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Shimin Li, Sherry Hu, Douglas McHugh, Alex Straiker, Joseph A. Bonanno; 2-Arachidonoylglycerol (2-AG) Induces Corneal Epithelial Cell Migration via Cannabinoid CB1 Receptors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1995.
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Cannabinoids are a group of ~70 compounds present in Cannabis plants. Best known for their psychoactive properties, they also possess immunosuppressive and anti-inflammatory properties, and have potential as therapeutic agents in alleviating such conditions as pain, nausea, diabetes, septic shock, rheumatoid arthritis, chronic hepatitis, and intraocular pressure in glaucoma. Some cannabinoids such as Δ9-THC are known to act through classical cannabinoid receptors (CB1, CB2) and potentially other putative receptors (e.g. GPR55, GPR119, GPR92 and GPR18). CB1 receptors are known to be present in the eye, but the distribution of the others remains poorly studied. Furthermore, a constellation of proteins involved in the produce of the endogenous cannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG), have been identified. In the present study, we examined the presence of five candidate cannabinoid receptors as well as 10 cannabinoid-related proteins in bovine anterior eyes and assessed 2-AG-induced corneal epithelial cell migration to provide insight for the medicinal potential of cannabinoids, particularly for wound healing during corneal injury.
Bovine eyes were dissected to collect corneal epithelium and endothelium, trabecular meshwork, and retina tissue. Primary corneal epithelial cells were obtained via dispase digestion. The expression of a panel of cannabinoid receptors (CB1, CB2 and several GPRs), enzymes for biosynthesis of AEA and 2-AG (NAPE-PLD, ABHDs, FAAH, NAAA, DGLα/β and MGL) and cannabinoid receptor interacting protein (CRIP1a) were examined by RT-PCR. CB1 protein was also examined by western blotting. 2-AG-induced epithelial cell migration was examined using a Boyden Chamber assay with Diff-Quik staining.
mRNA for CB1, GPR18, ABHD4, ABHD12, MGL and CRIP1a was detectable in the bovine corneal epithelium. CB1 protein was also found in this tissue, while CB2 was not detectable. 2-AG-induced corneal epithelial cell migration in a concentration-dependent manner with the peak at 100nM, which was able to enhance the migration by 6-fold when compared to the control. Furthermore, 2-AG induced-migration was blocked by a CB1 antagonist SR141716.
Our results demonstrate the presence of several additional components of the endocannabinoid signaling system in mammalian anterior eyes. Corneal epithelial cell migration is mediated via activation of cannabinoid receptor CB1 by 2-AG. This event may alter the cytokine profile and promote cornea wound healing.
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