Mucins on oral mucosal surfaces in dry mouth patients

Mucins are large glycoproteins which are present in saliva that coats the mucosal surfaces in the oral cavity, serving as a lubricant and anti-desiccant. Saliva on oral mucosal surfaces originates from different glands, and the mucins MUC5B and MUC7 are expressed in different glandular secretions, exhibiting different degrees of glycosylation. In dry mouth patients, the mucosal surface saliva is impaired due to decreases in salivary flow rate and reduced mucosal wetness, which could impact on levels and types of mucins present. Objective: To compare MUC5B and MUC7 in mucosal surface saliva samples collected from dry mouth patients with low salivary flow rates (<0.1ml/min) and those unable to produce a measurable amount of saliva (zero flow). Samples were also collected from healthy age matched controls. Methods: Unstimulated saliva was collected from patients and controls. Mucosal saliva was collected from four oral surfaces; anterior hard palate; buccal; anterior tongue and lower labial using sterile filter paper strips. Saliva samples were electrophoresed on SDS-PAGE gels and visualised with Periodic Acidic Schiff (PAS) or immunoblotting with specific antibodies. PAS stained mucin bands were semi-quantified using ImageJ software according to area and density. Results: MUC5B and MUC7 were present on all mucosal surfaces of all subjects including patients with ‘zero flow'. There were statistically significant reductions in MUC5B on the anterior tongue and MUC7 on the labial surface in patients compared to controls. Conclusion: The presence of MUC5B and MUC7 on mucosal surfaces in dry mouth patients with low salivary flow rates and even ‘zero' flow rates, suggests small volumes of saliva can coat oral mucosal surfaces and may be important in the function of the mucosa in dry mouth. Acknowledgements: NIHR Biomedical Research Centre at Guy's & St Thomas' NHS Foundation Trust.