To investigate the expression of MUC16 protein in tears and conjunctival cell membranes and MUC16 mRNA in conjunctival cells of Sjogren's syndrome (SS), keratoconjunctivitus sicca (KCS) and non-dry eyed (NDE) subjects. The relationship of tear flow and soluble MUC16 concentration was also measured.
Seventy-six subjects were recruited for this study: 25 SS (confirmed via American-European Consensus Criteria 2002), 25 KCS (confirmed by symptoms and Schirmer scores < or =10 mm) and 26 NDE. Tear flow was measured by the Schirmer test without anesthesia for 5 min. Tears were collected using an eye-wash technique. Protein and mRNA were isolated from conjunctival epithelial cells collected via impression cytology. Soluble and membrane bound MUC16 were quantified via western blotting and MUC16 mRNA was quantified by real time qPCR.
The SS group demonstrated significantly higher concentrations of soluble MUC16 (7.28 [SS] +/- 3.97 versus 3.35 [KCS] +/- 4.54 [p=0.004] and versus 1.61 [NDE] +/- 1.22 [p<0.001]) and MUC16 mRNA (4.66 [SS] +/- 5.06 versus 1.84 [KCS] +/- 2.26 [p=0.01] and 1.52 [NDE] +/- 1.04 [p=0.003]) compared to both KCS and NDE groups, respectively. No differences in soluble MUC16 or MUC16 mRNA were found between the KCS and NDE groups. Membrane bound MUC16 was similar in all three groups. No significant correlation was found between mean Schirmer values and any measure of MUC16 expression.
These results demonstrate that SS subjects display a significant increase in both soluble MUC16 and MUC16 mRNA concentrations compared to other forms of aqueous deficient dry eye and non dry-eyed individuals. There was no correlation between tear flow and soluble MUC16 concentration.