Microglia and macrophages are recruited to sites of retinal degeneration where local cytokines and chemokines determine protective or neurotoxic microglia responses. Defining the role of Ccl2-Ccr2 and Cx3cl1-Cx3cr1 signalling for retinal pathology is of particular interest because of its potential role in age-related macular degeneration (AMD). Ccl2, Ccr2, and Cx3cr1 signalling defects impair macrophage trafficking, but have, in several conflicting studies, been reported to show different degrees of age-related retinal degeneration. Ccl2/Cx3cr1 double knockout (CCDKO) mice show an early onset retinal degeneration and have been suggested as a model for AMD. In order to understand phenotypic discrepancies in different chemokine knockout lines and to study how defects in Ccl2 and/or Cx3cr1 signalling contribute to the described early onset retinal degeneration, we defined primary and secondary pathological events in CCDKO mice. To control for genetic background variability, we compared the original phenotype with that of single Ccl2, Cx3cr1 and Ccl2/Cx3cr1 double knockout mice obtained from backcrosses of CCDKO with C57Bl/6 mice. We found that the primary pathological event in CCDKO mice develops in the inferior outer nuclear layer independently of light around postnatal day P14. RPE and vascular lesions develop secondarily with increasing penetrance with age and are clinically similar to retinal telangiectasia not to choroidal neovascularisation. Furthermore, we provide evidence that a third autosomal recessive gene causes the degeneration in CCDKO mice and in all affected re-derived lines and subsequently demonstrated co-segregation of the naturally occurring RD8 mutation in the Crb1 gene. By comparing CCDKO mice with re-derived CCl2？/？/Crb1Rd8/RD8, Cx3cr1？/？/Crb1Rd8/RD8 and CCl2？/？/Cx3cr1？/？/Crb1Rd8/RD8 mice, we observed a differential modulation of the retinal phenotype by genetic background and both chemokine signalling pathways. These findings indicate that CCDKO mice are not a model of AMD, but a model for an inherited retinal degeneration that is differentially modulated by Ccl2-Ccr2 and Cx3cl1-Cx3cr1 chemokine signalling.
Jung S, Aliberti J, Graemmel P, Sunshine MJ, Kreutzberg GW, et al. (2000) Analysis of Fractalkine Receptor CX3CR1 Function by Targeted Deletion and Green Fluorescent Protein Reporter Gene Insertion. Mol Cell Biol 20: 4106–4114.
Joly S, Francke M, Ulbricht E, Beck S, Seeliger M, et al. (2009) Cooperative Phagocytes: Resident Microglia and Bone Marrow Immigrants Remove Dead Photoreceptors in Retinal Lesions. Am J Pathol 174: 2310–2323.
Eter N, Engel DR, Meyer L, Helb HM, Roth F, et al. (2008) In Vivo Visualization of Dendritic Cells, Macrophages, and Microglial Cells Responding to Laser-Induced Damage in the Fundus of the Eye. Invest Ophthalmol Vis Sci 49: 3649–3658.
Dzenko KA, Song L, Ge S, Kuziel WA, Pachter JS (2005) CCR2 expression by brain microvascular endothelial cells is critical for macrophage transendothelial migration in response to CCL2. Microvascular Research 70: 53–64.
Marchesi F, Locatelli M, Solinas G, Erreni M, Allavena P, et al. (2010) Role of CX3CR1/CX3CL1 axis in primary and secondary involvement of the nervous system by cancer. Journal of Neuroimmunology 224: 39–44.
Combadiere C, Feumi C, Raoul W, Keller N, Rodero M, et al. (2007) CX3CR1-dependent subretinal microglia cell accumulation is associated with cardinal features of age-related macular degeneration. J Clin Invest 117: 2920–2928.
Tuo J, Smith BC, Bojanowski CM, Meleth AD, Gery I, et al. (2004) The involvement of sequence variation and expression of CX3CR1 in the pathogenesis of age-related macular degeneration. FASEB J 18: 1297–1299.
Neale BM, Fagerness J, Reynolds R, Sobrin L, Parker M, et al. (2010) Genome-wide association study of advanced age-related macular degeneration identifies a role of the hepatic lipase gene (LIPC). PNAS 107: 7395–7400.
McKay GJ, Patterson CC, Chakravarthy U, Dasari S, Klaver CC, et al. (2011) Evidence of association of APOE with age-related macular degeneration - a pooled analysis of 15 studies. Hum Mutat 32: 1407–1416.
Jonas JB, Tao Y, Neumaier M, Findeisen P (2010) Monocyte Chemoattractant Protein 1, Intercellular Adhesion Molecule 1, and Vascular Cell Adhesion Molecule 1 in Exudative Age-Related Macular Degeneration. Arch Ophthalmol 128: 1281–1286.
Raoul W, Feumi C, Keller N, Lavalette S, Houssier M, et al. (2008) Lipid-bloated subretinal microglial cells are at the origin of drusen appearance in CX3CR1-deficient mice. Ophthalmic Res 40: 115–119.
Luhmann UFO, Robbie S, Munro PM, Barker SE, Duran Y, et al. (2009) The drusen-like phenotype in aging Ccl2 knockout mice is caused by an accelerated accumulation of swollen autofluorescent subretinal macrophages. Invest Ophthalmol Vis Sci 50: 5934–5943.
Tuo J, Bojanowski CM, Zhou M, Shen D, Ross RJ, et al. (2007) Murine Ccl2/Cx3cr1 Deficiency Results in Retinal Lesions Mimicking Human Age-Related Macular Degeneration. Invest Ophthalmol Vis Sci 48: 3827–3836.
West JB, Fu Z, Deerinck TJ, Mackey MR, Obayashi JT, et al. (2010) Structure–function studies of blood and air capillaries in chicken lung using 3D electron microscopy. Respiratory Physiology & Neurobiology 170: 202–209.
Zhou Y, Sheets KG, Knott EJ, Regan J, Tuo J, et al. (2011) Cellular and 3D optical coherence tomography assessment during the initiation and progression of retinal degeneration in the Ccl2/Cx3cr1-deficient mouse. Experimental Eye Research 93: 636–648.
Mehalow AK, Kameya S, Smith RS, Hawes NL, Denegre JM, et al. (2003) CRB1 is essential for external limiting membrane integrity and photoreceptor morphogenesis in the mammalian retina. Hum Mol Genet 12: 2179–2189.
van de Pavert SA, Kantardzhieva A, Malysheva A, Meuleman J, Versteeg I, et al. (2004) Crumbs homologue 1 is required for maintenance of photoreceptor cell polarization and adhesion during light exposure. Journal of Cell Science 117: 4169–4177.
Jaissle G, May C, van de Pavert S, Wenzel A, Claes-May E, et al. (2010) Bone spicule pigment formation in retinitis pigmentosa: insights from a mouse model. Graefe's Archive for Clinical and Experimental Ophthalmology 248: 1063–1070.
Silverman MD, Zamora DO, Pan Y, Texeira PV, Baek SH, et al. (2003) Constitutive and Inflammatory Mediator-Regulated Fractalkine Expression in Human Ocular Tissues and Cultured Cells. Investigative Ophthalmology & Visual Science 44: 1608–1615.
Rutar M, Natoli R, Valter K, Provis JM (2011) Early Focal Expression of the Chemokine Ccl2 by Müller Cells during Exposure to Damage-Inducing Bright Continuous Light. Investigative Ophthalmology & Visual Science 52: 2379–2388.
Blomster LV, Vukovic J, Hendrickx DAE, Jung S, Harvey AR, et al. (2011) CX3CR1 deficiency exacerbates neuronal loss and impairs early regenerative responses in the target-ablated olfactory epithelium. Molecular and Cellular Neuroscience 48: 236–245.
Ross RJ, Zhou M, Shen D, Fariss RN, Ding X, et al. (2008) Immunological protein expression profile in Ccl2/Cx3cr1 deficient mice with lesions similar to age-related macular degeneration. Experimental Eye Research 86: 675–683.