This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium-and plasmaderived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cellvessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro-and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Immune mechanisms are known to control the pathogenesis of atherosclerosis. However, the exact role of DCs, which are essential for priming of immune responses, remains elusive. We have shown here that the DC-derived chemokine CCL17 is present in advanced human and mouse atherosclerosis and that CCL17 + DCs accumulate in atherosclerotic lesions. In atherosclerosis-prone mice, Ccl17 deficiency entailed a reduction of atherosclerosis, which was dependent on Tregs. Expression of CCL17 by DCs limited the expansion of Tregs by restricting their maintenance and precipitated atherosclerosis in a mechanism conferred by T cells. Conversely, a blocking antibody specific for CCL17 expanded Tregs and reduced atheroprogression. Our data identify DC-derived CCL17 as a central regulator of Treg homeostasis, implicate DCs and their effector functions in atherogenesis, and suggest that CCL17 might be a target for vascular therapy.

SummaryTo understand the process of cardiac aging, it is of crucial importance to gain insight into the age-related changes in gene expression in the senescent failing heart. Age-related cardiac remodeling is known to be accompanied by changes in extracellular matrix (ECM) gene and protein levels. Small noncoding microRNAs regulate gene expression in cardiac development and disease and have been implicated in the aging process and in the regulation of ECM proteins. However, their role in age-related cardiac remodeling and heart failure is unknown. In this study, we investigated the aging-associated microRNA cluster 17-92, which targets the ECM proteins connective tissue growth factor (CTGF) and thrombospondin-1 (TSP-1). We employed aged mice with a failure-resistant (C57Bl6) and failure-prone (C57Bl6 · 129Sv) genetic background and extrapolated our findings to human age-associated heart failure. In aging-associated heart failure, we linked an aging-induced increase in the ECM proteins CTGF and TSP-1 to a decreased expression of their targeting microRNAs 18a, 19a, and 19b, all members of the miR-17-92 cluster. Failure-resistant mice showed an opposite expression pattern for both the ECM proteins and the microRNAs. We showed that these expression changes are specific for cardiomyocytes and are absent in cardiac fibroblasts. In cardiomyocytes, modulation of miR-18 ⁄ 19 changes the levels of ECM proteins CTGF and TSP-1 and collagens type 1 and 3. Together, our data support a role for cardiomyocyte-derived miR-18 ⁄ 19 during cardiac aging, in the fine-tuning of cardiac ECM protein levels. During aging, decreased miR-18 ⁄ 19 and increased CTGF and TSP-1 levels identify the failure-prone heart.

Note: The editorial process for this article was fully handled by Prof. G. Y. H. Lip, Editor-in-Chief.

Objective-High-shear perfusion of blood over collagen results in rapid platelet adhesion, aggregation, and procoagulant activity. We studied regulation of ␣2␤1 and ␣IIb␤3 integrin activation during thrombus formation on collagen. Methods and Results-Blockade of glycoprotein (GP) VI by 9O12 antibody or of P2Y purinergic receptors permitted platelet adhesion but reduced aggregate formation, fibrinogen binding, and activation of ␣2␤1 and ␣IIb␤3, as detected with antibodies IAC-1 and PAC1 directed against activation-dependent epitopes of these integrins. Combined blockade of GPVI and P2Y receptors and thromboxane formation abolished integrin activation but still allowed adhesion of morphologically unstimulated, nonprocoagulant platelets. Exogenous ADP partly restored the suppressive effect of GPVI blockade on integrin ␣2␤1 and ␣IIb␤3 activation. Adhesion was fully inhibited only with simultaneous blocking of GPVI and ␣2␤1, indicating that the integrin can support platelet-collagen binding in the absence of its activation. Blockade or absence of GPIb␣ only moderately influenced integrin activation and adhesion unless GPVI was inhibited. Conclusions-GPVI-and autocrine-released ADP induce affinity changes of ␣2␤1 and ␣IIb␤3 during thrombus formation on collagen under flow. These integrin changes are dispensable for adhesion but strengthen platelet-collagen interactions and thereby collagen-induced platelet activation. Key Words: ADP Ⅲ collagen Ⅲ glycoprotein VI Ⅲ integrins Ⅲ platelets Ⅲ thrombus P latelet integrins are critical in hemostasis. Abundantly expressed at the platelet surface, integrins are required for platelet interactions with subendothelial matrix components and for platelet-platelet interactions leading to aggregate and thrombus formation. 1 Integrin ␣2␤1 plays a role in platelet adhesion to collagen under static 2,3 and flow conditions. 4,5 Integrin ␣IIb␤3 allows platelets to bind to fibrinogen and von Willebrand factor (vWF) present on collagen and other platelets. 6 This leads to stable platelet adhesion and aggregate formation. 7 On resting platelets, these integrins are considered to be present in a low-affinity state. Intracellular signaling or ligand binding results in conformational changes of the integrins with a switch to higher-affinity states. 6 Agonists such as thrombin, collagen, ADP, and vWF induce ␣IIb␤3 activation and platelet aggregation. 8,9 Full integrin activation with ADP requires the P2Y 1 and P2Y 12 purinergic receptors. 10,11 Recent studies show that integrin ␣2␤1 can also be activated by inside-out signaling. 12,13 Thrombin and collagen turn this integrin into a high-affinity form, whereas ADP changes it to intermediate affinity. 13 Although much is known of the affinity and avidity changes of ␣IIb␤3 on isolated platelets especially, 8,14 regulation of integrin activation during thrombus formation is incompletely understood.In vivo studies as well as ex vivo experiments, in which blood was allowed to flow over collagen under arterial shear conditions, have indicated that glycop...