Effect of peripherally derived steroid hormones on the expression of steroidogenic enzymes in the rat choroid plexus

Peripherally derived steroids affect steroid production in the brain via the blood–brain barrier. However, steroid concentrations are lower in the cerebrospinal fluid than those in the blood, indicating restricted influx of steroids because of their metabolization by choroid plexus (CP) epithelial cells. Here, we analyzed the gene expression of steroidogenic enzymes [cholesterol side-chain cleavage enzyme (P450scc), 17α-hydroxylase/C17-C20 lyase (P450c17), 3β-hydroxysteroid dehydrogenase (3β -HSD), 17β-hydroxysteroid dehydrogenase type 1 (17β -HSD1), aromatase (Cyp19a1), and 5α-reductase type 1 (5α -R1)]. These genes were expressed to a lesser extent in the CP than in the testis and to a similar extent in the cerebral cortex. However, P450scc levels were higher in the CP than in the cerebral cortex, whereas Cyp19a1 levels showed the opposite trend. We also evaluated the effects of orchiectomy and testosterone on the expression of these genes. P450c17 and 5α -R1 levels were unaffected by orchiectomy, whereas P450scc and 3β -HSD levels were increased and decreased, respectively. Cyp19a1 expression increased upon testosterone treatment, whereas that of 17β -HSD decreased upon orchiectomy or administration of testosterone. Immunohistochemistry analysis revealed that 17β -HSD was expressed in the cytoplasm of CP epithelial cells. These results indicate that CP epithelial cells synthesize and convert the certain types of steroids to contribute to the homeostasis of steroids in the brain.