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

A novel immunofluorescence study of Lingual Salivary Glands in the Egyptian Tortoise (Testudo kleinmanni) and its ecological significance

The Egyptian tortoise (Testudo kleinmanni) is remarkably adapted to its harsh desert environment, a characteristic that is crucial for its survival under extreme conditions. This study was aimed at providing a deeper understanding of the lingual salivary gland structures in the Egyptian tortoise and examining how these structures help the tortoise manage hydration and nutrition in arid conditions. Utilizing a combination of light microscopy and immunofluorescence, this research introduced pioneering methods involving seven different antibodies, marking a first in the study of reptilian salivary glands. Our investigations categorized the tortoise's salivary glands into papillary and non-papillary types. The papillary glands were further classified into superficial, deep, interpapillary, and intraepithelial salivary glands, while non-papillary glands included superficial and deep lingual types. Structurally, these glands are organized into lobules, delineated by interlobular septa, and are equipped with a duct system comprising interlobular, intercalated, and main excretory ducts with gland openings on the tongue's surface and the papillae surfaces. Notably, the superficial glands displayed both tubuloalveolar and acinar configurations, whereas the deep lingual glands were exclusively acinar. Immunofluorescence results indicated that α-smooth muscle actin (α-SMA) was prevalent in myoepithelial cells, myofibroblasts, and blood vessels, suggesting their integral role in glandular function and support. E-cadherin was predominantly found in epithelial cells, enhancing cell adhesion and integrity, which are critical for efficient saliva secretion. Importantly, Mucin 1 (MUC1) and Mucin 5B (MUC5B) staining revealed that most glands were mucous in nature, with MUC5B specifically marking mucin within secretory cells, confirming their primary function in mucous secretion. PDGFRα and CD34 highlighted the presence of telocytes and stromal cells within the glandular and interlobular septa, indicating a role in structural organization and possibly in regenerative processes. Cytokeratin 14 expression was noted in the basal cells of the glands, underscoring its role in upholding the structural foundation of the epithelial barrier. In conclusion, this detailed morphological and immunological characterization of the Egyptian tortoise's salivary glands provides new insights into their complex structure and essential functions. These findings not only enhance our understanding of reptilian physiology but also underline the critical nature of salivary glands in supporting life in arid environments. This study's innovative use of a broad range of immunofluorescence markers opens new avenues for further research into the adaptive mechanisms of reptiles.

Rapid and visual detection of specific bacteria for saliva and vaginal fluid identification with the lateral flow dipstick strategy

Identification of body fluids is critical for crime scene reconstruction, and a source of investigation source of investigative leads. In recent years, microbial DNA analysis using sequencing and quantitative real-time polymerase chain reaction have been used to identify body fluids. However, these techniques are time-consuming, expensive, and require complex workflows. In this study, a new method for simultaneous detection of Streptococcus salivarius and Lactobacillus crispatus using polymerase chain reaction (PCR) in combination with a lateral flow dipstick (LFD) was developed to identify saliva and vaginal fluid in forensic samples. LFD results can be observed with the naked eye within 3 min with a sensitivity of 0.001 ng/µL DNA. The PCR-LFD assay was successfully used to detect S. salivarius and L. crispatus in saliva and vaginal fluid respectively, and showed negative results in blood, semen, nasal fluid, and skin. Moreover, saliva and vaginal fluid were detectable even at an extremely high mixing ratio of sample DNA (1:999). Saliva and vaginal fluid were identified in various mock forensic samples. These results indicate that saliva and vaginal fluid can be effectively detected by identifying S. salivarius and L. crispatus, respectively. Furthermore, we have shown that DNA samples used to identify saliva and vaginal fluid can also provide a complete short tandem repeat (STR) profile when used as source material for forensic STR profiling. In summary, our results suggest that PCR-LFD is a promising assay for rapid, simple, reliable, and efficient identification of body fluids.

High-Resolution Transcriptomic Landscape of the Human Submandibular Gland

Saliva-secreting and transporting cells are part of the complex cellular milieu of the human salivary gland, where they play important roles in normal glandular physiology and diseased states. However, comprehensive molecular characterization, particularly at single-cell resolution, is still incomplete, in part due to difficulty in procuring normal human tissues. Here, we perform an in-depth analysis of male and female adult human submandibular gland (SMG) samples by bulk RNA sequencing (RNA-seq) and examine the molecular underpinnings of the heterogeneous cell populations by single-cell (sc) RNA-seq. Our results from scRNA-seq highlight the remarkable diversity of clusters of epithelial and nonepithelial cells that reside in the SMG that is also faithfully recapitulated by deconvolution of the bulk-RNA data sets. Our analyses reveal complex transcriptomic heterogeneity within both the ductal and acinar subpopulations and identify atypical SMG cell types, such as mucoacinar cells that are unique to humans and ionocytes that have been recently described in the mouse. We use CellChat to explore ligand-receptor interactome predictions that likely mediate crucial cell-cell communications between the various cell clusters. Finally, we apply a trajectory inference method to investigate specific cellular branching points and topology that offers insights into the dynamic and complex differentiation process of the adult SMG. The data sets and the analyses herein comprise an extensive wealth of high-resolution information and a valuable resource for a deeper mechanistic understanding of human SMG biology and pathophysiology.

Internal reference genes with the potential for normalizing quantitative PCR results for oral fluid specimens

In basic research, testing of oral fluid specimens by real-time quantitative polymerase chain reaction (qPCR) has been used to evaluate changes in gene expression levels following experimental treatments. In diagnostic medicine, qPCR has been used to detect DNA/RNA transcripts indicative of bacterial or viral infections. Normalization of qPCR using endogenous and exogenous reference genes is a well-established strategy for ensuring result comparability by controlling sample-to-sample variation introduced during sampling, storage, and qPCR testing. In this review, the majority of recent publications in human (n = 136) and veterinary (n = 179) medicine did not describe the use of internal reference genes in qPCRs for oral fluid specimens (52.9% animal studies; 57.0% human studies). However, the use of endogenous reference genes has not been fully explored or validated for oral fluid specimens. The lack of valid internal reference genes inherent to the oral fluid matrix will continue to hamper the reliability, reproducibility, and generalizability of oral fluid qPCR assays until this issue is addressed.

Assessment of salivary alpha amylase and mucin-4 before and after non-surgical treatment of peri-implant mucositis

BACKGROUND

The present study was based on the null hypothesis that there is no difference in clinicoradiographic parameters and whole salivary alpha amylase (AA) and mucin-4 levels before and after non-surgical mechanical debridement (NSMD) of patients with peri-implant mucositis (PM). The aim was to assess whole salivary AA and mucin-4 levels before and after treatment of PM.

METHODS

Patients with PM (Group-1) and individuals without peri-implant diseases (Group-2) were included. Demographic data was collected and peri-implant modified plaque and bleeding indices (mPI and mBI, respectively), probing depth (PD) and crestal bone loss were measured at baseline. Levels of AA and mucin-4 were assessed in unstimulated whole saliva samples. All patients underwent full-mouth non-surgical periodontal therapy (NSPT) and NSMD; and clinical parameters and salivary biomarkers were re-assessed after 3 months. Level of significance was set at P < 0.01.

RESULTS

Twenty-six and 32 individuals were included in groups 1 and 2, respectively. None of the participants had periodontitis. At baseline clinical periodontal parameters (PI [P < 0.001], GI [P < 0.001], clinical AL [P < 0.001] and PD [P < 0.001]) were significantly high in Group-1 than Group-2. At 3-month follow-up, there was a statistically significant reduction in clinical periodontal and peri-implant parameters (PI [P < 0.01], GI [P < 0.01], and PD [P < 0.01]) in Group-1 compared with their baseline values. At baseline, salivary AA levels were significantly high in Group-1 than Group-2 (P < 0.01). At 3-month follow-up, there was no significant difference in whole salivary AA levels among patients in groups 1 and 2.

CONCLUSIONS

The AA and mucin-4 levels are potential biomarkers for evaluation of peri-implant diseases including PM. Mechanical instrumentation continues to be the most predictable treatment option for the management of peri-implant diseases.

Development and validation of an mRNA-based multiplex body fluid identification workflow and a rectal mucosa marker pilot study

Molecular identification of body fluids and tissues is crucial in order to understand the circumstances of crimes. For that reason, molecular investigations used to identify body fluids/tissues have increasingly been examined recently. Various studies have proved that messenger RNA (mRNA) profiling is a sensitive and robust method for body fluid/tissue identification. The forensically relevant body fluids/tissues blood, semen, saliva, vaginal secretion, menstrual blood and skin have all been detected successfully by applying suitable mRNA assay. However, rectal mucosa, which can be found as evidence in sexual assault cases, has been neglected in forensic investigations. So far there is no mRNA marker to detect rectal mucosa, although anal penetration occurs in a large number of sexual assaults (23.2% of female victims and 50% of male victims). In this study, specific and sensitive mRNA markers for forensically relevant body fluids were adapted and validated in an mRNA multiplex assay for routine casework. This included the implementation of a DNA/RNA re-extraction method for automated extraction that can be integrated into casework without loss of DNA. This re-extraction method and the mRNA multiplex assay were tested using casework samples. PCR-primers were designed for the identification of rectal mucosa and the more effective marker MUC12 was integrated into an extended multiplex assay. The result of our study is a highly specific and sensitive mRNA multiplex assay plus an automated DNA/RNA re-extraction method, that can be integrated into casework and identify rectal mucosa for the first time.

Building a Functional Salivary Gland for Cell-Based Therapy: More than Secretory Epithelial Acini

A few treatment options exist for patients experiencing xerostomia due to hyposalivation that occurs as a result of disease or injury to the gland. An opportunity for a permanent solution lies in the field of salivary gland replacement through tissue engineering. Recent success emboldens in the vision of producing a tissue-engineered salivary gland composed of differentiated salivary epithelial cells that are able to differentiate to form functional units that produce and deliver saliva to the oral cavity. This vision is augmented by advances in understanding cellular mechanisms that guide branching morphogenesis and salivary epithelial cell polarization in both acinar and ductal structures. Growth factors and other guidance cues introduced into engineered constructs help to develop a more complex glandular structure that seeks to mimic native salivary gland tissue. This review describes the separate epithelial phenotypes that make up the gland, and it describes their relationship with the other cell types such as nerve and vasculature that surround them. The review is organized around the links between the native components that form and contribute to various aspects of salivary gland development, structure, and function and how this information can drive the design of functional tissue-engineered constructs. In addition, we discuss the attributes of various biomaterials commonly used to drive function and form in engineered constructs. The review also contains a current description of the state-of-the-art of the field, including successes and challenges in creating materials for preclinical testing in animal models. The ability to integrate biomolecular cues in combination with a range of materials opens the door to the design of increasingly complex salivary gland structures that, once accomplished, can lead to breakthroughs in other fields of tissue engineering of epithelial-based exocrine glands or oral tissues.

Diversity of mucins in labial glands of infants

Mucins as highly glycosylated proteins comprise multiple functions like protection, homeostasis, immune defense, cell signaling. Various epithelial tissues including glandular structures express different specific mucin types. We investigated labial salivary glands in infants for the occurrence of MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, and MUC7 by immunohistochemistry. MUC1 and MUC4 were detected in serous and ductal glandular cells, partially intensified at the apical plasma membrane. MUC3 was found in ductal glandular cells and in myoepithelial cells. MUC5B exhibited a mosaic expression pattern in mucous glandular endpieces. MUC2 and MUC7 were abundant in serous acini. Glandular structures were negative for MUC5AC. A comprehensive study of specific mucins in labial salivary glands of infants was presented for the first time. As a representative of the minor salivary glands, labial glands are, due to their localization, directly exposed to environmental influences. The distribution of a broad spectrum of mucins in infantile labial glands indicates their importance early in human development to sustain oral health.

Importance of digestive mucus and mucins for designing new functional food ingredients

The mucus, mainly composed of the glycoproteins mucins, is a rheological substance that covers the intestinal epithelium and acts as a protective barrier against a variety of harmful molecules, microbial infection and varying lumen environment conditions. Alterations in the composition or structure of the mucus could lead to various diseases such as inflammatory bowel disease or colorectal cancer. Recent studies revealed that an exogenous intake of probiotic bacteria or other dietary components (such as bioactive peptides and probiotics) derived from food influence mucus layer properties as well as modulate gene expression and secretion of mucins. Therefore, the use of such components for designing new functional ingredients and then foods, could constitute a novel approach to preserve the properties of mucus. After presenting some aspects of the mucus and mucins in the gastrointestinal tract as well as mucus role in the gut health, this review will address role of dietary ingredients in improving mucus/mucin production and provides new suggestions for further investigations of how dietary ingredients/probiotics based functional foods can be developed to maintain or improve the gut health.

Assessing the prognostic significance of MUC4β in mucoepidermoid carcinoma of the salivary glands: An immunohistochemical study

Objectives

– Routine histopathological grading for salivary gland mucoepidermoid carcinoma (MEC) have failed to prognosticate these tumors, resulting in poor post-surgical outcomes. In developing countries, the lack of technologically advanced infrastructure curtails, efficient treatment modalities. This study aimed at determining if MUC4β can characterize salivary gland MEC and serve as a practical and inexpensive method to prognosticate salivary gland MEC.

Materials and methods

– Fifteen cases of archived paraffin embedded tissue blocks of mucoepidermoid carcinomas were reassessed for histopathological grading using Healey's system, modified by Batsakis and Luna and immunohistochemically evaluated for expression of MUC4β. Statistical analysis (Kappa statistics and Spearman's rho correlation coefficient) was performed to assess inter-observer reproducibility and to correlate the expression of MUC4β with the histopathological grade of the tumor.

Results

MUC4β expression is related to tumor differentiation in an inverse relationship. Two cases of high grade MEC were the exception to this rule.

Conclusion

Our study revealed that MUC4β alone cannot serve as a reliable prognostic marker due to its divergent tumor suppressor and oncogenic pathway. The role of MUC4β needs further evaluation and research so as to potentiate therapeutics depending upon its context dependent function, as a cancer marker or an oncogenic factor.

Methodology for the establishment of primary porcine vocal fold epithelial cell cultures

OBJECTIVE

A current lack of methods for epithelial cell culture significantly hinders our understanding of the role of the epithelial and mucus barriers in vocal fold health and disease. Our first objective was to establish reproducible techniques for the isolation and culture of primary porcine vocal fold epithelial cells. Our second objective was to evaluate the functional significance of cell cultures using an in vitro exposure to an inflammatory cytokine.

METHODS

Epithelial cells were isolated from porcine vocal folds and expanded in culture. Characterization of cultures was completed by immunostaining with markers for pan-cytokeratin (epithelial cells), vimentin (stromal cells), von Willebrand factor (endothelial cell), and MUC1 and MUC4 (mucin) glycoproteins. Established epithelial cell cultures were then exposed to the inflammatory cytokine tumor necrosis factor alpha (TNF-α) for 24-hours, and transcript expression of MUC1 and MUC4 was evaluated.

RESULTS

Reproducible, porcine vocal fold epithelial cell cultures, demonstrating cobblestone appearance characteristic of the typical morphology of epithelial cell cultures were created. Cells showed positive staining for pan-cytokeratin with limited expression of vimentin and von Willebrand factor. Epithelial cells also expressed MUC1 and MUC4. TNF-α significantly increased transcript expression of MUC4.

CONCLUSION

Here, we present the first report of successful culture of primary porcine vocal fold epithelial cells. Cultures will provide researchers with a valuable new in vitro tool to investigate vocal fold epithelium and mucus as well as the effects of common challenges, including inflammatory cytokines, on these barriers.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E355-E364, 2019.

MUC7 Level As A New Saliva Risk Factor For Dental Caries In Adult Patients

Purpose: Data currently available indicate the significance of salivary mucins MUC5B and MUC7 in the protection of teeth against caries. Our study aimed to determine the relationship between dental caries in adults and levels of MUC5B and MUC7. Methods: The studies were conducted on 45 adult subjects selected on the basis of dental examination and calculation of the DMFT (Decayed, Missing, and Filled Teeth) index. Among these patients, two research groups were distinguished: group 1 included 19 caries-free subjects (DMFT = 0); and group 2 included 26 patients with severe caries (DMFT > 13.9). Samples of whole unstimulated saliva were collected and centrifuged. MUC5B and MUC7 content in saliva supernatant were estimated using an enzyme-linked immunosorbent sandwich assay (ELISA). Analysis of the obtained data receiver operating characteristic (ROC) curves was employed to define relationships between the contents of the studied mucins and the detected dental caries. Results: In subjects from group 1, the mean level of MUC5B amounted to 0.63 ± 0.35 ng/ml and this was significantly higher than the concentration of mucin in patients of group 2, which amounted to 0.38 ± 0.32 ng/ml (p = 0.023). The mean level of MUC7 amounted to 5.47 ± 1.18 ng/ml and this was significantly higher than the level of the mucin in group 2, which was 1.39 ± 0.86 ng/ml (p< 0.0001). In parallel, a relationship was detected between levels of the examined mucins and manifestation of dental caries. For MUC7, the optimal cut-off value was obtained (i.e. corresponding to 100% sensitivity and specificity), amounting to 2.5 ng/ml for the detection of dental caries risk. Conclusions: Development of dental caries is linked to reduced concentrations of MUC5B and MUC7. The level of MUC7 may represent a significant parameter clinically suitable for evaluation of disease risk.

Oral epithelial MUC1 and oral health

OBJECTIVES

To provide information about MUC1, epithelial membrane-bound mucin, in terms of its role in oral health.

DESIGN

The expression and functional roles of MUC1 in the oral mucosa and salivary glands were reviewed. Information on the modulation of oral mucosal epithelial MUC1 expression compared with that of endometrial epithelial MUC1 expression was also reviewed. In addition, the possible associations between oral mucosal epithelial MUC1 and oral diseases were explored.

RESULTS

MUC1 is expressed in the oral mucosa and major and minor salivary glands. Protection of oral mucosal surfaces is believed to be the main function of oral mucosal epithelial MUC1. Its role in the salivary glands is thought to facilitate salivary flow through the ductal system. Information on the role of MUC1 in signal transduction and modulation of immune function in the oral cavity is sparse. However, the possible roles of MUC1 in dry mouth conditions, burning mouth syndrome, dental caries, and oral candidiasis have been suggested.

CONCLUSIONS

Despite limited information, it is clear that oral epithelial MUC1 plays an important role in oral health. Further research evaluating the physiological and pathological roles of MUC1 in the oral cavity is warranted.

Transcriptional profiling reveals gland-specific differential expression in the three major salivary glands of the adult mouse

RNA-Seq was used to better understand the molecular nature of the biological differences among the three major exocrine salivary glands in mammals. Transcriptional profiling found that the adult murine parotid, submandibular, and sublingual salivary glands express greater than 14,300 protein-coding genes, and nearly 2,000 of these genes were differentially expressed. Principle component analysis of the differentially expressed genes revealed three distinct clusters according to gland type. The three salivary gland transcriptomes were dominated by a relatively few number of highly expressed genes (6.3%) that accounted for more than 90% of transcriptional output. Of the 912 transcription factors expressed in the major salivary glands, greater than 90% of them were detected in all three glands, while expression for ~2% of them was enriched in an individual gland. Expression of these unique transcription factors correlated with sublingual and parotid specific subsets of both highly expressed and differentially expressed genes. Gene ontology analyses revealed that the highly expressed genes common to all glands were associated with global functions, while many of the genes expressed in a single gland play a major role in the function of that gland. In summary, transcriptional profiling of the three murine major salivary glands identified a limited number of highly expressed genes, differentially expressed genes, and unique transcription factors that represent the transcriptional signatures underlying gland-specific biological properties.

Mucins: Structural diversity, biosynthesis, its role in pathogenesis and as possible therapeutic targets

Mucins are the main structural components of mucus that create a selective protective barrier for epithelial surface and also execute wide range of other physiological functions. Mucins can be classified into two types, namely secreted mucins and membrane bounded mucins. Alterations in mucin expression or glycosylation and mislocalization have been seen in various types of pathological conditions such as cancers, inflammatory bowel disease and ocular disease, which highlight the importance of mucin in maintaining homeostasis. Hence mucins can be used as attractive target for therapeutic intervention. In this review, we discuss in detail about the structural diversity of mucins; their biosynthesis; its role in pathogenesis; regulation and as possible therapeutic targets.

Mucoepidermoid carcinoma-associated expression of MUC5AC, MUC5B and mucin-type carbohydrate antigen sialyl-Tn in the parotid gland

OBJECTIVES

The aberrant expression of mucins and mucin-type carbohydrates has been described in many types of cancer, including mucoepidermoid carcinoma (MEC), a malignant salivary gland tumor. In this study, we examined the aberrant expression patterns of mucins (MUC1, MUC4, MUC5AC and MUC5B), simple mucin-type carbohydrate antigens (Tn, sialyl-Tn and T) and mature carbohydrate antigens (Lewis^a and sulfo-Lewis^a antigens) in MEC originating from the parotid gland, which normally does not secrete mucins.

DESIGN

We conducted an immunohistochemical study to investigate the presence of mucins and carbohydrates in 24 MEC samples originating from the parotid gland and in surrounding normal tissue of the same gland in comparison 6 samples of normal salivary glands. The expression levels were compared with respect to the histological grading. Furthermore, 24 MEC samples from non-parotid salivary glands were included.

RESULTS

We observed loss of topology of membrane-bound MUC1 and MUC4, and de novo expression of MUC5AC, MUC5B and sialyl-Tn in MEC that originated in the parotid gland. Furthermore, mucins MUC1, MUC4 and carbohydrate antigens Tn, sialyl-Tn, T, Lewis^a and sulfo-Lewis^a were overexpressed in MEC samples compared to surrounding normal salivary gland tissues. MUC1 was expressed in both low- and high grade MECs, whereas MUC4 was not expressed in high grade MECs of the parotid gland.

CONCLUSION

During the development of MEC in the parotid gland, the genes for gel-forming secretory mucins are switched on. Besides these MEC tissues overexpress short oligosaccharides, suggesting that the glycosylation machinery is altered.

Pro-inflammatory Cytokines Up-regulate MUC1 Gene Expression in Oral Epithelial Cells

The membrane-bound mucin MUC1 is expressed ubiquitously on epithelial surfaces and is thought to provide protection from bacterial and chemical injury. The present study was undertaken to determine whether MUC1 was expressed in cultured oral epithelial cells and whether expression is modulated by pro-inflammatory mediators released as part of the host response to infection by oral pathogens. Northern and Western blotting experiments showed that KB cells express MUC1 mRNA and protein. When cells were treated with interleukins (IL-1β, IL-6), tumor necrosis factor-alpha (TNF-α), or interferon-gamma (IFN-γ), or combinations of these, real-time PCR demonstrated that MUC1 mRNA increased 1.4- to 3.2-fold. Interestingly, a significant increase in levels of MUC1 protein was also observed. While no effect was observed when KB cells were incubated with LPS from Porphyromonas gingivalis, infection of KB monolayers with this oral pathogen caused a 2.85-fold increase in MUC1 transcript levels. These results suggest that increased MUC1 synthesis may be a key element in the host response to infection with oral pathogens.

Glycomic profile of the human parotid gland between 18th and 26th week of fetal development

The formation of new and functional structural components of several organs, such as parotid glands, can be influenced by the glycocode. This study analyzed the glycobiology of parotid salivary gland tissue during fetal development using specific biochemical probes (lectins and antibodies). Eleven parotid gland samples from human fetuses were obtained from spontaneous abortions at 14-28 weeks of gestation, and tissue sections were analyzed for lectin histochemistry and immunohistochemistry. From the 18th to 26th week, Canavalia ensiformis agglutinin, wheat germ agglutinin, Ulex europaeus agglutinin-I, peanut agglutinin, Sambucus nigra agglutinin, and Vicia villosa agglutinin lectin staining were predominantly observed in the apical and/or basement membranes of the ducts and tubulo-acinar units. Moreover, the presence of galectin-1 was found in the membrane, cytoplasm, and nucleus of both structures. Conversely, Gal-3 and mucin-1 were restricted to the glandular ducts. The lectin staining pattern changed during the weeks evaluated. Nevertheless, the carbohydrate subcellular localization represented a key factor in the investigation of structural distribution profiles and possible roles of these glycans in initial parotid gland development. These findings are defined by their high biological value and provide an important base for the development of subsequent studies. (J Oral Sci 58, 353-360, 2016).

Salivary mucins in host defense and disease prevention

Mucus forms a protective coating on wet epithelial surfaces throughout the body that houses the microbiota and plays a key role in host defense. Mucins, the primary structural components of mucus that creates its viscoelastic properties, are critical components of the gel layer that protect against invading pathogens. Altered mucin production has been implicated in diseases such as ulcerative colitis, asthma, and cystic fibrosis, which highlights the importance of mucins in maintaining homeostasis. Different types of mucins exist throughout the body in various locations such as the gastrointestinal tract, lungs, and female genital tract, but this review will focus on mucins in the oral cavity. Salivary mucin structure, localization within the oral cavity, and defense mechanisms will be discussed. These concepts will then be applied to present what is known about the protective function of mucins in oral diseases such as HIV/AIDS, oral candidiasis, and dental caries.

Periodontal bone loss and risk of epithelial ovarian cancer

PURPOSE

Periodontitis, a chronic inflammatory response to pathogenic bacteria in the oral microbiome, is common among adults. It is associated with several medical conditions, including cardiovascular diseases, and potentially with esophageal, lung, oral, and pancreatic cancer. One of the proposed mechanisms behind these associations is systemic inflammation, which has also been implicated in ovarian cancer etiology. The aim of this study was to evaluate association between ovarian cancer and periodontal bone loss.

METHODS

The association between periodontal bone loss, a marker of periodontitis, and risk of epithelial ovarian cancer was estimated among 60,560 participants of the prospective Nurses' Health Study using Cox proportional hazards analysis. Competing risks analysis was used to estimate association by histologic subtype.

RESULTS

We did not observe an increased risk of ovarian cancer among participants with periodontal bone loss (HR 0.86, 95% CI 0.64-1.15). Among women younger than 69 years, periodontal bone loss was associated with a 40 % (HR 0.60, 95% CI 0.36-0.98) decreased ovarian cancer risk, while there was no association in women older than 69 (HR 1.09, 95% CI 0.75-1.58), although this difference did not reach statistical significance (p-heterogeneity = 0.06). We observed a suggestive decreased risk for serous tumors (HR 0.76, 95% CI 0.53-1.09). The number of natural teeth and root canals, other metrics of oral health, were not associated with ovarian cancer risk.

CONCLUSION

Our results do not support an increased ovarian cancer risk in women with periodontal bone loss; however, there was a significant decrease in risk in women younger than 69. Given the unexpected association between periodontal bone loss and ovarian cancer risk in younger women, further research is warranted.

Estimation of levels of salivary mucin, amylase and total protein in gingivitis and chronic periodontitis patients

BACKGROUND

Periodontal diseases are a group of inflammatory conditions resulting from interaction between a pathogenic bacterial biofilm and susceptible host's inflammatory response eventually leading to the destruction of periodontal structures and subsequent tooth loss. Hence, investigation of salivary proteins in individuals with periodontal diseases may be useful to enhance the knowledge of their roles in these diseases.

MATERIALS AND METHODS

This case-control study was conducted at A.B. Shetty Memorial Institute of Dental Sciences, Mangalore. The study comprised of 90 patients of age between 25-60 years who were clinically examined and divided into three groups of 30 each: namely clinically healthy, gingivitis and chronic periodontitis. These were classified according to the values of gingival index score, clinical attachment loss and probing pocket depth. Unstimulated saliva was collected and salivary mucin, amylase and total protein levels were determined.

STATISTICAL ANALYSIS

RESULTS obtained were tabulated and statistically analyzed using ANOVA test and Karl pearson's correlation test.

RESULTS

The results of the study showed an increased concentration of salivary mucin, amylase and total protein in gingivitis patients and increased levels of amylase and total protein in saliva of chronic periodontitis patients compared to healthy individuals which were statistically significant. A decrease in mucin concentration was observed in the periodontitis group compared to gingivitis group. A positive correlation was present between salivary mucin, amylase and total protein levels in the three groups.

CONCLUSION

Salivary mucin, amylase and total protein may serve as an important biochemical parameter of inflammation of the periodontium. Also, it can be hypothesized that various enzyme inhibitors might be useful as a part of host modulation therapy in the treatment of periodontal diseases.

Development of highly sensitive and specific mRNA multiplex system (XCYR1) for forensic human body fluids and tissues identification

The identification of human body fluids or tissues through mRNA-based profiling is very useful for forensic investigations. Previous studies have shown mRNA biomarkers are effective to identify the origin of biological samples. In this study, we selected 16 tissue specific biomarkers to evaluate their specificities and sensitivities for human body fluids and tissues identification, including porphobilinogen deaminase (PBGD), hemoglobin beta (HBB) and Glycophorin A (GLY) for circulatory blood, protamine 2 (PRM2) and transglutaminase 4 (TGM4) for semen, mucin 4 (MUC4) and human beta defensin 1(HBD1) for vaginal secretion, matrix metalloproteinases 7 and 11 (MMP7 and MMP11) for menstrual blood, keratin 4(KRT4) for oral mucosa, loricrin (LOR) and cystatin 6 (CST6) for skin, histatin 3(HTN3) for saliva, statherin (STATH) for nasal secretion, dermcidin (DCD) for sweat and uromodulin (UMOD) for urine. The above mentioned ten common forensic body fluids or tissues were used in the evaluation. Based on the evaluation, a reverse transcription (RT) PCR multiplex assay, XCYR1, which includes 12 biomarkers (i.e., HBB, GLY, HTN3, PRM2, KRT4, MMP11, MUC4, DCD, UMOD, MMP7, TGM4, and STATH) and 2 housekeeping genes [i.e., glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and 18SrRNA], was developed. This assay was further validated with real casework samples and mock samples (with both single source and mixture) and it was approved that XCYR1 is effective to identify common body fluids or tissues (i.e., circulatory blood, saliva, semen, vaginal secretion, menstrual blood, oral mucosa, nasal secretion, sweat and urine) in forensic casework samples.

Human prominin-1 (CD133) is detected in both neoplastic and non-neoplastic salivary gland diseases and released into saliva in a ubiquitinated form

Prominin-1 (CD133) is physiologically expressed at the apical membranes of secretory (serous and mucous) and duct cells of major salivary glands. We investigated its expression in various human salivary gland lesions using two distinct anti-prominin-1 monoclonal antibodies (80B258 and AC133) applied on paraffin-embedded sections and characterized its occurrence in saliva. The 80B258 epitope was extensively expressed in adenoid cystic carcinoma, in lesser extent in acinic cell carcinoma and pleomorphic adenoma, and rarely in mucoepidermoid carcinoma. The 80B258 immunoreactivity was predominately detected at the apical membrane of tumor cells showing acinar or intercalated duct cell differentiation, which lined duct- or cyst-like structures, and in luminal secretions. It was observed on the whole cell membrane in non-luminal structures present in the vicinity of thin-walled blood vessels and hemorrhagic areas in adenoid cystic carcinoma. Of note, AC133 labeled only a subset of 80B258–positive structures. In peritumoral salivary gland tissues as well as in obstructive sialadenitis, an up-regulation of prominin-1 (both 80B258 and AC133 immunoreactivities) was observed in intercalated duct cells. In most tissues, prominin-1 was partially co-expressed with two cancer markers: carcinoembryonic antigen (CEA) and mucin-1 (MUC1). Differential centrifugation of saliva followed by immunoblotting indicated that all three markers were released in association with small membrane vesicles. Immuno-isolated prominin-1–positive vesicles contained CEA and MUC1, but also exosome-related proteins CD63, flotillin-1, flotillin-2 and the adaptor protein syntenin-1. The latter protein was shown to interact with prominin-1 as demonstrated by its co-immunoisolation. A fraction of saliva-associated prominin-1 appeared to be ubiquitinated. Collectively, our findings bring new insights into the biochemistry and trafficking of prominin-1 as well as its immunohistochemical profile in certain types of salivary gland tumors and inflammatory diseases.

A simple identification method for vaginal secretions using relative quantification of Lactobacillus DNA

In criminal investigations there are some cases in which identifying the presence of vaginal secretions provides crucial evidence in proving sexual assault. However, there are no methods for definitively identifying vaginal secretions. In the present study, we focused on Lactobacillus levels in vaginal secretions and developed a novel identification method for vaginal secretions by relative quantification based on real time PCR. We designed a Lactobacillus conserved region primer pair (LCP) by aligning 16S rRNA gene sequences from major vaginal Lactobacillus species (Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus iners and Lactobacillus jensenii), and selected the human specific primer pair (HSP) as an endogenous control for relative quantification. As a result, the ΔCt (ΔCt=Ct[LCP]-Ct[HSP]) values of vaginal secretions (11 out of 12 samples) were significantly lower than those of saliva, semen and skin surface samples, and it was possible to discriminate between vaginal secretions and other body fluids. For the one remaining sample, it was confirmed that the predominant species in the microflora was not of the Lactobacillus genus. The ΔCt values in this study were calculated when the total DNA input used from the vaginal secretions was 10pg or more. Additionally, the ΔCt values of samples up to 6-months-old, which were kept at room temperature, remained unchanged. Thus, we concluded in this study that the simple ΔCt method by real time PCR is a useful tool for detecting the presence of vaginal secretions.

MUC4 as a diagnostic marker in cancer

BACKGROUND

Mucins are high molecular mass glycoproteins whose role in diagnosis, prognosis and therapy is being increasingly recognized owing to their altered expression in a variety of carcinomas. MUC4, a membrane-bound mucin encoded by a gene located on chromosome locus 3q29, is aberrantly expressed in several cancers including those of the bile duct, breast, colon, esophagus, ovary, lung, prostate, stomach and pancreas.

OBJECTIVE

This review considers the potential use of the MUC4 expression pattern in the diagnosis and prognosis of various cancers.

RESULTS/CONCLUSION

MUC4 expression is a specific marker of epithelial tumors and its expression correlates positively with the degree of differentiation in several cancers. Importantly, MUC4 has emerged as a specific marker of dysplasia, being expressed in the earliest dysplastic lesions preceding several malignancies, including lethal pancreatic cancer. The presence of MUC4-specific antibodies in the serum and of the transcript in peripheral blood mononuclear cells of cancer patients raises the possibility of it emerging as a new diagnostic biomarker for bedside application in high-risk individuals and those with established cancer.

The oral cavity as a biological barrier system: design of an advanced buccal in vitro permeability model

An important area for future research lies in finding a drug delivery system across or into the oral mucosa. However, to design such systems, simplified biological models are necessary so that the mechanisms and/or interactions of interest can readily be studied. The oral epithelium is covered by a complex mucus layer, which enables exchange of nutrients and provides lubrication. However, it has been demonstrated that mucus has an impact on the mobility of nanoparticles and drug molecules. Thus, we aimed to develop an advanced buccal in vitro model for studying transport of nanoparticles, taking the mucus layer into account. First, animal mucins (porcine gastric, bovine submaxillary) were compared with natural human mucin regarding chemical and morphological structure. Second, an "external" mucus layer was prepared by a film method and deposited onto an oral cell line (TR 146), cultured on transwells®. Adherence of the mucin fibers was evaluated and the viability of the model was assessed. Nanoparticle transport studies were performed with this advanced in vitro model and an ex vivo diffusion system. The results revealed that porcine mucin is most similar to human natural mucin in chemical structure and morphology. Both the bovine and porcine mucin fibers adhered onto the oral cells: Due to the different morphology of bovine mucin, the viability of the oral cells decreased, whereas porcine mucin maintained the viability of the model for more than 48 h. Comparison of in vitro data with ex vivo data suggested reliability of the advanced buccal in vitro model. Additionally, it was demonstrated that the mucus layer in the oral cavity also acts as a strong barrier for the mobility of nanoparticles.

Mucins and toll-like receptors: kith and kin in infection and cancer

Inflammation is underlying biological phenomenon common in infection and cancer. Mucins are glycoproteins which establish a physical barrier for undesirable entry of foreign materials through epithelial surfaces. A deregulated expression and an anomalous glycosylation pattern of mucins are known in large number of cancers. TLRs are class of receptors which recognize the molecular patterns of invading pathogens and activate complex inflammatory pathways to clear them. Aberrant expression of TLRs is observed in many cancers. A highly orchestrated action of mucins and TLRs is well evolved host defence mechanism; however, a link between the two in other non-infectious conditions has received less attention. Here we present an overview as to how mucins and TLRs give protection to the host and are deregulated during carcinogenesis. Further, we propose the possible mechanisms of cross-regulation between them in pathogenesis of cancer. As both mucins and TLRs are therapeutically important class of molecules, an understanding of the underlying molecular mechanisms connecting the two will open new avenues for the therapeutic targeting of cancer.

A multiplex (m)RNA-profiling system for the forensic identification of body fluids and contact traces

In current forensic practice, information about the possible biological origin of forensic traces is mostly determined using protein-based presumptive testing. Recently, messenger RNA-profiling has emerged as an alternative strategy to examine the biological origin. Here we describe the development of a single multiplex mRNA-based system for the discrimination of the most common forensic body fluids as well as skin cells. A DNA/RNA co-isolation protocol was established that results in DNA yields equivalent to our standard in-house validated DNA extraction procedure which uses silica-based columns. An endpoint RT-PCR assay was developed that simultaneously amplifies 19 (m)RNA markers. This multiplex assay analyses three housekeeping, three blood, two saliva, two semen, two menstrual secretion, two vaginal mucosa, three general mucosa and two skin markers. The assay has good sensitivity as full RNA profiles for blood, semen and saliva were obtained when using ≥0.05 μL body fluid starting material whereas full DNA profiles were obtained with ≥0.1 μL. We investigated the specificity of the markers by analysing 15 different sets of each type of body fluid and skin with each set consisting of 8 individuals. Since skin markers have not been incorporated in multiplex endpoint PCR assays previously, we analysed these markers in more detail. Interestingly, both skin markers gave a positive result in samplings of the hands, feet, back and lips but negative in tongue samplings. Positive identification (regarding both DNA- and RNA-profiling) was obtained for specimens stored for many years, e.g. blood (28 years-old), semen (28 years-old), saliva (6 years-old), skin (10 years-old) and menstrual secretion (4 years-old). The described approach of combined DNA- and RNA-profiling of body fluids and contact traces assists in the interpretation of forensic stains by providing information about not only the donor(s) that contributed to the stain but also by indicating which cell types are present.

Evaluation of mRNA marker specificity for the identification of five human body fluids by capillary electrophoresis

The identification of forensically relevant human body fluids through messenger RNA (mRNA) profiling is of interest to the forensic community. Previous studies have proposed several tissue-specific mRNA markers to achieve this goal. Seven markers for the following genes were selected for evaluation in this study: histatin 3 (HTN3) and statherin (STATH) for saliva, mucin 4 (MUC4) for vaginal secretions, matrix metalloproteinase 7 (MMP7) for menstrual blood, delta-aminolevulinate synthase 2 (ALAS2) for peripheral blood, and protamine 2 (PRM2) and transglutaminase 4 (TGM4) for semen. The expression of these markers was examined in each body fluid. All mRNA markers were present in their target body fluids. Peripheral blood and saliva showed little cross-reactivity with the selected markers. However, a high level of cross-reactivity was observed between the vaginal secretion marker MUC4 and saliva stains. Semen showed a high level of cross-reactivity with the selected markers. Co-expression of the predicted body fluid markers was detected in menstrual blood and vaginal secretion stains. The expression pattern of these mRNA markers varied through the menstrual cycle time points tested. Differences in gene expression levels and marker cross-reactivity were observed in the donors tested. Despite the presence of cross-reactivity and co-expression, each of the body fluids examined have distinct gene expression profiles, allowing for body fluid identification based on mRNA profiling.

Monoclonal antibodies recognizing the non-tandem repeat regions of the human mucin MUC4 in pancreatic cancer

The MUC4 mucin is a high molecular weight, membrane-bound, and highly glycosylated protein. It is a multi-domain protein that is putatively cleaved into a large mucin-like subunit (MUC4α) and a C-terminal growth-factor like subunit (MUC4β). MUC4 plays critical roles in physiological and pathological conditions and is aberrantly overexpressed in several cancers, including those of the pancreas, cervix, breast and lung. It is also a potential biomarker for the diagnosis, prognosis and progression of several malignancies. Further, MUC4 plays diverse functional roles in cancer initiation and progression as evident from its involvement in oncogenic transformation, proliferation, inhibition of apoptosis, motility and invasion, and resistance to chemotherapy in human cancer cells. We have previously generated a monoclonal antibody 8G7, which is directed against the TR region of MUC4, and has been extensively used to study the expression of MUC4 in several malignancies. Here, we describe the generation of anti-MUC4 antibodies directed against the non-TR regions of MUC4. Recombinant glutathione-S-transferase (GST)-fused MUC4α fragments, both upstream (MUC4α-N-Ter) and downstream (MUC4α-C-Ter) of the TR domain, were used as immunogens to immunize BALB/c mice. Following cell fusion, hybridomas were screened using the aforementioned recombinant proteins ad lysates from human pancreatic cell lines. Three anti MUC4α-N-Ter and one anti-MUC4α-C-Ter antibodies were characterized by several inmmunoassays including enzyme-linked immunosorbent assay (ELISA), immunoblotting, immunofluorescene, flow cytometry and immunoprecipitation using MUC4 expressing human pancreatic cancer cell lines. The antibodies also reacted with the MUC4 in human pancreatic tumor sections in immunohistochemical analysis. The new domain-specific anti-MUC4 antibodies will serve as important reagents to study the structure-function relationship of MUC4 domains and for the development of MUC4-based diagnostics and therapeutics.

Recent advances in mucin immunohistochemistry in salivary gland tumors and head and neck squamous cell carcinoma

This review focuses on the immunohistochemical expression of members of the MUC-type mucin family in salivary gland tumors and head and neck squamous cell carcinomas (HNSCC). Information is available on changes in the expression levels and distribution profiles of MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6 and MUC7 in tumors of the salivary glands; and of MUC1, MUC2 and MUC4 in HNSCC. In salivary gland tumors the expression patterns of MUC2, MUC3, MUC5AC and MUC6 appear to be very closely correlated with the histopathological tumor type indicating their potential use to improve diagnostic accuracy in salivary gland neoplasia. Some MUC-type mucins have emerged as valuable prognostic indicators in pleomorphic adenoma, mucoepidermoid carcinoma and HNSCC. Nine antibodies directed against different MUC1 antigens have thus far been examined in HNSCC of which monoclonal antibodies DF3, HMFG-1 and Ma695 have shown significant correlations with disease outcome. The importance of taking the specific anti-MUC antibody into consideration when comparing the results of different studies on MUC expression in salivary gland tumors and HNSCC is also highlighted in this review.

Development of human minor salivary glands: expression of mucins according to stage of morphogenesis

The formation of salivary glands entails the proliferation of epithelial cells from the stomatodeum into the underlying ectomesenchyme, culminating in a complex network of ducts and acinar bulbs. The extent to which mucins regulate this process is unknown, but they appear to mediate luminal space formation and maturation. Our aim was to examine mucin expression patterns during the morphogenesis of human salivary glands. Mucin expression - MUC1, 2, 3, 4, 5AC, 5B, 6, and 16 - was analyzed in specimens of developing human salivary glands, obtained from fetuses at 4-24 weeks' gestation, and fully developed salivary glands by immunohistochemistry. Expression patterns were analyzed qualitatively according to the development stage of the salivary glands. Mucins 1, 3, 4, 5B, and 16 were expressed during salivary gland development - being stronger in all ductal segments by the final phases of branching morphogenesis and in mature glands. Acinar cells were negative for most mucins, including MUC1 in mature salivary glands. Mucins 2, 5AC, and 6 were not expressed. Mucins MUC1, 3, 4, 5B, and 16 are expressed in developing human salivary glands and in mature glands, suggesting important roles in the maturation and maintenance of the ductal network.

Improving human forensics through advances in genetics, genomics and molecular biology

Forensic DNA profiling currently allows the identification of persons already known to investigating authorities. Recent advances have produced new types of genetic markers with the potential to overcome some important limitations of current DNA profiling methods. Moreover, other developments are enabling completely new kinds of forensically relevant information to be extracted from biological samples. These include new molecular approaches for finding individuals previously unknown to investigators, and new molecular methods to support links between forensic sample donors and criminal acts. Such advances in genetics, genomics and molecular biology are likely to improve human forensic case work in the near future.

MUC1 expression in the oral mucosal epithelial cells of the elderly

OBJECTIVE

MUC1 is primarily involved in the protection of epithelial surfaces. Decreases in oral mucosal defence can be a predisposing factor for the development of oral mucosal diseases in the elderly. The aim of this study was to compare MUC1 expression level in oral mucosal epithelial cells of the elderly with that of young adults.

DESIGN

Thirty elderly (mean age, 71.1±4.6 years) and thirty young (mean age, 26.4±2.4 years) adults (15 men and 15 women in each group) were included. Oral examination, including tooth, periodontal, and oral mucosal status, was performed and whole saliva samples were collected along with flow rate measurements. Precipitates of stimulated whole saliva were used for the evaluation of MUC1 expression using real-time PCR. Clarified supernatants were used for the measurement of pro-inflammatory cytokines, IL-1β, IL-6, and TNF-α.

RESULTS

There was a significant decrease in the amounts of MUC1 transcripts in elderly subjects compared with those of young subjects, a result seen in both men (0.589-fold) and women (0.547-fold). The MUC1 expression level was not correlated with salivary cytokine level but did show a significant positive correlation with the level of periodontal inflammation (r(s)=0.505, P<0.01) in the elderly group.

CONCLUSIONS

Oral mucosal defence provided by MUC1 was decreased in the elderly; this decrease may play a role in the development of oral mucosal diseases in the aged population.

Increased mucin 1 expression in recurrence and malignant transformation of salivary gland pleomorphic adenoma

AIMS

Pleomorphic adenoma (PA) is the most common salivary gland tumour with a tendency to recur (RPA) and a risk of malignant transformation. Mucin 1 (MUC-1) plays a role in the progression of many tumours and may be a marker to predict RPA. The aim of this study was to evaluate MUC-1 expression in different phases of the adenoma to carcinoma sequence.

METHODS AND RESULTS

Twenty-one cases of PA, 18 cases of RPA, three cases of RPA with focal transformation (TRPA) and 11 cases of carcinoma ex-pleomorphic adenoma (CXPA) were analysed immunohistochemically for MUC1 expression using an antibody to MUC1/DF3. MUC1 reactivity in RPA was stronger than that observed in PA and, in all the different carcinoma groups, MUC-1 expression was significantly higher in carcinoma than in RPA and PA.

CONCLUSION

This study has confirmed that MUC-1 is related to the recurrence of PA and that this molecule is associated with malignant transformation of PA with carcinoma cells overexpressing MUC-1.

MUC1 and the simple mucin-type antigens: Tn and Sialyl-Tn are differently expressed in salivary gland acini and ducts from the submandibular gland, the vestibular folds, and the soft palate

OBJECTIVE AND DESIGN

Autopsies of the submandibular gland, the vestibular folds and the soft palate from 65-87 old humans were examined to record the immunohistochemical expression of MUC1 and the simple mucin-type antigens Tn and Sialyl-Tn.

RESULTS

(1) The serous acini in the submucosal glands from the larynx and the soft palate expressed MUC1-associated glycans that were not detectable in the serous acini from the submandibular gland. (2) Virtually all the submucosal acini at oral site of the soft palate are mucous, and in contrast to mucous acini in the vestibular folds and submandibular gland, the palatinal acini in the submucosa underneath the oral mucosa showed a well-defined cytoplasmic reaction with anti-MUC1 antibodies as wells as with anti-Tn. (3) Both the mucous acini and the ducts at the oral site of the soft palate showed reaction for Sialyl-Tn while in the vestibular folds and in the submandibular gland expression for this carbohydrate was observed only in the acini. (4) The staining obtained after incubation with the Tn antibodies showed no cross localization with the staining obtained after incubation with an anti-A blood group antibody. (5) All the autopsies showed reaction in the glands after incubation with the MUC1 antibodies while some autopsies reacted with the anti-Tn antibodies and/or with the anti-Sialyl-Tn antibodies and others did not.

CONCLUSION

The mucin expression in the acini and ducts from the upper human aerodigestive tract strongly depended on the location of the glandular tissue.

Ultrastructural localization of salivary mucins MUC5B and MUC7 in human labial glands

As a result of their presence throughout the mouth in the submucosa or between muscle fibers, minor salivary glands secrete directly and continuously into the oral cavity, providing mucosal surfaces with highly glycosylated proteins that are active in bacterial aggregation and in oral tissue lubrication. In this study, we investigated the ultrastructural localization of the MUC5B and MUC7 mucins in human labial glands by means of a postembedding immunogold technique. Thin sections of normal human labial glands, obtained during surgery, were incubated with polyclonal antibodies to human salivary mucins MUC5B and MUC7, and then with gold-labeled secondary antibodies. Specific MUC5B reactivity was found in the secretory granules of mucous cells of all glands examined, and was associated with the luminal membrane of duct cells. MUC7 labeling was observed in the granules of both mucous and seromucous secretory cells of the glandular parenchyma. Quantitative analyses demonstrated that seromucous granules have higher immunogold labeling densities for MUC7 than mucous granules. Our immunohistochemical data extend the results of previous light microscopic studies of MUC5B and MUC7 localizations, pointing out the significant contribution of human labial glands in the secretion process of these two mucins.

A metaproteomic analysis of the human salivary microbiota by three-dimensional peptide fractionation and tandem mass spectrometry

Metagenomics uses gene expression patterns to understand the taxonomy and metabolic activities of microbial communities. Metaproteomics applies the same approach to community proteomes. Previously, we used a novel three-dimensional peptide separation method to identify over 2000 salivary proteins. This study used those data to carry out the first metaproteomic analysis of the human salivary microbiota. The metagenomic software MEGAN generated a phylogenetic tree, which was checked against the Human Oral Microbiome Database (HOMD). Pathway analyses were performed with the Clusters of Orthologous Groups and MetaCyc databases. Thirty-seven per cent of the peptides were identifiable only at the level of cellular organisms or bacteria. The rest were distributed among five bacterial phyla (61%), archea (0.5%), and viruses (0.8%); 29% were assignable at the genus level, and most belonged to Streptococcus (17%). Eleven per cent of all peptides could be assigned to species. Most taxa were represented in HOMD and they included well-known species such as periodontal pathogens. However, there also were 'exotic' species including aphid endosymbionts; plant, water, and soil bacteria; extremophiles; and archea. The pathway analysis indicated that peptides were linked to translation (37%), followed by glycolysis (19%), amino acid metabolism (8%), and energy production (8%). The taxonomic structure of the salivary metaproteome is very diverse but is dominated by streptococci. 'Exotic' species may actually represent close relatives that have not yet been sequenced. Salivary microbes appear to be actively engaged in protein synthesis, and the pathway analysis is consistent with the metabolism of salivary glycoproteins.