Effects of DNA methyltransferase inhibition on pattern separation performance in mice

Abstract

Introduction: Schizophrenia and anxiety disorders place a great burden on the patients suffering from it and on society. The cognitive symptoms of both diseases can be caused partly by impaired pattern separation. Pattern separation is the ability to make distinct representations out of highly overlapping information. Improving pattern separation could slow down the progression of the above mentioned disorders and thus improve the quality of life of the patients. Alterations in gene expression can lead to differences in pattern separation performance. Methylation of DNA is one of the epigenetic changes controlled by DNA methyltransferases (DNMT) that can alter such gene expression levels without changing the underlying DNA sequence. In this study, the DNMT inhibitor RG108 was given to mice in order to investigate its effect on pattern separation performance. Methods: 36 male C57BL/6 mice were used. Pattern separation performance was measured using the novel Object Pattern Separation task. It consists of two trials with two identical objects. In the second trial one of the objects is replaced along a vertical axis, while the second object stays in the same position. For the assessment of pattern separation the object is replaced at increasingly distinct locations. The most suitable inter-trial interval and position were assessed and pattern separation performance was measured after an intraperitoneal injection of either saline, 0.1mg/kg RG108 or 0.3mg/kg RG108. After 48 hours mice received a saline injection and pattern separation performance was measured again to check for carry-over effects. Lastly, a 24 hour inter-trial interval was used to unravel RG108 effects on long-term memory. After the behavioral task, the mice were decapitated and the dorsal hippocampus was dissected to quantify the expression of six target genes with qPCR. Results: RG108 leads to an acute, dose-dependent increase in pattern separation. This effect vanishes after 48 hours. Furthermore, RG108 administration is not sufficient to 89 enhance pattern separation in such a way that animals can still remember the object’s location after 24 hours. Whereas BDNF4, BDNF9, GRIA1, HDAC2 and HEY1 expressions do not change after acute administration of RG108, BDNF1 expression increases and can be the underlying reason for the improvement in pattern separation. Future studies are needed to reveal the possible methylation changes and to study the effect of chronic treatment with this drug.