Acidity and Acid-Sensing Ion Channels in the Normal and Alzheimer's Disease Brain

Fusion of brain imaging genetic data for alzheimer's disease diagnosis and causal factors identification using multi-stream attention mechanisms and graph convolutional networks

Correctly diagnosing Alzheimer's disease (AD) and identifying pathogenic brain regions and genes play a vital role in understanding the AD and developing effective prevention and treatment strategies. Recent works combine imaging and genetic data, and leverage the strengths of both modalities to achieve better classification results. In this work, we propose MCA-GCN, a Multi-stream Cross-Attention and Graph Convolutional Network-based classification method for AD patients. It first constructs a brain region-gene association network based on brain region fMRI time series and gene SNP data. Then it integrates the absolute and relative positions of the brain region time series to obtain a new brain region time series containing temporal information. Then long-range and local association features between brain regions and genes are sequentially aggregated by multi-stream cross-attention and graph convolutional networks. Finally, the learned brain region and gene features are input to the fully connected network to predict AD types. Experimental results on the ADNI dataset show that our model outperforms other methods in AD classification tasks. Moreover, MCA-GCN designed a multi-stage feature scoring process to extract high-risk genes and brain regions related to disease classification.

The impact of dietary acid load on super-agers with exceptional cognitive abilities: a propensity score analysis of national health and nutrition examination survey (NHANES) 2011-2014

OBJECTIVES

'Super-agers,' individuals over 80 with memory abilities comparable to those 20-30 years younger. The relationship between super-agers and dietary acid load (DAL) is an area that warrants further investigation. We aim to examine the link between DAL and super-agers and assess DAL's effects on cognitive functions across different age groups and cognitive domains.

DESIGN

Employing a cross-sectional analysis of the 2011-2014 National Health and Nutrition Examination Survey (NHANES) data, we utilized propensity score analysis and multivariate-adjusted regression to mitigate confounding factors.

SETTING

Older adults aged 60 and above in the United States.

PARTICIPANTS

Our primary analysis encompassed 985 older adults, supplemented by a sensitivity analysis with 2,522 participants.

MEASUREMENTS

DAL was assessed through potential renal acid load (PRAL), estimated net acid excretion (NAEes), and net endogenous acid production (NEAP) indices.

RESULTS

Super-agers demonstrate a preference for alkaline diets, shown by their lower DAL indices. After inverse probability of treatment weighting (IPTW), multivariate-adjusted logistic regression reveals that each unit reduction in NAEes and PRAL increases the chances of being a super-ager by 3.9% and 3.0%, respectively. The DAL's impact on cognitive function becomes more pronounced with age. Lower PRAL and NAEes scores are significantly linked to higher situational memory and overall cognitive performance scores in those over 70, with these effects being even more pronounced in participants over 80.

CONCLUSION

This research pioneers in demonstrating that super-agers prefer an alkaline diet, highlighting the potential role of alkaline diet in countering cognitive decline associated with aging.

Triggering of Major Brain Disorders by Protons and ATP: The Role of ASICs and P2X Receptors

Adenosine triphosphate (ATP) is well-known as a universal source of energy in living cells. Less known is that this molecule has a variety of important signaling functions: it activates a variety of specific metabotropic (P2Y) and ionotropic (P2X) receptors in neuronal and non-neuronal cell membranes. So, a wide variety of signaling functions well fits the ubiquitous presence of ATP in the tissues. Even more ubiquitous are protons. Apart from the unspecific interaction of protons with any protein, many physiological processes are affected by protons acting on specific ionotropic receptors-acid-sensing ion channels (ASICs). Both protons (acidification) and ATP are locally elevated in various pathological states. Using these fundamentally important molecules as agonists, ASICs and P2X receptors signal a variety of major brain pathologies. Here we briefly outline the physiological roles of ASICs and P2X receptors, focusing on the brain pathologies involving these receptors.

The role of microRNA-485 in neurodegenerative diseases

Neurodegenerative diseases (NDDs) are age-related disorders characterized by progressive neurodegeneration and neuronal cell loss in the central nervous system. Neuropathological conditions such as the accumulation of misfolded proteins can cause neuroinflammation, apoptosis, and synaptic dysfunction in the brain, leading to the development of NDDs including Alzheimer's disease (AD) and Parkinson's disease (PD). MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate gene expression post-transcriptionally via RNA interference. Recently, some studies have reported that some miRNAs play an important role in the development of NDDs by regulating target gene expression. MiRNA-485 (miR-485) is a highly conserved brain-enriched miRNA. Accumulating clinical reports suggest that dysregulated miR-485 may be involved in the pathogenesis of AD and PD. Emerging studies have also shown that miR-485 plays a novel role in the regulation of neuroinflammation, apoptosis, and synaptic function in the pathogenesis of NDDs. In this review, we introduce the biological characteristics of miR-485, provide clinical evidence of the dysregulated miR-485 in NDDs, novel roles of miR-485 in neuropathological events, and discuss the potential of targeting miR-485 as a diagnostic and therapeutic marker for NDDs.

A review for the pharmacological effects of paeoniflorin in the nervous system

Paeoniflorin, a terpenoid glycoside compound extracted from Paeonia lactiflora Pall, shows preventive and therapeutic effects in various types of nervous system disorders. However, to date, no comprehensive knowledge on the pharmacological effects of paeoniflorin on the nervous system is available online. Clarification of this issue may be useful for the development of paeoniflorin as a new drug for the treatment of nervous system disorders. To this end, the authors summarize the pharmacological aspects of paeoniflorin and its possible mechanisms, such as restoration of mitochondrial function; inhibition of neuroinflammation, oxidative stress, and cellular apoptosis; activation of adenosine A1 receptor, cAMP response element-binding protein (CREB) and extracellular signal-regulated kinase 1/2 (ERK1/2); or enhancement of brain-derived neurotrophic factor and serotonin function, in the prevention of disorders such as cerebral ischemia, subarachnoid hemorrhage, vascular dementia, Alzheimer's disease, Parkinson's disease, depression, post-traumatic syndrome disorder, and epilepsy, by reviewing the previously published literature.

Acidosis induces RIPK1-dependent death of glioblastoma stem cells via acid-sensing ion channel 1a

Eliciting regulated cell death, like necroptosis, is a potential cancer treatment. However, pathways eliciting necroptosis are poorly understood. It has been reported that prolonged activation of acid-sensing ion channel 1a (ASIC1a) induces necroptosis in mouse neurons. Glioblastoma stem cells (GSCs) also express functional ASIC1a, but whether prolonged activation of ASIC1a induces necroptosis in GSCs is unknown. Here we used a tumorsphere formation assay to show that slight acidosis (pH 6.6) induces necrotic cell death in a manner that was sensitive to the necroptosis inhibitor Nec-1 and to the ASIC1a antagonist PcTx1. In addition, genetic knockout of ASIC1a rendered GSCs resistant to acid-induced reduction in tumorsphere formation, while the ASIC1 agonist MitTx1 reduced tumorsphere formation also at neutral pH. Finally, a 20 amino acid fragment of the ASIC1 C-terminus, thought to interact with the necroptosis kinase RIPK1, was sufficient to reduce the formation of tumorspheres. Meanwhile, the genetic knockout of MLKL, the executive protein in the necroptosis cascade, did not prevent a reduction in tumor sphere formation, suggesting that ASIC1a induced an alternative cell death pathway. These findings demonstrate that ASIC1a is a death receptor on GSCs that induces cell death during prolonged acidosis. We propose that this pathway shapes the evolution of a tumor in its acidic microenvironment and that pharmacological activation of ASIC1a might be a potential new strategy in tumor therapy.

Simulation and Machine Learning Methods for Ion-Channel Structure Determination, Mechanistic Studies and Drug Design

Ion channels are expressed in almost all living cells, controlling the in-and-out communications, making them ideal drug targets, especially for central nervous system diseases. However, owing to their dynamic nature and the presence of a membrane environment, ion channels remain difficult targets for the past decades. Recent advancement in cryo-electron microscopy and computational methods has shed light on this issue. An explosion in high-resolution ion channel structures paved way for structure-based rational drug design and the state-of-the-art simulation and machine learning techniques dramatically improved the efficiency and effectiveness of computer-aided drug design. Here we present an overview of how simulation and machine learning-based methods fundamentally changed the ion channel-related drug design at different levels, as well as the emerging trends in the field.

Recent Advances in Acid-sensitive Ion Channels in Central Nervous System Diseases

Acid-sensitive ion channels (ASICs) are cationic channels activated by extracellular protons and widely distributed in the nervous system of mammals. It belongs to the ENaC/DEG family and has four coding genes: ASIC1, ASIC2, ASIC3, and ASIC4, which encode eight subunit proteins: ASIC1a, ASIC1b, ASIC1b2, ASIC2a, ASIC2b, ASIC3, ASIC4, and ASIC5. Different subtypes of ASICs have different distributions in the central nervous system, and they play an important role in various physiological and pathological processes of the central nervous system, including synaptic plasticity, anxiety disorders, fear conditioning, depression-related behavior, epilepsy, Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, malignant Glioma, pain, and others. This paper reviewed the recent studies of ASICs on the central nervous system to improve the understanding of ASICs' physiological functions and pathological effects. This article also provides a reference for studying the molecular mechanisms and therapeutic measures of nervous system-related diseases.

Acid-Sensing Ion Channels in Glial Cells

Acid-sensing ion channels (ASICs) are proton-gated cation channels and key mediators of responses to neuronal injury. ASICs exhibit unique patterns of distribution in the brain, with high expression in neurons and low expression in glial cells. While there has been a lot of focus on ASIC in neurons, less is known about the roles of ASICs in glial cells. ASIC1a is expressed in astrocytes and might contribute to synaptic transmission and long-term potentiation. In oligodendrocytes, constitutive activation of ASIC1a participates in demyelinating diseases. ASIC1a, ASIC2a, and ASIC3, found in microglial cells, could mediate the inflammatory response. Under pathological conditions, ASIC dysregulation in glial cells can contribute to disease states. For example, activation of astrocytic ASIC1a may worsen neurodegeneration and glioma staging, activation of microglial ASIC1a and ASIC2a may perpetuate ischemia and inflammation, while oligodendrocytic ASIC1a might be involved in multiple sclerosis. This review concentrates on the unique ASIC components in each of the glial cells and integrates these glial-specific ASICs with their physiological and pathological conditions. Such knowledge provides promising evidence for targeting of ASICs in individual glial cells as a therapeutic strategy for a diverse range of conditions.

Acid-sensing ion channels as potential therapeutic targets

Tissue acidification is associated with a variety of disease states, and acid-sensing ion channels (ASICs) that can sense changes in pH have gained traction as possible pharmaceutical targets. An array of modulators, ranging from small molecules to large biopharmaceuticals, are known to inhibit ASICs. Here, we summarize recent insights from animal studies to assess the therapeutic potential of ASICs in disorders such as ischemic stroke, various pain-related processes, anxiety, and cardiac pathologies. We also review the factors that present a challenge in the pharmacological targeting of ASICs, and which need to be taken into careful consideration when developing potent and selective modulators in the future.

Early detection of Alzheimer's disease using creatine chemical exchange saturation transfer magnetic resonance imaging

Detecting Alzheimer's disease (AD) at an early stage brings a lot of benefits including disease management and actions to slow the progression of the disease. Here, we demonstrate that reduced creatine chemical exchange saturation transfer (CrCEST) contrast has the potential to serve as a new biomarker for early detection of AD. The results on wild type (WT) mice and two age-matched AD models, namely tauopathy (Tau) and Aβ amyloidosis (APP), indicated that CrCEST contrasts of the cortex and corpus callosum in the APP and Tau mice were significantly reduced compared to WT counterpart at an early stage (6-7 months) (p < 0.011). Two main causes of the reduced CrCEST contrast, i.e. cerebral pH and creatine concentration, were investigated. From phantom and hypercapnia experiments, CrCEST showed excellent sensitivity to pH variations. From MRS results, the creatine concentration in WT and AD mouse brain was equivalent, which suggests that the reduced CrCEST contrast was dominated by cerebral pH change involved in the progression of AD. Immunohistochemical analysis revealed that the abnormal cerebral pH in AD mice may relate to neuroinflammation, a known factor that can cause pH reduction.

Hydrogen Sulfide Upregulates Acid-sensing Ion Channels via the MAPK-Erk1/2 Signaling Pathway

Hydrogen sulfide (H₂S) emerged recently as a new gasotransmitter and was shown to exert cellular effects by interacting with proteins, among them many ion channels. Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive Na⁺ channels activated by extracellular protons. ASICs are involved in many physiological and pathological processes, such as fear conditioning, pain sensation, and seizures. We characterize here the regulation of ASICs by H₂S. In transfected mammalian cells, the H₂S donor NaHS increased the acid-induced ASIC1a peak currents in a time- and concentration-dependent manner. Similarly, NaHS potentiated also the acid-induced currents of ASIC1b, ASIC2a, and ASIC3. An upregulation induced by the H₂S donors NaHS and GYY4137 was also observed with the endogenous ASIC currents of cultured hypothalamus neurons. In parallel with the effect on function, the total and plasma membrane expression of ASIC1a was increased by GYY4137, as determined in cultured cortical neurons. H₂S also enhanced the phosphorylation of the extracellular signal-regulated kinase (pErk1/2), which belongs to the family of mitogen-activated protein kinases (MAPKs). Pharmacological blockade of the MAPK signaling pathway prevented the GYY4137-induced increase of ASIC function and expression, indicating that this pathway is required for ASIC regulation by H₂S. Our study demonstrates that H₂S regulates ASIC expression and function, and identifies the involved signaling mechanism. Since H₂S shares several roles with ASICs, as for example facilitation of learning and memory, protection during seizure activity, and modulation of nociception, it may be possible that H₂S exerts some of these effects via a regulation of ASIC function.

Histamine and Corticosterone Modulate Acid Sensing Ion Channels (ASICs) Dependent Long-term Potentiation at the Mouse Anterior Cingulate Cortex

Increase in proton concentration [H⁺] or decrease in local and global extracellular pH occurs in both physiological and pathological conditions. Acid-sensing ion channels (ASICs), belonging to the ENaC/Deg superfamily, play an important role in signal transduction as proton sensor. ASICs and in particular ASIC1a (one of the six ASICs subunits) which is permeable to Ca²⁺, are involved in many physiological processes including synaptic plasticity and neurodegenerative diseases. Activity-dependent long-term potentiation (LTP) is a major type of long-lasting synaptic plasticity in the CNS, associated with learning, memory, development, fear and persistent pain. Neurons in the anterior cingulate cortex (ACC) play critical roles in pain perception and chronic pain and express ASIC1a channels. During synaptic transmission, acidification of the synaptic cleft presumably due to the co-release of neurotransmitter and H⁺ from synaptic vesicles activates postsynaptic ASIC1a channels in ACC of mice. This generates ASIC1a synaptic currents that add to the glutamatergic excitatory postsynaptic currents (EPSCs). Here we report that modulators like histamine and corticosterone, acting through ASIC1a regulate synaptic plasticity, reducing the threshold for LTP induction of glutamatergic EPSCs. Our findings suggest a new role for ASIC1a mediating the neuromodulator action of histamine and corticosterone regulating specific forms of synaptic plasticity in the mouse ACC.

Carnoquinolines Target Copper Dyshomeostasis, Aberrant Protein-Protein Interactions, and Oxidative Stress

Metal dysregulation, oxidative stress, protein modification, and aggregation are factors strictly interrelated and associated with neurodegenerative pathologies. As such, all of these aspects represent valid targets to counteract neurodegeneration and, therefore, the development of metal-binding compounds with other properties to combat multifactorial disorders is definitely on the rise. Herein, the synthesis and in-depth analysis of the first hybrids of carnosine and 8-hydroxyquinoline, carnoquinolines (CarHQs), which combine the properties of the dipeptide with those of 8-hydroxyquinoline, are reported. CarHQs and their copper complexes were characterized through several techniques, such as ESI-MS and NMR, UV/Vis, and circular dichroism spectroscopy. CarHQs can modulate self- and copper-induced amyloid-β aggregation. These hybrids combine the antioxidant activity of their parent compounds. Therefore, they can simultaneously scavenge free radicals and reactive carbonyl species, thanks to the phenolic group and imidazole ring. These results indicate that CarHQs are promising multifunctional candidates for neurodegenerative disorders and they are worthy of further studies.

Acid-sensing ion channels regulate nucleus pulposus cell inflammation and pyroptosis via the NLRP3 inflammasome in intervertebral disc degeneration

Objective

Lactate accumulation is an important factor in the intervertebral disc degeneration (IVDD). Currently, the effect and underlying mechanism of action of lactate on nucleus pulposus (NP) cell inflammation during IVDD are unclear. Previous studies have found that the NLRP3 inflammasome plays an important role in the regulation of NP inflammation. This study focused on the regulation of acid‐sensitive ion channels (ASICs) in relation to inflammation and the effect of NLRP3 on pyroptosis levels in NP cells under acidic conditions.

Design

For the in vitro experiments, human NP cells were exposed to 6 mM lactate solution; different groups were either treated with NLRP3 inhibitor or transfected with siRNA against NLRP3, siRNA against ASC or a mix of these, and mRNA and protein expression levels were then assessed. For the in vivo experiment, varying concentrations of lactate were injected into rat intervertebral discs and examined via magnetic resonance imaging (MRI) and histological staining.

Results

Extracellular lactate promoted NLRP3 inflammasome activation and degeneration of the NP extracellular matrix; furthermore, it increased the levels of inflammation and pyroptosis in the NP. Lactate‐induced NLRP3 inflammasome activation was blocked by ASIC inhibitors and NLRP3 siRNA.

Conclusions

Extracellular lactate regulates levels of intercellular reactive oxygen species (ROS) through ASIC1 and ASIC3. ROS activate the NF‐κB signalling pathway, thus promoting NLRP3 inflammasome activation and IL‐1β release, both of which promote NP degeneration.

[Acid-sensing ion channels differentially affect ictal-like and non-ictal-like epileptic activities of mouse hippocampal pyramidal neurons in acidotic extracellular pH]

OBJECTIVE

To investigate the effects of acid-sensing ion channels (ASICs) on electrophysiological epileptic activities of mouse hippocampal pyramidal neurons in the extracellular acidotic condition.

METHODS

We investigated effects of extracellular acidosis on epileptic activities induced by elevated extracellular K ⁺ concentration or the application of an antagonist of GABA_A receptors in perfusate of mouse hippocampal slices under field potential recordings. We also tested the effects of extracellular acidosis on neuronal excitability under field potential recording and evaluated the changes in epileptic activities of the neurons in response to pharmacological inhibition of ASICs using a specific inhibitor of ASICs.

RESULTS

Extracellular acidosis significantly suppressed epileptic activities of the hippocampal neurons by converting ictal-like epileptic activities to non-ictal-like epileptic activities in both high [K ⁺]o and disinhibition models, and also suppressed the intrinsic excitability of the neurons. ASICs inhibitor did not antagonize the inhibitory effect of extracellular acidosis on ictal epileptic activities and intrinsic neuronal excitability, but exacerbated non-ictal epileptic activities of the neurons in extracellular acidotic condition in both high [K⁺]o and disinhibition models.

CONCLUSIONS

ASICs can differentially modulate ictal-like and non-ictallike epileptic activities via its direct actions on excitatory neurons.

Zinc-mediated Neurotransmission in Alzheimer's Disease: A Potential Role of the GPR39 in Dementia

With more people reaching an advanced age in modern society, there is a growing need for strategies to slow down age-related neuropathology and loss of cognitive functions, which are a hallmark of Alzheimer's disease. Neuroprotective drugs and candidate drug compounds target one or more processes involved in the neurodegenerative cascade, such as excitotoxicity, oxidative stress, misfolded protein aggregation and/or ion dyshomeostasis. A growing body of research shows that a G-protein coupled zinc (Zn²⁺) receptor (GPR39) can modulate the abovementioned processes.

Zn²⁺ itself has a diverse activity profile at the synapse, and by binding to numerous receptors, it plays an important role in neurotransmission. However, Zn²⁺ is also necessary for the formation of toxic oligomeric forms of amyloid beta, which underlie the pathology of Alzheimer’s disease. Furthermore, the binding of Zn²⁺ by amyloid beta causes a disruption of zincergic signaling, and recent studies point to GPR39 and its intracellular targets being affected by amyloid pathology.

In this review, we present neurobiological findings related to Zn²⁺ and GPR39, focusing on its signaling pathways, neural plasticity, interactions with other neurotransmission systems, as well as on the effects of pathophysiological changes observed in Alzheimer's disease on GPR39 function.

Direct targeting of the GPR39 might be a promising strategy for the pharmacotherapy of zincergic dyshomeostasis observed in Alzheimer’s disease. The information presented in this article will hopefully fuel further research into the role of GPR39 in neurodegeneration and help in identifying novel therapeutic targets for dementia.

Intra-arterial Stem Cell Therapy Diminishes Inflammasome Activation After Ischemic Stroke: a Possible Role of Acid Sensing Ion Channel 1a

Studies from our lab demonstrated that 1 × 10⁵ intra-arterial mesenchymal stem cells (IA MSCs) at 6 h following ischemic stroke are efficacious owing to its maximum homing due to elevated stromal derived factor 1 (SDF1) in the tissue. Further, IA MSCs could abate the infarct progression, improve functional outcome, and decrease expression of calcineurin by modifying neuronal Ca²⁺ channels following ischemic stroke. Since stroke pathology also encompasses acidosis that worsens the condition; hence, the role of acid sensing ion channels (ASICs) in this context could not be overlooked. ASIC1a being the major contributor towards acidosis triggers Ca²⁺ ions overload which progressively contributes towards exacerbation of neuronal injury following ischemic insult. Inflammasome involvement in ischemic stroke is well reported as activated ASIC1a increases the expression of inflammasome in a pH-dependent manner to trigger inflammatory cascade. Hence, the current study aimed to identify if IA MSCs can decrease the production of inflammasome by attenuating ASIC1a expression to render neuroprotection. Ovariectomized Sprague Dawley (SD) rats exposed to middle cerebral artery occlusion (MCAo) for 90 min were treated with phosphate-buffered saline (PBS) or 1 × 10⁵ MSCs IA at 6 h to check for the expression of ASIC1a and inflammasome in different groups. Inhibition studies were carried out to explore the underlying mechanism. Our results demonstrate that IA MSCs improves functional outcome and oxidative stress parameters, and decreases the expression of ASIC1a and inflammasomes in the cortical brain region after ischemic stroke. This study offers a preliminary evidence of the role of IA MSCs in regulating inflammasome by modulating ASIC1a.

Curcuminoids and Novel Opportunities for the Treatment of Alzheimer's Disease: Which Molecules are Actually Effective?

BACKGROUND

Millions of people worldwide are suffering from Alzheimer's disease (AD), and there are only symptomatic treatments available for this disease. Thus, there is a great need to identify drugs capable of arresting or reversing AD. Constituents of the spice turmeric, in particular, curcuminoids, seem to be very promising, as evident from in vitro experiments and tests using animal models of AD. However, most of the clinical trials did not reveal any beneficial effects of curcuminoids in the treatment of AD. These controversies, including conflicting results of clinical trials, are thought to be related to bioavailability of curcuminoids, which is low unless it is enhanced by developing a special formulation. However, there is growing evidence suggesting that other reasons may be of even greater importance, but these avenues are less explored.

OBJECTIVE

Review relevant literature, and analyze potential reasons for the controversial results.

METHODOLOGY

Recent in vitro and preclinical studies; clinical trials (without a limiting period) were searched in PubMed and Google Scholar.

RESULTS

While recent in vitro and preclinical studies confirm the therapeutic potential of curcuminoids in the treatment of AD and cognitive dysfunctions, results of corresponding clinical trials remain rather controversial.

CONCLUSION

The controversial results obtained in the clinical trials may be in part due to particularities of the curcuminoid formulations other than bioavailability. Namely, it seems likely that the various formulations differ in terms of their minor turmeric constituent(s). We hypothesize that these distinctions may be of key importance for efficacy of the particular formulation in clinical trials. A testable approach addressing this hypothesis is suggested.

Subtype-selective inhibition of acid-sensing ion channel 3 by a natural flavonoid

AIMS

Acid-sensing ion channels (ASICs) are extracellular proton-gated cation channels that have been implicated in multiple physiological and pathological processes, and peripheral ASIC3 prominently participate into the pathogenesis of chronic pain, itch, and neuroinflammation, which necessitates the need for discovery and development of novel modulators in a subtype-specific manner.

METHODS

Whole-cell patch clamp recordings and behavioral assays were used to examine the effect of several natural compounds on the ASIC-mediated currents and acid-induced nocifensive behavior, respectively.

RESULTS

We identified a natural flavonoid compound, (-)-epigallocatechin gallate (EGCG, compound 11), that acts as a potent inhibitor for the ASIC3 channel in an isoform-specific way. The compound 11 inhibited ASIC3 currents with an apparent half maximal inhibitory concentration of 13.2 μmol/L when measured at pH 5.0. However, at the concentration up to 100 μmol/L, the compound 11 had no significant impacts on the homomeric ASIC1a, 1b, and 2a channels. In contrast to most of the known ASIC inhibitors that usually bear either basic or carboxylic groups, the compound 11 belongs to the polyphenolic family. In compound 11, both the chirality and the 3-hydroxyl group of its pyrogallol part, in addition to the integrity of the gallate part, are crucial for the inhibitory efficacy. Finally, EGCG was found significantly to decrease the acid-induced nocifensive behavior in mice.

CONCLUSION

Taken together, these results thus defined a novel backbone structure for small molecule drug design targeting ASIC3 channels to treat pain-related diseases.

Naked mole-rat cortical neurons are resistant to acid-induced cell death

Regulation of brain pH is a critical homeostatic process and changes in brain pH modulate various ion channels and receptors and thus neuronal excitability. Tissue acidosis, resulting from hypoxia or hypercapnia, can activate various proteins and ion channels, among which acid-sensing ion channels (ASICs) a family of primarily Na⁺ permeable ion channels, which alongside classical excitotoxicity causes neuronal death. Naked mole-rats (NMRs, Heterocephalus glaber) are long-lived, fossorial, eusocial rodents that display remarkable behavioral/cellular hypoxia and hypercapnia resistance. In the central nervous system, ASIC subunit expression is similar between mouse and NMR with the exception of much lower expression of ASIC4 throughout the NMR brain. However, ASIC function and neuronal sensitivity to sustained acidosis has not been examined in the NMR brain. Here, we show with whole-cell patch-clamp electrophysiology of cultured NMR and mouse cortical and hippocampal neurons that NMR neurons have smaller voltage-gated Na⁺ channel currents and more hyperpolarized resting membrane potentials. We further demonstrate that acid-mediated currents in NMR neurons are of smaller magnitude than in mouse, and that all currents in both species are reversibly blocked by the ASIC antagonist benzamil. We further demonstrate that NMR neurons show greater resistance to acid-induced cell death than mouse neurons. In summary, NMR neurons show significant cellular resistance to acidotoxicity compared to mouse neurons, contributing factors likely to be smaller ASIC-mediated currents and reduced NaV activity.

Role of ASIC1a in Aβ-induced synaptic alterations in the hippocampus

Acid-sensing ion channels (ASICs) are widely expressed in the mammalian central nervous system where they play a key role in synaptic transmission and in specific forms of memory. On the other hand, ASICs can be persistently active under pathological conditions contributing to neuronal damage in ischemic stroke, brain trauma, epilepsy and Parkinson's disease. However, to date no experimental evidence has linked ASICs to Alzheimer's disease (AD). Aim of the present work was to investigate, in CA1 pyramidal neurons, the possible involvement of ASIC1a in the Aβ-mediated effect on metabotropic glutamate (mGlu) receptor dependent transmission. We found that, in slices pretreated with Aβ, the pharmacological blockade of ASIC1a restored the increased intrinsic excitability following group I mGlu receptor activation. This suggests that, under certain conditions, ASIC1a might further contribute to the Aβ-related depolarizing response. We have recently demonstrated that ASIC1a is also involved long-term depression (LTD) induced either by low-frequency stimulation or by application of the group I mGlu receptor agonist DHPG. Here, we have shown that psalmotoxin-1, a selective blocker of ASIC1a, rescued the DHPG-LTD facilitation associated with genetic and non-genetic models of AD. Overall, these results suggest that a functional coupling between ASIC1a and mGlu receptors occurs and might contribute to the synaptic alterations associated with AD.

A Critical Assessment of Research on Neurotransmitters in Alzheimer's Disease

The purpose of this mini-forum, "Neurotransmitters and Alzheimer's Disease", is to critically assess the current status of neurotransmitters in Alzheimer's disease. Neurotransmitters are essential neurochemicals that maintain synaptic and cognitive functions in mammals, including humans, by sending signals across pre- to post-synaptic neurons. Authorities in the fields of synapses and neurotransmitters of Alzheimer's disease summarize the current status of basic biology of synapses and neurotransmitters, and also update the current status of clinical trials of neurotransmitters in Alzheimer's disease. This article discusses the prevalence, economic impact, and stages of Alzheimer's dementia in humans.