Roles of Estrogens in the Healthy and Diseased Oviparous Vertebrate Liver

Abstract

The liver is a vital organ that sustains multiple functions beneficial for the whole organism. It is sexually dimorphic, presenting sex-biased gene expression with implications for the phenotypic differences between males and females. Estrogens are involved in this sex dimorphism and their actions in the liver of several reptiles, fishes, amphibians, and birds are discussed. The liver participates in reproduction by producing vitellogenins (yolk proteins) and eggshell proteins under the control of estrogens that act via two types of receptors active either mainly in the cell nucleus (ESR) or the cell membrane (GPER1). Estrogens also control hepatic lipid and lipoprotein metabolisms, with a triglyceride carrier role for VLDL from the liver to the ovaries during oogenesis. Moreover, the activation of the vitellogenin genes is used as a robust biomarker for exposure to xenoestrogens. In the context of liver diseases, high plasma estrogen levels are observed in fatty liver hemorrhagic syndrome (FLHS) in chicken implicating estrogens in the disease progression. Fishes are also used to investigate liver diseases, including models generated by mutation and transgenesis. In conclusion, studies on the roles of estrogens in the non-mammalian oviparous vertebrate liver have contributed enormously to unveil hormone-dependent physiological and physiopathological processes.

Flammulina velutipes stem regulates oxidative damage and synthesis of yolk precursors in aging laying hens by regulating the liver–blood–ovary axis

“…During egg production, the liver produces large amounts of apolipoproteins, yolk proteins, and lipids, which are processed into yolk precursors that are transported through the blood to the ovary to promote oocyte maturation; therefore, their levels can affect egg production ( Nimpf and Schneider, 1991 ). In addition, the synthesis of yolk precursors is regulated by the production of estrogen in the ovary ( Tramunt et al, 2021 ). It is therefore essential to investigate the mechanism of action of the liver–blood–ovary axis to prolong the reproductive cycle in laying hens.…”

The different natural estrogens promote endothelial healing through distinct cell targets

“…The production of E4 is restricted to the fetal liver of males and females from great apes, including humans. This is particularly intriguing because so far, the liver was rather viewed as a target of estrogens in oviparous animals ( 27 ) and also in mammals ( 28 ). The conversion of the E3 into E4 by the liver suggests a peculiar position and status of this organ in the network of sex hormones.…”

Reproductive and Developmental Effects of Sex-Specific Chronic Exposure to Dietary Arsenic in Zebrafish (Danio rerio)

“…In female oviparous vertebrates like fish, reproduction is regulated by the HPG-L (hypothalamus–pituitary–gonad–liver) axis, as the liver plays a primary reproductive function by synthesizing and secreting vitellogenin under estrogen stimulation [ 27 ]. Vitellogenin ( Vtg ) is a lipoglycophosphoprotein absorbed by the growing oocytes in the ovary, and it serves as a major precursor of egg yolk proteins that are essential nutrients for future embryogenesis [ 28 ]. Chronic exposure to arsenic-contaminated polychaete worms was found to suppress the expression of the hepatic Vtg gene in female fish, indicating that arsenic can disrupt Vtg production by the liver [ 15 ].…”