Characterization of the Role of Apoptosis Inducing Factor (AIF) in Retina Under Normal Conditions and Retinal Detachment

Abstract

Purpose:: Apoptotic photoreceptor death is one of the major causes of visual loss after retinal detachment (RD). Previously, we reported the translocation of the apoptosis inducing factor (AIF) from the mitochondrial intermembrane space into the nucleus during RD and that AIF deficient mice (AIF-/Y) showed less apoptosis after RD. To further elucidate the role of retinal AIF, we quantified retinal expression of AIF in wild type (WT) and AIF deficient mice (AIF-/Y) under normal conditions and RD and examined blockage of AIF signaling by inhibiting mitochondria-dependent pathways.

Methods:: Eyes of WT and hemizygous AIF deficient mice were enucleated at 1, 3, and 6 months of age to determine retinal developmental differences. RD was induced by subretinal injection of sodium hyaluronate in age-matched WT and AIF (-/Y) mice. The animal’s eyes were enucleated on days 1, 3, and 7 after RD, and were analyzed using immunohistochemistry, TUNEL, transmission electron microscopy (TEM), RT-PCR and western blotting. HIV protease inhibitors (Nelfinavir/Ritonavir) were administered orally three times a day for 3 days during RD (125mg/kg, 13mg/kg). HIV tat BH4 protein was injected intraperitoneally before inducing RD (8mg/kg).

Results:: AIF mRNA was expressed constantly in WT mice and did not change after RD. AIF mRNA was significantly lower in AIF deficient mice. Western blotting also demonstrated constant expression of AIF in wildtype and significant loss in AIF deficient mice. Following RD, photoreceptor apoptosis was significantly lower in AIF deficient mice (2.4% of total photoreceptors) when compared to WT (5.1%, n=5 in each group, p=0.016). HIV protease inhibitors reduced photoreceptor apoptosis (1.6%, n=5, p<0.01) in the treated groups as did HIV tat BH4 protein (0.52%, n=5, p<0.01) 3 days after RD. AIF translocation from mitochondria to nucleus was partially inhibited in the treated groups.

Conclusions:: Our data suggest that AIF plays an important role in RD-induced photoreceptor apoptosis. Mice lacking AIF show a substantial protection against RD-induced neurodegeneration. AIF blockade by inhibiting mitochondria-dependent pathways also showed neuroprotective effects. AIF may thus offer a new therapeutic target for neuroprotection after RD.

Keywords: photoreceptors • apoptosis/cell death • neuroprotection