Sebocytes are the key regulators of androgen homeostasis in human skin.

The mRNA expression patterns of the androgen receptor and the androgen metabolizing enzymes 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase, 17beta-hydroxysteroid dehydrogenase, 5alpha-reductase, and 3alpha-hydroxysteroid dehydrogenase were investigated in three different cell populations originating from human skin, SZ95 sebocytes, HaCaT keratinocytes, and MeWo melanoma cells, by means of reverse transcription polymerase chain reaction. Restriction analysis of cDNA fragments was performed to identify isozymes of 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase and 3alpha-hydroxysteroid dehydrogenase. In addition, 3H-dihydroepiandrosterone and 3H-testosterone were used as substrates to determine the metabolic activity of these enzymes in SZ95 sebocytes, primary sebocyte cultures, and HaCaT keratinocytes. Furthermore, the effects of the selective 5alpha-reductase type 1 and 2 inhibitors, 4,7beta-dimethyl-4-aza-5alpha-cholestan-3-one and dihydrofinasteride, respectively, and of the 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase inhibitor cyproterone acetate on androgen metabolism were investigated. Androgen receptor mRNA was detected in SZ95 sebocytes and HaCaT keratinocytes but not in MeWo melanoma cells, whereas 3beta-hydroxysteroid dehydrogenase/Delta(5-4)-isomerase isotype 1 mRNA and metabolic activity were only found in SZ95 sebocytes. The enzyme activity could be inhibited by cyproterone acetate. Type 2 17beta-hydroxysteroid dehydrogenase, type 1 5alpha-reductase, and 3alpha-hydroxysteroid dehydrogenase mRNA were expressed in all three cell populations tested, whereas type 3 17beta-hydroxysteroid dehydrogenase mRNA could only be detected in SZ95 sebocytes. The major metabolic steps of testosterone in SZ95 sebocytes, primary sebocyte cultures, and HaCaT keratinocytes were its conversion to androstenedione by 17beta-hydroxysteroid dehydrogenase and further to 5alpha-androstanedione by 5alpha-reductase. The type 1 5alpha-reductase selective inhibitor 4,7beta-dimethyl-4-aza-5alpha-cholestan-3-one, but not the type 2 selective inhibitor dihydrofinasteride, inhibited 5alpha-reductase at low concentrations in SZ95 sebocytes and HaCaT keratinocytes. 5alpha-androstanedione was degraded to androsterone by 3alpha-hydroxysteroid dehydrogenase, which exhibited a stronger activity in HaCaT keratinocytes than in SZ95 sebocytes and in primary sebocyte cultures. Lower levels of 5alpha-dihydrotestosterone and 5alpha-androstanediol were also detected in all cells tested. Our investigations show that specific enzyme expression and activity in cultured sebocytes and keratinocytes seem to allocate different duties to these cells in vitro. Sebocytes are able to synthesize testosterone from adrenal precursors and to inactivate it in order to maintain androgen homeostasis, whereas keratinocytes are responsible for androgen degradation.