Intestinal commensal microbiota and cytokines regulate Fut2+ Paneth cells for gut defense

Paneth cells are intestinal epithelial cells that release antimicrobial peptides, such as α-defensin as part of host defense. Together with mesenchymal cells, Paneth cells provide niche factors for epithelial stem cell homeostasis. Here, we report two subtypes of murine Paneth cells, differentiated by their production and utilization of fucosyltransferase 2 (Fut2), which regulates α(1,2)fucosylation to create cohabitation niches for commensal bacteria and prevent invasion of the intestine by pathogenic bacteria. The majority of Fut2− Paneth cells were localized in the duodenum, whereas the majority of Fut2+ Paneth cells were in the ileum. Fut2+ Paneth cells showed higher granularity and structural complexity than did Fut2− Paneth cells, suggesting that Fut2+ Paneth cells are involved in host defense. Signaling by the commensal bacteria, together with interleukin 22 (IL-22), induced the development of Fut2+ Paneth cells. IL-22 was found to affect the α-defensin secretion system via modulation of Fut2 expression, and IL-17a was found to increase the production of α-defensin in the intestinal tract. Thus, these intestinal cytokines regulate the development and function of Fut2+ Paneth cells as part of gut defense.

Fatty acids produced by the gut microbiota dampen host inflammatory responses by modulating intestinal SUMOylation

The gut microbiota produces a wide variety of metabolites, which interact with intestinal cells and contribute to host physiology. These metabolites regulate intestinal cell activities by modulating either gene transcription or post-translational modifications of gut proteins. The effect of gut commensal bacteria on SUMOylation, an essential ubiquitin-like modification in intestinal physiology, remains however unknown. Here, we show that short chain fatty acids (SCFAs) and branched chain fatty acids (BCFAs) produced by the gut microbiota increase protein SUMOylation in different intestinal cell lines in a pH-dependent manner. We demonstrate that these metabolites induce an oxidative stress which inactivates intestinal deSUMOylases and promotes the hyperSUMOylation of chromatin-bound proteins. In order to determine the impact of these modifications on intestinal physiology, we focused on the NF-kappaB signaling pathway, a key player in inflammation known to be regulated by SUMOylation. We demonstrated that the hyperSUMOylation induced by SCFAs/BCFAs inhibits the activation of the NF-kappaB pathway in intestinal cells by blocking the degradation of the inhibitory factor IkappaBalpha in response to TNFalpha. This results in a decrease in pro-inflammatory cytokines expression, such as IL8 or CCL20, as well as a decrease in intestinal epithelial permeability in response to TNFalpha. Together, our results reveal that fatty acids produced by gut commensal bacteria regulate intestinal physiology by modulating SUMOylation and illustrate a new mechanism of dampening of host inflammatory responses by the gut microbiota.

Bacterial recognition by PGRP-SA and downstream signalling by Toll/DIF sustain commensal gut bacteria in Drosophila

The gut sets the immune and metabolic parameters for the survival of commensal bacteria. We report that in Drosophila, deficiency in bacterial recognition upstream of Toll/NF-κB signalling resulted in reduced density and diversity of gut bacteria. Translational regulation factor 4E-BP, a transcriptional target of Toll/NF-κB, mediated this host-bacteriome interaction. In healthy flies, Toll activated 4E-BP, which enabled fat catabolism, which resulted in sustaining of the bacteriome. The presence of gut bacteria kept Toll signalling activity thus ensuring the feedback loop of their own preservation. When Toll activity was absent, TOR-mediated suppression of 4E-BP made fat resources inaccessible and this correlated with loss of intestinal bacterial density. This could be overcome by genetic or pharmacological inhibition of TOR, which restored bacterial density. Our results give insights into how an animal integrates immune sensing and metabolism to maintain indigenous bacteria in a healthy gut.

Enteropathogenic Escherichia coli Mediates CoCrMo Particle-Induced Peri-Implant Osteolysis by Increasing Peripheral 5-HT

The human gut microbiota has been proven to have great effects on the regulation of bone health. However, the association between gut microbiota and particle-induced osteolysis, which is the primary cause of aseptic loosening, is still unknown. In this study, we used a combination of wide-spectrum antibiotics to eliminate the majority of gut microbiota and found that reduction of gut commensal bacteria significantly alleviated the progression of osteolysis, in which anaerobe was the biggest culprit in the exacerbation of osteolysis. Furthermore, colonization of enteropathogenic Escherichia coli (EPEC), a subspecies of anaerobe, could promote the development of particle-induced osteolysis by increasing the secretion of peripheral 5-hydroxytryptamine (5-HT) from the colon. Elevated 5-HT level decreased the phosphorylation of CREB and inhibited the proliferation of osteoblasts. Collectively, these results indicated EPEC colonization suppressed the bone formation and aggravated particle-induced osteolysis in vivo. Thus, clearance of EPEC is expected to become a potential preventive approach to treat debris-induced osteolysis and aseptic loosening.

Akkermansia Muciniphila induces chronic extramedullary hematopoiesis through cooperative IL-1R and TLR signals

Bacterial infections can activate and mobilize hematopoietic stem and progenitor cells (HSPCs) from the bone marrow (BM) to spleen, which is termed as extramedullary hematopoiesis (EMH). Recent studies suggest that commensal bacteria, particularly the microbiota, regulates not only the host immune system but also hematopoietic homeostasis. However, the impact of gut microbial species on hematopoietic pathology remains largely unknown. Here we found that systemic injection of Akkermansia muciniphila (A. m.), a mucin-degrading bacterium abundantly existing in the human gut rapidly activates BM myelopoiesis, and induces a slow but long-lasting hepato-splenomegaly, characterized by the expansion and differentiation of functional HSPCs, which we termed chronic EMH. Genetic deletion of Toll-like receptor-2 and -4 (TLR2/4) partially diminished A. m.-induced chronic EMH, while additional pharmacological inhibition of the interleukin-1 receptor (IL-1R) completely alleviated splenomegaly and EMH. Our results demonstrate that cooperative IL-1R- and TLR-mediated innate immune signals regulate commensal bacteria-driven EMH, which might be relevant for certain autoimmune disorders.

Antibacterial and antioxidant activity of different extracts obtained from Withania somnifera (Ashwagandha)

Ashwagandha (W. somnifera) is widely known as the queen of Indian Ayurveda. The objective of this study was to determine the antioxidant and antibacterial activity of the different parts of the Ashwagandha. The antioxidant activity of different extracts from different parts of Ashwagandha was determined using DPPH free radical scavenging method. Ashwaghanda root inhabiting bacteria was isolated using pour-plate technique. The agar well method and filter paper method were followed to assess the antibacterial activity of the extracts. Ethanol-water extracts (1:1 v/v) gave higher yield of extractable matter than methanol extracts. The antioxidant activity of fresh root extract was significantly higher than other parts of the plant (stem and leaves) as well as the plant material bought from open market. The minimal inhibitory concentration (MIC) values of Ethanol-water extract against MRSA, Candida Sp. and Salmonella Sp. were >256 mg/L. The commensal bacteria (Bacilli Sp.) inhabiting Ashwagandha roots displayed mild antibacterial activity against pathogenic P. aeruginosa. Keywords: Ashwaghanda, commensal bacteria, Antibacterial activity, Antioxidant activity, Crude extracts

Chemomicrobiome analysis of the ornithine molecule

Hepatoprotectors and prebiotic molecules that promote the growth of intestinal flora differ significantly in their effects on different representatives of the human microbiome. This work presents the results of a comparative chemomicrobiomic analysis of ornithine and reference molecules (S-ademetionine, ursodeoxycholic acid, lactulose, and fructose). For each of the studied molecules, estimates of the values of the area under the growth curve were obtained for a representative sample of human microbiota, which included 38 commensal bacteria (including bifidobacteria and lactobacilli) and the values of the minimum inhibitory concentrations (MIC) for 152 strains of pathogenic bacteria. It has been shown that ornithine, to a lesser extent than the reference molecules, stimulates the growth of pathogenic bacteria of the genera Aspergillus, Klebsiella, Pseudomonas, Staphylococcus and Candida fungi. Ornithine is also less likely to stimulate the growth of more aggressive bacteria (Biosafety Level 2) and to a greater extent less aggressive bacteria (Biosafety Level 1). By stimulating butyric and other short-chain fatty acid-producing microorganisms, ornithine can improve the profile of gut microbiota.

Xenobiotic receptors and the regulation of intestinal homeostasis - harnessing the chemical output of the intestinal microbiota

The commensal bacteria that reside in the gastrointestinal tract exist in a symbiotic relationship with the host, driving the development of the immune system and maintaining metabolic and tissue homeostasis in the local environment. The intestinal microbiota has the capacity to generate a wide array of chemical metabolites to which the cells of the intestinal mucosa are exposed. Host cells express xenobiotic receptors, such as the aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR), that can sense and respond to chemicals that are generated by non-host pathways. In this review, we will outline the physiological and immunological processes within the intestinal environment that are regulated by microbial metabolites through the activation of the AhR and PXR, with a focus on ligands generated by the step-wise catabolism of tryptophan.