To quantify and compare human mucin 1 (MUC1) protein and mRNA expression in tears and conjunctival epithelial cells collected from Sjogren's syndrome (SS), non-Sjogren's keratoconjunctivitus sicca (KCS) and non-dry eyed (NDE) control subjects.
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. Tears were collected using an eye-wash technique. Impression cytology was used to gather protein and mRNA from conjunctival epithelial cells. Soluble and membrane bound MUC1 were quantified via western blotting and MUC1 mRNA was quantified by real time qPCR.
The SS group demonstrated significantly higher concentrations of soluble MUC1 (0.12 +/- 0.11 [SS]; 0.013 +/- 0.02 [KCS; p=0.001]; 0.0023 +/- 0.0024 [NDE; p<0.001]) and MUC1 mRNA (3.18 +/- 1.44 [SS]; 1.79 +/- 1.18 [KCS; p<0.05]; 1.60 +/- 0.74 [NDE; p<0.05]) compared to both KCS and NDE groups. Soluble MUC1 expression was also higher in the KCS group compared to the NDE group (p=0.02), where as MUC1 mRNA expression was similar in both KCS and NDE groups. Membrane bound MUC1 expression differed only between the SS and NDE groups (0.005 +/- -0.003 [SS]; 0.003 +/- 0.002 [NDE; p=0.002]).
These results demonstrate that SS subjects express greater quantities of MUC1 protein and mRNA compared to both KCS and control subjects. Increased soluble MUC1 expression was also found in KCS subjects compared to controls. Membrane bound MUC1 was present in higher concentration in SS versus NDE only. These significant changes in MUC1 expression may represent compensatory or protective responses to chronic insult to the ocular surface.