Impact of Low Humidity on Damage-associated Molecular Patterns at the Ocular Surface during Dry Eye Disease

SIGNIFICANCE Dry eye is one of the leading causes for individuals to seek eye care, whereas the pathogenesis is poorly understood. One mechanism in which dry eye inflammation may ensue is by the release of damage-associated molecular patterns (DAMPs) by damaged cells to stimulate the production of cytokines and matrix metalloproteinases. Examining DAMP levels on the ocular surface during dry eye disease (DED) will increase our understanding of their potential involvement in the pathogenesis of DED. PURPOSE This study aimed to quantitate DAMPs, high-mobility group box 1 (HMGB1), and heat shock proteins on the ocular surface of normal and dry eye subjects and to examine the impact of low-humidity environment (LHE) on DAMPs and inflammation in dry eye subjects. METHODS Basal tears (10 to 20 mu L) and conjunctival impression cytology samples were analyzed for HMGB1, HSP-27, HSP-60, HSP-70, and HSP-90 alpha by ELISA or Luminex assays in normal (n = 15) and DED (n = 15) subjects. In addition, a subset of DED subjects were exposed to LHE for 2 hours. The level of DAMPs in the tear film was evaluated by ELISA or Luminex assay. Interleukin 6, interleukin 8, or metalloproteinase (MMP) 9 mRNA were quantitated by real-time polymerase chain reaction from conjunctival impression cytology samples. RESULTS Compared with age-matched normal subjects, HMGB1 was significantly elevated in the tear film of DED subjects (P = .03), whereas there was no significant difference in heat shock proteins. Conjunctival impression cytology samples revealed no significant difference in intracellular DAMP levels between both groups. After exposure to an LHE, there was an increase in corneal staining (P = .005), HSP-60 levels in the tear film (P = .01), and MMP-9 mRNA in the conjunctiva (P = .001). CONCLUSIONS Dry eye subjects had higher levels of HMGB1 in their tear film. Exposure to an LHE worsened corneal staining, increased conjunctival MMP-9 mRNA expression, and increased tear film HSP-60 levels. Larger studies are needed to understand the involvement of DAMPs in stimulating dry eye inflammation.