Purpose: Evidence suggests that chronically increased stress conditions in the anterior eye segment constitute major mechanisms involved in the pathobiology of pseudoexfoliation (PEX) syndrome. The expression of stress-related genes in eyes from patients with and without PEX syndrome/glaucoma was investigated to determine whether PEX syndrome is associated with an altered cellular stress response.
Methods: cDNA array hybridization, quantitative real-time PCR, Western blot analysis, and immunohistochemistry were applied to analyze the mRNA and protein expression of stress-related genes in anterior segment tissues of PEX eyes, with and without glaucoma, and to compare them with normal and glaucomatous control eyes.
Results: Hybridization of cDNA arrays identified a set of stress-related candidate genes for differential expression in PEX syndrome/glaucoma, of which 10 were confirmed by real-time PCR in ciliary processes and iris tissue. The expression of MAPKp38, heat shock proteins (HSP40, HSP60), and superoxide dismutase (SOD2) was increased up to threefold in PEX specimens. In contrast, a large set of cytoprotective gene products, including antioxidant defense enzymes (glutathione S-transferases mGST1 and GSTT1), ubiquitin-conjugating enzymes (UBE2A, UBE2B), the DNA repair protein MLH1, and the stress-inducible transcription factor GADD153, were found to be consistently downregulated up to threefold in PEX specimens on both the mRNA and protein levels.
Conclusions: The present findings provide evidence of alterations in cytoprotective mechanisms including antioxidant defense, proteasome function, endoplasmic reticulum-related stress response, and DNA repair in anterior segment tissues of PEX eyes. The resultant enhanced sensitivity and vulnerability to cellular stress conditions may therefore be one contributing factor in the pathobiology of PEX syndrome.