Inhibition of trophoblast invasiveness in vitro by immunoneutralization of leptin in the bat, Myotis lucifugus (Chiroptera)

In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and secreted by the placenta of many, but not all mammalian species. In mice, in which the placenta does not secrete leptin, exogenously added leptin stimulates invasiveness of early (but not late)-gestation trophoblast cells. We report a similar phenomenon occurs in Myotis lucifugus (little brown myotis), a species in which the placenta synthesizes and secretes leptin. Immunoneutralization of endogenously secreted leptin from cultured M. lucifugus trophoblast cells inhibited the ability of these cells to invade a matrigel matrix. The effect was not due to an inhibitory effect of the antibody on cell proliferation, nor was it a non-specific effect of antibody administration. Cell invasion was significantly reduced in untreated cells obtained from late-gestation placentas, and the antibody had no effect at that time. This occurred despite continued expression throughout gestation of the long (OBRb) and short (OBRa) isoforms of leptin receptor mRNA. This study suggests that an important function of leptin during pregnancy is an effect on trophoblast cell invasiveness, at a time when the placenta is becoming established. That this occurs in two phylogenetically unrelated and distant species, regardless of whether the placenta is a source of secreted leptin, suggests that this is a highly conserved reproductive action of leptin.