Amanda J. Reynolds

Hair follicle dermal cells differentiate into adipogenic and osteogenic lineages

Abstract: The adult hair follicle dermal papilla (DP) and dermal sheath (DS) cells are developmentally active cell populations with a proven role in adult hair follicle‐cycling activity and unique inductive powers. In stem cell biology, the hair follicle epithelium has recently been the subject of a great deal of investigation, but up to now, the follicle dermis has been largely overlooked as a source of stem cells. Following the sporadic appearance of muscle, lipid and bone‐type cells in discretely isolated follicle DP and DS cell primary cultures, we demonstrated that cultured papilla and sheath cell lines were capable of being directed to lipid and bone differentiation. Subsequently, for the first time, we produced clonal DP and DS lines that had extended proliferative capabilities. Dye exclusion has been reported to be an identifying feature of stem cells; therefore, clonal papilla and sheath lines with differing capacity to exclude rhodamine123 were cultured in medium known to induce adipocyte and osteocyte differentiation. Both DS‐ and DP‐derived clones showed the capacity to make lipid and to produce calcified material; however, different clones had varied behaviour and there was no obvious correlation between their stem cell capabilities and dye exclusion or selected gene expression markers. As a highly accessible source, capable of being discretely isolated, the follicle has important potential as a stem cell source for tissue engineering and cell therapy purposes. It will also be interesting to compare follicle dermal stem cell properties with the broader stem cell capabilities discovered in skin dermis and investigate whether, as we believe, the follicle is a key dermal stem cell niche. Finally, the discovery of stem cells in the dermis may have implications for certain pathologies in which abnormal differentiation occurs in the skin.

Trans-gender induction of hair follicles

Human follicle cells can be induced to grow in an incompatible host of the other sex.

Hair follicle dermal sheath cells: unsung participants in wound healing

The dermal sheath that surrounds the outside of the hair follicle contains progenitor cells that maintain and regenerate the dermal papilla, a key component for hair growth. Our contention is that dermal sheath cells have other roles. We believe that they can become wound healing fibroblasts and perform an important function in the repair of skin dermis after injury. The dermal sheath has close developmental and anatomical parallels with follicle outer root sheath, the epithelial component that contains the stem cells responsible for replacing skin epidermis. Dermal sheath cells also have a myofibroblast or wound healing phenotype, and in animals with high follicle densities differences in wound healing are observed in conjunction with changes in the hair growth cycle. Similarly, in human beings there are apparent differences in wound healing responses between hairy and non-hairy body sites. Moreover, clinical and experimental data suggest that the involvement of follicle-derived dermal cells results in qualitatively improved dermal repair. Therefore, in a therapeutic context, hair follicle dermal cells provide an accessible option for the creation of dermal or full skin equivalents that could both improve wound healing and reduce scarring. Indeed, given the inductive properties of adult hair follicle dermal cells, it is reasonable to envisage a tissue engineering approach for the production of a skin equivalent that will grow hair follicles when grafted.

Plasticity of hair follicle dermal cells in wound healing and induction

Abstract: The capacity of adult hair follicle dermal cells to participate in new follicle induction and regeneration, and to elicit responses from diverse epithelial partners, demonstrates a level of developmental promiscuity and influence far exceeding that of interfollicular fibroblasts. We have recently suggested that adult follicle dermal cells have extensive stem or progenitor cell activities, including an important role in skin dermal wound healing. Given that up to now tissue engineered skin equivalents have several deficiencies, including the absence of hair follicles, we investigated the capacity of follicle dermal cells to be incorporated into skin wounds; to form hair follicles in wound environments; and to create a hair follicle‐derived skin equivalent. In our study, we implanted rat follicle dermal cells labelled with a vital dye into ear and body skin wounds. We found that they were incorporated into the new dermis in a manner similar to skin fibroblasts, but that lower follicle dermal sheath also assimilated into hair follicles. Using different combinations of follicle dermal cells and outer root sheath epithelial cells in punch biopsy wounds, we showed that new hair follicles were formed only with the inclusion of intact dermal papillae. Finally by combining follicle dermal sheath and outer root sheath cells in organotypic chambers, we created a skin equivalent with characteristic dermal and epidermal architecture and a normal basement membrane – the first skin to be produced entirely from hair follicle cells. These data support the hypothesis that follicle dermal cells may be important in wound healing and demonstrate their potential usefulness in human skin equivalents and skin substitutes. While we have made progress towards producing skin equivalents that contain follicles, we suggest that the failure of cultured dermal papilla cells to induce follicle formation in wounds illustrates the complex role the follicle dermis may play in skin. We believe that it demonstrates a genuine dichotomy of activity for follicle cells within skin.

Trans-species hair growth induction by human hair follicle dermal papillae.

Abstract: A series of experimental bioassays has shown that the dermal papilla of the adult rodent vibrissa hair follicle retains unique inductive properties. In view of the many phenotypic and functional differences between specific hair follicle types, and the growing interest in hair follicle biology and disease, it remains important to establish that the human hair follicle dermal papilla has equivalent capabilities. In this study we tested the ability of human hair follicle papillae to induce hair growth when implanted into transected, athymic mouse vibrissa follicles. The implanted papillae that interacted with mouse follicle epithelium created new fibre‐producing follicle end bulbs. The origin of the papillae in the recombinant structures was confirmed using laser capture microdissection and human specific gender determination by PCR. The demonstration that intact adult human dermal papillae can induce hair growth has implications for molecular analysis of basic hair growth mechanisms, particularly since the study involved common epithelial–mesenchymal signalling and recognition properties across species. It also improves the prospects for a cell‐based clinical approach to hair follicle disorders.

Dermal-epidermal interactions—follicle-derived cell populations in the study of hair-growth mechanisms

All skin appendage development is initiated by a series of dermal-epidermal interactions. These continue to underpin adult hair follicle activities through the specialized follicular cell populations--indeed the inductive properties of isolated dermal papillae from adult vibrissa follicles are well established. Far less is known about the influence of adult follicle epidermis on dermal cells, or inductive properties of papilla cells from other follicle types. Cultured papilla cells, unusually, are able to support the proliferation of skin epidermal cells during simple association in culture, but do not produce more elaborate organization or differentiation. However, germinative epidermal cells from the follicle base are morphologically and behaviorally distinct from other epidermal populations, and in simple association with papilla cells interact to form complex structures with a distinct basal lamina. That hair follicle germinative cells have an important influence on dermal cells is further demonstrated by in vivo recombinations, where germinative cells interact with otherwise non-inductive follicle dermal sheath cells to initiate follicle formation and hair growth. In vitro, several follicle cell populations assembled within the capsule of a vibrissa follicle and grown in a three-dimensional culture system produce hair-type fibers. When cultured pelage follicle dermal papilla cells are implanted alone into footpad skin under controlled conditions, new pelage-type follicles and fibers are induced. This emphasizes the power and universal nature of inductive influences from papilla cells, and underlines the dermatologic potential of cell manipulations. The transdifferentiation of the footpad epidermis is a powerful biologic phenomenon normally only seen in embryonic-type association experiments.

Skin stem cells - a hairy issue.

The hair follicle is a major repository for epidermal stem cells. Learning more about the processes that regulate the differentiation of these cells will improve the prospects for skin replacement and treatments for skin cancers.

Hair follicle reconstruction in vitro

The in vitro creation of a follicular structure capable of hair growth from cultured adult cells has long been an aim of researchers in hair biology. Basal outer root sheath cells (ORS) attached to the hair follicle glassy membrane (GM) were isolated and cultured, where they revealed greater replicative potential and longevity than ORS cells from plucked fibres. Hair follicles were reconstructed in vitro using the collagenous shells of rat vibrissa follicles as natural containers for 4 hair follicle cell types. Basal ORS cells were initially seeded onto the residual vibrissa GM, and cultured dermal papilla, dermal sheath and germinative epidermal cells were then added. Histology revealed that after 2 or 3 weeks in combined culture, cell interactions and tissue morphogenesis had resulted in the formation of irregular but recognizable hair fibres, produced from unusual bulb structures. To our knowledge this represents the first example of adult cell populations instigating the de novo creation of hair fibres in a culture dish. While the usefulness of the current methodology relates immediately to hair growth research, the generation of hair follicles and fibres in vitro establishes the enormous potential of this type of interactive work for practical purposes.

Hair Follicle Stem Cells: Characteristics and Possible Significance

All four of the principle dermal and epidermal cell types from the adult hair follicle (dermal papilla and sheath, germinative epidermal and outer root sheath) can now be grown in culture. The germinative epidermal cells from the source of the hair fibre appear to be the most visually distinctive of these populations, but all four can be morphologically, synthetically and behaviourally distinguished from general interfollicular skin cells. The germinative population also most obviously exhibit many classical stem cell attributes, but the interactive and inductive capabilities of all of the cell types, in addition to their multipotential natures, highlights that they all share an intriguing level of developmental flexibility.

Genes that are differentially expressed in rat vibrissa follicle germinative epithelium in vivo show altered expression patterns after extended organ culture

Abstract: Hair growth depends on maintenance of signalling between the dermal papilla and the germinative epithelium (GE), from which the differentiated layers of the hair fibre originate. Because no molecular studies have been reported which concentrate specifically on GE cells either in vivo or in vitro, we prepared a cDNA library enriched for messages which were highly expressed in GE cells to identify genes that may be involved in hair growth control. Of 35 subtracted library clones sequenced, 23 shared extensive homology with previously determined cDNA sequences, including LEF‐1 and id4. Hair follicle organ culture models are often used to investigate the molecular basis of hair growth, although hair growth arrest occurs relatively rapidly in vitro. As an indicator of their role in follicle activities, we compared the expression of GE‐specific clones in different regions of freshly isolated vibrissa follicles, with the corresponding regions of growth arrested, cultured follicles. Changes in the expression of some of these clones indicates that they could be related to fundamental cellular activities in the follicle. A library enriched for GE‐specific clones therefore provides a useful source of candidate molecules for studies of follicular epithelial cell behaviour, both in vivo and in vitro.