Red blood cells (RBCs) influence rheology, and release ADP, ATP, and nitric oxide, suggesting a role for RBCs in hemostasis and thrombosis. Here, we provide evidence for a significant contribution of RBCs to thrombus formation. Anemic mice showed enhanced occlusion times upon injury of the carotid artery. A small population of RBCs was located to platelet thrombi and enhanced platelet activation by a direct cell contact via the FasL/FasR (CD95) pathway known to induce apoptosis. Activation of platelets in the presence of RBCs led to platelet FasL exposure that activated FasR on RBCs responsible for externalization of phosphatidylserine (PS) on the RBC membrane. Inhibition or genetic deletion of either FasL or FasR resulted in reduced PS exposure of RBCs and platelets, decreased thrombin generation, and reduced thrombus formation in vitro and protection against arterial thrombosis in vivo. Direct cell contacts between platelets and RBCs via FasL/FasR were shown after ligation of the inferior vena cava (IVC) and in surgical specimens of patients after thrombectomy. In a flow restriction model of the IVC, reduced thrombus formation was observed in FasL^–/– mice. Taken together, our data reveal a significant contribution of RBCs to thrombosis by the FasL/FasR pathway.

Aims/hypothesis: People with diabetes have an increased cardiovascular risk with an accelerated development of atherosclerosis and an elevated mortality rate after myocardial infarction. Therefore, cardioprotective effects of glucose-lowering therapies are of major importance for the pharmacotherapy of individuals with type 2 diabetes. For sodium–glucose cotransporter 2 inhibitors (SGLT2is), in addition to a reduction in blood glucose, beneficial effects on atherosclerosis, obesity, renal function and blood pressure have been observed. Recent results showed a reduced risk of worsening heart failure and cardiovascular deaths under dapagliflozin treatment irrespective of the diabetic state. However, the underlying mechanisms are yet unknown. Platelets are known drivers of atherosclerosis and atherothrombosis and disturbed platelet activation has also been suggested to occur in type 2 diabetes. Therefore, the present study investigates the impact of the SGLT2i dapagliflozin on the interplay between platelets and inflammation in atherogenesis. Methods: Male, 8-week-old LDL-receptor-deficient (Ldlr^−/−) mice received a high-fat, high-sucrose diabetogenic diet supplemented without (control) or with dapagliflozin (5 mg/kg body weight per day) for two time periods: 8 and 25 weeks. In a first translational approach, eight healthy volunteers received 10 mg dapagliflozin/day for 4 weeks. Results: Dapagliflozin treatment ameliorated atherosclerotic lesion development, reduced circulating platelet–leucocyte aggregates (glycoprotein [GP]Ib⁺CD45⁺: 29.40 ± 5.94 vs 17.00 ± 5.69 cells, p < 0.01; GPIb⁺lymphocyte antigen 6 complex, locus G⁺ (Ly6G): 8.00 ± 2.45 vs 4.33 ± 1.75 cells, p < 0.05) and decreased aortic macrophage infiltration (1.31 ± 0.62 vs 0.70 ± 0.58 ×10³ cells/aorta, p < 0.01). Deeper analysis revealed that dapagliflozin decreased activated CD62P-positive platelets in Ldlr^−/− mice fed a diabetogenic diet (3.78 ± 1.20% vs 2.83 ± 1.06%, p < 0.01) without affecting bleeding time (85.29 ± 37.27 vs 89.25 ± 16.26 s, p = 0.78). While blood glucose was only moderately affected, dapagliflozin further reduced endogenous thrombin generation (581.4 ± 194.6 nmol/l × min) × 10⁻⁹ thrombin vs 254.1 ± 106.4 (nmol/l × min) × 10⁻⁹ thrombin), thereby decreasing one of the most important platelet activators. We observed a direct inhibitory effect of dapagliflozin on isolated platelets. In addition, dapagliflozin increased HDL-cholesterol levels. Importantly, higher HDL-cholesterol levels (1.70 ± 0.58 vs 3.15 ± 1.67 mmol/l, p < 0.01) likely contribute to dapagliflozin-mediated inhibition of platelet activation and thrombin generation. Accordingly, in line with the results in mice, treatment with dapagliflozin lowered CD62P-positive platelet counts in humans after stimulation by collagen-related peptide (CRP; 88.13 ± 5.37% of platelets vs 77.59 ± 10.70%, p < 0.05) or thrombin receptor activator peptide-6 (TRAP-6; 44.23 ± 15.54% vs 28.96 ± 11.41%, p < 0.01) without affecting haemostasis. Conclusions/interpretation: We demonstrate that dapagliflozin-mediated atheroprotection in mice is driven by elevated HDL-cholesterol and ameliorated thrombin–platelet-mediated inflammation without interfering with haemostasis. This glucose-independent mechanism likely contributes to dapagliflozin’s beneficial cardiovascular risk profile. Graphical

Cardiovascular diseases (CVDs) are the leading cause of death globally—partly a consequence of increased population size and ageing—and are major contributors to reduced quality of life. Platelets play a major role in hemostasis and thrombosis. While platelet activation and aggregation are essential for hemostasis at sites of vascular injury, uncontrolled platelet activation leads to pathological thrombus formation and provokes thrombosis leading to myocardial infarction or stroke. Platelet activation and thrombus formation is a multistage process with different signaling pathways involved to trigger platelet shape change, integrin activation, stable platelet adhesion, aggregation, and degranulation. Apart from thrombotic events, thrombo-inflammation contributes to organ damage and dysfunction in CVDs and is mediated by platelets and inflammatory cells. Therefore, in the past, many efforts have been made to investigate specific signaling pathways in platelets to identify innovative and promising approaches for novel antithrombotic and anti-thrombo-inflammatory strategies that do not interfere with hemostasis. In this review, we focus on some of the most recent data reported on different platelet receptors, including GPIb-vWF interactions, GPVI activation, platelet chemokine receptors, regulation of integrin signaling, and channel homeostasis of NMDAR and PANX1.

Multiple receptors on platelets drive Alzheimer’s disease–associated amyloid deposits in brain vessels.

Background and Aims: Thrombocytopenia has been described in most patients with acute and chronic liver failure. Decreased platelet production and decreased half‐life of platelets might be a consequence of low levels of thrombopoietin (TPO) in these patients. Platelet production is tightly regulated to avoid bleeding complications after vessel injury and can be enhanced under elevated platelet destruction as observed in liver disease. Thrombopoietin (TPO) is the primary regulator of platelet biogenesis and supports proliferation and differentiation of megakaryocytes. Approach and Results: Recent work provided evidence for the control of TPO mRNA expression in liver and bone marrow (BM) by scanning circulating platelets. The Ashwell‐Morell receptor (AMR) was identified to bind desialylated platelets to regulate hepatic thrombopoietin (TPO) production by Janus kinase (JAK2)/signal transducer and activator of transcription (STAT3) activation. Two‐thirds partial hepatectomy (PHx) was performed in mice. Platelet activation and clearance by AMR/JAK2/STAT3 signaling and TPO production were analyzed at different time points after PHx. Here, we demonstrate that PHx in mice led to thrombocytopenia and platelet activation defects leading to bleeding complications, but unaltered arterial thrombosis, in these mice. Platelet counts were rapidly restored by up‐regulation and crosstalk of the AMR and the IL‐6 receptor (IL‐6R) to induce JAK2‐STAT3‐TPO activation in the liver, accompanied by an increased number of megakaryocytes in spleen and BM before liver was completely regenerated. Conclusions: The AMR/IL‐6R‐STAT3‐TPO signaling pathway is an acute‐phase response to liver injury to reconstitute hemostasis. Bleeding complications were attributable to thrombocytopenia and platelet defects induced by elevated PGI₂, NO, and bile acid plasma levels early after PHx that might also be causative for the high mortality in patients with liver disease.