The NLRP6 Inflammasome Recognizes Lipoteichoic Acid and Regulates Gram-Positive Pathogen Infection.

The activator and composition of the NLRP6 inflammasome remain poorly understood. We find that lipoteichoic acid (LTA), a molecule produced by Gram-positive bacteria, binds and activates NLRP6. In response to cytosolic LTA or infection with Listeria monocytogenes, NLRP6 recruited caspase-11 and caspase-1 via the adaptor ASC. NLRP6 activation by LTA induced processing of caspase-11, which promoted caspase-1 activation and interleukin-1ß (IL-1ß)/IL-18 maturation in macrophages. Nlrp6-/- and Casp11-/- mice were less susceptible to L. monocytogenes infection, which was associated with reduced pathogen loads and impaired IL-18 production. Administration of IL-18 to Nlrp6-/- or Casp11-/- mice restored the susceptibility of mutant mice to L. monocytogenes infection. These results reveal a previously unrecognized innate immunity pathway triggered by cytosolic LTA that is sensed by NLRP6 and exacerbates systemic Gram-positive pathogen infection via the production of IL-18.

Control of pathogens and pathobionts by the gut microbiota.

A dense resident microbial community in the gut, referred as the commensal microbiota, coevolved with the host and is essential for many host physiological processes that include enhancement of the intestinal epithelial barrier, development of the immune system and acquisition of nutrients. A major function of the microbiota is protection against colonization by pathogens and overgrowth of indigenous pathobionts that can result from the disruption of the healthy microbial community. The mechanisms that regulate the ability of the microbiota to restrain pathogen growth are complex and include competitive metabolic interactions, localization to intestinal niches and induction of host immune responses. Pathogens, in turn, have evolved strategies to escape from commensal-mediated resistance to colonization. Thus, the interplay between commensals and pathogens or indigenous pathobionts is critical for controlling infection and disease. Understanding pathogen-commensal interactions may lead to new therapeutic approaches to treating infectious diseases.

NOD1 and NOD2 in inflammatory and infectious diseases.

It has been long recognized that NOD1 and NOD2 are critical players in the host immune response, primarily by their sensing bacterial peptidoglycan-conserved motifs. Significant advances have been made from efforts that characterize their upstream activators, assembly of signaling complexes, and activation of downstream signaling pathways. Disruption in NOD1 and NOD2 signaling has also been associated with impaired host defense and resistance to the development of inflammatory diseases. In this review, we will describe how NOD1 and NOD2 sense microbes and cellular stress to regulate host responses that can affect disease pathogenesis and outcomes.

Gut microbiota and systemic immunity in health and disease.

The mammalian intestine is colonized by trillions of microorganisms that have co-evolved with the host in a symbiotic relationship. Although the influence of the gut microbiota on intestinal physiology and immunity is well known, mounting evidence suggests a key role for intestinal symbionts in controlling immune cell responses and development outside the gut. Although the underlying mechanisms by which the gut symbionts influence systemic immune responses remain poorly understood, there is evidence for both direct and indirect effects. In addition, the gut microbiota can contribute to immune responses associated with diseases outside the intestine. Understanding the complex interactions between the gut microbiota and the host is thus of fundamental importance to understand both immunity and human health.

The Nod2 sensor promotes intestinal pathogen eradication via the chemokine CCL2-dependent recruitment of inflammatory monocytes.

The intracellular sensor Nod2 is activated in response to bacteria, and the impairment of this response is linked to Crohn's disease. However, the function of Nod2 in host defense remains poorly understood. We found that Nod2-/- mice exhibited impaired intestinal clearance of Citrobacter rodentium, an enteric bacterium that models human infection by pathogenic Escherichia coli. The increased bacterial burden was preceded by reduced CCL2 chemokine production, inflammatory monocyte recruitment, and Th1 cell responses in the intestine. Colonic stromal cells, but not epithelial cells or resident CD11b+ phagocytic cells, produced CCL2 in response to C. rodentium in a Nod2-dependent manner. Unlike resident phagocytic cells, inflammatory monocytes produced IL-12, a cytokine that induces adaptive immunity required for pathogen clearance. Adoptive transfer of Ly6C(hi) monocytes restored the clearance of the pathogen in infected Ccr2-/- mice. Thus, Nod2 mediates CCL2-CCR2-dependent recruitment of inflammatory monocytes, which is important in promoting bacterial eradication in the intestine.

Understanding Covalent versus Spin-Orbit Coupling Contributions to Temperature-Dependent Electron Spin Relaxation in Cupric and Vanadyl Phthalocyanines.

Recent interest in transition-metal complexes as potential quantum bits (qubits) has reinvigorated the investigation of fundamental contributions to electron spin relaxation in various ligand scaffolds. From quantum computers to chemical and biological sensors, interest in leveraging the quantum properties of these molecules has opened a discussion of the requirements to maintain coherence over a large temperature range, including near room temperature. Here we compare temperature-, magnetic field position-, and concentration-dependent electron spin relaxation in copper(II) phthalocyanine (CuPc) and vanadyl phthalocyanine (VOPc) doped into diamagnetic hosts. While VOPc demonstrates coherence up to room temperature, CuPc coherence times become rapidly T1-limited with increasing temperature, despite featuring a more covalent ground-state wave function than VOPc. As rationalized by a ligand field model, this difference is ascribed to different spin-orbit coupling (SOC) constants for Cu(II) versus V(IV). The manifestation of SOC contributions to spin-phonon coupling and electron spin relaxation in different ligand fields is discussed, allowing for a further understanding of the competing roles of SOC and covalency in electron spin relaxation.

Nod1 Limits Colitis-Associated Tumorigenesis by Regulating IFN-γ Production.

Chronic intestinal inflammation is a major risk factor for the development of colorectal cancer. Nod1, a member of the Nod-like receptor (NLR) family of pattern recognition receptors, is a bacterial sensor that has been previously demonstrated to reduce susceptibility of mice to chemically induced colitis and subsequent tumorigenesis, but the mechanism by which it mediates its protection has not been elucidated. In this study, we show that Nod1 expression in the hematopoietic cell compartment is critical for limiting inflammation-induced intestinal tumorigenesis. Specifically, Nod1-deficient T cells exhibit impaired IFN-γ production during dextran sulfate sodium (DSS)-induced acute inflammation in vivo, and administration of the Nod1 ligand KF1B enhances IFN-γ responses by anti-CD3-activated T cells in vitro. Absence of IFN-γ signaling results in increased inflammation-associated tumors in mice, and adoptive transfer of Nod1(-/-) or IFNγ(-/-) T cells into T cell-deficient mice results in increased tumorigenesis as compared with T cell-deficient mice that were adoptively transferred with wild-type T cells. Collectively, these results suggest a previously unappreciated role for the innate immune receptor Nod1 in suppressing colitis-associated tumorigenesis through a T cell-mediated mechanism.

The Role of the Gut Microbiome in Colorectal Cancer.

There is increasing evidence that the gut microbiome, which consists of trillions of microbes representing over 1,000 species of bacteria with over 3 million genes, significantly impacts intestinal health and disease. The gut microbiota not only is capable of promoting intestinal homeostasis and antitumor responses but can also contribute to chronic dysregulated inflammation as well as have genotoxic effects that lead to carcinogenesis. Whether the gut microbiota maintains health or promotes colon cancer may ultimately depend on the composition of the gut microbiome and the balance within the microbial community of protective and detrimental bacterial populations. Disturbances in the normal balanced state of a healthful microbiome, known as dysbiosis, have been observed in patients with colorectal cancer (CRC); however, whether these alterations precede and cause CRC remains to be determined. Nonetheless, studies in mice strongly suggest that the gut microbiota can modulate susceptibility to CRC, and therefore may serve as both biomarkers and therapeutic targets.

Dissecting CD8+ NKT Cell Responses to Listeria Infection Reveals a Component of Innate Resistance.

A small pool of NK1.1(+) CD8(+) T cells is harbored among the conventional CD8(+) T cell compartment. Conclusions drawn from the analysis of immune responses mediated by cytotoxic CD8(+) T cells are often based on the total population, which includes these contaminating NK1.1(+) CD8(+) T cells. An unresolved question is whether NK1.1(+) CD8(+) cells are conventional T cells that acquire NK1.1 expression upon activation or delineation into memory phenotype or whether they are a distinct cell population that induces immune responses in a different manner than conventional T cells. To address this question, we used the Listeria monocytogenes model of infection and followed CD8(+) NK1.1(+) T cells and NK1.1(-) CD8(+) T cells during each phase of the immune response: innate, effector, and memory. Our central finding is that CD8(+) NK1.1(+) cells and conventional NK1.1(-) CD8(+) T cells both contribute to the adaptive immune response to Listeria, but only CD8(+) NK1.1(+) cells were equipped with the ability to provide a rapid innate immune response, as demonstrated by early and Ag-independent IFN-γ production, granzyme B expression, and degranulation. More importantly, purified conventional CD8(+) T cells alone, in the absence of any contaminating CD8(+) NK1.1(+) cells, were not sufficient to provide early protection to lethally infected mice. These results highlight the role of CD8(+) NK1.1(+) T cells in mounting early innate responses that are important for host defense and support the therapeutic potential of this subset to improve the effectiveness of protective immunity.

Development of an Integrated Pipeline for Profiling Microbial Proteins from Mouse Fecal Samples by LC-MS/MS.

Metaproteomics is one approach to analyze the functional capacity of the gut microbiome but is limited by the ability to evenly extract proteins from diverse organisms within the gut. Herein, we have developed a pipeline to optimize sample preparation of stool obtained from germ-free (GF) mice that were gavaged a defined community of 11 bacterial strains isolated from the human gut. With 64% more proteins identified, bead-beating was confirmed to be an indispensable step for the extraction of bacterial proteins, especially for Gram-positive bacteria. Bacterial enrichment from mouse fecal samples was further optimized by evaluating three different methods: (1) a high-speed differential centrifugation (HCE) or (2) a low-speed differential centrifugation (LCE) and (3) a filter-aided method (FA). The HCE method was associated with dramatic loss of bacteria and 71% less recovery of bacterial proteins than the LCE method. Compared with LCE, the FA method also showed dramatic loss of the amount of bacteria recovered and decreased protein identifications from Gram-positive bacteria in the stool samples. Ultimately, LCE may provide an alternative and complementary method for enriching bacteria from small amounts of mouse fecal samples, which could aid in investigating bacterial function in health and disease.

Role of Nlrp6 and Nlrp12 in the maintenance of intestinal homeostasis.

There has been significant interest in understanding how interactions between the host immune system and the gut microbiota regulate intestinal homeostasis. Recent data suggest that the Nod-like receptor (NLR) family of PRRs regulate both the composition of the gut microbiota and innate immune signaling pathways that prevent pathologic intestinal inflammation and tumorigenesis. In this review, we will focus on NLRP6 and NLRP12, two members of the NLR family that have emerged as important players in the maintenance of intestinal homeostasis, and discuss the signaling pathways engaged by these receptors as well as the current models of how these receptors protect against the development of colitis and tumorigenesis.

Nonidealities in CO2 Electroreduction Mechanisms Revealed by Automation-Assisted Kinetic Analysis.

In electrocatalysis, mechanistic analysis of reaction rate data often relies on the linearization of relatively simple rate equations; this is the basis for typical Tafel and reactant order dependence analyses. However, for more complex reaction phenomena, such as surface coverage effects or mixed control, these common linearization strategies will yield incomplete or uninterpretable results. Cohesive kinetic analysis, which is often used in thermocatalysis and involves quantitative model fitting for data collected over a wide range of reaction conditions, requires more data but also provides a more robust strategy for interrogating reaction mechanisms. In this work, we report a robotic system that improves the experimental workflow for collecting electrochemical rate data by automating sequential testing of up to 10 electrochemical cells, where each cell can have a different electrode, electrolyte, gas-phase reactant composition, and applied voltage. We used this system to investigate the mechanism of carbon dioxide electroreduction to carbon monoxide at several immobilized metal tetrapyrroles. Specifically, at cobalt phthalocyanine (CoPc), cobalt tetraphenylporphyrin (CoTPP), and iron phthalocyanine (FePc), we see signatures of complex reaction mechanisms, where observed bicarbonate and CO2 order dependences change with applied potential. We illustrate how phenomena such as electrolyte poisoning and potential-dependent degrees of rate control can explain the observed kinetic behaviors. Our mechanistic analysis suggests that CoPc and CoTPP share a similar reaction mechanism, akin to one previously proposed, whereas the mechanism for FePc likely involves a species later in the catalytic cycle as the most abundant reactive intermediate. Our study illustrates that complex reaction mechanisms that are not amenable to common Tafel and order dependence analyses may be quite prevalent across this class of immobilized metal tetrapyrrole electrocatalysts.

Opposing diet, microbiome, and metabolite mechanisms regulate inflammatory bowel disease in a genetically susceptible host.

Inflammatory bowel diseases (IBDs) are chronic conditions characterized by periods of spontaneous intestinal inflammation and are increasing in industrialized populations. Combined with host genetics, diet and gut bacteria are thought to contribute prominently to IBDs, but mechanisms are still emerging. In mice lacking the IBD-associated cytokine, interleukin-10, we show that a fiber-deprived gut microbiota promotes the deterioration of colonic mucus, leading to lethal colitis. Inflammation starts with the expansion of natural killer cells and altered immunoglobulin-A coating of some bacteria. Lethal colitis is then driven by Th1 immune responses to increased activities of mucin-degrading bacteria that cause inflammation first in regions with thinner mucus. A fiber-free exclusive enteral nutrition diet also induces mucus erosion but inhibits inflammation by simultaneously increasing an anti-inflammatory bacterial metabolite, isobutyrate. Our findings underscore the importance of focusing on microbial functions-not taxa-contributing to IBDs and that some diet-mediated functions can oppose those that promote disease.

A functional role for Nlrp6 in intestinal inflammation and tumorigenesis.

The nucleotide-binding oligomerization domain-like receptor (NLR) family member, Nlrp6, has been implicated in inflammasome signaling to activate caspase-1, which is essential for the production of mature IL-1ß and IL-18. However, a function for Nlrp6 in vivo has never been demonstrated. Due to the relative high expression of Nlrp6 in intestinal tissue, we hypothesized that Nlrp6 has a role in intestinal homeostasis. Indeed, Nlrp6-deficient mice are more susceptible to chemically induced colitis as well as colitis-induced tumorigenesis than wild-type (WT) mice. Nlrp6-deficient mice exhibited significantly more inflammation within the colon than WT mice after dextran sulfate sodium treatment. Their inability to resolve inflammation and repair damaged epithelium as efficiently as WT mice resulted in prolonged increases in epithelial proliferative activity that likely underlie the increased propensity for tumors in these mice during chronic inflammation. We further show that the activity of Nlrp6 in hematopoietic cells is critical for protection against inflammation-related colon tumorigenesis. This study highlights the importance of NLR function in maintaining intestinal homeostasis to prevent the development of aberrant inflammation and tumor development within the colon.

A steamed broccoli sprout diet preparation that reduces colitis via the gut microbiota.

Sulforaphane is a bioactive metabolite with anti-inflammatory activity and is derived from the glucosinolate glucoraphanin, which is highly abundant in broccoli sprouts. However, due to its inherent instability its use as a therapeutic against inflammatory diseases has been limited. There are few studies to investigate a whole food approach to increase sulforaphane levels with therapeutic effect and reduce inflammation. In the current study, using a mouse model of inflammatory bowel disease, we investigated the ability of steamed broccoli sprouts to ameliorate colitis and the role of the gut microbiota in mediating any effects. We observed that despite inactivation of the plant myrosinase enzyme responsible for the generation of sulforaphane via steaming, measurable levels of sulforaphane were detectable in the colon tissue and feces of mice after ingestion of steamed broccoli sprouts. In addition, this preparation of broccoli sprouts was also capable of reducing chemically-induced colitis. This protective effect was dependent on the presence of an intact microbiota, highlighting an important role for the gut microbiota in the metabolism of cruciferous vegetables to generate bioactive metabolites and promote their anti-inflammatory effects.

Salivary microbiome changes distinguish response to chemoradiotherapy in patients with oral cancer.

BACKGROUND: Oral squamous cell carcinoma (SCC) is associated with oral microbial dysbiosis. In this unique study, we compared pre- to post-treatment salivary microbiome in patients with SCC by 16S rRNA gene sequencing and examined how microbiome changes correlated with the expression of an anti-microbial protein. RESULTS: Treatment of SCC was associated with a reduction in overall bacterial richness and diversity. There were significant changes in the microbial community structure, including a decrease in the abundance of Porphyromonaceae and Prevotellaceae and an increase in Lactobacillaceae. There were also significant changes in the microbial community structure before and after treatment with chemoradiotherapy, but not with surgery alone. In patients treated with chemoradiotherapy alone, several bacterial populations were differentially abundant between responders and non-responders before and after therapy. Microbiome changes were associated with a change in the expression of DMBT1, an anti-microbial protein in human saliva. Additionally, we found that salivary DMBT1, which increases after treatment, could serve as a post-treatment salivary biomarker that links to microbial changes. Specifically, post-treatment increases in human salivary DMBT1 correlated with increased abundance of Gemella spp., Pasteurellaceae spp., Lactobacillus spp., and Oribacterium spp. This is the first longitudinal study to investigate treatment-associated changes (chemoradiotherapy and surgery) in the oral microbiome in patients with SCC along with changes in expression of an anti-microbial protein in saliva. CONCLUSIONS: The composition of the oral microbiota may predict treatment responses; salivary DMBT1 may have a role in modulating the oral microbiome in patients with SCC. After completion of treatment, 6 months after diagnosis, patients had a less diverse and less rich oral microbiome. Leptotrichia was a highly prevalent bacteria genus associated with disease. Expression of DMBT1 was higher after treatment and associated with microbiome changes, the most prominent genus being Gemella Video Abstract.

Unravelling specific diet and gut microbial contributions to inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic condition characterized by periods of spontaneous intestinal inflammation and is increasing in industrialized populations. Combined with host genetic predisposition, diet and gut bacteria are thought to be prominent features contributing to IBD, but little is known about the precise mechanisms involved. Here, we show that low dietary fiber promotes bacterial erosion of protective colonic mucus, leading to lethal colitis in mice lacking the IBD-associated cytokine, interleukin-10. Diet-induced inflammation is driven by mucin-degrading bacteria-mediated Th1 immune responses and is preceded by expansion of natural killer T cells and reduced immunoglobulin A coating of some bacteria. Surprisingly, an exclusive enteral nutrition diet, also lacking dietary fiber, reduced disease by increasing bacterial production of isobutyrate, which is dependent on the presence of a specific bacterial species, Eubacterium rectale. Our results illuminate a mechanistic framework using gnotobiotic mice to unravel the complex web of diet, host and microbial factors that influence IBD.

Cell-based proteome profiling of potential dasatinib targets by use of affinity-based probes.

Protein kinases (PKs) play an important role in the development and progression of cancer by regulating cell growth, survival, invasion, metastasis, and angiogenesis. Dasatinib (BMS-354825), a dual Src/Abl inhibitor, is a promising therapeutic agent with oral bioavailability. It has been used for the treatment of imatinib-resistant chronic myelogenous leukemia (CML). Most kinase inhibitors, including Dasatinib, inhibit multiple cellular targets and do not possess exquisite cellular specificity. Recent efforts in kinase research thus focus on the development of large-scale, proteome-wide chemical profiling methods capable of rapid identification of potential cellular (on- and off-) targets of kinase inhibitors. Most existing approaches, however, are still problematic and in many cases not compatible with live-cell studies. In this work, we have successfully developed a cell-permeable kinase probe (DA-2) capable of proteome-wide profiling of potential cellular targets of Dasatinib. In this way, highly regulated, compartmentalized kinase-drug interactions were maintained. By comparing results obtained from different proteomic setups (live cells, cell lysates, and immobilized affinity matrix), we found DA-2 was able to identify significantly more putative kinase targets. In addition to Abl and Src family tyrosine kinases, a number of previously unknown Dasatinib targets have been identified, including several serine/threonine kinases (PCTK3, STK25, eIF-2A, PIM-3, PKA C-α, and PKN2). They were further validated by pull-down/immunoblotting experiments as well as kinase inhibition assays. Further studies are needed to better understand the exact relevance of Dasatinib and its pharmacological effects in relation to these newly identified cellular targets. The approach developed herein should be amenable to the study of many of the existing reversible drugs/drug candidates.

Inflammasomes in intestinal inflammation and cancer.

Inflammasomes are multi-protein complexes that mediate activation of caspase-1, which promotes secretion of the proinflammatory cytokines interleukin-1ß and interleukin-18 and pyroptosis, a form of phagocyte cell death induced by bacterial pathogens. Members of the Nod-like receptor family (including Nlrp1, Nlrp3, and Nlrc4), the DNA sensor Aim2, the adaptor apoptosis-associated speck-like protein (ASC), and pro-caspase-1 are important components of inflammasomes. Stimulation with specific microbial and endogenous molecules leads to inflammasome assembly and caspase-1 activation. Inflammasomes are believed to mediate host defense against microbial pathogens and tissue homeostasis within the intestine, and their dysregulation might contribute to inflammatory diseases and intestinal cancer. Improving our understanding of inflammasome signaling pathways could provide insights into the pathogenesis of many gastrointestinal disorders and the development of therapeutic targets and approaches to treat diseases such as inflammatory bowel diseases and gastrointestinal cancers.

High fat stems tumor immune surveillance.

In a recent issue of Cell Stem Cell, Beyaz et al. show that high-fat diets promote tumorigenesis by reducing major histocompatibility complex (MHC) class II expression in intestinal stem cells. Dietary modulation of epithelial MHC II expression is regulated by the gut microbiota.