Nucleotide-binding oligomerization domain 2 signaling promotes hyperresponsive macrophages and colitis in IL-10-deficient mice.

IL-10 contributes to the maintenance of intestinal homeostasis via the regulation of inflammatory responses to enteric bacteria. Loss of IL-10 signaling results in spontaneous colitis in mice and early onset enterocolitis in humans. Nucleotide-binding oligomerization domain (NOD) 2 is an intracellular receptor of bacterial peptidoglycan products, and, although NOD2 mutations are associated with Crohn's disease, the precise role of NOD2 in the development of intestinal inflammation remains undefined. To determine the role of NOD2 in the development of colitis on the clinically relevant genetic background of IL-10-deficient signaling, we generated mice lacking IL-10 and NOD2 (IL-10(-/-)NOD2(-/-)). Loss of NOD2 in IL-10(-/-) mice resulted in significant amelioration of chronic colitis, indicating that NOD2 signaling promotes the development of intestinal inflammation in IL-10(-/-) mice. Contrary to previous reports investigating immune function in NOD2(-/-) mice, T cell proliferative capacity and IL-2 production were not impaired, and immune polarization toward type 1 immunity was not affected. However, loss of NOD2 in IL-10-deficient macrophages reduced IL-6, TNF-α, and IL-12p40 production in response to bacterial stimulation. Further analysis of the intrinsic macrophage response before the onset of inflammation revealed that, in the absence of IL-10, synergistic signaling between various TLRs and NOD2 resulted in hyperresponsive, proinflammatory macrophages, thus providing the appropriate immune environment for the development of colitis. Data presented in this study demonstrate that NOD2 signaling contributes to intestinal inflammation that arises through loss of IL-10 and provides mechanistic insight into the development of colitis in inflammatory bowel disease patients with impaired IL-10 signaling.

Host genetics and environmental factors regulate ecological succession of the mouse colon tissue-associated microbiota.

BACKGROUND: The integration of host genetics, environmental triggers and the microbiota is a recognised factor in the pathogenesis of barrier function diseases such as IBD. In order to determine how these factors interact to regulate the host immune response and ecological succession of the colon tissue-associated microbiota, we investigated the temporal interaction between the microbiota and the host following disruption of the colonic epithelial barrier. METHODOLOGY/PRINCIPAL FINDINGS: Oral administration of DSS was applied as a mechanistic model of environmental damage of the colon and the resulting inflammation characterized for various parameters over time in WT and Nod2 KO mice. RESULTS: In WT mice, DSS damage exposed the host to the commensal flora and led to a migration of the tissue-associated bacteria from the epithelium to mucosal and submucosal layers correlating with changes in proinflammatory cytokine profiles and a progressive transition from acute to chronic inflammation of the colon. Tissue-associated bacteria levels peaked at day 21 post-DSS and declined thereafter, correlating with recruitment of innate immune cells and development of the adaptive immune response. Histological parameters, immune cell infiltration and cytokine biomarkers of inflammation were indistinguishable between Nod2 and WT littermates following DSS, however, Nod2 KO mice demonstrated significantly higher tissue-associated bacterial levels in the colon. DSS damage and Nod2 genotype independently regulated the community structure of the colon microbiota. CONCLUSIONS/SIGNIFICANCE: The results of these experiments demonstrate the integration of environmental and genetic factors in the ecological succession of the commensal flora in mammalian tissue. The association of Nod2 genotype (and other host polymorphisms) and environmental factors likely combine to influence the ecological succession of the tissue-associated microflora accounting in part for their association with the pathogenesis of inflammatory bowel diseases.

Effects of cannabinoids on the anxiety-like response in mice.

Several pieces of anatomical, biochemical and pharmacological evidence indicate that the endocannabinoid system via CB1 receptors is implicated in the control of emotional behavior. However, previous studies have reported unclear and contradictory results concerning the role of cannabinoids in anxiety. The aim of the present study was to examine the influence of the cannabinoid agonist WIN 55,212-2 (1 and 5 mg/kg), the CB1 antagonist AM 281 (1, 2 and 4 mg/kg), the inhibitor of anandamide hydrolysis AACOCF3 (1 and 4 mg/kg) and the inhibitor of anandamide transporter AM404 (1 and 4 mg/kg) on the anxiety-like response in mice in the light/dark box test. WIN 55,212-2 (5 mg/kg) induced the anxiogenic-like effect accompanied by motor inhibition, AACOCF3 (4 mg/kg) induced the selective anxiolytic-like effect, whereas AM404 and AM281 were without effect. Pretreatment with AM281 (2 mg/kg) blocked the anxiogenic-like and sedative responses induced by WIN 55, 212-2, as well as the anxiolytic-like effect of AACOCF3. These results support the hypothesis that the endocannabinoid system is involved in the regulation of anxiety-like behavior, and also suggest that the inhibitors of anandamide hydrolysis might be potential anxiolytic drugs.