Mycoplasma fermentans interaction with monocytes/macrophages: molecular basis

Mycoplasma ovipneumoniae-derived lipid-associated membrane proteins induce cytokine secretion in mouse peritoneal macrophages through TLR2 signalling

BACKGROUND

Mycoplasma ovipneumoniae (M. ovi) is the causative agent of chronic non-progressive pneumonia in sheep, goats, bighorn, and wild small ruminants. However, the mechanism of infection and immune response to M. ovi remain unclear. Invading microbes express lipid-associated membrane proteins (LAMPs) on the cell surface that interact with host cells to facilitate infection, and are thus the major molecules recognised by the host immune system. Upon LAMP recognition, Toll-like receptor 2 (TLR2) and NLRP3 inflammasome sense the pathogens and signalling pathways for cytokine secretion. In this study, we investigated whether M. ovi and M. ovi-derived LAMPs are immuno-biologically active compounds capable of activating mouse peritoneal macrophages and explored the underlying mechanism.

RESULTS

After infection of wild-type mice with M. ovi, the expression of TLR2 and NLRP3 at the transcriptional and translational levels was determined with reverse transcription-polymerase chain reaction and flow cytometry. In addition, the cytokine levels and associated pathways were detected in infected wild-type, Tlr2^-/-, and Nlrp3^-/- mice via enzyme-linked immunosorbent assays and western blotting. The nuclear factor (NF)-κB and mitogen-activated protein kinase (MAPK) signalling pathways were found to mediate the expression of inflammatory cytokines in M. ovi or M. ovi-derived LAMP-infected peritoneal macrophages, and cytokines were not induced in Tlr2^-/- and/or Nlrp3^-/- macrophages.

CONCLUSION

Host cytokine production is activated in response to M. ovi-derived LAMPs through the NF-κB and MAPK signalling pathway via TLR2.

Comprehensive RNA-Seq profiling of the lung transcriptome of Bashbay sheep in response to experimental Mycoplasma ovipneumoniae infection

The Bashbay sheep (Ovis aries), an indigenous breed of Xinjiang, China, has many excellent characteristics. It is resistant to Mycoplasma ovipneumoniae infection, the causative agent of mycoplasma ovipneumonia, a chronic respiratory disease that is harmful to the sheep industry. To date, knowledge regarding the mechanisms responsible for M. ovipneumoniae pathogenesis in scant. Herein, we report the results of transcriptome profiling of lung tissues from Bashbay sheep experimentally infected with an M. ovipneumoniae strain at 4 and 14 days post-infection, in comparison to mock-infected animals (0 d). Transcriptome profiling was performed by deep RNA sequencing, using the Illumina platform. The analysis of differentially expressed genes was performed to determine concomitant gene-specific temporal patterns of mRNA expression in the lungs after M. ovipneumoniae infection. We found 1048 differentially expressed genes (575 up-regulated, 473 down-regulated) when comparing transcriptomic data at 4 and 0 days post-infection, and 2823 (1362 up-regulated, 1461 down-regulated) when comparing 14 versus 0 days post-infection. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the differentially expressed genes at 4 and 14 versus 0 days post-infection were enriched in 245 and 287 pathways, respectively, and the Toll-like receptor (TLR) signaling pathway was considered most closely related to MO infection (p < 0.01). Two pathways (LAMP-TLR2/TLR6-MyD88-MKK6-AP1-IL1B and LAMP-TLR8MyD88-IRF5-RANTES) were identified based on the TLR signaling pathway from differentially expressed genes related M. ovipneumoniae infection. Gene Ontology analysis showed that differentially expressed genes in different groups were enriched for 1580 and 4561 terms, where those most closely related to M. ovipneumoniae infection are positive regulators of inflammatory responses (p < 0.01). These results could aid in understanding how M. ovipneumoniae infection progresses in the lungs and may provide useful information regarding key regulatory pathways.

Comprehensive RNA-Seq profiling of the lung transcriptome of Argali hybrid sheep in response to experimental Mycoplasma ovipneumoniae infection

BACKGROUND

An experiment was conducted to reveal why the Argali hybrid sheep are susceptible to Mycoplasma ovipneumoniae infection, the causative agent of mycoplasma ovipneumonia, a chronic respiratory disease that is harmful to the sheep industry.

RESULTS

After nine Argali hybrid sheep, divided into three groups, were experimentally infected with an M. ovipneumoniae strain at 0, 4 and 14 days, transcriptome profiling of lung tissues was performed by deep RNA sequencing, using the Illumina platform. Analysis of differentially expressed genes was performed to determine concomitant gene-specific temporal patterns of mRNA expression in the lungs after M. ovipneumoniae infection. 156 differentially expressed genes (44 up-regulated, 112 down-regulated) were found when comparing transcriptomic data at 4 and 0 days post-infection, and 367 (35 up-regulated, 332 down-regulated) when comparing 14 versus 0 days post-infection. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the differentially expressed genes at 4 and 14 versus 0 days post-infection were enriched in 109 and 150 pathways, respectively, and the Primary immunodeficiency pathway was considered most closely related to MO infection (p < .01). Hyper-IgM syndrome was identified based on the B-cell Immunodeficiency signaling pathway from differentially expressed genes related to M. ovipneumoniae infection. Gene Ontology analysis showed that differentially expressed genes in different groups were enriched for 497 and 928 terms, where those most closely related to M. ovipneumoniae infection are ciliated motor damage (p < .01).

CONCLUSIONS

The situation that ciliary movement is significantly inhibited and B cells in immunodeficiency are possibly the most important reason why Argali hybrid sheep are susceptible to MO.

Potential of Maintaining a Healthy Vaginal Environment by Two Lactobacillus Strains Isolated from Cocoa Fermentation

Bacteria in the genera Mycoplasma and Ureaplasma do not have cell walls and therefore interact with host cells through lipid-associated membrane proteins (LAMP). These lipoproteins are important for both surface adhesion and modulation of host immune responses. Mycoplasma and Ureaplasma have been implicated in cases of bacterial vaginosis (BV), which can cause infertility, abortion, and premature delivery. In contrast, bacteria of the genus Lactobacillus, which are present in the vaginal microbiota of healthy women, are thought to inhibit local colonization by pathogenic microorganisms. The aim of the present study was to evaluate the in vitro interactions between lipoproteins of Mycoplasma and Ureaplasma species and vaginal lineage (HMVII) cells and to study the effect of Lactobacillus isolates from cocoa fermentation on these interactions. The tested Lactobacillus strains showed some important probiotic characteristics, with autoaggregation percentages of 28.55% and 31.82% for L. fermentum FA4 and L. plantarum PA3 strains, respectively, and percent adhesion values of 31.66 and 41.65%, respectively. The two strains were hydrophobic, with moderate to high hydrophobicity values, 65.33% and 71.12% for L. fermentum FA4 and L. plantarum PA3 in toluene. Both strains secreted acids into the culture medium with pH=4.32 and pH=4.33, respectively, and showed antibiotics susceptibility profiles similar to those of other lactobacilli. The strains were also able to inhibit the death of vaginal epithelial cells after incubation with U. parvum LAMP from 41.03% to 2.43% (L. fermentum FA4) and 0.43% (L. plantarum PA3) and also managed to significantly decrease the rate of cell death caused by the interaction with LAMP of M. hominis from 34.29% to 14.06% (L. fermentum FA4) and 14.61% (L. plantarum PA3), thus demonstrating their potential for maintaining a healthy vaginal environment.

Nrf2 regulates the inflammatory response, including heme oxygenase-1 induction, by mycoplasma pneumoniae lipid-associated membrane proteins in THP-1 cells

A series of inflammatory responses caused by Mycoplasma pneumoniae largely depend on the lipid-associated membrane proteins (LAMPs). Nuclear factor E2-related factor 2 (Nrf2), a transcription factor, is considered to be a critical modulator of inflammatory responses and cellular redox homeostasis. Monocytes play an important role in the invasion and immunity to resist pathogens. Here, we investigated the role of Nrf2 in the anti-inflammatory response stimulated by LAMPs using the human monocyte cell line THP-1. LAMPs were shown to affect the localization of Nrf2, and the levels of reactive oxygen species and inflammatory reactants, including nitric oxide (NO), prostaglandin E2 (PGE2) and cytokines (IL-6, IL-8), were highly elevated in LAMP-stimulated Nrf2-silenced THP-1 cells. Moreover, LAMPs induced the levels of mRNA and the expression of heme oxygenase-1 (HO-1). In summary, our results demonstrated that LAMPs cause nuclear translocation of Nrf2, which further suppresses the expression of inflammatory reactants in THP-1 cells.

Mycoplasma fermentans deacetylase promotes mammalian cell stress tolerance

Mycoplasma fermentans is a pathogenic bacterium that infects humans and has potential pathogenic roles in respiratory, genital and rheumatoid diseases. NAD⁺-dependent deacetylase is involved in a wide range of pathophysiological processes and our studies have demonstrated that expression of mycoplasmal deacetylase in mammalian cells inhibits proliferation but promotes anti-starvation stress tolerance. Furthermore, mycoplasmal deacetylase is involved in cellular anti-oxidation, which correlates with changes in the proapoptotic proteins BIK, p21 and BIM. Mycoplasmal deacetylase binds to and deacetylates the FOXO3 protein, similar with mammalian SIRT2, and affects expression of the FOXO3 target gene BIM, resulting in inhibition of cell proliferation. Mycoplasmal deacetylase also alters the performance of cells under drug stress. This study expands our understanding of the potential molecular and cellular mechanisms of interaction between mycoplasmas and mammalian cells.

Genome Sequence of Mycoplasma hyorhinis Isolated from Cell Cultures

Mycoplasmas are major contaminants of mammalian cell cultures. Here, the complete genome sequence of Mycoplasma hyorhinis recovered from Madin-Darby bovine kidney (MDBK) cells is reported.

Ureaplasma diversum Genome Provides New Insights about the Interaction of the Surface Molecules of This Bacterium with the Host

Whole genome sequencing and analyses of Ureaplasma diversum ATCC 49782 was undertaken as a step towards understanding U. diversum biology and pathogenicity. The complete genome showed 973,501 bp in a single circular chromosome, with 28.2% of G+C content. A total of 782 coding DNA sequences (CDSs), and 6 rRNA and 32 tRNA genes were predicted and annotated. The metabolic pathways are identical to other human ureaplasmas, including the production of ATP via hydrolysis of the urea. Genes related to pathogenicity, such as urease, phospholipase, hemolysin, and a Mycoplasma Ig binding protein (MIB)-Mycoplasma Ig protease (MIP) system were identified. More interestingly, a large number of genes (n = 40) encoding surface molecules were annotated in the genome (lipoproteins, multiple-banded antigen like protein, membrane nuclease lipoprotein and variable surface antigens lipoprotein). In addition, a gene encoding glycosyltransferase was also found. This enzyme has been associated with the production of capsule in mycoplasmas and ureaplasma. We then sought to detect the presence of a capsule in this organism. A polysaccharide capsule from 11 to 17 nm of U. diversum was observed trough electron microscopy and using specific dyes. This structure contained arabinose, xylose, mannose, galactose and glucose. In order to understand the inflammatory response against these surface molecules, we evaluated the response of murine macrophages J774 against viable and non-viable U. diversum. As with viable bacteria, non-viable bacteria were capable of promoting a significant inflammatory response by activation of Toll like receptor 2 (TLR2), indicating that surface molecules are important for the activation of inflammatory response. Furthermore, a cascade of genes related to the inflammasome pathway of macrophages was also up-regulated during infection with viable organisms when compared to non-infected cells. In conclusion, U. diversum has a typical ureaplasma genome and metabolism, and its surface molecules, including the identified capsular material, represent major components of the organism immunopathogenesis.

Mycoplasma hyopneumoniae-derived lipid-associated membrane proteins induce inflammation and apoptosis in porcine peripheral blood mononuclear cells in vitro

Mycoplasma hyopneumoniae is the causative agent of swine enzootic pneumonia (EP), a disease that causes considerable economic losss in swine industry. Lipid-associated membrane proteins (LAMPs) of mycoplasma play important roles in causing mycoplasma diseases. The present study explores the pathogenic mechanisms of M. hyopneumoniae LAMPs by elucidating their role in modulating the inflammation, apoptosis, and relevant signaling pathways of peripheral blood mononuclear cells (PBMCs) of pig. LAMP treatment inhibited the growth of PBMCs. Up-regulation of cytokines, such as IL-6 and IL-1β, as well as increased production of nitric oxide (NO) and superoxide anion were all detected in the supernatant of LAMPs-treated PBMCs. Furthermore, flow cytometric analysis using dual staining with annexin-V-FITC and propidium iodide (PI) showed that LAMPs of M. hyopneumoniae induced a time-dependent apoptosis in lymphocyts and monocytes from PBMCs, which was blocked by NOS inhibitor or antioxidant. In addition, LAMPs induced the phosphorylation of p38, the ratio of pro-apoptotic Bax protein to anti-apoptotic Bcl-2, activation of caspase-3 and caspase-8, and poly ADP-ribose polymerase (PARP) cleavage in PBMCs. These findings demonstrated that M. hyopneumoniae LAMPs induced the production of proinflammatory cytokines, NO and reactive oxygen species (ROS), and apoptosis of PBMCs in vitro through p38 MAPK and Bax/Bcl-2 signaling pathways, as well as caspase activation.

Mycoplasma gallisepticum lipid associated membrane proteins up-regulate inflammatory genes in chicken tracheal epithelial cells via TLR-2 ligation through an NF-κB dependent pathway

Mycoplasma gallisepticum-mediated respiratory inflammation in chickens is associated with accumulation of leukocytes in the tracheal submucosa. However the molecular mechanisms underpinning these changes have not been well described. We hypothesized that the initial inflammatory events are initiated upon ligation of mycoplasma lipid associated membrane proteins (LAMP) to TLRs expressed on chicken tracheal epithelial cells (TEC). To test this hypothesis, live bacteria or LAMPs isolated from a virulent (R_low) or a non-virulent (R_high) strain were incubated with primary TECs or chicken tracheae ex vivo. Microarray analysis identified up-regulation of several inflammatory and chemokine genes in TECs as early as 1.5 hours post-exposure. Kinetic analysis using RT-qPCR identified the peak of expression for most genes to be at either 1.5 or 6 hours. Ex-vivo exposure also showed up-regulation of inflammatory genes in epithelial cells by 1.5 hours. Among the commonly up-regulated genes were IL-1β, IL-6, IL-8, IL-12p40, CCL-20, and NOS-2, all of which are important immune-modulators and/or chemo-attractants of leukocytes. While these inflammatory genes were up-regulated in all four treatment groups, R_low exposed epithelial cells both in vitro and ex vivo showed the most dramatic up-regulation, inducing over 100 unique genes by 5-fold or more in TECs. Upon addition of a TLR-2 inhibitor, LAMP-mediated gene expression of IL-1β and CCL-20 was reduced by almost 5-fold while expression of IL-12p40, IL-6, IL-8 and NOS-2 mRNA was reduced by about 2–3 fold. Conversely, an NF-κB inhibitor abrogated the response entirely for all six genes. miRNA-146a, a negative regulator of TLR-2 signaling, was up-regulated in TECs in response to either R_low or R_high exposure. Taken together we conclude that LAMPs isolated from both R_high and R_low induced rapid, TLR-2 dependent but transient up-regulation of inflammatory genes in primary TECs through an NF-κB dependent pathway.

Sulfur compounds block MCP-1 production by Mycoplasma fermentans-infected macrophages through NF-κB inhibition

Background and aims

Hydrogen sulfide (H₂S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to a family of endogenous signaling mediators termed “gasotransmitters”. Recent studies suggest that H₂S modulates many cellular processes and it has been recognized to play a central role in inflammation, in the cardiovascular and nervous systems. By infecting monocytes/macrophages with Mycoplasma fermentans (M.F.), a well-known pro-inflammatory agent, we evaluated the effects of H₂S.

Methods

M.F.-infected cells were analyzed by ELISA and real time RT-PCR to detect the M.F. effects on MCP-1 and on MMP-12 expression. The role of two different H₂S donors (NaHS and GYY4137) on MF-infected cells was determined by treating infected cells with H₂S and then testing the culture supernatants for MCP-1 and on MMP-12 production by ELISA assay. In order to identify the pathway/s mediating H₂S- anti-inflammatory activity, cells were also treated with specific pharmaceutical inhibitors. Cytoplasmic and nuclear accumulation of NF-κB heterodimers was analyzed.

Results

We show that H₂S was able to reduce the production of pro-inflammatory cytokine MCP-1, that was induced in monocytes/macrophages during M.F. infection. Moreover, MCP-1 was induced by M.F. through Toll-like receptor (TLR)-mediated nuclear factor-κB (NF-κB) activation, as demonstrated by the fact that TLR inhibitors TIRAP and MyD88 and NF-κB inhibitor IKK were able to block the cytokine production. In contrast H₂S treatment of M.F. infected macrophages reduced nuclear accumulation of NF-κB heterodimer p65/p52.

Conclusions

Our data demonstrate that under the present conditions H₂S is effective in reducing Mycoplasma-induced inflammation by targeting the NF-κB pathway. This supports further studies for possible clinical applications.

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

Mycoplasma fermentans possesses unique α-glycolipid antigens (GGPL-I and GGPL-III) at the cytoplasm membrane, which carry a phosphocholine group at the sugar primary (6-OH) position. This paper describes a practical synthetic pathway to a GGPL-I homologue (C(16:0)) and its diastereomer, in which our one-pot α-glycosylation method was effectively applied. The synthetic GGPL-I isomers were characterized with (1)H NMR spectroscopy to determine the equilibrium among the three conformers (gg, gt, tg) at the acyclic glycerol moiety. The natural GGPL-I isomer was found to prefer gt (54%) and gg (39%) conformers around the lipid tail, while adopting all of the three conformers with equal probability around the sugar position. This property was very close to what we have observed with respect to the conformation of phosphatidylcholine (DPPC), suggesting that the Mycoplasma glycolipids GGPLs may constitute the cytoplasm fluid membrane together with ubiquitous phospholipids, without inducing stereochemical stress.

Proteomics characterization of cytoplasmic and lipid-associated membrane proteins of human pathogen Mycoplasma fermentans M64

Mycoplasma fermentans is a potent human pathogen which has been implicated in several diseases. Notably, its lipid-associated membrane proteins (LAMPs) play a role in immunomodulation and development of infection-associated inflammatory diseases. However, the systematic protein identification of pathogenic M. fermentans has not been reported. From our recent sequencing results of M. fermentans M64 isolated from human respiratory tract, its genome is around 1.1 Mb and encodes 1050 predicted protein-coding genes. In the present study, soluble proteome of M. fermentans was resolved and analyzed using two-dimensional gel electrophoresis. In addition, Triton X-114 extraction was carried out to enrich amphiphilic proteins including putative lipoproteins and membrane proteins. Subsequent mass spectrometric analyses of these proteins had identified a total of 181 M. fermentans ORFs. Further bioinformatics analysis of these ORFs encoding proteins with known or so far unknown orthologues among bacteria revealed that a total of 131 proteins are homologous to known proteins, 11 proteins are conserved hypothetical proteins, and the remaining 39 proteins are likely M. fermentans-specific proteins. Moreover, Triton X-114-enriched fraction was shown to activate NF-kB activity of raw264.7 macrophage and a total of 21 lipoproteins with predicted signal peptide were identified therefrom. Together, our work provides the first proteome reference map of M. fermentans as well as several putative virulence-associated proteins as diagnostic markers or vaccine candidates for further functional study of this human pathogen.

Promotion of arthritis and allergy in mice by aminoglycoglycerophospholipid, a membrane antigen specific to Mycoplasma fermentans

Mycoplasmas, which lack a cell wall and are the smallest self-replicating bacteria, have been linked to some chronic diseases, such as AIDS, rheumatoid arthritis (RA), and oncogenic transformation of cells. Their membrane components (lipoproteins and glycolipids) have been identified as possible causative factors in such diseases. Glycoglycerophospholipid (GGPL)-III, a unique phosphocholine-containing aminoglycoglycerophospholipid, is a major specific antigen of Mycoplasma fermentans, and has been detected in 38% of RA patients. Unlike those of lipoproteins, which induce inflammation via Toll-like receptor 2 (TLR2), the pathologic effects of GGPL-III are poorly understood. RA and metal allergies are chronic inflammatory diseases in which autoantigens have been implicated. Here, we examined the effects of chemically synthesized GGPL-III in murine arthritis and allergy models. GGPL-III alone exhibited little inflammatory effect, but promoted both collagen-induced arthritis and nickel (Ni) allergy, although less powerfully than Escherichia coli lipopolysaccharide. The augmenting effect of GGPL-III on Ni allergy was present in mice deficient in either T cells or active TLR4, but it was markedly weaker in mice deficient in macrophages, interleukin-1, or the histamine-forming enzyme histidine decarboxylase than in their control strains. These results suggest that GGPL-III may play roles in some types of chronic diseases via the innate immune system.

Mycoplasma genitalium lipoproteins induce human monocytic cell expression of proinflammatory cytokines and apoptosis by activating nuclear factor kappaB

This study was designed to investigate the molecular mechanisms responsible for the induction of proinflammatory cytokines gene expression and apoptosis in human monocytic cell line THP-1 stimulated by lipoproteins (LPs) prepared from Mycoplasma genitalium. Cultured cells were stimulated with M. genitalium LP to analyze the production of proinflammatory cytokines and expression of their mRNA by ELISA and RT-PCR, respectively. Cell apoptosis was also detected by Annexin V-FITC-propidium iodide (PI) staining and acridine orange (AO)-ethidium bromide (EB) staining. The DNA-binding activity of nuclear factor-κB (NF-κB) was assessed by electrophoretic mobility shift assay (EMSA). Results showed that LP stimulated THP-1 cells to produce tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 in a dose-dependent manner. The mRNA levels were also upregulated in response to LP stimulation. LPs were also found to increase the DNA-binding activity of NF-κB, a possible mechanism for the induction of cytokine mRNA expression and the cell apoptosis. These effects were abrogated by PDTC, an inhibitor of NF-κB. Our results indicate that M. genitalium-derived LP may be an important etiological factor of certain diseases due to the ability of LP to produce proinflammatory cytokines and induction of apoptosis, which is probably mediated through the activation of NF-κB.

Synthesis and characterization of a dipalmitoylated lipopeptide derived from paralogous lipoproteins of Mycoplasma pneumoniae

Genomic analysis of Mycoplasma pneumoniae revealed the existence of a large number of putative lipoprotein genes compared with the numbers in other bacteria. However, the pathogenic roles of M. pneumoniae lipoproteins are still obscure. In this study, we synthesized a lipopeptide (designated M. pneumoniae paralogous lipoprotein 1 [MPPL-1]) in which an S-dipalmitoylglyceryl cysteine was coupled to a peptide with a consensus sequence of a putative paralogous lipoprotein group characteristic of M. pneumoniae. The cytokine-inducing activity of MPPL-1 in human monocytic cells was much weaker (approximately 700-fold weaker) than that of the known mycoplasmal S-dipalmitoylated lipopeptide FSL-1 or MALP-2. MPPL-1 required Toll-like receptor (TLR2) to activate NF-kappaB-dependent gene transcription in HEK293 cells, although a 1,000-fold-larger amount of MPPL-1 was needed to exert activity similar to that of FSL-1 in the cells. TLR2-mediated recognition of MPPL-1 was synergistically upregulated by TLR6 but not by TLR1 or TLR10, although the activity was still weak. In addition, MPPL-1 did not antagonize FSL-1 recognition in human monocytic cells and TLR2/TLR6-expressing HEK293 cells. Thus, these results suggest that there is preferential selective recognition of diacylated lipopeptides due to the magnitude of an affinity with TLR2 and TLR6 and the roles of increased paralogous lipoprotein genes of M. pneumoniae in evasion of TLR2 recognition.

Interactions between mycoplasma lipid-associated membrane proteins and the host cells

Mycoplamas are a group of wall-less prokaryotes widely distributed in nature, some of which are pathogenic for humans and animals. There are many lipoproteins anchored on the outer face of the plasma membrane, called lipid-associated membrane proteins (LAMPs). LAMPs are highly antigenic and could undergo phase and size variation, and are recognized by the innate immune system through Toll-like receptors (TLR) 2 and 6. LAMPs can modulate the immune system, and could induce immune cells apoptosis or death. In addition, they may associate with malignant transformation of host cells and are also considered to be cofactors in the progression of AIDS.

Infection of human B lymphoma cells by Mycoplasma fermentans induces interaction of its elongation factor with the intracytoplasmic domain of Epstein-Barr virus receptor (gp140, EBV/C3dR, CR2, CD21)

Human cell lines are often infected by mycoplama strains. We have demonstrated that when infected by Mycoplasma fermentans, human B lymphoma cell proliferation increased strongly. These infected B cells expressed a p45 kDa protein which interacted with the intracellular domain of CD21, the EBV/C3d receptor. p45 analysis demonstrated that this is a new gene which encodes an elongation factor originating from Mycoplasma fermentans. p45 interaction with CD21 was specific, there being no interaction with CD19. This is the first demonstration that Mycoplasma fermentans, in infecting human B cells, generates a p45 Mycoplasma component that interacts with CD21, which is involved in B cell proliferation.

Pain in patients with chronic fatigue syndrome: Does nitric oxide trigger central sensitisation?

Previous studies have provided evidence supportive of the clinical importance of widespread pain in patients with chronic fatigue syndrome (CFS): pain severity may account for 26-34% of the variability in the CFS patient's activity limitations and participation restrictions. The etiology of widespread pain in CFS remains to be elucidated, but sensitisation of the central nervous system has been suggested to take part of CFS pathophysiology. It is hypothesised that a nitric oxide (NO)-dependent reduction in inhibitory activity of the central nervous system and consequent central sensitisation accounts for chronic widespread pain in CFS patients. In CFS patients, deregulation of the 2',5'-oligoadenylate synthetase/RNase L pathway is accompanied by activation of the protein kinase R enzyme. Activation of the protein kinase R and subsequent nuclear factor-kappaB activation might account for the increased production of NO, while infectious agents frequently associated with CFS (Coxsackie B virus, Epstein-Barr Virus, Mycoplasma) might initiate or accelerate this process. In addition, the evidence addressing behavioural changes in CFS patients fits the central sensitisation-hypothesis: catastrophizing, avoidance behaviour, and somatization may result in, or are initiated by sensitisation of the central nervous system.

Chronic fatigue syndrome: intracellular immune deregulations as a possible etiology for abnormal exercise response

The exacerbation of symptoms after exercise differentiates Chronic fatigue syndrome (CFS) from several other fatigue-associated disorders. Research data point to an abnormal response to exercise in patients with CFS compared to healthy sedentary controls, and to an increasing amount of evidence pointing to severe intracellular immune deregulations in CFS patients. This manuscript explores the hypothetical interactions between these two separately reported observations. First, it is explained that the deregulation of the 2-5A synthetase/RNase L pathway may be related to a channelopathy, capable of initiating both intracellular hypomagnesaemia in skeletal muscles and transient hypoglycemia. This might explain muscle weakness and the reduction of maximal oxygen uptake, as typically seen in CFS patients. Second, the activation of the protein kinase R enzyme, a characteristic feature in atleast subsets of CFS patients, might account for the observed excessive nitric oxide (NO) production in patients with CFS. Elevated NO is known to induce vasidilation, which may limit CFS patients to increase blood flow during exercise, and may even cause and enhanced postexercise hypotension. Finally, it is explored how several types of infections, frequently identified in CFS patients, fit into these hypothetical pathophysiological interactions.

Stimulation of human Toll-like receptor (TLR) 2 and TLR6 with membrane lipoproteins of Mycoplasma fermentans induces apoptotic cell death after NF-kappa B activation

Mycoplasmal membrane diacylated lipoproteins not only initiate proinflammatory responses through Toll-like receptor (TLR) 2 and TLR6 via the activation of the transcriptional factor NF-kappaB, but also initiate apoptotic responses. The aim of this study was to clarify the apoptotic machineries. Mycoplasma fermentans lipoproteins and a synthetic lipopeptide, MALP-2, showed cytocidal activity towards HEK293 cells transfected with a TLR2-encoding plasmid. The activity was synergically augmented by co-expression of TLR6, but not by co-expression of other TLRs. Under the condition of co-expression of TLR2 and TLR6, the lipoproteins could induce maximum NF-kappa B activation and apoptotic cell death in the cells 6 h and 24 h after stimulation respectively. Dominant-negative forms of MyD88 and FADD, but not IRAK-4, reduced the cytocidal activity of the lipoproteins. In addition, both dominant-negative forms also downregulated the activation of both NF-kappa B and caspase-8 in the cells. Additionally, the cytocidal activity was sufficiently attenuated by a selective inhibitor of p38 MAPK. These findings suggest that mycoplasmal lipoproteins can trigger TLR2- and TLR6-mediated sequential bifurcate responses: NF-kappa B activation as an early event, which is partially mediated by MyD88 and FADD; and apoptosis as a later event, which is regulated by p38 MAPK as well as by MyD88 and FADD.

Extracellular ATP regulates cell death of lymphocytes and monocytes induced by membrane-bound lipoproteins of Mycoplasma fermentans and Mycoplasma salivarium

The cytotoxicities of lipoproteins of Mycoplasma fermentans and Mycoplasma salivarium to a lymphocytic cell line, MOLT-4, and a monocytic cell line, HL-60, was upregulated by ATP added extracellularly in a dose-dependent manner. These lipoproteins induced ATP release and plasma membrane permeability increase in these cell lines. In addition, periodate-oxidized ATP, an antagonist for P2X purinergic receptors, suppressed the cytotoxicity of the lipoproteins, suggesting the possibility that P2X receptors for ATP play crucial roles in the cytotoxicity. Activation of caspase-3 induced by the lipoproteins, which was assessed by the cleavage of the synthetic substrate DEVD-pNA and the endogenous substrate poly(ADP-ribose) polymerase, was also upregulated and downregulated by extracellular ATP and periodate-oxidized ATP, respectively. On the basis of these results, this study suggests that mycoplasmal lipoproteins induce the permeability increase in lymphocytes and monocytes, by which ATP is released, and the ATP regulates the cytotoxicities of the lipoproteins to the cells, possibly by interaction with ATP receptors such as P2X purinergic receptors.

Chronic fatigue syndrome: a risk factor for osteopenia?

No data documenting a possible depletion of bone mineral density in patients with chronic fatigue syndrome (CFS) are currently available. However, recent pathophysiological observations in CFS patients may have deleterious consequences on bone density. Firstly, the deregulation of the 2,5A synthetase RNase L antiviral pathway and its associated channelopathy, implicates increased demands for calcium and consequent increased calcium-re-absorption from the skeletal system. Secondly, Mycoplasma fermentans which has been frequently associated with CFS, produces a lipopeptide, named 2-kDa macrophage-activating lipopeptide (MALP-2), which stimulates macrophages. MALP-2 has been shown to enhance bone resorption in a dose-dependent manner, at least in part by stimulating the formation of prostaglandins. Thirdly, decreased levels of insulin-like growth factor I (IGF-I) have been reported in CFS-patients. IGF-I is critical to the proliferation of osteoblasts. Consequently, depleted levels of IGF-I may shift the balance between osteoclastic and osteoblastic activity towards bone resorption.

Identification and functional mapping of the Mycoplasma fermentans P29 adhesin

Initial adherence interactions between mycoplasmas and mammalian cells are important for host colonization and may contribute to subsequent pathogenic processes. Despite significant progress toward understanding the role of specialized, complex tip structures in the adherence of some mycoplasmas, particularly those that infect humans, less is known about adhesins through which other mycoplasmas of this host bind to diverse cell types, even though simpler surface components are likely to be involved. We show by flow cytometric analysis that a soluble recombinant fusion protein (FP29), representing the abundant P29 surface lipoprotein of Mycoplasma fermentans, binds human HeLa cells and inhibits M. fermentans binding to these cells, in both a quantitative and a saturable manner, whereas analogous fusion proteins representing other mycoplasma surface proteins did not. Constructs representing nested N- or C-terminal truncations of FP29 allowed initial mapping of this specific adherence function to a central region of the P29 sequence containing a 36-amino-acid disulfide loop. A derivative of FP29 containing a mutation converting one participating Cys to Ser, precluding intrachain disulfide bond formation, retained full activity. Together these results suggest that the direct interaction of M. fermentans with a ligand on the HeLa cell surface involves a limited segment of the P29 surface lipoprotein and requires neither the disulfide bond nor the contribution of adjacent portions of the protein. Earlier results indicating phase-variable display of monoclonal antibody surface epitopes on P29, now recognized to be outside this ligand binding region, raise the possibility that variation of mycoplasma surface architecture might alter the presentation of the binding region and the adherence phenotype. Preliminary results further indicated that FP29 could inhibit binding to HeLa cells by Mycoplasma hominis, a distinct human mycoplasma species displaying the phase-variable adhesin Vaa, but not that by Mycoplasma capricolum, an organism infecting caprine species. This result raises the additional, testable possibility that a common host cell ligand for two human mycoplasma species may be recognized through structurally dissimilar adhesins that undergo phase variation by two distinct mechanisms, governing protein expression (Vaa) or surface masking (P29).

Site-specific proteolysis of the MALP-404 lipoprotein determines the release of a soluble selective lipoprotein-associated motif-containing fragment and alteration of the surface phenotype of Mycoplasma fermentans

The mature MALP-404 surface lipoprotein of Mycoplasma fermentans comprises a membrane-anchored N-terminal lipid-modified region responsible for macrophage activation (P. F. Mühlradt, M. Kiess, H. Meyer, R. Süssmuth, and G. Jung, J. Exp. Med. 185:1951-1958, 1997) and an external hydrophilic region that contains the selective lipoprotein-associated (SLA) motif defining a family of lipoproteins from diverse but selective prokaryotes, including mycoplasmas (M. J. Calcutt, M. F. Kim, A. B. Karpas, P. F. Mühlradt, and K. S. Wise, Infect. Immun. 67:760-771, 1999). This family generally corresponds to a computationally defined group of orthologs containing the basic membrane protein (BMP) domain. Two discrete lipid-modified forms of the abundant MALP product which vary dramatically in ratio among isolates of M. fermentans occur on the mycoplasma surface: (i) MALP-404, the full-length mature product, and (ii) MALP-2, the Toll-like receptor 2-mediated macrophage-activating lipopeptide containing the N-terminal 14 residues of the mature lipoprotein. The role of posttranslational processing in the biogenesis of MALP-2 from the prototype MALP-404 SLA-containing lipoprotein was investigated. Detergent phase fractionation of cell-bound products and N-terminal sequencing of a newly discovered released fragment (RF) demonstrated that MALP-404 was subject to site-specific proteolysis between residues 14 and 15 of the mature lipoprotein, resulting in the cell-bound MALP-2 and soluble RF products. This previously unknown mechanism of posttranslational processing among mycoplasmas suggests that specific cleavage of some surface proteins may confer efficient "secretion" of extracellular products by these organisms, with concurrent changes in the surface phenotype. This newly identified form of variation may have significant implications for host adaptation by mycoplasmas, as well as other pathogens expressing lipoproteins of the SLA (BMP) family.