Type-1 pericytes accumulate in the fibrotic region after myocardium infarction but do not express collagen. (A) Representative photomicrographs of longitudinal sections of myocardial tissue from Nestin-GFP/NG2-DsRed double-transgenic mice. Blood vessels with CD31+ endothelial cells are surrounded by Nestin-GFP–/NG2-DsRed+ (type-1) and Nestin-GFP+/NG2-DsRed+ (type-2) pericytes. All panels show the same area for different channels (CD31, NG2-DsRed, Nestin-GFP, Hoechst, and merged fluorescence). Region in yellow box shows type-1 and type-2 pericytes close to CD31+ blood vessels, magnified in (C). (B) Representative longitudinal sections of hearts 14 days post infarct from Nestin-GFP/NG2-DsRed double-transgenic mice. All panels show identical areas in the heart section (CD31 staining, NG2-DsRed, Nestin-GFP+, Hoechst, and merged fluorescence images). Region in yellow box shows area with high type-1 pericyte accumulation near areas with dense collagen production, magnified in (D). (C) Type-1 and type-2 pericytes close to CD31+ blood vessels, magnified from (A). (D) High type-1 pericyte accumulation near areas with dense collagen production, magnified from (B). Note that anti-type I collagen (Col) staining confirms that neither type-1 nor type-2 pericytes express Col I, although type-1 pericytes accumulate near the fibrotic area. (E) Quantification of type-1 and type-2 pericytes before and 14 days after infarction (n = 3 mice; 10 heart sections from each). Note that the number of type-1 pericytes increased significantly. (F) Percent of cells expressing Col I in the infarcted heart. Scale bars = 100 μm.