The cell's dilemma, or the story of cell death: an entertainment in three acts

Single-cell RNA-seq analyses inform necroptosis-associated myeloid lineages influence the immune landscape of pancreas cancer

Introduction

Tumor-infiltrating myeloid cells (TIMs) are key regulators in tumor progression, but the similarity and distinction of their fundamental properties in pancreatic ductal adenocarcinoma (PDAC) remain elusive.

Method

In this study, we conducted scRNA-seq data analysis of cells from 12 primary tumor (PT) tissues, 4 metastatic (Met) tumor tissues, 3 adjacent normal pancreas tissues (Para), and PBMC samples across 16 PDAC patients, and revealed a heterogeneous TIMs environment in PDAC.

Result

Systematic comparisons between tumor and non-tumor samples of myeloid lineages identified 10 necroptosis-associated genes upregulated in PDAC tumors compared to 5 upregulated in paratumor or healthy peripheral blood. A novel RTM (resident tissue macrophages), GLUL-SQSTM1- RTM, was found to act as a positive regulator of immunity. Additionally, HSP90AA1+HSP90AB1+ mast cells exhibited pro-immune characteristics, and JAK3+TLR4+ CD16 monocytes were found to be anti-immune. The findings were validated through clinical outcomes and cytokines analyses. Lastly, intercellular network reconstruction supported the associations between the identified novel clusters, cancer cells, and immune cell populations.

Conclusion

Our analysis comprehensively characterized major myeloid cell lineages and identified three subsets of myeloid-derived cells associated with necroptosis. These findings not only provide a valuable resource for understanding the multi-dimensional characterization of the tumor microenvironment in PDAC but also offer valuable mechanistic insights that can guide the design of effective immuno-oncology treatment strategies.

Exploring the Toxic Effects of ZEA on IPEC-J2 Cells from the Inflammatory Response and Apoptosis

Zearalenone (ZEA) is the most common fungal toxin contaminating livestock and poultry feeding, especially in pigs, causing severe toxic effects and economic losses. However, the mechanism of ZEA damage to the intestine is unknown. We constructed an in vitro model of ZEA toxicity in a porcine small intestinal epithelial cell (IPEC-J2) line. ZEA causes severe oxidative stress in porcine small intestine cells, such as the production of ROS and a significant decrease in the levels of antioxidant enzymes GSH, CAT, SOD, and T-AOC. ZEA also caused apoptosis in porcine small intestine cells, resulting in a significant reduction in protein and/or mRNA expression of apoptosis-related pathway factors such as P53, caspase 3, caspase 9, Bax, and Cyt-c, which in turn caused a significant decrease in protein and/or mRNA expression of inflammatory-related factors such as IL-1β, IL-2, Cox-2, NF-κD, NLRP3, IL-6, and IL -18, which in turn caused a significant increase in protein and/or mRNA expression levels. The final results suggest that ZEA can cause a severe toxic response in porcine small intestine cells, with oxidative stress, apoptotic cell death and inflammatory damage.

Kinases control of regulated cell death revealing druggable targets for Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder in the world. Motor impairment seen in PD is associated with dopaminergic neurotoxicity in the striatum, and dopaminergic neuronal death in the substantia nigra pars compacta. Cell death has a significant effect on the development and progression of PD. Extensive research over the last few decades has unveiled new regulated cell death (RCD) mechanisms that are not dependent on apoptosis such as necroptosis, ferroptosis, and others. In this review, we will overview the mechanistic pathways of different types of RCD. Unlike accidental cell death, RCD subroutines can be regulated and the RCD-associated kinases are potential druggable targets. Hence, we will address an overview and analysis of different kinases regulating apoptosis such as receptor-interacting protein kinase 1 (RIPK-1), RIPK3, mixed lineage kinase (MLK), Ataxia telangiectasia muted (ATM), cyclin-dependent kinase (CDK), death-associated protein kinase 1 (DAPK1), Apoptosis-signaling kinase-1 (ASK-1), and Leucine-rich repeat kinase-2 (LRRK2). In addition to the role of RIPK1, RIPK3, and Mixed Lineage Kinase Domain like Pseudokinase (MLKL) in necroptosis. We also overview functions of AMP-kinase (AMPK), protein kinase C (PKC), RIPK3, and ATM in ferroptosis. We will recap the anti-apoptotic, anti-necroptotic, and anti-ferroptotic effects of different kinase inhibitors in different models of PD. Finally, we will discuss future challenges in the repositioning of kinase inhibitors in PD. In conclusion, this review kicks-start targeting RCD from a kinases perspective, opening novel therapeutic disease-modifying therapeutic avenues for PD.

Catching a killer: Mechanisms of programmed cell death and immune activation in Amyotrophic Lateral Sclerosis

In the central nervous system (CNS), execution of programmed cell death (PCD) is crucial for proper neurodevelopment. However, aberrant activation of these pathways in adult CNS leads to neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). How a cell dies is critical, as it can drive local immune activation and tissue damage. Classical apoptosis engages several mechanisms to evoke "immunologically silent" responses, whereas other forms of programmed death such as pyroptosis, necroptosis, and ferroptosis release molecules that can potentiate immune responses and inflammation. In ALS, a fatal neuromuscular disorder marked by progressive death of lower and upper motor neurons, several cell types in the CNS express machinery for multiple PCD pathways. The specific cell types engaging PCD, and ultimate mechanisms by which neuronal death occurs in ALS are not well defined. Here, we provide an overview of different PCD pathways implicated in ALS. We also examine immune activation in ALS and differentiate apoptosis from necrotic mechanisms based on downstream immunological consequences. Lastly, we highlight therapeutic strategies that target cell death pathways in the treatment of neurodegeneration and inflammation in ALS.

Selenium deficiency causes apoptosis through endoplasmic reticulum stress in swine small intestine

Selenium (Se) plays a crucial role in intestinal health. However, the specific mechanism by which deficiency of Se causes intestinal damage remains unclear. This study was to explore whether Se deficiency can cause ER stress and induce apoptosis in swine small intestine. We established the Se deficiency swine model in vivo and the intestinal epithelial (IPEC-J2) cell Se deficiency model in vitro. The results of morphological observation showed that Se deficiency caused structural damage in intestinal villi and the decrease of goblet cell structure. The apoptotic characteristics such as nucleolar condensation, mitochondrial swelling, and apoptotic bodies were observed in the IPEC-J2 cells. The results of acridine orange/ethidium bromide and mitochondrial membrane potential fluorescence staining in vitro showed that there were more apoptotic cells in the Se-deficiency group than that in the control group. The protein and/or mRNA expression levels of Bax, Bcl-2, caspase 3, caspase 8, caspase 9, cytc, PERK, ATF6, IRE, XBP1, CHOP, GRP78, which are related to ER stress-apoptosis pathway, were significantly increased in the Se-deficient group which compared with the control group in vivo and in vitro were consistent. These results indicated that Se deficiency induced ER stress and increased the apoptosis in swine small intestine and IPEC-J2 cells and then caused the damage in swine small intestinal tissue. Besides, the results of gene expressions in our experiment proved that ER stress induced by Se deficiency promoted apoptosis. These results filled the blank in the mechanism of Se deficiency-induced intestinal injury in swine.

Endothelial Iron Homeostasis Regulates Blood-Brain Barrier Integrity via the HIF2α-Ve-Cadherin Pathway

The objective of this study was to investigate the molecular response to damage at the blood-brain barrier (BBB) and to elucidate critical pathways that might lead to effective treatment in central nervous system (CNS) pathologies in which the BBB is compromised. We have used a human, stem-cell derived in-vitro BBB injury model to gain a better understanding of the mechanisms controlling BBB integrity. Chemical injury induced by exposure to an organophosphate resulted in rapid lipid peroxidation, initiating a ferroptosis-like process. Additionally, mitochondrial ROS formation (MRF) and increase in mitochondrial membrane permeability were induced, leading to apoptotic cell death. Yet, these processes did not directly result in damage to barrier functionality, since blocking them did not reverse the increased permeability. We found that the iron chelator, Desferal© significantly decreased MRF and apoptosis subsequent to barrier insult, while also rescuing barrier integrity by inhibiting the labile iron pool increase, inducing HIF2α expression and preventing the degradation of Ve-cadherin specifically on the endothelial cell surface. Moreover, the novel nitroxide JP4-039 significantly rescued both injury-induced endothelium cell toxicity and barrier functionality. Elucidating a regulatory pathway that maintains BBB integrity illuminates a potential therapeutic approach to protect the BBB degradation that is evident in many neurological diseases.

Injury factors alter miRNAs profiles of exosomes derived from islets and circulation

Islets damage is a major abnormality underling diabetes. Recent studies suggested the value of exosomes in diagnosis. This study aimed to investigate the impact of injury factors on the miRNA profiles of islet exosomes and determine whether circulating exosomal miRNAs is suitable as biomarkers of islets damage. Islets were isolated from ICR mice and induced injury in vitro by mixed cytokines (Tumor Necrosis Factor-α, Interleukin -1β and Interferon-γ) or streptozotocin (STZ), and exosomes were derived from the cultural supernatant. Using miRNA microarray analysis, we found 22 and 11 differentially expressed miRNAs in islet exosomes of STZ and cytokines treatment, respectively, including 6 miRNAs as the intersection of two injured conditions. Thereinto, mmu-miR-375-3p and mmu-miR-129-5p could be validated by qRT-PCR. Then, Serum exosomes were isolated from STZ injected mice and subjects with various glucose metabolism states and diabetic duration. qRT-PCR demonstrated exosomal mmu-miR-375-3p dramatically increased in serum of STZ treated mouse prior to the disturbance of blood glucose and insulin. In human serum exosomes, hsa-miR-375-3p was elevated in new-onset diabetes patients. Overall, our results suggest that injury factors changed miRNA profiles of exosomes derived from islets and exosomal miR-375-3p showed promising potential as a biomarker of islets damage.

Regulated Cell Death Signaling Pathways and Marine Natural Products That Target Them

Our understanding of cell death used to consist in necrosis, an unregulated form, and apoptosis, regulated cell death. That understanding expanded to acknowledge that apoptosis happens through the intrinsic or extrinsic pathways. Actually, many other regulated cell death processes exist, including necroptosis, a regulated form of necrosis, and autophagy-dependent cell death. We also understand that apoptosis occurs beyond the intrinsic and extrinsic pathways with caspase independent forms of apoptosis existing. Our knowledge of the signaling continues to grow, and with that, so does our ability to target different parts of the pathways with small molecules. Marine natural products co-evolve with their targets, and these unique molecules have complex structures with exquisite biological activities and specificities. This article offers a review of our current understanding of the signaling pathways regulating cell death, and highlights marine natural products that can affect these signaling pathways.

Crashing the computer: apoptosis vs. necroptosis in neuroinflammation

Programmed cell death (PCD) plays critical roles in development, homeostasis, and both control and progression of a plethora of diseases, including cancer and neurodegenerative pathologies. Besides classical apoptosis, several different forms of PCD have now been recognized, including necroptosis. The way a cell dies determines the reaction of the surrounding environment, and immune activation in response to cell death proceeds in a manner dependent on which death pathways are activated. Apoptosis and necroptosis are major mechanisms of cell death that typically result in opposing immune responses. Apoptotic death usually leads to immunologically silent responses whereas necroptotic death releases molecules that promote inflammation, a process referred to as necroinflammation. Diseases of the nervous system, in particular neurodegenerative diseases, are characterized by neuronal death and progressive neuroinflammation. The mechanisms of neuronal death are not well defined and significant cross-talk between pathways has been suggested. Moreover, it has been proposed that the dying of neurons is a catalyst for activating immune cells in the brain and sustaining inflammatory output. In the current review we discuss the effects of apoptotis and necroptosis on inflammatory immune activation, and evaluate the roles of each cell death pathway in a variety of pathologies with specific focus on neurodegeneration. A putative model is proposed for the regulation of neuronal death and neuroinflammation that features a role for both the apoptotic and necroptotic pathways in disease establishment and progression.

Caspase-8: regulating life and death

Roles for cell death in development, homeostasis, and the control of infections and cancer have long been recognized. Although excessive cell damage results in passive necrosis, cells can be triggered to engage molecular programs that result in cell death. Such triggers include cellular stress, oncogenic signals that engage tumor suppressor mechanisms, pathogen insults, and immune mechanisms. The best-known forms of programmed cell death are apoptosis and a recently recognized regulated necrosis termed necroptosis. Of the two best understood pathways of apoptosis, the extrinsic and intrinsic (mitochondrial) pathways, the former is induced by the ligation of death receptors, a subset of the TNF receptor (TNFR) superfamily. Ligation of these death receptors can also induce necroptosis. The extrinsic apoptosis and necroptosis pathways regulate each other and their balance determines whether cells live. Integral in the regulation and initiation of death receptor-mediated activation of programmed cell death is the aspartate-specific cysteine protease (caspase)-8. This review describes the role of caspase-8 in the initiation of extrinsic apoptosis execution and the mechanism by which caspase-8 inhibits necroptosis. The importance of caspase-8 in the development and homeostasis and the way that dysfunctional caspase-8 may contribute to the development of malignancies in mice and humans are also explored.

50 years of The FEBS Journal: looking back as well as ahead

In this last issue of 2017, we're celebrating the 50th anniversary of The FEBS Journal. This Editorial considers how the journal has grown and changed from volume 1, issue 1 and outlines our exciting plans for the future.

MOMP, cell suicide as a BCL-2 family business

Apoptosis shapes development and differentiation, has a key role in tissue homeostasis, and is deregulated in cancer. In most cases, successful apoptosis is triggered by mitochondrial outer membrane permeabilization (MOMP), which defines the mitochondrial or intrinsic pathway and ultimately leads to caspase activation and protein substrate cleavage. The mitochondrial apoptotic pathway centered on MOMP is controlled by an intricate network of events that determine the balance of the cell fate choice between survival and death. Here we will review how MOMP proceeds and how the main effectors cytochrome c, a heme protein that has a crucial role in respiration, and second mitochondria-derived activator of caspase (SMAC), as well as other intermembrane space proteins, orchestrate caspase activation. Moreover, we discuss recent insights on the interplay of the upstream coordinators and initiators of MOMP, the BCL-2 family. This review highlights how our increasing knowledge on the regulation of critical checkpoints of apoptosis integrates with understanding of cancer development and has begun to translate into therapeutic clinical benefit.

Apoptosis and necroptosis of mouse hippocampal and parenchymal astrocytes, microglia and neurons caused by Angiostrongylus cantonensis infection

BACKGROUND

Angiostrongylus cantonensis has been the only parasite among Angiostrongylidae to cause human central nervous system infection characterized by eosinophilic meningitis or meningoencephalitis. The mechanism of the extensive neurological impairments of hosts caused by A. cantonensis larvae remains unclear. The aim of the present study was to investigate apoptosis, necroptosis and autophagy in the brains of mice infected with A. cantonensis, which will be valuable for better understanding the pathogenesis of angiostrongyliasis cantonensis.

METHODS

Functional and histological neurological impairments of brain tissues from mice infected with A. cantonensis were measured by the Morris water maze test and haematoxylin and eosin (H&E) staining, respectively. The transcriptional and translational levels of apoptosis-, necroptosis- and autophagy-related genes were quantified by quantitative real-time polymerase chain reaction (RT-PCR), and assessed by western blot and immunohistochemistry (IHC) analysis. Apoptotic and necroptotic cells and their distributions in infected brain tissues were analysed by flow cytometry and transmission electron microscopy (TEM).

RESULTS

Inflammatory response in the central nervous system deteriorated as A. cantonensis infection evolved, as characterized by abundant inflammatory cell infiltration underneath the meninges, which peaked at 21 days post-infection (dpi). The learning and memory capacities of the mice were significantly decreased at 14 dpi, indicating prominent impairment of their cognitive functions. Compared with those of the control group, the mRNA levels of caspase-3, -4, -6, and RIP3 and the protein levels of caspase-4, cleaved caspase-3, cleaved caspase-6, RIP3, and pRIP3 were obviously elevated. However, no changes in the mRNA or protein levels of FADD, Beclin-1 or LC3B were evident, indicating that apoptosis and necroptosis, but not autophagy, occurred in the brain tissues of mice infected with A. cantonensis. The quantitative RT-PCR, western blot, IHC, flow cytometry and TEM results further revealed the apoptotic and necroptotic microglia, astrocytes and neurons in the parenchymal and hippocampal regions of infected mice.

CONCLUSIONS

To our knowledge, we showed for the first time that A. cantonensis infection causes the apoptosis and necroptosis of microglia and astrocytes in the parenchymal and hippocampal regions of host brain tissues, further demonstrating the pathogenesis of A. cantonensis infection and providing potential therapeutic targets for the management of angiostrongyliasis.

Mitochondrial mechanisms of neuronal rescue by F-68, a hydrophilic Pluronic block co-polymer, following acute substrate deprivation

Global brain ischemia can lead to widespread neuronal death and poor neurologic outcomes in patients. Despite detailed understanding of the cellular and molecular mechanisms mediating neuronal death following focal and global brain hypoxia-ischemia, treatments to reduce ischemia-induced brain injury remain elusive. One pathway central to neuronal death following global brain ischemia is mitochondrial dysfunction, one consequence of which is the cascade of intracellular events leading to mitochondrial outer membrane permeabilization. A novel approach to rescuing injured neurons from death involves targeting cellular membranes using a class of synthetic molecules called Pluronics. Pluronics are triblock copolymers of hydrophilic poly[ethylene oxide] (PEO) and hydrophobic poly[propylene oxide] (PPO). Evidence is accumulating to suggest that hydrophilic Pluronics rescue injured neurons from death following substrate deprivation by preventing mitochondrial dysfunction. Here, we will review current understanding of the nature of interaction of Pluronic molecules with biological membranes and the efficacy of F-68, an 80% hydrophilic Pluronic, in rescuing neurons from injury. We will review data indicating that F-68 reduces mitochondrial dysfunction and mitochondria-dependent death pathways in a model of neuronal injury in vitro, and present new evidence that F-68 acts directly on mitochondria to inhibit mitochondrial outer membrane permeabilization. Finally, we will present results of a pilot, proof-of-principle study suggesting that F-68 is effective in reducing hippocampal injury induced by transient global ischemia in vivo. By targeting mitochondrial dysfunction, F-68 and other Pluronic molecules constitute an exciting new approach to rescuing neurons from acute injury.

Special Issue on Cell Death: Murder, mystery (and a little bit of mayhem) in Manhattan

This Special Issue on Cell Death comprises a series of 12 reviews that span a broad spectrum of topics within highly active research areas in the cell death field. We hope that you will find these pieces to be of interest; we certainly found them to be fresh and engaging and we are grateful to their authors for taking the time to write for The FEBS Journal.