# Mechanistic Characterization of Calcium-Activated Chloride Channels in Retinal  Pigment Epithelium

> **NIH NIH R01** · COLUMBIA UNIVERSITY HEALTH SCIENCES · 2020 · $53,670

## Abstract

Project Summary
 Ca2+-activated Cl- channels (CaCCs) open in response to increases of intracellular Ca2+ and
selectively conduct Cl- and other anions. To date, two families of CaCCs, namely BESTROPHINs
and TMEM16s, have been identified, among which three members- BESTROPHIN1 (BEST1),
TMEM16A and TMEM16B have been proposed to function in human retinal pigment epithelium
(RPE). BEST1 is predominantly expressed in RPE and genetically linked to a spectrum of retinal
degenerative disorders. However, Best1 knockout mice did not display any retinal phenotype or
Cl- current abnormality, arguing against the idea that BEST1 is an essential CaCC in RPE.
Although human and mice may have fundamental differences on the genetic requirement of
CaCCs in their RPEs, no direct evidence has been documented to support this hypothesis.
TMEM16A and TMEM16B, on the other hand, are widely expressed in a variety of cell types
including RPE. Their CaCC roles in RPE were suggested by studies in animal models and cell
lines, but have not yet been examined in human RPE. Therefore, the physiological contributions
of the three candidate CaCCs in human RPE still remain a mystery. This deficit is mainly due to
the technical challenges: 1) the accessibility to native human RPE cells is very limited, and it is
hard to perform gene manipulation with them; 2) currently available Cl- channel inhibitors cannot
effectively distinguish BEST1, TMEM16A and TMEM16B. In this proposal, we aim to use
multidisciplinary approaches, including CRISPR/Cas9-mediated genome editing, stem cell
technology, whole-cell patch clamp and X-ray crystallography, to define the functional CaCC(s)
in human RPE (in Aim 1), and to conduct an unprecedented mechanistic investigation on the
CaCC activity and physiological role of BEST1 (in Aims 2 and 3). Our proposed work will reveal
basic principles of CaCC function and regulation in human RPE, thereby making significant
contributions to multiple fields of research including calcium signaling, ion transport, membrane
protein structure and retinal physiology. Moreover, the pipelines established in this work can be
generally applied to study ion channels and/or genes of interest in other human organs.

## Key facts

- **NIH application ID:** 10133241
- **Project number:** 3R01GM127652-04S1
- **Recipient organization:** COLUMBIA UNIVERSITY HEALTH SCIENCES
- **Principal Investigator:** Tingting Yang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $53,670
- **Award type:** 3
- **Project period:** 2018-05-01 → 2023-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10133241

## Citation

> US National Institutes of Health, RePORTER application 10133241, Mechanistic Characterization of Calcium-Activated Chloride Channels in Retinal  Pigment Epithelium (3R01GM127652-04S1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10133241. Licensed CC0.

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