-
ENeuro Jun 2024Persistent activity in excitatory pyramidal cells is a putative mechanism for maintaining memory traces during working memory. We recently demonstrated persistent...
Persistent activity in excitatory pyramidal cells is a putative mechanism for maintaining memory traces during working memory. We recently demonstrated persistent interruption of firing in fast-spiking parvalbumin-expressing interneurons (PV-INs), a phenomenon which could serve as a substrate for persistent activity in pyramidal cells through disinhibition lasting hundreds of milliseconds. Here, we find that hippocampal CA1 PV-INs exhibit type 2 excitability, like striatal and neocortical PV-INs. Modelling and mathematical analysis showed that the slowly inactivating potassium current K1 contributes to type 2 excitability, enables the multiple firing regimes observed experimentally in PV-INs, and provides a mechanism for robust persistent interruption of firing. Using a fast/slow separation of times scales approach with the K1 inactivation variable as a bifurcation parameter shows that the initial inhibitory stimulus stops repetitive firing by moving the membrane potential trajectory onto a co-existing stable fixed point corresponding to a non-spiking quiescent state. As K1 inactivation decays, the trajectory follows the branch of stable fixed points until it crosses a subcritical Hopf bifurcation then spirals out into repetitive firing. In a model describing entorhinal cortical PV-INs without K1, interruption of firing could be achieved by taking advantage of the bistability inherent in type 2 excitability based on a subcritical Hopf bifurcation, but the interruption was not robust to noise. Persistent interruption of firing is therefore broadly applicable to PV-INs in different brain regions but is only made robust to noise in the presence of a slow variable, K1 inactivation. Persistent activity in neuronal networks is thought to provide a substrate for multiple forms of memory. The architecture of neuronal networks across many brain regions involves a small number of locally-projecting inhibitory neurons that control many excitatory pyramidal neurons which provide the output of the region. We propose that persistent silencing of fast-spiking parvalbumin-expressing inhibitory interneurons (PV-INs) can result in persistent activity of pyramidal neurons. We use a mathematical approach and computer simulations to show how a slowly changing state of a particular ion channel controls the long-lasting silence imposed by persistent interruption. Overall, our results provide a conceptual framework that positions the persistent interruption of PV-INs firing as a potential mechanism for persistent activity in pyramidal cells.
PubMed: 38886063
DOI: 10.1523/ENEURO.0190-24.2024 -
MedRxiv : the Preprint Server For... Jun 2024Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by a varying degree of severity that correlates with the reduction of SMN protein levels....
Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by a varying degree of severity that correlates with the reduction of SMN protein levels. Motor neuron degeneration and skeletal muscle atrophy are hallmarks of SMA, but it is unknown whether other mechanisms contribute to the spectrum of clinical phenotypes. Here, through a combination of physiological and morphological studies in mouse models and SMA patients, we identify dysfunction and loss of proprioceptive sensory synapses as key signatures of SMA pathology. We demonstrate that SMA patients exhibit impaired proprioception, and their proprioceptive sensory synapses are dysfunctional as measured by the neurophysiological test of the Hoffmann reflex (H-reflex). We further show that loss of excitatory afferent synapses and altered potassium channel expression in SMA motor neurons are conserved pathogenic events found in both severely affected patients and mouse models. Lastly, we report that improved motor function and fatigability in ambulatory SMA patients and mouse models treated with SMN-inducing drugs correlate with increased function of sensory-motor circuits that can be accurately captured by the H-reflex assay. Thus, sensory synaptic dysfunction is a clinically relevant event in SMA, and the H-reflex is a suitable assay to monitor disease progression and treatment efficacy of motor circuit pathology.
PubMed: 38883729
DOI: 10.1101/2024.06.03.24308132 -
Biochemical Pharmacology Jun 2024The voltage-dependent potassium channel Kv1.3 is a promising therapeutic target for the treatment of autoimmune and chronic inflammatory disorders. Kv1.3 blockers are...
The voltage-dependent potassium channel Kv1.3 is a promising therapeutic target for the treatment of autoimmune and chronic inflammatory disorders. Kv1.3 blockers are effective in treating multiple sclerosis (fampridine) and psoriasis (dalazatide). However, most Kv1.3 pharmacological antagonists are not specific enough, triggering potential side effects and limiting their therapeutic use. Functional Kv are oligomeric complexes in which the presence of ancillary subunits shapes their function and pharmacology. In leukocytes, Kv1.3 associates with KCNE4, which reduces the surface abundance and enhances the inactivation of the channel. This mechanism exerts profound consequences on Kv1.3-related physiological responses. Because KCNE peptides alter the pharmacology of Kv channels, we studied the effects of KCNE4 on Kv1.3 pharmacology to gain insights into pharmacological approaches. To that end, we used margatoxin, which binds the channel pore from the extracellular space, and Psora-4, which blocks the channel from the intracellular side. While KCNE4 apparently did not alter the affinity of either margatoxin or Psora-4, it slowed the inhibition kinetics of the latter in a stoichiometry-dependent manner. The results suggested changes in the Kv1.3 architecture in the presence of KCNE4. The data indicated that while the outer part of the channel mouth remains unaffected, KCNE4 disturbs the intracellular architecture of the complex. Various leukocyte types expressing different Kv1.3/KCNE4 configurations participate in the immune response. Our data provide evidence that the presence of these variable architectures, which affect both the structure of the complex and their pharmacology, should be considered when developing putative therapeutic approaches.
PubMed: 38880360
DOI: 10.1016/j.bcp.2024.116368 -
Stem Cell Research Jun 2024Lysosomes play crucial roles in regulating cell metabolism, and K channels are critical for controlling various aspects of lysosomal function. Additionally, lysosomal...
Lysosomes play crucial roles in regulating cell metabolism, and K channels are critical for controlling various aspects of lysosomal function. Additionally, lysosomal activity is essential for maintaining the quiescence of hematopoietic stem cells (HSCs) under both steady-state and stress conditions. Tmem175 is a lysosomal potassium channel protein. To further investigate the role of K channels in HSCs, our study employed knockout mice to examine the function of Tmem175. Our research findings demonstrate that the deletion of Tmem175 does not disrupt the functionality of HSCs in both stable and stressed conditions, including irradiation and intraperitoneal 5-FU injections. However, we did observe that the absence of Tmem175 impairs the long-term differentiation capacity of HSCs into myeloid differentiated subpopulation cells(In this paper, it is referred to simply as M cells)in HSC transplantation test, while promoting their differentiation into T cells. This suggests that Tmem175 plays a role in the lineage differentiation of HSCs without being essential for their self-renewal or long-term regenerative capabilities.
PubMed: 38878670
DOI: 10.1016/j.scr.2024.103469 -
The Journal of Biological Chemistry Jun 2024The voltage-gated potassium ion channel K11.1 plays a critical role in cardiac repolarization. Genetic variants that render Kv11.1 dysfunctional cause Long QT Syndrome...
The voltage-gated potassium ion channel K11.1 plays a critical role in cardiac repolarization. Genetic variants that render Kv11.1 dysfunctional cause Long QT Syndrome (LQTS), which is associated with fatal arrhythmias. Approximately 90% of LQTS-associated variants cause intracellular protein transport (trafficking) dysfunction, which pharmacological chaperones like E-4031 can rescue. Protein folding and trafficking decisions are regulated by chaperones, protein quality control factors, and trafficking machinery comprising the cellular proteostasis network. Here, we test whether trafficking dysfunction is associated with alterations in the proteostasis network of pathogenic Kv11.1 variants and whether pharmacological chaperones can normalize the proteostasis network of responsive variants. We used affinity-purification coupled with tandem mass tag-based quantitative mass spectrometry to assess protein interaction changes of wild-type (WT) K11.1 or trafficking-deficient channel variants in the presence or absence of E4031. We identified 572 core K11.1 protein interactors. Trafficking-deficient variants K11.1-G601S and K11.1-G601S-G965* had significantly increased interactions with proteins responsible for folding, trafficking, and degradation compared to WT. We confirmed previous findings that the proteasome is critical for K11.1 degradation. Our report provides the first comprehensive characterization of protein quality control mechanisms of K11.1. We find extensive interactome remodeling associated with trafficking-deficient K11.1 variants, and with pharmacological chaperone rescue of K11.1 cell surface expression. The identified protein interactions could be targeted therapeutically to improve K11.1 trafficking and treat Long QT Syndrome.
PubMed: 38876300
DOI: 10.1016/j.jbc.2024.107465 -
MBio Jun 2024Lymphocytic choriomeningitis virus (LCMV) is an enveloped and segmented negative-sense RNA virus classified within the family of the order. LCMV is associated with...
Lymphocytic choriomeningitis virus (LCMV) is an enveloped and segmented negative-sense RNA virus classified within the family of the order. LCMV is associated with fatal disease in immunocompromised populations and, as the prototypical arenavirus member, acts as a model for the many highly pathogenic members of the family, such as Junín, Lassa, and Lujo viruses, all of which are associated with devastating hemorrhagic fevers. To enter cells, the LCMV envelope fuses with late endosomal membranes, for which two established requirements are low pH and interaction between the LCMV glycoprotein (GP) spike and secondary receptor CD164. LCMV subsequently uncoats, where the RNA genome-associated nucleoprotein (NP) separates from the Z protein matrix layer, releasing the viral genome into the cytosol. To further examine LCMV endosome escape, we performed an siRNA screen which identified host cell potassium ion (K) channels as important for LCMV infection, with pharmacological inhibition confirming K channel involvement during the LCMV entry phase completely abrogating productive infection. To better understand the K-mediated block in infection, we tracked incoming virions along their entry pathway under physiological conditions, where uncoating was signified by separation of NP and Z proteins. In contrast, K channel blockade prevented uncoating, trapping virions within Rab7 and CD164-positive endosomes, identifying K as a third LCMV entry requirement. K did not increase GP-CD164 binding or alter GP-CD164-dependent fusion. Thus, we propose that K mediates uncoating by modulating NP-Z interactions within the virion interior. These results suggest K channels represent a potential anti-arenaviral target.IMPORTANCEArenaviruses can cause fatal human disease for which approved preventative or therapeutic options are not available. Here, using the prototypical LCMV, we identified K channels as critical for arenavirus infection, playing a vital role during the entry phase of the infection cycle. We showed that blocking K channel function resulted in entrapment of LCMV particles within late endosomal compartments, thus preventing productive replication. Our data suggest K is required for LCMV uncoating and genome release by modulating interactions between the viral nucleoprotein and the matrix protein layer inside the virus particle.
PubMed: 38874413
DOI: 10.1128/mbio.01684-23 -
Frontiers in Genetics 2024Long QT syndrome (LQTS) is an inherited malignant arrhythmia syndrome that poses a risk of sudden death. Variants in the Potassium Voltage-Gated Channel Subfamily H...
BACKGROUND
Long QT syndrome (LQTS) is an inherited malignant arrhythmia syndrome that poses a risk of sudden death. Variants in the Potassium Voltage-Gated Channel Subfamily H Member 2 () gene are known to cause Long QT syndrome through an autosomal dominant inheritance pattern. However, as of now, there have been no reports of any variant leading to Long QT syndrome exhibiting incomplete penetrance that is influenced by gender.
METHODS
Whole-exome sequencing (WES) was conducted on the proband to identify pathogenic variants. Subsequently, Sanger sequencing was employed to validate the identified likely pathogenic variants in all family members.
RESULTS
We analyzed a pedigree spanning three-generations afflicted by Long QT syndrome. WES revealed a novel missense variant (p.Val630Gly, c.1889 T>G) as the causative factor for the family's phenotype. Within this family, all three male carriers of the variant carriers exhibited the Long QT syndrome phenotype: one experienced sudden death during sleep, another received an implantable cardioverter defibrillator (ICD), and a younger man displayed a prolonged QTc interval without any instances of syncope or malignant arrhythmia to date. Interestingly, the middle-aged female carrier showed no Long QT Syndrome phenotype. However, her offspring, diagnosed with Turner syndrome (45, X) and also a carrier of this variant, experienced frequent syncope starting at 12 years old and was diagnosed with Long QT syndrome, leading to an ICD implantation when she was 15 years old. These observations suggest that the manifestation of Long QT syndrome associated with this KCNH2 variant exhibits incomplete penetrance influenced by gender within this family, indicating potential protective mechanisms against the syndrome in females affected by this variant.
CONCLUSION
Our investigation has led to the identification of a novel pathogenic variant responsible for Long QT syndrome within a familial context characterized by gender-selective, incomplete penetrance. This discovery highlights a unique pathogenic inheritance pattern for the gene associated with Long QT syndrome, and could potentially shed light on the distinct penetrance behaviors and patterns of the gene. This discovery broadens our exploration of the KCNH2 gene in cardiac arrhythmias, highlighting the intricate genetic dynamics behind Long QT syndrome.
PubMed: 38873110
DOI: 10.3389/fgene.2024.1409459 -
Anatolian Journal of Cardiology Jun 2024Mendelian forms of renin-angiotensin-aldosterone system (RAAS)-related hypertension, commonly referred to as monogenic hypertension, represent a rare but significant...
Mendelian forms of renin-angiotensin-aldosterone system (RAAS)-related hypertension, commonly referred to as monogenic hypertension, represent a rare but significant subset of hypertensive disorders characterized by genetic mutations that disrupt the normal physiological mechanisms of blood pressure regulation. This review focuses on elucidating the germline mutations affecting RAAS pathways that lead to distinct forms of heritable hypertension. By understanding the pathophysiological basis of conditions such as Gordon's syndrome, Liddle syndrome, congenital adrenal hyperplasia, and familial hyperaldosteronism types, this review aims to highlight the unique clinical features, diagnostic challenges, and therapeutic implications associated with these disorders. Recognizing specific clinical presentations and family histories indicative of monogenic hypertension is crucial for diagnosis, particularly as it often manifests as early-onset hypertension, abnormalities in potassium and blood pH, and occasionally, abnormal sexual development or related syndromes. Therefore, employing a targeted diagnostic approach through next-generation sequencing is essential to pinpoint the responsible genetic mutations, enabling accurate and individualized treatment plans. The critical importance of certain readily available specific channel blockers, such as thiazides or low-dose corticosteroids, in managing these disorders must be emphasized, as they play a key role in preventing serious complications, including cerebrovascular events. As advancements in genetic and molecular sciences continue to evolve, a deeper comprehension of the mechanisms underlying RAAS-related monogenic hypertension promises to revolutionize the management of this complex disorder, offering hope for more effective and individualized treatment options.
PubMed: 38872497
DOI: 10.14744/AnatolJCardiol.2024.4480 -
Biological Research Jun 2024Spreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is...
BACKGROUND
Spreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is repetitive and produces a metabolic overload that increases secondary damage. However, the mechanisms associated with the initiation and propagation of SD are unknown. Multiple lines of evidence indicate that persistent and uncontrolled opening of hemichannels could participate in the pathogenesis and progression of several neurological disorders including acute brain injuries. Here, we explored the contribution of astroglial hemichannels composed of connexin-43 (Cx43) or pannexin-1 (Panx1) to SD evoked by high-K stimulation in brain slices.
RESULTS
Focal high-K stimulation rapidly evoked a wave of SD linked to increased activity of the Cx43 and Panx1 hemichannels in the brain cortex, as measured by light transmittance and dye uptake analysis, respectively. The activation of these channels occurs mainly in astrocytes but also in neurons. More importantly, the inhibition of both the Cx43 and Panx1 hemichannels completely prevented high K-induced SD in the brain cortex. Electrophysiological recordings also revealed that Cx43 and Panx1 hemichannels critically contribute to the SD-induced decrease in synaptic transmission in the brain cortex and hippocampus.
CONCLUSIONS
Targeting Cx43 and Panx1 hemichannels could serve as a new therapeutic strategy to prevent the initiation and propagation of SD in several acute brain injuries.
Topics: Animals; Astrocytes; Connexins; Cortical Spreading Depression; Synaptic Transmission; Connexin 43; Male; Nerve Tissue Proteins; Cerebral Cortex; Neurons; Hippocampus; Rats, Sprague-Dawley; Rats; Potassium
PubMed: 38867288
DOI: 10.1186/s40659-024-00519-9 -
Proceedings of the National Academy of... Jun 2024The heart beats approximately 100,000 times per day in humans, imposing substantial energetic demands on cardiac muscle. Adenosine triphosphate (ATP) is an essential...
The heart beats approximately 100,000 times per day in humans, imposing substantial energetic demands on cardiac muscle. Adenosine triphosphate (ATP) is an essential energy source for normal function of cardiac muscle during each beat, as it powers ion transport, intracellular Ca handling, and actin-myosin cross-bridge cycling. Despite this, the impact of excitation-contraction coupling on the intracellular ATP concentration ([ATP]) in myocytes is poorly understood. Here, we conducted real-time measurements of [ATP] in ventricular myocytes using a genetically encoded ATP fluorescent reporter. Our data reveal rapid beat-to-beat variations in [ATP]. Notably, diastolic [ATP] was <1 mM, which is eightfold to 10-fold lower than previously estimated. Accordingly, ATP-sensitive K (K) channels were active at physiological [ATP]. Cells exhibited two distinct types of ATP fluctuations during an action potential: net increases (Mode 1) or decreases (Mode 2) in [ATP]. Mode 1 [ATP] increases necessitated Ca entry and release from the sarcoplasmic reticulum (SR) and were associated with increases in mitochondrial Ca. By contrast, decreases in mitochondrial Ca accompanied Mode 2 [ATP] decreases. Down-regulation of the protein mitofusin 2 reduced the magnitude of [ATP] fluctuations, indicating that SR-mitochondrial coupling plays a crucial role in the dynamic control of ATP levels. Activation of β-adrenergic receptors decreased [ATP], underscoring the energetic impact of this signaling pathway. Finally, our work suggests that cross-bridge cycling is the largest consumer of ATP in a ventricular myocyte during an action potential. These findings provide insights into the energetic demands of EC coupling and highlight the dynamic nature of ATP concentrations in cardiac muscle.
Topics: Myocytes, Cardiac; Adenosine Triphosphate; Excitation Contraction Coupling; Animals; Calcium; Heart Ventricles; Action Potentials; Sarcoplasmic Reticulum; Heart Rate; Humans; KATP Channels; Myocardial Contraction; Mice
PubMed: 38865270
DOI: 10.1073/pnas.2318535121