scholarly journals Arl8/ARL-8 functions in apoptotic cell removal by mediating phagolysosome formation inCaenorhabditis elegans

2013 ◽  
Vol 24 (10) ◽  
pp. 1584-1592 ◽  
Author(s):  
Ayaka Sasaki ◽  
Isei Nakae ◽  
Maya Nagasawa ◽  
Keisuke Hashimoto ◽  
Fumiko Abe ◽  
...  
Keyword(s):  
Germ Cells ◽  
Apoptotic Cell ◽  
Small Gtpase ◽  
Tissue Homeostasis ◽  
Apoptotic Cells ◽  
Loss Of Function ◽  
Efficient Removal ◽  
Phagosomal Maturation ◽  
Late Stages

Efficient clearance of apoptotic cells by phagocytes is important for development, tissue homeostasis, and the prevention of autoimmune responses. Phagosomes containing apoptotic cells undergo acidification and mature from Rab5-positive early to Rab7-positive late stages. Phagosomes finally fuse with lysosomes to form phagolysosomes, which degrade apoptotic cells; however, the molecular mechanism underlying phagosome–lysosome fusion is not fully understood. Here we show that the Caenorhabditis elegans Arf-like small GTPase Arl8 (ARL-8) is involved in phagolysosome formation and is required for the efficient removal of apoptotic cells. Loss of function of arl-8 results in the accumulation of apoptotic germ cells. Both the engulfment of the apoptotic cells by surrounding somatic sheath cells and the phagosomal maturation from RAB-5- to RAB-7-positive stages occur in arl-8 mutants. However, the phagosomes fail to fuse with lysosomes in the arl-8 mutants, leading to the accumulation of RAB-7-positive phagosomes and the delayed degradation of apoptotic cells. ARL-8 localizes primarily to lysosomes and physically interacts with the homotypic fusion and protein sorting complex component VPS-41. Collectively our findings reveal that ARL-8 facilitates apoptotic cell removal in vivo by mediating phagosome–lysosome fusion during phagocytosis.

scholarly journals The rapid in vivo evolution of Pseudomonas aeruginosa in ventilator-associated pneumonia patients leads to attenuated virulence

Open Biology ◽  
2017 ◽  
Vol 7 (9) ◽  
pp. 170029 ◽  
Author(s):  
Ke Wang ◽  
Yi-qiang Chen ◽  
May M. Salido ◽  
Gurjeet S. Kohli ◽  
Jin-liang Kong ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Opportunistic Pathogen ◽  
Ventilator Associated Pneumonia ◽  
Loss Of Function ◽  
Short Term ◽  
Airway Infections ◽  
Evolutionary Trajectories ◽  
Human Airways ◽  
Late Stages

Pseudomonas aeruginosa is an opportunistic pathogen that causes severe airway infections in humans. These infections are usually difficult to treat and associated with high mortality rates. While colonizing the human airways, P. aeruginosa could accumulate genetic mutations that often lead to its better adaptability to the host environment. Understanding these evolutionary traits may provide important clues for the development of effective therapies to treat P. aeruginosa infections. In this study, 25 P. aeruginosa isolates were longitudinally sampled from the airways of four ventilator-associated pneumonia (VAP) patients. Pacbio and Illumina sequencing were used to analyse the in vivo evolutionary trajectories of these isolates. Our analysis showed that positive selection dominantly shaped P. aeruginosa genomes during VAP infections and led to three convergent evolution events, including loss-of-function mutations of lasR and mpl , and a pyoverdine-deficient phenotype. Specifically, lasR encodes one of the major transcriptional regulators in quorum sensing, whereas mpl encodes an enzyme responsible for recycling cell wall peptidoglycan. We also found that P. aeruginosa isolated at late stages of VAP infections produce less elastase and are less virulent in vivo than their earlier isolated counterparts, suggesting the short-term in vivo evolution of P. aeruginosa leads to attenuated virulence.

scholarly journals Overexposure to apoptosis via disrupted glial specification perturbs Drosophila macrophage function and reveals roles of the CNS during injury

2020 ◽  
Author(s):  
Emma Louise Armitage ◽  
Hannah Grace Roddie ◽  
Iwan Robert Evans
Keyword(s):  
Inflammatory Responses ◽  
Apoptotic Cell ◽  
Calcium Waves ◽  
Apoptotic Cells ◽  
Phagocytic Cells ◽  
Macrophage Function ◽  
Apoptotic Cell Clearance ◽  
Cell Clearance ◽  
Wound Responses

AbstractApoptotic cell clearance by phagocytes is a fundamental process during development, homeostasis and the resolution of inflammation. However, the demands placed on phagocytic cells such as macrophages by this process, and the limitations these interactions impose on subsequent cellular behaviours are not yet clear. Here we seek to understand how apoptotic cells affect macrophage function in the context of a genetically-tractable Drosophila model in which macrophages encounter excessive amounts of apoptotic cells. We show that loss of the glial transcription factor repo, and corresponding removal of the contribution these cells make to apoptotic cell clearance, causes macrophages in the developing embryo to be challenged with large numbers of apoptotic cells. As a consequence, macrophages become highly vacuolated with cleared apoptotic cells and their developmental dispersal and migration is perturbed. We also show that the requirement to deal with excess apoptosis caused by a loss of repo function leads to impaired inflammatory responses to injury. However, in contrast to migratory phenotypes, defects in wound responses cannot be rescued by preventing apoptosis from occurring within a repo mutant background. In investigating the underlying cause of these impaired inflammatory responses, we demonstrate that wound-induced calcium waves propagate into surrounding tissues, including neurons and glia of the ventral nerve cord, which exhibit striking calcium waves on wounding, revealing a previously unanticipated contribution of these cells during responses to injury. Taken together these results demonstrate important insights into macrophage biology and how repo mutants can be used to study macrophage-apoptotic cell interactions in the fly embryo.Furthermore, this work shows how these multipurpose cells can be ‘overtasked’ to the detriment of their other functions, alongside providing new insights into which cells govern macrophage responses to injury in vivo.

scholarly journals Two Alternative Mechanisms That Regulate the Presentation of Apoptotic Cell Engulfment Signal in Caenorhabditis elegans

2007 ◽  
Vol 18 (8) ◽  
pp. 3180-3192 ◽  
Author(s):  
Victor Venegas ◽  
Zheng Zhou
Keyword(s):  
Caenorhabditis Elegans ◽  
Abc Transporter ◽  
Germ Cells ◽  
Mammalian Cells ◽  
Developmental Stages ◽  
Apoptotic Cell ◽  
Somatic Cells ◽  
Apoptotic Cells ◽  
Phospholipid Scramblase ◽  
Cell Engulfment

Phosphatidylserine exposed on the surface of apoptotic mammalian cells is considered an “eat-me” signal that attracts phagocytes. The generality of using phosphatidylserine as a clearance signal for apoptotic cells in animals and the regulation of this event remain uncertain. Using ectopically expressed mouse MFG-E8, a secreted phosphatidylserine-binding protein, we detected specific exposure of phosphatidylserine on the surface of apoptotic cells in Caenorhabditis elegans. Masking the surface phosphatidylserine inhibits apoptotic cell engulfment. CED-7, an ATP-binding cassette (ABC) transporter, is necessary for the efficient exposure of phosphatidylserine on apoptotic somatic cells, and for the recognition of these cells by phagocytic receptor CED-1. Alternatively, phosphatidylserine exposure on apoptotic germ cells is not CED-7 dependent, but instead requires phospholipid scramblase PLSC-1, a homologue of mammalian phospholipid scramblases. Moreover, deleting plsc-1 results in the accumulation of apoptotic germ cells but not apoptotic somatic cells. These observations suggest that phosphatidylserine might be recognized by CED-1 and act as a conserved eat-me signal from nematodes to mammals. Furthermore, the two different biochemical activities used in somatic cells (ABC transporter) and germ cells (phospholipid scramblase) suggest an increased complexity in the regulation of phosphatidylserine presentation in response to apoptotic signals in different tissues and during different developmental stages.

scholarly journals Persistence of apoptotic cells without autoimmune disease or inflammation in CD14−/− mice

2004 ◽  
Vol 167 (6) ◽  
pp. 1161-1170 ◽  
Author(s):  
Andrew Devitt ◽  
Kate G. Parker ◽  
Carol Anne Ogden ◽  
Ceri Oldreive ◽  
Michael F. Clay ◽  
...  
Keyword(s):  
Autoimmune Disease ◽  
Apoptotic Cell ◽  
Apoptotic Cells ◽  
Autoantibody Production ◽  
Apoptotic Cell Clearance ◽  
Cell Clearance ◽  
Surface Receptor ◽  
Anti Inflammatory

Interaction of macrophages with apoptotic cells involves multiple steps including recognition, tethering, phagocytosis, and anti-inflammatory macrophage responses. Defective apoptotic cell clearance is associated with pathogenesis of autoimmune disease. CD14 is a surface receptor that functions in vitro in the removal of apoptotic cells by human and murine macrophages, but its mechanism of action has not been defined. Here, we demonstrate that CD14 functions as a macrophage tethering receptor for apoptotic cells. Significantly, CD14−/− macrophages in vivo are defective in clearing apoptotic cells in multiple tissues, suggesting a broad role for CD14 in the clearance process. However, the resultant persistence of apoptotic cells does not lead to inflammation or increased autoantibody production, most likely because, as we show, CD14−/− macrophages retain the ability to generate anti-inflammatory signals in response to apoptotic cells. We conclude that CD14 plays a broad tethering role in apoptotic cell clearance in vivo and that apoptotic cells can persist in the absence of proinflammatory consequences.

scholarly journals Interaction of Apoptotic Cells with Macrophages Upregulates COX-2/PGE2and HGF Expression via a Positive Feedback Loop

2014 ◽  
Vol 2014 ◽  
pp. 1-17 ◽  
Author(s):  
Ji Yeon Byun ◽  
Young-So Youn ◽  
Ye-Ji Lee ◽  
Youn-Hee Choi ◽  
So-Yeon Woo ◽  
...  
Keyword(s):  
Positive Feedback ◽  
Tissue Repair ◽  
Feedback Loop ◽  
Apoptotic Cell ◽  
Raw 264.7 Cells ◽  
Apoptotic Cells ◽  
Positive Feedback Loop ◽  
Cox 2

Recognition of apoptotic cells by macrophages is crucial for resolution of inflammation, immune tolerance, and tissue repair. Cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and hepatocyte growth factor (HGF) play important roles in the tissue repair process. We investigated the characteristics of macrophage COX-2 and PGE2expression mediated by apoptotic cells and then determined how macrophages exposed to apoptotic cellsin vitroandin vivoorchestrate the interaction between COX-2/PGE2and HGF signaling pathways. Exposure of RAW 264.7 cells and primary peritoneal macrophages to apoptotic cells resulted in induction of COX-2 and PGE2. The COX-2 inhibitor NS-398 suppressed apoptotic cell-induced PGE2production. Both NS-398 and COX-2-siRNA, as well as the PGE2receptor EP2 antagonist, blocked HGF expression in response to apoptotic cells. In addition, the HGF receptor antagonist suppressed increases in COX-2 and PGE2induction. Thein vivorelevance of the interaction between the COX-2/PGE2and HGF pathways through a positive feedback loop was shown in cultured alveolar macrophages followingin vivoexposure of bleomycin-stimulated lungs to apoptotic cells. Our results demonstrate that upregulation of the COX-2/PGE2and HGF in macrophages following exposure to apoptotic cells represents a mechanism for mediating the anti-inflammatory and antifibrotic consequences of apoptotic cell recognition.

The liaison between apoptotic cells and macrophages – the end programs the beginning

2009 ◽  
Vol 390 (5/6) ◽  
Author(s):  
Andreas Weigert ◽  
Carla Jennewein ◽  
Bernhard Brüne
Keyword(s):  
Cell Death ◽  
Inflammatory Disease ◽  
Regulatory Mechanism ◽  
Current Knowledge ◽  
Apoptotic Cell ◽  
Tumor Development ◽  
Tissue Homeostasis ◽  
Human Diseases ◽  
Apoptotic Cells ◽  
Resolution Of Inflammation

AbstractThe efficient execution of apoptotic cell death with the clearance of apoptotic debris by phagocytes is a key regulatory mechanism ensuring tissue homeostasis. Failure in this execution program contributes to the pathogenesis of many human diseases. In this review, we describe the current knowledge regarding the interaction of apoptotic cells with their professional ‘captors’, the macrophages, with special emphasis on the immunological outcome. Removal of apoptotic cells must be considered as a process that actively delivers signals to polarize macrophages, which are fundamental for the resolution of inflammation. However, the sculpting of macrophage responses by apoptotic cells can be misused under certain inflammatory disease conditions, including tumor development.

Inhibition of Rho-dependent kinases ROCK I/II activates VEGF-driven retinal neovascularization and sprouting angiogenesis

2009 ◽  
Vol 296 (3) ◽  
pp. H893-H899 ◽  
Author(s):  
Jens Kroll ◽  
Daniel Epting ◽  
Katrin Kern ◽  
Christian T. Dietz ◽  
Yuxi Feng ◽  
...  
Keyword(s):  
Growth Factor ◽  
Small Gtpase ◽  
Vegf Receptor ◽  
Small Interfering Rnas ◽  
Loss Of Function ◽  
Sprouting Angiogenesis ◽  
Extracellular Signal ◽  
Specific Growth Factor

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that activates the small GTPase RhoA. While the role of RhoA for VEGF-driven endothelial migration and angiogenesis has been studied in detail, the function of its target proteins, the Rho-dependent kinases ROCK I and II, are controversially discussed. Using the mouse model of oxygen-induced proliferative retinopathy, ROCK I/II inhibition by H-1152 resulted in increased angiogenesis. This enhanced angiogenesis, however, was completely blocked by the VEGF-receptor antagonist PTK787/ZK222584. Loss-of-function experiments in endothelial cells revealed that inhibition of ROCK I/II using the pharmacological inhibitor H-1152 and ROCK I/II-specific small-interfering RNAs resulted in a rise of VEGF-driven sprouting angiogenesis. These functional data were biochemically substantiated by showing an enhanced VEGF-receptor kinase insert domain receptor phosphorylation and extracellular signal-regulated kinase 1/2 activation after inhibition of ROCK I/II. Thus our data identify that the inhibition of Rho-dependent kinases ROCK I/II activates angiogenesis both, in vitro and in vivo.

scholarly journals “Dead Cells Talking”: The Silent Form of Cell Death Is Not so Quiet

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Richard Jäger ◽  
Howard O. Fearnhead
Keyword(s):  
Cell Death ◽  
Cancer Therapy ◽  
Apoptotic Cell ◽  
Surrounding Tissue ◽  
Apoptotic Cells ◽  
Cancer Cell Proliferation ◽  
Loss Of Function ◽  
Molecular Events ◽  
Dying Cells

After more than twenty years of research, the molecular events of apoptotic cell death can be succinctly stated; different pathways, activated by diverse signals, increase the activity of proteases called caspases that rapidly and irreversibly dismantle condemned cell by cleaving specific substrates. In this time the ideas that apoptosis protects us from tumourigenesis and that cancer chemotherapy works by inducing apoptosis also emerged. Currently, apoptosis research is shifting away from the intracellular events within the dying cell to focus on the effect of apoptotic cells on surrounding tissues. This is producing counterintuitive data showing that our understanding of the role of apoptosis in tumourigenesis and cancer therapy is too simple, with some interesting and provocative implications. Here, we will consider evidence supporting the idea that dying cells signal their presence to the surrounding tissue and, in doing so, elicit repair and regeneration that compensates for any loss of function caused by cell death. We will discuss evidence suggesting that cancer cell proliferation may be driven by inappropriate or corrupted tissue-repair programmes that are initiated by signals from apoptotic cells and show how this may dramatically modify how we view the role of apoptosis in both tumourigenesis and cancer therapy.

scholarly journals Autophagosomes fuse to phagosomes and facilitate the degradation of apoptotic cells in Caenorhabditis elegans

eLife ◽  
2022 ◽  
Vol 11 ◽  
Author(s):  
Omar Peña-Ramos ◽  
Lucia Chiao ◽  
Xianghua Liu ◽  
Xiaomeng Yu ◽  
Tianyou Yao ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Apoptotic Cell ◽  
Adaptor Protein ◽  
Small Gtpase ◽  
Apoptotic Cells ◽  
Phagosome Maturation ◽  
Double Membrane ◽  
C Elegans ◽  
Intracellular Organelles ◽  
Cellular Components

Autophagosomes are double-membrane intracellular vesicles that degrade protein aggregates, intracellular organelles, and other cellular components. During the development of the nematode Caenorhabditis elegans, many somatic and germ cells undergo apoptosis. These cells are engulfed and degraded by their neighboring cells. We discovered a novel role of autophagosomes in facilitating the degradation of apoptotic cells using a real-time imaging technique. Specifically, the double-membrane autophagosomes in engulfing cells are recruited to the surfaces of phagosomes containing apoptotic cells and subsequently fuse to phagosomes, allowing the inner vesicle to enter the phagosomal lumen. Mutants defective in the production of autophagosomes display significant defects in the degradation of apoptotic cells, demonstrating the importance of autophagosomes to this process. The signaling pathway led by the phagocytic receptor CED-1, the adaptor protein CED-6, and the large GTPase dynamin (DYN-1) promotes the recruitment of autophagosomes to phagosomes. Moreover, the subsequent fusion of autophagosomes with phagosomes requires the functions of the small GTPase RAB-7 and the HOPS complex components. Further observations suggest that autophagosomes provide apoptotic cell-degradation activities in addition to and in parallel of lysosomes. Our findings reveal that, unlike the single-membrane, LC3-associated phagocytosis (LAP) vesicles reported for mammalian phagocytes, the canonical double-membrane autophagosomes facilitate the clearance of C. elegans apoptotic cells. These findings add autophagosomes to the collection of intracellular organelles that contribute to phagosome maturation, identify novel crosstalk between the autophagy and phagosome maturation pathways, and discover the upstream signaling molecules that initiate this crosstalk.

scholarly journals Charcot-Marie-Tooth 2B mutations in rab7 cause dosage-dependent neurodegeneration due to partial loss of function

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Smita Cherry ◽  
Eugene Jennifer Jin ◽  
Mehmet Neset Özel ◽  
Zhiyuan Lu ◽  
Egemen Agi ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Protein Function ◽  
Quantitative Imaging ◽  
Small Gtpase ◽  
Loss Of Function ◽  
Gain Of Function ◽  
Mutant Proteins ◽  
Charcot Marie Tooth ◽  
Function Mechanism

The small GTPase Rab7 is a key regulator of endosomal maturation in eukaryotic cells. Mutations in rab7 are thought to cause the dominant neuropathy Charcot-Marie-Tooth 2B (CMT2B) by a gain-of-function mechanism. Here we show that loss of rab7, but not overexpression of rab7 CMT2B mutants, causes adult-onset neurodegeneration in a Drosophila model. All CMT2B mutant proteins retain 10–50% function based on quantitative imaging, electrophysiology, and rescue experiments in sensory and motor neurons in vivo. Consequently, expression of CMT2B mutants at levels between 0.5 and 10-fold their endogenous levels fully rescues the neuropathy-like phenotypes of the rab7 mutant. Live imaging reveals that CMT2B proteins are inefficiently recruited to endosomes, but do not impair endosomal maturation. These findings are not consistent with a gain-of-function mechanism. Instead, they indicate a dosage-dependent sensitivity of neurons to rab7-dependent degradation. Our results suggest a therapeutic approach opposite to the currently proposed reduction of mutant protein function.

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