Abstract
Purpose:
The molecular principles for DHA uptake/retention in retinal pigment epithelial (RPE) cells and PRC are not understood. Here we demonstrate that the seven trans-membrane domain AdipoR1 protein, which displays an extracellular C terminal and thus is not a G protein nor does it signal as a G protein, regulates the DHA lipidome, and its ablation in mice triggers PRC degeneration.
Methods:
Two independent lines of AdipoR1 KO mice were developed by gene trapping and homologous recombination that leads to PRC degeneration. The role of AdipoR1 in PRC biology was explored by ERG, optical coherence tomography (OCT), histology, biochemistry, and LC-MS/MS-based lipidomics.
Results:
In situ hybridization shows AdipoR1 in PRC/RPE, whereas no specific signal was in mice lacking AdipoR1. This KO showed: a) progressive PRC degeneration (3-33 weeks of age by OCT and histology), attenuated ERGs, prolonged dark recovery and impaired retinol visual cycle; b) flecked retina resembling human fundus albipunctatis with intact vasculature (12-16 week-old); c) anti-F4/80-positive cells (activated macrophages) beneath the RPE, UV autofluorescence in RPE and macrophages, and undigested outer segment debris in RPE (by EM); d) TUNEL-positive cells in outer nuclear layer; e) specific reduction of retinal DHA, since arachidonic acid (esterified and free) and systemic DHA were unchanged; f) decreased DHA uptake in eye cups/RPE incubated with deuterium labeled-DHA; g) overexpression or silencing of AdipoR1 in human RPE cells leading to enhanced or decreased DHA uptake, respectively; and h) absence of PRC-specific very long chain polyunsatured fatty acids (VLC-PUFAs) along with unchanged ELOVL4 abundance.
Conclusions:
AdipoR1 is a novel molecular switch, independent of its cognate ligand adiponectin, that selectively controls the DHA lipidome in RPE cells and PRC. Moreover, this switch modulates DHA retention and conservation, and is required for PRC-specific elongation to VLC-PUFAs. Since the PRC DHA lipidome comprises endogenous cell survival responses, mimicking them to counteract early stages of retinal degenerative diseases will lead to a therapeutic paradigm shift.