Enterocyte-Derived TAK1 Signaling Prevents Epithelium Apoptosis and the Development of Ileitis and Colitis

Recent studies have revealed that TAK1 kinase is an essential intermediate in several innate immune signaling pathways. In this study, we investigated the role of TAK1 signaling in maintaining intestinal homeostasis by generating enterocytes-specific constitutive and inducible gene deleted TAK1 mice. We found that enterocyte-specific constitutive TAK1 deleted mice spontaneously developed intestinal inflammation as observed by histological analysis and enhanced expression of IL-1β, MIP2 and IL-6 around the time of birth, which was accompanied by significant enterocytes apoptosis. When TAK1 was deleted in the intestinal epithelium of 4-week-old mice using an inducible knockout system, enterocytes underwent apoptosis and intestinal inflammation developed within 2–3 days following the initiation of gene deletion. We found that enterocytes apoptosis and intestinal inflammation were strongly attenuated when enterocyte-specific constitutive TAK1 deleted mice were crossed to TNF receptor 1 (TNFR1)−/− mice. However, these mice later (>14 days) developed ileitis and colitis. Thus, TAK1 signaling in enterocytes is essential for preventing TNF-dependent epithelium apoptosis and the TNF-independent development of ileitis and colitis. We propose that aberration in TAK1 signaling might disrupt intestinal homeostasis and favor the development of inflammatory disease

Intestinal Epithelial-Derived TAK1 Signaling Is Essential for Cytoprotection against Chemical-Induced Colitis

We have previously reported that intestinal epithelium-specific TAK1 deleted mice exhibit severe inflammation and mortality at postnatal day 1 due to TNF-induced epithelial cell death. Although deletion of TNF receptor 1 (TNFR1) can largely rescue those neonatal phenotypes, mice harboring double deletion of TNF receptor 1 (TNFR1) and intestinal epithelium-specific deletion of TAK1 (TNFR1KO/TAK1(IE)KO) still occasionally show increased inflammation. This indicates that TAK1 is important for TNF-independent regulation of intestinal integrity.In this study, we investigated the TNF-independent role of TAK1 in the intestinal epithelium. Because the inflammatory conditions were sporadically developed in the double mutant TNFR1KO/TAK1(IE)KO mice, we hypothesize that epithelial TAK1 signaling is important for preventing stress-induced barrier dysfunction. To test this hypothesis, the TNFR1KO/TAK1(IE)KO mice were subjected to acute colitis by administration of dextran sulfate sodium (DSS). We found that loss of TAK1 significantly augments DSS-induced experimental colitis. DSS induced weight loss, intestinal damages and inflammatory markers in TNFR1KO/TAK1(IE)KO mice at higher levels compared to the TNFR1KO control mice. Apoptosis was strongly induced and epithelial cell proliferation was decreased in the TAK1-deficient intestinal epithelium upon DSS exposure. These suggest that epithelial-derived TAK1 signaling is important for cytoprotection and repair against injury. Finally, we showed that TAK1 is essential for interleukin 1- and bacterial components-induced expression of cytoprotective factors such as interleukin 6 and cycloxygenase 2.Homeostatic cytokines and microbes-induced intestinal epithelial TAK1 signaling regulates cytoprotective factors and cell proliferation, which is pivotal for protecting the intestinal epithelium against injury

Neuronal GPCR controls innate immunity by regulating noncanonical unfolded protein response genes

The unfolded protein response (UPR), which is activated when unfolded or misfolded proteins accumulate in the endoplasmic reticulum, has been implicated in the normal physiology of immune defense and in several human diseases, including diabetes, cancer, neurodegenerative disease, and inflammatory disease. In this study, we found that the nervous system controlled the activity of a noncanonical UPR pathway required for innate immunity in Caenorhabditis elegans. OCTR-1, a putative octopamine G protein-coupled catecholamine receptor (GPCR, G protein-coupled receptor), functioned in sensory neurons designated ASH and ASI to actively suppress innate immune responses by down-regulating the expression of noncanonical UPR genes pqn/abu in nonneuronal tissues. Our findings suggest a molecular mechanism by which the nervous system may sense inflammatory responses and respond by controlling stress-response pathways at the organismal level

Distinct Roles of Sensory Neurons in Mediating Pathogen Avoidance and Neuropeptide-Dependent Immune Regulation

Summary: Increasing evidence implies an extensive and universal interaction between the immune system and the nervous system. Previous studies showed that OCTR-1, a neuronal G-protein-coupled receptor (GPCR) analogous to human norepinephrine receptors, functions in sensory neurons to control the gene expression of both microbial killing pathways and the unfolded protein response (UPR) in Caenorhabditis elegans. Here, we found that OCTR-1-expressing neurons, ASH, are involved in controlling innate immune pathways. In contrast, another group of OCTR-1-expressing neurons, ASI, was shown to promote pathogen avoidance behavior. We also identified neuropeptide NLP-20 and AIA interneurons, which are responsible for the integration of conflicting cues and behaviors, as downstream components of the ASH/ASI neural circuit. These findings provide insights into a neuronal network involved in regulating pathogen defense mechanisms in C. elegans and might have broad implications for the strategies utilized by metazoans to balance the energy-costly immune activation and behavioral response. : Cao et al. show that chemosensory neurons have the ability to coordinate behavioral and immune responses upon bacterial infections in C. elegans. The underlying mechanisms involve interneurons and neuropeptide signaling and provide insights into tactics that may be used by animals when dealing with pathogen threats. Keywords: neural-immune communication, behavioral immunology, infection, innate immunity, neural circuit, host-pathogen interaction, p38, xbp-1, unfolded protein response, UP

Antitumor activity of the MEK inhibitor trametinib on intestinal polyp formation in Apc[Δ716] mice involves stromal COX-2

Extracellular signal-regulated kinase is an MAPK that is most closely associated with cell proliferation, and the MEK/ERK signaling pathway is implicated in various human cancers. Although epidermal growth factor receptor, KRAS, and BRAF are considered major targets for colon cancer treatment, the precise roles of the MEK/ERK pathway, one of their major downstream effectors, during colon cancer development remain to be determined. Using Apc[Δ716] mice, a mouse model of familial adenomatous polyposis and early-stage sporadic colon cancer formation, we show that MEK/ERK signaling is activated not only in adenoma epithelial cells, but also in tumor stromal cells including fibroblasts and vascular endothelial cells. Eight-week treatment of Apc[Δ716] mice with trametinib, a small-molecule MEK inhibitor, significantly reduced the number of polyps in the large size class, accompanied by reduced angiogenesis and tumor cell proliferation. Trametinib treatment reduced the COX-2 level in Apc[Δ716] tumors in vivo and in primary culture of intestinal fibroblasts in vitro. Antibody array analysis revealed that trametinib and the COX-2 inhibitor rofecoxib both reduced the level of CCL2, a chemokine known to be essential for the growth of Apc mutant polyps, in intestinal fibroblastsin vitro. Consistently, trametinib treatment reduced the Ccl2 mRNA level in Apc[Δ716] tumors in vivo. These results suggest that MEK/ERK signaling plays key roles in intestinal adenoma formation in Apc[Δ716] mice, at least in part, through COX-2 induction in tumor stromal cells

Loss of TAK1 disrupts homeostatic proliferation of the intestinal epithelium.

<p>A Distal colon was isolated from TNFR1KO and TNFR1KO/TAK1^IEKO mice treated with water or 2.5% DSS for 3 days. Mice were injected with 0.1 mg/g of 5-bromo-2′-deoxyuridine (BrdU) 2 h prior to sacrifice. Immunostaining for BrdU was performed and BrdU-positive cells were counted. Each bar represents a mean value±SE (N = 5 per group, ** = p<0.01). B Representative BrdU staining and H&E staining at 3 days DSS treatment. Original magnifications; ×200 (BrdU staining) and ×40 (H&E staining).</p