title: Resolution of Skin Fibrosis by Neutralization of the Antifibrinolytic Function of Plasminogen Activator Inhibitor 1.
abstract: OBJECTIVE
  Systemic sclerosis (SSc) is a fibrotic disease characterized by an obliterative vasculopathy with thrombosis and impairment of the coagulation-fibrinolysis balance. Plasminogen activator inhibitor 1 (PAI-1) is the major inhibitor of profibrinolytic plasminogen activators (PAs). This study was undertaken to evaluate the contribution of PAI-1 to SSc pathology in the skin.
  
  
  METHODS
  PAI-1 was evaluated in skin from patients with diffuse SSc (dSSc) and those with limited SSc (lSSc) by immunohistochemistry. The contribution of PAI-1 to SSc pathology was tested in vivo in murine graft-versus-host disease (GVHD) and bleomycin models of progressive skin fibrosis and in vitro in dermal human microvascular endothelial cells (HMVECs) using a monoclonal antibody that selectively prevents the binding of PAI-1 to PA.
  
  
  RESULTS
  Skin from patients with dSSc and those with lSSc showed increased PAI-1 levels in the epidermis and microvessel endothelium. PAI-1 neutralization in the GVHD model led to a dramatic, dose-dependent improvement in clinical skin score, concomitant with vasculopathy resolution, including a reduction in fibrinolysis regulators and vascular injury markers, as well as reduced inflammation. Resolution of vasculopathy and inflammation was associated with resolution of skin fibrosis, as assessed by reduction in collagen content and expression of key profibrotic mediators, including transforming growth factor β1 and tissue inhibitor of metalloproteinases 1. Similar to the GVHD model, PAI-1 neutralization reduced dermal inflammation and fibrosis in the bleomycin model. PAI-1 neutralization stimulated plasmin-mediated metalloproteinase 1 activation in dermal HMVECs.
  
  
  CONCLUSIONS
  Our findings indicate that neutralization of the antifibrinolytic function of PAI-1 resolves skin fibrosis by limiting the extent of initial vascular injury and connective tissue inflammation. These data suggest that PAI-1 represents an important checkpoint in disease pathology in human SSc.
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland, and Boston University School of Medicine, Boston, Massachusetts.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Lemaire
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Timothy
authors.initials: T
authors.lastname: Burwell
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Tracy
authors.initials: T
authors.lastname: Delaney
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Julie
authors.initials: J
authors.lastname: Bakken
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Lily
authors.initials: L
authors.lastname: Cheng
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Marlon C
authors.initials: MC
authors.lastname: Rebelatto
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Meggan
authors.initials: M
authors.lastname: Czapiga
authors.affiliation: MedImmune, Ltd., Cambridge, UK.
authors.forename: Isabelle
authors.initials: I
authors.lastname: de-Mendez
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Coyle
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Ronald
authors.initials: R
authors.lastname: Herbst
authors.affiliation: Boston University School of Medicine, Boston, Massachusetts.
authors.forename: Robert
authors.initials: R
authors.lastname: Lafyatis
authors.affiliation: MedImmune LLC, Gaithersburg, Maryland.
authors.forename: Jane
authors.initials: J
authors.lastname: Connor
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000633:toxicity; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D057134:Antibodies, Neutralizing / Q000494:pharmacology; D001761:Bleomycin / Q000633:toxicity; D016022:Case-Control Studies; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005355:Fibrosis / Q000139:chemically induced / Q000378:metabolism; D006086:Graft vs Host Disease / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D020781:Matrix Metalloproteinase 1 / Q000378:metabolism; D051379:Mice; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D010960:Plasminogen Activators / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D045743:Scleroderma, Diffuse / Q000378:metabolism*; D045745:Scleroderma, Limited / Q000378:metabolism*; D012867:Skin / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology
chemical_list: D000903:Antibiotics, Antineoplastic; D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D017395:Plasminogen Activator Inhibitor 1; D001761:Bleomycin; D010960:Plasminogen Activators; C522360:MMP1 protein, human; D020781:Matrix Metalloproteinase 1