Multifunctionality of PAI-1 in fibrogenesis: Evidence from obstructive nephropathy in PAI-1–overexpressing mice

Multifunctionality of PAI-1 in fibrogenesis: Evidence from obstructive nephropathy in PAI-1–overexpressing mice.BackgroundPlasminogen activator inhibitor-1 (PAI-1) has been implicated in the pathogenesis of chronic kidney disease based on its up-regulated expression and on the beneficial effects of PAI-1 inhibition or depletion in experimental models. PAI-1 is a multifunctional protein and the mechanisms that account for its profibrotic effects have not been fully elucidated.MethodsThe present study was designed to investigate PAI-1–dependent fibrogenic pathways by comparing the unilateral ureteral obstruction model (UUO) (days 3, 7, and 14) in PAI-1–overexpressing mice (PAI-1 tg) to wild-type mice, both on a C57BL6 background.ResultsFollowing UUO, total kidney PAI-1 mRNA and/or protein levels were significantly higher in the PAI-1 tg mice (N = 6 to 8/group) and fibrosis severity was significantly worse (days 3, 7, and 14), measured both as Sirius red–positive interstitial area (e.g., 10 ± 3.2% vs. 4.5 ± 1.0%) (day 14) and total kidney collagen (e.g., 11.1 ± 1.7 vs. 6.2 ± 1.3 μg/mg) (day 14). By day 14, the expression of two normal tubular proteins, E-cadherin and Ksp-cadherin, were significantly lower in the PAI-1 tg mice (3.2 ± 0.5% vs. 11.7 ± 5.9% and 2.6 ± 1.6) vs. 6.2 ± 0.8%, respectively), implying more extensive tubular damage. At least four fibrogenic pathways were differentially expressed in the PAI-1 tg mice. First, interstitial macrophage recruitment was more intense (P < 0.05 days 3 and 14). Second, interstitial myofibroblast density was greater (P < 0.05 days 3 and 7) despite similar numbers of proliferating tubulointerstitial cells. Third, transforming growth factor-β1 (TGF-β1) and collagen I mRNA were significantly higher. Finally, urokinase activity was significantly lower (P < 0.05 days 7 and 14) despite similar mRNA levels. Gene microarray studies documented that that the deletion of this single profibrotic gene had far-reaching consequences on renal cellular responses to chronic injury.ConclusionThese data provide further evidence that PAI-1 is directly involved in interstitial fibrosis and tubular damage via two primary overlapping mechanisms: early effects on interstitial cell recruitment and late effects associated with decreased urokinase activity.