Role Of DKK1 In Promoting Mesenchymal Stem Cell Migration

Mesenchymal stem cells(MSCs),a widely-studied adult stem cell population,are characterised by high proliferative and differentiation abilities,low immunogenicity,neuroprotective effects and potential of neural differentiation,highlighting the clinical applicability of these cells.However,studies have shown that only a small percentage of the transplanted MSCs can reach the lesions,leading to a very low rate of cell replacement.Many growth factors and cytokines have been found to act as strong chemoattractants for MSCs,such as HGF,VEGF,SDF,etc,which can be secreted in the injured area or inflammatory reaction area.Therefore,improving the ability of MSCs migration to chemotaxis factors is much yet to learn.Activation of Wnt/?-catenin signaling promotes the migration of MSCs.However,we found that DKK1,as a Wnt/?-catenin signaling inhibitor,did not inhibit cell migration at 100 ng/ml,instead it could promote the chemotactic response MSCs to HGF,while 400 ng/ml DKK1 inhibited mobility of MSCs and chemotactic migration to Wnt3 a and HGF.Further,we found that 100 ng/ml DKK1 could promote the nuclear translocation of ?-catenin,the expression of ABC(?-catenin activated form)protein,the target genes,Runx2 and Tiam1.Moreover,we constructed Ad-DKK1 adenoviral vector,increasing the expression of DKK1 in MSCs,and found that Ad-DKK1 can also inhibit Wnt/?-catenin signaling and inhibit the chemotactic migration of MSCs to Wnt3 a,indicating that high concentrations DKK1 can inhibit Wnt/?-catenin signal and suppress the migration of MSCs.The low concentration DKK1 not only promotes the migration of MSCs but also activates Wnt/?-catenin signaling.Studies have been shown that DKK1 can activate Wnt/PCP signal,so we also analyzed the effect of DKK1 on the phosphorylation of JNK in MSCs.We found that 100 ng/ml DKK1 can increase the phosphorylation of JNK and the JNK inhibitor treatment inhibited the promotion of DKK1 on the migration of MSCs,indicating that JNK may also be involved in DKK1-stimulated migration of MSCs.How does low concentration of DKK1 activate Wnt/?-catenin and JNK to promote MSCs migration? By reviewing the literature,we surmised that it may be related to the Frizzled3(Fzd3)receptor.We established a lentivirus interfering system and interfered with the expression of Fzd3 in MSCs and examined the effect of DKK1 on the migration of MSCs.We found that interfering Fzd3,100 ng/ml DKK1 could not promote the chemotactic migration of MSCs to Wnt3 a or HGF.This suggests that the promotion of DKK1 on the migration of MSCs may be through the Fzd3 receptor.In summary,for the first time,we found that 100 ng/ml DKK1 does not inhibit,but promotes the migration of MSCs,and activates Wnt/?-catenin and JNK,and that downregulating the Fzd3 expression blocks the effect of DKK1,indicating the critical role of Fzd3 in DKK1-stimulated migration of MSCs.