Regulation of hyaluronan (HA) synthesis and degradation is essential to maintenance of extracellular matrix homeostasis. We recently reported that HYBID (HYaluronan-Binding protein Involved in hyaluronan Depolymerization), also called KIAA1199, plays a key role in HA depolymerization in skin and arthritic synovial fibroblasts. However, regulation of HA metabolism mediated by HYBID and HA synthases (HASs) under stimulation with growth factors remains obscure. Here we report that TGF-1, basic FGF, EGF, and PDGF-BB commonly enhance total amount of HA in skin fibroblasts through up-regulation of HAS expression, but molecular size of newly produced HA is dependent on HYBID expression levels. Stimulation of HAS1/2 expression and suppression of HYBID expression by TGF-1 were abrogated by blockade of the MAPK and/or Smad signaling and the PI3K-Akt signaling, respectively. In normal human skin, expression of the TGF-1 receptors correlated positively with HAS2 expression and inversely with HYBID expression. On the other hand, TGF-1 upregulated HAS1/2 expression but exerted only a slight suppressive effect on HYBID expression in synovial fibroblasts from the patients with osteoarthritis or rheumatoid arthritis, resulting in the production of lower molecular weight HA compared with normal skin and synovial fibroblasts. These data demonstrate that although TGF-1, basic FGF, EGF, and PDGF-BB enhance HA production in skin fibroblasts, TGF-1 most efficiently contributes to production of high molecular weight HA by HAS up-regulation and HYBID down-regulation and suggests that inefficient downregulation of HYBID by TGF-1 in arthritic synovial fibroblasts may be linked to accumulation of depolymerized HA in synovial fluids in arthritis patients.
Hyaluronan (HA)3 is a nonsulfated linear glycosaminoglycan composed of repeating disaccharide units of -(1,3)-linked-Dglucuronic acid and -(1,4)-linked-N-acetyl-D-glucosamine. HA is ubiquitously present as a major component in vertebrate connective tissues such as skin and synovial membrane and contributes to space filling, lubrication, and cell proliferation and migration (1). The turnover of HA in most tissues is extraordinarily rapid; the half-life of HA in the skin, which contains about half of all HA in the body, is 1-1.5 days (2). Thus, the tight control of HA synthesis and degradation is necessary for this turnover and seems to finely balance the amounts of high molecular mass HA (1,000 -10,000 kDa) within tissues (1, 2). On the other hand, an imbalance of synthesis and degradation causes the accumulation of HA with different molecular weights, which is commonly observed in diseases such as arthritis and cancers (3-5). Synovial fluids from patients with osteoarthritis (OA) or rheumatoid arthritis (RA) contain lower molecular mass HA (as low as 200 kDa) than that from normal subjects, leading to decreased synovial viscosity and increased inflammatory responses (6). HA is synthesized by HA synthases (Has1, Has2, and Has3) at the cell membrane, and the expression of Has enzyme...