High cell density alters the ratio of type III to I collagen synthesis by fibroblasts.

HUMAN fibroblasts in culture synthesise both type I and type III collagen(1), with type I accounting for 70-90% of the total(2). In culture, the rates at which these proteins are synthesised is constant and apparently rather rigidly controlled(3). However, the proportions of these collagens differs in cells cultured with increased amounts of serum (increased type III/I)(4) as well as in cells obtained from patients with certain diseases. Cells from patients with the Ehlers-Danlos type IV syndrome make little or no type III collagen(5,6), whereas cells from patients with osteogenesis imperfecta have an increased type III/I (refs 7, 8). We have found that cells from some patients with systemic sclerosis (scleroderma), have a reduced type III/I ratio. However, as previously reported, these cells grew to a lower density than control cells(9). We report here that normal fibroblasts from human and guinea pig skin produce proportionally more type III collagen at high cell density, probably because of a reduction in the synthesis of type I collagen.