Assessing changes induced by in utero low protein dietary exposure in offspring development and behaviour

Abstract

Embryonic development involves temporal and spatial coordination of epigenetic processes, which are exquisitely sensitive to environmental influences and can have life-long implications for disease if disrupted. In this thesis, I examined the impact of gestational diet, specifically protein restriction, on the expression of cyclin-dependent kinase inhibitor C1 (Cdkn1c), a gene that is epigenetically regulated through genomic imprinting, during development and post-natally, with an allele-specific bioluminescent reporter mouse model. I showed that in utero low protein diet (LPD) exposure affects behaviour in adolescence and adulthood, through changes in the dopamine system at a transcriptional, cellular and metabolic level. Sensitisation experiments suggest that adult LPD mice are hypersensitive to cocaine, as they show increased locomotor activity compared to controls, and increased stereotypy at higher doses. Adult LPD mice also show hyperactivity and reduced anxiety, which are phenotypes frequently observed in hyperdopaminergic mouse models. Adolescent LPD mice demonstrated impaired motor function, in contrast to age-matched controls, based on open field and rotarod performance. However, I have shown this deficit to be transient and resolved by adulthood. Juvenile and adult LPD-exposed mice displayed a 25% increase in midbrain dopaminergic neuron numbers. Moreover, RNA analysis from adult midbrains showed a downregulation of the gene that encodes dopamine transporter (DAT) and upregulation of dopamine receptor 5 (D5) in LPD mice, with many other dopamine-related genes unaffected. A pilot RNA-seq experiment on midbrain neuronal nuclei identified 123 differentially expressed genes in LPD mice, affecting cholesterol synthesis and markers linked to neurodegeneration and early-life stress. Lastly, μPET imaging revealed elevated striatal dopamine synthesis capacity in adult LPD mice, recapitulating one of the hallmarks of schizophrenia, and in accordance with reports of gestational exposure to famine inferring increased susceptibility to schizophrenia. This work sheds light on consequences of early-life adversity and epigenetic disruption on embryonic brain development, behaviour and disease risk.