Macrophage accumulation is a prominent feature in most forms of human glomerulonephritis and correlates with renal dysfunction. Macrophages can directly mediate acute renal injury in animal models, but the mechanisms of macrophage activation required for mediating renal injury are unknown. This study examined whether activation of the Jun amino terminal kinase (JNK) signaling pathway is necessary for macrophage-mediated renal injury. An adoptive transfer model was used in which rats were

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... ed with sheep IgG (day Ϫ5), made leukopenic by administration of cyclophosphamide (CyPh) (day Ϫ2), and then injected with sheep anti-glomerular basement membrane (GBM) serum (day 0). Animals were then given an intravenous injection of bone marrow-derived macrophages (BMM) (day 1) and killed 24 h later (day 2). The induction of proteinuria and glomerular cell proliferation (PCNA ϩ cells) in CyPh-treated anti-GBM disease was dependent on transfer of BMM. Exposure of BMM to the specific JNK inhibitor, SP600125, for 3 h before adoptive transfer had no effect on glomerular accumulation of BMM in CyPhtreated anti-GBM disease. However, SP600125 treatment of BMM caused a 75% reduction in proteinuria and a 70% reduction in glomerular cell proliferation (P Ͻ 0.01 versus vehicle or untreated BMM). In conclusion, this study has defined a critical role for the JNK signaling pathway in macrophage-mediated renal injury.