Regulation of Cardiac Voltage-Gated Sodium Channel by Kinases: Roles of Protein Kinases A and C

Exercise-induced adaptation of neurons in the vertebrate locomotor system

Vertebrate neurons are highly dynamic cells that undergo several alterations in their functioning and physiologies in adaptation to various external stimuli. In particular, how these neurons respond to physical exercise has long been an area of active research. Studies of the vertebrate locomotor system's adaptability suggest multiple mechanisms are involved in the regulation of neuronal activity and properties during exercise. In this brief review, we highlight recent results and insights from the field with a focus on the following mechanisms: (a) alterations in neuronal excitability during acute exercise; (b) alterations in neuronal excitability after chronic exercise; (c) exercise-induced changes in neuronal membrane properties via modulation of ion channel activity; (d) exercise-enhanced dendritic plasticity; and (e) exercise-induced alterations in neuronal gene expression and protein synthesis. Our hope is to update the community with a cellular and molecular understanding of the recent mechanisms underlying the adaptability of the vertebrate locomotor system in response to both acute and chronic physical exercise.

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Protein kinase C regulates organic anion transporter 1 through phosphorylating ubiquitin ligase Nedd4-2

Background

Organic anion transporter 1 (OAT1) is a drug transporter expressed on the basolateral membrane of the proximal tubule cells in kidneys. It plays an essential role in the disposition of numerous clinical therapeutics, impacting their pharmacological and toxicological properties. The activation of protein kinase C (PKC) is shown to facilitate OAT1 internalization from cell surface to intracellular compartments and thereby reducing cell surface expression and transport activity of the transporter. The PKC-regulated OAT1 internalization occurs through ubiquitination, a process catalyzed by a E3 ubiquitin ligase, neural precursor cell expressed developmentally down-regulated 4–2 (Nedd4–2). Nedd4–2 directly interacts with OAT1 and affects ubiquitination, expression and stability of the transporter. However, whether Nedd4–2 is a direct substrate for PKC-induced phosphorylation is unknown.

Results

In this study, we investigated the role of Nedd4–2 phosphorylation in the PKC regulation of OAT1. The results showed that PKC activation enhanced the phosphorylation of Nedd4–2 and increased the OAT1 ubiquitination, which was accompanied by a decreased OAT1 cell surface expression and transport function. And the effects of PKC could be reversed by PKC-specific inhibitor staurosporine. We further discovered that the quadruple mutant (T197A/S221A/S354A/S420A) of Nedd4–2 partially blocked the effects of PKC on Nedd4–2 phosphorylation and on OAT1 transport activity.

Conclusions

Our investigation demonstrates that PKC regulates OAT1 likely through direct phosphorylation of Nedd4–2. And four phosphorylation sites (T197, S221, S354, and S420) of Nedd4–2 in combination play an important role in this regulatory process.

Protein Kinases Mediate Anti-Inflammatory Effects of Cannabidiol and Estradiol Against High Glucose in Cardiac Sodium Channels

Background: Cardiovascular anomalies are predisposing factors for diabetes-induced morbidity and mortality. Recently, we showed that high glucose induces changes in the biophysical properties of the cardiac voltage-gated sodium channel (Nav1.5) that could be strongly correlated to diabetes-induced arrhythmia. However, the mechanisms underlying hyperglycemia-induced inflammation, and how inflammation provokes cardiac arrhythmia, are not well understood. We hypothesized that inflammation could mediate the high glucose-induced biophyscial changes on Nav1.5 through protein phosphorylation by protein kinases A and C. We also hypothesized that this signaling pathway is, at least partly, involved in the cardiprotective effects of cannabidiol (CBD) and 17β-estradiol (E₂).

Methods and Results: To test these ideas, we used Chinese hamster ovarian (CHO) cells transiently co-transfected with cDNA encoding human Nav1.5 α-subunit under control, a cocktail of inflammatory mediators or 100 mM glucose conditions (for 24 h). We used electrophysiological experiments and action potential modeling. Inflammatory mediators, similar to 100 mM glucose, right shifted the voltage dependence of conductance and steady-state fast inactivation and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. We also used human iCell cardiomyocytes derived from inducible pluripotent stem cells (iPSC-CMs) as a physiologically relevant system, and they replicated the effects produced by inflammatory mediators observed in CHO cells. In addition, activators of PK-A or PK-C replicated the inflammation-induced gating changes of Nav1.5. Inhibitors of PK-A or PK-C, CBD or E₂ mitigated all the potentially deleterious effects provoked by high glucose/inflammation.

Conclusion: These findings suggest that PK-A and PK-C may mediate the anti-inflammatory effects of CBD and E₂ against high glucose-induced arrhythmia. CBD, via Nav1.5, may be a cardioprotective therapeutic approach in diabetic postmenopausal population.

KV1.5-KVβ1.3 Recycling Is PKC-Dependent

K_V1.5 channel function is modified by different regulatory subunits. K_Vβ1.3 subunits assemble with K_V1.5 channels and induce a fast and incomplete inactivation. Inhibition of PKC abolishes the K_Vβ1.3-induced fast inactivation, decreases the amplitude of the current K_V1.5–K_Vβ1.3 and modifies their pharmacology likely due to changes in the traffic of K_V1.5–K_Vβ1.3 channels in a PKC-dependent manner. In order to analyze this hypothesis, HEK293 cells were transfected with K_V1.5–K_Vβ1.3 channels, and currents were recorded by whole-cell configuration of the patch-clamp technique. The presence of K_V1.5 in the membrane was analyzed by biotinylation techniques, live cell imaging and confocal microscopy approaches. PKC inhibition resulted in a decrease of 33 ± 7% of channels in the cell surface due to reduced recycling to the plasma membrane, as was confirmed by confocal microscopy. Live cell imaging indicated that PKC inhibition almost abolished the recycling of the K_V1.5–K_Vβ1.3 channels, generating an accumulation of channels into the cytoplasm. All these results suggest that the trafficking regulation of K_V1.5–K_Vβ1.3 channels is dependent on phosphorylation by PKC and, therefore, they could represent a clinically relevant issue, mainly in those diseases that exhibit modifications in PKC activity.

MIR448 antagomir reduces arrhythmic risk after myocardial infarction by upregulating the cardiac sodium channel

Cardiac ischemia is associated with arrhythmias; however, effective therapies are currently limited. The cardiac voltage-gated sodium channel α subunit (SCN5A), encoding the Na_v1.5 current, plays a key role in the cardiac electrical conduction and arrhythmic risk. Here, we show that hypoxia reduces Na_v1.5 through effects on a miR, miR-448. miR-448 expression is increased in ischemic cardiomyopathy. miR-448 has a conserved binding site in 3′-UTR of SCN5A. miR-448 binding to this site suppressed SCN5A expression and sodium currents. Hypoxia-induced HIF-1α and NF-κB were major transcriptional regulators for MIR448. Moreover, hypoxia relieved MIR448 transcriptional suppression by RE1 silencing transcription factor. Therefore, miR-448 inhibition reduced arrhythmic risk after myocardial infarction. Here, we show that ischemia drove miR-448 expression, reduced Na_v1.5 current, and increased arrhythmic risk. Arrhythmic risk was improved by preventing Na_v1.5 downregulation, suggesting a new approach to antiarrhythmic therapy.

Ischemic induction of miR-448 negatively regulates the cardiac sodium channel Nav1.5, and inhibiting miR-448 raises Nav1.5 and reduces arrhythmic risk after myocardial infarction in mice.

JAK2 regulates Nav1.6 channel function via FGF14Y158 phosphorylation

BACKGROUND

Protein interactions between voltage-gated sodium (Nav) channels and accessory proteins play an essential role in neuronal firing and plasticity. However, a surprisingly limited number of kinases have been identified as regulators of these molecular complexes. We hypothesized that numerous as-of-yet unidentified kinases indirectly regulate the Nav channel via modulation of the intracellular fibroblast growth factor 14 (FGF14), an accessory protein with numerous unexplored phosphomotifs and required for channel function in neurons.

METHODS

Here we present results from an in-cell high-throughput screening (HTS) against the FGF14: Nav1.6 complex using >3000 diverse compounds targeting an extensive range of signaling pathways. Regulation by top kinase targets was then explored using in vitro phosphorylation, biophysics, mass-spectrometry and patch-clamp electrophysiology.

RESULTS

Compounds targeting Janus kinase 2 (JAK2) were over-represented among HTS hits. Phosphomotif scans supported by mass spectrometry revealed FGF14Y158, a site previously shown to mediate both FGF14 homodimerization and interactions with Nav1.6, as a JAK2 phosphorylation site. Following inhibition of JAK2, FGF14 homodimerization increased in a manner directly inverse to FGF14:Nav1.6 complex formation, but not in the presence of the FGF14Y158A mutant. Patch-clamp electrophysiology revealed that through Y158, JAK2 controls FGF14-dependent modulation of Nav1.6 channels. In hippocampal CA1 pyramidal neurons, the JAK2 inhibitor Fedratinib reduced firing by a mechanism that is dependent upon expression of FGF14.

CONCLUSIONS

These studies point toward a novel mechanism by which levels of JAK2 in neurons could directly influence firing and plasticity by controlling the FGF14 dimerization equilibrium, and thereby the availability of monomeric species for interaction with Nav1.6.

Regulation of organic anion transporters: Role in physiology, pathophysiology, and drug elimination

The members of the organic anion transporter (OAT) family are mainly expressed in kidney, liver, placenta, intestine, and brain. These transporters play important roles in the disposition of clinical drugs, pesticides, signaling molecules, heavy metal conjugates, components of phytomedicines, and toxins, and therefore critical for maintaining systemic homeostasis. Alterations in the expression and function of OATs contribute to the intra- and inter-individual variability of the therapeutic efficacy and the toxicity of many drugs, and to many pathophysiological conditions. Consequently, the activity of these transporters must be highly regulated to carry out their normal functions. This review will present an update on the recent advance in understanding the cellular and molecular mechanisms underlying the regulation of renal OATs, emphasizing on the post-translational modification (PTM), the crosstalk among these PTMs, and the remote sensing and signaling network of OATs. Such knowledge will provide significant insights into the roles of these transporters in health and disease.

Co-expression networks uncover regulation of splicing and transcription markers of disease

Gene co-expression networks based on gene expression data are usually used to capture biologically significant patterns, enabling the discovery of biomarkers and interpretation of regulatory relationships. However, the coordination of numerous splicing changes within and across genes can exert a substantial impact on the function of these genes. This is particularly impactful in studies of the properties of the nervous system, which can be masked in the networks that only assess the correlation between gene expression levels. A bioinformatics approach was developed to uncover the role of alternative splicing and associated transcriptional networks using RNA-seq profiles. Data from 40 samples, including control and two treatments associated with sensitivity to stimuli across two central nervous system regions that can present differential splicing, were explored. The gene expression and relative isoform levels were integrated into a transcriptome-wide matrix, and then Graphical Lasso was applied to capture the interactions between genes and isoforms. Next, functional enrichment analysis enabled the discovery of pathways dysregulated at the isoform or gene levels and the interpretation of these interactions within a central nervous region. In addition, a Bayesian biclustering strategy was used to reconstruct treatment-specific networks from gene expression profile, allowing the identification of hub molecules and visualization of highly connected modules of isoforms and genes in specific conditions. Our bioinformatics approach can offer comparable insights into the discovery of biomarkers and therapeutic targets for a wide range of diseases and conditions.

Propranolol inhibits neonatal Nav1.5 activity and invasiveness of MDA-MB-231 breast cancer cells: Effects of combination with ranolazine

The MDA-MB-231 cell line was used as a model of triple negative breast cancer to investigate the interaction of β-adrenergic receptor (β-AR) and voltage-gated sodium channel (VGSC). There was significant (86%) overlap in their expression. Short-term (acute) application of the β-AR antagonist propranolol (25 μM) led to reduction of peak current and quickening of current inactivation (the latter occurred only in 5% fetal bovine serum). Long-term (48 hr) incubation with propranolol (25 μM) resulted in several changes in VGSC characteristics: shifts in (a) current-voltage relationship and (b) steady-state inactivation, both to more negative potentials and (c) the slowing of recovery from inactivation. We then investigated the effects of propranolol and ranolazine, a blocker of VGSC activity, alone and in combination, on lateral motility and Matrigel invasion. These assays were carried out under hypoxic conditions more representative of tumor progression. Propranolol (2.5 and 25 μM) and ranolazine (5 μM), and their combination inhibited lateral motility. Also, propranolol (25 μM) and ranolazine (5 μM), and their combination inhibited invasion. However, no synergy was observed in the pharmacological combinations for both assays. Propranolol also significantly decreased total neonatal Nav1.5 protein expression, the predominant VGSC subtype expressed in these cells. We conclude (a) that β-AR and VGSC are functionally coupled in MDA-MB-231 cells; (b) that propranolol has direct blocking action on the VGSC; (c) that the action of propranolol is modulated by serum; and (d) that the antimetastatic cellular effects of propranolol and ranolazine are not additive.

Riluzole promotes neurological function recovery and inhibits damage extension in rats following spinal cord injury: a meta-analysis and systematic review

Spinal cord injury (SCI) is a devastating condition that has few treatment options. Riluzole, a sodium channel blocker used to treat amyotrophic lateral sclerosis, has been initially trialed in human SCI. We performed a systematic review to critically assess the efficacy of riluzole in locomotor recovery and damage extension in SCI rat models, and the potential for clinical translation. PubMed, Embase, Cochrane Library, and Chinese databases were searched from their inception date to March 2018. Two reviewers independently selected animal studies that evaluated neurological recovery and lesion area following riluzole treatment in SCI rat models, extracted data and assessed methodological quality. Pairwise meta-analysis, subgroup analysis, and network meta-analysis were performed to assess the effects of riluzole on SCI. Ten eligible studies were included. Two studies had high methodological quality. Overall, the Basso, Beattie, and Bresnahan scores were increased in riluzole-treated animals versus controls, and effect sizes showed a gradual increase from the 1st (five studies, n = 104, mean difference = 1.24, 95% CI = 0.11 to 2.37, p = 0.03) to 6th week after treatment (five studies, n = 120, mean difference = 2.34, 95% CI = 1.26 to 3.42, p < 0.0001). Riluzole was associated with improved outcomes in the inclined plane test and the tissue preservation area. Subgroup analyses suggested an association of locomotor recovery with riluzole dose. Network meta-analysis showed that 5 mg/kg riluzole exhibited greater protection than 2.5 and 8 mg/kg riluzole. Collectively, this review suggests that riluzole has a protective effect on SCI, with good safety and a clear mechanism of action and may be suitable for future clinical trials or applications. However, animal results should be interpreted with caution given the known limitations in animal experimental design and methodological quality.

Phosphorylation of cardiac voltage-gated sodium channel: Potential players with multiple dimensions

Cardiomyocytes are highly coordinated cells with multiple proteins organized in micro domains. Minor changes or interference in subcellular proteins can cause major disturbances in physiology. The cardiac sodium channel (Na_V1.5) is an important determinant of correct electrical activity in cardiomyocytes which are localized at intercalated discs, T‐tubules and lateral membranes in the form of a macromolecular complex with multiple interacting protein partners. The channel is tightly regulated by post‐translational modifications for smooth conduction and propagation of action potentials. Among regulatory mechanisms, phosphorylation is an enzymatic and reversible process which modulates Na_V1.5 channel function by attaching phosphate groups to serine, threonine or tyrosine residues. Phosphorylation of Na_V1.5 is implicated in both normal physiological and pathological processes and is carried out by multiple kinases. In this review, we discuss and summarize recent literature about the (a) structure of Na_V1.5 channel, (b) formation and subcellular localization of Na_V1.5 channel macromolecular complex, (c) post‐translational phosphorylation and regulation of Na_V1.5 channel, and (d) how these phosphorylation events of Na_V1.5 channel alter the biophysical properties and affect the channel during disease status. We expect, by reviewing these aspects will greatly improve our understanding of Na_V1.5 channel biology, physiology and pathology, which will also provide an insight into the mechanism of arrythmogenesis at molecular level.