Macrophage interferon regulatory factor 4 deletion ameliorates aristolochic acid nephropathy via reduced migration and increased apoptosis.

Kensuke Sasaki,Raymond C Harris,Jiaqi Tang,Yahua Zhang,Andrew S Terker,Aolei Niu,Juan Pablo Arroyo,Xiaofeng Fan,Stephanie R Bennett,Shirong Cao,Ming-Zhi Zhang,Suwan Wang

doi:10.1172/jci.insight.150723

Abstract

Aristolochic acid (AA) is the causative nephrotoxic alkaloid in AA nephropathy, which results in a tubulointerstitial fibrosis. AA causes direct proximal tubule damage as well as an influx of macrophages, although the role of macrophages in pathogenesis is poorly understood. Here, we demonstrate that AA directly stimulates migration, inflammation, and ROS production in macrophages ex vivo. Cells lacking interferon regulatory factor 4 (IRF4), a known regulator of macrophage migration and phenotype, had a reduced migratory response, though effects on ROS production and inflammation were preserved or increased relative to WT cells. Macrophage-specific IRF4-knockout mice were protected from both acute and chronic kidney effects of AA administration based on functional and histological analysis. Renal macrophages from kidneys of AA-treated macrophage-specific IRF4-knockout mice demonstrated increased apoptosis and ROS production compared with WT controls, indicating that AA directly polarizes macrophages to a promigratory and proinflammatory phenotype. However, knockout mice had reduced renal macrophage abundance following AA administration. While macrophages lacking IRF4 can adopt a proinflammatory phenotype upon AA exposure, their inability to migrate to the kidney and increased rates of apoptosis upon infiltration provide protection from AA in vivo. These results provide evidence of direct AA effects on macrophages in AA nephropathy and add to the growing body of evidence that supports a key role of IRF4 in modulating macrophage function in kidney injury.

Highlights

Aristolochic acid (AA) is the causative nephrotoxic alkaloid in aristolochic acid nephropathy (AAN)
Our findings provide mechanistic insight into the role of macrophages in the pathogenesis of AAN and the protective effect of interferon regulatory factor 4 (IRF4) deletion adds to the growing body of evidence that supports a key role of IRF4 in modulating macrophage function in kidney injury
AA led to increased macrophage migration and reactive oxygen species (ROS) production (Fig 1a, b)

Summary

Introduction

Aristolochic acid (AA) is the causative nephrotoxic alkaloid in aristolochic acid nephropathy (AAN). AAN presents clinically as a progressive interstitial fibrosis with decline in renal function and leads to end-stage kidney disease in patients with repeated exposure. While not commonly encountered by nephrologists in the United States, AAN is the cause of end-stage renal disease in up to 10% of the dialysis population in some endemic areas [4]. The toxic effects of AA on renal tubules are linked to epithelial cell G2/M arrest followed by an apoptotic and profibrotic response [5]. While these direct effects on renal epithelial cells are well documented, the roles of other cell types involved in the injury process remain largely unexplored in AAN, preventing a complete understanding of its pathogenesis

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Conclusion