To determine whether the relative amounts of mucin mRNA in the conjunctival epithelium and mucin protein in the tears are altered in patients with Sjögren syndrome compared with healthy individuals.
Tear fluid was collected from the inferior fornix of normal subjects (n = 17) and patients with Sjögren syndrome (n = 11) after instillation of 60 microL sterile water onto the ocular surface. Immediately after tear fluid collection, conjunctival epithelium was obtained by filter paper-stripping from the bulbar temporal region for mRNA isolation. Primers to nontandem repeat sequences of the gel-forming mucin MUC5AC and the membrane-spanning mucins MUC1 and MUC4 were used in real-time RT-PCR to determine relative abundance of MUC mRNA in patients with Sjögren syndrome in relation to that of normal subjects. Enzyme-linked immunosorbent assay was performed on neuraminidase-treated tears, using a polyclonal antibody against a synthetic peptide mimicking the deduced amino acid sequence from the D3 region of MUC5AC.
The number of RNA transcripts for the goblet cell-specific mucin MUC5AC in the conjunctival epithelium of patients with Sjögren syndrome was significantly lower than in normal individuals. No significant changes were detected when analyzing the mRNA levels of the mucins expressed by the stratified epithelium of the conjunctiva, MUC1 and MUC4. Protein levels of the goblet cell mucin MUC5AC were significantly reduced in the tear fluid of patients with Sjögren syndrome, corroborating mRNA data obtained using real-time RT-PCR.
The tear fluid of patients with Sjögren syndrome has reduced levels of the goblet cell-specific mucin MUC5AC, which correlates to decreased levels of conjunctival MUC5AC mRNA. The authors propose that deficiency of MUC5AC mucin in tears constitutes one of the mechanisms responsible for tear film instability in Sjögren syndrome.