Iodoacetic Acid Exposure Alters the Transcriptome in Mouse Ovarian Antral Follicles

The process of drinking water disinfection forms compounds known as disinfection byproducts (DBPs). Studies have shown that DBPs can be harmful to human and animal health. Iodoacetic acid (IAA) is a non-regulated DBP that is cytotoxic and genotoxic to mammalian cells. In addition, IAA has been shown to be an ovarian toxicant in vitro and in vivo. However, the mechanisms of action underlying IAA toxicity on ovarian follicles in vivo remain unclear. In this study, we determined whether IAA exposure alters gene expression patterns in ovarian antral follicles in mice. Adult female CD-1 mice were dosed with water or IAA (10 or 500mg/L) in the drinking water for 35-40 days. Antral follicles were dissected from the ovaries based on size (220–400?µm). Sera were collected to measure estradiol levels. RNA-sequencing was applied to uncover the global gene expression of the antral follicles in response to IAA exposure. RNA-sequencing analysis identified 410 and 653 differentially expressed genes (DEGs) in the 10 and 500mg/L IAA treatment groups (FDR < 0.1), respectively, compared to controls. Gene Ontology Enrichment analysis showed that DEGs were involved with RNA processing and regulation of angiogenesis (10mg/L) and the cell cycle, cell division, and mitotic nuclear division (500mg/L). In addition, Pathway Enrichment analysis showed that DEGs were involved in the phosphatidylinositol 3-kinase and protein kinase B (PI3K-Akt) signaling pathway, gonadotropin-releasing hormone (GnRH) signaling pathway, estrogen signaling pathway, and insulin signaling pathway (10mg/L). In the 500mg/L group, Pathway Enrichment analysis showed that DEGs were involved in the oocyte meiosis signaling pathway, GnRH signaling pathway, and oxytocin signaling pathway. In addition, RNA-sequencing analysis identified 809 DEGs when comparing the 10 and 500mg/L IAA groups (FDR < 0.1). DEGs were related to ribosome, translation, mRNA processing, oxidative phosphorylation, chromosome, cell cycle, cell division, protein folding, platelet activation, and the oxytocin signaling pathway. Moreover, IAA exposure significantly decreased estradiol levels (500mg/L) in serum compared to control. This study identified key candidate genes and pathways involved in IAA toxicity that could help to further understand the molecular mechanisms of IAA toxicity in ovarian follicles. Overall design: Murine mRNA profile of ovarian antral follicles. Adult female mice (40 days old) were dosed with vehicle (deionized, reverse osmosis filtered water) or IAA (10 or 500 mg/L) dissolved in reverse osmosis water for 35 days (n=5 per treatment group) via the drinking water. Two experiments were performed a month apart. In experiment 1, animals were exposed to only water (control) or 500mg/L of IAA in drinking water. In experiment 2, animals were exposed to only water (control) or 10mg/L of IAA in drinking water. Antral follicles were mechanically isolated from 1 individual mouse and submitted for mRNA sequencing as 1 experimenal unit. Global analyses combined control groups from both experiments for comparisons with IAA treated groups.