Functional role of TRPC channels in the regulation of endothelial permeability

Effects of aging on calcium channels in skeletal muscle

In skeletal muscle, calcium is not only essential to stimulate and sustain their contractions but also for muscle embryogenesis, regeneration, energy production in mitochondria, and fusion. Different ion channels contribute to achieving the various functions of calcium in skeletal muscles. Muscle contraction is initiated by releasing calcium from the sarcoplasmic reticulum through the ryanodine receptor channels gated mechanically by four dihydropyridine receptors of T-tubules. The calcium influx through store-operated calcium channels sustains the contraction and stimulates muscle regeneration. Mitochondrial calcium uniporter allows the calcium entry into mitochondria to stimulate oxidative phosphorylation. Aging alters the expression and activity of these different calcium channels, resulting in a reduction of skeletal muscle force generation and regeneration capacity. Regular physical training and bioactive molecules from nutrients can prevent the effects of aging on calcium channels. This review focuses on the current knowledge of the effects of aging on skeletal muscles' calcium channels.

The role of transient receptor potential channels in metastasis

Metastasis is the hallmark of failed tumor treatment and is typically associated with death due to cancer. Transient receptor potential (TRP) channels affect changes in intracellular calcium concentrations and participate at every stage of metastasis. Further, they increase the migratory ability of tumor cells, promote angiogenesis, regulate immune function, and promote the growth of tumor cells through changes in gene expression and function. In this review, we explore the potential mechanisms of action of TRP channels, summarize their role in tumor metastasis, compile inhibitors of TRP channels relevant in tumors, and discuss current challenges in research on TRP channels involved in tumor metastasis.

Investigating a Genetic Link Between Alzheimer's Disease and CADASIL-Related Cerebral Small Vessel Disease

Monogenic forms of Alzheimer's disease (AD) have been identified through mutations in genes such as APP, PSEN1, and PSEN2, whilst other genetic markers such as the APOE ε carrier allele status have been shown to increase the likelihood of having the disease. Mutations in these genes are not limited to AD, as APP mutations can also cause an amyloid form of cerebral small vessel disease (CSVD) known as cerebral amyloid angiopathy, whilst PSEN1 and PSEN2 are involved in NOTCH3 signalling, a process known to be dysregulated in the monogenic CSVD, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). The overlap between AD genes and causes of CSVD led to the hypothesis that mutations in other genes within the PANTHER AD-presenilin pathway may be novel causes of CSVD in a cohort of clinically suspicious CADASIL patients without a pathogenic NOTCH3 mutation. To investigate this, whole exome sequencing was performed on 50 suspected CADASIL patients with no NOTCH3 mutations, and a targeted gene analysis was completed on the PANTHER. ERN1 was identified as a novel candidate CSVD gene following predicted pathogenic gene mutation analysis. Rare variant burden testing failed to identify an association with any gene; however, it did show a nominally significant link with ERN1 and TRPC3. This study provides evidence to support a genetic overlap between CSVD and Alzheimer's disease.

G protein-coupled estrogen receptor regulates the KLF2-dependent eNOS expression by activating of Ca2+ and EGFR signaling pathway in human endothelial cells

G protein-coupled estrogen receptor (GPER) is important for maintaining normal blood vessel function by preventing endothelial cell dysfunction. It has been reported that G-1, an agonist of GPER, increases nitric oxide (NO) production through the phosphorylation of endothelial nitric oxide synthase (eNOS). However, the effect of GPER activation on eNOS expression has not been studied. Our results show that G-1 significantly increased the expression of eNOS and Kruppel-like factor 2 (KLF2) in human endothelial EA.hy926 cells. The individual silences of KLF2 and GPER attenuated G-1-induced eNOS expression. In addition, inhibition of the Gαq and Gβγ suppressed G-1-induced the expression of eNOS and KLF2 in EA.hy926 cells. Interestingly, these effects were similar in HUVECs. Furthermore, we found that GPER-mediated Ca²⁺ signaling increased the phosphorylation of CaMKKβ, AMPK, and CaMKIIα in the cells. The phosphorylation of histone deacetylase 5 (HDAC5) by activation of AMPK and CaMKIIα increased the expression of eNOS via transcriptional activity of KLF2. We further demonstrate that GPER activation increased the phosphorylation of Src, EGFR, ERK5, and MEF2C and consequently induced the expression of eNOS and KLF2. Meanwhile, inhibition of ERK5 and HDAC5 suppressed the expression of eNOS and KLF2 induced by G-1 in the cells. These findings suggest that GPER provides a novel mechanism for understanding the regulation of eNOS expression and is an essential therapeutic target in preventing cardiovascular-related endothelial dysfunction.

Correlation between classical transient receptor potential channel 1 gene polymorphism and microalbuminuria in patients with primary hypertension

OBJECTIVE

To investigate the correlation between transient receptor potential channel 1 (TRPC1) gene polymorphism and microalbuminuria in patients with primary hypertension. Methods: A total of 468 patients with primary hypertension were admitted to the Department of Hypertension of the First Affiliated Hospital of Xinjiang Medical University from April 2015 to November 2017. According to microalbuminuria, the patients were divided into two groups: high urinary albumin group (EH+mALB group, n = 71) and normal urinary microalbuminuria group (EH group, n = 397). The Sequenom detection technology was used for genotyping the single nucleotide polymorphism (SNP) sites of the TRPC1 gene, such as rs1382688, rs3821647, rs7638459, rs953239, and rs7621642.

RESULTS

(1) No significant differences were detected in gender, smoking history, drinking history, family history, course of hypertension, fasting blood glucose, urea, creatinine, triglyceride, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, glycosylated hemoglobin, vitamin D, homocysteine, and cystatin C between the two groups (P > .05). However, age, body mass index (BMI), 24-h mean systolic and diastolic blood pressure, and 24-h average pulse pressure were statistically significant (P < .05). (2) No significant difference was detected in the distribution frequency of the polymorphisms of the TRPC1 gene between the two groups (P > .05), while the genotype, allele, and recessive model of rs7638459 differed significantly difference (P < .05). (3) Logistic regression analysis showed that BMI and rs7638459 CC genotype were the risk factors of increased microalbuminuria in patients with primary hypertension.

CONCLUSION

TRPC1 gene polymorphism is associated with increased microalbuminuria in patients with primary hypertension. The CC genotype of rs7638459 may increase the risk of microalbuminuria in patients with essential hypertension, while BMI and rs7638459 CC genotype may be the risk factors of increased microalbuminuria in patients with primary hypertension.

Betulinic Acid Induces eNOS Expression via the AMPK-Dependent KLF2 Signaling Pathway

Betulinic acid (BA) is a natural pentacyclic triterpenoid with protective effects against inflammation, metabolic diseases, and cardiovascular diseases. We have previously shown that BA prevents endothelial dysfunction by increasing nitric oxide (NO) synthesis through activating endothelial nitric oxide synthase (eNOS) in human endothelial cells. However, the effect of BA on eNOS expression remains unclear. Thus, the aim of our study was to investigate the intracellular pathways associated with the effect of BA to regulate eNOS expression in human endothelial cells. BA significantly increased eNOS expression in a time- and concentration-dependent manner. Additionally, BA upregulated the expression of the transcription factor KLF2, which is known to regulate eNOS expression. KLF2 silencing in human endothelial cells attenuated the ability of BA to upregulate eNOS. BA also increased levels of intracellular Ca²⁺, activating CaMKKβ, CaMKIIα, and AMPK. Inhibition of the TRPC calcium channel abolished BA-mediated effects on intracellular Ca²⁺ levels. Moreover, BA increased the phosphorylation levels of ERK5, HDAC5, and MEF2C. Pretreatment of cells with compound C (AMPK inhibitor), LMK235 (HDAC5 inhibitor), and XMD8-92 (ERK5 inhibitor) attenuated the BA-induced eNOS expression. Collectively, these findings suggest that BA induces eNOS expression by activating the HDAC5/ERK5/KLF2 pathway in endothelial cells. The data presented here provide strong evidence supporting the use of BA to prevent endothelial dysfunction and treat vascular diseases, such as atherosclerosis.

Ca2+ release-activated Ca2+ channels are responsible for histamine-induced Ca2+ entry, permeability increase, and interleukin synthesis in lymphatic endothelial cells

The lymphatic functions in maintaining lymph transport, and immune surveillance can be impaired by infections and inflammation, thereby causing debilitating disorders, such as lymphedema and inflammatory bowel disease. Histamine is a key inflammatory mediator known to trigger vasodilation and vessel hyperpermeability upon binding to its receptors and evoking intracellular Ca²⁺ ([Ca²⁺]_i) dynamics for downstream signal transductions. However, the exact molecular mechanisms beneath the [Ca²⁺]_i dynamics and the downstream cellular effects have not been elucidated in the lymphatic system. Here, we show that Ca²⁺ release-activated Ca²⁺ (CRAC) channels, formed by Orai1 and stromal interaction molecule 1 (STIM1) proteins, are required for the histamine-elicited Ca²⁺ signaling in human dermal lymphatic endothelial cells (HDLECs). Blockers or antagonists against CRAC channels, phospholipase C, and H₁R receptors can all significantly diminish the histamine-evoked [Ca²⁺]_i dynamics in lymphatic endothelial cells (LECs), while short interfering RNA-mediated knockdown of endogenous Orai1 or STIM1 also abolished the Ca²⁺ entry upon histamine stimulation in LECs. Furthermore, we find that histamine compromises the lymphatic endothelial barrier function by increasing the intercellular permeability and disrupting vascular endothelial-cadherin integrity, which is remarkably attenuated by CRAC channel blockers. Additionally, the upregulated expression of inflammatory cytokines, IL-6 and IL-8, after histamine stimulation was abolished by silencing Orai1 or STIM1 with RNAi in LECs. Taken together, our data demonstrated the essential role of CRAC channels in mediating the [Ca²⁺]_i signaling and downstream endothelial barrier and inflammatory functions induced by histamine in the LECs, suggesting a promising potential to relieve histamine-triggered vascular leakage and inflammatory disorders in the lymphatics by targeting CRAC channel functions.

MicroRNA26a inhibits cisplatin-induced renal tubular epithelial cells apoptosis through suppressing the expression of transient receptor potential channel 6 mediated dynamin-related protein 1

Acute kidney injury (AKI) is a common adverse reaction of the anticancer drug. Among these chemotherapeutic agents, cisplatin, an effective chemotherapeutic drug, is extensively applied to the treatment of solid tumours, yet various adverse reactions, especially AKI, often limit their use. However, the pathogenesis of AKI caused by cisplatin remains poorly clarified. Therefore, we tested whether microRNAs, which have been certified as key regulators of disease are involved in this process. AKI mouse and HK2 cells were treated with cisplatin. Annexin V/PI staining and cleaved caspase-3 were used to assess apoptosis. Western blot analyses and qRT-PCR were used to evaluate the protein and mRNA level of TRPC6 and DRP1. miR-26a was remarkably decreased in cisplatin-induced AKI and in cisplatin co-cultured HK2 cells. Furthermore, we used a miR-26a mimics in vitro and found that apoptosis was alleviated than that in the control cells. We further verified that miR-26a protected against cisplatin-induced cell apoptosis by acting on transient receptor potential channel 6 (TRPC6) which can regulate the expression of dynamin-related protein 1 (DRP1), thus inhibited the mitochondrial apoptosis pathway. Therefore, the study unveiled that miR-26a/TRPC6/DRP1 is a novel protective pathway in cisplatin-induced AKI and may be targeted for the prevention and treatment of drug-related renal injury. SIGNIFICANCE OF THE STUDY: Our study found that miR-26a was significantly downregulated during cisplatin-induced AKI and during cisplatin co-cultured HK2 cells. Further, in vitro we used miR-26a mimic to intervene cells and found that apoptosis alleviated compared with control group. We further verified that miR-26a protected cisplatin-induced apoptosis by target transient receptor potential channel 6 (TRPC6) which can regulate the expression of dynamic-related protein 1 (DRP1) and inhibit the mitochondrial apoptosis pathway. Thus, miR-26a/TRPC6/DRP1 is a new protective pathway in cisplatin-induced AKI and may be targeted for the prevention and treatment of drug-related acute kidney injury.

Endothelial dysfunction in pulmonary arterial hypertension: an evolving landscape (2017 Grover Conference Series)

Endothelial dysfunction is a major player in the development and progression of vascular pathology in pulmonary arterial hypertension (PAH), a disease associated with small vessel loss and obstructive vasculopathy that leads to increased pulmonary vascular resistance, subsequent right heart failure, and premature death. Over the past ten years, there has been tremendous progress in our understanding of pulmonary endothelial biology as it pertains to the genetic and molecular mechanisms that orchestrate the endothelial response to direct or indirect injury, and how their dysregulation can contribute to the pathogenesis of PAH. As one of the major topics included in the 2017 Grover Conference Series, discussion centered on recent developments in four areas of pulmonary endothelial biology: (1) angiogenesis; (2) endothelial-mesenchymal transition (EndMT); (3) epigenetics; and (4) biology of voltage-gated ion channels. The present review will summarize the content of these discussions and provide a perspective on the most promising aspects of endothelial dysfunction that may be amenable for therapeutic development.

Endocardial TRPC-6 Channels Act as Atrial Mechanosensors and Load-Dependent Modulators of Endocardial/Myocardial Cross-Talk

Mechanoelectrical feedback may increase arrhythmia susceptibility, but the molecular mechanisms are incompletely understood. This study showed that mechanical stretch altered the localization, protein levels, and function of the cation-selective transient receptor potential channel (TRPC)-6 in atrial endocardial cells in humans, pigs, and mice. In endocardial/myocardial cross-talk studies, addition of media from porcine atrial endocardium (AE) cells altered the calcium (Ca²⁺) transient characteristics of human-induced pluripotent stem cell-derived cardiomyocytes. These changes did not occur with media from stretched AE cells. Our data suggested that endocardial TRPC-6-dependent paracrine signaling may modulate myocardial Ca²⁺ homeostasis under basal conditions and protect against stretch-induced atrial arrhythmias.

TRPC3- and ETB receptor-mediated PI3K/AKT activation induces vasogenic edema formation following status epilepticus

Status epilepticus (SE, a prolonged seizure activity) is a high risk factor of developing vasogenic edema, which leads to secondary complications following SE. In the present study, we investigated whether transient receptor potential canonical channel-3 (TRPC3) may link vascular endothelial growth factor (VEGF) pathway to NFκB/ET_B receptor axis in the rat piriform cortex during vasogenic edema formation. Following SE, TRPC3 and ET_B receptor independently activated phosphatidylinositol 3 kinase (PI3K)/AKT/eNOS signaling pathway. SN50 (a NFκB inhibitor) attenuated the up-regulations of eNOS, TRPC3 and ET_B receptor expressions following SE, accompanied by reductions in PI3K/AKT phosphorylations. Inhibition of SE-induced VEGF over-expression by leptomycin B also abrogated PI3K and AKT phosphorylations, but not TRPC3 expression. Wortmannin (a PI3K inhibitor) and 3CAI (an AKT inhibitor) effectively inhibited up-regulation of eNOS expressions and vasogenic edema lesion following SE. These findings indicate that PI3K/AKT may be common down-stream molecules for TRPC3- and ET_B receptor signaling pathways during vasogenic edema formation. In addition, the present data demonstrate for the first time that TRPC3 may integrate VEGF- and NFκB-mediated vasogenic edema formation following SE. Thus, we suggest that PI3K/AKT signaling pathway may be one of considerable therapeutic targets for vasogenic edema.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca²⁺-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Increasing extracellular Ca2+ sensitizes TNF-alpha-induced vascular cell adhesion molecule-1 (VCAM-1) via a TRPC1/ERK1/2/NFκB-dependent pathway in human vascular endothelial cells

Increasing circulating Ca²⁺ levels within the normal range has been reported to positively correlate with the incidence of fatal cardiovascular diseases (CVDs). However, limited studies have been able to delineate the potential mechanism(s) linking circulating Ca²⁺ to CVD. In this study, we exposed primary human umbilical vein endothelial cells (HUVECs) and human umbilical vein cell line (EA.hy926) to different extracellular Ca²⁺ to mimic the physiological state. Our data revealed that increasing extracellular Ca²⁺ significantly enhanced susceptibility to tumor necrosis factor (TNF)-alpha-stimulated vascular cell adhesion molecule (VCAM)-1 expression and monocytes adhesion. Knocking-down VCAM-1 by siRNA abolished calcium-induced monocytes adhesion on HUVECs. Follow up mechanistic investigations identified that extracellular Ca²⁺-increased calcium influx contributed to the activation of VCAM-1. This was mediated via upregulation of transient receptor potential channel (TRPC)1 in a nuclear factor (NF)κB-dependent manner. Most importantly, we found that a novel TRPC1-regulated extracellular signal-regulated kinase 1/2 (ERK1/2) pathway exclusively contributed to calcium-induced NFκB activation. This study provided direct evidence that increasing extracellular Ca²⁺ enhanced TNF-alpha-induced VCAM-1 activation and monocytes adhesion. Moreover, we identified a novel TRPC1/ERK1/2/NFκB signaling pathway mediating VCAM-1 activation and monocyte adhesion in this pathological process. Our studies indicate that blood calcium levels should be strictly monitored to help prevent CVD, and that TRPC1 might act as a potential target for the treatment and prevention against increased circulating calcium-enhanced CVDs.

Use of Noncontrast Computed Tomography and Computed Tomographic Perfusion in Predicting Intracerebral Hemorrhage After Intravenous Alteplase Therapy

Background and Purpose—

Intracerebral hemorrhage is a feared complication of intravenous alteplase therapy in patients with acute ischemic stroke. We explore the use of multimodal computed tomography in predicting this complication.

Methods—

All patients were administered intravenous alteplase with/without intra-arterial therapy. An age- and sex-matched case–control design with classic and conditional logistic regression techniques was chosen for analyses. Outcome was parenchymal hemorrhage on 24- to 48-hour imaging. Exposure variables were imaging (noncontrast computed tomography hypoattenuation degree, relative volume of very low cerebral blood volume, relative volume of cerebral blood flow ≤7 mL/min·per 100 g, relative volume of T max ≥16 s with all volumes standardized to z axis coverage, mean permeability surface area product values within T max ≥8 s volume, and mean permeability surface area product values within ipsilesional hemisphere) and clinical variables (NIHSS [National Institutes of Health Stroke Scale], onset to imaging time, baseline systolic blood pressure, blood glucose, serum creatinine, treatment type, and reperfusion status).

Results—

One-hundred eighteen subjects (22 patients with parenchymal hemorrhage versus 96 without, median baseline NIHSS score of 15) were included in the final analysis. In multivariable regression, noncontrast computed tomography hypoattenuation grade ( P <0.006) and computerized tomography perfusion white matter relative volume of very low cerebral blood volume ( P =0.04) were the only significant variables associated with parenchymal hemorrhage on follow-up imaging (area under the curve, 0.73; 95% confidence interval, 0.63–0.83). Interrater reliability for noncontrast computed tomography hypoattenuation grade was moderate (κ=0.6).

Conclusions—

Baseline hypoattenuation on noncontrast computed tomography and very low cerebral blood volume on computerized tomography perfusion are associated with development of parenchymal hemorrhage in patients with acute ischemic stroke receiving intravenous alteplase.

Roles of transient receptor potential channels in regulation of vascular and epithelial barriers

Transient receptor potential (TRP) channels are a ubiquitously expressed multi-family group of cation channels that are critical to signaling events in many tissues. Their roles have been documented in many physiologic and pathologic conditions. Nevertheless, direct studies of their roles in maintain barrier function in endothelial and epithelia are relatively infrequent. This seems somewhat surprising considering that calcium ion concentrations are known to regulate barrier function. This short review provides an introduction to TRP channels and reviews some of the work in which investigators directly studied the role of TRP channels in endothelial permeability to electric current, solute, or leukocytes during the inflammatory response.

Association between proximal internal carotid artery steno-occlusive disease and diffuse wall thickening in its petrous segment: a magnetic resonance vessel wall imaging study

PURPOSE

Significant stenosis or occlusion in carotid arteries may lead to diffuse wall thickening (DWT) in the arterial wall of downstream. This study aimed to investigate the correlation between proximal internal carotid artery (ICA) steno-occlusive disease and DWT in ipsilateral petrous ICA.

METHODS

Symptomatic patients with atherosclerotic stenosis (>0%) in proximal ICA were recruited and underwent carotid MR vessel wall imaging. The 3D motion sensitized-driven equilibrium prepared rapid gradient-echo (3D-MERGE) was acquired for characterizing the wall thickness and longitudinal extent of the lesions in petrous ICA and the distance from proximal lesion to the petrous ICA. The stenosis degree in proximal ICA was measured on the time-of-flight (TOF) images.

RESULTS

In total, 166 carotid arteries from 125 patients (mean age 61.0 ± 10.5 years, 99 males) were eligible for final analysis and 64 showed DWT in petrous ICAs. The prevalence of severe DWT in petrous ICA was 1.4%, 5.3%, 5.9%, and 80.4% in ipsilateral proximal ICAs with stenosis category of 1%-49%, 50%-69%, 70%-99%, and total occlusion, respectively. Proximal ICA stenosis was significantly correlated with the wall thickness in petrous ICA (r = 0.767, P < 0.001). Logistic regression analysis showed that proximal ICA stenosis was independently associated with DWT in ipsilateral petrous ICA (odds ratio (OR) = 2.459, 95% confidence interval (CI) 1.896-3.189, P < 0.001].

CONCLUSION

Proximal ICA steno-occlusive disease is independently associated with DWT in ipsilateral petrous ICA.

Role of transient receptor potential vanilloid 1 in regulating erythropoietin-induced activation of endothelial nitric oxide synthase

AIMS

Erythropoietin (EPO), the key hormone involved in erythropoiesis, beneficially affects endothelial cells (ECs), but the detailed mechanisms are yet to be completely understood. In this study, we investigated the role of transient receptor potential vanilloid type 1 (TRPV1), a ligand-gated non-selective calcium (Ca²⁺ ) channel, in EPO-mediated endothelial nitric oxide synthase (eNOS) activation and angiogenesis.

METHODS AND RESULTS

In ECs, EPO time dependently increased intracellular levels of calcium; this increase was abrogated by the Ca²⁺ chelators and pharmacological inhibitors of TRPV1 in bovine aortic ECs (BAECs) and TRPV1-transfected HEK293 cells. In addition, EPO-induced nitrite oxide (NO) production, phosphorylation of eNOS, Akt and AMP-activated protein kinase (AMPK) and the formation of TRPV1-Akt-AMPK-eNOS complex as well as tube formation were diminished by the pharmacological inhibition of TRPV1 in BAECs. Moreover, EPO time dependently induced the phosphorylation of phospholipase C-γ1 (PLC-γ1). Inhibition of PLC-γ1 activity blunted the EPO-induced Ca²⁺ influx, eNOS phosphorylation, TRPV1-eNOS complex formation and NO production. The phosphorylated level of eNOS increased in the aortas of EPO-treated wild-type (WT) mice or EPO-transgenic (Tg) mice but not in those of EPO-treated TRPV1-deficient (TRPV1^-/- ) mice or EPO-Tg/TRPV1^-/- mice. Matrigel plug assay showed that EPO-induced angiogenesis was abrogated in TRPV1 antagonist capsazepine-treated WT mice and TRPV1^-/- mice.

CONCLUSION

These findings indicate the EPO-induced Ca²⁺ influx via the activation of the PLC-γ1 signalling pathway, which leads to TRPV1 activation and consequently increases the association of the TRPV1-Akt-AMPK-eNOS complex, eNOS activation, NO production and angiogenesis.

Positive feedback role of TRPC3 in TNF-α-mediated vasogenic edema formation induced by status epilepticus independent of ETB receptor activation

Brain-blood barrier (BBB) disruption results in vasogenic edema, which is involved in the pathogenesis of epilepsy. Following status epilepticus (SE), up-regulated transient receptor potential canonical channel-3 (TRPC3), a Ca²⁺-permeable cation channels in endothelial cells, is relevant to vasogenic edema formation in the rat piriform cortex. In addition, pyrazole-3 (Pyr-3, a TRPC3 inhibitor) attenuated SE-induced vasogenic edema. However, the upstream regulators of TRPC3 expression in vasogenic edema formation have been unclear. In the present study, soluble tumor necrosis factor p55 receptor (sTNFp55R, a TNF-α inhibitor), SN50 (a nuclear factor-κB (NFκB) inhibitor), BQ-788 (an endothelin B (ET_B) receptor inhibitor) and Pyr-3 effectively prevented vasogenic edema following SE. sTNFp55R and SN50 (but not BQ-788) attenuated SE-induced up-regulation of endothelial TRPC3 expression. Pyr-3 ameliorated SE-induced NFκB p65-Thr435 phosphorylation and ET_B receptor expression. In addition, Pyr-3 mitigated NFκB p65-Thr435 phosphorylation induced by recombinant TNF-α. These findings indicate that TNF-α-mediated NFκB p65-Thr435 phosphorylation may up-regulate TRPC3 expression, which participates in vasogenic edema formation via increasing endothelial nitric oxide synthase expression following SE, independent of ET_B receptor activation. Therefore, we suggest that TRPC3 may be involved in a positive feedback loop of NFκB/ET_B receptor signaling pathway.

Loss of Transient Receptor Potential Ankyrin 1 Channel Deregulates Emotion, Learning and Memory, Cognition, and Social Behavior in Mice

The transient receptor potential ankyrin 1 (TRPA1) channel is a non-selective cation channel that helps regulate inflammatory pain sensation and nociception and the development of inflammatory diseases. However, the potential role of the TRPA1 channel and the underlying mechanism in brain functions are not fully resolved. In this study, we demonstrated that genetic deletion of the TRPA1 channel in mice or pharmacological inhibition of its activity increased neurite outgrowth. In vivo study in mice provided evidence of the TRPA1 channel as a negative regulator in hippocampal functions; functional ablation of the TRPA1 channel in mice enhanced hippocampal functions, as evidenced by less anxiety-like behavior, and enhanced fear-related or spatial learning and memory, and novel location recognition as well as social interactions. However, the TRPA1 channel appears to be a prerequisite for motor function; functional loss of the TRPA1 channel in mice led to axonal bundle fragmentation, downregulation of myelin basic protein, and decreased mature oligodendrocyte population in the brain, for impaired motor function. The TRPA1 channel may play a crucial role in neuronal development and oligodendrocyte maturation and be a potential regulator in emotion, cognition, learning and memory, and social behavior.

Thiol-Disulfide Exchange Reactions in the Mammalian Extracellular Environment

Disulfide bonds represent versatile posttranslational modifications whose roles encompass the structure, catalysis, and regulation of protein function. Due to the oxidizing nature of the extracellular environment, disulfide bonds found in secreted proteins were once believed to be inert. This notion has been challenged by the discovery of redox-sensitive disulfides that, once cleaved, can lead to changes in protein activity. These functional disulfides are twisted into unique configurations, leading to high strain and potential energy. In some cases, cleavage of these disulfides can lead to a gain of function in protein activity. Thus, these motifs can be referred to as switches. We describe the couples that control redox in the extracellular environment, examine several examples of proteins with switchable disulfides, and discuss the potential applications of disulfides in molecular biology.

ROS-activated calcium signaling mechanisms regulating endothelial barrier function

Increased vascular permeability is a common pathogenic feature in many inflammatory diseases. For example in acute lung injury (ALI) and its most severe form, the acute respiratory distress syndrome (ARDS), lung microvessel endothelia lose their junctional integrity resulting in leakiness of the endothelial barrier and accumulation of protein rich edema. Increased reactive oxygen species (ROS) generated by neutrophils (PMNs) and other inflammatory cells play an important role in increasing endothelial permeability. In essence, multiple inflammatory syndromes are caused by dysfunction and compromise of the barrier properties of the endothelium as a consequence of unregulated acute inflammatory response. This review focuses on the role of ROS signaling in controlling endothelial permeability with particular focus on ALI. We summarize below recent progress in defining signaling events leading to increased endothelial permeability and ALI.

Derinat Protects Skin against Ultraviolet-B (UVB)-Induced Cellular Damage

Ultraviolet-B (UVB) is one of the most cytotoxic and mutagenic stresses that contribute to skin damage and aging through increasing intracellular Ca²⁺ and reactive oxygen species (ROS). Derinat (sodium deoxyribonucleate) has been utilized as an immunomodulator for the treatment of ROS-associated diseases in clinics. However, the molecular mechanism by which Derinat protects skin cells from UVB-induced damage is poorly understood. Here, we show that Derinat significantly attenuated UVB-induced intracellular ROS production and decreased DNA damage in primary skin cells. Furthermore, Derinat reduced intracellular ROS, cyclooxygenase-2 (COX-2) expression and DNA damage in the skin of the BALB/c-nu mice exposed to UVB for seven days in vivo. Importantly, Derinat blocked the transient receptor potential canonical (TRPC) channels (TRPCs), as demonstrated by calcium imaging. Together, our results indicate that Derinat acts as a TRPCs blocker to reduce intracellular ROS production and DNA damage upon UVB irradiation. This mechanism provides a potential new application of Derinat for the protection against UVB-induced skin damage and aging.

Oxidative stress increases pulmonary vascular permeability in diabetic rats through activation of transient receptor potential melastatin 2 channels

OBJECTIVE

In vitro superoxide activates pulmonary endothelial TRPM2 channels and increases Kf . We hypothesized that pulmonary capillary Kf is increased in a model of type I diabetes due to elevated vascular superoxide and resultant TRPM2 channel activation.

METHODS

Type I diabetes was induced in Zucker rats using STZ. Half of the STZ animals were treated with apocynin, a NOX inhibitor. After four weeks, lung Kf was measured in the isolated lung in the presence or absence of TRPM2 inhibitors (2-APB and FA). In an additional set of experiments, Kf was measured in nondiabetic Zucker rats after applying the superoxide donor (PMS).

RESULTS

As compared to control rats, hyperglycemic rats exhibited increased vascular superoxide and Kf , along with decreased lung vascular TRPM2-L expression. Apocynin treatment reduced superoxide and Kf in hyperglycemic rats with no effect in control rats. TRPM2 channel inhibition decreased Kf in hyperglycemic rats with no effect in control rats. PMS increased the lung Kf in control rats, with TRPM2 inhibition attenuating this response.

CONCLUSION

Diabetic rats exhibit a TRPM2-mediated increase in lung Kf , which is associated with increased TRPM2 activation and increased vascular superoxide levels.

Pathobiology of acute respiratory distress syndrome

The unique characteristics of pulmonary circulation and alveolar-epithelial capillary-endothelial barrier allow for maintenance of the air-filled, fluid-free status of the alveoli essential for facilitating gas exchange, maintaining alveolar stability, and defending the lung against inhaled pathogens. The hallmark of pathophysiology in acute respiratory distress syndrome is the loss of the alveolar capillary permeability barrier and the presence of protein-rich edema fluid in the alveoli. This alteration in permeability and accumulation of fluid in the alveoli accompanies damage to the lung epithelium and vascular endothelium along with dysregulated inflammation and inappropriate activity of leukocytes and platelets. In addition, there is uncontrolled activation of coagulation along with suppression of fibrinolysis and loss of surfactant. These pathophysiological changes result in the clinical manifestations of acute respiratory distress syndrome, which include hypoxemia, radiographic opacities, decreased functional residual capacity, increased physiologic deadspace, and decreased lung compliance. Resolution of acute respiratory distress syndrome involves the migration of cells to the site of injury and re-establishment of the epithelium and endothelium with or without the development of fibrosis. Most of the data related to acute respiratory distress syndrome, however, originate from studies in adults or in mature animals with very few studies performed in children or juvenile animals. The lack of studies in children is particularly problematic because the lungs and immune system are still developing during childhood and consequently the pathophysiology of pediatric acute respiratory distress syndrome may differ in significant ways from that seen in acute respiratory distress syndrome in adults. This article describes what is known of the pathophysiologic processes of pediatric acute respiratory distress syndrome as we know it today while also presenting the much greater body of evidence on these processes as elucidated by adult and animal studies. It is also our expressed intent to generate enthusiasm for larger and more in-depth investigations of the mechanisms of disease and repair specific to children in the years to come.

MicroRNA-26a prevents endothelial cell apoptosis by directly targeting TRPC6 in the setting of atherosclerosis

Atherosclerosis, a chronic inflammatory disease, is the major cause of life-threatening complications such as myocardial infarction and stroke. Endothelial apoptosis plays a vital role in the initiation and progression of atherosclerotic lesions. Although a subset of microRNAs (miRs) have been identified as critical regulators of atherosclerosis, studies on their participation in endothelial apoptosis in atherosclerosis have been limited. In our study, we found that miR-26a expression was substantially reduced in the aortic intima of ApoE^−/− mice fed with a high-fat diet (HFD). Treatment of human aortic endothelial cells (HAECs) with oxidized low-density lipoprotein (ox-LDL) suppressed miR-26a expression. Forced expression of miR-26a inhibited endothelial apoptosis as evidenced by MTT assay and TUNEL staining results. Further analysis identified TRPC6 as a target of miR-26a, and TRPC6 overexpression abolished the anti-apoptotic effect of miR-26a. Moreover, the cytosolic calcium and the mitochondrial apoptotic pathway were found to mediate the beneficial effects of miR-26a on endothelial apoptosis. Taken together, our study reveals a novel role of miR-26a in endothelial apoptosis and indicates a therapeutic potential of miR-26a for atherosclerosis associated with apoptotic cell death.

Mechanisms regulating endothelial permeability

The endothelial monolayer partitioning underlying tissue from blood components in the vessel wall maintains tissue fluid balance and host defense through dynamically opening intercellular junctions. Edemagenic agonists disrupt endothelial barrier function by signaling the opening of the intercellular junctions leading to the formation of protein-rich edema in the interstitial tissue, a hallmark of tissue inflammation that, if left untreated, causes fatal diseases, such as acute respiratory distress syndrome. In this review, we discuss how intercellular junctions are maintained under normal conditions and after stimulation of endothelium with edemagenic agonists. We have focused on reviewing the new concepts dealing with the alteration of adherens junctions after inflammatory stimulus.

The essential role of transient receptor potential vanilloid 1 in simvastatin-induced activation of endothelial nitric oxide synthase and angiogenesis

AIMS

We investigated the role of transient receptor potential vanilloid receptor type 1 (TRPV1) in simvastatin-mediated activation of endothelial nitric oxide synthase (eNOS) and angiogenesis.

METHODS

Fluo-8 NW assay was for Ca(2+) detection; Griess's assay was for NO bioavailability; Western blotting and immunoprecipitation were for protein phosphorylation and interaction; tube formation and Matrigel plug assay were for angiogenesis.

RESULTS

In endothelial cells (ECs), treatment with simvastatin time-dependently increased intracellular level of Ca(2+). Pharmacological inhibition or genetic disruption of TRPV1 abrogated simvastatin-mediated elevation of intracellular Ca(2+) in ECs or TRPV1-transfected HEK293 cells. Loss of TRPV1 function abolished simvastatin-induced NO production and phosphorylation of eNOS and calmodulin protein kinase II (CaMKII) in ECs and in aortas of mice. Inhibition of TRPV1 activation prevented the simvastatin-elicited increase in the formation of TRPV1-Akt-CaMKII-AMPK-eNOS complex. In mice, Matrigel plug assay showed that simvastatin-evoked angiogenesis was abolished by TRPV1 antagonist and genetic ablation of TRPV1. Additionally, our results demonstrated that TRP ankyrin 1 (TRPA1) is the downstream effector in the simvastatin-activated TRPV1-Ca(2+) signalling and in the consequent NO production and angiogenesis as evidence by that re-expression of TRPA1 further augmented simvastatin-elicited Ca(2+) influx in TRPV1-expressed HEK293 cells and ablation of TRPA1 function profoundly inhibited the simvastatin-induced increase in the phosphorylation of eNOS and CaMKII, formation of TRPV1-Akt-CaMKII-AMPK-eNOS complex, NO bioavailability, tube formation and angiogenesis in ECs or mice.

CONCLUSION

Simvastatin-induced Ca(2+) influx may through the activation of TRPV1-TRPA1 signalling, which leads to phosphorylation of CaMKII, increases in the formation of TRPV1-CaMKII-AMPK-eNOS complex, eNOS activation, NO production and, ultimately, angiogenesis in ECs.

Extracellular disulfide bridges stabilize TRPC5 dimerization, trafficking, and activity

Crucial cysteine residues can be involved in the modulation of protein activity via the modification of thiol (-SH) groups. Among these reactions, disulfide bonds (S-S) play a key role in the folding, stability, and activity of membrane proteins. However, the regulation of extracellular cysteines in classical transient receptor potential (TRPC) channels remains controversial. Here, we examine the functional importance of the extracellular disulfide bond in TRPC5 in modulating channel gating and trafficking. Specifically, we investigated TRPC5 activity in transiently transfected HEK293 cells with wild-type (WT) or cysteine (C553 and C558) mutants in the pore loop. Using reducing agents, we determined that a disulfide linkage mediates the tetrameric formation of the TRPC5 channel. By measuring the TRPC5 current, we observed that C553S or C558S mutants completely lose channel activity induced by lanthanides or receptor stimulation. Co-expression of TRPC5 (WT) with mutants demonstrated a dominant-negative function in mutants, which inhibited the activity of TRPC5 (WT). We generated TRPC5-TRPC5 dimers and observed reduced activity of WT-mutant (C553S or C558S) dimers compared to WT-WT dimers. When pretreated with reducing agents for 12 h, the TRPC5 current decreased due to a reduction in membrane TRPC5 distribution. In addition, we identified a reduced expression of C553S mutant in plasma membrane. We analyzed a dimeric interaction of wild-type and mutant TRPC5 using co-immunoprecipitation and FRET method, indicating a weak interaction between dimeric partners. These results indicated that the disulfide bond between conserved extracellular cysteines, especially C553, is essential for functional TRPC5 activity by channel multimerization and trafficking.

TRPC5

Human canonical transient receptor potential channel 5 (TRPC5) has been cloned from the Xq23 region on chromosome X as a suspect in nonsyndromic mental retardation. TRPC5 is a Ca(2+)-permeable cation channel predominantly expressed in the CNS, including the hippocampus, cerebellum, amygdala, sensory neurons, and retina. It also shows more restricted expression in the periphery, notably in the kidney and cardiovascular system. Homotetrameric TRPC5 channels are primarily activated by receptors coupled to Gq and phospholipase C and/or Gi proteins, but TRPC5 channels may also gate in a store-dependent manner, which requires other partner proteins such TRPC1, STIM1, and Orai1. There is an impressive array of other activators of TRPC5 channels, such as nitric oxide, lysophospholipids, sphingosine-1-phosphate, reduced thioredoxin, protons, lanthanides, and calcium, and many can cause its direct activation. Moreover, TRPC5 shows constitutive activity, and it is responsive to membrane stretch and cold. Thus, TRPC5 channels have significant potential for synergistic activation and may serve as an important focal point in Ca(2+) signalling and electrogenesis. Moreover, TRPC5 functions in partnership with about 60 proteins, including TRPC1, TRPC4, calmodulin, IP3 receptors, NHERF, NCS-1, junctate, stathmin 2, Ca(2+)-binding protein 1, caveolin, and SESTD1, while its desensitisation is mediated by both protein kinases A and C. TRPC5 has a distinct voltage dependence shared only with its closest relative, TRPC4. Its unique N-shaped activation curve underlined by intracellular Mg(2+) block seems to be perfectly "shaped" to trigger action potential discharge, but not to grossly interfere with the action potential shape. The range of biological functions of TRPC5 channels is also impressive, from neurotransmission to control of axon guidance and vascular smooth muscle cell migration and contractility. Recent studies of Trpc5 gene knockouts begin to uncover its roles in fear, anxiety, seizures, and cold sensing.

New insights into TRP channels: Interaction with pattern recognition receptors

An increasing number of studies have implicated that the activation of innate immune system and inflammatory mechanisms are of importance in the pathogenesis of numerous diseases. The innate immune system is present in almost all multicellular organisms in response to pathogens or tissue injury, which is performed via germ-line encoded pattern-recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs) or dangers-associated molecular patterns (DAMPs). Intracellular pathways linking immune and inflammatory response to ion channel expression and function have been recently identified. Among ion channels, transient receptor potential (TRP) channels are a major family of non-selective cation-permeable channels that function as polymodal cellular sensors involved in many physiological and pathological processes. In this review, we summarize current knowledge about classifications, functions, and interactions of TRP channels and PRRs, which may provide new insights into their roles in the pathogenesis of inflammatory diseases.

Recruitment of dynamic endothelial Ca2+ signals by the TRPA1 channel activator AITC in rat cerebral arteries

OBJECTIVE

Stimulation of endothelial TRP channels, specifically TRPA1, promotes vasodilation of cerebral arteries through activation of Ca2+ -dependent effectors along the myoendothelial interface. However, presumed TRPA1-triggered endothelial Ca2+ signals have not been described. We investigated whether TRPA1 activation induces specific spatial and temporal changes in Ca2+ signals along the intima that correlates with incremental vasodilation.

METHODS

Confocal imaging, immunofluorescence staining, and custom image analysis were employed.

RESULTS

We found that endothelial cells of rat cerebral arteries exhibit widespread basal Ca2+ dynamics (44 ± 6 events/minute from 26 ± 3 distinct sites in a 3.6 × 10(4) μm2 field). The TRPA1 activator AITC increased Ca2+ signals in a concentration-dependent manner, soliciting new events at distinct sites. Origination of these new events corresponded spatially with TRPA1 densities in IEL holes, and the events were prevented by the TRPA1 inhibitor HC-030031. Concentration-dependent expansion of Ca2+ events in response to AITC correlated precisely with dilation of pressurized cerebral arteries (p = 0.93 by F-test). Correspondingly, AITC caused rapid endothelium-dependent suppression of asynchronous Ca2+ waves in subintimal smooth muscle.

CONCLUSIONS

Our findings indicate that factors that stimulate TRPA1 channels expand Ca2+ signal-effector coupling at discrete sites along the endothelium to evoke graded cerebral artery vasodilation.

Vasorelaxant action of an ethylacetate fraction of Euphorbia humifusa involves NO-cGMP pathway and potassium channels

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia humifusa Willd. (EH) is an important traditional Chinese medicine that has commonly been used for treating bacillary dysentery and enteritis in many Asian countries for thousands of years. EH has a wide variety of pharmacological actions such as antioxidant, hypotensive, and hypolipidemic effects. However, the mechanisms involved are to be defined.

AIM OF THE STUDY

The present study was performed to evaluate the cardiovascular effects of EH in rats.

MATERIALS AND METHODS

Methanol extract of EH (MEH) and ethylacetate fraction of the MEH (EEH) was examined for their vascular relaxant effects in phenylephrine-precontracted aortic rings. Effects of EEH on systolic blood pressure and heart rate were tested in Sprague-Dawley rats.

RESULTS

MEH and EEH induced vasorelaxation in a concentration-dependent manner. Endothelium-denudation abolished the EEH-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N(G)-nitro-L-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) significantly inhibited the EEH-induced vasorelaxation. EEH increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME or ODQ. Extracellular Ca(2+) depletion and treatments with thapsigargin, Gd(3+), and 2-aminoethyl diphenylborinate significantly attenuated the EEH-induced vasorelaxation. Wortmannin markedly attenuated the EEH-induced vasorelaxation. In addition, tetraethylammonium, iberiotoxin, and charybdotoxin, but not apamin, attenuated the EEH-induced vasorelaxation. Glibenclamide, indomethacin, atropine, and propranolol had no effects on the EEH-induced vasorelaxation. Furthermore, EEH decreased systolic blood pressure and heart rate in a concentration-dependent manner in rats.

CONCLUSIONS

The present study demonstrates that EEH induces endothelium-dependent vasorelaxation via eNOS-NO-cGMP signaling through the modification of intracellular Ca(2+), Ca(2+) entry, and large- and intermediate-conductance KCa channel homeostasis. The data also suggest that the Akt-eNOS pathway is involved in the EEH-induced vasorelaxation. EEH induces hypotension and bradycardia in vivo.

Double-stranded RNA attenuates the barrier function of human pulmonary artery endothelial cells

Circulating RNA may result from excessive cell damage or acute viral infection and can interact with vascular endothelial cells. Despite the obvious clinical implications associated with the presence of circulating RNA, its pathological effects on endothelial cells and the governing molecular mechanisms are still not fully elucidated. We analyzed the effects of double stranded RNA on primary human pulmonary artery endothelial cells (hPAECs). The effect of natural and synthetic double-stranded RNA (dsRNA) on hPAECs was investigated using trans-endothelial electric resistance, molecule trafficking, calcium (Ca²⁺) homeostasis, gene expression and proliferation studies. Furthermore, the morphology and mechanical changes of the cells caused by synthetic dsRNA was followed by in-situ atomic force microscopy, by vascular-endothelial cadherin and F-actin staining. Our results indicated that exposure of hPAECs to synthetic dsRNA led to functional deficits. This was reflected by morphological and mechanical changes and an increase in the permeability of the endothelial monolayer. hPAECs treated with synthetic dsRNA accumulated in the G1 phase of the cell cycle. Additionally, the proliferation rate of the cells in the presence of synthetic dsRNA was significantly decreased. Furthermore, we found that natural and synthetic dsRNA modulated Ca²⁺ signaling in hPAECs by inhibiting the sarco-endoplasmic Ca²⁺-ATPase (SERCA) which is involved in the regulation of the intracellular Ca²⁺ homeostasis and thus cell growth. Even upon synthetic dsRNA stimulation silencing of SERCA3 preserved the endothelial monolayer integrity. Our data identify novel mechanisms by which dsRNA can disrupt endothelial barrier function and these may be relevant in inflammatory processes.

Endothelial transient receptor potential conical channel (TRPC)-3 activation induces vasogenic edema formation in the rat piriform cortex following status epilepticus

Transient receptor potential canonical channel (TRPC) is a nonselective cation channel permeable to Ca(2+), which express in many cell types, including neurons. However the alterations in TRPC receptor expressions in response to status epilepticus (SE) have not been explored. Therefore, the present study was designated to elucidate the roles of TRPC3 in neuronal death and vasogenic edema within the rat piriform cortex (PC) following SE. In non-SE animals, TRPC3 immunoreactivity was abundantly detected in the PC. Following SE, TRPC3 immunoreactivity was increased in neurons. Furthermore, TRPC3 expression was detected in endothelial cells that did not contain it in non-SE animals. Loss of SMI-71 (a blood-brain barrier antigen) immunoreactivity was also observed in TRPC3 positive endothelial cells. In addition, FJB positive neurons and vasogenic edema were noticeably detected in the PC. To directly determine whether TRPC3 activation is correlated to SE-induced vasogenic edema formation and neuronal damages in the PC, the effect of Pyr-3 (a TRPC3 antagonist) on SE-induced insults were investigated. Pyr-3 infusion effectively attenuated vasogenic edema in the PC as compared to the vehicle. Therefore, our findings indicate that TRPC3 activation/overexpression induced by SE may involve BBB disruption and neuronal damages in the rat PC following SE. Therefore, the present study was TRPC3 may play an important role in SE-induced vasogenic edema formation through BBB disruptions in the rat PC.

Characterization of shear-sensitive genes in the normal rat aorta identifies Hand2 as a major flow-responsive transcription factor

Objective

Shear forces play a key role in the maintenance of vessel wall integrity. Current understanding regarding shear-dependent gene expression is mainly based on in vitro or in vivo observations with experimentally deranged shear, hence reflecting acute molecular events in relation to flow. Our objective was to combine computational fluid dynamic (CFD) simulations with global microarray analysis to study flow-dependent vessel wall biology in the aortic wall under physiological conditions.

Methods and Results

Male Wistar rats were used. Animal-specific wall shear stress (WSS) magnitude and vector direction were estimated using CFD based on aortic geometry and flow information acquired by magnetic resonance imaging. Two distinct flow pattern regions were identified in the normal rat aortic arch; the distal part of the lesser curvature being exposed to low WSS and a non-uniform vector direction, and a region along the greater curvature being subjected to markedly higher levels of WSS and a uniform vector direction. Microarray analysis identified numerous novel mechanosensitive genes, including Trpc4 and Fgf12, and confirmed well-known ones, e.g. Klf2 and Nrf2. Gene ontology analysis revealed an over-representation of genes involved in transcriptional regulation. The most differentially expressed gene, Hand2, is a transcription factor previously shown to be involved in extracellular matrix remodeling. HAND2 protein was endothelial specific and showed higher expression in the regions exposed to low WSS with disturbed flow.

Conclusions

Microarray analysis validated the CFD-defined WSS regions in the rat aortic arch, and identified numerous novel shear-sensitive genes. Defining the functional importance of these genes in relation to atherosusceptibility may provide important insight into the understanding of vascular pathology.

The vascular barrier-protecting hawthorn extract WS® 1442 raises endothelial calcium levels by inhibition of SERCA and activation of the IP3 pathway

WS® 1442 has been proven as an effective and safe therapeutical to treat mild forms of congestive heart failure. Beyond this action, we have recently shown that WS® 1442 protects against thrombin-induced vascular barrier dysfunction and the subsequent edema formation by affecting endothelial calcium signaling. The aim of the study was to analyze the influence of WS® 1442 on intracellular calcium concentrations [Ca(2+)](i) in the human endothelium and to investigate the underlying mechanisms. Using ratiometric calcium measurements and a FRET sensor, we found that WS® 1442 concentration-dependently increased basal [Ca(2+)](i) by depletion of the endoplasmic reticulum (ER) and inhibited a subsequent histamine-triggered rise of [Ca(2+)](i). Interestingly, the augmented [Ca(2+)](i) did neither trigger an activation of the contractile machinery nor led to a barrier breakdown (macromolecular permeability). It also did not impair endothelial cell viability. As assessed by patch clamp recordings, WS® 1442 did only slightly affect endothelial Na(+)/K(+)-ATPase, but increased [Ca(2+)](i) by inhibiting the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA) and by activating the inositol 1,4,5-trisphosphate (IP(3)) pathway. Most importantly, WS® 1442 did not induce store-operated calcium entry (SOCE), but even irreversibly prevented histamine-induced SOCE. Taken together, WS® 1442 prevented the deleterious hyperpermeability-associated rise of [Ca(2+)](i) by a preceding, non-toxic release of Ca(2+) from the ER. WS® 1442 interfered with SERCA and the IP(3) pathway without inducing SOCE. The elucidation of this intriguing mechanism helps to understand the complex pharmacology of the cardiovascular drug WS® 1442.

Malathion/Oxon and Lead Acetate Increase Gene Expression and Protein Levels of Transient Receptor Potential Canonical Channel Subunits TRPC1 and TRPC4 in Rat Endothelial Cells of the Blood–Brain Barrier

This study examined the effects of malathion and lead on transient receptor potential canonical channel TRPC1/TRPC4 channels in rat brain endothelial cells as a mechanism to explain previously noted blood–brain barrier (BBB) permeability induced by these compounds. Lead, malathion, malaoxon and combinations of these were assessed for protein levels and gene expression of TRPC1/C4 at 2, 4, 8, 16, and 24 hours after exposure. Changes in intracellular free calcium dynamics were also assessed. Compounds increased TRPC1 and TRPC4 protein levels as well as gene expression within 4 hours after exposure. Basal levels of intracellular free calcium were also elevated. Increases in gene and protein expression may be associated with an increase in the numbers of TRP channels, and the increases in intracellular calcium may be associated with activation of such channels. Therefore, upregulation and activation of the TRPC1/TRPC4 may be a mechanism by which these neurotoxicants affect BBB permeability.

Lung endothelial Ca2+ and permeability response to platelet-activating factor is mediated by acid sphingomyelinase and transient receptor potential classical 6

RATIONALE

Platelet-activating factor (PAF) increases lung vascular permeability within minutes by activation of acid sphingomyelinase (ASM) and a subsequent nitric oxide (NO)-inhibitable and Ca(2+)-dependent loss in barrier function.

OBJECTIVES

To elucidate the molecular mechanisms underlying this response.

METHODS

In isolated perfused rat and mouse lungs, endothelial Ca(2+) concentration ([Ca(2+)](i)) was quantified by real-time fluorescence imaging, and caveolae of endothelial cells were isolated and probed for Ca(2+) entry channels. Regulation of transient receptor potential classical (TRPC) 6-mediated currents in lung endothelial cells was assessed by patch clamp technique.

MEASUREMENTS AND MAIN RESULTS

PAF increased lung weight gain and endothelial [Ca(2+)](i). This response was abrogated by inhibitors of ASM or in ASM-deficient mice, and replicated by lung perfusion with exogenous ASM or C2-ceramide. PAF increased the caveolar abundance of TRPC6 channels, which was similarly blocked by ASM inhibition. PAF-induced increases in lung endothelial [Ca(2+)](i), vascular filtration coefficient, and edema formation were attenuated by the TRPC inhibitor SKF96365 and in TRPC6-deficient mice, whereas direct activation of TRPC6 replicated the [Ca(2+)](i) and edema response to PAF. The exogenous NO donor PapaNONOate or the cyclic guanosine 3',5'-monophosphate analog 8Br-cGMP blocked the endothelial [Ca(2+)](i) and permeability response to PAF, in that they directly blocked TRPC6 channels without interfering with their PAF-induced recruitment to caveolae.

CONCLUSIONS

The present findings outline a new signaling cascade in the induction of PAF-induced lung edema, in that stimulation of ASM causes recruitment of TRPC6 channels to caveolae, thus allowing for Ca(2+) influx and subsequent increases in endothelial permeability that are amplified in the absence of endothelial NO synthesis.

Regulation of cardiovascular TRP channel functions along the NO-cGMP-PKG axis

There is growing body of evidence that nitric oxide (NO)-cGMP-PKG signaling plays a central role in negative regulation of cardiovascular (CV) responses and its disorders through suppressed Ca(2+) dynamics. Other lines of evidence also reveal the stimulatory effects of this signaling on some CV functions. Recently, transient receptor potential (TRP) channels have received much attention as non-voltage-gated Ca(2+) channels involved in CV physiology and pathophysiology. Available information suggests that these channels undergo both inhibition and activation by NO via PKG-mediated phosphorylation and S-nitrosylation, respectively, and also act as upstream regulators to promote endothelial NO production. This review summarizes the roles of NO-cGMP-PKG signaling pathway, particularly in regulating TRP channel functions with their associated physiology and pathophysiology.

Heterotrimeric G proteins, focal adhesion kinase, and endothelial barrier function

Ligands by binding to G protein coupled receptors (GPCRs) stimulate dissociation of heterotrimeric G proteins into Gα and Gβγ subunits. Released Gα and Gβγ subunits induce discrete signaling cues that differentially regulate focal adhesion kinase (FAK) activity and endothelial barrier function. Activation of G proteins downstream of receptors such as protease activated receptor 1 (PAR1) and histamine receptors rapidly increases endothelial permeability which reverses naturally within the following 1-2 h. However, activation of G proteins coupled to the sphingosine-1-phosphate receptor 1 (S1P1) signal cues that enhance basal barrier endothelial function and restore endothelial barrier function following the increase in endothelial permeability by edemagenic agents. Intriguingly, both PAR1 and S1P1 activation stimulates FAK activity, which associates with alteration in endothelial barrier function by these agonists. In this review, we focus on the role of the G protein subunits downstream of PAR1 and S1P1 in regulating FAK activity and endothelial barrier function.

Klotho is associated with VEGF receptor-2 and the transient receptor potential canonical-1 Ca2+ channel to maintain endothelial integrity

Klotho is a circulating protein, and Klotho deficiency disturbs endothelial integrity, but the molecular mechanism is not fully clarified. We report that vascular endothelium in Klotho-deficient mice showed hyperpermeability with increased apoptosis and down-regulation of vascular endothelial (VE)-cadherin because of an increase in VEGF-mediated internal calcium concentration ([Ca(2+)]i) influx and hyperactivation of Ca(2+)-dependent proteases. Immunohistochemical analysis, the pull-down assay using Klotho-fixed agarose, and FRET confocal imaging confirmed that Klotho protein binds directly to VEGF receptor 2 (VEGFR-2) and endothelial, transient-receptor potential canonical Ca(2+) channel 1 (TRPC-1) and strengthens the association to promote their cointernalization. An in vitro mutagenesis study revealed that the second hydrolase domain of Klotho interacts with sixth and seventh Ig domains of VEGFR-2 and the third extracellular loop of TRPC-1. In Klotho-deficient endothelial cells, VEGF-mediated internalization of the VEGFR-2/TRPC-1 complex was impaired, and surface TRPC-1 expression increased 2.2-fold; these effects were reversed by supplementation of Klotho protein. VEGF-mediated elevation of [Ca(2+)]i was sustained at higher levels in an extracellular Ca(2+)-dependent manner, and normalization of TRCP-1 expression restored the abnormal [Ca(2+)]i handling. These findings provide evidence that Klotho protein is associated with VEGFR-2/TRPC-1 in causing cointernalization, thus regulating TRPC-1-mediated Ca(2+) entry to maintain endothelial integrity.

The role of transient receptor potential cation channels in Ca2+ signaling

The 28 mammalian members of the super-family of transient receptor potential (TRP) channels are cation channels, mostly permeable to both monovalent and divalent cations, and can be subdivided into six main subfamilies: the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and the TRPA (ankyrin) groups. TRP channels are widely expressed in a large number of different tissues and cell types, and their biological roles appear to be equally diverse. In general, considered as polymodal cell sensors, they play a much more diverse role than anticipated. Functionally, TRP channels, when activated, cause cell depolarization, which may trigger a plethora of voltage-dependent ion channels. Upon stimulation, Ca2+ permeable TRP channels generate changes in the intracellular Ca2+ concentration, [Ca2+]i, by Ca2+ entry via the plasma membrane. However, more and more evidence is arising that TRP channels are also located in intracellular organelles and serve as intracellular Ca2+ release channels. This review focuses on three major tasks of TRP channels: (1) the function of TRP channels as Ca2+ entry channels; (2) the electrogenic actions of TRPs; and (3) TRPs as Ca2+ release channels in intracellular organelles.

Sphingosine kinase inhibition alleviates endothelial permeability induced by thrombin and activated neutrophils

Inflammation and microvascular thrombosis are interrelated causes of acute lung injury in the systemic inflammatory response syndrome. Neutrophils (polymorphonuclear neutrophil [PMN]) and endothelial cells (EC) activated by systemic inflammatory response syndrome interact to increase pulmonary vascular permeability, but the interactions between PMN and EC are difficult to study. Recently, we reported that sphingosine 1-phosphate is a second messenger eliciting store-operated calcium entry (SOCE) in response to inflammatory agonists in both PMN and EC. Store-operated calcium entry is therefore a target mechanism for the therapeutic modulation of inflammatory PMN-EC interactions. Here, we isolated, modeled, and studied the effects of pharmacologic SOCE inhibition using real-time systems to monitor EC permeability after exposure to activated PMN. We created systems to continuously assess permeability of human pulmonary artery endothelial cells and human microvascular endothelial cells from lung. Endothelial cells show increased permeability after challenge by activated PMN. Such permeability increases can be attenuated by exposure of the cocultures to sphingosine kinase (SK) inhibitors (SKI-2, N,N-dimethylsphingosine [DMS]) or Ca2+ entry inhibitors (Gd3+, MRS-1845). Human microvascular endothelial cells from lung pretreated with SKI-2 or DMS showed decreased permeability when later exposed to activated PMN. Likewise, when PMNs were activated with thapsigargin (TG) in the presence of SKI-2, DMS, Gd, or MRS-1845, their ability to cause EC permeability subsequently was reduced. SKI-2 also inhibited the activation of human pulmonary artery ECs by thrombin. These studies will provide a firm mechanistic foundation for understanding how systemic SOCE inhibition may be used to prevent acute lung injury in vivo.

Cerebral ischemia-reperfusion injury in rats--a 3 T MRI study on biphasic blood-brain barrier opening and the dynamics of edema formation

Serial magnetic resonance imaging (MRI) was performed to investigate the temporal and spatial relationship between the biphasic nature of blood-brain barrier (BBB) opening and, in parallel, edema formation after ischemia-reperfusion (I/R) injury in rats. T(2)-weighted imaging combined with T(2)-relaxometry, mainly for edema assessment, was performed at 1 h after ischemia, after reperfusion, and at 4, 24 and 48 h after reperfusion. T(1)-weighted imaging was performed before and after gadolinium contrast at the last three time points to assess BBB integrity. The biphasic course of BBB opening with a significant reduction in BBB permeability at 24 h after reperfusion, associated with a progressive expansion of leaky BBB volume, was accompanied by a peak ipsilateral edema formation. In addition, at 4 h after reperfusion, edema formation could also be detected at the contralateral striatum as determined by the elevated T(2)-values that persisted to varying degrees, indicative of widespread effects of I/R injury. The observations of this study may indicate a dynamic temporal shift in the mechanisms responsible for biphasic BBB permeability changes, with complex relations to edema formation. Stroke therapy aimed at vasogenic edema and drug delivery for neuroprotection may also be guided according to the functional status of the BBB, and these findings have to be confirmed in human stroke.