title: Synergism of MSC-secreted HGF and VEGF in stabilising endothelial barrier function upon lipopolysaccharide stimulation via the Rac1 pathway.
abstract: BACKGROUND
  Mesenchymal stem cells (MSCs) stabilise endothelial barrier function in acute lung injury via paracrine hepatocyte growth factor (HGF). Vascular endothelial growth factor (VEGF), which is secreted by MSCs, is another key regulator of endothelial permeability; however, its role in adjusting permeability remains controversial. In addition, whether an interaction occurs between HGF and VEGF, which are secreted by MSCs, is not completely understood.
  
  
  METHODS
  We introduced a co-cultured model of human pulmonary microvascular endothelial cells (HPMECs) and MSC conditioned medium (CM) collected from MSCs after 24 h of hypoxic culture. The presence of VEGF and HGF in the MSC-CM was neutralised by anti-VEGF and anti-HGF antibodies, respectively. To determine the roles and mechanisms of MSC-secreted HGF and VEGF, we employed recombinant humanised HGF and recombinant humanised VEGF to co-culture with HPMECs. Additionally, we employed the RhoA inhibitor C3 transferase and the Rac1 inhibitor NSC23766 to inhibit the activities of RhoA and Rac1 in HPMECs treated with MSC-CM or VEGF/HGF with the same dosage as in the MSC-CM. Then, endothelial paracellular and transcellular permeability was detected. VE-cadherin, occludin and caveolin-1 protein expression in HPMECs was measured by western blot. Adherens junction proteins, including F-actin and VE-cadherin, were detected by immunofluorescence.
  
  
  RESULTS
  MSC-CM treatment significantly decreased lipopolysaccharide-induced endothelial paracellular and transcellular permeability, which was significantly inhibited by pretreatment with HGF antibody or with both VEGF and HGF antibodies. Furthermore, MSC-CM treatment increased the expression of the endothelial intercellular adherence junction proteins VE-cadherin and occludin and decreased the expression of caveolin-1 protein. MSC-CM treatment also decreased endothelial apoptosis and induced endothelial cell proliferation; however, the effects of MSC-CM treatment were inhibited by pretreatment with HGF antibody or with both HGF and VEGF antibodies. Additionally, the effects of MSC-CM and VEGF/HGF on reducing endothelial paracellular and transcellular permeability were weakened when HPMECs were pretreated with the Rac1 inhibitor NSC23766.
  
  
  CONCLUSIONS
  HGF secreted by MSCs protects the endothelial barrier function; however, VEGF secreted by MSCs may synergize with HGF to stabilise endothelial cell barrier function. Rac1 is the pathway by which MSC-secreted VEGF and HGF regulate endothelial permeability.
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. yiyiyang2004@163.com.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. chenqihong00@163.com.
authors.forename: Qi-Hong
authors.initials: QH
authors.lastname: Chen
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. airanliu2013@gmail.com.
authors.forename: Ai-Ran
authors.initials: AR
authors.lastname: Liu
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. xiupxu@126.com.
authors.forename: Xiu-Ping
authors.initials: XP
authors.lastname: Xu
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. hanjibin86@foxmail.com.
authors.forename: Ji-Bin
authors.initials: JB
authors.lastname: Han
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Nanjing, 210009, People's Republic of China. haiboq2000@163.com.
authors.forename: Hai-Bo
authors.initials: HB
authors.lastname: Qiu
mesh_terms: D000199:Actins / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D017209:Apoptosis; D015820:Cadherins / Q000378:metabolism; D002199:Capillary Permeability / Q000187:drug effects / Q000502:physiology*; D051242:Caveolin 1 / Q000378:metabolism; D002470:Cell Survival; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D017228:Hepatocyte Growth Factor / Q000037:antagonists & inhibitors / Q000502:physiology*; D006801:Humans; D008070:Lipopolysaccharides / Q000633:toxicity; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors / Q000502:physiology*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism; D000099152:Cadherin 5
chemical_list: D000199:Actins; D015703:Antigens, CD; D015820:Cadherins; D051242:Caveolin 1; D017077:Culture Media, Conditioned; D017228:Hepatocyte Growth Factor; D008070:Lipopolysaccharides; D042461:Vascular Endothelial Growth Factor A; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein; D000099152:Cadherin 5; C495540:CAV1 protein, human; C066855:HGF protein, human; C107953:RAC1 protein, human; C467484:VEGFA protein, human; C066737:RHOA protein, human