Reproduction Abstracts

Bovine placental lactogen (bPL) is a classical member of a prolactin (PRL) gene family expressed in the placenta. bPL exerts lactogenic activity similar to pituitary PRL, however, detailed information about the role of bPL during bovine gestation is still limited. The 16 k N-terminal fragments of PRL, generated by enzymatic cleavage, have angiostatic activities in human and rodents. In the present study, we examined the feasibility of N-terminal fragments of bPL following cleavage by placental enzymes. bPL (32 kDa) was cleaved by matrix metalloproteinase (MMP)-8, -9 and -13 resulting in the 25 kDa N-terminal fragments. Gelatinase and collagenase activities in placental explant culture media were confirmed by gelatin and casein zymographies, respectively. The expression of Mmp13 in the trophoblast was detected by in situ hybridization. Cleaved form of bPL was generated by recombinant expression and purified truncated protein was used for following studies. The cleaved N-terminal fragments of bPL did not stimulate the proliferation of Nb2 cells indicating the loss of lactogenic activity. Angiogenic or angiostatic activity of cleaved bPL was examined by using cultured bovine brain microvascular endothelial cells (BBMC). Cleaved bPL inhibited the proliferation of BBMC in vitro while intact bPL had no effect for BBMC growth. Results in the present study show that bPL is cleaved by placental MMPs and resulted N-terminal fragments inhibit the proliferation of BBMC in vitro. Angiostatic activity of cleaved bPL could be shared in specific mechanisms in the regulation of placental angiogenesis. (Supported by JSPS Grants-in-Aid for Scientific Research 2013-13351115.)