Histone Acetylation as an Epigenetic Regulator of Glaucoma-Associated Growth Factors in the Trabecular Meshwork

Glaucoma is a leading cause of blindness in the U.S. and worldwide. This disease leads to progressive, irreversible damage to the optic nerve and visual function. The primary risk factor of primary open angle glaucoma (POAG), the major type of glaucoma, is elevated intraocular pressure (IOP). IOP elevation in glaucoma patients is due to glaucomatous insults to the trabecular meshwork (TM) and compromised TM function, which increase aqueous humor outflow resistance. In the glaucomatous TM (GTM), there is excessive extracellular matrix (ECM) protein deposition. Many studies have suggested that cell signaling pathways, such as the transforming growth factor beta (TGF-β) and Wnt signaling pathways, play key roles in TM homeostasis. The growth factors that are associated with these pathways, including TGFβ2 and sFRP1, are increased in the GTM cells compared to normal TM cells. Little is known about the role of epigenetics in regulating glaucoma-associated growth factors in the TM. We hypothesize that histone acetylation is responsible for the increased expression of glaucoma associated factors in the TM. Primary human TM cell cultures were treated with 10nM Thailandepsin (TDP-A), a histone deacetylase inhibitor (HDACi), or 1% DMSO as vehicle control for 3 - 4 days. TM cells were a kind gift from Novartis. RNA was extracted for qPCR to compare gene expression. We also treated paired perfusion cultured bovine anterior segments with DMSO or TDP-A for 7 to 10 days. Additionally, we treated paired perfused anterior segments with TDP-A or TDP-A plus sFRP-1 or TGFβ receptor 1 inhibitors. The IOPs of the bovine eyes were continuously monitored. Data were analyzed by using Student’s t-test. P values less than 0.05 were considered significant. We found that TDP-A elevated the expression of sFRP-1 and TGFβ2 in TM cell cultures. Our bovine eye perfusion culture study also showed that TDP-A treatment increased the expression of sFRP-1 and TGFβ2 as well as significantly elevated IOP (n=9, p less than 0.05). Furthermore, use of sFRP-1 or TGFβ receptor 1 inhibitors decreased IOP. Histone acetylation may play an important role in the dysregulation of growth factors in the GTM. This mechanism provides a unique opportunity to elucidate the etiology of POAG. Also, TDP-A is a potent HDACi that can be used as a powerful research tool in glaucoma research.