Leptin receptor expression increases in placenta, but not hypothalamus, during gestation in Mus musculus and Myotis lucifugus.
In addition to effects on appetite and metabolism, the hormone leptin is required for reproduction in mammals. Maternal plasma leptin is increased above non-pregnant levels in all mammals thus far examined, including humans. The increase in plasma leptin appears to result in part from upregulation of adipose leptin secretion (e.g., in mice), or from production and secretion of leptin from the placenta (e.g., in humans and some bats). The placenta may also modulate maternal leptin levels via production of a plasma leptin-binding protein (mice, humans). Thus, the placenta plays a coordinating role in regulation of maternal leptin during pregnancy. In this study, the hypothesis that the placenta is also a target organ for leptin in diverse taxa was tested by examining the expression of leptin receptors (Ob-R) in placentae from species of distantly related mammalian taxa, Mus musculus (the laboratory mouse) and Myotis lucifugus (the little brown myotis, also called the little brown bat). A partial sequence of M. lucifugus Ob-R cDNA was first obtained and found to share approximately 78-88% homology at the nucleotide level with known mammalian Ob-R cDNAs. Using probes and primers designed from this sequence, receptor expression was detected in numerous tissues of M. lucifugus, including placenta, which expressed two major receptor isoforms as judged by molecular size. In both species, Ob-R mRNA expression in placenta significantly increased from early to late gestation. Expression of Ob-R mRNA was not affected by cAMP treatment in vitro. The increase in Ob-R mRNA expression in placenta was specific, since Ob-R mRNA expression did not change during gestation in either species in hypothalamus, the major site of the central actions of leptin. Thus, Ob-R is expressed in placenta throughout gestation in mice and bats, and its expression increases over the course of gestation, which raises the possibility that leptin may exert temporally distinct effects on placental growth or function throughout gestation. Because similar placenta-specific changes in leptin receptor expression occurred in species from distantly related mammalian taxa which collectively comprise approximately 70% of all known mammalian species, it is possible that placental actions of leptin are conserved across mammals, even in those species (such as the Swiss-Webster strain of mouse) in which the placenta does not itself produce leptin.