Activation of BKCa Channels Mediates Hippocampal Neuronal Death After Reoxygenation and Reperfusion

Hypoxic Regulation of the Large-Conductance, Calcium and Voltage-Activated Potassium Channel, BK

Hypoxia is a condition characterized by a reduction of cellular oxygen levels derived from alterations in oxygen balance. Hypoxic events trigger changes in cell-signaling cascades, oxidative stress, activation of pro-inflammatory molecules, and growth factors, influencing the activity of various ion channel families and leading to diverse cardiovascular diseases such as myocardial infarction, ischemic stroke, and hypertension. The large-conductance, calcium and voltage-activated potassium channel (BK) has a central role in the mechanism of oxygen (O₂) sensing and its activity has been related to the hypoxic response. BK channels are ubiquitously expressed, and they are composed by the pore-forming α subunit and the regulatory subunits β (β1–β4), γ (γ1–γ4), and LINGO1. The modification of biophysical properties of BK channels by β subunits underly a myriad of physiological function of these proteins. Hypoxia induces tissue-specific modifications of BK channel α and β subunits expression. Moreover, hypoxia modifies channel activation kinetics and voltage and/or calcium dependence. The reported effects on the BK channel properties are associated with events such as the increase of reactive oxygen species (ROS) production, increases of intracellular Calcium ([Ca²⁺]_i), the regulation by Hypoxia-inducible factor 1α (HIF-1α), and the interaction with hemeproteins. Bronchial asthma, chronic obstructive pulmonary diseases (COPD), and obstructive sleep apnea (OSA), among others, can provoke hypoxia. Untreated OSA patients showed a decrease in BK-β1 subunit mRNA levels and high arterial tension. Treatment with continuous positive airway pressure (CPAP) upregulated β1 subunit mRNA level, decreased arterial pressures, and improved endothelial function coupled with a reduction in morbidity and mortality associated with OSA. These reports suggest that the BK channel has a role in the response involved in hypoxia-associated hypertension derived from OSA. Thus, this review aims to describe the mechanisms involved in the BK channel activation after a hypoxic stimulus and their relationship with disorders like OSA. A deep understanding of the molecular mechanism involved in hypoxic response may help in the therapeutic approaches to treat the pathological processes associated with diseases involving cellular hypoxia.

Acupuncture ameliorates neurological function in rats with cerebral ischemia-reperfusion by regulating the opening of large-conductance Ca2+ -activated potassium channels

Acupuncture has a good effect on improving neurological function after cerebral ischemia-reperfusion, but there are few studies on the neuroprotective effect of acupuncture from the perspective of ion channel cellular electrophysiology. Studies have shown that the over activation of large-conductance Ca²⁺ -activated potassium channel （BKCa） after cerebral ischemia-reperfusion can reduce the excitability of neurons and induce apoptosis. This study intends to establish middle cerebral artery occlusion/reperfusion (MCAO/R) model, with acupuncture at GV26 as the intervention measure, using patch-clamp technique to record the electrophysiological changes of BKCa channel. The results showed that the neurological function score of MCAO/R rats was significantly decreased, and the conductance, open dwell time and open probability of BKCa channel in hippocampal CA1 neurons of MCAO/R rats were significantly increased. Acupuncture at GV26 could significantly improve the neurological function scores of MCAO/R rats, and reduce the conductance, open dwell time, and open probability of BKCa channel. The effect of acupuncture at GV26 was significantly better than acupuncture at non-acupuncture point. The neuroprotective effect of acupuncture at GV26 after cerebral ischemia-reperfusion may be related to regulating the electrophysiological characteristics of BKCa channel opening.

Endothelium-derived hydrogen sulfide acts as a hyperpolarizing factor and exerts neuroprotective effects via activation of large-conductance Ca2+ -activated K+ channels

BACKGROUND AND PURPOSE

Endothelium-derived hyperpolarizing factor (EDHF) has been suggested as a therapeutic target for vascular protection against ischaemic brain injury. However, the molecular entity of EDHF and its action on neurons remains unclear. This study was undertaken to demonstrate whether the hydrogen sulfide (H₂ S) acts as EDHF and exerts neuroprotective effect via large-conductance Ca²⁺ -activated K⁺ (BK_Ca /K_Ca 1.1) channels.

EXPERIMENTAL APPROACH

The whole-cell patch-clamp technology was used to record the changes of BK_Ca currents in rat neurons induced by EDHF. The cerebral ischaemia/reperfusion model of mice and oxygen-glucose deprivation/reoxygenation (OGD/R) model of neurons were used to explore the neuroprotection of EDHF by activating BK_Ca channels in these neurons.

KEY RESULTS

Increases of BK_Ca currents and membrane hyperpolarization in hippocampal neurons induced by EDHF could be markedly inhibited by BK_Ca channel inhibitor iberiotoxin or endothelial H₂ S synthase inhibitor propargylglycine. The H₂ S donor, NaHS-induced BK_Ca current and membrane hyperpolarization in neurons were also inhibited by iberiotoxin, suggesting that H₂ S acts as EDHF and activates the neuronal BK_Ca channels. Besides, we found that the protective effect of endothelium-derived H₂ S against mice cerebral ischaemia/reperfusion injury was disrupted by iberiotoxin. Importantly, the inhibitory effect of NaHS or BK_Ca channel opener on OGD/R-induced neuron injury and the increment of intracellular Ca²⁺ level could be inhibited by iberiotoxin but enhanced by co-application with L-type but not T-type calcium channel inhibitor.

CONCLUSION AND IMPLICATIONS

Endothelium-derived H₂ S acts as EDHF and exerts neuroprotective effects via activating the BK_Ca channels and then inhibiting the T-type calcium channels in hippocampal neurons.

[Acupuncture in the prevention and treatment of stroke: a review of foreign studies]

Acupuncture has been recommended by the World Health Organization (WHO) as an alternative and complementary method for treating stroke and a way to increase the effectiveness of rehabilitation. The data available in the literature suggest that acupuncture has a beneficial effect on the status of patients with stroke. The mechanism of action of acupuncture for stroke includes the following components: 1) stimulation of neurogenesis and cell proliferation in the CNS; 2) regulation of cerebral blood flow; 3) antiapoptosis; 4) regulation of neurotransmitters; 5) improvement of the neuronal synaptic function, stimulation of long-term potentiation; 6) stimulation of neuroplasticity; and 7) decrease in blood-brain barrier permeability. Acupuncture has been proven to have a positive impact on the restoration of stroke-related dysfunctions, such as motor disorders, spasticity, cognitive impairment, and dysphagia. The most commonly used acupuncture points for the treatment of motor disorders are GV20, GB20, LI4, ST36, SP6, LI11, GB39, and motor scalp area; those for the treatment of cognitive dysfunction are GV20 and EX-HN-1, and those for the treatment of dysphagia are GV20, GV16, and CV23. A review of the literature indicates that studies of the clinical potential of acupuncture in the treatment of complications and the prevention of stroke are insufficient. It is assumed that the international community's recent interest in acupuncture methods used in the treatment of stroke will lead to the emergence of new studies and publications.

BKCa channels regulate the immunomodulatory properties of WJ-MSCs by affecting the exosome protein profiles during the inflammatory response

Background

Wharton’s jelly-derived mesenchymal stem cells (WJ-MSCs) from the human umbilical cord have been studied extensively due to their immunomodulatory functions. Large-conductance Ca²⁺-activated K⁺ (BKCa channels) channels are involved in many inflammatory responses, but their involvement in the anti-inflammatory activity of WJ-MSCs is unknown. The underlying molecular mechanism, through which BKCa channels mediate the immunomodulation of WJ-MSC, which may include changes in exosomes proteomics, has not yet been clarified.

Methods

Alizarin staining, Oil Red O staining, and flow cytometry were used to identify WJ-MSCs, which were isolated from human umbilical cord Wharton’s jelly. BKCa channels were detected in WJ-MSCs using western blotting, real-time polymerase chain reaction (real-time PCR), and electrophysiology, and cytokine expression was examined using real-time PCR and enzyme-linked immunosorbent assays (ELISAs). Exosomes were characterized using transmission electron microscopy and nanoparticle tracking analysis. Proteomics analysis was performed to explore exosomal proteomic profiles.

Results

The cells derived from human umbilical cord Wharton’s jelly were identified as MSCs. BKCa channels were detected in the isolated WJ-MSCs, and the expression of these channels increased after lipopolysaccharide (LPS) stimulation. BKCa channels blockade in LPS-treated WJ-MSCs induced apoptosis and decreased interleukin-6 (IL-6) expression. Furthermore, THP-1 cells (human monocytic cell line) stimulated with LPS/interferon gamma (IFN-γ) produced more anti-inflammatory cytokines after treatment with exosomes derived from BKCa channel-knockdown WJ-MSCs (si-exo). We also observed altered expression of mitochondrial ATP synthase alpha subunit (ATP5A1), filamin B, and other proteins in si-exo, which might increase the anti-inflammatory activity of macrophages.

Conclusions

Our study described the functional expression of BKCa channels in WJ-MSCs, and BKCa channels regulated the immunomodulatory properties of WJ-MSCs by affecting the exosomal protein profiles during the inflammatory response.

Mitigating effect of paxilline against injury produced by Cd2+ in rat pheochromocytoma PC12 and ascites hepatoma AS-30D cells

On two rat cell lines, pheochromocytoma PC12 and ascites hepatoma AS-30D, and on rat liver mitochondria we studied action of paxilline (lipophilic mycotoxin from fungus Penicillium paxilli which is blocker of large-conductance potassium channels) against harmful effects of Cd(II) - one of the most dangerous toxic metals and environmental pollutants. We investigated an influence of paxilline on cell viability and mitochondrial function in the presence and in the absence of Cd²⁺. As found, paxilline protected partially from the Cd²⁺-induced cytotoxicity, namely taken in concentration of 1 μM it decreased the Cd²⁺-induced cell necrosis in average by 10-14 or 13-23% for AS-30D and PC12 cells, respectively. Nevertheless, paxilline did not affect the Cd²⁺-induced apoptosis of AS-30D cells. The alleviating concentration of paxilline reduced an intracellular production of reactive oxygen species (ROS) in PC12 cells intoxicated by Cd²⁺ and enhanced the ROS production in control AS-30D cells; however, it weakly affected mitochondrial membrane potential of the cells in the absence and in the presence of Cd²⁺. The ameliorative concentration of paxilline decreased the maximal respiration rates of control cells of both types after short-term (3-5 h) treatment with it while the rates reached their control levels after long-term (24-48 h) incubation with the drug. Paxilline was not protective against the Cd²⁺-induced membrane permeability and respiration rate changes in isolated rat liver mitochondria. As result, the mitochondrial electron transport chain was concluded to contribute in the mitigating effect of paxilline against the Cd²⁺-produced cell injury.

Tanshinone IIA Suppresses Hypoxia-induced Apoptosis in Medial Vestibular Nucleus Cells Via a Skp2/BKCa Axis

BACKGROUND

The aim of the present study was to investigate the protective effects of Tanshinone IIA (Tan IIA) on hypoxia-induced injury in the medial vestibular nucleus (MVN) cells.

METHODS

An in vitro hypoxia model was established using MVN cells exposed to hypoxia. The hypoxia-induced cell damage was confirmed by assessing cell viability, apoptosis and expression of apoptosis-associated proteins. Oxidative stress and related indicators were also measured following hypoxia modeling and Tan IIA treatment, and the genes potentially involved in the response were predicted using multiple GEO datasets.

RESULTS

The results of the present study showed that Tan IIA significantly increased cell viability, decreased cell apoptosis and decreased the ratio of Bax/Bcl-2 in hypoxia treated cells. In addition, hypoxia treatment increased oxidative stress in MVN cells, and treatment with Tan IIA reduced the oxidative stress. The expression of SPhase Kinase Associated Protein 2 (SKP2) was upregulated in hypoxia treated cells, and Tan IIA treatment reduced the expression of SKP2. Mechanistically, SKP2 interacted with large-conductance Ca2+-activated K+ channels (BKCa), regulating its expression, and BKCa knockdown alleviated the protective effects of Tan IIA on hypoxia induced cell apoptosis.

CONCLUSION

The results of the present study suggested that Tan IIA had a protective effect on hypoxia-induced cell damage through its anti-apoptotic and anti-oxidative activity via an SKP2/BKCa axis. These findings suggest that Tan IIA may be a potential therapeutic for the treatment of hypoxia-induced vertigo.

BKCa channel is a molecular target of vitamin C to protect against ischemic brain stroke

Epidemiological studies have demonstrated that vitamin C decreases the risk of stroke, which has generally been ascribed to its function as antioxidant and free radical scavenger. However, whether there is a defined molecular target for vitamin C on stroke is unknown. Utilizing middle cerebral artery occlusion (MCAO) in rats as a model for ischemic stroke, we demonstrated that long-term, low-dose administration of vitamin C prior to MCAO could exert significant neuroprotective effect on the brain damage. The long-term, low-dose vitamin C pretreated rats had decreased brain infarct size and decreased neurological deficit score compared with the vehicle or single high dose pretreated MCAO rats. Furthermore, electrophysiological experiments using patch clamp technique showed that vitamin C increased the whole-cell current of the large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel. Moreover, vitamin C increased the open probability of the channel without change its amplitude. Importantly, blockade of the BK_Ca channels abolished the neuroprotective effect of vitamin C on MCAO. Therefore, this study shows that long-term, low-dose pretreatment with vitamin C could reduce MCAO-induced brain damage through activation of the BK_Ca channels, suggesting that the BK_Ca channel is a molecular target of vitamin C on stroke.

Total flavones of Rhododendron simsii Planch flower protect rat hippocampal neuron from hypoxia-reoxygenation injury via activation of BKCa channel

OBJECTIVES

To study the effects of total flavones of Rhododendra simsii Planch flower (TFR) on hypoxia/reoxygenation (H/R) injury in rat hippocampal neurons and its underlying mechanism.

METHOD

Model of H/R was established in newborn rat primary cultured hippocampal neuron. Lactate dehydrogenase (LDH) and neuron-specific enolase (NSE) activity as well as malondialdehyde (MDA) content in cultured supernatants of the neurons were examined. Methyl thiazolyl tetrazolium assay and Hoechst33258 staining were, respectively, used to detect cell viability and apoptosis of neurons. Protein expression and current of BK_Ca channel were assessed by using Western blotting and whole-cell patch-clamp methods, respectively.

KEY FINDINGS

In the ranges of 3.7-300 mg/l, TFR significantly inhibited H/R-induced decrease of neuronal viability and increases of LDH, NSE and MDA in the supernatants as well as apoptosis; TFR 33.3, 100 and 300 mg/l markedly increased current of BK_Ca channel rather than the BK_Ca channel protein expression in the neurons.

CONCLUSIONS

Total flavones of R. simsii Planch flower had a protective effect against H/R injury in rat hippocampal neuron, and activation of BK_Ca channel may contribute to the neuroprotection.

Propofol Protects Hippocampal Neurons from Hypoxia-Reoxygenation Injury by Decreasing Calcineurin-Induced Calcium Overload and Activating YAP Signaling

Objectives

Propofol is a popular anesthetic drug that is neuroprotective. However, the mechanisms of propofol for hippocampal neuroprotection remain elusive. This study is aimed at investigating the neuroprotective effect and mechanism of propofol in hippocampal neurons exposed to ischemia-reperfusion (I/R) injury.

Methods

Hypoxia-reoxygenated (H/R) HT-22 cells were used to mimic I/R injury of the hippocampus in vitro. An MTT assay was used to determine cell viability. Cell apoptosis was detected by a TUNEL assay and a flow cytometry cell apoptosis assay. Expression levels of proteins were measured by Western blotting. Intracellular calcium was assessed by Fura-2/AM staining. Flow cytometry was used to determine the mitochondrial membrane potential (MMP). Coimmunoprecipitation was used to evaluate the stability of the FKBP-RyR complex. Calcineurin enzymatic activity was measured with a colorimetric method. YAP nuclear translocation was tested by immunofluorescence staining.

Results

H/R induced HT-22 cell viability depression, and apoptosis was reversed by propofol treatment. Propofol could alleviate H/R-induced intracellular calcium accumulation and MMP loss by inhibiting calcineurin activity and FKBP12.6-RyR disassociation in a concentration-dependent manner. In addition, YAP expression was crucial for propofol to protect HT-22 cell apoptosis from H/R injury. Propofol could activate YAP through dephosphorylation. Activated YAP stimulated the transcription of the Bcl2 gene, which promotes cellular survival. Our data also demonstrated that propofol activated YAP through the RhoA-Lats1 pathway without large G proteins or MST involvement. In addition, we showed that there was no interaction between calcineurin signaling and YAP activation in HT-22 cells.

Conclusions

Propofol protected hippocampal neurons from I/R injury through two independent signaling pathways, including the calcineurin/FKBP12.6-RyR/calcium overload pathway and the RhoA/Lats1/YAP/Bcl-2 pathway.

Large-conductance Ca(2+)-activated K(+) channel involvement in suppression of cerebral ischemia/reperfusion injury after electroacupuncture at Shuigou (GV26) acupoint in rats

Excess activation and expression of large-conductance Ca²⁺-activated K⁺ channels (BKCa channels) may be an important mechanism for delayed neuronal death after cerebral ischemia/reperfusion injury. Electroacupuncture can regulate BKCa channels after cerebral ischemia/reperfusion injury, but the precise mechanism remains unclear. In this study, we established a rat model of cerebral ischemia/reperfusion injury. Model rats received electroacupuncture of 1 mA and 2 Hz at Shuigou (GV26) for 10 minutes, once every 12 hours for a total of six times in 72 hours. We found that in cerebral ischemia/reperfusion injury rats, ischemic changes in the cerebral cortex were mitigated after electroacupuncture. Moreover, BKCa channel protein and mRNA expression were reduced in the cerebral cortex and neurological function noticeably improved. These changes did not occur after electroacupuncture at a non-acupoint (5 mm lateral to the left side of Shuigou). Thus, our findings indicate that electroacupuncture at Shuigou improves neurological function in rats following cerebral ischemia/reperfusion injury, and may be associated with down-regulation of BKCa channel protein and mRNA expression. Additionally, our results suggest that the Shuigou acupoint has functional specificity.

Functional Role of Mitochondrial and Nuclear BK Channels

BK channels are important for the regulation of many cell functions. The significance of plasma membrane BK channels in the control of action potentials, resting membrane potential, and neurotransmitter release is well established; however, the composition and functions of mitochondrial and nuclear BK (nBK) channels are largely unknown. In this chapter, we summarize the recent findings on the subcellular localization, biophysical, and pharmacological properties of mitochondrial and nBK channels and discuss their molecular identity and physiological functions.

Ion channel expression in the developing enteric nervous system

The enteric nervous system arises from neural crest-derived cells (ENCCs) that migrate caudally along the embryonic gut. The expression of ion channels by ENCCs in embryonic mice was investigated using a PCR-based array, RT-PCR and immunohistochemistry. Many ion channels, including chloride, calcium, potassium and sodium channels were already expressed by ENCCs at E11.5. There was an increase in the expression of numerous ion channel genes between E11.5 and E14.5, which coincides with ENCC migration and the first extension of neurites by enteric neurons. Previous studies have shown that a variety of ion channels regulates neurite extension and migration of many cell types. Pharmacological inhibition of a range of chloride or calcium channels had no effect on ENCC migration in cultured explants or neuritogenesis in vitro. The non-selective potassium channel inhibitors, TEA and 4-AP, retarded ENCC migration and neuritogenesis, but only at concentrations that also resulted in cell death. In summary, a large range of ion channels is expressed while ENCCs are colonizing the gut, but we found no evidence that ENCC migration or neuritogenesis requires chloride, calcium or potassium channel activity. Many of the ion channels are likely to be involved in the development of electrical excitability of enteric neurons.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging

SIGNIFICANCE

Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection.

RECENT ADVANCES

Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging.

CRITICAL ISSUES

Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit.

FUTURE DIRECTIONS

Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

Voltage-gated potassium channels at the crossroads of neuronal function, ischemic tolerance, and neurodegeneration

Voltage-gated potassium (Kv) channels are widely expressed in the central and peripheral nervous system and are crucial mediators of neuronal excitability. Importantly, these channels also actively participate in cellular and molecular signaling pathways that regulate the life and death of neurons. Injury-mediated increased K(+) efflux through Kv2.1 channels promotes neuronal apoptosis, contributing to widespread neuronal loss in neurodegenerative disorders such as Alzheimer's disease and stroke. In contrast, some forms of neuronal activity can dramatically alter Kv2.1 channel phosphorylation levels and influence their localization. These changes are normally accompanied by modifications in channel voltage dependence, which may be neuroprotective within the context of ischemic injury. Kv1 and Kv7 channel dysfunction leads to neuronal hyperexcitability that critically contributes to the pathophysiology of human clinical disorders such as episodic ataxia and epilepsy. This review summarizes the neurotoxic, neuroprotective, and neuroregulatory roles of Kv channels and highlights the consequences of Kv channel dysfunction on neuronal physiology. The studies described in this review thus underscore the importance of normal Kv channel function in neurons and emphasize the therapeutic potential of targeting Kv channels in the treatment of a wide range of neurological diseases.