Transient hyperproliferation of a transgenic human epidermis expressing hepatocyte growth factor

Hepatocyte growth factor (HGF) is a fibroblast-derived protein that affects the growth, motility, and differentiation of epithelial cells including epidermal keratinocytes. To investigate the role of HGF in cutaneous biology and to explore the possibility of using it in a tissue engineering approach, we used retroviral-mediated gene transfer to introduce the gene encoding human HGF into diploid human keratinocytes. Modified cells synthesized and secreted significant levels of HGF in vitro and the proliferation of keratinocytes expressing HGF was enhanced compared with control unmodified cells. To investigate the effects of HGF in vivo, we grafted modified keratinocytes expressing HGF onto athymic mice using acellular dermis as a substrate. When compared with controls, HGF-expressing keratinocytes formed a hyperproliferative epidermis. The epidermis was thicker, had more cells per length of basement membrane, and had increased numbers of Ki-67-positive proliferating cells, many of which were suprabasal in location. Hyperproliferation subsided and the epidermis was equivalent to controls by 2 weeks, a time frame that coincides with healing of the graft. Transient hyperproliferation may be linked to the loss of factors present in the wound that activate HGF. These data suggest that genetically modified skin substitutes secreting HGF may have applications in wound closure and the promotion of wound healing.