Figure 10. Heme oxygenase-1 mediates the difference in the secretome and the therapeutic effects of RG1-MSC-CM. MSCs were transfected with varying doses of HO-1 siRNA and nonspecific siRNA prior to RG1 stimulation. The protein levels of HO-1 (A), the secretion (B) and the mRNA expression (C) of VEGF, IL-6 and IL-10 from BM-MSCs were evaluated. ##, P < 0.05 versus control, **, P < 0.05 versus RG1-MSC-CM. NS-KD-RG1-MSC-CM: conditioned medium from non-specific siRNA transfected MSCs activated by RG1. HO-1-KD-RG1-MSC-CM: conditioned medium from HO-1 siRNA transfected MSCs activated by RG1. Administration of HO1-KD-RG1-MSC-CM partially abolished the therapeutic effect of RG1-MSC-CM on the apoptosis (D) and proliferation (E) of irradiated intestinal epithelial cells in vivo, which were evaluated by quantification of TUNEL-positive and PCNA-positive cells in the intestine, respectively. ##, P < 0.05 versus IR + DMEM-F12. **, P < 0.05 versus IR + RG1-MSC-CM. (F) The activity of NF-κB p65 in intestine on day 3 of experiment was measured by an ELISA-based assay directed against the p65 subunit of NF-κB. Data represent the mean ± SD (n=3). ##, P < 0.05 versus IR + DMEM-F12. **, P < 0.05 versus IR + RG1-MSC-CM. (G) The ability to improve the 14-days survival rate were partially reversed by administration of HO1-KD-RG1-MSC-CM. ##, P < 0.05 versus IR + DMEM-F12. **, P < 0.05 versus IR + RG1-MSC-CM. All data were analyzed by t-test or one-way ANOVA except as otherwise indicated.