DKK1 Promotes The Migration Of Mesenchymal Stem Cells Through CKAP4

Mesenchymal stem cells(MSCs)are multipotent mesoderm-derived cells with the advantages of easy sampling,multidirectional differentiation potential,low immunogenicity and have been emerged as a promising approach to cell transplantation therapy and therapeutic agents for tissue repair and regeneration.However,studies have shown that only a very limited number of transplanted MSCs can reach the injured tissues,which restricts their potential in clinical applications.Therefore,improving the migration ability of MSCs will help to enhance their therapeutic potential.Meanwhile,elucidating the cellular and molecular mechanisms regulating MSC migration will provide important theoretical and practical significance for the effective utilization of MSCs.Studies have shown that activation of Wnt/β-catenin signaling promotes MSC migration,and inhibition of it inhibits MSC migration.When we treated cells with the Wnt inhibitor Dickkopf-1(DKK1),we found that low concentration of DKK1 did not inhibit but promote Wnt/β-catenin signaling and MSC migration.Therefore,we investigated the molecular mechanism by which DKK1 regulates Wnt/β-catenin signaling and MSC migration.The activation of Wnt/β-catenin signaling is accompanied by phosphorylation of LRP6(low-density lipoprotein related protein 6).DKK1 competes with Wnt3a to bind LRP6 to inhibit its phosphorylation and thus inhibit Wnt/β-catenin signaling.To determine whether DKK1 affects the role of Wnt3a to regulate Wnt/β-catenin signaling by LRP6,we examined LRP6 phosphorylation and found that low concentration of DKK1,although promoting the activation of Wnt/β-catenin signaling,inhibited Wnt3a-induced LRP6 phosphorylation,suggesting that low concentration of DKK1 may activate Wnt/β-catenin signaling and promote MSCs migration through means other than LRP6 phosphorylation.We then found that MSCs express CKAP4(cytoskeleton associated protein 4),a receptor of DKK1,on the cell membrane,and that low concentration of DKK1 can not only activate Wnt/β-catenin signaling but also promote the phosphorylation of AKT.The phosphorylation of AKT can further inhibit the activity of GSK-3β,thereby reducing the degradation of β-catenin.In order to determine whether DKK1 can activate Wnt/β-catenin signaling through CKAP4,we constructed two DKK1 adenovirus vectors lacking different domains(ΔCRD1/ΔCRD2)to block the binding of DKK1 to CKAP4 or LRP6 respectively.It turned out that blocking the binding of DKK1 to CKAP4 inhibited Wnt3a-induced AKT phosphorylation,ABC accumulation and MSC migration,while only binding to CKAP4 promoted AKT phosphorylation,ABC accumulation and MSC migration.We further constructed an extracellular domain-deleted LRP6(LRP6-ΔE)to block the binding of DKK1 to LRP6,and found that low concentration of DKK1 can still promoted AKT activation,Wnt/β-catenin signaling and MSC migration,but the effect was weakened.In conclusion,we revealed that as an inhibitor of Wnt/β-catenin signaling,low concentration of DKK1 can activate this signal and promote the migration of MSCs.Our further research showed that DKK1 can induce AKT activation,activate Wnt/β-catenin signaling and promote MSC migration through CKAP4 but not LRP6,which provides a theoretical basis for improving the migration ability of MSCs and increasing the number of transplanted cells that migrate to the injury site.