P27 deletion enhances hematopoiesis by paracrine action of IL22 secreted from bone marrow mesenchymal stem cells.

Previous studies have reported that p27 deletion stimulates the proliferation of bone marrow mesenchymal stem cells (BM-MSCs) and their differentiation into osteoblasts, it also increases bone marrow hematopoietic progenitor cells (HPCs). However, it is unknown whether the enhanced hematopoiesis induced by p27 deficiency was associated with releasing hematopoietic stem cell (HSC) and HPC supporting factors by BM-MSCs. To answer this question, we cultured the BM-MSCs from wild-type (WT) or p27 knockout (KO) mice, analyzed their proliferation, apoptosis and osteogenesis and harvested their conditioned medium (CM); We also cultured the bone marrow cells (BMCs) with normal medium or CM from WT or KO BM-MSCs and analyzed changes of HSCs and HPCs and colony forming cells (CFCs). Our results showed that the proliferation and osteogenic differentiation of BM-MSCs were increased significantly and their apoptosis was reduced significantly in p27 deficient mice. Simultaneously, we demonstrated that the CM from p27 deficient BM-MSCs stimulated the expansion of HSCs/HPCs more dramatically than that from WT BM-MSCs. Five 2-fold up-regulated proteins were identified in the CM from p27 deficient BM-MSCs by protein chip assays, including interleukin-22 (IL-22), transforming growth factor-β type I receptor, tumor necrosis factor-related Apoptosis-inducing ligands, VE-cadherin and vascular endothelial growth factor B. We confirmed that expression of IL22 at both mRNA and protein levels were up-regulated significantly in p27 deficient BM-MSCs. The treatment of IL22 increased the percentages of HSCs and HPCs in BMC cultures and the number of CFCs in the colony formation assay, whereas the increased HSC/HPC expansion induced by the CM derived from p27 deficient BM-MSCs was blocked by the addition of anti-IL22 antibody in a dose dependent manner. We also found that the percentages of IL22R1, Stat3 and p-Stat3-S727 positive HSCs and HPCs were increased significantly in p27 deficient BMCs. Our findings in this study indicate that p27 deficiency stimulates HSC/HPC expansion by increasing secretion of IL22 by BM-MSCs and activating IL22-Stat3 signaling in HSCs and HPCs.