5A). Pparγ and Lxrα expression were clearly increased by 4- and 2-fold, respectively, in the liver of mice exposed to BPA-TDI only (Fig. 5A). We also measured the expression of sterol regulatory element binding protein 1c (SREBP-1c), a major regulator of de novo lipogenesis,27 of sterol regulatory element binding protein 2 (SREBP-2), which regulates cholesterol metabolism,28

and of carbohydrate response element binding protein (ChREBP), a transcriptional regulator of glucose and lipid metabolism.29 The expression of Srebp-1c, Srebp-2, and Chrebp exhibited an inverted U-shaped dose-response profile under the effect of BPA (Fig. 5B). This was also the case for insulin induced gene 1 (Insig1), but not for insulin induced Sirolimus gene 2 (Insig2), two negative regulators of SREBP-2 and SREBP-1c processing, respectively (Fig. 5B). The analysis by western blot of nuclear protein levels for ER and for the key regulators of lipogenesis SREBP-1C, CHREBP and LXR confirmed a specific effect of low BPA Selleckchem ICG-001 doses on the active protein levels of these transcription factors (Fig. 5C). To evaluate the consequences of increased expression of lipogenic genes, we stained hepatic neutral lipids with Oil-Red-O. The representative pictures in Fig. 6A illustrate a greater accumulation of lipids in the liver of mice exposed to BPA compared with control livers. Lipid droplets were larger and more numerous in the

livers click here of mice exposed to BPA-TDI compared with those exposed to BPA-NOAEL.

The quantification of liver lipid content confirmed these observations. BPA had no effect on hepatic total free cholesterol content (not shown). Liver triglycerides were significantly increased by approximately 60% and 65% in mice exposed to 50 and 500 μg BPA/kg/day, respectively, compared with control mice (Fig. 6B). Additionally, mice exposed to BPA-TDI also showed a significant increase in hepatic cholesteryl esters (Fig. 6B). The analysis of hepatic FA composition (Fig. 6C; Supporting Table 3) showed that exposure to 50 or 500 μg BPA/kg/day resulted in accumulation of palmitic (C16:0) and oleic acids (C18:1n-9), the major constituents of triglycerides and cholesteryl esters. Conversely, the proportions of polyunsaturated FA and of C18:0, which are found at higher levels in phospholipids, were reduced at these doses. Despite increased Elovl6 mRNA expression, the C18:0/C16:0 ratio was decreased at these doses. This may result from a combined increased synthesis of C16:0 by FAS and the efficient desaturation/elongation of C18:0 (as illustrated by the increased C18:1n-9/C18:0 ratio, Fig. 6D), both producing substrates for triglyceride synthesis. Our results show that the oral exposure of adult male mice to low BPA doses increases plasma insulin and hepatic mRNA and protein expression related to lipid biosynthesis.