Mucous Metaplasia Research Articles

Changes in expression of the endogenous β-galactoside-binding 14-kDa lectin of chick embryonic skin during epidermal differentiation

Changes in the expression pattern of the gene for the endogenous β-galactoside-binding 14-kDa lectin of chick embryo were examined immunohistochemically during epidermal differentiation in vivo and in vitro with special reference to detailed localization of the 14-kDa lectin. The gene expression was visualized by the HRP-staining method following in situ hybridization, in which sulfonated cDNA was employed as a probe. The 14-kDa lectin gene expression (mRNA) was detected mainly in the intermediate layer of the epidermis: it was faint in 13-day-old embryos, gradually increased in intensity during epidermal differentiation, and became intensely positive in 17-day-old embryo. The expression of the gene in skin explants was suppressed by vitamin A, which induces mucous metaplasia of the epidermis in vitro. The anti-14-kDa lectin reaction was positive mainly in the intermediate layer of the differentiating epidermis, coinciding chronologically with expression of the gene at the light microscopic level. Immunoelectron microscopy revealed that the positive reaction was primarily localized in desmosomes, in tonofilament bundles anchored to the desmosomes, along the outer surface of the plasma membrane, and in the intercellular space. Essentially the same staining pattern was observed in differentiating epidermis in vitro. The positive reaction was markedly reduced in the epidermis in which differentiation had been suppressed in vitro by the addition of vitamin A.

Inhibition by epidermal growth factor (EGF) of epidermal DNA synthesis in cultured chick embryonic skin pretreated with retinol and/or hydrocortisone: specific increment in EGF binding activity in both retinol- and hydrocortisone-pretreated epidermis without correlation to EGF-mediated inhibition of cell growth.

When tarsometatarsal skin of 13-day-old chick embryos that had been cultured in medium containing 5% delipidized FCS with or without retinol (20 microM) and/or hydrocortisone (20 nM) for 1 day was cultured in a chemically defined medium without either the hormone or retinol for 1 day, epidermal DNA synthesis of hydrocortisone- and/or retinol-pretreated skin was inhibited when compared to that of control skin. The addition of epidermal growth factor (EGF, 10 ng/ml) to retinol- or hydrocortisone-pretreated skin further inhibited the epidermal DNA synthesis. Epidermal DNA synthesis in retinol- and hydrocortisone-pretreated skin was more strongly inhibited than in retinol- or hydrocortisone-pretreated skin, but was not further inhibited by EGF. In epidermis which was induced to differentiation toward keratinization by hydrocortisone or mucous metaplasia by retinol, EGF inhibited DNA synthesis. The extent of [125I]-EGF binding to the epidermis of retinol- and hydrocortisone-pretreated skin was 160-180% that in control skin, with no change in affinity. Hence there is no correlation between EGF-binding and the mitogenic activity of EGF.

Histological features of the airways in asthma and COPD.

Asthma and chronic obstructive pulmonary disease (COPD) are complex conditions with imprecise definitions which make definitive morphological comparisons difficult. Broadly, the airways in asthma are occluded by tenacious plugs of exudate and mucus, there is fragility of airway surface epithelium, thickening of the reticular layer beneath the epithelial basal lamina and bronchial vessel congestion and oedema. There is increased inflammatory infiltrate comprising 'activated' lymphocytes and eosinophils with release of granular content in the latter, and there is enlargement of bronchial smooth muscle particularly in medium sized bronchi. Three conditions contribute to COPD. In chronic bronchitis there is mucous hypersecretion with enlargement of tracheo-bronchial submucosal glands and a disproportionate increase of mucous acini. In small (peripheral) airways disease, there is inflammation of bronchioli, mucous metaplasia and hyperplasia, with increased intralumenal mucus, increased wall muscle, fibrosis and airway stenoses. Respiratory bronchiolitis is a critically important early lesion which may predispose to the development of centrilobular emphysema. The severity of destruction of alveolar wall in emphysema appears to be the most important determinant of chronic deterioration of airflow.

Short term retinol treatment in vitro induces stable transdifferentiation of chick epidermal cells into mucus-secreting cells.

Epidermal mucous metaplasia of cultured skin can be induced by treatment with excess retinol for several days (Fell 1957). In the induction of mucous metaplasia, retinol primarily affects the dermal cells and retinol-pretreated dermis can alter epidermal differentiation towards secretory epithelium (Obinata et al. 1987). In this work, we found that mucous metaplasia could be induced by culturing 13-day-old chick embryonic tarsometatarsal skin in medium containing retinol (20 μM) for only 8-24 h, followed by culture in a chemically defined medium (BGJb) without retinol or serum for 6 days. The application of cycloheximide together with retinol during the first 8 h of culture inhibited epidermal mucous metaplasia during subsequent culture for 6 days in BGJb, indicating that induction of a signal(s) in the dermis by excess retinol requires protein synthesis. However, the presence of 20 nM hydrocortisone (Takata et al. 1981) throughout the culture period did not inhibit retinol-induced epidermal mucous metaplasia of the epidermis. This indicates that a brief treatment of the skin with excess retinol determines the direction of epithelial differentiation toward secretory epithelium; this is a simpler in vitro system for the induction of epidermal mucous metaplasia than those established before.

Modification of Mucin Gene Expression in Airway Disease

Mucus hypersecretion is a characteristic feature of several human airway diseases, including chronic bronchitis, cystic fibrosis, and asthma. Although its pathogenesis is poorly understood, hypersecretion apparently results from the abnormally large number of mucous cells found in hypersecretory airways. The factors giving rise to these mucous cells are unknown, but experimental evidence supports possible roles for both mitosis (mucous cell hyperplasia) and differentiation (mucous cell metaplasia). On the basis of the hypothesis that differentiation would require activation of mucin mRNA transcription, we have used mucin cDNA to monitor mucin mRNA levels in an animal model of chronic bronchitis. We first showed that a mucin gene (SMUC or MUC-2) cloned from the human intestine is also expressed in the human airways and is the same or homologous to genes expressed in other human mucin-producing organs. We next showed that a homologue of the SMUC gene is expressed in several animal species, including the rat. Finally, we showed that the induction of experimental chronic bronchitis by SO2 in rats is accompanied by the induction (from near zero baseline) of airway mucin mRNA. The induction by irritants of high steady-state levels of mucin mRNA may represent one of the early events in mucous cell differentiation and hypersecretion.

Morphology of the Airway Wall in Asthma and in Chronic Obstructive Pulmonary Disease

Asthma and chronic obstructive pulmonary disease (COPD) are complex conditions with imprecise definitions, which make definitive morphologic comparisons difficult. Broadly, the airways in asthma are occluded by tenacious plugs of exudate and mucus, and there is fragility of airway surface epithelium, thickening of the reticular layer beneath the epithelial basal lamina, and bronchial vessel congestion and edema. There is increased inflammatory infiltrate comprising "activated" lymphocytes and eosinophils with release of granular content in the latter, and there is enlargement of bronchial smooth muscle, particularly in medium-sized bronchi. Three conditions contribute to COPD. In chronic bronchitis there is mucous hypersecretion with enlargement of tracheobronchial submucosal glands and a disproportionate increase of mucous acini. In small or peripheral airways disease, there is inflammation of bronchioli and mucous metaplasia and hyperplasia, with increased intraluminal mucus, increased wall muscle, fibrosis, and airway stenoses. Respiratory bronchiolitis is a critically important early lesion that may predispose to the development of centrilobular emphysema. The severity of emphysema, rather than type, appears to be the most important determinant of chronic deterioration of airflow, and in this there may be significant loss of elastic recoil prior to the observed morphologic destruction of the acinus.

Stimulation by Bt2cAMP of epidermal mucous metaplasia in retinol-pretreated chick embryonic cultured skin, and its inhibition by herbimycin A, an inhibitor for protein-tyrosine kinase

Epidermal mucous metaplasia of cultured 13-day-old chick embryonic tarsometatarsal skin can be induced by culture in medium containing retinol (20 μM) for only 8–24 h and then in a chemically defined medium without vitamins or serum for 6 days. In the induction of mucous metaplasia, retinol primarily affects the dermal cells and a signal(s) induced in the dermis by excess retinol alters epidermal differentiation toward secretory epithelium. In this work we found that Bt2cAMP (2 mM) stimulated mucous metaplasia severalfold when added to retinol-pretreated skin but inhibited epidermal mucous metaplasia when added together with retinol. Forskolin (100 μM), an activator of adenylate cyclase, also stimulated mucous metaplasia when added to retinol-pretreated skin. On the other hand, transduction in the epidermal cells of a signal(s) induced in dermal cells by excess retinol was inhibited by herbimycin A (500 ng/ml), an inhibitor of protein-tyrosine kinases, and TPA (0.1 μM), an activator of protein kinase C. Hence these findings indicated that cAMP stimulated signal-induced mucous metaplasia, and that transduction of the signal(s) in the epidermal cells required protein-tyrosine kinase and was inhibited by protein kinase C.

Histologic characterization of mouse bronchiolar cell hyperplasia, metaplasia, and neoplasia induced intratracheally by 3-methylcholanthrene.

Female B6C3F1 mice were treated intratracheally with 3-methylcholanthrene (MCA) at intervals of once every 2 weeks for a total of six doses each of 222 micrograms or 457 micrograms/mouse per dose. Animals were necropsied when found dead, moribund, or at the end of the study 43 weeks after the first treatment. Controls were treated with the vehicle (0.2% gelatin saline) only. Lungs were fixed in neutral buffered formalin and processed for light microscopic evaluation. Proliferative and metaplastic bronchiolar cell alterations were seen both within bronchioles and in the alveolar parenchyma. In both locations, changes included hyperplasia of nonciliated cells, squamous cell metaplasia, presence of ciliated cells, and mucous cell metaplasia. Mucous cells were either positive for alcian blue or the periodic-acid Schiff's reaction (PAS), or appeared eosinophilic with hematoxylin and eosin (H&E) but colorless with PAS. Tumors seemed to develop from both extra- and intrabronchiolar areas of cellular proliferation and invaded pulmonary structures. The majority were squamous cell carcinomas and adenosquamous carcinomas, accompanied by a few mucinous cell tumors and some rare tumors that were largely composed of ciliated cells. Combinations of the different metaplastic changes were frequently present in these neoplasms. In summary, it appears that tumors originating from bronchiolar cells in mice show the same morphologic variability that is observed in hyperplastic and metaplastic bronchiolar cells within airways.

Pathology of bacterial gill disease: ultrastructure of branchial lesions

Abstract. The range of branchial lesions associated with bacterial gill disease (BGD) in rainbow trout, Oncorhynchus mykiss (Richardson), was investigated through the ultrastructural examination of 23 separate outbreaks of the disease condition within commercially reared stocks. Diseased branchial tissues had a large and diffusely distributed monomorphic population of filamentous bacteria which were strictly epicellular. Although bacterial colonization was restricted to the branchial cavity, it was neither site nor cell specific: epithelial and chloride cells of the lamellae, filaments and lining tissues of the branchial cavity were all uniformly affected. The bacteria possessed an extensive glycocalyx which appeared to facilitate adhesion to the apices of the microridged sub‐unit modifications of the cell surface. Sites of colonization were accompanied by a diffuse pattern of cellular degeneration and necrosis that was generally restricted to the outer layers of epithelium. The polarity and nature of these changes suggest that the mechanism of interaction between the bacteria and host cells includes progressive hydropic change as a sequel to primary membrane damage and consequent increased cell permeability. These cellular changes were accompanied by the range of stereotypical responses of the gill to damage frequently reported for BGD including lamellar fusion, epithelial hyperplasia, and squamous and mucous cell metaplasia, in addition to lamellar spongiosis.

Modification of mucin gene expression in the airways of rats exposed to sulfur dioxide

The molecular mechanisms mediating mucous cell metaplasia and hypersecretion in the respiratory tract are unknown. Previous work suggests that mucous metaplasia requires the induction of mucin gene expression. We are investigating this possibility by monitoring steady state levels of mucin mRNA in a model of mucous cell metaplasia induced by SO2 exposure. Male Sprague Dawley rats were exposed to 400 ppm SO2 gas in air for 3 h per day, 5 days per week for 0,1,2, or 3 weeks. Sham controls were exposed to air under similar conditions. After 3 weeks, morphological changes were apparent in the epithelium of SO2 exposed rats at all levels from the trachea to the distal airways. The epithelial thickness increased, as well as the number and size of glands in the trachea. Epithelial mucous (goblet) cells increased from 0 to 4.5 per mm in the trachea, 0.2 to 6.2 per mm in the main stem bronchi, and 0.2 to 22.7 per mm in the distal airways (mean values obtained for 3-6 tissue blocks per airway level per condition). In parallel experiments, we used SMUC41, a 950 bp human intestinal cDNA to isolate a human airway cDNA, HAM-1 from a cDNA library constructed in bacteriophage from human bronchial poly A+RNA. HAM-1 is a 90 bp cDNA encoding a threonine- and proline-rich peptide with 96% homology to the human intestinal cDNA SMUC-41. Next we probed total and poly A+ airway RNA from rats in each exposure condition with SMUC-41 or HAM-1. Blots were then stripped and reprobed with cDNA encoding beta actin. Densitometry values normalized for the amount of RNA loaded per lane (as determined by actin hybridization intensity) showed that mucin mRNA increased 8-9 fold as a function of SO2 exposure. This is consistent with the possibility that mucin gene transcription is induced by SO2 exposure, and may represent a primary event in the development of mucous metaplasia and hypersecretion.

Persistence of added retinoids in organ culture media during induction of mucous metaplasia and glandular morphogenesis in hamster cheek pouches

The retinoid concentration (determined colorimetrically) did not change significantly in retinyl acetate-supplemented (6 micrograms/ml) Eagle's Minimal Essential Medium containing 10% fetal calf serum when stored at -20 or 4 degrees C over 7 days. After the medium was incubated at 37 degrees C for 48 h, 37-49% of the retinoid remained, whether or not tissue (neonatal Syrian hamster cheek pouch) was present, and irrespective of explant age. The normal retinoid level in the tissue was approximately 0.25 micrograms per gram. Therefore, neonatal hamster cheek pouches, incubated in medium with the addition of 6 micrograms of retinyl acetate per ml of medium and undergoing mucous metaplasia and some mucous gland morphogenesis, were continually being exposed to retinoid levels which, though gradually decreasing, remained well above their normal physiological level.

Helicobacter pylori is not identified in areas of gastric metaplasia of gall bladder

Sections from 200 cholecystectomy specimens were searched microscopically for areas of gastric metaplasia and Helicobacter (Campylobacter) pylori colonization. The presence of gastric metaplasia was confirmed in 31 cases by the presence of tall columnar cells with abundant apical neutral mucin. Examination of haematoxylin and eosin and, in some cases, Warthin-Starry stained sections failed to demonstrate H. pylori in any of these 31 cases or in 29 other cases with 'bladder neck-type mucous gland metaplasia'. The failure of H. pylori to colonize areas of gastric metaplasia in the gall bladder confirms their intolerance to high concentrations of bile.

Campylobacter pylori and Its Role in Peptic Ulcer Disease

In almost all patients with genuine nondrug-induced duodenal or gastric ulcer there is evidence of gastric Campylobacter pylori colonization and concomitant inflammation. C. pylori is only demonstrable in the duodenal cap when there is "gastric mucus metaplasia." Suppression or eradication of C. pylori with antibiotic therapy may accelerate duodenal ulcer healing. The relapse rate of duodenal ulcer is less after temporary clearing or permanent eradication of C. pylori. As eradication of C. pylori reduces or eliminates gastric (and duodenal) inflammation, this renders the gastroduodenal mucosa less susceptible to reulceration. Interference with C. pylori status presumably explains the retardation of relapse of duodenal ulcer healing with colloidal bismuth subcitrate.

Histology of the major salivary glands.

Major salivary glands are characterized by the presence of numerous excretory units that consist of acini and a peculiar duct system. Under normal conditions, sebaceous glands are annexed to the duct system in the parotid and the submaxillary glands. The excretion of the saliva is assisted by the myoepithelial cells, which play an important role in the morphology of several kinds of salivary gland tumors. Interstitial lymphocytes give rise to the formation of lymph nodes in the parotid gland. Heterotopic salivary tissue is found in many locations throughout the head and neck. Age-induced variations and reactive changes include oncocyte proliferation, fatty infiltration, squamous and mucous metaplasia, hyperplasia, atrophy, and regeneration. An analysis of the normal salivary gland structure permits a morphogenetic approach to an understanding of the variability in histologic types of salivary gland tumors.

Endogenous beta-galactoside-binding lectin expression is suppressed in retinol-induced mucous metaplasia of chick embryonic epidermis.

The fate of endogenous beta-galactoside-binding lectin of chick embryo (14K type) was investigated during the course of skin differentiation. Lectin (14K) was found in keratinized epidermis and was localized mainly in the basal and intermediate cells. However, the protein lectin in the epidermis disappeared when the cultured skin was treated with vitamin A and mucous metaplasia was observed. The synthesis of lectin mRNA was also strongly suppressed by vitamin A in a concentration-dependent manner. On the other hand, in the dermis, in which the lectin was localized in the extracellular matrix, lectin expression was scarcely affected by vitamin A. These results indicated that the lectin was expressed in the keratinized epidermis but that its expression was suppressed in vitamin A-induced mucous-secreting epithelium. The suppression may be a result of a transition of the epidermal regulatory system to one of mucous-secreting epithelium. This is the first finding that 14K lectin expression might be regulated during the course of the epidermal differentiation.

The use of retinoids as probes for analyzing morphogenesis of glands from epithelial tissues.

Thirty-five years ago Honor Fell and Edward Mellanby were studying effects of high doses of vitamin A on skeletal development in chick embryos when they noticed that a piece of epidermis, accidentally included in an organ culture, had undergone mucous metaplasia. Further studies by Fell and others eventually led to an understanding of the important role of vitamin A in modulating epithelia in vivo. Fifteen years later another organ culture experiment showed me that excess vitamin A could also initiate the morphogenesis of branching and mucus-secreting glands from developing vibrissa follicles in upper lip skin of embryonic mice. Since then our group has shown that induction of this novel structure by naturally occurring retinoids resembles a normal embryonic induction in that it is stage-dependent, time-dependent, and irreversible. Tissue separation and recombination studies showed that isolated upper lip epidermis can form these glands when combined with retinoid-treated upper lip dermis. Untreated mouse epidermis can form similar glands after combination with chick dermis containing higher retinoid levels. The hamster cheek pouch, normally devoid of glandular structures, can also form mucous glands when treated with a retinoid, either in vivo or in vitro. Recombination studies in organ culture have now shown that mesenchyme exposed to retinoid is essential for gland morphogenesis from pouch epithelium. Evidence is accumulating that retinoic acid may even be the active morphogen in some normally developing systems.

Epithelial cell markers and proliferating cells in odontogenic jaw cysts

The expression of keratins, CEA, EMA, and rat liver antigen (RLA) and the presence of Ki67+ proliferating cells were studied in the epithelial linings of 50 odontogenic cysts using an indirect immunoperoxidase method on acetone-fixed frozen sections. All cysts were positive with monoclonal antibodies of broad keratin specificity (CK1, AE1-3), and between 40 and 100 per cent of epithelial cells expressed keratins 13 and 19. Keratins 7, 8, and 18 were rarely expressed although surface cells in areas of mucous metaplasia often expressed keratins 7 and 18. Expression of keratin 10/11 was related to the presence of a well-ordered epithelial lining and was detected in isolated cells in 4/32 non-keratinizing cysts and in the upper suprabasal cell layers of 17/18 keratocysts. Although CEA, EMA, and RLA were detected in the epithelium of all specimens, the pattern of expression of CEA and EMA differed between cyst types. Ki67+ proliferating cells were most prevalent in keratocyst epithelia, where they were usually found within lower suprabasal layers which were negative or weakly positive for keratins 10/11 and 13. These results indicate differences in keratin, CEA, and EMA expression between cyst types which appear to be dependent on epithelial differentiation/structure rather than cyst type or histogenesis. Although these differences may not be of diagnostic significance, the consistent expression of both keratins 13 and 19 may provide a useful marker of odontogenic epithelium in general.

Stability of the glandular morphogenesis produced by retinoids in the newborn hamster cheek pouch in vitro.

Retinoids can induce alterations in differentiation and morphogenesis in the hamster cheek pouch. In order to determine the stability of these changes, explants of neonatal pouch were exposed to 6 micrograms/ml of either retinyl acetate (RAc: 1.8 x 10(-5) M) or all-trans retinoic acid (RA: 2.0 x 10(-5) M) for an initial 3 of 7 days, out of a total of 21 days in organ culture. Three days of RAc or RA caused a delay in the differentiation and keratinization of the epithelium at least up to day 7 of culture. Additionally, two out of ten explants exposed to RA showed small downgrowths of epithelium into the stroma at 7 or 14 days. Seven days of exposure to either retinoid led to inhibition of epithelial keratinization, and produced a mucous metaplasia which was still seen at the end of the 21-day culture period. Periodic acid-Schiff (PAS)-positive, diastase-resistant material was present in the metaplastic epithelium, in intercellular, and in some instances, intracellular locations. An excess of either RAc or RA, for 7 days, induced persistent glandlike downgrowths of epithelium, suggesting that a stable alteration in the developmental program of the epithelium may have occurred. Many of these downgrowths possessed a lumen which was lined by cuboidal epithelium and contained PAS-positive, diastase-resistant secretory material. RA appeared more potent than RAc in inhibiting keratinization, in producing a mucous metaplasia, and in initiating glandlike downgrowths. The persistence of glandular downgrowths suggests that retinoids, either directly or indirectly, act in a manner similar to that of an embryonic inductor.

Eosinophil recruitment into guinea pig lungs after PAF-acether and allergen administration. Modulation by prostacyclin, platelet depletion, and selective antagonists.

Intravenous administration of PAF-acether to the guinea pig induces bronchoconstriction, hypotension, intravascular platelet aggregation, endothelial disruption, and platelet and neutrophil diapedesis. These effects are followed within 1 h by an eosinophilic infiltration into the bronchial walls, which was also noted after the administration of antigen to passively sensitized guinea pigs. Bronchoconstriction and eosinophil infiltration are 2 major features of asthma, and selective bronchial eosinophilia characterizes late asthmatic reactions. We compared the histologic effects of PAF-acether 6 and 24 h after its intravenous injection with those of experimental passive anaphylactic shock, which is used as a model for asthma. Six hours after PAF-acether or antigen (ovalbumin) administration, a marked lung eosinophil infiltration, particularly in the bronchial walls, was noted, together with mucous plugs containing eosinophils in the bronchial lumen. Epithelial desquamation was followed after 24 h by mucous metaplasia of the bronchial epithelium. These effects were not observed when the inactive metabolite lyso-PAF was used. Our results agree fully with the suggestion that the eosinophil mediates the pathophysiology of bronchial asthma and releases materials toxic for the respiratory epithelium. Two PAF-acether antagonists (BN 52021 and WEB 2086) prevented the eosinophil infiltration triggered by PAF-acether and by antigen. When PAF-acether or ovalbumin were injected into guinea pigs after antiplatelet serum or prostacyclin, the eosinophil infiltration was significantly reduced, suggesting that platelets or another adenylate cyclase-sensitive cell are important for the subsequent PAF-acether-induced eosinophil infiltration. Our results support an essential role for PAF-acether in an experimental model of allergic asthma.

Sequential histopathologic changes of type I, pre-type II and type II ostertagiasis in cattle

Yearling cattle in Louisiana were examined at monthly intervals for abomasal nematode burdens and histological lesions over a year. Tracer calves were grazed for 3 to 4 weeks and removed from pasture for 2 to 3 weeks, then slaughtered; a few animals were killed in extremis shortly after removal from pasture. Histological changes were correlated with worm burdens and characterized according to the type of Ostertagia ostertagi infection present. In cattle with acute Type I ostertagiosis, changes varied from eosinophil infiltration to glandular dilation and slight mucous cell hyperplasia with submucosal edema. During the summer months the cattle had worm burdens that were primarily early 4th stage larvae (EL 4), with changes characterized by minimal glandular dilation and mucous cell metaplasia and moderate lymphoid cell proliferation and with intramucosal migration of EL 4. In the autumn, the maturation of EL 4 produced the Type II syndrome with severe glandular changes, prominent mucosal hyperplasia and marked lymphoid cell accumulation. With increased duration of the pre-Type II interval, there was greater development of the subepithelial lymphoid tissue and increased frequency of epithelial globule leukocytes. The lymphoproliferation which occurred during the prolonged pre-Type II interval appeared to be related to the increased severity and mortality seen with the Type II ostertagiasis syndrome.