TNFα-induced lysosomal membrane permeability is downstream of MOMP and triggered by caspase-mediated NDUFS1 cleavage and ROS formation

Oxygen/Nitric Oxide Dual-Releasing Nanozyme for Augmenting TMZ-Mediated Apoptosis and Necrosis

Glioblastoma multiforme (GBM) is the most common and aggressive malignant brain tumor, with a poor prognosis. Temozolomide (TMZ) represents the standard chemotherapy for GBM but has limited efficacy due to poor targeting and a hypoxic tumor microenvironment (TME). To address these challenges, we developed a dual-gas-releasing, cancer-cell-membrane-camouflaged nanoparticle to deliver TMZ. This nanoceria, camouflaged with a cancer cell membrane (CCM-CeO2), targets explicitly GBM cells and accumulates in lysosomes, triggering the rapid release of TMZ. Additionally, CCM-CeO2 could release oxygen (O2) and nitric oxide (NO) in response to the TME. Synthesized using d-arginine, catalytic nanoceria could decompose excessive hydrogen peroxide (H2O2) in the TME to produce O2, while d-arginine could nonenzymatically react with H2O2 to generate NO. CCM-CeO2 could penetrate GBM spheroids to a depth of 148.3 ± 31 μm, with the O2 and NO produced, reducing HIF-1α protein expression. When loaded with TMZ, CCM-CeO2 could increase the intracellular ROS produced by TMZ, leading to lysosome membrane permeabilization and notably augmented apoptosis and necrosis in GBM cells. An in vitro antitumor assay using spheroids showed that CCM-CeO2 reduced the IC50 value of TMZ from 174.5 to 42.6 μg/mL, likely due to the catalase-like activity of nanoceria. These results suggest that alleviating hypoxia and increasing ROS produced by chemotherapeutics could be an effective therapeutic strategy for treating GBM.

Hepatic Alarmins and Mitochondrial Dysfunction under Residual Hyperlipidemic Stress Lead to Irreversible NAFLD

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease (NAFLD) includes a range of progressive disorders generated by excess lipid accumulation in the liver leading to hepatic steatosis and eventually fibrosis. We aimed to identify by high performance mass spectrometry-based proteomics the main signaling pathways and liver proteome changes induced by hypercholesterolemia in a rabbit atherosclerotic model that induced high accumulation of lipids in the liver.

METHODS

The effect of combined lipid-lowering drugs (statins and anti-PCSK9 monoclonal antibody) were used after the interruption of the hypercholesterolemic diet to identify also the potential mediators, such as alarmins, responsible for the irreversible NAFLD build up under the hyperlipidemic sustained stress.

RESULTS

Proteomic analysis revealed a number of proteins whose abundance was altered. They were components of metabolic pathways including fatty-acid degradation, glycolysis/gluconeogenesis, and nonalcoholic fatty liver disease. Mitochondrial dysfunction indicated alteration at the mitochondrial respiratory chain level and down-regulation of NADH: ubiquinone oxidoreductase. The expression of a majority of cytochromes (P4502E1, b5, and c) were up-regulated by lipid-lowering treatment. Long-term hyperlipidemic stress, even with a low-fat diet and lipid-lowering treatment, was accompanied by alarmin release (annexins, galectins, HSPs, HMGB1, S100 proteins, calreticulin, and fibronectin) that generated local inflammation and induced liver steatosis and aggressive fibrosis (by high abundance of galectin 3, fibronectin, and calreticulin).

CONCLUSIONS

The novel findings of this study were related to the residual effects of hyperlipidemic stress with consistent, combined lipid-lowering treatment with statin and inhibitor of PCSK9.

The novel antitumor compound clinopodiside A induces cytotoxicity via autophagy mediated by the signaling of BLK and RasGRP2 in T24 bladder cancer cells

In the study, we investigated the anti-cancer effect of clinopodiside A and the underlying mechanisms using T24 bladder cancer cells as an experimental model. We found that the compound inhibited the growth of the bladder cancer cells in vitro and in vivo in a in a concentration- and dose-dependent manner, respectively, which showed a combinational effect when used together with cisplatin. In the bladder cancer cells, clinopodiside A caused autophagy, which was mediated by the signaling of BLK and RasGRP2, independently. Inhibition of the autophagy by chemical inhibitor 3-methyladenine or by the inhibition of the signaling molecules attenuated the cytotoxicity of clinopodiside A. Further analyses showed that clinopodiside A acted in synergism with cisplatin which itself could trigger both autophagy and apoptosis, which occurred with concomitant enhancements in autophagy and the cisplatin-evoked apoptosis. In conclusion, our results suggest that clinopodiside A inhibits the growth of the bladder cancer cells via BLK- and RasGRP2-mediated autophagy. The synergistic effect between clinopodiside A and cisplatin is attributed to the increases in autophagy and autophagy-promoted apoptosis. Clinopodiside A is a promising investigational drug for the treatment of cancer, at least blabber, which can be used alone or in combination with clinical drug(s).

The Development and Survival of Thymic Epithelial Cells Require TSC1-Dependent Negative Regulation of mTORC1 Activity

Thymic epithelial cells (TECs) are critical for the development and generation of functionally competent T cells. Until now, the mechanism that regulates the survival of TECs is poorly understood. In the current study, we found that Tsc1 controls the homeostasis of medullary TECs (mTECs) by inhibiting lysosomal-mediated apoptosis pathway in mice. TEC-specific deletion of Tsc1 predominately decreased the cell number of mTECs and, to a lesser content, affected the development cortical TECs. The defect of mTECs caused by Tsc1 deficiency in mice impaired thymocyte development and peripheral T cell homeostasis. Mechanistically, Tsc1 deficiency did not affect the cell proliferation of mTECs but increased the apoptosis of mTECs significantly. RNA-sequencing analysis showed that pathways involved in lysosomal biogenesis, cell metabolism, and apoptosis were remarkably elevated in Tsc1-deficient mTECs compared with their wild-type counterparts. Tsc1-deficient mTECs exhibited overproduction of reactive oxygen species and malfunction of lysosome, with lysosome membrane permeabilization and the release of cathepsin B and cathepsin L to the cytosol, which then lead to Bid cleaved into active truncated Bid and subsequently intrinsic apoptosis. Finally, we showed that the impaired development of mTECs could be partially reversed by decreasing mTORC1 activity via haploinsufficiency of Raptor Thus, Tsc1 is essential for the homeostasis of mTECs by inhibiting lysosomal-mediated apoptosis through mTORC1-dependent pathways.

The intrinsic apoptotic pathway lies upstream of oxidative stress in multiple organs

Oxidative stress increases with age in multiple organ systems and is implicated in the development of age-related pathologies in them. Studies from our laboratory show that the intrinsic pathway proapoptotic proteins BAX and caspase-3 (CASP3) lie upstream of mitochondrial production of oxidative stress-inducing reactive species (RS) such as reactive oxygen and reactive nitrogen species (ROS and RNS) in apoptotic and nonapoptotic neurons in cell culture. Our objective in this study was to determine if these findings could be generalized to the development of oxidative stress in nonneuronal tissues in vivo. We first investigated the effect of genetic deletion of Bax on DNA damage in the liver, heart and kidneys of female mice of increasing ages (5, 14, 22 months). The organs of the aged mice showed increased oxidative DNA strand breaks compared to young animals (5 month). Ablation of Bax greatly reduced this damage. We next assessed lipid peroxidation, DNA oxidation, and protein tyrosine nitration to determine whether Casp3 deletion reduces oxidative stress in the hearts, livers, and kidneys of 12-month-old female mice. Lipid peroxides and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were much lower in organs from mice with depleted Casp3 than in those of wild type animals. Nitration of protein tyrosine residues, caused by RNS, was also significantly suppressed in the tissues of Casp3 null mice compared to those in wild type mice. Our findings indicate that BAX and CASP3 have a vital role in the generation of oxidative stress in organs of aged mice.

Oxidative damage of lysosomes in regulated cell death systems: Pathophysiology and pharmacologic interventions

Lysosomes are small specialized organelles containing a variety of different hydrolase enzymes that are responsible for degradation of all macromolecules, entering the cells through the endosomal system or originated from the internal sources. This allows for transport and recycling of nutrients and internalization of surface proteins for antigen presentation as well as maintaining cellular homeostasis. Lysosomes are also important storage compartments for metal ions and nutrients. The integrity of lysosomal membrane is central to maintaining their normal function, but like other cellular membranes, lysosomal membrane is subject to damage mediated by reactive oxygen species. This results in spillage of lysosomal enzymes into the cytoplasm, leading to proteolytic damage to cellular systems and organelles. Several forms of lysosomal dependent cell death have been identified in diseases. Examination of these events are important for finding treatment strategies relevant to cancer or neurodegenerative diseases as well as autoimmune deficiencies. In this review, we have examined the current literature on involvement of lysosomes in induction of programed cell death and have provided an extensive list of therapeutic approaches that can modulate cell death. Exploitation of these mechanisms can lead to novel therapies for cancer and neurodegenerative diseases.

Cathepsin G Inhibition by Serpinb1 and Serpinb6 Prevents Programmed Necrosis in Neutrophils and Monocytes and Reduces GSDMD-Driven Inflammation

Neutrophil granule serine proteases contribute to immune responses through cleavage of microbial toxins and structural proteins. They induce tissue damage and modulate inflammation if levels exceed their inhibitors. Here, we show that the intracellular protease inhibitors Serpinb1a and Serpinb6a contribute to monocyte and neutrophil survival in steady-state and inflammatory settings by inhibiting cathepsin G (CatG). Importantly, we found that CatG efficiently cleaved gasdermin D (GSDMD) to generate the signature N-terminal domain GSDMD-p30 known to induce pyroptosis. Yet GSDMD deletion did not rescue neutrophil survival in Sb1a.Sb6a^-/- mice. Furthermore, Sb1a.Sb6a^-/- mice released high levels of pro-inflammatory cytokines upon endotoxin challenge in vivo in a CatG-dependent manner. Canonical inflammasome activation in Sb1a.Sb6a^-/- macrophages showed increased IL-1β release that was dependent on CatG and GSDMD. Together, our findings demonstrate that cytosolic serpins expressed in myeloid cells prevent cell death and regulate inflammatory responses by inhibiting CatG and alternative activation of GSDMD.

Vulnerability of invasive glioblastoma cells to lysosomal membrane destabilization

The current clinical care of glioblastomas leaves behind invasive, radio‐ and chemo‐resistant cells. We recently identified mammary‐derived growth inhibitor (MDGI/FABP3) as a biomarker for invasive gliomas. Here, we demonstrate a novel function for MDGI in the maintenance of lysosomal membrane integrity, thus rendering invasive glioma cells unexpectedly vulnerable to lysosomal membrane destabilization. MDGI silencing impaired trafficking of polyunsaturated fatty acids into cells resulting in significant alterations in the lipid composition of lysosomal membranes, and subsequent death of the patient‐derived glioma cells via lysosomal membrane permeabilization (LMP). In a preclinical model, treatment of glioma‐bearing mice with an antihistaminergic LMP‐inducing drug efficiently eradicated invasive glioma cells and secondary tumours within the brain. This unexpected fragility of the aggressive infiltrating cells to LMP provides new opportunities for clinical interventions, such as re‐positioning of an established antihistamine drug, to eradicate the inoperable, invasive, and chemo‐resistant glioma cells from sustaining disease progression and recurrence.

CRISPR/Cas9 Knockout of Bak Mediates Bax Translocation to Mitochondria in response to TNFα/CHX-induced Apoptosis

TNFα/CHX-induced apoptosis is dependent on caspase-8 activation and regulated by Bcl-2. However, the specific participants and precise mechanisms underlying this apoptotic pathway are poorly understood. The proapoptotic proteins Bak and Bax—members of the Bcl-2 family—are essential for the functioning of the mitochondrial apoptotic pathway. In this study, we used the CRISPR/Cas9 system to knockout Bak in the human SH-SY5Y cell line and determined the effects of this knockout on TNFα/CHX-induced apoptosis. Our data showed that overexpression of Bcl-2 dramatically prevented TNFα/CHX-induced apoptosis, and then pro-apoptotic protein Bak was downregulated and became more resistant to TNFα/CHX-induced apoptosis, because both TNFα/CHX-induced PARP cleavage and caspase activation were blocked in BAK−/− cells or using specific siRNA, whereas Bax was dispensable in TNFα/CHX-induced apoptosis, as evidenced using specific siRNA. Bax translocated from the cytosol into the mitochondria in response to TNFα/CHX, and CRISPR/Cas9 knockout of Bak significantly decreased this translocation. These results indicate that TNFα/CHX-induced apoptosis does not occur in Bak−/− cells, suggesting that TNFα/CHX-induced apoptosis is Bak-dependent but Bax-independent.

Cardiac proteomics reveals the potential mechanism of microtubule associated protein 4 phosphorylation-induced mitochondrial dysfunction

Background

Our previous work suggested that microtubule associated protein 4 (MAP4) phosphorylation led to mitochondrial dysfunction in MAP4 phosphorylation mutant mice with cardiomyopathy, but the detailed mechanism was still unknown. Thus, the aim of this study was to investigate the potential mechanism involved in mitochondrial dysfunction responsible for cardiomyopathy.

Methods

The present study was conducted to explore the potential mechanism underlying the mitochondrial dysfunction driven by MAP4 phosphorylation. Strain of mouse that mimicked constant MAP4 phosphorylation (S737 and S760) was generated. The isobaric tag for relative and absolute quantitation (iTRAQ) analysis was applied to the heart tissue. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interaction (PPI) were all analyzed on the basis of differential expressed proteins (DEPs).

Results

Among the 72 cardiac DEPs detected between the two genotypes of mice, 12 were upregulated and 60 were downregulated. GO analysis showed the biological process, molecular function, and cellular component of DEPs, and KEGG enrichment analysis linked DEPs to 96 different biochemical pathways. In addition, the PPI network was also extended on the basis of DEPs as the seed proteins. Three proteins, including mitochondrial ubiquitin ligase activator of NF-κB 1, reduced form of nicotinamide adenine dinucleotide (NADH)-ubiquinone oxidoreductase 75 kDa subunit, mitochondrial and growth arrest, and DNA-damage-inducible proteins-interacting protein 1, which play an important role in the regulation of mitochondrial function, may correlate with MAP4 phosphorylation-induced mitochondrial dysfunction. Western blot was used to validate the expression of the three proteins, which was consistent with iTRAQ experiments.

Conclusions

These findings revealed that the DEPs caused by MAP4 phosphorylation in heart tissue using iTRAQ technique and may provide clues to uncover the potential mechanism of MAP4 phosphorylation-induced mitochondrial dysfunction.

Electronic supplementary material

The online version of this article (10.1186/s41038-019-0146-3) contains supplementary material, which is available to authorized users.

Role of autophagy in environmental neurotoxicity

Human exposure to neurotoxic pollutants (e.g. metals, pesticides and other chemicals) is recognized as a key risk factor in the pathogenesis of neurodegenerative disorders. Emerging evidence indicates that an alteration in autophagic pathways may be correlated with the onset of the neurotoxicity resulting from chronic exposure to these pollutants. In fact, autophagy is a natural process that permits to preserving cell homeostasis, through the seizure and degradation of the cytosolic damaged elements. However, when an excessive level of intracellular damage is reached, the autophagic process may also induce cell death. A correct modulation of specific stages of autophagy is important to maintain the correct balance in the organism. In this review, we highlight the critical role that autophagy plays in neurotoxicity induced by the most common classes of environmental contaminants. The understanding of this mechanism may be helpful to discover a potential therapeutic strategy to reduce side effects induced by these compounds.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

PreImplantation factor (PIF) therapy provides comprehensive protection against radiation induced pathologies

Acute Radiation Syndrome (ARS) may lead to cancer and death and has few effective countermeasures. Efficacy of synthetic PIF treatment was demonstrated in preclinical autoimmune and transplantation models. PIF protected against inflammation and mortality following lethal irradiation in allogeneic bone marrow transplant (BMT) model. Herein, we demonstrate that PIF imparts comprehensive local and systemic protection against lethal and sub-lethal ARS in murine models. PIF treatment 2 h after lethal irradiation led to 100% survival and global hematopoietic recovery at 2 weeks after therapy. At 24 h after irradiation PIF restored hematopoiesis in a semi-allogeneic BMT model. PIF-preconditioning provided improved long-term engraftment. The direct effect of PIF on bone marrow cells was also demonstrated in vitro: PIF promoted pre-B cell differentiation and increased immunoregulatory properties of BM-derived mesenchymal stromal cells. PIF treatment also improved hematopoietic recovery and reduced systemic inflammatory cytokine production after sub-lethal radiation exposure. Here, PIF also prevented colonic crypt and basal membrane damage coupled with reduced nitric oxide synthetase (iNOS) and increased (B7h1) expression. Global upper GI gene pathway analysis revealed PIF's involvement in protein-RNA interactions, mitochondrial oxidative pathways, and responses to cellular stress. Some effects may be attributed to PIF's influence on macrophage differentiation and function. PIF demonstrated a regulatory effect on irradiated macrophages and on classically activated M1 macrophages, reducing inflammatory gene expression (iNOS, Cox2), promoting protective (Arg1) gene expression and inducing pro-tolerance cytokine secretion. Notably, synthetic PIF is stable for long-term field use. Overall, clinical investigation of PIF for comprehensive ARS protection is warranted.

Lysosomotropism depends on glucose: a chloroquine resistance mechanism

There has been long-standing interest in targeting pro-survival autophagy as a combinational cancer therapeutic strategy. Clinical trials are in progress testing chloroquine (CQ) or its derivatives in combination with chemo- or radiotherapy for solid and haematological cancers. Although CQ has shown efficacy in preclinical models, its mechanism of action remains equivocal. Here, we tested how effectively CQ sensitises metastatic breast cancer cells to further stress conditions such as ionising irradiation, doxorubicin, PI3K-Akt inhibition and serum withdrawal. Contrary to the conventional model, the cytotoxic effects of CQ were found to be autophagy-independent, as genetic targeting of ATG7 or the ULK1/2 complex could not sensitise cells, like CQ, to serum depletion. Interestingly, although CQ combined with serum starvation was robustly cytotoxic, further glucose starvation under these conditions led to a full rescue of cell viability. Inhibition of hexokinase using 2-deoxyglucose (2DG) similarly led to CQ resistance. As this form of cell death did not resemble classical caspase-dependent apoptosis, we hypothesised that CQ-mediated cytotoxicity was primarily via a lysosome-dependent mechanism. Indeed, CQ treatment led to marked lysosomal swelling and recruitment of Galectin3 to sites of membrane damage. Strikingly, glucose starvation or 2DG prevented CQ from inducing lysosomal damage and subsequent cell death. Importantly, we found that the related compound, amodiaquine, was more potent than CQ for cell killing and not susceptible to interference from glucose starvation. Taken together, our data indicate that CQ effectively targets the lysosome to sensitise towards cell death but is prone to a glucose-dependent resistance mechanism, thus providing rationale for the related compound amodiaquine (currently used in humans) as a better therapeutic option for cancer.

A ROS-mediated lysosomal-mitochondrial pathway is induced by ginsenoside Rh2 in hepatoma HepG2 cells

Ginsenoside Rh2 (GRh2), isolated from Panax ginseng C. A. Meyer, has been proven as an anticancer compound both in vitro and in vivo. In the present study, we investigated the role of the lysosomes during the apoptosis of HepG2 cells induced by GRh2. The results showed that GRh2 significantly induced intracellular reactive oxygen species (ROS) generation in the HepG2 cells, which consequently resulted in early lysosomal membrane permeabilization with the release of cathepsin B (Cat B) to the cytosol. Western blot analysis showed that the released Cat B in the cytosol contributed to Bid cleavage. Subsequently mitochondrial damage was observed in the HepG2 cells. Interestingly, when the HepG2 cells were pre-treated with N-Acetyl-L-Cysteine (NAC) for 1 h, which inhibited ROS generation before being exposed to GRh2, the permeabilization of lysosomal membranes and the levels of Cat B in the cytosol were down-regulated. Moreover, mitochondrial damage was alleviated when the HepG2 cells were pre-treated with leupeptin (Leu). From the above results, it could be concluded that GRh2 induced apoptosis of the HepG2 cells through accumulation of ROS and activation of the lysosomal-mitochondrial apoptotic pathway involving the release of Cat B.

Strategies for Assaying Lysosomal Membrane Permeabilization

Late endosomal organelles have an acidic pH and contain hydrolytic enzymes to degrade cargo delivered either from the extracellular environment by endocytosis or from within the cell itself by autophagy. In the event of lysosomal membrane permeabilization (LMP), the contents of late endosomes and lysosomes can be released into the cytosol and then initiate apoptosis. Compounds that can trigger LMP are therefore candidates for the induction of apoptosis, in particular in anticancer therapy. Alternatively, drug-delivery systems, such as nanoparticles, can have side effects that can include LMP, which has toxic consequences for the cells. To determine when, to what extent, and with what consequences LMP occurs is therefore of paramount importance for the evaluation of new potentially LMP-inducing compounds. In this introduction, we provide an overview of some basic assays for assessing LMP, such as staining with lysosomotropic dyes and measurement of cysteine cathepsin activity, and discuss additional strategies for the detection of the release of endogenous lysosomal molecules or preloaded exogenous tracers into the cytosol.

The Use of Lysosomotropic Dyes to Exclude Lysosomal Membrane Permeabilization

Progressive lowering of pH is characteristic for the endocytic pathway and enables efficient degradation of molecules by hydrolytic enzymes at its distal end. The existence of the proton gradient over the endosomal/lysosomal membranes depends on the action of the vacuolar ATPase (v-ATPase). During lysosomal membrane permeabilization (LMP), protons leak through the destabilized membrane, resulting in loss of the pH gradient. Here, we present a protocol showing how this effect can be detected by staining cells with lysosomotropic dyes, which accumulate in acidic organelles after protonation. During LMP, cells lose the ability to retain these dyes and therefore appear pale. Among the most commonly used lysosomotropic dyes are LysoTracker reagents and acridine orange. Cells can be analyzed with a fluorescence microscope; however, flow-cytometric analysis enables fast, objective, and reliable evaluation of differences between samples. Advantages of the technique include the fact that sample preparation is relatively simple and can be scaled-up to test several different compounds or conditions. However, as we will discuss, cells treated with v-ATPase inhibitors also lose the pH gradient across lysosomal membranes and cannot be stained with lysosomotropic dyes, although this is not accompanied by LMP. Therefore, merely observing loss of staining is not in itself a proof of LMP.

The role of oxidative stress in citreoviridin-induced DNA damage in human liver-derived HepG2 cells

We hypothesize that citreoviridin (CIT) induces DNA damage in human liver-derived HepG2 cells through an oxidative stress mechanism and that N-acetyl-l-cysteine (NAC) protects against CIT-induced DNA damage in HepG2 cells. CIT-induced DNA damage in HepG2 cells was evaluated by alkaline single-cell gel electrophoresis assay. To elucidate the genotoxicity mechanisms, the level of oxidative DNA damage was tested by immunoperoxidase staining for 8-hydroxydeoxyguanosine (8-OHdG); the intracellular generation of reactive oxygen species (ROS) and reduced glutathione (GSH) were examined; mitochondrial membrane potential and lysosomal membranes' permeability were detected; furthermore, protective effects of NAC on CIT-induced ROS formation and CIT-induced DNA damage were evaluated in HepG2 cells. A significant dose-dependent increment in DNA migration was observed at tested concentrations (2.50-10.00 µM) of CIT. The levels of ROS, 8-OHdG formation were increased by CIT, and significant depletion of GSH in HepG2 cells was induced by CIT. Destabilization of lysosome and mitochondria was also observed in cells treated with CIT. In addition, NAC significantly decreased CIT-induced ROS formation and CIT-induced DNA damage in HepG2 cells. The data indicate that CIT induces DNA damage in HepG2 cells, most likely through oxidative stress mechanisms; that NAC protects against DNA damage induced by CIT in HepG2 cells; and that depolarization of mitochondria and lysosomal protease leakage may play a role in CIT-induced DNA damage in HepG2 cells.

The role of necroptosis in neurosurgical diseases

Programmed necrosis or necroptosis is an alternative form of cell death that is executed through a caspase-independent pathway. Necroptosis has been implicated in many pathological conditions. Genetic or pharmacological inhibition of necroptotic signaling has been shown to confer neuroprotection after traumatic and ischemic brain injury. Therefore, the necroptotic pathway represents a potential target for neurological diseases that are managed by neurosurgeons. In this review, we summarize recent advances in the understanding of necroptotic signaling pathways and explore the role of necroptotic cell death in craniocerebral trauma, brain tumors, and cerebrovascular diseases.

NLRX1 acts as tumor suppressor by regulating TNF-α induced apoptosis and metabolism in cancer cells

Chronic inflammation in tumor microenvironment plays an important role at different stages of tumor development. The specific mechanisms of the association and its role in providing a survival advantage to the tumor cells are not well understood. Mitochondria are emerging as a central platform for the assembly of signaling complexes regulating inflammatory pathways, including the activation of type-I IFN and NF-κB. These complexes in turn may affect metabolic functions of mitochondria and promote tumorigenesis. NLRX1, a mitochondrial NOD-like receptor protein, regulate inflammatory pathways, however its role in regulation of cross talk of cell death and metabolism and its implication in tumorigenesis is not well understood. Here we demonstrate that NLRX1 sensitizes cells to TNF-α induced cell death by activating Caspase-8. In the presence of TNF-α, NLRX1 and active subunits of Caspase-8 are preferentially localized to mitochondria and regulate the mitochondrial ROS generation. NLRX1 regulates mitochondrial Complex I and Complex III activities to maintain ATP levels in the presence of TNF-α. The expression of NLRX1 compromises clonogenicity, anchorage-independent growth, migration of cancer cells in vitro and suppresses tumorigenicity in vivo in nude mice. We conclude that NLRX1 acts as a potential tumor suppressor by regulating the TNF-α induced cell death and metabolism.

ROS signaling during granzyme B-mediated apoptosis

Reactive oxygen species (ROS) are involved in cell signaling, aging, and death and play a role in carcinogenesis. However, whether ROS are bystanders or active effectors of apoptosis was unclear until recently. New evidence shows that the killer lymphocyte protease granzyme B activates a conserved biochemical pathway centered on respiratory chain disruption to trigger mitocentric ROS-dependent apoptosis.

Rotenone impairs autophagic flux and lysosomal functions in Parkinson's disease

BACKGROUND

Rotenone is an environmental neurotoxin that induces accumulation of α-synuclein and degeneration of dopaminergic neurons in substantia nigra pars compacta (SNpc), but the molecular mechanisms are not fully understood. We investigated whether rotenone induced impairment of autophagic flux and lysosomal functions.

METHODS

Autophagy flux, accumulation of α-synuclein, lysosomal membrane integrity and neurodegeneration were assessed in the rotenone-treated rat model and PC12 cells, and the effects of the autophagy inducer trehalose on rotenone's cytotoxicity were also studied.

RESULTS

Rotenone administration significantly reduced motor activity and caused a loss of tyrosine hydroxylase in SNpc of Lewis rats. The degeneration of nigral dopaminergic neurons was accompanied by the deposition of α-synuclein aggregates, autophagosomes and redistribution of cathepsin D from lysosomes to the cytosol. In cultured PC12 cells, rotenone also induced increases in protein levels of α-synuclein, microtubule-associated protein 1 light chain 3-II, Beclin 1, and p62. Rotenone increased lysosomal membrane permeability as evidenced by leakage of N-acetyl-beta-d-glucosaminidase and cathepsin D, the effects were blocked by reactive oxygen species scavenger tiron. Autophagy inducer trehalose enhanced the nuclear translocation of transcription factor EB, accelerated the clearance of autophagosomes and α-synuclein and attenuated rotenone-induced cell death of PC12 cells. Meanwhile, administration of trehalose to rats in drinking water (2%) decreased rotenone-induced dopaminergic neurons loss in SNpc.

CONCLUSIONS

These studies indicate that the lysosomal dysfunction contributes to rotenone's neurotoxicity and restoration of lysosomal function could be a new therapeutic strategy for Parkinson's disease.

Granzyme B-induced mitochondrial ROS are required for apoptosis

Caspases and the cytotoxic lymphocyte protease granzyme B (GB) induce reactive oxygen species (ROS) formation, loss of transmembrane potential and mitochondrial outer membrane permeabilization (MOMP). Whether ROS are required for GB-mediated apoptosis and how GB induces ROS is unclear. Here, we found that GB induces cell death in an ROS-dependent manner, independently of caspases and MOMP. GB triggers ROS increase in target cell by directly attacking the mitochondria to cleave NDUFV1, NDUFS1 and NDUFS2 subunits of the NADH: ubiquinone oxidoreductase complex I inside mitochondria. This leads to mitocentric ROS production, loss of complex I and III activity, disorganization of the respiratory chain, impaired mitochondrial respiration and loss of the mitochondrial cristae junctions. Furthermore, we have also found that GB-induced mitocentric ROS are necessary for optimal apoptogenic factor release, rapid DNA fragmentation and lysosomal rupture. Interestingly, scavenging the ROS delays and reduces many of the features of GB-induced death. Consequently, GB-induced ROS significantly promote apoptosis.

Stat3 controls cell death during mammary gland involution by regulating uptake of milk fat globules and lysosomal membrane permeabilization

We have previously demonstrated that Stat3 regulates lysosomal-mediated programmed cell death (LM-PCD) during mouse mammary gland involution in vivo. However, the mechanism that controls the release of lysosomal cathepsins to initiate cell death in this context has not been elucidated. We show here that Stat3 regulates the formation of large lysosomal vacuoles that contain triglyceride. Furthermore, we demonstrate that milk fat globules (MFGs) are toxic to epithelial cells and that, when applied to purified lysosomes, the MFG hydrolysate oleic acid potently induces lysosomal leakiness. Additionally, uptake of secreted MFGs coated in butyrophilin 1A1 is diminished in Stat3-ablated mammary glands and loss of the phagocytosis bridging molecule MFG-E8 results in reduced leakage of cathepsins in vivo. We propose that Stat3 regulates LM-PCD in mouse mammary gland by switching cellular function from secretion to uptake of MFGs. Thereafter, perturbation of lysosomal vesicle membranes by high levels of free fatty acids results in controlled leakage of cathepsins culminating in cell death.

The role of iron and reactive oxygen species in cell death

The transition metal iron is essential for life, yet potentially toxic iron-catalyzed reactive oxygen species (ROS) are unavoidable in an oxygen-rich environment. Iron and ROS are increasingly recognized as important initiators and mediators of cell death in a variety of organisms and pathological situations. Here, we review recent discoveries regarding the mechanism by which iron and ROS participate in cell death. We describe the different roles of iron in triggering cell death, targets of iron-dependent ROS that mediate cell death and a new form of iron-dependent cell death termed ferroptosis. Recent advances in understanding the role of iron and ROS in cell death offer unexpected surprises and suggest new therapeutic avenues to treat cancer, organ damage and degenerative disease.