Inhibition of PARP-1 abrogates the effect of salidroside on HSC maintenance. (A) Deletion of Parp-1 abolishes salidroside-mediated increase in quiescent HSC frequency in stressed mice. Parp1^−/− mice as well as their WT littermates were pretreated with or without salidroside (75 μg/g body weight) followed by H₂O₂ (0.25 μmol/g body weight). BM cells were subjected to flow cytometry analysis for quiescent HSC (G₀ phase). Results are means ± SD of 3 independent experiments (n = 9 per group). (B) NU1025 treatment abolishes salidroside-mediated increase in quiescent HSC frequency in stressed mice. H₂O₂-treated (0.25 μmol/g body weight) WT mice were treated with or without salidroside (SD; 75μg/g body weight) and NU1025 (25 mg/kg body weight). BM cells were subjected to flow cytometry analysis for quiescent HSC. Results are means ± SD of 3 independent experiments (n = 9 per group). (C) The maintenance of HSC quiescence by salidroside requires Parp-1. 1000 LSK cells from WT or Parp1^−/− mice were injected to lethally irradiated WT recipients. Recipient mice were then subjected to salidroside and H₂O₂ treatments. Cycling donor-derived (CD45.2⁺) cells were assessed by Flow Cytometry analysis by pyronin Y staining. Representative images (top) and quantifications (bottom) were shown. Results are means ± SD of 3 independent experiments (n = 9 per group). (D) The enhancing effect of salidroside on the long-term repopulation abilities of stressed HSCs requires Parp1. Cells from primary recipients described in panel C were used for second transplantation by injecting 10 million whole BM cells to lethally irradiated WT recipients. Donor-derived cells were determined by flow cytometry analysis. Representative images (top) and quantifications (bottom) were shown. Results are means ± SD of 3 independent experiments (n = 9 per group).