4-Octyl itaconate attenuates renal tubular injury in db/db mice by activating Nrf2 and promoting PGC-1α-mediated mitochondrial biogenesis

<b>Objectives:</b> The aim of this study was to investigate the mechanism of itaconate’s potential effect in diabetic kidney disease. <b>Methods:</b> Renal immune responsive gene 1 (IRG1) levels were measured in db/db mice and streptozotocin (STZ) + high-fat diet (HFD)-induced diabetic mice. <i>Irg1</i> knockout mice were generated. db/db mice were treated with 4-octyl itaconate (4-OI, 50 mg/kg), a derivative of itaconate, for 4 weeks. Renal function and morphological changes were investigated. Ultrastructural alterations were determined by transmission electron microscopy. <b>Results:</b> Renal IRG1 levels were reduced in two diabetic models. STZ+HFD-treated <i>Irg1</i> knockout mice exhibited aggravated renal tubular injury and worsened renal function. Treatment with 4-OI lowered urinary albumin-to-creatinine ratio and blood urea nitrogen levels, and restored renal histological changes in db/db mice. It improved mitochondrial damage, increased expressions of peroxisome-proliferator-activated receptor γ coactivator-1α (PGC-1α) and mitochondrial transcription factor A (TFAM) in the renal cortex of db/db mice. These were confirmed <i>in vitro</i>; 4-OI improved high glucose-induced abnormal mitochondrial morphology and TFAM expression in HK-2 cells, effects that were inhibited by <i>PGC-1α</i> silencing. Moreover, 4-OI reduced the number of apoptotic cells in the renal cortex of db/db mice. Further study showed that 4-OI increased renal Nrf2 expression and decreased oxidative stress levels in db/db mice. In HK-2 cells, 4-OI decreased high glucose-induced mitochondrial ROS production, which was reversed by <i>Nrf2</i> silencing. <i>Nrf2</i> depletion also inhibited 4-OI-mediated regulation of PGC-1α, TFAM, and mitochondrial apoptotic protein expressions. <b>Conclusions:</b> 4-OI attenuates renal tubular injury in db/db mice by activating Nrf2 and promoting PGC-1α-mediated mitochondrial biogenesis.

**研究目的**：本研究旨在探讨衣康酸（itaconate）在糖尿病肾病中发挥潜在作用的分子机制。**研究方法**：本研究检测了db/db小鼠及链脲佐菌素（streptozotocin, STZ）联合高脂饮食（high-fat diet, HFD）诱导的糖尿病小鼠肾脏免疫应答基因1（renal immune responsive gene 1, IRG1）的表达水平。构建了<i>Irg1</i>基因敲除小鼠。对db/db小鼠给予衣康酸衍生物4-辛基衣康酸（4-octyl itaconate, 4-OI，50 mg/kg）干预，持续4周。观察小鼠肾脏功能及形态学变化，通过透射电子显微镜检测肾脏超微结构改变。**研究结果**：两种糖尿病模型小鼠的肾脏IRG1表达水平均降低。经STZ+HFD造模的<i>Irg1</i>基因敲除小鼠表现出更严重的肾小管损伤及肾功能恶化。4-OI干预可降低db/db小鼠的尿白蛋白/肌酐比值及血尿素氮水平，并改善其肾脏组织病理学改变。4-OI可改善db/db小鼠肾脏皮质的线粒体损伤，上调过氧化物酶体增殖物激活受体γ辅激活因子1α（PGC-1α）及线粒体转录因子A（TFAM）的表达。上述结果在<i>in vitro</i>实验中得到验证：4-OI可改善高糖诱导的HK-2细胞线粒体形态异常，并恢复其TFAM表达水平，而<i>PGC-1α</i>基因沉默可抑制该效应。此外，4-OI可减少db/db小鼠肾脏皮质的细胞凋亡数量。进一步研究显示，4-OI可上调db/db小鼠肾脏的核因子E2相关因子2（nuclear factor erythroid 2-related factor 2, Nrf2）表达，并降低其氧化应激水平。在HK-2细胞中，4-OI可减少高糖诱导的线粒体活性氧（reactive oxygen species, ROS）生成，而<i>Nrf2</i>基因沉默可逆转这一效应。<i>Nrf2</i>基因敲除同样可抑制4-OI介导的PGC-1α、TFAM及线粒体凋亡蛋白表达调控。**研究结论**：4-OI可通过激活Nrf2并促进PGC-1α介导的线粒体生物发生，减轻db/db小鼠的肾小管损伤。