Abstract
Purpose :
Transducin is a heterotrimeric G protein which is a component of this phototransduction cascade. The rod-specific Transducin α-subunit, Gnat1, is known to regulate light/dark adaptation by changing its subcellular localization depending on light. Our previous study revealed that Gnat1 translocation in rod photoreceptor cells under the light/dark conditions requires the E3 ligase Klhl18-mediated ubiquitination and degradation of Unc119, a Gnat1-binding protein. A mutation in the human UNC119 gene is known to be associated with cone-rod dystrophy; however, its underlying pathological mechanism remains unclear.
Methods :
In order to investigate the mechanism of cone-rod dystrophy caused by UNC119 mutation, we generated Unc119-deficient (Unc119-/-) mice. We performed ERG and histological analyses at 1 month (1M), 6 M, and 12M in the retina. In addition, we performed biochemical analyses using the HEK293T cell line to investigate whether and how the human UNC119 mutation affects the UNC119 function.
Results :
ERG analyses showed that photopic responses in Unc119-/- mice were lower than those in the control mice both at 1 M and 6 M. Unc119-/- mice exhibited reduced photopic and scotopic responses compared to those in control mice at 12 M. We immunostained cone and rod outer segments at 1M, 6M, and 12M. While we observed outer segments degeneration and mislocalization of cone opsins only in cones at 1M and 6M, disorganized rod and cone outer segments were observed in the Unc119-/- retina at 12M. Co-immunoprecipitation analysis showed that UNC119 binds to GNAT2 and NPHP3. In addition, we observed that human UNC119 mutation inhibits the interaction of UNC119 with GNAT1, GNAT2, and NPHP3.
Conclusions :
Our results suggest that the Unc119 deficiency leads to progressive photoreceptor degeneration, such as cone-rod dystrophy. GNAT1, GNAT2, and NPHP3 mutations are known to cause retinal degeneration diseases in human; therefore, human UNC119 mutation may inhibit these proteins function. Our current study will advance our understanding of the function of G proteins in the retina and the pathological mechanism of cone-rod dystrophy.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.