Role of Staphylococcus aureus Formate Metabolism during Prosthetic Joint Infection.

Biofilms are bacterial communities characterized by antibiotic tolerance. Staphylococcus aureus is a leading cause of biofilm infections on medical devices, including prosthetic joints, which represent a significant health care burden. The major leukocyte infiltrate associated with S. aureus prosthetic joint infection (PJI) is granulocytic myeloid-derived suppressor cells (G-MDSCs), which produce IL-10 to promote biofilm persistence by inhibiting monocyte and macrophage proinflammatory activity. To determine how S. aureus biofilm responds to G-MDSCs and macrophages, biofilms were cocultured with either leukocyte population followed by RNA sequencing. Several genes involved in fermentative pathways were significantly upregulated in S. aureus biofilm following G-MDSC coculture, including formate acetyltransferase (pflB), which catalyzes the conversion of pyruvate and coenzyme-A into formate and acetyl-CoA. A S. aureus pflB mutant (ΔpflB) did not exhibit growth defects in vitro. However, ΔpflB formed taller and more diffuse biofilm compared to the wild-type strain as revealed by confocal microscopy. In a mouse model of PJI, the bacterial burden was significantly reduced with ΔpflB during later stages of infection, which coincided with decreased G-MDSC influx and increased neutrophil recruitment, and ΔpflB was more susceptible to macrophage killing. Although formate was significantly reduced in the soft tissue surrounding the joint of ΔpflB-infected mice levels were increased in the femur, suggesting that host-derived formate may also influence bacterial survival. This was supported by the finding that a ΔpflBΔfdh strain defective in formate production and catabolism displayed a similar phenotype to ΔpflB. These results revealed that S. aureus formate metabolism is important for promoting biofilm persistence.

Interleukin-1beta triggers the expansion of circulating granulocytic myeloid-derived suppressor cell subset dependent on Erk1/2 activation.

Chronic inflammation contributes to cancer development and progression. Although interleukin-1beta (IL-1ß) has been observed to be associated with an general immune suppression of T cell response and the immunosuppression strongly correlates with accumulation of myeloid-derived suppressor cells (MDSCs), the relationship and mechanism between MDSCs expansion and IL-1ß expression remain ambiguous. Here, we showed that the concentration of IL-1ß was highly correlated with G-MDSC subset, rather than mo-MDSC subset. Recombinant IL-1ß increased the percentage of G-MDSCs in the blood of tumor-bearing mice, and IL-1Ra attenuated the accumulation of G-MDSCs in the tumor-bearing mice. In addition, the IL-1ß-overexpressing B16F10 cells induced higher level of G-MDSCs compared with wild-type B16F10 cells. Moreover, we found that the accumulation of G-MDSCs induced by IL-1ß was dependent on the activation of extracellular signal-regulated kinases 1 and 2 (Erk1/2). Collectively, these findings show a novel role of IL-1ß in G-MDSCs accumulation by activating Erk1/2, which suggests that IL-1ß elimination or Erk1/2 signaling blockade could decrease G-MDSCs generation and thereby improve host immunosurveillance.

Granulocytic and Monocytic Myeloid-Derived Suppressor Cells are Functionally and Prognostically Different in Patients with Chronic Myeloid Leukemia.

Myeloid-derived suppressor cells (MDSCs) represent phenotypically heterogeneous populations that suppress tumor-specific T-cell responses. MDSCs are produced from myeloid precursors in emergent states and are increased in several hematologic malignancies. We evaluated the differences in the levels and prognostic significance of MDSCs according to the clinical status of chronic myeloid leukemia (CML). The percentages and numbers of granulocytic (g)MDSCs and monocytic (m)MDSCs in peripheral blood (PB) and bone marrow (BM) aspirates were determined by five-color flow cytometry (HLA-DR/CD11b/CD15/CD33/CD14). The median BM-gMDSC% and PB-gMDSC% of the CML group were lower than those of the complete hematologic response (CHR) and control groups (P<0.001). In the CHR group, patients with major molecular response (MMR) showed higher median BM-gMDSC% than those without MMR (P=0.039). Conversely, the PB-mMDSC number of the CML group was higher than those of the CHR and control groups (P<0.001). Patients with high PB-gMDSC number exhibited superior survival to those with low PB-gMDSC number (P=0.021), and patients with high PB-mMDSC% showed inferior survival to those with low PB-mMDSC%, but there was no statistical significance (P=0.182). Increased gMDSCs at CHR may reflect non-leukemic granulopoiesis, and a high number of PB-gMDSCs suggests better prognosis in CML. However, mMDSCs may be associated with malignant conditions and poor prognosis.

Modulation of gut microbiota mediates berberine-induced expansion of immuno-suppressive cells to against alcoholic liver disease.

BACKGROUND: Berberine is an isoquinoline alkaloid compound derived from many herbs, which has been used extensively to improve liver function. But action mechanism of its hepatoprotection in alcoholic liver disease (ALD) is far from being clear. AIM: To investigate the underlying mechanism of berberine's therapeutic effect on ALD associated with gut microbiota-immune system axis. METHOD: An animal model fed with ethanol that mimics drinking pattern ideally in ALD patients was established. Liver function was evaluated by biochemical test and histological examination. Immune cells were detected by flow cytometry and feces samples were collected for 16S rRNA gene amplicon sequencing. RESULTS: We first reported the promising beneficial effect of berberine on ameliorating acute-on-chronic alcoholic hepatic damage and explored the underlying mechanism involving gut microbiota-immune system axis. Notably, berberine activated a population with immune suppressive function, defined as granulocytic- myeloid-derived suppressor cell (G-MDSC)-like population, in the liver of mice with alleviating alcohol-induced hepatic injury. Berberine remarkably enhanced the increase of G-MDSC-like cells in blood and liver and decreased cytotoxic T cells correspondingly. Suppression of G-MDSC-like population significantly attenuated the protective effect of berberine against alcohol. Berberine activated IL6/STAT3 signaling in in vitro culture of G-MSDCs-like population, while inhibition of STAT3 activity attenuated the activation of this population by berberine. Moreover, berberine changed the overall gut microbial community, primarily increased the abundance of Akkermansia muciniphila. Of note, depletion of gut microbiota abolished the inducing effect of berberine on G-MDSC-like population, and attenuated its hepatoprotective effect against alcohol in mice, suggesting intestinal flora might be involved in mediating the expansion of this protective population. CONCLUSION: Collectively, this study delivered insight into the role of immunosuppressive response in ALD, and facilitated the understanding of the pharmacological effects and action mechanisms of berberine.

Metformin inhibits the function of granulocytic myeloid-derived suppressor cells in tumor-bearing mice.

Metformin, an oral medicine broadly used for the treatment of type 2 diabetes, has been found to significantly improve tumor incidence and survival in large-scale clinical analysis. In recent years, the antitumor effect and mechanism of metformin have received much attention. Myeloid-derived suppressor cells (MDSCs), a major immunosuppressive cell type that accumulates in tumor-bearing hosts, can inhibit T cells and promote tumor immune escape. The mechanism by which metformin exerts its anti-tumor effect by regulating MDSCs remains unclear. Here, we found that metformin could inhibit the accumulation and suppressive capacity of G-MDSCs, delay tumor progression and elicit Th1 and CTL responses in murine colon cancer CT-26 cell-transplanted mice. In additionally, metformin could enhance the phosphorylation of AMPK, reduce STAT3 phosphorylation levels, and down-regulate the inhibitory function of G-MDSCs in vitro. These results suggest that metformin may be a potential clinical benefit for antitumor immunotherapy in tumor-bearing mice.

Hedgehog Signaling Links Chronic Inflammation to Gastric Cancer Precursor Lesions.

Since its initial discovery in Drosophila, Hedgehog (HH) signaling has long been associated with foregut development. The mammalian genome expresses 3 HH ligands, with sonic hedgehog (SHH) levels highest in the mucosa of the embryonic foregut. More recently, interest in the pathway has shifted to improving our understanding of its role in gastrointestinal cancers. The use of reporter mice proved instrumental in our ability to probe the expression pattern of SHH ligand and the cell types responding to canonical HH signaling during homeostasis, inflammation, and neoplastic transformation. SHH is highly expressed in parietal cells and is required for these cells to produce gastric acid. Furthermore, myofibroblasts are the predominant cell type responding to HH ligand in the uninfected stomach. Chronic infection caused by Helicobacter pylori and associated inflammation induces parietal cell atrophy and the expansion of metaplastic cell types, a precursor to gastric cancer in human subjects. During Helicobacter infection in mice, canonical HH signaling is required for inflammatory cells to be recruited from the bone marrow to the stomach and for metaplastic development. Specifically, polarization of the invading myeloid cells to myeloid-derived suppressor cells requires the HH-regulated transcription factor GLI1, thereby creating a microenvironment favoring wound healing and neoplastic transformation. In mice, GLI1 mediates the phenotypic shift to gastric myeloid-derived suppressor cells by directly inducing Schlafen 4 (slfn4). However, the human homologs of SLFN4, designated SLFN5 and SLFN12L, also correlate with intestinal metaplasia and could be used as biomarkers to predict the subset of individuals who might progress to gastric cancer and benefit from treatment with HH antagonists.

Cutaneous squamous cell carcinomas with markers of increased metastatic risk are associated with elevated numbers of neutrophils and/or granulocytic myeloid derived suppressor cells.

BACKGROUND: A subset of presenting cutaneous squamous cell carcinomas (CSCC) is high risk with respect to their high rates of recurrence, metastasis and patient death. The identification of such high risk CSCC is problematic. Neutrophil and granulocytic myeloid derived suppressor cell (G-MDSC) numbers are elevated in a number of cancers, but their association with current markers of high risk tumors in the setting of CSCC is unknown. OBJECTIVES: To assess circulating and tumor-localised neutrophil and G-MDSC populations for associations with high-risk tumor characteristics and overall survival (OS) in CSCC patients. METHODS: A retrospective clinical audit was performed of patients who had hospital operations for primary CSCC and did not have other malignancies or HIV. Therapeutically immuno-suppressed individuals (TII, n=129) and non-TII (n=29) were analysed separately with respect to the presence of high-risk tumor features and OS. In addition, 47 patients with prospectively collected blood and primary CSCC tumor samples were analysed to determine frequencies of circulating G-MDSC and tumor localised CD66b+ and CD8+ leukocytes. RESULTS: In the clinical audit of non-TII, high circulating neutrophil counts were associated with tumor thickness≥5mm, Clark level V and high T-stage. Univariate analysis showed elevated neutrophil count was a significant marker of poor OS, whilst tumor thickness remained the only independent histological predictor of OS after adjusting for age and immuno-suppression. The prospective study demonstrated that tumors≥5mm thick had significantly increased total and peri-tumorally localised CD66b+ leukocytes (comprising neutrophils and/or G-MDSC) and that elevated circulating G-MDSC numbers were associated with high T-stage tumors. CONCLUSIONS: This study demonstrates that the presence of high risk CSCC is associated with increased numbers of both circulating and tumor resident populations of neutrophils and/or G-MDSC. These cell types therefore merit further investigation with respect to their functional and prognostic significance in CSCC.