Fin56-induced ferroptosis is supported by autophagy-mediated GPX4 degradation and functions synergistically with mTOR inhibition to kill bladder cancer cells

Ferroptosis is a form of regulated cell death that emerges to be relevant for therapy-resistant and dedifferentiating cancers. Although several lines of evidence suggest that ferroptosis is a type of autophagy-dependent cell death, the underlying molecular mechanisms remain unclear. Fin56, a type 3 ferroptosis inducer, triggers ferroptosis by promoting glutathione peroxidase 4 (GPX4) protein degradation via a not fully understood pathway. Here, we determined that Fin56 induces ferroptosis and autophagy in bladder cancer cells and that Fin56-triggered ferroptosis mechanistically depends on the autophagic machinery. Furthermore, we found that autophagy inhibition at different stages attenuates Fin56-induced oxidative stress and GPX4 degradation. Moreover, we investigated the effects of Fin56 in combination with Torin 2, a potent mTOR inhibitor used to activate autophagy, on cell viability. We found that Fin56 synergizes with Torin 2 in cytotoxicity against bladder cancer cells. Collectively, our findings not only support the concept that ferroptosis is a type of autophagy-dependent cell death but imply that the combined application of ferroptosis inducers and mTOR inhibitors is a promising approach to improve therapeutic options in the treatment of bladder cancer.Subject terms: Macroautophagy, Macroautophagy     

Ghrelin induces autophagy and CXCR4 expression via the SIRT1/AMPK axis in lymphoblastic leukemia cell lines

T cell acute lymphoblastic leukemia (T-ALL) is one of the most frequent malignancies in children, and the CXCR4 receptor plays an important role in the metastasis of this malignancy. Ghrelin is a hormone with various functions including stimulation of the release of growth hormone and autophagy in cancer cells. Moreover, SIRT1 and AMPK (AMP-activated protein kinase) stimulate expression of proteins involved in autophagy. On the other hand, autophagic cell death can be an alternative target for cancer therapy, in the absence of apoptosis. The relationship between ghrelin and the SIRT1/AMPK axis and the resulting effects on autophagy, apoptosis, proliferation, and expression of CXCR4 and the ghrelin receptor (GHS-R1a), in Jurkat and Molt-4 human lymphoblastic cell lines was not previously clear. Here we demonstrate that SIRT1 expression is upregulated during the induction of autophagy by ghrelin, an effect that is inhibited by inactivation of SIRT1/AMPK axis. In addition, ghrelin can affect CXCR4 and GHS-R1a expression. In conclusion, this work reveals that ghrelin induces autophagy, invasion, and downregulation of ghrelin receptor expression via the SIRT1/AMPK axis in lymphoblastic cell lines. However, in these cell lines ghrelin-induced autophagy does not lead to cell death due to weak induction of apoptosis.     

GSTZ1 sensitizes hepatocellular carcinoma cells to sorafenib-induced ferroptosis via inhibition of NRF2/GPX4 axis

Increasing evidence supports that ferroptosis plays an important role in tumor growth inhibition. Sorafenib, originally identified as an inhibitor of multiple oncogenic kinases, has been shown to induce ferroptosis in hepatocellular carcinoma (HCC). However, some hepatoma cell lines are less sensitive to sorafenib-induced ferroptotic cell death. Glutathione S-transferase zeta 1 (GSTZ1), an enzyme in the catabolism of phenylalanine, suppresses the expression of the master regulator of cellular redox homeostasis nuclear factor erythroid 2-related factor 2 (NRF2). This study aimed to investigate the role and underlying molecular mechanisms of GSTZ1 in sorafenib-induced ferroptosis in HCC. GSTZ1 was significantly downregulated in sorafenib-resistant hepatoma cells. Mechanistically, GSTZ1 depletion enhanced the activation of the NRF2 pathway and increased the glutathione peroxidase 4 (GPX4) level, thereby suppressing sorafenib-induced ferroptosis. The combination of sorafenib and RSL3, a GPX4 inhibitor, significantly inhibited GSTZ1-deficient cell viability and promoted ferroptosis and increased ectopic iron and lipid peroxides. In vivo, the combination of sorafenib and RSL3 had a synergic therapeutic effect on HCC progression in Gstz1^−/− mice. In conclusion, this finding demonstrates that GSTZ1 enhanced sorafenib-induced ferroptosis by inhibiting the NRF2/GPX4 axis in HCC cells. Combination therapy of sorafenib and GPX4 inhibitor RSL3 may be a promising strategy in HCC treatment.Subject terms: Cancer therapeutic resistance, Cancer therapeutic resistance     

Acid sphingomyelinase-dependent autophagic degradation of GPX4 is critical for the execution of ferroptosis

Ferroptosis is a type of regulated cell death characterized by ROS accumulation and devastating lipid peroxidation (LPO). The role of acid sphingomyelinase (ASM), a key enzyme in sphingolipid metabolism, in the induction of apoptosis has been studied; however, to date its role in ferroptosis is unclear. In this study, we report that ASM plays a hitherto unanticipated role in promoting ferroptosis. Mechanistically, Erastin (Era) treatment results in the activation of ASM and generation of ceramide, which are required for the Era-induced reactive oxygen species (ROS) generation and LPO. Inhibition of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) or removal of intracellular ROS, significantly reduced Era-induced ASM activation, suggesting that NADPH oxidase-derived ROS regulated ASM-initiated redox signaling in a positive feedback manner. Moreover, ASM-mediated activation of autophagy plays a critical role in ferroptosis inducers (FINs)-induced glutathione peroxidase 4 (GPX4) degradation and ferroptosis activation. Genetic or pharmacological inhibition of ASM diminishes Era-induced features of autophagy, GPX4 degradation, LPO, and subsequent ferroptosis. Importantly, genetic activation of ASM increases ferroptosis in cancer cells induced by various FINs. Collectively, these findings reveal that ASM plays a novel role in ferroptosis that could be exploited to improve pathological conditions that link to ferroptosis.Subject terms: Lipid peroxides, Cancer models, Macroautophagy, Lipid signalling     

Ezetimibe ameliorates steatohepatitis via AMP activated protein kinase-TFEB-mediated activation of autophagy and NLRP3 inflammasome inhibition

Impairment in macroautophagy/autophagy flux and inflammasome activation are common characteristics of nonalcoholic steatohepatitis (NASH). Considering the lack of approved agents for treating NASH, drugs that can enhance autophagy and modulate inflammasome pathways may be beneficial. Here, we investigated the novel mechanism of ezetimibe, a widely prescribed drug for hypercholesterolemia, as a therapeutic option for ameliorating NASH. Human liver samples with steatosis and NASH were analyzed. For in vitro studies of autophagy and inflammasomes, primary mouse hepatocytes, human hepatoma cells, mouse embryonic fibroblasts with Ampk or Tsc2 knockout, and human or primary mouse macrophages were treated with ezetimibe and palmitate. Steatohepatitis and fibrosis were induced by feeding Atg7 wild-type, haploinsufficient, and knockout mice a methionine- and choline-deficient diet with ezetimibe (10 mg/kg) for 4 wk. Human livers with steatosis or NASH presented impaired autophagy with decreased nuclear TFEB and increased SQSTM1, MAP1LC3-II, and NLRP3 expression. Ezetimibe increased autophagy flux and concomitantly ameliorated lipid accumulation and apoptosis in palmitate-exposed hepatocytes. Ezetimibe induced AMPK phosphorylation and subsequent TFEB nuclear translocation, related to MAPK/ERK. In macrophages, ezetimibe blocked the NLRP3 inflammasome-IL1B pathway in an autophagy-dependent manner and modulated hepatocyte-macrophage interaction via extracellular vesicles. Ezetimibe attenuated lipid accumulation, inflammation, and fibrosis in liver-specific Atg7 wild-type and haploinsufficient mice, but not in knockout mice. Ezetimibe ameliorates steatohepatitis by autophagy induction through AMPK activation and TFEB nuclear translocation, related to an independent MTOR ameliorative effect and the MAPK/ERK pathway. Ezetimibe dampens NLRP3 inflammasome activation in macrophages by modulating autophagy and a hepatocyte-driven exosome pathway.     

Resveratrol attenuates vascular endothelial inflammation by inducing autophagy through the cAMP signaling pathway

Inflammation participates centrally in all stages of atherosclerosis (AS), which begins with inflammatory changes in the endothelium, characterized by expression of the adhesion molecules. Resveratrol (RSV) is a naturally occurring phytoalexin that can attenuate endothelial inflammation; however, the exact mechanisms have not been thoroughly elucidated. Autophagy refers to the normal process of cell degradation of proteins and organelles, and is protective against certain inflammatory injuries. Thus, we intended to determine the role of autophagy in the antiinflammatory effects of RSV in human umbilical vein endothelial cells (HUVECs). We found that RSV pretreatment reduced tumor necrosis factor α (TNF/TNFα)-induced inflammation and increased MAP1LC3B2 (microtubule-associated protein 1 light chain 3 β 2) expression and SQSTM1/p62 (sequestosome 1) degradation in a concentration-dependent manner. A bafilomycin A₁ (BafA1) challenge resulted in further accumulation of MAP1LC3B2 in HUVECs. Furthermore, autophagy inhibitors 3-methyladenine (3-MA), chloroquine as well as ATG5 and BECN1 siRNA significantly attenuated RSV-induced autophagy, which, subsequently, suppressed the downregulation of RSV-induced inflammatory factors expression. RSV also increased cAMP (cyclic adenosine monophosphate) content, the expression of PRKA (protein kinase A) and SIRT1 (sirtuin 1), as well as the activity of AMPK (AMP-activated protein kinase). RSV-induced autophagy in HUVECs was abolished in the presence of inhibitors of ADCY (adenylyl cyclase, KH7), PRKA (H-89), AMPK (compound C), or SIRT1 (nicotinamide and EX-527), as well as ADCY, PRKA, AMPK, and SIRT1 siRNA transfection, indicating that the effects of RSV on autophagy induction were dependent on cAMP, PRKA, AMPK and SIRT1. In conclusion, RSV attenuates endothelial inflammation by inducing autophagy, and the autophagy in part was mediated through the activation of the cAMP-PRKA-AMPK-SIRT1 signaling pathway.     

Resveratrol-activated AMPK/SIRT1/autophagy in cellular models of Parkinson's disease

Excessive misfolded proteins and/or dysfunctional mitochondria, which may cause energy deficiency, have been implicated in the etiopathogenesis of Parkinson's disease (PD). Enhanced clearance of misfolded proteins or injured mitochondria via autophagy has been reported to have neuroprotective roles in PD models. The fact that resveratrol is a known compound with multiple beneficial effects similar to those associated with energy metabolism led us to explore whether neuroprotective effects of resveratrol are related to its role in autophagy regulation. We tested whether modulation of mammalian silent information regulator 2 (SIRT1) and/or metabolic energy sensor AMP-activated protein kinase (AMPK) are involved in autophagy induction by resveratrol, leading to neuronal survival. Our results showed that resveratrol protected against rotenone-induced apoptosis in SH-SY5Y cells and enhanced degradation of α-synucleins in α-synuclein-expressing PC12 cell lines via autophagy induction. We found that suppression of AMPK and/or SIRT1 caused decrease of protein level of LC3-II, indicating that AMPK and/or SIRT1 are required in resveratrol-mediated autophagy induction. Moreover, suppression of AMPK caused inhibition of SIRT1 activity and attenuated protective effects of resveratrol on rotenone-induced apoptosis, further suggesting that AMPK-SIRT1-autophagy pathway plays an important role in the neuroprotection by resveratrol on PD cellular models.     

DGKζ depletion attenuates HIF-1α induction and SIRT1 expression,but enhances TAK1-mediated AMPKα phosphorylation under hypoxia

Cells cope with environmental changes through various mechanisms. Pathways involving HIF-1, SIRT1, and AMPK play major roles in energy homeostasis under stress conditions. Diacylglycerol kinase (DGK) constitutes an enzyme family that catalyzes conversion of diacylglycerol to phosphatidic acid. We reported earlier that energy depletion such as ischemia induces proteasomal degradation of DGKζ before cell death, suggesting involvement of DGKζ in energy homeostasis. This study examines how DGKζ depletion affects the regulation of HIF-1α, SIRT1, and AMPKα. Under hypoxia DGKζ depletion attenuates HIF-1α induction and SIRT1 expression, which might render cells vulnerable to energy stress. However, DGKζ depletion engenders enhanced AMPKα phosphorylation by upstream kinase TAK1 and an increase in intracellular ATP levels. Results suggest that DGKζ exerts a suppressive effect on TAK1 activity in the AMPK activation mechanism, and that DGKζ depletion might engender dysregulation of the AMPK-mediated energy sensor system.     

Aberrant SIRT6 expression contributes to melanoma growth: Role of the autophagy paradox and IGF-AKT signaling

Melanoma is among the most life-threatening cancers. The pathogenesis of melanoma has not been fully elucidated. Recently, dysregulated macroautophagy/autophagy has been found to play a critical but inconsistent role in modulating melanoma growth at different stages, with the regulatory mechanism unclear. The histone deacetylase SIRT6 (sirtuin 6) is a known autophagy regulator, and its involvement in cancer development has been reported. Therefore, we sought to determine the role of SIRT6 in melanoma growth and detect its possible link with autophagy in the current study. We initially observed that the expression of SIRT6 decreased in primary melanoma but increased in metastatic melanoma compared with melanocytic nevus. Notably, the expression of SIRT6 was significantly correlated with the expression of autophagy biomarkers including MAP1LC3/LC3 and SQSTM1/p62. Furthermore, SIRT6 suppressed the growth of primary melanoma but promoted metastatic melanoma development in an autophagy-dependent way in vitro. Moreover, SIRT6 exerted its regulation on melanoma growth via the IGF-AKT signaling pathway, and the intervention of AKT could partly reverse the effects of SIRT6 on melanoma growth by regulating autophagy. At last, we determined the effects of SIRT6 on melanoma development in vivo. Taken together, our findings demonstrate that the bimodal expression of SIRT6 at different melanoma stages plays a critical role in regulating melanoma growth through an autophagy-dependent manner, which indicates the potential of SIRT6 to be a biomarker and a therapeutic target in melanoma.     

肿瘤细胞死亡的一种新形式——铁死亡

铁死亡是近年来发现的一种程序性细胞死亡新形式,其主要特征是在发生于线粒体内的铁依赖性脂质过氧化物损伤诱导的细胞死亡。铁死亡细胞在形态、蛋白质及基因水平的变化均不同于细胞凋亡、坏死和自噬。2012年,铁死亡概念首次被提出后,铁死亡逐渐成为科学研究的热点。Erastin以及RSL3是铁死亡的诱导剂,谷胱甘肽过氧化物酶4（glutathione peroxidase 4,GPX4）是铁死亡的关键调节点,GPX4的表达量减少或活性降低均可诱导铁死亡的发生。胱氨酸-谷氨酸逆向转运蛋白（system Xc^-）可将细胞内的谷氨酸排出,同时将细胞外胱氨酸转运入细胞内,促进细胞内谷胱甘肽的合成,维持GPX4酶的活性。新近的研究表明,p62-keap1-Nrf2、P53-SAT1-ALOX15是铁死亡的关键调控通路,p53、BECN1以及BAP1是铁死亡的关键调节因子。Erastin以及RSL3可以选择性杀死RAS突变的肿瘤细胞,且越来越多的研究也证明,诱导肿瘤细胞铁死亡在免疫治疗以及逆转耐药方面均有着重要作用。因此,调控肿瘤细胞铁死亡很可能成为治疗肿瘤的新手段。本文就诱导肿瘤细胞铁死亡的机制及其进展作一综述。     

肿瘤细胞死亡的一种新形式——铁死亡

铁死亡是近年来发现的一种程序性细胞死亡新形式,其主要特征是在发生于线粒体内的铁依赖性脂质过氧化物损伤诱导的细胞死亡。铁死亡细胞在形态、蛋白质及基因水平的变化均不同于细胞凋亡、坏死和自噬。2012年,铁死亡概念首次被提出后,铁死亡逐渐成为科学研究的热点。Erastin以及RSL3是铁死亡的诱导剂,谷胱甘肽过氧化物酶4（glutathione peroxidase 4,GPX4）是铁死亡的关键调节点,GPX4的表达量减少或活性降低均可诱导铁死亡的发生。胱氨酸-谷氨酸逆向转运蛋白（system Xc^-）可将细胞内的谷氨酸排出,同时将细胞外胱氨酸转运入细胞内,促进细胞内谷胱甘肽的合成,维持GPX4酶的活性。新近的研究表明,p62-keap1-Nrf2、P53-SAT1-ALOX15是铁死亡的关键调控通路,p53、BECN1以及BAP1是铁死亡的关键调节因子。Erastin以及RSL3可以选择性杀死RAS突变的肿瘤细胞,且越来越多的研究也证明,诱导肿瘤细胞铁死亡在免疫治疗以及逆转耐药方面均有着重要作用。因此,调控肿瘤细胞铁死亡很可能成为治疗肿瘤的新手段。本文就诱导肿瘤细胞铁死亡的机制及其进展作一综述。     

Ferroptosis: Role of lipid peroxidation,iron and ferritinophagy

Ferroptosis is a form of regulated cell death that is dependent on iron and reactive oxygen species (ROS) and is characterized by lipid peroxidation. It is morphologically and biochemically distinct and disparate from other processes of cell death. As ferroptosis is induced by inhibition of cysteine uptake or inactivation of the lipid repair enzyme glutathione peroxidase 4 (GPX4), the process is favored by chemical or mutational inhibition of the cystine/glutamate antiporter and culminates in the accumulation of reactive oxygen species (ROS) in the form of lipid hydroperoxides. Excessive lipid peroxidation leads to death by ferroptosis and the phenotype is accentuated respectively by the repletion and depletion of iron and glutathione in cells. Furthermore, oxidized phosphatidylethanolamines (PE) harbouring arachidonoyl (AA) and adrenoyl moieties (AdA) have been shown as proximate executioners of ferroptosis. Induction of ferroptosis due to cysteine depletion leads to the degradation of ferritin (i.e. ferritinophagy), which releases iron via the NCOA4-mediated autophagy pathway. Evidence of the manifestation of ferroptosis in vivo in iron overload mice mutants is emerging. Thus, a concerted synchronization of iron availability, ROS generation, glutamate excess and cysteine deficit leads to ferroptosis. A number of questions on the molecular mechanisms of some features of ferroptosis are highlighted as subjects for future investigations.     

Saikosaponin A alleviates Staphylococcus aureus-induced mastitis in mice by inhibiting ferroptosis via SIRT1/Nrf2 pathway

Mastitis is a common and serious bacterial infection of the mammary gland. Saikosaponin A (SSA) is a triterpenoid saponin isolated from Bupleurum falcatum that has the ability to treat various diseases. However, little is known about the role of SSA in achieving mastitis remission. Here, we found that SSA alleviated Staphylococcus aureus (S. aureus)-induced mastitis by attenuating inflammation and maintaining blood-milk barrier integrity. Furthermore, S. aureus activated nuclear factor kappa B (NF-κB) pathway by upregulated p-p65 and p-IκB. S. aureus also induced ferroptosis in mammary gland in mice, mainly characterized by excessive iron accumulation, mitochondrial morphological changes and impaired antioxidant production. However, S. aureus-induced NF-κB activation and ferroptosis were prevented by SSA. Moreover, SAA could upregulate the expression of SIRT1, Nrf2, HO-1 and GPX4. And the inhibitory effects of SAA on inflammation and ferroptosis were reversed by SIRT1 inhibitor EX-527. In conclusion, SAA protected S. aureus-induced mastitis through suppressing inflammation and ferroptosis by activating SIRT1/Nrf2 pathway.     

WNK1 is an unexpected autophagy inhibitor

Autophagy is a cellular degradation pathway that is essential to maintain cellular physiology, and deregulation of autophagy leads to multiple diseases in humans. In a recent study, we discovered that the protein kinase WNK1 (WNK lysine deficient protein kinase 1) is an inhibitor of autophagy. The loss of WNK1 increases both basal and starvation-induced autophagy. In addition, the depletion of WNK1 increases the activation of the class III phosphatidylinositol 3-kinase (PtdIns3K) complex, which is required to induce autophagy. Moreover, the loss of WNK1 increases the expression of ULK1 (unc-51 like kinase 1), which is upstream of the PtdIns3K complex. It also increases the pro-autophagic phosphorylation of ULK1 at Ser555 and the activation of AMPK (AMP-activated protein kinase), which is responsible for that phosphorylation. The inhibition of AMPK by compound C decreases the magnitude of autophagy induction following WNK1 loss; however, it does not prevent autophagy induction. We found that the UVRAG (UV radiation resistance associated gene), which is a component of the PtdIns3K, binds to the N-terminal region of WNK1. Moreover, WNK1 partially colocalizes with UVRAG and this colocalization decreases when autophagy is stimulated in cells. The loss of WNK1 also alters the cellular distribution of UVRAG. The depletion of the downstream target of WNK1, OXSR1/OSR1 (oxidative-stress responsive 1) has no effect on autophagy, whereas the depletion of its relative STK39/SPAK (serine/threonine kinase 39) induces autophagy under nutrient-rich and starved conditions.     

Proline dehydrogenase (oxidase), a mitochondrial tumor suppressor, and autophagy under the hypoxia microenvironment

Proline dehydrogenase (oxidase, PRODH/POX), the first enzyme in the pathway of proline catabolism, has been identified as a mitochondrial, metabolic tumor suppressor, which is downregulated in a variety of human tumors. However, our recent findings show that PRODH/POX is upregulated by hypoxia in vitro and in vivo. The combination of low glucose and hypoxia produces additive effects on PRODH/POX expression. Both hypoxia and glucose depletion enhance PRODH/POX expression through AMP-activated protein kinase (AMPK) activation to promote tumor cell survival. Nevertheless, the mechanisms underlying PRODH/POX prosurvival functions are different for hypoxia and low-glucose conditions. Glucose depletion with or without hypoxia elevates PRODH/POX and proline utilization to supply ATP for cellular energy needs. Interestingly, under hypoxia PRODH/POX induces protective autophagy by generating reactive oxygen species (ROS). AMPK is the main initiator of stress-triggered autophagy. Thus, PRODH/POX acts as a downstream effector of AMPK in the activation of autophagy under hypoxia. This regulation was confirmed to be independent of the mechanistic target of rapamycin (MTOR) pathway, a major downstream target of AMPK signaling.     

Proline dehydrogenase (oxidase), a mitochondrial tumor suppressor,and autophagy under the hypoxia microenvironment

Proline dehydrogenase (oxidase, PRODH/POX), the first enzyme in the pathway of proline catabolism, has been identified as a mitochondrial, metabolic tumor suppressor, which is downregulated in a variety of human tumors. However, our recent findings show that PRODH/POX is upregulated by hypoxia in vitro and in vivo. The combination of low glucose and hypoxia produces additive effects on PRODH/POX expression. Both hypoxia and glucose depletion enhance PRODH/POX expression through AMP-activated protein kinase (AMPK) activation to promote tumor cell survival. Nevertheless, the mechanisms underlying PRODH/POX prosurvival functions are different for hypoxia and low-glucose conditions. Glucose depletion with or without hypoxia elevates PRODH/POX and proline utilization to supply ATP for cellular energy needs. Interestingly, under hypoxia PRODH/POX induces protective autophagy by generating reactive oxygen species (ROS). AMPK is the main initiator of stress-triggered autophagy. Thus, PRODH/POX acts as a downstream effector of AMPK in the activation of autophagy under hypoxia. This regulation was confirmed to be independent of the mechanistic target of rapamycin (MTOR) pathway, a major downstream target of AMPK signaling.     

Tetrandrine Ameliorates Traumatic Brain Injury by Regulating Autophagy to Reduce Ferroptosis

Traumatic brain injury (TBI) is the leading cause of death and disability in trauma patients. However, the effects and mechanism of autophagy after TBI remain unclear. This study aimed to investigate whether tetrandrine could ameliorate TBI through autophagy to reduce ferroptosis. A mice model for TBI was implemented. Behavioral and histomorphological experiments were performed to evaluate outcomes of the mice. The ferroptosis levels was detected by Perls staining. Enzyme-linked immunosorbent assay (ELISA) was applied to detect malondialdehyde (MDA), glutathione (GSH), and glutathione peroxidase 4 (GPX4) levels in the brain tissue. Western blot test was performed to detect Beclin 1, light chain 3 (LC3) II/I, p62, GPX4, SCL7A11, and ferritin heavy chain 1 (FTH1) levels, and the expression of LC3B, Beclin 1, GPX4, and FTH1 in the brain tissue was detected by immunofluorescence (IF). The behavioral and histomorphological results demonstrated that tetrandrine improved the neurological function and cerebral edema on days 1, 3, and 7 after TBI. The ELISA results suggested that tetrandrine reduced the MDA concentration and increased GSH concentration on days 1, 3, and 7 after TBI. IF staining and Perls staining reflected that tetrandrine promoted autophagy and inhibited ferroptosis on days 1, 3, and 7 after TBI, respectively. Tetrandrine further improved the neurological function, cerebral edema, autophagy, and ferroptosis on days 1, 3, and 7 after TBI after adding the autophagy inducer rapamycin. The effect of TET in alleviating TBI increased with the increase of time and dose. Tetrandrine ameliorated TBI by regulating autophagy to reduce ferroptosis, providing a new therapeutic strategy for TBI.

     

Autophagy induction by xanthoangelol exhibits anti‐metastatic activities in hepatocellular carcinoma

Xanthoangelol (XAG), a prenylated chalcone isolated from the Japanese herb Angelica keiskei Koidzumi, has been reported to exhibit antineoplastic properties. However, the specific anti‐tumor activity of XAG in human hepatocellular carcinoma (HCC), and the relevant mechanisms are not known. Herein, we evaluated the effect of XAG against HCC in vitro and in vivo. Although XAG treatment did not significantly reduce the viability of the Hep3B and Huh7 cell lines, it suppressed cell migration, invasion, and EMT. This anti‐metastatic effect of XAG was due to induction of autophagy, because treatment with the autophagy inhibitor 3‐methyadenine (3‐MA) or knockdown of the pro‐autophagy Beclin‐1 effectively abrogated the XAG‐induced suppression of metastasis. Mechanistically, XAG induced autophagy via activation of the AMPK/mTOR signaling pathway, and XAG treatment dramatically increased the expression of p‐AMPK while decreasing p‐mTOR expression. In addition, blocking AMPK/mTOR axis with compound C abrogated the autophagy‐mediated inhibition of metastasis. The murine model of HCC metastasis also showed that XAG effectively reduced the number of metastatic pulmonary nodules. Taken together, our results revealed that autophagy via the activation of AMPK/mTOR pathway is essential for the anti‐metastatic effect of XAG against HCC. These findings not only contribute to our understanding of the anti‐tumor activity of XAG but also provide a basis for its clinical application in HCC. Before this study, evidence of XAG on HCC was purely anecdotal; present study provides the first comprehensive assessments of XAG on HCC metastasis and investigates its underlying mechanism. Results suggest that XAG exerts anti‐metastatic properties against HCC through inducing autophagy which is mediated by the activation of AMPK/mTOR signaling pathway. This research extends our knowledge about the antineoplastic properties of XAG and suggests that induction autophagy may represent future treatment strategies for metastatic HCC.     

Legumain promotes tubular ferroptosis by facilitating chaperone-mediated autophagy of GPX4 in AKI

Legumain is required for maintenance of normal kidney homeostasis. However, its role in acute kidney injury (AKI) is still unclear. Here, we induced AKI by bilateral ischemia-reperfusion injury (IRI) of renal arteries or folic acid in lgmn^WT and lgmn^KO mice. We assessed serum creatinine, blood urea nitrogen, histological indexes of tubular injury, and expression of KIM-1 and NGAL. Inflammatory infiltration was evaluated by immunohistological staining of CD3 and F4/80, and expression of TNF-α, CCL-2, IL-33, and IL-1α. Ferroptosis was evaluated by Acsl4, Cox-2, reactive oxygen species (ROS) indexes H₂DCFDA and DHE, MDA and glutathione peroxidase 4 (GPX4). We induced ferroptosis by hypoxia or erastin in primary mouse renal tubular epithelial cells (mRTECs). Cellular survival, Acsl4, Cox-2, LDH release, ROS, and MDA levels were measured. We analyzed the degradation of GPX4 through inhibition of proteasomes or autophagy. Lysosomal GPX4 was assessed to determine GPX4 degradation pathway. Immunoprecipitation (IP) was used to determine the interactions between legumain, GPX4, HSC70, and HSP90. For tentative treatment, RR-11a was administrated intraperitoneally to a mouse model of IRI-induced AKI. Our results showed that legumain deficiency attenuated acute tubular injury, inflammation, and ferroptosis in either IRI or folic acid-induced AKI model. Ferroptosis induced by hypoxia or erastin was dampened in lgmn^KO mRTECs compared with lgmn^WT control. Deficiency of legumain prevented chaperone-mediated autophagy of GPX4. Results of IP suggested interactions between legumain, HSC70, HSP90, and GPX4. Administration of RR-11a ameliorated ferroptosis and renal injury in the AKI model. Together, our data indicate that legumain promotes chaperone-mediated autophagy of GPX4 therefore facilitates tubular ferroptosis in AKI.Subject terms: Necroptosis, Glomerulus, Acute kidney injury     

Cellular degradation systems in ferroptosis

In eukaryotic cells, macromolecular homeostasis requires selective degradation of damaged units by the ubiquitin-proteasome system (UPS) and autophagy. Thus, dysfunctional degradation systems contribute to multiple pathological processes. Ferroptosis is a type of iron-dependent oxidative cell death driven by lipid peroxidation. Various antioxidant systems, especially the system xc⁻-glutathione-GPX4 axis, play a significant role in preventing lipid peroxidation-mediated ferroptosis. The endosomal sorting complex required for transport-III (ESCRT-III)–dependent membrane fission machinery counteracts ferroptosis by repairing membrane damage. Moreover, cellular degradation systems play a dual role in regulating the ferroptotic response, depending on the cargo they degrade. The key ferroptosis repressors, such as SLC7A11 and GPX4, are degraded by the UPS. In contrast, the overactivation of selective autophagy, including ferritinophagy, lipophagy, clockophagy and chaperone-mediated autophagy, promotes ferroptotic death by degrading ferritin, lipid droplets, circadian proteins, and GPX4, respectively. Autophagy modulators (e.g., BECN1, STING1/TMEM173, CTSB, HMGB1, PEBP1, MTOR, AMPK, and DUSP1) also determine the ferroptotic response in a context-dependent manner. In this review, we provide an updated overview of the signals and mechanisms of the degradation system regulating ferroptosis, opening new horizons for disease treatment strategies.Subject terms: Cell biology, Molecular biology