Mucin In Response Research Articles

147 Human Lung Organoids Predict Response to Carbon-Based Nanomaterials and Model Pulmonary Fibrosis

Abstract Advances in in-vitro culture systems have stimulated an interest in more reliable testing approaches that predict nanomaterial toxicity. Lung organoids are one example, and display functions consistent with their in-vivo counterparts. Organoids have been used in a variety of applications, but studies have yet to interrogate their suitability for nanomaterial testing. Here, we report the step-wise development of multilineage lung organoids, and validate their potential as tools for predicting pulmonary toxicity of carbon-based nanomaterials. After 50-days of differentiation, the lung organoids exhibited the six major proximal (goblet/basal/club/ciliated) and distal (AECI/II) epithelial cell types of the adult lung. Using microinjection, we developed an exposure model to exploit the airspace-like lumen of the organoids for cargo delivery. We compared the impact of small nanometric (50-950nm, sGO) and large micrometric (4-41µm, lGO) graphene oxide sheets, with multi-walled carbon nanotubes (1-20µm, MWCNT) on lung organoids after 1/7/28d exposure. Consistent with in-vivo data, sGO and lGO exhibited a transient interaction with the alveolar epithelium, and did not induce any histoarchitectural changes indicative of fibrosis. Organoids did however produce 2.5-fold more mucins in response to lGO than sGO exposure, suggesting that a thicker mucin barrier is required to prevent lGO-induced damage. In contrast, MWCNT caused detrimental effects on organoid architecture. Its persistent interaction with the alveolar epithelium led to a pro-fibrotic phenotype, where MWCNT caused AECII to undergo epithelial-mesenchymal transition. With further development, our model may reduce the need for rodent inhalation studies in the assessment of lung toxicity.

Colonic MUC2 Mucin Is Stabilized By FCGBP To Resist Salmonella Enterica Invasion In Goblet Cells

MUC2 mucin produced by goblet cells form the colonic mucus bilayer as the first line of innate defense against pathogen invasion by forming a physical barrier between the lumen and the underlying single layer of mucosal epithelial cells. Goblet cells also produce a variety of proteins that are associated with the mucus layer. Of these proteins, FCGBP is of significant interest due to its structural similarities to MUC2 mucin with unknown functions. In this study, we elucidated the putative functions of FCGBP embedded in MUC2 mucin in response to Salmonella enterica adherence and invasion in human colonic goblet cells. We hypothesis that FCGBP is coordinately produced with MUC2 mucin to play an integral role in forming the protective mucus layer in innate host defense. The aims of the study are: 1) to determine if FCGBP alters the structural integrity of the mucus layer and 2) to quantify structural alterations of the mucus layer in S. enterica adherence and invasion of goblet cells.To investigate whether FCGBP impaired mucus barrier functions, two cell types were investigated: Wildtype LS174T (WT) MUC2 mucus‐producing goblet cells and LS174T cells with a missense mutation in FCGBP (FCGBP MS). To determine if FCGBP MS led to loss in barrier function in the mucus layer, S. enterica adherence and invasion, and 0.2, 1, and 2 µM fluorescent bead penetrability inoculated on WT and FCGBP MS monolayers were quantified. MUC2 and FCGBP mRNA and protein expression induced by S. enterica in WT and FCGBP MS goblet cells were analysed by RT‐PCR and Western blotting. Cell killing by S. enterica was determined by LDH assay. S. enterica induced pro‐inflammatory cytokines responses were analyzed by RT‐PCR and human focus 15‐plex cytokine and chemokine array.FCGBP MS cells exhibited significant loss in MUC2 mucus barrier function as quantified by fluorescent beads penetrability further towards the epithelial cell surface temporally as compared to WT cells independent of bead size. Adherence of live S. enterica was significantly increased in FCGBP MS but not WT cells and induced robust MUC2 mRNA expression and mucus secretion in a time‐dependent manner. Similarly, S. enterica elicited high expression of pro‐inflammatory cytokine mRNA and protein release in FCGBP MS as compared to WT cells. FCGBP MS were readily invaded by S. enterica that resulted in increased cell death as compared to WT cells.More S. enterica adhered, invaded, and killed FCGBP MS as compared to WT cells. Fluorescent beads penetrated the mucus layer closer to the cell surface in FCGBP MS cells. In WT goblet cells, FCGBP and MUC2 were coordinately upregulated in response to S. enterica. The concurrent increase in pro‐inflammatory cytokine expression in FCGBP MS cells in response to S. enterica suggests that bacteria directly interacted with the cell surface suggesting an impaired protective mucus layer. The overall trend for increased bacterial invasion, pro‐inflammatory response, and cell death in FCGBP MS demonstrates that FCGBP was critical in providing structural integrity of the mucus layer.

Targeting mucin hypersecretion in COVID-19 therapy.

Targeting mucin hypersecretion in COVID-19 therapy.

A198 COLONIC MUC2 MUCIN IS STABILIZED BY FCGBP TO RESIST SALMONELLA TYPHIMURIUM INVASION IN GOBLET CELLS

BackgroundThe colonic mucus bilayer is the first line of innate defense against pathogen invasion in the gut by forming a physical barrier between the lumen and the underlying single layer of mucosal epithelial cells. While MUC2 mucin is the primary component of the mucus layer, it also contains several mucus associated proteins of which FCGBP is of significant interest due to its structural similarities to MUC2 with unknown functions. Here we elucidated the functions of FCGBP in MUC2 mucin in response to S. typhimurium ( St) adherence and invasion in human colonic goblet cells.AimsHypothesis: FCGBP is coordinately produced with MUC2 mucin and plays an important role in innate host defense. The specific aims are:1. To determine if FCGBP alters the structural integrity of the mucus layer2. To determine the role of FCGBP in St adherence and invasion of goblet cellsMethodsTo investigate whether FCGBP impaired mucus barrier functions, wildtype LS174T (WT) MUC2 mucus-producing goblet cells and LS174T cells with a missense mutation in FCGBP (FCGBP MS) were used. To determine if FCGBP MS led to loss in barrier function, St adherence and invasion, and 0.2, 1, and 2 μM fluorescent bead penetration through the mucus monolayers were quantified. MUC2 and FCGBP mRNA and protein expression induced by St were analysed by RT-PCR and Western blotting. St-induced pro-inflammatory cytokines responses were analyzed by RT-PCR and human focus 15-plex cytokine and chemokine array. Cell killing was enumerated by LDH assay.ResultsFCGBP MS cells exhibited significant loss in MUC2 mucus barrier function as quantified by fluorescent beads penetration closer towards the epithelial cell surface temporally as compared to WT cells independent of bead size. Adherence of St was significantly increased in FCGBP MS cells and induced robust MUC2 mRNA and protein expressions in a time-dependent manner. Similarly, St elicited robust expression of pro-inflammatory cytokine mRNA and protein release in FCGBP MS as compared to WT cells. FCGBP MS were readily invaded by St that resulted in increased cell death as compared to WT cells.ConclusionsLoss of function by FCGBP MS, but not in WT cells, showed increased penetration of fluorescent beads through the mucus layer that resulted in increased St adherence, invasion, and cell death. In WT cells, FCGBP and MUC2 were coordinately upregulated in response to St. The concurrent increase in pro-inflammatory cytokine expression in FCGBP MS cells in response to St suggests that bacteria directly interacted with the cell surface indicative of an impaired mucus layer. The overall trend for increased bacterial invasion, pro-inflammatory response and cell death in FCGBP MS demonstrates that FCGBP was critical in providing structural integrity and protective functions of the mucus layer.Funding AgenciesCIHR

Chronic Inflammation in Ulcerative Colitis Causes Long-Term Changes in Goblet Cell Function.

Background & AimsOne of the features of ulcerative colitis (UC) is a defect in the protective mucus layer. This has been attributed to a reduced number of goblet cells (GCs). However, it is not known whether abnormal GC mucus secretion also contributes to the reduced mucus layer. Our aims were to investigate whether GC secretion was abnormal in UC and exists as a long-term effect of chronic inflammation.MethodsColonoids were established from intestinal stem cells of healthy subjects (HS) and patients with UC. Colonoids were maintained as undifferentiated (UD) or induced to differentiate (DF) and studied as three-dimensional or monolayers on Transwell filters. Total RNA was extracted for quantitative real-time polymerase chain reaction analysis. Carbachol and prostaglandin E2 mediated mucin stimulation was examined by MUC2 IF/confocal microscopy and transmission electron microscopy.ResultsColonoids from UC patients can be propagated over many passages; however, they exhibit a reduced rate of growth and transepithelial electrical resistance compared with HS. Differentiated UC colonoid monolayers form a thin and non-continuous mucus layer. UC colonoids have increased expression of secretory lineage markers ATOH1 and SPDEF, along with MUC2 positive GCs, but failed to secrete mucin in response to the cholinergic agonist carbachol and prostaglandin E2, which caused increased secretion in HS. Exposure to tumor necrosis factor α (5 days) reduced the number of GCs, with a greater percentage decrease in UC colonoids compared with HS.ConclusionsChronic inflammation in UC causes long-term changes in GCs, leading to abnormal mucus secretion. This continued defect in GC mucus secretion may contribute to the recurrence in UC.

MGSE Regulates Crosstalk from the Mucin Pathway to the TFE3 Pathway of the Golgi Stress Response.

The Golgi apparatus is an organelle where membrane or secretory proteins receive post-translational modifications such as glycosylation and sulfation, after which the proteins are selectively transported to their final destinations through vesicular transport. When the synthesis of secretory or membrane proteins is increased and overwhelms the capacity of the Golgi (Golgi stress), eukaryotic cells activate a homeostatic mechanism called the Golgi stress response to augment the capacity of the Golgi. Four response pathways of the Golgi stress response have been identified, namely the TFE3, CREB3, HSP47, and proteoglycan pathways, which regulate the general function of the Golgi, apoptosis, cell survival, and proteoglycan glycosylation, respectively. Here, we identified a novel response pathway that augments the expression of glycosylation enzymes for mucins in response to insufficiency in mucin-type glycosylation in the Golgi (mucin-type Golgi stress), and we found that expression of glycosylation enzymes for mucins such as GALNT5, GALNT8, and GALNT18 was increased upon mucin-type-Golgi stress. We named this pathway the mucin pathway. Unexpectedly, mucin-type Golgi stress induced the expression and activation of TFE3, a key transcription factor regulating the TFE3 pathway, suggesting that the activated mucin pathway sends a crosstalk signal to the TFE3 pathway. We identified an enhancer element regulating transcriptional induction of TFE3 upon mucin-type Golgi stress, and named it the mucin-type Golgi stress response element, of which consensus was ACTTCC(N9)TCCCCA. These results suggested that crosstalk from the mucin pathway to the TFE3 pathway has an important role in the regulation of the mammalian Golgi stress response.Key words: Golgi stress, mucin, TFE3, organelle autoregulation, organelle zone.

Protein Kinase Cδ Regulates Airway Mucin Secretion via Phosphorylation of MARCKS Protein

Mucin hypersecretion is a major pathological feature of many respiratory diseases, yet cellular mechanisms regulating secretion of mucin have not been fully elucidated. Previously, we reported that mucin hypersecretion induced by human neutrophil elastase involves activation of protein kinase C (PKC), specifically the delta-isoform (PKC delta). Here, we further investigated the role of PKC delta in mucin hypersecretion using both primary human bronchial epithelial cells and the human bronchial epithelial 1 cell line as in vitro model systems. Phorbol-12-myristate-13-acetate (PMA)-induced mucin hypersecretion was significantly attenuated by rottlerin, a PKC delta-selective inhibitor. Rottlerin also reduced PMA- or human neutrophil elastase-induced phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) protein in these cells. Both secretion and MARCKS phosphorylation were significantly enhanced by the PKC delta activator bryostatin 1. A dominant-negative PKC delta construct (pEGFP-N1/PKC delta K376R) transfected into human bronchial epithelial 1 cells significantly attenuated both PMA-induced mucin secretion and phosphorylation of MARCKS, whereas transfection of a wild-type construct increased PKC delta and enhanced mucin secretion and MARCKS phosphorylation. Similar transfections of a dominant-negative or wild-type PKC epsilon construct did not affect either mucin secretion or MARCKS phosphorylation. The results suggest that PKC delta plays an important role in mucin secretion by airway epithelium via regulation of MARCKS phosphorylation.

MUC5AC and MUC5B Mucins Increase in Cystic Fibrosis Airway Secretions during Pulmonary Exacerbation

Cystic fibrosis (CF) is believed to be associated with mucus hypersecretion; thus, the principal airway gel-forming mucins, MUC5AC and MUC5B, are also expected to be increased relative to non-CF secretions. However, we have shown that these mucins are decreased during stable CF disease. In this study, we determine if these mucins increase during a pulmonary exacerbation of CF. Expectorated sputum was collected from 11 adults with CF during stable disease and then during a pulmonary exacerbation and from 12 healthy control subjects. MUC5AC and MUC5B proteins were measured by Western blot. DNA content was measured using microfluorimetry. MUC5AC protein increased by 908% and MUC5B by 59% (p < 0.05 for both) during an exacerbation compared with periods of stable disease. During stable disease, the vol/vol quantity of MUC5AC protein was 89% less than normal mucus, and the mucin-associated sugars, measured using a lectin binding assay, were 46% less compared with normal mucus. The concentration of DNA in CF sputum did not increase during an exacerbation. During a CF exacerbation, concentration of secreted mucin increased to the amount found in mucus from normal subjects, suggesting that the capacity to secrete mucin in response to an infection or inflammatory stimulus is preserved in CF airways. This might help to protect the airway from injury.

A3Adenosine Receptor Signaling Contributes to Airway Mucin Secretion after Allergen Challenge

Mucin hypersecretion is a prominent feature of obstructive airway diseases such as asthma. Clara cells conditionally produce mucin in response to inflammatory signals in a process termed mucous metaplasia. This can be followed by mucin secretion stimulated by various signaling molecules. The cellular and molecular mechanisms that regulate mucin production and secretion are not well understood. Adenosine is a signaling nucleoside that has been implicated in airway diseases in which mucus obstruction is prominent. Furthermore, the A(3) adenosine receptor (A(3)AR) is upregulated in mucin-producing goblet cells of the airway, thereby implicating it in processes involved in mucous cell biology. Here we use genetic approaches to investigate the contribution of A(3)AR signaling to mucus production and secretion in a mouse model of allergen-induced pulmonary disease. We found that the degree of mucin production in response to allergen is similar in wild-type and A(3)AR-deficient mice, and that overexpression of this receptor in Clara cells neither induces mucin production itself, nor enhances mucin production in response to allergen challenge. Collectively, these experiments demonstrate that the A(3)AR is neither necessary nor sufficient for mucous cell metaplasia. In contrast to the lack of effect on mucin production, agonist-induced mucin secretion was increased in goblet cells overexpressing the A(3)AR, and was absent in A(3)AR-deficient mice. Thus, the A(3)AR contributes to mucin secretion in allergen-induced metaplasia. Signaling through this receptor may contribute to mucus airway obstruction seen in pulmonary disorders in which adenosine levels are elevated.

PANIN 1A OR DUCT GLANDS OF THE PANCREAS? ANATOMIC PROOF AND CHARACTERIZATION OF A SPECIALIZED COMPARTMENT OF THE DUCTAL SYSTEM

The PanIN-system is generally accepted as a classification and progression model of ductal lesions with increasing atypia. However, the origin of the earliest lesions (PanIN-1A) remains unclear. PanIN-1A are flat epithelial lesions with abundant supra-nuclear mucin but without atypia. The neoplastic nature of PanIN-1A is unclear, as they are consistently observed in otherwise histologically normal human pancreata. In several other species those “lesions” have been observed more frequently and described as mucin producing “duct glands”. However, their existence is controversial, because they could not be clearly distinguished from small branch ducts. The expression of Sonic Hedgehog (Shh), which had not been previously identified in the normal pancreas, drew our attention to these glands. Here we provide an anatomic proof of small, blind-ending outpouches in the normal pancreas of mice, rats and in one human pancreas using scanning electron microscopy of corrosion casts. These outpouches are unequally distributed within the ductal system: They are found more often in larger ducts but can be observed in intralobular ducts. Furthermore we show by immunohistochemistry that these outpouches may contain a specialized compartment of the ductal epithelium envolved in mucosal protection and repair. Several developmental genes, which are thought to be involved in tissue repair are specifically (Sonic Hedgehog) or predominantly (Pdx-1) expressed in these outpouches and upregulated in response to chronic inflammatory injury. Additionally, outpouches exhibit high mucin expression when compared to the normal ductal epithelium and upregulate the expression of mucins in response to chronic injury. This suggests that these glands play a role in mucosal protection. We suggest that the pancreatic ductal system has outpouches/glands with a specialized epithelium. These duct glands may correspond to PanIN-1A observed in normal pancreata. They may be a source of pancreatic regeneration and be involved in the formation of pancreatic cancer.

Control of mucin transcription by diverse injury-induced signaling pathways.

Mucin production is an evolutionarily ancient defense mechanism that is retained in mammals and operates at all mucosal surfaces to protect the host against pathogens and irritants. As in lower organisms, the mammalian mucosa (epithelium) produces mucin in response to diverse insults. Our studies aim to understand the intracellular signaling and gene regulation mechanisms mediating mucin production in response to clinically important insults. To date, we find that the signaling pathway triggered by each type of insult is distinct. Relatively common, however, is the involvement of the protein tyrosine kinase c-Src, the MAP kinase kinase MEK 1/2, and the transcription factor NF-kappaB. Basbaum C, Lemjabbar H, Longphre M, Li D, Gensch E, McNamara N. Control of mucin transcription by diverse injury-induced signaling pathways.

Induction of mucin gene expression in human colonic cell lines by PMA is dependent on PKC-epsilon.

Treatment of HT-29 cells with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), induces MUC2 expression. To investigate the role of PKC in regulating mucin genes in intestinal cells, we examined the regulation of MUC1, MUC2, MUC5AC, MUC5B, and MUC6 expression in two human mucin-producing colonic cell lines, T84 and HT29/A1. T84 and HT29/A1 cells (at 80-90% confluency) were exposed to 100 nM PMA for 0, 3, and 6 h. Twofold or greater increases in mRNA levels for MUC2 and MUC5AC were observed in both cell lines during this time period, whereas the levels of MUC1, MUC5B, and MUC6 mRNAs were only marginally affected. These results indicated that PKC differentially regulates mucin gene expression and that it may be responsible for altered mucin expression. Our previous results suggested that the Ca(2+)-independent PKC-epsilon isoform appeared to mediate PMA-regulated mucin exocytosis in these cell lines. To determine if PKC-epsilon was also involved in MUC2/MUC5AC gene induction, HT29/A1 cells were stably transfected with either a wild-type PKC-epsilon or a dominant-negative ATP-binding mutant of PKC-epsilon (PKC-epsilon K437R). Overexpression of the dominant-negative PKC-epsilon K437R blocked induction of both mucin genes, whereas PMA-induced mucin gene expression was not prevented by overexpression of wild-type PKC-epsilon. PMA-dependent MUC2 mucin secretion was also blocked in cells overexpressing the dominant-negative PKC-epsilon K437R. On the basis of these observations, PKC-epsilon appears to mediate the expression of two major gastrointestinal mucins in response to PMA as well as PMA-regulated mucin exocytosis.

Protein kinase C and Ca2+ activation of mucin secretion in airway goblet cells.

Airway goblet cells secrete mucin in response to ATP and uridine 5'-triphosphate (UTP), but the underlying signal transduction pathways are poorly understood. Cultures of SPOC1 cells (L. H. Abdullah, S. W. Davis, L. Burch, M. Yamauchi, S. H. Randell, P. Nettesheim, and C. W. Davis. Biochem. J. 316: 943-951, 1996) secreted mucin on exposure to phorbol 12-myristate 13-acetate (PMA) [apparent affinity (K0.5) approximately 100 nM] and ionomycin (K0.5 approximately 5 microM) almost fivefold over baseline. Thapsigargin also elicited secretion (K0.5 approximately 20 nM). Ionomycin and PMA together elicited approximately twice the secretion of either agent alone. Overnight exposure to half-maximal PMA abolished the response to maximal doses of UTP and PMA, whereas ionomycin was fully effective. Protein kinase C (PKC) activity in the membrane fraction was increased by maximal doses of PMA and UTP, whereas ionomycin had no effect. PKC inhibitors were relatively ineffective against PMA- and UTP-induced mucin secretion. Human and canine goblet cells in epithelial explants, by video microscopy, underwent exocytosis with ionomycin (1 microM) and PMA (0.1 or 1 microM). SPOC1 cell mucin secretion was not stimulated by forskolin, 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, or 8-bromoguanosine 3',5'-cyclic monophosphate. Cystic fibrosis transmembrane conductance regulator was not detected in SPOC1 cells by Western blotting, and its mRNA was detected by reverse transcriptase polymerase chain reaction (PCR) only as a very weak band and after 55 PCR cycles. Multidrug resistance (MDR1), however, was readily detected by Western blotting, and its mRNA was detected as a major band after 35 PCR cycles. Thus airway goblet cell mucin secretion, distal to receptor activation, may be regulated independently by Ca(2+)- and PKC-dependent pathways. Cystic fibrosis transmembrane conductance regulator and cyclic nucleotides, however, may not play a major role in this secretion.

Effects of histamine on mucin biosynthesis in rat gastric mucosa.

Mucin biosynthesis is stimulated by gastrin during the process of glycosylation in the corpus mucosa of the rat stomach. The purpose of this study was to clarify, using an organ culture technique, whether biosynthetic responses to histamine in the rat gastric mucin are the same as that to gastrin. Radiolabeled mucin was obtained from the corpus and antral mucosa of the rat stomach after in vitro incubation for 5 h with [3H]glucosamine (GlcN), [14C]threonine (Thr), and [35S]sulfate. Addition of histamine (10(-7)-10(-5) M) to the culture medium increased [3H]GlcN-labeled mucin in the corpus tissue in a concentration-dependent manner. In the antrum, there was no significant change in the biosynthetic activity of mucin in response to histamine. Histamine at 10(-5) M also increased the incorporation of both [35S]sulfate and [14C]Thr into the corpus mucin. These results indicate that histamine stimulates the biosynthesis of the mucin peptide, as well as the glycosylation step in the corpus, and suggest that the effect of histamine on mucin synthesis is distinct from that of gastrin.

Hypersecretion of mucin in response to inflammatory mediators by guinea pig tracheal epithelial cells in vitro is blocked by inhibition of nitric oxide synthase.

Primary cultures of guinea pig tracheal epithelial cells in air/liquid interface were exposed to one of four agents associated with airway inflammation: the peptide histamine (100 microM), the lipid mediator platelet-activating factor (1 microM), the cytokine tumor necrosis factor-alpha (15 ng/ml; specific activity 2.86 x 10(7) U/mg), or enzymatically generated reactive oxygen species (purine [500 microM]+xanthine oxidase [20 mU/ml]). Effects of each of these substances on release of mucin by guinea pig tracheal epithelial (GPTE) cells were measured using a monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA). Each secretagogue significantly enhanced release of mucin, but the stimulatory effect of each was inhibited by pre-(+)co-incubation of the cells with the competitive inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMA), but not by NG-monomethyl-D-arginine (D-NMA), the inactive stereoisomer that does not inhibit nitric oxide synthase. Neither L-NMA nor D-NMA affected mucin secretion by themselves. The results suggest that each of these inflammation-associated mediators provokes airway epithelial mucin secretion via a mechanism involving intracellular production of nitric oxide (NO) as a critical signaling molecule.

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.

Both crypt and villus intestinal goblet cells secrete mucin in response to cholinergic stimulation.

Computer-assisted morphometric analysis was used to quantify the effects of cholinergic stimulation on intestinal goblet cells. Within 5 min of stimulation (250 micrograms/kg carbachol sc), many crypt goblet cells were depleted of mucin secretory granules and their apical membranes had the deep cavitation that accompanies recent compound exocytotic activity. The percentage of crypt epithelial volume occupied by mucin secretory granules was decreased by 58.4% at 5 min and 45.9% at 60 min. Although villus goblet cells never showed signs of recent compound exocytosis, morphometric analysis revealed a 22.4% decrease in the percentage of villus epithelial volume occupied by mucin secretory granules within 5 min of stimulation and a 32.4% decrease by 60 min. The decrease in villus mucin stores was due to both a reduction in the volume of mucin in an average villus goblet cell and a drop in the number of recognizable goblet cells per square micrometer of villus epithelium. Mucin stores in both the crypt and villus regions were largely replenished by 4 h poststimulation.

Intestinal release of mucin in response to HCl and taurocholate: Effect of indomethacin

1. 1. Alkaline secretion and mucin output were analyzed along the gastrointestinal tract of a dog in response to luminal application of HC1 and taurocholate with and without pretreatment with indomethacin. 2. 2. Mucins derived from the different areas displayed similar contents of protein and carbohydrate but differed with respect to associated and covalently bound lipids. 3. 3. Application of HC1 or taurocholate in all the regions caused an increase in the output of mucins and HCO 3 −. However, mucins elaborated in response to HC1 exhibited higher total lipid content and were richer in phospholipids. 4. 4. Pretreatment with indomethacin prior to HC1 application led to a reduction in HCO 3 − and caused a decrease in mucin phospholipid content, but had no effect on HCO 3 − secretion and the lipid content of mucins elaborated in response to taurocholate. 5. 5. The results indicate that mucins elaborated along the gastrointestinal tract differ with respect to lipids, and that their output in response to HC1 is mediated by prostaglandins.