Benzopyrene Aggravates Nonalcoholic Liver Fatty Diseases in Female Mice Via the AHR/ERα Axis

Objective: Nonalcoholic fatty liver disease (NAFLD) is a prevalent liver condition worldwide, and the statistics show that men have a higher incidence and prevalence than women, but its toxicological mechanism is not completely clear. This research is intended to explore the role of BaP in NAFLD and to study how the environmental pollutant BaP influences the AHR/ERα axis to mediate the progression of NAFLD.

Methods: In this study, we established NAFLD models in vivo and in vitro by treating HepG2 cells with a high-fat diet and Oleic acid (OA) in C57BL/6J mice. Liver injury indexes ALT, AST, and lipid metabolism indexes TG and TC were evaluated to verify the success of modeling. Then, the model was treated with BaP, and the mRNA and protein expressions of CYP1A1, ERα, and SREBP-1c were evaluated by RT-PCR and WB, and the changes of liver fat were evaluated by HE and oil red O staining. Next, BaP was added into the cells treated with or without estradiol (E2), and the lipid metabolism in the cells was evaluated by oil red O staining, and whether the above levels of CYP1A1, ERα and SREBP-1c were changed.

Results: Our results show that after exposure to BaP, ERα protein levels in mice and cells are inhibited, mRNA and protein levels of SREBP-1c are reduced, and lipid metabolism processes are obstructed. The addition of E2 can reduce the increase of SREBP-1c mRNA and protein expression induced by OA, and reduce the deposition of lipids in cells. However, BaP treatment can weaken the action of E2 and destroy the protection of E2 in cells.

Conclusion: The results showed that E2 could reduce SREBP-1c mRNA and protein levels. BaP can stimulate AHR, leading to the degradation of ERα protein, reducing the binding of E2 to ERα, and aggravating the progression of NAFLD. This reveals the toxicological mechanism by which environmental pollutant BaP influences E2 to mediate NAFLD, and provides strong evidence for differences in NAFLD between the sexes.