Synergistic activation of vascular TRPC6 channel by receptor and mechanical stimulation via phospholipase C/diacylglycerol and phospholipase A2/omega-hydroxylase/20-HETE pathways

Mechanosensitive ion channels in glaucoma pathophysiology

Force sensing is a fundamental ability that allows cells and organisms to interact with their physical environment. The eye is constantly subjected to mechanical forces such as blinking and eye movements. Furthermore, elevated intraocular pressure (IOP) can cause mechanical strain at the optic nerve head, resulting in retinal ganglion cell death (RGC) in glaucoma. How mechanical stimuli are sensed and affect cellular physiology in the eye is unclear. Recent studies have shown that mechanosensitive ion channels are expressed in many ocular tissues relevant to glaucoma and may influence IOP regulation and RGC survival. Furthermore, variants in mechanosensitive ion channel genes may be associated with risk for primary open angle glaucoma. These findings suggest that mechanosensitive channels may be important mechanosensors mediating cellular responses to pressure signals in the eye. In this review, we focus on mechanosensitive ion channels from three major channel families-PIEZO, two-pore potassium and transient receptor potential channels. We review the key properties of these channels, their effects on cell function and physiology, and discuss their possible roles in glaucoma pathophysiology.

Transient receptor potential channels as an emerging target for the treatment of Alzheimer's disease: Unravelling the potential of pharmacological interventions

Alzheimer's disease (AD) is a devastating disorder with a multifaceted aetiology characterized by dementia, which later progresses to cognitive impairment. Significant efforts have been made to develop pharmacological interventions that slow down the pathogenesis of AD. However, conventional drugs have failed to satisfactorily treat AD and are more focussed towards symptomatic management. Thus, there is a gap in the literature regarding novel targets and modulators targeting them for the effective treatment of AD. Recent studies have demonstrated that modulation of transient receptor potential (TRP) channels has the potential to halt AD pathogenesis at an early stage and rescue hippocampal neurons from death. Amongst several members, TRP channels like TRPA1, TRPC6, TRPM2 and TRPV2 have shown promising results in the attenuation of neurobehavioural cognitive deficits as well as signalling pathways governing such cognitive decline. Furthermore, as these channels govern the ionic balance in the cell, their beneficial effects have also been known to maintain the homeostasis of Ca2+, which is the major culprit eliciting the vicious cycle of excitotoxicity, mitochondrial dysfunction, ROS generation and neurodegeneration. Despite such tremendous potential of TRP channel modulators, their clinical investigation remains elusive. Therefore, in the present review, we have discussed such agents in the light of TRP channels as molecular targets for the amelioration of AD both at the preclinical and clinical levels.

Pathophysiological significance and modulation of the transient receptor potential canonical 3 ion channel

Transient receptor potential canonical 3 (TRPC3) protein belongs to the TRP family of nonselective cation channels. Its activation occurs by signaling through a G protein-coupled receptor (GPCR) and a phospholipase C-dependent (PLC) pathway. Perturbations in the expression of TRPC3 are associated with a plethora of pathophysiological conditions responsible for disorders of the cardiovascular, immune, and central nervous systems. The recently solved cryo-EM structure of TRPC3 provides detailed inputs about the underlying mechanistic aspects of the channel, which in turn enables more efficient ways of designing small-molecule modulators. Pharmacologically targeting TRPC3 in animal models has demonstrated great efficacy in treating diseases including cancers, neurological disorders, and cardiovascular diseases. Despite extensive scientific evidence supporting some strong correlations between the expression and activity of TRPC3 and various pathophysiological conditions, therapeutic strategies based on its pharmacological modulations have not led to clinical trials. The development of small-molecule TRPC3 modulators with high safety, sufficient brain penetration, and acceptable drug-like profiles remains in progress. Determining the pathological mechanisms for TRPC3 involvement in human diseases and understanding the requirements for a drug-like TRPC3 modulator will be valuable in advancing small-molecule therapeutics to future clinical trials. In this review, we provide an overview of the origin and activation mechanism of TRPC3 channels, diseases associated with irregularities in their expression, and new development in small-molecule modulators as potential therapeutic interventions for treating TRPC3 channelopathies.

Functional, Structural and Proteomic Effects of Ageing in Resistance Arteries

The normal ageing process affects resistance arteries, leading to various functional and structural changes. Systolic hypertension is a common occurrence in human ageing, and it is associated with large artery stiffening, heightened pulsatility, small artery remodeling, and damage to critical microvascular structures. Starting from young adulthood, a progressive elevation in the mean arterial pressure is evidenced by clinical and epidemiological data as well as findings from animal models. The myogenic response, a protective mechanism for the microcirculation, may face disruptions during ageing. The dysregulation of calcium entry channels (L-type, T-type, and TRP channels), dysfunction in intracellular calcium storage and extrusion mechanisms, altered expression of potassium channels, and a change in smooth muscle calcium sensitization may contribute to the age-related dysregulation of myogenic tone. Flow-mediated vasodilation, a hallmark of endothelial function, is compromised in ageing. This endothelial dysfunction is related to increased oxidative stress, lower nitric oxide bioavailability, and a low-grade inflammatory response, further exacerbating vascular dysfunction. Resistance artery remodeling in ageing emerges as a hypertrophic response of the vessel wall that is typically observed in conjunction with outward remodeling (in normotension), or as inward hypertrophic remodeling (in hypertension). The remodeling process involves oxidative stress, inflammation, reorganization of actin cytoskeletal components, and extracellular matrix fiber proteins. Reactive oxygen species (ROS) signaling and chronic low-grade inflammation play substantial roles in age-related vascular dysfunction. Due to its role in the regulation of vascular tone and structural proteins, the RhoA/Rho-kinase pathway is an important target in age-related vascular dysfunction and diseases. Understanding the intricate interplay of these factors is crucial for developing targeted interventions to mitigate the consequences of ageing on resistance arteries and enhance the overall vascular health.

Inhibition and potentiation of the exercise pressor reflex by pharmacological modulation of TRPC6 in male rats

We determined the role played by the transient receptor potential canonical 6 (TRPC6) channel in evoking the mechanical component of the exercise pressor reflex in male decerebrated Sprague-Dawley rats. TRPC6 channels were identified by quadruple-labelled (DiI, TRPC6, neurofilament-200 and peripherin) immunohistochemistry in dorsal root ganglion (DRG) cells innervating the triceps surae muscles (n = 12). The exercise pressor reflex was evoked by statically contracting the triceps surae muscles before and after injection of the TRPC6 antagonist BI-749327 (n = 11; 12 μg kg-1 ) or SAR7334 (n = 11; 7 μg kg-1 ) or the TRPC6 positive modulator C20 (n = 11; 18 μg kg-1 ). Similar experiments were conducted while the muscles were passively stretched (n = 8-12), a manoeuvre that isolated the mechanical component of the reflex. Blood pressure, tension, renal sympathetic nerve activity (RSNA) and blood flow were recorded. Of the DRG cells innervating the triceps surae muscles, 85% stained positive for the TRPC6 antigen, and 45% of those cells co-expressed neurofilament-200. Both TRPC6 antagonists decreased the reflex pressor responses to static contraction (-32 to -42%; P < 0.05) and to passive stretch (-35 to -52%; P < 0.05), whereas C20 increased these responses (55-65%; P < 0.05). In addition, BI-749327 decreased the peak and integrated RSNA responses to both static contraction (-39 to -43%; P < 0.05) and passive stretch (-56 to -62%; P < 0.05), whereas C20 increased the RSNA to passive stretch only. The onset latency of the decrease or increase in RSNA occurred within 2 s of the onset of the manoeuvres (P < 0.05). Collectively, our results show that TRPC6 plays a key role in evoking the mechanical component of the exercise pressor reflex. KEY POINTS: The exercise pressor reflex plays a key role in the sympathetic and haemodynamic responses to exercise. This reflex is composed of two components, namely the mechanoreflex and the metaboreflex. The receptors responsible for evoking the mechanoreflex are poorly documented. A good candidate for this function is the transient receptor potential canonical 6 (TRPC6) channel, which is activated by mechanical stimuli and expressed in dorsal root ganglia of rats. Using two TRPC6 antagonists and one positive modulator, we investigated the role played by TRPC6 in evoking the mechanoreflex in decerebrated rats. Blocking TRPC6 decreased the renal sympathetic and the pressor responses to both contraction and stretch, the latter being a manoeuvre that isolates the mechanoreflex. In contrast, the positive modulator increased the pressor reflex to contraction and stretch, in addition to the sympathetic response to stretch. Our results provide strong support for a role played by the TRPC6 channel in evoking the mechanoreflex.

Transcriptomic profile of the mechanosensitive ion channelome in human cardiac fibroblasts

Human cardiac fibroblasts (HCFs) have mRNA transcripts that encode different mechanosensitive ion channels and channel regulatory proteins whose functions are not known yet. The primary goal of this work was to define the mechanosensitive ion channelome of HCFs. The most common type of cationic channel is the transient receptor potential (TRP) family, which is followed by the TWIK-related K+ channel (TREK), transmembrane protein 63 (TMEM63), and PIEZO channel (PIEZO) families. In the sodium-dependent NON-voltage-gated channel (SCNN) subfamily, only SCNN1D was shown to be highly expressed. Particular members of the acid-sensing ion channel (ASIC) (ASIC1 and ASIC3) subfamilies were also significantly expressed. The transcripts per kilobase million (TPMs) for Piezo 2 were almost 100 times less abundant than those for Piezo 1. The tandem of P domains in a weak inward rectifying K+ channel (TWIK)-2 channel, TWIK-related acid-sensitive K+ channel (TASK)-5, TASK-1, and the TWIK-related K1 (TREK-1) channel were the four most prevalent types in the K2P subfamily. The highest expression in the TRPP subfamily was found for PKD2 and PKD1, while in the TRPM subfamily, it was found for TRPM4, TRPM7, and TRPM3. TRPV2, TRPV4, TRPV3, and TRPV6 (all members of the TRPV subfamily) were also substantially expressed. A strong expression of the TRPC1, TRPC4, TRPC6, and TRPC2 channels and all members of the TRPML subfamily (MCOLN1, MCOLN2, and MCOLN3) was also shown. In terms of the transmembrane protein 16 (TMEM16) family, the HCFs demonstrated significant expression of the TMEM16H, TMEM16F, TMEM16J, TMEM16A, and TMEM16G channels. TMC3 is the most expressed channel in HCFs of all known members of the transmembrane channel-like protein (TMC) family. This analysis of the mechanosensitive ionic channel transcriptome in HCFs: (1) agrees with previously documented findings that all currently identified mechanosensitive channels play a significant and well recognized physiological function in elucidating the mechanosensitive characteristics of HCFs; (2) supports earlier preliminary reports that point to the most common expression of the TRP mechanosensitive family in HCFs; and (3) points to other new mechanosensitive channels (TRPC1, TRPC2, TWIK-2, TMEM16A, ASIC1, and ASIC3).

Mechanosensitive ion channel gene survey suggests potential roles in primary open angle glaucoma

Although glaucoma is a disease modulated by eye pressure, the mechanisms of pressure sensing in the eye are not well understood. Here, we investigated associations between mechanosensitive ion channel gene variants and primary open-angle glaucoma (POAG). Common (minor allele frequency > 5%) single nucleotide polymorphisms located within the genomic regions of 20 mechanosensitive ion channel genes in the K2P, TMEM63, PIEZO and TRP channel families were assessed using genotype data from the NEIGHBORHOOD consortium of 3853 cases and 33,480 controls. Rare (minor allele frequency < 1%) coding variants were assessed using exome array genotyping data for 2606 cases and 2606 controls. Association with POAG was analyzed using logistic regression adjusting for age and sex. Two rare PIEZO1 coding variants with protective effects were identified in the NEIGHBOR dataset: R1527H, (OR 0.17, P = 0.0018) and a variant that alters a canonical splice donor site, g.16-88737727-C-G Hg38 (OR 0.38, P = 0.02). Both variants showed similar effects in the UK Biobank and the R1527H also in the FinnGen database. Several common variants also reached study-specific thresholds for association in the NEIGHBORHOOD dataset. These results identify novel variants in several mechanosensitive channel genes that show associations with POAG, suggesting that these channels may be potential therapeutic targets.

Diversity of cells and signals in the cardiovascular system

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies, and challenges in examining cell and signal diversity, co-ordination and interrelationships involved in cardiovascular function. This paper originates from the topics of formal presentations and informal discussions from the Symposium, which aimed to develop a holistic view of how the multiple cell types in the cardiovascular system integrate to influence cardiovascular function, disease progression and therapeutic strategies. The first section describes the major cell types (e.g. cardiomyocytes, vascular smooth muscle and endothelial cells, fibroblasts, neurons, immune cells, etc.) and the signals involved in cardiovascular function. The second section emphasizes the complexity at the subcellular, cellular and system levels in the context of cardiovascular development, ageing and disease. Finally, the third section surveys the technological innovations that allow the interrogation of this diversity and advancing our understanding of the integrated cardiovascular function and dysfunction.

Use the force, fluke: Ligand-independent gating of Schistosoma mansoni ion channel TRPMPZQ

The parasitic flatworm ion channel, TRPMPZQ, is a non-selective cation channel that mediates Ca2+ entry and membrane depolarization when activated by the anthelmintic drug, praziquantel (PZQ). TRPMPZQ is conserved in all platyhelminth genomes scrutinized to date, with the sensitivity of TRPMPZQ in any particular flatworm correlating with the overall sensitivity of the worm to PZQ. Conservation of this channel suggests it plays a role in flatworm physiology, but the nature of the endogenous cues that activate this channel are currently unknown. Here, we demonstrate that TRPMPZQ is activated in a ligand-independent manner by membrane stretch, with the electrophysiological signature of channel opening events being identical whether evoked by negative pressure, or by PZQ. TRPMPZQ is therefore a multimodal ion channel gated by both physical and chemical cues. The mechanosensitivity of TRPMPZQ is one route for endogenous activation of this ion channel that holds relevance for schistosome physiology given the persistent pressures and mechanical cues experienced throughout the parasite life cycle.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Interruption of TRPC6-NFATC1 signaling inhibits NADPH oxidase 4 and VSMCs phenotypic switch in intracranial aneurysm

Intracranial aneurysm (IA) is a frequent cerebrovascular disorder with unclear pathogenesis. The vascular smooth muscle cells (VSMCs) phenotypic switch is essential for IA formation. It has been reported that Ca2+ overload and excessive reactive oxygen species (ROS) are involved in VSMCs phenotypic switch. The transient receptor potential canonical 6 (TRPC6) and NADPH oxidase 4 (NOX4) are the main pathway to participate in Ca2+ overload and ROS production in VSMCs. Ca2+ overload can activate calcineurin (CN), leading to nuclear factor of activated T cell (NFAT) dephosphorylation to regulate the target gene's transcription. We hypothesized that activation of TRPC6-NFATC1 signaling may upregulate NOX4 and involve in VSMCs phenotypic switch contributing to the progression of IA. Our results showed that the expressions of NOX4, p22phox, p47phox, TRPC6, CN and NFATC1 were significantly increased, and VSMCs underwent a significant phenotypic switch in IA tissue and cellular specimens. The VIVIT (NFATC1 inhibitor) and BI-749327 (TRPC6 inhibitor) treatment reduced the expressions of NOX4, p22phox and p47phox and the production of ROS, and significantly improved VSMCs phenotypic switch in IA rats and cells. Consistent results were obtained from IA Trpc6 knockout (Trpc6-/-) mice. Furthermore, the results also revealed that NFATC1 could regulate NOX4 transcription by binding to its promoter. Our findings reveal that interrupting the TRPC6-NFATC1 signaling inhibits NOX4 and improves VSMCs phenotypic switch in IA, and regulating Ca2+ homeostasis may be an important therapeutic strategy for IA.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Improvement of platelet preservation by inhibition of TRPC6

BACKGROUND

The preservation of platelets (PLTs) by room temperature (RT) oscillation limits their shelf life to between 4 and 7 days because of the decrease in PLT function. TRPC6 is a non-selective mechanically sensitive cation channel that has been shown to mediate Ca²⁺ signalling, implying a role in PLT activation during preservation by RT oscillation.

OBJECTIVES

This study was designed to investigate whether inhibition of TRPC6 can improve the RT preservation of PLTs and the possible underlying mechanism.

METHODS

Human PLTs from whole blood were stored at 22 ± 2°C with oscillation in plasma or M-sol (mixture of solutions). BI-749327, a specific TRPC6 inhibitor, was administered throughout the preservation period. PLT distribution width (PDW), mean platelet volume (MPV), maximum platelet aggregation rate (MAR) and average aggregation rate (AAR) were measured. The MTT method was used to assess the relative viability of PLTs. Flow cytometry was used to measure the changes of Ca²⁺ concentration in PLTs and phosphatidylserine (PS) exposure on the PLT surface, and western blotting was used to assess the expression changes of platelet TRPC6 and CD62P proteins.

RESULTS

Compared with the control group, inhibition of TRPC6 with BI-749327 significantly reduced the PDW, MPV and Ca²⁺ concentration, the MAR and AAR were significantly increased, the expression of TRPC6 and CD62P protein was significantly down-regulated in PLTs, and the PS exposure was significantly reduced on the PLT surface. However, these effects were all reversed by activation of TRPC6.

CONCLUSION

Inhibition of TRPC6 improves the quality of PLT preservation by inhibiting the Ca²⁺ signal mediated by TRPC6.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Mechanosensitive cation currents through TRPC6 and Piezo1 channels in human pulmonary arterial endothelial cells

Mechanosensitive cation channels and Ca2+ influx through these channels play an important role in the regulation of endothelial cell functions. Transient receptor potential canonical channel 6 (TRPC6) is a diacylglycerol-sensitive nonselective cation channel that forms receptor-operated Ca2+ channels in a variety of cell types. Piezo1 is a mechanosensitive cation channel activated by membrane stretch and shear stress in lung endothelial cells. In this study, we report that TRPC6 and Piezo1 channels both contribute to membrane stretch-mediated cation currents and Ca2+ influx or increase in cytosolic-free Ca2+ concentration ([Ca2+]cyt) in human pulmonary arterial endothelial cells (PAECs). The membrane stretch-mediated cation currents and increase in [Ca2+]cyt in human PAECs were significantly decreased by GsMTX4, a blocker of Piezo1 channels, and by BI-749327, a selective blocker of TRPC6 channels. Extracellular application of 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane permeable analog of diacylglycerol, rapidly induced whole cell cation currents and increased [Ca2+]cyt in human PAECs and human embryonic kidney (HEK)-cells transiently transfected with the human TRPC6 gene. Furthermore, membrane stretch with hypo-osmotic or hypotonic solution enhances the cation currents in TRPC6-transfected HEK cells. In HEK cells transfected with the Piezo1 gene, however, OAG had little effect on the cation currents, but membrane stretch significantly enhanced the cation currents. These data indicate that, while both TRPC6 and Piezo1 are involved in generating mechanosensitive cation currents and increases in [Ca2+]cyt in human PAECs undergoing mechanical stimulation, only TRPC6 (but not Piezo1) is sensitive to the second messenger diacylglycerol. Selective blockers of these channels may help develop novel therapies for mechanotransduction-associated pulmonary vascular remodeling in patients with pulmonary arterial hypertension.

Evaluation of the presence of TRPC6 channels in human vessels: A pilot study using immunohistochemistry

The TRPC6 channel is permeable to calcium ions as well as other ions and plays an important role in the physiology and pathophysiology of vessels. Findings from animal and cell culture experiments have shown its involvement in important vascular processes such as the Bayliss effect or endothelial-mediated vasodilatation. Furthermore, the relevance of TRPC6 channels in humans has become apparent based on diseases such as idiopathic pulmonary arterial hypertension, focal segmental glomerulosclerosis and atherosclerosis, amongst others. However, histological evidence that systematically detects TRPC6 channels in human vessels has not been provided to date. In this study, 40 vessel sections from nine body donors were obtained, processed and stained with a knockout-validated antibody against the TRPC6 protein using immunohistochemistry and western blotting. More than half of the samples yielded evidence of TRPC6 channel expression in the intima and adventitia. TRPC6 channels were detected in the tunica media in only one of 40 cases. TRPC6 detection in the human intima confirmed several demonstrated physiological aspects of the TRPC6 channels in the vasculature and may also be involved in associated human diseases. The near absence of TRPC6 channels in the tunica media was in contrast to a view that is primarily based on animal studies, from which its presence was assumed.

The CYP/20-HETE/GPR75 axis in hypertension

20-Hydroxyeicosatetraenoic acid (20-HETE) is a bioactive lipid generated from the ω-hydroxylation of arachidonic acid (AA) by enzymes of the cytochrome P450 (CYP) family, primarily the CYP4A and CYP4F subfamilies. 20-HETE is most notably identified as a modulator of vascular tone, regulator of renal function, and a contributor to the onset and development of hypertension and cardiovascular disease. 20-HETE-mediated signaling promotes hypertension by sensitizing the vasculature to constrictor stimuli, inducing endothelial dysfunction, and potentiating vascular inflammation. These bioactions are driven by the activation of the G-protein coupled receptor 75 (GPR75), a 20-HETE receptor (20HR). Given the capacity of 20-HETE signaling to drive pro-hypertensive mechanisms, the CYP/20-HETE/GPR75 axis has the potential to be a significant therapeutic target for the treatment of hypertension and cardiovascular diseases associated with increases in blood pressure. In this chapter, we review 20-HETE-mediated cellular mechanisms that promote hypertension, highlight important data in humans such as genetic variants in the CYP genes that potentiate 20-HETE production and describe recent findings in humans with 20HR/GPR75 mutations. Special emphasis is given to the 20HR and respective receptor blockers that have the potential to pave a path to translational and clinical studies for the treatment of 20-HETE-driven hypertension, and obesity/metabolic syndrome.

TRPC6, a therapeutic target for pulmonary hypertension

Idiopathic pulmonary arterial hypertension (PAH) is a fatal and progressive disease. Sustained vasoconstriction due to pulmonary arterial smooth muscle cell (PASMC) contraction and concentric arterial remodeling due partially to PASMC proliferation are the major causes for increased pulmonary vascular resistance and increased pulmonary arterial pressure in patients with precapillary pulmonary hypertension (PH) including PAH and PH due to respiratory diseases or hypoxemia. We and others observed upregulation of TRPC6 channels in PASMCs from patients with PAH. A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in PASMC triggers PASMC contraction and vasoconstriction, while Ca2+-dependent activation of PI3K/AKT/mTOR pathway is a pivotal signaling cascade for cell proliferation and gene expression. Despite evidence supporting a pathological role of TRPC6, no selective and orally bioavailable TRPC6 antagonist has yet been developed and tested for treatment of PAH or PH. In this study, we sought to investigate whether block of receptor-operated Ca2+ channels using a nonselective blocker of cation channels, 2-aminoethyl diphenylborinate (2-APB, administered intraperitoneally) and a selective blocker of TRPC6, BI-749327 (administered orally) can reverse established PH in mice. The results from the study show that intrapulmonary application of 2-APB (40 µM) or BI-749327 (3-10 µM) significantly and reversibly inhibited acute alveolar hypoxia-induced pulmonary vasoconstriction. Intraperitoneal injection of 2-APB (1 mg/kg per day) significantly attenuated the development of PH and partially reversed established PH in mice. Oral gavage of BI-749327 (30 mg/kg, every day, for 2 wk) reversed established PH by ∼50% via regression of pulmonary vascular remodeling. Furthermore, 2-APB and BI-749327 both significantly inhibited PDGF- and serum-mediated phosphorylation of AKT and mTOR in PASMC. In summary, the receptor-operated and mechanosensitive TRPC6 channel is a good target for developing novel treatment for PAH/PH. BI-749327, a selective TRPC6 blocker, is potentially a novel and effective drug for treating PAH and PH due to respiratory diseases or hypoxemia.

Vascular calcium signalling and ageing

Changes in cellular Ca²⁺ levels have major influences on vascular function and blood pressure regulation. Vascular smooth muscle cells (SMCs) and endothelial cells (ECs) orchestrate vascular activity in distinct ways, often involving highly specific fluctuations in Ca²⁺ signalling. Ageing is a major risk factor for cardiovascular diseases, but the impact of ageing per se on vascular Ca²⁺ signalling has received insufficient attention. We reviewed the literature for age-related changes in Ca²⁺ signalling in relation to vascular structure and function. Vascular tone dysregulation in several vascular beds has been linked to abnormal expression or activity of SMC voltage-gated Ca²⁺ channels, Ca²⁺ -activated K⁺ channels or TRPC6 channels. Some of these effects were linked to altered caveolae density, microRNA expression or 20-HETE abundance. Intracellular store Ca²⁺ handling was suppressed in ageing mainly via reduced expression of intracellular Ca²⁺ release channels, and Ca²⁺ reuptake or efflux pumps. An increase in mitochondrial Ca²⁺ uptake, leading to oxidative stress, could also play a role in SMC hypercontractility and structural remodelling in ageing. In ECs, ageing entailed diverse effects on spontaneous and evoked Ca²⁺ transients, as well as structural changes at the EC-SMC interface. The concerted effects of altered Ca²⁺ signalling on myogenic tone, endothelium-dependent vasodilatation, and vascular structure are likely to contribute to blood pressure dysregulation and blood flow distribution deficits in critical organs. With the increase in the world's ageing population, future studies should be directed at solving specific ageing-induced Ca²⁺ signalling deficits to combat the imminent accelerated vascular ageing and increased risk of cardiovascular diseases.

Endothelial upregulation of mechanosensitive channel Piezo1 in pulmonary hypertension

Piezo is a mechanosensitive cation channel responsible for stretch-mediated Ca2+ and Na+ influx in multiple types of cells. Little is known about the functional role of Piezo1 in the lung vasculature and its potential pathogenic role in pulmonary arterial hypertension (PAH). Pulmonary arterial endothelial cells (PAECs) are constantly under mechanic stretch and shear stress that are sufficient to activate Piezo channels. Here, we report that Piezo1 is significantly upregulated in PAECs from patients with idiopathic PAH and animals with experimental pulmonary hypertension (PH) compared with normal controls. Membrane stretch by decreasing extracellular osmotic pressure or by cyclic stretch (18% CS) increases Ca2+-dependent phosphorylation (p) of AKT and ERK, and subsequently upregulates expression of Notch ligands, Jagged1/2 (Jag-1 and Jag-2), and Delta like-4 (DLL4) in PAECs. siRNA-mediated downregulation of Piezo1 significantly inhibited the stretch-mediated pAKT increase and Jag-1 upregulation, whereas downregulation of AKT by siRNA markedly attenuated the stretch-mediated Jag-1 upregulation in human PAECs. Furthermore, the mRNA and protein expression level of Piezo1 in the isolated pulmonary artery, which mainly contains pulmonary arterial smooth muscle cells (PASMCs), from animals with severe PH was also significantly higher than that from control animals. Intraperitoneal injection of a Piezo1 channel blocker, GsMTx4, ameliorated experimental PH in mice. Taken together, our study suggests that membrane stretch-mediated Ca2+ influx through Piezo1 is an important trigger for pAKT-mediated upregulation of Jag-1 in PAECs. Upregulation of the mechanosensitive channel Piezo1 and the resultant increase in the Notch ligands (Jag-1/2 and DLL4) in PAECs may play a critical pathogenic role in the development of pulmonary vascular remodeling in PAH and PH.

Cardiovascular co-morbidities, inflammation and cerebral small vessel disease

Cerebral small vessel disease (cSVD) is the most common cause of vascular cognitive impairment and affects all levels of the brain's vasculature. Features include diverse structural and functional changes affecting small arteries and capillaries that lead to a decline in cerebral perfusion. Due to an aging population, incidence of cerebral small vessel disease (cSVD) is continually rising. Despite its prevalence and its ability to cause multiple debilitating illnesses, such as stroke and dementia, there are currently no therapeutic strategies for the treatment of cSVD. In the healthy brain, interactions between neuronal, vascular and inflammatory cells are required for normal functioning. When these interactions are disturbed, chronic pathological inflammation can ensue. The interplay between cSVD and inflammation has attracted much recent interest and this review discusses chronic cardiovascular diseases, particularly hypertension, and explores how the associated inflammation may impact on the structure and function of the small arteries of the brain in cSVD. Molecular approaches in animal studies are linked to clinical outcomes in patients and novel hypotheses regarding inflammation and cSVD are proposed that will hopefully stimulate further discussion and study in this important area.

Pleiotropic and Potentially Beneficial Effects of Reactive Oxygen Species on the Intracellular Signaling Pathways in Endothelial Cells

Endothelial cells (ECs) are exposed to molecular dioxygen and its derivative reactive oxygen species (ROS). ROS are now well established as important signaling messengers. Excessive production of ROS, however, results in oxidative stress, a significant contributor to the development of numerous diseases. Here, we analyze the experimental data and theoretical concepts concerning positive pro-survival effects of ROS on signaling pathways in endothelial cells (ECs). Our analysis of the available experimental data suggests possible positive roles of ROS in induction of pro-survival pathways, downstream of the G_i-protein-coupled receptors, which mimics insulin signaling and prevention or improvement of the endothelial dysfunction. It is, however, doubtful, whether ROS can contribute to the stabilization of the endothelial barrier.

TRPM7 is an essential regulator for volume-sensitive outwardly rectifying anion channel

Animal cells can regulate their volume after swelling by the regulatory volume decrease (RVD) mechanism. In epithelial cells, RVD is attained through KCl release mediated via volume-sensitive outwardly rectifying Cl^- channels (VSOR) and Ca²⁺-activated K⁺ channels. Swelling-induced activation of TRPM7 cation channels leads to Ca²⁺ influx, thereby stimulating the K⁺ channels. Here, we examined whether TRPM7 plays any role in VSOR activation. When TRPM7 was knocked down in human HeLa cells or knocked out in chicken DT40 cells, not only TRPM7 activity and RVD efficacy but also VSOR activity were suppressed. Heterologous expression of TRPM7 in TRPM7-deficient DT40 cells rescued both VSOR activity and RVD, accompanied by an increase in the expression of LRRC8A, a core molecule of VSOR. TRPM7 exerts the facilitating action on VSOR activity first by enhancing molecular expression of LRRC8A mRNA through the mediation of steady-state Ca²⁺ influx and second by stabilizing the plasmalemmal expression of LRRC8A protein through the interaction between LRRC8A and the C-terminal domain of TRPM7. Therefore, TRPM7 functions as an essential regulator of VSOR activity and LRRC8A expression.

Channelling the Force to Reprogram the Matrix: Mechanosensitive Ion Channels in Cardiac Fibroblasts

Cardiac fibroblasts (CF) play a pivotal role in preserving myocardial function and integrity of the heart tissue after injury, but also contribute to future susceptibility to heart failure. CF sense changes to the cardiac environment through chemical and mechanical cues that trigger changes in cellular function. In recent years, mechanosensitive ion channels have been implicated as key modulators of a range of CF functions that are important to fibrotic cardiac remodelling, including cell proliferation, myofibroblast differentiation, extracellular matrix turnover and paracrine signalling. To date, seven mechanosensitive ion channels are known to be functional in CF: the cation non-selective channels TRPC6, TRPM7, TRPV1, TRPV4 and Piezo1, and the potassium-selective channels TREK-1 and KATP. This review will outline current knowledge of these mechanosensitive ion channels in CF, discuss evidence of the mechanosensitivity of each channel, and detail the role that each channel plays in cardiac remodelling. By better understanding the role of mechanosensitive ion channels in CF, it is hoped that therapies may be developed for reducing pathological cardiac remodelling.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

Vascular Dysfunction in Diabetes and Obesity: Focus on TRP Channels

Transient receptor potential (TRP) superfamily consists of a diverse group of non-selective cation channels that has a wide tissue distribution and is involved in many physiological processes including sensory perception, secretion of hormones, vasoconstriction/vasorelaxation, and cell cycle modulation. In the blood vessels, TRP channels are present in endothelial cells, vascular smooth muscle cells, perivascular adipose tissue (PVAT) and perivascular sensory nerves, and these channels have been implicated in the regulation of vascular tone, vascular cell proliferation, vascular wall permeability and angiogenesis. Additionally, dysfunction of TRP channels is associated with cardiometabolic diseases, such as diabetes and obesity. Unfortunately, the prevalence of diabetes and obesity is rising worldwide, becoming an important public health problems. These conditions have been associated, highlighting that obesity is a risk factor for type 2 diabetes. As well, both cardiometabolic diseases have been linked to a common disorder, vascular dysfunction. In this review, we briefly consider general aspects of TRP channels, and we focus the attention on TRPC (canonical or classical), TRPV (vanilloid), TRPM (melastatin), and TRPML (mucolipin), which were shown to be involved in vascular alterations of diabetes and obesity or are potentially linked to vascular dysfunction. Therefore, elucidation of the functional and molecular mechanisms underlying the role of TRP channels in vascular dysfunction in diabetes and obesity is important for the prevention of vascular complications and end-organ damage, providing a further therapeutic target in the treatment of these metabolic diseases.

Transient receptor potential channel-dependent myogenic responsiveness in small-sized resistance arteries

It is well documented that the inherent ability of small arteries and arterioles to regulate intraluminal diameter in response to alterations in intravascular pressure determines peripheral vascular resistance and blood flow (termed myogenic response or pressure-induced vasoconstriction/dilation). This autoregulatory property of resistance arteries is primarily originated from mechanosensitive vascular smooth muscle cells (VSMCs). There are diverse biological apparatuses in the plasma membrane of VSMCs that sense mechanical stimuli and generate intracellular signals for the contractility of VSMCs. Although the roles of transient receptor potential (TRP) channels in pressure-induced vasoconstriction are not fully understood to date, TRP channels that are directly activated by mechanical stimuli (e.g., stretch of VSMCs) or indirectly evoked by intracellular molecules (e.g., inositol trisphosphate) provide the major sources of Ca²⁺ (e.g., Ca²⁺ influx or release from the sarcoplasmic reticulum) and in turn, evoke vascular reactivity. This review sought to summarize mounting evidence over several decades that the activation of TRP canonical, TRP melastatin, TRP vanilloid, and TRP polycystin channels contributes to myogenic vasoconstriction.

Novel Mechanistic Insights and Potential Therapeutic Impact of TRPC6 in Neurovascular Coupling and Ischemic Stroke

Ischemic stroke is one of the most disabling diseases and a leading cause of death globally. Despite advances in medical care, the global burden of stroke continues to grow, as no effective treatments to limit or reverse ischemic injury to the brain are available. However, recent preclinical findings have revealed the potential role of transient receptor potential cation 6 (TRPC6) channels as endogenous protectors of neuronal tissue. Activating TRPC6 in various cerebral ischemia models has been found to prevent neuronal death, whereas blocking TRPC6 enhances sensitivity to ischemia. Evidence has shown that Ca2+ influx through TRPC6 activates the cAMP (adenosine 3',5'-cyclic monophosphate) response element-binding protein (CREB), an important transcription factor linked to neuronal survival. Additionally, TRPC6 activation may counter excitotoxic damage resulting from glutamate release by attenuating the activity of N-methyl-d-aspartate (NMDA) receptors of neurons by posttranslational means. Unresolved though, are the roles of TRPC6 channels in non-neuronal cells, such as astrocytes and endothelial cells. Moreover, TRPC6 channels may have detrimental effects on the blood-brain barrier, although their exact role in neurovascular coupling requires further investigation. This review discusses evidence-based cell-specific aspects of TRPC6 in the brain to assess the potential targets for ischemic stroke management.

Early-life persistent vitamin D deficiency-induced cardiovascular dysfunction in mice is mediated by transient receptor potential C channels

BACKGROUND

Studies indicate that chronic vitamin D deficiency (VDD) may predispose to hypertension, yet, there is very little data characterizing its direct cardiac effects. Vitamin D modulates the function of transient receptor potential C cation channels (TRPC), which is a mechanosensitive cation channel that plays a role in cardiac slow-force responses to hemodynamic changes. The purpose of this study was to determine the cardiac effects of VDD and the potential role of TRPC.

METHODS

Three-week old mice were placed on a VDD or normal diet (ND) for 19 weeks. Mice were then implanted with radiotelemeters for the measurement of heart rate (HR) and heart rate variability (HRV), while a separate group was anesthetized to measure blood pressure (BP) and left ventricular function using an intraventricular probe. Animals were treated with a TRPC antagonist or vehicle after which they were challenged with dobutamine to measure cardiac responses.

RESULTS

VDD mice had significantly increased BP (72 ± 3 mmHg vs. 62 ± 2 mmHg) and left ventricular pressure (LVP) (84.6 ± 0.8 mmHg vs. 78.2 ± 2.0 mmHg), and decreased cardiac contractility (-3 % vs. + 11 %) and HR response (+8 % vs. + 13 %) to dobutamine when compared to ND. These responses were blocked by the TRPC antagonist. HRV decreased with increasing dobutamine doses in ND but not VDD mice, however, the antagonist had no effect.

CONCLUSION

VDD increases BP and alters cardiac mechanical function in mice, the latter appears to be mediated by TRPC, in particular TRPC6. Although the cardiac effects might be due to increased BP, it is likely that VDD also affects the function of the heart directly. This is the first study to demonstrate the potentially deleterious effects of VDD on cardiac function and the role of TRPC6 in this response.

Potential Drug Candidates to Treat TRPC6 Channel Deficiencies in the Pathophysiology of Alzheimer's Disease and Brain Ischemia

Alzheimer’s disease and cerebral ischemia are among the many causative neurodegenerative diseases that lead to disabilities in the middle-aged and elderly population. There are no effective disease-preventing therapies for these pathologies. Recent in vitro and in vivo studies have revealed the TRPC6 channel to be a promising molecular target for the development of neuroprotective agents. TRPC6 channel is a non-selective cation plasma membrane channel that is permeable to Ca²⁺. Its Ca²⁺-dependent pharmacological effect is associated with the stabilization and protection of excitatory synapses. Downregulation as well as upregulation of TRPC6 channel functions have been observed in Alzheimer’s disease and brain ischemia models. Thus, in order to protect neurons from Alzheimer’s disease and cerebral ischemia, proper TRPC6 channels modulators have to be used. TRPC6 channels modulators are an emerging research field. New chemical structures modulating the activity of TRPC6 channels are being currently discovered. The recent publication of the cryo-EM structure of TRPC6 channels should speed up the discovery process even more. This review summarizes the currently available information about potential drug candidates that may be used as basic structures to develop selective, highly potent TRPC6 channel modulators to treat neurodegenerative disorders, such as Alzheimer’s disease and cerebral ischemia.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

Revisiting the mechanism of hypoxic pulmonary vasoconstriction using isolated perfused/ventilated mouse lung

Hypoxic Pulmonary Vasoconstriction (HPV) is an important physiological mechanism of the lungs that matches perfusion to ventilation thus maximizing O2 saturation of the venous blood within the lungs. This study emphasizes on principal pathways in the initiation and modulation of hypoxic pulmonary vasoconstriction with a primary focus on the role of Ca2+ signaling and Ca2+ influx pathways in hypoxic pulmonary vasoconstriction. We used an ex vivo model, isolated perfused/ventilated mouse lung to evaluate hypoxic pulmonary vasoconstriction. Alveolar hypoxia (utilizing a mini ventilator) rapidly and reversibly increased pulmonary arterial pressure due to hypoxic pulmonary vasoconstriction in the isolated perfused/ventilated lung. By applying specific inhibitors for different membrane receptors and ion channels through intrapulmonary perfusion solution in isolated lung, we were able to define the targeted receptors and channels that regulate hypoxic pulmonary vasoconstriction. We show that extracellular Ca2+ or Ca2+ influx through various Ca2+-permeable channels in the plasma membrane is required for hypoxic pulmonary vasoconstriction. Removal of extracellular Ca2+ abolished hypoxic pulmonary vasoconstriction, while blockade of L-type voltage-dependent Ca2+ channels (with nifedipine), non-selective cation channels (with 30 µM SKF-96365), and TRPC6/TRPV1 channels (with 1 µM SAR-7334 and 30 µM capsazepine, respectively) significantly and reversibly inhibited hypoxic pulmonary vasoconstriction. Furthermore, blockers of Ca2+-sensing receptors (by 30 µM NPS2143, an allosteric Ca2+-sensing receptors inhibitor) and Notch (by 30 µM DAPT, a γ-secretase inhibitor) also attenuated hypoxic pulmonary vasoconstriction. These data indicate that Ca2+ influx in pulmonary arterial smooth muscle cells through voltage-dependent, receptor-operated, and store-operated Ca2+ entry pathways all contribute to initiation of hypoxic pulmonary vasoconstriction. The extracellular Ca2+-mediated activation of Ca2+-sensing receptors and the cell-cell interaction via Notch ligands and receptors contribute to the regulation of hypoxic pulmonary vasoconstriction.

The analgesic action of larixyl acetate, a potent TRPC6 inhibitor, in rat neuropathic pain model induced by spared nerve injury

Background

Neuropathic pain is a debilitating status that is insusceptible to the existing analgesics. It is important to explore the underlying pathophysiological changes and search for new pharmacological approaches. Transient receptor potential canonical 6 (TRPC6) is a mechanosensitive channel that is expressed by dorsal root ganglia and glial cells. It has been demonstrated that this channel in dorsal root ganglia plays essential roles in the formation of mechanical hyperalgesia in neuropathic pain. Recent pharmacological screening suggests that larixyl acetate (LA), a main constituent of larch resin, is able to selectively inhibit TRPC6 function. But whether LA is effective in treating neuropathic pain remains unknown. We investigated the efficacy of LA in rat neuropathic pain model, examined its effects on central neuroinflammation, and explored the possible molecular mechanisms by targeting the spinal dorsal horn.

Methods

Spared nerve injury (SNI) was conducted in Sprague-Dawley rats. Mechanical hypersensitivity and cold allodynia before and after single and multiple i.t. applications of LA at the dose of 3, 10, and 30 μM were evaluated by von Frey filament and acetone tests, respectively. Western blot, immunohistochemical, and immunocytochemical stainings were employed to examine the level and expression feature of ionized calcium-binding adaptor molecule 1 (Iba-1), glial fibrillary acidic protein (GFAP), TRPC6, and phosphorylated p38 kinase. The changes of cytokine concentrations, including that of TNF-α, IL-1β, IL-6, and IL-10, were also assessed by multiplex analysis. TRPC6 antisense strategy was finally adopted to investigate the action mechanisms of LA.

Results

Single application of LA on day 5 post injury caused dose-dependent inhibition of mechanical allodynia with the ED₅₀ value of 13.43 μM. Multiple applications of LA at 30 μM not only enhanced the analgesic efficacy but also elongated the effective duration without obvious influences on animal locomotor activities. Single and multiple administrations of LA at 30 μM played similar but weaker inhibitory effects on cold allodynia. In addition to behavioral improvements, multiple applications of LA for 6 days dose-dependently inhibited the upregulation of Iba-1, TNF-α, IL-1β, and IL-6, whereas had no obvious effects on the levels of GFAP and IL-10. Combined Western blot and immunostaining assays revealed that the expression of TRPC6 was significantly increased in both spinal dorsal horn after nerve injury and the cultured microglia challenged by LPS, which was however suppressed by the addition of LA at 30 μM or 10 μM, respectively. Further knockdown of TRPC6 with antisense oligodeoxynucleotide produced prominent analgesic effects in rats with SNI, accompanied by the reduced phosphorylation level of p38 in the microglia.

Conclusions

These data demonstrate that i.t. applied LA exhibits analgesic and anti-inflammatory action in neuropathic pain. The action of LA involves the suppression of TRPC6 and p38 signaling in the microglia. LA may be thus a promising pharmacological candidate for the treatment of intractable chronic pain.

It takes more than two to tango: mechanosignaling of the endothelial surface

The endothelial surface is a highly flexible signaling hub which is able to sense the hemodynamic forces of the streaming blood. The subsequent mechanosignaling is basically mediated by specific structures, like the endothelial glycocalyx building the top surface layer of endothelial cells as well as mechanosensitive ion channels within the endothelial plasma membrane. The mechanical properties of the endothelial cell surface are characterized by the dynamics of cytoskeletal proteins and play a key role in the process of signal transmission from the outside (lumen of the blood vessel) to the interior of the cell. Thus, the cell mechanics directly interact with the function of mechanosensitive structures and ion channels. To precisely maintain the vascular tone, a coordinated functional interdependency between endothelial cells and vascular smooth muscle cells is necessary. This is given by the fact that mechanosensitive ion channels are expressed in both cell types and that signals are transmitted via autocrine/paracrine mechanisms from layer to layer. Thus, the outer layer of the endothelial cells can be seen as important functional mechanosensitive and reactive cellular compartment. This review aims to describe the known mechanosensitive structures of the vessel building a bridge between the important role of physiological mechanosignaling and the proper vascular function. Since mutations and dysfunction of mechanosensitive proteins are linked to vascular pathologies such as hypertension, they play a potent role in the field of channelopathies and mechanomedicine.

Influence of connexin45 on renal autoregulation

Renal autoregulation is mediated by the myogenic response and tubuloglomerular feedback (TGF) working in concert to maintain renal blood flow and glomerular filtration rate despite fluctuations in renal perfusion pressure. Intercellular communication through gap junctions may play a role in renal autoregulation. We examine if one of the building blocks in gap junctions, connexin45 (Cx45), which is expressed in vascular smooth muscle cells, has an influence on renal autoregulatory efficiency. The isolated perfused juxtamedullary nephron preparation was used to measure afferent arteriolar diameter changes in response to acute changes in renal perfusion pressure. In segmental arteries, pressure myography was used to study diameter changes in response to pressure changes. Wire myography was used to study vasoconstrictor and vasodilator responses. A mathematical model of the vascular wall was applied to interpret experimental data. We found a significant reduction in the afferent arteriolar constriction in response to acute pressure increases in Cx45 knockout (KO) mice compared with wild-type (WT) mice. Abolition of TGF caused a parallel upward shift in the autoregulation curve of WT animals but had no effect in KO animals, which is compatible with TGF providing a basal tonic contribution in afferent arterioles whereas Cx45 KO animals were functionally papillectomized. Analysis showed a shift toward lower stress sensitivity in afferent arterioles from Cx45 KO animals, indicating that the absence of Cx45 may also affect myogenic properties. Finally, loss of Cx45 in vascular smooth muscle cells appeared to associate with a change in both structure and passive properties of the vascular wall.

TRPC Channels in Cardiac Plasticity

The heart flexibly changes its structure in response to changing environments and oxygen/nutrition demands of the body. Increased and decreased mechanical loading induces hypertrophy and atrophy of cardiomyocytes, respectively. In physiological conditions, these structural changes of the heart are reversible. However, chronic stresses such as hypertension or cancer cachexia cause irreversible remodeling of the heart, leading to heart failure. Accumulating evidence indicates that calcium dyshomeostasis and aberrant reactive oxygen species production cause pathological heart remodeling. Canonical transient receptor potential (TRPC) is a nonselective cation channel subfamily whose multimodal activation or modulation of channel activity play important roles in a plethora of cellular physiology. Roles of TRPC channels in cardiac physiology have been reported in pathological cardiac remodeling. In this review, we summarize recent findings regarding the importance of TRPC channels in flexible cardiac remodeling (i.e., cardiac plasticity) in response to environmental stresses and discuss questions that should be addressed in the near future.

Mechanisms of Synergistic Interactions of Diabetes and Hypertension in Chronic Kidney Disease: Role of Mitochondrial Dysfunction and ER Stress

PURPOSE OF REVIEW

To discuss the importance of synergistic interactions of diabetes mellitus (DM) and hypertension (HT) in causing chronic kidney disease and the potential molecular mechanisms involved.

RECENT FINDINGS

DM and HT are the two most important risk factors for chronic kidney disease (CKD) and development of end-stage renal disease (ESRD). The combination of HT and DM may synergistically promote the progression of renal injury through mechanisms that have not been fully elucidated. Hyperglycemia and other metabolic changes in DM initiate endoplasmic reticulum (ER) stress and mitochondrial (MT) adaptation in different types of glomerular cells. These adaptations appear to make the cells more vulnerable to HT-induced mechanical stress. Excessive activation of mechanosensors, possibly via transient receptor potential cation channel subfamily C member 6 (TRPC6), may lead to impaired calcium (Ca²⁺) homeostasis and further exacerbate ER stress and MT dysfunction promoting cellular apoptosis and glomerular injury. The synergistic effects of HT and DM to promote kidney injury may be mediated by increased intraglomerular pressure. Chronic activation of mechanotransduction signaling may amplify metabolic effects of DM causing cellular injury through a vicious cycle of impaired Ca²⁺ homeostasis, mitochondrial dysfunction, and ER stress.

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

Canonical Transient Receptor Potential Channels and Vascular Smooth Muscle Cell Plasticity

Vascular smooth muscle cells (VSMCs) play a pivotal role in the stability and tonic regulation of vascular homeostasis. VSMCs can switch back and forth between highly proliferative (synthetic) and fully differentiated (contractile) phenotypes in response to changes in the vessel environment. Abnormal phenotypic switching of VSMCs is a distinctive characteristic of vascular disorders, including atherosclerosis, pulmonary hypertension, stroke, and peripheral artery disease; however, how the control of VSMC phenotypic switching is dysregulated under pathological conditions remains obscure. Canonical transient receptor potential (TRPC) channels have attracted attention as a key regulator of pathological phenotype switching in VSMCs. Several TRPC subfamily member proteins—especially TRPC1 and TRPC6—are upregulated in pathological VSMCs, and pharmacological inhibition of TRPC channel activity has been reported to improve hypertensive vascular remodeling in rodents. This review summarizes the current understanding of the role of TRPC channels in cardiovascular plasticity, including our recent finding that TRPC6 participates in aberrant VSMC phenotype switching under ischemic conditions, and discusses the therapeutic potential of TRPC channels.

Myogenic vasoconstriction requires G12/G13 and LARG to maintain local and systemic vascular resistance

Myogenic vasoconstriction is an autoregulatory function of small arteries. Recently, G-protein-coupled receptors have been involved in myogenic vasoconstriction, but the downstream signalling mechanisms and the in-vivo-function of this myogenic autoregulation are poorly understood. Here, we show that small arteries from mice with smooth muscle-specific loss of G₁₂/G₁₃ or the Rho guanine nucleotide exchange factor ARHGEF12 have lost myogenic vasoconstriction. This defect was accompanied by loss of RhoA activation, while vessels showed normal increases in intracellular [Ca²⁺]. In the absence of myogenic vasoconstriction, perfusion of peripheral organs was increased, systemic vascular resistance was reduced and cardiac output and left ventricular mass were increased. In addition, animals with defective myogenic vasoconstriction showed aggravated hypotension in response to endotoxin. We conclude that G₁₂/G₁₃- and Rho-mediated signaling plays a key role in myogenic vasoconstriction and that myogenic tone is required to maintain local and systemic vascular resistance under physiological and pathological condition.

Calcium signals that determine vascular resistance

Small arteries in the body control vascular resistance, and therefore, blood pressure and blood flow. Endothelial and smooth muscle cells in the arterial walls respond to various stimuli by altering the vascular resistance on a moment to moment basis. Smooth muscle cells can directly influence arterial diameter by contracting or relaxing, whereas endothelial cells that line the inner walls of the arteries modulate the contractile state of surrounding smooth muscle cells. Cytosolic calcium is a key driver of endothelial and smooth muscle cell functions. Cytosolic calcium can be increased either by calcium release from intracellular stores through IP3 or ryanodine receptors, or the influx of extracellular calcium through ion channels at the cell membrane. Depending on the cell type, spatial localization, source of a calcium signal, and the calcium-sensitive target activated, a particular calcium signal can dilate or constrict the arteries. Calcium signals in the vasculature can be classified into several types based on their source, kinetics, and spatial and temporal properties. The calcium signaling mechanisms in smooth muscle and endothelial cells have been extensively studied in the native or freshly isolated cells, therefore, this review is limited to the discussions of studies in native or freshly isolated cells. This article is categorized under: Biological Mechanisms > Cell Signaling Laboratory Methods and Technologies > Imaging Models of Systems Properties and Processes > Mechanistic Models.

Transmembrane insertases and N-glycosylation critically determine synthesis, trafficking, and activity of the nonselective cation channel TRPC6

Transient receptor potential cation channel subfamily C member 6 (TRPC6) is a widely expressed ion channel. Gain-of-function mutations in the human TRPC6 channel cause autosomal-dominant focal segmental glomerulosclerosis, but the molecular components involved in disease development remain unclear. Here, we found that overexpression of gain-of-function TRPC6 channel variants is cytotoxic in cultured cells. Exploiting this phenotype in a genome-wide CRISPR/Cas screen for genes whose inactivation rescues cells from TRPC6-associated cytotoxicity, we identified several proteins essential for TRPC6 protein expression, including the endoplasmic reticulum (ER) membrane protein complex transmembrane insertase. We also identified transmembrane protein 208 (TMEM208), a putative component of a signal recognition particle-independent (SND) ER protein-targeting pathway, as being necessary for expression of TRPC6 and several other ion channels and transporters. TRPC6 expression was also diminished by loss of the previously uncharacterized WD repeat domain 83 opposite strand (WDR83OS), which interacted with both TRPC6 and TMEM208. Additionally enriched among the screen hits were genes involved in N-linked protein glycosylation. Deletion of the mannosyl (α-1,3-)-glycoprotein β-1,2-N-acetylglucosaminyltransferase (MGAT1), necessary for the generation of complex N-linked glycans, abrogated TRPC6 gain-of-function variant-mediated Ca2+ influx and extracellular signal-regulated kinase activation in HEK cells, but failed to diminish cytotoxicity in cultured podocytes. However, mutating the two TRPC6 N-glycosylation sites abrogated the cytotoxicity of mutant TRPC6 and reduced its surface expression. These results expand the targets of TMEM208-mediated ER translocation to include multipass transmembrane proteins and suggest that TRPC6 N-glycosylation plays multiple roles in modulating channel trafficking and activity.

Endurance exercise training restores atrophy-induced decreases of myogenic response and ionic currents in rat skeletal muscle artery

Atrophic limbs exhibit decreased blood flow and histological changes in the arteries perfusing muscles. However, the effect of atrophy on vascular smooth muscle function is poorly understood. Here, we investigated the effect of unilateral sciatic denervation on the myogenic response (MR) and the ionic currents in deep femoral artery (DFA) smooth muscles from Sprague-Dawley rats. Because denervated rats were capable of treadmill exercise (20 m/min, 30 min, 3 times/wk), the impact of exercise training on these effects was also assessed. Skeletal arteries were harvested 3 or 5 wk after surgery. Then skeletal arteries or myocytes were subjected to video analysis of pressurized artery, myography, whole-cell patch clamp, and real-time quantitative PCR to determine the effect of hindlimb paralysis in the presence/absence of exercise training on MR, contractility, ionic currents, and channel transcription, respectively. In sedentary rats, atrophy was associated with loss of MR in the DFA at 5 wk. The contralateral DFA had a normal MR. At 5 wk after surgery, DFA myocytes from the atrophic limbs exhibited depressed L-type Ca2+currents, GTPγS-induced transient receptor potential cation channel (TRPC)-like currents, 80 mM KCl-induced vasoconstriction, TRPC6 mRNA, and voltage-gated K+and inwardly rectifying K+currents. Exercise training abrogated the differences in all of these functions between atrophic side and contralateral side DFA myocytes. These results suggest that a probable increase in hemodynamic stimuli in skeletal artery smooth muscle plays an important role in maintaining MR and ionic currents in skeletal artery smooth muscle. This may also explain the observed benefits of exercise in patients with limb paralysis.

NEW & NOTEWORTHY Myogenic responses (MRs) in rat skeletal arteries feeding the unilateral atrophic hindlimb were impaired. In addition, the L-type Ca2+channel current, the TRPC6-like current, and TRPC6 mRNA levels in the corresponding myocytes decreased. Voltage-gated K+channel currents and inwardly rectifying K+channel currents were also attenuated in atrophic side myocytes. Exercise training effectively abrogated electrophysiological dysfunction of atrophic side myocytes and prevented loss of the MR.

Role of TRPC6 in Progression of Diabetic Kidney Disease

PURPOSE OF REVIEW

The underlining goal of this review is to offer a concise, detailed look into current knowledge surrounding transient receptor potential canonical channel 6 (TRPC6) in the progression of diabetic kidney disease (DKD).

RECENT FINDINGS

Mutations and over-activation in TRPC6 channel activity lead to the development of glomeruli injury. Angiotensin II, reactive oxygen species, and other factors in the setting of DKD stimulate drastic increases in calcium influx through the TRPC6 channel, causing podocyte hypertrophy and foot process effacement. Loss of the podocytes further promote deterioration of the glomerular filtration barrier and play a major role in the development of both albuminuria and the renal injury in DKD. Recent genetic manipulation with TRPC6 channels in various rodent models provide additional knowledge about the role of TRPC6 in DKD and are reviewed here. The TRPC6 channel has a pronounced role in the progression of DKD, with deviations in activity yielding detrimental outcomes. The benefits of targeting TRPC6 or its upstream or downstream signaling pathways in DKD are prominent.

TRPC6 inactivation does not affect loss of renal function in nephrotoxic serum glomerulonephritis in rats, but reduces severity of glomerular lesions

Canonical transient receptor potential-6 (TRPC6) channels have been implicated in a variety of chronic kidney diseases including familial and acquired forms of focal and segmental glomerulosclerosis (FSGS) and renal fibrosis following ureteral obstruction. Here we have examined the role of TRPC6 in progression of inflammation and fibrosis in the nephrotoxic serum (NTS) model of crescentic glomerulonephritis. This was assessed in rats with non-functional TRPC6 channels due to genomic disruption of an essential domain in TRPC6 channels (Trpc6^del/del rats) and wild-type littermates (Trpc6^wt/wt rats). Administration of NTS evoked albuminuria and proteinuria observed 4 and 28 days later that was equally severe in Trpc6^wt/wt and Trpc6^del/del rats. By 28 days, there were dense deposits of complement and IgG within glomeruli in both genotypes, accompanied by severe inflammation and fibrosis readily observed by standard histological methods, and also by increases in renal cortical expression of multiple markers (α-smooth muscle actin, vimentin, NLRP3, and CD68). Tubulointerstitial fibrosis appeared equally severe in Trpc6^wt/wt and Trpc6^del/del rats. TRPC6 inactivation did not protect against the substantial declines in renal function (increases in blood urea nitrogen, serum creatinine and kidney:body weight ratio) in NTS-treated animals, and increases in a urine maker of proximal tubule pathology (β2-macroglobulin) were actually more severe in Trpc6^del/del animals. By contrast, glomerular pathology, blindly scored from histology, and from renal cortical expression of podocin suggested a partial but significant protective effect of TRPC6 inactivation within the glomerular compartment, at least during the autologous phase of the NTS model.

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TRPC6 inactivation in rats does not affect declines in overall renal function in an autoimmune model of rapidly progressing glomerulonephritis.

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TRPC6 inactivation does not reduce renal fibrosis or tubulointerstitial disease in autoimmune glomerulonephritis, and may exacerbate proximal tubule dysfunction in this model.

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TRPC6 inactivation reduces glomerulosclerosis and podocyte loss in autoimmune glomerulonephritis in rats.

TRPC channels in exercise-mimetic therapy

Physical exercise yields beneficial effects on all types of muscle cells, which are essential for the maintenance of cardiovascular homeostasis and good blood circulation. Daily moderate exercise increases systemic antioxidative capacity, which can lead to the prevention of the onset and progression of oxidative stress-related diseases. Therefore, exercise is now widely accepted as one of the best therapeutic strategies for the treatment of ischemic (hypoxic) diseases. Canonical transient receptor potential (TRPC) proteins are non-selective cation channels activated by mechanical stress and/or stimulation of phospholipase C-coupled surface receptors. TRPC channels, especially diacylglycerol-activated TRPC channels (TRPC3 and TRPC6; TRPC3/6), play a key role in the development of cardiovascular remodeling. We have recently found that physical interaction between TRPC3 and NADPH oxidase (Nox) 2 under hypoxic stress promotes Nox2-dependent reactive oxygen species (ROS) production and mediates rodent cardiac plasticity, and inhibition of the TRPC3-Nox2 protein complex results in enhancement of myocardial compliance and flexibility similar to that observed in exercise-treated hearts. In this review, we describe current understanding of the roles of TRPC channels in striated muscle (patho)physiology and propose that targeting TRPC-based protein complexes could be a new strategy to imitate exercise therapy.

Role of age, Rho-kinase 2 expression, and G protein-mediated signaling in the myogenic response in mouse small mesenteric arteries

The myogenic response (MR) and myogenic tone (MT) in resistance vessels is crucial for maintaining peripheral vascular resistance and blood flow autoregulation. Development of MT involves G protein-coupled receptors, and may be affected by aging.

AIMS

(1) to estimate the mesenteric blood flow in myogenically active small mesenteric arteries; (2) to investigate the signaling from Gαq/11 and/or Gα12 activation to MT development; (3) to investigate the role of Rho-kinase 2 and aging on MT in mesenteric resistance arteries.

METHODS

we used pressure myography, quantitative real-time PCR, and immunolocalization to study small (<200 μm) mesenteric arteries (SMA) from young, mature adult, and middle aged mice.

RESULTS

Poiseuille flow calculations indicated autoregulation of blood flow at 60-120 mm Hg arterial pressure. Gαq/11 and Gα12 were abundantly expressed at the mRNA and protein levels in SMA. The Gαq/11 inhibitor YM-254890 suppressed MT development, and the Phosholipase C inhibitors U73122 and ET-18-OCH3 robustly inhibited it. We found an age-dependent increase in ROCK2 mRNA expression, and in basal MT. The specific ROCK2 inhibitor KD025 robustly inhibited MT in SMAs in all mice with an age-dependent variation in KD025 sensitivity. The inhibitory effect of KD025 was not prevented by the L-type Ca2+ channel activator BayK 8644. KD025 reversibly inhibited MT and endothelin-1 vasoconstriction in small pial arteries from Göttingen minipigs.

CONCLUSIONS

MT development in SMAs occurs through a Gαq/11 /PLC/Ca2+ -dependent pathway, and is maintained via ROCK2-mediated Ca2+ sensitization. Increased MT at mature adulthood can be explained by increased ROCK2 expression/activity.

Transient receptor potential (TRP) channels: a metabolic TR(i)P to obesity prevention and therapy

Cellular transport of ions, especially by ion channels, regulates physiological function. The transient receptor potential (TRP) channels, with 30 identified so far, are cation channels with high calcium permeability. These ion channels are present in metabolically active tissues including adipose tissue, liver, gastrointestinal tract, brain (hypothalamus), pancreas and skeletal muscle, which suggests a potential role in metabolic disorders including obesity. TRP channels have potentially important roles in adipogenesis, obesity development and its prevention and therapy because of their physiological properties including calcium permeability, thermosensation and taste perception, involvement in cell metabolic signalling and hormone release. This wide range of actions means that organ-specific actions are unlikely, thus increasing the possibility of adverse effects. Delineation of responses to TRP channels has been limited by the poor selectivity of available agonists and antagonists. Food constituents that can modulate TRP channels are of interest in controlling metabolic status. TRP vanilloid 1 channels modulated by capsaicin have been the most studied, suggesting that this may be the first target for effective pharmacological modulation in obesity. This review shows that most of the TRP channels are potential targets to reduce metabolic disorders through a range of mechanisms.