Hypomethylation of thrombospondin-1 promoter region is associated with reduced aqueous humor flow.

Prolonged use of dexamethasone (DEX) elevates intraocular pressure (IOP) and increases the risk of developing glaucoma. In a previous study, we demonstrate that DEX stimulates the expression of thrombospondin-1 (THBS1) in primary human trabecular meshwork (hTM) cells, and that inhibiting THBS1 expression prevents DEX-induced elevation of IOP in mice. Therefore, we investigate the mechanism by which DEX regulates THBS1 expression. Treatment with the DNA methylation inhibitors, 5-azacytosine (5-AC) or 5-aza-2'-deoxycytidine (5-aza-dC), upregulates THBS1 protein levels in vitro and in vivo, reduces outflow facility in perfused mouse eyes, and elevates IOP in mice. In primary hTM cells, 7-day DEX treatment results in hypomethylation of the THBS1 promoter region and reduces transcript levels of 2 DNA methyltransferases (DNMTs), DNMT1 and DNMT3A. Taken together, we show that DEX reduces expression of DNMTs and DNA methylation of the THBS1 promoter region, supporting a critical role for THBS1 in DEX-induced outflow reduction.