Ang1 increases EC proliferation but suppresses EC apoptosis during Flk-1⁺ MPC differentiation. Control or Ang1 was administered into Flk-1⁺ MPCs on days 0, 2, and 4 during OP9 coculture. (A) Images showing PHH3⁺ cells in CD144⁺ EC colonies on days 1.5, 2, 2.5, 3, and 3.5. Nuclei were stained with Hoechst. Scale bar represents 100 μm. (B) Comparison of number of PHH3⁺ ECs over time (n = 5). *P < .05 compared with control. (C) Representative FACS analyses of the populations of annexin⁺ apoptotic Flk-1⁺ cells and Flk-1⁻ cells on day 3. Numbers indicate percentages of each population. (D) Comparison of percentage of annexin⁺ apoptotic Flk-1⁺ cells and Flk-1⁻ cells on day 3 (n = 3). *P < .05 compared with control.