Key regulatory role of dermal fibroblasts in pigmentation as demonstrated using a reconstructed skin model: impact of photo-aging.

Christine Duval,Virginie Flouret,Françoise Bernerd,Emilie Bourreau,Catherine Cohen,Corinne Chagnoleau,Andrzej T Slominski

doi:10.1371/journal.pone.0114182

Abstract

To study cutaneous pigmentation in a physiological context, we have previously developed a functional pigmented reconstructed skin model composed of a melanocyte-containing epidermis grown on a dermal equivalent comprising living fibroblasts. The present studies, using the same model, aimed to demonstrate that dermal fibroblasts influence skin pigmentation up to the macroscopic level. The proof of principle was performed with pigmented skins differing only in the fibroblast component. First, the in vitro system was reconstructed with or without fibroblasts in order to test the global influence of the presence of this cell type. We then assessed the impact of the origin of the fibroblast strain on the degree of pigmentation using fetal versus adult fibroblasts. In both experiments, impressive variation in skin pigmentation at the macroscopic level was observed and confirmed by quantitative parameters related to skin color, melanin content and melanocyte numbers. These data confirmed the responsiveness of the model and demonstrated that dermal fibroblasts do indeed impact the degree of skin pigmentation. We then hypothesized that a physiological state associated with pigmentary alterations such as photo-aging could be linked to dermal fibroblasts modifications that accumulate over time. Pigmentation of skin reconstructed using young unexposed fibroblasts (n = 3) was compared to that of tissues containing natural photo-aged fibroblasts (n = 3) which express a senescent phenotype. A stimulation of pigmentation in the presence of the natural photo-aged fibroblasts was revealed by a significant increase in the skin color (decrease in Luminance) and an increase in both epidermal melanin content and melanogenic gene expression, thus confirming our hypothesis. Altogether, these data demonstrate that the level of pigmentation of the skin model is influenced by dermal fibroblasts and that natural photo-aged fibroblasts can contribute to the hyperpigmentation that is associated with photo-aging.

Highlights

In human skin, melanocytes that produce the melanin pigment accounting for the tegument color, lie at the dermal epidermal junction (DEJ), the boundary structure between the two major skin compartments, the epidermis and dermis
To demonstrate that the 3D skin model is capable of detecting the role of fibroblasts in the pigmentation process, we studied the effects of drastically different fibroblast conditions in the dermal equivalents
The absence of fibroblasts led to a significant increase in the mean melanocyte numbers by a factor of 3.3, while the mean melanin content increased by a factor of 10

Summary

Introduction

Melanocytes that produce the melanin pigment accounting for the tegument color, lie at the dermal epidermal junction (DEJ), the boundary structure between the two major skin compartments, the epidermis and dermis. Melanocytes in the basal layer of epidermis produce various amounts and types of melanins (eu/pheomelanins) within specific organelles called melanosomes that are transferred to neighboring epidermal keratinocytes. Important regulators of melanogenesis are the POMC derived peptides (aMSH, ACTH) found in both the epidermis and the dermis [1, 2]. They are produced by various cell types including keratinocytes, melanocytes, fibroblasts and endothelial cells. As proposed by Slominski et al [7], other positive regulators of pigmentation are melanin precursors such as L-Tyrosine and L-DOPA, which besides being major substrates of melanogenesis, can promote the proper folding and activity of tyrosinase and the formation and maturation of melanosomes

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