Betacellulin as a Potential Therapeutic Agent in Corneal Epithelial Wound Healing

Abstract

Purpose: : Experimentally it has been shown that epidermal growth factor (EGF) and its receptor (EGFR/ErbB1) are necessary and sufficient for promoting the cellular events associated with corneal epithelial wound healing. However, the clinical use of EGF has mixed results and there is no clear evidence that exogenous EGF can enhance wound healing of the corneal epithelium in patients. In an attempt to resolve the disparity between experimental and clinical data, the role of other EGFR ligands should be explored. Preliminary data from our lab, and others, indicated that betacellulin (BTC), an EGF-like ligand, induced corneal wound healing more efficaciously that EGF and therefore may be a potential therapeutic agent. The purpose of this study is to determine the molecular mechanisms that contribute to BTC’s enhanced efficacy.

Methods: : Porcine corneas were superficially wounded (epithelial layer) and treated with BTC, EGF, or media to assess qualitative and quantitative differences in ligand-mediated epithelial wound healing. Radiolabeled BTC (¹²⁵I-BTC) was used with immortalized and primary corneal epithelial cell cultures to determine ligand binding properties of BTC.

Results: : After 48 hours, the epithelial thickness of the wounded area in eyes treated with BTC is approximately 1.5-fold greater than those treated with EGF and 2-fold greater than media alone. The binding affinity of BTC in both immortalized and primary cells is consistent with published data and the number of available binding sites in immortalized cells is greater than those in primary cells. Unlabeled ligands BTC and EGF, but not neuregulin 4, were able to compete for ¹²⁵I-BTC binding to receptors. Additionally, BTC binding is less sensitive to acid dissociation than EGF binding.

Conclusions: : BTC mediates corneal epithelial wound healing at a greater rate than EGF. The binding properties of BTC are a likely mechanism for why BTC is a more efficacious ligand. Our data demonstrate that BTC binds with a higher affinity than EGF. Further, binding of BTC to receptors is less sensitive to changes in pH, indicating the ligand:receptor complex would stay intact longer. A third possibility is that BTC binds to an additional population of receptors that are either more prevalent or intrinsically more efficacious in mediating corneal epithelial wound healing.

Keywords: cornea: basic science • wound healing • growth factors/growth factor receptors