title: Lesion-targeted thrombopoietin potentiates vasculogenesis by enhancing motility and enlivenment of transplanted endothelial progenitor cells via activation of Akt/mTOR/p70S6kinase signaling pathway.
abstract: Thrombopoietin (TPO), a physiological regulator of megakaryocyte and platelet development, is a multifunctional positive regulator in early hematopoiesis by hematopoietic stem cells. In this study, we investigated the effect of TPO on endothelial progenitor cells (EPCs) for therapeutic vasculogenesis in vitro and in vivo, and the intracellular signaling mechanism exerting the activity of EPCs. 7-day culture-expanded EPCs derived from human peripheral blood mononuclear cells were applied to each assay. Flow cytometry demonstrated the expression of c-Mpl, the receptor of TPO, in cultured EPCs. In vitro experiments revealed enhanced migration and survival of cultured EPCs by TPO. In vivo, TPO was intramuscularly administered into the foci of ischemic hindlimbs in athymic nude mice, immediately followed by intravenous injection of cultured EPCs, to assess the booster effect of TPO on vascular regeneration. At day 4 post-transplantation, transplanted EPCs were 1.7-fold higher in TPO-treated animals compared to control. At day 28, blood perfusion was recovered in the TPO-treated group, accompanied by an increase in microvascular density. The signaling transduction pathway underlying TPO-mediated activities of cultured EPCs was assessed by Western blotting. TPO induced sequential phosphorylations of Akt to p70S6kinase through mTOR. Inhibition of the PI3-kinase/Akt/mTOR/p70S6kinase signaling pathway negated the biological functions of cultured EPCs, either migration (by LY294002 for PI3-kinase and Rapamycin for mTOR) or survival and tubulogenesis (by Rapamycin). These findings provide evidence that TPO possesses booster potential for therapeutic vasculogenesis, by activating the PI3-kinase/Akt/mTOR/p70S6kinase pathway crucial to the biological activities of EPCs.
authors.affiliation: Department of Regenerative Medicine, Tokai University School of Medicine, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Eguchi
authors.forename: Haruchika
authors.initials: H
authors.lastname: Masuda
authors.forename: Sangmon
authors.initials: S
authors.lastname: Kwon
authors.forename: Katsuya
authors.initials: K
authors.lastname: Shirakura
authors.forename: Tomoko
authors.initials: T
authors.lastname: Shizuno
authors.forename: Rie
authors.initials: R
authors.lastname: Ito
authors.forename: Michiru
authors.initials: M
authors.lastname: Kobori
authors.forename: Takayuki
authors.initials: T
authors.lastname: Asahara
mesh_terms: D000818:Animals; D002465:Cell Movement; D017690:Cell Transplantation; D042783:Endothelial Cells / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D011494:Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D013234:Stem Cells / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases; D013926:Thrombopoietin / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D013926:Thrombopoietin; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases