Expression of nitric oxide synthase-2 (NOS-2) in reactive astrocytes of the human glaucomatous optic nerve head

Inducible nitric oxide synthase (NOS-2) is abundantly present in the optic nerve heads of glaucoma patients. To determine the regulation of NOS-2 expression in the glaucomatous optic nerve head, the specific cells that express NOS-2 in the optic nerve heads of patients with primary open-angle glaucoma were studied by immunohistochemical double-labeling of NOS-2 and one of the characteristic cell markers for different cell types. Most of the labeling for NOS-2 was identified in reactive astrocytes that were clustered in the areas of nerve damage in the prelaminar and lamina cribrosa regions of the glaucomatous optic nerve heads. In vitro, the expression of GFAP and NOS-2 by reactive astrocytes of human optic nerve heads was demonstrated by immunocytochemistry and Western blot. In primary cultures of human lamina cribrosa astrocytes, stimulation by interferon-gamma and interleukin-1beta upregulated GFAP and induced expression of NOS-2 protein. At 24, 48 and 72 h of stimulation, NOS-2 appeared first in the Golgi body and then was sent out into the cytoplasm in granules. These results demonstrated that the astrocytes of human optic nerve head are capable of inducing the expression of NOS-2. Reactive astrocytes in the glaucomatous optic nerve heads apparently play an important role in local neurotoxicity to the axons of the retinal ganglion cells by producing excessive nitric oxide in glaucomatous optic neuropathy.