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1.
Int J Mol Sci ; 24(2)2023 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-36674886

RESUMO

Although the phagocytic activity of macrophages has long been studied, the involvement of microtubules in the process is not well understood. In this study, we improved the fixation protocol and revealed a dynamically rearranging microtubule network in macrophages, consisting of a basal meshwork, thick bundles at the cell edge, and astral microtubules. Some astral microtubules extended beneath the cell cortex and continued to form bundles at the cell edge. These microtubule assemblies were mutually exclusive of actin accumulation during membrane ruffling. Although the stabilization of microtubules with paclitaxel did not affect the resting stage of the macrophages, it reduced the phagocytic activity and membrane ruffling of macrophages activated with serum-MAF, which induced rapid phagocytosis. In contrast, the destabilization of microtubules with nocodazole enhanced membrane ruffling and the internalization of phagocytic targets suggesting an inhibitory effect of the microtubule network on the remodeling of the actin network. Meanwhile, the microtubule network was necessary for phagosome maturation. Our detailed analyses of cytoskeletal filaments suggest a phagocytosis control system involving Ca2+ influx, the destabilization of microtubules, and activation of actin network remodeling, followed by the translocation and acidification of phagosomes on the microtubule bundles.


Assuntos
Actinas , Fagocitose , Actinas/metabolismo , Fagocitose/fisiologia , Macrófagos/metabolismo , Microtúbulos/metabolismo , Citoesqueleto/metabolismo
2.
Curr Protoc ; 3(1): e638, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36622815

RESUMO

Microglia function as the tissue-specific resident macrophages of the nervous system, performing immune and non-immune functions. These functions are critical to development and to maintain homeostasis in the nervous system throughout the lifespan, and during brain injury or disease. One method by which microglia maintain homeostasis is phagocytosis of aberrant proteins, extracellular debris, synapses, or apoptotic cells. Phagocytic function can be changed by environmental or genetic risk factors that affect microglia. These protocols present a rapid and simple in vitro high-content imaging protocol for studying phagocytosis in the murine microglia BV-2 cell line. High-content imaging and analysis enable versatility of the assay, which can be used to test multiple experimental conditions, or as a screening tool. © 2023 Wiley Periodicals LLC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. Basic Protocol 1: Phagocytosis of fluorescently labeled particles Basic Protocol 2: Examining modifications to phagocytosis by test substances Basic Protocol 3: High content imaging and analysis of phagocytic cells.


Assuntos
Microglia , Fagocitose , Camundongos , Humanos , Animais , Microglia/metabolismo , Fagocitose/fisiologia , Fagócitos , Linhagem Celular , Sinapses
3.
Elife ; 112022 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-36508246

RESUMO

The centrosome decides which branch extending from the body of microglia will successfully engulf and clear away dead neurons.


Assuntos
Centrossomo , Microglia , Neurônios/fisiologia , Fagocitose/fisiologia
4.
Elife ; 112022 11 18.
Artigo em Inglês | MEDLINE | ID: mdl-36398880

RESUMO

During brain development, many newborn neurons undergo apoptosis and are engulfed by microglia, the tissue-resident phagocytes of the brain, in a process known as efferocytosis. A hallmark of microglia is their highly branched morphology characterized by the presence of numerous dynamic extensions that these cells use for scanning the brain parenchyma and engulfing unwanted material. The mechanisms driving branch formation and apoptotic cell engulfment in microglia are unclear. By taking a live-imaging approach in zebrafish, we show that while microglia generate multiple microtubule-based branches, they only successfully engulf one apoptotic neuron at a time. Further investigation into the mechanism underlying this sequential engulfment revealed that targeted migration of the centrosome into one branch is predictive of phagosome formation and polarized vesicular trafficking. Moreover, experimentally doubling centrosomal numbers in microglia increases the rate of engulfment and even allows microglia to remove two neurons simultaneously, providing direct supporting evidence for a model where centrosomal migration is a rate-limiting step in branch-mediated efferocytosis. Conversely, light-mediated depolymerization of microtubules causes microglia to lose their typical branched morphology and switch to an alternative mode of engulfment, characterized by directed migration towards target neurons, revealing unexpected plasticity in their phagocytic ability. Finally, building on work focusing on the establishment of the immunological synapse, we identified a conserved signalling pathway underlying centrosomal movement in engulfing microglia.


Assuntos
Microglia , Peixe-Zebra , Animais , Microglia/metabolismo , Fagocitose/fisiologia , Neurônios/metabolismo , Centrossomo
5.
Cells ; 11(21)2022 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-36359810

RESUMO

Microglia, the main immune modulators of the central nervous system, have key roles in both the developing and adult brain. These functions include shaping healthy neuronal networks, carrying out immune surveillance, mediating inflammatory responses, and disposing of unwanted material. A wide variety of pathological conditions present with microglia dysregulation, highlighting the importance of these cells in both normal brain function and disease. Studies into microglial function in the context of both health and disease thus have the potential to provide tremendous insight across a broad range of research areas. In vitro culture of microglia, using primary cells, cell lines, or induced pluripotent stem cell derived microglia, allows researchers to generate reproducible, robust, and quantifiable data regarding microglia function. A broad range of assays have been successfully developed and optimised for characterizing microglial morphology, mediation of inflammation, endocytosis, phagocytosis, chemotaxis and random motility, and mediation of immunometabolism. This review describes the main functions of microglia, compares existing protocols for measuring these functions in vitro, and highlights common pitfalls and future areas for development. We aim to provide a comprehensive methodological guide for researchers planning to characterise microglial functions within a range of contexts and in vitro models.


Assuntos
Microglia , Fagocitose , Microglia/metabolismo , Fagocitose/fisiologia , Quimiotaxia/fisiologia , Sistema Nervoso Central , Encéfalo/metabolismo
6.
PLoS Biol ; 20(10): e3001858, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-36279312

RESUMO

Cancer cells survive chemotherapy and cause lethal relapse by entering a senescent state that facilitates expression of many phagocytosis/macrophage-related genes that engender a novel cannibalism phenotype. We used biosensors and live-cell imaging to reveal the basic steps and mechanisms of engulfment by senescent human and mouse tumor cells. We show filamentous actin in predator cells was localized to the prey cell throughout the process of engulfment. Biosensors to various phosphoinositide (PI) species revealed increased concentration and distinct localization of predator PI(4) P and PI(4,5)P2 at the prey cell during early stages of engulfment, followed by a transient burst of PI(3) P before and following internalization. PIK3C2B, the kinase responsible for generating PI(3)P, was required for complete engulfment. Inhibition or knockdown of Clathrin, known to associate with PIK3C2B and PI(4,5)P2, severely impaired engulfment. In sum, our data reveal the most fundamental cellular processes of senescent cell engulfment, including the precise localizations and dynamics of actin and PI species throughout the entire process.


Assuntos
Citoesqueleto de Actina , Actinas , Camundongos , Animais , Humanos , Actinas/metabolismo , Citoesqueleto de Actina/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Fagocitose/fisiologia
7.
Nat Commun ; 13(1): 6233, 2022 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-36280666

RESUMO

Microglia are important immune cells in the central nervous system (CNS) that undergo turnover throughout the lifespan. If microglial debris is not removed in a timely manner, accumulated debris may influence CNS function. Clearance of microglial debris is crucial for CNS homeostasis. However, underlying mechanisms remain obscure. We here investigate how dead microglia are removed. We find that although microglia can phagocytose microglial debris in vitro, the territory-dependent competition hinders the microglia-to-microglial debris engulfment in vivo. In contrast, microglial debris is mainly phagocytosed by astrocytes in the brain, facilitated by C4b opsonization. The engulfed microglial fragments are then degraded in astrocytes via RUBICON-dependent LC3-associated phagocytosis (LAP), a form of noncanonical autophagy. Interference with C4b-mediated engulfment and subsequent LAP disrupt the removal and degradation of microglial debris, respectively. Together, we elucidate the cellular and molecular mechanisms of microglial debris removal in mice, extending the knowledge on the maintenance of CNS homeostasis.


Assuntos
Astrócitos , Microglia , Animais , Camundongos , Microglia/metabolismo , Fagocitose/fisiologia , Autofagia , Sistema Nervoso Central , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo
8.
Biochem Soc Trans ; 50(5): 1281-1291, 2022 10 31.
Artigo em Inglês | MEDLINE | ID: mdl-36281986

RESUMO

Phagocytosis triggered by the phospholipid phosphatidylserine (PS) is key for the removal of apoptotic cells in development, tissue homeostasis and infection. Modulation of PS-mediated phagocytosis is an attractive target for therapeutic intervention in the context of atherosclerosis, neurodegenerative disease, and cancer. Whereas the mechanisms of target recognition, lipid and protein signalling, and cytoskeletal remodelling in opsonin-driven modes of phagocytosis are increasingly well understood, PS-mediated phagocytosis has remained more elusive. This is partially due to the involvement of a multitude of receptors with at least some redundancy in functioning, which complicates dissecting their contributions and results in complex downstream signalling networks. This review focusses on the receptors involved in PS-recognition, the signalling cascades that connect receptors to cytoskeletal remodelling required for phagocytosis, and recent progress in our understanding of how phagocytic cup formation is coordinated during PS-mediated phagocytosis.


Assuntos
Doenças Neurodegenerativas , Fosfatidilserinas , Humanos , Fosfatidilserinas/metabolismo , Apoptose/fisiologia , Fagocitose/fisiologia , Transdução de Sinais/fisiologia
9.
Int J Mol Sci ; 23(19)2022 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-36233124

RESUMO

We previously described the participation of canonical phospholipase D isoforms (PLD1 and PLD2) in the inflammatory response of retinal pigment epithelium (RPE) cells exposed to high glucose concentrations (HG). Here, we studied the role of the PLD pathway in RPE phagocytic function. For this purpose, ARPE-19 cells were exposed to HG (33 mM) or to normal glucose concentration (NG, 5.5 mM) and phagocytosis was measured using pHrodo™ green bioparticles® or photoreceptor outer segments (POS). HG exposure for 48 and 72 h reduced phagocytic function of ARPE-19 cells, and this loss of function was prevented when cells were treated with 5 µM of PLD1 (VU0359595 or PLD1i) or PLD2 (VU0285655-1 or PLD2i) selective inhibitors. Furthermore, PLD1i and PLD2i did not affect RPE phagocytosis under physiological conditions and prevented oxidative stress induced by HG. In addition, we demonstrated PLD1 and PLD2 expression in ABC cells, a novel human RPE cell line. Under physiological conditions, PLD1i and PLD2i did not affect ABC cell viability, and partial silencing of both PLDs did not affect ABC cell POS phagocytosis. In conclusion, PLD1i and PLD2i prevent the loss of phagocytic function of RPE cells exposed to HG without affecting RPE function or viability under non-inflammatory conditions.


Assuntos
Fosfolipase D , Linhagem Celular , Células Cultivadas , Glucose/metabolismo , Humanos , Fagocitose/fisiologia , Fosfolipase D/genética , Fosfolipase D/metabolismo , Epitélio Pigmentado da Retina/metabolismo
10.
Front Cell Infect Microbiol ; 12: 1015386, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36299625

RESUMO

Sepsis is associated with a high risk of death, and the crosstalk between gut microbiota and sepsis is gradually revealed. Indole 3-propionic acid (IPA) is a gut microbiota-derived metabolite that exerts immune regulation and organ protective effects. However, the role of IPA in sepsis is not clear. In this study, the role of IPA in sepsis-related survival, clinical scores, bacterial burden, and organ injury was assessed in a murine model of cecal ligation and puncture-induced polymicrobial sepsis. Aryl hydrocarbon receptor (AhR) highly specific inhibitor (CH223191) was used to observe the role of AhR in the protection of IPA against sepsis. The effects of IPA on bacterial phagocytosis by macrophages were investigated in vivo and vitro. The levels of IPA in feces were measured and analyzed in human sepsis patients and patient controls. First, we found that gut microbiota-derived IPA was associated with the survival of septic mice. Then, in animal model, IPA administration protected against sepsis-related mortality and alleviated sepsis-induced bacterial burden and organ injury, which was blunted by AhR inhibitor. Next, in vivo and vitro, IPA enhanced the macrophage phagocytosis through AhR. Depletion of macrophages reversed the protective effects of IPA on sepsis. Finally, on the day of ICU admission (day 0), septic patients had significantly lower IPA level in feces than patient controls. Also, septic patients with bacteremia had significantly lower IPA levels in feces compared with those with non-bacteremia. Furthermore, in septic patients, reduced IPA was associated with worse clinical outcomes, and IPA in feces had similar prediction ability of 28-day mortality with SOFA score, and increased the predictive ability of SOFA score. These findings indicate that gut microbiota-derived IPA can protect against sepsis through host control of infection by promoting macrophages phagocytosis and suggest that IPA may be a new strategy for sepsis treatment.


Assuntos
Microbioma Gastrointestinal , Sepse , Animais , Humanos , Camundongos , Bactérias , Indóis/farmacologia , Macrófagos , Camundongos Endogâmicos C57BL , Fagocitose/fisiologia , Receptores de Hidrocarboneto Arílico , Sepse/microbiologia
11.
J Vis Exp ; (186)2022 08 18.
Artigo em Inglês | MEDLINE | ID: mdl-36063018

RESUMO

Microglia are the resident immune cells of myeloid origin that maintain homeostasis in the brain microenvironment and have become a key player in multiple neurological diseases. Studying human microglia in health and disease represents a challenge due to the extremely limited supply of human cells. Induced pluripotent stem cells (iPSCs) derived from human individuals can be used to circumvent this barrier. Here, it is demonstrated how to differentiate human iPSCs into microglia-like cells (iMGs) for in vitro experimentation. These iMGs exhibit the expected and physiological properties of microglia, including microglia-like morphology, expression of proper markers, and active phagocytosis. Additionally, documentation for isolating and labeling synaptosome substrates derived from human iPSC-derived lower motor neurons (i3LMNs) is provided. A live-cell, longitudinal imaging assay is used to monitor engulfment of human synaptosomes labeled with a pH-sensitive dye, allowing for investigations of iMG's phagocytic capacity. The protocols described herein are broadly applicable to different fields that are investigating human microglia biology and the contribution of microglia to disease.


Assuntos
Células-Tronco Pluripotentes Induzidas , Microglia , Diferenciação Celular/fisiologia , Citofagocitose , Humanos , Fagocitose/fisiologia , Sinaptossomos
12.
FASEB J ; 36(10): e22556, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-36165194

RESUMO

Outer segment phagocytosis (OSP) is a highly-regulated, biological process wherein photoreceptor outer segment (OS) tips are cyclically phagocytosed by the adjacent retinal pigment epithelium (RPE) cells. Often an overlooked retinal process, rhythmic OSP ensures the maintenance of healthy photoreceptors and vision. Daily, the photoreceptors renew OS at their base and the most distal, and likely oldest, OS tips, are phagocytosed by the RPE, preventing the accumulation of photo-oxidative compounds by breaking down phagocytosed OS tips and recycling useful components to the photoreceptors. Light changes often coincide with an escalation of OSP and within hours the phagosomes formed in each RPE cell are resolved. In the last two decades, individual molecular regulators were elucidated. Some of the molecular machinery used by RPE cells for OSP is highly similar to mechanisms used by other phagocytic cells for the clearance of apoptotic cells. Consequently, in the RPE, many molecular regulators of retinal phagocytosis have been elucidated. However, there is still a knowledge gap regarding the key regulators of physiological OSP in vivo between endogenous photoreceptors and the RPE. Understanding the regulation of OSP is of significant clinical interest as age-related macular degeneration (AMD) and inherited retinal diseases (IRD) are linked with altered OSP. Here, we review the in vivo timing of OSP peaks in selected species and focus on the reported in vivo environmental and molecular regulators of OSP.


Assuntos
Degeneração Macular , Epitélio Pigmentado da Retina , Humanos , Fagocitose/fisiologia , Fagossomos , Células Fotorreceptoras , Epitélio Pigmentado da Retina/fisiologia
13.
J Cell Biol ; 221(11)2022 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-36121394

RESUMO

Phagocytosis requires actin dynamics, but whether actomyosin contractility plays a role in this morphodynamic process is unclear. Here, we show that in the retinal pigment epithelium (RPE), particle binding to Mer Tyrosine Kinase (MerTK), a widely expressed phagocytic receptor, stimulates phosphorylation of the Cdc42 GEF Dbl3, triggering activation of MRCKß/myosin-II and its coeffector N-WASP, membrane deformation, and cup formation. Continued MRCKß/myosin-II activity then drives recruitment of a mechanosensing bridge, enabling cytoskeletal force transmission, cup closure, and particle internalization. In vivo, MRCKß is essential for RPE phagocytosis and retinal integrity. MerTK-independent activation of MRCKß signaling by a phosphomimetic Dbl3 mutant rescues phagocytosis in retinitis pigmentosa RPE cells lacking functional MerTK. MRCKß is also required for efficient particle translocation from the cortex into the cell body in Fc receptor-mediated phagocytosis. Thus, conserved MRCKß signaling at the cortex controls spatiotemporal regulation of actomyosin contractility to guide distinct phases of phagocytosis in the RPE and represents the principle phagocytic effector pathway downstream of MerTK.


Assuntos
Actomiosina , Miotonina Proteína Quinase , Fagocitose , Actinas/metabolismo , Actomiosina/metabolismo , Miosina Tipo II/metabolismo , Miotonina Proteína Quinase/metabolismo , Fagocitose/fisiologia , Proteínas Tirosina Quinases , Receptores Fc , c-Mer Tirosina Quinase/metabolismo
14.
Bioconjug Chem ; 33(10): 1837-1851, 2022 10 19.
Artigo em Inglês | MEDLINE | ID: mdl-36153839

RESUMO

Here, we explore whether PEGylation of antibodies can modulate their biodistribution to the eye, an organ once thought to be immune privileged but has recently been shown to be accessible to IV-administered large molecules, such as antibodies. We chose to PEGylate an anti-MerTK antibody, a target with known potential for ocular toxicity, to minimize biodistribution to retinal pigment epithelial cells (RPEs) in the eye by increasing the hydrodynamic volume of the antibody. We used site-specific conjugation to an engineered cysteine on anti-MerTK antibody to chemically attach 40-kDa branched or linear PEG polymers. Despite reduced binding to MerTK on cells, site-specifically PEGylated anti-MerTK retained similar potency in inhibiting MerTK-mediated macrophage efferocytosis of apoptotic cells. Importantly, we found that PEGylation of anti-MerTK significantly reduced MerTK receptor occupancy in RPE cells in both naïve mice and MC-38 tumor-bearing mice, with the branched PEG exhibiting a greater effect than linear PEG. Furthermore, similar to unconjugated anti-MerTK, PEGylated anti-MerTK antibody triggered type I IFN response and exhibited antitumor effect in syngeneic mouse tumor studies. Our results demonstrate the potential of PEGylation to control ocular biodistribution of antibodies.


Assuntos
Cisteína , Neoplasias , Camundongos , Animais , c-Mer Tirosina Quinase/metabolismo , Distribuição Tecidual , Cisteína/metabolismo , Fagocitose/fisiologia , Anticorpos/metabolismo , Neoplasias/metabolismo , Polietilenoglicóis/química , Polímeros/metabolismo , Pigmentos da Retina/metabolismo
15.
Mol Biol Cell ; 33(14): br24, 2022 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-36129777

RESUMO

Phagocytosis requires rapid remodeling of the actin cytoskeleton for extension of membrane protrusions and force generation to ultimately drive the engulfment of targets. The detailed mechanisms of phagocytosis have almost exclusively been studied in immortalized cell lines. Here, we make use of high-resolution imaging and novel biophysical approaches to determine the structural and mechanical features of phagocytosis by primary bone marrow-derived macrophages. We find that the signature behavior of these primary cells is distinct from macrophage-like cell lines; specifically, it is gentle, with only weak target constriction and modest polarization of the F-actin distribution inside the phagocytic cup. We show that long-tailed myosins 1e/f are critical for this organization. Deficiency of myo1e/f causes dramatic shifts in F-actin localization, reducing F-actin at the phagocytic cup base and enhancing F-actin-mediated constriction at the cup rim. Surprisingly, these changes can be almost fully reverted upon inhibition of another myosin motor protein, myosin-II. Hence, we show that the biomechanics and large-scale organization of phagocytic cups is tightly regulated through competing contributions from myosin-Ie/f and myosin-II.


Assuntos
Actinas , Fagocitose , Actinas/metabolismo , Constrição , Fagocitose/fisiologia , Citoesqueleto de Actina/metabolismo , Miosina Tipo II/metabolismo , Miosinas/metabolismo , Macrófagos/metabolismo , Proteínas do Citoesqueleto/metabolismo
16.
Pharmacol Ther ; 238: 108282, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-36130624

RESUMO

Efferocytosis (clearance of apoptotic cells by phagocytosis without inducing inflammation and autoimmunity) is an important mechanism in the resolution of inflammatory processes. Efficient efferocytosis inhibits the accumulation of apoptotic cells/debris and maintains homeostasis before the onset of necrosis (secondary necrosis), which promotes inflammation or injury. Moreover, the detection and clearance of apoptotic cells can promote anti-inflammatory responses. Defective efferocytosis is involved in the pathogenesis of several diseases, such as atherosclerosis, chronic inflammation, autoimmunity and cancer. Statins are 3-hydroxy-3-methylglutaryl coenzyme A-reductase inhibitors which exert cholesterol-lowering effects plus multiple pleiotropic properties, such as inhibition of inflammation and macrophage proliferation. Statins exhibit anti-inflammatory properties by reducing both the prenylation of signaling molecules with downregulation of gene expression and the expression of adhesion molecules, as well as the levels of cytokines and chemokines. Additionally, statins suppress the prenylation of GTPases, such as Rac-1, as a positive regulator of efferocytosis, and RhoA, as a negative regulator of efferocytosis. However, statins alter the membrane balance of Rho GTPases in efferocytosis toward Rac-1. Efferocytosis has modifiable targets, which can be exploited for the treatment of several diseases, although limited attention has been given to the mechanisms by which statins regulate efferocytosis and the resulting therapeutic implications. In this review, we will elaborate on the mechanisms underlying the modulation of apoptotic cell clearance by statins, which, in turn, inhibits uncontrolled inflammation and ensuing diseases.


Assuntos
Inibidores de Hidroximetilglutaril-CoA Redutases , Apoptose , Colesterol , Coenzima A/farmacologia , Citocinas , Humanos , Inibidores de Hidroximetilglutaril-CoA Redutases/farmacologia , Inibidores de Hidroximetilglutaril-CoA Redutases/uso terapêutico , Inflamação/tratamento farmacológico , Necrose/tratamento farmacológico , Oxirredutases , Fagocitose/fisiologia , Proteínas rho de Ligação ao GTP
17.
J Cell Sci ; 135(20)2022 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-36177600

RESUMO

The last step of cell death is cell clearance, a process critical for tissue homeostasis. For efficient cell clearance to occur, phagocytes and dead cells need to reciprocally signal to each other. One important phenomenon that is under-investigated, however, is that phagocytes not only engulf corpses but contribute to cell death progression. The aims of this study were to determine how the phagocytic receptor Draper non-autonomously induces cell death, using the Drosophila ovary as a model system. We found that Draper, expressed in epithelial follicle cells, requires its intracellular signaling domain to kill the adjacent nurse cell population. Kinases Src42A, Shark and JNK (Bsk) were required for Draper-induced nurse cell death. Signs of nurse cell death occurred prior to apparent engulfment and required the caspase Dcp-1, indicating that it uses a similar apoptotic pathway to starvation-induced cell death. These findings indicate that active signaling by Draper is required to kill nurse cells via the caspase Dcp-1, providing novel insights into mechanisms of phagoptosis driven by non-professional phagocytes.


Assuntos
Proteínas de Drosophila , Animais , Feminino , Proteínas de Drosophila/metabolismo , Fagocitose/fisiologia , Receptores Imunológicos , Drosophila/metabolismo , Morte Celular , Caspases , Apoptose/fisiologia , Proteínas Proto-Oncogênicas pp60(c-src)
18.
Elife ; 112022 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-35929733

RESUMO

The phagocytic receptor CED-1 mediates apoptotic cell recognition by phagocytic cells, enabling cell corpse clearance in Caenorhabditis elegans. Whether appropriate levels of CED-1 are maintained for executing the engulfment function remains unknown. Here, we identified the C. elegans E3 ubiquitin ligase tripartite motif containing-21 (TRIM-21) as a component of the CED-1 pathway for apoptotic cell clearance. When the NPXY motif of CED-1 was bound to the adaptor protein CED-6 or the YXXL motif of CED-1 was phosphorylated by tyrosine kinase SRC-1 and subsequently bound to the adaptor protein NCK-1 containing the SH2 domain, TRIM-21 functioned in conjunction with UBC-21 to catalyze K48-linked poly-ubiquitination on CED-1, targeting it for proteasomal degradation. In the absence of TRIM-21, CED-1 accumulated post-translationally and drove cell corpse degradation defects, as evidenced by direct binding to VHA-10. These findings reveal a unique mechanism for the maintenance of appropriate levels of CED-1 to regulate apoptotic cell clearance.


Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans , Animais , Apoptose/fisiologia , Cadáver , Caenorhabditis elegans/fisiologia , Proteínas de Caenorhabditis elegans/metabolismo , Humanos , Proteínas de Membrana/metabolismo , Fagocitose/fisiologia
19.
Biophys J ; 121(17): 3224-3241, 2022 09 06.
Artigo em Inglês | MEDLINE | ID: mdl-35927956

RESUMO

Macrophages use filopodia to withdraw particles toward the cell body for phagocytosis. This can require substantial forces, which the cell generates after bio-mechanical stimuli are transmitted to the filopodium. Adaptation mechanisms to mechanical stimuli are essential for cells, but can a cell iteratively improve filopodia pulling? If so, the underlying mechanic adaptation principles organized on the protein level are unclear. Here, we tackle this problem using optically trapped 1 µm beads, which we tracked interferometrically at 1 MHz during connection to the tips of dorsal filopodia of macrophages. We observe repetitive failures while the filopodium tries to pull the bead out of the optical trap. Analyses of mean bead motions and position fluctuations on the nano-meter and microsecond scale indicate mechanical ruptures caused by a force-dependent actin-membrane connection. We found that beads are retracted three times slower under any load between 5 and 40 pN relative to the no-load transport, which has the same speed as the actin retrograde flow obtained from fluorescent speckle tracking. From this duty ratio of pulling velocities, we estimated a continuous on/off binding with τoff = 2⋅τon, with measured off times τoff = 0.1-0.5 s. Remarkably, we see a gradual increase of filopodia pulling forces from 10 to 30 pN over time and after failures, which points toward an unknown adaptation mechanism. Additionally, we see that the attachment strength and friction between the bead and filopodium tip increases under load and over time. All observations are typical for catch-bond proteins such as integrin-talin complexes. We present a mechanistic picture of adaptive mechanotransduction, which formed by the help of mathematical models for repetitive tip ruptures and reconnections. The analytic mathematical model and the stochastic computer simulations, both based on catch-bond lifetimes, confirmed our measurements. Such catch-bond characteristics could also be important for other immune cells taking up counteracting pathogens.


Assuntos
Actinas , Pseudópodes , Actinas/metabolismo , Macrófagos/metabolismo , Mecanotransdução Celular , Fagocitose/fisiologia , Pseudópodes/metabolismo
20.
Int J Mol Sci ; 23(16)2022 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-36012733

RESUMO

In all mammalian species tested to date, rod photoreceptor outer segment renewal is a circadian process synchronized by light with a burst of outer segment fragment (POS) shedding and POS phagocytosis by the adjacent retinal pigment epithelium (RPE) every morning at light onset. Recent reports show that RPE phagocytosis also increases shortly after dark onset in C57BL/6 (C57) mice. Genetic differences between C57 mice and 129T2/SvEmsJ (129) mice may affect regulation of outer segment renewal. Here, we used quantitative methods to directly compare outer segment renewal in C57 and 129 mouse retina. Quantification of rhodopsin-positive phagosomes in the RPE showed that in 129 mice, rod POS phagocytosis after light onset was significantly increased compared to C57 mice, but that 129 mice did not show a second peak after dark onset. Cone POS phagosome content of RPE cells did not differ by mouse strain with higher phagosome numbers after light than after dark. We further quantified externalization of the "eat me" signal phosphatidylserine by outer segment tips, which precedes POS phagocytosis. Live imaging of retina ex vivo showed that rod outer segments extended PS exposure in both strains but that frequency of outer segments with exposed PS after light onset was lower in C57 than in 129 retina. Taken together, 129 mice lacked a burst of rod outer segment renewal after dark onset. The increases in rod outer segment renewal after light and after dark onset in C57 mice were attenuated compared to the peak after light onset in 129 mice, suggesting an impairment in rhythmicity in C57 mice.


Assuntos
Ritmo Circadiano , Segmento Externo da Célula Bastonete , Animais , Ritmo Circadiano/fisiologia , Mamíferos , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Fagocitose/fisiologia , Fagossomos , Fosfatidilserinas , Epitélio Pigmentado da Retina/fisiologia , Segmento Externo da Célula Bastonete/fisiologia
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