Cognitive recovery by chronic activation of the large-conductance calcium-activated potassium channel in a mouse model of Alzheimer's disease

Rosin: A comprehensive review on traditional uses, phytochemistry, and pharmacology

Rosin, a natural resin obtained from conifer trees, has a long history of use in traditional folk medicine for treating abscesses, wounds, carbuncles, and burns, etc. It has been employed in ancient Egypt, China, Nordic countries, and Turkey as a therapeutic remedy. This comprehensive review examines the traditional uses, phytochemistry, and pharmacology of rosin, and it provides a critical update on current knowledge of rosin and identifies potential therapeutic opportunities. The chemical composition of rosin is known to vary depending on factors such as botanical sources, geographical locations, and processing methods. Rosin acids, which account for over 90% of its primary chemical constituents, have been identified as the predominant compounds in rosin. Researchers have isolated approximately 50 compounds from rosin, with terpenoid rosin acids being the most prevalent. Furthermore, the review highlights the potential pharmacological activities of rosin and its constituents. Crude extracts and isolated rosin acids have demonstrated promising properties, including antimicrobial, anti-inflammatory, anti-tumor, insecticidal, wound healing, and anti-obesity effects. However, the review emphasizes that further research is needed, as existing studies are predominantly preliminary. Many of the reported bioactivities require further verification, and the underlying mechanisms of action remain largely unexplored. In conclusion, rosin has been extensively used in traditional medicine across different cultures, and its chemical composition has been confirmed to a significant extent. The pharmacological activities observed in crude extracts and isolated rosin acids support its traditional uses. Nevertheless, additional research is necessary to deepen our understanding of the pharmacological mechanisms underlying its effects.

Disruption of sphingomyelin synthase 2 gene alleviates cognitive impairment in a mouse model of Alzheimer's disease

The membrane raft accommodates the key enzymes synthesizing amyloid β (Aβ). One of the two characteristic components of the membrane raft, cholesterol, is well known to promote the key enzymes that produce amyloid-β (Aβ) and exacerbate Alzheimer's disease (AD) pathogenesis. Given that the raft is a physicochemical platform for the sound functioning of embedded bioactive proteins, the other major lipid component sphingomyelin may also be involved in AD. Here we knocked out the sphingomyelin synthase 2 gene (SMS2) in 3xTg AD model mice by hybridization, yielding SMS2KO mice (4S mice). The novel object recognition test in 9/10-month-old 4S mice showed that cognitive impairment in 3xTg mice was alleviated by SMS2KO, though performance in the Morris water maze (MWM) was not improved. The tail suspension test detected a depressive trait in 4S mice, which may have hindered the manifestation of performance in the wet, stressful environment of MWM. In the hippocampal CA1, hyperexcitability in 3xTg was also found alleviated by SMS2KO. In the hippocampal dentate gyrus of 4S mice, the number of neurons positive with intracellular Aβ or its precursor proteins, the hallmark of young 3xTg mice, is reduced to one-third, suggesting an SMS2KO-led suppression of syntheses of those peptides in the dentate gyrus. Although we previously reported that large-conductance calcium-activated potassium (BK) channels are suppressed in 3xTg mice and their recovery relates to cognitive amelioration, no changes occurred by hybridization. Sphingomyelin in the membrane raft may serve as a novel target for AD drugs.

Spatiotemporal development of the neuronal accumulation of amyloid precursor protein and the amyloid plaque formation in the brain of 3xTg-AD mice

The amyloid plaque is a hallmark of Alzheimer's disease. The accumulation of the amyloid precursor protein (APP) in the neuronal structure is assumed to lead to amyloid plaque formation through the excessive production of β-amyloid protein. To study the relationship between the neuronal accumulation of APP and amyloid plaque formation, we histologically analyzed their development in the different brain regions in 3xTg-AD mice, which express Swedish mutated APP (APPSWE) in the neurons. Observation throughout the brain revealed APPSWE-positive somata in the broad regions. Quantitative model analysis showed that the somatic accumulation of APPSWE developed firstly in the hippocampus from a very early age (<1 month) and proceeded slower in the isocortex. In line with this, the hippocampus was the first region to form amyloid plaques at the age of 9-12 months, while amyloid plaques were rarely observed in the isocortex. Females had more APPSWE-positive somata and plaques than males. Furthermore, amyloid plaques were observed in the lateral septum and pontine grey, which did not contain APPSWE-positive somata but only the APPSWE-positive fibers. These results suggested that neuronal accumulation of APPSWE, both in somatodendritic and axonal domains, is closely related to the formation of amyloid plaques.

Challenges in the Therapeutic Targeting of KCa Channels: From Basic Physiology to Clinical Applications

Calcium-activated potassium (KCa) channels are ubiquitously expressed throughout the body and are able to regulate membrane potential and intracellular calcium concentrations, thereby playing key roles in cellular physiology and signal transmission. Consequently, it is unsurprising that KCa channels have been implicated in various diseases, making them potential targets for pharmaceutical interventions. Over the past two decades, numerous studies have been conducted to develop KCa channel-targeting drugs, including those for disorders of the central and peripheral nervous, cardiovascular, and urinary systems and for cancer. In this review, we synthesize recent findings regarding the structure and activating mechanisms of KCa channels. We also discuss the role of KCa channel modulators in therapeutic medicine. Finally, we identify the major reasons behind the delay in bringing these modulators to the pharmaceutical market and propose new strategies to promote their application.

BK channels sustain neuronal Ca2+ oscillations to support hippocampal long-term potentiation and memory formation

Mutations of large conductance Ca2+- and voltage-activated K+ channels (BK) are associated with cognitive impairment. Here we report that CA1 pyramidal neuron-specific conditional BK knock-out (cKO) mice display normal locomotor and anxiety behavior. They do, however, exhibit impaired memory acquisition and retrieval in the Morris Water Maze (MWM) when compared to littermate controls (CTRL). In line with cognitive impairment in vivo, electrical and chemical long-term potentiation (LTP) in cKO brain slices were impaired in vitro. We further used a genetically encoded fluorescent K+ biosensor and a Ca2+-sensitive probe to observe cultured hippocampal neurons during chemical LTP (cLTP) induction. cLTP massively reduced intracellular K+ concentration ([K+]i) while elevating L-Type Ca2+ channel- and NMDA receptor-dependent Ca2+ oscillation frequencies. Both, [K+]i decrease and Ca2+ oscillation frequency increase were absent after pharmacological BK inhibition or in cells lacking BK. Our data suggest that L-Type- and NMDAR-dependent BK-mediated K+ outflow significantly contributes to hippocampal LTP, as well as learning and memory.

Ca2+- and Voltage-Activated K+ (BK) Channels in the Nervous System: One Gene, a Myriad of Physiological Functions

BK channels are large conductance potassium channels characterized by four pore-forming α subunits, often co-assembled with auxiliary β and γ subunits to regulate Ca2+ sensitivity, voltage dependence and gating properties. BK channels are abundantly expressed throughout the brain and in different compartments within a single neuron, including axons, synaptic terminals, dendritic arbors, and spines. Their activation produces a massive efflux of K+ ions that hyperpolarizes the cellular membrane. Together with their ability to detect changes in intracellular Ca2+ concentration, BK channels control neuronal excitability and synaptic communication through diverse mechanisms. Moreover, increasing evidence indicates that dysfunction of BK channel-mediated effects on neuronal excitability and synaptic function has been implicated in several neurological disorders, including epilepsy, fragile X syndrome, mental retardation, and autism, as well as in motor and cognitive behavior. Here, we discuss current evidence highlighting the physiological importance of this ubiquitous channel in regulating brain function and its role in the pathophysiology of different neurological disorders.

The modulation of potassium channels by estrogens facilitates neuroprotection

Estrogens, the sex hormones, have the potential to govern multiple cellular functions, such as proliferation, apoptosis, differentiation, and homeostasis, and to exert numerous beneficial influences for the cardiovascular system, nervous system, and bones in genomic and/or non-genomic ways. Converging evidence indicates that estrogens serve a crucial role in counteracting neurodegeneration and ischemic injury; they are thereby being considered as a potent neuroprotectant for preventing neurological diseases such as Alzheimer's disease and stroke. The underlying mechanism of neuroprotective effects conferred by estrogens is thought to be complex and multifactorial, and it remains obscure. It is well established that the K+ channels broadly expressed in a variety of neural subtypes determine the essential physiological features of neuronal excitability, and dysfunction of these channels is closely associated with diverse brain deficits, such as ataxia and epilepsy. A growing body of evidence supports a neuroprotective role of K+ channels in malfunctions of nervous tissues, with the channels even being a therapeutic target in clinical trials. As multitarget steroid hormones, estrogens also regulate the activity of distinct K+ channels to generate varying biological actions, and accumulated data delineate that some aspects of estrogen-mediated neuroprotection may arise from the impact on multiple K+ channels, including Kv, BK, KATP, and K2P channels. The response of these K+ channels after acute or chronic exposure to estrogens may oppose pathological abnormality in nervous cells, which serves to extend our understanding of these phenomena.

The Effect of 40-Hz White LED Therapy on Structure-Function of Brain Mitochondrial ATP-Sensitive Ca-Activated Large-Conductance Potassium Channel in Amyloid Beta Toxicity

Photobiomodulation therapy has become the focus of medical research in many areas such as Alzheimer's disease (AD), because of its modulatory effect on cellular processes through light energy absorption via photoreceptors/chromophores located in the mitochondria. However, there are still many questions around the underlying mechanisms. This study was carried out to unravel whether the function-structure of ATP-sensitive mitoBK_Ca channels, as crucial components for maintenance of mitochondrial homeostasis, can be altered subsequent to light therapy in AD. Induction of Aβ neurotoxicity in male Wistar rats was done by intracerebroventricular injection of Aβ1-42. After a week, light-treated rats were exposed to 40-Hz white light LEDs, 15 min for 7 days. Electrophysiological properties of mitoBK_Ca channel were investigated using a channel incorporated into the bilayer lipid membrane, and mitoBK_Ca-β2 subunit expression was determined using western blot analysis in Aβ-induced toxicity and light-treated rats. Our results describe that conductance and open probability (Po) of mitoBK_Ca channel decreased significantly and was accompanied by a Po curve rightward shift in mitochondrial preparation in Aβ-induced toxicity rats. We also showed a significant reduction in expression of mitoBK_Ca-β2 subunit, which is partly responsible for a leftward shift in BK_Ca Po curve in low calcium status. Interestingly, we provided evidence of a significant improvement in channel conductance and Po after light therapy. We also found that light therapy improved mitoBK_Ca-β2 subunit expression, increasing it close to saline group. The current study explains a light therapy improvement in brain mitoBK_Ca channel function in the Aβ-induced neurotoxicity rat model, an effect that can be linked to increased expression of β2 subunit.

The lateral entorhinal cortex is a hub for local and global dysfunction in early Alzheimer's disease states

Functional network activity alterations are one of the earliest hallmarks of Alzheimer's disease (AD), detected prior to amyloidosis and tauopathy. Better understanding the neuronal underpinnings of such network alterations could offer mechanistic insight into AD progression. Here, we examined a mouse model (3xTgAD mice) recapitulating this early AD stage. We found resting functional connectivity loss within ventral networks, including the entorhinal cortex, aligning with the spatial distribution of tauopathy reported in humans. Unexpectedly, in contrast to decreased connectivity at rest, 3xTgAD mice show enhanced fMRI signal within several projection areas following optogenetic activation of the entorhinal cortex. We corroborate this finding by demonstrating neuronal facilitation within ventral networks and synaptic hyperexcitability in projection targets. 3xTgAD mice, thus, reveal a dichotomic hypo-connected:resting versus hyper-responsive:active phenotype. This strong homotopy between the areas affected supports the translatability of this pathophysiological model to tau-related, early-AD deficits in humans.

Impact of β-Amyloids Induced Disruption of Ca2+ Homeostasis in a Simple Model of Neuronal Activity

Alzheimer’s disease is characterized by a marked dysregulation of intracellular Ca²⁺ homeostasis. In particular, toxic β-amyloids (Aβ) perturb the activities of numerous Ca²⁺ transporters or channels. Because of the tight coupling between Ca²⁺ dynamics and the membrane electrical activity, such perturbations are also expected to affect neuronal excitability. We used mathematical modeling to systematically investigate the effects of changing the activities of the various targets of Aβ peptides reported in the literature on calcium dynamics and neuronal excitability. We found that the evolution of Ca²⁺ concentration just below the plasma membrane is regulated by the exchanges with the extracellular medium, and is practically independent from the Ca²⁺ exchanges with the endoplasmic reticulum. Thus, disruptions of Ca²⁺ homeostasis interfering with signaling do not affect the electrical properties of the neurons at the single cell level. In contrast, the model predicts that by affecting the activities of L-type Ca²⁺ channels or Ca²⁺-activated K⁺ channels, Aβ peptides promote neuronal hyperexcitability. On the contrary, they induce hypo-excitability when acting on the plasma membrane Ca²⁺ ATPases. Finally, the presence of pores of amyloids in the plasma membrane can induce hypo- or hyperexcitability, depending on the conditions. These modeling conclusions should help with analyzing experimental observations in which Aβ peptides interfere at several levels with Ca²⁺ signaling and neuronal activity.

Amyloid β and Amyloid Precursor Protein Synergistically Suppress Large-Conductance Calcium-Activated Potassium Channel in Cortical Neurons

Intracellular amyloid β (Aβ) injection suppresses the large-conductance calcium-dependent potassium (BK) channel in cortical pyramidal cells from wild-type (WT) mice. In 3xTg Alzheimer’s disease (AD) model mice, intraneuronal Aβ is genetically programed to accumulate, which suppresses the BK channel. However, the mode of BK channel suppression remained unclarified. The present report revealed that only one (11A1) of the three anti-Aβ-oligomer antibodies that we examined, but not anti-monomer-Aβ-antibodies, was effective in recovering BK channel activity in 3xTg neurons. Antibodies against amyloid precursor protein (APP) were also found to be effective, suggesting that APP plays an essential part in this Aβ-oligomer-induced BK channel suppression in 3xTg neurons. In WT neurons, by contrast, APP suppressed BK channels by itself, which suggests that either APP or Aβ is sufficient to block BK channels, thus pointing to a different co-operativity of Aβ and APP in WT and 3xTg neurons. To clarify this difference, we relied on our previous finding that the scaffold protein Homer1a reverses the BK channel blockade in both WT and 3xTg neurons. In cortical neurons from 3xTg mice that bear Homer1a knockout (4xTg mice), neither anti-APP antibodies nor 11A1, but only the 6E10 antibody that binds both APP and Aβ, rescued the BK channel suppression. Given that Homer1a expression is activity dependent and 3xTg neurons are hyperexcitable, Homer1a is likely to be expressed sufficiently in 3xTg neurons, thereby alleviating the suppressive influence of APP and Aβ on BK channel. A unique way that APP modifies Aβ toxicity is thus proposed.

The role of nuclear Ca2+ in maintaining neuronal homeostasis and brain health

Nuclear Ca2+ has emerged as one of the most potent mediators of the dialogue between neuronal synapses and the nucleus that regulates heterochromatin states, transcription factor activity, nuclear morphology and neuronal gene expression induced by synaptic activity. Recent studies underline the importance of nuclear Ca2+ signaling in long-lasting, activity-induced adaptation and maintenance of proper brain function. Diverse forms of neuroadaptation require transient nuclear Ca2+ signaling and cyclic AMP-responsive element-binding protein (CREB1, referred to here as CREB) as its prime target, which works as a tunable switch to drive and modulate specific gene expression profiles associated with memory, pain, addiction and neuroprotection. Furthermore, a reduction of nuclear Ca2+ levels has been shown to be neurotoxic and a causal factor driving the progression of neurodegenerative disorders, as well as affecting neuronal autophagy. Because of its central role in the brain, deficits in nuclear Ca2+ signaling may underlie a continuous loss of neuroprotection in the aging brain, contributing to the pathophysiology of Alzheimer's disease. In this Review, we discuss the principles of the 'nuclear calcium hypothesis' in the context of human brain function and its role in controlling diverse forms of neuroadaptation and neuroprotection. Furthermore, we present the most relevant and promising perspectives for future studies.

Hippocampal hyperactivity in a rat model of Alzheimer's disease

Neuronal network dysfunction is a hallmark of Alzheimer's disease (AD). However, the underlying pathomechanisms remain unknown. We analyzed the hippocampal micronetwork in transgenic McGill-R-Thy1-APP rats (APPtg) at the beginning of extracellular amyloid beta (Aβ) deposition. We established two-photon Ca²⁺ -imaging in vivo in the hippocampus of rats and found hyperactivity of CA1 neurons. Patch-clamp recordings in brain slices in vitro revealed increased neuronal input resistance and prolonged action potential width in CA1 pyramidal neurons. We did neither observe changes in synaptic inhibition, nor in excitation. Our data support the view that increased intrinsic excitability of CA1 neurons may precede inhibitory dysfunction at an early stage of Aβ-deposition and disease progression.

Remodeling of projections from ventral hippocampus to prefrontal cortex in Alzheimer's mice

Emotional dysregulation often accompanies cognitive deficits in Alzheimer's disease (AD). The hippocampus, most notably damaged by AD pathology, is classified into the cognition-bound posterior and emotion-bound anterior hippocampi. Since the anterior hippocampus or its rodent counterpart, the ventral hippocampus (VH), sends dense afferents to the prefrontal cortex (PFC) and the basolateral amygdala (BLA), the two structures implicated in fear responses, we investigated whether these afferents are modified in 3xTg AD model mice. An anterograde dextrin tracer injected into VH revealed that axons in PFC were more ramified in 3xTg than wild-type (WT) mice, with the synaptic density reduced. The VH projections to BLA were not affected. Intracellular accumulation of amyloid β (Aβ) or Aβ-like immunoreactivity was found in PFC and BLA neurons alike. Behaviorally, in the 2-way active avoidance test, the frequency of chamber change was higher, with the test performance better, in 3xTg than WT mice, suggesting a distorted contextual fear in the 3xTg group. Given the essential involvement of parts of PFC in contextual fear responses and that of BLA in fear responses in general, the observed remodeling of VH-to-PFC afferents and the accumulation of intracellular Aβ in BLA and PFC pyramidal cells might exercise critical influences on enhanced avoidance behavior in 3xTg mice.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

Pathogenic Tau Causes a Toxic Depletion of Nuclear Calcium

Synaptic activity-induced calcium (Ca2+) influx and subsequent propagation into the nucleus is a major way in which synapses communicate with the nucleus to regulate transcriptional programs important for activity-dependent survival and memory formation. Nuclear Ca2+ shapes the transcriptome by regulating cyclic AMP (cAMP) response element-binding protein (CREB). Here, we utilize a Drosophila model of tauopathy and induced pluripotent stem cell (iPSC)-derived neurons from humans with Alzheimer's disease to study the effects of pathogenic tau, a pathological hallmark of Alzheimer's disease and related tauopathies, on nuclear Ca2+. We find that pathogenic tau depletes nuclear Ca2+ and CREB to drive neuronal death, that CREB-regulated genes are over-represented among differentially expressed genes in tau transgenic Drosophila, and that activation of big potassium (BK) channels elevates nuclear Ca2+ and suppresses tau-induced neurotoxicity. Our studies identify nuclear Ca2+ depletion as a mechanism contributing to tau-induced neurotoxicity, adding an important dimension to the calcium hypothesis of Alzheimer's disease.

BK channel density is regulated by endoplasmic reticulum associated degradation and influenced by the SKN-1A/NRF1 transcription factor

Ion channels are present at specific levels within subcellular compartments of excitable cells. The regulation of ion channel trafficking and targeting is an effective way to control cell excitability. The BK channel is a calcium-activated potassium channel that serves as a negative feedback mechanism at presynaptic axon terminals and sites of muscle excitation. The C. elegans BK channel ortholog, SLO-1, requires an endoplasmic reticulum (ER) membrane protein for efficient anterograde transport to these locations. Here, we found that, in the absence of this ER membrane protein, SLO-1 channels that are seemingly normally folded and expressed at physiological levels undergo SEL-11/HRD1-mediated ER-associated degradation (ERAD). This SLO-1 degradation is also indirectly regulated by a SKN-1A/NRF1-mediated transcriptional mechanism that controls proteasome levels. Therefore, our data indicate that SLO-1 channel density is regulated by the competitive balance between the efficiency of ER trafficking machinery and the capacity of ERAD.

Excitable cells, such as neurons and muscles, are essential for the movement and behavior of animals. These cells express a set of specific types of ion channels that allow the selective passage of ions across the plasma membrane. The alteration in the levels of these ion channels influences cell excitability and the function of excitable cells. The regulation of ion channel trafficking and targeting is an effective way to control the function of excitable cells. The BK SLO-1 channel is a calcium-activated potassium channel that reduces excitability at presynaptic axon terminals and sites of muscle excitation. In a C. elegans genetic study, authors found that the delayed exit of SLO-1 channels from the ER causes their degradation by a mechanism called ER-associated degradation (ERAD). Interestingly, the same components that directly mediate SLO-1 ERAD also process a key transcriptional factor that maintains proteasome levels, thus indirectly influencing SLO-1 degradation. These data show that the levels of SLO-1 channels are regulated by the competitive balance between the efficiency of ER trafficking machinery and the capacity of ERAD.

The monomers, oligomers, and fibrils of amyloid-β inhibit the activity of mitoBKCa channels by a membrane-mediated mechanism

A causative agent of Alzheimer's disease (AD) is a short amphipathic peptide called amyloid beta (Aβ). Aβ monomers undergo structural changes leading to their oligomerization or fibrillization. The monomers as well as all aggregated forms of Aβ, i.e., oligomers, and fibrils, can bind to biological membranes, thereby modulating membrane mechanical properties. It is also known that some isoforms of the large-conductance calcium-activated potassium (BK_Ca) channel, including the mitochondrial BK_Ca (mitoBK_Ca) channel, respond to mechanical changes in the membrane. Here, using the patch-clamp technique, we investigated the impact of full-length Aβ (Aβ_1-42) and its fragment, Aβ_25-35, on the activity of mitoBK_Ca channels. We found that all forms of Aβ inhibited the activity of the mitoBK_Ca channel in a concentration-dependent manner. Since monomers, oligomers, and fibrils of Aβ exhibit different molecular characteristics and structures, we hypothesized that the inhibition was not due to direct peptide-protein interactions but rather to membrane-binding of the Aβ peptides. Our findings supported this hypothesis by showing that Aβ peptides block mitoBK_Ca channels irrespective of the side of the membrane to which they are applied. In addition, we found that the enantiomeric peptide, D-Aβ_1-42, demonstrated similar inhibitory activity towards mitoBK_Ca channels. As a result, we proposed a general model in which all Aβ forms i.e., monomers, oligomers, and amyloid fibrils, contribute to the progression of AD by exerting a modulatory effect on mechanosensitive membrane components.

Calcium-activated potassium channels: implications for aging and age-related neurodegeneration

Population aging, as well as the handling of age-associated diseases, is a worldwide increasing concern. Among them, Alzheimer's disease stands out as the major cause of dementia culminating in full dependence on other people for basic functions. However, despite numerous efforts, in the last decades, there was no new approved therapeutic drug for the treatment of the disease. Calcium-activated potassium channels have emerged as a potential tool for neuronal protection by modulating intracellular calcium signaling. Their subcellular localization is determinant of their functional effects. When located on the plasma membrane of neuronal cells, they can modulate synaptic function, while their activation at the inner mitochondrial membrane has a neuroprotective potential via the attenuation of mitochondrial reactive oxygen species in conditions of oxidative stress. Here we review the dual role of these channels in the aging phenotype and Alzheimer's disease pathology and discuss their potential use as a therapeutic tool.

De novo loss-of-function KCNMA1 variants are associated with a new multiple malformation syndrome and a broad spectrum of developmental and neurological phenotypes

KCNMA1 encodes the large-conductance Ca2+- and voltage-activated K+ (BK) potassium channel α-subunit, and pathogenic gain-of-function variants in this gene have been associated with a dominant form of generalized epilepsy and paroxysmal dyskinesia. Here, we genetically and functionally characterize eight novel loss-of-function (LoF) variants of KCNMA1. Genome or exome sequencing and the participation in the international Matchmaker Exchange effort allowed for the identification of novel KCNMA1 variants. Patch clamping was used to assess functionality of mutant BK channels. The KCNMA1 variants p.(Ser351Tyr), p.(Gly356Arg), p.(Gly375Arg), p.(Asn449fs) and p.(Ile663Val) abolished the BK current, whereas p.(Cys413Tyr) and p.(Pro805Leu) reduced the BK current amplitude and shifted the activation curves toward positive potentials. The p.(Asp984Asn) variant reduced the current amplitude without affecting kinetics. A phenotypic analysis of the patients carrying the recurrent p.(Gly375Arg) de novo missense LoF variant revealed a novel syndromic neurodevelopmental disorder associated with severe developmental delay, visceral and cardiac malformations, connective tissue presentations with arterial involvement, bone dysplasia and characteristic dysmorphic features. Patients with other LoF variants presented with neurological and developmental symptoms including developmental delay, intellectual disability, ataxia, axial hypotonia, cerebral atrophy and speech delay/apraxia/dysarthria. Therefore, LoF KCNMA1 variants are associated with a new syndrome characterized by a broad spectrum of neurological phenotypes and developmental disorders. LoF variants of KCNMA1 cause a new syndrome distinctly different from gain-of-function variants in the same gene.

Potassium channels in the neuronal homeostasis and neurodegenerative pathways underlying Alzheimer's disease: An update

With more than 80 subunits, potassium (K⁺) channels represent a group of ion channels showing high degree of diversity and ubiquity. They play important role in the control of membrane depolarization and cell excitability in several tissues, including the brain. Controlling the intracellular and extracellular K⁺ flow in cells, they also modulate the hormone and neurotransmitter release, apoptosis and cell proliferation. It is therefore not surprising that an improper functioning of K⁺ channels in neurons has been associated with pathophysiology of a wide range of neurological disorders, especially Alzheimer's disease (AD). This review aims to give a comprehensive overview of the basic properties and pathophysiological functions of the main classes of K⁺ channels in the context of disease processes, also discussing the progress, challenges and opportunities to develop drugs targeting these channels as potential pharmacological approach for AD treatment.

The enantiomer pair of 24S- and 24R-hydroxycholesterol differentially alter activity of large-conductance Ca2+ -dependent K+ (slo1 BK) channel

24S-hydroxycholesterol (HC) is most abundant oxysterols in the brain, passes through blood brain barrier, and is therefore regarded as an intermediary for brain cholesterol elimination. We reported that large-conductance Ca²⁺ - and voltage-activated K⁺ (slo1 BK) channels are suppressed by this oxysterol, which is presumably intercalated into cell membrane to access the outer surface of the channel. Such an outer approach would make it difficult to interact with the inner, ion-conducting part of the channel. The present findings showed that 24R-HC, the racemic counterpart of 24S-HC, also suppressed slo1 BK channel but in a different voltage-dependent manner. There was a difference between the effects of the two enantiomers on activation kinetics but not on deactivation kinetics. It is suggested that the chirality contributes to the efficacy of channel blockers that act from outer lipophilic parts of channels, as with those which act on the inner, ion-permeable surface.

24S-hydroxycholesterol alters activity of large-conductance Ca2+-dependent K+ (slo1 BK) channel through intercalation into plasma membrane

Oxysterols, oxidization products of cholesterol, are regarded as bioactive lipids affecting various physiological functions. However, little is known of their effects on ion channels. Using inside-out patch clamp recording, we found that naturally occurring side-chain oxidized oxysterols, 20S‑hydroxycholesterol, 22R‑hydroxycholesterol, 24S‑hydroxycholestero, 25‑hydroxycholesterol, and 27‑hydroxycholesterol, induced current reduction of large-conductance Ca²⁺- and voltage-activated K⁺ (slo1 BK) channels heterologously expressed in HEK293T cells. In contrast with side-chain oxidized oxysterols, naturally occurring ring oxidized ones, 7α‑hydroxycholesterol and 7‑ketocholesterol were without effect. By using 24S‑hydroxycholesterol (24S‑HC), the major brain oxysterol, we explored the inhibition mechanism. 24S‑HC inhibited Slo1 BK channels with an IC₅₀ of ~2 μM, and decreased macroscopic current by ~60%. This marked current decrease was accompanied by a rightward shift in the conductance-voltage relationship and a slowed activation kinetics, with the deactivation kinetics unaltered. Furthermore, the membrane sterol scavenger γ‑cyclodextrin was found to rescue slo1 BK channels from the inhibition, implicating that 24S-HC may be intercalated into the plasma membrane to affect the channel. These findings unveil a novel physiological importance of oxysterols from a new angle that involves ion channel regulation.

Overexpression of Kcnmb2 in Dorsal CA1 of Offspring Mice Rescues Hippocampal Dysfunction Caused by a Methyl Donor-Rich Paternal Diet

BK channels are known regulators of neuronal excitability, synaptic plasticity, and memory. Our previous study showed that a paternal methyl donor-rich diet reduced the expression of Kcnmb2, which encodes BK channel subunit beta 2, and caused memory deficits in offspring mice. To explore the underlying cellular mechanisms, we investigated the intrinsic and synaptic properties of CA1 pyramidal neurons of the F1 offspring mice whose fathers were fed with either a methyl donor-rich diet (MD) or regular control diet (CD) for 6 weeks before mating. Whole-cell patch-clamp recordings of CA1 pyramidal neurons revealed a decrease in intrinsic excitability and reduced frequency of inhibitory post-synaptic currents in MD F1 mice compared to the CD F1 controls. AAV-based overexpression of Kcnmb2 in dorsal CA1 ameliorated changes in neuronal excitability, synaptic transmission, and plasticity in MD F1 mice. Our findings thus indicate that a transient paternal exposure to a methyl donor-rich diet prior to mating alters Kcnmb2-sensitive hippocampal functions in offspring animals.

Physiological Roles and Therapeutic Potential of Ca2+ Activated Potassium Channels in the Nervous System

Within the potassium ion channel family, calcium activated potassium (K_Ca) channels are unique in their ability to couple intracellular Ca²⁺ signals to membrane potential variations. K_Ca channels are diversely distributed throughout the central nervous system and play fundamental roles ranging from regulating neuronal excitability to controlling neurotransmitter release. The physiological versatility of K_Ca channels is enhanced by alternative splicing and co-assembly with auxiliary subunits, leading to fundamental differences in distribution, subunit composition and pharmacological profiles. Thus, understanding specific K_Ca channels’ mechanisms in neuronal function is challenging. Based on their single channel conductance, K_Ca channels are divided into three subtypes: small (SK, 4–14 pS), intermediate (IK, 32–39 pS) and big potassium (BK, 200–300 pS) channels. This review describes the biophysical characteristics of these K_Ca channels, as well as their physiological roles and pathological implications. In addition, we also discuss the current pharmacological strategies and challenges to target K_Ca channels for the treatment of various neurological and psychiatric disorders.

Impaired retention of depression-like behavior in a mouse model of Alzheimer's disease

By using a 5-day forced swimming test (FS) that we previously developed, swim immobility was induced in 3xTg Alzheimer's model mice and wild-type (WT) mice. After the initial 5-day FS, the next and last swimming session was performed at a 4-week interval, during which the immobility was reduced in 3xTg mice, but was maintained fully in WT mice. After FS, context-dependent fear learning was normally induced in WT mice, but was impaired in 3xTg mice, suggesting that FS may exaggerate cognitive deficits typical to 3xTg mice. Hippocampal long-term potentiation (LTP) at Schaffer collateral-CA1 synapses was suppressed by FS in WT mice, but not in 3xTg mice, indicating that FS modifies LTP in the WT mouse hippocampus, but not in 3xTg tissue. FS increased excitability of cingulate cortex pyramidal cells similarly in WT and 3xTg mice. Agreeing with our previous finding that expression of Homer1a protein is decreased in the cingulate cortex in harmony with FS-induced immobility, western blot showed that Homer1a expression is reduced by FS in the WT mice. In 3xTg mice, by contrast, FS failed to reduce Homer1a expression. The disrupted endurance of FS-induced immobility in 3xTg mice appears to be attributable to impaired cognition typical to this genotype. Failure of FS to alter LTP magnitude might be related to unaltered Homer1a expression after FS in 3xTg mice.

Stimulatory actions of a novel thiourea derivative on large-conductance, calcium-activated potassium channels

In this study, we examine whether an anti-inflammatory thiourea derivative, compound #326, actions on ion channels. The effects of compound #326 on Ca²⁺ -activated K⁺ channels were evaluated by patch-clamp recordings obtained in cell-attached, inside-out or whole-cell configuration. In pituitary GH₃ cells, compound #326 increased the amplitude of Ca²⁺ -activated K⁺ currents (I_K(Ca) ) with an EC₅₀ value of 11.6 μM, which was reversed by verruculogen, but not tolbutamide or TRAM-34. Under inside-out configuration, a bath application of compound #326 raised the probability of large-conductance Ca²⁺ -activated K⁺ (BK_Ca ) channels. The activation curve of BK_Ca channels was shifted to less depolarised potential with no modification of the gating charge of the curve; consequently, the difference of free energy was reduced in the presence of this compound. Compound #326-stimulated activity of BK_Ca channels is explained by a shortening of mean closed time, despite its inability to alter single-channel conductance. Neither delayed-rectifier nor erg-mediated K⁺ currents was modified. Compound #326 decreased the peak amplitude of voltage-gated Na⁺ current with no clear change in the overall current-voltage relationship of this current. In HEK293T cells expressing α-hSlo, compound #326 enhanced BK_Ca channels effectively. Intriguingly, the inhibitory actions of compound #326 on interleukin 1β in lipopolysaccharide-activated microglia were significantly reversed by verruculogen, whereas BK_Ca channel inhibitors suppressed the expressions of inducible nitric oxide synthase. The BK_Ca channels could be an important target for compound #326 if similar in vivo results occur, and the multi-functionality of BK_Ca channels in modulating microglial immunity merit further investigation.

Molecular Determinants of BK Channel Functional Diversity and Functioning

Large-conductance Ca2+- and voltage-activated K+ (BK) channels play many physiological roles ranging from the maintenance of smooth muscle tone to hearing and neurosecretion. BK channels are tetramers in which the pore-forming α subunit is coded by a single gene ( Slowpoke, KCNMA1). In this review, we first highlight the physiological importance of this ubiquitous channel, emphasizing the role that BK channels play in different channelopathies. We next discuss the modular nature of BK channel-forming protein, in which the different modules (the voltage sensor and the Ca2+ binding sites) communicate with the pore gates allosterically. In this regard, we review in detail the allosteric models proposed to explain channel activation and how the models are related to channel structure. Considering their extremely large conductance and unique selectivity to K+, we also offer an account of how these two apparently paradoxical characteristics can be understood consistently in unison, and what we have learned about the conduction system and the activation gates using ions, blockers, and toxins. Attention is paid here to the molecular nature of the voltage sensor and the Ca2+ binding sites that are located in a gating ring of known crystal structure and constituted by four COOH termini. Despite the fact that BK channels are coded by a single gene, diversity is obtained by means of alternative splicing and modulatory β and γ subunits. We finish this review by describing how the association of the α subunit with β or with γ subunits can change the BK channel phenotype and pharmacology.

Calycosin and Formononetin Induce Endothelium-Dependent Vasodilation by the Activation of Large-Conductance Ca2+-Activated K+ Channels (BKCa)

Calycosin and formononetin are two structurally similar isoflavonoids that have been shown to induce vasodilation in aorta and conduit arteries, but study of their actions on endothelial functions is lacking. Here, we demonstrated that both isoflavonoids relaxed rat mesenteric resistance arteries in a concentration-dependent manner, which was reduced by endothelial disruption and nitric oxide synthase (NOS) inhibition, indicating the involvement of both endothelium and vascular smooth muscle. In addition, the endothelium-dependent vasodilation, but not the endothelium-independent vasodilation, was blocked by BK_Ca inhibitor iberiotoxin (IbTX). Using human umbilical vein endothelial cells (HUVECs) as a model, we showed calycosin and formononetin induced dose-dependent outwardly rectifying K⁺ currents using whole cell patch clamp. These currents were blocked by tetraethylammonium chloride (TEACl), charybdotoxin (ChTX), or IbTX, but not apamin. We further demonstrated that both isoflavonoids significantly increased nitric oxide (NO) production and upregulated the activities and expressions of endothelial NOS (eNOS) and neuronal NOS (nNOS). These results suggested that calycosin and formononetin act as endothelial BK_Ca activators for mediating endothelium-dependent vasodilation through enhancing endothelium hyperpolarization and NO production. Since activation of BK_Ca plays a role in improving behavioral and cognitive disorders, we suggested that these two isoflavonoids could provide beneficial effects to cognitive disorders through vascular regulation.

Stressful learning paradigm precludes manifestation of cognitive ability in sphingomyelin synthase-2 knockout mice

Sphingomyelin synthases (SMSs) are enzymes converting ceramide to sphingomyelin. The behavioral phenotype attributed to their disruption has not been well described. We examined learning ability and hippocampal synaptic plasticity in mice deficient in SMS2 (SMS2 KO). In context-dependent fear learning and novel object recognition test, no difference in learning ability was detected in SMS2 KO and wild-type (WT) mice. By contrast, achievement of the Morris water maze (MWM) test was deteriorated in SMS2 KO mice. In the hippocampal CA1, while the basic synaptic transmission was normal, both short- and long-term synaptic plasticity was moderately suppressed. We interpret that the MWM test taking place in wet environment may represent learning paradigm under more stressful condition than those performed in dry conditions, and that the learning ability of SMS2 KO mice failed to manifest itself fully in stressful situations. In agreement, forced swimming induced depression-like behavior more easily in SMS2 KO mice. Mass spectrometry suggested a slightly altered species distribution of ceramide in the hippocampus of SMS2 KO mice. These findings support the proposal that altered synthesis of ceramide, which is the substrate of SMS2 and therefore expected to be modified in SMS2 KO mice, is associated with depression-like tendency in animal models and depressive disorder in humans.

BK Channels in the Central Nervous System

Large conductance Ca(2+)- and voltage-activated K(+) (BK) channels are widely distributed in the postnatal central nervous system (CNS). BK channels play a pleiotropic role in regulating the activity of brain and spinal cord neural circuits by providing a negative feedback mechanism for local increases in intracellular Ca(2+) concentrations. In neurons, they regulate the timing and duration of K(+) influx such that they can either increase or decrease firing depending on the cellular context, and they can suppress neurotransmitter release from presynaptic terminals. In addition, BK channels located in astrocytes and arterial myocytes modulate cerebral blood flow. Not surprisingly, both loss and gain of BK channel function have been associated with CNS disorders such as epilepsy, ataxia, mental retardation, and chronic pain. On the other hand, the neuroprotective role played by BK channels in a number of pathological situations could potentially be leveraged to correct neurological dysfunction.

Synthetic Studies on Tricyclic Diterpenoids: Direct Allylic Amination Reaction of Isopimaric Acid Derivatives

A selective synthesis of 7- or 14-nitrogen containing tricyclic diterpenoids was completed according to a strategy in which the key step was the catalyzed direct allylic amination of methyl 14α-hydroxy-15,16-dihydroisopimarate with a wide variety of nitrogenated nucleophiles. It was revealed that the selectivity of the reaction depends on the nature of nucleophile. The catalyzed reaction of the mentioned diterpenoid allylic alcohol with 3-nitroaniline, 3-(trifluoromethyl)aniline, and 4-(trifluoromethyl)aniline yield the subsequent 7α-, 7β- and 14αnitrogen-containing diterpenoids. The reaction with 2-nitroaniline, 4-nitro-2-chloroaniline, 4-methoxy-2-nitroaniline, phenylsulfamide, or tert-butyl carbamate proceeds with the formation of 7α-nitrogen-substituted diterpenoids as the main products.

Matrine improves cognitive impairment and modulates the balance of Th17/Treg cytokines in a rat model of Aβ1-42-induced Alzheimer's disease

Matrine (MAT) has been reported for its anti-inflammatory and neuroprotective effects. However, little is known about its effects on Th17/Treg cytokines and cognitive impairment in Alzheimer's disease (AD). In the present study, we injected Aβ_1-42 to the hippocampus of the rat to induce AD. Three groups of the AD rats were treated with MAT (25, 100 or 200 mg/kg/day, respectively) by intraperitoneal injection for 5 weeks. Levels of Th17 cell cytokines [interleukin (IL)-17A and IL-23] and regulatory T (Treg) cell cytokines [transforming growth factor β (TGF-β) and IL-35] in homogenates of the brain cortex and hippocampus were measured using enzyme-linked immunosorbent assay (ELISA) kits. The mRNA expressions of Th17 cell specific transcription factor RORγt and Treg cell specific transcription factor Foxp3 in the brain cortex and hippocampus were quantified by real-time RT-PCR. Learning and memory ability of the rats were evaluated by Morris water maze test and novel object recognition test. ELISA detections showed the AD rats had increased levels of IL-17A and IL-23 as well as decreased levels of TGF-β and IL-35. Matrine (100 and 200 mg/kg/day) significantly reversed the alternations of Th17/Treg cytokines induced by Aβ_1-42 injection, decreased RORγt mRNA expression, increased Foxp3 mRNA expression and improved the learning and memory ability in the AD rats. The findings demonstrated that the AD rats had imbalance of Th17/Treg cytokines in the brain. MAT could dose-dependently restore the balance of Th17/Treg cytokines and attenuate the cognitive impairment in AD rats.

Battling Alzheimer's Disease: Targeting SUMOylation-Mediated Pathways

SUMO (small ubiquitin-like modifier) conjugation is a critically important control process in all eukaryotic cells, because it acts as a biochemical switch and regulates the function of hundreds of proteins in many different pathways. Although the diverse functional consequences and molecular targets of SUMOylation remain largely unknown, SUMOylation is becoming increasingly implicated in the pathophysiology of Alzheimer's disease (AD). Apart from the central SUMO-modified disease-associated proteins, such as amyloid precursor protein, amyloid β, and tau, SUMOylation also regulates several other processes underlying AD. These are involved in inflammation, mitochondrial dynamics, synaptic transmission and plasticity, as well as in protective responses to cell stress. Herein, we review current reports on the involvement of SUMOylation in AD, and present an overview of potential SUMO targets and pathways underlying AD pathogenesis.