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.

TMEM132D, a new candidate for anxiety phenotypes: evidence from human and mouse studies.

The lifetime prevalence of panic disorder (PD) is up to 4% worldwide and there is substantial evidence that genetic factors contribute to the development of PD. Single-nucleotide polymorphisms (SNPs) in TMEM132D, identified in a whole-genome association study (GWAS), were found to be associated with PD in three independent samples, with a two-SNP haplotype associated in each of three samples in the same direction, and with a P-value of 1.2e-7 in the combined sample (909 cases and 915 controls). Independent SNPs in this gene were also associated with the severity of anxiety symptoms in patients affected by PD or panic attacks as well as in patients suffering from unipolar depression. Risk genotypes for PD were associated with higher TMEM132D mRNA expression levels in the frontal cortex. In parallel, using a mouse model of extremes in trait anxiety, we could further show that anxiety-related behavior was positively correlated with Tmem132d mRNA expression in the anterior cingulate cortex, central to the processing of anxiety/fear-related stimuli, and that in this animal model a Tmem132d SNP is associated with anxiety-related behavior in an F2 panel. TMEM132D may thus be an important new candidate gene for PD as well as more generally for anxiety-related behavior.

Proteomic-based genotyping in a mouse model of trait anxiety exposes disease-relevant pathways.

In our biomarker identification efforts, we have reported earlier on a protein that differs in its electrophoretic mobility between mouse lines bred either for high or low trait anxiety. The altered electrophoretic behavior of enolase phosphatase (EP) is now identified to be caused by two single-nucleotide polymorphisms. In both cases, the genetic polymorphism introduces an amino acid change in the protein's sequence resulting in differential mobility on SDS gels. This was shown by recombinantly expressing the two EP isoforms. Functional studies indicate that the EP isoform from the high anxiety mouse line has a lower enzymatic activity than does its low anxiety mouse counterpart. EP is a member of the methionine salvage pathway that is responsible for the synthesis of S-adenosyl-L-methionine, a natural compound with potential antidepressant activities. In addition, it is linked to the polyamine pathway whose members have functions in anxiety/depression-related behaviors. In a freely-segregating F2 panel, both single-nucleotide polymorphisms were significantly associated with locomotion-independent trait anxiety, further supporting a functional role of EP for this phenotype. The study shows that proteomic analysis can reveal genotypic differences relevant for the phenotype. The identified protein alterations, in turn, can expose metabolic pathways pertinent to the behavioral phenotype.