Stimulation of PAI‐1 in rabbit anti‐GBM glomerulonephritis

Abstract

It has previously been shown in human disease and animal models of glomerulonephritis (GN) that fibrin deposition is associated with a net reduction of glomerular fibrinolytic activity as a result of reduced expression of plasminogen activators and increased expression of plasminogen activator inhibitor type 1 (PAI‐1). Conditioned media (CM) prepared from cultured glomeruli of normal rabbits and rabbits 24 (Day 1) and 96 (Day 4) h after induction of anti‐GBM GN were compared for their effects on the synthesis of fibrinolytic molecules in human endothelial cells (EC). Only CM from Day 4 GN rabbits showed PAI‐1 protein stimulatory activity of up to 148% (P<0.05; n=3) above that of untreated EC. This was also seen at the mRNA level. Glomerulonephritis Day 4 CM showed significantly higher amounts of tumour necrosis factor (TNF) and thrombin and transforming growth factor‐β (TGF‐β) bioactivity in comparison to glomerular CM from normal rabbits. After high performance liquid chromatography (HPLC) of Day 4 GN CM, PAI‐1 stimulatory activity was found to correlate with the presence of interleukin 1 (IL‐1), TNF and TGF‐β. These results suggest a correlation between severity of anti‐GBM GN in a rabbit model, increased PAI‐1 synthesis and increased expression of TNF and TGF‐β. This may potentiate glomerular fibrin and extracellular matrix deposition in anti‐GBM GN, leading to glomerular crescent formation and eventual renal failure.