Distribution of TGF-beta Isoforms and Signaling Intermediates in Corneal Fibrotic Wound Repair

In this study, temporal and spatial distribution of three TGF-beta isoforms and their downstream signaling pathways including pSmad2 and p38MAPK were examined during fibrotic wound repair. In normal chick corneas, TGF-beta1, -2, and -3 were weakly detected in Bowman's layer (BL). In healing corneas, TGF-beta1 was primarily deposited in the fibrin clot and the unwounded BL. TGF-beta2 was highly expressed in healing epithelial and endothelial cells, and numerous active fibroblasts/myofibroblasts. TGF-beta3 was mainly detected in the unwound region of basal epithelial cells. alpha-Smooth muscle actin (alpha-SMA) was initially appeared in the posterior region of repairing stroma at day 3, and was detected in the entire healing stroma by day 7. Notably, alpha-SMA was absent in the central region of healing stroma by day 14, and its staining pattern was similar to those of TGF-beta2 and p38MAPK. By contrast, pSmad2 was mainly detected in the fibroblasts. In normal cornea, laminin was mainly detected in both epithelial basement membrane (BM) and Descemet's membrane (DM). By contrast to reconstitution of the BM in the wound region, the DM was not repaired although endothelial layer was regenerated, indicating that high levels of TGF-beta2 were released into the posterior region of healing stroma on day 14. High levels of alpha-SMA staining, shown in cultured repair stromal cells from healing corneas on day 14 and in TGF-beta2 treated normal stromal cells, were significantly reduced by p38MAPK inhibition. Collectively, this study suggests that TGF-beta2-mediated myofibroblast transformation is mediated, at least partly, by the p38MAPK pathway in vivo.