Summary

The dermal papilla is a discrete group of cells at the base of the hair follicle and is implicated in controlling the hair growth cycle. Early passage dermal papilla cells can induce hair growth in vivo, but, upon further culturing, this property is lost. In order to study the events occurring in hair induction, a representative dermal papilla cell line was required. We have transfected passage 1 rat vibrissa dermal papilla cells with a polyomavirus large T gene encoding a temperature-sensitive T antigen, and generated permanent cell lines in which the immortalizing function can be switched off by temperature shift. The cells established without crisis, resembled cells in the starting population, and retained the aggregative properties of early passage dermal papilla cells. Growth studies were performed on the immortalized cell lines, which showed that transferring the cells to the restrictive temperature for the large T gene product resulted in cell senescence or quiescence, and changes in morphology. Implantation of cell pellets into the ears of immunologically compatible rats showed that the immortal cells retained hair-inductive ability. Cytokines are believed to have an important role in the control of hair growth. The pattern of cytokine gene expression in the immortal cell lines was compared with early passage dermal papilla cells and a non-hair-inducing dermal papilla cell line, using reverse transcriptase-polymerase chain reaction. Epidermal growth factor, tumour necrosis factor, and interleukin-1a were detected in the immortalized and non-hair-inducing dermal papilla cell lines, but were absent in passage 2 dermal papilla cells. All other cytokines examined were detected in all the cell types under study. These results demonstrate that the polyomavirus large Ttsa-immortalized dermal papilla cell lines are very similar to passage 2 dermal papilla cells and thus provide a good model for hair growth studies. Cytokine expression profiles indicate that the expression of several cytokines may be implicated in hair induction. Further studies are under way to investigate the relationship between cytokine expression and the hair growth cycle.