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Daniel J. Gibson, Gregory S. Schultz; Initial Evidence for an Epithelial-to-Mesenchymal Transition Basis For Corneal Scarring. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1980.
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To investigate the source of cells which form a light scattering scar following a stroma penetrating wound to the cornea.
Twelve rabbits received bilateral central 6.0 mm diameter, 125 µm deep PTK wounds. Just prior to euthanization, each eye was anesthetized, the pupils dilated, and the wound was photographed. Two rabbits were euthanized at 30 min, 1 day, 2 days, 5 days, 7 days, and 10 days post-wounding and an 8.0 mm diameter punch encompassing the wound was collected, fixed, paraffin embedded and sectioned. One slide per eye was stained with H&E for general histological analysis. Immunohistochemical staining for α-smooth muscle actin (α-SMA) was used to identify myofibroblasts and staining for tenascin-C (TNC) was used to identify loci of EMT.
Corneal haze became apparent in the day 5 eyes and began as a ring of haze at the wound margin with occasional points of haze in the body of the wound. The haze then spread from the points of nucleation. Both the patterns of α-SMA and TNC staining mirrored the spreading pattern seen with the haze. General histological analysis revealed that during re-epithelialization: 1) an occasional epithelial cell was found to have partially invaded the wounded stroma, 2) that the remaining stromal fibroblasts were still apparent, 3) there was a significant number of neutrophils which had invaded the stroma and were associating with the stromal fibroblasts. At day 5 the entire wound volume was filled with epithelial-like cells. At the basal layer, the nuclei remained flattened and in places, a weak association between the basement stroma and the nascent epithelium was evidenced by blister-like formations with what appears to be a flattened nuclei at each the basal and apical surfaces. The distribution of this "blistering" mirrored the haze and IHC staining. Finally, the wound volume had been reconstituted with stroma-like tissue and the epithelium is restored to its typically thickness.
The spread of corneal haze and its molecular markers mirrors the pattern of re-epithelialization whereby both start at the wound margin and migrate towards the wound’s center. The co-localization of markers which also mirror the same spreading pattern for haze and EMT further strengthen the evidentiary basis underlying the theory that the light scattering regenerated stromal tissue is derived from the epithelium, not the stromal fibroblasts.
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