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.
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-β 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.
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.
Copyright © 2024 Reusswig, Dille, Krüger, Ortscheid, Feige, Gorressen, Fischer and Elvers.

KRAS is a small GTPase, ubiquitously expressed in mammalian cells, that functions as a molecular switch to regulate cell proliferation and differentiation. Oncogenic mutations that render KRAS constitutively active occur frequently in human cancers. KRAS must localize to the plasma membrane (PM) for biological activity. KRAS PM binding is mediated by interactions of the KRAS membrane anchor with phosphatidylserine (PtdSer), therefore, depleting PM PtdSer content abrogates KRAS PM binding and oncogenic function. From a genome-wide siRNA screen to search for genes that regulate KRAS PM localization, we identified a set of phosphatidylinositol (PI) 3-phosphatase family members: myotubularin-related (MTMR) proteins 2, 3, 4 and 7. Here we show that knockdown of MTMR 2/3/4/7 expression disrupts KRAS PM interactions. The molecular mechanism involves depletion of PM PI 4-phosphate (PI4P) levels, which in turn disrupts the subcellular localization and operation of oxysterol-binding protein related protein (ORP) 5, a PtdSer lipid transfer protein that maintains PM PtdSer content. Concomitantly, silencing MTMR 2/3/4/7 expression elevates PM levels of PI3P and reduces PM and total cellular levels of PtdSer. In summary we propose that the PI 3-phosphatase activity provided by MTMR proteins is required to generate PM PI for the synthesis of PM PI4P, which in turn, promotes the PM localization of PtdSer and KRAS.

Platelets play an important role in cardio- and cerebrovascular diseases. Abdominal aortic aneurysm (AAA) is a highly lethal, atherosclerotic-related disease with characteristic features of progressive dilatation of the abdominal aorta and degradation of the vessel wall accompanied by chronic inflammation. Platelet activation and pro-coagulant activity play a decisive role in the AAA pathology as they might trigger AAA development in both mice and men. The present study investigated the impact of the major platelet collagen receptor glycoprotein (GP)VI in cellular processes underlying AAA initiation and progression. Genetic deletion of GPVI offered protection of mice against aortic diameter expansion in experimental AAA. Mechanistically, GPVI deficiency resulted in decreased inflammation with reduced infiltration of neutrophils and platelets into the aortic wall. Further, remodelling of the aortic wall was improved in absence of GPVI, indicated by reduced MMP2/9 and OPN plasma levels and an enhanced α-SMA content within the aortic wall, accompanied by reduced cell apoptosis. As a result, an elevation in intima/media thickness and elastin content were observed in GPVI-deficient PPE mice, coursing a significantly reduced aortic diameter expansion and reduced aneurysm incidence. In AAA patients, enhanced plasma levels of soluble GPVI and fibrin, besides fibrin accumulation within the intraluminal thrombus (ILT) suggested that GPVI might serve as a biomarker and mediator in fibrin-supported stabilization of the ILT. In conclusion, our results emphasize the potential need for a GPVI-targeted anti-platelet therapy to reduce AAA initiation and progression, as well as to protect AAA patients from aortic rupture. Translational perspective Abdominal aortic aneurysm (AAA) is an atherosclerotic-related, cardiovascular disease (CVD) with high mortality. The impact of platelets in different cellular processes underlying AAA initiation and progression remains unclear.Therefore, we analysed the role of the major platelet collagen receptor GPVI in the pathogenesis of AAA. Results from platelet depleted mice and patients with AAA revealed a significant contribution of GPVI to the inflammatory response and remodelling process of the aorta. Further, elevated accumulation of fibrin, a recently identified ligand of GPVI in the intraluminal thrombus (ILT) and in the plasma of AAA patients, suggests that GPVI binding to fibrin plays a role in ILT formation and probably stabilization of the abdominal aorta. Furthermore, increased levels of sGPVI suggest that GPVI might serve as a clinical biomarker for AAA. Thus, therapeutic targeting of GPVI-mediated platelet activation might be an effective anti-thrombotic strategy for AAA patients.

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.
Copyright © 2023 Metz, Feige, de Biasi, Ehrenberg, Mulorz, Toska, Reusswig, Quast, Gerdes, Kelm, Schelzig and Elvers.

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 AAA 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 AAA, we analyzed the contribution of platelet Panx1 in the progression of AAA. We detected enhanced Panx1 plasma levels in AAA patients. In experimental AAA 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 AAA formation and progression. In conclusion, our data strongly supports the role of platelets in inflammatory responses in AAA via Panx1 channels and adds important knowledge about the significance of platelets in AAA pathology important for the establishment of an anti-platelet therapy for AAA patients.