Background: Autism spectrum disorder (ASD) has been associated with intrauterine growth restriction (IUGR), but the underlying mechanisms are unclear. Results: We found that the IUGR rat model induced by prenatal caffeine exposure (PCE) showed ASD-like symptoms, accompanied by altered gut microbiota and reduced production of indole 3-propionic acid (IPA), a microbiota-specific metabolite and a ligand of aryl hydrocarbon receptor (AHR). IUGR children also had a reduced serum IPA level consistent with the animal model. We demonstrated that the dysregulated IPA/AHR/NF-κB signaling caused by disturbed gut microbiota mediated the hippocampal microglia hyperactivation and neuronal synapse over-pruning in the PCE-induced IUGR rats. Moreover, postnatal IPA supplementation restored the ASD-like symptoms and the underlying hippocampal lesions in the IUGR rats. Conclusions: This study suggests that the microbiota-IPA-brain axis regulates ASD susceptibility in PCE-induced IUGR offspring, and supplementation of microbiota-derived IPA might be a promising interventional strategy for ASD with a fetal origin.

Prenatal dexamethasone exposure (PDE) induces multiorgan developmental toxicities in offspring. Here we verified the transgenerational inheritance effect of ovarian developmental toxicity by PDE and explored its intrauterine programming mechanism. Pregnant rats subcutaneously received 0.2 mg/kg/d dexamethasone from gestational day (GD) 9 to GD20. A subgroup was euthanized for fetuses on GD20, and the other group went on to spontaneous labor to produce F1 offspring. The adult F1 females were mated with normal males to produce the F2 and F3 generations. The PDE fetal rats exhibited ovarian mitochondrial structural abnormalities, decreased serum estradiol (E₂) levels, and lower expression levels of ovarian steroidogenic factor 1 (SF1), steroidal synthetases, and insulinlike growth factor 1 (IGF1). On postnatal week (PW) 6 and PW12, the PDE F1 offspring showed altered reproductive behavior and ovarian morphology. The serum E₂ level and ovarian expression of SF1, steroidal synthetases, and IGF1 were also decreased. The adult F3 offspring showed alterations in reproductive phenotype and ovarian IGF1, SF1, and steroidal synthetase expression similar to those of F1. PDE induces ovarian developmental toxicity and transgenerational inheritance effects. The mechanism by which this toxicity occurs may be related to PDE-induced low-functional programming of fetal ovarian IGF1/SF1 and steroidal synthetases.

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.