Induction of hair growth in ear wounds by cultured dermal papilla cells.

In the adult hair follicle the dermal papilla plays a crucial role in the dermal-epidermal interactions that control hair production and events of the growth cycle. It has previously been shown that cultured cells from rat vibrissa follicle dermal papillae can stimulate hair growth when implanted into amputated follicles. This study investigated the effects of implanting low-passage cultured papilla cells into small incisional wounds in the rat ear pinna. The groups of fibers that emerged from wound sites were much larger than local hairs, and often had vibrissa-type characteristics. Later-passage papilla cells or cultured skin fibroblasts failed to elicit the same response. Histology revealed that big follicles were formed when papilla cells were trapped between the cut edges of the epidermis. Abnormally large follicles were seen at wound sites many months post-operatively. Independent of epidermal influence, cultured papilla cells in the wound dermis formed rounded papilla-like aggregates that also persisted until biopsy. A previously described method of wrapping papilla cells in glabrous epidermis was less successful in percentage terms but resulted in the production of one very large vibrissa-type follicle and fiber. These results further illustrate that the inductive powers and developmental information retained by cultured dermal papilla cells parallel the properties of their embryonic precursors; the findings may have implications for human hair growth.

Human hair follicle regeneration following amputation and grafting into the nude mouse.

In this study we investigated the capacity of the human hair follicle to regenerate a fiber-forming bulb after its amputation. We removed the bases from terminal follicles from a variety of sites and transplanted the follicles onto athymic mice, either still attached to a skin graft or as subcutaneous implants of individual follicles. External hair growth was observed on the skin grafts, and histology of the follicles revealed restoration of dermal papillae and follicle bulb structures. This result suggests that the capacity of hair follicles to regenerate their lower structures after removal, which was first demonstrated on whisker follicles, may be a general phenomenon. It emphasizes the importance of specific cellular subpopulations within the follicle and the role of dermal-epidermal interactions in adult follicle activities.

Dermal collagen implants.

The feasibility of using preparations of cell-free, fibrous dermal collagen, prepared by trypsin-treatment of skin, for the repair of soft body tissues has been examined both as subcutaneous implants and as a replacement for dermis in skin wounds in rats. Increased collagen stability, and suppression or reduction of tissue antigenicity in collagen heterografts, was achieved by crosslinking with weak solutions of aldehydes while still allowing implant recellularization and revascularization. Tritium-labelled collagen turnover studies have shown that maintenance of collagen mass in implants crosslinked with glutaraldehyde occurs primarily by inhibition of loss of original implant collagen. Some of the in vitro growth characteristics of human fibroblasts on animal collagen preparations are also described.

Dermal-epidermal interactions.

The dermal papilla is established as a permanent and stable population of specialized fibroblasts that first appear as a cellular aggregate that interacts with the epidermis to ensure follicle development. Our experimental findings strongly suggest that thereafter the papilla, in association with the confluent lower dermal sheath, continues to interact with the follicular epidermis with the papilla cells, which retain their aggregative property, undergoing cyclic changes in size and synthetic activities in phase with the hair cycle. In these activities, the lower follicle dermis appears to act as a functional unit that retains key embryonic characteristics throughout the lifetime of the follicle, re-enacting its inductive influence over follicular epidermis to regulate the profound morphogenetic changes that occur during successive hair cycles and to determine the physical characteristics of the fibers produced. While epidermal mitotic inhibitors have been suggested as a controlling mechanism in the hair cycle, we have argued that the papilla provides potent factors that stimulate epidermal proliferation in the hair germ to initiate, and then sustain, anagen and also follicle morphogenesis. Our recent findings with cocultures of dermal papilla and epidermal cells, which demonstrated that papilla cells enhance epidermal cell attachment and proliferative activity, reinforces this supposition. Thus, it may prove that the intrinsically determined aspect of the hair cycle reflects and is dependent on an intrapapillary cycle of events. Furthermore, we have suggested that at another level of interaction the dermal component of the follicle may mediate the influence of systemic factors, which are known to modify this innately programmed pattern of follicle behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

An autoradiographic study of 3H-thymidine incorporation and distribution in the dermis of healing skin incisions in the pig.

The dermal response to injury in healing incisional wounds aged from 1 to 24 days was studied by in vitro and in vivo 3H-thymidine (3HT) labelling and the use of colcemid to induce metaphase arrest. In vitro 3HT labelling provided mean numbers (+/- s.e. mean) of labelled dermal cells/section within the incision and in 3 zones in the dermis up to 0.875 mm lateral to the incision. There was a progressive increase in the numbers of DNA-synthesizing cells in the incisions as granulation tissue developed from Day 1 to Day 7, and a sharp decline by Day 9. Immediately adjacent to the incision there was a dramatic increase in the number of labelled cells on Day 2, with reduced numbers laterally. This response, which was largely maintained up to 7 days, paralleled the cellular reaction around blood vessels and skin appendages but also included labelled dermal fibroblasts. The in vivo 3HT study, taken in conjunction with the colcemid and in vitro 3HT studies, supported the idea that during the development of granulation tissue there is a continual recruitment of paraincisional cells, including dermal fibroblasts, either by direct migration or by division and then migration, as well as by continued mitosis of cells already within the incision.

Oral cyclosporin A restores hair growth in the DEBR rat model for alopecia areata.

The Dundee experimental bald rat (DEBR) undergoes hair loss associated with the development of peri- and intrafollicular mononuclear cell infiltrates, as occurs in human alopecia areata. We studied the effect of orally administered cyclosporin A (10 mg/kg; 5 days/week for 7 weeks) on established lesional DEBR rats displaying extensive areas of hair loss. New hairs appeared after 10 days and there was simultaneous regrowth of hair over the whole body with restoration of a full pelt by 5 weeks. Semiquantitative histological examination of flank skin biopsies revealed early reduction of the cellular infiltrate associated with conversion of dystrophic anagen follicles to normal, hair-producing follicles. These results confirm the value of the DEBR model of alopecia areata in evaluating existing and new therapies for this disease in humans.

Changes in the synthesis, distribution and sulphation of glycosaminoglycans of cultured human skin fibroblasts upon ascorbate feeding.

The effect of ascorbic acid on the synthesis, distribution and sulphation of glycosaminoglycans by human skin fibroblasts has been examined. Medium was supplemented with ascorbate over several days, and cultures incubated with [3H]glucosamine and Na2(35)SO4 for 48 h, followed by analysis of the glycosaminoglycans in the medium, in collagenase and trypsin extracts, and in cell fractions. Ascorbate feeding resulted in a reduction in hyaluronate synthesis, which was the main 3H-labelled component and was distributed mainly in the medium fractions. Sulphated glycosaminoglycans showed a reduction in incorporation of 3H label, but increased sulphation following ascorbate feeding. In control cultures 53% of 3H-labelled sulphated glycosaminoglycans and 63% of 35S-labelled glycosaminoglycans were present in the medium fraction, while in ascorbate-fed cultures, 41% of 3H label and 38% 35S label were incorporated into medium-sulphated glycosaminoglycans. Ascorbate also caused an increase in cell density and in collagen production and deposition.

Reconstruction of full-thickness loss skin wounds using skin collagen allografts.

Sheets of allogeneic dermal collagen measuring 20 X 15 mm and prepared by trypsin treatment of full-thickness skin were grafted under skin flaps in rats. After 2 to 5 weeks the protective recipient skin was excised and replaced by split-thickness skin isografts which remained viable on their supportive collagen beds. On average such composite grafts maintained 84 per cent of their original size over 3 to 28 weeks and in contrast with split-thickness skin grafts achieved full-thickness reconstruction of the excised skin.

Immunohistological study of the development of the cellular infiltrate in the pelage follicles of the DEBR model for alopecia areata.

The Dundee experimental bald rat (DEBR) undergoes hair loss associated with perifollicular infiltrates of mononuclear cells (MNC), a pathological characteristic of human alopecia areata (AA). To investigate further the pathogenesis of the disease in this animal model, we have studied the development, composition and extent of the perifollicular MNC infiltration in young (6-week-old), prelesional (3-month-old), active lesional, and established lesional DEBR rats, using 6-week- and 6-month-old Wistar rats as normal controls. The proportions of hair follicles showing infiltration by MNC and their main subsets were determined using immunohistochemical staining of serial cryostat sections of flank skin biopsies. There was a good correlation between the degree of leucocyte (OX-1+) infiltration of anagen hair follicles and the development of hair loss. In 6-week-old DEBR skin, there were few perifollicular cells expressing MHC class II, with positively stained dendritic cells in the dermis above the sebaceous gland. There was a sparse perifollicular distribution of CD4+ cells (W3/25) and macrophages (ED-1+). No CD8+ cells (OX-8+) were seen associated with DEBR hair follicles, and only small numbers were present in Wistar rats. In prelesional DEBR rats there was an increased perifollicular presence of MHC class II+ cells, macrophages, and particularly of CD8+ cells, with little change in CD4+ cells. Active and established lesional rats, i.e. animals with overt loss of hair, showed a significant increase in the degree of MNC infiltration and the proportion of infiltrated follicles, the majority of which were in dystrophic anagen. In the perifollicular infiltrate the CD4+:CD8+ ratio was approximately 2:1. An intrafollicular infiltrate was prominent, and was composed of CD8+ cells and macrophages, with bulbar and suprabulbar keratinocytes expressing MHC class II antigens. CD4+ cells were not detected in follicular epithelium. ICAM-1 expression correlated with MNC infiltration. These results show marked similarities to lesional human AA. They also focus on a possible active role for CD8+ cells in the pathogenesis of hair loss in the DEBR rat.

Morphological changes associated with the growth cycle of vibrissal follicles in the rat.

Morphological changes which occur in the growth cycle of the rat vibrissal follicle during the transitional period between consecutive anagen phases are described. In contrast with pelage hair follicles, there is no shortening of the follicle, no formation of a papilla 'rest' and no close synchrony between club differentiation and follicle regression. Telogen is therefore considered to occur after loss of the matrix of the hair bulb and maximal diminution of the dermal papilla to a small aggregation of cells. These difference are discussed in relation to current nomenclature of the hair cycle and the function of the vibrissal follicle.