Abstract
Loss-of-function variant in the gene encoding the KCNQ4 potassium channel causes autosomal dominant nonsyndromic hearing loss (DFNA2), and no effective pharmacotherapeutics have been developed to reverse channel activity impairment. Phosphatidylinositol 4,5-bisphosphate (PIP2), an obligatory phospholipid for maintaining KCNQ channel activity, confers differential pharmacological sensitivity of channels to KCNQ openers. Through whole-exome sequencing of DFNA2 families, we identified three novel KCNQ4 variants related to diverse auditory phenotypes in the proximal C-terminus (p.Arg331Gln), the C-terminus of the S6 segment (p.Gly319Asp), and the pore region (p.Ala271_Asp272del). Potassium currents in HEK293T cells expressing each KCNQ4 variant were recorded by patch-clamp, and functional recovery by PIP2 expression or KCNQ openers was examined. In the homomeric expression setting, the three novel KCNQ4 mutant proteins lost conductance and were unresponsive to KCNQ openers or PIP2 expression. Loss of p.Arg331Gln conductance was slightly restored by a tandem concatemer channel (WT-p.R331Q), and increased PIP2 expression further increased the concatemer current to the level of the WT channel. Strikingly, an impaired homomeric p.Gly319Asp channel exhibited hyperactivity when a concatemer (WT-p.G319D), with a negative shift in the voltage dependence of activation. Correspondingly, a KCNQ inhibitor and chelation of PIP2 effectively downregulated the hyperactive WT-p.G319D concatemer channel. Conversely, the pore-region variant (p.Ala271_Asp272del) was nonrescuable under any condition. Collectively, these novel KCNQ4 variants may constitute therapeutic targets that can be manipulated by the PIP2 level and KCNQ-regulating drugs under the physiological context of heterozygous expression. Our research contributes to the establishment of a genotype/mechanism-based therapeutic portfolio for DFNA2.
Highlights
The KCNQ4 (Kv7.4) gene, which encodes a voltage-gated potassium channel protein, can cause autosomal dominant nonsyndromic hearing loss (DFNA2) when mutated[1,2,3,4], accounting for approximately 9% of all ADNSHL cases[5]
We further investigated whether the lost channel activity of these mutant proteins, especially in a homologous setting was restored by known KCNQ channel openers, such as retigabine (Ret, 10 μM), zinc pyrithione (ZnPy, 10 μM), or a combination of them (Ret/ZnPy)
In this study, we explored the application of genotype/pathophysiology-based customized pharmacology to functionally rescue impaired KCNQ4-mediated potassium currents related to novel DFNA2 variants
Summary
The KCNQ4 (Kv7.4) gene, which encodes a voltage-gated potassium channel protein, can cause autosomal dominant nonsyndromic hearing loss (DFNA2) when mutated[1,2,3,4], accounting for approximately 9% of all ADNSHL cases[5]. Over 30 variants have been shown to cause nonsyndromic sensorineural hearing loss (NSHL)[5,6,7,8]. KCNQ4 is highly expressed in the basolateral membrane of outer hair cells (OHCs) in the cochlea and is involved in the formation of M-type potassium currents that repolarize the cells, reduce cell excitability, and regulate many physiological responses[1,9]. The majority of KCNQ4 variants responsible for DFNA2 are clustered in the S5−S6 region, surrounding the ion permeating pore region (amino acids 271 −292). In the potassium ion selectivity com Received: 21 February 2021 Revised: 13 May 2021 Accepted: 9 June 2021 Published online: 28 July 2021
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
