On close histological observation of balded scalp biopsies, the miniaturization of terminal hairs is a distinguishing feature in AGA and is frequently associated with perifollicular fibrosis.The miniaturization of the hair follicles was found to be associated with a deposit of so-called "collagen or connective tissue streamers beneath the follicle” as well as a 2--2.5 times enlargement of the follicular dermal sheath composed of densely packed collagen bundles.
Previous reports showed that the DHT and Testosterone treatment elicited an increase in the steady state concentration of alpha 1 (I)-procollagen mRNA in human osteoblast-like osteosarcoma cells and that collagen synthesis was stimulated by androgen in mice. For that reason, perifollicular fibrosis rnay be another pathogenetic mechanisms of AGA, not a simple phenomenon usually seen in AGA.
Testosterone and DHT stimulates the transcription and protein expression of type I procollagen gene in follicular dermal fibroblats. This suggests that type I procollagen synthesis induction by Testosterone may be, in part, responsible for densely packed collagen bundles around miniaturized hair follicles leading to perifollicular fibrosis seen in AGA.
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