Ferroptosis is a phospholipid peroxidation-mediated and iron-dependent cell death form, involved in sepsis-induced organ injury and other lung diseases. Yes-associated protein 1 (YAP1), a key regulator of the Hippo signaling pathway, could target multiple ferroptosis regulators. Herein, this study aimed to explore the involvement of ferroptosis in the etiopathogenesis of sepsis-induced acute lung injury (ALI) and demonstrate that YAP1 could disrupt ferritinophagy and moderate sepsis-induced ALI. Cecal ligation and puncture (CLP) models were constructed in wild-type (WT) and pulmonary epithelium-conditional knockout (YAP1^f/f) mice to induce ALI, while MLE-12 cells with or without YAP1 overexpression were stimulated by lipopolysaccharide (LPS) in vitro. In-vivo modes showed that YAP1 knockout aggravated CLP-induced ALI and also accelerated pulmonary ferroptosis, as presented by the downregulated expression of GPX4, FTH1, and SLC7A11, along with the upregulated expression of SFXN1 and NCOA4. Transcriptome research identified these key genes and ferroptosis pathways involved in sepsis-induced ALI. In-vitro modes consistently verified that YAP1 deficiency boosted the ferrous iron accumulation and mitochondrial dysfunction in response to LPS. Furthermore, the co-IP assay revealed that YAP1 overexpression could prevent the degradation of ferritin to a mass of Fe²⁺ (ferritinophagy) via disrupting the NCOA4–FTH1 interaction, which blocked the transport of cytoplasmic Fe²⁺ into the mitochondria via the mitochondrial membrane protein (SFXN1), further reducing the generation of mitochondrial ROS. Therefore, these findings revealed that YAP1 could inhibit ferroptosis in a ferritinophagy-mediated manner, thus alleviating sepsis-induced ALI, which may provide a new approach to the therapeutic orientation for sepsis-induced ALI.

Kidney is one of the most vulnerable organs in sepsis, resulting in sepsis-associated acute kidney injury (SA-AKI), which brings about not only morbidity but also mortality of sepsis. Ferroptosis is a new kind of death type of cells elicited by iron-dependent lipid peroxidation, which participates in pathogenesis of sepsis. The aim of this study was to verify the occurrence of ferroptosis in the SA-AKI pathogenesis and demonstrate that post-treatment with irisin could restrain ferroptosis and alleviate SA-AKI via activating the SIRT1/Nrf2 signaling pathway. We established a SA-AKI model by cecal ligation and puncture (CLP) operation and an in vitro model in LPS-induced HK2 cells, respectively. Our result exhibited that irisin inhibited the level of ferroptosis and ameliorated kidney injury in CLP mice, as evidenced by reducing the ROS production, iron content, and MDA level and increasing the GSH level, as well as the alteration of ferroptosis-related protein (GPX4 and ACSL4) expressions in renal, which was consistent with the ferroptosis inhibitor ferrostatin-1 (Fer-1). Additionally, we consistently observed that irisin inhibited ROS accumulation, iron production, and ameliorated mitochondrial dysfunction in LPS-stimulated HK-2 cells. Furthermore, our result also revealed that irisin could activate SIRT1/Nrf2 signaling pathways both in vivo and vitro. However, the beneficial effects of irisin were weakened by EX527 (an inhibitor of SIRT1) in vivo and by SIRT1 siRNA in vitro. In conclusion, irisin could protect against SA-AKI through ferroptotic resistance via activating the SIRT1/Nrf2 signaling pathway.

The balance between M1 and M2 macrophage polarization is involved in the regulation of pulmonary inflammation. Nuclear factor erythroid-derived 2-like 2 (Nfe2l2, also known as Nrf2), a nuclear transcription factor, is reported to play protective roles in acute lung injury (ALI) and inflammation, and increasing evidence indicates that the protective effects of Nrf2 are closely related to autophagy. This study aimed to explore whether Nrf2 is involved in sepsis-induced acute pulmonary injury and inflammation and in the role of macrophage polarization in the process. In the present study, sepsis patients, an Nrf2 knockout mouse that underwent cecal ligation and puncture (CLP), and lipopolysaccharide (LPS)-treated macrophage cell lines were employed to investigate the potential functions of Nrf2 in sepsis-induced lung injury and the underlying mechanisms. Clinical studies showed that the NRF2 mRNA level was inversely correlated with pulmonary inflammation and disease severity in patients with sepsis. Analyses in a CLP-treated Nrf2 knockout mouse model indicated that an Nrf2 deficiency promoted a CLP-induced increase in M1 macrophage polarization and apoptosis and inhibited CLP-induced upregulation of the autophagy level in lung tissues. Experiments in RAW264.7 cells revealed that Nrf2 overexpression inhibited M1 macrophage polarization but promoted M2 macrophage polarization by improving the autophagy, and Nrf2 overexpression promoted PPARγ but inhibited NF-κB nuclear translocation. In conclusion, these results indicate that Nrf2 plays a protective role in sepsis-induced pulmonary injury and inflammation through the regulation of autophagy- and NF-κB/PPARγ-mediated macrophage polarization.

Background: The liver plays crucial roles in sepsis and is one of the major targets for sepsis-related injuries. Ferroptosis, a newly emerged form of lytic cell death, has been implicated in sepsis related organ failure. Yes-associated protein1 (YAP1), a key regulator of the Hippo signaling pathway, may be involved in ferroptosis development. This study aimed to elucidate the role of YAP1 in septic liver injury through regulating ferroptosis, especially ferritinophagy-mediated ferroptosis. Results: Cecal ligation and puncture (CLP) models were constructed in control (Yap1^flfl) and liver-conditional knockout mice (Yap1^fl/fl Alb-Cre) to induce septic liver injury, while LO2 cells with or without YAP1 overexpression/deletion were stimulated by lipopolysaccharide (LPS) in vitro. Our study showed YAP1 knockdown aggravated CLP-induced liver injury and inflammation, as well as accelerated hepatocyte ferroptosis, revealed by down-regulated expression of GPX4, FTH1 and SLC7A11, along with up-regulated expression of SFXN1 and NCOA4. Consistently, YAP1 deficiency aggravated LO2 cells ferroptosis, but YAP1 overexpression alleviated LPS-induced LO2 ferritinophagy, as evidenced by reduced mitochondrial ROS and Fe²⁺, along with down-regulated expression of SFXN1 and NCOA4. Further co-IP assay verified that YAP1 disrupted the interaction between NCOA4 and FTH1, thus prevent the degradation of ferritin to Fe²⁺, further reduced the ROS production and suppressed ferroptosis. Conclusion: YAP1 inhibits ferritinophagy-mediated ferroptosis in hepatocytes, and YAP1 deficiency aggravates sepsis-induced liver injury.