Hyaluronic acid in the normal and glaucomatous optic nerve

Abstract

Eighteen normal human eye-bank eyes (age: 18-81 years), five fetal eyes (16-24 weeks), 11 primary open-angle glaucoma (POAG) eyes (age: 76-89 years), and two Schnabel's cavernous optic atrophy eyes were examined using a biotinylated-hyaluronan binding protein to study the changes in the distribution of hyaluronic acid (HA) in the fetal, adult and glaucomatous optic nerve head. The vitreous body served as a positive control. Sections treated with Streptomyces hyaluronidase were used to confirm specificity. Monoclonal antibodies to myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) were used as additional controls. In fetal optic nerve, HA was localized in blood vessels, peripapillary sclera and the pial septae in the retrolaminar nerve. No staining was associated with axons. Staining for MBP was negative. In adults, HA was found surrounding the myelin sheaths in the retrolaminar nerve; staining decreased with age. In contrast, HA staining in myelinated peripheral nerves (e.g. ciliaries) remained unchanged with age. HA also was localized to the adventltia of arteries and veins throughout the posterior segment. Compared to age-matched normal eyes, HA staining was virtually absent around myelin sheaths of the retrolaminar nerve in POAG eyes. Similar changes were not found in other HA positive structures. In Schnabel's cavernous optic atrophy, HA was present in increased amount in the atrophic area, but virtually absent in the remaining retrolaminar nerve. HA staining was invariably positive in vitreous, and Streptomyces hyaluronidase treated sections were negative. In adults, staining of MBP was associated with the myelin sheath in the retrolaminar nerve. In contrast to HA, staining of MBP was unchanged with age and in POAG. In Schnabel's atrophy, MBP staining disappeared only in the atrophic area. HA in the retrolaminar optic nerve appears to be associated with the space-filling matrix between myelin sheaths. HA is not present in the oxon bundles prior to myelination of the optic nerve. HA in the retrolaminar optic nerve appears to decrease with age and is further reduced in POAG: however, corresponding changes are not found in MBP or in peripheral nerves. Perhaps, decreased amounts of HA is related to a higher susceptibility to elevated intraocular pressure or to optic nerve atrophy. In Schnabel's cavernous optic atrophy, HA is present in increased amount only in the atrophic area while MBP is markedly decreased, suggesting in situ production of HA in areas of optic nerve atrophy.