Although glial cells in the optic nerve head undergo a reactivation process in glaucoma, the role of glial cells during glaucomatous neurodegeneration of retinal ganglion cells is unknown. Using a coculture system in which retinal ganglion cells and glial cells are grown on different layers but share the same culture medium, we studied the influences of glial cells on survival of retinal ganglion cells after exposure to different stress conditions typified by simulated ischemia and elevated hydrostatic pressure. After the exposure to these stressors, we observed that glial cells secreted tumor necrosis factor-alpha (TNF-alpha) as well as other noxious agents such as nitric oxide into the coculture media and facilitated the apoptotic death of retinal ganglion cells as assessed by morphology, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and caspase activity. The glial origin of these noxious effects was confirmed by passive transfer experiments. Furthermore, retinal ganglion cell apoptosis was attenuated approximately 66% by a neutralizing antibody against TNF-alpha and 50% by a selective inhibitor of inducible nitric oxide synthase (1400W). Because elevated intraocular pressure and ischemia are two prominent stress factors identified in the eyes of patients with glaucoma, these findings reveal a novel glia-initiated pathogenic mechanism for retinal ganglion cell death in glaucoma. In addition, these findings suggest that the inhibition of TNF-alpha that is released by reactivated glial cells may provide a novel therapeutic target for neuroprotection in the treatment of glaucomatous optic neuropathy.

To study expression and location of matrix metalloproteinases (MMPs) and tumor necrosis factor ␣ (TNF-␣) in glaucomatous optic nerve heads, which are known to be secreted in response to a variety of neuronal injury.Methods: Four postmortem eyes from patients with primary open-angle glaucoma, 7 eyes from patients with normal-pressure glaucoma, and 4 eyes from age-matched normal donors were studied by immunohistochemistry. The sections of the optic nerve heads were examined after immunostaining with antibodies to MMPs (MMP-1, MMP-2, and MMP-3), TNF-␣, or TNF-␣ receptor 1. Results:The intensity of the immunostaining and the number of stained cells for MMPs, TNF-␣, or TNF-␣ receptor 1 were greater in the glaucomatous optic nerve heads, particularly in eyes with normal-pressure glaucoma compared with age-matched controls. Positive immunostaining was observed in all regions of the glauco-matous optic nerve heads, but most prominently in the postlaminar region. Immunostaining was observed mainly in glial cells and their processes around the axons and blood vessels and in pial septae. Conclusion:There is increased immunostaining for MMPs, TNF-␣ and TNF-␣ receptor 1 in the glaucomatous optic nerve head, which suggests increased expression of these proteins in glaucoma and thereby implies a role in the tissue remodeling and degenerative changes seen in glaucomatous optic nerve heads.Clinical Relevance: The MMPs and TNF-␣ may be components of astroglial activation that occurs in glaucomatous optic nerve heads. The biological alterations in the expression of these proteins may play a role in the progression of glaucomatous optic neuropathy.

The rebound tonometer was easy to use and accurately measured IOP in rats and mice. This technique, together with advances in genetic and other biological studies in rodents, will be valuable in the further understanding of the etiology and pathology of glaucoma.

Glaucomatous optic neuropathy causes blindness through the degeneration of retinal ganglion cells (RGCs

Objective: To examine tissue hypoxia in the retina and optic nerve head of glaucomatous eyes by the assessment of a transcription factor, hypoxia-inducible factor 1␣ (HIF-1␣), which is tightly regulated by the cellular oxygen concentration. Methods: Using immunohistochemical analysis, the cellular localization of HIF-1␣ was studied in the retina and optic nerve head of 28 human donor eyes with glaucoma compared with 20 control eyes from healthy donors matched for several characteristics. The relationship between the retinal regions that exhibited immunostaining for HIF-1␣ and functional damage was examined using visual field data. Results: There was an increase in the immunostaining for HIF-1␣ in the retina and optic nerve head of glaucomatous donor eyes compared with the control eyes. In addition, the retinal location of the increased immunostaining for HIF-1␣ in some of the glaucomatous eyes was closely concordant with the location of visual field defects recorded in these eyes. Conclusions: Because the regions of HIF-1␣ induction represent the areas of decreased oxygen delivery and hypoxic stress, information obtained from this study provides direct evidence that tissue hypoxia is present in the retina and optic nerve head of glaucomatous eyes, and hypoxic signaling is a likely component of the pathogenic mechanisms of glaucomatous neurodegeneration. Clinical Relevance: These findings support the presence of tissue hypoxia in the retina and optic nerve head of glaucomatous patients.