Retinoid binding proteins-expression patterns in the human placenta

The present study examined the expression and occurrence of different retinoid binding proteins in human first trimester and term placenta. At both stages, messenger RNA for the serum transport vehicle for retinol, retinol-binding protein (RBP), was detected only in decidual cells of the basal plate. In contrast, immunoreactive RBP (irRBP) was present in syncytiotrophoblast, core mesenchyme and lumen of vessels in placental villi and in mesenchyme and decidual cells of the basal plate. In villi of term placentae, however, staining for irRBP was lost in syncytiotrophoblasts and villous core mesenchyme. A putative placental RBP-receptor, approx 60-65kDa, was detected in the villous syncytiotrophoblast of both stages investigated. Immunoreactivity for the cellular retinol binding protein type I (CRBP I), was found in villous stromal cells and in decidual cells of the basal plate in sections of first trimester and term placenta. These results may suggest that maternal RBP-retinol is transferred across the chorionic villi to the fetal/villous circulation and that villous absorption of the complex is mediated via a placental RBP-receptor. Moreover, binding and possibly also metabolism of retinol may occur in the CRBP I positive villous stromal cells and decidual cells of the basal plate. In the latter, release of placental RBP-retinol may also be anticipated.