Bidirectional rescue of extreme genetic predispositions to anxiety: impact of CRH receptor 1 as epigenetic plasticity gene in the amygdala

The continuum of physiological anxiety up to psychopathology is not merely dependent on genes, but is orchestrated by the interplay of genetic predisposition, gene x environment and epigenetic interactions. Accordingly, inborn anxiety is considered a polygenic, multifactorial trait, likely to be shaped by environmentally driven plasticity at the genomic level. We here took advantage of the extreme genetic predisposition of the selectively bred high (HAB) and low anxiety (LAB) mouse model exhibiting high vs low anxiety-related behavior and tested whether and how beneficial (enriched environment) vs detrimental (chronic mild stress) environmental manipulations are capable of rescuing phenotypes from both ends of the anxiety continuum. We provide evidence that (i) even inborn and seemingly rigid behavioral and neuroendocrine phenotypes can bidirectionally be rescued by appropriate environmental stimuli, (ii) corticotropin-releasing hormone receptor 1 (Crhr1), critically involved in trait anxiety, shows bidirectional alterations in its expression in the basolateral amygdala (BLA) upon environmental stimulation, (iii) these alterations are linked to an increased methylation status of its promoter and, finally, (iv) binding of the transcription factor Yin Yang 1 (YY1) to the Crhr1 promoter contributes to its gene expression in a methylation-sensitive manner. Thus, Crhr1 in the BLA is critically involved as plasticity gene in the bidirectional epigenetic rescue of extremes in trait anxiety.

Genetic influences on the development of alcoholism

Alcoholism has a substantial heritability yet the detection of specific genetic influences has largely proved elusive. The strongest findings are with genes encoding alcohol metabolizing enzymes. A few candidate genes such as GABRA2 have shown robust associations with alcoholism. Moreover, it has become apparent that variants in stress-related genes such as CRHR1, may only confer risk in individuals exposed to trauma, particularly in early life. Over the past decade there have been tremendous advances in large scale SNP genotyping technologies allowing for genome-wide associations studies (GWAS). As a result, it is now recognized that genetic risk for alcoholism is likely to be due to common variants in very many genes, each of small effect, although rare variants with large effects might also play a role. This has resulted in a paradigm shift away from gene centric studies toward analyses of gene interactions and gene networks within biologically relevant pathways.

Family-based study of AVPR1B association and interaction with stressful life events on depression and anxiety in suicide attempts

The cortisol response to psychosocial stress may become dysregulated in stress-related disorders. It is potentiated by pituitary secretion of adrenocorticotropic hormone (ACTH), which is, in part, regulated by arginine vasopressin receptor-1B (AVPR1B). AVPR1B variants were previously reported to associate with mood and anxiety disorders. This study aims, for the first time, to investigate association of AVPR1B genetic variants with mood and anxiety outcomes in suicidal behavior.Using a family-based study design of 660 complete nuclear family trios with offspring who have made a suicide attempt (SA), we tested the direct association and linkage of AVPR1B single nucleotide polymorphisms (SNPs) with SA, as well as with depression and anxiety in SA. Main findings were the association and linkage of AVPR1B exon 1 SNP rs33990840 and a major 6-SNP haplotype representative of all common AVPR1B-SNPs, on the outcome of high Beck Depression Inventory scores in SA. By contrast, genetic associations with lifetime diagnoses of depression and anxiety in SA or gene-environment interactions between AVPR1B variants and stressful life events (SLEs) were not significant. An exploratory screen of interactions between AVPR1B and CRHR1 (corticotropin-releasing hormone receptor-1), the principal pituitary regulator of ACTH secretion, showed no support for gene-gene interactions on the studied outcomes. The results suggest that AVPR1B genetic variation, eg, non-synonymous SNP rs33990840 mediating putative consequences on ligand binding, has a role in SA etiology characterized by elevated depression symptoms, without involving AVPR1B-moderation of SLEs.

The influence of gene-environment interactions on the development of alcoholism and drug dependence

Alcoholism and drug dependence are common psychiatric disorders with a heritability of about 50%; therefore genetic and environmental influences are equally important. Early-life stress is a predictor of adolescent problem drinking/drug use and alcohol/drug dependence in adulthood, but moderating factors governing the availability of alcohol/drug are important. The risk-resilience balance for addiction may be due in part to the interaction between genetic variation and environment stressors (G × E); this has been confirmed by twin studies of inferred genetic risk. Measured genotype studies to detect G × E effects have used a range of alcohol consumption and diagnostic phenotypes and stressors ranging from early-life to adulthood past year life events. In this article, the current state of the field is critically reviewed and suggestions are put forth for future research.

Consolidation of remote fear memories involves Corticotropin-Releasing Hormone (CRH) receptor type 1-mediated enhancement of AMPA receptor GluR1 signaling in the dentate gyrus

Persistent dreadful memories and hyperarousal constitute prominent psychopathological features of posttraumatic stress disorder (PTSD). Here, we used a contextual fear conditioning paradigm to demonstrate that conditional genetic deletion of corticotropin-releasing hormone (CRH) receptor 1 within the limbic forebrain in mice significantly reduced remote, but not recent, associative and non-associative fear memories. Per os treatment with the selective CRHR1 antagonist DMP696 (3 mg/kg) attenuated consolidation of remote fear memories, without affecting their expression and retention. This could be achieved, if DMP696 was administered for 1 week starting as late as 24 h after foot shock. Furthermore, by combining electrophysiological recordings and western blot analyses, we demonstrate a delayed-onset and long-lasting increase in AMPA receptor (AMPAR) GluR1-mediated signaling in the dentate gyrus (DG) of the dorsal hippocampus 1 month after foot shock. These changes were absent from CRHR1-deficient mice and after DMP696 treatment. Inactivation of hippocampal GluR1-containing AMPARs by antisense oligonucleotides or philantotoxin 433 confirmed the behavioral relevance of AMPA-type glutamatergic neurotransmission in maintaining the high levels of remote fear in shocked mice with intact CRHR1 signaling. We conclude that limbic CRHR1 receptors enhance the consolidation of remote fear memories in the first week after foot shock by increasing the expression of Ca(2+)-permeable GluR1-containing AMPARs in the DG. These findings suggest both receptors as rational targets for the prevention and therapy, respectively, of psychopathology associated with exaggerated fear memories, such as PTSD.

Two HPA axis genes, CRHBP and FKBP5, interact with childhood trauma to increase the risk for suicidal behavior

Childhood trauma is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation. Both factors increase risk for suicidal behavior. Corticotropin releasing hormone (CRH) regulates the HPA axis and its actions are moderated by a high-affinity binding protein (CRHBP). We hypothesized that CRHBP variation and interaction with childhood trauma might influence suicidal behavior. Moreover, there might be an additive effect with FKPB5, another HPA axis gene previously associated with suicidality in this dataset. African Americans were recruited: 398 treatment seeking patients with substance dependence (90% men; 120 suicide attempters) and 432 non-substance dependent individuals (40% men; 21 suicide attempters). A total of 474 participants (112 suicide attempters) completed the Childhood Trauma Questionnaire (CTQ). Haplotype-tagging SNPs were genotyped across CRHBP and, for completeness, across CRH, CRHR1 and CRHR2. FKBP5 genotypes were available. Three CRHBP SNPs rs6453267, rs7728378 and rs10474485 showed a nominally significant interaction with the continuous CTQ score to predict suicide attempt; rs7728378 remained significant after FDR correction. There was an additive effect with FKBP5: in the group exposed to high trauma, the prevalence of suicide attempt was 0.35-0.30 in carriers of either the FKBP5 rs3800373 major homozygote or the CRHBP rs7728378 major homozygote and 0.58 in carriers of both major homozygotes. Individuals without either major homozygote were resilient to the effects of childhood trauma (suicide attempt prevalence 0.24). Main effects of CRHBP rs6453267 and CRHR1 rs9900679, both unique to African ancestry, were detected. CRHBP variation may predispose, independently and additively, to suicidal behavior in individuals who have experienced childhood trauma.

Modulation of corticotropin releasing factor (CRF) signaling through receptor splicing in mouse pituitary cell line AtT-20--emerging role of soluble isoforms

Previously, using cultured human epidermal keratinocytes we have demonstrated that the activity of CRF1 receptor can be modulated by the process of alternative splicing. This phenomenon has been further investigated in the mouse corticotroph AtT-20 cell line. In the cells, transiently transfected with the plasmids coding human CRF1 isoforms, only isoforms alpha and c have shown expression on the cell membrane. Other isoforms d, e, g and h had intracellular localization with the isoform e also found in the nucleus. Co-expression of the CRF1alpha (main form of the receptor) with isoforms d, f and g prevented its expression on the cell surface resulting in accumulation of CRF1alpha inside of the cell. s expected, CRF stimulated time and dose dependent activation of CRE, CARE, AP-1 transcription elements and POMC promoter in AtT-20 cells overexpressing human CRF1alpha, while having no effect on the AP-1 transcriptional activity in cells transfected with other isoforms (d, f, g and h). However, when cells were co-transfected with CRF1alpha and CRF1e or h the CRF stimulated transcriptional activity of CRE and AP-1 was amplified in comparison to the cells expressing solely CRF1alpha; the effect was more pronounced for CRF1h than for CRF1e. In contrast, the conditioned media from the cells overexpressing CRF1e and h inhibited the CRF induced transcriptional activity in cells overexpressing CRF1alpha. Media from cells expressing CRF1h were significantly more potent that from cells transfected with CRF1e. In summary, we have demonstrated that alternatively spliced CRF1 isoforms can regulate the cellular localization of CRF1alpha, and that soluble CRF1 isoforms can have a dual effect on CRF1alpha activity depending on the intracellular vs. extracellular localization.