Figure 4. Homed BM Sca-1⁺ cells stimulated proliferation of donor and host progenitor cells after MI.

(A) Coronary artery ligation was performed 12 weeks after the bone marrow (BM) reconstitution of old recipients with young Sca-1⁺ or Sca-1⁻ cells, and BrdU was given 1 day prior to myocardial infarction (MI), on the day of MI, and 1 day after MI. Cardiac proliferating cells were assessed 3 days post-MI (LAD3). Immunolabeling of myocardial sections permitting identification of cells which were either GFP⁺ (young BM cells; green) and/or BrdU⁺ (proliferating cells; red). Nuclei are stained blue with DAPI (B). Quantification of BrdU⁺ cells in the scar, border, and remote regions of the Sca-1⁺ [(YSca1⁺)-O] and Sca-1⁻ [(YSca1⁻)-O] chimeric hearts (C, n = 3/group). Representative confocal images of BrdU⁺/GFP⁺ donor cells in the scar region (D) and quantification of BrdU⁺/GFP⁺ donor cells (E, n = 3/group) and BrdU⁺/GFP⁻ host cells (F, n = 3/group) in the scar, border, and remote regions of chimeric hearts. Quantification of BrdU⁺/cKit⁺ cells in the GFP⁺ and GFP⁻ fraction (G, n = 3/group) in the scar, border, and remote regions of the Sca-1⁺ and Sca-1⁻ chimeric hearts. GFP⁺ (H, n = 4/group) and GFP⁺/Sca-1⁺ cells (I, n = 3–5/group) quantified by flow cytometry in chimeric hearts at baseline and 3 days post-MI. BrdU: 5-bromo-2′-deoxyuridine; DAPI: 4′,6-diamidino-2-phenylindole; LAD: ligation of left anterior coronary artery. Data analysis used two-way ANOVA followed by Bonferroni post-hoc tests for multiple comparisons (C,E,F,G,H,I). Data shown are mean ± SEM.