Hypoxic preconditioning promotes cell proliferation and decreases hydrogen peroxide- or belomycin-induced cell death in mesenchymal stem cells. (A) Mesenchymal stem cells (MSCs) were stained with 1 μM JC-10 for 30 minutes, and were then analyzed by flow cytometry. Owing to the dual wavelength emission of JC-10, most stained cells distributed at the double-positive region (top right quadrant). Electronic compensation was made to correct the bleed of the green (monomer) and red (aggregate) fluorescence signals into the FL2 and FL1 channels. Right column shows compensated data. The gated region represented the higher mitochondrial membrane potential cell population. The histogram on the right shows the quantification of three independent normoxia-preconditioned MSCs (NP-MSCs) and hypoxia-preconditioned MSCs (HP-MSCs) samples of JC-10 staining. (B) Cell number of NP-MSCs and HP-MSCs was determined by an automated cell counter. (C) Cell viability of NP-MSCs and HP-MSCs treated with the indicated H2O2 concentration for 1 hour as assessed by flow cytometric analysis with Annexin V/propidium iodide (PI) staining. Percentages of Annexin V/PI-double positive cells (dead cells population) are shown. (D) MTT assays of cell viability of bleomycin-treated mouse lung epithelial cells (MLE-12) in the presence of NP-MSC- or HP-MSC-conditioned medium for 48 hours. *P < 0.05, **P < 0.01, differences between HP-MSCs and the NP-MSC controls.