Ligand modulation of KCNQ-encoded (KV7) potassium channels in the heart and nervous system

Improved classification and pathogenicity assessment by comprehensive functional studies in a large data set of KCNQ2 variants

AIMS

The paucity of functional annotations on hundreds of KCNQ2 variants impedes the diagnosis and treatment of KCNQ2-related disorders. The aims of this work were to determine the functional properties of 331 clinical KCNQ2 variants, interpreted the pathogenicity of 331 variants using functional data，and explored the association between homomeric channel functions and phenotypes.

MAIN METHODS

We collected 145 KCNQ2 variants from 232 epilepsy patients and 186 KCNQ2 missense variants from the ClinVar database. Whole-cell patch-clamp recording was used to classify the function of 331 variants. Subsequently, we proposed 24 criteria for the pathogenicity interpretation of KCNQ2 variants and used them to assess pathogenicity of 331 variants. Finally, we analyzed the clinical phenotypes of patients carrying these variants, and explored the correlations between functional mechanisms and phenotypes.

KEY FINDINGS

In the homozygous state, 287 were classified as loss-of-function and 14 as gain-of-function. In the more clinically relative heterozygous state, 200 variants exhibited functional impairment, 121 of which showed dominant-negative effects on wild-type KCNQ2 subunits. After introducing functional data as strong-level evidence to interpret pathogenicity, over half of variants (169/331) were reclassified and 254 were classified as pathogenic/likely pathogenic. Moreover, dominant-negative effect and haploinsufficiency were identified as primary mechanisms in DEE/ID and SeLNE, respectively. The degree of impairment of channel function correlated with the phenotype severity.

SIGNIFICANCE

Our study reveals the possible cause of KCNQ2-related disorders at the molecular level, provides compelling evidence for clinical classification of KCNQ2 variants, and expands the knowledge of correlations between functional mechanisms and phenotypes.

Coronary and carotid artery dysfunction and KV7 overexpression in a mouse model of Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is an extremely rare genetic disease caused by expression of progerin, a lamin A variant that is also expressed at low levels in non-HGPS individuals. Although HGPS patients die predominantly from myocardial infarction and stroke, the mechanisms that provoke pathological alterations in the coronary and cerebral arteries in HGPS remain ill defined. Here, we assessed vascular function in the coronary arteries (CorAs) and carotid arteries (CarAs) of progerin-expressing LmnaG609G/G609G mice (G609G), both in resting conditions and after hypoxic stimulus. Wire myography, pharmacological screening, and gene expression studies demonstrated vascular atony and stenosis, as well as other functional alterations in progeroid CorAs and CarAs and aorta. These defects were associated with loss of vascular smooth muscle cells and overexpression of the KV7 family of voltage-dependent potassium channels. Compared with wild-type controls, G609G mice showed reduced median survival upon chronic isoproterenol exposure, a baseline state of chronic cardiac hypoxia characterized by overexpression of hypoxia-inducible factor 1α and 3α genes, and increased cardiac vascularization. Our results shed light on the mechanisms underlying progerin-induced coronary and carotid artery disease and identify KV7 channels as a candidate target for the treatment of HGPS.

Genetic Background of Epilepsy and Antiepileptic Treatments

Advanced identification of the gene mutations causing epilepsy syndromes is expected to translate into faster diagnosis and more effective treatment of these conditions. Over the last 5 years, approximately 40 clinical trials on the treatment of genetic epilepsies have been conducted. As a result, some medications that are not regular antiseizure drugs (e.g., soticlestat, fenfluramine, or ganaxolone) have been introduced to the treatment of drug-resistant seizures in Dravet, Lennox-Gastaut, maternally inherited chromosome 15q11.2-q13.1 duplication (Dup 15q) syndromes, and protocadherin 19 (PCDH 19)-clusterig epilepsy. And although the effects of soticlestat, fenfluramine, and ganaxolone are described as promising, they do not significantly affect the course of the mentioned epilepsy syndromes. Importantly, each of these syndromes is related to mutations in several genes. On the other hand, several mutations can occur within one gene, and different gene variants may be manifested in different disease phenotypes. This complex pattern of inheritance contributes to rather poor genotype-phenotype correlations. Hence, the detection of a specific mutation is not synonymous with a precise diagnosis of a specific syndrome. Bearing in mind that seizures develop as a consequence of the predominance of excitatory over inhibitory processes, it seems reasonable that mutations in genes encoding sodium and potassium channels, as well as glutamatergic and gamma-aminobutyric (GABA) receptors, play a role in the pathogenesis of epilepsy. In some cases, different pathogenic variants of the same gene can result in opposite functional effects, determining the effectiveness of therapy with certain medications. For instance, seizures related to gain-of-function (GoF) mutations in genes encoding sodium channels can be successfully treated with sodium channel blockers. On the contrary, the same drugs may aggravate seizures related to loss-of-function (LoF) variants of the same genes. Hence, knowledge of gene mutation-treatment response relationships facilitates more favorable selection of drugs for anticonvulsant therapy.

Emerging mechanisms involving brain Kv7 channel in the pathogenesis of hypertension

Hypertension is a prevalent health problem inducing many organ damages. The pathogenesis of hypertension involves a complex integration of different organ systems including the brain. The elevated sympathetic nerve activity is closely related to the etiology of hypertension. Ion channels are critical regulators of neuronal excitability. Several mechanisms have been proposed to contribute to hypothalamic-driven elevated sympathetic activity, including altered ion channel function. Recent findings indicate one of the voltage-gated potassium channels, Kv7 channels (M channels), plays a vital role in regulating cardiovascular-related neurons activity, and the expression of Kv7 channels is downregulated in hypertension. This review highlights recent findings that the Kv7 channels in the brain, blood vessels, and kidneys are emerging targets involved in the pathogenesis of hypertension, suggesting new therapeutic targets for treating drug-resistant, neurogenic hypertension.

Signaling pathways involved in NMDA-induced suppression of M-channels in corticotropin-releasing hormone neurons in central amygdala

Glutamate N-methyl-D-aspartate (NMDA) receptors (NMDARs) and Kv7/M channels are importantly involved in regulating neuronal activity involved in various physiological and pathological functions. Corticotropin-releasing hormone (CRH)-expressing neurons in the central nucleus of the amygdala (CeA) critically mediate autonomic response during stress. However, the interaction between NMDA receptors and Kv7/M channels in the CRH^CeA neurons remains unclear. In this study, we identified rat CRH^CeA neurons through the expression of an AAV viral vector-mediated enhanced green fluorescent protein (eGFP) driven by the rat CRH promoter. M-currents carried by Kv7/M channels were recorded using the whole-cell patch-clamp approach in eGFP-tagged CRH^CeA neurons in brain slices. Acute exposure to NMDA significantly reduced M-currents recorded from the CRH^CeA neurons. NMDA-induced suppression of M-currents was eliminated by chelating intracellular Ca²⁺ , supplying phosphatidylinositol 4,5-bisphosphate (PIP2) intracellularly, or blocking phosphoinositide3-kinase (PI3K). In contrast, inhibiting protein kinase C (PKC) or calmodulin did not alter NMDA-induced suppression of M-currents. Sustained exposure of NMDA decreased Kv7.3 membrane protein levels and suppressed M-currents, while the Kv7.2 expression levels remained unaltered. Pre-treatment of brain slices with PKC inhibitors alleviated the decreases in Kv7.3 and reduction of M-currents in CRH^CeA neurons induced by NMDA. PKC inhibitors did not alter Kv7.2 and Kv7.3 membrane protein levels and M-currents in CRH^CeA neurons. These data suggest that transient activation of NMDARs suppresses M-currents through the Ca²⁺ -dependent PI3K-PIP2 signaling pathway. In contrast, sustained activation of NMDARs reduces Kv7.3 protein expression and suppresses M-currents through a PKC-dependent pathway.

Behavior of KCNQ Channels in Neural Plasticity and Motor Disorders

The broad distribution of voltage-gated potassium channels (VGKCs) in the human body makes them a critical component for the study of physiological and pathological function. Within the KCNQ family of VGKCs, these aqueous conduits serve an array of critical roles in homeostasis, especially in neural tissue. Moreover, the greater emphasis on genomic identification in the past century has led to a growth in literature on the role of the ion channels in pathological disease as well. Despite this, there is a need to consolidate the updated findings regarding both the pharmacotherapeutic and pathological roles of KCNQ channels, especially regarding neural plasticity and motor disorders which have the largest body of literature on this channel. Specifically, KCNQ channels serve a remarkable role in modulating the synaptic efficiency required to create appropriate plasticity in the brain. This role can serve as a foundation for clinical approaches to chronic pain. Additionally, KCNQ channels in motor disorders have been utilized as a direction for contemporary pharmacotherapeutic developments due to the muscarinic properties of this channel. The aim of this study is to provide a contemporary review of the behavior of these channels in neural plasticity and motor disorders. Upon review, the behavior of these channels is largely dependent on the physiological role that KCNQ modulatory factors (i.e., pharmacotherapeutic options) serve in pathological diseases.