Inflammasomes are multi-protein complexes that function as sensors of endogenous or exogenous damage-associated molecular patterns. Here we show that deficiency of NLRP6 in mouse colonic epithelial cells results in reduced IL-18 levels and altered fecal microbiota characterized by expanded representation of the bacterial phyla Bacteroidetes (Prevotellaceae) and TM7. NLRP6 inflammasome-deficient mice were characterized by spontaneous intestinal hyperplasia, inflammatory cell recruitment, and exacerbation of chemical colitis induced by exposure to dextran sodium sulfate (DSS). Cross-fostering and cohousing experiments revealed that the colitogenic activity of this microbiota is transferable to neonatal or adult wild-type mice, leading to exacerbation of DSS colitis via induction of CCL5. Antibiotic treatment and electron microscopy studies further supported the role of Prevotellaceae as a key representative of this microbiota-associated phenotype. Altogether, perturbations in this inflammasome pathway, including NLRP6, ASC, caspase-1 and IL-18 may constitute a predisposing or initiating event in some cases of human IBD.

The current model of apoptosis holds that upstream signals lead to activation of downstream effector caspases. We generated mice deficient in the two effectors, caspase 3 and caspase 7, which died immediately after birth with defects in cardiac development. Fibroblasts lacking both enzymes were highly resistant to both mitochondrial and death receptor-mediated apoptosis, displayed preservation of mitochondrial membrane potential, and had defective nuclear translocation of apoptosis-inducing factor (AIF). Furthermore, the early apoptotic events of Bax translocation and cytochrome c release were also delayed. We conclude that caspases 3 and 7 are critical mediators of mitochondrial events of apoptosis.Mitochondria play a central role in apoptosis. Mitochondrial outer membrane permeabilization (MOMP) leads to release of proapoptotic factors such as cytochrome c and AIF (1). Furthermore, loss of mitochondrial membrane potential (Δψ m ) is thought to contribute to cell death by disruption of normal mitochondrial function (2, 3). Interaction of members of the Bcl-2 family of proteins regulates MOMP, the key event of cytochrome c release into the cytoplasm (3, 4). What is less clear, however, is the precise role of caspase proteases in mitochondrial events of apoptosis. Although upstream caspases, such as caspase 2 and caspase 8, affect mitochondrial events in both death-receptor and mitochondrial pathways of apoptosis, either directly or through interaction with Bcl-2 family members, the role of presumed downstream "effector" caspases in this process is less clear (5, 6). Therefore, we studied the two highly related effectors, caspase 3 and caspase 7, to elucidate their functions in apoptosis.* To whom correspondence should be addressed. richard.flavell@yale.edu. We generated caspase 7 −/− mice ( fig. S1), which were born in ratios consistent with Mendelian inheritance. They had normal appearance, organ morphology, and lymphoid development. When caspase 7 −/− mouse embryonic fibroblasts (MEFs) were treated with inducers of apoptosis, they exhibited a slight survival advantage as compared with wild-type MEFs. Apoptosis caused by a range of insults in other caspase 7 −/− cells proceeded normally, however, including the death of activated T cells following stimulation of the T cell receptor, thymocyte apoptosis, Fas-mediated death of B cells, and Fas-mediated death of hepatocytes ( fig. S2). Supporting Online MaterialCaspase 3, which is structurally similar to caspase 7, might compensate for the lack of caspase 7, which would lead to this relatively mild antiapoptotic phenotype (7,8). Thus, we bred caspase 7 −/− mice to caspase 3 −/− mice previously described by our laboratory (9). The embryonic stem cells containing the mutation were from the 129/SvJ genetic background. Mice derived from these embryonic stem cells were backcrossed six generations onto the C57BL/6 background. We obtained no live caspase 3 −/− /caspase 7 −/− double-knockout (DKO) mice when progeny were genotyped at an age of 10 to 14 days. DKO mic...

Chronic mucosal inflammation and tissue damage predisposes patients to the development of colorectal cancer (CRC)1. This association could be explained by the hypothesis that the same factors and pathways important for wound healing also promote tumorigenesis. A sensor of tissue damage should induce these factors to promote tissue repair and regulate their action to prevent development of cancer. IL-22, a cytokine of the IL-10 superfamily, plays an important role for colonic epithelial cell repair, and is increased in the blood and intestine of IBD patients2, 3. This cytokine can be neutralized by the soluble IL-22 receptor, known as the IL-22 binding protein (IL-22BP, IL-22RA2), however the significance of endogenous IL-22BP in vivo and the pathways that regulate this receptor are unknown4, 5. We describe herein that IL-22BP plays a crucial role in controlling tumorigenesis and epithelial cell proliferation in the colon. IL-22BP is highly expressed by dendritic cells (DC) in the colon in steady state conditions. Sensing of intestinal tissue damage via the NLRP3 or NLRP6 inflammasomes led to an IL-18-dependent down regulation of IL-22BP, thereby increasing the ratio of IL-22/IL-22BP. IL-22, which is induced during intestinal tissue damage, exerted protective properties during the peak of damage, but promoted tumor development if uncontrolled during the recovery phase.Thus the IL-22-IL-22BP axis critically regulates intestinal tissue repair and tumorigenesis in the colon.

Interleukin 23 (IL-23) and IL-17 have been linked to the pathogenesis of several chronic inflammatory disorders, including inflammatory bowel disease. Yet as an important function for IL-23 is emerging, the function of IL-17 in inflammatory bowel disease remains unclear. Here we demonstrate IL-17A-mediated protection in the CD45RBhi transfer model of colitis. An accelerated wasting disease elicited by T cells deficient in IL-17A correlated with higher expression of genes encoding T helper type 1-type cytokines in colon tissue. IL-17A also modulated T helper type 1 polarization in vitro. Furthermore, T cells deficient in the IL-17 receptor elicited an accelerated, aggressive wasting disease relative to that elicited by wild-type T cells in recipient mice. Our data demonstrate a protective function for IL-17 and identify T cells as not only the source but also a target of IL-17 in vivo.

SUMMARY Genome-wide studies have identified thousands of long noncoding RNAs (lncRNAs) lacking protein coding capacity. However, most lncRNAs are expressed at a very low level, and in most cases there is no genetic evidence to support their in vivo function. Malat1 (metastasis associated lung adenocarcinoma transcript 1) is among the most abundant and highly conserved lncRNAs, and it exhibits an uncommon 3′-end processing mechanism. In addition, its specific nuclear localization, developmental regulation, and dysregulation in cancer are suggestive of it having a critical biological function. We have characterized a Malat1 loss-of-function genetic model that indicates Malat1 is not essential for mouse pre- and post-natal development. Furthermore, depletion of Malat1 does not impact global gene expression, splicing factor level and phosphorylation status, or alternative pre-mRNA splicing. However, among a small number of genes that were dysregulated in adult Malat1 knockout mice, many were Malat1 neighboring genes, thus indicating a potential cis regulatory role of Malat1 gene transcription.