5 alpha-Reductase type 2 is constitutively expressed in the dermal papillaand connective tissue sheath of the hair follicle in vivo but not during culture in vitro

Recent studies suggest that 5 alpha -reductase type 2 (5 alpha R2) rather t han 5 alpha R1 plays a key role in the pathogenesis of male-pattern baldnes s. To clarify the localization of the androgen receptor (AR), 5aR1, and 5 a lpha R2 in the hair follicle, we investigated the expression of the corresp onding genes by RT-PCR using microdissected hair follicles. AR and 5 alpha R1 mRNAs were expressed in all portions of the hair follicle. By contrast, 5 alpha R2 mRNA was expressed only in mesenchymal portions that included th e dermal papilla and connective tissue sheath, and hardly any was expressed in epithelial portions. The intensity of expression of these genes in each portion of the hair follicles did not differ between follicles from baldin g and nonbalding scalp. We also examined the expression of these genes in c ultured fibroblasts derived from the dermal papilla and connective tissue s heath. Although expression of AR and 5 alpha R1 mRNAs was easily detected, there was no obvious expression of 5 alpha R2 mRNA in either type of cell. Type-specific inhibition of 5 alphaR activity by MK386 and MK906 confirmed these patterns of expression of 5 alphaR mRNA. Thus, the expression of 5 al pha R2 mRNA seems to be characteristic of freshly microdissected mesenchyma l portions of the hair follicle, but such expression might not be maintaine d in culture.