Rescue of the Corpus luteum from luteolysis by bovine trophoblast protein-1: an example of maternal recognition of pregnancy

RESUMO

Bovine trophoblast protein-1 (bTP-1) is an interferon molecule produced by trophectoderm tissue that plays a critical role in maintenance of luteal function during early pregnancy. Synthesis and secretion of bTP-1 begins as early as day 10 of pregnancy, is maximal around days 15-22, and continues to at least day 25. Bovine trophoblast protein-1 exists as a complex of up to 13 microheterogeneous glycoproteins in three molecular weight classes (21-22 kDa, 23-24 kDa and 26 kDa), with each molecular weight class having 4-5 isoelectric variants of pI 5.6-6.6. The several isoelectric variants of bTP-1 arise from different mRNA and the different size classes from differences in degree of glycosylation. As for other interferon-* molecules, bTP-1 possesses antiviral activity and inhibits lymphocyte proliferation. The major role of bTP-1, however, is to block endometrial secretion of prostaglandin F2* so as to prevent luteolysis. This effect of bTP-1 may be exerted through induction of an inhibitor in endometrial epithelial cells that blocks the conversion of arachidonic acid to prostaglandins. Interestingly, other interferon-* molecules can also block secretion of endometrial PGF2* in vitro and one of these, bovine interferon-*1 1, has been shown to be effective in extending luteal lifespan when administered intramuscularly. This latter finding raises the possibility of using systemically-administered bTP-1 or other interferon-* molecules for enhancing fertility. Before such schemes can be feasible, however procedures must be found to minimize side effects of interferon administration such as hyperthermia and a transient depression in circulating progesterone concentrations. Future research on bTP-1 will concentrate on developing practical systems for fertility enhancement using bTP-1 or related interferons as well as on problems of mechanism of action of bTP-1 and regulation of expression of the bTP-1 gene in trophectoderm