In vitro growth rates of epidermal cells derived from the skin of psoriatic patients and non-psoriatic controls

Normalized proliferation of normal and psoriatic keratinocytes by suppression of sAPPalpha-release

The soluble form of the beta-amyloid precursor protein (sAPPalpha) is known to function in the autocrine regulation of epidermal growth and repair. Here we show that its proteolytic release by alpha-secretase in normal human keratinocytes is susceptible to hydroxamic-acid-based zinc metalloproteinase inhibitors and suppressed by these inhibitors by 80%-90%. As various other growth factors participate in regulating epidermal growth we investigated whether the inhibitor-induced sAPPalpha-deficiency would affect keratinocyte proliferation. At optimal inhibitor concentrations the suppression of sAPPalpha-release was followed by a decline in proliferation by 50%-60%, indicating that sAPPalpha is a major growth factor that cannot be compensated for by other growth factors. This finding was the basis for the treatment of human lesional psoriatic keratinocytes with these inhibitors, which resulted in the normalization of their increased proliferation rates. The reversibility of these effects and the lack of toxicity underline the value of these inhibitors and suggest their therapeutic application in psoriatic skin diseases.

Comparative analysis of normal and psoriatic skin both in vivo and in vitro

The morphological and biochemical characteristics of psoriasis are well documented, but the pathogenesis of this disease is not clearly understood. A variety of in vitro models of psoriasis have been developed in attempts to identify the trigger factors, but no model so far reproduces the stable psoriatic phenotype accurately. In the present work, we initially checked the immunohistochemical distribution of proliferation/differentiation markers in psoriatic skin in vivo, and our results largely confirm previously reported data. However the study was performed using a new series of monoclonal antibodies to keratin. Subsequently we took normal or psoriatic skin biopsies, reconstructed skin equivalents using a recently described model and analysed the proliferation/differentiation status of the resulting epidermis. Dramatic morphological and antigenic differences were found between normal and psoriatic skin in vivo, but whatever the source of the initial biopsy, a unique in vitro phenotype was obtained in the reconstructed epidermis. This phenotype was marked by mild hyperproliferation and an altered distribution of differentiation-associated antigens suggesting a need for extracutaneous stimuli to maintain the psoriatic phenotype in vitro.

A study of protein synthesis in cells cultured from involved psoriatic skin

Using histochemical techniques an abnormal programme of epidermal differentiation has been well documented in psoriasis. In order to characterise further the biochemistry of this process we have cultured dermal fibroblasts and epidermal keratinocytes from involved psoriatic skin. This has facilitated metabolic radiolabelling of skin cells and analysis of protein synthesis by two-dimensional polyacrylamide gel electrophoresis. The expression of keratin and differentiation markers was identical to that of normal keratinocytes, suggesting that psoriatic epidermal differentiation is not truncated in vitro as has been postulated to be the case in vivo. Low molecular mass components (5-8.5 kDa), previously shown to be upregulated in suprabasal keratinocytes, were detected in epidermal fractions from psoriatic skin enriched for basal cells. Of special interest was a component of 26 kDa, pI 5.9, which was highly upregulated in psoriatic as compared to normal cultured keratinocytes and was not detected in fibroblasts. These findings are in accord with a qualitatively abnormal pattern of differentiation for keratinocytes in the involved psoriatic epidermis.

PUVA therapy damages psoriatic and normal lymphoid cells within milliseconds

Results of previous investigations have indicated that photochemotherapy (PUVA) attacks membranes of target cells. Using the combination of a stopped-flow technique and laser irradiation we were able to prove that the fast PUVA effect is explainable solely by the membrane damage. Lymphoid cells of healthy persons or psoriatics were taken, within 1 ms mixed with 8-methoxy-psoralen (8-MOP) at concentrations of 1.0, 0.1, and 0.5 microgram/ml, and then irradiated by a 337-nm laser pulse (0.5 mJ/cm2) lasting some picoseconds. Approximately 1 ms after administration of 8-MOP to the cell surface at least 10% of the cells were damaged, as could be judged using the standard trypan blue exclusion test. This happened at 8-MOP concentrations of 1.0 or 0.1 microgram/ml plus laser irradiation, but a concentration of 0.05 microgram/ml 8-MOP plus laser exposure did not cause any effect within 8 ms after mixing. There was no difference between using lymphoid cells from healthy persons or from psoriatics. The fact that only a very short time is necessary before cell damage occurs means that, as far as the fast PUVA effect is concerned, a photochemical reaction involving nuclear DNA can be discounted.

Increased DNA synthesis of uninvolved psoriatic epidermis is maintained in vitro

Clinically uninvolved psoriatic epidermis shows increased DNA synthesis in vivo. We have studied the DNA synthesis of cultured keratinocytes from uninvolved psoriatic skin. Trypsinized epidermal cells were plated on plastic dishes pre-coated with bovine collagen type I. In initial studies, normal human serum was found to be superior to fetal bovine in supporting the growth of human epidermal keratinocytes. Furthermore, keratinocyte cultures established in the presence of normal human serum produced large keratin proteins (68,000 daltons) indicating that the terminal steps in cell differentiation can occur in vitro. In subsequent experiments keratinocyte cultures were grown in medium supplemented with 10% normal human serum. Confluent cultures of keratinocytes from uninvolved psoriatic epidermis had an increased DNA synthesis determined both as the incorporation of [3H]thymidine and as the autoradiographic labelling index. The DNA synthesis of both normal and psoriatic keratinocyte cultures increased in response to incubation in medium with 10% psoriatic serum. The ability of keratinocytes from uninvolved psoriatic epidermis to maintain an increased DNA synthesis suggests the presence of an inherent defect within the population of epidermal keratinocytes in psoriasis. Such a culture system can be used as an in vitro model for the study of psoriasis.