Significance of the urokinase-type plasminogen activator and its receptor in the progression of focal segmental glomerulosclerosis in clinical and mouse models

Abstract

Background: suPAR biomarker generally considered a pathogenic factor in FSGS. However, studies have been published that dispute this conclusion. The current study was designed to investigate the roles of uPA and suPAR in FSGS in clinical and mouse models.

Methods: Clinical subjects including those with biopsy-proven FSGS and MCD were enrolled. To verify the role of uPA in FSGS, Adriamycin was used to induce FSGS in uPA knockout (uPA(-/-)) and BALB/c (WT) mice. Proteinuria and suPAR, the cleaved/intact forms of the circulating suPAR, and possible proteases involving cleavage of the suPAR were also studied.

Results: FSGS clinical cases presented significantly higher serum levels of suPAR and Cr and lower serum levels of uPA. In the mice model, the uPA(-/-) group exhibited faster disease progression and worsening proteinuria than the WT group. In addition, the uPA(-/-) group had higher plasma suPAR levels, glomerular cell apoptosis, and dysregulation of the Th1/Th2 balance. In an analysis of suPAR variants in FSGS, both the intact and cleaved forms of the suPAR were higher in clinical subjects and the mouse model. However, the process of suPAR cleavage was not mediated by enzymatic activities of the uPA, elastase, or cathepsin G.

Conclusions: A deficiency of uPA accelerated the progression of Adriamycin-induced mouse FSGS model. Decrease of serum uPA levels may be an indicator of the progression of FSGS in clinical subjects and animal models.

Fig. 1

Moderate correlation between human plasma soluble urokinase-type plasminogen activator (uPA) receptor (suPAR) and serum creatinine in combination of FSGS (red) and MCD (blue) clinical cases

Fig. 2

Deficiency of the urokinase-type plasminogen activator (uPA) accelerated the decrease of renal functions in a focal segmental glomerulosclerosis (FSGS) mouse model. a Proteinuria was expressed as total protein (mg/ml) over creatinine (mg/dl), and (b) plasma albumin was determined in wild-type (WT) and uPA^−/− groups during the course of the experiment until 4 weeks after Adriamycin treatment. ^# p < 0.05 vs. week 0 (W0); *p < 0.05 vs. the WT

Fig. 3

Deficiency of the urokinase-type plasminogen activator (uPA) exacerbated the severity of renal histopathological changes in a focal segmental glomerulosclerosis (FSGS) mouse model. At the end of the experiment, kidney samples were collected for a histopathological examination. a Representative sections from renal tissue in wild-type (WT) and uPA^−/− groups were evaluated with PAS staining (lines 1 and 2), colloidal iron staining (lines 3 and 4), and TUNEL staining (lines 5 and 6), at an original magnification of 400x. Semi-quantification analyses of PAS (b), colloidal iron (c), and TUNEL (d) staining are also presented. ^# p < 0.05 vs. week 0 (W0); *p < 0.05 vs. the WT

Fig. 4

Urokinase-type plasminogen activator (uPA)-deficient mice failed to generate a type 2 immune response in a focal segmental glomerulosclerosis (FSGS) mouse model. Plasma samples in the wild-type (WT) and uPA^−/− groups were collected at indicated time points to determine levels of immunoglobulin G1 (IgG1), IgG2a, and IgG3. Data are presented as the ratio of IgG1 over the combination of IgG2a and IgG3. ^# p < 0.05 vs. week 0 (W0); *p < 0.05 vs. the WT

Fig. 5

Plasma soluble urokinase-type plasminogen activator (uPA) receptor (suPAR) levels and expression patterns in a focal segmental glomerulosclerosis (FSGS) mouse model. a Plasma suPAR levels were determined in the wild-type (WT) and uPA^−/− groups during the course of the experiment until 4 weeks after Adriamycin treatment. b Immunoblot analysis of the expression of plasma suPAR variants in the WT (upper panel) and uPA^−/− (lower panel) groups at the indicated time points are presented. ^# p < 0.05 vs. week 0 (W0); *p < 0.05 vs. the WT

Fig. 6

Expression patterns of soluble urokinase-type plasminogen activator receptor (suPAR) variants in clinical subjects. Immunoblot analyses of expressions of serum suPAR variants in minimal-change disease (MCD) and focal segmental glomerulosclerosis (FSGS) clinical subjects are presented

Fig. 7

Neither elastase nor cathepsin G mediated cleavage of the soluble urokinase-type plasminogen activator (uPA) receptor (suPAR) in a focal segmental glomerulosclerosis (FSGS) mouse model. Plasma activities of elastase (a) and cathepsin G (b) were determined in the wild-type (WT) and uPA^−/− groups during the course of the experiment until 4 weeks after Adriamycin treatment. ^# p < 0.05 vs. week 0 (W0); *p < 0.05 vs. the WT