BACKGROUND & AIMS A high-fat diet (HFD) can cause serious health problems, including alteration of gastrointestinal transit, the exact mechanism of which is not clear. Several microRNAs (miRNAs) are involved in energy homeostasis, lipid metabolism, and HFD-induced weight gain. We investigated the role of miRNAs in HFD-induced damage to the enteric nervous system. METHODS Male mice were fed a HFD (60% calories from fat) or regular diets (18% calories from fat) for 11 weeks. Mice on regular diets and HFDs were given intraperitoneal injections of Mir375 inhibitor or a negative control. Body weights, food intake, stool indices, and gastrointestinal transit (following Evans blue gavage) were measured. An enteric neuronal cell line (IM-PEN) and primary enteric neurons were used for in vitro studies. RESULTS A HFD delayed intestinal transit, which was associated with increased apoptosis and loss of neurons from colonic myenteric neurons. Mice fed a low-palmitate HFD did not develop a similar phenotype. Palmitate caused apoptosis of enteric neuronal cells associated with mitochondrial dysfunction and endoplasmic reticulum stress. Palmitate significantly increased the expression of Mir375 in vitro; transfection of cells with a Mir375 inhibitor prevented the palmitate-induced enteric neuronal cell apoptosis. Mir375 expression was increased in myenteric ganglia of mice fed HFD, and associated with decreased levels of Mir375 target mRNAs, including Pdk1. Systemic injection of a Mir375 inhibitor for 5 weeks prevented HFD-induced delays in intestinal transit and morphologic changes. CONCLUSIONS HFD delay colonic transit, partly by inducing apoptosis in enteric neuronal cells. This effect is mediated by Mir375 and is associated with reduced levels of Pdk1. Mir375 might be targeted to increase survival of enteric neurons and gastrointestinal motility.

There is a well-documented association of matrix metalloproteinase-9 (MMP-9) and receptor Notch-1 overexpression in colon cancer. We recently showed that MMP-9 is also upregulated in colitis, where it modulates tissue damage and goblet cell differentiation via proteolytic cleavage of Notch-1. In this study, we investigated whether MMP-9 is critical for colitis-associated colon cancer (CAC). Mice that are wild type (WT) or MMP-9 nullizygous (MMP-9 −/− ) were used for in vivo studies and the human enterocyte cell line Caco2-BBE was used for in vitro studies. CAC was induced in mice using an established carcinogenesis protocol that involves exposure to azoxymethane followed by treatment with dextran sodium sulfate. MMP-9 −/− mice exhibited increased susceptibility to CAC relative to WT mice. Elevations in tumor multiplicity, size, and mortality were associated with increased proliferation and decreased apoptosis. Tumors formed in MMP-9

Background Neuro-immune interactions play a significant role in regulating the severity of inflammation. Our previous work demonstrated that neuropeptide Y (NPY) is up regulated in the enteric nervous system (ENS) during murine colitis, and that NPY knockout mice exhibit reduced inflammation. Here we investigated if NPY expression during inflammation is induced by tumor necrosis factor (TNF), the main pro-inflammatory cytokine. Methods Utilizing primary enteric neurons and colon explant cultures from WT and NPY knockout (NPY−/−) mice, we determined if NPY knockdown modulates TNF release and epithelial permeability. Further we assessed if NPY expression is inducible by TNF in enteric neuronal cells and mouse model of experimental colitis, utilizing the TNF inhibitors-etanercept (blocks transmembrane and soluble TNF) and XPro1595 (blocks soluble TNF only). Results We found that enteric neurons express TNF receptors (TNFR1 and R2). Primary enteric neurons from NPY−/− mice produced less TNF compared to WT. Further, TNF activated NPY promoter in enteric neurons via phospho-c-jun. NPY−/− mice had decreased intestinal permeability. In vitro, NPY increased epithelial permeability via phosphatidyl inositol-3-kinase (PI3-K)-induced pore-forming claudin-2. TNF inhibitors attenuated NPY expression in vitro and in vivo. TNF-inhibitor-treated colitic mice exhibited reduced NPY expression and inflammation, reduced oxidative stress, enhanced neuronal survival and improved colonic motility. XPro1595 had more protective effects on neuronal survival and motility compared to etanercept. Conclusions We demonstrate a novel TNF-NPY cross talk that modulates inflammation, barrier functions and colonic motility during inflammation. It is also suggested that selective blocking of soluble TNF maybe a better therapeutic option than using anti-TNF antibodies.