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Joana Galvao, Li Guo, Ana Raquel Santiago, Antonio Ambrosio, M Francesca Cordeiro; Adenosine A3 receptor agonist inhibits retinal ganglion cell apoptosis in vivo. Invest. Ophthalmol. Vis. Sci. 2013;54(15):433.
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© ARVO (1962-2015); The Authors (2016-present)
Adenosine receptors (AR) have been considered as potential therapeutic targets in neurodegenerative diseases, such as glaucoma. Adenosine and three of its four receptors have been identified at the level of retinal ganglion cell (RGC) layer. Our previous studies have shown that RGCs express the A3AR, and that the A3AR agonist is protective against an NMDA insult to retinal explants. In this study, we focused on assessing A3AR expression and the potential neuroprotective effects of a selective A3AR agonist, 2-Cl-IB-MECA, in two rat models of RGC degeneration: partial optic nerve transection (pONT) and ocular hypertension model (OHT).
OHT or pONT was induced in the left eye of Dark Agouti rats, with the opposite eye as control. A pilot study identified 1.2 µM 2-Cl-IB-MECA as the most effective dose at reducing DMSO induced RGC apoptosis in vivo. Both eyes of OHT or pONT were intravitreally injected with either 2-Cl-IB-MECA, PBS (vehicle) or 1.2 µM 2-Cl-IB-MECA + 1.2 µM MRS 1220 (A3AR antagonist) immediately before surgery. IOPs were measured regularly using a Tonolab. Animals were imaged to assess RGC apoptosis in vivo using DARC (Detection of Apoptosis in Retinal Cells) 7 days after pONT or three weeks after IOP elevation, previously described. Immunohistochemical analysis of A3AR expression and TUNEL was performed in 10 µm-thick retinal cryosections.
Treatment with the A3AR agonist resulted in a reduction of IOP in OHT eyes. DARC imaging analysis revealed that the A3AR agonist 2-Cl-IB-MECA significantly reduced RGC apoptosis (p < 0.01) to approximately 50% compared to vehicle treated pONT/OHT (mean 239±93.65 vs 449±84.58, respectively for pONT and mean 215±93.01 vs 409±154.58, respectively for OHT). Rats treated with both A3AR agonist and antagonist did not show significant difference from insult alone. Immunohistochemistry confirmed an increase in the number of apoptotic cells using TUNEL and showed a down regulation in the expression of A3AR in the RGC layer in the eyes with the insult compared to control.
In accordance with our previous findings, these results suggest that A3AR activation is neuroprotective against RGC apoptosis in vivo. Therefore, targeting A3AR and delineation of its relationship with RGC apoptosis could have great potential in the management of retinal neurodegeneration, such as glaucoma.
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