Fibrillin-rich microfibrils: structural modifications during ageing in normal human zonule.

Ageing is marked by ultrastructural and functional changes in most tissues. In part, these changes are caused by a loss of elasticity in the elastic fibers of the extracellular matrix. These fibers are composed of the protein elastin associated with microfibrils of 8 to 12 nm in diameter. Microfibrils contain fibrillins as major constituents. Mutations in fibrillin genes are considered as primary causes of Marfan syndrome, a genetic disorder with pathological manifestations in the cardiovascular and skeletal systems, in addition to dysfunctions in the eye. Fibrillin is also the major protein of the ciliary zonule fibers. During ageing, these fibers become more fragile, and concomitantly, an increased risk for ocular pathologies is observed. We have investigated structural modifications in fibrillin-rich microfibrils during ageing of human ciliary zonule. Observations using light microscopy and transmission electron microscopy after rotary shadowing allowed us to describe the organization of the zonule fibers and their insertion into the ciliary body. Our results emphasize qualitative differences between young and old zonules, which are likely due to modifications in the structure of microfibrils.