The release of nitric oxide from S-nitrosothiols promotes angiogenesis

Vitamin C deficiency induces hypoglycemia and cognitive disorder through S-nitrosylation-mediated activation of glycogen synthase kinase 3β

Vitamin C (VC, l-ascorbic acid) is an essential nutrient that plays a key role in metabolism and functions as a potent antioxidant in regulating the S-nitrosylation and denitrosylation of target proteins. The precise function of VC deprivation in glucose homeostasis is still unknown. In the absence of L-gulono-1,4-lactone oxidoreductase, an essential enzyme for the last step of VC synthesis, VC deprivation resulted in persistent hypoglycemia and subsequent impairment of cognitive functions in female but not male mouse pups. The cognitive disorders caused by VC deprivation were largely reversed when these female pups were given glucose. VC deprivation-induced S-nitrosylation of glycogen synthase kinase 3β (GSK3β) at Cys14, which activated GSK3β and inactivated glycogen synthase to decrease glycogen synthesis and storage under the feeding condition, while VC deprivation inactivated glycogen phosphorylase to decrease glycogenolysis under the fasting condition, ultimately leading to hypoglycemia and cognitive disorders. Treatment with Nω-Nitro-l-arginine methyl ester (l-NAME), a specific inhibitor of nitric oxide synthase, on the other hand, effectively prevented S-nitrosylation and activation of GSK3β in female pups in response to the VC deprivation and reversed hypoglycemia and cognitive disorders. Overall, this research identifies S-nitrosylation of GSK3β and subsequent GSK3β activation as a previously unknown mechanism controlling glucose homeostasis in female pups in response to VC deprivation, implying that VC supplementation in the prevention of hypoglycemia and cognitive disorders should be considered in the certain groups of people, particularly young females.

Repurposing PDE5 inhibitor tadalafil and sildenafil as anticancer agent against hepatocellular carcinoma via targeting key events of glucose metabolism and multidrug resistance

Hepatocellular carcinoma (HCC) has emerged as one of the most common and lethal cancers worldwide and is caused due to contamination of diets with aflatoxin B1 and chronic viral hepatitis. Recent reports suggest that phosphodiesterase-5 inhibitor (PDE5i) exhibits anticancer properties against several forms of cancer but till now has not been evaluated against HCC. We aimed to evaluate the anticancer property of phosphodiesterase-5 inhibitors (PDE5i) tadalafil and sildenafil against aflatoxin B1 HCC. Rats of HCC group were fed with 5% alcohol via drinking water for 3 weeks, followed by administration of AFB1 (1 mg/kg/bw, i.p.) at an interval of two subsequent days. PDE5i (tadalafil and sildenafil, 10 mg/kg bw) was administered along with drinking water after 6 weeks of treatment with AFB1 for 2 weeks. In the present investigation, in HCC elevation in the level of SGOT, SGPT, ALP, and urea vis-à-vis activity of key glycolytic enzyme LDH and mRNA expression of c-myc, Akt, LDH-A, and PFKFB3 was noted. Similarly, the level of multidrug resistance protein (MDR) and breast cancer resistance protein (BCRP/ABCG2) was elevated along with increased expression of angiogenesis marker (HIF-1α, VEGF, and TGF-β1) in HCC. Post-treatment with PDE5 inhibitor (tadalafil and sildenafil) downregulated and brought back the above parameters towards normal and out of two PDE5i (tadalafil and sildenafil), sildenafil effect was more potent as compared to tadalafil. Our findings demonstrate for the first time that PDE5 inhibitors tadalafil and sildenafil are able to prohibit the development and progression of aflatoxin B1 induced HCC.

α1G T-type calcium channel determines the angiogenic potential of pulmonary microvascular endothelial cells

Pulmonary microvascular endothelial cells (PMVECs) display a rapid angioproliferative phenotype, essential for maintaining homeostasis in steady-state and promoting vascular repair after injury. Although it has long been established that endothelial cytosolic Ca²⁺ ([Ca²⁺]_i) transients are required for proliferation and angiogenesis, mechanisms underlying such regulation and the transmembrane channels mediating the relevant [Ca²⁺]_i transients remain incompletely understood. In the present study, the functional role of the microvascular endothelial site-specific α_1G T-type Ca²⁺ channel in angiogenesis was examined. PMVECs intrinsically possess an in vitro angiogenic "network formation" capacity. Depleting extracellular Ca²⁺ abolishes network formation, whereas blockade of vascular endothelial growth factor receptor or nitric oxide synthase has little or no effect, suggesting that the network formation is a [Ca²⁺]_i-dependent process. Blockade of the T-type Ca²⁺ channel or silencing of α_1G, the only voltage-gated Ca²⁺ channel subtype expressed in PMVECs, disrupts network formation. In contrast, blockade of canonical transient receptor potential (TRP) isoform 4 or TRP vanilloid 4, two other Ca²⁺ permeable channels expressed in PMVECs, has no effect on network formation. T-type Ca²⁺ channel blockade also reduces proliferation, cell-matrix adhesion, and migration, three major components of angiogenesis in PMVECs. An in vivo study demonstrated that the mice lacking α_1G exhibited a profoundly impaired postinjury cell proliferation in the lungs following lipopolysaccharide challenge. Mechanistically, T-type Ca²⁺ channel blockade reduces Akt phosphorylation in a dose-dependent manner. Blockade of Akt or its upstream activator, phosphatidylinositol-3-kinase (PI3K), also impairs network formation. Altogether, these findings suggest a novel functional role for the α_1G T-type Ca²⁺ channel to promote the cell's angiogenic potential via a PI3K-Akt signaling pathway.

Antimicrobial activity of NO-releasing compounds against periodontal pathogens

This study describes the successful synthesis of nitric oxide (NO)-releasing compounds with biodegradable and injectable properties and demonstrates that the kinetics of NO release vary according to the type of NO donor. The antimicrobial activity of NO-releasing compounds against three common periodontal pathogens, i.e., Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Actinomyces israelii, was investigated using a susceptibility assay. Human gingival fibroblasts were treated with NO-releasing compounds at the minimum concentrations required for bacterial growth and cytotoxicity was evaluated using the MTT cell proliferation assay. Our results suggest that NO-releasing compounds can be used topically to treat both gram-negative and gram-positive periodontal pathogens. Comparison of the antimicrobial activity and cytotoxicity assay results between the NO-releasing compounds revealed that an NO donor comprising a macromolecule without surface charge, a lower instantaneous NO concentration, and an adequate supply of NO were associated with a strong bactericidal effect and low cytotoxicity. NO-releasing compounds with these properties may be suitable for treatment of periodontitis.

Alternative fluorimetric-based method to detect and compare total S-nitrosothiols in plants

Nitric oxide (NO) is an important signaling molecule occurring in virtually all organisms, whose mechanism of action relies mainly on its interaction with proteins or peptides by nitrosylation, forming compounds such as S-nitrosothiols (SNO). The Saville reaction and the ozone-based chemiluminescence method are the main techniques used for nitrosylated protein quantification. While the Saville assay is not very sensitive, the ozone-based chemiluminescence is expensive and time-consuming. Here we propose a method in which the protein-bound NO groups are exposed to UV light, cleaving the bond and allowing the quantification of the derived NO molecules by diamino-rhodamine (DAR) dyes. The DAR-based method was shown to be specific in plant tissues by pre-treatment of the samples with reducing agents and parallel EPR analysis. Spike-and-recovery assays revealed 72% recovery after a GSNO spike. Moreover, the method was significantly more sensitive than the Saville reaction, and this increase in sensitivity was crucial for detecting the reduced levels of nitrosylated proteins in plant species other than Arabidopsis. The method presented here is a suitable alternative to compare plant samples, allowing simple and fast detection of nitrosylated proteins.

Peroxynitrite is Involved in the Apoptotic Death of Cultured Cerebellar Granule Neurons Induced by Staurosporine, but not by Potassium Deprivation

Nitric oxide (NO) regulates numerous physiological process and is the main source of reactive nitrogen species (RNS). NO promotes cell survival, but it also induces apoptotic death having been involved in the pathogenesis of several neurodegenerative diseases. NO and superoxide anion react to form peroxynitrite, which accounts for most of the deleterious effects of NO. The mechanisms by which these molecules regulate the apoptotic process are not well understood. In this study, we evaluated the role of NO and peroxynitrite in the apoptotic death of cultured cerebellar granule neurons (CGN), which are known to experience apoptosis by staurosporine (St) or potassium deprivation (K5). We found that CGN treated with the peroxynitrite catalyst, FeTTPs were completely rescued from St-induced death, but not from K5-induced death. On the other hand, the inhibition of the inducible nitric oxide synthase partially protected cell viability in CGN treated with K5, but not with St, while the inhibitor L-NAME further reduced the cell viability in St, but it did not affect K5. Finally, an inhibitor of the soluble guanylate cyclase (sGC) diminished the cell viability in K5, but not in St. Altogether, these results shows that NO promotes cell survival in K5 through sGC-cGMP and promotes cell death by other mechanisms, while in St NO promotes cell survival independently of cGMP and peroxynitrite results critical for St-induced death. Our results suggest that RNS are differentially handled by CGN during cell death depending on the death-inducing conditions.

Vascular nitric oxide: Beyond eNOS

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

S-Nitrosothiol analysis via photolysis and amperometric nitric oxide detection in a microfluidic device

A 530 nm light emitting diode was coupled to a microfluidic sensor to facilitate photolysis of nitrosothiols (i.e., S-nitrosoglutathione, S-nitrosocysteine, and S-nitrosoalbumin) and amperometric detection of the resulting nitric oxide (NO). This configuration allowed for maximum sensitivity and versatility, while limiting potential interference from nitrate decomposition caused by ultraviolet light. Compared to similar measurements of total S-nitrosothiol content in bulk solution, use of the microfluidic platform permitted significantly enhanced analytical performance in both phosphate-buffered saline and plasma (6-20× improvement in sensitivity depending on nitrosothiol type). Additionally, the ability to reduce sample volumes from milliliters to microliters provides increased clinical utility. To demonstrate its potential for biological analysis, this device was used to measure basal nitrosothiol levels from the vasculature of a healthy porcine model.

Inflammatory stimuli induce inhibitory S-nitrosylation of the deacetylase SIRT1 to increase acetylation and activation of p53 and p65

Inflammation increases the abundance of inducible nitric oxide synthase (iNOS), leading to enhanced production of nitric oxide (NO), which can modify proteins by S-nitrosylation. Enhanced NO production increases the activities of the transcription factors p53 and nuclear factor κB (NF-κB) in several models of disease-associated inflammation. S-nitrosylation inhibits the activity of the protein deacetylase SIRT1. SIRT1 limits apoptosis and inflammation by deacetylating p53 and p65 (also known as RelA), a subunit of NF-κB. We showed in multiple cultured mammalian cell lines that NO donors or inflammatory stimuli induced S-nitrosylation of SIRT1 within CXXC motifs, which inhibited SIRT1 by disrupting its ability to bind zinc. Inhibition of SIRT1 reduced deacetylation and promoted activation of p53 and p65, leading to apoptosis and increased expression of proinflammatory genes. In rodent models of systemic inflammation, Parkinson's disease, or aging-related muscular atrophy, S-nitrosylation of SIRT1 correlated with increased acetylation of p53 and p65 and activation of p53 and NF-κB target genes, suggesting that S-nitrosylation of SIRT1 may represent a proinflammatory switch common to many diseases and aging.

Nitric oxide-releasing chitosan oligosaccharides as antibacterial agents

Secondary amine-functionalized chitosan oligosaccharides of different molecular weights (i.e., ~2500, 5000, 10,000) were synthesized by grafting 2-methyl aziridine from the primary amines on chitosan oligosaccharides, followed by reaction with nitric oxide (NO) gas under basic conditions to yield N-diazeniumdiolate NO donors. The total NO storage, maximum NO flux, and half-life of the resulting NO-releasing chitosan oligosaccharides were controlled by the molar ratio of 2-methyl aziridine to primary amines (e.g., 1:1, 2:1) and the functional group surrounding the N-diazeniumdiolates (e.g., polyethylene glycol (PEG) chains), respectively. The secondary amine-modified chitosan oligosaccharides greatly increased the NO payload over existing biodegradable macromolecular NO donors. In addition, the water-solubility of the chitosan oligosaccharides enabled their penetration across the extracellular polysaccharides matrix of Pseudomonas aeruginosa biofilms and association with embedded bacteria. The effectiveness of these chitosan oligosaccharides at biofilm eradication was shown to depend on both the molecular weight and ionic characteristics. Low molecular weight and cationic chitosan oligosaccharides exhibited rapid association with bacteria throughout the entire biofilm, leading to enhanced biofilm killing. At concentrations resulting in 5-log killing of bacteria in Pseudomonas aeruginosa (P. aeruginosa) biofilms, the NO-releasing and control chitosan oligosaccharides elicited no significant cytotoxicity to mouse fibroblast L929 cells in vitro.

UVC inhibits collagen biosynthesis through up-regulation of NF-κB p65 signaling in cultured fibroblasts

The effects of UVC on collagen biosynthesis, prolidase activity, expression of α₂β₁ integrin, IGF-I receptor, FAK, MAP-kinases (ERK1 and ERK2) and the transcription factor NF-κB p65 were evaluated in human dermal fibroblasts. Confluent fibroblasts were treated with UVC light at a rates of 30 and 60 J/m(2). It was found that UVC-dependent decrease in collagen biosynthesis was not accompanied by parallel decrease in prolidase activity and expression. Since insulin-like growth factor receptor (IGF-IR) and α₂β₁ integrin signaling are the most potent regulators of collagen biosynthesis, the effect of UVC on IGF-IR and α₂β₁ integrin receptor expressions were evaluated. It was found that the exposure of the cells to UVC contributed to decrease in α₂β₁ integrin receptor and FAK expression and to an increase in IGF-IR and pERK1, pERK2 expressions. It was accompanied by an increase in the expression of NF-κB p65, the known inhibitor of collagen gene expression. The data suggest that UVC-dependent decrease of collagen biosynthesis in cultured human skin fibroblasts results from decrease in α₂β₁ integrin receptor signaling and activation of NF-κB p65, that is responsible for down-regulation of collagen gene expression.

Modulation of thioacetamide-induced liver fibrosis/cirrhosis by sildenafil treatment

Sildenafil citrate is a phosphodiesterase-5 inhibitor, approved for the treatment of erectile dysfunction. It enhances nitric-oxide-induced vasodilatation and it promotes angiogenesis. A relationship between angiogenesis and hepatic fibrosis has long been speculated, where the 2 are believed to progress together. In this study, the ability of sildenafil (10 mg·(kg body mass)(-1), orally, once daily) to prevent and also reverse liver fibrosis/cirrhosis experimentally induced by thioacetamide injection (200 mg·kg(-1), intraperitoneal (i.p.), 3 times·week(-1)) in male Sprague-Dawley rats has been investigated. Sildenafil administration, either to prevent or to reverse liver fibrosis/cirrhosis significantly improved the estimated hepatic functions, reduced hepatic hydroxyproline and, in turn, hepatic collagen content, as well as reducing serum levels of the pro-fibrogenic mediator transforming growth factor β1. In co-ordination with such improvement, fibrosis grades declined and fibrosis retracted. Herein, the observed results provide evidence for the potential therapeutic efficacy of sildenafil as an antifibrotic agent.

Microfluidic amperometric sensor for analysis of nitric oxide in whole blood

Standard photolithographic techniques and a nitric oxide (NO) selective xerogel polymer were utilized to fabricate an amperometric NO microfluidic sensor with low background noise and the ability to analyze NO levels in small sample volumes (~250 μL). The sensor exhibited excellent analytical performance in phosphate buffered saline, including a NO sensitivity of 1.4 pA nM(-1), a limit of detection (LOD) of 840 pM, and selectivity over nitrite, ascorbic acid, acetaminophen, uric acid, hydrogen sulfide, ammonium, ammonia, and both protonated and deprotonated peroxynitrite (selectivity coefficients of -5.3, -4.2, -4.0, -5.0, -6.0, -5.8, -3.8, -1.5, and -4.0, respectively). To demonstrate the utility of the microfluidic NO sensor for biomedical analysis, the device was used to monitor changes in blood NO levels during the onset of sepsis in a murine pneumonia model.

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

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

Cyclic GMP protects endothelial progenitors from oxidative stress

Endothelial progenitor cells (EPCs) play a critical role in the repair of damaged blood vessels and/or in the growth of new ones in ischemic tissues. Elevated levels of oxygen radicals, which accumulate in the ischemic tissue, could compromise the angiogenic potential of EPCs. To determine if oxidative stress alters the angiogenic response of EPCs and to identify possible cellular targets that protect EPCs from the damaging effects of oxidative stress, we have investigated vascular development in embryonic bodies (EBs) under hyperoxic conditions. Murine EBs at differentiaton day 2 were cultured for 3 days under normoxic (21% O(2)) or hyperoxic (60% O(2)) conditions. Hyperoxic EBs showed a moderate reduction in Pecam-1, Vegfr-2, eNOS and Tie2 mRNA levels compared to normoxic EBs. However, immunostaining of hyperoxic EBs with antibodies against PECAM-1 after 1 week recovery at room air revealed a defective vasculature completely deficient in branches, while normoxic EBs developed a normal vascular plexus. Oxygen-induced defective vascular development correlated with a dramatic decrease in soluble guanylyl cyclase, phosphodiesterase (Pde) 4B and Pde4C mRNAs. Oxidative stress did not affect the expression of adenylyl cyclase 6 and Pde5. The abnormal vascular development caused by hyperoxia was reverted by pharmacological treatments that increased cGMP levels, such as 8-bromo-cGMP or 4-{[3',4'-(methylenedioxy)benzyl]amino}-6-methoxyquinazoline, a specific inhibitor of PDE5. These results indicated that oxidative stress inhibits vascular development from EPCs through its effects on levels of cyclic nucleotides and suggested that therapies that target cyclic nucleotide turnover may be useful in protecting vascular repair under oxidative conditions.

Pim-3 is expressed in endothelial cells and promotes vascular tube formation

Pim-3 is a member of proto-oncogene Pim family that encodes serine/threonine kinases. Pim proteins regulate both apoptosis and cellular metabolism by phosphorylating their substrates. Here, we report for the first time that Pim-3 is highly expressed at mRNA and protein levels in endothelial cells (ECs). We found that Pim-3 is concentrated at the cellular lamellipodia and co-localized with focal adhesion kinase (FAK). Pim-3 was dispersed from lamellipodia when ECs were treated with cytochalasin D, an inhibitor of actin polymerization. In addition, small-interfering RNA (siRNA)-mediated gene knockdown of Pim-3 significantly impaired EC spreading, migration, and proliferation, leading to a reduction in tube-like structure formation in a Matrigel assay. These results provide the novel evidence that Pim-3 plays an essential role in EC spreading and migration, suggesting that Pim-3 may be an important molecular target for the development of small-molecule inhibitors of angiogenesis.

Roles of the creatine kinase system and myoglobin in maintaining energetic state in the working heart

BACKGROUND

The heart is capable of maintaining contractile function despite a transient decrease in blood flow and increase in cardiac ATP demand during systole. This study analyzes a previously developed model of cardiac energetics and oxygen transport to understand the roles of the creatine kinase system and myoglobin in maintaining the ATP hydrolysis potential during beat-to-beat transient changes in blood flow and ATP hydrolysis rate.

RESULTS

The theoretical investigation demonstrates that elimination of myoglobin only slightly increases the predicted range of oscillation of cardiac oxygenation level during beat-to-beat transients in blood flow and ATP utilization. In silico elimination of myoglobin has almost no impact on the cytoplasmic ATP hydrolysis potential (DeltaGATPase). In contrast, disabling the creatine kinase system results in considerable oscillations of cytoplasmic ADP and ATP levels and seriously deteriorates the stability of DeltaGATPase in the beating heart.

CONCLUSION

The CK system stabilizes DeltaGATPase by both buffering ATP and ADP concentrations and enhancing the feedback signal of inorganic phosphate in regulating mitochondrial oxidative phosphorylation.

Type 5 phosphodiesterase expression is a critical determinant of the endothelial cell angiogenic phenotype

Type 5 phosphodiesterase (PDE5) inhibitors increase endothelial cell cGMP and promote angiogenesis. However, not all endothelial cell phenotypes express PDE5. Indeed, whereas conduit endothelial cells express PDE5, microvascular endothelial cells do not express this enzyme, and they are rapidly angiogenic. These findings bring into question whether PDE5 activity is a critical determinant of the endothelial cell angiogenic potential. To address this question, human full-length PDE5A1 was stably expressed in pulmonary microvascular endothelial cells. hPDE5A1 expression reduced the basal and atrial natriuretic peptide (ANP)-stimulated cGMP concentrations in these cells. hPDE5A1-expressing cells displayed attenuated network formation on Matrigel in vitro and also produced fewer blood vessels in Matrigel plug assays in vivo; the inhibitory actions of hPDE5A1 were reversed using sildenafil. To examine whether endogenous PDE5 activity suppresses endothelial cell angiogenic potential, small interfering RNA (siRNA) constructs were stably expressed in pulmonary artery endothelial cells. siRNA selectively decreased PDE5 expression and increased basal and ANP-stimulated cGMP concentrations in these conduit cells. PDE5 downregulation increased network formation on Matrigel in vitro and increased blood vessel formation in Matrigel plug assays in vivo. Collectively, our results indicate that PDE5 activity is an essential determinant of angiogenesis and suggest that PDE5 downregulation in microvascular endothelium imparts a stable, enhanced angiogenic potential to this cell type.

Atrial natriuretic peptide-initiated cGMP pathways regulate vasodilator-stimulated phosphoprotein phosphorylation and angiogenesis in vascular endothelium

Nitric oxide (NO)- and atrial natriuretic peptide (ANP)-initiated cGMP signaling cascades are important in the maintenance of cardiovascular homeostasis. The molecular signaling mechanisms downstream of cGMP are not well understood, however. We have used small interfering RNA (siRNA) approaches to specifically knock down a series of signaling proteins in bovine aortic endothelial cells, and we have combined biochemical analyses with physiological assays to investigate cGMP-mediated signal transduction pathways. Activation of particulate guanylate cyclase (GC-A) by ANP leads to a substantial, dose-dependent, rapid, and sustained increase in intracellular cGMP. In contrast, stimulation of soluble guanylate cyclase by NO yields only a weak and transient increase in cGMP. ANP-induced cGMP production is selectively suppressed by siRNA-mediated knockdown of GC-A. ANP greatly enhances the phosphorylation at Ser-239 of the vasodilator-stimulated phosphoprotein (VASP), a major substrate of cGMP-dependent protein kinase (PKG) that significantly influences actin dynamics. Moreover, the ANP-induced phosphorylation of VASP at Ser-239 is accompanied by increased actin stress fiber formation and enhanced endothelial tube formation. siRNA-mediated knockdown of GC-A, VASP, or PKG abolishes ANP-induced VASP Ser-239 phosphorylation, stress fiber formation, and endothelial tube formation. We have demonstrated similar findings in human umbilical vein endothelial cells, where ANP substantially enhances intracellular cGMP content, phosphorylation of VASP at Ser-239, and endothelial tube formation. Taken together, our findings suggest that ANP-mediated cGMP signal transduction pathways regulate PKG phosphorylation of VASP Ser-239 in endothelial cells, resulting in reorganization of the actin cytoskeleton and enhancement of angiogenesis.