Functional Cooperation between KCa3.1 and TRPV4 Channels in Bronchial Smooth Muscle Cell Proliferation Associated with Chronic Asthma

A review of the pathophysiology and the role of ion channels on bronchial asthma

Asthma is one of the main non-communicable chronic diseases and affects a huge portion of the population. It is a multifactorial disease, classified into several phenotypes, being the allergic the most frequent. The pathophysiological mechanism of asthma involves a Th2-type immune response, with high concentrations of allergen-specific immunoglobulin E, eosinophilia, hyperreactivity and airway remodeling. These mechanisms are orchestrated by intracellular signaling from effector cells, such as lymphocytes and eosinophils. Ion channels play a fundamental role in maintaining the inflammatory response on asthma. In particular, transient receptor potential (TRP), stock-operated Ca2+ channels (SOCs), Ca2+-activated K+ channels (IKCa and BKCa), calcium-activated chloride channel (TMEM16A), cystic fibrosis transmembrane conductance regulator (CFTR), piezo-type mechanosensitive ion channel component 1 (PIEZO1) and purinergic P2X receptor (P2X). The recognition of the participation of these channels in the pathological process of asthma is important, as they become pharmacological targets for the discovery of new drugs and/or pharmacological tools that effectively help the pharmacotherapeutic follow-up of this disease, as well as the more specific mechanisms involved in worsening asthma.

Bidirectional TRP/L Type Ca2+ Channel/RyR/BKCa Molecular and Functional Signaloplex in Vascular Smooth Muscles

TRP channels are expressed both in vascular myocytes and endothelial cells, but knowledge of their operational mechanisms in vascular tissue is particularly limited. Here, we show for the first time the biphasic contractile reaction with relaxation followed by a contraction in response to TRPV4 agonist, GSK1016790A, in a rat pulmonary artery preconstricted with phenylephrine. Similar responses were observed both with and without endothelium, and these were abolished by the TRPV4 selective blocker, HC067047, confirming the specific role of TRPV4 in vascular myocytes. Using selective blockers of BK_Ca and L-type voltage-gated Ca²⁺ channels (Ca_L), we found that the relaxation phase was inducted by BK_Ca activation generating STOCs, while subsequent slowly developing TRPV4-mediated depolarisation activated Ca_L, producing the second contraction phase. These results are compared to TRPM8 activation using menthol in rat tail artery. Activation of both types of TRP channels produces highly similar changes in membrane potential, namely slow depolarisation with concurrent brief hyperpolarisations due to STOCs. We thus propose a general concept of bidirectional TRP-Ca_L-RyR-BK_Ca molecular and functional signaloplex in vascular smooth muscles. Accordingly, both TRPV4 and TRPM8 channels enhance local Ca²⁺ signals producing STOCs via TRP-RyR-BK_Ca coupling while simultaneously globally engaging BK_Ca and Ca_L channels by altering membrane potential.

KCa3.1 differentially regulates trachea and bronchi epithelial gene expression in a chronic-asthma mouse model

Ion channels are potentially exploitable as pharmacological targets to treat asthma. This study evaluated the role of KCa3.1 channels, encoded by Kcnn4, in regulating the gene expression of mouse airway epithelium and the development of asthma traits. We used the ovalbumin (OVA) challenge as an asthma model in wild type and Kcnn4^-/- mice, performed histological analysis, and measured serum IgE to evaluate asthma traits. We analyzed gene expression of isolated epithelial cells of trachea or bronchi using mRNA sequencing and gene ontology and performed Ussing chamber experiments in mouse trachea to evaluate anion secretion. Gene expression of epithelial cells from mouse airways differed between trachea and bronchi, indicating regional differences in the inflammatory and transepithelial transport properties of proximal and distal airways. We found that Kcnn4 silencing reduced mast cell numbers, mucus, and collagen in the airways, and reduced the amount of epithelial anion secretion in the OVA-challenged animals. Additionally, gene expression was differentially modified in the trachea and bronchi, with Kcnn4 genetic silencing significantly altering the expression of genes involved in the TNF pathway, supporting the potential of KCa3.1 as a therapeutic target for asthma.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca²⁺ over Na ⁺ influx, TRPV5 and TRPV6 are only Ca²⁺ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

Treatment with senicapoc, a KCa3.1 channel blocker, alleviates hypoxemia in a mouse model for acute respiratory distress syndrome

BACKGROUND AND PURPOSE

Acute respiratory distress syndrome (ARDS) is characterized by pulmonary oedema and severe hypoxaemia. We investigated whether genetic deficit or blockade of calcium-activated potassium (KCa3.1) channels would counteract pulmonary oedema and hypoxaemia in ventilator-induced lung injury, an experimental model for ARDS.

EXPERIMENTAL APPROACH

KCa3.1 channel knockout mice were exposed to ventilator-induced lung injury. Control mice exposed to ventilator-induced lung injury were treated with the KCa3.1 channel inhibitor, senicapoc. The outcomes were oxygenation (PaO₂ /FiO₂ ratio), lung compliance, lung wet-to-dry weight, and protein and cytokines in bronchoalveolar lavage fluid (BALF).

KEY RESULTS

Ventilator-induced lung injury resulted in lung oedema, decreased lung compliance, a severe drop in PaO₂ /FiO₂ ratio, increased protein, neutrophils, and tumor necrosis factor-alpha (TNFα) in BALF from wild-type mice compared to KCa3.1 knockout mice. Pre-treatment with senicapoc (10-70 mg/kg) prevented the reduction in PaO₂ /FiO₂ ratio, decrease in lung compliance, increased protein, and TNFα. Senicapoc (30 mg/kg) reduced histopathological lung injury score and neutrophils in BALF. After injurious ventilation, administration of 30 mg/kg senicapoc also improved the PaO₂ /FiO₂ ratio and reduced lung injury score and neutrophils in the BALF compared to vehicle-treated mice. In human lung epithelial cells, senicapoc decreased TNFα-induced permeability.

CONCLUSIONS AND IMPLICATIONS

Genetic deficiency of KCa3.1 channels and senicapoc improved the PaO₂ /FiO₂ ratio and decreased the cytokines after a ventilator-induced lung injury. Moreover, senicapoc directly affects lung epithelial cells and blocks neutrophil infiltration of the injured lung. These findings open the perspective that blocking KCa3.1 channels is a potential treatment in ARDS-like disease.

Role of Transient Receptor Potential Vanilloid 4 in Vascular Function

Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed in systemic tissues and can be activated by many stimuli. TRPV4, a Ca²⁺-permeable cation channel, plays an important role in the vasculature and is implicated in the regulation of cardiovascular homeostasis processes such as blood pressure, vascular remodeling, and pulmonary hypertension and edema. Within the vasculature, TRPV4 channels are expressed in smooth muscle cells, endothelial cells, and perivascular nerves. The activation of endothelial TRPV4 contributes to vasodilation involving nitric oxide, prostacyclin, and endothelial-derived hyperpolarizing factor pathways. TRPV4 activation also can directly cause vascular smooth muscle cell hyperpolarization and vasodilation. In addition, TRPV4 activation can evoke constriction in some specific vascular beds or under some pathological conditions. TRPV4 participates in the control of vascular permeability and vascular damage, particularly in the lung capillary endothelial barrier and lung injury. It also participates in vascular remodeling regulation mainly by controlling vasculogenesis and arteriogenesis. This review examines the role of TRPV4 in vascular function, particularly in vascular dilation and constriction, vascular permeability, vascular remodeling, and vascular damage, along with possible mechanisms, and discusses the possibility of targeting TRPV4 for therapy.

Mimicking Antigen-Driven Asthma in Rodent Models-How Close Can We Get?

Asthma is a heterogeneous disease with increasing prevalence worldwide characterized by chronic airway inflammation, increased mucus secretion and bronchial hyperresponsiveness. The phenotypic heterogeneity among asthmatic patients is accompanied by different endotypes, mainly Type 2 or non-Type 2. To investigate the pathomechanism of this complex disease many animal models have been developed, each trying to mimic specific aspects of the human disease. Rodents have classically been employed in animal models of asthma. The present review provides an overview of currently used Type 2 vs. non-Type 2 rodent asthma models, both acute and chronic. It further assesses the methods used to simulate disease development and exacerbations as well as to quantify allergic airway inflammation, including lung physiologic, cellular and molecular immunologic responses. Furthermore, the employment of genetically modified animals, which provide an in-depth understanding of the role of a variety of molecules, signaling pathways and receptors implicated in the development of this disease as well as humanized models of allergic inflammation, which have been recently developed to overcome differences between the rodent and human immune systems, are discussed. Nevertheless, differences between mice and humans should be carefully considered and limits of extrapolation should be wisely taken into account when translating experimental results into clinical use.

Lack of Kcnn4 improves mucociliary clearance in muco-obstructive lung disease

Airway mucociliary clearance (MCC) is the main mechanism of lung defense keeping airways free of infection and mucus obstruction. Airway surface liquid volume, ciliary beating, and mucus are central for proper MCC and critically regulated by sodium absorption and anion secretion. Impaired MCC is a key feature of muco-obstructive diseases. The calcium-activated potassium channel KCa.3.1, encoded by Kcnn4, participates in ion secretion, and studies showed that its activation increases Na⁺ absorption in airway epithelia, suggesting that KCa3.1-induced hyperpolarization was sufficient to drive Na⁺ absorption. However, its role in airway epithelium is not fully understood. We aimed to elucidate the role of KCa3.1 in MCC using a genetically engineered mouse. KCa3.1 inhibition reduced Na⁺ absorption in mouse and human airway epithelium. Furthermore, the genetic deletion of Kcnn4 enhanced cilia beating frequency and MCC ex vivo and in vivo. Kcnn4 silencing in the Scnn1b-transgenic mouse (Scnn1b^tg/+), a model of muco-obstructive lung disease triggered by increased epithelial Na⁺ absorption, improved MCC, reduced Na⁺ absorption, and did not change the amount of mucus but did reduce mucus adhesion, neutrophil infiltration, and emphysema. Our data support that KCa3.1 inhibition attenuated muco-obstructive disease in the Scnn1b^tg/+ mice. K⁺ channel modulation may be a therapeutic strategy to treat muco-obstructive lung diseases.

Silencing the calcium-activated potassium channel KCa.3.1 improves mucociliary clearance in muco-obstructive lung disease by decreasing sodium absorption in the airways.

Downregulation of the Ca2+-activated K+ channel KCa3.1 in mouse preosteoblast cells treated with vitamin D receptor agonist

The maturity of osteoblasts by proliferation and differentiation in preosteoblasts is essential for maintaining bone homeostasis. The beneficial effects of vitamin D on bone homeostasis in mammals have been demonstrated experimentally and clinically. However, the direct actions of vitamin D on preosteoblasts remain to be fully elucidated. In this study, we found that the functional activity of intermediate-conductance Ca²⁺-activated K⁺ channels (K_Ca3.1) positively regulated cell proliferation in MC3T3-E1 cells derived from mouse preosteoblasts by enhancing intracellular Ca²⁺ signaling. We examined the effects of treatment with vitamin D receptor (VDR) agonist on the expression and activity of K_Ca3.1 by real-time PCR examination, Western blotting, Ca²⁺ imaging, and patch clamp analyses in mouse MC3T3-E1 cells. Following the downregulation of K_Ca3.1 transcriptional modulators such as Fra-1 and HDAC2, K_Ca3.1 activity was suppressed in MC3T3-E1 cells treated with VDR agonists. Furthermore, application of the K_Ca3.1 activator DCEBIO attenuated the VDR agonist-evoked suppression of cell proliferation rate. These findings suggest that a decrease in K_Ca3.1 activity is involved in the suppression of cell proliferation rate in VDR agonist-treated preosteoblasts. Therefore, K_Ca3.1 plays an important role in bone formation by promoting osteoblastic proliferation under physiological conditions.

TRPV4: A Physio and Pathophysiologically Significant Ion Channel

Transient Receptor Potential (TRP) channels are a family of ion channels whose members are distributed among all kinds of animals, from invertebrates to vertebrates. The importance of these molecules is exemplified by the variety of physiological roles they play. Perhaps, the most extensively studied member of this family is the TRPV1 ion channel; nonetheless, the activity of TRPV4 has been associated to several physio and pathophysiological processes, and its dysfunction can lead to severe consequences. Several lines of evidence derived from animal models and even clinical trials in humans highlight TRPV4 as a therapeutic target and as a protein that will receive even more attention in the near future, as will be reviewed here.

Transient receptor potential vanilloid 4 is a critical mediator in LPS mediated inflammation by mediating calcineurin/NFATc3 signaling

Transient Receptor Potential Vanilloid 4 (TRPV4) ion channel is thought to be an essential component of inflammatory response. However, its role and mechanism in regulating acute lung injury (ALI) and macrophages activation are not well characterized. In our study, we observe that blockade of TRPV4 using GSK2193874 or HC-067047 greatly improve the pneumonedema, the lung pathologic changes, the up-regulation of proinflammatory cytokines and the neutrophil infiltration in LPS-induced lung injury. In vitro, knockdown of TRPV4 in macrophages reduces the levels of pro-inflammatory cytokines, ROS production, Ca²⁺ concentration in cytoplasma and the activation of calcineurin/NFATc3 signaling. Importantly, change of extracellular Ca²⁺ in culture medium prevents LPS-induced NFATc3 nuclear translocation, up-regulation of proinflammatory cytokines and ROS production in macrophages. Inhibition of calcineurin with cyclosporine A, FK506 down-regulates the levels of NFATc3 nuclear translocation and proinflammatory cytokines expression. Our results demonstrate that TRPV4-dependent Ca²⁺ influx contributes to LPS-induced macrophage activation by calcineurin-NFATc3 pathway.

Involvement of ion channels in allergy

Allergic asthma is a complex disease, often characterized by an inappropriate Th2 response to normally harmless allergens. Epithelial cells damaged or activated by the allergen produce IL-33, TSLP and IL-25, activating ILC2 and dendritic cells. The latter migrate into lymph nodes where they induce Th2-cell commitment. Th2 and other type 2 innate inflammatory cells trigger inflammation and airway hyper-reactivity. The toolbox consisting of the ion channels varies from one cellular type to another and depends on its activation state, offering the possibility to design novel drugs in the field of allergy. We will discuss about some channels as calcium, nonselective cation, potassium and chloride channels that appear as good candidates in allergy.