AIPL1, A protein linked to blindness, is essential for the stability of enzymes mediating cGMP metabolism in cone photoreceptor cells

Defects in the photoreceptor-specific gene encoding aryl hydrocarbon receptor interacting protein like-1 (AIPL1) are linked to blinding diseases, including Leber congenital amaurosis (LCA) and cone dystrophy. While it is apparent that AIPL1 is needed for rod and cone function, the role of AIPL1 in cones is not clear. In this study, using an all-cone animal model lacking Aipl1, we show a light-independent degeneration of M- and S-opsin containing cones that proceeds in a ventral-to-dorsal gradient. Aipl1 is needed for stability, assembly and membrane association of cone PDE6, an enzyme crucial for photoreceptor function and survival. Furthermore, RetGC1, a protein linked to LCA that is needed for cGMP synthesis, was dramatically reduced in cones lacking Aipl1. A defect in RetGC1 is supported by our finding that cones lacking Aipl1 exhibited reduced levels of cGMP. These findings are in contrast to the role of Aipl1 in rods, where destabilization of rod PDE6 results in an increase in cGMP levels, which drives rapid rod degeneration. Our results illustrate mechanistic differences behind the death of rods and cones in retinal degenerative disease caused by deficiencies in AIPL1.