| Abstract |
The pluripotency of mouse embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can be maintained by feeder cells, which secrete leukemia inhibitory factor (LIF). We found that feeder cells provide a relatively low concentration (25 unit/ml) of LIF, which is insufficient to maintain the ESCs/iPSCs pluripotency in feeder free conditions. To identify additional factors involved in the maintenance of pluripotency, we carried out a global transcript expression profiling of mouse iPSCs cultured on feeder cells and in feeder-free (LIF-treated) conditions. This identified 17 significantly differentially expressed genes (adjusted p value <0.05) including seven chemokines overexpressed in iPSCs grown on feeder cells. Ectopic expression of these chemokines in iPSCs revealed that CC chemokine ligand 2 (Ccl2) induced the key transcription factor genes for pluripotency, Klf4, Nanog, Sox2, and Tbx3. Furthermore, addition of recombinant Ccl2 protein drastically increased the number of Nanog-green fluorescent protein-positive iPSCs grown in low-LIF feeder free conditions. We further revealed that pluripotency promotion by Ccl2 is mediated by activating the Stat3-pathway followed by Klf4 upregulation. We demonstrated that Ccl2-mediated increased pluripotency is independent of phosphoinositide 3-kinase and mitogen-activated protein kinase pathways and that Tbx3 may be upregulated by Klf4. Overall, Ccl2 cooperatively activates the Stat3-pathway with LIF in feeder-free conditions to maintain pluripotency for ESCs/iPSCs.
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