MMP-type endopeptidase activity in the cornea. Its evolution during organ culture storage at the Eye Bank. Effect of hyaluronan

[The irido-corneo-endothelial syndrome. The loss of the control of corneal endothelial cell cycle. A review]

The three major symptoms of the irido-corneo-endothelial syndrome are the alterations of the corneal endothelium and of the iris with a loss of the regulation of the cell cycle, and the progressive obstruction of the irido-corneal angle. This rare pathology attacks mainly young adult women. Most of the symptoms and complications originate from the excessive proliferation of the corneal endothelial cells accompanied by the evolution of their phenotype towards that of the epithelial cells. In normal conditions the corneal endothelial cells do not divide, they are blocked in the G1 stage of the cell cycle, mainly because of the action of the inhibitors of cyclin-dependent kinases. Still these cells retain a good capacity for proliferation, which can be induced by the down-regulation of the expression of the inhibitors of the cyclin-dependent kinases. This proliferative capacity declines with age and is also different according to the localization of the cells: it is more intense with those originating from the central area then in those from the peripheral area of the cornea. The age-related decline of the proliferative capacity is not due to the shortening of the telomers, but to the stress-induced accelerated senescence of the cells.

[Eye connective tissues: cornea and vitreous body]

The authors, ophtalmologist (Y.P.) and basic scientists (J.L.-R and L.R.), collaborated on eye-research since 1962 on normal and pathological aspects of eye tissues, considered as specialized forms of connective tissues, and on specific aspects of the physiology and pathology of the eye. This date coincides with the foundation of the French Society of Connective Tissues, which celebrates the 50th anniversary of its creation. We shall present here some of our work on the ontogenetic and phylogenetic aspects of the cornea, on its structure, function and regulation in normal and pathological states, taken from a large number of publications of our laboratories. Our work on cornea started with the study of the morphogenesis of its lamellar structure, made of collagen fibers and proteoglycans. This led us to the isolation and characterization of structural (or matrix) glycoproteins, a new class of matrix components, present also in all other connective tissues, and to the study of their biosynthesis by keratocytes. Corneal wounds and regeneration were also studied, as well as some corneal pathologies such as keratoconus. The confrontation of quantitative morphological methods with biochemical procedures were to yield important results on the mechanisms of the maintenance of corneal structure and function. Another series of studies concerned the vitreous where we detected, besides previously characterized components, such as hyaluronan and collagens, fibronectin which plays an important role in the adhesion of hyaluronan to the collagen network. Its age-dependent modifications were also studied, with a special focus on the role of reactive oxygen species (ROS)-mediated degradation of hyaluronan, especially important for the aging of the vitreous.