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Graphical abstract A proposed model illustrating the therapeutic effect of QCT on AKI. QCT inhibits the expression of ATF3. While ATF3 blocks the system Xc-, and then suppresses GPX4, inducing ferroptosis. In another side, ferroptotic cells secrete chemokines like CCL2, CCL7, induce the recruitment of macrophages, and then cause the inflammation in AKI. In summary, QCT ameliorates AKI through the inhibition on ferroptosis and the following inflammation., Highlights • Quercetin (QCT) inhibits ferroptosis but not apoptosis, necrosis or autophagy of renal proximal tubular epithelial cells, and ameliorates AKI induced by ischemia–reperfusion (I/R) or folic acid (FA). • Activation transcription factor 3 (ATF3) plays an important role in cell ferroptosis, while QCT significantly inhibits the expression of ATF3 and further blocks the downstream signaling pathway of ferroptosis. • Ferroptotic cells induce the recruitment and chemotaxis of macrophages through CCL2, triggering inflammation and enhancing tissue injury., Introduction Ferroptosis is an iron-dependent regulated necrosis and has been proven to contribute to the progress of acute kidney injury (AKI). Quercetin (QCT), a natural flavonoid which is commonly found in numerous fruits and vegetables, has extensive pharmacological effects, such as anti-oxidant, anti-inflammatory and anti-senescence effects. Objectives This study aims to explain whether ferroptosis is a therapeutic strategy to AKI, and to explore the effect of QCT on AKI ferroptosis. Methods NRK-52E cells and HK-2 cells were used for in vitro ferroptosis studies. Morphology of cells was detected by transmission electron microscopy. Lipid ROS was assayed using flow cytometry. In vivo, AKI was induced by ischemia–reperfusion (I/R) or folic acid (FA). To explore the molecular mechanisms, RNA-sequence analysis was performed. Transwell was used to detect macrophage migration. Results We discovered that quercetin (QCT), a natural flavonoid, inhibited ferroptosis in renal proximal tubular epithelial cells. QCT blocked the typical morphologic changes of ferroptotic cells by reducing the levels of malondialdehyde (MDA) and lipid ROS and increasing the levels of glutathione (GSH). Moreover, QCT ameliorated AKI induced by I/R or FA. RNA-sequence analysis highlighted activation transcription factor 3 (ATF3), as it was the dominant one among all the 299 down-regulated genes by QCT. Knockdown of ATF3 could significantly increase the levels of SLC7A11, GPX4 and increased the cell viability. In addition, ferroptotic cells were found to be extremely pro-inflammatory by recruiting macrophages through CCL2, while QCT inhibited the chemotaxis of macrophages induced by ferroptosis in AKI. Conclusions Collectively, these results identify QCT as a ferroptosis inhibitor and provide new therapeutic strategies for diseases related to ferroptosis.

Interleukin 6 (IL-6) is a pleiotropic cytokine that is elevated in inflammatory bowel disease. However, the role of IL-6 deficiency in colitis is not well-defined. Some IL-6 and IL-6 receptor antagonists are associated with severe gastrointestinal immune adverse effects, but the mechanisms of the effects are not clear. This study aimed to investigate the effect of IL-6 in ulcerative colitis in Il6-/- mice. Results indicated that physiological deficiency of IL-6 promoted the development of colitis. Moreover, IL-6 deficiency significantly increased the mRNA levels of monocytes chemokine Ccl2 and its receptor Ccr2 in colon tissues. Similarly, the percentage of Ly6Chigh monocytes and neutrophils were increased in the colon of Il6-/- mice. Intestinal crypts more strongly increased the migration of Il6-/- macrophages than wild-type ones. Moreover, Il6-/- macrophages promoted the migration of neutrophils. Most importantly, RS102895, an antagonist of CCR2, diminished chemotaxis of macrophages and inhibited colitis in Il6-/- mice. Collectively, these results indicate that Il6-/- macrophages migrate to inflamed colon tissues and recruit neutrophils, thereby promoting the effect of Il6-/- on colitis. This study expands our understanding on the effect of IL-6 deficiency in colitis and the development of gastrointestinal immune adverse effects.

Ferroptosis is a novel type of programmed cell death characterized by iron-dependent accumulation of lipid hydroperoxides to lethal levels. Accumulative studies have indicated diabetic nephropathy (DN) as an inflammatory disorder, which involved immune modulation both in the occurrence and progression of the disease. In addition, DN is also considered as the major threatening complication of Diabetes mellitus (DM). However, other forms of programmed cell death, such as autophagy, apoptosis and necrosis, have been reported to be associated with DN, while there are no effective drugs to alleviate the damage of DN. In this study, we explored whether ferroptosis was involved in the progression of DN both in vivo and in vitro. We first established DN models using streptozotocin (STZ) and db/db mice. Results showed significant changes of ferroptosis associated markers, like increased expression levels of acyl-CoA synthetase long-chain family member 4 (ACSL4) and decreased expression levels of glutathione peroxidase 4 (GPX4) in DN mice. Also lipid peroxidation products and iron content were increased in DN mice. Next, in vitro, ferroptosis inducer erastin or RSL3 could induce renal tubular cell death, while iron and high ACSL4 levels sensitised ferroptosis. Finally, ACSL4 inhibitor rosiglitazone (Rosi) was used in the development of DN, which improved survival rate and kidney function, reduced lipid peroxidation product MDA and iron content. In summary, we first found ferroptosis was involved in DN and ferroptosis might be as a future direction in the treatment of DN.