Aging Alters Functionally Human Dermal Papillary Fibroblasts but Not Reticular Fibroblasts: A New View of Skin Morphogenesis and Aging

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

Cellules souches de l'épiderme interfolliculaire humain : phénotypes et potentialités

Des cellules souches d'origines tissulaires distinctes ont en commun un certain nombre de caractéristiques fondamentales, parmi lesquelles la capacité d'autorenouvellement et le potentiel de régénération de leur tissu d'appartenance. Trouver des critères d'identification de populations particulières de cellules souches et comprendre les réseaux de signalisation responsables de leur état d'immaturité et du maintien de leur potentiel constituent des domaines de recherche majeurs qui conduiront à une connaissance plus aboutie de la physiologie normale des cellules souches adultes, et conséquemment à augmenter notre aptitude à les utiliser pour des thérapies régénératives. Cette synthèse traitera de différentes approches et modèles expérimentaux qui ont été développés dans ce domaine, et qui ont contribué à approfondir notre connaissance des cellules souches de l'épiderme interfolliculaire humain. L'une d'elle, basée sur des études transcriptionnelles menées à l'échelle du génome global, a consisté à rechercher des marqueurs moléculaires universels à tous les types de cellules souches. Dans d'autres approches, les cellules souches ont été étudiées de manière moins globale, en s'intéressant à certaines de leurs caractéristiques spécifiques. La compréhension des propriétés des cellules souches somatiques, comme leur état de quiescence ou leur potentiel de détoxification, ont notamment conduit à l'identification de phénotypes utilisables pour la sélection de sous-populations de kératinocytes possédant des propriétés de cellules souches. L'intérêt de ces différentes démarches sera discuté

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Age-related impact of Fp and Fr on the epidermal compartment in three-dimensional reconstructed skin.

<p>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 µm.</p

Secretion profiles of cytokines, MMPs and TIMPs by Fp and Fr as a function of donor's age.

<p>Evolution with age of the secretion profiles of Fp and Fr was analyzed by linear regression on a cohort of 16 different pairs of fibroblast samples obtained from independent donors, ranging from 19 to 74 years old. Secretion level of specific proteins was considered as significantly modulated with age when the correlation coefficient (R) was found >0.5 (in absolute value) and p<0.05 (*).</p

Age-related growth characteristics of Fp and Fr.

<p>Fp and Fr samples from 3 young (19 yr, 19 yr, and 26 yr) and 3 old donors (57 yr, 58 yr, and 67 yr) were cultured for 21 days. Cellular growth rate was estimated every 7 days after culture initiation. Data are expressed as cumulative expansion curves (means±SEM, n = 3 independent samples). (A) Comparison of growth rates of Fp and Fr from young donors. (B) Comparison of growth rates of Fp and Fr from old donors (*p<0.05; n.s. = not significant).</p

Evolution with age of Fp and Fr morphology.

<p>Fp and Fr samples from 3 young donors (19 yr, 21 yr, and 26 yr) and 3 old donors (57 yr, 62 yr, and 74 yr) were examined by flow cytometry according to the morphological parameters of size (forward scatter, FSC) and granularity (side scatter, SSC). FSC versus SSC dot plots corresponding to a typical pair of young [19 yr] Fp (A) and Fr (B), and a typical pair of old [74 yr] Fp (C) and Fr (D). Median FSC and SSC values were determined for the different samples. (E) Comparison of Fp and Fr FSC values in young and old donors (mean±SEM, n = 3). (F) Comparison of Fp and Fr SSC values in young and old donors (mean±SEM) (*p<0.05; n.s. = not significant). a.u. = arbitrary unit.</p

Histological characteristics of young and old human skin.

<p>Photographs shown correspond to histological sections of mammary skin biopsies obtained from a 19 year old (A) and a 74 year old donor (B). Sections were stained with hematoxylin, eosin, and saffron (HES). Scale bars = 50 µm. Dp = papillary dermis. Dr = reticular dermis.</p