MO266: Deficiency of Urokinase-Type Plasminogen Activator Exacerbates CBSA-Induced Membranous Nephropathy in Mice

Abstract BACKGROUND AND AIMS In nondiabetic population, primary membranous nephropathy (PMN) is the most common cause of idiopathic nephrotic syndrome in the world. Urokinase-type plasminogen activator (uPA) is one of the key members of fibrinolysis system, which functions as dissolving blood clots to prevent obstruction of blood vessels. Currently, the roles of uPA in PMN remain undefined. METHOD Six-week-old male mice with Plau wild-type and knockout in BALB/c strain were used to induce MN by cationic bovine serum albumin (cBSA). Biochemistry assays of blood and urine were measured by a Fuji Dri-Chem FDC NX 500 machine. Glomerular polyanions were determined by using Colloidal Iron Stain Kit. Reactive oxygen species (ROS) was detected by immunohistochemistry stained by 4-HNE antibody. TUNEL positivity in the kidneys of mice was determined using an ApopTag® Plus Peroxidase In Situ Apoptosis Kit. The deposition of immune complex in glomeruli was examined by a transmission electron microscope. Lymphocyte subsets were determined by flow cytometry. Serum concentrations of IgG1 and IgG2a were measured by ELISA. RESULTS It has been reported that BALB/c mice is an ideal strain for mimicking human PMN. Thus, we generated uPA deficient mice (Plau-/-) in BALB/c strain by backcrossing C.129S2-Plautm1Mlg/J mice with BALB/c wild-type mice to N10. Plau-/- mice exhibited severe urinary albumin-to-creatinine ratio significantly when compared with wild-type mice at 2 weeks post-cBSA administration. Consistently, cBSA-induced Plau-/- mice displayed higher serum creatinine, hypoalbuminemia and hypercholesterolemia than wild-type mice. Histologically, Plau-/- mice presented more severed glomerular basement thickening, IgG granular deposition, intensified podocyte effacement, irregular thickening of glomerular basement membrane and subepithelial deposits than wild-type mice. Attenuated colloidal iron stain was observed in Plau-/- mice when compared with wild-type mice. Moreover, elevated ROS and apoptosis in the kidneys of Plau-/- mice were observed. B lymphocyte subsets were enriched significantly in the Plau-/- mice with MN, suggesting that pathological aggravation of MN is associated with dominant B lymphocyte population. The enriched ratio of IgG1 to IgG2a further confirmed predominant Th2 subset in Plau-/- mice. CONCLUSION uPA deficiency enhances Th2 dominant immune response, leading to enhancement of ROS and apoptosis in the kidneys, which subsequently exacerbates the progression of MN. Maintenance of uPA homeostasis may be a promising therapeutic approach for MN management.