iPSC-derived RPE and retinal organoids from two phenotypically different Stargardt disease patients show differences in ABCA4 function

Stargardt disease is a phenotypically heterogeneous disease caused by bi-allelic mutations in the ABCA4 gene. We generated retinal pigment epithelium (RPE) cells, photoreceptor precursors (PhRPs), and retinal organoids (ROs) from two induced pluripotent stem (iPS) cell lines derived from two phenotypically different Stargardt disease patients. We observed that RPE cells from the patient with peripheral affectation showed reduced ABCA4 expression, reduced phagocytosis and digestion of photoreceptor outer segments (POSs), and accumulation of lipid byproducts. ROs from both patients show stunted segments, more rods, caspase-3 activation, and lipofuscin accumulation at week 45 of maturation. Phenotypical differences seen in Stargardt disease patients are caused by their specific ABCA4 variants, but cellular and molecular mechanisms underlying the process of photoreceptor degeneration are still poorly understood. Here, we suggest that peripheral phenotypes associated with these macular dystrophies can be linked to poor clearance of POSs by RPE cells, giving these cells a higher role in the pathogenesis of the disease.