Localization of collagen type III mRNA in normal human optic nerve heads

Previous studies using immunocytochemistry and electron microscopy have localized collagen type III (CIII) in the human optic nerve head (ONH). CIII is present in the core of the cribriform plates of the lamina cribrosa and increases with age. In this study, in situ hybridization was used to localize mRNA for CIII in specific cells in human fetal and adult ONH to determine its cellular origin and to provide temporal and regional information on the synthesis of CIII in the ONH. Human ONH from donors with no history of eye disease (16-24 weeks gestation and 6-75 years) were fixed, embedded and sectioned serially. Sections were hybridized with antisense riboprobe for CIII and controls with sense riboprobe and processed for ISH. Immunoperoxidase staining with antibodies against GFAP and von Willebrand factor was used to detect astrocytes and vascular endothelial cells respectively. Fetal ONH: CIII mRNA was localized in most blood vessels throughout the ONH in sections hybridized with antisense probe. The label was localized to endothelial cells of small vessels. Endothelial cells of central retinal vessels were not labeled. In the lamina cribrosa, CIII mRNA was localized to small vessels, but not to astrocytes. Fibroblasts of the peripapillary sclera were labelled with antisense probe. Young-Adult ONH: In the cribriform plates, lamina cribrosa cells hybridized the probe at all ages. Few astrocytes hybridized the probe. Some endothelial cells of small vessels were also labeled. In the insertion region, most vessels were labeled in young ONH, but very few, if any, in old adults. The apparent intensity of hybridization signal associated with blood vessels in adult ONH is markedly reduced with age. No hybridization was observed inside of nerve bundles consistent with the absence of mRNA inside axon and CIII in this location. Localization of mRNA for CIII to blood vessels in fetal lamina cribrosa suggests a vascular origin for CIII in the plates, and perhaps, for lamina cribrosa cells. In young and old lamina cribrosa, localization of CIII mRNA suggests lifelong synthesis of this protein in agreement with age-related increase of CIII in this tissue.