Cannabinoid-induced chemotaxis in bovine corneal epithelial cells

PURPOSE. Cannabinoid CB₁receptors are found in abundance in the vertebrate eye, with most tissue types expressing this receptor. However, the function of CB₁ receptors in corneal epithelial cells (CEC_s) is poorly understood. Interestingly, the corneas of CB1 knockout mice heal more slowly after injury via a mechanism proposed to involve protein kinase B (Akt) activation, chemokinesis, and cell proliferation. The current study examined the role of cannabinoids in CEC migration in greater detail. METHODS. We determined the role of CB₁ receptors in corneal healing. We examined the consequences of their activation on migration and proliferation in bovine CECs (bCEC_s). We additionally examined the mRNA profile of cannabinoid-related genes and CB1 protein expression as well as CB₁ signaling in bovine CEC_s. RESULTS. We now report that activation of CB1 with physiologically relevant concentrations of the synthetic agonist WIN55212-2 (WIN) induces bCEC migration via chemotaxis, an effect fully blocked by the CB1 receptor antagonist SR141716. The endogenous agonist 2- arachidonoylglycerol (2-AG) also enhances migration. Separately, mRNA for most cannabinoidrelated proteins are present in bovine corneal epithelium and cultured bCEC_s. Notably absent are CB₂ receptors and the 2-AG synthesizing enzyme diglycerol lipase-a (DAGL_a). The signaling profile of CB₁ activation is complex, with inactivation of mitogen-activated protein kinase (MAPK). Lastly, CB₁ activation does not induce bCEC proliferation, but may instead antagonize EGF-induced proliferation. CONCLUSIONS. In summary, we find that CB1-based signaling machinery is present in bovine cornea and that activation of this system induces chemotaxis.