Molecular and neurochemical evidence for the biosynthesis of dehydroepiandrosterone in the adult rat spinal cord

Various studies have indicated that exogenous dehydroepiandrosterone (DHEA) modulates several mechanisms in the CNS of rodents. As adult rodent glands do not secrete significant amounts of DHEA, its role as endogenous modulator of the CNS remains possible only if DHEA is produced by nerve cells. Therefore, the last decade has been marked by diverse unsuccessful investigations aiming to demonstrate the activity of cytochrome P450c17 (P450c17), the key DHEA-synthesizing enzyme, in adult rodent CNS. Here, we combined molecular, anatomical, cellular and neurochemical approaches to provide the first demonstration of the existence of P450c17 and bioactivity in adult rat spinal cord (SC). Real-time RT-PCR revealed P450c17 gene expression in all SC segments. Western blot analyses allowed identification of a specific P450c17 protein in the SC and immunohistochemical studies localized P450c17 in neurones and glial cells. Pulse-chase experiments combined with HPLC and radioactive steroid detection showed that SC slices converted [H-3]pregnenolone into [H-3]DHEA, a conversion markedly reduced by ketoconazole, a P450c17 inhibitor. Kinetics studies revealed accumulation of [H-3]DHEA newly synthesized by SC slices in the incubation medium as its amount declined slowly. This first cellular mapping of an active P450c17 in adult rodent SC suggests that endogenous DHEA synthesized in spinal neural networks may control various spinally-mediated activities.