The TRPC2 ion channel and pheromone sensing in the accessory olfactory system

The mammalian vomeronasal organ (VNO) has emerged as an excellent model to investigate the signaling mechanisms, mode of activation, biological function, and molecular evolution of transient receptor potential (TRP) channels in real neurons and real physiological systems. TRPC2, a member of the canonical TRPC subfamily, is highly localized to the dendritic tip of vomeronasal sensory neurons. Targeted deletion of the TRPC2 gene has established that TRPC2 plays a fundamental role in the detection of pheromonal signals by the VNO. TRPC2-deficient mice exhibit striking behavioral defects in the regulation of sexual and social behaviors. A novel Ca²⁺-permeable, diacylglycerol-activated cation channel found at the dendritic tip of vomeronasal neurons is severely defective in TRPC2 mutants, providing the first clear example of native diacylglycerol-gated cation channels in the mammalian nervous system. The TRPC2 gene has become an important marker for the evolution of VNO-dependent pheromone signaling in primates.     

Functional characterization and physiological relevance of the TRPC3/6/7 subfamily of cation channels

The mammalian transient receptor potential (TRP) superfamily of cation channels can be divided into six major families. Among them, the classical or canonical TRPC family is most closely related to Drosophila TRP, the founding member of the superfamily. All seven channels of this family designated TRPC1-7 share the common property of activation through phospholipase C (PLC)-coupled receptors, but their gating by receptor- or store-operated mechanisms is still controversial. The TRPC3, 6, and 7 channels are 75% identical and are also gated by direct exposure to diacylglycerols (DAG). TRPC3, 6, and 7 interact physically and, upon coexpression, coassemble to form functional tetrameric channels. This review will focus on the TRPC3/6/7 subfamily and describe their functional properties and regulation as homomers obtained from overexpression studies in cell lines. It will also summarize their heteromultimerization potential in vitro and in vivo and will present preliminary data concerning their physiological functions analyzed in isolated tissues with downregulated channel activity and gene-deficient mouse models.     

The role of mechanical tension on lipid raft dependent PDGF-induced TRPC6 activation

Canonical transient receptor potential channel 6 (TRPC6) can play an important role in governing how cells perceive the surrounding material environment and regulate Ca²⁺ signaling. We have designed a TRPC6 reporter based on fluorescence resonance energy transfer (FRET) to visualize the TRPC6-mediated calcium entry and hence TRPC6 activity in live cells with high spatiotemporal resolutions. In mouse embryonic fibroblasts (MEFs), platelet-derived growth factor BB (PDGF) can activate the TRPC6 reporter, mediated by phospholipase C (PLC). This TRPC6 activation occurred mainly at lipid rafts regions of the plasma membrane because disruption of lipid raft/caveolae by methyl-β-cyclodextrin (MβCD) or the expression of dominant-negative caveolin-1 inhibited the TRPC6 activity. Culturing cells on soft materials or releasing the intracellular tension by ML-7 reduced this PDGF-induced activation of TRPC6 without affecting the PDGF-regulated Src or inositol 1,4,5-trisphosphate (IP₃) receptor function, suggesting a specific role of mechanical tension in regulating TRPC6. We further showed that the release of intracellular tension had similar effect on the diffusion coefficients of TRPC6 and a raft marker, confirming a strong coupling between TRPC6 and lipid rafts. Therefore, our results suggest that the TRPC6 activation mainly occurs at lipid rafts, which is regulated by the mechanical cues of surrounding materials.     

足细胞损伤的诱导途径：血管紧张素Ⅱ-足细胞瞬时受体电位阳离子通道蛋白6信号通路

背景：瞬时受体电位阳离子通道蛋白6是足细胞上一种新发现的阳离子通道蛋白,是组成裂隙隔膜重要蛋白之一,其表达变化与糖尿病肾病蛋白尿密切相关。目的：观察高糖刺激对足细胞瞬时受体电位阳离子通道蛋白6表达的影响,探讨糖尿病肾病发生发展的可能机制。方法：以永生化小鼠足细胞（MPC5）作为实验对象,将其设为：正常糖组（D-葡萄糖5.6 mmol/L）;渗透压对照组（D-葡萄糖5.6 mmol/L＋甘露醇25 mmol/L）;高糖组（D-葡萄糖30 mmol/L）;缬沙坦组（D-葡萄糖30 mmol/L＋10-5结果与结论：与正常糖组相比,高糖组足细胞瞬时受体电位阳离子通道蛋白6、血管紧张素Ⅱ蛋白及 mRNA水平明显升高（P〈0.01）,nephrin mRNA及蛋白水平明显降低（P〈0.01）;与高糖组相比,缬沙坦组瞬时受体电位阳离子通道蛋白6、血管紧张素Ⅱ的表达显著降低（P〈0.05,P〈0.01）;高糖＋U73122组瞬时受体电位阳离子通道蛋白6、血管紧张素Ⅱ表达较高糖组明显下降（P〈0.05,P〈0.01）;渗透压对照组与正常糖组之间各因子差异无显著性意义（P〉0.05）。结果说明高糖可能通过血管紧张素Ⅱ-瞬时受体电位阳离子通道蛋白6反馈信号通路损伤足细胞,同时也为血管紧张素受体拮抗剂通过此通路保护足细胞而治疗糖尿病肾病的提供了一新的理论基础。 mol/L缬沙坦）;高糖＋U73122组（D-葡萄糖30 mmol/L＋10μmol/L磷脂酶抑制剂U73122）。各组细胞干预时间为48 h。采用荧光定量PCR和western-blot方法检测各组足细胞瞬时受体电位阳离子通道蛋白6、nephrin、血管紧张素ⅡmRNA和蛋白的表达。     

Agonist-evoked calcium entry in vascular smooth muscle cells requires IP3 receptor-mediated activation of TRPC1

Transient receptor potential canonical (TRPC) proteins have been proposed to function as plasma membrane Ca2+ channels activated by store depletion and/or by receptor stimulation. However, their role in the increase in cytosolic Ca2+ activated by contractile agonists in vascular smooth muscle is not yet elucidated. The present study was designed to investigate the functional and molecular properties of the Ca2+ entry pathway activated by endothelin-1 in primary cultured aortic smooth muscle cells. Measurement of the Ca2+ signal in fura-2-loaded cells allowed to characterize endothelin-1-evoked Ca2+ entry, which was resistant to dihydropyridine, and was blocked by 2-aminoethoxydiphenylborate (2-APB) and micromolar concentration of Gd3+. It was not activated by store depletion, but was inhibited by the endothelin ETA receptor antagonist BQ-123, and by heparin. On the opposite, thapsigargin-induced store depletion activated a Ca2+ entry pathway that was not affected by 2-APB, BQ-123 or heparin, and was less sensitive to Gd3+ than was endothelin-1-evoked Ca2+ entry. Investigation of the gene expression of TRPC isoforms by real-time RT-PCR revealed that TRPC1 was the most abundant. In cells transfected with TRPC1 small interfering RNA sequence, TRPC1 mRNA and protein expression were decreased by 72+/-3% and 86+/-2%, respectively, while TRPC6 expression was unaffected. In TRPC1 knockdown cells, both endothelin-1-evoked Ca2+ entry and store-operated Ca2+ entry evoked by thapsigargin were blunted. These results indicate that in aortic smooth muscle cells, TRPC1 is not only involved in Ca2+ entry activated by store depletion but also in receptor-operated Ca2+ entry, which requires inositol (1,4,5) triphosphate receptor activation.     

黄芪丹参水煎液抑制ISO诱导的大鼠心肌重构及其下调STIM1,TRPC1,CaN和NFATc3表达的机制

探讨黄芪丹参水煎液(HDD)对异丙肾上腺素(ISO)诱导大鼠心肌重构抑制作用和对STIM1,TRPC1,Ca M,Ca N,NFATc3表达的影响。皮下注射ISO(2.5 mg·kg~(-1)·d~(-1),14 d)建立大鼠心肌重构模型,随机分为对照组、ISO模型组、HDD5(HDD 5 g·kg~(-1)·d~(-1)+ISO)组、HDD10(HDD 10 mg·kg~(-1)·d~(-1)+ISO)组。干预4周后,计算心脏质量指数(HW/BW)和左心室质量指数(LVW/BW);超声心动图观察心肌结构;HE染色观察心肌组织病理学结构变化;ELISA检测血清中BNP,Ca N和Ca M kinasesⅡ的水平;Western blot检测左心室组织STIM1,TRPC1,p-Ca N,p-NFATc3和NFATc3蛋白的表达。结果显示,ISO组大鼠HW/BW和LVW/BW均大于HDD5组和HDD10组(P0.05);超声心动图检查结果显示,HDD能够抑制ISO诱导的LVEDD,LVESD增加;ELISA检测显示,HDD能明显抑制ISO致心肌重构大鼠血清中BNP,Ca N和Ca M kinasesⅡ含量的升高(P0.01)。Western blot检测结果显示,ISO组大鼠心肌组织STIM1,TRPC1,p-Ca N,p-NFATc3和NFATc3表达升高,HDD给药后心肌组织内STIM1,TRPC1,p-Ca N,p-NFATc3和NFATc3的表达均降低(P0.05)。结果表明,黄芪丹参水煎液具有抑制ISO致大鼠心肌重构的作用,其机制与下调STIM1,TRPC1,Ca M kinasesⅡ,p-Ca N/Ca N和pNFATc3/NFATc3表达有关。     

Pressure-induced and store-operated cation influx in vascular smooth muscle cells is independent of TRPC1

Among the classical transient receptor potential (TRPC) subfamily, TRPC1 is described as a mechanosensitive and store-operated channel proposed to be activated by hypoosmotic cell swelling and positive pipette pressure as well as regulated by the filling status of intracellular Ca(2+) stores. However, evidence for a physiological role of TRPC1 may most compellingly be obtained by the analysis of a TRPC1-deficient mouse model. Therefore, we have developed and analyzed TRPC1(-/-) mice. Pressure-induced constriction of cerebral arteries was not impaired in TRPC1(-/-) mice. Smooth muscle cells from cerebral arteries activated by hypoosmotic swelling and positive pipette pressure showed no significant differences in cation currents compared to wild-type cells. Moreover, smooth muscle cells of TRPC1(-/-) mice isolated from thoracic aortas and cerebral arteries showed no change in store-operated cation influx induced by thapsigargin, inositol-1,4,5 trisphosphate, and cyclopiazonic acid compared to cells from wild-type mice. In contrast to these results, small interference RNAs decreasing the expression of stromal interaction molecule 1 (STIM1) inhibited thapsigargin-induced store-operated cation influx, demonstrating that STIM1 and TRPC1 are mutually independent. These findings also imply that, as opposed to current concepts, TRPC1 is not an obligatory component of store-operated and stretch-activated ion channel complexes in vascular smooth muscle cells.     

The imprint of salivary secretion in autoimmune disorders and related pathological conditions

Xerostomia is a state of oral dryness associated with salivary gland dysfunction and is induced by stress, radiation and chemical therapy, various systemic and autoimmune diseases, and specific medications. Fluid secretion is interrupted by the stimulation of neurotransmitter-induced increase in cytosolic calcium ([Ca²⁺]_i) in salivary gland acinar cells, prompting the mobilization of ion channels and their transporters. Salivary fluid and protein secretion are principally dependent on parasympathetic and sympathetic nerves. Various inflammatory cytokines allied with lymphocytic infiltration cause glandular damage and Sjogren's syndrome, an autoimmune exocrinopathy associated with hyposalivation. A defect in IP₃Rs, a major calcium release channel, prompts inadequate agonist-induced [Ca²⁺]_i in acinar cells and deters salivary flow. The store-operated calcium entry-mediated Ca²⁺ movement into the acini activates K⁺ and Cl^? channels, which further opens a water channel protein, aquaporin-5, and triggers the release of fluid secretion from the salivary glands. The cellular mechanism of salivary gland dysfunction and hyposalivation has not yet been elucidated. In this review, we focused mainly on the proteins responsible for deficient saliva, the correlation between inflammation and salivation, autoimmune disorders and other ailments or complications associated with hyposalivation.