Evidence for a GPR18 Role in Chemotaxis, Proliferation, and the Course of Wound Closure in the Cornea

Abstract

Purpose: 

We previously showed that cannabinoid-related GPR18 receptors are present in the murine corneal epithelium, but their function remains unknown. The related CB₁ receptors regulate corneal healing, possibly via chemotaxis. We therefore examined a potential role for GPR18 in corneal epithelial chemotaxis and wound healing.

Methods: 

We examined GPR18 messenger RNA (mRNA) and protein expression in the cornea. We additionally examined GPR18 action in cultured bovine corneal epithelial cells (bCECs) using Boyden and tracking assays, as well as proliferation and signaling. Finally, we examined wound closure in murine corneal explants.

Results: 

GPR18 mRNA was upregulated with injury in the mouse cornea. GPR18 protein was present in basal epithelial cells of the mouse and cow and redistributed to the wound site upon injury. GPR18 ligand N-arachidonoylglycine induced bCEC chemotaxis. The endocannabinoid arachidonoylethanolamine also induced chemotaxis via fatty acid amide hydrolase–mediated metabolism to N-arachidonoylglycine. GPR18 receptor activation additionally induced bCEC proliferation. In an explant model, the GPR18 antagonist O-1918 slowed corneal epithelial cell migration and the rate of corneal wound closure.

Conclusions: 

Corneal GPR18 activation induced both chemotaxis and proliferation in corneal epithelial cells in vitro and impacted wound healing. GPR18 may contribute to the maintenance of corneal integrity.