Inhibition of TRPC5 channels by Ca2+-binding protein 1 in Xenopus oocytes

The transient receptor potential canonical type 5 (TRPC5) channel is a member of the channels that has been implicated in neurite extension and growth cone morphology of hippocampal neurons. Although homomeric TRPC5 channels are activated following stimulation of G_q/11-coupled receptors, the exact mechanism for this activation remains unresolved. Using two-electrode voltage clamp recordings, we show that the activity of TRPC5 channels expressed in Xenopus oocytes is dependent on the presence of Ca²⁺ at the extracellular as well as the cytoplasmic side of the plasma membrane. TRPC5 was activated by the stimulation of coexpressed M5 muscarinic receptors or by ionomycin. The TRPC5 activity was detectable with the presence of submillimolar levels of extracellular Ca²⁺, but it was eliminated by the injection of 5 mM 1,2-bis(o-aminophenoxy)ethane-N,N,N,N-tetraacetic acid into the oocytes. Lanthanum could substitute for extracellular Ca²⁺ to support TRPC5 activity. Coexpression of Ca²⁺-binding protein 1 (CaBP1), but not calmodulin (CaM), inhibited the TRPC5 activity, without affecting the cell surface expression of TRPC5 proteins. Using in vitro binding assays, we demonstrated direction interactions between CaBP1 and TRPC5. The CaBP1-binding sites at the C terminus of TRPC5 are closely localized, but not identical, to CaM-binding sites. We conclude that TRPC5 is a Ca²⁺-regulated channel, and its activity is negatively controlled by CaBP1.     

Physiological mechanisms of TRPC activation

TRPC (canonical transient receptor potential) channels are vertebrate homologs of the Drosophila photoreceptor channel, TRP. Considerable research has been brought to bear on the seven members of this family, especially with regard to their possible role in calcium entry. Unfortunately, the current literature presents a confusing picture, with different laboratories producing widely differing results and interpretations. It appears that ectopically expressed TRPC channels can be activated by phospholipase C products (generally, diacylglycerols), by stimulation of trafficking to the plasma membrane, or by depletion of intracellular Ca²⁺ stores. Here, I discuss the possibility that these diverse experimental findings arise because TRPC channels can, under both experimental as well as physiological conditions, be activated in three distinct ways, possibly depending on their subunit composition and/or signaling complex environment. The TRPCs may be unique among ion-channel subunit families in being able to participate in the assembly and function of multiple types of physiologically important ion channels.     

Effects of caveolin-1 and P-ERK1/2 on Ang II-induced glomerular mesangial cell proliferation

Abstract

This study explored the effects of caveolin-1, p-ERK1/2 and transient receptor potential channel 6 (TRPC6) on angiotensin II (Ang II)-induced glomerular mesangial cell (GMC) proliferation, and investigated the role of Ang II on GMC proliferation. GMC cultures were divided into Control, Ang II (Ang II 10^?7?mol/L), PD98059 (Ang II 10^?7?mol/L?+?PD98059 5?×?10^?5?mol/L) and MβCD groups (Ang II 10^?7?mol/L?+?MβCD 10^?2?mol/L). GMCs proliferation was measured by the methyl thiazolil tetracolium and trypan blue assays. The distribution of caveolin-1, p-ERK1/2 and TRPC6 was monitored by immunocytochemistry. Real time polymerase chain reaction (PCR) was used to assess mRNA expression of caveolin-1 and TRPC6. Western blot analysis was used to assess protein expression of caveolin-1, p-ERK1/2 and TRPC6. The results showed that Ang II promoted GMC proliferation. PD98059 and MβCD blocked Ang II-induced GMC proliferation, by 31.06% and 48.96%, respectively. In comparison with the control group, the expression of p-ERK1/2 and TRPC6 was significantly higher and caveolin-1 expression was significantly lower in the Ang II group. PD98059 markedly decreased p-ERK1/2 and TRPC6 expression and increased caveolin-1 expression. MβCD decreased the expression of p-ERK1/2 and TRPC6, but had no significant effect on caveolin-1 protein expression. These findings suggested that the intact caveolae structure was associated with Ang II-induced GMC proliferation, ERK1/2 activation and TRPC6 expression. And p-ERK1/2 acted as an upstream signal molecule for TRPC6. Moreover, p-ERK1/2 and caveolin-1 appeared to be inhibited reciprocally, thus regulated GMC proliferation by regulating TRPC6 expression.     

阿托伐他汀对ApoE基因敲除小鼠动脉粥样硬化病变中TRPC5表达的影响

目的:观察载脂蛋白E基因敲除(Apo E-/-)小鼠动脉粥样硬化斑块形成过程中血管平滑肌细胞瞬时受体电位通道5(TRPC5)蛋白的表达变化,以及阿托伐他汀药物干预对TRPC5的影响并探讨其作用机制。方法:将40只6周龄雄性Apo E-/-小鼠随机分为模型组和他汀干预组,高脂饲料喂养建立动脉粥样硬化模型。他汀干预组给予阿托伐他汀(20 mg·kg-1·d-1)灌胃,模型组给予等量生理盐水灌胃。20只同龄雄性野生型C57BL/6J小鼠给予普通饲料喂养作为正常对照组。各组小鼠分别喂养至20和30周龄,分别取10只取血并处死。取主动脉根部做石蜡切片行HE染色形态学观察,测量并计算斑块相对面积;免疫组织化学染色检测各组小鼠TRPC5蛋白表达变化。取胸腹段主动脉行实时荧光定量PCR,检测主动脉中TRPC5通道蛋白mRNA的表达水平。结果:与模型组相比,阿托伐他汀干预组的血脂明显下降,斑块总面积明显减小,TRPC5蛋白水平及mRNA含量明显下降;30周龄模型组的TRPC5蛋白表达稍高于20周龄模型组,但差异无统计学意义;30周干预组较20周干预组相比,TRPC5水平有降低趋势且差异有统计学意义。结论:阿托伐他汀可能通过下调TRPC5蛋白表达从而延缓动脉粥样硬化进程。     

瞬时受体电位通道蛋白6参与血管紧张素Ⅱ诱导足细胞损伤的信号传导机制

足细胞表达瞬时受体电位通道蛋白6(TRPC6),TRPC家族是一类能通透钙离子的非选择性阳离子通道,近年来,研究发现TRPC6参与了血管紧张素Ⅱ(AngⅡ)诱导足细胞损伤的病理生理过程.本文就TRPC6一般特性及参与AngⅡ诱导足细胞损伤的信号传导机制作一简述.     

Age-related autoregulatory dysfunction and cerebromicrovascular injury in mice with angiotensin II-induced hypertension

Hypertension in the elderly substantially contributes to cerebromicrovascular damage and promotes the development of vascular cognitive impairment. Despite the importance of the myogenic mechanism in cerebromicrovascular protection, it is not well understood how aging affects the functional adaptation of cerebral arteries to high blood pressure. Hypertension was induced in young (3 months) and aged (24 months) C57/BL6 mice by chronic infusion of angiotensin II (AngII). In young hypertensive mice, the range of cerebral blood flow autoregulation was extended to higher pressure values, and the pressure-induced tone of middle cerebral artery (MCA) was increased. In aged hypertensive mice, autoregulation was markedly disrupted, and MCAs did not show adaptive increases in myogenic tone. In young mice, the mechanism of adaptation to hypertension involved upregulation of the 20-HETE (20-hydroxy-5,8,11,14-eicosatetraenoic acid)/transient receptor potential cation channel, subfamily C (TRPC6) pathway and this mechanism was impaired in aged hypertensive mice. Downstream consequences of cerebrovascular autoregulatory dysfunction in aged AngII-induced hypertensive mice included exacerbated disruption of the blood–brain barrier and neuroinflammation (microglia activation and upregulation of proinflammatory cytokines and chemokines), which were associated with impaired hippocampal dependent cognitive function. Collectively, aging impairs autoregulatory protection in the brain of mice with AngII-induced hypertension, potentially exacerbating cerebromicrovascular injury and neuroinflammation.     

Canonical transient receptor potential channel subtype 3‐mediated hair cell Ca2+ entry regulates sound transduction and auditory neurotransmission

The physiological significance of canonical transient receptor potential (TRPC) ion channels in sensory systems is rapidly emerging. Heterologous expression studies show that TRPC3 is a significant Ca²⁺ entry pathway, with dual activation via G protein‐coupled receptor (GPCR)–phospholipase C–diacylglycerol second messenger signaling, and through negative feedback, whereby a fall in cytosolic Ca²⁺ releases Ca²⁺–calmodulin channel block. We hypothesised that the latter process contributes to cochlear hair cell cytosolic Ca²⁺ homeostasis. Confocal microfluorimetry with the Ca²⁺ indicator Fluo‐4 acetoxymethylester showed that, when cytosolic Ca²⁺ was depleted, Ca²⁺ re‐entry was significantly impaired in mature TRPC3^?/? inner and outer hair cells. The impact of this disrupted Ca²⁺ homeostasis on sound transduction was assessed with the use of distortion product otoacoustic emissions (DPOAEs), which constitute a direct measure of the outer hair cell transduction that underlies hearing sensitivity and frequency selectivity. TRPC3^?/? mice showed significantly stronger DPOAE (2f₁ ? f₂) growth functions than wild‐type (WT) littermates within the frequency range of best hearing acuity. This translated to hyperacusis (decreased threshold) measured by the auditory brainstem response (ABR). TRPC3^?/? and WT mice did not differ in the levels of temporary and permanent threshold shift arising from noise exposure, indicating that potential GPCR signaling via TRPC3 is not pronounced. Overall, these data suggest that the Ca²⁺ set‐point in the hair cell, and hence membrane conductance, is modulated by TRPC3s through their function as a negative feedback‐regulated Ca²⁺ entry pathway. This TPRC3‐regulated Ca²⁺ homeostasis shapes the sound transduction input–output function and auditory neurotransmission.     

Organization and function of TRPC channelosomes

TRPC proteins constitute a family of conserved Ca²⁺-permeable cation channels which are activated in response to agonist-stimulated PIP₂ hydrolysis. These channels were initially proposed to be components of the store-operated calcium entry channel (SOC). Subsequent studies have provided substantial evidence that some TRPCs contribute to SOC activity. TRPC proteins have also been shown to form agonist-stimulated calcium entry channels that are not store-operated but are likely regulated by PIP₂ or diacylglycerol. Further, and consistent with the presently available data, selective homomeric or heteromeric interactions between TRPC monomers generate distinct agonist-stimulated cation permeable channels. We suggest that interaction between TRPC monomers, as well as the association of these channels with accessory proteins, determines their mode of regulation as well as their cellular localization and function. Currently identified accessory proteins include key Ca²⁺ signaling proteins as well as proteins involved in vesicle trafficking, cytoskeletal interactions, and scaffolding. Studies reported until now demonstrate that TRPC proteins are segregated into specific Ca²⁺ signaling complexes which can generate spatially and temporally controlled [Ca²⁺]_i signals. Thus, the functional organization of TRPC channelosomes dictates not only their regulation by extracellular stimuli but also serves as a platform to coordinate specific downstream cellular functions that are regulated as a consequence of Ca²⁺ entry. This review will focus on the accessory proteins of TRPC channels and discuss the functional implications of TRPC channelosomes and their assembly in microdomains.     

过表达miR-607通过下调TRPC5表达抑制肝细胞癌的生长和转移

目的 研究miR-607异常表达在肝细胞癌（HCC）中的临床意义及对肝癌细胞生长转移的影响。方法 荧光定量PCR检测45对HCC及癌旁组织中miR-607表达,分析miR-607表达与患者临床病理特征间的相关性。通过转染miR-607 mimics提高HCC细胞（Huh-7和HCCLM3）内miR-607的表达水平。采用CCK-8、流式细胞仪、划痕愈合实验及transwell小室模型分别检测过表达miR-607对HCC细胞增殖、凋亡、迁移和侵袭的影响。双荧光素酶报告基因系统检测miR-607是否与潜在靶点TRPC5的mRNA 3'-非翻译区直接结合。Western blot检测过表达miR-607对HCC细胞内TRPC5、CCND1、MMP2表达及Akt磷酸化的影响。结果 MiR-607在HCC组织及HCC细胞中的表达水平均降低（P<0.05）;miR-607低表达与肿瘤直径>5 cm、血管侵犯及较晚TNM分期（III+IV）密切相关（P<0.05）。过表达miR-607抑制HCC细胞增殖、迁移、侵袭并诱导细胞凋亡（P<0.05）。双荧光素酶报告基因系统证实 miR-607 与 TRPC5 mRNA 3'-非翻译区直接结合（P<0.05）。过表达 miR-607 抑制HCC细胞内TRPC5、CCND1及MMP2表达并下调Akt的磷酸化水平（P<0.05）。结论 miR-607低表达与肝细胞癌恶性临床特征密切相关,miR-607可能通过下调TRPC5表达进而抑制Akt通路激活来发挥抗HCC生长转移作用。     

TRPC1蛋白在乳腺癌中表达及与临床病理参数的相关性

目的观察TRPC1蛋白在乳腺癌组织的表达及与临床病理参数的相关性。方法免疫组化法观察TRPC1蛋白在乳腺癌组织及癌旁组织中的表达,并分析其表达与临床病理参数的相关性。结果乳腺癌组织TRPC1蛋白表达率明显高于癌旁组织(P<0. 05)。TRPC1蛋白表达率与肿瘤的病理类型、临床分级、淋巴结转移、肿瘤大小、ERα及HER-2表达具有相关性(均P<0. 05),与患者年龄、绝经等无关(P>0. 05)。结论 TRPC1蛋白在乳腺癌组织高表达,并与乳腺癌分级、病理类型、ERα及HER-2表达具有相关性。