Macrophage’s Proinflammatory Response to a Mycobacterial Infection Is Dependent on Sphingosine Kinase-Mediated Activation of Phosphatidylinositol Phospholipase C, Protein Kinase C, ERK1/2, and Phosphatidylinositol 3-Kinase

Signaling controversy and future therapeutical perspectives of targeting sphingolipid network in cancer immune editing and resistance to tumor necrosis factor-α immunotherapy

Anticancer immune surveillance and immunotherapies trigger activation of cytotoxic cytokine signaling, including tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) pathways. The pro-inflammatory cytokine TNF-α may be secreted by stromal cells, tumor-associated macrophages, and by cancer cells, indicating a prominent role in the tumor microenvironment (TME). However, tumors manage to adapt, escape immune surveillance, and ultimately develop resistance to the cytotoxic effects of TNF-α. The mechanisms by which cancer cells evade host immunity is a central topic of current cancer research. Resistance to TNF-α is mediated by diverse molecular mechanisms, such as mutation or downregulation of TNF/TRAIL receptors, as well as activation of anti-apoptotic enzymes and transcription factors. TNF-α signaling is also mediated by sphingosine kinases (SphK1 and SphK2), which are responsible for synthesis of the growth-stimulating phospholipid, sphingosine-1-phosphate (S1P). Multiple studies have demonstrated the crucial role of S1P and its transmembrane receptors (S1PR) in both the regulation of inflammatory responses and progression of cancer. Considering that the SphK/S1P/S1PR axis mediates cancer resistance, this sphingolipid signaling pathway is of mechanistic significance when considering immunotherapy-resistant malignancies. However, the exact mechanism by which sphingolipids contribute to the evasion of immune surveillance and abrogation of TNF-α-induced apoptosis remains largely unclear. This study reviews mechanisms of TNF-α-resistance in cancer cells, with emphasis on the pro-survival and immunomodulatory effects of sphingolipids. Inhibition of SphK/S1P-linked pro-survival branch may facilitate reactivation of the pro-apoptotic TNF superfamily effects, although the role of SphK/S1P inhibitors in the regulation of the TME and lymphocyte trafficking should be thoroughly assessed in future studies.

Systematic analysis of lysine crotonylation in human macrophages responding to MRSA infection

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most commonly encountered bacteria found in healthcare clinics and has been ranked a priority 2 pathogen. Research is urgently needed to develop new therapeutic approaches to combat the pathogen. Variations in the pattern of protein posttranslational modifications (PTMs) of host cells affect physiological and pathological events, as well as therapeutic effectiveness. However, the role of crotonylation in MRSA-infected THP1 cells remains unknown. In this study, we found that crotonylation profiles of THP1 cells were altered after MRSA infection. It was then confirmed that lysine crotonylation profiles of THP1 cells and bacteria were different; MRSA infection inhibited global lysine crotonylation (Kcro) modification but partially elevated Kcro of host proteins. We obtained a proteome-wide crotonylation profile of THP1 cells infected by MRSA further treated by vancomycin, leading to the identification of 899 proteins, 1384 sites of which were down-regulated, and 160 proteins with 193 sites up-regulated. The crotonylated down-regulated proteins were mainly located in cytoplasm and were enriched in spliceosome, RNA degradation, protein posttranslational modification, and metabolism. However, the crotonylated up-regulated proteins were mainly located in nucleus and significantly involved in nuclear body, chromosome, ribonucleoprotein complex, and RNA processing. The domains of these proteins were significantly enriched on RNA recognition motif, and linker histone H1 and H5 families. Some proteins related to protecting against bacterial infection were also found to be targets of crotonylation. The present findings point to a comprehensive understanding of the biological functions of lysine crotonylation in human macrophages, thereby providing a certain research basis for the mechanism and targeted therapy on the immune response of host cells against MRSA infection.

Phospholipase C: underrated players in microbial infections

During bacterial infections, one or more virulence factors are required to support the survival, growth, and colonization of the pathogen within the host, leading to the symptomatic characteristic of the disease. The outcome of bacterial infections is determined by several factors from both host as well as pathogen origin. Proteins and enzymes involved in cellular signaling are important players in determining the outcome of host-pathogen interactions. phospholipase C (PLCs) participate in cellular signaling and regulation by virtue of their ability to hydrolyze membrane phospholipids into di-acyl-glycerol (DAG) and inositol triphosphate (IP3), which further causes the activation of other signaling pathways involved in various processes, including immune response. A total of 13 PLC isoforms are known so far, differing in their structure, regulation, and tissue-specific distribution. Different PLC isoforms have been implicated in various diseases, including cancer and infectious diseases; however, their roles in infectious diseases are not clearly understood. Many studies have suggested the prominent roles of both host and pathogen-derived PLCs during infections. PLCs have also been shown to contribute towards disease pathogenesis and the onset of disease symptoms. In this review, we have discussed the contribution of PLCs as a determinant of the outcome of host-pathogen interaction and pathogenesis during bacterial infections of human importance.

PET Study of Sphingosine-1-phosphate Receptor 1 Expression in Response to S. aureus Infection

Sphingosine-1-phosphate receptor 1 (S1PR1) plays a crucial role in infectious diseases. Targeting S1PR1 provides protection against pathogens, such as influenza viruses. This study is aimed at investigating S1PR1 in response to bacterial infection by assessing S1PR1 expression in S. aureus-infected mice. A rodent local muscle bacterial infection model was developed by injecting S. aureus to the lower hind limb of Balb/c mice. The changes of S1PR1 expression in response to bacterial infection and blocking treatment were assessed using ex vivo biodistribution and in vivo positron emission tomography (PET) after intravenous injection of an S1PR1-specific radiotracer [18F]TZ4877. The specificity of [18F]TZ4877 was assessed using S1PR1-specific antagonist, NIBR-0213, and S1PR1-specific DsiRNA pretreated the animals. Immunohistochemical studies were performed to confirm the increase of S1PR1 expression in response to infection. Ex vivo biodistribution data showed that the uptake of [18F]TZ4877 was increased 30.6%, 54.3%, 74.3%, and 115.3% in the liver, kidney, pancreas, and thymus of the infected mice, respectively, compared to that in normal control mice, indicating that S1PR1 is involved in the early immune response to bacterial infection. NIBR-0213 or S1PR1-specific DsiRNA pretreatment reduced the tissue uptake of [18F]TZ4877, suggesting that uptake of [18F]TZ4877 is specific. Our PET/CT study data also confirmed that infected mice have increased [18F]TZ4877 uptake in several organs comparing to that in normal control mice. Particularly, compared to control mice, a 39% increase of [18F]TZ4877 uptake was observed in the infected muscle of S. aureus mice, indicating that S1PR1 expression was directly involved in the inflammatory response to infection. Overall, our study suggested that S1PR1 plays an important role in the early immune response to bacterial infection. The uptake of [18F]TZ4877 is tightly correlated with the S1R1 expression in response to S. aureus infection. PET with S1PR1-specific radiotracer [18F]TZ4877 could provide a noninvasive tool for detecting the early S1PR1 immune response to infectious diseases.

Interaction of Trypanosoma cruzi Gp82 With Host Cell LAMP2 Induces Protein Kinase C Activation and Promotes Invasion

The surface molecule gp82 of metacyclic trypomastigote (MT) forms of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, mediates the host cell invasion, a process critical for the establishment of infection. Gp82 is known to bind to the target cell in a receptor-dependent manner, triggering Ca²⁺ signal, actin cytoskeleton rearrangement and lysosome spreading. The host cell receptor for gp82 was recently identified as LAMP2, the major lysosome membrane-associated protein. To further clarify the mechanisms of MT invasion, we aimed in this study at identifying the LAMP2 domain that interacts with gp82 and investigated whether target cell PKC and ERK1/2, previously suggested to be implicated in MT invasion, are activated by gp82. Interaction of MT, or the recombinant gp82 (r-gp82), with human epithelial HeLa cells induced the activation of Ca²⁺-dependent PKC and ERK1/2. The LAMP2 sequence predicted to bind gp82 was mapped and the synthetic peptide based on that sequence inhibited MT invasion, impaired the binding of r-gp82 to HeLa cells, and blocked the PKC and ERK1/2 activation induced by r-gp82. Treatment of HeLa cells with specific inhibitor of focal adhesion kinase resulted in inhibition of r-gp82-induced PKC and ERK1/2 activation, as well as in alteration of the actin cytoskeleton architecture. PKC activation by r-gp82 was also impaired by treatment of HeLa cells with inhibitor of phospholipase C, which mediates the production of diacylglycerol, which activates PKC, and inositol 1,4,5-triphosphate that releases Ca²⁺ from intracellular stores. Taken together, our results indicate that recognition of MT gp82 by LAMP2 induces in the host cell the activation of phosholipase C, with generation of products that contribute for PKC activation and the downstream ERK1/2. This chain of events leads to the actin cytoskeleton disruption and lysosome spreading, promoting MT internalization.

Whole Transcriptome Analysis of Chicken Bursa Reveals Candidate Gene That Enhances the Host's Immune Response to Coccidiosis

Coccidiosis is a major hazard to the chicken industry, but the host’s immune response to coccidiosis remains unclear. Here, we performed Eimeria coccidia challenge in 28-day-old ROSS 308 broilers and selected the bursa from the three most severely affected individuals and three healthy individuals for RNA sequencing. We obtained 347 DEGs from RNA-seq and found that 7 upregulated DEGs were enriched in Cytokine-cytokine receptor interaction pathway. As the DEGs with the highest expression abundance in these 7 genes, TNFRSF6B was speculated to participate in the process of host’s immune response to coccidiosis. It is showed that TNFRSF6B can polarize macrophages to M1 subtype and promote inflammatory cytokines expression. In addition, the expression of TNFRSF6B suppressed HD11 cells apoptosis by downregulating Fas signal pathway. Besides, TNFRSF6B-mediated macrophages immunity activation can be reversed by apoptosis. Overall, our study indicates that TNFRSF6B upregulated in BAE, is capable of aggravating the inflammatory response by inhibiting macrophages apoptosis via downregulating Fas signal pathway, which may participate in host’s immune response to coccidiosis.

Involvement of calcium in 50-Hz magnetic field-induced activation of sphingosine kinase 1 signaling pathway

Previously, we found that exposure to a 50-Hz magnetic field (MF) could induce human amniotic epithelial (FL) cell proliferation and sphingosine kinase 1 (SK1) activation, but the mechanism was not clearly understood. In the present study, the possible signaling pathways which were involved in SK1 activation induced by 50-Hz MF exposure were investigated. Results showed that MF exposure increased intracellular Ca²⁺ which was dependent on the L-type calcium channel, and induced Ca²⁺ -dependent phosphorylation of extracellular regulated protein kinase (ERK), SK1, and protein kinase C α (PKCα). Also, treatment with U0126, an inhibitor of ERK, could block MF-induced SK1 phosphorylation, but had no effect on PKCα phosphorylation. Also, the inhibitor of PKCα, Gö6976, had no effect on MF-induced SK1 activation in FL cells. In addition, the activation of ERK and PKCα could be abolished by SKI II, the inhibitor of SK1. In conclusion, the intracellular Ca²⁺ mediated the 50-Hz MF-induced SK1 activation which enhanced PKCα phosphorylation, and there might be a feedback mechanism between SK1 and ERK activation in responding to MF exposure in FL cells. Bioelectromagnetics. 9999:XX-XX, 2019. © 2019 Bioelectromagnetics Society.

ESAT-6 modulates Calcimycin-induced autophagy through microRNA-30a in mycobacteria infected macrophages

OBJECTIVE

Mycobacterium tuberculosis (M. tb) has a sumptuous repertoire of effector molecules to counter host defenses. Some of these antigens inhibit autophagy but the exact mechanism of this inhibition is poorly understood.

METHODS

Purified protein derivative (PPD) was fractionated using 10 (PPD 10, antigenic molecular weight > 10 kDa) and 3 (PPD 3, mol. weight > 3 kDa) kDa cutters. Effect of these fractions on Calcimycin-induced autophagy and intracellular mycobacterial viability was then studied using different experimental approaches.

RESULT

We found significant downregulation of autophagy by PPD 3 pre-treatment in Calcimycin-treated dTHP-1 cells compared to PPD 10. This reduction in autophagy also corroborated with the enhanced survival of mycobacteria in macrophages. We demonstrate that recombinant early secreted antigenic target 6 (rESAT-6) is responsible to inhibit Calcimycin-induced autophagy and enhance intracellular survival of mycobacteria. We also show that pre-treatment with rESAT-6 upregulates microRNA (miR)-30a-3p expression and vis-a-vis downregulates miR-30a-5p expression in Calcimycin-treated dTHP-1 cells. Transfection studies with either miR-30a-3p inhibitor or miR-30a-5p mimic clearly elucidated the opposing roles of miR-30a-3p and miR-30a-5p in rESAT-6 mediated mycobacterial survival through autophagy inhibition.

CONCLUSION

Taken together, our result evidently highlights that rESAT-6 enhances intracellular survival of mycobacteria by modulating miR-30a-3p and miR-30a-5p expression.

Brain-Derived Neurotrophic Factor in Brain Disorders: Focus on Neuroinflammation

Brain-derived neurotrophic factor (BDNF) is one of the most studied neurotrophins in the healthy and diseased brain. As a result, there is a large body of evidence that associates BDNF with neuronal maintenance, neuronal survival, plasticity, and neurotransmitter regulation. Patients with psychiatric and neurodegenerative disorders often have reduced BDNF concentrations in their blood and brain. A current hypothesis suggests that these abnormal BDNF levels might be due to the chronic inflammatory state of the brain in certain disorders, as neuroinflammation is known to affect several BDNF-related signaling pathways. Activation of glia cells can induce an increase in the levels of pro- and antiinflammatory cytokines and reactive oxygen species, which can lead to the modulation of neuronal function and neurotoxicity observed in several brain pathologies. Understanding how neuroinflammation is involved in disorders of the brain, especially in the disease onset and progression, can be crucial for the development of new strategies of treatment. Despite the increasing evidence for the involvement of BDNF and neuroinflammation in brain disorders, there is scarce evidence that addresses the interaction between the neurotrophin and neuroinflammation in psychiatric and neurodegenerative diseases. This review focuses on the effect of acute and chronic inflammation on BDNF levels in the most common psychiatric and neurodegenerative disorders and aims to shed some light on the possible biological mechanisms that may influence this effect. In addition, this review will address the effect of behavior and pharmacological interventions on BDNF levels in these disorders.

Effects of Baicalin on piglet monocytes involving PKC-MAPK signaling pathways induced by Haemophilus parasuis

Background

Haemophilus parasuis (HPS) is the causative agent of Glässer’s disease, characterized by arthritis, fibrinous polyserositis and meningitis, and resulting in worldwide economic losses in the swine industry. Baicalin (BA), a commonly used traditional Chinese medication, has been shown to possess a series of activities, such as anti-bacterial, anti-viral, anti-tumor, anti-oxidant and anti-inflammatory activities. However, whether BA has anti-apoptotic effects following HPS infection is unclear. Here, we investigated the anti-apoptotic effects and mechanisms of BA in HPS-induced apoptosis via the protein kinase C (PKC)–mitogen-activated protein kinase (MAPK) pathway in piglet’s mononuclear phagocytes (PMNP).

Results

Our data demonstrated that HPS could induce reactive oxygen species (ROS) production, arrest the cell cycle and promote apoptosis via the PKC–MAPK signaling pathway in PMNP. Moreover, when BA was administered, we observed a reduction in ROS production, suppression of cleavage of caspase-3 in inducing apoptosis, and inhibition of activation of the PKC–MAPK signaling pathway for down-regulating p-JNK, p-p38, p-ERK, p-PKC-α and PKC-δ in PMNP triggered by HPS.

Conclusions

Our data strongly suggest that BA can reverse the apoptosis initiated by HPS through regulating the PKC–MAPK signaling pathway, which represents a promising therapeutic agent in the treatment of HPS infection.

Aeromonas hydrophila-induced alterations in cytosolic calcium activate pro-apoptotic cPKC-MEK1/2-TNFα axis in infected headkidney macrophages of Clarias gariepinus

Alterations in intracellular-calcium (Ca²⁺)_i homeostasis is critical to Aeromonas hydrophila-induced headkidney macrophages (HKM) apoptosis of Clarias gariepinus, though the implications are poorly understood. Here, we describe the role of intermediate molecules of Ca^2+-signaling pathway that are involved in HKM apoptosis. We observed phosphoinositide-3-kinase/phospholipase C is critical for (Ca²⁺)_i release in infected HKM. Heightened protein kinase-C (PKC) activity and phosphorylation of MEK1/2-ERK1/2 was noted which declined in presence of 2-APB, Go6976 and PD98059, inhibitors to IP3-receptor, conventional PKC isoforms (cPKC) and MEK1/2 respectively implicating Ca²⁺/cPKC/MEK-ERK1/2 axis imperative in A. hydrophila-induced HKM apoptosis. Significant tumor necrosis factor-α (TNFα) production and its subsequent reduction in presence of MEK-ERK1/2 inhibitor U0126 suggested TNFα production downstream to cPKC-mediated signaling via MEK1/2-ERK1/2 pathway. RNAi and inhibitor studies established the role of TNFα in inducing caspase-8-mediated apoptosis of infected HKM. We conclude, alterations in A. hydrophila-induced (Ca²⁺)i alterations activate cPKC-MEK1/2-ERK1/2-TNFα signaling cascade triggering HKM apoptosis.

Aldose reductase inhibitors attenuate β-amyloid-induced TNF-α production in microlgia via ROS-PKC-mediated NF-κB and MAPK pathways

Microglia-mediated neuroinflammation is a key risk factor to the development of Alzheimer' disease (AD). Aldose reductase (AR) has been found to be widely involved in inflammation-related diseases; however, whether aldose reductase inhibitors (ARIs) could be used to treat neuroinflammation is rarely reported. This study aims to evaluate the anti-neuroinflammatory effects of two major ARIs of Sorbinil (Sor) and Zopolrestat (Zol) in β-amyloid protein (Aβ)-induced microglia (BV-2). We find that Sor and Zol significantly inhibit TNF-α, IL-1β, IL-6 production from microglia in response to Aβ stimulation. Mechanism study showed that Sor and Zol decreased the production of intracellular ROS which resulted in an effective inhibition on the phosphorylation of several protein kinase C (PKC) isoforms including PKCα/β, δ, ζ/λ and mu. Moreover, Sor and Zol inactivated PCK-associated IKKβ-IκB-NF-κB and mitogen-activated protein kinase (JNK, p38, ERK) inflammation pathways. In summary, our findings suggest that Sor and Zol could inhibit Aβ-induced neuroinflammation by regulating ROS/PKC-dependent NF-κB and MAPK signaling pathways, indicating that ARIs could be promising agents for treating inflammation-related neurodegenerative diseases such as AD.

Calcium and Superoxide-Mediated Pathways Converge to Induce Nitric Oxide-Dependent Apoptosis in Mycobacterium fortuitum-Infected Fish Macrophages

Mycobacterium fortuitum causes ‘mycobacteriosis’ in wide range of hosts although the mechanisms remain largely unknown. Here we demonstrate the role of calcium (Ca⁺²)-signalling cascade on M. fortuitum-induced apoptosis in headkidney macrophages (HKM) of Clarias sp. M. fortuitum could trigger intracellular-Ca⁺² influx leading to the activation of calmodulin (CaM), protein kinase C alpha (PKCα) and Calmodulin kinase II gamma (CaMKIIg). Gene silencing and inhibitor studies established the role of CaM in M. fortuitum pathogenesis. We noted that CaMKIIg activation is regulated by CaM as well as PKCα-dependent superoxide anions. This is altogether first report of oxidised CaMKIIg in mycobacterial infections. Our studies with targeted-siRNA and pharmacological inhibitors implicate CaMKIIg to be pro-apoptotic and critical for the activation of extra-cellular signal regulated kinase 1/2 (ERK1/2). Inhibiting the ERK1/2 pathway attenuated nitric oxide synthase 2 (NOS2)-induced nitric oxide (NO) production. Conversely, inhibiting the NOS2-NO axis by specific-siRNA and inhibitors down-regulated ERK1/2 activation suggesting the crosstalk between ERK1/2 and NO is essential for pathogenesis induced by the bacterium. Silencing the NOS2-NO axis enhanced intracellular bacterial survival and attenuated caspase-8 mediated activation of caspase-3 in the infected HKM. Our findings unveil hitherto unknown mechanism of M. fortuitum pathogenesis. We propose that M. fortuitum triggers intracellular Ca⁺² elevations resulting in CaM activation and PKCα-mediated superoxide generation. The cascade converges in common pathway mediated by CaMKIIg resulting in the activation of ERK1/2-NOS2 axis. The crosstalk between ERK1/2 and NO shifts the balance in favour of caspase dependent apoptosis of M. fortuitum-infected HKM.

Sphingosine-1-phosphate signaling: unraveling its role as a drug target against infectious diseases

Sphingosine-1-phosphate (S1P) signaling is reported in variety of cell types, including immune, endothelial and cancerous cells. It is emerging as a crucial regulator of cellular processes, such as apoptosis, cell proliferation, migration, differentiation and so on. This signaling pathway is initiated by the intracellular production and secretion of S1P through a cascade of enzymatic reactions. Binding of S1P to different S1P receptors (S1PRs) activates different downstream signaling pathways that regulate the cellular functions differentially depending upon the cell type. An accumulating body of evidence suggests that S1P metabolism and signaling is often impaired during infectious diseases; thus, its manipulation might be helpful in the treatment of such diseases. In this review, we summarize recent advances in our understanding of the S1P signaling pathway and its candidature as a novel drug target against infectious diseases.

Apigenin attenuates heart injury in lipopolysaccharide-induced endotoxemic model by suppressing sphingosine kinase 1/sphingosine 1-phosphate signaling pathway

Sepsis is a cluster of heterogeneous syndromes associated with progressive endotoxemic developments, ultimately leading to damage of multiple organs, including the heart. This study is to investigate the effects of apigenin on heart injury in lipopolysaccharide-induced endotoxemic rat model. Normal Wistar rats were randomly divided into four groups: control group, LPS group (15 mg/kg), LPS plus apigenin groups with different apigenin doses (50 mg/kg, 100 mg/kg). Serum levels of creatine kinase (CK), lactate dehydrogenase (LDH), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) were measured after the rats were sacrificed. SphK1/S1P signaling pathway proteins, cleaved caspase-3, cleaved caspase-9, Bax and Bcl-2 in heart were measured by Western blot. In vitro, we evaluated the protective effect of apigenin on rat embryonic heart-derived myogenic cell line H9c2 induced by LPS. Apigenin decreased serum levels of CK-MB, LDH, TNF-α, IL-6, IL-1β. SphK1/S1P signaling pathway proteins, cleaved caspase-3, cleaved caspase-9, Bax in heart were found inhibited and Bcl-2 increased in the apigenin groups in vivo. In addition, apigenin inhibited intracellular calcium, the MAPK pathway and SphK1/S1P signaling pathway in vitro. Apigenin exerts pronounced cardioprotection in rats subjected to LPS likely through suppressing myocardial apoptosis and inflammation by inhibiting the SphK1/S1P signaling pathway.

Sphingosine 1-phosphate: a potential molecular target for ovarian cancer therapy?

Sphingosine 1-phosphate (S1P) is an important signaling regulator involved in tumor progression in multiple neoplasms. However, the role of S1P in the pathogenesis of ovarian cancer remains unclear. Herein, we summarize recent advances in understanding the impact of S1P signaling in ovarian cancer progression. S1P, aberrantly produced in ovarian cancer patients, is involved in the regulation of key cellular processes that contribute to ovarian cancer initiation and progression. Moreover, agents that block the S1P signaling pathway inhibit ovarian cancer cell growth or induce apoptosis. Hence, current evidence suggests that S1P may become a potential molecular target for ovarian cancer therapy.

Alveolar macrophage innate response to Mycobacterium immunogenum, the etiological agent of hypersensitivity pneumonitis: role of JNK and p38 MAPK pathways

Mycobacterium immunogenum is an emerging pathogen of the immune-mediated lung disease hypersensitivity pneumonitis (HP) reported in machinists occupationally exposed to contaminated metal working fluid (MWF). However, the mechanism of its interaction with the host lung is unclear. Considering that alveolar macrophages play a central role in host defense in the exposed lung, understanding their interaction with the pathogen could provide initial insights into the underlying immunopathogenesis events and mechanisms. In the current study, M. immunogenum 700506, a predominant genotype isolated from HP-linked fluids, was shown to multiply intracellularly, induce proinflammatory mediators (TNF-α, IL-1α, IL-1β, IL-6, GM-CSF, NO) and cause cytotoxicity/cell death in the cultured murine alveolar macrophage cell line MH-S in a dose- and time-dependent manner. The responses were detected as early as 3h post-infection. Comparison of this and four additional genotypes of M. immunogenum (MJY-3, MJY-4, MJY-12, MJY-14) using an effective dose-time combination (100 MOI for 24h) showed these macrophage responses in the following order (albeit with some variations for individual response indicators). Inflammatory: MJY-3 ≥ 700506 > MJY-4 ≥ MJY-14 ≥ MJY-12; Cytotoxic: 700506 ≥ MJY-3 > MJY-4 ≥ MJY-12 ≥ MJY-14. In general, 700506 and MJY-3 showed a more aggressive response than other genotypes. Chemical blocking of either p38 or JNK inhibited the induction of proinflammatory mediators (cytokines, NO) by 700506. However, the cellular responses showed a somewhat opposite effect. This is the first report on M. immunogenum interactions with alveolar macrophages and on the identification of JNK- and p38- mediated signaling and its role in mediating the proinflammatory responses during these interactions.

The production of reactive oxygen species in TLR-stimulated granulocytes is not enhanced by hyperglycemia in diabetes

Toll-like receptors (TLRs) play an important role in several inflammatory diseases such as diabetes. The present study was to determine whether hyperglycemia in diabetes interferes in reactive oxygen species (ROS) production in granulocytes stimulated with either TLR2/zymosan, TLR4/lipopolysaccharide (LPS) or TLR2,4,9/concanavalin A (ConA). NADPH (nicotinamide adenine dinucleotide phosphate) oxidase and mitogen-activated protein kinase (MAPK) signaling pathways associated with ROS generation in TLR-stimulated granulocytes were evaluated. Our results demonstrate that ROS generation in resting granulocytes derived from patients suffering from Type 2 diabetes mellitus (T2DM) is significantly higher than that observed in equivalent cells from healthy controls. However, ROS formed by TLR-stimulated granulocytes from T2DM patients and healthy subjects were comparable. ROS production by TLR4,9 depends on NADPH-oxidase and MAPK signaling pathways. In contrast, the activation of TLR2 leads to ROS production by a mechanism that is dependent on NADPH oxidase but independent of the MAPK. In conclusion our results suggest that hyperglycemia in diabetes may prime cells metabolically for ROS generation but does not exert any significant effect on TLR-stimulated ROS production and possibly does not aggravate the development of ROS-dependent diabetic complications.

Identification of Leptospira interrogans phospholipase C as a novel virulence factor responsible for intracellular free calcium ion elevation during macrophage death

BACKGROUND

Leptospira-induced macrophage death has been confirmed to play a crucial role in pathogenesis of leptospirosis, a worldwide zoonotic infectious disease. Intracellular free Ca(2+) concentration ([Ca(2+)]i) elevation induced by infection can cause cell death, but [Ca(2+)]i changes and high [Ca(2+)]i-induced death of macrophages due to infection of Leptospira have not been previously reported.

METHODOLOGY/PRINCIPAL FINDINGS

We first used a Ca(2+)-specific fluorescence probe to confirm that the infection of L. interrogans strain Lai triggered a significant increase of [Ca(2+)]i in mouse J774A.1 or human THP-1 macrophages. Laser confocal microscopic examination showed that the [Ca(2+)]i elevation was caused by both extracellular Ca(2+) influx through the purinergic receptor, P2X7, and Ca(2+) release from the endoplasmic reticulum, as seen by suppression of [Ca(2+)]i elevation when receptor-gated calcium channels were blocked or P2X7 was depleted. The LB361 gene product of the spirochete exhibited phosphatidylinositol phospholipase C (L-PI-PLC) activity to hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP2) into inositol-1,4,5-trisphosphate (IP3), which in turn induces intracellular Ca(2+) release from endoplasmic reticulum, with the Km of 199 µM and Kcat of 8.566E-5 S(-1). Secretion of L-PI-PLC from the spirochete into supernatants of leptospire-macrophage co-cultures and cytosol of infected macrophages was also observed by Western Blot assay. Lower [Ca(2+)]i elevation was induced by infection with a LB361-deficient leptospiral mutant, whereas transfection of the LB361 gene caused a mild increase in [Ca(2+)]i. Moreover, PI-PLCs (PI-PLC-β3 and PI-PLC-γ1) of the two macrophages were activated by phosphorylation during infection. Flow cytometric detection demonstrated that high [Ca(2+)]i increases induced apoptosis and necrosis of macrophages, while mild [Ca(2+)]i elevation only caused apoptosis.

CONCLUSIONS/SIGNIFICANCE

This study demonstrated that L. interrogans infection induced [Ca(2+)]i elevation through extracellular Ca(2+) influx and intracellular Ca(2+) release cause macrophage apoptosis and necrosis, and the LB361 gene product was shown to be a novel PI-PLC of L. interrogans responsible for the [Ca(2+)]i elevation.

Early secreted antigenic target of 6 kDa (ESAT-6) protein of Mycobacterium tuberculosis induces interleukin-8 (IL-8) expression in lung epithelial cells via protein kinase signaling and reactive oxygen species

Early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis is critical for the virulence and pathogenicity of M. tuberculosis. IL-8, a major chemotactic cytokine for neutrophils and T lymphocytes, plays important roles in the development of lung injury. To further understand the role of ESAT-6 in lung pathology associated with tuberculosis development, we studied the effects of ESAT-6 on the regulation of IL-8 expression in lung epithelial cells. ESAT-6 induced IL-8 expression by increasing IL-8 gene transcription and mRNA stability. ESAT-6 induction of IL-8 promoter activity was dependent on nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) binding and sensitive to pharmacological inhibition of PKC and ERK and p38 MAPK pathways. ESAT-6 activated ERK and p38 MAPK phosphorylation and rapidly induced reactive oxygen species (ROS) production. Dimethylthiourea but not mannitol inhibited IL-8 induction by ESAT-6, further supporting the involvement of ROS in the induction of IL-8 expression. Exposure of mice to ESAT-6 induced localized inflammatory cell aggregate formation with characteristics of early granuloma concomitant with increased keratinocyte chemoattractant CXCL1 staining in bronchiolar and alveolar type II epithelial cells and alveolar macrophages. Our studies have identified a signal transduction pathway involving ROS, PKC, ERK, and p38 MAPKs and NF-κB and AP-1 in the ESAT-6 induction of IL-8 expression in lung epithelial cells. This has important implications for the understanding of lung innate immune responses to tuberculosis and the pathogenesis of lung injury in tuberculosis.

Nuclear phosphoinositide-specific phospholipase C β1 controls cytoplasmic CCL2 mRNA levels in HIV-1 gp120-stimulated primary human macrophages

HIV-1 envelope glycoprotein gp120 induces, independently of infection, the release of CCL2 from macrophages. In turn, this chemokine acts as an autocrine factor enhancing viral replication. In this study, we show for the first time that phosphoinositide-specific phospholipase C (PI-PLC) is required for the production of CCL2 triggered by gp120 in macrophages. Using a combination of confocal laser-scanner microscopy, pharmacologic inhibition, western blotting and fluorescence-activated cell sorter analysis, we demonstrate that gp120 interaction with CCR5 leads to nuclear localization of the PI-PLC β1 isozyme mediated by mitogen-activated protein kinase ERK-1/2. Notably, phosphatidylcholine-specific phospholipase C (PC-PLC), previously reported to be required for NF-kB-mediated CCL2 production induced by gp120 in macrophages, drives both ERK1/2 activation and PI-PLC β1 nuclear localization induced by gp120. PI-PLC β1 activation through CCR5 is also triggered by the natural chemokine ligand CCL4, but independently of ERK1/2. Finally, PI-PLC inhibition neither blocks gp120-mediated NF-kB activation nor overall accumulation of CCL2 mRNA, whereas it decreases CCL2 transcript level in the cytoplasm. These results identify nuclear PI-PLC β1 as a new intermediate in the gp120-triggered PC-PLC-driven signal transduction pathway leading to CCL2 secretion in macrophages. The finding that a concerted gp120-mediated signaling involving both PC- and PI-specific PLCs is required for the expression of CCL2 in macrophages suggests that this signal transduction pathway may also be relevant for the modulation of viral replication in these cells. Thus, this study may contribute to identify novel targets for therapeutic intervention in HIV-1 infection.

Indoleamine 2,3-dioxygenase (IDO) induced by Leishmania infection of human dendritic cells

Dendritic cells (DC) play a pivotal role in regulating immunity, establishing immunologically privileged tissue microenvironments and maintaining homoeostasis. It is becoming increasingly clear that one key mechanism that mediates many DC functions is production of the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO). For pathogens that cause chronic infection, exploitation of host DCs is a solution to establish and persist within a host. Leishmania parasites cause a range of clinical manifestations, all involving chronic infection, and are proficient at avoiding immune responses. We demonstrate here that infection of human myeloid-derived DC with L. major and L. donovani induces IDO expression using a mechanism that involves autocrine or paracrine stimulation with a DC-secreted factor. Leishmania-induced IDO suppresses allogeneic and tetanus toxoid-specific lymphocyte proliferation, an inhibition that is reversed with the IDO inhibitor, 1-methyl tryptophan (1-MT). Furthermore, IDO expression by human DC does not require live Leishmania infection, as parasite lysates also up-regulate IDO mRNA production. Our data suggest that one mechanism Leishmania parasites utilize to circumvent immune clearance may be to promote the induction of IDO among host DC within the infection microenvironment.

The role of sphingosine kinase 1 in patients with severe acute pancreatitis

OBJECTIVE

To investigate the role of sphingosine kinase 1 (SphK1)/sphingosine 1-phosphate (S1P) signaling in inflammatory response in severe acute pancreatitis (SAP).

BACKGROUND

SAP is an acute inflammatory process of the pancreas, which may lead to systemic inflammatory response syndrome and multiorgan dysfunction syndrome. SphK1 and its product S1P have been implicated in inflammatory response and various immune cell functions. However, the potential role for SphK1/S1P in inflammatory response in SAP is still unclear.

METHODS

Twenty-two patients with SAP were enrolled in this study. SphK1 expression on peripheral neutrophils, monocytes, and lymphocytes was evaluated by flow cytometry. SphK enzymatic activity in neutrophils and lymphocytes was measured using a radiometric assay. The expression of S1P1 and S1P3 mRNA was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The serum levels of tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1β), and IL-6 were measured by ELISA.

RESULTS

The expression of SphK1 and SphK activity were markedly increased in peripheral immune cells in the early stage of SAP and then reduced in the restoration stage in the patients. Moreover, we found that the level of S1P3 mRNA in peripheral neutrophils and lymphocytes of SAP patients was significantly elevated in the early stage as compared with the healthy volunteers, and it reduced in the restoration period. SphK1 expression on human peripheral neutrophils, monocytes, and CD4(+) T lymphocytes were positively correlated with the APACHE (Acute Physiological and Chronic Health Evaluation) II scores in patients with SAP. The levels of serum proinflammatory cytokines including TNF-α, IL-1β, and IL-6 showed similar shifts with intracellular SphK1 expression in SAP patients.

CONCLUSIONS

The authors identified a link between the SphK1 expression on peripheral immune cells and the severity of SAP. Observations showed a possible immunomodulating role for SphK1/S1P signaling in inflammatory response in SAP, suggesting that regulation of SphK1/S1P pathway may represent novel targets in the treatment of SAP.

Shaping up the membrane: diacylglycerol coordinates spatial orientation of signaling

Diacylglycerol signals by binding and activating C1 domain-containing proteins expressed principally in neuronal and immune tissues. This restricted expression profile suggests that diacylglycerol-regulated signals are particularly relevant in cell-cell communication processes in which active endocytosis and exocytosis take place. Not surprisingly, various experimental approaches have demonstrated a crucial role for diacylglycerol effectors and metabolizing enzymes in the control of immune responses, neuron communication and phagocytosis. Current research delineates a scenario in which coordinated decoding of diacylglycerol signals is translated into complex biological responses such as neuronal plasticity, T cell development or cytolytic killing. Diacylglycerol functions reach maximal diversity in these highly specialized systems in which signal intensity directly regulates distinct biological outcomes. This review brings together the most recent studies, emphasizing the contribution of compartmentalized DAG metabolism to orientated signaling events.

Exosomes released from M. tuberculosis infected cells can suppress IFN-γ mediated activation of naïve macrophages

Background

Macrophages infected with Mycobacterium tuberculosis (M.tb) are known to be refractory to IFN-γ stimulation. Previous studies have shown that M.tb express components such as the 19-kDa lipoprotein and peptidoglycan that can bind to macrophage receptors including the Toll-like receptor 2 resulting in the loss in IFN-γresponsiveness. However, it is unclear whether this effect is limited to infected macrophages. We have previously shown that M.tb-infected macrophages release exosomes which are 30–100 nm membrane bound vesicles of endosomal origin that function in intercellular communication. These exosomes contain mycobacterial components including the 19-kDa lipoprotein and therefore we hypothesized that macrophages exposed to exosomes may show limited response to IFN-γ stimulation.

Methodology/Principal Findings

Exosomes were isolated from resting as well as M.tb-infected RAW264.7 macrophages. Mouse bone marrow-derived macrophages (BMMØ) were treated with exosomes +/− IFN-γ. Cells were harvested and analyzed for suppression of IFN-γ responsive genes by flow cytometry and real time PCR. We found that exosomes derived from M.tb H37Rv-infected but not from uninfected macrophages inhibited IFN-γ induced MHC class II and CD64 expression on BMMØ. This inhibition was only partially dependent on the presence of lipoproteins but completely dependent on TLR2 and MyD88. The exosomes isolated from infected cells did not inhibit STAT1 Tyrosine phosphorylation but down-regulated IFN-γ induced expression of the class II major histocompatibity complex transactivator; a key regulator of class II MHC expression. Microarray studies showed that subsets of genes induced by IFN-γ were inhibited by exosomes from H37Rv-infeced cells including genes involved in antigen presentation. Moreover, this set of genes partially overlapped with the IFN-γ-induced genes inhibited by H37Rv infection.

Conclusions

Our study suggests that exosomes, as carriers of M.tb pathogen associated molecular patterns (PAMPs), may provide a mechanism by which M.tb may exert its suppression of a host immune response beyond the infected cell.

Reactive oxygen species-activated p38/ERK 1/2 MAPK signaling pathway in the Mycobacterium bovis bacillus Calmette Guérin (BCG)-induced CCL2 secretion in human monocytic cell line THP-1

BACKGROUND AND AIMS

CCL2 plays an important role in mycobacterial infection by inducing leukocyte recruitment and activation. Here we assess the role of reactive oxygen species (ROS) in the secretion of the CCL2 and the activation of mitogen-activated protein kinases (MAPKs) by human monocytic cells infected with Mycobacterium bovis bacillus Calmette Guérin (BCG).

METHODS

CCL2 mRNA and protein expression were measured by reverse transcriptase polymerase chain reaction (RT-PCR), quantitative PCR and ELISA. Kinase phosphorylation was determined by immunoblotting.

RESULTS

Treatment of human monocytic cells with M. bovis BCG activated rapid superoxide generation. mRNA expression of CCL2 was increased in M. bovis BCG-infected monocytic cells, and this increase was abrogated by administration of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenyleneiodonium (DPI). Importantly, M. bovis BCG-induced CCL2 protein secretion was also inhibited by the NADPH oxidase inhibitor DPI, the selective inhibitor of NADPH oxidase apocynin, the mitochondrial electron transfer chain subunit I inhibitor rotenone and H(2)O(2) scavenging enzyme catalase, indicating that the inhibition is through the NADPH/ROS pathway. Analysis of downstream signals showed that inhibition of NADPH oxidase inhibited M. bovis BCG-induced phosphorylation of MAPK (extracellular signal-regulated kinase (ERK) 1/2 and p38).

CONCLUSIONS

These results strongly suggest that NADPH oxidase-derived ROS-mediated activation of p38 and ERK 1/2 is essential for the M. bovis BCG-induced CCL2 production.

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence.

Sphingosine 1-phosphate, a key mediator of the cytokine network: juxtacrine signaling

Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite, which has emerged as an important signaling mediator participating in the regulation of multiple cellular processes. The discovery of a family of S1P receptors, together with the more recently identified intracellular targets, has provided fundamental understanding of the multi-faceted actions of S1P. Evidence from both in vitro and in vivo studies has implicated the S1P signaling system in the control of immunity, inflammation and many associated diseases. Enigmatically, S1P appears to have both pro- and anti-inflammatory effects depending on the cell context. Here, we review this emerging area and argue for a pivotal role for S1P, as a key mediator of the cytokine network, acting through juxtacrine signaling in the immune system.

The non-pathogenic mycobacteria M. smegmatis and M. fortuitum induce rapid host cell apoptosis via a caspase-3 and TNF dependent pathway

Background

The HIV pandemic raised the potential for facultative-pathogenic mycobacterial species like, Mycobacterium kansasii, to cause disseminating disease in humans with immune deficiencies. In contrast, non-pathogenic mycobacterial species, like M. smegmatis, are not known to cause disseminating disease even in immunocompromised individuals. We hypothesized that this difference in phenotype could be explained by the strong induction of an innate immune response by the non-pathogenic mycobacterial species.

Results

A comparison of two rapid-growing, non-pathogenic species (M. smegmatis and M. fortuitum) with two facultative-pathogenic species (M. kansasii and M. bovis BCG) demonstrated that only the non-pathogenic bacteria induced strong apoptosis in human THP-1 cells and murine bone marrow-derived macrophages (BMDM) and dendritic cells (BMDD). The phospho-myo-inositol modification of lipoarabinomannan (PI-LAM) isolated from non-pathogenic species may be one of the cell wall components responsible for the pro-inflammatory activity of the whole bacteria. Indeed, PI-LAM induces high levels of apoptosis and IL-12 expression compared to the mannosyl modification of LAM isolated from facultative-pathogenic mycobacteria. The apoptosis induced by non-pathogenic M. smegmatis was dependent upon caspase-3 activation and TNF secretion. Consistently, BALB/c BMDM responded by secreting large amounts of TNF upon infection with non-pathogenic but not facultative-pathogenic mycobacteria. Interestingly, C57Bl/6 BMDM do not undergo apoptosis upon infection with non-pathogenic mycobacteria despite the fact that they still induce an increase in TNF secretion. This suggests that the host cell signaling pathways are different between these two mouse genotypes and that TNF is necessary but not sufficient to induce host cell apoptosis.

Conclusion

These results demonstrate a much stronger induction of the innate immune response by non-pathogenic versus facultative-pathogenic mycobacteria as measured by host cell apoptosis, IL-12 and TNF cytokine induction. These observations lend support to the hypothesis that the strong induction of the innate immune response is a major reason for the lack of pathogenicity in fast-growing mycobacteria.

Sphingosine kinase-1 (SphK-1) regulates Mycobacterium smegmatis infection in macrophages

Sphingosine kinase-1 is known to mediate Mycobacterium smegmatis induced inflammatory responses in macrophages, but its role in controlling infection has not been reported to date. We aimed to unravel the significance of SphK-1 in controlling M. smegmatis infection in RAW 264.7 macrophages. Our results demonstrated for the first time that selective inhibition of SphK-1 by either D, L threo dihydrosphingosine (DHS; a competitive inhibitor of Sphk-1) or Sphk-1 siRNA rendered RAW macrophages sensitive to M. smegmatis infection. This was due to the reduction in the expression of iNOs, p38, pp-38, late phagosomal marker, LAMP-2 and stabilization of the RelA (pp-65) subunit of NF-kappaB. This led to a reduction in the generation of NO and secretion of TNF-alpha in infected macrophages. Congruently, overexpression of SphK-1 conferred resistance in macrophages to infection which was due to enhancement in the generation of NO and expression of iNOs, pp38 and LAMP-2. In addition, our results also unraveled a novel regulation of p38MAPK by SphK-1 during M. smegmatis infection and generation of NO in macrophages. Enhanced NO generation and expression of iNOs in SphK-1++ infected macrophages demonstrated their M-1(bright) phenotype of these macrophages. These findings thus suggested a novel antimycobacterial role of SphK-1 in macrophages.

A novel function of sphingosine kinase 1 suppression of JNK activity in preventing inflammation and injury

The mechanism underlying the protective effect of sphingosine kinase 1 (SphK1) in inflammatory injury is not clear. We demonstrated using SphK1-null mice (SphK1(-/-)) the crucial role of SphK1 in suppressing lipopolysaccharide-induced neutrophil oxidant production and sequestration in lungs and mitigating lung inflammatory injury. This effect of SphK1 was independent of the production of sphingosine 1-phosphate, the product of SphK1 activity. The anti-inflammatory effect of SphK1 in the lipopolysaccharide model was mediated through SphK1 interaction with JNK. SphK1 stabilization of JNK in turn inhibited JNK binding to the JNK-interacting protein 3 (JIP3) and thus abrogated the activation of NADPH oxidase and oxidant generation and resultant NF-kappaB activation. Therefore, SphK1-mediated down-regulation of JNK activity serves to dampen inflammation and tissue injury.

Role of host sphingosine kinase 1 in the lung response against Cryptococcosis

Cryptococcus neoformans is a fungal pathogen causing pulmonary infection and a life-threatening meningoencephalitis in human hosts. The fungus infects the host through inhalation, and thus, the host response in the lung environment is crucial for containment or dissemination of C. neoformans to other organs. In the lung, alveolar macrophages (AMs) are key players in the host lung immune response, and upon phagocytosis, they can kill C. neoformans by evoking an effective immune response through a variety of signaling molecules. On the other hand, under conditions not yet fully defined, the fungus is able to survive and proliferate within macrophages. Since the host sphingosine kinase 1 (SK1) regulates many signaling functions of immune cells, particularly in macrophages, in this study we determined the role of SK1 in the host response to C. neoformans infection. Using wild-type (SK1/2(+/+)) and SK1-deficient (SK1(-/-)) mice, we found that SK1 is dispensable during infection with a facultative intracellular wild-type C. neoformans strain. However, SK1 is required to form a host lung granuloma and to prevent brain infection by a C. neoformans mutant strain lacking the cell wall-associated glycosphingolipid glucosylceramide (Delta gcs1), previously characterized as a mutant able to replicate only intracellularly. Specifically, in contrast to those from SK1/2(+/+) mice, lungs from SK1(-/-) mice have no collagen deposition upon infection with C. neoformans Delta gcs1, and AMs from these mice contain significantly more C. neoformans cells than AMs from SK1/2(+/+) mice, suggesting that under conditions in which C. neoformans is more internalized by AMs, SK1 may become important to control C. neoformans infection. Indeed, when we induced immunosuppression, a host condition in which wild-type C. neoformans cells are increasingly found intracellularly, SK1(-/-) survived significantly less than SK1/2(+/+) mice infected with a facultative intracellular wild-type strain, suggesting that SK1 has an important role in controlling C. neoformans infection under conditions in which the fungus is predominantly found intracellularly.

Reduced transcript stabilization restricts TNF-alpha expression in RAW264.7 macrophages infected with pathogenic mycobacteria: evidence for an involvement of lipomannan

Despite the critical role that TNF-alpha plays in the containment of mycobacterial infection, the mechanisms involved in regulation of its expression by mycobacteria are poorly defined. We addressed this question by studying MAP, which causes a chronic enteritis in ruminants and is linked to human Crohn's disease. We found that in MAP infected macrophages, TNF-alpha gene expression was substantially lower than in macrophages infected with nonpathogenic MS or stimulated with LPS. TNF-alpha transcriptional one could not fully explain the differential TNF-alpha mRNA expression, suggesting that there must be a substantial contribution by post-transcriptional mechanisms.Accordingly, we found reduced TNF-alpha mRNA stability in MAP-infected macrophages. Further comparison of MAP- and MS-infected macrophages revealed that lower TNF-alpha mRNA stability combined with lower mRNA and protein expression in MAP-infected macrophages correlated with lower p38 MAPK phosphorylation. These findings were independent of viability of MAP and MS. We demonstrate that the major mycobacterial cell-wall lipoglycan LM of MAP and MS induced TNF-alpha mRNA transcription,but only the MS-LM induced p38 MAPK-dependent transcript stabilization. Overall, our data suggest that pathogenic mycobacteria cause weak p38 and TNF-alpha mRNA stabilization as a result of their structural cell-wall components such as LM and thereby, restrict TNF-alpha expression in macrophages.

Bile acid reflux contributes to development of esophageal adenocarcinoma via activation of phosphatidylinositol-specific phospholipase Cgamma2 and NADPH oxidase NOX5-S

Gastroesophageal reflux disease complicated by Barrett's esophagus (BE) is a major risk factor for esophageal adenocarcinoma (EA). However, the mechanisms of the progression from BE to EA are not fully understood. Besides acid reflux, bile acid reflux may also play an important role in the progression from BE to EA. In this study, we examined the role of phosphatidylinositol-specific phospholipase C (PI-PLC) and a novel NADPH oxidase NOX5-S in bile acid-induced increase in cell proliferation. We found that taurodeoxycholic acid (TDCA) significantly increased NOX5-S expression, hydrogen peroxide (H(2)O(2)) production, and cell proliferation in EA cells. The TDCA-induced increase in cell proliferation was significantly reduced by U73122, an inhibitor of PI-PLC. PI-PLCbeta1, PI-PLCbeta3, PI-PLCbeta4, PI-PLCgamma1, and PI-PLCgamma2, but not PI-PLCbeta2 and PI-PLCdelta1, were detectable in FLO cells by Western blot analysis. Knockdown of PI-PLCgamma2 or extracellular signal-regulated kinase (ERK) 2 mitogen-activated protein (MAP) kinase with small interfering RNAs (siRNA) significantly decreased TDCA-induced NOX5-S expression, H(2)O(2) production, and cell proliferation. In contrast, knockdown of PI-PLCbeta1, PI-PLCbeta3, PI-PLCbeta4, PI-PLCgamma1, or ERK1 MAP kinase had no significant effect. TDCA significantly increased ERK2 phosphorylation, an increase that was reduced by U73122 or PI-PLCgamma2 siRNA. We conclude that TDCA-induced increase in NOX5-S expression and cell proliferation may depend on sequential activation of PI-PLCgamma2 and ERK2 MAP kinase in EA cells. It is possible that bile acid reflux present in patients with BE may increase reactive oxygen species production and cell proliferation via activation of PI-PLCgamma2, ERK2 MAP kinase, and NADPH oxidase NOX5-S, thereby contributing to the development of EA.

Regulation of macrophage function by sphingosine-1-phosphate

The bioactive lipid sphingosine-1-phosphate (S1P) fulfils manifold tasks in the immune system acting in auto- and/or paracrine fashion. This includes regulation of apoptosis, migration and proliferation. Upon its generation by sphingosine kinases from plasma membrane sphingolipids, S1P can either act as a second messenger within cells or can be released from cells to occupy a family of specific G-protein-coupled receptors (S1P1-5). This diversity is reflected by the impact of S1P on macrophage biology and function. Over the last years it became apparent that the sphingosine kinase/S1P/S1P-receptor signalling axis in macrophages might play a central role in the pathogenesis of inflammatory diseases such as atherosclerosis, asthma, rheumatoid arthritis and cancer. Here, we summarize the current knowledge of the function of S1P in macrophage biology and discuss potential implications for pathology.

Regulation of endothelin-1-induced interleukin-6 production by Ca2+ influx in human airway smooth muscle cells

Endothelin-1 is considered to be an important mediator in the pathophysiology of asthma because it induces contraction, hypertrophy, and proliferation in airway smooth muscle cells as well as inflammatory responses in the airway. Airway smooth muscle cells have been suggested to contribute to airway inflammation in asthma by producing cytokines. Nevertheless, the role of intracellular Ca(2+) signal in cytokine production in human airway smooth muscle cells is still unclear. We investigated the mechanisms by which endothelin-1 induces production of interleukin (IL)-6, a pleiotropic cytokine, in primary cultured human airway smooth muscle cells. Levels of IL-6 protein and mRNA were significantly increased by endothelin-1 in dose- and time-dependent manners. Endothelin-1-induced IL-6 production was markedly attenuated by EGTA and various Ca(2+) channel inhibitors such as 3,5-bis(trifluoromethyl)-1H-pyrazole derivative (BTP-2), 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride (SKF96365), and nifedipine. Endothelin-1-induced increases in intracellular Ca(2+) concentrations were significantly inhibited in Ca(2+)-free solution and by BTP-2, SKF96365, and nifedipine. The IL-6 synthesis was also inhibited by the extracellular signal-regulated kinase (ERK)1/2 inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)-butadiene ethanolate (U0126) and the p38 inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), but not by the c-Jun NH2-terminal kinase inhibitor anthra[1,9-cd]-pyrazol-6-(2H)-one (SP600125). Endothelin-1 significantly upregulated phosphorylation of ERK1/2 and p38 but blocking Ca(2+) influx pathways did not inhibit either upregulation. These findings demonstrate that endothelin-1-induced IL-6 synthesis in airway smooth muscle cells occurs via two parallel but independent events that include Ca(2+) influx and activation of ERK1/2 and p38.

Coordinate regulation of sphingosine kinase and actin dynamics

The activation of lipid-modifying enzymes generally involves a physical change in their interactions with the membrane substrate. For sphingosine kinase, a predominantly cytosolic enzyme in resting cells, activation is accompanied by translocation to specific subsets of cellular membranes where catalysis occurs. As all eukaryotic membranes have a tightly associated filamentous actin skeleton, we investigated potential regulatory interactions between sphingosine kinase and actin. Sphingosine kinase 1 (SK1) exhibited constitutive- and stimulus-enhanced association with actin filaments and F-actin-enriched membrane fractions in both intact macrophages and an in vitro reconstitution assay, whereas SK1 bound G-actin only under stimulated conditions. Actin inhibitors disrupted SK1 localization and increased its enzymatic activity. Both the localization and the activity of SK1 were coordinately regulated with the actin cytoskeleton. The association of enzymes with the actin cytoskeleton and how this regulates their activities and functions are subjects of intense interest. Here, we describe the approach we used to investigate regulation of SK1. This provides general methods that can be used to examine the role of actin in regulating enzyme activity in macrophages and other myeloid cells.

Mycobacterium abscessus and M. avium trigger Toll-like receptor 2 and distinct cytokine response in human cells

Mycobacterium avium (MAV) and M. abscessus (MAB) are ubiquitous environmental organisms increasingly recognized to cause chronic lung disease in patients with apparently normal immune function. Little is yet known about their human pathophysiology. Our objective was to examine cytokine and chemokine responses (protein and gene expression) and signaling pathways triggered by reference and clinical isolates of MAB and MAV in human peripheral blood mononuclear cells, monocytes, and murine bone marrow-derived macrophages in vitro. MAB-induced TNF-alpha production was higher than that induced by MAV. IFN-gamma, IL-1beta, and the chemokines macrophage inflammatory protein-1alpha and regulated on activation, normal T cell expressed and secreted were equally up-regulated. Differences between MAB and MAV do not require replication and are heat stable. We found no differential effect due to rough or smooth colonies within the same species. Similar to MAV, MAB triggered mitogen-activated protein kinase (MAPK) signaling and nuclear factor-kappaB translocation. Induction of TNF-alpha was dependent on MAPK pathways, since pre-incubation of cells with signaling inhibitors led to more than 85% reduction in cytokine secretion. MAB also triggered a Toll-like receptor 2 (TLR2)-mediated response that led to TNF-alpha production by human monocytes. Accordingly, stimulation of murine TLR2- or myeloid differentiation factor 88-deficient bone marrow-derived macrophages did not elicit TNF-alpha, reinforcing a critical role for TLR2 in MAB-induced cell activation. We concluded that MAB signals human cells through MAPK and TLR2 pathways and triggers more pronounced pro-inflammatory cytokines and chemokines than MAV.

Prolactin induced production of cytokines in macrophages involves Ca++ and p42/44 MAP kinase signaling pathway

The immunomodulatory properties of prolactin (PRL) are well recognized. Recently, we have reported the activation and enhanced production of nitric oxide by macrophages on treatment with PRL. The involvement of protein tyrosine kinases, MAP kinases and Ca++ signaling in the enhanced nitric oxide production by macrophages on PRL treatment was also established. In the present study, it has been observed that PRL induces the intracellular release of Ca++; activates protein kinase C (PKC)-8 and p42/44 MAP kinase. The activation of PKC-delta was found to be inhibited by Pertussis toxin (PTX) (Galpha1-protein inhibitor) and H7 (PKC inhibitor). Pretreatment of macrophages with PTX, H7, TMB8 (intracellular Ca++ immobilizer) significantly down regulated the PRL induced intracellular Ca++ release and the activation of p42/44 MAP kinases. The involvement of Ca++ signaling and p42/44 MAP kinase in regulation of PRL induced IL-1beta and TNF-alpha production by macrophages has also been investigated. PRL is observed to induce the expression of transcription factors phospho-Elk-1, c-fos and phospho-c-myc. These observations clearly suggest the involvement of PKC-delta/Ca++/p42-44 MAP kinase cascade in PRL induced activation of murine peritoneal macrophages.

Human type II pneumocyte chemotactic responses to CXCR3 activation are mediated by splice variant A

Chemokine receptors control several fundamental cellular processes in both hematopoietic and structural cells, including directed cell movement, i.e., chemotaxis, cell differentiation, and proliferation. We have previously demonstrated that CXCR3, the chemokine receptor expressed by Th1/Tc1 inflammatory cells present in the lung, is also expressed by human airway epithelial cells. In airway epithelial cells, activation of CXCR3 induces airway epithelial cell movement and proliferation, processes that underlie lung repair. The present study examined the expression and function of CXCR3 in human alveolar type II pneumocytes, whose destruction causes emphysema. CXCR3 was present in human fetal and adult type II pneumocytes as assessed by immunocytochemistry, immunohistochemistry, and Western blotting. CXCR3-A and -B splice variant mRNA was present constitutively in cultured type II cells, but levels of CXCR3-B greatly exceeded CXCR3-A mRNA. In cultured type II cells, I-TAC, IP-10, and Mig induced chemotaxis. Overexpression of CXCR3-A in the A549 pneumocyte cell line produced robust chemotactic responses to I-TAC and IP-10. In contrast, I-TAC did not induce chemotactic responses in CXCR3-B and mock-transfected cells. Finally, I-TAC increased cytosolic Ca2+ and activated the extracellular signal-regulated kinase, p38, and phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B kinases only in CXCR3-A-transfected cells. These data indicate that the CXCR3 receptor is expressed by human type II pneumocytes, and the CXCR3-A splice variant mediates chemotactic responses possibly through Ca2+ activation of both mitogen-activated protein kinase and PI 3-kinase signaling pathways. Expression of CXCR3 in alveolar epithelial cells may be important in pneumocyte repair from injury.

Cross-talk at the crossroads of sphingosine-1-phosphate, growth factors, and cytokine signaling

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide array of biologic effects through its interaction with a family of five G protein-coupled receptors. Cytokines and growth factors interact with this signaling pathway in a variety of ways, including both activation and regulation of the expression of the enzymes that regulate synthesis and degradation of S1P. Not only do many growth factors and cytokines stimulate S1P production, leading to transactivation of S1P receptors, ligation of S1P receptors by S1P can also transactivate growth factor tyrosine kinase receptors and stimulate growth factor and cytokine signaling cascades. This review discusses the mechanisms involved in cross-talk between S1P, cytokines, and growth factors and the impact of that cross-talk on cell signaling and cell biology.

The regulation of dendritic cell function by calcium-signaling and its inhibition by microbial pathogens

Dendritic cells (DC) are the sentinels of the immune system, linking innate with adaptive responses. The functional responses of DC are subject to complex regulation and serve as targets for pathogens. Ca2+-mediated signal transduction pathways serve a central regulatory role in DC responses to diverse antigens, including TLR ligands, intact bacteria, and microbial toxins. This review summarizes the major mechanisms of Ca2+-signaling that DC utilize to regulate maturation and antigen presentation, including a Ca2+-calmodulin (CaM)-CaM kinase II pathway that is localized to phagosomes and is targeted by the human intracellular pathogen, Mycobacterium tuberculosis. Restoration of functional Ca2+ signaling in DC may provide a novel mechanism to enhance therapy and promote vaccine efficacy to infectious diseases, including tuberculosis.