Abstract
Abstract: :
Molecular interactions are important in the regulation corneal fibrillogenesis and development of a transparent cornea. Heterotypic type I/V collagen interactions as well as the interactions of lumican, keratocan and decorin with fibrils have been implicated in the regulation of differents steps in fibril assembly and growth. Purpose: To determine the mechanism(s) whereby type V collagen regulates corneal fibrillogenesis and at what specific stages the regulation occurs. Methods: A mouse model with a targeted deletion of col5a1 was utilized. Stromal matrix deposition was analyzed using biochemical, molecular and structural approaches in col5a1 haplo–insufficient and wild type litter mates. Corneal fibril structure was analyzed ultrastructurally. Results: The –/– mice were embryonic lethal before the cornea developed at approximately E10. The lethal phenotype was associated with a severe reduction in mesenchymal fibril deposition. Biochemical analyses of the dermis from +/– mice indicated less collagen deposition than the wild type controls which was consistent with morphological analyses of both dermis and corneal stroma. There were significant differences between the corneal stromas of col5a1 +/– and +/+ mice. (1) Collagen fibril diameter was inversely proportional to type V/type I collagen ratios. The mutant corneal fibrils were 25–35% larger than those from control corneas. (2) A reduction of type V collagen, in the col5a1 +/– corneas was associated with the assembly of significantly fewer fibrils compared to control corneas. (3) The +/– stroma were approximately 25% thinner than wild type stromas at comparable ages. Conclusions: These data indicate that type V collagen is a key regulator of fibril nucleation in the corneal stroma. The control of fibril initiation events associated with a total collagen pool also explains type V collagen’s role as a negative regulator of fibril diameter. The high corneal type V collagen content (10–20%) relative to other type I collagen containing tissues (1–5%) suggests that type V collagen and therefore control of initial fibril assembly, number and organization are key events in stromal development and maintenance of transparency.
Keywords: cornea: stroma and keratocytes • extracellular matrix • cornea: basic science