Pathophysiological implications of transient receptor potential channels in vascular function

Silencing of transient receptor potential canonical channel 4 inhibits endothelial progenitor cell angiogenesis by suppressing VEGF and SDF-1

OBJECTIVES

Endothelial progenitor cells (EPCs) play a crucial role in acquired angiogenesis and endothelial injury repair. Transient receptor potential canonical channel 4 (TRPC4), a key component of store-operated calcium channels, is essential for EPC function. While the role of TRPCs has been clarified in vascular diseases, the relationship between TRPC4 and EPC function, along with the underlying molecular mechanisms, remains unclear and requires further elucidation.

METHODS

EPCs were isolated from canine bone marrow and identified by morphology and flow cytometry. TRPC4 was transfected into EPCs using lentivirus or negative control, and its expression was assessed using real-time polymerase chain reaction (RT-PCR). Proliferation, migration, and tube formation were evaluated using Cell Counting Kit-8 (CCK-8), Transwell, and Matrigel assays, respectively. Levels of vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1 (SDF-1) were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

TRPC4 mRNA expression was significantly reduced in TRPC4-short hairpin RNA (shRNA) transfected EPCs compared to the normal control (NC)-shRNA groups. Migration and tube formation were significantly decreased after TRPC4 silencing, while proliferation showed no difference. Additionally, levels of SDF-1 and VEGF in EPCs were markedly reduced following TRPC4 silencing.

CONCLUSION

TRPC4 plays a crucial role in regulating angiogenesis in EPCs. Silencing of TRPC4 can lead to decreased angiogenesis by inhibiting VEGF and SDF-1 expression, suggesting that TRPC4 knockdown might be a novel therapeutic strategy for vascular diseases.

Functional roles and mechanisms of ginsenosides from Panax ginseng in atherosclerosis

Atherosclerosis (AS) is a leading cause of cardiovascular diseases (CVDs) and it results in a high rate of death worldwide, with an increased prevalence with age despite advances in lifestyle management and drug therapy. Atherosclerosis is a chronic progressive inflammatory process, and it mainly presents with lipid accumulation, foam cell proliferation, inflammatory response, atherosclerotic plaque formation and rupture, thrombosis, and vascular calcification. Therefore, there is a great need for reliable therapeutic drugs or remedies to cure or alleviate atherosclerosis and reduce the societal burden. Ginsenosides are natural steroid glycosides and triterpene saponins obtained mainly from the plant ginseng. Several recent studies have reported that ginsenosides have a variety of pharmacological activities against several diseases including inflammation, cancer and cardiovascular diseases. This review focuses on describing the different pharmacological functions and underlying mechanisms of various active ginsenosides (Rb1,-Rd, -F, -Rg1, -Rg2, and -Rg3, and compound K) for atherosclerosis, which could provide useful insights for developing novel and effective anti-cardiovascular drugs.

Gαi-mediated TRPC4 activation by polycystin-1 contributes to endothelial function via STAT1 activation

Hypertension and aneurysm are frequently associated with autosomal dominant polycystic kidney disease (ADPKD) caused by polycystin-1 (PC1) mutations, which is closely related to endothelial dysfunction. PC1 is an atypical G-protein-coupled receptor that activates G-proteins by self-cleavage; currently, however, the molecular and cellular mechanisms of the associated intracellular signaling and ion channel activation remain poorly elucidated. Here, we report an activation mechanism of a calcium-permeable canonical transient receptor potential 4 (TRPC4) channel by PC1 and its endothelial function. We found that the inhibitory Gα_i3 protein selectively bound to the G-protein-binding domain on the C-terminus of PC1. The dissociation of Gα_i3 upon cleavage of PC1 increased TRPC4 activity. Calcium influx through TRPC4 activated the transcription factor STAT1 to regulate cell proliferation and death. The down-regulation of PC1/TRPC4/STAT1 disrupted migration of endothelial cell monolayers, leading to an increase in endothelial permeability. These findings contribute to greater understanding of the high risk of aneurysm in patients with ADPKD.

Silencing of Transient Receptor Potential Channel 4 Alleviates oxLDL-induced Angiogenesis in Human Coronary Artery Endothelial Cells by Inhibition of VEGF and NF-κB

Background

Transient receptor potential channel 4 (TRPC4) plays central roles in endothelial cell function. The aim of this study was to investigate the silencing effects of TRPC4 on oxidized low-density lipoprotein (oxLDL)-induced angiogenesis in human coronary artery endothelial cells (HCAECs), as well as the underlying molecular mechanism involved in this process.

Material/Methods

HCAECs were transfected with small interfering RNA (siRNA) targeting TRPC4 (TRPC4-siRNA) or with a negative control (NC)-siRNA. The expression of TRPC4 was confirmed by real-time polymerase chain reaction (RT-PCR) and Western blotting. After the siRNA transfection, oxLDL was added to the medium. Cell proliferation, migration, and in vitro angiogenesis were determined by bromodeoxyuridine (BrdU) enzyme-linked immunosorbent assay (ELISA), Transwell assay and scratch-wound assay, respectively, and tube formation on Matrigel. Expression of vascular endothelial growth factor (VEGF) and nuclear factor (NF)-κB p65 were assessed by Western blotting.

Results

Both the mRNA and protein levels of TRPC4 were significantly reduced by transfection with TRPC4-siRNA compared to the control group or NC-siRNA group (P<0.05). Silencing of TRPC4 significantly decreased the cell proliferation, migration, and tube formation (all P<0.05). Furthermore, the expression levels of VEGF and NF-κB p65 were markedly lowered by silencing of TRPC4 in HCAECs.

Conclusions

These results suggest that silencing of TRPC4 alleviates angiogenesis induced by oxLDL in HCAECs through inactivation of VEGF and NF-κB. Suppression of TRPC4 might be an alternative therapeutic strategy for atherosclerotic neovascularization.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Ginsenoside-Rd, a purified component from panax notoginseng saponins, prevents atherosclerosis in apoE knockout mice

Recently, it was revealed that the dysfunction of transmembrane Ca(2+) transport, results in an increase in intracellular Ca(2+)[Ca(2+)](i), which is involved in the process of atherosclerosis. We previously demonstrated that ginsenoside-Rd, a purified component from panax notoginseng, is a voltage-independent Ca(2+) channels blocker. In this study, we investigated the effects of ginsenoside-Rd on atherosclerosis and the underlying mechanisms in apolipoprotein E deficient (apoE(-/-)) mice and RAW264.7 cells. Atherosclerotic plaques were stained by Red oil O staining. Ca(2+) influx was measured by Fura-2 dyed Mn(2+) quenching. Intracellular cholesterol and uptake of lipid was assayed by enzymatic, fluorometric method and DiI-labeled Ox-LDL. Western blot was used to determine protein expression. We found that Ginsenoside-Rd (20mg/kg/day. i.p.) significantly reduced the atherosclerotic plaque areas, oxidized low-density lipoprotein (ox-LDL) uptake and thapsigargin and l-oleoyl-2-acetyl-glycerol (OAG, membrane-permeable diacylglycerol analog)-induced Ca(2+) influx in macrophages from high-fat diet apoE(-/-) mice. In vitro, 20μM ginsenoside-Rd significantly inhibited ox-LDL-induced foam cell formation and the increase of thapsigargin- and OAG-induced Ca(2+) influx. Ox-LDL induced an increase in scavenger receptor A (SR-A) expression, and ginsenoside-Rd inhibited this effect of ox-LDL significantly. The results suggest that ginsenoside-Rd prevents the development of atherosclerosis. The underlying mechanism may be related to the inhibition of Ca(2+) influx through voltage-independent Ca(2+) channels, resulting in the inhibition of SR-A activity and expression, followed by reductions of ox-LDL uptake and cholesterol accumulation in macrophages.

Na+-independent, nifedipine-resistant rat afferent arteriolar Ca2+ responses to noradrenaline: possible role of TRPC channels

AIM

In rat afferent arterioles we investigated the role of Na(+) entry in noradrenaline (NA)-induced depolarization and voltage-dependent Ca(2+) entry together with the importance of the transient receptor potential channel (TRPC) subfamily for non-voltage-dependent Ca(2+) entry.

METHODS

R (340/380) Fura-2 fluorescence was used as an index for intracellular free Ca(2+) concentration ([Ca(2+)](i)). Immunofluorescence detected the expression of TRPC channels.

RESULTS

TRPC 1, 3 and 6 were expressed in afferent arteriolar vascular smooth muscle cells. Under extracellular Na(+)-free (0 Na) conditions, the plateau response to NA was 115% of the baseline R(340/380) (control response 123%). However, as the R(340/380) baseline increased (7%) after 0 Na the plateau reached the same level as during control conditions. Similar responses were obtained after blockade of the Na(+)/Ca(2+) exchanger. The L-type blocker nifedipine reduced the plateau response to NA both under control (from 134% to 116% of baseline) and 0 Na conditions (from 112% to 103% of baseline). In the presence of nifedipine, the putative TRPC channel blockers SKF 96365 (30 μm) and Gd(3+) (100 μm) further reduced the plateau Ca(2+) responses to NA (from 117% to 102% and from 117% to 110% respectively).

CONCLUSION

We found that Na(+) is not crucial for the NA-induced depolarization that mediates Ca(2+) entry via L-type channels. In addition, the results are consistent with the idea that TRPC1/3/6 Ca(2+) -permeable cation channels expressed in afferent arteriolar smooth muscle cells mediate Ca(2+) entry during NA stimulation.

Urotensin II-induced signaling involved in proliferation of vascular smooth muscle cells

The urotensin II receptor, bound by the ligand urotensin II, generates second messengers, ie, inositol triphosphate and diacylglycerol, which stimulate the subsequent release of calcium (Ca²⁺) in vascular smooth muscle cells. Ca²⁺ influx leads to the activation of Ca²⁺-dependent kinases (CaMK) via calmodulin binding, resulting in cellular proliferation. We hypothesize that urotensin II signaling in pulmonary arterial vascular smooth muscle cells (Pac1) and primary aortic vascular smooth muscle cells (PAVSMC) results in phosphorylation of Ca²⁺/calmodulin-dependent kinases leading to cellular proliferation. Exposure of Pac1 cultures to urotensin II increased intracellular Ca²⁺, subsequently activating Ca²⁺/calmodulin-dependent kinase kinase (CaMKK), and Ca²⁺/calmodulin-dependent kinase Type I (CaMKI), extracellular signal-regulated kinase (ERK 1/2), and protein kinase D. Treatment of Pac1 and PAVSMC with urotensin II increased proliferation as measured by ³H-thymidine uptake. The urotensin II-induced increase in ³H-thymidine incorporation was inhibited by a CaMKK inhibitor. Taken together, our results demonstrate that urotensin II stimulation of smooth muscle cells leads to a Ca²⁺/calmodulin-dependent kinase-mediated increase in cellular proliferation.

Combined therapy with renin-angiotensin system and calcium channel blockers in type 2 diabetic hypertensive patients with proteinuria: effects on soluble TWEAK, PTX3, and flow-mediated dilation

BACKGROUND AND OBJECTIVES

Soluble TNF-like weak inducer of apoptosis (sTWEAK) and long pentraxin-3 (PTX3) concentrations have been associated with endothelial function in patients with chronic kidney disease (CKD). This study tested the hypothesis that the improvement in endothelial function after initiation of angiotensin II receptor blocker (valsartan), calcium channel blocker (amlodipine) therapy, or a combination of both is directly linked to the normalization of sTWEAK and PTX3.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One-hundred-eight diabetic CKD stage I patients with hypertension (56% men, 46.7+/-5.3 years) were allocated to a 12-week intervention with amlodipine (10 mg/d), valsartan (160 mg/d), or their combination. Plasma levels of sTWEAK, PTX3, and flow-mediated dilation (FMD) were studied during the interventions.

RESULTS

All treatment strategies effectively increased FMD and reduced proteinuria, confirming a more prone reduction with the combined therapy. These improvements were followed by significant PTX3 reductions. Valsartan alone and in combination with amlodipine achieved significant incremental raises in sTWEAK plasma levels. More importantly, the changes observed in sTWEAK (beta=0.25, P=0.006) or PTX3 (beta=-0.24, P=0.007) plasma levels were independently associated with the improvement in ultrasonographically measured FMD.

CONCLUSIONS

This study shows that treatment with antihypertensive drugs improves FMD and normalizes proteinuria, PTX3, and sTWEAK in diabetic CKD stage I patients with hypertension. The improvement in FMD was independently associated with PTX3 and sTWEAK normalization. Two surrogate biomarkers of endothelial function are therefore identified with potential as therapeutic targets. The study was registered in clinicaltrials.gov as NCT00921570.

Ginsenoside Rd prevents glutamate-induced apoptosis in rat cortical neurons

1. The role of voltage-independent Ca(2+) entry in cell apoptosis has recently received considerable attention. It has been found that ginsenoside Rd significantly inhibits voltage-independent Ca(2+) entry. The aim of the present study was to investigate the protective effects of ginsenoside Rd against glutamate-induced apoptosis of rat cortical neurons. 2. Ginsenoside Rd significantly reduced glutamate-induced apoptotic morphological changes and DNA laddering. In comparison, nimodipine only had a weak effect. 3. Ginsenoside Rd (1, 3 and 10 micromol/L) concentration-dependently inhibited caspase 3 activation and expression of the p20 subunit of active caspase 3 (by 30 +/- 10%, 41 +/- 9% and 62 +/- 19%, respectively, compared with glutamate alone; P < 0.05), whereas 1 micromol/L nimodipine had no effect. 4. Glutamate decreased cell viability to 37.4 +/- 4.7 (n = 8) and evoked cell apoptosis. Ginsenoside Rd (1, 3, 10 and 30 micromol/L) concentration-dependently inhibited glutamate-induced cell death, increased cell viability and reduced apoptotic percentage (from 47.5 +/- 4.9% to 37.4 +/- 6.9%, 28.3 +/- 5.2% and 22.5 +/- 5.6%, respectively; P < 0.05). At 1 micromol/L, nimodipine had no effect on cell viability. Furthermore, although 1, 3, 10, 30 and 60 micromol/L ginsenoside Rd concentration-dependently inhibited glutamate-induced Ca(2+) entry by 8 +/- 2%, 24 +/- 4%, 40 +/- 7%, 49 +/- 8% and 50 +/- 8% (P < 0.05), respectively, nimodipine had no effect. 5. In conclusion, the results indicate that ginsenoside Rd prevents glutamate-induced apoptosis in rat cortical neurons and provide further evidence of the potential of voltage-independent Ca(2+) channel blockers as new neuroprotective drugs for the prevention of neuronal apoptosis and death induced by cerebral ischaemia.

Opposite regulation of KCNQ5 and TRPC6 channels contributes to vasopressin-stimulated calcium spiking responses in A7r5 vascular smooth muscle cells

Physiologically relevant concentrations of [Arg(8)]-vasopressin (AVP) induce repetitive action potential firing and Ca(2+) spiking responses in the A7r5 rat aortic smooth muscle cell line. These responses may be triggered by suppression of KCNQ potassium currents and/or activation of non-selective cation currents. Here we examine the relative contributions of KCNQ5 channels and TRPC6 non-selective cation channels to AVP-stimulated Ca(2+) spiking using patch clamp electrophysiology and fura-2 fluorescence measurements in A7r5 cells. KCNQ5 or TRPC6 channel expression levels were suppressed by short hairpin RNA constructs. KCNQ5 knockdown resulted in more positive resting membrane potentials and induced spontaneous action potential firing and Ca(2+) spiking. However physiological concentrations of AVP induced additional depolarization and increased Ca(2+) spike frequency in KCNQ5 knockdown cells. AVP activated a non-selective cation current that was reduced by TRPC shRNA treatment or removal of external Na(+). Neither resting membrane potential nor the AVP-induced depolarization was altered by knockdown of TRPC6 channel expression. However, both TRPC6 shRNA and removal of external Na(+) delayed the onset of Ca(2+) spiking induced by 25pM AVP. These results suggest that suppression of KCNQ5 currents alone is sufficient to excite A7r5 cells, but AVP-induced activation of TRPC6 contributes to the stimulation of Ca(2+) spiking.

Trpv4 induces collateral vessel growth during regeneration of the arterial circulation

The development of a collateral circulation (arteriogenesis), bypassing an arterial occlusion, is important for tissue survival, but it remains functionally defective. Micro array data of growing collateral vessels, exposed to chronically elevated fluid shear stress (FSS), showed increased transcription of the transient receptor potential cation channel, subfamily V, member 4 (Trpv4). Thus, the aim of this study was to investigate the role of the shear stress sensitive Trpv4 in transmitting this physical stimulus into an active growth response. qRT-PCR at different time points during the growth of collateral vessels after femoral artery ligature (FAL) in rats showed a strong positive correlation of Trpv4 transcription and the intensity of FSS. An increased protein expression of Trpv4 was localized in the FSS-sensing endothelium by means of confocal immunohistochemistry. Cultured porcine endothelial cells showed a dose-dependent expression of Trpv4 and an increased level of Ki67-positive cells upon treatment with 4alpha-Phorbol 12,13-didecanoate (4alphaPDD), a specific Trpv4 activator. This was also demonstrated by flow culture experiments. These results were confirmed by in vivo application of 4alphaPDD in rabbit hind limb circulation via an osmotic mini-pump after FAL. Trpv4 expression as well as Ki67-positive staining was significantly increased in collateral vessels. Finally, 4alphaPDD treatment after FAL led to a 61% (215.5 ml/min/mmHg versus 350 ml/min/mmHg) recovery of conductance when compared with the non-occluded artery. Cell culture and in vivo studies demonstrate that an FSS- or a 4alphaPDD-induced activation of Trpv4 leads to an active proliferation of vascular cells and finally triggers collateral growth. Trpv4, a well-known FSS-sensitive vasodilator, has hitherto not been implicated in active growth processes of collateral arteries. This new function may lead to new therapeutic strategies for the treatment of arterial occlusive diseases.

Nitric oxide-cGMP-protein kinase G pathway negatively regulates vascular transient receptor potential channel TRPC6

We investigated the inhibitory role of the nitric oxide (NO)-cGMP-protein kinase G (PKG) pathway on receptor-activated TRPC6 channels in both a heterologous expression system (HEK293 cells) and A7r5 vascular myocytes. Cationic currents due to TRPC6 expression were strongly suppressed (by approximately 70%) by a NO donor SNAP (100 microm) whether it was applied prior to muscarinic receptor stimulation with carbachol (CCh; 100 microm) or after G-protein activation with intracellular perfusion of GTPgammaS (100 microm). A similar extent of suppression was also observed with a membrane-permeable analogue of cGMP, 8Br-cGMP (100 microm). The inhibitory effects of SNAP and 8Br-cGMP on TRPC6 channel currents were strongly attenuated by the presence of inhibitors for guanylyl cyclase and PKG such as ODQ, KT5823 and DT3. Alanine substitution for the PKG phosphorylation candidate site at T69 but not at other sites (T14A, S28A, T193A, S321A) of TRPC6 similarly attenuated the inhibitory effects of SNAP and 8Br-cGMP. SNAP also significantly reduced single TRPC6 channel activity recorded in the inside-out configuration in a PKG-dependent manner. SNAP-induced PKG activation stimulated the incorporation of (32)P into wild-type and S321A-mutant TRPC6 proteins immunoprecipitated by TRPC6-specific antibody, but this was greatly attenuated in the T69A mutant. SNAP or 8Br-cGMP strongly suppressed TRPC6-like cation currents and membrane depolarization evoked by Arg(8)-vasopressin in A7r5 myocytes. These results strongly suggest that TRPC6 channels can be negatively regulated by the NO-cGMP-PKG pathway, probably via T69 phosphorylation of the N-terminal. This mechanism may be physiologically important in vascular tissues where NO is constantly released from vascular endothelial cells or nitrergic nerves.