Differential relaxing responses to particulate or soluble guanylyl cyclase activation on endothelial cells: a mechanism dependent on PKG-I alpha activation by NO/cGMP

Alterations of Cardiac Protein Kinases in Cyclic Nucleotide-Dependent Signaling Pathways in Human Ischemic Heart Failure

Objectives

Impaired protein kinase signaling is a hallmark of ischemic heart disease (IHD). Inadequate understanding of the pathological mechanisms limits the development of therapeutic approaches. We aimed to identify the key cardiac kinases and signaling pathways in patients with IHD with an effort to discover potential therapeutic strategies.

Methods

Cardiac kinase activity in IHD left ventricle (LV) and the related signaling pathways were investigated by kinomics, transcriptomics, proteomics, and integrated multi-omics approach.

Results

Protein kinase A (PKA) and protein kinase G (PKG) ranked on top in the activity shift among the cardiac kinases. In the IHD LVs, PKA activity decreased markedly compared with that of controls (62% reduction, p = 0.0034), whereas PKG activity remained stable, although the amount of PKG protein increased remarkably (65%, p = 0.003). mRNA levels of adenylate cyclases (ADCY 1, 3, 5, 9) and cAMP-hydrolysing phosphodiesterases (PDE4A, PDE4D) decreased significantly, although no statistically significant alterations were observed in that of PKGs (PRKG1 and PRKG2) and guanylate cyclases (GUCYs). The gene expression of natriuretic peptide CNP decreased remarkably, whereas those of BNP, ANP, and neprilysin increased significantly in the IHD LVs. Proteomics analysis revealed a significant reduction in protein levels of “Energy metabolism” and “Muscle contraction” in the patients. Multi-omics integration highlighted intracellular signaling by second messengers as the top enriched Reactome pathway.

Conclusion

The deficiency in cAMP/PKA signaling pathway is strongly implicated in the pathogenesis of IHD. Natriuretic peptide CNP could be a potential therapeutic target for the modulation of cGMP/PKG signaling.

A Real-Time, Plate-Based BRET Assay for Detection of cGMP in Primary Cells

Cyclic guanosine monophosphate (cGMP) is a second messenger involved in the regulation of numerous physiological processes. The modulation of cGMP is important in many diseases, but reliably assaying cGMP in live cells in a plate-based format with temporal resolution is challenging. The Förster/fluorescence resonance energy transfer (FRET)-based biosensor cGES-DE5 has a high temporal resolution and high selectivity for cGMP over cAMP, so we converted it to use bioluminescence resonance energy transfer (BRET), which is more compatible with plate-based assays. This BRET variant, called CYGYEL (cyclic GMP sensor using YFP-PDE5-Rluc8), was cloned into a lentiviral vector for use across different mammalian cell types. CYGYEL was characterised in HEK293T cells using the nitric oxide donor diethylamine NONOate (DEA), where it was shown to be dynamic, reversible, and able to detect cGMP with or without the use of phosphodiesterase inhibitors. In human primary vascular endothelial and smooth muscle cells, CYGYEL successfully detected cGMP mediated through either soluble or particulate guanylate cyclase using DEA or C-type natriuretic peptide, respectively. Notably, CYGYEL detected differences in kinetics and strength of signal both between ligands and between cell types. CYGYEL remained selective for cGMP over cAMP, but this selectivity was reduced compared to cGES-DE5. CYGYEL streamlines the process of cGMP detection in plate-based assays and can be used to detect cGMP activity across a range of cell types.

Neutrophil-Initiated Myocardial Inflammation and Its Modulation by B-Type Natriuretic Peptide: A Potential Therapeutic Target

Activation of neutrophils is a critically important component of the innate immune response to bacterial and chemical stimuli, and culminates in the “neutrophil burst”, which facilitates neutrophil phagocytosis via the release of superoxide anion radical (O₂⁻) from NADPH oxidase. Excessive and/or prolonged neutrophil activation results in substantial tissue injury and increases in vascular permeability—resulting in sustained tissue infiltration with neutrophils and monocytes, and persistent vasomotor dysfunction. Cardiovascular examples of such changes include acute and chronic systolic and diastolic heart failure (“heart failure with preserved ejection fraction”), and the catecholamine-induced inflammatory disorder takotsubo syndrome. We have recently demonstrated that B-type natriuretic peptide (BNP), acting via inhibition of activation of neutrophil NADPH oxidase, is an important negative modulator of the “neutrophil burst”, though its effectiveness in limiting tissue injury is partially lost in acute heart failure. The potential therapeutic implications of these findings, regarding the development of new means of treating both acute and chronic cardiac injury states, are discussed.

Pharmacodynamic interaction between intravenous nitroglycerin and oral sacubitril/valsartan (LCZ696) in healthy subjects

PURPOSE

Sacubitril/valsartan (LCZ696) and nitroglycerin share the second messenger cGMP and lower blood pressure. Given the potential for co-administration of both drugs in patients with heart failure, this study was designed to investigate the potential for a pharmacodynamic drug interaction affecting blood pressure.

METHODS

In this double-blind, placebo-controlled, randomised, crossover study, 40 healthy subjects received sacubitril/valsartan 200 mg bid (97/103 mg bid) or placebo for 5 days. Two hours after the morning dose of sacubitril/valsartan or placebo on day 5, subjects received intravenous nitroglycerin infusion at increasing doses up to 40 μg/min or placebo. Serial measurements of blood pressure (BP), heart rate, biomarkers and sacubitril/valsartan pharmacokinetics were conducted.

RESULTS

Administration of nitroglycerin alone led to a dose- and time-dependent decrease in supine systolic BP (SBP) and diastolic BP (DBP) which was similar when nitroglycerin was co-administered with sacubitril/valsartan. At the highest dose of nitroglycerin, the mean (95% CI) decrease from baseline of SBP/DBP was 19.54 (- 21.99, - 17.09)/12.38 (- 13.85, - 10.92) mmHg for nitroglycerin alone compared to 22.63 (- 25.06, - 20.21)/12.94 (- 14.38, - 11.49) mmHg when co-administered with sacubitril/valsartan. Co-administration of sacubitril/valsartan and nitroglycerin did not result in further plasma cGMP increase compared to sacubitril/valsartan alone. The co-administration of nitroglycerin and sacubitril/valsartan was safe and well tolerated and did not impact the pharmacokinetics of sacubitril/valsartan.

CONCLUSIONS

The results from this study demonstrate no pharmacodynamic drug interaction between nitroglycerin and sacubitril/valsartan in healthy subjects, suggesting that no change of dose selection and escalation recommendations or clinical monitoring during nitroglycerin administration is required.

Evaluation of Pharmacokinetic and Pharmacodynamic Drug-Drug Interaction of Sacubitril/Valsartan (LCZ696) and Sildenafil in Patients With Mild-to-Moderate Hypertension

Sacubitril/valsartan (LCZ696) is indicated for the treatment of patients with heart failure and reduced ejection fraction (HFrEF). Since patients with HFrEF may receive sacubitril/valsartan and sildenafil, both increasing cyclic guanosine monophosphate, the present study evaluated the pharmacokinetic and pharmacodynamic drug interaction potential between sacubitril/valsartan and sildenafil. In this open‐label, three‐period, single sequence study, patients with mild‐to‐moderate hypertension (153.8 ± 8.2 mmHg mean systolic blood pressure (SBP)) received a single dose of sildenafil 50 mg, sacubitril/valsartan 400 mg once daily for 5 days, and sacubitril/valsartan and sildenafil coadministration. When coadministered with sildenafil, the AUC and C_max of valsartan decreased by 29% and 39%, respectively. Coadministration of sacubitril/valsartan and sildenafil resulted in a greater decrease in BP (–5/–4/–4 mmHg mean ambulatory SBP/DBP/MAP (mean arterial pressure)) than with sacubitril/valsartan alone. Both treatments were generally safe and well tolerated in this study; however, the additional BP reduction suggests that sildenafil should be administered cautiously in patients receiving sacubitril/valsartan. Unique identifier: NCT01601470.

The Anti-fibrotic Actions of Relaxin Are Mediated Through a NO-sGC-cGMP-Dependent Pathway in Renal Myofibroblasts In Vitro and Enhanced by the NO Donor, Diethylamine NONOate

INTRODUCTION

The anti-fibrotic hormone, relaxin, has been inferred to disrupt transforming growth factor (TGF)-β1/Smad2 phosphorylation (pSmad2) signal transduction and promote collagen-degrading gelatinase activity via a nitric oxide (NO)-dependent pathway. Here, we determined the extent to which NO, soluble guanylate cyclase (sGC) and cyclic guanosine monophosphate (cGMP) were directly involved in the anti-fibrotic actions of relaxin using a selective NO scavenger and sGC inhibitor, and comparing and combining relaxin's effects with that of an NO donor.

METHODS AND RESULTS

Primary renal cortical myofibroblasts isolated from injured rat kidneys were treated with human recombinant relaxin (RLX; 16.8 nM), the NO donor, diethylamine NONOate (DEA/NO; 0.5-5 μM) or the combined effects of RLX (16.8 nM) and DEA/NO (5 μM) over 72 h. The effects of RLX (16.8 nM) and DEA/NO (5 μM) were also evaluated in the presence of the NO scavenger, hydroxocobalamin (HXC; 100 μM) or sGC inhibitor, ODQ (5 μM) over 72 h. Furthermore, the effects of RLX (30 nM), DEA/NO (5 μM) and RLX (30 nM) + DEA/NO (5 μM) on cGMP levels were directly measured, in the presence or absence of ODQ (5 μM). Changes in matrix metalloproteinase (MMP)-2, MMP-9 (cell media), pSmad2 and α-smooth muscle actin (α-SMA; a measure myofibroblast differentiation) (cell layer) were assessed by gelatin zymography and Western blotting, respectively. At the highest concentration tested, both RLX and DEA/NO promoted MMP-2 and MMP-9 levels by 25-33%, while inhibiting pSmad2 and α-SMA expression by up to 50% (all p < 0.05 vs. untreated and vehicle-treated cells). However, 5μM of DEA/NO was required to produce the effects seen with 16.8 nM of RLX over 72 h. The anti-fibrotic effects of RLX or DEA/NO alone were completely abrogated by HXC and ODQ (both p < 0.01 vs. RLX alone or DEA/NO alone), but were significantly enhanced when added in combination (all p < 0.05 vs. RLX alone). Additionally, the direct cGMP-promoting effects of RLX, DEA/NO and RLX+DEA/NO (which all increased cGMP levels by 12-16-fold over basal levels; all p < 0.01 vs. vehicle-treated cells) were significantly inhibited by pre-treatment of ODQ (all p < 0.05 vs. the respective treatments alone).

CONCLUSION

These findings confirmed that RLX mediates its TGF-β1-inhibitory and gelatinase-promoting effects via a NO-sGC-cGMP-dependent pathway, which was additively augmented by co-administration of DEA/NO.

Cyclic guanosine monophosphate compartmentation in human vascular smooth muscle cells

AIMS

The role of different vascular subtypes of phosphodiesterases (PDE) in cGMP compartmentalization was evaluated in human smooth muscle cells.

METHODS AND RESULTS

To understand how the cGMP conveys different information we infected smooth muscle cells with adenovirus containing mutants of the rat olfactory cyclic nucleotide-gated (CNG) channel-subunit and we recorded the associated cGMP-gated current (ICNG). The whole cell configuration of patch clamp technique was used to measure the ICNG and also the potassium current (IK) in human umbilical artery smooth muscle cells (HUASMC). ANP (0.1μM) induced a clear activation of basal ICNG, whereas SNP (100 μM) had a slight effect. The nonselective PDE inhibitor (IBMX; 100 μM), the PDE5 inhibitor (T0-156; 1 μM) and the PDE3 inhibitor (cilostamide; 10 μM), all had a tiny effects on the basal ICNG current. Concerning potassium channels, we observed that ANP and testosterone induced activation of IK and this activation is bigger than that elicited by SNP, cilostamide and T0-156. Cilostamide and T0-156 decreased the CNG stimulation induced by ANP and testosterone, suggesting that pGC pool is controlled by PDE3 and 5. Thus, the effects of SNP show the existence of two separated pools, one localized next to the plasma membrane and controlled by the PDE5 and PDE3, and a second pool localized in the cytosol of the cells that is regulated mainly by PDE3.

CONCLUSIONS

Our results show the existence of cGMP compartmentalization in human vascular smooth muscle cells and this phenomenon can open new perspectives concerning the examination of PDE families as therapeutic targets.

Grape seed proanthocyanidins prevent DOCA-salt hypertension-induced renal injury and its mechanisms in rats

Renal dysfunction is one of the major effects of DOCA (deoxycorticosterone acetate)-salt hypertension and there is an increasing amount of evidence that oxidative stress damages the function of the kidney. Grape seed proanthocyanidins (GSPE) have been reported to be potent anti-oxidants and free radical scavengers. The present study sought to investigate the ability of GSPE to prevent renal injury in DOCA-salt hypertensive rats and to explore the molecular mechanisms underlying its protective effects. A total of 54 Sprague Dawley (SD) rats were randomly divided into 7 groups: Sham group (n = 7), UnX-sham group (n = 8), DOCA-salt group (n = 8), GSPE150 group (150 mg kg(-1), n = 7), GSPE240 group (240 mg kg(-1), n = 8), GSPE384 group (384 mg kg(-1), n = 8) and ALM (amlodipine besylate tablets) group (5 mg kg(-1), n = 8), and treated for 4 weeks. Compared to sham group rats, renal injury was observed in DOCA-salt hypertensive group rats as the urine protein, KW/BW (kidney weight/body weight), degree of renal fibrosis, renal MDA (malondialdehyde) and Hyp (hydroxyproline) contents significantly increased (P < 0.01). Moreover, SOD (Superoxide Dismutase) activities decreased in the model group (P < 0.01). In contrast, DOCA-salt hypertensive rats treated with different dose of GSPE or ALM showed a significant improvement of renal injury with decreased urine protein, KW/BW, degree of renal fibrosis, renal total MDA and Hyp contents compared to the untreated group. In addition, SOD activities increased in the treatment group. Since the experimental modeling time was short, kidney damage occurs to a lesser extent. BUN (Blood Urea Nitrogen), Scr (Serum Creatinine) and UA (Uric Acid) contents did not appear significantly changed in all groups. Finally, the activation of JNK and p38 kinases in the kidney was suppressed in rats treated with GSPEs or ALM compared to the untreated group, suggesting that the inhibition of these kinase pathways by GSPE contributes to the improvement of renal function. Taking these results together, we conclude that the anti-hypertensive and anti-oxidative stress beneficial effects of GSPE on renal injury in rats with DOCA-salt hypertension occur via the attenuation of JNK and p38 activity.

Phosphodiesterase 5 inhibition ameliorates angiontensin II-induced podocyte dysmotility via the protein kinase G-mediated downregulation of TRPC6 activity

The emerging role of the transient receptor potential cation channel isotype 6 (TRPC6) as a central contributor to various pathological processes affecting podocytes has generated interest in the development of therapeutics to modulate its function. Recent insights into the regulation of TRPC6 have revealed PKG as a potent negative modulator of TRPC6 conductance and associated signaling via its phosphorylation at two highly conserved amino acid residues: Thr(69)/Thr(70) (Thr(69) in mice and Thr(70) in humans) and Ser(321)/Ser(322) (Ser(321) in mice and Ser(322) in humans). Here, we tested the role of PKG in modulating TRPC6-dependent responses in primary and conditionally immortalized mouse podocytes. TRPC6 was phosphorylated at Thr(69) in nonstimulated podocytes, but this declined upon ANG II stimulation or overexpression of constitutively active calcineurin phosphatase. ANG II induced podocyte motility in an in vitro wound assay, and this was reduced 30-60% in cells overexpressing a phosphomimetic mutant TRPC6 (TRPC6T70E/S322E) or activated PKG (P < 0.05). Pretreatment of podocytes with the PKG agonists S-nitroso-N-acetyl-dl-penicillamine (nitric oxide donor), 8-bromo-cGMP, Bay 41-2772 (soluble guanylate cyclase activator), or phosphodiesterase 5 (PDE5) inhibitor 4-{[3',4'-(methylenedioxy)benzyl]amino}[7]-6-methoxyquinazoline attenuated ANG II-induced Thr(69) dephosphorylation and also inhibited TRPC6-dependent podocyte motility by 30-60%. These data reveal that PKG activation strategies, including PDE5 inhibition, ameliorate ANG II-induced podocyte dysmotility by targeting TRPC6 in podocytes, highlighting the potential therapeutic utility of these approaches to treat hyperactive TRPC6-dependent glomerular disease.

Restoring nitric oxide cytosolic calcium regulation by cyclic guanosine monophosphate protein kinase I alpha transfection in coronary endothelial cells of spontaneously hypertensive rats

In microcoronary endothelial cells (RCEs) from spontaneously hypertensive rats (SHR), the nitric oxide (NO)/cyclic guanosine monophosphate (GMP)-dependent proteinkinase I (cGKI) pathway cannot regulate the cytosolic calcium ([Ca2+]i) dynamic as in RCEs from Wistar Kyoto rats (WKY). We investigated the altered downstream NO target in SHR cells and, since cGKI expression was low, whether the re-expression of cGKIα in SHR RCEs could restore NO calcium responsiveness. We measured [Ca2+]i dynamic by fura-2 imaging analysis and the cGKI level by RT-PCR and Western blot in SHR and WKY RCEs. Plasmids encoding for enhanced green fluorescence protein or cGKIα-enhanced green fluorescence protein were transiently transfected in SHR RCEs, and [Ca2+]i was evaluated. Angiotensin-II (AT-II) increased [Ca2+]i in a concentration-dependent way in both strains. Whereas in WKY, endogenously produced NO and cyclic GMP analog decreased the AT-II-induced [Ca2+]i transient, they were ineffective in SHR RCEs. The cGKI level was low in SHR cells. However, after cGKIα re-expression, endogenous NO decreased the AT-II-induced [Ca2+]i transient, while endothelial NO synthase and cGKI inhibition prevented it. The low expression of cGKI in SHR accounts for the absent regulation of the agonist-induced [Ca2+]i transient by the NO/cyclic GMP pathway. Studies on cGKI in humans could contribute to a better understanding of cardiovascular pathologies.

Nitric oxide decreases the expression of endothelin-converting enzyme-1 through mRNA destabilization

OBJECTIVE

Endothelial function depends on the equilibrium in the synthesis of vasoactive endothelial factors. It is well known that endothelin and nitric oxide (NO) exhibit reciprocal regulation. We assessed the ability of NO to regulate endothelin-converting enzyme-1 (ECE-1) expression in vascular endothelial cells.

METHODS AND RESULTS

Bovine aortic endothelial cells were incubated with 2 different NO donors as well as with a cyclic-GMP analog, dibutyryl-cGMP (dB-cGMP). ECE-1 protein content and mRNA expression were evaluated by Western blot and Northern blot, respectively, promoter activity by transfection experiments, ECE-1 activity by ELISA, and cGMP production by radioimmunoassay. Both NO donors decreased ECE-1 protein content, mRNA expression, and ECE-1 activity. ODQ, an inhibitor of soluble guanylyl cyclase, blocked those effects. NO donors raised cGMP levels, and dB-cGMP mimicked their effects on ECE-1 expression, which were blocked by KT5823, a nonspecific PKG inhibitor. The changes on ECE-1 expression were due to a destabilization on 3'-untranslated region (3'-UTR) of this mRNA, because the activity of a luciferase reporter construct containing the 3'-UTR of the ECE-1 gene was reduced by dB-cGMP in a PKG-dependent manner. The biological relevance of this regulation was confirmed in bovine aortic endothelial cells coincubated with macrophages in the presence of lipopolysaccharide, in eNOS-deficient mice, and in Wistar rats treated with NO donors. In every case, an inverse relationship was observed between NO and ECE-1 protein content.

CONCLUSION

Our results support that NO regulates ECE-1 expression through a cGMP/PKG-dependent regulatory mechanism at the post-transcriptional level via the 3'-UTR of the ECE-1 gene.

Relaxin regulates myofibroblast contractility and protects against lung fibrosis

Myofibroblasts are specialized contractile cells that participate in tissue fibrosis and remodeling, including idiopathic pulmonary fibrosis (IPF). Mechanotransduction, a process by which mechanical stimuli are converted into biochemical signals, regulates myofibroblast differentiation. Relaxin is a peptide hormone that mediates antifibrotic effects through regulation of collagen synthesis and turnover. In this study, we demonstrate enhanced myofibroblast contraction in bleomycin-induced lung fibrosis in mice and in fibroblastic foci of human subjects with IPF, using phosphorylation of the regulatory myosin light chain (MLC(20)) as a biomarker of in vivo cellular contractility. Compared with wild-type mice, relaxin knockout mice express higher lung levels of phospho-MLC(20) and develop more severe bleomycin-induced lung fibrosis. Exogenous relaxin inhibits MLC(20) phosphorylation and bleomycin-induced lung fibrosis in both relaxin knockout and wild-type mice. Ex vivo studies of IPF lung myofibroblasts demonstrate decreases in MLC(20) phosphorylation and reduced contractility in response to relaxin. Characterization of the signaling pathway reveals that relaxin regulates MLC(20) dephosphorylation and lung myofibroblast contraction by inactivating RhoA/Rho-associated protein kinase through a nitric oxide/cGMP/protein kinase G-dependent mechanism. These studies identify a novel antifibrotic role of relaxin involving the inhibition of the contractile phenotype of lung myofibroblasts and suggest that targeting myofibroblast contractility with relaxin-like peptides may be of therapeutic benefit in the treatment of fibrotic lung disease.

Nitric oxide counters the inhibitory effects of uremic toxin indoxyl sulfate on endothelial cells by governing ERK MAP kinase and myosin light chain activation

Uremic toxins such as indoxyl sulfate (IS) accumulate at a high level in end stage renal disease (ESRD) and can exhibit significant systemic endothelial toxicity leading to accelerated cardiovascular events. The precise molecular mechanisms by which IS causes endothelial dysfunction are unknown. We tested the hypothesis that IS negatively influences properties of endothelial cells, such as migration and tube formation, by depleting nitric oxide (NO) bioavailability, and that an NO donor can reverse these inhibitory effects. IS inhibited human umbilical vein endothelial cell (HUVEC) migration and formation of tubes on matrigel. Mechanistically, IS inhibited VEGF-induced NO release from HUVECs. An NO donor, SNAP, reversed IS-mediated inhibition of HUVEC migration as well as tube-formation. IS inhibited ERK 1/2 MAP kinase activity in a dose-dependent manner, but this was preserved by SNAP. Inhibition of ERK 1/2 with a pharmacological inhibitor (U0126) decreased HUVEC migration and tube formation; these effects too were prevented by SNAP. Further, IS stimulated activation of myosin light chain (MLC), potentially stimulating endothelial contractility, while SNAP decreased MLC activation. Thus, we conclude that the negative effects of IS on endothelial cells are prevented, to a major extent, by NO, via its divergent actions on ERK MAP kinase and MLC.

Kruppel-like factor 2 regulates endothelial barrier function

OBJECTIVE

A central function of the endothelium is to serve as a selective barrier that regulates fluid and solute exchange. Although perturbation of barrier function can contribute to numerous disease states, our understanding of the molecular mechanisms regulating this aspect of endothelial biology remains incompletely understood. Accumulating evidence implicates the Kruppel-like factor 2 (KLF2) as a key regulator of endothelial function. However, its role in vascular barrier function is unknown.

METHODS AND RESULTS

To assess the role of KLF2 in vascular barrier function in vivo, we measured the leakage of Evans blue dye into interstitial tissues of the mouse ear after treatment with mustard oil. By comparison with KLF2(+/+) mice, KLF2(+/-) mice exhibited a significantly higher degree of vascular leak. In accordance with our in vivo observation, adenoviral overexpression of KLF2 in human umbilical vein endothelial cells strongly attenuated the increase of endothelial leakage by thrombin and H(2)O(2) as measured by fluorescein isothiocyanate dextrans (FITC-dextran) passage. Conversely, KLF2 deficiency in human umbilical vein endothelial cells and primary endothelial cells derived from KLF2(+/-) mice exhibited a marked increase in thrombin and H(2)O(2)-induced permeability. Mechanistically, our studies indicate that KLF2 confers barrier-protection via differential effects on the expression of key junction protein occludin and modification of a signaling molecule (myosin light chain) that regulate endothelial barrier integrity.

CONCLUSIONS

These observations identify KLF2 as a novel transcriptional regulator of vascular barrier function.

PKG and PKC Are Down-Regulated during Cardiomyocyte Differentiation from Embryonic Stem Cells: Manipulation of These Pathways Enhances Cardiomyocyte Production

Understanding signal transduction mechanisms that drive differentiation of adult or embryonic stem cells (ESCs) is imperative if they are to be used to cure disease. While the list of signaling pathways regulating stem cell differentiation is growing, it is far from complete. Indentifying regulatory mechanisms and timecourse commitment to cell lineages is needed for generating pure populations terminally differentiated cell types, and in ESCs, suppression of teratoma formation. To this end, we investigated specific signaling mechanisms involved in cardiomyogenesis, followed by manipulation of these pathways to enhance differentiation of ESCs into cardiomyocytes. Subjecting nascent ESC-derived cardiomyocytes to a proteomics assay, we found that cardiomyogenesis is influenced by up- and down-regulation of a number of kinases, one of which, cGMP-dependent protein kinase (PKG), is markedly down-regulated during differentiation. Delving further, we found that manipulating the PKG pathway using PKG-specific inhibitors produced significantly more cardiomyocytes from ESCs when compared to ESCs left to differentiate without inhibitors. In addition, we found combinatorial effects when culturing ESCs in inhibitors to PKG and PKC isotypes. Consequently, we have generated a novel hypothesis: Down-regulation of PKG and specific PKC pathways are necessary for cardiomyogenesis, and when manipulated, these pathways produce significantly more cardiomyocytes than untreated ESCs.

C-type natriuretic peptide regulation of guanosine-3',5'-cyclic monophosphate production in human endothelial cells

In vascular smooth muscle cells, relaxant actions of guanosine--3',5'-cyclic monophosphate (cGMP) are well recognized, but there is increasing evidence that cGMP also plays regulatory roles in vascular endothelium. However, the autacoid and endocrine mechanisms controlling cGMP production in endothelium are not well understood. The objective of these studies was to examine the mechanisms of cGMP accumulation in human umbilical vein endothelial cells (HUVEC) in response to natriuretic peptides. Expression in HUVEC of natriuretic peptide receptors, particulate guanylyl cyclases (GC)-A and GC-B, was confirmed by RT-PCR and Western blot analysis. In the presence of the phosphodiesterase inhibitor IBMX 500 microM, 3 h incubation of HUVEC with B-type natriuretic peptide (BNP) (preferential GC-A agonist) or C-type natriuretic peptide (CNP) (preferential GC-B agonist) stimulated concentration-dependent increases in cGMP production. At 10 and 100 nM, we observed two to three-fold greater potency of CNP compared to BNP. In the absence of IBMX, CNP-stimulated cGMP accumulation was significantly less than cGMP accumulation in response to sodium nitroprusside 1 mM. This greater sensitivity of GC-B-derived cGMP to phosphodiesterases suggests compartmentalization of two pools of cGMP from particulate and soluble guanylyl cyclases. Although CNP 100 nM and 1 microM was observed to increase nitrite + nitrate (stable metabolites of NO) production in HUVEC two-fold above basal level, the soluble guanylyl cyclase inhibitor ODQ 10 microM did not significantly modify CNP-stimulated cGMP accumulation suggesting that endothelial actions of CNP may be NO-independent. In conclusion, these studies indicate functional signaling by natriuretic peptides in endothelial cells, supporting possible roles of these mediators in regulating endothelial cell function.

Hydrogen peroxide down-regulates inositol 1,4,5-trisphosphate receptor content through proteasome activation

Hydrogen peroxide (H(2)O(2)) is implicated in the regulation of signaling pathways leading to changes in vascular smooth muscle function. Contractile effects produced by H(2)O(2) are due to the phosphorylation of myosin light chain kinase triggered by increases in intracellular calcium (Ca(2+)) from intracellular stores or influx of extracellular Ca(2+). One mechanism for mobilizing such stores involves the phosphoinositide pathway. Inositol 1,4,5-trisphosphate (IP(3)) mobilizes intracellular Ca(2+) by binding to a family of receptors (IP(3)Rs) on the endoplasmic-sarcoplasmic reticulum that act as ligand-gated Ca(2+) channels. IP(3)Rs can be rapidly ubiquitinated and degraded by the proteasome, causing a decrease in cellular IP(3)R content. In this study we show that IP(3)R(1) and IP(3)R(3) are down-regulated when vascular smooth muscle cells (VSMC) are stimulated by H(2)O(2), through an increase in proteasome activity. Moreover, we demonstrate that the decrease in IP(3)R by H(2)O(2) is accompanied by a reduction in calcium efflux induced by IP(3) in VSMC. Also, we observed that angiotensin II (ANGII) induces a decrease in IP(3)R by activation of NADPH oxidase and that preincubation with H(2)O(2) decreases ANGII-mediated calcium efflux and planar cell surface area in VSMC. The decreased IP(3) receptor content observed in cells was also found in aortic rings, which exhibited a decreased ANGII-dependent contraction after treatment with H(2)O(2). Altogether, these results suggest that H(2)O(2) mediates IP(3)R down-regulation via proteasome activity.

Soluble guanylyl cyclase contributes to ventilator-induced lung injury in mice

High tidal volume (HV(T)) ventilation causes pulmonary endothelial barrier dysfunction. HV(T) ventilation also increases lung nitric oxide (NO) and cGMP. NO contributes to HV(T) lung injury, but the role of cGMP is unknown. In the current study, ventilation of isolated C57BL/6 mouse lungs increased perfusate cGMP as a function of V(T). Ventilation with 20 ml/kg V(T) for 80 min increased the filtration coefficient (K(f)), an index of vascular permeability. The increased cGMP and K(f) caused by HV(T) were attenuated by nitric oxide synthase (NOS) inhibition and in lungs from endothelial NOS knockout mice. Inhibition of soluble guanylyl cyclase (sGC) in wild-type lungs (10 muM ODQ) also blocked cGMP generation and inhibited the increase in K(f), suggesting an injurious role for sGC-derived cGMP. sGC inhibition also attenuated lung Evans blue dye albumin extravasation and wet-to-dry weight ratio in an anesthetized mouse model of HV(T) injury. Additional activation of sGC (1.5 muM BAY 41-2272) in isolated lungs at 40 min increased cGMP production and K(f) in lungs ventilated with 15 ml/kg V(T). HV(T) endothelial barrier dysfunction was attenuated with a nonspecific phosphodiesterase (PDE) inhibitor (100 muM IBMX) as well as an inhibitor (10 muM BAY 60-7550) specific for the cGMP-stimulated PDE2A. Concordantly, we found a V(T)-dependent increase in lung cAMP hydrolytic activity and PDE2A protein expression with a decrease in lung cAMP concentration that was blocked by BAY 60-7550. We conclude that HV(T)-induced endothelial barrier dysfunction resulted from a simultaneous increase in NO/sGC-derived cGMP and PDE2A expression causing decreased cAMP.

Ammonia inhibits the C-type natriuretic peptide-dependent cyclic GMP synthesis and calcium accumulation in a rat brain endothelial cell line

Recently we reported a decrease of C-type natriuretic peptide (CNP)-dependent, natriuretic peptide receptor 2 (NPR2)-mediated cyclic GMP (cGMP) synthesis in a non-neuronal compartment of cerebral cortical slices of hyperammonemic rats [Zielińska, M., Fresko, I., Konopacka, A., Felipo, V., Albrecht, J., 2007. Hyperammonemia inhibits the natriuretic peptide receptor 2 (NPR2)-mediated cyclic GMP synthesis in the astrocytic compartment of rat cerebral cortex slices. Neurotoxicology 28, 1260-1263]. Here we accounted for the possible involvement of cerebral capillary endothelial cells in this response by measuring the effect of ammonia on the CNP-mediated cGMP formation and intracellular calcium ([Ca2+]i) accumulation in a rat cerebral endothelial cell line (RBE-4). We first established that stimulation of cGMP synthesis in RBE-4 cells was coupled to protein kinase G (PKG)-mediated Ca2+ influx from the medium which was inhibited by an L-type channel blocker nimodipine. Ammonia treatment (1h, 5mM NH4Cl) evoked a substantial decrease of CNP-stimulated cGMP synthesis which was related to a decreased binding of CNP to NPR2 receptors, and depressed the CNP-dependent [Ca2+]i accumulation in these cells. Ammonia also abolished the CNP-dependent Ca2+ accumulation in the absence of Na+. In cells incubated with ammonia in the absence of Ca2+ a slight CNP-dependent increase of [Ca2+]i was observed, most likely representing Ca2+ release from intracellular stores. Depression of CNP-dependent cGMP-mediated [Ca2+]i accumulation may contribute to cerebral vascular endothelial dysfunction associated with hyperammonemia or hepatic encephalopathy.

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.

Differential regulation of endothelial cell permeability by cGMP via phosphodiesterases 2 and 3

Endothelial barrier dysfunction leading to increased permeability and vascular leakage is an underlying cause of several pathological conditions, including edema and sepsis. Whereas cAMP has been shown to decrease endothelial permeability, the role of cGMP is controversial. Endothelial cells express cGMP-inhibited phosphodiesterase (PDE)3A and cGMP-stimulated PDE2A. Thus we hypothesized that the effect of cGMP on endothelial permeability is dependent on the concentration of cGMP present and on the relative expression levels of PDE2A and PDE3A. When cAMP synthesis was slightly elevated with a submaximal concentration of 7-deacetyl-7-(O-[N-methylpiperazino]-gamma-butyryl)-dihydrochloride-forskolin (MPB-forskolin), we found that low doses of either atrial natriuretic peptide (ANP) or NO donors potentiated the inhibitory effects of MPB-forskolin on thrombin-induced permeability. However, this inhibitory effect of forskolin was reversed at higher doses of ANP or NO. These data suggest that cGMP at lower concentrations inhibits PDE3A and thereby increases a local pool of cAMP, whereas higher concentrations cGMP activates PDE2A, reversing the effect. Inhibitors of PDE3A mimicked the effect of low-dose ANP on thrombin-induced permeability, and inhibition of PDE2A reversed the stimulation of permeability seen with higher doses of ANP. Finally, increasing PDE2A expression with tumor necrosis factor-alpha reversed the inhibition of permeability caused by low doses of ANP. As predicted, the effect of tumor necrosis factor-alpha on permeability was reversed by a PDE2A inhibitor. These findings suggest that the effect of increasing concentrations of cGMP on endothelial permeability is biphasic, which, in large part, is attributable to the relative amounts of PDE2A and PDE3A in endothelial cells.

Regulation of renal ouabain-resistant Na+-ATPase by leptin, nitric oxide, reactive oxygen species, and cyclic nucleotides: implications for obesity-associated hypertension

This study examined the effect of leptin on renal ouabain-resistant Na(+)-ATPase, which drives the reabsorption of about 10% of sodium transported in the proximal tubule. Chronic leptin administration (0.25 mg/kg s.c. twice daily for seven days) increased Na(+)-ATPase activity by 62.9%. This effect was prevented by the coadministration of superoxide dismutase mimetic, tempol, or the NADPH oxidase inhibitor, apocynin (2 mM in the drinking water). Acutely administered NO donors decreased Na(+)-ATPase activity. This effect was abolished by soluble guanylate cyclase inhibitor, ODQ, but not by protein kinase G inhibitors. Exogenous cGMP reduced Na(+)-ATPase activity, but its synthetic analogues, 8-bromo-cGMP and 8-pCPT-cGMP, were ineffective. The inhibitory effect of NO donors and cGMP was abolished by EHNA, an inhibitor of cGMP-stimulated phosphodiesterase (PDE2). Exogenous cAMP analogue and dibutyryl-cAMP increased Na(+)-ATPase activity and abolished the inhibitory effect of cGMP. Finally, the administration of superoxide-generating mixture (xanthine oxidase+hypoxanthine) increased Na(+)-ATPase activity. The results suggest that nitric oxide decreases renal Na(+)-ATPase activity by stimulating cGMP, which in turn activates PDE2 and decreases cAMP concentration. Increased production of reactive oxygen species may lead to the elevation of Na(+)-ATPase activity by scavenging NO and limiting its inhibitory effect. Chronic hyperleptinemia is associated with increased Na(+)-ATPase activity due to excessive oxidative stress.

cGMP-dependent protein kinase in regulation of basal tone and in nitroglycerin- and nitric-oxide-induced relaxation in porcine coronary artery

Cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) may act as a critical enzyme for nitric-oxide-induced vasodilation. In this study, the role of PKG in regulation of basal tension and in relaxation induced by nitrovasodilators in coronary arteries was determined. Under basal conditions, Rp-8-Br-PET-cGMPS, a specific PKG inhibitor, evoked a significant contraction of isolated porcine coronary arteries, which was prevented by nitro-L: -arginine or the removal of the endothelium. Relaxation to nitroglycerin and (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA NONOate) in vessels preconstricted with U46619 was largely abolished by 1H-[1,2,4]oxadiazolo[4,3]quinoxalin-1-one (ODQ) and inhibited by 48 to 79% by Rp-8-Br-PET-cGMPS. Relaxation of the vessels to 8-Br-cGMP was inhibited by 56% by Rp-8-Br-PET-cGMPS. The basal activity of PKG but not that of cyclic adenosine monophosphate-dependent protein kinase (PKA) was inhibited by nitro-L: -arginine, ODQ, or Rp-8-Br-PET-cGMPS. The activity of PKG but not that of PKA was increased by nitroglycerin and DETA NONOate in intact vessels and increased by cGMP in the tissue homogenates. These effects were abolished by Rp-8-Br-PET-cGMPS but not by myristoylated PKI, a specific inhibitor of PKA. These results suggest that in porcine coronary arteries, PKG is involved in the regulation of basal tension and plays a primary role in relaxation induced by nitrovasodilators, whereas PKA may play a minor role.

Inhibition of Cytokine-Mediated Nitric Oxide Synthase Expression in Rat Insulinoma Cells by Scoparone

Cytokines produced by immune cells infiltrating pancreatic islets are important mediators of beta-cell destruction in insulin-dependent diabetes mellitus. Scoparone (6,7-dimethoxycoumarin) is known to have a wide range of pharmacological properties in vitro. In this study, the effects of scoparone on cytokine-induced beta-cell dysfunction were examined. Presence of scoparone significantly protected interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma)-mediated cytotoxicity of RINm5F, a rat insulinoma cell line, and preserved glucose-stimulated insulin secretion in rat pancreatic islets. Scoparone also resulted in a significant reduction in IL-1beta and IFN-gamma-induced nitric oxide (NO) production, a finding that correlated well with reduced levels of the inducible form of NO synthase (iNOS) mRNA and protein. The molecular mechanism by which scoparone inhibited iNOS gene expression appeared to involve the inhibition of NF-kappaB activation. These results revealed the possible therapeutic value of scoparone for the prevention of diabetes mellitus progression.

Compartmentation of cyclic nucleotide signaling in the heart: the role of cyclic nucleotide phosphodiesterases

A current challenge in cellular signaling is to decipher the complex intracellular spatiotemporal organization that any given cell type has developed to discriminate among different external stimuli acting via a common signaling pathway. This obviously applies to cAMP and cGMP signaling in the heart, where these cyclic nucleotides determine the regulation of cardiac function by many hormones and neuromediators. Recent studies have identified cyclic nucleotide phosphodiesterases as key actors in limiting the spread of cAMP and cGMP, and in shaping and organizing intracellular signaling microdomains. With this new role, phosphodiesterases have been promoted from the rank of a housekeeping attendant to that of an executive officer.

Nitric oxide regulates mitochondrial oxidative stress protection via the transcriptional coactivator PGC-1alpha

Nitric oxide (NO) has both prooxidant and antioxidant activities in the endothelium; however, the molecular mechanisms involved are still a matter of controversy. PGC-1alpha [peroxisome proliferators-activated receptor (PPAR) gamma coactivator 1-alpha] induces the expression of several members of the mitochondrial reactive oxygen species (ROS) detoxification system. Here, we show that NO regulates this system through the modulation of PGC-1alpha expression. Short-term (<12 h) treatment of endothelial cells with NO donors down-regulates PGC-1alpha expression, whereas long-term (>24 h) treatment up-regulates it. Treatment with the NOS inhibitor l-NAME has the opposite effect. Down-regulation of PGC-1alpha by NO is mediated by protein kinase G (PKG). It is blocked by the soluble guanylate cyclase (sGC) inhibitor ODQ and the PKG inhibitor KT5823, and mimicked by the cGMP analog 8-Br-cGMP. Changes in PGC-1alpha expression are in all cases paralleled by corresponding variations in the mitochondrial ROS detoxification system. Cells that transiently overexpress PGC-1alpha from the cytomeglovirus (CMV) promoter respond poorly to NO donors. Analysis of tissues from eNOS(-/-) mice showed reduced levels of PGC-1alpha and the mitochondrial ROS detoxification system. These data suggest that NO can regulate the mitochondrial ROS detoxification system both positively and negatively through PGC-1alpha.

Phosphodiesterase 5 inhibitor ameliorates renal resistance to atrial natriuretic peptide associated with obesity and hyperleptinemia

BACKGROUND

Abnormal neurohormonal regulation of renal sodium handling plays an important role in obesity-associated hypertension. We investigated the effect of experimental obesity on renal response to atrial natriuretic peptide (ANP).

METHODS

The effect of ANP was studied in three groups of rats: (1) lean controls, (2) animals made obese by a highly palatable diet, (3) rats treated with adipose tissue hormone, leptin, for 7 days to reproduce hyperleptinemia observed in obesity.

RESULTS

ANP administered at a dose of 50 pmol/kg min(-1) induced about a 3-fold lower increase in Na+ and cGMP excretion in obese and leptin-treated rats than in the control group. ANP decreased Na+,K+-ATPase activity in the renal medulla only in the control group. Natriuretic effect of exogenous cGMP was also impaired in obese and leptin-treated rats. In contrast, hydrolysis-resistant cGMP derivative, 8-bromo-cGMP exerted comparable natriuretic effects in all groups. Neutral endopeptidase inhibitor, phosphoramidon, and ANP clearance receptor antagonist, C-ANP, increased urinary ANP excretion in all groups to a similar level, but their natriuretic effect was impaired in obese and leptin-treated groups. A specific inhibitor of cGMP-degrading phosphodiesterase, zaprinast, had comparable natriuretic and Na+,K+-ATPase-lowering effects in all groups and restored normal sensitivity to ANP.

CONCLUSIONS

(1) Dietary-induced obesity is accompanied by impaired natriuretic effect of ANP, (2) ANP resistance in obesity may be accounted for by increased leptin level, (3) accelerated degradation of cGMP may contribute to ANP resistance associated with obesity and hyperleptinemia, suggesting that inhibiting cGMP-specific phosphodiesterases may be useful in the treatment of obesity-associated hypertension.

Cyclic guanosine monophosphate compartmentation in rat cardiac myocytes

BACKGROUND

Cyclic guanosine monophosphate (cGMP) is the common second messenger for the cardiovascular effects of nitric oxide (NO) and natriuretic peptides, such as atrial or brain natriuretic peptide, which activate the soluble and particulate forms of guanylyl cyclase, respectively. However, natriuretic peptides and NO donors exert different effects on cardiac and vascular smooth muscle function. We therefore tested whether these differences are due to an intracellular compartmentation of cGMP and evaluated the role of phosphodiesterase (PDE) subtypes in this process.

METHODS AND RESULTS

Subsarcolemmal cGMP signals were monitored in adult rat cardiomyocytes by expression of the rat olfactory cyclic nucleotide-gated (CNG) channel alpha-subunit and recording of the associated cGMP-gated current (ICNG). Atrial natriuretic peptide (10 nmol/L) or brain natriuretic peptide (10 nmol/L) induced a clear activation of ICNG, whereas NO donors (S-nitroso-N-acetyl-penicillamine, diethylamine NONOate, 3-morpholinosydnonimine, and spermine NO, all at 100 micromol/L) had little effect. The ICNG current was strongly potentiated by nonselective PDE inhibition with isobutyl methylxanthine (100 micromol/L) and by the PDE2 inhibitors erythro-9-(2-hydroxy-3-nonyl)adenine (10 micromol/L) and Bay 60-7550 (50 nmol/L). Surprisingly, sildenafil, a PDE5 inhibitor, produced a dose-dependent increase of I(CNG) activated by NO donors but had no effect (at 100 nmol/L) on the current elicited by atrial natriuretic peptide.

CONCLUSIONS

These results indicate that in rat cardiomyocytes (1) the particulate cGMP pool is readily accessible at the plasma membrane, whereas the soluble pool is not; and (2) PDE5 controls the soluble but not the particulate pool, whereas the latter is under the exclusive control of PDE2. Differential spatiotemporal distributions of cGMP may therefore contribute to the specific effects of natriuretic peptides and NO donors on cardiac function.

Nitric oxide regulates transforming growth factor-beta signaling in endothelial cells

Many forms of vascular disease are characterized by increased transforming growth factor (TGF)-beta1 expression and endothelial dysfunction. Smad proteins are a key step in TGF-beta-initiated signal transduction. We hypothesized that NO may regulate endothelial TGF-beta-dependent gene expression. We show that NO inhibits TGF-beta/Smad-regulated gene transactivation in a cGMP-dependent manner. NO effects were mimicked by a soluble analogue of cGMP. Inhibition of cGMP-dependent protein kinase 1 (PKG-1) or overexpression of dominant-negative PKG-1alpha suppressed NO/cGMP inhibition of TGF-beta-induced gene expression. Inversely, overexpression of PKG-1alpha catalytic subunit blocked TGF-beta-induced gene transactivation. Furthermore NO delayed and reduced phosphorylated Smad2/3 nuclear translocation, an effect mediated by PKG-1, whereas NG-nitro-L-arginine methyl ester augmented Smad phosphorylation and gene expression in response to TGF-beta. Aortas from endothelial NO synthase-deficient mice showed enhanced basal TGF-beta1 and collagen type I expression; endothelial cells from these animals showed increased Smad phosphorylation and transcriptional activity. Proteasome inhibitors prevented the inhibitory effect of NO on TGF-beta signaling. NO reduced the metabolic life of ectopically expressed Smad2 and enhanced its ubiquitination. Taken together, these results suggest that the endothelial NO/cGMP/PKG pathway interferes with TGF-beta/Smad2 signaling by directing the proteasomal degradation of activated Smad.

Drosophila soluble guanylyl cyclase mutants exhibit increased foraging locomotion: behavioral and genomic investigations

Genetic variation in the gene foraging (for) is associated with a natural behavioral dimorphism in the fruit fly, Drosophila melanogaster. Some larvae, called 'rovers', have increased foraging locomotion compared to others, called 'sitters', and this difference is directly related to for-encoded cGMP-dependent protein kinase (PKG) activity. Here we report that larvae with mutations in the gene dgcalpha1, which encodes a soluble guanylyl cyclase (sGC) subunit, have increases in both PKG activity and foraging locomotion. This is contrary to our original prediction that, based on the role of sGC in the synthesis of cGMP, dgcalpha1 mutant larvae would have deficient cGMP production leading to decreased PKG activation and thus reduced larval foraging locomotion. We performed DNA microarray analyses to compare transcriptional changes induced by a dgcalpha1 mutation in both rover and sitter wildtype genetic backgrounds. In either background, we identified many genes that are differentially transcribed, and interestingly, relatively few are affected in both backgrounds. Furthermore, several of these commonly affected genes are enhanced or suppressed in a background-dependent manner. Thus, genetic background has a critical influence on the molecular effects of this mutation. These findings will support future investigations of Drosophila foraging behavior.

Differential Regulation of Soluble Guanylyl Cyclase Expression and Signaling by Collagens: Involvement of Integrin-Linked Kinase

Glomerular diseases are characterized by an abnormal synthesis of extracellular matrix proteins, such as collagen type I. Evidence that growth on collagen type I downregulates soluble guanylyl cyclase (sGC) expression and the responsiveness of human mesangial cells to nitric oxide (NO) by activating specific integrin signals involving integrin-linked kinase (ILK) is presented. Human mesangial cells were grown on collagen type I or IV for 24 to 72 h. Compared with collagen IV, growth on collagen I reduced the protein expression and NO-stimulated enzyme activity of sGC. This downregulation was effected at the level of transcription, because steady-state sGC mRNA expression was reduced on collagen I, but inhibition of transcription with Actinomycin D revealed no differences in transcript stability between the two culture conditions. Collagen I also reduced the capacity of cells to relax in response to NO after H2O2 challenge and inhibited NO-induced phosphorylation of vasodilator-activated phosphoprotein, a target of cyclic guanine monophosphate-dependent protein kinase. Examination of the surface expression of integrins, the receptors for extracellular matrix components, revealed that alpha1 and alpha2 integrin subunits were more abundant on cells that were grown on collagen IV and that surface expression of beta1 integrin did not vary with collagen type. However, growth on collagen I induced beta1 integrin to adopt its active conformation, and this activation of beta1 integrin was accompanied by increased activity of its downstream effector ILK. Dominant-negative suppression of ILK signaling relieved the suppression of sGC expression and NO-induced vasodilator-activated phosphoprotein phosphorylation induced by collagen I.

Vascular endothelial cell cyclic nucleotide phosphodiesterases and regulated cell migration: implications in angiogenesis

Angiogenesis is necessary during embryonic development and wound healing but can be detrimental in pathologies, including cancer. Because initiation of angiogenesis involves migration and proliferation of vascular endothelial cells (VECs) and cAMP-elevating agents inhibit these events, such agents may represent a novel therapeutic avenue to controlling angiogenesis. Intracellular cAMP levels are regulated by their synthesis by adenylyl cyclases and hydrolysis by cyclic nucleotide phosphodiesterases (PDEs). In this report, we show that human VECs express variants of PDE2, PDE3, PDE4, and PDE5 families and demonstrate that the levels of these enzymes differ in VECs derived from aorta, umbilical vein, and microvascular structures. Selective inhibition of PDE2 did not increase cAMP in any VECs, whether in the absence or presence of forskolin, but it did inhibit migration of all VECs studied. Inhibition of PDE4 activity decreased migration, and in conjunction with forskolin, increased cAMP in all VECs studied. PDE3 inhibition potentiated forskolin-induced increases in cAMP and inhibited migration in VECs derived from aorta and umbilical vein but not in microvascular VECs. In experiments with combinations of PDE2, PDE3, and PDE4 inhibitors, a complex interaction between the abilities of these agents to limit human VEC migration was observed. Overall, our data are consistent with the hypothesis that PDE subtype inhibition allows different effects in distinct VEC populations and indicate that these agents may represent novel therapeutic agents to limit angiogenesis in complex human diseases.