Purpose: Visual loss secondary to retinal ischemia/hypoxia can be a serious complication of diabetic retinopathy, as well as other vascular insults. We used R28 retinal precursor cells, as well as primary rat retinal cell cultures, to test whether the neuroprotective growth factor IGF-1 would protect retinal cells from dying under conditions of hypoxia or serum-starvation. We also utilized three IGF-1 analogs ([LongR3], [Ala31], and [Leu24][Ala31]) with altered affinities for the IGF-1 receptor and/or IGF-1 binding proteins in order to address the mechanism(s) of IGF-1 neuroprotection.
Methods: Retinal cultures were subjected to hypoxia (95% N2/5% CO2 for 0-8 h), or serum-starvation (0% serum for 48 h). Experimental cultures were pre-treated for 24 h with 0-100 ng/ml of IGF-1 or its analogs. Retinal cultures were analyzed for the extent of cell death by trypan blue exclusion assay, TUNEL in situ, as well as ssDNA analysis specific for apoptosis.
Results: IGF-1 and all three IGF-1 analogs tested were able to inhibit neuroretinal cell death at a concentration of 50 ng/ml. Neuroprotection was evident under conditions of hypoxia or serum-starvation.
Conclusions: IGF-1, as well as IGF-1 analogs, improves survival of neuroretinal cells in vitro, under conditions of hypoxia or serum-starvation. Since all three IGF-1 analogs inhibit cell death to some degree, we interpret these results to mean that IGF-1-mediated inhibition of cell death does not depend upon strong affinities for the IGF-1 receptor or IGF-1 binding proteins. Further studies will reveal additional information as to the pathways responsible for IGF-1-mediated neuroprotection of retinal cells.