In vivo induction of hair growth by dermal cells isolated from hair follicles after extended organ culture

Successful hair follicle organ culture has been established for some time, but hair growth in vitro is limited and generally terminates prematurely in comparison with in vivo. The reasons why growth stops in culture are as ye t unknown. In this investigation, adult rat vibrissa follicles for which gr owth in culture is limited to about 10 d, were maintained in vitro for a mi nimum of 20 d after the hair shaft stopped growing. The pattern of fiber gr owth and long-term follicle pathology reflected the initial hair cycle stag e at the time of isolation. Furthermore, there was evidence that a group of follicles put into culture when in late anagen were attempting to cycle in vitro. Microscopy showed that, in spite of widespread pathologic changes t o the follicle epithelium, dermal cells in the follicle showed remarkable r esilience. Their viability was confirmed when primary cell cultures were es tablished from isolated dermal tissue. These cells labeled positively for a lpha -smooth muscle actin, an established marker of hair follicle dermal ce ll phenotype in vitro. Moreover, isolated dermal tissue induced hair growth when implanted into inactivated hair follicles in vivo. These data confirm that the cessation in hair growth is not due to a loss of the inductive ca pacity in the dermal component. Long-term organ culture may provide opportu nities to investigate factors that are expressed or lost during hair growth cessation. In addition it may be possible to develop this method further t o obtain a reliable and predictable model of hair follicle cycling in vitro .