Effects of hypoxic preconditioning on cytoprotective and regenerative gene expression in hypoxia-preconditioned mesenchymal stem cells. Quantitative real-time RT-PCR was performed to examine the relative expression levels of mRNAs. (A) Hypoxia-induced factor (HIF)-1α in mesenchymal stem cells (MSCs) after 6 to 24 hours exposure under 1.5% oxygen conditions. (B) The HIF-1α downstream target genes, erythropoietin receptor (EPOR) and vascular endothelial growth factor (VEGF), (C) pro- and anti-apoptotic factors, B-cell lymphoma 2-associated X protein (BAX) and B-cell lymphoma 2 (Bcl-2), and (D) anti-oxidants, catalase (CAT) and heme oxygenase 1 (HO-1), in normoxia-preconditioned MSCs (NP-MSCs; 20% O2 for 24 hours) and hypoxia-preconditioned MSCs (HP-MSCs; 1.5% O2 for 24 hours). (E) Western blot analysis was performed to detect the expression level of HIF-1α in MSCs after 2 to 48 hours incubation under the 1.5% oxygen condition. (F) Comparison of protein levels of HGF, VEGF, and HO-1 in NP-MSCs (20% O2 for 24 hours) and HP-MSCs (1.5% O2 for 24 hours) in western blot analysis. Mouse β-actin was used as the normalization control. (A-D) Open and filled bars indicate NP-MSCs and HP-MSCs, respectively. Values were normalized to β-actin and are expressed relative to the respective control group. *P < 0.05, **P < 0.01, ***P < 0.001.