Metabolic syndrome is a group of obesity-related metabolic abnormalities that increase an individual’s risk of developing type 2 diabetes and cardiovascular disease. Here, we show that mice genetically deficient in Toll-like receptor 5 (TLR5), a component of the innate immune system that is expressed in the gut mucosa and that helps defend against infection, exhibit hyperphagia and develop hallmark features of metabolic syndrome, including hyperlipidemia, hypertension, insulin resistance, and increased adiposity. These metabolic changes correlated with changes in the composition of the gut microbiota, and transfer of the gut microbiota from TLR5-deficient mice to wild-type germ-free mice conferred many features of metabolic syndrome to the recipients. Food restriction prevented obesity, but not insulin resistance, in the TLR5-deficient mice. These results support the emerging view that the gut microbiota contributes to metabolic disease and suggest that malfunction of the innate immune system may promote the development of metabolic syndrome.

Diabetes can result in loss of enteric neurons and subsequent gastrointestinal complications. The mechanism of enteric neuronal loss in diabetes is not known. We examined the effects of hyperglycemia on enteric neuronal survival and the effects of glial cell line-derived neurotrophic factor (GDNF) on modulating this survival. Exposure of primary enteric neurons to 20 mM glucose (hyperglycemia) for 24 hours resulted in a significant increase in apoptosis compared with 5 mM glucose (normoglycemia). Exposure to 20 mM glucose resulted in decreased Akt phosphorylation and enhanced nuclear translocation of forkhead box O3a (FOXO3a). Treatment of enteric neurons with GDNF ameliorated these changes. In streptozotocin-induced diabetic mice, there was evidence of myenteric neuronal apoptosis and reduced Akt phosphorylation. Diabetic mice had loss of NADPH diaphorase-stained myenteric neurons, delayed gastric emptying, and increased intestinal transit time. The pathophysiological effects of hyperglycemia (apoptosis, reduced Akt phosphorylation, loss of inhibitory neurons, motility changes) were reversed in diabetic glial fibrillary acidic protein-GDNF (GFAP-GDNF) Tg mice. In conclusion, we demonstrate that hyperglycemia induces neuronal loss through a reduction in Aktmediated survival signaling and that these effects are reversed by GDNF. GDNF may be a potential therapeutic target for the gastrointestinal motility disorders related to diabetes.

Background Gastrointestinal dysfunction is very common in diabetic patients. We assessed the changes in the colonic enteric nervous system using colectomy specimens and intestinal biopsies from diabetic subjects and age-matched controls. Methods In control and diabetic colons, we determined the total ganglion area (hematoxylin-eosin staining), changes in neuronal markers-protein gene product 9.5, peripherin, neuronal nitric oxide synthase (nNOS), neuropeptide Y (NPY), choline acetyl transferase (ChAT) and vasoactive intestinal peptide (by immunostaining), apoptosis (cleaved caspase-3 staining) and reduced glutathione levels. Superoxide dismutase mRNA was determined in enteric ganglia isolated by laser capture micro dissection. Isometric muscle recording was used to assess contraction and relaxation responses of colonic circular muscle strips. Apoptosis in enteric neurons under hyperglycemia in vitro was determined by cleaved caspase-3 Western blotting and protective effects of lipoic acid were evaluated. Key Results Diabetic subjects had higher incidence of lower gastrointestinal symptoms like constipation and diarrhea at baseline prior to surgery. Diabetic ganglia displayed significant decrease in ganglion size due to enhanced apoptosis and loss of peripherin, nNOS, NPY, and ChAT neurons.Reduced glutathione levels in the diabetic colon (HbA1C > 7%) were significantly less than the control, indicating increased oxidative stress. Colonic circular muscle strips from diabetic subjects showed impaired contraction and relaxation responses compared with the healthy controls. Hyperglycemia-induced cleaved caspase-3 in enteric neurons was reversed by lipoic acid. Conclusions & Inferences Our data demonstrate loss of enteric neurons in the colon due to increased oxidative stress and apoptosis which may cause the motility disturbances seen in human diabetes. Antioxidants may be of therapeutic value for preventing motility disorders in diabetes.

Background & AimsHigh-fat diet (HFD) feeding is associated with gastrointestinal motility disorders. We recently reported delayed colonic motility in mice fed a HFD for 11 weeks. In this study, we investigated the contributing role of gut microbiota in HFD-induced gut dysmotility.MethodsMale C57BL/6 mice were fed a HFD (60% kcal fat) or a regular/control diet (RD) (18% kcal fat) for 13 weeks. Serum and fecal endotoxin levels were measured, and relative amounts of specific gut bacteria in the feces were assessed by real-time polymerase chain reaction. Intestinal transit was measured by fluorescent-labeled marker and a bead expulsion test. Enteric neurons were assessed by immunostaining. Oligofructose (OFS) supplementation with RD or HFD for 5 weeks also was studied. In vitro studies were performed using primary enteric neurons and an enteric neuronal cell line.ResultsHFD-fed mice had reduced numbers of enteric nitrergic neurons and showed delayed gastrointestinal transit compared with RD-fed mice. HFD-fed mice had higher fecal Firmicutes and Escherichia coli and lower Bacteroidetes compared with RD-fed mice. OFS supplementation protected against enteric nitrergic neuron loss in HFD-fed mice, and improved intestinal transit time. OFS supplementation resulted in a reduction in fecal Firmicutes and Escherichia coli and serum endotoxin levels. In vitro, palmitate activation of TLR4 induced enteric neuronal apoptosis in a Phospho–c-Jun N-terminal kinase–dependent pathway. This apoptosis was prevented by a c-Jun N-terminal kinase inhibitor and in neurons from TLR4-/- mice.ConclusionsTogether our data suggest that intestinal dysbiosis in HFD-fed mice contribute to the delayed intestinal motility by inducing a TLR4-dependent neuronal loss. Manipulation of gut microbiota with OFS improved intestinal motility in HFD mice.