TNFR1 activation induced apoptosis of adult retinal ganglion cells in ischemic conditions or pure cell culture

Abstract

Abstract: : Purpose: TNFα was reported to increase in pathological conditions of the retina like glaucoma or diabetic retinopathy. Since TNFα can have opposite effects depending on activated receptors, we examined TNFR1 receptor localization in ischemic conditions and its effect in retinal cell cultures. Methods: Retinal ischemia was induced in one eye of adult Long Evans rats by increasing intraocular pressure (IOP) for one hour. At different times of reperfusion, TNFα and TNFR1 localizations were examined by immunohistochemistry on control and ischemic retinae. To characterize TNFα–related effects, exogenous TNFα, a TNFα neutralizing antibody and/or a TNFR1 neutralizing antibody were applied on either mixed adult retinal cell culture or pure adult retinal ganglion cells (RGCs) culture in ischemic or control conditions. Ischemic conditions were obtained by 48h–long hypoxia combined to hypoglycemia. RGCs survival was assessed and quantified by RGCs immunolabeling with the NF68 antibody. Results: TNFα and TNFR1 were not detected in the control rat retina. By contrast, following an ischemic insult, TNFα was detected in Müller glial cells while TNFR1 expression was localized in RGCs 48h after the ischemic episode. In retinal cell cultures, TNFα and TNFR1 were similarly localized in glial cells and RGCs, respectively. However, exogenous application of TNFα induced RGCs apoptosis in mixed retinal cell cultures only under ischemic conditions. By contrast, in purified RGCs cultures, 75% of RGCs were lost upon TNFα application even under normal culture conditions. Most RGCs were then rescued in the presence of the TNFR1 neutralizing antibody. Conclusions: These results indicate that ischemic conditions can induce TNFα and TNFR1 expressions in Müller glial cells and RGCs, respectively. They show further that TNFR1 activation triggers RGCs apoptosis in ischemic conditions or in purified RGCs. These observations suggest that the inhibition of TNFR1 activated apoptotic pathway could contribute to RGCs survival in retinal pathologies implying ischemic conditions.

Keywords: ganglion cells • cytokines/chemokines • ischemia