Dickkopf-2 knockdown protects against classic macrophage polarization and lipid loading by activation of...

Wnt/β-catenin signaling pathway plays an important role in regulation of macrophage activation implicated in the development of atherosclerosis. However, as a negative regulator of Wnt/β-catenin, the potential role of Dickkopf-2 (Dkk2) on macrophage activation remains unexplored.

Bone marrow-derived macrophages (BMDMs) and mouse peritoneal macrophages (MPMs) collected from ApoE knockout mice upon oxidation low lipoprotein (Ox-LDL) administration were performed to test the expression of Dkk2. The loss-of-function strategy using siRNA-Dkk2 was further utilized for the function of Dkk2. Inhibition of β-catenin with XAV939 (a β-catenin specific inhibitor) was further used for testing its effect on macrophage activation mediated by Dkk2 knockdown.

In the current study, real time-polymerase chain reaction analysis demonstrated that an up-regulated Dkk2 expression was observed in BMDMs and MPMs of ApoE knockout mice upon Ox-LDL administration, which was confirmed by western blot. The double immunofluorescence staining further exhibited that Dkk2 showed a strong immunoreactivity in BMDMs and primarily located in cytoplasm of macrophages. Dkk2 knockdown significantly decreased the genes related to classic M1 polarized macrophage but increased alternative M2 polarized macrophage markers. Moreover, Dkk2 silencing dramatically attenuated foam cell formation which was contributed by promoted markers' expression associated with cholesterol efflux but attenuated markers to cholesterol influx. Mechanistically, we observed that Dkk2 knockdown activated Wnt/β-catenin signaling by promoting β-catenin to translocate into the nuclei of macrophages, and XAV939 reversed the ameliorated effect of Dkk2 silencing macrophage activation. Taken together, these results suggested that downregulated Dkk2 expression in macrophages was responsible for the inactivation of macrophage through targeting Wnt/β-catenin pathway.