035 Hair growth in vitro.

M.P.Philpott. Centre for Cutaneous Research, St Bartholomew’s and the Royal London School of Medicine and Dentistry. QMW College. University of London. UK.

Since methods for the isolation and in vitro culture of human hair follicles were first published many researchers have used these models to investigate hair follicle biology. The major application of these models has been to investigate possible roles for growth factors in controlling hair follicle growth and differentiation. These studies have identified IGF-I, HGF and members of the FGF and TGF-â/BMP family as being possible key hair growth regulators. Moreover, these in vitro observations have been confirmed by in vivo data such as knockout mice, immunohistochemistry (IHC), in situ hybridisation (ISH) and RT-PCR. Human hair follicles can be switched from anagen to catagen by insulin/IGF-I withdrawal and some of these follicles appear to progress to a catagen like state. However, full human hair cycle in vitro is not achieved. To address this problem several workers have shown that cultured vibrissa follicles grow at rates that appear to reflect their in vivo status and also show cyclical changes in morphology. These observations suggest that cultured vibrissa follicles will prove to be an excellent model for in vitro hair cycle study. Human hair follicles have been used to investigate both the intermediary metabolism of hair growth, and the process of hair fibre formation. The next major step for those of us involved in the use of in vitro models will be to develop methods that permit genes to be knocked out in vitro using either antisense oligonucleotides, neutralising oligonucleotides or blocking peptides. Further work is required to characterise in vitro models of hair follicle cycling, especially those that use cultured vibrissa follicles. Such models could also be used to investigate stem cell trafficking. Also the development of mice, such as the c-Myc-ER transgenic, in which 4-hydroxytamoxifen (4OHT) is used to induce c-Myc overexpression may permit genes to be activated in vitro and their effects on hair follicles studied. Finally, the ultimate in vitro model would be one in which embryonic hair follicles can be stimulated to develop in vitro in skin equivalent models. With recent advances in which it has been demonstrated that, in vivo, embryonic mesoderm can stimulate adult epithelium to undergo hair follicle development. Perhaps such in vitro models are not so distant.