Fusobacterium nucleatum promotes M2 polarization of macrophages in the microenvironment of colorectal tumours via a TLR4-dependent mechanism

Autoinducer-2 of Fusobacterium nucleatum promotes macrophage M1 polarization via TNFSF9/IL-1β signaling

The effect of Fusobacterium nucleatum (F. nucleatum) autoinducer-2 (AI-2) on the polarization of macrophages and the underlying mechanism is not known. We investigated the effect of F. nucleatum AI-2 on the migration and polarization of cultured macrophages. We further screened AI-2-interacting proteins in macrophages using a quantitative proteomics strategy, and evaluated the expression of TNFSF9/TRAF1/p-AKT/IL-1β signaling in cultured macrophages and human colorectal cancer (CRC). The data showed that F. nucleatum AI-2 enhanced the mobility and M1 polarization of macrophages, possibly through TNFSF9/TRAF1/p-AKT/IL-1β signaling. Moreover, TNFSF9 and IL-1β expression was significantly increased in human CRCs when compared to normal colon (P < 0.05), and was associated with AI-2 concentration and increased survival. Together, our data suggested that AI-2 induced macrophage M1 polarization by activating the TNFSF9/IL-1β pathway. Thus, AI-2 may serve as a promising novel target for immunotherapy of gut microbiota-related diseases.

Fusobacterium nucleatum Aggravates the Progression of Colitis by Regulating M1 Macrophage Polarization via AKT2 Pathway

Disordered intestinal flora and discordant immune response are associated with the development of ulcerative colitis (UC). Recent work has described the ability of macrophages to undergo repolarization toward a proinflammatory M1 or anti-inflammatory M2 phenotype in response to particular bacterium-derived signals. Fusobacterium nucleatum (F. nucleatum, Fn) is a species of intestinal commensal bacteria with potential pathogenicity, but its association with UC and how it may contribute to progression of UC is largely unknown. In this study, we provide new evidence that F. nucleatum accumulated heavily in the intestine of UC patients and was accompanied by the secretion of IFN-γ and the skewing of M1 macrophages. Mechanistically, our data showed that F. nucleatum aggravated dextran sodium sulfate (DSS)-induced colitis in the production of Th1-related cytokines IFN-γ through the AKT2 signaling pathway in vitro and in vivo. To further confirm the disease-relevance of these shifts in macrophage repolarization in response to F. nucleatum, stimulated bone marrow-derived macrophages (BMDMs) were transferred into recipient mice with DSS colitis. This transfer resulted in increased disease activity and inflammatory cytokine production. Taken together, we show clearly that F. nucleatum can promote the progression of UC via proinflammatory M1 macrophage skewing, and targeting F. nucleatum or AKT2 signaling may be a viable means of blocking development of UC.

Autoinducer-2 of gut microbiota, a potential novel marker for human colorectal cancer, is associated with the activation of TNFSF9 signaling in macrophages

Objectives: The interaction between the quorum sensing (QS) molecules of gut microbiota and the immunity of colorectal cancer (CRC) has not been investigated before. Methods: We measured the concentration of autoinducer-2 (AI-2) in samples of stool, colorectal tissue, saliva and serum of CRC patients, and compared this to AI-2 levels in colorectal adenoma (AD) and normal colon mucosa (NC). To explore the activated signaling pathways involved, we utilized AI-2 extracted from Fusobacterium nucleatum to stimulate macrophages and validated these in vitro findings in human CRC tissues. Results: The AI-2 concentration in both colorectal tissue and stool of CRC patients was significantly higher when compared to that in AD and NC (all P values < .01). The AI-2 concentration along with the progression of CRC in both tissues and stools was significantly increased (P= .045，P= .0003, respectively). After AI-2 stimulation, TNFSF9 was the most significantly increased protein in macrophage cells (P < .01). TNFSF9 expression was significantly higher in CRC tissues when compared to NCs (P< .0001), which was mainly derived from macrophages in the tumor microenvironment. Moreover, AI-2 level was positively associated with CD3 + T cell numbers (P= .0462), and negatively associated with CD4/CD8 ratio (P= .0113) within CRC tissues. Conclusions: We demonstrated for the first time that AI-2 may serve as a novel marker for screening CRC in the clinic. AI-2 was associated with tumor immunity in CRCs through tumor-associated macrophages and CD4/CD8 ratio in a TNFSF9-dependent manner.

Inter-kingdom signaling between gut microbiota and their host

The crosstalk between prokaryotic bacteria and eukaryotic gut epithelial cells has opened a new field for research. Quorum sensing system (QS) molecules employed by gut microbiota may play an essential role in host-microbial symbioses of the gut. Recent studies on the gut microbiome will unveil evolved mechanisms of the host to affect bacterial QS and shape bacterial composition. Bacterial autoinducers (AIs) could talk to the host's gut by eliciting proinflammatory effects and modulating the activities of T lymphocyte, macrophage, dendritic cells, and neutrophils. In addition, the gut mucosa could interfere with bacterial AIs by degrading them or secreting AI mimics. Moreover, bacterial AIs and gut hormones epinephrine and noradrenaline may be interchangeable in the crosstalk between the microbiota and human gut. Therefore, inter-kingdom signaling between gut microbiota and host may provide a novel target in the management of gut microbiota-related conditions or diseases in the future.

Fusobacterium nucleatum Contributes to the Carcinogenesis of Colorectal Cancer by Inducing Inflammation and Suppressing Host Immunity

The presence of Fusobacterium nucleatum (F. nucleatum) in the gut is associated with the development of colorectal cancer (CRC). F. nucleatum promotes tumor development by inducing inflammation and host immune response in the CRC microenvironment. Adhesion to the intestinal epithelium by the cell surface proteins FadA, Fap2 and RadD expressed by F. nucleatum can cause the host to produce inflammatory factors and recruit inflammatory cells, creating an environment which favors tumor growth. Furthermore, F. nucleatum can induce immune suppression of gut mucosa by suppressing the function of immune cells such as macrophages, T cells and natural killer cells, contributing the progression of CRC.

Crosstalk between cancer cells and tumor associated macrophages is required for mesenchymal circulating tumor cell-mediated colorectal cancer metastasis

Background

Tumor-associated macrophages (TAMs) are major components of tumor microenvironment that frequently associated with tumor metastasis in human cancers. Circulating tumor cell (CTC), originating from primary tumor sites, is considered to be the precursors of tumor metastasis. However, the regulatory mechanism of TAMs in CTC-mediated tumor metastasis still remains unclear.

Methods

Immunohistochemical staining was used to detect the macrophages infiltration (CD68 and CD163), epithelial–mesenchymal transition (EMT) markers (E-cadherin and Vimentin) expression in serial sections of human colorectal cancer (CRC) specimens. Then, the correlations between macrophages infiltration and clinicopathologic features, mesenchymal CTC ratio, and patients’ prognosis were analyzed. A co-culture assay in vitro was used to evaluate the role of TAMs on CRC EMT, migration and invasion, and ELISA, luciferase reporter assay and CHIP were performed to uncover the underlying mechanism. Furthermore, an in vivo model was carried out to confirm the effect of TAMs on mesenchymal CTC-mediated metastasis.

Results

Clinically, CD163⁺ TAMs infiltrated in invasive front was associated with EMT, mesenchymal CTC ratio, and poor prognosis in patients with CRC. CRC–conditioned macrophages regulated EMT program to enhance CRC cells migration and invasion by secreting IL6. TAMs-derived IL6 activated the JAK2/STAT3 pathway, and activated STAT3 transcriptionally inhibited the tumor suppressor miR-506-3p in CRC cells. miR-506-3p, a key miRNA regulating FoxQ1, was downregulated in CRC cells, resulting in increased FoxQ1 expression, which in turn led to the production of CCL2 that promoted macrophage recruitment. Inhibition of CCL2 or IL6 broke this loop and reduced macrophage migration and mesenchymal CTC-mediated metastasis, respectively.

Conclusions

Our data indicates that TAMs induce EMT program to enhance CRC migration, invasion, and CTC-mediated metastasis by regulating the JAK2/STAT3/miR-506-3p/FoxQ1 axis, which in turn leads to the production of CCL2 that promote macrophage recruitment, revealing a new cross-talk between immune cells and tumor cells in CRC microenvironment.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0976-4) contains supplementary material, which is available to authorized users.