Maternal immune activation induces fetal epigenetic dysfunction, developmental perturbations in glutamatergic signalling and adult cognitive deficit in a rodent model for schizophrenia.

Introduction: Epidemiological studies demonstrate viral infection, resulting in maternal immune activation (mIA), during pregnancy is a risk factor for schizophrenia (SZ). We hypothesize that the maternal inflammatory response promotes epigenetic alterations in the fetal brain leading to changes in expression of key neurodevelopmental genes, which predisposes offspring to SZ. To test this hypothesis, we used our validated rat model for SZ, exposing pregnant dams to the viral mimetic polyinosinic: polycytidylic acid (poly(I:C)), which increases pro-inflammatory plasma cytokines, IL-6 and TNFα. Objectives: Establish DNA methylation patterns and associated gene/protein expression changes underpinning cognitive deficits in mIAoffspring. Methods: Pregnant Wistar rat dams were blindly assigned to receive 10mg/kg bodyweight poly(I:C) (mIA) or 0.9% saline (vehicle control) on gestational day (GD) 15 (N=8- 10/group). Adult offspring (Postnatal day (PD) 100) were assessed using the attentional setshifting task (ASST) for cognitive function underscored by prefrontal cortex (PFC) activity. Offspring PFC were dissected at multiple developmental timepoints (GD21, PD1, PD21, PD35 and PD100). DNA, RNA and protein were extracted for DNA methylation, mRNA (qPCR) and protein expression (WES) analysis, respectively (N=5-10/group). Data were analysed using general linear mixed models (GLMM). Results: Adult offspring exposed to mIA showed an increased number of trials and errors in the extra-dimensional shift phase of the ASST, indicative of a cognitive deficit. Global DNA methylation, Dnmt3a/b mRNA expression and DNMT activity were increased in GD21 mIA-fetuses, indicative of epigenetic alterations in response to mIA. mRNA analysis across developmental timepoints showed decreases in Reelin signalling genes (Reln, Dab1), and both decreases (Camk2b, Dlg4) and increases (Sgk1, Gpc4) in glutamatergic modulators in mIA-offspring. Protein analysis across postnatal timepoints showed a reduction in AMPA receptor (GRIA1) expression in PD21 and PD35 mIA-offspring but no changes in expression of NMDA receptors (NR2A, NR2B). However, we found a decrease in the NR2A:2B and NMDA: AMPA receptor ratios in adult mIA-offspring. Conclusions: Mia induced early alterations in DNA methylation together with persistent changes in the expression of glutamatergic signalling genes and an imbalance of glutamatergic receptor ratios. We suggest that developmentally imbalanced glutamatergic signalling in mIA-offspring may contribute to adult cognitive deficits, comparable to cognitive symptoms in SZ.