Fig. 4

hDPSCs suppress osteoarthritic macrophages partially by inactivating MAPK pathways. The JNK/SAPK, ERK/MAPK, and p38/MAPK pathways in macrophages were markedly activated by OASF in a time-dependent manner while exposure of osteoarthritic macrophages to hDPSCs conditional medium suppressed the activation of these pathways in macrophages (a). Additionally, specific chemical pathway inhibitors, including SB203580 (for p38/MAPK), PD98059 (for ERK/MAPK), and JNK inhibitor II (for JNK/SAPK) showed a similar effect on the immunophenotype, and expression of TNF-α, IL-12b, and IL-10 of osteoarthritic macrophages to that of hDPSCs. Notably, blockage of single pathway could not result in same suppression on osteoarthritic macrophage as that of hDPSCs (immunophenotypes in b and c, mRNA expression in d and protein secretion in e), *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, hDPSC group and inhibitor groups compared to osteoarthritic macrophage group) (b–e, ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, inhibitor groups compared to hDPSC group). hDPSCs, human dental pulp stem cells; IL-12b, interleukin 12; TNF-α, tumor necrosis factor α; IL-10, interleukin 10