title: The role of IGF-I in human skin and its appendages: morphogen as well as mitogen?
abstract: Previous studies have investigated the expression of insulin-like growth factor-I (IGF-I) and its receptor in cultured skin cells or in whole skin. In order to fully understand the role of IGF-I in the skin and its appendages, however, a comprehensive study that details the expression of IGF-I and the IGF-I receptor in sections of human skin is needed. Therefore, we now report an immunocytochemical and in situ hybridization localization study of the cell types expressing IGF-I and its receptor in human adult skin and its appendages. We have observed that (i) dermal fibroblasts produce IGF-I, (ii) the epidermal basal keratinocytes are IGF-I negative but IGF-I receptor positive, and (iii) the keratinocytes of the stratum granulosum produce IGF-I. These observations indicate either that the mitogenesis of the basal keratinocytes is regulated by IGF-I expressed both in the dermis and in the stratum granulosum, or that dermal fibroblasts are responsible for sequestering IGF-I to the basal keratinocytes and that the stratum granulosum-derived IGF-I may be an autocrine regulator of epidermal differentiation. The distribution of IGF-I and its receptor in the hair follicle indicates that IGF-I may be a morphogen, not a mitogen, at those sites, because their proliferating cells, but not their differentiating cells, are IGF-I receptor negative. Further, IGF-I receptor expression by the dermal papilla appears to be switched off during the transition from anagen to catagen, which implies a regulatory role for IGF-I during the hair growth cycle.
authors.affiliation: Department of Clinical Biochemistry, University of Cambridge, Addenbrookes Hospital, UK.
authors.forename: S M
authors.initials: SM
authors.lastname: Rudman
authors.forename: M P
authors.initials: MP
authors.lastname: Philpott
authors.forename: G A
authors.initials: GA
authors.lastname: Thomas
authors.forename: T
authors.initials: T
authors.lastname: Kealey
mesh_terms: D000328:Adult; D000818:Animals; D002454:Cell Differentiation; D015536:Down-Regulation; D005260:Female; D018859:Hair Follicle / Q000737:chemistry; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008934:Mitogens / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000032:analysis; D012867:Skin / Q000166:cytology*
chemical_list: D008934:Mitogens; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1