Immunohistochemical study on the distribution of voltage-gated K(+) channels in rat brain following transient focal ischemia

Proteomics on the role of muscone in the "consciousness-restoring resuscitation" effect of musk on ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Musk is a representative drug of aroma-relieving traditional Chinese medicine, and it is a commonly used traditional Chinese medicine for the treatment of ischemic stroke. Muscone is the core medicinal component of musk.

AIM OF THE STUDY

We sought to identify the target of muscone in the treatment of ischemic stroke using network pharmacology, an animal model of ischemic stroke, and differential proteomics.

MATERIALS AND METHODS

The drug targets of muscone in the treatment of ischemic stroke were predicted and analyzed using information derived from sources such as the Traditional Chinese Medicine Systems Pharmacology database and Swiss Target Prediction tool. The animal model of focal cerebral ischemia was established by suture-based occlusion of the middle cerebral artery of rats. The rats were divided into six groups: sham-operated control, model, musk, muscone1, muscone2, and muscone3. Neurological deficit scores were calculated after intragastric administration of musk or muscone. The microcirculation blood flow of the pia mater was detected using a laser speckle blood flow meter. The cerebral infarction rate was detected by 2,3,5-triphenyltetrazolium chloride staining. The necrosis rate of the cerebral cortex and the hippocampal neurons was detected by hematoxylin and eosin staining. Blood-brain barrier damage was detected by the Evans blue method. Quantitative proteomics analysis in the sham-operated control, model, and muscone groups was performed using tandem-mass-tags. Considering fold changes exceeding 1.2 as differential protein expression, the quantitative values were compared among groups by analysis of variance. Furthermore, a protein-protein interaction network was constructed, and differentially expressed proteins were analyzed by gene ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis.

RESULTS

Network pharmacology identified 339 targets for the intersection of 17 components of musk and cerebral ischemia-reperfusion injury. The GO and KEGG enrichment items mainly identified regulation of neuronal synaptic structure and transfer function, synaptic neurotransmitters, and receptor activity. Zoopery showed that the model group had a higher behavioral score, cerebral infarction rate, cortical and hippocampal neuron death rate, Evans blue exudation in the brain, and bilateral pia mater microcirculation blood flow differences than the sham-operated control group (P <0.01). Compared with the model group, the behavioral score, infarction rate, hippocampal neuronal mortality, and Evans blue content decreased significantly in the musk, muscone2, and muscone3 groups (P <0.05). Proteomic analysis showed that 160 genes were differentially expressed among the sham-operated control, model, and muscone groups. GO items with high enrichment included neuronal synapses, postsynaptic signal transduction, etc. KEGG items with high enrichment included cholinergic synapses, calcium signaling pathway, dopaminergic synapses, etc. Protein interaction analysis revealed that the top three protein pairs were Ndufa10/Ndufa6, Kcna2/Kcnab2, and Gsk3b/Traf6.

CONCLUSIONS

Muscone can reduce neuronal necrosis, protect the blood-brain barrier, and improve the neurological damage caused by cerebral ischemia via molecular mechanisms mainly involving the regulation of neuronal synaptic connections. Muscone is an important active component responsible for the "consciousness-restoring resuscitation" effect of musk on ischemic stroke.

Ion Channels in the Paraventricular Hypothalamic Nucleus (PVN); Emerging Diversity and Functional Roles

The paraventricular nucleus of the hypothalamus (PVN) is critical for the regulation of homeostatic function. Although also important for endocrine regulation, it has been referred to as the "autonomic master controller." The emerging consensus is that the PVN is a multifunctional nucleus, with autonomic roles including (but not limited to) coordination of cardiovascular, thermoregulatory, metabolic, circadian and stress responses. However, the cellular mechanisms underlying these multifunctional roles remain poorly understood. Neurones from the PVN project to and can alter the function of sympathetic control regions in the medulla and spinal cord. Dysfunction of sympathetic pre-autonomic neurones (typically hyperactivity) is linked to several diseases including hypertension and heart failure and targeting this region with specific pharmacological or biological agents is a promising area of medical research. However, to facilitate future medical exploitation of the PVN, more detailed models of its neuronal control are required; populated by a greater compliment of constituent ion channels. Whilst the cytoarchitecture, projections and neurotransmitters present in the PVN are reasonably well documented, there have been fewer studies on the expression and interplay of ion channels. In this review we bring together an up to date analysis of PVN ion channel studies and discuss how these channels may interact to control, in particular, the activity of the sympathetic system.

Hypothalamic Ion Channels in Hypertension

Hypertension is a prevalent and major health problem, involving a complex integration of different organ systems, including the central nervous system (CNS). The CNS and the hypothalamus in particular are intricately involved in the pathogenesis of hypertension. In fact, evidence supports altered hypothalamic neuronal activity as a major factor contributing to increased sympathetic drive and increased blood pressure. Several mechanisms have been proposed to contribute to hypothalamic-driven sympathetic activity, including altered ion channel function. Ion channels are critical regulators of neuronal excitability and synaptic function in the brain and, thus, important for blood pressure homeostasis regulation. These include sodium channels, voltage-gated calcium channels, and potassium channels being some of them already identified in hypothalamic neurons. This brief review summarizes the hypothalamic ion channels that may be involved in hypertension, highlighting recent findings that suggest that hypothalamic ion channel modulation can affect the central control of blood pressure and, therefore, suggesting future development of interventional strategies designed to treat hypertension.

15-oxo-ETE-induced internal carotid artery constriction in hypoxic rats is mediated by potassium channels

Our own study as well as others have previously reported that hypoxia activates 15-lipoxygenase (15-LO) in the brain, causing a series of chain reactions, which exacerbates ischemic stroke. 15-hydroxyeicosatetraenoic acid (15-HETE) and 15-oxo-eicosatetraenoic acid (15-oxo-ETE/15-KETE) are 15-LO-specific metabolites of arachidonic acid (AA). 15-HETE was found to be rapidly converted into 15-oxo-ETE by 15-hydroxyprostaglandin dehydrogenase (15-PGDH) in some circumstances. We have demonstrated that 15-HETE promotes cerebral vasoconstriction during hypoxia. However, the effect of 15-oxo-ETE upon the contraction of cerebral vasculature remains unclear. To investigate this effect and to clarify the underlying mechanism, we performed immunohistochemistry and Western blot to test the expression of 15-PGDH in rat cerebral tissue, examined internal carotid artery (ICA) tension in isolated rat ICA rings. Western blot and reverse transcription polymerase chain reaction (RT-PCR) were used to analyze the expression of voltage-gated potassium (Kv) channels (Kv2.1, Kv1.5, and Kv1.1) in cultured cerebral arterial smooth muscle cells (CASMCs). The results showed that the levels of 15-PGDH expression were drastically elevated in the cerebral of rats with hypoxia, and 15-oxo-ETE enhanced ICA contraction in a dose-dependent manner. This effect was more significant in the hypoxic rats than in the normoxic rats. We also found that 15-oxo-ETE significantly attenuated the expression of Kv2.1 and Kv1.5, but not Kv1.1. In conclusion, these results suggest that 15-oxo-ETE leads to the contraction of the ICA, especially under hypoxic conditions and that specific Kv channels may play an important role in 15-oxo-ETE-induced ICA constriction.

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.

Age-related changes in the distribution of Kv1.1 and Kv3.1 in rat cochlear nuclei

OBJECTIVES

To identify age-related changes in voltage-gated K(+) (Kv) channels that contribute to temporal processing in neurons of the central auditory system, we investigated the distribution of Kv1.1 and Kv3.1 in the auditory brainstem of adult and aged rats.

METHODS

Immunohistochemistry was performed in accordance with the free-floating method described earlier.

RESULTS

Among the auditory nuclei, only the posterior ventral cochlear nucleus (PVCN) showed age-related changes. Kv1.1 immunoreactivity was increased in the octopus cell bodies, while the staining intensity was significantly decreased in the neuropil. Image analysis demonstrated the specific increase in Kv1.1 immunoreactivity in aged cochlear nucleus neurons although the mean density of the entire selection was significantly decreased. In contrast, the number of Kv1.1-immunoreactive neurons was not significantly different between control and aged groups. The immunoreactivity for Kv3.1 was decreased in the octopus cells and neuropil of aged PVCN, which was confirmed by image analysis. The number of Kv3.1-positive cells was also significantly decreased in aged PVCN.

DISCUSSION

This study may provide useful data to compare age-related changes in Kv1.1 and Kv3.1 with known physiological properties of auditory neurons.

Single cell analysis of voltage-gated potassium channels that determines neuronal types of rat hypothalamic paraventricular nucleus neurons

The hypothalamic paraventricular nucleus (PVN), a site for the integration of both the neuroendocrine and autonomic systems, has heterogeneous cell composition. These neurons are classified into type I and type II neurons based on their electrophysiological properties. In the present study, we investigated the molecular identification of voltage-gated K+ (Kv) channels, which determines a distinctive characteristic of type I PVN neurons, by means of single-cell reverse transcription-polymerase chain reaction (RT-PCR) along with slice patch clamp recordings. In order to determine the mRNA expression profiles, firstly, the PVN neurons of male rats were classified into type I and type II neurons, and then, single-cell RT-PCR and single-cell real-time RT-PCR analysis were performed using the identical cell. The single-cell RT-PCR analysis revealed that Kv1.2, Kv1.3, Kv1.4, Kv4.1, Kv4.2, and Kv4.3 were expressed both in type I and in type II neurons, and several Kv channels were co-expressed in a single PVN neuron. However, we found that the expression densities of Kv4.2 and Kv4.3 were significantly higher in type I neurons than in type II neurons. Taken together, several Kv channels encoding A-type K+ currents are present both in type I and in type II neurons, and among those, Kv4.2 and Kv4.3 are the major Kv subunits responsible for determining the distinct electrophysiological properties. Thus these 2 Kv subunits may play important roles in determining PVN cell types and regulating PVN neuronal excitability. This study further provides key molecular mechanisms for differentiating type I and type II PVN neurons.

Hypoxia-induced 15-HETE enhances the constriction of internal carotid arteries by down-regulating potassium channels

Severe hypoxia induces the constriction of internal carotid arteries (ICA), which worsens ischemic stroke in the brain. A few metabolites are presumably involved in hypoxic vasoconstriction, however, less is known about how such molecules provoke this vasoconstriction. We have investigated the influence of 15-hydroxyeicosatetrienoic acid (15-HETE) produced by 15-lipoxygenase (15-LOX) on vasoconstriction during hypoxia. As showed in our results, 15-LOX level increases in ICA endothelia and smooth muscles. 15-HETE enhances the tension of ICA ring in a dose-dependent manner, as well as attenuates the activities and expression of voltage-gated potassium channels (Kv 1.5 and Kv 2.1). Therefore, the down-regulation of Kv channels by 15-HETE during hypoxia may weaken the repolarization of action potentials and causes a dominant influx of calcium ions to enhance smooth muscle tension and ICA constriction.

Rat neonatal immune challenge alters adult responses to cerebral ischaemia

Infection, inflammation, and hyperthermia associated with cerebral ischaemia are known to contribute to enhanced neuronal cell loss and more severe behavioural deficits. Because neonatal exposure to an immune challenge has been shown to alter the severity of inflammatory and febrile responses to a further immune challenge experienced in adulthood, we hypothesised that this could also alter temperature responses and neuronal survival after ischaemia. Thus, male Sprague-Dawley rats were treated at postnatal day 14 with a single injection of the bacterial endotoxin lipopolysaccharide (LPS) and were examined as adults for temperature changes, behavioural deficits, and neuronal cell loss associated with global cerebral ischaemia after a two-vessel occlusion (2VO). Neonatally LPS-treated rats showed behavioural differences in a novel object exploration paradigm, as well as altered temperature responses to the 2VO compared with neonatally saline-treated controls. Interestingly, these neonatally LPS-treated rats also showed increased cell loss in the central nucleus of the amygdala, a region that is important in the processing of emotional responses, but that is not usually examined in animal models of cerebral ischaemia. No differences were seen in the CA1, CA3, or dentate gyrus regions of the hippocampus. This work shows the importance of examining brain regions other than the hippocampus in association with global ischaemia. We also highlight the importance of the early period of development in programming an animal's ability to deal with injury such as cerebral ischaemia in adulthood.

Increase of delayed rectifier potassium currents in large aspiny neurons in the neostriatum following transient forebrain ischemia

Large aspiny (LA) neurons in the neostriatum are resistant to cerebral ischemia whereas spiny neurons are highly vulnerable to the same insult. Excitotoxicity has been implicated as the major cause of neuronal damage after ischemia. Voltage-dependent potassium currents play important roles in controlling neuronal excitability and therefore influence the ischemic outcome. To reveal the ionic mechanisms underlying the ischemia-resistance, the delayed rectifier potassium currents (Ik) in LA neurons were studied before and at different intervals after transient forebrain ischemia using brain slices and acute dissociation preparations. The current density of Ik increased significantly 24 h after ischemia and returned to control levels 72 h following reperfusion. Among currents contributing to Ik, the margatoxin-sensitive currents increased 24 h after ischemia while the KCNQ/M current remained unchanged after ischemia. Activation of protein kinase A (PKA) down-regulated Ik in both control and ischemic LA neurons, whereas inhibition of PKA only up-regulated Ik and margatoxin-sensitive currents 72 h after ischemia, indicating an active PKA regulation on Ik at this time. Protein tyrosine kinases had a tonic inhibition on Ik to a similar extent before and after ischemia. Compared with that of control neurons, the spike width was significantly shortened 24 h after ischemia due to facilitated repolarization, which could be reversed by blocking margatoxin-sensitive currents. The increase of Ik in LA neurons might be one of the protective mechanisms against ischemic insult.

Immunohistochemical study on the distribution of the voltage-gated potassium channels in the gerbil cerebellum

Although there have been many studies on the regional distribution of Kv channels in the rat and mouse cerebellum, there are no reports about Kv channel distribution in the gerbil, which is used as an ischemia animal model. Therefore, we aimed to investigate differences in the spatial patterning of Kv channel alpha-subunit isoforms in the gerbil cerebellum. The greatest concentration of Kv1.2 was found in the basket cell axon plexus and terminal regions around the Purkinje cells. Kv1.1 immunoreactivity was also concentrated in this area although the staining intensity was relatively lower. Both Purkinje cell layer and granular layer were intensely stained with anti-Kv1.3 and Kv1.6 antibodies, whereas immunoreactivities for Kv1.4 and Kv1.5 were detected in the Purkinje cell bodies with much lower intensity in the molecular and granular layers. In the cerebellar nuclei, the cell bodies of cerebellar output neurons showed strong immunoreactivities for Kv1.2, Kv1.4, and Kv1.6 with moderate staining for Kv1.3 and Kv1.5 in the cell bodies. This study on the differential localization patterns of Kv1 channel subunits in the gerbil cerebellum may provide helpful guidelines for correlating current types with particular channels and useful data for the future investigations on the pathological conditions such as ischemia and epilepsy.

Heterogeneous competition of Kv1 channel toxins with kaliotoxin for binding in rat brain: autoradiographic analysis

The alpha-subunits of Kv1 channels display characteristic distributions and restricted co-assembly in mammalian brain. The heterogeneous composition of Kv1 channels has made it difficult to use specific toxins to label brain structures. We used autoradiography to analyse the competitive behaviour of three Kv1 channel toxins--alpha-dendrotoxin, kaliotoxin, and mast cell degranulating peptide--for binding to kaliotoxin binding sites in various brain structures. IC(50) varied considerably between brain regions (by up to three orders of magnitude) for each ligand. alpha-dendrotoxin and kaliotoxin competed equally in some regions and to different extents in others, identifying two types of structure. Mast cell degranulating peptide competed with (125)I-kaliotoxin less efficiently than alpha-dendrotoxin and kaliotoxin, in all regions. Thus, differences in the capacity of these three toxins to bind to kaliotoxin binding sites provide evidence of major differences in the composition of the Kv1 channels constituting the kaliotoxin binding sites.

Enhancement of ischemia-induced tyrosine phosphorylation of Kv1.2 by vascular endothelial growth factor via activation of phosphatidylinositol 3-kinase

Our studies observed that, consistent with the literature, ischemic/hypoxic insults increased the expression of voltage-gated potassium channel (Kv) 1.2 potassium channel as well as elevating the endogenous level of vascular endothelial growth factor (VEGF) in neurons of adult rat brain following middle cerebral artery occlusion and in SH-SY5Y cells after hypoxia and glucose deprivation. Concomitantly, we also observed that ischemic injury increased the tyrosine phosphorylation of Kv 1.2 in in vivo and in vitro; the introduction of exogenous VEGF could attenuate cell death in in vitro models. Furthermore, we found that the protective effect of VEGF is mediated through its up-regulative actions on the tyrosine phosphorylation of Kv 1.2, which in turn has a direct influence on cell viability after ischemic insult. In substantiation of this result, we used anti-sense methodology to suppress the expression of endogenous VEGF, which significantly inhibited the tyrosine phosphorylation of Kv 1.2 and increased cell death elicited by ischemic/hypoxic injury. Finally, the enhancement of the tyrosine phosphorylation of the channel by VEGF in neuronal cells was significantly attenuated in the presence of wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-K), or genestin, an inhibitor of tyrosine kinase, thus suggesting that the phosphorylation of Kv 1.2 induced by VEGF is mechanistically linked to the PI3-K pathway.

Gene transcription of brain voltage-gated potassium channels is reversibly regulated by oxygen supply

Voltage-dependent potassium channels (Kv channels) are important determinants of brain electrical activity. Hypoxia may be an important modifier, because several voltage-gated K+ channels are reversibly blocked by acute hypoxia and are thought to act as oxygen sensors. Here we show, using the anoxia-tolerant turtle brain (Trachemys scripta) as a model, that brain Kv1 channel transcription is reversibly regulated by oxygen supply. We found that in turtle brains exposed to 4-h anoxia Kv1 transcripts were reduced to 18.5% of normoxic levels. Kv1 channel mRNA levels were restored to normal within 4 h of subsequent reoxygenation. Our results provide clear evidence that brain Kv channel expression is sensitive to oxygen supply and indicate an important mechanism that matches brain activity to oxygen supply.