A cellular model for the investigation of Fuchs' Endothelial Corneal Dystrophy

Fuchs' Endothelial Corneal Dystrophy is the most common corneal endotheliopathy, and a leading indication for corneal transplantation in the US. Relatively little is known about its underlying pathology. We created a cellular model of the disease focusing on collagen VIII alpha 2 (COL8A2), a collagen which is normally present in the cornea, but which is found in abnormal amounts and distribution in both early and late-onset forms of the disease. We performed cellular transfections using COL8A2 cDNAs including both wild-type and mutant alleles which are known to result in early-onset FECD. We used this cell model to explore the cellular production of wild-type and mutant monomeric and trimeric collagen VIII and measured production levels and patterns using Western blotting and immunofluorescence. We studied the thermal stability of the mutated collagen VIII helices using computer modeling, and further investigated these differences using collagen mimetic peptides. The Western blots demonstrated that similar amounts of wild-type and mutant collagen VIII monomers were produced in the cells. However, the levels of trimeric collagen peptide in the mutant-transfected cells were elevated. Intracellular accumulation of trimeric collagen VIII was confirmed on immunofluorescence studies. Both the computer model and the collagen mimetic peptides demonstrated that the L450W mutant was less thermally stable than either the Q455K or wild-type collagen VIII. Thus, although both mutant collagen VIII peptides were retained intracellularly, the biochemical reasons for the retention varied between genotypes. Collagen VIII mutations, which clinically result in Fuchs' Dystrophy, are associated with abnormal cellular accumulation of collagen VIII. Different collagen VIII mutations may act via distinct biochemical mechanisms to produce the FECD phenotype.