Aging Alters Functionally Human Dermal Papillary Fibroblasts but Not Reticular Fibroblasts: A New View of Skin Morphogenesis and Aging Sole` ne Mine, Nicolas O. Fortunel¤, Herve´ Pageon, Daniel Asselineau* L’Ore´al, Sciences du Vivant, Clichy, France Abstract Understanding the contribution of the dermis in skin aging is a key question, since this tissue is particularly important for skin integrity, and because its properties can affect the epidermis. Characteristics of matched pairs of dermal papillary and reticular fibroblasts (Fp and Fr) were investigated throughout aging, comparing morphology, secretion of cytokines, MMPs/ TIMPs, growth potential, and interaction with epidermal keratinocytes. We observed that Fp populations were characterized by a higher proportion of small cells with low granularity and a higher growth potential than Fr populations. However, these differences became less marked with increasing age of donors. Aging was also associated with changes in the secretion activity of both Fp and Fr. Using a reconstructed skin model, we evidenced that Fp and Fr cells do not possess equivalent capacities to sustain keratinopoiesis. Comparing Fp and Fr from young donors, we noticed that dermal equivalents containing Fp were more potent to promote epidermal morphogenesis than those containing Fr. These data emphasize the complexity of dermal fibroblast biology and document the specific functional properties of Fp and Fr. Our results suggest a new model of skin aging in which marked alterations of Fp may affect the histological characteristics of skin. Citation: Mine S, Fortunel NO, Pageon H, Asselineau D (2008) Aging Alters Functionally Human Dermal Papillary Fibroblasts but Not Reticular Fibroblasts: A New View of Skin Morphogenesis and Aging. PLoS ONE 3(12): e4066. doi:10.1371/journal.pone.0004066 Editor: Beth Sullivan, Duke University, United States of America Received July 31, 2008; Accepted November 26, 2008; Published December 30, 2008 Copyright: 2008 Mine et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was carried out at L’Ore´al research laboratories without external funding. The occurence of the publication has no consequence on financial interests for the authors or for the company. L’Ore´al taken as a private company has no role in study design, collection, or interpretation. Competing Interests: The authors have declared that no competing interests exist. * E-mail: dasselineau@rd.loreal.com ¤ Current address: CEA, Institut de Radiobiologie Cellulaire et Mole´culaire, Laboratoire de Ge´nomique et Radiobiologie de la Ke´ratinopo¨ıe`se, Evry, France Introduction Chronological aging is described as a time-dependant biological process leading to gradual changes in the structure and functions of all tissues that compose an organism. These modifications tend to decrease the capacity for adaptive responsiveness and wound healing, and therefore enhance its susceptibility to disorders and death. The genetic program that determines life span and aging is investigated using models of different species, including yeasts (Saccharomyces cerevisiae), worms (Caenorhabditis elegans), insects (Drosophila melanogaster), and mammals (Mus musculus) [1]. In humans, genetic diseases which display clinical signs of premature aging such as progeroid syndromes are an important source of information to identify molecular effectors involved in aging [2]. The importance of specific allelic polymorphisms in the predisposition of human beings to longevity or resistance to age- related disorders has been emphasized by studies of centenarians [3]. In addition to intrinsic genetic factors, chronological aging is controlled through epigenetic mechanisms and is affected by environmental parameters including nutrition [4], which clearly leads to consider this biological process as a complex multifactorial phenomenon. Skin represents a valuable model to study aging in humans, since it is widely affected by this process and is easily accessible. Modifications related to aging are particularly visible in human skin, which becomes wrinkled, lax, dry, and irregularly pigmented over time [5]. Aged skin is characterized by a flattening of the dermal-epidermal junction, a marked atrophy and a loss of elasticity of the dermal connective tissue [6], associated with a reduction and disorganization of its major extracellular matrix components, such as collagen and other elastic fibers [7], proteoglycans and glycosaminoglycans [8]. A histological charac- teristic of chronological aging in the epidermis is a decrease of tissue thickness [7]. Solar radiations are particularly studied as environmental factors promoting skin aging [9] and carcinogenesis [10]. UV lights have been shown to affect both epidermal keratinocytes [11] and dermal fibroblasts [12]. However, at present, age-related modifications of the different dermal fibroblast populations and the consequent effects on skin aging remain poorly understood. Human fibroblasts can be isolated from various connective tissues, including skin [13]. These cells exert important functions in the regulation of tissue structure and cellular microenvironment, by the production of extracellular matrix proteins [14], cytokines, growth factors [15], and matrix metalloproteinases [16]. The pioneering work of Hayflick has revealed that serially cultivated fibroblasts exhibit a limited capacity to divide in vitro [17,18]. This experimental model, termed replicative senescence, has been extensively investigated to approach in vitro the biology of fibroblast aging and senescence, at the cellular and molecular levels. Alterations of fibroblast properties, associated with aging or senescence, have been studied either in long-term cell cultures PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e4066