Tnf-α and calcium permeable ampa receptors on neurodegeneration in experimental glaucoma

J. CUEVA VARGAS; I. OSSWALD; N. UNSAIN; D. BOWIE; P. BARKER; A. DI POLO

New Orleans

Congreso; Neuroscience Meeting; 2012

Society for Neuroscience

Purpose: Progressive and irreversible degeneration of Retinal Ganglion Cells (RGCs) and their axons are the principal cause of visual field loss in glaucoma. The primary mechanism of RGC damage is still unclear. We have shown that TNF-α is a crucial regulator of neuronal glutamate receptors in the CNS, mediating the insertion of calcium permeable AMPA receptors (CP-AMPAR), resulting in loss of RGCs. We hypothesize that TNF-α serves as an important mediator of RGCs loss in glaucoma, by stimulating the insertion of CP-AMPAR on RGCs and thereby facilitating its death. Methods: Experimental glaucoma was induced in Brown Norways rats, consisting of an injection of 1.8 M NaCl into the episcleral vein. To demonstrate the role of TNF-α, a dose of Etanercept was injected into the glaucomatous eye. Additionally, to see if TNF-α is killing RGCs by activation of caspase-8, we injected the inhibitor Z-IETD-FMK. The presence of CP-AMPARs was determined using the Co2+ staining technique on retinas dissected from rats, 3 weeks after induction of high Intraocular Pressure (IOP). CP-AMPAR function was demonstrated injecting the selective antagonists GYKI 52466 and Philantotoxin (PhT) into the glaucomatous eye. The neuroprotective effect was determined by counting RGCs, which were backlabeled with DiI. The expression of TNF-α, TNF-R1 and TNF-R2 was determined by Western blot and RT-PCR. Results: We show that in glaucomatous eyes, the expression of TNF-α, TNF-R1 and TNF-R2 are upregulated. Furthermore, blocking the expression of TNF-α with Etanercept, conveys to a significant neuroprotection to RGCs. We also show that TNF-α is not acting solely through caspase-8 activation, suggesting that TNF-α kills RGCs by another mechanism. Our data also demonstrate the presence of CP-AMPAR on RGCs, and that the intraocular injection of GYKI 52466 and PhT, significantly reduces the loss of RGCs in experimental glaucoma. Conclusion: This study provides evidence that high IOP is involved in the upregulation of TNF-α and its receptors as well as CP-AMPARs. We suggest that CP-AMPAR could be upregulated by the presence of TNF-α and could be used as a target in future researches.