Initial Characterization Of Mitogenic Activity Of Ovine Corpora-Lutea From Early-Pregnancy

To characterize angiogenic factors produced by ovine corpora lutea (CL) during early pregnancy, two experiments were performed. In Experiment 1, luteal explants from days 12, 18, 24, and 30 (n = 4 ewes/day) after mating were incubated in serum-free medium for 6 h. Luteal-conditioned media (LCM) were evaluated for their ability to stimulate proliferation of endothelial and 3T3 cells, as well as migration of endothelial cells. Pools of the LCM (one pool/day) then were characterized biochemically. In Experiment 2, two pools of LCM from day 24 of pregnancy were evaluated for their effects on endothelial cell, 3T3 cell, and ovine luteal cell proliferation. These pools of LCM then were concentrated by ultrafiltration and subjected to heparin-agarose affinity chromatography with salt gradient (0-4 M NaCl in buffer) elution, and fractions were evaluated for mitogenic activity for endothelial and 3T3 cells. The resulting five peaks of mitogenic activity from heparin-agarose chromatography were characterized biochemically. The five peaks of mitogenic activity were further purified by using chromatography, then were concentrated and subjected to SDS-PAGE and Western analysis for FGF-2. Ovine CL from each day of early pregnancy secreted mitogens (P<0.05) for endothelial (285+/-8% of unconditioned media controls) and 3T3 (142+/-7%) cells as well as factors which stimulated migration of endothelial cell (153+/-8% of controls). LCM pool from day 24 of pregnancy also stimulated (P<0.05) proliferation of ovine luteal cells in a dose-dependent manner. In Experiment 1, mitogenic activity for endothelial cells was greater than 100 kDa, heat-labile, trypsin-sensitive and bound to DEAE-Sephacel and heparin-agarose columns, but not to a CM-Sepharose column. Antibody against FGF-1 did not affect mitogenic activity of LCM for endothelial and 3T3 cells, whereas treatment with FGF-2 antibody decreased (P<0.05) mitogenic activity of LCM for both endothelial and 3T3 cells. In Experiment 2, heparin-agarose affinity chromatography resolved five peaks of mitogenic activity: a non-heparin-binding peak that was specific for 3T3 cells, three heparin-binding peaks that were specific for endothelial cells, and one heparin-binding peak that was specific for 3T3 cells. In Experiment 2, heparin-, heat-, or trypsin-treatment and immunoneutralization with FGF-1 or FGF-2 antibodies influenced mitogenic activity of all of the peaks. Whereas SDS-PAGE demonstrated several bands of protein within each peak, Western analysis was unable to detect the presence of FGF-2 in any of the heparin-binding peaks. These data demonstrate that ovine CL from early pregnancy produce mitogenic factors that can be resolved into 5 separate peaks of activity with differing affinities for heparin. These data also indicate that the endothelial mitogens produced by CL of early pregnancy are immunologically related to, but biochemically distinct from FGF-2. Mitogens for endothelial and other cells likely play a role in regulation of luteal function during early pregnancy in sheep.