Hyaluronan affects protein and collagen synthesis by in vitro human skin fibroblasts M. A. Croce, 1 K. Dyne, 2 F. Boraldi, 1 D. Quaglino Jr, 1 G. Cetta, 2 R. Tiozzo, 1 I. Pasquali Ronchetti 1 Abstract. Given the importance of hyaluronan (HA) for the homeostasis of connective tissues during embryogenesis and aging and its role in tissue repair, the aim of the present study was to examine the effect of exogenous HA on the synthesis of total protein, collagen and HA by in vitro human dermal fibroblasts. With differences between different cell strains, HA, at concentrations between 0.5 and 1 mM, induced a significant decrease in total protein synthesised and secreted into the medium compared to controls (P < 0.05), and particularly in collagen ( 40%; P < 0.05). The ratios between collagen types I and III and between collagen types V and I were normal. Pulse and chase experiments showed that protein degradation was normal. The presence of exogenous HA did not affect HA synthesis. Data strongly indicate that a relatively high concentration of HA in the extracellular space, such as during development and in the first phases of tissue repair, would partially limit the deposition of the extracellular matrix, and of collagen in particular. This would suggest a role for HA in delaying tissue differentiation during embryogenesis and in preventing fibrosis and scar formation in fetus and in the early phases of wound healing. ß 2001 Harcourt Publishers Ltd Keywords: collagen synthesis, fibroblast, hyaluronan, hyaluronic acid, protein synthesis, wound healing Introduction Hyaluronan (HA) is a linear polysaccharidic chain made of repeating disaccharide units of glucuronic acid and acetyl-glucosamine. It is produced by eucaryotic and by a number of procaryotic cells and is mainly secreted into the extracellular space, where it contributes towards maintaining the architecture and visco-elastic properties of tissues and modulating cell functions via interaction with speci®c cell receptors (Knudson & Knudson, 1993; Savani et al., 1995; Van de Stople & Van der Saag, 1996; Entwistle et al., 1996; Toole & Gross, 1971; Fraser et al., 1997). Recently HA has also been found within the cell, both in the cytoplasm and in the nucleus, suggesting that this polysaccharide may exert rather complex roles in cell metabolism (Evanko & Wright, 1999). Extracellular matrix HA is prominent in development and in the early phases of wound healing, especially in foetuses where the repair process is scar-free (Entwistle et al., 1996). In contrast, its accumulation is reduced in adult tissues, where wound healing is charac- terized by scarring, or in keloids characterized by exuber- ant collagen deposition (Meyer et al., 2000). It has thus been suggested that extracellular HA might prevent ®brosis. To analyse whether this phenomenon is due to physical±chemical mechanisms, such as HA-mediated modulation of collagen deposition (Iocono et al., 1998) or to a direct effect on protein and collagen synthesis, high or low molecular weight HA was added to the cul- ture medium of normal human dermal ®broblasts and Tissue & Cell, 2001 33 (4) 326±331 ß 2001 Harcourt Publishers Ltd DOI: 10.1054/tice.2001.0180, available online at http://www.idealibrary.com Tissue &Cell 326 1 Department of Biomedical Sciences, University of Modena and Reggio Emilia, Modena, Italy. 2 Department of Biochemistry, University of Pavia, Italy Received 8 January 2001 Accepted 7 March 2001 Correspondence to: Professor Ivonne Pasquali-Ronchetti, Department of Biomedical Sciences, Via Campi, 287, 41100 Modena, Italy. Tel:  39 059 2055418; Fax:  39 059 2055426; E-mail: ronchett@mail.unimo.it