The tri-lineage differentiation potential and cytokine secretion of hUC-MSCs at various passages. a Adipogenic differentiation potential of hUC-MSCs at various passages (P3, P6, P15) was identified by Oil Red O staining (scale bar = 200 μm). b qRT-PCR analysis of the adipogenic markers (ADIPOQ, PPAR-γ, FABP4) in hUC-MSCs at various passages (P3, P6, P15). Data are shown as mean ± SEM (n = 3). *P < 0.05; NS, not significant. All values are normalized to the negative control (NC) group (= 1). c Osteogenic differentiation potential of hUC-MSCs at various passages (P3, P6, P15) was identified by Alizarin Red staining (scale bar = 200 μm). d qRT-PCR analysis of the osteogenic markers (RUNX2, BGLAP, COL2A1) in hUC-MSCs at various passages (P3, P6, P15). Data are shown as mean ± SEM (n = 3). *P < 0.05; NS, not significant. All values are normalized to the NC group (= 1). e Chondrogenic differentiation potential of hUC-MSCs at various passages (P3, P6, P15) was identified by Alcian Blue staining (scale bar = 200 μm). f qRT-PCR analysis of the chondrogenic markers (ACAN, SOX9, COL2A1) in hUC-MSCs at various passages (P3, P6, P15). Data are shown as mean ± SEM (n = 3). *P < 0.05; NS, not significant. All values are normalized to the NC group (= 1). g ELISA shows soluble cytokines (IL-6, IL-8, VEGF, G-CSF, HGF, TGF-β, TNF-α, PGE-2) in the supernatant of hUC-MSCs at various passages (P3, P6, P15) after 24 h culture in MSC medium. All values normalized to level (= 1) of cytokine concentration in P3. Data shown as mean ± SEM (n = 3). *P < 0.05; ***P < 0.001; NS, not significant.