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Matthew Kaufman, Britta White, Folami Lamoke, Sathish Sivaprakasam, Nagendra Singh, Pamela M Martin; GPR109A activation reduces macrophage infiltration and subsequent neurodegeneration in a non-autoimmune model of uveitis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5400.
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© ARVO (1962-2015); The Authors (2016-present)
Unregulated inflammation is implicated in a number of degenerative retinal diseases. Our prior in vitro studies demonstrate GPR109A, a G-protein coupled receptor expressed in monocytes/macrophages and retinal pigment epithelial cells, to be a potent modulator of inflammation. Our aim here was evaluate the protective effects of GPR109A activation in retina in vivo. To do so, we used mice with endotoxin-induced uveitis, a widely accepted model of acute retinal inflammation.
Wild-type (WT; Gpr109a+/+) and knockout (KO; Gpr109a-/-) C57BL/6J male mice (5 months old) were injected intraperitoneally with PBS (control) or GPR109A agonists, β-hydroxybutyrate (β-HB; 300 mg/kg) or niacin (60 mg/kg) for 4-consecutive days. On day 4, lipopolysaccharide (LPS; 4 mg/kg) was also injected. 16-24 h post-injection, whole blood and eyes were harvested. Circulating immune cells were quantified using a hematology analyzer (Horiba). Mouse multiplex chemokine arrays (R&D Systems), Western blotting, and immunohistofluorescence analyses were used to evaluate the retinal inflammatory protein profile. Retina/RPE tissues were homogenized and single cell suspensions were prepared and the number of cells positive for CD45, CD11b and F4/80 were quantified by flow cytometry. Cell death was assessed by routine TUNEL assay and caspase 3 Western blotting.
Significantly higher numbers of pro-inflammatory cytokines, chemokines and CD45/CD11b/F4-80 -positive cells were evident in control KO compared to WT retinas. LPS injection induced robust increases these parameters both in WT and KO retinas. Pre-treatment with niacin or β-HB abrogated significantly the LPS-induced effect in WT retinas but had little to no effect in KO retinas. Hematological analyses revealed a similar trend with respect to the number of circulating monocytes. The number of apoptotic (TUNEL and caspase 3 positive) retinal cells was reduced also with ligand treatment of WT retina, but no cell protective effects were evident in treated KO retinas.
Our current findings suggest GPR109A to be an ideal therapeutic target for curtailing pathologic inflammation in the retina, thereby preventing and treating retinal neurodegenerative diseases.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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