Different patterns of 5alpha-reductase expression, cellular distribution, and testosterone metabolism in human follicular dermal papilla cells.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study on cultured human cells
PubMed 18258185 · doi:10.1016/j.bbrc.2008.01.130
What was done
Human follicular dermal papilla cells derived from beard hair (bDPCs) and scalp hair (sDPCs) were evaluated in vitro alongside control dermal fibroblasts. The authors measured 5alpha-reductase type 1 and type 2 (5alphaR1 and 5alphaR2) mRNA levels by real-time RT-PCR, evaluated 5alphaR1 protein expression via Western blot, and determined its cellular distribution by immunofluorescence. Testosterone metabolism was quantified in intact cells using [14C]testosterone labeling, and enzymatic inhibition was compared between the 5alphaR1 inhibitor MK386 and the 5alphaR2 inhibitor finasteride.
What was found
5alphaR1 mRNA expression was highest in bDPCs, intermediate in sDPCs, and low but detectable in fibroblasts, whereas 5alphaR2 mRNA was minimally detectable across all three cell types. A 26 kDa 5alphaR1 protein band was observed in both DPC types but not in fibroblasts, with immunofluorescence confirming cytoplasmic rather than nuclear localization. Intact cell radiolabeling showed that testosterone was converted primarily into androstenedione (attributed to 17beta-HSD activity) and only in small amounts into DHT. 5alpha-reductase activity was greater in DPCs than in fibroblasts, and in bDPCs, the 5alphaR1 inhibitor MK386 exhibited greater inhibitory potency than finasteride. No exact numerical values or effect sizes were reported in the abstract.
Why it matters
These findings suggest that 5alphaR1, rather than 5alphaR2, is the primary 5alpha-reductase isozyme expressed in cultured human dermal papilla cells and that 17beta-HSD represents the dominant metabolic pathway for testosterone in this in vitro model.
Limits
The study is entirely in vitro using cultured cells, which may alter enzyme expression profiles compared to native in vivo tissue. The abstract provides no exact quantitative data, variance measures, or donor sample sizes.
Cited by
- supports The scalp skin has a high density and expression of 5-alpha reductase enzymes that locally convert testosterone to dihydrotestosterone (DHT).