Crosstalk of platelets with macrophages and fibroblasts aggravates inflammation, aortic wall stiffening, and osteopontin release in abdominal aortic aneurysm.

AIMS: Abdominal aortic aneurysm (AAA) is a highly lethal disease with progressive dilatation of the abdominal aorta accompanied by degradation and remodelling of the vessel wall due to chronic inflammation. Platelets play an important role in cardiovascular diseases, but their role in AAA is poorly understood. METHODS AND RESULTS: The present study revealed that platelets play a crucial role in promoting AAA through modulation of inflammation and degradation of the extracellular matrix (ECM). They are responsible for the up-regulation of SPP1 (osteopontin, OPN) gene expression in macrophages and aortic tissue, which triggers inflammation and remodelling and also platelet adhesion and migration into the abdominal aortic wall and the intraluminal thrombus (ILT). Further, enhanced platelet activation and pro-coagulant activity result in elevated gene expression of various cytokines, Mmp9 and Col1a1 in macrophages and Il-6 and Mmp9 in fibroblasts. Enhanced platelet activation and pro-coagulant activity were also detected in AAA patients. Further, we detected platelets and OPN in the vessel wall and in the ILT of patients who underwent open repair of AAA. Platelet depletion in experimental murine AAA reduced inflammation and ECM remodelling, with reduced elastin fragmentation and aortic diameter expansion. Of note, OPN co-localized with platelets, suggesting a potential role of OPN for the recruitment of platelets into the ILT and the aortic wall. CONCLUSION: In conclusion, our data strongly support the potential relevance of anti-platelet therapy to reduce AAA progression and rupture in AAA patients.

Flow Chamber Analyses in Cardiovascular Research: Impact of Platelets and the Intercellular Crosstalk with Endothelial Cells, Leukocytes, and Red Blood Cells.

Platelets are main drivers of thrombus formation. Besides platelet aggregate formation, platelets interact with different blood cells such as red blood and white blood cells (RBCs, WBCs) and endothelial cells (ECs), to promote thrombus formation and inflammation. In the past, the role of different proteins in platelet adhesion, activation, and aggregate formation has been analyzed using platelets/mice with a genetic loss of a certain protein. These knock-out mouse models have been investigated for changes in experimental arterial thrombosis or hemostasis. In this review, we focused on the Maastricht flow chamber, which is a very elegant tool to analyze thrombus formation under flow using whole blood or different blood cell components of genetically modified mice. Besides, the interaction of platelets with RBCs, WBCs, and ECs under flow conditions has been evaluated with regard to thrombus formation and platelet-mediated inflammation. Importantly, alterations in thrombus formation as emerged in the flow chamber frequently reflect arterial thrombosis in different mouse models. Thus, the results of flow chamber experiments in vitro are excellent indicators for differences in arterial thrombosis in vivo. Taken together, the Maastricht flow chamber can be used to (1) determine the severity of platelet alterations in different knock-out mice; (2) analyze differences in platelet adhesion, aggregation, and activation; (3) investigate collagen and non-collagen-dependent alterations of thrombus formation; and (4) highlight differences in the interaction of platelets with different blood/ECs. Thus, this experimental approach is a useful tool to increase our understanding of signaling mechanisms that drive arterial thrombosis and hemostasis.

Platelet pannexin-1 channels modulate neutrophil activation and migration but not the progression of abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) is a common disease and highly lethal if untreated. The progressive dilatation of the abdominal aorta is accompanied by degradation and remodeling of the vessel wall due to chronic inflammation. Pannexins represent anion-selective channels and play a crucial role in non-vesicular ATP release to amplify paracrine signaling in cells. Thus, pannexins are involved in many (patho-) physiological processes. Recently, Panx1 channels were identified to be significantly involved in abdominal aortic aneurysm formation through endothelial derived Panx1 regulated inflammation and aortic remodeling. In platelets, Panx1 becomes activated following activation of glycoprotein (GP) VI. Since platelets play a role in cardiovascular diseases including abdominal aortic aneurysm, we analyzed the contribution of platelet Panx1 in the progression of abdominal aortic aneurysm. We detected enhanced Panx1 plasma levels in abdominal aortic aneurysm patients. In experimental abdominal aortic aneurysm using the pancreatic porcine elastase (PPE) mouse model, a major contribution of platelet Panx1 channels in platelet activation, pro-coagulant activity of platelets and platelet-mediated inflammation has been detected. In detail, platelets are important for the migration of neutrophils into the aortic wall induced by direct cell interaction and by activation of endothelial cells. Decreased platelet activation and inflammation did not affect ECM remodeling or wall thickness in platelet-specific Panx1 knock-out mice following PPE surgery. Thus, aortic diameter expansion at different time points after elastase infusion of the aortic wall was unaltered in platelet-specific Panx1 deficient mice suggesting that the modulation of inflammation alone does not affect abdominal aortic aneurysm formation and progression. In conclusion, our data strongly supports the role of platelets in inflammatory responses in abdominal aortic aneurysm via Panx1 channels and adds important knowledge about the significance of platelets in abdominal aortic aneurysm pathology important for the establishment of an anti-platelet therapy for abdominal aortic aneurysm patients.

Platelets modulate cardiac remodeling via the collagen receptor GPVI after acute myocardial infarction.

Introduction: Platelets play an important role in cardiovascular diseases. After acute myocardial infarction, platelets display enhanced activation and migrate into the infarct zone. Furthermore, platelets trigger acute inflammation and cardiac remodeling leading to alterations in scar formation and cardiac function as observed in thrombocytopenic mice. GPVI is the major collagen receptor in platelets and important for platelet activation and thrombus formation and stability. Antibody induced deletion of GPVI at the platelet surface or treatment of mice with recombinant GPVI-Fc results in reduced inflammation and decreased infarct size in a mouse model of AMI. However, the role of GPVI has not been fully clarified to date. Methods/Results: In this study, we found that GPVI is not involved in the inflammatory response in experimental AMI using GPVI deficient mice that were analyzed in a closed-chest model. However, reduced platelet activation in response to GPVI and PAR4 receptor stimulation resulted in reduced pro-coagulant activity leading to improved cardiac remodeling. In detail, GPVI deficiency in mice led to reduced TGF-ß plasma levels and decreased expression of genes involved in cardiac remodeling such as Col1a1, Col3a1, periostin and Cthrc1 7 days post AMI. Consequently, collagen quality of the scar shifted to more tight and less fine collagen leading to improved scar formation and cardiac function in GPVI deficient mice at 21d post AMI. Conclusion: Taken together, this study identifies GPVI as a major regulator of platelet-induced cardiac remodeling and supports the potential relevance of GPVI as therapeutic target to reduce ischemia reperfusion injury and to improve cardiac healing.

Impact of Amyloid-ß on Platelet Mitochondrial Function and Platelet-Mediated Amyloid Aggregation in Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is characterized by an accumulation of amyloid ß (Aß) peptides in the brain and mitochondrial dysfunction. Platelet activation is enhanced in AD and platelets contribute to AD pathology by their ability to facilitate soluble Aß to form Aß aggregates. Thus, anti-platelet therapy reduces the formation of cerebral amyloid angiopathy in AD transgenic mice. Platelet mitochondrial dysfunction plays a regulatory role in thrombotic response, but its significance in AD is unknown and explored herein. METHODS: The effects of Aß-mediated mitochondrial dysfunction in platelets were investigated in vitro. RESULTS: Aß40 stimulation of human platelets led to elevated reactive oxygen species (ROS) and superoxide production, while reduced mitochondrial membrane potential and oxygen consumption rate. Enhanced mitochondrial dysfunction triggered platelet-mediated Aß40 aggregate formation through GPVI-mediated ROS production, leading to enhanced integrin αIIbß3 activation during synergistic stimulation from ADP and Aß40. Aß40 aggregate formation of human and murine (APP23) platelets were comparable to controls and could be reduced by the antioxidant vitamin C. CONCLUSIONS: Mitochondrial dysfunction contributes to platelet-mediated Aß aggregate formation and might be a promising target to limit platelet activation exaggerated pathological manifestations in AD.