Objective: Investigate changes in MUC7 O-glycans between Sjögren’s Syndrome (SjS) patients and healthy controls.
Method: MUC7 was isolated from unstimulated whole-mouth saliva (UWMS, n=12 patients, 13 controls) and lower labial residual mucosal saliva (RMS.LL, n=13 patients, 4 controls) by gel electrophoresis and transferred to PVDF membrane. Alcian blue stained MUC7 bands were excised and O-glycans released by reductive β-elimination and analysed by mass spectrometry. Oral dryness was assessed using two questionnaires and UWMS extensional rheology (spinnbarkeit) measured with the Neva-Meter.
Result: Objective and subjective measures of dryness showed significantly higher signs and complaint of dry mouth in patients (p<0.0001). Patient’s saliva showed a higher relative abundance of core 1 glycans (Galβ1-3GalNAc) compared to controls, which showed greater core 2 (GlcNAcβ1-6(Gal β1-3)GalNAc) abundance. Sulphated glycan was higher in patient saliva (significant in UWMS, p=0.035). Despite the majority of sugars being sialylated in both groups, total sialylated glycans (core 1 and 2) were lower in patients (UWMS p=0.03, RMS.LL p=0.032). Spinnbarkeit was significantly lower in patients (p<0.0001).
Conclusion: In SjS patients, MUC7 has a lower abundance of longer, sialylated and branched glycans. The altered mucin glycosylation may be linked with functional changes seen as loss of saliva lubricity and increased dryness.