Fp and Fr in Skin Aging Figure 8. Age-related impact of Fp and Fr on the epidermal compartment in three-dimensional reconstructed skin. Keratinocytes from the same batch were seeded onto dermal equivalents containing Fp or Fr from young or old donors. Typical histological sections of reconstructed skin samples made with collagen contracted lattices containing: (A) young Fp; (B) young Fr; (C) old Fp; (D) old Fr. Measurements of the thicknesses of total nucleated (E), cornified (F), granular (G), and spinous (H) keratinocyte layers in reconstructed skins generated in the presence of Fp or Fr from young or old donors. (I) to (L) Typical expression pattern of filaggrin in reconstructed skin epidermis generated in the presence of Fp or Fr from young or old donors. Scale bars = 50 mm. doi:10.1371/journal.pone.0004066.g008 Figure 9. Age-dependent effects of Fp and Fr on the morphology of reconstructed skin after grafting into nude mice. The histology of the different types of three-dimensional reconstructed skin samples was next observed 5 weeks after graft onto nude mice: (A) reconstructed skin containing young Fp; (B) young Fr; (C) old Fp; (D) old Fr. All histological sections were stained with hematoxylin, eosin, and saffron (HES). Scale bars = 50 mm. doi:10.1371/journal.pone.0004066.g009 The preferential evolution of the Fp population throughout aging may have important consequences on the biology of papillary dermis. In particular, reduction of the growth capacity of Fp may contribute to their decline in the papillary dermis of aged skin. Moreover, modifications of their secretion profile may have a wide impact on the biology of the tissue. Indeed, cytokines, growth factors, and MMPs/TIMPs, secreted by fibroblasts are involved in the regulation of a variety of biological processes, including inflammation [15,49], production and remodeling of extracellular matrix components [16,50], angiogenesis [51], as well as epithelial morphogenesis [52]. Modification of the Fp secretion profile may explain some of the structural changes in the superficial part of dermis, which have been previously associated with aging [6,53]. For example, the simultaneous increase of MMP-1, MMP-2 and MMP-3 production in Fp may trigger the degradation of collagenous and non-collagenous components of the extracellular matrix, and consequently contribute to the deterioration of the upper dermis and basement membrane. Changes in the secretion by fibroblasts of growth factor such as KGF throughout aging may partly explain the delayed wound healing observed in elderly people [54,55]. Recent reports have shown that dermal fibroblasts play a key role in the regulation of epidermal morphogenesis [56,57]. In particular, these cells have been shown to influence the formation of its basement membrane [58,59]. This prompted us to analyze the specific impact of Fp and Fr isolated from young and old adult human donors on the characteristics of three-dimensional reconstructed dermis and epidermis. Fibroblasts were embedded into type I collagen [60], and first tested for their capacity to Figure 10. Model of skin morphogenesis and aging. Preferential modifications of Fp characteristics throughout aging may have structural and physiological consequences not only on the dermis, but also on the epidermis. Cellular differentiation of epidermal keratinocytes and dermal fibroblasts may be symmetrically organized including upward differentiation of keratinocytes associated with downward differentiation of fibroblasts. This cellular organization may be altered during skin aging. doi:10.1371/journal.pone.0004066.g010 PLoS ONE | www.plosone.org 11 December 2008 | Volume 3 | Issue 12 | e4066