A Natural Mutation in Helix 5 of the Ligand Binding Domain of Glucocorticoid Receptor Enhances Receptor-Ligand Interaction

Genetic determinism of cortisol levels in pig

In facing the challenge of sustainability, animal breeding provides the option to improve animal robustness. In the search for new selection criteria related to robustness, the hypothalamic-pituitary-adrenocortical (HPA) axis is studied as a major neuroendocrine system involved in metabolic regulations and adaptive responses. Indeed, HPA axis activity is strongly influenced by genetic factors acting at several levels of the axis. The adrenocorticotropic hormone (ACTH) stimulation test has long been used to analyze interindividual and genetic differences in HPA axis activity in several species, including pigs. To uncover the genetic determinism of HPA activity and its influence on functional traits and robustness, a divergent selection experiment was carried out for three generations in a Large White pig population based on plasma cortisol levels measured one hour after injection of ACTH. In the present study the response to selection was very strong (confirming our previous studies), with a heritability value of cortisol level after ACTH injections reaching 0.64 (±0.03). The difference between the two divergent lines was around five genetic standard deviations after three selection steps. A genome-wide association study pointed out the importance of the glucocorticoid receptor gene (NR3C1) in this response. The measurement of plasma corticosteroid-binding globulin (CBG) binding capacity excluded any significant role of CBG in this selection process. The phenotypic effect of selection on body weight and growth rate was modest and/or inconsistent across generations. The HPA axis, a major neuroendocrine system involved in adaptation processes is highly heritable and responsive to genetic selection. The present experiment confirms the importance of glucocorticoid receptor polymorphism in genetic variation of HPA axis activity-in addition to the previously demonstrated role of CBG gene polymorphism. Further studies will explore the effect of this divergent selection on production and robustness.

Transcriptional signature of a hypersensitive glucocorticoid receptor variant in the neuroendocrine system suggests enhanced vulnerability to brain disorders

The natural substitution Ala610Val in the porcine glucocorticoid receptor (GRAla610Val) leads to a profound compensatory downregulation of the hypothalamic-pituitary-adrenal (HPA) axis in early ontogeny. In this study, we leveraged this unique animal model to explore mechanisms of HPA axis regulation and consequences of its genetically-based persistent hypoactivity. To this end, we examined transcriptional signature of GRAla610Val in the hypothalamus, hippocampus, amygdala and adrenal gland in resting conditions (i.e. baseline glucocorticoid level) using mRNA sequencing. In addition, we studied transcriptome responses to two different doses of dexamethasone in the hypothalamus and hippocampus, depending on GRAla610Val. Across tissues, GRAla610Val consistently influenced the expression of several clustered protocadherins, particularly PCDHB7. Clustered protocadherins play an important role in neuronal connectivity and are implicated in different neurobiological disorders. Moreover, in line with our previous findings in blood immune cells, we found higher expression of pro-inflammatory genes, including canonical members of the TLR4 signaling pathway, in the brain of Val carriers. While the pro-inflammatory priming occurs already at resting conditions in the amygdala, in hypothalamus and hippocampus this seems to be associated with a stronger downregulation of several marker genes of homeostatic microglia, such as SALL1, by dexamethasone in Val carriers. Regarding the regulation of the HPA axis, GRAla610Val showed a dose-dependent effect on the central regulator of the axis, CRH, suggesting a dynamic adaptation to the glucocorticoid hypersensitivity of the Val variant. In the adrenal gland, GRAla610Val appears to downregulate cortisol production by impairing mitochondrial function. Overall, the transcriptional signature of GRAla610Val provides strong evidence that GR hypersensitivity leads to increased susceptibility to brain disorders.

Clinical and functional heterogeneity associated with the disruption of retinoic acid receptor beta

PURPOSE

Dominant variants in the retinoic acid receptor beta (RARB) gene underlie a syndromic form of microphthalmia, known as MCOPS12, which is associated with other birth anomalies and global developmental delay with spasticity and/or dystonia. Here, we report 25 affected individuals with 17 novel pathogenic or likely pathogenic variants in RARB. This study aims to characterize the functional impact of these variants and describe the clinical spectrum of MCOPS12.

METHODS

We used in vitro transcriptional assays and in silico structural analysis to assess the functional relevance of RARB variants in affecting the normal response to retinoids.

RESULTS

We found that all RARB variants tested in our assays exhibited either a gain-of-function or a loss-of-function activity. Loss-of-function variants disrupted RARB function through a dominant-negative effect, possibly by disrupting ligand binding and/or coactivators' recruitment. By reviewing clinical data from 52 affected individuals, we found that disruption of RARB is associated with a more variable phenotype than initially suspected, with the absence in some individuals of cardinal features of MCOPS12, such as developmental eye anomaly or motor impairment.

CONCLUSION

Our study indicates that pathogenic variants in RARB are functionally heterogeneous and associated with extensive clinical heterogeneity.

Glucocorticoid receptor hypersensitivity enhances inflammatory signaling and inhibits cell cycle progression in porcine PBMCs

The consequences of glucocorticoid receptor (GR) hypersensitivity during infection have so far received little attention. We previously discovered that a natural gain-of-function Ala610Val substitution in the porcine GR aggravates response of pigs to lipopolysaccharide (LPS)-induced endotoxemia, which can be alleviated by dexamethasone (DEX) pretreatment. In this work, we investigated the relevant molecular basis of these phenotypes by transcriptomic profiling of porcine peripheral blood mononuclear cells (PBMCs) carrying different GR genotypes, in unstimulated conditions or in response to DEX and/or LPS in vitro. The Val allele differentially regulated abunda+nt genes in an additive-genetic manner. A subset of more than 200 genes was consistently affected by the substitution across treatments. This was associated with upregulation of genes related i.a. to endo-lysosomal system, lipid and protein catabolism, and immune terms including platelet activation, and antigen presentation, while downregulated genes were mainly involved in cell cycle regulation. Most importantly, the set of genes constitutively upregulated by Val includes members of the TLR4/LPS signaling pathway, such as LY96. Consequently, when exposing PBMCs to LPS treatment, the Val variant upregulated a panel of additional genes related to TLR4 and several other pattern recognition receptors, as well as cell death and lymphocyte signaling, ultimately amplifying the inflammatory responses. In contrast, when stimulated by DEX treatment, the Val allele orchestrated several genes involved in anti-inflammatory responses during infection. This study provides novel insights into the impact of GR hypersensitivity on the fate and function of immune cells, which may be useful for endotoxemia therapy.

A natural Ala610Val substitution causing glucocorticoid receptor hypersensitivity aggravates consequences of endotoxemia

Despite the crucial role of glucocorticoid receptor (GR) in proper immune responses, the effect of GR hypersensitivity on inflammation is rarely reported. To fill this knowledge gap, we exploited the natural gain-of-function substitution in the porcine glucocorticoid receptor (GR_Ala610Val) and challenged pigs carrying normal or hypersensitive GR using 50 µg/kg lipopolysaccharide (LPS) following pretreatment with either saline or single bolus of 60 µg/kg dexamethasone (DEX). The GR_Ala610Val substitution reduced baseline cortisol, adrenocorticotropic hormone (ACTH), and triglyceride concentration and granulocyte proportion whereas baseline platelet counts were elevated. Val-carriers, i.e. AlaVal as well as ValVal pigs, showed less LPS-induced cortisol rise but the cortisol fold change was similar in all genotypes. Differently, ACTH response to LPS was most significant in GR_Ala610Val heterozygotes (AlaVal). LPS-induced disorders, including sickness behaviors, anorexia, thrombocytopenia, cytokine production, and metabolic alterations were more intense in Val-carriers. On the other hand, Val-carriers were more sensitive to DEX effect than wild types (AlaAla) during endotoxemia, but not under unchallenged conditions. This is the first report revealing aggravated responses to endotoxemia by GR gain-of-function. Together, these results imply that GR hypersensitivity is difficult to diagnose but may represent a risk factor for endotoxemia and sepsis.

Omics Application in Animal Science-A Special Emphasis on Stress Response and Damaging Behaviour in Pigs

Increasing stress resilience of livestock is important for ethical and profitable meat and dairy production. Susceptibility to stress can entail damaging behaviours, a common problem in pig production. Breeding animals with increased stress resilience is difficult for various reasons. First, studies on neuroendocrine and behavioural stress responses in farm animals are scarce, as it is difficult to record adequate phenotypes under field conditions. Second, damaging behaviours and stress susceptibility are complex traits, and their biology is not yet well understood. Dissecting complex traits into biologically better defined, heritable and easily measurable proxy traits and developing biomarkers will facilitate recording these traits in large numbers. High-throughput molecular technologies (“omics”) study the entirety of molecules and their interactions in a single analysis step. They can help to decipher the contributions of different physiological systems and identify candidate molecules that are representative of different physiological pathways. Here, we provide a general overview of different omics approaches and we give examples of how these techniques could be applied to discover biomarkers. We discuss the genetic dissection of the stress response by different omics techniques and we provide examples and outline potential applications of omics tools to understand and prevent outbreaks of damaging behaviours.

Transcriptome Responses to Dexamethasone Depending on Dose and Glucocorticoid Receptor Sensitivity in the Liver

Tissue sensitivity to glucocorticoids is a key factor dictating outcome of their homeostatic and therapeutic action, whereby liver represents one of the major peripheral targets. Here, we used pigs carrying a natural gain-of-function glucocorticoid receptor (GR) variant Ala610Val (GR_Ala610Val) as a model to identify genes and pathways related to differential glucocorticoid sensitivity. Animals with different GR_Ala610Val genotypes were treated either with saline or two different doses of dexamethasone. Genome-wide transcriptional responses depending on treatment, genotype, and their interaction in the liver were investigated using mRNA sequencing. Dexamethasone induced vast transcriptional responses, with more than 30% of present genes being affected. Functional annotation of genes differentially expressed due to dexamethasone treatment suggested that genes related to inflammation respond more sensitively, despite absence of an immune stimulus. In contrast, genes involved in glucose metabolism and cancer appeared to be less sensitive. Analysis of genotype and genotype × treatment interaction revealed that clustered protocadherins, particularly PCDHB7, are most prominently affected by GR_Ala610Val, mainly depending on dose. GR_Ala610Val influenced also expression of a set of glucose metabolism related genes, including PPARGC1A and CEBPB, in the absence of dexamethasone though no differences in basal plasma glucose level were observed. This might represent an adaptive response, keeping balance between receptor sensitivity, and level of circulating endogenous glucocorticoids. Administration of low dexamethasone dose changed their expression pattern and induced higher glucose response in carriers of the hypersensitive Val receptor. Our findings suggest that GR_Ala610Val modulates tissue responses to glucocorticoids dynamically, depending on their circulating level.

A screening assay for Selective Dimerizing Glucocorticoid Receptor Agonists and Modulators (SEDIGRAM) that are effective against acute inflammation

It has been suggested that glucocorticoid receptor (GR) agonists that promote GR homodimerization more than standard glucocorticoids such as Dexamethasone could be more effective anti-inflammatory molecules against acute and life-threatening inflammatory conditions. To test this hypothesis, we set up a screening pipeline aimed at discovering such Selective Dimerizing GR Agonists and Modulators (SEDIGRAM). The pipeline consists of a reporter gene assay based on a palindromic glucocorticoid responsive element (GRE). This assay represents GR dimerization in human A549 lung epithelial cells. In the pipeline, this is followed by analysis of endogenous GRE-driven gene expression, a FRET assay confirming dimerization, and monitoring of in vitro and in vivo anti-inflammatory activity. In a proof of principle experiment, starting from seven candidate compounds, we identified two potentially interesting compounds (Cortivazol and AZD2906) that confer strong protection in a mouse model of aggressive TNF-induced lethal inflammation. A screening pipeline for SEDIGRAM may assist the search for compounds that promote GR dimerization and limit overwhelming acute inflammatory responses.