Kacper A. Wojtal

pH-dependent internalization of muramyl peptides from early endosomes enables Nod1 and Nod2 signaling

Nod1 and Nod2 are members of the Nod-like receptor family that detect intracellular bacterial peptidoglycan-derived muramyl peptides. The biological effects of muramyl peptides have been described for over three decades, but the mechanism underlying their internalization to the cytosol remains unclear. Using the human epithelial cell line HEK293T as a model system, we demonstrate here that Nod1-activating ligands entered cells through endocytosis, most likely by the clathrin-coated pit pathway, as internalization was dynamin-dependent but not inhibited by methyl-β-cyclodextrin. In the endocytic pathway, the cytosolic internalization of Nod1 ligands was pH-dependent, occurred prior to the acidification mediated by the vacuolar ATPase, and was optimal at pH ranging from 5.5 to 6. Similarly, the Nod2 ligand MDP was internalized into host cytosol through a similar pathway with optimal pH for internalization ranging from 5.5 to 6.5. Moreover, Nod1-activating muramyl peptides likely required processing by endosomal enzymes, prior to transport into the cytosol, suggesting the existence of a sterically gated endosomal transporter for Nod1 ligands. In support for this, we identified a role for SLC15A4, an oligopeptide transporter expressed in early endosomes, in Nod1-dependent NF-κB signaling. Interestingly, SLC15A4 expression was also up-regulated in colonic biopsies from patients with inflammatory bowel disease, a disorder associated with mutations in Nod1 and Nod2. Together, our results shed light on the mechanisms by which muramyl peptides get access to the host cytosol, where they are detected by Nod1 and Nod2, and might have implications for the understanding of human diseases, such as inflammatory bowel disease.

Changes in mRNA expression levels of solute carrier transporters in inflammatory bowel disease patients

Inflammatory bowel disease (IBD) is an inflammatory condition that affects the gastrointestinal tract. The solute carrier (SLC) superfamily of transporters comprise proteins involved in the uptake of drugs, hormones, and other biologically active compounds. The purpose of this study was to determine the mRNA expression levels of 15 solute carrier transporters in two regions of the intestine in IBD patients. Endoscopic biopsy specimens were taken from two locations (terminal ileum and colon) for histological examination and RNA extraction. We quantitatively measured the mRNA expression of 15 SLC transporters in 107 IBD patients (53 with Crohns disease and 54 with ulcerative colitis) and 23 control subjects. mRNA expression was evaluated using the quantitative reverse transcription-polymerase chain reaction technique. We observed that in the ileum of IBD patients, mRNA levels for serotonin transporter, equilibrative nucleoside transporter (ENT) 1, ENT2, and organic anion-transporting polypeptide (OATP) 2B1 were significantly elevated, whereas levels for apical sodium-dependent bile acid transporter (ASBT) and organic zwitterion/cation transporter (OCTN) 2 were significantly lower. In colon, mRNA levels for ENT1, ENT2, concentrative nucleoside transporter (CNT) 2, OATP2B1, and OATP4A1 were significantly higher, whereas mRNA levels for OCTN2 were significantly decreased. In inflamed colon of IBD patients the mRNA expression levels of ENT1, ENT2, CNT2, OATP2B1, OATP4A1, and peptide transporter 1 were significantly higher. We conclude that intestinal SLC mRNA levels are dysregulated in IBD patients, which may be linked to the inflammation of the tissue and provides an indication about the role of inflammatory signaling in regulation of SLC expression.

Protein tyrosine phosphatase nonreceptor type 2 regulates autophagosome formation in human intestinal cells

Background: Autophagy is a process of central importance for maintaining cell homeostasis, survival, and the regulation of inflammation. Recent studies associated variants within the gene loci, encoding protein tyrosine phosphatase nonreceptor type 2 (PTPN2), and autophagy genes, such as autophagy‐related 16‐like 1 (ATG16L1), with chronic inflammatory disorders, such as Crohns disease (CD). We show that PTPN2 regulates autophagy in human intestinal epithelial cells (IEC) and primary colonic lamina propria fibroblasts (CLPF). Methods: Protein analysis in IEC and CLPF was performed by western blotting. Autophagososme formation was assessed by LC3B immunofluorescence or immunohistochemistry. Human intestinal tissue samples were obtained from noninflammatory bowel disease (IBD) control or from CD patients and genotyped for disease‐associated PTPN2 or ATG16L1 variations. Results: Knockdown of PTPN2 causes impaired autophagosome formation and dysfunctional autophagy resulted in increased levels of intracellular Listeria monocytogenes (LM) and elevated IEC apoptosis in response to tumor necrosis factor (TNF) and interferon gamma (IFN‐&ggr;). Similar findings were observed in primary CLPF derived from CD patients carrying the CD‐associated PTPN2 variant. Presence of the ATG16L1 variant prevented the cytokine‐induced rise in PTPN2 protein, finally resulting in impaired LC3B‐II levels in IEC. Actively inflamed intestinal biopsies from CD patients carrying either ATG16L1 or PTPN2 genetic variants revealed aberrant LC3B expression patterns when compared with samples from non‐IBD control patients. Conclusions: Our results demonstrate that PTPN2 regulates autophagosome formation in human intestinal cells. We provide a model of how a dysfunction of the CD susceptibility genes, PTPN2 and/or ATG16L1, may contribute to the onset and perpetuation of chronic intestinal inflammation. (Inflamm Bowel Dis 2011;)

Titanium dioxide nanoparticles exacerbate DSS-induced colitis: role of the NLRP3 inflammasome

Objective Western lifestyle and diet are major environmental factors playing a role in the development of IBD. Titanium dioxide (TiO2) nanoparticles are widely used as food additives or in pharmaceutical formulations and are consumed by millions of people on a daily basis. We investigated the effects of TiO2 in the development of colitis and the role of the nucleotide-binding oligomerisation domain receptor, pyrin domain containing (NLRP)3 inflammasome. Design Wild-type and NLRP3-deficient mice with dextran sodium sulfate-induced colitis were orally administered with TiO2 nanoparticles. The proinflammatory effects of TiO2 particles in cultured human intestinal epithelial cells (IECs) and macrophages were also studied, as well as the ability of TiO2 crystals to traverse IEC monolayers and accumulate in the blood of patients with IBD using inductively coupled plasma mass spectrometry. Results Oral administration of TiO2 nanoparticles worsened acute colitis through a mechanism involving the NLRP3 inflammasome. Importantly, crystals were found to accumulate in spleen of TiO2-administered mice. In vitro, TiO2 particles were taken up by IECs and macrophages and triggered NLRP3-ASC-caspase-1 assembly, caspase-1 cleavage and the release of NLRP3-associated interleukin (IL)-1β and IL-18. TiO2 also induced reactive oxygen species generation and increased epithelial permeability in IEC monolayers. Increased levels of titanium were found in blood of patients with UC having active disease. Conclusion These findings indicate that individuals with a defective intestinal barrier function and pre-existing inflammatory condition, such as IBD, might be negatively impacted by the use of TiO2 nanoparticles.

Adaptation of iron transport and metabolism to acute high‐altitude hypoxia in mountaineers

Human iron homeostasis is regulated by intestinal iron transport, hepatic hepcidin release, and signals from pathways that consume or supply iron. The aim of this study was to characterize the adaptation of iron homeostasis under hypoxia in mountaineers at the levels of (1) hepatic hepcidin release, (2) intestinal iron transport, and (3) systemic inflammatory and erythropoietic responses. Twenty‐five healthy mountaineers were studied. Blood samples and duodenal biopsies were taken at baseline of 446 m as well as on day 2 (MG2) and 4 (MG4) after rapid ascent to 4559 m. Divalent metal‐ion transporter 1 (DMT‐1), ferroportin 1 (FP‐1) messenger RNA (mRNA), and protein expression were analyzed in biopsy specimens by quantitative reverse‐transcription polymerase chain reaction (RT‐PCR) and immunohistochemistry. Serum hepcidin levels were analyzed by mass spectrometry. Serum iron, ferritin, transferrin, interleukin (IL)−6, and C‐reactive protein (CRP) were quantified by standard techniques. Serum erythropoietin and growth differentiation factor 15 (GDF15) levels were measured by enzyme‐linked immunosorbent assay (ELISA). Under hypoxia, erythropoietin peaked at MG2 (P < 0.001) paralleled by increased GDF15 on MG2 (P < 0.001). Serum iron and ferritin levels declined rapidly on MG2 and MG4 (P < 0.001). Duodenal DMT‐1 and FP‐1 mRNA expression increased up to 10‐fold from baseline on MG2 and MG4 (P < 0.001). Plasma CRP increased on MG2 and MG4, while IL‐6 only increased on MG2 (P < 0.001). Serum hepcidin levels decreased at high altitude on MG2 and MG4 (P < 0.001). Conclusion: This study in healthy volunteers showed that under hypoxemic conditions hepcidin is repressed and duodenal iron transport is rapidly up‐regulated. These changes may increase dietary iron uptake and allow release of stored iron to ensure a sufficient iron supply for hypoxia‐induced compensatory erythropoiesis. (Hepatology 2013; 58:2153–2162)

Fc Gamma Receptor CD64 Modulates the Inhibitory Activity of Infliximab

Background Tumor necrosis factor (TNF) is an important cytokine in the pathogenesis of inflammatory bowel disease (IBD). Anti-TNF antibodies have been successfully implemented in IBD therapy, however their efficacies differ among IBD patients. Here we investigate the influence of CD64 Fc receptor on the inhibitory activity of anti-TNFs in cells of intestinal wall. Methods Intestinal cell lines, monocytes/macrophages and peripheral blood mononuclear cells (PBMCs) were used as models. The efficacies of adalimumab, infliximab and certolizumab-pegol were assessed by RT-PCR for target genes. Protein levels and localizations were examined by Western blotting and immunofluorescence. Antibody fragments were obtained by proteolytic digestion, immunoprecipitation and protein chip analysis. Knock-down of specific gene expression was performed using siRNAs. Results Infliximab had limited efficacy towards soluble TNF in cell types expressing Fc gamma receptor CD64. Both adalimumab and infliximab had lower efficacies in PBMCs of IBD patients, which express elevated levels of CD64. Infliximab-TNF complexes were more potent in activating CD64 in THP-1 cells than adalimumab, which was accompanied by distinct phospho-tyrosine signals. Blocking Fc parts and isolation of Fab fragments of infliximab improved its efficacy. IFN-γ-induced expression of CD64 correlated with a loss of efficacy of infliximab, whereas reduction of CD64 expression by either siRNA or PMA treatment improved inhibitory activity of this drug. Colonic mRNA expression levels of CD64 and other Fc gamma receptors were significantly increased in the inflamed tissues of infliximab non-responders. Conclusions CD64 modulates the efficacy of infliximab both in vitro and ex vivo, whereas the presence of this receptor has no impact on the inhibitory activity of certolizumab-pegol, which lacks Fc fragment. These data could be helpful in both predicting and evaluating the outcome of anti-TNF therapy in IBD patients with elevated systemic and local levels of Fc receptors.

cAMP-dependent protein kinase A and the dynamics of epithelial cell surface domains: Moving membranes to keep in shape

Cyclic adenosine monophosphate (cAMP) and cAMP‐dependent protein kinase A (PKA) are evolutionary conserved molecules with a well‐established position in the complex network of signal transduction pathways. cAMP/PKA‐mediated signaling pathways are implicated in many biological processes that cooperate in organ development including the motility, survival, proliferation and differentiation of epithelial cells. Cell surface polarity, here defined as the anisotropic organisation of cellular membranes, is a critical parameter for most of these processes. Changes in the activity of cAMP/PKA elicit a variety of effects on intracellular membrane dynamics, including membrane sorting and trafficking. One of the most intriguing aspects of cAMP/PKA signaling is its evolutionary conserved abundance on the one hand and its precise spatial–temporal actions on the other. Here, we review recent developments with regard to the role of cAMP/PKA in the regulation of intracellular membrane trafficking in relation to the dynamics of epithelial surface domains. BioEssays 30:146–155, 2008.

High altitude journeys and flights are associated with an increased risk of flares in inflammatory bowel disease patients

BACKGROUND AND AIMS Hypoxia can induce inflammation in the gastrointestinal tract. However, the impact of hypoxia on the course of inflammatory bowel disease (IBD) is poorly understood. We aimed to evaluate whether flights and/or journeys to regions lying at an altitude of >2000 m above the sea level are associated with flare-ups within 4 weeks of the trip. METHODS IBD patients with at least one flare-up during a 12-month observation period were compared to a group of patients in remission. Both groups completed a questionnaire. RESULTS A total of 103 IBD patients were included (43 with Crohns disease (CD): mean age 39.3 ± 14.6 years; 60 with ulcerative colitis (UC): mean age 40.4 ± 15.1 years). Fifty-two patients with flare-ups were matched to 51 patients in remission. IBD patients experiencing flare-ups had more frequently undertaken flights and/or journeys to regions >2000 m above sea level within four weeks of the flare-up when compared to patients in remission (21/52 [40.4%] vs. 8/51 [15.7%], p=0.005). CONCLUSIONS Journeys to high altitude regions and/or flights are a risk factor for IBD flare-ups occurring within 4 weeks of travel.

The effects of vitamin A on cells of innate immunity in vitro

Retinoid treatment is suggested to promote development of inflammatory bowel disease, although preclinical studies are not supportive. We evaluated the effect of retinoids on cytokine response in in vitro-differentiated human dendritic cells (ivDCs) and macrophages (ivMACs) derived from healthy human donors and in cultured human THP-1 cells. Effect on human intestinal epithelial cell integrity was also assessed. Each cell type was incubated (±lipopolysaccharide [LPS]) with all-trans retinoic acid (ATRA), 13-cis-RA (isotretinoin) and 4-oxo-13-cis-RA. Cytokine analysis was performed by array analysis. Cultured human endothelial colorectal adenocarcinoma (Caco-2) cells were incubated with these retinoids and media analyzed for leakage by spectrofluorometric analysis. ATRA consistently and significantly inhibited LPS-induced release of the pro-inflammatory cytokines tumor necrosis factor, interleukin (IL)-6, macrophage inflammatory protein (MIP)-1α and MIP-1β. All retinoids tested stimulated release of the anti-inflammatory cytokines granulocyte-macrophage colony-stimulating factor and IL-10, and also monocyte chemotactic protein-1, vascular endothelial growth factor and eotaxin-1. Incubation with retinoids did not significantly alter the permeability of Caco-2 monolayers. Pre-treatment of each cell type with retinoids promoted an anti-inflammatory cytokine profile with only minimal effect on intestinal epithelial cell permeability; consistent with in vivo studies.

Downregulation of duodenal SLC transporters and activation of proinflammatory signaling constitute the early response to high altitude in humans.

Solute carrier (SLC) transporters mediate the uptake of biologically active compounds in the intestine. Reduced oxygenation (hypoxia) is an important factor influencing intestinal homeostasis. The aim of this study was to investigate the pathophysiological consequences of hypoxia on the expression and function of SLCs in human intestine. Hypoxia was induced in human intestinal epithelial cells (IECs) in vitro (0.2; 1% O2 or CoCl2). For human in vivo studies, duodenal biopsies and serum samples were obtained from individuals (n = 16) acutely exposed to 4,554 meters above sea levels. Expression of relevant targets was analyzed by quantitative PCR, Western blotting, or immunofluorescence. Serum levels of inflammatory mediators and nucleosides were determined by ELISA and LC/MS-MS, respectively. In the duodenum of volunteers exposed to high altitude we observed decreased mRNA levels of apical sodium-dependent bile acid transporter (ASBT), concentrative nucleoside transporters 1/2 (CNT1/2), organic anion transporting polypeptide 2B1 (OATP2B1), organic cation transporter 2 (OCTN2), peptide transporter 1 (PEPT1), serotonin transporter (SERT), and higher levels of IFN-γ, IL-6, and IL-17A. Serum levels of IL-10, IFN-γ, matrix metalloproteinase-2 (MMP-2), and serotonin were elevated, whereas the levels of uridine decreased upon exposure to hypoxia. Hypoxic IECs showed reduced levels of equilibrative nucleoside transporter 2 (ENT2), OCTN2, and SERT mRNAs in vitro, which was confirmed on the protein level and was accompanied by activation of ERK1/2, increase of hypoxia-inducible factor (HIF) proteins, and production of IL-8 mRNA. Costimulation with IFN-γ and IL-6 during hypoxia further decreased the expression of SERT, ENT2, and CNT2 in vitro. Reduced oxygen supply affects the expression pattern of duodenal SLCs that is accompanied by changes in serum levels of proinflammatory cytokines and biologically active compounds demonstrating that intestinal transport is affected during systemic exposure to hypoxia in humans.