Smooth muscle α-actin is a marker for hair follicle dermis in vivo and in vitro

ABSTRACT We have examined the expression of smooth muscle α-actin in hair follicles in situ, and in hair follicle dermal cells in culture by means of immunohistochemistry. Smooth muscle "-actin was present in the dermal sheath component of rat vibrissa, rat pelage and human follicles. Dermal papilla cells within all types of follicles did not express the antigen. However, in culture a large percentage of both hair dermal papilla and dermal sheath cells were stained by this antibody. The same cells were negative when tested with an antibody to desmin. Overall, explant-derived skin fibroblasts had relatively low numbers of positively marked cells, but those from skin regions of high hair-follicle density displayed more smooth muscle α-actin expression than fibroblasts from areas with fewer follicles. 2-D SDS-PAGE confirmed that, unlike fibroblasts, cultured papillacells contained significant quantities of the α-actin isoform. The rapid switching on of smooth muscle α-actin expression by dermal papilla cells in early culture, contrasts with the behaviour of smooth muscle cells in vitro, and has implications for control of expression of the antigen in normal adult systems. The very high percentage of positively marked cultured papilla and sheath cells also provides a novel marker of cells from follicle dermis, and reinforces the idea that they represent a specialized cell population, contributing to the heterogeneity of fibroblast cell types in the skin dermis, and possibly acting as a source of myofibroblasts during wound healing.