Lactosaminoglycan assembly, cell surface expression, and release by mouse uterine epithelial cells

The Effect of Hyperglycemic Hyperinsulinemia on Small-Intestinal Mucosal Protein Synthesis in Patients After Surgical Stress

Hyperglycemic hyperinsulinemia cannot stimulate intestinal protein synthesis in healthy individuals but does so in conditions characterized by an altered somatotropic axis such as diabetes. Only in a state of growth hormone resistance (high growth hormone but low insulin like growth factor [IGF-1] concentrations), extra insulin may acutely reverse the impaired, growth-hormone-induced IGF-1 release, thereby exerting anabolic actions at the intestinal tract. Growth hormone resistance can be also found in patients after surgical stress. Therefore, we wanted to test the hypothesis whether hyperglycemic hyperinsulinemia would stimulate ileal protein synthesis in the latter condition. Mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) were used to directly determine the incorporation rate of 1-[(13)C]-leucine into ileal mucosal protein. All subjects had an ileostomy, which allowed easy access to the ileal mucosa, and consecutive sampling from the same tissue was performed during continuous isotope infusion (0.16 mumol/kg min). Isotopic enrichments and fractional protein synthesis were determined at baseline (period I) and after a 4-hour glucose infusion (170 mg/kg/h) or after infusion of saline (control group) (period II). In controls, ileal protein synthesis declined significantly during prolonged isotope infusion (period I: 1.11 +/- 0.14%/h, period II: 0.39 +/- 0.13%/h, p < .01). In contrast, ileal protein synthesis remained constant during glucose infusion (period I: 1.32 +/- 0.35%/h, period II: 1.33 +/- 0.21%/h, n.s. vs period I, but p < .005 vs the corresponding value at the end of period II in the control group). Using the continuous tracer infusion technique, ileal protein synthesis seemingly declines over a short time in control subjects. We found evidence that this artificial decline was due to mass effects of a rapidly turning over mucosa protein pool in which an isotopic plateau was reached during the experiment and of which the size amounted to approximately 4% of the total mixed protein pool. Maintenance of ileal protein synthesis during glucose infusion therefore indicates a rise of ileal protein synthesis in a slowly turning over protein pool. This effect in postsurgical patients would be compatible with the concept of intestinal insulin action to depend on the specific clinical state (eg, growth hormone resistance).

Effect of Amino Acid Infusion on Human Postoperative Colon Protein Synthesisin Situ

BACKGROUND

Amino acids are an integral part of parenteral nutrition because of their anabolic action helping to conserve body protein after surgical stress. At the gastrointestinal tract, an adequate supply of amino acids may be particularly important because of the gut's high rate of protein turnover, cell division, and proliferation. However, no information is available about the effects of amino acids on human intestinal protein metabolism after surgery.

METHODS

Studies were performed in postabsorptive patients 8-10 days after major abdominal surgery. Mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) were used to directly determine the incorporation rate of 1-[13C]-leucine into colon mucosal protein. All subjects had a colostomy, which allowed easy access to the colon mucosa, and consecutive sampling from the same tissue was performed during continuous isotope infusion (0.16 micromol/kg min). Isotopic enrichments were determined at baseline and after a 4-hour infusion of amino acids or after infusion of saline (control group).

RESULTS

Compared with baseline, infusion of amino acids reduced fractional colon protein synthesis significantly by -29.2 +/- 8.3%. This decrease was also significantly different from the corresponding (insignificant) change during saline infusion (+19.4 +/- 26.9%, p < .05 vs amino acid group).

CONCLUSIONS

After surgery, an amino acid infusion acutely reduces postoperative colon protein synthesis. This effect possibly may be attributed to interactions of specific amino acids (glutamine) with an altered intestinal immune system and enterocyte activity.

Ultrastructural studies of glycan changes in the apical surface of the uterine epithelium during pre-ovulatory and and pre-implantation stages in the marmoset monkey

It has been postulated that carbohydrates are involved in a variety of cell-cell interactions including blastocyst implantation. In primates, there are only limited investigations on the ultrastructural localisation of the cyclic changes in uterine epithelial surface carbohydrates. Our aim was to investigate such changes during the pre-ovulatory and pre-implantation stages of the reproductive cycle in the marmoset monkey. After fixation of endometrial tissues, avidin-ferritin lectin cytochemistry was employed for apical surface glycan detection at the ultrastructural level. Five lectins were used including Canavalia ensiformis (Con A), Lotus tetragonolobus (LTA), Glycine max (SBA), Phytolacca americana (PWM) and Triticum vulgaris (WGA). Morphometry was used to quantitate changes in the intensity of lectin staining by determining the total number of ferritin particles per unit length of membrane. Surface and intra-cytoplasmic vesicles, stained by the lectins, were also examined. Quantitative ferritin assessment showed that 1 day before presumed implantation (days 11 to 12 after ovulation in the marmoset monkey) there was a significant increase in Con A, LTA and SBA staining on the apical uterine epithelial plasma membrane compared to the pre-ovulatory phase and earlier stages of pregnancy (days 4-8 after ovulation). A significant increase in PWM was also detected from early pregnancy to pre-implantation stages. All lectins except WGA produced reproducible staining within reproductive cycle groups. The greatest variation and intensity of epithelial surface staining was observed with WGA and the weakest with LTA. The patchy staining with LTA compared with thick coverage by WGA indicated the complexity of the carbohydrate arrangement in the glycocalyx of the uterine surface plasma membrane. Reduction of WGA reactivity after neuraminidase treatment suggested that the lectin binding might be related to the presence of heavily sialylated apical uterine membrane glycoconjugates. This is the first high-resolution study in primates to report quantitative cyclic changes in fucosyl, galactosyl, glucosyl, and mannosyl sugar residues of the apical uterine epithelial glycocalyx. The findings support the concept that uterine epithelial glycocalyx surface carbohydrates play a role in preparing a receptive uterine surface.

Expression and characterization of a lactosaminoglycan-carrying glycoprotein of Zajdela hepatoma cell surface--structural analysis of the carbohydrate moiety

In poorly differentiated hepatoma cells, a glycoprotein carrying lactosaminoglycans is identified, and the structure of its glycan moiety is proposed. After membrane solubilization, protein fractionation by gel filtration, and electroelution, this glycoprotein (GPIII) was identified by its affinity for Datura stramonium lectin and its content in large glycopeptides. As shown by PAGE, GPIII has an apparent molecular mass of 100 kDa and is highly glycosylated (36%). It appears as an integral membrane glycoprotein. It is absent from normal hepatocytes, in that no heavy glycopeptides could be detected that bound to Datura lectin or to specific antiserum. The glycan moiety of GPIII has been analyzed according to carbohydrate composition, glycosidase treatment, affinity chromatography on immobilized pokeweed, Datura and Griffonia lectins, and by NMR and methylation analyses. The glycan is a N-linked tetraantennary lactosaminoglycan of 6.6 kDa, containing Gal, GlcNAc, Man, and NeuNAc in a 16:14:3:4 molar ratio, with an average of three repeating units/branch. Its beta-Gal residues are in the penultimate position and are linked in beta1-4 at least in four structural elements (three peripheral and one internal). It contains a very branched structure with Gal alpha1-3Gal beta1-4GlcNAc side chains linked in the C6 position to an inner Gal residue in a main branch. Alpha-Gal and NeuNAc residues [mainly NeuNAc alpha(2-3) linkage] are expressed as the nonreducing terminal groups. A possible structural model is proposed for this heterogeneous lactosaminoglycan, although no definitive structure can be established. That this lactosaminoglycan-carrying glycoprotein GPIII is not expressed in hepatocytes suggests its expression to be linked to the undifferentiated and/or malignant state of this hepatoma.

Synthesis and intracellular trafficking of Muc-1 and mucins by polarized mouse uterine epithelial cells

Mucins function as a protective layer rendering the apical surface of epithelial cells nonadhesive to a variety of microorganisms and macromolecules. Muc-1 is a transmembrane mucin expressed at the apical cell surface of mouse uterine epithelial cells (UEC) that disappears as UEC become receptive for embryo implantation (Surveyor, G. A., Gendler, S. J., Pemberton, L., Das, S. K., Chakraborty, I., Julian, J., Pimental, R. A., Wegner, C. W., Dey, S. K., and Carson, D. D. (1995) Endocrinology 136, 3639-3647). In the present study, the kinetics of Muc-1 assembly, cell surface expression, release, and degradation were examined in polarized mouse UEC in vitro. Mucins were identified as the predominant glycoconjugates synthesized, apically expressed, and vectorially released in both wild-type and Muc-1 null mice. When mucins were released, greater than 95% were directed to the apical compartment. Approximately half of the cell-associated mucins lost during a 24-h period were found in the apical compartment. Vectorial biotinylation detected apically disposed, cell-surface mucin and indicated that at least 34% of these mucins are released apically within 24 h. This suggests that release of mucin ectodomains is part of the mechanism of mucin removal from the apical cell surface of UEC. The half-lives of total cell-associated mucins and Muc-1 were 19.5 +/- 1 and 16.5 +/- 0.8 h, respectively. Muc-1 represented approximately 10% of the [3H]glucosamine-labeled, cell-associated mucins. Studies of the kinetics of intracellular transport of Muc-1 indicated transit times of 21 +/- 15 min from the rough endoplasmic reticulum to Golgi apparatus and 111 +/- 28 min from the Golgi apparatus to the cell surface. Collectively, these studies provide the first comprehensive description of Muc-1 and mucin maturation, metabolism, and release by polarized cells, as well as defining a major metabolic fate for mucins expressed by UEC. Normal metabolic processing appears to be sufficient to account for the removal of Muc-1 protein during the transition of UEC to a receptive state.

Sialyl-Lewis x and Sialyl-Lewis a are associated with MUC1 in human endometrium

Endometrial epithelial cells express MUC1 with increased abundance in the secretory phase of the menstrual cycle, when embryo implantation occurs. MUC1 is associated with the apical surface of epithelial cells and is also secreted, being detectable in uterine fluid at elevated levels in the implantation phase. However, its physiological role is uncertain; it may either inhibit intercellular adhesion by steric hindrance or carry carbohydrate recognition structures capable of mediating cell-cell interaction. Here we show that endometrial epithelium expresses both Sialyl-Lewis x (SLex) and Sialyl-Lewis a (SLea), with a distribution and pattern of menstrual cycle regulation similar to that of MUC1. Using Western blotting and double determinant ELISA of uterine flushings, we demonstrate that SLex is associated with MUC1 core protein. The endometrial carcinoma cell lines HEC1A and HEC1B are shown to express MUC1 in a mosaic pattern, while three other cell lines express much lower amounts. HEC1A expresses both SLex and SLea while HEC1B expresses SLea only. Immunoprecipitation has been used to demonstrate that SLea is associated with MUC1 in HEC1B cells, and both SLex and SLea are associated with MUC1 in HEC1A cells.

The endometrial cell surface and implantation. Expression of the polymorphic mucin MUC-1 and adhesion molecules during the endometrial cycle

The cell surface mucin MUC-1 is present in endometrial epithelial cells and their associated apical glycocalyx and is also released into gland lumens as a secretory product. MUC-1 mRNA and core protein are found at low levels in the proliferative phase of the cycle, but their abundance increases after ovulation. Endometrial MUC-1 has been found to carry sialokeratan sulphate chains and these show a dramatically increased abundance in cells and secretions in the post-ovulatory phase of the cycle, reaching a maximum in secretions 6-7 days after the LH peak. The apical epithelium also contains adhesion receptor molecules of the integrin and CD44 families. MUC-1 is large and highly glycosylated and probably extends farther from the cell surface than these 'conventional' glycoprotein receptors. It has the potential to inhibit sterically receptor-mediated cell-cell adhesion. However, it is also possible that MUC-1 displays specific (e.g., glycan) recognition structures for the initial attachment of the blastocyst or that the embryo may create a specialised microenvironment in which to implant.

WGA-binding, mucin glycoproteins protect the apical cell surface of mouse uterine epithelial cells

Expression of apical cell surface proteins and glycoproteins was examined in polarized primary cultures of mouse uterine epithelial cells (UEC). Lectin-gold cytochemistry revealed that wheat germ agglutinin (WGA) bound specifically to the components of the apical glycocalyx as well as intracellular vesicles. Double labeling with the pH sensitive dye 3-(2,4-dinitroanilino)-3'amino-N-methyldipropylamine (DAMP) demonstrated the acidic nature of the WGA-staining intracellular vesicles. The enzymatic and chemical sensitivities of the WGA binding sites on the apical cell surface were monitored both by WGA-gold staining as well as by 125I-WGA binding assays. In thin sections, a large fraction of these sites were removed by pronase; however, application of a wide variety of proteases, glycosidases, or chemical treatments to the apical surface of intact UEC failed to reduce WGA binding. In no case did treatments designed to remove sialic acids reduce 125I-WGA binding more than 12%. In contrast, endo-beta-galactosidase as well as a combination of beta-galactosidase with beta-hexosaminidase succeeded in removing 28% and 77% of these sites, respectively. These studies suggested that the majority of the apically disposed WGA binding sites involved N-acetylglucosamine residues rather than sialic acids and included lactosaminoglycans. Many of the proteins detected at the apical cell surface by lactoperoxidase-catalyzed radioiodination were WGA-binding glycoproteins. A major class of these glycoproteins displayed Mr > 200 kDa by SDS-PAGE and was heavily labeled metabolically by 3H-glucosamine or by vectorial labeling at the apical cell surface with galactosyl transferase and UDP-3H-galactose. Analyses of the 3H-labeled oligosaccharides labeled by either procedure indicated that a large fraction of the apically disposed WGA-binding oligosaccharides consisted of neutral, O-linked mucin-type structures with median MW of approximately 1,500. Oligosaccharides in this fraction were partially (15%) sensitive to endo-beta-galactosidase digestion and bound to Datura stramonium agglutinin (68%), demonstrating the presence of lactosaminoglycan sequences. UEC were an extremely effective barrier to attachment or invasion by either a highly invasive melanoma cell line, B16-BL6, or implantation-competent mouse blastocysts. In contrast, neither uterine stromal cells nor a non-polarizing UEC cell line, RL95, prevented B16-BL6 attachment.(ABSTRACT TRUNCATED AT 400 WORDS)

Implanting mouse embryo stain with a LNF-I bearing fluorescent probe at their mural trophectodermal side

Mouse embryos at implantation stage were stained successfully with lacto-N-fucopentaose I (LNF-I) bearing neoglycoprotein labeled with rhodamine synthesized by us for the first time. The fluorescent neoglycoproteins carrying LNF-II, -III, LND-I, or LNT failed to stain the embryos. The embryo was stained only at the cell surface of trophectoderm at the mural side. Since the attachment of the mouse embryo to the uteric epithelium occurs at its mural side trophectoderm and LNF-I is the key substance in mouse implantation (Lindenberg, S. et al, (1988) J. Reprod. Fert. 83, 149-158), the material stained with the probe carrying LNF-I appears to be the molecule responsive to attachment to the endometrium surface and leading to implantation.