title: Injured microenvironment directly guides the differentiation of engrafted Flk-1(+) mesenchymal stem cell in lung.
abstract: OBJECTIVE
  Time window is a key factor in the treatment of lung injury by mesenchymal stem cells (MSC) transplantation. This study was aimed to analyze the engraftment and differentiation behavior of MSC transplanted at different time points after lung irradiation, and the possible mechanisms were discussed.
  
  
  METHODS
  The thorax of C57BL/6 mice was exposed to 1400 cGy, then Flk-1(+)MSCs from enhanced green fluorescent protein C57BL/6 mice were systemically injected into C57BL/6 mice at 4 hours, 60 days, and 120 days post thoracic exposure, respectively. The engraftment and differentiation of Flk-1(+)MSC transplanted at different time points were evaluated. Lung tissue was collected and analyzed for fibrosis. Expression of transforming growth factor (TGF)-beta1 in the lung was qualified by semi-quantitative real-time reverse transcription polymerase chain reaction. In vitro, Flk-1(+)MSCs were cultured in epithelium induction media, together with damaged primary lung cells, supernatants of radiation-injured lung cells, or TGF-beta1 to find the possible factors that might effect Flk-1(+)MSC differentiation.
  
  
  RESULTS
  Cells injected immediately after injury were shown to differentiate into functional lung cells, such as epithelial and endothelial cells. Cells injected 2 months later were mostly located in the interstitial area and appeared as myofibrocyte. The in vivo lung microenvironments at different time points after injury were different from each other, especially TGF-beta1 expression. We demonstrated that cytokines secreted by irradiated lung cells could inhibit differentiation of Flk-1(+)MSCs into epithelial cells in vitro.
  
  
  CONCLUSIONS
  Flk-1(+)MSCs injected into the lung immediately after irradiation could differentiate into functional lung cells, while those injected at later stage after irradiation would be involved in fibrosis development. Thus our in vivo and in vitro studies demonstrated that differentiation of Flk-1(+)MSCs is controlled by the microenvironment.
authors.affiliation: Institute of Basic Medical Sciences Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Center of Excellence in Tissue Engineering, Beijing, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Yan
authors.forename: Yanning
authors.initials: Y
authors.lastname: Liu
authors.forename: Qin
authors.initials: Q
authors.lastname: Han
authors.forename: Mingyue
authors.initials: M
authors.lastname: Jia
authors.forename: Lianming
authors.initials: L
authors.lastname: Liao
authors.forename: Maili
authors.initials: M
authors.lastname: Qi
authors.forename: Robert Chunhua
authors.initials: RC
authors.lastname: Zhao
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D004847:Epithelial Cells / Q000187:drug effects; D007150:Immunohistochemistry; D008168:Lung / Q000473:pathology / Q000528:radiation effects; D055370:Lung Injury; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000096:biosynthesis; D011833:Radiation Injuries, Experimental / Q000628:therapy*; D017564:Radiation Pneumonitis / Q000628:therapy*; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D040301:Vascular Endothelial Growth Factor Receptor-2