Effects of phytoestrogens on growth-related and lipogenic genes in rainbow trout (Oncorhynchus mykiss)

This study determined whether estradiol (E2) or the phytoestrogens genistein and daidzein regulate expression of growth-related and lipogenic genes in rainbow trout. Juvenile fish (5 mon, 65.8 ± 1.8 g) received intraperitoneal injections of E2, genistein, or daidzein (5 μg/g body weight) or a higher dose of genistein (50 μg/g body weight). Liver and white muscle were harvested 24 h post-injection. In liver, expression of vitellogenin (vtg) and estrogen receptor alpha (era1) increased in all treatments and reflected treatment estrogenicity (E2 > genistein (50 μg/g) > genistein (5 μg/g) = daidzein (5 μg/g)). Estradiol and genistein (50 μg/g) reduced components of the growth hormone (GH)/insulin-like growth factor (IGF) axis in liver, including increased expression of IGF binding protein-2b1 (igfbp2b1) and reduced igfbp5b1. In liver E2 and genistein (50 μg/g) affected expression of components of the transforming growth factor beta signaling mechanism, reduced expression of ppar and rxr transcription factors, and increased expression of fatty acid synthesis genes srebp1, acly, fas, scd1, and gpat and lipid binding proteins fabp3 and lpl. In muscle E2 and genistein (50 μg/g) increased era1 and erb1 expression and decreased erb2 expression. Other genes responded to phytoestrogens in a manner that suggested regulation by estrogen receptor-independent mechanisms, including increased ghr2, igfbp2a, igfbp4, and igfbp5b1. Expression of muscle regulatory factors pax7 and myod was increased by E2 and genistein. These data indicate that genistein and daidzein affect expression of genes in rainbow trout that regulate physiological mechanisms central to growth and nutrient retention.