Abstract
Purpose :
Late-onset retinal degeneration (L-ORD) is an autosomal dominant disorder in which a missense mutation in the CTRP5 gene leads to retinal pigment epithelium (RPE) atrophy and choroidal neovascularization. CTRP5 is a paralogue of Adiponectin family proteins which regulate cell metabolism. We hypothesize that similar to Adiponectin, CTRP5 acts through Adiponectin Receptor 1 (AdipoR1). In L-ORD RPE cells, mutant CTRP5 forms oligomers with its WT counterpart which is believed to interfere with its apical secretion from RPE and reduce binding affinity toward AdipoR1. While in silico ligand/receptor modeling and immunogold labeling suggest an interaction between CTRP5 and AdipoR1, a direct interaction has yet to be confirmed. Here, we aim to biochemically investigate CTRP5-AdipoR1 protein interactions and provide a mechanism of L-ORD disease progression.
Methods :
Induced pluripotent stem cells (iPSCs) were generated from fibroblasts of skin biopsies of four siblings, two clinically and genotypically confirmed L-ORD patients with a pathogenic variant in CTRP5 (p.Ser163Arg), and two unaffected siblings that did not carry the pathogenic variant. Cell membrane preparations from iPSC-derived RPE (iRPE) were prepared using a cellular membrane protein extraction kit and, co-immunoprecipitation was conducted via Dynabead technology using AdipoR1 antibodies as the probe. The components of protein complexes were detected via Western blot.
Results :
From AdipoR1 probed protein complexes obtained through co-immunoprecipitation, we detected CTRP5 protein in healthy iRPE. However, in L-ORD-iRPE, we detected lower CTRP5, presumably due to the lower expression and lower AdiopR1 binding affinity of mutant CTRP5. This will be further examined by comparing the binding ability of AdipoR1 to tagged p.Ser163Arg CTRP5 and WT CTRP5.
Conclusions :
Compromised AdipoR1 and CTRP5 binding in L-ORD iRPE provides a mechanism for disease pathogenesis. Most notably, the presence of mutant CTRP5 could lead to chronically activated AdipoR1 resulting in sustained AMPK activation and RPE metabolic dysfunction. This data allows potential therapeutic opportunities directly through AdipoR1 and AMPK activity modulation thus circumventing the dominant behavior of the CTRP5 mutation in L-ORD patients.
This is a 2021 ARVO Annual Meeting abstract.