Redox-Dependent Modulation of T-Type Ca(2+) Channels in Sensory Neurons Contributes to Acute Anti-Nociceptive Effect of Substance P

A rapid protocol for distinguishing the quality of Sanshengyin and identifying potential markers by the "three-in-one" fingerprint profiles with antioxidant activity

It is imperative to establish a standardized model for the quality control of traditional prescriptions, exemplified by Sanshengyin (SSY). This study introduces a multi-component and multi-level "three-in-one" fingerprint quality evaluation system designed to predict the comprehensive quality of traditional Chinese medicine (TCM). Initially, a five-wavelength high-performance liquid chromatography (HPLC) fusion spectrum was developed to enhance the stability of SSY within the chromatographic system. Additionally, a quantification method was employed to streamline the calculation and visualization processes of ultraviolet (UV) and infrared (IR) spectral systems. Through this approach, chromatographic and spectral fingerprints were amalgamated into a holistic analytical strategy. The average linear quantitative fingerprint method (ALQFM) was employed to swiftly differentiate the grades of 17 sample batches. Additionally, six quality markers were identified for content determination. Correlation analysis between the total content of these quality markers and macroscopic quantitative similarity was conducted to assess the accuracy of ALQFM in evaluating the quality of TCM represented by SSY. Finally, the binary correlation analysis model was employed to investigate the correlation between antioxidant activity and fingerprint profiles, facilitating the prediction of potential bioactive compounds in SSY. This research offers a straightforward, cost-effective, and holistic approach for assessing the quality consistency of TCM. The method is recommended for adoption by medical institutions and enterprises to enhance the standardization of TCM quality control.

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

Constitutive activity of the dopamine (D5 ) receptor, highly expressed in CA1 hippocampal neurons, selectively reduces CaV 3.2 and CaV 3.3 currents

BACKGROUND AND PURPOSE

Ca_V 3.1-3 currents differentially contribute to neuronal firing patterns. Ca_V 3 are regulated by G protein-coupled receptors (GPCRs) activity, but information about Ca_V 3 as targets of the constitutive activity of GPCRs is scarce. We investigate the impact of D₅ recpetor constitutive activity, a GPCR with high levels of basal activity, on Ca_V 3 functionality. D₅ recpetor and Ca_V 3 are expressed in the hippocampus and have been independently linked to pathophysiological states associated with epilepsy.

EXPERIMENTAL APPROACH

Our study models were HEK293T cells heterologously expressing D₁ or D₅ receptor and Ca_V 3.1-3, and mouse brain slices containing the hippocampus. We used chlorpromazine (D₁ /D₅ inverse agonist) and a D₅ receptor mutant lacking constitutive activity as experimental tools. We measured Ca_V 3 currents and excitability parameters using the patch-clamp technique. We completed our study with computational modelling and imaging technique.

KEY RESULTS

We found a higher sensitivity to TTA-P2 (Ca_V 3 blocker) in CA1 pyramidal neurons obtained from chlorpromazine-treated animals compared with vehicle-treated animals. We found that Ca_V 3.2 and Ca_V 3.3-but not Ca_V 3.1-are targets of D₅ receptor constitutive activity in HEK293T cells. Finally, we found an increased firing rate in CA1 pyramidal neurons from chlorpromazine-treated animals in comparison with vehicle-treated animals. Similar changes in firing rate were observed on a neuronal model with controlled Ca_V 3 currents levels.

CONCLUSIONS AND IMPLICATIONS

Native hippocampal Ca_V 3 and recombinant Ca_V 3.2-3 are sensitive to D₅ receptor constitutive activity. Manipulation of D₅ receptor constitutive activity could be a valuable strategy to control neuronal excitability, especially in exacerbated conditions such as epilepsy.

Electrophysiological and computational analysis of Cav3.2 channel variants associated with familial trigeminal neuralgia

Trigeminal neuralgia (TN) is a rare form of chronic neuropathic pain characterized by spontaneous or elicited paroxysms of electric shock-like or stabbing pain in a region of the face. While most cases occur in a sporadic manner and are accompanied by intracranial vascular compression of the trigeminal nerve root, alteration of ion channels has emerged as a potential exacerbating factor. Recently, whole exome sequencing analysis of familial TN patients identified 19 rare variants in the gene CACNA1H encoding for Ca_v3.2T-type calcium channels. An initial analysis of 4 of these variants pointed to a pathogenic role. In this study, we assessed the electrophysiological properties of 13 additional TN-associated Ca_v3.2 variants expressed in tsA-201 cells. Our data indicate that 6 out of the 13 variants analyzed display alteration of their gating properties as evidenced by a hyperpolarizing shift of their voltage dependence of activation and/or inactivation resulting in an enhanced window current supported by Ca_v3.2 channels. An additional variant enhanced the recovery from inactivation. Simulation of neuronal electrical membrane potential using a computational model of reticular thalamic neuron suggests that TN-associated Ca_v3.2 variants could enhance neuronal excitability. Altogether, the present study adds to the notion that ion channel polymorphisms could contribute to the etiology of some cases of TN and further support a role for Ca_v3.2 channels.

Potent CaV3.2 channel inhibitors exert analgesic effects in acute and chronic pain models

Pain is the most common presenting physical symptom and a primary reason for seeking medical care, which chronically affects people's mental health and social life. Ca_V3.2 channel plays an essential role in the peripheral processing maintenance of pain states. This study was designed to identify novel drug candidates targeting the Ca_V3.2 channel. Whole-cell patch-clamp, cellular thermal shift assay, FlexStation, in vivo and in vitro Ca_V3.2 knock-down, site-directed mutagenesis, and double-mutant cycle analysis were employed to explore the pain-related receptors and ligand-receptor direct interaction. We found that toddaculin efficiently inhibits the Ca_V3.2 channel and significantly reduced the excitability of dorsal root ganglion neurons and pain behaviors. The Carbonyl group of coumarins directly interacts with the pore domain of Ca_V3.2 via van der Waals (VDW) force. Docking with binding pockets further led us to identify glycycoumarin, which exhibited more potent inhibition on the Ca_V3.2 channel and better analgesic activity than the parent compound. Toddaculin and its analog showed beneficial therapeutic effects in pain models. Toddaculin binding pocket on Ca_V3.2 might be a promising docking site for the design of drugs.

A population of in silico models identifies the interplay between Nav 1.8 conductance and potassium currents as key in regulating human dorsal root ganglion neuron excitability

Background: The Nav 1.8 sodium channel has a key role in generating repetitive action potentials in nociceptive human dorsal root ganglion neurons. Nav 1.8 is differentiated from other voltage-gated sodium channels by its unusually slow inactivation kinetics and depolarised voltage-dependence of activation. These features are particularly pronounced in the human Nav 1.8 channel and allow the channel to remain active during repolarisation. Gain-of-function mutations in Nav 1.8 have been linked to neuropathic pain and selective blockers of Nav 1.8 have been developed as potential new analgesics. However, it is not well understood how modulating the Nav 1.8 conductance alters neuronal excitability and how this depends on the balance of other ion channels expressed by nociceptive neurons. Methods: To investigate this, we developed a novel computational model of the human dorsal root ganglion neuron and used it to construct a population of models that mimicked inter-neuronal heterogeneity in ionic conductances and action potential morphology Results: By simulating changes to the Nav 1.8 conductance in the population of models, we found that moderately increasing the Nav 1.8 conductance led to increased firing rate, as expected, but increasing Nav 1.8 conductance beyond an inflection point caused firing rate to decrease. We found that the delayed rectifier and M-type potassium conductances were also critical for determining neuronal excitability. In particular, altering the delayed rectifier potassium conductance shifted the position of the Nav 1.8 inflection point and therefore the relationship between Nav 1.8 conductance and firing rate. Conclusions: Our results suggest that the effects of modulating Nav 1.8 in a nociceptive neuron can depend significantly on other conductances, particularly potassium conductances.

Junctophilin-4 facilitates inflammatory signalling at plasma membrane-endoplasmic reticulum junctions in sensory neurons

KEY POINTS

Rat somatosensory neurons express a junctional protein, junctophilin-4 (JPH4) JPH4 is necessary for the formation of store operated Ca²⁺ entry (SOCE) complex at the junctions between plasma membrane and endoplasmic reticulum in these neurons. Knockdown of JPH4 impairs endoplasmic reticulum Ca²⁺ store refill and junctional Ca²⁺ signalling in sensory neurons. In vivo knockdown of JPH4 in the dorsal root ganglion (DRG) sensory neurons significantly attenuated experimentally induced inflammatory pain in rats. Junctional nanodomain Ca²⁺ signalling maintained by JPH4 is an important contributor to the inflammatory pain mechanisms.

ABSTRACT

Junctions of endoplasmic reticulum and plasma membrane (ER-PM junctions) form signalling nanodomains in eukaryotic cells. ER-PM junctions are present in peripheral sensory neurons and are important for the fidelity of G protein coupled receptor (GPCR) signalling. Yet little is known about the assembly, maintenance and physiological role of these junctions in somatosensory transduction. Using fluorescence imaging, proximity ligation, super-resolution microscopy, in vitro and in vivo gene knockdown we demonstrate that a member of the junctophilin protein family, junctophilin-4 (JPH4), is necessary for the formation of store operated Ca²⁺ entry (SOCE) complex at the ER-PM junctions in rat somatosensory neurons. Thus we show that JPH4 localises to the ER-PM junctional areas and co-clusters with SOCE proteins STIM1 and Orai1 upon ER Ca²⁺ store depletion. Knockdown of JPH4 impairs SOCE and ER Ca²⁺ store refill in sensory neurons. Furthermore, we demonstrate a key role of the JPH4 and junctional nanodomain Ca²⁺ signalling in the pain-like response induced by the inflammatory mediator bradykinin. Indeed, an in vivo knockdown of JPH4 in the dorsal root ganglion (DRG) sensory neurons significantly shortened the duration of nocifensive behaviour induced by hindpaw injection of bradykinin in rats. Since the ER supplies Ca²⁺ for the excitatory action of multiple inflammatory mediators, we suggest that junctional nanodomain Ca²⁺ signalling maintained by JPH4 is an important contributor to the inflammatory pain mechanisms.

The Role of Kv7.2 in Neurodevelopment: Insights and Gaps in Our Understanding

Kv7.2 subunits encoded by the KCNQ2 gene constitute a critical molecular component of the M-current, a subthreshold voltage-gated potassium current controlling neuronal excitability by dampening repetitive action potential firing. Pathogenic loss-of-function variants in KCNQ2 have been linked to epilepsy since 1998, and there is ample functional evidence showing that dysfunction of the channel indeed results in neuronal hyperexcitability. The recent description of individuals with severe developmental delay with or without seizures due to pathogenic variants in KCNQ2 (KCNQ2-encephalopathy) reveals that Kv7.2 channels also have an important role in neurodevelopment. Kv7.2 channels are expressed already very early in the developing brain when key developmental processes such as proliferation, differentiation, and synaptogenesis play a crucial role in brain morphogenesis and maturation. In this review, we will discuss the available evidence for a role of Kv7.2 channels in these neurodevelopmental processes, focusing in particular on insights derived from KCNQ2-related human phenotypes, from the spatio-temporal expression of Kv7.2 and other Kv7 family member, and from cellular and rodent models, highlighting critical gaps and research strategies to be implemented in the future. Lastly, we propose a model which divides the M-current activity in three different developmental stages, correlating with the cell characteristics during these particular periods in neuronal development, and how this can be linked with KCNQ2-related disorders. Understanding these mechanisms can create opportunities for new targeted therapies for KCNQ2-encephalopathy.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Delineating an extracellular redox-sensitive module in T-type Ca2+ channels

T-type (Cav3) Ca²⁺ channels are important regulators of excitability and rhythmic activity of excitable cells. Among other voltage-gated Ca²⁺ channels, Cav3 channels are uniquely sensitive to oxidation and zinc. Using recombinant protein expression in HEK293 cells, patch clamp electrophysiology, site-directed mutagenesis, and homology modeling, we report here that modulation of Cav3.2 by redox agents and zinc is mediated by a unique extracellular module containing a high-affinity metal-binding site formed by the extracellular IS1–IS2 and IS3–IS4 loops of domain I and a cluster of extracellular cysteines in the IS1–IS2 loop. Patch clamp recording of recombinant Cav3.2 currents revealed that two cysteine-modifying agents, sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES) and N-ethylmaleimide, as well as a reactive oxygen species–producing neuropeptide, substance P (SP), inhibit Cav3.2 current to similar degrees and that this inhibition is reversed by a reducing agent and a zinc chelator. Pre-application of MTSES prevented further SP-mediated current inhibition. Substitution of the zinc-binding residue His¹⁹¹ in Cav3.2 reduced the channel's sensitivity to MTSES, and introduction of the corresponding histidine into Cav3.1 sensitized it to MTSES. Removal of extracellular cysteines from the IS1–IS2 loop of Cav3.2 reduced its sensitivity to MTSES and SP. We hypothesize that oxidative modification of IS1–IS2 loop cysteines induces allosteric changes in the zinc-binding site of Cav3.2 so that it becomes sensitive to ambient zinc.

Enhanced cell selectivity of hybrid peptides with potential antimicrobial activity and immunomodulatory effect

BACKGROUND

Hybridization is a useful strategy to bond the advantages of different peptides into novel constructions. We designed a series of AMPs based on the structures of a synthetic AMP KFA3 and a naturally-occurred host defense peptide substance P (SP) to obtain peptides retaining the high antibacterial activity of KFA3 and the immunomodulatory activity and low cytotoxicity of SP.

METHODS

Two repeats of KFA and different C terminal fragments of SP were hybridized, generating a series of novel AMPs (KFSP1-8). The antibacterial activities, host cell toxicity and immunomodulation were measured. The antibacterial mechanisms were investigated.

RESULTS

Hybrid peptides KFSP1-4 exerted substantial antibacterial activities against Gram-negative bacteria of standard strains and clinical drug-resistant isolates including E.coli, A.baumannii and P.aeruginosa, while showing little toxicity towards host cells. Compared with KFA3, moderate reduction in α-helix content and the interruption in α-helix continuality were indicated in CD spectra analysis and secondary-structure simulation in these peptides. Membrane permeabilization combined with time-kill studies and FITC-labeled imaging, indicated a selective membrane interaction of KFSP1 with bacteria cell membranes. By specially activating NK1 receptor, the hybrid peptides kept the ability of SP to induce intracellular calcium release and ERK1/2 phosphorylation, but unable to stimulate NF-κB phosphorylation. KFSP1 facilitated the survival of mouse macrophage RAW264.7, directly interacting with LPS and inhibiting the LPS-induced NF-κB phosphorylation and TNF-α expression.

CONCLUSION

Hybridization is a useful strategy to bond the advantages of different peptides. KFSP1 and its analogs are worth of advanced efforts to explore their potential applications as novel antimicrobial agents.

Ion Channels Involved in Substance P-Mediated Nociception and Antinociception

Substance P (SP), an 11-amino-acid neuropeptide, has long been considered an effector of pain. However, accumulating studies have proposed a paradoxical role of SP in anti-nociception. Here, we review studies of SP-mediated nociception and anti-nociception in terms of peptide features, SP-modulated ion channels, and differential effector systems underlying neurokinin 1 receptors (NK1Rs) in differential cell types to elucidate the effect of SP and further our understanding of SP in anti-nociception. Most importantly, understanding the anti-nociceptive SP-NK1R pathway would provide new insights for analgesic drug development.

Inhibitory Gi/O-coupled receptors in somatosensory neurons: Potential therapeutic targets for novel analgesics

Primary sensory neurons in the dorsal root ganglia and trigeminal ganglia are responsible for sensing mechanical and thermal stimuli, as well as detecting tissue damage. These neurons express ion channels that respond to thermal, mechanical, or chemical cues, conduct action potentials, and mediate transmitter release. These neurons also express a large number of G-protein coupled receptors, which are major transducers for extracellular signaling molecules, and their activation usually modulates the primary transduction pathways. Receptors that couple to phospholipase C via heterotrimeric G_q/11 proteins and those that activate adenylate cyclase via G_s are considered excitatory; they positively regulate somatosensory transduction and they play roles in inflammatory sensitization and pain, and in some cases also in inducing itch. On the other hand, receptors that couple to G_i/o proteins, such as opioid or GABA_B receptors, are generally inhibitory. Their activation counteracts the effect of G_s-stimulation by inhibiting adenylate cyclase, as well as exerts effects on ion channels, usually resulting in decreased excitability. This review will summarize knowledge on G_i-coupled receptors in sensory neurons, focusing on their roles in ion channel regulation and discuss their potential as targets for analgesic and antipruritic medications.

Zinc signaling and epilepsy

Evidence from both preclinical and clinical studies suggest the importance of zinc homeostasis in seizures/epilepsy. Undoubtedly, zinc, via modulation of a variety of targets, is necessary for maintaining the balance between neuronal excitation and inhibition, while an imbalance between excitation and inhibition underlies seizures. However, the relationship between zinc signaling and seizures/epilepsy is complex as both extracellular and intracellular zinc may produce either protective or detrimental effects. This review provides an overview of preclinical/behavioral, functional and molecular studies, as well as clinical data on the involvement of zinc in the pathophysiology and treatment of seizures/epilepsy. Furthermore, the potential of targeting elements associated with zinc signaling or homeostasis and zinc levels as a therapeutic strategy for epilepsy is discussed.

M-type K+ channels in peripheral nociceptive pathways

Pathological pain is a hyperexcitability disorder. Since the excitability of a neuron is set and controlled by a complement of ion channels it expresses, in order to understand and treat pain, we need to develop a mechanistic insight into the key ion channels controlling excitability within the mammalian pain pathways and how these ion channels are regulated and modulated in various physiological and pathophysiological settings. In this review, we will discuss the emerging data on the expression in pain pathways, functional role and modulation of a family of voltage-gated K+ channels called 'M channels' (KCNQ, Kv 7). M channels are increasingly recognized as important players in controlling pain signalling, especially within the peripheral somatosensory system. We will also discuss the therapeutic potential of M channels as analgesic drug targets.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc/.

Regulation of the CaV3.2 calcium channels in health and disease Regulácia CaV3.2 vápnikových kanálov v zdraví a chorobe

Family of T-type or low-voltage activated calcium channels consists of three members: CaV3.1, CaV3.2, and CaV3.3. CaV3.2 channel has almost identical biophysical properties as the CaV3.1 channel, but is distinguished by a specific tissue expression profile and a prominent role in several pathologies, including neuropathic pain, epilepsy, and dysregulation of cardiac rhythm. Further, it may be involved in phenotype of autism spectrum disorders, and amyotrophic lateral sclerosis. It represents a promising target for future pharmacotherapies.

Intracellular zinc activates KCNQ channels by reducing their dependence on phosphatidylinositol 4,5-bisphosphate

M-type (Kv7, KCNQ) potassium channels are proteins that control the excitability of neurons and muscle cells. Many physiological and pathological mechanisms of excitation operate via the suppression of M channel activity or expression. Conversely, pharmacological augmentation of M channel activity is a recognized strategy for the treatment of hyperexcitability disorders such as pain and epilepsy. However, physiological mechanisms resulting in M channel potentiation are rare. Here we report that intracellular free zinc directly and reversibly augments the activity of recombinant and native M channels. This effect is mechanistically distinct from the known redox-dependent KCNQ channel potentiation. Interestingly, the effect of zinc cannot be attributed to a single histidine- or cysteine-containing zinc-binding site within KCNQ channels. Instead, zinc dramatically reduces KCNQ channel dependence on its obligatory physiological activator, phosphatidylinositol 4,5-bisphosphate (PIP₂). We hypothesize that zinc facilitates interactions of the lipid-facing interface of a KCNQ protein with the inner leaflet of the plasma membrane in a way similar to that promoted by PIP₂ Because zinc is increasingly recognized as a ubiquitous intracellular second messenger, this discovery might represent a hitherto unknown native pathway of M channel modulation and provide a fresh strategy for the design of M channel activators for therapeutic purposes.