Estrogen induces estrogen receptor α expression and hepatocyte proliferation in late pregnancy.

Partial hepatectomy (PH) induces estradiol production, and then hepatocyte proliferation. Estradiol may play a role in triggering hepatocyte proliferation after PH. In this study, estradiol was injected to the Estrogen Receptor alpha (ERα) or ERβ KO mice. No increased hepatocyte proliferation was observed in ERα KO mice, indicates that ERα is involved in estradiol-induced hepatocyte proliferation. The ERα and ERβ KO mice are sterile, hence it is impossible to study ERα and ERβ function during pregnancy when the estrogen levels are highest. Using conditional mutagenesis technique, we made ERα hepatocyte KO mice, which are fertile. We used these mice for analyzing the hepatocyte ERα function during pregnancy. However, in the control mice, the maternal hepatocyte was proliferated higher in late pregnancy, but no pregnancy-induced hepatocyte proliferation was observed in KO mice. Hence, we conclude that the maternal hepatocyte ERα is involved in estradiol-induced hepatocyte proliferation in late pregnancy.