Dexamethasone Increases Expression of Pigment Epithelium Derived Factor (PEDF) in Perfused Human Anterior Segments from Post-Mortem Donor Eyes

Abstract

Abstract: : Purpose: Glaucoma, a disease characterized by retinal ganglion cell death is commonly associated with elevated intraocular pressure. Thirty to 40% of patients treated with glucocorticoids develop glaucoma. The mechanisms by which glucocorticoids cause steroid-induced glaucoma however are unknown. We have previously shown that PEDF, a neurotrophic factor secreted by retinal pigment epithelium cells, is also expressed in the human trabecular meshwork (HTM), the tissue responsible for regulating ocular pressure. In the present study, we investigated whether dexamethasone (DEX) plays a role in the regulation of PEDF expression in TM. Methods: Anterior segment organ cultures were prepared from paired eyes from post-mortem human donors. One eye of each pair was perfused with 0.1 µM DEX for 7 days while the contralateral was perfused with control medium. Primary HTM cells at 4^th passage were treated with DEX under the same conditions. PEDF mRNA levels from intact perfused TM as well as from HTM cells were measured using relative quantitative RT-PCR. PEDF protein levels were determined in the effluents from DEX-perfused eyes and in the conditioned media of HTM cells by Western blotting techniques. Results: In TM from organ cultures, PEDF mRNA increased 5.8 ± 0.5-fold (n=6) by 7 days of DEX treatment over contralateral controls. In DEX treated HTM cells, PEDF mRNA increased 1.4 to 3.8-fold (n=6) over vehicle treated cells during 7 days in culture. PEDF protein was detected extracellularly in both cultures. By day 8, the amount of PEDF secreted in the effluents of DEX treated organ cultures increased 3 to 5-fold (n=2) above controls. Correspondingly, PEDF protein levels in the media of DEX treated HTM cells increased by an average of 4-fold over the untreated controls by 8 days . Conclusions: DEX up-regulated PEDF gene expression and protein production in the TM of human anterior segments and cultured HTM cells . This is the first demonstration that PEDF gene expression is up-regulated by corticosteroids and that PEDF protein is secreted by anterior segment organ cultures and HTM cells in primary culture. By elevating levels of the neurotrophic factor PEDF, DEX may be triggering an adaptive mechanism to counteract DEX-induced glaucoma. Such a mechanism may also be used to prevent neurodegeneration of retinal ganglion cells.

Keywords: trabecular meshwork • corticosteroids • gene/expression