Aim: To characterize the expression and function of midkine (MK) in an in vitro embryonic stem cell (ESC) culture system.
Methods: To investigate the potential roles of MK, the expression of MK in ESCs was evaluated by RT-PCR and immunocytochemistry. The effects of MK on the self-renewal of ESCs were measured using alkaline phosphatase assays, immunocytochemistry, RT-PCR and colony-forming assays. The mechanism of the growth-promoting effect of MK in mESCs was assessed by cell cycle analysis and Western blot analysis.
Results: MK is expressed in mouse embryonic stem cells (mESCs), human embryonic stem cells (hESCs) and mouse embryonic fibroblasts (MEFs). MK promotes proliferation and self-renewal of mESCs both in feeder and feeder free culture systems. It also promotes self-renewal and proliferation of hESCs. Further study showed that MK promotes the growth of mESCs by inhibiting apoptosis while accelerating the progression toward the S phase, and enhances mESC self-renewal through PI3K/Akt signaling pathway.
Conclusion: MK plays profound roles in ESCs. MK/PTPzeta signaling pathway is a novel pathway in the signal network maintaining pluripotency of ESCs. The results extend our knowledge on pluripotency control of ESCs and the relationship between ESCs and cancers.