Programming for increased expression of hippocampal GAD67 mediated the hypersensitivity of the hypothalamic\u2013pituitary\u2013adrenal axis in male offspring rats with prenatal ethanol exposure

Juan Lu,Hui Wang,Chong Zhang,Ying Yu,Dan Xu,Qiang Li,Xia He,Zhexiao Jiao

doi:10.1038/s41419-018-0663-1

Abstract

An imbalance of excitatory and inhibitory signals in the brain has been proposed to be one of the main pathological features of various diseases related to hypothalamic–pituitary–adrenal axis (HPAA) dysfunction. Excessive glutamate release induces neuronal excitotoxicity, while glutamic acid decarboxylase (GAD) 67 promotes the transformation of excessive glutamate to γ-aminobutyric acid (GABA). Our previous studies demonstrated that prenatal ethanol exposure (PEE) causes foetal over-exposure to maternal corticosterone and hypersensitivity of the HPAA after birth, but its intrauterine programming mechanism is unknown. In this study, PEE was shown to lead to an enhanced potential excitatory ability of the hypothalamus and hypersensitivity of the HPAA, as well as mild abnormal hippocampal morphology, demethylation of the -1019 to -691-bp region in the hippocampal GAD67 promoter and upregulation of GAD67 expression accompanied by a reduction in glutamatergic neurons and increase in GABAergic neurons in PEE male offspring. Similar changes were also found in PEE male foetal rats. Furthermore, corticosterone increased the expression of the glucocorticoid receptor (GR) and GAD67 in foetal hippocampal H19-7 cells in a concentration-dependent manner, accompanied by demethylation of the GAD67 promoter, a decrease in glutamatergic neurons and increase in GABAergic neurons. The GR inhibitor, mifepristone, reversed the effects of corticosterone on H19-7 cells. These results suggested that PEE-induced excessive corticosterone can lead to upregulation of GAD67 through epigenetic modification mediated by the GR in the male foetal hippocampus, thereby weakening the negative regulation of the HPAA by the hippocampus and increasing the potential excitatory ability of the hypothalamus. These changes persisted until after birth, resulting in hypersensitivity of the HPAA. However, gender differences were observed in the hippocampal development, morphology and GAD67 expression associated with PEE. Programming for the increased expression of hippocampal GAD67 is a potential mechanism responsible for the hypersensitivity of the HPAA in PEE male rats.

Highlights

The hypothalamic–pituitary–adrenal axis (HPAA) is an important neuroendocrine axis involved in the stress response and metabolic regulation
Using this stable intrauterine growth retardation (IUGR) rat model induced by prenatal ethanol exposure (PEE), we demonstrated a hypersensitivity of the HPAA to chronic stress (CS) in male adult offspring, embodied by increased expression levels of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) in the hypothalamus and elevated levels of serum adrenocorticotropic hormone (ACTH) and corticosterone after CS (Fig. 1c–f)
GAD65 is the major synthase of glutamate to γ-aminobutyric acid (GABA), and Reelin is involved in its synaptic transmission and plasticity

Summary

Introduction

The hypothalamic–pituitary–adrenal axis (HPAA) is an important neuroendocrine axis involved in the stress response and metabolic regulation. Lu et al Cell Death and Disease (2018)9:659 environment can cause developmental programming alterations of the HPAA and have a permanent effect on neuroendocrine function[1,2,3]. Excessive maternal glucocorticoids inhibit the development of foetal HPAA function and alter glucose and lipid metabolism in peripheral tissues, eventually resulting in IUGR10, 11. These intrauterine neuroendocrine and metabolic changes can be extended to after birth even into adulthood, embodied by hypersensitivity of the HPAA to chronic stress (CS) and glucocorticoid-dependent changes in glucose and lipid metabolism in peripheral tissues in PEE offspring with a post-weaning high-fat diet, thereby causing metabolic syndrome and non-alcoholic fatty liver disease[10, 12]. Whether hypersensitivity of the HPAA to CS exists in PEE offspring fed a normal diet, whether gender differences exist in the mechanism resulting in HPAA hypersensitivity and whether epigenetic modification is involved in the hypersensitivity of the HPAA are unclear

Methods

Results

Conclusion