title: Human epicardial cell-conditioned medium contains HGF/IgG complexes that phosphorylate RYK and protect against vascular injury.
abstract: OBJECTIVE
  The aim of this study was to evaluate the paracrine activity of human epicardial-derived cells (hEPDCs) to screen for secreted vasoprotective factors and develop therapeutics to treat vascular reperfusion injury.
  
  
  RESULTS
  Epicardial cells support cardiac development, repair, and remodelling after injury in part, through paracrine activity. We hypothesized that secreted ligands from hEPDCs would protect vascular integrity after myocardial infarction (MI) with reperfusion. During simulated ischaemia in culture (24-48 h), concentrated hEPDC-conditioned medium (EPI CdM) increased survival of primary cardiac endothelial cells. In a rat MI model, EPI CdM treatment reduced vascular injury in vivo after reperfusion. By phospho-receptor tyrosine kinase (RTK) arrays, ELISA, and neutralizing antibody screens, we identified hepatocyte growth factor (HGF) as a key vasoprotective factor in EPI CdM. Unexpectedly, we observed that some of the HGF in EPI CdM formed complexes with polyclonal IgG. Following reperfusion, preparations of HGF/IgG complexes provided greater vascular protection than free HGF with IgG. HGF/IgG complexes localized to blood vessels in vivo and increased HGF retention time after administration. In subsequent screens, we found that 'related to tyrosine kinase' (RYK) receptor was phosphorylated after exposure of cardiac endothelial cells to HGF/IgG complexes, but not to free HGF with IgG. The enhanced protection conferred by HGF/IgG complexes was lost after antibody blockade of RYK. Notably, the HGF/IgG complex is the first 'ligand' shown to promote phosphorylation of RYK.
  
  
  CONCLUSIONS
  Early treatment with HGF/IgG complexes after myocardial ischaemia with reperfusion may rescue tissue through vasoprotection conferred by c-Met and RYK signalling.
authors.affiliation: Cellular, Molecular and Biomedical Sciences Graduate Program, University of Vermont, Colchester, VT, USA Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Krithika S
authors.initials: KS
authors.lastname: Rao
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Aronshtam
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Keara L
authors.initials: KL
authors.lastname: McElory-Yaggy
authors.affiliation: Cellular, Molecular and Biomedical Sciences Graduate Program, University of Vermont, Colchester, VT, USA Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bakondi
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: VanBuren
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA.
authors.forename: Burton E
authors.initials: BE
authors.lastname: Sobel
authors.affiliation: Department of Medicine and Cardiovascular Research Institute, University of Vermont, 208 South Park Drive, Ste 2, Colchester, VT 05446, USA Stem Cell Core, University of Vermont, Colchester, VT 05446, USA jeffrey.spees@uvm.edu.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Spees
mesh_terms: D000818:Animals; D017228:Hepatocyte Growth Factor / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D008297:Male; D009203:Myocardial Infarction / Q000378:metabolism*; D017202:Myocardial Ischemia / Q000378:metabolism; D011916:Rats, Inbred F344; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D057772:Vascular System Injuries / Q000378:metabolism*
chemical_list: C066855:HGF protein, human; D007074:Immunoglobulin G; D017228:Hepatocyte Growth Factor; C080836:RYK protein, human; D020794:Receptor Protein-Tyrosine Kinases; C485555:Ryk protein, rat
keywords: EPDC; Epicardial; HGF; Myocardial infarction; Precursor cell; Progenitor cell; Reperfusion