Myosin 1f is specifically required for neutrophil migration in 3D environments during acute inflammation

Neutrophils-biology and diversity

Neutrophils, the most abundant white blood cells in the human circulation, play crucial roles in various diseases, including kidney disease. Traditionally viewed as short-lived pro-inflammatory phagocytes that release reactive oxygen species, cytokines and neutrophil extracellular traps, recent studies have revealed their complexity and heterogeneity, thereby challenging this perception. Neutrophils are now recognized as transcriptionally active cells capable of proliferation and reverse migration, displaying phenotypic and functional heterogeneity. They respond to a wide range of signals and deploy various cargo to influence the activity of other cells in the circulation and in tissues. They can regulate the behavior of multiple immune cell types, exhibit innate immune memory, and contribute to both acute and chronic inflammatory responses while also promoting inflammation resolution in a context-dependent manner. Here, we explore the origin and heterogeneity of neutrophils, their functional diversity, and the cues that regulate their effector functions. We also examine their emerging role in infectious and non-infectious diseases with a particular emphasis on kidney disease. Understanding the complex behavior of neutrophils during tissue injury and inflammation may provide novel insights, thereby paving the way for potential therapeutic strategies to manage acute and chronic conditions. By deciphering their multifaceted role, targeted interventions can be developed to address the intricacies of neutrophil-mediated immune responses and improve disease outcomes.

Microfluidic device reveals new insights into impairment of neutrophil transmigration in patients with sepsis

Neutrophils need to migrate through tight tissue spaces to eliminate pathogens, but their movement is often hindered by their large and stiff nuclei. Neutrophil migration is impaired in sepsis patients, but it is unclear whether this defect is related to the deformability of their nuclei. Herein, we designed microfluidic devices with micron-scale narrow slits to simulate biological barriers. This setup allowed us to observe and record neutrophil movement and nuclear deformation in real-time. We also developed a method for morphological analysis to quantify nucleus deformation in numerous individual cells. Our studies showed that neutrophils from healthy individuals could adjust their nuclear shape to squeeze through these constrictions, whereas those from sepsis patients demonstrated less flexibility. Neutrophils with rigid nuclei struggled to pass through narrow gaps and were more likely to rupture under pressure. These findings suggest that the migration defects of neutrophils observed in sepsis may be attributed to the inability of neutrophils to deform their nuclei, highlighting the crucial role of microfluidic technologies in offering new insights into migration defects under pathological conditions.

BMP4-Induced Suppression of Breast Cancer Metastasis Is Associated with Inhibition of Cholesterol Biosynthesis

We reported previously that in preclinical models, BMP4 is a potent inhibitor of breast cancer metastasis and that high BMP4 protein levels predict favourable patient outcomes. Here, we analysed a breast cancer xenograft with or without enforced expression of BMP4 to gain insight into the mechanisms by which BMP4 suppresses metastasis. Transcriptomic analysis of cancer cells recovered from primary tumours and phosphoproteomic analyses of cancer cells exposed to recombinant BMP4 revealed that BMP4 inhibits cholesterol biosynthesis, with many genes in this biosynthetic pathway being downregulated by BMP4. The treatment of mice bearing low-BMP4 xenografts with a cholesterol-lowering statin partially mimicked the anti-metastatic activity of BMP4. Analysis of a cohort of primary breast cancers revealed a reduced relapse rate for patients on statin therapy if their tumours exhibited low BMP4 levels. These findings indicate that BMP4 may represent a predictive biomarker for the benefit of additional statin therapy in breast cancer patients.

Matrix mechanics regulate the polarization state of bone marrow-derived neutrophils through the JAK1/STAT3 signaling pathway

Matrix mechanics regulate essential cell behaviors through mechanotransduction, and as one of its most important elements, substrate stiffness was reported to regulate cell functions such as viability, communication, migration, and differentiation. Neutrophils (Neus) predominate the early inflammatory response and initiate regeneration. The activation of Neus can be regulated by physical cues; however, the functional alterations of Neus by substrate stiffness remain unknown, which is critical in determining the outcomes of engineered tissue mimics. Herein, a three-dimensional (3D) culture system made of hydrogels was developed to explore the effects of varying stiffnesses (1.5, 2.6, and 5.7 kPa) on the states of Neus. Neus showed better cell integrity and viability in the 3D system. Moreover, it was shown that the stiffer matrix tended to induce Neus toward an anti-inflammatory phenotype (N2) with less adhesion molecule expression, less reactive oxygen species (ROS) production, and more anti-inflammatory cytokine secretion. Additionally, the aortic ring assay indicated that Neus cultured in a stiffer matrix significantly increased vascular sprouting. RNA sequencing showed that a stiffer matrix could significantly activate JAK1/STAT3 signaling in Neus and the inhibition of JAK1 ablated the stiffness-dependent increase in the expression of CD182 (an N2 marker). Taken together, these results demonstrate that a stiffer matrix promotes Neus to shift to the N2 phenotype, which was regulated by JAK1/STAT3 pathway. This study lays the groundwork for further research on fabricating engineered tissue mimics, which may provide more treatment options for ischemic diseases and bone defects. STATEMENT OF SIGNIFICANCE.

The circadian neutrophil, inside-out

The circadian clock has sway on a myriad of physiological targets, among which the immune and inflammatory systems are particularly prominent. In this review, we discuss how neutrophils, the wildcard of the immune system, are regulated by circadian oscillations. We describe cell-intrinsic and extrinsic diurnal mechanisms governing the general physiology and function of these cells, from purely immune to homeostatic. Repurposing the concepts discovered in other cell types, we then speculate on various uncharted avenues of neutrophil-circadian relationships, such as topology, metabolism, and the regulation of tissue clocks, with the hope of identifying exciting new avenues of work in the context of circadian immunity.

The role of G protein-coupled receptor in neutrophil dysfunction during sepsis-induced acute respiratory distress syndrome

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.

Myo1f has an essential role in γδT intraepithelial lymphocyte adhesion and migration

γδT intraepithelial lymphocyte represents up to 60% of the small intestine intraepithelial compartment. They are highly migrating cells and constantly interact with the epithelial cell layer and lamina propria cells. This migratory phenotype is related to the homeostasis of the small intestine, the control of bacterial and parasitic infections, and the epithelial shedding induced by LPS. Here, we demonstrate that Myo1f participates in the adhesion and migration of intraepithelial lymphocytes. Using long-tailed class I myosins KO mice, we identified the requirement of Myo1f for their migration to the small intestine intraepithelial compartment. The absence of Myo1f affects intraepithelial lymphocytes' homing due to reduced CCR9 and α4β7 surface expression. In vitro, we confirm that adhesion to integrin ligands and CCL25-dependent and independent migration of intraepithelial lymphocytes are Myo1f-dependent. Mechanistically, Myo1f deficiency prevents correct chemokine receptor and integrin polarization, leading to reduced tyrosine phosphorylation which could impact in signal transduction. Overall, we demonstrate that Myo1f has an essential role in the adhesion and migration in γδT intraepithelial lymphocytes.

Class I Myosins, molecular motors involved in cell migration and cancer

Class I Myosins are a subfamily of motor proteins with ATPase activity and a characteristic structure conserved in all myosins: A N-Terminal Motor Domain, a central Neck and a C terminal Tail domain. Humans have eight genes for these myosins. Class I Myosins have different functions: regulate membrane tension, participate in endocytosis, exocytosis, intracellular trafficking and cell migration. Cell migration is influenced by many cellular components including motor proteins, like myosins. Recently has been reported that changes in myosin expression have an impact on the migration of cancer cells, the formation of infiltrates and metastasis. We propose that class I myosins might be potential markers for future diagnostic, prognostic or even as therapeutic targets in leukemia and other cancers.Abbreviations: Myo1g: Myosin 1g; ALL: Acute Lymphoblastic Leukemia, TH1: Tail Homology 1; TH2: Tail Homology 2; TH3: Tail Homology 3.

Atypical CXCL12 signaling enhances neutrophil migration by modulating nuclear deformability

To reach inflamed tissues from the circulation, neutrophils must overcome physical constraints imposed by the tissue architecture, such as the endothelial barrier or the three-dimensional (3D) interstitial space. In these microenvironments, neutrophils are forced to migrate through spaces smaller than their own diameter. One of the main challenges for cell passage through narrow gaps is the deformation of the nucleus, the largest and stiffest organelle in cells. Here, we showed that chemokines, the extracellular signals that guide cell migration in vivo, modulated nuclear plasticity to support neutrophil migration in restricted microenvironments. Exploiting microfabricated devices, we found that the CXC chemokine CXCL12 enhanced the nuclear pliability of mouse bone marrow–derived neutrophils to sustain their migration in 3D landscapes. This previously uncharacterized function of CXCL12 was mediated by the atypical chemokine receptor ACKR3 (also known as CXCR7), required protein kinase A (PKA) activity, and induced chromatin compaction, which resulted in enhanced cell migration in 3D. Thus, we propose that chemical cues regulate the nuclear plasticity of migrating leukocytes to optimize their motility in restricted microenvironments.

Roles of the nucleus in leukocyte migration

Leukocytes patrol our bodies in search of pathogens and migrate to sites of injury in response to various stimuli. Rapid and directed leukocyte motility is therefore crucial to our immunity. The nucleus is the largest and stiffest cellular organelle and a mechanical obstacle for migration through constrictions. However, the nucleus is also essential for 3D cell migration. Here, we review the roles of the nucleus in leukocyte migration, focusing on how cells deform their nuclei to aid cell motility and the contributions of the nucleus to cell migration. We discuss the regulation of the nuclear biomechanics by the nuclear lamina and how it, together with the cytoskeleton, modulates the shapes of leukocyte nuclei. We then summarize the functions of nesprins and SUN proteins in leukocytes and discuss how forces are exerted on the nucleus. Finally, we examine the mechanical roles of the nucleus in cell migration, including its roles in regulating the direction of migration and path selection.

Intravital calcium imaging in myeloid leukocytes identifies calcium frequency spectra as indicators of functional states

The assessment of leukocyte activation in vivo is mainly based on surrogate parameters, such as cell shape changes and migration patterns. Consequently, additional parameters are required to dissect the complex spatiotemporal activation of leukocytes during inflammation. Here, we showed that intravital microscopy of myeloid leukocyte Ca²⁺ signals with Ca²⁺ reporter mouse strains combined with bioinformatic signal analysis provided a tool to assess their activation in vivo. We demonstrated by two-photon microscopy that tissue-resident macrophages reacted to sterile inflammation in the cremaster muscle with Ca²⁺ transients in a distinct spatiotemporal pattern. Moreover, through high-resolution, intravital spinning disk confocal microscopy, we identified the intracellular Ca²⁺ signaling patterns of neutrophils during the migration cascade in vivo. These patterns were modulated by the Ca²⁺ channel Orai1 and Gα_i-coupled GPCRs, whose effects were evident through analysis of the range of frequencies of the Ca²⁺ signal (frequency spectra), which provided insights into the complex patterns of leukocyte Ca²⁺ oscillations. Together, these findings establish Ca²⁺ frequency spectra as an additional dimension to assess leukocyte activation and migration during inflammation in vivo.

The Taspase1/Myosin1f-axis regulates filopodia dynamics

The unique threonine protease Tasp1 impacts not only ordered development and cell proliferation but also pathologies. However, its substrates and the underlying molecular mechanisms remain poorly understood. We demonstrate that the unconventional Myo1f is a Tasp1 substrate and unravel the physiological relevance of this proteolysis. We classify Myo1f as a nucleo-cytoplasmic shuttle protein, allowing its unhindered processing by nuclear Tasp1 and an association with chromatin. Moreover, we show that Myo1f induces filopodia resulting in increased cellular adhesion and migration. Importantly, filopodia formation was antagonized by Tasp1-mediated proteolysis, supported by an inverse correlation between Myo1f concentration and Tasp1 expression level. The Tasp1/Myo1f-axis might be relevant in human hematopoiesis as reduced Tasp1 expression coincided with increased Myo1f concentrations and filopodia in macrophages compared to monocytes and vice versa. In sum, we discovered Tasp1-mediated proteolysis of Myo1f as a mechanism to fine-tune filopodia formation, inter alia relevant for cells of the immune system.

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Myosin1f is a nucleo-cytoplasmic shuttle protein temporarily located in the nucleus

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Myosin1f induces filopodia resulting in increased cellular adhesion and migration

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The protease Taspase1 cleaves Myosin1f, thereby impairing its function

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Taspase1 and Myosin1f inversely correlate in immune cell differentiation

Neutrophils in acute inflammation: current concepts and translational implications

Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.

Quantifying the Probing and Selection of Microenvironmental Pores by Motile Immune Cells

Immune cells are constantly on the move through multicellular organisms to explore and respond to pathogens and other harmful insults. While moving, immune cells efficiently traverse microenvironments composed of tissue cells and extracellular fibers, which together form complex environments of various porosity, stiffness, topography, and chemical composition. In this protocol we describe experimental procedures to investigate immune cell migration through microenvironments of heterogeneous porosity. In particular, we describe micro-channels, micro-pillars, and collagen networks as cell migration paths with alternative pore size choices. Employing micro-channels or micro-pillars that divide at junctions into alternative paths with initially differentially sized pores allows us to precisely (1) measure the cellular translocation time through these porous path junctions, (2) quantify the cellular preference for individual pore sizes, and (3) image cellular components like the nucleus and the cytoskeleton. This reductionistic experimental setup thus can elucidate how immune cells perform decisions in complex microenvironments of various porosity like the interstitium. The setup further allows investigation of the underlying forces of cellular squeezing and the consequences of cellular deformation on the integrity of the cell and its organelles. As a complementary approach that does not require any micro-engineering expertise, we describe the usage of three-dimensional collagen networks with different pore sizes. Whereas we here focus on dendritic cells as a model for motile immune cells, the described protocols are versatile as they are also applicable for other immune cell types like neutrophils and non-immune cell types such as mesenchymal and cancer cells. In summary, we here describe protocols to identify the mechanisms and principles of cellular probing, decision making, and squeezing during cellular movement through microenvironments of heterogeneous porosity. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Immune cell migration in micro-channels and micro-pillars with defined pore sizes Support Protocol 1: Epoxy replica of generated and/or published micro-structures Support Protocol 2: Dendritic cell differentiation Basic Protocol 2: Immune cell migration in 3D collagen networks of variable pore sizes.

Light-Sheet Scattering Microscopy to Visualize Long-Term Interactions Between Cells and Extracellular Matrix

Visualizing interactions between cells and the extracellular matrix (ECM) mesh is important to understand cell behavior and regulatory mechanisms by the extracellular environment. However, long term visualization of three-dimensional (3D) matrix structures remains challenging mainly due to photobleaching or blind spots perpendicular to the imaging plane. Here, we combine label-free light-sheet scattering microcopy (LSSM) and fluorescence microscopy to solve these problems. We verified that LSSM can reliably visualize structures of collagen matrices from different origin including bovine, human and rat tail. The quality and intensity of collagen structure images acquired by LSSM did not decline with time. LSSM offers abundant wavelength choice to visualize matrix structures, maximizing combination possibilities with fluorescently-labelled cells, allowing visualizing of long-term ECM-cell interactions in 3D. Interestingly, we observed ultrathin thread-like structures between cells and matrix using LSSM, which were not observed by normal fluorescence microscopy. Transient local alignment of matrix by cell-applied forces can be observed. In summary, LSSM provides a powerful and robust approach to investigate the complex interplay between cells and ECM.

ADAM8 signaling drives neutrophil migration and ARDS severity

Acute respiratory distress syndrome (ARDS) results in catastrophic lung failure and has an urgent, unmet need for improved early recognition and therapeutic development. Neutrophil influx is a hallmark of ARDS and is associated with the release of tissue-destructive immune effectors, such as matrix metalloproteinases (MMPs) and membrane-anchored metalloproteinase disintegrins (ADAMs). Here, we observed using intravital microscopy that Adam8-/- mice had impaired neutrophil transmigration. In mouse pneumonia models, both genetic deletion and pharmacologic inhibition of ADAM8 attenuated neutrophil infiltration and lung injury while improving bacterial containment. Unexpectedly, the alterations of neutrophil function were not attributable to impaired proteolysis but resulted from reduced intracellular interactions of ADAM8 with the actin-based motor molecule Myosin1f that suppressed neutrophil motility. In 2 ARDS cohorts, we analyzed lung fluid proteolytic signatures and identified that ADAM8 activity was positively correlated with disease severity. We propose that in acute inflammatory lung diseases such as pneumonia and ARDS, ADAM8 inhibition might allow fine-tuning of neutrophil responses for therapeutic gain.

Neutrophils Culture in Collagen Gel System

Neutrophils (Neu) migrate rapidly to damaged tissue and play critical roles in host defense and tissue homeostasis, including the intestinal epithelia injuries and immune responses. Although their important roles in these diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Moreover, the standard cell culturing on plastic plates (two-dimensional (2D) cultures) does not represent the actual microenvironment where cells reside in tissues. In this study, we developed a new three-dimensional (3D) culture system for human and mouse peripheral blood Neu, which is made of hydrogel. The Neu showed much better cell integrity and less cell debris in the 3D culture system compared to that in 2D culture system. Moreover, the 3D culture system was more suitable for the observation of neutrophil extracellular traps (NETs) stimulated by the classical stimulation phorbol ester (PMA), and other damage associated molecular patterns (DAMPs) such as Lipopolysaccharide (LPS)/ATP, interleukin-1 β (IL-1β) and tumor necrosis factor α (TNFα) than the 2D culture system. Moreover, NETs phenomenon in 3D culture system is similar to that in vivo. In addition, the 3D culture system was evaluated to co-culturing Neu and other parenchymal cells, such as colon mucosal epithelial cell lines. In conclusion, the 3D culture system could maintain better properties of Neu than that in 2D culture system and it may reduce the gap between in vitro an in vivo experimentations.

Myosin 1g and 1f: A Prospective Analysis in NK Cell Functions

NK cells are contained in the ILC1 group; they are recognized for their antiviral and antitumor cytotoxic capacity; NK cells also participate in other immune response processes through cytokines secretion. However, the mechanisms that regulate these functions are poorly understood since NK cells are not as abundant as other lymphocytes, which has made them difficult to study. Using public databases, we identified that NK cells express mRNA encoding class I myosins, among which Myosin 1g and Myosin 1f are prominent. Therefore, this mini-review aims to generate a model of the probable participation of Myosin 1g and 1f in NK cells, based on information reported about the function of these myosins in other leukocytes.

Complement C5a induces the formation of neutrophil extracellular traps by myeloid-derived suppressor cells to promote metastasis

Myeloid-derived suppressor cells (MDSCs) play a major role in cancer progression. In this study, we investigated the mechanisms by which complement C5a increases the capacity of polymorphonuclear MDSCs (PMN-MDSCs) to promote tumor growth and metastatic spread. Stimulation of PMN-MDSCs with C5a favored the invasion of cancer cells via a process dependent on the formation of neutrophil extracellular traps (NETs). NETosis was dependent on the production of high mobility group box 1 (HMGB1) by cancer cells. Moreover, C5a induced the surface expression of the HMGB1 receptors TLR4 and RAGE in PMN-MDSCs. In a mouse lung metastasis model, inhibition of C5a, C5a receptor-1 (C5aR1) or NETosis reduced the number of circulating-tumor cells (CTCs) and the metastatic burden. In support of the translational relevance of these findings, C5a was able to stimulate migration and NETosis in PMN-MDSCs obtained from lung cancer patients. Furthermore, myeloperoxidase (MPO)-DNA complexes, as markers of NETosis, were elevated in lung cancer patients and significantly correlated with C5a levels. In conclusion, C5a induces the formation of NETs from PMN-MDSCs in the presence of cancer cells, which may facilitate cancer cell dissemination and metastasis.

Myosin 1f-mediated activation of microglia contributes to the photoreceptor degeneration in a mouse model of retinal detachment

Photoreceptor death and neurodegeneration is the leading cause of irreversible vision loss. The inflammatory response of microglia plays an important role in the process of neurodegeneration. In this study, we chose retinal detachment as the model of photoreceptor degeneration. We found Myosin 1f was upregulated after retinal detachment, and it was specifically expressed in microglia. Deficiency of myosin 1f protected against photoreceptor apoptosis by inhibiting microglia activation. The elimination of microglia can abolish the protective effect of myosin 1f deficiency. After stimulation by LPS, microglia with myosin 1f deficiency showed downregulation of the MAPK and AKT pathways. Our results demonstrated that myosin 1f plays a crucial role in microglia-induced neuroinflammation after retinal injury and photoreceptor degeneration by regulating two classic inflammatory pathways and thereby decreasing the expression of inflammatory cytokines. Knockout of myosin 1f reduces the intensity of the immune response and prevents cell death of photoreceptor, suggesting that myosin 1f can be inhibited to prevent a decline in visual acuity after retinal detachment.

The spatio-temporal control of effector T cell migration

Effector T cells leave the lymph nodes armed with specialized functional attributes. Their antigenic targets may be located anywhere in the body, posing the ultimate challenge: how to efficiently identify the target tissue, navigate through a complex tissue matrix and, ultimately, locate the immunological insult. Recent advances in real-time in situ imaging of effector T cell migratory behaviour have revealed a great degree of mechanistic plasticity that enables effector T cells to push and squeeze their way through inflamed tissues. This process is shaped by an array of 'stop' and 'go' guidance signals including target antigens, chemokines, integrin ligands and the mechanical cues of the inflamed microenvironment. Effector T cells must sense and interpret these competing signals to correctly position themselves to mediate their effector functions for complete and durable responses in infectious disease and malignancy. Tuning T cell migration therapeutically will require a new understanding of this complex decision-making process.

MYO1F regulates antifungal immunity by regulating acetylation of microtubules

Each year, the global mortality rates for fungal diseases now exceed those for malaria and breast cancer and are currently comparable to those for tuberculosis and HIV. The limited scope of currently available antifungal drugs is the major factor underlying the observed high mortality rate. Here, we provide evidence that Myosin IF (MYO1F) plays a critical role in the mediating of signaling molecules “trafficking from membrane to cytoplasm,” and this process is essential for the antifungal signaling pathway activation. Moreover, we provide evidence that Sirt2 deacetylase inhibitors promote antifungal immunity and protect mice from lethal Candida albicans infection, which indicates that the Sirt2 could be a good therapeutic target for the antifungal drug development.

Opportunistic fungal infections have become one of the leading causes of death among immunocompromised patients, resulting in an estimated 1.5 million deaths each year worldwide. The molecular mechanisms that promote host defense against fungal infections remain elusive. Here, we find that Myosin IF (MYO1F), an unconventional myosin, promotes the expression of genes that are critical for antifungal innate immune signaling and proinflammatory responses. Mechanistically, MYO1F is required for dectin-induced α-tubulin acetylation, acting as an adaptor that recruits both the adaptor AP2A1 and α-tubulin N-acetyltransferase 1 to α-tubulin; in turn, these events control the membrane-to-cytoplasm trafficking of spleen tyrosine kinase and caspase recruitment domain-containing protein 9. Myo1f-deficient mice are more susceptible than their wild-type counterparts to the lethal sequelae of systemic infection with Candida albicans. Notably, administration of Sirt2 deacetylase inhibitors, namely AGK2, AK-1, or AK-7, significantly increases the dectin-induced expression of proinflammatory genes in mouse bone marrow–derived macrophages and microglia, thereby protecting mice from both systemic and central nervous system C. albicans infections. AGK2 also promotes proinflammatory gene expression in human peripheral blood mononuclear cells after Dectin stimulation. Taken together, our findings describe a key role for MYO1F in promoting antifungal immunity by regulating the acetylation of α-tubulin and microtubules, and our findings suggest that Sirt2 deacetylase inhibitors may be developed as potential drugs for the treatment of fungal infections.

HIF2α is a direct regulator of neutrophil motility

Orchestrated recruitment of neutrophils to inflamed tissue is essential during the initiation of inflammation. Inflamed areas are usually hypoxic, and adaptation to reduced oxygen pressure is typically mediated by hypoxia pathway proteins. However, it remains unclear how these factors influence the migration of neutrophils to and at the site of inflammation during their transmigration through the blood-endothelial cell barrier, as well as their motility in the interstitial space. Here, we reveal that activation of hypoxia-inducible factor 2 (HIF2α) as a result of a deficiency in HIF prolyl hydroxylase domain protein 2 (PHD2) boosts neutrophil migration specifically through highly confined microenvironments. In vivo, the increased migratory capacity of PHD2-deficient neutrophils resulted in massive tissue accumulation in models of acute local inflammation. Using systematic RNA sequencing analyses and mechanistic approaches, we identified RhoA, a cytoskeleton organizer, as the central downstream factor that mediates HIF2α-dependent neutrophil motility. Thus, we propose that the novel PHD2-HIF2α-RhoA axis is vital to the initial stages of inflammation because it promotes neutrophil movement through highly confined tissue landscapes.

MYO1F Regulates IgE and MRGPRX2-Dependent Mast Cell Exocytosis

The activation and degranulation of mast cells is critical in the pathogenesis of allergic inflammation and modulation of inflammation. Recently, we demonstrated that the unconventional long-tailed myosin, MYO1F, localizes with cortical F-actin and mediates adhesion and migration of mast cells. In this study, we show that knockdown of MYO1F by short hairpin RNA reduces human mast cell degranulation induced by both IgE crosslinking and by stimulation of the Mas-related G protein-coupled receptor X2 (MRGPRX2), which has been associated with allergic and pseudoallergic drug reactions, respectively. Defective degranulation was accompanied by a reduced reassembly of the cortical actin ring after activation but reversed by inhibition of actin polymerization. Our data show that MYO1F is required for full Cdc42 GTPase activation, a critical step in exocytosis. Furthermore, MYO1F knockdown resulted in less granule localization in the cell membrane and fewer fissioned mitochondria along with deficient mitochondria translocation to exocytic sites. Consistent with that, AKT and DRP1 phosphorylation are diminished in MYO1F knockdown cells. Altogether, our data point to MYO1F as an important regulator of mast cell degranulation by contributing to the dynamics of the cortical actin ring and the distribution of both the secretory granules and mitochondria.

Scopolamine promotes neuroinflammation and delirium-like neuropsychiatric disorder in mice

Postoperative delirium is a common neuropsychiatric syndrome resulting a high postsurgical mortality rate and decline in postdischarge function. Extensive research has been performed on both human and animal delirium-like models due to their clinical significance, focusing on systematic inflammation and consequent neuroinflammation playing a key role in the pathogenesis of postoperative cognitive dysfunctions. Since animal models are widely utilized for pathophysiological study of neuropsychiatric disorders, this study aimed at examining the validity of the scopolamine-induced delirium-like mice model with respect to the neuroinflammatory hypothesis of delirium. Male C57BL/6 mice were treated with intraperitoneal scopolamine (2 mg/kg). Neurobehavioral tests were performed to evaluate the changes in cognitive functions, including learning and memory, and the level of anxiety after surgery or scopolamine treatment. The levels of pro-inflammatory cytokines (IL-1β, IL-18, and TNF-α) and inflammasome components (NLRP3, ASC, and caspase-1) in different brain regions were measured. Gene expression profiles were also examined using whole-genome RNA sequencing analyses to compare gene expression patterns of different mice models. Scopolamine treatment showed significant increase in the level of anxiety and impairments in memory and cognitive function associated with increased level of pro-inflammatory cytokines and NLRP3 inflammasome components. Genetic analysis confirmed the different expression patterns of genes involved in immune response and inflammation and those related with the development of the nervous system in both surgery and scopolamine-induced mice models. The scopolamine-induced delirium-like mice model successfully showed that analogous neuropsychiatric changes coincides with the neuroinflammatory hypothesis for pathogenesis of delirium.

Analysis of miRNA and mRNA reveals core interaction networks and pathways of dexamethasone-induced immunosuppression in chicken bursa of Fabricius

Stress-induced immunosuppression is a serious problem affecting the production value of poultry, but its specific molecular mechanism has not yet been elucidated. We selected 7-day-old Gushi cocks as test animals and successfully established a stress-induced immunosuppression model by injecting 2.0 mg/kg (body weight) dexamethasone (Dex). We then constructed six cDNA libraries and two small RNA libraries of Bursa of Fabricius from the control group and the Dex group. RNA-seq results revealed 21,028 transcripts including 3920 novel transcripts; 500 miRNAs including 68 novel miRNAs were identified. Correlation analysis of miRNA, target genes and mRNA results indicated that the gga-miR-15 family, gga-miR-103-3p, gga-miR-456-3p, and gga-miR-27b-3p, as core differentially expressed miRNAs, may potentially regulate multiple genes which are involved in immune-related pathways; and that the core genes Suppressor of IKBKE 1 (SIKE1) and high mobility group AT-hook 2 (HMGA2) are associated with the miR-17 family (gga-miR-20a-5p, gga-miR-20b-5p, gga-miR-106-5p, and gga-miR-17-5p) and gga-let -7 family (gga-let-7b, gga-let-7i, gga-let-7c-5p, and gga-let-7f-5p). The interaction networks of mRNAs of significantly enrichment pathways and PPI (protein-protein interaction) networks showed that IL6, IL1B, IL8L1, CCL5, SOCS3, SOCS1, ITGB5, GSTA3, SQLE, FDFT1, FN1, IL18, IL10, MAPK11 and MAPK12 are network core nodes and that most of them are strongly associated with immune response. One of the candidate miRNAs, gga-miR-20b-5p, may play an important role in stress-induced immunosuppression. Luciferase assay and over-expression experiments suggested that gga-miR-20b-5p negatively regulated the expression of target gene SIKE1. These results provide better understanding of the mechanism of stress-induced immunosuppression in Gushi chicken bursa, and provide novel targets for subsequent research to improve poultry anti-stress capability.

Myosins and Disease

Myosins constitute a superfamily of actin-based molecular motor proteins that mediates a variety of cellular activities including muscle contraction, cell migration, intracellular transport, the formation of membrane projections, cell adhesion, and cell signaling. The 12 myosin classes that are expressed in humans share sequence similarities especially in the N-terminal motor domain; however, their enzymatic activities, regulation, ability to dimerize, binding partners, and cellular functions differ. It is becoming increasingly apparent that defects in myosins are associated with diseases including cardiomyopathies, colitis, glomerulosclerosis, neurological defects, cancer, blindness, and deafness. Here, we review the current state of knowledge regarding myosins and disease.

Long-Tailed Unconventional Class I Myosins in Health and Disease

Long-tailed unconventional class I myosin, Myosin 1E (MYO1E) and Myosin 1F (MYO1F) are motor proteins that use chemical energy from the hydrolysis of adenosine triphosphate (ATP) to produce mechanical work along the actin cytoskeleton. On the basis of their motor properties and structural features, myosins perform a variety of essential roles in physiological processes such as endocytosis, exocytosis, cell adhesion, and migration. The long tailed unconventional class I myosins are characterized by having a conserved motor head domain, which binds actin and hydrolyzes ATP, followed by a short neck with an isoleucine-glutamine (IQ) motif, which binds calmodulin and is sensitive to calcium, and a tail that contains a pleckstrin homology domain (PH), a tail homology 1 domain (TH1), wherein these domains allow membrane binding, a tail homology 2 domain (TH2), an ATP-insensitive actin-binding site domain, and a single Src homology 3 domain (SH3) susceptible to binding proline rich regions in other proteins. Therefore, these motor proteins are able to bind actin, plasma membrane, and other molecules (adaptor, kinases, membrane proteins) that contribute to their function, ranging from increasing membrane tension to molecular trafficking and cellular adhesion. MYO1E and MYO1F function in host self-defense, with a better defined role in innate immunity in cell migration and phagocytosis. Impairments of their function have been identified in patients suffering pathologies ranging from tumoral processes to kidney diseases. In this review, we summarize our current knowledge of specific features and functions of MYO1E and MYO1F in various tissues, as well as their involvement in disease.

Myo1e modulates the recruitment of activated B cells to inguinal lymph nodes

The inclusion of lymphocytes in high endothelial venules and their migration to the lymph nodes are critical steps in the immune response. Cell migration is regulated by the actin cytoskeleton and myosins. Myo1e is a long-tailed class I myosin and is highly expressed in B cells, which have not been studied in the context of cell migration. By using intravital microscopy in an in vivo model and performing in vitro experiments, we studied the relevance of Myo1e for the adhesion and inclusion of activated B cells in high endothelial venules. We observed reduced expression of integrins and F-actin in the membrane protrusions of B lymphocytes, which might be explained by deficiencies in vesicular trafficking. Interestingly, the lack of Myo1e reduced the phosphorylation of focal adhesion kinase (FAK; also known as PTK2), AKT (also known as AKT1) and RAC-1, disturbing the FAK-PI3K-RAC-1 signaling pathway. Taken together, our results indicate a critical role of Myo1e in the mechanism of B-cell adhesion and migration.

Intermittent rolling is a defect of the extravasation cascade caused by Myosin1e-deficiency in neutrophils

Neutrophil extravasation is a migratory event in response to inflammation that depends on cytoskeletal dynamics regulated by myosins. Myosin-1e (Myo1e) is a long-tailed class-I myosin that has not yet been studied in the context of neutrophil-endothelial interactions and neutrophil extravasation. Intravital microscopy of TNFα-inflamed cremaster muscles in Myo1e-deficient mice revealed that Myo1e is required for efficient neutrophil extravasation. Specifically, Myo1e deficiency caused increased rolling velocity, decreased firm adhesion, aberrant crawling, and strongly reduced transmigration. Interestingly, we observed a striking discontinuous rolling behavior termed "intermittent rolling," during which Myo1e-deficient neutrophils showed alternating rolling and jumping movements. Surprisingly, chimeric mice revealed that these effects were due to Myo1e deficiency in leukocytes. Vascular permeability was not significantly altered in Myo1e KO mice. Myo1e-deficient neutrophils showed diminished arrest, spreading, uropod formation, and chemotaxis due to defective actin polymerization and integrin activation. In conclusion, Myo1e critically regulates adhesive interactions of neutrophils with the vascular endothelium and neutrophil extravasation. Myo1e may therefore be an interesting target in chronic inflammatory diseases characterized by excessive neutrophil recruitment.

NCF2, MYO1F, S1PR4, and FCN1 as potential noninvasive diagnostic biomarkers in patients with obstructive coronary artery: A weighted gene co-expression network analysis

This study aims to explore the predictive noninvasive biomarker for obstructive coronary artery disease (CAD). By using the data set GSE90074, weighted gene co-expression network analysis (WGCNA), and protein-protein interactive network, construction of differentially expressed genes in peripheral blood mononuclear cells was conducted to identify the most significant gene clusters associated with obstructive CAD. Univariate and multivariate stepwise logistic regression analyses and receiver operating characteristic analysis were used to predicate the diagnostic accuracy of biomarker candidates in the detection of obstructive CAD. Furthermore, functional prediction of candidate gene biomarkers was further confirmed in ST-segment elevation myocardial infarction (STEMI) patients or stable CAD patients by using the datasets of GSE62646 and GSE59867. We found that the blue module discriminated by WGCNA contained 13 hub-genes that could be independent risk factors for obstructive CAD (P < .05). Among these 13 hub-genes, a four-gene signature including neutrophil cytosol factor 2 (NCF2, P = .025), myosin-If (MYO1F, P = .001), sphingosine-1-phosphate receptor 4 (S1PR4, P = .015), and ficolin-1 (FCN1, P = .012) alone or combined with two risk factors (male sex and hyperlipidemia) may represent potential diagnostic biomarkers in obstructive CAD. Furthermore, the messenger RNA levels of NCF2, MYO1F, S1PR4, and FCN1 were higher in STEMI patients than that in stable CAD patients, although S1PR4 showed no statistical difference (P > .05). This four-gene signature could also act as a prognostic biomarker to discriminate STEMI patients from stable CAD patients. These findings suggest a four-gene signature (NCF2, MYO1F, S1PR4, and FCN1) alone or combined with two risk factors (male sex and hyperlipidemia) as a promising prognostic biomarker in the diagnosis of STEMI. Well-designed cohort studies should be implemented to warrant the diagnostic value of these genes in clinical purpose.

Transcription Profiling of Monocyte-Derived Macrophages Infected In Vitro With Two Strains of Streptococcus agalactiae Reveals Candidate Pathways Affecting Subclinical Mastitis in Cattle

Macrophages are key cells of innate immune response and serve as the first line of defense against bacteria. Transcription profiling of bacteria-infected macrophages could provide important insights on the pathogenicity and host defense mechanisms during infection. We have examined transcription profiles of bovine monocyte-derived macrophages (bMDMs) isolated from the blood of 12 animals and infected in vitro with two strains of Streptococcus agalactiae. Illumina sequencing of RNA from 36 bMDMs cultures exposed in vitro to either one of two sequence types of S. agalactiae (ST103 or ST12) for 6 h and unchallenged controls was performed. Analyses of over 1,656 million high-quality paired-end sequence reads revealed 5,936 and 6,443 differentially expressed genes (p < 0.05) in bMDMs infected with ST103 and ST12, respectively, versus unchallenged controls. Moreover, 588 genes differentially expressed between bMDMs infected with ST103 versus ST12 were identified. Ingenuity pathway analysis of the differentially up-regulated genes in the bMDMs infected with ST103 revealed significant enrichment for granulocyte adhesion and diapedesis, while significant enrichment for the phagosome formation pathway was found among down-regulated genes. Moreover, Ingenuity pathway analysis of the differentially up-regulated genes in the bMDMs infected with ST12 showed significant enrichment for type 1/type 2 T helper cell activation, while the complement activation pathway was overrepresented in the down-regulated genes. Our study identified pathogen-induced regulation of key genes and pathways involved in the immune response of macrophages against infection but also likely involved in bacterial evasion of the host immune system. These results may contribute to better understanding of the mechanisms underlying subclinical infection such as bovine streptococcal mastitis.

Intraepithelial neutrophils in mammary, urinary and gall bladder infections

Neutrophil mobilization is a crucial response to protect the host against invading microorganisms. Neutrophil recruitment and removal have to be tightly regulated to prevent uncontrolled inflammation and excessive release of their toxic content causing tissue damage and subsequent organ dysfunctions. We show here the presence of live and apoptotic neutrophils in the cytoplasm of inflamed mammary, urinary and gall bladder epithelial cells following infection with E. coli and Salmonella bacteria. The entry process commenced with adherence of transmigrated neutrophils to the apical membrane of inflamed epithelial cells. Next, nuclear rearrangement and elongation associated with extensive actin polymerization enabled neutrophils to crawl and invaginate the apical membrane into cytoplasmic double membrane compartments. Scission of the invaginated cell membrane from the entry point and loss of these surrounding membranes released intracellular neutrophils into the cytoplasm where they undergone apoptotic death. The co-occurrence of this observation with bacterial invasion and formation of intracellular bacterial communities (IBCs) might link entry of infected neutrophils to the formation of IBCs and chronic carriage in E. coli mastitis and cystitis and Salmonella cholecystitis.

Neutrophil Recruitment: From Model Systems to Tissue-Specific Patterns

Neutrophil recruitment is not only vital for host defense, but also relevant in pathological inflammatory reactions, such as sepsis. Model systems have been established to examine different steps of the leukocyte recruitment cascade in vivo and in vitro under inflammatory conditions. Recently, tissue-specific recruitment patterns have come into focus, requiring modification of formerly generalized assumptions. Here, we summarize existing models of neutrophil recruitment and highlight recent discoveries in organ-specific recruitment patterns. New techniques show that previously stated assumptions of integrin activation and tissue invasion may need revision. Similarly, neutrophil recruitment to specific organs can rely on different organ properties, adhesion molecules, and chemokines. To advance our understanding of neutrophil recruitment, organ-specific intravital microscopy methods are needed.

Myo1f, an Unconventional Long-Tailed Myosin, Is a New Partner for the Adaptor 3BP2 Involved in Mast Cell Migration

Mast cell chemotaxis is essential for cell recruitment to target tissues, where these cells play an important role in adaptive and innate immunity. Stem cell factor (SCF) is a major chemoattractant for mast cells. SCF binds to the KIT receptor, thereby triggering tyrosine phosphorylation in the cytoplasmic domain and resulting in docking sites for SH2 domain-containing molecules, such as Lyn and Fyn, and the subsequent activation of the small GTPases Rac that are responsible for cytoskeletal reorganization and mast cell migration. In previous works we have reported the role of 3BP2, an adaptor molecule, in mast cells. 3BP2 silencing reduces FcεRI-dependent degranulation, by targeting Lyn and Syk phosphorylation, as well as SCF-dependent cell survival. This study examines its role in SCF-dependent migration and reveals that 3BP2 silencing in human mast cell line (LAD2) impairs cell migration due to SCF and IgE. In that context we found that 3BP2 silencing decreases Rac-2 and Cdc42 GTPase activity. Furthermore, we identified Myo1f, an unconventional type-I myosin, as a new partner for 3BP2. This protein, whose functions have been described as critical for neutrophil migration, remained elusive in mast cells. Myo1f is expressed in mast cells and colocalizes with cortical actin ring. Interestingly, Myo1f-3BP2 interaction is modulated by KIT signaling. Moreover, SCF dependent adhesion and migration through fibronectin is decreased after Myo1f silencing. Furthermore, Myo1f silencing leads to downregulation of β1 and β7 integrins on the mast cell membrane. Overall, Myo1f is a new 3BP2 ligand that connects the adaptor to actin cytoskeleton and both molecules are involved in SCF dependent mast cell migration.

Myosin1f-mediated neutrophil migration contributes to acute neuroinflammation and brain injury after stroke in mice

Background

During the acute stroke phase, neutrophils from the peripheral blood are first to arrive in the ischemic brain, which then attracts other immune cells that exacerbate neuroinflammation in the ischemic tissue. Myosin1f was reported to specifically mediate neutrophil migration in the peripheral tissues, but whether it plays a critical role in the neuroinflammatory response after ischemic stroke remains unknown. In this study, we aim to test the hypothesis that myosin1f-mediated neutrophil migration is critical in acute neuroinflammation induced by ischemic stroke.

Methods

Myosin1f ^−/− and wild type (WT) mice were subjected to transient middle cerebral artery occlusion (MCAO). To determine which cells determine myosin1f’s transmigration ability, bone marrow transplantation, neutrophil depletion, and adoptive neutrophil transfer were performed. The myosin1f RNA level was assessed in peripheral neutrophils by reverse transcription polymerase chain reaction (RT-PCR) at 1 day and 3 days after stroke. The infiltrating neutrophils were quantified by immunofluorescence staining and FACS at 72 h after reperfusion.

Results

The myosin1f ^−/− mice had significantly smaller infarctions than the myosin1f ^+/+ mice. Bone marrow transplantation from myosin1f ^−/− mice to recipient mice also had smaller infarctions compared to animals receiving bone marrow from myosin1f ^+/+ mice. By performing neutrophil depletion and adoptive transfer, we confirmed that myosin1f acts mainly in circulating neutrophils. RT-PCR showed that myosin1f gene expression was increased in the circulating blood neutrophils at 3 days after ischemia. The confocal immunostaining and FACS results confirmed that fewer neutrophils infiltrated into the ischemic brain in myosin1f ^−/− mice compared to WT mice.

Conclusions

Myosin1f determines neutrophil migration into the ischemic hemisphere, which directly affects stroke outcome.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1465-9) contains supplementary material, which is available to authorized users.

Class I myosins: Highly versatile proteins with specific functions in the immune system

Connections established between cytoskeleton and plasma membrane are essential in cellular processes such as cell migration, vesicular trafficking, and cytokinesis. Class I myosins are motor proteins linking the actin-cytoskeleton with membrane phospholipids. Previous studies have implicated these molecules in cell functions including endocytosis, exocytosis, release of extracellular vesicles and the regulation of cell shape and membrane elasticity. In immune cells, those proteins also are involved in the formation and maintenance of immunological synapse-related signaling. Thus, these proteins are master regulators of actin cytoskeleton dynamics in different scenarios. Although the localization of class I myosins has been described in vertebrates, their functions, regulation, and mechanical properties are not very well understood. In this review, we focused on and summarized the current understanding of class I myosins in vertebrates with particular emphasis in leukocytes.

Myosin 1F Regulates M1-Polarization by Stimulating Intercellular Adhesion in Macrophages

Intestinal macrophages are highly mobile cells with extraordinary plasticity and actively contribute to cytokine-mediated epithelial cell damage. The mechanisms triggering macrophage polarization into a proinflammatory phenotype are unknown. Here, we report that during inflammation macrophages enhance its intercellular adhesion properties in order to acquire a M1-phenotype. Using in vitro and in vivo models we demonstrate that intercellular adhesion is mediated by integrin-αVβ3 and relies in the presence of the unconventional class I myosin 1F (Myo1F). Intercellular adhesion mediated by αVβ3 stimulates M1-like phenotype in macrophages through hyperactivation of STAT1 and STAT3 downstream of ILK/Akt/mTOR signaling. Inhibition of integrin-αVβ3, Akt/mTOR, or lack of Myo1F attenuated the commitment of macrophages into a pro-inflammatory phenotype. In a model of colitis, Myo1F deficiency strongly reduces the secretion of proinflammatory cytokines, decreases epithelial damage, ameliorates disease activity, and enhances tissue repair. Together our findings uncover an unknown role for Myo1F as part of the machinery that regulates intercellular adhesion and polarization in macrophages.

The Neutrophil Nucleus: An Important Influence on Neutrophil Migration and Function

Neutrophil nuclear morphology has historically been used in haematology for neutrophil identification and characterisation, but its exact role in neutrophil function has remained enigmatic. During maturation, segmentation of the neutrophil nucleus into its mature, multi-lobulated shape is accompanied by distinct changes in nuclear envelope composition, resulting in a unique nucleus that is believed to be imbued with extraordinary nuclear flexibility. As a rate-limiting factor for cell migration, nuclear morphology and biomechanics are particularly important in the context of neutrophil migration during immune responses. Being an extremely plastic and fast migrating cell type, it is to be expected that neutrophils have an especially deformable nucleus. However, many questions still surround the dynamic capacities of the neutrophil nucleus, and which nuclear and cytoskeletal elements determine these dynamics. The biomechanics of the neutrophil nucleus should also be considered for their influences on the production of neutrophil extracellular traps (NETs), given this process sees the release of chromatin "nets" from nucleoplasm to extracellular space. Although past studies have investigated neutrophil nuclear composition and shape, in a new era of more sophisticated biomechanical and genetic techniques, 3D migration studies, and higher resolution microscopy we now have the ability to further investigate and understand neutrophil nuclear plasticity at an unprecedented level. This review addresses what is currently understood about neutrophil nuclear structure and its role in migration and the release of NETs, whilst highlighting open questions surrounding neutrophil nuclear dynamics.

Nuclear Deformation During Neutrophil Migration at Sites of Inflammation

Cell migration is indispensable for various biological processes including angiogenesis, wound healing, and immunity. In general, there are two different migration modes described, the mesenchymal migration mode and the amoeboid migration mode. Neutrophils rapidly migrate toward the sites of injury, infection, and inflammation using the amoeboid migration mode which is characterized by cell polarization and a high migration velocity. During site-directed trafficking of neutrophils from the blood stream into the inflamed tissue, neutrophils must first withstand shear stress while migrating on the 2-dimensional endothelial surface. Subsequently, they have to cross different physical barriers during the extravasation process including the squeezing through the compact endothelial monolayer that comprises the blood vessel, the underlining basement membrane and then the 3-dimensional meshwork of extracellular matrix (ECM) proteins in the tissue. Therefore, neutrophils have to rapidly switch between distinct migration modes such as intraluminal crawling, transmigration, and interstitial migration to pass these different confinements and mechanical barriers. The nucleus is the largest and stiffest organelle in every cell and is therefore the key cellular element involved in cellular migration through variable confinements. This review highlights the importance of nuclear deformation during neutrophil crossing of such confinements, with a focus on transendothelial migration and interstitial migration. We discuss the key molecular components involved in the nuclear shape changes that underlie neutrophil motility and squeezing through cellular and ECM barriers. Understanding the precise molecular mechanisms that orchestrate these distinct neutrophil migration modes introduces an opportunity to develop new therapeutic concepts for controlling pathological neutrophil-driven inflammation.

A Fundamental Role of Myh9 for Neutrophil Migration in Innate Immunity

Neutrophils are the first leukocytes to arrive at sites of injury during the acute inflammatory response. To maintain the polarized morphology during migration, nonmuscle myosins class II are essential, but studies using genetic models to investigate the role of Myh9 for neutrophil migration were missing. In this study, we analyzed the functional role of Myh9 on neutrophil trafficking using genetic downregulation of Myh9 in Vav-iCre⁺/Myh9^wt/fl mice because the complete knockout of Myh9 in the hematopoietic system was lethal. Migration velocity and Euclidean distance were significantly diminished during mechanotactic migration of Vav-iCre⁺/Myh9^wt/fl neutrophils compared with Vav-iCre^-/Myh9^wt/fl control neutrophils. Similar results were obtained for transmigration and migration in confined three-dimensional environments. Stimulated emission depletion nanoscopy revealed that a certain threshold of Myh9 was required to maintain proper F-actin dynamics in the front of the migrating cell. In laser-induced skin injury and in acute peritonitis, reduced Myh9 expression in the hematopoietic system resulted in significantly diminished neutrophil extravasation. Investigation of bone marrow chimeric mice in the peritonitis model revealed that the migration defect was cell intrinsic. Expression of Myh9-EGFP rescued the Myh9-related defects in two-dimensional and three-dimensional migration of Hoxb8-SCF cell-derived neutrophils generated from fetal liver cells with a Myh9 knockdown. Live cell imaging provided evidence that Myh9 was localized in branching lamellipodia and in the uropod where it may enable fast neutrophil migration. In summary, the severe migration defects indicate an essential and fundamental role of Myh9 for neutrophil trafficking in innate immunity.