Inducible nitric oxide synthase inhibition of weibel-palade body release in cardiac transplant rejection

TNF-α-activated eNOS signaling increases leukocyte adhesion through the S-nitrosylation pathway

Nitric oxide (NO) is a key factor in inflammation. Endothelial nitric oxide synthase (eNOS), whose activity increases after stimulation with proinflammatory cytokines, produces NO in endothelium. NO activates two pathways: 1) soluble guanylate cyclase-protein kinase G and 2) S-nitrosylation (NO-induced modification of free-thiol cysteines in proteins). S-nitrosylation affects phosphorylation, localization, and protein interactions. NO is classically described as a negative regulator of leukocyte adhesion to endothelial cells. However, agonists activating NO production induce a fast leukocyte adhesion, which suggests that NO might positively regulate leukocyte adhesion. We tested the hypothesis that eNOS-induced NO promotes leukocyte adhesion through the S-nitrosylation pathway. We stimulated leukocyte adhesion to endothelium in vitro and in vivo using tumor necrosis factor-α (TNF-α) as proinflammatory agonist. ICAM-1 changes were evaluated by immunofluorescence, subcellular fractionation, immunoprecipitation, and fluorescence recovery after photobleaching (FRAP). Protein kinase Cζ (PKCζ) activity and S-nitrosylation were evaluated by Western blot analysis and biotin switch method, respectively. TNF-α, at short times of stimulation, activated the eNOS S-nitrosylation pathway and caused leukocyte adhesion to endothelial cells in vivo and in vitro. TNF-α-induced NO led to changes in ICAM-1 at the cell surface, which are characteristic of clustering. TNF-α-induced NO also produced S-nitrosylation and phosphorylation of PKCζ, association of PKCζ with ICAM-1, and ICAM-1 phosphorylation. The inhibition of PKCζ blocked leukocyte adhesion induced by TNF-α. Mass spectrometry analysis of purified PKCζ identified cysteine 503 as the only S-nitrosylated residue in the kinase domain of the protein. Our results reveal a new eNOS S-nitrosylation-dependent mechanism that induces leukocyte adhesion and suggests that S-nitrosylation of PKCζ may be an important regulatory step in early leukocyte adhesion in inflammation.NEW & NOTEWORTHY Contrary to the well-established inhibitory role of NO in leukocyte adhesion, we demonstrate a positive role of nitric oxide in this process. We demonstrate that NO induced by eNOS after TNF-α treatment induces early leukocyte adhesion activating the S-nitrosylation pathway. Our data suggest that PKCζ S-nitrosylation may be a key step in this process.

Determination of Redox Status in Serum

Free radicals of oxidative and nitrosative stress can trigger both pro-inflammatory and anti-inflammatory responses. In the transplant setting, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced at the rejection site by different cell types including endothelial cells and macrophages. In particular, production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) seems to play an important role in promoting inflammation after exposure to inflammatory stimuli. In xenotransplantation, NO produced by iNOS upregulate multiple vasoactive substances, cytokines, chemokines, and growth factors, whereas production of NO by endothelial nitric oxide synthase (eNOS) could confer a protective effect to the graft. Accordingly, further research is needed to better understand the associated mechanisms in order to enhance protection and prevent tissue damage. Here, we describe simple methods to determine the redox state in serum that could be applied to animal models such as for xenotransplantation studies, as well as to clinical samples. Notably, caution should be taken when interpreting results of ROS and RNS measurements due to this dual role of free radicals in protecting and injuring the graft.

Pharmacological hypothesis: Nitric oxide-induced inhibition of ADAM-17 activity as well as vesicle release can in turn prevent the production of soluble endothelin-converting enzyme

Endothelin‐1 (ET‐1) and nitric oxide (NO) are two highly potent vasoactive molecules with opposing effects on the vasculature. Endothelin‐converting enzyme (ECE) and nitric oxide synthase (NOS) catalyse the production of ET‐1 and NO, respectively. It is well established that these molecules play a crucial role in the initiation and progression of cardiovascular diseases and have therefore become targets of therapy. Many studies have examined the mechanism(s) by which NO regulates ET‐1 production. Expression and localization of ECE‐1 is a key factor that determines the rate of ET‐1 production. ECE‐1 can either be membrane bound or be released from the cell surface to produce a soluble form. NO has been shown to reduce the expression of both membrane‐bound and soluble ECE‐1. Several studies have examined the mechanism(s) behind NO‐mediated inhibition of ECE expression on the cell membrane. However, the precise mechanism(s) behind NO‐mediated inhibition of soluble ECE production are unknown. We hypothesize that both exogenous and endogenous NO, inhibits the production of soluble ECE‐1 by preventing its release via extracellular vesicles (e.g., exosomes), and/or by inhibiting the activity of A Disintegrin and Metalloprotease‐17 (ADAM17). If this hypothesis is proven correct in future studies, these pathways represent targets for the therapeutic manipulation of soluble ECE‐1 production.

The Emerging Role of NETs in Venous Thrombosis and Immunothrombosis

Venous thrombosis (VT), a leading cause of morbidity and mortality worldwide, has recently been linked to neutrophil activation and release of neutrophil extracellular traps (NETs) via a process called NETosis. The use of various in vivo thrombosis models and genetically modified mice has more precisely defined the exact role of NETosis in the pathogenesis of VT. Translational large animal VT models and human studies have confirmed the presence of NETs in pathologic VT. Activation of neutrophils, with subsequent NETosis, has also been linked to acute infection. This innate immune response, while effective for bacterial clearance from the host by formation of an intravascular bactericidal "net," also triggers thrombosis. Intravascular thrombosis related to such innate immune mechanisms has been coined immunothrombosis. Dysregulated immunothrombosis has been proposed as a mechanism of pathologic micro- and macrovascular thrombosis in sepsis and autoimmune disease. In this focused review, we will address the dual role of NETs in the pathogenesis of VT and immunothrombosis.

N-ethylmaleimide‑sensitive factor siRNA inhibits the release of Weibel-Palade bodies in endothelial cells

The aim of the present study was to examine the effect of small interfering RNA (siRNA) methods on the expression of N‑ethylmaleimide sensitive factor (NSF) and Weibel‑Palade body (WPB) release in endothelial cells. A small hairpin RNA (shRNA), mediated with an adenovirus vector, was designed to target the N‑terminal functional area of NSF. Subsequently, viruses were transfected into human aortic endothelial cells. The mRNA and protein expression levels of NSF were detected using reverse transcription‑quantitative polymerase chain reaction and Western blot analyses, respectively, and the release of WPBs in the endothelial cells was examined using immunofluorescence. The mRNA expression of NSF in the endothelial cells, which were transfected with the adenoviruses carrying the NSF‑shRNA was significantly decreased, compared with the negative control group (P=0.035) and blank control group (P=0.02). In addition, the mRNA expression of NSF was gradually decreased as duration increased; there were marked differences between the 24, 48 and 72 h groups (P<0.05). The protein expression of NSF was significantly decreased in the experimental group, compared with the negative control group (P=0.004) and blank control group (P=0.031), however, no difference was observed between the negative control and blank control groups (P=0.249). The immunofluorescence staining showed that the release of WPBs in the endothelial cells induced with thrombin was inhibited markedly following transfection with the virus carrying the NSF‑shRNA. Therefore NSF‑siRNA inhibited the mRNA and protein expression levels of NSF, and inhibited the release of WPBs in endothelial cells induced with thrombin. These results suggested that NSF-siRNA may be valuable for preventing and treating atherosclerosis and acute coronary syndrome.

Low-dose benznidazole treatment results in parasite clearance and attenuates heart inflammatory reaction in an experimental model of infection with a highly virulent Trypanosoma cruzi strain

Chagas disease, caused by Trypanosoma cruzi, is the main cause of dilated cardiomyopathy in the Americas. Antiparasitic treatment mostly relies on benznidazole (Bzl) due to Nifurtimox shortage or unavailability. Both induce adverse drug effects (ADE) of varied severity in many patients, leading to treatment discontinuation or abandonment. Since dosage may influence ADE, we aimed to assess Bzl efficacy in terms of parasiticidal and anti-inflammatory activity, using doses lower than those previously reported. BALB/c mice infected with the T. cruzi RA strain were treated with different doses of Bzl. Parasitaemia, mortality and weight change were assessed. Parasite load, tissue infiltrates and inflammatory mediators were studied in the heart. Serum creatine kinase (CK) activity was determined as a marker of heart damage. The infection-independent anti-inflammatory properties of Bzl were studied in an in vitro model of LPS-treated cardiomyocyte culture. Treatment with 25 mg/kg/day Bzl turned negative the parasitological parameters, induced a significant decrease in IL-1β, IL-6 and NOS2 in the heart and CK activity in serum, to normal levels. No mortality was observed in infected treated mice. Primary cultured cardiomyocytes treated with Bzl showed that inflammatory mediators were reduced via inhibition of the NF-κB pathway. A Bzl dose lower than that previously reported for treatment of experimental Chagas disease exerts adequate antiparasitic and anti-inflammatory effects leading to parasite clearance and tissue healing. This may be relevant to reassess the dose currently used for the treatment of human Chagas disease, aiming to minimize ADE.

JAK2V617F-positive endothelial cells contribute to clotting abnormalities in myeloproliferative neoplasms

The Janus kinase 2 (JAK2) V617F mutation is the primary pathogenic mutation in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). Although thrombohemorrhagic incidents are the most common causes of morbidity and mortality in patients with MPNs, the events causing these clotting abnormalities remain unclear. To identify the cells responsible for the dysfunctional hemostasis, we used transgenic mice expressing JAK2V617F in specific lineages involved in thrombosis and hemostasis. When JAK2V617F was expressed in both hematopoietic and endothelial cells (ECs), the mice developed a significant MPN, characterized by thrombocytosis, neutrophilia, and splenomegaly. However, despite having significantly higher platelet counts than controls, these mice showed severely attenuated thrombosis following injury. Interestingly, platelet activation and aggregation in response to agonists was unaltered by JAK2V617F expression. Subsequent bone marrow transplants revealed the contribution of both endothelial and hematopoietic compartments to the attenuated thrombosis. Furthermore, we identified a potential mechanism for this phenotype through JAK2V617F-regulated inhibition of von Willebrand factor (VWF) function and/or secretion. JAK2V617F(+) mice display a condition similar to acquired von Willebrand syndrome, exhibiting significantly less high molecular weight VWF and reduced agglutination to ristocetin. These findings greatly advance our understanding of thrombohemorrhagic events in MPNs and highlight the critical role of ECs in the pathology of hematopoietic malignancies.

Relaxin protects rat lungs from ischemia-reperfusion injury via inducible NO synthase: role of ERK-1/2, PI3K, and forkhead transcription factor FKHRL1

INTRODUCTION

Early allograft dysfunction following lung transplantation is mainly an ischemia/reperfusion (IR) injury. We showed that relaxin-2 (relaxin) exerts a protective effect in lung IR, attributable to decreases in endothelin-1 (ET-1) production, leukocyte recruitment, and free radical generation. Here, we summarize our investigations into relaxin's signalling.

MATERIALS AND METHODS

Isolated rat lungs were perfused with vehicle or 5 nM relaxin (n = 6-10 each). Thereafter, experiments were conducted in the presence of relaxin plus vehicle, the protein kinase A inhibitors H-89 and KT-5720, the NO synthase (NOS) inhibitor L-NAME, the iNOS inhibitor 1400W, the nNOS inhibitor SMTC, the extracellular signal-regulated kinase-1/2 (ERK-1/2) inhibitor PD-98059, the phosphatidylinositol-3 kinase (PI3K) inhibitor wortmannin, the endothelin type-B (ETB) antagonist A-192621, or the glucocorticoid receptor (GR) antagonist RU-486. After 90 min ischemia and 90 min reperfusion we determined wet-to-dry (W/D) weight ratio, mean pulmonary arterial pressure (MPAP), vascular release of ET-1, neutrophil elastase (NE), myeloperoxidase (MPO), and malondialdehyde (MDA). Primary rat pulmonary vascular cells were similarly treated.

RESULTS

IR lungs displayed significantly elevated W/D ratios, MPAP, as well as ET-1, NE, MDA, and MPO. In the presence of relaxin, all of these parameters were markedly improved. This protective effect was completely abolished by L-NAME, 1400W, PD-98059, and wortmannin whereas neither PKA and nNOS inhibition nor ETB and GR antagonism were effective. Analysis of NOS gene expression and activity revealed that the relaxin-induced early and moderate iNOS stimulation is ERK-1/2-dependent and counter-balanced by PI3K. Relaxin-PI3K-related phosphorylation of a forkhead transcription factor, FKHRL1, paralleled this regulation. In pulmonary endothelial and smooth muscle cells, FKHRL1 was essential to relaxin-PI3K signalling towards iNOS.

CONCLUSION

In this short-time experimental setting, relaxin protects against IR-induced lung injury via early and moderate iNOS induction, dependent on balanced ERK-1/2 and PI3K-FKHRL1 stimulation. These findings render relaxin a candidate drug for lung preservation.

PPARγ ligand treatment inhibits cardiac inflammatory mediators induced by infection with different lethality strains of Trypanosoma cruzi

Trypanosoma cruzi (T. cruzi), the etiological agent of Chagas' disease, causes cardiac alterations in the host. Although the main clinical manifestations arise during the chronic stage, the mechanisms leading to heart damage develop early during infection. In fact, an intense inflammatory response is observed from acute stage of infection. Recently, peroxisome proliferator-activated receptors (PPARs) have attracted research interest due to their participation in the modulation of inflammation. In this work we addressed the role of 15-Deoxy-∆(12,14) ProstaglandinJ2 (15dPGJ2), a PPARγ natural ligand in the regulation of inflammatory mediators, in acute and chronic experimental mouse models of Chagas' disease with the RA and K98 T. cruzi strains, respectively. This work demonstrates that 15dPGJ2 treatment inhibits the expression and activity of inducible nitric oxide synthase (NOS2) as well as TNF-α and IL-6 mRNA levels. Also, expression and activity of metalloproteinases 2 (MMP-2) and 9 (MMP9) were inhibited by 15dPGJ2. Moreover GW9662, a specific PPARγ antagonist, revealed the participation of other signaling pathways since, in GW9662 presence, 15dPJG2 had a partial effect on the inhibition of inflammatory parameters in the acute model of infection. Accordingly, NF-κB activation was demonstrated, assessing p65 nuclear translocation in the hearts of infected mice with both T. cruzi strains. Such effect was inhibited after 15dPGJ2 treatment. Our findings support the concept that in vivo PPARγ and NF-κB pathways are implicated in the inhibitory effects of 15dPGJ2 on inflammatory mediators at different times depending on whether the infection is caused by the lethal or non-lethal T. cruzi strain.

Modulation of inflammatory response and parasitism by 15-Deoxy-Δ(12,14) prostaglandin J(2) in Trypanosoma cruzi-infected cardiomyocytes

Trypanosoma cruzi infection produces an intense inflammatory response in diverse tissues including the heart. The inflammatory reaction is critical for the control of the parasites' proliferation and evolution of Chagas disease. 15-Deoxy-Δ(12,14) prostaglandin J(2) (15dPGJ2) can repress the inflammatory response in many experimental models. However, the precise role of peroxisome proliferator-activated receptor γ (PPARγ) ligands in T. cruzi infection or in Chagas disease is poorly understood. This work reports the first evidence that 15dPGJ2 treatment increases the number of intracellular parasites as shown by fluorescence microscopy and it is also able to inhibit the expression and activity of different inflammatory enzymes such as inducible nitric oxide synthase (NOS-2), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9), as well as pro-inflammatory cytokine (TNF-α and IL-6) mRNA expression in neonatal mouse cardiomyocytes after T. cruzi infection. Transfection of cardiomyocytes with small interfering RNA (siRNA) induces silencing of PPARγ and impairs the effects of 15dPGJ2 on the modulation of pro-inflammatory enzymes. Moreover, transfection restores the ability of these cells to control the intracellular growth of T. cruzi. We also found that PPARγ-independent pathways are involved, since 15dPGJ2 also exerts its effect through extracellular signal-regulated kinases-mitogen-activated protein kinase (Erk-MAPK) and nuclear factor-κB (NF-κB). The use of specific pharmacological inhibitors confirmed these findings. Our data point out that 15dPGJ2 is a potent modulator of the inflammatory process and regulator of parasites growth through PPARγ-dependent and independent (Erk-MAPK- and NF-κB) pathways in T. cruzi infected neonatal cardiac cells.

15-deoxy-Delta12,14 prostaglandin GJ2 but not rosiglitazone regulates metalloproteinase 9, NOS-2, and cyclooxygenase 2 expression and functions by peroxisome proliferator-activated receptor gamma-dependent and -independent mechanisms in cardiac cells

Sepsis or endotoxemia produced by LPS followed by hypotension and multiorganic failure may lead to cardiac dysfunction contributing to mortality. Cardiac failure is usually associated to activation of nuclear factor kappaB (NF-kappaB) and mitogen-activated protein kinase (MAPK), which play an important role in proinflammatory enzymes expression. It has been shown that 15-deoxy-Delta12,14 prostaglandin J2 (15dPGJ2) can repress the inflammatory response by means of peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent and -independent mechanisms. However, its precise role in heart is poorly understood. In the present study, mouse neonatal cardiomyocytes were isolated and stimulated with LPS to investigate the role of PPARgamma-specific ligands 15dPGJ2 and rosiglitazone on cardiac inflammatory response. Inducible NO synthase, cyclooxygenase 2, and metalloproteinase 9 mRNA levels, protein expression, and activity were inhibited with 15dPGJ2 but not by rosiglitazone. Peroxisome proliferator-activated receptor gamma antagonist, GW9662, prevented all these 15dPGJ2 actions. To go inside the mechanisms by which 15dPGJ2 exerts inhibitory effects, cells were preincubated with specific chemical inhibitors of NF-kappaB and p38 MAPK, and we found that these signaling cascades are implicated in 15dPGJ2 action as well as PPARgamma. These results suggest that only the natural PPARgamma ligand, 15dPGJ2, but not the synthetic one, rosiglitazone, regulates the inflammatory response by inhibition of inducible NO synthase, cyclooxygenase 2, and metalloproteinase 9 expression. Moreover, our results offer an additional 15dPGJ2 mechanism of action, despite PPARgamma, showing NF-kappaB and p38 MAPK participation.

Endothelial von Willebrand factor release due to eNOS deficiency predisposes to thrombotic microangiopathy in mouse aging kidney

Endothelial dysfunction is critical in the decline of renal function with. By using endothelial nitric oxide synthase knockout (eNOSKO) mice, we tested the hypothesis that a lack of endothelial nitric oxide synthase accelerates renal injury in the aging kidney. In contrast to control mice and young eNOSKO mice, aging eNOSKO mice showed greater renal injury and in particular developed a thrombotic microangiopathy, with mesangiolysis, endothelial swelling, endothelial cell loss, double-contour appearance of glomerular basement membrane (GBM), and thrombus formation. Thrombi, which were composed of fibrin, platelets, and von Willebrand factor (vWF), were identified predominantly in glomerular capillaries and rarely in arterioles, but not in larger vessels. In the tubulointerstitium, tubular degeneration and macrophage infiltration were also prominent in aging eNOSKO mice. Intraluminal vWF deposition was accompanied with thrombus formation, whereas mesangial deposition of vWF was associated with mesangial matrix expansion. Furthermore, the mesangial vWF deposition was detectable in young eNOSKO mice in which severe glomerular injury had not yet developed. Finally, a higher level of serum P-selectin in eNOSKO mice was consistent with the vWF behavior and suggested exocytosis of the Weibel-Palade body by the endothelium. In conclusion, a lack of endothelial nitric oxide synthase resulted in the development of glomerular thrombotic microangiopathy. A lack of nitric oxide likely contributed to the release of vWF, leading to thrombus formation in this model.

Controlled delivery of nitric oxide inhibits leukocyte migration and prevents vasospasm in haptoglobin 2-2 mice after subarachnoid hemorrhage

OBJECTIVE

Cerebral vasospasm is the leading cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (SAH) occurs. The haptoglobin 2-2 genotype likely increases the risk for developing posthemorrhagic vasospasm, but potential treatments for vasospasm have never been tested in an animal model of this genotype. We used the nitric oxide (NO) donor diethylenetriamine (DETA)/NO incorporated into ethylene/vinyl acetate (EVAc) polymers to evaluate the efficacy of controlled NO repletion in a haptoglobin 2-2 mouse basilar artery SAH model.

METHODS

Mice were randomized to 3 groups: autologous blood injection and empty polymer implantation into the subarachnoid space (n = 16); blood injection and 30% DETA/NO-EVAc implantation (n = 20); and sham operation (n = 19). At 24 hours after surgery, activity level was assessed on a 3-point scale, and basilar arteries were processed for morphometric measurements. Leukocyte extravasation was assessed by immunohistochemistry (n = 12).

RESULTS

Treatment with controlled release of NO from DETA/NO-EVAc polymers after SAH resulted in a significant increase in basilar artery lumen patency (73.3% +/- 4.3% versus 96.5% +/- 4.3%, mean +/- standard error of the mean; P = 0.01), a significant improvement in activity after experimental SAH (2.14 +/- 0.14 versus 2.56 +/- 0.10 points; P = 0.025), and a significant decrease in extravasated leukocytes (21 +/- 4.55 versus 6.75 +/- 3.77 leukocytes per high-power field, untreated versus treated mice; P = 0.001).

CONCLUSION

Treatment with controlled release of NO prevented posthemorrhagic vasospasm in haptoglobin 2-2 mice, and mitigated neurological deficits, suggesting that DETA/NO-EVAc would be an effective therapy in patients with a genotype that confers higher risk for vasospasm after SAH. In addition to smooth muscle relaxation, inhibition of leukocyte migration may contribute to the therapeutic mechanism of NO.

The complex role of iNOS in acutely rejecting cardiac transplants

This review summarizes the evidence for a detrimental role of nitric oxide (NO) derived from inducible NO synthase (iNOS) and/or reactive nitrogen species such as peroxynitrite in acutely rejecting cardiac transplants. In chronic cardiac transplant rejection, iNOS may have an opposing beneficial component. The purpose of this review is primarily to address issues related to acute rejection, which is a recognized risk factor for chronic rejection. The evidence for a detrimental role is based upon strategies involving nonselective NOS inhibitors, NO neutralizers, selective iNOS inhibitors, and iNOS gene deletion in rodent models of cardiac rejection. The review is presented in the context of the impact on various components, including graft survival, histological rejection, and cardiac function, which may contribute to the process of graft rejection in toto. Possible limitations of each strategy are discussed in order to understand better the variance in published findings, including issues related to the potential importance of cell localization of iNOS expression. Finally, the concept of a dual role for NO and its downstream product, peroxynitrite, in rejection vs immune regulation is discussed.

Nitric oxide regulates vascular calcification by interfering with TGF- signalling

AIMS

Vascular calcification often occurs with advancing age, atherosclerosis, and metabolic disorders such as diabetes mellitus and end-stage renal disease. Vascular calcification is associated with cardiovascular events and increased mortality. Nitric oxide (NO) is crucial for maintaining vascular function, but little is known about how NO affects vascular calcification. The aim of this study was to examine the effect of NO on vascular calcification.

METHODS AND RESULTS

In this study, we examined the inhibitory effects of NO on calcification of murine vascular smooth muscle cells (VSMCs) in vitro. We measured calcium concentration, alizarin red staining, and alkaline phosphatase activity to examine the effect of NO on calcification of VSMCs and differentiation of VSMCs into osteoblastic cells. We also determined gene expression and levels of phosphorylation of Smad2/3 by RT-PCR and western blotting. NO inhibited calcification of VSMCs and differentiation of VSMCs into osteoblastic cells. An inhibitor of cyclic guanosine monophosphate (cGMP)-dependent protein kinase restored the inhibition by NO of osteoblastic differentiation and calcification of VSMCs. NO inhibited transforming growth factor-beta (TGF-beta)-induced phosphorylation of Smad2/3 and expression of TGF-beta-induced genes such as plasminogen activator inhibitor-1. In addition, NO inhibited expression of the TGF-beta receptor ALK5.

CONCLUSION

Our data show that NO prevents differentiation of VSMCs into osteoblastic cells by inhibiting TGF-beta signalling through a cGMP-dependent pathway. Our findings suggest that NO may play a beneficial role in atherogenesis in part by limiting vascular calcification.

Nitric oxide inhibits exocytosis of cytolytic granules from lymphokine-activated killer cells

NO inhibits cytotoxic T lymphocyte killing of target cells, although the precise mechanism is unknown. We hypothesized that NO decreases exocytosis of cytotoxic granules from activated lymphocytes. We now show that NO inhibits lymphokine-activated killer cell killing of K562 target cells. Exogenous and endogenous NO decreases the release of granzyme B, granzyme A, and perforin: all contents of cytotoxic granules. NO inhibits the signal transduction cascade initiated by cross-linking of the T cell receptor that leads to granule exocytosis. In particular, we found that NO decreases the expression of Ras, a critical signaling component within the exocytic pathway. Ectopic expression of Ras prevents NO inhibition of exocytosis. Our data suggest that Ras mediates NO inhibition of lymphocyte cytotoxicity and emphasize that alterations in the cellular redox state may regulate the exocytic signaling pathway.

The role of Rho-associated kinase in differential regulation by statins of interleukin-1beta- and lipopolysaccharide-mediated nuclear factor kappaB activation and inducible nitric-oxide synthase gene expression in vascular smooth muscle cells

An optimal level of NO has protective effects in atherosclerosis, whereas large amounts contribute to septic shock. To study how statins, the potent inhibitors of cholesterol synthesis, regulate NO in the vascular wall, we determined their effects on interleukin-1beta (IL-1beta)- and lipopolysaccharide (LPS)-induced NO production in aortic vascular smooth muscle cells (VSMCs). Compared with the large amounts of NO and inducible NO synthase (iNOS) protein expression induced by LPS, the responses of IL-1beta were modest. Various statins were found to inhibit LPS-induced iNOS expression and NO production, although they potentiated IL-1beta responses. In addition, fluvastatin increased IL-1beta-induced p65 nuclear translocation and nuclear factor kappaB (NF-kappaB) activity, although it inhibited those induced by LPS. To address the role of small G proteins in statin's actions, farnesyl transferase inhibitors [alpha-hydroxyfarne-sylphosphonic acid and (2S)-2-[[(2S)-2-[(2S,3S)-2-[(2R)-2-amino-3-mercaptopropyl]amino]-3-methylpentyl]oxy]-1-oxo-3-phenylpropyl]amino]-4-(methylsulfonyl)-butanoic acid 1-methylethyl ester (L-744382)], Rac inhibitor (NSC23766), and Rho-associated kinase (ROCK) inhibitor [N-(4-pyridyl)-4-(1-aminoethyl)cyclohexanecarboxamide dihydrochloride (Y-27632)] were used. We found that Y-27632 potentiated IL-1beta-induced iNOS expression, p65 nuclear translocation, IkappaB kinase (IKK), and NF-kappaB activation, whereas it had minimal effects on LPS-induced responses. In contrast, farnesyl transferase inhibitors blocked iNOS protein expression induced by LPS and IL-1beta, whereas NSC23766 had no effect. Further studies showed that LPS down-regulated Rho and ROCK activity, whereas IL-1beta increased them, suggesting a negative role of Rho and ROCK signaling, which is regulated in contrary manners by IL-1beta and LPS, in IKK/NF-kappaB activation. Through abrogating this negative signaling, statins differentially regulate iNOS expression induced by LPS and IL-1beta in VSMCs. These differential actions of statins on iNOS gene regulation might provide an additional explanation for the pleiotropic beneficial effects of statins.

Regulation of Weibel–Palade Body Exocytosis

Weibel-Palade bodies (WPBs) are endothelial granules that store von Willebrand factor (VWF), P-selectin, and other vascular modulators. Endothelial cells secrete WPBs in response to vascular injury, releasing VWF, which triggers platelet rolling, and externalizing P-selectin, which activates leukocyte trafficking. Endothelial exocytosis is one of the earliest responses to vascular damage and plays a pivotal role in thrombosis and inflammation. This review examines the regulation of WPB exocytosis-the exocytic machinery, activators, and inhibitors of exocytosis-and speculates about the development of novel anti-exocytic drugs.

HMG-CoA reductase inhibitors inhibit endothelial exocytosis and decrease myocardial infarct size

Three-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors protect the vasculature from inflammation and atherosclerosis by cholesterol dependent and cholesterol independent mechanisms. We hypothesized that HMG-CoA reductase inhibitors decrease exocytosis of Weibel-Palade bodies, endothelial cell granules whose contents promote thrombosis and vascular inflammation. We pretreated human aortic endothelial cells with simvastatin for 24 hours, then stimulated the cells with thrombin, and measured the amount of vWF released into the media. We then measured the effect of simvastatin on myocardial infarction in mice. Simvastatin decreased thrombin-stimulated Weibel-Palade body exocytosis by 89%. Simvastatin inhibited exocytosis in part by increasing synthesis of nitric oxide (NO), which S-nitrosylated N-ethylmaleimide sensitive factor (NSF), a critical regulator of exocytosis. Simvastatin treatment attenuated myocardial infarct size by 58% in wild-type but not eNOS knockout mice. Furthermore, simvastatin decreased endothelial exocytosis and neutrophil infiltration into ischemic-reperfused myocardium, which was mediated in part by P-selectin contained in Weibel-Palade bodies. However, simvastatin did not affect exocytosis and inflammation in myocardial infarcts of eNOS knockout mice. Inhibition of endothelial exocytosis is a novel mechanism by which HMG-CoA reductase inhibitors may reduce vascular inflammation, inhibit thrombosis, and protect the ischemic myocardium. These findings may explain part of the pleiotropic effects of statin therapy for patients with cardiovascular disease.

Antibody, complement and accommodation in ABO-incompatible transplants

Many facets of accommodation have been explored since this process was first observed in ABO-incompatible renal allografts over 17 years ago. Intriguing new pieces of the puzzle have emerged to be fitted into the picture in several places. For example, vascular endothelial cells can be stimulated to secrete substantial amounts of blood group A and B antigens linked to von Willebrand factor; the antibody response to A and B antigens stimulated by ABO-incompatible renal allografts can show epitope spreading; complement can inhibit inflammation through actions of some complement split products, particularly iC3b and C3a; endothelial cells can upregulate various cytoprotective mechanisms; and clinically, new protocols for achieving accommodation have been implemented with improved results.

Vascular endothelial growth factor regulation of Weibel-Palade-body exocytosis

Vascular endothelial growth factor (VEGF) not only regulates angiogenesis, vascular permeability, and vasodilation but also promotes vascular inflammation. However, the molecular basis for the proinflammatory effects of VEGF is not understood. We now show that VEGF activates endothelial cell exocytosis of Weibel-Palade bodies, releasing vasoactive substances capable of causing vascular thrombosis and inflammation. VEGF triggers endothelial exocytosis in part through calcium and phospholipase C-gamma (PLC-gamma) signal transduction. However, VEGF also modulates endothelial cell exocytosis by activating endothelial nitric oxide synthase (eNOS) production of nitric oxide (NO), which nitrosylates N-ethylmaleimide sensitive factor (NSF) and inhibits exocytosis. Thus, VEGF plays a dual role in regulating endothelial exocytosis, triggering pathways that both promote and inhibit endothelial exocytosis. Regulation of endothelial exocytosis may explain part of the proinflammatory effects of VEGF.

Sphingosine 1-phosphate activates Weibel-Palade body exocytosis

Sphingosine 1-phosphate (S1P) not only regulates angiogenesis, vascular permeability and vascular tone, but it also promotes vascular inflammation. However, the molecular basis for the proinflammatory effects of S1P is not understood. We now show that S1P activates endothelial cell exocytosis of Weibel-Palade bodies, releasing vasoactive substances capable of causing vascular thrombosis and inflammation. S1P triggers endothelial exocytosis in part through phospholipase C-gamma signal transduction. However, S1P also modulates endothelial cell exocytosis by activating endothelial nitric oxide synthase production of nitric oxide, which inhibits exocytosis. Thus S1P plays a dual role in regulating endothelial exocytosis, triggering pathways that both promote and inhibit endothelial exocytosis. Regulation of endothelial exocytosis may explain part of the proinflammatory effects of S1P.

Inhibition of inducible nitric-oxide synthase by activators of AMP-activated protein kinase: a new mechanism of action of insulin-sensitizing drugs

AMP-activated protein kinase (AMPK), an energy-sensing enzyme that is activated in response to cellular stress, is a critical signaling molecule for the regulation of multiple metabolic processes. AMPK has recently emerged as an attractive novel target for the treatment of obesity and type 2 diabetes because its activation increases fatty acid oxidation and improves glucose homeostasis. Here we show that pharmacological activation of AMPK by insulin-sensitizing drugs markedly inhibits inducible nitric-oxide synthase (iNOS), a proinflammatory mediator in endotoxic shock and in chronic inflammatory states including obesity-linked diabetes. AMPK-mediated iNOS inhibition was observed in several cell types (myocytes, adipocytes, macrophages) and primarily resulted from post-transcriptional regulation of the iNOS protein. AMPK activation in vivo also blunted iNOS induction in muscle and adipose tissues of endotoxin-challenged rats. Reduction of AMPK expression by small interfering RNA reversed the inhibitory effects of AMPK activators on iNOS expression and nitric oxide production in myocytes. These results indicate that AMPK is a novel anti-inflammatory signaling pathway and thus represents a promising therapeutic target for immune-inflammatory disorders.

Nitric Oxide Regulates Exocytosis by S-Nitrosylation of N-ethylmaleimide-Sensitive Factor

Nitric oxide (NO) inhibits vascular inflammation, but the molecular basis for its anti-inflammatory properties is unknown. We show that NO inhibits exocytosis of Weibel-Palade bodies, endothelial granules that mediate vascular inflammation and thrombosis, by regulating the activity of N-ethylmaleimide-sensitive factor (NSF). NO inhibits NSF disassembly of soluble NSF attachment protein receptor (SNARE) complexes by nitrosylating critical cysteine residues of NSF. NO may regulate exocytosis in a variety of physiological processes, including vascular inflammation, neurotransmission, thrombosis, and cytotoxic T lymphocyte cell killing.