Emerging mechanisms by which endocannabinoids and their derivatives modulate bacterial populations within the gut microbiome

Bioactive lipids such as endocannabinoids serve as important modulators of host health and disease through their effects on various host functions including central metabolism, gut physiology, and immunity. Furthermore, changes to the gut microbiome caused by external factors such as diet or by disease development have been associated with altered endocannabinoid tone and disease outcomes. These observations suggest the existence of reciprocal relationships between host lipid signaling networks and bacterial populations that reside within the gut. Indeed, endocannabinoids and their congeners such as N-acylethanolamides have been recently shown to alter bacterial growth, functions, physiology, and behaviors, therefore introducing putative mechanisms by which these bioactive lipids directly modulate the gut microbiome. Moreover, these potential interactions add another layer of complexity to the regulation of host health and disease pathogenesis that may be mediated by endocannabinoids and their derivatives. This mini review will summarize recent literature that exemplifies how N-acylethanolamides and monoacylglycerols including endocannabinoids can impact bacterial populations in vitro and within the gut microbiome. We also highlight exciting preclinical studies that have engineered gut bacteria to synthesize host N-acylethanolamides or their precursors as potential strategies to treat diseases that are in part driven by aberrant lipid signaling, including obesity and inflammatory bowel diseases

Iron and the intestinal microbiota in inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are chronic, immune-mediated disorders that are the result of inappropriate immune responses towards a subset of resident intestinal microbes in genetically susceptible individuals. Epidemiological studies have correlated dietary factors with increased risk for disease development, exacerbation and relapse in IBD patients. Iron is of particular interest because of the clinical concern of disease exacerbation upon oral iron supplementation in anemic IBD patients. Moreover, iron can selectively modulate the growth, physiology and function of numerous bacterial taxa, although the precise impact on specific resident intestinal bacteria remains largely unexplored. We therefore hypothesized that intestinal iron availability modulates the ecological structure and proinflammatory potential of the intestinal microbiota. To explore this hypothesis, we investigated how iron availability alters the composition of the intestinal microbiota and impacts the physiology and proinflammatory potential of adherent invasive Escherichia coli (AIEC), a distinct pathotype of enteric resident E. coli associated with IBD. In inflammation-resistant wild type mice, decreasing luminal iron concentrations during community assembly resulted in compositional changes consistent with a dysbiotic state, including a bloom in endogenous E. coli. Aggregation of the resident AIEC strain NC101, which is dependent on both cellulose production and iron availability, influenced subsequent interactions with macrophages. When monoassociated in germ free, inflammation-susceptible interleukin-10-deficient (Il10-/-) mice, abrogation of cellulose production in NC101 delayed onset of colitis, suggesting that cellulose may be a novel factor that enhances the proinflammatory potential of AIEC. Consistent with our in vivo observations, NC101 cellulose production corresponded with increased resistance against macrophage phagocytosis and enhanced macrophage proinflammatory responses when bacterial iron availability was restricted. When colonized with a complex microbiota, dietary iron supplementation also limited colitis development in Il10-/- mice. Taken together, these studies suggest that decreasing iron availability enhances the proinflammatory potential of the intestinal microbiota and highlight the complex interplay between host, microbial and environmental factors in the development of IBD.Doctor of Philosoph

Adherent-Invasive Escherichia coli Production of Cellulose Influences Iron-Induced Bacterial Aggregation, Phagocytosis, and Induction of Colitis

Adherent-invasive Escherichia coli (AIEC), a functionally distinct subset of resident intestinal E. coli associated with Crohn's disease, is characterized by enhanced epithelial adhesion and invasion, survival within macrophages, and biofilm formation. Environmental factors, such as iron, modulate E. coli production of extracellular structures, which in turn influence the formation of multicellular communities, such as biofilms, and bacterial interactions with host cells. However, the physiological and functional responses of AIEC to variable iron availability have not been thoroughly investigated. We therefore characterized the impact of iron on the physiology of AIEC strain NC101 and subsequent interactions with macrophages. Iron promoted the cellulose-dependent aggregation of NC101. Bacterial cells recovered from the aggregates were more susceptible to phagocytosis than planktonic cells, which corresponded with the decreased macrophage production of the proinflammatory cytokine interleukin-12 (IL-12) p40. Prevention of aggregate formation through the disruption of cellulose production reduced the phagocytosis of iron-exposed NC101. In contrast, under iron-limiting conditions, where NC101 aggregation is not induced, the disruption of cellulose production enhanced NC101 phagocytosis and decreased macrophage secretion of IL-12 p40. Finally, abrogation of cellulose production reduced NC101 induction of colitis when NC101 was monoassociated in inflammation-prone Il10 −/− mice. Taken together, our results introduce cellulose as a novel physiological factor that impacts host-microbe-environment interactions and alters the proinflammatory potential of AIEC

Enterococcus faecalis Gelatinase Mediates Intestinal Permeability via Protease-Activated Receptor 2

Microbial protease-mediated disruption of the intestinal epithelium is a potential mechanism whereby a dysbiotic enteric microbiota can lead to disease. This mechanism was investigated using the colitogenic, protease-secreting enteric microbe Enterococcus faecalis . Caco-2 and T-84 epithelial cell monolayers and the mouse colonic epithelium were exposed to concentrated conditioned media (CCM) from E. faecalis V583 and E. faecalis lacking the gelatinase gene ( gelE ). The flux of fluorescein isothiocyanate (FITC)-labeled dextran across monolayers or the mouse epithelium following exposure to CCM from parental or mutant E. faecalis strains indicated paracellular permeability. A protease-activated receptor 2 (PAR2) antagonist and PAR2-deficient (PAR2 −/− ) mice were used to investigate the role of this receptor in E. faecalis -induced permeability. Gelatinase (GelE) purified from E. faecalis V583 was used to confirm the ability of this protease to induce epithelial cell permeability and activate PAR2. The protease-mediated permeability of colonic epithelia from wild-type (WT) and PAR2 −/− mice by fecal supernatants from ulcerative colitis patients was assessed. Secreted E. faecalis proteins induced permeability in epithelial cell monolayers, which was reduced in the absence of gelE or by blocking PAR2 activity. Secreted E. faecalis proteins induced permeability in the colonic epithelia of WT mice that was absent in tissues from PAR2 −/− mice. Purified GelE confirmed the ability of this protease to induce epithelial cell permeability via PAR2 activation. Fecal supernatants from ulcerative colitis patients induced permeability in the colonic epithelia of WT mice that was reduced in tissues from PAR2 −/− mice. Our investigations demonstrate that GelE from E. faecalis can regulate enteric epithelial permeability via PAR2

Microbial-derived signals modulate numerous hallmarks of cancer through diverse mechanisms.

<p>Microbial-derived signals modulate numerous hallmarks of cancer through diverse mechanisms.</p

Members of the intestinal microbiota associated with cancer development and resistance.

<p>Members of the intestinal microbiota associated with cancer development and resistance.</p

Adherent-Invasive Escherichia coli Production of Cellulose Influences Iron-Induced Bacterial Aggregation, Phagocytosis, and Induction of Colitis

Adherent-invasive Escherichia coli (AIEC), a functionally distinct subset of resident intestinal E. coli associated with Crohn's disease, is characterized by enhanced epithelial adhesion and invasion, survival within macrophages, and biofilm formation. Environmental factors, such as iron, modulate E. coli production of extracellular structures, which in turn influence the formation of multicellular communities, such as biofilms, and bacterial interactions with host cells. However, the physiological and functional responses of AIEC to variable iron availability have not been thoroughly investigated. We therefore characterized the impact of iron on the physiology of AIEC strain NC101 and subsequent interactions with macrophages. Iron promoted the cellulose-dependent aggregation of NC101. Bacterial cells recovered from the aggregates were more susceptible to phagocytosis than planktonic cells, which corresponded with the decreased macrophage production of the proinflammatory cytokine interleukin-12 (IL-12) p40. Prevention of aggregate formation through the disruption of cellulose production reduced the phagocytosis of iron-exposed NC101. In contrast, under iron-limiting conditions, where NC101 aggregation is not induced, the disruption of cellulose production enhanced NC101 phagocytosis and decreased macrophage secretion of IL-12 p40. Finally, abrogation of cellulose production reduced NC101 induction of colitis when NC101 was monoassociated in inflammation-prone Il10(−/−) mice. Taken together, our results introduce cellulose as a novel physiological factor that impacts host-microbe-environment interactions and alters the proinflammatory potential of AIEC