uPAR Amplifies Macrophage Inflammation via NF-κB Pathway to Promote Fibrotic Transition Following Acute Kidney Injury.

AIMS: Persistent inflammation is recognized as a major driver of the acute kidney injury (AKI) to chronic kidney disease (CKD) transition, yet upstream macrophage-activation signals remain incompletely understood. Here, we investigated whether the urokinase receptor (uPAR), traditionally linked to matrix remodeling, functions instead as an inflammatory signaling hub that links kidney injury to chronic fibrotic remodeling. RESULTS: In a unilateral renal ischemia-reperfusion injury model, uPAR was induced during the fibrotic phase of postischemic kidney injury. Functional enhancement- and loss-of-function approaches revealed a striking dichotomy: exogenous urokinase (uPA) aggravated renal dysfunction, inflammation, oxidative stress, and fibrosis, whereas uPAR deletion was protective. Mechanistically, uPA/uPAR signaling amplified macrophage inflammatory responses, enhancing M1 polarization, pro-inflammatory cytokine production, reactive oxygen species generation, and NF-κB activation. Molecular docking, mutational modeling, and co-immunoprecipitation analyses revealed a previously underappreciated association between activated uPAR and toll-like receptor 4 (TLR4)-containing complexes. This interaction enhanced myeloid differentiation primary response gene 88-dependent NF-κB signaling and potentiated macrophage inflammatory amplification rather than initiating inflammation independently. NF-κB blockade abolished the pro-inflammatory effects of uPA/uPAR signaling, establishing the functional importance of this pathway. INNOVATION: We demonstrate that uPA-activated uPAR engages TLR4-associated signaling to intensify macrophage-driven inflammation, oxidative stress, and fibrotic remodeling. These findings redefine uPAR as a molecular switch governing maladaptive kidney repair and identify the uPA/uPAR-TLR4 signaling interface as a promising therapeutic target. CONCLUSION: Our findings suggest that the uPA/uPAR-TLR4 axis is involved in regulating the progression from AKI to fibrosis. Targeting this signaling node may represent a novel strategy to interrupt maladaptive repair and prevent CKD following AKI. Antioxid. Redox Signal. 00, 000-000.