Temporal and spatial distribution of TGF-ß isoforms and signaling intermediates in corneal regenerative wound repair

The present study analyzed the temporal and spatial expression of TGF-ß isoforms and activated pSmad2 and p38MAPK during epithelial debridement wound repair, using chick cornea by immunohistochemistry. Normal corneas showed low-level TGFßs staining. Following wounding, TGF-ß1 expression was strong in the Bowman's layer (BL). TGF-ß3 expression was confined to basal cells in the regenerating and unwounded regions, and was not detected in migrating epithelial, stromal or endothelial cells. In addition, TGF-ß3 treatment stimulated the proliferation of cultured epithelial cells. Our present findings seem to suggest that the TGF-ß3 signal may be required for epithelial cell proliferation. TGF-ß2 expression was strong in migrating and proliferating epithelial cells, many active migrating fibroblasts at the wound edge, endothelial cells and Descemet's membrane (DM). Although both nuclear pSmad2 and p38MAPK staining was observed in many basal epithelial cells, pSmad2 positive cells were co-localized with PCNA positive cells. Therefore, it seems likely that the pSmad2 signal may affect epithelial cell proliferation in healing corneas. Both pSmad2 and p38MAPK expression were also observed in endothelial cells. Interestingly, many active fibroblasts over the whole stroma in early wound healing at day 2 expressed nuclear pSmad2, but little if any cytoplasmic p38MAPK. Collectively, temporal/spatial up-regulation and distribution of the three TGF-ß isoforms, as well as concerted activation of both Smad2 and p38MAPK, appears to be a key aspect of regenerative corneal wound healing in the chick.