Résumé
Choroideremia (CHM) is an inherited retinal dystrophy (IRD) characterized by night blindness in childhood and a progressive loss of the peripheral visual field leading to legal blindness from the age of 40 years. These clinical signs are associated with the degeneration of the photoreceptors, retinal pigment epithelium (RPE) and choroid. CHM is caused by mutations in the CHM gene, which is located on the X chromosome and encodes the Rab Escort Protein 1 (REP1). REP1 is involved in the prenylation of Rab GTPases proteins, which are proteins that regulate intracellular vesicular trafficking. The absence of REP1 results in the under-prenylation of Rab proteins, and in particular Rab27a, in the retina. Rab27a is thought to modulate voltage-gated L-type calcium channels in the RPE. Thus, we wanted to investigate the functionality of these channels in human RPE from control and CHM individuals. To this end, we generated RPE from induced pluripotent stem cells (iPSCs) of patients and controls. Firstly, we showed the presence of L-type calcium channels at the basal pole of the control RPE. We also demonstrated their functionality by calcium imaging techniques following ATP stimulation. Next, using a pharmacological inhibitor, we showed their role in the phagocytosis of the outer segments of photoreceptors. Secondly, we identified for the first time the presence of a calcium signaling defect in the RPE derived from CHM patients, which is associated with deregulation of L-type calcium channels. We found that this was consistent with a deregulation of the gene expression of these channels subunits by RNAseq analysis. In conclusion, we validated our iPSC-derived RPE model as functional and highlighted a novel pathophysiological mechanism of CHM. This work underlines the potency of this model for the study of IRDs in general.