Extracellular matrix components in retrocorneal fibrous membrane in comparison to corneal endothelium and Descemet's membrane

To investigate the extracellular matrix macromolecules found in Descemet's membrane and in retrocorneal fibrous membrane (RCFM), and to examine whether the corneal endothelium has the capacity to produce both basement and non-basement membrane phenotypes.

Rabbit corneas with and without RCFM were analyzed by immunofluorescence using antibodies to 8 different collagens (basement membrane collagens: types IV and VIII; fibrillar collagens: types I and III; interfibrillar collagens: type VI and two spliced variant forms of type XII and one anchoring fiber: type VII), proteoglycans (perlecan and decorin), (beta)ig-h3 and laminin-1.

Normal corneal endothelium stains positively for all of the tested collagen types except type VII collagen. On the other hand, Descemet's membrane reacts positively only to the type IV collagen antibody. When non-collagenous components in normal cornea were examined, corneal endothelium stained positively for perlecan, decorin, (beta)ig-h3 and laminin, whereas Descemet's membrane staining for these proteins was negative. When collagenous components of RCFM were examined, RCFM stained positively for all of the tested collagen types except type IV collagen. When non-collagenous components of RCFM were examined, RCFM demonstrated a strong positive staining with decorin, (beta)ig-h3 and laminin, while perlecan staining was weak.

These observations suggest that corneal endothelium is able to produce both basement membrane phenotypes and non-basement membrane, fibrillar phenotypes. This in vivo study confirms our in vitro model of endothelial mesenchymal transformation, in which corneal endothelial cells are transformed to fibroblasts that are responsible for fibrosis.