Intelectin: a novel lipid raft-associated protein in the enterocyte brush border

Cell lineage identification and stem cell culture in a porcine model for the study of intestinal epithelial regeneration

Significant advances in intestinal stem cell biology have been made in murine models; however, anatomical and physiological differences between mice and humans limit mice as a translational model for stem cell based research. The pig has been an effective translational model, and represents a candidate species to study intestinal epithelial stem cell (IESC) driven regeneration. The lack of validated reagents and epithelial culture methods is an obstacle to investigating IESC driven regeneration in a pig model. In this study, antibodies against Epithelial Adhesion Molecule 1 (EpCAM) and Villin marked cells of epithelial origin. Antibodies against Proliferative Cell Nuclear Antigen (PCNA), Minichromosome Maintenance Complex 2 (MCM2), Bromodeoxyuridine (BrdU) and phosphorylated Histone H3 (pH3) distinguished proliferating cells at various stages of the cell cycle. SOX9, localized to the stem/progenitor cells zone, while HOPX was restricted to the +4/‘reserve’ stem cell zone. Immunostaining also identified major differentiated lineages. Goblet cells were identified by Mucin 2 (MUC2); enteroendocrine cells by Chromogranin A (CGA), Gastrin and Somatostatin; and absorptive enterocytes by carbonic anhydrase II (CAII) and sucrase isomaltase (SIM). Transmission electron microscopy demonstrated morphologic and sub-cellular characteristics of stem cell and differentiated intestinal epithelial cell types. Quantitative PCR gene expression analysis enabled identification of stem/progenitor cells, post mitotic cell lineages, and important growth and differentiation pathways. Additionally, a method for long-term culture of porcine crypts was developed. Biomarker characterization and development of IESC culture in the porcine model represents a foundation for translational studies of IESC-driven regeneration of the intestinal epithelium in physiology and disease.

Bacterial lipopolysaccharides stimulate production of XCL1, a calcium-dependent lipopolysaccharide-binding serum lectin, in Xenopus laevis

Xenopus laevis serum lectin XCL1 is a newly identified molecule of the XCGL (or X-lectin) family, a unique group of Ca(2+)-dependent lectins that have a fibrinogen-like domain. The XCL1 protein was purified from lipopolysaccharide (LPS)-stimulated frog sera by sequential affinity chromatography on heparin-acrylic beads and galactose-Sepharose. XCL1 comprises multiple oligomeric proteins consisting of 37-kDa subunit polypeptides, as revealed by sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) and Western blot analyses using the monoclonal antibody (mAb) produced against the recombinant XCL1 polypeptide. In the presence of Ca(2+), the protein bound to Escherichia coli, Staphylococcus aureus, LPS and galactose and the bound XCL1 was competitively eluted using ribose and xylose, and the elution was as efficient as that using EDTA, whereas elution using hexoses, GalNAc or GlcNAc was less effective. In reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses, XCL1 expression was ubiquitously detected in frog tissues, with relatively high levels in hematopoietic tissues including the spleen, liver and kidney. Intraperitoneal injection of E. coli, S. aureus or 100-300μg S-type LPS from various bacteria induced several-fold increases in serum XCL1 concentrations on day 3, and the elevated levels retained up to day 12. It also caused a remarkable increase of the splenic XCL1 expression on day 3, followed by a rapid decline to nearly nonstimulated control levels by day 7. The R-type LPS with shortened polysaccharide chains was less effective in inducing the serum XCL1 response, indicating that the sugar chains of LPS were important, if not essential, for the stimulation of XCL1 production. These results suggest that XCL1 is a pathogen recognition molecule involved in antimicrobial innate immunity in Xenopus.

Phenotype-genotype profiles in Crohn's disease predicted by genetic markers in autophagy-related genes (GOIA study II)

BACKGROUND

About 70 loci are associated with susceptibility to Crohn's disease (CD), particularly in pathways of innate immunity, autophagy, and pathogen recognition. Phenotype-genotype associations are inconsistent.

METHODS

CD susceptibility polymorphisms ATG16L1 rs2241880, ICAM1 rs5498, IL4 rs2070874, IL17F rs763780, IRGM rs13361189, ITLN1 rs2274910, LRRK2 rs11175593, and TLR4 rs4986790 were genotyped in a Portuguese population (511 CD patients, 626 controls) and assessed for association with CD clinical characteristics.

RESULTS

There is a significant association of CD with the single nucleotide polymorphisms (SNPs) in ATG16L1 (odds ratio [OR] 1.36 [1.15-1.60], P = 2.7 × 10(-6) for allele G), IRGM (OR 1.56 [1.21-1.93], P = 3.9 × 10(-4) for allele C), and ITLN1 (OR 1.55 [1.28-1.88], P = 4.9 × 10(-4) for allele C). These SNPs are associated with ileal location (OR, respectively, 1.49, 1.52, and 1.70), ileocolonic location (OR, respectively, 1.31, 1.57, and 1.68), and involvement of the upper digestive tract (OR, respectively for ATG16L1 and IRGM, 1.96 and 1.95). The risk genotype GG in ATG16L1 is associated with patients who respond to steroids (OR 1.89), respond to immunosuppressants (OR 1.77), and to biologic therapy (OR 1.89). The SNPs in ITLN1 and IRGM are both associated with a positive response to biologic therapy. The risk for ileal, ileocolonic, and upper digestive tract locations increases with the number of risk alleles (OR for three alleles, respectively, 7.10, 3.54, and 12.07); the OR for positive response to biologic therapy is 3.66.

CONCLUSIONS

A multilocus approach using autophagy-related genes provides insight into CD phenotype-genotype associations and genetic markers for predicting therapeutic responses.

Paneth cells and necrotizing enterocolitis: a novel hypothesis for disease pathogenesis

Current models of necrotizing enterocolitis (NEC) propose that intraluminal microbes destroy intestinal mucosa and activate an inflammatory cascade that ends in necrosis. We suggest an alternate hypothesis wherein NEC is caused by injury to Paneth cells (PCs) in the intestinal crypts. PCs are specialized epithelia that protect intestinal stem cells from pathogens, stimulate stem cell differentiation, shape the intestinal microbiota, and assist in repairing the gut. Our novel model of NEC uses neonatal mice and ablates PCs followed by enteral infection. We contrast this model with other animal examples of NEC and the clinical disease. Selective destruction of PCs using dithizone likely releases tumor necrosis factor-α and other inflammatory mediators. We propose that this event produces inflammation in the submucosa, generates platelet-activating factor, and induces a coagulopathy. The role of PCs in NEC is consistent with the onset of disease in preterm infants after a period of PC-related maturation, the central role of PCs in crypt-related homeostasis, the anatomic location of pneumatosis intestinalis close to the crypts, and the proximity of PCs to occluded blood vessels that cause coagulation necrosis of the intestinal villi. We offer this hypothesis to promote new thoughts about how NEC occurs and its potential prevention.

Chronic intestinal inflammation: inflammatory bowel disease and colitis-associated colon cancer

The inflammatory bowel diseases (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), are chronic inflammatory disorders of the intestine. The prevalence in the United States is greater than 200 cases per 100,000, with the total number of IBD patients between 1 and 1.5 million. CD may affect all parts of the gastrointestinal tract, from mouth to anus, but most commonly involves the distal part of the small intestine or ileum, and colon. UC results in colonic inflammation that can affect the rectum only, or can progress proximally to involve part of or the entire colon. Clinical symptoms include diarrhea, abdominal pain, gastrointestinal bleeding, and weight loss. A serious long-term complication of chronic inflammation is the development of colorectal cancer. A genetic basis for IBD had long been recognized based on the increased familial risk. However, significant discordance for CD in twins, and a much less robust phenotypic concordance for UC, suggested additional factors play a role in disease pathogenesis, including environmental factors. In the past several years, progress in understanding the molecular basis of IBD has accelerated, beginning with the generation of animal models of colitis and progressing to the identification of specific genetic markers from candidate gene, gene linkage, and genome-wide association analyses. Genetic studies have also resulted in the recognition of the importance of environmental factors, particularly the crucial role of the gut microbiota in CD and UC. Altered immune responses to the normal intestinal flora are key factors in IBD pathogenesis. In this research topic, the genetic basis of IBD, the genetic and cellular alterations associated with colitis-associated colon cancer, and the emerging role of the intestinal microbiota and other environmental factors will be reviewed.

Lactoferrin: an alternative view of its role in human biological fluids

Lactoferrin is a major component of biologically important mucosal fluids and of the specific granules of neutrophils. Understanding its biological function is essential for understanding neutrophil- and mucosal-mediated immunity. In this review, we reevaluate the in vivo functions of human lactoferrin (hLF) emphasizing in vivo studies and in vitro studies performed in biologically relevant fluids. We discuss the evidence in the literature that supports (or does not support) proposed roles for hLF in mucosal immunity and in neutrophil function. We argue that the current literature supports a microbiostatic role, but not a microbicidal role, for hLF in vivo. The literature also supports a role for hLF in inhibiting colonization and infection of epithelial surfaces by microorganisms and in protecting tissues from neutrophil-mediated damage. Using this information, we briefly discuss hLF in the context of the complex biological fluids in which it is found.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

Dietary cholesterol induces trafficking of intestinal Niemann-Pick Type C1 Like 1 from the brush border to endosomes

The transmembrane protein Niemann-Pick C1 Like 1 (NPC1L1) belongs to the Niemann-Pick C1 (NPC1) family of cholesterol transporters and is mainly expressed in the liver and the small intestine. NPC1L1 is believed to be the main transporter responsible for the absorption of dietary cholesterol. Like NPC1, NPC1L1 contains a sterol sensing domain, suggesting that it might be sensitive to dietary cholesterol. To test this hypothesis, mucosal explants were cultured in the presence or absence of cholesterol. In the absence of cholesterol NPC1L1 was localized mainly in the brush border of the enterocyte, colocalizing with the brush border enzyme aminopeptidase N (APN), and only a minor part was present in intracellular compartments. In contrast, following culture in the presence of cholesterol a major part of NPC1L1 was found in intracellular compartments positive for the early endosomal marker early endosome antigen 1, whereas only a minor fraction was left in the brush border. Neither APN, lactase, nor sucrase-isomaltase was endocytosed in parallel, demonstrating that this is a selective cholesterol-induced endocytosis of NPC1L1. Conceivably either the induced internalization could be due to NPC1L1 acting as an endocytic cholesterol receptor or it could be a mechanism to reduce the cholesterol uptake. The fluorescent cholesterol analog NBD-cholesterol readily labeled the cytoplasm also under conditions nonpermissible for endocytosis, arguing against a receptor-mediated uptake. We therefore propose that cholesterol is absorbed by NPC1L1 acting as a membrane transporter and that NPC1L1 is internalized to an endosomal compartment to reduce the absorption of cholesterol.

Recognition roles of the carbohydrate glycotopes of human and bovine lactoferrins in lectin-N-glycan interactions

BACKGROUND

Lactoferrin is an iron-binding protein belonging to the transferrin family. In addition to iron homeostasis, lactoferrin is also thought to have anti-microbial, anti-inflammatory, and anticancer activities. Previous studies showed that all lactoferrins are glycosylated in the human body, but the recognition roles of their carbohydrate glycotopes have not been well addressed.

METHODS

The roles of human and bovine lactoferrins involved in lectin-N-glycan recognition processes were analyzed by enzyme-linked lectinosorbent assay with a panel of applied and microbial lectins.

RESULTS AND CONCLUSIONS

Both native and asialo human/bovine lactoferrins reacted strongly with four Man-specific lectins - Concanavalia ensiformis agglutinin, Morniga M, Pisum sativum agglutinin, and Lens culinaris lectin. They also reacted well with PA-IIL, a LFuc>Man-specific lectin isolated from Pseudomonas aeruginosa. Both human and bovine lactoferrins also recognized a sialic acid specific lectin-Sambucus nigra agglutinin, but not their asialo products. Both native and asialo bovine lactoferrins, but not the human ones, exhibited strong binding with a GalNAc>Gal-specific lectin-Wisteria floribunda agglutinin. Human native lactoferrins and its asialo products bound well with four Gal>GalNAc-specific type-2 ribosome inactivating protein family lectins-ricin, abrin-a, Ricinus communis agglutinin 1, and Abrus precatorius agglutinin (APA), while the bovine ones reacted only with APA.

GENERAL SIGNIFICANCE

This study provides essential knowledge regarding the different roles of bioactive sites of lactoferrins in lectin-N-glycan recognition processes.

Lactoferrin targets T cells in the small intestine

BACKGROUND

Lactoferrin (Lf) belongs to the transferrin family of non-heme iron-binding proteins and is found in milk and mucosal secretions. Consequently, it is now considered a multifunctional protein mainly involved in both the innate and adaptive immune defenses of the organism against various pathogens, and Lf receptors have been identified at the surfaces of a number of different cells. In the small intestine Lf binds to the luminal surface, but its further interaction with the epithelial cells is controversial.

METHODS

In the present work, we studied the uptake of Lf in cultured mucosal explants of pig small intestine by immunofluorescence and immunogold microscopy.

RESULTS

Lf rapidly bound to the brush border and subsequently appeared in punctae in the apical cytoplasm, indicating internalization into an endosomal compartment. Essentially, no labeling was detected elsewhere in the enterocytes by 2 h incubation. However, in addition to enterocytes, a distinct subpopulation of cells in the lamina propria also took up Lf, most likely from the serosal side of the explants. None of these cells were apoptotic, nor did they belong to the predominant group of immunoglobulin-synthesizing plasma cells in the lamina propria. However, they were CD3(+), identifying them as T lymphocytes. Lf labeling of these cells was mainly seen in the cytosol, but occasionally nuclear staining was seen as well, suggesting a direct regulatory role of Lf.

CONCLUSION

We propose that Lf functions in the immune defense of the small intestinal mucosa by targeting the population of T cells in the lamina propria.

Downregulation of trefoil factor 3 gene expression in the colon of the senescence-accelerated mouse (SAM)-P6 revealed by oligonucleotide microarray analysis

Global comparison of the colonic gene expression profiles between 14-month-old senescenceaccelerated mouse (SAM)-P6 mice and SAM-R1 mice, a wild-type control, was conducted with an oligonucleotide microarray containing more than 5,000 mouse genes. Eight genes were upregulated more than two-fold and 94 genes were downregulated more than two-fold in SAM-P6 mice. The three cell defense genes intelectin1 (Itln1), trefoil factor 3 (intestinal) (Tff3) and "deleted in malignant brain tumors 1" (Dmbt1) were among those extensively downregulated. Quantitative RT-PCR analysis confirmed that Itln1 mRNA was almost undetectable in SAM-P6 colon, whereas it was readily detected in SAM-R1 colon. Colonic expression of both Tff3 and Dmbt1 mRNA was also substantially decreased, to one third and two thirds of the levels in SAM-R1 mice, respectively. A 14 kDa Tff3 dimer was detected by Western blotting in the colon of all three SAM-R1 mice, but was not present in three SAM-P6 mice. No upregulation of 3 cell defense genes was detected in 3-month-old SAM-R1 as well as SAM-P6 mice. These results suggest that a diminution of the intestinal trefoil factor system may be involved in the acceleration of aging in SAM-P6 mice.

The effect of lectins on the attachment and invasion of Enteromyxum scophthalmi (Myxozoa) in turbot (Psetta maxima L.) intestinal epithelium in vitro

The involvement of the lectin/carbohydrate interaction in the invasion of the turbot intestinal epithelium by Enteromyxum scophthalmi was studied in vitro using explants of turbot intestine and pre-treatment of parasite stages with the plant lectins of Canavalia ensiformis (Con A) and Glycine max (SBA). Both lectins inhibited the attachment and invasion of E. scophthalmi stages to the intestinal epithelium, though the inhibitory effect was higher for SBA than for Con A. Such results point to the involvement of N-acetyl-galactosamine (GalNAc) and galactose (Gal) residues and also of mannose/glucose residues in the E. scophthalmi-intestinal epithelium interaction. The inhibitory effect of both lectins on the parasite adhesion and penetration points to the interest of further studies to confirm the presence of putative lectins recognising GalNAc-Gal and mannose/glucose residues in turbot intestine. The obtained results demonstrated also the adequacy of turbot intestinal explants as an in vitro model to study the interaction with E. scophthalmi.

Prominin-1: a distinct cholesterol-binding membrane protein and the organisation of the apical plasma membrane of epithelial cells

The apical plasma membrane of polarized epithelial cells is composed of distinct subdomains, that is, planar regions and protrusions (microvilli, primary cilium), each of which are constructed from specific membrane microdomains. Assemblies containing the pentaspan glycoprotein prominin-1 and certain membrane lipids, notably cholesterol, are characteristic features of these microdomains in apical membrane protrusions. Here we highlight the recent findings concerning the molecular architecture of the apical plasma membrane of epithelial cells and its dynamics. The latter is illustrated by the budding and fission of prominin-1-containing membrane vesicles from apical plasma membrane protrusions, which is controlled, at least in part, by the level of membrane cholesterol and the cholesterol-dependent organization of membrane microdomains.

Transport of iron bound to recombinant human lactoferrin from rice and iron citrate across Caco-2 cell monolayers

The possibility of using recombinant human lactoferrin from rice (rhLF) makes it necessary to study its differences from the protein of milk. In this work, the binding of different iron-saturated forms of rhLF to Caco-2 cells was studied. Iron-saturated rhLF bound in higher proportion than the apo-form, but, the data obtained for specific binding were not compatible with receptor-mediated binding. Competition assays showed the same binding capacity for human milk lactoferrin as for rhLF to Caco-2 cells. Another basic protein of milk, lactoperoxidase, was found to compete with rhLF for binding to Caco-2 cell membranes, suggesting an electrostatic interaction. The transport of iron ((59)Fe) bound to rhLF and to citrate and the transport of rhLF ((125)I-labeled) were studied on Caco-2 monolayers. Transport of iron was found to be significantly greater when bound to citrate than to rhLF. The amount of intact lactoferrin that traversed the Caco-2 monolayers was very low, suggesting degradation of it across these cells.

Intelectin is required for IL-13-induced monocyte chemotactic protein-1 and -3 expression in lung epithelial cells and promotes allergic airway inflammation

Asthma is characterized by airway inflammation, mucus overproduction, airway hyperreactivity, and peribronchial fibrosis. Intelectin has been shown to be increased in airway epithelium of asthmatics. However, the role of intelectin in the pathogenesis of asthma is unknown. Airway epithelial cells can secrete chemokines such as monocyte chemotactic protein (MCP)-1 and -3 that play crucial roles in asthmatic airway inflammation. We hypothesized that intelectin plays a role in allergic airway inflammation by regulating chemokine expression. In a mouse allergic asthma model, we found that mRNA expression of intelectin-2 as well as MCP-1 and -3 in mouse lung was increased very early (within 2 h) after allergen challenge. Expression of intelectin protein was localized to mucous cells in airway epithelium. Treatment of MLE12 mouse lung epithelial cells with interleukin IL-13, a critical mediator of allergic airway disease, induced expression of intelectin-1 and -2 as well as MCP-1 and -3. When IL-13-induced intelectin-1 and -2 expression was inhibited by RNA interference, IL-13-induced extracellular signal-regulated kinase 1/2 phosphorylation and MCP-1 and -3 production by MLE12 cells was inhibited. Furthermore, inhibition of intelectin expression by airway transfection with shRNA targeting intelectin-1 and -2 attenuated allergen-induced airway inflammation. We conclude that intelectin, a molecule expressed by airway epithelial cells and upregulated in asthma, is required for IL-13-induced MCP-1 and -3 production in mouse lung epithelial cells and contributes to allergic airway inflammation.

The genetics of Crohn's disease

From epidemiological data, based on concordance data in family studies, via linkage analysis to genome-wide association studies, we and others have accumulated robust evidence implicating more than 30 distinct genomic loci involved in the genetic susceptibility to Crohn's disease (CD). These loci encode genes involved in a number of homeostatic mechanisms: innate pattern recognition receptors (NOD2/CARD15, TLR4, CARD9), the differentiation of Th17-lymphocytes (IL-23R, JAK2, STAT3, CCR6, ICOSLG), autophagy (ATG16L1, IRGM, LRRK2), maintenance of epithelial barrier integrity (IBD5, DLG5, PTGER4, ITLN1, DMBT1, XBP1), and the orchestration of the secondary immune response (HLA-region, TNFSF15/TL1A, IRF5, PTPN2, PTPN22, NKX2-3, IL-12B, IL-18RAP, MST1). While many of these loci also predispose to pediatric CD, an additional number of childhood-onset loci have been identified recently (e.g., TNFRSF6B). Not only has the identification of these loci improved our understanding of the pathophysiology of CD, this knowledge also holds real promise for clinical practice.

Role of gut microbiota in Crohn's disease

Crohn's disease (CD), a form of inflammatory bowel disease (IBD), provides a complex model of host-microbe interactions underpinning disease pathogenesis. Although there is not widespread agreement on the etiology of CD, there is evidence that microorganisms lead to the often severe inflammatory response characteristic of the disease. Despite several microbial candidates, no specific microbe has been considered pathogenic. Instead, the concept of the 'pathogenic community' has emerged from the evidence, whereby the stability of the microbial ecosystem of the healthy human gut is disrupted in response to host genetics and destabilized immunity, perhaps through changing public health practices leading to altered microbial exposures over time. We discuss the complex microbial ecosystem of the mammalian gut, the underlying genetic factors that predispose to CD, and how these gene variants may alter host-microbe interactions and propagate inflammation. Over the next 5 years, the increased understanding of genes involved in CD and the way in which individuals with variants of these genes respond differently to nutrients and drugs will enable the rational development of personalized therapies, using pharmacogenomic and nutrigenomic approaches.

Endocytic trafficking from the small intestinal brush border probed with FM dye

The small intestinal brush border functions as the body's main portal for uptake of dietary nutrients and simultaneously acts as the largest permeability barrier against pathogens. To enable this, the digestive enzymes of the brush border are organized in lipid raft microdomains stabilized by cross-linking galectins and intelectin, but little is known about the dynamic properties of this highly specialized membrane. Here, we probed the endocytic membrane trafficking from the brush border of organ-cultured pig intestinal mucosal explants by use of a fixable, lipophilic FM dye. The fluorescent dye readily incorporated into the brush border, and by 15 min faint but distinct punctae were detectable approximately 1 microm beneath the brush border, indicative of a constitutive endocytosis. The punctae represented a subpopulation of early endosomes confined to the actomyosin-rich terminal web region, and their number and intensity increased by 1 h, but trafficking further into the enterocyte was not observed except in immature epithelial cells of the crypts. A powerful ligand for receptor-mediated endocytosis, cholera toxin B subunit, increased apical endocytosis and caused membrane trafficking to proceed to compartments localized deeper into the cytoplasm of the enterocytes. Two major raft-associated brush border enzymes, alkaline phosphatase and aminopeptidase N, were excluded from endocytosis. We propose that the terminal web cytoskeleton, by inhibiting traffic from apical early endosomes further into the cell, contributes to the overall permeability barrier of the gut.

Galectin-2 at the enterocyte brush border of the small intestine

The brush border of pig small intestine is a local hotspot for beta-galactoside-recognizing lectins, as evidenced by its prominent labeling with fluorescent lectin PNA. Previously, galectins 3-4, intelectin, and lectin-like anti-glycosyl antibodies have been localized to this important body boundary. Together with the membrane glycolipids these lectins form stable lipid raft microdomains that also harbour several of the major digestive microvillar enzymes. In the present work, we identified a lactose-sensitive 14-kDa protein enriched in a microvillar detergent resistant fraction as galectin-2. Its release from closed, right-side-out microvillar membrane vesicles shows that at least some of the galectin-2 resides at the lumenal surface of the brush border, indicating that it plays a role in the organization/stabilization of the lipid raft domains. Galectin-2 was released more effectively from the membrane by lactose than was galectin-4, and surprisingly, it was also released by the noncanonical disaccharides sucrose and maltose. Furthermore, unlike galectin-4, galectin-2 was preferentially co-immunoisolated with sucrase-isomaltase rather than with aminopeptidase N. Together, these results show that the galectins are not simply redundant proteins competing for the same ligands but rather act in concert to ensure an optimal cross-linking of membrane glycolipids and glycoproteins. In this way, they offer a maximal protection of the brush border against exposure to bile, pancreatic enzymes and pathogens.

Expression of three intelectins in sheep and response to a Th2 environment

Sheep intelectin1 and sheep intelectin3 (sITLN1 and sITLN3) were cloned and sequenced. The amino acid sequences of sITLN1 and sITLN3 shared 86% and 91% homology with the previously cloned sheep intelectin2 (sITLN2), respectively. Expression of sITLN1 and sITLN3 transcript was demonstrated in abomasum, lung, colon and gastric lymph node, terminal rectum, skin, jejunum, mesenteric lymph node, ileal peyer’s patches, brain, kidney, liver, spleen, skin, ear pinna, heart and ovary in normal sheep tissues. sITLN2 transcript expression was restricted to the abomasal mucosa in normal sheep tissues. Using a non selective chicken anti-intelectin antibody, tissue intelectin protein was demonstrated in mucus neck cells in the abomasum, mucus cells in the colon, free mucus in ileum, goblet cells in the lung, small intestinal epithelium and brush border, epidermal layer of the skin and skin sebaceous glands. The expression of the three sITLN transcripts was examined in two nematode infections in sheep known to induce a Th2 response; a Teladorsagia circumcincta challenge infection model and a Dictyocaulus filaria natural infection. The three sITLN were absent in unchallenged naïve lambs and present in the abomasal mucosa of both naïve and immune lambs following T. circumcincta challenge infection. Upregulation of sITLN2 and sITLN3 was shown in sheep lung following D. filaria natural infection. Intelectins may play an important role in the mucosal response to nematode infections in ruminants.

Lipid raft organization and function in the small intestinal brush border

The enterocyte brush border of the small intestine is a highly specialized membrane designed to function both as a high capacity digestive/absorptive surface of dietary nutrients and a permeability barrier towards lumenal pathogens. It is characterized by an unusually high content of glycolipids (approximately 30% of the total microvillar membrane lipid), enabling the formation of liquid ordered microdomains, better known as lipid rafts. The glycolipid rafts are stabilized by galectin-4, a 36 kDa divalent lectin that cross-links galactosyl (and other carbohydrate) residues present on membrane lipids and several brush border proteins, including some of the major hydrolases. These supramolecular complexes are further stabilized by intelectin, a 35 kDa trimeric lectin that also functions as an intestinal lactoferrin receptor. As a result, brush border hydrolases, otherwise sensitive to pancreatic proteinases, are protected from untimely release into the gut lumen. Finally, anti-glycosyl antibodies, synthesized by plasma cells locally in the gut, are deposited on the brush border glycolipid rafts, protecting the epithelium from lumenal pathogens that exploit lipid rafts as portals for entry to the organism.

Copy number variation in the mouse genome: implications for the mouse as a model organism for human disease

Individuals within a species have genetic differences which ultimately result in the spectrum of phenotypic variation that we observe. Genetic variation exists at the nucleotide level in the form of single nucleotide polymorphisms (SNPs), and at a structural level as inversions, deletions and amplifications of larger stretches of nucleotides. Profiling of human and mouse genomes has identified numerous genomic segmental copy number variations (CNVs) throughout these genomes. Since inbred mice are widely used laboratory models for the study of both normal and disease biology, it is crucial that we understand the full scope of genetic variation, including CNVs, within these animals. These genetic differences can inform us about the history of a population or species, enlighten us on gene function, and guide our selection of a model system for the study of human disease.

Capture of heat-killed Mycobacterium bovis bacillus Calmette-Guérin by intelectin-1 deposited on cell surfaces

Intelectin is an extracellular animal lectin found in chordata. Although human and mouse intelectin-1 recognize galactofuranosyl residues included in cell walls of various microorganisms, the physiological function of mammalian intelectin had been unclear. In this study, we found that human intelectin-1 was a serum protein and bound to Mycobacterium bovis bacillus Calmette-Guérin (BCG). Human intelectin-1-binding to BCG was inhibited by Ca(2+)-depletion, galactofuranosyl disaccharide, ribose, or xylose, and was dependent on the trimeric structure of human intelectin-1. Although monomeric, mouse intelectin-1 bound to BCG, with its C-terminal region contributing to efficient binding. Human intelectin-1-transfected cells not only secreted intelectin-1 into culture supernatant but also expressed intelectin-1 on the cell surface. The cell surface intelectin-1 was not a glycosylphosphatidylinositol-anchored membrane protein. Intelectin-1-transfected cells captured BCG more than untransfected cells, and the BCG adherence was inhibited by an inhibitory saccharide of intelectin-1. Intelectin-1-preincubated cells took up BCG more than untreated cells, but the adhesion of intelectin-1-bound BCG was the same as that of untreated BCG. Mouse macrophages phagocytosed BCG more efficiently in medium containing mouse intelectin-1 than in control medium. These results indicate that intelectin is a host defense lectin that assists phagocytic clearance of microorganisms.

Decreased expression of intelectin 1 in the human airway epithelium of smokers compared to nonsmokers

Lectins are innate immune defense proteins that recognize bacterial cell wall components. Based on the knowledge that cigarette smoking is associated with an increased risk of infections, we hypothesized that cigarette smoking may modulate the expression of lectin genes in airway epithelium. Affymetrix microarrays were used to survey the expression of lectin genes in large airway epithelium from nine nonsmokers and 20 healthy smokers and in small airway epithelium from 13 nonsmokers and 20 healthy smokers. There were no changes (>2-fold change; p < 0.05) in lectin gene expression among healthy smokers compared with nonsmokers except for down-regulation of intelectin 1, a lectin that binds to galactofuranosyl residues in bacterial cell walls (large airway epithelium, p < 0.01; small airway epithelium, p < 0.01). This was confirmed by TaqMan RT-PCR in both large (p < 0.05) and small airway epithelium (p < 0.02). Immunohistochemistry assessment of airway biopsies demonstrated that intelectin 1 was expressed in secretory cells, while Western analysis confirmed the decreased expression of intelectin 1 in airway epithelium of healthy smokers compared with healthy nonsmokers (p < 0.02). Finally, compared with healthy nonsmokers, intelectin 1 expression was also decreased in small airway epithelium of smokers with lone emphysema and normal spirometry (n = 13, p < 0.01) and smokers with established chronic obstructive pulmonary disease (n = 14, p < 0.01). In the context that intelectin 1 plays a role in defense against bacteria, its down-regulation in response to cigarette smoking is another example of the immunomodulatory effects of smoking on the immune system and may contribute to the increase in susceptibility to infections observed in smokers.

Recombinant human intelectin binds bovine lactoferrin and its peptides

Intelectin (IntL), a lectin that exists on the brush border membrane of the small intestine, plays a role in the innate immune response and also acts as a receptor for lactoferrin (LF), an iron-binding glycoprotein found in milk and other secretions. Similar to human LF (hLF), bovine LF (bLF) has been shown to induce proliferation and differentiation of human enterocytes and to modulate their cytokine productions. To evaluate the interaction between human IntL (hIntL) and bLF, recombinant hIntL (rhIntL) conjugated with a tag sequence was examined for its ligand-binding capacity by using microtiter plates coated with LF or other proteins. Interestingly, rhIntL showed higher binding for bLF than hLF. It also bound pepsin hydrolysate of bLF, but to a lower degree than native bLF. A very low binding of rhIntL was observed for bovine serum albumin or transferrin. These findings suggest that hIntL acts as a receptor for bLF and its digested fragments.

Interleukin-4, interleukin-13, signal transducer and activator of transcription factor 6, and allergic asthma

Interleukin (IL)-4 and IL-13 share many biological activities. To some extent, this is because they both signal via a shared receptor, IL-4Ralpha. Ligation of IL-4Ralpha results in activation of Signal Transducer and Activator of Transcription factor 6 (STAT6) and Insulin Receptor Substrate (IRS) molecules. In T- and B-cells, IL-4Ralpha signaling contributes to cell-mediated and humoral aspects of allergic inflammation. It has recently become clear that IL-4 and IL-13 produced in inflamed tissues activate signaling in normally resident cells of the airway. The purpose of this review is to critically evaluate the contributions of IL-4- and IL-13-induced tissue responses, especially those mediated by STAT6, to some of the pathologic features of asthma including eosinophilic inflammation, airway hyperresponsiveness, subepithelial fibrosis and excessive mucus production. We also review the functions of some recently identified IL-4- and/or IL-13-induced mediators that provide some detail on molecular mechanisms and suggest an important contribution to host defense.

Genome-wide association defines more than 30 distinct susceptibility loci for Crohn's disease

Several risk factors for Crohn's disease have been identified in recent genome-wide association studies. To advance gene discovery further, we combined data from three studies on Crohn's disease (a total of 3,230 cases and 4,829 controls) and carried out replication in 3,664 independent cases with a mixture of population-based and family-based controls. The results strongly confirm 11 previously reported loci and provide genome-wide significant evidence for 21 additional loci, including the regions containing STAT3, JAK2, ICOSLG, CDKAL1 and ITLN1. The expanded molecular understanding of the basis of this disease offers promise for informed therapeutic development.

Crystallization and preliminary X-ray diffraction analysis of mouse galectin-4 N-terminal carbohydrate recognition domain in complex with lactose

Galectin-4 is thought to play a role in the process of tumour conversion of cells of the alimentary tract and the breast tissue; however, its exact function remains unknown. With the aim of elucidating the structural basis of mouse galectin-4 (mGal-4) binding specificity, we have undertaken X-ray analysis of the N-terminal domain, CRD1, of mGal-4 in complex with lactose (the basic building block of known galectin-4 carbohydrate ligands). Crystals of CRD1 in complex with lactose were obtained using vapour-diffusion techniques. The crystals belong to tetragonal space group P42(1)2 with unit-cell parameters a = 91.1, b = 91.16, c = 57.10 A and preliminary X-ray diffraction data were collected to 3.2 A resolution. An optimized crystallization procedure and cryocooling protocol allowed us to extend resolution to 2.1 A. Structure refinement is currently under way; the initial electron-density maps clearly show non-protein electron density in the vicinity of the carbohydrate binding site, indicating the presence of one lactose molecule. The structure will help to improve understanding of the binding specificity and function of the potential colon cancer marker galectin-4.

Identification, cloning and tissue localization of a rainbow trout (Oncorhynchus mykiss) intelectin-like protein that binds bacteria and chitin

Intelectins are a recently identified group of animal lectins involved in innate immune surveillance. This paper describes the primary structure, expression and immunohistochemical localization of a rainbow trout plasma intelectin (RTInt). RTInt exhibited calcium-dependent binding to N-acetylglucosamine (GlcNAc) and mannose conjugated Toyopearl Amino 650 M matrices. When GlcNAc eluates from chromatography matrices were analyzed by reducing 1D PAGE and Western blots, the lectin appeared as approximately 37 kDa and approximately 72 kDa bands. Similar analysis of plasma revealed a single 72 kDa band under reducing conditions. MALDI-TOF MS demonstrated five, approximately 37 kDa isoforms (pI 5.3-6.1) separated by 2D-PAGE. A 975 bp cDNA sequence obtained by RT-PCR from liver and spleen tissue encoded a 325 amino acid secretory protein with homology to human and murine intelectins, which bind bacterial components and are induced during parasitic infections. Gene expression and immunohistochemistry detected RTInt in gill, spleen, hepatic sinusoid, renal interstitium, intestine, skin, swim bladder and within leukocytes. Direct binding assays demonstrated the ability of RTInt to bind relevant bacterial and chitinous targets. These findings suggest that RTInt plays a role in innate immune defense against bacterial and chitinous microbial organisms.

Lgals6, a 2-million-year-old gene in mice: a case of positive Darwinian selection and presence/absence polymorphism

Duplications of genes are widely considered to be a driving force in the evolutionary process. The fate of such duplicated genes (paralogs) depends mainly on the early stages of their evolution. Therefore, the study of duplications that have already started to diverge is useful to better understand their evolution. We present here the example of a 2-million-year-old segmental duplication at the origin of the Lgals4 and Lgals6 genes in the mouse genome. We analyzed the distribution of these genes in samples from 110 wild individuals and wild-derived inbred strains belonging to eight mouse species from Mus (Coelomys) pahari to M. musculus and 28 laboratory strains. Using a maximum-likelihood method, we show that the sequence of the Lgals6 gene has evolved under the influence of strong positive selection that is likely to result in its neofunctionalization. Surprisingly, despite this selection pressure, the Lgals6 gene is present in some mouse species, but not all. Furthermore, even within the species and populations where it is present, the Lgals6 gene is never fixed. To explain this paradox, we propose different hypotheses such as balanced selection and neutral retention of ancient polymophism and we discuss this unexpected result with regard to known galectin properties and response to infections by pathogens.

Identification of omentin mRNA in human epicardial adipose tissue: comparison to omentin in subcutaneous, internal mammary artery periadventitial and visceral abdominal depots

OBJECTIVE

The purpose of this study was to determine the relative distribution of omentin and visfatin mRNA in human epicardial, peri-internal mammary, upper thoracic, upper abdominal and leg vein subcutaneous adipose tissue as well as the distribution of omentin in the nonfat cells and adipocytes of human omental adipose tissue.

BACKGROUND

Omentin is found in human omentum but not subcutaneous fat. Omentin and visfatin are considered markers of visceral abdominal fat.

RESEARCH DESIGN AND METHODS

The mRNA content of omentin and visfatin was measured by qRT-PCR analysis of fat samples removed from humans undergoing cardiac or bariatric surgery.

RESULTS

Omentin mRNA in internal mammary fat was 3.5%, that in the upper thoracic subcutaneous fat was 4.7% while that in the other subcutaneous fat depots was less than 1% of omentin in epicardial fat. The distribution of visfatin mRNA did not vary between the five depots. Omentin mRNA was preferentially expressed in the nonfat cells of omental adipose tissue since the omentin mRNA content of isolated adipocytes was 9% of that in nonfat cells, and similar results were seen for visfatin. The amount of omentin mRNA in differentiated adipocytes was 0.3% and that of visfatin 4% of that in nonfat cells. The amount of omentin mRNA in preadipocytes was virtually undetectable while that of visfatin was 3% of that in freshly isolated nonfat cells from omental adipose tissue.

CONCLUSION

Omentin mRNA is predominantly found in epicardial and omental human fat whereas visfatin mRNA is found to the same extent in epicardial, subcutaneous and omental fat.

Genetics of inflammatory bowel disease: clues to pathogenesis

INTRODUCTION OR BACKGROUND

It has long been recognized from epidemiological data that inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), have a strong genetic predisposition, interacting with unknown environmental drivers to render susceptible individuals at risk for relapsing intestinal inflammation. Substantial progress has been made in the last 2 years in characterizing the susceptibility genes involved.

SOURCES OF DATA

The recent acceleration in understanding has resulted from the use of new technologies of genome-wide association scanning in large panels of cases and controls.

AREAS OF AGREEMENT

Genome scans have robustly identified 11 susceptibility genes and loci and highlighted a number of new, previously unsuspected pathways as playing an important role in IBD pathogenesis-including the IL23 pathway in IBD overall and specific aspects of innate immunity (particularly NOD2 and the autophagy genes ATG16L1 and IRGM) in CD.

AREAS OF CONTROVERSY

The next challenge is to identify specific causal variants at each of the confirmed susceptibility loci and then characterize their biological impact on gene expression and function of the protein product.

GROWING POINTS

To date, most attention has focused on CD. A recent meta-analysis has increased the number of confirmed susceptibility loci to 32-more than for any other common disease to date. Attention is now turning to the use of the same techniques in UC to identify new, disease-specific genes and understand areas of overlap.

AREAS TIMELY FOR DEVELOPING RESEARCH

This review explores genetic clues to the pathogenesis of IBD derived from the growing list of confirmed IBD susceptibility genes, and briefly elaborates some of the important themes and overlaps that are becoming evident both within IBD and also with other complex diseases.

Intestinal alkaline phosphatase: selective endocytosis from the enterocyte brush border during fat absorption

Absorption of dietary fat in the small intestine is accompanied by a rise of intestinal alkaline phosphatase (IAP) in the serum and of secretion of IAP-containing surfactant-like particles from the enterocytes. In the present work, fat absorption was studied in organ cultured mouse intestinal explants. By immunofluorescence microscopy, fat absorption caused a translocation of IAP from the enterocyte brush border to the interior of the cell, whereas other brush-border enzymes were unaffected. By electron microscopy, the translocation occurred by a rapid (5 min) induction of endocytosis via clathrin-coated pits. By 60 min, IAP was seen in subapical endosomes and along membranes surrounding fat droplets. IAP is a well-known lipid raft-associated protein, and fat absorption was accompanied by a marked change in the density and morphology of the detergent-resistant membranes harboring IAP. A lipid analysis revealed that fat absorption caused a marked increase in the microvillar membrane contents of free fatty acids. In conclusion, fat absorption rapidly induces a transient clathrin-dependent endocytosis via coated pits from the enterocyte brush border. The process selectively internalizes IAP and may contribute to the appearance of the enzyme in serum and surfactant-like particles.

Cloning of a pig homologue of the human lactoferrin receptor: expression and localization during intestinal maturation in piglets

The presence of a small intestinal lactoferrin receptor (SI-LfR) has been suggested in the pig, but remains to be identified. LfR has been suggested to play a key role in the internalization of lactoferrin (Lf) and to facilitate absorption of iron bound to Lf. The aim of this study was to identify the pig SI-LfR cDNA, determine its mRNA and protein expression during different stages of intestinal development. The coding region of the pig LfR cDNA was cloned by PCR using conserved sequences among species. LfR mRNA expression and protein abundance were measured in proximal small intestine from piglets at 1 week (pre-weaning), 3 weeks (weaning) and 6 months (post-weaning) of age by quantitative real-time PCR (Q-PCR) and Western blot, respectively. Intestinal brush border membrane vesicles (BBMV) were also isolated to examine LfR abundance on the apical membrane. We determined the pig SI-LfR open reading frame (ORF) consists of 972 bp, resulting in a protein with a molecular mass approximately 135 kD and approximately 35 kD under non-reducing and reducing conditions, respectively. Using Q-PCR, we determined LfR expression significantly increased with age in the duodenum and reciprocally decreased in the jejunum. Intestinal LfR protein expression was maintained at all timepoints in the jejunum; however, in the duodenum LfR abundance reached maximum levels at 6 months. In BBMV fractions, LfR abundance significantly increased with age. Taken together our findings demonstrate the presence of a human SI-LfR homologue in pig, with mRNA and protein expression concomitantly regulated in the duodenum and inversely regulated in the jejunum. These findings suggest a mechanism by which pig Lf can be internalized in the intestine.

Differential structure and activity between human and mouse intelectin-1: human intelectin-1 is a disulfide-linked trimer, whereas mouse homologue is a monomer

Human intelectin-1 (hITLN-1) is a 120-kDa lectin recognizing galactofuranosyl residues found in cell walls of various microorganisms but not in mammalian tissues. Although mouse intelectin-1 (mITLN-1) has been identified previously, its biochemical properties and functional characteristics have not been studied. Therefore, we have compared structures and saccharide-binding specificities of hITLN-1 and mITLN-1 using recombinant proteins produced by mammalian cells. Recombinant hITLN-1 is a trimer, disulfide-linked through Cys-31 and Cys-48, and N-glycosylated at Asn-163. Despite 84.9% amino acid identity to hITLN-1, recombinant and intestinal mITLN-1 are unglycosylated 30-kDa monomers. Recombinant hITLN-1, as well as recombinant and intestinal mITLN-1 were purified by Ca(2+)-dependent adsorption to galactose-Sepharose. In competitive binding studies, hITLN-1 was eluted from galactose-Sepharose by 100 mM 2-deoxygalactose, a galactofuranosyl disaccharide, d-xylose, and both d- and l-ribose. In contrast, mITLN-1 was partially eluted by the galactofuranosyl disaccharide, and only minimally by the other saccharides indicating that the two intelectins have different saccharide-binding specificities. When the N- and C-terminal regions of hITLN-1 were replaced, respectively, with those of mITLN-1, galactose-Sepharose binding was associated with the C-terminal regions. Finally, hITLN-1 binding to galactose-Sepharose was not affected by the substitution of the Cys residues in the N-terminal region that are necessary for oligomer formation, nor was it affected by the removal of the N-linked oligosaccharide at Asn-163. Although both hITLN-1 and mITLN-1 recognize galactofuranosyl residues, our comparative studies, taken together, demonstrate that these intelectins have different quaternary structures and saccharide-binding specificities.

Innate immune defenses in the intestinal tract

PURPOSE OF REVIEW

Innate intestinal defenses are important for protection against ingested and commensal microbes. This review highlights recent new insights into innate immune effectors in the intestine.

RECENT FINDINGS

Intestinal epithelial cells, particularly Paneth cells, are the major producers of multiple peptides and proteins with antimicrobial activity in the intestine. The most abundant and diverse of these are the defensins. They are highly microbicidal in vitro and probably important in vivo, yet their physiologic functions remain incompletely understood. Relative defensin deficiency may be a risk factor for Crohn's disease and infectious diarrhea. Cathelicidin contributes to mucosal defense against epithelial-adherent bacterial pathogens, and helps to set a threshold for productive infection. Bactericidal/permeability-inducing protein has lipopolysaccharide-neutralizing capacity and kills bacteria when overexpressed in epithelial cells. Resistin-like molecule beta is important in mucosal defense against helminths due to its ability to inhibit worm chemotaxis. Antimicrobial lectins, particularly hepatocarcinoma-intestine-pancreas/pancreatic-associated protein, RegIII, and intelectin, can lyse bacteria or interfere with their attachment to epithelial cells.

SUMMARY

Discovery of an expanding set of antimicrobial effectors supports the evolutionary importance of innate intestinal defenses against microbial threats, but also underlines the physiologic and pharmacologic need for a better understanding of the respective functions of these molecules.