The Influence of Retinoids on Chemotaxis and Connective Tissue Synthesis of Fibroblasts

Retinoids exert very profound effects on fibroblast functions. Often they have been shown to lead to a reduction of collagen synthesis in vitro when applied directly to fibroblast cultures. In the skin, as a more complex system, they reveal even other activities and, for example, cause an induction of cytokines in the epidermis. This induction of several cytokines could further lead to an increased collagen production in the lower dermal fibroblasts. To investigate this hypothesis, we conducted several in vitro experiments. First, we studied the influence of three different retinoids [isotretinoin (Ro 4–3780), arotinoid methyl sulfone (Ro 14–9706) and arotinoid ethyl sulfone (Ro 15–1570)] on the chemotactic activity and proliferation of fibroblasts. Further, we tested the influence of conditioned media derived from retinoid-treated keratinocytes in comparison to directly applied retinoids on collagen type I and III synthesis of fibroblasts by northern and dot blot analysis. Finally, we observed the influence of these retinoids on TGF-β1 and of Ro 14–9706 on Il-1α and β expression in human primary keratinocytes by northern blot analysis. None of the retinoids tested were chemoattractive, but all inhibited the chemotactic response to fibroblast-conditioned medium. Also, proliferation was inhibited dose dependently. While Ro 4–3780 showed a concentration-dependent reduction of the α1(I) and α1(III) procollagen mRNA steady-state levels, low doses of Ro 14–9706 and Ro 15–1570 first of all increased collagen mRNA levels. Only high concentrations of these retinoids decreased the collagen levels in fibroblast cultures. The inhibiting effects observed with high concentrations of retinoids were abolished by the use of conditioned media derived from keratinocyte cultures treated with the same concentration of retinoids. Furthermore, higher levels of TGF-β1 mRNA were observed in keratinocyte cultures treated with 10-5 M sulfur-containing arotinoids compared with untreated controls or cultures treated with 10-5 M Ro 4–3780. Il-1α mRNA levels were raised up to 200% compared with control when 10-6 M Ro 14–9706 was applied. Il-1β mRNA levels were also elevated, but to a lesser extent. These data demonstrate that retimoids can act in an opposite manner on collagen synthesis when they were used in a more complex system instead of applied directly.