Retinoids stimulate leptin synthesis and secretion in human syncytiotrophoblast

The syncytiotrophoblast (ST), which forms the outer layer of the chorionic villi, is the endocrine unit of the human placenta. Bathing in the maternal blood of the intervillous space, the ST secretes its hormonal products dir ectly into the maternal circulation. Leptin is expressed in the ST and is s ecreted into the maternal circulation. However, its regulation and physiolo gical role during pregnancy remain poorly known. In the present work we use d the in vitro model of human cytotrophoblast differentiation into ST to st udy the effect of physiological and synthetic retinoids on leptin synthesis and secretion. Using specific antibodies we first illustrated by immunocyt ochemistry the expression of retinoic acid (RA) receptor a! and retinoid X receptor alpha (RXR alpha) in ST. We then observed that leptin messenger ri bonucleic acid and protein expression increased with in vitro ST formation. The 9-cis isomer of RA and the synthetic retinoid specific for RXRs (BMS 6 49) stimulated leptin messenger ribonucleic acid expression and secretion. In contrast, all-trans-RA and a RA cr-specific ligand had no effect. These results suggest that retinoids regulate leptin expression and highlight a r ole for RXR alpha in this process.