Review of hair follicle dermal cells

Abstract

Hair follicle stem cells in the epithelial bulge are responsible for the continual regeneration of the hair follicle during cycling. The bulge cells reside in a niche composed of dermal cells. The dermal compartment of the hair follicle consists of the dermal papilla and dermal sheath. Interactions between hair follicle epithelial and dermal cells are necessary for hair follicle morphogenesis during development and in hair reconstitution assays. Dermal papilla and dermal sheath cells express specific markers and possess distinctive morphology and behavior in culture. These cells can induce hair follicle differentiation in epithelial cells and are required in hair reconstitution assays either in the form of intact tissue, dissociated freshly prepared cells or cultured cells. This review will focus on hair follicle dermal cells since most therapeutic efforts to date have concentrated on this aspect of the hair follicle, with the idea that enriching hair-inductive dermal cell populations and expanding their number by culture while maintaining their properties, will establish an efficient hair reconstitution assay that could eventually have therapeutic implications.

Fig. 1

The structure of a hair follicle. The hair follicle stem cells (red) are located in a niche created by the dermal sheath and dermal papilla cells (green). In anagen, the dermal papilla leads the down-growth from the secondary germ and bulge cells to the formation of the bulb. In telogen, the dermal papilla resides adjacent to the secondary germ (yellow), which is derived from bulge stem cells during late catagen phase.

Fig. 2

Transposition of intact dermal tissue (A) or cultured dermal cells (B) into a dermal-epidermal junctional pocket created by dispase (C) or under amputated hair follicles (D) as a model for hair regeneration.

Fig. 3

Hair regeneration models using dissociated epidermal and dermal cells. The cells are either injected subcutaneously or seeded on a full-thickness wound protected by a chamber on the back of the immunodeficient host mouse.

Fig. 4

Subcutaneous injection of dissociated murine epidermal and dermal cells into the back skin of a nude mouse. (a) A nodule or “patch” with regenerated hair follicles can be observed from the undersurface of the skin in 2 weeks. (b) The histology shows formation of a cyst with hair follicles coming out from the cyst wall.

Fig. 4

Subcutaneous injection of dissociated murine epidermal and dermal cells into the back skin of a nude mouse. (a) A nodule or “patch” with regenerated hair follicles can be observed from the undersurface of the skin in 2 weeks. (b) The histology shows formation of a cyst with hair follicles coming out from the cyst wall.