[Frontiers in Bioscience S4, 157-166, January 1, 2012]
TRPC channels as prospective targets in atherosclerosis: terra incognita
Guillermo Vazquez1
1
TABLE OF CONTENTS
1. ABSTRACT
Transient Receptor Potential Canonical (TRPC) proteins are non-selective cation channels ubiquitously expressed throughout the cardiovascular system, where they participate as Ca2+/Na+-permeable channels and/or signaling platforms in various physiological and pathophysiological mechanisms. TRPCs have been implicated in essential hypertension, cardiac hypertrophy and endothelial dysfunction. Despite these pathologies being related, directly or indirectly to development of atherosclerotic lesions, the potential role of TRPCs in the pathogenesis of atherosclerosis remains unexplored. Recent studies from our laboratory showing an obligatory requirement of TRPC3 in the inflammatory signaling linked to monocycle recruitment to coronary endothelium, suggest for the first time potential pathophysiological relevance of a member of the TRPC group in atherogenesis. This brings about the question whether we can envision TRPCs as potential targets for diagnosis, prognosis and/or treatment of atherosclerosis. Here we revisit some of the existing knowledge on TRPCs and cardiovascular pathology and discuss it within the context of cellular/molecular processes related to atherogenesis. Potential limitations and advantages of TRPCs as prospectives targets in atherosclerosis are discussed and confronted against those of channel blockers currently in use.
2. TRANSIENT RECEPTOR POTENTIAL CANONICAL (TRPC) PROTEINS
Without question TRPC proteins stand up amongst the most important channel forming proteins in the vasculature, where they are expressed in all cell types composing the heart and vessel's wall, and also in hematopoietic cells, and participate, directly or indirectly, in Ca2+ signaling events required for modulation of a myriad of vascular functions (1; 2). The TRPC family belongs to the larger TRP superfamily of channel forming proteins and contains those TRP members most closely related to the original Drosophila melanogaster TRP protein (3; 4). TRPC proteins can be subgrouped on the basis of structural, pharmacological and functional properties: TRPC1, TRPC2 (a pseudogene in humans, old world monkeys and apes), TRPC3/6/7, and TRPC4/5 (4). Functional TRPC channels are made of homo- or hetero-tetrameric arrangements of four TRPC proteins with each subunit exhibiting a membrane topology which includes six transmembrane domains (TM1-TM6) separating cytoplasmic N- and C-termini, and a re-entry loop between TM5 and TM6 which lines the wall of the pore ( (4) and references therein). The presence of ankyrin repeats at the N-terminus and coiled-coil regions both at N- and C-ends -among other structural features that vary within individual members- enable TRPCs to interact with a diversity of signaling proteins, although this strongly depends on the particular TRPC subunit, cell type and expression conditions. Ectopic expression of TRPC proteins in homo- or heterologous expression systems renders non-voltage gated, non-selective Ca2+-permeable cation channels characteristically activated downstream receptor-stimulated phospholipases (v.g., PLC and/or PLD; see for instance (5)). This is also the situation in native conditions, as TRPC channels expressed at endogenous cellular levels take part in the action of several phospholipase-coupled receptors for peptides and growth factors that contribute to various aspects of vascular physiology, such as regulation of arterial tone, endothelial permeability, secretion, endothelial cell proliferation, apoptosis and survival, among others (2). It is important to keep in mind that in terms of permeability properties all TRPCs are non-selective for cations, which confers them the ability to also alter Ca2+ signaling by mediating Na+ influx, i.e., by altering membrane potential and modifying the driving force for Ca2+ entry (see (6) and references therein). The mechanisms underlying activation of TRPC channels are diverse, and is still controversial whether lessons learned from heterologous expression systems truly reflect mechanisms involved in TRPC regulation under native conditions (reviewed by us in (7; 8)). Despite this uncertainty, there is a great deal of in vitro and in vivo data documenting the participation of TRPCs in Ca2+/Na+ influx associated to vascular physiology (2; 9). Most importantly, accumulating evidence shows that TRPCs are indisputable players in the pathogenesis of cardiovascular disease (10; 11). Notably, it was not until we began to pay attention to which cellular and/or molecular events rely upon appropriate TRPC expression/function -regardless of the particular mechanism/s driving channel activation- that we started to move forward in better understanding the role of TRPCs in cardiovascular physiology and disease.
3. TRPC PROTEINS AND CARDIOVASCULAR DISEASE: QUID NOVIS?
For more than a decade now we have witnessed an increasing enthusiasm to learn more about the role of TRPC proteins in cardiovascular pathology. Because all members of the TRPC family are ubiquitously expressed along the vascular tree, it is not surprising that altered TRPC function and/or expression is frequently associated to a variety of vascular disease states (reviewed by us in (12); see also (3; 13)). For example, TRPC1, 4 and 6 participate in regulation of vascular tone and play a role in hypertension . TRPC1 and 6 modulate proliferation of vascular smooth muscle cells and may have implications in the development of both idiopathic and hypoxia-induced -acute and chronic- pulmonary hypertension (14; 15; 16; 17; 18; 19) as well as in the pathogenesis of intima hyperplasia (20; 21). More recently, the pro-proliferative role of TRPC6 in endothelium underscores a potential role for this TRPC member in angiogenesis and neovascularization (see section 4.4. below). Regulated Ca2+ entry through TRPC3 and 6 activates Nuclear Factor of Activated T cells (NFAT), a critical event in development of cardiac hypertrophy (22; 23). A significant amount of information on regulatory aspects of TRPC3 and 7 in lymphocytes has been derived from studies on both human and avian cells, and is likely that at least these closely related TRPC members may take part in immune responses mediated by B and T cells (24; 25; 26). Because those studies were conducted on cell lines, it remains to be explored if those findings represent relevant TRPC functions in intracellular signaling associated to the pathogenesis of inflammatory vascular disease in in vivo models. TRPC3, by yet to be known mechanisms, is upregulated in circulating monocytes from spontaneously hypertensive rats (27; 28) and that strongly correlates with increased regulated Ca2+ influx. Similarly, increased store-operated and diacylglycerol-regulated Ca2+ influx accompany augmented expression of TRPC3 and 5 in circulating monocytes from patients with essential hypertension (29; 30). The speculation has been made that this may account for the increased monocyte activation observed in hypertensive individuals with potential implications in promoting vascular disease in these patients - v.g., atherosclerosis- (30) but this notion has not been further explored. Expression of TRPC3 and 6 is increased in pre-glomerular arterioles from patients with malignant hypertension (31) and TRPC3 is also elevated in kidney endothelium obtained from renal cell carcinoma patients who had a history of hypertension, but not in those with normal blood pressure (32). Because TRPC3 is endowed with high constitutive, non-regulated activity (4; 33) it is plausible to speculate that upregulated channel expression may derive in increased constitutive Ca2+ and/or Na+ influx into endothelium and/or smooth muscle, and thus affect the basal activity of Ca2+/Na+ dependent signaling processes underlying vascular function. The best example that such phenomenon does indeed take place in vivo, is provided by the observation that constitutively active TRPC3 is upregulated in TRPC6 knockout mice and is responsible for enhanced contractility of aorta and cerebral arteries and elevated blood pressure (34). More recently, we showed that upregulated expression of TRPC3 in coronary endothelium promotes inflammatory signaling and supports regulated expression of cell adhesion molecules ( (35; 36); discussed in section 4.1 below).
4. TRPC PROTEINS AND ATHEROSCLEROSIS: QUO VADIS?
Atherosclerosis is a chronic disease of the arterial wall with a dominant inflammatory component that is present throughout all stages of the disease (37). Atherosclerosis is perhaps the best example of an inflammatory vascular disease arising as the result of a complex interplay between mechanisms that are intrinsic to the endothelium, such as endothelial dysfunction, cell adhesion-mediated recruitment of inflammatory cells, oxidative stress, and factors related to the individual genetics and its environment, such as metabolic disorders or lifestyle, among others (38; 39). Also, atherosclerotic lesions are the major vascular complication of diabetes, obesity and metabolic syndrome. It is not surprising then that atherosclerosis still constitutes the major cause of death in western societies, where in the United States only, one in five annual deaths are due to coronary artery disease, a manifestation of atherosclerosis of the coronary arteries, in both men and women (40). Most frequently, atherosclerotic lesions are present in epicardial coronaries, aorta, carotid or peripheral arteries, and the narrowing of the arterial lumen caused by lesion growth can lead to ischemia of the heart, brain, or extremities and eventually, infarction, stroke and/or complications derived from ischemic or thromboembolic events that follow plaque rupture (39; 41). The inflammatory response that takes place in the subintima plays a central role not only in the initiation of the atherosclerotic lesion, but also in its progression and the fate of the plaque at more advanced stages (reviewed in (41; 42)). At the cellular and molecular level, inflammatory signaling in the endothelial cell, the endothelial repertoire of constitutive and inducible cell adhesion molecules (CAMs) and the recruitment of circulating monocytes to the inflammation sites in the subintima, all constitute salient features that somehow determine progression of initial fatty streaks -lipid laden subendothelial macrophages- towards complex plaques that may later become unstable, life-threatening lesions.
Recent studies from our laboratory aimed at understanding the role of TRPC3 in regulated expression of CAMs and monocyte recruitment to coronary artery endothelium (vide infra) provided, for the first time, experimental support to the novel notion that TRPC3 - and perhaps other members of the TRPC group, vide infra- might play a signaling role in atherogenesis. Our findings and those from other groups -although the latter not directly aimed at studying atherosclerosis- suggest the existence of a novel relationship between expression and function of native TRPC proteins and cellular and molecular events that contribute to atherogenesis, suggesting pathophysiological relevance for TRPCs in this disease. The available evidence is briefly revisited in the following subsections and it was grouped, for a didactic purpose only, on the basis of observations that, although not originally intended to examine a role of TRPCs in atherogenesis, provide a potential link between TRPC function to molecular/cellular events and/or risk factors known to play a role in the pathogenesis of atherosclerosis. The sections below by no means intend to represent a thorough revision of existing literature in the field; rather, only those examples most representative in terms of their relevance to atherosclerosis have been chosen in order to illustrate our viewpoint. For further reading on TRPCs in cardiovascular disease the reader is referred to some recent reviews on the topic (see for instance, (2; 6; 11; 13; 43; 44)).
4.1. TRPCS IN REGULATED EXPRESSION OF CELL ADHESION MOLECULES AND INFLAMMATORY CELL RECRUITMENT
Recruitment of circulating monocytes to the endothelium and their migration to the subendothelial milieu where they differentiate into macrophages is one of the earliest cellular events in atherogenesis (37; 45). Nevertheless, monocyte infiltration takes place throughout all stages of lesion development and this perpetuation of monocyte/macrophage replenishment at the lesion site has a prominent role in the mechanisms that lead to plaque instability and rupture (46). Monocyte recruitment to the endothelium entails interaction of integrins on the monocyte surface with CAMs expressed on the endothelial cell, particularly selectins (v.g., E-selectin) and CAMs from the immunoglobulin superfamily such as intercellular cell adhesion-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Both ICAM-1 and VCAM-1 have a central function not only in mediating attachment and firm monocyte adhesion to the endothelial layer but also in the endothelial intracellular signaling that supports transmigration of the bound monocyte (47; 48; 49). Whereas it is clear that ICAM-1 and E-selectin contribute to monocyte recruitment, the role of VCAM-1 in this process is unique in that while ICAM-1 or E-selectin are mostly constitutively expressed in non-activated endothelium, VCAM-1 is absent or undetectable, but its expression is drastically upregulated when the endothelium is exposed to pro-atherogenic stimuli (50). For instance, in hypercholesterolemic animals both ICAM-1 and VCAM-1 are induced in early lesions. However, VCAM-1 expression is largely restricted to lesions, or to sites prone to lesion formation, and can also be detected even before the onset of visible fatty streaks, while ICAM-1 also extends to uninvolved aorta and lesion-protected regions (51). This dissimilar pattern strongly suggested different functions for ICAM-1 and VCAM-1, at least in lesion initiation. Pro-atherogenic factors such as tumor necrosis factor-α (TNFα), locally released nucleotides or oxidized low density lipoprotein (oxLDL) among others, are potent inducers of VCAM-1 expression (50). Oxidized LDL is of most relevance to atherogenesis, as endothelial permeability to apolipoprotein B-containing lipoproteins (i.e., LDL) and their retention and oxidation in the subendothelial space is decisive in triggering endothelial activation and monocyte recruitment. TNFα and nucleotides can be released abluminally or to the subendothelial milieu in response to ischemia, hypoxia, chemical or mechanical stress, and amplify the inflammatory response by promoting release of other inflammatory mediators (v.g., interleukin 6, monocyte chemoattractant protein-1 (52; 53). In human coronary artery endothelial cells (HCAECs) ATP is a potent inducer of VCAM-1 through a mechanism that requires activation of P2Y2 purinergic receptors and changes in intracellular Ca2+ ( (36) and references therein). In a recent study, we showed that in HCAECs native TRPC3 protein forms Ca2+-permeable channels that contribute to constitutive, non-regulated Ca2+ influx and also to receptor-regulated Ca2+ entry (36). Those studies showed that TRPC3 expression and its characteristic constitutive function are obligatory for ATP-induced VCAM-1 and monocyte adhesion. In a follow up work, we showed that TRPC3 constitutive function is also required for TNFα-induced expression of VCAM-1 in HCAECs (35). Using knockdown and overepxression approaches, it was demonstrated that it is indeed the constitutive, non-regulated function of TRPC3 rather than regulated channel activity, what is required for the signaling underlying VCAM-1 expression in these cells, through a mechanism that involves constitutive TRPC3-mediated Ca2+ influx for proper activation of NFκB, presumably through Ca2+-dependent activation of a Calmodulin/Calmodulin-dependent kinase axis (35). Notably, knockdown of TRPC3 in HCAECs also caused a significant reduction in TNFα-induced ICAM-1 expression and interleukin-1β-induced VCAM-1, suggesting that TRPC3 may exert a more general role in NFκB-dependent regulated-expression of CAMs by different pro-atherogenic stimuli, rather than a specific function in TNFα-induced VCAM-1. These findings represented the first direct indication that TRPC-mediated Ca2+ influx plays a role in the signaling driving expression of endothelial VCAM-1, underscoring for the first time a potential novel function of TRPC3 in atherogenesis and coronary artery disease.
4.2. Oxidative stress
Available evidence indicates that TRPC3 contributes not only to normal redox-dependent endothelial functions but to the signaling associated to oxidative stress, a critical component of endothelial dysfunction associated to atherogenesis (54; 55; 56). In porcine pulmonary artery endothelial cells native TRPC3 heteromultimerizes with TRPC4 to make non-selective cation channels that are sensitive to the redox status of the cell (54; 55). In addition, molecular and electrophysiological evidence suggests that TRPC3 is likely the peroxide-activated non-selective cation channel that mediates Na+ influx and membrane potential breakdown in calf pulmonary endothelium (57; 58). The mechanism by which TRPC-based channels sense redox status in the membrane microenvironment remains unknown. In HCAECs, TNFα-dependent generation of reactive oxygen species occurs mainly through activation of membrane associated NADPH oxidases (Nox2/Nox4A; (59)) and this contributes to TNFα-induced activation of the NFκB pathway. We recently showed that this process has a mandatory requirement for constitutive Ca2+ influx, presumably through native TRPC3 channels (35). Notably, in HCAECs NADPH oxidase-dependent generation of reactive oxygen species is necessary but not sufficient for full activation of NFκB by TNFα, and constitutive Ca2+ influx is required in order for the system to be fully operational (35).
4.3. Endothelial permeability
The ability of endothelial cells to undergo retraction under certain local or systemic conditions confers the endothelium with the ability to adjust its permeability to a variety of molecules and/or cells (v.g., during monocyte transendothelial migration). This also has pathophysiological relevance, as altered transcellular and/or paracellular endothelial cell permeability is now well recognized as a contributing factor to the pathogenesis of atherosclerosis (60). Notably, members of the TRPC family have been involved in the processes that regulate endothelial barrier function (61; 62). Of relevance to atherogenesis, TRPC6-mediated Ca2+ influx is obligatory for the inhibitory actions of lysophosphatidylcholine (LysoPC) on migration of bovine aortic endothelial cells (63; 64). TRPC6 is expressed in endothelium, macrophages and medial smooth muscle cells, and therefore it is conceivable that LysoPC, which is an important component of oxLDL at the lesion site, can act as a signaling mediator for LysoPC pro-inflammatory actions. The role of TRPC1, 4 and to some extent, TRPC6, in receptor-regulated lung endothelial permeability is well supported by both in vivo and in vitro studies (65; 66), but their participation in endothelial permeability in atherosclerosis prone arterial beds remains to be explored. Recently, endothelial hyperpermeability in Klotho deficient mice has been shown to be related to inefficient internalization of TRPC1, which results in augmented vascular endothelial growth factor (VEGF)-dependent Ca2+ influx and hyperactivity of Ca2+-dependent proteases (67).
4.4. Adventitial angiogenesis and plaque neovascularization
As the atherosclerotic lesion grows, new vessels can sprout from the adventitial vassa vasorum and neovascularize the growing plaque. Plaque neovascularization provides an additional entering route for inflammatory cell recruitment into the plaque, what derives into exacerbation of the inflammatory state and speeds up plaque growth. Most importantly, plaque neovascularization is an important contributing factor to the instability of the plaque and ultimately, its rupture and subsequent thromboembolic complications (46). VEGF is a central player in adventitial angiogenesis and neovascularization and whether its role in atherosclerotic lesion progression is beneficial of detrimental is still a matter of debate (68). Although not derived from vascular beds prone to atherosclerotic lesion development, human microvascular and umbilical vein endothelial cells migrate, sprout and proliferate in response to VEGF by a mechanism that requires TRPC6-mediated Ca2+ influx (69; 70). These results can be interpreted as suggestive of a potential role of TRPC6 in the signaling events that drive angiogenesis during plaque neovascularization. However, the impact of different cellular and molecular processes on lesion progression might also be significantly dependent upon the overall inflammatory/necrotic status of the plaque, and therefore it is possible that the function of TRPC6 in plaque neovascularization, if any at all, might have differential impacts depending on the plaque being at early or advanced stage. In vivo studies using mouse models of plaque destabilization -v.g., brachiocephalic artery in ApoE-/- mice (71; 72)- in mice lacking or overexpressing TRPC6 in particular vascular tissues will provide valuable information on this potentially critical role of TRPC6 in atherosclerosis.
4.5. Blood pressure
A significant amount of experimental evidence supports a role for TRPC proteins in smooth muscle cells of the systemic and pulmonary circulation where they seem to contribute to events related to systemic blood pressure and hypoxia-induced and idiopathic pulmonary hypertension ( (13; 73) and references therein). Monocytes isolated from patients with essential hypertension exhibit a significant increase in TRPC3 levels compared to cells from normotensive individuals, and that correlates with increased regulated Ca2+ influx (29; 30). TRPC3 was also found to be significantly higher in renal endothelium from patients with malignant hypertension (31) and patients with renal cell carcinoma with a history of elevated systolic blood pressure (32). This evidence however, only provides "guilt by association" and it does not answer a more fundamental question, i.e., whether increased levels of TRPC3 play a causative role in the pathogenesis of human hypertension. Evidence on the modulation of nitric oxide (NO) bioavailability through TRPC function as a potential mechanism linking channel activity to vasorelaxation and blood pressure is not yet available. However, NO levels seem to affect TRPC activity, and recent work points for a role of the NO/cGMP axis as a potential strong modulator of TRPC3 and 6 functions. Increasing NO levels either through guanylyl cyclase-linked agonists or by inhibition of cGMP-specific type 5 phosphodiesterase (PDE5; i.e., with sildenafil) inhibits the activities of TRPC3 and more robustly, TRPC6, resulting in a more vigorous and sustained PKG activity which is known to exert phosphorylation-mediated negative feedback of these TRPC proteins (see (74) and references therein). This mechanism has been proposed to be of relevance in PKG mediated modulation of vascular relaxation, and therefore blood pressure (75).
5. ATHEROSCLEROSIS, CHANNEL BLOCKERS AND TRPC PROTEINS AS PROSPECTIVE TARGETS: DO WE NEED MORE CHANNELS TO BLOCK?
The notion of Ca2+ influx exerting a permissive effect in atherogenesis has been recognized long before the concept of atherosclerosis as an inflammatory disease would fully develop (76; 77) and even before having available the significant amount of information that exists today regarding signaling pathways that directly or indirectly depend on Ca2+ influx in endothelium, vascular smooth muscle or macrophages. The realization that traditional L-type channel blockers in clinical use for other cardiovascular situations -v.g., hypertension, arrhythmias- have a beneficial effect on atherosclerosis, somehow centered the attention on their role on L-type channels in smooth muscle. On this ground, any action of L-type blockers on cells other than smooth muscle, and not expressing L-type channels -v.g., endothelium - were systematically attributed to "non-channel related" effects. This somewhat may explain the lack of a systematic exploration of the nature of other Ca2+-influx channels that may be involved in atherogenesis or of the mechanism/s linking Ca2+ entry to atherogenic processes. Our recent studies on TRPC3 in inflammatory signaling in coronary endothelium and those from others (vide supra) provide the first experimental support to the notion that non-L-type channels, in this case members of the TRPC group, might play a signaling role in atherogenesis. This concept immediately opens a spectrum of possibilities regarding potential exploitation of TRPCs -once their individual roles are elucidated- as novel molecular targets in diagnosis, prognosis and/or treatment of atherosclerosis. But how realistic is to think of TRPCs as prospective targets for this disease? This is a fundamental question particularly if we consider the following. First, TRPC proteins are ubiquitously expressed throughout tissues in the body, what imposes a limitation when strategies for selective vascular targeting are to be designed - v.g., endothelial vs. smooth muscle targeting- unless cell specific delivery is achieved. Second, provided this issue is resolved, targeting TRPCs will most likely be aimed at blocking channel function. This immediately raises the question whether targeting TRPCs would provide any additional benefit over what is currently available from clinical use of traditional CCBs whose anti-atherogenic effects have been known for quite some time (78; 79; 80; 81). Indeed, several randomized control clinical trials have shown that CCBs of the phenylalkylamine, benzothiazepine and dihydropyridine groups, historically used in the treatment of hypertension, arrythmias, cardiac hypertrophy, cardiac failure and angina pectoris (82; 83), reduce progression of atherosclerosis (reviewed in (81; 84; 85; 86). However, two critical aspects of CCBs in clinical use are worth mentioning. First, several vascular effects of CCBs -with exception of their action on smooth muscle cells and cardiomyocytes- are unrelated to their channel blocking properties and the underlying mechanism remains, for the most part, unknown. This is well exemplified by the effects of verapamil - a phenylalkylamine- or amlodipine - a dihydropyridine- on expression of endothelial CAMs. It has been shown that long term therapy with these CCBs results in a reduction in expression levels of VCAM-1 with the concomitant benefit derived from reduced recruitment of inflammatory cells (87; 88); these actions are not dependent on channel blockade -endothelium does not rely upon L-type channels for Ca2+ influx- but rather seem to be, at least in part, subsequent to an anti-oxidant effect of these CCBs by a poorly understood mechanism which may involve a scavenging action and/or preservation of superoxide dismutase activity (reviewed in (89)). That actions of this nature are not subsequent to channel blockade is better exemplified by the anti-oxidant and anti-apoptotic effects of the dihydropyridine nifedipine on endothelium, which can be completely recapitulated by BayW9798, a dihydropyridine structurally related to nifedipine but with no channel blocker activity (see (90) and references therein). Second, in those few instances where the vascular actions of CCBs do indeed reflect a Ca2+-influx blockade effect - v.g., nifedipine and verapamil blockade of L-type Ca2+ channels in arteriolar smooth muscle or cardiomyocytes, respectively, with the concomitant reduction in peripheral resistance and cardiac output- several side effects occur. Indeed, the most significant toxic effects of CCBs are direct extensions of their therapeutic actions. For example, persistent Ca2+ influx blockade can derive in serious cardiac depression, including cardiac arrest, bradycardia, atrioventricular block and heart failure; although these extreme effects have not been frequent in clinical use, side effects of intermediate caliber are observed in an important number of individuals undergoing CCB therapy. In addition, all prototypical CCBs -verapamil, nifedipine and diltiazem- interfere not only with L-type channels but also some non-selective cation channels including TRPCs. For example, verapamil suppresses both constitutive and regulated TRPC3 activity (36; 91). Verapamil's anti-inflammatory actions on endothelium, including a reduction in VCAM-1 expression and leukocyte adhesion (87; 92), have been historically thought to be unrelated to its channel blocker properties. Whereas verapamil is not specific for TRPC3, our recent observation that in coronary endothelial cells verapamil reduces VCAM-1 expression and monocyte binding to the same extent as knockdown of TRPC3 does (36), raises the question whether at least part of the anti-inflammatory actions of this CCB might be related to a non-L type channel blocker effect. Although additional studies are required to specifically address this notion, it is possible that actions of CCBs on non-L type channels may interfere, in vivo, with a myriad of signaling functions that depend upon proper operation of those channels. Based on these considerations, an immediate benefit can be envisaged from targeting TRPCs over current calcium channels, and that is the possibility of achieving efficient suppression of signaling events downstream TRPC-mediated Ca2+ influx with no interference on pathways usually affected by traditional L-type CCBs. Therefore, typical CCBs side effects are expected to be avoided or at least minimized. Crucial to achieve this goal is the development of subtype-specific inhibitors for TRPCs. As of this writing, no specific pharmacological inhibitors of TRPCs have been developed so far and none of the existing blockers that affect TRPC function - v.g., verapamil, SKF96365, flufenamate, hyperforin, among others; see for instance (93) and references therein- are selective enough to be expected to discriminate, in vivo, between TRPCs and other channels. In this regard, some progress has been recently made with pyrazole compounds (94), but their efficacy in vivo awaits further examination. An alternative approach that illustrates the possibility of specific TRPC targeting in the vasculature is provided by work showing that antibody-mediated targeting of extracellular domains of TRPC proteins may have therapeutic potential (21; 95). This strategy relies upon using antibodies to target the third extracellular loop of TRPCs -"E3 targeting"- which lies next to the pore region; this may impose both conformational and steric constraints to the pore which then results in abrogation of channel activity. The E3-targeting strategy was successfully applied to block TRPC1 (21) and TRPC5 (95) channel activities. Importantly, because of the exquisitely high selectivity and specificity that can be attained with antibodies, this strategy provides an opportunity to discriminate even between closely related members within the TRPC group -v.g., TRPC5 vs. TRPC4, see for instance (95) - with the potential benefit of minimizing side effects derived from incomplete selectivity of pharmacological blockers.
6. CONCLUDING REMARKS
The recognition of atherosclerosis as an inflammatory disease revolutionized the field regarding the way basic and clinical research efforts were conceived. For example, advances on the knowledge of molecular and cellular components involved in lesion development, such as the role of endothelial CAMs in monocyte recruitment, and appreciation of the fundamental role of the macrophage as a central player in lesion formation and progression, were rapidly and enthusiastically envisaged as promising new opportunities to develop anti-inflammatory therapies for the disease. However, evidence accumulated so far indicates that interfering at the level of one single target may render limited success (see (86; 96; 97)) and that dual or multiple targeting might be necessary to achieve results of clinical significance. This is not surprising considering the multifactorial nature of atherosclerosis and the diverse repertoire of receptors, signaling molecules and cell types that contribute to its pathogenesis. It is easy then to understand why characterization of new components of signaling events that contribute to monocyte recruitment, their migration to the subintima, factors involved in their differentiation to macrophage and events that modulate macrophage survival and/or apoptosis at the lesion site, is of fundamental importance to move forward in the development of new therapeutic and/or prognostic/diagnostic strategies for effective management of this disease. Within this context, studies aimed at understanding the role of TRPC proteins in atherogenesis have an unequivocal potential to make a major contribution into that direction. An invaluable step forward to achieve such goal will be the generation of genetically modified mouse models with conditional overexpression or knockout of one or more TRPC members in atherosclerosis relevant vascular cells in order to allow examination of the in vivo contribution of that particular TRPC in atherogenesis.
7. ACKNOWLEDGMENTS
Work at the author's laboratory is supported by a Scientist Development Grant from the American Heart Association (SDG0635250N to G.V.) and University of Toledo College of Medicine.
8. REFERENCES
1. B. Nilius, G. Droogmans, R. Wondergem. Transient receptor potential channels in endothelium: solving the calcium entry puzzle? Endothelium 10, 5-15 (2003)
doi:10.1080/10623320303356
PMid:12699072
2. X. Yao, C.J. Garland. Recent Developments in Vascular Endothelial Cell Transient Receptor Potential Channels. Circ Res 97, 853-863 (2005)
doi:10.1161/01.RES.0000187473.85419.3e
PMid:16254217
3. L.J. Wu, T.B. Sweet, D.E. Clapham. International Union of Basic and Clinical Pharmacology. LXXVI. Current progress in the mammalian TRP ion channel family. Pharmacol Rev 62, 381-404 (2010)
doi:10.1124/pr.110.002725
PMid:20716668
4. G. Vazquez, B.J. Wedel, O. Aziz, M. Trebak, J. Putney Jr. The mammalian TRPC cation channels. Biochim Biophy Acta 1742, 21-36 (2004)
PMid:15590053
5. G. Vazquez, J.Y. Tano, K. Smedlund. On the potential role of source and species of diacylglycerol in phospholipase-dependent regulation of TRPC3 channels. Channels (Austin, Tex.) 4, 232-240 (2010)
doi:10.4161/chan.4.3.12058
6. L. Birnbaumer. The TRPC class of ion channels: a critical review of their roles in slow, sustained increases in intracellular Ca2+ concentrations. Annu Rev Pharmacol Toxicol 49, 395-426 (2009)
doi:10.1146/annurev.pharmtox.48.113006.094928
PMid:19281310
7. J.W. Putney, Jr., M. Trebak, G. Vazquez, B. Wedel, G.S. Bird. Signalling mechanisms for TRPC3 channels. Novartis Found Symp 258, 123-133 (2004)
doi:10.1002/0470862580.ch9
8. M. Trebak, G. Vazquez, G.S. Bird, J.W. Putney, Jr. The TRPC3/6/7 subfamily of cation channels. Cell Calcium 33, 451-61 (2003)
doi:10.1016/S0143-4160(03)00056-3
9. B. Nilius, G. Droogmans. Ion Channels and Their Functional Role in Vascular Endothelium. Physiol Rev 81, 1415-1459 (2001)
PMid:11581493
10. B. Nilius, G. Owsianik, T. Voets, J.A. Peters. Transient Receptor Potential Cation Channels in Disease. Physiol Rev 87, 165-217 (2007)
doi:10.1152/physrev.00021.2006
PMid:17237345
11. J. Abramowitz, L. Birnbaumer. Physiology and pathophysiology of canonical transient receptor potential channels. FASEB J. 23, 297-328 (2009)
doi:10.1096/fj.08-119495
PMid:18940894 PMCid:2630793
12. J.Y. Tano, K. Smedlund, G. Vazquez. Endothelial TRPC3/6/7 Proteins at the Edge of Cardiovascular Disease. Cardiovasc Hematol Agents Med Chem 8, 76-86 (2010)
doi:10.2174/187152510790796138
13. A. Dietrich, H. Kalwa, B. Fuchs, F. Grimminger, N. Weissmann, and T. Gudermann. In vivo TRPC functions in the cardiopulmonary vasculature. Cell Calcium 42, 233-244 (2007)
doi:10.1016/j.ceca.2007.02.009
PMid:17433435
14. N. Weissmann, A. Dietrich, B. Fuchs, H. Kalwa, M. Ay, R. Dumitrascu, A. Olschewski, U. Storch, M. Mederos y Schnitzler, H.A. Ghofrani, R.T. Schermuly, O. Pinkenburg, W. Seeger, F. Grimminger, T. Gudermann. Classical transient receptor potential channel 6 (TRPC6) is essential for hypoxic pulmonary vasoconstriction and alveolar gas exchange. Proc Natl Acad Sci USA 103, 19093-19098 (2006)
doi:10.1073/pnas.0606728103
PMid:17142322 PMCid:1748182
15. M.J. Lin, G.P. Leung, W.M. Zhang, X.R. Yang, K.P. Yip, C.M. Tse, J.S. Sham. Chronic hypoxia-induced upregulation of store-operated and receptor-operated Ca2+ channels in pulmonary arterial smooth muscle cells: a novel mechanism of hypoxic pulmonary hypertension. Circ Res 95, 496-505 (2004)
doi:10.1161/01.RES.0000138952.16382.ad
PMid:15256480
16. N. Kunichika, J.W. Landsberg, Y. Yu, H. Kunichika, P.A. Thistlethwaite, L.J. Rubin, J.X. Yuan. Bosentan inhibits transient receptor potential channel expression in pulmonary vascular myocytes. Am J Respir Crit Care Med 170, 1101-1107 (2004)
doi:10.1164/rccm.200312-1668OC
PMid:15317671
17. Y. Yu, I. Fantozzi, C.V. Remillard, J.W. Landsberg, N. Kunichika, O. Platoshyn, D.D. Tigno, P.A. Thistlethwaite, L.J. Rubin, J.X. Yuan. Enhanced expression of transient receptor potential channels in idiopathic pulmonary arterial hypertension. Proc Natl Acad Sci USA 101, 13861-13866 (2004)
doi:10.1073/pnas.0405908101
PMid:15358862 PMCid:518765
18. M. Freichel, R. Vennekens, J. Olausson, M. Hoffmann, C. Muller, S. Stolz, J. Scheunemann, P. Weissgerber, V. Flockerzi. Functional role of TRPC proteins in vivo: lessons from TRPC-deficient mouse models. Biochem Biophys Res Commun 322, 1352-1358 (2004)
doi:10.1016/j.bbrc.2004.08.041
PMid:15336983
19. B. Fuchs, A. Dietrich, T. Gudermann, H. Kalwa, F. Grimminger, N. Weissmann. The role of classical transient receptor potential channels in the regulation of hypoxic pulmonary vasoconstriction. Adv Exp Med Biol 661, 187-200 (2010)
doi:10.1007/978-1-60761-500-2_12
PMid:20204731
20. S. Jung, R. Strotmann, G. Schultz, T.D. Plant. TRPC6 is a candidate channel involved in receptor-stimulated cation currents in A7r5 smooth muscle cells. Am J Physiol Cell Physiol 282, C347-C359 (2002)
21. B. Kumar, K. Dreja, S. Shah, A. Cheong, S.-Z. Xu, P. Sukumar, J. Naylor, A. Forte, M. Cipollaro, D. McHugh, P.A. Kingston, A.M. Heagerty, C.M. Munsch, A. Bergdahl, A. Hultgardh-Nilsson, M.F. Gomez, K.E. Porter, P. Hellstrand, D.J. Beech. Upregulated TRPC1 Channel in Vascular Injury In vivo and Its Role in Human Neointimal Hyperplasia. Circ Res 98, 557-563 (2006)
doi:10.1161/01.RES.0000204724.29685.db
PMid:16439693 PMCid:2633624
22. K. Kuwahara, Y. Wang, J. McAnally, J.A. Richardson, R. Bassel-Duby, J.A. Hill, E.N. Olson. TRPC6 fulfills a calcineurin signaling circuit during pathologic cardiac remodeling. J Clin Invest 116, 3114-3126 (2006)
doi:10.1172/JCI27702
PMid:17099778 PMCid:1635163
23. H. Nakayama, B.J. Wilkin, I. Bodi, J.D. Molkentin. Calcineurin-dependent cardiomyopathy is activated by TRPC in the adult mouse heart. FASEB J. 20, 1660-1670 (2006)
doi:10.1096/fj.05-5560com
PMid:16873889 PMCid:2693319
24. S. Philipp, B. Strauss, D. Hirnet, U. Wissenbach, L. Mery, V. Flockerzi, M. Hoth. TRPC3 mediates T-cell receptor-dependent calcium entry in human T-lymphocytes. J Biol Chem 278, 26629-26638 (2003)
doi:10.1074/jbc.M304044200
PMid:12736256
25. J. Lievremont, T. Numaga, G. Vazquez, L. Lemonnier, Y. Hara, E. Mori, M. Trebak, S. Moss, G. Bird, Y. Mori, J.W. Putney. The role of canonical receptor potential 7 (TRPC7) in B-cell receptor activated channels. J Biol Chem 280, 35346-35351 (2005)
doi:10.1074/jbc.M507606200
PMid:16123040
26. G. Vazquez, J.-P. Lievremont, G. St. J. Bird, J.W. Putney Jr. Human Trp3 forms both inositol trisphosphate receptor-dependent and receptor-independent store-operated cation channels in DT40 avian B lymphocytes. Proc Natl Acad Sci USA 98, 11777-11782 (2001)
doi:10.1073/pnas.201238198
PMid:11553786 PMCid:58806
27. D. Liu, A. Scholze, Z. Zhu, R. Kreutz, M. Wehland-von-Trebra, W. Zidek, M. Tepel. Increased Transient Receptor Potential Channel TRPC3 Expression in Spontaneously Hypertensive Rats. Am J Hypertens 18, 1503-1507 (2005)
doi:10.1016/j.amjhyper.2005.05.033
PMid:16280289
28. D.Y. Liu, A. Scholze, R. Kreutz, M. Wehland-von-Trebra, W. Zidek, Z.M. Zhu, M. Tepel. Monocytes from spontaneously hypertensive rats show increased store-operated and second messenger-operated calcium influx mediated by transient receptor potential canonical Type 3 channels. Am J Hypertens 20, 1111-1118 (2007)
doi:10.1016/j.amjhyper.2007.04.004
PMid:17903696
29. D. Liu, A. Scholze, Z. Zhu, K. Krueger, F. Thilo, A. Burkert, K. Streffer, S. Holz, C. Harteneck, W. Zidek, M. Tepel. Transient receptor potential channels in essential hypertension. J Hypertens 24, 1105-1114 (2006)
doi:10.1097/01.hjh.0000226201.73065.14
PMid:16685211
30. D.Y. Liu, F. Thilo, A. Scholze, A. Wittstock, Z.G. Zhao, C. Harteneck, W. Zidek, Z.M. Zhu, M. Tepel. Increased store-operated and 1-oleoyl-2-acetyl-sn-glycerol-induced calcium influx in monocytes is mediated by transient receptor potential canonical channels in human essential hypertension. J Hypertens 25, 799-808 (2007)
doi:10.1097/HJH.0b013e32803cae2b
PMid:17351372
31. F. Thilo, C. Loddenkemper, E. Berg, W. Zidek, M. Tepel. Increased TRPC3 expression in vascular endothelium of patients with malignant hypertension. Mod Pathol 22, 426-430 (2009)
doi:10.1038/modpathol.2008.200
PMid:19136933
32. F. Thilo, D. Baumunk, H. Krause, M. Schrader, K. Miller, C. Loddenkemper, A. Zakrzewicz, K. Krueger, W. Zidek, M. Tepel. Transient receptor potential canonical type 3 channels and blood pressure in humans. J Hypertens 27, 1217-1223 (2009)
doi:10.1097/HJH.0b013e32832a5a9f
PMid:19417689
33. A. Dietrich, H. Kalwa, B.R. Rost, T. Gudermann. The diacylgylcerol-sensitive TRPC3/6/7 subfamily of cation channels: functional characterization and physiological relevance. Pflugers Archiv Eur J Physiol 451, 72-80 (2005)
doi:10.1007/s00424-005-1460-0
PMid:15971081
34. Dietrich A, Mederos Y Schnitzler M, Gollasch M, Gross V, Storch U, Dubrovska G, Obst M, Yildirim E, Salanova B, Kalwa H, Essin K, Pinkenburg O, Luft FC, Gudermann T, and B. L. Increased vascular smooth muscle contractility in TRPC6-/- mice. Mol Cell Biol 25, 6980-6989 (2005)
doi:10.1128/MCB.25.16.6980-6989.2005
PMid:16055711 PMCid:1190236
35. K. Smedlund, J.-Y. Tano, G. Vazquez. The Constitutive Function of Native TRPC3 Channels Modulates Vascular Cell Adhesion Molecule-1 Expression in Coronary Endothelial Cells Through Nuclear Factor {kappa}B Signaling. Circ Res 106, 1479-1488 (2010)
doi:10.1161/CIRCRESAHA.109.213314
PMid:20360250
36. K. Smedlund, G. Vazquez. Involvement of Native TRPC3 Proteins in ATP-Dependent Expression of VCAM-1 and Monocyte Adherence in Coronary Artery Endothelial Cells. Arterioscler Thromb Vasc Biol 28, 2049-2055 (2008)
doi:10.1161/ATVBAHA.108.175356
PMid:18787184
37. I. Tabas, A. Tall, D. Accili. The Impact of Macrophage Insulin Resistance on Advanced Atherosclerotic Plaque Progression. Circ Res 106, 58-67 (2010)
doi:10.1161/CIRCRESAHA.109.208488
PMid:20056946
38. E.A. Kaperonis, C.D. Liapis, J.D. Kakisis, D. Dimitroulis, V.G. Papavassiliou. Inflammation and Atherosclerosis. Eur J Vasc Endovasc Surg 31, 386-393 (2006)
doi:10.1016/j.ejvs.2005.11.001
PMid:16359887
39. P. Libby, P.M. Ridker, A. Maseri. Inflammation and Atherosclerosis. Circ 105, 1135-1143 (2002)
doi:10.1161/hc0902.104353
PMid:11877368
40. A.H. Association, Heart Disease and Stroke Statistics. Update, Dallas TX, AHA. (2008)
41. A. Alsheikh-Ali, G. Kitsios, E. Balk, J. Lau, S. Ip. The vulnerable atherosclerotic plaque, scope of the literature. Ann Intern Med 153, 387-395 (2010)
PMid:20713770
42. G.K. Hansson. Inflammation, Atherosclerosis, and Coronary Artery Disease. N Engl J Med 352, 1685-1695 (2005)
doi:10.1056/NEJMra043430
PMid:15843671
43. A. Dietrich, V. Chubanov, H. Kalwa, B.R. Rost, T. Gudermann. Cation channels of the transient receptor potential superfamily: their role in physiological and pathophysiological processes of smooth muscle cells. Pharmacol Ther 112, 744-760 (2006)
doi:10.1016/j.pharmthera.2006.05.013
44. R. Inoue, L.J. Jensen, J. Shi, H. Morita, M. Nishida, A. Honda, Y. Ito. Transient receptor potential channels in cardiovascular function and disease. Circ Res 99, 119-131 (2006)
doi:10.1161/01.RES.0000233356.10630.8a
PMid:16857972
45. M.F. Linton, S. Fazio. Macrophages, inflammation, and atherosclerosis. Int J Obes Relat Metab Disord 27, S35-S40 (2003)
doi:10.1038/sj.ijo.0802498
PMid:14704742
46. R. Virmani, A.P. Burke, A. Farb, F.D. Kolodgie. Pathology of the Vulnerable Plaque. J Am Coll Cardiol 47, C13-C18 (2006)
doi:10.1016/j.jacc.2005.10.065
PMid:16631505
47. H.E. Matheny, T.L. Deem, J.M. Cook-Mills. Lymphocyte Migration Through Monolayers of Endothelial Cell Lines Involves VCAM-1 Signaling Via Endothelial Cell NADPH Oxidase. J Immunol 164, 6550-6559 (2000)
PMid:10843714
48. J. Cook-Mills, VCAM-1 signals during lymphocyte migration: role of reactive oxygen species Mol Immunol 39, 499-508 (2002)
doi:10.1016/S0161-5890(02)00206-7
49. H. Abdala-Valencia, J.M. Cook-Mills. VCAM-1 Signals Activate Endothelial Cell Protein Kinase C{alpha} via Oxidation. J Immunol 177, 6379-6387 (2006)
PMid:17056569 PMCid:2711556
50. E. Galkina, K. Ley. Vascular Adhesion Molecules in Atherosclerosis. Arterioscler Thromb Vasc Biol 27, 2292-2301 (2007)
doi:10.1161/ATVBAHA.107.149179
PMid:17673705
51. K. Iiyama, L. Hajra, M. Iiyama, H. Li, M. DiChiara, B.D. Medoff, M.I. Cybulsky. Patterns of Vascular Cell Adhesion Molecule-1 and Intercellular Adhesion Molecule-1 Expression in Rabbit and Mouse Atherosclerotic Lesions and at Sites Predisposed to Lesion Formation. Circ Res 85, 199-207 (1999)
PMid:10417402
52. D. Erlinge, G. Burnstock. P2 receptors in cardiovascular regulation and disease. Purinergic Signal 4, 1-20 (2008)
doi:10.1007/s11302-007-9078-7
PMid:18368530 PMCid:2245998
53. H. Zhang, Y. Park, J. Wu, X.p. Chen, S. Lee, J. Yang, K.C. Dellsperger, C. Zhang. Role of TNFalpha in vascular dysfunction. Clin Sci 116, 219-230 (2009)
doi:10.1042/CS20080196
PMid:19118493 PMCid:2620341
54. M. Poteser, A. Graziani, C. Rosker, P. Eder, I. Derler, H. Kahr, M.X. Zhu, C. Romanin, K. Groschner. TRPC3 and TRPC4 Associate to Form a Redox-sensitive Cation Channel: evidence for expression of native TRPC3-TRPC4 heteromeric channels in endothelial cells. J Biol Chem 281, 13588-13595 (2006)
doi:10.1074/jbc.M512205200
PMid:16537542
55. M. Balzer, B. Lintschinger, K. Groschner. Evidence for a role of Trp proteins in the oxidative stress-induced membrane conductances of porcine aortic endothelial cells. Cardiovasc Res 42, 543-549 (1999)
doi:10.1016/S0008-6363(99)00025-5
56. K. Groschner, C. Rosker, M. Lukas. Role of TRP channels in oxidative stress. Novartis Found Symp 258, 222-230 (2004)
doi:10.1002/0470862580.ch16
57. S.K. Koliwad, S.J. Elliott, D.L. Kunze. Oxidized glutathione mediates cation channel activation in calf vascular endothelial cells during oxidant stress. J Physiol 495, 37-49 (1996)
PMid:8866350 PMCid:1160723
58. S.K. Koliwad, D.L. Kunze, S.J. Elliott. Oxidant stress activates a non-selective cation channel responsible for membrane depolarization in calf vascular endothelial cells. J Physiol 491, 1-12 (1996)
PMid:9011602 PMCid:1158754
59. L.S. Yoshida, S. Tsunawaki. Expression of NADPH oxidases and enhanced H2O2-generating activity in human coronary artery endothelial cells upon induction with tumor necrosis factor-alpha. Int Pharmacol 8, 1377-1385 (2008)
60. L. Burnier, P. Fontana, A. Angelillo-Scherrer, B.R. Kwak. Intercellular Communication in Atherosclerosis. Physiol 24, 36-44 (2009)
doi:10.1152/physiol.00036.2008
PMid:19196650
61. D.M.R.M.A.B.M. Emily Vandenbroucke. Regulation of Endothelial Junctional Permeability. Ann New York Acad Sci 1123, 134-145 (2008)
doi:10.1196/annals.1420.016
PMid:18375586
62. R.D. Minshall, A.B. Malik. Transport across the endothelium: regulation of endothelial permeability. Handb Exp Pharmacol 176, 107-144 (2006)
doi:10.1007/3-540-32967-6_4
63. P. Chaudhuri, S.M. Colles, D.S. Damron, L.M. Graham. Lysophosphatidylcholine Inhibits Endothelial Cell Migration by Increasing Intracellular Calcium and Activating Calpain. Arterioscler Thromb Vasc Biol 23, 218-223 (2003)
doi:10.1161/01.ATV.0000052673.77316.01
64. P. Chaudhuri, S.M. Colles, M. Bhat, D.R. Van Wagoner, L. Birnbaumer, L.M. Graham. Elucidation of a TRPC6-TRPC5 Channel Cascade That Restricts Endothelial Cell Movement. Mol Biol Cell 19, 3203-3211 (2008)
doi:10.1091/mbc.E07-08-0765
PMid:18495872 PMCid:2488296
65. G.U. Ahmmed, A.B. Malik. Functional role of TRPC channels in the regulation of endothelial permeability. Pflugers Arch 451, 131-42 (2005)
doi:10.1007/s00424-005-1461-z
PMid:15988589
66. I. Singh, N. Knezevic, G.U. Ahmmed, V. Kini, A.B. Malik, D. Mehta. Galphaq-TRPC6-mediated Ca2+ Entry Induces RhoA Activation and Resultant Endothelial Cell Shape Change in Response to Thrombin. J Biol Chem 282, 7833-7843 (2007)
doi:10.1074/jbc.M608288200
PMid:17197445
67. T. Kusaba, M. Okigaki, A. Matui, M. Murakami, K. Ishikawa, T. Kimura, K. Sonomura, Y. Adachi, M. Shibuya, T. Shirayama, S. Tanda, T. Hatta, S. Sasaki, Y. Mori, H. Matsubara. Klotho is associated with VEGF receptor-2 and the transient receptor potential canonical-1 Ca2+ channel to maintain endothelial integrity. Proc Natl Acad Sci USA 107, 19308-19313 (2010)
doi:10.1073/pnas.1008544107
PMid:20966350
68. D.W. Losordo, J.M. Isner. Vascular endothelial growth factor-induced angiogenesis: crouching tiger or hidden dragon? Journal of the Am Coll Cardiol 37, 2131-2135 (2001)
doi:10.1016/S0735-1097(01)01298-0
69. R. Ge, Y. Tai, Y. Sun, K. Zhou, S. Yang, T. Cheng, Q. Zou, F. Shen, Y. Wang. Critical role of TRPC6 channels in VEGF-mediated angiogenesis. Cancer Lett 283, 43-51 (2009)
doi:10.1016/j.canlet.2009.03.023
PMid:19394138
70. M.A. Hamdollah Zadeh, C.A. Glass, A. Magnussen, J.C. Hancox, D.O. Bates. VEGF-mediated elevated intracellular calcium and angiogenesis in human microvascular endothelial cells in vitro are inhibited by dominant negative TRPC6. Microcirc 15, 605-614 (2008)
doi:10.1080/10739680802220323
PMid:18800249 PMCid:2635545
71. H. Williams, J.L. Johnson, K.G.S. Carson, C.L. Jackson. Characteristics of Intact and Ruptured Atherosclerotic Plaques in Brachiocephalic Arteries of Apolipoprotein E Knockout Mice. Arterioscler Thromb Vasc Biol 22, 788-792 (2002)
doi:10.1161/01.ATV.0000014587.66321.B4
72. N. Kae, S. Takeshi, C. Xian Wu, I. Akihisa, S. Kohji, K. Masafumi. Statin prevents plaque disruption in apoE-knockout mouse model through pleiotropic effect on acute inflammation. Atheroscler 206, 355-361 (2009)
doi:10.1016/j.atherosclerosis.2009.02.014
PMid:19296953
73. H. Watanabe, M. Murakami, T. Ohba, Y. Takahashi, H. Ito. TRP channel and cardiovascular disease. Pharmacol Ther 118, 337-51 (2008)
doi:10.1016/j.pharmthera.2008.03.008
74. J. Rowell, N. Koitabashi, D.A. Kass. TRP-ing up heart and vessels: canonical transient receptor potential channels and cardiovascular disease. J Cardiovasc Transl Res 3, 516-524 (2010)
doi:10.1007/s12265-010-9208-4
PMid:20652467
75. X. Yao. TRPC, cGMP-dependent protein kinases and cytosolic Ca2+. Handb Exp Pharmacol 527-540 (2007)
76. H. Orimo, Y. Ouchi. The Role of Calcium and Magnesium in the Development of Atherosclerosis. Ann New York Acad Sci 598, 444-457 (1990)
doi:10.1111/j.1749-6632.1990.tb42315.x
PMid:2248457
77. R.D. Phair. Cellular calcium and atherosclerosis: a brief review. Cell Calcium 9, 275 (1988)
doi:10.1016/0143-4160(88)90008-5
78. T.K. Biswas. Endothelium, atherosclerosis and calcium channel blockers. J Indian Med Assoc 101, 428-431 (2003)
PMid:14748381
79. I.F. Perez. Calcium channel blockers: do they have pleiotropic effects on atherosclerosis? J Hum Hypertens 14 Suppl 1, S96-9 (2000)
doi:10.1038/sj.jhh.1000994
80. A. Simon, J. Levenson. Effects of calcium channel blockers on atherosclerosis: new insights. Acta Cardiol 57, 249-255 (2002)
doi:10.2143/AC.57.4.2005421
PMid:12222691
81. G.B. Mancini. Antiatherosclerotic effects of calcium channel blockers. Prog Cardiovasc Dis 45, 1-20 (2002)
doi:10.1053/pcad.2002.122694
PMid:12138411
82. J.C. Somberg. The Calcium Channel Blockers. Am J Ther 2, 231-232 (1995)
doi:10.1097/00045391-199504000-00001
83. P. Trenkwalder. Antihypertensive treatment with calcium channel blockers: pharmacological pornography or useful intervention? Nephrol Dial Transplant 19, 17-20 (2004)
doi:10.1093/ndt/gfg431
84. R.P. Mason. Mechanisms of plaque stabilization for a charged calcium channel blocker in coronary artery disease. Pharmacotherapy 21, 209S-215S (2001)
doi:10.1592/phco.21.14.209S.34600
PMid:11560191
85. J. Scholze, T. Unger. The ALLHAT study (antihypertensive and lipid-lowering treatment to prevent heart attack trial): primary antihypertensive agents - diuretics vs calcium channel blockers vs angiotensin-converting enzyme inhibitors) Internist (Berl) 44, 1193-1195 (2003)
doi:10.1007/s00108-003-1028-z
PMid:14566471
86. A. Recio-Mayoral, J.C. Kaski, J.J.V. McMurray, J. Horowitz, D.J. Veldhuisen, W.J. Remme. Clinical Trials Update from the European Society of Cardiology Congress in Vienna, 2007: PROSPECT, EVEREST, ARISE, ALOFT, FINESSE, Prague-8, CARESS in MI and ACUITY. Cardiovasc Drugs Ther 21, 459-465 (2007)
doi:10.1007/s10557-007-6069-4
PMid:17992567
87. M. Yamaguchi, M. Kuzume, H. Nakano, K. Kumada. Verapamil suppressed lymphocyte adhesion to vascular endothelial cells via selective inhibition of VCAM-1 expression. Transpl Proc 30, 2955-2955 (1998)
doi:10.1016/S0041-1345(98)00885-9
88. T. Yoshii, M. Iwai, Z. Li, R. Chen, A. Ide, S. Fukunaga, A. Oshita, M. Mogi, J. Higaki, M. Horiuchi. Regression of Atherosclerosis by Amlodipine via Anti-Inflammatory and Anti-Oxidative Stress Actions. Hypertens Res 29, 457-466 (2006)
doi:10.1291/hypres.29.457
PMid:16940709
89. T. Godfraind. Antioxidant effects and the therapeutic mode of action of calcium channel blockers in hypertension and atherosclerosis. Phil Trans Royal Soc Biol Sci 360, 2259-2272 (2005)
doi:10.1098/rstb.2005.1774
PMid:16321796 PMCid:1569592
90. S.-i. Yamagishi, K. Nakamura, T. Matsui. Role of oxidative stress in the development of vascular injury and its therapeutic intervention by nifedipine. Cur Med Chem 15, 172-177 (2008)
doi:10.2174/092986708783330557
PMid:18220772
91. X. Zhu, M. Jiang, L. Birnbaumer. Receptor-activated Ca2+ Influx via Human Trp3 Stably Expressed in Human Embryonic Kidney (HEK)293 Cells evidence for a non-capacitative Ca2+ entry. J Biol Chem 273, 133-142 (1998)
doi:10.1074/jbc.273.1.133
PMid:9417057
92. J. Cuschieri, D. Gourlay, I. Garcia, S. Jelacic, R.V. Maier. Slow channel calcium inhibition blocks proinflammatory gene signaling and reduces macrophage responsiveness. J Trauma 52, 434-442 (2002)
doi:10.1097/00005373-200203000-00004
93. C. Harteneck, M. Gollasch. Pharmacological Modulation of Diacylglycerol-Sensitive TRPC3/6/7 Channels. Curr Pharm Biotechnol Nov 8 (2010)
94. S. Kiyonaka, K. Kato, M. Nishida, K. Mio, T. Numaga, Y. Sawaguchi, T. Yoshida, M. Wakamori, E. Mori, T. Numata, M. Ishii, H. Takemoto, A. Ojida, K. Watanabe, A. Uemura, H. Kurose, T. Morii, T. Kobayashi, Y. Sato, C. Sato, I. Hamachi, Y. Mori. Selective and direct inhibition of TRPC3 channels underlies biological activities of a pyrazole compound. Proc Natl Acad Sci 106, 5400-5405 (2009)
doi:10.1073/pnas.0808793106
PMid:19289841 PMCid:2664023
95. S.-Z. Xu, F. Zeng, M. Lei, J. Li, B. Gao, C. Xiong, A. Sivaprasadarao, D.J. Beech. Generation of functional ion-channel tools by E3 targeting. 23, 1289-1293 (2005)
96. D.J. Preiss, N. Sattar. Vascular cell adhesion molecule-1: a viable therapeutic target for atherosclerosis? Int J Clin Pract 61, 697-701 (2007)
doi:10.1111/j.1742-1241.2007.01330.x
PMid:17394445
97. K. Yonekawa, J.M. Harlan. Targeting leukocyte integrins in human diseases. J Leuk Biol 77, 129-140 (2005)
doi:10.1189/jlb.0804460
PMid:15548573
Abbreviations: CAM: Cell adhesion molecule, CCB: Calcium channel blocker, DHP: Dihydropyridine, HCAEC: Human coronary artery endothelial cells, HUVEC: human umbilical vein endothelial cells, ICAM-1: Intercellular cell adhesion molecule-1, NFAT: Nuclear factor of activated T cells, NFkB: Nuclear factor kappa B, NO: Nitric oxide, oxLDL: Oxidized low density lipoprotein, PLC: Phospholipase C, PLD: Phospholipase D, TNFa: Tumor necrosis factor alpha, TRPC: Transient Receptor Potential Canonical, VCAM-1 : Vascular cell adhesion molecule-1, VEGF: Vascular endothelial growth factor
Key words: Transient Receptor Potential Canonical Channels, Atherosclerosis, Cardiovascular Disease, Endothelial Dysfunction, Calcium Channels, Inflammatory Signaling, Review
Send correspondence to: Guillermo Vazquez, Department of Physiology and Pharmacology, University of Toledo College of Medicine. 3000 Arlington Av, Toledo OH 43614 USA, Tel: 419-383-5301, Fax 419-383-2871, E-mail:Guillermo.Vazquez@utoledo.edu