P34 DISASSEMBLING OF THE HUMAN HAIR FOLLICLE PIGMENTARY UNIT DURING IN VITRO INDUCED CATAGEN-LIKE REGRESSION

Rumio C., Donetti E., Barajon I, Imberti A., Castano P.; Institute of Human Anatomy, University of Milan, Via Mangiagalli 31, 20133  Milano / Italy

In animal models, it has been demonstrated that catagen-like events can be reproduced by different substances including dexamethasone (DEX). Based on this observation we have recently used this substance to develop an in vitro model to induce catagen-like alterations in human hair follicles

The aim of the present study has been to use this model to study the morphological modifications occurring to the different cell populations of the hair follicle during regression events. Our attention has been initially focused on melanocytes because of the known alterations occurring  to the bulbar pigmentary unit of animals, during the transition between anagen and catagen. In anagen phase melanocytes are located in pre-cortex matrix in contact with the basal membrane of the follicle papilla. Conversely during early spontaneous catagen, melanocytes migrate loosing their contact with the papilla. Only some follicles treated with DEX presented gross morphological alterations typical of the catagen phase where the bulb acquires a pear shaped appearance. However at the structural level all treated samples showed a disassembling of the bulbar pigmentary unit reminiscent of known early catagen modifications.  Melanocytes seemed to have lost their dendritic shape, assuming a undifferentiated aspect and to have migrated far from the hair papilla either clustering along the hair axis or towards the surrounding ORS. These data show that during such experimentally induced degeneration, melanocytes undergo modifications similar to those observed during spontaneous catagen. This finding support the idea that our DEX model in vitro can be used to study specific responses of cell population of the human hair follicle.