Sex-specific Effect of Maternal Immune Activation on Gene Expression in the Rat Placenta

Abstract Body : Background: The placenta is a temporary organ necessary for fetal growth and survival during pregnancy. Viral infections during pregnancy can trigger maternal immune activation (MIA) resulting in placental inflammation. Inflammation can compromise placental function and contribute to adverse pregnancy outcomes such as preeclampsia, fetal growth restriction, and neurodevelopmental disorders in offspring. Many of these complications manifest differently depending on the offspring sex, suggesting differential inflammatory responses between female and male placentas. The mechanisms underlying these sexually dimorphic inflammatory responses are not well understood. Therefore, the objective of this study is to characterize the gene expression profiles associated with female and male placental malfunction, resultant of MIA. We hypothesized that acute maternal exposure to a viral mimetic during late gestation would result in differential gene expression in female and male rat placentas.

Methods: On gestational day 18.5, pregnant Sprague-Dawley rats (N=4 per group) were intravenously injected with 4 mg/kg of the viral mimetic polyinosinic-polycytidylic acid (poly I:C), or an equal volume of saline (controls). Five hours following injection, pregnant dams were euthanized. Female and male placentas (determined by Kdm5c/5d genotyping of fetal tissue) were collected and processed for RNA-sequencing (RNA-seq). Partec Flow was utilized for RNA-seq analyses.

Results: There were 1,541 and 938 genes differentially expressed (P < 0.05, fold-change > 1.5) in female and male placentas, respectively, from poly I:C treated dams when compared to placentas from saline-injected dams. Female and male gene profiles showed that some genes were significantly upregulated in female placentas but not males (e.g., Socs2), and others were increased in males only (e.g., Gzma). This suggests that placentas exhibit sex-specific changes in the expression of a subset of genes following maternal poly I:C exposure. Gene ontology analysis confirmed that pathways such as 'inflammatory response' and 'response to virus' were significantly upregulated in both female and male placentas following maternal poly I:C exposure (P < 0.0001). Interestingly, pathways associated with vascular activation and vasoconstriction were also significantly upregulated in female and male placentas after maternal poly I:C exposure (P < 0.05). Notable genes associated with vascular activation and vasoconstriction that had increased expression in placental tissue after maternal poly I:C injections, included: Cxcl10 (5.5-fold), Cxcl11 (7.3-fold), Vcam1 (4.9-fold), Icam1 (1.7-fold), Edn1 (2.9-fold) and Vcan (3-fold; all P < 0.05).

Conclusion and Significance: Maternal poly I:C exposure increased the expression of genes associated with viral inflammation, vascular activation and vasoconstriction in both female and male placentas. A subset of genes showed altered expression profiles in a sex-specific manner. Future work will determine whether genes exhibiting altered expression profiles after maternal poly I:C exposure are similarly changed at the protein level, and if so, experiments will be done to determine their localization patterns. Collectively, these findings will provide insight into the influence of sex on the placenta's response to viral stimuli and provide opportunities to design targeted interventions to help mitigate adverse pregnancy outcomes following MIA.