Dermal papilla cells (DPC) are able to induce hair follicles. DPC tend to aggregate both in vitro and in vivo. This tendency is associated with their ability to induce hair growth. The use of DPC to treat alopecia is limited because human DPC lose their hair-inducing activity in culture. However, ovine DPC maintain these properties after extensive proliferation. We aim to characterise the molecular phenotype of ovine DPC aggregates, and to determine whether aggregating ovine DPC secrete factors that affect the aggregative behaviour or inductive potential of human DPC.
Expression of papilla markers in cultured ovine DPC was characterised by immunofluorescence and PCR. Ovine and human DPC were labelled with fluorescent dyes and mixed in culture to determine whether the human cells incorporate into aggregates formed by ovine cells. The effects of different culture substrates and medium compositions on aggregative behaviour were determined.
Ovine DPC aggregates expressed alkaline phosphatase, versican and delta, showing they have a similar phenotype to papillae in vivo. Ki67 staining showed that cell proliferation decreased as ovine DPC formed aggregates. In co-culture experiments, well-formed aggregates were produced by 9:1 human:ovine and 1:1 human:ovine DPC mixtures. In contrast, unmixed human DPC remained in a monolayer state after 18 days, indicating that ovine cells are required to initiate aggregation but the human cells are then able to incorporate into aggregates. Both human and ovine DPC had a higher tendency to aggregate in medium containing 20% lamb serum compared to 10% foetal calf serum, and on a type I collagen substrate compared to polystyrene or glass. The expression of papilla markers in aggregating human DPC will be described, as will the effect of co-culturing human with ovine DPC separated by a permeable membrane. In summary, ovine factors show potential for increasing the aggregative behaviour of human DPC in culture.