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  • Title: Cone Viability Is Affected by Disruption of Melatonin Receptors Signaling.
    Author: Gianesini C, Hiragaki S, Laurent V, Hicks D, Tosini G.
    Journal: Invest Ophthalmol Vis Sci; 2016 Jan 01; 57(1):94-104. PubMed ID: 26780313.
    Abstract:
    PURPOSE: Previous studies have demonstrated that melatonin has an important role in the modulation of photoreceptor viability during aging and may be involved in the pathogenesis of age-related macular degeneration.This hormone exerts its influence by binding to G-protein coupled receptors named melatonin receptor 1 (MT1) and 2 (MT2). Melatonin receptors 1 and 2 activate a wide variety of signaling pathways. METHODS: Melatonin-proficient mice (C3H/f+/+) and melatonin-proficient mice lacking MT1 or MT2 receptors (MT1-/- and MT2-/-) were used in this study. Mice were killed at the ages of 3 and 18 months, and photoreceptor viability was determined by counting nuclei number in the outer nuclear layer (ONL). Cones were identified by immunohistochemistry using peanut agglutinin (PNA) and green/red and blue opsin antibodies. Protein kinase B (AKT) and forkhead box O (FOXO1) were assessed by Western blotting and immunohistochemistry. RESULTS: The number of nuclei in the ONL was significantly reduced in C3Hf+/+, MT1-/-, and MT2-/- mice at 18 months of age with respect to 3-month-old animals. In 18-month-old MT1-/- and MT2-/- mice, but not in C3H/f+/+, the number of cones was significantly reduced with respect to young MT1-/- and MT2-/- mice or age-matched C3H/f+/+. In C3H/f+/+, activation of the AKT-FOXO1 pathway in the photoreceptors showed a significant difference between night and day. CONCLUSIONS: Our data indicate that disruption of MT1/MT2 heteromer signaling induces a reduction in the number of photoreceptors during aging and also suggest that the AKT-FOXO1 survival pathway may be involved in the mechanism by which melatonin protects photoreceptors.
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