Résumé
Objective: Choroideremia (CHM) is an inherited retinal disease characterized by a primarydegeneration of the retinal pigment epithelium (RPE). It is caused by a deficiency in Rab Escort Protein 1 (REP1), which is involved in the prenylation of Rab proteins. The aim of this work was to identify the pathophysiological changes, at the level of melanogenesis and the cytoskeleton, in the RPE derived from human-induced pluripotent stem cells (hiPSCs) of choroideremia patients. Methods: Studies were performed in parallel on iPSC-derived RPE from control and two CHM individuals. RNA sequencing was performed to identify genes deregulated at the level melanogenesis and the cytoskeleton. Transmission electron microscopy was used to evaluate melanogenesis, and atomic force microscopy (AFM) was used to evaluate the cytoskeleton. Results were validated via western blot and immunofluorescence studies. Results: Gene deregulation was detected at the level of melanogenesis and the cytoskeleton. There was no change in the overall number of melanosomes between control and CHM RPE, but in CHM RPE, there were significantly more premature (stage I) melanosomes. This was consistent with a downregulation of tyrosine (TYR), which is directly involved in melanogenesis. Moreover, melanosomes are transported through the cytoskeleton (microtubules). We detected alterations in the cytoskeleton, which were confirmed by significant differences in the cell area between control and CHM cells. In addition, this correlated with the high rigidity of the RPE detected by atomic force microscopy in CHM cells compared to controls. Conclusions: Melanogenesis is affected in the RPE of CHM patients and this is likely due to defects in the cytoskeleton along which the melanosomes are transported.