Abstract
Best vitelliform macular dystrophy (BD), autosomal dominant vitreoretinochoroidopathy (ADVIRC), and the autosomal recessive bestrophinopathy (ARB), together known as the bestrophinopathies, are caused by mutations in the bestrophin-1 (BEST1) gene affecting anion transport through the plasma membrane of the retinal pigment epithelium (RPE). To date, while no treatment exists a better understanding of BEST1-related pathogenesis may help to define therapeutic targets. Here, we systematically characterize functional consequences of mutant BEST1 in thirteen RPE patient cell lines differentiated from human induced pluripotent stem cells (hiPSCs). Both BD and ARB hiPSC-RPEs display a strong reduction of BEST1-mediated anion transport function compared to control, while ADVIRC mutations trigger an increased anion permeability suggesting a stabilized open state condition of channel gating. Furthermore, BD and ARB hiPSC-RPEs differ by the degree of mutant protein turnover and by the site of subcellular protein quality control with adverse effects on lysosomal pH only in the BD-related cell lines. The latter finding is consistent with an altered processing of catalytic enzymes in the lysosomes. The present study provides a deeper insight into distinct molecular mechanisms of the three bestrophinopathies facilitating functional categorization of the more than 300 known BEST1 mutations that result into the distinct retinal phenotypes.
Highlights
Bestrophin-1 (BEST1) belongs to the bestrophin family of four evolutionarily related genes (BEST1–4) that encode distinct integral membrane proteins [1]
Our results demonstrate that human induced pluripotent stem cells (hiPSCs)-retinal pigment epithelium (RPE) derived from Best vitelliform macular dystrophy (BD), autosomal dominant vitreoretinochoroidopathy (ADVIRC), and autosomal recessive bestrophinopathy (ARB) patients display specific properties in BEST1 expression, localization, degradation pathway, and ion gating processes
We show that autosomal dominant BEST1 mutations in BD and ADVIRC hiPSC-RPEs escape ER-associated degradation and instead are recognized by a post-ER quality control probably at the Golgi complex (BDIN) or on the cell surface (BDPM and ADVIRC) disassembling the mutant protein complexes in the lysosome
Summary
Bestrophin-1 (BEST1) belongs to the bestrophin family of four evolutionarily related genes (BEST1–4) that encode distinct integral membrane proteins [1]. In humans, they function as calcium-activated anion channels differing in expression regulation and tissue distribution [2,3]. While a typical phenotype presentation can be assigned to each of the distinct entities, a clear genotype-phenotype correlation is limited as individuals with BEST1-associated retinal defects present with a remarkable inter- and intra-familial phenotypic variability. An abnormal Arden ratio (light peak/dark trough ratio) in the electro-oculogram (EOG) response is regarded pathognomonic for the BEST1-associated clinical manifestations [11]
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