Maintaining Iron Homeostasis Is the Key Role of Lysosomal Acidity for Cell Proliferation

Iron-Deficiency in Atopic Diseases: Innate Immune Priming by Allergens and Siderophores

Although iron is one of the most abundant elements on earth, about a third of the world's population are affected by iron deficiency. Main drivers of iron deficiency are beside the chronic lack of dietary iron, a hampered uptake machinery as a result of immune activation. Macrophages are the principal cells distributing iron in the human body with their iron restriction skewing these cells to a more pro-inflammatory state. Consequently, iron deficiency has a pronounced impact on immune cells, favoring Th2-cell survival, immunoglobulin class switching and primes mast cells for degranulation. Iron deficiency during pregnancy increases the risk of atopic diseases in children, while both children and adults with allergy are more likely to have anemia. In contrast, an improved iron status seems to protect against allergy development. Here, the most important interconnections between iron metabolism and allergies, the effect of iron deprivation on distinct immune cell types, as well as the pathophysiology in atopic diseases are summarized. Although the main focus will be humans, we also compare them with innate defense and iron sequestration strategies of microbes, given, particularly, attention to catechol-siderophores. Similarly, the defense and nutritional strategies in plants with their inducible systemic acquired resistance by salicylic acid, which further leads to synthesis of flavonoids as well as pathogenesis-related proteins, will be elaborated as both are very important for understanding the etiology of allergic diseases. Many allergens, such as lipocalins and the pathogenesis-related proteins, are able to bind iron and either deprive or supply iron to immune cells. Thus, a locally induced iron deficiency will result in immune activation and allergic sensitization. However, the same proteins such as the whey protein beta-lactoglobulin can also transport this precious micronutrient to the host immune cells (holoBLG) and hinder their activation, promoting tolerance and protecting against allergy. Since 2019, several clinical trials have also been conducted in allergic subjects using holoBLG as a food for special medical purposes, leading to a reduction in the allergic symptom burden. Supplementation with nutrient-carrying lipocalin proteins can circumvent the mucosal block and nourish selectively immune cells, therefore representing a new dietary and causative approach to compensate for functional iron deficiency in allergy sufferers.

Friend or Foe: The Relativity of (Anti)oxidative Agents and Pathways

An element, iron, a process, the generation of reactive oxygen species (ROS), and a molecule, ascorbate, were chosen in our study to show their dual functions and their role in cell fate decision. Iron is a critical component of numerous proteins involved in metabolism and detoxification. On the other hand, excessive amounts of free iron in the presence of oxygen can promote the production of potentially toxic ROS. They can result in persistent oxidative stress, which in turn can lead to damage and cell death. At the same time, ROS—at strictly regulated levels—are essential to maintaining the redox homeostasis, and they are engaged in many cellular signaling pathways, so their total elimination is not expedient. Ascorbate establishes a special link between ROS generation/elimination and cell death. At low concentrations, it behaves as an excellent antioxidant and has an important role in ROS elimination. However, at high concentrations, in the presence of transition metals such as iron, it drives the generation of ROS. In the term of the dual function of these molecules and oxidative stress, ascorbate/ROS-driven cell deaths are not necessarily harmful processes—they can be live-savers too.

Dynamic O-GlcNAcylation coordinates ferritinophagy and mitophagy to activate ferroptosis

Ferroptosis is a regulated iron-dependent cell death characterized by the accumulation of lipid peroxidation. A myriad of facets linking amino acid, lipid, redox, and iron metabolisms were found to drive or to suppress the execution of ferroptosis. However, how the cells decipher the diverse pro-ferroptotic stress to activate ferroptosis remains elusive. Here, we report that protein O-GlcNAcylation, the primary nutrient sensor of glucose flux, orchestrates both ferritinophagy and mitophagy for ferroptosis. Following the treatment of ferroptosis stimuli such as RSL3, a commonly used ferroptosis inducer, there exists a biphasic change of protein O-GlcNAcylation to modulate ferroptosis. Pharmacological or genetic inhibition of O-GlcNAcylation promoted ferritinophagy, resulting in the accumulation of labile iron towards mitochondria. Inhibition of O-GlcNAcylation resulted in mitochondria fragmentation and enhanced mitophagy, providing an additional source of labile iron and rendering the cell more sensitive to ferroptosis. Mechanistically, we found that de-O-GlcNAcylation of the ferritin heavy chain at S179 promoted its interaction with NCOA4, the ferritinophagy receptor, thereby accumulating labile iron for ferroptosis. Our findings reveal a previously uncharacterized link of dynamic O-GlcNAcylation with iron metabolism and decision-making for ferroptosis, thus offering potential therapeutic intervention for fighting disease.

Iron Metabolism and Immune Regulation

Iron is a critical element for living cells in terrestrial life. Although iron metabolism is strictly controlled in the body, disturbance of iron homeostasis under certain type of condition leads to innate and adaptive immune response. In innate immunity, iron regulates macrophage polarizations, neutrophils recruitment, and NK cells activity. In adaptive immunity, iron had an effect on the activation and differentiation of Th1, Th2, and Th17 and CTL, and antibody response in B cells. In this review, we focused on iron and immune regulation and listed the specific role of iron in macrophage polarization, T-cell activation, and B-cells antibody response. In addition, correlations between iron and several diseases such as cancer and aging degenerative diseases and some therapeutic strategies targeting those diseases are also discussed.

Ferrous iron-activatable drug conjugate achieves potent MAPK blockade in KRAS-driven tumors

KRAS mutations drive a quarter of cancer mortality, and most are undruggable. Several inhibitors of the MAPK pathway are FDA approved but poorly tolerated at the doses needed to adequately extinguish RAS/RAF/MAPK signaling in the tumor cell. We found that oncogenic KRAS signaling induced ferrous iron (Fe2+) accumulation early in and throughout mutant KRAS-mediated transformation. We converted an FDA-approved MEK inhibitor into a ferrous iron-activatable drug conjugate (FeADC) and achieved potent MAPK blockade in tumor cells while sparing normal tissues. This innovation allowed sustainable, effective treatment of tumor-bearing animals, with tumor-selective drug activation, producing superior systemic tolerability. Ferrous iron accumulation is an exploitable feature of KRAS transformation, and FeADCs hold promise for improving the treatment of KRAS-driven solid tumors.

Heterogeneity of ferrous iron-containing endolysosomes and effects of endolysosome iron on endolysosome numbers, sizes, and localization patterns

Endolysosomes are key regulators of iron metabolism and are central to iron trafficking and redox signaling. Iron homeostasis is linked to endolysosome acidity and inhibition of endolysosome acidity triggers iron dysregulation. Because of the physiological importance and pathological relevance of ferrous iron (Fe2+ ), we determined levels of Fe2+ specifically and quantitatively in endolysosomes as well as the effects of Fe2+ on endolysosome morphology, distribution patterns, and function. The fluorescence dye FeRhoNox-1 was specific for Fe2+ and localized to endolysosomes in U87MG astrocytoma cells and primary rat cortical neurons; in U87MG cells the endolysosome concentration of Fe2+ ([Fe2+ ]el ) was 50.4 μM in control cells, 73.6 μM in ferric ammonium citrate (FAC) treated cells, and 12.4 μM in cells treated with the iron chelator deferoxamine (DFO). Under control conditions, in primary rat cortical neurons, [Fe2+ ]el was 32.7 μM. Endolysosomes containing the highest levels of Fe2+ were located perinuclearly. Treatment of cells with FAC resulted in endolysosomes that were less acidic, increased in numbers and sizes, and located further from the nucleus; opposite effects were observed for treatments with DFO. Thus, FeRhoNox-1 is a useful probe for the study of endolysosome Fe2+ , and much more work is needed to understand better the physiological significance and pathological relevance of endolysosomes classified according to their heterogeneous iron content Cover Image for this issue: https://doi.org/10.1111/jnc.15396.

Lysosomal iron recycling in mouse macrophages is dependent upon both LcytB and Steap3 reductases

Iron that is stored in macrophages as ferritin can be made bioavailable by degrading ferritin in the lysosome and releasing iron back into the cytosol. Iron stored in ferritin is found as Fe3+ and must be reduced to Fe2+ before it can be exported from the lysosome. Here we report that the lysosomal reductase Cyb561a3 (LcytB) and the endosomal reductase six-transmembrane epithelial antigen of prostate 3 (Steap3) act as lysosomal ferrireductases in the mouse macrophage cell line RAW264.7 converting Fe3+ to Fe2+ for iron recycling. We determined that when lysosomes were loaded with horse cationic ferritin, reductions or loss of LcytB or Steap3 using CRISPR/Cas9-mediated knockout technology resulted in decreased lysosomal iron export. Loss of both reductases was additive in decreasing lysosomal iron export. Decreased reductase activity resulted in increased transcripts for iron acquisition proteins DMT1 and transferrin receptor 1 (Tfrc1) suggesting that cells were iron limited. We show that transcript expression of LcytB and Steap3 is decreased in macrophages exposed to Escherichia coli pathogen UTI89, which supports a role for these reductases in regulating iron availability for pathogens. We further show that loss of LcytB and Steap3 in macrophages infected with UTI89 led to increased proliferation of intracellular UTI89 suggesting that the endolysosomal system is retaining Fe3+ that can be used for proliferation of intravesicular pathogens. Together, our findings reveal an important role for both LcytB and Steap3 in macrophage iron recycling and suggest that limiting iron recycling by decreasing expression of endolysosomal reductases is an innate immune response to protect against pathogen proliferation and sepsis.

Insufficient Iron Improves Pristane-Induced Lupus by Promoting Treg Cell Expansion

Trace element iron affects T cell biology, but the knowledge about the role of iron in regulating Treg cell expansion is limited. Treg cells play an important role in keeping peripheral T cell tolerance, increasing Treg cell expansion is a promising therapeutic method for SLE. Here we showed that iron deficiency promotes Treg cell expansion by reducing ROS accumulation, improving the disease progression of pristane-induced lupus. Increased oxidative stress inhibits Treg cell differentiation by inducing cell apoptosis. Our data suggest that altering iron metabolism promotes Treg cell expansion by preventing oxidation-induced cell death, which may provide a potential therapeutic strategy for SLE.

Effect of pH on the structure and function of cyclin-dependent kinase 6

Cyclin-dependent kinase 6 (CDK6) is an important protein kinase that regulates cell growth, development, cell metabolism, inflammation, and apoptosis. Its overexpression is associated with reprogramming glucose metabolism through alternative pathways and apoptosis, which ultimately plays a significant role in cancer development. In the present study, we have investigated the structural and conformational changes in CDK6 at varying pH employing a multi-spectroscopic approach. Circular dichroism (CD) spectroscopy revealed at extremely acidic conditions (pH 2.0–4.0), the secondary structure of CDK6 got significantly disrupted, leading to aggregates formation. These aggregates were further characterized by employing Thioflavin T (ThT) fluorescence. No significant secondary structural changes were observed over the alkaline pH range (pH 7.0–11.0). Further, fluorescence and UV spectroscopy revealed that the tertiary structure of CDK6 was disrupted under extremely acidic conditions, with slight alteration occurring in mild acidic conditions. The tertiary structure remains intact over the entire alkaline range. Additionally, enzyme assay provided an insight into the functional aspect of CDK at varying pH; CDK6 activity was optimal in the pH range of 7.0–8.0. This study will provide a platform that provides newer insights into the pH-dependent dynamics and functional behavior of CDK6 in different CDK6 directed diseased conditions, viz. different types of cancers where changes in pH contribute to cancer development.

Persister cancer cells: Iron addiction and vulnerability to ferroptosis

Ferroptosis is a unique type of non-apoptotic cell death resulting from the unrestrained occurrence of peroxidized phospholipids, which are subject to iron-mediated production of lethal oxygen radicals. This cell death modality has been detected across many organisms, including in mammals, where it can be used as a defense mechanism against pathogens or even harnessed by T cells to sensitize tumor cells toward effective killing. Conversely, ferroptosis is considered one of the main cell death mechanisms promoting degenerative diseases. Emerging evidence suggests that ferroptosis represents a vulnerability in certain cancers. Here, we critically review recent advances linking ferroptosis vulnerabilities of dedifferentiating and persister cancer cells to the dependency of these cells on iron, a potential Achilles heel for small-molecule intervention. We provide a perspective on the mechanisms reliant on iron that contribute to the persister cancer cell state and how this dependency may be exploited for therapeutic benefits.

Effect of calcium and magnesium on inflammatory cytokines in accidentally multiple fracture adults: A short-term follow-up

Calcium (Ca) and magnesium (Mg), which play an important role in several cellular processes, is essential for normal development of the skeleton and maintenance of tissue homeostasis. Deficiency of these elements might delay bone fracture recovery or accelerates bone loss. We aimed to examine whether supplementation of trace element (TE) promotes fracture healing in accidentally fracturing adults by involvement of inflammatory mechanism.A short-term follow-up in clinic was performed. Totally, 117 subjects diagnosed with multiple fractures by traffic accidents were recruited in this study. Serum Ca and Mg levels were measured by inductively coupled plasma atomic emission spectrophotometry. Short-term changes such as serum C-reactive protein, interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha in normal treatment and TE supplement groups were detected by enzyme-linked immunosorbent assay. Student t test and the Spearman correlation were performed to analyze the data.Significantly negative correlations between Ca (r = 0.7032; P < .001) and Mg (r = 0.2719; P < .05) and injury severity score were observed. Serum Ca and Mg were significantly increased at Day 5, 7, and 9 following TE supplements. After treatment, serum C-reactive protein, IL-1β, IL-6, and tumor necrosis factor alpha were significantly reduced whereas cytokine levels of the TE supplement group were found to be lower than that of the normal treatment group after Day 3.These findings suggest that Ca and Mg levels are associated with the injury severity of multiple fractures, and the supplement could reduce the inflammation, which may be beneficial for the bone recovery and disease process.

Lysosomal dysfunction impairs mitochondrial quality control and is associated with neurodegeneration in TBCK encephaloneuronopathy

Biallelic variants in the TBCK gene cause intellectual disability with remarkable clinical variability, ranging from static encephalopathy to progressive neurodegeneration (TBCK-Encephaloneuronopathy). The biological factors underlying variable disease penetrance remain unknown. Since previous studies had suggested aberrant autophagy, we tested whether mitophagy and mitochondrial function are altered in TBCK^−/− fibroblasts derived from patients exhibiting variable clinical severity. Our data show significant accumulation of mitophagosomes, reduced mitochondrial respiratory capacity and mitochondrial DNA content, suggesting impaired mitochondrial quality control. Furthermore, the degree of mitochondrial dysfunction correlates with a neurodegenerative clinical course. Since mitophagy ultimately depends on lysosomal degradation, we also examined lysosomal function. Our data show that lysosomal proteolytic function is significantly reduced in TBCK^−/− fibroblasts. Moreover, acidifying lysosomal nanoparticles rescue the mitochondrial respiratory defects in fibroblasts, suggesting impaired mitochondrial quality control secondary to lysosomal dysfunction. Our data provide insight into the disease mechanisms of TBCK Encephaloneuronopathy and the potential relevance of mitochondrial function as a biomarker beyond primary mitochondrial disorders. It also supports the benefit of lysosomal acidification strategies for disorders of impaired lysosomal degradation affecting mitochondrial quality control.

Targeting lysosomes in human disease: from basic research to clinical applications

In recent years, accumulating evidence has elucidated the role of lysosomes in dynamically regulating cellular and organismal homeostasis. Lysosomal changes and dysfunction have been correlated with the development of numerous diseases. In this review, we interpreted the key biological functions of lysosomes in four areas: cellular metabolism, cell proliferation and differentiation, immunity, and cell death. More importantly, we actively sought to determine the characteristic changes and dysfunction of lysosomes in cells affected by these diseases, the causes of these changes and dysfunction, and their significance to the development and treatment of human disease. Furthermore, we outlined currently available targeting strategies: (1) targeting lysosomal acidification; (2) targeting lysosomal cathepsins; (3) targeting lysosomal membrane permeability and integrity; (4) targeting lysosomal calcium signaling; (5) targeting mTOR signaling; and (6) emerging potential targeting strategies. Moreover, we systematically summarized the corresponding drugs and their application in clinical trials. By integrating basic research with clinical findings, we discussed the current opportunities and challenges of targeting lysosomes in human disease.

Iron Metabolism in Pancreatic Beta-Cell Function and Dysfunction

Iron is an essential element involved in a variety of physiological functions. In the pancreatic beta-cells, being part of Fe-S cluster proteins, it is necessary for the correct insulin synthesis and processing. In the mitochondria, as a component of the respiratory chain, it allows the production of ATP and reactive oxygen species (ROS) that trigger beta-cell depolarization and potentiate the calcium-dependent insulin release. Iron cellular content must be finely tuned to ensure the normal supply but also to prevent overloading. Indeed, due to the high reactivity with oxygen and the formation of free radicals, iron excess may cause oxidative damage of cells that are extremely vulnerable to this condition because the normal elevated ROS production and the paucity in antioxidant enzyme activities. The aim of the present review is to provide insights into the mechanisms responsible for iron homeostasis in beta-cells, describing how alteration of these processes has been related to beta-cell damage and failure. Defects in iron-storing or -chaperoning proteins have been detected in diabetic conditions; therefore, the control of iron metabolism in these cells deserves further investigation as a promising target for the development of new disease treatments.

miR-1 sustains muscle physiology by controlling V-ATPase complex assembly

Muscle function requires unique structural and metabolic adaptations that can render muscle cells selectively vulnerable, with mutations in some ubiquitously expressed genes causing myopathies but sparing other tissues. We uncovered a muscle cell vulnerability by studying miR-1, a deeply conserved, muscle-specific microRNA whose ablation causes various muscle defects. Using Caenorhabditis elegans, we found that miR-1 represses multiple subunits of the ubiquitous vacuolar adenosine triphosphatase (V-ATPase) complex, which is essential for internal compartment acidification and metabolic signaling. V-ATPase subunits are predicted miR-1 targets in animals ranging from C. elegans to humans, and we experimentally validated this in Drosophila. Unexpectedly, up-regulation of V-ATPase subunits upon miR-1 deletion causes reduced V-ATPase function due to defects in complex assembly. These results reveal V-ATPase assembly as a conserved muscle cell vulnerability and support a previously unknown role for microRNAs in the regulation of protein complexes.

NDST3 deacetylates α-tubulin and suppresses V-ATPase assembly and lysosomal acidification

Lysosomes are key organelles maintaining cellular homeostasis in health and disease. Here, we report the identification of N‐deacetylase and N‐sulfotransferase 3 (NDST3) as a potent regulator of lysosomal functions through an unbiased genetic screen. NDST3 constitutes a new member of the histone deacetylase (HDAC) family and catalyzes the deacetylation of α‐tubulin. Loss of NDST3 promotes assembly of the V‐ATPase holoenzyme on the lysosomal membrane and thereby increases the acidification of the organelle. NDST3 is downregulated in tissues and cells from patients carrying the C9orf72 hexanucleotide repeat expansion linked to the neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Deficiency in C9orf72 decreases the level of NDST3, and downregulation of NDST3 exacerbates the proteotoxicity of poly‐dipeptides generated from the C9orf72 hexanucleotide repeats. These results demonstrate a previously unknown regulatory mechanism through which microtubule acetylation regulates lysosomal activities and suggest that NDST3 could be targeted to modulate microtubule and lysosomal functions in relevant diseases.

Callyspongiolide kills cells by inducing mitochondrial dysfunction via cellular iron depletion

The highly cytotoxic marine natural product callyspongiolide holds great promise as a warhead of antibody-drug conjugate in cancer therapeutics; however, the mechanism underlying its cytotoxicity remains unclear. To elucidate how callyspongiolide kills cells, we employed label-free target identification with thermal stability-shift-based fluorescence difference in two-dimensional (2-D) gel electrophoresis (TS-FITGE), which allowed observation of a unique phenomenon of protein-spot separation on 2-D gels upon treatment with callyspongiolide at increasing temperatures. During our exploration of what proteins were associated with this phenomenon as well as why it happens, we found that callyspongiolide induces mitochondrial/lysosomal dysfunction and autophagy inhibition. Moreover, molecular biology studies revealed that callyspongiolide causes lysosomal dysfunction, which induces cellular iron depletion and leads to mitochondrial dysfunction and subsequent cytotoxicity. Notably, these effects were rescued through iron supplementation. Although our approach was unable to reveal the direct protein targets of callyspongiolide, unique phenomena observed only by TS-FITGE provided critical insight into the mechanism of action of callyspongiolide and specifically its cytotoxic activity via induction of mitochondrial dysfunction through cellular iron depletion caused by lysosomal deacidification, which occurred independent of known programmed cell death pathways.

In order to elucidate how callyspongiolide, a potent cytotoxic marine natural product, kills human lung cancer cells, Ha and Park employed TS-FITGE technique, a label-free target identification method with thermal stability-shift-based fluorescence difference in 2-D gel electrophoresis, allowing them to observe protein-spot separation upon treatment in increasing temperatures. They found that callyspongiolide induces lysosomal dysfunction followed by mitochondrial dysfunction as well as iron depletion, which sheds light on the mechanism of action of callyspongiolide.

Mitochondrial-derived compartments facilitate cellular adaptation to amino acid stress

Amino acids are essential building blocks of life. However, increasing evidence suggests that elevated amino acids cause cellular toxicity associated with numerous metabolic disorders. How cells cope with elevated amino acids remains poorly understood. Here, we show that a previously identified cellular structure, the mitochondrial-derived compartment (MDC), functions to protect cells from amino acid stress. In response to amino acid elevation, MDCs are generated from mitochondria, where they selectively sequester and deplete SLC25A nutrient carriers and their associated import receptor Tom70 from the organelle. Generation of MDCs promotes amino acid catabolism, and their formation occurs simultaneously with transporter removal at the plasma membrane via the multivesicular body (MVB) pathway. The combined loss of vacuolar amino acid storage, MVBs, and MDCs renders cells sensitive to high amino acid stress. Thus, we propose that MDCs operate as part of a coordinated cell network that facilitates amino acid homeostasis through post-translational nutrient transporter remodeling.

Atg8ylation as a general membrane stress and remodeling response

The yeast Atg8 protein and its paralogs in mammals, mammalian Atg8s (mAtg8s), have been primarily appreciated for their participation in autophagy. However, lipidated mAtg8s, including the most frequently used autophagosomal membrane marker LC3B, are found on cellular membranes other than autophagosomes. Here we put forward a hypothesis that the lipidation of mAtg8s, termed 'Atg8ylation', is a general membrane stress and remodeling response analogous to the role that ubiquitylation plays in tagging proteins. Ubiquitin and mAtg8s are related in sequence and structure, and the lipidation of mAtg8s occurs on its C-terminal glycine, akin to the C-terminal glycine of ubiquitin. Conceptually, we propose that mAtg8s and Atg8ylation are to membranes what ubiquitin and ubiquitylation are to proteins, and that, like ubiquitylation, Atg8ylation has a multitude of downstream effector outputs, one of which is autophagy.

Down the Iron Path: Mitochondrial Iron Homeostasis and Beyond

Cellular iron homeostasis and mitochondrial iron homeostasis are interdependent. Mitochondria must import iron to form iron–sulfur clusters and heme, and to incorporate these cofactors along with iron ions into mitochondrial proteins that support essential functions, including cellular respiration. In turn, mitochondria supply the cell with heme and enable the biogenesis of cytosolic and nuclear proteins containing iron–sulfur clusters. Impairment in cellular or mitochondrial iron homeostasis is deleterious and can result in numerous human diseases. Due to its reactivity, iron is stored and trafficked through the body, intracellularly, and within mitochondria via carefully orchestrated processes. Here, we focus on describing the processes of and components involved in mitochondrial iron trafficking and storage, as well as mitochondrial iron–sulfur cluster biogenesis and heme biosynthesis. Recent findings and the most pressing topics for future research are highlighted.

GOT1 inhibition promotes pancreatic cancer cell death by ferroptosis

Cancer metabolism is rewired to support cell survival in response to intrinsic and environmental stressors. Identification of strategies to target these adaptions is an area of active research. We previously described a cytosolic aspartate aminotransaminase (GOT1)-driven pathway in pancreatic cancer used to maintain redox balance. Here, we sought to identify metabolic dependencies following GOT1 inhibition to exploit this feature of pancreatic cancer and to provide additional insight into regulation of redox metabolism. Using pharmacological methods, we identify cysteine, glutathione, and lipid antioxidant function as metabolic vulnerabilities following GOT1 withdrawal. We demonstrate that targeting any of these pathways triggers ferroptosis, an oxidative, iron-dependent form of cell death, in GOT1 knockdown cells. Mechanistically, we reveal that GOT1 inhibition represses mitochondrial metabolism and promotes a catabolic state. Consequently, we find that this enhances labile iron availability through autophagy, which potentiates the activity of ferroptotic stimuli. Overall, our study identifies a biochemical connection between GOT1, iron regulation, and ferroptosis.

The lysosome as a master regulator of iron metabolism

Intracellular iron fulfills crucial cellular processes, including DNA synthesis and mitochondrial metabolism, but also mediates ferroptosis, a regulated form of cell death driven by lipid-based reactive oxygen species (ROS). Beyond their established role in degradation and recycling, lysosomes occupy a central position in iron homeostasis and integrate metabolic and cell death signals emanating from different subcellular sites. We discuss the central role of the lysosome in preserving iron homeostasis and provide an integrated outlook of the regulatory circuits coupling the lysosomal system to the control of iron trafficking, interorganellar crosstalk, and ferroptosis induction. We also discuss novel studies unraveling how deregulated lysosomal iron-handling functions contribute to cancer, neurodegeneration, and viral infection, and can be harnessed for therapeutic interventions.

Endophilin A2 regulates B-cell endocytosis and is required for germinal center and humoral responses

Antigen‐specific B‐cell responses require endosomal trafficking to regulate antigen uptake and presentation to helper T cells, and to control expression and signaling of immune receptors. However, the molecular composition of B‐cell endosomal trafficking pathways and their specific roles in B‐cell responses have not been systematically investigated. Here, we report high‐throughput identification of genes regulating B‐cell receptor (BCR)‐mediated antigen internalization using genome‐wide functional screens. We show that antigen internalization depends both on constitutive, clathrin‐mediated endocytosis and on antigen‐induced, clathrin‐independent endocytosis mediated by endophilin A2. Although endophilin A2‐mediated endocytosis is dispensable for antigen presentation, it is selectively required for metabolic support of B‐cell proliferation, in part through regulation of iron uptake. Consequently, endophilin A2‐deficient mice show defects in GC B‐cell responses and production of high‐affinity IgG. The requirement for endophilin A2 highlights a unique importance of clathrin‐independent intracellular trafficking in GC B‐cell clonal expansion and antibody responses.

Targeting iron metabolism in cancer therapy

Iron is a critical component of many cellular functions including DNA replication and repair, and it is essential for cell vitality. As an essential element, iron is critical for maintaining human health. However, excess iron can be highly toxic, resulting in oxidative DNA damage. Many studies have observed significant associations between iron and cancer, and the association appears to be more than just coincidental. The chief characteristic of cancers, hyper-proliferation, makes them even more dependent on iron than normal cells. Cancer therapeutics are becoming as diverse as the disease itself. Targeting iron metabolism in cancer cells is an emerging, formidable field of therapeutics. It is a strategy that is highly diverse with regard to specific targets and the various ways to reach them. This review will discuss the importance of iron metabolism in cancer and highlight the ways in which it is being explored as the medicine of tomorrow.

CYB561A3 is the Key Lysosomal Iron Reductase Required for Burkitt B-cell Growth and Survival

Epstein-Barr virus (EBV) causes endemic Burkitt lymphoma, the leading childhood cancer in sub-Saharan Africa. Burkitt cells retain aspects of germinal center B-cell physiology with MYC-driven B-cell hyperproliferation, yet little is presently known about their iron metabolism. CRISPR/Cas9 analysis highlighted the little studied ferrireductase CYB561A3 as critical for Burkitt proliferation, but not for that of closely related EBV-transformed lymphoblastoid cells or nearly all other Cancer Dependency Map cell lines. Burkitt CYB561A3 knockout induced profound iron starvation, despite ferritinophagy and plasma membrane transferrin upregulation. Elevated concentrations of ascorbic acid, a key CYB561 family electron donor or the labile iron source ferrous citrate rescued Burkitt CYB561A3 deficiency. CYB561A3 knockout caused catastrophic lysosomal and mitochondrial damage and impaired mitochondrial respiration. By contrast, lymphoblastoid B-cells with the transforming EBV latency III program were instead dependent on the STEAP3 ferrireductase. These results highlight CYB561A3 it as an attractive therapeutic Burkitt lymphoma target.

Genome-wide CRISPRi/a screens in human neurons link lysosomal failure to ferroptosis

Single-cell transcriptomics provide a systematic map of gene expression in different human cell types. The next challenge is to systematically understand cell-type-specific gene function. The integration of CRISPR-based functional genomics and stem cell technology enables the scalable interrogation of gene function in differentiated human cells. Here we present the first genome-wide CRISPR interference and CRISPR activation screens in human neurons. We uncover pathways controlling neuronal response to chronic oxidative stress, which is implicated in neurodegenerative diseases. Unexpectedly, knockdown of the lysosomal protein prosaposin strongly sensitizes neurons, but not other cell types, to oxidative stress by triggering the formation of lipofuscin, a hallmark of aging, which traps iron, generating reactive oxygen species and triggering ferroptosis. We also determine transcriptomic changes in neurons after perturbation of genes linked to neurodegenerative diseases. To enable the systematic comparison of gene function across different human cell types, we establish a data commons named CRISPRbrain.

Ferronostics: Measuring Tumoral Ferrous Iron with PET to Predict Sensitivity to Iron-Targeted Cancer Therapies

Although cancer has been known for decades to harbor an insatiable appetite for iron, only recently has the chemistry emerged to exploit this altered state therapeutically, by targeting the expanded cytosolic labile iron pool (LIP) of the cancer cell. The state of the art includes therapies that react with the LIP to produce cytotoxic radical species (in some cases also releasing drug payloads) and molecules that exacerbate LIP-induced oxidative stress to trigger ferroptosis. Effectively implementing LIP-targeted therapies in patients will require biomarkers to identify those tumors with the most elevated LIP and thus most likely to succumb to LIP-targeted interventions. Toward this goal, we tested whether tumor uptake of the novel LIP-sensing radiotracer 18F-TRX aligns with tumor sensitivity to LIP-targeted therapies. Methods:18F-TRX uptake was assessed in vivo among 10 subcutaneous and orthotopic human xenograft models. Glioma and renal cell carcinoma were prioritized because these tumors have the highest relative expression levels of STEAP3, the oxidoreductase that reduces ferric iron to the ferrous oxidation state, in the Broad Institute Cancer Cell Line Encyclopedia. The antitumor effects of the LIP-activated prodrug TRX-CBI, which releases the DNA alkylator CBI, were compared in mice bearing U251 or PC3 xenografts, tumors with high and intermediate levels of 18F-TRX uptake, respectively. Results:18F-TRX showed a wide range of tumor accumulation. An antitumor assessment study showed that the growth of U251 xenografts, the model with the highest 18F-TRX uptake, was potently inhibited by TRX-CBI. Moreover, the antitumor effects against U251 were significantly greater than those observed for PC3 tumors, consistent with the relative 18F-TRX-determined LIP levels in tumors before therapy. Lastly, a dosimetry study showed that the estimated effective human doses for adult male and female mice were comparable to those of other 18F-based imaging probes. Conclusion: We report the first evidence-to our knowledge-that tumor sensitivity to an LIP-targeted therapy can be predicted with a molecular imaging tool. More generally, these data bring a new dimension to the nuclear theranostic model by showing a requirement for imaging to quantify, in situ, the concentration of a metastable bioanalyte toward predicting tumor drug sensitivity.

Tributyltin Oxide Exposure During in vitro Maturation Disrupts Oocyte Maturation and Subsequent Embryonic Developmental Competence in Pigs

Tributyltin oxide (TBTO), an organotin compound, has been demonstrated to have toxic effects on several cell types. Previous research has shown that TBTO impairs mouse denuded oocyte maturation. However, limited information is available on the effects of TBTO exposure on livestock reproductive systems, especially on porcine oocytes in the presence of dense cumulus cells. In the present research, we evaluated the effects of TBTO exposure on porcine oocyte maturation and the possible underlying mechanisms. Porcine cumulus-oocyte complexes were cultured in maturation medium with or without TBTO for 42 h. We found that TBTO exposure during oocyte maturation prevented polar body extrusion, inhibited cumulus expansion and impaired subsequent blastocyst formation after parthenogenetic activation. Further analysis revealed that TBTO exposure not only induced intracellular reactive oxygen species (ROS) accumulation but also caused a loss of mitochondrial membrane potential and reduced intracellular ATP generation. In addition, TBTO exposure impaired porcine oocyte quality by disrupting cellular iron homeostasis. Taken together, these results demonstrate that TBTO exposure impairs the porcine oocyte maturation process by inducing intracellular ROS accumulation, causing mitochondrial dysfunction, and disrupting cellular iron homeostasis, thus decreasing the quality and impairing the subsequent embryonic developmental competence of porcine oocytes.

Loss of zebrafish atp6v1e1b, encoding a subunit of vacuolar ATPase, recapitulates human ARCL type 2C syndrome and identifies multiple pathobiological signatures

The inability to maintain a strictly regulated endo(lyso)somal acidic pH through the proton-pumping action of the vacuolar-ATPases (v-ATPases) has been associated with various human diseases including heritable connective tissue disorders. Autosomal recessive (AR) cutis laxa (CL) type 2C syndrome is associated with genetic defects in the ATP6V1E1 gene and is characterized by skin wrinkles or loose redundant skin folds with pleiotropic systemic manifestations. The underlying pathological mechanisms leading to the clinical presentations remain largely unknown. Here, we show that loss of atp6v1e1b in zebrafish leads to early mortality, associated with craniofacial dysmorphisms, vascular anomalies, cardiac dysfunction, N-glycosylation defects, hypotonia, and epidermal structural defects. These features are reminiscent of the phenotypic manifestations in ARCL type 2C patients. Our data demonstrates that loss of atp6v1e1b alters endo(lyso)somal protein levels, and interferes with non-canonical v-ATPase pathways in vivo. In order to gain further insights into the processes affected by loss of atp6v1e1b, we performed an untargeted analysis of the transcriptome, metabolome, and lipidome in early atp6v1e1b-deficient larvae. We report multiple affected pathways including but not limited to oxidative phosphorylation, sphingolipid, fatty acid, and energy metabolism together with profound defects on mitochondrial respiration. Taken together, our results identify complex pathobiological effects due to loss of atp6v1e1b in vivo.

Cutis laxa syndromes are pleiotropic disorders of the connective tissue, characterized by skin redundancy and variable systemic manifestations. Cutis laxa syndromes are caused by pathogenic variants in genes encoding structural and regulatory components of the extracellular matrix or in genes encoding components of cellular trafficking, metabolism, and mitochondrial function. Pathogenic variants in genes coding for vacuolar-ATPases, a multisubunit complex responsible for the acidification of multiple intracellular vesicles, cause type 2 cutis laxa syndromes, a group of cutis laxa subtypes further characterized by neurological, skeletal, and rarely cardiopulmonary manifestations. To investigate the pathomechanisms of vacuolar-ATPase dysfunction, we generated zebrafish models that lack a crucial subunit of the vacuolar-ATPases. The mutant zebrafish models show morphological and functional features reminiscent of the phenotypic manifestations in cutis laxa patients carrying pathogenic variants in ATP6V1E1. In-depth analysis at multiple -omic levels identified biological signatures that indicate impairment of signaling pathways, lipid metabolism, and mitochondrial respiration. We anticipate that these data will contribute to a better understanding of the pathogenesis of cutis laxa syndromes and other disorders involving defective v-ATPase function, which may eventually improve patient treatment and management.

Colorectal cancer cells utilize autophagy to maintain mitochondrial metabolism for cell proliferation under nutrient stress

Cancer cells reprogram cellular metabolism to maintain adequate nutrient pools to sustain proliferation. Moreover, autophagy is a regulated mechanism to break down dysfunctional cellular components and recycle cellular nutrients. However, the requirement for autophagy and the integration in cancer cell metabolism is not clear in colon cancer. Here, we show a cell-autonomous dependency of autophagy for cell growth in colorectal cancer. Loss of epithelial autophagy inhibits tumor growth in both sporadic and colitis-associated cancer models. Genetic and pharmacological inhibition of autophagy inhibits cell growth in colon cancer–derived cell lines and patient-derived enteroid models. Importantly, normal colon epithelium and patient-derived normal enteroid growth were not decreased following autophagy inhibition. To couple the role of autophagy to cellular metabolism, a cell culture screen in conjunction with metabolomic analysis was performed. We identified a critical role of autophagy to maintain mitochondrial metabolites for growth. Loss of mitochondrial recycling through inhibition of mitophagy hinders colon cancer cell growth. These findings have revealed a cell-autonomous role of autophagy that plays a critical role in regulating nutrient pools in vivo and in cell models, and it provides therapeutic targets for colon cancer.

Static Magnetic Field (0.2-0.4 T) Stimulates the Self-Renewal Ability of Osteosarcoma Stem Cells Through Autophagic Degradation of Ferritin

Static magnetic field (SMF) can alter cell fate decisions in many ways. However, the effects of SMF on cancer stem cells (CSCs) are little-known. In this particular study, we evaluate the biological effect of moderate-intensity SMF on osteosarcoma stem cells (OSCs) and try to clarify the underlying mechanisms of action. First, we demonstrated that prolonged exposure to SMF induced the proliferation and tumorsphere formation in K7M2 and MG63 OSCs. Moreover, SMF promoted the release of ferrous iron (Fe²⁺ ) and provoked reactive oxygen species (ROS) in OSCs. Interestingly, SMF evidently triggered the autophagic degradation of ferritin, which is characterized by the activation of microtubule-associated protein 1 light chain 3 (LC3) and nuclear receptor co-activator 4 (NCOA4), and downregulation of ferritin heavy chain 1 (FTH1) in OSCs. Particularly, the colony-forming ability of K7M2 OSCs promoted by SMF was obviously abolished by using a small interfering RNA (siRNA) against NCOA4. Finally, treatment of the tumor-bearing mice with SMF did not affect the tumor volume or tumor mass, nor pulmonary metastasis of K7M2 OSCs, but the SMF-treated K7M2 OSCs caused a preference of pulmonary metastasis in a mouse model, which suggested that SMF might induce the metastatic characteristic of OSCs. Consequently, this paper demonstrates for the first time that the cumulative SMF exposure promoted the self-renewal ability of OSCs via autophagic degradation of ferritin, implying that ferritinophagy may be a potential molecular target for cancer. © 2021 Bioelectromagnetics Society.

Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles

Gold-silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold-silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.

The marker of cobalamin deficiency, plasma methylmalonic acid, may help identifying lysosomal iron trapping in patients. Its possible utility for heart failure

Iron deficiency is known to aggravate the prognosis of patients with heart failure. Iron has functions in the mitochondrial respiratory chain. In patients with reduced mitochondrial respiration, the mitochondrial ratio between the level of nicotinamide adenine dinucleotide and its reduced form decreases. Due to the mitochondrial-lysosomal interplay, decreased mitochondrial respiration also leads to inhibition of lysosomal hydrolysis. As a result, cobalamin and iron will be trapped in lysosomes. This will, even if iron and cobalamin have been consumed and absorbed in sufficient amounts, lead to their functional deficiencies.1 Functional iron deficiency can further impede mitochondrial respiration. Increased plasma levels of methylmalonic acid were shown to predict all-cause and cardiovascular mortality in the general population. Treatments targeting mitochondrial and lysosomal function may correct the functional deficiencies and improve prognosis in a subgroup of patients with heart failure, notably those with skeletal muscle wasting. Methylmalonic acid levels may be used for monitoring response to treatment, thereby identifying patients of the subgroup in which disease outcome may improve.

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Iron deficiency hampers mitochondrial respiration, and this aggravates heart failure.

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Mitochondrial respiration oxidizes NADH and is required for lysosomal hydrolysis.

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Reduced respiration will therefore trap cobalamin and iron in lysosomes.

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Plasma methylmalonic acid levels will increase and can be used as a marker.

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NAD ⁺ precursors may liberate iron and cobalamin and improve mitochondrial respiration.

Ribosome Recycling by ABCE1 Links Lysosomal Function and Iron Homeostasis to 3' UTR-Directed Regulation and Nonsense-Mediated Decay

Nonsense-mediated decay (NMD) is a pathway that degrades mRNAs containing premature termination codons. Here we describe a genome-wide screen for NMD factors that uncovers an unexpected mechanism that broadly governs 3' untranslated region (UTR)-directed regulation. The screen reveals that NMD requires lysosomal acidification, which allows transferrin-mediated iron uptake, which, in turn, is necessary for iron-sulfur (Fe-S) cluster biogenesis. This pathway maintains the activity of the Fe-S cluster-containing ribosome recycling factor ABCE1, whose impaired function results in movement of ribosomes into 3' UTRs, where they displace exon junction complexes, abrogating NMD. Importantly, these effects extend beyond NMD substrates, with ABCE1 activity required to maintain the accessibility of 3' UTRs to diverse regulators, including microRNAs and RNA binding proteins. Because of the sensitivity of the Fe-S cluster of ABCE1 to iron availability and reactive oxygen species, these findings reveal an unanticipated vulnerability of 3' UTR-directed regulation to lysosomal dysfunction, iron deficiency, and oxidative stress.

Lysosomal nitric oxide determines transition from autophagy to ferroptosis after exposure to plasma-activated Ringer's lactate

Non-thermal plasma (NTP), an engineered technology to generate reactive species, induces ferroptosis and/or apoptosis specifically in various-type cancer cells. NTP-activated Ringer's lactate (PAL) is another modality for cancer therapy at preclinical stage. Here we found that PAL induces selective ferroptosis of malignant mesothelioma (MM) cells, where non-targeted metabolome screening identified upregulated citrulline-nitric oxide (^.NO) cycle as a PAL target. ^.NO probe detected biphasic peaks transiently at PAL exposure with time-dependent increase, which was responsible for inducible ^. NO synthase (iNOS) overexpression through NF-κB activation. ^.NO and lipid peroxidation occupied lysosomes as a major compartment with increased TFEB expression. Not only ferrostatin-1 but inhibitors for ^. NO and/or iNOS could suppress this ferroptosis. PAL-induced ferroptosis accompanied autophagic process in the early phase, as demonstrated by an increase in essential amino acids, LC3B-II, p62 and LAMP1, transforming into the later phase with boosted lipid peroxidation. Therefore, ^.NO-mediated lysosomal impairment is central in PAL-induced ferroptosis.

An energetics perspective on geroscience: mitochondrial protonmotive force and aging

Mitochondria are organelles that provide energy to cells through ATP production. Mitochondrial dysfunction has long been postulated to mediate cellular declines that drive biological aging. Many well-characterized hallmarks of aging may involve underlying energetic defects that stem from loss of mitochondrial function with age. Why and how mitochondrial function declines with age is an open question and one that has been difficult to answer. Mitochondria are powered by an electrochemical gradient across the inner mitochondrial membrane known as the protonmotive force (PMF). This gradient decreases with age in several experimental models. However, it is unclear if a diminished PMF is a cause or a consequence of aging. Herein, we briefly review and define mitochondrial function, we summarize how PMF changes with age in several models, and we highlight recent studies that implicate PMF in aging biology. We also identify barriers that must be addressed for the field to progress. Emerging technology permits more precise in vivo study of mitochondria that will allow better understanding of cause and effect in metabolic models of aging. Once cause and effect can be discerned more precisely, energetics approaches to combat aging may be developed to prevent or reverse functional decline.

Dichloroacetate attenuates the stemness of colorectal cancer cells via trigerring ferroptosis through sequestering iron in lysosomes

Colorectal cancer stem cell (CSC) has been regarded to be the root of colorectal cancer progression. However, there is still no effective therapeutic method targeting colorectal CSC in clinical application. Here, we investigated the effects of dichloroacetate (DCA) on colorectal cancer cell stemness. We showed that DCA could reduce colorectal cancer cell stemness in a dose-dependent manner, which is evident by the decreased expression of stemness markers, tumor cell sphere-formation and cell migration ability. In addition, it was found that DCA trigerred the ferroptosis of colorectal CSC, which is characterized as the upregulation of iron concentration, lipid peroxides, and glutathione level, and decreased cell viability. Mechanistic studies demonstrated that DCA could sequester iron in lysosome and thus trigger ferroptosis, which is necessary for DCA-mediated attenuation on colorectal cancer cell stemness. Taken together, this work suggests that DCA might be a colorectal CSC-killer.

Lysosome (Dys)function in Atherosclerosis-A Big Weight on the Shoulders of a Small Organelle

Atherosclerosis is a progressive insidious chronic disease that underlies most of the cardiovascular pathologies, including myocardial infarction and ischemic stroke. The malfunctioning of the lysosomal compartment has a central role in the etiology and pathogenesis of atherosclerosis. Lysosomes are the degradative organelles of mammalian cells and process endogenous and exogenous substrates in a very efficient manner. Dysfunction of these organelles and consequent inefficient degradation of modified low-density lipoproteins (LDL) and apoptotic cells in atherosclerotic lesions have, therefore, numerous deleterious consequences for cellular homeostasis and disease progression. Lysosome dysfunction has been mostly studied in the context of the inherited lysosomal storage disorders (LSDs). However, over the last years it has become increasingly evident that the consequences of this phenomenon are more far-reaching, also influencing the progression of multiple acquired human pathologies, such as neurodegenerative diseases, cancer, and cardiovascular diseases (CVDs). During the formation of atherosclerotic plaques, the lysosomal compartment of the various cells constituting the arterial wall is under severe stress, due to the tremendous amounts of lipoproteins being processed by these cells. The uncontrolled uptake of modified lipoproteins by arterial phagocytic cells, namely macrophages and vascular smooth muscle cells (VSMCs), is the initial step that triggers the pathogenic cascade culminating in the formation of atheroma. These cells become pathogenic "foam cells," which are characterized by dysfunctional lipid-laden lysosomes. Here, we summarize the current knowledge regarding the origin and impact of the malfunctioning of the lysosomal compartment in plaque cells. We further analyze how the field of LSD research may contribute with some insights to the study of CVDs, particularly how therapeutic approaches that target the lysosomes in LSDs could be applied to hamper atherosclerosis progression and associated mortality.

A genome-wide copper-sensitized screen identifies novel regulators of mitochondrial cytochrome c oxidase activity

Copper is essential for the activity and stability of cytochrome c oxidase (CcO), the terminal enzyme of the mitochondrial respiratory chain. Loss-of-function mutations in genes required for copper transport to CcO result in fatal human disorders. Despite the fundamental importance of copper in mitochondrial and organismal physiology, systematic identification of genes that regulate mitochondrial copper homeostasis is lacking. To discover these genes, we performed a genome-wide screen using a library of DNA-barcoded yeast deletion mutants grown in copper-supplemented media. Our screen recovered a number of genes known to be involved in cellular copper homeostasis as well as genes previously not linked to mitochondrial copper biology. These newly identified genes include the subunits of the adaptor protein 3 complex (AP-3) and components of the cellular pH-sensing pathway Rim20 and Rim21, both of which are known to affect vacuolar function. We find that AP-3 and Rim mutants exhibit decreased vacuolar acidity, which in turn perturbs mitochondrial copper homeostasis and CcO function. CcO activity of these mutants could be rescued by either restoring vacuolar pH or supplementing growth media with additional copper. Consistent with these genetic data, pharmacological inhibition of the vacuolar proton pump leads to decreased mitochondrial copper content and a concomitant decrease in CcO abundance and activity. Taken together, our study uncovered novel genetic regulators of mitochondrial copper homeostasis and provided a mechanism by which vacuolar pH impacts mitochondrial respiration through copper homeostasis.

Lysosomal retargeting of Myoferlin mitigates membrane stress to enable pancreatic cancer growth

Lysosomes must maintain the integrity of their limiting membrane to ensure efficient fusion with incoming organelles and degradation of substrates within their lumen. Pancreatic cancer cells upregulate lysosomal biogenesis to enhance nutrient recycling and stress resistance, but it is unknown whether dedicated programmes for maintaining the integrity of the lysosome membrane facilitate pancreatic cancer growth. Using proteomic-based organelle profiling, we identify the Ferlin family plasma membrane repair factor Myoferlin as selectively and highly enriched on the membrane of pancreatic cancer lysosomes. Mechanistically, lysosomal localization of Myoferlin is necessary and sufficient for the maintenance of lysosome health and provides an early acting protective system against membrane damage that is independent of the endosomal sorting complex required for transport (ESCRT)-mediated repair network. Myoferlin is upregulated in human pancreatic cancer, predicts poor survival and its ablation severely impairs lysosome function and tumour growth in vivo. Thus, retargeting of plasma membrane repair factors enhances the pro-oncogenic activities of the lysosome.

Quercetin induces p53-independent cancer cell death through lysosome activation by the transcription factor EB and Reactive Oxygen Species-dependent ferroptosis

BACKGROUND AND PURPOSE

Cancer cells exhibit more dependence on iron and enhanced sensitivity to iron-dependent, programmed cell death (ferroptosis) than normal cells. Quercetin exerts anti-cancer effects, but the underlying molecular mechanism is largely unknown. In this study, we aimed to investigate the involvement of lysosome function and ferroptosis in the anti-cancer potential of quercetin.

EXPERIMENTAL APPROACH

We used MTT assays and DNA content analysis to evaluate the cytotoxicity, colony formation assay to investigate cell proliferation, and flow cytometry and confocal microscopy to detect lysosomal acidification and protease enzyme activity. Western blotting, cell subfractionation, RT-PCR and siRNA transfection were used to establish molecular mechanisms of action.

KEY RESULTS

Quercetin is known to promote p53-independent cell death in various cancer cell lines. Although quercetin induces autophagy, genetic silencing of Atg7 fails to affect quercetin-induced cell death. In contrast, both lysosome inhibitors and knockdown of the transcription factor EB can prevent quercetin-induced cell death, suggesting the involvement of lysosome. Next, quercetin is found to induce lysosomal activation sequentially through nuclear translocation of EB and transcriptional activation of lysosomal genes. Notably, quercetin promoted lysosome-dependent ferritin degradation and free iron release. This action and quercetin-induced ROS generation synergistically resulted in lipid peroxidation and ferroptosis. Furthermore, Bid may link ferroptosis with apoptosis to cause cell death.

CONCLUSION AND IMPLICATIONS

Quercetin induced EB-mediated lysosome activation and increased ferritin degradation leading to ferroptosis and Bid-involved apoptosis. Results from this study may expand our current knowledge about the mechanism of quercetin as an anti-cancer agent.

Similarities and interplay between senescent cells and macrophages

Senescence is a cellular program that prevents the replication of old, damaged, or cancerous cells. Senescent cells become growth arrested and undergo changes in their morphology, chromatin organization, and metabolism, and produce a bioactive secretome. This secretome, the senescence-associated secretory phenotype (SASP), mediates many of the pathophysiological effects associated with senescent cells, for example, recruiting and activating immune cells such as macrophages. The relation between senescent cells and macrophages is intriguing: senescent cells recruit macrophages, can induce them to undergo senescence, or can influence their polarization. Senescent cells and macrophages share multiple phenotypic characteristics; both have a high secretory status, increased lysosome numbers, or the ability to activate the inflammasome. Senescent cells accumulate during aging and disease, and killing them results in widespread benefits. Here we discuss similarities between senescent cells and macrophages and interpret the latest developments in macrophage biology to understand the molecular mechanisms of cellular senescence. We describe evidence and effects of senescence in macrophages and speculate on the ontogeny of the senescent-like state in macrophages. Finally, we examine the macrophage-senescent cell interplay and its impact on macrophage effector functions during inflammatory conditions and in the tumor microenvironment.

Human Adrenocortical Carcinoma (NCI-H295R) Cell Line as an In Vitro Cell Culture Model for Assessing the Impact of Iron on Steroidogenesis

The aim of this in vitro study was to examine the dose-dependent effects of iron as a potential endocrine disruptor in relation to the release of sexual steroid hormones by a human adrenocortical carcinoma (NCI-H295R) cell line. The cells were exposed to different concentrations (3.90, 62.50, 250, 500, 1000 μM) of FeSO4.7H2O and compared with the control group (culture medium without FeSO4.7H2O). Cell viability was measured by the metabolic activity assay. Quantification of sexual steroid production was performed by enzyme-linked immunosorbent assay. Following 48 h culture of the cells in the presence of FeSO4.7H2O, significantly (P < 0.001) increased production of progesterone was observed at the lowest concentration (3.90 μM) of FeSO4.7H2O, whereas the lowest release of progesterone by NCIH295R cells was noted after addition of 1000 μM of FeSO4.7H2O, which did not elicit cytotoxic action (P > 0.05). Testosterone production was substantially increased at the concentrations ≤ 62.50 μM of FeSO4.7H2O. Lower levels of testosterone were recorded in the groups with higher concentrations (≥ 250 μM) of FeSO4.7H2O (P > 0.05). The presented data suggest that iron has no endocrine disruptive effect on the release of sexual steroid hormones, but its toxicity may be reflected at other points of the steroidogenesis pathway.

Ferrous Iron-Dependent Pharmacology

The recent emergence of oxidation state selective probes of cellular iron has produced a more nuanced understanding of how cells utilize this crucial nutrient to empower enzyme function, and also how labile ferrous iron contributes to iron-dependent cell death (ferroptosis) and other disease pathologies including cancer, bacterial infections, and neurodegeneration. These findings, viewed in light of the Fenton chemistry promoted by ferrous iron, suggest a new category of therapeutics exhibiting ferrous iron-dependent pharmacology. While still in its infancy, this nascent field draws inspiration from the remarkable activity and tremendous clinical impact of the antimalarial artemisinin. Here, we review recent insights into the role of labile ferrous iron in biology and disease, and describe new therapeutic approaches designed to exploit this divalent transition metal.

Serum lipoprotein-derived fatty acids regulate hypoxia-inducible factor

Oxygen regulates hypoxia-inducible factor (HIF) transcription factors to control cell metabolism, erythrogenesis, and angiogenesis. Whereas much has been elucidated about how oxygen regulates HIF, whether lipids affect HIF activity is un-known. Here, using cultured cells and two animal models, we demonstrate that lipoprotein-derived fatty acids are an independent regulator of HIF. Decreasing extracellular lipid supply inhibited HIF prolyl hydroxylation, leading to accumulation of the HIFα subunit of these heterodimeric transcription factors comparable with hypoxia with activation of downstream target genes. The addition of fatty acids to culture medium suppressed this signal, which required an intact mitochondrial respiratory chain. Mechanistically, fatty acids and oxygen are distinct signals integrated to control HIF activity. Finally, we observed lipid signaling to HIF and changes in target gene expression in developing zebrafish and adult mice, and this pathway operates in cancer cells from a range of tissues. This study identifies fatty acids as a physiological modulator of HIF, defining a mechanism for lipoprotein regulation that functions in parallel to oxygen.

Distinct photo-oxidation-induced cell death pathways lead to selective killing of human breast cancer cells

Lack of effective treatments for aggressive breast cancer is still a major global health problem. We have previously reported that photodynamic therapy using methylene blue as photosensitizer (MB-PDT) massively kills metastatic human breast cancer, marginally affecting healthy cells. In this study, we aimed to unveil the molecular mechanisms behind MB-PDT effectiveness and specificity towards tumor cells. Through lipidomics and biochemical approaches, we demonstrated that MB-PDT efficiency and specificity rely on polyunsaturated fatty acid-enriched membranes and on the better capacity to deal with photo-oxidative damage displayed by non-tumorigenic cells. We found out that, in tumorigenic cells, lysosome membrane permeabilization is accompanied by ferroptosis and/or necroptosis. Our results also pointed at a cross-talk between lysosome-dependent cell death (LDCD) and necroptosis induction after photo-oxidation, and contributed to broaden the understanding of MB-PDT-induced mechanisms and specificity in breast cancer cells. Therefore, we demonstrated that efficient approaches could be designed on the basis of lipid composition and metabolic features for hard-to-treat cancers. The results further reinforce MB-PDT as a therapeutic strategy for highly aggressive human breast cancer cells.