Inulin fibre promotes microbiota-derived bile acids and type 2 inflammation.

Dietary fibres can exert beneficial anti-inflammatory effects through microbially fermented short-chain fatty acid metabolites^1,2, although the immunoregulatory roles of most fibre diets and their microbiota-derived metabolites remain poorly defined. Here, using microbial sequencing and untargeted metabolomics, we show that a diet of inulin fibre alters the composition of the mouse microbiota and the levels of microbiota-derived metabolites, notably bile acids. This metabolomic shift is associated with type 2 inflammation in the intestine and lungs, characterized by IL-33 production, activation of group 2 innate lymphoid cells and eosinophilia. Delivery of cholic acid mimics inulin-induced type 2 inflammation, whereas deletion of the bile acid receptor farnesoid X receptor diminishes the effects of inulin. The effects of inulin are microbiota dependent and were reproduced in mice colonized with human-derived microbiota. Furthermore, genetic deletion of a bile-acid-metabolizing enzyme in one bacterial species abolishes the ability of inulin to trigger type 2 inflammation. Finally, we demonstrate that inulin enhances allergen- and helminth-induced type 2 inflammation. Taken together, these data reveal that dietary inulin fibre triggers microbiota-derived cholic acid and type 2 inflammation at barrier surfaces with implications for understanding the pathophysiology of allergic inflammation, tissue protection and host defence.

Interleukin-33 Induces the Enzyme Tryptophan Hydroxylase 1 to Promote Inflammatory Group 2 Innate Lymphoid Cell-Mediated Immunity.

Group 2 innate lymphoid cells (ILC2s) regulate immunity, inflammation, and tissue homeostasis. Two distinct subsets of ILC2s have been described: steady-state natural ILC2s and inflammatory ILC2s, which are elicited following helminth infection. However, how tissue-specific cues regulate these two subsets of ILC2s and their effector functions remains elusive. Here, we report that interleukin-33 (IL-33) promotes the generation of inflammatory ILC2s (ILC2INFLAM) via induction of the enzyme tryptophan hydroxylase 1 (Tph1). Tph1 expression was upregulated in ILC2s upon activation with IL-33 or following helminth infection in an IL-33-dependent manner. Conditional deletion of Tph1 in lymphocytes resulted in selective impairment of ILC2INFLAM responses and increased susceptibility to helminth infection. Further, RNA sequencing analysis revealed altered gene expression in Tph1 deficient ILC2s including inducible T cell co-stimulator (Icos). Collectively, these data reveal a previously unrecognized function for IL-33, Tph1, and ICOS in promoting inflammatory ILC2 responses and type 2 immunity at mucosal barriers.

Modulation of the fungal mycobiome is regulated by the chitin-binding receptor FIBCD1.

Host-microbiota interactions are critical in regulating mammalian health and disease. In addition to bacteria, parasites, and viruses, beneficial communities of fungi (the mycobiome) are important modulators of immune- and tissue-homeostasis. Chitin is a major component of the fungal cell wall, and fibrinogen C containing domain 1 (FIBCD1) is a chitin-binding protein; however, the role of this molecule in influencing host-mycobiome interactions in vivo has never been examined. Here, we identify direct binding of FIBCD1 to intestinal-derived fungi and demonstrate that epithelial-specific expression of FIBCD1 results in significantly reduced fungal colonization and amelioration of fungal-driven intestinal inflammation. Collectively, these results identify FIBCD1 as a previously unrecognized microbial pattern recognition receptor through which intestinal epithelial cells can recognize and control fungal colonization, limit fungal dysbiosis, and dampen intestinal inflammation.

Response to Fungal Dysbiosis by Gut-Resident CX3CR1+ Mononuclear Phagocytes Aggravates Allergic Airway Disease.

Sensing of the gut microbiota, including fungi, regulates mucosal immunity. Whether fungal sensing in the gut can influence immunity at other body sites is unknown. Here we show that fluconazole-induced gut fungal dysbiosis has persistent effects on allergic airway disease in a house dust mite challenge model. Mice with a defined community of bacteria, but lacking intestinal fungi were not susceptible to fluconazole-induced dysbiosis, while colonization with a fungal mixture recapitulated the detrimental effects. Gut-resident mononuclear phagocytes (MNPs) expressing the fractalkine receptor CX3CR1 were essential for the effect of gut fungal dysbiosis on peripheral immunity. Depletion of CX3CR1+ MNPs or selective inhibition of Syk signaling downstream of fungal sensing in these cells ameliorated lung allergy. These results indicate that disruption of intestinal fungal communities can have persistent effects on peripheral immunity and aggravate disease severity through fungal sensing by gut-resident CX3CR1+ MNPs.

ß2-adrenergic receptor-mediated negative regulation of group 2 innate lymphoid cell responses.

The type 2 inflammatory response is induced by various environmental and infectious stimuli. Although recent studies identified group 2 innate lymphoid cells (ILC2s) as potent sources of type 2 cytokines, the molecular pathways controlling ILC2 responses are incompletely defined. Here we demonstrate that murine ILC2s express the ß2-adrenergic receptor (ß2AR) and colocalize with adrenergic neurons in the intestine. ß2AR deficiency resulted in exaggerated ILC2 responses and type 2 inflammation in intestinal and lung tissues. Conversely, ß2AR agonist treatment was associated with impaired ILC2 responses and reduced inflammation in vivo. Mechanistically, we demonstrate that the ß2AR pathway is a cell-intrinsic negative regulator of ILC2 responses through inhibition of cell proliferation and effector function. Collectively, these data provide the first evidence of a neuronal-derived regulatory circuit that limits ILC2-dependent type 2 inflammation.

Polygenic Risk of Spasmodic Dysphonia is Associated With Vulnerable Sensorimotor Connectivity.

Spasmodic dysphonia (SD), or laryngeal dystonia, is an isolated task-specific dystonia of unknown causes and pathophysiology that selectively affects speech production. Using next-generation whole-exome sequencing in SD patients, we computed polygenic risk score from 1804 genetic markers based on a genome-wide association study in another form of similar task-specific focal dystonia, musician's dystonia. We further examined the associations between the polygenic risk score, resting-state functional connectivity abnormalities within the sensorimotor network, and SD clinical characteristics. We found that the polygenic risk of dystonia was significantly associated with decreased functional connectivity in the left premotor/primary sensorimotor and inferior parietal cortices in SD patients. Reduced connectivity of the inferior parietal cortex was correlated with the age of SD onset. The polygenic risk score contained a significant number of genetic variants lying near genes related to synaptic transmission and neural development. Our study identified a polygenic contribution to the overall genetic risk of dystonia in the cohort of SD patients. Associations between the polygenic risk and reduced functional connectivity of the sensorimotor and inferior parietal cortices likely represent an endophenotypic imaging marker of SD, while genes involved in synaptic transmission and neuron development may be linked to the molecular pathophysiology of this disorder.

The neuropeptide neuromedin U stimulates innate lymphoid cells and type 2 inflammation.

The type 2 cytokines interleukin (IL)-4, IL-5, IL-9 and IL-13 have important roles in stimulating innate and adaptive immune responses that are required for resistance to helminth infection, promotion of allergic inflammation, metabolic homeostasis and tissue repair. Group 2 innate lymphoid cells (ILC2s) produce type 2 cytokines, and although advances have been made in understanding the cytokine milieu that promotes ILC2 responses, how ILC2 responses are regulated by other stimuli remains poorly understood. Here we demonstrate that ILC2s in the mouse gastrointestinal tract co-localize with cholinergic neurons that express the neuropeptide neuromedin U (NMU). In contrast to other haematopoietic cells, ILC2s selectively express the NMU receptor 1 (NMUR1). In vitro stimulation of ILC2s with NMU induced rapid cell activation, proliferation, and secretion of the type 2 cytokines IL-5, IL-9 and IL-13 that was dependent on cell-intrinsic expression of NMUR1 and Gαq protein. In vivo administration of NMU triggered potent type 2 cytokine responses characterized by ILC2 activation, proliferation and eosinophil recruitment that was associated with accelerated expulsion of the gastrointestinal nematode Nippostrongylus brasiliensis or induction of lung inflammation. Conversely, worm burden was higher in Nmur1-/- mice than in control mice. Furthermore, use of gene-deficient mice and adoptive cell transfer experiments revealed that ILC2s were necessary and sufficient to mount NMU-elicited type 2 cytokine responses. Together, these data indicate that the NMU-NMUR1 neuronal signalling circuit provides a selective mechanism through which the enteric nervous system and innate immune system integrate to promote rapid type 2 cytokine responses that can induce anti-microbial, inflammatory and tissue-protective type 2 responses at mucosal sites.

Nonmonotonic diffusion of particles among larger attractive crowding spheres.

We study the diffusive motion of particles among fixed spherical crowders. The diffusers interact with the crowders through a combination of a hard-core repulsion and a short-range attraction. The long-time effective diffusion coefficient of the diffusers is found to depend nonmonotonically on the strength of their attraction to the crowders. That is, for a given concentration of crowders, a weak attraction to the crowders enhances diffusion. We show that this counterintuitive fact can be understood in terms of the mesoscopic excess chemical potential landscape experienced by the diffuser. The roughness of this excess chemical potential landscape quantitatively captures the nonmonotonic dependence of the diffusion rate on the strength of crowder-diffuser attraction; thus, it is a purely static predictor of dynamic behavior. The mesoscopic view given here provides a unified explanation for enhanced diffusion effects that have been found in various systems of technological and biological interest.

Macromolecular crowding as a regulator of gene transcription.

Studies of macromolecular crowding have shown its important effects on molecular transport and interactions in living cells. Less clear is the effect of crowding when its influence is incorporated into a complex network of interactions. Here, we explore the effects of crowding in the cell nucleus on a model of gene transcription as a network of reactions involving transcription factors, RNA polymerases, and DNA binding sites for these proteins. The novelty of our approach is that we determine the effects of crowding on the rates of these reactions using Brownian dynamics and Monte Carlo simulations, allowing us to integrate molecular-scale information, such as the shapes and sizes of each molecular species, into the rate equations of the model. The steady-state cytoplasmic mRNA concentration shows several regimes with qualitatively different dependences on the volume fraction, ϕ, of crowding agents in the nucleus, including a broad range of parameter values where it depends nonmonotonically on ϕ, with maximum mRNA production occurring at a physiologically relevant value. The extent of this crowding dependence can be modulated by a variety of means, suggesting that the transcriptional output of a gene can be regulated jointly by the local level of macromolecular crowding in the nucleus, together with the local concentrations of polymerases and DNA-binding proteins, as well as other properties of the gene's physical environment.

Coarsening dynamics of domains in lipid membranes.

We investigate isothermal diffusion and growth of micron-scale liquid domains within membranes of free-floating giant unilamellar vesicles with diameters between 80 and 250 µm. Domains appear after a rapid temperature quench, when the membrane is cooled through a miscibility phase transition such that coexisting liquid phases form. In membranes quenched far from a miscibility critical point, circular domains nucleate and then progress within seconds to late stage coarsening in which domains grow via two mechanisms 1), collision and coalescence of liquid domains, and 2), Ostwald ripening. Both mechanisms are expected to yield the same growth exponent, α = 1/3, where domain radius grows as time(α). We measure α = 0.28 ± 0.05, in excellent agreement. In membranes close to a miscibility critical point, the two liquid phases in the membrane are bicontinuous. A quench near the critical composition results in rapid changes in morphology of elongated domains. In this case, we measure α = 0.50 ± 0.16, consistent with theory and simulation.