Fig. 6

HAPs activated ERK1/2 signaling in hWJ-MSCs indirectly co-cultured with HUVECs. a Immunofluorescence of HIF-1α performed in HUVECs treated with/without HAPs for 18 h. b The fluorescence intensity of HIF-1α from part (a). c The extracellular concentration of HIF-1α in the culture medium of HUVECs treated with/without HAPs for 18 h was measured via ELISA. Scale bars: 20 μm. *P < 0.05; **P < 0.01; ***P < 0.001 versus control; ^##P < 0.01; ^###P < 0.001 versus the np20 group. Cells without HAPs treatment were used as the control group. hWJ-MSCs were treated with CM for 24 h. d Western blot analysis indicating activation of key kinases in the ERK1/2 pathways. e Densitometric measurements of p-ERK1/2 from part (b). **P < 0.01; ***P < 0.001 versus control; ^##P < 0.01, ^###P < 0.001 versus 2-MeOE2( −) group. Cells incubated in CM without HAP treatment were used as the control group. Abbreviations: HAPs hydroxyapatite particles, m-HAP micro-sized HAP particles, hWJ-MSCs human umbilical cord Wharton’s jelly-derived mesenchymal stem cells, HUVECs human umbilical vein endothelial cells, ERK extracellular signal-regulated kinase, HIF-1α hypoxia-inducible factor 1α