50 Aging of Skin Cells in Culture

The study of age-related changes in the physiology, biochemistry, and molecular biology of isolated skin cell populations in culture has greatly expanded the understanding of the fundamental aspects of skin aging. In modern biogerontology, the terms ‘‘cellular aging,’’ ‘‘cell senescence,’’ or ‘‘replicative senescence’’ most commonly imply the study of normal diploid cells in culture, which during serial subcultivation undergo a multitude of changes culminating in the permanent cessation of cell division. This process of cellular aging in vitro is generally known as the Hayflick phenomenon, and the limited division potential of normal cells is called the Hayflick limit, in recognition of the observations first reported by Leonard Hayflick in 1961 [1]. With respect to skin aging, three main cell types have been studied extensively with respect to cellular aging in vitro: dermal fibroblasts, epidermal keratinocytes, and melanocytes [2–7]. The aim of this chapter is to describe the experimental system of aging of skin cells in culture, to provide an overview of the age-related changes in the structural and functional aspects of cells including physiological, biochemical, and molecular changes, and to evaluate the use of such a system in testing and developing effective interventions for maintaining and/or re-achieving a healthy skin during aging.