Androgen and progesterone metabolism in the central and peripheral nervous system

This paper summarizes the most recent data obtained in the authors' laboratory on the metabolism of testosterone and progesterone in neurons, in the glia, and in neuroblastoma cells. The activities of the 5α-reductase (the enzyme that converts testosterone into dihydrotestosterone, DHT), and of the 3α-hydroxysteroid dehydrogenase (the enzyme that converts DHT into 5α-androstane-3α,17β-diol, 3α-diol) have been first evaluated in primary cultures of neurons, oligodendrocytes and type-1 and -2 astrocytes, obtained from the fetal or neonatal rat brain. All the cultures were used on the fifth day. The formation of DHT or 3α-diol was evaluated incubating the different cultures with labeled testosterone or DHT as substrates. The results obtained indicate that the formation of DHT takes place preferentially in neurons; however, type-2 astrocytes and oligodendrocytes also possess considerable 5α-reductase activity, while type-1 astrocytes show a much lower enzymatic concentration. A completely different localization was observed for 3α-hydroxysteroid dehydrogenase; the formation of 3α-diol appears to be prevalently, if not exclusively, present in type-1 astrocytes; 3α-diol is formed in very low yields by neurons, type-2 astrocytes and oligodendrocytes. The compartmentalization of two strictly correlated enzymes (5α-reductase and 3α-hydroxysteroid dehydrogenase) in separate central nervous system (CNS) cell populations suggests the simultaneous participation of neurons and glial cells in the 5α-reductive metabolism of testosterone. Subsequently it has been shown that, similarly to what happens when testosterone is used as the substrate, the 5α-reductase which metabolizes progesterone into 5α-pregnane-3,20-dione (DHP) shows a significantly higher activity in neurons than in glial cells; however, type-1 and -2 astrocytes as well as oligodendrocytes also possess some ability to 5α-reduce progesterone. On the other hand, 3α-hydroxysteroid dehydrogenase, the enzyme which converts DHP into 5α-pregnane-3α-ol-20-one, appears to be present mainly in type-1 astrocytes; much lower levels of this enzyme are present in neurons and in type-2 astrocytes. At variance with the previous results obtained using androgens as precursors, oligodendrocytes show considerable 3α-hydroxysteroid dehydrogenase activity, even if this is statistically lower than that present in type-1 astrocytes. The existence of isoforms of the enzyme involved in androgen and progesterone metabolism is discussed.Finally, the ability of the human neuroblastoma cell line SH-SY5Y to metabolize androgens and progesterone was studied incubating the cells in the presence of labeled testosterone or progesterone to measure, respectively, the formation of DHT or DHP (5α-reductase activity). 3α-Hydroxysteroid dehydrogenase activity was studied by evaluating the conversion of labeled DHT into 3α-diol. The results demonstrate that undifferentiated neuroblastoma cells possess a significant 5α-reductase activity, as shown by the considerable conversion of testosterone into DHT; moreover, this enzymatic activity seems to be significantly stimulated following cell differentiation induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), but not after differentiation induced by retinoic acid (RA). The 5α-reductase present in SH-SY5Y cells is also able to convert progesterone into DHP. In undifferentiated cell, this conversion is about 8 times higher than that of testosterone into DHT. Under the influences of TPA and RA, the formation of DHP follows the same pattern observed for that of DHT. SH-SY5Y cells also appear to possess the enzyme 3α-hydroxysteroid dehydrogenase, since they are able to convert DHT into 3α-diol. This enzymatic activity is not altered following TPA-induced differentiation, and appears to be decreased following treatment with RA. It is suggested that the SH-SY5Y cell line may represent a useful “in vitro” model for the study of the mechanisms involved in the control of androgen and progesterone metabolism in nervous cells.