5α-Reductase Type 2 Is Constitutively Expressed in the Dermal Papilla and Connective Tissue Sheath of the Hair Follicle in Vivo But Not during Culture in Vitro 1

Abstract

Recent studies suggest that 5-reductase type 2 (5R2) rather than 5R1 plays a key role in the pathogenesis of male-pattern baldness. To clarify the localization of the androgen receptor (AR), 5R1, and 5R2 in the hair follicle, we investigated the expression of the corresponding genes by RT-PCR using microdissected hair follicles. AR and 5R1 mRNAs were expressed in all portions of the hair follicle. By contrast, 5R2 mRNA was expressed only in mesenchymal portions that included the 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 balding and nonbalding scalp. We also examined the expression of these genes in cultured fibroblasts derived from the dermal papilla and connective tissue sheath. Although expression of AR and 5R1 mRNAs was easily detected, there was no obvious expression of 5R2 mRNA in either type of cell. Type-specific inhibition of 5R activity by MK386 and MK906 confirmed these patterns of expression of 5R mRNA. Thus, the expression of 5R2 mRNA seems to be characteristic of freshly microdissected mesen-chymal portions of the hair follicle, but such expression might not be maintained in culture. (J Clin Endocrinol Metab 86: 2875-2880, 2001)