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Blood Jul 2022The extravasation of leukocytes is a critical step during inflammation that requires the localized opening of the endothelial barrier. This process is initiated by the...
The extravasation of leukocytes is a critical step during inflammation that requires the localized opening of the endothelial barrier. This process is initiated by the close interaction of leukocytes with various adhesion molecules such as ICAM-1 on the surface of endothelial cells. Here we reveal that mechanical forces generated by leukocyte-induced clustering of ICAM-1 synergize with fluid shear stress exerted by the flowing blood to increase endothelial plasma membrane tension and to activate the mechanosensitive cation channel PIEZO1. This leads to increases in [Ca2+]i and activation of downstream signaling events including phosphorylation of tyrosine kinases sarcoma (SRC) and protein tyrosine kinase 2 (PYK2), as well as of myosin light chain, resulting in opening of the endothelial barrier. Mice with endothelium-specific Piezo1 deficiency show decreased leukocyte extravasation in different inflammation models. Thus, leukocytes and the hemodynamic microenvironment synergize to mechanically activate endothelial PIEZO1 and subsequent downstream signaling to initiate leukocyte diapedesis.
Topics: Animals; Endothelial Cells; Endothelium, Vascular; Inflammation; Intercellular Adhesion Molecule-1; Ion Channels; Leukocytes; Mice; Transendothelial and Transepithelial Migration
PubMed: 35443048
DOI: 10.1182/blood.2021014614 -
Immunity Sep 2021The migration of neutrophils from the blood circulation to sites of infection or injury is a key immune response and requires the breaching of endothelial cells (ECs)...
The migration of neutrophils from the blood circulation to sites of infection or injury is a key immune response and requires the breaching of endothelial cells (ECs) that line the inner aspect of blood vessels. Unregulated neutrophil transendothelial cell migration (TEM) is pathogenic, but the molecular basis of its physiological termination remains unknown. Here, we demonstrated that ECs of venules in inflamed tissues exhibited a robust autophagic response that was aligned temporally with the peak of neutrophil trafficking and was strictly localized to EC contacts. Genetic ablation of EC autophagy led to excessive neutrophil TEM and uncontrolled leukocyte migration in murine inflammatory models, while pharmacological induction of autophagy suppressed neutrophil infiltration into tissues. Mechanistically, autophagy regulated the remodeling of EC junctions and expression of key EC adhesion molecules, facilitating their intracellular trafficking and degradation. Collectively, we have identified autophagy as a modulator of EC leukocyte trafficking machinery aimed at terminating physiological inflammation.
Topics: Animals; Autophagy; Chemotaxis, Leukocyte; Endothelial Cells; Human Umbilical Vein Endothelial Cells; Humans; Inflammation; Intercellular Junctions; Mice; Mice, Inbred C57BL; Neutrophil Infiltration; Neutrophils; Transendothelial and Transepithelial Migration
PubMed: 34363750
DOI: 10.1016/j.immuni.2021.07.012 -
Immunity Oct 2023Engagement of platelet endothelial cell adhesion molecule 1 (PECAM, PECAM-1, CD31) on the leukocyte pseudopod with PECAM at the endothelial cell border initiates...
Engagement of platelet endothelial cell adhesion molecule 1 (PECAM, PECAM-1, CD31) on the leukocyte pseudopod with PECAM at the endothelial cell border initiates transendothelial migration (TEM, diapedesis). We show, using fluorescence lifetime imaging microscopy (FLIM), that physical traction on endothelial PECAM during TEM initiated the endothelial signaling pathway. In this role, endothelial PECAM acted as part of a mechanotransduction complex with VE-cadherin and vascular endothelial growth factor receptor 2 (VEGFR2), and this predicted that VEGFR2 was required for efficient TEM. We show that TEM required both VEGFR2 and the ability of its Y1175 to be phosphorylated, but not VEGF or VEGFR2 endogenous kinase activity. Using inducible endothelial-specific VEGFR2-deficient mice, we show in three mouse models of inflammation that the absence of endothelial VEGFR2 significantly (by ≥75%) reduced neutrophil extravasation by selectively blocking diapedesis. These findings provide a more complete understanding of the process of transmigration and identify several potential anti-inflammatory targets.
Topics: Animals; Mice; Cell Adhesion; Cell Movement; Endothelium, Vascular; Mechanotransduction, Cellular; Platelet Endothelial Cell Adhesion Molecule-1; Transendothelial and Transepithelial Migration; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-2
PubMed: 37643615
DOI: 10.1016/j.immuni.2023.08.001 -
Advances in Immunology 2016The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. Neutrophil recruitment to inflamed... (Review)
Review
The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. Neutrophil recruitment to inflamed tissues occurs in a well-defined stepwise manner, which includes elements of neutrophil rolling, firm adhesion, and crawling onto the endothelial cell surface before transmigrating across the endothelial barrier. This latter step known as diapedesis can occur at the endothelial cell junction (paracellular) or directly through the endothelial cell body (transcellular). The extravasation cascade is controlled by series of engagement of various adhesive modules, which result in activation of bidirectional signals to neutrophils and endothelial cells for adequate cellular response. This review will focus on recent advances in our understanding of mechanism of leukocyte crawling and diapedesis, with an emphasis on leukocyte-endothelial interactions and the signaling pathways they transduce to determine the mode of diapedesis, junctional or nonjunctional. I will also discuss emerging evidence highlighting key differences in the two modes of diapedesis and why it is clinically important to understand specificity in the regulation of diapedesis.
Topics: Animals; Cell Adhesion; Cell Adhesion Molecules; Cell Communication; Endothelial Cells; Endothelium, Vascular; Humans; Inflammation; Leukocytes; Neutrophils; Signal Transduction; Transendothelial and Transepithelial Migration
PubMed: 26791857
DOI: 10.1016/bs.ai.2015.09.001 -
Nature Reviews. Immunology Mar 2013Neutrophils have traditionally been thought of as simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions. More recently, it... (Review)
Review
Neutrophils have traditionally been thought of as simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions. More recently, it has become apparent that neutrophils are, in fact, complex cells capable of a vast array of specialized functions. Although neutrophils are undoubtedly major effectors of acute inflammation, several lines of evidence indicate that they also contribute to chronic inflammatory conditions and adaptive immune responses. Here, we discuss the key features of the life of a neutrophil, from its release from bone marrow to its death. We discuss the possible existence of different neutrophil subsets and their putative anti-inflammatory roles. We focus on how neutrophils are recruited to infected or injured tissues and describe differences in neutrophil recruitment between different tissues. Finally, we explain the mechanisms that are used by neutrophils to promote protective or pathological immune responses at different sites.
Topics: Adaptive Immunity; Animals; Bone Marrow Cells; Cell Adhesion; Cell Death; Cell Differentiation; Cellular Senescence; Chemokines; Chemotaxis, Leukocyte; Endothelium, Vascular; Humans; Immunity, Innate; Inflammation; Mice; Neutrophil Activation; Neutrophil Infiltration; Neutrophils; Receptors, Chemokine; Transendothelial and Transepithelial Migration; Wound Healing
PubMed: 23435331
DOI: 10.1038/nri3399 -
Immunity Dec 2018Neutrophils require directional cues to navigate through the complex structure of venular walls and into inflamed tissues. Here we applied confocal intravital microscopy...
Neutrophils require directional cues to navigate through the complex structure of venular walls and into inflamed tissues. Here we applied confocal intravital microscopy to analyze neutrophil emigration in cytokine-stimulated mouse cremaster muscles. We identified differential and non-redundant roles for the chemokines CXCL1 and CXCL2, governed by their distinct cellular sources. CXCL1 was produced mainly by TNF-stimulated endothelial cells (ECs) and pericytes and supported luminal and sub-EC neutrophil crawling. Conversely, neutrophils were the main producers of CXCL2, and this chemokine was critical for correct breaching of endothelial junctions. This pro-migratory activity of CXCL2 depended on the atypical chemokine receptor 1 (ACKR1), which is enriched within endothelial junctions. Transmigrating neutrophils promoted a self-guided migration response through EC junctions, creating a junctional chemokine "depot" in the form of ACKR1-presented CXCL2 that enabled efficient unidirectional luminal-to-abluminal migration. Thus, CXCL1 and CXCL2 act in a sequential manner to guide neutrophils through venular walls as governed by their distinct cellular sources.
Topics: Animals; Abdominal Muscles; Chemokine CXCL1; Chemokine CXCL2; Duffy Blood-Group System; Endothelial Cells; Gene Expression Profiling; Gene Expression Regulation; Intercellular Junctions; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Neutrophils; Receptors, Cell Surface; Transendothelial and Transepithelial Migration; Tumor Necrosis Factor-alpha
PubMed: 30446388
DOI: 10.1016/j.immuni.2018.09.018 -
Immunity Nov 2010Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These... (Review)
Review
Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These contain proteins that enable the neutrophil to deliver lethal hits against microorganisms, but also to cause great tissue damage. Neutrophils circulate in the blood as dormant cells. At sites of infection, endothelial cells capture bypassing neutrophils and guide them through the endothelial cell lining whereby the neutrophils are activated and tuned for the subsequent interaction with microbes. Once in tissues, neutrophils kill microorganisms by microbicidal agents liberated from granules or generated by metabolic activation. As a final act, neutrophils can extrude stands of DNA with bactericidal proteins attached that act as extracellular traps for microorganisms.
Topics: Animals; Anti-Infective Agents; Bone Marrow; Cell Adhesion; Cell Adhesion Molecules; Exocytosis; Hematopoiesis; Hematopoietic Stem Cells; Humans; Infections; Mice; Neutrophils; Phagocytosis; Secretory Vesicles; Transendothelial and Transepithelial Migration
PubMed: 21094463
DOI: 10.1016/j.immuni.2010.11.011 -
Immunity Nov 2014Leukocyte migration through activated venular walls is a fundamental immune response that is prerequisite to the entry of effector cells such as neutrophils, monocytes,... (Review)
Review
Leukocyte migration through activated venular walls is a fundamental immune response that is prerequisite to the entry of effector cells such as neutrophils, monocytes, and effector T cells to sites of infection, injury, and stress within the interstitium. Stimulation of leukocytes is instrumental in this process with enhanced temporally controlled leukocyte adhesiveness and shape-changes promoting leukocyte attachment to the inner wall of blood vessels under hydrodynamic forces. This initiates polarized motility of leukocytes within and through venular walls and transient barrier disruption facilitated sequentially by stimulated vascular cells, i.e., endothelial cells and their associated pericytes. Perivascular cells such as macrophages and mast cells that act as tissue inflammatory sentinels can also directly and indirectly regulate the exit of leukocytes from the vascular lumen. In this review, we discuss current knowledge and open questions regarding the mechanisms involved in the interactions of different effector leukocytes with peripheral vessels in extralymphoid organs.
Topics: Blood Vessels; Cell Adhesion; Endothelium, Vascular; Humans; Inflammation; Integrins; Leukocytes; Macrophages; Mast Cells; Neutrophils; T-Lymphocytes; Transendothelial and Transepithelial Migration
PubMed: 25517612
DOI: 10.1016/j.immuni.2014.10.008 -
Blood May 2019Neutrophils represent the first line of cellular defense against invading microorganism by rapidly moving across the blood-endothelial cell (EC) barrier and exerting... (Review)
Review
Neutrophils represent the first line of cellular defense against invading microorganism by rapidly moving across the blood-endothelial cell (EC) barrier and exerting effector cell functions. The neutrophil recruitment cascade to inflamed tissues involves elements of neutrophil rolling, firm adhesion, and crawling onto the EC surface before extravasating by breaching the EC barrier. The interaction between neutrophils and ECs occurs via various adhesive modules and is a critical event determining the mode of neutrophil transmigration, either at the EC junction (paracellular) or directly through the EC body (transcellular). Once thought to be a homogenous entity, new evidence clearly points to the plasticity of neutrophil functions. This review will focus on recent advances in our understanding of the mechanism of the neutrophil transmigration process. It will discuss how neutrophil-EC interactions and the subsequent mode of diapedesis, junctional or nonjunctional, can be context dependent and how this plasticity may be exploited clinically.
Topics: Animals; Cell Adhesion; Cell Communication; Endothelial Cells; Humans; Inflammation; Neutrophils; Transendothelial and Transepithelial Migration
PubMed: 30898863
DOI: 10.1182/blood-2018-12-844605 -
Nature Communications Nov 2022Neutrophil diapedesis is an immediate step following infections and injury and is driven by complex interactions between leukocytes and various components of the blood...
Neutrophil diapedesis is an immediate step following infections and injury and is driven by complex interactions between leukocytes and various components of the blood vessel wall. Here, we show that perivascular mast cells (MC) are key regulators of neutrophil behaviour within the sub-endothelial space of inflamed venules. Using confocal intravital microscopy, we observe directed abluminal neutrophil motility along pericyte processes towards perivascular MCs, a response that created neutrophil extravasation hotspots. Conversely, MC-deficiency and pharmacological or genetic blockade of IL-17A leads to impaired neutrophil sub-endothelial migration and breaching of the pericyte layer. Mechanistically, identifying MCs as a significant cellular source of IL-17A, we establish that MC-derived IL-17A regulates the enrichment of key effector molecules ICAM-1 and CXCL1 in nearby pericytes. Collectively, we identify a novel MC-IL-17A-pericyte axis as modulator of the final steps of neutrophil diapedesis, with potential translational implications for inflammatory disorders driven by increased neutrophil diapedesis.
Topics: Transendothelial and Transepithelial Migration; Neutrophils; Pericytes; Interleukin-17; Mast Cells
PubMed: 36396641
DOI: 10.1038/s41467-022-34695-7