Activated Platelets Upregulate ß2 Integrin Mac-1 (CD11b/CD18) on Dendritic Cells, Which Mediates Heterotypic Cell-Cell Interaction.

Recent evidence suggests interaction of platelets with dendritic cells (DCs), while the molecular mechanisms mediating this heterotypic cell cross-talk are largely unknown. We evaluated the role of integrin Mac-1 (αMß2, CD11b/CD18) on DCs as a counterreceptor for platelet glycoprotein (GP) Ibα. In a dynamic coincubation model, we observed interaction of human platelets with monocyte-derived DCs, but also that platelet activation induced a sharp increase in heterotypic cell binding. Inhibition of CD11b or GPIbα led to significant reduction of DC adhesion to platelets in vitro independent of GPIIbIIIa, which we confirmed using platelets from Glanzmann thrombasthenia patients and transgenic mouse lines on C57BL/6 background (GPIbα-/-, IL4R-GPIbα-tg, and muMac1 mice). In vivo, inhibition or genetic deletion of CD11b and GPIbα induced a significant reduction of platelet-mediated DC adhesion to the injured arterial wall. Interestingly, only intravascular antiCD11b inhibited DC recruitment, suggesting a dynamic DC-platelet interaction. Indeed, we could show that activated platelets induced CD11b upregulation on Mg2+-preactivated DCs, which was related to protein kinase B (Akt) and dependent on P-selectin and P-selectin glycoprotein ligand 1. Importantly, specific pharmacological targeting of the GPIbα-Mac-1 interaction site blocked DC-platelet interaction in vitro and in vivo. These results demonstrate that cross-talk of platelets with DCs is mediated by GPIbα and Mac-1, which is upregulated on DCs by activated platelets in a P-selectin glycoprotein ligand 1-dependent manner.

Novel Aspects Targeting Platelets in Atherosclerotic Cardiovascular Disease-A Translational Perspective.

Platelets are important cellular targets in cardiovascular disease. Based on insights from basic science, translational approaches and clinical studies, a distinguished anti-platelet drug treatment regimen for cardiovascular patients could be established. Furthermore, platelets are increasingly considered as cells mediating effects "beyond thrombosis", including vascular inflammation, tissue remodeling and healing of vascular and tissue lesions. This review has its focus on the functions and interactions of platelets with potential translational and clinical relevance. The role of platelets for the development of atherosclerosis and therapeutic modalities for primary and secondary prevention of atherosclerotic disease are addressed. Furthermore, novel therapeutic options for inhibiting platelet function and the use of platelets in regenerative medicine are considered.

Complement links platelets to innate immunity.

The complement system is a versatile part of our immune system. Various intersection points of complement with other cells and molecules of the immune response are well described. Platelets are classically conceived as cells of hemostasis. In recent years, however, several functions of platelets "beyond thrombosis" were discovered. This review depicts the crosstalk of platelets with components of the immune system in the context of thrombo-inflammation. In particular, the various ways, in which platelets interact with the complement system, are illustrated. Platelets cannot only aggravate vascular inflammation and cardiovascular diseases, but they also contribute to organ remodeling and tissue homeostasis. Here, we portray the role of complement factors associated with platelet activation in tissue remodeling. Importantly, the clinical relevance of this platelet-complement crosstalk is addressed. A focus lies on thrombo-inflammatory disorders, other diseases with thrombo-embolic mechanisms or complications, but also autoimmune diseases. Finally, we draw attention to the growing body of evidence on the role of complement-platelet crosstalk in cardiovascular diseases. For future clinical, translational and basic science approaches, this crosstalk may prove a fruitful area of research in order to procure novel therapeutic and diagnostic targets in cardiovascular medicine and previously less addressed diseases featuring a platelet-complement axis.

Platelets and the Role of P2X Receptors in Nociception, Pain, Neuronal Toxicity and Thromboinflammation.

P2X receptors belong to a family of cation channel proteins, which respond to extracellular adenosine 5'-triphosphate (ATP). These receptors have gained increasing attention in basic and translational research, as they are central to a variety of important pathophysiological processes such as the modulation of cardiovascular physiology, mediation of nociception, platelet and macrophage activation, or neuronal-glial integration. While P2X1 receptor activation is long known to drive platelet aggregation, P2X7 receptor antagonists have recently been reported to inhibit platelet activation. Considering the role of both P2X receptors and platelet-mediated inflammation in neuronal diseases such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, and stroke, targeting purinergic receptors may provide a valuable novel therapeutic approach in these diseases. Therefore, the present review illuminates the role of platelets and purinergic signaling in these neurological conditions to evaluate potential translational implications.

CaMKII activity contributes to homeometric autoregulation of the heart: A novel mechanism for the Anrep effect.

KEY POINTS: The Anrep effect represents the alteration of left ventricular (LV) contractility to acutely enhanced afterload in a few seconds, thereby preserving stroke volume (SV) at constant preload. As a result of the missing preload stretch in our model, the Anrep effect differs from the slow force response and has a different mechanism. The Anrep effect demonstrated two different phases. First, the sudden increased afterload was momentary equilibrated by the enhanced LV contractility as a result of higher power strokes of strongly-bound myosin cross-bridges. Second, the slightly delayed recovery of SV is perhaps dependent on Ca2+ /calmodulin-dependent protein kinase II activation caused by oxidation and myofilament phosphorylation (cardiac myosin-binding protein-C, myosin light chain 2), maximizing the recruitment of available strongly-bound myosin cross-bridges. Short-lived oxidative stress might present a new facet of subcellular signalling with respect to cardiovascular regulation. Relevance for human physiology was demonstrated by echocardiography disclosing the Anrep effect in humans during handgrip exercise. ABSTRACT: The present study investigated whether oxidative stress and Ca2+ /calmodulin-dependent protein kinase II (CaMKII) activity are involved in triggering the Anrep effect. LV pressure-volume (PV) analyses of isolated, preload controlled working hearts were performed at two afterload levels (60 and 100 mmHg) in C57BL/6N wild-type (WT) and CaMKII-double knockout mice (DKOCaMKII ). In snap-frozen WT hearts, force-pCa relationship, H2 O2 generation, CaMKII oxidation and phosphorylation of myofilament and Ca2+ handling proteins were assessed. Acutely raised afterload showed significantly increased wall stress, H2 O2 generation and LV contractility in the PV diagram with an initial decrease and recovery of stroke volume, whereas end-diastolic pressure and volume, as well as heart rate, remained constant. Afterload induced increase in LV contractility was blunted in DKOCaMKII -hearts. Force development of single WT cardiomyocytes was greater with elevated afterload at submaximal Ca2+ concentration and associated with increases in CaMKII oxidation and phosphorylation of cardiac-myosin binding protein-C, myosin light chain and Ca2+ handling proteins. CaMKII activity is involved in the regulation of the Anrep effect and associates with stimulation of oxidative stress, presumably starting a cascade of CaMKII oxidation with downstream phosphorylation of myofilament and Ca2+ handling proteins. These mechanisms improve LV inotropy and preserve stroke volume within few seconds.

Functional Relevance of the Anaphylatoxin Receptor C3aR for Platelet Function and Arterial Thrombus Formation Marks an Intersection Point Between Innate Immunity and Thrombosis.

BACKGROUND: Platelets have distinct roles in the vascular system in that they are the major mediator of thrombosis, critical for restoration of tissue integrity, and players in vascular inflammatory conditions. In close spatiotemporal proximity, the complement system acts as the first line of defense against invading microorganisms and is a key mediator of inflammation. Whereas the fluid phase cross-talk between the complement and coagulation systems is well appreciated, the understanding of the pathophysiological implications of such interactions is still scant. METHODS: We analyzed coexpression of the anaphylatoxin receptor C3aR with activated glycoprotein IIb/IIIa on platelets of 501 patients with coronary artery disease using flow cytometry; detected C3aR expression in human or murine specimen by polymerase chain reaction, immunofluorescence, Western blotting, or flow cytometry; and examined the importance of platelet C3aR by various in vitro platelet function tests, in vivo bleeding time, and intravital microscopy. The pathophysiological relevance of C3aR was scrutinized with the use of disease models of myocardial infarction and stroke. To approach underlying molecular mechanisms, we identified the platelet small GTPase Rap1b using nanoscale liquid chromatography coupled to tandem mass spectrometry. RESULTS: We found a strong positive correlation of platelet complement C3aR expression with activated glycoprotein IIb/IIIa in patients with coronary artery disease and coexpression of C3aR with glycoprotein IIb/IIIa in thrombi obtained from patients with myocardial infarction. Our results demonstrate that the C3a/C3aR axis on platelets regulates distinct steps of thrombus formation such as platelet adhesion, spreading, and Ca2+ influx. Using C3aR-/- mice or C3-/- mice with reinjection of C3a, we uncovered that the complement activation fragment C3a regulates bleeding time after tail injury and thrombosis. Notably, C3aR-/- mice were less prone to experimental stroke and myocardial infarction. Furthermore, reconstitution of C3aR-/- mice with C3aR+/+ platelets and platelet depletion experiments demonstrated that the observed effects on thrombosis, myocardial infarction, and stroke were specifically caused by platelet C3aR. Mechanistically, C3aR-mediated signaling regulates the activation of Rap1b and thereby bleeding arrest after injury and in vivo thrombus formation. CONCLUSIONS: Overall, our findings uncover a novel function of the anaphylatoxin C3a for platelet function and thrombus formation, highlighting a detrimental role of imbalanced complement activation in cardiovascular diseases.

Differential retrotranslocation of mitochondrial Bax and Bak.

The Bcl-2 proteins Bax and Bak can permeabilize the outer mitochondrial membrane and commit cells to apoptosis. Pro-survival Bcl-2 proteins control Bax by constant retrotranslocation into the cytosol of healthy cells. The stabilization of cytosolic Bax raises the question whether the functionally redundant but largely mitochondrial Bak shares this level of regulation. Here we report that Bak is retrotranslocated from the mitochondria by pro-survival Bcl-2 proteins. Bak is present in the cytosol of human cells and tissues, but low shuttling rates cause predominant mitochondrial Bak localization. Interchanging the membrane anchors of Bax and Bak reverses their subcellular localization compared to the wild-type proteins. Strikingly, the reduction of Bax shuttling to the level of Bak retrotranslocation results in full Bax toxicity even in absence of apoptosis induction. Thus, fast Bax retrotranslocation is required to protect cells from commitment to programmed death.

Platelets induce apoptosis via membrane-bound FasL.

After tissue injury, both wound sealing and apoptosis contribute to restoration of tissue integrity and functionality. Although the role of platelets (PLTs) for wound closure and induction of regenerative processes is well established, the knowledge about their contribution to apoptosis is incomplete. Here, we show that PLTs present the death receptor Fas ligand (FasL) on their surface after activation. Activated PLTs as well as the isolated membrane fraction of activated PLTs but not of resting PLTs induced apoptosis in a dose-dependent manner in primary murine neuronal cells, human neuroblastoma cells, and mouse embryonic fibroblasts. Membrane protein from PLTs lacking membrane-bound FasL (FasL(△m/△m)) failed to induce apoptosis. Bax/Bak-mediated mitochondrial apoptosis signaling in target cells was not required for PLT-induced cell death, but increased the apoptotic response to PLT-induced Fas signaling. In vivo, PLT depletion significantly reduced apoptosis in a stroke model and an inflammation-independent model of N-methyl-d-aspartic acid-induced retinal apoptosis. Furthermore, experiments using PLT-specific PF4Cre(+) FasL(fl/fl) mice demonstrated a role of PLT-derived FasL for tissue apoptosis. Because apoptosis secondary to injury prevents inflammation, our findings describe a novel mechanism on how PLTs contribute to tissue homeostasis.

Macrophage migration inhibitory factor limits activation-induced apoptosis of platelets via CXCR7-dependent Akt signaling.

RATIONALE: Macrophage migration inhibitory factor (MIF) is released on platelet activation. Circulating MIF could potentially regulate platelets and thereby platelet-mediated inflammatory and regenerative mechanisms. However, the effect of MIF on platelets is unknown. OBJECTIVE: The present study evaluated MIF in regulating platelet survival and thrombotic potential. METHODS AND RESULTS: MIF interacted with CXCR4-CXCR7 on platelets, defining CXCR7 as a hitherto unrecognized receptor for MIF on platelets. MIF internalized CXCR4, but unlike CXCL12 (SDF-1α), it did not phosphorylate Erk1/2 after CXCR4 ligation because of the lack of CD74 and failed in subsequent CXCR7 externalization. MIF did not alter the activation status of platelets. However, MIF rescued platelets from activation and BH3 mimetic ABT-737-induced apoptosis in vitro via CXCR7 and enhanced circulating platelet survival when administered in vivo. The antiapoptotic effect of MIF was absent in Cxcr7(-/-) murine embryonic cells but pronounced in CXCR7-transfected Madin-Darby canine kidney cells. This prosurvival effect was attributed to the MIF-CXCR7-initiated PI3K-Akt pathway. MIF induced CXCR7-Akt-dependent phosphorylation of BCL-2 antagonist of cell death (BAD) both in vitro and in vivo. Consequentially, MIF failed to rescue Akt(-/-) platelets from thrombin-induced apoptosis when challenged ex vivo, also in prolonging platelet survival and in inducing BAD phosphorylation among Akt(-/-) mice in vivo. MIF reduced thrombus formation under arterial flow conditions in vitro and retarded thrombotic occlusion after FeCl3-induced arterial injury in vivo, an effect mediated through CXCR7. CONCLUSION: MIF interaction with CXCR7 modulates platelet survival and thrombotic potential both in vitro and in vivo and thus could regulate thrombosis and inflammation.

Platelet bound oxLDL shows an inverse correlation with plasma anaphylatoxin C5a in patients with coronary artery disease.

Both oxidized lipids as well as the complement system contribute to atherothrombosis. The expression of complement receptors correlates with the expression of platelet activation markers, and platelet bound oxidized low-density lipoprotein (oxLDL) modulates platelet function. In the present study, we investigated the relationship of markers of complement activation, the anaphylatoxins C5a and C3a, and oxidized low-density lipoprotein. Two hundred and seven patients with coronary artery disease (CAD) were analyzed in this study. Using enzyme-linked immunosorbent assays, plasma levels of oxLDL, C3a, and C5a were measured. Moreover, we assessed platelet bound oxLDL by flow cytometry. The overall level of C5a in the troponin negative group (stable angina (SA) and unstable angina (UA)) compared to the troponin positive group (non-ST-elevation myocardial infarction (NSTEMI) and ST-elevation myocardial infarction (STEMI)) did not differ significantly (62.7 ± 32.4 ng/ml versus 65.8 ± 40.3 ng/ml). While C5a and C3a showed a significant correlation with each other (r = 0.25, p < 0.001), there was no statistically significant relationship between C3a and platelet bound oxLDL (r = 0.06, p = 0.37). Furthermore, plasma oxLDL did not correlate with either C3a or C5a. However, we observed a moderate, yet significant negative correlation between plasma C5a and platelet bound oxLDL (r = -0.15, p = 0.04). Partial correlation analysis correcting for the presence of acute coronary syndrome (ACS), troponin status or the subgroups SA, UA, NSTEMI, or STEMI did not alter this correlation substantially. Interestingly, flow cytometric analysis of human platelets showed increased expression of C5aR and P-selectin after in vitro stimulation with oxLDL. In conclusion, the complement anaphylatoxin C5a shows an inverse correlation with platelet bound oxLDL. The relationship of oxidized lipids to particular complement components may add to the platelet-lipid interplay in atherogenesis and trigger future clinical and mechanistic studies.

The Inflammatory Role of Platelets: Translational Insights from Experimental Studies of Autoimmune Disorders.

Beyond their indispensable role in hemostasis, platelets have shown to affect the development of inflammatory disorders, as they have been epidemiologically and mechanistically linked to diseases featuring an inflammatory reaction in inflammatory diseases like multiple sclerosis, rheumatoid arthritis and inflammatory bowel disorders. The identification of novel molecular mechanisms linking inflammation and to platelets has highlighted them as new targets for therapeutic interventions. In particular, genetic and pharmacological studies have identified an important role for platelets in neuroinflammation. This review summarizes the main molecular links between platelets and inflammation, focusing on immune regulatory factors, receptors, cellular targets and signaling pathways by which they can amplify inflammatory reactions and that make them potential therapeutic targets.

SDF-1α induces differential trafficking of CXCR4-CXCR7 involving cyclophilin A, CXCR7 ubiquitination and promotes platelet survival.

Platelet-derived SDF-1α (CXCL12) mediates inflammatory and regenerative mechanisms. The present study characterizes the effect of SDF-1α ligation in platelets. SDF-1α (0-100 µM) dose and time dependently caused internalization of its receptor CXCR4 (28.9 ± 1.6 vs. 16.1 ± 1.9 in SDF-1α-treated platelets), coupled to the surface externalization of CXCR7 (65.5 ± 8 vs. 162.8 ± 27.6 following SDF-1α treatment), both in vitro and in vivo. This was inhibited in the presence of AMD3100 (100 µM), CXCR4 blocking and vesicular transport inhibitors (brefeldin A, 10 µM; rapamycin, 100 nM). SDF-1α/CXCR-4-mediated CXCR7 translocation was significantly reduced by inhibitors of ERK1/2-(U0126-10 µM) and cyclophilinA (CyPA)-(NIM811-10 µM) by 28 and 46%, respectively. Further, SDF-1α-induced downstream phosphorylation of Erk1/2 led to CyPA-dependent ubiquitination of CXCR7, which is essential for its surface translocation. CyPA-PPIase-activity inhibitor NIM-811, Erk1/2, and E1-ligase inhibitor-(PYR-41-25 µM) significantly abolished SDF-1α-driven CXCR7 ubiquitination and subsequent surface translocation. SDF-1α induced CXCR7 ubiquitination, and its surface exposure was observed in wild-type murine platelets, but not in CyPA-deficient platelets. SDF-1α/CXCR4-CyPA-dependent CXCR7 translocation and its subsequent ligation attenuated activation-induced apoptosis both in vitro and when administered in vivo. This antiapoptotic effect of SDF-1α was abrogated by blocking CXCR7, also significantly affected in Cypa(-/-) platelets. Thus, we decipher a novel mechanism, whereby SDF-1α regulates relative receptor availability in circulating platelets and exerts its prosurvival benefits.-Chatterjee, M., Seizer, P., Borst, O., Schönberger, T., Mack, A., Geisler, T., Langer, H. F., May, A. E., Vogel, S., Lang, F., Gawaz, M. SDF-1α induces differential trafficking of CXCR4-CXCR7 involving cyclophilin A, CXCR7 ubiquitination and promotes platelet survival.

Platelets contribute to the pathogenesis of experimental autoimmune encephalomyelitis.

RATIONALE: Multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE), are inflammatory disorders of the central nervous system (CNS). The function of platelets in inflammatory and autoimmune pathologies is thus far poorly defined. OBJECTIVE: We addressed the role of platelets in mediating CNS inflammation in EAE. METHODS AND RESULTS: We found that platelets were present in human MS lesions as well as in the CNS of mice subjected to EAE but not in the CNS from control nondiseased mice. Platelet depletion at the effector-inflammatory phase of EAE in mice resulted in significantly ameliorated disease development and progression. EAE suppression on platelet depletion was associated with reduced recruitment of leukocytes to the inflamed CNS, as assessed by intravital microscopy, and with a blunted inflammatory response. The platelet-specific receptor glycoprotein Ibα (GPIbα) promotes both platelet adhesion and inflammatory actions of platelets and targeting of GPIbα attenuated EAE in mice. Moreover, targeting another platelet adhesion receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), also reduced EAE severity in mice. CONCLUSIONS: Platelets contribute to the pathogenesis of EAE by promoting CNS inflammation. Targeting platelets may therefore represent an important new therapeutic approach for MS treatment.

Engagement of αIIbß3 (GPIIb/IIIa) with ανß3 integrin mediates interaction of melanoma cells with platelets: a connection to hematogenous metastasis.

A mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remain poorly understood. Here, we used murine B16 melanoma cells to observe functional aspects of how platelets contribute to the process of hematogenous metastasis. We found that platelets interfere with a distinct step of the metastasis cascade, as they promote adhesion of melanoma cells to the endothelium in vitro under shear conditions. Constitutively active platelet receptor GPIIb/IIIa (integrin αIIbß3) expressed on Chinese hamster ovary cells promoted melanoma cell adhesion in the presence of fibrinogen, whereas blocking antibodies to aνß3 integrin on melanoma cells or to GPIIb/IIIa significantly reduced melanoma cell adhesion to platelets. Furthermore, using intravital microscopy, we observed functional platelet-melanoma cell interactions, as platelet depletion resulted in significantly reduced melanoma cell adhesion to the injured vascular wall in vivo. Using a mouse model of hematogenous metastasis to the lung, we observed decreased metastasis of B16 melanoma cells to the lung by treatment with a mAb blocking the aν subunit of aνß3 integrin. This effect was significantly reduced when platelets were depleted in vivo. Thus, the engagement of GPIIb/IIIa with aνß3 integrin interaction mediates tumor cell-platelet interactions and highlights how this interaction is involved in hematogenous tumor metastasis.

Binding of oxidized low-density lipoprotein on circulating platelets is increased in patients with acute coronary syndromes and induces platelet adhesion to vascular wall in vivo--brief report.

OBJECTIVE: Hyperlipidemia is associated with platelet hyperactivity. In the present study, we evaluated the binding of oxidized low-density lipoprotein (oxLDL) on the surface of circulating platelets in patients with stable coronary artery disease and acute coronary syndromes and its possible association with platelet activation. Furthermore, the role of oxLDL binding on platelet adhesion to collagen and endothelial cells in vitro as well as after carotid ligation in mice was investigated. METHODS AND RESULTS: Using flow cytometry, patients with acute coronary syndromes (n=174) showed significantly enhanced oxLDL binding compared with patients with stable coronary artery disease (n=182; P=0.007). Platelet-bound oxLDL positively correlated with the degree of platelet activation (expression of P-selectin and activated fibrinogen receptor; P<0.001 for both). Plasma oxLDL was increased in patients with acute coronary syndromes compared with stable angina pectoris patients. Preincubation of isolated platelets with oxLDL, but not with native LDL, resulted in enhanced platelet adhesion to collagen and activated endothelial cells under high shear stress in vitro, as well as after carotid ligation in C57BL/6J mice and apolipoprotein E(-/-) mice fed a high cholesterol diet. CONCLUSIONS: Increased platelet-bound oxLDL in patients with acute coronary syndromes may play an important role in atherothrombosis, thus providing a potential future therapeutic target.

Improved mid-term stability of MR reduction with an increased number of clips after percutaneous mitral valve repair in functional MR.

Background: Percutaneous mitral valve repair (PMVR) has evolved to be a standard procedure in suitable patients with mitral regurgitation (MR) not accessible for open surgery. Here, we analyzed the influence of the number and positioning of the clips implanted during the procedure on MR reduction analyzing also sub-collectives of functional and degenerative MR (DMR). Results: We included 410 patients with severe MR undergoing PMVR using the MitraClip® System. MR and reduction of MR were analyzed by TEE at the beginning and at the end of the PMVR procedure. To specify the clip localization, we sub-divided segment 2 into 3 sub-segments using the segmental classification of the mitral valve. Results: We found an enhanced reduction of MR predominantly in DMR patients who received more than one clip. Implantation of only one clip led to a higher MR reduction in patients with functional MR (FMR) in comparison to patients with DMR. No significant differences concerning pressure gradients could be observed in degenerative MR patients regardless of the number of clips implanted. A deterioration of half a grade of the achieved MR reduction was observed 6 months post-PMVR independent of the number of implanted clips with a better stability in FMR patients, who got 3 clips compared to patients with only one clip. Conclusions: In patients with FMR, after 6 months the reduction of MR was more stable with an increased number of implanted clips, which suggests that this specific patient collective may benefit from a higher number of clips.

Effector T cell chemokine IP-10 predicts cardiac recovery and clinical outcomes post-myocardial infarction.

Background and aims: Preclinical data suggest that activation of the adaptive immune system is critical for myocardial repair processes in acute myocardial infarction. The aim of the present study was to determine the clinical value of baseline effector T cell chemokine IP-10 blood levels in the acute phase of ST-segment elevation myocardial infarction (STEMI) for the prediction of the left ventricular function changes and cardiovascular outcomes after STEMI. Methods: Serum IP-10 levels were retrospectively quantified in two independent cohorts of STEMI patients undergoing primary percutaneous coronary intervention. Results: We report a biphasic response of the effector T cell trafficking chemokine IP-10 characterized by an initial increase of its serum levels in the acute phase of STEMI followed by a rapid reduction at 90min post reperfusion. Patients at the highest IP-10 tertile presented also with more CD4 effector memory T cells (CD4 TEM cells), but not other T cell subtypes, in blood. In the Newcastle cohort (n=47), patients in the highest IP-10 tertile or CD4 TEM cells at admission exhibited an improved cardiac systolic function 12 weeks after STEMI compared to patients in the lowest IP-10 tertile. In the Heidelberg cohort (n=331), STEMI patients were followed for a median of 540 days for major adverse cardiovascular events (MACE). Patients presenting with higher serum IP-10 levels at admission had a lower risk for MACE after adjustment for traditional risk factors, CRP and high-sensitivity troponin-T levels (highest vs. rest quarters: HR [95% CI]=0.420 [0.218-0.808]). Conclusion: Increased serum levels of IP-10 in the acute phase of STEMI predict a better recovery in cardiac systolic function and less adverse events in patients after STEMI.

Platelets regulate ischemia-induced revascularization and angiogenesis by secretion of growth factor-modulating factors.

In ischemic tissue, platelets can modulate angiogenesis. The specific factors influencing this function, however, are poorly understood. Here, we characterized the complement anaphylatoxin C5a-mediated activation of C5a receptor 1 (C5aR1) expressed on platelets as a potent regulator of ischemia-driven revascularization. We assessed the relevance of the anaphylatoxin receptor C5aR1 on platelets in patients with coronary artery disease as well as those with peripheral artery disease and used genetic mouse models to characterize its significance for ischemia and growth factor-driven revascularization. The presence of C5aR1-expressing platelets was increased in the hindlimb ischemia model. Ischemia-driven angiogenesis was significantly improved in C5aR1-/- mice but not in C5-/- mice, suggesting a specific role of C5aR1. Experiments using the supernatant of C5a-stimulated platelets suggested a paracrine mechanism of angiogenesis inhibition by platelets by means of antiangiogenic CXC chemokine ligand 4 (CXCL4, PF4). Lineage-specific C5aR1 deletion verified that the secretion of CXCL4 depends on C5aR1 ligation on platelets. Using C5aR1-/-CXCL4-/- mice, we observed no additional effect in the revascularization response, underscoring a strong dependence of CXCL4 secretion on the C5a-C5aR1-axis. We identified a novel mechanism for inhibition of neovascularization via platelet C5aR1, which was mediated by the release of antiangiogenic CXCL4.

Modification of the GRACE Risk Score for Risk Prediction in Patients With Acute Coronary Syndromes.

Importance: The Global Registry of Acute Coronary Events (GRACE) risk score, a guideline-recommended risk stratification tool for patients presenting with acute coronary syndromes (ACS), does not consider the extent of myocardial injury. Objective: To assess the incremental predictive value of a modified GRACE score incorporating high-sensitivity cardiac troponin (hs-cTn) T at presentation, a surrogate of the extent of myocardial injury. Design, Setting, and Participants: This retrospectively designed longitudinal cohort study examined 3 independent cohorts of 9803 patients with ACS enrolled from September 2009 to December 2017; 2 ACS derivation cohorts (Heidelberg ACS cohort and Newcastle STEMI cohort) and an ACS validation cohort (SPUM-ACS study). The Heidelberg ACS cohort included 2535 and the SPUM-ACS study 4288 consecutive patients presenting with a working diagnosis of ACS. The Newcastle STEMI cohort included 2980 consecutive patients with ST-elevation myocardial infarction treated with primary percutaneous coronary intervention. Data were analyzed from March to June 2023. Exposures: In-hospital, 30-day, and 1-year mortality risk estimates derived from an updated risk score that incorporates continuous hs-cTn T at presentation (modified GRACE). Main Outcomes and Measures: The predictive value of continuous hs-cTn T and modified GRACE risk score compared with the original GRACE risk score. Study end points were all-cause mortality during hospitalization and at 30 days and 1 year after the index event. Results: Of 9450 included patients, 7313 (77.4%) were male, and the mean (SD) age at presentation was 64.2 (12.6) years. Using continuous rather than binary hs-cTn T conferred improved discrimination and reclassification compared with the original GRACE score (in-hospital mortality: area under the receiver operating characteristic curve [AUC], 0.835 vs 0.741; continuous net reclassification improvement [NRI], 0.208; 30-day mortality: AUC, 0.828 vs 0.740; NRI, 0.312; 1-year mortality: AUC, 0.785 vs 0.778; NRI, 0.078) in the derivation cohort. These findings were confirmed in the validation cohort. In the pooled population of 9450 patients, modified GRACE risk score showed superior performance compared with the original GRACE risk score in terms of reclassification and discrimination for in-hospital mortality end point (AUC, 0.878 vs 0.780; NRI, 0.097), 30-day mortality end point (AUC, 0.858 vs 0.771; NRI, 0.08), and 1-year mortality end point (AUC, 0.813 vs 0.797; NRI, 0.056). Conclusions and Relevance: In this study, using continuous rather than binary hs-cTn T at presentation, a proxy of the extent of myocardial injury, in the GRACE risk score improved the mortality risk prediction in patients with ACS.