Novel KCNQ4 variants in different functional domains confer genotype- and mechanism-based therapeutics in patients with nonsyndromic hearing loss

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.

Behavior of KCNQ Channels in Neural Plasticity and Motor Disorders

“…This concept focuses on hippocampal formation and two principal cell types: pyramidal neurons and granular cells. Specifically, the pyramidal neurons are composed of diverse branching of dendritic neurons, which are responsible for synaptic communication with other neurons [ 49 , 50 ]. The morphological formation of these neurons within the hippocampus leads to the further subfield classification of pyramidal cells in what is known as Cornu Ammonus (CA), divided into CA1, CA2, and CA3 [ 49 , 50 ].…”

“…Specifically, the pyramidal neurons are composed of diverse branching of dendritic neurons, which are responsible for synaptic communication with other neurons [ 49 , 50 ]. The morphological formation of these neurons within the hippocampus leads to the further subfield classification of pyramidal cells in what is known as Cornu Ammonus (CA), divided into CA1, CA2, and CA3 [ 49 , 50 ]. These regions serve an important role in localizing KCNQ channel function in synaptic plasticity [ 49 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 ].…”

“…The morphological formation of these neurons within the hippocampus leads to the further subfield classification of pyramidal cells in what is known as Cornu Ammonus (CA), divided into CA1, CA2, and CA3 [ 49 , 50 ]. These regions serve an important role in localizing KCNQ channel function in synaptic plasticity [ 49 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 ]. Within synaptic plasticity, two major models involved in the application of neural plasticity are long-term potentiation (LTP) and long-term depression (LTD) [ 59 ].…”

“…It was initially found that pharmacologic KCNQ channel inhibition via linopirdine reduced spike frequency adaptation (SFA) in CA1 pyramidal neurons in vitro, but only after the initial spike [ 49 , 50 ]. Following this initial discovery, it was also found that KCNQ channel modulation also plays a role in after hyperpolarization, which ultimately supports the notion that KCNQ channels contribute to AP [ 66 ].…”

“…This plays a key role in maintaining the K + gradient for channel mechanosensation to carry K + into hair cells to stimulate auditory sensation [ 14 , 38 ]. KCNQ4 mutations are often associated with auditory hearing loss and have therefore been a key target in developing pharmacotherapeutic options for hearing loss [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. KCNQ5 is most expressed in neural tissue, including the retinal pigment epithelium [ 48 ].…”