Kevin Croce

Accumulation of Tissue Factor into Developing Thrombi In Vivo Is Dependent upon Microparticle P-Selectin Glycoprotein Ligand 1 and Platelet P-Selectin

Using a laser-induced endothelial injury model, we examined thrombus formation in the microcirculation of wild-type and genetically altered mice by real-time in vivo microscopy to analyze this complex physiologic process in a system that includes the vessel wall, the presence of flowing blood, and the absence of anticoagulants. We observe P-selectin expression, tissue factor accumulation, and fibrin generation after platelet localization in the developing thrombus in arterioles of wild-type mice. However, mice lacking P-selectin glycoprotein ligand 1 (PSGL-1) or P-selectin, or wild-type mice infused with blocking P-selectin antibodies, developed platelet thrombi containing minimal tissue factor and fibrin. To explore the delivery of tissue factor into a developing thrombus, we identified monocyte-derived microparticles in human platelet–poor plasma that express tissue factor, PSGL-1, and CD14. Fluorescently labeled mouse microparticles infused into a recipient mouse localized within the developing thrombus, indicating that one pathway for the initiation of blood coagulation in vivo involves the accumulation of tissue factor– and PSGL-1–containing microparticles in the platelet thrombus expressing P-selectin. These monocyte-derived microparticles bind to activated platelets in an interaction mediated by platelet P-selectin and microparticle PSGL-1. We propose that PSGL-1 plays a role in blood coagulation in addition to its known role in leukocyte trafficking.

Platelet Expression Profiling and Clinical Validation of Myeloid-Related Protein-14 as a Novel Determinant of Cardiovascular Events

Background— Platelets participate in events that immediately precede acute myocardial infarction. Because platelets lack nuclear DNA but retain megakaryocyte-derived mRNAs, the platelet transcriptome provides a novel window on gene expression preceding acute coronary events. Methods and Results— We profiled platelet mRNA from patients with acute ST-segment–elevation myocardial infarction (STEMI, n=16) or stable coronary artery disease (n=44). The platelet transcriptomes were analyzed and single-gene models constructed to identify candidate genes with differential expression. We validated 1 candidate gene product by performing a prospective, nested case-control study (n=255 case-control pairs) among apparently healthy women to assess the risk of future cardiovascular events (nonfatal myocardial infarction, nonfatal stroke, and cardiovascular death) associated with baseline plasma levels of the candidate protein. Platelets isolated from STEMI and coronary artery disease patients contained 54 differentially expressed transcripts. The strongest discriminators of STEMI in the microarrays were CD69 (odds ratio 6.2, P<0.001) and myeloid-related protein-14 (MRP-14; odds ratio 3.3, P=0.002). Plasma levels of MRP-8/14 heterodimer were higher in STEMI patients (17.0 versus 8.0 &mgr;g/mL, P<0.001). In the validation study, the risk of a first cardiovascular event increased with each increasing quartile of MRP-8/14 (Ptrend<0.001) such that women with the highest levels had a 3.8-fold increase in risk of any vascular event (P<0.001). Risks were independent of standard risk factors and C-reactive protein. Conclusions— The platelet transcriptome reveals quantitative differences between acute and stable coronary artery disease. MRP-14 expression increases before STEMI, and increasing plasma concentrations of MRP-8/14 among healthy individuals predict the risk of future cardiovascular events.

Vascular Inflammation and Repair: Implications for Re-Endothelialization, Restenosis, and Stent Thrombosis

The cellular and molecular processes that control vascular injury responses after percutaneous coronary intervention involve a complex interplay among vascular cells and progenitor cells that control arterial remodeling, neointimal proliferation, and re-endothelialization. Drug-eluting stents (DES) improve the efficacy of percutaneous coronary intervention by modulating vascular inflammation and preventing neointimal proliferation and restenosis. Although positive effects of DES reduce inflammation and restenosis, negative effects delay re-endothelialization and impair endothelial function. Delayed re-endothelialization and impaired endothelial function are linked to stent thrombosis and adverse clinical outcomes after DES use. Compared with bare-metal stents, DES also differentially modulate mobilization, homing, and differentiation of vascular progenitor cells involved in re-endothelialization and neointimal proliferation. The effects of DES on vascular inflammation and repair directly impact clinical outcomes with these devices and dictate requirements for extended-duration dual antiplatelet therapy.

NF-κB Directs Dynamic Super Enhancer Formation in Inflammation and Atherogenesis

Proinflammatory stimuli elicit rapid transcriptional responses via transduced signals to master regulatory transcription factors. To explore the role of chromatin-dependent signal transduction in the atherogenic inflammatory response, we characterized the dynamics, structure, and function of regulatory elements in the activated endothelial cell epigenome. Stimulation with tumor necrosis factor alpha prompted a dramatic and rapid global redistribution of chromatin activators to massive de novo clustered enhancer domains. Inflammatory super enhancers formed by nuclear factor-kappa B accumulate at the expense of immediately decommissioned, basal endothelial super enhancers, despite persistent histone hyperacetylation. Mass action of enhancer factor redistribution causes momentous swings in transcriptional initiation and elongation. A chemical genetic approach reveals a requirement for BET bromodomains in communicating enhancer remodeling to RNA Polymerase II and orchestrating the transition to the inflammatory cell state, demonstrated in activated endothelium and macrophages. BET bromodomain inhibition abrogates super enhancer-mediated inflammatory transcription, atherogenic endothelial responses, and atherosclerosis in vivo.

Myeloid-Related Protein-8/14 Is Critical for the Biological Response to Vascular Injury

Background— Myeloid-related protein (MRP)-8 (S100A8) and MRP-14 (S100A9) are members of the S100 family of calcium-modulated proteins that regulate myeloid cell function and control inflammation, in part, through activation of Toll-like receptor-4 and the receptor for advanced glycation end products. A transcriptional profiling approach in patients with acute coronary syndromes identified MRP-14 as a novel predictor of myocardial infarction. Further studies demonstrated that elevated plasma levels of MRP-8/14 heterodimer predict increased risk of first and recurrent cardiovascular events. Beyond its serving as a risk marker, whether MRP-8/14 participates directly in vascular inflammation and disease remains unclear. Methods and Results— We evaluated vascular inflammation in wild-type and MRP-14–deficient (MRP-14−/−) mice that lack MRP-8/14 complexes with experimental arterial injury, vasculitis, or atherosclerosis. After femoral artery wire injury, MRP-14−/− mice had significant reductions in leukocyte accumulation, cellular proliferation, and neointimal formation compared with wild-type mice. In a cytokine-induced local Shwartzman-like reaction that produces thrombohemorrhagic vasculitis, MRP-14−/− mice had significant reductions in neutrophil accumulation, lesion severity, and hemorrhagic area. In response to high-fat feeding, mice doubly deficient in apolipoprotein E and MRP-8/14 complexes had attenuation in atherosclerotic lesion area and in macrophage accumulation in plaques compared with mice deficient in apolipoprotein E alone. Conclusion— This study demonstrates that MRP-8/14 broadly regulates vascular inflammation and contributes to the biological response to vascular injury by promoting leukocyte recruitment.

Macrophage-Derived Matrix Vesicles An Alternative Novel Mechanism for Microcalcification in Atherosclerotic Plaques

Rationale: We previously showed that early calcification of atherosclerotic plaques associates with macrophage accumulation. Chronic renal disease and mineral imbalance accelerate calcification and the subsequent release of matrix vesicles (MVs), precursors of microcalcification. Objective: We tested the hypothesis that macrophage-derived MVs contribute directly to microcalcification. Methods and Results: Macrophages associated with regions of calcified vesicular structures in human carotid plaques (n=136 patients). In vitro, macrophages released MVs with high calcification and aggregation potential. MVs expressed exosomal markers (CD9 and TSG101) and contained S100A9 and annexin V. Silencing S100A9 in vitro and genetic deficiency in S100A9−/− mice reduced MV calcification, whereas stimulation with S100A9 increased calcification potential. Externalization of phosphatidylserine after Ca/P stimulation and interaction of S100A9 and annexin V indicated that a phosphatidylserine-annexin V-S100A9 membrane complex facilitates hydroxyapatite nucleation within the macrophage-derived MV membrane. Conclusions: Our results support the novel concept that macrophages release calcifying MVs enriched in S100A9 and annexin V, which contribute to accelerated microcalcification in chronic renal disease. # Novelty and Significance {#article-title-18}Rationale: We previously showed that early calcification of atherosclerotic plaques associates with macrophage accumulation. Chronic renal disease and mineral imbalance accelerate calcification and the subsequent release of matrix vesicles (MVs), precursors of microcalcification. Objective: We tested the hypothesis that macrophage-derived MVs contribute directly to microcalcification. Methods and Results: Macrophages associated with regions of calcified vesicular structures in human carotid plaques (n=136 patients). In vitro, macrophages released MVs with high calcification and aggregation potential. MVs expressed exosomal markers (CD9 and TSG101) and contained S100A9 and annexin V. Silencing S100A9 in vitro and genetic deficiency in S100A9−/− mice reduced MV calcification, whereas stimulation with S100A9 increased calcification potential. Externalization of phosphatidylserine after Ca/P stimulation and interaction of S100A9 and annexin V indicated that a phosphatidylserine-annexin V-S100A9 membrane complex facilitates hydroxyapatite nucleation within the macrophage-derived MV membrane. Conclusions: Our results support the novel concept that macrophages release calcifying MVs enriched in S100A9 and annexin V, which contribute to accelerated microcalcification in chronic renal disease.

Systemic Delivery of MicroRNA-181b Inhibits Nuclear Factor-κB Activation, Vascular Inflammation, and Atherosclerosis in Apolipoprotein E–Deficient Mice

Rationale: Activated nuclear factor (NF)-&kgr;B signaling in the vascular endothelium promotes the initiation and progression of atherosclerosis. Targeting endothelial NF-&kgr;B may provide a novel strategy to limit chronic inflammation. Objective: To examine the role of microRNA-181b (miR-181b) in endothelial NF-&kgr;B signaling and effects on atherosclerosis. Methods and Results: MiR-181b expression was reduced in the aortic intima and plasma in apolipoprotein E–deficient mice fed a high-fat diet. Correspondingly, circulating miR-181b in the plasma was markedly reduced in human subjects with coronary artery disease. Systemic delivery of miR-181b resulted in a 2.3-fold overexpression of miR-181b in the aortic intima of apolipoprotein E–deficient mice and suppressed NF-&kgr;B signaling revealed by bioluminescence imaging and reduced target gene expression in the aortic arch in apolipoprotein E–deficient/NF-&kgr;B-luciferase transgenic mice. MiR-181b significantly inhibited atherosclerotic lesion formation, proinflammatory gene expression and the influx of lesional macrophages and CD4+ T cells in the vessel wall. Mechanistically, miR-181b inhibited the expression of the target gene importin-&agr;3, an effect that reduced NF-&kgr;B nuclear translocation specifically in the vascular endothelium of lesions, whereas surprisingly leukocyte NF-&kgr;B signaling was unaffected despite a 7-fold overexpression of miR-181b. Our findings uncover that NF-&kgr;B nuclear translocation in leukocytes does not involve importin-&agr;3, but rather importin-&agr;5, which miR-181b does not target, highlighting that inhibition of NF-&kgr;B signaling in the endothelium is sufficient to mediate miR-181b’s protective effects. Conclusions: Systemic delivery of miR-181b inhibits the activation of NF-&kgr;B and atherosclerosis through cell-specific mechanisms in the vascular endothelium. These findings support the rationale that delivery of miR-181b may provide a novel therapeutic approach to treat chronic inflammatory diseases such as atherosclerosis.

IL-17 and TNF-α Sustain Neutrophil Recruitment during Inflammation through Synergistic Effects on Endothelial Activation

IL-17A (IL-17) is the signature cytokine produced by Th17 cells and has been implicated in host defense against infection and the pathophysiology of autoimmunity and cardiovascular disease. Little is known, however, about the influence of IL-17 on endothelial activation and leukocyte influx to sites of inflammation. We hypothesized that IL-17 would induce a distinct pattern of endothelial activation and leukocyte recruitment when compared with the Th1 cytokine IFN-γ. We found that IL-17 alone had minimal activating effects on cultured endothelium, whereas the combination of TNF-α and IL-17 produced a synergistic increase in the expression of both P-selectin and E-selectin. Using intravital microscopy of the mouse cremaster muscle, we found that TNF-α and IL-17 also led to a synergistic increase in E-selectin–dependent leukocyte rolling on microvascular endothelium in vivo. In addition, TNF-α and IL-17 enhanced endothelial expression of the neutrophilic chemokines CXCL1, CXCL2, and CXCL5 and led to a functional increase in leukocyte transmigration in vivo and CXCR2-dependent neutrophil but not T cell transmigration in a parallel-plate flow chamber system. By contrast, endothelial activation with TNF-α and IFN-γ preferentially induced the expression of the integrin ligands ICAM-1 and VCAM-1, as well as the T cell chemokines CXCL9, CXCL10, and CCL5. These effects were further associated with a functional increase in T cell but not neutrophil transmigration under laminar shear flow. Overall, these data show that IL-17 and TNF-α act in a synergistic manner to induce a distinct pattern of endothelial activation that sustains and enhances neutrophil influx to sites of inflammation.

Leukocyte Engagement of Platelet Glycoprotein Ibα via the Integrin Mac-1 Is Critical for the Biological Response to Vascular Injury

Background— Leukocyte-platelet interactions are critical in the initiation and progression of atherosclerosis as well as restenosis. Although the leukocyte integrin Mac-1 (αMβ2, CD11b/CD18) has been implicated in the firm adhesion and transmigration of leukocytes at sites of platelet deposition, the precise αMβ2 counterligand responsible for mediating adhesion-strengthening interactions between neutrophils and platelets in vivo has not previously been identified. Methods and Results— Our previous studies have established the P201-K217 sequence in the αMI domain as the binding site for platelet glycoprotein (GP) Ibα. Here we report that antibody targeting of αM(P201-K217) reduced αMβ2-dependent adhesion to GP Ibα but not other αMβ2 ligands, including fibrinogen, intercellular adhesion molecule-1, and junctional adhesion molecule-3. Anti-αM(P201-K217) inhibited the firm adhesion of both human and murine leukocytes to adherent platelets under laminar flow conditions. In a mouse femoral artery wire injury model, antibody targeting of αM(P201-K217) reduced leukocyte accumulation after injury that was accompanied by inhibition of cellular proliferation and neointimal thickening. Conclusions— This study demonstrates that GP Ibα is a physiologically relevant ligand for αMβ2 and that integrin engagement of GP Ibα is critical to leukocyte function and the biological response to vascular injury. These observations establish a molecular target for selectively disrupting leukocyte-platelet complexes that promote inflammation in thrombosis and restenosis.

Proteins of the exocytotic core complex mediate platelet alpha-granule secretion. Roles of vesicle-associated membrane protein, SNAP-23, and syntaxin 4.

To understand the molecular basis of granule release from platelets, we examined the role of vesicle-associated membrane protein, SNAP-23, and syntaxin 4 in α-granule secretion. A vesicle-associated membrane protein, SNAP-23, and syntaxin 4 were detected in platelet lysate. These proteins form a SDS-resistant complex that disassembles upon platelet activation. To determine whether these proteins are involved in α-granule secretion, we developed a streptolysin O-permeabilized platelet model of α-granule secretion. Streptolysin O-permeabilized platelets released α-granules, as measured by surface expression of P-selectin, in response to Ca2+ up to 120 min after permeabilization. Incubation of streptolysinO-permeabilized platelets with an antibody directed against vesicle-associated membrane protein completely inhibited Ca2+-induced α-granule release. Tetanus toxin cleaved platelet vesicle-associated membrane protein and inhibited Ca2+-induced α-granule secretion from streptolysinO-permeabilized platelets. An antibody to syntaxin 4 also inhibited Ca2+-induced α-granule release by approximately 75% in this system. These results show that vesicle-associated membrane protein, SNAP-23, and syntaxin 4 form a heterotrimeric complex in platelets that disassembles with activation and demonstrate that α-granule release is dependent on vesicle SNAP receptor-target SNAP receptor (vSNARE-tSNARE) interactions.