title: mTOR inhibition induces endothelial progenitor cell death.
abstract: Immunosuppressants are necessary to prevent graft rejection after solid organ transplantation. However, they are also known to have significant side effects, including endothelial toxicity. Endothelial progenitor cells originate in the bone marrow and are recognized by their angiogenic and endothelial reparative properties. The effects of the immunosuppressants cyclosporine A (CyA), tacrolimus and rapamycin were analyzed on endothelial progenitor-like cells. Rapamycin induced rapid cell death, even at concentrations much lower than those used clinically, in peripheral blood mononuclear cells (PBMC) cultured to favor outgrowth of endothelial progenitors. Cyclosporine A and tacrolimus had no significant effects at clinical concentrations. The effect of rapamycin was specific to endothelial progenitor cells, in particular to the early stages of differentiation, as a lesser effect was observed in late outgrowth endothelial progenitors, mature aortic endothelial cells, and macrophages derived from the same PBMCs. The mechanism of cell death appeared to be apoptosis; however, its induction was probably multifactorial and did not depend on caspase or cathepsin activation. In conclusion, rapamycin induces endothelial progenitor cell death, possibly because it blocks survival signals given by growth factors critically required by these cells.
authors.affiliation: Department of Medicine, Toronto General Hospital, Faculty of Medicine, University of Toronto, Ontario, Canada.
authors.forename: S G
authors.initials: SG
authors.lastname: Miriuka
authors.forename: V
authors.initials: V
authors.lastname: Rao
authors.forename: M
authors.initials: M
authors.lastname: Peterson
authors.forename: L
authors.initials: L
authors.lastname: Tumiati
authors.forename: D H
authors.initials: DH
authors.lastname: Delgado
authors.forename: R
authors.initials: R
authors.lastname: Mohan
authors.forename: D
authors.initials: D
authors.lastname: Ramzy
authors.forename: D
authors.initials: D
authors.lastname: Stewart
authors.forename: H J
authors.initials: HJ
authors.lastname: Ross
authors.forename: T K
authors.initials: TK
authors.lastname: Waddell
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000473:pathology*; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology*; D013234:Stem Cells / Q000473:pathology*; D058570:TOR Serine-Threonine Kinases; D016559:Tacrolimus / Q000494:pharmacology
chemical_list: D007166:Immunosuppressive Agents; D000081082:Phosphoinositide-3 Kinase Inhibitors; D016572:Cyclosporine; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus; D016559:Tacrolimus