Urokinase Promotes Redundantly Intratubular C3a-Formation But Not ENaC-Driven Hypertension in DOCA/Salt Kidney Injury

uPA (urokinase-type plasminogen activator) inhibitors mitigate salt retention, plasmin, and complement activation in acute proteinuric kidney diseases. We hypothesized that in chronic kidney injury with albuminuria, uPA contributes to hypertension and complement-dependent tissue inflammation and injury.

Wild-type and uPA KO (knockout) mice underwent either sham surgery or unilateral nephrectomy, followed by insertion of deoxycorticosterone acetate (DOCA)- or sham pellets and a high (4%) or control (0.5%) sodium chloride diet for 21 days. Glomerular filtration rate was estimated by transcutaneous fluorescein-isothiocyanate-sinistrin, and arterial blood pressure was recorded continuously by indwelling femoral catheters. Urine was analyzed for albumin, plasmin(ogen), electrolytes, kidney injury markers (neutrophil gelatinase-associated lipocalin), and complement proteins (C3, C3a). Kidney tissue was examined for neutrophil gelatinase-associated lipocalin, epithelial sodium channel, C3, C3a, C5a, cytokines, inflammation, and macrophage polarization markers (CD16⁺CD32⁺, CD163⁺).

DOCA-salt increased diuresis, Na⁺ excretion, albuminuria, tubular injury markers, and single-kidney glomerular filtration rate, with no genotype-dependent differences. Blood pressure increased by ≈30 mm Hg within 2 days and then stabilized, with no genotype difference for up to 15 days. DOCA-salt wild-type mice showed elevated urinary protease activity, plasmin, C3, and C3a, while these were mitigated in KO mice. In the kidney, DOCA-salt increased IL-6 (interleukin 6), MCP-1 (monocyte chemoattractant protein-1), MIP-1α (macrophage inflammatory protein 1 alpha), and TNF (tumor necrosis factor), while TNF and IP-10 (interferon gamma-induced protein-10) were reduced in KO mice. CD16⁺CD32⁺ macrophages predominated over CD163⁺ macrophages in DOCA-salt kidney tissue across genotypes.

While not essential for filtration barrier injury, glomerular filtration rate decline, and hypertension in DOCA-salt-induced kidney injury, uPA, through plasmin, generates anaphylatoxins with effects on specific cytokines.