Rat-colonic, mucus glycoprotein

Glycosylation of IgA1 and pathogenesis of IgA nephropathy

IgA nephropathy, described in 1968 as IgA-IgG immune-complex disease, is an autoimmune disease. Galactose-deficient IgA1 is recognized by unique autoantibodies, resulting in the formation of pathogenic immune complexes that ultimately induce glomerular injury. Thus, formation of the galactose-deficient IgA1-containing immune complexes is a critical factor in the pathogenesis of IgA nephropathy. Studies of molecular defects of IgA1 can define new biomarkers specific for IgA nephropathy that can be developed into clinical assays to aid in the diagnosis, assessment of prognosis, and monitoring of disease progression.

Analysis of the genome sequence of Lactobacillus gasseri ATCC 33323 reveals the molecular basis of an autochthonous intestinal organism

This study presents the complete genome sequence of Lactobacillus gasseri ATCC 33323, a neotype strain of human origin and a native species found commonly in the gastrointestinal tracts of neonates and adults. The plasmid-free genome was 1,894,360 bp in size and predicted to encode 1,810 genes. The GC content was 35.3%, similar to the GC content of its closest relatives, L. johnsonii NCC 533 (34%) and L. acidophilus NCFM (34%). Two identical copies of the prophage LgaI (40,086 bp), of the Sfi11-like Siphoviridae phage family, were integrated tandomly in the chromosome. A number of unique features were identified in the genome of L. gasseri that were likely acquired by horizontal gene transfer and may contribute to the survival of this bacterium in its ecological niche. L. gasseri encodes two restriction and modification systems, which may limit bacteriophage infection. L. gasseri also encodes an operon for production of heteropolysaccharides of high complexity. A unique alternative sigma factor was present similar to that of B. caccae ATCC 43185, a bacterial species isolated from human feces. In addition, L. gasseri encoded the highest number of putative mucus-binding proteins (14) among lactobacilli sequenced to date. Selected phenotypic characteristics that were compared between ATCC 33323 and other human L. gasseri strains included carbohydrate fermentation patterns, growth and survival in bile, oxalate degradation, and adhesion to intestinal epithelial cells, in vitro. The results from this study indicated high intraspecies variability from a genome encoding traits important for survival and retention in the gastrointestinal tract.

Biochemical characterization of rat colonic mucins secreted in response to Entamoeba histolytica

Invasion of the colonic mucosa by Entamoeba histolytica trophozoites is preceded by colonic mucus depletion. The aim of our studies was to determine whether E. histolytica caused a differential secretion of mucin species in a rat colonic loop model. Mucus secretion in response to amoebae was followed by release of acid-precipitable 3H-glucosamine metabolically labelled glycoproteins and in vitro labelling of glycoprotein secretion with NaB3H4. The secretory response consisted of high-Mr goblet cell mucins and an increase in the secretion of low-Mr nonmucin glycoproteins as determined by Sepharose 4B column chromatography. High-Mr mucins subfractionated by Cellex-E (ECTEOLA) ion-exchange chromatography demonstrated a minor neutral and a major acidic mucin (greater than 98%) species. Marked differences between the neutral and acidic mucin species were indicated by immunogenicity and amino acid compositions. Thin-section histochemistry of rat colons confirmed secretion of neutral and acidic mucins in response to E. histolytica and demonstrated secretory activity from goblet cells from both the crypts and interglandular epithelium. E. histolytica mucus secretagogue activity was generalized and may function to deplete the host's protective mucus layer, facilitating invasion by the parasites.

Characterization of cell surface carbohydrate receptors for Entamoeba histolytica adherence lectin

Binding and cytolysis of Chinese hamster ovary (CHO) cells by Entamoeba histolytica trophozoites is inhibitable by galactose (Gal) or N-acetyl-D-galactosamine (GalNAc). To better define the carbohydrate receptor for E. histolytica, we compared the binding and cytolytic target properties of 10 CHO glycosylation mutants. Each mutant expresses a uniquely altered array of N- and/or O-linked cell surface carbohydrates. Amebic adherence was reduced when lactosamine-containing N-linked carbohydrates were essentially absent (Lec1 mutant), almost undetectable when Gal and GalNAc residues were absent on both N- and O-linked carbohydrates (ldlD.Lec1 mutant), and enhanced for mutants with increased terminal Gal residues (Lec2 and Lec3). Parental CHO cells treated with neuraminidase to expose Gal residues behaved like Lec2 mutants. Binding of purified Gal or GalNAc lectin to parental, Lec1, ldlD.Lec1, and Lec2 mutant CHO cells corroborated the adherence results. The suitability of CHO cell mutants as targets for amebic cytolysis correlated with their glycosylation phenotype: the Lec1 mutants were less susceptible than parental CHO cells, the ldlD.Lec1 mutants were highly resistant, and the Lec2 mutants required higher concentrations of Gal for inhibition. The E. histolytica Gal or GalNAc adherence lectin bound preferentially to beta 1-6-branched, N-linked carbohydrates lacking terminal sialic acid or fucose residues. However, amebic lectin binding to either N- or O-linked cell surface carbohydrates was sufficient to initiate parasite cytolytic activity.

Analysis of cancer-associated colonic mucin by ion-exchange chromatography: evidence for a mucin species of lower molecular charge and weight in cancer

Cancer-associated mucins in the colon are antigenically distinct and glycosylated differently from their normal counterparts. Mucin-rich glycoconjugate preparations were made from nine non-neoplastic colons, seven colon cancers, and two different xenografts from mucin-producing human colon cancer cell lines, and radiolabeled with 3H. The preparation was applied to a DEAE-cellulose ion-exchange column, and eluted with a discontinuous ascending NaCl gradient resulting in seven discrete fractions or 'species'. Over half of the 3H-labeled glycoconjugates from specimens of non-neoplastic colonic epithelium eluted in fraction V (eluted with 0.25 NaCl). Significantly less of the 3H-labeled glycoconjugates from specimens of colon cancer eluted in fraction V (34%, P less than 0.0005), and there were significant increases in glycoconjugates eluted in fractions IV (P less than 0.008), III (P less than 0.0005), and II (P less than 0.028). Additional samples were prepared without the radiolabeling procedures, chromatographed on a DEAE-cellulose ion-exchange column, and analyzed for monosaccharide content. Each of the fractions contained the monosaccharides expected in mucin-type glycoproteins, but only sialic acid was differentially expressed in the seven fractions or 'species', occurring principally in the more charged species. However, differences in sialic acid content were not sufficient to explain the differences in retention on the ion-exchange column, nor were differences in O-acetylation of the mucins. Mucin-type glycoconjugates from colon cancers are relatively less charged than those from the normal colon, and elute at lower ionic strengths. Of interest, cancer-associated mucins appear to be of lower molecular weight than their normal counterparts. Additional studies of oligosaccharide and apomucin structure will be required to explain the molecular basis of these differences in charge.

The colonic goblet cell and glycoprotein heterogeneity

Mucin glycoproteins are an important 'nonspecific' host defense at the interface of mucosal surface and lumen. However insights into structural and functional features of these enormously complex and heterogeneous glycoproteins have been markedly limited. In recent studies, the presence of several distinct colonic mucin glycoproteins has been demonstrated and their oligosaccharide side chains extensively characterized through conventional structural analysis and utilization of monoclonal antibodies. Glycoprotein diversity has been found to arise from previously unrecognized functional heterogeneity of colonic goblet cells. Rates of biosynthesis and secretion of different HCM glycoproteins appear to vary. In addition, a selective reduction in HCM glycoprotein IV has been demonstrated in specific association with ulcerative colitis. Finally preliminary studies suggest that additional alterations in colonic glycoconjugates may be present in ulcerative colitis mucosa.

The complexity of mucins

Mucins represent the main components of gel-like secretions, or mucus, secreted by mucosae or some exocrine glands. These high-molecular-weight glycoproteins are characterized by the large number of carbohydrate chains O-glycosidically linked to the peptide. The determination of mucin molecular weight and conformation has been controversial for several reasons: 1) the methods used to solubilize mucus and to purify mucins are different and 2) the molecules have a strong tendency to aggregate or to bind to other molecules (peptides or lipids). Recently, electron microscopy has shown the filamentous shape of most mucins and their polydisperse character which, in some secretions, might correspond to a polymorphism of the peptide part of these molecules. The recent development of high pressure liquid chromatography and high-resolution proton NMR spectroscopy has allowed major progress in the structural study of mucin carbohydrate chains. These chains may have from 1 to about 20 sugars and bear different antigenic determinants, such as A, B, H, I, i, X, Y or Cad antigens. In some mucins, such as human respiratory mucins, the carbohydrate chain diversity is remarkable, which raises many questions. Mucins are molecules located at the interface between mucosae and the external environment. The carbohydrate chain diversity might allow many interactions between mucins and microorganisms and play a major role in the colonization or the defense of mucosae.

Aberrant expression of monoclonal antibody-defined colonic mucosal antigens in inflammatory bowel disease

Human proximal colon from patients with inflammatory bowel disease and from controls was studied by two techniques to detect tumor-associated antigen expression. A panel of four murine monoclonal antibodies that recognize tumor-associated antigens was used to test purified colonic mucins for epitope expression by radioimmunoassay and to test formalin-fixed, deparaffinized sections of colon by the immunoperoxidase technique. The panel included monoclonal antibodies 19-9, B72.3, DU-PAN-2, and CSLEX1. Colonic mucins were purified from uninvolved surgical specimens by gel filtration with Sepharose 4B and cesium chloride-guanidine hydrochloride density gradient ultracentrifugation. Purified mucins from uninvolved colonic mucosal specimens from 4 of 7 patients with ulcerative colitis expressed one or more of these epitopes by radioimmunoassay, whereas mucins from 6 disease controls did not. Reactivity patterns were heterogeneous. Immunoperoxidase testing demonstrated staining with two or more antibodies in 14 of 18 involved inflammatory bowel disease segments, whereas control sections rarely stained with these antibodies, with the exception of 19-9. Sections of uninvolved mucosa from 4 of 9 patients with ulcerative colitis stained with two or more antibodies. Staining patterns were heterogeneous. The results demonstrate that colonic expression of tumor-associated epitopes occurs frequently in involved segments from both patients with ulcerative colitis and with Crohn's disease, whereas only patients with ulcerative colitis frequently expressed these epitopes in uninvolved segments.

Rat and human colonic mucins bind to and inhibit adherence lectin of Entamoeba histolytica

Establishment of adherence by Entamoeba histolytica is mediated by a 170-kD Gal/GalNAc inhibitable lectin and is required for cytolysis and phagocytosis of mammalian target cells. We studied the biochemical mechanisms of the in vitro interaction between rat and human colonic mucins and axenic E. histolytica trophozoites. Crude mucus prevented amebic adherence to Chinese hamster ovary (CHO) cells by up to 70%. Purification of the colonic mucins by Sepharose 4B chromatography, nuclease digestion, and cesium chloride gradient centrifugation resulted in a 1,000-fold enrichment of the inhibitory mucins. Purified rat mucin inhibited amebic adherence to and cytolysis of homologous rat colonic epithelial cells. Oxidation and enzymatic cleavage of rat mucin Gal and GalNAc residues completely abrogated mucin inhibition of amebic adherence. The binding of rat 125I-mucin to amebae was galactose specific, saturable, reversible, and pH dependent. A monoclonal antibody specific for the 170-kD amebic Gal/GalNAc lectin completely inhibited the binding of rat 125I-mucin. Rat mucin bound to Affigel affinity purified the amebic lectin from conditioned medium. Colonic mucin glycoproteins act as an important host defense by binding to the parasite's adherence lectin, thus preventing amebic attachment to and cytolysis of host epithelial cells.

Organ specific antigens of the human gastrointestinal tract

We previously reported the characterization of a normal adult colonic mucin antigen which contained an organ specific immunodeterminant [Tissue Antigen 11, 362 (1978)]. In the present study we have investigated mucins produced at other levels of the gastrointestinal tract in order to determine if regional specificities exist. Mucins were isolated from normal adult stomach, jejunum, ileum and colon and used to prepare antisera in rabbits. By radioimmunoassay at least four distinct specificities were observed. Gastric, ileal and colonic mucins were shown to contain immunodeterminants which were organ specific. Antiserum directed toward jejunal mucin determinants was reactive with the entire gastrointestinal tract. However, by heterologous inhibition analyses employing purified mucins as inhibiting antigens, the anti-jejunum antiserum was shown to be capable of discriminating a determinant present in much higher epitope density within small intestinal mucins as compared to mucins of the stomach and colon. Thus, it appeared that immunologic determinants present within mucin type glycoproteins of the gastrointestinal tissues exhibit anatomic specificity. In each case the structure of the immunodeterminant was, or was dependent upon the presence of a sialic acid derivative.

Development of anti-human colonic mucin monoclonal antibodies. Characterization of multiple colonic mucin species

Structural relationships between colonic mucin species were assessed using a library of monoclonal antibodies (MAbs) directed against purified human colonic mucin (HCM). After immunization of mice with purified mucin from normal human colonic mucosa, 14% of 1,920 fusion products screened were positive for anti-HCM activity in a solid-phase assay. Patterns of selective binding by hybridomas to six discrete HCM species (I-VI) separated by DEAE-cellulose chromatography suggested the presence of both shared and species-specific antigenic determinants among HCM species I-VI. 23 anti-HCMs MAbs (7 IgM, 7 IgG1, and 9 IgG2) demonstrating a range of anti-HCM species specificities, were produced and used to study structural relationships between mucin species. Binding of various mucin species by individual anti-HCM MAbs was shown by competitive solid-phase radioimmunoassay to reflect the presence of identical epitopes on the different species. Adsorption of HCM species on a variety of affinity resins prepared with anti-HCM MAbs demonstrated that binding to multiple mucin species by a single MAb was related to intrinsic structural determinants. Four anti-HCM MAbs recognized protease-sensitive antigenic structures, which suggests that they may be directed to core HCM proteins. 12 of the anti-HCM MAbs were shown by solid-phase assay to recognize either complete (n = 5) or partial (n = 7) isolated colonic mucin oligosaccharide side chains of defined structure. Collectively, these data show the presence of both shared and unique antigenic structural determinants among colonic mucin species. Chromatographic heterogeneity of mucin glycoproteins seems to be related to the existence of biologically significant subclasses in the normal human colon.

The influence of bisacodyl and deacetylbisacodyl on mucus secretion, mucus synthesis and electrolyte movements in the rat colon in vivo

The effect of the diphenolic laxatives bisacodyl and deacetylbisacodyl on mucus secretion and fluid, sodium and potassium net transport was studied in rat colon perfused in vivo. Mucus output in the effluent was determined as total protein-bound hexose. Deacetylbisacodyl was more potent than the parent compound and was used to investigate dose-response relationships. At a low concentration (0.1 mg/dl), mucus and potassium secretion were stimulated whereas sodium and fluid absorption were inhibited, or converted to secretion, only at higher concentrations (0.5-3.0 mg/dl). All effects were dose-dependent and reversible within 1 h. With longer lasting perfusion of deacetylbisacodyl, mucus appeared in two peaks, one initial peak and another after 4 h. The late peak contained newly synthetized glycoproteins as indicated by the incorporation of intravenously injected [14C]galactose. It is concluded that stimulation of mucus secretion and synthesis contributes to the laxative action of bisacodyl. The effects of low versus high concentrations suggests that part of the potassium secretion is due to mucus release.

Binding of lectins to goblet cell mucin in malignant and premalignant colonic epithelium in the CF-1 mouse

The lectin peanut agglutinin binds to mucin secreted by neoplastic but not normal human colonic epithelial cells. Peanut agglutinin was found to bind to mucin secreted by experimentally induced neoplasms in the distal colons of CF-1 mice, but not in the distal colons of control animals. Serial examination of colonic tissues after exposure to carcinogen has revealed the "cancer-associated" mucin in histologically normal but potentially premalignant epithelium. Thus, in the chemical carcinogen-rodent model, a diffuse alteration in glycoprotein structure is found in that part of the murine colon that subsequently develops cancer, and this precedes the appearance of neoplastic tissue. Changes in mucin structure may prove to be useful in the identification of premalignant gastrointestinal epithelium in certain humans at high risk for colon cancer.

Composition of human colonic mucin. Selective alteration in inflammatory bowel disease

Human colonic mucin has been isolated from mucosal scrapings of fresh surgical specimens of normal controls as well as patients with Crohn's colitis and ulcerative colitis. Following sonication and ultracentrifugation, mucin fractions were separated from other soluble colonic glycoproteins by Sepharose 4B chromatography. After nuclease digestion, cesium chloride gradient centrifugation of the excluded material yielded colonic mucin with an average buoyant density of 1.52 g/ml. Subsequent chromatography of the apparently homogeneous colonic mucin on DEAE-cellulose revealed the presence of at least six distinct mucin species (mucin I-VI). Each mucin species was found to have a distinctive hexose, hexosamine, sialic acid, and sulfate content as well as blood group substance activities. Mucin from five patients with Crohn's colitis was found to represent a mixture of at least six discrete species comparable to those isolated from normal colonic specimens. However, in mucin from eight patients with ulcerative colitis there was a marked and selective reduction of one component mucin subclass, designated species IV. Normal mucin and mucin from patients with Crohn's disease contained 48 +/- 17 and 42 +/- 12 mg of species IV/g, while mucin from patients with ulcerative colitis had 5 +/- 3 mg/g solubilized glycoprotein. The selective absence of species IV was found in preparations from both sigmoid (n = 7) and ascending (n = 4) colon and could not be accounted for by an overall decrease in total mucin content. The selective reduction of species IV was also found in mucin isolated from relatively noninflamed colonic mucosa of patients with ulcerative colitis. The carbohydrate composition and blood group activities of the remaining five mucin species were similar to their normal counterparts. Based on the results to date, there appears to be an underlying selective decrease of one colonic mucin subclass in ulcerative colitis.

Independence of the activation of mucus and potassium secretion on the inhibition of sodium and water absorption by deoxycholate in rat colon

The dose dependence of the influence of deoxycholic acid (DOC) on fluid and sodium absorption, transmural potential difference (PD), permeability of 14C-erythritol and secretion of potassium and mucus (protein bound hexoses) was measured in the in vivo perfused rat colon. The following results were obtained: 1. The threshold concentration for the inhibitory effect of DOC on fluid and sodium absorption is 2 mmol. In order to decrease PD and increase the colonic permeability for 14C-erythritol the same concentration was needed. 2. In contrast, DOC stimulated potassium and mucus secretion even in a fourfold lower concentration (0.5 mmol). No difference in the responsiveness of the descending and ascending colon was observed. 3. It is concluded that the identical dose dependency of the effect of DOC on fluid and sodium movement, PD, and permeability of the colonic mucosa is consistent with the interpretation that the secretagogue effect of DOC is mediated by an increase in permeability. However, because of their greater sensitivity, mucus and potassium secretion obviously are affected by a different mechanism. It is speculated that mucus and potassium are secreted together by the mucus producing cells of the colonic mucosa under the influence of DOC.

Influence of osmolality, short chain fatty acids and deoxycholic acid on mucus secretion in the rat colon

Mucus secretion into the rat colon has been measured in situ using a single perfusion technique. Protein, sialic acid and hexose concentrations in the perfusion solution were found to give reliable estimates of mucus output if samples were homogenized prior to analysis. Mucus output as indicated by an increase in the concentration of mucus constituents was higher when the solution was hypotonic (270 mosm . kg-1) or hypertonic (370 mosm . kg-1) than when isotonic solutions (320 mosm . kg-1) were used. The proportion of hexoses and sialic acid to protein was 23 and 14% at low, 23 and 11% at high osmolality, and 21 and 13% when isotonic solutions were used. Deoxycholic acid (DCA, 4 mmol . 1(-1)) increased the net secretion of mucus constituents 3 fold, whereas short chain fatty acids (SCFA) had no effect. Mucus composition during all treatments did not change significantly, even when stimulated with DCA. When mucus was released from the epithelial surface by previous perfusion with a DCA containing solution, net water and SCFA absorption rates and mucus output were significantly lowered for 2 to 3 h. However, no correlation between mucus secretion and SCFA absorption was found, indicating that a role for mucus as a diffusion barrier to SCFA is unlikely. Mucus output, which indicates the amount of mucus released from the epithelial surface, probably depends on the direction of net water movement, which follows the osmotic gradient between colon lumen and blood.

Purification and composition of colonic epithelial mucin

Colonic mucin was purified from homogenized scrapings of rat colonic epithelial cells using gel filtration and ion-exchange chromatography. High molecular weight water-soluble mucin was separated from low molecular weight proteins by gel exclusion chromatography on Sepharose 4B, and was further separated into two major mucin fractions and several non-mucin fractions on DEAE-cellulose. Fraction IV, the major mucin, was a sulphated glycoprotein with 62% carbohydrate by weight, and high concentrations of serine and threonine. A more acidic mucin, fraction V, had similar composition. Approx. 85% of the sialic acid of fractions IV and V were removed after incubation with Clostridium perfringens neuraminidase. Blood group A but not group H activity was present in fractions III, IV, and V. Ultracentrifugation experiments showed that fraction IV migrated as a single peak, whereas fraction V contained two components. Our study indicates that colonic mucin consists of at least two closely related acidic high molecular weight glycoproteins which can be separated from non-mucin contaminants by ion-exchange chromatography.

A comparison of [3H]galactose and [3H]fucose uptake with the morphological and histochemical changes observed in mucous secretion in chemically induced rat colonic carcinoma

The alterations in carbohydrate metabolism which occur in the distal colon of rats during carcinogenesis induced by dimethylhydrazine were investigated using [3H]galactose and [3H]fucose as glycoprotein precursors. A statistically significant decrease in [3H]galactose uptake was observed in dysplastic epithelia. These findings are consistent with the alterations in mucin composition with predominance of sialomucins shown in these areas by histochemical methods. Furthermore, changes in the gradient of [3H]galactose incorporation along the crypt epithelium were also found in the histological and histochemically non-involved colonic mucosa of dimethylhydrazine-treated rats, as compared with controls. No significant variations were seen in [3H]fucose incorporation. These results correlate well with our previous histochemical observations and are further evidence of the profound alterations in glycoprotein synthesis affecting the whole colonic mucosa during carcinogenesis.