DNA methylation patterns of FKBP5 regulatory regions in brain and blood of humanized mice and humans.

Humanized mouse models can be used to explore human gene regulatory elements (REs), which frequently lie in non-coding and less conserved genomic regions. Epigenetic modifications of gene REs, also in the context of gene x environment interactions, have not yet been explored in humanized mouse models. We applied high-accuracy measurement of DNA methylation (DNAm) via targeted bisulfite sequencing (HAM-TBS) to investigate DNAm in three tissues/brain regions (blood, prefrontal cortex and hippocampus) of mice carrying the human FK506-binding protein 5 (FKBP5) gene, an important candidate gene associated with stress-related psychiatric disorders. We explored DNAm in three functional intronic glucocorticoid-responsive elements (at introns 2, 5, and 7) of FKBP5 at baseline, in cases of differing genotype (rs1360780 single nucleotide polymorphism), and following application of the synthetic glucocorticoid dexamethasone. We compared DNAm patterns in the humanized mouse (N = 58) to those in human peripheral blood (N = 447 and N = 89) and human postmortem brain prefrontal cortex (N = 86). Overall, DNAm patterns in the humanized mouse model seem to recapitulate DNAm patterns observed in human tissue. At baseline, this was to a higher extent in brain tissue. The animal model also recapitulated effects of dexamethasone on DNAm, especially in peripheral blood and to a lesser extent effects of genotype on DNAm. The humanized mouse model could thus assist in reverse translation of human findings in psychiatry that involve genetic and epigenetic regulation in non-coding elements.

Cacna1c deficiency in forebrain glutamatergic neurons alters behavior and hippocampal plasticity in female mice.

CACNA1C, coding for the α1 subunit of L-type voltage-gated calcium channel (LTCC) Cav1.2, has been associated with multiple psychiatric disorders. Clinical studies have revealed alterations in behavior as well as in brain structure and function in CACNA1C risk allele carriers. These findings are supported by rodent models of Cav1.2 deficiency, which showed increased anxiety, cognitive and social impairments as well as a shift towards active stress-coping strategies. These behavioral alterations were accompanied by functional deficits, such as reduced long-term potentiation (LTP) and an excitation/inhibition (E/I) imbalance. However, these preclinical studies are largely limited to male rodents, with few studies exploring sex-specific effects. Here, we investigated the effects of Cav1.2 deficiency in forebrain glutamatergic neurons in female conditional knockout (CKO) mice. CKO mice exhibited hyperlocomotion in a novel environment, increased anxiety-related behavior, cognitive deficits, and increased active stress-coping behavior. These behavioral alterations were neither influenced by the stage of the estrous cycle nor by the Nex/Neurod6 haploinsufficiency or Cre expression, which are intrinsically tied to the utilization of the Nex-Cre driver line for conditional inactivation of Cacna1c. In the hippocampus, Cav1.2 inactivation enhanced presynaptic paired-pulse facilitation without altering postsynaptic LTP at CA3-CA1 synapses. In addition, CA1 pyramidal neurons of female CKO mice displayed a reduction in dendritic complexity and spine density. Taken together, our findings extend the existing knowledge suggesting Cav1.2-dependent structural and functional alterations as possible mechanisms for the behavioral alterations observed in female Cav1.2-Nex mice.

The Activating Transcription Factor 3 (Atf3) Homozygous Knockout Mice Exhibit Enhanced Conditioned Fear and Down Regulation of Hippocampal GELSOLIN.

The genetic and molecular basis underlying fear memory formation is a key theme in anxiety disorder research. Because activating transcription factor 3 (ATF3) is induced under stress conditions and is highly expressed in the hippocampus, we hypothesize that ATF3 plays a role in fear memory formation. We used fear conditioning and various other paradigms to test Atf3 knockout mice and study the role of ATF3 in processing fear memory. The results demonstrated that the lack of ATF3 specifically enhanced the expression of fear memory, which was indicated by a higher incidence of the freeze response after fear conditioning, whereas the occurrence of spatial memory including Morris Water Maze and radial arm maze remained unchanged. The enhanced freezing behavior and normal spatial memory of the Atf3 knockout mice resembles the fear response and numbing symptoms often exhibited by patients affected with posttraumatic stress disorder. Additionally, we determined that after fear conditioning, dendritic spine density was increased, and expression of Gelsolin, the gene encoding a severing protein for actin polymerization, was down-regulated in the bilateral hippocampi of the Atf3 knockout mice. Taken together, our results suggest that ATF3 may suppress fear memory formation in mice directly or indirectly through mechanisms involving modulation of actin polymerization.