Identification of Cholecystokinin by Genome-Wide Profiling as Potential Mediator of Serotonin-Dependent Behavioral Effects of Maternal Separation in the Amygdala

Abstract

Converging evidence suggests a role of serotonin (5-hydroxytryptamine, 5-HT) and tryptophan hydroxylase 2 (TPH2), the rate-limiting enzyme of 5-HT synthesis in the brain, in modulating long-term, neurobiological effects of early-life adversity. Here, we aimed at further elucidating the molecular mechanisms underlying this interaction, and its consequences for socio-emotional behaviors, with a focus on anxiety and social interaction. In this study, adult, male Tph2 null mutant ( Tph2 -/- ) and heterozygous ( Tph2 +/- ) mice, and their wildtype littermates ( Tph2 +/+ ) were exposed to neonatal, maternal separation (MS) and screened for behavioral changes, followed by genome-wide RNA expression and DNA methylation profiling. In Tph2 -/- mice, brain 5-HT deficiency profoundly affected socio-emotional behaviors, i.e., decreased avoidance of the aversive open arms in the elevated plus-maze (EPM) as well as decreased prosocial and increased rule breaking behavior in the resident-intruder test when compared to their wildtype littermates. Tph2 +/- mice showed an ambiguous profile with context-dependent, behavioral responses. In the EPM they showed similar avoidance of the open arm but decreased prosocial and increased rule breaking behavior in the resident-intruder test when compared to their wildtype littermates. Notably, MS effects on behavior were subtle and depended on the Tph2 genotype, in particular increasing the observed avoidance of EPM open arms in wildtype and Tph2 +/- mice when compared to their Tph2 -/- littermates. On the genomic level, the interaction of Tph2 genotype with MS differentially affected the expression of numerous genes, of which a subset showed an overlap with DNA methylation profiles at corresponding loci. Remarkably, changes in methylation nearby and expression of the gene encoding cholecystokinin, which were inversely correlated to each other, were associated with variations in anxiety-related phenotypes. In conclusion, next to various behavioral alterations, we identified gene expression and DNA methylation profiles to be associated with TPH2 inactivation and its interaction with MS, suggesting a gene-by-environment interaction-dependent, modulatory function of brain 5-HT availability.

Serotonin deficiency induced after brain maturation rescues consequences of early life adversity

“…A slightly altered expression of Maoa in amygdala and hippocampus may point to specific compensatory mechanisms due to MS 53 . Furthermore, MS exposed mice showed altered expression of Htr1a and Htr2a in the raphe independent of Tph2 icKO, which is in line with previous MS studies 76 , 77 . Alterations in 5-HT receptors in target regions of 5-HT neurons have previously been associated with altered anxiety and exploratory behavior 78 .…”

Serotonergic modulation of normal and abnormal brain dynamics: The genetic influence of the TPH2 G-703T genotype and DNA methylation on wavelet variance in children and adolescents with and without ADHD

“…Gene expression is, furthermore, defined by TPH2 ’s DNA methylation levels [ 11 , 12 ]. DNA methylation is an epigenetic modification in which a methyl group is added to cytosine in cytosine–phosphate–guanine (CpG) sites.…”

Long-Term Impact of Social Isolation and Molecular Underpinnings

“…Notably, its mammalian homolog cholecystokinin (CCK) regulates aggression and anxiety and has been implicated in panic disorder (Zwanzger et al, 2012;Katsouni et al, 2013). CCK transcription can also be modulated by other stressors such as maternal separation (Weidner et al, 2019). In rodents, chronic social isolation stress can trigger widespread changes in the transcription of protein-coding and non-coding genes (Karelina et al, 2009;Wallace et al, 2009;Liu et al, 2012a;Jin et al, 2016;Kumari et al, 2016;Verma et al, 2016Verma et al, , 2018Zelikowsky et al, 2018;Mavrikaki et al, 2019;Chang et al, 2020).…”