Dickkopf-1 Enhances Inflammatory Interaction Between Platelets and Endothelial Cells and Shows Increased Expression in Atherosclerosis

Abstract

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

Activation of Platelets byAspergillus fumigatusand Potential Role of Platelets in the Immunopathogenesis of Aspergillosis

“…DKK-1 is a major regulator of the Wnt signaling pathway, a complex cascade of mediators that have been shown to be involved in a wide range of physiological and pathophysiological responses, such as inflammation, angiogenesis, and regulation of cell survival (14). Recently, we reported that DKK-1 also may play a major role in platelet-dependent endothelial activation and inflammation (22), and Wnt signaling has been shown to be involved in the pathogenesis of various disorders ranging from cancer to atherosclerosis and septicemia (14,22). It is tempting to hypothesize that DKK-1 and the Wnt pathway could also be involved in A. fumigatus-induced inflammation and vascular pathology.…”

“…Third, in contrast to the effects of conidia and hyphae on the membrane expression of CD62P and CD63, only hyphae induced a significant increase in the release of RANTES and CD40L, with a particularly pronounced effect on CD40L. Fourth, we have recently shown that upon activation, platelets may release significant amounts of DKK-1, an important regulator of the wingless (Wnt) signaling pathways, which are involved in inflammation and vascular development (22), and notably, hyphae, but not conidia, induced a marked release of DKK-1 upon platelet activation. Finally, while combined stimulation with SFLLRN and swollen conidia or hyphae showed an enhancing effect on CD40L, the combination of SFLLRN and resting or swollen conidia attenuated the SFLLRN-induced release of RANTES and DKK-1.…”

Platelet-derived Wnt antagonist Dickkopf-1 is implicated in ICAM-1/VCAM-1–mediated neutrophilic acute lung inflammation

“…8 The blood was collected into 3.8% sodium citrate, pH 7.4 (2:1, volume) by cardiac puncture, and centrifuged at 250g for 10 minutes to obtain the platelet-rich plasma (PRP). For platelet stimulation, PRP was treated with 100 mM thrombin receptor activating peptide (SFLLRN; Sigma-Aldrich) for the indicated times and then centrifuged at 657g for 7 minutes.…”

“…7 Platelets also aggregate with neutrophils or monocytes via cell surface P-selectin and provide supportive juxtacrine and paracrine signals. [7][8][9] By interacting with endothelial cells, activated platelets cause increases in vascular permeability and promote the release of proinflammatory cytokines (interleukin-6…”

“…8,10 Platelet components are found in the bronchoalveolar (BAL) fluid from ARDS patients. 11 However, it remains unclear whether platelets directly affect the functions of the alveolar epithelium during the development of ALI.…”