Zinc supplementation selectively decreases fetal hepatocyte DNA synthesis and insulin-like growth factor II gene expression in primary culture

Abstract

Zinc is important for normal cell growth and differentiation, DNA synthesis, and gene expression. IGF-II is a fetal growth and differentiation factor whose regulation is largely unknown. To assess the effect of zinc (Zn) on fetal hepatocyte IGF-II expression and DNA synthesis, primary cultures of ovine fetal hepatocytes were studied in serum-free medium containing 1 μmol/L Zn or supplemented to 10 or 50 μmol/L Zn. Fetal hepatocyte DNA synthesis, Zn and protein content, IGF-II mRNA, and IGF binding protein production were measured. Zn concentration in medium increased slightly in unsupplemented dishes, from 1 to 1.5 μmol/L; however, Zn concentration declined by 4 and 8 μmol/L over 24 h in culture medium supplemented to contain either 10 or 50 μmol/L Zn (p < 0.05). Zn content of cell pellets increased 155 and 204% after 24 h in supplemented cultures compared with unsupplemented controls, demonstrating uptake of Zn by the liver cells. Media Zn supplementation to 10 and 50 μmol/ L decreased 3H-thymidine incorporation of cells in culture by 11 and 13%, respectively, compared with 1 μmol/L Zn (p = 0.001). Addition of Zn caused a progressive 2- to 3fold decline in the nuclear labeling index of fetal hepatocytes, whereas the labeling index of nonhepatocytes increased almost 2-fold at 50 μmol/L compared with 1 μmol/ L Zn. Associated with decreased hepatocyte DNA synthesis, IGF-II mRNA abundance declined by almost 30%. IGF binding protein content of conditioned medium did not change with added Zn. Cellular DNA and protein contents did not vary after 24 h in culture with either 1, 10, or 50 μmol/L Zn, suggesting that Zn was not toxic to the cells. We conclude that Zn selectively decreases fetal hepatocyte proliferation in primary culture, whereas nonparenchymal cell growth is not inhibited. Some of this response may be caused by decreased expression of IGF-II, an autocrine growth factor for fetal hepatocytes. © 1994 International Pediatric Research Foundation, Inc.