Nitric oxide synthase-2 in human optic nerve head astrocytes induced by elevated pressure in vitro

Objective: To determine whether astrocytes of the human optic nerve head ca n induce nitric oxide synthase-2 (NOS-2) in response to elevated hydrostati c pressure as a mechanism for directly damaging the axons of the retinal ga nglion cells in glaucoma. Methods: Primary cultures of astrocytes from human optic nerve heads were p laced in chambers, either pressurized at elevated hydrostatic pressure (60 mm Hg) or maintained at ambient pressure. The induction of NOS-2 was studie d by immunocytochemistry, immunoblot, and semiquantitative reverse transcri ption polymerase chain reaction. Results: In astrocyte cultures under ambient pressure, NOS-2 was almost und etectable. In astrocyte cultures under elevated hydrostatic pressure for 24 , 48, and 72 hours, intensive labeling of NOS-2 in the Golgi body and the c ytoplasm was observed by immunocytochemistry and intense bands of NOS-2 wer e detected by immunoblotting. As detected by semiquantitative reverse trans cription polymerase chain reaction, the messenger RNA level of NOS-2 increa sed significantly in the astrocytes under elevated hydrostatic pressure wit hin 12 hours, peaking earlier than the protein level of NOS-2. Conclusion: Elevated hydrostatic pressure induces the astrocytes of the hum an optic nerve head to express NOS-2. Clinical Relevance: In glaucoma, the appearance of the neurodestructive NOS -2 in astrocytes of the optic nerve head may be a primary response to eleva ted intraocular pressure, in vivo, and therefore damaging to the axons of t he retinal ganglion cells.