Eine neue Methode zur Darstellung des Stratum corneum

Keratinocyte stem cells, label-retaining cells and possible genome protection mechanisms

Stem cells are the crucial cells upon which the entire tissue is dependent. Here we define and discuss what is meant by and known about keratinocyte stem cells. One way in which these cells have been studied is by their ability to retain radioactivity labelled thymidine for long periods of time (label retaining cells, LRCs). The underlying mechanism has been assumed in the past to be slow cycling but a more likely explanation is the selective segregation of old and new DNA strands (Cairns's hypothesis). Experiments in the small intestine indicate that the stem cells here are selectively sorting their DNA and becoming LRCs. A possible role for p53 in stem cell biology is presented.

Scanning electron microscopy of skin surface and the internal structure of corneocyte in normal human skin. An application of the osmium-dimethyl sulfoxide-osmium method

A horny layer of normal human skin prepared according to the newly developed osmium-dimethyl sulfoxide-osmium method was examined using scanning electron microscopy. On the skin surface, cytomembranes of the uppermost corneocytes frequently had unilateral, very slightly flat-elevated, zonal areas along the junctions between the corneocytes. The uppermost corneocytes peeled off along the junctions, leaving the remnants of their cell bodies in the junctional areas. In the cracked surface, cytomembranes of the corneocytes protruded from the plane of their cytoplasmic surface. In the lateral junction between the corneocytes, the cytomembranes of the corneocytes were in tight contact with each other, while occasionally the marginal bands had become detached from the cytomembranes. In the vertical connection, cleavages formed between the cytomembranes of the corneocytes. There were thick woollen thread-like structures about 10-30 nm thick in the cytoplasm of the corneocytes. They formed fine irregular meshworks, with their tips projecting digitally: Transmission electron microscopy revealed these structures as most likely being keratin bundles transformed during processing.

Rate of loss of tritiated thymidine label in basal cells in mouse epithelial tissues

A subpopulation of epithelial cells which retains a tritiated thymidine label (termed label-retaining cells, LRCs) has been previously demonstrated in skin and oral mucosae of mice and hamsters. To examine the rate of decrease in the number of LRCs and the changes in degree of labelling, young mice were labelled with tritiated thymidine and the rate at which label was diluted from basal keratinocytes assessed for up to 90 days. The number of LRCs in each tissue examined decreased from 15 to 90 days after labelling with the epidermal tissues maintaining a higher percentage of LRCs than the oral mucosae. Grain counts for LRCs in each tissue at each time period indicated that the number of silver grains overlying LRCs also decreased with time. The observed decrease in numbers of LRCs and the change in their degree of labelling with time suggest that such cells divide slowly, a property associated with stem cells.

The rate of corneocyte formation in microscopic lesions in patients with active psoriasis

Microscopic lesions in active psoriasis were identified after careful examination with a magnifying glass in areas free of macroscopic lesions and of hair follicles. Biopsies were excised without anesthesia, immediately frozen and cryostat-sectioned. Care was taken to preserve the horny layer which was stained to reveal corneocyte membranes and nuclei when present. The interlocking sheets of corneocyte layers made it feasible to outline and trace intercellular spaces parallel to the surface and count the number of corneocyte layers between pairs of these. It was assumed that the location of such a space in the horny layer indicates the period of time from its formation. This information was used to assess the rate of corneocyte layer formation at specified intervals of time. The result shows that adjacent areas of the horny layer could be compared and relative rates of corneocyte layer formation computed. In the parakeratotic part of the early lesions of psoriasis studied the rate of corneocyte layer formation was 15 times higher than that in the non-involved skin. The peak rate, coincident with parakeratosis, was preceded by a number of thickened corneocyte layers. These also showed an increased rate of formation, up to 6.6 times that in non-involved skin. There was no acanthosis in the lesions studied. A subepidermal cellular infiltrate was observed. Periods of rapid corneocyte formation with parakeratosis were often short (not more than one day). These were interrupted by periods with a lower rate. The relationship between corneocyte morphology and stratum corneum kinetics is a distinct feature in the early psoriatic lesion.

Advances in epithelial kinetics--an oral view

There is growing evidence that the basal layer of stratified squamous epithelia consists of cells of differing proliferative capacities and behaviour. These can be classified as stem cells, transient amplifying cells and post-mitotic maturing cells, the most important of which appear to be the stem cells which may be present throughout life and are responsible for all cell production under steady-state conditions. Recent stem cell concepts are reviewed for epidermis, intestinal crypt and oral mucosa and are compared with tissues such as bone marrow and testes which have for some time been thought to operate in a similar manner. These concepts are applied to several pathological conditions of oral epithelia in an attempt to explain some of the changes observed.

Effects of dermatitis, stripping, and steroids on the morphology of corneocytes. A new bioassay

This study was designed to investigate the effects of increased or decreased epidermal turnover on the morphology of human corneocytes. The desquamating portion of the stratum corneum was sampled with the detergent scrub technique using Triton X-100. The following parameters were measured: size (surface micron2), shape (regular, irregular), nuclear inclusions, trabeculae, and numerical counts. Specimens were obtained from adult males with allergic contact dermatitis (N=18); with tretinoin-induced dermatitis (N=11); after cellophane stripping (N=11); and after treatment of these conditions with topical steroids (N=40). Data from 250,000 cells were analyzed statistically. The reproducibility of the method is good (r=0.934). Corneocytes from skin of patients with allergic contact dermatitis differed from those of normal skin: they were 15% smaller and of irregular shape with asymmetrical trabeculae; 50% were nucleated and about 3 times as many cells were collected per cm2 skin surface. Tretinoin and stripping produced similar but more pronounced effects. Topical steroids significantly improved all parameters (p less 0.01). Betamethasone-17-dipropionate was more effective than the valerate. This bioassay permits sensitive measurements of corneocyte morphology in conditions with altered epidermal cellular kinetics. It provides a method to evaluate steroid effectiveness.

Effects of alkaline on horny layer cellularity

The microscopical changes of plantar Str. corneum after immersion in alkaline were investigated. For this purpose a test system was used in which unexcised skin of guinea pig hind feet was exposed and subsequently analysed by the FITC-staining method. The effect of KOH on the Str. corneum consisted in an immediate swelling of the outer cell layers which was followed by a further increase in cell volume. Cells became separated layer by layer after maximal swelling. There is a high and constant rate of cell loss, when treated superficial cells are repeatedly removed as compared to permanent immersion. Thus, the buffering capacity of the treated outer cell layers has a rate limiting effect upon alkaline-induced cell loss in the Str. corneum.

"Keratolytic" effect of salicylic acid

The "keratolytic" effect of salicylic acid was examined in guinea-pig skin. Using a fluorescent staining method the str. corneum cells could be seen to rapidly become detached. The cellular walls remained unchanged. This drug therefore appears to primarily reduce the intercellular cohesiveness of the horny cells.

A model implicating the Langerhans cell in keratinocyte proliferation control

A tentative model is presented which is based on existing data and our own cell kinetic and morphological observations in mice. The model suggests that the epidermal Langerhans cell plays a role in proliferation control of keratinocytes and may also act as an epidermal stem cell.

Ordered structure of the epidermis

Recent reports on the ordered structure of the epidermis are reviewed. The regular relationship between Langerhans cells and cell columns in the mouse is not typical of the epidermis of other animals. The pattern of mitotic activity previously described in mouse epidermis has also been demonstrated in the hamster, which suggests control of keratinocyte activity rather than the exclusion of keratinocytes from the central region beneath cell columns. These findings are discussed in relation to mechanisms which may be responsible for the formation of cell columns.