Disease and damage at the level of Descemet's membrane/corneal endothelium can result in production of retrocorneal fibrous membrane (RCFM). Corneal endothelium in vivo responds to diverse types of pathology by converting to fibroblast-like cells. Experimentally induced RCFMs in rabbit eyes produce type I collagen as the predominant species, in contrast to type IV collagen that is synthesized by corneal endothelial cells. Furthermore, in an in vitro model in which polymorphonuclear leukocytes (PMNs) modulate type IV collagen-synthesizing endothelial cells to type I collagen-synthesizing cells, such modulated endothelial cells share phenotypic characteristics with the cells in retrocorneal fibrous membranes; the major collagen is type I,k which can form fibrous interstitial extracellular matrices between multiple layers of the modulated cells. Thus, corneal endothelial modulation is involved in phenotypic switches in collagen gene expression. The control mechanism of collagen gene expression in both normal and modulated corneal endothelial cells has now been partially characterized and it can be shown that the amounts of collagen mRNAs do not account for the amount of translated proteins in endothelial cells. This suggests that there is, at least in part, translational regulation of collagen gene expression in corneal endothelial cells. Furthermore, it appears that corneal endothelial modulation exerts a profound effect on the stability of alpha2(I) and alpha2(IV) collagen mRNAs, confirming that translational regulation plays an important role in collagen gene expression by endothelial cells and in their modulation. The mechanisms of translational regulation would be studied further using a combination of molecular biology techniques and protein chemistry. The 3'-untranslated and 5' regions of collagen mRNAs from normal and form modulated endothelial cells would be analyzed with either full-length type I collagen cDNAs or type IV collagen cDNAs coding for these regions to ascertain whether any structural alteration of the mRNA leads to translational regulation. Ribonucleoproteins that modulate the stability and translatability of types I and IV collagen mRNAs would be isolated and characterized. Finally, by studying the collagen gene expression during early stages of modulation, the question of how the corneal endothelium modulation factor affects translational regulation of collagen would also be studied.
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