Mononuclear phagocyte biophysiology influences brain transendothelial and tissue migration: implication for HIV-1-associated dementia

A Meta-Analysis Study to Infer Voltage-Gated K+ Channels Prognostic Value in Different Cancer Types

Potassium channels are often highly expressed in cancer cells with respect to healthy ones, as they provide proliferative advantages through modulating membrane potential, calcium homeostasis, and various signaling pathways. Among potassium channels, Shaker type voltage-gated Kv channels are emerging as promising pharmacological targets in oncology. Here, we queried publicly available cancer patient databases to highlight if a correlation exists between Kv channel expression and survival rate in five different cancer types. By multiple gene comparison analysis, we found a predominant expression of KCNA2, KCNA3, and KCNA5 with respect to the other KCNA genes in skin cutaneous melanoma (SKCM), uterine corpus endometrial carcinoma (UCEC), stomach adenocarcinoma (STAD), lung adenocarcinoma (LUAD), and lung squamous cell carcinoma (LUSC). This analysis highlighted a prognostic role of KCNA3 and KCNA5 in SKCM, LUAD, LUSC, and STAD, respectively. Interestingly, KCNA3 was associated with a positive prognosis in SKCM and LUAD but not in LUSC. Results obtained by the analysis of KCNA3-related differentially expressed genes (DEGs); tumor immune cell infiltration highlighted differences that may account for such differential prognosis. A meta-analysis study was conducted to investigate the role of KCNA channels in cancer using cancer patients’ datasets. Our study underlines a promising correlation between Kv channel expression in tumor cells, in infiltrating immune cells, and survival rate.

Functional Potassium Channels in Macrophages

Macrophages are the predominant component of innate immunity, which is an important protective barrier of our body. Macrophages are present in all organs and tissues of the body, their main functions include immune surveillance, bacterial killing, tissue remodeling and repair, and clearance of cell debris. In addition, macrophages can present antigens to T cells and facilitate inflammatory response by releasing cytokines. Macrophages are of high concern due to their crucial roles in multiple physiological processes. In recent years, new advances are emerging after great efforts have been made to explore the mechanisms of macrophage activation. Ion channel is a class of multimeric transmembrane protein that allows specific ions to go through cell membrane. The flow of ions through ion channel between inside and outside of cell membrane is required for maintaining cell morphology and intracellular signal transduction. Expressions of various ion channels in macrophages have been detected. The roles of ion channels in macrophage activation are gradually caught attention. K⁺ channels are the most studied channels in immune system. However, very few of published papers reviewed the studies of K⁺ channels on macrophages. Here, we will review the four types of K⁺ channels that are expressed in macrophages: voltage-gated K⁺ channel, calcium-activated K⁺ channel, inwardly rectifying K⁺ channel and two-pore domain K⁺ channel.

The contribution of ion channels to shaping macrophage behaviour

The expanding roles of macrophages in physiological and pathophysiological mechanisms now include normal tissue homeostasis, tissue repair and regeneration, including neuronal tissue; initiation, progression, and resolution of the inflammatory response and a diverse array of anti-microbial activities. Two hallmarks of macrophage activity which appear to be fundamental to their diverse cellular functionalities are cellular plasticity and phenotypic heterogeneity. Macrophage plasticity allows these cells to take on a broad spectrum of differing cellular phenotypes in response to local and possibly previous encountered environmental signals. Cellular plasticity also contributes to tissue- and stimulus-dependent macrophage heterogeneity, which manifests itself as different macrophage phenotypes being found at different tissue locations and/or after different cell stimuli. Together, plasticity and heterogeneity align macrophage phenotypes to their required local cellular functions and prevent inappropriate activation of the cell, which could lead to pathology. To execute the appropriate function, which must be regulated at the qualitative, quantitative, spatial and temporal levels, macrophages constantly monitor intracellular and extracellular parameters to initiate and control the appropriate cell signaling cascades. The sensors and signaling mechanisms which control macrophages are the focus of a considerable amount of research. Ion channels regulate the flow of ions between cellular membranes and are critical to cell signaling mechanisms in a variety of cellular functions. It is therefore surprising that the role of ion channels in the macrophage biology has been relatively overlooked. In this review we provide a summary of ion channel research in macrophages. We begin by giving a narrative-based explanation of the membrane potential and its importance in cell biology. We then report on research implicating different ion channel families in macrophage functions. Finally, we highlight some areas of ion channel research in macrophages which need to be addressed, future possible developments in this field and therapeutic potential.

The voltage-gated potassium channel KV1.3 as a therapeutic target for venom-derived peptides

The voltage-gated potassium channel K_V1.3 is a well-established therapeutic target for a range of autoimmune diseases, in addition to being the site of action of many venom-derived peptides. Numerous studies have documented the efficacy of venom peptides that target K_V1.3, in particular from sea anemones and scorpions, in animal models of autoimmune diseases such as rheumatoid arthritis, psoriasis and multiple sclerosis. Moreover, an analogue of the sea anemone peptide ShK (known as dalazatide) has successfully completed Phase 1 clinical trials in mild-to-moderate plaque psoriasis. In this article we consider other potential therapeutic applications of inhibitors of K_V1.3, including in inflammatory bowel disease and neuroinflammatory conditions such as Alzheimer's and Parkinson's diseases, as well as fibrotic diseases. We also summarise strategies for facilitating the entry of peptides to the central nervous system, given that this will be a pre-requisite for the treatment of most neuroinflammatory diseases. Venom-derived peptides that have been reported recently to target K_V1.3 are also described. The increasing number of autoimmune and other conditions in which K_V1.3 is upregulated and is therefore a potential therapeutic target, combined with the fact that many venom-derived peptides are potent inhibitors of K_V1.3, suggests that venoms are likely to continue to serve as a rich source of new pharmacological tools and therapeutic leads targeting this channel.

Voltage Gated Potassium Channel Kv1.3 Is Upregulated on Activated Astrocytes in Experimental Autoimmune Encephalomyelitis

Kv1.3 is a voltage gated potassium channel that has been implicated in pathophysiology of multiple sclerosis (MS). In the present study we investigated temporal and cellular expression pattern of this channel in the lumbar part of spinal cords of animals with experimental autoimmune encephalomyelitis (EAE), animal model of MS. EAE was actively induced in female Dark Agouti rats. Expression of Kv1.3 was analyzed at different time points of disease progression, at the onset, peak and end of EAE. We here show that Kv1.3 increased by several folds at the peak of EAE at both gene and protein level. Double immunofluorescence analyses demonstrated localization of Kv1.3 on activated microglia, macrophages, and reactive astrocytes around inflammatory lesions. In vitro experiments showed that pharmacological block of Kv1.3 in activated astrocytes suppresses the expression of proinflammatory mediators, suggesting a role of this channel in inflammation. Our results support the hypothesis that Kv1.3 may be a therapeutic target of interest for MS and add astrocytes to the list of cells whose activation would be suppressed by inhibiting Kv1.3 in inflammatory conditions.

Diabetes Mellitus and Ischemic Heart Disease: The Role of Ion Channels

Diabetes mellitus is one the strongest risk factors for cardiovascular disease and, in particular, for ischemic heart disease (IHD). The pathophysiology of myocardial ischemia in diabetic patients is complex and not fully understood: some diabetic patients have mainly coronary stenosis obstructing blood flow to the myocardium; others present with coronary microvascular disease with an absence of plaques in the epicardial vessels. Ion channels acting in the cross-talk between the myocardial energy state and coronary blood flow may play a role in the pathophysiology of IHD in diabetic patients. In particular, some genetic variants for ATP-dependent potassium channels seem to be involved in the determinism of IHD.

Exenatide Inhibits the KCa3.1 Channels of Aortic Vascular Smooth Muscle in Diabetic Rats

BACKGROUND

KCa3.1 ion channels play an important role during atherosclerosis. We aimed to investigate the effect of exenatide on KCa3.1 expression in aortic vascular smooth muscle cells (VSMCs) of diabetic rats.

METHODS

Sprague-Dawley rats were randomly divided into normal control (NC), diabetes model (DM), and exenatide treatment (ET) groups. Hematoxylin and eosin and α-actin immunohistochemical staining were used to detect changes in rat aortic vascular smooth muscle. Quantitative RT-PCR and Western blot analysis were used to detect changes in KCa3.1 mRNA and protein levels, respectively.

RESULTS

Aortic tissue staining in the DM group revealed an absence of smooth or integrated endothelium, increased smooth muscle cell proliferation in the media, smooth muscle hyperplasia, disorganized smooth muscle cells, and an increased number of collagen fibers, relative to the NC and ET groups. KCa3.1 mRNA expression was higher in the DM group than in the NC and ET groups. Similarly, the KCa3.1 protein level was higher in the DM group than in the NC and ET groups. The KCa3.1 protein level did not significantly differ between the ET and NC groups.

CONCLUSIONS

Exenatide could inhibit the expression of the KCa3.1 channel in VSMCs of diabetic rats.

Venom-derived peptide inhibitors of voltage-gated potassium channels

Voltage-gated potassium channels play a key role in human physiology and pathology. Reflecting their importance, numerous channelopathies have been characterised that arise from mutations in these channels or from autoimmune attack on the channels. Voltage-gated potassium channels are also the target of a broad range of peptide toxins from venomous organisms, including sea anemones, scorpions, spiders, snakes and cone snails; many of these peptides bind to the channels with high potency and selectivity. In this review we describe the various classes of peptide toxins that block these channels and illustrate the broad range of three-dimensional structures that support channel blockade. The therapeutic opportunities afforded by these peptides are also highlighted. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Mechanisms of the Immunological Effects of Volatile Anesthetics: A Review

Volatile anesthetics (VAs) have been in clinical use for a very long time. Their mechanism of action is yet to be fully delineated, but multiple ion channels have been reported as targets for VAs (canonical VA targets). It is increasingly recognized that VAs also manifest effects outside the central nervous system, including on immune cells. However, the literature related to how VAs affect the behavior of immune cells is very limited, but it is of interest that some canonical VA targets are reportedly expressed in immune cells. Here, we review the current literature and describe canonical VA targets expressed in leukocytes and their known roles. In addition, we introduce adhesion molecules called β2 integrins as noncanonical VA targets in leukocytes. Finally, we propose a model for how VAs affect the function of neutrophils, macrophages, and natural killer cells via concerted effects on multiple targets as examples.

Effects of Intermediate-Conductance Ca(2+)-Activated K(+) Channels on Human Endometrial Carcinoma Cells

The objective of this study was to investigate the effect of intermediate-conductance Ca(2+)-activated K(+) (KCa3.1) channels on the cell proliferation, cell cycle, apoptosis, migration, and invasion in endometrial cancer (EC) cells. Human EC cell lines HEC-1-A and Ishikawa were cultured in vitro and transfected with recombinant plasmid containing KCa3.1-targeting shRNA. RT-qPCR and Western blot were used to examine the mRNA and protein expression levels of KCa3.1 channels in transfected cells. In addition, the specific inhibitor of KCa3.1, TRAM-34, was used to examine the effect of KCa3.1 blockage on migration capacity and invasiveness of EC cells using transwell assay. Proliferation and apoptotic rates of EC cells transfected with KCa3.1 shRNA or treated with TRAM-34 were analyzed using MTT, BrdU incorporation assay, and flow cytometry. Expression of cell cycle proteins and metalloproteinase-2 (MMP-2) was evaluated by RT-qPCR and Western blotting. TRAM-34 treatment and KCa3.1 silencing using shRNA dramatically suppressed both the mRNA and protein expression of KCa3.1 channels (P < 0.01) compared with control groups. Blockage of KCa3.1 by TRAM-34 treatment and KCa3.1 shRNA transfection exerted inhibitory effect on cell growth of both EC cell lines, as demonstrated by increased cell population at G0-G1 phase and decreased cell population at S phase. However, both the treatments did not result in significant changes in the apoptotic rate (P > 0.05) compared to controls. Protein expressions of cyclin D1, cyclin E, and survivin were significantly decreased in the experimental groups comparing to control. We showed that TRAM-34 treatment led to significantly inhibited migration, invasion, and MMP-2 expression in HEC-1-A and Ishikawa cells, compared with the control group (P < 0.01). Blockage of KCa3.1 channel activity or expression inhibits cell proliferation and cell cycle progression without inducing apoptosis in EC cells. Moreover, TRAM-34 could reduce the ability of EC cells to migrate and invade, which might be related to reduced expression of MMP-2.

Ion channels in innate and adaptive immunity

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.

Role of the potassium channel KCa3.1 in diabetic nephropathy

There is an urgent need to identify novel interventions for mitigating the progression of diabetic nephropathy. Diabetic nephropathy is characterized by progressive renal fibrosis, in which tubulointerstitial fibrosis has been shown to be the final common pathway of all forms of chronic progressive renal disease, including diabetic nephropathy. Therefore targeting the possible mechanisms that drive this process may provide novel therapeutics which allow the prevention and potentially retardation of the functional decline in diabetic nephropathy. Recently, the Ca2+-activated K+ channel KCa3.1 (KCa3.1) has been suggested as a potential therapeutic target for nephropathy, based on its ability to regulate Ca2+ entry into cells and modulate Ca2+-signalling processes. In the present review, we focus on the physiological role of KCa3.1 in those cells involved in the tubulointerstitial fibrosis, including proximal tubular cells, fibroblasts, inflammatory cells (T-cells and macrophages) and endothelial cells. Collectively these studies support further investigation into KCa3.1 as a therapeutic target in diabetic nephropathy.

Inflammatory status of transmigrating primary rat monocytes in a novel perfusion model simulating blood flow

It remains unclear whether monocyte infiltration plays a protective or detrimental role in neurodegenerative disease. The present study characterizes the inflammatory status of primary monocytes in a novel in vitro perfusion model. Monocytes under perfusion do not undergo elevated cell death. However, perfusion does lead to altered morphology, which can be counteracted by anti-inflammatory drugs. Functional studies indicate that cytokine levels are significantly reduced in perfusion compared to stationary conditions and enhanced with brain slices or capillary endothelial cells. Understanding monocyte properties could lead to refined treatment and new ways to interfere with inflammation in diseased brains.

Therapeutic potential of KCa3.1 blockers: recent advances and promising trends

The Ca(2+)-activated K(+) channel K(Ca)3.1 regulates membrane potential and calcium signaling in erythrocytes, activated T and B cells, macrophages, microglia, vascular endothelium, epithelia, and proliferating vascular smooth muscle cells and fibroblasts. K(Ca)3.1 has therefore been suggested as a potential therapeutic target for diseases such as sickle cell anemia, asthma, coronary restenosis after angioplasty, atherosclerosis, kidney fibrosis and autoimmunity, where activation and excessive proliferation of one or more of these cell types is involved in the pathology. This article will review the physiology and pharmacology of K(Ca)3.1 and critically examine the available preclinical and clinical data validating K(Ca)3.1 as a therapeutic target.

Mononuclear phagocytes in the pathogenesis of neurodegenerative diseases

Brain mononuclear phagocytes (MP, bone marrow monocyte-derived macrophages, perivascular macrophages, and microglia) function to protect the nervous system by acting as debris scavengers, killers of microbial pathogens, and regulators of immune responses. MP are activated by a variety of environmental cues and such inflammatory responses elicit cell injury and death in the nervous system. MP immunoregulatory responses include secretion of neurotoxic factors, mobilization of adaptive immunity, and cell chemotaxis. This incites tissue remodelling and blood-brain barrier dysfunction. As disease progresses, MP secretions engage neighboring cells in a vicious cycle of autocrine and paracrine amplification of inflammation leading to tissue injury and ultimately destruction. Such pathogenic processes tilt the balance between the relative production of neurotrophic and neurotoxic factors and to disease progression. The ultimate effects that brain MP play in disease revolves "principally" around their roles in neurodegeneration. Importantly, common functions of brain MP in neuroimmunity link highly divergent diseases (for example, human immunodeficiency virus type-one associated dementia, Alzheimer's disease and Parkinson's disease). Research into this process from our own laboratories and those of others seek to harness MP inflammatory processes with the intent of developing therapeutic interventions that block neurodegenerative processes and improve the quality of life in affected people.

Cl- channels are expressed in human normal monocytes: a functional role in migration, adhesion and volume change

Increased adhesion and diapedesis of monocytes appear to be primary initiating factors in the pathophysiology of occlusive vascular diseases, including atherosclerosis and restenosis. However, the underlying mechanisms of transendothelial migration and invasion of monocytes into the blood vessels are not known. Alterations in ion channels on the cell membrane are generally involved in induced changes in shape and volume. In the present study, we investigated the expression and functional role of chloride channels in freshly isolated human blood monocytes. The Cl- currents in whole-cells were measured by the patch-clamp technique. We observed whole cell Cl- currents, which were time-independent and outwardly rectifying. The chloride channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and R(+)-[(6,7-dichloro-2-cyclopentyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5yl)-oxy]acetic acid 94 (IAA94) attenuated the Cl- currents. NPPB and IAA94 also inhibited chemotaxis of monocytes, as measured in Boyden chemotactic chambers, with the same sensitivity. NPPB but not IAA94, increased the cell volume as measured by shape change, and decreased tumour necrosis factor (TNF)-alpha-induced monocyte adhesion to endothelial cells. These results suggest that monocytes contain Cl- channels which regulate transendothelial migration of monocytes, due presumably to an alteration in cell volume.

Is repetitive opportunistic infection in AIDS patients the effective mechanism for neurodegeneration in terms of endlessly amplifying cytokine/chemokine effect?

With strict reference to how AIDS dementia somehow evolves from HIV infection through stages of initial monocyte-macrophage stimulation via a series of transendothelial and infiltrative events, it is perhaps significant to consider systemic body involvement by the HIV-associated processes to culminate in a concerted series of effects involving cascades and amplifications of action of cytokines and chemokines. Indeed, in terms that would implicate neurons only secondarily in AIDS dementia, one might perhaps consider HIV-1-dementia as an effective result of ongoing inflammation in the brain dependent not only on macrophage-microglial activation and replication, but also on glial participation in an overall process particularly conducive to increasing the brain HIV-1 load. In effect, perhaps, HIV encephalitis would constitute a system of mutually self-enhancing series of events ranging from macrophage-monocyte activation and replication on the one hand, and also HIV-1-induced cellular effects on the other that would result in progressively amplifying neuronal injury induced by cytokines and chemokines in AIDS patients suffering from repetitive opportunistic infections.

HIV-1-associated dementia: a metabolic encephalopathy perpetrated by virus-infected and immune-competent mononuclear phagocytes

Infection of the nervous system by HIV-1 commonly causes a broad range of cognitive, behavioral, and motor abnormalities called, in its most severe form, HIV-1-associated dementia (HAD). HAD is a metabolic encephalopathy caused by productive viral infection of brain mononuclear phagocytes (MPs) (perivascular and parenchymal brain macrophages and microglia) and sustained by paracrine-amplified, inflammatory, neurotoxic responses. MP neurotoxins are, in large measure, homeostatic secretory products that can have a negative effect on neuronal cell function when produced in abundance. Proinflammatory cytokines, chemokines, platelet-activating factor, arachidonic acid and its metabolites, nitric oxide, quinolinic acid, progeny virions, and viral structural and regulatory proteins are all included as part of these cellular and viral toxic elements. In addition, neuronal damage can occur directly by engaging specific receptors or through inducing widespread inflammatory activities in brain tissue that ultimately induce neuronal demise. The mechanisms for immune-and viral-mediated neural injury in HAD are made more striking by the effects of abused drugs on cognitive function. Ultimately, linkages between neuronal function and disordered MP immunity will provide insights into how HIV-1 infection of the brain leads to compromised mental function as well as providing clues into the pathogenesis of other neurodegenerative disorders.