Cytosolic free calcium elevation mediates the phagosome-lysosome fusion during phagocytosis in human neutrophils

Tracking the Cellular Degradation of Silver Nanoparticles: Development of a Generic Kinetic Model

Understanding the degradation of nanoparticles (NPs) after crossing the cell plasma membrane is crucial in drug delivery designs and cytotoxicity assessment. However, the key factors controlling the degradable kinetics remain unclear due to the absence of a quantification model. In this study, subcellular imaging of silver nanoparticles (AgNPs) was used to determine the intracellular transfer of AgNPs, and single particle ICP-MS was utilized to track the degradation process. A cellular kinetic model was subsequently developed to describe the uptake, transfer, and degradation behaviors of AgNPs. Our model demonstrated that the intracellular degradation efficiency of AgNPs was much higher than that determined by mimicking testing, and the degradation of NPs was highly influenced by cellular factors. Specifically, deficiencies in Ca or Zn primarily decreased the kinetic dissolution of NPs, while a Ca deficiency also resulted in the retardation of NP transfer. The biological significance of these kinetic parameters was strongly revealed. Our model indicated that the majority of internalized AgNPs dissolved, with the resulting ions being rapidly depurated. The release of Ag ions was largely dependent on the microvesicle-mediated route. By changing the coating and size of AgNPs, the model results suggested that size influenced the transfer of NPs into the degradation process, whereas coating affected the degradation kinetics. Overall, our developed model provides a valuable tool for understanding and predicting the impacts of the physicochemical properties of NPs and the ambient environment on nanotoxicity and therapeutic efficacy.

Lysosomal Cu(I)/Cu(II) Dependence of Antimicrobial Ability of Oyster Hemocytes and Regulation of Phagolysosomal System

Copper (Cu) is hyperaccumulated in oyster hemocytes and is an essential trace metal indispensable for diverse innate immune functions. However, the roles of Cu in oyster immune defense are still unclear. In this study, Cu exposure enhanced the phagocytosis of zymosan by increasing the number and length of filopodia, as well as mitochondrial ROS (mitoROS) production mainly in granulocytes, followed by semigranulocytes and agranulocytes. The intracellular calcium level increased to promote the phagosome-lysosome fusion after Cu exposure. The enhancement of phagosomal acidification and mitochondrion-phagosome juxtaposition were also found in granulocytes after Cu exposure. These results indicated that Cu could regulate the phagolysosomal system to enhance the antimicrobial ability of oyster hemocytes with the assistance of mitoROS. Furthermore, Cu(I) and Cu(II) were predominately located in lysosomes, and degranulation may provide a mechanism for exposing Cu to bacteria to prevent their survival and proliferation. Specifically, we showed that the newly formed Cu(I) arising from lysosomal Cu(II) moved to lysosomes and mitochondria in activated hemocytes to induce strong immune responses. The ability of the transformation of Cu(I) from Cu(II) followed granulocytes > semigranlocytes > agranulocytes, indicating that granulocytes played important roles in immune functions of oysters. Our results provided new insights into the understanding of antimicrobial effects of Cu in oyster hemocytes.

Blood metabolomics and impacted cellular mechanisms during transition into lactation in dairy cows that develop metritis

The objective of this study was to identify metabolites associated with metritis and use them for identification of cellular mechanisms affected during transition into lactation. Holstein cows (n = 104) had blood collected in the prepartum period (d -14 ± 6 relative to calving), at calving (d 0), and at the day of metritis diagnosis (d 7 ± 2 after calving). Cows with reddish or brownish, watery, and fetid discharge were diagnosed with metritis (n = 52). Cows with metritis were paired with herdmates without metritis (n = 52) based on days in milk. The metabolome of plasma samples was evaluated using untargeted gas chromatography time-of-flight mass spectrometry. Univariate analyses included t-tests and fold change analyses. Metabolites with false discovery rate adjusted P ≤ 0.10 on t-tests were used for partial least squares discriminant analysis coupled with permutational analysis using 2,000 permutations. Metabolites with false discovery rate adjusted P ≤ 0.10 on t-tests were also used for enriched pathway analyses and identification of cellular processes. Cows that developed metritis had affected cellular processes associated with lower amino acid metabolism in the prepartum period, greater lipolysis, cell death, and oxidative stress at calving and at metritis diagnosis, and greater leukocyte activation at calving, but lower immune cell activation at metritis diagnosis. In summary, cows that developed metritis had plasma metabolomic changes associated with greater lipolysis, oxidative stress, and a dysregulated immune response which may predispose cows to metritis development.

The formation and function of the neutrophil phagosome

Neutrophils are the most abundant circulating leukocyte and are crucial to the initial innate immune response to infection. One of their key pathogen-eliminating mechanisms is phagocytosis, the process of particle engulfment into a vacuole-like structure called the phagosome. The antimicrobial activity of the phagocytic process results from a collaboration of multiple systems and mechanisms within this organelle, where a complex interplay of ion fluxes, pH, reactive oxygen species, and antimicrobial proteins creates a dynamic antimicrobial environment. This complexity, combined with the difficulties of studying neutrophils ex vivo, has led to gaps in our knowledge of how the neutrophil phagosome optimizes pathogen killing. In particular, controversy has arisen regarding the relative contribution and integration of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived antimicrobial agents and granule-delivered antimicrobial proteins. Clinical syndromes arising from dysfunction in these systems in humans allow useful insight into these mechanisms, but their redundancy and synergy add to the complexity. In this article, we review the current knowledge regarding the formation and function of the neutrophil phagosome, examine new insights into the phagosomal environment that have been permitted by technological advances in recent years, and discuss aspects of the phagocytic process that are still under debate.

Neutrophils in the Pathogenesis of Rheumatic Diseases

Rheumatic diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), are a group of auto-inflammatory disorders associated with substantial morbidity and mortality. One unifying feature of these diseases is the presence of abnormal neutrophils exhibiting dysregulated neutrophil extracellular trap (NET) release, reactive oxygen species (ROS) production, degranulation, and pro-inflammatory cytokines secretion. Moreover, the release of autoantigens associated with NETs promotes the generation of autoantibodies and a breakdown of self-tolerance, thereby perpetuating inflammation and tissue injury in these patients. In recent years, targeted therapies directed at neutrophilic effector functions have shown promising results in the management of rheumatic diseases. In this review, we will highlight the emerging roles of neutrophils in the onset and progression of rheumatic diseases, and further discuss current and future therapeutic approaches targeting the pathogenic functions of neutrophils, which can modulate inflammation and hence improve patients' survival and quality of life.

Efferocytosis requires periphagosomal Ca2+-signaling and TRPM7-mediated electrical activity

Efficient clearance of apoptotic cells by phagocytosis, also known as efferocytosis, is fundamental to developmental biology, organ physiology, and immunology. Macrophages use multiple mechanisms to detect and engulf apoptotic cells, but the signaling pathways that regulate the digestion of the apoptotic cell cargo, such as the dynamic Ca²⁺ signals, are poorly understood. Using an siRNA screen, we identify TRPM7 as a Ca²⁺-conducting ion channel essential for phagosome maturation during efferocytosis. Trpm7-targeted macrophages fail to fully acidify or digest their phagosomal cargo in the absence of TRPM7. Through perforated patch electrophysiology, we demonstrate that TRPM7 mediates a pH-activated cationic current necessary to sustain phagosomal acidification. Using mice expressing a genetically-encoded Ca²⁺ sensor, we observe that phagosome maturation requires peri-phagosomal Ca²⁺-signals dependent on TRPM7. Overall, we reveal TRPM7 as a central regulator of phagosome maturation during macrophage efferocytosis.

Efficient removal of apoptotic cells by phagocytosis underlies tissue development, wound repair, host defense and organ homeostasis. Here, authors identify TRPM7 as a regulator of cargo acidification and Ca2+ signaling during apoptotic cell clearance.

FIB-SEM-based analysis of Borrelia intracellular processing by human macrophages

Borrelia burgdorferi is the causative agent of Lyme disease, a multisystemic disorder affecting primarily skin, joints and nervous system. Successful internalization and intracellular processing of borreliae by immune cells, like macrophages, is decisive for the outcome of a respective infection. Here, we use, for the first time, focused ion beam scanning electron microscopy tomography (FIB-SEM tomography) to visualize the interaction of borreliae with primary human macrophages with high resolution. We report that interaction between macrophages and the elongated and highly motile borreliae can lead to formation of membrane tunnels that extend deeper into the host cytoplasm than the actual phagosome, most probably as a result of partial extrication of captured borreliae. We also show that membrane tubulation at borreliae-containing phagosomes, a process suggested earlier as a mechanism leading to phagosome compaction but hard to visualize in live-cell imaging, is apparently a frequent phenomenon. Finally, we demonstrate that the endoplasmic reticulum (ER) forms multiple STIM1-positive contact sites with both membrane tunnels and phagosome tubulations, confirming the important role of the ER during uptake and intracellular processing of borreliae.

Monitoring Phosphoinositide Fluxes and Effectors During Leukocyte Chemotaxis and Phagocytosis

The dynamic re-organization of cellular membranes in response to extracellular stimuli is fundamental to the cell physiology of myeloid and lymphoid cells of the immune system. In addition to maintaining cellular homeostatic functions, remodeling of the plasmalemma and endomembranes endow leukocytes with the potential to relay extracellular signals across their biological membranes to promote rolling adhesion and diapedesis, migration into the tissue parenchyma, and to ingest foreign particles and effete cells. Phosphoinositides, signaling lipids that control the interface of biological membranes with the external environment, are pivotal to this wealth of functions. Here, we highlight the complex metabolic transitions that occur to phosphoinositides during several stages of the leukocyte lifecycle, namely diapedesis, migration, and phagocytosis. We describe classical and recently developed tools that have aided our understanding of these complex lipids. Finally, major downstream effectors of inositides are highlighted including the cytoskeleton, emphasizing the importance of these rare lipids in immunity and disease.

Does the Nutritional Composition of Dairy Milk Based Recovery Beverages Influence Post-exercise Gastrointestinal and Immune Status, and Subsequent Markers of Recovery Optimisation in Response to High Intensity Interval Exercise?

This study aimed to determine the effects of flavored dairy milk based recovery beverages of different nutrition compositions on markers of gastrointestinal and immune status, and subsequent recovery optimisation markers. After completing 2 h high intensity interval running, participants (n = 9) consumed a whole food dairy milk recovery beverage (CM, 1.2 g/kg body mass (BM) carbohydrate and 0.4 g/kg BM protein) or a dairy milk based supplement beverage (MBSB, 2.2 g/kg BM carbohydrate and 0.8 g/kg BM protein) in a randomized crossover design. Venous blood samples, body mass, body water, and breath samples were collected, and gastrointestinal symptoms (GIS) were measured, pre- and post-exercise, and during recovery. Muscle biopsies were performed at 0 and 2 h of recovery. The following morning, participants returned to the laboratory to assess performance outcomes. In the recovery period, carbohydrate malabsorption (breath H₂ peak: 49 vs. 24 ppm) occurred on MBSB compared to CM, with a trend toward greater gut discomfort. No difference in gastrointestinal integrity (i.e., I-FABP and sCD14) or immune response (i.e., circulating leukocyte trafficking, bacterially-stimulated neutrophil degranulation, and systemic inflammatory profile) markers were observed between CM and MBSB. Neither trial achieved a positive rate of muscle glycogen resynthesis [-25.8 (35.5) mmol/kg dw/h]. Both trials increased phosphorylation of intramuscular signaling proteins. Greater fluid retention (total body water: 86.9 vs. 81.9%) occurred on MBSB compared to CM. Performance outcomes did not differ between trials. The greater nutrient composition of MBSB induced greater gastrointestinal functional disturbance, did not prevent the post-exercise reduction in neutrophil function, and did not support greater overall acute recovery.

Cellular and molecular complementary immune stress markers for the model species Dreissena polymorpha

This study aimed to combine cellular and molecular analyses for better detail the effects of various stresses on a sentinel species of freshwater invertebrate. For this purpose, the hemocytes of the zebra mussel, Dreissena polymorpha, were exposed to different stresses at two different intensities, high or low: chemical (cadmium and ionomycin), physical (ultraviolet B), or biological ones (Cryptosporidium parvum and Toxoplasma gondii). After exposure, flow cytometry and droplet digital PCR analyses were performed on the same pools of hemocytes. Several responses related to necrosis, apoptosis, phagocytosis, production of nitric oxide and expression level of several genes related to the antioxidant, detoxification and immune systems were evaluated. Results showed that hemocyte integrity was compromised by both chemical and physical stress, and cellular markers of phagocytosis reacted to ionomycin and protozoa. While cadmium induced oxidative stress and necrosis, ionomycin tends to modulate the immune response of hemocytes. Although both biological stresses led to a similar immune response, C. parvum oocysts induced more effects than T. gondii, notably through the expression of effector caspases gene and an increase in hemocyte necrosis. This suggests different management of the two protozoa by the cell. This work provides new knowledge of biomarkers in the zebra mussel, at both cellular and molecular levels, and contributes to elucidate the mechanisms of action of different kinds of stress in this species.

Unconventional role of lysosomes in phagocytosis

Lysosomes are generally thought to be required only for the late stages of phagosome maturation, providing the proton pumps (V-ATPases) and hydrolases needed to acidify and degrade the ingested prey. A recent paper by Davis et al. (EMBO J. [2020], doi:10.15252/embj.2019104058) reports the involvement of lysosomes at a much earlier stage, namely in scission of phagosomes from the plasma membrane. Here we analyze these findings, highlighting a number of unexpected observations and unresolved questions.

The Impact of a Dairy Milk Recovery Beverage on Bacterially Stimulated Neutrophil Function and Gastrointestinal Tolerance in Response to Hypohydration Inducing Exercise Stress

The study aimed to determine the impact of a dairy milk recovery beverage immediately after endurance exercise on leukocyte trafficking, neutrophil function, and gastrointestinal tolerance markers during recovery. Male runners (N = 11) completed two feeding trials in randomized order, after 2 hr of running at 70% V˙O2max, fluid restricted, in temperate conditions (25 °C, 43% relative humidity). Immediately postexercise, the participants received a chocolate-flavored dairy milk beverage equating to 1.2 g/kg body mass carbohydrate and 0.4 g/kg body mass protein in one trial, and water volume equivalent in another trial. Venous blood and breath samples were collected preexercise, postexercise, and during recovery to determine the leukocyte counts, plasma intestinal fatty acid binding protein, and cortisol concentrations, as well as breath H2. In addition, 1,000 µl of whole blood was incubated with 1 μg/ml Escherichia coli lipopolysaccharide for 1 hr at 37 °C to determine the stimulated plasma elastase concentration. Gastrointestinal symptoms and feeding tolerance markers were measured preexercise, every 15 min during exercise, and hourly postexercise for 3 hr. The postexercise leukocyte (mean [95% confidence interval]: 12.7 [11.6, 14.0] × 109/L [main effect of time, MEOT]; p < .001) and neutrophil (10.2 [9.1, 11.5] × 109/L; p < .001) counts, as well as the plasma intestinal fatty acid binding protein (470 pg/ml; +120%; p = .012) and cortisol (236 nMol/L; +71%; p = .006) concentrations, were similar throughout recovery for both trials. No significant difference in breath H2 and gastrointestinal symptoms was observed between trials. The total (Trial × Time, p = .025) and per cell (Trial × Time, p = .001) bacterially stimulated neutrophil elastase release was greater for the chocolate-flavored dairy milk recovery beverage (+360% and +28%, respectively) in recovery, compared with the water trial (+85% and -38%, respectively). Chocolate-flavored dairy milk recovery beverage consumption immediately after exercise prevents the decrease in neutrophil function during the recovery period, and it does not account for substantial malabsorption or gastrointestinal symptoms over a water volume equivalent.

Sialic Acid-Siglec-E Interactions During Pseudomonas aeruginosa Infection of Macrophages Interferes With Phagosome Maturation by Altering Intracellular Calcium Concentrations

Pseudomonas aeruginosa (PA) is commonly associated with nosocomial and chronic infections of lungs. We have earlier demonstrated that an acidic sugar, sialic acid, is present in PA which is recognized and bound by sialic acid binding immunoglobulin type lectins (siglecs) expressed on neutrophils. Here, we have tried to gain a detailed insight into the immunosuppressive role of sialic acid-siglec interactions in macrophage-mediated clearance of sialylated PA (PA^+Sia). We have demonstrated that PA^+Sia shows enhanced binding (~1.5-fold) to macrophages due to additional interactions between sialic acids and siglec-E and exhibited more phagocytosis. However, internalization of PA^+Sia is associated with a reduction in respiratory burst and increase in anti-inflammatory cytokines secretion which is reversed upon desialylation of the bacteria. Phagocytosis of PA^+Sia is also associated with reduced intracellular calcium ion concentrations and altered calcium-dependent signaling which negatively affects phagosome maturation. Consequently, although more PA^+Sia was localized in early phagosomes (Rab5 compartment), only fewer bacteria reach into the late phagosomal compartment (Rab7). Possibly, this leads to reduced phagosome lysosome fusion where reduced numbers of PA^+Sia are trafficked into lysosomes, compared to PA^−Sia. Thus, internalized PA^+Sia remain viable and replicates intracellularly in macrophages. We have also demonstrated that such siglec-E-sialic acid interaction recruited SHP-1/SHP-2 phosphatases which modulate MAPK and NF-κB signaling pathways. Disrupting sialic acid-siglec-E interaction by silencing siglec-E in macrophages results in improved bactericidal response against PA^+Sia characterized by robust respiratory burst, enhanced intracellular calcium levels and nuclear translocation of p65 component of NF-κB complex leading to increased pro-inflammatory cytokine secretion. Taken together, we have identified that sialic acid-siglec-E interactions is another pathway utilized by PA in order to suppress macrophage antimicrobial responses and inhibit phagosome maturation, thereby persisting as an intracellular pathogen in macrophages.

Calcium Signaling Commands Phagosome Maturation Process

Phagosome-lysosome (P-L) fusion is one of the central immune-effector responses of host. It is known that phagosome maturation process is associated with numerous signaling cascades and among these, important role of calcium (Ca²⁺) signaling has been realized recently. Ca²⁺ plays key roles in actin rearrangement, activation of NADPH oxidase and protein kinase C (PKC). Involvement of Ca²⁺ in these cellular processes directs phagosomal maturation process. Some of the intracellular pathogens have acquired the strategies to modulate Ca²⁺ associated pathways to block P-L fusion process. In this review we have described the mechanism of Ca²⁺ signals that influence P-L fusion by controlling ROS, actin and PKC signaling cascades. We have also discussed the strategies implemented by the intracellular pathogens to manipulate Ca²⁺ signaling to consequently subvert P-L fusion. A detail study of factors associated in manipulating Ca²⁺ signaling may provide new insights for the development of therapeutic tools for more effective treatment options against infectious diseases.

ArhGAP12 plays dual roles in Stabilin-2 mediated efferocytosis: Regulates Rac1 basal activity and spatiotemporally turns off the Rac1 to orchestrate phagosome maturation

The rapid and precise clearance of apoptotic cells (efferocytosis) involves a series of phagocytic processes through which apoptotic cells are recognized, engulfed, and degraded within phagocytes. The Rho-family GTPases critically rearrange the cytoskeleton for these phagocytic processes, but we know little about the mechanisms by which regulatory proteins control the spatiotemporal activities of the Rho-family GTPases. Here, we identify ArhGAP12 as a functional GTPase-activating protein (GAP) of Rac1 during Stabilin-2 mediated efferocytosis. ArhGAP12 constitutively forms a complex with the phosphatidylserine receptor, Stabilin-2, via direct interaction with the downstream protein, GULP, but is released from the complex when Stabilin-2 interacts with apoptotic cells. When the phagocytic cup is closed and the apoptotic cell is surrounded by the phagosomal membrane, ArhGAP12 localizes to the phagocytic cup via a specific interaction with phosphatidylinositol-4,5-bisphosphate, which is transiently biosynthesized in the phagocytic cup. Down-regulation of ArhGAP12 results in sustained Rac1 activity, arrangement of F-actin, and delayed phagosome-lysosome fusion. Our results collectively suggest that ArhGAP12 carries dual roles in Stabilin-2 mediated efferocytosis: it binds to GULP/Stabilin-2 and switches off Rac1 basal activity and switches on the Rac1 by releasing itself from the complex. In addition, the spatiotemporal membrane targeting of ArhGAP12 inactivates Rac1 in a time-specific and spatially coordinated manner to orchestrate phagosome maturation. This may shed light on how other RhoGAPs spatiotemporally inactivate Rac or Cdc42 during phagocytosis by various cells, in different circumstances.

Early neutropenia on day 8 treated with adjuvant Docetaxel-based chemotherapy in early breast cancer patients: Putative mechanisms within the neutrophil pool system

Most chemotherapy regimens cause neutropenic nadirs between days 10 and 14, and administration of granulocyte colony-stimulating factor (G-CSF) support relies on this timing. In docetaxel (DOC)-based chemotherapy, the frequency of febrile neutropenia (FN) and the G-CSF dose administered varied greatly between studies. Our study goal was to forecast the necessary dose of G-CSF by comparing day 8 neutropenia with putative changes within the neutrophil pool. We conducted a retrospective observational analysis of 242 early breast cancer patients who had received adjuvant DOC-based chemotherapy (DOC group) compared with 43 patients who had received FEC chemotherapy (FEC group). Patients who were given a standard dose and had a blood test on day 8 in the 1st cycle were eligible. In the DOC group, patients routinely received prophylactic administration of G-CSF (150 μg/body) on day 3 and received additional G-CSF based on a blood test on day 8. Results of the day 8 blood test showed that severe neutropenia (<500/mm3, average 494/mm3) was observed in 152 out of 242 (62.8%) patients in the DOC group, while in the FEC group (n = 43), neutropenia was ambiguous (average 1,741/mm3). In the FEC group, 9 out of 43 patients (20.9%) and in the DOC group, 27 out of 242 patients (11.1%) experienced FN. In the DOC group, day 8 neutropenia was predictive for FN in a logistic regression model (OR 0.79 [95% CI: 0.655-0.952], p = 0.013). Among 214 patients under 70 years old, the planned chemotherapy cycle was completed in 190 (88.8%) patients who also received the maximum dose of G-CSF (150 μg/body) four times, while 23 patients could not complete the planned chemotherapy cycle, but only five because of FN-related complications. Patients treated with DOC should be treated for primary prophylaxis with G-CSF support at an earlier time starting with a relatively small dose.

Cervico-vaginal mucus (CVM) - an accessible source of immunologically informative biomolecules

Cervico-vaginal mucus (CVM), the product of epithelial cells lining the uterus, cervix and vagina, is secreted to facilitate uterine lubrication and microbial clearance. Predominantly composed of water and mucins, CVM also contains high levels of immuno-active proteins such as immunoglobulin A (IgA), lactoferrin and lysozyme which protect against infection by blocking adhesion and mediating microbial killing. The repertoire of cytokines, chemokines and antimicrobial peptides is predominantly generated by the secretions of endometrial epithelial cells into the uterine lumen and concentrated in the CVM. The quantity and relative proportions of these inflammatory biomarkers are affected by diverse factors including the estrus cycle and health status of the animal and therefore potentially provide important diagnostic and prognostic indicators. We propose that measuring molecular signatures in bovine CVM could be a useful approach to identifying and monitoring genital tract pathologies in beef and dairy cows.

Lysophosphatidylcholine Promotes Phagosome Maturation and Regulates Inflammatory Mediator Production Through the Protein Kinase A-Phosphatidylinositol 3 Kinase-p38 Mitogen-Activated Protein Kinase Signaling Pathway During Mycobacterium tuberculosis Infection in Mouse Macrophages

Tuberculosis is caused by the infectious agent Mycobacterium tuberculosis (Mtb). Mtb has various survival strategies, including blockade of phagosome maturation and inhibition of antigen presentation. Lysophosphatidylcholine (LPC) is a major phospholipid component of oxidized low-density lipoprotein and is involved in various cellular responses, such as activation of second messengers and bactericidal activity in neutrophils. In this study, macrophages were infected with a low infectious dose of Mtb and treated with LPC to investigate the bactericidal activity of LPC against Mtb. In macrophages infected with Mtb strain, H37Ra or H37Rv, LPC suppressed bacterial growth; however, this effect was suppressed in bone marrow-derived macrophages (BMDMs) isolated from G2A (a G protein-coupled receptor involved in some LPC actions) knockout mice. LPC also promoted phagosome maturation via phosphatidylinositol 3 kinase (PI3K)–p38 mitogen-activated protein kinase (MAPK)-mediated reactive oxygen species production and intracellular Ca²⁺ release during Mtb infection. In addition, LPC induced increased levels of intracellular cyclic adenosine monophosphate (cAMP) and phosphorylated glycogen synthase kinase 3 beta (GSK3β) in Mtb-infected macrophages. Protein kinase A (PKA)-induced phosphorylation of GSK3β suppressed activation of NF-κB in LPC-treated macrophages during Mtb infection, leading to decreased secretion of pro-inflammatory cytokines and increased secretion of anti-inflammatory cytokines. These results suggest that LPC can effectively control Mtb growth by promoting phagosome maturation via cAMP-induced activation of the PKA–PI3K–p38 MAPK pathway. Moreover, LPC can regulate excessive production of pro-inflammatory cytokines associated with bacterial infection of macrophages.

Extension of chemotactic pseudopods by nonadherent human neutrophils does not require or cause calcium bursts

Global bursts in free intracellular calcium (Ca²⁺) are among the most conspicuous signaling events in immune cells. To test the common view that Ca²⁺ bursts mediate rearrangement of the actin cytoskeleton in response to the activation of G protein-coupled receptors, we combined single-cell manipulation with fluorescence imaging and monitored the Ca²⁺ concentration in individual human neutrophils during complement-mediated chemotaxis. By decoupling purely chemotactic pseudopod formation from cell-substrate adhesion, we showed that physiological concentrations of anaphylatoxins, such as C5a, induced nonadherent human neutrophils to form chemotactic pseudopods but did not elicit Ca²⁺ bursts. By contrast, pathological or supraphysiological concentrations of C5a often triggered Ca²⁺ bursts, but pseudopod protrusion stalled or reversed in such cases, effectively halting chemotaxis, similar to sepsis-associated neutrophil paralysis. The maximum increase in cell surface area during pseudopod extension in pure chemotaxis was much smaller-by a factor of 8-than the known capacity of adherent human neutrophils to expand their surface. Because the measured rise in cortical tension was not sufficient to account for this difference, we attribute the limited deformability to a reduced ability of the cytoskeleton to generate protrusive force in the absence of cell adhesion. Thus, we hypothesize that Ca²⁺ bursts in neutrophils control a mechanistic switch between two distinct modes of cytoskeletal organization and dynamics. A key element of this switch appears to be the expedient coordination of adhesion-dependent lock or release events of cytoskeletal membrane anchors.

Armed for destruction: formation, function and trafficking of neutrophil granules

Neutrophils respond nearly instantly to infection, rapidly deploying a potent enzymatic and chemical arsenal immediately upon entering an infected site. This capacity for rapid and potent responses is endowed by stores of antimicrobial proteins contained in readily mobilizable granules. These granules contain the proteins necessary to mediate the recruitment, chemotaxis, antimicrobial function and NET formation of neutrophils. Four granule types exist, and are sequentially deployed as neutrophils enter infected sites. Secretory vesicles are released first, enabling recruitment of neutrophils out of the blood. Next, specific and gelatinase granules are released to enable neutrophil migration and begin the formation of an antimicrobial environment. Finally, azurophilic granules release potent antimicrobial proteins at the site of infection and into phagosomes. The step-wise mobilization of these granules is regulated by calcium signaling, while specific trafficking regulators and membrane fusion complexes ensure the delivery of granules to the correct subcellular site. In this review, we describe neutrophil granules from their formation through to their deployment at the site of infection, focusing on recent developments in our understanding of the signaling pathways and vesicular trafficking mechanisms which mediate neutrophil degranulation.

Inseparable tandem: evolution chooses ATP and Ca2+ to control life, death and cellular signalling

From the very dawn of biological evolution, ATP was selected as a multipurpose energy-storing molecule. Metabolism of ATP required intracellular free Ca(2+) to be set at exceedingly low concentrations, which in turn provided the background for the role of Ca(2+) as a universal signalling molecule. The early-eukaryote life forms also evolved functional compartmentalization and vesicle trafficking, which used Ca(2+) as a universal signalling ion; similarly, Ca(2+) is needed for regulation of ciliary and flagellar beat, amoeboid movement, intracellular transport, as well as of numerous metabolic processes. Thus, during evolution, exploitation of atmospheric oxygen and increasingly efficient ATP production via oxidative phosphorylation by bacterial endosymbionts were a first step for the emergence of complex eukaryotic cells. Simultaneously, Ca(2+) started to be exploited for short-range signalling, despite restrictions by the preset phosphate-based energy metabolism, when both phosphates and Ca(2+) interfere with each other because of the low solubility of calcium phosphates. The need to keep cytosolic Ca(2+) low forced cells to restrict Ca(2+) signals in space and time and to develop energetically favourable Ca(2+) signalling and Ca(2+) microdomains. These steps in tandem dominated further evolution. The ATP molecule (often released by Ca(2+)-regulated exocytosis) rapidly grew to be the universal chemical messenger for intercellular communication; ATP effects are mediated by an extended family of purinoceptors often linked to Ca(2+) signalling. Similar to atmospheric oxygen, Ca(2+) must have been reverted from a deleterious agent to a most useful (intra- and extracellular) signalling molecule. Invention of intracellular trafficking further increased the role for Ca(2+) homeostasis that became critical for regulation of cell survival and cell death. Several mutually interdependent effects of Ca(2+) and ATP have been exploited in evolution, thus turning an originally unholy alliance into a fascinating success story.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Induction of Live Cell Phagocytosis by a Specific Combination of Inflammatory Stimuli

Conditions of severe hyper-inflammation can lead to uncontrolled activation of macrophages, and the ensuing phagocytosis of live cells. However, relationships between inflammatory stimuli and uncontrolled phagocytosis of live cells by macrophages are poorly understood. To identify mediators of this process, we established phagocytosis assays of live cells by stimulating macrophages with CpG DNA, interferon-γ, and anti-interleukin-10 receptor antibody. In this model, various cell surface receptors were upregulated on macrophages, and phagocytosis of live cells was induced in a Rac1-dependent manner. Subsequent inhibition of the ICAM-1, VCAM-1, and both of these receptors abolished in vitro and in vivo phagocytosis of live T cells, myeloid cells, and B cells, respectively. Specifically, the reduction in lymphocyte numbers due to in vivo activation of macrophages was ameliorated in Icam-1-deficient mice. In addition, overexpression of ICAM-1 or VCAM-1 in non-phagocytic NIH3T3 cells led to active phagocytosis of live cells. These data indicate molecular mechanisms underlying live cell phagocytosis induced by hyper-inflammation, and this experimental model will be useful to clarify the pathophysiological mechanisms of hemophagocytosis and to indicate therapeutic targets.

The Transcription Factor EB Links Cellular Stress to the Immune Response

The transcription factor EB (TFEB) is the master transcriptional regulator of autophagy and lysosome biogenesis. Recent advances have led to a paradigm shift in our understanding of lysosomes from a housekeeping cellular waste bin to a dynamically regulated pathway that is efficiently turned up or down based on cellular needs. TFEB coordinates the cellular response to nutrient deprivation and other forms of cell stress through the lysosome system, and regulates a myriad of cellular processes associated with this system including endocytosis, phagocytosis, autophagy, and lysosomal exocytosis. Autophagy and the endolysosomal system are critical to both the innate and adaptive arms of the immune system, with functions in effector cell priming and direct pathogen clearance. Recent studies have linked TFEB to the regulation of the immune response through the endolysosmal pathway and by direct transcriptional activation of immune related genes. In this review, we discuss the current understanding of TFEB's function and the molecular mechanisms behind TFEB activation. Finally, we discuss recent advances linking TFEB to the immune response that positions lysosomal signaling as a potential target for immune modulation.

Rabs on the fly: Functions of Rab GTPases during development

The organization of intracellular transport processes is adapted specifically to different cell types, developmental stages, and physiologic requirements. Some protein traffic routes are universal to all cells and constitutively active, while other routes are cell-type specific, transient, and induced under particular conditions only. Small GTPases of the Rab (Ras related in brain) subfamily are conserved across eukaryotes and regulate most intracellular transit pathways. The complete sets of Rab proteins have been identified in model organisms, and molecular principles underlying Rab functions have been uncovered. Rabs provide intracellular landmarks that define intracellular transport sequences. Nevertheless, it remains a challenge to systematically map the subcellular distribution of all Rabs and their functional interrelations. This task requires novel tools to precisely describe and manipulate the Rab machinery in vivo. Here we discuss recent findings about Rab roles during development and we consider novel approaches to investigate Rab functions in vivo.

Suppression of Protective Responses upon Activation of L-Type Voltage Gated Calcium Channel in Macrophages during Mycobacterium bovis BCG Infection

The prevalence of Mycobacterium tuberculosis (M. tb) strains eliciting drug resistance has necessitated the need for understanding the complexities of host pathogen interactions. The regulation of calcium homeostasis by Voltage Gated Calcium Channel (VGCCs) upon M. tb infection has recently assumed importance in this area. We previously showed a suppressor role of VGCC during M. tb infections and recently reported the mechanisms of its regulation by M. tb. Here in this report, we further characterize the role of VGCC in mediating defence responses of macrophages during mycobacterial infection. We report that activation of VGCC during infection synergistically downmodulates the generation of oxidative burst (ROS) by macrophages. This attenuation of ROS is regulated in a manner which is dependent on Toll like Receptor (TLR) and also on the route of calcium influx, Protein Kinase C (PKC) and by Mitogen Activation Protein Kinase (MAPK) pathways. VGCC activation during infection increases cell survival and downmodulates autophagy. Concomitantly, pro-inflammatory responses such as IL-12 and IFN-γ secretion and the levels of their receptors on cell surface are inhibited. Finally, the ability of phagosomes to fuse with lysosomes in M. bovis BCG and M. tb H37Rv infected macrophages is also compromised when VGCC activation occurs during infection. The results point towards a well-orchestrated strategy adopted by mycobacteria to supress protective responses mounted by the host. This begins with the increase in the surface levels of VGCCs by mycobacteria and their antigens by well-controlled and regulated mechanisms. Subsequent activation of the upregulated VGCC following tweaking of calcium levels by molecular sensors in turn mediates suppressor responses and prepare the macrophages for long term persistent infection.

Potential of Ca2+ in Mycobacterium tuberculosis H37Rv Pathogenesis and Survival

The host-pathogen interaction and involvement of calcium (Ca²⁺) signaling in tuberculosis infection is crucial and plays a significant role in pathogenesis. Ca²⁺ is known as a ubiquitous second messenger that could control multiple processes and is included in cellular activities like division, motility, stress response, and signaling. However, Ca²⁺ is thought to be a regulative molecule in terms of TB infection but its binding relation with proteins/substrates molecules which are influenced with Ca²⁺ concentrations in host-pathogen interaction requires attention. So, in this review, our primary goal is to focus on some Ca²⁺ substrates/proteins and their imperative involvement in pathogenesis, which is unclear. We have discussed several Ca²⁺-binding substrate and protein that affect intracellular mechanism of infected host cell. The major involvement of these proteins/substrates including calmodulin (CaM), calpain, annexin, surfactant protein A (SP-A), surfactant protein D (SP-D), calprotectin (MRP8/14), and PE_PGRS family protein are considered to be significant; however, their detailed understanding in mycobacterium infection is limited. In this aspect, this study will help in adding up our understanding in TB biology and additionally in the development of new therapeutic approach to reduce TB pandemic worldwide.

The Role of Calcium and Magnesium Ions in Uptake of β-Amyloid Peptides by Microglial Cells

Amyloid peptides 1-40 and 1-42 (Aβ 1-40 and Aβ 1-42) are major components of diffuse and neuritic senile plaques present in the brain of patients with Alzheimer's disease. Their interaction with microglial cells was studied using a system partly mimicking these plaques, which consisted in heat-killed yeast particles coated with either Aβ 1-40 or Aβ 1-42. Using these particles, it has been shown in our laboratory that LRP is involved mainly in the elimination of Aβ 1-42-coated heat-killed yeast particles and partly in that of Aβ 1-40-coated heat-killed yeast particles by microglial cells in culture. We show here that in the presence of calcium and magnesium ions extracellular chelators, namely EDTA (for both ions) and EGTA (for calcium ions), the internalization of coated heat-killed particles was impaired. In the presence of BAPTA-AM, an intracellular chelator of calcium ions and thapsigargin, an inhibitor of the endoplasmic reticulum calcium pump, no effect was observed on the phagocytosis of Aβ 1-40-coated heat-killed yeast particles, whereas that of Aβ 1-42-coated heat-killed yeast particles was affected. These results suggest that different signaling mechanisms are involved after the internalization of Aβ 1-40 and Aβ 1-42.

Neutrophil extracellular traps release induced by Leishmania: role of PI3Kγ, ERK, PI3Kσ, PKC, and [Ca2+]

Upon in vitro stimulation, neutrophils undergo a cell death named netosis. This process is characterized by extracellular release of chromatin scaffold associated with granular and cytoplasmic proteins, which together, ensnare and kill microbes. We have previously described that interaction of Leishmania amazonensis with human neutrophils leads to the release of neutrophil extracellular traps, which trap and kill the parasite. However, the signaling leading to Leishmania induced netosis is still unknown. Thus, we sought to evaluate signaling events that drive L. amazonensis induced neutrophil extracellular trap release from human neutrophils. Here, we found that PI3K, independently of protein kinase B, has a role in parasite-induced netosis. We also described that the main isoforms involved are PI3Kγ and PI3Kδ, which work in reactive oxygen species-dependent and -independent ways, respectively. We demonstrated that activation of ERK downstream of PI3Kγ is important to trigger reactive oxygen species-dependent, parasite-induced netosis. Pharmacological inhibition of protein kinase C also significantly decreased parasite-induced neutrophil extracellular trap release. Intracellular calcium, regulated by PI3Kδ, represents an alternative reactive oxygen species-independent pathway of netosis stimulated by L. amazonensis Finally, intracellular calcium mobilization and reactive oxygen species generation are the major regulators of parasite-induced netosis. Our results contribute to a better understanding of the signaling behind netosis induced by interactions between Leishmania and neutrophils.

The role of STIM and ORAI proteins in phagocytic immune cells

Phagocytic cells, such as neutrophils, macrophages, and dendritic cells, migrate to sites of infection or damage and are integral to innate immunity through two main mechanisms. The first is to directly neutralize foreign agents and damaged or infected cells by secreting toxic substances or ingesting them through phagocytosis. The second is to alert the adaptive immune system through the secretion of cytokines and the presentation of the ingested materials as antigens, inducing T cell maturation into helper, cytotoxic, or regulatory phenotypes. While calcium signaling has been implicated in numerous phagocyte functions, including differentiation, maturation, migration, secretion, and phagocytosis, the molecular components that mediate these Ca(2+) signals have been elusive. The discovery of the STIM and ORAI proteins has allowed researchers to begin clarifying the mechanisms and physiological impact of store-operated Ca(2+) entry, the major pathway for generating calcium signals in innate immune cells. Here, we review evidence from cell lines and mouse models linking STIM and ORAI proteins to the control of specific innate immune functions of neutrophils, macrophages, and dendritic cells.

Direct In Vivo Manipulation and Imaging of Calcium Transients in Neutrophils Identify a Critical Role for Leading-Edge Calcium Flux

Calcium signaling has long been associated with key events of immunity, including chemotaxis, phagocytosis, and activation. However, imaging and manipulation of calcium flux in motile immune cells in live animals remain challenging. Using light-sheet microscopy for in vivo calcium imaging in zebrafish, we observe characteristic patterns of calcium flux triggered by distinct events, including phagocytosis of pathogenic bacteria and migration of neutrophils toward inflammatory stimuli. In contrast to findings from ex vivo studies, we observe enriched calcium influx at the leading edge of migrating neutrophils. To directly manipulate calcium dynamics in vivo, we have developed transgenic lines with cell-specific expression of the mammalian TRPV1 channel, enabling ligand-gated, reversible, and spatiotemporal control of calcium influx. We find that controlled calcium influx can function to help define the neutrophil's leading edge. Cell-specific TRPV1 expression may have broad utility for precise control of calcium dynamics in other immune cell types and organisms.

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca²⁺ -release channels, as well as signalling by cyclic nucleotides and Ca²⁺ . Ca²⁺ -binding proteins (calmodulin, centrin) and Ca²⁺ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H⁺ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca²⁺ -channels, exocyst complexes and Ca²⁺ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.

Junctate boosts phagocytosis by recruiting endoplasmic reticulum Ca2+ stores near phagosomes

Local intracellular Ca(2+) elevations increase the efficiency of phagocytosis, a process that is essential for innate and adaptive immunity. These local Ca(2+) elevations are generated in part by the store-operated Ca(2+) entry (SOCE) sensor STIM1, which recruits endoplasmic reticulum (ER) cisternae to phagosomes and opens phagosomal Ca(2+) channels at ER-phagosome junctions. However, residual ER-phagosome contacts and periphagosomal Ca(2+) hotspots remain in Stim1(-/-) cells. Here, we tested whether junctate (also called ASPH isoform 8), a molecule that targets STIM1 to ER-plasma-membrane contacts upon Ca(2+)-store depletion, cooperates with STIM1 at phagosome junctions. Junctate expression in Stim1(-/-) and Stim1(-/-); Stim2(-/-) phagocytic fibroblasts increased phagocytosis and periphagosomal Ca(2+) elevations, yet with only a minimal impact on global SOCE. These Ca(2+) hotspots were only marginally reduced by the SOCE channel blocker lanthanum chloride (La(3+)) but were abrogated by inositol trisphosphate receptor inhibitors 2-APB and xestospongin-C, revealing that unlike STIM1-mediated hotspots, junctate-mediated Ca(2+) originates predominantly from periphagosomal Ca(2+) stores. Accordingly, junctate accumulates near phagosomes and elongates ER-phagosome junctions in Stim1(-/-) cells. Thus, junctate mediates an alternative mechanism for generating localized Ca(2+) elevations within cells, promoting Ca(2+) release from internal stores recruited to phagosomes, thereby boosting phagocytosis.

Role of intracellular free calcium in killing Penicillium marneffei within human macrophages

Increases in cytosolic Ca(2+) concentration ([Ca(2+)]c) promote phagocyte antimicrobial responses. Here, we investigated macrophages stimulated by Penicillium marneffei (P. marneffei). [Ca(2+)]c was determined in macrophages loaded with the fluorescent calcium probe Fura 2/AM as they were stimulated by P. marneffei. We found that P. marneffei induced an increase in [Ca(2+)]c in human macrophages. Further, increased [Ca(2+)]c with the ionophore A23187 promoted phagosomal acidification and maturation and reduced intracellular replication of P. marneffei in P. marneffei-infected human macrophages, whereas decreased [Ca(2+)]c with the chelation MAPTAM decreased TNF-α production, inhibited phagosomal acidification and maturation and increased intracellular replication of P. marneffei. These data indicate that Ca(2+) signaling may play an important role in controlling the replication of P. marneffei within macrophages.

Regulation of L-type Voltage Gated Calcium Channel CACNA1S in Macrophages upon Mycobacterium tuberculosis Infection

We demonstrated earlier the inhibitory role played by Voltage Gated Calcium Channels (VGCCs) in regulating Mycobacterium tuberculosis (M. tb) survival and pathogenesis. In this report, we investigated mechanisms and key players that regulate the surface expression of VGCC-CACNA1S by Rv2463 and M. tb infection in macrophages. Our earlier work identified Rv2463 to be expressed at early times post infection in macrophages that induced suppressor responses to dendritic cells and macrophages. Our results in this study demonstrate a role of MyD88 independent TLR pathway in mediating CACNA1S expression. Dissecting the role for second messengers, we show that calcium homeostasis plays a key role in CACNA1S expression during M. tb infection. Using siRNAs against molecular sensors of calcium regulation, we show an involvement of ER associated Stromal Interaction Molecules 1 and 2 (STIM1 and STIM2), and transcription factor pCREB, towards CACNA1S expression that also involved the MyD88 independent pathway. Interestingly, reactive oxygen species played a negative role in M. tb mediated CACNA1S expression. Further, a cross-regulation of ROS and pCREB was noted that governed CACNA1S expression. Characterizing the mechanisms governing CACNA1S expression would improve our understanding of the regulation of VGCC expression and its role in M. tb pathogenesis during M. tb infection.

Erythropoietin Receptor Antagonist Suppressed Ectopic Hemoglobin Synthesis in Xenografts of HeLa Cells to Promote Their Destruction

The aim of this study is to explore a cause-oriented therapy for patients with uterine cervical cancer that expresses erythropoietin (Epo) and its receptor (EpoR). Epo, by binding to EpoR, stimulates the proliferation and differentiation of erythroid progenitor cells into hemoglobin-containing red blood cells. In this study, we report that the HeLa cells in the xenografts expressed ε, γ, and α globins as well as myoglobin (Mb) to produce tetrameric α2ε2 and α2γ2 and monomeric Mb, most of which were significantly suppressed with an EpoR antagonist EMP9. Western blotting revealed that the EMP9 treatment inhibited the AKT-pAKT, MAPKs-pMAPKs, and STAT5-pSTAT5 signaling pathways. Moreover, the treatment induced apoptosis and suppression of the growth and inhibited the survival through disruption of the harmonized hemoprotein syntheses in the tumor cells concomitant with destruction of vascular nets in the xenografts. Furthermore, macrophages and natural killer (NK) cells with intense HIF-1α expression recruited significantly more in the degenerating foci of the xenografts. These findings were associated with the enhanced expressions of nNOS in the tumor cells and iNOS in macrophages and NK cells in the tumor sites. The treated tumor cells exhibited a substantial number of perforations on the cell surface, which indicates that the tumors were damaged by both the nNOS-induced nitric oxide (NO) production in the tumor cells as well as the iNOS-induced NO production in the innate immune cells. Taken together, these data suggest that HeLa cells constitutively acquire ε, γ and Mb synthetic capacity for their survival. Therefore, EMP9 treatment might be a cause-oriented and effective therapy for patients with squamous cell carcinoma of the uterine cervix.

Immobilized IL-8 Triggers Phagocytosis and Dynamic Changes in Membrane Microtopology in Human Neutrophils

The interaction of leukocytes with surface bound ligands can be limited by the location of the molecules relative to the surface topology of the cell. In this report, we examine the dynamic response of neutrophils to IL-8-fractalkine chimera immobilized on bead surfaces, taking into account changes in receptor occupancy resulting from changes in surface topography. As a readout for receptor signaling, we observe the dynamics of calcium release in neutrophils following contact with the IL-8 coated surface. After a delay that depended on the initial area of contact and the surface density of IL-8, the cell began to phagocytose the IL-8 coated bead. This appeared to be a pre-requisite for release of calcium, which typically followed shortly after the initiation of phagocytosis. In separate experiments, effective kinetic coefficients for the formation of bonds between immobilized IL-8 and receptors on the cell surface were determined. Using these coefficients, we were able to estimate the number of bound receptors in the nascent contact zone. Kinetic modeling of the signaling response predicted that cell spreading and a concomitant increase in the density of occupied receptors would be required for the experimentally observed calcium dynamics. Postulating that there is an increase in receptor occupancy resulting from smoothing of the cell surface as it is stretched over the bead enabled us to obtain model predictions consistent with experimental observations. This study reveals the likely importance of membrane microtopology as a rate-limiting property and potential means of regulation of cell responses stimulated by two-dimensional surface interactions.

Active calpain in phagocytically competent human neutrophils: electroinjection of fluorogenic calpain substrate

Calpain has been implicated in the apparent expansion of neutrophil plasma membrane that accompanies cell spreading and phagocytosis. In order to test this hypothesis, an internally quenched fluorescent peptide substrate of calpain-1 which increased in fluorescence on cleavage, was micro-electroinjected into neutrophils. The fluorescence intensity increased in a significant number of neutrophils, including those which appeared to be in a morphologically resting (spherical) state. In order to test whether calpain was activated by an elevation of cytosolic Ca(2+) during the injection, Ca(2+) chelators were added to the injectate and cytosolic free Ca(2+) in the receiving neutrophil was simultaneously monitored. It was shown that this approach could be used without raising Ca(2+) within the injected cell. Despite this, approximately 75% of individual neutrophils had calpain activity which consumed the substrate within approx. 100 s. It was found that all neutrophils had elevated calpain activity were phagocytically competent; whereas neutrophils with low or undetectable calpain activity failed to undergo phagocytosis. This association was consistent with the hypothesis that calpain activity within neutrophils was necessary for them to undergo efficient phagocytosis.

Phosphoinositides in phagocytosis and macropinocytosis

Professional phagocytes provide immunoprotection and aid in the maintenance of tissue homeostasis. They perform these tasks by recognizing, engulfing and eliminating pathogens and endogenous cell debris. Here, we examine the paramount role played by phosphoinositides in phagocytosis and macropinocytosis, two major endocytic routes that mediate the uptake of particulate and fluid matter, respectively. We analyze accumulating literature describing the molecular mechanisms whereby phosphoinositides translate environmental cues into the complex, sophisticated responses that underlie the phagocytic and macropinocytic responses. In addition, we exemplify virulence strategies involving modulation of host cell phosphoinositide signaling that are employed by bacteria to undermine immunity. This article is part of a Special Issue entitled Phosphoinositides.

Neutrophils at work

In this Review we discuss data demonstrating recently recognized aspects of neutrophil homeostasis in the steady state, granulopoiesis in 'emergency' conditions and interactions of neutrophils with the adaptive immune system. We explore in vivo observations of the recruitment of neutrophils from blood to tissues in models of blood-borne infections versus bacterial invasion through epithelial linings. We examine data on novel aspects of the activation of NADPH oxidase and the heterogeneity of phagosomes and, finally, consider the importance of two neutrophil-derived biological agents: neutrophil extracellular traps and ectosomes.

Involvement of Mannose Receptor in Glycopeptidolipid-Mediated Inhibition of Phagosome-Lysosome Fusion

We previously reported that glycopeptidolipid (GPL) isolated from Mycobacterium avium serovar 4 inhibited phagosome-lysosome (P-L) fusion when macrophages phagocytosed heat-killed Staphylococcus aureus (SA). In the present study we analyzed the underlying inhibitory mechanism of GPL coated on SA. Elimination of oligosaccharide from GPL abrogated its inhibitory activity. GPL did not inhibit P-L fusion of opsonized SA phagocytosed via complement receptors. The inhibitory activity of GPL was competitively reduced by the presence of alpha-methyl-D-mannoside and anti-mannose receptor antibody, suggesting that inhibition of P-L fusion by GPL is mediated through mannose receptor. Recruitment of early endosome antigen 1 and Ca2+/calmodulin kinase II in human macrophage-like THP-1 cells were significantly suppressed by GPL, indicating that GPL inhibits steps for leading to the P-L fusion.

Calcium regulation in the protozoan model, Paramecium tetraurelia

Early in eukaryotic evolution, the cell has evolved a considerable inventory of proteins engaged in the regulation of intracellular Ca(2+) concentrations, not only to avoid toxic effects but beyond that to exploit the signaling capacity of Ca(2+) by small changes in local concentration. Among protozoa, the ciliate Paramecium may now be one of the best analyzed models. Ciliary activity and exo-/endocytosis are governed by Ca(2+) , the latter by Ca(2+) mobilization from alveolar sacs and a superimposed store-operated Ca(2+) -influx. Paramecium cells possess plasma membrane- and endoplasmic reticulum-resident Ca(2+) -ATPases/pumps (PMCA, SERCA), a variety of Ca(2+) influx channels, including mechanosensitive and voltage-dependent channels in the plasma membrane, furthermore a plethora of Ca(2+) -release channels (CRC) of the inositol 1,4,5-trisphosphate and ryanodine receptor type in different compartments, notably the contractile vacuole complex and the alveolar sacs, as well as in vesicles participating in vesicular trafficking. Additional types of CRC probably also occur but they have not been identified at a molecular level as yet, as is the equivalent of synaptotagmin as a Ca(2+) sensor for exocytosis. Among established targets and sensors of Ca(2+) in Paramecium are calmodulin, calcineurin, as well as Ca(2+) /calmodulin-dependent protein kinases, all with multiple functions. Thus, basic elements of Ca(2+) signaling are available for Paramecium.

The Calmodulin-like calcium binding protein EhCaBP3 of Entamoeba histolytica regulates phagocytosis and is involved in actin dynamics

Phagocytosis is required for proliferation and pathogenesis of Entamoeba histolytica and erythrophagocytosis is considered to be a marker of invasive amoebiasis. Ca²⁺ has been found to play a central role in the process of phagocytosis. However, the molecular mechanisms and the signalling mediated by Ca²⁺ still remain largely unknown. Here we show that Calmodulin-like calcium binding protein EhCaBP3 of E. histolytica is directly involved in disease pathomechanism by its capacity to participate in cytoskeleton dynamics and scission machinery during erythrophagocytosis. Using imaging techniques EhCaBP3 was found in phagocytic cups and newly formed phagosomes along with actin and myosin IB. In vitro studies confirmed that EhCaBP3 directly binds actin, and affected both its polymerization and bundling activity. Moreover, it also binds myosin 1B in the presence of Ca²⁺. In cells where EhCaBP3 expression was down regulated by antisense RNA, the level of RBC uptake was reduced, myosin IB was found to be absent at the site of pseudopod cup closure and the time taken for phagocytosis increased, suggesting that EhCaBP3 along with myosin 1B mediate the closure of phagocytic cups. Experiments with EhCaBP3 mutant defective in Ca²⁺ -binding showed that Ca²⁺ binding is required for phagosome formation. Liposome binding assay revealed that EhCaBP3 recruitment and enrichment to membrane is independent of any cellular protein as it binds directly to phosphatidylserine. Taken together, our results suggest a novel pathway mediating phagocytosis in E. histolytica, and an unusual mechanism of modulation of cytoskeleton dynamics by two calcium binding proteins, EhCaBP1 and EhCaBP3 with mostly non-overlapping functions.

Entamoeba histolytica is one of the major causes of morbidity and mortality in developing countries. Phagocytosis plays an important role in both survival and virulence and has been used as a virulence marker. Inhibition of phagocytosis leads to a defect in cellular proliferation. Therefore, the molecules that participate in phagocytosis are good targets for developing new drugs. However, the molecular mechanism of the process is still largely unknown. Here, we demonstrate that Calmodulin-like calcium binding protein EhCaBP3 is involved in erythrophagocytosis. We show this by a number of different approaches including immunostaining of actin, myosin1B, EhCaBP1 and EhCaBP3 during uptake of RBC; over expression and down regulation of EhCaBP3, and over expression of calcium defective mutant of EhCaBP3. Our analysis suggests that EhCaBP3 can regulate actin dynamics. Along with actin and myosin 1B it can participate in both initiation and formation of phagosomes. The Ca²⁺-bound form of this protein is required only for progression from cups into early phagosomes but not for initiation. Our results demonstrate the complex role of Ca²⁺ binding proteins, EhCaBP1 and EhCaBP3 in regulation of phagocytosis in the protist parasite E. histolytica and the novel mechanisms of manipulating actin dynamics at multiple levels.