Intravitreous Injection of TNF– Induces Ocular Cell Death Activation and Apoptosis Under Specific Conditions

Abstract

Abstract: : Purpose: To investigate the effects of intravitreal injections of TNF–α on the rat retina. Methods: An experimental model of optic neuropathy in rats was developed using intravitreal injection of TNF–α. The level of glial fibrillary acid protein (GFAP); protein kinase C (PKC); TNFR–1(P55); TNFR–2(P75) and TNF–induced apoptosis were evaluated. Rats were sacrificed at 5, 18, 48 hours or 6 days after injection of PBS or TNF–α (final concentrations: 2U, 20U, 200U and 20U TNF–α + PKC–ζ–specific inhibitor). The eyes were enucleated and studied. Half of the eyes were used for immunohistology including TUNEL reaction. The remaining eyes were dissected, the retinas isolated, the proteins extracted and identified by Western Blot. Results: Control animals injected with PBS showed a transient and weak GFAP activation within 18 hours after injection. Injection of TNF–α induced the expression and activation of GFAP positive cells. Low doses of TNF–α stimulated the expression of PKC–ζ, consistent with the activation of bipolar cells. High doses of TNF–α however, inhibited the expression of PKC–ζ. Intravitreal injection of TNF–α stimulated the expression of TNFR–1 (P55) more than that of TNFR–2 (P75). When PKC–ζ–specific inhibitor was injected in parallel with TNF–α, apoptotic cells were observed in the inner nuclear and ganglion cell layers. The cornea, iris and ciliary body were also sensitive to 20 and 200 units intravitreal TNF–α. 18 hours after injection, we observed apoptosis in the corneal stroma, the corneal endothelium and the posterior iris epithelium. Conclusions: The intravitreal injection of TNF–α allowed us to establish an experimental model to study the early stages of the effects of TNF–α leading to the degeneration of retinal cells. This model provided a quantitative assessment of GFAP modulation and the potential effects of PKC–ζ in cellular survival.

Keywords: neuro-ophthalmology: optic nerve • retinal degenerations: cell biology • cytokines/chemokines