title: Mechanisms underlying the antifibrotic properties of noninhibitory PAI-1 (PAI-1R) in experimental nephritis.
abstract: Administration of a mutant, noninhibitory PAI-1 (PAI-1R), reduces disease in experimental glomerulonephritis. Here we investigated the importance of vitronectin (Vn) binding, PAI-1 stability and protease binding in this therapeutic effect using a panel of PAI-1 mutants differing in half-life, protease binding, and Vn binding. PAI-1R binds Vn normally but does not inhibit proteases. PAI-1AK has a complete defect in Vn binding but retains full inhibitory activity, with a short half-life similar to wild-type (wt)-PAI-1. Mutant 14-lb is identical to wt-PAI-1 but with a longer half-life. PAI-1K has defective Vn binding, inhibits proteases normally, and has a long half-life. In vitro wt-PAI-1 dramatically inhibited degradation of mesangial cell ECM while the AK mutant had much less effect. Mutants 14-1b and PAI-1K, like wt-PAI-1, inhibited matrix degradation but PAI-1R failed to reverse this inhibition although PAI-1R reversed the wt-PAI-1-induced inhibition of ECM degradation in a plasmin-, time-, and dose-dependent manner. Thus the ability of PAI-1 to inhibit ECM degradation is dependent both on its antiproteinase activity and on maintaining an active conformation achieved either by Vn binding or mutation to a stable form. Administration of these PAI-1 mutants to nephritic rats confirmed the in vitro data; only PAI-1R showed therapeutic effects. PAI-1K did not bind to nephritic kidney, indicating that Vn binding is essential to the therapeutic action of PAI-1R. The ability of PAI-1R to remain bound to Vn even in a high-protease environment is very likely the key to its therapeutic efficacy. Furthermore, because both PAI-1R and 14-1b bound to the nephritic kidney in the same pattern and differ only in their ability to bind proteases, lack of protease inhibition is also keyed to PAI-1R's therapeutic action.
authors.affiliation: Fibrosis Research Laboratory, Division of Nephrology, University of Utah School of Medicine, Salt Lake City, UT 84108, USA.
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Huang
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Border
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lawrence
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Noble
mesh_terms: D000818:Animals; D024042:Collagen Type I / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005921:Glomerulonephritis / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism*; D007518:Isoantibodies; D008297:Male; D050527:Mesangial Cells / Q000378:metabolism; D009154:Mutation; D010447:Peptide Hydrolases / Q000378:metabolism*; D010503:Periodic Acid-Schiff Reaction; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism*; D011507:Proteinuria / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D019096:Vitronectin / Q000378:metabolism*
chemical_list: D024042:Collagen Type I; D007518:Isoantibodies; D017395:Plasminogen Activator Inhibitor 1; D011994:Recombinant Proteins; D053773:Transforming Growth Factor beta1; D019096:Vitronectin; C035678:anti-Thy antibody; D010447:Peptide Hydrolases