Glucocorticoid receptor binding in three different cell types in major depressive disorder: lack of evidence of receptor binding defect

Human Derived Dermal Fibroblasts as in Vitro Research Tool to Study Circadian Rhythmicity in Psychiatric Disorders

A number of psychiatric disorders are defined by persistent or recurrent sleep-wake disturbances alongside disruptions in circadian rhythm and altered clock gene expression. Circadian rhythms are present not only in the hypothalamic suprachiasmatic nucleus but also in peripheral tissues. In this respect, cultures of human derived dermal fibroblasts may serve as a promising new tool to investigate cellular and molecular mechanisms underlying the pathophysiology of mental illness. In this article, we discuss the advantages of fibroblast cultures to study psychiatric disease. More specifically, we provide an update on recent advances in modeling circadian rhythm disorders using human fibroblasts.

Human Dermal Fibroblast: A Promising Cellular Model to Study Biological Mechanisms of Major Depression and Antidepressant Drug Response

BACKGROUND

Human dermal fibroblasts (HDF) can be used as a cellular model relatively easily and without genetic engineering. Therefore, HDF represent an interesting tool to study several human diseases including psychiatric disorders. Despite major depressive disorder (MDD) being the second cause of disability in the world, the efficacy of antidepressant drug (AD) treatment is not sufficient and the underlying mechanisms of MDD and the mechanisms of action of AD are poorly understood.

OBJECTIVE

The aim of this review is to highlight the potential of HDF in the study of cellular mechanisms involved in MDD pathophysiology and in the action of AD response.

METHODS

The first part is a systematic review following PRISMA guidelines on the use of HDF in MDD research. The second part reports the mechanisms and molecules both present in HDF and relevant regarding MDD pathophysiology and AD mechanisms of action.

RESULTS

HDFs from MDD patients have been investigated in a relatively small number of works and most of them focused on the adrenergic pathway and metabolism-related gene expression as compared to HDF from healthy controls. The second part listed an important number of papers demonstrating the presence of many molecular processes in HDF, involved in MDD and AD mechanisms of action.

CONCLUSION

The imbalance in the number of papers between the two parts highlights the great and still underused potential of HDF, which stands out as a very promising tool in our understanding of MDD and AD mechanisms of action.

Glucocorticoid receptor number and affinity differ between peripheral blood mononuclear cells and granulocytes in domestic pigs

The aim of the present study was to characterize the number and affinity of glucocorticoid receptors (GR) in peripheral blood mononuclear cells (PBMC) and granulocytes of domestic pigs because glucocorticoid signaling is considered important for animal health and welfare. To investigate GR binding characteristics in intact porcine immune cells, blood samples of 6 castrated male pigs were collected via indwelling vein catheters. Porcine PBMC and granulocytes were isolated using two-layer density gradients, followed by radioligand binding assays to determine the number of GR sites per cell and the dissociation constant K_d as a measure for GR binding affinity. The present study revealed a greater number of GR sites per cell (P = 0.039) in PBMC (mean ± SEM: 1,953 ± 207 sites/cell) compared to granulocytes (1,561 ± 159 sites/cell) in domestic pigs. Furthermore, porcine PBMC had a higher GR binding affinity than porcine granulocytes (P = 0.003) as the dissociation constant K_d of PBMC (1.8 ± 0.2 nM) was lower than that of granulocytes (3.5 ± 0.4 nM). Our results point to differences in underlying mechanisms of glucocorticoid signaling in different porcine leukocyte populations.

Human dermal fibroblasts in psychiatry research

In order to decipher the disease etiology, progression and treatment of multifactorial human brain diseases we utilize a host of different experimental models. Recently, patient-derived human dermal fibroblast (HDF) cultures have re-emerged as promising in vitro functional system for examining various cellular, molecular, metabolic and (patho)physiological states and traits of psychiatric disorders. HDF studies serve as a powerful complement to postmortem and animal studies, and often appear to be informative about the altered homeostasis in neural tissue. Studies of HDFs from patients with schizophrenia (SZ), depression, bipolar disorder (BD), autism, attention deficit and hyperactivity disorder and other psychiatric disorders have significantly advanced our understanding of these devastating diseases. These reports unequivocally prove that signal transduction, redox homeostasis, circadian rhythms and gene*environment (G*E) interactions are all amenable for assessment by the HDF model. Furthermore, the reported findings suggest that this underutilized patient biomaterial, combined with modern molecular biology techniques, may have both diagnostic and prognostic value, including prediction of response to therapeutic agents.

Brain-immune interactions and disease susceptibility

Many studies have established the routes by which the immune and central nervous (CNS) systems communicate. This network of connections permits the CNS to regulate the immune system through both neuroendocrine and neuronal pathways. In turn, the immune system signals the CNS through neuronal and humoral routes, via immune mediators and cytokines. This regulatory system between the immune system and CNS plays an important role in susceptibility and resistance to autoimmune, inflammatory, infectious and allergic diseases. This review focuses on the regulation of the immune system via the neuroendocrine system, and underlines the link between neuroendocrine dysregulation and development of major depressive disorders, autoimmune diseases and osteoporosis.

Glucocorticoid receptor function in vitro in patients with major depression

Clinical studies have demonstrated an impairment of glucocorticoid receptor (GR)-mediated negative feedback on the hypothalamic--pituitary--adrenal (HPA) axis in patients with major depression (GR resistance), and its resolution by antidepressant treatment. Interestingly, a number of studies have also demonstrated that GR function is reduced in vitro, in peripheral tissues of depressed patients, as shown by a decreased sensitivity to the effects of glucocorticoids on immune and metabolic functions. This paper reviews the in vitro studies that have examined GR function in patients with major depression, and the possible molecular mechanisms involved in GR resistance. Since several studies have demonstrated similar regulation of GR in the brain and in peripheral tissues in humans, and given limited access to brain GR in clinical populations, this review claims that in vitro studies are of particular relevance to understand the molecular mechanisms underlying GR abnormalities in patients with major depression and its regulation by antidepressant treatment.

Vasoconstrictor response to topical beclomethasone in major depression

Overactivity of the hypothalamic-pituitary-adrenal (HPA) axis has been frequently described in depression. Due to the closed-loop nature of the HPA axis, one possible cause of this overactivity may be a defect in negative feedback regulation, in particular an abnormality of the glucocorticoid receptor (GR). In the present study, the vasoconstrictor response to the topical glucocorticoid, beclomethasone, was used to examine GR function in depression. Topical beclomethasone was applied in four concentrations (10 microl each of 3, 10, 30 and 100 microg/ml) to the forearms of 22 subjects with major depression and their age- and sex-matched controls. Skin blanching responses were compared between the depressed and control groups and, within the depressed group, on the basis of the modified dexamethasone suppression test (DST), between cortisol suppressors and non-suppressors. Depressed subjects demonstrated a significantly reduced vasoconstrictor response compared to controls (P=0.0001). No difference was detected between cortisol suppressors and non-suppressors in their skin blanching responses. These findings suggest that peripheral GR function is abnormal in depression but that the reduced vasoconstrictor response to beclomethasone is not necessarily a secondary effect of hypercortisolaemia or HPA axis overactivity.

Glucocorticoid receptors in major depression: relevance to pathophysiology and treatment

Hyperactivity of the hypothalamic--pituitary--adrenal (HPA) axis has been reliably observed in patients with major depression. One of the primary features of this HPA axis hyperactivity is reduced sensitivity to the inhibitory effects of the glucocorticoid dexamethasone on the production of adrenocorticotropic hormone and cortisol during the dexamethasone suppression test and, more recently, the dexamethasone--corticotropin-releasing hormone test. Because the effects of glucocorticoids are mediated by intracellular receptors including, most notably, the glucocorticoid receptor (GR), a number of studies have considered the possibility that the number and/or function of GRs are reduced in depressed patients. Moreover, whether antidepressants act by reversing these putative GR changes has been examined. The extant literature on GR receptors in major depression was reviewed along with studies examining the impact of antidepressants on the GR. The data support the hypothesis that the function of the GR is reduced in major depression in the absence of clear evidence of decreased GR expression. The data also indicate that some antidepressants have direct effects on the GR, leading to enhanced GR function and increased GR expression. Hypotheses regarding the mechanism of these receptor changes involve relevant second messenger pathways that regulate GR function. The findings indicate that the GR is an important molecular target in major depression. Further elucidation of the biochemical and molecular mechanisms involved in GR changes in major depression is an exciting frontier that will no doubt lead to new insights into the pathophysiology and treatment of affective disorders.

Psychoneuroendocrinology of depression. Hypothalamic-pituitary-adrenal axis

Among the more consistent observations in patients with major depression is dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis presenting as elevation of basal cortisol, dexamethasone-mediated negative feedback resistance, increased cerebrospinal fluid levels of corticotropin-releasing factor (CRF), and a blunted adrenocorticotropic hormone (ACTH) response to challenge with exogenous CRF. These features appear to be state, rather than trait markers, and are normalized upon successful treatment. These pathophysiologic adaptations may arise from defects in central drive to the neuroendocrine hypothalamus, disruption of normal adrenocortical hormone receptor function or a modification of HPA axis function at any level. Functional assessment of the HPA axis is thought to provide a window into central nervous system operation that may be of diagnostic value in this and other affective disorders regardless of whether CRF and glucocorticoids are directly involved in the origin of major depression or merely exacerbate the consequences of other primary defects.

Opposing effects of ERK and JNK-p38 MAP kinases on apoptosis

Apoptosis plays an important role during neuronal development, and defects in apoptosis may underlie various neurodegenerative disorders. To characterize molecular mechanisms that regulate neuronal apoptosis, the contributions to cell death of mitogen-activated protein (MAP) kinase family members, including ERK (extracellular signal-regulated kinase), JNK (c-JUN NH2-terminal protein kinase), and p38, were examined after withdrawal of nerve growth factor (NGF) from rat PC-12 pheochromocytoma cells. NGF withdrawal led to sustained activation of the JNK and p38 enzymes and inhibition of ERKs. The effects of dominant-interfering or constitutively activated forms of various components of the JNK-p38 and ERK signaling pathways demonstrated that activation of JNK and p38 and concurrent inhibition of ERK are critical for induction of apoptosis in these cells. Therefore, the dynamic balance between growth factor-activated ERK and stress-activated JNK-p38 pathways may be important in determining whether a cell survives or undergoes apoptosis.