Alteration of Conjunctival Mucin Gene Expression in Tear-deficient Dry Eye Syndrome

Abstract

Abstract: : Purpose: There is scarce information reported on ocular mucin gene alteration induced by Dry Eye Syndrome (DES). Levels of MUC1, MUC4, and MUC5AC has been studied in Sjögren's syndrome, being significantly decreased only MUC5AC levels. The present study investigates mRNA levels of the ocular mucins MUC1, MUC2, MUC4, MUC5AC, and MUC7 in conjunctival impression cytology (CIC) samples of moderate to severe tear-deficient DES compared to healthy subjects. Methods: Two filters were applied to the superior and inferior bulbar conjunctiva of 38 DES patients and of 43 healthy donors. Total RNA was extracted, and retrotranscription followed by real time PCR was performed to examine the mRNA of ocular mucin genes MUC1, MUC2, MUC4, MUC5AC and MUC7, using SYBR^® Green I dye for their detection. Levels of mucin genes were normalized for a housekeeping gene, GAPDH. The relative quantity of MUC mRNA in patients with DES in relation to that of normal individuals was determined. Data of mucin genes were analyzed using a logarithmic transformation to obtain a distribution closer to normal. Results: The number of RNA transcripts for MUC1, MUC2, MUC4 and MUC5AC, but not for MUC7, was significantly lower (p<0.01) in conjunctival epithelium from patients with DES compared to normal donors. Table 1 represents negative logarithmic relative expression (mean±SEM) of mucin transcripts to GAPDH transcripts. Conclusions: The conjunctival epithelium of DES patients has significantly reduced levels of mRNAs for the ocular mucins MUC1, MUC2, MUC4 and MUC5AC, while levels of MUC7 remain unaltered. These findings further support an alteration in the mucin layer of the tear film of DES patients and might be further used for diagnostic and therapeutic purposes.  

Keywords: cornea: tears/tear film/dry eye • cornea: surface mucins • conjunctiva