Apoptotic endometrial caspase-3 mediated phospholipase a2 activation, a critical component in programing uterine receptivity.

The objective of this study was to determine the consequence of uterine apoptotic caspase-3 activation on day 1 post coitus (dpc) in the pregnant mouse. We previously demonstrated that during pregnancy uterine caspase-3 activation isolated to the myometrial compartment is largely non-apoptotic and controls uterine quiescence. In this study we determined that uterine caspase-3 activation on 1 dpc may play a critical role in regulating endometrial PGE2 synthesis though iPLA2 activation. These analyses provide novel insight into the molecular mechanisms that regulate previously reported increases in endometrial PGE2 synthesis in very early pregnancy, that act to enhance uterine receptivity. We have identified the site and impact of that uterine apoptotic caspase-3 activation utilizing uteri isolated from non-pregnant control animals at estrous and diestrous and from control pregnant mice at 1-19 dpc. In addition, uteri were isolated from non-ligated controls (GD), unilateral (UL) and bilateral ligated (BL) uterine horn mouse models at 1, 3 and 6 dpc. Uteri were examined for apoptotic indices, such as caspase-3 activation and TUNEL staining. Immunohistochemical analysis was performed to identify the site of apoptotic caspase-3 activation. The presence of the truncated form of phospholipase A2 (tiPLA2) was examined as a measure of apoptotic caspase-3 mediated iPLA2 activation. Our analysis determined that apoptotic caspase-3 and iPLA2 activation were limited to the endometrial compartments of the control and unilateral uteri on 1dpc and were not found in the bilateral ligated uterine horn on 3 or 6 dpc. Our data indicates that the presence of a conceptus on 1 dpc triggers an increase in endometrial apoptotic caspase-3 mediated iPLA2 activation. iPLA2 when activated causes the hydrolysis of fatty acids resulting in arachidonic acid release and production of PGE2, which in early pregnancy has been demonstrated to act in a leutoprotective manner, prolonging progesterone synthesis and promoting uterine receptivity.