Since trunk skin (or non-palmoplantar skin) is less durable under mechanical stress than sole skin (palm, plantar or palmoplantar skin), conventional trunk-derived skin grafts (including the trunk dermis) commonly result in erosion and ulceration when transplanted on to plantar
wounds caused by various
injuries including,
diabetes mellitus or
collagen diseases (including
systemic sclerosis,
polyarthritis nodosa and
rheumatoid arthritis). However, trunk-derived epidermis can adopt a plantar phenotype, characterized by
keratin 9 expression,
hypopigmentation and thick suprabasal layers, through factors derived from plantar dermal fibroblasts in the
wounds. Thus, intractable plantar
wounds with exposed bones can be treated with the combination of bone marrow exposure,
occlusive dressing and epidermal grafting. The higher expression of dickkopf 1 (DKK1), an inhibitor of canonical Wnt/
beta-catenin signals, in the plantar dermis partly explains these phenomena. Thus, mesenchymal-epithelial interactions play important roles not only in embryogenesis (the embryonic development) but also in maintaining the homeostasis of adult tissue. The topographical (site-specific) interactions of
growth factors and substances, including DKKs,
fibroblast growth factors (FGFs) and
transforming growth factor-beta (
TGF-beta) family
proteins including
bone morphogenetic proteins (BMPs), may explain the site-specific differences in the skin in addition to the expression patterns of HOX genes and sonic hedgehogs (Shhs). We review the importance of dermal-epidermal interactions in tissue homeostasis and regeneration, especially in palms and soles.