Peroxynitrite resistance of sarco/endoplasmic reticulum Ca2+ pump in pig coronary artery endothelium and smooth muscle

IP3R and RyR channels are involved in traffic-related PM2.5-induced disorders of calcium homeostasis

Traffic-related PM_2.5 can result in immune system damage and diseases; however, the possible mechanism of its effect remains unclear. Calcium (Ca²⁺) is a critical signaling molecule in a variety of cells. Indeed, Ca²⁺ is involved in numerous basic functions, including cell growth and death. In this study, Jurkat T cells were used to explore the possible mechanisms of PM_2.5-elicited intracellular Ca²⁺signal responses. The results indicate that PM_2.5 could raise the level of intracellular Ca²⁺ concentration ([Ca²⁺]i). The [Ca²⁺]i in Jurkat T cells significantly decreased after treatment with heparin as an inhibitor of inositol trisphosphate receptors (IP3 R), or procaine as an inhibitor of ryanodine receptors (RyR). The expression of calmodulin (CAM) protein decreased in a time-dependent manner after exposure to PM_2.5, whereas the activity of Ca²⁺-Mg²⁺-ATPase seemed to show a slight drop trend after exposure to PM_2.5. Our findings demonstrate that PM_2.5 stimulation to Jurkat T cells would result in an increase in [Ca²⁺]i, which is modulated by IP3 R and RyR, as well as CAM.

Endoplasmic reticulum stress in insulin resistance and diabetes

The endoplasmic reticulum is the main intracellular Ca(2+) store for Ca(2+) release during cell signaling. There are different strategies to avoid ER Ca(2+) depletion. Release channels utilize first Ca(2+)-bound to proteins and this minimizes the reduction of the free luminal [Ca(2+)]. However, if release channels stay open after exhaustion of Ca(2+)-bound to proteins, then the reduction of the free luminal ER [Ca(2+)] (via STIM proteins) activates Ca(2+) entry at the plasma membrane to restore the ER Ca(2+) load, which will work provided that SERCA pump is active. Nevertheless, there are several noxious conditions that result in decreased activity of the SERCA pump such as oxidative stress, inflammatory cytokines, and saturated fatty acids, among others. These conditions result in a deficient restoration of the ER [Ca(2+)] and lead to the ER stress response that should facilitate recovery of the ER. However, if the stressful condition persists then ER stress ends up triggering cell death and the ensuing degenerative process leads to diverse pathologies; particularly insulin resistance, diabetes and several of the complications associated with diabetes. This scenario suggests that limiting ER stress should decrease the incidence of diabetes and the mobility and mortality associated with this illness.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

Reactive nitrogen species: molecular mechanisms and potential significance in health and disease

Reactive nitrogen species (RNS) are various nitric oxide-derived compounds, including nitroxyl anion, nitrosonium cation, higher oxides of nitrogen, S-nitrosothiols, and dinitrosyl iron complexes. RNS have been recognized as playing a crucial role in the physiologic regulation of many, if not all, living cells, such as smooth muscle cells, cardiomyocytes, platelets, and nervous and juxtaglomerular cells. They possess pleiotropic properties on cellular targets after both posttranslational modifications and interactions with reactive oxygen species. Elevated levels of RNS have been implicated in cell injury and death by inducing nitrosative stress. The aim of this comprehensive review is to address the mechanisms of formation and removal of RNS, highlighting their potential cellular targets: lipids, DNA, and proteins. The specific importance of RNS and their paradoxic effects, depending on their local concentration under physiologic conditions, is underscored. An increasing number of compounds that modulate RNS processing or targets are being identified. Such compounds are now undergoing preclinical and clinical evaluations in the treatment of pathologies associated with RNS-induced cellular damage. Future research should help to elucidate the involvement of RNS in the therapeutic effect of drugs used to treat neurodegenerative, cardiovascular, metabolic, and inflammatory diseases and cancer.

Modulation by simvastatin of iberiotoxin-sensitive, Ca2+-activated K+ channels of porcine coronary artery smooth muscle cells

BACKGROUND AND PURPOSE

Statins (3-hydroxy-3-methyl-glutaryl coenzyme A (HMG CoA) reductase inhibitors) have been demonstrated to reduce cardiovascular mortality. It is unclear how the expression level of HMG CoA reductase in cardiovascular tissues compares with that in cells derived from the liver. We hypothesized that this enzyme exists in different cardiovascular tissues, and simvastatin modulates the vascular iberiotoxin-sensitive Ca2+-activated K(+) (BK(Ca)) channels.

EXPERIMENTAL APPROACHES

Expression of HMG CoA reductase in different cardiovascular preparations was measured. Effects of simvastatin on BK(Ca) channel gatings of porcine coronary artery smooth muscle cells were evaluated.

KEY RESULTS

Western immunoblots revealed the biochemical existence of HMG CoA reductase in human cardiovascular tissues and porcine coronary artery. In porcine coronary artery smooth muscle cells, extracellular simvastatin (1, 3 and 10 microM) (hydrophobic), but not simvastatin Na+ (hydrophilic), inhibited the BK(Ca) channels with a minimal recovery upon washout. Isopimaric acid (10 microM)-mediated enhancement of the BK(Ca) amplitude was reversed by external simvastatin. Simvastatin Na+ (10 microM, applied internally), markedly attenuated isopimaric acid (10 microM)-induced enhancement of the BK(Ca) amplitude. Reduced glutathione (5 mM; in the pipette solution) abolished simvastatin -elicited inhibition. Mevalonolactone (500 microM) and geranylgeranyl pyrophosphate (20 microM) only prevented simvastatin (1 and 3 microM)-induced responses. simvastatin (10 microM ) caused a rottlerin (1 microM)-sensitive (cycloheximide (10 microM)-insensitive) increase of PKC-delta protein expression.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrated the biochemical presence of HMG CoA reductase in different cardiovascular tissues, and that simvastatin inhibited the BK(Ca) channels of the arterial smooth muscle cells through multiple intracellular pathways.

Ca2+-pumps and Na2+-Ca2+-exchangers in coronary artery endothelium versus smooth muscle

Vascular endothelial cells (EC) and smooth muscle cells (SMC) require a decrease in cytoplasmic Ca²⁺ concentration after activation. This can be achieved by Ca²⁺ sequestration by the sarco-/endoplasmic reticulum Ca²⁺ pumps (SERCA) and Ca²⁺ extrusion by plasma membrane Ca²⁺ pumps (PMCA) and Na⁺–Ca²⁺-exchangers (NCX). Since the two cell types differ in their structure and function, we compared the activities of PMCA, NCX and SERCA in pig coronary artery EC and SMC, the types of isoforms expressed using RT-PCR, and their protein abundance using Western blots. The activity of NCX is higher in EC than in SMC but those of PMCA and SERCA is lower. Consistently, the protein abundance for NCX protein is higher in EC than in SMC and those of PMCA and SERCA is lower. Based on RT-PCR experiments, the types of RNA present are as follows: EC for PMCA1 while SMC for PMCA4 and PMCA1; EC for SERCA2 and SERCA3 and SMC for SERCA2. Both EC and SMC express NCX1 (mainly NCX1.3). PMCA, SERCA and NCX differ in their affinities for Ca²⁺ and regulation. Based on these observations and the literature, we conclude that the tightly regulated Ca²⁺ removal systems in SMC are consistent with the cyclical control of contractility of the filaments and those in EC are consistent with Ca²⁺ regulation of the endothelial nitric oxide synthase near the cell surface. The differences between EC and SMC should be considered in therapeutic interventions of cardiovascular diseases.

Alcohol-induced blood?brain barrier dysfunction is mediated via inositol 1,4,5-triphosphate receptor (IP3R)-gated intracellular calcium release

The blood-brain barrier (BBB) formed by brain microvascular endothelial cells (BMVEC), pericytes and astrocytes controls the transport of ions, peptides and leukocytes in and out of the brain. Tight junctions (TJ) composed of TJ proteins (occludin, claudins and zonula occludens) ensure the structural integrity of the BMVEC monolayer. Neuropathologic studies indicated that the BBB was impaired in alcohol abusers; however, the underlying mechanism of BBB dysfunction remains elusive. Using primary human BMVEC, we previously demonstrated that oxidative stress induced by ethanol (EtOH) metabolism in BMVEC activated myosin light chain kinase (MLCK), resulting in the enhanced phosphorylation of either cytoskeletal or TJ proteins, and in BBB impairment. We proposed that EtOH metabolites stimulated inositol 1,4,5-triphosphate receptor (IP(3)R)-operated intracellular calcium (Ca(2+)) release, thereby causing the activation of MLCK in BMVEC. Indeed, treatment of primary human BMVEC with EtOH or its metabolites resulted in the increased expression of IP(3)R protein and IP(3)R-gated intracellular Ca(2+) release. These functional changes paralleled MLCK activation, phosphorylation of cytoskeletal/TJ proteins, loss of BBB integrity, and enhanced leukocyte migration across BMVEC monolayers. Inhibition of either EtOH metabolism or IP(3)R activation prevented BBB impairment. These findings suggest that EtOH metabolites act as signaling molecules for the activation of MLCK via the stimulation of IP(3)R-gated intracellular Ca(2+) release in BMVEC. These putative events can lead to BBB dysfunction in the setting of alcoholism, and to neuro-inflammatory disorders promoting leukocyte migration across the BBB.

Fructose-induced peroxynitrite production is mediated by methylglyoxal in vascular smooth muscle cells

Methylglyoxal (MG), a highly reactive molecule, has been implicated in the development of insulin resistance. We investigated whether fructose, a precursor of MG, induced ONOO(-) generation and whether this process was mediated via endogenously increased MG formation. Fructose significantly increased MG generation in vascular smooth muscle cells (VSMCs) in a concentration and time dependent manner. The intracellular production of MG was increased by 153+/-23% or 259+/-28% after cells were treated 6 h with fructose (15 mM or 30 mM), compared with production from untreated cells (p<0.01, n=4 for each group). A significant increase in the production of ONOO(-), NO, and O(2)(*-), was found in the cells treated with fructose (15 mM) or MG (10 microM). Fructose- or MG-induced ONOO(-) generation was significantly inhibited by MG scavengers, including reduced glutathione or N-acetyl-l-cysteine, and by O(2)(*-) or NO inhibitors, such as diphenylene iodonium, superoxide dismutase or N-nitro-l-arginine methyl ester. Moreover, an enhanced iNOS expression was also observed in the cells treated directly with MG which was significantly inhibited when co-application with N-acetyl-l-cysteine. Our results demonstrated that fructose is capable of inducing a significant increase in ONOO(-) production, which is mediated by an enhanced formation of endogenous MG in VSMCs.

Modulation by homocysteine of the iberiotoxin-sensitive, Ca2+ -activated K+ channels of porcine coronary artery smooth muscle cells

We evaluated the acute effect of homocysteine on the iberiotoxin-sensitive, Ca(2+)-activated K(+) (BK(Ca)) channels of the porcine coronary artery smooth muscle cells. NS 1619 (1 to 30 microM) caused a concentration-dependent enhancement of the BK(Ca) amplitude (recorded using the whole-cell, membrane-rupture configuration) only with an elevated [Ca(2+)](i) of approximately 444 nM, but not with [Ca(2+)](i) of approximately 100 nM. Homocysteine (30 microM) caused a small inhibition ( approximately 16%) of the BK(Ca) amplitude ([Ca(2+)](i)= approximately 444 nM), and a greater inhibition ( approximately 77%) was observed with 100 microM NADH present in the pipette solution. The inhibition persisted after washing. With NADPH (100 microM), a smaller magnitude of inhibition ( approximately 34%) of the BK(Ca) amplitude was recorded. The NS 1619-mediated enhancement of the BK(Ca) amplitude (with elevated [Ca(2+)](i) plus NADH in the pipette) was attenuated by homocysteine. The homocysteine-mediated inhibition of the BK(Ca) amplitude was suppressed by Tiron (10 mM) or diphenylene iodonium (30 nM), applied alone, but not by superoxide dismutase (500 U/ml) and catalase (500 U/ml). Generation of superoxide (O(2)(-)) of the smooth muscle cells (with NADH presence), measured using the lucigenin-enhanced chemiluminescence, was markedly increased by angiotensin II (100 nM) and homocysteine (30 microM). The chemiluminescence signal was sensitive to apocynin (300 microM) or Tiron, applied alone, but not to superoxide dismutase and catalase. In conclusion, our results demonstrate that acute homocysteine application inhibits the iberiotoxin-sensitive BK(Ca) channels (with elevated [Ca(2+)](i) and NADH present) which is probably caused by the NADH oxidase activation and the concomitant generation of intracellular superoxide.

Is methylglyoxal a causative factor for hypertension development?This paper is one of a selection of papers published in this Special Issue, entitled Young Investigator's Forum

Hypertension is a life-threatening disease that is associated with increased cardiovascular risks. Causes and mechanisms for hypertension development remain poorly understood. Methylglyoxal (MG), a highly reactive molecule, is a metabolite of sugar. Increased circulation and tissue levels of MG have been documented not only in diabetes but also in hypertension. Many recent studies also link MG-induced vascular damage to the pathogenic process of hypertension. As such, an etiological role of MG in hypertension development is proposed.

Peroxynitrite causes endoplasmic reticulum stress and apoptosis in human vascular endothelium: implications in atherogenesis

OBJECTIVE

Peroxynitrite, a potent oxidant generated by the reaction of NO with superoxide, has been implicated in the promotion of atherosclerosis. We designed this study to determine whether peroxynitrite induces its proatherogenic effects through induction of endoplasmic reticulum (ER) stress.

METHODS AND RESULTS

Human vascular endothelial cells treated with Sin-1, a peroxynitrite generator, induced the expression of the ER chaperones GRP78 and GRP94 and increased eIF2alpha phosphorylation. These effects were inhibited by the peroxynitrite scavenger uric acid. Sin-1 caused the depletion of ER-Ca2+, an effect known to induce ER stress, resulting in the elevation of cytosolic Ca2+ and programmed cell death (PCD). Sin-1 treatment was also found, via 3-nitrotyrosine and GRP78 colocalization, to act directly on the ER. Adenoviral-mediated overexpression of GRP78 in endothelial cells prevented Sin-1-induced PCD. Consistent with these in vitro findings, 3-nitrotyrosine was observed and colocalized with GRP78 in endothelial cells of early atherosclerotic lesions from apolipoprotein E-deficient mice.

CONCLUSIONS

Peroxynitrite is an ER stress-inducing agent. Its effects include the depletion of ER-Ca2+, a known mechanism of ER stress induction. The observation that 3-nitrotyrosine-containing proteins colocalize with markers of ER stress within early atherosclerotic lesions suggests that peroxynitrite contributes to atherogenesis through a mechanism involving ER stress.

Ascorbate uptake in pig coronary artery endothelial cells

Although smooth muscle and endothelial cells in pig coronary artery are morphologically and functionally distinct, ascorbate uptake has been characterized only in smooth muscle cells. Ascorbate transporters in kidney and intestinal epithelial cells differ from those in smooth muscle. We examined ascorbate transport and mRNA expression of sodium-dependent vitamin C transporters (SVCT) by RT-PCR in the pig coronary artery endothelial cell cultures. When 14C-ascorbate uptake in endothelial cells was examined as 14C or by HPLC, the two values did not differ from each other. 14C-ascorbate uptake was Na(+)-dependent, stereoselective for L-ascorbate and inhibited by sulfinpyrazone. The kinetic characteristics of the uptake were: Km = 27 +/- 3 microM (Hill coefficient = 1) for ascorbate and Km = 73 +/- 14 mM (Hill coefficient = 2) for Na+. Surprisingly, endothelial cells had similar kinetic parameters as smooth muscle cells, except for a slightly lower uptake velocity in endothelial cells. Comparison with the smooth muscle showed that both tissue types expressed mRNA for SVCT2. Endothelial cells differ from epithelial cells which express mainly SVCT1 but resemble smooth muscle cells in this respect.