iMSC exosome delivers hsa-mir-125b-5p and strengthens acidosis resilience through suppression of ASIC1 protein in cerebral ischemia-reperfusion.

Acid-sensing ion channel 1 (ASIC1) is critical in acidotoxicity and significantly contributes to neuronal death in cerebral stroke. Pharmacological inhibition of ASIC1 has been shown to reduce neuronal death. However, the potential of utilizing exosomes derived from pluripotent stem cells to achieve inhibition of Asic1 remains to be explored. Developing qualified exosome products with precise and potent active ingredients suitable for clinical application is also ongoing. Here, we adopt small RNA-seq to interrogate the miRNA contents in exosomes of pluripotent stem cell induced mesenchymal stem cell (iMSC). RNA-seq was used to compare the oxygen-glucose deprivation-damaged neurons before and after the delivery of exosomes. We used Western blot to quantify the Asic1 protein abundance in neurons before and after exosome treatment. An in vivo test on rats validated the neuroprotective effect of iMSC-derived exosome and its active potent miRNA hsa-mir-125b-5p. We demonstrate that pluripotent stem cell-derived iMSCs produce exosomes with consistent miRNA contents and sustained expression. These exosomes efficiently rescue injured neurons, alleviate the pathological burden, and restore neuron function in rats under oxygen-glucose deprivation stress. Furthermore, we identify hsa-mir-125b-5p as the active component responsible for inhibiting the Asic1a protein and protecting neurons. We validated a novel therapeutic strategy to enhance acidosis resilience in cerebral stroke by utilizing exosomes derived from pluripotent stem cells with specific miRNA content. This holds promise for cerebral stroke treatment with the potential to reduce neuronal damage and improve clinical patient outcomes.

Group II metabotropic glutamate receptor activation attenuates acid-sensing ion channel currents in rat primary sensory neurons.

Acid-sensing ion channels (ASICs) play an important role in pain associated with tissue acidification. Peripheral inhibitory group II metabotropic glutamate receptors (mGluRs) have analgesic effects in a variety of pain conditions. Whether there is a link between ASICs and mGluRs in pain processes is still unclear. Herein, we show that the group II mGluR agonist LY354740 inhibited acid-evoked ASIC currents and action potentials in rat dorsal root ganglia neurons. LY354740 reduced the maximum current response to protons, but it did not change the sensitivity of ASICs to protons. LY354740 inhibited ASIC currents by activating group II mGluRs. We found that the inhibitory effect of LY354740 was blocked by intracellular application of the Gi/o protein inhibitor pertussis toxin and the cAMP analogue 8-Br-cAMP and mimicked by the protein kinase A (PKA) inhibitor H-89. LY354740 also inhibited ASIC3 currents in CHO cells coexpressing mGluR2 and ASIC3 but not in cells expressing ASIC3 alone. In addition, intraplantar injection of LY354740 dose-dependently alleviated acid-induced nociceptive behavior in rats through local group II mGluRs. Together, these results suggested that activation of peripheral group II mGluRs inhibited the functional activity of ASICs through a mechanism that depended on Gi/o proteins and the intracellular cAMP/PKA signaling pathway in rat dorsal root ganglia neurons. We propose that peripheral group II mGluRs are an important therapeutic target for ASIC-mediated pain.

Complex alterations in inflammatory pain and analgesic sensitivity in young and ageing female rats: involvement of ASIC3 and Nav1.8 in primary sensory neurons.

OBJECTIVE AND DESIGN: Our aim was to determine an age-dependent role of Nav1.8 and ASIC3 in dorsal root ganglion (DRG) neurons in a rat pre-clinical model of long-term inflammatory pain. METHODS: We compared 6 and 24 months-old female Wistar rats after cutaneous inflammation. We used behavioral pain assessments over time, qPCR, quantitative immunohistochemistry, selective pharmacological manipulation, ELISA and in vitro treatment with cytokines. RESULTS: Older rats exhibited delayed recovery from mechanical allodynia and earlier onset of spontaneous pain than younger rats after inflammation. Moreover, the expression patterns of Nav1.8 and ASIC3 were time and age-dependent and ASIC3 levels remained elevated only in aged rats. In vivo, selective blockade of Nav1.8 with A803467 or of ASIC3 with APETx2 alleviated mechanical and cold allodynia and also spontaneous pain in both age groups with slightly different potency. Furthermore, in vitro IL-1ß up-regulated Nav1.8 expression in DRG neurons cultured from young but not old rats. We also found that while TNF-α up-regulated ASIC3 expression in both age groups, IL-6 and IL-1ß had this effect only on young and aged neurons, respectively. CONCLUSION: Inflammation-associated mechanical allodynia and spontaneous pain in the elderly can be more effectively treated by inhibiting ASIC3 than Nav1.8.

Mutagenesis of the Peptide Inhibitor of ASIC3 Channel Introduces Binding to Thumb Domain of ASIC1a but Reduces Analgesic Activity.

Acid-sensing ion channels (ASICs), which act as proton-gating sodium channels, have garnered attention as pharmacological targets. ASIC1a isoform, notably prevalent in the central nervous system, plays an important role in synaptic plasticity, anxiety, neurodegeneration, etc. In the peripheral nervous system, ASIC1a shares prominence with ASIC3, the latter well established for its involvement in pain signaling, mechanical sensitivity, and inflammatory hyperalgesia. However, the precise contributions of ASIC1a in peripheral functions necessitate thorough investigation. To dissect the specific roles of ASICs, peptide ligands capable of modulating these channels serve as indispensable tools. Employing molecular modeling, we designed the peptide targeting ASIC1a channel from the sea anemone peptide Ugr9-1, originally targeting ASIC3. This peptide (A23K) retained an inhibitory effect on ASIC3 (IC50 9.39 µM) and exhibited an additional inhibitory effect on ASIC1a (IC50 6.72 µM) in electrophysiological experiments. A crucial interaction between the Lys23 residue of the A23K peptide and the Asp355 residue in the thumb domain of the ASIC1a channel predicted by molecular modeling was confirmed by site-directed mutagenesis of the channel. However, A23K peptide revealed a significant decrease in or loss of analgesic properties when compared to the wild-type Ugr9-1. In summary, using A23K, we show that negative modulation of the ASIC1a channel in the peripheral nervous system can compromise the efficacy of an analgesic drug. These results provide a compelling illustration of the complex balance required when developing peripheral pain treatments targeting ASICs.

Mambalgin-3 potentiates human acid-sensing ion channel 1b under mild to moderate acidosis: Implications as an analgesic lead.

Acid-sensing ion channels (ASICs) are expressed in the nervous system, activated by acidosis, and implicated in pain pathways. Mambalgins are peptide inhibitors of ASIC1 and analgesic in rodents via inhibition of centrally expressed ASIC1a and peripheral ASIC1b. This activity has generated interest in mambalgins as potential therapeutics. However, most mechanism and structure-activity relationship work on mambalgins has focused on ASIC1a, and neglected the peripheral analgesic target ASIC1b. Here, we compare mambalgin potency and mechanism of action at heterologously expressed rat and human ASIC1 variants. Unlike the nanomolar inhibition at ASIC1a and rodent ASIC1b, we find mambalgin-3 only weakly inhibits human ASIC1b and ASIC1b/3 under severe acidosis, but potentiates currents under mild/moderate acidosis. Our data highlight the importance of understanding the activity of potential ASIC-targeting pharmaceuticals at human channels.

Lycocasine A, a Lycopodium Alkaloid from Lycopodiastrum casuarinoides and Its Acid-Sensing Ion Channel 1a Inhibitory Activity.

A novel Lycopodium alkaloid, lycocasine A (1), and seven known Lycopodium alkaloids (2-8), were isolated from Lycopodiastrum casuarinoides. Their structures were determined through NMR, HRESIMS, and X-ray diffraction analysis. Compound 1 features an unprecedented 5/6/6 tricyclic skeleton, highlighted by a 5-aza-tricyclic[6,3,1,02,6]dodecane motif. In bioactivity assays, compound 1 demonstrated weak inhibitory activity against acid-sensing ion channel 1a.

The Phytochemical, Quercetin, Attenuates Nociceptive and Pathological Pain: Neurophysiological Mechanisms and Therapeutic Potential.

Although phytochemicals are plant-derived toxins that are primarily produced as a form of defense against insects or microbes, several lines of study have demonstrated that the phytochemical, quercetin, has several beneficial biological actions for human health, including antioxidant and inflammatory effects without side effects. Quercetin is a flavonoid that is widely found in fruits and vegetables. Since recent studies have demonstrated that quercetin can modulate neuronal excitability in the nervous system, including nociceptive sensory transmission via mechanoreceptors and voltage-gated ion channels, and inhibit the cyclooxygenase-2-cascade, it is possible that quercetin could be a complementary alternative medicine candidate; specifically, a therapeutic agent against nociceptive and pathological pain. The focus of this review is to elucidate the neurophysiological mechanisms underlying the modulatory effects of quercetin on nociceptive neuronal activity under nociceptive and pathological conditions, without inducing side effects. Based on the results of our previous research on trigeminal pain, we have confirmed in vivo that the phytochemical, quercetin, demonstrates (i) a local anesthetic effect on nociceptive pain, (ii) a local anesthetic effect on pain related to acute inflammation, and (iii) an anti-inflammatory effect on chronic pain. In addition, we discuss the contribution of quercetin to the relief of nociceptive and inflammatory pain and its potential clinical application.

Physiological insight into the conserved properties of Caenorhabditis elegans acid-sensing degenerin/epithelial sodium channels.

Acid-sensing ion channels (ASICs) are members of the diverse family of degenerin/epithelial sodium channels (DEG/ENaCs). They perform a wide range of physiological roles in healthy organisms, including in gut function and synaptic transmission, but also play important roles in disease, as acidosis is a hallmark of painful inflammatory and ischaemic conditions. We performed a screen for acid sensitivity on all 30 subunits of the Caenorhabditis elegans DEG/ENaC family using two-electrode voltage clamp in Xenopus oocytes. We found two groups of acid-sensitive DEG/ENaCs characterised by being either inhibited or activated by increasing proton concentrations. Three of these acid-sensitive C. elegans DEG/ENaCs were activated by acidic pH, making them functionally similar to the vertebrate ASICs. We also identified three new members of the acid-inhibited DEG/ENaC group, giving a total of seven additional acid-sensitive channels. We observed sensitivity to the anti-hypertensive drug amiloride as well as modulation by the trace element zinc. Acid-sensitive DEG/ENaCs were found to be expressed in both neurons and non-neuronal tissue, highlighting the likely functional diversity of these channels. Our findings provide a framework to exploit the C. elegans channels as models to study the function of these acid-sensing channels in vivo, as well as to study them as potential targets for anti-helminthic drugs. KEY POINTS: Acidosis plays many roles in healthy physiology, including synaptic transmission and gut function, but is also a key feature of inflammatory pain, ischaemia and many other conditions. Cells monitor acidosis of their surroundings via pH-sensing channels, including the acid-sensing ion channels (ASICs). These are members of the degenerin/epithelial sodium channel (DEG/ENaC) family, along with, as the name suggests, vertebrate ENaCs and degenerins of the roundworm Caenorhabditis elegans. By screening all 30 C. elegans DEG/ENaCs for pH dependence, we describe, for the first time, three acid-activated members, as well as three additional acid-inhibited channels. We surveyed both groups for sensitivity to amiloride and zinc; like their mammalian counterparts, their currents can be blocked, enhanced or unaffected by these modulators. Likewise, they exhibit diverse ion selectivity. Our findings underline the diversity of acid-sensitive DEG/ENaCs across species and provide a comparative resource for better understanding the molecular basis of their function.

Neuropeptides and degenerin/epithelial Na+ channels: a relationship from mammals to cnidarians.

Ion channels of the degenerin (DEG)/epithelial Na+ channel (ENaC) family serve diverse functions ranging from mechanosensation over Na+ reabsorption to H+ sensing and neurotransmission. However, several diverse DEG/ENaCs interact with neuropeptides; some are directly activated, whereas others are modulated by neuropeptides. Two questions arise: does this interaction have a common structural basis and does it have an ancient origin? Current evidence suggests that RFamide neuropeptides activate the FMRFamide-activated Na+ channels (FaNaCs) of invertebrates via binding to a pocket at the external face of their large extracellular domain. It is likely that RFamides might activate DEG/ENaCs from the freshwater polyp Hydra (the HyNaCs) via binding to a similar pocket, although there is not yet any experimental evidence. In contrast, RFamide neuropeptides modulate acid-sensing ion channels (ASICs) from vertebrates via binding to a central cavity enclosed by ß-sheets of the extracellular domain. Dynorphin opioid peptides, for their part, bind to the acidic pocket of ASICs, which might be evolutionarily related to the peptide binding pocket of FaNaCs, but instead of opening the channels they work as antagonists to stabilize its closed state. Moreover, peptides interacting with DEG/ENaCs from animals of different phyla, although having similar sequences, are evolutionarily unrelated to each other. Collectively, it appears that despite a seemingly similar interaction with similar peptides, the interaction of DEG/ENaCs with neuropeptides has diverse structural bases and many origins.

Comparative analysis defines a broader FMRFamide-gated sodium channel family and determinants of neuropeptide sensitivity.

FMRFamide (Phe-Met-Arg-Phe-amide, FMRFa) and similar neuropeptides are important physiological modulators in most invertebrates, but the molecular basis of FMRFa activity at its receptors is unknown. We therefore sought to identify the molecular determinants of FMRFa potency against one of its native targets, the excitatory FMRFa-gated sodium channel (FaNaC) from gastropod mollusks. Using molecular phylogenetics and electrophysiological measurement of neuropeptide activity, we identified a broad FaNaC family that includes mollusk and annelid channels gated by FMRFa, FVRIamides, and/or Wamides (or myoinhibitory peptides). A comparative analysis of this broader FaNaC family and other channels from the overarching degenerin (DEG)/epithelial sodium channel (ENaC) superfamily, incorporating mutagenesis and experimental dissection of channel function, identified a pocket of amino acid residues that determines activation of FaNaCs by neuropeptides. Although this pocket has diverged in distantly related DEG/ENaC channels that are activated by other ligands but enhanced by FMRFa, such as mammalian acid-sensing ion channels, we show that it nonetheless contains residues that determine enhancement of those channels by similar peptides. This study thus identifies amino acid residues that determine FMRFa neuropeptide activity at FaNaC receptor channels and illuminates the evolution of ligand recognition in one branch of the DEG/ENaC superfamily of ion channels.

Accessibility of ENaC extracellular domain central core residues.

The epithelial Na+ channel (ENaC)/degenerin family has a similar extracellular architecture, where specific regulatory factors interact and alter channel gating behavior. The extracellular palm domain serves as a key link to the channel pore. In this study, we used cysteine-scanning mutagenesis to assess the functional effects of Cys-modifying reagents on palm domain ß10 strand residues in mouse ENaC. Of the 13 ENaC α subunit mutants with Cys substitutions examined, only mutants at sites in the proximal region of ß10 exhibited changes in channel activity in response to methanethiosulfonate reagents. Additionally, Cys substitutions at three proximal sites of ß and γ subunit ß10 strands also rendered mutant channels methanethiosulfonate-responsive. Moreover, multiple Cys mutants were activated by low concentrations of thiophilic Cd2+. Using the Na+ self-inhibition response to assess ENaC gating behavior, we identified four α, two ß, and two γ subunit ß10 strand mutations that changed the Na+ self-inhibition response. Our results suggest that the proximal regions of ß10 strands in all three subunits are accessible to small aqueous compounds and Cd2+ and have a role in modulating ENaC gating. These results are consistent with a structural model of mouse ENaC that predicts the presence of aqueous tunnels adjacent to the proximal part of ß10 and with previously resolved structures of a related family member where palm domain structural transitions were observed with channels in an open or closed state.

Aggressive migration in acidic pH of a glioblastoma cancer stem cell line in vitro is independent of ASIC and KCa3.1 ion channels, but involves phosphoinositide 3-kinase.

The microenvironment of proliferative and aggressive tumours, such as the brain tumour glioblastoma multiforme (GBM), is often acidic, hypoxic, and nutrient deficient. Acid-sensing ion channels (ASICs) are proton-sensitive Na+ channels that have been proposed to play a role in pH sensing and in modulation of cancer cell migration. We previously reported that primary glioblastoma stem cells (GSCs), which grow as multicellular tumour spheroids, express functional ASIC1a and ASIC3, whereas ASIC2a is downregulated in GSCs. Using a 2.5D migration assay, here we report that acidic pH dramatically increased migration of GSCs of the pro-neural subtype. Pharmacological blockade as well as CRISPR-Cas9-mediated gene knock-out of ASIC1a or stable overexpression of ASIC2a, however, revealed that neither ASIC1a nor ASIC3, nor downregulation of ASIC2a, mediated the aggressive migration at acidic pH. Therefore, we tested the role of two other proteins previously implicated in cancer cell migration: the Ca2+-activated K+ channel KCa3.1 (KCNN4) and phosphoinositide 3-kinase (PI3K). While pharmacological blockade of KCa3.1 did also not affect migration, blockade of PI3K decreased migration at acidic pH to control levels. In summary, our study reveals a strongly enhanced migration of GSCs at acidic pH in vitro and identifies PI3K as an important mediator of this effect.

Upregulation of acid sensing ion channels is associated with esophageal hypersensitivity in GERD.

Proton pump inhibitors (PPIs) are the mainstay of therapy for gastroesophageal reflux disease (GERD) but up to 60% of patients have inadequate response to therapy. Acid sensing ion channels (ASICs) play important roles in nociception. This study aimed to investigate whether the increased expression of ASICs results in neuronal hyperexcitability in GERD. Esophageal biopsies were taken from GERD patients and healthy subjects to compare expression of ASIC1 and 3. Next, gene and protein expression of ASIC1 and 3 from esophageal mucosa and dorsal root ganglia (DRG) neurons were measured by qPCR, Western-blot and immunofluorescence in rodent models of reflux esophagitis (RE), non-erosive reflux disease (NERD), and sham operated groups. Excitability of DRG neurons in the GERD and sham groups were also tested by whole-cell patch-clamp recordings. We demonstrated that ASIC1 and 3 expression were significantly increased in patients with RE compared with healthy controls. This correlated positively with symptom severity of heartburn and regurgitation (p < .001). Next, ASIC1 and 3 gene and protein expression in rodent models of RE and NERD were similarly increased in esophageal mucosa as well as T3-T5 DRG neurons compared with sham operation. DRG neurons from RE animals showed hyperexcitability compared with sham group. However, intrathecal injection of ASIC specific inhibitors, PcTx1 and APTEx-2, as well as silencing ASIC1 and 3 genes with specific siRNAs prevented visceral hypersensitivity. Overall, upregulation of ASIC1 and 3 may lead to visceral hypersensitivity in RE and NERD and may be a potential therapeutic target for PPI non-responsive patients.

Automated Patch Clamp Screening of Amiloride and 5-N,N-Hexamethyleneamiloride Analogs Identifies 6-Iodoamiloride as a Potent Acid-Sensing Ion Channel Inhibitor.

Acid-sensing ion channels (ASICs) are transmembrane sensors of extracellular acidosis and potential drug targets in several disease indications, including neuropathic pain and cancer metastasis. The K+-sparing diuretic amiloride is a moderate nonspecific inhibitor of ASICs and has been widely used as a probe for elucidating ASIC function. In this work, we screened a library of 6-substituted and 5,6-disubstituted amiloride analogs using a custom-developed automated patch clamp protocol and identified 6-iodoamiloride as a potent ASIC1 inhibitor. Follow-up IC50 determinations in tsA-201 cells confirmed higher ASIC1 inhibitory potency for 6-iodoamiloride 94 (hASIC1 94 IC50 = 88 nM, cf. amiloride 11 IC50 = 1.7 µM). A similar improvement in activity was observed in ASIC3-mediated currents from rat dorsal root ganglion neurons (rDRG single-concentration 94 IC50 = 230 nM, cf. 11 IC50 = 2.7 µM). 6-Iodoamiloride represents the amiloride analog of choice for studying the effects of ASIC inhibition on cell physiology.

Cancer-nerve interplay in cancer progression and cancer-induced bone pain.

INTRODUCTION: Cancer-induced bone pain (CIBP) is one of the most common and debilitating complications associated with bone metastasis. Although our understanding of the precise mechanism is limited, it has been known that bone is densely innervated, and that CIBP is elicited as a consequence of increased neurogenesis, reprogramming, and axonogenesis in conjunction with sensitization and excitation of sensory nerves (SNs) in response to the noxious stimuli that are derived from the tumor microenvironment developed in bone. Recent studies have shown that the sensitized and excited nerves innervating the tumor establish intimate communications with cancer cells by releasing various tumor-stimulating factors for tumor progression. APPROACHES: In this review, the role of the interactions of cancer cells and SNs in bone in the pathophysiology of CIBP will be discussed with a special focus on the role of the noxious acidic tumor microenvironment, considering that bone is in nature hypoxic, which facilitates the generation of acidic conditions by cancer. Subsequently, the role of SNs in the regulation of cancer progression in the bone will be discussed together with our recent experimental findings. CONCLUSION: It is suggested that SNs may be a newly-recognized important component of the bone microenvironment that contribute to not only in the pathophysiology of CIBP but also cancer progression in bone and dissemination from bone. Suppression of the activity of bone-innervating SNs, thus, may provide unique opportunities in the treatment of cancer progression and dissemination, as well as CIBP.

Mechanism and site of action of big dynorphin on ASIC1a.

Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there is a great interest in understanding the in vivo regulation of ASICs, especially by endogenous neuropeptides that potently modulate ASICs. The most potent endogenous ASIC modulator known to date is the opioid neuropeptide big dynorphin (BigDyn). BigDyn is up-regulated in chronic pain and increases ASIC-mediated neuronal death during acidosis. Understanding the mechanism and site of action of BigDyn on ASICs could thus enable the rational design of compounds potentially useful in the treatment of pain and ischemic stroke. To this end, we employ a combination of electrophysiology, voltage-clamp fluorometry, synthetic BigDyn analogs, and noncanonical amino acid-mediated photocrosslinking. We demonstrate that BigDyn binding results in an ASIC1a closed resting conformation that is distinct from open and desensitized states induced by protons. Using alanine-substituted BigDyn analogs, we find that the BigDyn modulation of ASIC1a is primarily mediated through electrostatic interactions of basic amino acids in the BigDyn N terminus. Furthermore, neutralizing acidic amino acids in the ASIC1a extracellular domain reduces BigDyn effects, suggesting a binding site at the acidic pocket. This is confirmed by photocrosslinking using the noncanonical amino acid azidophenylalanine. Overall, our data define the mechanism of how BigDyn modulates ASIC1a, identify the acidic pocket as the binding site for BigDyn, and thus highlight this cavity as an important site for the development of ASIC-targeting therapeutics.

New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction.

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.

ASIC1a stimulates the resistance of human hepatocellular carcinoma by promoting EMT via the AKT/GSK3ß/Snail pathway driven by TGFß/Smad signals.

Multidrug resistance is the main obstacle to curing hepatocellular carcinoma (HCC). Acid-sensing ion channel 1a (ASIC1a) has critical roles in all stages of cancer progression, especially invasion and metastasis, and in resistance to therapy. Epithelial to mesenchymal transition (EMT) transforms epithelial cells into mesenchymal cells after being stimulated by extracellular factors and is closely related to tumour infiltration and resistance. We used Western blotting, immunofluorescence, qRT-PCR, immunohistochemical staining, MTT, colony formation and scratch healing assay to determine ASIC1a levels and its relationship to cell proliferation, migration and invasion. ASIC1a is overexpressed in HCC tissues, and the amount increased in resistant HCC cells. EMT occurred more frequently in drug-resistant cells than in parental cells. Inactivation of ASIC1a inhibited cell migration and invasion and increased the chemosensitivity of cells through EMT. Overexpression of ASIC1a upregulated EMT and increased the cells' proliferation, migration and invasion and induced drug resistance; knocking down ASIC1a with shRNA had the opposite effects. ASIC1a increased cell migration and invasion through EMT by regulating α and ß-catenin, vimentin and fibronectin expression via the AKT/GSK-3ß/Snail pathway driven by TGFß/Smad signals. ASIC1a mediates drug resistance of HCC through EMT via the AKT/GSK-3ß/Snail pathway.

Potentiation of ASIC currents by lysophosphatidic acid in rat dorsal root ganglion neurons.

Lysophosphatidic acid (LPA) is a phospholipid which has been implicated in pain. Acid-sensing ion channels (ASICs) are important players in pain associated with tissue acidification. However, it is still unclear whether there is a link between LPA signaling and ASICs in pain processes. Herein, we show that a functional interaction between them in rat dorsal root ganglia (DRG) neurons. Pre-application of LPA enhanced ASIC-mediated and acid-evoked inward currents in a concentration-dependent manner. LPA shifted the concentration-response curve for protons upwards, with an increase of 41.79 ± 4.71% in the maximal current response of ASICs to protons in the presence of LPA. Potentiation of ASIC currents by LPA was blocked by the LPA1 receptor antagonist Ki16198, but not by the LPA2 receptor antagonist H2L5185303. The LPA-induced potentiation was also prevented by intracellular application of either G protein inhibitor or protein kinase C (PKC) inhibitor, but not by Rho inhibitor. LPA also enhanced ASIC3 currents in CHO cells co-expressing ASIC3 and LPA1 receptors, but not in cells expressing ASIC3 alone. Moreover, LPA increased the amplitude of the depolarization and the number of spikes induced by acid stimuli. Finally, LPA exacerbated acid-induced nociceptive behaviors in rats. These results suggested that LPA enhanced ASIC-mediated electrophysiological activity and nociception via a LPA1 receptor and its downstream PKC rather than Rho signaling pathway, which provided a novel peripheral mechanism underlying the sensitization of pain.

Role of ASIC1a in Normal and Pathological Synaptic Plasticity.

Acid-sensing ion channels (ASICs), members of the degenerin/epithelial Na+ channel superfamily, are broadly distributed in the mammalian nervous system where they play important roles in a variety of physiological processes, including neurotransmission and memory-related behaviors. In the last few years, we and others have investigated the role of ASIC1a in different forms of synaptic plasticity especially in the CA1 area of the hippocampus. This review summarizes the latest research linking ASIC1a to synaptic function either in physiological or pathological conditions. A better understanding of how these channels are regulated in brain circuitries relevant to synaptic plasticity and memory may offer novel targets for pharmacological intervention in neuropsychiatric and neurological disorders.