## 3 Results
None of them had the expression changed with estrogen deprivation with the exception of Nr1i1, in which mRNA levels fluctuated negatively with estrogen levels (Figure 4), as observed in the jejunum (Figure 3). As for jejunum, Mmp7 and Muc2 mRNA levels were also quantified. Other genes included markers of permeability involved in the intestinal barrier, specifically Tip1, Cldn2, and Ocdn which encode zonula occludens 1 (ZO-1), claud 2, and occludin, respectively. Additionally, genes encoding transcription factors involved in the differentiation of the different cell lineages in the intestine. For example, the protein atonal homog 1 (ATOH1) is essential for the formation of intestinal secretory cells (goblet, enteroendocrine, and Paneth cells). Neurogenin 3 (NGN3) is required for enteroendocrine differentiation. On this panel of genes, no significant impact on any of the measured genes was observed following ovariectomy and E2 replacement with the exception of Muc2 in the ileum and Tip1 and Atoh-1 in the colon (Figure 4, Figures S3 and S4). Exposure of ovariectomized mice to the pollutant mixture decreased the levels of Muc2 and Tip1 mRNA in the ileum compared to Ovx mice. Impact of Estrogens and of the Pollutant Mixture on the Expression of Genes Related to Bile Acid Biosynthesis in the Gut and Liver  
The synthesis of bile acids (BA) from cholesterol in the liver is strictly regulated by a negative feedback mechanism through a process known as enterohepatic circulation which refers to the circulation of BA from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte, and return to the liver through the portal vein. The complex scenario largely depends on the expression levels of specific bile acid efflux and uptake transporters within the liver and ileum, which are regulated by the farnesoid X receptor, FXR [35; 36]. Therefore, we focused on a panel of genes dedicated to the process of BA biosynthesis, in the liver and ileum of the four groups of mice. In the ileum, the expression of Nr1h4 encoding FXR did not vary between groups unlike Slc10a2 encoding the ileal sodium/bile acid cotransporter, also known as apical sodium-bile acid transporter (ASBT) and ileal bile acid transporter (IBAT). Specifically, the data showed significant upregulation in Ovx mice as compared to Sham mice, which was not demonstrated in the ileum of Ovx mice, whether E2-replaced or exposed to pollutants (Figure 4). In addition, fgf15 encoding fibroblast growth factor 15, which plays an important role in feedback inhibition of hepatic bile acid synthesis, has lowered mRNA levels in E2-replaced Ovx mice compared to Ovx mice. Ovx mice exposed to pollutants had levels in the same range as E2-replaced Ovx mice (Figure 4). In the liver, ovariectomy caused a significant decrease in the mRNA levels of Abcb11 (Figure 5), which encodes the bile salt export pump (BSEP), an ATP-dependent transporter localized to the canalicular membrane and which directs the efflux of BAs from hepatocytes into the bile. Along with the decrease in Abcb11, we showed a significant increase in the levels of Scl10a1 mRNA (Figure 5), which encodes the sodium/bile acid co-transporter also known as the Na + -taurocholate co-transporter polypeptide (NTCP) or liver bile acid transporter (LBAT) and permits re-entry of bile salts in hepatocytes. E2 replacement in Ovx mice prevented BA accumulation in hepatocytes through enhancing Abcb11 and reducing Scl10a1 mRNA levels as compared to Ovx mice (Figure 5). Pollutants did not modify the expression pattern of the BA transporters, Abcb11, and Scl10a1 (Figure 5). Moreover, we measured the expression levels of different genes related to cholesterol biosynthesis such as Lepr and Insig2, encoding the leptin receptor and the insulin-induced gene 2 [37; 38]. While data showed no changes following ovariectomy, Lepr was strongly enhanced and Insig2 was strongly decreased in E2-replaced Ovx mice compared to Ovx mice. However, pollutant exposure did not affect these parameters (Figure 5).