Caspase activity and regulation in the rat corpus luteum (CL) during pregnancy and following prostaglandin F2 alpha (PGF-2a) administration

PELUFFO, MC; STOUFFER, RL; TESONE, M

Omaha, Nebraska

Congreso; 39th SSR Annual Meeting; 2006

SSR (Society for the Study of Reproduction)

Apoptosis is involved in the regression of the CL in many species, but the molecular mechanisms involved are still unknown. Therefore, studies were designed to study the expression and activity of four caspases believed to contribute to the initial (eg, caspases-2, -8 and –9) and final (eg, caspase-3) apoptotic events in the CL during pregnancy and after injection of the physiological luteolysin, PGF-2a, in rats. CLs were dissected from ovaries obtained at different stages of pregnancy (days, 7, 17, 19 and 21 of gestation) and postpartum (day 1 and 4). In addition, on day 14 of pregnancy, rats were injected with PGF-2a and ovaries were collected at 0, 8, 16, 24 and 36 h after injection.  CL proteins were isolated for assessment of fluorometric caspase activity.  Ovaries (n = 6-7) were fixed for immunohistochemistry (IHC) of caspase-2, -3, -8, -9. Specific antibodies for the four caspases recognize both the inactive and the active forms. During pregnancy, the activity for the four caspases was significantly greater on day 19 as compared to all the other groups (p<0.05). IHC analyses showed specific staining for the caspases in luteal cells (large and small), as well as, in the endothelial cells. High protein expression for caspase-2 and -3 was observed at day 7, 17, 19 and 21 of pregnancy (before luteolysis), followed by a decrease in postpartum. In contrast, caspase-8 and -9 protein expression showed no changes during pregnancy, followed by a decrease at day 1 and an increase at day 4 postpartum. PGF-2a injection triggered an increase (P<0.05) in activity of all four caspases 36 h post treatment. There were no major changes in the caspase-2, -8 and –9 inmunostaining at any time, whereas caspase-3 appeared higher at 24 and 36 h post treatment. These results suggest an important role for this protease family during luteolysis in pregnancy, as well as an important role for PGF-2a in caspase regulation, in the rat CL. Supported by: ANPCYT and RR00163.