Searching for the genetic basis of impaired placentation in the Dahl salt sensitive rat model of superimposed preeclampsia

Abstract

Preeclampsia, a hypertensive disorder of pregnancy, is a leading cause of maternal and fetal morbidity and mortality worldwide. Despite the rising prevalence and severity of this disease, the initiating factors responsible for the development of preeclampsia remain unknown. While it is hypothesized that impaired placentation precedes the maternal syndrome of preeclampsia, specific factors that contribute to altered vascular remodeling at the maternal‐fetal interface have not yet been identified. We have recently characterized the Dahl salt sensitive rat (Dahl S) on a 0.3% NaCl diet as a spontaneous model of superimposed preeclampsia, and here we use this model to investigate potential genetic factors that contribute to the impaired placental vasculogenesis we have observed in this model. Sprague Dawley (SD) rats were used for comparison as a model of healthy pregnancy and normal placentation. Female Dahl S and SD rat strains were each mated, and implantation sites in the uterus were isolated on gestational days (GD) 7, 10, and 14 (n=4–5/group). Uterine samples from virgin (GD0) rats were also obtained, and placental samples were isolated on GD14 (n=5/group). RNA was isolated, whole transcriptome analysis was performed using Affymetrix GeneChips, and data analyzed using GeneSifter and Ingenuity Pathway Analysis (IPA) software. A preliminary analysis of microarray data (fold‐change >1.5; p<0.05) between SD and Dahl S showed a number of genes differentially expressed at GD 0 (466 genes), 7 (714), 10 (679), and 14 (512). At GD 0–10, few genes [e.g., fibronectin type III domain containing 7 and Cd86 (involved in T‐cell activation and proliferation)] were significantly different using more stringent B&H FDR (P<0.05), suggesting there are small/relatively subtle changes between the strains that lead to strong physiological difference. However, by GD14 (the beginning of the “third trimester” in the rat), 33 genes were significantly different between SD and S using more stringent statistical criteria. This analysis revealed greater expression of genes involved in cellular responses to hypoxia and oxidative stress (e.g. lactoperoxidase and prolactin family 8, subfamily a, member 2) in the Dahl S rat. Using a 2‐way ANOVA to look at changes that occur between groups and over time (strain X time interaction), gene differences between strains were 466 (FDR, p<0.05); with time were 1727 (FDR; p<0.001); and for strain X time there were only two [mast cell protease 10 and zinc metallopeptidase, STE24 homolog (S. cerevisiae) with most stringent FDR]. When the statistical criteria was relaxed (p<0.05), the number of strain X time genes was much greater (n=847). Currently, we are working to perform a more systematic analysis, including identification of major biological functions, canonical pathways, and gene networks to place the gene differences in context of physiological changes. The identification of these specific pathways that lead to impaired placentation in this model of preeclampsia will provide clues to understanding the pathogenesis of the disease.