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A. M. Suburo, M. Sgroi, M. A. Cubilla, M. Iribarne, A. Berra; Cannabinoid Receptors and Corneal Epithelium Repair. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6297.
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© ARVO (1962-2015); The Authors (2016-present)
We have previously shown expression of cannabinoid receptors CB1 and CB2 in conjunctival epithelium. Activation of these receptors stimulated conjunctival cell growth in vitro and blocked TNF-alfa dependent signaling pathways. Therefore, we investigated the presence of CB1 and CB2 in the cornea and their response to epithelial lesions.
Male Balb-c mice (4-6 weeks-old, n = 12) were handled according to the ARVO Statement for the Use of Animals. After general and topical anesthesia, a paper soaked in 20% ethanol was applied on the right central cornea (30 sec.). Swabbing removed remaining dead cells. Left eyes served as controls. Mice were euthanatized 4 or 24 hours after surgery. Immunohistochemical detection of CB1 and CB2 was made in corneal cryosections.
Little CB1 immunoreactivity was detected in normal corneas, being restricted to small patches of the limbus. By contrast, moderate CB2 immunoreactivity appeared in limbar cells and basal epithelial layers of the normal cornea. Immunoreactivity was higher in the limbus and periphery of the cornea than in its central region. 4 hours after surgery, CB1 appeared in most limbal cells, whereas CB2 immunoreactivity increased in the limbus and cornea. Small CB2+ cells also appeared in the corneal stroma. High expression of cannabinoid receptors remained after 24 hours, when the epithelial lamina had recovered its continuity.
Both CB1 and CB2 were present in corneal epithelial cells. However, CB2 immunoreactivity was always stronger than CB1 immunoreactivity. This was a consistent difference with conjunctival epithelium, showing similar CB1 and CB2 immunoreactivities.Limbal cells displayed the highest CB1 and CB2 immunoreactivities, both in control and lesioned eyes. Localization of immunoreactivity in control eyes indicated that CB2+ cells probably represent limbal stem cells and transit amplifyings cells. Increase of immunostaining intensity and number of epithelial CB2+ cells following injury suggests that these receptors might be involved in the regulation of cell proliferation and differentiation. Since limbal CB1 immunoreactivity increased after corneal lesion, a similar role can be postulated for this receptor. Small round CB2+ cells infiltrating the stroma after corneal injury probably represent immune/inflammatory cells. Further experiments are required to understand the role of each receptor in proliferation, differentiation and inflammation of corneal tissues.
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