title: Exosome poly-ubiquitin inhibits platelet activation, downregulates CD36 and inhibits pro-atherothombotic cellular functions.
abstract: BACKGROUND
  Activated platelets shed microparticles from plasma membranes, but also release smaller exosomes from internal compartments. While microparticles participate in athero-thrombosis, little is known of exosomes in this process.
  
  
  METHODS
  Ex vivo biochemical experiments with human platelets and exosomes, and FeCl3 -induced murine carotid artery thrombosis.
  
  
  RESULTS
  Both microparticles and exosomes were abundant in human plasma. Platelet-derived exosomes suppressed ex vivo platelet aggregation and reduced adhesion to collagen-coated microfluidic channels at high shear. Injected exosomes inhibited occlusive thrombosis in FeCl3 -damaged murine carotid arteries. Control platelets infused into irradiated, thrombocytopenic mice reconstituted thrombosis in damaged carotid arteries, but failed to do so after prior ex vivo incubation with exosomes.CD36 promotes platelet activation, and exosomes dramatically reduced platelet CD36.CD36 is also expressed by macrophages, where it binds and internalizes oxidized LDL and microparticles, supplying lipid to promote foam cell formation. Platelet exosomes inhibited oxidized-LDL binding and cholesterol loading into macrophages. Exosomes were not competitive CD36 ligands, but instead sharply reduced total macrophage CD36 content. Exosomal proteins, in contrast to microparticle or cellular proteins, were highly adducted by ubiquitin. Exosomes enhanced ubiquitination of cellular proteins, including CD36, and blockade of proteosome proteolysis with MG-132 rescued CD36 expression. Recombinant unanchored K48 poly-ubiquitin behaved similarly to exosomes, inhibiting platelet function, macrophage CD36 expression and macrophage particle uptake.
  
  
  CONCLUSIONS
  Platelet-derived exosomes inhibit athero-thrombotic processes by reducing CD36-dependent lipid loading of macrophages and by suppressing platelet thrombosis. Exosomes increase protein ubiquitination and enhance proteasome degradation of CD36.
authors.affiliation: Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland, OH, USA; Department of Molecular Medicine, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: S
authors.initials: S
authors.lastname: Srikanthan
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.forename: R L
authors.initials: RL
authors.lastname: Silverstein
authors.forename: T M
authors.initials: TM
authors.lastname: McIntyre
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D018955:CD36 Antigens / Q000097:blood*; D002340:Carotid Artery Diseases / Q000097:blood / Q000139:chemically induced / Q000517:prevention & control*; D055252:Cell-Derived Microparticles / Q000378:metabolism; D002712:Chlorides; D002784:Cholesterol / Q000097:blood; D003094:Collagen / Q000378:metabolism; D004195:Disease Models, Animal; D055354:Exosomes / Q000378:metabolism*; D005290:Ferric Compounds; D005487:Foam Cells / Q000378:metabolism; D006801:Humans; D008077:Lipoproteins, LDL / Q000097:blood; D008810:Mice, Inbred C57BL; D015539:Platelet Activation; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation; D017713:Platelet Transfusion; D025821:Polyubiquitin / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis; D015398:Signal Transduction; D013921:Thrombocytopenia / Q000097:blood; D013927:Thrombosis / Q000097:blood / Q000139:chemically induced / Q000517:prevention & control*; D013997:Time Factors; D054875:Ubiquitination
chemical_list: D018955:CD36 Antigens; D002712:Chlorides; D005290:Ferric Compounds; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D025821:Polyubiquitin; D003094:Collagen; D002784:Cholesterol; D046988:Proteasome Endopeptidase Complex; C024555:ferric chloride
keywords: CD36 protein; cell-derived microparticles; exosomes; platelets; thrombosis