Type V collagen synthesis and deposition by chicken embryo corneal fibroblasts in vitro

Chick embryo corneal fibroblasts were grown in culture to study the processes whereby fibroblasts regulate the deposition and organization of the collagenous, secondary stroma. The effects of an existing type I collagen substratum, cell density, and serum concentration on type V collagen synthesis were investigated. Type V collagen represented approximately 20% of the total fibrillar collagen synthesized, regardless of whether the cells were subcultured, grown on untreated or collagen-coated plastic, grown under confluent or subconfluent conditions, or grown in the presence of low (0.1%) or high (10.0%) serum concentrations. The synthesis of type V collagen remained constant at 20% of the total collagen when cells were grown in 1.0% serum, even though total collagen synthesis increased nearly twofold when compared to total synthesis in 0.1% or 10.0% serum. Immunocytochemistry with anti-collagen, type-specific monoclonal antibodies revealed a homogeneous population of cells synthesizing types I and V collagen. The fibrils deposited by cells grown in a three-dimensional collagen matrix contained a helical epitope on the type V molecule that was inaccessible unless the fibrillar structure was disrupted, mimicking the situation in situ. The production in vitro of heterotypic fibrils, with a constant I/V ratio and molecular packing mimicking the natural stroma, offers opportunities for studying in more detail this important process, which is essential for optical transparency.