Abstract: Objective: To investigate that Ox-LDL inhibits endothelial differentiation of bone marrow mesenchymal stem cells (MSCs) in rats and its underlying mechanism. Methods: Cultured MSCs were divided into four groups: blank groups, Ox-LDL groups (5μg/ml Ox-LDL), Ox-LDL+NAC groups (5μg/ml Ox-LDL and pre-treated NAC), and negative groups (5μg/ml nLDL). Cellular morphology, endothelial Marker and differentiation efficiency as well as signal of oxidative and pathway protein were detected after induction by Western blot, real–time PCR. Results: MSCs can differentiate into endothelial cells with expression of endothelial marker vWF,Flk-1 and CD31 at the mRNA and protein level and appearance of vascular morphology, ox-LDL obvious weaken endothelial differentiation of MSCs (P<0.05), but NAC can reverse the inhibited effect of ox-LDL, the amount of ROS in Ox-LDL groups was more higher than that in Ox-LDL+NAC groups(P<0.05), The expression of phosphorylated Akt became decreased distinctly after treatment with ox-LDL(P<0.05), NAC can restore its expression close to normal. Conclusion：ox-LDL can inhibit endothelial differentiation of MSCs via ROS, NAC restore partly or completely inhibited effect of ox-LDL，Akt signaling also played a critical role.

Key words: oxidized low density lipoprotein, Rat bone marrow mesenchymal stem cells, endothlial cells, differentiation.