Patient-specific mutations impair BESTROPHIN1's essential role in mediating Ca²⁺-dependent Cl^- currents in human RPE.

Abstract

Mutations in the human <i>BEST1</i> gene lead to retinal degenerative diseases displaying progressive vision loss and even blindness. BESTROPHIN1, encoded by <i>BEST1</i>, is predominantly expressed in retinal pigment epithelium (RPE), but its physiological role has been a mystery for the last two decades. Using a patient-specific iPSC-based disease model and interdisciplinary approaches, we comprehensively analyzed two distinct <i>BEST1</i> patient mutations, and discovered mechanistic correlations between patient clinical phenotypes, electrophysiology in their RPEs, and the structure and function of BESTROPHIN1 mutant channels. Our results revealed that the disease-causing mechanism of <i>BEST1</i> mutations is centered on the indispensable role of BESTROPHIN1 in mediating the long speculated Ca²⁺-dependent Cl^- current in RPE, and demonstrate that the pathological potential of <i>BEST1</i> mutations can be evaluated and predicted with our iPSC-based 'disease-in-a-dish' approach. Moreover, we demonstrated that patient RPE is rescuable with viral gene supplementation, providing a proof-of-concept for curing <i>BEST1</i>-associated diseases.