Effects of Mycoplasma fermentans incognitus on differentiation of THP-1 cells

Resolvin D2 attenuates LPS-induced macrophage exhaustion

Early in sepsis, a hyperinflammatory response is dominant, but later, an immunosuppressive phase dominates, and the host is susceptible to opportunistic infections. Anti-inflammatory agents may accelerate the host into immunosuppression, and few agents can reverse immunosuppression without causing inflammation. Specialized pro-resolving mediators (SPMs) such as resolvin D2 (RvD2) have been reported to resolve inflammation without being immunosuppressive, but little work has been conducted to examine their effects on immunosuppression. To assess the effects of RvD2 on immunosuppression, we established a model of macrophage exhaustion using two lipopolysaccharide (LPS) treatments or hits. THP-1 monocyte-derived macrophages were first treated with RvD2 or vehicle for 1 h. One LPS hit increased NF-κB activity 11-fold and TNF-α release 60-fold compared to unstimulated macrophages. RvD2 decreased LPS-induced NF-κB activity and TNF-α production but increased bacterial clearance. Two LPS hits reduced macrophage bacterial clearance and decreased macrophage NF-κB activity (45%) and TNF-α release (75%) compared to one LPS hit, demonstrating exhaustion. RvD2 increased NF-κB activity, TNF-α release, and bacterial clearance following two LPS hits compared to controls. TLR2 inhibition abolished RvD2-mediated changes. In a mouse sepsis model, splenic macrophage response to exogenous LPS was reduced compared to controls and was restored by in vivo administration of RvD2, supporting the in vitro results. If RvD2 was added to monocytes before differentiation into macrophages, however, RvD2 reduced LPS responses and increased bacterial clearance following both one and two LPS hits. The results show that RvD2 attenuated macrophage suppression in vitro and in vivo and that this effect was macrophage-specific.

Withaferin A Associated Differential Regulation of Inflammatory Cytokines

A role of inflammation-associated cytokines/chemokines has been implicated in a wide variety of human diseases. Here, we investigated the regulation of inflammatory cytokines released by monocyte-derived THP-1 cells following treatment with the dietary agent withaferin A (WFA). Membrane-based cytokine array profiling of the culture supernatant from adenosine triphosphate-stimulated WFA-treated THP-1 cells showed differential regulation of multiple cytokines/chemokines. A selected group of cytokines/chemokines [interleukin-1 beta (IL-1β), CCL2/MCP-1, granulocyte-macrophage colony stimulating factor, PDGF-AA, PTX3, cystatin-3, relaxin-2, TNFRSF8/CD30, and ACRP30] was validated at the transcription level using qPCR. In silico analysis for transcriptional binding factors revealed the presence of nuclear factor-kappa B (NF-κB) in a group of downregulated cytokine gene promoters. WFA treatment of THP-1 cells blocks the nuclear translocation of NF-kB and corresponds with the reduced levels of cytokine secretion. To further understand the differential expression of cytokines/chemokines, we showed that WFA alters the nigericin-induced co-localization of NLRP3 and ASC proteins, thereby inhibiting caspase-1 activation, which is responsible for the cleavage and maturation of pro-inflammatory cytokines IL-1β and IL-18. These data suggest that dietary agent WFA concurrently targets NF-κB and the inflammasome complex, leading to inhibition of IL-1β and IL-18, respectively, in addition to differential expression of multiple cytokines/chemokines. Taken together, these results provide a rationale for using WFA to further explore the anti-inflammatory mechanism of cytokines/chemokines associated with inflammatory diseases.

Visfatin contributes to the differentiation of monocytes into macrophages through the differential regulation of inflammatory cytokines in THP-1 cells

Visfatin is a novel multifunctional adipocytokine with inflammatory properties. Although a link between visfatin and atherosclerosis has recently been suggested, its actions in the development of atherosclerosis remain unknown. Therefore, we investigated a potential role and underlying mechanism(s) of visfatin in monocytes/macrophages differentiation, a critical early step in atherogenesis, using phorbol-12-myristate-13-acetate (PMA)-stimulated THP-1 cell models. The co-incubation of PMA with visfatin-induced CD36 expression with a concomitant increase in the phagocytosis of latex beads compared with PMA alone treatment. Moreover, visfatin markedly increased interleukin (IL)-1β secretion by enhancing IL-1β mRNA stability in a short-term incubation. Visfatin also significantly elevated the secretion of IL-6 as well as IL-1β in a longer incubation period, which was partially suppressed by nuclear factor-κB (NF-κB) inhibitor, BAY11-7082, and c-Jun-N-terminal kinase (JNK) inhibitor, SP600125. Furthermore, silencing IL-1β successfully blocked IL-6 secretion, CD36 expression, and NF-κB activation in response to visfatin. Collectively, these results suggest that visfatin enhances the IL-1β-dependent induction of IL-6 and CD36 via distinct signaling pathways mediated by JNK and NF-κB, respectively, and consequently, leading to the acceleration of monocytes/macrophages differentiation.

Methionine sulfoxide reductase A (MsrA) deficient Mycoplasma genitalium shows decreased interactions with host cells

Mycoplasma genitalium is an important sexually transmitted pathogen that affects both men and women. In genital-mucosal tissues, it initiates colonization of epithelial cells by attaching itself to host cells via several identified bacterial ligands and host cell surface receptors. We have previously shown that a mutant form of M. genitalium lacking methionine sulfoxide reductase A (MsrA), an antioxidant enzyme which converts oxidized methionine (Met(O)) into methionine (Met), shows decreased viability in infected animals. To gain more insights into the mechanisms by which MsrA controls M. genitalium virulence, we compared the wild-type M. genitalium strain (G37) with an msrA mutant (MS5) strain for their ability to interact with target cervical epithelial cell lines (HeLa and C33A) and THP-1 monocytic cells. Infection of epithelial cell lines with both strains revealed that MS5 was less cytotoxic to HeLa and C33A cell lines than the G37 strain. Also, the MS5 strain was more susceptible to phagocytosis by THP-1 cells than wild type strain (G37). Further, MS5 was less able to induce aggregation and differentiation in THP-1 cells than the wild type strain, as determined by carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling of the cells, followed by counting of cells attached to the culture dish using image analysis. Finally, MS5 was observed to induce less proinflammatory cytokine TNF-α by THP-1 cells than wild type G37 strain. These results indicate that MsrA affects the virulence properties of M. genitalium by modulating its interaction with host cells.

Transcription profiles of LPS-stimulated THP-1 monocytes and macrophages: a tool to study inflammation modulating effects of food-derived compounds

An assay was developed to study inflammation-related immune responses of food compounds on monocytes and macrophages derived from THP-1 cell line. First strategy focused on the effects after stimulation with either lipopolysaccharide (LPS) or Concanavalin A (ConA). Gene expression kinetics of inflammation-related cytokines (IL-1β, IL-6, IL-8, IL-10 and TNF-α), inflammation-related enzymes (iNOS and COX-2), and transcription factors (NF-κB, AP-1 and SP-1) were analyzed using RT-PCR. Time dependent cytokine secretion was investigated to study the inflammation-related responses at protein level. LPS stimulation induced inflammation-related cytokine, COX-2 and NF-κB genes of THP-1 monocytes and THP-1 macrophages with the maximum up-regulation at 3 and 6 h, respectively. These time points, were subsequently selected to investigate inflammation modulating activity of three well known immuno-modulating food-derived compounds; quercetin, citrus pectin and barley glucan. Co-stimulation of LPS with either quercetin, citrus pectin, or barley glucan in THP-1 monocytes and macrophages showed different immuno-modulatory activity of these compounds. Therefore, we propose that simultaneously exposing THP-1 cells to LPS and food compounds, combined with gene expression response analysis are a promising in vitro screening tool to select, in a limited time frame, food compounds for inflammation modulating effects.

Endogenous Jmjd6 gene product is expressed at the cell surface and regulates phagocytosis in immature monocyte-like activated THP-1 cells

A jumonji domain containing gene 6 (Jmjd6), previously referred to as phosphatidylserine receptor (PSR) gene, plays an important role in cell differentiation and development of multiple organs, although mechanisms of its action are not known. The Jmjd6 gene product was initially identified as a membrane protein that participates in phagocytosis. However, the later findings that recombinant Jmjd6 in expression systems was targeted to the nucleus challenged the role of Jmjd6 as a membrane receptor. Using immunocytochemistry approach we studied the subcellular distribution of endogenous Jmjd6 protein in THP-1 cells activated with phorbol 12-myristate 13 acetate (PMA). We found that treatment with PMA stimulated Jmjd6 expression in the cytosol of activated cells. Furthermore, Jmjd6 initially appeared at the cell surface of immature phagocytes (1-2 days after activation) but then translocated into the nucleus of differentiated macrophage-like cells (5-9 days after activation). Anti-Jmjd6 antibodies suppressed the engulfment of dead cell corpses by THP-1 cells expressing the Jmjd6 at the cell surface. These data indicate that Jmjd6 serves as a membrane-associated receptor that regulates phagocytosis in immature macrophages but is dispensable for phagocytosis and has other functions when it is expressed in the cytosol and nucleus of mature macrophage-like cells.

The novel angiogenic inhibitor, angiocidin, induces differentiation of monocytes to macrophages

We previously showed that angiocidin, a tumor and vascular associated protein, is a potent inhibitor of angiogenesis and tumor growth. Angiocidin is a multidomain protein that exerts its antiangiogenic activity through multiple mechanisms, including effects on cell matrix interaction. Here, we describe another activity of angiocidin that may contribute to its antitumor activity. We show that angiocidin activates monocytes to secrete a mixture of proinflammatory cytokines and induces them to differentiate into macrophage-like cells. Using the monocytic cell line THP-1, we show that angiocidin induces the cells to become adherent and phagocytic, express macrophage markers, and secrete matrix metalloproteinase-9. Microarray analysis of control and angiocidin-treated THP-1 cells revealed that angiocidin up-regulated p105/p50, p100/p52, and rel B, components of the nuclear factor-kappaB (NF-kappaB) pathway. We confirmed the microarray data and showed that angiocidin induced phosphorylation of I kappa beta, p50, and p65 and translocation of p50 and p65 to the nucleus. We also showed that angiocidin activated up-stream mediators of NF-kappaB, such as the mitogen-activated protein kinase (MAPK) pathway and phosphoinositide-3 kinase (PI3K). Blockage of NF-kappaB and MAPK activation with small molecule inhibitors completely prevented angiocidin-mediated secretion of cytokines from THP-1 cells, but did not inhibit their adhesive phenotype. Blocking PI3K inhibited both secretion of cytokines, as well as the adhesive phenotype. These data suggest that angiocidin activates monocytes to secrete cytokines and differentiates them to a macrophage-like phenotype through at least two pathways mediated by MAPK and NF-kappaB, as well as PI3K.

Intervertebral disc cells as competent phagocytes in vitro: implications for cell death in disc degeneration

INTRODUCTION

Apoptosis has been reported to occur in the intervertebral disc. Elsewhere in the body, apoptotic cells are cleared from the system via phagocytosis by committed phagocytes such as macrophages, reducing the chance of subsequent inflammation. These cells, however, are not normally present in the disc. We investigated whether disc cells themselves can be induced to become phagocytic and so have the ability to ingest and remove apoptotic disc cells, minimising the damage to their environment.

METHOD

Bovine nucleus pulposus cells from caudal intervertebral discs were grown in culture and exposed to both latex particles (which are ingested by committed phagocytes) and apoptotic cells. Their response was monitored via microscopy, including both fluorescent and video microscopy, and compared with that seen by cell lines of monocytes/macrophages (THP-1 and J774 cells), considered to be committed phagocytes, in addition to a nonmacrophage cell line (L929 fibroblasts). Immunostaining for the monocyte/macrophage marker, CD68, was also carried out.

RESULTS

Disc cells were able to ingest latex beads at least as efficiently, if not more so, than phagocytic THP-1 and J774 cells. Disc cells ingested a greater number of beads per cell than the committed phagocytes in a similar time scale. In addition, disc cells were able to ingest apoptotic cells when cocultured in monolayer with a UV-treated population of HeLa cells. Apoptotic disc cells, in turn, were able to stimulate phagocytosis by the committed macrophages. CD68 immunostaining was strong for THP-1 cells but negligible for disc cells, even those that had ingested beads.

CONCLUSION

In this study, we have shown that intervertebral disc cells are capable of behaving as competent phagocytes (that is, ingesting latex beads) and apoptotic cells. In terms of number of particles, they ingest more than the monocyte/macrophage cells, possibly due to their greater size. The fact that disc cells clearly can undergo phagocytosis has implications for the intervertebral disc in vivo. Here, where cell death is reported to be common yet there is normally no easy access to a macrophage population, the endogenous disc cells may be encouraged to undergo phagocytosis (for example, of neighbouring cells within cell clusters).

Transcriptional profiling of the LPS induced NF-kappaB response in macrophages

Background

Exposure of macrophages to bacterial products such as lipopolysaccharide (LPS) results in activation of the NF-κB transcription factor, which orchestrates a gene expression programme that underpins the macrophage-dependent immune response. These changes include the induction or repression of a wide range of genes that regulate inflammation, cell proliferation, migration and cell survival. This process is tightly regulated and loss of control is associated with conditions such as septic shock, inflammatory diseases and cancer. To study this response, it is important to have in vitro model systems that reflect the behaviour of cells in vivo. In addition, it is necessary to understand the natural differences that can occur between individuals. In this report, we have investigated and compared the LPS response in macrophage derived cell lines and peripheral blood mononuclear cell (PBMC) derived macrophages.

Results

Gene expression profiles were determined following LPS treatment of THP-1 cells for 1 and 4 hours. LPS significantly induced or repressed 72 out of 465 genes selected as being known or putative NF-κB target genes, which exhibited 4 temporal patterns of expression. Results for 34 of these genes, including several genes not previously identified as LPS target genes, were validated using real time PCR. A high correlation between microarray and real time PCR data was found. Significantly, the LPS induced expression profile of THP-1 cells, as determined using real time PCR, was found to be very similar to that of human PBMC derived macrophages. Interestingly, some differences were observed in the LPS response between the two donor PBMC macrophage populations. Surprisingly, we found that the LPS response in U937 cells was dramatically different to both THP-1 and PBMC derived macrophages.

Conclusion

This study revealed a dynamic and diverse transcriptional response to LPS in macrophages, involving both the induction and repression of gene expression in a time dependent manner. Moreover, we demonstrated that the LPS induced transcriptional response in the THP-1 cell line is very similar to primary PBMC derived macrophages. Therefore, THP-1 cells represent a good model system for studying the mechanisms of LPS and NF-κB dependent gene expression.

The inhibitory effect of Mycoplasma fermentans on tumour necrosis factor (TNF)-alpha-induced apoptosis resides in the membrane lipoproteins

Mycoplasma have been shown to be involved in the alteration of several eukaryotic cell functions, such as cytokine production, gene expression and more. We have previously reported that infection of human myelomonocytic U937 cell line with live Mycoplasma fermentans (M. fermentans) inhibited tumour necrosis factor (TNF-alpha)-induced apoptosis. Mycoplasmal membrane lipoproteins are considered to be the most potent initiators of inflammatory reactions in mycoplasmal infections. The aim of this study was to clarify whether the inhibitory effect on TNFalpha-induced apoptosis is exerted by M. fermentans lipoproteins (LPMf). A significant reduction in TNFalpha-induced apoptosis was demonstrated by stimulation of U937 cells with M. fermentans total proteins, LPMf or MALP-2 (M. fermentans synthetic lipopeptide), but not with M. fermentans hydrophilic protein preparation (AqMf). To investigate the mechanism of M. fermentans antiapoptotic effect, the reduction of mitochondrial transmembrane potential (delta psi m) was measured. M. fermentans total proteins LPMf and MALP-2, but not AqMf, inhibited the reduction of delta psi m. In addition, M. fermentans total proteins LPMf and MALP-2, but not AqMf, downregulated the formation of active caspase-8. NF-kappaB was transactivated in cells treated with M. fermentans lipoproteins, and was essential for host cell survival, but not for the inhibition of TNFalpha-induced apoptosis by LPMf. Our results suggest that the inhibitory effect exerted by M. fermentans on TNFalpha-induced apoptosis in U937 cells is due to the membrane lipoproteins of these bacteria.

Mycoplasma fermentans inhibits tumor necrosis factor alpha-induced apoptosis in the human myelomonocytic U937 cell line

Mycoplasma fermentans (M. fermentans) was shown to be involved in the alteration of several eukaryotic cell functions (i.e. cytokine production, gene expression), and was suggested as a causative agent in arthritic diseases involving impaired apoptosis. We investigated whether M. fermentans has a pathogenic potential by affecting tumor necrosis factor (TNF)alpha-induced apoptosis in the human myelomonocytic U937 cell line. A significant reduction in the TNFalpha-induced apoptosis (approximately 60%) was demonstrated upon either infection with live M. fermentans or by stimulation with non-live M. fermentans. To investigate the mechanism of M. fermentans antiapoptotic effect, the reduction of mitochondrial transmembrane potential (DeltaPsim) and the protease activity of caspase-8 were measured. In the infected cells, the reduction of DeltaPsim was inhibited (approximately 75%), and an approximately 60% reduction of caspase-8 activity was measured. In conclusion, M. fermentans significantly inhibits TNFalpha-induced apoptosis in U937 cells, and its effect is upstream of the mitochondria and upstream of caspase-8.

Chlamydia pneumoniae infection induces differentiation of monocytes into macrophages

Migration and differentiation of monocytes to the intima of blood vessels may be a crucial first step in the development of atherosclerosis associated with Chlamydia (Chlamydophila) pneumoniae. However, the involvement of C. pneumoniae infection in such steps is not clear. In the present study, therefore, the differentiation-inducing activity of C. pneumoniae to monocytes was examined. Human THP-1 monocytic cell line cells were infected with C. pneumoniae, and the differentiation of monocytes to macrophages was assessed by cell morphology, phagocytic activity, and expression of a cell surface adhesion molecule. The monocytic cells infected with viable bacteria markedly differentiated into macrophages associated with diffused cell morphology, increased uptake of polystyrene beads and increased ICAM-1 (intercellular adhesion molecule 1) expression on the cell surfaces. Heat-killed bacteria did not induce any morphological changes or increase of phagocytosis, but they did induce an increase of cell surface ICAM-1 expressions in THP-1 monocytic cells. The antibiotic minocycline treatment of infected cells resulted in marked inhibition of the cell differentiation as well as C. pneumoniae growth in the cells, but not ICAM-1 expression. In addition, the experiments with human peripheral blood monocytes infected with C. pneumoniae also showed the differentiation of macrophages assessed by morphological change and phagocytic activity. These results indicate that C. pneumoniae infection may directly induce the differentiation of monocytes to macrophages. However, antigenic stimulation of monocytes with bacteria may not be sufficient for a full macrophage differentiation.