Lipopolysaccharide Transiently Activates THP-1 Cell Adhesion

A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Assay Identifies Nilotinib as an Inhibitor of Inflammation in Acute Myeloid Leukemia

Inflammatory responses are important in cancer, particularly in the context of monocyte-rich aggressive myeloid neoplasm. We developed a label-free cellular phenotypic drug discovery assay to identify anti-inflammatory drugs in human monocytes derived from acute myeloid leukemia (AML), by tracking several features ionizing from only 2500 cells using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. A proof-of-concept screen showed that the BCR-ABL inhibitor nilotinib, but not the structurally similar imatinib, blocks inflammatory responses. In order to identify the cellular (off-)targets of nilotinib, we performed thermal proteome profiling (TPP). Unlike imatinib, nilotinib and other later-generation BCR-ABL inhibitors bind to p38α and inhibit the p38α-MK2/3 signaling axis, which suppressed pro-inflammatory cytokine expression, cell adhesion, and innate immunity markers in activated monocytes derived from AML. Thus, our study provides a tool for the discovery of new anti-inflammatory drugs, which could contribute to the treatment of inflammation in myeloid neoplasms and other diseases.

Substrate Viscoelasticity Amplifies Distinctions between Transient and Persistent LPS-Induced Signals

Macrophages settle in heterogeneous microenvironments rendered by other cells and extracellular matrices. It is well known that chemical stimuli direct macrophage behavior; however, the contributions of viscosity, which increases in inflammatory tissues but not in tumors, are ignored in immune responses including effective activation and timely attenuation. This paper demonstrates that transient lipopolysaccharide (LPS)-treated macrophages benefit from elastic substrates, whereas viscoelastic substrates with similar storage moduli support the inflammatory responses of macrophages under persistent stimulations and consequently amplify the distinctions between the transient and persistent LPS-induced transcriptional programs. Actin filaments (F-actin) fluctuate in line with transcriptional profiles and can be mathematically predicted by a clutch-like model. Moreover, viscosity modifies immune responses through transcription factors NF-κB and C/EBPδ, which act as switches discriminating transient and persistent infections. Interestingly, enhanced immune responses, consistent with the lower activated states, are attenuated promptly by the actin nucleation-related translocation of ATF3 to nuclei. These findings suggest that the substrate viscoelasticity induces more intense inflammation only in the case of persistent infection and promotes more sensitively perceiving the duration of infection through the F-actin correlated transcription factors. In addition, it may facilitate the cognition of immune response in inflammatory and cancerous microenvironments and have a wide range of applications in inflammatory regulations.

Aggregatibacter actinomycetemcomitans Leukotoxin Activates the NLRP3 Inflammasome and Cell-to-Cell Communication

Carriers of highly leukotoxic genotypes of Aggregatibacter actinomycetemcomitans are at high risk for rapid degradation of tooth-supporting tissues. The leukotoxin (LtxA) expressed by this bacterium induces a rapid pro-inflammatory response in leukocytes that results in cell death. The aim of the present study was to increase the understanding of LtxA-induced leukocyte activation mechanisms and of possible associated osteoclast differentiation. The effect of LtxA on activation of the inflammasome complex was studied in THP-1 wild type and in NLRP3- and ASC knockout cells. Cell-to-cell communication was assessed by fluorescent parachute assays, and THP-1 differentiation into osteoclast-like cells was investigated microscopically. The results showed that LtxA induced inflammatory cell death, which involved activation of the NLRP3 inflammasome and gap junction cell-to-cell communication. THP-1 cells treated with lipopolysaccharide (LPS) and LtxA together differentiated into an osteoclast-like phenotype. Here, LPS prevented LtxA-mediated cell death but failed to induce osteoclast differentiation on its own. However, pit formation was not significantly enhanced by LtxA. We conclude that A. actinomycetemcomitans leukotoxicity mediates activation of the NLRP3 inflammasome and cell-to-cell communication in the induced pro-inflammatory cell death. In addition, LtxA stimulated differentiation towards osteoclasts-like cells in LPS-treated THP-1 cells.

LPS Induces mTORC1 and mTORC2 Activation During Monocyte Adhesion

Monocyte adhesion is a crucial step in transmigration and can be induced by lipopolysaccharide (LPS). Here, we studied the role of mammalian target of rapamycin (mTOR) complexes, mTORC1 and mTORC2, and PKC in this process. We used THP-1 cells, a human monocytic cell line, to investigate monocyte adhesion under static and flow conditions. We observed that 1.0 μg/mL LPS increased PI3K/mTORC2 pathway and PKC activity after 1 h of incubation. WYE-354 10⁻⁶ M (mTORC2/mTORC1 inhibitor) and 10⁻⁶ M wortmannin avoided monocyte adhesion in culture plates. In addition, WYE also blocked LPS-induced CD11a expression. Interestingly, rapamycin and WYE-354 blocked both LPS-induced monocyte adhesion in a cell monolayer and actin cytoskeleton rearrangement, confirming mTORC1 involvement in this process. Once activated, PKC activates mTORC1/S6K pathway in a similar effect observed to LPS. Activation of the mTORC1/S6K pathway was attenuated by 10⁻⁶ M U0126, an MEK/ERK inhibitor, and 10⁻⁶ M calphostin C, a PKC inhibitor, indicating that the MEK/ERK/TSC2 axis acts as a mediator. In agreement, 80 nM PMA (a PKC activator) mimicked the effect of LPS on the activation of the MEK/ERK/TSC2/mTORC1/S6K pathway, monocyte adhesion to ECV cells and actin cytoskeleton rearrangement. Our findings show that LPS induces activation of mTOR complexes. This signaling pathway led to integrin expression and cytoskeleton rearrangement resulting in monocyte adhesion. These results describe a new molecular mechanism involved in monocyte adhesion in immune-based diseases.

A new cryptic cationic antimicrobial peptide from human apolipoprotein E with antibacterial activity and immunomodulatory effects on human cells

Cationic antimicrobial peptides (AMPs) possess fast and broad-spectrum activity against both Gram-negative and Gram-positive bacteria, as well as fungi. It has become increasingly evident that many AMPs, including those that derive from fragments of host proteins, are multifunctional and able to mediate various immunomodulatory functions and angiogenesis. Among these, synthetic apolipoprotein-derived peptides are safe and well tolerated in humans and have emerged as promising candidates in the treatment of various inflammatory conditions. Here, we report the characterization of a new AMP corresponding to residues 133-150 of human apolipoprotein E. Our results show that this peptide, produced either by chemical synthesis or by recombinant techniques in Escherichia coli, possesses a broad-spectrum antibacterial activity. As shown for several other AMPs, ApoE (133-150) is structured in the presence of TFE and of membrane-mimicking agents, like SDS, or bacterial surface lipopolysaccharide (LPS), and an anionic polysaccharide, alginate, which mimics anionic capsular exo-polysaccharides of several pathogenic microorganisms. Noteworthy, ApoE (133-150) is not toxic toward several human cell lines and triggers a significant innate immune response, assessed either as decreased expression levels of proinflammatory cytokines in differentiated THP-1 monocytic cells or by the induction of chemokines released from PBMCs. This novel bioactive AMP also showed a significant anti-inflammatory effect on human keratinocytes, suggesting its potential use as a model for designing new immunomodulatory therapeutics.

Extract from Acanthopanax senticosus prevents LPS-induced monocytic cell adhesion via suppression of LFA-1 and Mac-1

A crude extract from Acanthopanax senticosus (AS) has drawn increased attention because of its potentially beneficial activities, including anti-fatigue, anti-stress, anti-gastric-ulcer, and immunoenhancing effects. We previously reported that AS crude extract exerts anti-inflammatory activity through blockade of monocytic adhesion to endothelial cells. However, the underlying mechanisms remained unknown, and so this study was designed to investigate the pathways involved. It was confirmed that AS extract inhibited lipopolysaccharide (LPS)-induced adhesion of monocytes to endothelial cells, and we found that whole extract was superior to eleutheroside E, a principal functional component of AS. A series of PCR experiments revealed that AS extract inhibited LPS-induced expression of genes encoding lymphocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1) in THP-1 cells. Consistently, protein levels and cell surface expression of LFA-1 and Mac-1 were noticeably reduced upon treatment with AS extract. This inhibitory effect was mediated by the suppression of LPS-induced degradation of IκB-α, a known inhibitor of nuclear factor-κB (NF-κB). In conclusion, AS extract exerts anti-inflammatory activity via the suppression of LFA-1 and Mac-1, lending itself as a potential therapeutic galenical for the prevention and treatment of various inflammatory diseases.

Hypertonic Saline Attenuates the Pro-metastatic Effects of LPS by Reducing Tumor Cell Migration, Proliferation and MMP-9 Expression

Background

Lipopolysaccharide (LPS) promotes tumor metastases. The aim of this study was to determine the ability of a hypertonic environment to attenuate the pro metastatic properties of LPS both in vitro, and in vivo.

Methods

LPS stimulated, and unstimulated, 4T1 tumor cells were cultured in either an isotonic or hypertonic environment. The effect on invasion, migration, pro-matellomatrixproteinase 9 (proMMP-9) expression, proliferation, and microscopic cell structure was assessed. Lung metastases were induced in C57 mice with systemic hypertonicity in unstimulated and stimulated mice. The metastatic burden was assessed by estimation of lung/body weight ratio, pleural nodules and clonogenic assay.

Results

In vitro, a hypertonic environment reduced proMMP-9 expression (0.012 versus 1.16, P < 0.001) invasion (0.06 versus 0.119, P = 0.005), tumor cell proliferation (0.035 versus 0.041, P = 0.001), while inducing structural changes to tumor cells reducing overall cell volume. In vivo, the induction of transient systemic hypertonicity reduced metastatic burden as demonstrated by reduced lung nodules (4 versus 8, P = 0.004) and colonies on clonogenic assay (12 versus 43, P = 0.04).

Conclusion

The in vitro exposure of tumor cells to a hypertonic environment reduces tumor cell migration and proliferation. Transient systemic hypertonicity can reduce the metastatic burden following intra-operative exposure to LPS in vivo.

αVβ3-integrin expression through ERK activation mediates cell attachment and is necessary for production of tumor necrosis factor alpha in monocytic THP-1 cells stimulated by phorbol myristate acetate

Macrophages play a key role in inflammation. Activated macrophages express adhesion molecules and produce tumor necrosis factor alpha (TNFα). Integrins are the main adhesion molecules that mediate binding to the extracellular matrix and they are involved in intracellular pathways. In the present study, human monocytic THP-1 cell adhesion to uncoated plastic plate was examined to investigate the regulatory mechanism of TNFα secretion. Addition of phorbol myristate acetate (PMA) for THP-1 cell activation induced cell adhesion in parallel with TNFα production. Among the mitogen-activated protein kinase pathways, the protein kinase C (PKC)-extracellular signal-regulated kinase (ERK) pathway was involved in αVβ3-integrin expression and PMA-induced cell adhesion. Flow cytometry and reverse transcription - quantitative polymerase chain reaction analysis revealed increased expression of matrix-binding integrins including integrin-αVβ3. Blockade of αVβ3-integrin by a specific antibody suppressed cell adhesion and TNFα production. These findings indicate that TNFα production from THP-1 cells is PKC-ERK, αVβ3-integrin and adhesion-dependent and its related pathway could be a target for TNFα-related diseases.

Oligomeric amyloid-beta(1-42) induces THP-1 human monocyte adhesion and maturation

Amyloid-beta (Abeta) is a naturally occurring 40- or 42-residue peptide fragment with a primary role in Alzheimer's disease (AD). Aggregated Abeta accumulates as both dense core plaques and diffuse deposits in the brains of AD patients. Abeta plaques are surrounded by activated microglia, some of which are believed to be derived from peripheral blood monocytes that have infiltrated the central nervous system and differentiated into phagocytes in response to Abeta. We have modeled this process using THP-1 human monocytes and found Abeta(1-42) to be as effective as phorbol myristate acetate at differentiating THP-1 monocytes based on cell adhesion, fibronectin binding, CD11b cell-surface expression, and morphological changes. Cell adhesion studies and atomic force microscopy imaging revealed an inverse correlation between Abeta(1-42)-induced monocyte maturation and aggregation progression. Freshly reconstituted Abeta(1-42) solutions were the most effective, yet continued aggregation reduced, and eventually abolished, the ability to induce monocyte adhesion. Abeta(1-40), lower aggregation concentrations of Abeta(1-42), and an aggregation-restricted Abeta(1-42) L34P mutant had little effect on monocyte adhesion under the same conditions as Abeta(1-42). These findings implicated an oligomeric, but not monomeric or fibrillar, Abeta(1-42) aggregation species in the monocyte maturation process. The rapidly-formed Abeta(1-42) oligomers were distinct from Abeta-derived diffusible ligands which did not elicit significant THP-1 monocyte adhesion. These data demonstrate that a specific oligomeric Abeta(1-42) aggregation species can potently initiate the THP-1 monocyte maturation process.

Different functions of monocyte subsets in familial hypercholesterolemia: potential function of CD14+ CD16+ monocytes in detoxification of oxidized LDL

The study was undertaken to investigate whether the two major monocyte subsets defined by the surface markers CD14(+)CD16(+) and CD14(++)CD16(-) show differences in their responses to hypercholesterolemia. Monocytes were rapidly isolated from the blood of hypercholesterolemic, low-density lipoprotein (LDL) receptor-defective familial hypercholesterolemia (FH) patients and from control persons. Using flow cytometry and uptake, adhesion, and phagocytosis assays as well as laser scanning microscopy, we found significant differences between the monocyte subsets. FH-CD14(+)CD16(+) monocytes exhibit an increased uptake of oxidized LDL (oxLDL) via CD36, whereas FH-CD14(++)CD16(-) monocytes preferentially take up native LDL (nLDL). FH-CD14(+)CD16(+) monocytes have an increased expression of surface proteins CD68, stabilin-1, and CD11c and a higher adherence to activated endothelial cells in response to oxLDL and nLDL stimulation. In addition, all CD14(+)CD16(+) monocytes have an increased ability for phagocytosis and a higher resistance to phagocytosis impairment by oxLDL compared with CD14(++)CD16(-) monocytes. We conclude that FH-CD14(+)CD16(+) monocytes have specialized functions in the uptake of oxLDL at activated endothelial cell surfaces, and we hypothesize that these functions are critical for the clearance of oxLDL deposits and apoptotic cells from the vessel wall under hyperlipidemic conditions.

Therapy with hydroxyurea is associated with reduced adhesion molecule gene and protein expression in sickle red cells with a concomitant reduction in adhesive properties

Propagation of the vaso-occlusive process in sickle cell anaemia (SCA) is a complex process involving the adhesion of steady-state SCA patients red cells and reticulocytes to the vascular endothelium. The effect of hydroxyurea therapy (HUT) on the adhesive properties of sickle cells and the expression of adhesion molecule genes by erythroid cells of SCA individuals is not yet fully understood. The expressions of the CD36 gene and the VLA-4-integrin subunit genes, CD49d (alpha-subunit) and CD29 (beta-subunit), were compared in the reticulocytes of steady-state SCA patients and patients on HUT using real-time PCR. Basal adhesion of red cells from these subjects was also compared using static adhesion assays, as was surface protein expression, using flow cytometry. Basal sickle red cell adhesion to fibronectin was significantly greater than that of normal cells (P < 0.01); in contrast, HUT was associated with significantly lower levels (P < 0.01) of red cell adhesion that were similar to those of control cells; this decrease could not be justified solely by altered reticulocyte numbers in this population. Accordingly, flow cytometry demonstrated that reticulocytes from patients on HUT had significantly lower CD36 and CD49d surface expressions (P < 0.01) and, importantly, significantly lower expressions of the CD36, CD49d and CD29 genes (P < 0.05) than reticulocytes of SCA patients not on HUT. Taken together, data support the hypothesis that HUT reduces the adhesive properties of sickle cells and that this decrease appears to be mediated, at least in part, by a decrease in the gene and, consequently, surface protein expression of adhesion molecules such as VLA-4 and CD36.

Organic dust-induced activation, adhesion to substrate and expression of intercellular adhesion molecules in THP-1 monocytes

Inhalation of organic dust in a swine confinement building induces systemic reactions, increased bronchial responsiveness and intense airway inflammation in previously unexposed, healthy subjects. These effects are self-limiting, but chronic respiratory symptoms are frequently observed in swine confinement workers. The present study was aimed at investigating organic dust-induced activation of the monocytic leukemia cell line, THP-1. Unstimulated THP-1 cells proliferate in suspension but cultivation for several days in medium with complete dust or 0.22-mu-filtered suspension, caused a subset of the THP-1 cells to adhere to the substratum. As assessed by transmission light- and indirect immunofluorescence microscopy, dust-stimulated adherent THP-1 cells adopted macrophage-like morphology and expressed vimentin. Intercellular adhesion molecule (ICAM)-1 was expressed in all dust-activated adherent cells, but only in 1% of the unstimulated cells in suspension. Sialoadhesin, a macrophage marker, was detected in dust-stimulated adherent THP-1 cells but not in the parental monocytes. Serum factors were required for the dust-induced expression of sialoadhesin, but not for adhesion to substrate or expression of ICAM-1. In addition, morphology and expression of vascular endothelial growth factor (VEGF) of dust-stimulated adherent cells equalled that of PMA-differentiated THP-1 cells, but the PMA-differentiated cells exhibited weak sialoadhesin labelling. In conclusion, exposure to organic dust from a swine confinement building activated a subset of THP-1 monocytes inducing expression of intercellular adhesion molecules, which are important in inflammation. The sustained adhesion to substrate indicates that organic dust from a swine confinement building may contain agents that prevent deactivation and detachment of the cells.