MECHANISMS OF RE-EPITHELIALIZATION OF SKIN WOUNDS

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DESCRIPTION: Reepithelialization of skin wounds requires four sequential steps by the epidermal keratinocyte: activation, migration, hyperproliferation, and differentiation. It has been found that suprabasal, differentiating keratinocytes are the major source of epithelial cells that become activated and then migrate to cover the wound surface. Therefore, their program of gene expression must change from one devoted to producing an inflexible, solid squame to one which is consistent with and will promote active movement. Within the first day after injury, suprabasal keratinocytes at the wound edge begin to express a special set of keratin filament subunit proteins -- keratins 6, 16, and 17, associated with a polarized reorganization of the keratin filament network, a reduction in cell-cell adhesion, hypertrophy, and the onset of migration of cells at the wound margin. The applicant's previous work showed that experimental overexpression of K16 in keratinocytes interferes with the normal intracellular distribution of keratin filaments, such that the filaments become short, lose their association with cell surface desmosomes, and collapse around the nucleus, which may permit the cells to change shape so as to favor migration. The applicant has also generated transgenic mice that chronically express K16 in the basal keratinocytes of the epidermis. These mice develop alopecia and chronic, non-healing wounds later in life and exhibit a slower healing rate of acute wounds. The objective of this proposal is to test the hypothesis that proper expression and then suppression of K16 and K17 is essential for normal wound healing and to determine the molecular mechanism by which these keratins perform their functions. Transgenic mice K16 or K17 knockout mice (having these genes disrupted by homologous recombination) will be generated and studied for their wound healing ability. The filament forming abilities of K16 with K5 as a partner will be determined in a new transgenic mouse construct, and mutational and chimeric protein analyses will be done to determine the domain of K16 responsible for its filament-disrupting properties. A possible redundancy of function of K16 and K17 will be investigated. Wound healing in the already constructed K16-overexpressing transgenic mice will be characterized in detail, and the migration ability of cells cultured from these animals will be measured to determine the molecular basis for the impaired reepithelialization and susceptibility to chronic wounds of these animals. Considering that K6, K16, and K17 are also expressed in psoriasis and squamous cell carcinoma, the results of the proposed research should help understand important aspects of these diseases in addition to clinical conditions of impaired wound healing.