IL-25 Treatment Improves Metabolic Syndrome in High-Fat Diet and Genetic Models of Obesity.

INTRODUCTION: Endemic obesity is considered the driving force for the dramatic increase in incidence of type 2 diabetes (T2D). There is mounting evidence that chronic, low-grade inflammation driven by Th1/Th17 cells and M1 macrophages, is a critical link between obesity and insulin resistance. IL-25 promotes development of a Th2 immune response and M2 macrophages that counteract the inflammation associated with obesity and T2D. METHODS: Mice were fed a high-fat diet (HFD) for 16 weeks and then treated with IL-25 or BSA as a control for 21 days. Body weight, blood glucose levels, intraperitoneal glucose tolerance, and gene expression were evaluated in mice treated with BSA or IL-25. Ob/ob mice fed a normal control diet were also treated with BSA or IL-25 and body weight and blood glucose levels were measured. Transepithelial electrical resistance and sodium-linked glucose absorption were determined in muscle-free small intestinal tissue and glucose absorption assessed in vitro in intestinal epithelial and skeletal muscle cell lines. RESULTS: Administration of IL-25 to HFD fed mice reversed glucose intolerance, an effect mediated in part by reduction in SGLT-1 activity and Glut2 expression. Importantly, the improved glucose tolerance in HFD mice treated with IL-25 was maintained for several weeks post-treatment indicating long-term changes in glucose metabolism in obese mice. Glucose intolerance was also reversed by IL-25 treatment in genetically obese ob/ob mice without inducing weight loss. In vitro studies demonstrated that glucose absorption was inhibited by IL-25 treatment in the epithelial IPEC-1 cells but increased glucose absorption in the L6 skeletal muscle cells. This supports a direct cell-specific effect of IL-25 on glucose metabolism. CONCLUSION: These results suggest that the IL-25 pathway may be a useful target for the treatment of metabolic syndrome.

Bidirectional brain-gut interactions and chronic pathological changes after traumatic brain injury in mice.

OBJECTIVES: Traumatic brain injury (TBI) has complex effects on the gastrointestinal tract that are associated with TBI-related morbidity and mortality. We examined changes in mucosal barrier properties and enteric glial cell response in the gut after experimental TBI in mice, as well as effects of the enteric pathogen Citrobacter rodentium (Cr) on both gut and brain after injury. METHODS: Moderate-level TBI was induced in C57BL/6mice by controlled cortical impact (CCI). Mucosal barrier function was assessed by transepithelial resistance, fluorescent-labelled dextran flux, and quantification of tight junction proteins. Enteric glial cell number and activation were measured by Sox10 expression and GFAP reactivity, respectively. Separate groups of mice were challenged with Cr infection during the chronic phase of TBI, and host immune response, barrier integrity, enteric glial cell reactivity, and progression of brain injury and inflammation were assessed. RESULTS: Chronic CCI induced changes in colon morphology, including increased mucosal depth and smooth muscle thickening. At day 28 post-CCI, increased paracellular permeability and decreased claudin-1 mRNA and protein expression were observed in the absence of inflammation in the colon. Colonic glial cell GFAP and Sox10 expression were significantly increased 28days after brain injury. Clearance of Cr and upregulation of Th1/Th17 cytokines in the colon were unaffected by CCI; however, colonic paracellular flux and enteric glial cell GFAP expression were significantly increased. Importantly, Cr infection in chronically-injured mice worsened the brain lesion injury and increased astrocyte- and microglial-mediated inflammation. CONCLUSION: These experimental studies demonstrate chronic and bidirectional brain-gut interactions after TBI, which may negatively impact late outcomes after brain injury.

Type 3 muscarinic receptors contribute to intestinal mucosal homeostasis and clearance of Nippostrongylus brasiliensis through induction of TH2 cytokines.

Despite increased appreciation for the role of nicotinic receptors in the modulation of and response to inflammation, the contribution of muscarinic receptors to mucosal homeostasis, clearance of enteric pathogens, and modulation of immune cell function remains relatively undefined. Uninfected and Nippostrongylus brasiliensis-infected wild-type and type 3 muscarinic receptor (M3R)-deficient (Chrm3(-/-)) mice were studied to determine the contribution of M3R to mucosal homeostasis as well as host defense against the TH2-eliciting enteric nematode N. brasiliensis Intestinal permeability and expression of TH1/TH17 cytokines were increased in uninfected Chrm3(-/-) small intestine. Notably, in Chrm3(-/-) mice infected with N. brasiliensis, small intestinal upregulation of TH2 cytokines was attenuated and nematode clearance was delayed. In Chrm3(-/-) mice, TH2-dependent changes in small intestinal function including smooth muscle hypercontractility, increased epithelial permeability, decreased epithelial secretion and absorption, and goblet cell expansion were absent despite N. brasiliensis infection. These findings identify an important role for M3R in host defense and clearance of N. brasiliensis, and support the expanding role of cholinergic muscarinic receptors in maintaining mucosal homeostasis.

Mechanisms Involved in the Development of the Chronic Gastrointestinal Syndrome in Nonhuman Primates after Total-Body Irradiation with Bone Marrow Shielding.

In this study, nonhuman primates (NHPs) exposed to lethal doses of total body irradiation (TBI) within the gastrointestinal (GI) acute radiation syndrome range, sparing ∼5% of bone marrow (TBI-BM5), were used to evaluate the mechanisms involved in development of the chronic GI syndrome. TBI increased mucosal permeability in the jejunum (12-14 Gy) and proximal colon (13-14 Gy). TBI-BM5 also impaired mucosal barrier function at doses ranging from 10-12.5 Gy in both small intestine and colon. Timed necropsies of NHPs at 6-180 days after 10 Gy TBI-BM5 showed that changes in small intestine preceded those in the colon. Chronic GI syndrome in NHPs is characterized by continued weight loss and intermittent GI syndrome symptoms. There was a long-lasting decrease in jejunal glucose absorption coincident with reduced expression of the sodium-linked glucose transporter. The small intestine and colon showed a modest upregulation of several different pro-inflammatory mediators such as NOS-2. The persistent inflammation in the post-TBI-BM5 period was associated with a long-lasting impairment of mucosal restitution and a reduced expression of intestinal and serum levels of alkaline phosphatase (ALP). Mucosal healing in the postirradiation period is dependent on sparing of stem cell crypts and maturation of crypt cells into appropriate phenotypes. At 30 days after 10 Gy TBI-BM5, there was a significant downregulation in the gene and protein expression of the stem cell marker Lgr5 but no change in the gene expression of enterocyte or enteroendocrine lineage markers. These data indicate that even a threshold dose of 10 Gy TBI-BM5 induces a persistent impairment of both mucosal barrier function and restitution in the GI tract and that ALP may serve as a biomarker for these events. These findings have important therapeutic implications for the design of medical countermeasures.

Type 3 Muscarinic Receptors Contribute to Clearance of Citrobacter rodentium.

BACKGROUND: The role of muscarinic receptors in mucosal homeostasis, response to enteric pathogens, and modulation of immune cell function is undefined. METHODS: The contribution of type 3 muscarinic receptors (M3R) to mucosal homeostasis within the colon and host defense against Citrobacter rodentium was determined in uninfected and C. rodentium-infected WT and M3R-deficient (Chrm3) mice. In addition, WT and Chrm3 bone marrow-derived macrophages were studied to determine the ability of M3R to modulate macrophage phenotype and function. RESULTS: In Chrm3 mice, clearance of C. rodentium was delayed despite an amplified TH1/TH17 response. Delayed clearance of C. rodentium from Chrm3 mice was associated with prolonged adherence of bacteria to colonic mucosa, decreased goblet cell number, and decreased mucin 2 gene expression. Treatment of bone marrow-derived macrophages with bethanechol, a muscarinic-selective agonist, induced a classically activated macrophage phenotype, which was dependent on M3R expression. Chrm3 bone marrow-derived macrophages retained their ability to attain a classically activated macrophage phenotype when treated with the TH1 cytokine IFN-γ. CONCLUSIONS: In Chrm3 mice, mucin production is attenuated and is associated with prolonged adherence of C. rodentium to colonic mucosa. The immune response, as characterized by production of TH1/TH17 cytokines, in C. rodentium-infected Chrm3 mice is intact. In addition, M3R activity promotes the development of classically activated macrophages. Our data establish a role for M3R in host defense against C. rodentium through effects on goblet cell mucus production and in the modulation of macrophage phenotype and function.