title: Inhibition of p38 mitogen-activated protein kinase promotes ex vivo hematopoietic stem cell expansion.
abstract: Hematopoietic stem cell (HSC) self-renewal is tightly regulated by a complex crosstalk between many cell-intrinsic regulators and a variety of extrinsic signals from the stem cell niche. In this study, we examined whether the p38 mitogen-activated protein kinase (p38) is one of the intrinsic regulators that can negatively regulate HSC self-renewal in vitro and whether inhibition of p38 activity with a small molecule inhibitor can promote HSC expansion ex vivo. The results from this study showed that sorted mouse bone marrow Lin(-)Sca1(+)c-kit(+) cells (LSK(+) cells) exhibited selective activation of p38 after culture in a serum-free medium supplemented with 100 ng/mL stem cell factor, thrombopoietin, and Flt3 ligand. The activation of p38 was associated with a significant reduction in HSCs and induction of apoptosis and cellular senescence in LSK(+) cells and their progeny. Addition of the specific p38 inhibitor SB203580 (SB, 5 μM) to the culture inhibited the activation of p38 in LSK(+) cells, which led to increase in HSC self-renewal and ex vivo expansion as shown by the cobblestone area forming cell assay, competitive repopulation, and serial transplantation. The increase in HSC expansion is likely attributable to SB-mediated inhibition of HSC apoptosis and senescence and upregulation of HoxB4 and CXCR4. These findings suggest that p38 plays an important role in the regulation of HSC self-renewal in vitro and inhibition of p38 activation with a small molecule inhibitor may represent a novel approach to promote ex vivo expansion of HSCs.
authors.affiliation: Department of Pathology, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Joshua
authors.initials: J
authors.lastname: Kellner
authors.forename: Lingbo
authors.initials: L
authors.lastname: Liu
authors.forename: Daohong
authors.initials: D
authors.lastname: Zhou
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D048708:Cell Growth Processes; D049109:Cell Proliferation; D017690:Cell Transplantation / Q000379:methods; D002478:Cells, Cultured; D016922:Cellular Senescence; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology*; D019718:Receptors, CXCR4 / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015854:Up-Regulation; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C514936:CXCR4 protein, mouse; D004791:Enzyme Inhibitors; D018398:Homeodomain Proteins; C513262:Hoxb4 protein, mouse; D007093:Imidazoles; D011725:Pyridines; D019718:Receptors, CXCR4; D014157:Transcription Factors; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580