t-PA promotes glomerular plasmin generation and matrix degradation in experimental glomerulonephritis.
BACKGROUND
In addition to its well-known role in degrading fibrin, recent evidence suggests that plasmin degrades matrix proteins and activates prometalloproteinases. Plasmin is generated from plasminogen by tissue plasminogen activator (t-PA). We hypothesized that t-PA treatment increases plasmin generation in nephritic glomeruli and degrades pathological matrix leading to a therapeutic reduction in matrix accumulation.


METHODS
Anti-Thy-1 nephritis was induced by injection of OX-7 antibody. Rats were given twice daily intravenous injections of saline (disease control group) or human recombinant t-PA (rt-PA; 1 mg/kg body weight) on days 3 through 5. Proteinuria, glomerular matrix protein staining, and glomerular mRNA levels for transforming growth factor-beta 1 (TGF-beta 1), fibronectin, and plasminogen activator inhibitor type 1 (PAI-1) were evaluated at day 6. Localization of rt-PA, plasmin generation by glomeruli in vitro, and glomerular production and content of active TGF-beta1 were also investigated.


RESULTS
Compared with disease control animals, proteinuria and staining score for periodic acid-Schiff (2.75 +/- 0.17 vs. 1.41 +/- 0.09), fibronectin-EDA+ (19 +/- 2 vs. 14 +/- 1), laminin (35 +/- 2 vs. 25 +/- 2), type I collagen (33 +/- 1 vs. 21 +/- 3), and type IV collagen (27 +/- 2 vs. 23 +/- 1) were significantly reduced in treated rats (P < 0.01). Glomerular TGF-beta 1, fibronectin, and PAI-1 mRNA levels were unchanged. rt-PA colocalized with fibrin along glomerular capillary walls and in the mesangium. Nephritic glomeruli in vitro had decreased plasmin activity, which was elevated by an in vivo presacrifice injection of rt-PA. Glomerular production and content of active TGF-beta 1 were unchanged by the rt-PA injection.


CONCLUSIONS
: These results show that injected rt-PA binds to fibrin in nephritic glomeruli, thus increasing plasmin generation and promoting pathological matrix degradation without activating latent TGF-beta. Agents that increase plasmin generation, such as t-PA, may have potential as antifibrotic therapies.
Haraguchi
M
M
Fibrosis Research Laboratory, Division of Nephrology, University of Utah, Salt Lake City, Utah 84108, USA.
Border
W A
WA
Huang
Y
Y
Noble
N A
NA
D000818:Animals; D002478:Cells, Cultured; D005109:Extracellular Matrix / Q000378:metabolism / Q000473:pathology; D005337:Fibrin / Q000032:analysis / Q000378:metabolism; D005340:Fibrinogen / Q000032:analysis / Q000378:metabolism; D005341:Fibrinolysin / Q000096:biosynthesis* / Q000378:metabolism; D005353:Fibronectins / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D005923:Glomerulosclerosis, Focal Segmental / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D007678:Kidney Glomerulus / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D008297:Male; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics; D010960:Plasminogen Activators / Q000032:analysis / Q000494:pharmacology*; D011507:Proteinuria / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018800:Thy-1 Antigens; D010959:Tissue Plasminogen Activator / Q000032:analysis / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000235:genetics; D053773:Transforming Growth Factor beta1
D005353:Fibronectins; D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; D018800:Thy-1 Antigens; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D005337:Fibrin; D005340:Fibrinogen; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin