Diet, microbiota, and the mucus layer: The guardians of our health

The intestinal tract is an ecosystem in which the resident microbiota lives in symbiosis with its host. This symbiotic relationship is key to maintaining overall health, with dietary habits of the host representing one of the main external factors shaping the microbiome-host relationship. Diets high in fiber and low in fat and sugars, as opposed to Western and high-fat diets, have been shown to have a beneficial effect on intestinal health by promoting the growth of beneficial bacteria, improve mucus barrier function and immune tolerance, while inhibiting pro-inflammatory responses and their downstream effects. On the contrary, diets low in fiber and high in fat and sugars have been associated with alterations in microbiota composition/functionality and the subsequent development of chronic diseases such as food allergies, inflammatory bowel disease, and metabolic disease. In this review, we provided an updated overview of the current understanding of the connection between diet, microbiota, and health, with a special focus on the role of Western and high-fat diets in shaping intestinal homeostasis by modulating the gut microbiota

The Goblet Cell Protein Clca1 (Alias mClca3 or Gob-5) Is Not Required for Intestinal Mucus Synthesis, Structure and Barrier Function in Naive or DSS- Challenged Mice

The secreted, goblet cell-derived protein Clca1 (chloride channel regulator, calcium-activated-1) has been linked to diseases with mucus overproduction, including asthma and cystic fibrosis. In the intestine Clca1 is found in the mucus with an abundance and expression pattern similar to Muc2, the major structural mucus component. We hypothesized that Clca1 is required for the synthesis, structure or barrier function of intestinal mucus and therefore compared wild type and Clca1-deficient mice under naive and at various time points of DSS (dextran sodium sulfate)-challenged conditions. The mucus phenotype in Clca1-deficient compared to wild type mice was systematically characterized by assessment of the mucus protein composition using proteomics, immunofluorescence and expression analysis of selected mucin genes on mRNA level. Mucus barrier integrity was assessed in-vivo by analysis of bacterial penetration into the mucus and translocation into sentinel organs combined analysis of the fecal microbiota and ex-vivo by assessment of mucus penetrability using beads. All of these assays revealed no relevant differences between wild type and Clca1-deficient mice under steady state or DSS-challenged conditions in mouse colon. Clca1 is not required for mucus synthesis, structure and barrier function in the murine colon

Microbial experience through housing in a farmyard-type environment alters intestinal barrier properties in mouse colons

Abstract To close the gap between ultra-hygienic research mouse models and the much more environmentally exposed conditions of humans, we have established a system where laboratory mice are raised under a full set of environmental factors present in a naturalistic, farmyard-type habitat—a process we have called feralization. In previous studies we have shown that feralized (Fer) mice were protected against colorectal cancer when compared to conventionally reared laboratory mice (Lab). However, the protective mechanisms remain to be elucidated. Disruption of the protective intestinal barrier is an acknowledged player in colorectal carcinogenesis, and in the current study we assessed colonic mucosal barrier properties in healthy, feralized C57BL/6JRj male mice. While we found no effect of feralization on mucus layer properties, higher expression of genes encoding the mucus components Fcgbp and Clca1 still suggested mucus enforcement due to feralization. Genes encoding other proteins known to be involved in bacterial defense (Itln1, Ang1, Retnlb) and inflammatory mechanisms (Zbp1, Gsdmc2) were also higher expressed in feralized mice, further suggesting that the Fer mice have an altered intestinal mucosal barrier. These findings demonstrate that microbial experience conferred by housing in a farmyard-type environment alters the intestinal barrier properties in mice possibly leading to a more robust protection against disease. Future studies to unravel regulatory roles of feralization on intestinal barrier should aim to conduct proteomic analyses and in vivo performance of the feralized mice intestinal barrier

Obesity-associated microbiota contributes to mucus layer defects in genetically obese mice

The intestinal mucus layer is a physical barrier separating the tremendous number of gut bacteria from the host epithelium. Defects in the mucus layer have been linked to metabolic diseases, but previous studies predominantly investigated mucus function during high-caloric/low-fiber dietary interventions, thus making it difficult to separate effects mediated directly through diet quality from potential obesity-dependent effects. As such, we decided to examine mucus function in mouse models with metabolic disease to distinguish these factors. Here we show that, in contrast to their lean littermates, genetically obese (ob/ob) mice have a defective inner colonic mucus layer that is characterized by increased penetrability and a reduced mucus growth rate. Exploiting the coprophagic behavior of mice, we next co-housed ob/ob and lean mice to investigate if the gut microbiota contributed to these phenotypes. Co-housing rescued the defect of the mucus growth rate, whereas mucus penetrability displayed an intermediate phenotype in both mouse groups. Of note, non-obese diabetic mice with high blood glucose levels displayed a healthy colonic mucus barrier, indicating that the mucus defect is obesity- rather than glucose-mediated. Thus, our data suggest that the gut microbiota community of obesity-prone mice may regulate obesity-associated defects in the colonic mucosal barrier, even in the presence of dietary fiber

Transglutaminase 3 crosslinks the secreted gel-forming mucus component Mucin-2 and stabilizes the colonic mucus layer

The colonic mucus layer is organized as a two-layered system providing a physical barrier against pathogens and simultaneously harboring the commensal flora. The factors contributing to the organization of this gel network are not well understood. In this study, the impact of transglutaminase activity on this architecture was analyzed. Here, we show that transglutaminase TGM3 is the major transglutaminase-isoform expressed and synthesized in the colon. Furthermore, intrinsic extracellular transglutaminase activity in the secreted mucus was demonstrated in vitro and ex vivo. Absence of this acyl-transferase activity resulted in faster degradation of the major mucus component the MUC2 mucin and changed the biochemical properties of mucus. Finally, TGM3-deficient mice showed an early increased susceptibility to Dextran Sodium Sulfate-induced colitis. Here, we report that natural isopeptide cross-linking by TGM3 is important for mucus homeostasis and protection of the colon from inflammation, reducing the risk of colitis

The Nlrp6 inflammasome is not required for baseline colonic inner mucus layer formation or function

The inner mucus layer (IML) is a critical barrier that protects the colonic epithelium from luminal threats and inflammatory bowel disease. Innate immune signaling is thought to regulate IML formation via goblet cell Nlrp6 inflammasome activity that controls secretion of the mucus structural component Muc2. We report that isolated colonic goblet cells express components of several inflammasomes; however, analysis of IML properties in multiple inflammasome-deficient mice, including littermate-controlled Nlrp6−/−, detect a functional IML barrier in all strains. Analysis of mice lacking inflammasome substrate cytokines identifies a defective IML in Il18−/− mice, but this phenotype is ultimately traced to a microbiota-driven, Il18-independent effect. Analysis of phenotypic transfer between IML-deficient and IML-intact mice finds that the Bacteroidales family S24-7 (Muribaculaceae) and genus Adlercrutzia consistently positively covary with IML barrier function. Together, our results demonstrate that baseline IML formation and function is independent of inflammasome activity and highlights the role of the microbiota in determining IML barrier function

Strategies to facilitate implementation and sustainability of large system transformations : a case study of a national program for improving quality of care for elderly people

BACKGROUND: Large-scale change initiatives stimulating change in several organizational systems in the health and social care sector are challenging both to lead and evaluate. There is a lack of systematic research that can enrich our understanding of strategies to facilitate large system transformations in this sector. The purpose of this study was to examine the characteristics of core activities and strategies to facilitate implementation and change of a national program aimed at improving life for the most ill elderly people in Sweden. The program outcomes were also addressed to assess the impact of these strategies. METHODS: A longitudinal case study design with multiple data collection methods was applied. Archival data (n = 795), interviews with key stakeholders (n = 11) and non-participant observations (n = 23) were analysed using content analysis. Outcome data was obtained from national quality registries. RESULTS: This study presents an approach for implementing a large national change program that is characterized by initial flexibility and dynamism regarding content and facilitation strategies and a growing complexity over time requiring more structure and coordination. The description of activities and strategies show that the program management team engaged a variety of stakeholders and actor groups and accordingly used a palate of different strategies. The main strategies used to influence change in the target organisations were to use regional improvement coaches, regional strategic management teams, national quality registries, financial incentives and annually revised agreements. Interactive learning sessions, intense communication, monitor and measurements, and active involvement of different experts and stakeholders, including elderly people, complemented these strategies. Program outcomes showed steady progress in most of the five target areas, less so for the target of achieving coordinated care. CONCLUSIONS: There is no blue-print on how to approach the challenging task of leading large scale change programs in complex contexts, but our conclusion is that more attention has to be given to the multidimensional strategies that program management need to consider. This multidimensionality comprises different strategies depending on types of actors, system levels, contextual factors, program progress over time, program content, types of learning and change processes, and the conditions for sustainability

<i>Clca1</i>^<i>-/-</i> has no effect on mucus growth, responsiveness and penetrability in <i>Clca1</i>^<i>-/-</i> mice.

<p>(A) After flushing distal colon explants, mucus thickness and growth were similar in <i>Clca1</i>^<i>-/-</i> mice (dotted lines) compared to WT (filled lines). After CCh stimulation, an increase in mucus thickness compared to unstimulated explants was observed both in WT and in <i>Clca1</i>^<i>-/-</i> mice. Ctrl = control. (B) The growth rate was constant during unstimulated conditions whereas a significant growth rate increase in response to CCh was evident in both groups shortly after its addition. No significant difference was observed between the groups. Ctrl = control. (C) <i>Ex vivo</i> mucus penetrability assessment using bacteria-sized beads (1 μm, red) and confocal microscopy was performed. Representative z-stack projections from WT and <i>Clca1</i>^<i>-/-</i> mucus 30 minutes after tissue mounting both showed a clear separation between the tissue (blue) and the beads (red). Scale bars 50 μm. (D) The impenetrable mucus thickness, measured as the distance between the tissue and the sedimented beads in the confocal z-stacks did not differ between WT and <i>Clca1</i>^<i>-/-</i> mice. ns = non-significant. (E) FISH with a general bacterial 16S probe (EUB338, red), counterstained for Muc2 (anti-MUC2-C3, green) and DNA (Hoechst 34580, blue) in sections from distal colon confirmed the impenetrability of the inner mucus layer both in WT and <i>Clca1</i>^<i>-/-</i> mice with a clear separation of the tissue and bacteria. i = inner mucus layer. Scale bars 100 μm. n = 5 per group. Data are presented as mean ± SEM. ^## p < 0.01, ^### p < 0.001 for WT Ctrl vs. WT CCh; ****p < 0.0001 for <i>Clca1</i>^<i>-/-</i> Ctrl vs. <i>Clca1</i>^<i>-/-</i> CCh.</p