Activation of c-Fos and c-Jun in Optic Nerve Head Astrocytes of Monkeys with Unilateral Ocular Hypertension and in Human Astrocytes Exposed to Hydrostatic Pressure in Vitro

Abstract

Abstract: : Purpose: To determine whether immediate early gene (IEG) products c-fos and c-jun are activated in astrocytes from the optic nerve head (ONH) of monkeys with laser-induced elevated intraocular pressure (IOP) and human ONH astrocytes exposed to elevated hydrostatic pressure (HP) in vitro. Methods: Four Rhesus monkeys with laser-induced unilateral elevated IOP (33.8±7.91 mm Hg) for 15.7±5.7 weeks were used; the contralateral eye served as normal control (18.6±1.66 mmHg). Sagittal sections of the ONH were immunostained with antibodies against glial fibrillary acidic protein (GFAP), gene products c-fos and c-jun, and the nuclear stain DAPI. Sections were examined and scanned using fluorescence microscopy with three different filters. GFAP+ astrocytes were identified in standardized areas and the number of nuclei stained with c-fos and c-jun per total number of astrocyte nuclei was counted. After normalization between the experimental and control ONH, we performed statistical analysis. To confirm nuclear translocation of transcription factors in vitro, we exposed human ONH astrocytes to hydrostatic pressure (60 mm Hg) for different times, stained and counted labeled nuclei as above. Results: In all eyes with ocular hypertension, nuclear c-fos localized to 77.8±7.42% of the astrocytes compared to 22.2±7.42% in controls and c-jun localized to 67.5±4.36% of the astrocytes compared to 32.5±4.36% in controls (p<0.05). In vitro exposure to HP increased nuclear translocation of c-fos by 56.0±18.1% after 30 min and by 50.7±13.7% after 1.5h compared to 28.2±14.5% in controls. Nuclear translocation increased for c-jun by 53.0±14.0% after 30 min exposure to HP compared to 35.4±12.7 % in controls and by 53.4±12.4% after 1.5 h (p<0.05). The number of c-jun and c-fos labeled nuclei decreased after exposure to HP for 3 h. Conclusions: Nuclear localization of c-fos and c-jun, in ONH astrocytes exposed to elevated IOP in vivo and to elevated HP in vitro indicates activation of IEGs, which may be involved in optic nerve degeneration in glaucoma. The results illustrate how pressure acting as a short-term stimulus on ONH astrocytes in vitro, can also activate c-jun and c-fos in the vivo model with chronic IOP elevation.

Keywords: transcription factors • lamina cribrosa • animal model