TASK-3 knockout mice exhibit exaggerated nocturnal activity, impairments in cognitive functions, and reduced sensitivity to inhalation anesthetics

The "TASK" of Breathing: Anesthetic Relevance of Background Two-Pore Domain Potassium Channels as Therapeutic Targets for Respiratory Control

Background (leak) potassium (K+) currents, the main contributors to resting membrane potential in excitable cells, are mediated by channels of the 2-pore domain (K2P) family. In the respiratory system, the TWIK-related acid-sensitive K+ channel (TASK) subfamily is proposed to mediate key functions in the carotid body type I glomus cells, central chemoreceptors and respiratory center, pulmonary arteries, and upper airway musculature. K2P channels are also located throughout the central nervous system, notably in the hypoglossal motor neurone pool, regions involved in sleep-wake regulation and pain perception. Being sensitive to general anesthetics, K2P channels may mediate both the adverse respiratory effects and hypnotic actions of many anesthetics. Therefore, they offer potential as pharmacological targets to reverse postoperative respiratory depression, ameliorate anesthetic risks of obstructive sleep apnea, improve ventilation-perfusion matching, and even assist in the active recovery from hypnotic effects of anesthesia during emergence from surgery.

Intravenous anesthetics have differential effects on human potassium channels

General anesthetics are widely used in the clinic and greatly promote the development of surgery. However, the incidence of cardiovascular and respiratory complications caused by general anesthetics is still high, and the underlying mechanisms remain incompletely understood. Potassium channels are widely expressed in the heart and blood vessels and participate in regulating blood pressure, heart rate, and other physiological parameters. Whether they are directly affected by intravenous general anesthetics is unclear. Here, we independently express four classes of potassium channels, TASK-1, TASK-3, Kv1.5, Kv2.1, Kir2.1, SK1 and SK3, in Xenopus oocytes. The effects of propofol, pentobarbital and ketamine on these channels are evaluated by their current change. We find that propofol and ketamine potentiate TASK-3 and SK3 current respectively, while pentobarbital and ketamine inhibit SK1 current. To identify the key residues in TASK-3, SK1 and SK3 that interact with intravenous anesthetics, we predict homology models of the three channels and perform molecular docking simulations. The results show that propofol forms a hydrogen bond with Q126 of TASK-3, ketamine forms a hydrogen bond with S290 of SK1 and S467 of SK3, while pentobarbital forms hydrogen bonds with S330 and T358 of SK1. As these potassium channels are closely related to respiratory system regulation, cardiac rhythm and vasodilation, our study provides a new perspective for further study on the mechanism of general anesthetics-induced respiratory and circulatory side effects.

The TWIK-related acid sensitive potassium 3 (TASK-3) channel contributes to the different effects of anesthetics on the growth and metastasis of ovarian cancer cells

Different anesthetics exert different effects on the long-term outcomes of various cancers. The TWIK-related acid sensitive potassium 3 (TASK-3) channel is an important target of anesthetics and is upregulated in various cancers. However, the role and underlying mechanism of TASK-3 channel in the effects of anesthetics on ovarian cancer remain unknown. Here, we tested whether the TASK-3 channel contributes to the effects of anesthetics on ovarian cancers. We found that the TASK-3 channel was overexpressed in human ovarian cancer and ovarian cancer cell lines. Clinically relevant concentrations of lidocaine, as a TASK-3 channel inhibitor, exert inhibitory effects on tumor growth and metastasis of ovarian cancer cells in vitro and in vivo, whereas the TASK-3 channel potent activator sevoflurane had protumor effects and propofol had no significant effects on tumor growth and metastasis of ovarian cancer. Knockdown of the TASK-3 channel by TASK-3 shRNA attenuated the effects of lidocaine and sevoflurane. Moreover, mitochondrial TASK-3 channel contributes to the effects of lidocaine and sevoflurane on the mitochondrial functions of ovarian cancer. Taken together, the TASK-3 channel, especially the mitochondrial TASK-3 (MitoTASK-3) channel, is a molecular substrate for the effects of lidocaine and sevoflurane on the tumor growth and metastasis of ovarian cancer.

TASK-3, two-pore potassium channels, contribute to circadian rhythms in the electrical properties of the suprachiasmatic nucleus and play a role in driving stable behavioural photic entrainment

Stable and entrainable physiological circadian rhythms are crucial for overall health and well-being. The suprachiasmatic nucleus (SCN), the primary circadian pacemaker in mammals, consists of diverse neuron types that collectively generate a circadian profile of electrical activity. However, the mechanisms underlying the regulation of endogenous neuronal excitability in the SCN remain unclear. Two-pore domain potassium channels (K2P), including TASK-3, are known to play a significant role in maintaining SCN diurnal homeostasis by inhibiting neuronal activity at night. In this study, we investigated the role of TASK-3 in SCN circadian neuronal regulation and behavioural photoentrainment using a TASK-3 global knockout mouse model. Our findings demonstrate the importance of TASK-3 in maintaining SCN hyperpolarization during the night and establishing SCN sensitivity to glutamate. Specifically, we observed that TASK-3 knockout mice lacked diurnal variation in resting membrane potential and exhibited altered glutamate sensitivity both in vivo and in vitro. Interestingly, despite these changes, the mice lacking TASK-3 were still able to maintain relatively normal circadian behaviour.

Circadian Clock and Hypoxia

The timing of life on Earth is remarkable: between individuals of the same species, a highly similar temporal pattern is observed, with shared periods of activity and inactivity each day. At the individual level, this means that over the course of a single day, a person alternates between two states. They are either upright, active, and communicative or they lie down in a state of (un)consciousness called sleep where even the characteristic of neuronal signals in the brain shows distinctive properties. The circadian clock governs both of these time stamps-activity and (apparent) inactivity-making them come and go consistently at the same approximate time each day. This behavior thus represents the meeting of two pervasive systems: the circadian clock and metabolism. In this article, we will describe what is known about how the circadian clock anticipates daily changes in oxygen usage, how circadian clock regulation may relate to normal physiology, and to hypoxia and ischemia that can result from pathologies such as myocardial infarction and stroke.

TREK-1 and TREK-2 Knockout Mice Are Not Resistant to Halothane or Isoflurane

BACKGROUND

A variety of molecular targets for volatile anesthetics have been suggested, including the anesthetic-sensitive potassium leak channel, TREK-1. Knockout of TREK-1 is reported to render mice resistant to volatile anesthetics, making TREK-1 channels compelling targets for anesthetic action. Spinal cord slices from mice, either wild type or an anesthetic- hypersensitive mutant, Ndufs4, display an isoflurane-induced outward potassium leak that correlates with their minimum alveolar concentrations and is blocked by norfluoxetine. The hypothesis was that TREK-1 channels conveyed this current and contribute to the anesthetic hypersensitivity of Ndufs4. The results led to evaluation of a second TREK channel, TREK-2, in control of anesthetic sensitivity.

METHODS

The anesthetic sensitivities of mice carrying knockout alleles of Trek-1 and Trek-2, the double knockout Trek-1;Trek-2, and Ndufs4;Trek-1 were measured. Neurons from spinal cord slices from each mutant were patch clamped to characterize isoflurane-sensitive currents. Norfluoxetine was used to identify TREK-dependent currents.

RESULTS

The mean values for minimum alveolar concentrations (± SD) between wild type and two Trek-1 knockout alleles in mice (P values, Trek-1 compared to wild type) were compared. For wild type, minimum alveolar concentration of halothane was 1.30% (0.10), and minimum alveolar concentration of isoflurane was 1.40% (0.11); for Trek-1tm1Lex, minimum alveolar concentration of halothane was 1.27% (0.11; P = 0.387), and minimum alveolar concentration of isoflurane was 1.38% (0.09; P = 0.268); and for Trek-1tm1Lzd, minimum alveolar concentration of halothane was 1.27% (0.11; P = 0.482), and minimum alveolar concentration of isoflurane was 1.41% (0.12; P = 0.188). Neither allele was resistant for loss of righting reflex. The EC50 values of Ndufs4;Trek-1tm1Lex did not differ from Ndufs4 (for Ndufs4, EC50 of halothane, 0.65% [0.05]; EC50 of isoflurane, 0.63% [0.05]; and for Ndufs4;Trek-1tm1Lex, EC50 of halothane, 0.58% [0.07; P = 0.004]; and EC50 of isoflurane, 0.61% [0.06; P = 0.442]). Loss of TREK-2 did not alter anesthetic sensitivity in a wild-type or Trek-1 genetic background. Loss of TREK-1, TREK-2, or both did not alter the isoflurane-induced currents in wild-type cells but did cause them to be norfluoxetine insensitive.

CONCLUSIONS

Loss of TREK channels did not alter anesthetic sensitivity in mice, nor did it eliminate isoflurane-induced transmembrane currents. However, the isoflurane-induced currents are norfluoxetine-resistant in Trek mutants, indicating that other channels may function in this role when TREK channels are deleted.

EDITOR’S PERSPECTIVE

Advances in the Understanding of Two-Pore Domain TASK Potassium Channels and Their Potential as Therapeutic Targets

TWIK-related acid-sensitive K⁺ (TASK) channels, including TASK-1, TASK-3, and TASK-5, are important members of the two-pore domain potassium (K_2P) channel family. TASK-5 is not functionally expressed in the recombinant system. TASK channels are very sensitive to changes in extracellular pH and are active during all membrane potential periods. They are similar to other K_2P channels in that they can create and use background-leaked potassium currents to stabilize resting membrane conductance and repolarize the action potential of excitable cells. TASK channels are expressed in both the nervous system and peripheral tissues, including excitable and non-excitable cells, and are widely engaged in pathophysiological phenomena, such as respiratory stimulation, pulmonary hypertension, arrhythmia, aldosterone secretion, cancers, anesthesia, neurological disorders, glucose homeostasis, and visual sensitivity. Therefore, they are important targets for innovative drug development. In this review, we emphasized the recent advances in our understanding of the biophysical properties, gating profiles, and biological roles of TASK channels. Given the different localization ranges and biologically relevant functions of TASK-1 and TASK-3 channels, the development of compounds that selectively target TASK-1 and TASK-3 channels is also summarized based on data reported in the literature.

Variable allelic expression of imprinted genes at the Peg13, Trappc9, Ago2 cluster in single neural cells

Genomic imprinting is an epigenetic process through which genes are expressed in a parent-of-origin specific manner resulting in mono-allelic or strongly biased expression of one allele. For some genes, imprinted expression may be tissue-specific and reliant on CTCF-influenced enhancer-promoter interactions. The Peg13 imprinting cluster is associated with neurodevelopmental disorders and comprises canonical imprinted genes, which are conserved between mouse and human, as well as brain-specific imprinted genes in mouse. The latter consist of Trappc9, Chrac1 and Ago2, which have a maternal allelic expression bias of ∼75% in brain. Findings of such allelic expression biases on the tissue level raise the question of how they are reflected in individual cells and whether there is variability and mosaicism in allelic expression between individual cells of the tissue. Here we show that Trappc9 and Ago2 are not imprinted in hippocampus-derived neural stem cells (neurospheres), while Peg13 retains its strong bias of paternal allele expression. Upon analysis of single neural stem cells and in vitro differentiated neurons, we find not uniform, but variable states of allelic expression, especially for Trappc9 and Ago2. These ranged from mono-allelic paternal to equal bi-allelic to mono-allelic maternal, including biased bi-allelic transcriptional states. Even Peg13 expression deviated from its expected paternal allele bias in a small number of cells. Although the cell populations consisted of a mosaic of cells with different allelic expression states, as a whole they reflected bulk tissue data. Furthermore, in an attempt to identify potential brain-specific regulatory elements across the Trappc9 locus, we demonstrate tissue-specific and general silencer activities, which might contribute to the regulation of its imprinted expression bias.

Gain and loss of TASK3 channel function and its regulation by novel variation cause KCNK9 imprinting syndrome

BACKGROUND

Genomics enables individualized diagnosis and treatment, but large challenges remain to functionally interpret rare variants. To date, only one causative variant has been described for KCNK9 imprinting syndrome (KIS). The genotypic and phenotypic spectrum of KIS has yet to be described and the precise mechanism of disease fully understood.

METHODS

This study discovers mechanisms underlying KCNK9 imprinting syndrome (KIS) by describing 15 novel KCNK9 alterations from 47 KIS-affected individuals. We use clinical genetics and computer-assisted facial phenotyping to describe the phenotypic spectrum of KIS. We then interrogate the functional effects of the variants in the encoded TASK3 channel using sequence-based analysis, 3D molecular mechanic and dynamic protein modeling, and in vitro electrophysiological and functional methodologies.

RESULTS

We describe the broader genetic and phenotypic variability for KIS in a cohort of individuals identifying an additional mutational hotspot at p.Arg131 and demonstrating the common features of this neurodevelopmental disorder to include motor and speech delay, intellectual disability, early feeding difficulties, muscular hypotonia, behavioral abnormalities, and dysmorphic features. The computational protein modeling and in vitro electrophysiological studies discover variability of the impact of KCNK9 variants on TASK3 channel function identifying variants causing gain and others causing loss of conductance. The most consistent functional impact of KCNK9 genetic variants, however, was altered channel regulation.

CONCLUSIONS

This study extends our understanding of KIS mechanisms demonstrating its complex etiology including gain and loss of channel function and consistent loss of channel regulation. These data are rapidly applicable to diagnostic strategies, as KIS is not identifiable from clinical features alone and thus should be molecularly diagnosed. Furthermore, our data suggests unique therapeutic strategies may be needed to address the specific functional consequences of KCNK9 variation on channel function and regulation.

Minimum Alveolar Concentration of Isoflurane in Rats Chronically Treated with the Synthetic Cannabinoid WIN 55,212-2

Simple Summary

The minimum alveolar concentration of isoflurane (inhaled anesthetic required to prevent movement in 50% of subjects exposed to a supramaximal noxious stimulus) was determined in 24 male rats chronically treated with the synthetic cannabinoid WIN 55,212-2 to evaluate the interaction of isoflurane with chronically administered cannabinoid agonist. The minimum alveolar concentration was determined in one group without treatment, in rats treated for 21 days with WIN 55,212-2, and another group 8 days after stopping treatment for 21 days with cannabinoid. We believe it is necessary to study the effects of chronic consumption of these substances on the requirements of inhalation anesthetics in patients that will be submitted to general anesthesia. The administration for 21 days of WIN 55,212-2 increases the minimum alveolar concentration of isoflurane in rats; this effect does not disappear after 8 days of discontinuing treatment with the synthetic cannabinoid.

Abstract

The minimum alveolar concentration MAC of isoflurane was measured in rats chronically treated with WIN 55,212-2. Methods: The MAC of isoflurane was determined in 24 male rats from expiratory samples at time of tail clamping under the following conditions: without treatment MAC(_ISO), in rats treated for 21 days with WIN 55,212-2 MAC(_{ISO + WIN55}), and in rats 8 days after stopping treatment with WIN 55,212-2 (MAC_{ISO + WIN55 + 8D}). Results: The MAC(_ISO) was 1.32 ± 0.06. In the MAC(_{ISO + WIN55}) group, the MAC increased to 1.69 ± 0.09 (28%, p-value ≤ (0.0001). Eight days after stopping treatment with WIN55, the MAC did not decrease significantly, 1.67 ± 0.07 (26%, p-value ≤ 0.0001). Conclusions: The administration of WIN 55,212-2 for 21 days increases the MAC of isoflurane in rats. This effect does not disappear 8 days after discontinuation of treatment with the synthetic cannabinoid.

Contribution of Neuronal and Glial Two-Pore-Domain Potassium Channels in Health and Neurological Disorders

Two-pore-domain potassium (K2P) channels are widespread in the nervous system and play a critical role in maintaining membrane potential in neurons and glia. They have been implicated in many stress-relevant neurological disorders, including pain, sleep disorder, epilepsy, ischemia, and depression. K2P channels give rise to leaky K⁺ currents, which stabilize cellular membrane potential and regulate cellular excitability. A range of natural and chemical effectors, including temperature, pressure, pH, phospholipids, and intracellular signaling molecules, substantially modulate the activity of K2P channels. In this review, we summarize the contribution of K2P channels to neuronal excitability and to potassium homeostasis in glia. We describe recently discovered functions of K2P channels in glia, such as astrocytic passive conductance and glutamate release, microglial surveillance, and myelin generation by oligodendrocytes. We also discuss the potential role of glial K2P channels in neurological disorders. In the end, we discuss current limitations in K2P channel researches and suggest directions for future studies.

Effects of general anesthetics on synaptic transmission and plasticity

General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.

Two-Pore Domain Potassium Channel in Neurological Disorders

K2P channel is the leaky potassium channel that is critical to keep up the negative resting membrane potential for legitimate electrical conductivity of the excitable tissues. Recently, many substances and medication elements are discovered that could either straightforwardly or in a roundabout way influence the 15 distinctive K⁺ ion channels including TWIK, TREK, TASK, TALK, THIK, and TRESK. Opening and shutting of these channels or any adjustment in their conduct is thought to alter the pathophysiological condition of CNS. There is no document available till now to explain in detail about the molecular mechanism of agents acting on K2P channel. Accordingly, in this review we cover the current research and mechanism of action of these channels, we have also tried to mention the detailed effect of drugs and how the channel behavior changes by focusing on recent advances regarding activation and modulation of ion channels.

Modulation of TASK-1/3 channels at the hypoglossal motoneuron pool and effects on tongue motor output and responses to excitatory inputs in vivo: implications for strategies for obstructive sleep apnea pharmacotherapy

Obstructive sleep apnea (OSA) occurs exclusively during sleep due to reduced tongue motor activity. Withdrawal of excitatory inputs to the hypoglossal motor nucleus (HMN) from wake to sleep contributes to this reduced activity. Several awake-active neurotransmitters with inputs to the HMN (e.g. serotonin [5-HT]) inhibit K+ leak mediated by TASK-1/3 channels on hypoglossal motoneurons, leading to increased neuronal activity in vitro. We hypothesize that TASK channel inhibition at the HMN will increase tongue muscle activity in vivo and modulate responses to 5-HT. We first microperfused the HMN of anesthetized rats with TASK channel inhibitors: doxapram (75 μM, n = 9), A1899 (25 μM, n = 9), ML365 (25 μM, n = 9), acidified artificial cerebrospinal fluid (ACSF, pH = 6.25, n = 9); and a TASK channel activator terbinafine (50 μM, n = 9); all with and without co-applied 5-HT (10 mM). 5-HT alone at the HMN increased tongue motor activity (202.8% ± 45.9%, p < 0.001). However, neither the TASK channel inhibitors, nor activator, at the HMN changed baseline tongue activity (p > 0.716) or responses to 5-HT (p > 0.127). Tonic tongue motor responses to 5-HT at the HMN were also not different (p > 0.05) between ChAT-Cre:TASKf/f mice (n = 8) lacking TASK-1/3 channels on cholinergic neurons versus controls (n = 10). In freely behaving rats (n = 9), microperfusion of A1899 into the HMN increased within-breath phasic tongue motor activity in wakefulness only (p = 0.005) but not sleep, with no effects on tonic activity across all sleep-wake states. Together, the findings suggest robust maintenance of tongue motor activity despite various strategies for TASK channel manipulation targeting the HMN in vivo, and thus currently do not support this target and direction for potential OSA pharmacotherapy.

High-Frequency rTMS Improves Cognitive Function by Regulating Synaptic Plasticity in Cerebral Ischemic Rats

Poststroke cognitive impairment (PSCI) is one of the most severe sequelae of stroke and lacks effective treatment. Previous studies have shown that high-frequency repetitive transcranial magnetic stimulation (rTMS) may be a promising PSCI therapeutic approach, but the underlying mechanism is unclear. To uncover the effect of rTMS on PSCI, a transient middle cerebral artery occlusion (tMCAO) model was established. Modified Neurological Severity Score (mNSS) test and Morris Water Maze (MWM) test were performed to assess the neurological and cognitive function of rats. Furthermore, to explore the underlying mechanism, differentially expressed genes (DEGs) in the hippocampus of rats in the rTMS group and tMCAO group were compared using RNA sequencing. Then, bioinformatics analysis, including gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and protein-protein interaction (PPI) network analysis, was conducted to elaborate these DEGs. Our results indicated that high-frequency rTMS could significantly improve neurological and cognitive function, according to mNSS and MWM tests. We found 85 DEGs, including 71 upregulated genes and 14 downregulated genes, between the rTMS group and tMCAO group. The major functional category was related to chemical synaptic transmission modulation and several DEGs were significantly upregulated in processes related to synaptic plasticity, such as glutamatergic synapses. Calb2, Zic1, Kcnk9, and Grin3a were notable in PPI analysis. These results demonstrate that rTMS has a beneficial effect on PSCI, and its mechanism may be related to the regulation of synaptic plasticity and functional genes such as Calb2, Zic1, Kcnk9, and Grin3a in the hippocampus.

Sevoflurane depresses neurons in the medial parabrachial nucleus by potentiating postsynaptic GABAA receptors and background potassium channels

Despite persistent clinical use for over 170 years, the neuronal mechanisms by which general anesthetics produce hypnosis remain unclear. Previous studies suggest that anesthetics exert hypnotic effects by acting on endogenous arousal circuits. Recently, it has been shown that the medial parabrachial nucleus (MPB) is a novel wake-promoting component in the dorsolateral pons. However, it is not known whether and how the MPB contributes to anesthetic-induced hypnosis. Here, we investigated the action of sevoflurane, a widely used volatile anesthetic agent that best represents the drug class of halogenated ethers, on MPB neurons in mice. Using in vivo fiber photometry, we found that the population activities of MPB neurons were inhibited during sevoflurane-induced loss of consciousness. Using in vitro whole-cell patch-clamp recordings, we revealed that sevoflurane suppressed the firing rate of MPB neurons in concentration-dependent and reversible manners. At a concentration equal to MAC of hypnosis, sevoflurane potentiated synaptic GABA_A receptors (GABA_A-Rs), and the inhibitory effect of sevoflurane on the firing rate of MPB neurons was completely abolished by picrotoxin, which is a selective GABA_A-R antagonist. At a concentration equivalent to MAC of immobility, sevoflurane directly hyperpolarized MPB neurons and induced a significant decrease in membrane input resistance by increasing a basal potassium conductance. Moreover, pharmacological blockade of GABA_A-Rs in the MPB prolongs induction and shortens emergence under sevoflurane inhalation at MAC of hypnosis. These results indicate that sevoflurane inhibits MPB neurons through postsynaptic GABA_A-Rs and background potassium channels, which contributes to sevoflurane-induced hypnosis.

Two-Pore Domain Potassium Channels as Drug Targets: Anesthesia and Beyond

Two-pore domain potassium (K2P) channels stabilize the resting membrane potential of both excitable and nonexcitable cells and, as such, are important regulators of cell activity. There are many conditions where pharmacological regulation of K2P channel activity would be of therapeutic benefit, including, but not limited to, atrial fibrillation, respiratory depression, pulmonary hypertension, neuropathic pain, migraine, depression, and some forms of cancer. Up until now, few if any selective pharmacological regulators of K2P channels have been available. However, recent publications of solved structures with small-molecule activators and inhibitors bound to TREK-1, TREK-2, and TASK-1 K2P channels have given insight into the pharmacophore requirements for compound binding to these sites. Together with the increasing availability of a number of novel, active, small-molecule compounds from K2P channel screening programs, these advances have opened up the possibility of rational activator and inhibitor design to selectively target K2P channels.

Imprinted genes in clinical exome sequencing: Review of 538 cases and exploration of mouse-human conservation in the identification of novel human disease loci

Human imprinting disorders cause a range of dysmorphic and neurocognitive phenotypes, and they may elude traditional molecular diagnosis such exome sequencing. The discovery of novel disorders related to imprinted genes has lagged behind traditional Mendelian disorders because current diagnostic technology, especially unbiased testing, has limited utility in their discovery. To identify novel imprinting disorders, we reviewed data for every human gene hypothesized to be imprinted, identified each mouse ortholog, determined its imprinting status in the mouse, and analyzed its function in humans and mice. We identified 17 human genes that are imprinted in both humans and mice, and have functional data in mice or humans to suggest that dysregulated expression would lead to an abnormal phenotype in humans. These 17 genes, along with known imprinted genes, were preferentially flagged 538 clinical exome sequencing tests. The identified genes were: DIRAS3 [1p31.3], TP73 [1p36.32], SLC22A3 [6q25.3], GRB10 [7p12.1], DDC [7p12.2], MAGI2 [7q21.11], PEG10 [7q21.3], PPP1R9A [7q21.3], CALCR [7q21.3], DLGAP2 [8p23.3], GLIS3 [9p24.2], INPP5F [10q26.11], ANO1 [11q13.3], SLC38A4 [12q13.11], GATM [15q21.1], PEG3 [19q13.43], and NLRP2 [19q13.42]. In the 538 clinical cases, eight cases (1.7%) reported variants in a causative known imprinted gene. There were 367/758 variants (48.4%) in imprinted genes that were not known to cause disease, but none of those variants met the criteria for clinical reporting. Imprinted disorders play a significant role in human disease, and additional human imprinted disorders remain to be discovered. Therefore, evolutionary conservation is a potential tool to identify novel genes involved in human imprinting disorders and to identify them in clinical testing.

Inhibition of histone deacetylation rescues phenotype in a mouse model of Birk-Barel intellectual disability syndrome

Mutations in the actively expressed, maternal allele of the imprinted KCNK9 gene cause Birk-Barel intellectual disability syndrome (BBIDS). Using a BBIDS mouse model, we identify here a partial rescue of the BBIDS-like behavioral and neuronal phenotypes mediated via residual expression from the paternal Kcnk9 (Kcnk9^pat) allele. We further demonstrate that the second-generation HDAC inhibitor CI-994 induces enhanced expression from the paternally silenced Kcnk9 allele and leads to a full rescue of the behavioral phenotype suggesting CI-994 as a promising molecule for BBIDS therapy. Thus, these findings suggest a potential approach to improve cognitive dysfunction in a mouse model of an imprinting disorder.

Birk-Barel intellectual disability is an imprinting syndrome due to maternally-only transmitted mutations of KCNK9/TASK3. Here authors are using a heterozygous deletion of the active maternal Kcnk9 allele to model the disease and show phenotypic rescue by HDAC inhibition.

Optimizing functional outcome endpoints for stroke recovery studies

Novel therapeutic intervention that aims to enhance the endogenous recovery potential of the brain during the subacute phase of stroke has produced promising results. The paradigm shift in treatment approaches presents new challenges to preclinical and clinical researchers alike, especially in the functional endpoints domain. Shortcomings of the "neuroprotection" era of stroke research are yet to be fully addressed. Proportional recovery observed in clinics, and potentially in animal models, requires a thorough reevaluation of the methods used to assess recovery. To this end, this review aims to give a detailed evaluation of functional outcome measures used in clinics and preclinical studies. Impairments observed in clinics and animal models will be discussed from a functional testing perspective. Approaches needed to bridge the gap between clinical and preclinical research, along with potential means to measure the moving target recovery, will be discussed. Concepts such as true recovery of function and compensation and methods that are suitable for distinguishing the two are examined. Often-neglected outcomes of stroke, such as emotional disturbances, are discussed to draw attention to the need for further research in this area.

A Small-Molecule Compound Selectively Activates K2P Channel TASK-3 by Acting at Two Distant Clusters of Residues

The TASK-3 channel is a member of the K2P family that is important for the maintenance of the resting membrane potential. Previous studies have demonstrated that the TASK-3 channel is involved in several physiologic and pathologic processes, including sleep/wake control, cognition, and epilepsy. However, there is still a lack of selective pharmacological tools for TASK-3, which limits further research on channel function. In this work, using a high-throughput screen, we discovered that N-(2-((4-nitro-2-(trifluoromethyl)phenyl)amino)ethyl)benzamide (NPBA) showed excellent potency and selectivity as a novel TASK-3 activator. The molecular determinants of NPBA activation were then investigated by combining chimera and mutagenesis analysis. Two distant clusters of residues located at the extracellular end of the second transmembrane domain (A105 and A108) and the intracellular end of the third transmembrane domain (E157) were found to be critical for NPBA activation. We then compared the essentials of the actions of NPBA with inhalation anesthetics that nonselectively activate TASK-3 and found that they may activate TASK-3 channels through different mechanisms. Finally, we transplanted the three residues A105, A108, and E157 into the TASK-1 channel, which resists NPBA activation, and the constructed mutant TASK-1(G105A, V108A, A157E) showed dramatically increased activation by NPBA, confirming the importance of these two distant clusters of residues. SIGNIFICANCE STATEMENT: TASK-3 channels conduct potassium and are involved in various physiological and pathological processes. However, the lack of selective modulators has hindered efforts to increase our understanding of the physiological roles of TASK-3 channels. By using a high-throughput screen, we identified NPBA as a potent and selective TASK-3 activator, and we show that NPBA is a more potent activator than terbinafine, the only reported TASK-3 selective activator to date. We also show here that NPBA has outstanding selectivity for TAS-3 channels. These characteristics make NPBA a promising pharmacological probe for research focused on defining TASK-3 channel function(s). In addition, we identified two distant clusters of residues as determinants of NPBA activation providing new molecular clues for the understanding of the gating mechanism of K2P channels.

Selective Knockdown of TASK3 Potassium Channel in Monoamine Neurons: a New Therapeutic Approach for Depression

Current pharmacological treatments for major depressive disorder (MDD) are severely compromised by both slow action and limited efficacy. RNAi strategies have been used to evoke antidepressant-like effects faster than classical drugs. Using small interfering RNA (siRNA), we herein show that TASK3 potassium channel knockdown in monoamine neurons induces antidepressant-like responses in mice. TASK3-siRNAs were conjugated to cell-specific ligands, sertraline (Ser) or reboxetine (Reb), to promote their selective accumulation in serotonin (5-HT) and norepinephrine (NE) neurons, respectively, after intranasal delivery. Following neuronal internalization of conjugated TASK3-siRNAs, reduced TASK3 mRNA and protein levels were found in the brainstem 5-HT and NE cell groups. Moreover, Ser-TASK3-siRNA induced robust antidepressant-like behaviors, enhanced the hippocampal plasticity, and potentiated the fluoxetine-induced increase on extracellular 5-HT. Similar responses, yet of lower magnitude, were detected for Reb-TASK3-siRNA. These findings provide substantial support for TASK3 as a potential target, and RNAi-based strategies as a novel therapeutic approach to treat MDD.

Regulatory Effect of General Anesthetics on Activity of Potassium Channels

General anesthesia is an unconscious state induced by anesthetics for surgery. The molecular targets and cellular mechanisms of general anesthetics in the mammalian nervous system have been investigated during past decades. In recent years, K⁺ channels have been identified as important targets of both volatile and intravenous anesthetics. This review covers achievements that have been made both on the regulatory effect of general anesthetics on the activity of K⁺ channels and their underlying mechanisms. Advances in research on the modulation of K⁺ channels by general anesthetics are summarized and categorized according to four large K⁺ channel families based on their amino-acid sequence homology. In addition, research achievements on the roles of K⁺ channels in general anesthesia in vivo, especially with regard to studies using mice with K⁺ channel knockout, are particularly emphasized.

CCR2-dependent monocytes/macrophages exacerbate acute brain injury but promote functional recovery after ischemic stroke in mice

Rationale: Peripheral blood monocytes are recruited into the ischemic brain and transform into macrophages after stroke. Nevertheless, the exact role of CCR2-dependent monocytes/macrophages in brain injury after stroke remains elusive.

Methods: We used CCR2 knockout (KO) mice and the CCR2 pharmacological inhibitor, propagermanium (PG), to address the role of CCR2-dependent monocytes/macrophages in the acute stage and neurological functional recovery after middle cerebral artery (MCA) occlusion and reperfusion.

Results: CCR2 KO resulted in smaller infarct size and lower mortality than in wild type (WT) mice, when measured 3 days after stroke. However, from 5 to 28 days after stroke, the KO mice had higher mortality and showed no obvious neurological functional recovery. In addition, WT mice treated with PG had similar stroke outcomes compared with CCR2 KO, as measured by T2 weighted MRI. Flow cytometry and real-time PCR analyses suggest that monocyte-derived macrophages (MoDMs) in the stroke brains mainly polarized to pro-inflammatory macrophages at the early stage, but gradually switched to anti-inflammatory macrophages at 7 days after stroke. In addition, adoptive transfer of anti-inflammatory macrophages into CCR2 KO mice at 4 and 6 days after stroke alleviated mortality and promoted neurological recovery.

Conclusion: CCR2-dependent monocytes/macrophages are a double-edged sword; they worsen acute brain injury, but are essential for neurological recovery by promoting anti-inflammatory macrophage polarization.

Actions of Propofol on Neurons in the Cerebral Cortex

Propofol is primarily a hypnotic, and is widely used for induction and maintenance of anesthesia, as well as for sedation in various medical procedures. The exact mechanisms of its action are not well understood, although its neural mechanisms have been explored in in vivo and in vitro experiments. Accumulating evidence indicates that one of the major targets of propofol is the cerebral cortex. The principal effect of propofol is considered to be the potentiation of GABA_A receptor-mediated inhibitory synaptic currents, but propofol has additional roles in modulating ion channels, including voltage-gated Na⁺ channels and several K⁺ channels. We focus on the pharmacological actions of propofol on cerebrocortical neurons, particularly at the cellular and synaptic levels.

Abnormal respiration under hyperoxia in TASK-1/3 potassium channel double knockout mice

Despite intensive research, the exact function of TASK potassium channels in central and peripheral chemoreception is still under debate. In this study, we investigated the respiration of unrestrained TASK-3 (TASK-3^-/-) and TASK-1/TASK-3 double knockout (TASK-1/3^-/-) adult male mice in vivo using a plethysmographic device. Ventilation parameters of TASK-3^-/- mice were normal under control condition (21% O₂) and upon hypoxia and hypercapnia they displayed the physiological increase of ventilation. TASK-1/3^-/- mice showed increased ventilation under control conditions. This increase of ventilation was caused by increased tidal volumes (V_T), a phenomenon similarly observed in TASK-1^-/- mice. Under acute hypoxia, TASK-1/3^-/- mice displayed the physiological increase of the minute volume. Interestingly, this increase was not related to an increase of the respiratory frequency (f_R), as observed in wild-type mice, but was caused by a strong increase of V_T. This particular respiratory phenotype is reminiscent of the respiratory phenotype of carotid body-denervated rodents in the compensated state. Acute hypercapnia (5% CO₂) stimulated ventilation in TASK-1/3^-/- and wild-type mice to a similar extent; however, at higher CO₂ concentrations (>5% CO₂) the stimulation of ventilation was more pronounced in TASK-1/3^-/- mice. At hyperoxia (100% O₂), TASK-1^-/-, TASK-3^-/- and wild-type mice showed the physiological small decrease of ventilation. In sharp contrast, TASK-1/3^-/- mice exhibited an abnormal increase of ventilation under hyperoxia. In summary, these measurements showed a grossly normal respiration of TASK-3^-/- mice and a respiratory phenotype of TASK-1/3^-/- mice that was characterized by a markedly enhanced tidal volume, similar to the one observed in TASK-1^-/- mice. The abnormal hyperoxia response, exclusively found in TASK-1/3^-/- double mutant mice, indicates that both TASK-1 and TASK-3 are essential for the hyperoxia-induced hypoventilation. The peculiar respiratory phenotype of TASK-1/3 knockout mice is reminiscent of the respiration of animals with long-term carotid body dysfunction. Taken together, TASK-1 and TASK-3 appear to serve specific and distinct roles in the complex processes underlying chemoreception and respiratory control.

KCNK9 imprinting syndrome-further delineation of a possible treatable disorder

Patients with KCNK9 imprinting syndrome demonstrate congenital hypotonia, variable cleft palate, normal MRIs and EEGs, delayed development, and feeding problems. Associated facial dysmorphic features include dolichocephaly with bitemporal narrowing, short philtrum, tented upper lip, palatal abnormalities, and small mandible. This disorder maps to chromosomal region 8q24, and it is caused by a specific missense mutation 770G>A in exon 2, replacing glycine at position 236 by arginine (G236R) in the maternal copy of KCNK9 within this locus. KCNK9 (also called TASK3) encodes a member of the two pore- domain potassium channel (K2P) subfamily. This gene is normally imprinted with paternal silencing, thus a mutation in the maternal copy of the gene will result in disease, whereas a mutation in the paternal copy will have no effect. Exome sequencing in four new patients with developmental delay and central hypotonia revealed de novo G236R mutations. Older members of a previously reported Arab-Israeli family have intellectual disability of variable severity, persistent feeding difficulties in infancy with dysphagia of liquids and dysphonia with a muffled voice in early adulthood, generalized hypotonia, weakness of proximal muscles, elongated face with narrow bitemporal diameter, and reduced facial movements. We describe the clinical features in four recently recognized younger patients and compare them with those found in members of the originally reported Arab-Israeli family and suggest this may be a treatable disorder. © 2016 Wiley Periodicals, Inc.

New Perspectives on Genomic Imprinting, an Essential and Multifaceted Mode of Epigenetic Control in the Developing and Adult Brain

Mammalian evolution entailed multiple innovations in gene regulation, including the emergence of genomic imprinting, an epigenetic regulation leading to the preferential expression of a gene from its maternal or paternal allele. Genomic imprinting is highly prevalent in the brain, yet, until recently, its central roles in neural processes have not been fully appreciated. Here, we provide a comprehensive survey of adult and developmental brain functions influenced by imprinted genes, from neural development and wiring to synaptic function and plasticity, energy balance, social behaviors, emotions, and cognition. We further review the widespread identification of parental biases alongside monoallelic expression in brain tissues, discuss their potential roles in dosage regulation of key neural pathways, and suggest possible mechanisms underlying the dynamic regulation of imprinting in the brain. This review should help provide a better understanding of the significance of genomic imprinting in the normal and pathological brain of mammals including humans.

TASK Channels on Basal Forebrain Cholinergic Neurons Modulate Electrocortical Signatures of Arousal by Histamine

Basal forebrain cholinergic neurons are the main source of cortical acetylcholine, and their activation by histamine elicits cortical arousal. TWIK-like acid-sensitive K(+) (TASK) channels modulate neuronal excitability and are expressed on basal forebrain cholinergic neurons, but the role of TASK channels in the histamine-basal forebrain cholinergic arousal circuit is unknown. We first expressed TASK channel subunits and histamine Type 1 receptors in HEK cells. Application of histamine in vitro inhibited the acid-sensitive K(+) current, indicating a functionally coupled signaling mechanism. We then studied the role of TASK channels in modulating electrocortical activity in vivo using freely behaving wild-type (n = 12) and ChAT-Cre:TASK(f/f) mice (n = 12), the latter lacking TASK-1/3 channels on cholinergic neurons. TASK channel deletion on cholinergic neurons significantly altered endogenous electroencephalogram oscillations in multiple frequency bands. We then identified the effect of TASK channel deletion during microperfusion of histamine into the basal forebrain. In non-rapid eye movement sleep, TASK channel deletion on cholinergic neurons significantly attenuated the histamine-induced increase in 30-50 Hz activity, consistent with TASK channels contributing to histamine action on basal forebrain cholinergic neurons. In contrast, during active wakefulness, histamine significantly increased 30-50 Hz activity in ChAT-Cre:TASK(f/f) mice but not wild-type mice, showing that the histamine response depended upon the prevailing cortical arousal state. In summary, we identify TASK channel modulation in response to histamine receptor activation in vitro, as well as a role of TASK channels on cholinergic neurons in modulating endogenous oscillations in the electroencephalogram and the electrocortical response to histamine at the basal forebrain in vivo.

SIGNIFICANCE STATEMENT

Attentive states and cognitive function are associated with the generation of γ EEG activity. Basal forebrain cholinergic neurons are important modulators of cortical arousal and γ activity, and in this study we investigated the mechanism by which these neurons are activated by the wake-active neurotransmitter histamine. We found that histamine inhibited a class of K(+) leak channels called TASK channels and that deletion of TASK channels selectively on cholinergic neurons modulated baseline EEG activity as well as histamine-induced changes in γ activity. By identifying a discrete brain circuit where TASK channels can influence γ activity, these results represent new knowledge that enhances our understanding of how subcortical arousal systems may contribute to the generation of attentive states.

HCN1 Channels Contribute to the Effects of Amnesia and Hypnosis but not Immobility of Volatile Anesthetics

BACKGROUND

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) subtype 1 (HCN1) channels have been identified as targets of ketamine to produce hypnosis. Volatile anesthetics also inhibit HCN1 channels. However, the effects of HCN1 channels on volatile anesthetics in vivo are still elusive. This study uses global and conditional HCN1 knockout mice to evaluate how HCN1 channels affect the actions of volatile anesthetics.

METHODS

Minimum alveolar concentrations (MACs) of isoflurane and sevoflurane that induced immobility (MAC of immobility) and/or hypnosis (MAC of hypnosis) were determined in wild-type mice, global HCN1 knockout (HCN1) mice, HCN1 channel gene with 2 lox-P sites flanking a region of the fourth exon of HCN1 (HCN1) mice, and forebrain-selective HCN1 knockout (HCN1: cre) mice. Immobility of mice was defined as no purposeful reactions to tail-clamping stimulus, and hypnosis was defined as loss of righting reflex. The amnestic effects of isoflurane and sevoflurane were evaluated by fear-potentiated startle in these 4 strains of mice.

RESULTS

All MAC values were expressed as mean ± SEM. For MAC of immobility of isoflurane, no significant difference was found among wild-type, HCN1, HCN1, and HCN1: cre mice (all ~1.24%-1.29% isoflurane). For both HCN1 and HCN1: cre mice, the MAC of hypnosis for isoflurane (each ~1.05% isoflurane) was significantly increased over their nonknockout controls: HCN1 versus wild-type (0.86% ± 0.03%, P < 0.001) and HCN1: cre versus HCN1 mice (0.84% ± 0.03%, P < 0.001); no significant difference was found between HCN1 and HCN1: cre mice. For MAC of immobility of sevoflurane, no significant difference was found among wild-type, HCN1, HCN1, and HCN1: cre mice (all ~2.6%-2.7% sevoflurane). For both HCN1 and HCN1: cre mice, the MAC of hypnosis for sevoflurane (each ~1.90% sevoflurane) was significantly increased over their nonknockout controls: HCN1 versus wild-type (1.58% ± 0.05%, P < 0.001) and HCN1: cre versus HCN1 mice (1.56% ± 0.05%, P < 0.001). No significant difference was found between HCN1 and HCN1: cre mice. By fear-potentiated startle experiments, amnestic effects of isoflurane and sevoflurane were significantly attenuated in HCN1 and HCN1: cre mice (both P < 0.002 versus wild-type or HCN1 mice). No significant difference was found between HCN1 and HCN1: cre mice.

CONCLUSIONS

Forebrain HCN1 channels contribute to hypnotic and amnestic effects of volatile anesthetics, but HCN1 channels are not involved in the immobilizing actions of volatile anesthetics.

Acute rhabdomyolysis and inflammation

Rhabdomyolysis results from the rapid breakdown of skeletal muscle fibers, which leads to leakage of potentially toxic cellular content into the systemic circulation. Acquired causes by direct injury to the sarcolemma are most frequent. The inherited causes are: i) metabolic with failure of energy production, including mitochondrial fatty acid ß-oxidation defects, LPIN1 mutations, inborn errors of glycogenolysis and glycolysis, more rarely mitochondrial respiratory chain deficiency, purine defects and peroxysomal α-methyl-acyl-CoA-racemase defect (AMACR), ii) structural causes with muscle dystrophies and myopathies, iii) calcium pump disorder with RYR1 gene mutations, iv) inflammatory causes with myositis. Irrespective of the cause of rhabdomyolysis, the pathology follows a common pathway, either by the direct injury to sarcolemma by increased intracellular calcium concentration (acquired causes) or by the failure of energy production (inherited causes), which leads to fiber necrosis. Rhabdomyolysis are frequently precipitated by febrile illness or exercise. These conditions are associated with two events, elevated temperature and high circulating levels of pro-inflammatory mediators such as cytokines and chemokines. To illustrate these points in the context of energy metabolism, protein thermolability and the potential benefits of arginine therapy, we focus on a rare cause of rhabdomyolysis, aldolase A deficiency. In addition, our studies on lipin-1 (LPIN1) deficiency raise the possibility that several diseases involved in rhabdomyolysis implicate pro-inflammatory cytokines and may even represent primarily pro-inflammatory diseases. Thus, not only thermolability of mutant proteins critical for muscle function, but also pro-inflammatory cytokines per se, may lead to metabolic decompensation and rhabdomyolysis.

Involvement of leak K+ channels in neurological disorders

TWIK-related acid-sensitive K⁺ (TASK) channels give rise to leak K⁺ currents which influence the resting membrane potential and input resistance. The wide expression of TASK1 and TASK3 channels in the central nervous system suggests that these channels are critically involved in neurological disorders. It has become apparent in the past decade that TASK channels play critical roles for the development of various neurological disorders. In this review, I describe evidence for their roles in ischemia, epilepsy, learning/memory/cognition and apoptosis.

The family of K2P channels: salient structural and functional properties

Potassium channels participate in many biological functions, from ion homeostasis to generation and modulation of the electrical membrane potential. They are involved in a large variety of diseases. In the human genome, 15 genes code for K(+) channels with two pore domains (K2P ). These channels form dimers of pore-forming subunits that produce background conductances finely regulated by a range of natural and chemical effectors, including signalling lipids, temperature, pressure, pH, antidepressants and volatile anaesthetics. Since the cloning of TWIK1, the prototypical member of this family, a lot of work has been carried out on their structure and biology. These studies are still in progress, but data gathered so far show that K2P channels are central players in many processes, including ion homeostasis, hormone secretion, cell development and excitability. A growing number of studies underline their implication in physiopathological mechanisms, such as vascular and pulmonary hypertension, cardiac arrhythmias, nociception, neuroprotection and depression. This review gives a synthetic view of the most noticeable features of these channels.

The role of K₂p channels in anaesthesia and sleep

Tandem two-pore potassium channels (K_2Ps) have widespread expression in the central nervous system and periphery where they contribute to background membrane conductance. Some general anaesthetics promote the opening of some of these channels, enhancing potassium currents and thus producing a reduction in neuronal excitability that contributes to the transition to unconsciousness. Similarly, these channels may be recruited during the normal sleep-wake cycle as downstream effectors of wake-promoting neurotransmitters such as noradrenaline, histamine and acetylcholine. These transmitters promote K_2P channel closure and thus an increase in neuronal excitability. Our understanding of the roles of these channels in sleep and anaesthesia has been largely informed by the study of mouse K_2P knockout lines and what is currently predicted by in vitro electrophysiology and channel structure and gating.

Targeting two-pore domain K(+) channels TREK-1 and TASK-3 for the treatment of depression: a new therapeutic concept

Depression is a disease that is particularly frequent, affecting up to 20% of the population in Western countries. The origins of this pathology involve multiple genes as well as environmental and developmental factors leading to a disorder that remains difficult to treat. Several therapies for depression have been developed and these mainly target monoamine neurotransmitters. However, these treatments are not only associated with numerous adverse effects, but they are also ineffective for more than one-third of patients. Therefore, the need to develop new concepts to treat depression is crucial. Recently, studies using knockout mouse models have provided evidence for a crucial role of two members of the two-pore domain potassium channel (K2P ) family, tandem P-domain weak inward rectifying K(+) (TWIK)-related K(+) channel 1 (TREK-1) and TWIK-related acid-sensitive K(+) channel 3 (TASK-3) in the pathophysiology of depression. It is believed that TREK-1 and TASK-3 antagonists could lead to the development of new antidepressants. Herein, we describe the discovery of spadin, a natural peptide released from the maturation of the neurotensin receptor-3 (also known as sortilin), which specifically blocks the activity of the TREK-1 channel and displays particular antidepressant properties, with a rapid onset of action and the absence of adverse effects. The development of such molecules may open a new era in the field of psychiatry.

Silencing the KCNK9 potassium channel (TASK-3) gene disturbs mitochondrial function, causes mitochondrial depolarization, and induces apoptosis of human melanoma cells

TASK-3 (KCNK9 or K2P9.1) channels are thought to promote proliferation and/or survival of malignantly transformed cells, most likely by increasing their hypoxia tolerance. Based on our previous results that suggested mitochondrial expression of TASK-3 channels, we hypothesized that TASK-3 channels have roles in maintaining mitochondrial activity. In the present work we studied the effect of reduced TASK-3 expression on the mitochondrial function and survival of WM35 and A2058 melanoma cells. TASK-3 knockdown cells had depolarized mitochondrial membrane potential and contained a reduced amount of mitochondrial DNA. Compared to their scrambled shRNA-transfected counterparts, they demonstrated diminished responsiveness to the application of the mitochondrial uncoupler [(3-chlorophenyl)hydrazono]malononitrile (CCCP). These observations indicate impaired mitochondrial function. Further, TASK-3 knockdown cells presented reduced viability, decreased total DNA content, altered cell morphology, and reduced surface area. In contrast to non- and scrambled shRNA-transfected melanoma cell lines, which did not present noteworthy apoptotic activity, almost 50 % of the TASK-3 knockdown cells exhibited strong Annexin-V-specific immunofluorescence signal. Sequestration of cytochrome c from the mitochondria to the cytosol, increased caspase 3 activity, and translocation of the apoptosis-inducing factor from mitochondria to cell nuclei were also demonstrated in TASK-3 knockdown cells. Interference with TASK-3 channel expression, therefore, induces caspase-dependent and -independent apoptosis of melanoma cells, most likely via causing mitochondrial depolarization. Consequently, TASK-3 channels may be legitimate targets of future melanoma therapies.

Screening individuals with intellectual disability, autism and Tourette's syndrome for KCNK9 mutations and aberrant DNA methylation within the 8q24 imprinted cluster

The phenotype overlap between autism spectrum disorders (ASD) & intellectual disabilities (ID) is mirrored at the genetic level, with common genes being reported mutated in variety of developmental disabilities. However despite widespread genetic screening for mutations, in approximately 40-60% of childhood developmental disorders the genetic cause remains unknown. Several genome-wide linkage screens in ASD have identified a locus mapping to distal 8q. We have recently identified a novel brain-specific imprinted cluster at this location, which contains the reciprocally expressed maternal KCNK9 and paternally expressed non-coding PEG13 transcripts, the latter located within an intron of TRAPPC9. Interestingly, mutations of KCNK9 and TRAPPC9 have been reported in Birk-Barel mental retardation and non-syndromic familial forms of ID, respectively. Here, we report a genetic screen for KCNK9 coding mutations and potential epigenetic aberrations that could result in deregulated imprinting in a cohort of 120 ID, 86 ASD and 86 Tourette syndrome patients. Fifteen of the ID patients had clinical characteristics overlapping with Birk-Barel syndrome. Sequencing of the two coding exons of KCNK9 failed to identify pathologic mutations, with only one variant, rs2615374, being present with allele frequencies similar to those described in dbSNP database. DNA methylation profiling of the KCNK9 and TRAPPC9 promoters, the maternally methylated PEG13 DMR and a long-range enhancer region were normal in all patients. Our findings suggest that mutations of KCNK9 or epigenetic disturbances within the PEG13 imprinted cluster do not significantly contribute to the cause of the developmental disabilities tested in this study.

Novel approach identifies SNPs in SLC2A10 and KCNK9 with evidence for parent-of-origin effect on body mass index

The phenotypic effect of some single nucleotide polymorphisms (SNPs) depends on their parental origin. We present a novel approach to detect parent-of-origin effects (POEs) in genome-wide genotype data of unrelated individuals. The method exploits increased phenotypic variance in the heterozygous genotype group relative to the homozygous groups. We applied the method to >56,000 unrelated individuals to search for POEs influencing body mass index (BMI). Six lead SNPs were carried forward for replication in five family-based studies (of ∼4,000 trios). Two SNPs replicated: the paternal rs2471083-C allele (located near the imprinted KCNK9 gene) and the paternal rs3091869-T allele (located near the SLC2A10 gene) increased BMI equally (beta = 0.11 (SD), P<0.0027) compared to the respective maternal alleles. Real-time PCR experiments of lymphoblastoid cell lines from the CEPH families showed that expression of both genes was dependent on parental origin of the SNPs alleles (P<0.01). Our scheme opens new opportunities to exploit GWAS data of unrelated individuals to identify POEs and demonstrates that they play an important role in adult obesity.

Recovery of current through mutated TASK3 potassium channels underlying Birk Barel syndrome

TASK3 (TWIK-related acid-sensitive K(+) channel 3) potassium channels are members of the two-pore-domain potassium channel family. They are responsible for background leak potassium currents found in many cell types. TASK3 channels are genetically imprinted, and a mutation in TASK3 (G236R) is responsible for Birk Barel mental retardation dysmorphism syndrome, a maternally transmitted developmental disorder. This syndrome may arise from a neuronal migration defect during development caused by dysfunctional TASK3 channels. Through the use of whole-cell electrophysiologic recordings, we have found that, although G236R mutated TASK3 channels give rise to a functional current, this current is significantly smaller in an outward direction when compared with wild-type (WT) TASK3 channels. In contrast to WT TASK3 channels, the current is inwardly rectifying. Furthermore, the current through mutated channels is differentially sensitive to a number of regulators, such as extracellular acidification, extracellular zinc, and activation of Gαq-coupled muscarinic (M3) receptors, compared with WT TASK3 channels. The reduced outward current through mutated TASK3_G236R channels can be overcome, at least in part, by both a gain-of-function additional mutation of TASK3 channels (A237T) or by application of the nonsteroidal anti-inflammatory drug flufenamic acid (FFA; 2-{[3-(trifluoromethyl)phenyl]amino}benzoic acid). FFA produces a significantly greater enhancement of current through mutated channels than through WT TASK3 channels. We propose that pharmacologic enhancement of mutated TASK3 channel current during development may, therefore, provide a potentially useful therapeutic strategy in the treatment of Birk Barel syndrome.

Immunocytochemical localization of TASK-3 protein (K2P9.1) in the rat brain

Among all K2P channels, TASK-3 shows the most widespread expression in rat brain, regulating neuronal excitability and transmitter release. Using a recently purified and characterized polyclonal monospecific antibody against TASK-3, the entire rat brain was immunocytochemically analyzed for expression of TASK-3 protein. Besides its well-known strong expression in motoneurons and monoaminergic and cholinergic neurons, TASK-3 expression was found in most neurons throughout the brain. However, it was not detected in certain neuronal populations, and neuropil staining was restricted to few areas. Also, it was absent in adult glial cells. In hypothalamic areas, TASK-3 was particularly strongly expressed in the supraoptic and suprachiasmatic nuclei, whereas other hypothalamic nuclei showed lower protein levels. Immunostaining of hippocampal CA1 and CA3 pyramidal neurons showed strongest expression, together with clear staining of CA3 mossy fibers and marked staining also in the dentate gyrus granule cells. In neocortical areas, most neurons expressed TASK-3 with a somatodendritic localization, most obvious in layer V pyramidal neurons. In the cerebellum, TASK-3 protein was found mainly in neurons and neuropil of the granular cell layer, whereas Purkinje cells were only faintly positive. Particularly weak expression was demonstrated in the forebrain. This report provides a comprehensive overview of TASK-3 protein expression in the rat brain.

Identification of a pharmacological target for genioglossus reactivation throughout sleep

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is a significant public health problem caused by repeated episodes of upper airway closure that occur only during sleep. Attempts to treat OSA pharmacologically have been unsuccessful because there has not been identification of a target operating at cranial motor nuclei, blockade of which can reactivate pharyngeal muscle activity throughout sleep. Increasing potassium conductance is a common mechanism by which state-dependent neuromodulators reduce motoneuron excitability. Therefore, we aimed to determine if potassium channel blockade is an effective strategy to reactivate the pharyngeal musculature throughout sleep.

DESIGN PARTICIPANTS AND INTERVENTIONS

In rats chronically instrumented for recording sleep-wake states and respiratory motor activities, we locally microperfused pharmacological agents into the hypoglossal motor pool to modulate potassium channels of three major classes: inwardly rectifying, two-pore domain, and voltage-gated.

MEASUREMENTS AND RESULTS

Microperfusion of the inwardly rectifying potassium channel blocker, barium, as well as the voltage-gated potassium channel blockers, tetraethylammonium and 4-aminopyridine, increased tonic and respiratory-related genioglossus activities throughout nonrapid eye movement (non-REM) and rapid eye movement (REM) sleep to 133-300% of levels present during baseline wakefulness. In contrast, microperfusion of methanandamide (TWIK-related acid-sensitive potassium [TASK] channel blocker/cannabinoid receptor agonist) activated genioglossus in wakefulness but not in sleep.

CONCLUSIONS

These findings establish proof-of-principle that targeted blockade of certain potassium channels at the hypoglossal motor pool is an effective strategy for reversing upper airway hypotonia and causing sustained reactivation of genioglossus throughout nonrapid eye movement and rapid eye movement sleep. These findings identify an important new direction for translational approaches to the pharmacological treatment of obstructive sleep apnea.

Acid sensitive background potassium channels K2P3.1 and K2P9.1 undergo rapid dynamin-dependent endocytosis

Acid-sensitive, two-pore domain potassium channels, K(2P)3.1 and K(2P)9.1, are implicated in cardiac and nervous tissue responses to hormones, neurotransmitters and drugs. K(2P)3.1 and K(2P)9.1 leak potassium from the cell at rest and directly impact membrane potential. Hence altering channel number on the cell surface drives changes in cellular electrical properties. The rate of K(2P)3.1 and K(2P)9.1 delivery to and recovery from the plasma membrane determines both channel number at the cell surface and potassium leak from cells. This study examines the endocytosis of K(2P)3.1 and K(2P)9.1. Plasma membrane biotinylation was used to follow the fate of internalized GFP-tagged rat K(2P)3.1 and K(2P)9.1 transiently expressed in HeLa cells. Confocal fluorescence images were analyzed using Imaris software, which revealed that both channels are endocytosed by a dynamin-dependent mechanism and over the course of 60 min, move progressively toward the nucleus. Endogenous endocytosis of human K(2P)3.1 and K(2P)9.1 was examined in the lung carcinoma cell line, A549. Endogenous channels are endocytosed over a similar time-scale to the channels expressed transiently in HeLa cells. These findings both validate the use of recombinant systems and identify an endogenous model system in which K(2P)3.1 and K(2P)9.1 trafficking can be further studied.