Potential effect of resistin on the ET-1-increased reactions of blood pressure in rats and Ca2+ signaling in vascular smooth muscle cells

Deleterious effect in endothelin receptor-mediated coronary artery smooth muscle contractility in high-salt diet rats

BACKGROUND AND AIMS

High-salt diet has been suggested to increase the risk of heart disease. However, the mechanisms underlying coronary artery tension dysfunction caused by high-salt diet are unclear. Previous studies have shown that coronary artery spasm is often induced by endothelin-1 (ET-1) and thromboxane, leading to myocardial ischemia, while the store-operated Ca²⁺ entry (SOCE) function of coronary smooth muscle is very important in this process.

METHODS AND RESULTS

Tension measurements of endothelium-denuded coronary artery ring segments showed that vasocontraction induced by U46619, ET-1, orSTIM1/Orai1-mediated SOCE was significantly lower in 4% high-salt diet rats than in control rats fed a regular diet. The results of western blotting and immunohistochemistry assays showed lower expression levels of endothelial receptors ET_A and ET_B, STIM1 and Orai1 in coronary artery of high-salt intake rats compared with control rats. Fibrosis was observed by using Masson's trichrome staining and picrosirius red staining. The plasma ET-1 concentration in high-salt diet rats was significantly higher than that of controls. The interventricular septum and posterior wall of high-salt diet rats were significantly thickened.

CONCLUSION

Our findings indicated that coronary artery tension was significantly decreased in 4% high-salt diet rats and that this decrease may be due to the change of endothelin receptor and its downstream pathway SOCE related protein expression in coronary artery. Coronary fibrosis was observed in rats fed with high-salt diet. This study provides potential mechanistic insights into high-salt intake-induced heart disease.

Evidence that resistin acts on the mechanical responses of the mouse gastric fundus

Resistin, among its several actions, has been reported to exert central anorexigenic effects in rodents. Some adipokines which centrally modulate food intake have also been reported to affect the activity of gastric smooth muscle, whose motor responses represent a source of peripheral signals implicated in the control of the hunger-satiety cycle through the gut-brain axis. On this basis, in the present experiments, we investigated whether resistin too could affect the mechanical responses in the mouse longitudinal gastric fundal strips. Electrical field stimulation (EFS) elicited tetrodotoxin- and atropine-sensitive contractile responses. Resistin reduced the amplitude of the EFS-induced contractile responses. This effect was no longer detected in the presence of L-NNA, a nitric oxide (NO) synthesis inhibitor. Resistin did not influence the direct muscular response to methacholine. In the presence of carbachol and guanethidine, EFS elicited inhibitory responses whose amplitude was increased by resistin. L-NNA abolished the inhibitory responses evoked by EFS, indicating their nitrergic nature. In the presence of L-NNA, resistin did not have any effect on the EFS-evoked inhibitory responses. Western blot and immunofluorescence analysis revealed a significant increase in neuronal nitric oxide synthase (nNOS) expression in neurons of the myenteric plexus following resistin exposure. In conclusion, the present results offer the first evidence that resistin acts on the gastric fundus, likely through a modulatory action on the nitrergic neurotransmission.

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

Combinatorial roles of mitochondria and cGMP/PKG pathway in the generation of neuronal free Zn2+ under the presence of nitric oxide

BACKGROUND

Nitric oxide (NO), which possesses both protective and toxic properties, has been observed to have a complicated biphasic character within various types of tissues, including neuronal cells. NO was also found to cause the increase of another important signaling molecular Zn (termed as NZR). The molecular mechanism of NZR has been extensively investigated, but the source of Zn is present of a major candidate that is yet to be answered. The NO-protein kinase G (PKG) pathway, mitochondria, and metallothioneins (MTs), are all proposed to be the individual source of NZR. However, this hypothesis remains inconclusive. In this study, we examined the function of PKG signaling cascades, the mitochondria storage, and MT-1 during NZR of living PC12 cells.

METHODS

We applied live-cell imaging in combination with pharmacological inhibitors and activators as well as in vitro Zn assay to dissect the functions of the above candidates in NZR.

RESULTS

Two mechanisms, namely, mitochondria as the only Zn source and the opening of NO-PKG-dependent mitochondrial ATP-sensitive potassium channels (mKATP) as the key to releasing NO-induced increase in mitochondrial Zn, were proven to be the two critical paths of NZR in neuronal-related cells.

CONCLUSION

This new finding provides a reasonable explanation to previously existing and contradictory conclusions regarding the function of mitochondria/mKATP and PKG signaling on the molecular mechanism of NZR.

TRPP2 associates with STIM1 to regulate cerebral vasoconstriction and enhance high salt intake-induced hypertensive cerebrovascular spasm

Cerebrovascular spasm is a life-threatening event in salt-sensitive hypertension. The relationship between store-operated calcium entry (SOCE) and vasoconstriction in hypertension has not been fully clarified. This study investigated the changes in cerebrovascular contractile responses in high salt intake-induced hypertension and the functional roles of the main components of SOCE, namely, polycystin-2 (TRPP2), stromal interaction molecule 1 (STIM1), and Orai3. Polycystic kidney disease 2 (which encodes TRPP2) knockout mice displayed decreased cerebrovascular SOCE-induced contraction. The blood pressure of age-matched rats fed a normal or high-salt diet for 4 weeks was monitored weekly using noninvasive tail-cuff plethysmography. The systolic blood pressure of the rats fed a high-salt diet was significantly higher than that of controls. Western blotting and immunohistochemical results showed that these hypertensive rats expressed higher levels of cerebrovascular TRPP2, STIM1, and Orai3 than controls. Cerebrovascular tension measurements of the basilar artery indicated that SOCE-mediated contraction was significantly increased in hypertensive rats compared with control rats. In addition, SOCE-mediated contraction was decreased in the basilar arteries of rats pretreated with the SOCE inhibitor BTP-2 (10 μM) or transfected with TRPP2-specific or STIM1-specific small interfering RNA. Staining with 2,3,5-triphenyltetrazolium chloride (TTC) was used to quantify the infarcted brain area 24 h after middle cerebral artery occlusion, a model of ischemic stroke, in rodents. The infarcted brain area was significantly greater in hypertensive rats and significantly lower in BTP-2-treated rats than in controls. Taken together, these findings indicate that SOCE-induced contraction may be overactive in the basilar arteries of salt-sensitive hypertensive rats, suggesting the dysregulation of TRPP2 and SOCE and its other components.

Adipokines at the crossroad between obesity and cardiovascular disease

Obesity, and especially excessive visceral adipose tissue accumulation, is considered as a low-grade inflammatory state that is responsible for adipocyte dysfunction and associated metabolic disorders. Adipose tissue displays endocrine functions by releasing pro- or antiinflammatory bioactive molecules named adipokines. An altered expression of these molecules, provoked by obesity or adipocyte dysregulation, contributes to major metabolic diseases such as insulin resistance and type 2 diabetes mellitus that are important risk factors for cardiovascular disease. However, obesity is also characterised by the expansion of perivascular adipose tissue that acts locally via diffusion of adipokines into the vascular wall. Local inflammation within blood vessels induced by adipokines contributes to the onset of endothelial dysfunction, atherosclerosis and thrombosis, but also to vascular remodelling and hypertension. A fast expansion of obesity is expected in the near future, which will rapidly increase the incidence of these cardiovascular diseases. The focus of this review is to summarise the link between metabolic and cardiovascular disease and discuss current treatment approaches, limitations and future perspectives for more targeted therapies.

A short review of adipokines, smooth muscle and uterine contractility

Obesity is a major health problem worldwide. The prevalence of obesity is increasing in both developed and developing countries. In the UK, for example, 60% of adults are overweight and 25% are obese. Obesity is associated with many pathological complications including respiratory, cardiovascular and endocrine, but it also affects fertility and is associated with many reproductive complications. This has led us and others to investigate links between women with high BMI, pregnancy outcome and uterine function. These studies in turn have led investigators to ask how obesity can have such an impact on reproduction and, as part of this, to consider the role of the adipokines released from adipose tissues. Our focus in this short review is on adipokines and myometrial activity, and for completeness we overview their effects on other smooth muscles. To date four adipokines (leptin, visfatin, apelin and ghrelin) have been investigated and all affect myometrial contractility, but some more potently than others. We consider the possible mechanisms involved in how adipokines may modify uterine contractility, and discuss the potential impact on labor and delivery.

Resveratrol inhibits the intracellular calcium increase and angiotensin/endothelin system activation induced by soluble uric acid in mesangial cells

Resveratrol (Resv) is natural polyphenol found in grapes. This study evaluated the protective effect of Resv against the effects of uric acid (UA) in immortalized human mesangial cells (ihMCs). ihMCs were preincubated with Resv (12.5 µM) for 1 h and treated with UA (10 mg/dL) for 6 or 12 h. The intracellular calcium concentration [Ca²⁺]i was quantified by fluorescence using flow cytometry. Angiotensinogen (AGT) and pre-pro endothelin-1 (ppET-1) mRNA were assayed by quantitative real-time RT-PCR. Angiotensin II (AII) and endothelin-1 (ET-1) were assayed by ELISA. UA significantly increased [Ca²⁺]i. Pre-incubation with Resv significantly reduced the change in [Ca²⁺]i induced by UA. Incubation with UA for 6 or 12 h also increased AGT mRNA expression and AII protein synthesis. Resv blunted these increases in AGT mRNA expression and AII protein. Incubation with UA in the ihMCs increased ppET-1 expression and ET-1 protein synthesis at 6 and 12 h. When ihMCs were pre-incubated with Resv, UA had a significantly diminished effect on ppET-1 mRNA expression and ET-1 protein synthesis at 6 and 12 h, respectively. Our results suggested that UA triggers reactions including AII and ET-1 production in mesangial cells. The renin-angiotensin system may contribute to the pathogenesis of renal function and chronic kidney disease. Resv can minimize the impact of UA on AII, ET-1 and the increase of [Ca²⁺]i in mesangial cells, suggesting that, at least in part, Resv can prevent the effects of soluble UA in mesangial cells.

Ca(2+) handling alterations and vascular dysfunction in diabetes

More than 65% of patients with diabetes mellitus die from cardiovascular disease or stroke. Hyperglycemia, due to either reduced insulin secretion or reduced insulin sensitivity, is the hallmark feature of diabetes mellitus. Vascular dysfunction is a distinctive phenotype found in both types of diabetes and could be responsible for the high incidence of stroke, heart attack, and organ damage in diabetic patients. In addition to well-documented endothelial dysfunction, Ca(2+) handling alterations in vascular smooth muscle cells (VSMCs) play a key role in the development and progression of vascular complications in diabetes. VSMCs provide not only structural integrity to the vessels but also control myogenic arterial tone and systemic blood pressure through global and local Ca(2+) signaling. The Ca(2+) signalosome of VSMCs is integrated by an extensive number of Ca(2+) handling proteins (i.e. channels, pumps, exchangers) and related signal transduction components, whose function is modulated by endothelial effectors. This review summarizes recent findings concerning alterations in endothelium and VSMC Ca(2+) signaling proteins that may contribute to the vascular dysfunction found in the diabetic condition.

Activation of ERK1/2 by store-operated calcium entry in rat parotid acinar cells

The regulation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) plays a critical role in a variety of cellular processes, including transcription, protein activation, vesicle trafficking, and ion movement across epithelial cells. In many cells, the activation of phospholipase C-coupled receptors hydrolyzes membrane phosphoinositides and produces the depletion of endoplasmic reticulum Ca²⁺ stores, followed by the sustained elevation of [Ca²⁺]_i from Ca²⁺ entry across the plasma membrane via store-operated Ca²⁺ entry (SOCE). Ca²⁺ entry is also increased in a store-independent manner by arachidonate-regulated Ca²⁺ (ARC) channels. Using rat parotid salivary gland cells, we examined multiple pathways of Ca²⁺ entry/elevation to determine if they activated cell signaling proteins and whether this occurred in a pathway-dependent manner. We observed that SOCE activates extracellular signal-related kinases 1 and 2 (ERK1/2) to ∼3-times basal levels via a receptor-independent mechanism when SOCE was initiated by depleting Ca²⁺ stores using the endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin (TG). TG-initiated ERK1/2 phosphorylation increased as rapidly as that initiated by the muscarinic receptor agonist carbachol, which promoted an increase to ∼5-times basal levels. Notably, ERK1/2 phosphorylation was not increased by the global elevation of [Ca²⁺]_i by Ca²⁺ ionophore or by Ca²⁺ entry via ARC channels in native cells, although ERK1/2 phosphorylation was increased by Ca²⁺ ionophore in Par-C10 and HSY salivary cell lines. Agents and conditions that blocked SOCE in native cells, including 2-aminoethyldiphenyl borate (2-APB), SKF96363, and removal of extracellular Ca²⁺, also reduced TG- and carbachol-stimulated ERK1/2 phosphorylation. TG-promoted ERK1/2 phosphorylation was blocked when SRC and Protein Kinases C (PKC) were inhibited, and it was blocked in cells pretreated with β-adrenergic agonist isoproterenol. These observations demonstrate that ERK1/2 is activated by a selective mechanism of Ca²⁺ entry (SOCE) in these cells, and suggest that ERK1/2 may contribute to events downstream of SOCE.

Rosmarinic acid administration attenuates diabetes-induced vascular dysfunction of the rat aorta

OBJECTIVES

Oxidative stress as well as inflammation processes are engaged in diabetic vascular complications. Rosmarinic acid, a natural phenol antioxidant carboxylic acid, was found to have multiple biological activity, including anti-inflammatory and antitumour effects, which are a consequence of its inhibition of the inflammatory processes and of reactive oxygen species scavenging. The aim of this work was to study effects of rosmarinic acid administration on vascular impairment induced by experimental diabetes in rats.

METHODS

Diabetes was induced by streptozocin (3 × 30 mg/kg daily, i.p.) in Wistar rats. Rosmarinic acid was administered orally (50 mg/kg daily). Ten weeks after streptozocin administration, the aorta was excised for functional studies, evaluation by electron microscopy and real time PCR analysis.

KEY FINDINGS

In the aorta of diabetic rats, decreased endothelium-dependent relaxation was accompanied by overexpression of interleukin-1β, tumour necrosis factor-α, preproendothelin-1 and endothelin converting enzyme-1. Structural alterations in the endothelium, detected by electron microscopy, indicated aortic dysfunction caused by diabetes. The diabetes-induced aortic disorders were prevented by rosmarinic acid administration.

CONCLUSIONS

Rosmarinic acid protected aortic endothelial function and ultrastructure against diabetes-induced damage. Both antioxidant and anti-inflammatory effects of rosmarinic acid seemed to participate in the mechanism of this protection.

Pathogenic role of store-operated and receptor-operated ca(2+) channels in pulmonary arterial hypertension

Pulmonary circulation is an important circulatory system in which the body brings in oxygen. Pulmonary arterial hypertension (PAH) is a progressive and fatal disease that predominantly affects women. Sustained pulmonary vasoconstriction, excessive pulmonary vascular remodeling, in situ thrombosis, and increased pulmonary vascular stiffness are the major causes for the elevated pulmonary vascular resistance (PVR) in patients with PAH. The elevated PVR causes an increase in afterload in the right ventricle, leading to right ventricular hypertrophy, right heart failure, and eventually death. Understanding the pathogenic mechanisms of PAH is important for developing more effective therapeutic approach for the disease. An increase in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC migration and proliferation which lead to pulmonary vascular wall thickening and remodeling. It is thus pertinent to define the pathogenic role of Ca²⁺ signaling in pulmonary vasoconstriction and PASMC proliferation to develop new therapies for PAH. [Ca²⁺]_cyt in PASMC is increased by Ca²⁺ influx through Ca²⁺ channels in the plasma membrane and by Ca²⁺ release or mobilization from the intracellular stores, such as sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER). There are two Ca²⁺ entry pathways, voltage-dependent Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCC) and voltage-independent Ca²⁺ influx through store-operated Ca²⁺ channels (SOC) and receptor-operated Ca²⁺ channels (ROC). This paper will focus on the potential role of VDCC, SOC, and ROC in the development and progression of sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling in PAH.

Adipokines and the cardiovascular system: mechanisms mediating health and disease

This review focuses on the role of adipokines in the maintenance of a healthy cardiovascular system, and the mechanisms by which these factors mediate the development of cardiovascular disease in obesity. Adipocytes are the major cell type comprising the adipose tissue. These cells secrete numerous factors, termed adipokines, into the blood, including adiponectin, leptin, resistin, chemerin, omentin, vaspin, and visfatin. Adipose tissue is a highly vascularised endocrine organ, and different adipose depots have distinct adipokine secretion profiles, which are altered with obesity. The ability of many adipokines to stimulate angiogenesis is crucial for adipose tissue expansion; however, excessive blood vessel growth is deleterious. As well, some adipokines induce inflammation, which promotes cardiovascular disease progression. We discuss how these 7 aforementioned adipokines act upon the various cardiovascular cell types (endothelial progenitor cells, endothelial cells, vascular smooth muscle cells, pericytes, cardiomyocytes, and cardiac fibroblasts), the direct effects of these actions, and their overall impact on the cardiovascular system. These were chosen, as these adipokines are secreted predominantly from adipocytes and have known effects on cardiovascular cells.

Orai1 calcium channels in the vasculature

Orai1 was discovered in T cells as a calcium-selective channel that is activated by store depletion. Recent studies suggest that it is expressed and functionally important also in blood vessels, not only because haematopoietic cells can incorporate in the vascular wall but also because Orai1 is expressed and functional in vascular smooth muscle cells and endothelial cells. This article summarises the arising observations in this new area of vascular research and debates underlying issues and challenges for future investigations. The primary focus is on vascular smooth muscle cells and endothelial cells. Specific topics include Orai1 expression; Orai1 roles in store-operated calcium entry and ionic currents of store-depleted cells; blockade of Orai1-related signals by Synta 66 and other pharmacology; activation or regulation of Orai1-related signals by physiological substances and compartments; stromal interaction molecules and the relationship of Orai1 to other ion channels, transporters and pumps; transient receptor potential canonical channels and their contribution to store-operated calcium entry; roles of Orai1 in vascular tone, remodelling, thrombus formation and inflammation; and Orai2 and Orai3. Overall, the observations suggest the existence of an additional, previously unrecognised, calcium channel of the vascular wall that is functionally important particularly in remodelling but probably also in certain vasoconstrictor contexts.