Loss of classical transient receptor potential 6 channel reduces allergic airway response

TRPC6 is ubiquitously present in lymphatic tissues: A study using samples from body donors

Transient receptor potential canonical channel 6 (TRPC6) is a non-selective cation channel that is activated by diacylglycerol. It belongs to the TRP superfamily, is expressed in numerous tissues and has been shown to be associated with diseases, such as focal segmental glomerulosclerosis, idiopathic pulmonary arterial hypertension and cardiac hypertrophy. The investigation of the channel in human lymphoid tissues has thus far been limited to mRNA analysis or the western blotting of isolated lymphoid cell lines. The present study aimed to detect the channel in human lymphoid tissue using immunohistochemistry. For this purpose, lymphatic tissues were obtained from body donors. The lymphatic organs analyzed included the lymph nodes, spleen, palatine tonsil, gut-associated lymphoid tissues (ileum and vermiform appendix) and thymus. A total of 102 samples were obtained and processed for hematoxylin and eosin (H&E) staining. The H&E staining method was employed to identify five samples with good morphology. In total, three samples of the palatine tonsil of patients were included. Immunostaining was carried out using a knockout-validated anti-TRPC6 antibody. As shown by the results, using immunohistochemical staining, the presence of TRPC6 was confirmed in all the analyzed lymphatic tissue samples. Lymphocytes in lymph nodes, spleen, palatine tonsil, thymus, and gut-associated lymphatic tissues in ileum and vermiform appendix exhibited a positive staining signal. The follicle-associated epithelium of the palatine tonsil, ileum and appendix also demonstrated staining. Vessels of the lymphatic organs, particularly the trabecular arteries of the spleen, the submucosal vessels of the appendix and ileum, as well as the high endothelial venules in the palatine tonsils and lymphatic vessels of the lymph nodes expressed TRPC6 protein. TRPC6 in follicles may be involved in the immune response. TRPC6 in high endothelial venules suggests a role in leukocyte migration. The role of TRPC6 and other channels of the TRP family in lymphatic organs warrant further investigations to elucidate whether TRP channels are a pharmacological target.

TRP Ion Channels in Immune Cells and Their Implications for Inflammation

The transient receptor potential (TRP) ion channels act as cellular sensors and mediate a plethora of physiological processes, including somatosensation, proliferation, apoptosis, and metabolism. Under specific conditions, certain TRP channels are involved in inflammation and immune responses. Thus, focusing on the role of TRPs in immune system cells may contribute to resolving inflammation. In this review, we discuss the distribution of five subfamilies of mammalian TRP ion channels in immune system cells and how these ion channels function in inflammatory mechanisms. This review provides an overview of the current understanding of TRP ion channels in mediating inflammation and may offer potential avenues for therapeutic intervention.

A Putative Role for TRPC6 in Immune-Mediated Kidney Injury

Excessive activation of the immune system is the cause of a wide variety of renal diseases. However, the pathogenic mechanisms underlying the aberrant activation of the immune system in the kidneys often remain unknown. TRPC6, a member of the Ca2+-permeant family of TRPC channels, is important in glomerular epithelial cells or podocytes for the process of glomerular filtration. In addition, TRPC6 plays a crucial role in the development of kidney injuries by inducing podocyte injury. However, an increasing number of studies suggest that TRPC6 is also responsible for tightly regulating the immune cell functions. It remains elusive whether the role of TRPC6 in the immune system and the pathogenesis of renal inflammation are intertwined. In this review, we present an overview of the current knowledge of how TRPC6 coordinates the immune cell functions and propose the hypothesis that TRPC6 might play a pivotal role in the development of kidney injury via its role in the immune system.

Transient Receptor Potential (TRP) Channels in Airway Toxicity and Disease: An Update

Our respiratory system is exposed to toxicants and pathogens from both sides: the airways and the vasculature. While tracheal, bronchial and alveolar epithelial cells form a natural barrier in the airways, endothelial cells protect the lung from perfused toxic compounds, particulate matter and invading microorganism in the vascular system. Damages induce inflammation by our immune response and wound healing by (myo)fibroblast proliferation. Members of the transient receptor potential (TRP) superfamily of ion channel are expressed in many cells of the respiratory tract and serve multiple functions in physiology and pathophysiology. TRP expression patterns in non-neuronal cells with a focus on TRPA1, TRPC6, TRPM2, TRPM5, TRPM7, TRPV2, TRPV4 and TRPV6 channels are presented, and their roles in barrier function, immune regulation and phagocytosis are summarized. Moreover, TRP channels as future pharmacological targets in chronic obstructive pulmonary disease (COPD), asthma, cystic and pulmonary fibrosis as well as lung edema are discussed.

The effect of Ma-Xin-Gan-Shi decoction on asthma exacerbated by respiratory syncytial virus through regulating TRPV1 channel

ETHNOPHARMACOLOGICAL RELEVANCE

The incidence and mortality of bronchial asthma are increasing, and respiratory syncytial virus (RSV) is widely regarded as the common cause of clinical exacerbation of asthma. Ma-Xing-Gan-Shi decoction (MXGSD), a classic traditional Chinese medicine prescription, is well-known for treating respiratory diseases, while the mechanism of effecting on RSV-exacerbated asthma remains to be explored.

AIM OF THE STUDY

In this study, we investigated the mechanism by which MXGSD exerts a protective effect on asthma exacerbated by RSV in vivo and in vitro.

MATERIALS AND METHODS

MXGSD is composed of four Chinese medicine, including Ephedra intermedia Schrenk & C.A.Mey. (herbaceous stem, 27g), Prunus armeniaca L. (dry seed, 27g), Glycyrrhiza uralensis Fisch. (radix and rhizome, 18g), and Gypsum fibrosum (main component: CaSO4·2H2O, 54g). In the present study, the exacerbated asthmatic mice model with the treatment of OVA plus RSV was replicated, and accompanied by the TMT proteomic analysis and further experimental investigations. Then, the protective effect of MXGSD (13.2, 6.6, 3.3 g/kg/d, 7d) on the mice treated by OVA plus RSV, and the mechanism of regulating TRPV1 was explored. In addition, the intracellular Ca2+ concentration of 16HBE cells pretreated with MXGSD medicated serum was also tested after stimulation with the TRPV1 agonist capsaicin.

RESULTS

The results suggested that MXGSD could reduce the levels of inflammation cells, airway hyperresponsiveness, and pathological damage of lung tissue. TMT quantitative proteomics analysis and further experimental exploration revealed that MXGSD could reduce the levels of IL-4, IL-13, PGE2, and SP in BAL and down-regulate the expression of TRPV1 mRNA and protein in lung tissue. Furthermore, 16HBE cells stimulated by capsaicin showed an increased intracellular Ca2+ concentration, while the pretreatment of MXGSD medicated serum could reduce it.

CONCLUSION

MSGSD showed a protective effect on RSV-exacerbated asthma, which may be related to its regulation of TRPV1 expression and reduction of Th2 cytokines and neurogenic inflammatory mediators. It may provide an objective basis and reference for the clinical application of MXGSD.

Distribution and Assembly of TRP Ion Channels

In the last several decades, a large family of ion channels have been identified and studied intensively as cellular sensors for diverse physical and/or chemical stimuli. Named transient receptor potential (TRP) channels, they play critical roles in various aspects of cellular physiology. A large number of human hereditary diseases are found to be linked to TRP channel mutations, and their dysregulations lead to acute or chronical health problems. As TRP channels are named and categorized mostly based on sequence homology rather than functional similarities, they exhibit substantial functional diversity. Rapid advances in TRP channel study have been made in recent years and reported in a vast body of literature; a summary of the latest advancements becomes necessary. This chapter offers an overview of current understandings of TRP channel distribution and subunit assembly.

Heteromeric TRP Channels in Lung Inflammation

Activation of Transient Receptor Potential (TRP) channels can disrupt endothelial barrier function, as their mediated Ca²⁺ influx activates the CaM (calmodulin)/MLCK (myosin light chain kinase)-signaling pathway, and thereby rearranges the cytoskeleton, increases endothelial permeability and thus can facilitate activation of inflammatory cells and formation of pulmonary edema. Interestingly, TRP channel subunits can build heterotetramers, whereas heteromeric TRPC1/4, TRPC3/6 and TRPV1/4 are expressed in the lung endothelium and could be targeted as a protective strategy to reduce endothelial permeability in pulmonary inflammation. An update on TRP heteromers and their role in lung inflammation will be provided with this review.

Transient Receptor Potential Canonical (TRPC) Channels: Then and Now

Twenty-five years ago, the first mammalian Transient Receptor Potential Canonical (TRPC) channel was cloned, opening the vast horizon of the TRPC field. Today, we know that there are seven TRPC channels (TRPC1-7). TRPCs exhibit the highest protein sequence similarity to the Drosophila melanogaster TRP channels. Similar to Drosophila TRPs, TRPCs are localized to the plasma membrane and are activated in a G-protein-coupled receptor-phospholipase C-dependent manner. TRPCs may also be stimulated in a store-operated manner, via receptor tyrosine kinases, or by lysophospholipids, hypoosmotic solutions, and mechanical stimuli. Activated TRPCs allow the influx of Ca2+ and monovalent alkali cations into the cytosol of cells, leading to cell depolarization and rising intracellular Ca2+ concentration. TRPCs are involved in the continually growing number of cell functions. Furthermore, mutations in the TRPC6 gene are associated with hereditary diseases, such as focal segmental glomerulosclerosis. The most important recent breakthrough in TRPC research was the solving of cryo-EM structures of TRPC3, TRPC4, TRPC5, and TRPC6. These structural data shed light on the molecular mechanisms underlying TRPCs' functional properties and propelled the development of new modulators of the channels. This review provides a historical overview of the major advances in the TRPC field focusing on the role of gene knockouts and pharmacological tools.

Modulation of Transient Receptor Potential Channels 3 and 6 Regulates Osteoclast Function with Impact on Trabecular Bone Loss

Enhanced osteoclast formation and function is a fundamental cause of alterations to bone structure and plays an important role in several diseases impairing bone quality. Recent work revealed that TRP calcium channels 3 and 6 might play a special role in this context. By analyzing the bone phenotype of TRPC6-deficient mice we detected a regulatory effect of TRPC3 on osteoclast function. These mice exhibit a significant decrease in bone volume per tissue volume, trabecular thickness and -number together with an increased number of osteoclasts found on the surface of trabecular bone. Primary bone marrow mononuclear cells from TRPC6-deficient mice showed enhanced osteoclastic differentiation and resorptive activity. This was confirmed in vitro by using TRPC6-deficient RAW 264.7 cells. TRPC6 deficiency led to an increase of TRPC3 in osteoclasts, suggesting that TRPC3 overcompensates for the loss of TRPC6. Raised intracellular calcium levels led to enhanced NFAT-luciferase reporter gene activity in the absence of TRPC6. In line with these findings inhibition of TRPC3 using the specific inhibitor Pyr3 significantly reduced intracellular calcium concentrations and normalized osteoclastic differentiation and resorptive activity of TRPC6-deficient cells. Interestingly, an up-regulation of TRPC3 could be detected in a cohort of patients with low bone mineral density by comparing micro array data sets of circulating human osteoclast precursor cells to those from patients with high bone mineral density, suggesting a noticeable contribution of TRP calcium channels on bone quality. These observations demonstrate a novel regulatory function of TRPC channels in the process of osteoclastic differentiation and bone loss.

The Role of TRP Channels in Allergic Inflammation and its Clinical Relevance

Allergy refers to an abnormal adaptive immune response to non-infectious environmental substances (allergen) that can induce various diseases such as asthma, atopic dermatitis, and allergic rhinitis. In this allergic inflammation, various immune cells, such as B cells, T cells, and mast cells, are involved and undergo complex interactions that cause a variety of pathophysiological conditions. In immune cells, calcium ions play a crucial role in controlling intracellular Ca2+ signaling pathways. Cations, such as Na+, indirectly modulate the calcium signal generation by regulating cell membrane potential. This intracellular Ca2+ signaling is mediated by various cation channels; among them, the Transient Receptor Potential (TRP) family is present in almost all immune cell types, and each channel has a unique function in regulating Ca2+ signals. In this review, we focus on the role of TRP ion channels in allergic inflammatory responses in T cells and mast cells. In addition, the TRP ion channels, which are attracting attention in clinical practice in relation to allergic diseases, and the current status of the development of therapeutic agents that target TRP channels are discussed.

Intravascular adhesion and recruitment of neutrophils in response to CXCL1 depends on their TRPC6 channels

Abstract

Here we report a novel role for TRPC6, a member of the transient receptor potential (TRPC) channel family, in the CXCL1-dependent recruitment of murine neutrophil granulocytes. Representing a central element of the innate immune system, neutrophils are recruited from the blood stream to a site of inflammation. The recruitment process follows a well-defined sequence of events including adhesion to the blood vessel walls, migration, and chemotaxis to reach the inflammatory focus. A common feature of the underlying signaling pathways is the utilization of Ca²⁺ ions as intracellular second messengers. However, the required Ca²⁺ influx channels are not yet fully characterized. We used WT and TRPC6^−/− neutrophils for in vitro and TRPC6^−/− chimeric mice (WT mice with WT or TRPC6^−/− bone marrow cells) for in vivo studies. After renal ischemia and reperfusion injury, TRPC6^−/− chimeric mice had an attenuated TRPC6^−/− neutrophil recruitment and a better outcome as judged from the reduced increase in the plasma creatinine concentration. In the cremaster model CXCL1-induced neutrophil adhesion, arrest and transmigration were also decreased in chimeric mice with TRPC6^−/− neutrophils. Using atomic force microscopy and microfluidics, we could attribute the recruitment defect of TRPC6^−/− neutrophils to the impact of the channel on adhesion to endothelial cells. Mechanistically, TRPC6^−/− neutrophils exhibited lower Ca²⁺ transients during the initial adhesion leading to diminished Rap1 and β₂ integrin activation and thereby reduced ICAM-1 binding. In summary, our study reveals that TRPC6 channels in neutrophils are crucial signaling modules in their recruitment from the blood stream in response to CXCL1.

Key point

Neutrophil TRPC6 channels are crucial for CXCL1-triggered activation of integrins during the initial steps of neutrophil recruitment.

TRPC6 modulates adhesion of neutrophils to airway epithelial cells via NF-κB activation and ICAM-1 expression with ozone exposure

Ozone (O₃) is a major component of air pollution, which has been associated with airway inflammation characterized by the influx of neutrophils in asthmatic subjects. Canonical transient receptor potential 6 (TRPC6) channel is recently identified as a target of oxidative stress which is involved in airway inflammation. However, the regulatory role of TRPC6 in airway epithelial cells and neutrophils has not yet been illuminated in detail. In this study, we investigated the role of TRPC6 in neutrophil adhesion to airway epithelial cells exposed to O₃ in vivo and in vitro approaches. Using transgenic mice, the results showed that TRPC6-deficiency attenuated O₃-induced neutrophil recruitment to airway epithelial cells and intercellular adhesion molecule-1 (ICAM-1) expression. In vitro, O₃ induced ICAM-1 expression and neutrophil adhesion to 16HBE cells (human airway epithelial cell line) and which were reduced by both TRPC6 silencing short hairpin RNA (shRNA) and TRPC6 inhibitor Larixyl Acetate (LA). We also confirmed that TRPC6-dependent Ca²⁺ entry and NF-κB activation in 16HBE cells were required for ICAM-1-mediated neutrophil adhesion exposed to O₃. In conclusion, this study demonstrated the contribution of TRPC6 to O₃-induced neutrophil adhesion to airway epithelial cells via NF-κB activation and ICAM-1 expression, which may provide new potential concepts for preventing and treating air pollutant-related inflammatory lung diseases.

Modulators of Transient Receptor Potential (TRP) Channels as Therapeutic Options in Lung Disease

The lungs are essential for gas exchange and serve as the gateways of our body to the external environment. They are easily accessible for drugs from both sides, the airways and the vasculature. Recent literature provides evidence for a role of Transient Receptor Potential (TRP) channels as chemosensors and essential members of signal transduction cascades in stress-induced cellular responses. This review will focus on TRP channels (TRPA1, TRPC6, TRPV1, and TRPV4), predominantly expressed in non-neuronal lung tissues and their involvement in pathways associated with diseases like asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), lung fibrosis, and edema formation. Recently identified specific modulators of these channels and their potential as new therapeutic options as well as strategies for a causal treatment based on the mechanistic understanding of molecular events will also be evaluated.

Ion channels as therapeutic antibody targets

It is now well established that antibodies have numerous potential benefits when developed as therapeutics. Here, we evaluate the technical challenges of raising antibodies to membrane-spanning proteins together with enabling technologies that may facilitate the discovery of antibody therapeutics to ion channels. Additionally, we discuss the potential targeting opportunities in the anti-ion channel antibody landscape, along with a number of case studies where functional antibodies that target ion channels have been reported. Antibodies currently in development and progressing towards the clinic are highlighted.

The TRPC6 intronic polymorphism, associated with the risk of neurological disorders in systemic lupus erythematous, influences immune cell function

Patients with systemic lupus erythematosus (SLE) carrying a TT genotype for the rs7925662 single nucleotide polymorphism (SNP) in the transient receptor potential canonical channel 6 (TRPC6) gene are more likely to develop neuropsychiatric manifestations (NPSLE). We functionally characterised the effects of TRPC6 on peripheral blood mononuclear cells from 18 patients with SLE and 8 healthy controls with a known genotype. TRPC6 influenced calcium currents, apoptosis rates and cytokine secretion in a disease- and genotype-dependent manner. Cells from TT patients with NPSLE were more dependent on TRPC6 for the generation of calcium currents.

Transient Receptor Potential Channels and Chronic Airway Inflammatory Diseases: A Comprehensive Review

Chronic airway inflammatory diseases remain a major problem worldwide, such that there is a need for additional therapeutic targets and novel drugs. Transient receptor potential (TRP) channels are a group of non-selective cation channels expressed throughout the body that are regulated by various stimuli. TRP channels have been identified in numerous cell types in the respiratory tract, including sensory neurons, airway epithelial cells, airway smooth muscle cells, and fibroblasts. Different types of TRP channels induce cough in sensory neurons via the vagus nerve. Permeability and cytokine production are also regulated by TRP channels in airway epithelial cells, and these channels also contribute to the modulation of bronchoconstriction. TRP channels may cooperate with other TRP channels, or act in concert with calcium-dependent potassium channels and calcium-activated chloride channel. Hence, TRP channels could be the potential therapeutic targets for chronic airway inflammatory diseases. In this review, we aim to discuss the expression profiles and physiological functions of TRP channels in the airway, and the roles they play in chronic airway inflammatory diseases.

Ion Channels and Transporters in Inflammation: Special Focus on TRP Channels and TRPC6

Allergy and autoimmune diseases are characterised by a multifactorial pathogenic background. Several genes involved in the control of innate and adaptive immunity have been associated with diseases and variably combine with each other as well as with environmental factors and epigenetic processes to shape the characteristics of individual manifestations. Systemic or local perturbations in salt/water balance and in ion exchanges between the intra- and extracellular spaces or among tissues play a role. In this field, usually referred to as elementary immunology, novel evidence has been recently acquired on the role of members of the transient potential receptor (TRP) channel family in several cellular mechanisms of potential significance for the pathophysiology of the immune response. TRP canonical channel 6 (TRPC6) is emerging as a functional element for the control of calcium currents in immune-committed cells and target tissues. In fact, TRPC6 influences leukocytes’ tasks such as transendothelial migration, chemotaxis, phagocytosis and cytokine release. TRPC6 also modulates the sensitivity of immune cells to apoptosis and influences tissue susceptibility to ischemia-reperfusion injury and excitotoxicity. Here, we provide a view of the interactions between ion exchanges and inflammation with a focus on the pathogenesis of immune-mediated diseases and potential future therapeutic implications.

Trpc6 inactivation confers protection in a model of severe nephrosis in rats

Abstract

Mutations in canonical transient receptor potential-6 (TRPC6) channels give rise to rare familial forms of focal and segmental glomerulosclerosis (FSGS). Here we examined a possible role for TRPC6 in the progression of chronic puromycin aminonucleoside (PAN) nephrosis in Sprague-Dawley rats, a classic model of acquired nephrotic syndromes. We used CRISPR/Cas9 technology to delete a 239-bp region within exon 2 of the Trpc6 gene (Trpc6^del allele). Trpc6^del/del rats expressed detectable Trpc6 transcripts missing exon 2, and TRPC6 proteins could be detected by immunoblot of renal cortex. However, the abundance of Trpc6 transcripts and TRPC6 protein in renal cortex was much lower than in Trpc6^wt/wt littermates, and functional TRPC6 channels could not be detected in whole-cell recordings from glomerular cells cultured from Trpc6^del/del animals, possibly because of disruption of ankyrin repeats 1 and 2. During the chronic phase of PAN nephrosis, Trpc6^del/del rats had reduced urine albumin excretion, reduced serum cholesterol and triglycerides, and improved azotemia compared to wild-type Trpc6^wt/wt littermates. Glomerulosclerosis was severe during chronic PAN nephrosis in Trpc6^wt/wt rats but was markedly reduced in Trpc6^del/del littermates. Trpc6^del/del animals also had less severe tubulointerstitial fibrosis as assessed by several biochemical and histological analyses, as well as reduced foot process effacement and glomerular basement thickening compared to Trpc6^wtt/wt controls. None of the manipulations in this study affected the abundance of TRPC5 channels in renal cortex. TRPC3 was increased in PAN nephrosis and in Trpc6^del/del rats. These data support a role for TRPC6 channels in driving an acquired form of secondary FSGS.

Key messages

We examined aminonucleoside nephrosis in rats with wild type and inactivated TRPC6.

TRPC6 channels were inactivated by CRISPR/Cas9 editing of the Trpc6 gene.

TRPC6 inactivation reduced albuminuria in the chronic but not the acute phase.

TRPC6 inactivation reduced glomerulosclerosis and ultrastructural changes.

TRPC6 inactivation also reduced interstitial changes and renal fibrosis.

Electronic supplementary material

The online version of this article (10.1007/s00109-018-1648-3) contains supplementary material, which is available to authorized users.

TRPC3 overexpression and intervention in airway smooth muscle of ovalbumin-induced hyperresponsiveness and remodeling

Transient receptor potential canonical channel 3 (TRPC3) proteins function as non-voltage-gated Ca²⁺ -permeable channels and play divergent roles in many processes of pathophysiology. The purpose of this study was to determine the relationship between TRPC3 expression and airway hyperresponsiveness and remodeling in ovalbumin-induced asthmatic Kunming mice. Mice were sensitized and challenged by ovalbumin to establish asthmatic model. Hematoxylin-eosin staining, hydroxyproline assay, and isometric tracheal ring force measurement were used to evaluate airway remodeling and hyperresponsiveness in asthmatic mice. Western blot was performed to detect the expression of TRPC3 proteins. MTT assay was used to measure the proliferation of airway smooth muscle cells. TRPC3 protein expression increased in airway smooth muscle of asthmatic mice. GdCl₃ , a nonspecific TRPC blocker, attenuated the contractile force of airway smooth muscle. Fetal bovine serum stimulated airway smooth muscle cells proliferation and augmented TRPC3 protein expression. Both TRPC3 blockade by GdCl₃ or specific TRPC3 antibodies and gene silencing by siRNA inhibited the proliferation of airway smooth muscle cells. In contrast, the current drugs treatment for asthma such as Dexamethasone and Aminophylline had no effects on TRPC3 protein overexpression. Therefore, TRPC3 protein overexpression may be involved in airway smooth muscle hyperresponsiveness and remodeling in asthmatic mice, providing evidence for a new direction of asthma pathogenesis research and a new target for drug intervention.

TRPC6 contributes to LPS-induced inflammation through ERK1/2 and p38 pathways in bronchial epithelial cells

receptor potential canonical (TRPC) channels are presently an emerging target for airway disorders. Recent evidence has indicated that TRPC6 as a member of the TRPC family plays an important role in airway inflammation, but its precise function in bronchial epithelial cells remains unclear. The aim of this study was to investigate the role of TRPC6 in Toll-like receptor 4 (TLR4)-mediated inflammation in human bronchial epithelial cells stimulated by endotoxin [lipopolysaccharide (LPS)]. Hyp9 is a simplified phloroglucinol derivative of hyperforin that highly selectively activates TRPC6 channels. The results show that the activation of TRPC6 by Hyp9 induced the production of interleukin (IL)-8 and IL-6. LPS was also able to induce the release of IL-8 and IL-6, which was significantly aggravated by Hyp9 and reduced by knockdown of TRPC6. Treatment with LPS not only chronically induced the expression of TRPC6 mRNA and protein in a TLR4-dependent manner but also acutely increased Ca²⁺ influx through TRPC6 channels. In addition, LPS-induced overexpression of TRPC6 and Ca²⁺ influx were associated with the phosphorylation of phosphatidylinositol 3-kinase (PI3K) and Akt. Importantly, TRPC6 was required for the activation of ERK1/2, p38, and NF-κB. In conclusion, these data reveal that LPS induced the overexpression of TRPC6 and TRPC6-dependent Ca²⁺ influx via the TLR4/PI3K/Akt pathway resulting in Ca²⁺ mobilization, which subsequently promoted the activation of ERK1/2, p38, and NF-κB and the inflammatory response in bronchial epithelial cells.

TRPC Channels in Health and Disease

This chapter offers a brief introduction of the functions of TRPC channels in non-neuronal systems. We focus on three major organs of which the research on TRPC channels have been most focused on: kidney, heart, and lung. The chapter highlights on cellular functions and signaling pathways mediated by TRPC channels. It also summarizes several inherited diseases in humans that are related to or caused by TRPC channel mutations and malfunction. A better understanding of TRPC channels functions and the importance of TRPC channels in health and disease should lead to new insights and discovery of new therapeutic approaches for intractable disease.

Transendothelial migration: unifying principles from the endothelial perspective

Transendothelial migration (TEM) of polymorphonuclear leukocytes (PMN) involves a carefully orchestrated dialog of adhesion and signaling events between leukocyte and endothelial cell. This article focuses on the contribution of endothelial cells to transmigration. The initiation of TEM itself generally requires interaction of PECAM on the leukocyte with PECAM at the endothelial cell border. This is responsible for the transient elevation of cytosolic-free calcium ions in endothelium that is required for TEM and for recruitment of membrane from the lateral border recycling compartment (LBRC). TEM requires LBRC to move to the site at which TEM will take place and for VE-cadherin to move away. Targeting of the LBRC to this site likely precedes movement of VE-cadherin and may play a role in clearing VE-cadherin from the site of TEM. The process of TEM can be dissected into steps mediated by distinct pairs of PMN/endothelial interacting molecules. CD99 regulates a step at or close to the end of TEM. CD99 signals through soluble adenylyl cyclase to activate PKA to trigger ongoing targeted recycling of the LBRC. Paracellular transmigration predominates (≥90% of events) in the cremaster muscle circulation, but transcellular migration may be more important at sites such as the blood-brain barrier. Both processes involve many of the same molecules and recruitment of the LBRC.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca²⁺-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Roles of transient receptor potential channels in regulation of vascular and epithelial barriers

Transient receptor potential (TRP) channels are a ubiquitously expressed multi-family group of cation channels that are critical to signaling events in many tissues. Their roles have been documented in many physiologic and pathologic conditions. Nevertheless, direct studies of their roles in maintain barrier function in endothelial and epithelia are relatively infrequent. This seems somewhat surprising considering that calcium ion concentrations are known to regulate barrier function. This short review provides an introduction to TRP channels and reviews some of the work in which investigators directly studied the role of TRP channels in endothelial permeability to electric current, solute, or leukocytes during the inflammatory response.

Transient receptor potential (TRP) channels as molecular targets in lung toxicology and associated diseases

The lungs as the gateways of our body to the external environment are essential for gas exchange. They are also exposed to toxicants from two sides, the airways and the vasculature. Apart from naturally produced toxic agents, millions of human made chemicals were produced since the beginning of the industrial revolution whose toxicity still needs to be determined. While the knowledge about toxic substances is increasing only slowly, a paradigm shift regarding the proposed mechanisms of toxicity at the plasma membrane emerged. According to their broad-range chemical reactivity, the mechanism of lung injury evoked by these agents has long been described as rather unspecific. Consequently, therapeutic options are still restricted to symptomatic treatment. The identification of molecular down-stream effectors in cells was a major step forward in the mechanistic understanding of the action of toxic chemicals and will pave the way for more causal and specific toxicity testing as well as therapeutic options. In this context, the involvement of Transient Receptor Potential (TRP) channels as chemosensors involved in the detection and effectors of toxicant action is an attractive concept intensively discussed in the scientific community. In this review we will summarize recent evidence for an involvement of TRP channels (TRPA1, TRPC4, TRPC6, TRPV1, TRPV4, TRPM2 and TRPM8) expressed in the lung in pathways of toxin sensing and as mediators of lung inflammation and associated diseases like asthma, COPD, lung fibrosis and edema formation. Specific modulators of these channels may offer new therapeutic options in the future and will endorse strategies for a causal, specifically tailored treatment based on the mechanistic understanding of molecular events induced by lung-toxic agents.

Inhibitory effects of a standardized extract of Justicia pectoralis in an experimental rat model of airway hyper-responsiveness

OBJECTIVE

Justicia pectoralis is a plant useful for the treatment of respiratory diseases. Here, we studied the antiasthmatic properties of a standardized extract of J. pectoralis (Jp).

METHODS

Ovalbumin (OVA)-sensitized rats were actively challenged with saline or OVA to study airway hyper-responsiveness after oral treatment with saline or Jp. The ability of Jp to inhibit hyper-reactivity was evaluated in isolated trachea mounted in isolated organ bath chamber.

KEY FINDINGS

Using KCl or carbachol as contractile agents, tracheal rings of OVA-challenged rats contracted with higher magnitude than trachea of rats challenged with saline. Such hyper-responsive phenotype of OVA-challenged tissues decreased with Jp administration. In Ca⁺ -free medium, Jp or its major constituent coumarin inhibited preferentially the contractions induced by Ca²⁺ addition in tissues of OVA-challenged rats stimulated with KCl or acetylcholine. In tissues depleted of their internal Ca⁺ stores in the presence of thapsigargin, Jp inhibited the contraction induced by capacitative Ca²⁺ entry. By gavage, Jp abolished the increase caused by challenge with OVA on the levels of IL-1β and TNF-α in the bronchoalveolar fluid and also impaired the changes in gene expression of canonical transient receptor proteins.

CONCLUSIONS

Jp has antiasthmatic properties in an experimental model that reproduces tracheal hyper-reactivity.

Distal airways are protected from goblet cell metaplasia by diminished expression of IL-13 signalling components

BACKGROUND

Increased mucus production is a critical factor impairing lung function in patients suffering from bronchial asthma, the most common chronic inflammatory lung disease worldwide.

OBJECTIVE

This study aimed at investigating whether goblet cell (GC) metaplasia and mucus production are differentially regulated in proximal and distal airways.

METHODS

Female Balb/c mice were sensitized to ovalbumin (OVA) and challenged with an OVA-aerosol on two consecutive days for 1 week (acute) or 12 weeks (chronic). Real-time RT-PCR analysis was applied on microdissected airways.

RESULTS

In acutely and chronically OVA-challenged mice, GC metaplasia and mucus production were observed in proximal but not in distal airways. In contrast, inflammation reflected by the infiltration of eosinophils and expression of the TH2-type cytokines IL-4 and IL-13 was increased in both proximal and distal airways. Abundance of IL-13Rα1 was lower in distal airways of healthy control mice. Under acute and chronic OVA-exposure, activation of IL-13Rα1-dependent signalling cascade, reflected by Spdef and Foxo3A transcription factors, was attenuated in distal compared to proximal airways.

CONCLUSION AND CLINICAL RELEVANCE

These data indicate that distal airways might be less sensitive to IL-13-induced GC metaplasia and mucus production through lower expression of IL-13Rα1 and attenuated activation of downstream signalling. This might represent a protective strategy to prevent mucus plugging of distal airways and thus impaired ventilation of attached alveoli.

Modulating Innate and Adaptive Immunity by (R)-Roscovitine: Potential Therapeutic Opportunity in Cystic Fibrosis

(R)-Roscovitine, a pharmacological inhibitor of kinases, is currently in phase II clinical trial as a drug candidate for the treatment of cancers, Cushing's disease and rheumatoid arthritis. We here review the data that support the investigation of (R)-roscovitine as a potential therapeutic agent for the treatment of cystic fibrosis (CF). (R)-Roscovitine displays four independent properties that may favorably combine against CF: (1) it partially protects F508del-CFTR from proteolytic degradation and favors its trafficking to the plasma membrane; (2) by increasing membrane targeting of the TRPC6 ion channel, it rescues acidification in phagolysosomes of CF alveolar macrophages (which show abnormally high pH) and consequently restores their bactericidal activity; (3) its effects on neutrophils (induction of apoptosis), eosinophils (inhibition of degranulation/induction of apoptosis) and lymphocytes (modification of the Th17/Treg balance in favor of the differentiation of anti-inflammatory lymphocytes and reduced production of various interleukins, notably IL-17A) contribute to the resolution of inflammation and restoration of innate immunity, and (4) roscovitine displays analgesic properties in animal pain models. The fact that (R)-roscovitine has undergone extensive preclinical safety/pharmacology studies, and phase I and II clinical trials in cancer patients, encourages its repurposing as a CF drug candidate.

TRPC channel modulators and their potential therapeutic applications

The transient receptor potential canonical (TRPC) channels have gained interest as potential therapeutic targets for respiratory diseases, neurological disorders, cardiovascular disorders, pain, cancer and several other pathological conditions. The TRPC receptor family consists of seven isoforms (C1-C7) and has been divided into three subfamilies based on structural and functional similarities. Several pharmaceutical companies and academic institutes are currently exploring the potential of these nonselective cation channels as therapeutic targets using small molecule inhibitors or modulators. This review covers patents on TRPC receptor modulators published from 2002 to 2014. The review mainly focuses on TRPC receptor target biology, small and large molecule modulators and their therapeutic potential.

Second Messenger-Operated Calcium Entry Through TRPC6

Canonical transient receptor potential 6 (TRPC6) proteins assemble into heteromultimeric structures forming non-selective cation channels. In addition, many TRPC6-interacting proteins have been identified like some enzymes, channels, pumps, cytoskeleton-associated proteins, immunophilins, or cholesterol-binding proteins, indicating that TRPC6 are engaged into macromolecular complexes. Depending on the cell type and the experimental conditions used, TRPC6 activity has been reported to be controlled by diverse modalities. For instance, the second messenger diacylglycerol, store-depletion, the plant extract hyperforin or H2O2 have all been shown to trigger the opening of TRPC6 channels. A well-characterized consequence of TRPC6 activation is the elevation of the cytosolic concentration of Ca(2+). This latter response can reflect the entry of Ca(2+) through open TRPC6 channels but it can also be due to the Na(+)/Ca(2+) exchanger (operating in its reverse mode) or voltage-gated Ca(2+) channels (recruited in response to a TRPC6-mediated depolarization). Although TRPC6 controls a diverse array of biological functions in many tissues and cell types, its pathophysiological functions are far from being fully understood. This chapter covers some key features of TRPC6, with a special emphasis on their biological significance in kidney and blood cells.

Transient receptor potential (TRP) channels as a therapeutic target for intervention of respiratory effects and lethality from phosgene

Phosgene (CG), a toxic inhalation and industrial hazard, causes bronchoconstriction, vasoconstriction and associated pathological effects that could be life threatening. Ion channels of the transient receptor potential (TRP) family have been identified to act as specific chemosensory molecules in the respiratory tract in the detection, control of adaptive responses and initiation of detrimental signaling cascades upon exposure to various toxic inhalation hazards (TIH); their activation due to TIH exposure may result in broncho- and vasoconstriction. We studied changes in the regulation of intracellular free Ca(2+) concentration ([Ca(2+)]i) in cultures of human bronchial smooth muscle cells (BSMC) and human pulmonary microvascular endothelial cells (HPMEC) exposed to CG (16ppm, 8min), using an air/liquid interface exposure system. CG increased [Ca(2+)]i (p<0.05) in both cell types, The CG-induced [Ca(2+)]i was blocked (p<0.05) by two types of TRP channel blockers, SKF-96365, a general TRP channel blocker, and RR, a general TRPV (vanilloid type) blocker, in both BSMC and HPMEC. These effects correlate with the in vivo efficacies of these compounds to protect against lung injury and 24h lethality from whole body CG inhalation exposure in mice (8-10ppm×20min). Thus the TRP channel mechanism appears to be a potential target for intervention in CG toxicity.

Identification and Validation of Larixyl Acetate as a Potent TRPC6 Inhibitor

Classical or canonical transient receptor potential 6 (TRPC6), a nonselective and Ca(2+)-permeable cation channel, mediates pathophysiological responses within pulmonary and renal diseases that are still poorly controlled by current medication. Thus, controlling TRPC6 activity may provide a promising and challenging pharmacological approach. Recently identified chemical entities have demonstrated that TRPC6 is pharmacologically targetable. However, isotype-selectivity with regard to its closest relative, TRPC3, is difficult to achieve. Reasoning that balsams, essential oils, or incense materials that are traditionally used for inhalation may contain biologic activities to block TRPC6 activity, we embarked on a natural compound strategy to identify new TRPC6-blocking chemical entities. Within several preparations of plant extracts, a strong TRPC6-inhibitory activity was found in conifer balsams. The biologic activity was associated with nonvolatile resins, but not with essential oils. Of various conifers, the larch balsam was unique in displaying a marked TRPC6-prevalent mode of action. By testing the main constituents of larch resin, we identified larixol and larixyl acetate as blockers of Ca(2+) entry and ionic currents through diacylglycerol- or receptor-activated recombinant TRPC6 channels, exhibiting approximately 12- and 5-fold selectivity compared with its closest relatives TRPC3 and TRPC7, respectively. No significant inhibition of more distantly related TRPV or TRPM channels was seen. The potent inhibition of recombinant TRPC6 by larixyl acetate (IC50 = 0.1-0.6 µM) was confirmed for native TRPC6-like [Ca(2+)]i signals in diacylglycerol-stimulated rat pulmonary artery smooth muscle cells. In isolated mouse lungs, larix-6-yl monoacetate (CAS 4608-49-5; larixyl acetate; 5 µM) prevented acute hypoxia-induced vasoconstriction. We conclude that larch-derived labdane-type diterpenes are TRPC6-selective inhibitors and may represent a starting point for pharmacological TRPC6 modulation within experimental therapies.

Transient Receptor Potential (TRP) channels in T cells

The transient receptor potential (TRP) family of ion channels is widely expressed in many cell types and plays various physiological roles. Growing evidence suggests that certain TRP channels are functionally expressed in the immune system. Indeed, an increasing number of reports have demonstrated the functional expression of several TRP channels in innate and adaptive immune cells and have highlighted their critical role in the activation and function of these cells. However, very few reviews have been entirely dedicated to this subject. Here, we will summarize the recent findings with regards to TRP channel expression in T cells and discuss their emerging role as regulators of T cell activation and functions. Moreover, these studies suggest that beyond their pharmaceutical interest in pain management, certain TRP channels may represent potential novel therapeutic targets for various immune-related diseases.

TRPC6 is the endothelial calcium channel that regulates leukocyte transendothelial migration during the inflammatory response

Weber et al. identify TRPC6 as the calcium channel mediating the transient increase in endothelial cytosolic free calcium concentration required for transendothelial migration of leukocytes during the inflammatory response.

Leukocyte transendothelial migration (TEM) is a tightly regulated, multistep process that is critical to the inflammatory response. A transient increase in endothelial cytosolic free calcium ion concentration (↑[Ca²⁺]_i) is required for TEM. However, the mechanism by which endothelial ↑[Ca²⁺]_i regulates TEM and the channels mediating this ↑[Ca²⁺]_i are unknown. Buffering ↑[Ca²⁺]_i in endothelial cells does not affect leukocyte adhesion or locomotion but selectively blocks TEM, suggesting a role for ↑[Ca²⁺]_i specifically for this step. Transient receptor potential canonical 6 (TRPC6), a Ca²⁺ channel expressed in endothelial cells, colocalizes with platelet/endothelial cell adhesion molecule-1 (PECAM) to surround leukocytes during TEM and clusters when endothelial PECAM is engaged. Expression of dominant-negative TRPC6 or shRNA knockdown in endothelial cells arrests neutrophils apically over the junction, similar to when PECAM is blocked. Selectively activating endothelial TRPC6 rescues TEM during an ongoing PECAM blockade, indicating that TRPC6 functions downstream of PECAM. Furthermore, endothelial TRPC6 is required for trafficking of lateral border recycling compartment membrane, which facilitates TEM. Finally, mice lacking TRPC6 in the nonmyeloid compartment (i.e., endothelium) exhibit a profound defect in neutrophil TEM with no effect on leukocyte trafficking. Our findings identify endothelial TRPC6 as the calcium channel mediating the ↑[Ca²⁺]_i required for TEM at a step downstream of PECAM homophilic interactions.

TRPC6 regulates cell cycle progression by modulating membrane potential in bone marrow stromal cells

BACKGROUND AND PURPOSE

Ca(2+) influx is important for cell cycle progression, but the mechanisms involved seem to vary. We investigated the potential roles of transient receptor potential (TRP) channels and store-operated Ca(2+) entry (SOCE)-related molecules STIM (stromal interaction molecule)/Orai in the cell cycle progression of rat bone marrow stromal cells (BMSCs), a reliable therapeutic resource for regenerative medicine.

EXPERIMENTAL APPROACH

PCR and immunoblot analyses were used to examine mRNA and protein levels, fluorescence imaging and patch clamping for Ca(2+) influx and membrane potential measurements, and flow cytometry for cell cycle analysis.

KEY RESULTS

Cell cycle synchronization of BMSCs revealed S phase-specific enhancement of TRPC1, STIM and Orai mRNA and protein expression. In contrast, TRPC6 expression decreased in the S phase and increased in the G1 phase. Resting membrane potential (RMP) of BMSCs was most negative and positive in the S and G1 phases, respectively, and was accompanied by an enhancement and attenuation of SOCE respectively. Chemically depolarizing/hyperpolarizing the membrane erased these differences in SOCE magnitude during the cell cycle. siRNA knockdown of TRPC6 produced a negative shift in RMP, increased SOCE and caused redistribution of BMSCs with increased populations in the S and G2 /M phases and accumulation of cyclins A2 and B1. A low concentration of Gd(3+) (1 μM) suppressed BMSC proliferation at its concentration to inhibit SOC channels relatively specifically.

CONCLUSIONS AND IMPLICATIONS

TRPC6, by changing the membrane potential, plays a pivotal role in controlling the SOCE magnitude, which is critical for cell cycle progression of BMSCs. This finding provides a new therapeutic strategy for regulating BMSC proliferation.

TRP Channels in Respiratory Pathophysiology: the Role of Oxidative, Chemical Irritant and Temperature Stimuli

There is rapidly growing evidence indicating multiple and important roles of Ca(2+)- permeable cation TRP channels in the airways, both under normal and disease conditions. The aim of this review was to summarize the current knowledge of TRP channels in sensing oxidative, chemical irritant and temperature stimuli by discussing expression and function of several TRP channels in relevant cell types within the respiratory tract, ranging from sensory neurons to airway smooth muscle and epithelial cells. Several of these channels, such as TRPM2, TRPM8, TRPA1 and TRPV1, are discussed in much detail to show that they perform diverse, and often overlapping or contributory, roles in airway hyperreactivity, inflammation, asthma, chronic obstructive pulmonary disease and other respiratory disorders. These include TRPM2 involvement in the disruption of the bronchial epithelial tight junctions during oxidative stress, important roles of TRPA1 and TRPV1 channels in airway inflammation, hyperresponsiveness, chronic cough, and hyperplasia of airway smooth muscles, as well as TRPM8 role in COPD and mucus hypersecretion. Thus, there is increasing evidence that TRP channels not only function as an integral part of the important endogenous protective mechanisms of the respiratory tract capable of detecting and ensuring proper physiological responses to various oxidative, chemical irritant and temperature stimuli, but that altered expression, activation and regulation of these channels may also contribute to the pathogenesis of respiratory diseases.

Guinea pig models of asthma

Described in this unit are methods for establishing guinea pig models of asthma. Sufficient detail is provided to enable investigators to study bronchoconstriction, cough, airway hyperresponsiveness, inflammation, and remodeling.

Classical Transient Receptor Potential 1 (TRPC1): Channel or Channel Regulator?

In contrast to other Classical Transient Receptor Potential TRPC channels the function of TRPC1 as an ion channel is a matter of debate, because it is often difficult to obtain substantial functional signals over background in response to over-expression of TRPC1 alone. Along these lines, heterologously expressed TRPC1 is poorly translocated to the plasma membrane as a homotetramer and may not function on its own physiologically, but may rather be an important linker and regulator protein in heteromeric TRPC channel tetramers. However, due to the lack of specific TRPC1 antibodies able to detect native TRPC1 channels in primary cells, identification of functional TRPC1 containing heteromeric TRPC channel complexes in the plasma membrane is still challenging. Moreover, an extended TRPC1 cDNA, which was recently discovered, may seriously question results obtained in heterologous expression systems transfected with shortened cDNA versions. Therefore, this review will focus on the current status of research on TRPC1 function obtained in primary cells and a TRPC1-deficient mouse model.

Ca2+ handling and sensitivity in airway smooth muscle: emerging concepts for mechanistic understanding and therapeutic targeting

Free calcium ions within the cytosol serve as a key secondary messenger system for a diverse range of cellular processes. Dysregulation of cytosolic Ca(2+) handling in airway smooth muscle (ASM) has been implicated in asthma, and it has been hypothesised that this leads, at least in part, to associated changes in both the architecture and function of the lung. Significant research is therefore directed towards furthering our understanding of the mechanisms which control ASM cytosolic calcium, in addition to those regulating the sensitivity of its downstream effector targets to calcium. Key aspects of the recent developments in this field were discussed at the 8th Young Investigators' Symposium on Smooth Muscle (2013, Groningen, The Netherlands), and are outlined in this review.

Applications of mouse airway epithelial cell culture for asthma research

Primary airway epithelial cell culture provides a valuable tool for studying cell differentiation, cell-cell interactions, and the role of immune system factors in asthma pathogenesis. In this chapter, we discuss the application of mouse tracheal epithelial cell cultures for the study of asthma biology. A major advantage of this system is the ability to use airway epithelial cells from mice with defined genetic backgrounds. The in vitro proliferation and differentiation of mouse airway epithelial cells uses the air-liquid interface condition to generate well-differentiated epithelia with characteristics of native airways. Protocols are provided for manipulation of differentiation, induction of mucous cell metaplasia, genetic modification, and cell and pathogen coculture. Assays for the assessment of gene expression, responses of cells, and analysis of specific cell subpopulations within the airway epithelium are included.

Channelopathies

Channelopathies are a heterogeneous group of disorders resulting from the dysfunction of ion channels located in the membranes of all cells and many cellular organelles. These include diseases of the nervous system (e.g., generalized epilepsy with febrile seizures plus, familial hemiplegic migraine, episodic ataxia, and hyperkalemic and hypokalemic periodic paralysis), the cardiovascular system (e.g., long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia), the respiratory system (e.g., cystic fibrosis), the endocrine system (e.g., neonatal diabetes mellitus, familial hyperinsulinemic hypoglycemia, thyrotoxic hypokalemic periodic paralysis, and familial hyperaldosteronism), the urinary system (e.g., Bartter syndrome, nephrogenic diabetes insipidus, autosomal-dominant polycystic kidney disease, and hypomagnesemia with secondary hypocalcemia), and the immune system (e.g., myasthenia gravis, neuromyelitis optica, Isaac syndrome, and anti-NMDA [N-methyl-D-aspartate] receptor encephalitis). The field of channelopathies is expanding rapidly, as is the utility of molecular-genetic and electrophysiological studies. This review provides a brief overview and update of channelopathies, with a focus on recent advances in the pathophysiological mechanisms that may help clinicians better understand, diagnose, and develop treatments for these diseases.

TRPC6: physiological function and pathophysiological relevance

TRPC6 is a non-selective cation channel 6 times more permeable to Ca(2+) than to Na(+). Channel homotetramers heterologously expressed have a characteristic doubly rectifying current-voltage relationship and are directly activated by the second messenger diacylglycerol (DAG). TRPC6 proteins are also regulated by specific tyrosine or serine phosphorylation and phosphoinositides. Given its specific expression pattern, TRPC6 is likely to play a number of physiological roles which are confirmed by the analysis of a Trpc6 (-/-) mouse model. In smooth muscle Na(+) influx through TRPC6 channels and activation of voltage-gated Ca(2+) channels by membrane depolarisation is the driving force for contraction. Permeability of pulmonary endothelial cells depends on TRPC6 and induces ischaemia-reperfusion oedema formation in the lungs. TRPC6 was also identified as an essential component of the slit diaphragm architecture of kidney podocytes and plays an important role in the protection of neurons after cerebral ischaemia. Other functions especially in immune and blood cells remain elusive. Recently identified TRPC6 blockers may be helpful for therapeutic approaches in diseases with highly activated TRPC6 channel activity.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

Nuclear factor κB mediates suppression of canonical transient receptor potential 6 expression by reactive oxygen species and protein kinase C in kidney cells

This study was carried out to explore the molecular mechanism for down-regulation of TRPC6 expression in the reactive oxygen species (ROS)/PKC signaling in kidney cells. In cultured human mesangial cells, H2O2 and TNF-α inhibited TRPC6 mRNA expression in a time-dependent manner. Inhibition of NF-κB reversed both H2O2- and phorbol 12-myristate 13-acetate (PMA)-induced decrease in TRPC6 protein expression. Activation of NF-κB by knocking down IκBα using siRNA could mimic the suppressive effect of ROS/PKC on TRPC6. a Ca(2+) imaging study showed that activation and inhibition of NF-κB significantly decreased and increased the TRPC6-mediated Ca(2+) entry, respectively. Further experiments showed that PMA, but not its inactive analog 4α-phorbol 12, 13-didecanoate (4α-PDD), caused phosphorylation of IκBα and stimulated the nuclear translocation of NF-κB p50 and p65 subunits. The PMA-dependent IκBα phosphorylation was significantly inhibited by Gö6976. Electrophoretic mobility shift assay revealed that PMA stimulated DNA binding activity of NF-κB. Furthermore, specific knockdown of p65, but not p50, prevented an H2O2 inhibitory effect on TRPC6 protein expression, suggesting p65 as a predominant NF-κB subunit repressing TRPC6. In agreement with a major role of p65, chromatin immunoprecipitation assays showed that PMA treatment induced p65 binding to the TRPC6 promoter. Moreover, PMA treatment increased the association of p65 with histone deacetylase (HDAC) and decreased histone acetylation at the TRPC6 promoter. Consistently, knockdown of HDAC2 by siRNA or inhibition of HDAC with trichostatin A prevented a H2O2-induced decrease in TRPC6 mRNA and protein expressions, respectively. Taken together, our findings imply an important role of NF-κB in a negative regulation of TRPC6 expression at the gene transcription level in kidney cells.