Role Of Transient Receptor Potential Canonical Channels Research Articles

Role of Transient Receptor Potential Canonical Channels in Heart Physiology and Pathophysiology.

Transient receptor potential canonical (TRPC) channels are involved in the regulation of cardiac function under (patho)physiological conditions and are closely associated with the pathogenesis of cardiac hypertrophy, arrhythmias, and myocardial infarction. Understanding the molecular mechanisms and the regulatory pathway/locus of TRPC channels in related heart diseases will provide potential new concepts for designing novel drugs targeting TRPC channels. We will present the properties and regulation of TRPC channels and their roles in the development of various forms of heart disease. This article provides a brief review on the role of TRPC channels in the regulation of myocardial function as well as how TRPC channels may serve as a therapeutic target in heart failure and cardiac arrhythmias including atrial fibrillation.

Involvement of TRPC4 and 5 Channels in Persistent Firing in Hippocampal CA1 Pyramidal Cells

Persistent neural activity has been observed in vivo during working memory tasks, and supports short-term (up to tens of seconds) retention of information. While synaptic and intrinsic cellular mechanisms of persistent firing have been proposed, underlying cellular mechanisms are not yet fully understood. In vitro experiments have shown that individual neurons in the hippocampus and other working memory related areas support persistent firing through intrinsic cellular mechanisms that involve the transient receptor potential canonical (TRPC) channels. Recent behavioral studies demonstrating the involvement of TRPC channels on working memory make the hypothesis that TRPC driven persistent firing supports working memory a very attractive one. However, this view has been challenged by recent findings that persistent firing in vitro is unchanged in TRPC knock out (KO) mice. To assess the involvement of TRPC channels further, we tested novel and highly specific TRPC channel blockers in cholinergically induced persistent firing in mice CA1 pyramidal cells for the first time. The application of the TRPC4 blocker ML204, TRPC5 blocker clemizole hydrochloride, and TRPC4 and 5 blocker Pico145, all significantly inhibited persistent firing. In addition, intracellular application of TRPC4 and TRPC5 antibodies significantly reduced persistent firing. Taken together these results indicate that TRPC4 and 5 channels support persistent firing in CA1 pyramidal neurons. Finally, we discuss possible scenarios causing these controversial observations on the role of TRPC channels in persistent firing.

Novel findings of 18β-glycyrrhetinic acid on sRAGE secretion through inhibition of transient receptor potential canonical channels in high-glucose environment.

Enhancing soluble receptor for advanced glycation endproducts (sRAGE) is considered as a potent strategy for diabetes therapy. sRAGE secretion is regulated by calcium and transient receptor potential canonical (TRPC) channels. However, the role of TRPC channels in diabetes remains unknown. 18β-Glycyrrhetinic acid (18β-GA), produced from liquorice, has shown antidiabetic properties. This study was aimed to investigate the effect of 18β-GA on sRAGE secretion via TRPC channels in high glucose (HG)-induced THP-1 cells. HG treatment enhanced TRPC3 and TRPC6 expression and consequently caused reactive oxygen species (ROS) accumulation mediated through p47 nicotinamide-adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase (iNOS) associated with uncoupling protein 2 (UCP2) decline and lower sRAGE secretion. Interestingly, 18β-GA showed the dramatic effects similar to Pyr3 or 2-aminoethyl diphenyl borinate inhibitors and effectively reversed HG-elicited mechanisms including that blocking TRPC3 and TRPC6 protein expressions, suppressing intracellular [Ca2+] concentration, decreasing expressions of ROS, p47s, and iNOS, but increasing UCP2 level and promoting sRAGE secretion. Therefore, 18β-GA provides a potential implication to diabetes mellitus and its complications.

Role of TRPC Channels in Store-Operated Calcium Entry.

Store-operated calcium entry (SOCE) is a ubiquitous Ca(2+) entry pathway that is activated in response to depletion of Ca(2+) stores within the endoplasmic reticulum (ER) and contributes to the control of various physiological functions in a wide variety of cell types. The transient receptor potential canonical (TRPC) channels (TRPCs 1-7), that are activated by stimuli leading to PIP2 hydrolysis, were first identified as molecular components of SOCE channels. TRPC channels show a miscellany of tissue expression, physiological functions and channel properties. However, none of the TRPC members display currents that resemble I CRAC. Intensive search for the CRAC channel component led to identification of Orai1 and STIM1, now established as being the primary constituents of the CRAC channel. There is now considerable evidence that STIM1 activates both Orai1 and TRPC1 via distinct domains in its C-terminus. Intriguingly, TRPC1 function is not only dependent on STIM1 but also requires Orai1. The critical functional interaction between TRPC1 and Orai1, which determines the activation of TRPC1, has also been identified. In this review, we will discuss current concepts regarding the role of TRPC channels in SOCE, the physiological functions regulated by TRPC-mediated SOCE, and the complex mechanisms underlying the regulation of TRPCs, including the functional interactions with Orai1 and STIM1.

Abstract 19629: Expression and Role of TRPC Channels in Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Store-operated Ca 2+ entry (SOCE) is a mechanism for increasing cytosolic Ca 2+ (Ca i 2+ ) load after the SR/ER Ca 2+ depletion in many cell types. Our previous study has implicated SOCE, which is at least partially mediated by transient receptor potential canonical (TRPC) channels, exists in adult mouse ventricular myocytes, and contributes to the generation of spontaneous SR Ca 2+ release and triggered arrhythmias. However, it is unclear if this mechanism also exists in human cardiac myocytes. In the present study, we investigate the expression and role of TRPC channels in cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) (purchased from Cellular Dynamics). Abundant distributions of TRPC3 and 6 channels were detected in the plasma membrane of hiPSC-CMs using immunocytochemical staining. Ca i 2+ was imaged in fluo-4-AM loaded cells. A SOCE (F/F 0 = 1.75 ± 0.08, n = 47) was observed in hiPSC-CMs when the external Ca 2+ concentration ([Ca 2+ ] o ) was switched from 0 to 1 mM after SR Ca 2+ was completely depleted by caffeine (20 mM) and thapsigargin (10 µM). The SOCE was inhibited by non-selective TRPC blockers gadolinium (F/F 0 = 1.05 ± 0.03, n = 13) and SKF-96265 (F/F 0 = 1.04 ± 0.03, n = 17), respectively, compared to control (p<0.05). Whereas, the SOCE in hiPSC-CMs was significantly reduced only by pretreatment with anti-TRPC6 antibody (F/F 0 = 1.38 ± 0.06, n = 15, p<0.05), but not with anti-TRPC1 (F/F 0 = 1.93 ± 0.19, n = 8) or anti-TRPC3 antibodies (F/F 0 = 1.49 ± 0.05, n = 14), indicating TRPC6 channels are essential for SOCE in hiPSC-CMs. In addition, the hiPSC-CMs exhibit a property of spontaneous rhythmic beating. After SR Ca 2+ depletion, spontaneous Ca 2+ waves reappeared via refilling from the extracellular Ca 2+ source, suggesting the involvement of SOCE in the generation of spontaneous Ca 2+ waves. This idea was confirmed by the application of TRPC blockers, including gadolinium, SKF-96265 and Pyr3, all of which showed mild to potent inhibitory effects on the spontaneous Ca 2+ waves. In conclusion, we demonstrated the existence of SOCE in hiPSC-CMs. SOCE mediated by TRPC channels, especially the TRPC6, may act as an important mechanism of controlling Ca 2+ handling and arrhythmogenesis in the developing human heart.

Mechanisms controlling neurite outgrowth in a pheochromocytoma cell line: The role of TRPC channels

Transient Receptor Potential Canonical (TRPC) channels are implicated in modulating neurite outgrowth. The expression pattern of TRPCs changes significantly during brain development, suggesting that fine-tuning TRPC expression may be important for orchestrating neuritogenesis. To study how alterations in the TRPC expression pattern affect neurite outgrowth, we used nerve growth factor (NGF)-differentiated rat pheochromocytoma 12 (PC12) cells, a model system for neuritogenesis. In PC12 cells, NGF markedly up-regulated TRPC1 and TRPC6 expression, but down-regulated TRPC5 expression while promoting neurite outgrowth. Overexpression of TRPC1 augmented, whereas TRPC5 overexpression decelerated NGF-induced neurite outgrowth. Conversely, shRNA-mediated knockdown of TRPC1 decreased, whereas shRNA-mediated knockdown of TRPC5 increased NGF-induced neurite extension. Endogenous TRPC1 attenuated the anti-neuritogenic effect of overexpressed TRPC5 in part by forming the heteromeric TRPC1-TRPC5 channels. Previous reports suggested that TRPC6 may facilitate neurite outgrowth. However, we found that TRPC6 overexpression slowed down neuritogenesis, whereas dominant negative TRPC6 (DN-TRPC6) facilitated neurite outgrowth in NGF-differentiated PC12 cells. Consistent with these findings, hyperforin, a neurite outgrowth promoting factor, decreased TRPC6 expression in NGF-differentiated PC12 cells. Using pharmacological and molecular biological approaches, we determined that NGF up-regulated TRPC1 and TRPC6 expression via a p75(NTR)-IKK(2)-dependent pathway that did not involve TrkA receptor signaling in PC12 cells. Similarly, NGF up-regulated TRPC1 and TRPC6 via an IKK(2) dependent pathway in primary cultured hippocampal neurons. Thus, our data suggest that a balance of TRPC1, TRPC5, and TRPC6 expression determines neurite extension rate in neural cells, with TRPC6 emerging as an NGF-dependent "molecular damper" maintaining a submaximal velocity of neurite extension.

TRPC channel-mediated neuroprotection by PDGF involves Pyk2/ERK/CREB pathway

Platelet-derived growth factor-BB (PDGF) has been reported to provide tropic support for neurons in the central nervous system. The protective role of PDGF on dopaminergic neurons, especially in the context of HIV-associated dementia (HAD), however, remains largely unknown. Herein we demonstrate that exogenous PDGF was neuroprotective against toxicity induced by HIV-1 Tat in primary midbrain neurons. Furthermore, we report the involvement of transient receptor potential canonical (TRPC) channels in PDGF-mediated neuroprotection. TRPC channels are Ca2+-permeable, nonselective cation channels with a variety of physiological functions. Blocking TRPC channels with either a blocker or short interfering RNAs (specific for TRPC 5 and 6) in primary neurons resulted in suppression of both PDGF-mediated neuroprotection as well as elevations in intracellular Ca2+. PDGF-mediated neuroprotection involved parallel but distinct ERK/CREB and PI3K/Akt pathways. TRPC channel blocking also resulted in suppression of PDGF-induced Pyk2/ERK/CREB activation, but not Akt activation. Relevance of these findings in vivo was further corroborated by intrastriatal injections of PDGF and HIV-1 Tat in mice. Administration of PDGF was able to rescue the dopaminergic neurons in the substantia nigra from Tat-induced neurotoxicity. This effect was attenuated by pre-treatment of mice with the TRP blocker, thus underscoring the novel role of TRPC channels in the neuroprotection mediated by PDGF.

Involvement of TRPC Channels in CCL2-Mediated Neuroprotection against Tat Toxicity

Chemokine (C-C motif) ligand 2 (CCL2), also known as monocyte chemoattractant protein-1, plays a critical role in leukocyte recruitment and activation. In the present study, we identify an additional role for CCL2 that of neuroprotection against HIV-1 transactivator protein (Tat) toxicity in rat primary midbrain neurons. Furthermore, we report the involvement of transient receptor potential canonical (TRPC) channels in CCL2-mediated neuroprotection. TRPC are Ca(2+)-permeable, nonselective cation channels with a variety of physiological functions. Blockage of TRPC channels resulted in suppression of both CCL2-mediated neuroprotection and intracellular Ca(2+) elevations. Parallel but distinct extracellular signal-regulated kinase (ERK)/cAMP response element-binding protein (CREB) and Akt/nuclear factor kappaB (NF-kappaB) pathways were involved in the CCL2-mediated neuroprotection. Blocking TRPC channels and specific downregulation of TRPC channels 1 and 5 resulted in suppression of CCL2-induced ERK/CREB activation but not Akt/NF-kappaB activation. In vivo relevance of these findings was further corroborated in wild-type and CCR2 knock-out mice. In the wild-type but not CCR2 knock-out mice, exogenous CCL2 exerted neuroprotection against intrastriatal injection of HIV-1 Tat. These findings clearly demonstrate a novel role of TRPC channels in the protection of neurons against Tat through the CCL2/CCR2 axis.

Functional role of TRPC channels in the regulation of endothelial permeability

The endothelial cells (ECs) form a semipermeable barrier between the blood and the tissue. An important function of the endothelium is to maintain the integrity of the barrier function of the vessel wall. Ca(2+) signaling in ECs plays a key role in maintaining the barrier integrity. Transient receptor potential canonical (TRPC) channels are mammalian homologs of Drosophila TRP Ca(2+)-permeable channels expressed in EC. TRPC channels are thought to function as a Ca(2+) entry channel operated by store-depletion as well as receptor-activated channels in a variety of cell types, including ECs. Inflammatory mediators such as thrombin, histamine, bradykinin, and others increase endothelial permeability by actin polymerization-dependent EC rounding and formation of inter-endothelial gaps, a process critically dependent on the increase in EC cytosolic [Ca(2+)] ([Ca(2+)](i)). Increase in endothelial permeability depends on both intracellular Ca(2+) release and extracellular Ca(2+) entry through TRPC channels. This review summarizes recent findings on the role of TRPC channels in the mechanism of Ca(2+) entry in ECs, and, in particular, the role of TRPC channels in regulating endothelial barrier function.

Sensing the Right Path

During nervous system development, axonal growth cones find their way to their targets with the help of various chemoattractant and chemorepellant cues. Several neurite guidance signals modulate calcium influx into the growth cone, but the underlying mechanisms and the specific channels involved have been unclear (see Gomez). Now two groups, Li et al. and Wang and Poo, provide evidence implicating transient receptor potential canonical (TRPC) channels--a family of channels known for mediating sensory responses--in the response to the chemoattractants brain-derived neurotrophic factor (BDNF) and netrin-1. Wang and Poo performed perforated whole-cell patch clamp analysis of cultured Xenopus spinal neurons and found that netrin-1 elicited membrane depolarization that was inhibited by an antibody to its receptor, DDC. Netrin-induced current present during pharmacological blockade of most voltage-dependent ion channels was inhibited by SKF-96365, which blocks TRP channels, as was a similar current produced by BDNF. Further, growth cone turning in response to netrin-1 or BDNF was abolished by SKF-96365. Injection of morpholino oligonucleotides (MOs) that knocked down xTRPC1 expression inhibited the putative TRP currents and abolished growth cone turning in response to a netrin-1 gradient. Moreover, MO or SKF-96365 abolished the netrin-induced increase in growth cone calcium concentration. Li et al. investigated TRPC channels in BDNF-mediated guidance of cultured cerebellar granule cells, which was blocked by antibodies to the TrkB receptor, incubation with a membrane-permeable calcium chelator, or pharmacological depletion of intracellular calcium stores. Although pharmacological blockade of several voltage-sensitive sodium and calcium channels had no effect on growth cone turning elicited by BDNF, turning was abolished by SKF-96365, as well as by pharmacological inhibition of phospholipase C (PLC), phosphatidylinositol 3-kinase (PI3K), or blockade of the inositol 1,4,5-trisphosphate receptor (IP 3 R). In contrast, a PLC activator elicited turning, an effect that depended on extracellular calcium and was abolished by SKF-96365. BDNF increased growth cone calcium concentration, an effect that depended on both calcium influx and release from internal stores and that was reduced by SKF-96365, pharmacological inhibition of PLC, or IP 3 R blockade. BDNF-induced turning was abolished by siRNA directed against TRPC3 or by overexpression of dominant-negative mutant forms of TRPC3 or TRPC6. Thus, activation of TRPC channels appears to play a key role in calcium-dependent neurite pathfinding in response to both netrin-1 and BDNF. Y. Li, Y.-C. Jia, K. Cui, N. Li, Z.-Y. Zheng, Y.-Z. Wang, X.-B. Yuan, Essential role of TRPC channels in the guidance of nerve growth cones by brain-derived neurotrophic factor. Nature 434 , 894-898 (2005). [PubMed] G. X. Wang, M.-M. Poo, Requirement of TRPC channels in netrin-1-induced chemotropic turning of nerve growth cones. Nature 434 , 898-904 (2005). [PubMed] T. Gomez, Channels for pathfinding. Nature 434 , 835-838 (2005). [PubMed]