Gene Therapy Successfully Restores Retinal Function and Delays Degeneration in a Mouse Model of CNGB1-linked Retinitis Pigmentosa

Abstract

Purpose : Retinitis pigmentosa type 45 (RP45) is an autosomal-recessively inherited blinding disease caused by mutations in the cyclic nucleotide gated channel subunit beta 1 (CNGB1) gene. The disease leads to progressive retinal degeneration affecting rod photoreceptors and subsequently cone photoreceptors. Gene augmentation therapy using recombinant adeno-associated virus (rAAV) vectors poses a tangible and potentially curative therapeutic option. In this study, we developed a novel gene augmentation therapy for rod-targeted delivery of human CNGB1 using an rAAV5 (rAAV5.hCNGB1) and evaluated its efficacy in the Cngb1 knockout (Cngb1^-/-) mouse model of RP45.

Methods : We designed a novel rAAV vector optimized for specific and efficient expression of full-length human CNGB1 in rods under the control of a short human rhodopsin promoter (hRHO194), and packaged it with AAV serotype 5. Increasing doses of rAAV5.hCNGB1 were delivered subretinally in 4-week-old Cngb1^-/- mice and the therapeutic effect was assessed short-, mid- and long-term. Transgene expression and retinal morphology were investigated via immunohistochemistry. Visual recovery was analyzed in vivo by electroretinography (ERG) while morphological preservation was monitored via spectral-domain optical coherence tomography (SD-OCT). Additionally, spatial navigation was tested by a visual Water Maze to evaluate the processing of visual information in treated mice.

Results : Treatment with rAAV5.hCNGB1 achieved substantial preservation of rod and cone photoreceptors in Cngb1^-/- mice. Furthermore, we show that the supplemented hCNGB1 was capable of forming functional heteromeric rod CNG channels with the endogenous mouse CNGA1 subunit leading to recovery of rod photoreceptor function. CNGB1 expression increased dose-dependently and resulted in increased ERG-b-wave amplitudes and therefore in enhanced visual acuity in Cngb1^-/- mice. Moreover, Cngb1^-/- mice were able to process the gained retinal function and showed significant improvement when navigating in the dark. This rescue effect persisted for at least 9 months post injection.

Conclusions : The novel rAAV5.CNGB1 vector supports efficient and specific human CNGB1 protein expression in affected murine rod photoreceptors resulting in recovered rod function and deceleration of retinal degeneration in the Cngb1^-/- mouse model of RP45.

This is a 2021 ARVO Annual Meeting abstract.