In vivo, epidermal cells are committed to terminal differentiation in which they undergo a series of morphological and biochemical changes. In vitro, keratinocytes are able to undergo some steps of this differentiation process only. In view of the fact that in vivo skin is continuously subjected to mechanical stress, we investigated the stimulation of differentiation of transformed keratinocytes by mechanical stimulation. The cells, grown in plastic culture dishes, were periodically treated with weights exerting a pressure of 0.015 Ncm-2. This stimulation lasted from 1 to 4 days. Then keratinocytes were examined using indirect immunofluorescence, 3H-thymidine and 14C-amino acid incorporation, SDS polyacrylamide gel electrophoresis, and Western blotting. Following pressure treatment, the previously monolayered keratinocytes locally grew up to several layers, the number of horny scales increased and, after 4 days, the pattern of cytokeratin was modified. The total amount of keratin increased, forming granular accumulations, while the proliferation rate of the cells decreased. Both the 67 kDa and 49.5 kDa keratin subunits increased in stimulated cells. Moreover, a weak keratin band of 44 kDa appeared that was not present in controls. The results demonstrate that cyclic pressure promotes differentiation of cultivated epidermal cells.
Nicotine is rapidly taken up by human keratinocytes (HaCaT cells) and after 3 h the uptake is approximately 50% of maximum. Cotinine, a metabolite of nicotine, was detected, thus demonstrating the metabolism of nicotine in HaCaT cells. Low nicotine concentrations (0.1–200 µg/ml) did not influence the incorporation rate of thymidine into DNA or ami-no acids into proteins. Inhibition of DNA and protein synthesis was only observed at concentrations > 200 µg/ml. After application of 400 µg/ml nicotine, the cells were vacuolated. This process was reversed after nicotine withdrawal. At low nicotine concentrations, no changes in microtubules and actin filaments could be detected. However, in the presence of nicotine (1-10µg/ml), keratin filaments showed a more orderly pattern that controls, and the expression of the suprabasal keratins 1 and 10/11 was induced and increased according to the concentration of nicotine. The number of cornified envelopes also increased markedly. Nicotine concentrations > 100 µg/ml led to a disarrangement of keratin filaments and to a decrease in keratin expression and cornified envelope formation. Our results suggest that nicotine at concentrations up to 100 µg/ml is not an irritant but may induce cornification of the skin.
Faeces samples taken from 343 patients with psoriasis and 581 patients with atopic dermatitis were subjected to mycological examination. Yeasts were detected in 68% of the psoriatics and in 70% of the patients with atopic dermatitis but in only 54% of the controls (n = 50). Qualitative analysis revealed a predominance of Candida albicans. Non-pathogenic yeasts constituted only 1% in each of these groups. Of the hyphomycetes, Geotrichum candidum occurred in 22% of the psoriatics, in 10% of the atopic dermatitis patients and in 3% of the controls. Aspergillus species were found in 1% of the patients but not in the controls. Stool samples collected on three consecutive days from 141 patients were examined for yeasts. Qualitative correlation between all three samples was shown in 95% of the patients and quantitative correlation in 38%. Deviations were mainly of exponential magnitude. Germ cell concentration of 10(4) cells per ml and above were measured in 38% of the psoriatics and in 28% of the atopic dermatitis patients but in only 22% of the test subjects with healthy skin. There was no correlation between the concentration levels of yeasts in the faeces and the extent of psoriasis or atopic dermatitis.
Eumelanogenesis of human skin melanocytes requires at least three enzymes: tyrosinase, TRP 1, and TRP 2. The regulation of these enzymes on transcriptional level was detected in a semiquantitative attempt. The total RNA of melanocytes was reverse-transcripted and followed by a PCR with degenerated primers for all three enzymes. The amplification products were related to each other densitometrically. We examined five different culture conditions: 1) melanocytes in a popular phorbolester containing F-10-medium, 2) melanocytes in a co-culture medium with EGF, 3) melanocytes in a co-culture medium with high calcium, 4) melanocytes co-cultured with keratinocytes in EGF containing co-culture medium, and 5) melanocytes co-cultured with keratinocytes in co-culture medium with high calcium. Melanocytes cultured in phorbolester containing F-10-medium featured transcripts of tyrosinase, TRP 1, and TRP 2 in the ratio 45:45:10. The same results were obtained for melanocytes co-cultured with keratinocytes under the two different culture conditions. In melanocytes cultured alone in co-culture media only TRP 1-transcripts were present. It is likely that under co-culture conditions a keratinocyte-derived factor supports the transcription of all three enzymes. For melanocytes in the phorbolester-containing melanocyte medium a proteinkinase C dependent regulation of transcription seems possible.
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