Spatiotemporal characteristics of myeloid subsets during experimental neovascularization.Figure 6Experimental setup. TAM was applied to 6 weeks old Cx3cr1CreERT2:Rosa26-tdTomato mice leading to the excision of the stop sequence followed by robust Tomato expression in microglia. At the age of 14 weeks (8 weeks post TAM) three focal argon laser burns were applied to each retina to induce microglia activation and subsequent choroidal neovascularization (CNV). Analysis was performed on days (d) 3, 7, 14, 28 and 56, respectively. Above: Representative funduscopic pictures from living healthy Cx3cr1CreERT2:Rosa26-tdTomato mice on d0. Funduscopy and red fluorescence visualize the fundus and regular distribution of tomato+ microglia before the laser-induced lesion formation. Below: Corresponding immunofluorescence pictures. Non-lesioned retina show a regular pattern of Iba1+ (green) tomato+ (red) retinal microglia while macrophages are absent on the retinal pigment epithelium (RPE) under native conditions. Pictures are representative for six mice analyzed in one experiment. Scale bars represents 50 µm. c) Above: In vivo funduscopy on d7 post lesion. Funduscopic and red fluorescence image depict the lesions (encircled with dashed white lines) and accumulation of tomato+ microglia in Cx3cr1CreERT2:Rosa26-tdTomato mice. Intraperitoneal fluorescein application was performed to label retinal vessels and areas of choroidal neovascularization. Below: Representative immunofluorescence for Iba1 (green) in Cx3cr1CreERT2:Rosa26-tdTomato mice. Resident retinal microglia are Iba1+tomato+ (asterisks) whereas blood-derived myeloid cells are Iba1+tomato- (arrows) and accumulate at sites of laser-induced CNV. Overlay is shown left. Typical pictures from six mice obtained from one independent experiment are shown. Scale bars represents 50 µm. d) Percentage (left) and absolute numbers (right) of myeloid subsets in the retina at different time points post lesion. Red columns, red lines and red symbols represent tomato*Iba1+ microglia in Cx3cr1CreERT2:Rosa26-tdTomato mice whereas green columns, green lines and green symbols represent blood-derived tomato-Iba1+ myeloid cells. Left, Wilcoxon test at d3 (ns p = 0.0625), d28 (ns, p = 0.25) and d56 (ns p = 0.125) and paired t test at d7 (***p < 0.0001 and d14 (***p < 0.0001; right, absolute numbers Kruskal-Wallis test (tomato*Iba1+ *p < 0.05, tomato-Iba1+ ** p < 0.01). Data represent means ± s.e.m. from at least three mice per group (two to six lesion per mouse) out of one (d0, d14, d28, d56) or two (d7, d14) independent experiments. e) Distribution (left) and absolute numbers (right) of myeloid cells in the RPE at different time points following laser-induced lesion. Red columns, red lines and red symbols represent Iba1+ microglia in Cx3cr1CreERT2:Rosa26-tdTomato mice. Green columns, green lines and green symbols represent blood-derived Iba1+tomato- myeloid cells. Left, paired t test at d3, d7, d14 (**p < 0.01, ***p < 0.001), Wilcoxon test at d28 and d56 (ns p > 0.05); right, absolute numbers Kruskal-Wallis test (ns p > 0.05). Data represent means ± s.e.m. from at least three mice per group (two to six lesion per mouse) out of one (d0, d14, d28, d56) or two (d7, d14) independent experiments. f,g)Flow cytometric measurement of tomato expression in 14 weeks old Cx3cr1CreERT2:Rosa26-tdTomato mice eight weeks after TAM treatment (f) or with no treatment (g). Red lines represent the tomato signal and black lines the corresponding CreER-negative control. Data are presented as mean ± s.e.m. from four mice analyzed in one experiment.