Objective Inflammatory bowel diseases (IBDs) feature multiple cellular stress responses, including endoplasmic reticulum (ER) unfolded protein responses (UPRs). UPRs represent autoregulatory pathways that adjust organelle capacity to cellular demand. A similar mechanism, mitochondrial UPR (mtUPR), has been described for mitochondria. ER UPR in intestinal epithelial cells (IECs) contributes to the development of intestinal inflammation, and since mitochondrial alterations and dysfunction are implicated in the pathogenesis of IBDs, the authors characterised mtUPR in the context of intestinal inflammation. Methods Truncated ornithine transcarbamylase was used to selectively induce mtUPR in a murine IEC line. Dextran sodium sulphate (DSS) was administered to PKR (double-stranded-RNA-activated protein kinase) knockout mice to induce IEC stress in vivo and to test for their susceptibility to DSS-induced colitis. Expression levels of the mitochondrial chaperone chaperonin 60 (CPN60) and PKR were quantified in IECs from patients with IBDs and from murine models of colitis using immunohistochemistry and Western blot analysis. Results Selective mtUPR induction by truncated ornithine transcarbamylase transfection triggered the phosphorylation of eukaryotic translation initiation factor (eIF) 2α and cJun through the recruitment of PKR. Using pharmacological inhibitors and small inhibitory RNA, the authors identified mtUPR-induced eIF2α phosphorylation and transcription factor activation (cJun/AP1) as being dependent on the activities of the mitochondrial protease ClpP and the cytoplasmic kinase PKR. Pkr−/− mice failed to induce CPN60 in IECs upon DSS treatment at early time points and subsequently showed an almost complete resistance to DSS-induced colitis. Under inflammatory conditions, primary IECs from patients with IBDs and two murine models of colitis exhibited a strong induction of the mtUPR marker protein CPN60 associated with enhanced expression of PKR. Conclusion PKR integrates mtUPR into the disease-relevant ER UPR via eIF2α phosphorylation and AP1 activation. Induction of mtUPR and PKR was observed in IECs from murine models and patients with IBDs. The authors’ results indicate that PKR might link mitochondrial stress to intestinal inflammation.

Evidence has linked genetic predisposition and environmental exposures to the worldwide pandemic of inflammatory bowel diseases (IBD), but underlying biochemical events remain largely undefined. Here, we studied the gradual development of colitis in Interleukin 10 deficient mice using a combination of (i) histopathological analysis of intestinal sections, (ii) metabolic profiling of blood plasma, and (iii) measurement of plasma inflammatory biomarkers. Data integration using chemometric tools, including Independent Component Analysis, provided a new strategy for measuring and mapping the metabolic effects associated with the development of intestinal inflammation at the age of 1, 8, 16, and 24 weeks. Chronic inflammation appeared at 8 weeks and onward, and was associated with altered cecum and colon morphologies and increased inflammatory cell infiltration into the mucosa and the submucosa. Blood plasma profiles provided additional evidence of loss of energy homeostasis, impaired metabolism of lipoproteins and glycosylated proteins. In particular, IL-10-/-mice were characterized by decreased levels of VLDL and increased concentrations of LDL and polyunsaturated fatty acids, which are related to the etiology of IBD. Moreover, higher levels of lactate, pyruvate, citrate and lowered glucose suggested increased fatty acid oxidation and glycolysis, while higher levels of free amino acids reflected muscle atrophy, breakdown of proteins and interconversions of amino acids to produce energy. These integrated system investigations demonstrate the potential of metabonomics for investigating the mechanistic basis of IBD, and it will provide novel avenues for management of IBD.

Toll-like receptors (TLRs) play an important role in the recognition of microbial molecular patterns of infectious and commensal bacteria and their expression in various tissues including the intestinal epithelium orchestration of the innate and adaptive immune defense mechanisms. Changes in the TLR signaling pathways due to host genetic predispositions may turn a physiological response into a pathological situation including failure of bacterial clearance and development of chronic inflammation. The aim of this study was to characterize the role of TLR2 or TLR4 deficiency in epithelial cell stress responses under noninflamed and inflamed conditions using TLR-deficient mice and TLR(-/-) cross-bred IL-10-deficient mice as a model for genetically driven experimental colitis. Primary intestinal epithelial cells (IEC) were isolated from specific-pathogen-free wild-type, TLR2-, TLR4-, IL-10-, IL-10XTLR2- and IL-10XTLR4-deficient mice at the age of 1, 8, and 16 weeks. Histopathological analysis showed absence of tissue pathology (score 0-12) in distal colon sections of TLR2- and TLR4-deficient mice. In addition, TLR2- but not TLR4-deficient mice cross-bred to the IL-10-deficient background develop moderate colitis, suggesting different effects of these pattern recognition receptors in regulating disease mechanisms. Proteome analysis revealed significantly regulated proteins associated with endoplasmic reticulum (ER) and mitochondrial stress responses in the epithelium. In contrast to TLR2(-/-) and IL-10XTLR2(-/-) mice, the induction of the ER-associated chaperone grp-78 was dissociated from the activation of proapoptotic caspase 3 cleavage in noninflamed TLR4(-/-) and IL10XTLR4(-/-) mice. These results suggest that ER-associated cellular stress responses play an important role in epithelial cells homeostasis leading to beneficial but also deleterious effects. We hypothesize that ER stress-associated processes in the absence of TLR2 and TLR4 differentially affect host responses and epithelial functions under conditions of genetically driven chronic intestinal inflammation.