Human optic nerve head astrocytes as a target for endothelin-1

PURPOSE. To determine whether human optic nerve head astrocytes (hONAs) are target cells for the actions of endothelin (ET)-I, a potent vasoactive peptide, by causing astrocyte proliferation, as occurs in glaucomatous optic nerve heads. ET-1 levels are elevated in glaucomatous eyes, and administration of ET-1 to the retina causes glial activation and optic nerve damage in animal models in a manner similar to that observed in glaucoma. METHODS. Well-characterized hONAs were used in this study. Cell proliferation of hONAs was assessed, after ET-1 treatment under serum-free culture conditions, with both a formazan assay and [³H] thymidine uptake. ET receptor involvement for cell proliferation was determined with BQ788 (an ET_B antagonist), BQ610 (an ET_A antagonist), PD142893 (an ET_A/B mixed antagonist), and sarafotoxin 6C (S6C; an ETB agonist). ET-1-induced intracellular calcium ([Ca²⁺]_i) in hONAs was measured by fura-2 imaging. RT-PCR was used to determine whether hONAs express mRNA for preproET-1, ET_A, and ET_B receptors. RESULTS. ET-1 (10 and 100 nM) caused a time-dependent proliferation of hONAs, which was completely blocked by PD142893, as detected by two different cell proliferation assays. The effects of ET-1 were blocked by BQ788 and were also mimicked by S6C, indicative of the involvement of ET_B receptor activation. ET-1-induced elevation in [Ca²⁺]_i, and cell proliferation were both blocked completely by the ETA antagonist BQ610, suggesting ETA receptor involvement. The hONAs expressed mRNA for ET_A and ET_B, receptors as well as preproET-1, suggesting that these cells may also be a source for ET-1 in the optic nerve head. CONCLUSIONS. ET-1 induces astroglial proliferation in cultured human optic nerve head astrocytes through ET_A/B receptor activation. This is similar to the proliferation of ET-1 in brain astrocytes. These findings suggest that ET-1, which is elevated in glaucoma, could cause proliferation of ONAs in the optic nerve head.