Differential expression of salivary mucin bacterial aggregating activity with caries status

The impact of MUC5B gene on dental caries

OBJECTIVE

To identify the impact of MUC5B polymorphisms on dental caries.

METHODS

A case-control study was performed with patients recruited at Pontifícia Universidade Católica do Paraná. These individuals were aged 12 years old or more. Dental caries was diagnosed using the International Caries Detection and Assessment System, and the effects of socioeconomic, dietary, and hygiene factors on dental caries were investigated. Furthermore, buccal cells were collected, and their DNA was extracted and amplified using PCR. Uni-, bi-, and multivariate analyses were performed.

RESULTS

Two hundred patients were recruited, 100 were assigned to the case group and 100 to the control group. In the bivariate analysis, the following variables showed significant results: ethnicity (p = .008), biofilm (p < .001), and gingivitis (p < .001). The MUC5B gene affected dental caries with the markers rs2735733 (p < .001), rs2249073 (p < .001), and rs2857476 (p < .001). In the multivariate analysis, the biofilm variable remained significant (p = .026), as did the following markers from the MUC5B gene: rs2735733 (p = .019), rs2249073 (p < .025), and rs2857476 (p < .005).

CONCLUSION

Genetic variations in the MUC5B gene can influence dental caries.

Salivary mucin 19 glycoproteins: innate immune functions in Streptococcus mutans-induced caries in mice and evidence for expression in human saliva

Saliva functions in innate immunity of the oral cavity, protecting against demineralization of teeth (i.e. dental caries), a highly prevalent infectious disease associated with Streptococcus mutans, a pathogen also linked to endocarditis and atheromatous plaques. Gel-forming mucins are a major constituent of saliva. Because Muc19 is the dominant salivary gel-forming mucin in mice, we studied Muc19(-/-) mice for changes in innate immune functions of saliva in interactions with S. mutans. When challenged with S. mutans and a cariogenic diet, total smooth and sulcal surface lesions are more than 2- and 1.6-fold higher in Muc19(-/-) mice compared with wild type, whereas the severity of lesions are up to 6- and 10-fold higher, respectively. Furthermore, the oral microbiota of Muc19(-/-) mice display higher levels of indigenous streptococci. Results emphasize the importance of a single salivary constituent in the innate immune functions of saliva. In vitro studies of S. mutans and Muc19 interactions (i.e. adherence, aggregation, and biofilm formation) demonstrate Muc19 poorly aggregates S. mutans. Nonetheless, aggregation is enhanced upon adding Muc19 to saliva from Muc19(-/-) mice, indicating Muc19 assists in bacterial clearance through formation of heterotypic complexes with salivary constituents that bind S. mutans, thus representing a novel innate immune function for salivary gel-forming mucins. In humans, expression of salivary MUC19 is unclear. We find MUC19 transcripts in salivary glands of seven subjects and demonstrate MUC19 glycoproteins in glandular mucous cells and saliva. Similarities and differences between mice and humans in the expression and functions of salivary gel-forming mucins are discussed.

Reorganisation of the salivary mucin network by dietary components: insights from green tea polyphenols

The salivary mucins that include MUC5B (gel-forming) and MUC7 (non-gel-forming) are major contributors to the protective mucus barrier in the oral cavity, and it is possible that dietary components may influence barrier properties. We show how one dietary compound, the green tea polyphenol epigallocatechin gallate (EGCG), can substantially alter the properties of both the polymeric MUC5B network and monomeric MUC7. Using rate-zonal centrifugation, MUC5B in human whole saliva and MUC5B purified from saliva sedimented faster in the presence of EGCG. The faster sedimentation by EGCG was shown to be greater with increasing MUC5B concentration. Particle tracking microrheology was employed to determine the viscosity of purified MUC5B solutions and showed that for MUC5B solutions of 200-1600 µg/mL, EGCG caused a significant increase in mucin viscosity, which was greater at higher MUC5B concentrations. Visualisation of the changes to the MUC5B network by EGCG was performed using atomic force microscopy, which demonstrated increased aggregation of MUC5B in a heterogeneous manner by EGCG. Using trypsin-resistant, high-molecular weight oligosaccharide-rich regions of MUC5B and recombinant N-terminal and C-terminal MUC5B proteins, we showed that EGCG causes aggregation at the protein domains of MUC5B, but not at the oligosaccharide-rich regions of the mucin. We also demonstrated that EGCG caused the majority of MUC7 in human whole saliva to aggregate. Furthermore, purified MUC7 also underwent a large increase in sedimentation rate in the presence of EGCG. In contrast, the green tea polyphenol epicatechin caused no change in the sedimentation rate of either MUC5B or MUC7 in human whole saliva. These findings have demonstrated how the properties of the mucin barrier can be influenced by dietary components. In the case of EGCG, these interactions may alter the function of MUC5B as a lubricant, contributing to the astringency (dry puckering sensation) of green tea.

Sampling human indigenous saliva peptidome using a lollipop-like ultrafiltration probe: simplify and enhance peptide detection for clinical mass spectrometry

Although human saliva proteome and peptidome have been revealed they were majorly identified from tryptic digests of saliva proteins. Identification of indigenous peptidome of human saliva without prior digestion with exogenous enzymes becomes imperative, since native peptides in human saliva provide potential values for diagnosing disease, predicting disease progression, and monitoring therapeutic efficacy. Appropriate sampling is a critical step for enhancement of identification of human indigenous saliva peptidome. Traditional methods of sampling human saliva involving centrifugation to remove debris may be too time-consuming to be applicable for clinical use. Furthermore, debris removal by centrifugation may be unable to clean most of the infected pathogens and remove the high abundance proteins that often hinder the identification of low abundance peptidome. Conventional proteomic approaches that primarily utilize two-dimensional gel electrophoresis (2-DE) gels in conjugation with in-gel digestion are capable of identifying many saliva proteins. However, this approach is generally not sufficiently sensitive to detect low abundance peptides/proteins. Liquid chromatography-Mass spectrometry (LC-MS) based proteomics is an alternative that can identify proteins without prior 2-DE separation. Although this approach provides higher sensitivity, it generally needs prior sample pre-fractionation and pre-digestion with trypsin, which makes it difficult for clinical use. To circumvent the hindrance in mass spectrometry due to sample preparation, we have developed a technique called capillary ultrafiltration (CUF) probes. Data from our laboratory demonstrated that the CUF probes are capable of capturing proteins in vivo from various microenvironments in animals in a dynamic and minimally invasive manner. No centrifugation is needed since a negative pressure is created by simply syringe withdrawing during sample collection. The CUF probes combined with LC-MS have successfully identified tryptic-digested proteins. In this study, we upgraded the ultrafiltration sampling technique by creating a lollipop-like ultrafiltration (LLUF) probe that can easily fit in the human oral cavity. The direct analysis by LC-MS without trypsin digestion showed that human saliva indigenously contains many peptide fragments derived from various proteins. Sampling saliva with LLUF probes avoided centrifugation but effectively removed many larger and high abundance proteins. Our mass spectrometric results illustrated that many low abundance peptides became detectable after filtering out larger proteins with LLUF probes. Detection of low abundance saliva peptides was independent of multiple-step sample separation with chromatography. For clinical application, the LLUF probes incorporated with LC-MS could potentially be used in the future to monitor disease progression from saliva.

Identification of salivary mucin MUC7 binding proteins from Streptococcus gordonii

BACKGROUND

The salivary mucin MUC7 (previously known as MG2) can adhere to various strains of streptococci that are primary colonizers and predominant microorganisms of the oral cavity. Although there is a growing interest in interaction between oral pathogens and salivary mucins, studies reporting the specific binding sites on the bacteria are rather limited. Identification and characterization of the specific interacting proteins on the bacterial cell surface, termed adhesins, are crucial to further understand host-pathogen interactions.

RESULTS

We demonstrate here, using purified MUC7 to overlay blots of SDS-extracts of Streptococcus gordonii cell surface proteins, 4 MUC7-binding bands, with apparent molecular masses of 62, 78, 84 and 133 kDa from the Streptococcus gordonii strain, PK488. Putative adhesins were identified by in-gel digestion and subsequent nanoLC-tandem mass spectrometry analysis of resultant peptides. The 62 kDa and 84 kDa bands were identified as elongation factor (EF) Tu and EF-G respectively. The 78 kDa band was a hppA gene product; the 74 kDa oligopeptide-binding lipoprotein. The 133 kDa band contained two proteins; alpha enolase and DNA-directed RNA polymerase, beta' subunit. Some of these proteins, for example alpha enolase are expected to be intracellular, however, flow cytometric analysis confirmed its location on the bacterial surface.

CONCLUSION

Our data demonstrated that S. gordonii expressed a number of putative MUC7 recognizing proteins and these contribute to MUC7 mucin binding of this streptococcal strain.

Functional domain of bovine milk lactoferrin which inhibits the adherence of Streptococcus mutans cells to a salivary film

The bovine lactoferrin molecule and relatively long lactoferrin fragments containing residues 473 to 538 strongly inhibited adherence of Streptococcus mutans to saliva-coated hydroxyapatite beads. Each cysteine residue in Lf411 (residues 473 to 538) was replaced by a serine residue, and the mutants Lf411-C481S and Lf411-C532S strongly inhibited S. mutans adherence. These results suggest that the functional domain of lactoferrin that binds to a salivary film lies in residues 473 to 538 and that the region might be concealed by disulfide bond formation between Cys481 and Cys532 in the Lf411 fragment.

Binding of salivary glycoprotein-secretory immunoglobulin A complex to the surface protein antigen of Streptococcus mutans

The interaction between a surface protein antigen (PAc) of Streptococcus mutans and human salivary agglutinin was analyzed with a surface plasmon resonance biosensor. The major component sugars of the salivary agglutinin were galactose, fucose, mannose, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylneuraminic acid. Binding of salivary agglutinin to PAc was calcium dependent and heat labile and required a pH greater than 5. Binding was significantly inhibited by N-acetylneuraminic acid and alpha2,6-linked sialic acid-specific lectin derived from Sambucus sieboldiana in a dose-dependent manner. Pretreatment of the salivary agglutinin with sialidase reduced the binding activity of the agglutinin to the PAc molecule. The agglutinin was dissociated into high-molecular-mass glycoprotein and secretory immunoglobulin A (sIgA) components by electrophoretic fractionation in the presence of 1% sodium dodecyl sulfate and 1% 2-mercaptoethanol. Neither of the components separated by electrophoretic fractionation, high-molecular-mass glycoprotein or sIgA, bound to the PAc molecule. Furthermore, the high-molecular-mass glycoprotein strongly inhibited the binding of the native salivary complex to PAc. These results suggest that the complex formed by the high-molecular-mass salivary glycoprotein and sIgA is essential for the binding reaction and that the sialic acid residues of the complex play an important role in the interaction between the agglutinin and PAc of S. mutans.

Salivary mucins in oral mucosal defense

1. Salivary mucins are well recognized as an important factor in the preservation of the health of the oral cavity. These large glycoproteins play a major role in the formation of protective coatings covering tooth enamel and oral mucosa, which act as a dynamic functional barrier capable of modulating the untoward effects of oral environment, and are of significance to the processes occurring within the epithelial perimeter of mucosal defense. 2. Based on macromolecular characteristics, the mucins in saliva fall into high (> 1000 kDa) and low (200-300 kDa) molecular weight forms. The two forms, although differ with respect to bacterial clearance ability, display virtually identical carbohydrate chain make-up, ranging in size from 3 to 16 sugar units. 3. Of the two mucin forms, the low molecular weight form more efficient in bacterial aggregation, predominates in saliva and oral mucosal mucus coat of caries-resistant individuals, while the level of the high molecular weight form is higher in caries-susceptible subjects. The saliva of caries-resistant individuals also exhibits greater activity of protease capable of conversion of the high molecular weight mucin to the low molecular weight form. 4. The bacterial aggregating activity of salivary mucins appears to be associated with sulfomucins rather than sialomucins. While the removal of sialic acid causes only partial loss in mucin aggregating capacity, a complete loss in the bacterial aggregating activity occurs following mucin desulfation. 5. The mucins in oral mucosal mucus coat interact with the epithelial surfaces through specific membrane receptors. This interaction apparently involves the carbohydrate moiety of mucin molecule and may be rendered vulnerable to disruption by opportunistic bacteria colonizing the oral mucosa. 6. Salivary sulfo- and sialomucins actively participate in the modulation of the oral mucosal calcium channel activity through the inhibition of EGF-stimulated channel protein tyrosine phosphorylation. This function of salivary mucins is of paramount importance to mucosal calcium homeostasis.

Does variability in salivary protein concentrations influence oral microbial ecology and oral health?

Salivary protein interactions with oral microbes in vitro include aggregation, adherence, cell-killing, inhibition of metabolism, and nutrition. Such interactions might be expected to influence oral ecology. However, inconsistent results have been obtained from in vivo tests of the hypothesis that quantitative variation in salivary protein concentrations will affect oral disease prevalence. Results may have been influenced by choices made during study design, including saliva source, stimulation status, control for flow rate, and assay methods. Salivary protein concentrations also may be subject to circadian variation. Values for saliva collected at the same time of day tend to remain consistent within subjects, but events such as stress, inflammation, infection, menstruation, or pregnancy may induce short-term changes. Long-term factors such as aging, systemic disease, or medication likewise may influence salivary protein concentrations. Such sources of variation may increase the sample size needed to find statistically significant differences. Clinical studies also must consider factors such as human population variation, strain and species differences in protein-microbe interactions, protein polymorphism, and synergistic or antagonistic interaction between proteins. Salivary proteins may form heterotypic complexes with unique effects, and different proteins may exert redundant effects. Patterns of protein-microbe interaction also may differ between oral sites. Future clinical studies must take those factors into account. Promising approaches might involve meta-analysis or multi-center studies, retrospective and prospective longitudinal designs, short-term measurement of salivary protein effects, and consideration of individual variation in multiple protein effects such as aggregation, adherence, and cell-killing.

Nature vs. nurture in dental caries

Why are some people more resistant to dental caries than others? Certainly diet plays a part, but are there hereditary factors that affect caries development? This report explores genetic components that appear related to caries resistance and susceptibility.