Experimental Dry Eye Stimulates Production of Inflammatory Cytokines and MMP-9 and Activates MAPK Signaling Pathways on the Ocular Surface


Presented by:

Lihui Luo, De-Quan Li, Amish Doshi, William Farley, Rosa M. Corrales, and Stephen C. Pflugfelder

 

Purpose

 

To evaluate whether experimentally induced dry eye in mice activates mitogen-activated protein kinase (MAPK) signaling pathways, c-Jun N-terminal kinases (JNK), extracellular-regulated kinases (ERK), and p38 and stimulates ocular surface inflammation.

 

Methods

 

129SvEv/CD-1 mixed mice aged 6 to 8 weeks were treated with systemic scopolamine and exposure to an air draft for different lengths of time, from 4 hours to 10 days. Untreated mice were used as the control. The concentrations of IL-1β and TNF-α in tear fluid washings and in corneal and conjunctival epithelia were measured by ELISA. MMP-9 in tear washings was evaluated by zymography, and gelatinase activity in the cornea and conjunctiva was determined by in situ zymography. Corneal and conjunctival epithelia were lysed in RIPA buffer for Western blot with MAPK antibodies, or they were lysed in 4 M guanidium thiocyanate solution for extraction of total RNA, which was used to determine gene expression by semiquantitative RT-PCR, real-time PCR, and gene array.

 

Results

 

Compared with those in age-matched control subjects, the concentrations of IL-1β and MMP-9 in tear fluid washings and the concentrations of IL-1β and TNF-α and gelatinolytic activity in the corneal and conjunctival epithelia were significantly increased in mice receiving treatments to induce dry eye after 5 or 10 days. The expression of IL-1β, TNF-α, and MMP-9 mRNA by the corneal and conjunctival epithelia was also stimulated in mice treated for 5 or 10 days. The levels of phosphorylated JNK1/2, ERK1/2, and p38 MAPKs in the corneal and conjunctival epithelia were markedly increased as early as 4 hours after treatment, and they remained elevated up to 5 days.

 

Conclusions

 

Experimental dry eye stimulates expression and production of IL-1β, TNF-α, and MMP-9 and activates MAPK signaling pathways on the ocular surface. MAPKs are known to stimulate the production of inflammatory cytokines and MMPs, and they could play an important role in the induction of these factors that have been implicated in the pathogenesis of dry eye disease.

 

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