Dextran sulfate sodium upregulates MAPK signaling for the uptake and subsequent intracellular survival of Brucella abortus in murine macrophages

Transcriptome Landscape of Intracellular Brucella ovis Surviving in RAW264.7 Macrophage Immune System

Brucella ovis infection results in genital damage and epididymitis in rams, placental inflammation and rare abortion in ewes, and neonatal mortality in lambs. However, the mechanism underlying B. ovis infection remains unclear. In the present study, we used prokaryotic transcriptome sequencing to identify the differentially expressed genes (DEGs) between wild-type B. ovis and intracellular B. ovis in RAW264.7 macrophages. Gene ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed, and quantitative reverse transcriptase PCR (qRT-PCR) was used to validate the top 10 upregulated and downregulated DEGs. The results showed that 212 genes were differentially expressed, including 68 upregulated and 144 downregulated genes, which were mainly enriched in 30 GO terms linked to biological process, cellular component, and molecular function. KEGG analysis showed that the DEGs were enriched in the hypoxia-inducible factor 1 (HIF-1) signaling pathway, mitogen-activated protein kinase (MAPK) signaling pathway, beta-alanine metabolism, and quorum sensing pathway. BME_RS01160, BME_RS04270, BME_RS08185, BME_RS12880, BME_RS25875, predicted_RNA865, and predicted_RNA953 were confirmed with the transcriptome sequencing data. Hence, our findings not only reveal the intracellular parasitism of B. ovis in the macrophage immune system, but also help to understand the mechanism of chronic B. ovis infection.

Formyl peptide receptor 2 (FPR2) antagonism is a potential target for the prevention of Brucella abortus 544 infection

Here, we explore the potential role of formyl peptide receptor 2 (FPR2) during Brucella abortus infection. FPR2 manipulation affected B. abortus internalization but not its growth within macrophages. During the activation of FPR2 induced by its agonist AGP-8694, a high level of Brucella uptake was accompanied by an increase in ERK phosphorylation, while intracellular survival at 24 h postincubation was observed to be associated with slightly reduced nitrite accumulation but augmented superoxide anion production. Attenuated secretion of IL-6 and IL-10 were observed 48 h postincubation in the bone marrow-derived macrophages (BMDMs) treated with the FPR2 antagonist WRW4. An opposite pattern of bacterial uptake was observed upon treatment with the FPR2 antagonist, but no significant changes in the activation of MAPKs or the production of nitrite or superoxide anion were observed. Interestingly, AGP-8694 treatment of mice did not lead to differences in spleen or liver weight but slightly enhanced bacterial proliferation was observed in the spleen. Although the weights of the spleen or liver did not differ, WRW4 treatment led to reduced bacterial proliferation in the spleen. Furthermore, FPR2 antagonist treatment was associated with high serum levels of the proinflammatory cytokines IL-12, TNF-α, IFN-γ and MCP-1, while the production of TNF-α was inhibited in AGP-8694-treated mice. IL-6 and IL-10 levels were slightly increased in AGP-8694-treated mice at 24 h postinfection. Our findings demonstrated the contribution of FPR2 via manipulating this receptor using its reported agonist AGP-8694 and antagonist WRW4 in both in vitro and in vivo systems. Although activation of the receptor did not consistently induced Brucella infection, FPR2 inhibition may be a promising strategy to treat brucellosis in animals which encourages further investigation.

Adenosine receptor Adora2b antagonism attenuates Brucella abortus 544 infection in professional phagocyte RAW 264.7 cells and BALB/c mice

Brucella as a stealthy intracellular pathogen avoids activation of innate immune response. Here we investigated the contribution of an adenosine receptor, Adora2b, during Brucella infection in professional phagocyte RAW 264.7 cells and in a murine model. Adora2b-deficient cells showed attenuated Brucella internalization and intracellular survival with enhanced release of IL-6, TNF-α, IL-12 and MCP-1. In addition, blockade of Adora2b using MRS 1754 treatment in mice resulted in increased total weight of the spleens but suppressed bacterial burden in these organs accompanied by elevated levels of IL-6, IFN-γ, TNF-α, IL-12 and MCP-1, while reduced IL-10. Overall, we proposed that the Adora2b participates in the successful phagocytic pathway and intracellular survival of Brucella in RAW 264.7 cells, and could be a potential therapeutic target for the treatment of acute brucellosis in animals.

A Chemical Genetics Screen Reveals Influence of p38 Mitogen-Activated Protein Kinase and Autophagy on Phagosome Development and Intracellular Replication of Brucella neotomae in Macrophages

Brucella is an intracellular bacterial pathogen that causes chronic systemic infection in domesticated livestock and poses a zoonotic infectious risk to humans. The virulence of Brucella is critically dependent on its ability to replicate and survive within host macrophages. Brucella modulates host physiological pathways and cell biology in order to establish a productive intracellular replicative niche. Conversely, the host cell presumably activates pathways that limit infection. To identify host pathways contributing to this yin and yang during host cell infection, we performed a high-throughput chemical genetics screen of known inhibitors and agonists of host cell targets to identify host factors that contribute to intracellular growth of the model pathogen Brucella neotomae Using this approach, we identified the p38 mitogen-activated protein (MAP) kinase pathway and autophagy machinery as both a linchpin and an Achilles' heel in B. neotomae's ability to coopt host cell machinery and replicate within macrophages. Specifically, B. neotomae induced p38 MAP kinase phosphorylation and autophagy in a type IV secretion system-dependent fashion. Both p38 MAP kinase stimulation and an intact autophagy machinery in turn were required for phagosome maturation and intracellular replication. These findings contrasted with those for Legionella pneumophila, where chemical inhibition of the p38 MAP kinase pathway and autophagy factor depletion failed to block intracellular replication. Therefore, results from a chemical genetics screen suggest that intersections of the MAP kinase pathways and autophagy machinery are critical components of Brucella's intracellular life cycle.

Tannic acid-mediated immune activation attenuates Brucella abortus infection in mice

Brucellosis is an emerging infectious disease affecting humans and animals. In this study, we investigated the in vitro and in vivo effects of tannic acid (TA) against Brucella abortus infection. After infection, F-actin polymerization and mitogen-activated protein kinases (MAPKs) (ERK 1/2 and p38α) phosphorylation were reduced in TA-treated cells compared with that in control cells. The mice were infected via an intraperitoneal route and were orally given TA or phosphate-buffered saline for 14 days. Spleen weights of the TA-treated and control mice were not different; however, splenic proliferation of B. abortus was significantly reduced in the TA-treated group. Immune response analysis showed that, compared with the control group, non-infected TA-treated mice displayed increased levels of interferon-γ (IFN-γ), monocyte chemoattractant protein-1 (MCP-1), and interleukin-10 at 3 days post-infection and a further increase in IFN-γ and MCP-1 at 14 days post-infection. In contrast, compared with the control group, infected TA-treated mice displayed elevated levels of IFN-γ at 3 days post-infection, which continued to increase at 14 days post-infection, as was also observed for tumor necrosis factor. Taken together, the results showing TA activation of cytokine production and inhibition of bacterial proliferation in the host highlight a potential use of TA treatment in the control of Brucella infection.

The host immune enhancing agent Korean red ginseng oil successfully attenuates Brucella abortus infection in a murine model

ETHNOPHARMACOLOGICAL RELEVANCE

Panax ginseng Meyer (Araliaceae), is one of the most valuable traditional Chinese medicines and is used for the treatment of various human diseases. In this study, we elucidated the protective mechanism of the essential oil from Korean red ginseng (RGO) against Brucella infection.

MATERIALS AND METHODS

The effects of RGO on Brucella abortus viability, NO production, uptake and intracellular growth in macrophages were investigated. Mice were intraperitoneally infected with B. abortus and orally treated with RGO for 14 days. The weights and bacterial numbers from each spleen were monitored, and the sera were evaluated for cytokine production.

RESULTS

B. abortus viability was not affected, whereas NO production, internalization and intracellular replication were inhibited in RGO-treated macrophages. Bacterial adherence, F-actin polymerization and MAPK signaling protein phosphorylation (ERK1/2, JNK and p38α) were reduced and the co-localization of B. abortus-containing phagosomes with LAMP-1 was augmented in RGO-treated cells compared to untreated cells. RGO displayed protective effects against cell damage by inhibiting nitrite production during B. abortus infection in macrophages. Moreover, the spleen weight and bacterial burden were lower in the RGO-treated group than in the control group. The uninfected RGO-treated mice displayed increased TNF-α and IFN-γ production, whereas the B. abortus-infected RGO-treated mice showed reduced IL-10 production compared to the control.

CONCLUSION

RGO exhibits protective effects against B. abortus infection in vitro and in vivo, which emphasize the beneficial effects of RGO in the prevention and treatment of brucellosis.