CB1 Cannabinoid Receptor is a Target for Neuroprotection in Light Induced Retinal Degeneration

In the last few years, an increasing interest in the neuroprotective effect of cannabinoids has taken place. The aim of the present work was to study the effects of modulating cannabinoid receptor 1 (CB1) in the context of light induced retinal degeneration (LIRD), using an animal model that resembles many characteristics of human age-related macular degeneration (AMD) and other degenerative diseases of the outer retina. Sprague Dawley rats (n = 28) were intravitreally injected in the right eye with either a CB1 agonist (ACEA), or an antagonist (AM251). Contralateral eyes were injected with respective vehicles as controls. Then, rats were subjected to continuous illumination (12,000 lux) for 24 h. Retinas from 28 animals were processed by GFAP-immunohistochemistry (IHC), TUNEL technique, Western blotting (WB), or qRT-PCR. ACEA-treated retinas showed a significantly lower number of apoptotic nuclei in the outer nuclear layer (ONL), lower levels of activated Caspase-3 by WB, and lower levels of glial reactivity by both GFAP-IHC and WB. qRT-PCR revealed that ACEA significantly decreased the expression of Bcl-2 and CYP1A1. Conversely, AM251-treated retinas showed a higher number of apoptotic nuclei in the ONL, higher levels of activated Caspase-3 by WB, and higher levels of glial reactivity as determined by GFAP-IHC and WB. AM251 increased the expression of Bcl-2, Bad, Bax, Aryl hydrocarbon Receptor (AhR), GFAP, and TNFα. In summary, the stimulation of the CB1 receptor, previous to the start of the pathogenic process, improved the survival of photoreceptors exposed to LIRD. The modulation of CB1 activity may be used as a neuroprotective strategy in retinal degeneration and deserves further studies.