Cone Phosphodiesterase-6?' Subunit Augments Cone PDE6 Holoenzyme Assembly and Stability in a Mouse Model Lacking Both Rod and Cone PDE6 Catalytic Subunits.

ABSTRACT: Rod and cone phosphodiesterase 6 (PDE6) are key effector enzymes of the vertebrate phototransduction pathway. Rod PDE6 consists of two catalytic subunits PDE6? and PDE6? and two identical inhibitory PDE6? subunits, while cone PDE6 is composed of two identical PDE6?' catalytic subunits and two identical cone-specific PDE6?' inhibitory subunits. Despite their prominent function in regulating cGMP levels and therefore rod and cone light response properties, it is not known how each subunit contributes to the functional differences between rods and cones. In this study, we generated an rd10/cpfl1 mouse model lacking rod PDE6? and cone PDE6?' subunits. Both rod and cone photoreceptor cells are degenerated with age and all PDE6 subunits degrade in rd10/cpfl1 mice. We expressed cone PDE6?' in both rods and cones of rd10/cpfl1 mice by adeno-associated virus (AAV)-mediated delivery driven by the ubiquitous, constitutive small chicken ?-actin promoter. We show that expression of PDE6?' rescues rod function in rd10/cpfl1 mice, and the restoration of rod light sensitivity is attained through restoration of endogenous rod PDE6? and formation of a functional PDE6?'? complex. However, improved photopic cone responses were achieved only after supplementation of both cone PDE6?' and PDE6?' subunits but not by PDE6?' treatment alone. We observed a two fold increase of PDE6?' levels in the eyes injected with both PDE6?' plus PDE6?' relative to eyes receiving PDE6?' alone. Despite the presence of both PDE6?' and PDE6?, the majority of PDE6?' formed functional complexes with PDE6?', suggesting that PDE6?' has a higher association affinity for PDE6?' than for PDE6?. These results suggest that the presence of PDE6?' augments cone PDE6 assembly and enhances its stability. Our finding has important implication for gene therapy of PDE6?'-associated achromatopsia.

SUBMITTER: Deng WT 

PROVIDER: S-EPMC6046437 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature