Binding of Anti-SSA Antibodies to Apoptotic Fetal Cardiocytes Stimulates Urokinase Plasminogen Activator (uPA)/uPA Receptor-Dependent Activation of TGF-β and Potentiates Fibrosis

Abstract

In congenital heart block (CHB), binding of maternal anti-SSA/Ro antibodies to fetal apoptotic cardiocytes impairs their removal by healthy cardiocytes and increases uPA/uPAR-dependent plasmin activation. Since the uPA/uPAR system plays a role in TGF beta activation, we evaluated whether anti-Ro binding to apoptotic cardiocytes enhances plasmin-mediated activation of TGF beta thereby promoting a profibrosing phenotype. Supernatants from co-cultures of healthy cardiocytes and apoptotic cardiocytes bound by IgG from a mother whose child had CHB (apo-CHB-IgG) exhibited significantly increased levels of active TGF beta compared to supernatants from co-cultures of healthy cardiocytes and apoptotic cardiocytes preincubated with IgG (apo-nl-IgG) from a healthy donor. Treatment of the culture medium with anti-TGF beta antibody or TGF beta inhibitor (SB431542) abrogated the luciferase response thereby confirming TGF beta dependency. Increased uPA levels and activity were present in supernatants generated from cocultures of healthy cardiocytes and apo-CHB-IgG cardiocytes compared to healthy cardiocytes and and apo nl-IgG cardiocytes, respectively. Treatment of apo-CHB-IgG cardiocytes with anti-uPAR or anti-uPA antibodies or plasmin inhibitor aprotinin prior to coculturing with healthy cardiocytes attenuated TGF beta activation. Supernatants derived from cocultures of healthy cardiocytes and apo-CHB-IgG cardiocytes promoted Smad2 phosphorylation and fibroblast transdifferentiation as evidenced by increased SMAc and collagen expression, which decreased when fibroblasts were treated with supernatants from cocultures pretreated with uPAR antibodies. These data suggest that binding of anti-Ro antibodies to apoptotic cardiocytes triggers TGF beta activation, by virtue of increasing uPAR-dependent uPA activity, thus initiating and amplifying a cascade of events that promote myofibroblast transdifferentiation and scar.

Serum Biomarkers of Inflammation, Fibrosis, and Cardiac Function in Facilitating Diagnosis, Prognosis, and Treatment of Anti-SSA/Ro–Associated Cardiac Neonatal Lupus

“…Studies by Briassouli et al (4,17) revealed that uPA/uPAR inhibition attenuated TGF-β activation in supernatants of apoptotic cardiocytes exposed to anti-SSA/Ro and that cord blood uPA, uPAR, and plasminogen were elevated in cardiac NL cases in univariate analysis (4,17). In applying multivariate analysis to the previously reported results, uPA, uPAR, and plasminogen remained significantly associated with development of cardiac NL and associated with disease severity.…”

“…The former disease is clinically identified as congenital heart block and/or cardiomyopathy (1,2). Injury to the developing heart is postulated to occur secondary to a proinflammatory and profibrotic cascade initiated following transplacental passage of maternal autoantibodies to SSA/Ro and/or SSB/La ribonucleoproteins (2–4). Detection occurs most often between the gestational ages (GA) of 16 and 24 weeks of pregnancy (2).…”

Soluble urokinase plasminogen activator receptor levels reflect organ damage in systemic lupus erythematosus

“…57 The same authors also recently suggested that an autoantibody-triggered uPAR-dendent increase in plasmin activity may activate transforming growth factor-β, which in turn could promote fibrosis. 58 Speculatively, altered expression/shedding of uPAR may be affected by autoantibodies and reflect, or even contribute to, a deficient waste disposal process.…”

Pathogenic effects of maternal antinuclear antibodies during pregnancy in women with lupus

“…In addition, TGF-induces the trans-differentiation of cardiac fibroblasts, leading to fibrosis and AV node scaring, 62 and stimulates the plasminogen activator receptor, which feeds the fibrotic process. 63 The toxic effect of anti-Ro52 antibodies on the conduction system is dose-dependent. Studies have demonstrated that these antibodies alter cardiomyocyte calcium homeostasis.…”