A novel role for the cytokine granulocyte-macrophage colony- stimulating factor (GM-CSF) in the induction of mRNA for ovine interferon tau (oIFN).

Abstract

During pregnancy the sheep conceptus produces various proteins, most notably oIFNr (ovine trophoblast protein-1, oTP-1). Their production is enhanced by various cytokines/growth factors. To study the role of GM-CSF in the reproductive tract of nonpregnant and pregnant ewes, the temporal expression and cellular sites of synthesis of GM-CSF mRNA were determined. GM-CSF mRNA was detected by in situ hybridization in luminal and glandular epithelium of uterine endometrium of both nonpregnant ewes. GM-CSF expression was restricted to the uterine luminal and glandular epithelial cells at all stages of gestation. GM-CSF mRNA was also detected in the cytoplasm of trophoblastic cells of the conceptus. Higher levels of GM-CSF mRNA expression were observed in pregnant ewes compared to that of non-pregnangt ewes and the conceptus. Total cellular RNA extracted from conceptuses cultured with various cytokines was characterized for relative amounts of oIFNr mRNA by northern blot analysis. GM-CSF increased oIFNr mRNA in a dose dependent fashion with maximal induction at 300 Vlml hrGM-CSF. IL-3 increased conceptus oIFNr mRNA in a dose dependent manner with maximal induction in conceptuses treated with 75 Vlml IL-3. IL-6 increased oIFNr mRNA regardless of doses tested. Retinoic acid (RA) alone had no effect on oIFNr mRNA, but when combined with GM-CSF added to cultures simultaneously, conceptus oIFNr mRNA was not increased suggesting that RA down regulated GM-CSF induction of oIFNr in vitro. These results document that the GM-CSF gene is expressed in non-pregnant and pregnant ewes, specifically in uterine luminal and glandular epithelial cells. The presence of GM-CSF transcripts in trophoblastic cells of the conceptus suggests a major role for GM-CSF in the dynamic development of the conceptus and the induction of oIFNr in a paracrine manner. Collectively, these results suggests that a well established communication exists between the developing conceptus and the endometrium during pregnancy establishment.