In-situ hybridization localized MUC7 mucin gene expression to the mucous acinar cells of human and MUC7-transgenic mouse salivary glands

Transcriptomic profiling and the first spatial expression analysis of candidate genes in the salivary gland of the East Asian medicinal leech, Hirudo nipponia

Hirudo nipponia, a blood-sucking leech native to East Asia, possesses a rich repertoire of active ingredients in its saliva, showcasing significant medical potential due to its anticoagulant, anti-inflammatory, and antibacterial effects against human diseases. Despite previous studies on the transcriptomic and proteomic characteristics of leech saliva, which have identified medicinal compounds, our knowledge of tissue-specific transcriptomes and their spatial expression patterns remains incomplete. In this study, we conducted an extensive transcriptomic profiling of the salivary gland tissue in H. nipponia based on de novo assemblies of tissue-specific transcriptomes from the salivary gland, teeth, and general head region. Through gene ontology (GO) analysis and hierarchical clustering, we discovered a novel set of anti-coagulant factors-i.e., Hni-Antistasin, Hni-Ghilanten, Hni-Bdellin, Hni-Hirudin-as well as a previously unrecognized immune-related gene, Hni-GLIPR1 and uncharacterized salivary gland specific transcripts. By employing in situ hybridization, we provided the first visualization of gene expression sites within the salivary gland of H. nipponia. Our findings expand on our understanding of transcripts specifically expressed in the salivary gland of blood-sucking leeches, offering valuable resources for the exploration of previously unidentified substances with medicinal applications.

Integrity of the Intestinal Barrier: The Involvement of Epithelial Cells and Microbiota-A Mutual Relationship

Simple Summary

The gastrointestinal tract is a complex organization of various types of epithelial cells forming a single layer of the mucosal barrier, the host mucosal immune system, and microorganisms termed as gut microbiota inhabiting this area. The mucosal barrier, including physical and chemical factors, spatially segregates gut microbiota and the host immune system preventing the development of immune response directed towards non-pathogenic commensals and dietary antigens. However, for the maintenance of the integrity of the mucosal surfaces, cross-talk between epithelial cells and microbiota is required. The microbiome and the intestinal epithelium developed a complex dependence necessary for sustaining intestinal homeostasis. In this review, we highlight the role of specific epithelial cell subtypes and their role in barrier arrangement, the mechanisms employed by them to control intestinal microbiota as well as the mechanisms utilized by the microbiome to regulate intestinal epithelial function. This review will provide information regarding the development of inflammatory disorders dependent on the loss of intestinal barrier function and composition of the intestinal microbiota.

Abstract

The gastrointestinal tract, which is constantly exposed to a multitude of stimuli, is considered responsible for maintaining the homeostasis of the host. It is inhabited by billions of microorganisms, the gut microbiota, which form a mutualistic relationship with the host. Although the microbiota is generally recognized as beneficial, at the same time, together with pathogens, they are a permanent threat to the host. Various populations of epithelial cells provide the first line of chemical and physical defense against external factors acting as the interface between luminal microorganisms and immunocompetent cells in lamina propria. In this review, we focus on some essential, innate mechanisms protecting mucosal integrity, thus responsible for maintaining intestine homeostasis. The characteristics of decisive cell populations involved in maintaining the barrier arrangement, based on mucus secretion, formation of intercellular junctions as well as production of antimicrobial peptides, responsible for shaping the gut microbiota, are presented. We emphasize the importance of cross-talk between gut microbiota and epithelial cells as a factor vital for the maintenance of the homeostasis of the GI tract. Finally, we discuss how the imbalance of these regulations leads to the compromised barrier integrity and dysbiosis considered to contribute to inflammatory disorders and metabolic diseases.

The Role of the Gastrointestinal Mucus System in Intestinal Homeostasis: Implications for Neurological Disorders

Mucus is integral to gut health and its properties may be affected in neurological disease. Mucus comprises a hydrated network of polymers including glycosylated mucin proteins. We propose that factors that influence the nervous system may also affect the volume, viscosity, porosity of mucus composition and subsequently, gastrointestinal (GI) microbial populations. The gut has its own intrinsic neuronal network, the enteric nervous system, which extends the length of the GI tract and innervates the mucosal epithelium. The ENS regulates gut function including mucus secretion and renewal. Both dysbiosis and gut dysfunction are commonly reported in several neurological disorders such as Parkinson's and Alzheimer's disease as well in patients with neurodevelopmental disorders including autism. Since some microbes use mucus as a prominent energy source, changes in mucus properties could alter, and even exacerbate, dysbiosis-related gut symptoms in neurological disorders. This review summarizes existing knowledge of the structure and function of the mucus of the GI tract and highlights areas to be addressed in future research to better understand how intestinal homeostasis is impacted in neurological disorders.

Oral Bacterial and Fungal Microbiome Impacts Colorectal Carcinogenesis

Host's physiology is significantly influenced by microbiota colonizing the epithelial surfaces. Complex microbial communities contribute to proper mucosal barrier function, immune response, and prevention of pathogen invasion and have many other crucial functions. The oral cavity and large intestine are distant parts of the digestive tract, both heavily colonized by commensal microbiota. Nevertheless, they feature different proportions of major bacterial and fungal phyla, mostly due to distinct epithelial layers organization and different oxygen levels. A few obligate anaerobic strains inhabiting the oral cavity are involved in the pathogenesis of oral diseases. Interestingly, these microbiota components are also enriched in gut inflammatory and tumor tissue. An altered microbiota composition - dysbiosis - and formation of polymicrobial biofilms seem to play important roles in the development of oral diseases and colorectal cancer. In this review, we describe the differences in composition of commensal microbiota in the oral cavity and large intestine and the mechanisms by which microbiota affect the inflammatory and carcinogenic response of the host.

The gastrointestinal mucus system in health and disease

Mucins--large, highly glycosylated proteins--are important for the luminal protection of the gastrointestinal tract. Enterocytes have their apical surface covered by transmembrane mucins and goblet cells produce the secreted gel-forming mucins that form mucus. The small intestine has a single unattached mucus layer, which in cystic fibrosis becomes attached, accounting for the intestinal manifestations of this disease. The stomach and colon have two layers of mucus; the inner layer is attached and the outer layer is less dense and unattached. In the colon, the outer mucus layer is the habitat for commensal bacteria. The inner mucus layer is impervious to bacteria and is renewed every hour by surface goblet cells. The crypt goblet cells have the ability to restitute the mucus layer by secretion, for example after an ischaemic challenge. Proteases of certain parasites and some bacteria can cleave mucins and dissolve the mucus as part of their pathogenicity. The inner mucus layer can, however, also become penetrable to bacteria by several other mechanisms, including aberrations in the immune system. When bacteria reach the epithelial surface, the immune system is activated and inflammation is triggered. This mechanism might occur in some types of ulcerative colitis.

Mutations in centrosomal protein CEP152 in primary microcephaly families linked to MCPH4

Primary microcephaly is a rare condition in which brain size is substantially diminished without other syndromic abnormalities. Seven autosomal loci have been genetically mapped, and the underlying causal genes have been identified for MCPH1, MCPH3, MCPH5, MCPH6, and MCPH7 but not for MCPH2 or MCPH4. The known genes play roles in mitosis and cell division. We ascertained three families from an Eastern Canadian subpopulation, each with one microcephalic child. Homozygosity analysis in two families using genome-wide dense SNP genotyping supported linkage to the published MCPH4 locus on chromosome 15q21.1. Sequencing of coding exons of candidate genes in the interval identified a nonconservative amino acid change in a highly conserved residue of the centrosomal protein CEP152. The affected children in these two families were both homozygous for this missense variant. The third affected child was compound heterozygous for the missense mutation plus a second, premature-termination mutation truncating a third of the protein and preventing its localization to centrosomes in transfected cells. CEP152 is the putative mammalian ortholog of Drosphila asterless, mutations in which affect mitosis in the fly. Published data from zebrafish are also consistent with a role of CEP152 in centrosome function. By RT-PCR, CEP152 is expressed in the embryonic mouse brain, similar to other MCPH genes. Like some other MCPH genes, CEP152 shows signatures of positive selection in the human lineage. CEP152 is a strong candidate for the causal gene underlying MCPH4 and may be an important gene in the evolution of human brain size.

Functional analysis of human MUC7 mucin gene 5'-flanking region in lung epithelial cells

The human MUC7 gene encodes a low-molecular-mass mucin glycoprotein that functions in modulation of microbial flora in the oral cavity and respiratory tracts. MUC7 gene expression is tissue- and cell-specific, with dominant expression in salivary gland acinar cells. To begin to understand the molecular mechanisms responsible for controlling MUC7 gene expression, we analyzed the promoter activity of MUC7 5'-flanking region in a human lung epithelial cell line A549. We demonstrated that MUC7 gene is expressed constitutively in this cell line and is upregulated by TNF-alpha stimulation. The promoter activities of a 2,762-bp fragment of the human genomic DNA (-2,732/+30 bp) and its deletion series, subcloned into a luciferase reporter vector, were characterized at the basal level and under stimulation by TNF-alpha. The results indicated that the minimal functional MUC7 promoter is in the region of -138/+30 bp. This region also revealed the greatest increase in the promoter activity upon TNF-alpha stimulation. Two putative AP1-binding elements and one NF-kappaB-binding element were identified within the proximal promoter. Further analyses demonstrated that mutations of these elements dramatically reduced specific DNA-protein binding ability and reporter gene expression. AP1 elements played an essential role in the constitutive expression, while the NF-kappaB element was crucially important in the response to TNF-alpha stimulation, demonstrating that TNF-alpha activates MUC7 transcription via NF-kappaB signaling pathway.

Regulation of mucin expression: mechanistic aspects and implications for cancer and inflammatory diseases

Mucins are large multifunctional glycoproteins whose primary functions are to protect and lubricate the surfaces of epithelial tissues lining ducts and lumens within the human body. Several lines of evidence also support the involvement of mucins in more complex biological processes such as epithelial cell renewal and differentiation, cell signaling, and cell adhesion. Recent studies have uncovered the role of select mucins in the pathogenesis of cancer, underscoring the importance of a detailed knowledge about mucin biology. Under normal physiological conditions, the production of mucins is optimally maintained by a host of elaborate and coordinated regulatory mechanisms, thereby affording a well-defined pattern of tissue-, time-, and developmental state-specific distribution. However, mucin homeostasis may be disrupted by the action of environmental and/or intrinsic factors that affect cellular integrity. This results in an altered cell behavior that often culminates into a variety of pathological conditions. Deregulated mucin production has indeed been associated with numerous types of cancers and inflammatory disorders. It is, therefore, crucial to comprehend the underlying basis of molecular mechanisms controlling mucin production in order to design and implement adequate therapeutic strategies for combating these diseases. Herein, we discuss some physiologically relevant regulatory aspects of mucin production, with a particular emphasis on aberrations that pertain to pathological situations. Our views of the achievements, the conceptual and technical limitations, as well as the future challenges associated with studies of mucin regulation are exposed.

Patterns of secretion of mucins and non-mucin glycoproteins in human submandibular/sublingual secretion

The present investigation has characterised the influence of gustatory stimulation and duration of stimulation on the secretion pattern of salivary mucins MG1 and MG2 and non-mucin glycoproteins in submandibular/sublingual secretion (SMSL). Resting SMSL was collected for three 2 min intervals and stimulated SMSL was collected for ten 1 min intervals from six healthy subjects. Flow rates and total protein were significantly different under the two conditions. The secretion patterns of these proteins under resting and stimulated conditions was examined on periodic acid-Schiff reagent (PAS)-stained polyacrylamide gels using a Kodak Digital-Science Image Station. Image analyses revealed that the level of MG1 increased and the level of MG2 remained nearly the same after stimulation. Six other major glycoproteins (designated Band 1-6) were identified on the basis of their electrophoretic mobilities and immuno-reactivity on Western blots. After stimulation the intensity of Band 1 (lactoferrin and peroxidase) and Band 2 (amylase) decreased whereas the intensity of Band 3 (carbonic anhydrase), Band 4 (proline-rich glycoprotein) and Bands 5 and 6 (basic glycosylated proline-rich proteins) increased. These patterns probably reflect secretion from preformed vesicles since de novo synthesis would be unexpected within the time frame of these experiments. The variable patterns observed suggest that mucins and non-mucin glycoproteins in SMSL derive from different subsets of secretory vesicles, some of which may originate in mucous and others in serous acini, as well as in ductal cells. Quantification of mucins was performed by image analysis technology using purified MG1 and MG2 standards. Finally, the present investigation has shown that the secretory patterns of mucins and non-mucin glycoproteins from submandibular/sublingual glands are complex and represent an important aspect of salivary gland physiology.

Electron microscopic immunogold localization of salivary mucins MG1 and MG2 in human submandibular and sublingual glands

The human salivary mucins MG1 and MG2 are well characterized biochemically and functionally. However, there is disagreement regarding their cellular and glandular sources. The aim of this study was to define the localization and distribution of these two mucins in human salivary glands using a postembedding immunogold labeling method. Normal salivary glands obtained at surgery were fixed in 3% paraformaldehyde-0.1% glutaraldehyde and embedded in Lowicryl K4M or LR Gold resin. Thin sections were labeled with rabbit antibodies to MG1 or to an N-terminal synthetic peptide of MG2, followed by gold-labeled goat anti-rabbit IgG. The granules of all mucous cells of the submandibular and sublingual glands were intensely reactive with anti-MG1. No reaction was detected in serous cells. With anti-MG2, the granules of both mucous and serous cells showed reactivity. The labeling was variable in both cell types, with mucous cells exhibiting a stronger reaction in some glands and serous cells in others. In serous granules, the electron-lucent regions were more reactive than the dense cores. Intercalated duct cells near the acini displayed both MG1 and MG2 reactivity in their apical granules. In addition, the basal and lateral membranes of intercalated duct cells were labeled with anti-MG2. These results confirm those of earlier studies on MG1 localization in mucous cells and suggest that MG2 is produced by both mucous and serous cells. They also indicate differences in protein expression patterns among salivary serous cells.

Expression of membrane-associated mucins MUC1 and MUC4 in major human salivary glands

Mucins are high molecular weight glycoproteins secreted by salivary glands and epithelial cells lining the digestive, respiratory, and reproductive tracts. These glycoproteins, encoded in at least 13 distinct human genes, can be subdivided into gel-forming and membrane-associated forms. The gel-forming mucin MUC5B is secreted by mucous acinar cells in major and minor salivary glands, but little is known about the expression pattern of membrane-associated mucins. In this study, RT-PCR and Northern blotting demonstrated the presence of transcripts for MUC1 and MUC4 in both parotid and submandibular glands, and in situ hybridization localized these transcripts to epithelial cells lining striated and excretory ducts and in some serous acinar cells. The same cellular distribution was observed by immunohistochemistry. Soluble forms of both mucins were detected in parotid secretion after immunoprecipitation with mucin-specific antibodies. These studies have shown that membrane-associated mucins are produced in both parotid and submandibular glands and that they are expressed in different cell types than gel-forming mucins. Although the function of these mucins in the oral cavity remains to be elucidated, it is possible that they both contribute to the epithelial protective mucin layer and act as receptors initiating one or more intracellular signal transduction pathways.

Immunoquantification of human salivary mucins MG1 and MG2 in stimulated whole saliva: factors influencing mucin levels

While more and more is known about the structure and function of human salivary mucins, there is relatively little information on quantification of these glycoconjugates in whole saliva and on factors influencing their secretion. The goal of the present work was to develop capture ELISAs that would allow for rapid, inexpensive, and reliable measurement of the salivary mucins MG1 and MG2, and to use these immunological procedures to investigate the significance of age, gender, flow rate, and protein concentration on mucin levels in whole saliva. Previously, we described a rabbit polyclonal antibody against MG1 (Troxler et al., 1995) and a rabbit polyclonal peptide antibody against an epitope in the N-terminal region of MG2 (Liu et al., 1999) which were used to develop the capture ELISAs. We verified the accuracy and specificity of these assays by showing correct measurement of known quantities of purified MG1 or MG2 added to whole saliva and lack of cross-reactivity between mucins and heterologous antisera on Western blots or in ELISAs. Whole saliva was collected from 60 subjects under conditions of masticatory stimulation, flow rates were recorded, and mucin concentrations were determined. The results showed that the mean concentration of MG1 and MG2 was 23.3 +/- 14.6 mg% and 13.3 +/- 11.6 mg%, respectively, and that mucins constitute approximately 16% of the total protein in whole saliva. No significant correlations were found between mucin levels and age or flow rate; however, a significant correlation was found between MG2 levels and total protein concentration. Furthermore, there were statistically significant gender differences in flow rate and MG1 levels, but not in MG2 levels. The availability of these immunoassays for quantification of MG1 and MG2 will help to elucidate the role of mucin in oral health and disease.