Objective-Based on the emerging importance of the wingless (Wnt) pathways in inflammation and vascular biology, we hypothesized a role for Dickkopf-1 (DKK-1), a major modulator of Wnt signaling, in atherogenesis and plaque destabilization. Methods and Results-We report increased levels of DKK-1 in experimental (ApoE Ϫ/Ϫ mice) and clinical (patients with coronary artery disease ͓nϭ80͔ and patients with carotid plaque ͓nϭ47͔) atherosclerosis, both systemically (serum) and within the lesion, with particularly high levels in advanced and unstable disease. We identified platelets as an important cellular source of DKK-1 as shown by in vitro experiments and by immunostaining of thrombus material obtained at the site of plaque rupture in patients with acute ST-elevation myocardial infarction, with strong immunoreactivity in platelet aggregates. Our in vitro experiments identified a role for platelet-and endothelialderived DKK-1 in platelet-dependent endothelial activation, promoting enhanced release of inflammatory cytokines. These inflammatory effects of DKK-1 involved inhibition of the Wnt/␤-catenin pathway and activation of nuclear factor B. Key Words: atherosclerosis Ⅲ endothelium Ⅲ inflammation Ⅲ platelets P roteins from the wingless (Wnt) signaling pathways are involved in diverse developmental and physiological processes, including cardiac and vascular development. Wnt signals are transduced to the canonical and the noncanonical pathways for control of cell fate, cell movement, and tissue polarity. 1 The Wnt pathways are regulated by multiple families of secreted antagonists including soluble frizzled related receptors and dickkopfs (DKK). The best studied of these is DKK-1, which dampens Wnt signaling by binding to the low-density lipoprotein receptor-related protein (LRP)5/6 and a cell surface coreceptor, Kremen-1, promoting internalization of the receptor complex. 2 In adults, DKK-1 has been implicated in bone disease, cancer, and brain ischemia, and most recently, the destructive effect of tumor necrosis factor ␣ (TNF␣) on joints in rheumatoid arthritis was found to involve DKK-1. 2,3 Also, serum levels of DKK-1 give prognostic information in patients with multiple myeloma and other malignancies as well as in patients with osteoarthritis. 4,5 Recent evidence points to an important role of the Wnt signaling pathways in the regulation of inflammation. Thus, activation of the canonical Wnt/␤-catenin pathway induces proliferation and survival of endothelial cells, enhances monocyte adhesion, and regulates transendothelial migration of monocytes. 6 -9 Moreover, activation of the noncanonical pathway has been shown to regulate inflammatory responses of human monocytes and macrophages in vitro. 10,11 However, the interaction between the different proteins in the Wnt family is rather complex, and the role Conclusion-Our

Traditionally, platelets are known to play an important role in hemostasis, thrombosis, and wound healing, but increasing evidence suggests that activated platelets also may promote inflammation. Platelet-induced modulation of inflammation seems to involve platelet expression of ligands in the tumor necrosis factor (TNF) superfamily such as CD40 ligand and Fas ligand. The present study demonstrates that LIGHT, another member of the TNF superfamily, is associated with platelets and is released as a soluble ligand on platelet activation. The release of LIGHT involves GP IIb/IIIa-dependent mechanisms and action of metal-dependent proteases as well as intracellular processes such as actin polymerization. We also report that platelet-derived LIGHT is biologically active and can induce an inflammatory response in monocytes and particularly within endothelial cells measured as up-regulation of adhesion molecules and release of chemokines. Moreover, we demonstrate that thrombus material, obtained at the site of plaque rupture in patients with acute myocardial infarction, contains platelet-associated LIGHT, suggesting that LIGHT-mediated inflammation also is operating in vivo within an inflamed and thrombotic vessel wall. The data may suggest a pathogenic role for platelet-derived LIGHT in atherogenesis and plaque destabilization as well as in other inflammatory disorders involving leukocyte infiltration into the vessel wall. IntroductionThe traditional role of platelets as mediators of hemostasis and thrombosis is well documented. Increasing evidence suggests that activated platelets also play a key role in inflammation. Hence, on activation platelets release and express inflammatory mediators, induce an inflammatory response in adjacent leukocytes and endothelial cells, and respond with activation to several of the mediators produced by these cells. [1][2][3][4][5][6] Such interactions between platelets and leukocytes/endothelial cells seem to play a pathogenic role in atherosclerosis as well as in other immune-mediated disorders.Several platelet-derived mediators, such as chemokines and prostaglandins, appear to be involved in platelet-mediated inflammation. 1 Recently, much attention has been focused on the role of platelet-associated CD40 ligand (CD40L), a ligand in the tumor necrosis factor (TNF) superfamily, in this inflammatory loop between platelets and other cells. Thus, platelet-associated CD40L may interact with CD40, which is constitutively expressed on a wide range of cells, such as macrophages, endothelial cells, and vascular smooth muscle cells, resulting in various inflammatory responses. 7,8 Moreover, platelet-derived FasL, another member of the TNF superfamily, was recently shown to induce apoptosis in Fas ϩ tumor cells, further suggesting a role for ligands of this cytokine superfamily in platelet-mediated immune responses. 9 LIGHT, the name of which is derived from "homologous to lymphotoxins, exhibits inducible expression, and competes with herpes simplex virus (HSV) glycoprotein D for herpes virus...

Activin A, a member of the transforming growth factor (TGF)-beta superfamily, is involved in regulation of tissue remodeling and inflammation. Herein, we wanted to explore a role for activin A in pulmonary hypertension (PH). Circulating levels of activin A and its binding protein follistatin were measured in patients with PH (n = 47) and control subjects (n = 14). To investigate synthesis and localization of pulmonary activin A, we utilized an experimental model of hypoxia-induced PH. In mouse lungs, we also explored signaling pathways that can be activated by activin A, such as phosphorylation of Smads, which are mediators of TGF-beta signaling. Possible pathophysiological mechanisms initiated by activin A were explored by exposing pulmonary arterial smooth muscle cells in culture to this cytokine. Elevated levels of activin A and follistatin were found in patients with PH, and activin A levels were significantly related to mortality. Immunohistochemistry of lung autopsies from PH patients and lungs with experimental PH localized activin A primarily to alveolar macrophages and bronchial epithelial cells. Mice with PH exhibited increased pulmonary levels of mRNA for activin A and follistatin in the lungs, and also elevated pulmonary levels of phosphorylated Smad2. Finally, we found that activin A increased proliferation and induced gene expression of endothelin-1 and plasminogen activator inhibitor-1 in pulmonary artery smooth muscle cells, mediators that could contribute to vascular remodeling. Our findings in both clinical and experimental studies suggest a role for activin A in the development of various types of PH.