TRPA1 promotes the maturation of embryonic stem cell-derived cardiomyocytes by regulating mitochondrial biogenesis and dynamics

BACKGROUND

Cardiomyocytes derived from pluripotent stem cells (PSC-CMs) have been widely accepted as a promising cell source for cardiac drug screening and heart regeneration therapies. However, unlike adult cardiomyocytes, the underdeveloped structure, the immature electrophysiological properties and metabolic phenotype of PSC-CMs limit their application. This project aimed to study the role of the transient receptor potential ankyrin 1 (TRPA1) channel in regulating the maturation of embryonic stem cell-derived cardiomyocytes (ESC-CMs).

METHODS

The activity and expression of TRPA1 in ESC-CMs were modulated by pharmacological or molecular approaches. Knockdown or overexpression of genes was done by infection of cells with adenoviral vectors carrying the gene of interest as a gene delivery tool. Immunostaining followed by confocal microscopy was used to reveal cellular structure such as sarcomere. Staining of mitochondria was performed by MitoTracker staining followed by confocal microscopy. Calcium imaging was performed by fluo-4 staining followed by confocal microscopy. Electrophysiological measurement was performed by whole-cell patch clamping. Gene expression was measured at mRNA level by qPCR and at protein level by Western blot. Oxygen consumption rates were measured by a Seahorse Analyzer.

RESULTS

TRPA1 was found to positively regulate the maturation of CMs. TRPA1 knockdown caused nascent cell structure, impaired Ca²⁺ handling and electrophysiological properties, and reduced metabolic capacity in ESC-CMs. The immaturity of ESC-CMs induced by TRPA1 knockdown was accompanied by reduced mitochondrial biogenesis and fusion. Mechanistically, we found that peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), the key transcriptional coactivator related to mitochondrial biogenesis and metabolism, was downregulated by TRPA1 knockdown. Interestingly, overexpression of PGC-1α ameliorated the halted maturation induced by TRPA1 knockdown. Notably, phosphorylated p38 MAPK was upregulated, while MAPK phosphatase-1 (MKP-1), a calcium-sensitive MAPK inhibitor, was downregulated in TRPA1 knockdown cells, suggesting that TRPA1 may regulate the maturation of ESC-CMs through MKP-1-p38 MAPK-PGC-1α pathway.

CONCLUSIONS

Taken together, our study reveals the novel function of TRPA1 in promoting the maturation of CMs. As multiple stimuli have been known to activate TRPA1, and TRPA1-specific activators are also available, this study provides a novel and straightforward strategy for improving the maturation of PSC-CMs by activating TRPA1. Since a major limitation for the successful application of PSC-CMs for research and medicine lies in their immature phenotypes, the present study takes a big step closer to the practical use of PSC-CMs.

Cytosolic delivery of CDK4/6 inhibitor p16 protein using engineered protein crystals for cancer therapy

The tumor suppressor p16 protein is an endogenous CDK4/6 inhibitor. Inactivation of its encoding gene is found in nearly half of human cancers. Restoration of p16 function via adenovirus-based gene delivery has been shown to be effective in suppressing aberrant cell growth in many types of cancer, however, the potential risk of insertional mutagenesis in genomic DNA remains a major concern. Thus, there has been great interest in developing efficient strategies to directly deliver proteins into cells as an alternative that can avoid such safety concerns while achieving a comparable therapeutic effect. Nevertheless, intracellular delivery of protein therapeutics remains a challenge. Our group has recently developed a protein delivery platform based on an engineered Pos3Aa protein that forms sub-micrometer-sized crystals in Bacillus thuringiensis cells. In this report, we describe the further development of this platform (Pos3AaTM) via rationally designed site-directed mutagenesis, and its resultant potency for the delivery of cargo proteins into cells. Pos3AaTM-based fusion protein crystals are shown to exhibit improved release of their cargo proteins as demonstrated using a model mCherry protein. Importantly, this Pos3AaTM platform is able to mediate the efficient intracellular delivery of p16 protein with significant endosomal escape, resulting in p16-mediated inhibition of CDK4/6 kinase activity and Rb phosphorylation, and as a consequence, significant cell cycle arrest and cell growth inhibition. These results validate the ability of these improved Pos3AaTM crystals to mediate enhanced cytosolic protein delivery and highlight the potential of using protein therapeutics as selective CDK4/6 inhibitors for cancer therapy. STATEMENT OF SIGNIFICANCE: Cytosolic delivery of bioactive therapeutic proteins capable of eliciting therapeutic benefit remains a significant challenge. We have previously developed a protein delivery platform based on engineered Pos3Aa protein crystals with excellent cell-permeability and endosomal escape properties. In this report, we describe the rational design of an improved Pos3Aa triple mutant (Pos3AaTM) with enhanced cargo release. We demonstrate that Pos3AaTM-mCherry-p16 fusion crystals can efficiently deliver p16 protein, a CDK4/6 inhibitor frequently inactivated in human cancers, into p16-deficient UM-SCC-22A cells, where it promotes significant G1 cell cycle arrest and cell growth inhibition. These results highlight the ability of the Pos3AaTM platform to promote potent cytosolic delivery of protein therapeutics, and the efficacy of p16 protein delivery as an effective strategy for treating cancer.

Remdesivir induces persistent mitochondrial and structural damage in human induced pluripotent stem cell derived cardiomyocytes

AIMS

Remdesivir is a prodrug of an adenosine triphosphate analogue and is currently the only drug formally approved for the treatment of hospitalised COVID-19 patients. Nucleoside/nucleotide analogues have been shown to induce mitochondrial damage and cardiotoxicity, and this may be exacerbated by hypoxia, which frequently occurs in severe COVID-19 patients. Although there have been few reports of adverse cardiovascular events associated with remdesivir, clinical data are limited. Here, we investigated whether remdesivir induced cardiotoxicity using an in vitro human cardiac model.

METHODS AND RESULTS

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were exposed to remdesivir under normoxic and hypoxic conditions to simulate mild and severe COVID-19 respectively. Remdesivir induced mitochondrial fragmentation, reduced redox potential and suppressed mitochondrial respiration at levels below the estimated plasma concentration under both normoxic and hypoxic conditions. Non-mitochondrial damage such as electrophysiological alterations and sarcomere disarray were also observed. Importantly, some of these changes persisted after the cessation of treatment, culminating in increased cell death. Mechanistically, we found that inhibition of DRP1, a regulator of mitochondrial fission, ameliorated the cardiotoxic effects of remdesivir, showing that remdesivir-induced cardiotoxicity was preventable and excessive mitochondrial fission might contribute to this phenotype.

CONCLUSIONS

Using an in vitro model, we demonstrated that remdesivir can induce cardiotoxicity in hiPSC-CMs at clinically relevant concentrations. These results reveal previously unknown potential side-effects of remdesivir and highlight the importance of further investigations with in vivo animal models and active clinical monitoring to prevent lasting cardiac damage to patients.

TRANSLATIONAL PERSPECTIVE

Adult cardiomyocytes have limited ability to regenerate, thus treatment-induced cardiotoxicity can potentially cause irreparable harm. Remdesivir is currently the only FDA approved treatment for COVID-19 but clinical safety data are limited. Using human pluripotent stem cell-derived cardiomyocytes, we revealed that remdesivir induced persistent mitochondrial and structural abnormalities at clinically relevant concentrations. We advise confirmatory experiments in in vivo animal models, investigations of cardioprotective strategies, and closer patient monitoring such that treatment-induced cardiotoxicity does not contribute to the long term sequelae of COVID-19 patients.

Extracellular and Intracellular Angiotensin II Regulate the Automaticity of Developing Cardiomyocytes via Different Signaling Pathways

Angiotensin II (Ang II) plays an important role in regulating various physiological processes. However, little is known about the existence of intracellular Ang II (iAng II), whether iAng II would regulate the automaticity of early differentiating cardiomyocytes, and the underlying mechanism involved. Here, iAng II was detected by immunocytochemistry and ultra-high performance liquid chromatography combined with electrospray ionization triple quadrupole tandem mass spectrometry in mouse embryonic stem cell–derived cardiomyocytes (mESC-CMs) and neonatal rat ventricular myocytes. Expression of AT₁R-YFP in mESC-CMs revealed that Ang II type 1 receptors were located on the surface membrane, while immunostaining of Ang II type 2 receptors (AT₂R) revealed that AT₂R were predominately located on the nucleus and the sarcoplasmic reticulum. While extracellular Ang II increased spontaneous action potentials (APs), dual patch clamping revealed that intracellular delivery of Ang II or AT₂R activator C21 decreased spontaneous APs. Interestingly, iAng II was found to decrease the caffeine-induced increase in spontaneous APs and caffeine-induced calcium release, suggesting that iAng II decreased spontaneous APs via the AT₂R- and ryanodine receptor–mediated pathways. This is the first study that provides evidence of the presence and function of iAng II in regulating the automaticity behavior of ESC-CMs and may therefore shed light on the role of iAng II in fate determination.

TRPC7 regulates the electrophysiological functions of embryonic stem cell-derived cardiomyocytes

Background

Biological pacemakers consisting of pluripotent stem cell-derived cardiomyocytes are potentially useful for treating bradycardia. However, tachyarrhythmia caused by derived cardiomyocytes themselves is one of main barriers hampering their clinical translation. An in-depth understanding of the mechanisms underlying the spontaneous action potential (a.k.a. automaticity) might provide potential approaches to solve this problem. The aim of this project is to study the role of canonical transient receptor potential isoform 7 (TRPC7) channels in regulating the automaticity of embryonic stem cell-derived cardiomyocytes (ESC-CMs).

Methods and results

By Western blotting, the expression of TRPC7 was found to be increased during the differentiation of mouse ESC-CMs (mESC-CMs). Adenovirus-mediated TRPC7 knockdown decreased while overexpression increased the frequency of Ca²⁺ transients (CaTs), local Ca²⁺ releases (LCRs), and action potentials (APs) as detected by confocal microscopy and whole-cell patch-clamping. TRPC7 was found to be positively associated with the activity of ryanodine receptor 2 (RyR2), sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA), and sodium-calcium exchanger (NCX) but not hyperpolarization-activated, cyclic nucleotide-gated channel (HCN), and inositol trisphosphate receptor (IP3R). Knockdown or overexpression of TRPC7 did not alter the expression of HCN4, Cav1.3, Cav3.1, Cav3.2, IP3R1, RyR2, and SERCA but positively regulated the phosphorylation of RyR2 at S2814 and phospholamban (PLN) at T17. Moreover, the positive regulation of APs by TRPC7 was Ca²⁺-dependent, as overexpression of N-terminus of TRPC7 (dominant negative of TRPC7) which diminished the Ca²⁺ permeability of TRPC7 decreased the AP frequency.

Conclusions

TRPC7 regulates the automaticity of mESC-CMs through two mechanisms. On the one hand, TRPC7 positively regulates the intracellular Ca²⁺ clock through the regulation of activities of both RyR2 and SERCA; on the other hand, TRPC7 also positively regulates the membrane clock via its influence on NCX activity. Altogether, our study reveals that TRPC7 is a potential drug target to manipulate the action potential firing rate of pluripotent stem cell-derived cardiomyocyte-based biological pacemakers to prevent tachyarrhythmia, a condition that might be encountered after transplantation.

TRPV1 channels regulate the automaticity of embryonic stem cell-derived cardiomyocytes through stimulating the Na+ /Ca2+ exchanger current

Calcium controls the excitation-contraction coupling in cardiomyocytes. Embryonic stem cell-derived cardiomyocytes (ESC-CMs) are an important cardiomyocyte source for regenerative medicine and drug screening. Transient receptor potential vanilloid 1 (TRPV1) channels are nonselective cation channels that permeate sodium and calcium. This study aimed to investigate whether TRPV1 channels regulate the electrophysiological characteristics of ESC-CMs. If yes, what is the mechanism behind? By immunostaining and subcellular fractionation, followed by western blotting, TRPV1 was found to locate intracellularly. The staining pattern of TRPV1 was found to largely overlap with that of the sarco/endoplasmic reticulum Ca²⁺ -ATPase, the sarcoplasmic reticulum (SR) marker. By electrophysiology and calcium imaging, pharmacological blocker of TRPV1 and the molecular tool TRPV1β (which could functionally knockdown TRPV1) were found to decrease the rate and diastolic depolarization slope of spontaneous action potentials, and the amplitude and frequency of global calcium transients. By calcium imaging, in the absence of external calcium, TRPV1-specific opener increased intracellular calcium; this increase was abolished by preincubation with caffeine, which could deplete SR calcium store. The results suggest that TRPV1 controls calcium release from the SR. By electrophysiology, TRPV1 blockade and functional knockdown of TRPV1 decreased the Na⁺ /Ca2⁺ exchanger (NCX) currents from both the forward and reverse modes, suggesting that sodium and calcium through TRPV1 stimulate the NCX activity. Our novel findings suggest that TRPV1 activity is important for regulating the spontaneous activity of ESC-CMs and reveal a novel interplay between TRPV1 and NCX in regulating the physiological functions of ESC-CMs.

Contamination profiles and health impact of benzothiazole and its derivatives in PM2.5 in typical Chinese cities

Although benzothiazole and its derivatives (BTHs) are considered emerging contaminants in diverse environments and organisms, little information is available about their contamination profiles and health impact in ambient particles. In this study, an optimized method of ultrasound-assisted extraction coupled with the selected reaction monitoring (SRM) mode of GC-EI-MS/MS was applied to characterize and analyze PM_2.5-bound BTHs from three cities of China (Guangzhou, Shanghai, and Taiyuan) during the winter of 2018. The total BTH concentration (ΣBTHs) in PM_2.5 samples from the three cities decreased in the order of Guangzhou > Shanghai > Taiyuan, independently of the PM_2.5 concentration. Despite the large variation in concentration of ΣBTHs in PM_2.5, 2-hydroxybenzothiazole (OTH) was always the predominant compound among the PM_2.5-bound BTHs and accounted for 50-80% of total BTHs in the three regions. Results from human exposure assessment and toxicity screening indicated that the outdoor exposure risk of PM_2.5-bound BTHs in toddlers was much higher than in adults, especially for OTH. The developmental and reproduction toxicity of OTH was further explored in vivo and in vitro. Exposure of mouse embryonic stem cells (mESCs) to OTH for 48 h significantly increased the intracellular reactive oxygen species (ROS) and induced DNA damage and apoptosis via the functionally activating p53 expression. In addition, the growth and development of zebrafish embryos were found to be severely affected after OTH treatment. An overall metabolomics study was conducted on the exposed zebrafish larvae. The results indicated that exposure to OTH inhibited the phenylalanine hydroxylation reaction, which further increased the accumulation of toxic phenylpyruvate and acetylphenylalanine in zebrafish. These findings provide important insights into the contamination profiles of PM_2.5-bound BTHs and emphasize the health risk of OTH.

Chemical identity and cardiovascular toxicity of hydrophobic organic components in PM2.5

Numerous experimental and epidemiological studies have demonstrated that exposure to PM_2.5 may result in pathogenesis of several major cardiovascular diseases (CVDs), which can be attributed to the combined adverse effects induced by the complicated components of PM_2.5. Organic materials, which are major components of PM_2.5, contain thousands of chemicals, and most of them are environmental hazards. However, the contamination profile and contribution to overall toxicity of PM_2.5-bound organic components (OCs) have not been thoroughly evaluated yet. Herein, we aim to provide an overview of the literature on PM_2.5-bound hydrophobic OCs, with an emphasis on the chemical identity and reported impairments on the cardiovascular system, including the potential exposure routes and mechanisms. We first provide an update on the worldwide mass concentration and composition data of PM_2.5, and then, review the contamination profile of PM_2.5-bound hydrophobic OCs, including constitution, concentration, distribution, formation, source, and identification. In particular, the link between exposure to PM_2.5-bound hydrophobic OCs and CVDs and its possible underlying mechanisms are discussed to evaluate the possible risks of PM_2.5-bound hydrophobic OCs on the cardiovascular system and to provide suggestions for future studies.

PinX1t, a Novel PinX1 Transcript Variant, Positively Regulates Cardiogenesis of Embryonic Stem Cells

Background

Pin2/TRF1‐interacting protein, PinX1, was previously identified as a tumor suppressor. Here, we discovered a novel transcript variant of mPinX1 (mouse PinX1), mPinX1t (mouse PinX1t), in embryonic stem cells (ESCs). The aims of this investigation were (1) to detect the presence of mPinX1 and mPinX1t in ESCs and their differentiation derivatives; (2) to investigate the role of mPinX1 and mPinX1t on regulating the characteristics of undifferentiated ESCs and the cardiac differentiation of ESCs; (3) to elucidate the molecular mechanisms of how mPinX1 and mPinX1t regulate the cardiac differentiation of ESCs.

Methods and Results

By 5′ rapid amplification of cDNA ends, 3′ rapid amplification of cDNA ends, and polysome fractionation followed by reverse transcription–polymerase chain reaction, mPinX1t transcript was confirmed to be an intact mRNA that is actively translated. Western blot confirmed the existence of mPinX1t protein. Overexpression or knockdown of mPinX1 (both decreased mPinX1t expression) both decreased while overexpression of mPinX1t increased the cardiac differentiation of ESCs. Although both mPinX1 and mPinX1t proteins were found to bind to cardiac transcription factor mRNAs, only mPinX1t protein but not mPinX1 protein was found to bind to nucleoporin 133 protein, a nuclear pore complex component. In addition, mPinX1t‐containing cells were found to have a higher cytosol‐to‐nucleus ratio of cardiac transcription factor mRNAs when compared with that in the control cells. Our data suggested that mPinX1t may positively regulate cardiac differentiation by enhancing export of cardiac transcription factor mRNAs through interacting with nucleoporin 133.

Conclusions

We discovered a novel transcript variant of mPinX1, the mPinX1t, which positively regulates the cardiac differentiation of ESCs.

Adipose-derived stem cells and cancer cells fuse to generate cancer stem cell-like cells with increased tumorigenicity

Adipose-derived stem cells (ADSCs) are a type of mesenchymal stem cells isolated from adipose tissue and have the ability to differentiate into adipogenic, osteogenic, and chondrogenic lineages. Despite their great therapeutic potentials, previous studies showed that ADSCs could enhance the proliferation and metastatic potential of breast cancer cells (BCCs). In this study, we found that ADSCs fused with BCCs spontaneously, while breast cancer stem cell (CSC) markers CD44⁺ CD24^-/low EpCAM⁺ were enriched in this fusion population. We further assessed the fusion hybrid by multicolor DNA FISH and mouse xenograft assays. Only single nucleus was observed in the fusion hybrid, confirming that it was a synkaryon. In vivo mouse xenograft assay indicated that the tumorigenic potential of the fusion hybrid was significantly higher than that of the parent tumorigenic triple-negative BCC line MDA-MB-231. We had compared the fusion efficiency between two BCC lines, the CD44-rich MDA-MB-231 and the CD44-poor MCF-7, with ADSCs. Interestingly, we found that the fusion efficiency was much higher between MDA-MB-231 and ADSCs, suggesting that a potential mechanism of cell fusion may lie in the dissimilarity between these two cell lines. The cell fusion efficiency was hampered by knocking down the CD44. Altogether, our findings suggest that CD44-mediated cell fusion could be a potential mechanism for generating CSCs.

Acute exposure to triphenyl phosphate inhibits the proliferation and cardiac differentiation of mouse embryonic stem cells and zebrafish embryos

Attention has recently paid to the interaction of triphenyl phosphate (TPHP) and body tissues, particularly within the reproductive and development systems, due to its endocrine-disrupting properties. However, the acute effects of TPHP on early embryonic development remain unclear. Here, we used mouse embryonic stem cells (mESC) and zebrafish embryos to investigate whether TPHP is an embryo toxicant. First, we found that continuous exposure of TPHP decreased the proliferation and increased the apoptotic populations of mESCs in a concentration-dependent manner. Results of mass spectrometry showed that the intracellular concentration of TPHP reached 39.45 ± 7.72 µg/g w/w after 3 hr of acute exposure with TPHP (38.35 μM) but gradually decreased from 3 hr to 48 hr. Additionally, DNA damage was detected in mESCs after a short-term treatment with TPHP, which in turn, activated DNA damage responses, leading to cell cycle arrest by changing the expression levels of p53, proliferating cell nuclear antigen, and Y15-phosphorylated Cdk I. Furthermore, our results revealed that short-term treatment with TPHP disturbed cardiac differentiation by decreasing the expression levels of Oct4, Sox2, and Nanog and transiently reduced the glycolysis capacity in mESCs. In zebrafish embryos, exposure to TPHP resulted in broad, concentration-dependent developmental defects and coupled with heart malformation and reduced heart rate. In conclusion, the two models demonstrate that acute exposure to TPHP affects early embryonic development and disturbs the cardiomyogenic differentiation.

Cyanidin-3-o-glucoside directly binds to ERα36 and inhibits EGFR-positive triple-negative breast cancer

Anthocyanins have been shown to inhibit the growth and metastatic potential of breast cancer (BC) cells. However, the effects of individual anthocyanins on triple-negative breast cancer (TNBC) have not yet been studied. In this study, we found that cyanidin-3-o-glucoside (Cy-3-glu) preferentially promotes the apoptosis of TNBC cells, which co-express the estrogen receptor alpha 36 (ERα36) and the epidermal growth factor receptor (EGFR). We demonstrated that Cy-3-glu directly binds to the ligand-binding domain (LBD) of ERα36, inhibits EGFR/AKT signaling, and promotes EGFR degradation. We also confirmed the therapeutic efficacy of Cy-3-glu on TNBC in the xenograft mouse model. Our data indicates that Cy-3-glu could be a novel preventive/therapeutic agent against the TNBC co-expressed ERα36/EGFR.

Functional Characterization of MicroRNA-27a-3p Expression in Human Polycystic Ovary Syndrome

The goal of this study was to characterize the function of microRNA-27a-3p (miR-27a-3p) in polycystic ovary syndrome (PCOS). miR-27a-3p expression was analyzed in excised granulosa cells (GCs) from 21 patients with PCOS and 12 normal patients undergoing in vitro fertilization cycle treatments and in 17 nontreated cuneiform ovarian resection PCOS samples and 13 control ovarian samples from patients without PCOS. We found that the expression of miR-27a-3p was significantly increased in both excised GCs and the ovaries of patients with PCOS compared with the controls. Insulin treatment of the human granulosa-like tumor cell line (KGN) resulted in decreased downregulated expression of miR-27a-3p, and this effect appeared to be mediated by signal transducer and activator of transcription STAT1 and STAT3. The overexpression of miR-27a-3p in KGN cells inhibited SMAD5, which in turn decreased cell proliferation and promoted cell apoptosis. After KGN cells were stimulated with insulin for 48 hours, there was increased expression of SMAD5 protein and decreased apoptosis. Additionally, knockdown/overexpression of SMAD5 in KGN cells reduced/increased cell number and promoted/inhibited cell apoptosis. Insulin-stimulated primary GCs isolated from patients with PCOS, in contrast to normal GCs or KGN cells, did not exhibit decreased miR-27a-3p expression. The differences in the expression levels in KGN cells and human PCOS GCs are likely explained by increased miR-27a-3p expression in the GCs caused by insulin resistance in PCOS. Taken together, our data provided evidence for a functional role of miR-27a-3p in the GCs' dysfunction that occurs in patients with PCOS.

MicroRNA-27a-3p affects estradiol and androgen imbalance by targeting Creb1 in the granulosa cells in mouse polycytic ovary syndrome model

Polycystic ovary syndrome (PCOS) is a common endocrine abnormality in women characterized by a menstrual disturbance with chronic anovulation and hyperandrogenism, polycystic ovaries, and insulin resistance. MicroRNAs (miRNAs) are important fine-tune regulators involved in various physiological and pathological processes, but their actions are not fully understood. In this study, we observed the increased expression of miR-27a-3p in the ovaries of mice with PCOS and explored its functions in primary mouse granulosa cells (mGCs) and the mouse granulosa-like tumor cell line, KK-1, using several approaches. QPCR results showed that miR-27a-3p expression was significantly higher in mGCs at the preantral follicle (PrF) stage. Using flow cytometry and hormone analysis, we found that overexpression of miR-27a-3p promoted apoptosis and inhibited estradiol (E₂) production in KK-1 cells. Moreover using a luciferase assay and Western blotting analysis, we verified that the gene of cyclic AMP response element (CRE)-binding protein 1 (Creb1) was a potential target of miR-27a-3p, which in effect hindered the expression of its downstream factor cytochrome P450 family 19 subfamily A polypeptide 1 (Cyp19a1). With the decrease of aromatase activity, testosterone (T) is reduced to dihydrotestosterone (DHT) and this exerts its effect of upregulation of the miR-27a-3p expression. The imbalance of androgen and E₂ levels affected by miR-27a-3p and its function of promoting GC apoptosis could be involved in the pathophysiology of PCOS. Our results indicate that miR-27a-3p in PCOS GCs may play an important role in ovarian follicular development and provide new insights into GC dysfunction in PCOS.

Role of inducible nitric oxide synthase in endothelium-independent relaxation to raloxifene in rat aorta

BACKGROUND AND PURPOSE

Raloxifene can induce both endothelium-dependent and -independent relaxation in different arteries. However, the underlying mechanisms by which raloxifene triggers endothelium-independent relaxation are still incompletely understood. The purpose of present study was to examine the roles of NOSs and Ca²⁺ channels in the relaxant response to raloxifene in the rat isolated, endothelium-denuded aorta.

EXPERIMENTAL APPROACH

Changes in isometric tension, cGMP, nitrite, inducible NOS protein expression and distribution in response to raloxifene in endothelium-denuded aortic rings were studied by organ baths, radioimmunoassay, Griess reaction, western blot and immunohistochemistry respectively.

KEY RESULTS

Raloxifene reduced the contraction to CaCl₂ in a Ca²⁺ -free, high K⁺ -containing solution in intact aortic rings. Raloxifene also acutely relaxed the aorta primarily through an endothelium-independent mechanism involving NO, mostly from inducible NOS (iNOS) in vascular smooth muscle layers. This effect of raloxifene involved the generation of cGMP and nitrite. Also, it was genomic in nature, as it was inhibited by a classical oestrogen receptor antagonist and inhibitors of RNA and protein synthesis. Raloxifene-induced stimulation of iNOS gene expression was partly mediated through activation of the NF-κB pathway. Raloxifene was more potent than 17β-estradiol or tamoxifen at relaxing endothelium-denuded aortic rings by stimulation of iNOS.

CONCLUSIONS AND IMPLICATIONS

Raloxifene-mediated vasorelaxation in rat aorta is independent of a functional endothelium and is mediated by oestrogen receptors and NF-κB. This effect is mainly mediated through an enhanced production of NO, cGMP and nitrite, via the induction of iNOS and inhibition of calcium influx through Ca²⁺ channels in rat aortic smooth muscle.

Cancer-Associated Fibroblasts Regulate Tumor-Initiating Cell Plasticity in Hepatocellular Carcinoma through c-Met/FRA1/HEY1 Signaling

Like normal stem cells, tumor-initiating cells (T-ICs) are regulated extrinsically within the tumor microenvironment. Because HCC develops primarily in the context of cirrhosis, in which there is an enrichment of activated fibroblasts, we hypothesized that cancer-associated fibroblasts (CAFs) would regulate liver T-ICs. We found that the presence of α-SMA(+) CAFs correlates with poor clinical outcome. CAF-derived HGF regulates liver T-ICs via activation of FRA1 in an Erk1,2-dependent manner. Further functional analysis identifies HEY1 as a direct downstream effector of FRA1. Using the STAM NASH-HCC mouse model, we find that HGF-induced FRA1 activation is associated with the fibrosis-dependent development of HCC. Thus, targeting the CAF-derived, HGF-mediated c-Met/FRA1/HEY1 cascade may be a therapeutic strategy for the treatment of HCC.

TRPV3 Channel Negatively Regulates Cell Cycle Progression and Safeguards the Pluripotency of Embryonic Stem Cells

Embryonic stem cells (ESCs) have tremendous potential for research and future therapeutic purposes. However, the calcium handling mechanism in ESCs is not fully elucidated. Aims of this study are (1) to investigate if transient receptor potential vanilloid-3 (TRPV3) channels are present in mouse ESCs (mESCs) and their subcellular localization; (2) to investigate the role of TRPV3 in maintaining the characteristics of mESCs. Western blot and immunocytochemistry showed that TRPV3 was present at the endoplasmic reticulum (ER) of mESCs. Calcium imaging showed that, in the absence of extracellular calcium, TRPV3 activators camphor and 6-tert-butyl-m-cresol increased the cytosolic calcium. However, depleting the ER store in advance of activator addition abolished the calcium increase, suggesting that TRPV3 released calcium from the ER. To dissect the functional role of TRPV3, TRPV3 was activated and mESC proliferation was measured by trypan blue exclusion and MTT assays. The results showed that TRPV3 activation led to a decrease in mESC proliferation. Cell cycle analysis revealed that TRPV3 activation increased the percentage of cells in G2 /M phase; consistently, Western blot also revealed a concomitant increase in the expression of inactive form of cyclin-dependent kinase 1, suggesting that TRPV3 activation arrested mESCs at G2 /M phase. TRPV3 activation did not alter the expression of pluripotency markers Oct-4, Klf4 and c-Myc, suggesting that the pluripotency was preserved. Our study is the first study to show the presence of TRPV3 at ER. Our study also reveals the novel role of TRPV3 in controlling the cell cycle and preserving the pluripotency of ESCs.

A novel missense mutation in CCDC88C activates the JNK pathway and causes a dominant form of spinocerebellar ataxia

Background

Spinocerebellar ataxias (SCAs) are a group of clinically and genetically diverse and autosomal-dominant disorders characterised by neurological deficits in the cerebellum. At present, there is no cure for SCAs. Of the different distinct subtypes of autosomal-dominant SCAs identified to date, causative genes for only a fraction of them are currently known. In this study, we investigated the cause of an autosomal-dominant SCA phenotype in a family that exhibits cerebellar ataxia and pontocerebellar atrophy along with a global reduction in brain volume.

Methods and results

Whole-exome analysis revealed a missense mutation c.G1391A (p.R464H) in the coding region of the coiled-coil domain containing 88C (CCDC88C) gene in all affected individuals. Functional studies showed that the mutant form of CCDC88C activates the c-Jun N-terminal kinase (JNK) pathway, induces caspase 3 cleavage and triggers apoptosis.

Conclusions

This study expands our understanding of the cause of autosomal-dominant SCAs, a group of heterogeneous congenital neurological conditions in humans, and unveils a link between the JNK stress pathway and cerebellar atrophy.

Regulation of multiple transcription factors by reactive oxygen species and effects of pro-inflammatory cytokines released during myocardial infarction on cardiac differentiation of embryonic stem cells

BACKGROUND

The mechanism of how reactive oxygen species (ROS) regulate cardiac differentiation in the long-run is unclear and the effect of pro-inflammatory cytokines secreted during myocardial infarction on the cardiac differentiation of embryonic stem cells (ESCs) is unknown. The aims of this study were 1) to investigate the effect of ROS on cardiac differentiation and the regulations of transcription factors in ESC differentiation cultures and 2) to investigate the effect of pro-inflammatory cytokines on the expression of cardiac structural genes and whether this effect is mediated through ROS signaling.

METHODS

ESCs were differentiated using hanging drop method. Degree of cardiac differentiation was determined by the appearance of beating embryoid bodies (EBs) and by the expression of cardiac genes using real-time PCR and Western blot. Intracellular ROS level was examined by confocal imaging.

RESULTS

H2O2-treated EBs were found to have enhanced cardiac differentiation in the long run as reflected by, firstly, an earlier appearance of beating EBs, and secondly, an upregulation in cardiac structural protein expression at both mRNA and protein levels. Also, ROS upregulated the expression of several cardiac-related transcription factors, and increased the post-translationally-activated transcription factors SRF and AP-1. IL-1β, IL-10, IL-18 and TNF-α upregulated the expression of cardiac structural proteins and increased the ROS level in differentiating EBs. In addition, ROS scavenger reversed the cardiogenic effect of IL-10 and IL-18.

CONCLUSIONS

These results demonstrated that ROS enhance cardiac differentiation of ESCs through upregulating the expression and activity of multiple cardiac-related transcription factors. IL-1β, IL-10, IL-18 and TNF-α enhance cardiac differentiation and ROS may serve as the messenger in cardiogenic signaling from these cytokines.

Differential effects of estrogen/androgen on the prevention of nonalcoholic fatty liver disease in the male rat

It is important to clarify the distinct contributions of estrogen/estrogen receptor (ER) and androgen/androgen receptor (AR) signaling and their reciprocal effects on the regulation of hepatic lipid homeostasis. We studied the molecular mechanisms underlying the preventive effects of estradiol (E2), dihydrotestosterone (DHT), or E2+DHT on high-fat diet-induced nonalcoholic fatty liver disease (NAFLD) in an orchidectomized Sprague-Dawley (SD) rat model. E2 is shown to be associated with decreased fatty acid synthesis in hepatic zone 3-specific manner by increasing the phosphorylation of acetyl coenzyme-A carboxylase via an ERα-mediated pathway. DHT is shown to be associated with decreased lipid accumulation and cholesterol synthesis in a hepatic zone 1-specific manner by increasing expression of carnitine palmitotyltransferase1 and phosphorylation of 3-hydroxy-3-methyl-glutaryl-CoA reductase via an AR-mediated pathway. E2+DHT showed an additive positive effect and normalized all three impaired zones of the liver. Gene expression changes in human severe liver steatosis were similar to those of experimental rat NAFLD. Steroids reversed the histopathological NAFLD changes, likely by decreasing fatty acid and cholesterol synthesis and increasing β-oxidation. The diverse steroid effects (ER/AR) on NAFLD prevention in male rats indicate the potential applicability of ER/AR modulators for NAFLD treatment.

Prostacyclin receptor-dependent inhibition of human erythroleukemia cell differentiation is STAT3-dependent

We have previously demonstrated that activation of prostacyclin (IP) receptors in human erythroleukemia (HEL) cells phosphorylates the signal transducer and activator of transcription 3 (STAT3) via Gα(s) and Gα(16) hybrid signalling. This current study was designed to determine if functional responses to cicaprost in HEL cells were dependent on STAT3 phosphorylation. Cicaprost significantly enhanced the rapid change in HEL cell morphology induced by phorbol-12-myristate-13-acetate (PMA), and this effect was inhibited by the IP receptor antagonist RO1138452 and a STAT3 inhibitory peptide. Other indicators of PMA-induced HEL cell differentiation, such as increased expression of CD41/CD61 and an increase in cell complexity/granularity, were inhibited by cicaprost in an IP receptor-dependent and STAT3-dependent manner. Although thrombopoietic cytokines promote megakaryocytic differentiation and platelet production via activation of STAT3, the predominant STAT3-dependent effects of cicaprost in HEL cells were inhibitory towards the process of PMA-induced megakaryocytopoeisis.

The Ethanol Extract of Fructus trichosanthis Promotes Fetal Hemoglobin Production via p38 MAPK Activation and ERK Inactivation in K562 Cells

Pharmacological stimulation of fetal hemoglobin (HbF) expression may be a promising approach for the treatment of beta-thalassemia. In this study, the effects of Fructus trichosanthis (FT) were investigated in human erythroleukemic K562 cells for their gamma-globin mRNA and HbF-induction activities. The role of signaling pathways, including extracellular regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), was also investigated. It was found that the ethanol extract of FT significantly increased gamma-globin mRNA and HbF levels, determined by real-time reverse transcription polymerase chain reaction and enzyme linked immunosorbent assay, respectively, in dose- and time-dependent manner. Total Hb (THb) levels were also elevated in the concentrations without cytotoxicity (<80 μg mL(-1)). Pre-treatment with p38 MAPK inhibitor SB203580 blocked the stimulatory effects of FT extract in total and HbF induction. In contrast, no change in HbF was observed when treated with ERK inhibitor PD98059. Furthermore, FT ethanol extract activated p38 MAPK and inhibited ERK signaling pathways in K562 cells, as revealed in western blotting analysis. In addition, SB203580 significantly abolished p38 MAPK activation when the cells were treated with FT. In summary, the ethanol extract of FT was found to be a potent inducer of HbF synthesis in K562 cells. The present data delineated the role of ERK and p38 MAPK signaling as molecular targets for pharmacologic stimulation of HbF production upon FT treatment.

Relative contribution of individual oxidized components in ox-LDL to inhibition on endothelium-dependent relaxation in rat aorta

BACKGROUND AND AIM

Oxidized low-density lipoprotein (ox-LDL) causes atherosclerosis and endothelial dysfunction. No study up to the present date has examined the relative contribution of all the oxidized components in ox-LDL to inhibition on vascular function. Our aim was to investigate the effects of individual oxidized components at concentrations similar to those in ox-LDL on the impairment of endothelium-dependent relaxation in rat aorta.

METHODS AND RESULTS

Rat thoracic aorta was pre-treated with lysophosphatidylcholine (LPC), cholesterol oxidized products (COPs), oxidized linoleic acid (ox-18:2) and oxidized linolenic acid (ox-18:3) at concentrations similar to those in human ox-LDL. Ox-LDL as a whole caused 61% inhibition while LPC, COPs and ox-18:2 at concentrations similar to those in ox-LDL caused 12%, 24% and 19% inhibition, respectively, on endothelium-dependent relaxation, suggesting that COPs produced the most adverse effect followed by ox-18:2 and LPC in an additional way. Three COPs including 7-ketocholesterol, 7α-hydroxycholesterol and 7β-hydroxycholesterol showed inhibition on endothelium-dependent relaxation with E(max) being reduced to 79-87% compared with the control E(max) (95%). At Western blot analysis phosphorylation of eNOS at Ser1177 site and total eNOS were not altered by ox-LDL treatment, indicating that ox-LDL did not affect nitric oxide (NO) synthesis capacity. Ox-LDL might react directly with NO and lower NO bioavailability.

CONCLUSION

The present study demonstrated the relative contribution of individual oxidized components in ox-LDL in the inhibition of endothelium-dependent relaxation in rat aorta. This inhibitory effect could be caused by the reduction of NO bioactivity.

Differential gene expressions in atrial and ventricular myocytes: insights into the road of applying embryonic stem cell-derived cardiomyocytes for future therapies

Myocardial infarction has been the leading cause of morbidity and mortality in developed countries over the past few decades. The transplantation of cardiomyocytes offers a potential method of treatment. However, cardiomyocytes are in high demand and their supply is extremely limited. Embryonic stem cells (ESCs), which have been isolated from the inner cell mass of blastocysts, can self-renew and are pluripotent, meaning they have the ability to develop into any type of cell, including cardiomyocytes. This suggests that ESCs could be a good source of genuine cardiomyocytes for future therapeutic purposes. However, problems with the yield and purity of ESC-derived cardiomyocytes, among other hurdles for the therapeutic application of ESC-derived cardiomyocytes (e.g., potential immunorejection and tumor formation problems), need to be overcome before these cells can be used effectively for cell replacement therapy. ESC-derived cardiomyocytes consist of nodal, atrial, and ventricular cardiomyocytes. Specifically, for treatment of myocardial infarction, transplantation of a sufficient quantity of ventricular cardiomyocytes, rather than nodal or atrial cardiomyocytes, is preferred. Hence, it is important to find ways of increasing the yield and purity of specific types of cardiomyocytes. Atrial and ventricular cardiomyocytes have differential expression of genes (transcription factors, structural proteins, ion channels, etc.) and are functionally distinct. This paper presents a thorough review of differential gene expression in atrial and ventricular myocytes, their expression throughout development, and their regulation. An understanding of the molecular and functional differences between atrial and ventricular myocytes allows discussion of potential strategies for preferentially directing ESCs to differentiate into chamber-specific cells, or for fine tuning the ESC-derived cardiomyocytes into specific electrical and contractile phenotypes resembling chamber-specific cells.

4-aminopyridine-sensitive K+ channels contributes to NaHS-induced membrane hyperpolarization and relaxation in the rat coronary artery

The present study aimed at examining the role of potassium channels and endothelium in relaxations induced by sodium hydrogen sulphide (NaHS), which is the donor of gaseous hydrogen sulphide (H(2)S) and the effect of NaHS on endothelium-dependent relaxations in rat coronary arteries. Rat coronary arteries were suspended in a myograph for force measurement and changes of the membrane potential in arteries were determined by membrane potential-sensitive fluorescence dye. NaHS relaxed coronary arteries pre-contracted by U46619 and the relaxation was significantly less in high KCl-contracted rings. NaHS-induced relaxations were reduced by 4-aminopyridine (4-AP) but unaffected by glibenclamide, iberiotoxin, N(G)-nitro-L-arginine methyl ester, ODQ, indomethacin or by endothelium removal. The inhibitory effect of 4-AP was absent in NaHS-induced relaxations in high KCl-contracted rings. Addition of NaHS caused membrane hyperpolarization and this effect was inhibited by 4-AP but not by glibenclamide. NaHS causes endothelium-independent relaxations in rat coronary arteries partially through activation of 4-AP-sensitive potassium channel and ensuring hyperpolarization. Other potassium channels, Na(+)-K(+) pump or endothelium-derived relaxing factors play little role.

Therapeutically relevant concentrations of raloxifene dilate pressurized rat resistance arteries via calcium-dependent endothelial nitric oxide synthase activation

OBJECTIVE

Selective estrogen receptor modulators (SERMs) inhibit constriction of mammalian conduit arteries. However, it is unknown whether SERMs at therapeutically achievable concentrations could reduce vascular tone in resistance arteries. The present study aimed to examine roles of Ca(2+) influx in endothelium and endothelial nitric oxide synthase (eNOS) activation in dilatations induced by raloxifene, a second-generation SERM in myogenically active arteries.

METHODS AND RESULTS

Small mesenteric arteries from Sprague-Dawley rats were isolated and mounted in a pressure myograph for measurement of changes in vessel diameter. [Ca(2+)](i) images on native endothelial cells of intact arteries were determined by the fluorescence imaging technique, and phosphorylation of eNOS was assayed by Western blotting. Raloxifene (0.3 to 10 nmol/L) produced dilatations on established steady myogenic constriction. Female rat arteries dilated significantly more in response to raloxifene than male arteries. Raloxifene-induced dilatations of female arteries were blunted by N(G)-nitro-l-arginine methyl ester but unaffected by 1400W, charybdotoxin plus apamin, wortmannin, or LY294002. Raloxifene (3 nmol/L) triggered rises in endothelial cell [Ca(2+)](i) and increased eNOS phosphorylation at Ser1177. Both effects were greater in arteries from female rats than in arteries from male rats. Increases in endothelial cell [Ca(2+)](i) and in eNOS phosphorylation were prevented by removal of extracellular Ca(2+) ions. Finally, ICI 182,780 did not affect the raloxifene-stimulated rise in endothelial cell [Ca(2+)](i), eNOS phosphorylation, and vasodilatations. Chronic raloxifene treatment reduced myogenic constriction in arteries from female but not male rats.

CONCLUSION

Raloxifene at therapeutically relevant concentrations inhibits myogenic constriction by an NO-dependent mechanism that causally involves the elevated [Ca(2+)](i) in endothelial cells and subsequent eNOS activation. Raloxifene dilates resistance arteries more effectively in female rats, indicating its significant gender-related action on endothelial cells in microcirculation.

Raloxifene, tamoxifen and vascular tone

1. Oestrogen deficiency causes progressive reduction in endothelial function. Despite the benefits of hormone-replacement therapy (HRT) evident in earlier epidemiological studies, recent randomized trials of HRT for the prevention of heart disease found no overall benefit. Instead, HRT users had higher incidences of stroke and heart attack. Most women discontinue HRT because of its many side-effects and/or the increased risk of breast and uterine cancer. This has contributed to the development of selective oestrogen receptor modulators (SERMs), such as tamoxifen and raloxifene, as alternative oestrogenic agents. 2. A SERM is a molecule that binds with high affinity to oestrogen receptors but has tissue-specific effects distinct from oestrogen, acting as an oestrogen agonist in some tissues and as an antagonist in others. Clinical and animal studies suggest multiple cardiovascular effects of SERMs. For example, raloxifene lowers serum levels of cholesterol and homocysteine, attenuates oxidation of low-density lipoprotein, inhibits endothelial-leucocyte interaction, improves endothelial function and reduces vascular smooth muscle tone. 3. Available evidence suggests that raloxifene and tamoxifen are capable of acting directly on both endothelial cells and the underlying vascular smooth muscle cells and cause a multitude of favourable modifications of the vascular wall, which jointly contribute to improved local blood flow. The outcome of the Raloxifene Use for the Heart (RUTH) trial will determine whether raloxifene, currently approved for the treatment of post-menopausal osteoporosis, could substitute for HRT in alleviating cardiovascular symptoms in post-menopausal women.

Ectopic expression of systemic RNA interference defective protein in embryonic stem cells

RNA interference (RNAi), a post-transcriptional gene silencing mechanism originally described in Caenorhabditis elegans, involves sequence-specific mRNA degradation mediated by double-stranded RNAs (dsRNAs). Passive dsRNA uptake has been uniquely observed in C. elegans due to the expression of systemic RNA interference defective-1 (SID-1). Here we investigated the ability of ectopic SID-1 expression to enable passive cellular uptake of short interfering RNA (siRNA) or double stranded RNA (dsRNA) in pluripotent mouse embryonic stem cells (mESCs). When SID-1-GFP and the Firefly luciferase reporter gene (luc(Fir)) were co-expressed in mESCs, luc(Fir) activity could be suppressed by simple incubation with dsRNAs/siRNAs that were designed to specifically target luc(Fir). By contrast, suppression was not observed in mESCs expressing luc(Fir) and GFP alone or when either GFP- or SID-1-GFP-expressing cells were incubated with control dsRNAs/siRNAs (non-silencing or Renilla luciferase-specific). These results may lead to high-throughput experimental strategies for studying ESC differentiation and novel approaches to genetically inhibit or eliminate the tumorigenicity of ESCs.

Tamoxifen and estrogen attenuate enhanced vascular reactivity induced by estrogen deficiency in rat carotid arteries

Recent clinical trials showed that estrogen usage in postmenopausal women did not affect coronary heart disease incidence, in contrast to several laboratory studies showing that estrogen decreased vascular reactivity. We speculated that, in some arteries, estrogen deficiency enhances endothelial function to compensate for the increased vascular smooth muscle reactivity. In this study, we examined the role of endothelium-derived vasoactive factors and the influence of in vivo estrogen and/or tamoxifen treatment on vascular reactivity of estrogen-deficient rats. Common carotid arteries were isolated from sham-operated (control), ovariectomized (Ovx), estrogen- or tamoxifen-treated Ovx rats, and Ovx rats co-treated with estrogen and tamoxifen. U46619 or phenylephrine induced similar contractions in endothelium-intact rings from all groups. Interestingly, removal of endothelium unmasked enhanced contractions in Ovx rats, which was prevented by estrogen, tamoxifen, or estrogen+tamoxifen treatment. Contractions to high K(+) were higher in both endothelium-intact and endothelium-denuded arteries from Ovx rats. Estrogen or tamoxifen treatment normalized high K(+)-induced contraction. A gap junction blocker, 18alpha-glycyrrhetinic acid, revealed enhanced contractions to U46619 in the absence or presence of l-NNA. Western blotting showed enhanced expressions of gap junctional connexin 43 in Ovx group. This study suggests that ovariectomy increases functional expression of gap junction-mediated endothelium-derived hyperpolarizing factor. Also, vascular effects of ovariectomy can be reversed by estrogen, tamoxifen or estrogen+tamoxifen treatment, suggesting that tamoxifen confers estrogenic effects in the vascular system.

Raloxifene prevents endothelial dysfunction in aging ovariectomized female rats

Lack of an appropriate animal model has delayed the better understanding of mechanisms related to higher cardiovascular risk in women after menopause. The aging female rat may share some menopausal changes observed in women. However, most studies have attempted to mimic menopause by ovariectomizing young (6-12 weeks old) animals without taking into accounts the influence of aging and of declining ovarian function. Therefore, the present study examined changes in vascular reactivity in the aging (15 months old) female rat after ovariectomy and the effects of chronic raloxifene therapy on vascular reactivity and eNOS protein expression. Aortic rings were prepared from the three experimental groups of rats: sham-operated control, ovariectomized and ovariectomized aging rats receiving daily oral administration of raloxifene for 3 months. Aortic rings were suspended in organ baths for the measurement of isometric tension. Rings with endothelium contracted significantly more to phenylephrine after inhibition of nitric oxide/cyclic GMP-signaling pathway by L-NAME or ODQ (as an index of basal nitric oxide release) in control and raloxifene-treated ovariectomized rats than in ovariectomized rats. This effect was abolished upon mechanical removal of the endothelium. Phenylephrine induced greater contractions only in rings with endothelium from ovariectomized rats as compared with control rats and raloxifene treatment normalized this response. In the presence of L-NAME or ODQ, phenylephrine-induced contraction was similar in rings from the three groups. Rings relaxed more to thapsigargin and acetylcholine in raloxifene-treated ovariectomized rats than in ovariectomized rats. There was no significant difference in aortic eNOS protein contents among the different groups. These results suggest that chronic oral administration of raloxifene to aging ovariectomized female rats augmented the bioavailability of endothelial nitric oxide in isolated aortic rings without altering eNOS protein levels.

A multifunctional aromatic residue in the external pore vestibule of Na+ channels contributes to the local anesthetic receptor

Voltage-gated Na(+) (Na(v)) channels are responsible for initiating action potentials in excitable cells and are the targets of local anesthetics (LA). The LA receptor is localized to the cytoplasmic pore mouth formed by the S6 segments from all four domains (DI-DIV) but several outer pore-lining residues have also been shown to influence LA block (albeit somewhat modestly). Many of the reported amino acid substitutions, however, also disrupt the inactivated conformations that favor LA binding, complicating the interpretation of their specific effects on drug block. In this article, we report that an externally accessible aromatic residue in the Na(v) channel pore, DIV-Trp1531, when substituted with cysteine, completely abolished LA block (e.g., 300 microM mexiletine induced a use-dependent block with 65.0 +/- 2.9% remaining current and -11.0 +/- 0.6 mV of steady-state inactivation shift of wild-type (WT) channels versus 97.4 +/- 0.7% and -2.4 +/- 2.1 mV of W1531C, respectively; p < 0.05) without destabilizing fast inactivation (complete inactivation at 20 ms at -20 mV; V(1/2) = -70.0 +/- 1.6 mV versus -48.6 +/- 0.5 mV of WT). W1531C also abolished internal QX-222 block (200 microM; 98.4 +/- 3.4% versus 54.0 +/- 3.2% of WT) without altering drug access. It is interesting that W1531Y restored WT blocking behavior, whereas W1531A channels exhibited an intermediate phenotype. Together, our results provide novel insights into the mechanism of drug action, and the structural relationship between the LA receptor and the outer pore vestibule.

A Multifunctional Aromatic Residue in the External Pore Vestibule of Na+ Channels Contributes to the Local Anesthetic Receptor

Voltage-gated Na(+) (Na(v)) channels are responsible for initiating action potentials in excitable cells and are the targets of local anesthetics (LA). The LA receptor is localized to the cytoplasmic pore mouth formed by the S6 segments from all four domains (DI-DIV) but several outer pore-lining residues have also been shown to influence LA block (albeit somewhat modestly). Many of the reported amino acid substitutions, however, also disrupt the inactivated conformations that favor LA binding, complicating the interpretation of their specific effects on drug block. In this article, we report that an externally accessible aromatic residue in the Na(v) channel pore, DIV-Trp1531, when substituted with cysteine, completely abolished LA block (e.g., 300 microM mexiletine induced a use-dependent block with 65.0 +/- 2.9% remaining current and -11.0 +/- 0.6 mV of steady-state inactivation shift of wild-type (WT) channels versus 97.4 +/- 0.7% and -2.4 +/- 2.1 mV of W1531C, respectively; p < 0.05) without destabilizing fast inactivation (complete inactivation at 20 ms at -20 mV; V(1/2) = -70.0 +/- 1.6 mV versus -48.6 +/- 0.5 mV of WT). W1531C also abolished internal QX-222 block (200 microM; 98.4 +/- 3.4% versus 54.0 +/- 3.2% of WT) without altering drug access. It is interesting that W1531Y restored WT blocking behavior, whereas W1531A channels exhibited an intermediate phenotype. Together, our results provide novel insights into the mechanism of drug action, and the structural relationship between the LA receptor and the outer pore vestibule.

Critical intra-linker interactions of HCN1-encoded pacemaker channels revealed by interchange of S3-S4 determinants

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels contribute to the spontaneous rhythmic activities in cardiac and neuronal cells. Recently, we reported that the S3-S4 linker of HCN1 channels influences activation, and that part of the linker is helical with the determinants G231, M232, and E235 clustered on one side. Here we explored the undefined role of the G(231)E(235)M(232) triplet by systematic substitutions. Replacing G231 or M232 next to the "neighboring" E235 in the S3-S4 helix with an anionic residue (i.e., G231E, M232E) rendered channels non-functional although they were localized on the membrane surface. Interestingly, this loss of function could be readily rescued either by introducing a countercharge at position 235 (G231E/E235R, M232E/E235R) or by interchanging residues 231 or 232 and 235 (G231E/E235G, M232E/E235M). We conclude that residues 231, 232, and 235 are in close spatial proximity to each other, and uniquely interact with one another to shape the phenotypes of HCN channels.

Differential regulation of K+ and Ca2+ channel gene expression by chronic treatment with estrogen and tamoxifen in rat aorta

The beneficial effect of estrogen on the vascular system is partly associated with its ability to reduce vascular contractility. Estrogen acutely activates large-conductance Ca(2+)-activated K(+) channel (BK(Ca)) and inhibits L-type voltage-gated Ca(2+) channel (VGCC) in vascular smooth muscle cells. However, a long-term influence of estrogen, estrogen deficiency, or selective estrogen receptor modulators on gene expression of these ion channels is unclear. This study was therefore aimed to determine the relative mRNA expression levels of alpha- and beta-subunits of BK(Ca), K(V)1.5 subtype of delayed rectifier K(+) channel (K(V)), and alpha(1C) subunit of L-type VGCC in endothelium-denuded aortas from female rats by a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. Rats were divided into four experimental groups: (i) sham-operated control, (ii) ovariectomized, (iii) ovariectomized with 17 beta-estradiol treatment and (iv) ovariectomized with tamoxifen treatment. The results showed that ovariectomy decreased the mRNA expression of K(V)1.5 while it increased the mRNA expression of alpha(1C) subunit of L-type VGCC. Ovariectomy-induced modulation of gene expression of these ion channels was completely prevented in ovariectomized rats receiving chronic treatment with estrogen or tamoxifen. In contrast, the expression levels of genes encoding both alpha- and beta-subunits of BK(Ca) remained the same in the four animal groups. The present study has provided the first line of evidence suggesting the long-term beneficial effects of estrogen and tamoxifen therapy on vascular ion channel expressions, which may be an important mechanism by which the favorable modulation of vessel tone by estrogen or selective estrogen receptor modulators is mediated.

Dissecting the structural and functional roles of the S3-S4 linker of pacemaker (hyperpolarization-activated cyclic nucleotide-modulated) channels by systematic length alterations

If or Ih, a key player in neuronal and cardiac pacing, is encoded by the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel gene family. We have recently reported that the S3-S4 linker (i.e. residues 229EKGMDSEVY237 of HCN1) prominently influences the activation phenotypes of HCN channels and that part of the linker may conform a secondary helical structure. Here we further dissected the structural and functional roles of this linker by systematic alterations of its length. In contrast to voltage-gated K+ channels, complete deletion of the S3-S4 linker (Delta229-237) did not produce functional channels. Similarly, the deletions Delta229-234, Delta232-234, and Delta232-237 also abolished normal current activity. Interestingly, Delta229-231, Delta233-237, Delta234-237, Delta235-237, Delta229-231/Delta233-237, Delta229-231/Delta234-237, and Delta229-231/Delta235-237 all yielded robust hyperpolarization-activated inward currents, indicating that loss-of-function caused by deletion could be rescued by keeping the single functionally important residue Met232 alone. Whereas shortening the linker by deletion generally shifted steady-state activation in the depolarizing direction (e.g. DeltaV1/2 of Delta229-231, Delta233-237, Delta235-237 > +10 mV relative to wild type), linker prolongation by duplicating the entire linker (Dup229-237) or by glutamine insertion (InsQ233Q, InsQQ233QQ and InsQQQ233QQQ, or Ins237QQQ) produced length-dependent progressive hyperpolarizing activation shifts (-35 mV < DeltaV1/2 < -4 mV). Based on these results, we conclude that only Met232 is prerequisite for channels to function, but the length and other constituents of the S3-S4 linker shape the ultimate activation phenotype. Our results also highlight several evolutionary similarities and differences between HCN and voltage-gated K+ channels. Manipulations of the S3-S4 linker length may provide a flexible approach to customize HCN gating for engineering electrically active cells (such as stem cell-derived neuronal and cardiac pacemakers) for gene- and cell-based therapies.

Development of Effective Therapeutics Targeting the GABAA Receptor: Naturally Occurring Alternatives

The enhancement of GABA-mediated synaptic transmission underlies the pharmacotherapy of various neurological diseases. GABAA receptors are thus targets for neuroactive drugs, including classical benzodiazepines, mediating their anxiolytic, hypnotic and anticonvulsant effects via the benzodiazepine site (BZS). Based on findings that low intrinsic efficacy and subtype selectivity can greatly improve the specificity of drugs targeting the BZS, recent research has identified possible drug leads with apparently little side effects. In particular, drug leads of natural sources have been identified as promising candidates. This review describes the advances in the design of effective therapeutics targeting the GABAA receptor, focusing on the more recent research on naturally occurring drug leads. This includes discussion on the isolation of neuroactive alkaloids and flavonoids from herbal medicines and their rational development based on structure-activity relationships studies. Interest in the development of effective therapeutics from natural sources is clear and awaits to be seen whether their medicinal potential can be fulfilled.

Inhibition of nitric oxide/cyclic GMP-mediated relaxation by purified flavonoids, baicalin and baicalein, in rat aortic rings

The dried roots of Scutellaria baicalensis Georgi (Huangqin) are widely used in traditional Chinese medicine. We purified two flavonoids, baicalin and baicalein from S. baicalensis Georgi and examined their effects on isolated rat aortic rings. Baicalin (3-50 microM) inhibited endothelium/nitric oxide (NO)-dependent relaxation induced by acetylcholine (Ach) or cyclopiazonic acid (CPA). Baicalein at 50 microM abolished Ach-induced relaxation and markedly reduced CPA-induced relaxation. Treatment with 1mM L-arginine partially but significantly reversed the effects of baicalin (50 microM) or baicalein (50 microM) on Ach-induced relaxation. In endothelium-denuded rings, treatment with baicalin, baicalein or methylene blue partially inhibited relaxations induced by the NO donors, sodium nitroprusside (SNP) and hydroxylamine. Both flavonoids markedly reduced the increase in cyclic GMP levels stimulated by Ach in endothelium-intact rings and by SNP in endothelium-denuded rings. In contrast, exposure of endothelium-denuded rings to baicalin or baicalein did not affect relaxations induced by pinacidil or NS 1619, putative K+ channel activators. Neither flavonoids affected agonist-induced increase in the endothelial [Ca2+]i. Our results indicate that baicalin and baicalein attenuated NO-mediated aortic relaxation and cyclic GMP increases, likely through inhibition of NO-dependent guanylate cyclase activity.

Contribution of Na+ -Ca2+ exchanger to pinacidil-induced relaxation in the rat mesenteric artery

1 Pinacidil relaxes blood vessels through opening the K(ATP) channels with a resultant membrane hyperpolarization and inhibition of Ca(2+) influx. The aim of this study was to examine the mechanisms thereby pinacidil induces K(+) channel-independent relaxation in isolated endothelium-denuded rat mesenteric artery. 2 Pinacidil-induced relaxation was inhibited by glibenclamide (1-10 micro M) in phenylephrine-preconstricted rings, but was unaffected by glibenclamide after inhibition of K(+) channels and VGCCs. Pinacidil-induced K(+) channel-independent relaxation remained unchanged after treatment with cyclopiazonic acid (10 micro M), thapsigargin (1 micro M), ouabain (100 micro M), propranolol (10 micro M), Rp-cAMPS triethylamine (30 micro M), L-NNA (100 micro M), or ODQ (10 micro M). 3 Pinacidil induced more relaxant effect in the presence of nifedipine than in the presence of 60 mM K(+) plus nifedipine. Pretreatment with Na(+)-Ca(2+) exchanger inhibitors, nickel (30-300 micro M) or benzamil (20 micro M) attenuated pinacidil-induced relaxation in normal or in nifedipine-containing solution. Pinacidil (1 micro M) produced less relaxant effect with decreasing extracellular Na(+) concentration. Na(+)-free condition abolished the inhibitory effect of benzamil. Both nickel and benzamil inhibited pinacidil-induced relaxation in the presence of glibenclamide (10 micro M). Nickel (300 micro M) did not affect the relaxant response to sodium nitroprusside. 4 Pinacidil relaxed the rings preconstricted by active phorbol and U46619 with similar potency. 5 The present results indicate that stimulation of the forward mode Na(+)-Ca(2+) exchange pathway is in part responsible for pinacidil-induced K(+) channel-independent vasorelaxation. Pinacidil also induces K(+) channel-dependent but VGCCs-independent relaxation. The PKC-mediated cellular pathway may be a target site for pinacidil only in higher concentrations.

Inhibition of tumor-induced angiogenesis and matrix-metalloproteinase expression in confrontation cultures of embryoid bodies and tumor spheroids by plant ingredients used in traditional chinese medicine

Tumor-induced angiogenesis is a prerequisite for excessive tumor growth. Blood vessels invade the tumor tissue after degradation of the extracellular matrix scaffold by matrix metalloproteinases (MMPs). Inhibition of MMPs has been therefore suggested to be a useful tool to abolish neoangiogenesis of solid tumors. In the present study, antioxidative plant ingredients used in traditional Chinese medicine were investigated for their capacity to down-regulate MMP expression and to inhibit angiogenesis in embryonic stem cell-derived embryoid bodies and tumor-induced angiogenesis in confrontation cultures consisting of embryoid bodies and multicellular DU-145 prostate tumor spheroids. Embryoid bodies transiently expressed MMP-1, MMP-2, and MMP-9 during the time of differentiation of capillary-like structures. In confrontation cultures, MMP expression was increased compared with control tumor spheroids and embryoid bodies cultivated separately. The increased expression of MMPs in confrontation cultures was a result of elevated levels of reactive oxygen species (ROS) upon confrontation culture and was totally abolished in the presence of the free radical scavenger vitamin E. Incubation of embryoid bodies with baicalein, epicatechin, berberine, and acteoside, which are herbal ingredients used in traditional Chinese medicine, significantly inhibited angiogenesis in embryoid bodies and decreased intracellular ROS levels. Tumor-induced angiogenesis in confrontation cultures was totally abolished in the presence of the free radical scavenger vitamin E. Because herbal ingredients down-regulated MMP expression, we conclude that ROS generated during confrontation culture induce the expression of MMPs that are necessary for endothelial cell invasion into the tumor tissue.