The skin equivalent model: developments and perspectives.

Three-dimensional culture systems have been developed to mimic natural interactions among cells and between cells and the extracellular matrix. The “skin equivalent ” is a 3-D co-culture system of fibroblasts and keratinocytes used as a covering surface in extended wounds, and as a model for studying the influence of each cell type on the synthesis of the extracellular matrix. In the present study, a three-dimensional scaffold made of chitosan, glycosaminoglycans and collagen has been colonised by keratinocytes from newborn foreskin an by fibroblasts isolated from donors of different ages. In the skin equivalent, the neo-synthesized connective tissue is characterized by the presence of amorphous elastic fibers, strengthening the usefulness of this three-dimensional model as a powerful tool for investigating connective tissue metabolism in different physiological (i.e. aging) and pathological conditions. Interestingly, when fibroblasts isolated from aged donors were cultured in vitro, even though in the presence of abundant nutrients and growth factors, their old phenotype appeared not to be completely overcome, indicating that aging is the result of a continuous remodelling controlled by epigenetic as well as genetic factors. Finally, the aged phenotype of fibroblasts seems to exert a stronger influence on keratinocytes compared to that of keratinocytes on fibroblasts.