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CF Marfurt, HJ Woo, E Bentley, A Whiteman, C Murphy; NGF and trkA Expression are Increased in Canine Corneal Epithelium Following Chronic Epithelial Wounding . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4226.
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Purpose: NGF is expressed within the corneal epithelium under basal physiological conditions and is released into the tear film following corneal injuries. To further investigate the role of NGF in corneal epithelial wound healing, we examined the effect of chronic corneal epithelial abrasions and spontaneous chronic corneal epithelial defects (SCCED) on the expression of NGF and its high affinity receptor, trkA, in the canine cornea. Methods: Immunohistochemical analyses were performed on frozen-sectioned corneas from normal dogs, dogs with SCEED of 2-6 months duration, and dogs subjected to repeated corneal epithelial abrasions. In the latter group, unilateral 8-mm axial corneal abrasions were created weekly for 8 weeks by mechanical scraping; the animals were then euthanized 3 days after the final defect was made, at which time a small epithelial defect still remained. Results: Corneal epithelium of normal dogs contained minimal levels of NGF and trkA immunoreactivity. The staining was located predominantly, if not exclusively, in the basal epithelial cells, and was somewhat stronger in the limbal and conjunctival basal cells. Corneal epithelium in the (regenerated) mechanically wounded corneas, and in the SCEED corneas, demonstrated considerable upregulation of trkA immunostaining, but only minimal increases in NGF immunostaining, compared to normal corneas. TrkA staining in the chronically wounded corneas was confined to the basal epithelium, but in the SCEED specimens the staining extended also into the winged cell layers. Cells in both groups demonstrated a particularly strong band of trkA immunostaining on the basal surfaces of the basal epithelial cells, in apparent contact with the basal lamina. NGF-immunoreactive nerves were observed in the corneal epithelium and stroma of normal dogs, provided that the specimens were immersion-fixed for no longer than 4 hours. Conclusion: NGF and its trkA receptor are expressed under basal physiological conditions in the canine corneal epithelium and are increased following chronic epithelial mechanical wounding and in animals with SCEED. These data suggest a probable role for NGF in corneal epithelial maintenance and wound healing.
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