Collagen fibril organization and its association with glycosaminoglycans in human, pig, and mouse cornea.

The primary objective of the present study was to characterize the species-specific effects of GAGs on the microstructure of corneal extracellular matrix (ECM). To this end, the keratanase enzyme was used to remove GAGs from human, pig, and mouse corneal ECM. Then, transmission electron microscopy (TEM) was done to determine the microstructure of samples before and after GAG depletion. In particular, TEM images were analyzed using ImageJ software to determine the diameter of collagen fibrils and interfibrillar spacing (IFS). An insignificant change in the average collagen fibril diameter of human (28.7 nm->28.8 nm), porcine (34.7 nm->35.2 nm), and murine (33.0 nm->33.4 nm) was observed because of GAG depletion. The enzyme treatment significantly increased the average IFS from 45.8 nm, 53.0 nm, and 54.6 nm to 48.9 nm, 57.3 nm and 61.5 nm in human, porcine, and murine corneal samples, respectively (α < 0.05). The effects of GAGs on microstructural properties of corneal ECM were discussed in terms of their ability to form tiny bridges between collagen fibrils and their net negative charge density. It was concluded that, despite existing differences among collagen fibril diameter and IFS of human, porcine, and mouse cornea, GAG depletion showed relatively similar effects on the microstructure of their ECM. The findings of the present study may help explain the pathological effects associated with changes in GAG content and offer a basis for better understanding of interspecies variations in biomechanical response of cornea.