PCSK9 (Proprotein Convertase Subtilisin/Kexin 9) Enhances Platelet Activation, Thrombosis, and Myocardial Infarct Expansion by Binding to Platelet CD36

Abstract

Background: Proprotein convertase subtilisin/kexin 9 (PCSK9), mainly secreted by the liver and released into the blood, elevates plasma low-density lipoprotein (LDL) cholesterol by degrading LDL receptor. Pleiotropic effects of PCSK9 beyond lipid-metabolism have been shown. However, the direct effects of PCSK9 on platelet activation and thrombosis, as well as the underlying mechanisms, still remain unclear. Methods: We detected the direct effects of PCSK9 on agonists-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, α granule release, spreading, and clot retraction. These studies were complemented by in vivo analysis of FeCl3-injured mouse mesenteric arteriole thrombosis. We also investigated the underlying mechanisms. Using myocardial infarct (MI) model, we explored the effects of PCSK9 on microvascular obstruction and infarct expansion post-MI. Results: PCSK9 directly enhances agonists-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, P-selection release from α granules, spreading, and clot retraction. In line, PCSK9 enhances in vivo thrombosis in a FeCl3-injured mesenteric arteriole thrombosis mouse model, while PCSK9 inhibitor evolocumab ameliorates its enhancing effects. Mechanism studies revealed that PCSK9 binds to platelet CD36 and thus activates Src kinase and mitogen-activated protein kinase (MAPK)- extracellular signal-regulated kinase 5 and c-Jun N-terminal kinase, increases the generation of reactive oxygen species, as well as activates the p38MAPK/cytosolic phospholipase A2/cyclooxygenase-1/thromboxane A 2 signaling pathways downstream of CD36 to enhance platelet activation. Using CD36 knockout mice, we showed the enhancing effects of PCSK9 on platelet activation are CD36 dependent. Consistently and importantly, aspirin abolishes the enhancing effects of PCSK9 on platelet activation and in vivo thrombosis. Finally, we showed that PCSK9 activating platelet CD36 aggravates microvascular obstruction and promotes MI expansion post-MI. Conclusions: PCSK9 in plasma directly enhances platelet activation and in vivo thrombosis, as well as MI expansion post-MI, by binding to platelet CD36 and thus activating the downstream signaling pathways. PCSK9 inhibitors or aspirin abolish the enhancing effects of PCSK9, supporting the use of aspirin in patients with high plasma PCSK9 levels in addition to PCSK9 inhibitors to prevent thrombotic complications.

Polymorphisms of rs2483205 and rs562556 in the PCSK9 gene are associated with coronary artery disease and cardiovascular risk factors

“…Recent studies revealed that PCSK9 inhibitors prevent CVD through mechanisms other than only reducing LDL-C levels. Several new effects of PCSK9 on diseases, such as insulin resistance and thrombus, have been revealed 13 , 17 .…”

“…Previously, most studies on the PCSK9 gene were focused on several polymorphisms, such as E670G or R46L, and the findings suggested that the PCSK9 gene was significantly associated with LDL-C levels and CAD 10 – 12 . Recently, an increasing number of studies have implied that PCSK9 might affect CAD beyond its effects on lipids and that it also interacts with cardiovascular risk factors, such as insulin resistance 13 , 14 , inflammation 15 , platelet activation 16 , and thrombosis 17 . However, these multieffects of PCSK9 are still unclear, and whether there are novel genetic targets of PCSK9 that could be applied to therapy for atherosclerotic cardiovascular disease (ASCVD) with safer, more efficient, and pleiotropic effects requires further exploration.…”

TNFɑ-induced LDL cholesterol accumulation involve elevated LDLR cell surface levels and SR-B1 downregulation in human arterial endothelial cells

“…Notwithstanding, PCSK9 also downregulates other receptors in the LDLR family [79,80], and binds the scavenger receptor, CD36, concurrent with thrombosis [97,99]. Thus, the effect of increasing LDLR in the athero-protective effects of PCSK9, beyond lowering serum LDL concentration, is more complex.…”

TNFɑ-induced LDL cholesterol accumulation involve elevated LDLR cell surface levels and SR-B1 downregulation in human arterial endothelial cells

“…General upregulation of the LDLR receptor function through inhibition of PCSK9 have been reported to bene t against coronary artery disease [97,98]. Notwithstanding, PCSK9 also downregulates other receptors in the LDLR family [79,80], and binds the scavenger receptor, CD36, concurrent with thrombosis [97,99]. Thus, the effect of increasing LDLR in the athero-protective effects of PCSK9, beyond lowering serum LDL concentration, is more complex.…”