title: Endothelial induction of fgl2 contributes to thrombosis during acute vascular xenograft rejection.
abstract: Thrombosis is a prominent feature of acute vascular rejection (AVR), the current barrier to survival of pig-to-primate xenografts. Fibrinogen-like protein 2 (fgl2/fibroleukin) is an inducible prothrombinase that plays an important role in the pathogenesis of fibrin deposition during viral hepatitis and cytokine-induced fetal loss. We hypothesized that induction of fgl2 on the vascular endothelium of xenografts contributes to thrombosis associated with AVR. We first examined fgl2 as a source of procoagulant activity in the pig-to-primate combination. The porcine fgl2 (pfgl2) was cloned and its chromosomal locus was identified. Recombinant pfgl2 protein expressed in vitro was detected on the cell surface and generated thrombin from human prothrombin. Studies of pig-to-baboon kidney xenografts undergoing AVR in vivo revealed induction of pfgl2 expression on graft vascular endothelial cells (ECs). Cultured porcine ECs activated by human TNF-alpha in vitro demonstrated induction of pfgl2 expression and enhanced activation of human prothrombin. The availability of gene-targeted fgl2-deficient mice allowed the contribution of fgl2 to the pathogenesis of AVR to be directly examined in vivo. Hearts heterotopically transplanted from fgl2(+/+) and fgl2(+/-) mice into Lewis rats developed AVR with intravascular thrombosis associated with induction of fgl2 in graft vascular ECs. In contrast, xenografts from fgl2(-/-) mice were devoid of thrombosis. These observations collectively suggest that induction of fgl2 on the vascular endothelium plays a role in the pathogenesis of AVR-associated thrombosis. Manipulation of fgl2, in combination with other interventions, may yield novel strategies by which to overcome AVR and extend xenograft survival.
authors.affiliation: Multi-Organ Transplant Program, Institute of Medical Science, and Department of Surgery, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Anand
authors.initials: A
authors.lastname: Ghanekar
authors.forename: Michael
authors.initials: M
authors.lastname: Mendicino
authors.forename: Hao
authors.initials: H
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: He
authors.forename: Mingfeng
authors.initials: M
authors.lastname: Liu
authors.forename: Robert
authors.initials: R
authors.lastname: Zhong
authors.forename: M James
authors.initials: MJ
authors.lastname: Phillips
authors.forename: Gary A
authors.initials: GA
authors.lastname: Levy
authors.forename: David R
authors.initials: DR
authors.lastname: Grant
mesh_terms: D000208:Acute Disease; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002874:Chromosome Mapping; D003001:Cloning, Molecular / Q000379:methods; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D004789:Enzyme Activation; D005340:Fibrinogen / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D006084:Graft Rejection / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D016027:Heart Transplantation / Q000276:immunology* / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D010215:Papio; D011516:Prothrombin / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000494:pharmacology; D013552:Swine; D013917:Thrombin / Q000378:metabolism; D013927:Thrombosis / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D014183:Transplantation, Heterologous / Q000276:immunology* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: C095202:FGL2 protein, human; C490637:Fgl2 protein, mouse; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D011516:Prothrombin; D005340:Fibrinogen; D013917:Thrombin