scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Macrophages target Listeria monocytogenes by two discrete non-canonical autophagy pathways.

05 Sep 2021-Autophagy (Informa UK Limited)-pp 1-18
TL;DR: Flexneri et al. as mentioned in this paper characterized a second non-canonical autophagy pathway targeting L.m. containing phagosomes, which is induced by damage caused to the phagosomal membrane by the pore-forming toxin of Listeria monocytogenes.
Abstract: Non-canonical autophagy pathways decorate single-membrane vesicles with Atg8-family proteins such as MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3). Phagosomes containing the bacterial pathogen Listeria monocytogenes (L.m.) can be targeted by a non-canonical autophagy pathway called LC3-associated phagocytosis (LAP), which substantially contributes to the anti-listerial activity of macrophages and immunity. We here characterized a second non-canonical autophagy pathway targeting L.m.-containing phagosomes, which is induced by damage caused to the phagosomal membrane by the pore-forming toxin of L.m., listeriolysin O. This pore-forming toxin-induced non-canonical autophagy pathway (PINCA) was the only autophagic pathway evoked in tissue macrophages deficient for the NADPH oxidase CYBB/NOX2 that produces the reactive oxygen species (ROS) that are required for LAP induction. Similarly, also bone marrow-derived macrophages (BMDM) exclusively targeted L.m. by PINCA as they completely failed to induce LAP because of insufficient production of ROS through CYBB, in part, due to low expression of some CYBB complex subunits. Priming of BMDM with proinflammatory cytokines such as TNF and IFNG/IFNγ increased ROS production by CYBB and endowed them with the ability to target L.m. by LAP. Targeting of L.m. by LAP remained relatively rare, though, preventing LAP from substantially contributing to the anti-listerial activity of BMDM. Similar to LAP, the targeting of L.m.-containing phagosomes by PINCA promoted their fusion with lysosomes. Surprisingly, however, this did not substantially contribute to anti-listerial activity of BMDM. Thus, in contrast to LAP, PINCA does not have clear anti-listerial function suggesting that the two different non-canonical autophagy pathways targeting L.m. may have discrete functions.Abbreviations: actA/ActA: actin assembly-inducing protein A; ATG: autophagy-related; BMDM: Bone marrow-derived macrophages; CALCOCO2/NDP52: calcium-binding and coiled-coil domain-containing protein 2; CYBA/p22phox: cytochrome b-245 light chain; CYBB/NOX2: cytochrome b(558) subunit beta; E. coli: Escherichia coli; IFNG/IFNγ: interferon gamma; L.m.: Listeria monocytogenes; LAP: LC3-associated phagocytosis; LGALS: galectin; LLO: listeriolysin O; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; NCF1/p47phox: neutrophil cytosol factor 1; NCF2/p67phox: neutrophil cytosol factor 2; NCF4/p67phox: neutrophil cytosol factor 4; Peritoneal macrophages: PM; PINCA: pore-forming toxin-induced non-canonical autophagy; plc/PLC: 1-phosphatidylinositol phosphodiesterase; PMA: phorbol 12-myristate 13-acetate; RB1CC1/FIP200: RB1-inducible coiled-coil protein 1; ROS: reactive oxygen species; S. aureus: Staphylococcus aureus; S. flexneri: Shigella flexneri; SQSTM1/p62: sequestosome 1; S. typhimurium: Salmonella typhimurium; T3SS: type III secretion system; TNF: tumor necrosis factor; ULK: unc-51 like autophagy activating kinase; PM: peritoneal macrophages; WT: wild type.
Citations
More filters
Journal ArticleDOI
TL;DR: The nature of the LAP mechanism is outlined, recent insights into its interplay with bacterial pathogens are discussed, and parts of the autophagic machinery to label the cargo-containing phagosomes for lysosomal degradation are discussed.
Abstract: Cells of the innate immune system continuously patrol the extracellular environment for potential microbial threats that are to be neutralized by phagocytosis and delivery to lysosomes. In addition, phagocytes employ autophagy as an innate immune mechanism against pathogens that succeed to escape the phagolysosomal pathway and invade the cytosol. In recent years, LC3-associated phagocytosis (LAP) has emerged as an intermediate between phagocytosis and autophagy. During LAP, phagocytes target extracellular microbes while using parts of the autophagic machinery to label the cargo-containing phagosomes for lysosomal degradation. LAP contributes greatly to host immunity against a multitude of bacterial pathogens. In the pursuit of survival, bacteria have developed elaborate strategies to disarm or circumvent the LAP process. In this review, we will outline the nature of the LAP mechanism and discuss recent insights into its interplay with bacterial pathogens.

12 citations

Journal ArticleDOI
TL;DR: Many microbes secrete virulence factors to inhibit ROS production and/or the V-ATPase-ATG16L1 axis to slow LC3 recruitment and avoid degradation in lysosomes to protect against infection.
Abstract: The delivery of pathogens to lysosomes for degradation provides an important defense against infection. Degradation is enhanced when LC3 is conjugated to endosomes and phagosomes containing pathogens to facilitate fusion with lysosomes. In phagocytic cells, TLR signaling and Rubicon activate LC3-associated phagocytosis (LAP) where stabilization of the NADPH oxidase leads to sustained ROS production and raised vacuolar pH. Raised pH triggers the assembly of the vacuolar ATPase on the vacuole membrane where it binds ATG16L1 to recruit the core LC3 conjugation complex (ATG16L1:ATG5-12). This V-ATPase-ATG16L1 axis is also activated in nonphagocytic cells to conjugate LC3 to endosomes containing extracellular microbes. Pathogens provide additional signals for recruitment of LC3 when they raise vacuolar pH with pore-forming toxins and proteins, phospholipases, or specialized secretion systems. Many microbes secrete virulence factors to inhibit ROS production and/or the V-ATPase-ATG16L1 axis to slow LC3 recruitment and avoid degradation in lysosomes.

4 citations

Journal ArticleDOI
TL;DR: This review focuses on defensins and calprotectin as AMPs that appear to work cooperatively to fortify the epithelial barrier against infection, and the contribution of both AMPs to candidiasis as a fungal infection and periodontitis resulting from bacterial dysbiosis.
Abstract: The recent epidemic caused by aerosolized SARS-CoV-2 virus illustrates the importance and vulnerability of the mucosal epithelial barrier against infection. Antimicrobial proteins and peptides (AMPs) are key to the epithelial barrier, providing immunity against microbes. In primitive life forms, AMPs protect the integument and the gut against pathogenic microbes. AMPs have also evolved in humans and other mammals to enhance newer, complex innate and adaptive immunity to favor the persistence of commensals over pathogenic microbes. The canonical AMPs are helictical peptides that form lethal pores in microbial membranes. In higher life forms, this type of AMP is exemplified by the defensin family of AMPs. In epithelial tissues, defensins, and calprotectin (complex of S100A8 and S100A9) have evolved to work cooperatively. The mechanisms of action differ. Unlike defensins, calprotectin sequesters essential trace metals from microbes, which inhibits growth. This review focuses on defensins and calprotectin as AMPs that appear to work cooperatively to fortify the epithelial barrier against infection. The antimicrobial spectrum is broad with overlap between the two AMPs. In mice, experimental models highlight the contribution of both AMPs to candidiasis as a fungal infection and periodontitis resulting from bacterial dysbiosis. These AMPs appear to contribute to innate immunity in humans, protecting the commensal microflora and restricting the emergence of pathobionts and pathogens. A striking example in human innate immunity is that elevated serum calprotectin protects against neonatal sepsis. Calprotectin is also remarkable because of functional differences when localized in epithelial and neutrophil cytoplasm or released into the extracellular environment. In the cytoplasm, calprotectin appears to protect against invasive pathogens. Extracellularly, calprotectin can engage pathogen-recognition receptors to activate innate immune and proinflammatory mechanisms. In inflamed epithelial and other tissue spaces, calprotectin, DNA, and histones are released from degranulated neutrophils to form insoluble antimicrobial barriers termed neutrophil extracellular traps. Hence, calprotectin and other AMPs use several strategies to provide microbial control and stimulate innate immunity.

3 citations

Journal ArticleDOI
Jin Yuan, Qiu-Li Zhang, Shihua Chen, Min Yan, Lei Yue 
TL;DR: The mechanism of LAP in resistance to bacterial infection and the ways in which bacteria escape LAP are summarized to provide new clues for developing novel therapeutic strategies for bacterial infectious diseases.
Abstract: LC3-associated phagocytosis (LAP) is a noncanonical autophagy process reported in recent years and is one of the effective mechanisms of host defense against bacterial infection. During LAP, bacteria are recognized by pattern recognition receptors (PRRs), enter the body, and then recruit LC3 onto a single-membrane phagosome to form a LAPosome. LC3 conjugation can promote the fusion of the LAPosomes with lysosomes, resulting in their maturation into phagolysosomes, which can effectively kill the identified pathogens. However, to survive in host cells, bacteria have also evolved strategies to evade killing by LAP. In this review, we summarized the mechanism of LAP in resistance to bacterial infection and the ways in which bacteria escape LAP. We aim to provide new clues for developing novel therapeutic strategies for bacterial infectious diseases.

3 citations

Journal ArticleDOI
TL;DR: In this article , molecular differences and similarities between LC3-associated phagocytosis (LAP), PINCA and xenophagy in macrophages during bacterial infections are discussed.
Abstract: Macrophages remove bacteria from the extracellular milieu via phagocytosis. While most of the engulfed bacteria are degraded in the antimicrobial environment of the phagolysosome, several bacterial pathogens have evolved virulence factors, which evade degradation or allow escape into the cytosol. To counter this situation, macrophages activate LC3-associated phagocytosis (LAP), a highly bactericidal non-canonical autophagy pathway, which destroys the bacterial pathogens in so called LAPosomes. Moreover, macrophages can also target intracellular bacteria by pore-forming toxin-induced non-canonical autophagy (PINCA), a recently described non-canonical autophagy pathway, which is activated by phagosomal damage induced by bacteria-derived pore-forming toxins. Similar to LAP, PINCA involves LC3 recruitment to the bacteria-containing phagosome independently of the ULK complex, but in contrast to LAP, this process does not require ROS production by Nox2. As last resort of autophagic targeting, macrophages activate xenophagy, a selective form of macroautophagy, to recapture bacteria, which evaded successful targeting by LAP or PINCA through rupture of the phagosome. However, xenophagy can also be hijacked by bacterial pathogens for their benefit or can be completely inhibited resulting in intracellular growth of the bacterial pathogen. In this perspective, we discuss the molecular differences and similarities between LAP, PINCA and xenophagy in macrophages during bacterial infections.

2 citations

References
More filters
Journal ArticleDOI
TL;DR: As discussed in this Review, autophagy has multitiered immunological functions that influence infection, inflammation and immunity.
Abstract: It is increasingly understood that autophagy is an ancient defence mechanism that has become incorporated into numerous immunological pathways. As discussed in this Review, its immunological roles include the elimination of microorganisms, the control of inflammation, the regulation of antigen presentation and lymphocyte homeostasis, and the secretion of immune mediators.

1,549 citations

Journal ArticleDOI
20 Dec 2007-Nature
TL;DR: It is shown that a particle that engages TLRs on a murine macrophage while it is phagocytosed triggers the autophagosome marker LC3 to be rapidly recruited to the phagosome in a manner that depends on theAutophagy pathway proteins ATG5 and ATG7; this process is preceded by recruitment of beclin 1 and phosphoinositide-3-OH kinase activity.
Abstract: Phagocytosis and autophagy are two ancient, highly conserved processes involved, respectively, in the removal of extracellular organisms and the destruction of organisms in the cytosol. Autophagy, for either metabolic regulation or defence, involves the formation of a double membrane called the autophagosome, which then fuses with lysosomes to degrade the contents, a process that has similarities with phagosome maturation. Toll-like-receptor (TLR) engagement activates a variety of defence mechanisms within phagocytes, including facilitation of phagosome maturation, and also engages autophagy. Therefore we speculated that TLR signalling might link these processes to enhance the function of conventional phagosomes. Here we show that a particle that engages TLRs on a murine macrophage while it is phagocytosed triggers the autophagosome marker LC3 to be rapidly recruited to the phagosome in a manner that depends on the autophagy pathway proteins ATG5 and ATG7; this process is preceded by recruitment of beclin 1 and phosphoinositide-3-OH kinase activity. Translocation of beclin 1 and LC3 to the phagosome was not associated with observable double-membrane structures characteristic of conventional autophagosomes, but was associated with phagosome fusion with lysosomes, leading to rapid acidification and enhanced killing of the ingested organism.

1,206 citations

Journal ArticleDOI
TL;DR: A panel of leading experts in the field attempts here to define several autophagy‐related terms based on specific biochemical features to formulate recommendations that facilitate the dissemination of knowledge within and outside the field of autophagic research.
Abstract: Over the past two decades, the molecular machinery that underlies autophagic responses has been characterized with ever increasing precision in multiple model organisms. Moreover, it has become clear that autophagy and autophagy-related processes have profound implications for human pathophysiology. However, considerable confusion persists about the use of appropriate terms to indicate specific types of autophagy and some components of the autophagy machinery, which may have detrimental effects on the expansion of the field. Driven by the overt recognition of such a potential obstacle, a panel of leading experts in the field attempts here to define several autophagy-related terms based on specific biochemical features. The ultimate objective of this collaborative exchange is to formulate recommendations that facilitate the dissemination of knowledge within and outside the field of autophagy research.

1,095 citations

Journal ArticleDOI
TL;DR: This fundamental discrepancy explains why most surface markers identified on in vitro generated macrophages do not translate to the in vivo situation and is justified by comparing the gene lists positively or negatively correlated with the ratio of IL-12 and arginase 1 in transcriptomes of LPS-treated peritoneal macrophades.
Abstract: Macrophages are found in tissues, body cavities, and mucosal surfaces. Most tissue macrophages are seeded in the early embryo before definitive hematopoiesis is established. Others are derived from blood monocytes. The macrophage lineage diversification and plasticity are key aspects of their functionality. Macrophages can also be generated from monocytes in vitro and undergo classical (LPS+IFN-γ) or alternative (IL-4) activation. In vivo, macrophages with different polarization and different activation markers coexist in tissues. Certain mouse strains preferentially promote T-helper-1 (Th1) responses and other Th2 responses. Their macrophages preferentially induce iNOS or arginase and have been called M1 and M2, respectively. In many publications, M1 and classically activated and M2 and alternatively activated are used interchangeably. We tested whether this is justified by comparing the gene lists positively [M1(=LPS+)] or negatively [M2(=LPS-)] correlated with the ratio of IL-12 and arginase 1 in transcriptomes of LPS-treated peritoneal macrophages with in vitro classically (LPS, IFN-γ) versus alternatively activated (IL-4) bone marrow-derived macrophages, both from published datasets. Although there is some overlap between in vivo M1(=LPS+) and in vitro classically activated (LPS+IFNγ) and in vivo M2(=LPS-) and in vitro alternatively activated macrophages, many more genes are regulated in opposite or unrelated ways. Thus, M1(=LPS+) macrophages are not equivalent to classically activated, and M2(=LPS-) macrophages are not equivalent to alternatively activated macrophages. This fundamental discrepancy explains why most surface markers identified on in vitro generated macrophages do not translate to the in vivo situation. Valid in vivo M1/M2 surface markers remain to be discovered.

977 citations

Journal ArticleDOI
16 Feb 2012-Nature
TL;DR: It is shown in human cells that galectin 8 (also known as LGALS8), a cytosolic lectin, is a danger receptor that restricts Salmonella proliferation and serves as a versatile receptor for vesicle-damaging pathogens.
Abstract: Galectin 8, a cytosolic lectin, is shown to function as a danger receptor that detects damaged vesicles and protects cells from bacterial infection by inducing autophagy. The galectins are carbohydrate-binding proteins that have a range of functions inside and outside the cell. They accumulate in the cytosol, which is normally devoid of complex carbohydrates, making them prime candidates for danger and/or pattern-recognition receptors. Here galectin-8 is identified as a danger receptor that protects cells against bacterial infection. It binds to host glycans exposed on bacteria-containing vesicles and recruits the ubiquitin-binding autophagy receptor NDP52 to clear the cytosol of invading bacteria. Autophagy defends the mammalian cytosol against bacterial infection1,2,3. Efficient pathogen engulfment is mediated by cargo-selecting autophagy adaptors that rely on unidentified pattern-recognition or danger receptors to label invading pathogens as autophagy cargo, typically by polyubiquitin coating4,5,6,7,8,9. Here we show in human cells that galectin 8 (also known as LGALS8), a cytosolic lectin, is a danger receptor that restricts Salmonella proliferation. Galectin 8 monitors endosomal and lysosomal integrity and detects bacterial invasion by binding host glycans exposed on damaged Salmonella-containing vacuoles. By recruiting NDP52 (also known as CALCOCO2), galectin 8 activates antibacterial autophagy. Galectin-8-dependent recruitment of NDP52 to Salmonella-containing vesicles is transient and followed by ubiquitin-dependent NDP52 recruitment. Because galectin 8 also detects sterile damage to endosomes or lysosomes, as well as invasion by Listeria or Shigella, we suggest that galectin 8 serves as a versatile receptor for vesicle-damaging pathogens. Our results illustrate how cells deploy the danger receptor galectin 8 to combat infection by monitoring endosomal and lysosomal integrity on the basis of the specific lack of complex carbohydrates in the cytosol.

843 citations