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Regulation by P2X₇: Epithelial Migration and Stromal Organization in the Cornea

¹From the Departments of Biochemistry and ³Ophthalmology, Boston University School of Medicine, Boston, Massachusetts; and the ²Department of Anatomy and Reparative Medicine, The George Washington University, Washington, DC.

PURPOSE. Previously, the authors demonstrated that BzATP, a P2X₇ receptor agonist, enhanced corneal epithelial migration in vitro. The goal here was to characterize the role of the P2X₇ receptor in the repair of in vivo corneal epithelial debridement wounds and in the structural organization of the corneal stroma.

METHODS. Epithelial debridement was performed on P2X₇ knockout (P2X₇^–/–) and wild-type (WT) mice, and eyes were harvested after 16 hours. Corneas were stained with Richardson vital stain, and the wound area was recorded. Corneas were fixed and prepared for light microscopic, immunohistochemical, and electron microscopic analysis. Cuprolinic blue staining was performed to analyze stromal proteoglycans (PGs). Real-time PCR was performed to examine the expression of stromal collagens.

RESULTS. P2X₇ was present in the WT corneal epithelium but was not detected in P2X₇^–/– mice. Pannexin-1, a protein demonstrated to interact with P2X₇, was absent from the wound edge in P2X₇^–/–. This was associated with a trend toward delayed corneal reepithelialization. Stromal ultrastructure and collagen alignment were altered in P2X₇^–/–, and collagen fibrils had smaller diameters with a larger interfibrillar distances. Expression of collagen alpha1(I) and alpha3(v) was reduced. There were 30% fewer sulfated PGs along fibrils in the P2X₇^–/– stroma.

CONCLUSIONS. In the absence of the P2X₇ receptor, the expression of proteins in the corneal epithelium was altered and wound healing was compromised. Loss of receptor resulted in morphologic changes in the stroma, including changes in alignment of collagen fibrils, decreased expression of collagen, and smaller fibrils with fewer PGs per fibril.