Cyclic AMP (cAMP) and cGMP regulate a myriad of cellular functions, such as metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system. Considerable effort over the last 20 years has allowed identification of the cellular components involved in the synthesis of cyclic nucleotides, as well as effectors of cyclic nucleotide-mediated signaling. More recently, a central role for cyclic nucleotide phosphodiesterase (PDE) has also been elaborated in many cell types, including those involved in regulating the activities of the cardiovascular system. In this review, we introduce the PDE families whose members are expressed in cells of the cardiovascular system including cardiomyocytes, vascular smooth muscle cells, and vascular endothelial cells. Because cell behavior is a dynamic process influenced by numerous factors, we will attempt to emphasize how changes in the activity, expression, and targeting of PDE influence cyclic nucleotide-mediated regulation of the behavior of these cells.The cyclic nucleotides cAMP and cGMP regulate a myriad of cellular functions, including metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system (Antoni, 2000;Klein, 2002). Although early work identified cAMP and cGMP as second messengers and led to the discovery of the proteins involved in coordinating the synthesis, degradation, and cellular actions of cyclic nucleotides, early models describing how these systems allowed cyclic nucleotide-mediated regulation of multiple cellular functions underestimated the levels of flexibility and specialization involved. In this context, recent work has identified large numbers of receptor (Marchese et al., 1999;Lucas et al., 2000), adenylyl cyclase (Hanoune and Defer, 2001), guanylyl cyclase (Garbers, 1999;Lucas et al., 2000), heterotrimeric G-protein (Marchese et al., 1999), and cyclic nucleotide phosphodiesterase (PDE) (Beavo and Reifsnyder, 1990;Beavo, 1995;Conti et al., 1995;Manganiello and Degerman, 1999;Conti, 2000;Conti and Jin, 2000;Houslay and Kolch, 2000;Soderling and Beavo, 2000;Francis et al., 2001;Houslay and Adams, 2003) protein families. Although many of the cellular effects of cAMP and cGMP are coordinated through their activation of cyclic nucleotide-dependent protein kinases (Lincoln et al., 1995), several other effectors are now known. Thus, cyclic nucleotidegated ion channels (Yau, 1994), cAMP-activated guanine nucleotide exchange factors (de Rooij et al., 1998;Kawasaki et al., 1998), and cyclic nucleotide PDEs have each been shown to transduce cyclic nucleotide-encoded information (Beavo and Reifsnyder, 1990;Beavo, 1995;Conti et al., 1995;Manganiello and Degerman, 1999;Conti, 2000;Conti and Jin, 2000;Houslay and Kolch, 2000;Soderling and Beavo, 2000;Francis et al., 2001;Houslay and Adams, 2003). More recently, an appreciation of the impact of regulated anchoring/targeting of cyclic nucleotide-regulated proteins to discrete subcell...

Thrombocytopenia has been consistently reported following the administration of adenoviral gene transfer vectors. The mechanism underlying this phenomenon is currently unknown. In this study, we have assessed the influence of von Willebrand Factor (VWF) and P-selectin on the clearance of platelets following adenovirus administration. In mice, thrombocytopenia occurs between 5 and 24 hours after adenovirus delivery. The virus activates platelets and induces platelet-leukocyte aggregate formation. There is an associated increase in platelet and leukocyte-derived microparticles. Adenovirus-induced endothelial cell activation was shown by VCAM-1 expression on virus-treated, cultured endothelial cells and by the release of ultra-large molecular weight multimers of VWF within 1 to 2 hours of virus administration with an accompanying elevation of endothelial microparticles. In contrast, VWF knockout (KO) mice did not show significant thrombocytopenia after adenovirus administration. We have also shown that adenovirus interferes with adhesion of platelets to a fibronectincoated surface and flow cytometry revealed the presence of the Coxsackie adenovirus receptor on the platelet surface. We conclude that VWF and P-selectin are critically involved in a complex platelet-leukocyteendothelial interplay, resulting in platelet activation and accelerated platelet clearance following adenovirus administration. IntroductionAcute thrombocytopenia has been consistently reported following intravenous administration of adenovirus. [1][2][3] Thrombocytopenia is transient and vector dose-dependent but the mechanism underlying this adverse event currently remains unclear.P-selectin is a member of the selectin family of cell adhesion molecules that mediate binding to specific carbohydrate-containing ligands. The protein is localized in the ␣ granules of platelets and the Weibel-Palade bodies of endothelial cells. 4,5 The most clearly identified ligand for P-selectin is PSGL-1, which is detected on the majority of leukocytes and also present in small amounts on platelets. 6,7 P-selectin supports initial tethering of leukocytes to activated endothelial cells and to activated platelets and mediates leukocyte rolling on the endothelial cell surface. 8 A soluble form of P-selectin resulting from proteolytic shedding of the extracellular domain has been detected in human 9 and mouse 10 plasma and was found to maintain the requirements for ligand binding. 11 Elevated levels of plasma P-selectin are seen in a variety of inflammatory, autoimmune, and thrombotic disorders. 12,13 A critical step in the response to vascular injury is the interaction between platelets and the adhesive protein von Willebrand factor (VWF), which mediates platelet translocation and adhesion to the exposed subendothelium. 14 VWF binding to platelets is mediated through platelet GPIb and this interaction acts as a complementary binding event to the tethering of leukocytes to platelets through a Mac1-P-selectin interaction. 15 Furthermore, activation of the endothelium is...

Elbatarny, Hisham S., and Donald H. Maurice. Leptin-mediated activation of human platelets: involvement of a leptin receptor and phosphodiesterase 3A-containing cellular signaling complex.

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 G1␤ (PKG1␤)-containing signaling complex, reported previously to coordinate cGMP-mediated inhibition of inositol-1, 4, 5-trisphosphate receptor type 1 (IP 3R1)-mediated Ca 2؉ -release. PKG1␤ and PDE5 did not interact in subcellular fractions devoid of IP 3R1 and were not recruited to IP3R1-enriched membranes in response to cGMP-elevating agents. Activation of platelet PKG promoted phosphorylation and activation of the PDE5 fraction tethered to the IP 3R1-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.calcium ͉ PKG

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