible in γδ T-lymphocytes belonged to immune system response, oxidative phosphorylation and the spliceosome. In this study, we predicted the likely events in lymphocyte response to systemic bacterial infection and identified proteins which can be used as markers specific for each lymphocyte subpopulation.

The FKBP51 Glucocorticoid Receptor Co-Chaperone: Regulation, Function, and Implications in Health and Disease

Among the chaperones and co-chaperones regulating the glucocorticoid receptor (GR), FK506 binding protein (FKBP) 51 is the most intensely investigated across different disciplines. This review provides an update on the role of the different co-chaperones of Hsp70 and Hsp90 in the regulation of GR function. The development leading to the focus on FKBP51 is outlined. Further, a survey of the vast literature on the mechanism and function of FKBP51 is provided. This includes its structure and biochemical function, its regulation on different levels—transcription, post-transcription, and post-translation—and its function in signaling pathways. The evidence portraying FKBP51 as a scaffolding protein organizing protein complexes rather than a chaperone contributing to the folding of individual proteins is collated. Finally, FKBP51’s involvement in physiology and disease is outlined, and the promising efforts in developing drugs targeting FKBP51 are discussed.

Impaired Spinal Glucocorticoid Receptor Signaling Contributes to the Attenuating Effect of Depression on Mechanical Allodynia and Thermal Hyperalgesia in Rats with Neuropathic Pain

Although depression-induced altered pain perception has been described in several laboratory and clinical studies, its neurobiological mechanism in the central nervous system (CNS), particularly in the spinal dorsal horn, remains unclear. Therefore, in this study, we aimed to clarify whether nociceptive sensitivity of neuropathic pain is altered in the olfactory bulbectomy (OB) model of depression and whether glucocorticoid receptor (GR), which is involved in the etio-pathologic mechanisms of both major depression and neuropathic pain, contributes to these processes in the spinal dorsal horn of male Sprague-Dawley rats. The results showed that mechanical allodynia and thermal hyperalgesia induced by spinal nerve ligation (SNL) were attenuated in OB-SNL rats with decreased spinal GR expression and nuclear translocation, whereas non-olfactory bulbectomy (NOB)-SNL rats showed increased spinal GR nuclear translocation. In addition, decreased GR nuclear translocation with normal mechanical nociception and hypoalgesia of thermal nociception were observed in OB-Sham rats. Intrathecal injection (i.t.) of GR agonist dexamethasone (Dex; 4 μg/rat/day for 1 week) eliminated the attenuating effect of depression on nociceptive hypersensitivity in OB-SNL rats and aggravated neuropathic pain in NOB-SNL rats, which was associated with the up-regulation of brain-derived neurotrophic factor (BDNF), TrkB and NR2B expression in the spinal dorsal horn. The present study shows that depression attenuates the mechanical allodynia and thermal hyperalgesia of neuropathic pain and suggests that altered spinal GR-BDNF-TrkB signaling may be one of the reasons for depression-induced hypoalgesia.

A focused Real Time PCR strategy to determine GILZ expression in mouse tissues

Glucocorticoid-Induced Leucine Zipper (GILZ) is a glucocorticoid-inducible gene that mediates glucocorticoid anti-inflammatory effects. GILZ and the isoform L-GILZ are expressed in a variety of cell types, especially of hematopoietic origin, including macrophages, lymphocytes and epithelial cells, and strongly upregulated upon glucocorticoid treatment.

A quantitative analysis of GILZ expression in mouse tissues is technically difficult to perform because of the presence of a pseudogene and the high homology of GILZ gene with other genes of TSC22 family. We here propose specific primer pairs to be used in Real Time PCR to avoid unwanted amplification of GILZ pseudogene and TSC-22 family member d1iso3. These primer pairs were used to determine GILZ and L-GILZ expression, in either untreated or in vivo and in vitro dexamethasone-treated tissues. Results indicate that GILZ and L-GILZ are upregulated by glucocorticoids, being GILZ more sensitive to glucocorticoid induction than L-GILZ, but they are differently expressed in all examined tissues, confirming a different role in specific cells. An inappropriate primer pair amplified also GILZ pseudogene and TSC22d1iso3, thus producing misleading results. This quantitative evaluation may be used to better characterize the role of GILZ and L-GILZ in mice and may be translated to humans.