The chronic phase following toxin-induced acute kidney injury (AKI) is characterized by robust inflammation and progressive kidney fibrosis. Interferon regulatory factor 4 (IRF-4) is a type of multifunctional transcription factor that has been deeply linked to inflammation and fibrotic diseases. However, the role of IRF-4 in kidney damage and renal fibrosis after toxin-induced AKI remain to be explored. In this work, we examined the effect of IRF-4 deficiency on inflammation and kidney fibrosis in an AKI-chronic kidney disease (CKD) transition model induced by folic acid (FA) injury. We showed that FA treatment resulted in severe acute tubular injury followed by inflammatory reaction and interstitial fibrosis in wild-type mice. A sharp elevation of IRF-4 levels was observed in FA-injured kidneys. IRF-4 knockout led to a substantial reduction of extracellular matrix (ECM) proteins deposition and inhibited myofibroblasts transformation in the kidneys of mice subjected to FA treatment. In addition, IRF-4 ablation impaired F4/80⁺ macrophages and CD3⁺ T lymphocytes infiltration into the FA-injured kidneys. Loss of IRF-4 reduced the production of inflammatory molecules such as CXCL16, IL-18, IL-6, and TGF-β1 in the kidneys in response to FA stress. Following FA injury, the kidneys of IRF-4 knockout mice had fewer bone marrow-derived myofibroblasts than wild-type controls. Moreover, IRF-4 disruption inhibited macrophages to myofibroblasts differentiation in the kidneys in response to FA stimuli. In vitro, IL-4 stimulated expression of α-smooth muscle actin and ECM proteins and promoted M2 macrophages to myofibroblasts transition in mouse bone marrow-derived monocytes, which was abolished in the absence of IRF-4. Thus, we identified an important role of IRF-4 in the pathogenesis of progressive CKD following FA-induced AKI.

毒素引起的急性肾损伤（AKI）后的慢性阶段的特点是强烈的炎症和进行性肾纤维化。干扰素调节因子 4 (IRF-4) 是一种多功能转录因子，与炎症和纤维化疾病密切相关。然而，IRF-4 在毒素诱导的 AKI 后肾损伤和肾纤维化中的作用仍有待探索。在这项工作中，我们研究了 IRF-4 缺乏对叶酸 (FA) 损伤诱导的 AKI-慢性肾病 (CKD) 转变模型中炎症和肾纤维化的影响。我们发现，FA 治疗会导致野生型小鼠严重急性肾小管损伤，随后出现炎症反应和间质纤维化。在 FA 损伤的肾脏中观察到 IRF-4 水平急剧升高。 IRF-4 敲除导致细胞外基质 (ECM) 蛋白沉积大幅减少，并抑制接受 FA 治疗的小鼠肾脏中肌成纤维细胞的转化。此外，IRF-4 消融损害了 F4/80 ⁺巨噬细胞和 CD3 ⁺ T 淋巴细胞浸润到 FA 损伤的肾脏中。 IRF-4 的缺失会减少肾脏中 CXCL16、IL-18、IL-6 和 TGF-β1 等炎症分子的产生，以应对 FA 应激。 FA 损伤后，IRF-4 敲除小鼠的肾脏中骨髓来源的肌成纤维细胞数量少于野生型对照小鼠。此外，IRF-4 破坏抑制了肾脏中巨噬细胞对 FA 刺激的反应，向肌成纤维细胞分化。在体外，IL-4刺激α-平滑肌肌动蛋白和ECM蛋白的表达，并促进小鼠骨髓源性单核细胞中M2巨噬细胞向肌成纤维细胞的转变，而在IRF-4不存在的情况下，这种转变被消除。 因此，我们确定了 IRF-4 在 FA 诱导的 AKI 后进行性 CKD 发病机制中的重要作用。