Macrophage-NLRP3 Activation Promotes Right Ventricle Failure in Pulmonary Arterial Hypertension.

Rationale: Pulmonary arterial hypertension (PAH) often results in death from right ventricular failure (RVF). NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3)-macrophage activation may promote RVF in PAH. Objectives: Evaluating the contribution of the NLRP3 inflammasome in RV macrophages to PAH RVF. Methods: Rats with decompensated RV hypertrophy (monocrotaline [MCT] and Sugen-5416 hypoxia [SuHx]) were compared with compensated RV hypertrophy rats (pulmonary artery banding). Echocardiography and right heart catheterization were performed. Macrophages, atrial natriuretic peptides, and fibrosis were evaluated by microscopy or flow cytometry. NLRP3 inflammasome activation and cardiotoxicity were confirmed by immunoblot and in vitro strategies. MCT rats were treated with SC-144 (a GP130 antagonist) or MCC950 (an NLRP3 inhibitor). Macrophage-NLRP3 activity was evaluated in patients with PAH RVF. Measurements and Main Results: Macrophages, fibrosis, and atrial natriuretic peptides were increased in MCT and SuHx RVs but not in left ventricles or pulmonary artery banding rats. Although MCT RV macrophages were inflammatory, lung macrophages were antiinflammatory. CCR2+ macrophages (monocyte-derived) were increased in MCT and SuHx RVs and highly expressed NLRP3. The macrophage-NLRP3 pathway was upregulated in patients with PAH with decompensated RVs. Cultured MCT monocytes showed NLRP3 activation, and in coculture experiments resulted in cardiomyocyte mitochondrial damage, which MCC950 prevented. In vivo, MCC950 reduced NLRP3 activation and regressed pulmonary vascular disease and RVF. SC-144 reduced RV macrophages and NLRP3 content, prevented STAT3 (signal transducer and activator of transcription 3) activation, and improved RV function without regressing pulmonary vascular disease. Conclusions: NLRP3-macrophage activation occurs in the decompensated RV in preclinical PAH models and patients with PAH. Inhibiting GP130 or NLRP3 signaling improves RV function. The concept that PAH RVF results from RV inflammation rather than solely from elevated RV afterload suggests a new therapeutic paradigm.

Phosphodiesterase 1C integrates store-operated calcium entry and cAMP signaling in leading-edge protrusions of migrating human arterial myocytes.

In addition to maintaining cellular ER Ca2+ stores, store-operated Ca2+ entry (SOCE) regulates several Ca2+-sensitive cellular enzymes, including certain adenylyl cyclases (ADCYs), enzymes that synthesize the secondary messenger cyclic AMP (cAMP). Ca2+, acting with calmodulin, can also increase the activity of PDE1-family phosphodiesterases (PDEs), which cleave the phosphodiester bond of cAMP. Surprisingly, SOCE-regulated cAMP signaling has not been studied in cells expressing both Ca2+-sensitive enzymes. Here, we report that depletion of ER Ca2+ activates PDE1C in human arterial smooth muscle cells (HASMCs). Inhibiting the activation of PDE1C reduced the magnitude of both SOCE and subsequent Ca2+/calmodulin-mediated activation of ADCY8 in these cells. Because inhibiting or silencing Ca2+-insensitive PDEs had no such effects, these data identify PDE1C-mediated hydrolysis of cAMP as a novel and important link between SOCE and its activation of ADCY8. Functionally, we showed that PDE1C regulated the formation of leading-edge protrusions in HASMCs, a critical early event in cell migration. Indeed, we found that PDE1C populated the tips of newly forming leading-edge protrusions in polarized HASMCs, and co-localized with ADCY8, the Ca2+ release activated Ca2+ channel subunit, Orai1, the cAMP-effector, protein kinase A, and an A-kinase anchoring protein, AKAP79. Because this polarization could allow PDE1C to control cAMP signaling in a hyper-localized manner, we suggest that PDE1C-selective therapeutic agents could offer increased spatial specificity in HASMCs over agents that regulate cAMP globally in cells. Similarly, such agents could also prove useful in regulating crosstalk between Ca2+/cAMP signaling in other cells in which dysregulated migration contributes to human pathology, including certain cancers.

Endothelial BMPR2 Loss Drives a Proliferative Response to BMP (Bone Morphogenetic Protein) 9 via Prolonged Canonical Signaling.

OBJECTIVE: Pulmonary arterial hypertension is a disease of proliferative vascular occlusion that is strongly linked to mutations in BMPR2-the gene encoding the BMPR-II (BMP [bone morphogenetic protein] type II receptor). The endothelial-selective BMPR-II ligand, BMP9, reverses disease in animal models of pulmonary arterial hypertension and suppresses the proliferation of healthy endothelial cells. However, the impact of BMPR2 loss on the antiproliferative actions of BMP9 has yet to be assessed. Approach and Results: BMP9 suppressed proliferation in blood outgrowth endothelial cells from healthy control subjects but increased proliferation in blood outgrowth endothelial cells from pulmonary arterial hypertension patients with BMPR2 mutations. This shift from growth suppression to enhanced proliferation was recapitulated in control human pulmonary artery endothelial cells following siRNA-mediated BMPR2 silencing, as well as in mouse pulmonary endothelial cells isolated from endothelial-conditional Bmpr2 knockout mice (Bmpr2EC-/-). BMP9-induced proliferation was not attributable to altered metabolic activity or elevated TGFß (transforming growth factor beta) signaling but was linked to the prolonged induction of the canonical BMP target ID1 in the context of BMPR2 loss. In vivo, daily BMP9 administration to neonatal mice impaired both retinal and lung vascular patterning in control mice (Bmpr2EC+/+) but had no measurable effect on mice bearing a heterozygous endothelial Bmpr2 deletion (Bmpr2EC+/-) and caused excessive angiogenesis in both vascular beds for Bmpr2EC-/- mice. CONCLUSIONS: BMPR2 loss reverses the endothelial response to BMP9, causing enhanced proliferation. This finding has potential implications for the proposed translation of BMP9 as a treatment for pulmonary arterial hypertension and suggests the need for focused patient selection in clinical trials.

Phosphodiesterase 4D7 selectively regulates cAMP-mediated control of human arterial endothelial cell transcriptomic responses to fluid shear stress.

Human arterial endothelial cells (HAECs) regulate their phenotype by integrating signals encoded in the frictional forces exerted by flowing blood, fluid shear stress (FSS). High laminar FSS promotes establishment of adaptive HAEC phenotype protective against atherosclerosis, whereas low or disturbed FSS cause HAECs to adopt atheroprone phenotypes. A vascular endothelial cadherin (VE cadherin)-based mechanosensory complex allows HAECs to regulate barrier function, cell morphology,/ and gene expression in response to FSS. Previously, we reported that this mechanosensor integrated exchange protein activated by cAMP (EPAC1) and a PDE4D gene derived cyclic nucleotide phosphodiesterase (PDE), but had not identified the PDE4D variant involved. Our hypothesis here was that only one of the two ∼100 kDa PDE4D variants expressed in HAECs coordinated these responses. Now, we show one unique PDE4D splice variant, PDE4D7, controls transcriptional responses of HAECs to FSS while another, PDE4D5, does not. Adaptive transcriptional responses of HAECs subjected to laminar FSS in vitro were blunted in cells in which PDE4D7 was silenced, but unaffected in cells with silenced PDE4D5. This work identifies a specific therapeutic target for the treatment or prevention of atherosclerosis and improves our understanding of the role of cAMP signaling in modulating mechanosensory signal transduction in the vascular endothelium.

Liquid Degradable Poly(trimethylene-carbonate-co-5-hydroxy-trimethylene carbonate): An Injectable Drug Delivery Vehicle for Acid-Sensitive Drugs.

Liquid, injectable hydrophobic polymers have advantages as degradable drug delivery vehicles; however, polymers examined for this purpose to date form acidic degradation products that may damage acid-sensitive drugs. Herein, we report on a new viscous liquid vehicle, poly(trimethylene carbonate-co-5-hydroxy-trimethylene carbonate), which degrades through intramolecular cyclization producing glycerol, carbon dioxide, and water-soluble trimethylene carbonate. Copolymer degradation durations from weeks to months were achieved with the 5-hydroxy-trimethylene carbonate (HTMC) content of the oligomer having the greatest impact on the degradation rate, with oligomers possessing a higher HTMC content degrading fastest. The degradation products were non-cytotoxic towards 3T3 fibroblasts and RAW 264.7 macrophages. These copolymers can be injected manually through standard gauge needles and, importantly, during in vitro degradation, the microenvironmental pH within the oligomers remained near neutral. Complete and sustained release of the acid-sensitive protein vascular endothelial growth factor was achieved, with the protein remaining highly bioactive throughout the release period. These copolymers represent a promising formulation for local and sustained release of acid sensitive drugs.

Leptin influences the excitability of area postrema neurons.

The area postrema (AP) is a circumventricular organ with important roles in central autonomic regulation. This medullary structure has been shown to express the leptin receptor and has been suggested to have a role in modulating peripheral signals, indicating energy status. Using RT-PCR, we have confirmed the presence of mRNA for the leptin receptor, ObRb, in AP, and whole cell current-clamp recordings from dissociated AP neurons demonstrated that leptin influenced the excitability of 51% (42/82) of AP neurons. The majority of responsive neurons (62%) exhibited a depolarization (5.3 ± 0.7 mV), while the remaining affected cells (16/42) demonstrated hyperpolarizing effects (-5.96 ± 0.95 mV). Amylin was found to influence the same population of AP neurons. To elucidate the mechanism(s) of leptin and amylin actions in the AP, we used fluorescence resonance energy transfer (FRET) to determine the effect of these peptides on cAMP levels in single AP neurons. Leptin and amylin were found to elevate cAMP levels in the same dissociated AP neurons (leptin: % total FRET response 25.3 ± 4.9, n = 14; amylin: % total FRET response 21.7 ± 3.1, n = 13). When leptin and amylin were coapplied, % total FRET response rose to 53.0 ± 8.3 (n = 6). The demonstration that leptin and amylin influence a subpopulation of AP neurons and that these two signaling molecules have additive effects on single AP neurons to increase cAMP, supports a role for the AP as a central nervous system location at which these circulating signals may act through common intracellular signaling pathways to influence central control of energy balance.

Cyclic nucleotide phosphodiesterases (PDEs): coincidence detectors acting to spatially and temporally integrate cyclic nucleotide and non-cyclic nucleotide signals.

The cyclic nucleotide second messengers cAMP and cGMP each affect virtually all cellular processes. Although these hydrophilic small molecules readily diffuse throughout cells, it is remarkable that their ability to activate their multiple intracellular effectors is spatially and temporally selective. Studies have identified a critical role for compartmentation of the enzymes which hydrolyse and metabolically inactivate these second messengers, the PDEs (cyclic nucleotide phosphodiesterases), in this specificity. In the present article, we describe several examples from our work in which compartmentation of selected cAMP- or cGMP-hydrolysing PDEs co-ordinate selective activation of cyclic nucleotide effectors, and, as a result, selectively affect cellular functions. It is our belief that therapeutic strategies aimed at targeting PDEs within these compartments will allow greater selectivity than those directed at inhibiting these enzymes throughout the cells.

Phosphodiesterase 4 activity uniquely regulates ciliary cAMP-dependent 3T3-L1 adipogenesis.

Recent evidence indicates that the presence of a primary cilium (PC), and of selective cAMP signaling within this smallest of organelles, promotes adipogenic differentiation of 3T3-L1 preadipocytes incubated in media supplemented with either a natural (docosahexaenoic acid, DHA), or a synthetic (TUG-891), free fatty acid receptor 4 (FFAR4) agonist. Indeed, in this earlier work, activation of ciliary FFAR4 in 3T3-L1 cells was correlated with selective increases in PC cAMP and adipogenesis in these cells. However, this study was silent on the role of local PC cAMP phosphodiesterases (PDEs)-mediated events in regulating these adipogenic responses and on the identity of cAMP PDEs that could regulate the "pool" of ciliary cAMP accessed by FFAR4 agonists. In this context, we have identified the PDEs expressed by 3T3-L1 preadipocytes and showed that of these, only PDE4 inhibition promotes FFAR4-mediated adipogenesis. We propose that this work will identify more selective therapeutic targets through which to control adipogenesis, and perhaps the differentiation of other stem cells in which ciliary cAMP is critical.

Phosphodiesterase 4D regulates baseline sarcoplasmic reticulum Ca2+ release and cardiac contractility, independently of L-type Ca2+ current.

RATIONALE: Baseline contractility of mouse hearts is modulated in a phosphatidylinositol 3-kinase-γ-dependent manner by type 4 phosphodiesterases (PDE4), which regulate cAMP levels within microdomains containing the sarcoplasmic reticulum (SR) calcium ATPase type 2a (SERCA2a). OBJECTIVE: The goal of this study was to determine whether PDE4D regulates basal cardiac contractility. METHODS AND RESULTS: At 10 to 12 weeks of age, baseline cardiac contractility in PDE4D-deficient (PDE4D(-/-)) mice was elevated mice in vivo and in Langendorff perfused hearts, whereas isolated PDE4D(-/-) cardiomyocytes showed increased whole-cell Ca2+ transient amplitudes and SR Ca2+content but unchanged L-type calcium current, compared with littermate controls (WT). The protein kinase A inhibitor R(p)-adenosine-3',5' cyclic monophosphorothioate (R(p)-cAMP) lowered whole-cell Ca2+ transient amplitudes and SR Ca2+ content in PDE4D(-/-) cardiomyocytes to WT levels. The PDE4 inhibitor rolipram had no effect on cardiac contractility, whole-cell Ca2+ transients, or SR Ca2+ content in PDE4D(-/-) preparations but increased these parameters in WT myocardium to levels indistinguishable from those in PDE4D(-/-). The functional changes in PDE4D(-/-) myocardium were associated with increased PLN phosphorylation but not cardiac ryanodine receptor phosphorylation. Rolipram increased PLN phosphorylation in WT cardiomyocytes to levels indistinguishable from those in PDE4D(-/-) cardiomyocytes. In murine and failing human hearts, PDE4D coimmunoprecipitated with SERCA2a but not with cardiac ryanodine receptor. CONCLUSIONS: PDE4D regulates basal cAMP levels in SR microdomains containing SERCA2a-PLN, but not L-type Ca2+ channels or ryanodine receptor. Because whole-cell Ca2+ transient amplitudes are reduced in failing human myocardium, these observations may have therapeutic implications for patients with heart failure.

Potential therapeutic applications of phosphodiesterase inhibition in prostate cancer.

OBJECTIVE: Phosphodiesterases (PDEs) play a role in controlling cyclic nucleotide action, including cyclic guanosine monophosphate (cGMP). Previous studies have ascribed a protective role of cGMP signaling on hypoxia-mediated cancer progression. Herein, we determine their potential role in hypoxia-mediated chemoresistance and immune escape. MATERIALS AND METHODS: Phosphodiesterase assays were used to measure PDE activity in prostate cancer cell lines (DU145, PC3). Immunoblots were performed to determine the presence of PDEs in human prostate tissue samples. The effect of PDE inhibition on hypoxia-induced chemoresistance (compared to normoxic controls, 20% O2) was determined using clonogenic assays. Flow cytometry was used to determine the effects of PDE inhibition on surface MHC class I-related chain A (MICA), a natural killer (NK) cell-activating ligand. A mouse model was used to evaluate the in vivo effects of PDE inhibition on the growth of human prostate cancer cells. RESULTS: PDE5 and PDE11 were the most prominent PDEs in the cell lines, representing between 86 and 95% of the total cGMP-specific PDE activity. Treatment of DU-145 cells with a PDE inhibitor significantly reduced the hypoxia-associated acquisition of resistance to doxorubicin, with a mean 51% reduction in surviving fraction compared to controls (p < 0.001, ANOVA). As well, PDE inhibition completely reversed (p = 0.02, ANOVA) hypoxia-induced shedding of the immune stimulatory molecule, MICA, and attenuated the growth of human prostate tumor xenografts in an NK cell-competent murine model (p = 0.03, Wilcoxon, Mann-Whitney). CONCLUSIONS: These results suggest a rationale for future studies on the potential therapeutic applications of PDE inhibitors in men with prostate cancer.

A phosphodiesterase 3B-based signaling complex integrates exchange protein activated by cAMP 1 and phosphatidylinositol 3-kinase signals in human arterial endothelial cells.

Enzymes of the phosphodiesterase 3 (PDE3) and PDE4 families each regulate the activities of both protein kinases A (PKAs) and exchange proteins activated by cAMP (EPACs) in cells of the cardiovascular system. At present, the mechanisms that allow selected PDEs to individually regulate the activities of these two effectors are ill understood. The objective of this study was to determine how a specific PDE3 variant, namely PDE3B, interacts with and regulates EPAC1-based signaling in human arterial endothelial cells (HAECs). Using several biochemical approaches, we show that PDE3B and EPAC1 bind directly through protein-protein interactions. By knocking down PDE3B expression or by antagonizing EPAC1 binding with PDE3B, we show that PDE3B regulates cAMP binding by its tethered EPAC1. Interestingly, we also show that PDE3B binds directly to p84, a PI3Kγ regulatory subunit, and that this interaction allows PI3Kγ recruitment to the PDE3B-EPAC1 complex. Of potential cardiovascular importance, we demonstrate that PDE3B-tethered EPAC1 regulates HAEC PI3Kγ activity and that this allows dynamic cAMP-dependent regulation of HAEC adhesion, spreading, and tubule formation. We identify and molecularly characterize a PDE3B-based "signalosome" that integrates cAMP- and PI3Kγ-encoded signals and show how this signal integration regulates HAEC functions of importance in angiogenesis.

Cyclic AMP phosphodiesterase 4D (PDE4D) Tethers EPAC1 in a vascular endothelial cadherin (VE-Cad)-based signaling complex and controls cAMP-mediated vascular permeability.

Vascular endothelial cell (VEC) permeability is largely dependent on the integrity of vascular endothelial cadherin (VE-cadherin or VE-Cad)-based intercellular adhesions. Activators of protein kinase A (PKA) or of exchange protein activated by cAMP (EPAC) reduce VEC permeability largely by stabilizing VE-Cad-based intercellular adhesions. Currently, little is known concerning the nature and composition of the signaling complexes that allow PKA or EPAC to regulate VE-Cad-based structures and through these actions control permeability. Using pharmacological, biochemical, and cell biological approaches we identified and determined the composition and functionality of a signaling complex that coordinates cAMP-mediated control of VE-Cad-based adhesions and VEC permeability. Thus, we report that PKA, EPAC1, and cyclic nucleotide phosphodiesterase 4D (PDE4D) enzymes integrate into VE-Cad-based signaling complexes in human arterial endothelial cells. Importantly, we show that protein-protein interactions between EPAC1 and PDE4D serve to foster their integration into VE-Cad-based complexes and allow robust local regulation of EPAC1-based stabilization of VE-Cad-based adhesions. Of potential translational importance, we mapped the EPAC1 peptide motif involved in binding PDE4D and show that a cell-permeable variant of this peptide antagonizes EPAC1-PDE4D binding and directly alters VEC permeability. Collectively, our data indicate that PDE4D regulates both the activity and subcellular localization of EPAC1 and identify a novel mechanism for regulated EPAC1 signaling in these cells.

Compartmentation and compartment-specific regulation of PDE5 by protein kinase G allows selective cGMP-mediated regulation of platelet functions.

It is generally accepted that nitric oxide (NO) donors, such as sodium nitroprusside (SNP), or phosphodiesterase 5 (PDE5) inhibitors, including sildenafil, each impact human platelet function. Although a strong correlation exists between the actions of NO donors in platelets and their impact on cGMP, agents such as sildenafil act without increasing global intra-platelet cGMP levels. This study was undertaken to identify how PDE5 inhibitors might act without increasing cGMP. Our data identify PDE5 as an integral component of a protein kinase G1beta (PKG1beta)-containing signaling complex, reported previously to coordinate cGMP-mediated inhibition of inositol-1, 4, 5-trisphosphate receptor type 1 (IP(3)R1)-mediated Ca(2+)-release. PKG1beta and PDE5 did not interact in subcellular fractions devoid of IP(3)R1 and were not recruited to IP(3)R1-enriched membranes in response to cGMP-elevating agents. Activation of platelet PKG promoted phosphorylation and activation of the PDE5 fraction tethered to the IP(3)R1-PKG complex, an effect not observed for the nontethered PDE5. Based on these findings, we elaborate a model in which PKG selectively activates PDE5 within a defined microdomain in platelets and propose that this mechanism allows spatial and temporal regulation of cGMP signaling in these cells. Recent reports indicate that sildenafil might prove useful in limiting in-stent thrombosis and the thrombotic events associated with the acute coronary syndromes (ACS), situations poorly regulated with currently available therapeutics. We submit that our findings may define a molecular mechanism by which PDE5 inhibition can differentially impact selected cellular functions of platelets, and perhaps of other cell types.

Formulation parameters governing sustained protein delivery from degradable viscous liquid aliphatic polycarbonates.

Viscous liquid degradable polymers have advantages as drug depots for sustained protein delivery. We have created a new aliphatic polycarbonate for this purpose, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), which upon degradation retains a near neutral micro-environmental pH. As such, this copolymer is highly suited to the delivery of acid sensitive proteins. We show that the mechanism of protein release from this liquid copolymer is consistent with the formation of super-hydrated regions as a result of the osmotic activity of the solution formed upon distributed protein particle dissolution. Protein release can be manipulated by controlling polymer hydrophobicity which can be adjusted by molecular weight and choice of initiator. Moreover, protein release is highly dependent on protein solubility which impacts the osmotic activity of the solution formed upon dissolution of the protein particles while protein molecular size and isoelectric point are not as influential. As demonstrated by the release of highly bioactive vascular endothelial growth factor, formulations of this copolymer are suitable for prolonged delivery of protein therapeutics.

cAMP-Specific phosphodiesterase-4 enzymes in the cardiovascular system: a molecular toolbox for generating compartmentalized cAMP signaling.

Cyclic AMP regulates a vast number of distinct events in all cells. Early studies established that its hydrolysis by cyclic nucleotide phosphodiesterases (PDEs) controlled both the magnitude and the duration of its influence. Recent evidence shows that PDEs also act as coincident detectors linking cyclic-nucleotide- and non-cyclic-nucleotide-based cellular signaling processes and are tethered with great selectively to defined intracellular structures, thereby integrating and spatially restricting their cellular effects in time and space. Although 11 distinct families of PDEs have been defined, and cells invariably express numerous individual PDE enzymes, a large measure of our increased appreciation of the roles of these enzymes in regulating cyclic nucleotide signaling has come from studies on the PDE4 family. Four PDE4 genes encode more than 20 isoforms. Alternative mRNA splicing and the use of different promoters allows cells the possibility of expressing numerous PDE4 enzymes, each with unique amino-terminal-targeting and/or regulatory sequences. Dominant negative and small interfering RNA-mediated knockdown strategies have proven that particular isoforms can uniquely control specific cellular functions. Thus the protein kinase A phosphorylation status of the beta(2) adrenoceptor and, thereby, its ability to switch its signaling to extracellular signal-regulated kinase activation, is uniquely regulated by PDE4D5 in cardiomyocytes. We describe how cardiomyocytes and vascular smooth muscle cells selectively vary both the expression and the catalytic activities of PDE4 isoforms to regulate their various functions and how altered regulation of these processes can influence the development, or resolution, of cardiovascular pathologies, such as heart failure, as well as various vasculopathies.

Formation of extracellular matrix-digesting invadopodia by primary aortic smooth muscle cells.

Invasion of the subendothelial space by vascular smooth muscle cells (VSMCs) contributes to the development and progression of diverse cardiovascular diseases. In this report we show that the expression of activated versions of Src, Cdc42 and Rac1, or a kinase-dead but open form of the p21-activated kinase (PAK1), induces primary rat aorta VSMCs to form extracellular matrix-degrading actin-rich protrusions that are morphologically similar to the invadopodia formed by highly invasive tumor cells. The matrix-degrading structures are enriched in known markers for invadopodia, including cortactin and tyrosine-phosphorylated cortactin and contain the matrix metalloproteinases MMP-9 and MT1-MMP and the urokinase plasminogen activator receptor (uPAR). In contrast to other cell types, invadopodia formation in VSMCs is only weakly supported by the phorbol ester PBDu. Invadopodia formation by Src was dependent on Cdc42, Rac, and ERK, but not on p38 MAPK. Invadopodia formation induced by kinase-dead PAK1 required Src and ERK activity and a direct interaction with the exchange factor PIX. VSMCs embedded in a three-dimensional collagen matrix formed actin- and cortactin-rich extensions that penetrated through holes in the matrix, suggesting that invadopodia-like structures are formed in a three-dimensional environment.

Both protein kinase A and exchange protein activated by cAMP coordinate adhesion of human vascular endothelial cells.

cAMP regulates integrin-dependent adhesions of vascular endothelial cells (VECs) to extracellular matrix proteins, their vascular endothelial cadherin-dependent intercellular adhesions, and their proliferation and migration in response to growth and chemotactic factors. Previously, we reported that cAMP-elevating agents differentially inhibited migration of human VECs isolated from large vascular structures (macro-VECs, human aortic endothelial cells [HAECs]) or small vascular structures (micro-VECs, human microvascular endothelial cells [HMVECs]) and that cAMP hydrolysis by phosphodiesterase (PDE)3 and PDE4 enzymes was important in coordinating this difference. Here we report that 2 cAMP-effector enzymes, namely protein kinase (PK)A and exchange protein activated by cAMP (EPAC), each regulate extracellular matrix protein-based adhesions of both macro- and micro-VECs. Of interest and potential therapeutic importance, we report that although specific pharmacological activation of EPAC markedly stimulated adhesion of micro-VECs to extracellular matrix proteins when PKA was inhibited, this treatment only modestly promoted adhesion of macro-VECs. Consistent with an important role for cAMP PDEs in this difference, PDE3 or PDE4 inhibitors promoted EPAC-dependent adhesions in micro-VECs when PKA was inhibited but not in macro-VECs. At a molecular level, we identify multiple, nonoverlapping, PKA- or EPAC-based signaling protein complexes in both macro- and micro-VECs and demonstrate that each of these complexes contains either PDE3B or PDE4D but not both of these PDEs. Taken together, our data support the concept that adhesion of macro- and micro-VECs is differentially regulated by cAMP and that these differences are coordinated through selective actions of cAMP at multiple nonoverlapping signaling complexes that contain PKA or EPAC and distinct PDE variants.

PI3Kgamma is required for PDE4, not PDE3, activity in subcellular microdomains containing the sarcoplasmic reticular calcium ATPase in cardiomyocytes.

We recently showed that phosphoinositide-3-kinase-gamma-deficient (PI3Kgamma(-/-)) mice have enhanced cardiac contractility attributable to cAMP-dependent increases in sarcoplasmic reticulum (SR) Ca(2+) content and release but not L-type Ca(2+) current (I(Ca,L)), demonstrating PI3Kgamma locally regulates cAMP levels in cardiomyocytes. Because phosphodiesterases (PDEs) can contribute to cAMP compartmentation, we examined whether the PDE activity was altered by PI3Kgamma ablation. Selective inhibition of PDE3 or PDE4 in wild-type (WT) cardiomyocytes elevated Ca(2+) transients, SR Ca(2+) content, and phospholamban phosphorylation (PLN-PO(4)) by similar amounts to levels observed in untreated PI3Kgamma(-/-) myocytes. Combined PDE3 and PDE4 inhibition caused no further increases in SR function. By contrast, only PDE3 inhibition affected Ca(2+) transients, SR Ca(2+) loads, and PLN-PO(4) levels in PI3Kgamma(-/-) myocytes. On the other hand, inhibition of PDE3 or PDE4 alone did not affect I(Ca,L) in either PI3Kgamma(-/-) or WT cardiomyocytes, whereas simultaneous PDE3 and PDE4 inhibition elevated I(Ca,L) in both groups. Ryanodine receptor (RyR(2)) phosphorylation levels were not different in basal conditions between PI3Kgamma(-/-) and WT myocytes and increased in both groups with PDE inhibition. Our results establish that L-type Ca(2+) channels, RyR(2), and SR Ca(2+) pumps are regulated differently in distinct subcellular compartments by PDE3 and PDE4. In addition, the loss of PI3Kgamma selectively abolishes PDE4 activity, not PDE3, in subcellular compartments containing the SR Ca(2+)-ATPase but not RyR(2) or L-type Ca(2+) channels.

An EPAC1/PDE1C-Signaling Axis Regulates Formation of Leading-Edge Protrusion in Polarized Human Arterial Vascular Smooth Muscle Cells.

Pharmacological activation of protein kinase A (PKA) reduces migration of arterial smooth muscle cells (ASMCs), including those isolated from human arteries (HASMCs). However, when individual migration-associated cellular events, including the polarization of cells in the direction of movement or rearrangements of the actin cytoskeleton, are studied in isolation, these individual events can be either promoted or inhibited in response to PKA activation. While pharmacological inhibition or deficiency of exchange protein activated by cAMP-1 (EPAC1) reduces the overall migration of ASMCs, the impact of EPAC1 inhibition or deficiency, or of its activation, on individual migration-related events has not been investigated. Herein, we report that EPAC1 facilitates the formation of leading-edge protrusions (LEPs) in HASMCs, a critical early event in the cell polarization that underpins their migration. Thus, RNAi-mediated silencing, or the selective pharmacological inhibition, of EPAC1 decreased the formation of LEPs by these cells. Furthermore, we show that the ability of EPAC1 to promote LEP formation by migrating HASMCs is regulated by a phosphodiesterase 1C (PDE1C)-regulated "pool" of intracellular HASMC cAMP but not by those regulated by the more abundant PDE3 or PDE4 activities. Overall, our data are consistent with a role for EPAC1 in regulating the formation of LEPs by polarized HASMCs and show that PDE1C-mediated cAMP hydrolysis controls this localized event.