Corneal collagens

Cornea is a highly differentiated tissue rich in extracellular matrix (ECM) specifically distributed in space in order to insure its dual role - trans parency and protection of inner eye-tissues. Corneal ECM is especially rich in collagens. Since the characterisation of a number of distinct collagen types it appeared that most of them are present in the cornea. Their synthe sis follows a specific program of sequential expression of the different co llagen types to be synthesised during the development and maturation of the cornea. The precise regulation of the diameter and orientation of fibers, and of the interfibrillar spaces is partially at least attributed to intera ctions between glycosaminoglycans and collagens. This 'program' of vectoria l collagen synthesis and GAG-collagen interactions changes also with age an d in several pathological conditions as corneal dystrophies and wound heali ng. The Maillard reaction, especially in diabetes, is one of these importan t factors involved in age-dependent modifications of corneal structure and function. Far from being inert, corneal collagens were shown to have relati vely short half-lives. The biosynthesis of corneal collagens was studied al so during wound healing. The refibrillation of wounded corneas does not fol low the original 'program' of ECM-synthesis as shown by the comparative stu dy of wound healing using biochemical and morphometric methods. This review recapitulates briefly previous and recent studies on corneal collagens in order to present to clinicians and scientists an overview of the state of t he art of this important field at the intersection of eye research and matr ix biology. (C) 2001 Editions scientifiques et medicales Elsevier SAS.