Changes in keratinocyte maturation during wound healing.

Changes in the presence and distribution of maturation markers in human epidermis following injury have been studied with the goal of understanding the nature of keratinocyte responses to environmental stress. Wound healing has been compared with normal, uninjured epidermis, psoriatic epidermis, and cultured keratinocytes. To distinguish keratinization pathways expressed during wound healing, we have used fluorescence microscopy to detect the maturation markers involucrin, transglutaminase, filaggrin, and staining by Ψ-3, AE-1, and AE-3 an- tibodies, Ulex europeus agglutinin (UEA) and Helix pomatia agglutinin. We have also followed the synthesis of keratins by one- arid two-dimensional electrophoresis. We have used two types of epidermal injury: tape stripping to remove the stratum corneum and suction blisters to remove the full thickness of the epidermis. Following tape stripping, keratinocytes showed changes in the pattern of keratin synthesis within 8.5 h. These included the appearance of keratins 6 and 16 and reduction of synthesis (to 72% of untreated skin) of keratin 1. Two- dimensional gels also showed changes in isoelectric distribution of keratin 1. Alterations in the patterns of staining with AE-1, anti-involucrin, UEA, and antitransglutaminase were visible within 15 h. Within 24 h of suction blister injury, changes in staining patterns characteristic of regenerative maturation were visible as far as 1 mm from the edge of the blister. On the third day after injury, a tongue of keratinocytes, displaying regenerative maturation markers, extended across the de- nuded blister floor. We observed a hierarchy of the various markers of regenerative maturation during healing (AE-1, deep staining by anti-involucrin and UEA appearing early and being lost late, while Ψ-3 antigen appeared later for a shorter time), suggesting participation of both regenerative and normal maturation pathways together rather than all-or-nothing switching of one pathway to the other. Cells displaying the basal cell marker recognized by VM-1 antibody were sen beneath the keratinocyte tongue after blister injury, and on the distal half of the superficial surface. None of these cells were Ψ-3 positive although some retained involucrin and some, near the tip, expressed AE-1. The more proximal part of the superficial surface of the tongue was occupied by cells producing filaggrin, a marker of normal maturation. We infer that keratinocytes move through the center of the tongue, reaching the surface near the tip. Cells migrating onto the basement membrane lose maturation markers and become basal cells. The first sign of restoration of normal maturation after injury was in the synthesis of keratins. By 48h after tape stripping, very little residual synthesis of keratins 6 and 16 was seen, while keratins 1, 2, and 10 were overproduced by comparison with untreated skin. From about 3–4 days onward, the patterns of staining with Ψ-3 and AE-1 antibodies, anti-involucrin, antitransglutaminase, and UEA returned to normal. In the cases of Ψ-3 and AE-1 antibodies, staining was lost first from the most superficial layers of the epidermis, finally remaining in a single suprabasal layer. We conclude that expression of these antigens may be switched off and the antigens destroyed or masked during the maturation of a keratinocyte. Moreover, normal maturation is favored close to the stratum corneum. Keratinocytes in culture and in psoriatic skin express maturation markers very similar to those seen following epidermal injury. We conclude that the keratinization pathway expressed under these conditions is related to wound healing.