Pathogenic Stimuli Research Articles

Comprehensive review of lipocalin 2-mediated effects in lung inflammation.

Lipocalin-2 (LCN2) is an inflammatory mediator best known for its role as an innate acute-phase protein. LCN2 mediates the innate immune response to pathogens by sequestering iron, thereby inhibiting pathogen growth. Although LCN2 and its bacteriostatic properties are well studied, other LCN2 functions in the immune response to inflammatory stimuli are less well understood, such as its role as a chemoattractant and involvement in the regulation of cell migration and apoptosis. In the lungs, most studies thus far investigating the role of LCN2 in the immune response have looked at pathogenic inflammatory stimuli. Here, we compile data that explore the role of LCN2 in the immune response to various inflammatory stimuli in an effort to differentiate between protective versus detrimental roles of LCN2.

NETosis and the Immune System in COVID-19: Mechanisms and Potential Treatments.

NETosis is a form of neutrophil death leading to the release of extracellular chromatin and the assembling of proteins, including antiviral proteins, primed by an initial pathogenic stimulus. Under certain specific conditions, neutrophils can exhibit a double-edged activity. This event has been implicated in COVID-19 among other conditions. Neutrophil extracellular traps (NETs) are involved in the pathogenesis of COVID-19 by promoting a pro-inflammatory and a procoagulant state leading to multiorgan failure. This particular form of host defense promoted by neutrophils is closely related to the well-known cytokine storm observed in severe COVID-19 patients. These two elements therefore represent possible targets for treatment of severe SARS-CoV-2 infections.

Functional and Stress Response Analysis of Heat Shock Proteins 40 and 90 of Giant River Prawn (Macrobrachium rosenbergii) under Temperature and Pathogenic Bacterial Exposure Stimuli.

The aims of this research were to perform molecular characterization and biofunctional analyses of giant river prawn Hsp40 and Hsp90 genes (Mr-hsp40 and Mr-hsp90) under various stress conditions. Comparisons of the nucleotide and amino acid sequences of Mr-hsp40 and Mr-hsp90 with those of other species showed the highest similarity scores with crustaceans. Under normal conditions, expression analysis using quantitative real-time RT-PCR (qRT-PCR) indicated that Mr-hsp40 was highly expressed in the gills and testis, and Mr-hsp90 expression was observed in all tissues, with the highest expression in the ovary. The expression patterns of Mr-hsp40 and Mr-hsp90 transcripts under Aeromonas hydrophila challenge and heat–cold shock conditions were examined in gills, the hepatopancreas and hemocytes, at 0, 3, 6, 12, 24, 48 and 96 h by qRT-PCR. Under bacterial challenge, Mr-hsp40 displayed variable expression patterns in all tissues examined during the tested periods. In contrast, upregulated expression of Mr-hsp90 was quickly observed from 3 to 12 h in the gills and hepatopancreas, whereas obviously significant upregulation of Mr-hsp90 was observed in hemocytes at 12–96 h. Under temperature shock conditions, upregulation of Mr-hsp40 expression was detected in all tested tissues, while Mr-hsp90 expression was quickly upregulated at 3–48 h in all tissues in response to 35 °C conditions, and conditions of 35 and 25 °C stimulated its expression in gills and the hepatopancreas at 12 and 48 h, respectively. Silencing analyses of these two genes were successfully conducted under normal, high-temperature (35 °C) and A. hydrophila infection conditions. Overall, knockdown of Mr-hsp40 and Mr-hsp90 effectively induced more rapid and higher mortality than in the PBS control and GFP induction groups in temperature and infectious treatments. Evidence from this study clearly demonstrated the significant functional roles of Mr-hsp40 and Mr-hsp90, which are crucially involved in cellular stress responses to both temperature and pathogenic bacterial stimuli.

Phase separation in immune signalling.

Immune signalling pathways convert pathogenic stimuli into cytosolic events that lead to the resolution of infection. Upon ligand engagement, immune receptors together with their downstream adaptors and effectors undergo substantial conformational changes and spatial reorganization. During this process, nanometre-to-micrometre-sized signalling clusters have been commonly observed that are believed to be hotspots for signal transduction. Because of their large size and heterogeneous composition, it remains a challenge to fully understand the mechanisms by which these signalling clusters form and their functional consequences. Recently, phase separation has emerged as a new biophysical principle for organizing biomolecules into large clusters with fluidic properties. Although the field is still in its infancy, studies of phase separation in immunology are expected to provide new perspectives for understanding immune responses. Here, we present an up-to-date view of how liquid-liquid phase separation drives the formation of signalling condensates and regulates immune signalling pathways, including those downstream of T cell receptor, B cell receptor and the innate immune receptors cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene I protein (RIG-I). We conclude with a summary of the current challenges the field is facing and outstanding questions for future studies.

The lymphatics in kidney health and disease.

The mammalian vascular system consists of two networks: the blood vascular system and the lymphatic vascular system. Throughout the body, the lymphatic system contributes to homeostatic mechanisms by draining extravasated interstitial fluid and facilitating the trafficking and activation of immune cells. In the kidney, lymphatic vessels exist mainly in the kidney cortex. In the medulla, the ascending vasa recta represent a hybrid lymphatic-like vessel that performs lymphatic-like roles in interstitial fluid reabsorption. Although the lymphatic network is mainly derived from the venous system, evidence supports the existence of lymphatic beds that are of non-venous origin. Following their development and maturation, lymphatic vessel density remains relatively stable; however, these vessels undergo dynamic functional changes to meet tissue demands. Additionally, new lymphatic growth, or lymphangiogenesis, can be induced by pathological conditions such as tissue injury, interstitial fluid overload, hyperglycaemia and inflammation. Lymphangiogenesis is also associated with conditions such as polycystic kidney disease, hypertension, ultrafiltration failure and transplant rejection. Although lymphangiogenesis has protective functions in clearing accumulated fluid and immune cells, the kidney lymphatics may also propagate an inflammatory feedback loop, exacerbating inflammation and fibrosis. Greater understanding of lymphatic biology, including the developmental origin and function of the lymphatics and their response to pathogenic stimuli, may aid the development of new therapeutic agents that target the lymphatic system.

The Roles of Phospholipase A2 in Phagocytes.

Phagocytic cells, such as macrophages, neutrophils, and dendritic cells, ingest particles larger than about 0.5 μM and thereby clear microbial pathogens and malignant cells from the body. These phagocytic cargoes are proteolytically degraded within the lumen of phagosomes, and peptides derived from them are presented on Major Histocompatibility Complexes (MHC) for the activation of T cells. Mammalian PLA2 isozymes belong to a large family of enzymes that cleave phospholipids at the second position of the glycerol backbone, releasing a free fatty acid and a lysolipid moiety. In human macrophages, at least 15 different PLA2 forms are expressed, and expression of many of these is dependent on pathogenic stimulation. Intriguing questions are why so many PLA2 forms are expressed in macrophages, and what are the functional consequences of their altered gene expression after encountering pathogenic stimuli. In this review, we discuss the evidence of the differential roles of different forms of PLA2 in phagocytic immune cells. These roles include: lipid signaling for immune cell activation, initial phagocytic particle uptake, microbial action for the killing and degradation of ingested microbes, and the repair of membranes induced by oxygen radicals. We also discuss the roles of PLA2 in the subsequent digestion of ingested phagocytic cargoes for antigen presentation to T cells.

Blueberry Treatment Administered Before and/or After Lipopolysaccharide Attenuates Neuroinflammation and Oxidative Stress in Rat Microglial Cells

ObjectivesNeuroinflammation and oxidative stress (OS) are implicated as mediators of cognitive decline and neurodegenerative diseases. Microglia, the primary immune cells of the central nervous system (CNS), are key regulators of inflammation and OS in the CNS. Blueberries (BB) are rich in anti-inflammatory and antioxidant polyphenols and reduce inflammation and OS when administered to microglia before pathogenic stimuli such as lipopolysaccharide (LPS). However, the therapeutic value of BBs administered to microglial cells after activation by LPS on inflammation and OS has not been examined. This study investigated the potential differential effects of pre-, post-, and pre-/post-BB on LPS-induced inflammation and OS in rat microglia. MethodsRat microglia were pre-treated with freeze-dried BB diluted in media (0.5 mg/mL) or control media (C) for 24 h, incubated overnight with LPS (0 or 100 ng/mL), and post-treated with BB or C for 24 h. Standard immunochemical techniques were used to measure biomarkers of inflammation and OS, including nitrite, tumor necrosis factor alpha (TNFɑ), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Data were analyzed using two-way ANOVAs with treatment group (pre-/post-BB) and LPS exposure as experimental factors. Post-hoc testing was performed using Tukey’s test to determine differences among groups. ResultsPreliminary results showed that all BB treatments (pre-, post- and pre-/post-BB) reduced LPS-induced nitrite and TNFɑ relative to no BB (P < 0.01). Pre-BB was more effective at reducing nitrite than post-BB (P < 0.01), although neither was significantly different than pre-/post-BB. In contrast, the attenuating effects of pre-BB and post-BB on TNFɑ were not different from each other, although both treatments were more beneficial than pre-/post-BB (P < 0.001). Compared to no BB, both pre-BB and post-BB, although not pre-/post-BB reduced LPS-induced iNOS expression (P < 0.05), and only pre-BB attenuated COX2 expression (P < 0.01). ConclusionsResults suggest that BBs can target the downstream effects of microglial activation in addition to preventing stressor-induced neuroinflammation and OS. Therefore, although potentially more effective, BBs may not need to be present prior to microglial activation for beneficial effects. Funding SourcesSupported by USDA intramural funding.

FC 099DECLINING PERITONEAL HOST DEFENCES REVEALED BY EX-VIVO CYTOKINE RELEASE ASSAY OF PERITONEAL DIALYSIS EFFLUENT CELLS

Abstract Background and Aims Infectious complications occur in a significant proportion of PD patients, limiting long-term applicability. Reduced peritoneal immune-competence, caused by the continuous exposure to PD-fluids, has been described as a therapy-related pathomechanisms, prompting the need for a tool to assess the functional peritoneal immune status. We established an ex-vivo stimulation assay to test host defence mechanisms in only 9ml of PD-effluent. The aim of this study was to analyse basal inflammation and immune-competence in the general PD population at routine conditions to evaluate the assay as surrogate parameter of immune competence and linking it to PD vintage and clinical outcome parameters. Method 147 of 284 (51.8%) adult and paediatric PD patients treated between April 2013 and September 2020 at the local Department of Nephrology were included in the analysis. The study was approved by the local ethics committee and was conducted in accordance with the Declaration of Helsinki. Patients were exclusively treated with neutral pH/multi-chamber PD fluids during the glucose dwells. The majority of the 558 included PD-effluent samples were obtained during standard 4-hours peritoneal equilibration tests (PET) with 3.86% glucose containing PDF. Samples from the pre-PET dwell and at PET time points 1-hour and 4-hours were collected and immediately processed. Additional effluent samples were obtained during unscheduled hospitalization and in the event of an acute peritonitis. Effluent samples were collected directly from the drainage bags into standard 9 ml additive-free sample tubes. For ex-vivo stimulation, 100 ng/ml toll-like receptor (TLR) 4 agonist LPS and TLR2 agonist Pam3Cys were added to the effluent in the 9 ml collection tubes in duplicates and incubated at 37°C for 24h. Unstimulated samples kept in parallel were used as controls. IL-6 and TNF-α concentrations were measured with ELISA in the supernatants. Results Ex-vivo stimulation of peritoneal cells significantly increased the IL-6 and TNF-α release compared to unstimulated controls and resulted in a dwell-time dependent increase, with a significant lower cytokine released at the 1h PET time point. To assess local inflammation IL-6 levels of crude effluent were determined. IL-6 concentrations remained stable over time on PD. Interestingly, we were able to show higher IL-6 levels in CAPD patients in comparison to APD. As chronic exposure to PD-fluids has been shown to dampen the peritoneal immune competence, consecutive peritoneal effluent bags, obtained from patients were analysed. In this subcohort of 183 4h-PET effluents we found a decline in cytokine secretion with time on PD (IL-6 r=-0.27, p=0.00015, TNFa r=-0.25, p=0.00071). In a subgroup the ex-vivo cytokine release of effluent samples from patients with an acute peritonitis was assessed. IL-6 levels of acute peritonitis effluent samples did not differ from the stimulated IL-6 levels of effluent samples without acute peritonitis (2.45 pg/mL vs 2.31 pg/mL, p=0.85, t-test) suggesting that the assay seemingly represents the in-vivo host-defence cytokine release accurately. Conclusion The study provides evidence of a correlation of declining local host defence and duration of PD-therapy. It supports the hypothesis of PD duration-dependent progressive impairment of the ability of the peritoneal immune cells to secrete cytokines in response to a pathogenic stimulus and thereby dampening the global peritoneal immuno-competence. This suggests the utility of this clinically feasible ex-vivo induced cytokine-release assay in peritoneal effluent as a surrogate of the functional peritoneal immune competence. Future analyses need to evaluate the assay as a tool to predict common clinical outcomes and define reference values to facilitate stratification of patient populations, clinical staging and to guide novel therapeutic interventions.

Investigating the age and sex associated mucosal immune landscape of urinary bladder

Abstract The incidence of BC is four times higher in males than females, however, females tend to present with a more aggressive disease, a poorer response to immunotherapy, and suffer worse clinical outcomes. Our recent novel findings demonstrated sexual dimorphism in the tumor immune microenvironment of non-muscle invasive bladder cancer, which is primarily treated with local immunotherapy. Investigating sexual dimorphism in the clinical journey of BC beyond the static local immune landscapes remains a challenge. With similarities in mucosal immune physiology between humans and mice, and the recently reported age-associated pathogenic stimuli independent inflammation observed female murine bladders, we conducted a comprehensive evaluation of the sex and age-related immune alterations in healthy murine bladders. Bulk-RNA sequencing and multiplex immunofluorescence based spatial immune profiling of normal murine bladders from male and female mice of the ages 3, 6, 9, 12, 15, and 18 months were performed. Preliminary findings from the transcriptomic analysis showed a highly altered immune landscape that exhibited sex differences in aged bladders. Spatial profiling of using markers specific to macrophages (CD163, CD11b), T lymphocytes (CD3, CD8), B lymphocytes (Pax5), activated dendritic cells (CD208), high endothelial venules (PNAd), inflammatory cells (Ly6G) and the PD-L1 immune checkpoint, showed sex and age associated differences. Older female mice had a higher density of tertiary lymphoid structures/lymphoid aggregates compared to both young female and male equivalents. Findings from this study will allow the appropriate modeling in pre-clinical studies evaluating immunotherapeutic agents for NMIBC treatment.

IL-33 sensitizes mast cells to respond to a second alarmin, ATP, but not PAMPs.

Abstract Barrier defenses must respond rapidly to pathogen infection but avoid responses to innocuous antigens or microbes. Aberrant recognition can lead to hypersensitivity and/or chronic inflammatory conditions. Barrier tissues actively release alarmins such as IL-33 in response to cell stress helping to identify pathogenic stimuli. Additional alarmin molecules such as ATP, uric acid crystals, and HMBG protein have also been identified but it remains unclear how the innate immune system integrates these multiple signals. We have used mast cells to address how IL-33 and ATP signals interact. While best known for their role in IgE-mediated allergic responses, mast cells readily produce inflammatory cytokines in response to either IL-33 or ATP. Measuring secreted IL-6, TNF alpha and IL-13 we found that bone marrow-derived and peritoneal mast cells had a 3–6-fold increased response to ATP when sensitized by pretreatment with IL-33. This synergistic effect was observed at relatively low ATP concentrations (&amp;lt;300μM) and required &amp;lt;1hr exposure to IL-33. Stimulating with PAMPs (LPS, LTA, poly I:C, ß-glucan) failed to show any enhancement with IL-33 pretreatment. Inhibitor studies indicated that the P2X3 receptor and the NFAT transcription factor mediated the ATP response. To test IL-33 and ATP synergy in vivo, we assessed eosinophil mobilization to the peritoneal cavity in mice. Consistent with the in vitro studies, co-administration of IL-33 and ATP increased eosinophil numbers compared to either alarmin alone. These results support the hypothesis that alarmins collaborate to surpass a threshold level of barrier stress necessary to initiate an inflammatory immune response.

Immunology of biodegradable nanoparticles: a brief overview on a wide growing field

Immunity is continuously evolving by evolutionary mechanisms shaped by pathogenic stimuli of different kinds. Man-made nanomaterials (NMs) have been developed in the last decades and represent a novel challenge for our immune system, especially when applied to medical science. Toxicological studies of such nanoparticles (NPs) revealed that size, shape, and surface chemistry are key parameters to understand their noxious effects on cellular mechanisms. Less is known on the immune reactions to NMs since prolonged exposure data are not so detailed as the results for acute administration. The importance of immunity to biocompatible NPs is underlined by their increasing use as drug or gene delivery carriers in common pharmaceutical preparations and vaccines. In the latter case, the immunomodulatory properties of NMs allow their use also as efficient adjuvants to enhance the innate immune response. In the current manuscript, the authors discuss the main concepts in this fast-growing field by restricting our view to NMs with consolidated application in biomedicine.

Long-COVID syndrome-associated brain fog and chemofog: Luteolin to the rescue.

COVID‐19 leads to severe respiratory problems, but also to long‐COVID syndrome associated primarily with cognitive dysfunction and fatigue. Long‐COVID syndrome symptoms, especially brain fog, are similar to those experienced by patients undertaking or following chemotherapy for cancer (chemofog or chemobrain), as well in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) or mast cell activation syndrome (MCAS). The pathogenesis of brain fog in these illnesses is presently unknown but may involve neuroinflammation via mast cells stimulated by pathogenic and stress stimuli to release mediators that activate microglia and lead to inflammation in the hypothalamus. These processes could be mitigated by phytosomal formulation (in olive pomace oil) of the natural flavonoid luteolin.

Decoding Mast Cell-Microglia Communication in Neurodegenerative Diseases.

Microglia, resident immune cells of the central nervous system (CNS), play a pivotal role in immune surveillance and maintenance of neuronal health. Mast cells are also important resident immune cells of the CNS but they are underappreciated and understudied. Both microglia and mast cells are endowed with an array of signaling receptors that recognize microbes and cellular damage. As cellular sensors and effectors in the CNS, they respond to many CNS perturbations and have been implicated in neuroinflammation and neurodegeneration. Mast cells contain numerous secretory granules packaged with a plethora of readily available and newly synthesized compounds known as ‘mast cell mediators’. Mast cells act as ‘first responders’ to a pathogenic stimuli and respond by degranulation and releasing these mediators into the extracellular milieu. They alert other glial cells, including microglia to initiate neuroinflammatory processes that culminate in the resolution of injury. However, failure to resolve the pathogenic process can lead to persistent activation, release of pro-inflammatory mediators and amplification of neuroinflammatory responses, in turn, resulting in neuronal dysfunction and demise. This review discusses the current understanding of the molecular conversation between mast cells and microglia in orchestrating immune responses during two of the most prevalent neurodegenerative diseases, namely Alzheimer’s disease and Parkinson’s disease. Here we also survey the potential emerging therapeutic approaches targeting common pathways in mast cells and microglia to extinguish the fire of inflammation.

What Will B Will B: Identifying Molecular Determinants of Diverse B-Cell Fate Decisions Through Systems Biology.

B-cells are the poster child for cellular diversity and heterogeneity. The diverse repertoire of B lymphocytes, each expressing unique antigen receptors, provides broad protection against pathogens. However, B-cell diversity goes beyond unique antigen receptors. Side-stepping B-cell receptor (BCR) diversity through BCR-independent stimuli or engineered organisms with monoclonal BCRs still results in seemingly identical B-cells reaching a wide variety of fates in response to the same challenge. Identifying to what extent the molecular state of a B-cell determines its fate is key to gaining a predictive understanding of B-cells and consequently the ability to control them with targeted therapies. Signals received by B-cells through transmembrane receptors converge on intracellular molecular signaling networks, which control whether each B-cell divides, dies, or differentiates into a number of antibody-secreting distinct B-cell subtypes. The signaling networks that interpret these signals are well known to be susceptible to molecular variability and noise, providing a potential source of diversity in cell fate decisions. Iterative mathematical modeling and experimental studies have provided quantitative insight into how B-cells achieve distinct fates in response to pathogenic stimuli. Here, we review how systems biology modeling of B-cells, and the molecular signaling networks controlling their fates, is revealing the key determinants of cell-to-cell variability in B-cell destiny.

Gold nanoparticles synergize with bacterial lipopolysaccharide to enhance class A scavenger receptor dependent particle uptake in neutrophils and augment neutrophil extracellular traps formation

Gold nanoparticles (AuNPs) are extensively utilized in biomedical fields. However, their potential interaction with host cells has not been comprehensively elucidated. In this study, we demonstrated a size-dependent effect of AuNPs to synergize with bacterial lipopolysaccharide (LPS) in promoting neutrophil extracellular traps (NETs) release in human peripheral neutrophils. Mechanistically, LPS was more efficient to contact with 10 nm AuNPs and promote their uptake in neutrophils compared to 40 and 100 nm AuNPs, leading to a synergistic upregulation of class A scavenger receptor (SRA) which mediated AuNPs uptake and triggered activation of extracellular regulated protein kinase (ERK) and p38. Blocking SRA or inhibiting ERK and p38 activation remarkably abrogated the effect of AuNPs and LPS to induce NETs formation. Further experiments demonstrated that AuNPs and LPS augmented the production of cytosolic reactive oxygen species (ROS) in p38 and ERK dependent manner, through upregulating and activating NADPH oxidase 2 (NOX2). Accordingly, scavenging of ROS or inhibiting the NOX2 dampened NETs release induced by combined AuNPs and LPS treatment. AuNPs and LPS also synergized to upregulate reactive oxygen species modulator 1 (ROMO1) via activating ERK, thereby increasing mitochondrial ROS generation and promoting the release of NETs. In summary, we provide new evidences about the synergy of AuNPs and LPS to augment cellular responses in neutrophils, which implicates the need to consider the amplifying effect by pathogenic stimuli when utilizing nanomaterials in infectious or inflammatory conditions.

NF-κB signalling as a pharmacological target in COVID-19: potential roles for IKKβ inhibitors.

Coronavirus disease 2019 (COVID-19) has been characterized by lymphopenia as well as a proinflammatory cytokine storm, which are responsible for the poor prognosis and multiorgan defects. The transcription factor nuclear factor-κB (NF-κB) modulates the functions of the immune cells and alters the gene expression profile of different cytokines in response to various pathogenic stimuli, while many proinflammatory factors have been known to induce NF-κB signalling cascade. Besides, NF-κB has been known to potentiate the production of reactive oxygen species (ROS) leading to apoptosis in various tissues in many diseases and viral infections. Though the reports on the involvement of the NF-κB signalling pathway in COVID-19 are limited, the therapeutic benefits of NF-κB inhibitors including dexamethasone, a synthetic form of glucocorticoid, have increasingly been realized. Considering the fact, the abnormal activation of the NF-κB resulting from severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection might be associated with the pathogenic profile of immune cells, cytokine storm and multiorgan defects. Thus, the pharmacological inactivation of the NF-κB signalling pathway can strongly represent a potential therapeutic target to treat the symptomatology of COVID-19. This article signifies pharmacological blockade of the phosphorylation of inhibitor of nuclear factor kappa B kinase subunit beta (IKKβ), a key downstream effector of NF-κB signalling, for a therapeutic consideration to attenuate COVID-19.

Differing Alterations of Odor Volatiles Among Pathogenic Stimuli.

Alterations of the volatile metabolome (the collection of volatiles present in secretions and other emanations) that occur in response to inflammation can be detected by conspecifics and chemometric analyses. Using a model system where mouse urinary metabolites are altered by treatment with lipopolysaccharide (found in the outer cell membrane of gram-negative bacteria), we hypothesized that alteration of body odor volatiles will vary according to the pathogen responsible for inducing the inflammation. We tested this hypothesis by treating mice with different immunogens that engage different immune signaling pathways. Results suggest that alterations of body odor volatiles resulting from inflammation do contain detailed information about the type of pathogen that instigated the inflammation and these differences are not merely dependent on the severity of the inflammatory event. These results are encouraging for the future of differential medical diagnosis of febrile diseases by analysis of the volatile metabolome. In particular, our data support the possibility that bacterial infections can be differentiated from viral infections such that antibiotic drug stewardship could be drastically improved by reducing unneeded treatments with antibiotics.

Lateral diffusion of CD14 and TLR2 in macrophage plasma membrane assessed by raster image correlation spectroscopy and single\xa0particle tracking

The diffusion of membrane receptors is central to many biological processes, such as signal transduction, molecule translocation, and ion transport, among others; consequently, several advanced fluorescence microscopy techniques have been developed to measure membrane receptor mobility within live cells. The membrane-anchored receptor cluster of differentiation 14 (CD14) and the transmembrane toll-like receptor 2 (TLR2) are important receptors in the plasma membrane of macrophages that activate the intracellular signaling cascade in response to pathogenic stimuli. The aim of the present work was to compare the diffusion coefficients of CD14 and TLR2 on the apical and basal membranes of macrophages using two fluorescence-based methods: raster image correlation spectroscopy (RICS) and single particle tracking (SPT). In the basal membrane, the diffusion coefficients obtained from SPT and RICS were found to be comparable and revealed significantly faster diffusion of CD14 compared with TLR2. In addition, RICS showed that the diffusion of both receptors was significantly faster in the apical membrane than in the basal membrane, suggesting diffusion hindrance by the adhesion of the cells to the substrate. This finding highlights the importance of selecting the appropriate membrane (i.e., basal or apical) and corresponding method when measuring receptor diffusion in live cells. Accurately knowing the diffusion coefficient of two macrophage receptors involved in the response to pathogen insults will facilitate the study of changes that occur in signaling in these cells as a result of aging and disease.

Enhanced Free Fatty Acid Uptake Via CD36 Promotes a Metabolic Switch to B-Oxidation within Hematopoietic Stem Cells in Response to Acute Infection

Acute infection is known to promote rapid differentiation of hematopoietic stem cells (HSC) and expansion of leukocytes. Metabolic changes in the HSC underpin the mammalian response to pathogenic stimuli however, knowledge of how this occurs is not fully understood. Here we investigate the immunometabolic changes which facilitate HSC expansion in response to acute infection. We created a novel in vivo transplant model to understand if the immune response to infection involves the acquisition of free fatty acids (FFA) by HSCs in the bone marrow (BM). We transduced CD45.1 lineage negative, c-kit positive cells with firefly luciferase and transplanted into CD45.2 animals. Post engraftment animals were treated with lipopolysaccharide (LPS). Live animal imaging confirmed activation of luciferase in the BM, demonstrating in vivo, uptake of long chain FFA by haematopoietic cells in response to LPS. To confirm the specific haematopoietic stem and/or progenitor cells (HSPC) with increased lipids during infection, mice were treated with S.typhimurium for 72h then sacrificed Analysis of LSK, MPP and HSC populations (LN-, CD117+, Sca1+, CD48-, CD150+ and CD34+) showed increased intracellular BODIPY 493/503 neutral lipid dye and uptake of Bodipy FL-C12 (FFA linked to bodipy) at 72 h compared to control non-infected animals. Together, these experiments show that HSC, multipotent progenitor (MPP) and LSK (LN-, CD117+, Sca1+) cells all acquire FFA in response to bacterial infection. Seahorse mitochondrial stress test confirmed increased oxygen consumption levels in HSC from LPS (16 hours) and S.typhimurium (72 hours) treated C57BL/6. LSK metabolic activity for different substrates was assessed LSKs from LPS treated animals had an increased dependency on β-oxidation when compared to control cells. Moreover, the β-oxidation inhibitor etomoxir blocks LSK basal metabolism and reduced HSC expansion as measured by Ki-67 staining in LPS and S.typhimurium treated animals. To understand the importance of β-oxidation in HSC expansion in response to infection we first measured CPT1A expression in HSC. RNA analysis confirmed CPT1A was increased in sorted HSCs in response to LPS. Next we transplanted WTor CPT1A KD cells into WT animals, and treated with LPS. HSC expansion as measured by Ki-67 staining was inhibited in the CPT1A KD cells in response to LPS, thus confirming the importance of β-oxidation based metabolism in HSC expansion. To determine how FFA are transported into the HSC we analysed the expression of known genes to be involved in lipid uptake. HSC sorted from LPS and S.typhimurium treated animals had increased CD36 mRNA expression compared to control. C57BL/6 mice were pre-treated with the CD36 inhibitor sulfosuccinimidyl oleate (SSO) before injection with LPS. HSCs had had less lipids, lower maximal respiration and reduced cycling when compared to animals treated with LPS alone. In a similar way CD36 KO animals were treated with LPS for 16 h, no increased FFA uptake or increased lipid content or HSC cycling was observed. Seahorse mitochondrial stress test confirmed CD36-/- LSK have increased basal ECAR but no change in basal OCR in response to S.typhimurium infection. Moreover, CD36-/- LSK have reduced dependency on β-oxidation. To determine if the uptake of FFA response is specific to HSC we transplanted CD36+/+ (CD45.1) LK into CD36-/- (CD45.2) animals. We found that CD36 expression was elevated in CD36+/+ HSC transplanted into CD36-/- treated with LPS, normal uptake of FFA, an increase in lipid content and cycling of HSCs. In addition, transplanted WT CD36+/+ (CD45.1) LSK into CD36-/- (CD45.2) animals reversed the metabolic phenotype observed in CD36-/- in response to LPS. We transplanted WT(CD36+/+) or CD36KO (WT(CD36-/-)) LSK into WT animals infected with S. typhimurium for 4 days. WT(CD36-/-) transplanted animals showed enhanced mortality, increased weight loss and increased liver injury. We also observed less HSC cycling and a reduced lipid content in HSC from WT(CD36-/-) compared to WT(CD36+/+). These findings expand the mechanistic understanding of the interplay between HSC and the bone marrow microenvironment, and in doing so explains how immunometabolic reprogramming of HSCs during infection supports the metabolic demands of HSCs in response to a pathogenic challenge without which results in increased susceptibility to infection. Disclosures Bowles: AbbVie: Research Funding; Janssen: Research Funding. Rushworth:AbbVie: Research Funding; Janssen: Research Funding.

Distinct Molecular Pattern-Induced Calcium Signatures Lead to Different Downstream Transcriptional Regulations via AtSR1/CAMTA3.

Plants encrypt the perception of different pathogenic stimuli into specific intracellular calcium (Ca2+) signatures and subsequently decrypt the signatures into appropriate downstream responses through various Ca2+ sensors. Two microbe-associated molecular patterns (MAMPs), bacterial flg22 and fungal chitin, and one damage-associated molecular pattern (DAMP), AtPep1, were used to study the differential Ca2+ signatures in Arabidopsis leaves. The results revealed that flg22, chitin, and AtPep1 induced distinct changes in Ca2+ dynamics in both the cytosol and nucleus. In addition, Flg22 and chitin upregulated the expression of salicylic acid-related genes, ICS1 and EDS1, whereas AtPep1 upregulated the expression of jasmonic acid-related genes, JAZ1 and PDF1.2, in addition to ICS1 and EDS1. These data demonstrated that distinct Ca2+ signatures caused by different molecular patterns in leaf cells lead to specific downstream events. Furthermore, these changes in the expression of defense-related genes were disrupted in a knockout mutant of the AtSR1/CAMTA3 gene, encoding a calmodulin-binding transcription factor, in which a calmodulin-binding domain on AtSR1 was required for deciphering the Ca2+ signatures into downstream transcription events. These observations extend our knowledge regarding unique and intrinsic roles for Ca2+ signaling in launching and fine-tuning plant immune response, which are mediated by the AtSR1/CAMTA3 transcription factor.