Endothelin-1, endothelin A and B receptor expression and their pharmacological properties in GFAP negative human lamina cribrosa cells

Primary open angle glaucoma (POAG) is a progressive optic neuropathy, characterized, in part by extensive extra cellular matrix remodeling and collapse of the lamina cribrosa (LC). Endothelin-1 (ET-1), a potent vasoactive peptide and its receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB), have been implicated in glaucomatous optic neuropathy. In this study we examined the expression of ET-1 and its receptors in GFAP negative LC cells. RT-PCR analysis revealed that LC cells express both ETA, ETB receptors and prepro- ET-1, the primary gene transcript of ET-1. A dose-dependent increase in intra-cellular calcium concentrations was observed in the presence of 1, 10 and 100 nM ET-1. Increased intracellular calcium concentrations were blocked by the ETA selective antagonist BQ610 but not by the ETB specific antagonist BQ788. Desensitization to ETA-mediated increase in intracellular calcium was observed in LC cells following pre-treatment with ET-1 for 24 h. Western blot analysis of LC cells treated with ET-1 for 24 h revealed a decreased expression of ETA receptor protein at 1, 10 and 100 nM concentrations, while a dose dependent increase in the ETB receptor was observed with a significant increase at 100 nM. Quantitative PCR showed a dose-dependent decrease in ETA receptor mRNA levels and an increase in the mRNA levels of ETB receptors. A Griess colorimetric assay was used to measure the NO released from LC cells and ET-1 induced a dose-dependent increase in NO release which was significant at 100 nM concentration. ET-1 induced NO release was significantly blocked by BQ788, an ETB selective antagonist, and as well as BQ610, an ETA selective antagonist. These results suggested that human lamina cribrosa cells expressed functional ETA and ETB receptors and their expression and function was altered in response to prolong exposure to ET-1. This may have an implication in the normal physiology of LC cells and in POAG subjects where elevated levels of ET-1 could impact LC function.