Inhibition of Receptor Interacting Protein Kinase Delays Necrotic Cone Photoreceptor Cell Death in a Mouse Model of Inherited Retinal Degeneration

Abstract

Purpose: : Retinitis pigmentosa (RP) is an incurable retinal disease resulting from loss of photoreceptors, primarily rods and secondarily cones. Rod photoreceptor death is caused by genetic mutations, most of which are expressed exclusively in rod cells, with apoptotic features. In contrast, mechanism and features of cone cell death remain largely unknown. In this study, we investigated a possible role for programmed necrosis mediated by receptor-interacting protein (RIP) kinase in a mouse model of RP, and establish a novel therapeutic interventions.

Methods: : The eyes of rd10 mice, which have a missense mutation in Pde6b, and wild-type C57BL6 mice were used for the experiments. Expression levels of RIP3, a key regulator of programmed necrosis, were measured by quantitative real-time PCR and Western blotting. Rd10 mice were crossed with Rip3-/- mice or were systemically injected with the RIP kinase inhibitor necrostatin-1. Rod and cone cell death was evaluated by transmission electron microscopy and immunohistochemistry. Retinal function was measured by electroretinogram.

Results: : RIP3 expression, a key regulator of programmed necrosis, was elevated in the phase of cone degeneration. While rd10 mice lacking Rip3 developed rod degeneration comparable to control rd10 mice, they displayed a significant reduction in cone cell loss. Ultrastructural analysis of rd10 mouse retina revealed that a substantial fraction of dying cones were accompanied by necrotic morphology, which was rescued by Rip3 deficiency. Additionally, pharmacological treatment with RIP kinase inhibitor attenuated histological and functional deficits of cones in rd10 mice.

Conclusions: : These findings demonstrate that distinct cell death mechanisms are involved in rod and cone cell death in rd10 mice and that cone cell death is mediated by necrotic mechanisms involving RIP kinase, suggesting the RIP kinase pathway as a potential target to protect cone-mediated central vision loss in RP patients.

Keywords: retinal degenerations: hereditary • neuroprotection • apoptosis/cell death