Project description:Neural control of visceral organ function is essential for homeostasis and health. Intestinal peristalsis is critical for digestive physiology and host defence and is often dysregulated in gastrointestinal (GI) disorders. Luminal factors, such as diet and microbiota regulate neurogenic programs of gut motility, but the underlying molecular mechanisms remain unclear. Here we show that the transcription factor Aryl hydrocarbon Receptor (AhR) functions as a biosensor in intestinal neural circuits linking their functional output to the microbial environment of the gut lumen. Using nuclear RNA sequencing of mouse enteric neurons representing distinct intestinal segments and microbiota states, we demonstrate that the intrinsic neural networks of the colon exhibit unique transcriptional profiles controlled by the combined effects of host genetic programmes and microbial colonisation. Microbiota-induced expression of AhR in neurons of the distal gastrointestinal tract enables them to respond to the luminal environment and induce expression of neuron-specific effector mechanisms. Neuron-specific deletion of Ahr or constitutive overexpression of its negative feedback regulator CYP1A1, results in reduced peristaltic activity of the colon, similar to that observed in microbiota-depleted mice. Finally, expression of Ahr in enteric neurons of antibiotic-treated mice partially restores intestinal motility. Taken together, our experiments identify AhR signalling in enteric neurons as a regulatory node that integrates the luminal environment with the physiological output of intestinal neural circuits towards gut homeostasis and health. The enteric nervous system (ENS) encompasses the intrinsic neural networks of the gastrointestinal (GI) tract, which regulate most aspects of intestinal physiology, including peristalsis. In addition to host-specific genetic programmes, microbiota and diet have emerged as critical regulators of gut tissue physiology and changes in the microbial composition of the lumen often accompany GI disorders. We found that gut environmental sensor Aryl hydrocarbon receptor (AhR) is induced in colonic neurons in response to microbiota colonisation and regulates intestinal peristalsis in an AhR ligand-dependent manner. In this experiment, we used RNA sequencing to identify genes regulated in mouse colonic neurons by AhR activation.

Project description:Neural control of visceral organ function is essential for homeostasis and health. Intestinal peristalsis is critical for digestive physiology and host defence and is often dysregulated in gastrointestinal (GI) disorders. Luminal factors, such as diet and microbiota regulate neurogenic programs of gut motility, but the underlying molecular mechanisms remain unclear. Here we show that the transcription factor Aryl hydrocarbon Receptor (AhR) functions as a biosensor in intestinal neural circuits linking their functional output to the microbial environment of the gut lumen. Using nuclear RNA sequencing of mouse enteric neurons representing distinct intestinal segments and microbiota states, we demonstrate that the intrinsic neural networks of the colon exhibit unique transcriptional profiles controlled by the combined effects of host genetic programmes and microbial colonisation. Microbiota-induced expression of AhR in neurons of the distal gastrointestinal tract enables them to respond to the luminal environment and induce expression of neuron-specific effector mechanisms. Neuron-specific deletion of Ahr or constitutive overexpression of its negative feedback regulator CYP1A1, results in reduced peristaltic activity of the colon, similar to that observed in microbiota-depleted mice. Finally, expression of Ahr in enteric neurons of antibiotic-treated mice partially restores intestinal motility. Taken together, our experiments identify AhR signalling in enteric neurons as a regulatory node that integrates the luminal environment with the physiological output of intestinal neural circuits towards gut homeostasis and health. The enteric nervous system (ENS) encompasses the intrinsic neural networks of the gastrointestinal (GI) tract, which regulate most aspects of intestinal physiology, including peristalsis. In addition to host-specific genetic programmes, microbiota and diet have emerged as critical regulators of gut tissue physiology and changes in the microbial composition of the lumen often accompany GI disorders. However the molecular mechanisms by which gut enviromental factors regulate ENS homeostasis remain unknown. In order to address this issue, we used RNA sequencing to identify genes specifically upregulated in mouse colonic neurons in response to microbial colonisation.

Project description:Proteases constitute the largest enzyme gene family in vertebrates with intracellular and secreted proteases having critical roles in cellular and organ physiology. Intestinal tract contains diverse set of proteases mediating digestion, microbial responses, epithelial and immune signaling. Transit of chyme through the intestinal tract results in significant suppression of proteases. Although endogenous protease inhibitors have been identified, the broader mechanisms underlying protease regulation in the intestinal tract remains unclear. The objective of this study was to determine microbial regulation of proteolytic activity in intestinal tract using phenotype of post-infection irritable bowel syndrome, a condition characterized by high fecal proteolytic activity. Proteases of host pancreatic origin (chymotrypsin like pancreatic elastase 2A, 3B and trypsin 2) drove proteolytic activity. Of the 14 differentially abundant taxa, high proteolytic activity state was characterized by complete absence of the commensal Alistipes putredinis. Germ free mice had very high proteolytic activity (10-fold of specific-pathogen free mice) which dropped significantly upon humanization with microbiota from healthy volunteers. In contrast, high proteolytic activity microbiota failed to inhibit it, a defect that corrected with fecal microbiota transplant as well as addition of A. putredinis. These mice also had increased intestinal permeability similar to that seen in patients. Microbiota β-glucuronidases mediate bilirubin deconjugation and unconjugated bilirubin is an inhibitor of serine proteases. We found that high proteolytic activity patients had lower urobilinogen levels, a product of bilirubin deconjugation. Mice colonized with β-glucuronidase overexpressing E. coli demonstrated significant inhibition of proteolytic activity and treatment with β-glucuronidase inhibitors increased it. The findings establish that specific commensal microbiota mediates effective inhibition of host pancreatic proteases and maintains intestinal barrier function through the production of β-glucuronidases. This suggests an important homeostatic role for commensal intestinal microbiota.

Project description:Traumatic brain injury (TBI) initiates not only complex neurovascular and glial changes within the brain but also pathophysiological responses that extend beyond the central nervous system. The peripheral response to TBI has become an intensive area of research, as these systemic perturbations can induce dysfunction in multiple organ systems. As there are no approved therapeutics for TBI, it is imperative that we investigate the peripheral response to TBI to identify targets for future intervention. Of particular interest is the gastrointestinal (GI) system. Even in the absence of polytrauma, brain-injured individuals are at increased risk of suffering from GI-related morbidity and mortality. Symptoms such as intestinal dysmotility, inflammation, ulceration, and fecal incontinence can drastically diminish quality of life. The GI tract is inhabited by trillions of microbes that have been implicated as modulators of many neurological disorders. Clinical and preclinical studies implicate gut dysbiosis, a pathological imbalance in the normally symbiotic microbiota, as both a consequence of TBI as well as a contributing factor to brain damage. However, our understanding of this interplay is still limited. While relatively little is known about the effects of TBI on the structure and function of the GI tract, prior studies report that experimental TBI induces intestinal barrier dysfunction and morphological changes. To confirm these findings in the current model of TBI, male C57BL/6J mice underwent a sham control or a controlled cortical impact (CCI) procedure to induce a contusive brain injury, and intestinal permeability was assessed at 4 h, 8 h, 1 d, and 3 d post-injury. An acute, transient increase in permeability was observed at 4 h after CCI. Histological analyses of the ileum and colon at multiple time points from 4 h to 4 wks revealed no overt morphological changes, suggesting that CCI induced a short-lived physiologic dysfunction without major structural alterations to the GI tract. As the microbiome is a modulator of GI physiology, we performed 16s gene sequencing on fecal samples collected prior to and over the first month after CCI or sham injury. Microbial community diversity was assessed using common metrics of alpha and beta diversity. Alpha diversity was lower in the CCI injury group and beta diversity differed among groups, although these effects were not observed in all metrics. Subsequent differential abundance analysis revealed that the phylum Verrucamicrobiota was increased in CCI mice at 1, 2, and 3 d post-injury when compared to sham mice. Subsequent qPCR identified the Verrucamicrobiota species as Akkermansia Muciniphila, an obligate anaerobe that resides in and helps regulate the intestinal mucus layer and barrier. To determine whether TBI promotes changes to the GI tract favorable for the proliferation of A. muciniphila, mucus-producing goblet cells and the level of GI hypoxia were evaluated. Goblet cell density in the medial colon was significantly increased at 1 d, while colon hypoxia was significantly increased at 3 d. Taken together, these studies show that CCI induces transient intestinal barrier dysfunction followed by increased goblet cell density and hypoxia in the colon with a concomitant increase in A. muciniphila that may suggest a compensatory response to systemic stress after TBI.

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