Distinct profiles of abnormal ganglion cell activity in two forms of Leber’s congenital amaurosis (LCA): Implications for therapy

Abstract

Purpose: To help improve therapy for Leber's congenital amaurosis (LCA), we sought to better understand differences in the abnormalities of inner retinal neurophysiology particular to its varied genetic forms. We studied mice with mutations in 1) Rpe65, the gene affected in the only form currently treatable with gene therapy; and 2) Cep290, the most commonly affected gene. We also assessed the effectiveness of gene therapy in reversing these abnormalities in Rpe65-/- mice, at the level of single cell and circuit physiology.

Methods: Using in vitro multielectrode recording, we measured retinal ganglion cell (RGC) activity in rd12 (Rpe65-/-), rd16 (Cep290-/-), and wild type (wt) mouse retinas. We compared spontaneous and light-evoked activity (full field flashes or pseudorandom checkerboard stimuli) from perinatal to adult ages. Some rd12 RGCs were recorded 7-90 days following subretinal injection of a viral vector to transfect photoreceptors with normal RPE65 (AAV2/1-hRPE65).

Results: Before eye-opening, normal developmental waves of correlated firing appeared in both rd12 and rd16 RGCs. Spontaneous hyperactivity emerged shortly after eye opening in both strains, but was more prominent in rd12. The frequency spectrum of spontaneous activity in rd16 cells included several peaks, indicating a rhythmic oscillatory component (similar to some other degenerate strains). In contrast, rd12 RGCs lacked such rhythmicity and had a broad frequency spectrum. Untreated rd12 RGCs had no light responses at any age, while rd16 cells had reduced responses at early ages but decayed slowly. Gene therapy restored robust light-evoked responses in many rd12 RGCs, with multiple recognizable response types and some reliable receptive field maps. However, treatment after first eye opening did not prevent hyperactivity, which was associated with less precise receptive fields. Only treatment prior to eye opening prevented hyperactivity and preserved more normal receptive field architecture in some cases.

Conclusions: Our results provide a high resolution view of distinct abnormalities in RGC activity particular to Rpe65- or Cep290-based LCA. They indicate that the ability of gene therapy to reverse different abnormalities in visual processing varies, and depends on optimizing the age of treatment administration. These principles may guide further improvements in gene therapy and other treatments.

Keywords: 695 retinal degenerations: cell biology • 531 ganglion cells • 508 electrophysiology: non-clinical