Altered hypothalamic DNA methylation and stress-induced hyperactivity in a novel model of early life stress

Abstract

Early life stress during childhood is associated with a number of psychiatric disorders that manifest across the life course. Preterm birth is a profound stressor, and an important cause of cognitive impairment, as well as neurodevelopmental and psychiatric disorders. However, the mechanisms that link events during the early neonatal period with later functional problems are poorly understood. We developed a novel mouse model of early life stress (modified maternal separation; MMS) with specific relevance to preterm birth (PTB) and hypothesised it would affect the hypothalamic transcriptome and DNA methylome and impact on behaviour in adulthood. MMS consisted of repeatedly stimulating pups for 1.5 hours/day, whilst separated from their mother, from postnatal day (P)4-6. 3' RNA sequencing and DNA methylation immunoprecipitation (meDIP) sequencing was performed on the hypothalamus at P6. Behaviour was assessed with the elevated plus and open field mazes, and in-cage monitoring at 3-4 months of age. Although MMS was only associated with subtle changes in gene expression there were widespread alterations in DNA methylation. Notably, differentially methylated regions were enriched for synapse-associated loci. MMS also resulted in hyperactivity in the elevated plus and open field mazes, but in-cage monitoring revealed that this was not representative of habitual hyperactivity. In conclusion we describe a novel model of early life stress with relevance to PTB, with marked effects on DNA methylation in the hypothalamus and with stress-specific hyperactivity in young adulthood. We suggest that these results have implications for the understanding of early life stress mediated effects on brain development.

Early life stress and LPS interact to modify the mouse cortical transcriptome in the neonatal period

“…Among the DEGs associated with MMS was Zfhx2 (Zinc Finger Homeobox 2), which plays a role in neuronal differentiation ( Komine et al., 2012 ) and is expressed in sensory neurons ( Habib et al., 2017 ); abnormalities in Zfhx2 associate with behavioural abnormalities including hyperactivity and anxiety ( Komine et al., 2012 ). This is of interest as we identified stress-induced hyperactivity following MMS ( Fitzgerald et al., 2020 ). We also observed enrichment of the GO term ‘response to cytokine’ with MMS.…”

“…On P3, PBS (autoclave sterilised) or 1 ​mg/kg LPS ( Silva et al., 2019 ) (Merck Life Science, Dorset, UK; Escherichia coli O111:B4) were administered intraperitoneally. MMS was performed ( Fitzgerald et al., 2020 ) between 13:30–15:00 on P4–P6. MMS and LPS ​+ ​MMS pups were placed on a heating pad adjacent to the home-cage, where the control and LPS groups remained.…”