Integrin And Tgf-β Signaling: Involvement In Two Types Of Corneal Wound Healing

Abstract

Purpose: : To examine the interplay between integrins and the TGF-β signaling pathway in two types of corneal injuries, epithelial debridement and keratectomy.

Methods: : Transgenic mice, K12^rtTA/rtTA/Tet-O-Cre/Tbr2^f/f, lacking the TGF-β receptor II (Tbr2^ceΔ/ceΔ) from the corneal epithelium by doxycycline induction, were used to examine the signaling pathways involved in the healing process. Transgenic mice were fed doxycylcine chow for 4 weeks and were then subjected to epithelial debridement or keratectomy. Transgenic K12^rtTA/rtTA/Tet-O-Cre/Tbr2^f/f (Tbr2^cef/cef) mice were fed normal chow and also subjected to epithelial debridement and keratectomy. Mice were sacrificied at 30 min, 1 h, 2 h, 6 h, and 16 h following corneal wounding and corneas were collected and subjected to immunohistochemistry for components of various signaling pathways including TGF-β, MAPK, and integrins. Mice at the later time points, i.e., 2 h, 6 h, and 16 h, were injected with BrdU 2 h prior to sacrifice to examine proliferation. All reported research was conducted in compliance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and approved by the IACUC of the University of Cincinnati.

Results: : Differences exist in the signaling cascades involved in the healing process following either a simple epithelial debridement or keratectomy. While initially both types of healing initiate the TGF-β signaling pathway, in debridement wounds Smad 7 is upregulated followed by a shift towards activation of p38MAPK, while this does not occur in keratectomy wounds. Interestingly, in the absence of TGF-β signaling there is delayed activation of p38MAPK at the wound edge following epithelium debridement; in contrast p38MAPK activation was observed in keratectomy. Integrin expression profiles also differ between the two types of injuries, with α1-integrin being more prevalent at the wound edge following keratectomy versus debridement; however, this expression is lacking in the absence of TGF-β signaling.

Conclusions: : These data show that different signaling pathways are utilized to heal various types of corneal injury. These initial observations suggest that part of the difference lies in the integrins expressed at the wound edge.

Keywords: cornea: epithelium • transgenics/knock-outs • wound healing