Ccr2 suppression by minocycline in Cx3cr1/Ccr2-visualized inherited retinal degeneration

Retinal inflammation accelerates photoreceptor cell death (PCD) caused by retinal degeneration. Minocycline, a semisynthetic broad-spectrum tetracycline antibiotic, has previously been reported to show PCD rescue effect in retinal degeneration. The purpose of this study was to assess the effect of minocycline on Cx3cr1 and Ccr2 expression in retinal degeneration. Mertk-/-Cx3cr1GFP/+Ccr2RFP/+ mice, which enabled observation of Cx3cr1- and Ccr2-expression pattern in inherited retinal degeneration, were used to test the effect of minocycline. Minocycline was systemically administered to Mertk-/-Cx3cr1GFP/+Ccr2RFP/+ mice. For observing the effect of minocycline on Cx3cr1 and Ccr2 expression, administration was started on 4-week-old mice and continued for 2 weeks. To assess the PCD rescue effect, minocycline was administered to 6-week-old mice for 2 weeks. The expression pattern of Cx3cr1-GFP and Ccr2-RFP were observed on retinal and retinal pigment epithelium (RPE) flat-mounts. The severity of retinal degeneration was assessed on retinal sections. Minocycline administration suppressed Ccr2 expression in Mertk-/-Cx3cr1GFP/+Ccr2RFP/+ mice as observed in retinal and RPE flat-mounts. On the contrary, Cx3cr1 expression was not affected by minocycline administration. Retinal degeneration is ameliorated in minocycline administered Mertk-/-Cx3cr1GFP/+Ccr2RFP/+ mice. In conclusions, Minocycline suppression of Ccr2 expression correlates to amelioration of retinal degeneration.