Non-selective cation channel activity is required for lysophosphatidylcholine-induced monocyte migration

The role of transient receptor potential (TRP) channels in phagocytosis: A comprehensive review

When host cells are exposed to foreign particles, dead cells, or cell hazards, a sophisticated process called phagocytosis begins. During this process, macrophages, dendritic cells, and neutrophils engulf the target by expanding their membranes. Phagocytosis of apoptotic cells is called efferocytosis. This process is of significant importance as billions of cells are eliminated daily without provoking inflammation. Both phagocytosis and efferocytosis depend on Ca2+ signaling. A big family of Ca2+ permeable channels is transient receptor potentials (TRPs) divided into nine subfamilies. We aimed to review their roles in phagocytosis. The present review article shows that various TRP channels such as TRPV1, 2, 3, 4, TRPM2, 4, 7, 8, TRPML1, TRPA1, TRPC1, 3, 5, 6 have roles at various stages of phagocytosis. They are involved in the phagocytosis of amyloid β, α-synuclein, myelin debris, bacteria, and apoptotic cells. In particular, TRPC3 and TRPM7 contribute to efferocytosis. These effects are mediated by changing Ca2+ signaling or targeting intracellular enzymes such as Akt. In addition, they contribute to the chemotaxis of phagocytic cells towards targets. Although a limited number of studies have assessed the role of TRP channels in phagocytosis and efferocytosis, their findings indicate that they have critical roles in these processes. In some cases, their ablation completely abolished the phagocytic function of the cells. As a result, TRP channels are potential targets for developing new therapeutics that modulate phagocytosis.

Optimized flow cytometric detection of transient receptor potential vanilloid-1 (TRPV1) in human hematological malignancies

The ectopic overexpression of transient receptor potential vanilloid-1 (TRPV1) has been detected in numerous solid cancers, including breast, prostate, pancreatic, and tongue epithelium cancer. However, the expression of TRPV1 in hematological malignancies remains unknown. Here we show through in silico analysis that elevated TRPV1 mRNA expression occurs in a range of hematological malignancies and presents an optimized flow cytometry method to rapidly assess TRPV1 protein expression for both cell lines and primary patient samples. Three anti-TRPV1 antibodies were evaluated for intracellular TRPV1 detection using flow cytometry resulting in an optimized protocol for the evaluation of TRPV1 in hematological malignant cell lines and patients' peripheral blood mononuclear cells (PBMC). Overexpression of TRPV1 was observed in THP-1 (acute monocytic leukemia) and U266B1 (multiple myeloma, MM), but not U937 (histiocytic lymphoma) compared to healthy PBMC. TRPV1 was also detected in all 49 patients including B-cell non-Hodgkin's lymphoma (B-NHL), MM, and others and 20 healthy controls. TRPV1 expression was increased in 8% of patients (MM = 2, B-NHL = 2). In conclusion, we provide an optimized flow cytometry method for routine expression analysis of clinical samples and show that TRPV1 is increased in a subset of patients with hematological malignancies.

The cation channel TRPM8 influences the differentiation and function of human monocytes

Monocytes are mononuclear phagocytes that can differentiate to a variety of cell fates under the influence of their microenvironment and hardwired commitment. We found that inhibition of TRPM8 in human blood CD14⁺ monocytes during a critical 3‐h window at the beginning of their differentiation into macrophages led to enhanced survival and LPS‐driven TNFα production after 24 h. TRPM8 antagonism also promoted LPS‐driven TNFα production in CD14⁺ monocytes derived from the intestinal mucosa. Macrophages that had been derived for 6 days under blockade of TRPM8 had impaired phagocytic capacity and were transcriptionally distinct. Most of the affected genes were altered in a way that opposed normal monocyte to macrophage differentiation indicating that TRPM8 activity promotes aspects of this differentiation programme. Thus, we reveal a novel role for TRPM8 in regulating human CD14⁺ monocyte fate and function.

Transient receptor potential ankyrin 1 contributes to the lysophosphatidylcholine-induced oxidative stress and cytotoxicity in OLN-93 oligodendrocyte

Transient receptor potential ankyrin 1 (TRPA1), the non-selective cation channel, was found that can mediate the generation of multiple sclerosis, while the mechanism is still controversial. Lysophosphatidylcholine (LPC) is a critical trigger of multiple sclerosis which results from the syndrome of neuronal inflammation and demyelination. In this work, we suggested that TRPA1 can mediate the LPC-induced oxidative stress and cytotoxicity in OLN-93 oligodendrocyte. The expression of TRPA1 in OLN-93 was detected by using quantitative real-time PCR (qRT-PCR) and immunofluorescence. The calcium overload induced by LPC via TRPA1 was detected by calcium imaging. The mechanism of LPC-induced mitochondrial reactive oxygen species (mtROS) generation, mitochondria membrane depolarization, nitric oxide (NO) increase, and development of superoxide production via TRPA1 was verified by using confocal imaging. The cell injury elicited by LPC via TRPA1 was confirmed by both CCK-8 and LDH cytotoxicity detection. These results indicate that TRPA1 plays an important role of the LPC-induced oxidative stress and cell damage in OLN-93 oligodendrocyte. Therefore, inhibition of TRPA1 may protect the LPC-induced demyelination.

Transient receptor potential ankyrin 1 contributes to the ATP-elicited oxidative stress and inflammation in THP-1-derived macrophage

P2X7 receptor (P2X7R) is an ATP-gated non-selective cation channel which mediates ATP-induced inflammation in macrophages. Transient receptor potential (TRP) receptors are nociceptors in cellular membrane which can perceive the stimuli of environmental irritant. The interaction between TRP channels and P2X7R has been found while the details about inflammation are still unclear. In this study, we suggested that transient receptor potential ankyrin 1 (TRPA1), a member of TRP superfamily, participates in ATP-induced oxidative stress and inflammation in human acute monocytic leukemia cell line (THP-1)-derived macrophage. The co-localization between TRPA1 and P2X7R was detected using immunofluorescence in THP-1-derived macrophage and transfected human embryonic kidney cell line (HEK293T). The mechanism by which ATP or 3'-O-(4-Benzoylbenzoyl)-ATP (BzATP) induces the activation of macrophages was verified by calcium imaging, mitochondrial reactive oxygen species (mtROS) detection, mitochondrial membrane potential (∆Ψ_m) measurement, flow cytometry, enzyme-linked immunosorbent assay (ELISA), western blotting, CCK-8 assay, and the lactate dehydrogenase (LDH) release cytotoxic assay. The BzATP and ATP induced calcium overload, mitochondria injury, interleukin-1β (IL-1β) secretion, and cytotoxicity can be inhibited by TRPA1 antagonists. These results indicated that TRPA1 can co-localize with P2X7R and mediate ATP-induced oxidative stress and inflammation. Therefore, the inhibition of TRPA1 may provide a potential therapy for ATP-elicited inflammatory diseases, including atherosclerosis.

2-Aminoethyldiphenyl Borinate: A Multitarget Compound with Potential as a Drug Precursor

BACKGROUND

Boron is considered a trace element that induces various effects in systems of the human body. However, each boron-containing compound exerts different effects.

OBJECTIVE

To review the effects of 2-Aminoethyldiphenyl borinate (2-APB), an organoboron compound, on the human body, but also, its effects in animal models of human disease.

METHODS

In this review, the information to showcase the expansion of these reported effects through interactions with several ion channels and other receptors has been reported. These effects are relevant in the biomedical and chemical fields due to the application of the reported data in developing therapeutic tools to modulate the functions of the immune, cardiovascular, gastrointestinal and nervous systems.

RESULTS

Accordingly, 2-APB acts as a modulator of adaptive and innate immunity, including the production of cytokines and the migration of leukocytes. Additionally, reports show that 2-APB exerts effects on neurons, smooth muscle cells and cardiomyocytes, and it provides a cytoprotective effect by the modulation and attenuation of reactive oxygen species.

CONCLUSION

The molecular pharmacology of 2-APB supports both its potential to act as a drug and the desirable inclusion of its moieties in new drug development. Research evaluating its efficacy in treating pain and specific maladies, such as immune, cardiovascular, gastrointestinal and neurodegenerative disorders, is scarce but interesting.

Transient Receptor Potential Ankyrin 1 Contributes to Lysophosphatidylcholine-Induced Intracellular Calcium Regulation and THP-1-Derived Macrophage Activation

Lysophosphatidylcholine (LPC) is a major atherogenic lipid that stimulates an increase in mitochondrial reactive oxygen species (mtROS) and the release of cytokines under inflammasome activation. However, the potential receptors of LPC in macrophages are poorly understood. Members of the transient receptor potential (TRP) channel superfamily, which is crucially involved in transducing environmental irritant stimuli into nociceptor activity, are potential receptors of LPC. In this study, we investigated whether LPC can induce the activation of transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily. The functional expression of TRPA1 was first detected by quantitative real-time polymerase chain reaction (qRT-PCR), western blotting and calcium imaging in human acute monocytic leukemia cell line (THP-1)-derived macrophages. The mechanism by which LPC induces the activation of macrophages through TRPA1 was verified by cytoplasmic and mitochondrial calcium imaging, mtROS detection, a JC-1 assay, enzyme-linked immunosorbent assay, the CCK-8 assay and the lactate dehydrogenase (LDH) cytotoxic assay. LPC induced the activation of THP-1-derived macrophages via calcium influx, and this activation was suppressed by potent and selective inhibitors of TRPA1. These results indicated that TRPA1 can mediate mtROS generation, mitochondrial membrane depolarization, the secretion of IL-1β and cytotoxicity through cellular and mitochondrial Ca²⁺ influx in LPC-treated THP-1-derived macrophages. Therefore, the inhibition of TRPA1 may protect THP-1-derived macrophages against LPC-induced injury.

Decisive role of P42/44 mitogen-activated protein kinase in Δ9-tetrahydrocannabinol-induced migration of human mesenchymal stem cells

In past years, medical interest in Δ⁹-tetrahydrocannabinol (THC), the major psychoactive ingredient of the Cannabis plant, has been renewed due to the elucidation of the endocannabinoid system and diverse other receptor targets involved in biological cannabinoid effects. The present study therefore investigates the impact of THC on the migration of mesenchymal stem cells (MSCs) which are known to be involved in various regenerative processes such as bone healing. Using Boyden chamber assays, THC was found to increase the migration of adipose-derived MSCs. Migration by THC was almost completely suppressed by the CB₁ receptor antagonist AM-251 and to a lesser extent by the CB₂ receptor antagonist AM-630. By contrast, the TRPV1 antagonist capsazepine as well as the G protein-coupled receptor 55 (GRP55) agonist O-1602 did not significantly interfere with the promigratory effect of THC. Furthermore, increased migration by THC was fully suppressed by PD98059, an inhibitor of p42/44 mitogen-activated protein kinase (MAPK) activation, and was accompanied by a time-dependent activation of this pathway accordingly. In line with the migration data, additional inhibitor experiments pointed towards a decisive role of the CB₁ receptor in conferring THC-induced activation of p42/44 MAPK. Collectively, this study demonstrates THC to exert a promigratory effect on MSCs via a CB₁ receptor-dependent activation of p42/44 MAPK phosphorylation. This pathway may be involved in regenerative effects of THC and could be a target of pharmacological intervention.

Rutaecarpine Reverses the Altered Connexin Expression Pattern Induced by Oxidized Low-density Lipoprotein in Monocytes

Adhesion of monocytes to the vascular endothelium is crucial in atherosclerosis development. Connexins (Cxs) which form hemichannels or gap junctions, modulate monocyte-endothelium interaction. We previously found that rutaecarpine, an active ingredient of the Chinese herbal medicine Evodia, reversed the altered Cx expression induced by oxidized low-density lipoprotein (ox-LDL) in human umbilical vein endothelial cells, and consequently decreases the adhesive properties of endothelial cells to monocytes. This study further investigated the effect of rutaecarpine on Cx expression in monocytes exposed to ox-LDL. In cultured human monocytic cell line THP-1, ox-LDL rapidly reduced the level of atheroprotective Cx37 but enhanced that of atherogenic Cx43, thereby inhibiting adenosine triphosphate release through hemichannels. Pretreatment with rutaecarpine recovered the expression of Cx37 but inhibited the upregulation of Cx43 induced by ox-LDL, thereby improving adenosine triphosphate-dependent hemichannel activity and preventing monocyte adhesion. These effects of rutaecarpine were attenuated by capsazepine, an antagonist of transient receptor potential vanilloid subtype 1. The antiadhesive effects of rutaecarpine were also attenuated by hemichannel blocker 18α-GA. This study provides additional evidence that rutaecarpine can modulate Cx expression through transient receptor potential vanilloid subtype 1 activation in monocytes, which contributes to the antiadhesive properties of rutaecarpine.

Alleviation of Microglial Activation Induced by p38 MAPK/MK2/PGE2 Axis by Capsaicin: Potential Involvement of other than TRPV1 Mechanism/s

Exaggerated inflammatory responses in microglia represent one of the major risk factors for various central nervous system’s (CNS) associated pathologies. Release of excessive inflammatory mediators such as prostaglandins and cytokines are the hallmark of hyper-activated microglia. Here we have investigated the hitherto unknown effects of capsaicin (cap) - a transient receptor potential vanilloid 1 (TRPV1) agonist- in murine primary microglia, organotypic hippocampal slice cultures (OHSCs) and human primary monocytes. Results demonstrate that cap (0.1–25 µM) significantly (p < 0.05) inhibited the release of prostaglandin E₂ (PGE₂)_, 8-iso-PGF_2α, and differentially regulated the levels of cytokines (TNF-α, IL-6 & IL-1β). Pharmacological blockade (via capsazepine & SB366791) and genetic deficiency of TRPV1 (TRPV1^−/−) did not prevent cap-mediated suppression of PGE₂ in activated microglia and OHSCs. Inhibition of PGE₂ was partially dependent on the reduced levels of PGE₂ synthesising enzymes, COX-2 and mPGES-1. To evaluate potential molecular targets, we discovered that cap significantly suppressed the activation of p38 MAPK and MAPKAPK2 (MK2). Altogether, we demonstrate that cap alleviates excessive inflammatory events by targeting the PGE₂ pathway in in vitro and ex vivo immune cell models. These findings have broad relevance in understanding and paving new avenues for ongoing TRPV1 based drug therapies in neuroinflammatory-associated diseases.

Regulation of thermoTRPs by lipids

The family of Transient Receptor Potential (TRP) ion channels is constituted by 7 subfamilies among which are those that respond to temperature, the thermoTRPs. These channels are versatile molecules of a polymodal nature that have been shown to be modulated in various fashions by molecules of a lipidic nature. Some of these molecules interact directly with the channels on specific regions of their structures and some of these promote changes in membrane fluidity or modify their gating properties in response to their agonists. Here, we have discussed how some of these lipids regulate the activity of thermoTRPs and included some of the available evidence for the molecular mechanisms underlying their effects on these channels.

KCa 3.1-a microglial target ready for drug repurposing?

Over the past decade, glial cells have attracted attention for harboring unexploited targets for drug discovery. Several glial targets have attracted de novo drug discovery programs, as highlighted in this GLIA Special Issue. Drug repurposing, which has the objective of utilizing existing drugs as well as abandoned, failed, or not yet pursued clinical development candidates for new indications, might provide a faster opportunity to bring drugs for glial targets to patients with unmet needs. Here, we review the potential of the intermediate-conductance calcium-activated potassium channels KCa 3.1 as the target for such a repurposing effort. We discuss the data on KCa 3.1 expression on microglia in vitro and in vivo and review the relevant literature on the two KCa 3.1 inhibitors TRAM-34 and Senicapoc. Finally, we provide an outlook of what it might take to harness the potential of KCa 3.1 as a bona fide microglial drug target. GLIA 2016;64:1733-1741.

Sub-Chronic Neuropathological and Biochemical Changes in Mouse Visual System after Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (r-mTBI) results in neuropathological and biochemical consequences in the human visual system. Using a recently developed mouse model of r-mTBI, with control mice receiving repetitive anesthesia alone (r-sham) we assessed the effects on the retina and optic nerve using histology, immunohistochemistry, proteomic and lipidomic analyses at 3 weeks post injury. Retina tissue was used to determine retinal ganglion cell (RGC) number, while optic nerve tissue was examined for cellularity, myelin content, protein and lipid changes. Increased cellularity and areas of demyelination were clearly detectable in optic nerves in r-mTBI, but not in r-sham. These changes were accompanied by a ~25% decrease in the total number of Brn3a-positive RGCs. Proteomic analysis of the optic nerves demonstrated various changes consistent with a negative effect of r-mTBI on major cellular processes like depolymerization of microtubules, disassembly of filaments and loss of neurons, manifested by decrease of several proteins, including neurofilaments (NEFH, NEFM, NEFL), tubulin (TUBB2A, TUBA4A), microtubule-associated proteins (MAP1A, MAP1B), collagen (COL6A1, COL6A3) and increased expression of other proteins, including heat shock proteins (HSP90B1, HSPB1), APOE and cathepsin D. Lipidomic analysis showed quantitative changes in a number of phospholipid species, including a significant increase in the total amount of lysophosphatidylcholine (LPC), including the molecular species 16:0, a known demyelinating agent. The overall amount of some ether phospholipids, like ether LPC, ether phosphatidylcholine and ether lysophosphatidylethanolamine were also increased, while the majority of individual molecular species of ester phospholipids, like phosphatidylcholine and phosphatidylethanolamine, were decreased. Results from the biochemical analysis correlate well with changes detected by histological and immunohistochemical methods and indicate the involvement of several important molecular pathways. This will allow future identification of therapeutic targets for improving the visual consequences of r-mTBI.

"TRP inflammation" relationship in cardiovascular system

Despite considerable advances in the research and treatment, the precise relationship between inflammation and cardiovascular (CV) disease remains incompletely understood. Therefore, understanding the immunoinflammatory processes underlying the initiation, progression, and exacerbation of many cardiovascular diseases is of prime importance. The innate immune system has an ancient origin and is well conserved across species. Its activation occurs in response to pathogens or tissue injury. Recent studies suggest that altered ionic balance, and production of noxious gaseous mediators link to immune and inflammatory responses with altered ion channel expression and function. Among plausible candidates for this are transient receptor potential (TRP) channels that function as polymodal sensors and scaffolding proteins involved in many physiological and pathological processes. In this review, we will first focus on the relevance of TRP channel to both exogenous and endogenous factors related to innate immune response and transcription factors related to sustained inflammatory status. The emerging role of inflammasome to regulate innate immunity and its possible connection to TRP channels will also be discussed. Secondly, we will discuss about the linkage of TRP channels to inflammatory CV diseases, from a viewpoint of inflammation in a general sense which is not restricted to the innate immunity. These knowledge may serve to provide new insights into the pathogenesis of various inflammatory CV diseases and their novel therapeutic strategies.

Regulation of TRP channels by steroids: Implications in physiology and diseases

While effects of different steroids on the gene expression and regulation are well established, it is proven that steroids can also exert rapid non-genomic actions in several tissues and cells. In most cases, these non-genomic rapid effects of steroids are actually due to intracellular mobilization of Ca(2+)- and other ions suggesting that Ca(2+) channels are involved in such effects. Transient Receptor Potential (TRP) ion channels or TRPs are the largest group of non-selective and polymodal ion channels which cause Ca(2+)-influx in response to different physical and chemical stimuli. While non-genomic actions of different steroids on different ion channels have been established to some extent, involvement of TRPs in such functions is largely unexplored. In this review, we critically analyze the literature and summarize how different steroids as well as their metabolic precursors and derivatives can exert non-genomic effects by acting on different TRPs qualitatively and/or quantitatively. Such effects have physiological repercussion on systems such as in sperm cells, immune cells, bone cells, neuronal cells and many others. Different TRPs are also endogenously expressed in diverse steroid-producing tissues and thus may have importance in steroid synthesis as well, a process which is tightly controlled by the intracellular Ca(2+) concentrations. Tissue and cell-specific expression of TRP channels are also regulated by different steroids. Understanding of the crosstalk between TRP channels and different steroids may have strong significance in physiological, endocrinological and pharmacological context and in future these compounds can also be used as potential biomedicine.

Rise and Fall of Kir2.2 Current by TLR4 Signaling in Human Monocytes: PKC-Dependent Trafficking and PI3K-Mediated PIP2 Decrease

LPSs are widely used to stimulate TLR4, but their effects on ion channels in immune cells are poorly known. In THP-1 cells and human blood monocytes treated with LPS, inwardly rectifying K(+) channel current (IKir,LPS) newly emerged at 1 h, peaked at 4 h (-119 ± 8.6 pA/pF), and decayed afterward (-32 ± 6.7 pA/pF at 24 h). Whereas both the Kir2.1 and Kir2.2 mRNAs and proteins were observed, single-channel conductance (38 pS) of IKir,LPS and small interfering RNA-induced knockdown commonly indicated Kir2.2 than Kir2.1. LPS-induced cytokine release and store-operated Ca(2+) entry were commonly decreased by ML-133, a Kir2 inhibitor. Immunoblot, confocal microscopy, and the effects of vesicular trafficking inhibitors commonly suggested plasma membrane translocation of Kir2.2 by LPS. Both IKir,LPS and membrane translocation of Kir2.2 were inhibited by GF109203X (protein kinase C [PKC] inhibitor) or by transfection with small interfering RNA-specific PKCε. Interestingly, pharmacological activation of PKC by PMA induced both Kir2.1 and Kir2.2 currents. The spontaneously decayed IKir,LPS at 24 h was recovered by PI3K inhibitors but further suppressed by an inhibitor of phosphatidylinositol(3,4,5)-trisphosphate (PIP3) phosphatase (phosphatase and tensin homolog). However, IKir,LPS at 24 h was not affected by Akt inhibitors, suggesting that the decreased phosphatidylinositol(4,5)-bisphosphate availability, that is, conversion into PIP3 by PI3K, per se accounts for the decay of IKir,LPS. Taken together, to our knowledge these data are the first demonstrations that IKir is newly induced by TLR4 stimulation via PKC-dependent membrane trafficking of Kir2.2, and that conversion of phosphatidylinositol(4,5)-bisphosphate to PIP3 modulates Kir2.2. The augmentation of Ca(2+) influx and cytokine release suggests a physiological role for Kir2.2 in TLR4-stimulated monocytes.

Activation of mitochondrial transient receptor potential vanilloid 1 channel contributes to microglial migration

Microglia, the resident immune cells in the brain, survey the environment of the healthy brain. Microglial migration is essential for many physiological and pathophysiological processes. Although microglia express some members of the transient receptor potential (TRP) channel family, there is little knowledge regarding the physiological roles of TRP channels in microglia. Here, we explored the role of TRP vanilloid 1 (TRPV1), a channel opened by capsaicin, heat, protons, and endovanilloids, in microglia. We found that application of capsaicin induced concentration-dependent migration in microglia derived from wild-type mice but not in those derived from TRPV1 knockout (TRPV1-KO) mice. Capsaicin-induced microglial migration was significantly inhibited by co-application of the TRPV1 blocker SB366791 and the Ca(2+) chelator BAPTA-AM. Using RT-PCR and immunocytochemistry, we validated that TRPV1 was expressed in microglia. Electrophysiological recording, intracellular Ca(2+) imaging, and immunocytochemistry indicated that TRPV1 was localized primarily in intracellular organelles. Treatment with capsaicin induced an increase in intramitochondrial Ca(2+) concentrations and mitochondrial depolarization. Furthermore, microglia derived from TRPV1-KO mice showed delayed Ca(2+) efflux compared with microglia derived from wild-type mice. Capsaicin-induced microglial migration was inhibited by membrane-permeable antioxidants and MAPK inhibitors, suggesting that mitochondrial TRPV1 activation induced Ca(2+) -dependent production of ROS followed by MAPK activation, which correlated with an augmented migration of microglia. Moreover, a mixture of three endovanilloids augmented microglial migration via TRPV1 activation. Together, these results indicate that mitochondrial TRPV1 plays an important role in inducing microglial migration. Activation of TRPV1 triggers an increase in intramitochondrial Ca(2+) concentration and following depolarization of mitochondria, which results in mtROS production, MAPK activation, and enhancement of chemotactic activity in microglia.

TRPM7 regulates proliferation and polarisation of macrophages

Ion channels play pivotal roles in regulating important functions of macrophages, such as cytokine and chemokine production, migration, proliferation, phagocytosis and others. In this study, we have identified the transient receptor potential cation channel, subfamily M, member 7 (TRPM7) for the first time in macrophages. TRPM7 activity is differentially regulated in macrophages, i.e. current density in TRPM7 is significantly larger in anti-inflammatory M2-type macrophages than in untreated and in pro-inflammatory M1-type macrophages, whereas mRNA levels of TRPM7 remain unchanged upon cell polarisation. The specific TRPM7 inhibitors NS8593 and FTY720 abolish proliferation of macrophages induced by interleukin-4 (IL-4) and macrophage colony-stimulating factor (M-CSF), respectively, whereas proliferation arrest was not accompanied by induction of apoptosis or necrosis in macrophages. Furthermore, NS8593 and FTY720 prevented polarisation of macrophages towards the anti-inflammatory M2 phenotype. Inhibition of TRPM7 reduced IL-4-induced upregulation of arginase-1 (Arg1) mRNA levels and Arg1 activity, and abolished the inhibitory effects of IL-4 or M-CSF on LPS-induced TNF-α production by macrophages. In summary, our data suggest a main role of TRPM7 in the regulation of macrophage proliferation and polarisation.

[Study on novel mechanism underlying analgesia targeting TRPV1]

Transient receptor potential protein (TRP) channels are distributed in pain pathways including primary afferent neurons and function as transduction of various noxious stimuli to innocuous stimuli. TRP channels are considered as molecular basis of chronic pain. Targeting TRPs may lead to novel class of analgesics, and so drug-discovery efforts are focused on TRP agonists and its antagonists. Few products have, however, been placed on the market, because most of candidates have adverse effects. A lesion or disease of the somatosensory nervous system causes neuropathic pain, a type of chronic pain. Neuropathic pain is intolerable and obstinate and therefore, debilitates the affected patients. A great deal of effort has been made to develop medicine targeting molecules involved in neuropathic pain, whereby the promising therapeutically targeted molecules have been identified. Neuroinflammation, based on pathological alteration in crosstalk between nervous system and immune system, has been a focus of attention as pathological mechanism involved in development of neuropathic pain. Recently, we used an animal model for neuropathic pain to find the possibility that neuropathic pain was exacerbated by adipokines derived from perineural adipocytes distributed in injured peripheral neurons. A working hypothesis is therefore proposed that the perineural adipocytes interacts with the immune cells, which also have TRPV1, in injured peripheral nerve, followed by a paracrine loop involving proinflammatory cytokines, chemokines and adipokines derived from them which aggravates and prolongs pain. Here, we overview the developmental status in TRPV1-targetting analgesics and illustrate our recent findings in terms of neuroinflammation.

Discovery of novel disease-specific and membrane-associated candidate markers in a mouse model of multiple sclerosis

Multiple sclerosis is a chronic demyelinating disorder characterized by the infiltration of auto-reactive immune cells from the periphery into the central nervous system resulting in axonal injury and neuronal cell death. Experimental autoimmune encephalomyelitis represents the best characterized animal model as common clinical, histological, and immunological features are recapitulated. A label-free mass spectrometric proteomics approach was used to detect differences in protein abundance within specific fractions of disease-affected tissues including the soluble lysate derived from the spinal cord and membrane protein-enriched peripheral blood mononuclear cells. Tissues were harvested from actively induced experimental autoimmune encephalomyelitis mice and sham-induced ("vehicle" control) counterparts at the disease peak followed by subsequent analysis by nanoflow liquid chromatography tandem mass spectrometry. Relative protein quantitation was performed using both intensity- and fragmentation-based approaches. After statistical evaluation of the data, over 500 and 250 differentially abundant proteins were identified in the spinal cord and peripheral blood mononuclear cell data sets, respectively. More than half of these observations have not previously been linked to the disease. The biological significance of all candidate disease markers has been elucidated through rigorous literature searches, pathway analysis, and validation studies. Results from comprehensive targeted mass spectrometry analyses have confirmed the differential abundance of ∼ 200 candidate markers (≥ twofold dysregulated expression) at a 70% success rate. This study is, to our knowledge, the first to examine the cell-surface proteome of peripheral blood mononuclear cells in experimental autoimmune encephalomyelitis. These data provide a unique mechanistic insight into the dynamics of peripheral immune cell infiltration into CNS-privileged sites at a molecular level and has identified several candidate markers, which represent promising targets for future multiple sclerosis therapies. The mass spectrometry proteomics data associated with this manuscript have been deposited to the ProteomeXchange Consortium with the data set identifier PXD000255.

Calcium influx through the TRPV1 channel of endothelial cells (ECs) correlates with a stronger adhesion between monocytes and ECs

PURPOSE

Atherosclerosis is thought to be initiated by the transendothelial migration of monocytes. In the early stage of this process, the adhesion of monocytes to endothelial cells is supported by an increase in the intracellular concentration of calcium ion ([Ca(2+)]i) in endothelial cells. However, the main source of Ca(2+) has been unclear. In this study, the changes in ionic transmittance and [Ca(2+)]i due to the adhesion of monocytes were continuously measured by an electrophysiological technique and fluorescent imaging. Especially, we focused on transient receptor potential vanilloid channel 1 (TRPV1) as a Ca(2+) channel that could influence the adhesion of monocytes.

MATERIAL AND METHODS

Whole-cell current was continuously recorded in human umbilical vein endothelial cells (HUVECs) by a patch electrode.

RESULTS

The adhesion of monocytes (THP-1) induced a transient inward current in HUVECs, as well as an elevation of [Ca(2+)]i. This inward element was abolished by the application of 100 nM SB366,791, a selective antagonist of TRPV1 channel. Furthermore, SB366,791 significantly decreased the number of THP-1 cells that adhered to HUVECs (control: 231 ± 38, SB366,791: 96 ± 16 cells/mm2).

CONCLUSION

These results suggest that an inward calcium current via the TRPV1 channels of endothelial cells correlates with a stronger adhesion between monocytes and endothelial cells.

Role of ion channels and transporters in cell migration

Cell motility is central to tissue homeostasis in health and disease, and there is hardly any cell in the body that is not motile at a given point in its life cycle. Important physiological processes intimately related to the ability of the respective cells to migrate include embryogenesis, immune defense, angiogenesis, and wound healing. On the other side, migration is associated with life-threatening pathologies such as tumor metastases and atherosclerosis. Research from the last ≈ 15 years revealed that ion channels and transporters are indispensable components of the cellular migration apparatus. After presenting general principles by which transport proteins affect cell migration, we will discuss systematically the role of channels and transporters involved in cell migration.

Patch clamp protocols to study ion channel activity in microglia

Microglia express a variety of ion channels, which can be distinguished based on their ion selectivity into K(+), H(+), Na(+), Ca(2+), nonselective cation, and Cl(-) channels. With respect to their activation mode, voltage-, Ca(2+)-, calcium release-, G protein-, swelling-, and stretch-activated ion channels have been described in microglia. The best method to study the activity of microglial ion channels is the patch clamp technique. The activity of microglial ion channels under physiological conditions is best explored using the perforated patch clamp technique, which allows recordings of membrane potential or ion currents, while the intracellular milieu of the cells remains intact. In whole-cell patch clamp recordings, application of specific voltage protocols with defined intra- and extracellular solutions allows precise identification of a certain ion channel type in microglia as well as the investigation of the channel's biophysical and pharmacological properties. This chapter summarizes patch clamp protocols optimal for recording and analysis of microglial ion channel activity in vitro and in situ.

Macrophage function in atherosclerosis: potential roles of TRP channels

Cation channels of the Transient Receptor Potential Canonical (TRPC) group, which belong to the larger TRP superfamily of channel proteins, are critical players in cardiovascular disease. Recent studies underscored a role of TRPC3 in macrophage survival and efferocytosis, two critical events in atherosclerosis lesion development. Also, other members of the TRP channel superfamily are found expressed in monocytes/macrophages, where they participate in processes that might be of significance to atherogenesis. These observations set a framework for future studies aimed at defining the ultimate functions not only of TRPC3, but probably other TRP channels, in macrophage biology. The purpose of this manuscript is to provide a timely revision of existing evidence on the role of members of the TRP channel superfamily, in particular TRPCs, in macrophages and discuss it in the context of the macrophage's function in atherogenesis.

Increased migration of monocytes in essential hypertension is associated with increased transient receptor potential channel canonical type 3 channels

Increased transient receptor potential canonical type 3 (TRPC3) channels have been observed in patients with essential hypertension. In the present study we tested the hypothesis that increased monocyte migration is associated with increased TRPC3 expression. Monocyte migration assay was performed in a microchemotaxis chamber using chemoattractants formylated peptide Met-Leu-Phe (fMLP) and tumor necrosis factor-α (TNF-α). Proteins were identified by immunoblotting and quantitative in-cell Western assay. The effects of TRP channel-inhibitor 2–aminoethoxydiphenylborane (2-APB) and small interfering RNA knockdown of TRPC3 were investigated. We observed an increased fMLP-induced migration of monocytes from hypertensive patients compared with normotensive control subjects (246±14% vs 151±10%). The TNF-α-induced migration of monocytes in patients with essential hypertension was also significantly increased compared to normotensive control subjects (221±20% vs 138±18%). In the presence of 2-APB or after siRNA knockdown of TRPC3 the fMLP-induced monocyte migration was significantly blocked. The fMLP-induced changes of cytosolic calcium were significantly increased in monocytes from hypertensive patients compared to normotensive control subjects. The fMLP-induced monocyte migration was significantly reduced in the presence of inhibitors of tyrosine kinase and phosphoinositide 3-kinase. We conclude that increased monocyte migration in patients with essential hypertension is associated with increased TRPC3 channels.

Integration of transient receptor potential canonical channels with lipids

Transient receptor potential canonical (TRPC) channels are the canonical (C) subset of the TRP proteins, which are widely expressed in mammalian cells. They are thought to be primarily involved in determining calcium and sodium entry and have wide-ranging functions that include regulation of cell proliferation, motility and contraction. The channels are modulated by a multiplicity of factors, putatively existing as integrators in the plasma membrane. This review considers the sensitivities of TRPC channels to lipids that include diacylglycerols, phosphatidylinositol bisphosphate, lysophospholipids, oxidized phospholipids, arachidonic acid and its metabolites, sphingosine-1-phosphate, cholesterol and some steroidal derivatives and other lipid factors such as gangliosides. Promiscuous and selective lipid sensing have been detected. There appear to be close working relationships with lipids of the phospholipase C and A₂ enzyme systems, which may enable integration with receptor signalling and membrane stretch. There are differences in the properties of each TRPC channel that are further complicated by TRPC heteromultimerization. The lipids modulate activity of the channels or insertion in the plasma membrane. Lipid microenvironments and intermediate sensing proteins have been described that include caveolae, G protein signalling, SEC14-like and spectrin-type domains 1 (SESTD1) and podocin. The data suggest that lipid sensing is an important aspect of TRPC channel biology enabling integration with other signalling systems.

Inflammation-related gene expression by lipid oxidation-derived products in the progression of atherosclerosis

Vascular areas of atherosclerotic development persist in a state of inflammation, and any further inflammatory stimulus in the subintimal area elicits a proatherogenic response; this alters the behavior of the artery wall cells and recruits further inflammatory cells. In association with the inflammatory response, oxidative events are also involved in the development of atherosclerotic plaques. It is now unanimously recognized that lipid oxidation-derived products are key players in the initiation and progression of atherosclerotic lesions. Oxidized lipids, derived from oxidatively modified low-density lipoproteins (LDLs), which accumulate in the intima, strongly modulate inflammation-related gene expression, through involvement of various signaling pathways. In addition, considerable evidence supports a proatherogenic role of a large group of potent bioactive lipids called eicosanoids, which derive from oxidation of arachidonic acid, a component of membrane phospholipids. Of note, LDL lipid oxidation products might regulate eicosanoid production, modulating the enzymatic degradation of arachidonic acid by cyclooxygenases and lipoxygenases; these enzymes might also directly contribute to LDL oxidation. This review provides a comprehensive overview of current knowledge on signal transduction pathways and inflammatory gene expression, modulated by lipid oxidation-derived products, in the progression of atherosclerosis.

Role of myosin light chain kinase in cardiotrophin-1-induced cardiac myofibroblast cell migration

Chemotactic movement of myofibroblasts is recognized as a common means for their sequestration to the site of tissue injury. Following myocardial infarction (MI), recruitment of cardiac myofibroblasts to the infarct scar is a critical step in wound healing. Contractile myofibroblasts express embryonic smooth muscle myosin, α-smooth muscle actin, as well as collagens I and III. We examined the effects of cardiotrophin-1 (CT-1) in the induction of primary rat ventricular myofibroblast motility. Changes in membrane potential (Em) and Ca2+entry were studied to reveal the mechanisms for induction of myofibroblast migration. CT-1-induced cardiac myofibroblast cell migration, which was attenuated through the inhibition of JAK2 (25 μM AG490), and myosin light chain kinase (20 μM ML-7). Inhibition of K+channels (1 mM tetraethylammonium or 100 μM 4-aminopyridine) and nonselective cation channels by 10 μM gadolinium (Gd3+) significantly reduced migration in the presence of CT-1. CT-1 treatment caused a significant increase in myosin light chain phosphorylation, which could be inhibited by incubation in Ca2+-free conditions or by application of AG490, ML-7, and W7 (100 μM; calmodulin inhibitor). Monitoring myofibroblast membrane potential with potentiometric fluorescent DiBAC4( 3 ) dye revealed a biphasic response to CT-1 consisting of an initial depolarization followed by hyperpolarization. Increased intracellular Ca2+, as assessed by fluo 3, occurred immediately after membrane depolarization and attenuated at the time of maximal hyperpolarization. CT-1 exerts chemotactic effects via multiple parallel signaling modalities in ventricular myofibroblasts, including changes in membrane potential, alterations in intracellular calcium, and activation of a number of intracellular signaling pathways. Further study is warranted to determine the precise role of K+currents in this process.

Lysophosphatidylcholine- and MCP-1-induced chemotaxis of monocytes requires potassium channel activity

One of the earliest cellular responses in atherogenesis is the focal recruitment of circulating monocytes, while the most important atherogenic chemoattractants are monocyte chemoattractant protein-1 (MCP-1) and lysophosphatidylcholine (LPC). Invading monocytes transform into activated macrophages and foam cells, which stimulate inflammatory processes and promote atherosclerosis. In this study, we have searched for common mechanisms involved in MCP-1- and LPC-stimulated monocyte migration. We have found that migration of THP-1 monocytes stimulated with MCP-1 was reduced upon inhibition of G(i/o) proteins with pertussis toxin and upon inhibition of platelet activating factor receptors with BN52021, whereas LPC-stimulated monocyte chemotaxis remained unaffected by both inhibitors. Furthermore, Cl(-) channels were only required for MCP-1-induced chemotaxis. However, activity of voltage-gated K+ channels and of Ca2+-activated K+ channels was found to be involved in migration of monocytes stimulated with either MCP-1 or LPC. Inhibition of voltage-gated K+ channels with 4-aminopyridine or margatoxin partially inhibited MCP-1- and LPC-stimulated migration of monocytes. Blockade of Ca2+-activated K+ channels with TRAM-34 also partially reduced migration of MCP-1- and LPC-stimulated monocytes. Simultaneous inhibition of voltage-gated and Ca2+-activated K+ channels abolished MCP-1- and LPC-induced chemotaxis of monocytes. Thus, K+ channel inhibition may represent a novel powerful strategy to reduce monocyte infiltration and subsequent inflammation in atherosclerosis.