Comprehensive analysis of glomerular mRNA expression of pro- and antithrombotic genes in atypical haemolytic-uremic syndrome (aHUS)

Abstract

Atypical haemolytic-uremic syndrome (aHUS) is, in most cases, due to hereditary or acquired defects in complement regulation and a life-threatening disease. Despite the rapidly grown knowledge about the primary defects in aHUS, the pathogenesis that links complement dysregulation with microthrombus formation in aHUS is still unknown. Thus, we examined the glomerular microvascular expression of pro- and antithrombotic genes. Glomeruli were microdissected from 12 archival paraffin-embedded biopsies with aHUS and from seven control biopsies. Glomerular mRNA expression was quantified by single real-time PCR reactions after preamplification. In addition immunostains were performed for plasminogen activator inhibitor 1 (PAI-1) and for tissue plasminogen activator (tPA). Results were compared between cases and controls and with clinical data. Glomeruli in aHUS had increased mRNA expression of antifibrinolytic, prothrombotic PAI-1, antithrombotic thrombomodulin (THBD) and CD73 and decreased expression of profibrinolytic, antithrombotic tPA compared to controls. Impaired fibrinolysis due to increased microvascular expression of the antifibrinolytic PAI-1 in combination with the decreased expression of the profibrinolytic tPA seems to be a final common pathway in renal thrombotic microangiopathy that is also effective in aHUS. The concomitant induction of antithrombotic transcripts likely indicates counterregulatory efforts, demonstrating that the capillary bed is not a passive victim of complement attack. Future research should investigate if and how complement activation could induce the reported shift in the expression of PAI-1 and tPA.

Comprehensive Genetic Analysis of Complement and Coagulation Genes in Atypical Hemolytic Uremic Syndrome

“…30 The role of coagulation activity in aHUS patients has been evaluated at the mRNA level in one study, in which gene expression was quantitated in glomeruli from archival paraffinembedded renal biopsies. 34 Expression of antifibrinolytic, prothrombotic plasminogen activator inhibitor-1 and antithrombotic thrombomodulin were increased, and expression of profibrinolytic, antithrombotic tissue plasminogen activator was decreased compared with controls, suggesting that reduction of fibrinolysis is important in aHUS. 34 Plasminogen-related studies on typical HUS, however, have yielded equivocal results.…”

“…34 Expression of antifibrinolytic, prothrombotic plasminogen activator inhibitor-1 and antithrombotic thrombomodulin were increased, and expression of profibrinolytic, antithrombotic tissue plasminogen activator was decreased compared with controls, suggesting that reduction of fibrinolysis is important in aHUS. 34 Plasminogen-related studies on typical HUS, however, have yielded equivocal results. [35][36][37][38][39] Some studies have reported that inhibition of fibrinolysis precedes and may be the cause of renal injury, 35 with plasma levels of plasminogen activator inhibitor-1 inversely correlating with improvement in renal function.…”

Acute Kidney Injury and Hemolytic Anemia Secondary to <b><i>Mycoplasma pneumoniae</i></b> Infection

“…However, ultrastructural evidence of endothelial cell swelling, loss of fenestration, and expansion of the subendothelial space together with occasional mesangiolysis was indicative of glomerular microangiopathic injury. Experimental studies demonstrated the ability of the glomeruli to release fibrinolytic and antithrombotic factors under certain conditions [23][24][25] . We can speculate that in our case these protective mechanisms may have contributed to preventing microthrombi formation until an effective therapy was started.…”

Endothelial cells: source, barrier, and target of defensive mediators

“…57,88 Binding Interestingly, micro-dissected glomeruli from aHUS patients had increased mRNA expression of antifibrinolytic, prothrombotic PAI-1, antithrombotic TM and CD73 and decreased expression of profibrinolytic, antithrombotic t-PA compared to controls. 89 The concomitant induction of antithrombotic transcripts likely indicates counter regulatory efforts, demonstrating that the capillary bed is not a passive victim of complement attack. Future research is needed to uncover whether and how complement activation could alter the balance between the expression of PAI-1 and t-PA and what is their role in aHUS.…”