Distinct expression requirements and rescue strategies for BEST1 loss- and gain-of-function mutations

Elife. 2021 Jun 1;10:e67622. doi: 10.7554/eLife.67622.


Genetic mutation of the human BEST1 gene, which encodes a Ca2+-activated Cl- channel (BEST1) predominantly expressed in retinal pigment epithelium (RPE), causes a spectrum of retinal degenerative disorders commonly known as bestrophinopathies. Previously, we showed that BEST1 plays an indispensable role in generating Ca2+-dependent Cl- currents in human RPE cells, and the deficiency of BEST1 function in patient-derived RPE is rescuable by gene augmentation (Li et al., 2017). Here, we report that BEST1 patient-derived loss-of-function and gain-of-function mutations require different mutant to wild-type (WT) molecule ratios for phenotypic manifestation, underlying their distinct epigenetic requirements in bestrophinopathy development, and suggesting that some of the previously classified autosomal dominant mutations actually behave in a dominant-negative manner. Importantly, the strong dominant effect of BEST1 gain-of-function mutations prohibits the restoration of BEST1-dependent Cl- currents in RPE cells by gene augmentation, in contrast to the efficient rescue of loss-of-function mutations via the same approach. Moreover, we demonstrate that gain-of-function mutations are rescuable by a combination of gene augmentation with CRISPR/Cas9-mediated knockdown of endogenous BEST1 expression, providing a universal treatment strategy for all bestrophinopathy patients regardless of their mutation types.

Keywords: bestrophin-1 (BEST1); calcium-activated chloride channel (CaCC); gain-of-function; gene therapy; human; molecular biophysics; retinal diseases; retinal pigment epithelium (RPE); structural biology.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bestrophins / genetics*
  • Bestrophins / metabolism
  • CRISPR-Cas Systems
  • Chlorides / metabolism
  • Gain of Function Mutation*
  • Genetic Predisposition to Disease
  • Genetic Therapy
  • HEK293 Cells
  • Humans
  • Loss of Function Mutation*
  • Membrane Potentials
  • Phenotype
  • Retinal Degeneration / diagnosis
  • Retinal Degeneration / genetics*
  • Retinal Degeneration / metabolism
  • Retinal Degeneration / therapy
  • Retinal Pigment Epithelium / metabolism


  • BEST1 protein, human
  • Bestrophins
  • Chlorides